The Dinuclear Zirconocene Complex [(Cp2Zr)2(μ‐Me)(μ‐C2Ph)] as a Platform for Small Molecule Activation

TL;DR

A new zirconocene complex is shown to activate small molecules and form unique hydride complexes through various reactions.

Contribution

The study introduces a dinuclear zirconocene complex as a versatile platform for small molecule activation and hydride complex formation.

Findings

The complex catalyzes amine borane dehydrocoupling and forms a hydride-bridged alkynyl complex.

Reactions with hydrogen produce a trinuclear hydride-bridged complex with a unique carbon environment.

Reactions with nitriles involve coordination and reduction of substrates.

Abstract

The dinuclear title compound [(Cp2Zr)2(μ‐Me)(μ‐C2Ph)] 5 was prepared from a zirconocene alkynyl methyl complex and Rosenthal's zirconocene source [Cp2Zr(py)(η
2‐Me3SiC2SiMe3)] in a formal comproportionation reaction. This complex shows catalytic activity for the dehydrocoupling of amine boranes, with a dinuclear hydride‐bridged alkynyl complex 6 being formed as a catalytically relevant species. The structure of this complex was confirmed for the first time by single‐crystal X‐ray analysis. The reaction of complex 5 with hydrogen results in hydrogenation of the alkynyl ligand, yielding a highly labile trinuclear hydride‐bridged complex as a possible intermediate of zirconocene dihydride/ethylbenzene formation. This complex shows an unusual distorted planar tetracoordinate environment at the central carbon atom positioned between the three Zr centers. The reaction of complex 5 with 2‐cyanopyridine and acetonitrile is characterized by a reduction of the substrates. The herein reported reactivity of complex 5 demonstrates the remarkable potential of well‐established dinuclear zirconocenes to stabilize unusual bond situations, which were analyzed comprehensively using spectroscopic, structural, and computational methods.

The reported dinuclear zirconocene alkynyl methyl complex represents a multifaceted platform for the activation of small molecules. While reduction reactions furnish unusual di‐ and trinuclear hydride complexes, reactions with nitriles result in coordination and reduction of the substrate. Detailed structural and computational analysis gives insights into the structure and bonding of these species.

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