Reactions of the Dirhenium(II) Complexes Re₂X₄(dppm)₂ (X = Cl, Br; dppm = Ph₂PCH₂PPh₂) with Isocyanides. 10. Synthesis and Characterization of the Complex [Re₂Br₃(μ-dppm)₂(CO)₂(CNXyl)]O₃SCF₃ and Several Isomeric Forms of [Re₂Br₃(μ-dppm)₂(CO)(CNXyl)₂]Y (Y = PF₆, O₃SCF₃)^†

Abstract

The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re2Br3(μ-dppm)2(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O3SCF3 (3a), PF6 (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re2Br3(μ-dppm)2(CO)(CNXyl)2]+. Two forms have very similar bis(μ-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(μ-Br)2(μ-dppm)2Re(CNXyl)2]Y (Y = O3SCF3 (4a/4a‘), PF6 (4b/4b‘)), while the third is an open bioctahedron [(XylNC)2BrRe(μ-dppm)2ReBr2(CO)]Y (Y = O3SCF3 (5a), PF6 (5b)). While the analogous chloro complex cation [Re2Cl3(μ-dppm)2(CO)(CNXyl)2]+ was previously shown to exist in three isomeric forms, only one of these has been found to be structurally similar to the bromo complexes (i.e. the isomer analogous to 5a and 5b). The reaction of 3a with CO gives the salt [Re2Br3(μ-dppm)2(CO)2(CNXyl)]O3SCF3 (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(μ-Br)(μ-CO)(μ-dppm)2ReBr(CO)]+ has an all-cis arrangement of π-acceptor ligands. The Re−Re distances in the structures of 4b‘, 5a, and 7 are 3.0456(8), 2.3792(7), and 2.5853(13) Å, respectively, and accord with formal Re−Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re2Br3(μ-dppm)2(CO)(CNXyl)2](PF6)0.78(ReO4)0.22·CH2Cl2 (4b‘) at 295 K:  monoclinic space group P21/n (No. 14) with a = 19.845(4) Å, b = 16.945(5) Å, c = 21.759(3) Å, β = 105.856(13)°, V = 7038(5) Å3, and Z = 4. The structure was refined to R = 0.060 (Rw = 0.145) for 14 245 data (Fo2 > 2σ(Fo2)). Crystal data for [Re2Br3(μ-dppm)2(CO)(CNXyl)2]O3SCF3·C6H6 (5a) at 173 K:  monoclinic space group P21/n (No. 14) with a = 14.785(3) Å, b = 15.289(4) Å, c = 32.067(5) Å, β = 100.87(2)°, V =7118(5) Å3, and Z = 4. The structure was refined to R = 0.046 (Rw = 0.055) for 6962 data (I > 3.0σ(I)). Crystal data for [Re2Br3(μ-dppm)2(CO)2(CNXyl)]O3SCF3·Me2CHC(O)Me (7) at 295 K:  monoclinic space group P21/n (No. 14) with a = 14.951(2) Å, b = 12.4180(19) Å, c = 40.600(5) Å, β = 89.993(11)°, V = 7537(3) Å3, and Z = 4. The structure was refined to R = 0.074 (Rw = 0.088) for 6595 data (I > 3.0σ(I))