James N. Spencer

Inclusion complexes of alcohols with α-cyclodextrin

Calorimetric studies of the inclusion complexes of straight and branched alcohols and of diols with alpha-cyclodextrin (α-CD) have been carried out in water solvent. The data suggest that straight and branched chain alcohols enter the cavity of α-CD alkyl end first. The hydroxyl group hydrogen bonds to the outer oxygen ring of the cyclodextrin. For branched chain alcohols the longer alkyl part of the molecule penetrates the α-CD cavity up to the hydroxyl group. Diols form two hydrogen bonds to the outer oxygen ring of the cyclodextrin with some penetration into its interior.

Complexation of Inorganic Anions and Small Organic Molecules with Alpha-Cyclodextrin in Water

The complexation of esters, amides, carboxylic acids, and inorganic ions with alpha-cyclodextrin (α-CD) in aqueous medium was studied by calorimetry. Thermodynamic parameters for the formation of the host–guest complex have been determined. All these processes seem to be enthalpy driven. The entire ester molecule probably penetrates the α-CD cavity. The carboxylic acids hydrogen bond to the α-CD while the alkyl part of the acid enters the cavity. Amides undergo only a weak interaction with the host molecule α-CD. Larger anions interact more strongly with α-CD than do smaller anions; this may be, in part, due to the relative ease of desolvation of the larger anion. The cation seems to play some role in the complexation process with α-CD.

Solvent effects on host-guest complexation

Complex formation between 15-crown-5 and malononitrile was studied in twelve solvents by calorimetry. Thermodynamic parameters for the crown ether adduct were determined and used in a LFER analysis to ascertain the solvent effects on the complexation process. Enthalpy of solution data show that malononitrile is solvated by electron pair donation by the solvents and the crown ether is solvated by donating electron pairs to the solvents. The complex is more solvated than the monomers.

Structure and equilibria in triorganolead halide adduct formation

Abstract The Lewis acidities of triorganolead halides have been studied by 31P and 207Pb NMR spectroscopy and by calorimetry. The formation of 1:1 adducts with a variety of mono- and bidentate bases was demonstrated by the linearity of the plots of chemical shift versus (shift/conc.) 1 2 . The 207Pb chemical shifts of the bidentate adducts indicated only 5-coordinate lead and hence the absence of chelation. Towards triphenyllead chloride basicities varied in the order triethylphosphine oxide > tributylphosphine oxide ⩾ triphenylphosphine oxide > DMSO > tributylphosphine ⩾ pyridine. Triphenyllead chloride was found to be a stronger acid (larger K) than both triphenyllead bromide and triethyllead chloride. The effects of solvent on the equilibrium constants paralleled the trend reported previously for organotin halides. The equilibrium constant for adduct formation with triphenylphosphine oxide (TPPO) is slightly larger for triphenyllead chloride relative to triphenyltin chloride, confirming the expected increase in acidities down Group 14. X-Ray diffraction studies of triphenylphosphine oxide adducts of triphenyllead bromide and triphenyltin chloride showed both structures to be trigonal bipyramidal with the phenyl groups on the equatorial positions. Additionally, the structures are crystallographically isomorphous.

Complex formation between α-cyclodextrin and amines in water and DMF solvents

Complexation between α-cyclodextrin (α-CD) and aliphatic amines in water and DMF solvents was studied by calorimetry. Amines form complexes with α-CD in both solvents but the nature of the complexes is quite different. In DMF the amines donate a hydrogen from the amine N−H group to the cyclodextrin forming a normal hydrogen bonded complex. In DMF solutions with large amine concentrations, complexes other than 1∶1 are observed. In contrast, in aqueous environment the amines form inclusion complexes in which the amine alkyl group penetrates the α-CD cavity and is stabilized by van der Waals interactions. The equilibrium constants for the complexes formed in water solvent increase with increasing alkyl chain length due to an entropy effect.

The Lewis acidities of organotin halides toward tributylphosphine and tributylphosphine oxide: the effect of the donor site

Abstract The stoichiometry of the adducts formed by tributylphosphine (TBP) and tributylphosphine oxide (TBPO) with organotin halides in benzene was determined by 31 P NMR spectroscopy and by calorimetry. Except for two cases, all adducts were found to have 1/1 stoichiometry. For the MeSnCl 3 /TBP and the Me 2 SnCl 2 /TBPO systems there was evidence for a small amount of 1/2 adduct. Both techniques indicate no adduct formation between triorganotin halides and TBP, whereas the equilibrium constants for the 1/1 adducts of TBPO with triorganotin halides range from 150 to 300. With the diorgano- and monoorgano-tin halides, however, the equilibrium constants for 1/1 adduct formation with TBP are the same as or greater than those for TBPO. Enthalpy changes determined by calorimetry show the same reversal of basicity, which can be attributed to steric repulsions in the weakly acidic triorgano derivatives with TBP. These repulsions are overwehlmed by the greater intrinsic tin-phosphorus dative bond strength in the di- and mono-organotin halide adducts.

The stoichiometry of organotin trihalides in solution

Abstract The formation of Lewis acid-base adducts of the organotin trihalides, CH 3 SnCl 3 , C 4 H 9 SnCl 3 , and C 6 H 5 SnCl 3 , with acetonitrile, DMA, triphenylphosphine oxide (TPPO), and triethylphosphine oxide (TEPO) were studied by calorimetry and NMR spectroscopy. Schematic mapping of the calorimetry results for the TPPO adducts in benzene showed that the data are best fit by the assumption of simultaneous formation of 1 1 and 1 2 adducts. For the C 6 H 5 SnCl 3 -TPPO system K 1 = 4.3 X 10 4 , K 2 = 55, Δ H 1 = −13.3 kcal/mol, and Δ H 2 = −10.8 kcal/mol. These equilibrium constants correspond to 93% 1 1 adduct and 1 2 adduct at equilibrium after the acid and base are mixed in equimolar (0.1 M ) concentrations. Thus, for this system and all others studied the 1 1 adduct predominates. Equilibrium constants for the formation of the 1 1 adducts were determined by 119 Sn or 31 P NMR spectroscopy from the shifts obtained in a series of equimolar mixtures of acid and base. These constants vary from approximately 1 for the acetonitile adducts to greater than 10 5 for TEPO and reveal the expected basicity order TEPO > TPPO > DMA > acetonitile.

The structure and Lewis acidity of some triorganotin carboxylates

A series of tributyltin carboxylates and one triphenyltin carboxylate were prepared by reaction of the tin oxide with the appropriate carboxylic acid. The tin-119 chemical shift of each compound in chloroform and, for the solid carboxylates, in the solid state was determined. A comparison of the solution (109–157 ppm) and solid state shifts (−53 to +45 ppm) indicates that the compounds exist primarily as monomeric 4-coordinate species in solution and as 5-coordinate, presumably polymeric species in the solid state. The Lewis acidity of the compounds toward triethylphosphine oxide (TEPO) was determined by recording the 31P chemical shift in a mixture of the carboxylate and TEPO in toluene as a function of concentration. Predominant 1 : 1 adduct formation was observed with equilibrium constants ranging from 5 to 320. The magnitude of the constant can be explained by the electronic effects of the substituents surrounding the tin.

The formation of organotin halide adducts with triethylphosphine oxide

The Lewis acid-base interactions of organotin mono-, di-, and tri-halides with triethylphosphine oxide (TEPO) were investigated by determining the 31P chemical shift of equimolar mixtures of the acid and base in benzene. The concentration dependence of this shift was used to determine the equilibrium constant for formation the 11 adduct. The acceptor number of the acid was obtained from the 31P chemical shift of the adduct and by extrapolation of the 31P shift to infinite dilution. Equilibrium constants for the complexes of the same acids with both TEPO and triphenylphosphine oxide (TPPO) were correlated by multiple regression analysis with these acceptor numbers (AN) and the molar refractivities (MR) of the acids. Enthalpy changes for the formation of adducts with TPPO were also found to correlate with AN aNd MR.

The formation of organotin halide adducts with 1,2-bis(diphenylphosphine oxy)ethane and methyldiphenylphosphine oxide

Abstract The acidities of a series of organotin halides toward the bidentate base 1,2-bis(diphenylphosphine oxy)ethane ([C6H5)2P(O)CH2]2, EDPO) were determined by monitoring the 31P chemical shift of equimolar mixtures of acid and base as a function of concentration in chloroform. Additional studies used the analogous Lewis monodentate base methyldiphenylphosphine oxide (MPPO) and the Lewis base triphenylphosphine oxide (TPPO). In all cases, formation of a 1 1 adduct was found to predominate. Comparison of the equilibrium constants for specific organotin halides showed that EDPO and MPPO have comparable base strengths in chloroform. TPPO is a weaker base than either EDPO or MPPO in chloroform. Tin-119 NMR indicated that the organotin halide-EDPO adducts have 5-coordination at tin with no chelation of the base.