Isomerization in Metal-Metal Bonded M2L10 Systems Involving Cis and Trans Sets of Bis(diphenylphosphino)methane Ligands

Article abstract of DOI:10.1021/ja00223a021

The reactions of the dirhenium(III) complexes Re2(O2CR)4X2 (R = CH3, C2H5, C6H5; X = Cl, Br), Re2(O2CR)2X4L2 (R = CH3, C2H5; X = Cl, Br; L = H2O, 4-methylpyridine, DMF, DMSO), and (n-Bu4N)2Re2X8 (X = Cl, Br) with Ph2PCH2PPh2 (abbreviated dppm) or, in the case of (n-Bu4N)2Re2X8, Ph2CH2PPh2/acetate mixtures affords the reduced complexes Re2(O2CR)X4(dppm)2 and cis- and trans-Re2(O2CR)2X2(dppm)2 depending upon the choice of reaction conditions.The thermolysis of Re2(O2CR)X4(dppm)2 provides a high yield synthetic route to Re2X4(dppm)2 (X = Cl, Br), a procedure that can be adapted to produce Re2I4(dppm)2 directly from Re2(O2CCH3)2I4.nH2O.The cis and trans isomers of the triply bonded dirhenium(II) compounds Re2(O2CR)2X2(dppm)2 can be oxidized to paramagnetic cis-PF6 and trans-PF6 by <(η⁵-C5H5)2Fe>PF6 and (C7H7)PF6, respectively.The structures of representative members of these groups of new complexes have been established by X-ray crystallography, viz., Re2(O2CCH3)Cl4(dppm)2.2(CH3)2CO (1), cis-Re2(O2CCH3)2Cl2(dppm)2 (2), and trans-PF6.CH2Cl2 (3).Complex 1 crystallizes in the monoclinic space group P2₁/c with the following unit cell dimensions: a = 12.720 (2) Angstroem, b = 35.593 (5) Angstroem, c = 9.405 (2) Angstroem, β = 104.36 (1) deg, V = 5610 (3) Angstroem³, and Z = 4.The structure was refined to R = 0.036 and R_w = 0.055 for 5822 data with F² > 3.0?(F²).The structure contains symmetrically bridging acetate and dppm ligands and is based upon an eclipsed M2L10 geometry, with two axial and two equatorial Re-Cl bonds.The Re-Re distance is 2.300 (1) Angstroem, which is in accord with the presence of a Re-Re bond of order 3.5.The unit cell dimensions for complexes 2 and 3, which crystallize in the monoclinic space groups P2₁/c and C2/c, respectively, are as follows: for 2, a = 14.634 (6) Angstroem, b = 15.190 (5) Angstroem, c = 24.281 (6) Angstroem, β = 107.24 (3) deg, V = 5155 (6) Angstroem³, and Z = 4; for 3, a = 22.853 (5) Angstroem, b = 18.712 (3) Angstroem, c = 14.236 (4) Angstroem, β = 107.48 (2) deg, V = 5807 (4) Angstroem³, and Z = 4.The structure of 2 was refined to R = 0.045 and R_w = 0.061 for 4468 data with F² > 3.0?(F²), whereas for 3 the refinement gave R = 0.034 and R_w = 0.049 for 2936 data with F² > 3.0?(F²).Both complexes contain pairs of bridging acetate and dppm ligands and axial Re-Cl bonds.In 2 the pairs of acetate (and dppm) ligands are cis to one another, while they assume a trans disposition in 3.The Re-Re distance is 2.315 (1) Angstroem in 2 and 2.275 (1) Angstroem in 3.