Carbon Extrusion in 1,2‐Dicarba‐<i>closo</i>‐dodecaboranes: Regioselective Boron Substitution in Ten‐Vertex <i>closo</i>‐Monocarbaborane Anions

Anders als ikosaedrische Carborane gehen 13‐eckige Carborane bei der Reaktion mit Nucleophilen keine Deborierung ein, sondern extrudieren unter Clusterverengung ein Käfig‐Kohlenstoffatom und bilden ikosaedrische Monocarboran‐Anionen. Im vorgeschlagenen Mechanismus spaltet der nucleophile Angriff eine CKäfig‐CKäfig‐Bindung und bildet neue CKäfig‐B‐Bindungen, um die Integrität des Clusters aufrechtzuerhalten, bevor eine Wasserstoffwanderung das ikosaedrische Endprodukt erzeugt (siehe Schema).

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Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions

Bakardjiev

Holub

Macháček

et al. 2015

Angewandte Chemie

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Reactions between the arachno-6,9-C 2 B 8 H 14 (1)d icarbaborane and acyl chlorides,R COCl (2), are subject to stereocontrol that completely changes the nature of the reaction products.W hile most chlorides produce the 8-R-nido-7,8,9-C 3 B 8 H 11 (3)t ricarbollides (by skeletal alkylcarbonation = SAC), bulky RCOCls (2; where R = 1-adamantyl, 2a;1 -mesityl, 2b;9 -anthranyl, 2c;1 -naphthyl, 2d)i n1 ,2-dichloroethane (DCE) in the presence of triethylamine at 40-60 8 8Cg ave as eries of entirely different 1-R-2-CH 3 -closo-1,6-C 2 B 8 H 8 (4)d icarbaboranes upon acidification with conc.H 2 SO 4 (by exosleletal alkylmehylation = EAM). Both types of reactions seem to proceed via ac ommon [8-R-nido-7,8,9-C 3 Recently,wehave demonstrated that reactions of the [arachno-6,9-C 2 B 8 H 13 ] À (1 À )a nion and various acyl chlorides,R COCl (2), in the presence of tert-amine bases (Et 3 N [1] or proton sponge [2] )i nC H 2 Cl 2 ,f ollowed by in situ acidification of the anion 3 À thus formed with conc. H 2 SO 4 ,g enerate as eries of neutral alkyl and aryl tricarbollides (11-vertex nido tricarbaboranes) [3] 8-R-nido-7,8,9-C 3 B 8 H 11 (3)( where R = linear alkyl and simple aryl groups, see also pathway Ao fS cheme 1). These so-called skeletal alkylcarbonation (SAC) reactions are consistent with an aldol-type condensation between the RCO group and openface hydrogen atoms on the dicarbaborane 1, [2] which is associated with the insertion of the RC unit into the structure of 1 À under elimination of three extra hydrogen atoms as H 2 O and HCl. Ther eactions thus result in an effective Rtricarbaborane cross-coupling.H owever,j ust recently we have found that reaction in Equation (1) surprisingly proceeds in an entirely different manner when acyl chlorides with bulky (sterically demanding) R-substituents are used as reaction components.Initial results of this study are presented herein.Scheme 1( pathway B) shows that treatment of the arachno-6,9-C 2 B 8 H 14 (1)dicarbaborane with bulky acyl chlorides,R COCl (2)( where R = 1-adamantyl = adm, 2a;1 -mesityl = mes, 2b;9 -anthranyl = anth, 2c;1 -naphthyl = naph, 2d)i n1 ,2-dichloroethane (DCE) in the presence of triethylamine (deprotonation agent generating in situ the 1 À Scheme 1. Stereocontrol in COCl reactions. Most chlorides (path A, SAC reactions) produce tricarbollides 8-R-nido-7,8,9-C 3 B 8 H 11 (3)w hile bulky chlorides (path B) induce cage rearrangement with resulting alkylmethylation (EAM) to form the disubstituted 1-R-2-CH 3 -closo-1,6-C 2 B 8 H 8 (4)c ompounds.

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Carbon Extrusion in 1,2‐Dicarba‐closo‐dodecaboranes: Regioselective Boron Substitution in Ten‐Vertex closo‐Monocarbaborane Anions

Cited by 7 publications

References 29 publications

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K₂[3‐NC‐closo‐B₁₁F₁₀]

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K₂[3‐NC‐closo‐B₁₁F₁₀]

Reaction of 13‐Vertex Carboranes with Nucleophiles: Unprecedented Cage‐Carbon Extrusion and Formation of Monocarba‐closo‐dodecaborate Anions

Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions

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Carbon Extrusion in 1,2‐Dicarba‐closo‐dodecaboranes: Regioselective Boron Substitution in Ten‐Vertex closo‐Monocarbaborane Anions

Cited by 7 publications

References 29 publications

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K2[3‐NC‐closo‐B11F10]

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K2[3‐NC‐closo‐B11F10]

Reaction of 13‐Vertex Carboranes with Nucleophiles: Unprecedented Cage‐Carbon Extrusion and Formation of Monocarba‐closo‐dodecaborate Anions

Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions

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Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K₂[3‐NC‐closo‐B₁₁F₁₀]

Kohlenstoff‐Extrusion/Cluster‐Kontraktion: Synthese des fluorierten Cyano‐closo‐undecaborats K₂[3‐NC‐closo‐B₁₁F₁₀]