REAPPRAISAL OF THE FLUXIONAL BEHAVIOR OF RU3(MU-H)(MU-3-ETA-2-CCTBU)(CO)9 AND EVIDENCE FOR THE CONCERTED ROTATION OF THE RU(CO)2(PME2PH) GROUP IN THE ENANTIOMERIZATION OF RU3(MU-H)(MU-3-ETA-2-CCTBU)(CO)8(PME2PH)

The fluxional behavior of the alkynyl cluster Ru3(mu-H)(mu(3)-eta(2)-C = CtBu)(CO)9 (1) has been reinvestigated by variable-temperature C-13 NMR spectroscopy and also by 2D EXSY and 1D magnetization transfer experiments. Three processes have been established. The lowest energy process is a tripodal rotation of the unique Ru(CO)3 group, with DELTA-G double-ended-dagger = 59.1 kJ mol-1. Two further higher energy processes result in complete carbonyl scrambling without intermetallic CO migration: (i) the rotation of the alkynyl ligand around the metal triangle coupled with hydride migration, DELTA-G double-ended-dagger = 67.0 kJ mol-1, and (ii) a tripodal rotation in the two equivalent Ru(CO)3 groups, DELTA-G double-ended-dagger = 72.0 kJ mol-1. The derivative Ru3(mu-H)(mu(3)-eta(2)-C = CtBu)(CO)8(PMe2Ph) (2) has been prepared and the fluxional behavior examined. Crystal data for 2: monoclinic, space group P2(1)/n, a = 10.1257 (7) angstrom, b = 21.432 (2) angstrom c = 12.440 (1) angstrom, beta = 90.448 (6)-degrees, V = 2699.6 (4) angstrom 3, R (R(w)) = 0.028 (0.039) for 4189 independent, absorption-corrected data. The PMe2Ph ligand substitutes in an equatorial position on the unique Ru(CO)3 group. Three isomers exist in solution, the major one corresponding to the crystal structure. Exchange within the Ru(CO)2(PMe2Ph) group in this isomer occurs as a concerted rotation, resulting in cluster enantiomerization, with DELTA-H double-ended-dagger = 57.3 kJ mol-1 and DELTA-S double-ended-dagger = 35.0 J mol-1 K-1.