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The absorption spectra of a series of dithiocarboxylates were investigated in the ultraviolet-visible region. Two questions that this study aimed to address were as follows: (1) What transitions give rise to the features in the electronic spectra? And (2) what are the long- and short-range substituent effects on the absorption spectra? A series of 11 dithiocarboxylates were prepared as organic soluble salts. Time-dependent density functional theory (TDDFT) was used to calculate excited state energies and oscillator strengths of electronic transitions. TDDFT at the CAM-B3LYP/def2-TZVPD level of theory predicts two low-energy n → π* transitions and two π → π* transitions at higher energy, consistent with the experimental spectra. This state ordering and density is in contrast to the better studied thiocarbonyls for which only two transitions within the singlet manifold appear in the UV-visible region. For derivatives of dithiobenzoate, the energy of the three lowest energy states are insensitive to changes to substituents para to the dithiocarboxylate group. In contrast, the energy of the highest ππ* state varies by 0.78 eV. This work shows that the results of TDDFT calculations can be used to predict the electronic absorption spectra of dithiocarboxylates, providing a useful tool for designing dithiocarboxylate light absorbers.

The synthesis and catalytic activity of several classes of NHC–Ni(0) pre-catalysts stabilized by electron-withdrawing alkenes are described. Variations in the structure of fumarate and acrylate ligands modulate the reactivity and stability of the NHC–Ni(0) pre-catalysts and lead to practical and versatile catalysts for a variety of transformations. The catalytic activity and efficiency of representative members of this class of catalysts have been evaluated in reductive couplings of aldehydes and alkynes and in N-arylations of aryl chlorides.

The mechanism of nickel(0)-catalyzed reductive coupling of aldehydes and alkynes has been studied. Extensive double-labeling crossover studies have been conducted. While previous studies illustrated that phosphine- and N-heterocyclic carbene-derived catalysts exhibited differing behavior, the origin of these effects has now been evaluated in detail. Many variables, including ligand class, sterics of the ligand and alkyne, temperature, and ring size being formed in intramolecular versions, all influence the extent of crossover observed. A computational evaluation of these effects suggests that dimerization of a key metallacyclic intermediate provides the origin of crossover. Protocols that proceed with crossover are typically less efficient than those without crossover given the thermodynamic stability and low reactivity of the dimeric metallacycles involved in crossover pathways.