Amidoamine-based dendrimers with end-grafted Pd–Fe units: Synthesis, characterization and their use in the Heck reaction

The synthesis and characterization of novel amidoamine-based metallodendrimers with heterobimetallic end-grafted amidoferrocenyl-palladium-allyl chloride units is described. Dendrimer (Fe((η5-C5H4PPh2)(η5-C5H4))C(O)HNCH2CH2NHC(O)CH2CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NH-C(O)(Fe(η5-C5H4)(η5-C5H4PPh2)))2]2 (9-Fe) and the corresponding metal species (Fe((η5-C5H4PPh2(Pd(η3-C3H5)Cl))(η5-C5H4))C(O)HNCH2CH2NHC(O)CH2CH2)N[CH2CH2N(CH2CH2C(O)NHCH2CH2NHC(O)(Fe(η5-C5H4)(η5-C5H4PPh2(Pd(η3-C3H5)Cl))))2]2 (9-Fe–Pd) were prepared by a consecutive divergent synthesis methodology including addition–amidation cycles, standard peptide coupling, and coordination procedures. For comparative reasons also the monomeric and dimeric molecules (Fe(η5-C5H4PPh2)(η5-C5H4C(O)NHnC3H7)) (5-Fe) and [Fe(η5-C5H4PPh2)(η5-C5H4C(O)NHCH2)]2 (6-Fe) as well as N(CH2CH2C(O)NHCH2CH2NHC(O)(Fe(η5-C5H4)(η5-C5H4PPh2)))3 (7-Fe) and [CH2N(CH2CH2C(O)NHCH2CH2NHC(O)(Fe(η5-C5H4)(η5-C5H4PPh2)))2]2 (8-Fe) were prepared from Fe(η5-C5H4PPh2)(η5-C5H4CO2H) (3). Using [Pd(η3-C3H5)Cl]2 (4) as palladium source heterobimetallic metallodendrimers (Fe(η5-C5H4PPh2(Pd(η3-C3H5)Cl))(η5-C5H4C(O)NHnC3H7)) (5-Fe–Pd), [Fe(η5-C5H4PPh2(Pd(η3-C3H5)Cl))(η5-C5H4C(O)NHCH2)]2 (6-Fe–Pd), N(CH2CH2C(O)NHCH2CH2NHC(O)(Fe(η5-C5H4)(η5-C5H4PPh2(Pd(η3-C3H5)Cl))))3 (7-Fe–Pd) and [CH2N(CH2CH2C(O)NHCH2CH2NHC(O)(Fe(η5-C5H4)(η5-C5H4PPh2(Pd(η3-C3H5)Cl))))2]2 (8-Fe–Pd) were synthesized. Additionally, seleno-phosphines of 5-Fe–Se and 9-Fe–Se, respectively, were prepared by addition of elemental selenium to 5-Fe or 9-Fe to estimate their σ-donor properties. The palladium-containing amidoamine supports are catalytically active in the Heck–Mizoroki cross-coupling of iodobenzene with tert-butyl acrylate. The catalytic data are compared to those obtained for the appropriate mononuclear and dinuclear compounds 5-Fe–Pd and 6-Fe–Pd. This comparison confirms a positive cooperative effect. The mercury drop test showed that (nano)particles were formed during catalysis, following on heterogeneous carbon–carbon cross-coupling.