REACTIVITY OF THE LINEAR TETRANUCLEAR RUTHENIUM CLUSTER RU4(CO)10[CH3C=C(H)C(H)=NC(H)(CH3)2]2 TOWARD CO - REGIOSELECTIVE ALIPHATIC C-H ACTIVATION PROCESSES AND THE X-RAY CRYSTAL-STRUCTURE OF RU2(CO)6[CH3CC(H)C(H)N=C(CH3)2]1

The linear tetranuclear cluster RU4(CO)10[CH3C=C(H)C(H)=N-i-Pr]2 (3a) reacts with CO at ambient temperature under exclusion of light to give ultimately Ru4(CO)14[CH3C=C(H)C(H)=N-i-Pr]2 (11a). During this conversion the coordination of the two MAD-yl ligands is changed from the bridging sigma-(N)-sigma(C)-eta-2(C=N):eta-2(C=C) (7e) to the chelating sigma-(N)-sigma-(CO (3e) mode. The compounds RU4(CO)12[CH3C=C(H)C-(H)=N-i-Pr]2 (9a), containing one 7e- and one 3e-donating MAD-yl ligand, and RU4(CO)13[CH3C=C(H)C(H)=N-i-Pr]2 (10a), containing one 5e-donating (sigma-(N)-sigma-(C)-eta-2(C=C) and one 3e-donating MAD-yl ligand, were shown to be intermediates during the formation of 11a. Complete conversion of 3a into 9a takes about 12 h, into 10a about 3 days, and into 11a about 2 weeks. These conversions are reversible; i.e., heating or irradiating a solution of 11a results in the re-formation of 3a. Compound 11a, which has been characterized by IR and H-1 and C-13 NMR Spectroscopy and elemental analysis, is proposed to contain a linear tetraruthenium cluster core in which the metal centers are connected via metal-metal bonds only. Thermolysis of 3a under CO (1 atm, 80-degrees-C, heptane) results in the breakdown of the tetranuclear cluster core with formation of two dinuclear compounds, RU2(CO)6[CH3C=C(H)CH2N-i-Pr] (1a; 40%) and RU2(CO)6[CH2CC(H)C(H)=N-i-Pr] (4a; 40%). Thermolysis of 3a under 11 atm of CO results in the formation of 4a, RU3(CO)12, and CH3C(H)=C(H)C(H)=N-i-Pr. Photolysis of 3a under CO also results in the breakdown of the cluster core, but in this case Ru2(CO)6[CH3CC(H)C(H)N=C(CH3)2] (12a), Ru3(CO)12, and CH3C(H)=C(H)C(H)=N-i-Pr are formed. The X-ray crystal structure of 12a has been determined. Crystals Of C13H11NO6RU2 are triclinic, space group P1BAR, a = 6.799 (2) angstrom, b = 10.098 (2) angstrom, c = 12.676 (3) angstrom, alpha = 84.70 (2)-degrees, beta = 82.91 (2)-degrees, gamma = 74.36 (2)-degrees, Z = 2, R = 0.035, and R(W) = 0.050. Possible mechanisms for the regioselective C-H activation processes, which are based on the hemilability of the MAD-yl ligand and which are dependent on the way 3a is activated, as well as the subsequent intramolecular H migrations and H additions, are discussed.