Electrophile-Induced Cyclizations of Chiral Rhenium Ethynyl and C2Li Complexes of the Formula (.eta.5-C5Me5)Re(NO)(PPh3)(C.tplbond.CX): Synthesis, Structure, and Reactivity of Unusual 1,3-Dimetalated Cyclic C4H3 and C4H4 Species
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Reactions of (η5-C5Me5)Re(NO)(PPh3)(C≡CH) (1) or (η5-C5Me5)Re(NO)(PPh3)(C≡CLi) (2) and ZnCl2 (≥1.2 equiv) give the meso dirhenium complex (4). Samples contain up to 10% of the corresponding dl diastereomer (total yield 94—38%). Mechanisms involving adventitious water and initial electrophilic attack upon Cβ of 1 are proposed. Accordingly, addition of 0.5 equiv of HBF4·OEt2 to 1 (CH2Cl2, 25 °C) gives the analogous dirhenium tetrafluoroborate salt 5 (85%). However, addition of 1 to 2.0 equiv of HBF4·OEt2(THF, -80 °C) gives the vinylidene complex [(η5-C5Me5)Re(NO)(PPh3)(=C=CH2)]+BF4-(6; 86%). Reaction of 1 and 6 (CH2Cl2)25 °C) also gives 5 (94%). The crystal structure of 4 shows rhenium—carbon bonds of 2.00(1)—2.03(1) Å, intermediate between single and double bonds and consistent with a delocalized structure based upon Re—C=CHC(CH2)=Re+ resonance forms. NMR data establish 12.1-12.6 kcal/mol rotational barriers. Reaction of 5 and HBF4·OEt2 gives the cyclobuta-1,3-diylidene complex (SR,RS)-[(η5-C5Me5)Re(NO)(PPh3)=CCH2C(CH2)=)-(Ph3P)(ON)Re(η5-C5Me5)]2+(BF4-)2 (8) in quantitative NMR yields. Upon all workups attempted, 8 reverts to 5. © 1995, American Chemical Society. All rights reserved.
author list (cited authors)
Weng, W., Bartik, T., Johnson, M. T., Arif, A. M., & Gladysz, J. A.