REACTIONS OF THE DIRHENIUM(II) COMPLEXES RE(2)X(4)(DPPM)(2) (X=CL,BR DPPM=PH(2)PCH(2)PPH(2)) WITH ISOCYANIDES .10. SYNTHESIS AND CHARACTERIZATION OF THE COMPLEX [RE2BR3(MU-DPPM)(2)(CO)(2)(CNXYL)]O3SCF3 AND SEVERAL ISOMERIC FORMS OF [RE2BR3(MU-DPPM)(2)(CO)(CNXYL)(2)]Y (Y=PF6, O3SCF3)

The reactions of the unsymmetrical, coordinatively unsaturated dirheni um(II) complexes [Re2Br3(mu-dppm)(2)(CO)(CNXyl)]Y (CNXyl)]Y (XylNC = 2 ,6-dimethylphenyl isocyanide; Y = O3SCF3 (3a), PF6 (3b)) with XylNC af ford at least three isomeric forms of the complex cation [Re2Br3(mu-dp pm)(2)(CO)(CNXyl)(2)](divided by). Two forms have very similar bis(mu- halo)-bridged edge-sharing bioctahedral structures of the type [(CO)Br Re(mu-Br)(2)(mu-dppm)(2)Re(CNXyl)(2)]Yx (Y = O3SCF3 (4a/4a'), PF6 (4b/ 4b')), while the third is an open bioctahedron [(XyINC)(2)BrRe(mu-dppm )(2)ReBr2(CO)]Y (Y = O3SCF3 (5a), PF6 (5b)). While the analogous chlor o complex cation [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been fou nd 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 [Re 2Br3(mu-dppm)(2)(CO)(2)(CNXyl)]O3SCF3(7), in which the edge-sharing bi octahedral cation [(XylNC)BrRe(mu-Br)(mu-CO)(mu-dppm)(2)ReBr(CO)](+) h as an all-cis arrangement of pi-acceptor ligands. The Re-Re distances in the structures of 4b', 5a, and 7 are 3.0456(8), 2.3792(7), and 2.58 53(13) Angstrom, respectively, and accord with formal Re-Re bond order s of 1, 3, and 2, respectively. Crystal data for mu-dppm)(2)(CO)(CNXyl )(2)](PF6)(0.78)(ReO4)(0.22). CH2Cl2 (4b') at 295 K: monoclinic space group P2(l)/n (No. 14) with a = 19.845(4) Angstrom, b = 16.945(5) Angs trom, c = 21.759(3) Angstrom, beta = 105.856(13)degrees, V = 7038(5) A ngstrom(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F-0(2) > 2 sigma(F-0(2))). Crystal data for [R e2Br3(mu-dppm)(2)(Co)(CNXyl)(2)], SCF3 . C6H6 (5a) at 173 K: monoclini c space group P2(l)/n (No. 14) with a = 14.785(3) Angstrom, b = 15.289 (4) Angstrom, c = 32.067(5) Angstrom, beta = 100.87(2)degrees, V =7118 (5) Angstrom(3), and Z = 4. The structure was refined to R = 0.060 (R( w) = 0.055) for 6962 data (I > 3.0 sigma(I)). Crystal data for [Re2Br3 (mu-dppm)(2)(CO)(2)(CNXyl)]O3SCF3 . Me(2)CHC(O)Me (7) at 295 K: monocl inic space group P2(l)/n (No. 14) with a = 14.951(2) Angstrom, b = 12. 4180(19) Angstrom, c = 40.600(5) Angstrom, beta = 89.993(11)degrees, V = 7537(3) Angstrom(3), and Z = 4. The structure was refined to R = 0. 074 (R(w) = 0.088) for 6595 data(I > 3.0 sigma(I)).