FLUXIONAL BEHAVIOR OF THE SIGMA,PI-VINYL COMPLEXES OS2(MU-CH=C(H)PH)(MU-BR)(CO)6-N(PPH3)N (N = 1, 2) - USE OF C-13(H-1) NOE AND OS-187-C-13COUPLINGS IN ASSIGNMENT OF CARBONYLS

The fluxional behavior of the complexes Os2{mu-CH=C(H)Ph}(A-Br)(CO)6-n (PPh3)n (1, n = 1; 2, n = 2) has been examined quantitatively by C-13 and P-31 1D magnetization transfer and 2D EXSY measurements. Complex 1 , which exists in solution as the two isomers la and lb, shows three i ndependent exchange processes at 273 K: tripodal rotations of the Os(C O)3 groups in the major isomer 1a (k = 5.18 s-1) and minor isomer 1b ( k = 0.25 s-1) and a sigma,pi-vinyl flip leading to the interconversion of la and lb (k = 2.37 s-1). Complex 2 in solution shows a single exc hange process, a sigma,pi-vinyl flip with k = 0.53 s-1 at 265 K. Cryst al data for 2: monoclinic, space group P2(1)/c, a = 14.256(1) angstrom , b = 11.650(1) angstrom, c = 25.841(2) angstrom, beta = 90.243(5)-deg rees, V = 4291.9(5) angstrom3, R (R(w)) = 0.030 (0.032) for 6231 indep endent absorption-corrected data to theta = 26-degrees. Couplings to O s-187 were observed for both complexes, and these were used in conjunc tion with C-13{H-1} and C-13 DQF-COSY experiments to provide unambiguo us assignments of all carbonyl resonances.