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

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)Cl-2] to afford the expected cationic Pd-Cl complex 6. The reaction of [Pd(COD)Cl-2] and [Pd(eta(3)-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 1phospha-barrelenes 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 x 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 degrees C using 2% of the catalyst.