Review moleculesCarbones and Carbon Atom as Ligands in Transition Metal Complexes
Review Lili Zhao 1, Chaoqun Chai 1, Wolfgang Petz 2,* and Gernot Frenking 1,2,*
Carbones and Carbon1 Institute Atomof Advanced as Synthesis, Ligands School of Chem inistry Transition and Molecular Engineering, Jiangsu National Metal Complexes Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China; [email protected] (L.Z.); [email protected] (C.C.) 2 Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, 1 1 2, 1,2, Lili Zhao , Chaoqun Chai , WolfgangD-35043 Marburg, Petz * andGermany Gernot Frenking * 1 Institute of Advanced Synthesis,* Correspondence: School of Chemistry [email protected] and Molecular Engineering, (W Jiangsu.P.); [email protected] National (G.F.) Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China; [email protected] (L.Z.);Received: [email protected] 23 August 2020; Accepted: (C.C.) 15 October 2020; Published: 23 October 2020 2 Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, D-35043 Marburg, Germany * Correspondence: [email protected]: This review (W.P.); [email protected] experimental and (G.F.) theoretical studies of transition metal
complexes with two types of novel metal-carbon bonds. One type features complexes with Academic Editors: Yves Canac and Carlo Santini carbones CL2 as ligands, where the carbon(0) atom has two electron lone pairs which engage Received: 23 August 2020; Accepted: 15 October 2020; Published: 26 October 2020 in double (σ and π) donation to the metal atom [M]⇇CL2. The second part of this review Abstract: This review summarizesreports experimental complexes and which theoretical have a studies neutral of carbon transition atom metal C as complexes ligand. Carbido complexes with with two types of novel metal-carbonnaked carbon bonds. atoms One typemay featuresbe considered complexes as endpoint with carbones of the CL series2 as [M]-CR3 → [M]-CR2 → ligands, where the carbon(0) atom[M]-CR has → two [M]-C. electron This review lone pairs includes which some engage work in doubleon uranium (σ and andπ) cerium complexes, but it donation to the metal atom [M]does⇔CL not2. The present second a complete part of this coverage review reportsof actinide complexes and lanthanide which have complexes with carbone or a neutral carbon atom C as ligand.carbide Carbido ligands. complexes with naked carbon atoms may be considered as endpoint of the series [M]-CR [M]-CR [M]-CR [M]-C. This review includes some work 3 → 2 → → on uranium and cerium complexes,Keywords: but itcarbone does not complexes; present a completecarbido complexes; coverage of transition actinide andmetal complexes; chemical lanthanide complexes with carbonebonding or carbide ligands.
Keywords: carbone complexes; carbido complexes; transition metal complexes; chemical bonding
1. Introduction 1. Introduction Transition metal compounds with metal-carbon bonds are the backbone of organometallic Transition metal compoundschemistry. with metal-carbonMolecules with bonds M-C aresingle the bonds backbone are already of organometallic known since 1849 when Frankland chemistry. Molecules with M-Creported single bonds the accidental are already synthesis known since of diethyl 1849 when zinc Frankland while attempting reported to the prepare free ethyl radicals accidental synthesis of diethyl zinc[1,2]. while Molecules attempting with to a prepare[M]=CR free2 double ethyl radicalsbond (carbene [1,2]. Molecules complexes) with or a [M]≡CR triple bond a [M]=CR double bond (carbene(carbyne complexes) complexes) or a [M]wereCR synthesized triple bond much (carbyne later complexes) [3–6]. Two were types of compounds with 2 ≡ synthesized much later [3–6].metal-carbon Two types of compoundsdouble or withtriple metal-carbon bonds having double different or triple types bonds of bonds are generally having different types of bondsdistinguished, are generally which distinguished, are named which after arethe named people afterwho theisolated people them who first. Fischer-type carbene isolated them first. Fischer-typeand carbenecarbyne andcomplexes carbyne are complexes best described are best in describedterms of dative in terms bonds of following the Dewar– (–)(─) (+(+)) dative bonds following the Dewar–Chatt–DuncanChatt–Duncan (DCD) (DCD) model model [7,8] [7,8 ][M] [M]⇄CRCR2 2andand [M ] CR CR ,, whereas Schrock-type whereas Schrock-type alkylidenesalkylidenes and alkylidynes and alkylidynes are assumed are toassumed have electron-sharing to have electron-sharing double and double and triple bonds triple bonds [M]=CR and [M][M]=CRCR [9–211 and]. [M]≡CR [9–11]. 2 ≡ This review deals with transitionThis metalreview complexes deals with with transition metal-carbon metal complexes bonds to with two typesmetal-carbon of bonds to two types ligands, which have only recentlyof ligands, been isolatedwhich have and only theoretically recently been studied. isolated One and type theoretically of ligand are studied. One type of ligand carbones CL2 [12], which are carbon(0)are carbones compounds CL2 [12], which with two are dativecarbon(0) bonds compounds to a carbon with atom two in dative the bonds to a carbon atom excited 1D state L C¯ L wherein the the excited carbon 1 atomD state retains L→C ← itsL four where valence the carbon electrons atom as retains two lone its pairs four valence electrons as two → ← that can serve as four-electronlone donors pairs [13 that,14 ].can Thus, serve carbones as four-electron CL2 are four-electrondonors [13,14]. donor Thus, ligands carbones CL2 are four-electron whereas carbenes CR2 are two-electrondonor ligands donors. whereas Carbenes carbenes have a formallyCR2 are two-electron [15] vacant p( donors.π) orbital Carbenes that have a formally [15] can accept electrons in donor-acceptorMolecules 2020 complexes, 25, x; doi: FOR M PEERCR2 REVIEWwhereas carbones are double (σ and π) www.mdpi.com/journal/molecules donors in complexes [M]CL2. A good Lewis acid acceptor fragment A for a carbene complex has a vacant σ orbital and an occupied π orbital whereas a suitable acceptor for a carbone is a double Lewis acid with vacant σ and π orbitals as shown in Figure1a,b. If the Lewis acid A has an occupied π orbital, it would lead to π repulsion with the π lone pair of the carbone CL2, whereby the repulsive interaction is reduced if L is a good π acceptor (Figure1c). The two electron lone pairs of a carbone may bind
Molecules 2020, 25, 4943; doi:10.3390/molecules25214943 www.mdpi.com/journal/molecules Molecules 2020, 25, x FOR PEER REVIEW 2 of 54
vacantMolecules p(2020π), 25orbital, x FOR PEERthat canREVIEW accept electrons in donor-acceptor complexes M⇄CR2 whereas2 of 54 carbones are double (σ and π) donors in complexes [M]⇇CL2. A good Lewis acid acceptor fragmentvacant p( πA) fororbital a carbene that cancomplex accept has electrons a vacant in σ donor-acceptororbital and an occupied complexes π orbitalM⇄CR whereas2 whereas a suitablecarbones acceptor are double for a( σcarbone and π is) donorsa double in Lewis complexes acid with [M] ⇇vacantCL2. A σ andgood π Lewisorbitals acid as shownacceptor in Figurefragment 1a,b. A Iffor the a carbeneLewis acid complex A has hasan occupied a vacant πσ orbital,orbital andit would an occupied lead to π π repulsion orbital whereas with the a πsuitable lone pair acceptor of the for carbone a carbone CL2 ,is whereby a double the Lewis repulsive acid with interaction vacant σ is and reduced π orbitals if L asis ashown good inπ MoleculesacceptorFigure2020 ,1a,b.25 ,(Figure 4943 If the 1c).Lewis The acid two A haselectron an occupied lone pairs π orbital, of a itcarbone would leadmay to bind π repulsion to one withor two the2 of 48 monodentateπ lone pair of Lewis the carbone acids A CL or 2protons, whereby or tothe a repulsivesingle bidentate interaction Lewis is acid reduced as shown if L isin aFigure good 1.π Theacceptor large (Figure second 1c).proton The affinity two electron is a characteristic lone pairs featureof a carbone of carbones, may bindwhich to distinguishes one or two to onethemmonodentate or two from monodentate carbenes Lewis acids[16]. Lewis Ex A amplesor acidsprotons of A all or cases to protons a single are known or bidentate to a singleand areLewis bidentate described acid as Lewis shownbelow. acid in Figure as shown 1. in FigureThe1. Thelarge large second second proton proton affinity a ffi nityis a ischaracteristic a characteristic feature feature of carbones, of carbones, which which distinguishes distinguishes themthem from from carbenes carbenes [16]. [16]. Examples Examples of allof casesall cases are are known known and and are are described described below. below.
(a) (b)
(a) (b)
(c) (d)
Figure 1. Schematic representation(c) of the most important orbital(d) interactions between carbene
ligands CR2 and carbones CL2 with Lewis acids A.(a) Carbene complex with a monodentate Figure 1. Schematic representation of the most important orbital interactions between carbene ligands LewisFigure acid;1. Schematic (b) Carbone representation with a bidentate of the mostLewis impo acid;rtant (c) Carboneorbital interactions with a monodentate between carbene Lewis CR2 and carbones CL2 with Lewis acids A.(a) Carbene complex with a monodentate Lewis acid; acid;ligands (d ) CRCarbone2 and carboneswith two CLmonodentate2 with Lewis Lewis acids acids. A.(a ) Carbene complex with a monodentate (b) Carbone with a bidentate Lewis acid; (c) Carbone with a monodentate Lewis acid; (d) Carbone with Lewis acid; (b) Carbone with a bidentate Lewis acid; (c) Carbone with a monodentate Lewis two monodentate Lewis acids. Itacid; is important (d) Carbone to with realize two thatmonodentate the two electronLewis acids. lone-pairs of a carbone CL2 may additionally Itengage is important in π-backdonation to realize that to the the ligands two electron L whose lone-pairs strength of depends a carbone on CLthe availabilitymay additionally of vacant engage 2 in π-backdonationπ orbitalsIt is important of the to ligands the to ligands realize L. Stronger that L whose the π two acceptor strength electron ligands depends lone-pairs L enhance on theof a availabilitycarbone the π-backdonation CL2of may vacant additionally Lπ←orbitalsC→L of the ligandswhichengage leads L.in Strongerπ-backdonation to widerπ acceptorbending to the angles ligands ligands at LtheL enhancewhose carbon strength theatomπ -backdonation(Figure depends 2). on The the significant L availabilityC¯ L bending which of vacant leads of to freeπ orbitals C(CO) of2 [17,18]the ligands can straightforwardlyL. Stronger π acceptor be explained ligands L in enhance terms ofthe dative π-backdonation← bonding→ in L ←carbonC →L wider bending angles at the carbon atom (Figure2). The significant bending of free C(CO) 2 [17,18] suboxidewhich leads C3 Oto2 wider[19,20]. bending The π angles-acceptor at the strength carbon atomof ligands (Figure L 2).thus The modulatessignificant bendingthe donor of can straightforwardly be explained in terms of dative bonding in carbon suboxide C3O2 [19,20]. interactionfree C(CO) 2of [17,18] the carbone can straightforwardly CL2. be explained in terms of dative bonding in carbon The π-acceptor strength of ligands L thus modulates the donor interaction of the carbone CL2. suboxide C3O2 [19,20]. The π-acceptor strength of ligands L thus modulates the donor interaction of the carbone CL2.
Figure 2. Calculated and (in parentheses) experimental bond angles of carbones CL with different Figure 2. Calculated and (in parentheses) experimental bond angles of carbones2 CL2 with
ligandsdifferent L and ligands partial chargesL and partial∆q of charges the divalent Δq of the carbon divalent atom. carbon The dataatom. are The taken data from are taken [19]. from [19]. The followingFigure 2. Calculated list gives and some (in essentialparentheses) features experimental of carbones bond angles and theirof carbones differences CL2 with to carbenes. different ligands L and partial charges Δq of the divalent carbon atom. The data are taken from At the same time we want to stress that the distinction between carbenes and carbones are just a useful [19]. classification of compounds, which are a helpful model to explain the structures and reactivity of molecules. Nature does not exhibit a strict distinction line and there are complexes with electronic structures that have intermediate features between both classes of compounds. Carbenes and carbones are two ordering principles like ionic and covalent bonding. Intermediate cases are common and yet, the two concepts are essential ingredients of chemistry. The first part of this review summarizes experimental and theoretical work about transition metal complexes with carbone ligands [M]-CL2.
1. Carbones are neutral carbon(0) compounds of the general formula CL2, which possess two electron lone pairs of electrons of σ and π symmetry, respectively. 2. Carbones CL have dative σ bonds L C L and weaker π backdonation L C L which 2 → ← ← → resemble donor-acceptor bonds in transition metal complexes. Molecules 2020, 25, 4943 3 of 48
3. The carbon atom of carbones has very large electron densities and thus, unusually large negative partial charges. 4. In contrast to carbenes, carbones exhibit high first and second proton affinities (PAs) in the region of about 290 and 150–190 kcal/mol, respectively. The second PA is a sensitive probe for the divalent C(0) character of a CL2 molecule. Carbones can take up one and two protons with + 2+ formation of [HCL2] cations or [H2CL2] dications, respectively. 5. Carbones have a bent equilibrium geometry where the bending angle becomes wider when the ligand L is a better π acceptor. 6. Carbones can take up one or two monodentate Lewis acids A building the complexes A C(L ) ← 2 and A C(L ) A or one bidentate Lewis acid A⇔C(L ). ← 2 → 2 To the thematic of carbones several review articles were reported previously; A general overview on species that bear two lone pairs of electrons at the same C-center are summarized in [21], transition metal adducts of carbones are described in [22], and those of main group fragments in [23]. Two contributions, [24] and [25], in the series Structure and Bonding (Springer Edition) also deal with carbone transition metal addition compounds. The second type of transition metal complexes with a carbon ligand features species with a naked neutral carbon atom as a ligand [M]-C, which can be considered as endpoint of the series [M]-CR3 [M]-CR2 [M]-CR [M]-C. Complexes with negatively charged carbon - → → → ligands [M]-C− , which are isoelectronic to nitride complexes [M]-N and are termed as carbides, were synthesized in 1997 by Cummins [26]. The first neutral carbon complex [M]-C, which was prepared and structurally characterized was reported in 2002 by by Heppert and co-workers [27]. They isolated the diamagnetic 16 valence electron ruthenium complexes [(PCy3)LCl2Ru(C)] (L = PCy and 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene; Cy = Cyclohexyl) by a metathesis facilitated reaction. Quantum chemical calculations of model compounds suggested that the Ru-C bond in the complexes is best described by an electron-sharing double bond like in Schrock carbenes, which is reinforced by a donor bond [Ru]=→C| [28]. The field of neutral carbon complexes was systematically explored in recent years by Bendix [29]. This review summarizes in its second part the research in transition metal complexes with a naked carbon atom as ligand [M]-C that has been accomplished since 2002. The review includes some work on uranium and cerium complexes, but it does not present a complete coverage of actinide and lanthanide complexes with carbone or carbide ligands.
2. Transition Metal Complexes with Carbone Ligands [M]-CL2
2.1. Transition Metal Addition Compounds of Symmetrical Carbones C(PR3)2 Molecules 2020, 25, x FOR PEER REVIEW 4 of 54 Among the existing carbones with a symmetric P-C-P skeleton, five species (1a–1e) are known todayFrom as donorother ligandslinear or to variousbent carbones transition with metal this fragments skeleton, as no outlined transition in Figure metal3. Fromcomplexes other linearare ordescribed bent carbones so far. with this skeleton, no transition metal complexes are described so far.
Figure 3. Symmetric carbones 1a–1e as ligands for transition metal complexes. Figure 3. Symmetric carbones 1a–1e as ligands for transition metal complexes.
In 1961, 1a was detected by Ramirez [30], and 1b–1d stem from the laboratory of Schmidbaurs group [31]. Later on, a series of related carbones were synthesized, but for which transition metal complexes are unknown so far. Quite recently the new amino substituted carbone 1e was published together with Zn and Rh addition compounds (See Scheme 1) [32]. In the 31P NMR spectra singlets at about −4.50 (1a), −6.70 (1b), −29.6 (1c), −22.45 (1d), and 12.5 ppm (1e) confirm the symmetric array of the compounds. All carbones have a bent structure but a linear form of 1a is realized if crystallized from benzene [33,34]. 1a has a short P-C distance of 1.633(4) Å and the P-C-P angle amounts to 130.1(6)° [35]. The carbone 1b exhibits a slightly longer P-C distance of 1.648(4) Å and the introduction of two less bulky methyl groups allows a more acute P-C-P angle of 121.8(3)° [36]. 1d has similar P-C bond distances of 1.645(12) Å 1.653(14) Å and the acutest P-C-P angle in this series of 116.7(7)° [37,38]. For 1c, gas phase electron diffraction studies result in a P-C distance of 1.594(3) Å and a P-C-P angle of 147.6(5)° assuming an apparent non-linearity but linearity in the average structure [37]. All structural parameters of 1e are close to those of 1a (P-C = 1.632(2) Å, P-C-P angle = 136.5(3)° [32].
Molecules 2020, 25, x FOR PEER REVIEW 4 of 54
From other linear or bent carbones with this skeleton, no transition metal complexes are described so far.
Figure 3. Symmetric carbones 1a–1e as ligands for transition metal complexes. Molecules 2020, 25, 4943 4 of 48
In 1961, 1a was detected by Ramirez [30], and 1b–1d stem from the laboratory of SchmidbaursIn 1961, 1a wasgroup detected [31]. Later by Ramirezon, a series [30 ],of and related 1b–1d carbones stem from were the synthesized, laboratory but of Schmidbaurs for which grouptransition [31]. Latermetal on, complexes a series of are related unknown carbones so fa werer. Quite synthesized, recently butthe fornew which amino transition substituted metal complexescarbone 1e are was unknown published so far. together Quite with recently Zn and the newRh addition amino substitutedcompounds carbone (See Scheme1e was 1) published[32]. In togetherthe 31P with NMR Zn andspectra Rh additionsinglets compoundsat about −4.50 (See (1a Scheme), −6.701)[ (1b32),]. − In29.6 the (1c 31P), − NMR22.45 spectra(1d), and singlets 12.5 at aboutppm 4.50(1e) (confirm1a), 6.70 the (1b symmetric), 29.6 (1c array), 22.45 of the (1d ),compounds. and 12.5 ppm All ( 1ecarbones) confirm have the symmetrica bent structure array of − − − − thebut compounds. a linear form All carbonesof 1a is haverealized a bent if crystallized structure but from a linear benzene form [33,34]. of 1a is realized1a has a if short crystallized P-C fromdistance benzene of 1.633(4) [33,34]. Å1a andhas the a shortP-C-P P-Cangle distance amounts of to 1.633(4) 130.1(6)° Å and[35]. theThe P-C-P carbone angle 1b exhibits amounts a to 130.1(6)slightly◦ [35 longer]. The P-C carbone distance1b exhibits of 1.648(4) a slightly Å and longer the introduction P-C distance ofof two 1.648(4) less bulky Å and methyl the introduction groups of twoallows less a bulkymore acute methyl P-C-P groups angle allows of 121.8(3)° a more acute[36]. 1d P-C-P has similar angle of P-C 121.8(3) bond◦ distances[36]. 1d has of 1.645(12) similar P-C bondÅ 1.653(14) distances Å of and 1.645(12) the acutest Å 1.653(14) P-C-P Å angle and thein acutestthis series P-C-P of 116.7(7)° angle in this[37,38]. series For of 1c 116.7(7), gas phase◦ [37,38 ]. Forelectron1c, gas phasediffraction electron studies diffraction result studiesin a P-C result distance in a of P-C 1.594(3) distance Å ofand 1.594(3) a P-C-P Å andangle a P-C-Pof 147.6(5)° angle of 147.6(5)assuming◦ assuming an apparent an apparent non-linearity non-linearity but linearity but linearity in the in average the average structure structure [37]. [37 All]. Allstructural structural parametersparameters of 1eof 1eare are close close to thoseto those of 1aof (P-C1a (P-C= 1.632(2) = 1.632(2) Å, Å, P-C-P P-C-P angle angle= 136.5(3)= 136.5(3)°◦ [32 [32].].
Scheme 1. Selected transition metal compounds with the carbone 1a as two electron donor ligand; (a) MI, (b) CdI2,(c) UCl4,(d) Fe(N{SiMe3}2)2,(e) ZnI2. In Table1, transition metal addition compounds between carbones with the P-C-P core are collected. All compounds show longer P-C bonds than the basic carbones as consequence of the competition of the occupied p orbital at C(0) between the two P-σ* orbitals and those of A.
Table 1. Transition metal complexes with the carbones 1a to 1e including C-M and P-C bond lengths and P-C-P angles and 31PNMR shifts in ppm.
1-M 31P NMR C-M P-C P-C-P Ref Transition metal complexes with the carbone 1a 1a-Ni(CO)2 19.20 1.990(3) 1.677(3) 1.676(3) 132.13(16) [39] 1a-Ni(CO)3 9.92 2.110(3) 1.681(3) 1.674(3) 124.58(19) [39] 1a-ZnI2 17.8 2.000(9) 1.691(9) 1.703(8) 128.3(6) [40] 1a-CdI(µ I2)CdI-1a 18.5 2.25(1) 1.700(9) 1.68(1) 124.8(7) [40] [1a-Hg-1a][Hg2Cl6] 21.2 2.057(6) 2.082(7) 1.731(6) 1.706(6) 1.737(6) 1.702(7) 124.2(4) 125.7(3) [41] [1a-Ag-1a]I 13.6 2.115(8) 2.134(7) 1.656(7) 1.690(7) 1.667(7) 1.663(7) 128.5(5) 129.1(5) [42] [1a-Cu-1a]I 15.8 1.944(5) 1.951(5) 1.683(6) 1.688(6) 1.673(6) 1.694(5) 125.6(3) 128.3(3) [41] [1a-ReO3][ReO4] 29.5 1.997(7) 1.771(8) 123.1(4) [43] Molecules 2020, 25, 4943 5 of 48
Table 1. Cont.
1-M 31P NMR C-M P-C P-C-P Ref 1a-CuCl 16.5 1.906(2) nr 123.8(1) [44] 1a-Cu-C5H5 8.5 nr nr nr [45] 1a-Cu-C5Me5 7.5 1.922(6) 1.668(5) 1.660(6) 136.0(4) [45] 1a-CuPPh3 3.7 nr nr nr [45] 1a-AgCl 16.5 nr nr nr [44] 1a-AgCp* 6.5 nr nr nr [45] 1a-Au-C C-R ≡ nr 2.082(2) 1.688(2) 1.682(2) 133.64(13) [46] R = C6H4NO2-p 1a-Au-CH(COMe)2 nr nr nr nr [46] 1a-AuCl 13.7 14.4 nr nr nr [44] [1a-Ir(COD)]PF6 nr nr nr nr [47] 1a-VCl3 21.13 2.050(3) 1.712(2) 1.722(2) 123.6(2) [48] 1a-FeCl (µ Cl2)FeCl-1a par 2.043(7) 1.689(7) 1.712(7) 121.3(4) [49] 1a-Fe[N(SiMe3)2]2 par 2.147(2) 1.702(2) 1.720(2) 120.0(1) [50] 1a-FeCl2 par 2.055(8) 1.709(7) 1.702(7) 122.7(5) [49] 1a-Fe(CH2Ph)2 par 2.097(5) 1.694(5) 1.671(5) 124.5(3) [49] 1a-FeCl[N(TMS)2] par nr nr nr [49] 1a-FeOTf[N(TMS)2] par 2.040(3) 1.701(3) 1.704(3) 122.1(2) [49] 1a-UCl4 nr 2.411(3) 1.705(3) 1.719(3) 125.05(16) [51] 1a-(AuCl)2 21.2 2.078(3) 2.074(3) 1.776(3) 1.776(3) 117.30(15) [46] [1aH-Ag-1aH](BF4)3 23.6 2.221(5) 1.770(7) 1.779(7) 119.9(4) [52] [1aH-Au-1aH](OTf)3 26.1 nr nr nr [46] [1aH-AuCl](OTf) 22.1 nr nr nr [46] Transition metal complexes with the carbone 1b 1b-Fe[N(SiMe3)2]2 par 2.100(2) 1.694(2) 1.696(1) 120.8(9) [50] 1b-Ni(CO)3 2.6 2.091(2) 1.683(2) 1.673(2) 122.3(1) [53] 1b-Ni2(CO)5 12.1 2.080(5) 2.070(5) 1.742(5) 1.743(5) 117.1(3) [53] [1bH-AuC6F5](CF3SO3) 22.7 2.029(6) 1.781(2) 1.792(2) 119.1 [54] [1bH-AuCl](CF3SO3) 22.1 nr nr nr [54] Transition metal complexes with the carbone 1c [1c-W(CO)2(Tp*)]PF6 36 2.11(1) 1.75(2) 1.77(1) 114.5(8) [55] 1c-(AuMe)2 nr nr nr nr [56] Transition metal complexes with the carbone 1d 1d-Ni(CO)3 3.5 2.0661(9) 1.712(2) 1.722(2) 117.19(9) [48] Transition metal complexes with the carbone 1e Molecules 2020, 25, x FOR PEER REVIEW 6 of 54 1e-ZnCl2 28.9 1.994(2) 1.686(2) 125.3(1) [32] 1e-Rh(CO)(acac) 32.9 2.092(3) 1.685(3) 128.56(17) [32] 1e-Rh(CO)(acac) 32.9 2.092(3) 1.685(3) 128.56(17) [32]
OccupiedOccupied d d orbitals orbitals of of Ni Ni in in thethe 1a-Ni(CO)1a-Ni(CO)33 complex elongate elongate the the C-Ni C-Ni bond bond toto a carbone a carbone (2.110(2.110 Å) Å) [39 ][39] but but this this leads leads to a to relative a relative short short bond bond length length to a NHCto a NHC (1.971 (1.971 Å) moiety Å) moiety [57]. In [57]. contrast, In UClcontrast,4 leads toUCl a4 short leads bond to a short to a carbone bond to (2.411 a carbone Å) [51 (2.411] indicating Å) [51] anindicating appreciable an appreciable U-C double U-C bond characterdouble andbond a longcharacter one toand a NHC a long base one (2.612 to a NHC Å) [58 base,59]. (2.612 Å) [58,59]. + The cation [1a-ReO3] holds the longest one with 1.771(8) Å indicating an appreciable C=Re The cation [1a-ReO3]+ holds the longest one with 1.771(8) Å indicating an appreciable C=Re double bond character. This feature applies also in part to 1a-UCl4 and 1c-W(CO)2N3 with elongated P-Cdouble bonds(See bond Schemecharacter.2); This a partial feature C-U applies double also bond in part is confirmed to 1a-UCl by4 and theoretical 1c-W(CO) calculations.2N3 with elongated P-C bonds(See Scheme 2); a partial C-U double bond3+ is confirmed by theoretical Similar long P-C bonds are found in the trication [1aH-Ag-1aH] , in 1a-(AuCl)2(See Scheme3), calculations. Similar long P-C bonds are found in the trication [1aH-Ag-1aH]3+, in and in 1b-Ni2(CO)5(See Scheme4), where the carbone provides each two electrons to two accepting Lewis1a-(AuCl) acids as2(See depicted Scheme in 3), Figure and1 ind. 1b-Ni2(CO)5(See Scheme 4), where the carbone provides each two electrons to two accepting Lewis acids as depicted in Figure 1d.
Scheme 2. Transition metal complex with the carbone 1c as two and four electron donor ligand. Scheme 2. Transition metal+ complex with the carbone 1c as two and four electron donor ligand. (a) [Tp*(CO)2W CPMe3] /PMe3,(b) 1c/2 MeAuPMe3. (a) [Tp*(CO)2≡W≡CPMe3]+/PMe3, (b) 1c/2 MeAuPMe3.
Scheme 3. Selected transition metal compounds with the carbone 1a as four electron donor ligand.
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1e-Rh(CO)(acac) 32.9 2.092(3) 1.685(3) 128.56(17) [32]
Occupied d orbitals of Ni in the 1a-Ni(CO)3 complex elongate the C-Ni bond to a carbone (2.110 Å) [39] but this leads to a relative short bond length to a NHC (1.971 Å) moiety [57]. In contrast, UCl4 leads to a short bond to a carbone (2.411 Å) [51] indicating an appreciable U-C double bond character and a long one to a NHC base (2.612 Å) [58,59].
The cation [1a-ReO3]+ holds the longest one with 1.771(8) Å indicating an appreciable C=Re double bond character. This feature applies also in part to 1a-UCl4 and 1c-W(CO)2N3 with elongated P-C bonds(See Scheme 2); a partial C-U double bond is confirmed by theoretical calculations. Similar long P-C bonds are found in the trication [1aH-Ag-1aH]3+, in 1a-(AuCl)2(See Scheme 3), and in 1b-Ni2(CO)5(See Scheme 4), where the carbone provides each two electrons to two accepting Lewis acids as depicted in Figure 1d.
Scheme 2. Transition metal complex with the carbone 1c as two and four electron donor ligand. Molecules 2020, 25, 4943 6 of 48 (a) [Tp*(CO)2W≡CPMe3]+/PMe3, (b) 1c/2 MeAuPMe3.
MoleculesScheme 2020 3., 25Selected, x FOR PEER transition REVIEW metal compounds with the carbone 1a as four electron donor ligand. 7 of 54 Scheme 3. Selected transition metal compounds with the carbone 1a as four electron donor ligand.
Scheme 4. Selected transition metal complexes with the carbone 1b as two and four electron donor Scheme 4. Selected transition metal complexes with the carbone 1b as two and four electron ligand. (a) Ni(CO)4,(b) Ni(CO)4 under CO atm, (c) Fe(N{SiMe3}2)2,(d) AuX(tht). donor ligand. (a) Ni(CO)4, (b) Ni(CO)4 under CO atm, (c) Fe(N{SiMe3}2)2, (d) AuX(tht). The P-C-P angles are in the range between 115 and 132 reflecting the required space of the The P-C-P angles are in the range between 115°◦ and 132°◦ reflecting the required space of appropriate Lewis acid. The 31P NMR shift of the carbone 1a amounts to about 5 ppm and those the appropriate Lewis acid. The 31P NMR shift of the carbone 1a amounts to about− −5 ppm and of the related addition compounds are shifted to lower fields and range between 4 ppm and 30 ppm. those of the related addition compounds are shifted to lower fields and range between 4 ppm All iron(II) complexes of 1a and 1b are paramagnetic and 31P NMR spectra could not be obtained. and 30 ppm. All iron(II) complexes of 1a and 1b are paramagnetic and 31P NMR spectra could For the 31P NMR spectrum of the carbone 1b, a shift of 6.70 ppm was recorded [31]. With exception not be obtained. − of 1b-Ni(CO) which resonate at 2.6 ppm, low field shifts between 12 and 22 ppm were found when 1b For the3 31P NMR spectrum of the carbone 1b, a shift of −6.70 ppm was recorded [31]. With act as a four electron donor [40]. exception of 1b-Ni(CO)3 which resonate at 2.6 ppm, low field shifts between 12 and 22 ppm Further, 1e-ZnCl (See Scheme5)[ 32] and 1a-ZnI [53] have closely related structural parameters were found when 1b2 act as a four electron donor [40].2 but exhibit shorter C-Zn bond lengths than to related NHC-addition compounds (∆ = 0.051 Å) [60]. Further, 1e-ZnCl2 (See Scheme 5) [32] and 1a-ZnI2 [53] have closely related structural In both compounds a nearly perpendicular array of the ZnX and the PCP plane are found. No tendency parameters but exhibit shorter C-Zn bond lengths than 2to related NHC-addition compounds (Δ for an additional N-coordination to the amino ligand of 1e is recorded for the ZnCl2 addition compound. = 0.051 Å) [60]. In both compounds a nearly perpendicular array of the ZnX2 and the PCP plane In contrast the Rh-C distances in 1e-Rh(CO) (acac) are longer (∆ = 0.117 Å) than in the corresponding are found. No tendency for an additional2 N-coordination to the amino ligand of 1e is recorded for the ZnCl2 addition compound. In contrast the Rh-C distances in 1e-Rh(CO)2(acac) are longer (Δ = 0.117 Å) than in the corresponding NHC compound [61] and a partial π interaction was found by DFT calculation. Rh also shows no tendency for coordination of the adjacent amino groups [32].
Scheme 5. Selected transition metal complex with the carbone 1e as two electron donor ligand.
Molecules 2020, 25, x FOR PEER REVIEW 7 of 54
Scheme 4. Selected transition metal complexes with the carbone 1b as two and four electron
donor ligand. (a) Ni(CO)4, (b) Ni(CO)4 under CO atm, (c) Fe(N{SiMe3}2)2, (d) AuX(tht).
The P-C-P angles are in the range between 115° and 132° reflecting the required space of the appropriate Lewis acid. The 31P NMR shift of the carbone 1a amounts to about −5 ppm and those of the related addition compounds are shifted to lower fields and range between 4 ppm and 30 ppm. All iron(II) complexes of 1a and 1b are paramagnetic and 31P NMR spectra could not be obtained. For the 31P NMR spectrum of the carbone 1b, a shift of −6.70 ppm was recorded [31]. With exception of 1b-Ni(CO)3 which resonate at 2.6 ppm, low field shifts between 12 and 22 ppm were found when 1b act as a four electron donor [40]. Further, 1e-ZnCl2 (See Scheme 5) [32] and 1a-ZnI2 [53] have closely related structural parameters but exhibit shorter C-Zn bond lengths than to related NHC-addition compounds (Δ = 0.051 Å) [60]. In both compounds a nearly perpendicular array of the ZnX2 and the PCP plane Moleculesare2020 found., 25, 4943No tendency for an additional N-coordination to the amino ligand of 1e is recorded7 of 48 for the ZnCl2 addition compound. In contrast the Rh-C distances in 1e-Rh(CO)2(acac) are longer (Δ = 0.117 Å) than in the corresponding NHC compound [61] and a partial π interaction was π NHCfound compound by DFT [61 calculation.] and a partial Rh alsointeraction shows no te wasndency found for bycoordination DFT calculation. of the adjacent Rh also amino shows no tendencygroups for [32]. coordination of the adjacent amino groups [32].
Molecules 2020, 25, x FOR PEER REVIEW 8 of 54 Scheme 5. Selected transition metal complex with the carbone 1e as two electron donor ligand. Scheme 5. Selected transition metal complex with the carbone 1e as two electron donor ligand. 2.2. Transition Metal Addition Compounds of Carbones C(PR3)2 with an Additional Pincer Function 2.2. Transition Metal Addition Compounds of Carbones C(PR3)2 with an Additional Pincer Function Starting material for 2a is not the free carbone Ph2P-CH2-PPh2-C-PPh2-CH2-PPh2, which Starting material for 2a is not the free carbone Ph2P-CH2-PPh2-C-PPh2-CH2-PPh2, which could could not be prepared so far, but the dication [Ph2P-CH2-PPh2-CH2-PPh2-CH2-PPh2]2+ as not be prepared so far, but the dication [Ph P-CH -PPh -CH -PPh -CH -PPh ]2+ as reported reported by Peringer [62]. Later on, Sundermeyer2 2studied2 the2 deprotonation2 2 2of the cation by Peringer [62]. Later on, Sundermeyer studied the deprotonation of the cation [Ph P-CH - [Ph2P-CH2-PPh2-CH-PPh2-CH2-PPh2]+ by quantum chemical methods giving more or less stable2 2 + PPhtautomers2-CH-PPh 2of-CH 2a2, -PPhsee Figure2] by 4. quantum Deprotonation chemical of methodsthe tautomer giving C of more 2a generates or less stable the anionic tautomers of 2apincer, see Figureligand4 [Ph. Deprotonation2P-CH-PPh2-CH-PPh of the2-CH-PPh tautomer2]− C[2c] of− [63].2a generates The same the working anionic group pincer also ligand [Ph2publishedP-CH-PPh the2-CH-PPh X-ray structure2-CH-PPh of2 ]the− [ 2c]pincer− [63 ligand]. The same2b with working the P-C-P group angle also of published 133.76(13)° the and X-ray structureP-C distances of the pincer of 1.633(2) ligand and2b with1.642(2) the Å; P-C-P the 31 angleP NMR of 133.76(13)shift δ = −5.6◦ and ppm P-C [64]. distances of 1.633(2) and 31 1.642(2) Å;Various the Pcationic NMR shiftcomplexesδ = 5.6 where ppm re [64ported]. with the pincer ligand 2a (See Figure 4) and − groupVarious 10 cationicmetal halides complexes and one where dicati reportedon with withthe group the pincer 11 metal ligand Au.2a The(See 31P Figure NMR4 shifts) and range group 10 metalbetween halides 32 and and one 41 dicationppm(See with Table the 2). group As with 11 metal1a the Au.carbone The 31carbonP NMR atom shifts of 2a range is basic between enough 32 and 41 ppm(Seeto accept Table a proton2). As to with generate1a the complexes carbone carbon of the atomtype of2aH2a-MClis basic dications enough with to accept all group a proton 10 to generateelements complexes (See Scheme of the 6). type 2aH-MCl dications with all group 10 elements (See Scheme6).
Figure 4. Tripodal basic pincer ligand 2a with its tautomers, the anionic pincer ligand 2cH and the Figure 4. Tripodal basic pincer ligand 2a with its tautomers, the anionic pincer ligand 2cH−- and pyridyl pincer ligand 2b. the pyridyl pincer ligand 2b.
Table 2. Transition metal complexes with the phosphine based pincer ligands 2a and the pyridyl based pincer ligand 2b; C-M and P-C distances are included and 31P NMR shifts in ppm.
31P C-M P-C P-C-P Ref NMR Transition metal complexes with the tripodal carbone 2a [2a-(PdCl)]Cl 34.5 2.062(2) 1.694(3) 124.9(2) [62,65] [2a-(NiCl)]Cl 36.4 1.942(4) 1.6925(18) 125.1(2) [65] [2a-(NiCl)]2NiCl4 nr 1.930(7) 1.696(7) 1.701(7) 126.3(4) [65] [2a-(PtCl)]Cl 35.7 2.060(4) 1.692(5) 124.86(15) [65] [2a-(NiMe)][AlCl2Me2] 31.8 1.959 1.697 120.9 [66] [2a-(AuCl)]TfO2 nr 2.080(8) 1.723(8) 124.5(5) [67] [2a-(AuCl)](NO3)2 40.8 2.060(3) 1.721(3) 125.1(2) [67] [2a-(AuI)](TfO)2 41.1 2.082(8) 1.723(8) 124.9(5) [67]
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Table 2. Transition metal complexes with the phosphine based pincer ligands 2a and the pyridyl based pincer ligand 2b; C-M and P-C distances are included and 31P NMR shifts in ppm.
31P NMR C-M P-C P-C-P Ref Transition metal complexes with the tripodal carbone 2a [2a-(PdCl)]Cl 34.5 2.062(2) 1.694(3) 124.9(2) [62,65] [2a-(NiCl)]Cl 36.4 1.942(4) 1.6925(18) 125.1(2) [65] [2a-(NiCl)]2NiCl4 nr 1.930(7) 1.696(7) 1.701(7) 126.3(4) [65] [2a-(PtCl)]Cl 35.7 2.060(4) 1.692(5) 124.86(15) [65] [2a-(NiMe)][AlCl2Me2] 31.8 1.959 1.697 120.9 [66] [2a-(AuCl)]TfO2 nr 2.080(8) 1.723(8) 124.5(5) [67] [2a-(AuCl)](NO3)2 40.8 2.060(3) 1.721(3) 125.1(2) [67] [2a-(AuI)](TfO)2 41.1 2.082(8) 1.723(8) 124.9(5) [67] [2aH-PdCl]Cl2 42.4 2.102(3) 1.803(3) 121.9(2) [62] [2aH-PtCl]Cl2 44.4 2.106(4) 1.811(4) 1.823(4) 120.4(2) [62] [2aH-NiCl]Cl2 32.7 1.990 1.801–1.834 121.1 [65,66] [2aH-(CuCl)]PF6 nr 2.304(2) 1.745(2) 125.26(14) [63] 2a-(CuCl)2 20.4 2.2041 1.718 122.86(14) [63] 2a-(CuI)2 22.5 2.4936 1.717 126.3(4) [63] 2a-(CuSPh)2 19.8–19.0 2.195 1.712 126.9(7) [63] Transition metal complexes with the tripodal carbone 2b 2b-(CeBr THF) 10.2 2.597(6) 1.672(6) 122.5(4) [68] 3 − 2b-(CeBr)-2b nr 2.573(6) 2.597(6) 1.684(7) 120.5(4) [68] 2b-(UCl4) nr 2.471(7) 1.696(7) 121.3(4) [41] 2b-(TiCl3)[57] 18.24 2.144(6) 1.670(3) 1.670(3) 129.9(4) [64] 2b-(Cr(CO)3) 6.97 2.212(2) 1.651(3) 1.650(3) 133.6(2) [64] 2b-(MnCl2) par 2.1843(14) 1.6671(17) 1.6636(17) 127.70(9) [64] 2b-(CoCl2) par 2.015(6) 1.680(7) 1.661(7) 127.5(3) [64] 2b-[Mo2(CO)7] 9.49 2.355(4) 1.722(4) 1.724(4) 120.4(2) [64] [2b-(PdCl)]Cl 31.6 2.004(4) 1.689(4) 1.676(4) 132.4 [64] 2b-[Ni2(CO)4] 34.20 2.0635(18) 1.7142(18) nr [64] 2.0912(18) 1.7146(18) 2b-(Cu2Cl2) 21.4 nr 1.714(3) 121.51(14) [63] 1.718(2) 2b-(Cu2I2) 21.5 nr 1.679(5) 128.5(3) [63] 1.702(5) [2b-Cu2(PPh3)2](PF6)2 32.9 nr 1.709(10) 126.8(6) [63] 1.693(9) 2b-Cu2(PC6H4OMe)2](PF6)2 32.8 nr 1.707(3) 123.64(18) [63] 1.710(3) [2b-Cu2(DPEPhos)](PF6)2 29.7 nr 1.710(4) 124.0(2) [63] [2b-Cu2(XantPhos)](PF6)2 34.9 nr 1.712(4) 1.7064(19) 122.10(11) [63] [2b-Cu2(dppf)](PF6)2 36.5 nr 1.7211(18) 1.730(6) 121.8(4) [63] 2b-Cu2(SC6F5)2 23.1 nr 1.717(6) 1.710(3) 123.70(17) [63] 1.710(3) 2b-Cu2(Carb)2 22.8 nr 1.726(2) 120.45(15) [63] 1.728(2) Transition metal complex with 2cH 23.6 2.196(3) 1.761(3) 124.26(17) [63] 2cH-(CuPPh ) 3 1.777(3) Molecules 2020, 25, 4943 9 of 48 Molecules 2020, 25, x FOR PEER REVIEW 10 of 54
Scheme 6. Selected compounds with the pincer ligands 2a and 2aH. (a) MCl with a mixture of dppm Scheme 6. Selected compounds with the pincer ligands 2a and 2aH. (a) MCl2 2 with a mixture of and 2 eq. of CS ,(b) AuCl(tht)/HNO ,(c) HCl. (d) two eq. of CuX. (e) 2 nBuLi, [Cu(NCMe) ]PF /PPh . dppm and 22 eq. of CS2, (b) AuCl(tht)/HNO3 3, (c) HCl. (d) two eq. of CuX. (e) 42 nBuLi,6 3
[Cu(NCMe)4]PF6/PPh3. A series of complexes with the N,C,N pincer ligand sym-bis(2-pyridyl) tetraphenylcarbodiphosphorane (2b) were reported recently by the group of Sundermeyer. A series of complexes with the N,C,N pincer ligand Remarkable is the molybdenum complex 2b-[Mo (CO) ] in which 2b provides four pairs of electrons sym-bis(2-pyridyl)tetraphenylcarbodiphosphorane2 (72b) were reported recently by the group of for donation to a Mo2 unit with an Mo-Mo separation of 3.0456(5) Å [64]. This coordination mode is Sundermeyer. Remarkable is the molybdenum complex 2b-[Mo2(CO)7] in which 2b provides continued in a series of dicopper complexes presented by the same working group and prepared four pairs of electrons for donation to a Mo2 unit with an Mo-Mo separation of 3.0456(5) Å [64]. as depicted in Scheme7. The addition of [Cu]PF to 2b followed by treatment with two eq. of PR This coordination mode is continued in a series6 of dicopper complexes presented by the same 3 generated the cationic complexes [2b-(CuPPh3)](PF6)2 and [2b-(CuP{C6H4OMe}3](PF6)2, respectively; 6 working group and prepared as depicted in Scheme 7. The addition tof [Cu]PF to 2b followed 2b-(CuCarb)2 was obtained from 2b-(CuCl)2 and two eq. of CarbH/NaO Bu (CarbH = carbazol) [63]. by treatment with two eq. of PR3 generated the cationic complexes [2b-(CuPPh3)](PF6)2 and [2b-(CuP{C6H4OMe}3](PF6)2, respectively; 2b-(CuCarb)2 was obtained from 2b-(CuCl)2 and two eq. of CarbH/NaOtBu (CarbH = carbazol) [63].
Molecules 2020, 25, 4943 10 of 48 Molecules 2020, 25, x FOR PEER REVIEW 11 of 54
Scheme 7. Selected compounds with the pincer ligand 2b as two and four electron donor. (a) CeBr3 Scheme 7. Selected compounds with the pincer ligand 2b as two and four electron donor. (a) in THF, (b) UCl4,(c) 2 eq. of Mo(CO)3(NCMe)3,(d) 2 eq. of Ni(CO)4,(e) 2 eq. of CuX, (f) 2 eq. of CeBr3 in THF, (b) UCl4, (c) 2 eq. of Mo(CO)3(NCMe)3, (d) 2 eq. of Ni(CO)4, (e) 2 eq. of CuX, (f) 2 [Cu]PF6/1 eq. of P-P. eq. of [Cu]PF6/1 eq. of P-P. 2+ For the cationic complexes [2b-Cu2(P-P)] the chelating ligands are: DPEPhos = bis[(2- diphenylphosphino)phenyl]For the cationic complexes ether, XantPhos [2b-Cu2(P-P)]= 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene,2+ the chelating ligands are: DPEPhos = dppfbis[(2-diphenylphosphino)phe= 1,10-bis(diphenyl-phosphino)ferrocenenyl] . Theether, germinal nature of bothXantPhos Cu(I) centers leads= to Cu-Cu4,5-bis(diphenylphosphino)-9,9 distances in the range of 2.55–2.67-dimethylxanthene, Å. Most of the Cu(I) complexes showdppf photoluminescence upon= irradiation1,10-bis(diphenyl-phosphino)ferrocene. with UV light at room temperature The [63 ].germinal nature of both Cu(I) centers leads to Cu-Cu distances in the range of 2.55–2.67 Å. Most of the Cu(I) complexes show Further, 2cH-CuPPh3 is an example of a complex with a deprotonated form of 2a and longer P-C distancesphotoluminescence are observed upon due to irradiation the protonation with UV of thelight central at room carbon temperature atom [63 [63].].
3 2.3. TransitionFurther, Metal 2cH Addition-CuPPh Compoundsis an example of Carbones of a complex C(PR3)2 with ana Additionaldeprotonated Ortho form Metallated of 2a and Pincerlonger Function P-C distances are observed due to the protonation of the central carbon atom [63].
The source for the Rh complex 3a-Rh(PMe3)2H was the half pincer compound 5a-Rh(C6H8) 2.3. Transition Metal Addition Compounds of Carbones C(PR3)2 with an Additional Ortho Metallated (vide infra) upon reacting with PMe under loss of cod (see Scheme8). 3a-Pt(SMe ) forms upon Pincer Function 3 2 reacting 1a with [Me2Pt(SMe2)]2 and loss of 4 molecules of CH4 [69]. PEt3 replaces the labile bonded SMe2 groupThe source of 3a-Pt(SMe for the2 )Rh to complex produce 3a3a--PtEtRh(PMe3, which3)2H was is transformed the half pincer with compound P(OPh)3 into 5a-Rh(C3a-Pt(OPh)6H8) 3. 2+ The(vide dication infra)[ 3aupon-PtPEt reacting3(µ-Ag with2)Et 3PMePPt-33a under] was loss obtainedof cod (see upon Scheme addition 8). 3a-Pt(SMe of AgOTf2) forms to 3a -PtPEtupon 3. Accordingreacting to1a the with carbone [Me2Pt(SMe C atom2)] as2 and four loss electron of 4 donormolecules the Pt of complexes CH4 [69]. withPEt3 µreplaces-Ag functions the labile show longbonded Pt-C distances SMe2 group between of 3a-Pt(SMe 1.737 and2) to 1.749 produce Å (mean 3a-PtEt values)3, which and theis transformed31PNMR shifts with are P(OPh) in the3 narrow into range3a-Pt(OPh) of 33 and3. 36The ppm dication (See Table [3a-3PtPEt)[ 703].(μ More-Ag2)Et complicated3PPt-3a]2+ iswas the obtained formation upon of 3a addition-Pt(CO), whichof AgOTf stems fromto the3a-PtPEt hydrolysis3. According of the relatedto the 3acarbone-Pt(CCl C2 )atom complex as four (not electron isolated) donor [71]. the Pt complexes with μ-Ag functions show long Pt-C distances between 1.737 and 1.749 Å (mean values) and the
Molecules 2020, 25, x FOR PEER REVIEW 12 of 54
31PNMR shifts are in the narrow range of 33 and 36 ppm (See Table 3) [70]. More complicated is Molecules 2020, 25, 4943 11 of 48 the formation of 3a-Pt(CO), which stems from the hydrolysis of the related 3a-Pt(CCl2) complex (not isolated) [71].
SchemeScheme 8. 8.Selected Selected addition addition compounds compounds withwith thethe pincer ligand 3a 3a and and 3aH 3aH and and those those with with the the Ag-bridged cations or dication, respectively. (a) from 3aH-PtCl via 3a-Pt(CCl ) and H O, (b) PMe , Ag-bridged cations or dication, respectively. (a) from 3aH-PtCl via 3a-Pt(CCl2 2) and2 H2O, (b) 3 (c) from 5a-Pt(C H ) (see Scheme 11) and CHCl , (d) PPh , (e) 2 AgOTf. PMe3, (c) from8 5a11-Pt(C8H11) (see Scheme 11) and3 CHCl33, (d) PPh3, (e) 2 AgOTf. Table 3. Transition metal complexes with ortho metallated tripodal pincer ligand 3a derived from 1a andTable the related 3. Transition pincer ligand metal 3bcomplexesand 31P NMRwith orth shifts.o metallated tripodal pincer ligand 3a derived from 1a and the related pincer ligand 3b and 31P NMR shifts. 3-M 31P NMR C-M P-C P-C-P Ref 3-M 31P NMR C-M P-C P-C-P Ref TransitionTransition metal metal complexes complexes withwith the tripodal tripodal ligand ligand 3a 3a 3a3a--Rh(PMeRh(PMe3)32)H2H 8.56 8.56 2.203(3) 2.203(3) 1.674(3) 1.674(3) 138.32(18) 138.32(18) [69] [69] 3a3a--PtSMePtSMe2 2 30.4230.42 nr nrnr nrnr nr[69] [69] 3a-3a-PtCOPtCO 41.5 41.5 2.037(5) 2.037(5) 1.706(3) 1.706(3) 128.4(3) 128.4(3) [71][71] 3a3a--PtPEtPtPEt3 3 28.528.5 2.067(2) 2.067(2) 1.697(2) 1.697(2) 124.88(14) 124.88(14) [70] [70] 3a3a--PtP(OPh)PtP(OPh)3 3 nrnr nr nrnr nrnr nr[70] [70] [3a[3a--PtPEtPtPEt33(μµ-AgPPh-AgPPh3)33](OTf))3](OTf) 32.5 32.5 2.130(4) 2.130(4) 1.737 1.737 126.0(2) 126.0(2) [70] [70] [3a[3a--PtP(OPh)PtP(OPh)33((μµ-AgPEt-AgPEt3](OTf)3](OTf) 36.0 36.0 2.105(3) 2.105(3) 1.743 1.743 122.9(2) 122.9(2) [70] [70] [[3a3a--PtPEtPtPEt33(μ(µ-Ag-Ag2)Et2)Et3PPt-3PPt-3a](OTf)3a](OTf)2 2 33.433.4 2.128(3) 2.128(3) 1.749 1.749 125.29(18) 125.29(18) [70] [70] 3aH-3aH-PtClPtCl 27.9 27.9 2.077(6) 2.077(6) 1.796(6) 1.796(6) 123.4(4) 123.4(4) [71][71] TransitionTransition metal metal complexes complexes withwith the tripodal tripodal ligand ligand 3b 3b 3b-Pt(CO) 46.9 2.002(5) nr 133.3(3) [72] Molecules 2020, 25, x FOR PEER REVIEW 13 of 54
Molecules 20203b-, 25Pt(CO), x FOR PEER REVIEW 46.9 2.002(5) nr 133.3(3) [72] 13 of 54 Molecules 2020, 25, 4943 12 of 48
The carbone3b-Pt(CO) complex 3b-Pt(CO)46.9 was obtained2.002(5) from reactingnr the yldiide133.3(3) platinum complex[72] (see Scheme 9) with 1 atm CO that inserts into the N-Si bond of the yldiide. TheThe carbone carbone complex complex3b 3b-Pt(CO)-Pt(CO) was was obtainedobtained from reacting reacting the the yldiide yldiide platinum platinum complex complex (see(see Scheme Scheme9) with 9) with 1 atm 1 atm CO CO that that inserts inserts into into the the N-Si N-Si bond bond of the of the yldiide. yldiide.
Scheme 9. Two mesomeric forms of 3b-Pt(CO); 3ba favors a tricarbene coordination at Pt(0) Schemewhereas 9. Two 3bb mesomeric is consistent forms Pt(II) of 3bforming-Pt(CO); two3ba C-Ptfavors s-bonds a tricarbene similar coordination to 3a-Pt(CO). at Pt(0)The whereasshort Scheme 9. Two mesomeric forms of 3b-Pt(CO); 3ba favors a tricarbene coordination at Pt(0) 3bbcentralis consistent C-Pt bond Pt(II) length forming of 2.002 two C-PtÅ indicates s-bonds a similarpartial doubly to 3a-Pt(CO). donation The of short the carbone central C-PtC atom bond whereas 3bb is consistent Pt(II) forming two C-Pt s-bonds similar to 3a-Pt(CO). The short lengthas shown of 2.002 in Figure Å indicates 5. The a planar partial environment doubly donation at Pt ofis typical the carbone for Pt(II) C atom and assupports shown this in Figure view 5. central C-Pt bond length of 2.002 Å indicates a partial doubly donation of the carbone C atom The[72]. planar environment at Pt is typical for Pt(II) and supports this view [72]. as shown in Figure 5. The planar environment at Pt is typical for Pt(II) and supports this view [72]. Ph2 Ph2 Ph2 Ph2 P P P P C Ph2 C Ph2 N Ph2 Ph2N P P P P MC CN MC CN
Me3SiO OSiMe3 M C M C 3a Me3SiO 3b OSiMe3 Figure 5. Bis-ortho metallated pincer complexes 3a and 3b. Figure3a 5. Bis-ortho metallated pincer complexes 3a3b and 3b. 2.4. Transition Metal Complexes with P-C-P Five Membered Ring 2.4. Transition Metal ComplexesFigure 5. Bis-ortho with P-C-P metallated Five Membered pincer complexes Ring 3a and 3b. The carbone 4 (see Figure6) was obtained by deprotonation of the cation [ 4H]+. According to two + P atoms2.4. TransitionThe in di carbonefferent Metal chemical4 (see Complexes Figure environments wi6) thwas P-C-P obtained twoFive doubletsMembered by deprotonation in Ring the 31 P NMRof thespectrum cation [4H] were. According recorded at 31 δ to two P atoms in different2 chemical environments two doublets in the P NMR spectrum were = 60.0Theand carbone 71.5 ppm; 4 (seeJPP Figure= 153 Hz.6) was From obtained X-ray determinationby deprotonation stem of the the P-C(1) cation and [4H] P-C(2)+. According distances recorded at δ = 60.0 and 71.5 ppm; 2JPP = 153 Hz. From X-ray determination stem the P-C(1) and of 1.644(19) and 1.657(17) Å, respectively, and the P-C-P angle amounts to31 104.82(10)◦ [73]. The bond P-C(2)to two Pdistances atoms in ofdifferent 1.644(19) chemical and 1.657(17) environments Å, respectively, two doublets and in the the P-C-P P NMR angle spectrum amounts were to lengths (see Table 4) are close to that reported2 for the carbone 1a. 104.82(10)°recorded at [73].δ = 60.0 The and bond 71.5 lengths ppm; (seeJPP =Table 153 Hz. 4) are From close X-ray to that determination reported for stem the carbonethe P-C(1) 1a .and P-C(2) distances of 1.644(19) and 1.657(17) Å, respectively, and the P-C-P angle amounts to 104.82(10)° [73]. The bond lengths (see Table 4) are close to that reported for the carbone 1a.
Molecules 2020, 25, 4943 13 of 48 Molecules 2020,, 25,, xx FORFOR PEERPEER REVIEWREVIEW 14 of 54
Figure 6. Structure of compound 4. Figure 6. Structure of compound 4.4. Table 4. Transition metal complexes with the cyclic carbone 4, containing 31P NMR shifts and relevant Table 4. Transition metal complexes with the cyclic carbone 4, containing 3131P NMR shifts and structuralTable 4. parameters. Transition metal complexes with the cyclic carbone 4, containing P NMR shifts and relevant structural parameters. 4-M 31P NMR M-C P1-C P2-C P-C-P Ref 4-M 3131P NMR M-C P11-C-C PP22-C-C P-C-PP-C-P RefRef 4-PdCl(π-C3H5) 61.2 71.9 (225) 2.120(2) 1.673(2) 1.694(2) 106.66(13) [73] 4-PdCl(π-C-C33H55)) 61.2 71.9 (225) 2.120(2) 1.673(2) 1.694(2) 106.66(13) [73] 4-RhCl(nbd) 64.6 75.7 (230) 2.115(18) 1.676(18) 1.702(18) 106.86(10) [73] 4-RhCl(nbd) 64.6 75.7 (230) 2.115(18) 1.676(18) 1.702(18) 106.86(10) [73] 4-Rh(CO)2Cl 68.2 75.6 (224) nr nr nr [73] 4-Rh(CO)2Cl 68.2 75.6 (224) nr nr nr [73] 4-AuOBut4-Rh(CO)2Cl 64.168.2 60.4 75.6 (225) (224) 2.018(6) nr 1.674(7) nr 1.687(7) 108.5(4) nr [73] [ 74] 4-AuOButt 64.1 60.4 (225) 2.018(6) 1.674(7) 1.687(7) 108.5(4) [74] 4-CuOBut4-AuOBu 69.864.1 62.6 60.4 (195) (225) 1.8923(15) 2.018(6) 1.6763(15) 1.674(7) 1.687(7) 1.6887(15) 108.5(4) 106.90(8) [74] [ 74] t 4-4-CuClCuOBut 63.269.8 70.6 62.6 (186) (195) 1.8914(19) 1.8923(15) 1.6763(15) 1.6700(19) 1.6887(15) 1.6869(19) 106.90(8) 107.20(11) [74] [ 74] 4-CuCl 63.2 70.6 (186) 1.8914(19) 1.6700(19) 1.6869(19) 107.20(11) [74]
FromFrom the the cyclic cyclic and and asymmetric asymmetric carbone carbone4 six4 sixsix transition transitiontransition metal metalmetal complexes complexescomplexes (see (see(see Scheme SchemeScheme 10 10)10)) are knownare known in which in which the ligand the ligand acts as twoacts electronas two electron donor via donor the Cvia atom. the C As atom. in the As starting in the compoundstarting compound2 4 the P22-C bond distances are slightly longer1 than P11-C bond. Addition of CuCl and 4 thecompound P -C bond 4 the distances P -C bond are distances slightly longerare slightly than longer P -C bond. than P Addition-C bond. of Addition CuCl and of CuCl AuCl(SMe and 2) AuCl(SMe+ 2) to 4H++/tBuOK generates the compounds 4-CuOtBu and 4-AuOtBu, respectively. In to AuCl(SMe4H /tBuOK2) to generates 4H /tBuOK the generates compounds the compounds4-CuOtBu and 4-CuO4-AuOtBu andtBu, 4 respectively.-AuOtBu, respectively. In CH3Cl In2 or CH3Cl2 or CHCl3 4-CuOtBu is converted into 4-CuCl [74]. 4-Rh(CO)2Cl stems from the reaction CHClCH3Cl4-CuO2 or CHCltBu3 is 4- convertedCuOtBu is intoconverted4-CuCl into [74 4].-CuCl4-Rh(CO) [74]. 42-Rh(CO)Cl stems2Cl from stems the from reaction the reaction of 4 with of 4 with [{RhCl(CO)2}2] [73]. 4-CuOtBu and 4-AuOtBu catalyze the hydroamination or [{RhCl(CO)of 4 with2} 2[{RhCl(CO)][73]. 4-CuO2}2t]Bu [73]. and 44-CuO-AuOttBuBu catalyzeand 4-AuO thet hydroaminationBu catalyze the orhydroamination hydroalkoxylation or of acrylonitrilehydroalkoxylation [74]. of acrylonitrile [74].
i Scheme 10. Selected complexes with the cyclic carbone 4.R = Pr. a) [{PdCl(allyl)}2], b) [{RhCl(nbd)}2]. i Scheme 10. Selected complexes with the cyclic carbone 4.. RR == iPr. a) [{PdCl(allyl)}22],], b)b) 2.5. Transition Metal Complexes with Asymmetric P-C-P Ligands [{RhCl(nbd)}[{RhCl(nbd)}22].]. Several asymmetric carbones with orthometallation (5a-M, 5d-M), with an additional donor 2.5. Transition Metal Complexes with Asymmetric P-C-P Ligands function2.5. Transition (5c), or Metal with Complexes a functionalized with Asymmetric phenyl ringP-C-P (5b Ligands) were reported that form TM complexes (see FigureSeveral7). asymmetric carbones withwith orthometallationorthometallation ((5a-M,, 5d-M), with an additional donor function (5c), or with a functionalized phenyl ring (5b) were reported that form TM complexes (see Figure 7).
Molecules 2020, 25, 4943 14 of 48 Molecules 2020, 25, x FOR PEER REVIEW 15 of 54
Figure 7. Structures of compounds 5a-M, 5b, 5c and 5d-M. Figure 7. Structures of compounds 5a-M, 5b, 5c and 5d-M. 1 The neutral asymmetric carbone 5b (X = PPh2) has the structural parameters P -C = 1.642(2), 2 The neutral asymmetric carbone 5b (X = PPh2) has the structural parameters P1-C = P -C = 1.636(1) Å, and a P-C-P angle of 140.74(8)◦ (see Table5); the P atoms resonate at δ = 6.9 1.642(2), P2-C =2 1.636(1) Å, and a P-C-P angle of 140.74(8)°1 (see Table 5); the P 2atoms resonate −at and 3.4 ppm ( JPP = 93 Hz) [75]. Those of 5c are P -C = 1.6416(16) Å, P -C = 1.6398(17) Å, δ =− −6.9 and −3.4 ppm (2JPP = 93 Hz) [75]. Those of 5c are P1-C = 1.6416(16) Å, P2-C = 1.6398(17) Å, and P-C-P = 133.25(10)◦ [76]. Three complexes in which the carbone 1a is half-side orthometallated formingand P-C-P5a-M complexes= 133.25(10)° are described[76]. Three [69, 73complexes,77]. in which the carbone 1a is half-side orthometallated forming 5a-M complexes are described [69,73,77]. Table 5. Transition metal complexes with the unsymmetrical carbones 5a–5d; 31P NMR shifts in ppm. Table 5. Transition metal complexes with the unsymmetrical carbones 5a–5d; 31P NMR shifts in 31 2 1 2 ppm.5-M P NMR ( JPP) M-C P -C P -C P-C-P Ref. Transition metal complexes of 5a-M 31 2 1 2 5a-Ptcod(C5-M8 H11) 14.9P NMR 5.7 (59.8) ( JPP) 2.072(3)M-C 1.694(4) P -C P 1.716(4)-C P-C-P 114.8(2) Ref. [77] 5a-Rhcod(p) 10.15 12.40Transition (50.9) metal complexes 2.165(2) of 5a-M 1.693(2) 1.692(2) 124.50(13) [69] 5a-PdC3H5 39.8 9.9 (54) nr1.694(4) nr nr [73] 5a-Ptcod(C8H11) 14.9 5.7Transition (59.8) metal complexes2.072(3) with the carbone 5b 114.8(2) [77] 1.716(4) 5b-AuCl (X = PPh2) 8.6 18.7 (52) 2.043 1.701(4) 1.696(2) 126.0(2) [75] 1.693(2) 5b-AuCl5a- (XRhcod(p)= PPh2-AuCl) 10.15 25.6 12.40 20.2 (47) (50.9) 2.165(2) 2.037(3) 1.690(3) 1.689(3)124.50(13) 131.4(2) [69] [75 ] 5b-(AuCl) 1.692(2) 2 25.4 26.9 2.089 2.064 1.774(5) 1.763(5) 123.6(3) [75] (X =5a-PPhPdC2-AuCl)3H5 39.8 9.9 (54) nr nr nr [73] 5b-PtMe (X = Me) 19.3 nr nr nr [78] 2 Transition metal complexes with the carbone 5b Transition metal complexes with the carbone 5c 1.701(4) 5c-UCl4 2 par 2.461(5) 1.699(5) 1.711(5) 120.6(3) [41] 5b-AuCl (X=PPh+ ) 8.6 18.7 (52) 2.043 126.0(2) [75] [5cAuPPh3] 19.70 15.03 (30.7) 2.067(9) 1.688(9)1.696(2) 1.707(9) 124.3(5) [76] + [5c(CuCl)(AuPPh5b-AuCl 3)] 39.7 26.2 (m) 2.111(4) Au 1.981(5) Cu 1.732(5)1.690(3) 1.750(5) 120.2(3) [76] [5c(AuCl)(AuPPh )]+ 25.635.4 27.520.2 (m)(47) 2.080(9) Au2.037(3)2 2.127(8) Au1 1.756(9)131.4(2) 119.3(5) [75] [76 ] (X=PPh2-AuCl)3 1.689(3) Transition metal complexes with the carbone 5d-M 5b-(AuCl)2 1.774(5) 5d-Pt-5d 25.419.3 26.9 2.089 nr 2.064 nr123.6(3) nr [75] [78 ] (X=PPh2-AuCl) 1.763(5) 5b-PtMe2 (X = Me) 19.3 nr nr nr [78] As depicted in Scheme 11Transition, three neutral metal complexes complexes with of the1a carboneare known 5c in which one of its phenyl 31 group is orthometallated to produce the 5a-M core. The P NMR shift1.699(5) of the unchanged PPh3 group 5c-UCl4 par 2.461(5) 120.6(3) [41] range between about 6 and 13 ppm whereas for the orthometallated side1.711(5) shifts between 15 and 40 ppm 1.688(9) where recorded.[5cAuPPh3] Both+ P-C19.70 distances 15.03 (30.7) do not differ markedly2.067(9) and amount to about 1.700124.3(5) Å. [76] 1.707(9) 2.111(4) Au 1.981(5) 1.732(5) [5c(CuCl)(AuPPh3)]+ 39.7 26.2 (m) 120.2(3) [76] Cu 1.750(5) 2.080(9) Au2 2.127(8) [5c(AuCl)(AuPPh3)]+ 35.4 27.5 (m) 1.756(9) 119.3(5) [76] Au1 Transition metal complexes with the carbone 5d-M 5d-Pt-5d 19.3 nr nr nr [78]
Molecules 2020, 25, x FOR PEER REVIEW 16 of 54
MoleculesAs 2020depicted, 25, x FOR in PEERScheme REVIEW 11, three neutral complexes of 1a are known in which one of its16 of 54 phenyl group is orthometallated to produce the 5a-M core. The 31P NMR shift of the unchanged As depicted in Scheme 11, three neutral complexes of 1a are known in which one of its PPh3 group range between about 6 and 13 ppm whereas for the orthometallated side shifts phenyl group is orthometallated to produce the 5a-M core. The 31P NMR shift of the unchanged between 15 and 40 ppm where recorded. Both P-C distances do not differ markedly and PPh3 group range between about 6 and 13 ppm whereas for the orthometallated side shifts amount to about 1.700 Å. Moleculesbetween2020 , 1525, 4943and 40 ppm where recorded. Both P-C distances do not differ markedly and15 of 48 amount to about 1.700 Å.
Scheme 11. Selected structures of transition metal complexes with the carbone 5a; (a) ½ 1 Scheme[PdCl(allyl); 11. Selected (b) 1/3 structures [PtI2(cod)]; of ( transitionc) ¼ [RhCl(cod)]. metal complexes All complexes with are the formed carbone upon5a; (a) release2 [PdCl(allyl); of the Scheme 11. +Selected1 structures of transition metal complexes with the carbone 5a; (a)+ ½ (b)cation 1/3 [PtI [21aH(cod)];] . (c) 4 [RhCl(cod)]. All complexes are formed upon release of the cation [1aH] . [PdCl(allyl); (b) 1/3 [PtI2(cod)]; (c) ¼ [RhCl(cod)]. All complexes are formed upon release of the cation [1aH]+. AllAll complexes complexes shown shown in in Scheme Scheme 12 12have have a furthera further PPh PPh2 function2 function at at the the ortho ortho position position of of one phenylone phenyl group of group1a. In of the 1a complex. In the 5bcomplex-(AuCl) 5b2 the-(AuCl) carbone2 the provides carbone four provides electrons four for electrons donation for with All complexes shown in Scheme 12 have a further PPh2 function at the ortho position of typicaldonation long P-Cwith distances typical long of about P-C distances 1.770 Å [ 75of ].about 1.770 Å [75]. one phenyl group of 1a. In the complex 5b-(AuCl)2 the carbone provides four electrons for donation with typical long P-C distances of about 1.770 Å [75].
SchemeScheme 12. Selected12. Selected structures structures of transition of transition metal complexes metal complexes with the carbone with the5b. (a)carbone [AuCl(tht)], 5b. (a) (b) 2 [AuCl(tht),[AuCl(tht)], 3 [AuCl(tht)]. (b) 2 [AuCl(tht), 3 [AuCl(tht)]. Scheme 12. Selected structures of transition metal complexes with the carbone 5b. (a) The[AuCl(tht)], paramagnetic (b) 2 5c[AuCl(tht),-UCl4 exhibits 3 [AuCl(tht)]. a short C-U distance indicative for a double dative bond of the carbone C atom as in 2b-UCl4 and was obtained by reacting UCl4 with the dication 5c-H2/NaHMDS. Upon further coordination of the pyridyl group (U-N = 2.537(4) Å) the U atom attains the coordination number 6 [41]. + [5c-AuPPh3] was obtained from reacting the carbone 5c with [PPh3AuCl]/Na[SbCl6] (see Scheme 13). In the cationic complex [5c-(CuCl)((AuPPh3)]SbF6, the carbone 5c acts as a six-electron donor with a Cu-N distance of 2.267(6) Å and Cu-Au separation of 2.8483(10) Å. The Cu and Cl atoms Molecules 2020, 25, x FOR PEER REVIEW 17 of 54
The paramagnetic 5c-UCl4 exhibits a short C-U distance indicative for a double dative bond of the carbone C atom as in 2b-UCl4 and was obtained by reacting UCl4 with the dication 5c-H2/NaHMDS. Upon further coordination of the pyridyl group (U-N = 2.537(4) Å) the U atom attains the coordination number 6 [41]. [5c-AuPPh3]+ was obtained from reacting the carbone 5c with [PPh3AuCl]/Na[SbCl6] (see Scheme 13). In the cationic complex [5c-(CuCl)((AuPPh3)]SbF6, the carbone 5c acts as a Molecules 2020, 25, 4943 16 of 48 six-electron donor with a Cu-N distance of 2.267(6) Å and Cu-Au separation of 2.8483(10) Å. The Cu and Cl atoms are each disordered over two positions with occupancy of about 0.8 to 0.2. areIf each CuCl disordered is replaced over by two AuCl positions as in [ with5c-(AuCl)(AuPPh occupancy of3)]SbF about6 0.8the to C-AuPPh 0.2. If CuCl3 distance is replaced is slightly by AuCl aselongated in [5c-(AuCl)(AuPPh and no coordination3)]SbF6 the C-AuPPhof the pyridyl3 distance N atom is slightly is observed. elongated The and Au-Au no coordination separation of is the pyridylwith 3.1274(6) N atom is Å observed. too long Thefor a Au-Au metallophilic separation interaction. is with 3.1274(6) In both compounds, Å too long for the a metallophiliccarbone C interaction.atom constitutes In both a compounds,chiral center theaccording carbone to C four atom chemical constitutes different a chiral substituents center according and acts toas foura chemicalfour-electron different donor. substituents The PPh and3 group acts as resonates a four-electron between donor. 15 and The 27 PPh ppm3 group [76]. resonates In the related between 15symmetric and 27 ppm pyridyl-free [76]. In the relatedcomplex symmetric 1a-(AuCl) pyridyl-free2, slightly shorter complex C-Au1a-(AuCl) (2.076(3)2, slightlyÅ) were shorter recorded C-Au (2.076(3)accompanied Å) were by recorded longer P-C accompanied (1.776(3) Å) by bond longer lengths P-C (1.776(3) [51]. Å) bond lengths [51].
Scheme 13. Selected structures of transition metal complexes with the mono pyridyl substituted carboneScheme5c. 13. Selected structures of transition metal complexes with the mono pyridyl substituted carbone 5c. 2.6. Transition Metal Complexes of Carbones with Cyclobutadiene 2.6. Transition Metal Complexes of Carbones with Cyclobutadiene The carbones 6a and 6b (see Figure8) can also be seen as an all-carbon four-membered ring bent alleneThe (CBA);carbones6a 6ais and stable 6b for (see several Figure hours 8) can at also20 bebut seen decomposes as an all-carbon when warmedfour-membered up to 5 . − ◦ − ◦ Thering optimized bent allene geometry (CBA); reveals6a is stable a very for acute several allene hours bond at − angle20° but of decomposes 85.0◦ and coplanarity when warmed of the up ring carbonto −5°. atoms The optimized including geometry the two nitrogen reveals atoms.a very acute The C allene=C bonds bond of angle the alleneof 85.0° fragment and coplanarity amount to 1.423of the Å and ring are carbon significantly atoms longerincluding than the in typicaltwo ni lineartrogen allenes atoms. (1.31 The Å).C=C Short bonds CN of bonds the ofallene 1.36 Å indicatefragment some amount double to bond 1.423 character. Å and are The significantly CCC carbon longer atom resonatesthan in typical in the 13linearC NMR allenes spectrum (1.31 Å). at 151 ppm.Short The CN first bonds and second of 1.36 proton Å indicate affinities some (PAs) double are very bond high amountingcharacter. toThe 307 C andCC 152carbon kcal/ molatom [79 ]. Molecules 2020, 25, x FOR PEER REVIEW 18 of 54 resonates in the 13C NMR spectrum at 151 ppm. The first and second proton affinities (PAs) are very high amounting to 307 and 152 kcal/mol [79].
Figure 8. Structures of compounds 6a and 6b. The molecular orbitals show that the HOMO and HOMO-1 have clearly the largest coefficients at The molecular orbitals show that the HOMO and HOMO-1 have clearly the largest the central carbon atom and exhibit the typical shape of lone-pair molecular orbitals with σ (HOMO) and coefficients at the central carbon atom and exhibit the typical shape of lone-pair molecular orbitals with σ (HOMO) and π (HOMO-1) symmetry; however, with reversed order with respect to CDPs and CDCs. To emphasize the proximity of 6 to CDP carbones, we use the same symbolism mimicking a metal. The free CBA 6b could not be obtained, but only the cationic 6bH+ and 6bH22+ are known and used as starting compounds for the syntheses of the related transition metal complexes [80]. The 13C NMR shifts of the central carbon atom are shifted to higher fields relative to the starting free carbone ranging between 124 and 139 ppm (see Table 6).
Table 6. Transition metal complexes with the all carbon ligand 6; 13C NMR shifts (in ppm) of the donating carbon atom. Distances in Å, angles in deg.
13C NMR C-M C-C C-C-C Ref. Transition metal complexes with the carbone 6a 6a-RhCl(cod) 136.6 2.038(5) 1.405(6) 88.4(3) [79] 6a-IrCl(cod) 138.6 nr nr nr [79] 6a-RhCl(CO)2 124.7 nr nr nr [79] 6a-IrCl(CO)2 129.2 nr nr nr [79] Transition metal complexes with the carbone 6b 6b-W(CO)5 130.1 2.319(3) 1.419(4) 88.0(2) [80] 6b-AuCl 123.6 2.001(4) 1.409(5) 90.5(3) [80] 6b-RhCl(CO)2 131.2 2.0602(14) 1.4102(19) 89.73(11) [80]
All complexes of the CBA 6a where obtained by reacting the freshly prepared free carbone 6a at −20° with [{MCl(cod)}2] complexes (M = Rh, Ir). The cod ligand can be replaced by bubbling CO through solutions of 6a-MCl(cod) to produce the related 6a-MCl(CO)2 compounds (see Scheme 14) [79].
Molecules 2020, 25, 4943 17 of 48
π (HOMO-1) symmetry; however, with reversed order with respect to CDPs and CDCs. To emphasize the proximity of 6 to CDP carbones, we use the same symbolism mimicking a metal. + 2+ The free CBA 6b could not be obtained, but only the cationic 6bH and 6bH2 are known and used as starting compounds for the syntheses of the related transition metal complexes [80]. The 13C NMR shifts of the central carbon atom are shifted to higher fields relative to the starting free carbone ranging between 124 and 139 ppm (see Table6).
Table 6. Transition metal complexes with the all carbon ligand 6; 13C NMR shifts (in ppm) of the donating carbon atom. Distances in Å, angles in deg.
13C NMR C-M C-C C-C-C Ref. Transition metal complexes with the carbone 6a 6a-RhCl(cod) 136.6 2.038(5) 1.405(6) 88.4(3) [79] 6a-IrCl(cod) 138.6 nr nr nr [79] 6a-RhCl(CO)2 124.7 nr nr nr [79] 6a-IrCl(CO)2 129.2 nr nr nr [79] Transition metal complexes with the carbone 6b 6b-W(CO)5 130.1 2.319(3) 1.419(4) 88.0(2) [80] 6b-AuCl 123.6 2.001(4) 1.409(5) 90.5(3) [80] 6b-RhCl(CO)2 131.2 2.0602(14) 1.4102(19) 89.73(11) [80]
All complexes of the CBA 6a where obtained by reacting the freshly prepared free carbone 6a at 20 with [{MCl(cod)} ] complexes (M = Rh, Ir). The cod ligand can be replaced by bubbling CO − ◦ 2 throughMolecules solutions 2020, 25, x of FOR6a-MCl(cod) PEER REVIEW to produce the related 6a-MCl(CO)2 compounds (see Scheme 14)[1979 of]. 54
Scheme 14. Selected structures of complexes with the cyclic carbones 6a and 6b. Preparation see text. Scheme 14. Selected structures of complexes with the cyclic carbones 6a and 6b. Preparation Transitionsee text. metal complexes with 6b as ligand were obtained by reacting 1,1,2,4-tetrapiperidino-1 -buten-3-yne with (a) [(tht)AuCl], (b) [RhCl(CO)2]2, and (c) [(NMe3)W(CO)5] during the reaction rearrangementTransition of themetal starting complexes buten-3-yne with to 6b has6b occurredas ligand [80 ]. were obtained by reacting 1,1,2,4-tetrapiperidino-1-buten-3-yne with (a) [(tht)AuCl], (b) [RhCl(CO)2]2, and (c) 2.7.[(NMe Carbodicyclopropenylidene3)W(CO)5] during the reaction rearrangement of the starting buten-3-yne to 6b has occurred [80]. Stephan described the first carbodicarbene stabilized by flanking cyclopropylidenes, named carbodicyclopropylidene 7 (see Figure9)[81]. 2.7. Carbodicyclopropenylidene Stephan described the first carbodicarbene stabilized by flanking cyclopropylidenes, named carbodicyclopropylidene 7 (see Figure 9) [81].
Figure 9. Possible description of the bonding in the carbone 7.
Neither the neutral singlet 1,2-diphenylcyclopropenylidene as carbene ligand L in 7 nor the carbone tetraphenylcarbodicyclopropenyliden (CDC) 7 itself are stable compounds at room temperature. The free carbene L has only been observed in an argon matrix isolated at 10 K and 7 could be characterized in solution by low temperature NMR spectroscopy; for the central carbon atom a 13C NMR shift at δ = 133 ppm was recorded at −60 °C. The first and second proton affinities of 7 were determined to be 283 and 153 kcal/mol, respectively. The molecular structure of 7 was determined by computational methods. Calculations reveal that the central carbon atom is in a linear environment the C-C distances were calculated at 1.308 Å and the C-C-C angle to 180°. The energy difference between the linear allenic structure and the bent arrangement is shallow amounting to 6.6 kcal/mol for a
Molecules 2020, 25, x FOR PEER REVIEW 19 of 54
Scheme 14. Selected structures of complexes with the cyclic carbones 6a and 6b. Preparation see text.
Transition metal complexes with 6b as ligand were obtained by reacting 1,1,2,4-tetrapiperidino-1-buten-3-yne with (a) [(tht)AuCl], (b) [RhCl(CO)2]2, and (c) [(NMe3)W(CO)5] during the reaction rearrangement of the starting buten-3-yne to 6b has occurred [80].
2.7. Carbodicyclopropenylidene Stephan described the first carbodicarbene stabilized by flanking cyclopropylidenes, Moleculesnamed2020 carbodicyclopropylidene, 25, 4943 7 (see Figure 9) [81]. 18 of 48
Figure 9. Possible description of the bonding in the carbone 7. Figure 9. Possible description of the bonding in the carbone 7. Neither the neutral singlet 1,2-diphenylcyclopropenylidene as carbene ligand L in 7 nor the carbone tetraphenylcarbodicyclopropenylidenNeither the neutral singlet 1,2-diphenylcyclopropenylidene (CDC) 7 itself are stable compounds as carbene at ligand room L temperature. in 7 nor Thethe free carbone carbene tetraphenylcarbo L has only beendicyclopropenyliden observed in an argon (CDC) matrix 7 itself isolatedare stable at compounds 10 K and 7 atcould room be characterizedtemperature. in The solution free carbene by low L temperature has only been NMR obse spectroscopy;rved in an argon for thematrix central isolated carbon at 10 atom K and a 13 C NMR7 could shift atbeδ characterized= 133 ppm was in recordedsolution atby low60 C.temperature NMR spectroscopy; for the central − ◦ carbonThe first atom and a 13 secondC NMR proton shift aatffi δnities = 133 of ppm7 were was determined recorded at to − be60 283°C. and 153 kcal/mol, respectively. TheMolecules molecularThe 2020 first, 25 structure and, x FOR second PEER of 7 REVIEW protonwas determined affinities of by 7 computational were determined methods. to be 283 Calculations and 153 kcal/mol, reveal that20 of 54 therespectively. central carbon The atom molecular is in a linear structure environment of 7 was the C-Cdetermined distances by were computational calculated at 1.308methods. Å and bending angle of 140° and 10 kcal/mol for 130°. The highest occupied molecular orbital theCalculations C-C-C angle reveal to 180 that◦. Thethe energycentral carbon difference atom between is in a thelinear linear environment allenic structure the C-C and distances the bent (HOMO) and HOMO-1 of 7 are degenerate and incorporate the p(π) orbitals of the C2-C1-C2a arrangementwere calculated is shallow at 1.308 amounting Å and tothe 6.6 C-C-C kcal/mol angle for ato bending 180°. The angle energy of 140 difference◦ and 10 kcal between/mol for the 130 ◦. fragment. Thelinear highest allenic occupied structure molecular and the orbital bent (HOMO) arrangement and HOMO-1 is shallow of 7amountingare degenerate to 6.6 and kcal/mol incorporate for a the The central C atom is more negatively charged (−0.19 a.u.) than the adjacent C atoms, p(π ) orbitals of the C2-C1-C2a fragment. suggesting nucleophilic character [81]. The central C atom is more negatively charged ( 0.19 a.u.) than the adjacent C atoms, suggesting The addition compounds [7-AuNHC-Ad](OTf)− and [7-AuNHC-Dipp](OTf) (see Table 7) nucleophilic character [81]. were prepared from reacting [7H]+ with KHMDS and the related (NHC)AuOTf at −45°(see The addition compounds [7-AuNHC-Ad](OTf) and [7-AuNHC-Dipp](OTf) (see Table7) were Scheme 15) [81]. prepared from reacting [7H]+ with KHMDS and the related (NHC)AuOTf at 45 (see Scheme 15)[81]. − ◦ Table 7. Complexes with the carbone 7. 13C NMR shifts (in ppm) of the donating carbon atom. Table 7. Complexes with the carbone 7. 13C NMR shifts (in ppm) of the donating carbon atom. 13C 7-M 7-M 13C NMRM-C M-C C-C C-C-CC-C-C Ref. Ref. NMR 2.071(6) [7-AuNHC-Ad](OTf) 92.72.071(6) nr nr [81] [7-AuNHC-Ad](OTf) 92.7 2.047(6) nr nr [81] [7-AuNHC-Dipp](OTf) 98.02.047(6) nr nr nr [81] [7-AuNHC-Dipp](OTf) 98.0 nr nr nr [81] +
NN Ad Ad
a [7H]+ Au
Ph C Ph
Ph Ph
7-AuNHC-Ad Scheme 15. Selected structures of complexes with the cyclo propylidene stabilized carbone 7. (a) KHMDSScheme /15.(NHC)AuOTf. Selected structures of complexes with the cyclo propylidene stabilized carbone 7. (a) KHMDS/(NHC)AuOTf.
2.8. Carbodicarbenes Carbodicarbenes, CDCs, are neutral compounds where a bare carbon atom with its four electrons is stabilized by two NHC ligands which plays the role of a phosphine group as in carbodiphosphoranes, CDPs. Theoretical studies have demonstrated that this class of compounds could be stable and their existence was predicted by Frenking [82] and short times later realized by the group of Bertrand [83]. Structural and spectroscopic parameters of the following symmetric CDCs (see Figure 10) are available: 8a, C-C = 1.343(2) Å, C-C-C = 134.8(2)°, 13C NMR 110.2 ppm [83]; 8b, C-C = 1.333(2) Å and 1.324(2) Å, C-C-C = 143.61(15)° [84]; 8c, C-C = 1.335(5) Å, C-C-C = 136.6(5)° (see Table 8) [85].
Molecules 2020, 25, 4943 19 of 48
2.8. Carbodicarbenes Carbodicarbenes, CDCs, are neutral compounds where a bare carbon atom with its four electrons is stabilized by two NHC ligands which plays the role of a phosphine group as in carbodiphosphoranes, CDPs. Theoretical studies have demonstrated that this class of compounds could be stable and their existence was predicted by Frenking [82] and short times later realized by the group of Bertrand [83]. Structural and spectroscopic parameters of the following symmetric CDCs (see Figure 10) are 13 available: 8a, C-C = 1.343(2) Å, C-C-C = 134.8(2)◦, C NMR 110.2 ppm [83]; 8b, C-C = 1.333(2) Å and 1.324(2)Molecules Å, 2020 C-C-C, 25, x= FOR143.61(15) PEER REVIEW◦ [84]; 8c, C-C = 1.335(5) Å, C-C-C = 136.6(5)◦ (see Table8)[85]. 21 of 54
Figure 10. Symmetrical CDCs from which transition metal complexes are known. Figure 10. Symmetrical CDCs from which transition metal complexes are known. Table 8. Collection of transition metal complexes with the CDCs 8a–8h. 13C NMR shifts of the central carbonTable atom 8. Collection (in ppm). of transition metal complexes with the CDCs 8a–8h. 13C NMR shifts of the central carbon atom (in ppm). 13C NMR M-C C-C C-C-C Ref. .13C NMR M-C C-C C-C-C Ref. Transition metal complexes with the CDC 8a Transition metal complexes with the CDC 8a 8a-RhCl(CO)2 64.1 2.089(7) 1.398(10) 121.2(7) [83] 8a-RhCl(CO)2 64.1 2.089(7) 1.398(10) 121.2(7) [83] 8a-RuCl2(=CHPh)NHC 73.01 mes 2.2069(18) 1.352(3) 1.429(3) 119.84(17) [86] 8a-RuCl2(=CHPh)NHC 73.01 mes i 2.2069(18) 1.352(3) 1.429(3) 119.84(17) [86] 8a-RuCl2(=CHPh)NHC 73.4 Pr 2.210(7) 1.345(11) 1.439(9) 116.9(6) [86] i 8a-RuCl2(=CHPh)NHC 73.4Transition Pr metal2.210(7) complexes with1.345(11) the CDC 1.439(9)8b 116.9(6) [86] [8b-PdCl]+ Transitionnr metal complexes 1.973(3) with 1.369(5)the CDC 1.398(5) 8b 126.5(3) [84] + 2+ [8b[8b-PdCl]-Fe0.5] nr 1.973(3)2.018(3) 1.369(5) 1.374(3)1.398(5) 126.5(3) 128.4(3) [84] [87 ] 2+ 3+ [8b-[8bFe-Fe0.50.5] ] 2.018(3)1.968(4) 1.374(3) 1.387(6) 128.4(3) 125.2(4) [87] [87 ] 3+ 4+ [8b-[8bFe-Fe0.50.5] ] 1.968(4)1.928(3) 1.387(6) 1.407(4) 125.2(4) 125.4(2) [87] [87 ] [8b-Fe0.5]4+ Transition metal1.928(3) complexes with the1.407(4) CDC 8c 125.4(2) [87] 8c-PdClC3H5 Transitionnr metal complexes 2.207(4) with 1.404(5)the CDC 1.377(5) 8c 119.7(4) [85] 8c-8cPdClC-RhCl(CO)3H5 2 nr 63.72.207(4) 2.109(2) 1.404(5) 1.411(3) 1.377(5) 1.385(3) 119.7(4) 117.4(2) [85] [85 ] 8d 8c-RhCl(CO)2 Transition63.7 metal2.109(2) complexes with1.411(3) the CDC1.385(3) 117.4(2) [85] 8d--RhCl(CO)2 Transition metal complexes2.123(2) with 1.416(3)the CDC 1.368(3) 8d 116.8(2) [85] Transition metal complexes with the asymmetric CDC 8e 8d--RhCl(CO)2 2.123(2) 1.416(3) 1.368(3) 116.8(2) [85] 8e-PdCl (POR) nr 2.0398(18) 1.395(3) 1.328(3) 119.20(16) [88] 2 3Transition metal complexes with the asymmetric CDC 8e 8e-PdCl2PPh3 nr 2.063(2) 1.383(3) 1.409(3) tP 115.63(19) [89] 8e-PdCl2(POR)3 nr 2.0398(18) 1.395(3) 1.328(3) 119.20(16) [88] 8e-PdCl2PTol3 nr 2.049(4) 1.374(7) 1.412(8) tP 117.7(4) [89] 8e-PdCl2PPh3 nr 2.063(2) 1.383(3) 1.409(3) tP 115.63(19) [89] 8e-PdCl2PCy3 nr 2.111(2) 1.343(3) 1.415(4) tP 123.6(2) [89] 8e-PdCl2PTol3 Transitionnr metal complexes2.049(4) with the 1.374(7) asymmetric 1.412(8) CDC tP 8f 117.7(4) [89] 8e-8fPdCl-RhCl(CO)2PCy3 2 nr 67.12.111(2) 2.117(2) 1.343(3) 1.369(3) 1.415(4) 1.424(3) tP 123.6(2) 117.8(2) [89] [90 ] Transition metal complexes withwith thethe asymmetricasymmetric CDCCDC 8g8f 8f-RhCl(CO)2 67.1 2.117(2) 1.369(3)1.374(2) 1.424(3)NHC 117.8(2) [90] 8g-RhCl(CO)2 63.2 2.1164(17) 118.77(16) [90] Transition metal complexes with the asymmetric1.420(3) CDC 8g 8g-RhCl(CO)2 Transition63.2 metal complexes2.1164(17) with the1.374(2) asymmetricNHC 1.420(3) CDC 8h 118.77(16) [90] 8h-IrCl(CO)2 Transition metalnr complexes nrwith the asymmetric nr CDC 8h nr [91] 8h-IrCl(cod) 166.4 nr nr nr [91] 8h-IrCl(CO)2 nr nr nr nr [91] 8h-IrCl(cod) 166.4 nr nr nr [91]
Structural parameters of the unsymmetrical CDCs (see Figure 11) are: 8e, C-C = 1.3401(16) Å and 1.3455(16), C-C-C 137.55(12)°. For 8f, no data are available [90]. 8g: C-C = 1.344(3) Å and, 1.318(3) Å, C-C-C = 146.11(19)° [90]. 8h was obtained at −60° by reacting 8hH+ with KMDS, and characterized spectroscopically. On warming to room temperature, it dimerizes. 13C NMR: δ = 105.5 ppm (see Table 8) [91].
Molecules 2020, 25, 4943 20 of 48
Structural parameters of the unsymmetrical CDCs (see Figure 11) are: 8e, C-C = 1.3401(16) Å and 1.3455(16), C-C-C 137.55(12)◦. For 8f, no data are available [90]. 8g: C-C = 1.344(3) Å and, 1.318(3) Å, C-C-C = 146.11(19) [90]. 8h was obtained at 60 by reacting 8hH+ with KMDS, and characterized ◦ − ◦ spectroscopically. On warming to room temperature, it dimerizes. 13C NMR: δ = 105.5 ppm
(seeMolecules Table8 2020)2020 [91,, ].2525,, xx FORFOR PEERPEER REVIEWREVIEW 2222 ofof 5454
Figure 11. Unsymmetrical CDCs from which transition metal complexes are reported. Figure 11. Unsymmetrical CDCs from which transition metal complexes are reported. Further, 8a-RhCl(CO)2 was prepared by addition of a suspension of 8a (see Scheme 16) in benzene to Further, 8a-RhCl(CO)2 was prepared2+ by addition2+ of a suspension of 8a (see Scheme 16) in a solutionFurther, of [RhCl(CO) 8a-RhCl(CO)2]2 [83].2 was [8b-Fe prepared0.5] contains by addition Fe in of octahedral a suspension environment of 8a (see coordinated Scheme 16) by in two 2+ 2+ moleculesbenzene of to8b a .solution Fe(II) can of be [RhCl(CO) successively22]]22 [83].[83]. oxidized [[8b-Fe to0.50.5 the]]2+ contains correspondingcontains FeFe2+ inin tri-, octahedraloctahedral tetra-, and environmentenvironment pentacationic speciescoordinatedcoordinated [87]. byby twotwo moleculesmolecules ofof 8b.. Fe(II)Fe(II) cancan bebe successivelysuccessively oxidizedoxidized toto thethe correspondingcorresponding tri-,tri-, tetra-,tetra-, andand pentacationicpentacationic speciesspecies [87].[87].
Scheme 16. Selected structures of transition metal complexes with symmetric CDCs 8a and 8b; Scheme 16. SelectedSelected structuresstructures ofof transitiontransition metalmetal complexescomplexes withwith symmetricsymmetric CDCsCDCs 8a8a andand 8b8b;; (a) Fe(OTf)2(MeCN)2. ((aa)) Fe(OTf)Fe(OTf)22(MeCN)(MeCN)2.2.
The addition compounds 8c-RhCl(CO)2 and 8d-RhCl(CO)2 where obtained upon reacting the The addition compounds 8c-RhCl(CO)22 andand 8d-RhCl(CO)22 wherewhere obtainedobtained uponupon reactingreacting appropriate carbone 8c or 8d with [RhCl(CO)2]2. Similarly, the addition of [Pd(allyl)Cl]2 to 8c leads to thethe appropriateappropriate carbonecarbone 8c oror 8d with [RhCl(CO)22]]22.. Similarly,Similarly, thethe additiaddition of [Pd(allyl)Cl]22 toto the allyl complex 8c-PdCl(C3H5)[85]. 8c leadsleads toto thethe allylallyl complexcomplex 8c-PdCl(C-PdCl(C33H55)) [85].[85]. As depicted in Scheme 17, introduction of PdCl22P(OiPr)33 toto 8e affordedafforded thethe complexcomplex 8e-PdCl-PdCl22P(OiPr)33;; itit featuresfeatures aa squaresquare planarplanar PdPd centercenter withwith aa shortshort interatomicinteratomic distancedistance ofof oneone phosphite oxygen atom and the carbon atom of thethe NHCNHC moleculemolecule ofof 2.8902.890 ÅÅ thatthat isis smallersmaller thanthan thethe sumsum ofof vanvan derder WaalsWaals radii.radii. ThisThis indiindicatescates strongstrong attractiveattractive interactioninteraction betweenbetween thethe atoms [88]. The three Pd complexes 8e-PdCl-PdCl22PPh33,, 8e-PdCl-PdCl22PTol33,, andand 8e-PdCl-PdCl22PCy33 werewere obtained by reacting the carbone 8e withwith thethe appropriateappropriate PdClPdCl22PR33;; betweenbetween thethe NHCNHC andand thethe aromatic phosphine substituents (Ph or Tol) an unexpected π--π interactioninteraction waswas detected.detected. OneOne
Molecules 2020, 25, 4943 21 of 48
As depicted in Scheme 17, introduction of PdCl2P(OiPr)3 to 8e afforded the complex 8e-PdCl2P(OiPr)3; it features a square planar Pd center with a short interatomic distance of one phosphite oxygen atom and the carbon atom of the NHC molecule of 2.890 Å that is smaller than theMolecules sum of 2020 van, 25 der, x FOR Waals PEER radii. REVIEW This indicates strong attractive interaction between the atoms [2388 of]. 54 The three Pd complexes 8e-PdCl2PPh3, 8e-PdCl2PTol3, and 8e-PdCl2PCy3 were obtained by reacting the carbonePhMolecules and8e 2020withone, 25 theTol, x FOR appropriategroup PEER REVIEWare PdClnearly 2PR parallel3; between to thethe NHC imidazole and the rings aromatic with phosphine centroid-centroid substituents23 of 54 (Phdistances or Tol) an of unexpected 3.25 Å (Ph) πand-π interaction 3.30 Å (Tol), was respectively detected. One [89]. Ph and one Tol group are nearly parallel to thePh imidazoleand one ringsTol group with centroid-centroid are nearly parallel distances to the of 3.25imidazole Å (Ph) andrings 3.30 with Å (Tol), centroid-centroid respectively [89 ]. distances of 3.25 Å (Ph) and 3.30 Å (Tol), respectively [89].
Scheme 17. Selected structural representation of 8e-PdCl2P(OiPr)3 (a) PdCl2P(OiPr) 3.
Scheme 17. Selected structural representation of 8e-PdCl2P(OiPr)3 (a) PdCl2P(OiPr)3. 8f-RhCl(CO)Scheme 217. and Selected 8g-RhCl(CO) structural representation2 stem from of reacting8e-PdCl2 P(OtheiPr) appropriate3 (a) PdCl2P(O carboneiPr)3. with [RhCl(CO)2]2 [90]. The cod ligand of [Ir(cod)Cl]2 was replaced by bubbling CO through a 8f-RhCl(CO)2 and 8g-RhCl(CO)2 stem from reacting the appropriate carbone with [RhCl(CO)2]2 [90]. mixture8f-RhCl(CO) with 8h to2 generateand 8g-RhCl(CO) the complex2 stem 8h-IrCl(CO) from 2reacting [91]. the appropriate carbone with The cod ligand of [Ir(cod)Cl]2 was replaced by bubbling CO through a mixture with 8h to generate the [RhCl(CO)Some 2experimental]2 [90]. The cod findings ligand indicate of [Ir(cod)Cl] that carbodicarbenes2 was replaced also by havebubbling catalytic CO throughproperties a complex 8h-IrCl(CO)2 [91]. formixtureSome a wide experimentalwith range 8h to of generate transformations, findings the indicatecomplex which that 8h-IrCl(CO)carbodicarbenes are currently2 [91]. being also actively have catalytic studied properties by several for a widegroups. rangeSome ofExamples experimental transformations, have findingsbeen which reported indicate are currently such that beingcarbodicarbenesas hydrogenation actively studied also of by haveinert several catalytic olefins groups. properties[92], Examples C-C havecross-couplingfor beena wide reported range reactions suchof transformations, as [84], hydrogenation intermolecular which of inert arehydroamination currently olefins [92 being], C-C[93] actively cross-couplingand hydroheteroarylation studied reactionsby several [84 ], intermolecular[groups.94]. It seems Examples hydroamination that this have area been is [still93 ]reported andin an hydroheteroarylation infant such stadium as hydrogenation and it [ 94can]. Itbe seems expectedof inert that thatolefins this CDCs area [92], is may still C-C inbe an infantfoundcross-coupling stadium useful andas reactionscatalyst it can be for [84], expected other intermolecular reactions. that CDCs mayhydroamination be found useful [93] as and catalyst hydroheteroarylation for other reactions. [94]. It seems that this area is still in an infant stadium and it can be expected that CDCs may be 2.9.2.9.found Tridentate Tridentate useful Cyclic as Cyclic catalyst Diphosphino Diphosphino for other CDCs CDCs reactions. The carbones9a 9a and9b 9b in Figure 12 are functionalized carbodicarbene in which the 2.9.The Tridentate carbones Cyclicand Diphosphinoin Figure CDCs 12 are functionalized carbodicarbene in which the donating carbondonating atom carbon is part atom of a seven is part membered of a seven ring. membered ring. The carbones 9a and 9b in Figure 12 are functionalized carbodicarbene in which the donating carbon atom is part of a seven membered ring.
Figure 12. Hypothetical free carbones 9a and 9b. Figure 12. Hypothetical free carbones 9a and 9b. The neutral 9a and 9b could not be isolated, source for transition metal complexes are the related cations The9aH +neutraland 9bH 9a +and(see 9bFigure Table could9 12.)[ not93 Hypothetical]. be isolated, free source carbones for 9atransition and 9b. metal complexes are the related cations 9aH+ and 9bH+ (see Table 9) [93]. The neutral 9a and 9b could not be isolated, source for transition metal complexes are the related cations 9aH+ and 9bH+ (see Table 9) [93].
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TableTable 9. Transition9. Transition metal metal complexes complexes with with the the carbonescarbones 9a9a and 9b;; 1313CC NMR NMR signal signal of ofthe the central central donatingdonating carbon carbon atom. atom.
13 9-M9-M C 13NMRC NMR M-CM-C C-C C-C C-C-C C-C-C Ref. Ref. Transition metal complexes with the carbone 9a Transition metal complexes with the carbone 9a 9a-RhCl 73.0 nr nr nr [93] 9a-RhCl 73.0 nr nr nr [93] [9a-RhNCMe]+ nr 2.043 1.398 1.387 nr [93] [9a-RhNCMe]+ nr 2.043 1.398 1.387 nr [93] [9a-Rh(CO)]BF4 nr nr nr nr [93] [9a-Rh(CO)]BF4 nr nr nr nr [93] [9a-Rh(styrene)]BF nr 2.075(2) 1.404(3)1.404(3) 1.391(3) 121.7(2) [94] [9a-Rh(styrene)]BF4 4 nr 2.075(2) 121.7(2) [94] [9aH-Rh(CO)](BF4)2 nr nr1.391(3) nr nr [94] [9aH-Rh(CO)](BF4)2 Transitionnr metal complexesnr with the carbone nr 9b nr [94] 9b-RhClTransition 73.4 metal complexes nr with the carbone nr 9b nr [93] [9b-RhNCMe]BF-RhCl 4 73.4 nrnr nr nr nr nr nr [93[93]] [9b-RhNCMe]BF[9b-Rh(CO)]BF4 4 nr nrnr nr nr nr nr nr [93[93]] [9b-Rh(CO)]BF4 nr nr nr nr [93]
TheThe neutral neutral complexes complexes9a-RhCl 9a-RhCl and and9b-RhCl 9b-RhCl (see Scheme(see Scheme 18) where 18) where prepared prepared upon reactingupon + + thereacting cations 9aHthe cationsor 9bH 9aH, respectively+ or 9bH+, withrespectively [Rh(cod)Cl] with2/NaOMe; [Rh(cod)Cl] if treated2/NaOMe; with AgBFif treated4/MeCN with the cationicAgBF spezies4/MeCN [ 9athe-Rh(MeCN)]BF cationic spezies4 and [9a [9b-Rh(MeCN)]BF-Rh(MeCN)]BF4 4and, respectively, [9b-Rh(MeCN)]BF were isolated.4, respectively, The related carbonylwere isolated. complexes The [9arelated-Rh(CO)]BF carbonyl4 and complexes [9b-Rh(CO)]BF [9a-Rh(CO)]BF4 formed4 and similarly [9b-Rh(CO)]BF upon reaction4 formed with + [Rh(CO)similarly2Cl] upon2/NaOMe reaction [93 ].with The [Rh(CO) styrene2Cl] complex2/NaOMe [9a [93].-Rh(styrene)] The styrenewas complex obtained [9a-Rh(styrene)] upon treating+ thewas related obtained chloro upon complex treating with styrenethe related/NaBAr chloro4; the styrenecomplex complex with styrene/NaBAr catalyzes the hydroarylation4; the styrene of + 2+ dienes. Protonation of [9a-Rh(CO)] with HBF OEt generates [9aH-Rh(CO)] in+ which the carbone complex catalyzes the hydroarylation of dienes.4· 2 Protonation of [9a-Rh(CO)] with HBF4·OEt2 actsgenerates as four-electron [9aH-Rh(CO)] donor2+ [94 in]. which the carbone acts as four-electron donor [94].
SchemeScheme 18. 18. SelectedSelected structures of of transition transition metal metal complexes complexes with with the carbones the carbones 9a and9a 9band. (a)9b . (a) [Rh(cod)Cl] /NaOMe, (b) 9a-RhCl/styrene/NaBF . [Rh(cod)Cl]2/NaOMe, (b) 9a-RhCl/styrene/NaBF4. 2.10. Tetraaminoallene (TAA) Transition Metal Complexes 2.10. Tetraaminoallene (TAA) Transition Metal Complexes The 13C NMR shift of the central carbon atom amounts to 142.8 ppm. The first and second PAs of The 13C NMR shift of the central carbon atom amounts to 142.8 ppm. The first and second 10 are 282.5 and 151.6 kcal/mol, respectively [16,82]. PAs of 10 are 282.5 and 151.6 kcal/mol, respectively [16,82]. The salt [10-AuPPh3]SbF6 in Scheme 19 is the only transition metal complex of TAA (see Figure 13), The salt [10-AuPPh3]SbF6 in Scheme 19 is the only transition metal complex of TAA (see which has been reported so far. Both carbene moieties are planar, but are tilted relative to each other, Figure 13), which has been reported so far. Both carbene moieties are planar, but are tilted to relieve allylic strain. The Au-C bond lengths amounts to 2.072(3) Å and the slightly different C-C relative to each other, to relieve allylic strain. The Au-C bond lengths amounts to 2.072(3) Å and dative bonds has interatomic distances of 1.406(5) and 1.424(5) Å. The central C-C-C bond angle is the slightly different C-C dative bonds has interatomic distances of 1.406(5) and 1.424(5) Å. The reported with 118.5(3)◦ [95]. central C-C-C bond angle is reported with 118.5(3)° [95].
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Scheme 19. Preparation of [10-AuPPh3]SbF6; a) AuClPPh3/NaSbF6.
SchemeScheme 19. 19.Preparation Preparation ofof [10[10-AuPPh-AuPPh33]SbF]SbF66;; a)a) AuClPPhAuClPPh33/NaSbF/NaSbF66.. Scheme 19. Preparation of [10-AuPPh3]SbF6; a) AuClPPh3/NaSbF6.
Figure 13. Bonding description of tetraaminoallene (TAA) (10). TAA’s may have a bent Figure 13. Bonding description of tetraaminoallene (TAA) (10). TAA’s may have a bent geometry geometryFigure 13. with Bonding hidden description or masked pairsof tetraaminoallene of electrons, which (TAA) are delocalized(10). TAA’s but may serve have as doublea bent with hidden or masked pairs of electrons, which are delocalized but serve as double donor orbitals in Figuredonorgeometry orbitals13. with Bonding in hidden complexes description or masked with CO ofpairs 2tetraaminoallene and of CSelectrons,2 [96]. which (TAA) are (delocalized10). TAA’s butmay serve have as adouble bent complexes with CO2 and CS2 [96]. geometrydonor orbitals with inhidden complexes or masked with COpairs2 and of electrons,CS2 [96]. which are delocalized but serve as double 2.11.2.11. Transition donorTransition orbitals Metal Metal in Complexes complexes Complexes of with Carbonesof Carbones CO2 and with CSwith the2 [96]. the P-C-C P-C-C Skeleton Skeleton 2.11. Transition Metal Complexes of Carbones with the P-C-C Skeleton 2.11.Mixed MixedTransition carbene-phosphine carbene-phosphine Metal Complexes stabilized stabilizedof Carbones carbones carbones with the from P-C-Cfrom the the Skeleton working working group group of of Bestmann Bestmann (1974) (1974) and Alkarazoand AlkarazoMixed (2009). carbene-phosphine (2009). stabilized carbones from the working group of Bestmann (1974) Mixed carbene-phosphine stabilized carbones from the working group of Bestmann (1974) andThe AlkarazoThe crystal crystal structure(2009). structure of 11aof 11ain Figurein Figure 14 reveals14 reveals a planar a planar configuration configuration of the of carbenethe carbene ligand and Alkarazo (2009). C(OEt)ligand2The. ShortC(OEt) crystal P-C2. Short andstructure C-C P-C distances andof 11a C-C in indicate distances Figure some 14 indicate reveals p back some donation;a planar p back configuration P-C donation;= 1.682(4)Å, P-C of C-C=the 1.682(4)Å, =carbene1.316(10) The crystal2 structure of 11a in Figure 14 reveals a planar configuration of the carbene Å,C-Cligand C-C-C = 1.316(10) 125.6C(OEt)◦ (see. Å,Short TableC-C-C P-C 10 125.6° )[and97]. C-C (see distancesTable 10) [97].indicate some p back donation; P-C = 1.682(4)Å, ligandC-C = 1.316(10)C(OEt)2. Å,Short C-C-C P-C 125.6° and C-C (see distances Table 10) indicate[97]. some p back donation; P-C = 1.682(4)Å, C-C = 1.316(10) Å, C-C-C 125.6° (see Table 10) [97]. C OEt C NMe2 Ph P C C OEt Ph3P C C NMe2 3 C OEt C NMe Ph3P C Ph3P C 2 Ph3P COEt Ph3P COEt OEt OEt 11aOEt 11bOEt 11a 11b Figure 14. In compounds 11 the C(0) atoms are stabilized by a phophine or a carbene ligand. 11a 11b Figure 14. In compounds 11 the C(0) atoms are stabilized by a phophine or a carbene ligand. 31 TableFigure 10. Transition 14. In compounds metal complexes 11 the C(0) with atoms the mixed are stabilized carbones by11a a phophineand 11b. orP a NMR carbene shifts ligand. in ppm. TableFigure 10. 14. Transition In compounds metal 11 complexes the C(0) atomswith the are mixed stabilized carbones by a phophine11a and 11b. or a31 carbeneP NMR shiftsligand. in 11-M 31P NMR M-C P-C C-C P-C-C Ref. Table 10. Transition metal complexes with theppm. mixed carbones 11a and 11b. 31P NMR shifts in Transition metal complexes with the carbone 11a 31 Table 10. Transition metal complexes with theppm. mixed carbones 11a and 11b. P NMR shifts in 11-M 31P NMR M-C P-C C-C P-C-C Ref. 11a-RhCl(CO)2 25.1 nrppm. nr nr [98] 11-M11a-AuCl 31PTransition 26.7 NMR metal 2.014(16) complexes M-C with1.7449(16) the carbone P-C 1.362(2) C-C 11a 114.30(12) P-C-C [98] Ref. 31 11a-RhCl(CO)11a11-M-(AuCl) 2 2 PTransition28.125.1 NMR metal 2.081(4) complexes M-C2.103(4)nr with 1.785(4) the carbone P-C 1.425(6)nr C-C 11a 114.2(3) P-C-Cnr [98] Ref.[98] Transition metal complexes with the carbone 11b 11a-11aRhCl(CO)-AuCl 2 Transition26.725.1 metal complexes2.014(16)nr with 1.7449(16)the carbonenr 1.362(2) 11a 114.30(12)nr [98] 11b-AuCl 22.2 nr nr nr [98] 11a-11a-11aRhCl(CO)(AuCl)-AuCl 2 2 25.128.126.7 2.081(4)2.014(16)nr 2.103(4) 1.7449(16) 1.785(4)nr 1.425(6) 1.362(2) 114.30(12) 114.2(3)nr [98] 11a-11a(AuCl)-AuCl 2 Transition26.728.1 metal2.081(4) complexes2.014(16) 2.103(4) with 1.7449(16)the 1.785(4) carbone 1.425(6) 1.362(2) 11b 114.30(12) 114.2(3) [98] [98] 11a-11b-(AuCl)AuCl 2 28.122.2 2.081(4)nr 2.103(4) 1.785(4)nr 1.425(6) 114.2(3)nr [98] The neutral Rh complexTransition11a-RhCl(CO) metal complexes2 was obtainedwith the carbone from reacting11b the carbone 11a with 11b-AuCl Transition22.2 metal complexesnr with the carbonenr 11b nr [98] [Rh(CO)2Cl]2. Similarly, the complex 11b-AuCl results from reaction of 11b with AuCl(SMe2) 11b-AuCl 22.2 nr nr nr [98] (Scheme 20)[98].
Molecules 2020, 25, x FOR PEER REVIEW 26 of 54 Molecules 2020, 25, x FOR PEER REVIEW 26 of 54 The neutral Rh complex 11a-RhCl(CO)2 was obtained from reacting the carbone 11a with Molecules 2020, 25, x FOR PEER REVIEW 26 of 54 [Rh(CO)The2 Cl]neutral2. Similarly, Rh complex the complex 11a-RhCl(CO) 11b-AuCl2 was results obtained from from reaction reacting of 11b the withcarbone AuCl(SMe 11a with2)
(Scheme 220) 2[98]. 2 [Rh(CO)The neutralCl] . Similarly, Rh complex the complex 11a-RhCl(CO) 11b-AuCl2 was results obtained from from reaction reacting of 11bthe carbonewith AuCl(SMe 11a with) Molecules 2020, 25, 4943 24 of 48 [Rh(CO)(Scheme2 Cl]20)2 .[98]. Similarly, the complex 11b-AuCl results from reaction of 11b with AuCl(SMe2) (Scheme 20) [98].
Scheme 20. Selected structural representation of transition metal complexes of 11a. (a) one equiv.Scheme of 20.AuCl(SMe Selected2), structural(b) two equiv. representation of AuCl(SMe of 2).transition metal complexes of 11a. (a) one Scheme 20. Selected structural representation of transition metal complexes of 11a.(a) one equiv. of Schemeequiv. of 20. AuCl(SMe Selected2 ),structural (b) two equiv. representation of AuCl(SMe of 2transition). metal complexes of 11a. (a) one 2.12.AuCl(SMe Transition2), ( bMetal) two Complexes equiv. of AuCl(SMe of Carbones2). with the P-C-Si Skeleton equiv. of AuCl(SMe2), (b) two equiv. of AuCl(SMe2). 2.12.2.12. Transition TheTransition neutral Metal Metal compound Complexes Complexes 12 of Carbonesinof CarbonesFigure with 15 with is the a thecarbone P-C-Si P-C-Si Skeleton in Skeleton which the C(0) atom is stabilized by 2.12.a donorThe TransitionThe neutral stabilized neutral compound Metal compound silylene Complexes12 and in12 Figure aofin phosphineCarbones Figure 15 is 15 awith carboneligand.is a the carbone P-C-Si in which in Skeleton which the C(0) the atomC(0) atom is stabilized is stabilized by a donor by stabilizeda donorThe silylene stabilizedneutral andcompound silylene a phosphine and 12 ina phosphine ligand.Figure 15 isligand. a carbone in which the C(0) atom is stabilized by a donor stabilized silylene and a phosphine ligand.
Figure 15. Carbone complex reported by Kato et al. [99]. Figure 15. Carbone complex reported by Kato et al. [99]. Figure 15. Carbone complex reported by Kato et al. [99]. The crystal structure of a related compound to 12 (a cyclopentene instead of a cyclohexene The crystal structureFigure of a 15. related Carbone compound complex reported to 12 (a by cyclopentene Kato et al. [99]. instead of a cyclohexene ring)ring) shows Theshows crystal a P-C a P-C distancestructure distance of of 1.6226(4) aof related 1.6226(4) Å compound and Å Si-Cand distanceSi-C to 12 distance (a cyclopentene of 1.6844(4) of 1.6844(4) Å; instead the Å; Si-C-P theof a Si-C-P anglecyclohexene amountsangle amounts to 140.03(3)°. to 140.03(3)ring)The shows crystal◦. a P-C structure distance of aof related 1.6226(4) compound Å and Si-Cto 12 distance(a cyclopentene of 1.6844(4) instead Å; ofthe a cyclohexeneSi-C-P angle Addition of CuCl generates the complex 12-CuCl. No spectroscopic or structural details ring)amountsAddition shows to 140.03(3)°. ofa P-C CuCl distance generates of 1.6226(4) the complex Å and12-CuCl. Si-C distance No spectroscopic of 1.6844(4) or Å; structural the Si-C-P details angle are are available [99]. availableamountsAddition [99 to]. 140.03(3)°. of CuCl generates the complex 12-CuCl. No spectroscopic or structural details are availableAddition [99]. of CuCl generates the complex 12-CuCl. No spectroscopic or structural details 2.13.2.13. Transition Transition Metal Metal Complexes Complexes of Carbonesof Carbones with with the the P-C-S P-C-S Skeleton Skeleton are available [99]. 2.13.A seriesATransition series of of carbones Metal carbones Complexes (13a (13a, 13b, 13bof) inCarbones) Figurein Figure with 16 based16 the based P-C-S on on a Skeleton P-C-S a P-C-S core core containing containing the the neutral neutral S(IV) ligands2.13.S(IV) TransitionA SPhligands series2=NMe SPhof Metal carbones (Figure2=NMe Complexes (Figure16 (13a) were, of13b 16) Carbones reported) werein Figure reported with by Fujii 16the based P-C-S by [100 Fujii ]. onSkeleton [100].a P-C-S core containing the neutral S(IV)A ligands series ofSPh carbones2=NMe (Figure(13a, 13b 16)) inwere Figure reported 16 based by Fujii on a[100]. P-C-S core containing the neutral S(IV) ligands SPh2=NMe (Figure 16) were reported by Fujii [100].
Figure 16. Carbone complexes reported by Fujii et al. [100].
Crystal structures and 31P NMR shifts of the following basic carbones are available (see Table 11): 13a, δ = 2.64 ppm; 13b, δ = 1.39 ppm, P-C = 1.663(2) Å, S-C = 1.602(2) Å, P-C-S = 125.59(15)◦. − − The authors revealed a high electron density at the central carbon atom. Molecules 2020, 25, x FOR PEER REVIEW 27 of 54
Figure 16. Carbone complexes reported by Fujii et al. [100].
Crystal structures and 31P NMR shifts of the following basic carbones are available (see MoleculesTable2020 11):, 25 13a,, 4943 δ = −2.64 ppm; 13b, δ = −1.39 ppm, P-C = 1.663(2) Å, S-C = 1.602(2) Å, P-C-S25 of= 48 125.59(15)°. The authors revealed a high electron density at the central carbon atom.
Table 11. Collection of transition metal complexes with the carbones 13a and 13b. 31P NMR signals Table 11. Collection of transition metal complexes with the carbones 13a and 13b. 31P NMR (in ppm) are given. signals (in ppm) are given. 31 13-M13-M 31P NMRP NMR M-CM-C P-C P-C S-C S-C P-C-S P-C-S Ref Ref Transition metal complexes with the carbone 13a based on a P-C-S corecore 13a-AgCl13a-AgCl 10.8 10.8 2.131 2.131 1.711 1.711 1.648 1.648 121.9 121.9 [100[100]] [13a-[AuPPh13a-AuPPh3](OTf)3](OTf) 15.2 15.2 nr nrnr nr nr nr [100[100]] [13a-[(AuPPh13a-(AuPPh3)2](OTf)3)2](OTf)2 2 29.729.7 nr nrnr nr nr nr [100[100]] Transition metal complexes with the carbone 13b based on a P-C-S core 13b-AgCl13b-AgCl 9.13 9.13 2.098 2.098 1.728 1.728 1.636 1.636 119.1 119.1 [100[100]] [13b-AuPh3](SbF6) 12.88 nr nr nr [100] [13b-AuPh3](SbF6) 12.88 nr nr nr [100] [13b-(AuPPh3)2](SbF6)2 27.45 2.127 2.118 1.788 1.737 115.6 [100] [13b-(AuPPh3)2](SbF6)2 27.45 2.127 2.118 1.788 1.737 115.6 [100] [13b-Ag-13b][OTf) 8.43 2.160 1.707 1.635 121.8 127.0 [100] [13b-Ag-13b][OTf) 8.43 2.160 1.707 1.635 121.8 127.0 [100] [13bH-AuPPh3](OTf)2 17.1 2.106 1.817 1.782 116.3 [100] [13bH-AuPPh3](OTf)2 17.1 2.106 1.817 1.782 116.3 [100]
+ + TheThe addition addition products products13a -AgCl13a-AgCl and 13band-AgCl 13b-AgCl were were obtained obtained from reactingfrom reacting [13aH] [13aHor [13bH]+ or ] , respectively[13bH]+, respectively with ion exchange with ion resin exchange (Cl− form) resin and(Cl- Agform)2O/CH and2Cl Ag2.2O/CH For the2Cl other2. For productsthe other see Schemeproducts 21[100 see]. Scheme 21 [100].
SchemeScheme 21. 21.Selected Selected structures structures with with the the carbones carbones13a 13aund und13b 13b:(: (aa)) 0.5 eq. of of AgOTf, AgOTf, (b ()b 2) 2eq. eq. of of AuCl(PPh )/2 eq. of AgSbF ,(c) 1 eq. of AuCl(PPh )/1 eq. of AgSbF ,(d) ion exchange (OH form), 1 eq. AuCl(PPh3 3)/2 eq. of AgSbF6 6, (c) 1 eq. of AuCl(PPh3 3)/1 eq. of 6AgSbF6, (d) ion exchange− (OH- of AuClPPh /1 eq. of AgOTf [100]. form), 1 eq.3 of AuClPPh3/1 eq. of AgOTf [100]. Addition of TM fragments to 13a or 13b in Scheme 21 elongates P-C and S-C bond length as Addition of TM fragments to 13a or 13b in Scheme 21 elongates P-C and S-C bond length reported for 1a. That of [13bH-AuPPh3](OTf)2 in which 13b acts as four-electron donor are elongated as reported for 1a. That of [13bH-AuPPh3](OTf)2 in which 13b acts as four-electron donor are to normal single bonds [100]. elongated to normal single bonds [100]. 2.14. Transition Metal Complex with a P-C-S Core Possessing a Neutral S(II) Ligand
The carbone 14 in Figure 17 contains a phosphine and a S(II) ligand with a free pair of electrons to stabilize the C(0) atom. However, the bare 14 could not be isolated, but only the protonated cation [14H]+ and used as starting material [101]. Molecules 2020, 25, x FOR PEER REVIEW 28 of 54 Molecules 2020, 25, x FOR PEER REVIEW 28 of 54
2.14.2.14. TransitionTransition MetalMetal ComplexComplex withwith aa P-P-C-SC-S CoreCore PossessingPossessing aa NeutralNeutral S(II)S(II) LigandLigand TheThe carbonecarbone 1414 inin FigureFigure 1717 containscontains aa phosphinephosphine andand aa S(II)S(II) ligandligand withwith aa freefree pairpair ofof electrons to stabilize the C(0) atom. However, the bare 14 could not be isolated, but only the Moleculeselectrons2020, 25 ,to 4943 stabilize the C(0) atom. However, the bare 14 could not be isolated, but only the26 of 48 + protonatedprotonated cationcation [[14H14H]]+ andand usedused asas startingstarting materialmaterial [101].[101].
FigureFigureFigure 17. 17.17. Mixed MixedMixed PP andand S S stabilized stabilized carbonecarbone carbone 141414.. .
The transitionThe transition metal metal complex complex [14 -CuN(SiMe[14-CuN(SiMe) ](OTf)3)2](OTf) was was prepared prepared upon upon reacting reacting [ 14H[14H]]++ with The transition metal complex [14-CuN(SiMe3 2 3)2](OTf) was prepared upon reacting [14H]+ KHMDSwithwith/ CuCl. KHMDS/CuCl.KHMDS/CuCl. X-ray analysis X-rayX-ray analysisanalysis reveals arevealsreveals Cu-C a distancea Cu-CCu-C distancedistance of 1.903(4) ofof 1.903(4)1.903(4) Å and ÅÅ the andand P-C thethe and P-CP-C S-C andand distances S-CS-C amountdistancesdistances to 1.709(5) amountamount and to 1.677(5)to 1.709(5)1.709(5) Å, respectively.andand 1.677(5)1.677(5) AsÅ,Å, foundrespectively.respectively. in carbone AsAs found additionfound inin compoundscarbonecarbone additionaddition of 13a and 13b thecompoundscompounds P-C distance ofof 13a13a is longerandand 13b13b than thethe the P-CP-C S-C distancedistance distance. isis longerlonger An acute thanthan P-C-S thethe S-CS-C angle distance.distance. of 115.3(2) AnAn acuteacute◦ was P-C-SP-C-S recorded. 31 31 The angleangleP NMR ofof 115.3(2)°115.3(2)° signal is waswas shifted recorded.recorded. to lower TheThe fields 31PP NMRNMR at 66.5 signalsignal ppm isis shifted [shifted101]. toto lowerlower fieldsfields atat 66.566.5 ppmppm [101].[101].
2.15.2.15.2.15. Transition TransitionTransition Metal MetalMetal Complexes ComplexesComplexes of Carbones ofof CarbonesCarbones with withwith the thethe S-C-S S-C-SS-C-S Skeleton SkeletonSkeleton In theInIn carbones thethe carbonescarbones15 (carbodisulfanes, 1515 (carbodisulfanes,(carbodisulfanes, CDS) CDS)CDS) the the centralthe centralcentral carbon carboncarbon atom atomatom is stabilized isis stabilizedstabilized by by twoby twotwo neutral S(II) ligandsneutralneutral S(II)S(II) (15a ligands),ligands or S(II), ((15a15a S(IV)),), oror groupsS(II),S(II), S(IV)S(IV) (15b groupsgroups), or two ((15b15b S(IV)),), oror two (two15c S(IV))S(IV) ligands ((15c15c) (see) ligandsligands Figure (see(see 18 FigureFigure). 18).18).
CC CC CC Ph S SPh Ph2S SPh2 Ph2S SPh2 Ph22S SPh22 Ph2S SPh2 Ph2S SPh2 NMeNMe NMeNMe NMeNMe
15a 15b 15a 15b 1515cc Figure 18. Sulfur based carbones 15 as ligands for transition metal complexes. FigureFigure 18.18. SulfurSulfur basedbased carbonescarbones 1515 asas ligandsligands forfor transitiontransition metalmetal complexes.complexes. The molecular structure of 15a was investigated computationally (see Table 12)[102]. For the carbones theTheThe following molecularmolecular parameters structurestructure ofof were 15a15a waswas recorded: investigatedinvestigated15b, C-S computationallycomputationallyII 1.707(2), C-S (see(seeIV 1.648(2), TableTable 12)12) S-C-S [102].[102]. 106.67(14). ForFor II IV 13C NMR,thethe carbonescarbonesδ = 35.4 thethe ppm followingfollowing [103]. 15c parametersparameters, S-C 1.635(4), werewere 1.636(2); recorded:recorded: S-C-S 15b15b,, 116.8(2) C-SC-SII 1.707(2),1.707(2), [104]. C-S SimilarC-SIV 1.648(2),1.648(2), to CDCs S-C-SS-C-S the first 13 and second106.67(14).106.67(14). PAs 13 ofCC NMR,15bNMR,amount δδ == 35.435.4 to ppmppm 288.0 [103].[103]. and 15c 184.415c,, S-CS-C kcal 1.635(4),1.635(4),/mol, respectively. 1.636(2);1.636(2); S-C-SS-C-S 116.8(2)116.8(2) [104].[104]. SimilarSimilar toto CDCsCDCs thethe firstfirst andand secondsecond PAsPAs ofof 15b15b amountamount toto 288.0288.0 andand 184.4184.4 kcal/mol,kcal/mol, respectively.respectively. Table 12. Transition metal complexes with selected bond length (Å) and angles (deg) of the carbone Table 12. Transition metal complexes with selected bond length (Å) and angles (deg) of the ligandsTable15a to12.15c Transition. 13C NMR metal signal complexes (in ppm) with of theselected central bond carbon length atom. (Å) and angles (deg) of the 13 carbonecarbone ligandsligands 15a15a toto 15c15c.. 13CC NMRNMR signalsignal (in(in ppm)ppm) ofof thethe centralcentral carboncarbon atom.atom. 13 II II II 15-M C NMR13 C-M S -CII SII -M-SII Ref. 15-M15-M 13CC NMRNMR C-M C-M S SII-C-C SSII-M-S-M-SII Ref.Ref. 15a-AgCl not obs 2.058(8) 1.707(8)1.707(8) 1.698(8) 107.3(5) [102] 15a-AgCl not obs 2.058(8) 1.707(8) 107.3(5) [102] [15a-AuPPh15a-3]OTfAgCl 65.4not obs nr 2.058(8) 1.698(8) nr 107.3(5) nr [102] [102 ] [15a-(AuPPh ) ]2+ not obs 2.116(6) 2.084(5) 1.782(6)1.698(8) 1.767(6) 115.4(3) [102] [15a-AuPPh3 2 3]OTf 65.4 nr nr nr [102] [15a-AuPPh2+3]OTf 65.4 nr nr nr [102] [15aH-AuPPh3] 66.0 2.090(7) 1.837(7) 1.805(7) 104.4 [102] 2+ 2.116(6) 1.782(6) [15a-(AuPPh3)2] 2+ Transitionnot metal obs complexes2.116(6) with the CDS1.782(6)15b 115.4(3) [102] [15a-(AuPPh3)2] not obs 2.084(5) 1.767(6) 115.4(3) [102] C-M2.084(5) SII-C1.767(6) SIV-C SII-M-SIV 1.837(7) [15b-AuPPh[15aH-3AuPPh]OTf3]2+ 67.466.0 nr2.090(7) 1.837(7) nr 104.4 nr [102] [102 ] [15aH-AuPPh3]2+ 66.0 2.090(7) 104.4 [102] [15b-Ag-15b]OTf not obs 2.111(7) 2.097(7) 1.718(6)1.805(7)1.805(7) 1.664(7) 106.3(6) [102,105] Transition metal complexes with the CDS 15b [15b-(AuPPh3)2](OTf)2 Transitionnot obs metal2.130(3) complexes 2.103(3) with 1.792(3)the CDS 1.746(3) 15b 106.27(18) [102] C-M SII-C SIV-C SII-M-SIV [15b-Ag2-15b](OTf) 2 not obs nrC-M SII nr-C SIV-C SII-M-S nrIV [105] [15b-AuPPh3]OTf 67.4 nr nr nr [102] [15b-Ag[15b-4-15bAuPPh](OTf)34]OTf not obs67.4 2.192 2.187nr nrnr nr nr [102] [105 ] [15bH-AuPPh ](OTf) 72.1 2.098(3)2.111(7) 1.796(3)1.718(6) 1.789(3) 106.83(17)[102,10 [102] [15b-Ag-3 15b]OTf2 not obs 2.111(7) 1.718(6) 106.3(6) [102,10 [15b-Ag-15b]OTf Transitionnot metal obs complexes with the CDS 15c 106.3(6) 2.097(7)2.097(7) 1.664(7)1.664(7) 5]5] C-M SIV-C SIV-M-SIV
[15c-AuPPh3]OTf 65.1 nr nr nr [102] 15c-AgCl not obs 2.134(3) 1.690(3) 1.678(3) 112.16(14) [102] [15c-(AuPPh3)2](OTf)2 not obs 2.126(4) 2.125(4) 1.789(4) 1.735(5) 112.5(2) [102] [15c-Ag-15c]OTf 40.0 2.116 2.127 1.671–1.696 114.6 115.6 [105] [15c-Ag2-15c](OTf)2 43.1 2.147 1.666 1.696 114.7 [105] [15c-Ag4-15c](OTf)4 nr 2.228 2.193 nr nr [105] {[15c-(AuPPh3)2AgOTf](OTf)4}2 nr 2.139 2.108 1.757 1.747 116.8 [102] Molecules 2020, 25, x FOR PEER REVIEW 29 of 54
2.130(3) 1.792(3) [15b-(AuPPh3)2](OTf)2 not obs 106.27(18) [102] 2.103(3) 1.746(3) [15b-Ag2-15b](OTf)2 not obs nr nr nr [105] [15b-Ag4-15b](OTf)4 not obs 2.192 2.187 nr nr [105] 1.796(3) [15bH-AuPPh3](OTf)2 72.1 2.098(3) 106.83(17) [102] 1.789(3) Transition metal complexes with the CDS 15c C-M SIV-C SIV-M-SIV [15c-AuPPh3]OTf 65.1 nr nr nr [102] 1.690(3) 15c-AgCl not obs 2.134(3) 112.16(14) [102] 1.678(3) 2.126(4) 1.789(4) [15c-(AuPPh3)2](OTf)2 not obs 112.5(2) [102] 2.125(4) 1.735(5) [15c-Ag-15c]OTf 40.0 2.116 2.127 1.671–1.696 114.6 115.6 [105] [15c-Ag2-15c](OTf)2 43.1 2.147 1.666 1.696 114.7 [105] Molecules 2020[15c, 25-Ag, 49434-15c](OTf)4 nr 2.228 2.193 nr nr [105]27 of 48 {[15c-(AuPPh3)2AgOTf](OTf)4}2 nr 2.139 2.108 1.757 1.747 116.8 [102]
+ + 15a15a--AgClAgCl was was obtained obtained from [15aHfrom] [upon15aH treating] upon with treating Ag2O /CHwith2Cl 2Ag. The2O/CH salt [2Cl15a2.-AuPPh The salt3]OTf formed[15a-AuPPh reacting3]OTf the bare formed15a withreacting AuCl(PPh the bare3) 15a followed with AuCl(PPh by addition3) offollowed NaTfO by in THF.addition [15a of-(AuPPh NaTfO3 )2] (OTf)in THF.2 and [ [15a15aH-(AuPPh-AuPPh3)23](OTf)](SbF62) and are sketched[15aH-AuPPh in Scheme3](SbF 226) are[102 sketched]. in Scheme 22 [102].
Scheme 22. Selected of complexes with the carbone 15a. (a) 2 eq AuCl(PPh3), (b) AuCl(PPh3)2.
[15bScheme-AuPPh 22.3]OTf Selected was of obtained complexes analogously with the carbone formed 15a. from (a) 2 reacting eq AuCl(PPh15b with3), (b) AuCl(PPh AuCl(PPh33)2 followed. byMolecules addition 2020 of, NaTfO25, x FOR in PEER THF. REVIEW For the other compounds, see Scheme 23[102]. 30 of 54
[15b-AuPPh3]OTf was obtained analogously formed from reacting 15b with AuCl(PPh3) followed by addition of NaTfO in THF. For the other compounds, see Scheme 23 [102].
Scheme 23. Selected of complexes with the carbone 15b. (a) 0.5 eq AgOTf, (b) 1.0 eq AgOTf, (c) 2.0 eq Scheme 23. Selected of complexes with the carbone 15b. (a) 0.5 eq AgOTf, (b) 1.0 eq AgOTf, (c) AgOTf, (d) 2 eq AuCl(PPh3), (e) AuCl(PPh3). 2.0 eq AgOTf, (d) 2 eq AuCl(PPh3), (e) AuCl(PPh3).
The preparation of [15c-AuPPh3]OTf and 15c-AgCl follows the procedure outlined for the related 15b compounds [102]. For the other compounds, see Scheme 24 [102,105]. The hetero hexametallic cluster {[15c-(AuPPh3)2AgOTf](OTf)4}2 is supported by two carbone ligands that adopt a κ4C,C’,N,N’ coordination mode. The Au-Ag separation amounts to 3.003 Å [102].
Molecules 2020, 25, 4943 28 of 48
The preparation of [15c-AuPPh3]OTf and 15c-AgCl follows the procedure outlined for the related 15b compounds [102]. For the other compounds, see Scheme 24[ 102,105]. The hetero hexametallic 4 cluster {[15c-(AuPPh3)2AgOTf](OTf)4}2 is supported by two carbone ligands that adopt a κ C,C’,N,N’ coordinationMolecules 2020 mode., 25, x FOR The PEER Au-Ag REVIEW separation amounts to 3.003 Å [102]. 31 of 54
Scheme 24. Selected complexes with the carbone ligand 15c; (a) AgOTf, (b) 0.5 eq AgOTf, (c) 1.0 eq Scheme 24. Selected complexes with the carbone ligand 15c; (a) AgOTf, (b) 0.5 eq AgOTf, (c) 1.0 AgOTf, (d) 2.0 eq AgOTf. {[15c-(AuPPh3)2AgOTf](OTf)4}2 is dimeric linked by two OTf anions. eq AgOTf, (d) 2.0 eq AgOTf. {[15c-(AuPPh3)2AgOTf](OTf)4}2 is dimeric linked by two OTf 13Canions. NMR signals of the donating C(0) atoms (if available) of all addition compounds of 15a to 15c are less shielded than that of the basic carbones [102]. 13C NMR signals of the donating C(0) atoms (if available) of all addition compounds of 15a 2.16.to 15c Transition are less Metal shielded Complexes than that of Carbones of the basic with thecarbones S-C-Se [102]. Skeleton (16) Compound 16 in Figure 19 is the first carbone containing a Se(II) compound together with a S(IV) 2.16. Transition Metal Complexes of Carbones with the S-C-Se Skeleton (16) one as ligand for stabilization of a C(0) atom. Compound 16 in Figure 19 is the first carbone containing a Se(II) compound together with a S(IV) one as ligand for stabilization of a C(0) atom.
Figure 19. Carbone with Se and S based ligands L.
Molecules 2020, 25, x FOR PEER REVIEW 31 of 54
Scheme 24. Selected complexes with the carbone ligand 15c; (a) AgOTf, (b) 0.5 eq AgOTf, (c) 1.0 eq AgOTf, (d) 2.0 eq AgOTf. {[15c-(AuPPh3)2AgOTf](OTf)4}2 is dimeric linked by two OTf anions.
13C NMR signals of the donating C(0) atoms (if available) of all addition compounds of 15a to 15c are less shielded than that of the basic carbones [102].
2.16. Transition Metal Complexes of Carbones with the S-C-Se Skeleton (16) in MoleculesCompound2020, 25, 4943 16 Figure 19 is the first carbone containing a Se(II) compound together with29 of 48 a S(IV) one as ligand for stabilization of a C(0) atom.
Molecules 2020, 25, x FOR PEER REVIEW 32 of 54 Figure 19. Carbone with Se and S based ligands L. Figure 19. Carbone with Se and S based ligands L. The tetranuclear complex [16-Ag4-16]4+ contains a rhomboidal [Ag4]4+ core surrounded by 4+ 4+ twoThe carbones tetranuclear 16 (see complex Table [ 1613).-Ag In4- 16this] andcontains in [16H a rhomboidal-Ag-16H]3+[Ag the4 ]donatingcore surrounded C(0) acts byas twoa carbonesfour-electron16 (see donor Table (see13). Scheme In this and25) [105]. in [16H -Ag-16H]3+ the donating C(0) acts as a four-electron donor (see Scheme 25)[105]. Table 13. Transition metal complexes with selected bond length (Å) and angles (deg) of the Tablecarbone 13. Transition 16. 13C NMR metal signal complexes (in ppm) with of selectedthe central bond carbon length atom. (Å) and angles (deg) of the carbone 16. 13C NMR signal (in ppm) of the central carbon atom. 16-M 13C NMR C-M C-S C-Se S-C-Se Ref. [16-Ag-1616-M](OTf) not13C obs. NMR C-Mnr C-S C-Senr S-C-Senr Ref.[105] [16-[Ag16-Ag-2-16](OTf)16](OTf)2 not52.7 obs. nrnr nrnr nrnr [105[105]] 1.714(5) [16-[16Ag-Ag4-162-](OTf)16](OTf)4 2 not52.7 obs 2.174(5) nr nr106.4(3) nr [105[105]] 1.714(5)1.923(6) [16-Ag -16](OTf) not obs 2.174(5) 106.4(3) [105] 4 4 1.923(6)1.772(5) 2.164(4)2.164(4) 1.772(5)1.771(5) 1.771(5) [16H[16H-Ag--Ag-16H](BF16H](BF4)3 4)3 notnot obs obs 103.8(2)103.8(2) [103[103]] 2.177(4)2.177(4) 1.936(4)1.936(4) 1.948(5) 1.948(5) + Me 2+ Me N Ph2Se Ph Se SPh 2 2 C Ag N C Ag C SPh2 Ph2S Ph2S SePh2 N Ag C N Me SePh2 a b Me 16 d c [16-Ag -16](OTf) [16-Ag-16](OTf) 2 2
3+ Me Ph Ph 4+ Se Ag N Ph2Se H SPh2 C Ag NMe SPh C Ag C Ph2S 2
Ph2S H SePh 2 MeN Ag C N Ag Se Me Ph Ph
[16H-Ag-16H ](BF4)3 [16-Ag4-16](OTf)4 Scheme 25. 16 Scheme 25.Transition Transition metal metal complexes complexes with with the the carbone carbone as16 twoas two and and four four electron electron donor. donor. (a) 0.5(a) eq AgOTf, (b) 1 eq AgOTf, (c) 2.0 eq AgOTf, (d) AgBF4/CH2Cl2. 0.5 eq AgOTf, (b) 1 eq AgOTf, (c) 2.0 eq AgOTf, (d) AgBF4/CH2Cl2. 3. Transition Metal Carbido Complexes [M]-C 3. Transition Metal Carbido Complexes [M]-C The second part of this review summarizes the research of transition metal complexes with a naked carbonThe second atom part as ligand of this [M]-C. review They summarizes are often the termed research as carbides,of transition but metal the bonding complexes situation with is clearlya naked different carbon from atom well-known as ligand carbides[M]-C. They of the are alkaline often andtermed alkaline as carbides, earth elements but the E, bonding which are situation is clearly different from well-known carbides of the alkaline and alkaline 1earth salt compounds of acetylene EnC2. The electron configuration of carbon atom in the D state elements E, which are salt compounds of acetylene EnC2. The electron configuration of carbon atom in the 1D state (2s22px22py02pz0) is perfectly suited for dative bonding with a transition metal following the DCD model [7] in terms of σ donation and π backdonation [M] C|. Carbon complexes [M]-C may thus be considered as carbone complexes [M]-CL2 without the ligands L at the carbon atoms. A theoretical study showed in 2000 that the 18 valence electron (VE) complex [(CO)4Fe(C)] is an energy minimum structure with a rather strong Fe-C bond [106]. However, such 18 VE systems could not be synthesized as isolated species but were only found as ligands where the lone-pair electron at the carbon atom serves as donor (see below). It seems that the electron lone-pair at carbon in the 18 VE complexes [M]-C makes the adducts too reactive to become isolated.
Review Carbones and Carbon Atom as Ligands in Transition Metal Complexes
Lili Zhao 1, Chaoqun Chai 1, Wolfgang Petz 2,* and Gernot Frenking 1,2,*
1 Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China; [email protected] (L.Z.); [email protected] (C.C.) 2 Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse 4, D-35043 Marburg, Germany * Correspondence: [email protected] (W.P.); [email protected] (G.F.)
Received: 23 August 2020; Accepted: 15 October 2020; Published: 23 October 2020
Abstract: This review summarizes experimental and theoretical studies of transition metal complexes with two types of novel metal-carbon bonds. One type features complexes with carbones CL2 as ligands, where the carbon(0) atom has two electron lone pairs which engage in double (σ and π) donation to the metal atom [M]⇇CL2. The second part of this review reports complexes which have a neutral carbon atom C as ligand. Carbido complexes with naked carbon atoms may be considered as endpoint of the series [M]-CR3 → [M]-CR2 → [M]-CR → [M]-C. This review includes some work on uranium and cerium complexes, but it does not present a complete coverage of actinide and lanthanide complexes with carbone or carbide ligands.
Keywords: carbone complexes; carbido complexes; transition metal complexes; chemical bonding
1. Introduction Transition metal compounds with metal-carbon bonds are the backbone of organometallic chemistry. Molecules with M-C single bonds are already known since 1849 when Frankland reported the accidental synthesis of diethyl zinc while attempting to prepare free ethyl radicals [1,2]. Molecules with a [M]=CR2 double bond (carbene complexes) or a [M]≡CR triple bond
(carbyneMolecules complexes)2020, 25, 4943 were synthesized much later [3–6]. Two types of compounds with 30 of 48 metal-carbon double or triple bonds having different types of bonds are generally distinguished, which are named after the people who isolated them first. Fischer-type carbene 2 2 0 0 and(2s carbyne2px 2p ycomplexes2pz ) is perfectly are best suited described for dative in terms bonding of dative with abonds transition following metal the following Dewar– the DCD ─ Chatt–Duncanmodel [7] in terms(DCD) of σmodeldonation [7,8] and [M]π backdonation⇄CR2 and [M [M]( )] C CR|. Carbon(+), whereas complexes Schrock-type [M]-C may thus alkylidenesbe considered and asalkylidynes carbone complexes are assumed [M]-CL to 2havewithout electron-sharing the ligands L atdouble the carbon and triple atoms. bonds A theoretical [M]=CRstudy2 showedand [M] in≡CR 2000 [9–11]. that the 18 valence electron (VE) complex [(CO)4Fe(C)] is an energy minimum structureThis review with adeals rather with strong transition Fe-C bond metal [106 complexes]. However, with such metal-carbon 18 VE systems bonds could to nottwo be types synthesized of asligands, isolated which species have but only were recently only foundbeen isolated as ligands and wheretheoretically the lone-pair studied. electron One type at theof ligand carbon atom areserves carbones as donor CL2 [12], (see which below). are Itcarbon(0) seems that compounds the electron with lone-pair two dative at carbonbonds to in a the carbon 18 VE atom complexes in [M]-Cthe excited makes 1D the state adducts L→C ← tooL where reactive the to carbon become atom isolated. retains its four valence electrons as two lone pairsIt came that ascan a serve surprise as four-electron when Heppert donors and co-workers [13,14]. Thus, reported carbones in 2002 CL2 theare firstfour-electron neutral adducts donorwith ligands a naked whereas carbon atom carbenes as a ligand, CR2 are which two-electron are the formally donors. 16 Carbenes VE diamagnetic have a rutheniumformally [15] complexes Molecules[(PCy 20203)LCl, 252,Ru(C)] x; doi: FOR (L= PEERPCy REVIEW and 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene; www.mdpi.com/journ Cy = Cyclohexyl)al/molecules [27 ]. A subsequent bonding analysis of the model compound [(Me3P)2Cl2Ru-C] considered five different models A–E for the Ru-C bonds that are shown in Figure 20[ 28]. It turned out that the best description for the bonding interactions is a combination of electron-sharing and dative bonds. An energy decomposition analysis [107] suggested that the model B provides the most faithful account of the bond, where the σ bond and the π bond in the Cl2M plane come from electron-sharing interactions Cl M=C whereas the π bond in the P M plane is due to backdonation (Me P) Ru C. The compounds 2 2 3 2 → [(PCy3)LCl2Ru(C)] should therefore be considered as 18 VE Ru(IV) adducts. The following section summarizes the research of transition metal complexes with a naked carbon atom as ligand [M]-C that has been accomplished since 2002.
FigureFigure 20. 20.Bonding Bonding models models (A– (EA)– forE) for the the bonding bonding between between a transition a transition metal metal (TM) (TM) and and a naked a naked carbon atomcarbon in the atom compound in the compound [(R3P)2Cl2 Ru-C].[(R3P)2Cl2Ru-C].
3.1. The System RuCl2(PCy3)2C ([Ru]C) By far the most known complexes with carbido ligands that have been synthesized and structurally characterized are ruthenium adducts. The progress in the chemistry of ruthenium carbido complexes was reviewed in 2012 by Takemoto and Matsuzaka [108]. In the following, we summarize the present knowledge on ruthenium carbido complexes which has been reported in the literature. The X-ray analysis of [Ru]C in Figure 21 exhibits a Ru-C distance of 1.632(6) Å. A signal at 471.8 ppm was attributed to the ligand carbon atom [109]. A general route to carbon complexes is described in [110].
Molecules 2020, 25, x; doi: FOR PEER REVIEW www.mdpi.com/journal/molecules Molecules 2020, 25, 4943 31 of 48 Molecules 2020, 25, x FOR PEER REVIEW 34 of 54 Molecules 2020, 25, x FOR PEER REVIEW 34 of 54
Figure 21. The [Ru]C core. FigureFigure 21.21. The [Ru]C core. core.
Addition of PdCl2(SMe2)2 gives the complex [Ru]C→PdCl2(SMe2), while with AdditionAddition of PdCl of2(SMe PdCl2)2(SMegives2)2 thegives complex the [Ru]CcomplexPdCl [Ru]C2(SMe→PdCl2), while2(SMe with2), while Mo(CO) with5(NMe 3) Mo(CO)5(NMe3) the carbonyl complex [Ru]C→Mo(CO)→5 is generated (see Table 14) [29,109]. A the carbonylMo(CO) complex5(NMe3) [Ru]Cthe carbonylMo(CO) complex5 is generated [Ru]C→Mo(CO) (see Table5 is generated 14)[29,109 (see]. ATable series 14) of [29,109]. [Ru]C APtCl 2L series of [Ru]C→PtCl2L→ complexes were obtained by Bendix from reacting the dimeric complex→ complexes were obtained→ by2 Bendix from reacting the dimeric complex {[Ru]C PtCl ] with various series of [Ru]C PtCl L complexes were obtained by Bendix from reacting the dimerict 2 2complex {[Ru]C→PtCl2]2 with various ligands L (L =t PPh3, PCy3, P(OPh)3, AsPh3,→ CN Bu, CNCy). ligands{[Ru]C L (L→=PtClPPh2]32, with PCy 3various, P(OPh) ligands3, AsPh L3 ,(L CN = Bu,PPh3 CNCy)., PCy3, P(OPh) Complexes3, AsPh with3, CN bridgingtBu, CNCy). ligands L Complexes with bridging ligands L such as {[Ru]C→PtCl2]2bipy, {[Ru]C→PtCl2]2pyz, and such asComplexes {[Ru]C PtClwith2 ]2bridgingbipy, {[Ru]C ligandsPtCl L such2]2pyz, as and{[Ru]C {[Ru]C→PtCl2PtCl]2bipy,2]2 pym{[Ru]C formed→PtCl2 upon]2pyz, displacingand {[Ru]C→→PtCl2]2pym formed → upon displacing ethylene→ from the related ethylene{[Ru]C from→ thePtCl related2]2pym (C formedH )PtCl -L-PtClupon (CdisplacingH ) by [Ru]C. ethylene {[Ru]C fromPtCl] (µthe-Cl)pz related results from (C2H4)PtCl2-L-PtCl2(C2H24) by4 [Ru]C.2 {[Ru]C2 →2PtCl]4 2(μ-Cl)pz results from an ethylene2 complex (C2H4)PtCl2-L-PtCl2(C2H4) by [Ru]C. {[Ru]C→PtCl]2(μ-Cl)pz results from→ an ethylene complex an ethyleneand [Ru]C complex as depicted and [Ru]C in Scheme as depicted 26 [111]. in A Scheme series of 26 Pt,[ 111Pd,]. Rh, A Ir, series Ag, ofRu Pt,complexes Pd, Rh, were Ir, Ag, Ru and [Ru]C as depicted in Scheme 26 [111]. A series of Pt,13 Pd, Rh, Ir, Ag, Ru complexes were complexespresented were by presented Bendix with by Bendix X-ray data with and X-ray 13C data NMR and shiftsC of NMR the ligand shifts carbon of the ligandatom ranging carbon atom presented by Bendix with X-ray data and 13C NMR shifts of the ligand carbon atom ranging rangingbetween between 340 340 and and 412 412 ppm ppm [112]. [112 Sulfur]. Sulfur containing containing TM complexes TM complexes with the with metals the metals Pd, Pt, Pd, Au, Pt, Au, between 340 and 412 ppm [112]. Sulfur containing TM complexes with the metals Pd, Pt, Au, and Cuand stem Cu fromstem from the same the same laboratory. laboratory. The The sulfur sulfur ligands ligands are are ttcn ttcn= =1,4,7-trithiacyclononane 1,4,7-trithiacyclononane and and Cu stem from the same laboratory. The sulfur ligands are ttcn = 1,4,7-trithiacyclononane S4(MCp*)and3 S(see4(MCp*) Figure3 (see 22 Figure)[113]. 22) [113]. and S4(MCp*)3 (see Figure 22) [113].
Figure 22. Spezification of ligands of Table 14. Figure 22. Spezification of ligands of Table 14. Table 14. Selected structuralFigure (in Å and22. Spezification deg) and spectroscopic of ligands of Table (13C 14. NMR in ppm) details of [Ru]C additionTable compounds. 14. Selected structural (in Å and deg) and spectroscopic (13C NMR in ppm) details of Table 14. Selected structural (in Å and deg) and spectroscopic (13C NMR in ppm) details of [Ru]C addition compounds. [Ru]C addition compounds. 13C NMR Ru-C M-C Ru-C-M Ref 13C NMR Ru-C M-C Ru-C-M ref 13 [Ru]C PdCl (SMe→ ) 381.23C NMR 1.662(2) Ru-C 1.946(2)M-C Ru-C-M 175.1(1) ref [109] → [Ru]C2 PdCl2 2(SMe2) 381.23 1.662(2) 1.946(2) 175.1(1) [109] {[Ru]C[Ru]CPdCl→PdCl} 2(SMe2) 380.9381.23 1.662(2) nr 1.946(2) nr 175.1(1) nr[109] [112] {[Ru]C3 →− PdCl3}- 380.9 nr nr nr [112] → → - [Ru]C Mo(CO){[Ru]C→ PdCl3} 446.31380.9 nrnr nr nr nr nr[112] [109] → [Ru]C Mo(CO)5 5 446.31 nr nr nr [109] [Ru]C [Ru]CPtCl →PyMo(CO)5 350.34446.31 nrnr nr nr nr nr[109] [29,111] [Ru]C2 →PtCl2Py 350.34 nr nr nr [29,111] → → [Ru]C PtCl [Ru]CNCr(dbm)→ PtCl2Py nr350.34 1.676(2)nr 1.899(2)nr nr 174.5(1)[29,111] [29] → [Ru]C2 PtCl2NCr(dbm)2 2 nr 1.676(2) 1.899(2) 174.5(1) [29] {[Ru]C[Ru]CPtCl→PtCl} 2NCr(dbm)2 344.7nr 1.676(2) nr 1.899(2) nr 174.5(1) nr[29] [29,112] {[Ru]C3 −→PtCl3}- 344.7 nr nr nr [29,112] → → - {[Ru]C {[Ru]CPtCl }→PtCl3} 326.23344.7 1.676(8)nr 1.871(8)nr nr 1796(4)[29,112] [ 29,111] →{[Ru]C2 2 PtCl2}2 326.23 1.676(8) 1.871(8) 1796(4) [29,111] [Ru]C PtCl{[Ru]CPPh→PtCl2}2 388.81326.23 1672(2)1.676(8) 1.871(8) 1.983(2) 1796(4) 173.7(1) [29,111] [111] [Ru]C2 →PtCl3 2PPh3 388.81 1672(2) 1.983(2) 173.7(1) [111] → → [Ru]C PtCl[Ru]CP(OPh)→ PtCl2PPh3 387.54388.81 1.659(2)1672(2) 1.983(2) 2.001(2) 173.7(1) 179.3(2) [111] [111] → [Ru]C2 PtCl23P(OPh)3 387.54 1.659(2) 2.001(2) 179.3(2) [111] [Ru]C [Ru]CPtCl →AsPhPtCl2P(OPh)3 374.68387.54 1.670(2)1.659(2) 2.001(2) 1.949(2) 179.3(2) 171.9(2) [111] [111] [Ru]C2 →PtCl3 2AsPh3 374.68 1.670(2) 1.949(2) 171.9(2) [111] → → t [Ru]C PtCl[Ru]CCNPtClBu2AsPh3 376.26374.68 1.661(2)1.670(2) 1.949(2) 1.967(6) 171.9(2) 176.5(3) [111] [111] [Ru]C2 →PtCl2CNtBu 376.26 1.661(2) 1.967(6) 176.5(3) [111] → → t [Ru]C PtCl[Ru]CCNCyPtCl2CN Bu 376.04376.26 1.661(2) nr 1.967(6) nr 176.5(3) nr[111] [111] [Ru]C2 →PtCl2CNCy 376.04 nr nr nr [111] → → [Ru]C [Ru]CPtCl PCyPtCl2CNCy 396.77376.04 1.666(3)nr 1.971(2)nr nr 174.5(2)[111] [111] → 2 3 [Ru]C PtCl (dmso) 349.0 [112] → 2 {[Ru]C PtCl } bipy 348.27 1.679(3) 1.891(4) 171.4(2) [111] → 2 2 {[Ru]C PtCl } pyz 342.48 1.668(6) 1.895(6) 176.3(3) [111] → 2 2 Molecules 2020, 25, x FOR PEER REVIEW 35 of 54 Molecules 2020, 25, 4943 32 of 48 Molecules 2020, 25, x FOR PEER REVIEW 35 of 54 [Ru]C→PtCl2PCy3 396.77 1.666(3) 1.971(2) 174.5(2) [111] → [Ru]C PtCl→ 2(dmso) 349.0 [112] [Ru]C PtCl2PCy3 396.77Table 14.1.666(3)Cont. 1.971(2) 174.5(2) [111] {[Ru]C→PtCl2}2bipy 348.27 1.679(3) 1.891(4) 171.4(2) [111] [Ru]C→PtCl2(dmso) 349.0 [112]
{[Ru]C→PtCl2}2pyz 13 342.48 1.668(6) 1.895(6) 176.3(3) [111] {[Ru]C→PtCl2}2bipy C NMR348.27 Ru-C1.679(3) 1.891(4) M-C 171.4(2) Ru-C-M [111] Ref {[Ru]C→PtCl2}2pym 341.36 1.678(3) 1.893(3) 176.0(2) [111] {[Ru]C→PtCl2}2pyz 342.48 1.668(6) 1.895(6) 176.3(3) [111] {[Ru]C PtCl→ 2}2pym2 341.36 1.678(3) 1.893(3) 176.0(2) [111] {[Ru]C→{[Ru]CPtCl}→PtCl(μ2-Cl)pz}2pym 355.09341.36 1.678(4)1.678(3) 1.893(3)1.909(4) 176.0(2)169.9(2) [111][111] {[Ru]C PtCl}2(µ→-Cl)pz 355.09 1.678(4) 1.909(4) 169.9(2) [111] → [Ru]C→ AuCl2 395.3 nr nr nr [112] [Ru]C{[Ru]CAuClPtCl} (μ-Cl)pz 395.3355.09 1.678(4) nr 1.909(4) nr 169.9(2) nr [111] [112] {[Ru]C→→Au→←C[Ru]}+ 395.3 nr nr nr [112] {[Ru]C Au[Ru]CC[Ru]}AuCl+ 395.3395.3 nrnr nr nr nr nr[112] [112] {[Ru]C→ →←IrCl(CO)→ ←←C[Ru]}+ 397.4 nr nr nr [112] {[Ru]C IrCl(CO){[Ru]C AuC[Ru]}C[Ru]} 397.4395.3 nrnr nr nr nr nr[112] [112] → →→ ← ← {[Ru]C{[Ru]C{[Ru]CRh(CO)}Rh(CO)}IrCl(CO)(µ-Cl)2(μ-Cl)C[Ru]}2 396.4 396.4397.4 nr nr nr nr nr nr nr nr [112] [112] [112] → →→ 2 2 [Ru]C{[Ru]C[Ru]CRhCl(cod)Rh(CO)}RhCl(cod)2(μ -Cl)2 411.7411.7396.4 nrnr nr nrnr nr nr nr nr [112][112] [112] → → [Ru]C[Ru]C[Ru]CIrCl(cod)→IrCl(cod)RhCl(cod) 387.6387.6411.7 nrnrnr nrnr nr nrnr nr[112][112] [112] →→ → {[Ru]C{[Ru]CAg(4[Ru]C0Ag(4-H-terpy)}IrCl(cod)′-H-terpy)} 433.5433.5387.6 nr nrnr nr nr nr nr nr nr[112] [112] [112] → → → {[Ru]C{[Ru]C{[Ru]CAg(40Ag(4-Ph-terpy)}Ag(4′-Ph-terpy)}′-H-terpy)} 433.1433.1433.5 nr nr nr nr nr nr nr nr nr [112] [112] [112] → → [Ru]C{[Ru]C[Ru]CAg(ttcn)→Ag(4Ag(ttcn)′-Ph-terpy)} nr433.1nr 1.653(4)1.653(4) nr 1.876(4) 1.876(4) nr 177.3(2) nr 177.3(2) [112][112] [112] → [Ru]C [Ru]CCu(ttcn)→→Ag(ttcn) nrnr 1.622(7)1.653(4) 1.876(4) 2.098(7) 177.3(2) 176.9(5) [112] [112] [Ru]C→ Cu(ttcn) nr 1.622(7) 2.098(7) 176.9(5) [112] [Ru]C Pd-S[Ru]C→(MoCp*)→Cu(ttcn) nrnr 1.672(3)1.622(7) 2.098(7) 1.971(3 176.9(5) 178.3(2) [112] [112] [Ru]C→ 4Pd-S4(MoCp*)3 3 nr 1.672(3) 1.971(3 178.3(2) [112] [Ru]C [Ru]CPt-S (MoCp*)→Pd-S4(MoCp*)3 nrnr 1.689(7)1.672(3) 1.971(3 1.896(7) 178.3(2) 178.2(5) [112] [112] [Ru]C→4 Pt-S4(MoCp*)3 3 nr 1.689(7) 1.896(7) 178.2(5) [112] → → [Ru]C [Ru]CPd-S→4(WCp*)Pt-S4(MoCp*)3 3 nrnr 1.668(5)1.689(7) 1.896(7) 1.959(5) 178.2(5) 178.1(3) [112] [112] [Ru]C→ Pd-S4(WCp*)3 nr 1.668(5) 1.959(5) 178.1(3) [112] [Ru]C [Ru]CPt-S4(WCp*)→Pd-S4(WCp*)3 3 nrnr 1.699(9)1.668(5) 1.959(5) 1.874(9) 178.1(3) 178.8(6) [112] [112] [Ru]C→ →Pt-S4(WCp*)3 nr 1.699(9) 1.874(9) 178.8(6) [112] [Ru]C→Pt-S4(WCp*)3 nr 1.699(9) 1.874(9) 178.8(6) [112]
SchemeScheme 26. 26.Selected Selected [Ru]C [Ru]C→MM carbido carbido complexescomplexes and synthesis of of {[Ru]C {[Ru]C→PtCl}PtCl}2(μ(-Cl)pz.µ-Cl)pz. Scheme 26. Selected [Ru]C→M carbido complexes and synthesis of {[Ru]C→PtCl}2(μ-Cl)pz. NHCNHC 3.2. The3.2. System The System RuCl RuCl2(PCy2(PCy3)(NHC)C3)(NHC)C ( ( [Ru]C)[Ru]C) 3.2. The System RuCl2(PCy3)(NHC)C (NHC[Ru]C) The X-rayThe X-ray analysis analysis of NHC of NHC[Ru]C[Ru]C in in Figure Figure 23 23 exhibits exhibits aa Ru-CRu-C distance of of 1.605(2) 1.605(2) Å. Å. A Asignal signal at The X-ray analysis of NHC[Ru]C in Figure 23 exhibits a Ru-C distance of 1.605(2) Å. A signal 471.5at ppm 471.5 was ppm attributed was attributed to the to ligand the ligand carbon carb atom.on atom. No No addition addition compoundscompounds were were described described so at 471.5 ppm was attributed to the ligand carbon atom. No addition compounds were described far [27so]. far [27]. so far [27].
Figure 23. The NHC[Ru]C core.
Molecules 2020, 25, x FOR PEER REVIEW 36 of 54
Molecules 2020, 25, x FOR PEER REVIEW Figure 23. The NHC[Ru]C core. 36 of 54 Molecules 2020, 25, x FOR PEER REVIEW 36 of 54 Molecules3.3. The2020 System, 25, 4943 (NHC)Cl3RuC- (NHC[Ru]Figure-C) 23. The NHC[Ru]C core. 33 of 48 Figure 23. The NHC[Ru]C core. Treating the carbene complex (NHC)Cl2(PCy3)Ru=CH2 in Figure 24 at 55° in benzene 3.3. The System (NHC)Cl3RuC- (NHC[Ru]-C) generated the neutral complexNHC depicted in Figure 25. X-ray analysis revealed a Ru1-C distance 3.3.3.3. The The System System (NHC)Cl (NHC)Cl3RuC3RuC− (- (NHC[Ru][Ru]−-C)C) of 1.698(4)Treating Å andthe thecarbene Ru2-C complex distance (NHC)Clof 1.875(4)2(PCy Å with3)Ru=CH a Ru-C-Ru2 in Figure angle of24 160.3(2)°.at 55° in Inbenzene the 13C Treating the carbene complex (NHC)Cl (PCy )Ru=CH in Figure 24 at 55 in benzene generated generatedNMRTreating the bridgingthe theneutral carbene C atom complex resonatescomplex depicted (NHC)Clat the in2 typicalFigure2(PCy3 value25.3)Ru=CH X-ray 2of 414.0 analysis2 in ppmFigure revealed [114]. 24◦ at a 55°Ru 1-Cin distancebenzene 1 theofgenerated neutral 1.698(4) complex theÅ and neutral the depicted Ru complex2-C in distance Figure depicted 25of. 1.875(4) X-rayin Figure analysis Å with25. X-ray revealed a Ru-C-Ru analysis a Ru angle revealed-C distance of 160.3(2)°. a Ru of1 1.698(4)-C In distance the Å13C and 2 13 theNMRof Ru 1.698(4)-C the distance bridging Å and ofthe C 1.875(4) atomRu2-C resonates distance Å with a atof Ru-C-Ru the1.875(4) typical angle Å valuewith of a 160.3(2)of Ru-C-Ru 414.0◦ ppm. In angle the [114]. ofC 160.3(2)°. NMR the In bridging the 13C C atomNMR resonates the bridging at the C typical atom valueresonates of 414.0 at the ppm typical [114 ].value of 414.0 ppm [114].
Figure 24. The NHC[RuCl3]-C core.
Figure 24. The NHC[RuCl3]-C core. NHC Figure 24. The NHC[RuCl ]-−C core. Figure 24. The [RuCl3] C core.
Figure 25. Structural representation of the Ru carbido complex Ru2(NHC) 2(≡C)Cl3H.
Figure 25. Structural representation of the Ru carbido complex Ru2(NHC)2( C)Cl3H. 3.4. The systemFigure RuClX(PCy 25. Structural3)2 Crepresentation ([Ru]XC) of the Ru carbido complex Ru2(NHC)2(≡C)Cl3H. 3.4. The systemFigure RuClX(PCy 25. Structural) C ([Ru]XC)representation of the Ru carbido complex Ru2(NHC)2(≡C)Cl3H. Various carbido complexes3 2 were reported in which one or both chloride ions in [Ru]C are 3.4. The system RuClX(PCy3)2C ([Ru]XC) replacedVarious by carbido X (X = complexesBr, I, CN, NCO, werereported NCS) (see in Figure which one26). or{[Ru](MeCN)C}OTf both chloride ions is in the [Ru]C first are cationic replaced 3.4. The system RuClX(PCy3)2C ([Ru]XC) bycarbido X (XVarious= complexBr, I, carbido CN, which NCO, complexes is NCS) also (seestartingwere Figure reported point 26 ). forin {[Ru](MeCN)C}OTf whichmost ofone the or substitutedboth chloride is the carbido first ions cationic in complexes. [Ru]C carbido are complexreplacedX-rayVarious data which by for X carbido is(X {[Ru](MeCN)C}OTf, also = Br, startingcomplexes I, CN, NCO, point were NCS) for[Ru](CN) reported most (see of 2FigureC, thein [Ru](Br)C, which substituted 26). {[Ru](MeCN)C}OTfone and or carbido both[Ru](NCO)C chloride complexes. is areions the available firstin X-ray [Ru]C cationic data (see are for replaced by X (X = Br, I, CN, NCO, NCS) (see Figure 26). {[Ru](MeCN)C}OTf is the first cationic {[Ru](MeCN)C}OTf,carbidoTable 15) complex [115]. which [Ru](CN) is 2alsoC, [Ru](Br)C, starting point and [Ru](NCO)Cfor most of the are availablesubstituted (see carbido Table 15 complexes.) [115]. X-raycarbido data complex for {[Ru](MeCN)C}OTf, which is also starting [Ru](CN) point2C, for [Ru](Br)C, most of theand substituted [Ru](NCO)C carbido are available complexes. (see TableX-ray 15)data [115]. for {[Ru](MeCN)C}OTf, [Ru](CN)2C, [Ru](Br)C, and [Ru](NCO)C are available (see Table 15) [115].
Figure 26. Carbido compounds of [Ru]XC with various X.
Molecules 2020, 25, x FOR PEER REVIEW 37 of 54
Molecules 2020, 25, 4943 Figure 26. Carbido compounds of [Ru]XC with various X. 34 of 48
Table 15. Carbido complexes with the [Ru]XC core. Table 15. Carbido complexes with the [Ru]XC core. 13C NMR Ru-C M-C Ru-C-M Ref 13 {[Ru](MeCN)C}OTf C464.75 NMR Ru-C nr M-C nr Ru-C-M nr [115] Ref {[Ru](MeCN)C}OTf[Ru](CN)2C 464.75464.70 nrnr nr nr nr [115] [115] [Ru](CN)[Ru](F)C2C 464.70474.58 nrnr nr nr nr [115] [115] [Ru](F)C 474.58 nr nr nr [115] [Ru](Br)C[Ru](Br)C 471.38471.38 nrnr nr nr nr [115] [115] [Ru](I)C[Ru](I)C 469.74469.74 nrnr nr nr nr [115] [115] [Ru](CN)C[Ru](CN)C 474.91474.91 nrnr nr nr nr [115] [115] [Ru](NCO)C[Ru](NCO)C 473.51473.51 nrnr nr nr nr [115] [115] [Ru](NCS)C[Ru](NCS)C 477.50477.50 nrnr nr nr nr [115] [115]
3.5.3.5. The The Systems Systems OsCl OsCl2(PCy2(PCy3)23C)2C and and OsI OsI2(PCy2(PCy3)32)C2C ([OsX]C)([OsX]C) TheThe carbido carbido complexes complexes [OsX]C [OsX]C in Figure in Figure 27 were 27 studiedwere studied by X-ray by analysis.X-ray analysis. The most The important most structuralimportant parameter structural is the parameter Os-C separation, is the Os-C which separation, for X = Cl which amounts for toX 1.689(5)= Cl amounts Å [116 to]. Single-crystal1.689(5) Å X-ray[116]. di ffSingle-crystalraction reveals X-ray that diffraction molecular reveals [OsX]C that adopts molecular an approximately [OsX]C adopts square-pyramidal an approximately core 13 geometry,square-pyramidal with the carbido core geometry, ligand occupying with the carbid the apicalo ligand position occupying and a shortthe apical Os-C position bond. In and the a C NMRshort spectrum Os-C bond. the signalIn the 13 atC 471.8 NMR ppm spectrum for X =theCl signal was attributed at 471.8 ppm to the for ligand X = Cl carbonwas attributed atom. It to was synthesizedthe ligand via carbon S-atom atom. abstraction It was from synthesized the thiocarbonyl via S-atom complex abstraction Os(CS)(PCy from3)2Cl the2 by thiocarbonyl Ta(OSi-t-Bu3 )3. Thecomplex diiodo derivativeOs(CS)(PCy was3)2 synthesizedCl2 by Ta(OSi- fromt-Bu [OsCl]C3)3. The upon diiodo reacting derivative with 10 eqwas of Mesynthesized3SiI and exhibits from a 13 C[OsCl]C NMR signal upon atreacting 446.14 with ppm. 10 eq of Me3SiI and exhibits a 13C NMR signal at 446.14 ppm.
Figure 27. The [Os]C core.
3.6. The System [Tp*Mo(CO)3 C]− ([Mo]−C) 3.6. The System [Tp*Mo(CO)≡3≡C] − ([Mo] −C) The reaction between Tp*Mo(CO)2CCl (see Figure 28) and KFeCp(CO)2 generates the carbido The reaction between Tp*Mo(CO)2CCl (see Figure 28) and KFeCp(CO)2 generates the complex [Mo]C FeCp(CO)2 (see Table 16)[117]; see alternative synthesis from Tp*Mo(CO)2C-Li and carbido complex→ [Mo]C→FeCp(CO)2 (see Table 16) [117]; see alternative synthesis from ClFeCp(CO)2 [118]. When Tp*Mo(CO)2CSe was allowed to react with [Ir(NCMe)(CO)(PPh3)2]BF4 the Tp*Mo(CO)2C-Li and ClFeCp(CO)2 [118]. When Tp*Mo(CO)2CSe was allowed to react with tetranuclear carbido complex (µ-Se2)[Ir2-{[Mo]C}2(CO)2(PPh3)2] was obtained (see Figure 29)[119]. [Ir(NCMe)(CO)(PPh3)2]BF4 the tetranuclear carbido complex (μ-Se2)[Ir2-{[Mo]C}2(CO)2(PPh3)2] AMolecules solution 2020 of, 25 Tp*Mo(CO), x FOR PEER2 REVIEWCBr in THF was treated with BuLi followed by addition of HgCl38 of2 54 was obtained (see Figure 29) [119]. A solution of Tp*Mo(CO)2CBr in THF was treated with BuLi resulted in the formation of the carbido complex [Mo]C Hg C[Mo] [120]. The platinum complex followed by addition of HgCl2 resulted in the→ formation← of the carbido complex [Mo]C Pt(PPh3)2Br was prepared from reacting [(HB(pz)3]Mo(CO)2CBr with [(PPh3)2Pt(C2H4)] [121]. [Mo]C→ →Hg←C[Mo] [120]. The platinum complex [Mo]C→Pt(PPh3)2Br was prepared from reacting [(HB(pz)3]Mo(CO)2CBr with [(PPh3)2Pt(C2H4)] [Error! Reference source not found.].
Figure 28. The [Mo]−C core. Tp* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]− or [HB(pz)3]−. Figure 28. The [Mo]−C core. Tp* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]− or
[HB(pz)3]−.
。 Table 16. Compounds with [Mo]−C core with Tp* = [HB(pzMe2)3] − or [HB(pz)3] −
Mo-C M-C Mo-C-M 13C NMR Ref Tp* is [HB(pzMe2)3]− [Mo]C→FeCp(CO)2 1.819(6) 1.911(8) 172.2(5) 381 [117] 171.3(3) (μ-Se2)[Ir2-{[Mo]C}2(CO)2(PPh3)2] 1.843(5) 1.974(5) 286.1 [119] 168.2(3) [Mo]C→Hg←C[Mo] nr nr nr 373 [120] [Mo]C→AuPPh3 nr nr nr nr [122] Tp* is [HB(pz)3]−
[Mo]C→Pt(PPh3)2Br nr nr nr 339.0 [121]
Figure 29. Selected structure of compounds with the [Mo]−C moiety.
3.7. Unique Mo Carbido Complex A further unique carbido complex was described recently as shown in Figure 30. A signal at 360.8 ppm in the 13C NMR spectrum was assigned to the ligand carbon atom [123].
Figure 30. The carbido complex with the P2(CO)Mo≡C core.
3.8. The System [Tp*W(CO)3≡C]− ([W]−C)
Reaction of [W]C-Li(THF) with NiCl2(PEt3)2 produced the complex [W]C→NiCl(PEt3)2 in Figure 31 [124]. Similarly, with [W]C-Li(THF) and FeCl(CO)2Cp or HgCl2 the compounds [W]C→Fe(CO)2Cp and [W]C→Hg←C[W], respectively, were obtained. [W]C→AuPEt3 was prepared from reacting [W]C→SnMe3 with AuCl(SMe2) followed by addition of PEt3. A similar
Molecules 2020, 25, x FOR PEER REVIEW 38 of 54 Molecules 2020, 25, x FOR PEER REVIEW 38 of 54
Figure 28. The [Mo]−C core. Tp* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]− or Figure 28. The [Mo]−C core. Tp* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]− or Molecules[HB(pz)2020, 25,3 4943]−. 35 of 48 [HB(pz)3]−.
。 Table 16. Compounds with [Mo]−C core with Tp* = [HB(pzMe2)3] − or [HB(pz)3] −。 Table 16. Compounds with [Mo]−C core with Tp* = [HB(pzMe2)3] − or [HB(pz)3] − Table 16. Compounds with [Mo]−C core with Tp* = [HB(pzMe2)3]− or [HB(pz)3]−. 13 Mo-C M-C Mo-C-M 13 C NMR Ref Mo-C M-C Mo-C-M 13C NMR Ref Mo-CTp* is [HB(pzMe M-C2)3]− Mo-C-M C NMR Ref Tp* is [HB(pzMe2)3]− [Mo]C→FeCp(CO)2 1.819(6) 1.911(8) 172.2(5) 381 [117] [Mo]C→FeCp(CO)2 1.819(6)Tp* is [HB(pzMe1.911(8)2) 3]− 172.2(5) 381 [117] [Mo]C FeCp(CO)2 1.819(6) 1.911(8) 172.2(5)171.3(3) 381 [117] (μ-Se2)[Ir2-{[Mo]C}→2(CO)2(PPh3)2] 1.843(5) 1.974(5) 171.3(3) 286.1 [119] (μ-Se(µ2-Se)[Ir2)[Ir-{[Mo]C}-{[Mo]C}2(CO)(CO)2(PPh(PPh3)2] ) ]1.843(5) 1.843(5) 1.974(5) 1.974(5) 171.3(3) 168.2(3) 286.1 [119[119]] 2 2 2 2 3 2 168.2(3)168.2(3) [Mo]C[Mo]C→Hg←HgC[Mo]C[Mo] nr nr nrnr nrnr 373 [120[120]] [Mo]C→Hg→←C[Mo]← nr nr nr 373 [120] [Mo]C[Mo]C→AuPPhAuPPh3 3 nr nr nrnr nrnr nr [122[122]] [Mo]C→AuPPh→ 3 nr nr nr nr [122] Tp* is [HB(pz) ] − Tp* is [HB(pz)33]− Tp* is [HB(pz)3]− [Mo]C Pt(PPh3)2Br nr nr nr 339.0 [121] [Mo]C→Pt(PPh→ 3)2Br nr nr nr 339.0 [121] [Mo]C→Pt(PPh3)2Br nr nr nr 339.0 [121]
Figure 29. − Figure 29. SelectedSelected structure structure ofof compoundscompounds withwith thethe [Mo][Mo]−CC moiety. moiety. 3.7. Unique Mo Carbido Complex 3.7. Unique Mo Carbido Complex A furtherA further unique unique carbido carbido complex complex was was described described recently recently as as shown shown in in Figure Figure 30 30.. AA signalsignal at A further 13unique carbido complex was described recently as shown in Figure 30. A signal 360.8 ppm in the C NMR13 spectrum was assigned to the ligand carbon atom [123]. at 360.8 ppm in the 13C NMR spectrum was assigned to thethe ligandligand carboncarbon atomatom [123].[123].
FigureFigure 30.30. TheThe carbidocarbido complexcomplex withwith thethe PP22(CO)Mo(CO)Mo≡C core. Figure 30. The carbido complex with the P2(CO)Mo≡C core.
3.8. The System [Tp*W(CO)3 C]− ([W]−C) 3.8. The System [Tp*W(CO)≡3≡C]− ([W]−C) 3.8. The System [Tp*W(CO)3≡C]− ([W]−C) Reaction of [W]C-Li(THF) with NiCl2(PEt3)2 produced the complex [W]C NiCl(PEt3)2 in Reaction of [W]C-Li(THF) with NiCl2(PEt3)2 produced the complex [W]C→→NiCl(PEt3)2 in 2 3 2 → 3 2 Figure Reaction31[ 124]. of [W]C-Li(THF) Similarly, with with [W]C-Li(THF) NiCl (PEt ) produced and FeCl(CO) the complex2Cp or HgCl[W]C2 NiCl(PEtthe compounds) in Figure 31 [124]. Similarly, with [W]C-Li(THF) and FeCl(CO)2Cp or HgCl2 the compounds 2 2 [W]CFigureFe(CO) 31 [124].2Cp andSimilarly, [W]C withHg C[W],[W]C-Li(THF) respectively, and wereFeCl(CO) obtained.Cp [W]Cor HgClAuPEt the 3compoundswas prepared [W]CMolecules→ → Fe(CO)2020, 25, 2xCp FOR and PEER [W]C REVIEW→ →←Hg ←C[W], respectively, were obtained.→ [W]C→AuPEt3 was39 of 54 → 2 → ← → 3 from[W]C reactingFe(CO) [W]CCp SnMeand [W]C3 with AuCl(SMeHg C[W],2) followedrespectively, by addition were obtained. of PEt3. A[W]C similarAuPEt reactionwas with prepared from reacting→ [W]C→SnMe3 with AuCl(SMe2) followed by addition of PEt3. A similar AuCl(PPhprepared) yieldedfrom reacting [W]C [W]CAuPPh→SnMe. [W]C3 withAuAsPh AuCl(SMeand2)[W]C followedAuPPh by additionform a of tetrameric PEt3. A similar assembly reaction3 with AuCl(PPh3) yielded3 [W]C→AuPPh3.3 [W]C→AuAsPh3 and3 [W]C→AuPPh3 form a → → → as depictedtetrameric in assembly Figure 32 .as The depicted X-ray analysis in Figure of 32. the The tetrameric X-ray analysis unit revealed of the Au-C tetrameric distances unit of revealed 1.995 and 2.078Au-C Å and distances the W-C of distance1.995 and is 2.078 1.877 Å Å and [122 the]. W-C distance is 1.877 Å [122].
Figure 31. The [W]−C core. T* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]−. Figure 31. The [W]-C core. T* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]−.
W
C
Au Au W W =W(CO) Tp* C C 2
Au Au W C W
Figure 32. Tetrameric unit from [W]C→AuAsPh3 and [W]C→AuPPh3 [122].
The terpyridine complex salt {[W]C→Pt(terpy)}PF6 was obtained from [W]C-Li and [PtCl(terpy)]PF6; the neutral complex [W]C→PtCl(terpyC[W]) (see Figure 33) was prepared from the same starting material and [PtCl2(phen)] (see Table 17) [Error! Reference source not found.].
Figure 33. Structural representation of [W]C→Pt complexes [Error! Reference source not found.].
Table 17. Compounds with [W]-C core. Tp* = [HB(pzMe2)3]−.
W-C M-C W-C-M 13C NMR Ref
[W]C→NiCl(PEt3)2 nr nr nr nr [124]
[W]C→Fe(CO)2Cp nr nr nr nr [122]
[W]C→Hg←C[W] nr nr nr nr [122]
Molecules 2020, 25, x FOR PEER REVIEW 39 of 54 Molecules 2020, 25, x FOR PEER REVIEW 39 of 54
reaction with AuCl(PPh3) yielded [W]C→AuPPh3. [W]C→AuAsPh3 and [W]C→AuPPh3 form a reaction with AuCl(PPh3) yielded [W]C→AuPPh3. [W]C→AuAsPh3 and [W]C→AuPPh3 form a tetrameric assembly as depicted in Figure 32. The X-ray analysis of the tetrameric unit revealed Au-C distances of 1.995 and 2.078 Å and the W-C distance is 1.877 Å [122].
Molecules 2020, 25, 4943 36 of 48 Figure 31. The [W]-C core. T* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]−. Figure 31. The [W]-C core. T* = tris(3,5-dimethylpyrazolyl)borate, [HB(pzMe2)3]−.
W W C C Au Au W Au Au W W =W(CO)2Tp* C C W =W(CO)2Tp* C C
Au Au W Au Au W C C W W
FigureFigure 32. Tetrameric 32. Tetrameric unit unit from from [W]C [W]C→AuAsPhAuAsPh3 and3 and [W]C [W]C→AuPPhAuPPh3 [122].3 [122]. Figure 32. Tetrameric unit from [W]C→→AuAsPh3 and [W]C→AuPPh→ 3 [122].
The terpyridine complex salt {[W]C→Pt(terpy)}PF6 was obtained from [W]C-Li and The terpyridineThe terpyridine complex saltcomplex {[W]C salt Pt(terpy)}PF{[W]C→Pt(terpy)}PF6 was obtained6 was obtained from [W]C-Li from [W]C-Li and [PtCl(terpy)]PF and 6; [PtCl(terpy)]PF6; the neutral complex→ [W]C→PtCl(terpyC[W]) (see Figure 33) was prepared the neutral[PtCl(terpy)]PF complex [W]C6; thePtCl(terpyC[W]) neutral complex (see[W]C Figure→PtCl(terpyC[W]) 33) was prepared (see Figure from 33) the was same prepared starting material from the same starting→ material and [PtCl2(phen)] (see Table 17) [Error! Reference source not and [PtCl2from(phen)] the (seesameTable starting 17 material) [125]. and [PtCl2(phen)] (see Table 17) [Error! Reference source not found.].
Molecules 2020, 25, x FOR PEER REVIEW 40 of 54
[W]C→AuAsPh3 nr nr nr nr [122]
[W]C→AuPPh3 nr nr nr nr [122]
[W]C→AuPEt3 nr nr nr 397.7 [122]
[Error! Referen ce {[W]C→Pt(terpy)}PF6 1.835(5) 1.938(5) 176.3(3) 368 FigureFigure 33. Structural 33. Structural representation representation of [W]C→Pt ofcomplexes [W]C [PtError! complexes Reference [125 source]. not Figure 33. Structural representation of [W]C→Pt complexes→ [Error! Reference source not source found.]. found.]. not Table 17. Compounds with [W]−C core. Tp* = [HB(pzMe2)3]−. found.] Table 17. Compounds with [W]-C core. Tp* = [HB(pzMe2)3]−. Table 17. CompoundsW-C with [W] M-C-C core. Tp* W-C-M = [HB(pzMe132C)3] NMR−. Ref [Error! W-C M-C W-C-M 13C NMR Ref [W]C NiCl(PEt ) W-C nrM-C nr W-C-M nr nr13C NMR [124] Ref → 3 2 Referen [W]C Fe(CO)2Cp nr nr nr nr [122] [W]C→NiCl(PEt→ 3)2 nr nr nr nr [124]ce [W]C[W]C→PtCl(terpyC[W])[W]C→NiCl(PEtHg 3)2C[W] 1.853(14)nr nr 1.890(14) nr nr 173.4(9) nr nr nr 331.3 nr [122][124] → ← source [W]C[W]C→Fe(CO)AuAsPh2Cp 3 nr nr nr nr nr nr nr nr [122][122] [W]C→Fe(CO)→ 2Cp nr nr nr nr [122]not [W]C AuPPh nr nr nr nr [122] → 3 found.] [W]C→[W]CHg←C[W]AuPEt nr nr nr nr nr nr 397.7 nr [122][122] [W]C→Hg←→C[W] 3 nr nr nr nr [122] {[W]C Pt(terpy)}PF 1.835(5) 1.938(5) 176.3(3) 368 [125] → 6 [W]C PtCl(terpyC[W]) 1.853(14) 1.890(14) 173.4(9) 331.3 [125] →
3.9. The Systems N3MoC and O3MoC 3.9. The Systems N3MoC and O3MoC The potassium salt of NMOC- in Figure 34 is dimeric with two K+ ions bridging two anions The potassium salt of NMOC in Figure 34 is dimeric with two K+ ions bridging two anions and and can be transformed with− the crown ethers 2.0-benzo-15-crown-5 and 1.0 2,2,2-crypt into the can be transformedrelated ion pairs. with X-ray the crown analysis ethers of the 2.0-benzo-15-crown-5 crown ether salt revealed and a Mo-C 1.0 2,2,2-crypt distance of into 1.713(9) therelated Å ion pairs. X-ray[26,126]. analysis of the crown ether salt revealed a Mo-C distance of 1.713(9) Å [26,126].
N O Figure 34. The [ Mo]−C and [ W]−C core. Figure 34. The [NMo]−C and [OW]−C core.
The complex [OW]C→Ru(CO)2Cp was prepared from reacting [OW]C-Et with Ru(C≡CMe)(CO)2Cp under loss of MeCCEt. The ligand C atom resonates at 237.3 ppm (1JWC = 290.1 Hz). Distances are W-C = 1.75(2) Å, Ru-C = 2.09(2) Å and the W-C-Ru angle amounts to 177(2) ° [127].
3.10. Symmetrically Bridged Carbido Complexes M=C=M
3.10.1. The Fe=C=Fe Core
[Fe(TPP)]2C was obtained from FeIII(TPP)Cl in the presence of iron powder by reacting with CI4 (TPP = 5, 10, 15, 20-tetraphenylporphyrin; according to FeII the complex is diamagnetic
Molecules 2020, 25, 4943 37 of 48
O O The complex [ W]C Ru(CO)2Cp was prepared from reacting [ W]C-Et with Ru(C CMe)(CO)2Cp → 1 ≡ under loss of MeCCEt. The ligand C atom resonates at 237.3 ppm ( JWC = 290.1 Hz). Distances are W-C = 1.75(2) Å, Ru-C = 2.09(2) Å and the W-C-Ru angle amounts to 177(2) ◦ [127].
3.10. Symmetrically Bridged Carbido Complexes M=C=M
3.10.1. The Fe=C=Fe Core
III [Fe(TPP)]2C was obtained from Fe (TPP)Cl in the presence of iron powder by reacting with II CI4 (TPP = 5, 10, 15, 20-tetraphenylporphyrin; according to Fe the complex is diamagnetic [128]. The complex was also obtained upon reacting Fe(TPP) with Me3SiCCl3 [129]; see also [130]. An X-ray analysis was performed in [131] and later in [130]. The Mössbauer spectrum is published in [132]. [Fe(TTP)]2C (TTP = tetratolylporphyrine) was similarly obtained from Fe(TTP) with Me3SiCCl3 [129]. [Fe(oep)]2C (oep = octaethylporphyrine) was prepared from [ClFe(oep)] and HCCl3 and studied by X-ray analysis ans Mössbauer spectroscopy (see Table 18)[132].
Table 18. Fe-C distances (in Å) and Fe-C-Fe angles (in deg). 13C NMR of the bridging carbon atom in ppm.
13C NMR Fe-C Fe-C Fe-C-Fe Ref
[Fe(TPP)]2C nr 1.683(1) 1.675 180 [130,131] [Fe(TTP)]2C nr nr nr nr [129] [Fe(oep)]2C nr 1.6638(9) 1.6638(9) 179.5(3) [132] (TPP)Fe=C=Fe(CO)4 nr nr nr nr [121] (TCNP)Fe=C=Fe(CO)4 nr nr nr nr [121] [Fe(pc)]2C nr nr nr nr [95] {[Fe(pc)]2C}(I3)0.66 nr nr nr nr [95] [(py)Fe(pc)]2C nr 1.69(2) 1.69(2) 177.5(8) [133] [(1-meim)Fe(pc)]2C nr 1.70(1) 1.70(1) 178(1) [134] [(4-Mepy)Fe(pc)]2C nr nr nr nr [133] [(pip)Fe(pc)]2C nr nr nr nr [133] [(thf)Fe(pc)]2C nr 1.71(2) 1.64(2) 180(1) [130] [(thf)(TPP)Fe=C=Fe(pc)(thf)] nr 1.71(1) 1.65(1) 179(1) [130] (Bu4N)2{[(F)Fe(pc)]2C} nr 1.687(4) 1.687(4) 179.5(3) [135] (Bu4N)2{[(Cl)Fe(pc)]2C} nr nr nr nr [135] (Bu4N)2{[(Br)Fe(pc)]2C} nr nr nr nr [135]
The mixed carbido compounds (TPP)Fe=C=Fe(CO)4, and (TCNP)Fe=C=Fe(CO)4 (TCNP = Tetrakis- p-cyanophenylporphyrinate) were synthesized from [(TPP)FeCCl2] or (TCNP)FeCCl2 and [Na2Fe(CO)4]; characterization proceeded via IR spectroscopy [121]. [Fe(pc)]2C was prepared from [ClFe(pc)]− and KOH/HCCl3 [132], or from Fe(pc) and CI4 in the presence of sodium dithionite [95,136], see also [134]. It also forms upon hydrolysis of (Bu4N)2 {[(F)Fe(pc)]2C}in acetone [135]. Oxidation with I2 generates {[Fe(pc)]2C}(I3)0.66 which was characterized by IR, Mössbauer spectroscopy and powder X-ray diffraction [95]. A series of six-coordinate N-Base adducts of µ-carbido phthalocyanine complexes were reported. The pyridine adduct [(py)Fe(pc)]2C was obtained y dissolution of [Fe(pc)]2C in warm pyridine [133] and characterized by Mössbauer spectroscopy [136] and X-ray analysis [133]. [Fe(pc)(1-meim)}2C was similarly obtained as the TPP derivate; starting with pcFe and CI4 followed by addition of sodium dithionite gave the µ-carbido bridged dimer; an X-ray diffraction analysis was reportedd (1-meim = 1-methylimidazole, pc = phthalocyanine) [134]. [(4-Mepy)Fe(pc)]2C and [(pip)Fe(pc)]2C were similarly obtained and studied by IR and Mössbauer spectroscopy [136]. [(thf)Fe(pc)]2C forms on dissolving [Fe(pc)] in THF. The asymmetric µ-carbido complex [(thf)(TPP)Fe=C=Fe(pc)(thf)] stems from the reaction of [FeCCl2(TPP)] with [Fe(pc)]-; both compounds were characterized by X-ray analyses [130]. Molecules 2020, 25, 4943 38 of 48
Anionic six-coordinate µ-carbido complexes (Bu4N)2{[(hal)Fe(pc)]2C}were reported (hal = F. Cl. Br) and obtained from reacting [Fe(pc)]2C with (Bu4N)(hal) (F: RT, Cl: 115◦, Br: 140◦) in solution (F) and in a melt [135].
3.10.2. The Rh=C=Rh Core
[Rh(PEt3)2(SGePh3)]2C was obtained upon reacting Rh(PEt3)2(SGePh3)CS with Rh(PEt3)3(Bpin) via the intermediate mixed carbido complex (SGePh3)(PEt3)2Rh=C=Rh(PEt3)2(SBpin) which rearranges to this complex and [Rh(PEt3)2(SBpin)]2. The X-ray analysis was performed (see Table 19)[137] [Rh(PEt3)2(SBpin)]2C was prepared earlier by the same working group from Rh(PEt3)3(Bpin) and 0,5 eq of CS2 (X-ray data (see Table 19). Addition of MeOH generated the carbido complex [Rh(PEt3)2(SH)]2C[138]. [Rh(Cl)(PPh3)2]2C resulted from reacting the thiocarbonyl complex 1 Rh(Cl)(PPh3)2CS with HBCat. The central C atom resonates at 424 ppm (t, JRhC = 47 Hz). In the chloro complex the chloride ion can be replaced with K[(H2B(pz)2], K[(H2B(pzMe2)2], or K[(HB(pz)3] to produce the carbido complexes [Rh(H2B(pz)2)(PPh3)]2C, [Rh(H2B(pzMe2)2)(PPh3)]2C, and [Rh(HB(pz)3)(PPh3)]2C, respectively (see Figure 35). The unusual asymmetric carbido complex I [Rh2H(µ-C)(µ-C6H4PPh2-2){HB(pzMe2)3}2] contains a Rh atom with a shorter Rh-C distance, while the RhIII –C distance is longer [139].
Table 19. Rh-C distances (in Å) and Rh-C-Rh angles (in deg). 13C NMR of the bridging carbon atom in ppm.
13C NMR Rh-C Rh-C Rh-C-Rh Ref 1 [Rh(PEt3)2(SGePh3)]2C 425.8, JRhC = 47 1.788(4) 1.798(4) 175.6(2) [137] [Rh(PEt3)2(SBpin)]2C nr 1.790(7) 1.766(7) 176.1(4) [137,138] [Rh(PEt3)2(SH)]2C nr nr nr nr [137] 1 [Rh(Cl)(PPh3)2]2C 424.4, JRhC = 47 1.7828(19) 1.7828(19) nr [139] [Rh(H2B(pz)2)(PPh3)]2C nr 1.7644(11) 1.7644(11) 169.1(7) [139] [Rh(H2B(pzMe2)2)(PPh3)]2C nr 1.7794(9) 1.7794(9) 168.8(6) [139] [Rh(HB(pz)3)(PPh3)]2C nr 1.7761(7) 1.7761(7) 163.7(4) [139] [Rh H(µ-C)(µ-C H PPh -2){HB(pzMe ) } ] 447.2 1J = 40, 50 1.740(6) 1.818(6) 165.9(3) [139] Molecules2 2020, 625,4 x FOR2 PEER REVIEW2 3 2 RhC 44 of 54
Figure 35. Selected structures of Rh=C=Rh complexes. Figure 35. Selected structures of Rh=C=Rh complexes.
3.10.3. The Ru=C=Ru Core
The tetranuclear carbido complex [Ru(PEt3)Cl(μ-Cl3)RuAr]2C was prepared from the reaction of [(p-cymene)Ru(μ-Cl)3RuCl(C2H4)-(PCy3)] with HCCH in THF. X-ray analysis adopts Ru-C distances of 1.877(9) Å and a Ru-C-Ru angle of 178.8(9)°(see Figure 36) [140].
Figure 36. Structural representation of the Ru carbido complex [Ru(PEt3)Cl(μ-Cl3)RuAr]2C.
Five coordinate [Ru(pc)]2C with pc = phthalocyaninate was obtained from H[RuCl2(pc)] and CCl2 (in situ from KOH/HCCl3) [Error! Reference source not found.]. The related pyridine adduct with six-coordinate Ru(IV) [(py)Ru(pc)]2C was obtained upon dissolution of [Ru(pc)]2C in warm pyridine. X-ray analysis revealed a Ru-C distance of 1.77(1) Å and a Ru-C-Ru angle of 174.5(8)° [Error! Reference source not found.].
3.10.4. .The Re=C=Re Core
The unique carbido complex [Re(CO)2Cp]2C in Figure 37 results from reaction of [Re(thf)(CO)2(η-C5H5)], CS2, and PPh3 (with the aim of the thiocarbonyl complex [Re(CS)(CO)(η-C5H5)]) as by-product in small amounts. X-ray analysis revealed Re-C distances of 1.882(14) and 1.881(14) Å and a Re-C-Re angle of 173.3(7)°. A 13C NMR shift for the bridging carbon atom at δ = 436.4 ppm was measured [141].
Molecules 2020, 25, x FOR PEER REVIEW 44 of 54
Molecules 2020, 25, 4943 39 of 48 Figure 35. Selected structures of Rh=C=Rh complexes.
3.10.3.3.10.3. The The Ru Ru=C=Ru=C=Ru Core Core
TheThe tetranuclear tetranuclear carbido carbido complex complex [Ru(PEt [Ru(PEt3)Cl(µ3-Cl)Cl(3)RuAr]μ-Cl3)RuAr]2C was2C preparedwas prepared from the from reaction the of [(preaction-cymene)Ru( of [(pµ-cymene)Ru(-Cl)3RuCl(Cμ2H-Cl)4)-(PCy3RuCl(C3)]2 withH4)-(PCy HCCH3)] with in THF. HCCH X-ray in analysis THF. X-ray adopts analysis Ru-C adopts distances ofRu-C 1.877(9) distances Å and aof Ru-C-Ru 1.877(9) angleÅ and of a 178.8(9)Ru-C-Ru◦(see angle Figure of 178.8(9)°(see 36)[140]. Figure 36) [140].
Figure 36. Structural representation of the Ru carbido complex [Ru(PEt3)Cl(µ-Cl3)RuAr]2C. Figure 36. Structural representation of the Ru carbido complex [Ru(PEt3)Cl(μ-Cl3)RuAr]2C.
Five coordinate [Ru(pc)]2C with pc = phthalocyaninate was obtained from H[RuCl2(pc)] and CCl2 Five coordinate [Ru(pc)]2C with pc = phthalocyaninate was obtained from H[RuCl2(pc)] (in situ from KOH/HCCl3)[132]. The related pyridine adduct with six-coordinate Ru(IV) [(py)Ru(pc)]2C and CCl2 (in situ from KOH/HCCl3) [Error! Reference source not found.]. The related pyridine was obtained upon dissolution of [Ru(pc)]2C in warm pyridine. X-ray analysis revealed a Ru-C distance adduct with six-coordinate Ru(IV) [(py)Ru(pc)]2C was obtained upon dissolution of [Ru(pc)]2C of 1.77(1) Å and a Ru-C-Ru angle of 174.5(8)◦ [136]. in warm pyridine. X-ray analysis revealed a Ru-C distance of 1.77(1) Å and a Ru-C-Ru angle of 3.10.4.174.5(8)° The Re[Error!=C= ReReference Core source not found.]. The unique carbido complex [Re(CO) Cp] C in Figure 37 results from reaction of [Re(thf)(CO) 3.10.4. .The Re=C=Re Core 2 2 2 (η-C5H5)], CS2, and PPh3 (with the aim of the thiocarbonyl complex [Re(CS)(CO)(η-C5H5)]) as by-productThe inunique small amounts.carbido complex X-ray analysis [Re(CO) revealed2Cp]2C Re-C in distancesFigure 37 of 1.882(14)results from and 1.881(14)reaction Åof and 2 5 5 2 13 3 a Re-C-Re[Re(thf)(CO) angle(η of-C 173.3(7)H )], CS◦.A, andC NMR PPh shift (with for thethe bridging aim of carbon the atomthiocarbonyl at δ = 436.4 complex ppm was measured[Re(CS)(CO)(Molecules 2020 [141, ].25η,-C x FOR5H5)]) PEER as REVIEWby-product in small amounts. X-ray analysis revealed Re-C distances45 of 54 of 1.882(14) and 1.881(14) Å and a Re-C-Re angle of 173.3(7)°. A 13C NMR shift for the bridging carbon atom at δ = 436.4 ppm was measured [141].
Figure 37. Structural representation of the Re carbido complex [Re(CO)2Cp]2C. Figure 37. Structural representation of the Re carbido complex [Re(CO)2Cp]2C. 3.10.5. The W=C=W Core 3.10.5. The W=C=W Coret t The oxo complex ( Bu3SiO)2(O)W=C=WCl2(OSi Bu3)2 in Figure 38 formed in high yield from t t 13 thermolysisThe oxo of [(siloxo) complex2Cl(CO)W] ( Bu3SiO)2 2in(O)W=C=WCl toluene with2(OSi lossBu of3 CO;)2 in in Figure the C 38 NMR formed spectrum in high the yield carbide 13 C atomfrom resonatesthermolysis at ofδ = [(siloxo)379.142 ppmCl(CO)W] (JWC =2 in200, toluene 180 Hz). with Degradation loss of CO; in of the (silox)C NMR4C1 spectrum2W2(CNAr) t t 13 complexthe carbide afforded C theatom imido resonatesµ-carbido at compoundδ = 379.14 (ppmBu3SiO) (JWC2(NR)W = 200,= C180=WCl Hz).2(OSi DegradationBu3)2; the ofC the NMR shift(silox) of the4C1µ2-CW2 atom(CNAr) appears complex at δ = 406.25 afforded ppm. X-ray the analysis imido revealed μ a-carbido tetrahedral tungstencompound core t t 13 with( Bu a3 W-CSiO) distance2(NR)W=C=WCl of 1.994(17)2(OSi ÅBu (W3)12); andthe aC distorted NMR shift square-pyramidal of the μ-C atom tungsten appears core at with δ = 406.25 a shorter distanceppm. X-ray of 1.796(17) analysis Å (Wrevealed2). The a W-C-W tetrahedral bond tungsten angle amounts core with to 176.0(12) a W-C ◦distance[142]. of 1.994(17) Å (W1) and a distorted square-pyramidal tungsten core with a shorter distance of 1.796(17) Å (W2). The W-C-W bond angle amounts to 176.0(12)° [Error! Reference source not found.].
Figure 38. Structural representation of the W carbido complexes
(tBu3SiO)2(NR)W=C=WCl2(OSitBu3)2 and (tBu3SiO)2(O)W=C=WCl2(OSitBu3)2.
3.11. Asymmetrically Bridged Carbido Complex Fe=C=M
3.11.1. The Fe=C=Re Core
The asymmetrical carbido complex (TPP)Fe=C=Re(CO)4Re(CO)5 in Figure 39 was prepared upon reacting the dichlorocarbene complex (TPP)Fe=CCl2 with 2 eq of pentacarbonylrhenate, [Re(CO)5]−, under release of CO and 2 Cl−; TPP is tetraphenylporphyrin. Crystals were analyzed by X-ray diffraction and revealed a Fe=C distance of 1.605(13) Å and a C=Re distance of 1.957(12) Å. The Fe-C-Re angle amounts to 173.3(9)°; the Fe-C distance is somewhat smaller than in [(TPP)Fe]2C and the Re-C distance is appreciable longer than in [Re(CO)2Cp]2C. In the 13C NMR spectrum the central carbido C atom resonates at 211.7 ppm [143].
Figure 39. Structural representation of the Fe=C=Re carbido complex (TPP)Fe=C=Re2(CO)9.
Molecules 2020, 25, x FOR PEER REVIEW 45 of 54
Molecules 2020, 25, x FOR PEER REVIEW 45 of 54
Figure 37. Structural representation of the Re carbido complex [Re(CO)2Cp]2C.
3.10.5. The W=C=WFigure 37. Core Structural representation of the Re carbido complex [Re(CO)2Cp]2C.
The oxo complex (tBu3SiO)2(O)W=C=WCl2(OSitBu3)2 in Figure 38 formed in high yield 3.10.5. The W=C=W Core from thermolysis of [(siloxo)2Cl(CO)W]2 in toluene with loss of CO; in the 13C NMR spectrum
the carbideThe oxo C complex atom resonates (tBu3SiO) at2(O)W=C=WCl δ = 379.14 ppm2(OSi t(JBuWC3) 2 =in 200, Figure 180 38Hz). formed Degradation in high of yield the from(silox) thermolysis4C12W2(CNAr) of [(siloxo) complex2Cl(CO)W] afforded2 in toluene thewith lossimido of CO; inμ -carbidothe 13C NMR compound spectrum t t 13 the( Bu 3carbideSiO)2(NR)W=C=WCl C atom resonates2(OSi Bu at3 )2δ; the= 379.14 C NMR ppm shift (JWC of = the200, μ -C180 atom Hz). appears Degradation at δ = of406.25 the (silox)ppm. X-ray4C12W analysis2(CNAr) revealedcomplex a tetrahedral afforded tungsten the core withimido a W-Cμ -carbidodistance of 1.994(17)compound Å ((WtBu1)3 SiO)and2 (NR)W=C=WCla distorted square-pyramidal2(OSitBu3)2; the 13tungstenC NMR coreshift withof the a μshorter-C atom distance appears of at 1.796(17) δ = 406.25 Å ppm.(W2). TheX-ray W-C-W analysis bond revealed angle amountsa tetrahedral to 176.0(12)° tungsten [Error! core withReference a W-C source distance not of found. 1.994(17)]. Å (W1) and a distorted square-pyramidal tungsten core with a shorter distance of 1.796(17) Å Molecules 2020, 25, 4943 40 of 48 (W2). The W-C-W bond angle amounts to 176.0(12)° [Error! Reference source not found.].
Figure 38. Structural representation of the W carbido complexes (tBu3SiO)2(NR)W=C=WCl2(OSitBu3)2 and (tBu3SiO)2(O)W=C=WCl2(OSitBu3)2. t t Figure 38. Structural representation of the W carbido complexes ( Bu3SiO)2(NR)W=C=WCl2(OSi Bu3)2 Figuret 38. Structural trepresentation of the W carbido complexes and ( Bu3SiO)2(O)W=C=WCl2(OSi Bu3)2. 3.11. (AsymmetricallytBu3SiO)2(NR)W=C=WCl Bridged 2Carbido(OSitBu3 )Complex2 and (tBu Fe=C=M3SiO)2(O)W=C=WCl 2(OSitBu3)2. 3.11. Asymmetrically Bridged Carbido Complex Fe=C=M 3.11.3.11.1. Asymmetrically The Fe=C=Re BridgedCore Carbido Complex Fe=C=M 3.11.1. The Fe=C=Re Core The asymmetrical carbido complex (TPP)Fe=C=Re(CO)4Re(CO)5 in Figure 39 was 3.11.1. The Fe=C=Re Core preparedThe asymmetrical upon reacting carbido complexthe dichlorocarbene (TPP)Fe=C=Re(CO) complex4Re(CO) (TPP)Fe=CCl5 in Figure 392 waswith prepared 2 eq uponof − − reactingpentacarbonylrhenate,The the dichlorocarbeneasymmetrical [Re(CO) carbido complex5] , complexunder (TPP)Fe release =(TPP)Fe=C=Re(CO)CCl of2 with CO and 2 eq 2 of Cl pentacarbonylrhenate,4;Re(CO) TPP is 5tetraphenylporphyrin. in Figure [Re(CO)39 was5 ]−, underpreparedCrystals release were upon of analyzed CO reacting and 2by Cl X-ra−the; TPPy diffractiondichlorocarbene is tetraphenylporphyrin. and revealed complex a Fe=C (TPP)Fe=CCl Crystals distance were of2 1.605(13) analyzedwith 2 Åeq byand X-rayof a diffpentacarbonylrhenate,C=Reraction distance and revealed of 1.957(12) a Fe[Re(CO)=C Å. distance 5The]−, under Fe-C-Re of 1.605(13) release angle Åof andCOamounts aand C= Re2 toCl distance −173.3(9)°;; TPP is of tetraphenylporphyrin. 1.957(12)the Fe-C Å. distance The Fe-C-Re is angleCrystalssomewhat amounts were smaller to analyzed 173.3(9) than◦ ;by in the X-ra[(TPP)Fe] Fe-Cy diffraction distance2C and is and somewhatthe revealedRe-C distance smaller a Fe=C thanis distance appreciable in [(TPP)Fe] of 1.605(13) longer2C and Åthan theand Re-Cin a 13 13 distanceC=Re[Re(CO) isdistance appreciable2Cp]2C. of In 1.957(12)the longer C NMR thanÅ. The in spectrum [Re(CO) Fe-C-Re 2theCp] angle central2C. Inamounts the carbidoC NMRto C173.3(9)°; atom spectrum resonates the the Fe-C central at distance211.7 carbido ppm is C atomsomewhat[143]. resonates smaller at 211.7 than ppm in [143 [(TPP)Fe]]. 2C and the Re-C distance is appreciable longer than in [Re(CO)2Cp]2C. In the 13C NMR spectrum the central carbido C atom resonates at 211.7 ppm [143].
Molecules 2020, 25, x FOR PEER REVIEW 46 of 54 Figure 39. Structural representation of the Fe=C=Re carbido complex (TPP)Fe=C=Re (CO) . 3.11.2. The Fe=C=Mn Core 2 9 Figure 39. Structural representation of the Fe=C=Re carbido complex (TPP)Fe=C=Re2(CO)9. 3.11.2. The Fe=C=Mn Core The carbido bridged di-manganese complex (TCNP)Fe=C=Mn2(CO)9 (TCNP = Figure 39. Structural representation of the Fe=C=Re carbido complex (TPP)Fe=C=Re2(CO)9. tetrakis(p-cyanophenyl)porphyrinate)The carbido bridged di-manganese (see complex Figure 40) (TCNP)Fe was synthesized=C=Mn2(CO) from9 [(TCNP)Fe=CCl(TCNP = tetrakis2]
(p-cyanophenyl)porphyrinate)and two eq. of Na(Mn(CO)5 (seein THF Figure and 40 characterized) was synthesized with elemental from [(TCNP)Fe analysis,= CClIR, 2and] and UV two eq.spectroscopy of Na(Mn(CO) [Error!5 in THF Reference and characterized source not found. with elemental]. analysis, IR, and UV spectroscopy [121].
Figure 40. Structural representation of the Fe=C=Mn carbido complex (TCNP)Fe=C=Mn2(CO)9. Figure 40. Structural representation of the Fe=C=Mn carbido complex (TCNP)Fe=C=Mn2(CO)9. 3.11.3. The Fe=C=Cr Core 3.11.3. The Fe=C=Cr Core Two compounds with the Fe=C=Cr core have been reported by the group of Beck and characterized by elementalTwo compounds analysis, IR, with and UVthe spectroscopy. Fe=C=Cr core Thus, have (TPP)Fe been reported=C=Cr(CO) by 5theand group (TAP)Fe of =BeckC=Cr(CO) and 5 (seecharacterized Figure 41) were by elemental prepared uponanalysis, reacting IR, and the relatedUV spectroscopy. dichlorocarbene Thus, iron (TPP)Fe=C=Cr(CO) complexes [(L)Fe5 =andCCl 2] with(TAP)Fe=C=Cr(CO) Na2[Cr(CO)5] in THF5 (see (TAP Figure= tetrakis(p-methoxyphenyl)porphyrinate)41) were prepared upon reacting the related [121]. dichlorocarbene iron complexes [(L)Fe=CCl2] with Na2[Cr(CO)5] in THF (TAP = tetrakis(p-methoxyphenyl)porphyrinate) [Error! Reference source not found.].
Figure 41. Structural representation of the Fe=C=Cr carbido complexes (TPP)Fe=C=Cr(CO)5 and
(TAP)Fe=C=Cr(CO)5.
4. Conclusions The experimental and theoretical research with regard transition metal complexes with carbone ligands [M]-CL2 and carbido complexes [M]-C has blossomed in the recent past and it can be foreseen that it will remain a very active area of organometallic chemistry in the future. The well-known family of transition metal complexes with C1-bonded carbon ligands that comprise alkyl (CR3), carbene (CR2), and carbyne (CR) groups has been extended by carbones (CL2) and carbido (C) ligands. The summary of recent work, which is described in this review, indicates that carbone and carbido complexes are still largely terra incognita and that many new discoveries can be expected.
Author Contributions: Conceptualization and writing of the first draft, W.P. and G.F. Checking and partial visualization L.Z. and C.C. All authors have read and agreed to the published version of the manuscript.
Funding: The work at Marburg was financially supported by the Deutsche Forschungsgemeinschaft. L.Z. and G.F acknowledge the financial support from Nanjing Tech University (grant number 39837132 and 39837123), National Natural Science Foundation of China (Grant No. 21703099 and 21993044), Natural
Molecules 2020, 25, x FOR PEER REVIEW 46 of 54
3.11.2. The Fe=C=Mn Core
The carbido bridged di-manganese complex (TCNP)Fe=C=Mn2(CO)9 (TCNP = tetrakis(p-cyanophenyl)porphyrinate) (see Figure 40) was synthesized from [(TCNP)Fe=CCl2] and two eq. of Na(Mn(CO)5 in THF and characterized with elemental analysis, IR, and UV spectroscopy [Error! Reference source not found.].
Figure 40. Structural representation of the Fe=C=Mn carbido complex (TCNP)Fe=C=Mn2(CO)9.
3.11.3. The Fe=C=Cr Core Two compounds with the Fe=C=Cr core have been reported by the group of Beck and characterized by elemental analysis, IR, and UV spectroscopy. Thus, (TPP)Fe=C=Cr(CO)5 and (TAP)Fe=C=Cr(CO)5 (see Figure 41) were prepared upon reacting the related dichlorocarbene iron complexes [(L)Fe=CCl2] with Na2[Cr(CO)5] in THF (TAP = Moleculestetrakis(p-methoxyphenyl)porphyrinate)2020, 25, 4943 [Error! Reference source not found.]. 41 of 48
Figure 41. Structural representation of the Fe=C=Cr carbido complexes (TPP)Fe=C=Cr(CO)5 and 5 (TAP)FeFigure=C 41.=Cr(CO) Structural5. representation of the Fe=C=Cr carbido complexes (TPP)Fe=C=Cr(CO) and (TAP)Fe=C=Cr(CO)5. 4. Conclusions 4. TheConclusions experimental and theoretical research with regard transition metal complexes with carbone ligandsThe [M]-CL experimental2 and carbido and complexes theoretical [M]-C research has blossomed with regard in thetransition recent pastmetal and complexes it can be foreseen with thatcarbone it will remainligands a [M]-CL very active2 and area carbido of organometallic complexes [M]-C chemistry has blossomed in the future. in the The recent well-known past and family it of transitioncan be foreseen metal complexesthat it will withremain C1-bonded a very active carbon area ligands of organometallic that comprise chemistry alkyl (CR3 ),in carbene the future. (CR 2), andThe carbyne well-known (CR) groups family has of been transition extended metal by carbones complexes (CL with2) and C1-bonded carbido (C) carbon ligands. ligands The summary that of recentcomprise work, alkyl which (CR is3),described carbene (CR in this2), and review, carbyne indicates (CR) that groups carbone has andbeen carbido extended complexes by carbones are still largely(CL2) terra and incognitacarbido (C) and ligands. that many The newsummary discoveries of recent can work, be expected. which is described in this review, indicates that carbone and carbido complexes are still largely terra incognita and that many Author Contributions: Conceptualization and writing of the first draft, W.P. and G.F. Checking and partial visualizationnew discoveries L.Z. and can C.C. be All expected. authors have read and agreed to the published version of the manuscript. Funding: AuthorThe Contributions: work at Marburg Conceptualization was financially and supported writing byof thethe Deutschefirst draft, Forschungsgemeinschaft. W.P. and G.F. Checking L.Z. and and G.F acknowledge the financial support from Nanjing Tech University (grant number 39837132 and 39837123), Nationalpartial Natural visualization Science L.Z. Foundation and C.C. of ChinaAll authors (Grant have No. 21703099read and and agreed 21993044), to the Natural published Science version Foundation of the of Jiangsumanuscript. Province for Youth (Grant No: BK20170964), and SICAM Fellowship from Jiangsu National Synergetic Innovation Center for Advanced Materials. Funding: The work at Marburg was financially supported by the Deutsche Forschungsgemeinschaft. L.Z. Conflicts of Interest: The authors declare no conflict of interest. and G.F acknowledge the financial support from Nanjing Tech University (grant number 39837132 and 39837123), National Natural Science Foundation of China (Grant No. 21703099 and 21993044), Natural References
1. Frankland, E. Über die Isolierung der Organischen Radicale. Justus Liebigs Ann. Chem. 1849, 71, 171–213.
[CrossRef] 2. Seyferth, D. Zinc Alkyls, Edward Frankland, and the Beginnings of Main-Group Organometallic Chemistry. Organomet. Chem. 2001, 20, 2940–2955. [CrossRef] 3. Fischer, E.O.M. A Zur Frage eines Wolfram-Carbonyl-Carben Komplexes. Angew. Chem. 1964, 76, 645. [CrossRef] 4. Fischer, E.O.; Kreis, G.; Kreiter, C.G.; Müller, J.; Huttner, G.; Lorenz, H. Trans-Halogeno[alkyl(aryl)carbyne] tetracarbonyl Complexes of Chromium, Molybdenum, and Tungsten—A New Class of Compounds Having a Transition Metal-Carbon Triple Bond. Angew. Chem. Int. Ed. 1973, 12, 564–565. [CrossRef] 5. Schrock, R.R. Alkylcarbene Complex of Tantalum by Intramolecular Alpha-Hydrogen Abstraction. J. Am. Chem. Soc. 1974, 96, 6796–6797. [CrossRef] 6. McLain, S.J.; Wood, C.D.; Messerle, L.W.; Schrock, R.R.; Hollander, F.J.; Youngs, W.J.; Churchill, M.R. Multiple Metal-Carbon Bonds. Thermally Stable Tantalum Alkylidyne Complexes and the Crystal Structure of
Ta(.eta.5-C5Me5)(CPh)(PMe3)2Cl. J. Am. Chem. Soc. 1978, 100, 5962–5964. [CrossRef] 7. Dewar, M.J.S. A Review of Π Complex Theory. Bull. Soc. Chim. Fr. 1951, 18, C79. 8. Chatt, J.; Duncanson, L.A. 586. Olefin Co-Ordination Compounds. Part III. Infra-Red Spectra and Structure: Attempted Preparation of Acetylene Complexes. J. Chem. Soc. 1953, 1, 2939–2947. [CrossRef] 9. Vyboishchikov, S.F.; Frenking, G. Theoretical Studies of Organometallic Compounds, Part 29-Structure and Bonding of Low-Valent (Fischer-Type) and High-Valent (Schrock-Type) Transition Metal Carbene Complexes. Chem. Eur. J. 1998, 4, 1428–1438. [CrossRef] 10. Vyboishchikov, S.F.; Frenking, G. Structure and Bonding of Low-Valent (Fischer-Type) and High-Valent (Schrock-Type) Transition Metal Carbyne Complexes. Chem. Eur. J. 1998, 4, 1439–1448. [CrossRef] 11. Jerabek, P.; Schwerdtfeger, P.; Frenking, G. Dative and Electron-Sharing Bonding in Transition Metal Compounds. J. Comput. Chem. 2019, 40, 247–264. [CrossRef][PubMed] Molecules 2020, 25, 4943 42 of 48
12. Frenking, G.; Tonner, R. Divalent Carbon(0) Compounds. Pure Appl. Chem. 2009, 81, 597–614. [CrossRef] 13. Frenking, G.; Tonner, R.; Klein, S.; Takagi, N.; Shimizu, T.; Krapp, A.; Pandey, K.K.; Parameswaran, P. New Bonding Modes of Carbon and Heavier Group 14 Atoms Si–Pb. Chem. Soc. Rev. 2014, 43, 5106–5139. [CrossRef][PubMed] 14. Frenking, G.; Hermann, M.; Andrada, D.M.; Holzmann, N. Donor–Acceptor Bonding in Novel Low-Coordinated Compounds of Boron and Group 14 Atoms C–Sn. Chem. Soc. Rev. 2016, 45, 1129–1144. [CrossRef] 15. Frenking, G.; Solà, M.; Vyboishchikov, S.F. Chemical bonding in transition metal carbene complexes. J. Organomet. Chem. 2005, 690, 6178–6204. [CrossRef] 16. Tonner, R.; Heydenrych, G.; Frenking, G. First and Second Proton Affinities of Carbon Bases. Chem. Phys. Chem. 2008, 9, 1474–1481. [CrossRef][PubMed] 17. Jensen, P.; Johns, J.W.C. The Infrared Spectrum of Carbon Suboxide in the ν6 Fundamental Region: Experimental Observation and Semirigid Bender Analysis. J. Mol. Spectrosc. 1986, 118, 248–266. [CrossRef] 18. Koput, J. An ab Initio Study on the Equilibrium Structure and CCC Bending Energy Levels of Carbon Suboxide. Chem. Phys. Lett. 2000, 320, 237–244. [CrossRef] 19. Tonner, R.; Frenking, G. Divalent Carbon(0) Chemistry, Part 1: Parent Compounds. Chem. Eur. J. 2008, 14, 3260–3272. [CrossRef] 20. Frenking, G. Dative Bonds in Main-Group Compounds: A Case for More Arrows! Angew. Chem. Int. Ed. 2014, 53, 6040–6046. [CrossRef] 21. Fustier-Boutignon, M.; Nebra, N.; Mézailles, N. Geminal Dianions Stabilized by Main Group Elements. Chem. Rev. 2019, 119, 855–8700. [CrossRef][PubMed] 22. Petz, W.; Frenking, G. Carbodiphosphoranes and Related Ligands. Top. Organomet. Chem. 2010, 30, 49–92.
23. Petz, W. Addition Compounds between Carbones, CL2, and Main Group Lewis Acids: A New Glance at Old and New Compounds. Coord. Chem. Rev. 2015, 291, 1–27. [CrossRef] 24. Alcarazo, M. Synthesis, Structure, and Reactivity of Carbidiphosphoranes, Carbodicarbenes and Related Species. Struct. Bond. 2018, 177, 25–50. 25. Liu, S.; Chen, W.C.; Ong, T.G. Synthesis and Structure of Carbodicarbenes and Their Application in Catalysis. Struct. Bond. 2018, 177, 51–72. 26. Peters, J.C.; Odom, A.L.; Cummins, C.C. A Terminal Molybdenum Carbide Prepared by Methylidyne Deprotonation. Chem. Commun. 1997, 20, 1995–1996. [CrossRef] 27. Carlson, R.G.; Gile, M.A.; Heppert, J.A.; Mason, M.H.; Powell, D.R.; Velde, D.V.; Vilain, J.M. The Metathesis-Facilitated Synthesis of Terminal Ruthenium Carbide Complexes: A Unique Carbon Atom Transfer Reaction. J. Am. Chem. Soc. 2002, 124, 1580–1581. [CrossRef] 28. Krapp, A.; Pandey, K.K.; Frenking, G. Transition Metal Carbon Complexes. A Theoretical Study. J. Am. − Chem. Soc. 2007, 129, 7596–7610. [CrossRef] 29. Reinholdt, A.; Bendix, J. Platinum(ii) as an Assembly Point for Carbide and Nitride Ligands. Chem. Commun. 2019, 55, 8270–8273. [CrossRef]
30. Ramirez, F.; Desai, N.B.; Hansen, B.; McKelvie, N. Hexaphenylcarbodiphosphorane, (C6H5)3PCP(C6H5)3. J. Am. Chem. Soc. 1961, 83, 3539–3540. [CrossRef] 31. Hussain, M.S.; Schmidbaur, H. Ein Gemischt Methyl/Phenyl-Substituiertes Carbodiphosphoran. Darstellung, Reaktionen und verwandte Verbindungen. Z. Nat. B 1976, 31, 721–726. 32. Kroll, A.; Steinert, H.; Scharf, L.T.; Scherpf, T.; Mallick, B.; Gessner, V.H. A Diamino-Substituted Carbodiphosphorane as Strong C-Donor and Weak N-Donor: Isolation of Monomeric Trigonal-Planar L ZnCl . Chem. Commun. 2020, 56, 8051–8054. [CrossRef][PubMed] · 2 33. Quinlivan, P.J.; Parkin, G. Flexibility of the Carbodiphosphorane, (Ph3P)2C: Structural Characterization of a Linear Form. Inorg. Chem. 2017, 56, 5493–5497. [CrossRef] 34. Böttger, S.; Gruber, M.; Münzer, J.E.; Bernard, G.M.; Kneusels, N.-J.H.; Poggel, C.; Klein, M.; Hampel, F.; Neumülöler, B.; Sundermeyer, J.; et al. Solvent-Induced Bond-Bending Isomerism in Hexaphenyl Carbodiphosphorane: Decisive Dispersion Interactions in the Solid State. Inorg. Chem. 2020, 59, 12054–12064. 35. Vincent, A.T.; Wheatley, P.J. Crystal Structure of Bis(triphenylphosphoranylidene)methane
[hexaphenylcarbodiphosphorane, Ph3P:C:PPh3]. J. Chem. Soc. Dalton Trans. 1972, 5, 617–622. [CrossRef] 36. Schmidbaur, H.; Hasslberger, G.; Deschler, U.; Schubert, U.; Kappenstein, C.; Frank, A. Problem of the Structure
of Carbodiphosphoranes, R3PCPR3—New Aspects. Angew. Chem. Int. Ed. 1979, 18, 408–409. [CrossRef] Molecules 2020, 25, 4943 43 of 48
37. Schubert, U.; Kappenstein, C.; Milewskimahrla, B.; Schmidbaur, H. Molecular and Crystal-Structures of 2 Carbodiphosphoranes with P-C-P Bond Angles near 120-Degrees. Chem. Ber. Recl. 1981, 114, 3070–3078. [CrossRef] 38. Schmidbaur, H.; Costa, T.; Milewskimahrla, B.; Schubert, U. Ring-Strained Carbodiphosphoranes. Angew. Chem. Int. Ed. 1980, 19, 555–556. [CrossRef]
39. Petz, W.; Weller, F.; Uddin, J.; Frenking, G. Reaction of Carbodiphosphorane Ph3P=C=PPh3 with Ni(CO)4. Experimental and Theoretical Study of the Structures and Properties of (CO)3NiC(PPh3)2 and (CO)2NiC(PPh3)2. Organometallics 1999, 18, 619–626. [CrossRef] 40. Flosdorf, K.; Jiang, D.D.; Zhao, L.L.; Neumüller, B.; Frenking, G.; Kuzu, I. An Experimental and Theoretical 2 2 Study of the Structures and Properties of CDPMe-Ni(CO)3 and Ni-2(CO)4(µ -CO)(µ -CDPMe). Eur. J. Inorg. Chem. 2019, 2019, 4546–4554. [CrossRef]
41. Petz, W.; Neumüller, B.; Klein, S.; Frenking, G. Syntheses and Crystal Structures of [Hg{C(PPh3)2}2][Hg2I6] and [Cu{C(PPh3)2}2]I and Comparative Theoretical Study of Carbene Complexes [M(NHC)2] with Carbone + + + 2+ 2+ 2+ Complexes [M{C(PH3)2}2] (M = Cu , Ag , Au , Zn , Cd , Hg ). Organometallics 2011, 30, 3330–3339. [CrossRef] 42. Petz, W.; Öxler, F.; Neumüller, B. Syntheses and Crystal Structures of Linear Coordinated Complexes of Ag+ + with the Ligands C(PPh3)2 and (HC{PPh3}2) . J. Organomet. Chem. 2009, 694, 4094–4099. [CrossRef] 43. Sundermeyer, J.; Weber, K.; Peters, K.; von Schnering, H.G. Modeling Surface Reactivity of Metal Oxides: Synthesis and Structure of an Ionic Organorhenyl Perrhenate Formed by Ligand-Induced Dissociation of
Covalent Re2O7. Organometallics 1994, 13, 2560–2562. [CrossRef] 44. Schmidbaur, H.; Zybill, C.E.; Müller, G.; Krüger, C. Coinage Metal Complexes of Hexaphenylcarbodiphosphorane–Organometallic Compounds with Coordination Number 2. Angew. Chem. Int. Ed. 1983, 22, 729–730. [CrossRef] 45. Zybill, C.; Mueller, G. Mononuclear Complexes of Copper(I) and Silver(I) Featuring the Metals Exclusively Bound to Carbon. Synthesis and Structure of (.eta.5-Pentamethylcyclopentadienyl)[(triphenylphosphonio) (triphenylphosphoranylidene)methyl]Copper(I). Organometallics 1987, 6, 2489–2494. [CrossRef] 46. Vicente, J.; Singhal, A.R.; Jones, P.G. New Ylide , Alkynyl , and Mixed Alkynyl/Ylide Gold(I) Complexes. − − − Organometallics 2002, 21, 5887–5900. [CrossRef] 47. Kaska, W.C.; Reichelderfer, R.F. The Interaction of Hexaphenylcarbodiphosphorane with Iridium Olefin Cations. Metalation of Coordinated Ligands. J. Organomet. Chem. 1974, 78, C47–C50. [CrossRef] 48. Münzer, J.E.; Kuzu, I.; Philipps-Universität Marburgdisabled, Marburg, Germany. Unpublished results. Private communication to WP. 49. Pranckevicius, C.; Iovan, D.A.; Stephan, D.W. Three and Four Coordinate Fe Carbodiphosphorane Complexes. Dalton Trans. 2016, 45, 16820–16825. [CrossRef] 50. Kneusels, N.J.H.; Münzer, J.E.; Flosdorf, K.; Jiang, D.; Neumüller, B.; Zhao, L.; Eichhöfer, A.; Frenking, G.; Kuzu, I. Double Donation in Trigonal Planar Iron–Carbodiphosphorane Complexes—A Aoncise Study on Their Spectroscopic and Electronic Properties. Dalton Trans. 2020, 49, 2537–2546. [CrossRef] 51. Su, W.; Pan, S.; Sun, X.; Wang, S.; Zhao, L.; Frenking, G.; Zhu, C. Double Dative Bond between Divalent Carbon(0) and Uranium. Nat. Commun. 2018, 9, 4997. [CrossRef] 52. Tonner, R.; Oexler, F.; Neumuller, B.; Petz, W.; Frenking, G. Carbodiphosphoranes: The Chemistry of Divalent Carbon(0). Angew. Chem. Int. Ed. 2006, 45, 8038–8042. [CrossRef][PubMed]
53. Petz, W.; Neumüller, B. Reaction of C(PPh3)2 with MI2 Compounds (M = Zn, Cd) - Formation and Crystal Structures of [I2Zn{C(PPh3)2}], [(I2Cd{C(PPh3)2})2] and the Salt-Like Compounds (HC{PPh3}2)[MI3(THF)] and (HC{PPh3}2)2[ZnI4]. Eur. J. Inorg. Chem. 2011, 31, 4889–4895. [CrossRef] 54. Romeo, I.; Bardají, M.; Concepción Gimeno, M.; Laguna, M. Gold(I) Complexes Containing the Cationic Ylide Ligand Bis(methyldiphenylphosphonio)methylide. Polyhedron 2000, 19, 1837–1841. [CrossRef] 55. Bruce, A.E.; Gamble, A.S.; Tonker, T.L.; Templeton, J.L. Cationic Phosphonium Carbyne and Bis(phosphonium)
Carbene Tungsten Complexes: [Tp’(OC)2WC(PMe3)n][PF6] (n = 1, 2). Organometallics 1987, 6, 1350–1352. [CrossRef] 56. Schmidbaur, H.; Gasser, O. The Ambident Ligand Properties of Bis(trimethylphosphoranylidene)methan. Angew. Chem. Int. Ed. 1976, 15, 502–503. [CrossRef] Molecules 2020, 25, 4943 44 of 48
57. Dorta, R.; Stevens, E.D.; Scott, N.M.; Costabile, C.; Cavallo, L.; Hoff, C.D.; Nolan, S.P. Steric and Electronic
Properties of N-Heterocyclic Carbenes (NHC): A Detailed Study on Their Interaction with Ni(CO)4. J. Am. Chem. Soc. 2005, 127, 2485–2495. [CrossRef] 58. Pugh, D.; Wright, J.A.; Freeman, S.; Danopoulos, A.A. ‘Pincer’ Dicarbene Complexes of Some Early Transition Metals and Uranium. Dalton Trans. 2006, 6, 775–782. [CrossRef] 59. Gardner, B.M.; McMaster, J.; Liddle, S.T. Synthesis and Structure of a Dis-N-Heterocyclic Carbene Complex of Uranium Tetrachloride Exhibiting Short Cl C Carbene Contacts. Dalton Trans. 2009, 35, 6924–6926. ··· [CrossRef]
60. Doddi, A.; Gemel, C.; Seidel, R.W.; Winter, M.; Fischer, R.A. Coordination Complexes of TiX4 (X = F, Cl) with a Bulky N-Heterocyclic Carbene: Syntheses, Characterization and Molecular Structures. Polyhedron 2013, 52, 1103–1108. [CrossRef] 61. Datt, M.S.; Nair, J.J.; Otto, S. Synthesis and Characterisation of Two Novel Rh(I) Carbene Complexes: Crystal
Structure of [Rh(acac)(CO)(L1)]. J. Organomet. Chem. 2005, 690, 3422–3426. [CrossRef] 62. Stallinger, S.; Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P. Novel Route to Carbodiphosphoranes Producing a New P,C,P Pincer Carbene Ligand. Chem. Commun. 2007, 510–512. [CrossRef] 63. Klein, M.; Demirel, N.; Schinabeck, A.; Yersin, H.; Sundermeyer, J. Cu(I) Complexes of Multidentate N,C,N- and P,C,P-Carbodiphosphorane Ligands and Their Photoluminescence. Molecules 2020, 25, 3990. [CrossRef] 64. Klein, M.; Xie, X.; Burghaus, O.; Sundermeyer, J. Synthesis and Characterization of a N,C,N-Carbodiphosphorane Pincer Ligand and Its Complexes. Organometallics 2019, 38, 3768–3777. [CrossRef] 65. Reitsamer, C.; Stallinger, S.; Schuh, W.; Kopacka, H.; Wurst, K.; Obendorf, D.; Peringer, P. Novel Access to Carbodiphosphoranes in the Coordination Sphere of Group 10 Metals: Template Synthesis and Protonation
of PCP Pincer Carbodiphosphorane Complexes of C(dppm)2. Dalton Trans. 2012, 41, 3503–3514. [CrossRef] 66. Maser, L.; Herritsch, J.; Langer, R. Carbodiphosphorane-Based Nickel Pincer Complexes and Their (de)Protonated Analogues: Dimerisation, Ligand Tautomers and Proton Affinities. Dalton Trans. 2018, 47, 10544–10552. [CrossRef][PubMed] 67. Reitsamer, C.; Hackl, I.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P. Gold(I) and Gold(III) Complexes + of the [CH(dppm)2] and C(dppm)2 PCP Pincer Ligand Systems. J. Organomet. Chem. 2017, 830, 150–154. [CrossRef] 68. Su, W.; Pan, S.; Sun, X.; Zhao, L.; Frenking, G.; Zhu, C. Cerium–Carbon Dative Interactions Supported by Carbodiphosphorane. Dalton Trans. 2019, 48, 16108–16114. [CrossRef] 69. Kubo, K.; Jones, N.D.; Ferguson, M.J.; McDonald, R.; Cavell, R.G. Chelate and Pincer Carbene Complexes of
Rhodium and Platinum Derived from Hexaphenylcarbodiphosphorane, Ph3PCPPh3. J. Am. Chem. Soc. 2005, 127, 5314–5315. [CrossRef][PubMed] 70. Kubo, K.; Okitsu, H.; Miwa, H.; Kume, S.; Cavell, R.G.; Mizuta, T. Carbon(0)-Bridged Pt/Ag Dinuclear and Tetranuclear Complexes Based on a Cyclometalated Pincer Carbodiphosphorane Platform. Organometallics 2017, 36, 266–274. [CrossRef] 71. Petz, W.; Neumüller, B. New Platinum Complexes with Carbodiphosphorane as Pincer Ligand via Ortho Phenyl Metallation. Polyhedron 2011, 30, 1779–1784. [CrossRef] 72. Lin, G.; Jones, N.D.; Gossage, R.A.; McDonald, R.; Cavell, R.G. A Tris(carbene) Pincer Complex: Monomeric Platinum Carbonyl with Three Bound Carbene Centers. Angew. Chem. Int. Ed. 2003, 42, 4054–4057. [CrossRef] 73. Marrot, S.; Kato, T.; Gornitzka, H.; Baceiredo, A. Cyclic Carbodiphosphoranes: Strongly Nucleophilic σ-Donor Ligands. Angew. Chem. Int. Ed. 2006, 45, 2598–2601. [CrossRef][PubMed] 74. Corberán, R.; Marrot, S.; Dellus, N.; Merceron-Saffon, N.; Kato, T.; Peris, E.; Baceiredo, A. First Cyclic Carbodiphosphoranes of Copper(I) and Gold(I) and Their Application in the Catalytic Cleavage of X H − Bonds (X = N and O). Organometallics 2009, 28, 326–330. [CrossRef] 75. Yogendra, S.; Schulz, S.; Hennersdorf, F.; Kumar, S.; Fischer, R.; Weigand, J.J. Reductive Ring Opening of a Cyclo-Tri(phosphonio)methanide Dication to a Phosphanylcarbodiphosphorane: In Situ UV-Vis Spectroelectrochemistry and Gold Coordination. Organometallics 2018, 37, 748–754. [CrossRef] 76. Alcarazo, M.; Radkowski, K.; Mehler, G.; Goddard, R.; Fürstner, A. Chiral Heterobimetallic Complexes of Carbodiphosphoranes and Phosphinidene–Carbene Adducts. Chem. Commun. 2013, 49, 3140–3142. [CrossRef][PubMed] Molecules 2020, 25, 4943 45 of 48
77. Petz, W.; Kutschera, C.; Neumüller, B. Reaction of the Carbodiphosphorane Ph3PCPPh3 with Platinum(II) and -(0) Compounds: Platinum Induced Activation of C H Bonds. Organometallics 2005, 24, 5038–5043. − [CrossRef] 78. Baldwin, J.C.; Kaska, W.C. The Interaction of Hexaphenylcarbodiphosphorane with the Trimethylplatinum(IV) Cation. Inorg. Chem. 1979, 18, 686–691. [CrossRef] 79. Melaimi, M.; Parameswaran, P.; Donnadieu, B.; Frenking, G.; Bertrand, G. Synthesis and Ligand Properties of a Persistent, All-Carbon Four-Membered-Ring Allene. Angew. Chem. Int. Ed. 2009, 48, 4792–4795. [CrossRef] 80. Hackl, L.; Petrov, A.R.; Bannenberg, T.; Freytag, M.; Jones, P.G.; Tamm, M. Dimerisation of Dipiperidinoacetylene: Convenient Access to Tetraamino-1,3-Cyclobutadiene and Tetraamino-1,2-Cyclobutadiene Metal Complexes. Chem. Eur. J. 2019, 25, 16148–16155. [CrossRef] 81. Pranckevicius, C.; Liu, L.; Bertrand, G.; Stephan, D.W. Synthesis of a Carbodicyclopropenylidene: A Carbodicarbene Based Solely on Carbon. Angew. Chem. Int. Ed. 2016, 55, 5536–5540. [CrossRef]
82. Tonner, R.; Frenking, G. C(NHC)2: Divalent Carbon(0) Compounds with N-Heterocyclic Carbene Ligands—Theoretical Evidence for a Class of Molecules with Promising Chemical Properties. Angew. Chem. Int. Ed. 2007, 46, 8695–8698. [CrossRef][PubMed] 83. Dyker, C.A.; Lavallo, V.; Donnadieu, B.; Bertrand, G. Synthesis of an Extremely Bent Acyclic Allene (A “Carbodicarbene”): A Strong Donor Ligand. Angew. Chem. Int. Ed. 2008, 47, 3206–3209. [CrossRef] 84. Hsu, Y.C.; Shen, J.S.; Lin, B.C.; Chen, W.C.; Chan, Y.T.; Ching, W.M.; Yap, G.P.A.; Hsu, C.P.; Ong, T.G. Synthesis and Isolation of an Acyclic Tridentate Bis(pyridine)carbodicarbene and Studies on Its Structural Implications and Reactivities. Angew. Chem. Int. Ed. 2015, 54, 2420–2424. [CrossRef] 85. Chen, W.C.; Hsu, Y.C.; Lee, C.Y.; Yap, G.P.A.; Ong, T.G. Synthetic Modification of Acyclic Bent Allenes (Carbodicarbenes) and Further Studies on Their Structural Implications and Reactivities. Organometallics 2013, 32, 2435–2442. [CrossRef] 86. Liberman-Martin, A.L.; Grubbs, R.H. Ruthenium Olefin Metathesis Catalysts Featuring a Labile Carbodicarbene Ligand. Organometallics 2017, 36, 4091–4094. [CrossRef] 87. Chan, S.C.; Gupta, P.; Engelmann, X.; Ang, Z.Z.; Ganguly, R.; Bill, E.; Ray, K.; Ye, S.F.; England, J. Observation of Carbodicarbene Ligand Redox Noninnocence in Highly Oxidized Iron Complexes. Angew. Chem. Int. Ed. 2018, 57, 15717–15722. [CrossRef] 88. Chen, W.C.; Shih, W.C.; Jurca, T.; Zhao, L.L.; Andrada, D.M.; Peng, C.J.; Chang, C.C.; Liu, S.K.; Wang, Y.P.; Wen, Y.S.; et al. Carbodicarbenes: Unexpected π-Accepting Ability during Reactivity with Small Molecules. J. Am. Chem. Soc. 2017, 139, 12830–12836. [CrossRef][PubMed] 89. Shih, W.C.; Chiang, Y.T.; Wang, Q.; Wu, M.C.; Yap, G.P.A.; Zhao, L.; Ong, T.G. Invisible Chelating Effect Exhibited between Carbodicarbene and Phosphine through π–π Interaction and Implication in the Cross-Coupling Reaction. Organometallics 2017, 36, 4287–4297. [CrossRef] 90. Chen, W.C.; Shen, J.S.; Jurca, T.; Peng, C.J.; Lin, Y.H.; Wang, Y.P.; Shih, W.C.; Yap, G.P.A.; Ong, T.G. Expanding the Ligand Framework Diversity of Carbodicarbenes and Direct Detection of Boron Activation in the
Methylation of Amines with CO2. Angew. Chem. Int. Ed. 2015, 54, 15207–15212. [CrossRef][PubMed] 91. Ruiz, D.A.; Melaimi, M.; Bertrand, G. Carbodicarbenes, Carbon(0) Derivatives, Can Dimerize. Chem. Asian J. 2013, 8, 2940–2942. [CrossRef] 92. Pranckevicius, C.; Fan, L.; Stephan, D.W. Cyclic Bent Allene Hydrido-Carbonyl Complexes of Ruthenium: Highly Active Catalysts for Hydrogenation of Olefins. J. Am. Chem. Soc. 2015, 137, 5582–5589. [CrossRef] 93. Goldfogel, M.J.; Roberts, C.C.; Meek, S.J. Intermolecular Hydroamination of 1,3-Dienes Catalyzed by Bis(phosphine)carbodicarbene–Rhodium Complexes. J. Am. Chem. Soc. 2014, 136, 6227–6230. [CrossRef] 94. Roberts, C.C.; Matías, D.M.; Goldfogel, M.J.; Meek, S.J. Lewis Acid Activation of Carbodicarbene Catalysts for Rh-Catalyzed Hydroarylation of Dienes. J. Am. Chem. Soc. 2015, 137, 6488–6491. [CrossRef] 95. Fürstner, A.; Alcarazo, M.; Goddard, R.; Lehmann, C.W. Coordination Chemistry of Ene-1,1-diamines and a Prototype “Carbodicarbene”. Angew. Chem. Int. Ed. 2008, 47, 3210–3214. [CrossRef][PubMed] 96. Paoletti, A.M.; Pennesi, G.; Rossi, G.; Ercolani, C. A New Approach to Cofacially Assembled Partially Oxidized Metal Phthalocyanine Low Dimensional Solids: Synthesis, Structure, and Electrical
Conductivity Properties of the Fe(IV) Containing Species [(PcFe)2C](l3)0.66 Obtained by I2 Doping of (m-Carbido)bis[phthalocyaninatoiron(IV)]. Inorg. Chem. 1995, 34, 4780–4784. 97. Burzlaff, H.; Voll, U.; Bestmann, H.J. Die Kristall- und Molekülstruktur des (2,2-Diäthoxyvinyliden) -triphenylphosphorans. Chem. Ber. 1974, 107, 1949–1956. [CrossRef] Molecules 2020, 25, 4943 46 of 48
98. Alcarazo, M.; Lehmann, C.W.; Anoop, A.; Thiel, W.; Furstner, A. Coordination Chemistry at Carbon. Nat. Chem. 2009, 1, 295–301. [CrossRef] 99. Troadec, T.; Wasano, T.; Lenk, R.; Baceiredo, A.; Saffon-Merceron, N.; Hashizume, D.; Saito, Y.; Nakata, N.; Branchadell, V.; Kato, T. Donor-Stabilized Silylene/Phosphine-Supported Carbon(0) Center with High Electron Density. Angew. Chem. Int. Ed. 2017, 56, 6891–6895. [CrossRef][PubMed] 100. Morosaki, T.; Wang, W.W.; Nagase, S.; Fujii, T. Synthesis, Structure, and Reactivities of Iminosulfane- and Phosphane-Stabilized Carbones Exhibiting Four-Electron Donor Ability. Chem. Eur. J. 2015, 21, 15405–15411. [CrossRef][PubMed] 101. Pascual, S.; Asay, M.; Illa, O.; Kato, T.; Bertrand, G.; Saffon-Merceron, N.; Branchadell, V.; Baceiredo, A.
Synthesis of a Mixed Phosphonium-Sulfonium Bisylide R3P=C=SR2. Angew. Chem. Int. Ed. 2007, 46, 9078–9080. [CrossRef] 102. Morosaki, T.; Iijima, R.; Suzuki, T.; Wang, W.W.; Nagase, S.; Fujii, T. Synthesis, Electronic Structure, and Reactivities of Two-Sulfur-Stabilized Carbones Exhibiting Four-Electron Donor Ability. Chem. Eur. J. 2017, 23, 8694–8702. [CrossRef] 103. Morosaki, T.; Suzuki, T.; Wang, W.W.; Nagase, S.; Fujii, T. Syntheses, Structures, and Reactivities of Two Chalcogen-Stabilized Carbones. Angew. Chem. Int. Ed. 2014, 53, 9569–9571. [CrossRef]
104. Fujii, T.; Ikeda, T.; Mikami, T.; Suzuki, T.; Yoshimura, T. Synthesis and Structure of (MeN)Ph2S=C=SPh2(NMe). Angew. Chem. Int. Ed. 2002, 41, 2576–2578. [CrossRef] 105. Morosaki, T.; Suzuki, T.; Fujii, T. Syntheses and Structural Characterization of Mono-, Di-, and Tetranuclear Silver Carbone Complexes. Organometallics 2016, 35, 2715–2721. [CrossRef] 106. Chen, Y.; Petz, W.; Frenking, G. Is It Possible to Synthesize a Low-Valent Transition Metal Complex with
a Neutral Carbon Atom as Terminal Ligand? A Theoretical Study of (CO)4FeC. Organometallics 2000, 19, 2698–2706. [CrossRef] 107. Zhao, L.; von Hopffgarten, M.; Andrada, D.M.; Frenking, G. Energy Decomposition Analysis. Wires Comput. Mol. Sci. 2018, 8, e1345. [CrossRef] 108. Takemoto, S.; Matsuzaka, H. Recent Advances in the Chemistry of Ruthenium Carbido Complexes. Coord. Chem. Rev. 2012, 256, 574–588. [CrossRef] 109. Hejl, A.; Trnka, T.M.; Day, M.W.; Grubbs, R.H. Terminal Ruthenium Carbido Complexes as σ-Donor Ligands. Chem. Commun. 2002, 21, 2524–2525. [CrossRef] 110. Caskey, S.R.; Stewart, M.H.; Kivela, J.E.; Sootsman, J.R.; Johnson, M.J.A.; Kampf, J.W. Two Generalizable Routes to Terminal Carbido Complexes. J. Am. Chem. Soc. 2005, 127, 16750–16751. [CrossRef] 111. Reinholdt, A.; Bendix, J. Weakening of Carbide–Platinum Bonds as a Probe for Ligand Donor Strengths. Inorg. Chem. 2017, 56, 12492–12497. [CrossRef] 112. Reinholdt, A.; Vibenholt, J.E.; Morsing, T.J.; Schau-Magnussen, M.; Reeler, N.E.A.; Bendix, J. Carbide Complexes as π-Acceptor Ligands. Chem. Sci. 2015, 6, 5815–5823. [CrossRef] 113. Reinholdt, A.; Herbst, K.; Bendix, J. Delivering Carbide Ligands to Sulfide-Rich Clusters. Chem. Commun. 2016, 52, 2015–2018. [CrossRef][PubMed] 114. Hong, S.H.; Day, M.W.; Grupps, R.H. Decomposition of a Key Intermediate in Ruthenium-Catalyzed Olefin Metatesis Reactions. J. Am. Chem. Soc. 2004, 126, 7414–7415. [CrossRef][PubMed] 115. Morsing, T.J.; Reinholdt, A.; Sauer, S.P.A.; Bendix, J. Ligand Sphere Conversions in Terminal Carbide Complexes. Organometallics 2016, 35, 100–105. [CrossRef] 116. Stewart, M.H.; Johnson, M.J.A.; Kampf, J.W. Terminal Carbido Complexes of Osmium: Synthesis, Structure, and Reactivity Comparison to the Ruthenium Analogues. Organometallics 2007, 26, 5102–5110. [CrossRef] 117. Etienne, M.; White, P.S.; Templeton, J.L. An Agostic.mu.-Methyne Molybdenum-Iron Complex from
Protonation of a.mu.-Carbide Precursor, Tp’(CO)2Mo.tplbond.CFe(CO)2Cp. J. Am. Chem. Soc. 1991, 113, 2324–2325. [CrossRef] 118. Cordiner, L.R.; Hill, A.F.; Wagler, J. Facil Generation of Lithiocarbyne Complexes; [M( CLi)(CO) ≡ 2 {HB(pzMe2)3}] (M = Mo, W; pz = Pyrazol-1-yl). Organometallics 2008, 27, 5177–5179. [CrossRef] 119. Cade, I.A.; Hill, A.F.; McQueen, C.M.A. Iridium Molybdenum Carbido Complex via C Se − − Activation of a Selenocarbonyl Ligand: (µ-Se )[Ir {C Mo(CO) (Tp*)} (CO) (PPh ) ](Tp* = Hydrotris 2 2 ≡ 2 2 2 3 2 (dimethylpyrazolyl)borate). Organometallics 2009, 28, 6639–6641. [CrossRef] Molecules 2020, 25, 4943 47 of 48
120. Colebatch, A.L.; Cordiner, R.L.; Hill, A.F.; Nguyen, K.T.H.D.; Shang, R.; Willis, A.C. A Bis-Carbyne (Ethanediylidyne) Complex via the Catalytic Demercuration of a Mercury Bis(carbido) Complex. Organometallics 2009, 28, 4394–4399. [CrossRef]
121. Knauer, W.; Beck, W. Carbide Bridged Complexes [HB(pz)3(OC)2Mo=C-Pt(PPh3)2Br], [(TPP)Fe=C-M (CO)4-M(CO)5] (M = Mn, Re), [(TPP)Fe=C=Cr(CO)5], TPP)Fe=C=Fe(CO)4] (pz- 3,5-dimethylpyrazol-1-yl; TPP Tetraphenylporphyrinate) from Halogeno-Carbyne and -Carbene Complexes. Z. Anorg. Allg. Chem. 2008, 634, 2241–2245. [CrossRef] 122. Borren, E.S.; Hill, A.F.; Shang, R.; Sharma, M.; Willis, A.C. A Golden Ring: Molecular Gold Carbido Complexes. J. Am. Chem. Soc. 2013, 135, 4942–4945. [CrossRef] 123. Buss, J.A.; Agapie, T. Mechanism of Molybdenum-Mediated Carbon Monoxide Deoxygenation and Coupling: Mono- and Dicarbyne Complexes Precede C–O Bond Cleavage and C–C Bond Formation. J. Am. Chem. Soc. 2016, 138, 16466–16477. [CrossRef][PubMed] 124. Hill, A.F.; Sharma, M.; Willis, A.C. Heterodinuclear Bridging Carbido and Phosphoniocarbyne Complexes. Organometallics 2012, 31, 2538–2542. [CrossRef] 125. Frogley, B.J.; Hill, A.F. Tungsten–Platinum µ-Carbido and µ-Methylidyne Complexes. Chem. Commun. 2019, 55, 12400–12403. [CrossRef][PubMed] 126. Agapie, T.; Diaconescu, P.L.; Cummins, C.C. Methine (CH) Transfer via a Chlorine Atom Abstraction/Benzene-Elimination Strategy: Molybdenum Methylidyne Synthesis and Elaboration to a Phosphaisocyanide Complex. J. Am. Chem. Soc. 2002, 124, 2412–2413. [CrossRef][PubMed]
127. Latesky, S.L.; Selegue, J.P. Preparation and Structure of [(Me3CO)3W.tplbond.C-Ru(CO)2(Cp)], a Heteronuclear,.mu.2-Carbide Complex. J. Am. Chem. Soc. 1987, 109, 4731–4733. [CrossRef] 128. Mansuy, D.; Lecomte, J.P.; Chottard, J.C.; Bartoli, J.F. Formation of a Complex with a Carbide Bridge between Two Iron Atoms from the Reaction of (Tetraphenylporphyrin)iron(II) with Carbon Tetraiodide. Inorg. Chem. 1981, 20, 3119–3121. [CrossRef] 129. Battioni, J.-P.; Dupre, D.; Mansuy, D. Reactions du Trichloromethyl-Trimethyl-Silane avec des Ferrotetra-Aryl-Porphyrines. J. Organometal. Chem. 1981, 414, 303–309. [CrossRef] 130. Galich, L.; Kienast, A.; Hückstädt, H.; Homborg, H. Syntheses, Spectroscopical Properties, and Crystal Structures of Binuclear Homo- and Heteroleptic µ-Carbido Complexes of Iron(IV) with Phthalocyaninate and Tetraphenylporphyrinate Ligands. Z. Anorg. Allg. Chem. 1998, 624, 1235–1242. [CrossRef] 131. Goedken, V.L.; Deakin, M.R.; Bottomley, L.A. Molecular Stereochemistry of a Carbon-Bridged Metalloporphyrin: µ-Carbido-Bid(5,10,15,20-tetraphenylporphinatoiron). J. Chem. Soc. Chem. Commun. 1982, 11, 607–608. [CrossRef] 132. Kienast, A.; Galich, L.; Murray, K.S.; Moubaraki, B.; Lazarev, G.; Cashion, J.D.; Homborg, H. M-Carbido Dipophyrinates and Diphthalocyaninates of Iron and Ruthenium. J. Porphyr. Phthalocyanines 1997, 1, 141–157. [CrossRef] 133. Kienast, A.; Bruhn, C.; Homborg, H. Synthesis, Properties, and Crystal Structure of µ-Carbidodi (pyridinephthalocyaninato(2-)Iron(IV)) and -Ruthenium(IV). Z. Anorg. Allg. Chem. 1997, 623, 967–972. [CrossRef] 134. Rossi, G.; Goedken, V.L.; Ercolani, C. µ-Carbido-Bridged Iron Phthalocyanine Dimers: Synthesis and Characterization. J. Chem. Soc. Chem. Commun. 1988, 1, 46–47. [CrossRef] 135. Kienast, A.; Homborg, H. Synthese und Eigenschaften von Bis(tetra(n-butyl)ammonium)-l- carbidodi(halogenophthalocyaninato(2-)ferraten(IV)); Kristallstruktur von Bis(tetra(n-butyl)ammonium)-µ -carbidodi(fluorophthalocyaninato(2-)ferrat(IV))-Trihydrat. Z. Anorg. Chem. 1998, 624, 107–112. [CrossRef] 136. Ercolani, C.; Gardini, M.; Goedken, V.L.; Pennesi, G.; Rossi, G.; Russo, U.; Zanonato, P. High-Valent Iron Phthalocyanine Five- and Six-Coordinated µ-Carbido Dimers. Inorg. Chem. 1989, 28, 3097–3099. [CrossRef]
137. Ahrens, T.; Schmiedecke, B.; Braun, T.; Herrmann, R.; Laubenstein, R. Activation of CS2 and COS at a Rhodium(I) Germyl Complex: Generation of CS and Carbido Complexes. Eur. J. Inorg. Chem. 2017, 3, 713–722. [CrossRef] 138. Kalläne, S.I.; Braun, T.; Teltewskoi, M.; Braun, B.; Herrmann, R.; Laubenstein, R. Remarkable Reactivity of a
Rhodium(i) Boryl Complex Towards CO2 and CS2: Isolation of a Carbido Complex. Chem. Commun. 2015, 51, 14613–14616. [CrossRef] 139. Barnett, H.J.; Burt, L.K.; Hill, A.F. Simple Generation of a Dirhodium µ-Carbido Complex via Thiocarbonyl Reduction. Dalton Trans. 2018, 47, 9570–9574. [CrossRef] Molecules 2020, 25, 4943 48 of 48
140. Solari, E.; Antonijevic, S.; Gauthier, S.; Scopelliti, R.; Severin, K. Formation of a Ruthenium mu-Carbide Complex with Acetylene as the Crbon Source. Eur. J. Inorg. Chem. 2007, 3, 367–371. [CrossRef]
141. Young, R.D.; Hill, A.F.; Cavigliasso, G.E.; Stranger, R. [(µ-C){Re(CO)2(η-C5H5)}2]: A Surprisingly Simple Bimetallic Carbido Complex. Angew. Chem. Int. Ed. 2013, 52, 3699–3702. [CrossRef] 142. Miller, R.L.; Wolczanski, P.T.; Rheingold, A.L. Carbide Formation via Carbon Monoxide Dissociation Across a W W Bond. J. Am. Chem. Soc. 1993, 115, 10422–10423. [CrossRef] ≡ 143. Beck, W.; Knauer, W.; Robl, C. Synthesis and Structure of the Novel µ-Carbido Complex [(TPP)Fe=C=Re
(CO)4Re(CO)5]. Angew. Chem. Int. Ed. 1990, 29, 318–320. [CrossRef]
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