AIM and ELF Electronic Structure/G2 and G3 π-Bond Energy Relationship for Doubly Bonded Silicon Species, H₂SiX (X = E¹⁴H₂, E¹⁵H, E¹⁶)¹

Abstract

π-Bond energies in doubly bonded silicon species, H 2 SidX (X ) E 14 H 2 , E 15 H, E 16 ), were determined using G2 and G3 procedures. In addition, the distribution of electron density in the internuclear area between silicon and the element in H 2 SidX and H 3 Si-XH was estimated using quantum-topological approaches AIM (MP2/6-311++G(2d,p)) and ELF (HF/6-311++G(2d,p)). Both parameters, an increase of electron density at the critical point of the silicon-element bond and π-bond energy, appeared to correlate linearly, increasing on going from group 14 to group 16 elements. The contribution of the ion-component to the SidE π-bond energy increases as the negative inductive effect of the element grows, attaining the maximum for silanone.

Advances in Phosphasilene Chemistry

“…Clearly, the properties of heteronuclear >Si=P‐ analogues might be classified as a balanced intermediate between these border examples of mononuclear bonds. In general, thermodynamic stability of the Si=P bond in phosphasilenes is higher than that of disilene Si=Si analogues, but lower than that of phosphaalkene C=P analogues. Similarly, a single σ(Si−P)‐bond is less stable than a single σ(C−P)‐bond.…”

“…Clearly,t he properties of heteronuclear > Si=P-analogues might be classified as ab alanced intermediate between these border examples of mononuclear bonds. In general, thermodynamic stabilityo ft he Si=Pb ond in phosphasilenes is higher than that of disilene Si=Si analogues, [26] but lower than that of phosphaalkeneC =Pa nalogues. Similarly,asingle s(SiÀP)-bond is less stable than as ingle s(CÀP)-bond.I nf act, the single SiÀP bond of silylphosphanes is even highly reactive:t he cleavage of these bondsi nr eactions with suitable polar compounds often proceeds under mild conditions in ap redictable manner.…”

“…The calculated Wiberg bond index (WBI) for the Si=P bond in H 2 Si=PH was found to be 1.97, and the bond dissociation energy (BDE) is 75.0 kcal mol −1[31] at the B97‐D/6‐31G(d) level of theory. The π‐bond energy, D π (Si=P), of 4 (36.6/35.9 kcal mol −1 ) is higher than that of the parent disilene H 2 Si=SiH 2 (27.3/25.6 kcal mol −1 ) and close to that of the parent silene H 2 Si=CH 2 (39.6/37.7 kcal mol −1 ) . The HOMO and LUMO in 4 correspond to the π(Si=P) and π*(Si=P) orbitals, respectively, while the HOMO−1 is the n(P) orbital .…”

“…The pbond energy, D p (Si=P), of 4 (36.6/35.9 kcal mol À1 )i sh igher than that of the parent disilene H 2 Si=SiH 2 (27.3/25.6 kcal mol À1 )a nd close to that of the parents ilene H 2 Si=CH 2 (39.6/37.7 kcal mol À1 ). [26] The HOMO and LUMO in 4 correspond to the p(Si=P) and p*(Si=P) orbitals, respectively,w hile the HOMOÀ1i st he n(P) orbital. [32] This energy distribution reflects ag eneral trend for phosphasilenes.…”

A Tetrasilicon Analogue of Bicyclo[1.1.0]but‐1(3)‐ene Containing a Si=Si Double Bond with an Inverted Geometry

“…100 kJ mol À1 ]. [24,27] TheUV/Vis spectrum of 1 in hexane exhibits aweak and broad band at circa 400 nm (e 2300) that tails into circa 500 nm (band I), as well as abroad intense band at 346 nm (e 15 000, band II;F igure 6). Thes hape of the absorption spectrum is in good agreement with that obtained from quantum chemical calculations at the TD-B3PW91-D3/B2// B3PW91-D3/B1 (B2: 6-311 + G(3d) [Si], 6-31 + G(d) [C,H]) level of theory ( Figure S12).…”