In recent years, the olefin metathesis reaction has attracted widespread attention as a versatile carbon−carbon bond-forming method. Many new applications have become possible because of major advances in catalyst design. State-of-the-art ruthenium catalysts are not only highly active but also compatible with most functional groups and easy to use. This Account traces the ideas and discoveries that were instrumental in the development of these catalysts, with particular emphasis on (PCy3)2Cl2RuCHPh and its derivatives. The discussion includes an analysis of trends in catalyst activity, a description of catalysts coordinated with N-heterocyclic carbene ligands, and an overview of ongoing work to improve the activity, stability, and selectivity of this family of L2X2RuCHR complexes.

http://web4.uwindsor.ca/users/j/jlichaa/reference.nsf/0/10ff8b04ff3a317885256d88005720f6/$FILE/acr-2001-34-18-metath-grubbs.pdf

The Development of L2X2RuCHR Olefin Metathesis Catalysts: An Organometallic Success Story

9-Fluorenylmethoxycarbonyl (Fmoc) amino acids were first used for solid phase peptide synthesis a little more than a decade ago. Since that time, Fmoc solid phase peptide synthesis methodology has been greatly enhanced by the introduction of a variety of solid supports, linkages, and side chain protecting groups, as well as by increased understanding of solvation conditions. These advances have led to many impressive syntheses, such as those of biologically active and isotopically labeled peptides and small proteins. The great variety of conditions under which Fmoc solid phase peptide synthesis may be carried out represents a truly "orthogonal" scheme, and thus offers many unique opportunities for bioorganic chemistry.

Solid phase peptide synthesis utilizing 9‐fluorenylmethoxycarbonyl amino acids

Dynamic covalent chemistry relates to chemical reactions carried out reversibly under conditions of equilibrium control. The reversible nature of the reactions introduces the prospects of "error checking" and "proof-reading" into synthetic processes where dynamic covalent chemistry operates. Since the formation of products occurs under thermodynamic control, product distributions depend only on the relative stabilities of the final products. In kinetically controlled reactions, however, it is the free energy differences between the transition states leading to the products that determines their relative proportions. Supramolecular chemistry has had a huge impact on synthesis at two levels: one is noncovalent synthesis, or strict self-assembly, and the other is supramolecular assistance to molecular synthesis, also referred to as self-assembly followed by covalent modification. Noncovalent synthesis has given us access to finite supermolecules and infinite supramolecular arrays. Supramolecular assistance to covalent synthesis has been exploited in the construction of more-complex systems, such as interlocked molecular compounds (for example, catenanes and rotaxanes) as well as container molecules (molecular capsules). The appealing prospect of also synthesizing these types of compounds with complex molecular architectures using reversible covalent bond forming chemistry has led to the development of dynamic covalent chemistry. Historically, dynamic covalent chemistry has played a central role in the development of conformational analysis by opening up the possibility to be able to equilibrate configurational isomers, sometimes with base (for example, esters) and sometimes with acid (for example, acetals). These stereochemical "balancing acts" revealed another major advantage that dynamic covalent chemistry offers the chemist, which is not so easily accessible in the kinetically controlled regime: the ability to re-adjust the product distribution of a reaction, even once the initial products have been formed, by changing the reaction's environment (for example, concentration, temperature, presence or absence of a template). This highly transparent, yet tremendously subtle, characteristic of dynamic covalent chemistry has led to key discoveries in polymer chemistry. In this review, some recent examples where dynamic covalent chemistry has been demonstrated are shown to emphasise the basic concepts of this area of science.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/1521-3773%2820020503%2941%3A9%3C1460%3A%3AAID-ANIE11111460%3E3.0.CO%3B2-N

Dynamic covalent chemistry.

Recent advances in olefin metathesis and its application in organic synthesis

The fascinating story of olefin (or alkene) metathesis (eq
1) began almost five decades ago, when Anderson and
Merckling reported the first carbon-carbon double-bond
rearrangement reaction in the titanium-catalyzed polymerization of norbornene. Nine years later, Banks and Bailey reported “a new disproportionation reaction . . . in which olefins are converted to homologues of shorter and longer carbon chains...”. In 1967, Calderon and co-workers named this metal-catalyzed redistribution of carbon-carbon double bonds olefin metathesis, from the Greek word “μeτάθeση”, which means change of position. These contributions have since served as the foundation for an amazing research field, and olefin metathesis currently represents a powerful transformation in chemical synthesis, attracting a vast amount of interest both in industry and academia.

https://core.ac.uk/download/pdf/4884240.pdf

Ruthenium-based heterocyclic carbene-coordinated olefin metathesis catalysts.

Preface. Abbreviations. Introduction: The Olefin Metathesis Reaction. Brief History. The Metal Carbene Mechanism. Equilibria and Stereoselectivity. Survey of Catalyst Systems: Group IV. Group V. GroupVI. Group VII. Group VIII. Photochemically Activated Catalysts. The Metal Carbene/Metallacyclobutane Mechanism: Evidence from Cross-Metathesis Reactions. Evidence from the Stereochemistry of Metathesis of Internal Olefins. Evidence from Ring-Opening Metathesis Polymerization (ROMP). Evidence from the reactions of Well-Defined Metal Carbene Complexes. Evidence from the Reactions of Metallacyclobutane Complexes. Evidence of Initiating Species in Systems with Non-Carbene Catalysts. Theoretical Treatments. Related Reactions: [2+2] Reactions Between Compounds Containing Multiple Bonds. Relationship to Ziegler-Natta Polymerization. Involvement of Three-Membered Ring Compounds in Metathesis Reactions. Ethene and Terminal Alkenes: Ethene. Propene. But-1-ene and its Derivatives. Pent-1-ene and its Derivatives. Hex-1-ene and its Derivatives. Higher Acyclic Terminal Alkenes. Acyclic Disubstituted and Trisubstituted Ethenes. Cis/trans Isomerization. Pent-2-ene and 4-Substituted Derivatives. Hex-2-ene and 4-Methylhex-2-ene.Hept-2-ene and Hept-3-ene. Higher Acyclic Internal Olefins. Stereoselectivity in the Metathesis of Acyclic Olefins. 1,1-Disubstituted Olefins. Trisubstituted Ethenes. Acyclic Functionalized Alkenes: Esters. Other Carbonyl-Containing Compounds. Ethers. Amines. Nitriles. Chlorides and Bromides. Sulfides and Sulfonates. Silancs and Germanes. Phospanes. Acyclic Dienes: Double Bonds Linked only by C Atoms. Double Bonds Linked by C and Si, Ge orSn Atoms. Double Bonds Linked by C and N Atoms. Double Bonds Linked by C, Si, and O Atoms. Divinylferrocene. Some Further Applications in Organic Synthesis. Copolymers by Metathesis Condensation. Cross-Metathesis Between Acyclic Compounds: Ethene.Propene. Butenes. Pentenes. Hexenes. Higher Olefins. Functionalized Olefins. Acetylenes: Metathesis Reactions Involving Total Cleavage of the C=C bond. Metathesis Reactions Involving Cleavage of Two of the thress C=C Bonds. Metathesis Reactions of Enynes and Dienynes. Other Metathesis Routes to Polyacetylenes. Ring-Opening Metathesis Polymerization: General Aspects: Thermodynamic Aspects. Efficiency of Initiation. The Use of Chain-Transfer Agents. Molecular Weight Distributions. Polymer Micostructure. Monocyclic Alkenes and Polyenes: Four-Membered Rings. Five-Membered Rings. Six-Membered Rings. Seven-Membered Rings. Eight-Membered Rings. Nine-Membered Rings. Ten-Membered Rings. Twelve-Membered and Other Rings. Polycyclic Alkenes: Monomers Containing a Fused Cyclobutene Ring. Monomers Containing a Fused Cyclopentene Ring and One Double Bond. Monomers Containing a Fused Cyclopentene Ring and More than One Double Bond. Bicyclo[2.2.1] Compounds Containing Heteroatoms in the Ring System. Other Bicyclic Compounds. Copolymers of Cycloalkenes: Direct Metathesis Copolymerization. Cyclic Co-Oligomers. Block Copolymers by Sequential Addition of Monomers to Living Systems. Block Copolymers by Modification of Homopolymers. Comb and GraftCopolymers. Copolymers by ROMP in Conjunction with Radical Reactions. Cross-Metathesis Between Cyclic and Acyclic Olefins: End-Groups and Telomers. Dependence of Molecular Weight on [M 2]/[M 1]. Kinetic Data. Degradation of UnsaturatedPolymers by Metathesis: Degradation by Intramolecular Metathesis. Applications of the Olefin Metathesis Reaction: The Phillips Triolefin Process. The Neohexene Process. The Shell Higher Olefins Process. Other Multistage Processes Involving Metathesis. The Isoamylene Process. (Circle around alpha and omega) ((-Diolefins. trans-Poly(1-Pentenylene). trans-Poly(1-octenylene). Polymers of Norhornene. Polymers of Norbornene Derivatives. Miscellaneous. Bibliography. Subject Index.

Olefin metathesis and metathesis polymerization

A mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts is developed which differs significantly from previous mechanisms in the proposal that it proceeds via a 1,2-hydrogen shift from the α-carbon of the polymer chain and formation of metallocycle and carbene intermediates.

Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

13C NMR spectra were obtained for polymers made by ring-opening polymerization of cyclopentene and bicyclo[2.2.1]hept-2-ene respectively. The fraction of cis double bonds could be determined with much greater precision from 13C NMR spectra than from IR spectra and varied from 0,66 to 0,31 for the samples of poly(1-pentenylene), (2), and from 1,0 to 0,14 for the samples of poly(1,3-cyclopentylenevinylene), (4). This is the first time an all-cis polymer of 4 has been reported.



The spectra of 2 showed a cis (upfield) and trans (downfield) peak for each of CH and α-CH2, but only one peak for β-CH2. The spectra of 4 showed multiple fine structure, the main splittings corresponding to a cis (upfield) and trans (downfield) peak for α-CH, and a reverse line order for the other three carbons; subsidiary splittings were observed for all but the olefinic carbons, interpreted in terms of sensitivity of the chemical shifts to the cis/trans structure at the next nearest double bond. A complete interpretation of the line orders in 4 is given in terms of steric compression effects. The possibility that ring tacticity accounts for some of the fine structure cannot be entirely discounted.



The stereochemistry of 4 is discussed in relation to the four possible modes of addition of monomer to a carbene chain carrier during polymerization.

The 13C NMR spectra of poly(1‐pentenylene) and poly(1,3‐cyclopentylenevinylene)

This chapter discusses general aspects of the group of metathesis reactions, such as the effect of ring size on polymerizability, the formation of cyclic oligomers, living systems, molecular weight distributions, and stereochemistry For addition polymerization processes of any kind, of which ring-opening metathesis polymerization (ROMP) is a particular case, the boundary between polymerizabilty and nonpolymerizabilty, corresponding to ∆G negative and positive respectively, is very distinct Metal carbene complexes used as initiators (I) are not always fully consumed before the monomer (M) has been completely polymerized This can happen when the propagation rate constant kp is somewhat greater than the initiation rate constant ki  In nonliving systems, the initiating species may be generated over a period of time, and the termination reactions are generally not well defined In some cases, there will also be backbiting reactions leading to the formation of cyclic oligomers

Ring-Opening Metathesis Polymerization: General Aspects

About one hundred samples of poly(1,3-cyclopentylenevinylene) (2) were prepared by ring-opening polymerization of norbornene using a variety of metathesis catalysts based mainly on WCl6 or MoCl5, with EtAlCl2, BuLi, Ph4Sn, and (CH2CHCH2)4Sn as cocatalysts, and with methyl acrylate, diethyl maleate or diethyl fumarate as additives. Ir, Re, V, and Os compounds were also used as catalysts. The double bond pair sequences, trans-trans (tt), trans-cis (tc) etc. were determined from the 13C NMR spectra of these samples and the ratios rt(=tt/tc) and rc(=cc/ct) examined as a function of the fraction of double bonds σc having cis structure. For σc up to 0,35 all polymers showed random distribution of cis and trans structures (rtrc = 1), corresponding to a single type of propagating species. Polymers having σc = 0,35–0,85 invariably gave rtrc ≥ 1, with values greater than 5 in some cases. It is proposed that steric crowding of the active site leads both to high values of σc and to restriction of rotation about the metal-carbene bond of the propagating metalcarbene species, such as to give rise to kinetically distinct conformations which tend to regenerate their own kind on addition of monomer.

Kenneth J. Ivin

Papers

Olefin metathesis and metathesis polymerization

Mechanism for the stereospecific polymerization of olefins by Ziegler–Natta catalysts

The 13C NMR spectra of poly(1‐pentenylene) and poly(1,3‐cyclopentylenevinylene)

Ring-Opening Metathesis Polymerization: General Aspects

Cis‐trans double bond distribution in poly(1,3‐cyclopentylenevinylene); dependence on metathesis catalyst, cocatalyst, and additives