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Polymer Rings and Chains Consisting of Doubly Silyl‐Bridged Metallocenes
Author(s) -
Köhler Frank H.,
Schell Andreas,
Weber Bernd
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021115)8:22<5219::aid-chem5219>3.0.co;2-h
Subject(s) - ferrocene , cyclopentadienyl complex , chemistry , cyclopentadiene , silylation , metallocene , nickelocene , polymer chemistry , nuclear magnetic resonance spectroscopy , crystallography , stereochemistry , polymer , organic chemistry , polymerization , electrode , electrochemistry , catalysis
Abstract With the formation of novel organometallic macromolecules in mind, the polycondensation of transition metal ions and bridged cyclopentadienyl ligands was studied. To this end solvated salts MX 2 (M=Fe, Ni, and Cr) were treated with a ligand that consisted of two doubly silyl‐bridged cyclopentadienyl anions. For M=Fe and diluted solutions a series of rings ○ i was obtained that consisted of a minimum of six (○ 6 ) and up to 17 (○ 17 ) ferrocene moieties in the backbone. They were separated partly by medium pressure liquid chromatography. The macrocycles were established by high‐resolution MALDI‐TOF mass spectroscopy which also yielded the molecular weight, the polydispersion, and the mean ring size, χ n , of the mixture of reaction products. When the reaction temperature was decreased from 25 °C to −20 °C, χ n increased from 8.1 to 10.8. Ferrocene‐containing chains, Λ j , with 2≤ j ≤12 were obtained in addition to rings in the presence of water; the terminal groups were cyclopentadiene moieties. The reaction of two ferrocene‐fused cyclopentadienyl anions with [FeCl 2 (thf) 1.5 ] gave chains consisting of exclusively uneven numbers of ferrocenes. For M=Ni and Cr the formation of doubly silyl‐bridged nickelocenes and chromocenes was proven by NMR spectroscopy. MALDI‐TOF mass spectroscopy showed nickelocene‐containing chains accompanied by some rings. For M=Fe the H,H‐DQF COSY spectra established the structure of ○ 7 , ○ 8 , and ○ 9 . The oxidation of the ferrocene‐containing ring ○ 7 with I 2 , NOPF 6 , and AgPF 6 gave ionic species [○ 7 ] n + which suffered from low stability. The ring‐closing reaction is discussed, and the relative abundance of the various rings is related to MNDO calculations.