Breaking Chemistry's Strongest Bond:Can Three-Coordinate[M{N(R)Ar}3]Complexes Cleave Carbon Monoxide?

摘要

The reaction pathway for the interaction of CO with three-coordi nate Ta~(III),W~(III)and Re~(III)complexes(modelled on the experimental[M{N-(tBu)Ar}3]system)has been explored by using density functional methods.Calculations show that CO binds with out a barrier to[Re(NH2)3],forming the encounter complex[OC-Re-(NH2)3],which is stabilized by approx=280 kJ mol-1 relative to the reactants.The binding of[Ta(NH2)3]to the oxygen terminus of CO is inhibited by a barrier of only 20 kJ mol-1 and is fol lowed by spontaneous cleavage of the C-O bond to form the products[C-Re(NH2)3]and[O-Ta(NH2)3].The sa lient features of the potential energy surface are more favourable to CO cleavage than the analogous N2 cleav age by[Mo(NH2)3],which is less exo thermic(335 vs.467 kJ mol-1)and is impeded by a significant barrier(66 kJ mol-1).The Re~(III)/Ta~(III)/CO system therefore appears to be an excellent candidate for cleaving the exceptional ly strong C-O bond under mild labora tory conditions.The related W~(III)/Ta~(III)dimer,which significantly weakens but does not cleave the CO bond,may be a suitable alternative when the chemistry is to be performed on activated CO rather than on the strongly bound oxide and carbide cleavage products.