Imine ligand

Evans et al. reported that the bis(imine)-copper (II) complex 25, prepared from chiral bis(imine) ligand and Cu(OTf)2, is also an effective chiral Lewis acid catalyst [34] (Scheme 1.44, Table 1.18). By tuning the aryl imine moiety, the bis(2,6-dichlor-ophenylimine) derivative was found to be suitable. Although the endojexo selectivity for 3-alkenoyloxazolidinones is low, significant improvement is achieved with the thiazolidine-2-thione analogs, for which both dienophile reactivity and endojexo selectivity are enhanced. 

In 1996, Cavell described the synthesis of neutral P(VI) compound 37 containing a divalent tridentate diphenol imine ligand and three chlorine atoms by the reaction of a bis silylated Schiff base with PCI5 to give 37 after elimination of two equivalents of Me3SiCl (Scheme 7) [51]. 

Zhang et al. [49] prepared a chiral ruthenium complex coordinated by a pyridine-bis(imine) ligand (structure 43 in Scheme 21). 

Sulflnyl imines ligands have been also largely used as copper-chelates for the asymmetric Diels-Alder reaction. Ellman et al. [105] reported their use as ligands, the chirality being solely introduced by the presence of siflfoxide moieties. They thus prepared novel sulflnyl imines 74 and 75 in analogy to the... 

Scheme 1.50 Test reaction with P/N-sulfinyl-imine ligand.

Moreover, a few chiral ferrocenylsulfur-imine ligands were investigated in the palladium-catalysed asymmetric allylic alkylation of 1,3-diphenylpropenyl acetate and cyclohexenyl acetate with dimethyl maionate (Scheme... 

Scheme 1.75 Ferrocene-based sulfur-imine ligands for Pd-catalysed allylic alkylations.

Scheme 8.12 Hydrogenations of olefins with BINOL-derived A -phosphino sulfox-imine ligands.

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. 

Because an FI catalyst has a pair of non-symmetric phenoxy-imine ligands, it potentially possesses five isomers stemming from the coordination modes of ligands. Zr-, Ti-, and Hf-FI catalysts 1-3 display three sets of signals in XH NMR, attributed to the imine proton, suggesting that these FI catalysts exist as isomeric mixtures in solution, which is probably an intrinsic feature of FI catalysts. On the basis of the symmetry of the possible isomers A-E (Fig. 10), as well as the relative formation... 

We and others have revealed that syndiospecific propylene polymerization is exclusively initiated by 1,2-insertion followed by 2,1-insertion as the principal mode of polymerization [64]. This is the first example of a predominant 2,1-insertion mechanism for chain propagation exhibited by a group 4 metal-based catalyst. The unusual preference for 2,1-regiochemistry displayed by the Ti-FI catalysts compared with the Zr- and Hf-FI catalysts is apparently inconsistent with the crys-tallographically characterized structures, which indicate that the Ti is shielded more by the phenoxy-imine ligands and thus possesses higher steric compression. The reason for the unusual preference in the regiochemistry of Ti-FI catalysts is unclear at the present time. 

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. 

Chelating bis(imine) ligands such asA-alkyl(2-pyridyl)methanimine (AlkPMI) have also been successfully utilized in copper-mediated ATRP [74,75,76,77,78]. In... 

To date, the most frequently used ligand for combinatorial approaches to catalyst development have been imine-type ligands. From a synthetic point of view this is logical, since imines are readily accessible from the reaction of aldehydes with primary or secondary amines. Since there are large numbers of aldehydes and amines that are commercially available the synthesis of a variety of imine ligands with different electronic and steric properties is easily achieved. Additionally, catalysts based on imine ligands are useful in a number of different catalytic processes. Libraries of imine ligands have been used in catalysts of the Strecker reaction, the aza-Diels-Alder reaction, diethylzinc addition, epoxidation, carbene insertions, and alkene polymerizations. 

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