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 (μ-Br)2[κ2-N2′,C1-1-Pd-2-{(2′-RCHNC6H4)C6H4}]2 [1a (R = 2,4,6-trimethoxyphenyl), 1b (R = 2,6-dichlorophenyl) and 1c (R = 2,6-difluorophenyl)] and (μ-Br)2[κ2-N2′,C1-1-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 (μ-Br)2[κ2-N2′,C1-1-Pd-2-{(2′-RCHNC6H4)C6H4}-cis-1,2-(CO2Me)2–CC]2 [2a (R = 2,4,6-trimethoxyphenyl), 2b (R = 2,6-dichlorophenyl) and 2c (R = 2,6-difluorophenyl)] and (μ-Br)2[κ2-N2′,C1-1-Pd-2-{(2′-NH2C6H4)C6H4}-cis-1,2-(CO2Me)2–CC]2 (2d), which derived from the monoinsertion of the alkyne into the palladium–carbon σ 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-{[κ2-N2′,C1-1-Pd-2-{(Z-2′-RCHNC6H4)C6H4}-cis-1,2-(CO2Me)2–CC]Br(PPh3)} and trans-P,P-{[κ1-C1-1-Pd-2-{(E-2′-RCHNC6H4)C6H4}-cis-1,2-(CO2Me)2–CC]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-{[κ1-C1-1-Pd-2-{(E-2′-RCHNC6H4)C6H4}-cis-1,2-(CO2Me)2–CC]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-κ2-N2′,C1-1-Pd-2-{(2′-NH2C6H4)C6H4}-1,2-(CO2Me)2–CC]Br(PPh3)} (compound 3d). Notably, the 31P{1H} 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].

The synthesis and characterization of the organopalladium compounds shown below are reported.Figure optionsDownload as PowerPoint slide