REACTIONS OF THE NEOHEXYL IODIDE COMPLEX [(ETA-5-C5H5)RE(NO)(PPH3)(ICH2CH2C(CH3)3)]+BF4- AND NUCLEOPHILES - STEREOCHEMISTRY OF CARBON-IODINE BOND-CLEAVAGE IN HIGHLY ACCELERATED SN2 REACTIONS

Reaction of (eta-5-C5H5)Re(NO)(PPh3)(CH3), ICH2CH2C(CH3)3 (2), and HBF4.OEt2 in C6H5Cl gives neohexyl iodide complex [(eta-5-C5H5)Re(NO)(PPh3)(ICH2CH2C(CH3)3)]+BF4- (3, 81%). Complex 3 and PPh3 react (-40-degrees-C, CD2Cl2) to give [Ph3PCH2CH2C(CH3)3]+BF4- (7) and (eta-5-C5H5)Re(NO)(PPh3)(I) (6) in > 99% spectroscopic yields. Complex 3 and [Ph3P-N-PPh3]+Br- (PPN+Br-) react (-40-degrees-C, CD2Cl2) to give BrCH2CH2C(CH3)3 (8) and 6 in 97-99% spectroscopic yields. Deuterated neohexyl halides erythro-ICHDCHDC(CH3)3 (erythro-2-d2), threo-2-d2, erythro-8-d2, and threo-8-d2 are prepared via (eta-5-C5H5)2Zr(Cl)(X) compounds. The labeled complexes erythro-3-d2 and threo-3-d2 are synthesized, and analogous reactions with PPN+Br- and PPh3 are conducted. Diastereomer ratios of the products 8-d2 and 7-d2, and all preceding deuterated compounds, are analyzed by 500-MHz H-1{H-2} NMR spectroscopy. In all cases, the carbon-iodine bond in 3-d2 is cleaved with essentially complete inversion of configuration at carbon.