Insertion of One, Two, and Three Molecules of Alkyne into the Pd−C Bond of Ortho-palladated Primary and Secondary Arylalkylamines

The ortho-metalated complex [Pd2{κ2(C,N)-C6H4CH2CH2NHMe-2}2(μ-Br)2] (1) can be prepared by refluxing a 1:1 mixture of Pd(OAc)2 and N-methylphenethylamine in acetonitrile, followed by addition of an excess of NaBr. Complex 1 reacts with PPh3 to give the mononuclear derivative [Pd{κ2(C,N)-C6H4CH2CH2NHMe-2}Br(PPh3)] (2). The cationic complex [Pd{κ2(C,N)-C6H4CH2CH2NHMe-2}(py)2]ClO4 (3) can be obtained by reacting 1 with AgClO4 and pyridine. The previously reported complex [Pd2{κ2(C,N)-C6H4CH2NHCH2Ph-2}2(μ-Br)2] (A) reacts with PhCCCO2R (R = Me, Et) to give the monoinserted derivatives [Pd2{κ2(C,N)-C(Ph)C(CO2R)C6H4CH2NHCH2Ph-2}2(μ-Br)2] (R = Me (4a), Et (4b)). These dimers react with neutral ligands (L = PPh3, tBuNC) in a 2:1 molar ratio to afford the monomeric complexes [Pd{κ2(C,N)-C(Ph)C(CO2R)C6H4CH2NHCH2Ph-2}Br(L)] (L = PPh3, R = Me (5a), Et (5b); L = tBuNC, R = Me (6a), Et (6b)). The complexes [Pd2{κ2(C,N)-C6H3CH2NH2-2,X-5}2(μ-Br)2] (X = Cl (C), F (D), NO2 (E)) react with RCCR (R = Et, Ph) to give [Pd{κ2(C,N)-C(R)C(R)C(R)C(R)C6H3CH2NH2-2,X-5}Br] (X = Cl, R = Et (7a), Ph (7b); X = F, R = Et (8a), Ph (8b); X = NO2, R = Ph (9)) through a double insertion of the alkyne into the Pd−C bond. Complexes A and D react with PhCCCO2R in molar ratio 1:6−7 to afford a mixture of di-inserted head-to-tail and tail-to-tail isomers [Pd{κ2(C,N)-C(R′)C(R′′)C(Ph)C(CO2R)C6H4CH2NHCH2Ph-2}Br] (R = Me, R′ = Ph, R′′ = CO2Me (10a); R = Me, R′ = CO2Me, R′′ = Ph (10b); R = Et, R′ = Ph, R′′ = CO2Et (11a); R = Et, R′ = CO2Et, R′′ = Ph (11b)) and [Pd{κ2(C,N)-C(R′)C(R′′)C(Ph)C(CO2Et)C6H3CH2NH2-2,F-5}Br] (R′ = Ph, R′′ = CO2Et (12a); R′ = CO2Et, R′′ = Ph (12b)). CO further inserts into the Pd−C bond of complexes 7a,b and 8a,b to give the 10-membered palladacycles [Pd2{κ2(C,N)-C(O)C(R)C(R)C(R)C(R)C6H3CH2NH2-2,X-5}2(μ-Br)2] (X = Cl, R = Et (13a), Ph (13b); X = F, R = Et (14a), Ph (14b)). Complexes A−E, [Pd2{κ2(C,N)-C6H4CH2CR2NH2-2}2(μ-X)2] (X = Br, R = H (F); X = Cl, R = Me, (G)) and 1 react with dimethylacetylene dicarboxylate (DMAD) to yield the tri-inserted products [Pd{κ3(O,C,N)-OC(OMe){C5(CO2Me)4}C(CO2Me)C6H3CH2NHR-2,R′-5}Br] (R = H, R′ = OMe (15), Cl (16), F (17); R = CH2Ph, R′ = H (18)) and [Pd{κ3(O,C,N)-OC(OMe){C5(CO2Me)4}C(CO2Me)C6H4CH2CR2NHR′-2}X] (X = Br, R = R′ = H (19); X = Cl, R = Me, R′ = H (20); X = Cl, R = H, R′ = Me (21)), which contain a cyclopentadienyl unit. Complex 18 reacts with TlOTf and neutral ligands to give [Pd{κ3(O,C,N)-OC(OMe){C5(CO2Me)4}C(CO2Me)C6H4CH2NHCH2Ph-2}(L)]OTf (L = H2O (22), py (23)). Reaction of complex A with an excess of 2-butyne for long periods of time affords the coordination derivative 24, probably emerging from tri-insertion of the alkyne into the Pd−C bond, followed by an internal cyclization and β-hydrogen abstraction. When complex G reacts with an excess of 2-butyne and TlOTf, the tri-inserted product 25 is obtained, which also contains a C5R5 unit, although in this case, coordination around the palladium atom is completed by one CC bond of the cyclopentadienyl unit. The crystal structures of complexes 2, 5a, 6b, 7a, 7b·3DMSO, 9, 14a·2DMSO, 18, 21, 24, and 25 have been solved by X-ray diffraction. In all these structures, the palladium atom shows a distorted or slightly distorted square-planar environment, except in complex 14a, where Pd(II) exhibits a distorted trigonal-bipyramidal geometry.