The chemical properties of alicyclic heterocycles are similar to those of the corresponding chain compounds. Compound: Tris(triphenylphosphine)chlororhodium, is researched, Molecular C54H45ClP3Rh, CAS is 14694-95-2, about Mechanistic insights into rhodium-catalyzed enantioselective allylic alkylation for quaternary stereogenic centers, the main research direction is phenylbutanal rhodium catalyst enantioselective alkylation mechanism transition state structure.Product Details of 14694-95-2.
Installing quaternary stereogenic carbon is an arduous task of contemporary importance in the domain of asym. catalysis. To this end, an asym. allylic alkylation of α,α-disubstituted aldehydes by using allyl benzoate in the presence of Wilkinson’s catalyst [Rh(Cl)(PPh3)3], (R)-BINOL-P(OMe) as the external ligand, and LiHMDS as the base has been reported to offer high enantioselectivity. The mechanistic details of this important reaction remain vague, which prompted us to undertake a detailed d. functional theory (SMD(THF)/B3LYP-D3) investigation on the nature of the potential active catalyst, energetic features of the catalytic cycle, and the origin of high enantioselectivity. We note that a chloride displacement from the native Rh-phosphine [Rh(Cl)(PPh3)3] by BINOL-P(OMe) phosphite and an ensuing MeCl elimination can result in the in situ formation of a Rh-phosphonate [Rh(BINOL-P=O)(PPh3)3]. A superior energetic span (δE) noted with such a Rh-phosphonate suggests that it is likely to serve as an active catalyst. The uptake of allyl benzoate by the active catalyst followed by the turnover determining C-O bond oxidative addition furnishes a Rh-π-allyl intermediate, which upon interception by (Z)-Li-enolate (derived from α,α-disubstituted aldehyde) in the enantiocontrolling C-C bond generates a quaternary stereogenic center. The addition of the re prochiral face of the (Z)-Li-enolate to the Rh-bound allyl moiety leading to the R enantiomer of the product is found to be 2.4 kcal mol-1 more preferred over the addition through its si face. The origin of the stereochem. preference for the re face addition is traced to improved noncovalent interactions (NCIs) and less distortion in the enantiocontrolling C-C bond formation transition state than that in the si face addition Computed enantioselectivity (96%) is in very good agreement with the exptl. value (92%), so is the overall activation barrier (δE of 17.1 kcal mol-1), which is in conformity with room temperature reaction conditions.
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Reference:
Phosphine ligand,
Chiral phosphine ligands in asymmetric synthesis. Molecular structure and absolute configuration of (1,5-cyclooctadiene)-(2S,3S)-2,3-bis(diphenylphosphino)butanerhodium(I) perchlorate tetrahydrofuran solvate