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.