Reactions of the dirhenium(II) complexes Re2X4(mu-dppm)(2) (X = Cl, Br; dppm = Ph2PCH2PPh2) with isocyanides. 19. Studies of the reactions of five structural isomers of Re2Cl2(mu-dppm)(2)(CO)(CNXyl)(3) that lead to the dirhenium(I) complexes [Re-2(mu-Cl)(mu-CO)(mu-dppm)(2)(CNXyl)(4)]O3SCF3 and [Re2Cl(mu-dppm)(2)(CO)(CNXyl)(3)(NCCH3)]O3SCF3

Three of the five known isomers of Re2Cl2(mu-dppm)(2)(CO)(CNXyl)(3) (labele d 4 "-8 " in accord with earlier work) react with 1 equiv each of XylNC and TlO3SCF3 in benzene to produce the symmetrical dirhenium(I) complex [Re-2( mu-Cl)(mu-Co)(mu-dppm)(2)(CNXyl)(4)]O3SCF3 (I) in good yield. Isomers 4 ", 6 ", and 8 " are converted to I, while 5 " gives an unidentified mixture an d isomer 7 " is unreactive. When the reactions of 4 ", 5 ", 6 ", and 8 " wi th TlO3SCF3 are carried out in acetonitrile in the absence of XylNC, the co mpound [Re2Cl(mu-dppm)(2)(CO)(CNXyl)(3)(NCCH3)]O3SCF3 can be isolated in th ree stable isomeric forms (A-C). Isomer B is unreactive, while A and C reac t with XylNC in benzene to afford I. Single-crystal X-ray structure determi nations have been carried out on compounds I and B.