Carbonylation solid support catalysts

In 2007, Wiles et al. (2007c) demonstrated the ability to employ solid-supported catalysts in series within an EOF-based microreactor. As summarized in Scheme 39, the model reaction sequence involved combining a previously investigated acid-catalyzed deprotection with a base-catalyzed condensation reaction to enable the synthesis of a,(3-unsaturated carbonyl compounds from dimethyl acetals. 

The same authors (77) also investigated the Michael addition of nitromethane to a,/l-unsaturated carbonyl compounds such as methyl crotonate, 3-buten-2-one, 2-cyclohexen-l-one, and crotonaldehyde in the presence of various solid base catalysts (alumina-supported potassium fluoride and hydroxide, alkaline earth metal oxides, and lanthanum oxide). The reactions were carried out at 273 or 323 K the results show that SrO, BaO, and La203 exhibited practically no activity for any Michael additions, whereas MgO and CaO exhibited no activity for the reaction of methyl crotonate and 3-buten-2-one, but low activities for 2-cyclohexen-l-one and crotonaldehyde. The most active catalysts were KF/alumina and KOH/alumina for all of the Michael additions tested. 

Many catalysts do not use metals in their pure reduced metallic forms. Anchored organometallic complexes are often analogs of homogenous catalysts fixed on a solid support. In particular, titanate complexes both in solution and in supported form have been found to be especially active in transesterifications of simple esters.It was proposed that titanates catalyze the transesterification reaction through a Lewis acid mechanism where the reactant ester and metal form a Lewis complex activating the carbonyl groups for a nucleophilic attack by the reactant alcohol. The tetrahedral intermediate that is formed breaks down into the product alcohol and an ester-metal Lewis... 

If the latter reaction proceeds through a closed transition state (e.g., 5 in Scheme 7.2), good diastereocontrol can be expected in the case of trans- and cis-CrotylSiCl3 (2b/2c) [14, 15]. Here, the anh-diastereoisomer 3b should be obtained from trans-crotyl derivative 2b, whereas the syn-isomer 3c should result from the reaction of the cis-isomer 2c (Scheme 7.2). Furthermore, this mechanism creates an opportunity for transferring the chiral information if the Lewis base employed is chiral. Provided that the Lewis base dissociates from the silicon in the intermediate 6 at a sufficient rate, it can act as a catalyst (rather than as a stoichiometric reagent). Typical Lewis bases that promote the allylation reaction are the common dipolar aprotic solvents, such as dimethylformamide (DMF) [8,12], dimethyl sulfoxide (DMSO) [8, 9], and hexamethylphosphoramide (HMPA) [9, 16], in addition to other substances that possess a strongly Lewis basic oxygen, such as various formamides [17] (in a solution or on a solid support [7, 8, 18]), urea derivatives [19], and catecholates [10] (and their chiral modifications [5c], [20]). It should be noted that, upon coordination to a Lewis base, the silicon atom becomes more Lewis acidic (vide infra), which facilitates its coordination to the carbonyl in the cyclic transition state 5. 

Comely, A. C., Gibson, S. E., Hales, N. J. Polymer-supported cobalt carbonyl complexes as novel solid-phase catalysts of the Pauson-Khand reaction. Chem. Common. 2000, 305-306. 

In a very recent article, Cole-Hamilton described new approaches to catalyst separation, recovery, and recycling [32]. He states that, to his knowledge, only one commercial example of a homogeneous catalyst heterogenized on a solid support is presently in use, i.e., for the carbonylation of methanol. Chan et aL, in their 2002 review on recoverable catalysts, came to the same conclusion [15]. These two statements are in full agreement with our experience. Although many publications and in particular patent applications show the potential interest of the chemical industry in this field, it was not possible to find more confirmed production processes. It will be seen from what follows that many attempts have been made to use and develop immobihzed catalyst systems,but in all cases they suffered from missing economy. Nevertheless, we feel that it is important to demonstrate what has been tried so far. 

For instance substitution chlorination of organic compounds produces hydrogen chloride which must simultaneously desorb back in the gas phase to prevent supersaturation of the liquid phase. Another industrially important process involves "supported liquid phase catalyst", where the reactants have to be transferred from a bulk gas to a liquid reaction phase while the products are released back into the gas phase. Here the catalyst is in the form of a melt on a solid support and it finds applications in alkylation, carbonylation, hydroformylation and oxidation of inorganic and organic compounds. The subject matter was recently reviewed delicately by Villadsen and Liv-berg (11,12). Other examples of these interesting systems are shown in Table 6. 

The Mizoroki-Heck reaction promoted by microwave irradiation was first described by Laihed and Hallberg [205]. For easy catalyst recovery, solid-supported systems were often used. An a-heteroatom-substituted carbonyl linker has been utilized in solid-phase approaches to oxinolines by Pummerer cyclization [206]. The reaction performed with s/c = 20 in the presence of phosphine ligands (ratio ligand/palladium-precursor = 1 1) in 88-99% yield at 7 h reaction time. 

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