Syntheses and properties of hydride-cyanamide and derived hydrogen-cyanamide complexes of molybdenum(IV). Crystal structure of [MoH2(NCNH2)2(Ph2PCH2CH2PPh2)2][BF4]2

The first hydride-cyanamide (or -cyanoguanidine) complexes of molybdenum, [MoH2(NCR)2(dppe)2][BF4]2(R = NH21a, NMe21b, NEt21c or NC(NH2)21d; dppe = Ph2PCH2CH2PPh2), have been prepared by treatment of [MoH4(dppe)2] in THF with the appropriate cyanamide (or cyanoguanidine) in the presence of HBF4. Reaction of 1a with a base leads to the bis(hydrogen-cyanamide)[or bis (hydrogen-cyananoimide)] complex trans-[Mo(NCNH)2(dppe)2][BF4]22 or to the bis(cyanoimide) complex trans-[Mo(NCN)2(dppe)2]3, via base-catalysed or base-promoted dehydrogenation, whereas cathodically-induced dehydrogenation appears to form [MoH2(NCNH) (NCNH2)(dppe)2]+4. The spectroscopic properties of the complexes are also reported along with their electrochemical behaviours and the molecular structure of 1a as established by X-ray crystallography which indicates the presence of the NCNH2 ligands involved in two hydrogen bonds connecting the ions in dimeric units.