Anorganische Chemie, Universität Duisburg-Essen, Universitätsstrasse 5, 45117 Essen, Germany.
Chemistry. 2010 Jul 26;16(28):8307-18. doi: 10.1002/chem.201000028.
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.
[(DIPPnacnac)MgNH(R)BH(3)]型配合物已被制备（DIPPnacnac=CH{(CMe)(2,6-iPr(2)C(6)H(3)N)}(2))。以下是使用的取代基 R：H、Me、iPr、DIPP（DIPP=2,6-二异丙基苯基）。配合物[(DIPPnacnac)MgNH(2)BH(3)].THF、[{(DIPPnacnac)MgNH(iPr)BH(3)}(2)]和[(DIPPnacnac)MgNH(DIPP)BH(3)]的结构已被确定。Mg 酰胺硼烷配合物的分解温度（90-110°C）明显高于相应的 Ca 酰胺硼烷配合物（20-110°C）。具有较小 R 取代基（H、Me）的配合物产生了分解产物的混合物，其中一种可以作为 [{(DIPPnacnac)Mg}(2)(H(3)B-NMe-BH-NMe)].THF 进行结构表征。[{(DIPPnacnac)MgNH(iPr)BH(3)}(2)] 干净地分解为[(DIPPnacnac)MgH]，其被表征为二聚体 THF 加合物。具有较大 DIPP 取代基的酰胺硼烷配合物分解为硼酰胺配合物[(DIPPnacnac)MgN(DIPP)BH(2)]，其结构已被确定为其 THF 加合物。双金属 Mg 酰胺硼烷配合物在较低温度（60-90°C）下分解，并显示出不同的分解途径。这里呈现的双核 Mg 酰胺硼烷配合物基于直接通过 N-N 键偶联（缩写为 NN）或通过 2,6-吡啶亚基桥（缩写为 PYR）偶联的 DIPPnacnac 单元。[PYR-{Mg(nBu)}(2)]、[PYR-{MgNH(iPr)BH(3)}(2)]、[NN-{MgNH(iPr)BH(3)}(2)]THF 和分解产物[PYR-Mg(2)(iPrN-BH-iPrN-BH(3))]和[NN-Mg(2)(iPrN-BH-iPrN-BH(3))].THF 的晶体结构被呈现。可以从这些研究中得出以下结论：i）金属酰胺硼烷配合物分解的第一步是β-氢化物消除，导致形成金属氢化物配合物和 R(H)N=BH(2)，ii）取决于金属的性质，金属氢化物要么稳定且可以分离，要么进一步反应，iii）具有较小 R 取代基的酰胺硼烷阴离子分解为二阴离子物种（RN-BH-RN-BH(3))(2-)，而较大取代基导致形成硼酰胺 RN==BH(2)(-)，iv）两个 Mg 酰胺硼烷单元的强制接近导致在显著较低的温度下分解，并干净地遵循 BNBN 途径。
