Protonation of bis[1,2-bis(diethylphosphino)ethane]bis(dinitrogen)-molybdenum and -tungsten with fluoroboric acid–diethyl ether (1/1) in benzene; crystal and molecular structure of bis[1,2- bis(diethylphosphino)ethane]fluoro[hydrazido(2–)]tungsten tetrafluoroborate

Abstract

The reaction of HBF₄·Et₂O with [W(N₂)₂(depe)₂] in benzene can, depending upon the conditions, give rise to [WF(NNH₂)(depe)₂]BF₄, [WF(NNH₃)(depe)₂][BF₄]₂, or [WH(F)(NNH₂)(depe)₂][BF₄]₂. The compounds are to some extent interconvertible. The structures have been completely elucidated using ³¹P and ¹⁵N n.m.r. spectroscopy, and the X-ray crystal structure of [WF(NNH₂)(depe)₂]BF₄ has been determined. This reveals no unusual bond distances, but an extensive system of hydrogen bonding. The parallel reaction of [Mo(N₂)₂(depe)₂] yields only one product, tentatively formulated as [Mo(BF₄)(NNH₂)(depe)₂]BF₄. The relevance of these observations to the mechanism of the protonation of complexed dinitrogen is discussed.