The Dynamics of the β-Agostic Isopropyl Complex (ArNC(R)−C(R)NAr)Pd(CH(CH2-μ-H)(CH3))+BAr4‘-(Ar = 2,6-C6H3(i-Pr)2):  Evidence for In-Place Rotation versus Dissociation of the Agostic Methyl Group

Tempel, Daniel J.; Brookhart, Maurice

doi:10.1021/om971137+

Cited by 66 publications

(107 citation statements)

References 19 publications

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“…Such a polymerization catalyst was prepared by the reaction of (COD) 2 Ni with hexafluoroacetylacetone 41. Recently, Brookhart et al4–8 obtained excellent results by using nickel diimine derivatives activated by MAO. Therefore, we also examined the reaction of ethylene with Ni(acac) 2 / MMAO, Ni(1,3‐tBu 2 ‐acac) 2 ( 13 )/MMAO, and Ni[1,3‐ (CF 3 ) 2 ‐acac] 2 (14 )/MMAO.…”

Section: Resultsmentioning

confidence: 99%

“…The polymerization of ethylene with Ni complexes to high molecular weight polymers was reported by Keim et al,1–3 and more recently Brookhart et al4–8 obtained particularly brilliant results in the polymerization of ethylene by using nickel aromatic diimine derivatives as catalysts activated by methylaluminoxane (MAO). Palladium diimine complexes also showed a high catalytic activity for the polymerization of ethylene.…”

Section: Introductionmentioning

confidence: 98%

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Glyceryl‐S‐Acyl Carrier Protein as an Intermediate in the Biosynthesis of Tetronate Antibiotics

Sun¹,

Hong²,

Gillies³

et al. 2007

ChemBioChem

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The biosynthetic pathway to the unusual tetronate ring of certain polyketide natural products, including the antibiotics abyssomicin and tetronomycin (TMN) and the antitumour compound chlorothricin (CHL), is presently unknown. The gene clusters governing chlorothricin and tetronomycin biosynthesis both contain a gene encoding an atypical member of the FkbH family of enzymes, which has previously been shown to synthesise glyceryl-S-acyl carrier protein (ACP) as the first step in production of unusual extender units for modular polyketide biosynthesis. We show here that purified recombinant FkbH-like protein, Tmn16, from the TMN gene cluster catalyses the efficient transfer of a glyceryl moiety from D-1,3-bisphosphoglycerate (1,3-BPG) to either of the dedicated ACPs, Tmn7a and ChlD2, to form glyceryl-S-ACP, which directly implicates this compound as an intermediate in tetronate biosynthesis as well. Neither Tmn16 nor Tmn7a produced glyceryl-S-ACP when incubated, respectively, with analogous ACP and FkbH-like proteins from a known extender-unit pathway; this indicates a highly selective channelling of glycolytic metabolites into tetronate biosynthesis.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Glyceryl‐S‐Acyl Carrier Protein as an Intermediate in the Biosynthesis of Tetronate Antibiotics

Sun¹,

Hong²,

Gillies³

et al. 2007

ChemBioChem

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“…The classical view of this process is that insertion occurs to form an unsaturated species followed by C-C bond rotation and return of a different ␤-hydrogen to metal as shown in Scheme 6 Upper. There is growing evidence (74)(75)(76)(77)(78)(79) C ␣ -C ␤ bond as shown in Scheme 6 Lower. The unsaturated metal center never relinquishes contact with electron density in ␤-CH bonds.…”

Section: Role Of Agostic Interactions In Reaction Intermediates and Tmentioning

confidence: 99%

Agostic interactions in transition metal compounds

Brookhart

Green

Parkin

2007

Proc. Natl. Acad. Sci. U.S.A.

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“…Mechanistic studies on these well-defined α-diimine Ni(II) and Pd(II) olefin polymerization catalysts have shown some critical features (Chart 1): [8][9][10][11][12][13][14][15][16][17] (1) the formation of branches results from a unique "chain walking" β-agostic alkyl intermediate via multiple processes of β-H elimination and reinsertion with opposite regiochemistry. (2) For Ni(II) species, ethylene trapping and insertion are competitive with chain walking, and thus the degree of branching is dependent on pressure and temperature; however, the branching density and the distribution of short chain branches are not sensitive to pressure and temperature for Pd(II) species because the rate of chain walking is much faster (ca.…”

Section: Introductionmentioning

confidence: 99%

Unsymmetrical Strategy Makes Significant Differences in α‐Diimine Nickel and Palladium Catalyzed Ethylene (Co)Polymerizations

Zhang

et al. 2020

ChemCatChem

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Ligand steric bulk is one of the most important parameters on determining activity, polymer molecular weight, and branching density in α-diimine Ni(II) and Pd(II) catalyzed ethylene polymerization. In this contribution, we delineated an unsymmetrical strategy to shed light on the effect of steric bulk in α-diimine species via the unsymmetrically pentiptycenyl/dibenzhydryl αdiimine Ni(II) and Pd(II) catalysts Ipty/Ph-Ni and Ipty/Ph-Pd versus symmetrical pentiptycenyl analogues Ipty-Ni and Ipty-Pd and symmetrical dibenzhydryl analogues Ph-Ni and Ph-Pd. In the Ni(II) catalyzed ethylene polymerization, new features have been revealed: (1) with the increase of steric bulk (Ph-Ni > Ipty/Ph-Ni > Ipty-Ni), in a relatively long 30 min polymer molecular weights increase, yet Ipty/Ph-Ni produces the high-est molecular weight (1230 kDa) in a short 5 min; (2) with increasing steric bulk, branching density first rises and then falls, liking a downward parabola. In the Pd(II) catalyzed ethylene polymerization, increasing steric bulk enhanced activity and molecular weight or not, dependent on temperature, but usually decreased branching density. Consequently, Ipty/Ph-Pd gave the highest activity and the highest molecular weight (412 kDa) at challenging high temperature of 70°C. Plausible insights have been given to address these differences from previous results. Notably, unsymmetrical Ni(II) and Pd(II) catalysts also enabled copolymerizations of ethylene with various polar comonomers.[a] X.Precise Synthesis of Unsymmetrical α-Diimine Ni(II) and Pd(II) Catalysts. It is well-known that, compared to symmetrical compounds, the synthesis of unsymmetrical compounds is usually more difficult. With significant efforts, a high-yield pathway without tedious column chromatography is shown in Scheme 1 for the synthesis of pentiptycenyl/dibenzhydryl substituted α-diimine ligand Ipty/Ph-L, where installing dibenzhydryl substituent firstly and then pentiptycenyl substituent is the key procedure. Treatment of sterically demanding α-diimine ligand Ipty/Ph-L with the precursor NiBr 2 (DME) or PdMeCl(COD) readily afforded the desired unsymmetrical Ni(II) catalyst Ipty/ Ph-Ni and Pd(II) catalyst Ipty/Ph-Pd, respectively, in excellent yields (> 87 %). For comparison, symmetrical Ni(II) catalysts Ipty-Ni and Ph-Ni and Pd(II) catalysts Ipty-Pd and Ph-Pd were also prepared by known methods (Chart 2). [21,65] Both Ni(II) catalyst Ipty/Ph-Ni and Pd(II) catalyst Ipty/Ph-Pd were comprehensively characterized by multiple methods to identify their structure and purity. Ipty/Ph-Ni was confirmed by 1 H NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction analysis (Figure 1). Note that the Ni(II) species is paramagnetic, but a clear spectrum without obviously broad signals is rarely obtained after several adjustments on NMR parameters. By comparison, the diamagnetic Pd(II) species was easily determined by 1 H, 13 C, and 2D NMR spectroscopy, elemental analysis, and X-ray diffraction analysis (Figure 1). Ethylene (Co)Polymerizations wit...

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The Dynamics of the β-Agostic Isopropyl Complex (ArNC(R)−C(R)NAr)Pd(CH(CH₂-μ-H)(CH₃))⁺BAr₄‘^-(Ar = 2,6-C₆H₃(i-Pr)₂): Evidence for In-Place Rotation versus Dissociation of the Agostic Methyl Group

Cited by 66 publications

References 19 publications

Glyceryl‐S‐Acyl Carrier Protein as an Intermediate in the Biosynthesis of Tetronate Antibiotics

Glyceryl‐S‐Acyl Carrier Protein as an Intermediate in the Biosynthesis of Tetronate Antibiotics

Agostic interactions in transition metal compounds

Unsymmetrical Strategy Makes Significant Differences in α‐Diimine Nickel and Palladium Catalyzed Ethylene (Co)Polymerizations

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