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Reactivity of TpMe2-Supported Yttrium Alkyl Complexes toward Aromatic N-Heterocycles: Ring-Opening or C[DOUBLE BOND]C Bond Formation Directed by C[BOND]H Activation

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Abstract

Unusual chemical transformations such as three-component combination and ring-opening of N-heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of TpMe2-supported yttrium alkyl complexes with aromatic N-heterocycles. The scorpionate-anchored yttrium dialkyl complex [TpMe2Y(CH2Ph)2(THF)] reacted with 1-methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24-membered rare-earth metallomacrocyclic compound [TpMe2Y(μ-N,C-Im)(η2-N,C-Im)]6 (1; Im=1-methylimidazolyl) through two kinds of C–H activations at the C2- and C5-positions of the imidazole ring. However, [TpMe2Y(CH2Ph)2(THF)] reacted with two equivalents of 1-methylbenzimidazole to afford a C–C coupling/ring-opening/C–C coupling product [TpMe2Y{η3-(N,N,N)-N(CH3)C6H4NHCH[DOUBLE BOND]C(Ph)CN(CH3)C6H4NH}] (2). Further investigations indicated that [TpMe2Y(CH2Ph)2(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring-opening product {(TpMe2)Y[μ-η21-SC6H4N(CH[DOUBLE BOND]CHPh)](THF)}2 (3). Moreover, the mixed TpMe2/Cp yttrium monoalkyl complex [(TpMe2)CpYCH2Ph(THF)] reacted with two equivalents of 1-methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [TpMe2CpY(μ-N,C-Im)]3 (5), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [TpMe2Y(Im-TpMe2)] (7; Im-TpMe2=1-methyl-imidazolyl-TpMe2) and [Cp3Y(HIm)] (8; HIm=1-methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C[DOUBLE BOND]C bond through multiple C–H activations.

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