MECHANISTIC STUDY OF THE CARBONYLATION OF NITROBENZENE CATALYZED BY THE [RH(CO)4]- NITROGEN BASE SYSTEM - X-RAY STRUCTURE OF [PPN][RH(CO)2ON(C6H3CL2)C(O)O]

[PPN] [Rh(CO)4] (1) reacts with ArNO2 or ArNO to yield the same product (Ar = Ph, 2; Ar = 3,4-Cl2-C6H3, 3). The reaction of 1 with nitrosoarenes also produces the corresponding azoxyarenes. The product was structurally characterized in the case of Ar = 3,4-dichlorophenyl and was shown to be [PPN][Rh(CO)2ON(C6H3Cl2)C(O)O] (3). Crystal data for 3: C45H33Cl2N2O5P2Rh.C4H8O, M(r) = 989.64, triclinic, space group P1BAR (No. 2), a = 10.798(4) angstrom, b = 9.889(6) angstrom, c = 21.648(6) angstrom, a = 89.77(1)degrees, beta = 96.00(1)degrees, gamma = 92.71(1)degrees, V = 2296(2) angstrom2, Z = 2, D()c = 1.431 g cm-3, Mo Kalpha radiation (lambda = 0.710 73 angstrom), mu(Mo Kalpha) = 6.00 cm-1, R = 0.037 (R(w) = 0.047) for 5299 independent reflections having I > 3sigma(I). Both of the reactions proceed through electron transfer to the nitroso or nitro derivative. Reaction of 2 and 3 with MeOH and CO produced the corresponding amine or the methyl carbamate, depending on the experimental conditions. The reaction of 3 with MeOH/CO was faster in the presence of nitrogen bases, and aniline was shown to be an intermediate in the synthesis of the carbamate. When the same reaction was performed in the presence of a large excess of nitrosobenzene, the two isomeric mixed azoxybenzenes 3,4-Cl2-C6H3N(O)=NPh and 3,4-Cl2-C6H3N=N(O)Ph were the largely dominant products, which strongly suggests the intermediate formation of a nitrene complex.