The syntheses and structures of coordinatively unsaturated aryloxy-hydride complexes of molybdenum, Mo(PMe3)4(OAr)H: reversible CH bond activation and comparison with their tungsten analogues

Abstract Mo(PMe 3 ) 6 reacts with ArOH (Ar=2,4,6-C 6 H 2 Me 3 , 2,6-C 6 H 3 Pr i 2 ) to give coordinatively unsaturated aryloxy-hydride derivatives Mo(PMe 3 ) 4 (OAr)H. The formation of Mo(PMe 3 ) 4 (OAr)H is in marked contrast to the cyclometalated products of CH bond activation 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 of the ortho substituents to yield cyclometalated derivatives that are thermodynamically unstable with respect to the aryloxy-hydride derivatives.