Winfried Steffen

Conjugated Organometallic Polymers Containing Vollhardt's Cyclobutadiene Complex: Aggregation and Morphologies

Organometallic polymers were prepared by acyclic diyne metathesis (ADIMET) or by Pd-catalyzed coupling of 1,3-diethynylcyclobutadiene(cyclopentadienyl)cobalt with a suitably substituted diiodobenzene. The polymers obtained by Heck coupling show a degree of polymerization (Pn) of 20-60. The monomers for ADIMET were made by the Pd-catalyzed coupling of [1,3-bis(trimethylsilylethynyl)-2,4-bis(trimethylsilyl)cyclobutadiene](cyclopentadienyl)cobalt to 1-bromo-2,5-dialkyl-4-propynylbenzenes in the presence of KOH in yields of 40-48%. The monomers carry hexyl, ethylhexyl, and (S)-3,7-dimethyloctyl side chains. Polymerization of the propynylated monomers furnishes organometallic polymers with a Pn of up to 230 arylene-ethynylene units. The polymers were fully characterized by polarizing microscopy, transmission electron microscopy, circular dichroism, differential scanning calorimetry, and X-ray diffraction (XRD). They show nematic, lyotropic liquid crystalline phases as well as chiroptical properties from which aggregation in poor solvents and in the solid state can be concluded. Lamellar or irregular honeycomb-shaped morphologies in these organometallic polymers can be detected by electron microscopy.

Synthesis and Structural Characterization of Organometallic Cyclynes: Novel Nanoscale, Carbon‐Rich Topologies

A combination of Pd- and Cu-catalyzed couplings make the ferrocene and cyclobutadiene(cyclopentadienylcobalt)-based halfwheels and the cyclobutadiene(cyclopentadienylcobalt)-based seco-wheel accessible. These targets can formally be constructed by fusing two or three organometallic benzohexadehydro[14]annulenes along an alkyne unit. In addition, a ferrocene-based, enlarged version of the half wheel was prepared. This target compound is obtained by formally fusing two organometallic benzododecadehydro[18]annulenes. Single crystal structures of three target molecules, the cyclobutadiene complex C51H37Co, the ferrocene derivativ eC 51H36Fe, and the cyclobutadiene complex C69H59Co were performed to verify the proposed geometries. # 2003 Published by Elsevier Science B.V.

Synthesis and structural characterization of organometallic cyclynes: novel nanoscale, carbon-rich topologies

A combination of Pd- and Cu-catalyzed couplings make the ferrocene and cyclobutadiene(cyclopentadienylcobalt)-based half-wheels and the cyclobutadiene(cyclopentadienylcobalt)-based seco-wheel accessible. These targets canformally be constructed by fusing two or three organometallic benzohexadehydro[l4]annulenes along an alkyne unit. In addition, a ferrocene-based, enlarged version of the half wheel was prepared. This target compound is obtained by formally fusing two organometallic benzododecadehydro[18]annulenes. Single crystal structures of three target molecules, the cyclobutadiene complex C 1 5 H 1 7 Co, the ferrocene derivative C 1 5 H 3 6 Fe, and the cyclobutadiene complex C 6 9 H 5 9 Co were performed to verify the proposed geometries.

Is ferrocene more aromatic than benzene

A combination of Pd-catalyzed arene–alkynyl couplings and Cu(OAc)2-promoted internal alkyne dimerization furnishes novel ferrocene-based dehydroannulenes in high yield.

Generation of bis(iminoalkyl)pyridine cobalt(i) cations under metal alkyl free conditions that polymerize etheneDedicated to Professor Helmut Werner on the occasion of his 70th birthday.

Treatment of the bis(iminoethyl)- or bis(iminobenzyl)pyridine cobalt dichlorides 3a,b with ″butadiene-magnesium″ (a, R = CH3) or methyllithium (b, R = Ph) yields the corresponding bis(iminoalkyl)pyridine cobalt(I) chloride complexes 7a,b. Chloride abstraction with Li[B(C6F5)4] in toluene generates the corresponding cations (9) which are low activity catalysts for the polymerization of ethene. The pyridine-stabilized [bis(iminoethyl)pyridineCo(I)(NC5H5)+] [B(C6F5)4−] salt was characterized by X-ray diffraction.