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  1. Free, publicly-accessible full text available July 10, 2024
  2. We shed light on the mechanism and rate-determining steps of the electrochemical carboxylation of acetophenone as a function of CO 2 concentration by using a robust finite element analysis model that incorporates each reaction step. Specifically, we show that the first electrochemical reduction of acetophenone is followed by the homogeneous chemical addition of CO 2 . The electrochemical reduction of the acetophenone-CO 2 adduct is more facile than that of acetophenone, resulting in an Electrochemical–Chemical–Electrochemical (ECE) reaction pathway that appears as a single voltammetric wave. These modeling results provide new fundamental insights into the complex microenvironment in CO 2 -rich media that produces an optimum electrochemical carboxylation rate as a function of CO 2 pressure.
    Free, publicly-accessible full text available May 9, 2024
  3. Manganese ([Mn(CO) 3 ]) and rhenium tricarbonyl ([Re(CO) 3 ]) complexes represent a workhorse family of compounds with applications in a variety of fields. Here, the coordination, structural, and electrochemical properties of a family of mono- and bimetallic [Mn(CO) 3 ] and [Re(CO) 3 ] complexes are explored. In particular, a novel heterobimetallic complex featuring both [Mn(CO) 3 ] and [Re(CO) 3 ] units supported by 2,2′-bipyrimidine (bpm) has been synthesized, structurally characterized, and compared to the analogous monomeric and homobimetallic complexes. To enable a comprehensive structural analysis for the series of complexes, we have carried out new single crystal X-ray diffraction studies of seven compounds: Re(CO) 3 Cl(bpm), anti -[{Re(CO 3 )Cl} 2 (bpm)], Mn(CO) 3 Br(bpz) (bpz = 2,2′-bipyrazine), Mn(CO) 3 Br(bpm), syn - and anti -[{Mn(CO 3 )Br} 2 (bpm)], and syn -[Mn(CO 3 )Br(bpm)Re(CO) 3 Br]. Electrochemical studies reveal that the bimetallic complexes are reduced at much more positive potentials (Δ E ≥ 380 mV) compared to their monometallic analogues. This redox behavior is consistent with introduction of the second tricarbonyl unit which inductively withdraws electron density from the bridging, redox-active bpm ligand, resulting in more positive reduction potentials. [Re(CO 3 )Cl] 2 (bpm) was reducedmore »with cobaltocene; the electron paramagnetic resonance spectrum of the product exhibits an isotropic signal (near g = 2) characteristic of a ligand-centered bpm radical. Our findings highlight the facile synthesis as well as the structural characteristics and unique electrochemical behavior of this family of complexes.« less
  4. Abstract

    Ligands based upon the 4,5‐diazafluorene core are an important class of emerging ligands in organometallic chemistry, but the structure and electronic properties of these ligands have received less attention than they deserve. Here, we show that 9,9′‐dimethyl‐4,5‐diazafluorene (Me2daf) can stabilize low‐valent complexes through charge delocalization into its conjugated π‐system. Using a new platform of [Cp*Rh] complexes with three accessible formal oxidation states (+III, +II, and +I), we show that the methylation in Me2daf is protective, blocking Brønsted acid‐base chemistry commonly encountered with other daf‐based ligands. Electronic absorption spectroscopy and single‐crystal X‐ray diffraction analysis of a family of eleven new compounds, including the unusual Cp*Rh(Me2daf), reveal features consistent with charge delocalization driven by π‐backbonding into the LUMO of Me2daf, reminiscent of behavior displayed by the workhorse 2,2′‐bipyridyl ligand. Taken together with spectrochemical data demonstrating clean conversion between oxidation states, our findings show that 9,9′‐dialkylated daf‐type ligands are promising building blocks for applications in reductive chemistry and catalysis.

  5. 4,5-diazafluorene (daf) and 9,9’-dimethyl-4,5-diazafluorene (Me2daf) are structurally similar to the important ligand 2,2’-bipyridine (bpy), but significantly less is known about the redox and spectroscopic properties of metal complexes containing Me2daf as a ligand than those containing bpy. New complexes Mn(CO)3Br(daf) (2), Mn(CO)3Br(Me2daf) (3), and [Ru(Me2daf)3](PF6)2 (5) have been prepared and fully characterized to understand the influence of the Me2daf framework on their chemical and electrochemical properties. Structural data for 2, 3, and 5 from single-crystal X-ray diffraction analysis reveal a distinctive widening of the daf and Me2daf chelate angles in comparison to the analogous Mn(CO)3(bpy)Br (1) and [Ru(bpy)3]2+ (4) complexes. Electronic absorption data for these complexes confirm the electronic similarity of daf, Me2daf, and bpy, as spectra are dominated in each case by metal-to-ligand charge transfer bands in the visible region. However, the electrochemical properties of 2, 3, and 5 reveal that the redox-active Me2daf framework in 3 and 5 undergoes reduction at a slightly more negative potential than that of bpy in 1 and 4. Taken together, the results indicate that Me2daf could be useful for preparation of a variety of new redox-active compounds, as it retains the useful redox-active nature of bpy but lacks the acidic, benzylic C–Hmore »bonds that can induce secondary reactivity in complexes bearing daf.« less