1,2-CH Bond Activation of Pyridine across a Transient Titanium Alkylidene Radical and Re-Formation of the Ti═CHtBu Moiety,Organometallics

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1,2-CH Bond Activation of Pyridine across a Transient Titanium Alkylidene Radical and Re-Formation of the Ti═CHtBu Moiety
Organometallics ( IF 2.5 ) Pub Date : 2017-12-29 00:00:00 , DOI: 10.1021/acs.organomet.7b00770
Takashi Kurogi ₁ , Matthias E. Miehlich ₂ , Dominik Halter ₂ , Daniel J. Mindiola ₁

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Reduction of the titanium alkylidene [(PNP)Ti═CH^tBu(OTf)] (PNP^– = N[2-PⁱPr₂-4-methylphenyl]₂^–) with KC₈ in the presence of pyridine results in formation of the transient titanium(III) alkylidene radical [(PNP)Ti═CH^tBu)] (A) or the adduct [(PNP)Ti═CH^tBu)(NC₅H₅)] (B), which activates the C–H bond of pyridine to form the titanium(III) pyridyl alkyl complex [(PNP)Ti(CH₂^tBu)(η²-NC₅H₄)] (1) in 64% yield as brown microcrystals. Low-temperature X-band EPR spectroscopy and single-crystal X-ray diffraction studies confirm the identity of 1 as a d¹ metal-centric radical with superhyperfine coupling to one nitrogen atom and having a side-on pyridyl moiety, which results in formation of the two isomeric forms 1a,b. Oxidation of 1 with [FeCp*₂][OTf] cleanly promotes α-hydrogen abstraction to re-form [(PNP)Ti═CH^tBu(OTf)] with concurrent elimination of pyridine and FeCp*₂. Re-formation of the alkylidene moiety most likely stems from an intermediate such as [(PNP)Ti(CH₂^tBu)(η²-NC₅H₄)(OTf)] (C).

中文翻译：

吡啶的1,2-CH键活化跨过暂态钛亚烷基和Ti═CH的重新形成^吨卜物部分

钛亚烷基的还原[（PNP）Ti═CH^吨卜（OTF）]（PNP ^- = N [2-P^我镨₂ -4-甲基苯基] ₂^-）与KC ₈在吡啶结果在地层的存在瞬态钛（III）亚烷基[（PNP）Ti═CH^吨丁基）]（甲）或加合物[（PNP）Ti═CH^吨卜）（NC ₅ H ^ ₅）]（乙），其激活与c吡啶基烷基络合物[（PNP）的Ti（CH吡啶-H键以形成钛（III）₂^吨卜）（η ² -NC ₅ H ^ ₄）]（1），为棕色微晶，产率为64％。低温X波段EPR光谱和单晶X射线衍射研究证实1的身份为ad ^1以金属为中心的自由基，具有与一个氮原子的超超精细偶联，并具有侧吡啶基部分，导致形成吡啶基。两个同分异构形式1a，b。氧化1与[FeCp * ₂ ] [光学传递函数]干净地促进α-夺氢重新形成[（PNP）Ti═CH^吨BU（OTF）]与吡啶和FeCp *并发消除₂。亚烷基部分的重整很可能源自中间体，例如[[PNP）Ti（CH ₂^t Bu）（η² -NC ₅ H ₄）（OTf）]（C）。

更新日期：2017-12-31

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