Tin in Catalysis

Abstract

In numerous natural products and synthetic compounds, ester moieties constitute major organic functional groups. Consequently, (trans)esterification reactions are widely applied in industry, 1 e.g. in the synthesis of fatty acid esters, 2,3 of polyesters 4−9 and of macrolides. 10 More specifically, polylactones and polylactides are multipurpose, bio-compatible and -degradable polyesters, which are suitable for biomedical and pharmaceutical applications. 11−14 Tin-based Lewis acids like mono-and dialkyltin compounds 4,15−19 and tetraalkyldistannoxane derivatives 8,20−22 are very efficient catalysts for transesterification reactions under mild conditions. A considerable drawback in the use of these organotin compounds in organic synthesis is the difficulty of their quantitative removal from the reaction mixture, because some organotin compounds are toxic. These limitations to the exploitation of such reagents and/or catalysts in biomedical and pharmaceutical synthesis applications 23,24 have been recently overcome by exploring alternative and less toxic catalysts, and by the improvement of workup procedures of several types of homogeneous organotin catalysts. Otera et al. have described the synthesis and catalytic activity of perfluoroalkyl distannoxanes, which combine the advantages of efficient catalysis based on organotins with fluorous biphasic technology. 21,25 These types of organotin catalysts, being highly soluble in fluorocarbon solvents, provide solutions which become perfectly miscible with the organic reaction phase upon heating. After cooling the reaction mixture, phase separation is observed and the catalyst returns into the fluorous phase, making it easily and repeatedly recyclable. Another strategy to alleviate the aforementioned toxicity issue, involves grafting the organotin reagent onto an insoluble solid support. 26−28 In this way, other types of environmentally friendly organotin catalysts, which can easily be removed from the desired reaction products by simple filtration of the insoluble support to which they are grafted, are being designed. The forecasted deliverables of such systems include improved catalyst recycling ability and a better control

Dinuclear Organotin Building Blocks and their Conversion into a Tetranuclear Macrocycle Containing Sn−O−Sn Linkages

“…[69] For comparison, the chemical shifts of Me 4 Sn, Me 3 SnCl and Me 3 SnI are 0.0, + 164 and + 39 ppm, respectively. [69] Accordingly, the 29 Si NMR spectra revealed non-equivalent silicon nuclei with signals in the range of À 2.6 to À 2.0 ppm for the biphenylÀ Si(CH 3 ) 2 CH 2 À and in the range of 2.3 to 2.9 ppm for the À CH 2 Si(CH 3 ) 3 silicon atoms. The shielding effect on the silicon atom attached to the aromatic biphenyl connector is confirmed by comparison with the 29 Si NMR spectra of the CpFe[C 5 H 4 Si(CH 3 ) 2 CH 2 ]-substituted analogues BD4-BD6, for which the chemical shifts are all negative (À 2.5 to À 1.3 ppm) in comparison to Me 4 Si.…”

“…terephthalate, 2,5-pyridinedicarboxylate, 3,5-pyridinedicarboxylate and piperazine-bis-dithiocarbamate, respectively, as ligands. [66] In order to generate larger macrocycles, herein we explored the combination of building block BD2 with the small oxide anion O 2À , which due to the large biphenyl connector is not able to facilitate The number, multiplicity and integration of the signals in the 1 H, 13 C, 29 Si and 119 Sn NMR spectra (see Figures S35-S39 and Tables S5-S6, ESI) for the product indicate a highly symmetric and conformationally flexible molecular structure, in agreement with the expected macrocyclic compound (M1). Figure 3 shows a comparison of the 1 H and 119 Sn NMR spectra of M1 and building block BD2, illustrating evident chemical shift differences.…”

“…[11,[24][25][26][27] Being Lewis acids, four-coordinate tin compounds count on the possibility of coordination number increase, enabling linkages with other compounds, e. g. solvent or guest molecules. [28] Because of these attributes, organotin compounds with interesting properties concerning the catalysis of transesterification and CÀ C coupling reactions, [29][30] anion and molecular recognition, [31][32][33][34][35] materials chemistry, [36][37][38] or biological activity [39][40][41][42] have been developed.…”

Organotin(IV) complexes with 2-acetylpyridine benzoyl hydrazones: antimicrobial activity

“…18 Tin compounds present applications as PVC stabilizers, 19 for chemical vapor decomposition (CVD), 20 in non-linear optics 21 and in catalyses. 22 Organotin complexes present innumerous pharmacological applications as antitumorals, 23 antimicrobials 24,25 and biocides. 26 The cytotoxic activity of a variety of organotin complexes against tumor cell lines has been demonstrated by some of us.…”

Synthesis, characterization and thermodynamic studies of complexes of dimethyl, diethyl, and diphenyltin(IV) dichlorides with (2H)-1,4-benzothiazine-2,3-(4H)-dione dioxime

“…Organotin(IV) complexes have a wide range of applications such as PVC stabilizers [1], for chemical vapor decomposition (CVD) [2], in non-linear optics [3] and in catalyses [4][5][6]. Organotin complexes present innumerous pharmacological applications as antitumorals [7], antimicrobials [8,9] and biocides [10] and locking agent in the formation of dinuclear complexes [11].…”