Binuclear methylene- and alkyne-bridged complexes of rhodium not containing accompanying metalmetal bonds

The alkyne-bridged “A-Frame” complex, [Rh2Cl2(μ-CF3C2CF3(DPM)2] (DPM  Ph2PCH2PPh2), reacts with diazomethane to give the unusual species, [Rh2Cl2(μ-CH2(μ-CF3C2CF3)(DPM)2] (2) in which the two DPM ligands, the methylene and the hexafluoro-2-butyne groups bridge the metals with no accompanying RhRh bond. Attempts to produce a methylene-bridged complex from the analogous carbonyl-bridged “A-frame”, [Rh2Cl2(μ-CO)(DPM)2], were unsuccessful as this species did not react with diazomethane. An X-ray structure determination has been carried out on compound 2. This complex crystallizes in the tetragonal space group P41 with a 21.334(3), c 14.574(2) A, V=6633.2 A3 and Z = 4. On the basis of 3669 unique observations and 291 parameters varied the structure has converged to R = 0.034 and Rw = 0.039. The RhRh separation of 3.466(1) A indicates that there is no RhRh bond and the wide RhCRh angle at the bridged methylene group (119.5(5)°) is also consistent with the absence of metalmetal bonding. The methylene group in compound 2 is found to be unreactive towards CO, H2 and protic acids, probably in part because it is protected in the pocket between the two metals, however compound 2 did react with PMe3 to yield a complex mix of products, from which [Rh2Cl(μ-Cl)(μ-CH2)(μ-CF3C2CF3)(PMe3)5] (3) crystallized in low yield. This complex crystallizes with two molar equivalents of CH2Cl2 in the monoclinic space group P21/n with a 11.519(2), b 14.689(7), c 25.250(5) A, β 93.00(2)°. V 4266.7 A3 and Z = 4. Based on 4614 unique observations and 396 parameters varied the structure has converged to R = 0.063 and Rw = 0.095. Compound 3 is unusual in that it has resulted from the replacement of the two bridging bidentate DPM groups in 2 by five monodentate PMe3 ligands. Both rhodium atoms have octahedral geometries in which they share a common face, bridged by the methylene, the alkyne and one chloro group. The RhRh separation of 3.1338(7) A is consistent with the absence of metalmetal bonding, which is substantiated by the relatively large RhCH2Rh angle of 100.1(3)°.