Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

Preparation of the dimeric starting compound [(C5H2tBu3-1,2,4)­Fe­(μ-Br)]2 (1) gave a small amount of its green sodium bromide adduct [(C5H2tBu3-1,2,4)­Fe­(μ-Br)2Na­(DME)2] (2). Reduction of 1 under argon in the presence of diphenylacetylene yielded dark red [(C5H2tBu3-1,2,4)­Fe­(μ-CPh)]2 (3) containing two bridging benzylidyne ligands resulting from diphenylacetylene scission. The dicobalt methylidyne complex [{(C5HiPr4)­Co}2(μ-CH)­(μ-H)] (5) was obtained in high yield from the reaction of [(C5HiPr4)­Co­(μ-Cl)]2 (4) with two equivalents of methylmagnesium chloride. According to DFT calculations the dinuclear alkylidyne complexes 3 and 5 contain d6 metal centers, namely, iron­(II) (3) and cobalt­(III) (5). Whereas the benzylidyne ligands of the iron complex 3 display an empty orbital of pz character at the bridging carbon atom, the pz orbital of the methylidyne carbon in the dicobalt complex 5 is filled with a lone pair of electrons.