Matching Items (2)

129505-Thumbnail Image.png

Preparation and Hydrosilylation Activity of a Molybdenum Carbonyl Complex That Features a Pentadentate Bis(imino)pyridine Ligand

Description

Attempts to prepare low-valent molybdenum complexes that feature a pentadentate 2,6-bis(imino)pyridine (or pyridine diimine, PDI) chelate allowed for the isolation of two different products. Refluxing Mo(CO)[subscript 6] with the pyridine-substituted

Attempts to prepare low-valent molybdenum complexes that feature a pentadentate 2,6-bis(imino)pyridine (or pyridine diimine, PDI) chelate allowed for the isolation of two different products. Refluxing Mo(CO)[subscript 6] with the pyridine-substituted PDI ligand, [superscript PyEtP]DI, resulted in carbonyl ligand substitution and formation of the respective bis(ligand) compound ([superscript PyEt]PDI)[subscript 2]Mo (1). This complex was investigated by single-crystal X-ray diffraction, and density functional theory calculations indicated that 1 possesses a Mo(0) center that back-bonds into the π*-orbitals of the unreduced PDI ligands. Heating an equimolar solution of Mo(CO)[subscript 6] and the phosphine-substituted PDI ligand, [superscript Ph2PPr]PDI, to 120 °C allowed for the preparation of ([superscript Ph2PPr]PDI)Mo(CO) (2), which is supported by a κ5-N,N,N,P,P-[superscript Ph2PPr]PDI chelate. Notably, 1 and 2 have been found to catalyze the hydrosilylation of benzaldehyde at 90 °C, and the optimization of 2-catalyzed aldehyde hydrosilylation at this temperature afforded turnover frequencies of up to 330 h[superscript –1]. Considering additional experimental observations, the potential mechanism of 2-mediated carbonyl hydrosilylation is discussed.

Contributors

Agent

Created

Date Created
  • 2014-09-01

129517-Thumbnail Image.png

Catalytic Hydrogen Evolution by Fe(II) Carbonyls Featuring a Dithiolate and a Chelating Phosphine

Description

Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P[subscript 2] [bdt = benzene-1,2-dithiolate; P[subscript 2] = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal

Two pentacoordinate mononuclear iron carbonyls of the form (bdt)Fe(CO)P[subscript 2] [bdt = benzene-1,2-dithiolate; P[subscript 2] = 1,1′-diphenylphosphinoferrocene (1) or methyl-2-{bis(diphenylphosphinomethyl)amino}acetate (2)] were prepared as functional, biomimetic models for the distal iron (Fe[subscript d]) of the active site of [FeFe]-hydrogenase. X-ray crystal structures of the complexes reveal that, despite similar ν(CO) stretching band frequencies, the two complexes have different coordination geometries. In X-ray crystal structures, the iron center of 1 is in a distorted trigonal bipyramidal arrangement, and that of 2 is in a distorted square pyramidal geometry. Electrochemical investigation shows that both complexes catalyze electrochemical proton reduction from acetic acid at mild overpotential, 0.17 and 0.38 V for 1 and 2, respectively. Although coordinatively unsaturated, the complexes display only weak, reversible binding affinity toward CO (1 bar). However, ligand centered protonation by the strong acid, HBF[subscript 4]·OEt[subscript 2], triggers quantitative CO uptake by 1 to form a dicarbonyl analogue [1(H)-CO][superscript +] that can be reversibly converted back to 1 by deprotonation using NEt[subscript 3]. Both crystallographically determined distances within the bdt ligand and density functional theory calculations suggest that the iron centers in both 1 and 2 are partially reduced at the expense of partial oxidation of the bdt ligand. Ligand protonation interrupts this extensive electronic delocalization between the Fe and bdt making 1(H)[superscript +] susceptible to external CO binding.

Contributors

Agent

Created

Date Created
  • 2014-09-01