Valence isomerization of 2-phospha-4-silabicyclo[1.1.0]butane: a high-level ab initio study

Abstract

The rearrangements for 2-phospha-4-silabicyclo[1.1.0]butane, analogous to the valence isomerization of the hydrocarbons bicyclobutane, 1,3-butadiene, and cyclobutene, were studied at the (U)QCISD(T)/6-311+G**//(U)QCISD/6-31G* level of theory. The monocyclic 1,2-dihydro-1,2-phosphasiletes are shown to be the thermodynamically preferred product, in contrast to the isomerization of the hydrocarbons, which favors the 1,3-butadiene structure. Furthermore, an unprecedented direct isomerization pathway to the 1,2-dihydro-1,2-phosphasiletes was identified. This pathway is competitive with the isomerization via the open-chain butadienes and becomes favorable when electron-donating substituents are present on silicon.

mTRAQ‐based quantification of potential endometrial carcinoma biomarkers from archived formalin‐fixed paraffin‐embedded tissues

“…For example, reaction of alkynes with the second‐generation Grubbs catalyst gives stable η 3 ‐vinylcarbene complexes ( 1 , Mes=2,4,6‐Me 3 C 6 H 2 ) that form after rearrangement of the initial ruthenium cyclobutenes ( B ) 6. 7 These puckered metal η 3 ‐vinylcarbene complexes8 ( C ) are highly potent and represent the key intermediate in enyne metathesis,9 alkyne polymerization (via D ),10 and the versatile Fischer carbene mediated Dötz (benzannulation) reaction (which involves complexes such as 2 ) 11. 12…”

Vielseitige Reaktivität eines elektrophilen Phosphasilens gegenüber anionischen Nukleophilen: Substitution oder Metall‐Amino‐Austausch

“…34] Die Ringçffnung des resultierenden Ylids[8]-Me,d ie zu einem instabilen 1-Phospha-1,3,4-trisilabutadien[9]-Me führt, ist nur leicht endergonisch mit DG =+6.3 kcal mol À1 ,w enngleich mit einer erheblichen Energiebarriere von DG ¼ 6 =+ 21.2 kcal mol À1 .D er letzte Schritt des Weges zum Bicyclo-[1.1.0]butan-Analogon 5-Me überkompensiert dies,indem er mit DG = À28.1 kcal mol À1 exergonisch ist, in Übereinstimmung mit bekannten Isomerisierungen von 1,3-Butadien zu Bicyclo[1.1.0]butan in Systemen der dritten Periode [35]. Ein alternativer Mechanismus über direkte Extrusion von SiR 2 aus[4]i st unwahrscheinlich, basierend auf der viel hçheren Energiebarriere von DG ¼ 6 =+38.3 kcal mol À1 .Wiez ue rwarten ist die SiTip 2 -Einheit, die im experimentellen Fall freigesetzt wird, zu kurzlebig für die Beobachtung:Zusätzlich zu den Signalen des Produkts 5 zeigt die Roh-Reaktionsmischung jedoch zwei weitere29 Si-NMR-Signale bei d = À21.5 und À25.1 ppm im Verhältnis 2:3, die wir dem Diastereomerengemisch von 10 zuordnen (Schema 2) [13].…”

From a Si3‐Cyclopropene to a Si3S‐Bicyclo[1.1.0]butane to a Si3S‐Cyclopropene to a Si3S2‐Bicyclo[1.1.0]butane: Back‐and‐Forth, and In‐Between

“…However,t hat was of alittle help because it resulted in amixture of several isomers of 3-d 6 ,inwhich the labeled tBu 2 (CD 3 )Si substituents were scrambled over the cyclic sp 3 -Si, two cyclic sp 2 -Si and Satoms. [8] Such nonselective distribution of the deuterium label in 3-d 6 is apparently indicative of competing pathways operating in the isomerization process.O ne such pathway may involve the initial bicyclo[1.1.0]butane 2 (0 kcal mol À1 , for the H-substituted model) [9] ring opening with the formation of intermediate 1-thia-2,3,4-trisilabuta-1,3-diene D 2 Si1 = Si3(H)-Si2(H) = S1 (Int1, + 5kcal mol À1 ), [10] followed by its ring closure forming the final cyclopropene 3 (+ 15 kcal mol À1 )w ith the overall migration of the D-substituent from the bridging position Si1 in 2 to the sulfur atom S1 in 3 ( Figure 1: pathway A). To get more insight into the mechanistic pathways,w en ext performed ak inetic analysis of the thermal isomerization of 2 to 3.…”