Chattopadhyay Swarup, Deb Tapash, Ma Huaibo, Petersen Jeffrey L, Young Victor G, Jensen Michael P
Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701, USA.
Inorg Chem. 2008 Apr 21;47(8):3384-92. doi: 10.1021/ic702417w. Epub 2008 Mar 15.
Five new pseudotetrahedral nickel(II) arylthiolate complexes Tp (R,Me)Ni-SR' [(Tp (R,Me)) (-) = 2,2,2-kappa (3)-hydridotris(3-R,5-methylpyrazolyl)borate; R = Me, R' = C 6H 5 (Ph), 2,4,6-C 6H 2(CH 3) 3 (Mes); R = Ph, R' = C 6H 5 (Ph), 2,4,6-C 6H 2(CH 3) 3 (Mes), and 2,6-C 6H 3(CH 3) 2 (Xyl)] were prepared by metathesis reactions of known chloride complexes with sodium arylthiolate salts in THF. The new products were fully characterized. The effect of increasing bulk of substituents at the proximal 3-pyrazolyl and ortho-thiolate positions represented in this series was evident in spectroscopic studies (UV-vis-NIR, (1)H NMR) of the product complexes. Increased steric contact induced red-shifting of nickel-thiolate ligand to metal charge transfer (LMCT) bands and enhanced contact shifts of arylthiolate protons with the paramagnetic ( S = 1) nickel(II) ion. These spectroscopic effects arise from structural distortion of the nickel(II)-thiolate bond revealed by X-ray crystal structure determinations of the structural extremes of the series, Tp (Me,Me)Ni-SPh and Tp (Ph,Me)Ni-SXyl. The distortion consists of a significantly increased tilting of the Ni-S bond from an ideal trigonal axis and increased linearity of the Ni-S-R angle that alters covalency of the Ni-S coordinate bond. Reactivity of the nickel-thiolate linkage toward electrophilic alkylation with MeI is also significantly affected, showing enhanced rates according to two distinct competing mechanisms, direct bimolecular alkylation of intact complex and rate-limiting unimolecular dissociation of free thiolate. Possible biochemical relevance of these observations to tetrahedral nickel(II) centers in metalloenzymes is considered.
通过已知的氯化物配合物与芳基硫醇钠在四氢呋喃中进行复分解反应，制备了五种新型的拟四面体镍（II）芳基硫醇配合物Tp（R，Me）Ni-SR'[（Tp（R，Me））（-）= 2,2,2-κ（3）-氢三（3-R，5-甲基吡唑基）硼酸盐；R = 甲基，R' = 苯基（Ph），2,4,6-三甲基苯基（Mes）；R = 苯基，R' = 苯基（Ph），2,4,6-三甲基苯基（Mes），以及2,6-二甲基苯基（Xyl）]。对新产物进行了全面表征。在该系列中，近端3-吡唑基和邻位硫醇盐位置上取代基体积增大的影响，在产物配合物的光谱研究（紫外可见近红外光谱、氢核磁共振）中很明显。空间接触增加导致镍-硫醇盐配体到金属电荷转移（LMCT）带发生红移，并增强了芳基硫醇盐质子与顺磁性（S = 1）镍（II）离子的接触位移。这些光谱效应源于该系列结构极端情况Tp（Me，Me）Ni-SPh和Tp（Ph，Me）Ni-SXyl的X射线晶体结构测定所揭示的镍（II）-硫醇盐键的结构畸变。这种畸变包括Ni-S键相对于理想三角轴的倾斜显著增加，以及Ni-S-R角的线性增加，这改变了Ni-S配位键的共价性。镍-硫醇盐键对用甲基碘进行亲电烷基化反应的反应性也受到显著影响，根据两种不同的竞争机制显示出反应速率增强，即完整配合物的直接双分子烷基化和游离硫醇盐的限速单分子解离。考虑了这些观察结果与金属酶中四面体镍（II）中心可能的生化相关性。
