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，既作为硼化反应中的反应中间体，也由于这类配体的配位化学性质。特别地，二氨基硼基配体已被描述为多齿配体的结构单元，特别是具有E-B-E供体原子组（E：P、N等）的钳形配体。与人们的极大兴趣相反，只有相当有限的合成方法可用于合成二氨基硼基配体。已建立的方法都或多或少地受限于可接近的金属或关于配体框架。特别地，二氨基硼基钳形配体目前只能通过将B-H键氧化加成到低氧化态的金属前体上来获得。在此，二氨基硼基配体通过σ键复分解或氧化加成通过pinB-B（NR）2C 6 H4型不对称乙硼烷（4）衍生物的选择性B-B键活化获得。此外，所需的乙硼烷（4）衍生物似乎在合成上很容易获得并且在配体取代模式方面是通用的;因此，这里也克服了合成限制。 该项目旨在加强初步研究，并进一步发展该方法在过渡金属和配体框架方面的范围，但特别是对硼基钳形配体的构建。基于对不对称乙硼烷（4）衍生物合成的详细系统研究和优化，将提供新的取代模式。使用这些数据，应该可以获得具有取代基R“的二硼烷（4）衍生物（RO）2B-B（NR”R ""）2，所述取代基R“含有作为二氨基硼基配体的合适前体的额外给体原子。在第二部分中，合成的不对称乙硼烷（4）衍生物将与选择的过渡金属络合物反应以获得二氨基硼基（钳形）络合物。所得的二氨基硼基（钳）配合物将详细表征光谱以及结构，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键活化过程的影响以及二氨基硼配体的配位化学性质。最后，某些获得的硼基（钳形）络合物将作为催化相关转化（例如铱催化的C-H硼基化）中的（预）催化剂进行测试。

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.