X-RAY STRUCTURE, EXAFS STUDIES, AND FLUXIONAL BEHAVIOR OF RU3PT(MU-H)(MU(3)-COME)(CO)(10)(PR(3))

Reaction of Pt(PR(3))(nb)(2) (R = Cy or Pr-i; nb = bicyclo[2.2.1]hept- 2-ene) with 1 mole equiv of Ru-3(mu-H)(mu-COMe)(CO)(10) (1) affords th e title cluster Ru3Pt(mu(3)-H)(mu(3)-COMe)(CO)(10)(PR(3)) (2a, R = Cy; 2b, R = Pr-i) in similar to 50% yield. Crystal data for (2a): monocli nic, space group P2(1)/c, a = 19.1198(8) Angstrom, b = 10.0226(7) Angs trom, c = 19.8234(12) Angstrom, beta = 107.978(4)degrees, V = 3613.3(4 ) Angstrom(3), R(R(w) = 0.028 (0.032) for 4897 independent, observed [ I > 2.5 sigma(I)] absorption corrected data. The metal framework consi sts of an essentially regular tetrahedron, with Pt-Ru = 2.760(1)-2.903 (1) Angstrom, and Ru-Ru = 2.754(1)-2.972(1) Angstrom. The methoxymethy lidyne ligand asymmetrically bridges the Ru-3 face, with Ru-C = 1.973( 6)-2.597(6) Angstrom. Pt(L(III))-edge and Ru K-edge EXAFS spectra on 2 a indicate that a similar structure is maintained in tetrahydrofuran s olution. Two fluxional processes involving CO exchange are observed fo r 2b by variable-temperature NMR spectroscopy. The lowest energy proce ss results in complete equilibration of all Ru-bound CO ligands, and i t is rapid at all accessible temperatures. A second, higher energy pro cess results in complete CO scrambling.