Labios Liezel A, Millard Matthew D, Rheingold Arnold L, Figueroa Joshua S
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Mail Code 0358, La Jolla, California 92093-0358, USA.
J Am Chem Soc. 2009 Aug 19;131(32):11318-9. doi: 10.1021/ja905338x.
Mg metal reduction of the divalent precursor PdCl(2)(CNAr(Dipp2))(2) (Dipp = 2,6-diisopropylphenyl) provides the isolable, two-coordinate Pd(0) bis-isocyanide, Pd(CNAr(Dipp2))(2), which is the first stable monomeric isocyanide complex of zerovalent palladium. Variable temperature (1)H NMR and FTIR studies on Pd(CNAr(Dipp2))(2) in the presence of added CNAr(Dipp2) revealed that free and coordinated isocyanide undergo rapid exchange, but the components do not form a stable tris-isocyanide complex. Bis-isocyanide Pd(CNAr(Dipp2))(2) is active for oxidative addition reactions and readily reacts with benzyl chloride and mesityl bromide to form Pd(Cl)(Bz)(CNAr(Dipp2))(2) and Pd(Br)(Mes)(CNAr(Dipp2))(2), respectively. Room-temperature Suzuki-Miyaura cross-coupling reactions are mediated by Pd(CNAr(Dipp2))(2). Coordinatively and electronically unsaturated substrates also react with Pd(CNAr(Dipp2))(2). Addition of thallium(I) triflate (TlOTf) to Pd(CNAr(Dipp2))(2) results in the salt [TlPd(CNAr(Dipp2))(2)]OTf, while addition of O(2) results in the peroxo complex (eta(2)-O)Pd(CNAr(Dipp2))(2). Most remarkably, 2 equiv of nitrosobenzene react with Pd(CNAr(Dipp2))(2) to form the square planar complex (kappa(1)-N-PhNO)(2) Pd(CNAr(Dipp2))(2), the geometry of which strongly suggests the formation of a divalent Pd center. With the aid of density functional theory calculations, this valence change is rationalized in terms of a formal reduction of the bond order in each NO unit to 1.5.
用镁金属还原二价前体PdCl₂(CNAr(Dipp₂))₂（Dipp = 2,6 - 二异丙基苯基）可得到可分离的二配位零价钯双异腈配合物Pd(CNAr(Dipp₂))₂，它是零价钯的首个稳定单体异腈配合物。在加入CNAr(Dipp₂)的情况下，对Pd(CNAr(Dipp₂))₂进行变温¹H NMR和FTIR研究表明，游离的和配位的异腈会快速交换，但各组分不会形成稳定的三异腈配合物。双异腈配合物Pd(CNAr(Dipp₂))₂对氧化加成反应具有活性，并且容易与苄基氯和均三甲苯基溴反应，分别形成Pd(Cl)(Bz)(CNAr(Dipp₂))₂和Pd(Br)(Mes)(CNAr(Dipp₂))₂。室温下的铃木 - 宫浦交叉偶联反应由Pd(CNAr(Dipp₂))₂介导。配位和电子不饱和的底物也能与Pd(CNAr(Dipp₂))₂反应。向Pd(CNAr(Dipp₂))₂中加入三氟甲磺酸铊（TlOTf）会生成盐[TlPd(CNAr(Dipp₂))₂]OTf，而加入O₂则会生成过氧配合物(η² - O)Pd(CNAr(Dipp₂))₂。最引人注目的是，2当量的亚硝基苯与Pd(CNAr(Dipp₂))₂反应形成平面正方形配合物(kappa¹ - N - PhNO)₂Pd(CNAr(Dipp₂))₂，其几何结构强烈表明形成了二价钯中心。借助密度泛函理论计算，这种价态变化可以从每个NO单元中键级形式上降低到1.5的角度进行合理解释。
