Binuclear Molybdenum Carbonyls Bridged Both by Hydride and by Bidentate Phosphine Ligands. Crystal and Molecular Structures of Salts of (μ-H)(μ-Ph2P(CH2)nPPh2)Mo2(CO)8- (n=1-4) and Their Reactions with Acids

Article abstract of DOI:10.1021/ja00321a016

Reaction of Et4N⁺ and Ph4P⁺ salts of μ-HMo2(CO)10^- with bidentate phosphine ligands in refluxing THF yielded salts of μ-HMo2(CO)8(Ph2P(CH2)nPPh2)^-, n=1-4, designated as anions 1^-, 2^-, 3^-, and 4^-.X-ray crystal structure analyses for two of the new compounds were carried out, and the following parameters were obtained.Ph4P⁺1^-: P2₁/c, Z=4, a=13.886(6) Angstroem, b=18.545(9) Angstroem, c=20.156(6) Angstroem, β=91.03(4) deg, V=5190(4) Angstroem³, R=0.0413 for 4402 reflections with /F₀/>=3?/F₀/.Et4N⁺4^-: P1, Z=2, a=8.760(2) Angstroem, b=13.940(4) Angstroem, c=19.686(4) Angstroem, α=105.75(2) deg, β=93.59(2) deg, γ=97.38(2) deg, V=2282(1) Angstroem³, R=0.0471 for 4720 reflections with /F₀/>=3?/F₀/.Anions 1^- and 4^- are bridged by both H^- and the bidentate ligands and show overall bent, staggered configurations with P₁-Mo₁-Mo₂-P₂ torsion angles of 21 deg for 1^- and 42 deg for 4^-.Similar framework bends (the intersection angle of (OC)_ax-Mo vectors) of ca. 160 deg and similar Mo₁-H-Mo₂ angles of ca. 131 deg are observed for 1^- and 4^-.The Mo...Mo separation in 1^- is 3.4028(8) Angstroem and in 4^- it is 3.4995(8) Angstroem.The distance between the P-donor atoms in 1^- is 3.19 Angstroem and in 4^- it is 5.08 Angstroem.In 4^- the hydride bridge is directed into the area underneath the ligand bridge (the (CH2)4 unit), whereas in 1^- the plane of the hydride bridge is roughly perpendicular to the P-CH2-P bridge.The observed ligand substitution site selection was rationalized on the basis of the best match of bridge ligand donor site separation and intermetal ligand coordination site separation in the bent, staggered form of the parent μ-HMo2(CO)10^-.A specific synthesis of the dibridged neutral bimetallics (μ-Ph2P(CH2)nPPh2)(μ-Ph2P(CH2)2PPh2)Mo2(CO)8 (n=1,2) and (μh2As(CH2)2AsPPh2)(μ-Ph2P(CH2)2PPh2)Mo2(CO)8 has been based on low-temperature protonation of 2^- in the presence of other bidentate ligands.