Unsymmetrical Diborane(4) Derivatives (RO)2B-B(NR´R´´)2 as Precursors for Diamino Boryl Complexes: From modular Synthesis to tailored ligands

过渡金属的二氨基硼基配合物目前被广泛研究，既是作为硼化反应的活性中间体，也是由于这类配体的配位化学性质。特别是二氨基硼基配体被描述为多齿配体的构建单元，特别是具有E- b -E给体原子集（E: P， N等）的钳形配体。与极大的兴趣相反，只有相当有限的合成方法可用于合成二氨基硼基配体。所建立的方法都或多或少地受到可及金属或配体框架的限制。特别是二氨基硼基钳形配体目前只能通过在低氧化态的金属前驱体上氧化加成B-H键来获得。申请人最近报告了一种新的二氨基硼基配体的合成途径，似乎克服了目前的合成限制。在这里，二氨基硼基配体是由pinB-B(NR)2C6H4型的不对称二硼烷(4)衍生物通过sigma键复分解或氧化加成选择性的B-B键激活而得到的。此外，所需的二硼烷(4)衍生物就配体取代模式而言，似乎在合成上易于接近和通用；因此，这里也克服了综合的限制。本项目旨在加强过渡金属和配体框架方面的初步研究和进一步发展该方法的范围，特别是在硼酸螯合体的构建方面。在对不对称二硼烷(4)衍生物的合成进行详细的系统研究和优化的基础上，将获得新的取代模式。利用这些数据，二硼烷(4)衍生物（RO）2B-B(NR ' R ‘)2显示取代基R ’含有额外的供体原子，是二氨基硼基配体的合适前体。在第二部分中，合成的不对称二硼烷(4)衍生物将与选定的过渡金属配合物反应，以获得二氨基硼基（钳形）配合物。所得到的二氨基硼基（钳形）配合物将在光谱和结构上进行详细的表征，但特别是关于它们的反应性。在此基础上，系统地研究了配体取代方式对B-B键激活过程和二氨基硼基配体配位化学性质的影响。最后，某些获得的硼基（钳形）配合物将在催化相关转化中作为（预）催化剂进行测试，例如铱催化的C-H硼化反应。

Diaminoboryl complexes of transition metals are currently intensively studied, both as reactive intermediates in borylation reactions as well as due to the coordination chemical properties of this remarkable class of ligands. In particular diamino boryl ligands have been described as building blocks of multidentate ligands, especially pincer ligands with an E-B-E donor atom set (E: P, N, etc.). In contrast to the great interest only rather limited synthetic methods are available to synthesise diamino boryl ligands. The established methods are all more or less limited either regarding the accessible metals or regarding the ligand framework. Especially diamino boryl pincer ligands are currently only accessible by oxidative addition of a B-H bond onto a metal precursor in a low oxidation state.The applicant recently reported on a new synthetic route to diamino boryl ligands that appears to overcome the present synthetic limitations. Here, the diamino boryl ligand is obtained by the selective B-B bond activation of an unsymmetrical diborane(4) derivative of the type pinB-B(NR)2C6H4 either by sigma bond metathesis or by oxidative addition. Moreover, the required diborane(4) derivatives appear synthetically well accessible and versatile with regard to the ligand substitution pattern; hence, also here synthetic limitations are overcome. This project aims to intensify the preliminary studies and develop the scope of this method further with regard to the transition metals as well as the ligand framework, but in particular towards the construction of boryl pincer ligands. Building on a detailed systematic study and optimisation of the synthesis of the unsymmetrical diborane(4) derivative new substitution patterns will be made available. Using these data diborane(4) derivatives (RO)2B-B(NR´R´´)2 exhibiting substituents R´ containing additional donor atoms that are suitable precursors for diamino boryl ligands should be accessible. In a second part the synthesised unsymmetrical diborane(4) derivatives will be reacted with selected transition metal complexes in order to obtain diamino boryl (pincer) complexes. The obtained diamino boryl (pincer) complexes will be characterised in detail spectroscopically as well as structurally but especially regarding their reactivity. In connection with this the impact of the ligands substitution pattern on the B-B bond activation process and the coordination chemical properties of the diamino boryl ligand will be studied systematically. Finally, certain of the obtained boryl (pincer) complexes will be tested as (pre-)catalysts in catalytically relevant transformations, e.g. iridium catalysed C-H borylation.