Metal and halogen dependence of the rate effect in hydroamination/cyclization of unactivated aminoalkenes: Synthesis, characterization, and catalytic rates of CCC-NHC hafnium and zirconium pincer complexes

Clark, Wesley D.; Cho, Joon; Valle, Henry U.; Hollis, T. Keith; Valente, E.

doi:10.1016/j.jorganchem.2013.11.001

Cited by 33 publications

(11 citation statements)

References 84 publications

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“…The preparation of this compound was based on previously published methods [19,23]. 2,6-Bis(1-imidazolyl)pyridine (0.201 g, 0.095 mmol), bromoethane (0.70 ml, 0.94 mmol), and 3.0 mL of xylenes were added to a thick-walled glass tube.…”

Section: Synthesis Of the Pyridyl-spaced Bis-imidazolium Based Proligmentioning

confidence: 99%

Synthesis and structure of palladium(II) complexes supported by bis-NHC pincer ligands for the electrochemical activation of CO2

et al. 2017

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A series of bis-NHC pincer complexes of palladium(II) have been prepared and characterized. These pyridyl-spaced dicarbene complexes ([(PDCR)Pd(MeCN)](PF6)2) were synthesized with substituents of varying steric bulk at the wingtip positions, which include R = methyl, ethyl, isopropyl, cyclohexyl, mesityl and 2,6-diisopropylphenyl. The synthesis of this library of complexes was accomplished either by direct metallation of the prerequisite pyridyl-spaced bis-imidazolium proligands with Pd(OAc)2 or via treatment with Ag2O to afford the corresponding silver carbenes, which were then transmetallated onto palladium. Solid-state structures for each of the [(PDCR)Pd(MeCN)](PF6)2 derivatives were obtained via X-ray crystallography and allowed for the steric properties of each PDCR ligand to be evaluated by two methods. These analyses, which included calculation of the percent buried volume (%VBur) and solid angles of the PDCR ligands, served to characterize the steric environment around the palladium center in each of the complexes that was prepared. Finally, voltammetry and controlled potential electrolysis studies were performed to characterize the redox chemistry of the [(PDCR)Pd(MeCN)](PF6)2 derivatives and assess if they could electrocatalyze the reduction of CO2. The influence of the steric properties of the PDCR ligand on the electrochemistry of the resulting complexes [(PDCR)Pd(MeCN)](PF6)2 is also discussed.

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Section: Synthesis Of the Pyridyl-spaced Bis-imidazolium Based Proligmentioning

confidence: 99%

Synthesis and structure of palladium(II) complexes supported by bis-NHC pincer ligands for the electrochemical activation of CO2

et al. 2017

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“…Materials and Equipment. (BBIB)X 2 salts were prepared following the procedure given elsewhere, 28 and all other chemicals were purchased from Sigma-Aldrich. SERS spectra were acquired using the LabRam HR800 confocal Raman microscope system with a 633 nm HeNe Raman excitation laser.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Counterion Effects on Electrolyte Interactions with Gold Nanoparticles

et al. 2016

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Electrolyte interactions with nanoparticles (NPs) at the solid/liquid interfaces are highly complicated as the charged species can be directly adsorbed onto the NP surfaces, confined in the diffusion layer immediately surrounding the NPs, and dispersed in bulk solutions. Existing studies on electrolyte interactions with NPs are based primarily on the electrical double layer theory that focuses mainly on electrolyte interactions with NPs with fixed pre-existing charges. Demonstrated herein is a comprehensive study of counterion effects during the electrolyte bindings to gold nanoparticles (AuNPs), including halide-induced AuNP aggregation and fusion, quantitative cation and anion coadsorption, selective cation and anion displacement on AuNPs, and surface-enhanced Raman spectroscopic features of the ionic species adsorbed onto AuNP surfaces. In contradiction to previous reports that electrolyte effects are anion-specific, we demonstrated that cations can play a dominant role in the halide-induced AuNP aggregation and fusion and the ion-exchange processes on AuNP surfaces. Mechanistically, these counterion effects are due to the cooperative and competitive cation and anion binding to AuNPs and AuNP-facilitated cation and anion interactions. The insights provided in this work should be of broad importance for NP research and applications in which electrolyte/NP interactions are ubiquitously implicated.

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“…However, their dissociation from oxophilic metals was partially prevented by designing multidentate anionic carbon, nitrogen, and oxygen-functionalized NHC ligands [ 5 , 13 , 15 , 16 , 17 ]. Anchoring such functionalized NHC ligands to oxophilic metals has proved to be a successful approach for developing catalysts, notably of group 4 metals, for the (oligo-)polymerization of olefins [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], hydroamination/cyclization of aminoalkenes [ 30 , 31 , 32 , 33 , 34 , 35 , 36 ], controlled ring-opening polymerization of rac -lactide [ 37 , 38 , 39 , 40 ], and more recently, for the copolymerization of epoxides with CO 2 [ 41 , 42 , 43 , 44 , 45 ].…”

Section: Introductionmentioning

confidence: 99%

Unsaturated and Benzannulated N-Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO2

et al. 2020

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Tridentate, bis-phenolate N-heterocyclic carbenes (NHCs) are among the ligands giving the most selective and active group 4-based catalysts for the copolymerization of cyclohexene oxide (CHO) with CO2. In particular, ligands based on imidazolidin-2-ylidene (saturated NHC) moieties have given catalysts which exclusively form polycarbonate in moderate-to-high yields even under low CO2 pressure and at low copolymerization temperatures. Here, to evaluate the influence of the NHC moiety on the molecular structure of the catalyst and its performance in copolymerization, we extend this chemistry by synthesizing and characterizing titanium complexes bearing tridentate bis-phenolate imidazol-2-ylidene (unsaturated NHC) and benzimidazol-2-ylidene (benzannulated NHC) ligands. The electronic properties of the ligands and the nature of their bonds to titanium are studied using density functional theory (DFT) and natural bond orbital (NBO) analysis. The metal–NHC bond distances and bond strengths are governed by ligand-to-metal s- and p-donation, whereas back-donation directly from the metal to the NHC ligand seems to be less important. The NHC p-acceptor orbitals are still involved in bonding, as they interact with THF and isopropoxide oxygen lone-pair donor orbitals. The new complexes are, when combined with [PPN]Cl co-catalyst, selective in polycarbonate formation. The highest activity, albeit lower than that of the previously reported Ti catalysts based on saturated NHC, was obtained with the benzannulated NHC-Ti catalyst. Attempts to synthesize unsaturated and benzannulated NHC analogues based on Hf invariably led, as in earlier work with Zr, to a mixture of products that include zwitterionic and homoleptic complexes. However, the benzannulated NHC-Hf complexes were obtained as the major products, allowing for isolation. Although these complexes selectively form polycarbonate, their catalytic performance is inferior to that of analogues based on saturated NHC.

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Metal and halogen dependence of the rate effect in hydroamination/cyclization of unactivated aminoalkenes: Synthesis, characterization, and catalytic rates of CCC-NHC hafnium and zirconium pincer complexes

Cited by 33 publications

References 84 publications

Synthesis and structure of palladium(II) complexes supported by bis-NHC pincer ligands for the electrochemical activation of CO2

Synthesis and structure of palladium(II) complexes supported by bis-NHC pincer ligands for the electrochemical activation of CO2

Counterion Effects on Electrolyte Interactions with Gold Nanoparticles

Unsaturated and Benzannulated N-Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO2

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