STRUCTURAL CHARACTERIZATION OF ALKYNE AND VINYLIDENE ISOMERS OF [RU(C2H2)(PME2PH)2(CP)][BF4]

The reaction of [RuCl(PMe2Ph)2(Cp)] with ethyne and TlBF4 in dichloromethane leads to [Ru(eta-2-HC=CH)(PMe2Ph)2(Cp)][BF4] (2), an unusual eta-2-alkyne complex of a d6 metal center. This ethyne complex smoothly rearranges to its vinylidene isomer, [Ru(C=CH2)(PMe2Ph)2(Cp)][BF4] (4), above ca. 60-degrees-C in acetone solution. The eta-2-ethyne to vinylidene conversion can also be carried out by deprotonation of 2 to give [Ru(C=CH)(PMe2Ph)2(CP)] (3), followed by protonation of 3 to give exclusively vinylidene isomer 4. Structures of both 2 and 4 were determined by X-ray diffraction. Aside from the difference in the geometry of the C2H2 ligands, the structures are nearly identical. Crystal data with Mo K-alpha (lambda = 0.7107 angstrom) radiation at 297 K are as follows: 2, C23H29BF4P2Ru, a = 23.099 (3) angstrom, b = 9.203 (2) angstrom, c = 11.344 (3) angstrom, orthorhombic space group Pca2(1) (No. 29), Z = 4, R = 0.054, R(w) = 0.074; 4, C23H29F4P2Ru, a = 23.270 (3) angstrom, b = 9.290 (1) angstrom, c = 11.3659 (8) angstrom, orthorhombic space group Pca2(1) (No. 29), Z = 4, R = 0.035, R(w) = 0.044.