crystals Article Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of 2 [(µ2-dppm)2Cu2(η -BH4)2] Dichloromethane Solvate Natalia V. Belkova 1 ID , Igor E. Golub 1,2 ID , Evgenii I. Gutsul 1, Konstantin A. Lyssenko 1, Alexander S. Peregudov 1, Viktor D. Makhaev 3, Oleg A. Filippov 1 ID , Lina M. Epstein 1, Andrea Rossin 4 ID , Maurizio Peruzzini 4 and Elena S. Shubina 1,* ID 1 A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences (INEOS RAS), 119991 Moscow, Russia; [email protected] (N.V.B.); [email protected] (I.E.G.); [email protected] (E.I.G.); [email protected] (K.A.L.); [email protected] (A.S.P.); [email protected] (O.A.F.); [email protected] (L.M.E.) 2 Inorganic Chemistry Department, Peoples’ Friendship University of Russia (RUDN University), 117198 Moscow, Russia 3 Institute of Problems of Chemical Physics, Russian Academy of Sciences (IPCP RAS), 142432 Moscow, Russia; [email protected] 4 Istituto di Chimica dei Composti Organometallici Consiglio Nazionale delle Ricerche (ICCOM CNR), 50019 Sesto Fiorentino, Italy; [email protected] (A.R.); [email protected] (M.P.) * Correspondence: [email protected]; Tel.: +7-495-135-5085 Academic Editor: Sławomir J. Grabowski Received: 18 September 2017; Accepted: 17 October 2017; Published: 20 October 2017 Abstract: Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(µ2-dppm)2Cu2(η2-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. The rare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. Keywords: copper(I); diphosphine; dppm ligand; tetrahydroborate; binuclear complex; crystal structure; conformations; polymorph; hydride-halogen bonding 1. Introduction The concept of cooperative catalytic effects [1] in multinuclear transition metal systems led to the broad development and extensive investigation of the chemistry of transition metal complexes, bearing “short-bite” ligands that are able to lock two or more metallocenters in close proximity [2–7]. Such compounds are of great interest due to their catalytic activity including the transformation of small molecules on metal centres [8,9], they can also be used as synthetic models of enzyme action [10–12]. Phosphines are ubiquitous ligands in transition metal chemistry. Among various types of diphosphine ligands, bis-(diphenylphosphino)methane (dppm) is one of the very efficient bridging ligands [2]. As other diphosphine ligands it is able to chelate metals, but rarely acts as a bidentate ligand (η2-dppm), forming a strained four-membered cycle (Scheme1)[ 13–17]. Rather, it has a tendency to 1 act as either a monodentate (η -dppm) or bridging bidentate ligand (µ2-dppm) [18]. Many examples Crystals 2017, 7, 318; doi:10.3390/cryst7100318 www.mdpi.com/journal/crystals Crystals 2017, 7, 318 2 of 17 Crystals 2017, 7, 318 2 of 17 Crystals 2017, 7, 318 2 of 17 ofexamples binuclear of complexes binuclear containingcomplexes thecont eight-memberedaining the eight-membered ring M(µ2-dppm) ring2 MM(' μare2-dppm) known2M' with are a varietyknown examplesofwith metals a variety andof binuclear stereochemistriesof metals complexes and stereochemistries [18 cont]. aining the [18]. eight-membered ring M(μ2-dppm)2M' are known with a variety of metals and stereochemistries [18]. 2 1 M(η -dppm) M(η -dppm) M2(μ2-dppm) 2 1 M(η -dppm) M(η -dppm) M2(μ2-dppm) SchemeScheme 1.1. Possible coordination modesmodes ofof dppmdppm ligandligand inin transitiontransition metalmetal complexes.complexes. Scheme 1. Possible coordination modes of dppm ligand in transition metal complexes. TheThe Cu(I)-dppmCu(I)-dppm complexescomplexes areare emergingemerging classclass ofof polynuclearpolynuclear complexes,complexes, thatthat areare drawingdrawing considerableconsiderableThe Cu(I)-dppm attention complexes because of of are their their emerging photophysi photophysical classcal of properties propertiespolynuclear [19–22] [19 complexes,–22 ]and and prospective prospective that are drawinguse use as as a considerableacatalyst catalyst [23–25] [23 attention–25 and] and a sensorbecause a sensor for of forvarious their various photophysi organic organic basescal bases properties[26] and [26] anions and[19–22] anions [27]. and Binuclear [ 27prospective]. Binuclear Cu(I) use species Cu(I)as a catalystspeciespossess possess[23–25]an enhanced and an enhanceda reactivity sensor for reactivitytoward various organic organic toward azides bases organic in [26]copper-catalysed azides and anions in copper-catalysed [27]. azide-alkyne Binuclear cycloadditionCu(I) azide-alkyne species possesscycloadditioncompared an enhancedto monomeric compared reactivity tocopper monomeric toward complexes organic copper [28–35] azides complexes .in Copper(I) copper-catalysed [28– tetrahydrobo35]. Copper(I) azide-alkynerates tetrahydroborates with cycloaddition phosphine withcomparedligands phosphine featuring to monomeric ligands relative featuring copperstability complexes relativeto air oxygen stability [28–35] an tod. moisture airCopper(I) oxygen are tetrahydrobo and used moisture as selectiverates are used withreducing asphosphine selective agents ligandsreducing[36–40], featuring catalystsagents [ 36ofrelative– phot40],osensitized catalysts stability ofto isomerization photosensitizedair oxygen an ofd moisturedienes isomerization [41–43] are used ofand dienes ashydrolytic selective [41–43 dehydrogenation ]reducing and hydrolytic agents [36–40],dehydrogenationof ammonia catalysts borane of of phot ammonia[44].osensitized Since borane metal isomerization tetrahydroborates [44]. Since of metal dienes tetrahydroborateshave [41–43] great and potential hydrolytic have in greathydrogendehydrogenation potential storage in ofhydrogentechnology ammonia storage [45–50], borane technology as[44]. catalysts Since [45 metal –[51–55]50], astetrahydroborates catalystsand select [51ive–55 reducing] andhave selective gr agentseat potential reducing [56–61] in their agents hydrogen structural [56– 61storage] their and technologystructuraldynamic properties and [45–50], dynamic ashave catalysts properties been [51–55]actively have beenand investigat activelyselectiveed investigated reducing[52,62–64]. agents [These52,62 [56–61]– 64studies]. These their revealed studies structural revealeddifferent and dynamic properties− have− been actively investigated [52,62–64]. These studies revealed different differentmodes of modes BH4 coordination of BH4 coordination to the metal to the atom, metal which atom, can which behave can as behave mono-, as mono-,bi-, or tridentate bi-, or tridentate ligand − modesligand[64]. [of64 BH]. 4 coordination to the metal atom, which can behave as mono-, bi-, or tridentate ligand [64]. − − OurOur studies studies of intermolecular of intermolecular interactions interactions of BH4 [65,66] of BH and4 several[65,66] metal and tetrahydroborates several metal − tetrahydroborates[67–70]Our with studies proton of [67 intermolecular –donors70] with have proton showninteractions donors the vers haveof BHatility shown4 [65,66] of dihydrogen the and versatility several bonded metal of dihydrogen tetrahydroborates(DHB) complexes bonded (DHB)[67–70]formed complexes withand their proton crucial formed donors role and havein their the shown crucialreactivity rolethe of invers these theatility reactivity compounds. of dihydrogen of these In partic compounds. bondedular, we (DHB) have In particular, showncomplexes that we formedhavethe formation shown and their that of bifurcatecrucial the formation role DHB in thecomplexes of bifurcatereactivity involving DHBof these complexes bothcompounds. bridging involving In and partic bothterminalular, bridging we hydride have and shown hydrogens terminal that the formation of2 bifurcate DHB complexes2 involving both bridging and terminal hydride hydrogens hydrideof (Ph3P) hydrogens2Cu(η -BH4) of(Scheme (Ph3P) 22)Cu( is ηprerequisite-BH4) (Scheme for the2) subsequent is prerequisite proton for transfer the subsequent and dimerization proton 2 oftransferto (Phoccur3P) and2 Cu([67].η dimerization -BHContinuing4) (Scheme to these occur2) is prerequisitestudies, [67]. Continuing we forattempted the thesesubsequent studies,the synthesis proton we attempted transferof (η2-dppm)Cu( and the dimerization synthesisη2-BH of4) to 2 occur [67]. 2Continuing these studies, we attempted the synthesis of (η2-dppm)Cu(η2-BH4) (followingη -dppm)Cu( the ηpublished-BH4) following recipe [71]. the published However, recipe in our [71 hands,]. However, it gave, in ourinstead, hands, a binuclear it gave, instead, dimer following the published recipe [71]. However, in our hands, 2it gave, instead, a 2binuclear dimer abearing binuclear two dimer bridging bearing μ2-dppm two bridgingligands betweenµ2-dppm the ligands two {Cu( betweenη -BH4 the)} moieties. two {Cu( Hereinη -BH 4we)} moieties.describe 2 bearingHereinits spectroscopic wetwo describe bridging characterization its μ spectroscopic2-dppm ligands and characterization betweenanalysis theof polymorphic two and {Cu( analysisη -BH structures of4)} polymorphicmoieties. of itsHerein dichloromethane