1,1,1-Trisborylalkanes as Precursors for Dicarbapentaboranes(5) − Synthesis, Reactivity, and Structures ofcloso-1,5-Bis(neopentyl)-2,3,4-trichloro-1,5-dicarbapentaborane and Its Derivatives

Abstract

Keywords: Alkynes / Boranes / Boron / Catechol / HydroborationThe treatment of 3,3-dimethyl-1-butynyllithium with boron trichloride followed by double hydroboration with HBCl 2 afforded 1,1,1-tris(dichloroboryl)-3,3-dimethylbutane (1a), characterized as its catechol derivative 1b. Analogously, three isomers (3a, 4a, and 5a) were obtained with trimethylsilylacetylide and identified as catechol derivatives 3b, 4b, and 5b. On heating, 1a formed 2,3,4-trichloro-1,5-dicarba-closopentaborane(5) (6a) with elimination of boron trichloride.[a]

exo ‐ endo Isomerism of Carboranes: Unusual Geometries of C 2 B 5 X 7 ( X =Cl, Br) and C 2 B 7 Cl 9Keller1, Conrad2, Hofmann3 2023ChemistrySelect

“…One of the few alternative routes to five-vertex closocarboranes was reported 2002 by Siebert et al with the synthesis and X-ray structure of 1,5-dineopentyl-2,3,4-trichloro-1,5-dicarba-closo-pentaborane(5) by pyrolysis of a bulky tris(dichloroboryl)alkane. [12] Both the 11 B (δ = 22.1 ppm) and 13 C (δ = 94 ppm) chemical shifts are in good agreement with the signals found for 1 and 3.…”

exo ‐ endo Isomerism of Carboranes: Unusual Geometries of C 2 B 5 X 7 ( X =Cl, Br) and C 2 B 7 Cl 9Keller1, Conrad2, Hofmann3 2023ChemistrySelect

“…One of the few alternative routes to five-vertex closocarboranes was reported 2002 by Siebert et al with the synthesis and X-ray structure of 1,5-dineopentyl-2,3,4-trichloro-1,5-dicarba-closo-pentaborane(5) by pyrolysis of a bulky tris(dichloroboryl)alkane. [12] Both the 11 B (δ = 22.1 ppm) and 13 C (δ = 94 ppm) chemical shifts are in good agreement with the signals found for 1 and 3.…”

A `tetrameric' 3,4-di-p-tolyl-1,2,5-oxadiborole derivative

“…1, different BÐO bond lengths are observed. The BÐO distances between atom O1 and the sp 2 -hybridized atoms B1 and B2 [1.353 (2) and 1.363 (2) A Ê , respectively] lie in the range of comparable BÐO bond lengths found in catecholborylalkanes, C 6 H 4 O 2 BR (BÐO = 1.39 A Ê ; Bayer et al, 2002), and in oxadiboroles [BÐO = 1.374 (3) A Ê ; Ko È ster et al, 1994]. The B2ÐO2, B1ÐO3, B6ÐO4 and B8ÐO5 bond lengths in (II) are elongated [1.414 (2)±1.433 (2) A Ê ] because of the threefold coordination of the O atoms.…”

Small boranes, carboranes, and heterocarboranes

“…For the synthesis of 9a, the tris(dichloroboryl)neopentylmethane (18a) is needed [13]. It is obtained via lithiation of 3,3-dimethyl-1-butyne, followed by boron/lithium exchange to give the intermediate Me 3 C-C≡C-BCl 2 , which then is hydroborated with HBCl 2 prepared in situ.…”

“…The 11 B NMR signal of 9b is shifted to δ = 17.3. Further replacements of the chloro substituents of 9a were possible with Me 3 CC 2 Li, PhC 2 Li, and Me 3 SiNMe 2 to give the tris(acetylenic) derivatives 9c and 9d, as well as the trisamino compound 9e [13].…”

exo ‐ endo Isomerism of Carboranes: Unusual Geometries of C 2 B 5 X 7 ( X =Cl, Br) and C 2 B 7 Cl 9Keller1, Conrad2, Hofmann3 2023ChemistrySelect

“…One of the few alternative routes to five-vertex closocarboranes was reported 2002 by Siebert et al with the synthesis and X-ray structure of 1,5-dineopentyl-2,3,4-trichloro-1,5-dicarba-closo-pentaborane(5) by pyrolysis of a bulky tris(dichloroboryl)alkane. [12] Both the 11 B (δ = 22.1 ppm) and 13 C (δ = 94 ppm) chemical shifts are in good agreement with the signals found for 1 and 3.…”

A `tetrameric' 3,4-di-p-tolyl-1,2,5-oxadiborole derivative

“…1, different BÐO bond lengths are observed. The BÐO distances between atom O1 and the sp 2 -hybridized atoms B1 and B2 [1.353 (2) and 1.363 (2) A Ê , respectively] lie in the range of comparable BÐO bond lengths found in catecholborylalkanes, C 6 H 4 O 2 BR (BÐO = 1.39 A Ê ; Bayer et al, 2002), and in oxadiboroles [BÐO = 1.374 (3) A Ê ; Ko È ster et al, 1994]. The B2ÐO2, B1ÐO3, B6ÐO4 and B8ÐO5 bond lengths in (II) are elongated [1.414 (2)±1.433 (2) A Ê ] because of the threefold coordination of the O atoms.…”

Small boranes, carboranes, and heterocarboranes

“…For the synthesis of 9a, the tris(dichloroboryl)neopentylmethane (18a) is needed [13]. It is obtained via lithiation of 3,3-dimethyl-1-butyne, followed by boron/lithium exchange to give the intermediate Me 3 C-C≡C-BCl 2 , which then is hydroborated with HBCl 2 prepared in situ.…”

“…The 11 B NMR signal of 9b is shifted to δ = 17.3. Further replacements of the chloro substituents of 9a were possible with Me 3 CC 2 Li, PhC 2 Li, and Me 3 SiNMe 2 to give the tris(acetylenic) derivatives 9c and 9d, as well as the trisamino compound 9e [13].…”

exo ‐ endo Isomerism of Carboranes: Unusual Geometries of C 2 B 5 X 7 ( X =Cl, Br) and C 2 B 7 Cl 9Keller1, Conrad2, Hofmann3 2023ChemistrySelect

“…One of the few alternative routes to five-vertex closocarboranes was reported 2002 by Siebert et al with the synthesis and X-ray structure of 1,5-dineopentyl-2,3,4-trichloro-1,5-dicarba-closo-pentaborane(5) by pyrolysis of a bulky tris(dichloroboryl)alkane. [12] Both the 11 B (δ = 22.1 ppm) and 13 C (δ = 94 ppm) chemical shifts are in good agreement with the signals found for 1 and 3.…”

A `tetrameric' 3,4-di-p-tolyl-1,2,5-oxadiborole derivative

“…1, different BÐO bond lengths are observed. The BÐO distances between atom O1 and the sp 2 -hybridized atoms B1 and B2 [1.353 (2) and 1.363 (2) A Ê , respectively] lie in the range of comparable BÐO bond lengths found in catecholborylalkanes, C 6 H 4 O 2 BR (BÐO = 1.39 A Ê ; Bayer et al, 2002), and in oxadiboroles [BÐO = 1.374 (3) A Ê ; Ko È ster et al, 1994]. The B2ÐO2, B1ÐO3, B6ÐO4 and B8ÐO5 bond lengths in (II) are elongated [1.414 (2)±1.433 (2) A Ê ] because of the threefold coordination of the O atoms.…”

Small boranes, carboranes, and heterocarboranes

“…For the synthesis of 9a, the tris(dichloroboryl)neopentylmethane (18a) is needed [13]. It is obtained via lithiation of 3,3-dimethyl-1-butyne, followed by boron/lithium exchange to give the intermediate Me 3 C-C≡C-BCl 2 , which then is hydroborated with HBCl 2 prepared in situ.…”

“…The 11 B NMR signal of 9b is shifted to δ = 17.3. Further replacements of the chloro substituents of 9a were possible with Me 3 CC 2 Li, PhC 2 Li, and Me 3 SiNMe 2 to give the tris(acetylenic) derivatives 9c and 9d, as well as the trisamino compound 9e [13].…”