Showing papers by "Stanislav Groysman published in 2016"

Synthesis and Characterization of a Stable High-Valent Cobalt Carbene Complex

Abstract: The formally CoIV carbene Co(OR)2(═CPh2) is formed upon the reaction of diphenyldiazomethane with the cobalt bis(alkoxide) precursor Co(OR)2(THF)2. Structural, spectroscopic, and theoretical studies demonstrate that Co(OR)2(═CPh2) has significant high-valent CoIV═CPh2 character with non-negligible spin density on the carbene moiety.

Ambiguous electrocatalytic CO2 reduction behaviour of a nickel bis(aldimino)pyridine pincer complex

Abstract: The electrochemical properties of two Ni(NNN)X2 pincer complexes are reported where X = Cl or Br and NNN is N,N'-(2,6-diisopropylphenyl)bis-aldiminopyridine. Cyclic voltammetry under 1 atm of CO2 suggests electrocatalytic CO2 reduction activity, however, bulk electrolysis shows a poor Faradaic efficiency for CO evolution with a high Faradaic yield for H2 evolution.

Synthesis of a mononuclear, non-square-planar chromium(ii) bis(alkoxide) complex and its reactivity toward organic carbonyls and CO2.

Abstract: In this paper, we report the synthesis and reactivity of a rare mononuclear chromium(II) bis(alkoxide) complex, Cr(OR′)2(THF)2, that is supported by a new bulky alkoxide ligand (OR′ = di-t-butyl-(3,5-diphenylphenyl)methoxide). The complex is prepared by protonolysis of square-planar Cr(N(SiMe3)2)2(THF)2 with HOR′. X-ray structure determination disclosed that Cr(OR′)2(THF)2 features a distorted seesaw geometry, in contrast to nearly all other tetra-coordinate Cr(II) complexes, which are square-planar. The reactivity of Cr(OR′)2(THF)2 with aldehydes, ketones, and carbon dioxide was investigated. Treatment of Cr(OR′)2(THF)2 with two equivalents of aromatic aldehydes ArCHO (ArCHO = benzaldehyde, 4-anisaldehyde, 4-trifluorbenzaldehyde, and 2,4,6-trimethylbenzaldehyde) leads cleanly to the formation of Cr(IV) diolate complexes Cr(OR′)2(O2C2H2Ar2) that were characterized by UV-vis and IR spectroscopies and elemental analysis; the representative complex Cr(OR′)2(O2C2H2Ph2) was characterized by X-ray crystallography. In contrast, no reductive coupling was observed for ketones: treatment of Cr(OR′)2(THF)2 with one or two equivalents of benzophenone forms invariably a single ketone adduct Cr(OR′)2(OCPh2) which does not react further. QM/MM calculations suggest the steric demands prevent ketone coupling, and demonstrate that a mononuclear Cr(III) bis-aldehyde complex with partially reduced aldehydes is sufficient for C–C bond formation. The reaction of Cr(OR′)2(THF)2 with CO2 leads to the insertion of CO2 into a Cr–OR′ bond, followed by complex rearrangement to form a diamagnetic dinuclear paddlewheel complex Cr2(O2COR′)4(THF)2, that was characterized by NMR, UV-vis, and IR spectroscopy, and X-ray crystallography.

Discrete Complexes of 3d Metals with Monodentate Bulky Alkoxide Ligands and Their Reactivity in Bond Activation and Bond Formation Reactions

Abstract: This review focuses on the design, synthesis, and reactivity of low-coordinate base transition metal complexes supported by bulky alkoxide ligands. The unique electronic features of alkoxide ligands result in strongly electrophilic character at the metal centers, which enhances reactivity of metal-bound substrates and facilitates their transformation. However, insufficiently bulky alkoxide ligands tend to form oligomeric and polymeric aggregates, thus circumventing well-defined reactivity at isolated metal centers. This review examines first the requirements for the attainment of mononuclear complexes in alkoxide ligand environments. Coordination chemistry of the most prominent alkoxide ligands [OCR3] is discussed, with particular emphasis on the impact of the R group on the nuclearity of the resulting complex and the number of alkoxide ligands bound to it. Next, the behavior of such complexes in group transfer chemistry and ensuing reactivity is examined. While several previously synthesized alkoxide lig...