Primary and Secondary Vinylarsines: Synthesis, Stability and Characterization

Primary α-Phosphino- and α-Arseno-Nitriles, Analogues of α-Aminonitriles

More than 170 years after the synthesis of α-aminonitriles by the reaction of Strecker, α-phosphinonitriles, and α-arsenonitriles have been prepared and characterized by NMR and IR spectroscopy. For the simplest derivatives, the reaction was carried out by reaction of cyanomethyltributylstannane with phosphorus or arsenic trichloride, followed by a chemoselective reduction of the dichlorophosphine and dichloroarsine formed to the corresponding primary phosphine and arsine. The phosphinoacetonitrile can be stored at -80 °C for months in its pure state, but arsenoacetonitrile decomposes at this temperature. Chiral compounds can be synthesized from C-substituted cyano-1-alkyltributylstannanes. In 1H NMR spectroscopy, these chiral phosphines and arsines display diastereotopic protons for the PH2 and AsH2 groups, a property never observed for the NH2 group of α-aminonitriles. This work paves the way for further studies on the chemistry of these compounds, including a comparative chemistry of these phosphorus and arsenic derivatives with the well-known α-aminonitriles.

Acidity Trends in α,β-Unsaturated Sulfur, Selenium, and Tellurium Derivatives: Comparison with C-, Si-, Ge-, Sn-, N-, P-, As-, and Sb-Containing Analogues

The gas-phase acidity of CH3-CH2XH (X=S, Se, Te), CH2=CHXH (X=S, Se, Te) and PhXH (X=S, Se) compounds was measured by means of Fourier transform ion cyclotron resonance mass spectrometry. To analyze the role that unsaturation plays on the intrinsic acidity of these systems, a parallel theoretical study, in the framework of the G2 and the G2(MP2) theories, was carried out for all ethyl, ethenyl (vinyl), ethynyl, and phenyl O-, S-, Se-, and Te-containing derivatives. Unsaturated compounds are stronger acids than their saturated analogues, because of the strong pi-electron donor ability of the heteroatoms that contributes to a large stabilization of the unsaturated anions. Ethynyl derivatives are stronger acids than vinyl compounds, while phenyl derivatives have an intrinsic acidity intermediate between that of the corresponding vinyl and ethynyl analogues. The CH2=CHXH vinyl compounds (enol-like) behave systematically as slightly stronger acids than their CH3-C(H)X (keto-like) tautomers. Vinyl derivatives are stronger acids than ethyl compounds, because the anion stabilization attributable to unsaturation is greater than that undergone in the neutral compounds. Conversely, the enhanced acidity of the ethynyl derivatives with respect to the vinyl compounds is due to two concomitant effects, the stabilization of the anion and the destabilization of the neutral compound. The acidities of ethyl, vinyl, and ethynyl derivatives containing heteroatoms of Groups 14, 15, and 16 of the periodic table are closely related, and reflect the differences in electronegativity of the CH3CH2-, CH2=CH-, and CH[triple chemical bond]C- groups.

Rotational Spectrum of Vinylarsine

The rotational spectrum of vinylarsine in the ground state has been studied in the range 7-320 GHz. The spectra of a syn conformer and a gauche conformer have been unambiguously assigned on the basis of the existence of a b-type or a c-type spectrum. Rotational constants, quartic, and some sextic centrifugal distortion constants were derived. For the syn form, measurements of low J aR0,1 transitions in a pulsed-nozzle Fourier transform microwave spectrometer (FTMWS) enabled the determination of the diagonal elements of the quadrupole tensor, as well as two spin-rotation constants. Ab initio calculations performed at the MP2 level using the 6-311++G(3df, 3pd) basis set reproduced experimental rotational constants within 0.2%. Copyright 1998 Academic Press.

Vinylmercury Hydrides: Synthesis and Spectroscopic Characterization

The first vinylmercury hydrides, and among them the parent compound, have been prepared by a chemoselective reduction of the corresponding vinylmercury chlorides with tributylstannane in the presence of a radical inhibitor. These hydrides have been characterized on the basis of their spectral data ((1)H, (13)C, and (199)Hg NMR spectroscopy and mass spectrometry). The photoelectron spectra of the ethenylmercury hydride displays bands at 9.79, 10.13, 11.41, and 13.20 eV. On the basis of photoelectron spectra and ab initio quantum chemical calculations some (d-p)pi interaction between the vinyl pi-system and the mercury d-orbitals could be concluded. Vinylmercury hydrides have been condensed and then revaporized in vacuum at low temperature, but they exhibit a very low stability at room temperature even diluted in toluene (tau(1/2) approximately 1 min); elemental mercury and the corresponding divinylmercury were formed under these conditions.