Cooperative effects in π-ligand bridged dinuclear complexes XXII. New dinuclear bis(cyclopentadienediyl)ketone complexes containing molybdenum, tungsten, cobalt and iron

Hydrolysis of the siloxyfulvene compounds {M}[η5-C5H4C(OTMS)(C5Me4)] ({M}=Mo(CO)3Me: 1a; {M}=W(CO)3Me: 1b) affords {M}[η5-C5H4C(O)(C5Me4H)] ({M}=Mo(CO)3Me: 3a; {M}=W(CO)3Me: 3b) which are suitable precursors for the synthesis of dinuclear complexes. The reactivity of the molybdenum and the tungsten compounds shows remarkable differences: heating of 3a with Co2(CO)8 in the presence of 3,3-dimethylbut-1-ene reveals the heterodinuclear complex Me(CO)3Mo[(η5(Mo)–C5H4)C(O)(η5(Co)–C5Me4)]Co(CO)2 (4a) along with the homodinuclear complex (CO)2Co[(η5-C5H4)C(O)(η5-C5Me4)]Co(CO)2 (5), the comparable reaction of 3b with Co2(CO)8 results in the formation of the heterodinuclear complex Me(CO)3W[(η5(W)–C5H4)C(O)(η5(Co)–C5Me4)]Co(CO)2 (4b) only. The metal–metal bound complexes [(η5(M)–C5H4)C(O)(η5(M′)–C5Me4)]MM′(CO)6 (M–M′) (M=W, M′=Mo: 8; M=M′=W: 9; M=M′=Mo: 10) are synthesized from the reaction of 3a or 3b with M′(CO)3(EtCN)3 (M′=Mo, W). When Mo(CO)6 is used in place of Mo(CO)3(EtCN)3 10 can also be obtained in addition to [(η5-C5H3Me)C(O)(η5-C5Me4)]Mo2(CO)6 (Mo–Mo) (12) as an unexpected by-product. In complex 12 the cyclopentadienyl ligand is regioselectively methylated in the vicinal position to the bridge-head atom. The synthesis of [(η5(Mo)–C5H4)C(O)(η5(Fe)–C5Me4)]MoFe(CO)5 (Mo–Fe) (14) is achieved by reaction of 3a with Fe(CO)3(C8H14). An X-ray diffraction study of the mononuclear siloxyfulvene Me(CO)3W[η5-C5H4C(OSiMe2t-Bu)(C5Me4)] (2) proves the fulvene-like structure of the uncoordinated tetramethylated cyclo-C5-moiety.