简介
二氯二(三环己基瞵)钯是一种常见的钯催化剂和膦配体络合物,在常温常压下表现为黄色固体粉末。它在卤化物溶剂如二氯甲烷、氯仿中的溶解度中等,但可溶于苯和甲苯,并且不溶于水、醇类、丙酮、乙醚、石油醚及正己烷。
用途
作为有机合成及药物分子制备中的常用催化剂,尤其在Suzuki偶联反应中有广泛的应用。有趣的是,在某些情况下,将钯催化剂与三环己基膦预先制备成络合物能提高催化效果。这可能是因为预先形成的络合物能够避免金属钯与多个膦配体进行配位。此外,已有报道指出可以通过二氯二(三环己基瞵)钯作为母体来合成其他类型的钯催化剂。
合成方法
在丙酮溶剂中回流搅拌三环己基膦和二氯化钯数小时后,固体过滤即为目标产物二氯二(三环己基瞵)钯。分离得到的产物最好保存于惰性气体氛围中,如手套箱内,以防止三环己基膦被氧化。
环境危害
作为一种含有卤素和重金属的有机化合物,二氯二(三环己基瞵)钯对水环境具有较大危害。因此,在处理该物质时,请勿让未经稀释或大量产品接触地下水、水道或污水系统。
PdCl2L2-type complexes with phosphines (L = PPhx(C6F5)3-x (x = 0-3)), phosphites (L = P(OMe)3, P(OPh)3, P(OEt)3), and phosphinites (L = PPh2(OC6F5), PPh2(O-3,5-F2C6H3), PPh2(OEt), PPh2(O-n-Bu), PPh2(O-t-Bu)) were synthesized and characterized by UV-vis and 31P NMR methods. PdCl2L2 complexes with less sterically demanding phosphines (Θ < 140°) exist as cis isomers, which is confirmed by the X-ray structure of cis-PdCl2[PPh2(OEt)]2. These complexes react with CO in the presence of NEt3 forming Pd(CO)xLy (x + y = 4) type carbonyls characterized by IR spectra. All PdCl2L2 complexes studied are active as precursors of benzyl bromide carbonylation catalysts at 40°C and 1 atm CO; however, the activity of the cis isomers is higher than that of the trans isomers. The highest yields of the carbonylation product, phenylacetic acid methyl ester, were obtained using cis-PdCl2[P(OMe)3]2 (92%), cis-PdCl2[P(OPh)3]2 (89%), and cis-PdCl2[PPh2(O-n-Bu)]2 (78%) as catalyst precursors.Key words: palladium complexes, fluorinated phosphines, benzyl bromide carbonylation.