ISSN:
0009-2940
Keywords:
Carbene complexes / Metallacycles, chiral / trans-C=C bonds in medium-sized heterocycles / Metallocene complexes, hent / Zirconium complexes
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Stereochemical Aspects with Metallacyclic Nine-Membered Zirconoxycarbene Complexes from Coupling (Butadiene)-zirconocene, Hexacarbonyltungsten, and Ketones or AldehydesReaction of (butadiene)zirconocene complexes with M(CO)6 (M =Cr, W) and subsequently with ketones or aldehydes O=CR1R2 (R1, R2 = H, alkyl, alkenyl, or aryl) produces the metallacyclic nine-membered zirconoxycarbene complexes (7a-r. The complexes trans-7 contain chiral metallacyclic ring systems. Starting from many ketones two diastereomeric compounds trans-7 and trans-7′ are obtained. From the dynamic 1H-NMR spectra an activation barrier of ΔG(317K)=16.5 ± 0.4 kcal/mol has been estimated fro the trans-7k [(2R*)(4,5,6-pS*)] → trans-7k′ [(2R*)(4,5,6-pR*)] rearrangement. For the tert-alkyl-substituted nine-membered metalacycles trans-7f-h only the respective (2R*)(4,5,6-pS*) isomers have been found Starting from aldehydes with less sterically demanding alkyl groups mixtures of the trans-7 [(2R*)(4,5,6-pS*)] compounds and their cis-7 isomers are obtained. Using the more bulky bis(tert-butylcyclopentadienyl)zirconium moiety for coupling butadiene and W(CO)6 with simple aldehydes leads to a large excess of the trans-isomers (e. g. R1 = H, R2 = i-C3H7: trans-7q: Cis7q = 90: 10).
Additional Material:
1 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19901230429
Permalink
