Joseph W. Burley

Further study of estertin trichlorides, Cl3SnCH2CH2CO2R. Lewis acidity towards acetonitrile. Crystal structure of Cl3SnCH2CH2CO2Pr-i

Abstract Crystals of Cl 3 SnCH 2 CH 2 CO 2 Pri-i are orthorhombic, space group P 2 1 2 1 2 1 with a 9.638(6), b 10.004(7) and c 12.848(8) A. The tin atom is five-coordinate with two chlorines and carbon equatorial and the remaining chlorine and the carbonyl oxygen axial, in a distorted trigonal-bipyramidal arrangement: (SnCl) ax 2.389(3), average (SnCl) eq 2.320(2), SnC 2.142(9), SnO 2.337(5) A. Apart from the equatorial chlorine and the terminal carbons in the isopropyl group, all non-hydrogen atoms are essentially coplanar. The molecule approaches C 2 v symmetry although not constrained to do so by the crystallographic space group. In MeCN solution, the compounds Cl 3 SnCH 2 CH 2 CO 2 R (I, R = Me, Pr-i, C 6 H 4 X (X = p -MeO, H, p -Cl, o -MeO or C 6 H 3 Cl 2 -2,4) form as equilibrium mixtures of 1/1 and 2/1 MeCN/I complexes; the chelate ring is broken in the 2/1 complexes. Equilibrium constants indicate that the strength of the intramolecular SnO coordination in I increases with the electron releasing ability of the R group.

β-substituted alkyltin halides : II. Dialkyltin dihalides: mechanistic and spectroscopic aspects☆

Abstract Hydrogen halides, tin and α,β-unsaturated carbonyl compounds react together under mild conditions to give mixtures of β-substituted alkyltin trihalides and bis(β-substituted alkyl)tin dihalides: acrylonitrile is also active. Spectroscopic data for a number of pure functionally substituted dialkyltin compounds is presented. The monoalkyltin compounds are almost certainly formed by the in-situ formation of trihalogenostannanes from hydrogen halides and tin. Several possible mechanisms are discussed for the formation of the dialkyltin compounds. The substituted monoalkyltin compounds react with tin to give the corresponding dialkyltin compounds as well as products which are believed to be relatively stable tin—tin species.

Lewis acidity of carboxyethyltin chlorides, Cl3SnCH2CH2CO2R and Cl2Sn(CH2CH2CO2R)2

Abstract The Lewis acidity of estertin chlorides, Cl 3 SnCH 2 CH 2 CO 2 R (R = Me, Pr i , Ph and H) and Cl 2 Sn(CH 2 CH 2 CO 2 R) 2 (R = Me and Pr i ) has been investigated. Stability constants ( K 1 , K 2 and K 3 ) for adducts of these Lewis acids with nitrogen donors, e.g. D = bipy, phen, py, quinoline and aniline, have been determined in CH 2 Cl 2 solution at 25 ± 1°C by UV and IR methods. From comparisons of stability constants, the following conclusions can be made: (i) Cl 3 SnCH 2 CH 2 CO 2 Me appears as strong a Lewis acid as MeSnCl 3 towards bidentate ligands and a single py molecule (from K 1 values); (ii) Cl 3 SnCH 2 CH 2 CO 2 Me · D (D = monodentate ligand) is a poorer acceptor than MeSnCl 3 · D but comparable to Me 2 SnCl 2 (using K 2 and K 3 values) towards D, and (iii) Cl 2 Sn(CH 2 CH 2 CO 2 R) 2 is a weaker acceptor than Cl 2 SnMe 2 towards phen and bipy (from K 3 values). Qualitatively it was established that for Cl 3 SnCH 2 CH 2 CO 2 R, the sequence of acidity is R = Ph > Me > Pr i > H towards bipy. Adducts of Cl 3 SnCH 2 CH 2 CO 2 Me and Cl 2 Sn(CH 2 CH 2 CO 2 Me) 2 with phen and bipy have similar Mosbauer parameters to those for other phen and bipy adducts of organotin trichloride and diorganotin dichloride.

Crystal structure and coordination chemistry of Cl3SnCH2CH2CH2CO2Et

Abstract The crystal and molecular structure of Cl3SnCH2CH2CH2CO2Et is reported. Crystals of Cl3SnCH2CH2CH2CO2Et are monoclinic, space group P21/c with a 8.0242(5), b 11.571(5), c 13.129(12) A and β 104.54(6)°. The tin atom is 5 coordinate with two chlorines and carbon equatorial and the remaining chlorine and the carbonyl oxygen axial, in a distorted trigonal bipyramidal arrangement: (SnCl)ax 2.382(4) A, average (SnCl)eq 2.310(3), SnC 2.125(12), SnO 2.405(8) A. The six-membered chelate ring is slightly boat-shaped. Coordination of the carbonyl group to tin persists in solution but is broken on complexation to Cl3SnCH2CH2CH2CO2Et by strong nitrogen donors (2,2′-bipyridyl, 1,10-phenanthroline and pyridine (2 moles)). Comparison of the formation constants for adducts of Cl3Sn(CH2)nCO2Et (A, n  2 or 3), both chelates with monodentate donors, D, suggests comparable acceptor strengths for A (n  2) and A (n  3) for 1/1 adduct formation but that A (n  2) is a weaker acceptor for 2D/A formation.

The synthesis and infrared spectra of organotin(IV) mercaptoester chlorides

Abstract We have prepared several butyltin mercaptoesters and butyltin mercaptoester chlorides of the general formula BunSn(S(CH2)1–2CO2R)mCl4−(n + m) (n = 1, m = 1–3; n = 2, m = 1–2) and we have studied, in some detail, their infrared spectra in the carbonyl region. The butyltin mercaptoester chlorides exist not as pure compounds but as mixtures in equilibrium with the respective butyltin mercaptoesters and butyltin chlorides. Our results suggest that anhydrous reactions between butyltin chlorides and isooctylthioglycolate give almost entirely butyltin isooctylthioglycolate chlorides in contrast to the findings of Herber and Stapfer [J. Organometal. Chem., 66 (1974) 425] who concluded that these reagents gave trans isomers of butyltin isooctylthioglycolates.

A possible mechanism to explain the synergistic effects exhibited by mixtures of alkyltin mercaptoesters as stabilisers for PVC

Abstract The phenomenon of synergism observed with mixtures of mono- and dialkyltin stabilisers for PVC has been recognised and exploited for many years, but remains largely unexplained. Whilst a similar effect in mixed metal (Ba/Cd or Ca/Zn) carboxylate stabilisers has been explained, mechanistic studies of the organotin systems have not appeared. Infra-red spectroscopy has now been used to study the Cl/mercaptoester exchange equilibria of alkyltin mercaptoester (isooctylthioglycollate) chlorine compounds which are undoubtedly produced when the organotin mercaptoesters act as PVC stabilisers. The exchange process is shown to be facile, even at ambient temperatures, and a regenerative mechanism, based on these observations, is proposed to explain the synergistic effect.

A study of mercaptoester/chlorine exchange equilibria exhibited by β-carboalkoxyethyltin compounds

Abstract 60 MHz proton NMR data confirms that Cl/mercaptoester exchange reactions in butyl- and β-carbobutoxyethyltin compounds occur readily in deuterochloroform at 35°C. The positions of dibutyl-, monobutyl- and mixed mono-/dibutyltin equilibria are dictated by intramolecular carbonyl to tin coordination from the mercaptoester groups. In the analogous β-carbobutoxyethyltin systems the corresponding equilibria are perturbed by the competing carbonyl to tin coordination from the β-carbobutoxyethyl groups. These results are correlated with the activity of alkyltin and β-carboalkoxyethyltin stabilisers in PVC.

Acidity of Cl3SnCH2CH2CO2H

Abstract Interaction of Cl 3 SnCH 2 CH 2 CO 2 H with aniline bases in CH 2 Cl 2 solution has been studied by UV-visible spectroscopy. As measured by the extents of complexation with the bases, Cl 3 SnCH 2 CH 2 CO 2 H is a stronger acid than the corresponding esters, Cl 3 SnCH 2 CH 2 CO 2 R (Lewis acids) and also very much more stronger than the Bronsted acid, CH 3 CH 2 CO 2 H. The enhanced Bronsted acidity arises from the stabilisation of the anion, Cl 3 SnCH 2 CH 2 CO 2 − , by the intramolecular coordination of the tin centre by the carboxylate group.

Redistribution reactions of β-carboalkoxyethyltin compounds

Abstract Carboalkoxyethyltin compounds undergo redistribution reactions at faster rates than similar unsubstituted alkyltin compounds. In redistribution reactions between SnCI4and carboalkoxyethyltin compounds stable intermolecular complexes are formed. Rate enhancement is explained in terms of intra- and intermolecular coordination effects. Where strong intermolecular coordination effects are observed, specific electrophilic cleavage of the carboalkoxyethyl group can occur in preference to alkyl cleavage in mixed carboalkoxyethylalkyltin compounds. The presence of a β-ester function can catalyse both alkyl/chlorine and alkyl/alkyl′ exchange reactions.

New synthesis of β-substituted alkyltin halides via halogenostannane intermediates

β-Substituted ethyltin trihalides and bis-(β-substituted ethyl)tin dihalides can be prepared via the in situ reaction of αβ-unsaturated carbonyl compounds with active halogenostannane intermediates produced from halogen acids and tin(II) chloride or halogen acids and metallic tin, respectively.