LIGAND-EXCHANGE OR REDUCTION AT MULTIPLY-BONDED DIMETAL UNITS OF MOLYBDENUM AND RHENIUM BY 2,6-BIS(DIPHENYLPHOSPHINO)PYRIDINE

Reaction of 2,6-bis(diphenylphosphino)pyridine (bdppp or (Ph2P)(2)Py)) with K4Mo2Cl8 in refluxing methanol gives Mo2Cl4(bdppp)(2) (1) with r etention of the quadruple Mo-Mo bond. However, the quadruply bonded oc tachlorodirhenate(III) anion, Re2Cl82-, reacts with bdppp under simila r conditions to afford Re2Cl4(bdppp)2 (2), which has a triply bonded d irhenium(II) core, Re-2(4+). An intermediate species, [(Bu4N)-N-n][Re2 Cl7(bdppp)] (3), containing an Re-2(6+) core and only one bridging bdp pp ligand has also been isolated. The crystal structures of complexes 1-3 have been investigated by X-ray crystallography. In all cases the potentially tridentate bdppp acts as a bidentate ligand using one N an d one of the P atoms, leaving the second phosphorus atom noncoordinate d. The crystallographic parameters for these structures are as follows : Mo2Cl4(bdppp)(2). 2CH(2)Cl(2) (1 . 2CH(2)Cl(2)), monoclinic space gr oup P2(1)/c with a = 15.475(2) Angstrom, b = 11.5958(7) Angstrom, c = 16.7637 (6) Angstrom, beta = 98.178(5)degrees, Z = 2; Re-2-Cl-4(bdppp) (2) (2), monoclinic space group P2(1)/n with a = 16.173(2) Angstrom, b = 11.285(1) Angstrom, c = 28.771 (4) Angstrom, beta = 96.17(1)degrees , Z = 4. [(Bu4N)-N-n][Re2Cl7(bdppp)]. CH2Cl2 (3 . CH2Cl2), triclinic s pace group P (1) over bar with a = 16.054(2) A, b = 18.562(3) Angstrom , c = 20.205 (6) A, a = 89.71(2)degrees, P = 73.21(1)degrees, gamma = 73.47(2)degrees, Z = 4.