CHEMISTRY OF [CP-ASTERISK-RH(MU-CL)]2 AND ITS DIOXYGEN AND NITROSOBENZENE INSERTION PRODUCTS

Treating [Cp*Rh(mu-Cl)Cl]2(CP* =C5Me5 = pentamethylcyclopentadienyl) with excess Na(Hg) (0.4%) in CH2Cl2 gives deep blue [Cp*Rh(mu-Cl)]2 (l). Crystals of 1 from toluene/petroleum ether are monoclinic (C2/c) with a = 33.068(8) angstrom, b = 13.173(3) angstrom, c = 16.810(4) angstrom, beta = 117.77(2)-degrees, V = 6479.4 angstrom3, and Z = 12. The structure consists of two independent, nearly identical molecules (one on a 2-fold axis and the other in a general position) with short Rh-Rh bonds (2.623 angstrom average), bridging chlorides, and eta5-Cp* ligands. Methylene chloride solutions of 1 react rapidly with dioxygen at temperatures slightly above -78-degrees-C to give an unstable (above ca. -15-degrees-C in CD2Cl2) unsymmetrical, dioxygen adduct [(Cp*Rh)2(mu-Cl)(Cl)(mu,eta1:eta2-02)] (2). Complex 2 is fluxional on the NMR time scale. The addition of PPh3 to cold solutions of 2 gives Cp*RhCl2(PPh3) and the unstable(above ca. 0-degrees-C in CD2Cl2) complex Cp*Rh(02)(PPh3) (3). With excess PMe3, 2 gives the fulvene complex [(eta4-C5Me4CH2)Rh(PMe3)3]Cl (4). Crystals of 4 from CH2Cl2/petroleum ether are monoclinic (C2/c) with a = 16.618(5) angstrom, b = 12.074(6) angstrom, c = 27.319(7) angstrom, beta = 99.04(2)-degrees, V = 5413 angstrom3, and Z = 8. Treating 1 with PhNO at 22-degrees-C gives [(Cp*Rh)2-(mu-Cl)(Cl)(mu,eta1:eta2-PhNO)] (5) which, by NMR and a crystal structure determination, has a structure similar to that proposed for 2. Crystals of 5 from toluene/hexane are triclinic (P1BAR) with a = 9.290(3) angstrom, b = 17.830(3) angstrom, c = 8.941(3) angstrom, alpha = 92.60(2)-degrees, beta = 110.87(3)-degrees, gamma = 104.36(2)-degrees, V = 1325.9 angstrom3, and Z = 2. The structure consists of an eta1:eta2-bound PhNO ligand (bridging the two eta5-Cp*Rh centers via the nitrogen atom), a bridging Cl, and a terminal Cl bound to the eta1-Rh center. A chloride ion is removed from 5 with TIBF4 to give the first mu,eta2:eta2-nitrosobenzene complex, [(Cp*Rh)2(mu-Cl)(mu,eta2:eta2-PhNO)]BF4 (6). Crystals of 6 from CH2Cl2/petroleum ether are monoclinic (P2(1)/c) with a = 10.933(4) angstrom, b = 15.166(6) angstrom, c = 18.136(10) angstrom, beta = 95.33(4)-degrees, V = 2994 angstrom3, and Z = 4. The Na/Hg reduction of 5 in the presence of PhNO and TIBF4 gives [Cp*Rh(mu,eta1:eta2-PhNO)]2 (7). Treating the nitrosobenzene complexes with CO gives up to 35% yields of PhNCO.