Diffusion and NOE NMR Studies on Multicationic DAB‐Organoruthenium Dendrimers: Size‐Dependent Noncovalent Self‐Assembly to Megamers and Ion Pairing

Abstract

New multicationic organoruthenium dendrimers (RuPF(6)-Dabn, n = 2, 4, 8, 16) have been synthesized by coupling of [Ru(eta(6)-p-cymene)(kappa(3)-dpk-OCH(2)CH(2)OH)]X (1PF(6), dpk = 2,2'-dipyridyl ketone, X = PF(6)) with 1,4-diaminobutane (DAB) and polypropylenimine dendrimer DAB-dendr-(NH(2))(n) {n=4, 8, 16} mediated by 1,1'-carbonyldiimidazole (CDI). The intermediate in the synthesis, [Ru(eta(6)-p-cymene)(kappa(3)-dpk-OCH(2)CH(2)OC(O)Im]X (2PF(6), Im = imidazole, X = PF(6)) has been isolated and characterized by single-crystal XRD. The intra- and supramolecular structures in a solution of RuPF(6)-Dabn dendrimer have been investigated by multidimensional and multinuclear NMR techniques. Diffusion NMR experiments on dilute solutions indicated that the linear distance between two metal centers (14.9-22.1 A depending on the dendrimer generation) is much greater than the diameter of 1PF(6) (9.9 A). (19)F,(1)H-HOESY NMR experiments (HOESY = heteronuclear Overhauser effect spectroscopy) showed that the counterion is positioned on the surface of the dendrimers and assumes the same relative anion-cation orientation as in 2PF(6). Diffusion NMR experiments on RuPF(6)-Dabn dendrimers in CD(2)Cl(2) at different concentrations revealed a process of supramolecular assembly of dendrimers to megamers that is strongly favored for the highest generations. Megamer formation is coupled with an increased fraction of free ions (alpha) and a consequent reduction in ion-paired ruthenium centers. Graphs of alpha versus C(Ru) (the concentration of ruthenium centers) showed a minimum for RuPF(6)-Dab4, RuPF(6)-Dab8, and RuPF(6)-Dab16 at a position coinciding with the significant presence of supramolecular dendritic dimers. The tendency to ion pairing decreases as the dendrimer generation increases.

Fluoride‐Promoted Esterification with Imidazolide‐Activated Compounds: A Modular and Sustainable Approach to Dendrimers

“…However, competitive inhibition was observed when a stronger electron acceptor, such as the non-activated acid, was added in excess, and full conversion was not reached after 18 h. Consequently, FPE relies heavily on minimizing the Scheme 2. All carboxylic acids were activated to imidazolide derivatives and then subjected to the established esterification protocol, leading to an array of functionalized pseudo-G4 dendrimers (14)(15)(16)(17)(18)(19) with yields above 90 %. Table 1: Comparison of strategies toward acetonide-protected bis-MPA dendrimers.…”

“…In materials science, polymer chemists often capitalize on verified synthetic concepts that generate complex macromolecular structures. [13][14] However, the synthesis of dendrimers based on polyester was thus far less successful, with low yields and long reaction times. Thus, to enable the transfer of click chemistry from the synthesis of small molecules to more complex macromolecules, the applicability of the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) was originally demonstrated by the formation of a library of dendrimers.…”

Cyclometalated IrIII Complexes with Substituted 1,10‐Phenanthrolines: A New Class of Efficient Cationic Organometallic Second‐Order NLO Chromophores

“…The fractions (a in Table 3) of ions, ion pairs, and ion quadruples (necessary to account for the slightly higher value of V H + with respect to V H IP ) were calculated with the assumption that only dissociated ion pairs, ion pairs, and ion quadruples were present in CH 2 Cl 2 solution. [24] The value of a ranges from 0.80 (3 10 À5 m) to 0.40 (saturated solution, 16 10 À3 m) for 1 b-PF 6 , whereas 1 b-C 12 H 25 SO 3 shows only marginal dissociation (a 0.05) in all the range of the concentrations investigated, confirming the stronger tendency to form ion pairing of the C 12 H 25 SO 3 À counterion when compared to PF 6 À . Some other trends can be deduced from Table 3.…”

“…D t data were treated as described in the literature. [19][20][21][22][23][24] The measurement uncertainty was estimated by determining the standard deviation of m by performing experiments with different D values. Standard propagation of error analysis yielded a standard deviation of approximately 3-4 % in the hydrodynamic radius and 10 % in the hydrodynamic volumes and a.…”

Characterization of Halogen Bonded Adducts in Solution by Advanced NMR Techniques

“…More quantitative information can be useful in determining the molecular weight distribution for polymers [78], the purity and composition of functionalized carbon nanotubes [79], the formation of ion pairs and quadruples [80][81][82][83], or, in the case of neutral species, of supramolecular adducts [84,85].…”