The First Carbodiphosphorane Complex with Two Palladium Centers Attached to the CDP Carbon: Assembly of a Single-Stranded di-Pd Helicate by the PCP Pincer ligand C(dppm)2

The reaction of the protonated PCP pincer carbodiphosphorane (CDP) complex [PdCl(CH(dppm)2)]Cl2 (1) with [PdCl2(MeCN)2] results in the opening of one ring of the pincer structure and affords the betaine [Pd2Cl5(CH(dppm)2)] (2). The [CH(dppm)2]+ ligand forms a five-membered chelate ring with the Pd(1)Cl2 moiety via the protonated CDP carbon (positively charged) and one phosphine functionality and bridges to the anionic Pd(2)Cl3 fragment via the second phosphine phosphorus. The complex is chiral due to a stereocenter at the protonated CDP carbon atom. Treatment of 2 with water effects deprotonation of the CDP carbon, C–H activation at one methylene group, and the coordination of the second Pd to the CDP carbon. The resulting tricyclic complex [Pd2Cl3(C(dppm)(Ph2CHPh2))] (3) is the first compound with two Pd centers coordinated to a CDP carbon. Compound 3 forms a single-stranded helicate structure and exhibits two interdependent carbon stereocenters, resulting in only two possible enantiomers. The complexes 2·2CH2Cl2 and 3·3CH2Cl2 crystallize in the chiral space group P21, whereby a spontaneous resolution of the enantiomers occurs in both cases.

质子化的PCP钳式羰基膦磷烷[PdCl(CH(dppm)2)]Cl2(1)与[PdCl2(MeCN)2]的反应导致钳式结构中的一个环的开启，从而得到胆碱[Pd2Cl5(CH(dppm)2)](2)。[CH(dppm)2]+配体通过质子化的CDP碳（带正电荷）和一个膦功能团与Pd(1)Cl2基团形成五元螯合环，并通过第二个膦磷桥接到阴离子Pd(2)Cl3片段。由于质子化的CDP碳原子上的立体中心，该复合物具有手性。2与水的处理导致CDP碳去质子化，一个亚甲基的C-H活化，以及第二个Pd与CDP碳的配位。所得的三环复合物[Pd2Cl3(C(dppm)(Ph2CHPh2))] (3)是第一个与CDP碳配位有两个Pd中心的化合物。化合物3形成单链螺旋结构，并展现出两个相互依赖的碳立体中心，从而仅产生两种可能的对映异构体。复合物2·2CH2Cl2和3·3CH2Cl2分别结晶于手性空间群P21中，在此两种情况下均自发地对映异构体进行了分离。