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(bimcaHomo)] (2) have been developed. The first route relies on the direct transmetalation of the in situ generated lithium complex [Li­(bimcaHomo)] with CoCl­(PPh3)3. The second route is a two-step synthesis that consists of the transmetalation of [Li­(bimcaHomo)] with CoCl2 followed by reduction of the Co­(II) complex to yield the desired Co­(I) complex 2. The analogous iridium complex [Ir­(bimcaHomo)] (4) was prepared by transmetalation of [Li­(bimcaHomo)] or [K­(bimcaHomo)] with [Ir­(μ-Cl)­(COD)]2. The catalytic activity of complexes 2 and 4 in the epoxide isomerization was tested in the absence and presence of H2. When [M­(bimcaHomo)] (M = Ir (4), Rh (3)) was exposed to 1 bar of H2 at 80 °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(bimcan‑Bu)­(H)2]2 (7) and [Rh­(bimcan‑Bu)­(H)2]2 (8).