SYNTHESIS AND CHARACTERIZATION OF A FAMILY OF NITRILE-SUBSTITUTED TRIANGULAR HYDRIDOCARBONYL RHENIUM CLUSTERS, [RE3(MU-H)3(CO)12-N(NCME)N](N=1-3) - X-RAY CRYSTAL-STRUCTURES OF [RE3(MU-H)3(CO)11(NCME)] AND [RE3(MU-H)3(CO)9(NCME)3]

Different routes to the new family of cluster compounds [Re3(μ-H)3(CO)12-n(NCMe)n] (n = 1-3), containing substitution labile nitrile ligands, are described. The interconversions within the members of the family have been investigated and the stepwise replacement of the MeCn groups with CO has been demonstrated. The reaction of [Re3(μ-H)3(CO)12] with Me3NO in controlled ratios (1:1 or 1:2) for progressive decarbonylation, in the presence of nitrile, is found not be selective, and leads to mixtures of substituted derivatives. On the contrary with a 1:3 ratio the trisubstituted derivative is obtained quantitatively. The crystal structures of the derivatives with n = 1 (1) and 3(3) are reported. Compound (1) crystallizes in the monoclinic space group P21/n, with a = 8.417(2), b = 15.282(4), c = 16.540(4) Å, β = 97.70(2)°, and Z = 4. Compound (3) gives triclinic crystals, space group P1, with a = 8.761(2), b = 9.403(2), c = 15.079(3) Å, α = 92.45(2), β = 94.02(2), γ = 108.38(2)°, and Z = 2. The structures were solved by Patterson and Fourier methods, and refined by full-matrix least squares on the basisi of 1 121(1) and 3129(3) significant counter data, to final values of the conventional R index of 0.035(1) and 0.019(3), respectively. Both structures contain an almost equilateral Re3 triangle, with all the edges bridged by hydride ligands. The mean values of the Re-Re bonds are 3.258 and 3.284 Å for compounds (1) and (3), respectively. The acetonitrile ligands always occupy axial position. N.m.r. data in solution have shown the presence of only one isomer for each compound.