New Hydroxylated Cyclic and Acyclic Silylenes Via DFT
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ORIGINAL PAPER
New Hydroxylated Cyclic and Acyclic Silylenes Via DFT Mojgan Ayoubi-Chianeh 1
&
Mohamad Z. Kassaee 1
Received: 27 May 2020 / Accepted: 1 October 2020 # Springer Nature B.V. 2020
Abstract We have scrutinized thirteen new derivatives of cyclic and acyclic silylenes and compared their structural and thermodynamic parameters, at M06-2X/6–311++G** level of theory. The cyclic three- and five-membered silylenes include (2-hydroxy)cyclopropasilylene-2ene (1), (2,3-dihydroxy)cyclopropasilylene-2-ene (2), (2-hydroxy)cyclopentasilylene-2,4-diene (3), and (2,5dihydroxy)cyclopentasilylene-2,4-diene (4). The acyclic isomers consist of hydroxypropa-2-silylene (1′), (1,3-dihydroxy)propa-2silylene (2′), (2-hydroxy)penta-3-silylene (3′), (2-hydroxy)penta-3-silylene-1,4-diene (3″), (2,4-dihydroxy)penta-3-silylene (4′), and (2,4-dihydroxy)penta-3-silylene-1,4-diene (4″). In addition, keto forms of 3″ (3”K) and 4″ (4”K1 and 4”K2) along with protonated forms of silylenes (1H, 1’H, 2H, 2’H, 3H, 3’H, 3”H, 3”K-H, 4H, 4’H, 4”H, 4”K1-H, and 4”K2-H) are investigated for determining their proton affinities (PAs) and intramolecular hydrogen bondings (IHBs). The results show that 4′ shows the lowest singlet-triplet energy gap (ΔEs-t = −19.03 eV) and band gap (ΔEH-L = −2.01 eV) and the highest nucleophilicity (N = 4.02 eV), chemical potential (μ = −3.38 eV), and PA (382.85 kcal/mol) which correlates with its strongest IHB. Atoms in molecules (AIM) analysis represents the highest electron density (ρ(r) = 0.033) at bond critical point (BCP) of IHB in 4′. The natural bond orbital (NBO) analysis shows the highest value of second-order perturbation stabilization energy (E2 = 7.85 kcal/mol) for 4′ which is in consistent with the lowest bond length of IHB (1.84 Å). Furthermore, the infrared (IR) spectroscopy indicates the lowest vibrational frequency of O-H bond νOH(νOH= 3542.87 cm−1) which verifies the strong IHB of 4′. The overall order of the IHB strength is 4′ > 4” > 4’H > 4”H > 2’ > 2’H. Keywords Silylene . Hydrogen bond . AIM . NBO . DFT
1 Introduction Silylenes are typically highly reactive and have short lifetimes at low temperatures [1]. The innovative discovery of the first stable silylene by Denk et al. in 1994 [2] became a landmark in silicon chemistry. Silylenes usually are stabilized by incorporation into a cyclic framework, especially by electron donating groups [3–9]. With regard to reactivity, the vacant coordination site of silylene together with lone pair of electrons provide a platform for many applications in synthesis and industry. Silylenes have been widely used for preserving the transition metals, generating strong bases, semiconductors, photonics, electroluminescence (EL), and light-emitting diodes (LEDs) [10–12]. They almost prefer singlet ground states, thus, larger singlet-triplet energy gap (ΔEs-t) implies * Mohamad Z. Kassaee [email protected] 1
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
more stable silylene [13]. Apeloig and Sekiguchi showed that elect
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