Reactions of the Dirhenium(II) Complexes Re<sub>2</sub>X<sub>4</sub>(μ-dppm)<sub>2</sub> (X = Cl, Br; dppm = Ph<sub>2</sub>PCH<sub>2</sub>PPh<sub>2</sub>) with Isocyanides. 11. A Triply Bonded Dirhenium Complex Containing a Labile Acetonitrile Ligand. Synthesis, Structural Characterization, and Reactivity of [(XylNC)(CH<sub>3</sub>CN)ClRe(μ-dppm)<sub>2</sub>ReCl<sub>2</sub>(CO)]O<sub>3</sub>SCF<sub>3</sub>
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The reaction of the open bioctahedral form of Re2Cl4(μ-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(μ-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) Å) 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(μ-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(μ-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 [Re2(μ-CO)(μ-Cl)(μ-dppm)2Cl2(CO)(CNXyl)]O3SCF3 (5).
