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Synthesis of 1-Phosphabarrelene Phosphine Sulfide Substituted Palladium(II) Complexes:  Application in the Catalyzed Suzuki Cross-Coupling Process and in the Allylation of Secondary Amines

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posted on 14.03.2005, 00:00 by Olivier Piechaczyk, Marjolaine Doux, Louis Ricard, Pascal le Floch
The reactivity of 2-phosphine sulfide substituted phosphinines toward alkynes was examined. 2,6-bis(diphenylphosphine sulfide)-3,5-diphenylphosphinine 2 reacts with diphenylacetylene to yield the corresponding 1-phosphabarrelene derivative 3, resulting from the [4 + 2] cycloaddition. Compound 2 and 2-(diphenylphosphine sulfide)-3-methyl-5,6-diphenylphosphinine 1 react with dimethyl acetylenedicarboxylate in a similar fashion to yield the expected 1-phosphabarrelenes 4 and 5, respectively. Ligand 3 acts as a tridentate ligand in its reaction with [Pd(COD)Cl2] to afford the expected cationic Pd−Cl complex 6. The reaction of [Pd(COD)Cl2] and [Pd(η3-C3H5)Cl]2 with ligand 5 yielded the corresponding complexes 7 and 8, in which the ligand behaves as a bidentate ligand. Complex 8 was isolated as a cationic derivative after chloride abstraction with AgOTf. DFT calculations, carried out at the B3LYP/6-311+G(d,p) level of theory, have shown that formation of 1-phosphabarrelenes is thermodynamically favored when dimethyl acetylenedicarboxylate is used as the alkyne. Complexes 6 and 8 proved to be very active catalysts in the Suzuki−Miyaura reaction, which allows the synthesis of functionalized biphenyl derivatives from the coupling of bromoarenes with phenylboronic acid (TON up to 7 × 106 using complex 8 as catalyst). The cationic complex 8 also catalyzes the coupling between allyl alcohol and secondary amines to afford the corresponding N-allylamines in toluene at 70 °C using 2% of the catalyst.

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