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

Reaction of the Ir-III complex [(Tp(Me2))Ir(C6H5)(2)(N-2)] (1 center dot N-2) with ortho-cresol (2-methylphenol) occurs with cleavage of the O-H and two C-(sp(3))-H bonds of the phenol and formation of the electrophilic hydride alkylidene derivative [(Tp(Me2))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 [(Tp(Me2))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 center dot N-2 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.