A Two‐Coordinate Cyclic (Alkyl)(amino)silylene: Balancing Thermal Stability and Reactivity

Abstract

Ac rystalline two-coordinate cyclic (alkyl)-(amino)silylene (1)w as successfully synthesized and isolated. Its 29 Si NMR and UV/Vis spectra indicate that the electronic properties of 1 fall between those of cyclic dialkylsilylenes and diaminosilylenes.A tv ery low temperature,t he color of as olution of 1 turned from colorless to yellow,w hichw as monitored by UV/Vis spectroscopy. DFT calculations supported the hypothesis that head-to-head dimers (disilenes) with avery long Si-Si distance are formed at such lowtemperatures. Although 1 is thermally stable,i tr eadily undergoes cycloadditions,S i ÀHi nsertions,a nd photochemical reactions with benzenesimilar to dialkylsilylenes.Athigher temperatures, 1 is also susceptible to intermolecular benzylic C À Hi nsertion reactions,aswell as unprecedented dehydrogenation reactions with cyclohexa-1,4-diene and 9,10-dihydroanthracene to afford benzenea nd anthracene,respectively.

Exceptionally Strong Electron‐Donating Ability of Bora‐Ylide Substituent vis‐à‐vis Silylene and Silylium Ion

“…Heterocyclic silylene 2 is stable in solution at RT and was isolated as highly air-sensitive reddish orange crystals from aconcentrated THF solution at 25 8 8C(63 %yield). In the 29 Si-NMR spectrum, abroad signal appears at significantly downfield (295.4 ppm), which is in good agreement with the formation of the two-coordinate silylene 2.T his signal is considerably downfield compared to the chemical shifts of NHSis II and III (78-112 ppm), [6] but in the similar range as bis-ylide-stabilized silylene IV (213 ppm), [11] (amino)(ylide)silylene V (200 ppm), [12] cyclic alkyl(amino)silylene (275 ppm) [20] and dithiolate silylene (285 ppm). [21] Nevertheless it is far upfield compared to acyclicm ono(amino)silylenes (440-443 ppm) [19c, 22] or cyclic dialkylsilylene (567 ppm).…”

“…In the 29 Si-NMR spectrum, abroad signal appears at significantly downfield (295.4 ppm), which is in good agreement with the formation of the two-coordinate silylene 2.T his signal is considerably downfield compared to the chemical shifts of NHSis II and III (78-112 ppm), [6] but in the similar range as bis-ylide-stabilized silylene IV (213 ppm), [11] (amino)(ylide)silylene V (200 ppm), [12] cyclic alkyl(amino)silylene (275 ppm) [20] and dithiolate silylene (285 ppm). Heterocyclic silylene 2 is stable in solution at RT and was isolated as highly air-sensitive reddish orange crystals from aconcentrated THF solution at 25 8 8C(63 %yield).…”

A Stable N‐Hetero‐Rh‐Metallacyclic Silylene

“…In the 29 Si NMR spectrum, ad oublet of doublets appears significantly downfield (d = 302 ppm, J SiRh = 34.7 Hz, J SiP3 = 26.5 Hz) compared to that observed for the precursor 4 (d = 21.7 ppm, dddd, J SiRh = 92.3 Hz, J SiP = 214.2, 50.2, and 23.8 Hz), which is in good agreement with at wo-coordinate silylene moiety in 5.This signal is also considerably downfield compared to the chemical shifts of NHSi species II-V (d = 78-213 ppm), [11][12][13][14][15][16] but falls in the range of cyclic (amino)-(bora-ylide)silylene VI (d = 296 ppm), [17] cyclic alkyl-(amino)silylene VII (d = 275 ppm), [18] and dithiolate silylene (d = 285 ppm). In the 29 Si NMR spectrum, ad oublet of doublets appears significantly downfield (d = 302 ppm, J SiRh = 34.7 Hz, J SiP3 = 26.5 Hz) compared to that observed for the precursor 4 (d = 21.7 ppm, dddd, J SiRh = 92.3 Hz, J SiP = 214.2, 50.2, and 23.8 Hz), which is in good agreement with at wo-coordinate silylene moiety in 5.This signal is also considerably downfield compared to the chemical shifts of NHSi species II-V (d = 78-213 ppm), [11][12][13][14][15][16] but falls in the range of cyclic (amino)-(bora-ylide)silylene VI (d = 296 ppm), [17] cyclic alkyl-(amino)silylene VII (d = 275 ppm), [18] and dithiolate silylene (d = 285 ppm).…”

“…[6][7][8][9][10] In addition to the classical NHSi compounds II [11][12][13] and III, [14] other stable cyclic silylenes IV-VIII,w ith various substitution patterns,h ave been synthesized. [15][16][17][18][19] Furthermore,i th as been clearly established that the nature of the substituents (electronegativity, s-donating ability, bulkiness etc.) has as ignificant influence on their properties and reactivity.…”

Bonding Relationship between Silicon and Germanium with Group 13 and Heavier Elements of Groups 14–16

“…The earlier reported examples of disilenes had either a π‐donor (e. g. amino group) or a π‐acceptor group (e. g. boryl, anthryl or transition metal) [21] . The reaction of 2‐aminodisilenide ( 11 ) [22] with B ‐chloro‐9‐borabicyclo[3.3.1]nonane and isopropyl bromide gave disilenes 12 (59% yield) and 13 (40% yield), respectively (Scheme 6).…”