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((η 5 -C 5 H 4 PPh 2 )(η 5 -C 5 H 4 ))C(O)HNCH 2 CH 2 NHC(O)CH 2 CH 2 )N[CH 2 CH 2 N(CH 2 CH 2 C(O)NHCH 2 CH 2 NH-C(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 ))) 2 ] 2 ( 9 - Fe ) and the corresponding metal species (Fe((η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 5 )Cl))(η 5 -C 5 H 4 ))C(O)HNCH 2 CH 2 NHC(O)CH 2 CH 2 )N[CH 2 CH 2 N(CH 2 CH 2 C(O)NHCH 2 CH 2 NHC(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 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 5 H 4 PPh 2 )(η 5 -C 5 H 4 C(O)NH n C 3 H 7 )) ( 5 - Fe ) and [Fe(η 5 -C 5 H 4 PPh 2 )(η 5 -C 5 H 4 C(O)NHCH 2 )] 2 ( 6 - Fe ) as well as N(CH 2 CH 2 C(O)NHCH 2 CH 2 NHC(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 ))) 3 ( 7 - Fe ) and [CH 2 N(CH 2 CH 2 C(O)NHCH 2 CH 2 NHC(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 ))) 2 ] 2 ( 8 - Fe ) were prepared from Fe(η 5 -C 5 H 4 PPh 2 )(η 5 -C 5 H 4 CO 2 H) ( 3 ). Using [Pd(η 3 -C 3 H 5 )Cl] 2 ( 4 ) as palladium source heterobimetallic metallodendrimers (Fe(η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 5 )Cl))(η 5 -C 5 H 4 C(O)NH n C 3 H 7 )) ( 5 - Fe – Pd ), [Fe(η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 5 )Cl))(η 5 -C 5 H 4 C(O)NHCH 2 )] 2 ( 6 - Fe – Pd ), N(CH 2 CH 2 C(O)NHCH 2 CH 2 NHC(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 5 )Cl)))) 3 ( 7 - Fe – Pd ) and [CH 2 N(CH 2 CH 2 C(O)NHCH 2 CH 2 NHC(O)(Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 4 PPh 2 (Pd(η 3 -C 3 H 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.