Catalysts late-transition-metal

FWA Fluorescence whitening agent LTMC Late transition metal catalyst... 

With the exception of LDPE, polyolefins like other polyethylenes and polypropylene, which represent the largest amount of vinyl-type polymers produced in the world, are neither synthesized by radical nor by classical ionic polymerisation processes. Different types of polymerisation catalysts are in use for these purposes. The Cr-based Phillips catalyst, Ziegler-Natta type catalysts, metallocene or other more recently discovered catalysts, including late transition metal catalysts, are all characterized by their propagation step where the olefin monomer inserts into a carbon-transition metal link. ... 

Based on an early process discovered by Natta in the 1950s, soluble transition metal catalysts like metallocenes were developed mainly in the 1950s as initiators for polyolefin syntheses. Others are still now under investigation, like the so-called LTM (for "late transition metal") catalysts. Metallocenes seem... 

Late Transition Metal Catalysts for the Copolymerization of Olefins and Polar Monomers... 

P, N, O, S, or C based, which favor covalent bonding and stabilize low oxidation states) due to the metals higher electronegativity and lower oxidation states [24], In recent years, late transition metal catalysts [25-29] have attracted attention not only for the polymerization of a-olefins, but more importantly for the copolymerization of hydrocarbon monomers with readily available polar monomers such as acrylates, vinyl ethers, and vinyl acetate [27 and references therein]. 

In addition to the foregoing late transition metal catalyst developments, which have led to the discovery of sophisticated palladium systems capable of the catalytic (coordination) copolymerization of ethylene with acrylates, there have also been some interesting studies into systems where it eventually transpired that the mechanism was actually free radical rather than catalytic. 

After five decades of catalyst research there is slowly emerging a family of discrete late transition metal catalysts that are capable of generating high molecular weight, linear, random copolymers of ethylene and polar comonomers such as acrylates. Further advances in the efficiency of these catalysts will likely give rise to new families of commercial polyolefins with a wealth of new performance properties imparted by the polar groups attached to the polymer backbone. 

The recent progress surveyed in this review shows the promise that late transition metal catalysts can provide in the production of new materials. We will continue our exploration of new catalyst design for the synthesis of new functional materials with unconventional topologies. Given the unique features of late transition-metal polymerization catalysts and further improvement in catalyst stability and activity for copolymerization with polar comonomers, the future of designing novel functional polymeric materials with late-transition-metal catalysts is very promising. 

To date, the reductive cyclization of allenic alkenes remains undeveloped. However, the reductive cyclization of activated alkene partners in the form of 1,3-dienes and conjugated enones has been achieved using late transition metal catalysts. Indeed, the hydrosilylative dimerization of 1,3-dienes reported in 1969 appears to be the first reductive... 

The very first example of the catalytic reductive cyclization of an acetylenic aldehyde involves the use of a late transition metal catalyst. Exposure of alkynal 78a to a catalytic amount of Rh2Co2(CO)12 in the presence of Et3SiH induces highly stereoselective hydrosilylation-cyclization to provide the allylic alcohol 78b.1 8 This rhodium-based catalytic system is applicable to the cyclization of terminal alkynes to form five-membered rings, thus complementing the scope of the titanocene-catalyzed reaction (Scheme 54). 

Figure 1. Late transition metal catalysts for olefin polymerization of current interest...

Theoretical studies have been carried out on all the late transition metal catalysts la [10-13], lb [14] and lc [15] in Figure 1. It is not the objective here to review all the computational results. We shall instead describe the general mechanistic insight that has been gained from the theoretical studies with the main emphasis on Brookhart s bis-imine catalysts. The experimental work on late transition metal olefin polymerization catalysts has been reviewed recently by Ittel [16] et al. 

The conventional hydrosilylation of alkenes catalyzed by late transition metal catalysts such as Speier s catalyst are generally assumed to proceed by... 

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

In2000, Hashmi and coworkers reported that certain alkynyl furans (151) undergo rapid cycloisomerization to give bicyclic phenols (152) in the presence of AUCI3 at room temperature (Equation 9.16) [51]. A number of late-transition metal catalysts promote this transformation [52]. Echavarren and coworkers have studied the Pt-catalyzed variant [53], which is believed to proceed via a mechanism involving Pt-cydopropylcarbene intermediates [54]. 

Compared to early transition metals, the number of group 8-10 transition metal catalysts for the polymerization of substituted acetylenes has been relatively small except for Rh. However, unique aspects of these late transition metal catalysts have been revealed which cannot be seen in early transition metals and conventional Rh catalysts. 

Regarding the co-polymerization of hydrocarbon and polar monomers, late transition metal catalysts have provided the most significant advances to date because of their lower oxophilicity and thus greater functional-group tolerance than early transition metal catalysts, although group 4 metallocene catalysts are known to promote the co-polymer-ization of olefins and non-vinyl polar monomers with masked functional groups. 

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