Insight into the Formation of Highly Strained [1]Ferrocenophanes with Boron in Bridging Position

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• 作者：Hridaynath Bhattacharjee ; Jonathon D. Martell ; Elaheh Khozeimeh Sarbisheh ; Saeid Sadeh ; J. Wilson Quail ; Jens Müller
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 27, 2016
• 年：2016
• 卷：35
• 期：12
• 页码：2156-2164
• 全文大小：447K
• 年卷期：0
• ISSN：1520-6041

文摘

Four planar-chiral, enantiomerically pure ferrocene dibromides (3^R1R2; [(CHR¹R²)BrH₃C₅]₂Fe) equipped with two CHR¹R² groups in α position to bromine were synthesized. From the four C₂ symmetrical species, two are already known [CHR¹R² = CHMe₂ (3^MeMe), CHEt₂ (3^EtEt)] and two are new compounds [CHR¹R² = R-CHEtMe (3^EtMe), S-CHMeEt (3^MeEt)]. The dibromides 3^R1R2 were in situ converted into dilithio ferrocene derivatives and reacted with Cl₂BNiPr₂ resulting in mixtures of bora[1]ferrocenophanes (4^R1R2) and 1,1′-bis(boryl)ferrocenes (5^R1R2). The aim of this investigation was to test the hypothesis that the alkyl group that is oriented approximately perpendicular to the Cp ring, i.e., R², affects the outcome of the salt-metathesis reaction. The obtained product ratios 4^R1R2:5^R1R2 were determined by ¹H NMR spectroscopy and revealed that systems with the same R² group gave similar 4^R1R2:5^R1R2 ratios (1.0:0.51 and 1.0:0.49 for R² = Me; 1.0:0.30 and 1.0:0.27 for R² = Et), confirming the hypothesis. Shown by DFT calculations (B3PW91/6-311+G(d,p)), reaction paths resulting in either product 4^R1R2 or product 5^R1R2 are both concerted steps.