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

Reactions of (eta(5)-C(5)Me(5))Re(NO)(PPh(3))(C drop CH) (1) or (eta(5 )-C(5)Me(5))Re(NO)(PPh(3))(C drop CLi) (2) and ZnCl2(greater than or e qual to 1.2 equiv) give the meso dirhenium complex SR,RS)-[(eta(5)-C(5 )Me(5))Re(NO)(PPh(3))-(<radical anion>C<radical anion>CH<radical anion >C(CH2)<radcial )P)(ON)Re(eta(5)-C(5)Me(5))](+)([Zn2Cl6](2-))(1/2) (4) ). Samples contain up to 10% of the corresponding dl diastereomer (tot al yield 94-38%). Mechanisms involving adventitious water and initial electrophilic attack upon C-beta of 1 are proposed. Accordingly, addit ion of 0.5 equiv of HBF4.OEt(2) to 1 (CH2Cl2, 25 degrees C) gives the analogous dirhenium tetrafluoroborate salt 5 (85%). However, addition of 1 to 2.0 equiv of HBF4.OEt(2) (THF, -80 degrees C) gives the vinyli dene complex eta(5)-C(5)Me(5))Re(NO)(PPh(3))(=C=CH2)](BF4)-B-+- (BF4-( 6;86%). Reaction of 1 and 6 (CH2Cl2, 25 degrees C) also gives 5 (94%). The crystal structure of 4 shows rhenium-carbon bonds of 2.00(1)-2.03 (1) Angstrom, intermediate between single and double bonds and consist ent with a delocalized structure based upon Re-C=CHC(CH2)=Re+ resonanc e forms. NMR data establish 12.1-12.6 kcal/mol Re rotational barriers. Reaction of 5 and HBF4.OEt(2) gives the cyclobuta-1,3-diylidene compl ex (SR,RS)-[(eta(5)-C(5)Me(5))Re(NO)(PPh(3))(=CCH2C (Ph(3)P)(ON)Re(eta (5)-C(5)Me(5))]2(+)(BF4-)(2) (8) in quantitative NMR yields. Upon all workups attempted, 8 reverts to 5.