Imines transition metal complexes

In this contribution, we describe the discovery and application of phenoxy-imine ligated early transition metal complexes (FI catalysts) for olefin polymerization, including the concept behind our catalyst design, the discovery and the polymerization behavior of FI catalysts, and their applications to new polyolefinic materials. 

Among the highly active catalysts introduced above, bis(phenoxy-imine) early transition metal complexes (Fig. 9) in particular show strikingly high activities for the polymerization of ethylene [14, 51-54]. 

Asymmetric hydrogenations catalyzed by supported transition metal complexes have included use of both chiral support materials (poly-imines, polysaccharides, and polyalcohols), and bonded chiral phosphines, although there have been only a few reports in this area. 

Early transition-metal complexes have been some of the first well-defined catalyst precursors used in the homogeneous hydrogenation of alkenes. Of the various systems developed, the biscyclopentadienyl Group IV metal complexes are probably the most effective, especially those based on Ti. The most recent development in this field has shown that enantiomerically pure ansa zirconene and titanocene derivatives are highly effective enantioselective hydrogenation catalysts for alkenes, imines, and enamines (up to 99% ee in all cases), whilst in some cases TON of up to 1000 have been achieved. 

In summary, the reduction of ketones and aldehydes can both be performed with MPV and transition-metal complexes as catalysts. Reductions of alkenes, al-kynes, and imines require transition-metal catalysts MPV reductions with these substrates are not possible. 

Terminal alkynes readily react with coordinatively unsaturated transition metal complexes to yield vinylidene complexes. If the vinylidene complex is sufficiently electrophilic, nucleophiles such as amides, alcohols or water can add to the a-carbon atom to yield heteroatom-substituted carbene complexes (Figure 2.10) [129 -135]. If the nucleophile is bound to the alkyne, intramolecular addition to the intermediate vinylidene will lead to the formation of heterocyclic carbene complexes [136-141]. Vinylidene complexes can further undergo [2 -i- 2] cycloadditions with imines, forming azetidin-2-ylidene complexes [142,143]. Cycloaddition to azines leads to the formation of pyrazolidin-3-ylidene complexes [143] (Table 2.7). 

Catalytic asymmetric reduction of unsaturated compounds is one of the most reliable methods used to synthsize the corresponding chiral saturated products. Chiral transition metal complexes repeatedly activate an organic or inorganic hydride source, and transfer the hydride to olefins, ketones, or imines from one... 

Ethers, sulfides, amines, carbonyl compounds, and imines are among the frequently encountered Lewis bases in the ylide formation from such metal carbene complex. The metal carbene in the ylide formation can be divided into stable Fisher carbene complex and unstable reactive metal carbene intermediates. The reaction of the former is thus stoichiometric and the latter is usually a transition metal complex-catalyzed reaction of a-diazocarbonyl compounds. The decomposition of a-diazocarbonyl compounds with catalytic transition metal complex has been the most widely used approach to generate reactive metal carbenes. For compressive reviews, see Refs 1,1a. 

Asymmetric hydrometallation of ketones and imines with H-M (M = Si, B, Al) catalyzed by chiral transition-metal complexes followed by hydrolysis provides an effective route to optically active alcohols and amines, respectively. Asymmetric addition of metal hydrides to olefins provides an alternative and attractive route to optically active alcohols or halides via subsequent oxidation of the resulting metal-carbon bonds (Scheme 2.1). 

A review has appeared on the synthesis of enantiomerically enriched aziridines by the addition of nitrenes to alkenes and of carbenes to imines.45 A study of the metal-catalysed aziridination of imines by ethyl diazoacetate found that mam group complexes, early and late transition metal complexes, and rare-earth metal complexes can catalyse the reaction.46 The proposed mechanism did not involve carbene intermediates, the role of the metal being as a Lewis acid to complex the imine lone pah. Ruthenium porphyrins were found to be efficient catalysts for the cyclopropana-tion of styrenes 47 High diastereoselectivities in favour of the //-product were seen but the use of chiral porphyrins gave only low ees. 

The metal-catalyzed oxidation of imines using molecular oxygen as the final oxidant and aldehydes as co-reductants has been studied223. Various transition metal complexes have been tested as catalysts and it is found that cobalt complexes can catalyze the selective oxidation of imines to oxaziridines in good yield (ca 80%) (Scheme 4). 

Low-valence transition metal complexes of a-diimine ligands are highly colored because of the presence of low-energy metal to a-diimine charge transfer (MLCT) transitions. For a series of d6-M(CO)., (a-diimine) (M=Cr,Mo,W) and d8- M (CO)3 (a-diimine) (M =Fe, Ru) complexes, we have studied the spectroscopic and photochemical properties (1-10). The a-diimine ligands used are 1,4-diaza-1,3-butadiene (R-DAB), pyridine-2-car-baldehyde-imine (PyCa), 2,2 -bipyridine (bipy) or 1,10-phenanthroline (phen) molecules. A close relationship was deduced between the photochemical behavior of these complexes and their resonance Raman (rR) spectra, obtained by excitation into the low-energy MLCT band. 

Jorgensen has studied the oxidation of imines 137 to oxaziridines 138 catalyzed by transition metal complexes using molecular oxygen as the stoichiometric oxidant. Optimized... 

Attempts to achieve asymmetric nitrene insertion reactions catalyzed by chiral transition metal complexes have also been performed [41,42]. The reaction of the nosyl-imine derivative as the nitrene donor with indane 61 catalyzed by the chiral rhodium complex 63 gave the optically active allyl amine 62 in good yield and moderate ee (Eq. (15)) [41],... 

Metal complexes enable one to employ molecules that are thermally unreactive toward cycloadditions by taking advantage of their ability to be activated through complexation. Most of the molecules activated by transition-metal complexes involve C-C unsaturated bonds such as alkynes, alkenes, 1,3-dienes, allenes, and cyclopropanes. In contrast, carbonyl functionalities such as aldehydes, ketones, esters, and imines seldom participate in transition-metal-catalyzed carbonylative cycloaddition reactions. Recently, such a transformation was reported via the use of ruthenium complexes. 

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