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.

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