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Use of the new ligand P(CH2CH2PCy2)3 in the synthesis of dihydrogen complexes of iron(II) and ruthenium(II)
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1993
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The novel bulky and basic tetradentate ligand P(CH<sub>2</sub>CH<sub>2</sub>PCy<sub>2</sub>)<sub>3</sub> (PP<sub>3</sub>Cy) is synthesized by the LiN(i-Pr)<sub>2</sub>-catalyzed addition reaction of dicyclohexylphosphine (HPCy<sub>2</sub>) to P(CHCH<sub>2</sub>)<sub>3</sub>. Treatment of RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub> with PP<sub>3</sub>Cy produces the five-coordinate square-pyramidal complex [RuCl(PP<sub>3</sub>Cy)]Cl, which is converted into [RuCl(PP<sub>3</sub>Cy)]BPh<sub>4</sub> when treated with NaBPh<sub>4</sub>. Similarly, FeCl<sub>2</sub> reacts with PP<sub>3</sub>Cy to give [FeCl(PP<sub>3</sub>Cy)]Cl. The structure of the tetraphenylborate salt [FeCl(PP<sub>3</sub>Cy)]BPh<sub>4</sub> is trigonal bipyramidal around Fe(II); crystals are monoclinic, space group P2<sub>1</sub>/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) Å<sup>3</sup> for Z = 4; R = 0.065. Reaction of [RuCl(PP<sub>3</sub>Cy)]Cl with excess NaBH<sub>4</sub> in THF yields mer-RuH(η<sup>2</sup>-BH<sub>4</sub>)(η<sup>3</sup>-PP<sub>3</sub>Cy-BH<sub>3</sub>), where the tetraphosphine is bound via three P atoms to ruthenium and the BH<sub>3</sub> is bound to a dangling terminal PCy<sub>2</sub> group of the tetraphosphine. The monohydride complex RuHCl(PP<sub>3</sub>Cy) is obtained from the reaction of [RuCl(PP<sub>3</sub>Cy)]Cl with excess NaOMe in refluxing THF. The η<sup>2</sup>-dihydrogen complex [RuH(η<sup>2</sup>-H<sub>2</sub>)(PP<sub>3</sub>Cy)]BPh<sub>4</sub> is synthesized by treating [RuCl(PP<sub>3</sub>Cy)]BPh<sub>4</sub> with 1 equiv of NaBH<sub>4</sub> under an atmosphere of dihydrogen. The analogous iron complex is also described. The nonclassical structures of [MH(η<sup>2</sup>-H<sub>2</sub>)(PP<sub>3</sub>Cy)]BPh<sub>4</sub> (M = Fe, Ru) are established by <sup>1</sup>H, <sup>31</sup>P, and T<sub>1</sub> NMR measurements and the observation of a <sup>1</sup>J(HD) coupling constant of 28 Hz in the isotopomer [RuD(HD)(PP<sub>3</sub>Cy)]<sup>+</sup>. Despite the steric bulk of the ligand, the complexes adopt an octahedral geometry, [MH(H<sub>2</sub>)(PP<sub>3</sub>Cy)]<sup>+</sup>, instead of a trigonal-bipyramidal ligand geometry with an H<sub>3</sub> ligand.