ZERO-VALENT GROUP-6 COMPLEXES OF 1,2,4,5-TETRAKIS(DIPHENYLPHOSPHINO) BENZENE

The tetradentate ligand, 1,2,4,5-tetrakis(diphenylphosphino)benzene (T PPB) (1),has been utilised to prepare linked Group 6 carbonyl complexe s [{M(CO)(4)}(2)(mu-TPPB)] (M=Cr, Mo, W) (2a-c), fac,fac-[{Mo(CO)(3)(M eCN)}(2)(mu-TPPB)] (3), fac,fac-[{Mo(CO)(3)(pph(3))}(2)(mu-TPPB)] (4), fac,fac-[{Mo(CO)(3)(eta(1)-DPPE)}(2)(mu-TPPB)] (5) and both cis and t rans isomers of [{M(CO)(2)(eta(2)-DPPE)}(2)(mu-TPPB)] (M = Mo, W) (6b- c). Attempts to prepare oligomers or polymers were unsuccessful, furth er reaction of 2b with TPPB afforded [(eta(2)-TPPB){Mo(CO)(2)}(mu-TPPB ){Mo(CO)(4)}] (7). The molecular structures of 1, 2b and 2c . 2THF hav e been determined by X-ray crystallography. Crystal data: for 1, monoc linic, space group P2(1)/a, a = 11.1954(21), b = 15.8671(27), c = 12.3 605(25) Angstrom, beta = 99.981(15)degrees, V = 2162.46 Angstrom(3), Z = 2; for 2b, monoclinic, space group P2(1)/a, a = 18.9560(33), b = 13 .1023(33), c = 23.0303(50) Angstrom, beta = 99.516(15)degrees, V = 564 1.25 Angstrom(3), Z = 4; for 2c . 2THF, orthorhombic, space group Pnmn , a = 13.2676(37), b = 15.1089(45), c = 18.8811(35) Angstrom, V = 3786 .64 Angstrom(3), Z = 2.