22092-92-8Relevant articles and documents
Mechanism of metal-free hydrogen transfer between amine-boranes and aminoboranes
Leitao, Erin M.,Stubbs, Naomi E.,Robertson, Alasdair P. M.,Helten, Holger,Cox, Robert J.,Lloyd-Jones, Guy C.,Manners, Ian
, p. 16805 - 16816 (2012)
The kinetics of the metal-free hydrogen transfer from amine-borane Me 2NH?BH3 to aminoborane iPr2N=BH 2, yielding iPr2NH?BH3 and cyclodiborazane [Me2N-BH2]2 via transient Me 2N=BH2, have been investigated in detail, with further information derived from isotopic labeling and DFT computations. The approach of the system toward equilibrium was monitored in both directions by 11B{1H} NMR spectroscopy in a range of solvents and at variable temperatures in THF. Simulation of the resulting temporal-concentration data according to a simple two-stage hydrogen transfer/dimerization process yielded the rate constants and thermodynamic parameters attending both equilibria. At ambient temperature, the bimolecular hydrogen transfer is slightly endergonic in the forward direction (ΔG1° (295) = 10 ± 7 kJ?mol-1; ΔG 1(295) = 91 ± 5 kJ?mol-1), with the overall equilibrium being driven forward by the subsequent exergonic dimerization of the aminoborane Me2N=BH2 (ΔG 2°(295) = -28 ± 14 kJ?mol-1). Systematic deuterium labeling of the NH and BH moieties in Me 2NH?BH3 and iPr2N=BH2 allowed the kinetic isotope effects (KIEs) attending the hydrogen transfer to be determined. A small inverse KIE at boron (kH/kD = 0.9 ± 0.2) and a large normal KIE at nitrogen (kH/kD = 6.7 ± 0.9) are consistent with either a pre-equilibrium involving a B-to-B hydrogen transfer or a concerted but asynchronous hydrogen transfer via a cyclic six-membered transition state in which the B-to-B hydrogen transfer is highly advanced. DFT calculations are fully consistent with a concerted but asynchronous process.
Polyaminoborane main chain scission using N-heterocyclic carbenes; Formation of donor-stabilised monomeric aminoboranes
Stubbs, Naomi E.,Jurca, Titel,Leitao, Erin M.,Woodall, Christopher H.,Manners, Ian
supporting information, p. 9098 - 9100 (2013/09/24)
The reaction of N-heterocyclic carbenes with polyaminoboranes [MeNH-BH 2]n or [NH2-BH2]n at 20 °C led to depolymerisation and the formation of labile, monomeric aminoborane-NHC adducts, RNH-BH2-NHC (R = Me or H); a similar NHC adduct of Ph2NBCl2 was characterized by single crystal X-ray diffraction.
Synthesis and the thermal and catalytic dehydrogenation reactions of amine-thioboranes
Robertson, Alasdair P. M.,Haddow, Mairi F.,Manners, Ian
, p. 8254 - 8264 (2012/09/22)
A series of trimethylamine-thioborane adducts, Me3N· BH2SR (R = tBu [2a], nBu [2b], iPr [2c], Ph [2d], C6F 5 [2e]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH2-SPh]3 (9) and C6F 5SBH2·SMe2 (10) with Me2NH and iPr2NH successfully yielded the adducts Me2NH· BH2SR (R = Ph [11a], C6F5 [12a]) and iPr 2NH·BH2SR (R = Ph [11b], C6F5 [12b]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me2N=BH 2, derived from the cyclic dimer [Me2N-BH 2]2 (13), and iPr2N=BH2 (14), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R2NH·BH2SR′ (R = Me, iPr; R′ = tBu, nBu, iPr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R2N= BH(SR′). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, 11a/11b and 12a/12b were also investigated. Adducts 11b and 12b were cleanly dehydrogenated to yield iPr2N=BH(SPh) (22) and iPr2N=BH(SC6F5) (23), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh(μ-Cl)cod]2 in the case of the former species. Similar studies with adduct 11a evidenced a competitive elimination of H2 and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue 12a was found to be resistant to dehydrogenation.
