ABSTRACT
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)](O(3)SCF(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)](n+) 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' '.
ABSTRACT
The reaction of the open bioctahedral form of Re(2)Cl(4)(&mgr;-dppm)(2)(CO)(CNXyl) (1), where XylNC = 2,6-dimethylphenyl isocyanide, with TlO(3)SCF(3) in the presence of acetonitrile proceeds with retention of stereochemistry at the dirhenium unit to afford the complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(NCCH(3))]O(3)SCF(3) (3). The single-crystal X-ray structure determination of 3 shows that a Re&tbd1;Re bond is retained (the Re-Re distance is 2.378(3) Å) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with TlO(3)SCF(3) in a noncoordinating solvent to produce the unsymmetrical complex [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)]O(3)SCF(3) (2), through loss of this same chloride ligand of 1 and CO transfer from the adjacent Re center. The acetonitrile ligand of 3 is very labile and is readily displaced by XylNC and t-BuNC, with retention of stereochemistry, to produce complexes of stoichiometry [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(CNR)]O(3)SCF(3) (R = Xyl, 4a; R = t-Bu, 4b). In a noncoordinating solvent, the nitrile ligand of 3 is lost and 2 is formed following CO transfer; this conversion is reversed upon the reaction of 2 with acetonitrile. When 3 is treated with CO, the acetonitrile ligand is again displaced, but in this instance the reaction is accompanied by a structure change to produce an edge-sharing bioctahedral complex of the type [Re(2)(&mgr;-CO)(&mgr;-Cl)(&mgr;-dppm)(2)Cl(2)(CO)(CNXyl)]O(3)SCF(3) (5).
ABSTRACT
The reactions of the unsymmetrical, coordinatively unsaturated dirhenium(II) complexes [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)]Y (XylNC = 2,6-dimethylphenyl isocyanide; Y = O(3)SCF(3) (3a), PF(6) (3b)) with XylNC afford at least three isomeric forms of the complex cation [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+). Two forms have very similar bis(&mgr;-halo)-bridged edge-sharing bioctahedral structures of the type [(CO)BrRe(&mgr;-Br)(2)(&mgr;-dppm)(2)Re(CNXyl)(2)]Y (Y = O(3)SCF(3) (4a/4a'), PF(6) (4b/4b')), while the third is an open bioctahedron [(XylNC)(2)BrRe(&mgr;-dppm)(2)ReBr(2)(CO)]Y (Y = O(3)SCF(3) (5a), PF(6) (5b)). While the analogous chloro complex cation [Re(2)Cl(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](+) was previously shown to exist in three isomeric forms, only one of these has been found 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(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3) (7), in which the edge-sharing bioctahedral cation [(XylNC)BrRe(&mgr;-Br)(&mgr;-CO)(&mgr;-dppm)(2)ReBr(CO)](+) has 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 2.5853(13) Å, respectively, and accord with formal Re-Re bond orders of 1, 3, and 2, respectively. Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)](PF(6))(0.78)(ReO(4))(0.22).CH(2)Cl(2) (4b') at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 19.845(4) Å, b = 16.945(5) Å, c = 21.759(3) Å, beta = 105.856(13) degrees, V = 7038(5) Å(3), and Z = 4. The structure was refined to R = 0.060 (R(w) = 0.145) for 14 245 data (F(o)(2) > 2sigma(F(o)(2))). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(CNXyl)(2)]O(3)SCF(3).C(6)H(6) (5a) at 173 K: monoclinic space group P2(1)/n (No. 14) with a = 14.785(3) Å, b = 15.289(4) Å, c = 32.067(5) Å, beta = 100.87(2) degrees, V=7118(5) Å(3), and Z = 4. The structure was refined to R = 0.046 (R(w) = 0.055) for 6962 data (I > 3.0sigma(I)). Crystal data for [Re(2)Br(3)(&mgr;-dppm)(2)(CO)(2)(CNXyl)]O(3)SCF(3).Me(2)CHC(O)Me (7) at 295 K: monoclinic space group P2(1)/n (No. 14) with a = 14.951(2) Å, b = 12.4180(19) Å, c = 40.600(5) Å, beta = 89.993(11) degrees, V = 7537(3) Å(3), and Z = 4. The structure was refined to R = 0.074 (R(w) = 0.088) for 6595 data (I > 3.0sigma(I)).
