Further studies on the reactivity of complexes of the type cis-Re 2(μ-O 2CR) 2X 2(μ-dppm) 2. The structural characterization of cis-Re 2(μ-O 2CCH 3) 2(NCBH 3) 2(μ-dppm) 2 and [Re 2Cl 3(μ-dppm) 2(1,2-C 6H 4(CN) 2) 2]PF 6

Abstract

The reactions of cis-Re 2(O 2CC 2H 5) 2Cl 2(dppm) 2 (dppm = Ph 2PCH 2PPh 2) with the nitriles RCN (R = CH 3 or C 2H 5) in the presence of HBF 4·Et 2O or HPF 6 (aq.) afford salts of the cis-[Re 2Cl 2(dppm) 2(NCR) 4] 2+ cations. Studies on the reactivity of cis- [Re 2Cl 2(dppm) 2(NCC 2H 5) 4](PF 6) 2 with CO in acetone show that the mixed carbonyl-nitrile complexes [Re 2Cl 3(dppm) 2(CO) 2(NCC 2H 5)]PF 6 and Re 2Cl 3(dppm) 2(CO) 2(NCC 2H 5) are the major products; these reactions involve the displacement of nitrile by CO and the uptake of Cl − through the sacrifice of a portion of the starting dirhenium complex. Attempts to grow crystals of cis-[Re 2Cl 2(dppm) 2(NCC 2H 5) 4](PF 6) 2 led to its conversion to [Re 2Cl 3(dppm) 2(NCC 2H 5) 2]PF 6. The related complex [Re 2Cl 3(dppm) 2(1,2- C 6H 4(CN) 2) 2]PF 6 has been prepared by the reaction of Re 2Cl 4(dppm) 2 with 1,2-C 6H 4(CN) 2 and KPF 6 in acetone, and its structure established by X-ray crystallography. The crystallographic data are as follows: orthorhombic space group P2 12 12 1, a = 18.242(6), b = 19.197(6), c = 19.789(6) Å, V = 6929(7) Å 3 and Z = 4. The structure was refined to R = 0.081 (R w = 0.098) for 3511 data with I> 3.0σ( I). The structure, which can be represented as [Cl 2Re(μ-dppm) 2ReCl(1,2-C 6H 4(CN) 2) 2]PF 6, contains monodentate 1,2 -C 6H 4(CN) 2 ligands and possesses a staggered rotational geometry. The Re—Re bond length is 2.265(1) Å. The reaction of cis-Re 2(O 2CCH 3) 2Cl 2(dppm) 2 with NaBH 3CN in THF gives cis-Re 2(O 2CCH 3) 2(NCBH 3) 2(dppm) 2, in which the structure of the parent complex is retained but with N-bound cyanotrihydroborato ligands in place of the axially bound chlorides. The crystallographic data for cis-Re 2(O 2CCH 3) 2(NCBH 3) 2(dppm) 2·CH 2Cl 2 are as follows: orthorhombic space group Pbca, a = 18.072(2), b = 19.982(2), c = 31.795(6) Å, V= 11481(5) Å 3 and Z = 8. The structure was refined to R = 0.035 ( R w = 0.045) for 4613 data with I > 3.0σ( I). The Re—Re bond distance in this complex is 2.2938(7) Å.