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Palladium- and Nickel-Catalyzed Carbon-Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes.

ABSTRACT: Palladium and nickel catalysts promoted highly selective carbon-carbon bond insertion reactions with di-tert-butyl-alkylidenesilacyclopropanes. Pd(PPh(3))(4) was demonstrated to be the optimal catalyst, allowing for a variety of carbon-carbon pi-bond insertion reactions. Depending on the nature of the carbon-carbon pi bond, the insertion reaction proceeded with either direct insertion into the carbon(sp(2))-silicon bond or with allylic transposition. Ring-substituted alkylidenesilacyclopropanes required a nickel catalyst to afford insertion products. Using Ni(cod)(2) as the carbon-carbon bond insertion catalyst, new double alkyne insertion products and alkene isomerization products were observed.

SUBMITTER: Buchner KM

PROVIDER: S-EPMC2856941 | biostudies-literature | 2010 Mar

REPOSITORIES: biostudies-literature

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Palladium- and Nickel-Catalyzed Carbon-Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes.

Buchner Kay M KM Woerpel K A KA

Organometallics 20100301 7

Palladium and nickel catalysts promoted highly selective carbon-carbon bond insertion reactions with di-tert-butyl-alkylidenesilacyclopropanes. Pd(PPh(3))(4) was demonstrated to be the optimal catalyst, allowing for a variety of carbon-carbon pi-bond insertion reactions. Depending on the nature of the carbon-carbon pi bond, the insertion reaction proceeded with either direct insertion into the carbon(sp(2))-silicon bond or with allylic transposition. Ring-substituted alkylidenesilacyclopropanes ...[more]

PMID: 20419110

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Project description:Through the combination of reaction kinetics (both stoichiometric and catalytic), solution- and solid-state characterization of arylpalladium(II) arylsilanolates, and computational analysis, the intermediacy of covalent adducts containing Si-O-Pd linkages in the cross-coupling reactions of arylsilanolates has been unambiguously established. Two mechanistically distinct pathways have been demonstrated: (1) transmetalation via a neutral 8-Si-4 intermediate that dominates in the absence of free silanolate (i.e., stoichiometric reactions of arylpalladium(II) arylsilanolate complexes), and (2) transmetalation via an anionic 10-Si-5 intermediate that dominates in the cross-coupling under catalytic conditions (i.e., in the presence of free silanolate). Arylpalladium(II) arylsilanolate complexes bearing various phosphine ligands have been isolated, fully characterized, and evaluated for their kinetic competence under thermal (stoichiometric) and anionic (catalytic) conditions. Comparison of the rates for thermal and anionic activation suggested, but did not prove, that intermediates containing the Si-O-Pd linkage were involved in the cross-coupling process. The isolation of a coordinatively unsaturated, T-shaped arylpalladium(II) arylsilanolate complex ligated with t-Bu3P allowed the unambiguous demonstration of the operation of both pathways involving 8-Si-4 and 10-Si-5 intermediates. Three kinetic regimes were identified: (1) with 0.5-1.0 equiv of added silanolate (with respect to arylpalladium bromide), thermal transmetalation via a neutral 8-Si-4 intermediate; (2) with 1.0-5.0 equiv of added silanolate, activated transmetalation via an anionic 10-Si-5 intermediate; and (3) with >5.0 equiv of added silanolate, concentration-independent (saturation) activated transmetalation via an anionic 10-Si-5 intermediate. Transition states for the intramolecular transmetalation of neutral (8-Si-4) and anionic (10-Si-5) intermediates have been located computationally, and the anionic pathway is favored by 1.8 kcal/mol. The energies of all intermediates and transition states are highly dependent on the configuration around the palladium atom.

Dataset Information

Palladium- and Nickel-Catalyzed Carbon-Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes.

Publications

Palladium- and Nickel-Catalyzed Carbon-Carbon Bond Insertion Reactions with Alkylidenesilacyclopropanes.

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