Reductive nitrosylation of tetraoxometallates. Part 3. Generation of {Mo(NO)}4, {Mo(NO)2}4, and {Mo(NO)2}6 moieties: synthesis of 2,2′- bipyridine, 1,10-phenanthroline, thiocyanato-, and diethyldithiocarbamato-complexes of mono- and di-nitrosylmolybdenum directly from MoO42– in aqueous and aerobic media

Abstract

In an aqueous aerobic medium MoO₄^2– can be reductively nitrosylated using excess of NH₂OH·HCl and SCN^– in the range pH 4–4.5, generating selectively the {Mo(NO)}⁴ moiety. This has been confirmed by synthesising complexes of the types [Mo(NO)(NH₂O)(NCS)₄]^2–, [Mo(NO)(NH₂O)(S₂CNEt₂)₂], and the isomeric [Mo(NO)(NH₂O)(NCS)₂(L–L)][L–L = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] almost in quantitative yield. However, if the same reaction is conducted at pH 5.2–5.4 a selective generation of the {Mo(NO)₂}⁴ moiety occurs leading to the stereoselective synthesis of [Mo(NO)₂(NHO)(NCS)₄]^2– and [Mo(NO)₂(NHO)(NCS)₂(L–L)]. In the range pH 5.7–6 the initially formed Mo(NO)³⁺ species undergoes disproportionation to a formally molybdenum(0) species, {Mo(NO)₂}⁶, viz.[Mo(NO)₂(NCS)₄]^2– or [Mo(NO)₂(NCS)₂(L–L)] along with an oxomolybdenum(V) species, viz.[Mo₂O₄(NCS)₆]^4– or [Mo₂O₄(NCS)₂(L–L)₂]. Here also, the dinitrosylmolybdenum moiety is formed stereoselectively.