Ligating similarities between the novel five-electron-donor η4-P3C2But2(R)H ring system, (R=CH(SiMe3)2) and the η5-cyclopentadienyl ring. Syntheses, crystal and molecular structures of [Co2(CO)5(μ-P3C2But2CH(SiMe3)2)] and [Co(CO)2(η4-P3C2But2H(CH(SiMe3)2]

Treatment of the 1,2,4-triphosphole, P3C2But2(CH(SiMe3)2), with [Co2(CO)8] in THF under mild conditions affords the binuclear complex [Co2(CO)5(μ-P3C2But2CH(SiMe3)2)], in which the ring acts as a six-electron-donor. Under slightly more vigorous reaction conditions an H-transfer reaction occurs (presumably from the solvent) to afford the mononuclear compound [Co(CO)2(P3C2But2H(CH(SiMe3)2)] containing an η4-ligated five-electron-donor P3C2But2H(CH(SiMe3)2 ring system. The molecular structures of both compounds have been determined by single-crystal X-ray diffraction studies.