Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)

Abstract

We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2− dianion to form the [closo-1-CB11H12]− anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70–90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]− to [closo-1-CB11H12]−, and CCl2 and CBr2, which require more.

Synthesis of closo-CB11H12– Salts Using Common Laboratory Reagents

“…The precursor can then be used to synthesize the [CB 11 H 12 ] − anion, by insertion of CCl 2 sourced from chloroform, as previously documented by Michl and co-workers . This method was believed to be the safer option than the alternatives that use toxic reagents to form the initial carbon insertion into decaborane (B 10 H 14 ) ,,, or use expensive niche compounds such as CF 3 SiMe 3 . , Initially, the Michl method (Scheme d) was used where Me 3 NH­[B 11 H 14 ] was deprotonated to [B 11 H 13 ] 2– by NaH, before carbene insertion. NaOEt formed in situ, by deprotonation of ethanol by NaH, was then used to deprotonate CHCl 3 , forming CCl 2 .…”

“…However, after deprotonation of [B 11 H 14 ] − to [B 11 H 13 ] 2– by NaH and elimination of the trimethylamine cation, dihalocarbene, (CX 2 ), is formed in situ and inserts into the cage. CX 2 is sourced by (d) the treatment of CHCl 3 with a base to form CCl 2 or (e) the formation of CF 2 from CF 3 SiMe 3 with either a pressure tube or using LiCl/TBAB as an initiator . (RNCs most commonly used are tert -butyl isocyanide or cyclohexyl isocyanide) TBAB = tetrabutylammonium bromide.…”

“…Deprotonation of [B 11 H 14 ] − to [B 11 H 13 ] 2– with NaH in tetrahydrofuran (THF) followed by the insertion of dichlorocarbene from chloroform (CHCl 3 ) was found to synthesize [CB 11 H 12 ] − (Scheme d) . However, this method must be undertaken under inert gas, has a low overall yield (∼20–25%), is difficult to scale up, and produces side products such as the [2-EtO-CB 11 H 12 ] − and [2-Cl-CB 11 H 12 ] − anions. , Two similar methods using difluorocarbene (CF 2 ) to insert into [B 11 H 13 ] 2– were published in 2019 (Scheme e). , Both of them use trimethyl­(trifluoromethyl)­silane (CF 3 SiMe 3 ) or Ruppert’s reagent as a source of difluorocarbene to be inserted in a one-pot synthesis (Scheme e). , Similar to other syntheses using Me 3 NH­[B 11 H 14 ], NaH is used to deprotonate [B 11 H 14 ] − to [B 11 H 13 ] 2– , before reacting with CF 3 SiMe 3 in an Ace pressure tube to ensure the volatile reagent’s evaporation, at 60 °C for 3 days . An overall yield of 95% could be achieved, with the reaction successfully scaled from 1.5 g of Me 3 NH­[B 11 H 14 ] to 15 g of starting material.…”

Polyhalogenated Bicyclo[1.1.1]pentane-1,3-dicarboxylic Acids

“…Minima found by MM2 were optimized using the B3LYP-D3BJ/6-311+G­(d,p) level of theory, which was also used in our previous work . The B3LYP functional has been shown to accurately describe reaction pathways for cage compounds, , while the presence of nonbonding interactions necessitated the use of D3BJ corrections …”

“…Minima found by MM2 were optimized using the B3LYP-D3BJ/6-311+G(d,p) level of theory, which was also used in our previous work. 33 The B3LYP functional has been shown to accurately describe reaction pathways for cage compounds, 40,41 while the presence of nonbonding interactions necessitated the use of D3BJ corrections. 42 The chlorination and reduction pathways and acidities were investigated by using the same B3LYP-D3BJ/6-311+G(d,p) level of theory with the SMD implicit solvent model (benzene for reduction, water for acidity), 43 including zero-point vibrations.…”