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

Abstract

A borylidene–phosphorane, the lightest phosphoranylidene, which is stabilized by an N‐heterocyclic carbene ligand, was synthesized and fully characterized. Experimental electron density analysis and DFT calculations indicate an enhanced ylene character (rather than an ylide character) with an exceptionally strong B→P π‐back bonding related to the less electronegative boron compared to phosphorus.

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

“…[12] Since the first isolation of ab orylene stabilized by two cyclic alkyl-amino carbenes (cAAC) VII by Bertrand et al, [13] several stable borylene complexes with different ligands have been described VIII, IX. [16,17] Of particular interest, these boron species,b eing isoelectronic with amines,p resent an ucleophilic three-coordinate boron center with al one-pair, [13,14] and it has been clearly demonstrated that they can be used as s-donating ligands for transition metals. [16,17] Of particular interest, these boron species,b eing isoelectronic with amines,p resent an ucleophilic three-coordinate boron center with al one-pair, [13,14] and it has been clearly demonstrated that they can be used as s-donating ligands for transition metals.…”

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

“…[26] These results clearly demonstrate the remaining silanone character of 2 despite its significant electronic perturbation by the strongly electrondonating amino and phosphonium bora-ylide substituents. Therefore,t he Si1ÀO1 and PÀBbond lengths are elongated and the Si1ÀBbond length is shorten (Si1ÀO1 1.553 ,P ÀB1 .852 ,S i1ÀB1 .865 ) relative to those observed for 2 (Si1 À O1 1.5432 (12) ,B À P 1.8175 (16) ,S i1 À B1 .8985 (15) ;F igure 5, left). Although no significant NMR data differences were observed between 8 ( 29 Si NMR:7 0.9 and 77.7 ppm, 11 (3);C 1-P1-B1 133.15 (15),N 2-P1- C11 14.29(14), N2-P1-B1 110.32- (14).…”

“…[6] Recently,e asy-to-handle silanones stabilized as donor-acceptor or donor complexes,h ave been reported. Herein we report that the introduction of as trongly donating phosphonium boraylide substituent considerably extends the lifetime of silanone 2 (t 1/2 = 4days,a tR T), which allows easier manipulation to study its properties and reactivity.Recently,w eh ave described that the electropositive boron-based substituent (phosphonium bora-ylide), [16,17] with an exceptionally strong electron donating character,i s able to efficiently stabilize highly reactive species such as Nheterocyclic silylene 1,the related silylium ion and transitionmetal-silylene complexes featuring at rigonal-planar geometry around the silicon center. [15] Therefore,t heir synthetic use is still limited because of the scarcity and limited lifetime (0.5-5 h, at RT for VI).…”

“…Recently,w eh ave described that the electropositive boron-based substituent (phosphonium bora-ylide), [16,17] with an exceptionally strong electron donating character,i s able to efficiently stabilize highly reactive species such as Nheterocyclic silylene 1,the related silylium ion and transitionmetal-silylene complexes featuring at rigonal-planar geometry around the silicon center. [18] We thus have considered the use of the same set of substituents for the stabilization of the silanone moiety.T aking into account the better donating ability of phosphonium bora-ylide function than that of classical (carbo)ylides, [18] we can expect abetter stabilization effect with this substituent set than that used for the previously persistent silanone VI.…”

“…1-40.8 ppm). [16] The 11 BNMR resonance is shifted upfield at d = À24.3 ppm (J PB = 190.2 Hz) relative to that of silylene 1 (15.3 ppm), [15] suggesting ad ecreased p-interaction between bora-ylide function and the silicon center.The IR spectroscopy of 2 shows asignal at 1130 cm À1 in C 6 D 6 which was assigned to the Si=O stretching. The 31 PNMR spectrum displays aquartet signal at d = 48.3 ppm ( 1 J PB = 190.9 Hz) in the same region as observed for the starting silylene 1 (38.0 ppm).…”