Pd-Catalyzed Cross-Coupling of Chloroarene-Cr(CO)₃ Complexes with Stabilized Organoindium (III) Reagents Under Remarkably Mild Conditions

Abstract

The palladium catalyzed cross-methylation of intramolecularly stabilized dimethylindium (III) compounds (3 and 4) with different chloroarene-Cr(CO)₃ complexes have been studied. Under mild conditions (40 °C in THF, 3 h) high yields (up to 96%) of the coupling products were obtained in the presence of 1-10 mol% of PdCl₂(PPh₃)₂. With MeMgCl almost no conversion was observed under the same conditions.

Key words

arene-chromium complexes - indium(III) reagents - palladium - catalysis - cross-coupling - methylation

References

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13

Typical Experimental Procedure: The indium reagent 4 [0.5 mmol of In(III), 123 mg], PdCl₂(PPh₃)₂ (1 mol%, 3.6 mg) and 1 (0.5 mmol, 124 mg) were placed in flame dried Schlenk-flask equipped with a reflux condenser, evacuated and flushed with argon. Deoxygenated anhydrous THF (3 mL) was added via syringe and the reaction mixture was placed in an oil bath pre-heated to 40 C. After stirring at 40 °C for 3 h under an argon atmosphere, the reaction mixture was cooled to ambient temperature, diluted with MTBE (5 mL), filtered trough a short pad of silica, washed with MTBE and concentrated under reduced pressure. The residue was purified by chromatography on silica (10 g) with cyclohexane-ethyl acetate = 10:1 to give 108 mg (95%) of the product 5 as a yellow crystalline solid with >97% purity according to HPLC analysis. Mp 81-82 °C (ref. [16a] 80-81 °C); ¹H NMR (250 MHz, CDCl₃) δ = 5.36-5.41 (m, 2 H), 5.10-5.14 (m, 3 H), 2.17 (s, 3 H); ¹³C NMR (62.5 MHz, CDCl₃) δ = 233.2, 109.6, 94.4, 92.8, 89.6, 20.8; FT-IR(neat): 1443, 1857, 1950 cm^-1.

14

Compound rac-7: Mp 83-84 °C (ref. [16b] 84-85 °C); ¹H NMR (250 MHz, CDCl₃) δ = 6.15 (dd, 1 H), 5.55 (dt, 1 H), 5.12 (dt, 1 H), 5.03 (dd, 1 H), 3.85 (s, 3 H), 2.49 (s, 3 H); ¹³C NMR (62.5 MHz , CDCl₃) δ = 231.2, 166.3, 111.9, 95.4, 92.2, 90.1, 87.5, 52.6, 21.2; FT-IR(neat): 1433, 1719, 1881, 1963 cm^-1.

15

Compound rac-9: Mp 94-96 °C (ref. [16b] not given); ¹H NMR (250 MHz, CDCl₃) δ = 5.56 (dd, 1 H), 5.34 (dd, 1 H), 5.24 (dt, 1 H), 5.10 (dt, 1 H), 2.30 (s, 3 H); ¹³C NMR (62.5 MHz, CDCl₃) δ = 232.0, 111.7, 107.9, 93.7, 93.1, 90.8, 90.4, 19.4; FT-IR(neat): 1445, 1865, 1958 cm^-1.