STRUCTURE AND REACTIVITY OF RUTHENIUM HALF-SANDWICH COMPOUNDS - CRYSTAL AND MOLECULAR-STRUCTURE AND ACETONITRILE EXCHANGE KINETICS AND MECHANISM OF RU(ETA-6-C6H6)(CH3CN)3(2+) AND RU(ETA-5-C5H5)(CH3CN)3+

[Ru(eta-6-C6H6)(CH3CN)3](PF6)2 crystallizes in the monoclinic space group P2(1)/c with a = 11.087 (3) angstrom, b = 12.779 (6) angstrom, c = 14.238 (10) angstrom, beta = 100.44 (4)degrees (125 K), and Z = 4. The structure was refined to R = 0.022 for 3635 reflections with I(o) > 3-sigma(I(o)). Average distances, corrected for thermal motion, are Ru-N = 2.059 (4) angstrom, Ru-C = 2.188 (2) angstrom, (C-C)ring = 1.408 (4) angstrom, N-C = 1.133 (3) angstrom, (C-C)an (an = acetonitrile) = 1.453 (1) angstrom, and Ru-center of ring = 1.675 angstrom. The torsional angle describing the relative arrangement of the benzene ring and the acetonitrile ligands is 12.2-degrees. [Ru(eta-5-C5H5)(CH3CN)3]BF4.0.5CH3CN crystallizes in the monoclinic space group I2/a with a = 23.684 (6) angstrom, b = 6.913 (2) angstrom, c = 21.550 (3) angstrom, beta = 111.84 (1)degrees (296 K), and Z = 8. The structure was refined to R = 0.022 for 2226 reflections with I(o) > 3-sigma(I(o)). After correction for thermal motion average distances are Ru-N = 2.090 (1) angstrom, Ru-C = 2.141 (2) angstrom, (C-C)ring = 1.396 (7) angstrom, N-C = 1.135 (3) angstrom, (C-C)an = 1.450 (4) angstrom, and Ru-center of ring = 1.781 angstrom. Acetonitrile exchange rates at variable temperature and pressure were determined by H-1 NMR spectroscopy. For Ru(eta-6-C6H6)(CH3CN)3(2+) the results are k(298 K) = 4.07 x 10(-5) s-1, DELTA-H* = 102.5 kJ mol-1, DELTA-S* = 15.0 J K-1 mol-1, and DELTA-V* = 2.4 cm3 mol-1; for Ru(eta-5-C5H5)(CH3CN)3+k(298 K) = 5.6 s-1, DELTA-H* = 86.5 kJ mol-1, DELTA-S* = 59.6 J K-1 mol-1, and DELTA-V* = 11.1 cm3 mol-1. For the benzene compound an interchange mechanism (I) applies whereas for the C5H5-species a dissociative pathway (D) is followed. The correlation between structural properties and kinetic behavior is discussed in terms of a simple bonding model.