Charles D. Schaeffer

Nuclear magnetic resonance studies of the bonding in aryltrimethylsilanes and germanes, aryldimethylphosphines and arsines, and arylmethylsulfides

Abstract Methyl chemical shifts and 13 C-H coupling constants were measured for the title compounds. Reasonably good (r>0.9) linear correlations between chemical shifts and Hammett σ-constants were found for all series, and the relative slopes of these lines were interpreted in terms of the mode of transmission of substituent effects to the methyl site. The effects of the Si(CH 3 ) 3 , Ge(CH 3 ) 3 , P(CH 3 ) 2 , As(CH 3 ) 2 , and SCH 3 groups on the methyl chemical shifts and coupling constants of toluenes, anisoles, and dimethylanilines were also determined and related to the electronic nature of these groups.

The relative stabilities of the copper hydroxyl sulphates

Abstract The literature contains considerable disagreements on the relative stabilities of the members of the copper hydroxyl sulphate family. Titration of copper sulphate with sodium hydroxide is claimed by some to produce only brochantite, while other reports indicate that antlerite and a dihydrate of antlerite are produced in the titration. Most stability field diagrams show that antlerite is the more stable stoichiomer at pH 4 and sulphate activity of 0.05-1. We have reexamined this stoichiometric family by titration of aqueous copper sulphate with sodiumhydroxide and sodium carbonate, reverse titration of sodiumhydroxide with copper sulphate and simultaneous addition of copper sulphate and sodium hydroxide at a variety of mole ratios, concentrations, temperatures and reaction times. We have also explored the reaction of copper hydroxide with copper sulphate and the reaction of weak bases, such as sodium acetate, sodium carbonate and urea, with copper sulphate. Our work indicates that: (1) antlerite is not formed in reactions of 0.05 to 1.2 м CuSO4 with 0.05-1.0 м NaOH or Na2CO3 at room temperature; (2) antlerite is formed in the addition of small concentrations of base (≤0.01 м) to 1 м CuSO4 at 80ºC, but not at room temperature or with 0.01 м CuSO4 at 80ºC; (3) the formation of Cu5(SO4)2(OH)6‧4H2O occurs at large Cu2+ to base mole ratios; (4) the compound described in the literature as antlerite dihydrate is actually Cu5(SO4)2(OH)6‧4H2O; (5) at mole ratios of Cu2+ to OH- ranging from 2:1 to 1:2 the predominant product is brochantite; and (6) brochantite and Cu5(SO4)2(OH)6‧4H2O are converted to antlerite in the presence of 1 м CuSO4 (the latter requires temperatures of 80ºC or greater). The Ksp (ion activity product) values of antlerite and brochantite were determined to be 2.53 (0.01)×10-48 and 1.01 (0.01)×10-69, respectively, using atomic absorption spectroscopy and Visual MINTEQ after equilibration in solutions of varying ionic strength and pH for six days. These values are in good agreement with those from the literature. However, after 6 months, antlerite in contact with solution is partially converted to brochantite and hence is metastable with a relatively low conversion rate. The Ksp value for antlerite must therefore be considered approximate. The relative stabilities of the copper hydroxyl sulphates are rationalized using appropriate equations and Gibbs energy calculations. A Gibbs free energy of formation for Cu5(SO4)2(OH)6‧4H2O of -3442 kJ/mol was obtained from the simple salt approximation. The very restricted conditions required for the formation of antlerite are rationalized with a stability field diagram at 80ºC.

Use of 73Ge NMR spectroscopy for the study of electronic interactions.

The lack of understanding of the structural and electronic factors that affect the often difficult to observe germanium resonance has been a major deterrent to studies of bonding interactions at germanium. We utilized the symmetrical system GeR 4 to determine what structural factors inherent in the R group affect the shape and position of the (73)Ge resonance. The (73)Ge resonances of symmetrical tetrakis germanium compounds of the type GeR 4 (R = alkyl, aryl), GeX 4 (X = F, Cl, Br, I), Ge(OR) 4 (R = alkyl, methoxyalkyl, dimethylaminoalkyl), Ge(NR 2) 4 (R = alkyl), and Ge(SR) 4 (R = alkyl, dimethylaminoalkyl) were examined for evidence of intramolecular coordination. Although many of these compounds have sharp resonances due to idealized tetrahedral symmetry with relatively long relaxation times, others have broad or no observable resonances due to fast quadrupolar relaxation. We hypothesize that the perturbation of symmetry by even weak Lewis interactions or conformational changes causes broadening of the resonance before the interaction can become sufficiently strong to cause the significant low-frequency shift generally associated with hypercoordination in most nuclei. Intermolecular coordination to GeCl 4 is believed to be responsible for the low-frequency shifts in (73)Ge resonances and the associated changes in peak widths in mixtures with bases such as tributylphosphine oxide (TBPO) and triethylphosphine oxide (TEPO). Adduct formation with these bases is confirmed by broad (31)P resonances that are resolved into five peaks at -40 degrees C. The exchange-broadened resonances due to the 1:1 and 1:2 TEPO adducts are also observed at -40 degrees C in the (73)Ge spectrum. Thus, relatively strong bonding to the germanium in GeCl 4 results in both low-frequency shifts and broadening of the resonance. The broad (73)Ge resonances that occur in some compounds may be in part due to exchange as well as quadrupolar relaxation.

Multinuclear NMR spectroscopic studies of aryltrimethylsilanes and aryldimethylphosphaneboranes

Abstract Proton, boron-11, carbon-13, silicon-29, and phosphorus-31 NMR chemical shifts and coupling constants are reported for nine ortho- and 2,6-disubstituted aryltrimethylsilanes and five similarly substituted aryldimethylphosphaneboranes. Resonances in the natural-abundance carbon-13 NMR spectra for both sets of derivatives are assigned on the basis of additivity relationships, proton-coupled spectra, and relative magnitudes of | J(31P13C) | coupling constants. Carbon-13 chemical shifts and |1J(13C1H) | coupling constants indicate that the P(BH3)(CH3)2 group is electron-withdrawing. The 13C chemical shifts of aryl C(5) carbons can be attributed to steric inhibition of resonance of about the same magnitude as that produced by ortho-Si(CH3)3. Chemical shift and coupling constant data from previous work are expanded in terms of Tafts dual substituent constants σ1 and σR0. Least squares solutions of these equations for aryldimethylphosphaneborane derivatives provide values of 0.41 for σ1 and 0.04 for σR0 for the P(BH3)(CH3)2 group. These constants produce reasonable agreement with observed 13C chemical shifts and coupling constants in the ortho derivatives.

THE SYNTHESIS, STRUCTURE AND LEWIS ACIDITY OF BIDENTATE ORGANOTIN ALKANES AND CARBOXYLATES

A series of bis(diphenylbromostannyl)alkanes of the type (C6H5)2BrSn(CH2)nSnBr(C6H5)2, where η = 6,10 and 12, and a series of bis(tributylstannyl)carboxylates of the type (n-C4H9)3Sn02C(CH2)nC02Sn(nC4H9)3 , where η = 2,6,10,12 and 14, were prepared. Tin-119 solid state NMR of the carboxylates indicated that the compounds contain five-coordinate, structurally-equivalent tins in the solid state. Adduct formation with triethylphosphine oxide (TEPO) for both the alkanes and carboxylates was monitored by phosphorus-31 NMR. Equilibrium constants for the alkanes were approximately independent of chain length from η = 6 to 12, while for the carboxylates, the constants for η = 2 and η = 14 were small. Equilibrium constants for the intermediate chains were approximately the same. Solid state NMR shows that the 1:1 TEPO adduct of the η = 12 carboxylate contains two different tin atoms, both of which are five-coordinate, and that the adduct is probably not symmetrically chelated.