trans-[Pt(BCat′)Me(PCy3)2]: An Experimental Case Study of Reductive Elimination Processes in Pt-Boryls through Associative Mechanisms
trans-[Pt(BCat′)Me(PCy3)2]: An Experimental Case Study of Reductive Elimination Processes in Pt-Boryls through Associative Mechanisms
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DOI：
10.1002/chem.201101823
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发表时间：
2011-10-01
影响因子：
4.3
通讯作者：
Seeler, Fabian
中科院分区：
文献类型：
--
作者：
Braunschweig, Holger;Bertermann, Ruediger;Seeler, Fabian
以反式-[Pt(BCat') Br(PCy3)(2)]为原料，与石灰盐还原反应合成了稳定的反式-（烷基）（硼基）铂配合物[Pt(BCat') Me(PCy3)(2)] (Cat'= Cat-4- tbu; Cy=环己基=C6H11)，并对其进行了表征。对标题化合物的反应性研究表明，在80℃下，在四周内完全还原消除了Cat'BMe。这一过程可以通过添加各种炔来加速，从而导致形成相应的h -炔铂配合物，其中[Pt(eta(2)- meccme)-(PCy3)(2)]通过x射线晶体学表征。在与螯合膦的反应中，由于瞬时还原消除过程，反式标题化合物转化为顺式衍生物仍然不成功。Cat(2)B(2)处理trans-[Pt（BCat’）Me(PCy3)(2)]，生成CatBMe和Cat’bme。在对该反应的进一步研究过程中，发现了两种难以区分的反应机制：1)在还原消除之前，六坐标铂中心的缔合形成；2)B-B和C-Pt键的s键复合。机制1为这两种甲基硼烷的形成提供了一个直接的解释。在[Pt(PCy3)(2)]存在下，二硼烷(4)Cat(2)B(2)和Cat'B-2(2)，在亚化学计量量的Cat(2)B(2)(2)存在下，从反式-[Pt(BCat') Me(PCy3)(2)]中完全还原消除CatBMe或Cat' bme，以及Cat(2)B(2)氧化加成[Pt(PCy3)(2)]的可逆性的证据，所有支持机制2，由顺序平衡反应组成。进一步研究了顺式-[Pt(BCat)(2)(PCy3)(2)]和顺式-[Pt(BCat')(2)(PCy3)(2)]的固态分子结构。这两种硼基配合物的B-B分离时间都很短，这表明这两种硼基配体与PtII中心的结合比相关的硼基配体更松散。
A stable trans-(alkyl) (boryl) platinum complex trans-[Pt(BCat') Me(PCy3)(2)] (Cat'= Cat-4-tBu; Cy= cyclohexyl=C6H11) was synthesised by salt metathesis reaction of trans-[Pt( BCat')Br(PCy3)(2)] with LiMe and was fully characterised. Investigation of the reactivity of the title compound showed complete reductive elimination of Cat'BMe at 80 degrees C within four weeks. This process may be accelerated by the addition of a variety of alkynes, thereby leading to the formation of the corresponding h 2-alkyne platinum complexes, of which [Pt(eta(2)-MeCCMe)-(PCy3)(2)] was characterised by X-ray crystallography. Conversion of the trans-configured title compound to a cis derivative remained unsuccessful due to an instantaneous reductive elimination process during the reaction with chelating phosphines. Treatment of trans-[Pt(BCat') Me(PCy3)(2)] with Cat(2)B(2) led to the formation of CatBMe and Cat'BMe. In the course of further investigations into this reaction, indications for two indistinguishable reaction mechanisms were found: 1) associative formation of a six-coordinate platinum centre prior to reductive elimination and 2) s-bond metathesis of B-B and C-Pt bonds. Mechanism 1 provides a straightforward explanation for the formation of both methylboranes. Scrambling of diboranes(4) Cat(2)B(2) and Cat'B-2(2) in the presence of [Pt(PCy3)(2)], fully reductive elimination of CatBMe or Cat'BMe from trans-[Pt(BCat') Me(PCy3)(2)] in the presence of sub-stoichiometric amounts of Cat(2)B(2), and evidence for the reversibility of the oxidative addition of Cat(2)B(2) to [Pt(PCy3)(2)] all support mechanism 2, which consists of sequential equilibria reactions. Furthermore, the solid-state molecular structure of cis-[Pt(BCat)(2)(PCy3)(2)] and cis-[Pt(BCat')(2)(PCy3)(2)] were investigated. The remarkably short B-B separations in both bis(boryl) complexes suggest that the two boryl ligands in each case are more loosely bound to the PtII centre than in related bis(boryl) species.