On the Coordination Chemistry of Bis- and Trisphosphinimine Containing Ligands

Webb, Duncan; Hayes, Paul G.

doi:10.1016/b978-0-08-102688-5.00090-8

Cited by 2 publications

(3 citation statements)

References 90 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…What makes these ligands so intriguing is their unique electronic structure; they can act as both strong σand π-donors due to their ylide-like structure. 42,55 Therefore, it was thought that phosphinimines and/or phosphinimides would be well suited for stabilizing high oxidation state, coordinatively unsaturated ruthenium carbene complexes that are common intermediates during OM. Additionally, phosphinimides have been used in place of cyclopentadienyl ligands for d 0 metallocene olefin polymerization catalysts.…”

Section: ■ Introductionmentioning

confidence: 94%

“…Phosphinimines are an underutilized class of ligands for late-transition metals that are beginning to receive more and more attention, especially as chelating donors for catalytic applications . Monodentate phosphinimines, however, are quite rare on ruthenium, whereas monodentate phosphinimide complexes are a bit more common. − Moreover, while phosphinimides have been utilized in early transition-metal-based alkyne metathesis, to the best of our knowledge, phosphinimines and phosphinimides have not been used in ruthenium-based OM catalysts.…”

Section: Introductionmentioning

confidence: 99%

“…Monodentate phosphinimines, however, are quite rare on ruthenium, whereas monodentate phosphinimide complexes are a bit more common. − Moreover, while phosphinimides have been utilized in early transition-metal-based alkyne metathesis, to the best of our knowledge, phosphinimines and phosphinimides have not been used in ruthenium-based OM catalysts. What makes these ligands so intriguing is their unique electronic structure; they can act as both strong σ- and π-donors due to their ylide-like structure. , Therefore, it was thought that phosphinimines and/or phosphinimides would be well suited for stabilizing high oxidation state, coordinatively unsaturated ruthenium carbene complexes that are common intermediates during OM. Additionally, phosphinimides have been used in place of cyclopentadienyl ligands for d 0 metallocene olefin polymerization catalysts. − A significant benefit seen for phosphinimide ligands was that they provided steric protection to the catalysts, but they also facilitated alkene binding because the bulkiness of the ligand was further removed from the metal due to the nitrogen spacer .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Ruthenium Phosphinimine Complex as a Fast-Initiating Olefin Metathesis Catalyst with Competing Catalytic Cycles

2022

View full text Add to dashboard Cite

A ruthenium-based olefin metathesis (OM) catalyst bearing a monodentate triphenylphosphinimine ligand, Ru1, was synthesized, characterized, and its activity for the homocoupling of terminal alkenes was investigated. Utilizing 1-hexene as a model substrate, the empirical rate law for Ru1 was found to be first-order in alkene and complex (indicating that both species were involved in the rate-limiting step), with a rate constant of 0.697 ± 0.050 M–1 s–1. Moreover, the experimentally determined activation parameters ΔS ⧧ and ΔH ⧧ (−48.7 ± 5.1 eu and 3.19 ± 0.15 kcal/mol, respectively) were consistent with an associative or associative interchange ligand substitution reaction. When considering the ΔG ⧧ (298 K) value of 17.7 kcal/mol, Ru1 ranked among the fastest initiating ruthenium-based OM catalysts reported in the literature. Density functional theory (DFT) calculations were also performed to explore potential catalytic mechanisms. Two pathways were considered: a traditional mechanism where the phosphinimine ligand de-coordinated and an alternative mechanism where the phosphine donor de-coordinated. Although the energy differences between the two pathways were typically fairly small (1.4–3.5 kcal/mol), the alternative pathway with phosphine de-coordination was energetically more favorable. It is anticipated, however, that both cycles are working in tandem during the catalytic reaction. In addition to kinetic studies, the stability of Ru1 was explored using 1-hexene as a model substrate. The phosphinimine catalyst was found to be mildly oxygen-sensitive and moisture-tolerant. Furthermore, Ru1 was determined to be prone to bimolecular decomposition, through the crystallographic characterization of a key degradation product. There was also strong evidence for NH exchange between the tricyclohexylphosphine and triphenylphosphinimine moieties. Lastly, the substrate scope of Ru1 in regard to α-olefins was explored. Catalytic efficiency dropped with more electron-deficient alkenes, as well as with increasing steric bulk on the substrate, which was consistent with the proposed catalytic mechanism.

show abstract

Section: ■ Introductionmentioning

confidence: 94%