REACTIONS OF ORGANIC HALIDES WITH THE CARBONYL ANIONS [RH(CO)4]-, [IR(CO)4]- - CRYSTAL AND MOLECULAR-STRUCTURE OF [PPN][IRBR2(CO)2(CH2CO2ME)2] AND OF [PPN][IR(CO)2(CH2CN)2] (PPN+ = [(PH3P)2N]+)

By reaction of [PPN][Ir(CO)4] (1, PPN = [(Ph3P)2N+]) with BrCH2R (R = CO2Me, CN, Ph), the anionic derivatives, all cis-[PPN][IrBr2(CO)2(CH2R)2] [R = CO2Me (3a), CN (3b), Ph (3c)] have been obtained. The structure of these compounds, suggested by IR and NMR data, has been unambiguously clarified in the case of compound 3a by X-ray crystallography. Compound 3a crystallizes in the triclinic space group P1, with a = 9.882 (2), b = 14.642 (3), c = 16.076 (3) Å, α = 105.59 (2), β = 102.44 (2), γ = 99.52 (2)°, Z = 2. R = 0.036 and Rw = 0.046 for 5595 reflections with I > 3σ(I). Analogous reactions carried out on [PPN][Rh(CO)4] (2) allowed only the isolation of cis-[PPN][RhBr2(CO)2] (9). Spectroscopic studies have shown that intermediates in these reactions are the complexes cis-[PPN][MBr(CO)2(CH2R)] [M = Rh, R = CO2Me, CN (4a,b); M = Ir, R = CO2Me, CN (5a,b)]. By carbonylation of 3c at atmospheric pressure, the anionic iridium bis-acyl derivative [PPN][IrBr2(CO)2(COCH2Ph)2] (6) has been identified by spectroscopic measurements. The reaction is reversible, and by bubbling dinitrogen into a solution of 6, compound 3c is re-formed. On the other hand, the reaction of 1 with PhCH2COCl gave the monoacyl derivative, [PPN][IrCl3(CO)2(COCH2Ph)] (7). By treatment of compound 3b with sodium methoxide, a complex reaction was observed, from which it was possible to isolate only the complex [PPN][Ir(CO)2(CH2CN)2] (8), the structure of which was determined by single-crystal X-ray diffraction. Compound 8 is triclinic, space group P1, with a = 9.684 (1), b = 13.994 (1), c = 15.055 (1) Å, α = 74.92 (1), β = 85.89 (1), γ = 74.67 (1)°, Z = 2. R = 0.039 and Rw = 0.058 for 3934 reflections with I > 3σ(I). Compounds 1 and 2 have been tested as catalysts in the carbonylation of PhCH2Br, showing a low catalytic activity and a poor selectivity in the formation of PhCH2COOH.