Synthesis, molecular structure, and reactivity of rhodium(I) complexes with diazoalkanes and related substrates as ligands

A series of (diazoalkane)rhodium(I) compounds of the general composition traps-[RhCl(N2CRR')(PiPr(3))(2)] with R = R'= Ph, p-C6H4Me, p-C6H4Cl and R = Ph, R' =p-C6H4Me, o-C6H4Me, CH3, CH2Ph, CF3 has been prepared from the dimer [RhCl(PiPr(3))(2)](2) (1) and the diazoalkane. This preparative route has also been extended to complexes in which the N2C unit(s) of 1,4-C6H4{C(Ph)N-2}2, 9-diazofluorene, 9,10-anthraquinone-9-diazide, and 3-methyl-1,4-naphthoquinone-1-diazide is (are) linked to a 14-electron [RhCl(PiPr(3))(2)] fragment. While C(CO2Et)(2)N-2 behaves as expected and affords upon treatment with 1 the complex trans[RhCl{N2C(CO2Et)(2)}(PiPr(3))(2)), CH(CO2Et)N-2 reacts with the same starting material to give the dinitrogen derivative traps-[RhCl(N-2)(PiPr(3))(2)] (12). The reactions of traps-[RhCl(C2H4)(PiPr(3))(2)] (2) with both N2CC4Cl4 and N2CC4Ph4 afford trans-[RhCl(N2CC4X4)(PiPr(3))(2)] (X = Cl, Ph), and the same type of ligand exchange takes place by treatment of traps-[RhCl(C2H4)(SbtPr(3))(2)] with N2CC4Cl4. The reactions of trans-[RhCl(N2CRR')(PiPr(3))(2)] (3-7, where R and R' are aryl) with excess ethene give, instead of a disubstituted cyclopropane, exclusively the trisubstituted olefin CH3CH=CRR'. The reaction of 1 with PhC(R)NNH2 (R = Ph, Me) proceeds mainly by orthometalation to yield the six-coordinate rhodium(III) complexes [Rh(H)Cl kappa(2)-C,N-C6H4C(NNH2)R}(PiPr(3))(2)]; of these, that with R = Ph reacts with Al2O3 to give trans- [RhCl(N2CPh2)(PiPr(3))(2)] and 12. The alkynylrhodium(I) derivatives trans- [Rh(Cequivalent toCX)(C2H4)(PiPr(3))(2)] (X = H, tBu) behave similarly to 2 and afford upon treatment with Ph2CN2 and C12H8CN2 the corresponding diazoalkane compounds trans- [Rh(Cequivalent toCX)(N2CRR')(PiPr(3))(2)] by ligand exchange. The reaction of 2 with the diazo ketones RC(O)C(Ph)N-2 (R = Ph, Me) leads to complexes of the general composition [RhCl{N2C(Ph)C(O)Ph}(PiPr(3))(2)], in which the diazo ketone is probably coordinated in a chelating fashion to the metal center. The keto ester derivative (CH3)(2)CHCH2CH2C(O)C(CO2Me)N-2 reacts with 2 to give a mixture of two isomers, one of which could be separated by fractional crystallization. The supposed chelating bonding mode of the diazo ligand in this compound via the terminal nitrogen and the keto oxygen could be confirmed by an X-ray crystal structure analysis.