Mixed chloride/amine complexes of dimolybdenum(II,II). 2. Reactions of Mo2Cl4(NHEt2)(4) with monodentate and bidentate phosphines. New type of compounds Mo2Cl4(diphosphine)(4)

The complex Mo2Cl4(NHEt2)(4) (1) undergoes facile substitution reactions of the amine ligands by phosphines to give compounds with the same core struc ture, Mo2Cl4(phosphine)(4), where the phosphine is PMe3 (2), PMe2Ph (3), PH Et2 (4), dmpm (bis(dimethylphosphino)methane) (5), or dmpe (1,2-bis(dimethy lphosphino)ethane) (6). Complexes of the type M2X4L4 are well-known with mo nodentate ligands, but there is no previous crystallographically verified e xample of the M2X4L4 type of compound in which L is a potentially bidentate ligand acting as a unidentate ligand. Mo2Cl4(eta(1)-dmpm)(4) (5) can be is olated in good yield as the kinetic product of the substitution reaction at room temperature. When a solution of 5 in THF is heated, transformation in to the more stable compound Mo2Cl4(mu-dmpm)(2) (7) takes place. Mo2Cl4(eta( 1)-dmpe)(4) (6) is stable in solution in the presence of free phosphine and can be detected by NMR. Over time it converts to a polymeric material whic h precipitates from the solution. For dppm (bis(diphenylphosphino)methane) (8) and dppa (bis(diphenylphosphino)amine) (9), only products of the stoich iometry Mo2Cl4(diphosphine)(2) were obtained. The crystal structures of the complexes 4 and 5 have been investigated by X-ray diffraction. The crystal lographic parameters for them are as follows: for 4, orthorhombic space gro up Pbcn with a = 7.6015(8) Angstrom, b = 20.120(8) Angstrom, c = 19.070(6) Angstrom, and Z = 4; for 5, hexagonal space group P6(4)22 with a = 12.396(1 ) Angstrom, c = 22.960(2) Angstrom, and Z = 3. Both structures have a Mo2Cl 4P4 core where the phosphorus atoms are trans one to another on each metal center. The Mo-Mo distances of 2.137(1) Angstrom (4) and 2.137(1) Angstrom (5) are consistent with quadruple bonding.