CO2 Derivatives of Molecular Tin Compounds. Part 1: † Hemicarbonato and Carbonato Complexes

inorganics

Review CO2 Derivatives of Molecular Tin Compounds. Part 1: † Hemicarbonato and Carbonato Complexes

Laurent Plasseraud

Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR-CNRS 6302, Université de Bourgogne Franche-Comté, 9 avenue A. Savary, F-21078 Dijon, France; [email protected] Paper dedicated to Professor Georg Süss-Fink on the occasion of his 70th birthday. † Received: 31 March 2020; Accepted: 24 April 2020; Published: 29 April 2020

Abstract: This review focuses on organotin compounds bearing hemicarbonate and carbonate ligands, and whose molecular structures have been previously resolved by single-crystal X-ray diffraction analysis. Most of them were isolated within the framework of studies devoted to the reactivity of tin precursors with carbon dioxide at atmospheric or elevated pressure. Alternatively, and essentially for the preparation of some carbonato derivatives, inorganic carbonate salts such as K2CO3, Cs2CO3, Na2CO3 and NaHCO3 were also used as coreagents. In terms of the number of X-ray structures, carbonate compounds are the most widely represented (to date, there are 23 depositions in the Cambridge Structural Database), while hemicarbonate derivatives are rarer; only three have so far been characterized in the solid-state, and exclusively for diorganotin complexes. For each compound, the synthesis conditions are first specified. Structural aspects involving, in particular, the modes of coordination of the hemicarbonato and carbonato moieties and the coordination geometry around tin are then described and illustrated (for most cases) by showing molecular representations. Moreover, when they were available in the original reports, some characteristic spectroscopic data are also given for comparison (in table form). Carbonato complexes are arbitrarily listed according to their decreasing number of hydrocarbon substituents linked to tin atoms, namely tri-, di-, and mono-organotins. Four additional examples, involving three CO2 derivatives of C,N-chelated stannoxanes and one of a trinuclear nickel cluster Sn-capped, are also included in the last part of the chapter.

Keywords: tin complexes; carbon dioxide ﬁxation; hypervalent compounds; X-ray crystallography

1. Introduction

Over the past fifty years, the coordination of CO2 on metal centers has aroused great interest, mobilizing numerous groups around the world; even today, it continues to fascinate the community of inorganic and organometallic chemists. Pioneering works in this area are to be credited to M. E. Vol’pin et al., who highlighted in 1969 the formation of a rhodium-phosphine complex with a carbon dioxide adduct [1]. To our knowledge, the first resolution of an X-ray crystal structure showing the metal-coordination of a CO2 molecule is to be attributed to M. Aresta et al., for the characterization of a nickel complex stabilized by triscyclohexilphosphines [2]. Since then, a multitude of CO2 coordination modes has been revealed at the solid state, showing an important diversity of structures and involving most of transition metal atoms [3,4]. Knowledge in the field has regularly been reviewed and updated [5]. Nature has also been an important source of inspiration for chemists in this area. Thus, the zinc-based active site of carbonic anhydrase has been widely used as a model for the design of metal complexes in order to mimic the catalytic role of the enzyme toward carbon dioxide [6].

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Nowadays,Nowadays, thethe organometallic organometallic chemistry chemistry of of metal–CO metal–CO2 complexes2 complexes remains remains a topical a topical research research area whicharea which is closely is linkedclosely to linked the fields to ofthe materials fields (COof materials2-capture) (CO and2-capture) catalysis (COand2 -transformation).catalysis (CO2- Indeed,transformation). beyond the Indeed, purely beyond fundamental the purely aspect, fundamental CO2-coordination aspect, on CO a metallic2-coordination center canon bea metallic viewed ascenter a key-step can be viewed facilitating as a itskey-step activation facilitating and conversion its activation into and useful conversion chemicals. into Inuseful this chemicals. way, carbon In dioxidethis way, appears carbon todioxide be a potentialappears to renewable be a potential C1 raw renewable material, C1 rather raw material, than a waste,rather than offering a waste, new opportunitiesoffering new opportunities for chemical reactionsfor chemical [7– 9reactions]. Currently, [7–9]. a Currently, great level a of great attention level isof beingattention paid is tobeing the designpaid to of the porous design coordination of porous coordination polymers (PCPs) poly ormers metal–organic (PCPs) or metal–or frameworksganic (MOF), frameworks owing to(MOF), their absorptionowing to their properties absorption [10], butproperties also transforming [10], but COalso2 [transforming11]. Thus, the CO chemical2 [11]. utilizationThus, the ofchemical carbon dioxideutilization has of become carbon a crucialdioxide issue, has become in particular a crucial in view issue, of thein particular environmental in view challenges of the environmental that humanity haschallenges to face, that i.e., (i)humanity the depletion has to offa fossilce, i.e., carbon (i) the resources, depletion andof fossil (ii) the carbon continuous resources, increase and in(ii) CO the2 emissionscontinuous and increase its consequences in CO2 emissions on the and climate. its consequences on the climate. FromFrom aa coordination coordination chemistry chemistry point point of view,of view, the reactivitythe reactivity of main of groupmain metalgroup elements metal elements (groups 13–15)(groups with 13–15) carbon with dioxide carbon hasdioxide been, has up been, to now, up relativelyto now, relatively underreviewed underreviewed in the literature. in the literature. Within theWithin framework the framework of our previousof our previous studies studies in this in field, this field, and usingand using the supportthe support of the of the online online portal portal of theof the Cambridge Cambridge Structural Structural Database Database (WebCSD) (WebCSD) [12 [12],], we we herein herein focus focus specifically specifically on on an an inventory inventory of X-rayof X-ray crystallographic crystallographic structures structures of of tin tin compounds compounds resulting resulting from from reactivity reactivity withwith carboncarbon dioxide. ToTo the best best of of our our knowledge, knowledge, tin tin complexes complexes directly directly bearing bearing a CO a2-coordinated CO2-coordinated molecule molecule have never have neverbeen isolated been isolated in the in solid the solid state. state. However, However, CO CO2-adducts2-adducts of oftin tin complexes complexes exist exist in in the the form form ofof hemicarbonate,hemicarbonate, carbonate,carbonate, carbamate,carbamate, formate and phosphinoformate derivatives, and are generally obtainedobtained fromfrom insertion insertion reactions reactions by reactingby reacting carbon carbon dioxide dioxide (under (under atmospheric atmospheric pressure orpressure requiring or highrequiring pressure) high withpressure) precursors with precursors having Sn–X having bonds Sn–X (X = bondsO, N, H,(X P).= O, In N, some H, cases,P). In alternatively,some cases, inorganicalternatively, carbonate inorganic salts carbonate are also used salts as are reagents. also used Herein, as reagents. we will focus Herein, exclusively we will onfocus hemicarbonato exclusively andon hemicarbonato carbonato tin derivatives.and carbonato These tin two derivatives. distinctfamilies These two of compounds distinct families are successively of compounds detailed are thereafter,successively with detailed a particular thereafter, focus uponwith a the particular synthetic focus and structural upon the aspects.synthetic This and inventory structural highlights aspects. theThis hypervalence inventory highlights of tin atoms the hypervalence in hemicarbonate of tin atoms and carbonatein hemicarbonate derivatives, and carbonate which preferentially derivatives, adoptwhich penta-preferentially and hexa-coordination adopt penta- and modes, hexa-coordination with trigonal bipyramidalmodes, with and trigonal octahedral bipyramidal geometries, and respectively.octahedral geometries, An example respectively. of a heptacoordinated An example of tin a heptacoordinated atom is also described tin atom in is Section also described 3.2, which in isSection devoted 3.2, towhich carbonato is devoted tin complexes. to carbonato In tin addition, complexes. and In when addition, they wereand when available they inwere the available original 119 publications,in the original the publications, relevant spectroscopic the relevant data spectroscopic resulting from data the resulting CO2 reactivity from (inthe particular, CO2 reactivity IR, Sn(in andparticular,13C NMR IR, in119Sn solution and 13C and NMR in solid in solution state) are and also in solid specified. state) For are comparison, also specified. summary For comparison, tables of structuralsummary tables and spectroscopic of structural dataand spectroscopic are presented data at the are end presented of each at section the end (Tables of each1–10 section). The (Tables other aforementioned1–10). The other CO aforementioned2-adduct families, CO i.e.,2-adduct carbamato-, families, formato- i.e., carbamato-, and phosphino- formato- formato and phosphino- complexes, areformato not included complexes, herein are andnot included will be the herein subject and of will a later be inventory.the subject of a later inventory.

2.2. Hemicarbonato Tin ComplexesComplexes

TheThe synthesissynthesis ofof linearlinear organicorganic carbonates,carbonates, alsoalso calledcalled carboniccarbonic esters,esters, (RO)(RO)22CO, fromfrom carboncarbon dioxidedioxide andand alcoholsalcohols attractedattracted a lotlot ofof attentionattention duringduring thethe 1990s1990s andand 2000s.2000s. ThisThis reaction,reaction, whichwhich isis basedbased onon thethe directdirect useuse ofof COCO22 as a C1-synthon (Scheme1 1),), alsoalso hashas thethe advantageadvantageof of producingproducing only only waterwater asas aa byproduct.byproduct. Thus, this synthesis pathway, leadingleading toto organicorganic carbonates,carbonates, ﬁtsfits wellwell withwith thethe conceptconcept ofof sustainablesustainable chemistrychemistry and constitutesconstitutes a safersafer andand greenergreener alternativealternative routeroute comparedcompared toto historicalhistorical usesuses involvinginvolving phosgenephosgene andand carboncarbon monoxidemonoxide [[13].13].

Scheme 1.1. Reaction scheme leading to dialkyl carbonatescarbonates from carboncarbon dioxidedioxide andand alcohols.alcohols.

MostMost previousprevious academic academic studies studies on theon topicthe topic focused focused on the on direct the synthesis direct synthesis of dimethyl of carbonatedimethyl (DMCcarbonate with (DMC R = with–CH 3R), = the –CH simplest3), the simplest of the linear of the organiclinear organi carbonates,c carbonates, by reacting by reacting directly directly CO2 withCO2 with methanol. methanol. Indeed, Indeed, in additionin addition to to being being a modela model reaction, reaction, DMC DMC is is considered considered aa greengreen andand environmentallyenvironmentally sustainable molecule [[14],14], usable as a solvent as well as aa reagentreagent inin numerousnumerous applications,applications, e.g., forfor biodieselbiodiesel productionproduction [[15].15]. Thus, numerousnumerous investigationsinvestigations involving the useuse ofof homogeneous, heterogeneous and supported catalysts have been conducted to produce this molecule catalytically [16]. With regards to the molecular approach, in the early 1990s, J. Kizlink reported

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Inorganics 2020, 8, x FOR PEER REVIEW 3 of 26 homogeneous,Inorganics 2020, 8, x heterogeneous FOR PEER REVIEW and supported catalysts have been conducted to produce this molecule3 of 26 catalytically [16]. With regards to the molecular approach, in the early 1990s, J. Kizlink reported preliminary works describing the potential role of tin complexes, in particular Sn(IV) alkoxides [17– preliminarypreliminary worksworks describing describing the the potential potential role role of of tin ti complexes,n complexes, in particularin particular Sn(IV) Sn(IV) alkoxides alkoxides [17 –[17–19]. 19]. In fact, as early as 1967, Bloodworth et al. highlighted the reactivity of tri-n-butyltin methoxide In19]. fact, In fact, as early as early as 1967,as 1967, Bloodworth Bloodworth et al.et al. highlighted highlighted the the reactivity reactivity of of tri- tri-nn-butyltin-butyltin methoxidemethoxide with carbon dioxide, demonstrating the facile insertion of CO2 in the Sn-OMe bond and leading to withwith carboncarbon dioxide, demonstrating the the facile facile insertion insertion of of CO CO2 2inin the the Sn-OMe Sn-OMe bond bond and and leading leading to (n-Bu)3Sn(OMe)(OCO2Me) (1). The authors observed, however, that the insertion does not take place to(n-Bu) (n-Bu)3Sn(OMe)(OCO3Sn(OMe)(OCO2Me)2Me) (1). (The1). Theauthors authors observed, observed, however, however, that the that insertion the insertion does doesnot take not place take with tributyltin phenoxide [20]. Later, in 1984, Blunden et al. monitored the reaction by 119Sn{1H} placewith tributyltin with tributyltin phenoxide phenoxide [20]. Later, [20]. in Later, 1984, in Blunden 1984, Blunden et al. monitored et al. monitored the reaction the by reaction 119Sn{1 byH} 119NMR 1spectroscopy, in toluene at 30 °C, and showed a notable move of the chemical shift, i.e., from NMRSn{ spectroscopy,H} NMR spectroscopy, in toluene at in 30 toluene °C, and at showed 30 ◦C, anda notable showed move a notableof the chemical move of shift, the chemicali.e., from +95.5 ppm (n-Bu3SnOMe) to −27 ppm (1) in the presence of CO2 [21]. In a more recent study, D. shift,+95.5 i.e.,ppm from (n-Bu+395.5SnOMe) ppm to (n -Bu−273 ppmSnOMe) (1) in to the27 presence ppm (1) inof theCO2 presence [21]. In a of more CO2 recent[21]. Instudy, a more D. Ballivet-Tkatchenko et al. systematically investig− ated the reactivity of tributyltin derivatives, n- recentBallivet-Tkatchenko study, D. Ballivet-Tkatchenko et al. systematically et al. investig systematicallyated the investigatedreactivity of the tributyltin reactivity derivatives, of tributyltin n- Bu3SnOR (R = Me; i-Pr; t-Bu; SnBu3) with CO2, observing, on the basis of the recorded values of derivatives,Bu3SnOR (Rn -Bu= Me;3SnOR i-Pr; (R t-Bu;= Me; SnBui-Pr;3) twith-Bu; SnBuCO2, 3observing,) with CO2 ,on observing, the basis on of the the basis recorded of the values recorded of δ119Sn{1H} NMR,119 1the presence of five-coordinate tin atoms in the carbonated species [22]. In 1999, by valuesδ119Sn{1 ofH}δ NMR,Sn{ theH} NMR,presence the of presence five-coordinate of five-coordinate tin atoms in tin the atoms carbonated in the carbonatedspecies [22]. species In 1999, [22 by]. focusing more specifically on the evolution of the tin precursor during the methanol carbonation Infocusing 1999, bymore focusing specifically more specificallyon the evolution on the of evolution the tin precursor of the tin during precursor the methanol during the carbonation methanol reaction (Scheme 1), T. Sakakura et al. elucidated the structure of Me2Sn(OMe)2 and its CO2 insertion carbonationreaction (Scheme reaction 1), T. (Scheme Sakakura1), T.et Sakakuraal. elucidated et al. the elucidated structure the of Me structure2Sn(OMe) of Me2 and2Sn(OMe) its CO2 insertion2 and its product, Me2Sn(OMe)(OCO2Me) (2), which corresponded to the first characterization by X-ray COproduct,2 insertion Me2Sn(OMe)(OCO product, Me2Sn(OMe)(OCO2Me) (2), which2Me) corresponded (2), which corresponded to the first tocharacterization the first characterization by X-ray crystallography of a hemicarbonate of tin complex [23]. Compound 2 was synthesized by treating a bycrystallography X-ray crystallography of a hemicarbonat of a hemicarbonatee of tin complex of tin [23]. complex Compound [23]. Compound 2 was synthesized2 was synthesized by treating by a sample of Me2Sn(OMe)2 with an excess of CO2 (Scheme 2). treatingsample of a sampleMe2Sn(OMe) of Me2 Sn(OMe)with an excess2 with of an CO excess2 (Scheme of CO 22).(Scheme 2).

Scheme 2. Reaction scheme leading to compound 2. SchemeScheme 2.2. Reaction scheme leadingleading toto compoundcompound 22..

Single-crystals of of 2 were2 were isolated isolated from froma CO2-saturated a CO -saturated CH2Cl2-Et CH2O Clsolution-Et O at solution 4 °C. At the at solid- 4 C. Single-crystals of 2 were isolated from a CO2-saturated2 CH2Cl2-Et2O2 solution2 2 at 4 °C. At the solid-◦ state, 2 adopts a dimeric structure via two bridging methoxy groups forming a centrosymmetric Atstate, the 2 solid-state,adopts a dimeric2 adopts structure a dimeric via two structure bridging via methoxy two bridging groups methoxy forming groupsa centrosymmetric forming a centrosymmetricSn2O2 four-membered Sn O four-memberedring (Figure 1). ring Each (Figure tin atom1). Each of tin2 is atom linked of 2 tois linkeda hemicarbonato to a hemicarbonato ligand Sn2O2 four-membered2 2 ring (Figure 1). Each tin atom of 2 is linked to a hemicarbonato ligand ligand(methylcarbonato, (methylcarbonato, –OCO2 –OCOMe), η1Me),-O-coordinatedη1-O-coordinated in the interminal the terminal position. position. The two The Sn two atoms Sn atoms are five- are (methylcarbonato, –OCO2Me), η2 1-O-coordinated in the terminal position. The two Sn atoms are five- ﬁve-coordinatedcoordinated and andadopt adopt a trigonal a trigonal bipyramidal bipyramidal (TBP) (TBP) geometry. geometry. The The Sn Sn2OO2 ringring and and hemicarbonato hemicarbonato coordinated and adopt a trigonal bipyramidal (TBP) geometry. The Sn22O22 ring and hemicarbonato fragments are nearby coplanar. The methyl chains bound to Sn are positioned on either side of the fragmentsfragments areare nearbynearby coplanar.coplanar. TheThe methylmethyl chainschains boundbound to Sn areare positionedpositioned onon eithereither sideside ofof thethe inorganic plane. inorganicinorganic plane.plane.

Figure 1. MolecularMolecular structure structure of of 2,, adapted adapted from from [23] [23] (Copyright 1999, American Chemical Society )) Figure 1. Molecular structure of 2, adapted from [23] (Copyright 1999, American Chemical Society) (MERCURY view).view). Hydrogen atomsatoms are omitted forfor clarityclarity (Sn(Sn lightlight blue,blue, OO red,red, CC grey).grey). (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, O red, C grey).

Analysis of 2 by IR spectroscopy corroborates the insertion of CO22 by showing a strong vibration Analysis of 21 by IR spectroscopy corroborates the insertion of CO2 by showing119 1 a strong vibration band at 1682 cm−1. .In In solution solution in in CDCl CDCl3,3 at, at low low temperature temperature (− (5050 °C),◦C), the the 119Sn{Sn{1H}H} NMR NMR spectrum spectrum of band at 1682 cm−1. In solution in CDCl3, at low temperature (−−50 °C), the 119Sn{1H} NMR spectrum of of2 displays2 displays one one sharp sharp signal signal at δ at = δ−171= 171ppm, ppm, which which is in isline in linewith with pentacoordinated pentacoordinated tin atoms, tin atoms, and 2 displays one sharp signal at δ = −171− ppm, which is in line with pentacoordinated tin atoms, and therefore supports the preservation of the dimer structure. At room temperature, the signal becomes therefore supports the preservation of the dimer structure. At room temperature, the signal becomes broader; the authors then suggest a dissociation process leading to a mononuclear complex having broader; the authors then suggest a dissociation process leading to a mononuclear complex having an intramolecularly coordinated carbonyl group [23]. Regarding the reactivity, the thermolysis of 2 an intramolecularly coordinated carbonyl group [23]. Regarding the reactivity, the thermolysis of 2

Inorganics 2020, 8, 31 4 of 26 and therefore supports the preservation of the dimer structure. At room temperature, the signal becomes broader; the authors then suggest a dissociation process leading to a mononuclear complex InorganicsInorganics 20202020,, 88,, xx FORFOR PEERPEER REVIEWREVIEW 44 ofof 2626 having an intramolecularly coordinated carbonyl group [23]. Regarding the reactivity, the thermolysis of(180(1802 °C,(180°C, 300300◦C, atmatm 300 ofof atm COCO22 of)) leadsleads CO2 )toto leads thethe formationformation to the formation ofof DMCDMC with ofwith DMC aa reasonablereasonable with a reasonable yieldyield (58%/Sn).(58%/Sn). yield InIn (58% parallelparallel/Sn). Inwithwith parallel thisthis work,work, with this studyingstudying work, studyingthethe reactivityreactivity the reactivity ofof thethe di-di- ofnn-butyl the-butyl di- nanalogue,analogue,-butyl analogue, nn-Bu-Bu22Sn(OMe)Sn(OMe)n-Bu2Sn(OMe)22 withwith carboncarbon2 with carbondioxide,dioxide, dioxide, D.D. Ballivet-TkatchenkoBallivet-Tkatchenko D. Ballivet-Tkatchenko etet al.al. acquiredacquired et al. acquired spectroscopicspectroscopic spectroscopic evidenceevidence evidence ofof thethe offormationformation the formation ofof thethe of COCO the22-- COadduct,adduct,2-adduct, nn-Bu-Bu22nSn(OMe)(OCOSn(OMe)(OCO-Bu2Sn(OMe)(OCO22Me)Me) ((233Me))) [22,24].[22,24]. (3)[ 22 WhenWhen,24]. aa When samplesample a sample ofof 33 waswas of treatedtreated3 was under treatedunder vacuumvacuum under vacuum atat roomroom attemperature,temperature, room temperature, itsits noncarbonatednoncarbonated its noncarbonated precprecursorursor precursor waswas quicklyquickly was recovered,recovered, quickly recovered, demodemonstratingnstrating demonstrating thatthat thethe insertioninsertion that the ofof insertionCOCO22 isis easilyeasily of CO reversible.reversible.2 is easily AlthoughAlthough reversible. 33 waswas Although notnot characterizedcharacterized3 was not characterizedbyby X-rayX-ray crystallography,crystallography, by X-ray crystallography, aa comparablecomparable astructurestructure comparable toto compoundcompound structure to22 waswas compound proposedproposed2 was basedbased proposed onon thethe spectroscopicspectroscopic based on the spectroscopic data.data. data. InIn 2006, 2006, using using aa comparablecomparable approach,approach, approach, D.D. D. Ballivet-TkatchenkoBallivet-Tkatchenko Ballivet-Tkatchenko etet et al.al. al. publishedpublished published thethe the reactivityreactivity reactivity ofof ofnn-Bu-Bun-Bu22Sn(OPr-Sn(OPr-2Sn(OPr-ii))22 towarditoward)2 toward carboncarbon carbon dioxidedioxide dioxide (Scheme(Scheme (Scheme 3),3),3 leadingleading), leading toto tothethe the formationformation formation ofof of thethe the COCO CO22-adduct,-adduct,2-adduct, nn-- nBuBu-Bu22Sn(OPr-Sn(OPr-2Sn(OPr-ii)(OCO)(OCOi)(OCO22Pr-Pr-2Pr-ii)) i(()(44))4 [25].[25].)[25 ].Again,Again, Again, thethe the reactionreaction reaction waswas was alsoalso also foundfound found toto to bebe be exothermicexothermic exothermic and and reversible reversiblereversible (under(under vacuumvacuumvacuum andandand atatat roomroomroom temperature).temperature).temperature). TheThe infraredinfrared spectrumspectrumspectrum ofof 44 showsshowsshows characteristiccharacteristiccharacteristic υυυ(CO(CO(CO33)) 1 absorptionabsorption bandsbands atat 1668–16151668–16151668–1615 andandand 128412841284 cmcmcm−−−11.. IsolatedIsolated asas single-crystals, single-crystals, 44 waswas analyzed analyzed by by X-rayX-ray crystallography,crystallography, revealing revealingrevealing a a dimerica dimericdimeric structure, structstructure,ure, showing showingshowing a similar aa similarsimilar core corecore to complex toto complexcomplex2 [22 ]22. Each[22].[22]. Each tinEach atom tintin ofatomatom4 is pentacoordinatedofof 44 isis pentacoordinatedpentacoordinated and bears andand in the bearsbears terminal inin thethe position termintermin analal isopropylcarbonatopositionposition anan isopropylcarbonatoisopropylcarbonato group resulting groupgroup from theresultingresulting CO2 insertion fromfrom thethe into COCO a22 Sn–OPr-insertioninsertioni bond.intointo aa TheSn–OPr-Sn–OPr- authorsii bond.bond. mentioned TheThe authorsauthors a weak mentionedmentioned interaction aa between weakweak interactioninteraction carbonyl oxygenbetween and carbonyl tin atoms oxygen [Sn O(C)and tin= 2.9114(12) atoms [Sn···O(C) Å]. A slightly = 2.9114(12) shorter Å]. distance A slightly was alsoshorter measured distance in was the between carbonyl oxygen··· and tin atoms [Sn···O(C) = 2.9114(12) Å]. A slightly shorter distance was casealso ofmeasured2 [Sn O(C) in the= 2.822case of Å]. 2 [Sn···O(C) = 2.822 Å]. also measured··· in the case of 2 [Sn···O(C) = 2.822 Å].

SchemeScheme 3.3. ReactionReaction schemescheme leadingleading toto compoundcompound 44..

AsAs partpart ofof thisthis samesame studystudy [[25],[25],25], thethe authorsauthorsauthors alsoalso consideredconsidered thethe reactivityreactivity ofof aa distannoxanedistannoxanedistannoxane species,species, [[nn-Bu-Bu22(((iii-PrO)Sn]-PrO)Sn]-PrO)Sn]22OO towardtoward carbon carbon dioxide dioxide (Scheme (Scheme 4 4).4).).

SchemeScheme 4.4. ReactionReaction schemescheme leadingleading toto compoundcompound 55..

Again,Again, greatgreat reactivityreactivity waswas observedobserved and and the the carb carbonationcarbonationonation was was also also reported reported as as being being reversible, reversible, on condition that the sample be kept under vacuum overnight. The CO insertion was monitored by onon conditioncondition thatthat thethe samplesample bebe kekeptpt underunder vacuumvacuum overnight.overnight. TheThe COCO22 insertioninsertion waswas monitoredmonitored byby 1 5 υ −1 infraredinfrared spectroscopyspectroscopyspectroscopy showingshowingshowing 55 characteristic characteristiccharacteristic υυ(CO(CO(CO333)) absorptionabsorptionabsorption bandsbandsbands atatat 1647–16271647–16271647–1627 andandand 128612861286 cm cmcm−−1.. RecrystallizationRecrystallization in in diethyletherdiethylether at at 4 4 ◦°C°CC promotedpromoted thethe growthgrowth ofof suitablesuitablesuitable single-crystals,single-crystals,single-crystals, ﬁnallyfinallyfinally n i i n 5 5 characterizedcharacterized asasas (((nn-Bu)-Bu)-Bu)222((ii-PrO)SnOSn(OCO-PrO)SnOSn(OCO222Pr-Pr-ii)()(nn-Bu)-Bu)22 ((55).). TheThe The X-rayX-ray crystallographiccrystallographic structure structurestructure ofof 55 waswas described describeddescribed as asas a centrosymmetric aa centrosymmetriccentrosymmetric dimeric dimericdimeric structure strustru withcturecture a built-inwithwith aa ladder-typebuilt-inbuilt-in ladder-typeladder-type arrangement arrangementarrangement exhibiting twoexhibitingexhibiting distinct twotwo tin distinctdistinct centers tintin in cent thecent exo-ersers inin and thethe endo- exo-exo- andand cyclic endo-endo- positions. cycliccyclic positions.positions. Again, as Again,Again, wtih 4 asas, the wtihwtih insertion 44,, thethe insertioninsertion of CO2 1 i η O 1 intoofof COCO the22 intointo Sn–OPr- thethe Sn–OPr-Sn–OPr-bond resultedii bondbond inresultedresulted the formation inin thethe formation offormation two isopropylcarbonato ofof twotwo isopropylcarbonatoisopropylcarbonato groups, - groups,groups,-coordinated ηη1--OO-- tocoordinatedcoordinated Sn, and exclusively toto Sn,Sn, andand exclusivelyexclusively located on locatedlocated the two onon exocyclic thethe twotwo exocyclic tinexocyclic atoms tintin (Figure atomsatoms2 ).(Figure(Figure All tin 2).2). atomsAllAll tintin ofatomsatoms5 are ofof pentacoordinated55 areare pentacoordinatedpentacoordinated in a distorted inin aa distorteddistorted trigonal trigonaltrigonal bipyramid bipyramidbipyramid (TBP) and (TBP)(TBP) are linked andand areare via linkedlinked oxygen viavia atoms oxygenoxygen according atomsatoms toaccordingaccording a zigzag toto arrangement, aa zigzagzigzag arrangement,arrangement, as commonly asas commonlycommonly observed for observedobserved distannoxanes forfor distannoxanesdistannoxanes [26]. [26].[26].

Inorganics 2020, 8, 31 5 of 26 InorganicsInorganics 20202020,, 88,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 2626

FigureFigure 2.2. MolecularMolecular structurestructure ofof 55,, adapted adaptedadapted from from [25] [[25]25] (Copyright (Copyright 2006, 2006,2006, RoyalRoyal Society Society of of Chemistry Chemistry)) (MERCURY(MERCURY view).view).view). HydrogenHydrogen atomsatomatomss areare omittedomitted forforfor clarityclarityclarity (Sn(Sn(Sn lightlightlight blue,blue,blue, OOO red,red,red, C CC grey). grey).grey).

Recently,Recently, on on the the basisbasis ofof of NMRNMR NMR spectroscopyspectroscopy spectroscopy experimentsexperiments experiments atat at highhigh high pressure,pressure, pressure, carriedcarried carried outout out underunder under 5050 50barbar bar ofof COCO of2 CO2 pressurepressure2 pressure atat 8080 at °C,°C, 80 eithereither◦C, either inin isopropanol-isopropanol- in isopropanol-dd88 oror toluene-toluene-d8 or toluene-dd88,, thethe existenceexistenced8, the existence ofof aa speciesspecies of with awith species fourfour withisopropylcarbonateisopropylcarbonate four isopropylcarbonate groupsgroups andand groups arisingarising and fromfrom arising 55 waswas from alsoalso 5suggestedsuggestedwas also [27] suggested[27] (Scheme(Scheme [27 5).5).] (Scheme Thus,Thus, compoundcompound5). Thus, compound66,, formulatedformulated6, formulated asas {[{[nn-Bu-Bu22Sn(OCOSn(OCO as {[n-Bu22Pr-Pr-2Sn(OCOii))22]]22O}O}22,, would2wouldPr-i)2] 2resultresultO}2, would fromfrom thethe result additionaladditional from the reactivityreactivity additional ofof reactivity 55 viavia thethe ofinsertioninsertion5 via the ofof insertionCOCO22 intointo ofthethe CO twotwo2 into remainingremaining the two noncarbonatednoncarbonated remaining noncarbonated isopropoxyisopropoxy isopropoxyligands.ligands. However,However, ligands. toto However, date,date, thethe toexistenceexistence date, the inin existence thethe solid-statesolid-state in the ofof solid-state suchsuch aa tetracarbonatetracarbona of such a tetracarbonatedtedted distannoxanedistannoxane distannoxane complexcomplex remainsremains complex toto remainsbebe confirmedconfirmed to be conﬁrmedbyby X-rayX-ray crystallography.crystallography. by X-ray crystallography.

SchemeScheme 5.5.5. MolecularMolecularMolecular representation representationrepresentation of ofof the thethe plausible plausiplausibleble tetrahemicarbonato tetrahemicarbonatotetrahemicarbonato distannoxane distannoxanedistannoxane6 resulting 66 resultingresulting from

thefromfrom reactivity thethe reactivityreactivity of 5 with ofof 55 CO withwith2; adaptedCOCO22;; adaptedadapted from from [from27] (Copyright [27][27] (Copyright(Copyright 2015, 2015,Elsevier2015, ElsevierElsevier). ).).

InIn thethethe past, past,past, and andand still stillstill within withinwithin the thethe framework frameworkframework of of theof thethe selective selectiveselective synthesis synthesissynthesis of dimethyl ofof dimethyldimethyl carbonate carbonatecarbonate from fromfrom CO2 andCOCO22 methanolandand methanolmethanol (Scheme (Scheme1(Scheme), D. Ballivet-Tkatchenko 1),1), D.D. Ballivet-TkatchenkoBallivet-Tkatchenko et al. reported etet the al.al. synthesis reportedreported and the characterizationthe synthesissynthesis andand by volumetry,characterizationcharacterization multinuclear byby volumetry,volumetry, NMR and multinuclearmultinuclear IR spectroscopies NMNMRR of andand a methylcarbonato IRIR spectroscopiesspectroscopies analogue ofof aa ofmethylcarbonatomethylcarbonato5, characterized asanalogueanalogue 1-methoxy-3-methylcarbonatotetrabutyldistannoxane, ofof 55,, characterizedcharacterized asas 1-methoxy-3-methylcarbonatotetrabutyldistannoxane,1-methoxy-3-methylcarbonatotetrabutyldistannoxane, [(n-Bu)2(MeO)SnOSn(OCO2Me)(n-Bu)] 2[([((7nn),-- andBu)Bu)22(MeO)SnOSn(OCO(MeO)SnOSn(OCO resulting from a 1:122Me)(Me)( adductnn-Bu)]-Bu)] with22 ((77),), and COand2 resultingresulting[28]. However, fromfrom aa 1:11:1 the adductadduct X-ray withwith structure COCO22 [28].[28]. of 7 However,However,has not yetthethe beenX-rayX-ray resolved. structurestructure ofof 77 hashas notnot yetyet beenbeen resolved.resolved. InIn termsterms ofof reactivity,reactivity, ititit isisis acceptedacceptedaccepted thatthatthat distannoxanedistdistannoxaneannoxane derivativesderivatives produceproduce onlyonly tracestraces ofof DMCDMC fromfrom carboncarbon dioxide dioxide and and methanol, methanol,methanol, even eveneven under under elevated elevated conditionsconditions ofof temperaturetemperature andand pressurepressure [[ 22288].8].]. Moreover,Moreover, monoalkoxidesmonoalkoxides of of triorganostannanestriorganostatriorganostannanesnnanes are are knownknown toto bebe inactiveinactive [[23][23]23]... To To date,date, thethe mostmost eefficientefficientﬃcient molecularmolecularmolecular species speciesspecies for for thefor DMCthethe DMCDMC synthesis synthesisynthesi remainsss remainsremains dialkoxides dialkoxidesdialkoxides of diorganostannanes. ofof diorganostannanes.diorganostannanes. Dimethyl DimethylDimethyl andand di-di-nn-butyl-butyl derivativesderivatives areare thethe mostmost studiedstudied species,species, andand areare oftenoften usedused asas modelsmodels forfor

Inorganics 2020, 8, 31 6 of 26 and di-n-butyl derivatives are the most studied species, and are often used as models for theoretical calculations and simulations [29–31], as well as precursors for grafting reactions on solid supports [32].

Table 1. Comparison of selected structural parameters found in hemicarbonates of organotin complexes.

CSD Entry Sn–O(C) C–O(Sn) C=O O–C–O O–C=O Compounds Deposition Ref. (Å) (Å) (Å) (deg) (deg) Number 1.292(4) FATVOL [(CH ) Sn(OCH )(OCO CH )] (2) 2.192(2) 1.201(4) 115.9(3) 125.9(3) [23] 3 2 3 2 3 2 1.353(4) 119276 1.290(2) 125.19(16) MEPJAT [(n-Bu) Sn(OPr-i)(OCO Pr-i)] (4) 2.1696(12) 1.224(2) 117.27(15) [25] 2 2 2 1.350(2) 117.53(16) 614750 1.293(6) 125.1(5) MEPJEX [(n-Bu) (i-PrO)SnOSn(OCO Pr-i)(n-Bu)] (5) 2.159(4) 1.233(6) 111.6(6) [25] 2 2 2 1.336(7) 123.3(5) 614751

Table 2. Selection of spectroscopic data (NMR and IR) assigned to hemicarbonates of tin complexes.

119 1 13 1 Sn{ H} NMR C{ H} NMR IR υ(CO3) Compounds 1 Ref. (δ, ppm) (δ, ppm) cm− a b (n-Bu)3Sn(OMe)(OCO2Me) (1) 27.0 158.4 1600 [20–22] − 170.91 b − (s, 50 ◦C) b [(CH3)2Sn(OCH3)(OCO2CH3)]2 (2) − 159.19 1682 [23] 171.91 b − (br, +25 ◦C)

b b 1655 [(n-Bu)2Sn(OMe)(OCO2Me)]2 (3) 213.0 156.0 [24] − 1303 b 209.5 b 1668–1615 [(n-Bu)2Sn(OPr-i)(OCO2Pr-i)]2 (4) − 158.24 [25] (br) 1284 b 185.9 b 1647–1627 [(n-Bu)2(i-PrO)SnOSn(OCO2Pr-i)(n-Bu)]2 (5) − 156.95 [25] 209.6 b 1286 − c 218.0 c {[n-Bu2Sn(OCO2Pr-i)2]2O}2 (6) − 157.0 1678–1591 [25] 229.0 c − b 176.6 b 1715, 1670, and [(n-Bu)2(MeO)SnOSn(OCO2Me)(n-Bu)]2 (7) − 157.99 [28] 208.5 b 1629 1300 − a b c Measured in toluene-d8, at 30 ◦C; measured in CDCl3; measured in toluene-d8, under CO2 pressure (50 bar).

3. Carbonato Tin Complexes Carbonate derivatives of organotin complexes have been discovered since the 19th century [33]. However, they have only studied more deeply since the 1960s, ﬁrst by Mossbauer and infrared spectroscopy [34,35], then from the 1980s by NMR spectroscopy in solution as well as in solid-state [36]. Since then, several crystallographic determinations of carbonato tin complexes have been resolved. The X-ray structures elucidated for these compounds are listed and described below as a function of the decreasing number of alkyl ligands linked to the tin atom, i.e., from triorgano- to monoorganotin. Finally, three CO2 derivatives of chelated stannoxanes and one of a trinuclear Sn-capped nickel cluster are also described in the last part of this chapter.

3.1. Triorganotin Derivatives The first X-ray crystallographic analysis of such a compound was resolved in 1983 by E.R.T. Tiekink, who reported the crystal structure of bis(trimethyltin)carbonate, (Me3Sn)2CO3 (8) at room temperature [37]. A few years later, A. Sebald et al. reproduced the measurement at lower temperatures (200 K), leading to a similar structure [38]. Compound 8 was obtained by passing a stream of dry carbon dioxide through a toluene solution of trimethyltin hydroxyde. The slow evaporation at room temperature led to the growth of colorless crystals. The structure of 8 can be described as a polymeric zigzag chain consisting of SnMe3 moieties bridged by carbonate dianions (Figure3). Two distinct sites Inorganics 2020, 8, x FOR PEER REVIEW 7 of 26 InorganicsInorganics2020 2020, ,8 8,, 31 x FOR PEER REVIEW 7 ofof 2626 (Figure 3). Two distinct sites of tin atoms can be observed: (i) those located in the main chain exhibit (Figurea trigonal 3). bipyramidalTwo distinct geometrysites of tin whose atoms equatorialcan be observed: plane is(i) occupiedthose located by three in the methyl main chain substituents exhibit ofa tintrigonal atoms bipyramidal can be observed: geometry (i) those whose located equatorial in the main plane chain is exhibitoccupied a trigonal by three bipyramidal methyl substituents geometry whoseand the equatorial apical positions plane is occupiedby two oxygen by three atoms, methyl (ii) substituents pendant SnMe and3 the groups, apical connected positions by according two oxygen to a andsyndiotactic the apical modes, positions are by in two a tetrahedral oxygen atoms, arrangement. (ii) pendant The SnMe 119Sn3 groups, cross polarizationconnected according magic-angle to a atoms,syndiotactic (ii) pendant modes, SnMe are3 ingroups, a tetrahedral connected arrangement. according to The a syndiotactic 119Sn cross modes, polarization are in amagic-angle tetrahedral arrangement.spinning nuclear The 119magneticSn cross resona polarizationnce (CP magic-angle MAS NMR) spinning data support nuclear th magneticis structural resonance feature (CP by MAS also spinningshowing nucleartwo distinct magnetic resonances resona nceat +123.3 (CP MAS ppm NMR) (four-coordinate data support tin th atom)is structural and − 62.2feature ppm by (five- also NMR)showing data two support distinct this resonances structural at feature +123.3 by ppm also (four-coordinate showing two distinct tin atom) resonances and −62.2 at + 123.3ppm ppm(five- coordinate tin atom) [38]. (n-Bu3Sn)2CO3 (9) could be synthesized in the same way from a solution of (four-coordinate tin atom) and 62.2 ppm (five-coordinate tin atom) [38]. (n-Bu3Sn)2CO3 (9) could be coordinate tin atom) [38]. (n-Bu−3Sn)2CO3 (9) could be synthesized119 in1 the same way from a solution of synthesizedtoluene bis(tri- in then-butyltin) same way oxide from by a solution reacting of with toluene CO bis(tri-2. The n-butyltin)Sn{ H} NMR oxide spectrum by reacting showed with CO two. toluene bis(tri-n-butyltin) oxide by reacting with CO2. The 119Sn{1H} NMR spectrum showed two2 Thebroad119 Sn{resonances1H} NMR (δ spectrum= +82 and showed−66.7 ppm), two suggesting broad resonances a structure (δ = analogous +82 and to66.7 8. However, ppm), suggesting obtained broad resonances (δ = +82 and −66.7 ppm), suggesting a structure analogous− to 8. However, obtained aas structure a viscous analogous oil, to our to knowledg8. However,e, the obtained solid-state as structure a viscous of oil, 9 has to our not knowledge,yet been resolved the solid-state by X-ray ascharacterization a viscous oil, to[21]. our In knowledg 1992, A. Sebalde, the solid-state et al., in a structure low temperature, of 9 has notsingle yet crystalbeen resolved X-ray diffraction by X-ray structurecharacterization of 9 has not[21]. yet In been1992, resolved A. Sebald by et X-ray al., in characterization a low temperature, [21]. In single 1992, crystal A. Sebald X-ray et al., diffraction in a low temperature,study, determined single crystalthe structure X-ray di offfraction the isobutyl study, determinedanalogue, (i the-Bu structure3Sn)2CO3 of(10 the) [38]. isobutyl Compound analogue, 10 study, determined the structure of the isobutyl analogue, (i-Bu3Sn)2CO3 (10) [38]. Compound 10 crystallized in the same space group as 8 (P212121) and also showed a one-dimensional, zigzag chain- (i-Bu3Sn)2CO3 (10)[38]. Compound 10 crystallized in the same space group as 8 (P212121) and also crystallizedlike polymeric in theorganization. same space However, group as 8compared (P212121) andto 8 ,also in 10 showed the repeating a one-dimensional, syndiotactic zigzagmotif is chain- more showedlike polymeric a one-dimensional, organization. zigzag However, chain-like compared polymeric to 8, in organization. 10 the repeating However, syndiotactic compared motif to 8is, inmore10 thecomplex repeating and syndiotacticinvolves two motif pendant is more Sn( complexi-Bu)3 units and (Figure involves 4). two pendant Sn(i-Bu) units (Figure4). complex and involves two pendant Sn(i-Bu)3 units (Figure 4). 3

Figure 3. Molecular structure of 8, adapted from [37,38] (Copyright 1986, Elsevier) (MERCURY view). Figure 3. Molecular structure of 8, adapted from [37,38] (Copyright 1986, Elsevier) (MERCURY view). FigureHydrogen 3. Molecular atoms are structure omitted offor 8 clarit, adaptedy (Sn from light [37,38]blue, O (Copyright red, C grey). 1986, Elsevier) (MERCURY view). HydrogenHydrogen atomsatoms are are omitted omitted for for clarity clarity (Sn (Sn light light blue, blue, O O red, red, C C grey). grey).

FigureFigure 4. 4.Molecular Molecular structurestructure ofof10 10,, adaptedadapted fromfrom [[38]38](Copyright (Copyright 1992,1992,Elsevier Elsevier)) (MERCURY(MERCURY view).view). HydrogenFigure 4. Molecular atoms and structure –CH(CH of) 10groups, adapted of i -Bufrom groups [38] (Copyright are omitted 1992, for clarityElsevier (Sn) (MERCURY light blue, Oview). red, Hydrogen atoms and –CH(CH33)22 groups of i-Bu groups are omitted for clarity (Sn light blue, O red, CHydrogenC grey). grey). atoms and –CH(CH3)2 groups of i-Bu groups are omitted for clarity (Sn light blue, O red, C grey). Since then, three additional exemplars of triorganotin carbonates have been characterized by Since then, three additional exemplars of triorganotin carbonates have been characterized by X- X-raySince diﬀraction then, three analysis. additional These exemplars compounds of alltriorgan resultotin from carbonates direct atmospheric have been CO characterized2 capture. Thus,by X- ray diffraction analysis. These compounds all result from direct atmospheric CO2 capture. Thus, in ray diffraction analysis. These compounds all result from direct atmospheric CO2 capture. Thus, in

Inorganics 2020, 8, 31 8 of 26

Inorganics 2020, 8, x FOR PEER REVIEW 8 of 26 in 2008, J.-F. Ma et al. reported the synthesis and characterization of the salt [(Ph3Sn)3(CO3)(EtOH)3]Cl (11) isolated at room temperature and under ambient air, from a mixture of EtONa, Ph SnCl and 2008, J.-F. Ma et al. reported the synthesis and characterization of the salt [(Ph3Sn)3(CO3)(EtOH)3 3]Cl tris(2-benzimidazolylmethyl)(11) isolated at room temperature amine (ntb) and inunder EtOH ambient/CHCl 3air,(Scheme from a6 )[mixture39]. Compound of EtONa, Ph113cocrystallizedSnCl and withtris(2-benzimidazolylmethyl) one ntb molecule and one amine water (ntb) molecule. in EtOH/CHCl The structure3 (Scheme of the 6) cationic [39]. Compound trinuclear 11 cluster + [(Ph3Sn)cocrystallized3(CO3)(EtOH) with3 one] reveals ntb molecule a central and carbonato one water molecule. anion exhibiting The structure a syn-anti of the µcationic3 coordination trinuclear mode cluster [(Ph3Sn)3(CO3)(EtOH)3]+ reveals a central carbonato anion exhibiting a syn-anti μ3 and connectingcluster [(Ph three3Sn)3(CO (EtOH)Ph3)(EtOH)33]Sn reveals moieties. a central Sn atoms carbonato are ﬁve-coordinated anion exhibiting ina a TBP syn-anti environment. μ3 The equatorialcoordination plane mode isand occupied connecting by three three (EtOH)Ph phenyl3Sn substituents moieties. Sn andatoms the are apical five-coordinated positions in by a two TBP environment. The equatorial plane is occupied by three phenyl substituents and the apical oxygenTBP atoms environment. (Figure5 The). From equatorial a supramolecular plane is occupied point by of three view, phenyl O–H substituentsN hydrogen and bonds the apical involving positions by two oxygen atoms (Figure 5). From a+ supramolecular point··· of view, O–H···N hydrogen coordinated ethanol of [(Ph3Sn)3(CO3)(EtOH)3] and aromatic+ nitrogen atoms of ntb lead to a bonds involving coordinated ethanol of [(Ph3Sn)3(CO3)(EtOH)3]+ and aromatic nitrogen atoms of ntb three-dimensional network. lead to a three-dimensional network.

SchemeScheme 6. 6.Reaction Reaction scheme scheme leading to to compound compound 11.11 .

FigureFigure 5. Molecular 5. Molecular structure structure of the of cation the cation of 11, adaptedof 11, adapted from [39 from] (Copyright [39] (Copyright 2008, Elsevier 2008, )Elsevier (MERCURY) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, O red, C grey). view).(MERCURY Hydrogen view). atoms Hydrogen are omitted atom fors are clarity omitted (Sn for light clarity blue, (Sn O light red, blue, C grey). O red, C grey). More recently, I. Haiduc and M. Andruh et al. isolated two new specimens as single crystals MoreMore recently, recently, I. Haiduc I. Haiduc and and M. M. Andruh Andruh etet al.al. isolated two two new new specimens specimens as single as single crystals crystals based on a trinuclear carbonato-centered core [40]: [(Ph3SnCl)2(μ3-CO3)(Ph3Sn)(Hbpa)]·H2O (12) and based on a trinuclear carbonato-centered core [40]: [(Ph3SnCl)2(µ3-CO3)(Ph3Sn)(Hbpa)] H2O(12) and 1∞[(Ph3SnCl)(Ph3Sn)2(μ3-CO3)(bpa)]·H2O (13). They were obtained by reacting triphenyltin chloride 1 [(Ph3SnCl)(Ph3Sn)2(μ3-CO3)(bpa)]·H2O (13). They were obtained by reacting triphenyltin· chloride [(Ph3SnCl)(Ph3Sn)2(µ3-CO3)(bpa)] H2O(13). They were obtained by reacting triphenyltin chloride ∞ with 1,2-bis (4-pyridyl)ethane (bpa)· in methanol and aqueous ammonia. Only the reaction with 1,2-bistemperature (4-pyridyl)ethane differed in the (bpa) synthesis in methanol protocol: and ataqueous 4 °C for ammonia.12, and at Onlyroomthe temperature reaction temperature for 13. diﬀeredCompound in the synthesis 12 consists protocol: of a discrete at 4trinuclear◦C for 12 complex, and at (Figure room temperature6), while 13 is fora one-dimensional13. Compound 12 consistscoordination of a discrete polymer trinuclear describing complex a zigzag (Figure chain6), (Figur whilee 7).13 Inis both a one-dimensional cases, the carbonato coordination group exhibits polymer describinga central a zigzagposition, chain comparable (Figure to7 11).,In bound both to cases, three tin the atoms carbonato and acting group as syn-anti exhibits μ a3-ligand. central All position, tin atoms are five-coordinated and display a TBP geometry in which equatorial positions are occupied comparableatoms are to five-coordinated11, bound to threeand display tin atoms a TBP and geomet actingry in aswhich syn-anti equatorialµ3-ligand. positions All are tin occupied atoms are ﬁve-coordinatedby phenyls groups. and display The authors a TBP claimed geometry that in alkaline which reaction equatorial conditions positions (20% are ammonia occupied aqueous by phenyls solution) promote the capture of atmospheric CO2, leading to carbonato triorganotins 12 and 13. groups.solution) The promote authors the claimed capture that of atmospheric alkaline reaction CO2, leading conditions to carbonato (20% triorganotins ammoniaaqueous 12 and 13. solution) promote the capture of atmospheric CO2, leading to carbonato triorganotins 12 and 13.

Inorganics 2020, 8, x FOR PEER REVIEW 9 of 26 Inorganics 2020, 8, 31 9 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 9 of 26

Figure 6. Molecular structure of 12, adapted from [40] (Copyright 2015, Elsevier) (MERCURY view). FigureHydrogenFigure 6. Molecular 6. atoms Molecular are structure omittedstructure of for of12 12clarity, adapted, adapted (Sn fromlightfrom blue, [[40]40] (Copyright (CopyrightO red, N 2015,dark 2015, Elsevierblue,Elsevier dark) (MERCURY) blue, (MERCURY Cl green,view). view). C Hydrogengrey).Hydrogen atoms atoms are omittedare omitted for clarityfor clarity (Sn (Sn light light blue, blue, O red,O red, N darkN dark blue, blue, dark dark blue, blue, Cl Cl green, green, C C grey). grey).

FigureFigureFigure 7. 7.Molecular Molecular7. Molecular structure structure structure of of of13 13 13,, adapted,adapted adapted fromfrom [40] [[40]40] (Copyright (Copyright 2015, 2015, 2015, Elsevier ElsevierElsevier) [Sn) [Sn) [Snlight light light blue, blue, blue, O Ored, red, O red, N darkN darkN dark blue, blue, blue, Cl Cl green, Cl green, green, C C grey]. Cgrey]. grey]. Hydrogen Hydrogen Hydrogen atomsat atomsoms areare omitted forfor for clarityclarity clarity (MERCURY (MERCURY (MERCURY view). view). view).

TableTable 3. Comparison3. Comparison of of selected selected structural structural parameters parameters found inin carbonatescarbonates of of triorganotin triorganotin complexes. complexes. Table 3. Comparison of selected structural parameters found in carbonates of triorganotin complexes. C–O CSD Entry Compounds Sn–O(C) (Å) C–O O–C–O (deg) CSD Entry Ref. Compounds Sn–O(C) (Å) (Å) O–C–O (deg) Deposition Number Ref. (Å) DepositionCSD EntryNumber Compounds Sn–O(C)2.247(6) (Å) 1.264(12) C–O (Å) O–C–O118.1(8) (deg) Ref. 2.247(6) 1.264(12) 118.1(8) DepositionDOKDOW Number 2.261(6) 1.267(12) 119.1(8) DOKDOW [37] 2.261(6)2.247(6) 1.267(12)1.264(12) 119.1(8)118.1(8) 1143774 [37] 2.031(7) 1.315(11) 122.9(8) DOKDOW1143774 (Me3Sn)2CO3 (8) 2.031(7)2.261(6) 1.315(11)1.267(12) 122.9(8)119.1(8) [37] (Me(Me3Sn)3Sn)22COCO33(8) (8) 2.031(5) 1.263(7) 117.4(5) 1143774 2.031(5)2.031(7) 1.263(7)1.315(11) 117.4(5)122.9(8) DOKDOW01 2.258(4) 1.301(7) 120.1(5) DOKDOW01 [38] 2.258(4)2.031(5) 1.301(7)1.263(7) 120.1(5)117.4(5) 1143775 [38] 2.248(4) 1.289(7) 122.8(16) DOKDOW011143775 2.248(4)2.258(4) 1.289(7)1.301(7) 122.8(16)120.1(5) [38] 2.014(12) 1.247(23) 115.4(15) 1143775 2.014(12)2.063(12)2.248(4) 1.247(23)1.227(21)1.289(7) 117.3(16)115.4(15)122.8(16) 2.063(12)2.253(11)2.014(12) 1.227(21)1.300(22)1.247(23) 118.8(15)117.3(16)115.4(15) YACKUI (i-Bu3Sn)2CO3 (10) [39] 2.253(11)2.258(13)2.063(12) 1.300(22)1.300(23)1.227(21) 120.2(17)118.8(15)117.3(16) 1298365YACKUI (i-Bu3Sn)2CO3 (10) [39] 2.258(13)2.261(12)2.253(11) 1.300(23)1.311(22)1.300(22) 122.5(17)120.2(17)118.8(15) 1298365YACKUI (i-Bu3Sn)2CO3 (10) [39] 2.261(12)2.272(13)2.258(13) 1.311(22)1.321(22)1.300(23) 125.8(16)122.5(17)120.2(17) 1298365 2.261(12) 1.311(22) 122.5(17) 2.272(13) 1.321(22) 125.8(16) TIWROH [(Ph3Sn)3(CO3)(EtOH)3]·(ntb)·Cl·H20 (11) 2.272(13)2.164(5) 1.26(1)1.321(22) 120.0(8)125.8(16) [40] 656567TIWROH [(Ph3Sn)3(CO3)(EtOH)3]·(ntb)·Cl·H20 (11) 2.164(5)2.133(5) 1.273(9)1.26(1) 120.3(6) 120.0(8) TIWROH [40] [(Ph3Sn)3(CO3)(EtOH)3] (ntb) Cl H20 (11) 2.164(5) 1.26(1) 120.0(8) QUKMIU656567 [40] [(Ph3SnCl)2(μ3-CO3)(Ph·3Sn)(Hbpa)]·H· · 2O (12) 2.251(5) 1.278(8) 118.9(6) 656567 [41] 2.133(5) 1.273(9) 120.3(6) 1052912 2.137(5)2.133(5) 1.294(8)1.273(9) 120.9(6)120.3(6) QUKMIU [(Ph3SnCl)2(μ3-CO3)(Ph3Sn)(Hbpa)]·H2O (12) 2.251(5) 1.278(8) 118.9(6) QUKMIU [41] [(Ph31SnCl)∞[(Ph32SnCl)(Ph(µ3-CO33)(PhSn)23(Sn)(Hbpa)]μ3-CO3)(bpa)]·HH2O2O (12) (13) 2.142(3)2.251(5) 1.277(6)1.278(8) 120.0(5)118.9(6) QUKMOA1052912 [42] [41] · 2.137(5) 1.294(8) 120.9(6) 1052912 2.137(5) 1.294(8) 120.9(6) 1∞[(Ph3SnCl)(Ph3Sn)2(μ3-CO3)(bpa)]·H2O (13) 2.142(3) 1.277(6) 120.0(5) QUKMOA [42] 2.142(3) 1.277(6) 120.0(5) 1 QUKMOA [(Ph3SnCl)(Ph3Sn)2(µ3-CO3)(bpa)] H2O (13) 2.234(4) 1.277(7) 119.6(5) [42] ∞ · 1052913 2.135(3) 1.289(7) 120.5(5) Inorganics 2020, 8, x FOR PEER REVIEW 10 of 26

2.234(4) 1.277(7) 119.6(5) 1052913 2.135(3) 1.289(7) 120.5(5) Inorganics 2020, 8, 31 10 of 26

Table 4. Selection of spectroscopic data (NMR and IR) assigned to carbonates of triorganotin Tablecomplexes. 4. Selection of spectroscopic data (NMR and IR) assigned to carbonates of triorganotin complexes.

119 1 119 13 1 13 Sn{119H}Sn{ 1H} Sn119 MASSn MAS 13C{C{H}1H} 13CC MAS MAS IR IR 3 CompoundsCompounds NMRNMR NMRNMR NMRNMR NMRNMR υ(COυ(CO3) ) Ref. Ref. 1 −1 (δ, ppm)(δ, ppm) (δiso(,δ ppm)iso, ppm) (δ(δ, ,ppm) ppm) (δ(iδsoisoppm) ppm) cm−cm +123.5+123.5 1553,1553, 1534 1534 (Me3Sn)(Me2COSn)3 (8)CO (8) n/a n/a n/an/a 163.8163.8 [35,38[35,38]] 3 2 3 −62.262.2 1379,1379, 1072 1072 − +82.0+ a82.0 a (n-Bu3Sn)(n-Bu2CO3Sn)3 (9)2CO 3 (9) n/a n/an/a n/a n/n/aa n/an/a [21] [21] a66.7 a −66.7− +86.5+86.5 b b (i-Bu3Sn)2CO3 (10) +101.7b 75.1 162.2b 163.3 n/a [38] (i-Bu3Sn)2CO3 (10) +101.7 −75.1− 162.2 163.3 n/a [38] 96.4 −96.4− [(Ph3Sn)3(CO3)(EtOH)3] (ntb) Cl H20 (11) n/a n/a n/a n/a 1455 [39] [(Ph3Sn)3(CO3)(EtOH)3]·(ntb)·Cl·H· 2·0 (11)· n/a n/a n/a n/a 1455 [39] 1428 [(Ph3SnCl)[(Ph3SnCl)2(μ3-CO2(µ33-CO)(Ph33)(PhSn)(Hbpa)]·H3Sn)(Hbpa)]2OH 2O (12) n/a n/a n/a n/a 1428 [40] · n/a n/a n/a n/a 829 [40] (12) 829 1 1428 1∞[(Ph3SnCl)(Ph[(Ph3SnCl)(Ph3Sn)23(Sn)μ3-CO2(µ33-CO)(bpa)]·H3)(bpa)]2OH 2O (13) n/a n/a n/a n/a 1428 [40] ∞ · n/a n/a n/a n/a 896 [40] 896 (13) a b Measured in toluene, at 30 ◦C; measured in CDCl3. a Measured in toluene, at 30 °C; b measured in CDCl3.

3.2. Diorganotin Derivatives Carbonato derivatives of of di diorganotinsorganotins also also aroused aroused great great interest interest in in the the 70s 70s and and 80s. 80s. In In1976, 1976, R. R.G. Goel G. Goel et al. et published al. published a synthesis a synthesis and spectroscopic and spectroscopic characterization characterization of (Me2 ofSn) (Me2O(CO2Sn)3)2 O(COby reacting3) by reactingan aqueous an solution aqueous of solution potassium of carbonate potassium with carbonate an acetone with solution an acetone of dimethyltin solution dichloride of dimethyltin [41]. dichlorideSimilarly, (PhSn) [41]. Similarly,2O(CO3) was (PhSn) prepared2O(CO3 )from was preparedcesium carbon fromate cesium and carbonatediphenyltin and dichloride diphenyltin in 119 dichloridemethanol solution in methanol at ambient solution attemperature. ambient temperature. Mainly based Mainly on based119Sn Mössbauer on Sn Mössbauer and infrared and infraredspectroscopic spectroscopic data, a polymeric data, a polymeric oxycarbonate oxycarbonate structure structure was suggested was suggested for these forcompounds these compounds (Scheme (Scheme7). Some7 years). Some later, years P. J. later, Smith P. J.et Smith al. extended et al. extended this work this by work publishing by publishing the spectroscopic the spectroscopic data of datanew ofdialkyltin new dialkyltin derivatives derivatives (R = Et, (RPr=, Bu,Et, Pr,Oct), Bu, still Oct), suggesting still suggesting a network a network organization organization based on based Goel’s on Goel’smodel model[42]. The [42 structure]. The structure is supposed is supposed to contain to containintermolecularly intermolecularly bridging bridging carbonate carbonate groups, groups,as well as wellfour-membered as four-membered Sn2O2 rings. Sn2O 2 rings.

SchemeScheme 7. 7.Goel’s Goel’s modelmodel proposedproposed for diorganotin oxycar oxycarbonates,bonates, adapted adapted from from [41,42] [41,42] (Copyright (Copyright 1983, Elsevier). 1983, Elsevier).

Regarding X-ray crystallographic structures, di diorganotinorganotin derivatives are the most represented carbonato tintin complexes complexes in in CSD. CSD. To ourTo knowledge,our knowledge, up to up now, to twelvenow, depositionstwelve depositions have been have reported, been correspondingreported, corresponding to ten distinct to ten compounds. distinct compound The ﬁrsts. structure The first of structure such a compound of such a wascompound reported was in 1997reported by R. in Borsdorf 1997 by R. et al.Borsdorf for [(n -Buet al.2Sn-Pyr) for [(n-Bu2(CO2Sn-Pyr)3)] (14)[2(CO43].3)] Compound (14) [43]. Compound14 was isolated 14 was as isolated orange crystalsas orange from crystals the reactionfrom the in reaction methanol in methanol involving involving an equimolar an equimolar mixture ofmixturen-Bu2 SnOof n-Bu and2SnO methyl and 2 2-pyridylmethylidenehydrazinecarbodithioate (HPyr), and in the presence of NaHCO3. CO3 − is 2 1 coordinated to two tin atoms according to a µ2-κ :η coordination mode (Figure8). The tin atoms Inorganics 2020, 8, x FOR PEER REVIEW 11 of 26

methyl 2-pyridylmethylidenehydrazinecarbodithioate (HPyr), and in the presence of NaHCO3. CO32− Inorganics 2020, 8, 31 11 of 26 is coordinated to two tin atoms according to a μ2-κ2:η1 coordination mode (Figure 8). The tin atoms present two distinct environments. One can be considered heptacoordinated with, in particular, a presentbond of two 2.506(6) distinct Å environments. between carbonyl One can oxygen be considered and tin heptacoordinatedatom, and the second with, in pentacoordinated, particular, a bond ofalthough 2.506(6) Sn–O Å between and Sn–N carbonyl interactions oxygen andmeasuring tin atom, 2.826(6) and the and second 2.777(7) pentacoordinated, Å, respectively, although exist (Figure Sn–O and8). Sn–N interactions measuring 2.826(6) and 2.777(7) Å, respectively, exist (Figure8).

Figure 8. Molecular structure of 14, adapted from [43] [43] (Copyright 1997, WILEY-VCH VERLAG GMBH & CO. KGAA) (MERCURY view).view). Hydrogen atoms ar aree omitted for clarity and for each n-butyl-butyl chain; chain; only the α-carbon atoms bonded to tin are shown (Sn light blue, O red, N dark blue, S yellow, yellow, C grey).

Several carbonate derivatives of organooxotinorganooxotin clusters have also been isolated and characterized in thethe solid-state.solid-state. It It has been known for a longlong timetime thatthat organooxotinorganooxotin clustersclusters assembledassembled by Sn–OSn–O bonds lead to a rich diversity of architectures with variable nuclearities (from discrete mononuclear compounds to complex clusters and multidimensionalmultidimensional networks). Several review articles have been dedicated to their astonishing topologies [[44,45].44,45]. Re Regardinggarding the class of carbonates, the most common structure recorded forfor diorganotin derivativesderivatives consistsconsists ofof a raft-like arrangement based on two almost planar Sn55O5 ladders,ladders, and and connected connected by by two two carbonato carbonato liga ligands.nds. All All tin tin atoms atoms display display a a TBP TBP geometry, geometry, and bear two alkyl ligands in equatorial positions. To our knowledge, four X-ray depositions of this type of compound have have been been identified identified to to date. date. The The first first example, example, [(R [(R2SnO)2SnO)3(R3(R2SnOH)2SnOH)2(CO2(CO3)]23 )](152 ()15 (R) (R= –CH= –CH2C6H2C5),6H was5), wasisolated isolated by J.-F. by J.-F. Ma Maet al., et al.,studying studying the the hydrolysis hydrolysis of ofdibenzyltin dibenzyltin dichloride dichloride in inethanol ethanol in inthe the presence presence of of atmospheric atmospheric CO CO2 2[46].[46]. Compound Compound 1515 cancan also also be be synthesized and characterized asas toluene toluene solvate solvate by reactingby reacting dibenzyltin dibenzyltin oxide oxide with dimethylwith dimethyl carbonate carbonate in the presence in the ofpresence toluene of and toluene methanol and methanol [47]. Meanwhile, [47]. Meanwhile, for compound for compound15, the four 15, cornersthe four of corners the inorganic of the frameworkinorganic framework are occupied are byoccupied four bridging by four hydroxyl bridging groupshydroxyl by groups changing by thechanging reaction the conditions reaction (andconditions addition (and of addition hypnone). of hypnone). J.-F. Ma et J.-F. al. Ma succeeded et al. succeeded in isolating in isolatin an ethanolate–modifiedg an ethanolate–modified cluster [(Rcluster2SnO) [(R3(R2SnO)2SnOH)3(R2SnOH)(R2SnOC(R2SnOC2H5)(CO2H53)(CO)]2 (R3)]2= (R–CH = –CH2C62HC56H)(516) ().16). In In16 16,, twotwo diagonallydiagonally oppositeopposite hydroxyl groups were replaced by two ethanolate groups. Later, a decanuclear cluster in which the four µμ-OH-OH groupsgroups were were substituted substituted was was obtained obtained in in 2006 2006 by by D. D. Ballivet-Tkatchenko Ballivet-Tkatchenko et al. et exploredal. explored the directthe direct synthesis synthesis of dimethyl of dimethyl carbonate carbonate from COfrom2 and CO methanol2 and methanol (Scheme (Scheme1), R = –CH 1), R3) = in –CH the presence3) in the ofpresence di-n-butyldimethoxystannane. of di-n-butyldimethoxystannane. During experiments During experime of recycling,nts of i.e., recycling, by repeating i.e., catalyticby repeating runs undercatalytic 200 runs bar under of CO 2002 at bar 150 of◦C, CO single-crystals2 at 150 °C, single-crystals of [(n-Bu2SnO) of 3[((n-Bu2SnO)SnOCH3(n-Bu3)2(CO2SnOCH3)]2 (317)2(CO) were3)]2 grown(17) were from grown a methanol from a methanol solution at solution room temperature at room temperature [48]. Thus, [48]. the Thus, four corners the four of corners17 areoccupied of 17 are byoccupied four methoxy by four bridgingmethoxy groupsbridging (Figure groups9). (Figure Their 9). presence Their presence was suspected was suspected to be directly to be relateddirectly torelated the formation to the formation of DMC. of InDMC. addition, In addition, and during and during recycling recycling runs carried runs carried out in out the in presence the presence of 2,2 dimethoxypropaneof 2,2 dimethoxypropane (usually (usually used asused dehydrating as dehydrati agent),ng agent), S. R. SanapureddyS. R. Sanapureddy and L.and Plasseraud L. Plasseraud also suspectedalso suspected the existence the existence of a close of a close relationship relationship between between [(n-Bu [(2SnO)n-Bu32SnO)(n-Bu32(nSnOCH-Bu2SnOCH3)2(CO3)32(CO)]2 (173)])2 and(17) theand oxycarbonate,the oxycarbonate, (n-Bu (n2Sn)-Bu22O(COSn)2O(CO3)[493)]. [49].

Inorganics 2020, 8, 31 12 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 12 of 26

FigureFigure 9.9. Molecular structure ofof 1717,, highlightinghighlighting thethe occupationoccupation ofof thethe fourfour cornerscorners byby –OCH–OCH33 ligands, adaptedadapted fromfrom [48 [48]] (Copyright (Copyright 2006, 2006,Elsevier Elsevier) (MERCURY) (MERCURY view). view). Hydrogen Hydrog atomsen atoms are omitted are omitted for clarity for andclarity for and each forn-butyl each n chain;-butyl onlychain; the onlyα-carbon the α-carbon atoms atoms bonded bonded to tin to are tin shown are shown (Sn light (Sn light blue, blue, O red, O Cred, grey). C grey).

Subsequently,Subsequently, L.L. PlasseraudPlasseraud andand R.R. WillemWillem etet al.al. publishedpublished twotwo alternativealternative syntheticsynthetic routesroutes leadingleading to to compound compound 1717: (i): from (i) from di-n-butyltin di-n-butyltin oxide, oxide, in a sealed in a vial sealed and in vial the and presence in the of DMC, presence (ii) offrom DMC, a chlorinated (ii) from organotin a chlorinated complex organotin n-Bu2Sn(OCH complex3)Cl,n -Bugenerated2Sn(OCH in 3situ)Cl, from generated n-Bu2Sn(OCH in situ3) from2 and nn-Bu-Bu22Sn(OCHSnCl2, and3)2 andin nthe-Bu 2presenceSnCl2, and of inK2 theCO3 presence. An ethoxy of K 2COanalogue3. An ethoxyof 17, analogue[(n-Bu2SnO) of 317(n-, [(Bun-Bu2SnOC2SnO)2H35)(2n(CO-Bu23)]SnOC2 (18),2 Hwas5)2 (COalso3 synthesized)]2 (18), was by also applying synthesized the sealed by applying vial method the sealed and using vial method diethyl andcarbonate using diethylas reactant. carbonate Moreover, as reactant. 17 Moreover,and 18 were17 and fully18 werecharacterized fully characterized in solution insolution by 1D byNMR 1D NMRinvestigations, investigations, as well as wellas by as by1H-1119H-Sn119 2DSn 2Dheteronuclear heteronuclear correlation correlation spectroscopy spectroscopy experiments experiments [[50].50]. Remarkably,Remarkably, these these decanucleardecanuclear speciesspecies displayingdisplaying raft-likeraft-like structuresstructures areare characterizedcharacterized inin solutionsolution byby threethree 119119Sn{1H}H} resonances resonances exhibiting exhibiting a a 1:2: 1:2:22 intensity ratio, in full agreement with X-ray structures. ForFor 1717,, aa comparablecomparable ﬁngerprintfingerprint waswas recordedrecorded at at the the solid-state. solid-state. ByBy changingchanging the the nature nature of theof the two two alkyl alkyl ligands ligands linked linked to tin, ato different tin, a different framework framework was achieved. was Thus,achieved. when Thus, a di-tert-butyltin when a di-tert-butyltin oxide suspension oxide in methanol suspension is treated in methanol with an aqueousis treated solution with an of Naaqueous2CO3, itsolution results inof theNa formation2CO3, it results of needle-like in the crystalsformation characterized of needle-like as [( t-Bucrystals2Sn) 3O(OH)characterized2]CO3 3MeOH as [(t- · (Bu19)[2Sn)51].3O(OH) The use2]CO of3 acetone·3MeOH instead (19) [51]. of methanolThe use of during acetone the instead synthesis of leadsmethanol to an during analogous the synthesis complex, crystallizingleads to an analogous with three moleculescomplex, crystallizing of water and with one ofthree acetone, molecules [(t-Bu 2ofSn) water3O(OH) and2]CO one3 of3H acetone,2O acetone [(t- · · (Bu20).2Sn) Complex 3O(OH)192]COwas3·3H also2O·acetone isolated by(20 D.). Complex Ballivet-Tkatchenko 19 was also et isolated al. during by theD. Ballivet-Tkatchenko study of the reactivity et ofal. di-tduringert-butyldimethoxystannane the study of the reactivity for of the di-t synthesisert-butyldimethoxystannane of dimethyl carbonate for fromthe synthesis carbon dioxide of dimethyl and methanolcarbonate [52from]. The carbon skeleton dioxide of 19 andand methanol20 consists [52]. of The an almost skeleton planar of 19 Sn and3O3 20core. consists Thetwo of an outer almost tin atomsplanar are Sn3 linkedO3 core. to The a carbonato two outer ligand tin atoms acting are as alinked bidentate to a chelating carbonato ligand ligand according acting as to a a bidentate syn–syn coordinationchelating ligand mode. according The three to tina syn–syn atoms are coordinati pentacoordinatedon mode. The in a three distorted tin atoms TBP arrangement. are pentacoordinated They are connectedin a distorted to twoTBPtert-butyl arrangement. ligands They located are connected in the equatorial to two tert-butyl plane, and ligands their located coordination in the equatorial sphere is completedplane, and by their three coordination oxygen atoms, sphere coming is completed from µ3-O, byµ-OH three or oxygenµ-CO3 ligandsatoms, (Figurecoming 10 from). H. μ Reuter3-O, μ-OH and H.or Wilbertsμ-CO3 ligands also qualified (Figure this 10). type H. of Reuter topology and as H. a butterfly Wilberts structure also qualified resulting this from type two of four-membered topology as a tin-oxygenbutterfly structure rings, fused resulting together from [51]. Intwo solution, four-membe althoughred verytin-oxygen slightly soluble,rings, fused these compoundstogether [51]. were In characterizedsolution, although by a pairvery of slightly119Sn{1 soluble,H} resonances these compounds (1:2 ratio) corresponding were characterized to two by pentacoordinate a pair of 119Sn{1 tinH} environmentsresonances (1:2 [52 ratio)]. corresponding to two pentacoordinate tin environments [52].

Inorganics 2020, 8, x FOR PEER REVIEW 13 of 26

Inorganics 2020, 8, 31 13 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 13 of 26

Figure 10. Molecular structure of 19 and 20, adapted from [51,52] (Copyright 2006, Elsevier) (MERCURY view). Hydrogen atoms and solvent molecules are omitted for clarity (Sn light blue, O red, C grey). FigureFigure 10. 10. MolecularMolecular structurestructure of 19ofand 1920 and, adapted 20, adapted from [51,52 from] (Copyright [51,52] 2006, (CopyrightElsevier) (MERCURY 2006, Elsevier) Interestingly,(MERCURYview). Hydrogen the view). trinuclear atomsHydrogen and framework solvent atoms molecules and solventdescribe are omittedmoleculesd above for clarityare was omitted (Sn subsequently light for blue, clarity O red, (Sn isolated C grey).light blue, as building-O red, C grey). blocks in moreInterestingly, complex the skeletons trinuclear framework of organooxotins. described above Firstly, was subsequently in 2010, J. isolatedBeckmann as building-blocks et al. reported the multinuclearin more complexhypercoordinated skeletons of organooxotins. organostannoxane Firstly, in 2010, J. Beckmanncarbonate et al. reportedcluster the [t- Interestingly, the trinuclear framework described above was subsequently isolated as building- Bu2Sn(OH)OSnR(OH)multinuclear hypercoordinated2OC(OSnt-Bu organostannoxane2OH)2(O)SnR(OH)(H carbonate2O)] cluster2 [(Rt-Bu 2Sn(OH)OSnR(OH)= 2,6-Mes2C62HOC(OSn3) (21t- ) [53]. blocks in more complex skeletons of organooxotins. Firstly, in 2010, J. Beckmann et al. reported the CompoundBu2OH) 212 (O)SnR(OH)(Hwas prepared2O)]2 (Rby= 2,6-Mespurging2C 6Hwith3)(21 )[an53 ].excess Compound of 21COwas2 prepareda mixture by purging of trans-[2,6- multinuclearwith an excess ofhypercoordinated CO2 a mixture of trans-[2,6-Mesorganostannoxane2C6H3Sn(O)(OH)] 3 andcarbonate (t-Bu2SnO) incluster THF. The [t- Mes2C6H3Sn(O)(OH)]3 and (t-Bu2SnO) in THF. The authors described the unusual structure of 21 as Bu2Sn(OH)OSnR(OH)authors described the2OC(OSn unusualt-Bu structure2OH)2(O)SnR(OH)(H of 21 as the assembly2O)]2 of(R two = trinuclear 2,6-Mes OC(OSn2C6H3)t -Bu(212)2)O- [53]. the assembly of two trinuclear OC(OSnt-Bu2)2O-(2,6-Mes2C6H3)Sn(OH)2 moieties connected to a Compound(2,6-Mes2 C216H 3)Sn(OH)was prepared2 moieties by connected purging to awith central an four-membered excess of CO (t-Bu2 2aSnOH) mixture2 ring of via trans two -[2,6- central four-membered (t-Bu2SnOH)2 ring via two (2,6-Mes2C6H3)(OH)Sn(OH)2 units (Figure 11). Mes(2,6-Mes2C6H3Sn(O)(OH)]2C6H3)(OH)Sn(OH)3 and (t2-Buunits2SnO) (Figure in THF.11). The authors described the unusual structure of 21 as the assembly of two trinuclear OC(OSnt-Bu2)2O-(2,6-Mes2C6H3)Sn(OH)2 moieties connected to a central four-membered (t-Bu2SnOH)2 ring via two (2,6-Mes2C6H3)(OH)Sn(OH)2 units (Figure 11).

Figure 11. Molecular structure of 21, adapted from [53] (Copyright 2010, WILEY-VCH VERLAG GMBH Figure 11. Molecular structure of 21, adapted from [53] (Copyright 2010, WILEY - VCH VERLAG & CO. KGAA t Figure 11. Molecular) (MERCURY structure view). of 21 Hydrogen, adapted atoms from are [53] omitted (Copyright for clarity 2010, and WILEY for each - R VCH and -BuVERLAG GMBH &substituent, CO. KGAA only) (MERCURY the α-carbon atom view). bonded Hydrogen to tin is shownatoms (Sn are light omitted blue, O for red, clarity C grey). and for each R and t-Bu substituent,GMBH & CO. only KGAA the) (MERCURY α-carbon atom view). bonded Hydrogen to tin atoms is show are omittedn (Sn light for clarityblue, O and red, for C each grey). R and t-Bu substituent, only the α-carbon atom bonded to tin is shown (Sn light blue, O red, C grey).

Recently, P. Svec and L. Plasseraud et al., studying the reactivity of [LCN(n-Bu)2Sn]+[CB11H12]− (LCN Recently, P. Svec and L. Plasseraud et al., studying the reactivity of [LCN(n-Bu)2Sn]+[CB11H12]− (LCN = 2-(N,N-dimethylaminomethyl)phenyl) for the synthesis of DMC from CO2 and methanol, isolated = 2-(N,N-dimethylaminomethyl)phenyl) for the synthesis of DMC from CO2 and methanol, isolated a newa newcarbonate carbonate of oforganooxotin organooxotin with with a a decanucleardecanuclear structure andand characterizedcharacterized it asit as[(n -[(n- 2+. − Bu)20SnBu)1020OSn2(OMe)10O2(OMe)6(CO6(CO3)2] 3)22[CB]2+.2[CB11H1112H]12 ](−22 (22) )[54]. [54]. The The corecore of 22 cancan bebe described described as asconsisting consisting of aof a centralcentral tetranuclear tetranuclear fragment fragment of ofth eth distannoxanee distannoxane type, type, withwith a characcharacteristicteristic ladder ladder structure, structure, linked linked by twoby carbonatotwo carbonato ligands ligands (syn-syn (syn-syn μ3 μ) to3) to two two trinuclear trinuclear fragmentsfragments (Figure (Figure 12). 12). Highly Highly soluble soluble in THF, in THF, 22 was22 alsowas alsofully fully characterized characterized by by NMR NMR spectroscopy. spectroscopy.

Inorganics 2020, 8, 31 14 of 26

CN + Recently, P. Svec and L. Plasseraud et al., studying the reactivity of [L (n-Bu)2Sn] [CB11H12]− CN (L = 2-(N,N-dimethylaminomethyl)phenyl) for the synthesis of DMC from CO2 and methanol, isolated a new carbonate of organooxotin with a decanuclear structure and characterized it as [(n-Bu) Sn O (OMe) (CO ) ]2+ 2[CB H ] (22)[54]. The core of 22 can be described as consisting 20 10 2 6 3 2 · 11 12 − of a central tetranuclear fragment of the distannoxane type, with a characteristic ladder structure, linked by two carbonato ligands (syn-syn µ3) to two trinuclear fragments (Figure 12). Highly soluble Inorganicsin THF, 202022, 8,was x FOR also PEER fully REVIEW characterized by NMR spectroscopy. 14 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 14 of 26

FigureFigure 12. Molecular12. MolecularMolecular structure structure structure of of of 22 2222, ,adapted, adapted adapted from from [54] [[54]54] (Copyright(Copyright (Copyright 2018, 2018, 2018, The The Royal Royal Society Society of Chemistry of Chemistry and andThe TheCentre CentreCentre National NationalNational de dede la la laRecherche Recherche Recherche Scientiﬁque ScientifiqueScientifique) (MERCURY)) (MERCURY(MERCURY view). view). view). Hydrogen Hydrogen Hydrogen atoms atoms atoms are are omitted omittedare omitted for for clarityforclarity clarity and and forfor for eacheach eachn -butyln-butyl n-butyl chain; chain; chain; only only only the the carbon carboncarbon atom atom atom bonded bo bondednded to tin to istotin shown tin is shown is shown (Sn light(Sn light(Sn blue, light blue, O red, blue, O O red,C grey). C grey). red, C grey).

Finally, by purging a mixture of di-tert-butyltin oxide and di- p-anisyltellurium oxide in solution Finally, by purging a mixture of di-tert-butyltin oxide and di-p-anisyltellurium oxide in solution in chloroform chloroform with with carbon carbon dioxide dioxide (for (for 15 15 min min an andd at at room room temperature) temperature) (Scheme (Scheme 8),8 ),J. J.Beckmman Beckmman et in chloroformal.et al.isolated isolated with an anunprecedented carbon unprecedented dioxide tellurastannoxane tellurastannoxane(for 15 min and frameworkat framework room temperature) containing containing two(Scheme two carbonato carbonato 8), J. Beckmmanmoieties, moieties, et al. isolatedcharacterized an unprecedented as [(pp-MeOC-MeOC66H44 )2tellurastannoxaneTeOSn(TeOSn(t-Bu2)CO)CO3}}22] ]((framework2323))[ [55].55]. By By applying applyingcontaining the the same sametwo synthetic syntheticcarbonato protocol protocol moieties, characterizedand using using as( (pp-Me -Me[(p-MeOC2NC2NC6H6H4)642HTeO)24TeO)2 TeOSn(as astellurium telluriumt-Bu2 )COprecursor, precursor,3}2] (23 the) [55]. the same sameBy group applying group achieved achieved the same a yield a synthetic yield of 95%, of 95%, protocol[(p- and Me[(usingp-Me2NC 26(NCHp-Me4)62TeOSn(H24NC)2TeOSn(6Ht-Bu4)2TeO2t)CO-Bu 23as})CO2] tellurium(324}2),]( 24which), whichprecursor, constitutes constitutes the another same another groupexample example achieved of of a a tellurastannoxane a yield of 95%, [(p- Me2NCcarbonate6H4)2TeOSn( clustert [[56].-Bu56].2 CompoundsCompounds)CO3}2] (24),23 23 andwhich and24 24 exhibit exhibitconstitutes a a comparable comparable another inorganic inorganic example skeleton skeleton of a which whichtellurastannoxane consists consists of carbonateofan an almost almost cluster planar planar [56]. Sn2 CompoundsTeSn22CTe22OC82Ocore.8 core. 23 In bothandIn both 24 cases, exhibitcases, the Snthe a atoms comparableSn atoms adopt adopt a inorganic TBP a geometryTBP geometry skeleton and the andwhich Te the atoms consistsTe are considered to be hexacoordinated in octahedral environments via the presence of intramolecular of anatoms almost are planar considered Sn2Te to2C 2beO8 core.hexacoordinated In both cases, in octahedralthe Sn atoms environments adopt a TBP via geometrythe presence and ofthe Te intramolecularTe O contacts (involvingTe···O contacts oxygen (involving atoms of carbonateoxygen atoms moieties). of carbonate The coordination moieties). mode The ofcoordination carbonates atoms ···are considered to2 1be hexacoordinated in octahedral environments via the presence of modecan be of deﬁned carbonates as µ2 -canκ : ηbe, i.e.,defined as monodentate as μ2-κ2:η1, i.e., ligand as monodentate of a tellurium ligand atom andof a chelatingtellurium aatom tin atom and intramolecular Te···O contacts (involving oxygen atoms of carbonate moieties). The coordination chelating(Figures 13 a tinand atom 14). (Figures 13 and 14). mode of carbonates can be defined as μ2-κ2:η1, i.e., as monodentate ligand of a tellurium atom and chelating a tin atom (Figures 13 and 14).

Scheme 8. ReactionReaction scheme scheme leading to compounds 23 and 24..

Scheme 8. Reaction scheme leading to compounds 23 and 24.

Inorganics 2020, 8, x FOR PEER REVIEW 14 of 26

Figure 12. Molecular structure of 22, adapted from [54] (Copyright 2018, The Royal Society of Chemistry and The Centre National de la Recherche Scientifique) (MERCURY view). Hydrogen atoms are omitted for clarity and for each n-butyl chain; only the carbon atom bonded to tin is shown (Sn light blue, O red, C grey).

Finally, by purging a mixture of di-tert-butyltin oxide and di-p-anisyltellurium oxide in solution in chloroform with carbon dioxide (for 15 min and at room temperature) (Scheme 8), J. Beckmman et al. isolated an unprecedented tellurastannoxane framework containing two carbonato moieties, characterized as [(p-MeOC6H4)2TeOSn(t-Bu2)CO3}2] (23) [55]. By applying the same synthetic protocol and using (p-Me2NC6H4)2TeO as tellurium precursor, the same group achieved a yield of 95%, [(p- Me2NC6H4)2TeOSn(t-Bu2)CO3}2] (24), which constitutes another example of a tellurastannoxane carbonate cluster [56]. Compounds 23 and 24 exhibit a comparable inorganic skeleton which consists of an almost planar Sn2Te2C2O8 core. In both cases, the Sn atoms adopt a TBP geometry and the Te atoms are considered to be hexacoordinated in octahedral environments via the presence of intramolecular Te···O contacts (involving oxygen atoms of carbonate moieties). The coordination mode of carbonates can be defined as μ2-κ2:η1, i.e., as monodentate ligand of a tellurium atom and chelating a tin atom (Figures 13 and 14).

Inorganics 2020, 8, 31 15 of 26 Scheme 8. Reaction scheme leading to compounds 23 and 24.

Inorganics 2020, 8, x FOR PEER REVIEW 15 of 26

Figure 13. Molecular structure of 23, adapted from [55] (Copyright 2004, WILEY-VCH VERLAG GMBH Figure 13. Molecular structure of 23, adapted from [55] (Copyright 2004, WILEY-VCH VERLAG GMBH & CO. KGAA) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, Te apricot, & CO. KGAA) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, Te apricot, O red, C grey). O red, C grey).

Figure 14. Molecular structure of 24, adapted from [56] (Copyright 2004, International Union of Figure 14. Molecular structure of 24, adapted from [56] (Copyright 2004, International Union of Crystallography) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, Te apricot, Crystallography) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, Te apricot, N dark blue, O red, C grey). N dark blue, O red, C grey).

Inorganics 2020, 8, 31 16 of 26

Table 5. Comparison of selected structural parameters found in carbonates of diorganotin complexes.

C–O C=O O–C=O CSD Entry Compounds Sn–O(C) (Å) O–C–O (9) Ref. (Å) (Å) (deg) Deposition Number 2.506(6) 1.326(11) 122.9(9) RACXIC [(n-Bu Sn-Pyr) (CO )] (14) 2.229(7) 1.260(11) 118.4(9) [43] 2 2 3 1.284(11) 118.7(9) 106460 2.195(6) MADDOL [(R SnO) (R SnOH) (CO )] (15) 2.094(2) 1.304(4) 125.5(3) 232628 [46] 2 3 2 2 3 2 1.237(4) 114.5(3) (R = –CH2C6H5) 2.113(2) 1.315(4) 122.0(3) MAHQIX [47] 763719 [(R SnO) (R SnOH) R SnOC H )(CO )] (16) 2.095(4) 1.298(7) 121.8(6) MADFUT 2 3 2 ( 2 2 5 3 2 1.240(8) 116.4(6) [46] (R = –CH2C6H5) 2.116(4) 1.302(7) 121.8(6) 232628 [(R SnO) (R SnOCH ) (CO )] (17) 2.111(6) 1.291(11) 1.243(10) 123.2(8) DIFLAG 2 3 2 3 2 3 2 115.0(7) [48] (R = –n-Bu) 2.110(6) 1.277(10 121.6(8) 1140489 JELZAC 2.140(4) 1.280(7) 120.3(6) 278211 [51] [(t-Bu2Sn)3O(OH)2]CO3 3MeOH (19) 2.119(4) 1.266(7) 120.6(7) · 1.310(7) 119.0(5) JELZAC01 [52] 968891 2.125(2) 1.295(3) 120.0(2) YONZOS [(t-Bu2Sn)3O(OH)2]CO3 3H2O acetone (20) 1.250(3) 120.0(2) [51] · · 2.128(2) 1.295(3) 120.0(2) 968892 2.11(1) 1.25(2) 117(1) [t-Bu Sn(OH)OSnR(OH) OC(OSnt-Bu OH) (O)SnR(OH)(H O)] SUMXUU 2 2 2 2 2 2 2.18(1) 1.27(2) 119(1) [53] (21) 749950 2.270(9) 1.28(2) 124(1) 2.11(1) 1.24(2) 125(1) 2+ TEWXUR [(n-Bu)20Sn10O2(OMe)6(CO3)2] 2[CB11H12] (22) 2.158(9) 1.29(2) 121(1) [54] · − 1590299 2.18(1) 1.28(2) 115(1) 2.307(2) 1.278(3) 124.7(2) FERVAA [(p-MeOC H ) TeOSn(t-Bu )CO } ] (23) 2.094(2) 1.329(3) 120.9(2) [55] 6 4 2 2 3 2 233184 2.481(2) a 1.259(3)a 114.4(2) 1.282(6) 123.7(5) 2.313(3) GAKNOW [(p-Me NC H ) TeOSn(t-Bu )CO } ] (24) 1.326(6) 122.0(5) [56] 2 6 4 2 2 3 2 2.085(3) 259086 1.252(6)a 114.3(5) a C–O(Te) bond. Inorganics 2020, 8, 31 17 of 26

Table 6. Selection of spectroscopic data (NMR and IR) assigned to carbonates of diorganotin complexes.

119 1 119 13 1 13 Sn{ H} NMR Sn MAS NMR C{ H} NMR C MAS NMR IR υ(CO3) Number Compounds 1 (δ, ppm) (δiso, ppm) (δ, ppm) (δiso ppm) cm− Ref.

a n/a a 1420 [(n-Bu2Sn-Pyr)2(CO3)] (14) 374.9 167.9 n/a [43] − 885 304.7 a [(R2SnO)3(R2SnOH)2(CO3)]2 (15) − 1537 244.5 a n/a 164.0 n/a [46,47] (R = –CH2C6H5) − 1363 242.6 a − 233.9 a 235 c [(R2SnO)3(R2SnOCH3)2(CO3)]2 (17) − − 1539 177.7 a 181 c 163.7 a 164 [48,50] (R = –n-Bu) − − 1373 171.2 a 174 c − − 234 b [(R2SnO)3(R2SnOC2H5)2(CO3)]2 (18) − 1535 178 b n/a n/a n/a [50] (R = –n-Bu) − 1374 173 b − 1500 297 a (1549 e) [(t-Bu2Sn)3O(OH)2]CO3 3MeOH (19) − n/a n/a n/a [24,52] · 265 a 1354 − (1291 e) 211.8 d 2+ − d [(n-Bu)20Sn10O2(OMe)6(CO3)2] 2[CB11H12]− 207.6 · − n/a 163.5 n/a [54] (22) 177.2 d − 164.3 d − a 258.3 a [(p-MeOC6H4)2TeOSn(t-Bu2)CO3}2] (23) − 262.4 165.4 165.6 n/a [55] − a a [(p-Me2NC6H4)2TeOSn(t-Bu2)CO3}2] (24) 257.9 267.5 165.4 n/a n/a [56] − − a b c 117 119 d Measured in CDCl3; measured in C6D6; the solid-state Sn rather than the Sn NMR spectrum was recorded because of local radio interferences; measured in THF-d8; e after overnight in vacuum at room temperature. Inorganics 2020, 8, 31 18 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 18 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 18 of 26

3.3. Monoorganotin Derivatives 3.3. Monoorganotin Derivatives To our knowledge, the sole example of monoorganotin carbonate characterized by an X-ray To ourour knowledge,knowledge, thethe solesole exampleexample ofof monoorganotinmonoorganotin carbonatecarbonate characterized by an X-ray crystallographic structure was reported by J. Beckmann et al. in 2009 [57]. K6[MeSn(O)CO3]6·14H2O crystallographic structurestructure waswas reportedreported bybyJ. J. Beckmann Beckmann et et al. al. in in 2009 2009 [ 57[57].]. K K6[MeSn(O)CO6[MeSn(O)CO3]3]66·14H14H22O (25) was isolated from the reaction of SnCl2 with methyl iodide and aqueous KOH in the presence· of ((25)) waswas isolatedisolated fromfrom thethe reactionreaction ofof SnClSnCl22 with methyl iodide and aqueous KOH in the presence of carbon dioxide (Scheme 9). Interestingly, the authors report that post-treatment of 25 with hot water carbon dioxide (Scheme9 9).). Interestingly,Interestingly, thethe authorsauthors reportreport thatthat post-treatmentpost-treatment ofof 25 with hot water leads to polymeric methylstannonic acid, [MeSn(O)OH]n. From a structural point of view, the anionic leadsleads toto polymeric methylstannonicmethylstannonic acid,acid, [MeSn(O)OH][MeSn(O)OH]nn.. From a structural structural point of view, view, the anionic moiety [MeSn(O)CO3]66−6 exhibits an hexameric structure of prismatic type, also called drum, the two moiety [MeSn(O)CO 33]]66− −exhibitsexhibits an an hexameric hexameric structure structure of pr ofismatic prismatic type, type, also also called called drum, drum, the two the faces of which consist of two Sn3O6 six-membered rings bridged by six bidentate CO322− anions, twofaces faces of which of which consist consist of oftwo two Sn Sn3O36O six-membered6 six-membered rings rings brid bridgedged by by six six bidentate COCO332− anions, coordinated to two distinct tin atoms (Scheme 10). All tin atoms are hexacoordinated. Compound 25 coordinated toto twotwo distinctdistinct tintin atomsatoms (Scheme(Scheme 1010)).. All tin atomsatoms areare hexacoordinated.hexacoordinated. Compound 25 was also characterized by 119Sn and 13C CP MAS NMR spectroscopy, showing three resonances for waswas alsoalso characterizedcharacterized by by119 119SnSn andand13 13CC CPCP MAS MAS NMR NMR spectroscopy, spectroscopy, showing showing three three resonances resonances for for tin tin (at −474, −481 and −486 ppm) and two sets of three signals for carbon, attributed to carbonate (at (attin (at474, −474,481 −481 and and486 −486 ppm) ppm) and and two two sets sets of three of three signals signals for carbon, for carbon, attributed attributed to carbonate to carbonate (at 164.2, (at 164.2,− 162.2,− 160.7− ppm) and methyl groups, respectively, which was considered as being in 162.2,164.2, 160.7162.2, ppm) 160.7 and ppm) methyl and groups, methyl respectively, groups, respectively, which was consideredwhich was as beingconsidered in agreement as being with in agreement with the crystallographic structure (Table 7). theagreement crystallographic with the crystallog structure (Tableraphic7 structure). (Table 7).

Scheme 9. Reaction scheme leading to compound 25. Scheme 9. Reaction scheme leading to compound 25..

SchemeScheme 10.10.Schematic Schematic representation representation of theof drumthe drum structure structure of anion of of anion25, adapted of 25, from adapted [57] (Copyright from [57] Scheme 10. Schematic representation of the drum structure of anion of 25, adapted from [57] 2009,(CopyrightAmerican 2009, Chemical American Society Chemical). The Society six bridging). The carbonatesix bridging ligands carbonate are depicted ligands byare red depicted lines. by red (Copyright 2009, American Chemical Society). The six bridging carbonate ligands are depicted by red lines. lines. Table 7. Selection of structural parameters found in 25. Table 7. Selection of structural parameters found in 25. Table 7. Selection of structural parameters found in 25. CSD Entry Sn–O(C) C–O(Sn) C=O O–C–O O–C=O CSD Entry Compound Sn–O(C) C–O(Sn) C=O O–C–O O–C=O DepositionCSD Entry Ref. Compound Sn–O(C) (Å)C–O(Sn) (Å)C=O (Å)O–C–O(deg) O–C=O(deg) Deposition Ref. Compound (Å) (Å) (Å) (deg) (deg) DepositionNumber Ref. (Å) (Å) (Å) (deg) (deg) Number 1.30(1) Number 2.167(8)1.30(1) 2.167(8) 1.30(1) 1.29(1) 2.167(8) 2.129(6)1.29(1) 120(1) 2.129(6) 1.29(1) 1.32(2) 1.24(1) 120(1) 2.129(6) 2.106(7) 121(1) 120(1)119(1) ZELPEN K6[MeSn(O)CO3]6 14H2O (25) 1.32(2) 1.32(2)1.24(1) 1.24(2) [57] K6[MeSn(O)CO3]6·14H· 2O 2.106(7) 2.140(8)1.32(2) 1.24(1) 121(1)122(1) 119(1)119(1) ZELPEN751878 K6[MeSn(O)CO3]6·14H2O 2.106(7) 1.32(2) 1.28(2)1.24(2) 1.25(1)121(1) 119(1) ZELPEN [57] (25) 2.140(8) 2.107(9)1.32(2) 1.24(2) 122(1) 119(1)119(1) 751878 [57] (25) 2.140(8) 1.28(2) 1.25(1)1.25(1) 122(1) 119(1) 751878 2.107(9) 2.122(7)1.28(2) 1.25(1) 119(1) 2.107(9) 1.25(1) 1.30(1) 119(1) 2.122(7) 1.25(1) 2.122(7) 1.30(1) 1.30(1) 3.4. C,N-Chelated Derivatives 3.4. C,N-Chelated Derivatives 3.4. C,N-Chelated Derivatives The first structural resolution by X-ray determination of a C,Y-chelated organotin compound The first structural resolution by X-ray determination of a C,Y-chelated organotin compound datesThe back first to structural 1968, when resolution Yoshida by and X-ray Kasai determination et al. reported of a the C,Y crystal-chelated and organotin molecular compound structure dates back to 1968, when Yoshida and Kasai et al. reported the crystal and molecular structure of Bis- ofdates Bis-(1,2-diethoxycarbonyl-ethyl)tin back to 1968, when Yoshida and Kasai Dibromide et al. reported [58]. Thereafter, the crystal this and field mo oflecular organotin structure chemistry of Bis- (1,2-diethoxycarbonyl-ethyl)tin Dibromide [58]. Thereafter, this field of organotin chemistry aroused aroused(1,2-diethoxycarbonyl-ethyl)tin a strong interest, being firstlyDibromide reviewed [58]. byTher J.T.B.H.eafter, Jastrzebskithis field of and organotin G. van chemistry Koten in 1983 aroused [59]. a strong interest, being firstly reviewed by J.T.B.H. Jastrzebski and G. van Koten in 1983 [59]. a strong interest, being firstly reviewed by J.T.B.H. Jastrzebski and G. van Koten in 1983 [59]. Nowadays, research groups of the University of Pardubice (Czech Republic) are still very active in Nowadays, research groups of the University of Pardubice (Czech Republic) are still very active in

Inorganics 2020, 8, 31 19 of 26 InorganicsInorganics 20202020,, 88,, xx FORFOR PEERPEER REVIEWREVIEW 1919 ofof 2626

Nowadays,thisthis field,field, focusingfocusing research onon groups bothboth thethe of structuralstructural the University aspectaspect of andand Pardubice onon thethe reactivityreactivity (Czech Republic) ofof CC,,NN-chelated-chelated are still organotinsorganotins very active [60],[60], in thisinin particularparticular ﬁeld, focusing towardtoward on carboncarbon both the dioxidedioxide structural [61].[61]. aspect and on the reactivity of C,N-chelated organotins [60], in particularThus,Thus, inin toward 2009,2009, A.A. carbon RRůůžižičč dioxidekaka etet al.al. [published61published]. aa studystudy devodevotedted toto thethe reactivityreactivity ofof thethe C,NC,N-chelated-chelated stannoxane,stannoxane,Thus, in {{2-[(CH{{2-[(CH 2009, A.33) R)22NCHNCH ˚užiˇckaet22]]22CC66H al.H44}}2 published2Sn(Sn(μμ-O)}-O)}22 a[62].[62]. study ThisThis devoted compoundcompound to the isis reactivity reportedreported of totothe reactreactC,N easilyeasily-chelated andand stannoxane,rapidlyrapidly withwith {{2-[(CH COCO22 inin3 )2airairNCH toto 2 ]leadlead2C6H to4to} 2 Sn(thetheµ -O)}cycliccyclic2 [ 62oxo-carbonato-bridgedoxo-carbonato-bridged]. This compound is dinuclear reporteddinuclear tocomplexcomplex react easily {{2-{{2- and[(CH[(CH3 rapidly3))22NCHNCH22]] with22CC66HH44} CO}22Sn(Sn(2μμin-O)(-O)( airμμ-CO-CO to33 lead)) ((2626).). to AA yield theyield cyclic ofof 84%84% oxo-carbonato-bridged waswas alsoalso obtainedobtained forfor thethe dinuclear preparationpreparation complex ofof 2626 {{2-[(CHbyby bubblingbubbling3)2NCH drieddried2]2C 6COCOH42}2 2 Sn(intointoµ -O)(aa EtEtµ22-COOO solutionsolution3)(26). A ofof yield {{2-[(CH{{2-[(CH of 84%33))22NCH wasNCH also22]]22CC6 obtained6HH44}}22Sn(Sn(μμ-O)} for-O)} the22 (Scheme(Scheme preparation 11).11). ofAccordingAccording26 by bubbling toto thethe X-rayX-ray dried structure,structure, CO2 into athethe Et two2twoO solution tintin atomsatoms of exhibitexhibit {{2-[(CH twotwo3)2 NCHdistinctdistinct2]2 coordinationCcoordination6H4}2Sn(µ-O)} geometries.geometries.2 (Scheme OneOne 11). Accordingcancan bebe viewedviewed to the asas X-ray hexacoordinatedhexacoordinated structure, the inin two aa distortdistort tin atomseded octahedronoctahedron exhibit two arrangement,arrangement, distinct coordination andand thethe geometries. secondsecond asas Onepentacoordinatedpentacoordinated can be viewed (TBP);(TBP); as hexacoordinated thethe nitrogennitrogen atomatom in of aof distorted oneone ofof thethe octahedron twotwo LLCNCN ligandsligands arrangement, isis notnot boundbound and toto the thethe second tintin atomatom as 119 1 CN pentacoordinated(Figure(Figure 15).15). However,However, (TBP); inin the CDClCDCl nitrogen33 solution,solution, atom thethe ofone 119Sn{Sn{ of1 theH}H} NMR twoNMR L spectrumspectrumligands revealreveal is nots bounds onlyonly oneone to the resonance,resonance, tin atom 119 1 (Figurebeyondbeyond 15 −−300).300 However, ppmppm andand in CDClslightlyslightly3 solution, dependentdependent the ononSn{ temperattemperatH} NMRure,ure, spectrum supportingsupporting reveals thethe onlypresencepresence one resonance, ofof aa six-six- beyondcoordinatecoordinate300 tintin ppm species.species. and slightlyMoreover,Moreover, dependent thethe authorsauthors on temperature, reportreport thethe possiblepossible supporting useuse of theof 2626 presence asas anan activeactive of asix-coordinate precursorprecursor forfor − tinthethe species. catalyticcatalytic Moreover, synthesissynthesis of theof propylenepropylene authors report carbonatecarbonate the possible fromfrom COCO use22 andand of propylene26propyleneas an active oxide,oxide, precursor withwith anan forestimatedestimated the catalytic yieldyield synthesisofof 5%5% [62].[62]. of propylene carbonate from CO2 and propylene oxide, with an estimated yield of 5% [62].

SchemeScheme 11.11. ReactionReaction schemescheme leadingleading toto compoundcompound 2626..

FigureFigure 15.15. MolecularMolecular structure structure of of 2626,, adaptedadapted fromfrom [[62][62]62] (Copyright(Copyright(Copyright 2009,2009, AmericanAmerican ChemicalChemical Society Society)) (MERCURY(MERCURY(MERCURY view). view).view). HydrogenHydrogen atomsatomsatoms areareare omittedomittedomitted for forfor clarityclarityclarity (Sn(Sn(Sn lightlightlight blue,blue,blue, NNN darkdark blue,blue, OO red,red, CC grey).grey).

InIn 2012,2012, R.R. Jambor Jambor andand A.A. R Rů ˚užiˇckaetůžižiččkaka etet al. al. enriched enriched this this family family of carbonate carbonate derivatives by by isolating isolating twotwo newnewnew compounds, compounds,compounds, i.e., i.e.,i.e., L( L(L(nnn-Bu)SnCO-Bu)SnCO-Bu)SnCO333( (27(2727))) and andand L(Ph)SnCO L(Ph)SnCOL(Ph)SnCO3 3(3 28((2828),),), with withwith L LL= ==2,6-(Me 2,6-(Me2,6-(Me22NCH2NCHNCH22)2))222CC66HH33 [63].[63].[63]. TheseThese complexescomplexes werewere obtainedobtained accordingaccording toto thethe samesame protocolprotocol ofof synthesis,synthesis, i.e.,i.e., byby bubblingbubbling carboncarbon µ µ dioxidedioxide throughthrough toluenetoluene solutionssolutions ofof [L([L([L(nnn-Bu)Sn(-Bu)Sn(-Bu)Sn(μμ-O)]-O)]-O)]22 andand [L(Ph)Sn([L(Ph)Sn(μμ-O)]-O)]22 forfor one one hour hour atat roomroom temperaturetemperature (Scheme(Scheme 1212).12).). Alternatively,Alternatively, they they can can also alsoalso be be obtained obtained under under COCO22 pressurepressure (2 (2 bar) bar) byby mixingmixing drydry iceice withwith toluenetoluene solutionssolutions ofof organotinorganotin precursorsprecursors forfor 22 h.h.h. Compounds Compounds 2727 andand 2828 havehave beenbeen characterizedcharacterizedcharacterized by byby X-ray, X-ray,X-ray, with with bothwith presentingbothboth presenpresen comparabletingting comparablecomparable structures structuresstructures (Figure 16 ), (Figure(Figure i.e., mononuclear 16),16), i.e.,i.e., complexesmononuclearmononuclear in complexes whichcomplexes the in tinin whichwhich atom the isthe hexacoordinated tintin atomatom isis hexacoordinatedhexacoordinated in a strongly inin distorted aa stronglystrongly octahedron distorteddistorted octahedronoctahedron geometry, geometry,geometry, andand OO,,OO-chelated,-chelated, symmetrically,symmetrically, byby aa carbonatecarbonate moiety,moiety, leadingleading toto aa four-memberedfour-membered ringring 119 1 (Figure(Figure 16).16). InIn CDClCDCl33 solution,solution, 2727 andand 28,28, areare characterizedcharacterized byby oneone 119Sn{Sn{1H}H} NMRNMR resonanceresonance locatedlocated

Inorganics 2020, 8, 31 20 of 26 andInorganicsO,O-chelated, 2020, 8, x FOR symmetrically, PEER REVIEW by a carbonate moiety, leading to a four-membered ring (Figure20 16of ).26 Inorganics 2020, 8, x FOR PEER REVIEW 20 of 26 119 1 In CDCl3 solution, 27 and 28, are characterized by one Sn{ H} NMR resonance located at δ = 379.2 at δ = −379.2 and −314.0 ppm, respectively, and supporting the hexacoordination observed− at the andat δ =314.0 −379.2 ppm, and respectively, −314.0 ppm, and respectively, supporting and the hexacoordinationsupporting the hexacoordination observed at the solid-stateobserved at for the tin solid-state− for tin atoms. In addition, the authors claimed that the CO2 fixation by 27 and 28 was atoms.solid-state In addition, for tin atoms. the authors In additi claimedon, the that authors the CO claimed2 ﬁxation that by the27 COand2 fixation28 was reversible,by 27 and 28 with was tin reversible, with tin precursors being quantitatively recovered by heating for 2 h under argon. precursorsreversible, beingwith tin quantitatively precursors being recovered quantitatively by heating recovered for 2 h under by heating argon. for 2 h under argon.

SchemeSchemeScheme 12.12. 12. Reaction Reaction scheme scheme leading leading to to to compounds compounds compounds 2727 27 andand and 2828 .28 . .

Figure 16. Molecular structure of 27 (left) and 28 (right), adapted from [63] (Copyright 2011, Elsevier) FigureFigure 16. 16. Molecular Molecular structure structure of of 27 27 (left) (left) and and 28 28 (right), (right), adapted adapted from from [63] [63] (Copyright (Copyright 2011, 2011, Elsevier Elsevier) ) (MERCURY view). Hydrogen atoms are omitted for clarity (Sn light blue, N dark blue, O red, C grey). (MERCURY(MERCURY view). view). Hydrogen Hydrogen atoms atoms are are omitted omitted for for clarity clarity (Sn (Sn light light blue, blue, N Ndark dark blue, blue, O red,O red, C grey). C grey).

TableTableTable 8.8. 8. Comparison ComparisonComparison of of selected ofselected selected structural structural structural parameters parameters parameters found found in found incarbonates carbonates in carbonates of ofC, NC-chelated,N-chelated of C, Norganotin-chelated organotin organotincomplexes.complexes. complexes. Sn– C– CSD Entry Sn– C– C=O O–C–O O−C=O CSDCSD Entry Entry Compounds O(C) Sn–O(C)O(Sn) C–O(Sn)C=O C=OO–C–OO–C–O OO−C=OC=O Deposition Ref. CompoundsCompounds O(C) O(Sn) (Å) (deg) (deg) DepositionDeposition Ref.Ref. (Å) (Å) (Å) (Å) (deg)(deg) (deg)(deg)− (Å)(Å) (Å)(Å) NumberNumberNumber {{2-[(CH3)2NCH2]2C6H4}2Sn(μ- 2.079(4) 1.312(2) 121.4(5) YUMVEI 3 2 2 2 6 4 2 {{2-[(CH{{2-[(CH3)2NCH) NCH2]2C]6CH4H}2Sn(} Sn(µ-O)(μ- µ-CO2.079(4)3) 2.079(4) 1.312(2)1.312(2) 1.215(8) 116.5(5) 121.4(5)121.4(5) YUMVEIYUMVEI [62] O)(μ-CO3) (26) 2.080(4) 1.322(2) 1.215(8)1.215(8) 116.5(5) 116.5(5) 122.1(5) 119276 [62][62] O)(μ-CO(26)3) (26) 2.080(4)2.080(4) 1.322(2)1.322(2) 122.1(5)122.1(5) 119276119276 L(n-Bu)SnCO3 (27) 2.110(2) 1.333(4) 124.2(3) PAJMEU L(n-Bu)SnCO3 (27) 2.110(2) 1.333(4) 124.2(3) PAJMEU L(n-Bu)SnCO3 (27) 2.110(2) 1.333(4)1.223(4) 111.6(3) 124.2(3) PAJMEU [63] (L = 2,6-(Me2NCH2)2C6H3) 2.125(2) 1.325(4) 1.223(4)1.223(4) 111.6(3) 111.6(3) 124.2(3) 835513 [63][63] (L (L= 2,6-(Me= 2,6-(Me2NCH2NCH2)2C2)62HC36)H 3) 2.125(2)2.125(2) 1.325(4)1.325(4) 124.2(3)124.2(3) 835513835513 L(Ph)SnCO3 (28) 2.099(3) 1.331(6) 124.4(4) PAJMOE L(Ph)SnCOL(Ph)SnCO3 (28)(28) 2.099(3)2.099(3) 1.331(6)1.331(6) 1.221(5) 110.6(4) 124.4(4)124.4(4) PAJMOEPAJMOE [63] (L = 2,6-(Me2NCH2)23C6H3) 2.107(3) 1.322(6) 1.221(5)1.221(5) 110.6(4) 110.6(4) 125.0(4) 835515 [63][63] (L (L= 2,6-(Me= 2,6-(Me2NCH2NCH2)2C2)62HC36)H 3) 2.107(3)2.107(3) 1.322(6)1.322(6) 125.0(4)125.0(4) 835515835515

InorganicsInorganics2020 2020, 8, ,8 31, x FOR PEER REVIEW 2121 ofof 26 26

Table 9. Selection of spectroscopic data (NMR and IR) assigned to carbonates of C,N-chelated Tableorganotin 9. Selection complexes. of spectroscopic data (NMR and IR) assigned to carbonates of C,N-chelated organotin complexes. 119Sn{1H} 13C{1H} IR 119Sn{1H} NMR 13C{1H} NMR IR υ(CO ) CompoundsCompounds NMR NMR υ(CO3) 3 Ref. δ δ 1 ( , ppm)(δ, ppm) ((δ,, ppm) cmcm−1− a,b 309.2−309.2 a,b d,e {{2-[(CH3)2NCH2]2C6H4}2Sn(µ-O)(µ-CO3) (26) − 161.9 d,e 1587 [62] {{2-[(CH3)2NCH2]2C6H4}2Sn(μ-O)(μ-CO3) (26) 315.8 a,c 161.9 1587 [62] − −315.8 a,c L(n-Bu)SnCO3 (27)3 d,e d,e L(n-Bu)SnCO (27) 314.0 d,e 163.9 d,e n/a [63] (L = 2,6-(Me2NCH2)2C6H3) − −314.0 163.9 n/a [63] (L = 2,6-(Me2NCH2)2C6H3)

L(Ph)SnCO3 (28)3 d,e d,e L(Ph)SnCO (28) 379.2 d,e 163.5 d,e n/a [63] (L = 2,6-(Me2NCH2)2C6H3) − −379.2 163.5 n/a [63] (L = 2,6-(Me2NCH2)2C6H3) a b c d e Measured in toluene-d8 or benzene-d6; at 350 K; at 220 K; measured in CDCl3; at 300 K. a Measured in toluene-d8 or benzene-d6; b at 350 K; c at 220 K; d measured in CDCl3; e at 300 K.

3.5. Heteronuclear Cluster 3.5. Heteronuclear Cluster AlthoughAlthough the the following following compound compound cannot cannot be considered be considered an organotin an organotin derivative derivative (no Sn-C (no bond), Sn-C webond), thought we thought it would it bewould interesting be interesting to include to include it in this it review.in this review. To our To knowledge, our knowledge, this is this the onlyis the exampleonly example of a carbonate of a carbonate derivative derivat forive this for family this family of compound. of compound. InIn 2005, 2005, E. E. Sim Simón-Mansoón-Manso and and C. P.Kubiak C. P. Kubiak published published the reactivity the reactivity of the trihydroxystannyl-capped of the trihydroxystannyl- cluster [Ni3(µ-dppm)3(µ3-Cl)(µ3-Sn(OH)3], in solution in CH2Cl2 or THF, with carbon dioxide capped cluster [Ni3(μ-dppm)3(μ3-Cl)(μ3-Sn(OH)3], in solution in CH2Cl2 or THF, with carbon dioxide 2 (bubbling) leading to the formation of the carbonate cluster [Ni3(µ-dppm)3(µ3-Cl)(µ3-Sn(OH)(η -CO3)]2 (bubbling) leading to the formation of the carbonate cluster [Ni3(μ-dppm)3(μ3-Cl)(μ3-Sn(OH)(η - (29)[64]. The nucleophilic addition of CO on the µ -Sn(OH) moiety of the starting cluster causes CO3)] (29) [64]. The nucleophilic addition2 of CO2 on3 the μ3-Sn(OH)3 3 moiety of the starting cluster ancauses immediate an immediate color change, color change, from dark from blue dark to purple,blue to andpurple, is accompanied and is accompanied by the elimination by the elimination of one waterof one molecule. water molecule. The reaction The is reportedreaction tois bereported completely to be reversible. completely The Snreversible. atom is hexacoordinatedThe Sn atom is inhexacoordinated a highly distorted in a octahedral highly distorted coordination octahedral geometry. coordination The coordination geometry. ofTh thee coordination carbonato ligand of the tocarbonato the tin atom ligand forms to the a strained tin atom four-membered forms a strained ring four-membered (Figure 17). By ring infrared, (Figure the 17). absorption By infrared, bands the 1 characteristicabsorption bands of carbonate characteristic are observed of carbonate at 1634 are and observed 1669 cm at− .1634 Interestingly, and 1669 thecm− authors1. Interestingly, described the a comparable reactivity of the cluster [Ni (µ-dppm) (µ -Cl)(µ -Sn(OH) ] toward 1,2-epoxybutane, authors described a comparable reactivity3 of the cluster3 3 [Ni33(μ-dppm)33(μ3-Cl)(μ3-Sn(OH)3] toward leading1,2-epoxybutane, to a 1,2-diolate leading tin clusterto a 1,2-diolate via a ring-opening tin cluster additionvia a ring-opening [64]. addition [64].

FigureFigure 17. 17.Molecular Molecular structure structure of of29 29,, adapted adapted from from [ 64[64]] (Copyright (Copyright 2005, 2005,WILEY-VCH WILEY-VCH VERLAG VERLAG GMBH GMBH && CO. CO. KGAA KGAA) (MERCURY) (MERCURY view). view). Hydrogen Hydrogen atoms atoms and and phenyl phenyl groups groups are are omitted omitted for for clarity clarity (Sn (Sn light light blue,blue, Ni Ni green, green, P P orange, orange, Cl Cl light light green, green, O O red, red, C C grey). grey).

Inorganics 2020, 8, 31 22 of 26

Table 10. Selection of structural parameters found in 29.

CSD Entry Sn–O(C) C–O(Sn) C=O O–C–O O–C=O Compound Deposition Ref. (Å) (Å) (Å) (deg) (deg) Number [Ni (µ-dppm) (µ -Cl)(µ -Sn(OH)(η2-CO )] 2.121(3) 1.325(6) 123.9(4) FIXWEP 3 3 3 3 3 1.223(6) 111.8(4) [64] (29) 2.148(3) 1.323(5) 124.3(4) 250077

4. Conclusions In conclusion, this structural inventory revealed a notable number of tin compounds bearing hemicarbonato and carbonato ligands (26 CSD entries). They were discovered over a period of forty years, sometimes accidentally, but most often in the context of studies devoted to reactivity toward carbon dioxide. These compounds highlight a rich diversity of architectures, from mononuclear complex to polynuclear clusters, showing various modes of coordination (summarized in Scheme 13). From a structural point of view, the tin atom preferentially adopts a trigonal bipyramidal or an octahedral geometry. When available, spectroscopic data rather correctly corroborate the resolved structures, even for the most complex, and show that in most cases, they are kept intact in solution. In general, the formation of hemicarbonato tin complexes results from the facile insertion of carbon dioxide at atmospheric pressure into Sn–OR bonds. Their formation has been intimately linked to the direct carbonation reaction of alcohols. Organotin compounds are thus recognized as the most efficient molecular precursors for the transformation of carbon dioxide into linear alkyl carbonates. With regards to carbonato tin complexes, the majority were obtained by directly reacting an organometallic tin precursor (very often an oxide derivative) with carbon dioxide. Alternatively, in some cases, inorganic carbonate salts were also used. This last class of compounds is the most abundant and varied from a structural point of view. However, several factors are decisive for the structure of the final edifice, in particular the reaction conditions and the number and nature of the ligands linked to the tin atom. In view of the diversity of the resolved structures and their relatively small number, the combination of these parameters still provides important perspectives in terms of the synthesis and design of new compounds. Finally, it appears that organotins exhibit a high reactivity with carbon dioxide, leading to its fixation, or even conversion. Thus, the CO2 derivatives of molecular compounds of tin can truly be considered as a class of compounds in their own right. As mentioned at the beginning of this article, other types of CO2-adducts of tin complexes are known, such as carbamates, formates, and phosphinoformates. These derivatives can also result from the insertion of CO2 into Sn–X bonds (X = N, H, P), and they will be the subject of a future structural inventory. Inorganics 2020, 8, 31 23 of 26 Inorganics 2020, 8, x FOR PEER REVIEW 23 of 26

SchemeScheme 13. 13.Summary Summary ofof thethe coordinationcoordination modes modes observed observed for for hemicarbonato hemicarbonato andand carbonato carbonato tin tin complexescomplexes and and described described in in this this review review (based(based on on X-ray X-ray crystallographic crystallographic structures). structures).

Funding: L.P. thanks the Centre National de la Recherche Scientifique (C.N.R.S-France) and the University of Funding:BourgogneL.P. Franche-Comté thanks the Centre for financial National support. de la Recherche Scientifique (C.N.R.S-France) and the University of Bourgogne Franche-Comté for financial support. Conflicts of Interest: The author declares no conflict of interest. Conflicts of Interest: The author declares no conflict of interest.

Inorganics 2020, 8, 31 24 of 26

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