Novel Nucleophilic Aluminyl Anions in Small Molecule Activation and Transition-Metal Chemistry
Final Report Abstract
Unlike the stable C=O bonds in ketones, the heavier E=O bonds (E = Si, Ge, Sn or Pb) are strongly polarized, rendering them especially prone to oligomerize. Herein, a series of novel boryl-supported amidinato-tetrylenes [B][R2C(NR1)2]E: ([B] = B{(NDippCH)2}, Dipp = 2,6- iPr2C6H3, E = Si, Ge, Sn or Pb; R1 = tBu or Dipp; R2 = Ph, tBu or NiPr2) have been synthesized and fully characterized. By utilizing the strong σ-donating nature of the boryl group, the first boryl amidinato-silanone [B][PhC(NtBu)2]Si=O and germanone [B][PhC(NtBu)2]Ge=O have been isolated at room temperature successfully by subjecting the respective silylene [B][PhC(NtBu)]Si: and germylene [B][PhC(NtBu)]Ge: to N2O. The boryl amidinato-silanone and -germanone are comprehensively characterized spectroscopically and structurally. Additionally, DFT calculations are performed, which reveals partial polarization in Si=O bond of silanone and Ge=O of germanone. Intriguingly, the reaction of N 2O with stannylene [B][PhC(NtBu)2]Sn: leads to the formation of a dimer {[B][PhC(NtBu)2]SnO}2 featuring a Sn2O2 four-membered ring. When employing bulkier stannylenes [B][(tBu)C(NDipp)2]Sn: and [B][(NiPr)C(NDipp)2]Sn: to react with N2O, it is observed that the dimerization process is prohibited. Instead, unexpected products boryloxy-stannylene [BO][RC(NDipp)2]Sn: (R = Ph or tBu) are obtained probably resulting from the migration of the boryl group from the Sn atom to the O atom. In contrast, the boryl plumbylene [PhC(NDipp)2]Pb: displays inertness towards oxygenation reagents. Subsequently, we explore the reactivity of the polarized E=O bonds in silanone and germanone towards small molecules. Surprisingly, gemarnone shows no reactivity towards CO2 and decomposed at the ammonia atmosphere. On the other hand, silanone could facilely react with CO2 to give a stable silicon carbonate species [B][PhC(NtBu)2]SiCO3. Notably, the exposure of silanone to NH3 leads to the successful isolation of the reactive sila-hemiaminal [B][PhC(NtBu)2]Si(OH)(NH2) at -30 oC. An investigation of the NH3 activation mechanism based on DFT calculations reveals a unique initial step. This step involves a hydrogen bond interaction between ammonia and the silanone, in contrast to the traditional ammonia coordination mode. In the final stage of the mechanism, the liberation of one Namidinate atom from the silicon center, followed by the formation of a hydrogen bond between the OH group and the release N atom, substantially contributes the stabilization of the sila-hemiaminal. These findings offer valuable insights into the intriguing reaction between silanone and NH3, while also providing an effective synthetic route to access the elusive sila-hemiaminal compound.
Publications
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Boryl Ancillary Ligands: Influencing Stability and Reactivity of Amidinato‐Silanone and Germanone Systems in Ammonia Activation. Angewandte Chemie, 136(20).
Wang, Yuwen; Crumpton, Agamemnon E.; Ellwanger, Mathias A.; McManus, Caitilín & Aldridge, Simon
