Insertion of internal acetylenes into orthopalladated α-methylbenzylamine. Crystal structure of [Pd{C(Ph)C(Ph)C(Ph)C(Ph)C6H4CH(Me)NH2}Br]

Abstract

The complex [Pd{C₆H₄CH(Me)NH₂}(Me₂CO)₂]ClO₄ reacted with diphenylacetylene to give [Pd₂(η⁵-C₅Ph₅)₂(µ-η²-PhCCPh)]. A pathway for this reaction is suggested. Species related with the postulated intermediates can be isolated starting from [{Pd[C₆H₄CH(Me)NH₂](µ-Br)}₂] which reacts with disubstituted alkynes (RCCR, R = CO₂Me or Ph) to afford [Pd{C(R)C(R)C(R)C(R)C₆H₄CH(Me)NH₂}Br](R = CO₂Me 1a or Ph 1b) through a double insertion of the alkyne into the Pd–C bond. Complex 1a reacted with 1 equivalent of MeO₂CCCCO₂Me to give the tri-insertion reaction product 2. These are the first products of alkyne insertion into a cyclopalladated primary amine. Neutral ligands, such as pyridine (py) or CO, can break the Pd–π-olefinic bond in 1a to give the corresponding adducts [Pd{C(R)C(R)C(R)C(R)C₆H₄CH(Me)NH₂}Br(L)](R = CO₂Me; L = py 3 or CO 4). Complexes 1a and 1b reacted with AgClO₄(1 : 1) in acetone to afford AgBr and [Pd{C(R)C(R)C(R)C(R)C₆H₄CH(Me)NH₂}(solv)]ClO₄(R = CO₂Me, solv = H₂O 5a; R = Ph, solv = Me₂CO 5b). The reaction of complex 1a with AgClO₄(1 : 1) and excess of pyridine gave the cationic complex [Pd{C(R)C(R)C(R)C(R)C₆H₄CH(Me)NH₂}(py)₂]ClO₄6(R = CO₂Me). The crystal structure of complex 1b has been determined by X-ray diffraction. The palladium atom is bonded to Br, N, C(1) and to the midpoint of the C(3)–C(4) double bond in a distorted square-planar geometry.