Well‐Defined Metallodendrimers by Site‐Specific Complexation

Abstract

Strong multiple complexation of transition metal ions, Cu(II), Zn(I1) and Ni(I1) with different generations of well-defined poly(propy1ene imine) dendrimers as multi(tridentate) li-metal ions from 2 up to 32.gands has been used to construct nanoscopic assemblies of defined structure and size incorporating a distinct number of Metal-containing architectures of nanoscopic dimensions are thought to create new materials with promising electronic, magnetic or catalytic properties [']. Polyniers with metal-coordinating side g r o~p s [~%~] or amphiphilic assembliesr41 are most commonly used in this field. However, their three-dimensional architectures are less defined, due to the polydispersity of polymers and the dynamic character of amphiphilic assemblies. Recently, well-defined structures of dendritic macromolecules, like 1 (Scheme l), have become available. These macromolecules emanate from a central core with a branching point at each monomer unit and possesb a defined number of generations and end groups [5]. Therefore, dendrimers are well suited for nanoscopic materials, e.g. in the complexation of metals. Organometallic complexes have been used in the construction of assembly points of dendritic branched6 91 and in end-group functionalization of dendrimers['"-"1. I 2It has been reported that the bis(3-aminopropy1)aminc functionality acts as a strongly complexing tridentate coordinating site for various transition metals (2)['3-'01. Cu(I1j complexes with his( 3-aminopropy1)amine are formed with high equilibrium constants of K = loi4 M-1[i71. Furthermore detailed insight into many complexes is obtained from single crystal X-ray data. Here we demonstrate that, with different generations of poly(propy1ene imine) dendrimers [DAB-dendr-(NH,),,; n 4, 8, 16, 32, 641 as multifunctional ligands, it is possible to prepare metal-containing nanoscopic structures incorporating a well-defined number of up to 32 transition metal ions such as Cu(llj, Zn(lI), and Ni(I1). Essential to this result is the combination of the high degree of definition attainable for poly(propy1ene imine) dendrimers and the metal-coordinating properties of the bis(3-aminopropy1)aniine end groups.Poly(propy1ene imme) dendrimers are synthesized in a stepwise manner from a central core, leading to a doubling of the end groups in every next generation up to 64 for the fifth generation (1) [18]. A high degree of definition of these structures has been established with electrospray mass spectroscopy, revealing a monodispersity of 1.0018 for the highest generation (1, n = 64)[191. The addition of metal(I1)chloride (MC12, with M = Cu, Zn, and Ni) in methanol to methanolic solutions of the dendrimers of different generations yielded the exclusive formation of the dendritic polybis(3-arninopropy1)amine-MCl2 complexes. We have studied both the formation and the structure of these metallodendrimers with a number of different techniques.Addition of CuC12 to different of generations poly(propylene imine) dendrimers in methanol resuIts in the immediate formation of...

Metallodendrimers: Structural Diversity and Functional Behavior

“…Most recently, Meiers group has reported multiple complexation of copper, zinc, and nickel ions with the multiple tridentate binding environments in poly(propylene imine) dendrimers to construct nanoscopic assemblies of defined structure and size incorporating a distinct number (2 to 32) of metal ions. [71] PAMAM dendrimers complexed with metals have been the subject of additional studies and have experienced a push towards applications. The molecular dynamics of vanadyl-chelate complexes attached to the surface of PAM-AM dendrimers was explored by calculating their rotational correlation times derived from EPR spectra.…”

Iron‐Containing Poly(propylene imine) Dendromesogens with Photoactive Properties

“…The EPR spectrum of the complexes recorded in the Q (hn 2 ¼ 1.2 cm À1 ) band does not contain the lines with g 2 ¼ 4. the range of variation of the parameter of the axial crystal field: 0.3 cm À1 <D<0.6 cm À1 for the second type of paramagnetic centers. [26] Based on the results obtained from EPR spectra and literature data mentioned above [17,[20][21][22] the following local environment for iron ions can be suggested. The first type of paramagnetic (MA 3 B 3 ) centers (signal g 1 ¼ 2) is formed by coordination of three nitrogen atoms, two of which belong to amido groups, and the third one-to amino groups.…”

Dense-shell glycodendrimers: UV/Vis and electron paramagnetic resonance study of metal ion complexation

“…(ii) In comparison with the n CuD value for the parent PPI dendrimers in MeOH (Bosman et al 1997), most glycodendrimers possess a similar Cu(II) complexation capacity. Thus, the n CuD value of glycodendrimers 2, 3, 4, 6 and 7 differs only in the range of 6-12% from those of the parent dendrimers.…”