DIMETHOXYBIPHENYL-2,2'-DIYL)BIS(DIPHENYLPHOSPHINE) (MEO-BIPHEP) AS A 6-ELECTRON DONOR IN [RU(ETA(5)-C8H11)(MEO-BIPHEP)](- COORDINATION OF ABIARYL DOUBLE-BOND, AS SHOWN BY C-13 NMR AND X-RAY CRYSTALLOGRAPHY() CATIONS )

The reaction of the MeO-BIPHEP complex Ru(OAc)(2)(1a) (1a = '-diyl)bis (bis(3,5-di-tert-butylphenyl)phosphine), with HBF4 and 1,5-COD affords [RU(eta(5)-C8H11)(1a)]BF4 (4), in which la functions as a 6e donor to Ru(II) via an unexpected coordination of one of the biaryl double bon ds. The isopropyl analog [RU(eta(5)-C8H11)(1b)]CF3-CO2 (6; 1b = thoxyb iphenyl-2,2'-diyl)bis(diisopropylphosphine)) was prepared by starting from [Ru(CF3CO2)(2)(1,5-COD)](2) and reveals the same eta(4)-bonding m ode. Both complexes were characterized by detailed multidimensional NM R studies, and the X-ray structure for 6 is reported. Although the P-3 1 chemical shifts for this new eta(4)-bonding mode are informative, th e C-13 resonance positions for the coordinated biaryl carbons are a mo re reliable criterion for recognizing this type of interaction. These chemical shift data are difficult to obtain using routine C-13 measure ments, and a long-range C-13,H-1-correlation is recommended as the met hod of choice. Complex 4 exhibits dynamic behavior in solution, as sho wn by 2-D NOESY. This exchange process can be rationalized by assuming that the doubt bond dissociates; however, complex 6 does not show an analogous exchange process at ambient temperature.