Redox potential–structure relationships in metal complexes. Part 2. The influence of trans-substituents upon the redox properties of certain dinitrogen complexes of molybdenum and tungsten and some carbonyl analogues: inner-sphere versus outer-sphere electron transfer in the alkylation of co-ordinated dinitrogen

Abstract

The preparation of some new anionic dinitrogen complexes of the type trans-[M(N₂)X(dppe)₂]^– is described (M = Mo or W; X = SCN, CN, or N₃; dppe = Ph₂PCH₂CH₂PPh₂) together with their monocarbonyl analogues(M = Mo). Relationships between E_½^ox, ν(N₂), and ν(CO) of these complexes and those of [M(N₂)(NCR)(dppe)₂] and the standard series [Cr(CO)₅(L or X^–)] have allowed us to identify the formation of a labile ammine complex [Mo(N₂)(NH₃)(dppe)₂] in tetrahydrofuran and to predict E_½^ox and ν(N₂) for as yet unsynthesised complexes related to those described. Furthermore, aspects of the reactivity of the co-ordinated dinitrogen ligand have been correlated with the ‘electron-richness’ of the complex (as measured by E_½^ox) with particular reference to (a) inner-sphere versus outer-sphere electron-transfer alkylation of co-ordinated dinitrogen to give organodiazenido-complexes and (b) the protonation of [M(N₂)(NCR)(dppe)₂] complexes which give the new hydrazido(2–)-salts, [M(N₂H₂)(NCR)(dppe)₂][HSO₄]₂, with retention of the trans-RCN ligand.