Bis(iminoxolene)iridium Anion and Alkyls: How Does Ligand Redox Noninnocence Interface with Oxidative Addition?

Abstract

The bis(iminoxolene) complex (Diso)₂IrCl (Diso = N-(2,6-diisopropylphenyl)-4,6-di-tert-butyl-2-imino-o-benzoquinone) is reduced by two equivalents of sodium naphthalenide to give square planar, diamagnetic Na[(Diso)₂Ir]. The anionic iridium center acts as a nucleophile to primary and secondary alkyl and allyl halides to give square pyramidal iridium alkyls. Benzoyl chloride reacts to give an iridium benzoyl complex. Organoiridium complexes are also formed by reaction of (Diso)₂IrCl with Grignard reagents, and treatment with acetone in the presence of base gives the κ¹ carbon-bonded enolate complex (Diso)₂IrCH₂COCH₃. The solid-state structures of the primary alkyls show significant inclinations of the iridium–carbon bond away from the 2-fold axis of the square pyramid, apparently for steric reasons. The relative reactivity of substrates and exclusive formation of (Diso)₂Ir(5-hexenyl) from 6-bromo-1-hexene indicate that primary alkyl halides react by an S_N2 mechanism. Structural data suggest that the oxidative addition is about 70% metal-centered, consistent with nucleophilic behavior that is analogous to that of other square planar group 9 anions.