Hydroboration of metal-carbon triple bonds

Hydroboration reactions of Fischer carbyne metal complexes [M(=CR)X(CO)(2)] (X = eta-C5R5 or tpb'; tpb' = tris(3,5-dimethylpyrazolyl)hydroborate) were studied. Depending on R and X two types of hydroboration products were for med, namely the alpha-boryl-eta(3)-benzyl metal complexes [M(C5R5)(CO)(2){( BEt2)C(H)(C6H4Me-4)}] (M = W, R-5 = MMe4Et; M = Mo, R = Me) and the novel b orylmetal complexes [M(tpb')(CO)(2){eta(2)-B(R')CH2R}] (M = W, R' = Et, R = C6H4Me-4 or Me; M = Mo, R' = Et, R = C6H4Me-4; M = W, R' = Ph, R = C6H4Me- 4 or Me). beta-Agostic CHM interactions are present between the metal and t he boryl ligands. Labelling experiments involving "DBEt2" showed selective transfer of deuterium to the former carbyne carbon, with only deuterium par ticipating in the agostic interaction. From [W(=CR)(C5Me5)(CO)(2)] 2 (R = M e or SiPh3) and "HBEt2" the complex trans-[W(C5Me5)(CO)(2)(H)(C2H4)] was ob tained as the sole organometallic compound. Deuterium labelling experiments confirmed transfer of hydrogen from the borane to the carbyne complex. In polar solvents, [W(eta-C5Me5)(CO)(2){(BEt2)C(H)C6H4Me-4}] and the eta-C5Me4 Et analogues were at least partially (30-100%) converted into [W(eta-C5R5') (CO)(2)(H)(C2H4)] (R' = Me, R-5' = Me4Et) and unknown boron containing prod ucts. From an acetone solution of the alpha-borylbenzyl eta-C5Me4Et complex crystals of a new product were isolated. Its unusual structure results fro m disruption of the boryl group, incorporation of two molecules of acetone to give a 1,3-dioxa-2-boracyclohexane ring system, conversion of the benzyl ligand into an eta(4)-2-methyl-5-exo-methylenehexa-1,3-diene ligand and th e formation of an acetyl group on the tungsten.