[Co(NHC)(CO)₃]: Isolation and Reactivity Study of a Model 17-Electron Species in the Oxo Process

Abstract

Metrics & MoreArticle Recommendations * sı Supporting InformationABSTRACT: [Co(L)(CO) 3 ] 2 (L = CO or PR 3 ) catalyzed hydroformylation of olefins is among the most successful homogeneous organometallic catalysis. The bimetallic [Co(L)(CO) 3 ] 2 complex exists in equilibrium with its mononuclear 17electron [Co(L)(CO) 3 ] metalloradical. However, isolation of the mononuclear metalloradical is unknown, and hence the role of this species in the catalytic cycle is difficult to study. Herein, we report the isolation of [Co(L)(CO) 3 ] using ringexpanded N-heterocyclic carbene (reNHC) ligands. Isolation of this complex enabled us to examine feasibility of putative termolecular H 2 activation by the [Co(L)(CO) 3 ] metalloradicals. The kinetic experiments revealed that [Co(reNHC)(CO) 3 ] does not activate H 2 via a previously proposed termolecular mechanism but via a bimolecular mechanism. The result obtained here will contribute to design a cobalt carbonyl complex that activates H 2 under mild conditions and to develop a more energy efficient oxo process based on economical cobalt catalysts.

Markovnikov Hydrosilylation of Alkynes with Tertiary Silanes Catalyzed by Dinuclear Cobalt Carbonyl Complexes with NHC Ligation

“…Complex 5 can be viewed as an analog of (IPr)­Co 2 (CO) 5 and has been fully characterized by various spectroscopic methods. Its molecular structure (Figure S5) is similar to [(6-Mes) 2 Co 2 (CO) 2 (μ-CO) 2 ] (6-Mes = 1,3-dimesityl-1,4,5,6-tetrahydro-pyrimidine-3-ylidene) reported recently …”

“…Its molecular structure (Figure S5) is similar to [(6-Mes) 2 Co 2 (CO) 2 (μ-CO) 2 ] (6-Mes = 1,3dimesityl-1,4,5,6-tetrahydro-pyrimidine-3-ylidene) reported recently. 47 Testing the catalytic performance of 1−5 in the catalytic reactions of PhCCH with HSiEt 3 then revealed the higher catalytic activity of the mono(NHC)-dicobalt bridging alkyne complex 2 over the other complexes. Monitoring the kinetic profile of the reaction at 60 °C with 1 as catalyst revealed that the reaction involves an apparent induction period (ca.…”

Direct observation of reversible bond homolysis by 2D EXSY NMR

“…4d). The molecular weight (449.17 g mol À1 ), tetrahedral geometry, and charge neutrality of 4 make this molecule the closest structural analog to the tetrahedral 56 and neutral [Co(SIMes)(CO) 3 ] radical (449.41 g mol À1 ) with practically identical molecular weights. 2D DOSY NMR spectra recorded at 24 C showed complete sets of signals from 2-Mes and 4 (Fig.…”

“…71 The ligand steric effect is a reliable way to control metal-metal bond strength. 13,56,[72][73][74] In contrast, the ligand electronic effect on metal-metal bond strength is not fully understood 23,68,75 partly due to the lack of an appropriate system to study ligand steric and electronic effects separately. 23 .…”

Synthesis of d10 N-Heterocyclic Carbene Complexes with a Perimidine Scaffold

“…Remarkably, the case for six-membered-ring NHCs is reversed. The saturated variants have dominated the literature and conjugated examples based on a perimidine scaffold are rare (Figure A). − To date, the complexes that have been characterized are restricted to group 8–10 transition metals with d electron counts of 6 or 8. (Figure B).…”