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ИСТИНА ЦЭМИ РАН |
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To the best of our knowledge, the rich collection of known optically active palladacycles does not contain any structures combining such powerful chirality sources as axial and planar one. The aim of our work was to develop route to such cyclopalladated compound. We take, as a starting ligand, the phosphite HL, which was prepared (as diastereomer mixture) by reaction of the generated in situ from (Sa)-BINOL phosphachloridite with the racemic 4-hydroxy[2.2]paracyclophane. NMR 31P spectra shows the presence of two diastereomer forms in equimolar proportions. Two ways of the phosphite diastereomer separation were used: (i) optical resolution of the free ligand, and (ii) its diastereomer separation on the enantiopure cyclopalladated matrix. Absolute configuration could be preliminary defined from NOE data. Numerous attempts of the phosphite HL cyclopalladation inevitably failed due to the palladium(0) formation.The activation of the aromatic C-H bond was achieved only by the thermolysis of the phosphite HL with [PdCl2(PhCN)2] mixture or by classical two-step path via the coordination intermediate 2. Unfortunately, the mixture of two diastereomers of the dimer 1 was prepared with poor yields (13-14%). Sterical congestion leads to the absence of regioselectivity during the coordination of the auxiliary ligand – PPh3. Each of two mononuclear adducts gives the mixture of cis(PP) and trans-(PP)-isomers.