Quadruply bonded complexes containing η2- or η3-tridentate phosphine ligands; syntheses, structures and 31P{1H} NMR spectra of Mo2Cl4(η3-etp) (L).

Article abstract of DOI:10.1016/s0020-1693(97)05961-6

The reactive complex Mo₂Cl₄(η³-etp) (CH₃OH) (etP = Ph₂PCH₂CH₂P(Ph)CH₂CH ₂PPh₂) (1) was synthesized by reacting (NH₄)₅Mo₂Cl₉ with 1 equiv. of etp in CH₃OH. Reactions of 1 with PMe₃ and PEt₃ in THF gave Mo₂Cl₄(η³-etp) (PMe₃) (2) and Mo₂Cl₄(η³-etp)(PEt₃) (3) respectively. The complex α-Mo₂Cl₄(η²-etp)₂ (4) was synthesized by refluxing Mo₂Cl₄(η³-etp)(CH₃OH) with 1 equiv. of etp in CH₃OH, where η³-etp is transformed to η²-etp. Complex 4 can also be prepared by reacting (NH₄)₅Mo₂Cl₉ with 2 equiv. of etp in refluxing CH₃OH. Their UV-Vis and ³¹PNMR spectra were recorded and the structures of 3 and 4 were determined. Crystal data for 3·C₇H₈: space group P2_l/n, a = 11.846(2), b = 29.349(3), c = 15.429(3) A?, β = 112.52(1)°, V = 4955(2) A?³, Z = 4, with final residuals R = 0.0797 and R_w = 0.0811. Crystal data for 4·2C₇H₈: space group P2₁/c, a = 14.555(2), b = 14.988(2), c = 20.220(3) A?, β = 106.80(1)°, V = 4222(1) A?³, Z = 2, with final residuals R = 0.0882 and R_w = 0.0893. The etp ligands in 1-3 are coordinated to the Mo centers in tridentate fashion with chelating/bridging bonding modes. The etp ligands in 4 are chelated to the Mo centers in bidentate fashion through the central phosphorus atom and one terminal phosphorus atom. Complex 4 appears to be the first binuclear biligate complex chelated by linear tridentate ligands. Study of the ³¹P{¹H} NMR spectrum of 3 leads to the conclusion that the through metal-metal quadruple bonding coupling |³J_p-Mo-Mo-P| is in the range from 18.18 to 24.28 Hz for complexes of the type Mo₂Cl₄(η³-etp)(L) (L = monodentate ligand).