arsaalkyne
In chemistry, a arsaalkyne (IUPAC name: alkylidynearsane) is an organoarsenic compound containing a triple bond between arsenic and carbon with the general chemical formula {{chem2|R\sC\tAs}}. Arsaalkynes are rare, especially in comparison with the phosphaalkynes. The parent {{chem2|H\sC\tAs}} has been characterized spectroscopically, otherwise the only arsaalkynes have bulky organic substituents.{{cite journal |doi=10.1039/B806771F|title=Methylidynearsine (HC≡As): Synthesis and Direct Characterization by UV-Photoelectron Spectroscopy and Mass Spectrometry |year=2008 |last1=Guillemin |first1=Jean-Claude |last2=Chrostowska |first2=Anna |last3=Dargelos |first3=Alain |last4=Nguyen |first4=Thi Xuan Mai |last5=Graciaa |first5=Alain |last6=Guenot |first6=Pierre |journal=Chemical Communications |issue=35 |pages=4204–4206 |pmid=18802530}}
Synthesis and isolation
Arsaalkynes are produced by dehydrohalogenation or related base-induced elimination reactions. The case of HCAs is illustrative:
:{{Chem2|Cl\sCH2\sAsH2 + 2 Na2CO3 → H\sC\tAs + 2 NaHCO3 + 2 NaCl}}
Owing to the principles of the double bond rule, arsaalkynes tend to oligomerize more readily than the phosphorus analogues. Thus attempts to prepare {{chem2|Me3C\sC\tAs}} produce the tetramer, which has a cubane structure.{{cite journal |doi=10.1002/anie.199301031|title=Synthesis and Structure of the Arsaalkyne Tetramer (AsCtBu)4 and its Fe(CO)4 Derivative |year=1993 |last1=Hitchcock |first1=Peter B. |last2=Johnson |first2=Julian A. |last3=Nixon |first3=John F. |journal=Angewandte Chemie International Edition in English |volume=32 |pages=103–104}} The very bulky substituent {{chem2|\sC6H2}}-2,4,6-{{chem2|(t\-Bu)3}} does however allow the crystallization of the monomeric arsaalkyne. Its As-C bond length is 1.657(7) Å.{{cite journal |doi=10.1039/C39940002061|title=Synthesis, Crystal and Molecular Structure of the First Metal Complex [Pt(PPh3)2{η2-As≡C(C6H2But3)}] Derived from an Arsaalkyne |year=1994 |last1=Hitchcock |first1=Peter B. |last2=Jones |first2=Cameron |last3=Nixon |first3=John F. |journal=J. Chem. Soc., Chem. Commun. |issue=18 |pages=2061–2062}}