119Sn spin–lattice relaxation times and nuclear Overhauser enhancement factors in some organotin compounds

Dipole-dipole relaxation via non-bonded protons is an important relaxation mechanism for¹¹⁹Sn in tri-n-propyltin and tri-n -butyltin compounds. This causes a negative nuclear Overhauser effect, arising from the negative magnetogyric ratio, which in some cases nulls the signal. The relative contributions from the spin-rotation and dipole-dipole mechanisms vary: larger molecules have lower spin-rotation and higher dipolar relaxation rates. The practical significance of large nuclear Overhauser enhancement factors in recording ¹¹⁹Sn spectra and the relation of the dipole-dipole contribution to the molecular motion and of the spin-rotation contribution to the absolute shift scale for ¹¹⁹Sn are discussed.     

Structures and relationship between the 119SnNMR chemical shifts and pKa of their parent acids in organotin (I∇) carboxylates

Ten di-n-butyltin(I∇) carboxylates [(ⁿBu₂Sn-OCOR′)₂O]₂ and ⁿBu₂Sn(OCOR′)₂ (R′ = CCl₃, CHCl₂, CH₂Cl, PhCH = CH, and 2,2,3,3-tetramethylcyclopropyl) were synthesized and characterized by IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and elemental analysis. Together with other series of organotin(I∇) carboxylates, their structural features were discussed. The relationship between the ¹¹⁹Sn NMR chemical shifts in the organotin(I∇) carboxylates [(ⁿBu₂SnOCOR′)₂O]₂, ⁿBu₂Sn(OCOR′)₂, ⁿBu₃SnOCOR′, Ph₃SnOCOR′ and the pK_a values of their parent acids R′COOH was studied. The results have shown that the log[-δ(¹¹⁹Sn)] of the same series of carboxylates is linearly related to the pK_a of R′COOH. It seems that the better is the linearity between the log[−δ(¹¹⁹Sn)] and the pK_a, the more analogous are the structures of the same series of carboxylates. © 1996 John Wiley & Sons, Inc.     

Fourier transform NMR investigations of organotin compounds : VIII. Propenyl- and isopropenyl-tin compounds; detection and identification of isomers using 119Sn and 13c NMR

Starting from the equilibrium mixture of cis- and trans-1-bromo-1-propene, isomeric mixtures of compounds Me_n Sn(CH=GHMe)_4-n (n = 0–3) have been prepared and studied. While proton NMR only allows distinction between the methyltin signals of the various isomers (except where n = 3), the ¹³C spectra show separate signals for almost all isomeric carbons even when n = 0. In the ¹¹⁹Sn spectra the signals due to the various isomers are separated by ca. 20 ppm for a given value of n; the peak areas can be used to estimate the proportions of cis- and trans-propenyl residues present in the mixtures. Addition of 2-bromo-propene to the starting 1-bromo-1-propenes leads to the formation of further isomers, which can in all cases be observed and identified in the ¹¹⁹Sn spectra; ¹¹⁹Sn shifts can be calculated using the shifts for the Me₃SnC₃H₅ isomers as increments.     

Carbon-13 chemical shifts of bicyclic compounds

¹³C NMR absorption spectra of 50 bicyclic hydrocarbons, alcohols and ketones have been measured, in addition to some terpenes. The ¹³C chemical shifts are approximately additive for similar compounds and can be used for the determination of molecular structure; they differ for endo- and exo-isomers, just as in proton spectra. These quite regular and predictable ¹³C shift differences are much larger and are caused by the 1,4-nonbonded interaction between atoms heavier than hydrogen, not by magnetic anisotropy effects.     

Carbon-13 fourier transform NMR studies of organotin compounds : III. Carbon-13 chemical shifts and tin-119—carbon-13 spin—spin coupling constants in acyclic,monocyclic and bicyclic organostannanes

Carbon-13 NMR parameters for 33 organotin compounds with a variety of structurul features were investigated in order to obtain information about the relationship between their structure and ¹³C NMR parameters. It was found that the substitution of a proton by a trialkyltin group generally produces an upfield shift for the directly bonded carbon. The γ-nuclei usually resonate at lower fields except where there is appreciable steric strain while the β-carbons undergo relatively constant shifts of approximately 3.5 to 4.5 ppm to lower fields. The magnitude of direct bond coupling Jz-sfnc;¹J(¹¹⁹Sn¹³C)z-sfnc; is influenced by the hybridization of the tin and the directly attached carbon atoms. In rigid organitins, the vicinal coupling constants show a Karplus type variation. In aliphatic organotins, the values of the vicinal¹¹⁹Sn¹³C coupling indicates a flexible molecular framework with a clear cut preference for certain conformations.     

13C and 119Sn NMR spectra of Di-n-butyltin(IV) compounds

The ¹³C and ¹¹⁹Sn NMR spectra of a set of di-n-butyltin(IV) compounds and their complexes in coordinating and non-coordinating solvents have been studied. The results have shown that it is possible to describe semiquantitatively the shape of coordination polyhedra of these compounds from analysis of their δ(¹¹⁹Sn) and ¹J(¹¹⁹Sn-¹³C) parameters. The values of δ(¹¹⁹Sn) define the regions with different coordination numbers of the central tin atom, so that four-coordinate compounds have δ(¹¹⁹Sn) ranging from about + 200 to −60 ppm, five-coordinate compounds, −90 to −190 ppm, and six-coordinate compounds, −210 to −400 ppm. The values of ¹J(¹¹⁹Sn-¹³C) were used for the calculation of the CSnC angle in the coordination polyhedron of individual compounds.     

13C and 119Sn NMR spectra of some tribenzyltin(IV) compounds

The ¹³C and ¹¹⁹Sn NMR spectra of some tribenzyltin(IV) compounds and their complexes in coordinating and non-coordinating solvents have been studied. The δ(¹¹⁹Sn) chemical shifts and coupling constants ¹J(¹¹⁹Sn, ¹³C) clearly depend on the coordination number of the central tin atom and the geometry of its coordination polyhedra. Approximate ranges of the characteristic values of both the NMR parameters were determined for various configurational types of tribenzyltin compound. The ¹³C and ¹¹⁹Sn NMR parameters found are indicative of a distinct interaction between the polarized σ(SnC) bond and adjacent π-electron system of the aromatic ring(s).     

Solid-state and high-resolution liquid 119Sn NMR spectroscopy of some monomeric, two-coordinate low-valent tin compounds: very large chemical shift anisotropies

High-resolution liquid- and solid-state 119Sn NMR spectroscopy was used to study the bonding environment in the series of monomeric, two-coordinate Sn(II) compounds of formula Sn(X)C6H3-2,6-Trip2 (X = Cl, Cr(eta 5-C5H5)(CO)3, t-Bu, Sn(Me)2C6H3-2,6-Trip2; Trip = C6H2-2,4,6-i-Pr3). The trends in the principal components of the chemical shift tensor extracted from the solid-state NMR data were consistent with the structures determined by X-ray crystallography. Furthermore, the spectra for the first three compounds displayed the largest 119Sn NMR chemical shift anisotropies (up to 3798 ppm) of any tin compound for which data are currently available. Relaxation time based calculations for the dimetallic compound 2,6-Trip2H3C6Sn-Sn(Me)2C6H3-2,6-Trip2 suggests that the chemical shift anisotropy for the two-coordinate tin center may be as much as ca. 7098 ppm, which is as broad as the 1 MHz bandwidth of the NMR spectrometer.     

Occurrence and chemical speciation analysis of organotin compounds in the environment: A review

Environmental concerns regarding organotin compounds have increased remarkably in the past 20 years, due in large part to the use of these compounds as active components in antifouling paints [mainly tributyltin (TBT)] and pesticide formulations [mainly triphenyltin (TPhT)]. Their direct introduction into the environment, their bio-accumulation and the high toxicity of these compounds towards “non-target” organisms (for example: oysters and mussels) causes environmental and economic damage around the world. As a consequence, the presence and absence of organotin compounds is currently monitored in a range of environmental matrices (e.g., water, sediment and shellfish) to examine the utility of controls meant to regulate the level of contamination as required in some EC Directives and the Water Framework Directive 2000/60/EC. To evaluate the environmental distribution and fate of these compounds and to determine the effectives of legal provisions adopted by a number of countries, a variety of analytical methods have been developed for organotin determination in the environment. Most of these methods include different steps such as extraction, derivatisation and clean up. The aim of the present review is to evaluate the environmental distribution, fate and chemical speciation of organotin compounds in the environment.     

13C Fourier transform studies of organotin compounds : I. 119Sn-13C spin-spin coupling constants

¹¹⁹Sn-¹³C coupling constants have been measured for fourteen organotin compounds including aliphatic, unsaturated and cyclic derivatives yielding results which indicate that these parameters have great potential for revealing information concerning structures and conformations of organotin compounds and of other compounds into which organotin groups can be conveniently introduced.     

Theoretical study on metal NMR chemical shifts: Germanium compounds

Germanium chemical shifts were studied theoretically by the ab initio molecular orbital method. The compounds studied were GeMe_4?xCl_x and GeMe_4?xH_x(x = 0–4). The calculated values of the germanium chemical shifts agreed well with the available experimental values. The germanium chemical shift is due to the p-electron mechanism that reflects the ligand electronic effect on the p-p* excitation term in the second-order paramagnetic term. For GeMe_4?xH_x, the chemical shift is almost linear to the number of the ligand, x. On the other hand, a U-shaped dependence is predicted for the chemical shifts of the GeMe_4?xCl_x series and is shown to be caused by the strong and nonadditive electron-withdrawing ability of the Cl ligand. The diamagnetic contribution is relatively small for the chemical shift and is determined solely by a structural factor. © 1994 John Wiley & Sons, Inc.     

13C NMR chemical shifts of some highly-branched acyclic compounds

A study has been made of the ¹³C chemical shifts of a number of acyclic alkanes, alkenes, nitriles and ketones which contain quaternary carbon atoms. Similar data have also been obtained for the series of compounds involved in the synthesis of triisopropylacetic acid. Substituent effects and steric factors in these highly substituted compounds are discussed in relation to the chemical shifts.     

Shielding constants of tin 119Sn nuclei

A number of organotin compounds have been studied using the heteronuclear double resonance H¹-{Sn¹¹⁹}. The tin chemical shifts have been tabulated and discussed on the basis of the concept of electronegativity. The highfield displacement is found attributable to the filling of the 5d-orbitals of the tin atom.