Experimental and Computational Studies on the Iridium Activation of Aliphatic and Aromatic C-H Bonds of Alkyl Aryl Ethers and Related Molecules

Abstract

Reaction of the IrIII complex [(TpMe2)Ir(C6H5)2(N2)] (1⋅N2) with ortho-cresol (2-methylphenol) occurs with cleavage of the O-H and two C(sp3)-H bonds of the phenol and formation of the electrophilic hydride alkylidene derivative [(TpMe2)Ir(H){=C(H)C6H4-o-O}] (2). The analogous reaction of 2-ethylphenol gives a related product 3. Both 2 and 3 have been shown to be identical to the minor, unidentified products of the already reported reactions of 1 with anisole and phenetole, respectively. Thus, in addition to the route that leads to the known heteroatom-stabilized hydride carbene [(TpMe2)Ir(H){=C(H)OC6H4- o-}] (B), anisole can react with 1 with cleavage of the O=CH3 bond and formation of a new carbon–carbon bond. In contrast, only C-H bond-activation products with structures akin to B result from 1⋅N2 and 3,5-dimethylanisole (complex 8) or 4-fluoroanisole (9). Using anisole as a model, a computational study of the triple C-H bond activation (two aliphatic C-H bonds plus an ortho-metalation reaction) that is responsible for the formation of these heteroatom-stabilized hydride carbenes has been undertaken.