Arylthiolate Coordination and Reactivity at Pseudotetrahedral Nickel(II) Centers: Modulation by Noncovalent Interactions

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• 作者：Swarup Chattopadhyay ; Tapash Deb ; Huaibo Ma ; Jeffrey L. Petersen ; Victor G. Young Jr. ; Michael P. Jensen
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：April 21, 2008
• 年：2008
• 卷：47
• 期：8
• 页码：3384 - 3392
• 全文大小：813K
• 年卷期：v.47,no.8(April 21, 2008)
• ISSN：1520-510X

文摘

Five new pseudotetrahedral nickel(II) arylthiolate complexes Tp^R,MeNi−SR′ [(Tp^R,Me)⁻ = 2,2,2-κ³-hydridotris(3-R,5-methylpyrazolyl)borate; R = Me, R′ = C₆H₅ (Ph), 2,4,6-C₆H₂(CH₃)₃ (Mes); R = Ph, R′ = C₆H₅ (Ph), 2,4,6-C₆H₂(CH₃)₃ (Mes), and 2,6-C₆H₃(CH₃)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, ¹H 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,MeNi−SPh and Tp^Ph,MeNi−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.