COORDINATION CHEMISTRY OF NITRILES AND CYANAMIDE AT ELECTRON-RICH METAL CENTERS

The reactions of various nitriles with dinitrogen or isocyanide complexes presenting an electron-rich d6 transition metal site are described and shown to give the following compounds: the nitrile complexes [ReCl(NCR)(dppe)2] (R = alkyl or aryl; dppe = Ph2PCH2CH2PPh2), [Re(NCR)2(dppe)2][BF4] or [Re(N2)(NCR)(dppe)2][BF4], derived from the reactions of NCR with trans-[ReCl(N2)(dppe)2]; the cyanamide compounds trans-[Re(CNR)(NCNH2)(dppe)2][BF4] (which can undergo deprotonation to the corresponding hydrogen cyanamide, NCNH, complexes), from the reaction of NCNH2 with trans-[ReCl(CNR)(dppe)2]; the cyanoimido complexes trans-[M(NCN)2(dppe)2] (M = Mo or W), from the dehydrogenation reaction of NCNH2 with trans-[M(N2)2(dppe)2]; and the trimethylsilyl isocyanide species trans-[ReCl(CNSiMe3)(dppe)2], from the reaction of trimethylsilyl cyanide (NCSiMe3) with trans-[ReCl(N2)(dppe)2]. The neutral organonitrile complexes undergo protonation either at the nitrile ligand or at the metal, to give the methyleneamido or the hydrido complexes [ReCl(N=CHR)(dppe)2]+ or [ReHCl(NCR)(dppe)2]+, respectively; further protonation of nitriles to amines and hydrocarbons or coupling with alkynes, although in very low yields, have been detected at some Mo(0) phosphinic centres. Moreover, reaction of the trimethylsilyl isocyanide complex with MeOH or with BBF4 affords trans-[ReCl(CNH)(dppe)2] or trans-[ReCl(CNH2)(dppe)2][BF4], with the simplest isocyanide or aminocarbyne ligands, respectively. The electrochemical behaviour of those complexes is also outlined and shown to involve electroinduced dehydrogenation or deprotonation reactions for the cyanamido methyleneamido or hydrido complexes.