A kinetic study on pyridine exchange reactions at a bis(μ-acetato)(μ-oxo)diruthenium(III) center:: effects of monodentate and bidentate N-heterocyclic ligands cis to the oxo bridge

被引:20
作者
Abe, M [1 ]
Mitani, A [1 ]
Ohsawa, A [1 ]
Herai, M [1 ]
Tanaka, M [1 ]
Sasaki, Y [1 ]
机构
[1] Hokkaido Univ, Grad Sch Sci, Div Chem, Kita Ku, Sapporo, Hokkaido 0600810, Japan
关键词
diruthenium complexes; ligand-exchange reactions; pyridine; oxo; H-1 NMR spectroscopy; activation parameters; redox potentials;
D O I
10.1016/S0020-1693(01)00780-0
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
A series of (mu-oxo)bis(mu-acetato)diruthenium(III) complexes containing two pyridine (py) ligands and varied N-heterocyclic ligands in the positions trans and cis to mu-O, respectively, have been prepared to study py/py-d(5) exchange reactions using H-1 NMR spectroscopy. The diruthenium(III) complexes under investigation are [Ru-2(mu-O)(mu-CH3COO)(2)(py)(6)](PF6)(2) (1), [Ru-2(mu-O)(mu-CH3COO)(2)(bpy)(2)(py)(2)](PF6)(2) (2). [Ru-2(mu-O)(mu-CH3COO)(2)(acpy)(4)(py)(2)](FF6)(2) (3). and [Ru-2(mu-O)(mu-CH3COO)(2)(dmbpy)(2)-(py)(2)](PF6)(2) (4), where bpy=2,2'-bipyridine, acpy=4-acetylpyridine, and dmbpy=4,4'-dimethyl-2,2'-bipyridine. Pseudo-first order rate constants for the ligand-exchange reactions are 10(-6)-10(-5) s(-1) for 1-4 in CD3CN at 298 K. It is found that the rate of the py/py-d(5) exchange reactions is controlled by the electronic nature of the cis-oriented ancillary ligands, while the exchange mechanisms are tuned principally by the ligand steric factors. The activation parameters (DeltaHdouble dagger and DeltaSdagger) indicate that exchange reactions proceed through the dissociative (D) or the interchange dissociative (I-d) mechanism for 1 and 3. Negative DeltaSdouble dagger values observed for 2 and 4 suggest a significant contribution of incoming ligands to the exchange pathway. The kinetic and thermodynamic parameters for the diruthenium series and the corresponding data for Ru-based oxo bridged trinuclear complexes established previously are compared and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
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页码:158 / 167
页数:10
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