Self-Adaptable Catalysts:  Substrate-Dependent Ligand Configuration

Abstract

Pd(II) allyl and Pd(0) olefin complexes containing the configurationally labile ligand 1,2-bis-[4,5-dihydro-3H-dibenzo[c-e]azepino]ethane were studied as models for intermediates in Pd-catalyzed allylic alkylations. According to NMR and DFT studies, the ligand prefers C(s) conformation in both eta3-1,3-diphenylpropenyl and eta3-cyclohexenyl Pd(II) complexes, whereas in Pd(0) olefin complexes it adopts different conformations in complexes derived from the two types of allyl systems in both solution and, as verified by X-ray crystallography, in the solid state. These results demonstrate that the Pd complex is capable of adapting its structure to the reacting substrate. The different structural preferences also provide an explanation for the behavior of 1,3-diphenyl-2-propenyl acetate and 2-cyclohexenyl acetate in Pd-catalyzed allylic alkylations using pseudo-C2 and pseudo-C(s) symmetric ligands.

Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

“…For the sake of completeness it may be interesting to cite the works of Gade, Spek, and Privalov in which ligands or olefins not described in Schemes 1 and 2 were used. However, no particular structural news arose from those studies [87][88][89].…”

H(OEt2)2[P(1,2‐O2C6Cl4)3]: Synthesis, Characterization, and Application as a Single‐Component Initiator for the Carbocationic Polymerization of Olefins

“…To date, most cationic initiator development has focused on group 13-element-based systems that are conceptually derived from classical Lewis acids (BF 3 3 ] À } which, along with related systems, has attracted considerable attention as an enantiomerically pure anion. [9][10][11][12] We have previously reported…”

Palladium-Catalyzed Enantioselective Allylic Substitution

“…The 3-position of the quinazoline and the substituents of the phosphine have been found to be very important in tuning the reactivity in catalysis. In asymmetric allylic alkylation, the enantioselectivity decreased in the presence of a bulky group such as adamantyl (adm) in the 3-position (Table 20) [81,82] In another approach, both of the binding atoms were surrounded by a binaphthyl unit, as in L48 [83]. Efficiency seemed maximal when the conformation of both binaphthyl units was the same (both S or both R) (Fig.…”