Reaction of a 14-Vertex Carborane with Nucleophiles: Formation of nido-C₂B₁₂, nido-C₂B_11, and closo-CB₁₁ Carborane Anions

Abstract

Nucleophilic reactions of a 14-vertex closo-carborane are reported. 2,3-(CH(2))(3)-2,3-C(2)B(12)H(12) (1) reacts with MeOH at 70 degrees C to give closo-CB(11) anions [1,2-(CH(2))(3)CH(OMe)-1-CB(11)H(10)](-) ([2a](-)), [1,2-(CH(2))(2)CH(OMe)CH(2)-1-CB(11)H(10)](-) ([2b](-)), and [1,2-(CH(2))(2)CH horizontal lineCH-1-CB(11)H(10)](-) ([2c](-)). It is suggested that [2c](-) is an intermediate for the isomerization from [2a](-) to [2b](-). Treatment of 1 with MeOH/Me(3)N, (t)BuOK or LiNMe(2) affords nido-C(2)B(12) species [8,9-(CH(2))(3)-mu-11,12-(Nu)BH-8,9-C(2)B(11)H(11)](-) (Nu = MeO ([3a](-)), (t)BuO ([3b](-)), and Me(2)N ([3c](-))). In the presence of acid such as HCl, anions [3](-) are converted to 1. However, [3](-) undergo deboration reaction, in the presence of bases, to generate a nido-C(2)B(11) anion [8,9-(CH(2))(3)-8,9-C(2)B(11)H(12)](-) ([4](-)) that can also be formed directly from the reaction of 1 with excess CsF or piperidine. Mechanistic studies show that [3a](-) is the first intermediate in the reaction of 1 with MeOH and [4](-) is unlikely an intermediate.

Selective cage boron/carbon extrusion reaction of 13-vertex carborane μ-1,2-(CH2)3–1,2-C2B11H11: formation of nido-CB10, closo-CB10, and closo-C2B10 species

“…Complex 3 has a very low solubility in common polar solvents such as CH 2 Cl 2 , MeOH, THF and acetone, but is soluble in DMSO and Py. The proton-coupled 11 B NMR spectrum exhibited a 1 : 9 : 1 pattern with all peaks being broad and unresolved. 16 The signal of the characteristic CH unit attached to two boron atoms was observed at 0.52 ppm in the 1 H NMR spectrum and at 14.9 ppm in the 13 C NMR spectrum.…”

“…10 14-Vertex carboranes can react with nucleophiles to yield either the closo-CB 11 monoanions in MeOH solution or deborated product nido-C 2 B 11 anion in THF. 11 Such versatile reactivities toward nucleophiles prompt us to investigate the effects of nucleophiles on the formation of products. It is found that 13-vertex carboranes can be selectively converted into nido-CB 10 , closo-CB 10 , and closo-C 2 B 10 species under appropriate reaction conditions.…”

Supercarboranes: Achievements and perspectives

“…Reaction of μ-2,3-(CH 2 ) 3 -2,3-C 2 B 12 H 12 with MeOH proceeds extremely sluggishly at ambient temperature, and is incomplete after one month. This reaction can be accelerated by heating at 70°C and completed in 2 d, affording the 12-vertex CB 11 -anions [μ-1,2-(CH 2 ) 3 CH(OMe)-1-CB 11 H 10 ] -, [μ-1,2-(CH 2 ) 2 CH(OMe)CH 2 -1-CB 11 H 10 ] -, and [μ-1,2-(CH 2 ) 2 CH=CH-1-CB 11 H 10 ] -(Scheme 10) [27]. NMR experiments suggest that [μ-1,2-(CH 2 ) 3 CH(OMe)-1-CB 11 H 10 ] -is initially formed and isomerized to [μ-1,2-(CH 2 ) 2 CH(OMe)CH 2 -1-CB 11 H 10 ] -upon heating probably via a [μ-1,2-(CH 2 ) 2 CH=CH-1-CB 11 H 10 ] -intermediate.…”

“…These complexes have very similar structural features with the nucleophiles bound to the bridging boron atom, which is the most electrophilic site in the 14-vertex closo-carborane. Treatment of the 14-vertex nido-C 2 B 12 monoanions ) 3 -μ-11,12-(Nu)BH-8,9-C 2 B 11 H 11 ] -(Nu = MeO, tBuO, or Me 2 N) with HCl regenerates the CAd 14-vertex closo-carborane μ-2,3-(CH 2 ) 3 -2,3-C 2 B 12 H 12 [27].…”

Reaction of N-heterocyclic carbenes with 13-vertex closo-carboranes: synthesis and structural characterization of zwitterionic salts of 13-vertex nido-carboranes

“…5 1,2-(CH 2 ) n -1,2-C 2 B 11 H 11 (n = 3, 4) reacts also with various nucleophiles to give the cage boron and/or carbon extrusion products closo-CB 11 − , nido-CB 10 − , closo-CB 10 − , or closo-C 2 B 10 depending on the nature of the nucleophiles. [15][16][17][18][19] On the other hand, 12-vertex o-carboranes react with Nheterocyclic carbenes (NHCs) to give the imidazolium salts of carborane anions, 20 or 1 : 2 adducts of nido-carboranecarbene, 21 or zwitterionic salts of imidazolium nido-carboranyl 22 depending upon the size of NHCs. The results show that a sterically demanding NHC, 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, can stabilize the first intermediate in the deboration reaction of o-carboranes with nucleophiles.…”