Rhodium(I) Complexes of the Conformationally Rigid IBioxMe4 Ligand: Preparation of Mono‑, Bis‑, and Tris-ligated NHC Complexes

The preparation and characterization of a series of mono-, bis-, and tris-ligated rhodium­(I) complexes of Glorius’ conformationally rigid bioxazoline-derived N-heterocyclic carbene ligand IBioxMe4 are described. Through reaction of [Rh­(COE)2Cl]2 (COE = cis-cyclooctene) with isolated IBioxMe4, [Rh­(IBioxMe4)­(COE)­Cl]2 (1), trans-[Rh­(IBioxMe4)2(COE)­Cl] (2), and [Rh­(IBioxMe4)3Cl] (3) were each isolated by careful choice of the reaction conditions. Further substitution and salt metathesis reactions of 1–3 were investigated, and derivatives containing CO, norbornadiene, and cyclopentadienyl ancillary ligands were readily isolated. Notably, halide abstraction from 2 and 3 using Na­[BArF4] (ArF = 3,5-C6H3(CF3)2) resulted in the formation of low-coordinate T-shaped cis-[Rh­(IBioxMe4)2(COE)]­[BArF4] (9) and [Rh­(IBioxMe4)3]­[BArF4] (11). The solid-state structures of 2, 9, and 11 each feature IBioxMe4 ligands that bind unusually with tilted coordination geometries.