Synthesis and Reactivity of Cobalt(I) and Iridium(I) Complexes Bearing a Pentadentate N-Homoallyl-Substituted Bis(NHC) Pincer Ligand

Two methods for the synthesis of the bis(imidazolin-2-ylidene)carbazolide cobalt(I) complex [Co-(bimca(Homo))] (2) have been developed. The first route relies on the direct transmetalation of the in situ generated lithium complex [Li(bimca(Homo))] with CoCl(PPh3)(3). The second route is a two-step synthesis that consists of the transmetalation of [Li(bimca(Homo))] with CoCl2 followed by reduction of the Co(II) complex to yield the desired Co(I) complex 2. The analogous iridium complex [Ir(bimca(Homo))] (4) was prepared by transmetalation of [Li(bimca(Homo))] or [K(bimca(Homo))] with [Ir(mu-Cl)(COD)](2). The catalytic activity of complexes 2 and 4 in the epoxide isomerization was tested in the absence and presence of H-2. When [M(bimca(Homo))] (M = Ir (4), Rh (3)) was exposed to 1 bar of H-2 at 80 degrees C, single crystals formed whose X-ray structure analyses revealed the hydrogenation of the N-homoallyl moieties and formation of the dimeric hydrido complexes [Ir(bimca(n-Bu))(H)(2)](2) (7) and [Rh(bimca(n-Bu))(H)(2)](2) (8).