Determination of the Absolute Configuration of CN-Palladacycles by ³¹P{¹H} NMR Spectroscopy Using (1R,2S,5R)-Menthyloxydiphenylphosphine as the Chiral Derivatizing Agent: Efficient Chirality Transfer in Phosphinite Adducts

Abstract

A series of (1R)-MenOPPh2 phosphinite derivatives of α-arylalkylaminate CN-palladacycles of known absolute configuration was prepared. Their structure and stereochemistry were determined using different experimental (NMR spectroscopy and X-ray diffraction) and theoretical (density functional theory calculation) methods. Despite the conformational mobility of the phosphinite reagent and the highly remote position of its stereocenters from those of the cyclopalladated amine, efficient chirality transfer in the phosphinite cyclopalladated complexes was established. On the basis of these results, a new method for the determination of the absolute configuration of chiral CN-palladacycles was elaborated using the (1R)-MenOPPh2 phosphinite as a highly sensitive referee ligand and in situ 31P­{1H} NMR spectroscopy as a control method. The proposed approach is a remarkable addition to the classical NMR techniques, increasing their versatility and excluding the isolation of the phosphinite derivatives.

Recent Advances in Multinuclear NMR Spectroscopy for Chiral Recognition of Organic Compounds

“…The enantiopurity determination is carried out in situ, without any complications from geometric isomerism or palladacycle dechelation. Continuing this work, the same authors applied this method to determine the absolute configuration of the CN -palladacycles [ 65 ]. The results were based on 31 P-NMR chiral discrimination, density function theory (DFT) calculations and X-ray data.…”

Conformational Mobility and Proton Transfer in Hydrogen-Bonded Dimers and Trimers of Phosphinic and Phosphoric Acids

“…For example, isotropic 31 P NMR chemical shifts, δP, could be used to estimate the π-accepting properties of carbenes in a series of carbine–phosphinidene adducts . The 31 P NMR spectroscopy also could be used to distinguish between nonequivalent isomers of organometallic complexes , and between enantiomers of chiral molecules. , Moreover, the sensitivity of δP to the noncovalent interactions was used to construct various scales of Brønsted and Lewis acidities . Most often, trialkylphosphines (R 3 P) and trialkylphosphine oxides (R 3 PO) are used as phosphorous probes.…”

Design, synthesis and applications of chiral functionalized phosphapalladacycles

“…These compounds are well established and successfully applied as derivatizing agents 19 , catalysts 20 , palladium sources 21 , promoters 22 , templates 23 , and antiproliferatives [24][25] .…”

“…The absolute configuration of the major enantiomer was determined to be S. The synthesis and application of ortho-palladated C-N complexes have been well established [1][2]229 . In particular, the N-donor palladacycle initially developed by Wild and co-workers 183,185,230 has been employed in a wide variety of catalytic asymmetric reactions, for example, as the catalyst in a Overman rearrangement reaction 174 , as either a catalyst precursor or promoter in hydrophosphination 22,231 , hydroamination 232 , Heck [233][234][235] , and Suzuki reaction and as an optical resolution reagent for various chiral ligands 19,183 . In contrast to the predominantly sigma-donating effect of the nitrogen-metal bond in the azapalladacycle complexes, π-back-bonding effect is well established to be present in the phosphapalladacycle complexes, which leads to different catalytic reactivity of the resulting metal-phosphine complex when compared to the azapalladacycle 108 .…”