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

Abstract

The synthesis and characterization of novel amidoamine-based metallodendrimers with heterobimetallic end-grafted amidoferrocenyl-palladium-allyl chloride units is described. Dendrimer (Fe((η 5-C 5H 4PPh 2)(η 5-C 5H 4))C(O)HNCH 2CH 2NHC(O)CH 2CH 2)N[CH 2CH 2N(CH 2CH 2C(O)NHCH 2CH 2NH-C(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2))) 2] 2 ( 9- Fe) and the corresponding metal species (Fe((η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)Cl))(η 5-C 5H 4))C(O)HNCH 2CH 2NHC(O)CH 2CH 2)N[CH 2CH 2N(CH 2CH 2C(O)NHCH 2CH 2NHC(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)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(η 5-C 5H 4PPh 2)(η 5-C 5H 4C(O)NH n C 3H 7)) ( 5- Fe) and [Fe(η 5-C 5H 4PPh 2)(η 5-C 5H 4C(O)NHCH 2)] 2 ( 6- Fe) as well as N(CH 2CH 2C(O)NHCH 2CH 2NHC(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2))) 3 ( 7- Fe) and [CH 2N(CH 2CH 2C(O)NHCH 2CH 2NHC(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2))) 2] 2 ( 8- Fe) were prepared from Fe(η 5-C 5H 4PPh 2)(η 5-C 5H 4CO 2H) ( 3). Using [Pd(η 3-C 3H 5)Cl] 2 ( 4) as palladium source heterobimetallic metallodendrimers (Fe(η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)Cl))(η 5-C 5H 4C(O)NH n C 3H 7)) ( 5- Fe– Pd), [Fe(η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)Cl))(η 5-C 5H 4C(O)NHCH 2)] 2 ( 6- Fe– Pd), N(CH 2CH 2C(O)NHCH 2CH 2NHC(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)Cl)))) 3 ( 7- Fe– Pd) and [CH 2N(CH 2CH 2C(O)NHCH 2CH 2NHC(O)(Fe(η 5-C 5H 4)(η 5-C 5H 4PPh 2(Pd(η 3-C 3H 5)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.