First enantiopure phosphapalladacycle with a palladium bonded stereogenic carbon as the sole chirality sourceстатья
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Аннотация:First enantiomerically pure phosphapalladacycle bearing an asymmetric carbon directly bonded to a palladium atom as a single chirality source was prepared by the resolution of racemic dimer {Pd(eta2-L)(myu-Cl)}2 (1), where L = 2-But2PC6H4CHMe, using (R,R)-stilbendiamine as an auxiliary ligand. Double recrystallization of a 1:1 mixture of diastereomers (S,RR)-4a and (R,RR)-4b from MeCN affords one of them, (S,RR)-4a, as a single isomer (>98% de, 31P{1H} NMR data). Another diastereomerically pure complex, (R,SS)-4c, was isolated by the same method using (S,S)-stilbendiamine as a resolving agent. This diastereomer (R,SS)-4c was converted into the enantiopure dimer (R,R)-1 (>98% ee, 31P{1H} NMR data) by the diamine protonation with dilute acetic acid at 5 oC. Dimer (R,R)-1 is configurationally stable at high temperatures up to at least 110 oC. The absolute configuration of the C*-stereocenter in dimer (S,S)-1 was
established by an X-ray diffraction study of its precursor (S,RR)-4a.