RETENTION OF DINITROGEN IN THE REACTIONS OF SOME DIAZOALKANES WITH A DIRHODIUM COMPLEX - CRYSTAL AND MOLECULAR-STRUCTURES OF (ETA-C5H5)2RH2(CF3C2CF3.CO.N2CRR'), RR'=MEPH AND (T-BU)2

Upon treatment of (eta-C5H5)2Rh2(mu-CO)(mu-eta2-CF3C2CF3) (1) with the diazo compounds N2CRR' (RR'=Ph2, MePh, Me(CF3), Ph(CF3)), the complexes (eta-C5H5)2Rh2{CF3C2CF3.CO.N2CRR'} (2a-2d) are formed. They do not lose nitrogen upon attempted thermolysis or photolysis. The crystal structure of the complex 2b (RR'=MePh) was determined by X-ray crystallography: orthorhombic, Pbca, Z=8, a=25.28(1), b=19.84(1), c=9.031(7) angstrom. The molecular structure shows that there has been end-to-end condensation of the components CF3C2CF3, CO and N2CMePh to produce a single bridging ligand, C(CF3)=C(CF3)C(=O)N{N=C(Ph)Me}. It is attached to one Rh atom from a terminal alkene-carbon and a nitrogen lone pair; the same nitrogen atom is covalently bonded to the second Rh atom which is also pi-bonded to the alkene function. Spectroscopic results indicate that the other complexes have analogous structures. The reaction of 1 with N2C(t-Bu)2 gives a related product (eta-C5H5)2Rh2{CF3C2CF3.CO.N2C(t-Bu)2} (5), but crystal structure determination reveals a vastly different ligand arrangement. The crystals are orthorhombic, Pbca, Z=8, a=27.679(3), b=11.560(1), c=15.924(1) angstrom. This complex incorporates a cyclic ligand C-N-N-C(t-Bu)2-O with the first ring carbon incorporated into an allylic group C-C(CF3)-C(CF3). The allylic side chain is sigma-pi attached to the Rh-Rh bond; a ring nitrogen also forms a dative bond with one Rh atom. A minor product (eta-C5H5)2Rh2(mu-CO){CF3C2CF3.CMePh} (3) is also formed in the reaction with N2CMePh; this undergoes decarbonylation during chromatography to give (eta-C5H5)2Rh2{CF3C2CF3.CMePh} (4).