School of Life Sciences, Department of Chemistry, University of Sussex, Falmer, Brighton, BN1 9QJ, UK.
Dalton Trans. 2018 Oct 23;47(41):14531-14539. doi: 10.1039/c8dt02654h.
The reaction of the bis(pentalene)dititanium complex Ti2(μ:η5,η5-Pn†)2 (Pn† = C8H4(1,4-SiiPr3)2) (1) with the N-heterocyclic carbene 1,3,4,5-tetramethylimidazol-2-ylidene results in intramolecular C-H activation of an isopropyl substituent to form a tucked-in hydride (3). Whilst pyridine will also effect this cyclometallation reaction to form (5), the pyridine analogue of (3), the bases 1,2,4,5-tetramethyl-imidazole, 2,6-lutidine, DABCO or trimethylphosphine are ineffective. The reaction of (1) with 2,6-dichloro-pyridine affords crystallographically characterised (6) which is the product of oxidative addition of one of the C-Cl bonds in 2,6-dichloro-pyridine across the Ti-Ti double bond in (1). The tucked-in hydride (3) reacts with hydrogen to afford a dihydride complex (4) in which the tuck-in process has been reversed; detailed experimental and computational studies on this reaction using D2, HD or H2/D2 support a mechanism for the formation of (4) which does not involve σ-bond metathesis of H2 with the tucked-in C-H bond in (3). The reaction of (3) with tBuCCH yields the corresponding acetylide hydrido complex (7), where deuteration studies show that again the reaction does not proceed via σ-bond metathesis. Finally, treatment of (3) with HCl affords the chloro-derivative (9) [(NHC)Ti(μ-H)Ti{(μ,η5:η5)Pn†}2Cl], whereas protonation with [NEt3H]BPh4 yielded a cationic hydride (10) featuring an agostic interaction between a Ti centre and an iPr Me group.
双（五并苯）二钛配合物 Ti2(μ:η5,η5-Pn†)2（Pn†=C8H4(1,4-SiiPr3)2）（1）与 N-杂环卡宾 1,3,4,5-四甲基咪唑-2-亚基反应，导致异丙基取代基的分子内 C-H 活化，形成缩进的氢化物（3）。虽然吡啶也会影响这种环金属化反应，形成（5），即（3）的吡啶类似物，但碱 1,2,4,5-四甲基咪唑、2,6- 二甲基吡啶、DABCO 或三甲基膦无效。（1）与 2,6-二氯吡啶反应得到结晶学表征的（6），这是（1）中 Ti-Ti 双键穿过的一个 C-Cl 键的氧化加成产物。缩进的氢化物（3）与氢气反应得到二氢化物配合物（4），其中缩进过程已被逆转；使用 D2、HD 或 H2/D2 对该反应进行的详细实验和计算研究支持了一种形成（4）的机制，该机制不涉及 σ-键重排，H2 与（3）中的缩进 C-H 键之间的 σ-键重排。（3）与 tBuCCH 的反应得到相应的炔基氢化物配合物（7），其中氘代研究表明，该反应也不通过 σ-键重排进行。最后，（3）与 HCl 反应得到氯衍生物（9）[(NHC)Ti(μ-H)Ti{(μ,η5:η5)Pn†}2Cl]，而用[NEt3H]BPh4 质子化得到阳离子氢化物（10），其中 Ti 中心和异丙基 Me 基团之间存在氢键相互作用。
