Dr Tomas Lebl
Tel: 01334 463788
Senior Scientific Officer for Solution State NMR
Fax: 01334 463808

Research Philosophy

The explosive growth of NMR spectroscopy during the last five decades is reflected in the vast number of applications. Nowadays, NMR spectroscopy represents the most versatile and informative technique for the elucidation of structures, dynamics and kinetics in solution. However, this rapid development means that only a fraction of the analytical potential offered by modern NMR spectroscopy is usually exploited by the research chemists. Thus, I try to participate in various scientific projects as a NMR specialist encouraging and research chemists and students to utilise modern NMR techniques. In former times, my work involved scientific projects dealing mainly with organotin compounds. Some of them are described below.

Now, I cooperate with various researchers within the School of Chemistry, the Centre of Bimolecular Sciences and Sasol Technology Research Laboratory. Therefore my field of interest is widening and involves the organic chemistry, biochemistry and homogeneous catalysis.

(3-Methoxypropyl)stannanes

Organotin compounds have revealed a wide spectrum of biological merits. Antitumor properties in vitro against a wide panel of tumour cell lines of human origin are rather well known. It has been proposed that anticancer reagents could also be used against trypanosomal diseases (human sleeping sickness and domesticated live stock diseases). Recently, it was found that several organotin thiolates exhibit high in vitro levels of activity compared with the arsenic derivatives used for chemotherapy. However, antitumor and trypanocidal efficiency of organotin derivatives seems to be limited by their low water solubility. Various sets of (3-methoxypropyl)stannanes have been prepared as organotin compounds with considerable water solubility. Although no or only negligible antitumor activity was found, promising trypanocidal activity was observed for some (3-methoxypropyl)stannanes.

The 3-methoxypropyl group can be bonded either as monodentate ligand (A) or as a bidentate C,O-chelating ligand (B).

OCchelate

To distinguish between those two binding modes in solution might be a crucial issue of structural research. In order to find a indicator of existence and eventually strength of O-Sn coordination, structures of (3-methoxypropylstannanes) were studied using X-ray crystallography, 119Sn CP/MAS NMR in the solid state and by 1H, 13C, 17O, 119Sn NMR in solutions of non-coordinating solvent (CDCl 3) and coordinating solvent (dmso-d6). J( 1H, 119Sn) Coupling constants, crucial to the study, were acquired by 1D 1H, 119Sn HMQC and 2D 1H, 119Sn J-HMBC heteronuclear correlations.

2-Functionalised Vinylstannanes

Organometallics containing not only M-C bonds as reactive sites but also other centres of high reactivity represent a very interesting field of organometallic chemistry. Introduction of a heteroatom Y (Y is a Group 14-17 element) into an organoligand can have a profound influence on the structure, stability and reactivity of organometallic compounds and consequently open the possibility of entirely new reactions. If organometallic compounds with Lewis-basic 2-functionalised ethyl ligands LxM─CH 2─CH 2YR n (YR n = NR 2, OR, Cl, …; R = alkyl, aryl, H) are treated with suitable electrophiles, they can undergo elimination reaction, so-called heterolytic fragmentation.

HF

On the other hand, in organotin compounds with 2-substituted vinyl ligands R'3SnCH=CHYRn, the electrophile attacks preferably at the α-carbon atom and a cleavage of the Sn-C bond takes place where significant difference in reactivity of stereoisomers is observed.

Esub

Kinetic studies were carried out using 1H NMR. 1H- 119Sn HMQC spectra were employed to analyse complex mixtures of products.

Recent Publications

  1. A Comparative Assessment of the Effect of the Lewis Acidity of the Central Tin Atom on Intramolecular Coordination of (3-Methoxypropyl)stannanes T. Lébl, P. Zoufalá, C. Brun Eur. J. Inorg. Chem. 2005, 2536-2544.
  2. Monomeric Triorganotin(IV) Fluorides Containing a C,N-Chelating Ligand J. Bareš, P. Novák, M. Nádvorník, R. Jambor, T. Lébl, I. Císařová, A. Růžička, J. Holeček Organometallics 2004, 23, 2967-2971.
  3. Kinetics of the Protodestannylation of Substituted Vinylstannanes Dymák, J. Holeček T. Lébl Main Group Met. Chem., 2004, 27, 33-50.
  4. Synthesis, structural study, in vitro antitumour and trypanocidal activity of tetrakis(3-methoxypropyl)- tin and (3-methoxypropyl)tin chlorides T. Lébl, A. Smička, J. Brus, C. Bruhn Eur.J. Inorg. Chem., 2003, 143148.
  5. Reinvestigation of reaction of (2-ethoxyvinyl)stannanes with acetyl bromide T. Lébl, J. Holeček, M. Dymák, D. Steinborn Collect. Czech. Chem. Commun., 2002, 67, 587-591.
  6. Synthesis, Characterisation and Reactivity of 2-Functionalised vinylstannanes T. Lébl, D. Steinborn, J. Holeček, M. Dymak J. Organomet. Chem., 2001, 625, 86-94.

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Last updated:19 August, 2005