Sharma Alpesh K, Joshi Hemant, Bhaskar Renu, Kumar Satyendra, Singh Ajai K
Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016, India.
Dalton Trans. 2017 Feb 21;46(8):2485-2496. doi: 10.1039/c7dt00083a.
Schiff base ligands (L1: sulfated and L2: selenated) having a ferrocene core synthesized by reacting ferrocene-carboxaldehyde with 2-(phenylthio/seleno)ethylamine on treatment with NaPdCl in the presence of NaOAc give cyclopalladated complexes [Pd(L1/L2-H)Cl] (1/2). Complex 1 of a sulfated Schiff base L1, on reacting with one equivalent of triphenylphosphine gives complex [Pd(L1-H)PPhCl] (3), formed due to cleavage of a Pd-S bond. With 2 such a reaction does not occur, as a Pd-Se bond being stronger than that of its sulfur analogue does not get cleaved. L1, L2 and their complexes 1-3 were authenticated with HR-MS, H, C{H} and Se{H} NMR spectroscopy. The single crystal structures of 1-3 were determined with X-ray diffraction. Palladium in all three complexes has nearly a square planar geometry. The Pd-S, Pd-Se and Pd-P bond distances are 2.4249(12), 2.5058(14) and 2.2445(17) Å respectively. The catalytic activity of complexes 1-3 was explored for O-arylation of phenol and Suzuki-Miyaura coupling (SMC) of phenylboronic acid with aryl bromides and chlorides. The optimum reaction time for SMC of ArBr is 3 h whereas for ArCl it is 6 h. The TON values of O-arylation catalyzed with complexes 1-3 are up to ∼170 (TOF, 28 h) and SMC ∼9300 (TOF, 3100 h) for the reaction time of the order of 3 and 6 h respectively. The catalytic process is somewhat more efficient with 2 (Pd bonded with a selenoether group), than 3, followed by 1.
通过使二茂铁甲醛与2-(苯硫基/苯硒基)乙胺反应合成的具有二茂铁核心的席夫碱配体（L1：硫酸化的和L2：硒化的），在醋酸钠存在下用NaPdCl处理时得到环钯化配合物[Pd(L1/L2-H)Cl]（1/2）。硫酸化席夫碱L1的配合物1与一当量的三苯基膦反应得到配合物[Pd(L1-H)PPhCl]（3），这是由于Pd-S键的断裂而形成的。对于2，不会发生这样的反应，因为Pd-Se键比其硫类似物的键更强，不会断裂。L1、L2及其配合物1-3通过高分辨质谱、氢谱、碳氢相关谱和硒氢相关谱进行了鉴定。1-3的单晶结构通过X射线衍射确定。所有三种配合物中的钯几乎具有平面正方形几何构型。Pd-S、Pd-Se和Pd-P键长分别为2.4249(12)、2.5058(14)和2.2445(17) Å。研究了配合物1-3对苯酚的O-芳基化以及苯基硼酸与芳基溴化物和氯化物的铃木-宫浦偶联（SMC）的催化活性。ArBr的SMC的最佳反应时间为3小时，而ArCl的最佳反应时间为6小时。配合物1-3催化的O-芳基化的TON值在反应时间约为3小时和6小时时分别高达约170（TOF，28小时）和SMC约9300（TOF，3100小时）。催化过程中，2（钯与硒醚基团键合）比3更有效率，其次是1。
