New Transformations of Unsaturated Hydrocarbons with Polynuclear Complexes of Pd (I)

近年来，钯配合物催化剂在有机合成领域中的应用日益受到人们的关注。在大多数催化中，关键中间体被认为具有Pd（0）和Pd（II）的氧化态。然而，迫切需要彻底改变这一方法。本课题的目的是通过研究含烯丙基、炔丙基、乙烯基、炔基和卡宾等桥联配体的多核Pd（I）配合物的制备、结构和反应，为下一代的合成方法奠定分子水平的基础。首先，制备了含4个和6个乙腈配体的Pd（I）-Pd（I）配合物，这些配合物很容易被不饱和烃等弱配体取代。X-射线结构测定证实了两个PPh_3配体与具有四个乙腈配体的Pd（I）-Pd（I）单元的配位。该配合物与两当量的。苯乙炔，得到Pd-Pd络合物，其含有通过乙炔的头-尾二聚化制备的桥连丁烯二亚基配体。在Pd（0）配合物存在下，由六个乙腈配体组成的Pd（I）-Pd（I）配合物与1，8-二苯基辛四烯反应，得到了由两个四烯配体与Pd_4链配位的新型夹心配合物。然后合成了含桥联二烯和联烯配体的Pd（I）-Pd（I）配合物，通过NMR、X-射线衍射和分子轨道计算确定了它们的结构。这些研究表明，相当大的电子密度通过背键相互作用从Pd-Pd σ轨道流向有机配体的反键MO。

Increasing attention has been paid to rapid progress in the field of organic synthesis by means of palladium complex based catalyst. In most of the catalysis, key intermediates are believed to have the oxidation state of Pd (0) and Pd(II). However, there is an urgent need to revolutionize this methodology. The aim of the present project is to lay a molecular level basis for the synthetic method of the next generation by studying preparation, structure and reactions of polynuclear Pd (I) complexes containing bridging ligands such as allyl, propargyl, vinyl, alkynyl, and carbene. First of all, the Pd (I)-Pd (I) complexes containing 4 and 6 acetonitrile ligands, which can readily be replaced by weak ligands such as unsaturated hydrocarbons, have been prepared. X-ray structure determination established coordination of two PPh_3 ligands to the Pd (I)-Pd (I) unit having four acetonitrile ligands. This complex reacted with two equiv. phenylacetylene to give the Pd-Pd complex containing the bridging butenediylidene ligand made by head-to-tail dimerization of the acetylene. The Pd (I)-Pd (I) complex having six acetonitrile ligands reacted with 1, 8-diphenyloctatetraene in the presence of Pd (0) complex to give novel sandwich complex made by two tetraen ligands coordinating to the linear Pd_4 chain. Next the Pd (I)-Pd (I) complexes containing bridging diene and allene ligands were synthesized, and their structures determined by NMR and X-ray analysis as well as by MO calculation. These studies established that considerable electron density flows from the Pd-Pd σ orbital to the antibonding MO of the organic ligand through back bonding interaction.