Use of the new ligand P(CH2CH2PCy2)3 in the synthesis of dihydrogen complexes of iron(II) and ruthenium(II)

The novel bulky and basic tetradentate ligand P(CH2CH2PCy2)3 (PP3Cy) is synthesized by the LiN(i-Pr)2-catalyzed addition reaction of dicyclohexylphosphine (HPCy2) to P(CHCH2)3. Treatment of RuCl2(PPh3)3 with PP3Cy produces the five-coordinate square-pyramidal complex [RuCl(PP3Cy)]Cl, which is converted into [RuCl(PP3Cy)]BPh4 when treated with NaBPh4. Similarly, FeCl2 reacts with PP3Cy to give [FeCl(PP3Cy)]Cl. The structure of the tetraphenylborate salt [FeCl(PP3Cy)]BPh4 is trigonal bipyramidal around Fe(II); crystals are monoclinic, space group P21/c, with a = 12.699(4) Å, b = 29.046(16) Å, c = 17.026(7) Å, β = 103.14(3)°, and V = 6116(5) Å3 for Z = 4; R = 0.065. Reaction of [RuCl(PP3Cy)]Cl with excess NaBH4 in THF yields mer-RuH(η2-BH4)(η3-PP3Cy-BH3), where the tetraphosphine is bound via three P atoms to ruthenium and the BH3 is bound to a dangling terminal PCy2 group of the tetraphosphine. The monohydride complex RuHCl(PP3Cy) is obtained from the reaction of [RuCl(PP3Cy)]Cl with excess NaOMe in refluxing THF. The η2-dihydrogen complex [RuH(η2-H2)(PP3Cy)]BPh4 is synthesized by treating [RuCl(PP3Cy)]BPh4 with 1 equiv of NaBH4 under an atmosphere of dihydrogen. The analogous iron complex is also described. The nonclassical structures of [MH(η2-H2)(PP3Cy)]BPh4 (M = Fe, Ru) are established by 1H, 31P, and T1 NMR measurements and the observation of a 1J(HD) coupling constant of 28 Hz in the isotopomer [RuD(HD)(PP3Cy)]+. Despite the steric bulk of the ligand, the complexes adopt an octahedral geometry, [MH(H2)(PP3Cy)]+, instead of a trigonal-bipyramidal ligand geometry with an H3 ligand.