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The synthesis of alkylphosphine-substituted α-diimine (DI) ligands and their subsequent addition to Ni(COD) 2 allowed for the preparation of ( iPr2PPr DI)Ni and ( tBu2PPr DI)Ni . The solid state structures of both compounds were found to feature a distorted tetrahedral geometry that is largely consistent with the reported structure of the diphenylphosphine-substituted variant, ( Ph2PPr DI)Ni . To explore and optimize the synthetic utility of this catalyst class, all three compounds were screened for benzaldehyde hydrosilylation activity at 1.0 mol% loading over 3 h at 25 °C. Notably, ( Ph2PPr DI)Ni was found to be the most efficient catalyst while phenyl silane was the most effective reductant. A broad scope of aldehydes and ketones were then hydrosilylated, and the silyl ether products were hydrolyzed to afford alcohols in good yield. When attempts were made to explore ester reduction, inefficient dihydrosilylation was noted for ethyl acetate and no reaction was observed for several additional substrates. However, when an equimolar solution of allyl acetate and phenyl silane was added to 1.0 mol% ( Ph2PPr DI)Ni , complete ester C–O bond hydrosilylation was observed within 30 min at 25 °C to generate propylene and PhSi(OAc) 3 . The scope of this reaction was expanded to include six additional allyl esters, and under neat conditions, turnover frequencies of up to 990 h −1 were achieved. This activity is believed to be the highest reported for transition metal-catalyzed ester C–O bond hydrosilylation. Proposed mechanisms for ( Ph2PPr DI)Ni -mediated carbonyl and allyl ester C–O bond hydrosilylation are also discussed.
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Chain‐growth polycondensation via the substituent effect: Investigation of the monomer structure on synthesis of poly(N‐octyl‐benzamide)
Abstract A systematic study of the behavior of different leaving groups on a variety of ester‐based monomers was performed for the chain‐growth polycondensation synthesis of poly(N‐octyl benzamide). Linear and branched alkane esters were compared with their phenyl analogs using both computational and experimental methods. Kinetic experiments along with qualitative solubility observations were used, with the aid of nuclear magnetic resonance spectroscopy and gel‐permeation chromatography, to determine progress of the reaction, molecular weights, and molecular weight distributions. It was found that the reactivity of the monomer's ester group depends more on the stability of the leaving alkoxide than the electrophilicity of the carbonyl carbon, which contradicts previous literature. The order of reactivity increases for the alkyl esters with decreasing steric hindrance and decreasing pKa of the substituent. For the phenyl ester derivatives, the more electron withdrawing character of a para substituent increases the reactivity of the ester group, due to the higher resonance stabilization of the leaving phenoxide anion, not due to an increase in the electrophilicity of the carbonyl carbon.
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- Award ID(s):
- 2024448
- PAR ID:
- 10453520
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Polymer Science
- Volume:
- 58
- Issue:
- 17
- ISSN:
- 2642-4150
- Page Range / eLocation ID:
- p. 2389-2406
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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