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

过渡金属双氨基硼基配合物是当前研究的热点，它既是硼化反应中的活性中间体，又是这类重要配体的配位化学性质。尤其是二氨基硼基配体被描述为多齿配体，特别是具有E-B-E给体原子组(E：P，N等)的钳形配体。与人们的极大兴趣形成鲜明对比的是，目前仅有相当有限的合成方法可用于合成二氨基硼配体。已建立的方法都或多或少地受到限制，无论是关于可获得的金属还是关于配体骨架。尤其是二氨基硼钳状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。申请人最近报道了一种新的二氨基硼配体的合成路线，该路线似乎克服了目前的合成限制。这里，二氨基硼配体是通过Sigma键易位或通过氧化加成，通过类型PinB-B(NR)2C6H4型的不对称二硼烷(4)衍生物的选择性B-B键激活而获得的。此外，所需的二硼烷(4)衍生物在配体取代模式方面表现出很好的可及性和多功能性；因此，这里也克服了合成限制。该项目旨在加强对过渡金属和配体骨架的初步研究，并进一步扩大这一方法的适用范围，特别是在构建硼钳形配体方面。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，将提供新的取代模式。使用这些数据，二硼烷(4)衍生物(RO)2B-B(NR‘R’)2显示的取代基R‘含有额外的供体原子，这些原子是二氨基硼配体的合适前体。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，以得到二氨基硼基(钳形)配合物。所获得的二氨基硼基(钳形)络合物将在光谱和结构上进行详细的表征，尤其是关于它们的反应性。有鉴于此，我们将系统地研究配体取代方式对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)配合物将被测试为催化相关转化的(前)催化剂，例如Ir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.