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Stereochemische Aspekte bei metallacyclischen Neunring‐Zirconoxycarbenkomplexen aus (Butadien)zirconocen, Hexacarbonylwolfram und Ketonen oder Aldehyden
Author(s) -
Erker Gerhard,
Sosua Friedrich,
Noe Ralf
Publication year - 1990
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19901230429
Subject(s) - chemistry , diastereomer , steric effects , alkyl , moiety , aryl , cis–trans isomerism , medicinal chemistry , stereochemistry , aldehyde , catalysis , organic chemistry
Stereochemical Aspects with Metallacyclic Nine‐Membered Zirconoxycarbene Complexes from Coupling (Butadiene)‐zirconocene, Hexacarbonyltungsten, and Ketones or Aldehydes Reaction of (butadiene)zirconocene complexes with M(CO) 6 (M =Cr, W) and subsequently with ketones or aldehydes O=CR 1 R 2 (R 1 , R 2 = 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 1 H‐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. R 1 = H, R 2 = i‐C 3 H 7 : trans ‐ 7q : Cis 7q = 90: 10).