Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Chemistry. 2011 Oct 10;17(42):11828-37. doi: 10.1002/chem.201101823. Epub 2011 Sep 7.
A stable trans-(alkyl)(boryl) platinum complex trans-[Pt(BCat')Me(PCy(3))(2)] (Cat'=Cat-4-tBu; Cy=cyclohexyl=C(6)H(11)) was synthesised by salt metathesis reaction of trans-[Pt(BCat')Br(PCy(3))(2)] with LiMe and was fully characterised. Investigation of the reactivity of the title compound showed complete reductive elimination of Cat'BMe at 80 °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 η(2) -alkyne platinum complexes, of which [Pt(η(2)-MeCCMe)(PCy(3))(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(PCy(3))(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) σ-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'(2)B(2) in the presence of [Pt(PCy(3))(2)], fully reductive elimination of CatBMe or Cat'BMe from trans-[Pt(BCat')Me(PCy(3))(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(PCy(3))(2)] all support mechanism 2, which consists of sequential equilibria reactions. Furthermore, the solid-state molecular structure of cis-[Pt(BCat)(2)(PCy(3))(2)] and cis-[Pt(BCat')(2)(PCy(3))(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 Pt(II) centre than in related bis(boryl) species.
一种稳定的反式-(烷基)(硼)铂配合物反式-[Pt(BCat')Me(PCy(3))(2)]（Cat'=Cat-4-tBu；Cy=环己基=C(6)H(11)）通过反式-[Pt(BCat')Br(PCy(3))(2)]与 LiMe 的盐交换反应合成，并进行了充分的表征。对标题化合物的反应性研究表明，Cat'BMe 在 80°C 下完全消除，在四周内完成。该过程可以通过添加各种炔烃来加速，从而导致形成相应的η(2)-炔烃铂配合物，其中[Pt(η(2)-MeCCMe)(PCy(3))(2)]通过 X 射线晶体学进行了表征。由于与螯合膦反应过程中瞬时消除消除反应，将反式构型的标题化合物转化为顺式衍生物仍然不成功。用 Cat(2)B(2)处理反式-[Pt(BCat')Me(PCy(3))(2)]导致 CatBMe 和 Cat'BMe 的形成。在对该反应的进一步研究过程中，发现了两种无法区分的反应机制的迹象：1）在消除消除之前形成六配位铂中心的缔合形成，和 2）B-B 和 C-Pt 键的σ键交换。机制 1 为两种甲基硼烷的形成提供了直接的解释。在[Pt(PCy(3))(2)]存在下，二硼烷(Cat(2)B(2)和 Cat'(2)B(2))的 scrambling，反式-[Pt(BCat')Me(PCy(3))(2)]中 CatBMe 或 Cat'BMe 的完全消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除消除 3）在存在亚化学计量的 Cat(2)B(2)的情况下，从反式-[Pt(BCat')Me(PCy(3))(2)]中完全消除 CatBMe 或 Cat'BMe，以及 Cat(2)B(2)对[Pt(PCy(3))(2)]的氧化加成的可逆性证据都支持由顺序平衡反应组成的机制 2。此外，还研究了顺式-[Pt(BCat)(2)(PCy(3))(2)]和顺式-[Pt(BCat')(2)(PCy(3))(2)]的固态分子结构。两种双硼配合物中明显较短的 B-B 分离表明，每个配合物中的两个硼基配体与 Pt(II)中心的结合比相关的双硼基物种更松。
