Combined experimental and computational studies on the nature of aromatic C-H activation by octahedral ruthenium(II) complexes:: Evidence for σ-bond metathesis from Hammett studies

被引:40
作者
DeYonker, Nathan J.
Foley, Nicholas A.
Cundari, Thomas R.
Gunnoe, T. Brent
Petersen, Jeffrey L.
机构
[1] Univ N Texas, Dept Chem, CASCaM, Denton, TX 76203 USA
[2] N Carolina State Univ, Dept Chem, Raleigh, NC 27695 USA
[3] W Virginia Univ, C Eugene Bennett Dept Chem, Morgantown, WV 26506 USA
关键词
D O I
10.1021/om7009057
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Octahedral ruthenium complexes of the type TpRu(L)(NCMe)R [Tp = hydridotris(pyrazolyl)borate; R = alkyl or aryl; L = CO or PMe3] have been shown previously to initiate the C-H activation of aromatic substrates. In order to probe the nature of the C-H activation step, reaction rates have been theoretically obtained for the conversion of TpRu(L)(eta(2)-C,C-C6H5X)Me to TpRu(L)(p-C6H4X) and CH4 where X is varied among Br, Cl, CN, F, H, NH2, NO2, and OMe. A linear Hammett correlation is calculated with a positive rho value of 2.6 for L = CO and 3.2 for L = PMe3. Calculated kinetic data for the aromatic C-H activations indicate that an electrophilic aromatic substitution mechanism is unlikely. While experiments cannot fully replicate the entire range of calculated Hammett plots, reactivity trends are consistent with the calculations that suggest activation barriers to overall metal-mediated arene C-H bond cleavage are reduced by the presence of electron-withdrawing groups in the position para to the site of activation. Previous mechanistic studies, as well as the structure and imaginary vibrational modes of the present transition states, validate that the C-H-activation for this family of TpRu complexes occurs through a sigma-bond metathesis-type pathway.
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页码:6604 / 6611
页数:8
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