Synthesis of Ferrocene Bridged bis(2-Indenyl) Ligands

Abstract

An optimised synthesis of 1,1′-bis(2-indenyl)ferrocene in 47% yield from the Pd(0)-catalysed cross coupling between 1,1′-zincated ferrocene and 2-bromo-indene is described along with the formation of (2-indenyl) ferrocene in 40% yield. The analogous synthesis of planar chiral derivatives gave either pure N,N-dimethyl-1-[2-(2-indenyl)ferrocenyl]ethylamine (74%) or N,N-dimethyl-1-[2,1′-bis(2-indenyl)ferrocenyl]ethylamine (26%) dependent upon the amount of Pd(0) catalyst used.

Key words

ferrocene carbanions - coupling - metallocene ligands

References

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7

The structure assigned to each new compound is in accord with IR, ¹H and ¹³C NMR, MS, HRMS and/or elemental analysis.

9

Generated the same way as in ref. [6]

18

A solution of 1,1′-dilithioferrocene/TMEDA complex (5.37 mmol) in THF (30 mL) was added to a solution of anhyd ZnCl₂ (731 mg, 5.37 mmol) in THF (25 mL) at 0 °C. The resulting orange slurry was warmed to r.t. and stirred for 1 h. In a separate Schlenk flask DIBAL (0.54 mL of a 1.0 M soln in hexanes, 0.54 mmol) was added to a yellow slurry of Pd(PPh₃)Cl₂ (188 mg, 0.27 mmol) in THF (5 mL) at r.t. The resulting black homogeneous solution was added to the ferrocenylzinc chloride slurry and the resulting brown/black solution heated to reflux for 12 h. After cooling to r.t. brine (50 mL) was added and the mixture extracted with CH₂Cl₂ (2 × 100 mL). The combined organic layers were dried (MgSO₄), filtered and concentrated in vacuo to yield a brown solid which was purified by flash chromatography [silica gel, gradient elution: 0 to 25% CH₂Cl₂/petrol (bp 40-60 °C)] to give in order of elution; ferrocene (40 mg, 4%). (2-indenyl)ferrocene(15) as an orange crystalline solid (650 mg, 40%); The spectral data were identical to the literature (ref. [6] ).
1,1′-bis(2-indenyl)ferrocene(9) as a red crystalline solid (1.05g, 47%). Mp 240 °C. ¹H NMR (250 MHz, CDCl₃): δ = 3.50 (4 H, s, 2 × CH ₂ ), 4.26 (4 H, t, J = 1.8 Hz, Cp-H), 4.43 (4 H, t, J = 1.8 Hz, Cp-H), 6.7 (2 H, s, 2 × Ind-H), 7.05-7.30 (8 H, m, 2 × Ar). ¹³C NMR (62.9 MHz, CDCl₃): δ = 39.7, 67.7, 70.2, 82.2, 119.9, 123.4, 123.7, 124.6, 126.5, 142.5, 145.1, 145.7. HRMS (EI⁺): M⁺ C₂₈H₂₂Fe calcd: 414.107. Found: 414.107.