Catalytic and mechanistic studies of a highly active and E-selective Co(ii) PNN^H pincer catalyst system for transfer-semihydrogenation of internal alkynes

Abstract

Herein we report the application of a Co(II) PNNH pincer catalyst system (PNNH = 2-(5-(t-butyl)-1H-pyrazol-3-yl)-6-(dialkylphosphinomethyl)pyridine) for the highly E-selective transfer semihydrogenation of internal diaryl alkynes using methanol and ammonia borane...

Cobalt-catalysed nucleophilic fluorination in organic carbonates

“…M06-L has also been shown to perform reasonably well in predicting the spin state of Co complexes, 39,49 and has demonstrated a good performance on catalytic studies of related systems. 52–54 M06 and B3LYP are hybrid functionals very commonly used in catalysis, and have also been applied to related processes. 40,55–58 The Gibbs energy results for the reaction mechanism of the Co–F assisted nucleophilic fluorination reaction of benzoyl chloride ( vide infra ) are provided in Table S2,† and, as somehow expected, there is a relatively big dispersion in the results, B3LYP and M06-L providing similar activation barriers (15.3 and 16.7 kcal mol −1 , respectively), while M06 predicts an intermediate value (23.7 kcal mol −1 ), and TPSS and TPSSh provide the highest one (29.1 and 30.7 kcal mol −1 , respectively).…”

“…M06-L has also been shown to perform reasonably well in predicting the spin state of Co complexes, 39,49 and has demonstrated a good performance on catalytic studies of related systems. [52][53][54] M06 and B3LYP are hybrid functionals very commonly used in catalysis, and have also been applied to related processes. 40,[55][56][57][58] The Gibbs energy results for the reaction mechanism of the Co-F assisted nucleophilic fluorination reaction of benzoyl chloride…”

“…Moreover, in operando 31 P NMR, spectra show exclusively the presence of 3. This way, given its reported good performance in the study of reaction mechanisms, [52][53][54] we consider the M06-L functional for the proposal and discussion of the reaction mechanism.…”

Hydrogenation and Cross-Coupling Reactions Catalyzed by Mn, Fe, and Co Aromatic Pincer Complexes

“…41 Cobalt compounds have also demonstrated promising activity in alkene hydrogenation. 42,43 In 2005, the Budzelaar group investigated the activity of two cobalt−diimine−pyridine complexes, 7 and 8, in the hydrogenation of alkenes. 44 In the mechanism of this reaction, the stoichiometric reaction of 7 with molecular hydrogen releases the trimethylsilyl methyl ligand, and a diamagnetic hydride complex, (NNN)CoH (I) is formed, in which an olefin insertion in the Co−H bond takes place to yield the alkyl derivative (II).…”

Rhodium(I) PNN Pincer Complexes with Proton‐responsive Ligands: Synthesis, Characterisation, and Catalytic Dehydrocoupling of Amine Boranes

“…[10] This observation of significant differences when changing the metal using the identical pincer ligand prompted us to investigate the influence of other potentially cooperative phosphine-based ligands in combination with group 9 metals. Based on previous work on a Co system bearing a pyridinepyrazole PNN(H) ligand, that was initially reported by Caulton and co-workers, [11] for catalytic transfer semihydrogenation of alkynes using H 3 B•NH 3 as the hydride source, [12] we now present the coordination chemistry of this ligand at Rh I along with a study of selected complexes for the dehydrocoupling of amine boranes (Figure 1b). The pyrazole moiety was chosen as a highly versatile functional group that can not only act as a proton shuttle during dehydrogenation of the amine borane or as a directing group for controlling the BÀ N bond formation event during oligomerisation via hydrogen bonding, but also undergo ligand-to-metal tautomerisation (i. e., from a square planar L(H)-M to an octahedral LÀ M(H) complex) to produce a potentially active Rh III hydride species.…”