Synthesis and structures of tungsten (1-pyridinio)imido complexes and their facile N-N bond cleavage

摘要

The tungsten (1-pyridinio)imido complexes [WX2(NNC5H4OMe)(L)(PMe2Ph)(2)](+), [WX2(NNC5H2Me3)(L)(PMe2Ph)(2)](+), and [WCl2{NNC5H2(COOEt)(2)Ph}(L)(PMe2Ph)(2)](+) (X = Cl, Br; L = CO, C2H4, PMe2Ph) were synthesized by the reaction of the salts of pyrylium cations with the hydrazido complexes [WX2(NNH2)(L)(PMe2Ph)(2)], which were derived from the dinitrogen complex cis-[W(N-2)(2)(PMe2Ph)(4)]. The complexes obtained were characterized by spectroscopic measurements as well as crystallographic studies of cis,mer-[WBr2(NNC5H4OMe-4)(PMe2Ph)(3)][PF6], cis, trans-[WCl2(NNC5H4OMe-4)(CO)(PMe2Ph)(2)][ClO4], cis, trans- [WCl2(NNC5H2Me3-2,4,6)(CO)(PMe2Ph)(2)][OTf] (OTf = OSO2CF3), and cis,trans-[WCl2(NNC5H4OMe-4)(C2H4)(PMe2Ph)(2)][ClO4], which revealed that the N-N bond distances of these (1-pyridinio)imido complexes are shorter than those of the trialkyl- or unsubstituted hydrazidium complexes so far reported. The (1-pyridinio)imido complexes with a pi-acidic ligand (CO or C2H4) undervent smooth N-N bond cleavage on reaction with cobaltocene under ambient conditions to liberate the pyridines in moderate to high yields. In some reactions that were conducted in the presence of HNEt3-Cl, the corresponding imido (NH) complexes were recovered as the metal products. The (1-pyridinio)imido complexes also reacted with KOH in MeOH to give the pyridines and ammonia in high yields. These reactions provide the first examples of N-N bond cleavage of well-defined hydrazidium complexes and accomplish the synthesis of pyridines from molecular nitrogen under mild conditions. [References: 51]