Reactions of benzylrhenium complexes (.eta.5-C5H5)Re(NO)(L)(CH2Ar) with Ph3C+PF6. Analysis of the Re-C.alpha. rotamers involved in .alpha.-hydride abstraction Academic Article uri icon

abstract

  • Sequential reaction of [(η5-C5H5)Re(NO)(PMe3)(CO) +BF4- (4) with CH3ONa, C6H5MgBr, and then BH3·THF gives (η5-C5H5)Re(NO)(PMe3)(CH 2C6H5) (7, 15%). Reaction of [η5-C5H5)Re(NO)(PPh3)(= CH2)]+PF6- with o-CH3C6H4MgBr and mesitylmagnesium bromide gives (η5-C5H5)Re(NO)(PPh3)(LH 2-(2-C6H4CH3)) (8,52%) and (η5-C5H5)Re(NO)(PPh3)(CH 2(2,4,6-C6H2(CH3)3)) (9, 78%), respectively. Reactions of Ph3C+PF6- with 7, 8, and 9 are examined and compared to that of Ph3C+PF6- with (η5-C5H5)Re-(NO)(PPh3)(CH 2C6H5) (1). With 1, the pro-R Hα is abstracted to give sc-[(η5-C5H5)Re(NO)(PPh3)(= CHC6H5)]+PF6- (2k). In contrast, 9 undergoes exclusively pro-S Hα abstraction to give ac-[(η5-C5H5)-Re(NO)(PPh 3)(=CH(2,4,6-C6H2(CH3) 3))]+PF6- (12t). With 8, both the pro-R and pro-S Hα are abstracted to give approximately equal amounts of sc- and ac-[(η5-C5H5)Re(NO)(PPh 3)(=CH(2-C6H4CH3))] +PF6- (11k and 11t). With 7, the pro-S Hα is abstracted to give aC-[(η5-C5H5)Re(NO)(PMe 3)(=CHC6H5)]+PF6- (13t). These data are discussed within the context of the Curtin-Hammett principle. Photolysis of 12t and 13t at -78°C gives ca. 50:50 mixtures of t/k (ac/sc) Re=C isomers, but in the dark at 25°C ≳99:≲1 equilibrium mixtures are reestablished. For 12k → 12t, ΔH‡ = 18.8 ± 0.3 kcal/mol and ΔS‡ = 0.5 ± 1.1 eu. Reaction of 13t with Li(C2H5)3BD gives a (77 ± 1):(23 ± 1) mixture of (η5-C5H5)Re(NO)(PMe3)(CHDC 6H5) diastereomers. © 1984 American Chemical Society.

author list (cited authors)

  • Kiel, W. A., Buhro, W. E., & Gladysz, J. A.

citation count

  • 24

publication date

  • June 1984