Polyolefins ligands

This review of some aspects of the organometallic chemistry of iridium is certainly not exhaustive. There have been some types of complexes that have receive little notice such as those containing polyolefinic ligands and related compounds. Also, there are other organic transformations that may be catalyzed by iridium complexes. However, throughout this chapter the reader has been directed to a number of primary references as well as a number of review articles that will delve into some areas of iridium organometallic chemistry more deeply. 

Complexes containing two cyclic polyolefinic ligands will be included in this section if one of the rings is cyclopentadienyl. 

The above achievements depend highly on both the recent advances in rational catalyst design with the aid of computational science represented by DFT calculations and the wide range of catalyst design possibilities that are afforded by FI catalysts. These possibilities are derived from the readily varied steric and electronic properties of the phenoxy-imine ligands. It is expected that future research on FI catalysts will provide opportunities to produce additional polyolefin-based materials with unique microstructures and a chance to study catalysis and mechanisms for olefin polymerization. 

Since their discovery over a decade ago, late transition metal a-diimine polymerization catalysts have offered new opportunities in the development of novel materials. The Ni(II) catalysts are highly active and attractive for industrial polyolefin production, while the Pd(II) catalysts exhibit unparalleled functional group tolerance and a propensity to form unusually branched polymers from simple monomers. Much of the success of these catalysts derives from the properties of the a-diimine ligands, whose steric bulk is necessary to accelerate the insertion process and inhibit chain transfer. 

Lehn and coworkers52 reported the synthesis, crystal structure and dinuclear copper(I) complexes of tris-carotenoid macrobicyclic ligands. The macrobicycles 89 and 90 were obtained in good yields in a one-step macrobicyclisation condensation between the tripode N(CH2CH2NH2)3 and the polyolefinic dialdehydes 93 and 94. 

The physiological hormone for the RARs is all-frans-retinoic acid RA 221 and that for the RXRs is its geometric isomer, 9-czs-retinoic acid (9-czs-RA 222) [320]. However, these polyolefinic hormones are of only limited use in elucidating the precise biological roles of each receptor family. Synthetic ligands that specifically activate only the RXR or RAR hormonal pathway and which cannot be converted into forms that activate the other pathway would be of much greater use in this regard. 

The first metal-olefin complex was reported in 1827 by Zeise, but, until a few years ago, only palladium(II), platinum(Il), copper(I), silver(I), and mercury(II) were known to form such complexes (67, 188) and the nature of the bonding was not satisfactorily explained until 1951. However, recent work has shown that complexes of unsaturated hydrocarbons with metals of the vanadium, chromium, manganese, iron, and cobalt subgroups can be prepared when the metals are stabilized in a low-valent state by ligands such as carbon monoxide and the cyclopentadienyl anion. The wide variety of hydrocarbons which form complexes includes olefins, conjugated and nonconjugated polyolefins, cyclic polyolefins, and acetylenes. 

Hydrocarbon ligands, overview, 6, 127-151 ]3-Hydrocarbon ligands, overview, 6, 127-151 ]4-Hydrocarbon ligands, overview, 6, 127-151 Hydrocarbon polyolefin monomers, co-polymerizations,... 

Polyolefin cyclization.1 This Pd(0) catalyst in combination with a phosphine ligand and acetic acid effects cyclization of polyunsaturated substrates to polycyclic products in one step (zipper reaction). However, a triple bond is required for initiation. This polyolefin cyclization has been used to prepare tetra- and pentaspirocycles, as a mixture of only two stereoisomers. 

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