Monoinsertion of but-2-ynedioic acid dimethyl ester into palladium-carbon σ bonds of cyclopalladated compounds derived from biphenyl-2-ylamine:: X-ray molecular structure of biphenyl-2-yl-(2,4,6-trimethoxy-benzylidene)-amine

Dinuclear cyclopalladated compounds (mu-Br)2[kappa(2)-N2',Cl-1-Pd-2-{(2'-RCH=NC6H4)C6H4}](2) [1a (R = 2,4,6-trimethoxyphenyl), 1b (R = 2,6-dichlorophenyl) and 1c (R = 2,6-difluorophenyl)] and (mu-Br)(2)[kappa(2)-N-2',Cl-1-Pd-2-{(2'-NH2C6H4)C6H4}](2) (1d) reacted with but-2-ynedioic acid dimethyl ester (molar ratio 1-2) to afford the dinuclear cyclopalladated compounds (mu-Br)(2)[kappa(2)-N2',Cl-1-Pd-2-{(2'-RCH=NC6H4)C6H4}-cis-1,2-(CO2Me)(2)-C=C](2) [2a (R = 2,4,6-trimethoxyphenyl), 2b (R = 2,6-dichlorophenyl) and 2c (R = 2,6-difluorophenyl)] and (mu-Br)(2)[kappa(2)-N2',Cl-1-Pd-2-{(2'-NH2C6H4)C6H4}-cis-1,2-(CO2Me)(2)-C=C](2) (2d), which derived from the monoinsertion of the alkyne into the palladium-carbon sigma bonds of the cyclopalladated dimers 1. Compounds 2a and 2b reacted with PPh3 (molar ratio 1-4) to give a mixture of the mononuclear compound trans-N,P-{[kappa(2)-N2',Cl-1-Pd-2-{(Z-2'-RCH=NC6H4)C6H4}-cis-1,2-(CO2Me)(2)-C=C]Br(PPh3)} and trans-P,P-{[kappa(1)-Cl-1-Pd-2-{(E-2'-RCH=NC6H4)C6H4)-cis-1,2(CO2Me)(2)-C=C]Br(PPh3)(2)} in a molar ratio of 1-2 and ca. 1-12, respectively. Compound 2c reacted with PPh3 in a molar ratio 1-4 giving trans-P,P-{[kappa(1)-Cl-1-Pd-2-{(E-2'-RCH=NC6H4)C6H4}-cis-1,2-(CO2Me)(2)-C=C]Br(PPh3)(2)} (R=2,6-difluorophenyl)-(compound 4c) and compound 2d reacted with PPh3 in a molar ratio of 1-2, affording the mononuclear cyclopalladated compound trans-N,P-{[cis-kappa(2) -N2',Cl-1-Pd-2-{(2'-NH2C6H4)C6H4}-1,2-(CO2Me)(2)-C=C]Br(PPh3)} (compound 3d). Notably, the P-31{H-1} NMR of compounds 4 produced an AB spin system, showing that compounds 4 were chiral. In addition, we report the X-ray molecular structure of the E isomer of the free Schiff base a [biphenyl-2-yl-(2,4,6-trimethoxy-benzylidene)-amine]. (c) 2005 Elsevier Ltd. All rights reserved.