Four‐, Five‐, and Six‐Coordinate Silicon(IV) Complexes: Reactivity of the Donor‐Stabilized Silylenes [iPrNC(Ph)NiPr]₂Si and [iPrNC(NiPr₂)NiPr]₂Si Towards Me₃SiN₃ and PhSCH₂N₃

Abstract

Bis(amidinato)silylene 1 and the analogous bis(guanidinato)silylene 2 reacted with Me3SiN3 to form compounds 3 [a five‐coordinate silicon(IV) complex with an Si=N double bond] and 4 [a four‐coordinate silicon(IV) complex with an Si=N double bond], respectively. For compound 3, a dynamic equilibrium between a five‐ and four‐coordinate silicon(IV) species in solution was observed (at –95 °C, these species are stable on the NMR spectroscopic timescale), whereas 4 is four‐coordinate in solution. Treatment of 1 with PhSCH2N3 afforded compound 5 (isolated as 5a·5b·0.5n‐C6H14), which is a cocrystallizate of the diastereomers 5a and 5b with half an n‐hexane molecule in the asymmetric unit. The diastereomers 5a and 5b [six‐coordinate silicon(IV) complexes with an unsubstituted methyleneamido ligand and an SiN5S skeleton] differ only in their interchanged positions of their thiophenolato and methyleneamido ligands. In solution, a dynamic equilibrium between 5a and 5b was observed.

A closer look into close packing: pentacoordinated silicon in a high-pressure polymorph of danburite

“…To the best of our knowledge, danburite-II is the first example of a high-pressure phase possessing silicon in a fivefold coordination only. Moreover, the geometry of a trigonal bipyramid has not previously been reported before for silicates, although it is known in metal-organic compounds (Rappoport & Apeloig, 1998;Baus et al, 2013;Wagler et al, 2014;Mü ck et al, 2016).…”

Reactions of main group compounds with azides forming organic nitrogen-containing species

“…117 In 2015, Tacke et al studied the reactivity of silylenes Si9 towards azides (Scheme 65d). 118 Treatment of bis(amidinato)silylene Si9a with TMSN 3 afforded the five-coordinate silaimine compound Si9a-P1 in 69% yield. The reaction of Si9a with PhSCH 2 N 3 resulted in the formation of Si9a-P2 featuring the six-coordinate Si center via a rearrangement similar to the formation of Si8-P2 .…”

A Theoretical Investigation of Novel Sila- and Germa-Spirocyclic Imines and Their Relevance for Electron-Transporting Materials and Drug Discovery

“…Conspicuously, the negative NICS(0.5) value above Si 6 in TSISSNU-19 is 1.17 ppm larger than the NICS(1) value. (2) As is also apparent in Table 14, the isotropic NICS values above the ring plane and closer to the spiro center Si 6 ununiformly start in both TSISSNU-19 and TISSNU-19, with positive NICS) iso values indicating anti-aromatic character, which then change to negative and small values (<1 ppm), signifying very weak diamagnetic aromatic character (nonaromatic). ( 3) The out-of-plane zz-components of the shielding tensor NICS zz values in Table 15 show generally similar tendency, like (NICS) iso , upon moving to larger distances above the spiro center Si 6 and equally above the ring geometric center, as well as above the reference position of the Bq atoms closer to the spiro center.…”

“…It is widely accepted that the bioisosteric substitution of carbon atoms by silicon in drugs and biologically active molecular systems could lead to a noticeable modification of their initial properties and, in most cases, to an appreciable enhancement of their biological activity and specific functionality. Aside from being less electronegative and possessing a larger atomic radius than carbon, silicon differs from carbon by its hypervalency [1,2] and its capability for forming 5-and 6-coordinated complexes.…”