CHIRAL TUNGSTEN(II) ETA(1)-KETONE AND ETA(1)-ALDEHYDE COMPLEXES

The neutral complex Tp'(CO)(PhC drop CMe)WI(Tp' = hydridotris(3,5-dimethylpyrazolyl)berate) reacts with lithium dimethylcuprate to effect net replacement of the iodide ligand by a methyl group. The resulting methyl complex Tp'(CO)(PhC drop CMe)WMe (1) can be protonated in the presence of ketones (acetone, 2-butanone, acetophenone, and 3,3-dimethyl-2-butanone) or aldehydes (benzaldehyde and trimethylacetaldehyde) to afford cationic eta(1)-ketone or eta(1)-aldehyde complexes [Tp'(CO)(PhC drop CMe)W(eta(1)-O double bond CRR')](+) (2a-d and 3a,b). These complexes exist as a mixture of E and Z isomers about the C double bond O bond, as judged by variable temperature NMR studies. Barriers for isomer interconversion range from 11 to 15 kcal/mol. Addition of hydride to complexes 2a-c and 3a,b with K[HB(sec-Bu(3))] as the hydride-transfer reagent yields neutral alkoxide complexes of the type Tp'(CO)(PhC drop CMe)WOCHRR'. Hydride transfer from K[HB(sec-Bu(3))] to the 2-butanone complex 2b gives a 3:2 mixture of metal alkoxide diastereomers Tp'(Co)(PhC drop CMe)WOCHMeEt (5b), while the acetophenone complex 2c gives an 1 1:2 mixture of metal alkoxides Tp'(CO)(PhC drop CMe)WOCHMePh (5c). Regeneration of cationic ketone or aldehyde complexes can be achieved by addition of 2 equiv of acid to the alkoxide complexes in the presence of the appropriate ketone or aldehyde. An X-ray structure of one tungsten alkoxide species, Tp'(CO)(PhC drop CMe)WOCH(2)(t)Bu (6b) (space group P2(1)/c, a = 16.261(5) Angstrom, b = 17.044(5) Angstrom, c = 12.673(4) Angstrom, Z = 4, R = 0.037, R(W) = 0.044), is reported.