| Abstract
| - The reactions of the unsymmetrical, coordinatively unsaturateddirhenium(II) complexes[Re2Br3(μ-dppm)2(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y =O3SCF3 (3a), PF6(3b)) with XylNC afford at leastthree isomeric forms of the complex cation[Re2Br3(μ-dppm)2(CO)(CNXyl)2]+.Two forms have very similarbis(μ-halo)-bridged edge-sharing bioctahedral structures of thetype[(CO)BrRe(μ-Br)2(μ-dppm)2Re(CNXyl)2]Y(Y = O3SCF3(4a/4a‘), PF6(4b/4b‘)), while the third is an openbioctahedron[(XylNC)2BrRe(μ-dppm)2ReBr2(CO)]Y(Y = O3SCF3 (5a),PF6 (5b)). While the analogous chlorocomplex cation[Re2Cl3(μ-dppm)2(CO)(CNXyl)2]+was previously shown to exist in three isomeric forms, only one ofthese has been found to be structurally similarto the bromo complexes (i.e. the isomer analogous to 5a and5b). The reaction of 3a with CO gives thesalt[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−Redistances in thestructures of 4b‘, 5a, and7 are 3.0456(8), 2.3792(7), and 2.5853(13)Å, respectively, and accord with formalRe−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 groupP21/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, andZ = 4. The structure was refined toR= 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 173K: 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. Thestructure was refined to R = 0.046(Rw = 0.055)for 6962 data (I> 3.0σ(I)). Crystaldata for[Re2Br3(μ-dppm)2(CO)2(CNXyl)]O3SCF3·Me2CHC(O)Me(7) at295 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 6595data(I> 3.0σ(I)).
- The reactions of theunsymmetrical, coordinatively unsaturated dirhenium(II) complexes[Re2Br3(μ-dppm)2(CO)(CNXyl)]Y(3) (XylNC = 2,6-dimethylphenyl isocyanide; Y =O3SCF3, PF6) with XylNC affordat least three isomeric forms of the complex cation[Re2Br3(μ-dppm)2(CO)(CNXyl)2]+.Two forms have very similar bis(μ-halo)-bridgededge-sharing bioctahedral structures of the type[(CO)BrRe(μ-Br)2(μ-dppm)2Re(CNXyl)2]Y(4) (Y = O3SCF3,PF6), while the third is an open bioctahedron[(XylNC)2BrRe(μ-dppm)2ReBr2(CO)]Y(5) (Y = O3SCF3,PF6). The Re−Re distances in the structures of4 (Y = PF6) and 5 (Y =O3SCF3) are 3.0456(8) and2.3792(7) Å, respectively, and accord with formal Re−Re bondorders of 1 and 3.
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