Synthesis, structure, and reactions of chiral rhenium vinylidene and acetylide complexes of the formula [(.eta.5-C5H5)Re(NO)(PPh3)(X)]n+. Vinylidene complexes that are formed by stereospecific C.beta. electrophilic attack, exist as two Re=C=C geometric isomers, and undergo stereospecific C.alpha. nucleophilic attack.
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Sequential reactions of acyl complexes ( 5 -C 5 H 5 )Re(NO)(PPh 3 )(COCH 2 R) (2: R = H (a), CH 3 (b), C 6 H 5 (c), 1-naphthyl (d)) with (CF 3 SO 2 ) 2 O (0.5 equiv), base (1.0 equiv), and (CF 3 SO 2 ) 2 O (0.5 equiv) give vinylidene complexes [( 5 -C 5 H 5 )Re(N0)(PPh3)(=C=CHR)] + CF 3 SO 3- (3a-d CF 3 SO 3- , 63-95%). Complexes 3b-dCF 3 SO 3- crystallize as (95 2):(5 2), >99:1, and >99:1 mixtures of sc/ac Re=C==C geometric isomers but equilibrate to (50 2):(50 2), (80 2):(20 2) and (80 2):(20 2) mixtures in CD 2 C1 2 . Photolysis gives (50 2):(50 2) photostationary states. An X-ray crystal structure of sc-3dPF 6- (Re=C 1.840 (17) ) shows a P-Re-C -C Np torsion angle of 161.5, placing the naphthyl substituent anti to the bulky PPh 3 ligand. Reactions of 3a-dCF 3 SO 3- with base give acetylide complexes ( 5 -C 5 H 5 )Re-(NO)(PPh 3 )(CCR) (6a-d, 59-93%). Reactions of 6b-d with CF 3 SO 3 H (-78 C, assayed by NMR) give (98 2):(2 2), >99:1, and >99:1 mixtures of ac- and sc-3b-dCF 3 SO 3- . Analogous C methylation reactions (6b-c) are similarly stereospecific. This high 1, 3-asymmetric induction is ascribed to electrophilic attack upon C of 6b-d from a direction opposite to the PPh 3 ligand, giving the less stable Re=C=C isomer with the C substituent syn to the PPh 3 ligand. Rates of ac-3b-dCF 3 SO 3- sc-3b-dCF 3 SO 3- isomerization give H* = 20.8, 16.9, 18.6 kcal/mol and S* = -5.7, -15.5, -10.5 eu. A crystal structure of 6b (Re-C a 2.066 (7) ) shows the ReCCCH 3 linkage to be essentially linear. Reactions of ac- and sc-3bCF 3 SO 3- with P(CH 3 ) 3 give (Z)- and (E)-[( 5 -C 5 H5)Re(NO)(PPh 3 )(C(P(CH 3 ) 3 )=CHCH 3 )] + CF 3 SO 3- , respectively, indicating preferential attack upon the C face opposite to PPh 3 . 1988, American Chemical Society. All rights reserved.
