Nickel-Catalyzed Cross-Coupling Reactions of Aryltitanium(IV) Alkoxides with Aryl Halides

Abstract

A nickel-catalyzed cross-coupling reaction between aryltitanium(IV) alkoxides and various functionalized aryl halides is described. The reaction requires Ni(acac)₂ (0.5 mol%), a phosphine or an N-heterocyclic carbene ligand (NHC ligand; 0.5-1.0 mol%) and proceeds at 25 °C within 1-24 hours.

Key words

organotitanium reagents - cross-coupling - nickel

References and Notes

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• 6e

  The NHC ligand itself is generated by deprotonation with the organometallic reagent. See also references above.

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14

Not using NMP leads to heterogeneous reactions and lower yields.

15

Typical Procedure for the Cross-Coupling Reaction; Preparation of Biphenyl-4-carboxylic Acid Ethyl Ester ( 3a): A flame-dried flask equipped with a magnetic stirring bar, an argon inlet, and a septum was charged with a Ti(OEt)₄ solution (1.0 mL, 1.5 M in THF). First phenyl-magnesium chloride (0.84 mL, 1.79 M in THF) was added dropwise at 0 °C, then Ni(acac)₂ (1.3 mg, 0.005 mmol), ligand 4 (2.1 mg, 0.005 mmol) and 4-bromobenzoic acid ethyl ester (2a; 229 mg, 1.00 mmol) were added. The reaction mixture was stirred for 3 h at r.t. Then the mixture was quenched with a sat. NH₄Cl solution and extracted with Et₂O. Column chromatography (pentane-Et₂O, 9:1) of the crude residue yielded 3a as colorless solid (215 mg, 95%).