MIXED-VALENCE DIRHENIUM ALKYLIDYNE COMPLEXES OF THE TYPE [RE-2(MU-CL)(MU-CO)(CCH(2)R)CL-2(L)(MU-DPPM)(2)](N+) (R=N-PR, N-BU L=CO, XYLNC N=0, 1) POSSESSING VERY UNSYMMETRICAL STRUCTURES

A series of mixed-valence, unsymmetrical, dirhenium alkylidyne complexes of the type [(L)ClRe(mu-Cl)(mu-Co)(mu-dppm)(2)Re(drop CCH(2)R)Cl]X (dppm = Ph(2)PCH(2)PPh(2); L = CO, xylC; R n-Pr, n-Bu; X = PF6, SO3CF3) have-been formed via the ring-opening reactions of the 3-metallafuran complexes [Re-2(mu-Cl)(mu-COC(R)CH)Cl-2(L) (mu-dppm)(2)]X. These paramagnetic complexes (one unpaired electron) can be reduced to their diamagnetic congeners (L)CIRe-(mu-Cl)(CI mu-Cl)(mu-CO)(mu-dppm)(2)Re(drop CCH(2)R)Cl, which show well-defined H-1 and P-31 NMR spectra. X-ray crystallographic structure determinations have been carried out on representative members of the ionic and neutral sets of complexes, viz., [Re-2(mu-Cl)(mu-CO)(drop CCH2-n-Bu)Cl-2(CNxyl)(mu-dppm)(2)]SO3CF3. O.5CH(2)Cl(2) (7d) and Re-2(mu-Cl)(mu-CO)(drop CCH2-n-Pr)Cl-2(CNxyl)(mu-dppm)(2) .2CH(2)Cl(2) (8a). The structures of the dirhenium units in these two compounds are essentially the same; the principal difference is the Re-Re distance, which increases from 2.817(2) Angstrom in 7d to 3.039(1) Angstrom in 8a. The Re drop C distances involving the alkylidyne ligands are typical for this type of unit (1.74(3) Angstrom in 7d; 1.70(1) Angstrom in 8a). Both complexes have a semibridging CO ligand, the Re-C distances being 1.93(3) and 2.57(4) Angstrom in 7d and 1.87(1) and 2.62(1) Angstrom in 8a. Crystal data for 7d: space group Pnma (No. 62) with a = 24.482(5) Angstrom, b = 15.377(3) Angstrom, c = 17.904(4) Angstrom, V = 6740(4) Angstrom(3), and Z = 4. The structure was refined to R = 0.056 (R(w) = 0.069) for 2650 data with I > 3.0 sigma(I). Crystal data for 8a: space group Pnma (No. 62) with a = 24.383(4) Angstrom, b = 15.420(3) Angstrom, c = 17.614(3) Angstrom, V = 6622(4) Angstrom(3), and Z = 4. The structure was refined to R = 0.034 (R(w) = 0.042) for 3569 data with I > 3.0 sigma(I).