SYNTHESIS, EXTENDED HUCKEL MOLECULAR-ORBITAL CALCULATIONS, AND X-RAY-DIFFRACTION STRUCTURE OF THE PENTAMETHYLCYCLOPENTADIENYLRUTHENIUM COMPLEX CP-ASTERISK-RU(NO)(2,3-QUINOXALINEDIOLATE)

The reaction between Cp*Ru(NO)Cl-2 and the heterocyclic compound 2,3-quinoxalinediol in the presence of methanolic KOH leads to the formation of the new piano-stool compound Cp*Ru(NO)(2,3-quinoxalinediolate) (1). Product isolation and characterization by solution spectroscopic methods (H-1 and C-13 NMR and IR) are described. The solid-state structure of Cp*Ru(NO)(2,3-quinoxalinediolate) confirms the replacement of each chloride ligand in Cp*Ru(NO)Cl-2 by an oxygen group of the 2,3-quinoxalinediol ligand. Cp*Ru(NO)(2,3-quinoxalinediolate) crystallizes in the orthorhombic space group Pbca, a = 14.846(1) Angstrom, b = 12.718(1) Angstrom, c = 18.255(2) Angstrom, V = 3446.7(5) Angstrom(3), Z = 8, d(calc) = 1.643 g . cm(-3); R = 0.0364, R(w) = 0.0393 for 1245 observed reflections with I > 3 sigma(I). The observed Ru-N-O bond angle of 156.3(7)degrees in the X-ray structure of 1 confirms the nonlinear nature of the nitrosyl linkage. This bend in the nitrosyl moiety away from the quinoxalinediolate ligand presumably results from solid-state packing forces and does not derive from electronic interactions, on the basis of extended Huckel molecular orbital calculations. The MO properties of 1 are compared with other Cp*Ru(NO)-substituted complexes previously synthesized in these laboratories.