Polymeric Schiff base complexes

A polymeric Schiff base complex gave reversible dioxygen addition 159 the oxygen could be liberated in vacuum and above 200 °C. 

Polymeric Schiff-base Complex 4 from Bisphenol A and a Dihydroxy-Substituted Schiff-base Complex (Section 6.1) [19]... 

The ruthenium indenylidene Schiff base complexes XXVIIIa and XXVIIId, synthesized by Verpoort, were evaluated in atom-transfer radical polymerization of methyl methacrylate. The polymerization was initiated by ethyl 2-bromo-2-methyl-... 

As reported by Spassky et al. [62], aluminum complexes of Schiff bases as initiators exhibit much lower activities than aluminum porphyrins for the ringopening polymerization of epoxides. In fact, the polymerization of PO (500 equiv) using a Schiff base complex (Salphen)AlCl (13) as initiator proceeded extremely slowly at room temperature to attain only 4% conversion in 8 d. Even at 80 °C, the polymerization was slow, and required 6 d for completion, affording a polymer with broad and bimodal MWD (Fig. 32A). 

Ring-opening metathesis polymerization was conducted by Verpoort et al. (4) using cyclooctene with a ruthenium Schiff base complex, (V), and proceeded with a monomer-to-catalyst ratio of 150,000 1, respectively. 

Although most oxovanadium(IV) complexes are blue, some Schiff base complexes may vary from yellow to maroon. Earlier suggestions that such colours, together with reductions in the V—O frequencies from 950-1000 to 800-850 cm-1, indicate polymerization or VO VO VO interaction are erroneous. Even for coordination environments which are very similar, the V=0 lengths may be very different, the vanadyl oxygens being exposed to the influence of the neighbouring molecules in the crystal.384... 

Recent work has also highlighted two classes of inorganic complexes that have interesting antimalarial activity (1) metal-N402 Schiff base complexes and (2) porphyrins. The mechanism of action for these complexes is discussed. The use of these complexes as probes for the elucidation of structure-activity relationships in heme polymerization inhibitor design and the loci of drug resistance is also detailed. 

The first enantiomer-selective polymerization was performed with propylene oxide (172) as a monomer [245], The polymerization was carried out with a ZnEt2/(+)-bor-neol or ZnEt2/(-)-menthol initiator system. The obtained polymer was optically active and the unreacted monomer was rich in (S)-isomer. Various examples are known concerning the polymerization and copolymerization of 172 [246-251 ]. A Schiff base complex 173 has been shown to be an effective catalyst In the polymerization at 60°C, the enantiopurity of the remaining monomer was 9% ee at 50% monomer conversion [250],... 

The ability of monomeric Schiff base complexes or polymeric Schiff base ligands to absorb solvent molecules is well-known. Sawodny et al.27) found that the polymer Schiff base complexes exhibit this property much more markedly. The polymers were prepared by the polycondensation reaction of polymer ligands of the Schiff base (29) with metal salts (Eq. 8). The adsorption of solvent is reversible and the ability is dependent upon the nature of the central metal atom and of the ring size around the metal. This profile suggests that the above polymers can be used as a molecular sieve. 

Some Co(l) macrocyclic complexes have been implicated in C-H activation reactions. The observation of N-H exchange with solvent CD3CN in solutions of Co(l) cyclam derivatives has been interpreted as evidence for C-H activation by a mechanism involving oxidative addition of CD3CN to the Co(l) center. Co(I) Schiff-base complexes have been proposed to be important intermediates in ethene polymerization. Treatment of Co(ll) complexes containing 2,6-bis(imino)pyridyl ligands with MAO leads to highly... 

One of the most powerful catalysts of the Mukaiyama aldol reaction is a chiral Ti(IV)-Schiff base complex 91 prepared from Ti(0 Pr)4 and enantiomerically pure salicylaldimine reported by Carreira [103-105]. This catalyst furnished aldol adducts in good yields and with excellent enantioselectivity. The Ti(IV)-Schiff base catalyst system is unique among the aldol catalysts yet reported in terms of operational simplicity, catalyst efficiency, chirality transfer, and substrate generality. Because the Ti(IV)-Schiff base complexes are remarkably efficient catalysts for the addition of ketene acetals to a wide variety of aldehydes, the polymeric version of catalyst 92 was prepared [106]. The activity and enantioselectivity of the polymer-supported chiral Ti(IV)-Schiff base complex were, however, much lower than were obtained from the low-molecular-weight catalyst (Eq. 28). 

Molecular mechanics calculations have been reported for a number of gadolinium complexes, including those with EDTA, dtpa, dtpa-bma and do3a. Other molecular mechanics calculations using a simple force field, computable on a PC, have been reported for [Gd(edta)(OH2)3] and a variety of Schiff base complexes. NMR and EPR studies are also reported on a number of compounds of this type. In the solid state, [La(pedta)(H20)].2H20 (pedta = A-(pyiid-2-ylmethyl)ethylenediamine-N,N, N -triacetate) adopts a polymeric structure, giving 10-coordinate La in solution, luminescence results for the Eu complex indicate three coordinated water molecules. ... 

Complexes of ligands with O-donors and two or three N-donors are known. The kinetics of the outer-sphere oxidation of cis-aq uaoxovanad i u m (IV) complexes of [2-(pyridylmethyl)imino]diacet-ate and its derivatives were determined.675 Complexes with Schiff bases have been used to mimic the structure and chemistry of vanadium bromoperoxidase.275 The ligation of an imidazole functionality in the ligand has been found to readily dissociate, and is important to the functional aspects of this complex.275 A variety of five-coordinate complexes with tridentate Schiff base complexes have been prepared, several of which have been found to form supramolecular polymeric structures through association between the V=0 groups in a V=0 V=0 V=0 pattern (140).627... 

Recently, Spassky has demonstrated that the chiral Schiff base complex 4 is highly selective for the kinetic resolution polymerization of rac-lactide [34]. At 50% conversion, the residual monomer is approximately 80% ee (Rr s=20) (Scheme 3). In addition, the polylactides exhibit narrow molecular weight distributions, consistent with the absence of significant transesterification. 

The structure of the Schiff-base complex bis(salicylaldehyde)ethylenedi-iminodimethyltin dichloride, MeaSnClaCsalenHjj), consists of polymeric... 

On the other side, a totally insoluble cross-linked Schiff-base complex was prepared as follows. The glycidyl ether of bisphenol A was reacted with a Schiff-base chelate (prepared from 2,4-dihydroxybenzaldehyde and 1,3-diaminopropane followed by metallation) in a molar ratio of, for example, 6 1 at 150-200 °C to obtain the polymer 4 as shown in Eq. 6-3 (see Experiment 6-1, Section 6.6) [19]. Polymeric copper complexes in particular exhibit good thermal stabilities and good mechanical properties such as tensile strength. 

Low molecular weight Schiff base complexes of many metals are well known and in the case of aromatic ligands these tend to have high thermal stability. Polymeric Schiff bases likewise have been well reported, and although many of these have the Schiff base appended as a substituent on a vinyl polymer backbone, others have the Schiff base residue as part of the mainchain. The latter continue to complex metals very well [140, 141] and one early paper reports the use of a Mn(II) polymeric complex in the aerobic oxidation of cumene at 30-100°C [142]. Indeed there is an implication in the paper that the polymer complex is stable to 200°C when complexed O2 tends to be liberated. Wohrle s group have also studied polymeric Schiff bases extensively, again mostly with pendant groups. However, they have reported a mainchain poly Schiff base [143], its complexation with Co(II), Ni(II) and Cu(II), and use of the supported complexes as catalysts in quadricyclane isomerisation to norbornadiene. 

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