Synthesis of isomeric B-methylated tantalum carboranes, (Me2N)3TaC2B9H10Me†

Fox, Mark A.; Howard, Judith A. K.; Hughes, Andrew K.; Malget, John M.; Yufit, Dimitrii S.

doi:10.1039/b103353k

Cited by 22 publications

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“…A 11 B{ 1 H}-11 B{ 1 H} COSY spectrum of [HNMe 3 ][1] in (CD 3 ) 2 CO was obtained in an attempt to assign these resonances to {closo-C 2 B 10 } or {nido-C 2 B 9 } components. By analogy with the spectra of [7,8-nido-C 2 B 9 H 12 ] − 19 and 1,2-closo-C 2 B 10 H 12 , 20 it seems reasonable to suggest that the two highest frequency resonances are due to the {closo-C 2 B 10 } cage and the four lowest frequency resonances are due to the {nido-C 2 B 9 } cage, but beyond this it was not possible to deconvolute the entire spectrum of [ ] (3) were isolated in yields of 8 and 19%, respectively. Both compounds were initially characterised by elemental microanalysis and EI mass spectrometry, the latter clearly showing the molecular ion peaks as a characteristic envelope due to the two naturally-occurring boron isotopes.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

“…H 12 ],20 [3-( p-cymene)-3,1,2-closo-RuC 2 B 9 H 11 ], 26 [3-Cp-3,1,2-closo-CoC 2 B 9 H 11 ] 23 and [2-Cp-2,1,8-closo-CoC 2 B 9 H 11 ] 25. …”

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Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

et al. 2015

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Examples of singly-metallated derivatives of 1,1'-bis(o-carborane) have been prepared and spectroscopically and structurally characterised. Metallation of [7-(1'-1',2'-closo-C2B10H11)-7,8-nido-C2B9H10](2-) with a {Ru(p-cymene)}(2+) fragment affords both the unisomerised species [1-(1'-1',2'-closo-C2B10H11)-3-(p-cymene)-3,1,2-closo-RuC2B9H10] (2) and the isomerised [8-(1'-1',2'-closo-C2B10H11)-2-(p-cymene)-2,1,8-closo-RuC2B9H10] (3), and 2 is easily transformed into 3 with mild heating. Metallation with a preformed {CoCp}(2+) fragment also affords a 3,1,2-MC2B9-1',2'-C2B10 product [1-(1'-1',2'-closo-C2B10H11)-3-Cp-3,1,2-closo-CoC2B9H10] (4), but if CoCl2/NaCp is used followed by oxidation the result is the 2,1,8-CoC2B9-1',2'-C2B10 species [8-(1'-1',2'-closo-C2B10H11)-2-Cp-2,1,8-closo-CoC2B9H10] (5). Compound 4 does not convert into 5 in refluxing toluene, but does do so if it is reduced and then reoxidised, perhaps highlighting the importance of the basicity of the metal fragment in the isomerisation of metallacarboranes. A computational study of 1,1'-bis(o-carborane) is in excellent agreement with a recently-determined precise crystallographic study and establishes that the {1',2'-closo-C2B10H11} fragment is electron-withdrawing compared to H.

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confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

et al. 2015

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“…12 The patterns of 11 B resonances for 1-8 are summarised in Table 1, together with <d 11 B>, the weighted average 11 B chemical shift. Also given are <d 11 B> values for the reference compounds 1,2-closo-C 2 B 10 H 12 (-11.12), 14 1,7-closo-C 2 B 10 H 12 (-12.44), 14 1,12closo-C 2 B 10 H 12 (-14.7), 15 and 1,2-Ph 2 -1,2-closo-C 2 B 10 H 10 (-8.98). 16 In moving from 1,2-closo-C 2 B 10 H 12 to 1,2-Ph 2 -1,2-closo-C 2 B 10 H 10 <d 11 B> shifts to higher frequency by ca.…”

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Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

et al. 2011

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The icosahedral carboranes 1-C(6)F(5)-2-Ph-1,2-closo-C(2)B(10)H(10) (1), 1-(4'-F(3)CC(6)H(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (2), 1,2-(4'-F(3)CC(6)H(4))(2)-1,2-closo-C(2)B(10)H(10) (3), 1-(4'-H(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (4), 1-(4'-F(3)CC(6)F(4))-2-Ph-1,2-closo-C(2)B(10)H(10) (5), 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10) (6), 1,7-(4'-F(3)CC(6)F(4))(2)-1,7-closo-C(2)B(10)H(10) (7) and 1,12-(4'-F(3)CC(6)F(4))(2)-1,12-closo-C(2)B(10)H(10) (8), with fluorinated aryl substituents on cage carbon atoms, have been prepared in good to high yields and characterised by microanalysis, (1)H, (11)B and (19)F NMR spectroscopies, mass spectrometry, single-crystal X-ray diffraction and (spectro)electrochemistry. By analysis of <δ(11)B>, the weighted average (11)B chemical shift, a ranking order for the ortho carboranes 1-6 is established based on the combined electron-withdrawing properties of the C-substituents, and is in perfect agreement with that established independently by electrochemical study. In a parallel computational study the effects of a wide range of different substituents on the redox properties of carboranes have been probed by comparison of ΔE values, where ΔE is the energy gap between the DFT-optimised [7,9-R(2)-7,9-nido-C(2)B(10)](2-) anion and its DFT-optimised basket-shaped first oxidation product. The overall conclusion from the NMR spectroscopic, electrochemical and computational studies is that strongly electron withdrawing substituents significantly stabilise [7,9-nido-C(2)B(10)](2-) dianions with respect to oxidation, and that the best practical substituent is 4-F(3)CC(6)F(4). Thus attention focussed on the reduction of 1,2-(4'-F(3)CC(6)F(4))(2)-1,2-closo-C(2)B(10)H(10), compound 6. The sequence 6/[6](-)/[6](2-) appears reversible on the cyclic voltammetric timescale but on the longer timescale of macroelectrolysis the radical anion is only partially stable. EPR study of the electrogenerated monoanions from the ortho-carboranes 1-6 confirms the cage-centred nature of the redox processes. In contrast, the reduction of the meta- and para-carboranes 7 and 8, respectively, appears to be centred on the aromatic substituents, a conclusion supported by the results of DFT calculation of the LUMOs of compounds 6-8. Bulk 2-electron reduction of 6 affords a dianion which is remarkably stable to reoxidation, surviving for several hours in the open laboratory in the absence of halogenated solvents.

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“…13 In every other case the initial metallation is of a 7,8-nido-C 2 B 9 anion followed by isomerisation of the 3,1,2-MC 2 B 9 species thus formed (sometimes only transiently) into the 4,1,2-MC 2 B 9 final product. 13 In every other case the initial metallation is of a 7,8-nido-C 2 B 9 anion followed by isomerisation of the 3,1,2-MC 2 B 9 species thus formed (sometimes only transiently) into the 4,1,2-MC 2 B 9 final product.…”

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Reduction-induced facile isomerisation of metallacarboranes: synthesis and crystallographic characterisation of 4-Cp-4,1,2-closo-CoC₂B₉H₁₁

2015

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Synthesis of isomeric B-methylated tantalum carboranes, (Me2N)3TaC2B9H10Me†

Cited by 22 publications

References 50 publications

Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

Reduction-induced facile isomerisation of metallacarboranes: synthesis and crystallographic characterisation of 4-Cp-4,1,2-closo-CoC₂B₉H₁₁

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Synthesis of isomeric B-methylated tantalum carboranes, (Me2N)3TaC2B9H10Me†

Cited by 22 publications

References 50 publications

Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

Icosahedral metallacarborane/carborane species derived from 1,1′-bis(o-carborane)

Spectroscopic, structural, computational and (spectro)electrochemical studies of icosahedral carboranes bearing fluorinated aryl groups

Reduction-induced facile isomerisation of metallacarboranes: synthesis and crystallographic characterisation of 4-Cp-4,1,2-closo-CoC2B9H11

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Reduction-induced facile isomerisation of metallacarboranes: synthesis and crystallographic characterisation of 4-Cp-4,1,2-closo-CoC₂B₉H₁₁