REACTIONS OF THE DIRHENIUM(II) COMPLEXES RE(2)X(4)(MU-DPPM)(2) (X=CL,BR DPPM=PH(2)PCH(2)PPH(2)) WITH ISOCYANIDES .11. A TRIPLY BONDED DIRHENIUM COMPLEX CONTAINING A LABILE ACETONITRILE LIGAND - SYNTHESIS, STRUCTURAL CHARACTERIZATION, AND REACTIVITY O

摘要

The reaction of the open bioctahedral form of Re2Cl4(mu-dppm)(2)(CO)(CNXyl) (1), where XylNC = 2,6-dimethylphenyl isocyanide, with TlO3SCF3 in the presence of acetonitrile proceeds with retention of stereochemistry at the dirhenium unit to afford the complex [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)(NCCH3)]O3SCF3 (3). The single-crystal X-ray structure determination of 3 shows that a Re=Re bond is retained (the Re-Re distance is 2.378(3) Angstrom) and that it is the chloride ligand trans to the XylNC ligand of 1 which is labilized. Complex 1 reacts with TlO3SCF3 in a noncoordinating solvent to produce the unsymmetrical complex [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)]O3SCF3 (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 [Re2Cl3(mu-dppm)(2)(CO)(CNXyl)(CNR)]O3SCF3 (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(mu-CO)(mu-Cl)(mu-dppm)(2)Cl-2(CO)(CNXyl)]O3SCF3 (5). [References: 18]