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首页> 外文期刊>Organometallics >Intramolecular C-H activation reactions derived from a terminal titanium neopentylidene functionality. Redox-controlled 1,2-addition and alpha-hydrogen abstraction reactions
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Intramolecular C-H activation reactions derived from a terminal titanium neopentylidene functionality. Redox-controlled 1,2-addition and alpha-hydrogen abstraction reactions

机译：分子内C-H活化反应衍生自末端新戊基亚钛基官能团。氧化还原控制的1,2-加成和α-氢提取反应

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摘要

Alkylation of the terminal neopentylidene titanium(IV) complex (L-1)Ti=(CHBu)-Bu-t(OTf) (L-1(-) = [Ar]NC(Me)CHC(Me)N[Ar], Ar = 2,6-(CHMe2)(2)C6H3) with LiCH2SiMe3 resulted in formation of the alkylidene-alkyl species (L-1)Ti=(CHBu)-Bu-t(CH2SiMe3) (1) in 82% yield. Compound 1 was fully characterized, and the molecular structure disclosed a four-coordinate titanium complex having significant a-hydrogen agostic interaction and possessing terminal alkylidene and alkyl functionalities. Attempts to alkylate (L-1)Ti=(CHBu)-Bu-t(OTf) with KCH2Ph in THF resulted in clean deprotonation of the methyl group attached to the beta-carbon of the diketiminate ligand to form the four-coordinate titanium(IV) neopentylidene-tetrahydrofuran complex (L-2)Ti=(CHBu)-Bu-t(THF) (2; L-2(2-) = [Ar]NC(Me)CH(CH2)N[Ar], 64% isolated yield). Complex 2 was fully characterized and revealed a low-coordinate titanium(IV) in a C-1 environment, which is supported by a chelating bis-anilide ligand. Alkylation of the alkylidene derivative (L-3)Ti=CHtBu(OTf) (L-3(-) = [Ar]NC(Bu-t)CHC(Bu-t)N[Ar1, Ar = 2,6-(CHMe2)(2)C6H3) with LiCH2SiMe3 or KCH2Ph resulted in clean formation of (L3)Ti=CHtBu(R) (R = CH2SiMe3 (3), CH2Ph (4)). Complexes 3 and 4 were fully characterized, and the structure of 4 was determined by single-crystal X-ray diffraction studies. Complex 1 was found to decompose rapidly to several products, of which the titanacycle Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CHC(Me)N[2,6-(CMe2)(CHMe2)C6H3](CH2Si(Me)(3)) (5) and dimer [Ti= NAr([Ar]NC(Me)CHC(mu-CH2)=(CHBu)-Bu-t)](2) (6) were formed. Complex 5 was prepared in better yield through an independent synthesis involving Ti[2,6-(CMe2)(CHMe2)C6H3]NC(Me)CHC(Me)N[2,6-(CMe2)(CHMe2)C6H3](OTf) and LiCH2SiMe3. In THF complex 6 dissociated into the corresponding monomer ((BuHC)-Bu-t=C(CH2)CHC(CH3)N[Ar])Ti=NAr(THF) (8), quantitatively. Unlike complex 1, complexes 3 and 4 are kinetically more stable to intramolecular Wittig-like and C-H abstraction reactions. It was also found that one-electron reduction of the four-coordinate titanium alkylidene complexes (L-1)Ti=(CHBu)-Bu-t(OTf) and (L-3)Ti=(CHBu)-Bu-t(OTf) afforded the Ti(III) metallacycles ([Ar]NC(R)CHC(R)N[2,6-(CHMe2)(CH(CH2)(Me))C6H3])(TiCH2Bu)-Bu-t (L-4(2-), R = Me (9); L-5(2-), R = tBu (10)), both resulting from 1,2-addition of the proximal isopropyl CH3 group across the Ti=CHtBu bond. One-electron oxidation of 10 with AgOTf promotes a-abstraction to generate back the alkylidene precursor (L3)Ti=CHtBu(OTf). The redox-controlled 1,2-addition and alpha-abstraction reactions are specific only to the isopropyl methyl attached to the aryl group of the beta-diketiminate ligand.
机译：末端新戊叉基钛（IV）络合物（L-1）Ti =（CHBu）-Bu-t（OTf）的烷基化（L-1（-）= [Ar] NC（Me）CHC（Me）N [Ar] ，用LiCH 2 SiMe 3，Ar ＝ 2，6-（CHMe 2）（2）C 6 H 3）导致亚烷基-烷基物质（L-1）Ti ＝（CHBu）-Bu-t（CH 2 SiMe 3）（1）的形成，产率为82％。 。对化合物1进行了充分表征，并且分子结构揭示了具有显着的α-氢原子相互作用且具有末端亚烷基和烷基官能团的四配位钛络合物。尝试用KCH2Ph在THF中烷基化（L-1）Ti =（CHBu）-Bu-t（OTf）导致与二酮基配体的β-碳相连的甲基的干净脱质子化反应，形成四配位的钛（ IV）新亚戊基-四氢呋喃配合物（L-2）Ti =（CHBu）-Bu-t（THF）（2; L-2（2-）= [Ar] NC（Me）CH（CH2）N [Ar]，分离产率为64％）。配合物2已得到充分表征，并显示出在C-1环境中低配位的钛（IV），并由螯合的双苯胺配体支撑。亚烷基衍生物（L-3）Ti = CHtBu（OTf）的烷基化（L-3（-）= [Ar] NC（Bu-t）CHC（Bu-t）N [Ar1，Ar = 2,6-（ CHMe2）（2）C6H3）与LiCH2SiMe3或KCH2Ph导致（L3）Ti = CHtBu（R）（R = CH2SiMe3（3），CH2Ph（4））的干净形成。对配合物3和4进行了充分表征，并通过单晶X射线衍射研究确定了4的结构。发现复合物1迅速分解为几种产物，其中钛环Ti [2,6-（CMe2）（CHMe2）C6H3] NC（Me）CHC（Me）N [2,6-（CMe2）（CHMe2）C6H3 ]（CH2Si（Me）（3））（5）和二聚体[Ti = NAr（[Ar] NC（Me）CHC（mu-CH2）=（CHBu）-Bu-t）]（2）（6）形成。通过涉及Ti [2,6-（CMe2）（CHMe2）C6H3] NC（Me）CHC（Me）N [2,6-（CMe2）（CHMe2）C6H3]（OTf）的独立合成以更高的产率制备了配合物5 ）和LiCH2SiMe3。在THF络合物6中，定量解离成相应的单体（（BuHC）-Bu-t = C（CH2）CHC（CH3）N [Ar]）Ti = NAr（THF）（8）。与复合物1不同，复合物3和4对分子内Wittig样和C-H提取反应在动力学上更稳定。还发现四配位的亚烷基钛配合物（L-1）Ti =（CHBu）-Bu-t（OTf）和（L-3）Ti =（CHBu）-Bu-t（ OTf）提供了Ti（III）金属环（[Ar] NC（R）CHC（R）N [2,6-（CHMe2）（CH（CH2）（Me））C6H3]）（TiCH2Bu）-Bu-t（ L-4（2-），R = Me（9）; L-5（2-），R = tBu（10）），两者均来自于Ti = CHtBu的近端异丙基CH3基团的1,2-加成键。用AgOTf对10进行单电子氧化可促进a的吸收，从而生成亚烷基前体（L3）Ti = CHtBu（OTf）。氧化还原控制的1，2-加成反应和α-抽象反应仅对与β-二酮化配体的芳基相连的异丙基甲基具有特异性。

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