Synthesis of trans-[Mo(N2)2(dippe)2][dippe = 1,2-bis(diisopropylphosphino)ethane] and related derivatives, protonation of co-ordinated dinitrogen and crystal structures of trans-[MoF(NNH2)(dippe)2][BF4] and trans-[MoCl2(dippe)2][BF4]

Abstract

Reduction of [MoCl₃(thf)₃](thf = tetrahydrofuran) with sodium dispersion or sodium amalgam in the presence of dinitrogen and 1,2-bis(diisopropylphosphino)ethane (dippe) gave low, but reproducible, yields of the bis(dinitrogen) complex trans-[Mo(N₂)₂(dippe)₂]1. This reacted very slowly with H₂ to yield the known tetrahydride [MoH₄(dippe)₂]2, which is more conveniently prepared by reaction of [MoCl₄(MeCN)₂] with dippe and Na[BH₄]. Complex 1 reacted with 2 equivalents of HBF₄ in Et₂O to give the hydrazido(2–) complex trans-[MoF(NNH₂)(dippe)₂][BF₄], the crystal structure of which has been determined. When the reduction of [MoCl₃(thf)₃] in the presence of dippe was performed under argon instead of dinitrogen the yellow, 16-electron, paramagnetic complex [MoCl₂(dippe)₂]4 was obtained. In accordance with its co-ordinatively unsaturated character, 4 reacted with CO in thf yielding seven-coordinate, diamagnetic [MoCl(CO)₂(dippe)₂]Cl 5. It also underwent one-electron oxidation by reaction with Ag[BF₄] in CH₂Cl₂, furnishing 15-electron [MoCl₂(dippe)₂][BF₄]6, the crystal structure of which was also determined.