ELECTROPHILE-INDUCED CYCLIZATIONS OF CHIRAL RHENIUM ETHYNYL AND C2LI COMPLEXES OF THE FORMULA (ETA(5)-C(5)ME(5))RE(NO)(PPH(3))(C-CX) - SYNTHESIS, STRUCTURE, AND REACTIVITY OF UNUSUAL 1,3-DIMETALLATED CYCLIC C4H3 AND C4H(4) SPECIES
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Reactions of (5-C5Me5)Re(NO)(PPh3)(CCH) (1) or (5-C5Me5)Re(NO)(PPh3)(CCLi) (2) and ZnCl2 (1.2 equiv) give the meso dirhenium complex (4). Samples contain up to 10% of the corresponding dl diastereomer (total yield 9438%). Mechanisms involving adventitious water and initial electrophilic attack upon C of 1 are proposed. Accordingly, addition of 0.5 equiv of HBF4OEt2 to 1 (CH2Cl2, 25 C) gives the analogous dirhenium tetrafluoroborate salt 5 (85%). However, addition of 1 to 2.0 equiv of HBF4OEt2(THF, -80 C) gives the vinylidene complex [(5-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 rheniumcarbon bonds of 2.00(1)2.03(1) , intermediate between single and double bonds and consistent with a delocalized structure based upon ReC=CHC(CH2)=Re+ resonance forms. NMR data establish 12.1-12.6 kcal/mol rotational barriers. Reaction of 5 and HBF4OEt2 gives the cyclobuta-1,3-diylidene complex (SR,RS)-[(5-C5Me5)Re(NO)(PPh3)=CCH2C(CH2)=)-(Ph3P)(ON)Re(5-C5Me5)]2+(BF4-)2 (8) in quantitative NMR yields. Upon all workups attempted, 8 reverts to 5. 1995, American Chemical Society. All rights reserved.
