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Seven‐Membered Heterodimetallic Ring Systems from (Conjugated Diene) Group 4 Metallocene Complexes and Organoaluminium Reagents
Author(s) -
Erker Gerhard,
Noe Ralf,
Wingbermühle Doris
Publication year - 1994
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.19941270503
Subject(s) - chemistry , metallocene , agostic interaction , iodide , medicinal chemistry , substituent , yield (engineering) , reagent , zirconium , polymer chemistry , nmr spectra database , stereochemistry , metal , organic chemistry , materials science , physics , astronomy , metallurgy , polymerization , spectral line , polymer
The ( s‐trans/s‐cis ‐η 4 ‐butadiene)zirconocene reagent adds dimethylaluminium chloride to yield the heterodimetallacyclic main group/transition‐metal system 2b , containing a seven‐membered metallacyclic framework that exhibits a “π‐agostic” s̀‐allyl zirconium interaction. Similar compounds ( 2c–f, 5a, 6 ) are obtained upon reaction of (butadiene)zirconocene with Et 2 All and (butadiene)hafnocene with Me 2 AlCl or Et 2 AlI. Addition of Me 2 AlCl or Et 2 AlI to (isoprene)zirconocene proceeds regioselectively to yield the corresponding heterodimetallacycles bearing the methyl substituent at C‐3 (i.e. near to the attached aluminium center). The iodide‐bridged heterodimetallacycles exhibit dynamic NMR spectra that indicate a rapid enantiomerization process on the NMR time scale (ΔG± ent ≈ 11–12 kcal mol −1 ). It is assumed that this automerization reaction proceeds by rate‐limiting aluminium‐halogen bond cleavage leading to an acyclic mixed metal heterodimetallic intermediate. This process is markedly inhibited by the presence of excess diethylaluminium iodide.