Preparation and Properties of Phosphaethynes Bearing Bulky Aryl Groups with Electron-Donating Substituents at the Para Position

Phosphaethynes bearing a 2,6-di-tert-butyl-4-(dimethylamino)phenyl, 2,6-di-tert-butyl-4-methoxyphenyl, or 2,6-di-tert-butylphenyl group were prepared. A (31)P NMR spectroscopic investigation of the chemical shifts indicated that electron-donating groups at the para position cause shifts to a higher field. Bathochromic shifts caused by the electron-donating groups were apparently observed in UV-vis spectra. The structure of 2-[2,6-di-tert-butyl-4-(dimethylamino)phenyl]-1-phosphaethyne was analyzed by X-ray crystallography.

2,6-Diisopropylphenylphosphane: A new, bulky primary phosphane and its mono- and disilylated Si(CH3)3 and Si(CH3)2-t-Bu derivatives — A synthetic, crystallographic, and dynamic NMR investigation

The bulky primary phosphane 2,6-diisopropylphenylphosphane, DipPH2, has been prepared from 1-bromo-2,6-diisopropylbenzene via the reaction of the Grignard reagent with PCl3. The resulting mixed phosphonous dihalides DipP(Cl,Br)2 are reduced with LiAlH4 to yield the title compound in reasonable yield and on a synthetically useful scale. DipPH2 is also used to prepare the monosilylated derivatives DipPHSi(CH3)3 and DipPH{Si(CH3)2-t-Bu} as well as the disilylated compounds DipP{Si(CH3)3}2 and DipP{Si(CH3)2-t-Bu}2. All products have been fully characterized by IR, mass, and NMR spectroscopy. The crystal structure of DipPH{Si(CH3)2-t-Bu} was determined from single-crystal diffraction data: C18H33PSi, P21/c, Z = 4, a = 8.5768(10), b = 28.104(3), c = 8.1102(4) Å, β = 93.341(3)° (R = 0.0518). Changes in the NMR spectrum of DipPH{Si(CH3)2-t-Bu} were observed over the temperature range 178–380 K. Barrier heights were determined from the peak separation at low temperature and the coalescence points: ΔG‡ [Formula: see text] 40 kJ mol–1 for C(aryl)—P bond rotation and [Formula: see text] 72 kJ mol–1 for pyramidal inversion at phosphorus.Key words: crystal structure, 2,6-diisopropylphenyl, bulky substituents, steric congestion, dynamic NMR, primary phosphane, silyl phosphane.