Comparative regiochemistry of protonation of (eta(6)-C6H5R)(1,1 ',1 ''-tris(2-diphenylphosphinomethyl)ethane)Mo(0) (R = H, Me and SiMe3)

Our previous mechanistic studies of 1 (R = H) demonstrate it is protonated to give a metal-hydride via a mechanism that involves indirect exo attack o n the arene ligand followed by endo proton transfer to the metal. The tolue ne derivative 1 (R = Me) reacts via a similar mechanism with unusual ortho/ meta/para = 61:36:3% selectivity. In contrast, the first equivalent of prot on hydrolyzes the TMS group of 1 (R = SiMe3) under surprisingly mild condit ions and the second equivalent reacts with the product 1 (R = H) to give th e metal-hydride via the aforementioned indirect mechanism. (C) 2001 Elsevie r Science B.V. All rights reserved.