STEREOSELECTIVE AND REGIOSELECTIVE MULTIPLE ADDITIONS TO COMPLEX-BOUND CYCLOOCTATETRAENE IN [CPFE(ETA-6-COT)]+
BEURSKENS PT, BOSMAN WP, BRUSSAARD HC, HECK J, GEBBINK RJM, MATERS M, SMITS JMM
JOURNAL OF ORGANOMETALLIC CHEMISTRY 469 (2): 197-203 MAY 2 1994

Abstract:
The cationic complex [CpFe(eta6-Cot)]+ (Cot = cyclooctatetraene) 1 has been shown to be very suitable for high yield nucleophilic additions. The nucleophiles Nu - (Nu = HC(CO2Me)2, 2a; HC(CO, Et)2, 2b; NMe 2, 2c; H, 2d) add exclusively at the Cot ring, and stereoselectively in exo position with respect to the metal centre. Subsequently, the electrophilic addition of H+ to the neutral compound CpFe(2-6-eta-C8H8-1-exo-Nu) generates the new cationic product [CpFe(2-7-eta-C8H9-l-exo-Nu)]+ (4), which can add a second nucleophile revealing an exo, exo-1,7-disubstituted cyclooctadienyl ligand. The X-ray structure analysis of the methyl malonate compound 2a (space group P2(1)/c, a = 19.083(l) angstrom, b = 7.9169(5) angstrom, c = 11.278(2) angstrom, beta = 106.77(1)-degrees, R(merge) = 0.062) shows the eta2-6 coordination mode of the cyclo-C8-ligand, the exo-position of the Nu-substituent, and the endo-position of the hydrogen atom at the sp3 carbon atom of the C8-ring confirmed by residual electron density. The cyclo-C8-ring is bent, and the angle between the two best planes, which are defined by C-7, C-8, C-1 and C-2-C-6, amounts to 122.7-degrees.