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Diastereospecific Coupling of Imines by Low‐Valent Titanium: An Experimental and Computational Study
Author(s) -
Kumar Akshai,
Samuelson Ashoka G.
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201001256
Subject(s) - chemistry , titanium , alkoxide , phenylsilane , computational chemistry , molecular orbital , photochemistry , molecule , catalysis , organic chemistry
The reaction of phenylsilane (PhSiH 3 ) and titanium(IV) isopropoxide [Ti(O i Pr) 4 ] generates low‐valent titanium alkoxides that reduce and reductively couple imines. The C–C coupling reaction is diastereospecific, with exclusive formation of the (±)‐isomer. The yield is dependent on the concentration of titanium(IV) isopropoxide used. Using imines with varying electronic demand revealed that the coupling is most efficient for unsubstituted imines. The involvement of a trimeric titanium biradical species is invoked to explain the observed concentration dependence and diastereospecificity in the reaction. Multilayer ONIOM (“our own n‐layered integrated molecular orbital and molecular mechanics”) calculations were carried out on the plausible intermediates involved by using the Guassian 09 suite of programs. Formation of the trimeric biradical species leading to the formation of the (±)‐isomer is more favored than formation of the trimeric biradical species, which leads to the meso ‐isomer. Similar calculations with dimeric intermediates do not predict the (±)‐selectivity. Mass spectral analysis of the reaction mixture indicates the presence of a trimeric titanium alkoxide species.