Reactions of Doubly Bridged Biscyclopentadienes with Molybdenum (Tungsten) Carbonyl

Dimolybdenum complexes (X)(Y)[(η5-C5H3)Mo(CO)3]2 [Y = Me2Si, X = Me2C, (CH2)5C, CH2;
Y = Ph2Si, X= Me2C] and desilylation products (X)[(η5-C5H4)Mo(CO)3]2 were obtained from
the reactions of carbon and silicon doubly bridged biscyclopentadiene ligands (X)(Y)(C5H4)2
with Mo(CO)6 in refluxing xylene. When these ligands reacted with W(CO)6, under similar
conditions, in addition to ditungsten complexes (X)(Y)[(η5-C5H3)W(CO)3]2 [X = Me2C; Y =
Me2Si, Ph2Si] and desilylation products (X)[(η5-C5H4)W(CO)3]2, a class of structurally novel
complexes (X)(η5-C5H3)(η5,η1-C5H3)[(Y)W(CO)3][W(CO)3] [for X = Me2C, (CH2)5C; Y = Me2Si] with a W−Si bond were also isolated. The reactions of carbon and germanium doubly
bridged biscyclopentadiene ligands (X)(Me2Ge)(C5H4)2 [X = Me2C, (CH2)5C] with Mo(CO)6
or W(CO)6 gave similar novel complexes (X)(η5-C5H3)(η5,η1-C5H3)[(Me2Ge)M(CO)3][M(CO)3]
[X = Me2C, (CH2)5C; M = Mo, W] with a M−Ge bond. The reactions also produced
degermylation products. However, the corresponding dimolybdenum or ditungsten complexes
were not isolated in these cases. The molecular structures of 2, 6, 8, 10, 11, 13, 14, 15, 19,
21, 22, 25t, and 26t have been determined by X-ray diffraction. The M−M distances in
complexes 2 [3.4328(12) Å], 8 [3.453(2) Å], and 11 [3.403(2) Å] are conspicuously elongated
and are in fact the longest ever reported among the biscyclopentadienyl dimolybdenum or
ditungsten complexes. The factors affecting the structures of dimolybdenum or ditungsten
complexes are discussed.