Reactions of the Dirhenium(II) Complexes Re(2)X(4)(&mgr;-dppm)(2) (X = Cl, Br; dppm = Ph(2)PCH(2)PPh(2)) with Isocyanides. 18.(1) The Isolation and Characterization of Isomers of the [Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)](2+) Cation and Its Monocationic and Neutral Congeners.

The reactions of the multiply bonded dirhenium(II) complexes Re(2)Cl(4)(&mgr;-dppm)(2)(CO), Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl), and [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3) (dppm = Ph(2)PCH(2)PPh(2); Xyl = 2,6-dimethylphenyl) with the requisite number of equivalents of TlO(3)SCF(3) and XylNC lead to three, non-interconvertible, structural isomers of the complex Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3)(2) (4a, 5a, and 6a; a signifies a triflate salt). Each of these complexes undergoes two reversible one-electron reductions which afford the redox pairs 4a'/4' ', 5a'/5' ', and 6a'/6' ', respectively. While 4a' and 4' ' have 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 establishing the existence of coupled redox/isomerization reactions. Solutions of 6a' in acetonitrile and 6' ' in benzene slowly convert to the new isomers 7a' and 8' ', respectively, which are in turn found to be members of the redox series 7'/7' ' and 8/8'/8' '. In all, the Re(2)Cl(2)(&mgr;-dppm)(2)(CO)(CNXyl)(3) species (n = 2, 1, or 0) have been found to exist in seven distinct structural 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 carried out on the seven complexes 4' ', 5a, 6a, 6a', 6' ', 7a', and 7' '.