Formation of Eta2-Side-Bonded Aryl Nitrile Complexes from 4-Metallaisoxazolin-5-One Species and Their Application in the Thermal and Photochemical Activation of C-H Bonds

摘要

Coordinatively unsaturated 16-electron metal species are believed to be the active intermediates responsible for the remarkable intermolecular activation of a variety of saturated and aromatic hydrocarbons. The success of these reactions with typically unreactive carbon-hydrogen bonds of hydrocarbons must be attributed to the unique structural and electronic features of these metal-containing moieties that stabilize the intermolecular oxidative addition product with respect to reductive elimination of hydrocarbon from the substituted metal center. As has been pointed out in recent review papers a number of favorable factors are necessary to allow fragments such as '(n5-C5Me5)Ir(PMe3)', '(n5-C5Me5)Ir(CO)', and '(n5-C5H5)Re(PMe3)2' to insert into C-H bonds. These include (i) the strength of the M-C and M-H bonds in the oxidative addition product, (ii) a sterically uncongested metal center that appears to promote intermolecular C-H activation (as opposed to the more common intramolecular cyclometallation), and (iii) suitable acceptor and donar orbitals that can interact with the sigma C-H and sigma C-H orbitals of the alkane. The synthesis of five-membered 4-metallaisoxazolin-5-one metallacycles formed by the 1,3-dipolar cycloaddition of aryl nitrile N-oxides to the M-CO bond of low-valent carbonyl complexes (Scheme IV) have recently been communicated. We have now extended this reaction to include a variety of low-valent metal carbonyl complexes of rhodium and iridium, and a full report detailing the syntheses of these metallacycles will be published shortly. Reprints. (MJM)