SELECTIVE ACTIVATION OF ONE METHYL KETONE ENANTIOFACE VIA SIGMA-BINDING TO A CHIRAL TRANSITION-METAL TEMPLATE - SYNTHESIS, STRUCTURE, AND REACTIVITY OF RHENIUM KETONE COMPLEXES [(ETA-5-C5H5)RE(NO)(PPH3)(ETA-1-O=C(CH3)R)]+X-

Reactions of dichloromethane complex [η6-C5H5)Re(NO)(PPh3)(ClCH2Cl)]+X- (2+X-: X- = BF4-, PF6-) and O=C(CH3)R (R = (a) CH3, (b) CH2CH3, (c) CH(CH3)2, (d) C(CH3)3; (e) C6H5) give ketone complexes [(η5-C5H5)-Re(NO)(PPh3)(η1-0=C(CH3)R)]+X- (3a-e+X-, 79-89%). Crystal structures (3a,e+PF6-) show N-Re-O-C torsion angles of 21-9°, one C-O face to be shielded by the bulky PPh3 ligand, and rhenium cis to CH3. The E/Z methyl groups in 3a+BF4- rapidly exchange (∆C*133K =6 kcal/mol). Both K(sec-C4H9)3BH and formyl complex (η5-C5H5)Re(NO)(PPh3)(CHO) (7) reduce 3a-e+X- to alkoxide complexes (RS, SR)-(η5-C5H5)Re(NO)(PPh3)(OCH(CH3)R) (5) in high yields and 75-99% de. The structure of (RS, SR)-5e is verified crystallographically and is consistent with hydride addition from a direction anti to the PPh3 ligand. Analogous reactions starting with optically active 2+BF4- give optically active ketone and alkoxide complexes with retention of configuration at rhenium. Reactions of (+)-(RS)-5b-e, (+)-(S)-C6H5(CH3O)(F3C)CC(=O)Cl, and 4-(dimcthylamino)pyridine give esters (RS)-C6H5(CH3O)(F3C)CC(==O)OCH(CH3)R (95-99%) in de that closely match those of (+)-(RS)-5b-e. Reactions of (+)-(RS)5c,d and (-)-(S)-C6H5(CH3O)(F3C)CC(=O)OH give alcohols (S)HOCH(R)CH3 and carboxylatc complex (+)-(RS)-(η5-C5H5)Re(NO)(PPh3)(OC(=O)C(CF3)(OCH3)C6H5) (92-93%, ≥99% de). Reaction of (+)-(RS)-5e with HBF4-O(C2H5)2 and then 2-butanone gives 1-phenylethanol (71%) and (+)-(RS)-3b+BF4* (78%, 93% cc). © 1990, American Chemical Society. All rights reserved.