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 = NCE t). These complexes react further with three equivalents of phosphite P(OR')3 (R' = Me or Et) at room temperature giving dicarbonyl tris(pho sphite) complexes [M(CO)2{P(OR')3}3/(SnRCl2)Cl] (2; M = Mo or W; R = B u or Ph; R' = Me or Et) through displacement of the two nitriles and o ne 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 re placed, leading to tricarbonyls [M(CO)3(TMTU)2(SnRCl2)Cl] (3, M = Mo o r W; R = Bu or Ph).