Synthesis and reactivity towards carbon monoxide of an optically active endo five-membered ortho-cyclopalladated imine: X-ray molecular structure of trans-(μ-Cl)2[Pd(κ2-C,N-(R)-C6H4-CHN-CHMe-Ph)]2

(R)-1-Phenylethyl-benzylidene-amine (1) reacted with Pd(OAc)2 in acetic acid at 60 °C under nitrogen affording the acetato-bridged dinuclear endo five-membered ortho-cyclopalladated compound (μ-OAc)2[Pd(κ2-C,N-(R)-C6H4-CHN-CHMe-Ph)]2 (2) in 65% yield. Compound 2 was converted by a metathesis reaction with LiCl into the corresponding chloro-bridged dinuclear cyclopalladated compound (μ-Cl)2[Pd(κ2-C,N-(R)-C6H4-CHN-CHMe-Ph)]2 (3). 1H NMR of CDCl3 solutions of compounds 2 and 3 treated separately with py-d5, (R)-1-phenylethylamine and racemic 1-phenylethylamine were consistent with the endo cyclopalladated structure and the R absolute configuration of the chiral carbon atoms of compounds 2 and 3. Compounds 2 and 3 reacted with carbon monoxide in methanol affording, as major compounds, methyl 2-formylbenzoate (91% chemical yield) and the epimers of 3-methoxy-2-[(R)-1-phenylethyl]isoindolin-1-one (64% chemical yield) in ca. 20% diastereomeric excess, respectively. The trans isomer of compound 3 crystallized in the P21 monoclinic space group with a = 10.430(4) Å, b = 12.082(8) Å, c = 11.168(4) Å and β = 95.20(3)° and presented C–H⋯Cl intramolecular and C–H⋯Pd intermolecular non-conventional hydrogen bonds.

Graphical abstractThe synthesis, structure and reactivity towards carbon monoxide of an optically active endo cyclopalladated imine are described. The co-ligands of the palladium atom control the selectivity of the carbonylation reaction and permit the preparation of 3-methoxy-2-[(R)-1-phenylethyl]isoindolin-1-one in 64% chemical yield and 20% diastereomeric excess.Figure optionsDownload full-size imageDownload as PowerPoint slide