Ligating similarities between the novel five-electron-donor eta(4)-P3C2Bu2t(R)H ring system (R = CH(SiMe3)(2)) and the eta(5)-cyclopentadienyl ring. Syntheses, crystal and molecular structures of [Co-2(CO)(5)(mu-(P3C2Bu2CH)-C-t(SiMe3)(2))] and [Co(CO)(2)(eta(4)-(P3C2Bu2H)-H-t(CH(SiMe3)(2)]

Treatment of the 1,2,4-triphosphole, P3C2Bu2t(CH(SiMe3)(2)), with [Co-2(CO) (8)] in THF under mild conditions affords the binuclear complex [Co-2(CO)(5 )(mu-(P3C2Bu2CH)-C-t(SiMe3)(2)], in which the ring acts as a six-electron d onor. Under slightly more vigorous reaction conditions an H-transfer reacti on occurs (presumably from the solvent) to afford the mononuclear compound [Co(CO)(2)((P3C2Bu2H)-H-t(CH(SiMe3)(2)] containing an eta(4)-ligated five-e lectron-donor (P3C2Bu2H)-H-t(CH(SiMe3)(2) ring system. The molecular struct ures of both compounds have been determined by single-crystal X-ray diffrac tion studies. (C) 2000 Elsevier Science S.A. All rights reserved.