Preparation of NHC–ruthenium complexes and their catalytic activity in metathesis reaction

Cyclic ruthenium-alkylidene catalysts for ring-expansion metathesis polymerization

A series of cyclic Ru-alkylidene catalysts have been prepared and evaluated for their efficiency in ring-expansion metathesis polymerization (REMP). The catalyst structures feature chelating tethers extending from one N-atom of an N-heterocyclic carbene (NHC) ligand to the Ru metal center. The catalyst design is modular in nature, which provided access to Ru complexes having varying tether lengths, as well as electronically different NHC ligands. Structural impacts of the tether length were unveiled through (1)H NMR spectroscopy as well as single-crystal X-ray analyses. Catalyst activities were evaluated via polymerization of cyclooctene, and key data are provided regarding propagation rates, intramolecular chain transfer, and catalyst stabilities, three areas necessary for the efficient synthesis of cyclic poly(olefin)s via REMP. From these studies, it was determined that while increasing the tether length of the catalyst leads to enhanced rates of polymerization, shorter tethers were found to facilitate intramolecular chain transfer and release of catalyst from the polymer. Electronic modification of the NHC via backbone saturation was found to enhance polymerization rates to a greater extent than did homologation of the tether. Overall, cyclic Ru complexes bearing 5- or 6-carbon tethers and saturated NHC ligands were found to be readily synthesized, bench-stable, and highly active catalysts for REMP.

Ruthenium-indenylidene complexes: powerful tools for metathesis transformations

Ruthenium-indenylidene complexes represent a class of robust and efficient pre-catalysts for olefin metathesis reactions. In this feature article, we provide an overview of the various complexes belonging to this family and summarise their use in various applications. The relation between the nature of ancillary ligands around the metal coordination sphere of these complexes and their catalytic activity is also discussed.

Cyclic (amino)[bis(ylide)]carbene as an anionic bidentate ligand for transition-metal complexes

The 3-(triphenylphosphonio)-N-(2,6-diisopropylphenyl)pyrrole reacts with 2 equiv of methyllithium to afford a lithium adduct in which a cyclic (amino)[bis(ylide)]carbene, a novel type of NHC, acts as a 1,4-bidentate ligand via the carbene center and the exocyclic ylidic carbon. This species readily undergoes transmetalation reactions, which allows for the synthesis of a variety of transition-metal complexes.

Flexible coordination of the carboxylate ligand in tin(ii) amides and a 1,3-diaza-2,4-distannacyclobutanediyl

A series of tin(II) amido complexes possessing m-terphenyl carboxylate ligands have been prepared. These complexes, namely [(Me(3)Si)(2)NSn(mu-O(2)CC(6)H(2)Ph(3))](2), [(Me(3)Si)(2)NSn(mu-O(2)CC(6)H(3)Mes(2))](2), and [(Me(3)Si)(2)NSn(mu-O(2)CC(6)H(2)Mes(2)Me)](2) [Mes = 2,4,6-trimethylphenyl], are the first structurally characterized examples of tin(II) carboxylate complexes exhibiting discrete Sn(2)O(4)C(2) heterocyclic cores. Initial reactivity studies led to the isolation of a 1,3-diaza-2,4-distannacyclobutanediyl, [(Mes(2)C(6)H(3)CO(2))Sn(mu-NSiMe(3))](2). This molecule possesses a Sn(2)N(2) heterocyclic core and it was crystallised as both the CH(2)Cl(2) and Et(2)O solvates. Although the tin atoms in this molecule have a formal oxidation state of 3+, preliminary computational studies on this molecule suggest that it is best described as a ground state singlet. Finally, the X-ray crystal structure of (CH(2)Cl)(Cl)Sn[N(SiMe(3))(2)](2), the product of oxidative addition of CH(2)Cl(2) to Sn[N(SiMe(3))(2)](2), is also presented herein.