NEW HALOGEN-BRIDGED DINUCLEAR EDGE-SHARING AND FACE-SHARING BIOCTAHEDRAL TUNGSTEN(III) COMPLEXES, W2X6(PR3)N, WHERE X=CL OR BR, PR3=PME3, PME2PH, OR PBU3, AND N = 4 OR 3 - CRYSTAL-STRUCTURES OF W2CL6(PME2PH)4, W2CL6(PME2PH)3, AND W2BR6(PME2PH)3

The reduction of WCl4 by 1 equiv of reducing agent, either Na/Hg or NaB(C2H5)3H, in toluene followed by the addition of 2 equiv (or an excess) of phosphine ligand produced the edge-sharing compound W2Cl6(PMe2Ph)4 (1) in high yield. The face-sharing compounds W2Cl6(PMe2Ph)3 (2) and W2Cl6(PBu3)3 (3) were prepared by reacting WCl4 with 1 equiv of reducing agent (Na/Hg for 2 and NaB(C2H5)3H in THF for 3) in toluene followed by the addition of 1.5 equiv of the appropriate phosphine ligand. The first bromo-bridged dinuclear complexes W2Br6(PMe2Ph)3 (4a) and W2Br6(PMe3)3 (5) were synthesized by reducing WBr5 with 2 equiv of reducing agent (Na/Hg for 4a and NaB (C2H5)3H in toluene for 5) in toluene followed by the addition of 1.5 equiv of PMe2Ph and PMe3, respectively. Compounds 1, 2, and 4a,b have been structurally characterized by X-ray diffraction studies. Compound 4 (4a,b) exists in two different crystalline forms. Crystal data: for 1, space group C2/c, a = 17.577 (2) angstrom, b = 11.200 (1) angstrom, c = 21.001 (3) angstrom, beta = 108.25 (2)-degrees, V = 3934 (2) angstrom 3, and Z = 4; for 1, space group PlBAR, a = 9.796 (2) angstrom, b = 12.603 (2) angstrom, c = 13.856 (3) angstrom, alpha = 76.51 (2)-degrees, beta = 82.66 (2)-degrees, gamma = 73.47 (1)-degrees, V = 1591 (1) angstrom 3, and Z = 2; for 4a, space group PlBAR, a = 9.896 (3) angstrom, b = 12.866 (4) angstrom, c = 14.246 (3) angstrom, alpha = 75.62 (2)-degrees, beta = 82.95 (2)-degrees, gamma = 74.07 (2)-degrees, V = 1687 (1) angstrom 3, and Z = 2; for 4b, space group PlBAR, a = 10.665 (2) angstrom, b = 16.009 (5) angstrom, c = 10.154 (3) angstrom, alpha = 98.12 (2)-degrees, beta = 101.92 (2)-degrees, gamma = 79.95 (2)-degrees, V = 1660 (1) angstrom 3, and Z = 2. In all these complexes, the W-W bond distances 2.6950 (3) (1), 2.4433 (4) (2), 2.4768 (9) (4a), and 2.4496 (6) angstrom (4b) indicate strong metal-metal bonding. The face-sharing compounds 2 and 4b have the shortest W-W bond distances in any neutral halogen-bridged dinuclear tungsten(III) complexes so far reported. The average W-X(b)-W bond angle in the edge-sharing compound 1 is 68.98 (3)-degrees and those in the face-sharing compounds are 58.45 [4], 56.28 [3], and 55.32 [2]-degrees for 2, 4a, and 4b respectively. Compounds 3 and 5 have been characterized by a P-31{H-1} NMR spectrum and an electronic spectrum (similar to that of 4), respectively.