These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: cis-Beta-bis(carbonyl) ruthenium-salen complexes: X-ray crystal structures and remarkable catalytic properties toward asymmetric intramolecular alkene cyclopropanation.
    Author: Xu ZJ, Fang R, Zhao C, Huang JS, Li GY, Zhu N, Che CM.
    Journal: J Am Chem Soc; 2009 Apr 01; 131(12):4405-17. PubMed ID: 19275149.
    Abstract:
    cis-Beta-[Ru(II)(salen(A))(CO)(2)] (salen(A) = N,N'-bis(3-R(1)-5-R(2)-salicylidene)-1,2-cyclohexenediamine dianion; R(1) = R(2) = Bu(t), 1a; R(1) = Pr(i), R(2) = H, 1b; R(1) = Bu(t), R(2) = H, 1c) complexes were prepared by treating Ru(3)(CO)(12) with the respective H(2)salen(A) in 1,2,4-trichlorobenzene and structurally characterized by X-ray crystallography. Complexes 1a-c catalyze intramolecular cyclopropanation of trans-allylic diazoacetates N(2)CHCO(2)CH(2)CH=CHR (3, R = Ph, 4-ClC(6)H(4), 4-BrC(6)H(4), 4-MeC(6)H(4), 4-MeOC(6)H(4), 2-MeC(6)H(4), 2-furanyl) under light irradiation to give cyclopropyl lactones 4 in up to 96% yield and up to 98% ee. DFT calculations on intramolecular cyclopropanation of 3a (R = Ph) with model catalyst cis-beta-[Ru(II)(salen(A0))(CO)(2)] (salen(A0) = N,N'-bis(salicylidene)-1,2-cyclohexenediamine dianion) reveal the intermediacy of both cis-beta- and trans-[Ru(salen(A0))(CHCO(2)CH(2)CH=CHPh)(CO)] bearing salen(A0) in a nonplanar and planar coordination mode, respectively, with the cis-beta-carbene species being a major intermediate in the catalytic carbenoid transfer reaction. The intramolecular cyclopropanation from the cis-beta-carbene species is the most favorable pathway and features an early transition state and an asynchronous concerted [2 + 1] addition mechanism. Enantioselectivities in the reactions involving [Ru(salen(A0))(CHCO(2)CH(2)CH=CHPh)(CO)] were predicted to be 77% ee for the trans-carbene species and 96% ee for the cis-beta-carbene species; the former dramatically increases to 98% ee, whereas the latter slightly increases to 99% ee, upon replacing salen(A0) with salen(A1) (R(1) = R(2) = B(t)). The observed variation in enantioselectivity (90-98% ee) for the conversion of 3a to 4a catalyzed by 1a-c could result from an equilibrium between cis-beta (major) and trans (minor) ruthenium-carbene intermediates.
    [Abstract] [Full Text] [Related] [New Search]