Barriers for arene C-H bond activation in platinum(II) η2-arene intermediates
Barriers for arene C-H bond activation in platinum(II) η2-arene intermediates
复制标题
DOI：
10.1021/om020526n
复制
发表时间：
2002-12-09
期刊：
影响因子：
2.8
通讯作者：
Templeton, JL
中科院分区：
文献类型：
--
作者：
Norris, CM;Reinartz, S;Templeton, JL
Tp‘Pt(Ar)(H)(R)[Tp’=氢化三(3，5二甲基吡唑基)硼酸盐；Ar=芳基；R=H，C6H5与[H(OEt2)(2)][BAR‘(4)][BAR’4=四(3，5-三氟甲基苯基)硼酸盐]形成阳离子铂(II)ETA(2)-芳烃配合物[Kappa(2)-(HTP‘)Pt(ETA(2)-Har)(R)1[BAR’(4)][Ar=C6H5，R=H(2)；Ar=MeC6H4，R=H(4)；Ar=3，6-Me2C6H3，R=H(6)；Ar=R=C6H5(8)]。通过变温核磁共振测量，计算了配合物6在183K时铂在ETA(2)-对二甲苯环上的迁移势垒为9.4kcal/mol。阳离子苯络合物2与氢化物配位体之间氢交换的Eyring分析表明，DeltaH(双匕首)=11.7+/-0.5kcal mol(-1)，deltas(双匕首)=-3.8+/-2cal mol(-1)K(-1)。这个过程被认为是通过芳烃C-H氧化加成得到五配位的铂(IV)苯基二氢化合物中间体2a。基态ETA(2)-芳烃加合物与相邻氢化物配体的分离使得芳烃C-H键的氧化加成势垒(DeltaG(双匕首))被测得对甲苯加合物4中的对氢为13.3千卡/摩尔，对二甲苯加合物6为13.6千卡/摩尔，对二甲苯加合物6为14.2千卡/摩尔。两个TP‘臂的平均环境是C，对称的ETA(2)-苯加合物S的核磁共振可观察到的特征。它可能是通过具有C对称性的五配位铂(IV)二苯氢化物中间体Sa发生的，允许芳烃C-H氧化加成的势垒计算为12.9kcal/mol。苯氢化物2和苯苯加合物8中芳烃C-H(D)键氧化加成反应的动力学同位素效应在259K和241K分别为k(H)/k(D)=3.0和4.7。这些数据提供了对芳烃C-H键活化的能量学的洞察。
Protonation of platinum(IV) complexes of the type Tp'Pt(Ar)(H)(R) [Tp' = hydridotris(3,5dimethylpyrazolyl)borate; Ar = aryl; R = H, C6H5] with [H(OEt2)(2)][BAr'(4)][BAr'4 = tetrakis(3,5-trifluoromethylphenyl)borate] results in the formation of cationic platinum(II) eta(2)-arene complexes [kappa(2)-(HTp')Pt(eta(2)-HAr)(R)1 [BAr'(4)] [Ar = C6H5, R = H (2); Ar = MeC6H4, R = H (4); Ar = 3,6-Me2C6H3, R = H (6); Ar = R = C6H5 (8)]. A barrier of 9.4 kcal/mol for platinum migration around the eta(2)-p-xylene ring was calculated for complex 6 at 183 K following variable-temperature NMR measurements. Eyring analysis of hydrogen exchange between the bound benzene and the hydride ligand for cationic benzene complex 2 indicates DeltaH(double dagger) = 11.7 +/- 0.5 kcal mol(-1) and DeltaS(double dagger) = -3.8 +/- 2 cal mol(-1)K(-1). This process is assumed to proceed via arene C-H oxidative addition to give the five-coordinate platinum(IV) phenyl dihydride intermediate 2a. Isolation of ground state eta(2)-arene adducts with adjacent hydride ligands has allowed the barrier to oxidative addition for arene C-H bonds (DeltaG(double dagger)) to be measured as 13.3 kcal/mol for the p-hydrogen and 13.6 kcal/mol for the m-hydrogens in the toluene adduct 4 and 14.2 kcal/mol for the p-xylene adduct 6. Averaging of the environments for two Tp' arms is an NMR observable feature for the C, symmetric eta(2)-benzene phenyl adduct S. This dynamic process, which presumably occurs via a five-coordinate platinum(IV) diphenyl hydride intermediate Sa with C, symmetry, allows the barrier for arene C-H oxidative addition to be calculated as 12.9 kcal/mol. Kinetic isotope effects for oxidative addition of the arene C-H(D) bond in the benzene hydride adduct 2 and the benzene phenyl adduct 8 were determined to be k(H)/k(D) = 3.0 at 259 K and 4.7 at 241 K, respectively. These data provide insight into the energetics of arene C-H bond activation.