The role of phosphine in cobalt-catalyzed carbonylative polymerization of N-alkylaziridine

Xu, Hongfei; LeGall, Nathalie; Li, Jia; Brennessel, William W.; Kucera, Benjamin E.

doi:10.1016/j.jorganchem.2005.03.050

Cited by 12 publications

(4 citation statements)

References 54 publications

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“…Crystals of [Co(CO) 3 (PEtPh 2 )(COMe)] suitable for an X-ray crystallographic study were obtained, and the molecular structure is shown in Figure . The complex adopts a distorted trigonal bipyramidal geometry with axial acetyl and phosphine ligands, in common with the structures of a number of complexes of this type that have been reported previously (e.g., for L = PPh 3 , P( o -tolyl) 3 , PMe 2 Ph, P(4-FC 6 H 4 ) 3 , PCy 3 , P(3–F–C 6 H 4 ) 3 ). − The metal–ligand bond distances for [Co(CO) 3 (PEtPh 2 )(COMe)] are very similar to those for other members of the series, but it is notable that the Co–P distances for the P( o -tolyl) 3 and PCy 3 variants (∼2.31 and 2.28 Å, respectively) are somewhat longer than the average for the remainder (∼2.25 Å). This presumably reflects greater steric congestion.…”

Section: Resultssupporting

confidence: 69%

Ligand Effects on Reactivity of Cobalt Acyl Complexes

et al. 2012

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Hydrogenolysis reactions of cobalt acyl complexes, [Co(CO)3(L)(COR)] (L = phosphine, R = Me, n Pr) have been monitored using in situ IR spectroscopy at moderate temperatures (<75 °C) and pressures (<25 bar). The reactions provide a model for the product-formation step in phosphine-modified, cobalt-catalyzed hydroformylation. The reaction kinetics are dependent on L, with the fastest rate being observed for the complex containing n-pentyl-9-phosphabicyclo[4.2.1]nonane (a 5-PhobPC5). The observed dependence of rate on H2 and CO pressure is consistent with a mechanism involving initial CO dissociation, followed by reaction of [Co(CO)2(L)(COR)] with H2. Isotopic exchange experiments, monitored by IR spectroscopy, demonstrate that both terminal and acetyl carbonyls of [Co(CO)3(L)(COR)] exchange with free 13CO. Kinetic data are also reported for reactions of [Co(CO)3(L)(COR)] with triphenyltinhydride. A zero-order dependence on [Ph3SnH] (at large excess) and positive values of ΔS ‡ demonstrate rate-determining CO dissociation. For a series of less bulky, symmetrical phosphines, the rates follow the sequence PEt3 < PMe2Ph ∼ PEtPh2 < PPh3 < P(4-ClC6H4)3, in accord with their electron-donating strength. Higher rates are found for more bulky phosphines, and the fastest rate is again found for L = a 5-PhobPC5. Calculations using density functional theory indicate that the CO dissociation energy for [Co(CO)3(L)(COMe)] is influenced by the stereoelectronic properties of L, with steric bulk having a substantial effect. X-ray crystal structures are reported for [Co(CO)3(PEtPh2)(COMe)], [Co(CO)3(s-PhobPC5)]2, and [Co(CO)3(a 5-PhobPC5)]2.

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Section: Resultssupporting

confidence: 69%

Ligand Effects on Reactivity of Cobalt Acyl Complexes

et al. 2012

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“…Continuous progress in this area has been hampered by the fact that acyl‐Co(CO) 4 cannot be readily modified. Substitution of a CO ligand with another ligand invariably (perhaps with the exception of PF 3 ) retards the reactivity of the acyl group toward nucleophiles . The problem is particularly impairing for the epoxide COP since even acyl‐Co(CO) 4 is barely reactive enough.…”

Section: Methodsmentioning

confidence: 99%

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

Dai

Peng

et al. 2018

Angew Chem Int Ed

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Zwitterionic structure is necessary for Ni complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the Ni center imparts sufficient electrophilicity to the Ni-acyl bond for it to react with cyclic ethers to give an acyl-cyclic ether oxonium intermediate, while the ligand-centered anionic charge ensures that the resultant oxonium cation is ion-paired with the Ni nucleophile. The current catalysts give non-alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.

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“…This was a significant finding as the incorporation of THF does not occur in the related aziridine systems. [175][176][177]182,183 Further probing of the incorporation of THF led to the finding that increased azetidine concentration produced polymers with lower degrees of ester incorporation. This suggests that the reaction of the active chain end with THF is favored when the azetidine concentration is low.…”

Section: Copolymers Of Azetidines With Comentioning

confidence: 99%

“…The cobalt catalyzed carbonylative polymerization of azetidine does have a drawback in that the formation of γ-lactam also occurs. This reaction was attributed to "back-biting", 178 rather than catalyst decomposition 183 due to the continued living character of the polymerizations. Jia further hypothesized that this back-biting reaction occurs at the acylazetidinium intermediate, and not the acyl-Co(CO) 4 intermediate.…”

Section: Copolymers Of Azetidines With Comentioning

confidence: 99%