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Synthesis and Stereoselective Interconversion of Chiral 1‐Aza‐3,6‐diphosphacycloheptanes
Author(s) -
Musina Elvira I.,
Karasik Andrey A.,
Balueva Anna S.,
Strelnik Igor D.,
Fesenko Tatiana I.,
Dobrynin Alexey B.,
Gerasimova Tatiana P.,
Katsyuba Sergey A.,
Kataeva Olga N.,
Lönnecke Peter,
HeyHawkins Evamarie,
Sinyashin Oleg G.
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201101337
Subject(s) - chemistry , ethylamine , stereoselectivity , cationic polymerization , medicinal chemistry , stereochemistry , diastereomer , platinum , chelation , catalysis , organic chemistry
Cyclic seven‐membered bisphosphanes, namely 1‐aza‐3,6‐diphosphacycloheptanes 3 – 5 ( 3 : 3,6‐diphenyl‐1‐(1‐phenylethyl)‐1‐aza‐3,6‐diphosphacycloheptane; 4 : 1‐[(1 R )‐1‐(4′‐methoxyphenyl)ethyl]‐3,6‐diphenyl‐1‐aza‐3,6‐diphosphacycloheptane; 5 : 3,6‐diphenyl‐1‐[(1 R )‐1‐phenylpropyl]‐1‐aza‐3,6‐diphosphacycloheptane), with chiral exocyclic substituents at the nitrogen positions have been synthesized, with the prevailing formation of meso stereoisomers (P R P S ) as kinetically controlled products, by stereoselective condensation of 1,2‐bis(phenylphosphanyl)ethane, formaldehyde and primary optically pure amines, namely ( S )‐(–)‐1‐phenylethylamine, ( R )‐(+)‐1‐phenylethylamine, ( R )‐(+)‐1‐phenylpropylamine, ( R )‐(+)‐1‐(4′‐methoxyphenyl)ethylamine. The meso stereoisomers of bisphosphanes 3 RSS , 3 – 5 RSR readily form neutral and cationic P,P‐chelate complexes 6 – 9 with platinum(II) ( 6 : cis ‐dichloro‐(3 R ,6 S )‐3,6‐diphenyl‐1‐[(1 S )‐1‐phenylethyl]‐1‐aza‐3,6‐diphosphacycloheptaneplatinum(II); 7 : cis ‐dichloro‐(3 R ,6 S )‐1‐[(1 R )‐1‐(4′‐methoxyphenyl)ethyl]‐3,6‐diphenyl‐1‐aza‐3,6‐diphosphacycloheptaneplatinum(II); 8 :bis{(3 R ,6 S )‐[(1 R )‐3,6‐diphenyl‐1‐(1‐phenylethyl)‐1‐aza‐3,6‐diphosphacycloheptane]}platinum(II) dichloride; 9 : bis{(3 R ,6 S )‐3,6‐diphenyl‐1‐[(1 R )‐1‐phenylpropyl]‐1‐aza‐3,6‐diphosphacycloheptane}platinum(II) dichloride). The fast and selective formation of the cationic complex ( 9 ) of the meso isomer 5 RSR allowed for the separation of the 5 RRR and 5 SSR isomers of the bisphosphane 5 . In solution, selective stereoconversion of the pure 3 RSS , 3 RSR and 4 RSR isomers into a mixture containing 3 RRS , 3 SSR and 4 SSR stereoisomers as the predominant products was observed. As a result, the stereoconversion is accompanied by a change in not only the value but also in the sign of the specific rotation, [ α ] D 20 . The ratio of the stereoisomers in an equilibrium mixture of 3 C( S ) ( 3 RSS / 3 RRS / 3 SSS in a 24:48:28 ratio) is in accord with their relative energies that were calculated with the B3LYP/6‐31G* basis. Kinetic studies of the stereoconversion of bisphosphane 3 C( S ) have been performed. The rate constants that were determined are indicative of a bimolecular interconversion mechanism, which is supposedly the reason for the relatively low activation energies for inversion at phosphorus. Molecular structures were obtained, by X‐ray crystal structure analysis, for the meso 3 RSS and 3 RRS stereoisomers of the N ‐( S )‐1‐phenylethyl‐substituted bisphosphanes and for 4 RSR .