Deprotonation of a Borohydride: Synthesis of a Carbene‐Stabilized Boryl Anion

Abstract

An acidic hydride! Thanks to the presence of a π-acceptor cyclic (alkyl)(amino)carbene (CAAC) and of two electron-withdrawing nitrile groups, a borohydride reacts with a base to give a carbenestabilized boryl anion, which reacts with carbon and metal electrophiles at the boron center.

Synthesis of a Tri(gold)boride Complex (Cy3P)B[AuP(o-Tol)3]3

“…The favorable 3 : 3 stoichiometric relation of suitable functions in Cy 3 PBH 2 SiMe 3 on the one hand, and in reagents of the type [(LAu) 3 O] + on the other hand, appeared to offer the right conditions for the envisaged metathesis. It should be noted that similar effects have now been demonstrated for carbene-boranes [1].…”

“…As summarized in a recent publication [1], within only a short period there have been various successful synthetic approaches to generate compounds with boride centers in various coordination environments [2 -4]. Reflecting the general movement in ligand chemistry from tertiary phosphines to carbenes, most of the newly designed systems are based on the latter, which proved to be more variable and more efficient in stabilizing boride functions.…”

From Borane to Borylene without Reduction: Ambiphilic Behavior of a Monovalent Silylisonitrile Boron Species

“…[13] In reports related to this work, the groups of Finze and Bertrand showed that multiple electron-withdrawing cyano substituents at anionic or neutral hydroboron species cause aB ÀHb ond umpolung, which enables deprotonation to dianion VII [14] or the cAACstabilized boryl anion VIII. [15] Inspired by these results we surmised that as ingle cyano group may suffice to induce aB ÀHb ond umpolung in [(cAAC)BH 2 (CN)] [16] (1,c AAC = 1-(2,6-i Pr 2 C 6 H 3 )-3,3,5,5-tetramethylpyrrolidin-2-ylidene) and enable deprotonation. To better understand the nucleophilic nature of the boronbound hydrogens,p artial charges (NBO) were calculated on BH 3 ,[ (cAAC)BH 3 ], and 1 at the BP86/def2-SVP level (see the Supporting Information, Figure S47).…”

“…An X-ray structure analysis of 2 revealed adimeric structure in which the boron centers are sp 2 -hybridized (S(B) = 360.0(2)8 8), and the lithium cations bridge end-on over the cyano ligands ( Figure 2, see Table S1 for selected bond lengths and angles), similarly to VII and VIII. [14,15] Both B À Cbonds in 2 (B1-C1 1.447(3), B1-C21 1.529(3) )are significantly shorter than in the dicyanoboryl anion VIII (1.473(2) and 1.553(2) ,r espectively), [15] pointing to ah igher degree of p-backdonation from the formally anionic boron center to the cyano and cAACligands in 2 than in VIII.P lots of the frontier molecular orbitals (Table S1). [15] Compound 2 also reacted as at ypical boron nucleophile with ar ange of soft, heavier triorganotetrelchlorides,C lER 3 (R = Me,E = Sn;R = Ph, E = Ge,S n, Pb), yielding the corresponding colorless boranes,[(cAAC)BH(CN)(ER 3 )] (4-6;Scheme 1c).…”

“…[14,15] Both B À Cbonds in 2 (B1-C1 1.447(3), B1-C21 1.529(3) )are significantly shorter than in the dicyanoboryl anion VIII (1.473(2) and 1.553(2) ,r espectively), [15] pointing to ah igher degree of p-backdonation from the formally anionic boron center to the cyano and cAACligands in 2 than in VIII.P lots of the frontier molecular orbitals (Table S1). [15] Compound 2 also reacted as at ypical boron nucleophile with ar ange of soft, heavier triorganotetrelchlorides,C lER 3 (R = Me,E = Sn;R = Ph, E = Ge,S n, Pb), yielding the corresponding colorless boranes,[(cAAC)BH(CN)(ER 3 )] (4-6;Scheme 1c). While an umber of germyl-, stannyl-, and plumbylboranes have been reported, they are usually synthesized by salt metathesis of ah aloborane with aL iER 3 precursor [17] rather than by the inverse-polarity reaction of ab oron nucleophile with ClER 3 .…”