MOLECULAR-ORBITAL STUDY OF THE BONDING AND REACTIVITY OF THE DIISOCYANIDE COMPLEXES TRANS-[MO(CNR)2(PH2PCH2CH2PPH2)2] AND DERIVED AMINOCARBYNE COMPOUNDS

The bonding, structure, properties and reaction patterns of the isocyanide and aminocarbyne-type complexes of molybdenum have been investigated with the aid of EHMO-SCCC calculations and of frontier orbital theory. The results indicate that (i) beta-protonation of a ligating isocyanide, in either the trans-[Mo(CNMe)2(dppe)2](1) or trans-[Mo(CNHMe)(CNMe)(dppe)2]+, is predominantly charge-controlled, whereas the alpha-nucleophilic attack at the dicarbene-type complex trans-[Mo(CNHMe)2(dppe)2]2+ is orbitally controlled, and (ii) electrophilic attack should preferentially occur at the Mo atom of a molybdenum complex involving linear isocyanide ligands but at the N atoms of a complex with bent isocyanide ligands. The conversion of the hydride into the aminocarbyne complex, the oxidation of 1, and its oxidative-addition reactions with halogens are interpreted in terms of FMO theory.