Thermal decomposition of mono- and bimetallic magnesium amidoborane complexes.
Thermal decomposition of mono- and bimetallic magnesium amidoborane complexes.
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DOI：
10.1002/chem.201000028
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发表时间：
2010-07
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影响因子：
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通讯作者：
Jan Spielmann;D. Piesik;S. Harder
中科院分区：
文献类型：
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作者：
Jan Spielmann;D. Piesik;S. Harder
(DIPPnacnac=CH{(CMe)(2，6-iPr(2)C(6)H(3)N)}(2)).合成了[(DIPPnacnAc)MgNH(R)BH(3)]型配合物使用了以下取代基R：H、Me、IPR、DIPP(DIPP=2，6-二异丙基苯基)。[(DIPPnAc-NAc)MgNH(2)BH(3)].THF，[{(DIPPnAc)MgNH(IPR)BH(3)}(2)]和[(DIPPnAc)MgNH(DIPP)BH(3)].与相应的钙胺硼烷络合物(20-110摄氏度)相比，镁胺硼烷络合物的分解温度(90-110摄氏度)要高得多。具有较小R取代基(H，Me)的络合物的分解产物为[{(DIPPnacnac)Mg}(2)(H(3)B-NME-BH-NME)].THF，[{(DIPP-nacnac)MgNH(IPR)BH(3)}(2)]干净地分解为[(DIPPnacnac)MGH]，表征为二聚四氢呋喃加合物。具有较大DIPP取代基的酰胺硼烷络合物分解为[(DIPPnacnac)MGN(DIPP)BH(2)]，结构表征为其四氢呋喃加合物。双金属镁酰胺硼配合物在较低温度(60-90℃)下分解，表现出不同的分解途径。本文所介绍的双核镁胺硼烷配合物是基于DIPPnacnac单元，这些单元通过N-N键(简称NN)或通过2，6-吡啶桥(简称PYR)直接偶联。报道了[PYR-{Mg(NBU)}(2)]、[PYR-{MgNH(IPR)BH(3)}(2)]、[NN-{MgNH(IPR)BH(3)}(2)]THF及其分解产物[PYR-Mg(2)(iPrN-BH-iPrN-BH(3))]和[NN-Mg(2)(iPrN-BH-iPrN-BH(3))]的晶体结构。从这些研究中可以得出以下结论：i)金属胺基硼烷络合物分解的第一步是β-氢化物消除，这导致形成金属氢化物络合物和R(H)N=BH(2)，ii)根据金属的性质，金属氢化物是稳定的并且可以被分离或它进一步反应，iii)具有小R取代基的氨基硼烷阴离子分解成双阴离子物种(RN-BH-RN-BH(3))(2-)，而大的取代基导致形成BN==BH(2)(-)和iv)两个镁基胺基团的强化接近导致在显著较低的温度下分解，并且干净地沿着BNBN途径进行。
Complexes of the type [(DIPPnacnac)MgNH(R)BH(3)] have been prepared (DIPPnacnac=CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2)). The following substituents R have been used: H, Me, iPr, DIPP (DIPP=2,6-diisopropylphenyl). Complexes [(DIPPnac- nac)MgNH(2)BH(3)].THF, [{(DIPPnac- nac)MgNH(iPr)BH(3)}(2)] and [(DIPPnacnac)MgNH(DIPP)BH(3)] were structurally characterised. The Mg amidoborane complexes decompose at a significantly higher temperature (90-110 degrees C) than the corresponding Ca amidoborane complexes (20-110 degrees C). The complexes with the smaller R substituents (H, Me) gave a mixture of decomposition products of which one could be structurally characterised as [{(DIPPnacnac)Mg}(2)(H(3)B-NMe-BH-NMe)].THF. [{(DIPP- nacnac)MgNH(iPr)BH(3)}(2)] cleanly decomposed to [(DIPPnacnac)MgH], which was characterised as a dimeric THF adduct. The amidoborane complex with the larger DIPP-substituent decomposed into a borylamide complex [(DIPPnacnac)MgN(DIPP)BH(2)], which was structurally characterised as its THF adduct. Bimetallic Mg amidoborane complexes decompose at lower temperatures (60-90 degrees C) and show a different decomposition pathway. The dinuclear Mg amidoborane complexes presented here are based on DIPPnacnac units that are either directly coupled through N-N bonding (abbreviated NN) or through a 2,6-pyridylene bridge (abbreviated PYR). Crystal structures of [PYR-{Mg(nBu)}(2)], [PYR-{MgNH(iPr)BH(3)}(2)], [NN-{MgNH(iPr)BH(3)}(2)]THF and the decomposition products [PYR-Mg(2)(iPrN-BH-iPrN-BH(3))] and [NN-Mg(2)(iPrN-BH-iPrN-BH(3))].THF are presented. The following conclusions can be drawn from these studies: i) The first step in the decomposition of a metal amidoborane complex is beta-hydride elimination, which results in formation of a metal hydride complex and R(H)N=BH(2), ii) depending on the nature of the metal, the metal hydride is either stable and can be isolated or it reacts further, iii) amidoborane anions with small R substituents decompose into the dianionic species (RN-BH-RN-BH(3))(2-), whereas large substituents result in formation of the borylamide RN==BH(2)(-) and iv) enforced proximity of two Mg amidoborane units results in decomposition at a significantly lower temperature and cleanly follows the BNBN pathway.