Phosphasila-, phosphagerma-, and phosphaarsaallenes --P=C=E (E = Si,Ge, As) and arsa- and diarsaallenes --As=C=E" (E" = C,As)

The paper reviews the contribution from our group to the studies of heteroallenes. The transient 1,3-phosphasilaallene ArP=C=Si(Ph)Tip (Ar = 2,4,6-tri-tert-butylphenyl, Tip = 2,4,6-triisopropylphenyl) and 1,3-phosphagermaallene ArP=C=GeMes₂ (Mes = 2,4,6-trimethylphenyl) were characterized below –40 °C by NMR spectroscopy and chemical trapping. These compounds dimerize above –40 °C through two routes. With increased steric hindrance on germanium, the phosphagermaallene ArP=C=Ge(Bu^t)Tip was stabilized as monomer at room temperature. 3-Chloro-2-lithio-1,3-phosphasilapropene ArP=C(Li)Si(Cl)CMeR₂ (CMeR₂ = 9-methylfluorenyl) behaves, at least in some cases, as a synthetic equivalent of the functionalizable allene ArP=C=Si(Cl)CMeR₂. Arsaallene ArAs=C=CR₂, phosphaarsaallenes ArP=C=AsAr and ArP=C=AsDmt (Dmt = 2,6-dimesityl-4-methylphenyl), and diarsaallene ArAs=C=AsAr exhibit a higher thermal, air, and moisture stability than the above phosphasilaallenes and phosphagermaallenes. The physicochemical data for the arsaallenes and diarsaallenes, particularly, their X-ray structural parameters, display a bonding system close to allenes. On going down the Periodic table, the stabilization becomes more difficult. For this reason, tin allenic derivatives are very rare and antimony allenic compounds have not yet been isolated.     

New Halo Compounds of Si,P, As,AND Sb Bearing a Bulky Substituted Fluorenyl Group

New halo compounds of Si, P, As, and Sb, potential precursors of doubly-bonded derivatives of these elements, have been synthesized: dichloro-and difluorosilanes 2–6 bearing a methylfluorenyl group and a second substituent of various size (Me, Ph, Mes, R₂CMe); dichlorophosphines 13 and 14, fluoro- and difluoroarsines 15 and 16 and fluorostibine 17, substituted by the diphenyl (or dimesityl) phosphinofluorenyl group. Phosphine oxide and sulfide 9 and 10 also have been prepared.

     

The electronic structure of a diarsaallene –As=C=As– and a phosphaarsaallene –P=C=As–: UV photoelectron spectroscopy and theoretical studies

The electronic properties of a diarsaallene ArAs=C=AsAr and a phosphaarsaallene ArP=C=AsAr (Ar: 2,4,6-tri-tert-butylphenyl) have been investigated by using UV photoelectron spectroscopy and by density functional calculations on model compounds [(CH₃)₂C₆H₃Pn=C=AsC₆H₃(CH₃)₂, Pn: As, P]. Moreover, a comparison of the geometrical and electronic structures of the parent heteroallenes with those of the arsaethene H₂C=AsH and phosphaethene H₂C=PH has also been undertaken in order to determine the magnitude of the interaction between the π bond and the pnictogen lone pair n_Pn.