Donor-Stabilized Silacyclobutanone: A Precursor of 1-Silaketene via Retro-[2 + 2]-Cycloaddition Reaction at Room Temperature

Abstract

The synthesis of donor-stabilized silacyclobutanone 2 was successfully realized by the reaction of silacyclopropylidene 1 with benzaldehyde in the presence of a Lewis acid catalyst. Of particular interest, silacyclobutanone 2 evolves at room temperature via a retro-[2 + 2]-cycloaddition reaction, leading to an original NHC-stabilized 1-silaketene 4 and cis-stilbene.

Donor/Acceptor‐Stabilized 1‐Silaketene: Reversible [2+2] Cycloaddition with Pyridine and Evolution by an Olefin Metathesis Reaction

“…Complex 8 is sufficiently stable to be isolated as yellow crystals from a toluene solution (yield: 69 %), and it was fully characterized by NMR spectroscopy as well as by X‐ray diffraction analysis (Figure ) . The structure of 8 is similar to that of previously reported NHC‐stabilized 1‐silaketene . Of particular interest, the formation of 8 can be explained by an intramolecular cross‐metathesis reaction involving the silaketene functionality and the vinyl fragment of transient 1‐silaketene 2‐Py .…”

“…Since the discovery of efficient methods to stabilize silanones by coordination of donor/acceptor ( VI ) or donor ligands ( VII ) by Driess et al., remarkable progress has been made in silanone chemistry . We have recently described the synthesis of a donor‐stabilized silacyclobutanone IV , which evolves at room temperature through a [2+2] cycloreversion, leading to a donor‐stabilized 1‐silaketene V (type IX ) and cis ‐stilbene, similar to the “Chauvin intermediate” metallacycle I (Figure ) . However, the irreversible dimerization of 1‐silaketene V via the silanone to afford a thermally stable cyclic siloxane, prevents any application of this unique phenomenon for metal‐free olefin metathesis.…”

The Lightest Element Phosphoranylidene: NHC‐Supported Cyclic Borylidene–Phosphorane with Significant B=P Character

“…Them olecular structure of 3 reveals at rigonal planar geometry around the boron atom (sum of angles at B = 359.38 8;F igure 1). [11b] Thee xceptionally strong p-back donation from the three-coordinate Ba tom to the s* P-N orbitals induces abnormally elongated PÀN2 and PÀN3 bonds (1.7595(6) and 1.7290(7) )c ompared to those observed in related phosphonium ylides, [24] and phosphanylidene-phosphoranes [10] (1.674-1.681 ). Indeed, this bond is much longer than those observed for other borylene complexes with cyclic CAACs( 1.462-1.518 ) [15] or oxazoli-2-ylidenes (1.496-1.511 ) [17] ligands, presenting as ubstantial BÀCm ultiple-bond character.…”

Cyclic (Amino)(Phosphonium Bora‐Ylide)Silanone: A Remarkable Room‐Temperature‐Persistent Silanone

“…[4] Silanones present as trongly polarized Si=Od ouble bond (Si d+ ÀO dÀ )w ith ac onsiderably large bond energy difference between SiO-p and SiO-s bonds, [5] and therefore,t hey easily oligomerize to give polysiloxanes. [7][8][9][10][11] Nevertheless,t he synthesis of stable threecoordinate silanone derivatives remains ad ifficult task, although the heavier analogue germanone III,well kinetically stabilized by bulky aryl substituents,h as been isolated by Matsuo/Tamao et al [12] At present only three examples are reported:1 )the transition-metal-substituted silanone IV, isolated at RT by Filippou et al, [13] 2) the cyclic dialkylsilanone V,c haracterized in situ at À80 8 8Cb yt he group of Iwamoto, [14] and 3) the relatively persistent (amino)-(ylide)silanones VI,r eported by us. [7][8][9][10][11] Nevertheless,t he synthesis of stable threecoordinate silanone derivatives remains ad ifficult task, although the heavier analogue germanone III,well kinetically stabilized by bulky aryl substituents,h as been isolated by Matsuo/Tamao et al [12] At present only three examples are reported:1 )the transition-metal-substituted silanone IV, isolated at RT by Filippou et al, [13] 2) the cyclic dialkylsilanone V,c haracterized in situ at À80 8 8Cb yt he group of Iwamoto, [14] and 3) the relatively persistent (amino)-(ylide)silanones VI,r eported by us.…”

“…[6] Recently,e asy-to-handle silanones stabilized as donor-acceptor or donor complexes,h ave been reported. [7][8][9][10][11] Nevertheless,t he synthesis of stable threecoordinate silanone derivatives remains ad ifficult task, although the heavier analogue germanone III,well kinetically stabilized by bulky aryl substituents,h as been isolated by Matsuo/Tamao et al [12] At present only three examples are reported:1 )the transition-metal-substituted silanone IV, isolated at RT by Filippou et al, [13] 2) the cyclic dialkylsilanone V,c haracterized in situ at À80 8 8Cb yt he group of Iwamoto, [14] and 3) the relatively persistent (amino)-(ylide)silanones VI,r eported by us. [15] Therefore,t heir synthetic use is still limited because of the scarcity and limited lifetime (0.5-5 h, at RT for VI).…”