Unexpected bonding mode of the diboran(4)yl ligand: combining the boryl motif with a dative Pt-B interaction.
Unexpected bonding mode of the diboran(4)yl ligand: combining the boryl motif with a dative Pt-B interaction.
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二硼烷（4）基配体的意外键合模式：硼基基序与配位 Pt-B 相互作用相结合
DOI：
10.1002/anie.201102593
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发表时间：
2011
影响因子：
--
通讯作者：
T. Kupfer
中科院分区：
文献类型：
--
作者：
H. Braunschweig;A. Damme;T. Kupfer
在过去的15年中，二硼烷(4)作为高价值试剂在不饱和有机底物的催化功能化中变得越来越重要在这方面，通常观察到的二硼烷(4)对催化活性物质的反应性，通常是一种低价过渡金属配合物，由BÀB键的氧化加成产生顺式-bis（硼基）物质组成例如，四烷氧二硼烷(4)在Pd0或Pt0中心的氧化加成已被广泛应用于有机化学中，以制备各种底物进行Suzuki-Miyaura型偶联反应除了BÀB键断裂外，卤化物取代的二硼烷(4)潜在地提供了氧化加成硼-卤化物键的机会，最终导致过渡金属二硼烷(4)基物质的形成。后一种方法被证明可以很容易地处理各种取代卤化硼XBR2，并已广泛用于制备过渡金属硼基配合物相比之下，卤化物取代的二硼烷(4)的反应性的相关研究仍然很少，这与前面提到的二硼烷(4)作为试剂在有机化学中的高度重要性有些令人惊讶。到目前为止，文献中只出现了一项相关研究。1999年，Norman小组研究了B2 (NMe2) 2Cl2对[(η2-C2H4) Pt (PPh3) 2]的反应性。然而，在这种情况下，从实验结果中无法推断出BÀCl键氧化加成的证据，而只验证了BÀB键激活产生的产物，即顺式-[(Ph3P) 2Pt {B-(NMe2)(Cl)} 2]和反式-[(Ph3P) 2Pt (Cl){B (NMe2)(Cl)}].[3]我们小组开发了一种过渡金属地硼(4)基配合物的替代方法。我们证明了双硼(4)基段可以很容易地通过B2 (NMe2) X2 （X= Cl,[4] Br,[5] I[6]）与阴离子半夹心羰基物质M ' -[CpM (CO) n]（M ' = Na， K； M= Mo， W, Fe, Ru）的盐消除反应引入。由于我们对过渡金属硼化学的长期兴趣，我们最近开始重新考虑卤化物取代的二硼烷(4)对低价铂配合物的反应性，并评估在BÀB键存在下BÀX键的选择性氧化加成是否可能。考虑到Norman和同事的经验，我们推断含有更多反应性BÀBr键的二硼烷(4)可能更适合这一目的。这一假设被证明是正确的，我们能够分离出trans-[(Et3P) 2Pt (Br)-{B (Mes) B (Mes)(Br)}](1)和trans-[(iPr3P) 2Pt (Br){B-(NMe2) B (NMe2)(Br)}](2)，它们都是通过在各自的铂前驱体上氧化加成一个BÀBr键来制备的。正如后面所讨论的，1的固态结构具有一种迄今为止未知的diboran (4) yl配体的键合模式，即在第二个硼中心上有一个意想不到的附加的PtÀB键，从而在一个分子中结合了两种电子精密PtÀB相互作用。在早期，由于硼中心的电子缺乏，金属硼键对过渡金属碱度概念的发展起了重要作用。[1f, 2d， 7]尽管这类相互作用早在20世纪60年代就已被假设，但直到1999年，硼烷钌[HRu {B (mt) 3}(PPh3)]（mt= 2-磺胺基-1-甲基咪唑）的第一个支撑式共轭MÀB键的例子才在结构上得到证实，而非支撑式共轭MÀB键的结构证据仍然难以获得。在过去的十年中，大量被支持的物种在结构上…
During the last 15 years, diboranes (4) have become increasingly important as high-value reagents in the catalytic functionalization of unsaturated organic substrates.[1] In this regard, the commonly observed reactivity of diboranes (4) towards the catalytic active species, which is usually a lowvalent transition-metal complex, consists of the oxidative addition of the BÀB bond to generate cis-bis (boryl) species.[1] For instance, the oxidative addition of tetraalkoxydiboranes (4) to Pd0 or Pt0 centers has been widely applied in organic chemistry to prepare diverse substrates for Suzuki–Miyaura type coupling reactions.[1] In addition to BÀB bond cleavage, halide substituted diboranes (4) potentially offer the opportunity for oxidative addition of a boron–halide bond eventually resulting in the formation of transition-metal diboran (4) yl species. The latter process was shown to proceed readily for a variety of substituted boron halides XBR2, and has been used extensively in the preparation of transitionmetal boryl complexes.[2] By contrast, related studies on the reactivity of halide substituted diboranes (4) still remain scarce, which is somewhat surprising regarding the aforementioned high significance of diboranes (4) as reagents in organic chemistry. Only a single relevant study has appeared in the literature so far. In 1999 the group of Norman studied the reactivity of B2 (NMe2) 2Cl2 towards [(η2-C2H4) Pt (PPh3) 2]. In this case however, no evidence for the oxidative addition of the BÀCl bond could be deduced from the experimental results, and exclusively products arising from BÀB bond activation were verified, that is, cis-[(Ph3P) 2Pt {B-(NMe2)(Cl)} 2] and trans-[(Ph3P) 2Pt (Cl){B (NMe2)(Cl)}].[3] An alternative approach towards transition-metal diboran (4) yl complexes has been developed in our group. We demonstrated that the diboran (4) yl moiety can be readily introduced by salt elimination reactions of B2 (NMe2) X2 (X= Cl,[4] Br,[5] I [6]) with anionic half-sandwich carbonyl species M’-[CpM (CO) n](M’= Na, K; M= Mo, W, Fe, Ru). Owing to our longstanding interest in transition-metal boron chemistry, we recently began to reconsider the reactivity of halide-substituted diboranes (4) towards lowvalent platinum complexes and to evaluate the question, whether a selective oxidative addition of BÀX bonds is possible in the presence of a BÀB bond. Bearing the experiences of Norman and co-workers in mind, we reasoned that diboranes (4) containing more reactive BÀBr bonds might be better suited for this purpose. This assumption proved to be true and we were able to isolate trans-[(Et3P) 2Pt (Br)-{B (Mes) B (Mes)(Br)}](1) and trans-[(iPr3P) 2Pt (Br){B-(NMe2) B (NMe2)(Br)}](2), each prepared by oxidative addition of one BÀBr bond to the respective platinum precursors. As discussed later on, the solid-state structure of 1 features a hitherto unknown bonding mode of the diboran (4) yl ligand, that is, an unexpected additional dative PtÀB bond to the second boron center, thus combining two types of electronprecise PtÀB interaction in one molecule. In the early days, dative metal boron bonds played an important role in the development of the concept of transition-metal basicity due to the electron deficiency of the boron center.[1 f, 2d, 7] Even though these kind of interactions had already been postulated in the 1960s, it was not until 1999 that the first example of a supported dative MÀB bond was structurally substantiated for the ruthenium boratrane [HRu {B (mt) 3}(PPh3)](mt= 2-sulfanyl-1-methylimidazole),[8] while structural evidence for unsupported dative MÀB bonds still remains elusive. During the last decade a large number of supported species have been structurally …
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