Hydrosilylation Induced by N→Si Intramolecular Coordination: Spontaneous Transformation of Organosilanes into 1‐Aza‐Silole‐Type Molecules in the Absence of a Catalyst |
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Authors: | Miroslav Novák Dr. Libor Dostál Dr. Mercedes Alonso Prof. Frank De Proft Dr. Aleš Růžička Prof. Antonín Lyčka Dr. Roman Jambor |
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Affiliation: | 1. Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 95, 53210, Pardubice (Czech Republic);2. Eenheid Algemene Chemie (ALGC), Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussels (Belgium);3. Research Institute for Organic Syntheses (VUOS a.s.), Rybitví 296, CZ‐533 54 Pardubice (Czech Republic) |
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Abstract: | Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph2L1SiH ( 1 a ), PhL1SiH2 ( 2 a ), Ph2L2SiH ( 3 a ), and PhL2SiH2 ( 4 a ) containing a CH?N imine group (in which L1 is the C,N‐chelating ligand {2‐[CH?N(C6H3‐2,6‐iPr2)]C6H4}? and L2 is {2‐[CH?N(tBu)]C6H4}?) yielded 1‐[2,6‐bis(diisopropyl)phenyl]‐2,2‐diphenyl‐1‐aza‐silole ( 1 ), 1‐[2,6‐bis(diisopropyl)phenyl]‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 2 ), 1‐tert‐butyl‐2,2‐diphenyl‐1‐aza‐silole ( 3 ), and 1‐tert‐butyl‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 4 ), respectively. Isolated organosilicon amides 1 – 4 are an outcome of the spontaneous hydrosilylation of the CH?N imine moiety induced by N→Si intramolecular coordination. Compounds 1–4 were characterized by NMR spectroscopy and X‐ray diffraction analysis. The geometries of organosilanes 1 a – 4 a and their corresponding hydrosilylated products 1 – 4 were optimized and fully characterized at the B3LYP/6‐31++G(d,p) level of theory. The molecular structure determination of 1 – 3 suggested the presence of a Si?N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor–acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si?N bond is highly polarized pointing to a predominantly zwitterionic Si+N? bond in 1 – 4 . Since compounds 1 – 4 are hydrosilylated products of 1 a – 4 a , the free energies (ΔG298), enthalpies (ΔH298), and entropies (ΔH298) were computed for the hydrosilylation reaction of 1 a – 4 a with both B3LYP and B3LYP‐D methods. On the basis of the very negative ΔG298 values, the hydrosilylation reaction is highly exergonic and compounds 1 a – 4 a are spontaneously transformed into 1 – 4 in the absence of a catalyst. |
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Keywords: | density functional calculations hydrosilylation intramolecular coordination NMR spectroscopy silicon |
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