Aluminum-porphyrin complex

The CO2 activation reactions seen for aluminum porphyrins are also observed for In(Por)Me (Por = OEP, TPP), which will insert CO2 in the presence of pyridine and under irradiation by visible light to give the acetato complex In(Por)OC(0)Me. The indium acetato product has been characterized by X-ray crystallography, whereas in the aluminum complex it was observed only by spectroscopy. An alternative synthesis of the acetato complex is by treatment of ln(Por)Cl by alumina and water, followed by acetic acid. For the indium and... 

The key point of the high-speed living polymerization is the steric suppression of an undesired reaction between the nucleophilic growing species and the Lewis acid, for which not only the steric bulk of the Lewis acid but also that of the porphyrin ligand is considered important. The benefit of using a Lewis acid holds even for the aluminum complexes with phthalocyanine (11), tetraazaannulene (12), and. Schiff bases (13-15). As initiators, these complexes exhibit much lower activity for the polymerization of PO than aluminum porphyrin 1 (X=C1). 

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). 

As already described, aluminum complexes of tetra-azaannulene (9) and phthalocyanine (10) have much lower reactivities than aluminum porphyrins for the polymerization of epoxides (11). However, in the presence of appropriate Lewis acids such as 44 or 45, the polymerizations with these initiators take place rapidly to give polyethers with fairly narrow MWD. ... 

In 1990, Valentine reported that redox inactive complexes of zinc, as well as aluminum-porphyrin complex [(TPP)AICI], could catalyze the epoxidation of olefins by PhIO [37]. The results for [(TPP)AICI] were later revised when it was discovered that use of ultrapure aluminum yielded no epoxide, and that contamination by traces of iron in the original aluminum complex was likely responsible for catalytic epoxidation [38]. 

Scheme 32 Organoalumlnum compounds used as substitute of aluminum porphyrins Schiff base (a) and calixarene aluminum complexes (b).

Porphyrin, octaethyl-, aluminum hydroxide complex cyclic voltammetry, 4, 399 <73JA5140)... 

Although the majority of metal complexes developed for PDT have porphyrin-style ligands, there are exceptions (e.g., compounds (53) and (54) to (57)). The aluminum(III) complex of hypocrellin B (59) provides another example. Compound (59) is an oligomeric system where n is about 9 the material is water soluble, has Amax(DMSO) 614 nm, and generates both superoxide and singlet oxygen on irradiation ([Pg.987]

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

Relatively few organometallic aluminum porphyrin complexes have been reported, unlike the heavier Group 13 elements for which more extensive series of compounds have been reported. However, the reaction chemistry of the aluminum porphyrins has been much more extensively studied and exhibits features not replicated by the heavier elements. For this reason the aluminum porphyrin complexes are discussed separately. 

Aluminum, Gallium, Indium, and Thallium Porphyrin Complexes, M(Por)R... 

Aluminum porphyrins first came to attention with the discovery that the simple alkyl complex Al(TPP)Et was capable of activating CO2 under atmospheric pressure. Both irradiation with visible light and addition of 1-methylimidazole were required for the reaction, which was proposed to proceed by initial coordination of the base to aluminum. The aluminum porphyrin containing direct product of CO2 insertion was not isolated, but was proposed on the basis of IR data to be (TPP)A10C(0)Et, which was then treated with HCl gas, presumably liberating propanoic acid, subsequently isolated as the butyl or methyl ester after reaction with 1-butanol or diazomethane, respectively [Eq. (5)]. Insertion of CO2 into the Al—C bond of an ethylaluminum phthalocyanine complex has also been reported. ... 

Both CO2 activation and enolate formation are combined in the preparation of malonic acid derivatives. The reaction of CO2 with methacrylic esters or methacry-lonitrile and under visible light irradiation produced the corresponding aluminum porphyrin malonate complex. When diethylzinc was added to this system, Al(TPP)Et could be regenerated by axial ligand exchange reactions, and the malonic acid derivatives were formed catalytically with respect to the aluminum porphyrins in a one-pot photosynthetic route (Scheme 1). The first step in this... 

Although photochemically induced cleavage of Al—C bonds in the aluminum porphyrin complexes has been exploited in several applications, relatively little is known about the intimate mechanism of this process. Similar reactivity is observed for the organo-gallium and indium porphyrins, and for these elements... 

All three hydroxo species [M(OEP)(Me)(OH)] (M = P, As, Sb]) are sufficiently acidic to react with the aluminum porphyrin complex Al(OEP)Me, which is known to eliminate methane on reaction with protic reagents. Three novel binuclear... 

Although anionic polymerization of cyclic ethers is generally limited to oxiranes, there are reports of successful oxetane and tetrahydrofuran polymerizations in the presence of a Lewis acid. Aluminum porphyrin alone does not polymerize oxetane, but polymerization proceeds in the presence of a Lewis acid [Sugimoto and Inoue, 1999]. Similarly, THF is polymerized by sodium triphenylmethyl in the presence of a Lewis acid such as aluminum alkoxide [Kubisa and Penczek, 1999]. The Lewis acid complexes at the ether oxygen, which weakens (polarizes) the carbon-oxygen bond and enhances nucleophilic attack. 

PO proceeded in a living manner to yield highly regioregular polyethers with narrow MWDs. These authors also developed the immortal polymerization of epoxides where polymers with narrow MWDs were obtained with the number of polymer chains exceeding the number of initial aluminum-porphyrin complexes (Scheme I). The key in the immortal polymerization is a reversible chain transfer, which is much more rapid than the chain propagation. In the presence of an alcohol (R OH) as a chain-transfer reagent, an aluminum-porphyrin complex with a growing species reacts with R OH reversibly, so that the polymerization takes place from all the molecules of aluminum-porphyrin complex and R OH. 

Aluminum-porphyrin complex lb with an alkoxide ligand also demonstrates the same reactivity as la in the presence of only 0.1 mol.% of 2a. The polymerization rate with lb/2a catalyst system is dependent on the concentration of 2a in the range from 0.025 to 2.5 mol.%, the increase of 2a results in more rapid polymerization. On the other hand, molecular weight and the number of polymer chains are independent of the molar ratio of 2a to... 

Table 1 Polymerization of terminal epoxides catalyzed by aluminum-porphyrin complexes...

Cationic polymerization of alkylene oxides generally produces low molecular weight polymers, although some work [26] seems to indicate that this difficulty can be overcome by the presence of an alcohol (Fig. 1.3). Higher molecular weight polyethylene oxides can be prepared by a coordinated nucleophilic mechanism that employs such catalysts as alkoxides, oxides, carbonates, and carboxylates, or chelates of alkaline earth metals (Fig. 1.4). An aluminum-porphyrin complex is claimed to generate immortal polymers from alkylene oxides that are totally free from termination reaction [27]. 

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