Evidence for the ready insertion of rhodium into a carbon–hydrogen bond of ethylene; crystal and molecular structure of µ-but-2-ene-µ-ethylene-bis-(η 5 -1-methylindenyl)dirhodium

But-2-yne reacts with [Rh(C2H4)2(η5-C9H7)] or [Rh(C2H4)2(η5-1-MeC9H6)] to give respectively [Rh2(CHCH2)(CMeCHMe)(η5-C9H7)2], [Rh2(C4Me4)(η5-C9H7)2], [Rh2(CHCH2)(CMeCHMe)(η5-1-MeC9H6)], and [Rh2-(C4Me4)(η5-1-MeC9H6)2] the structure of the 1-methyl analogue of the divinyl complex being established by X-ray crystallography; treatment of the dirhodium divinyl complex with carbon monoxide affords [Rh(CO)2(η5-C9H7)] and the ketone CH2CH·COC(Me)C(H)Me.