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George A Olah - One of the best experts on this subject based on the ideXlab platform.
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ab initio giao ccsd t calculated 13c 11b nmr chemical shift relationships in isoelectronic hypercoordinate carbonium and Boronium as well as carbenium and borenium ions
Journal of Physical Chemistry A, 2013Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Good linear correlations between GIAO–CCSD(T) calculated 11B NMR chemical shifts of hypercoordinate Boronium 1–6b and borenium 7–9b ions and 13C NMR chemical shifts of the corresponding isoelectronic carbonium 1–6a and carbenium 7–9a ions, respectively, were found.
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structures and stabilities of higher coordinate onium Boronium dications x bh3 and x bh5 x nh3 ph3 h2o and h2s
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Structures of higher coordinate onium-Boronium dications (X+BH3+ 1–4a and X+BH5+ 1–4d; X = NH3, PH3, H2O, and H2S) were calculated by using the ab initio method at the MP2/6-311+G** level. All of the dications 1–4a contain a four-coordinate boron atom with a three-center two-electron bond involving boron and two hydrogens. On the other hand, all the dications 1–4d contain a six-coordinate boron atom with two three-center two-electron bonds. The thermodynamics of the complexations of 1–4a and H2 to form 1–4d were computed. Deprotonations of 1–4d were found to be substantially endothermic.
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ab initio giao mp2 calculated structures and 11 b 13 c nmr chemical shift relationship in hypercoordinate onium carbonium dications and isoelectronic onium Boronium cations
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium–carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-Boronium cation analogs. Structures and 13C and 11B NMR chemical shifts of the onium-carbonium dications and the corresponding isoelectronic and isostructural onium-Boronium cations were calculated with the ab initio/GIAO-MP2 method. The data show a good linear correlation between 11B and 13C NMR chemical shifts, indicating that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated onium ions and dications.
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calculated 11b 13c nmr chemical shift relationship in hypercoordinate methonium and Boronium ions
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium-carbonium continuum was extended to include hypercoordinated protonated methanes and their boron analogs. The 11B NMR chemical shifts of the hypercoordinated hydriodo boron compounds and the 13C NMR chemical shifts of the corresponding isoelectronic and isostructural carbocations were calculated by using the GIAO-MP2 method. The data show good linear correlation between 11B and 13C NMR chemical shifts, which indicates that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated hydriodo compounds.
Golam Rasul - One of the best experts on this subject based on the ideXlab platform.
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ab initio giao ccsd t calculated 13c 11b nmr chemical shift relationships in isoelectronic hypercoordinate carbonium and Boronium as well as carbenium and borenium ions
Journal of Physical Chemistry A, 2013Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Good linear correlations between GIAO–CCSD(T) calculated 11B NMR chemical shifts of hypercoordinate Boronium 1–6b and borenium 7–9b ions and 13C NMR chemical shifts of the corresponding isoelectronic carbonium 1–6a and carbenium 7–9a ions, respectively, were found.
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structures and stabilities of higher coordinate onium Boronium dications x bh3 and x bh5 x nh3 ph3 h2o and h2s
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Structures of higher coordinate onium-Boronium dications (X+BH3+ 1–4a and X+BH5+ 1–4d; X = NH3, PH3, H2O, and H2S) were calculated by using the ab initio method at the MP2/6-311+G** level. All of the dications 1–4a contain a four-coordinate boron atom with a three-center two-electron bond involving boron and two hydrogens. On the other hand, all the dications 1–4d contain a six-coordinate boron atom with two three-center two-electron bonds. The thermodynamics of the complexations of 1–4a and H2 to form 1–4d were computed. Deprotonations of 1–4d were found to be substantially endothermic.
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ab initio giao mp2 calculated structures and 11 b 13 c nmr chemical shift relationship in hypercoordinate onium carbonium dications and isoelectronic onium Boronium cations
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium–carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-Boronium cation analogs. Structures and 13C and 11B NMR chemical shifts of the onium-carbonium dications and the corresponding isoelectronic and isostructural onium-Boronium cations were calculated with the ab initio/GIAO-MP2 method. The data show a good linear correlation between 11B and 13C NMR chemical shifts, indicating that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated onium ions and dications.
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calculated 11b 13c nmr chemical shift relationship in hypercoordinate methonium and Boronium ions
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium-carbonium continuum was extended to include hypercoordinated protonated methanes and their boron analogs. The 11B NMR chemical shifts of the hypercoordinated hydriodo boron compounds and the 13C NMR chemical shifts of the corresponding isoelectronic and isostructural carbocations were calculated by using the GIAO-MP2 method. The data show good linear correlation between 11B and 13C NMR chemical shifts, which indicates that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated hydriodo compounds.
Anthony F Hill - One of the best experts on this subject based on the ideXlab platform.
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synthetic and structural studies of phosphine coordinated Boronium salts
Dalton Transactions, 2017Co-Authors: Anthony F Hill, Jas S WardAbstract:The reaction of BrH2B·SMe2 with primary and secondary phosphines affords a range of Boronium salts of the form [H2B(PR3)2]Br (PR3 = PHCy21; PHPh2, 2; PH2Cy, 3), which have been fully characterised including solid-state determinations. Reactions of bulky tertiary phosphines, e.g., PCy3 and PPh3, with BrH2B·SMe2 do not proceed beyond the phosphine-stabilised bromoborane adducts, however, the smaller tertiary phosphine PMe2Ph readily proceeds to form [H2B(PMe2Ph)2]Br (4). The formation of the unsymmetrical Boronium salts [H2B(PH2Cy)(PHCy2)]Br (5) and [H2B(PHCy2)(PHPh2)]Br (6) was observed by in situ NMR spectroscopy, however, the compounds were found to spontaneously disproportionate to their respective homophosphine Boronium cations, even on prolonged storage in solution at -78 °C. Di- and triphosphines were found to form ring-closed Boronium salts to afford [H2B(κ2-P,P'-diphosphine)]Br (diphosphine = dppe, 7; dcpe, 8; dmpe, 9; dppf, 10; dppf with [AsF6]- counterion, 11; amphos, 12). The analogous methodology with Br2HB·SMe2 proved less generally applicable due to an accessible decomposition pathway being available to Boronium salts bearing primary and secondary phosphines, leading to the formation of phosphonium salts, although [BrHB(dcpe)]Br (13), [BrHB(PMe2Ph)2]Br (14) and [BrHB(amphos)]Br (15) were synthesised with varying degrees of success. Reaction of BrH2B·SMe2 with diphars afforded the Boronium salt [H2B(κ2-P,P'-diphars)]Br (16), which featured two pendant arsine arms. Similarly, triphos was found to react with BrH2B·SMe2 to give [H2B(κ2-P,P'-triphos)]Br (17), which featured a pendant phosphine arm. Substitution of the bromide counter anion with either hexafluoroarsenate or hexfluoroantimonate anions revealed weak hydrogen bonds between the P-H bonds of the Boronium cations and the anions, that appeared through NMR studies to be retained in solution (where hydrogen bonding order was determined to be Br- > [SbF6]-/[AsF6]-). This was further demonstrated by comparison of solid-state structures and solution NMR data of 1 with [H2B(PHCy2)2][SbF6] (18), 4 with [H2B(PMe2Ph)2][AsF6] (19) and 17 with [H2B(triphos)][AsF6] (20).
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1 1 bis n methylimidazole 2 trimethylsilyl 1 boracyclohexa 1 4 diene chloride a stable intermediate or tangent en route to 1 n methylimidazole borabenzene
Journal of the American Chemical Society, 2012Co-Authors: Ian A Cade, Anthony F HillAbstract:The reaction of 1-chloro-2-(trimethylsilyl)-1-boracylohexa-2,5-diene (1) with N-methylimidazole (NMI) results not in the anticipated borabenzene adduct [(NMI)→BC5H5] (3) but rather the title imidazole-stabilized cyclic Boronium salt [(NMI)2BC5H5SiMe3-2]Cl ([2]Cl), which represents a rare example of a trapped intermediate or possible tangent en route to a neutral borabenzene adduct (3) which may be obtained by heating [2]Cl under vacuum.
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1,1-Bis(N-methylimidazole)-2-(trimethylsilyl)-1-boracyclohexa-1,4-diene Chloride: A Stable Intermediate or Tangent en Route to 1-(N-Methylimidazole)borabenzene?
2012Co-Authors: Ian A Cade, Anthony F HillAbstract:The reaction of 1-chloro-2-(trimethylsilyl)-1-boracylohexa-2,5-diene (1) with N-methylimidazole (NMI) results not in the anticipated borabenzene adduct [(NMI)→BC5H5] (3) but rather the title imidazole-stabilized cyclic Boronium salt [(NMI)2BC5H5SiMe3-2]Cl ([2]Cl), which represents a rare example of a trapped intermediate or possible tangent en route to a neutral borabenzene adduct (3) which may be obtained by heating [2]Cl under vacuum
G Surya K Prakash - One of the best experts on this subject based on the ideXlab platform.
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ab initio giao ccsd t calculated 13c 11b nmr chemical shift relationships in isoelectronic hypercoordinate carbonium and Boronium as well as carbenium and borenium ions
Journal of Physical Chemistry A, 2013Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Good linear correlations between GIAO–CCSD(T) calculated 11B NMR chemical shifts of hypercoordinate Boronium 1–6b and borenium 7–9b ions and 13C NMR chemical shifts of the corresponding isoelectronic carbonium 1–6a and carbenium 7–9a ions, respectively, were found.
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structures and stabilities of higher coordinate onium Boronium dications x bh3 and x bh5 x nh3 ph3 h2o and h2s
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:Structures of higher coordinate onium-Boronium dications (X+BH3+ 1–4a and X+BH5+ 1–4d; X = NH3, PH3, H2O, and H2S) were calculated by using the ab initio method at the MP2/6-311+G** level. All of the dications 1–4a contain a four-coordinate boron atom with a three-center two-electron bond involving boron and two hydrogens. On the other hand, all the dications 1–4d contain a six-coordinate boron atom with two three-center two-electron bonds. The thermodynamics of the complexations of 1–4a and H2 to form 1–4d were computed. Deprotonations of 1–4d were found to be substantially endothermic.
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ab initio giao mp2 calculated structures and 11 b 13 c nmr chemical shift relationship in hypercoordinate onium carbonium dications and isoelectronic onium Boronium cations
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium–carbonium ion continuum was extended to include hypercoordinated onium-carbonium dications and the isoelectronic onium-Boronium cation analogs. Structures and 13C and 11B NMR chemical shifts of the onium-carbonium dications and the corresponding isoelectronic and isostructural onium-Boronium cations were calculated with the ab initio/GIAO-MP2 method. The data show a good linear correlation between 11B and 13C NMR chemical shifts, indicating that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated onium ions and dications.
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calculated 11b 13c nmr chemical shift relationship in hypercoordinate methonium and Boronium ions
Proceedings of the National Academy of Sciences of the United States of America, 1998Co-Authors: Golam Rasul, G Surya K Prakash, George A OlahAbstract:The Boronium-carbonium continuum was extended to include hypercoordinated protonated methanes and their boron analogs. The 11B NMR chemical shifts of the hypercoordinated hydriodo boron compounds and the 13C NMR chemical shifts of the corresponding isoelectronic and isostructural carbocations were calculated by using the GIAO-MP2 method. The data show good linear correlation between 11B and 13C NMR chemical shifts, which indicates that the same factors that determine the chemical shifts of the boron nuclei also govern the chemical shifts of carbon nuclei of these hypercoordinated hydriodo compounds.
Ian A Cade - One of the best experts on this subject based on the ideXlab platform.
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haloboration of internal alkynes with Boronium and borenium cations as a route to tetrasubstituted alkenes
ChemInform, 2013Co-Authors: James R Lawson, Ewan R Clark, Ian A Cade, Sophia A Solomon, Michael J InglesonAbstract:Vinyl boronates are extremely useful precursors, especially for the formation of new C–C bonds by cross-coupling and conjugate addition reactions.1, 2 Although alkyne hydroboration is a powerful synthetic route,3, 4 it is not applicable to the synthesis of trisubstituted vinyl boronates. Thus, alternative regio- and stereospecific methods are needed, particularly for subsequent use in the formation of tetrasubstituted alkenes,5–7 as the production of these important biologically active compounds as single isomers by classical methods is challenging.8 One simple approach to trisubstituted vinyl boronates is the functionalization of internal alkynes by metal-catalyzed 1,2-carboboration9–13 and 1,1-carboboration.14 The introduction of two selectively transformable moieties onto an internal alkyne should enable ready access to tetrasubstituted alkenes by successive cross-coupling reactions. Significant progress has been made in this area, particularly in the dimetalation of internal alkynes to provide two nucleophilic sites of distinct reactivity.15–19 The haloboration of internal alkynes is an attractive alternative to dimetalation, as it generates ambivalent synthetic intermediates that contain both a nucleophilic and an electrophilic position.20 These synthetic intermediates are ideally suited for the diversity-oriented synthesis of tetrasubstituted alkenes. To date, the application of alkyne haloboration with boron trihalides (BX3) has been limited to terminal alkynes, and has proved an effective route to produce trisubstituted alkenes with excellent regio- and stereoselectivity.21–25 The haloboration of internal alkynes is unsuccessful with BCl3, and it is either slow25 or produces isomeric mixtures susceptible to B–C bond cleavage when BBr3 is used.21, 26 Recent calculations found that the haloboration of internal alkynes with BCl3 is endothermic, but as the Lewis acidity of BX3 increases (Cl
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1 1 bis n methylimidazole 2 trimethylsilyl 1 boracyclohexa 1 4 diene chloride a stable intermediate or tangent en route to 1 n methylimidazole borabenzene
Journal of the American Chemical Society, 2012Co-Authors: Ian A Cade, Anthony F HillAbstract:The reaction of 1-chloro-2-(trimethylsilyl)-1-boracylohexa-2,5-diene (1) with N-methylimidazole (NMI) results not in the anticipated borabenzene adduct [(NMI)→BC5H5] (3) but rather the title imidazole-stabilized cyclic Boronium salt [(NMI)2BC5H5SiMe3-2]Cl ([2]Cl), which represents a rare example of a trapped intermediate or possible tangent en route to a neutral borabenzene adduct (3) which may be obtained by heating [2]Cl under vacuum.
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1,1-Bis(N-methylimidazole)-2-(trimethylsilyl)-1-boracyclohexa-1,4-diene Chloride: A Stable Intermediate or Tangent en Route to 1-(N-Methylimidazole)borabenzene?
2012Co-Authors: Ian A Cade, Anthony F HillAbstract:The reaction of 1-chloro-2-(trimethylsilyl)-1-boracylohexa-2,5-diene (1) with N-methylimidazole (NMI) results not in the anticipated borabenzene adduct [(NMI)→BC5H5] (3) but rather the title imidazole-stabilized cyclic Boronium salt [(NMI)2BC5H5SiMe3-2]Cl ([2]Cl), which represents a rare example of a trapped intermediate or possible tangent en route to a neutral borabenzene adduct (3) which may be obtained by heating [2]Cl under vacuum