7-COORDINATE MOLYBDENUM-TIN AND TUNGSTEN-TIN COMPLEXES CONTAINING PHOSPHITES AND TETRAMETHYLTHIOUREA - X-RAY STRUCTURE OF [MO(CO)2(P(OME)3)3(SNBUCL2)CL]

[M(CO)3(nitrile)3] react with SnRCl3 (R = Bu or Ph) to produce [M(CO)3(nitrile)2(SnRCl2)Cl] (1; M = Mo, nitrile = NCMe; M = W, nitrile = NCEt). These complexes react further with three equivalents of phosphite P(OR')3 (R' = Me or Et) at room temperature giving dicarbonyl tris(phosphite) complexes [M(CO)2{P(OR')3}3/(SnRCl2)Cl] (2; M = Mo or W; R = Bu or Ph; R' = Me or Et) through displacement of the two nitriles and one CO. The dicarbonyl tris(phosphite) complexes are produced even when only two equivalents of phosphite are added to the reaction mixture. In contrast, when the tricarbonyl bis(nitrile) compounds 1 react with an excess of tretramethylthiourea (TMTU), only the two nitriles are replaced, leading to tricarbonyls [M(CO)3(TMTU)2(SnRCl2)Cl] (3, M = Mo or W; R = Bu or Ph).