Preparation and NMR Spectroscopy of (1,2-Bis(diphenylphosphino)ethane)(η³-1,3-diarylallyl)- palladium Tetrafluoroborates. Correlation of Chemical Shifts with Hammett Substituent Constants and with the Regioselectivity of Nucleophilic Attack

Abstract

13C NMR chemical shifts of the terminal allyl carbon atoms C-1 and C-3 of (1,2-bis(diphenylphosphino)ethane)(η3-1,3-diarylallyl)palladium tetrafluoroborates correlate with σ Hammett substituent constants. For each complex the chemical shift at lower field indicates the site of preferred attack by soft nucleophiles in the Tsuji−Trost reaction.

Electronic effect of ionic‐pair substituents

“…IR, MS, and NMR( 1 H, 13 C and 15 N) spectral properties were correlated with σ and/or atomic Mulliken charges and bond orders . Among them, 13 C NMR chemical shifts have been successfully correlated to both positive charge density and regioselectivity of nucleophilic attack with substituted 1,3‐diphenylallylpalladium complexes with chiral ligands by Hammett analysis . The transmission of substituent effects across the palladium center to the alkyl carbons is monitored by 13 C NMR and X‐ray crystallography as a way to probe electronic asymmetry in chiral ligand design .…”

Density Functional Study on the Regioselectivity of Nucleophilic Attack in 1,3-Disubstituted (Diphosphino)(η3-allyl)palladium Cations

“…To make clear the role of electronic effects on the regioselectivity in the absence of any steric interference, some of us have studied Pd(0)-catalyzed allylations of soft nucleophiles with 1,3-diarylallyl systems . These reactions involve the (η 3 -allyl)palladium complexes 4 (L/L = PPh 3 /PPh 3 or Ph 2 PCH 2 CH 2 PPh 2 ) featuring para-substituted aryl rings (Figure ) that confer equal steric requirements but different electronic requirements at both ends of the allylic system.…”

“…These reactions involve the (η 3 -allyl)palladium complexes 4 (L/L = PPh 3 /PPh 3 or Ph 2 PCH 2 CH 2 PPh 2 ) featuring para-substituted aryl rings (Figure ) that confer equal steric requirements but different electronic requirements at both ends of the allylic system. Complexes 4 (Ar 1 = 4-ClPh, 4-MeOPh, Ar 2 = 4-NO 2 Ph;16a Ar 1 = Ph, Ar 2 = 4-MeOPh 16b ) were studied, and the experimental conclusion is clear: the nucleophilic attack takes place preferentially at the terminus remote from the most electron-withdrawing group …”

Synthesis and structural features of α-acyloxy-(η3-allyl)palladium complexes

“…13 C NMR shifts of the allylic carbons. It is well known [48,49] that 13 C NMR shift values of the allylic carbons are strongly influenced by the substituent and ligand effects. Accordingly, the acetoxy substituted C1 carbon in 1b (108.9 ppm) is less shielded ( Table 2) than the corresponding carbon in 1a (105.4 ppm).…”