We
report the synthesis of bimetallic Pd(I) and Pd(II) complexes
with bidentate 2-phosphinoimidazole ligands and their catalytic activity
to generate substituted naphthalenes. This process involves the coupling
of an aryl iodide and 2 equiv of a ketone via sequential ketone α-arylation
and then annulation to generate disubstituted and tetrasubstituted
naphthalenes in a regioselective manner. Excellent substrate scope
for both aryl iodide and ketone partners is demonstrated, including
that for heteroaryl iodides. Bimetallic Pd complexes are much more
reactive than monometallic Pd catalysts in this transformation. Density
functional theory calculations, isotope effect experiments, and substrate
competition experiments were used to examine bimetallic mechanisms,
reactivity, and selectivity.
We describe a proof-of-concept study in which peptide-bound enamine and thiourea catalysts are used to facilitate the conjugate addition of cyclohexanone to nitroolefins. Our bifunctional peptide scaffold is modified to optimize the local environment around both catalysts to enhance both reactivity and enantioselectivity, affording selectivities of ≤95% ee. Circular dichroism, nuclear magnetic resonance nuclear Overhauser effect studies, and molecular dynamics simulations verify the helical structure of our catalyst in solution and the importance of the secondary structure in catalysis.
We report the catalytic activity of two phosphinoimidazolederived bimetallic palladium complexes in Pd-catalyzed amination reactions. Our studies demonstrate that the starting oxidation state (Pd(I) or Pd(II)) of the dimeric complex has a significant effect on the efficiency of the catalytic reaction. The corresponding Pd(I) complex shows higher reactivity in Buchwald−Hartwig aminations, while the Pd(II) complex is much more reactive in carbonylative amination reactions. These new dimeric palladium complexes provide good to excellent reactivity and yields in the amination reactions tested.
We report the synthesis of bimetallic Pd(I) and Pd(II) complexes scaffolded on bidentate 2-phosphinoimidazole
ligands. These complexes display unique catalytic activity and enable the expeditious formation of 1,3-disubstituted naphthalenes via an unprecedented coupling of
aryl iodides and methyl ketones in the presence of silver triflate. Excellent substrate
scope for naphthalene formation is also demonstrated. Mechanistic studies suggest
that the transformation proceeds via Pd-catalyzed arylation of a methyl ketone, followed by cyclization with a second equivalent of ketone. Importantly, this ketone
arylation processes occurs under oxidizing conditions, suggesting involvement of
higher oxidation state dimeric Pd catalysts. Based on experiments and DFT calculations, we propose a mechanism involving high oxidation state Pd(III) bimetallic catalysis. These new bimetallic complexes
possess reactivity that is not seen with monometallic Pd catalysts and we confirm the importance of the palladium catalyst
for both arylation and cyclization for naphthalene formation.
We report the synthesis of bimetallic Pd(I) and Pd(II) complexes scaffolded on bidentate 2-phosphinoimidazole
ligands. These complexes display unique catalytic activity and enable the expeditious formation of 1,3-disubstituted naphthalenes via an unprecedented coupling of
aryl iodides and methyl ketones in the presence of silver triflate. Excellent substrate
scope for naphthalene formation is also demonstrated. Mechanistic studies suggest
that the transformation proceeds via Pd-catalyzed arylation of a methyl ketone, followed by cyclization with a second equivalent of ketone. Importantly, this ketone
arylation processes occurs under oxidizing conditions, suggesting involvement of
higher oxidation state dimeric Pd catalysts. Based on experiments and DFT calculations, we propose a mechanism involving high oxidation state Pd(III) bimetallic catalysis. These new bimetallic complexes
possess reactivity that is not seen with monometallic Pd catalysts and we confirm the importance of the palladium catalyst
for both arylation and cyclization for naphthalene formation.
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