三核铬（III）配合物[Cr(3)(μ(3)-O)(μ-RCO(2))(6)(H(2)O)(3)]⁺（R = H、CH(3)、CH(3)CH(2)、CH(2)Cl、CHCl(2)、CH(3)OCH(2)、(CH(3))(3)C、CH(2)ClCH(2)、(CH(3)CH(2))(2)CH）中用二甲基乙酰胺取代末端水配体的动力学研究。从活化体积和桥连羧酸根配体的取代基效应阐明反应机理

Kinetic Study on the Substitution of Dimethylacetamide for the Terminal Aqua Ligands in the Trinuclear Chromium(III) Complexes [Cr(3)(&mgr;(3)-O)(&mgr;-RCO(2))(6)(H(2)O)(3)](+) (R = H, CH(3), CH(3)CH(2), CH(2)Cl, CHCl(2), CH(3)OCH(2), (CH(3))(3)C, CH(2)ClCH(2), (CH(3)CH(2))(2)CH). Elucidation of the Mechanism from the Activation Volumes and the Substituent Effects of Bridging Carboxylate Ligands.

作者信息

Fujihara Takashi, Aonahata Jun, Kumakura Shigekazu, Nagasawa Akira, Murakami Kazuhiro, Ito Tasuku

机构信息

Department of Chemistry, Faculty of Science, Saitama University, Urawa, Saitama 338-8570, Japan, Department of Chemistry, Faculty of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan, and Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578, Japan.

出版信息

Inorg Chem. 1998 Jul 27;37(15):3779-3784. doi: 10.1021/ic980001g.

DOI:10.1021/ic980001g

PMID:11670479

Abstract

The substitution of dimethylacetamide (dma) for the terminal aqua ligands in the carboxylate-bridged trinuclear chromium(III) complex Cr(3)(&mgr;(3)-O)(&mgr;-RCO(2))(6)(H(2)O)(3) (R = H, CH(3), CH(3)CH(2), CH(2)Cl, CHCl(2), CH(3)OCH(2), (CH(3))(3)C, CH(2)ClCH(2), (CH(3)CH(2))(2)CH) in dma was kinetically studied by UV-visible absorption at 25-50 degrees C and 0.1-232 MPa. The time course is uniphasic over all three steps of the ligand replacement. The substitution rate k varied from 2.4(1) x 10(-)(5) (R = CHCl(2)) to 9.49(2) x 10(-)(3) (R = C(CH(3))(3)) s(-)(1) depending on the substituent R at 40 degrees C. Large positive activation parameters DeltaH() (98-123 kJ mol(-)(1)), DeltaS() (29-81 J K(-)(1) mol(-)(1)), and DeltaV() (12.4-21.3 cm(3) mol(-)(1)) for all the complexes suggested a dissociative activation mode (D or I(d) mechanism). It is similar to those for terminal ligand substitution of acetate-bridged trinuclear complexes of ruthenium(III) and rhodium(III) with a &mgr;(3)-O ligand and molybdenum with two &mgr;(3)-O ligands. Examination of the substituent effect disclosed a linear relationship between k and Taft's electronic parameters, as well as pK(a) (RCOOH), indicating that the sigma-donor ability of the bridging carboxylate affects the strength of the Cr-OH(2) bond in the cis position. The crystals of [Cr(3)(&mgr;(3)-O)(&mgr;-RCO(2))(6)(H(2)O)(3)][B(C(6)H(5))(4)].nH(2)O (R = H (1b), n = 6; R = CH(3) (2b), n = 2) were found to be triclinic with space group P&onemacr;, a = 9.2080(8) Å, b = 14.724(2) Å, and c = 15.308(2) Å, alpha = 79.369(6) degrees, beta = 86.513(8) degrees, gamma = 79.823(8) degrees, Z = 2, and V = 2006.5(4) Å(3) and with space group P&onemacr;, a = 8.848(6) Å, b = 15.057(7) Å, c = 17.375(8) Å, alpha = 107.82(3) degrees, beta = 104.57(4) degrees, gamma = 92.27(4) degrees, Z = 2, and V = 2116(2) Å(3), respectively. The relatively longer Cr-OH(2) distances (average 2.03(1) and 2.06(2) Å for 1b and 2b, respectively) than those of the mononuclear chromium(III) aqua complexes, due to a trans effect of the central oxide ion and the additional cis effect of the bridging carboxylate, play a role in accelerating the dissociative substitution for the terminal ligands.

摘要

在25至50摄氏度和0.1至232兆帕的条件下，通过紫外可见吸收光谱对在二甲基乙酰胺（dma）中，用二甲基乙酰胺取代羧酸根桥联的三核铬（III）配合物[Cr(3)(μ(3)-O)(μ-RCO(2))(6)(H(2)O)(3)]⁺（R = H、CH(3)、CH(3)CH(2)、CH(2)Cl、CHCl(2)、CH(3)OCH(2)、(CH(3))(3)C、CH(2)ClCH(2)、(CH(3)CH(2))(2)CH）末端水配体的过程进行了动力学研究。在配体取代的所有三个步骤中，时间进程都是单相的。取代速率k在40摄氏度时，根据取代基R的不同，从2.4(1)×10⁻⁵（R = CHCl(2)）变化到9.49(2)×10⁻³（R = C(CH(3))(3)）s⁻¹。所有配合物的大的正活化参数ΔH⁰（98 - 123 kJ mol⁻¹）、ΔS⁰（29 - 81 J K⁻¹ mol⁻¹）和ΔV⁰（12.4 - 21.3 cm³ mol⁻¹）表明是离解活化模式（D或I(d)机制）。这与钌（III）和铑（III）的带有μ(3)-O配体的乙酸根桥联三核配合物以及钼的带有两个μ(3)-O配体的配合物的末端配体取代情况相似。取代基效应的研究揭示了k与塔夫脱电子参数以及pK(a)（RCOOH）之间的线性关系，表明桥联羧酸根的σ供体能力影响顺式位置上Cr - OH₂键的强度。发现[Cr(3)(μ(3)-O)(μ-RCO(2))(6)(H(2)O)(3)][B(C(6)H(5))(4)].nH(2)O（R = H (1b)，n = 6；R = CH(3) (2b)，n = 2）的晶体为三斜晶系，空间群为Pī，a = 9.2080(8) Å，b = 14.724(2) Å，c = 15.308(2) Å，α = 79.369(6)°，β = 86.513(8)°；γ = 79.823(8)°；Z = 2；V = 2006.5(4) Å³，以及空间群为Pī，a = 8.848(6) Å，b = 15.057(7) Å，c = 17.375(8) Å，α = 107.82(3)°，β = 104.57(4)°，γ = 92.27(4)°，Z = 2，V = 2116(2) Å³。由于中心氧离子的反位效应和桥联羧酸根的额外顺式效应，与单核铬（III）水合配合物相比，相对较长的Cr - OH₂距离（1b和2b分别平均为2.03(1)和2.06(2) Å）在加速末端配体的离解取代中起作用。