Stabilisation effects of ferrocenylalkyl groups on hydrides of heavier main group elements

摘要

New hydrides of heavier p-block main group elements with a ferrocenylalkyl moiety, Fc(CH₂)nEHm (Fc = (CpFeC₅H₄-); E = P, As, Si, Ge or Se; n = 1, 2, 4, 6 or 11; m = 1, 2 or 3) and FcCH₂P(R)H (R = CH₃, C₆H₁₁ or p-CH₂C₆H₄NO₂), have been synthesised and characterised. Although some precursors of the desired hydrides, i.e. Fc(Cl)C=C(SnCl₃)H and (FcCH₂Te)₂, which are also new compounds, could be prepared, the syntheses of the corresponding desired hydrides, FcCH₂EHn, were unsuccessful probably due to their extreme instabilities. Some related primary phosphanes, [CpFeC₅H₃(CH₂OH)(CH₂PH₂)], RcCH₂PH₂ and Fc(CH₂)₆PH₂∙BH₃, phosphane oxide, FcCH₂P(O)H₂, and phosphinic acid, FcCH₂P(O)(OH)H, were also synthesised and reported. The X-ray crystal structures of Fc(CH₂)₆PH₂∙BH3 and FcCH₂SeCN are also presented in the present thesis.The stability of the hydrides of heavier p-block main group elements with a ferrocenyl or ruthenocenylalkyl moiety under ambient conditions has been investigated using NMR and/or IR spectroscopy. Ferrocenylalkyl and ruthenocenylmethyl primary phosphanes, Fc(CH₂)nPH₂ (n = 4, 6 or 11) and RcCH₂PH₂, respectively, exhibited a remarkable stability towards air oxidation in solution, i.e. ~1 year. In contrast, the secondary phosphanes were not as stable as expected, rapidly oxidising over several weeks or months. General trend for the oxidative stability of the secondary phosphanes could not be elucidated on the basis of the electronegativity, size or degree of conjugation of the substituent on the phosphorus. Ferrocenylmethyl primary arsane, FcCH₂AsH₂, was also unexpectedly air-sensitive, having been readily oxidised as a neat liquid or in solution upon the exposure to air.Ferrocenylethyl primary silane, Fc(CH₂)₂SiH₃, was stable both as a neat liquid and also in solution. It could be purified on a TLC plate in air and also stored in solution for up to 7 months. On the other hand, ferrocenylmethyl primary germane, FcCH₂GeH₃, was unstable, almost completely decomposing left overnight in solution, which was indicated by the disappearance of the germane proton NMR signal by ¹H NMR spectroscopy.Ferrocenylalkyl selenols, Fc(CH₂)nSeH (n = 1 or 4), were both found to be unstable as neat liquids or in solution. Handling the compounds in air caused significant oxidation, resulting in the formation of the corresponding diselenides which are the common oxidation products of selenols. Ferrocenylmethyl selenol, FcCH₂SeH, was completely oxidised in solution in air in 5 days while ferrocenylbutyl selenol, Fc(CH₂)₄SeH, in 3 days. The rapid oxidation of the latter was also observed by IR spectroscopy over a period of 10 minutes when exposed to air as a neat liquid.The oxidative stability of the air-sensitive primary phosphanes, PhPH₂ and camphylPH₂, in the presence of ferrocene, FcH, or its derivative, FcCH₂PH₂, in solution, was studied by ³¹P NMR spectroscopy. The study showed that the primary phosphanes could be stabilised by simple addition of FcH or FcCH₂PH₂. The corresponding ³¹P NMR study using known antioxidants, diphenyl picryl hydrazyl (DPPH) or nitrosobutane, in place of the ferrocene species also exhibited that PhPH₂ could be stabilised by addition of an antioxidant. These results suggest that FcH and FcCH₂PH₂ can be used to stabilise air-sensitive primary phosphanes in solution by simply adding them, probably acting as radical scavengers.