Charles G. Moreland

Synthesis and characterization of tetraalkylammonium salts of bis(5,6-dihydro-1,4-dithiin-2,3-dithiolato)cobaltate(III). Crystal structure of [(C4H9)4N]2[Co(DDDT)2]2

Abstract The reaction between CoCl2·6H2O and K2DDDT (the potassium salt of 1,2-dithiolene 5,6-dihydro-1,4- dithiin-2,3-dithiolate) under an argon atmosphere yields a dimeric dianion which can be isolated as a tetraalkylammonium salt. Constant potential electrolysis of the formally Co(III) product yields a Co(II) species. Both complexes are extremely sensitive to air in solution. The solid Co(III) product, however, is sufficiently air stable to allow a structural analysis of the tetrabutylammonium salt. The crystal belongs to the monoclinic space group C2/c with unit cell dimensions of a=23.626(3), b=16.915(3), c= 16.294(2) A, β=101.62(1)°, Z=8. The coordination around the cobalt atom is best described as square pyramid with an average basal CoS bond length of 2.197(1) A and an apical CoS distance of 2.328(1) A. The dimeric structure allows for S…S contacts in the crystal lattice as short as 3.22 A. The structure refined to R=0.037 and Rw=0.053. The frozen glass ESR spectrum of the Co(II) complex exhibits three sets of eight lines with g1=1.933, g2=2.067 and g3=2.860. A cyclic voltammogram contains a two-electron reversible wave, a quasi-reversible one- electron wave and a reversible one-electron wave indicating a four-member electrochemical series: [Co- (DDDT)2]2o[Co(DDDT)2]2− ⇄[Co(DDDT)2]22−⇄2Co(DDDT)22−. The solid-state 13C NMR spectrum shows different resonances for carbons in the double bonds of the ligand, consistent with splitting of the C=C stretch in the IR spectrum.

Substituent and solvent effects on the 31P NMR chemical shifts of substituted diethyl phenylphosphonates

Abstract The effect of various substituent groups on the 31P NMR chemical shifts of a series of substituted diethyl phenylphosphonates in acetone and ethanol has been observed. The linear correlation of the 31P chemical shifts with the Hammett σ constants was opposite to that expected on the basis of the electron-withdrawing ability of the substituent as was also found in the case of the acid analogs. Several hydrogen-bonding “mechanisms” are proposed to account for the solvent effect on the chemical shifts of both the esters and the acids.

Substituent effects on the 31P NNIR chemical shifts of substituted phenylphosphonic acids

Abstract The effect of various substituent groups on the 31 P NMR chemical shift of a series of substituted phenylphosphonic acids has been investigated in three different solvents: acetone, ethanol, and aqueous sodium hydroxide solution. The chemical shifts were found to be linearly related to the Hammett sigma constants and the Taft σ R and σ I parameters. The correlation was opposite to that expected on the basis of the electron withdrawing ability of the substituents. The effect of the substituents was found to be additive and constant.

Predictive schemes for the reactivity of borane carbonyl and the stability of carbonyltrihydroborate anions, BH3C(O)X−

The reactivity of borane carbonyl (BH3CO) and its isoelectronic counterpart the acetylium cation (CH3CO+) are compared resulting in the formulation of (carbonyl)trihydroborate anions, BH3C(O)X−, which are isoelectronic and isostructural with organic carbonyls. By analogy with the ease of reduction of organic carbonyl compounds by hydroborate, the relative stability towards self-reduction-oxidation (hydride transfer from boron to carbonyl carbon) in BH3C(O)X− is proposed. The postulated order, with increasing stability is BH3C(O)Cl− < BH3C(O)H− < BH3C(O)R− < BH3C(O)OR− < BH3C(O)NR−2 < BH3C(O)O2−. Experimental results of this study together with known chemistry are shown to be consistent with the proposed order. Further, it is suggested that a similar predictive scheme may be applicable to the chemistry of the amine-carboxyboranes (boron analogues of α-amino acids) and their derivatives.

New Chemical Reactivity in Aromatic Dithiocarbamate and Monothiocarbamate Ligands: Syntheses of Mo2L4·2THF (L = Pyrrole or indole monothiocarbamate or pyrrole dithiocarbamate) and Mo2L4 (L = indoline monothiocarbamate)

Abstract The reactions between Mo2(C2H3O2)4 and several new dithio- and monothiocarbamates have been studied. The first example of a dimolybdenum compound of a dithiocarbamate with the “molybdenum acetate” structure is reported (Mo2L4·2THF; L = pyrrole dithiocarbamate). In addition, the synthesis of Mo2L′4·2THF (L′ = pyrrole monothiocarbamate, indole monothiocarbamate, indole dithiocarbamate) and Mo2L″4 (L″ = indoline monothiocarbamate) are reported. A discussion of the unique stabilization of the dithiocarbamate bridge by “aromatic” dithio- and monothiocarbamates is presented.

SYNTHESES AND CHARACTERIZATION OF 1,3-DITHIEPIN-2-CARBODITHIOLATE AND ITS ALKYLATED DERIVATIVES

Abstract The synthesis and characterization of a new series of organo-sulfur compounds which contain the tetrathioethylene unit are reported. A single crystal structure study of one of these compounds, 2-(1,3-dithiolan-2-ylid-ene)-1,3-dithiepin was carried out. The crystals belong to space group P1 with α=8.634(2) A, b=15.658(4) A, c=8.196(2) A, α=75.79(2)°, β=103.11(2)°, δ=102.70(2)°, R=0.058 for 1886 reflections I > 3 [sgrave](I), and D x=1.493, D m=1.46, for Z=4. The packing of molecules does show stacking with three close contacts between sulfurs having the following distances: 3.6477 A, 3.5860 A, and 3.5782 A. Further characterization by 1H and 13C NMR, electrochemistry, and MO calculations show these compounds to be quite different from the parent TTF in many aspects.

Carbon-13 nuclear magnetic resonance spectra of 5-alkyl-5-(1-methylbutyl)barbituric acids

The natural-abundance 13C n.m.r. spectra of 5-alkyl-5-(1-methylbutyl)barbituric acids have been obtained. All resonances were assigned by chemical shift comparisons including the analysis of deuteriated analogues and the use of single-frequency, off-resonance decoupling. Chemical shift nonequivalence was observed between the carbonyl C-4 and C-6 atoms. This chemical shift difference is very sensitive to changes in the 5-alkyl substituent, thus indicating that 13C n.m.r. spectroscopy should be of considerable value in detecting steric effects and conformational changes in other optically active 5,5-dialkylbarbituric acids.

19F nuclear magnetic resonance investigation of some benzotrifluoride derivatives

Abstract 19F NMR chemical shifts for a number of para-substituted and meta-substituted benzotrifluoride derivatives are reported. The study includes results of the chemical shift dependence on solvent and electronic factors. These results are examined in terms of possible negative hyperconjugation and p−π interactions. The contribution of the paramagnetic term in the explanation of the 19F chemical shifts of the benzotrifluoride derivatives is discussed.