Abstract
Metathesis has persisted through the years as a formidable synthetic
approach to various unsaturated organic molecules and macromolecules.
The 21st century developments in olefin metathesis continue to feature
more efficient and selective, well-defined metathesis catalysts.
Due to the easily regulated steric and electronic properties of ‘pseudo-halide’ derivatives,
their study has launched a new milestone in ruthenium- and molybdenum-based catalysis.
Synthesizing ‘pseudo-halide’ derivatives often
entails replacing halide ligands with easily modified carboxylates,
perfluorocarboxylates, phenoxides, isocyanates, isothiocyanates,
pyridines, nitrates, and trifluoromethanesulfonates. This account
elucidates the recent advances in ‘pseudo-halide’-containing
olefin metathesis, including synthetic approaches to obtain new
catalysts and optimization of the ligand sphere. Several innovations
in Ru- and Mo-alkylidenes that concern initiation efficiency, reactivity,
stereoselectivity, supported catalysis, cyclopolymerization, and
copolymerization are described. Refinement of the anionic ‘pseudo-halide’ ligands
has enabled the perfection of Ru- and Mo-based metathesis catalysts
in both reactivity and selectivity. These advances have led to stereoselectivity
in polymerizations, improved copolymerization affinity, and the
regioselective cyclopolymerization of 1,6-heptadiynes to result
in conjugated polymers solely based on five-membered repeat units.
1 Introduction
2 Catalyst Synthesis
2.1 Modified Ru-Alkylidene-Based Metathesis Catalysts
2.1.1 Halides, Alkoxides, and Aryloxides
2.1.2 Bidentate or Monodentate Carboxylates
2.1.3 Nitrates and Trifluoromethanesulfonates
2.1.4 Isocyanates and Isothiocyanates
2.2 Modified Mo-Alkylidene-Based Metathesis Catalysts
2.2.1 Bidentate or Monodentate Carboxylates
2.3 Supported Catalysts
3 Characterization and Structural Effects
3.1 General Procedures
3.2 X-ray Structures
3.3 ¹ H and ¹³ C
NMR Shifts of the Alkylidene Resonances
4 Catalysis in Organic Synthesis
4.1 Ring-Closing Metathesis (RCM)
4.2 Other Metathesis Reactions
5 Catalysis in Polymerization
5.1 Ring-Opening Metathesis Polymerization (ROMP)
5.1.1 2-Norbornene (NBE)
5.1.2 Cyclooctene (COE)
5.1.3 cis -1,5-Cyclooctadiene (COD)
5.2 Cyclopolymerization of 1,6-Heptadiynes
5.2.1 Diethyl Dipropargylmalonate (DEDPM)
5.2.2 Other 1,6-Heptadiynes
5.3 Copolymerization
5.3.1 Copolymers via Ring-Opening Metathesis Polymerization (ROMP)
5.3.2 Copolymers of 1,6-Heptadiynes with Acetylene
6 Summary and Outlook
Key words
alkylidenes - olefin metathesis - catalysis - ruthenium - molybdenum - ring-closing metathesis - ring-opening metathesis polymerization - cyclopolymerization - 1,6-heptadiynes
