15628-18-9Relevant academic research and scientific papers
Studies on the α and β isomers of complexes of the type Re2X4(LL)2. Structural characterization of α- and β-Re2Cl4(dppee)2 (dppee = cis-Ph2PCH=CHPPh2)
Bakir, Mohammed,Cotton, F. Albert,Falvello, Larry R.,Vidyasagar,Wallon, Richard A.
, p. 2460 - 2466 (2008/10/08)
The first structural study on a pair of α and β isomers of dirhenium(II) of the type Re2X4(LL)2 (X = Cl, Br; LL = bidentate phosphine ligand) has been carried out in the case of X = Cl and LL = cis-Ph2PCH=CHPPh2 (dppee). Crystals of α-Re2Cl4(dppee)2·n-PrOH, which were grown from CH2Cl2/n-propyl alcohol, crystallize in the triclinic space group P1 with the following unit cell dimensions: a = 13.485 (3) A?, b = 17.556 (5) A?, c = 11.952 (3) A?, a = 87.24 (2)°, β = 100.12 (2)°, γ = 110.66 (2)°, V = 2606 (3) A? 3, and Z = 4. The structure was refined to R = 0.037 (Rw = 0.048), with quality of fit 1.403, for 5384 data with Fo2 > 3σ(Fo2). There are two crystallographically independent molecules, which are essentially identical structurally with an average Re≡Re distance of 2.258 A?. The centrosymmetric molecules contain chelating dppee ligands and possess an eclipsed rotational geometry. The isomer β-Re2Cl4(dppee)2 crystallizes in the monoclinic system, space group P21/n, with a = 16.917 (2) A?, b = 12.992 (4) A?, c = 22.990 (7) A?, β = 106.86 (2)°, V = 4836 (4) A?3, and Z = 4. The structure was refined to residuals of R = 0.088 and Rw = 0.074 and quality of fit 2.389 for 3002 data with Fo2 > 3σ(Fo2). Refinement of the structure was complicated by a disorder in which a second set of rhenium atoms (20% occupancy) was found, centered at the same point as the principal pair (80% occupancy), and with the Re-Re vector roughly perpendicular to that of the primary Re2 unit. The Re≡Re distance was refined to 2.242 (3) A? for the major component of the disorder. The molecules possess an overall staggered geometry in which the dppee ligands bridge the two metal centers. The resulting six-membered ring conformations in both the principal and minor molecules are of the type well-known for cyclohexene, namely, a flattened chair or half-chair. Synthetic procedures have been developed for the preparation of α-Re2X4(dppe)2 (X = Cl, Br; dppe = Ph2PCH2CH2PPh2), complexes whose β isomers have been reported previously. The first successful chemical oxidation of α isomers of dirhenium(II) has been accomplished; α-Re2Cl4(LL)2 complexes (LL = cis-Ph2PCH=CHPPh2, Ph2P(CH2)3PPh2) have been oxidized by (Cp2Fe)PF6 in CH2Cl2 to give paramagnetic α-[Re2Cl4(LL)2]PF6.
