Thermal Dealkylation of Tri-<i>n</i>-octylborane: Effect of Lewis Bases on Extent and Regioselectivity

Mzinyati, A.; Jaganyi, Deogratius

doi:10.1021/ie801303g

Cited by 4 publications

(4 citation statements)

References 27 publications

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“…A further limitation will be the occurrence of other undesired thermal decomposition reactions at high temperature . While a high equilibrium concentration of free olefin at mild temperatures would suggest a relatively simple dehydroboration reaction is possible, , this is clearly not the case. In the following sections, we investigate the involvement of intermediates from dehydroboration in alkylborane rearrangements.…”

Section: Results and Discussionmentioning

confidence: 99%

“…200 °C without decomposition. , A report from Rosenblum from around the same time suggests that heating tri- n -butylborane under vacuum results in slow formation of butene and n Bu 2 B 2 H 4 (2–10 days, 90–130 °C), while tri- n -decylborane was reported to yield 1-decene and n Dec 4 B 2 H 2 during distillation at 180 °C and 10 –3 Torr, although no time frame was reported . More recently Jaganyi has reported that tri- n -octylborane (BOct 3 ) forms appreciable equilibrium concentrations of free 1-octene when it is heated in a closed NMR tube, even at 50 °C, where 6.8% 1-octene relative to BOct 3 was reported (up to 13.9% at 200 °C). On the basis of this work, a boron-based internal olefin to α-olefin isomerization process was proposed, as shown in Scheme , although this was not actually demonstrated experimentally .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Thermal Dehydroboration: Experimental and Theoretical Studies of Olefin Elimination from Trialkylboranes and Its Relationship to Alkylborane Isomerization and Transalkylation

2014

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The free energies of reaction calculated in Gaussian (1 atm standard state concentration) were converted to 1 M standard state values in order to calculate the equilibrium data in Figure 3. The concentration at 1 atm, [1 atm], at each temperature is given by PV/RT, from which the entropy correction, S corr , is given by -Rln(1/[1 atm]). Applying this correction to each of the reactants leads to the corrected ∆G react values given in Table S1. Supporting InformationRadkiewicz-Poutsma and co-workers 4 , raised the concern that B3LYP geometry optimization, as implemented in the CBS-QB3 scheme, may lead to a poor geometry for the borane-olefin π-complex, and as such the energetics from CBS-QB3 may be incorrect for the weak R 2 BH-olefin complexes studied herein. This could also have an influence on the free energy barrier for olefin dissociation in these cases. In addressing this, we first discuss the findings of Gilbert and Radkiewicz-Poutsma, and then evaluate the effect of different methods on our results.Gilbert 3 evaluated various DFT methods as well as MP2 for predicting both the geometry and dissociation energy of amineborane dative bonds. It was found that B3LYP predicts B-N bond dissociation energies (BDEs) that are lower than found experimentally, and also predicts B-N bond distances that are too long. Radkiewicz-Poutsma and co-workers 4 extended the study of amine-borane dative bonds. They found that the poor performance of B3LYP in calculating the B-N BDE is due to how this method calculates the energy of the dative bond, rather than being due to the geometry resulting from optimization with the B3LYP method. Bond energies resulting from high level single point calculations on B3LYP geometries were found to be reliable, and CCSD(T) calculations were relatively insensitive to whether an MP2 or B3LYP geometry was used, despite MP2 leading to a tighter B-N bond. This is consistent with the PES corresponding to the dative bond B-N distance being very flat. Both authors found that the MP2 method leads to more reliable B-N bond distances, and MP2 BDEs were closer to experimental or CCSD(T) values. We note that our work has not employed B3LYP energies (apart from thermal corrections to Gibbs free energy); in all cases higher level composite energies on B3LYP geometries have been obtained. We also note that while validating theoretical studies of propene hydroboration (more directly analogous to our work), Singleton 1 found B3LYP to be reliable for energy calculations.We have investigated the effect of MP2 geometry optimization by studying elimination and re-addition of propene from B i Pr 3 , as shown in Figure 5(a) of the main article. CBS-QB3 optimisation in this case led to the loosest post-elimination borane-olefin complex encountered in this work, presumably for steric reasons. The B-C α distance in the i Pr 2 BH••••propene complex is 4.5 Å in this case. The transition structures (elimination and re-addition), π-complex and separated products (propene and i Pr 2 BH) have been re-optimized at the MP2/6-31+G(...

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermal Dehydroboration: Experimental and Theoretical Studies of Olefin Elimination from Trialkylboranes and Its Relationship to Alkylborane Isomerization and Transalkylation

2014

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“…In the final step, β-hydrogen elimination together with rapid removal of the olefin furnish the α-olefin selectively. For boron-hydrides the first two steps (insertion, isomerisation) are reasonably facile, 16,17 but we found the elimination step 18 to be unsuccessful. 13 For alkylaluminium the situation is reversed and it was demonstrated that α-olefins may be removed from tri-nalkylaluminium with very high selectivity (>97%).…”

Section: Introductionmentioning

confidence: 83%

Cobalt-bis(imino)pyridine complexes as catalysts for hydroalumination–isomerisation of internal olefins

Weliange¹,

McGuinness²,

Gardiner³

et al. 2016

Dalton Trans.

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The insertion of α- and internal octenes (hydroalumination) and chain walking isomerisation at di-n-octylaluminium hydride [Al(Oct)2H], catalysed by bis(imino)pyridine-Co complexes has been investigated by NMR spectroscopy. The Co-based catalysts promote efficient hydroalumination of 1-octene. Internal olefins are partially hydroaluminated, with isomerisation to the primary alkyls, but the catalyst responsible appears to deactivate rapidly. The reaction between the Co precatalysts and [Al(Oct)2H] generates a Co-hydride species, likely to be a hydride bridged dinuclear Co and Al complex. This species is reactive towards α-olefins but inert towards internal olefins. In contrast to hydroalumination, the catalysts promote efficient hydroboration, where insertion and isomerisation of internal octenes goes to completion. The differences between the systems may be partially ascribed to formation of an active mononuclear Co catalyst in the borane system versus a less active Co/Al dinuclear complex in hydroalumination.

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“…For alkylboranes, the first two steps are reasonably facile, 15,16 but we were unable to effect elimination and isolation of α-olefins on a preparative scale, 13 despite reports to the contrary. 17,18 On the other hand, we showed that α-olefins can be removed from tri-n-alkylaluminium with very high selectivity (>97%), but in this case insertion and isomerisation of internal olefins was unsuccessful. 14 The reaction of [Al(n-Alk) 2 H] with internal olefins reaches an equilibrium position (ca.…”

Section: Introductionmentioning

confidence: 87%

Insertion and isomerisation of internal olefins at alkylaluminium hydride: catalysis with zirconocene dichloride

Weliange¹,

McGuinness²,

Gardiner³

et al. 2015

Dalton Trans.

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The insertion of internal olefins (hydroalumination) and chain walking isomerisation at di-n-octylaluminium hydride [Al(Oct)2H], promoted by zirconocene dichloride [Cp2ZrCl2] has been studied. The reaction between [Cp2ZrCl2] and [Al(Oct)2H] in non-polar solvents leads to clusters containing bridging hydride ligands between Zr and Al. This system promotes hydroalumination of 1-octene but is largely ineffective for internal octenes (2-, 3-, 4-octene). In tetrahydrofuran the Zr-Al hydride clusters formed are more reactive and catalyse insertion and isomerisation of internal olefins to primary metal-alkyls, although this is accompanied by catalyst deactivation. Elimination and removal of 1-octene from the system post insertion/isomerisation was attempted, but it was found that the presence of the Zr catalyst leads to back-isomerisation to internal octenes, along with further decomposition with n-octane formation. Some possible pathways of catalyst decomposition, involving reduction of Zr and alkane elimination, have been studied theoretically.

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Thermal Dealkylation of Tri-n-octylborane: Effect of Lewis Bases on Extent and Regioselectivity

Cited by 4 publications

References 27 publications

Thermal Dehydroboration: Experimental and Theoretical Studies of Olefin Elimination from Trialkylboranes and Its Relationship to Alkylborane Isomerization and Transalkylation

Thermal Dehydroboration: Experimental and Theoretical Studies of Olefin Elimination from Trialkylboranes and Its Relationship to Alkylborane Isomerization and Transalkylation

Cobalt-bis(imino)pyridine complexes as catalysts for hydroalumination–isomerisation of internal olefins

Insertion and isomerisation of internal olefins at alkylaluminium hydride: catalysis with zirconocene dichloride

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