CATIONIC HYDROGEN COMPLEXES OF RHENIUM .2. SYNTHESIS, REACTIVITY, ANDCOMPETITION STUDIES

Cationic rhenium dihydrogen complexes, [Re(H-2)(PR3)(2)(CO)(3)]B(Ar')( 4)(PR3=PCy3, PiPr(3), PiPrPh(2), PPh3; Ar'=3,5-((CF3)(2)C6H3), have be en prepared by the protonation of ReX(PR3)(2)(CO)(3) (X=H, CH3) with [ H(Et2O)(2)]B(Ar')(4) under a hydrogen atmosphere. Deuterium is incorpo rated into the H-2 ligand when placed under a D-2 atmosphere and large J(HD) values (30-33 Hz) are consistent with a dihydrogen formulation. Relaxation data indicate very short T-1min for these complexes. These complexes are susceptible to heterolytic cleavage of dihydrogen, and the reactivity with several bases has been investigated. Under vacuum or argon atmosphere the complexes readily lose hydrogen to form 16-ele ctron complexes. In the solid state, [Re(PCy3)(2)(CO)(3)]B(Ar')(4) exh ibits an agostic interaction to a beta C-H bond of the phosphine ligan d. Variable-temperature P-31{H-1} NMR spectra of [Re(PCy3)(2)(CO)(3)]B (Ar')(4) indicate a dynamic process involving hindered rotation about the Re-P bond. Competition studies have been conducted, and the hydrog en binding affinity is higher for [Re(H-2)(PCy3)(2)(CNtBu)(3)]B(Ar')(4 ), (5) than for [Re(H-2)(PCy3)(2)(CO)(3)]B(Ar')(4) (2a). Similar exper iments also find that 5 also binds hydrogen preferentially over W(H-2( PCy3)(2)(CO)(3).