Reversible C−H Bond Activation in Coordinatively Unsaturated Molybdenum Aryloxy Complexes, Mo(PMe3)4(OAr)H: Comparison with Their Tungsten Analogs

Mo(PMe 3 ) 6 reacts with ArOH (Ar = C 6 H 2 Me 3, C 6 H 3 Pr i 2 ) to give aryloxy−hydride derivatives Mo(PMe 3 ) 4 (OAr)H in contrast to the cyclometalated derivatives that are obtained for the corresponding tungsten system. Deuterium labeling and magnetization transfer studies, however, demonstrate that the coordinatively unsaturated molybdenum complexes Mo(PMe 3 ) 4 (OAr)H are in fact kinetically capable of intramolecular oxidative addition of a C−H bond to yield cyclometalated derivatives but that the products so obtained are thermodynamically unstable with respect to the aryloxy−hydride derivatives.