An important development in recent synthesis strategies is the formation of electronically coupled one and two-dimensional organic systems for potential applications in nanoscale molecule-based devices. Here, we assemble one-dimensional spin chains by covalently linking basic molecular building blocks on a Au(111) surface. Their structural properties are studied by scanning tunneling microscopy and the Kondo effect of the basic molecular blocks inside the chains is probed by scanning tunneling spectroscopy. Tunneling spectroscopic images reveal the existence of separate Kondo regions within the chains while density functional theory calculations unveil antiferromagnetic coupling between the spin centers.

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The migration of a Zr center between adjacent carbon atoms of a Zr-bound alkyl group is investigated by a density functional study of alternative reaction paths available to a (C5H5)2Zr−alkyl cation. This migration is found to occur by the classical reaction route, i.e. by β-H transfer, olefin rotation, and reinsertion into the Zr−H bond without loss of the olefin ligand, rather than by a concerted Zr/H exchange. The activation barrier is determined to decrease from 75 kJ/mol for the degenerate isomerization of a zirconocene ethyl cation to 49 kJ/mol for the isomerization of a primary to a secondary zirconocene propyl cation and 41 kJ/mol for its back-reaction. It is further reduced to 40 kJ/mol for the isomerization of a primary to a tertiary zirconocene isobutyl cation and 31 kJ/mol for its reverse, which model the isomerization process competing with stereoregular chain growth in zirconocene-based catalysts. The facility with which the zirconocene isobutyl cation transfers its β-H atom is connected with a particularly soft stretching vibration of the agostic β-C−H bond. Substantial stabilization of positive charge at the β-carbon atom by two alkyl substituents appears to be the cause. Reaction paths by which an olefin ligand in an intervening isomerization intermediate can change its coordination from one enantioface to the other have also been identified.

The influence of silylene-bridged bis(indenyl) ligand substitution, especially benzannelation and 2-methyl substitution, on methylaluminoxane-activated metallocene-catalyzed ethene/1-octene copolymerization in toluene at 40 °C was investigated. 2-Methyl substitution gave significantly higher molecular masses at the expense of catalyst activity, whereas benzannelation promoted 1-octene incorporation and randomness of the resulting poly(ethene-co-1-octene) copolymers. Force field calculations based on steric arguments were used to explain experimental copolymerization results. Activation energy differences between ethene and 1-octene insertion accounted for improved 1-octene incorporation in the case of benzannelated metallocenes. According to 13 C-NMR microstructure analysis, copolymerization followed first-order Markov statistics.