Reactions of the dirhenium(II) complexes Re2X4(mu-dppm)(2) (X = Cl, Br ; dppm = Ph2PCH2PPh2) with isocyanides. 18. The isolation and characterizationof isomers of the [Re2Cl2(mu-dppm)(2)(CO)(CNXyl)(3)](2+) cation and its monocationic and neutral congeners

The reactions of the multiply bonded dirhenium(II) complexes Re2Cl4(mu-dppm )(2)(CO) Re2Cl4(mu-dppm)(2)(CO)(CNXyl), and [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)( 2)]O3SCF3 (dppm = Ph2PCH2PPh2: Xyl = 2,6-dimethylphenyl) with the requisite number of equivalents of TIO3SCF3 and XylNC lead to three, non-interconver tible, structural isomers of the complex [Re2Cl2(mu-dppm)(2)(CO)(CNXyl)(3)] (O3SCF3)(2) (4a, 5a, and 6a; a signifies a triflate salt). Each of these co mplexes undergoes two reversible one-electron reductions which afford the r edox pairs 4a'/4 ", 5a'/5 ", and 6a'/6 ", respectively. While 4a' and 4 " h ave structures which are very similar to that of 4a, the complexes 5a'/5 " and 6a'/6 " have structures which differ from 5a and 6a, thereby establishi ng the existence of coupled redox/isomerization reactions. Solutions of 6a' in acetonitrile and 6 " in benzene slowly convert to the new isomers 7a' a nd 8 ", respectively, which are in turn found to be members of the redox se ries 7'/7 " and 8/8'/8 ". In all, the [Re2Cl2(mu-dppm)(2)(CO)(CNXyl)(3)](n) species (n = 2, 1, or 0) have been found to exist in seven distinct struc tural forms which possess Re-Re bond orders of 3, 2, 1.5, 1, or 0 depending on the specific bioctahedral structure which is assumed and the charge on the complex. Single-crystal X-ray structure determinations have been carrie d out on the seven complexes 4 ". 5a, 6a, 6a', 6 ", 7a', and 7 ".