Synthesis and properties of guanidine-pyridine hybridligands and structural characterisation of their mono- and bis(chelated) cobalt complexes

Hoffmann, Alexander; Börner, Janna; Flörke, Ülrich; Herres‐Pawlis, Sonja

doi:10.1016/j.ica.2008.06.002

Cited by 55 publications

(59 citation statements)

References 21 publications

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“…In general, the calculated reaction proceeds analogously to the mechanisms analyzed by Gibson et al: [15] The transition states TS1 and TS2 are in good accordance in each approach with regard to the reaction path and the energy profile, but due to the required transformation of the coordination sphere (departure of guanidine ligand and approach of the lactide) the guanidine system exhibits an additional pretransition state TS0. The highest free energy of activation for the first ROP step in the ketiminate system was calculated to be 106 kJ mol À1 .…”

supporting

confidence: 62%

“…The guanidine ligands themselves display intense absorptions at 347 nm (8800 L mol À1 cm À1 ) and 371 nm (1320 L mol À1 cm À1 ) for DMEGqu and TMGqu, respectively. [15] This p-p* transition of the aromatic quinoline system can be traced in the polymer. Remarkably, the distinct intensity difference of the two ligands shows up in the UV absorption spectra of the corresponding polymer samples as well.…”

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confidence: 98%

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Mechanism of the Living Lactide Polymerization Mediated by Robust Zinc Guanidine Complexes

Börner

Vieira

Pawlis

et al. 2011

Chemistry A European J

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Zinc bis(chelate) guanidine complexes promote living lactide polymerization at elevated temperatures. By means of kinetic and spectroscopic analyses the mechanism has been elucidated for these special initiators that make use of neutral N-donor ligands. The neutral guanidine function initiates the polymerization by a nucleophilic ring-opening attack on the lactide molecule. DFT calculations on the first ring-opening step show that the guanidine is able to act as a nucleophile. Three transition states were located for ligand rearrangement, nucleophilic attack, and ring-opening. The second ring-opening step was modeled as a representation for the chain growth because here, the lactate alcoholate opens the second lactide molecule via two transition states (nucleophilic attack and ring-opening). Additionally, the resulting reaction profile proceeds overall exothermically, which is the driving force for the reaction. The experimental and calculated data are in good agreement and the presented mechanism explains why the polymerization proceeds without co-initiators.

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supporting

confidence: 62%

mentioning

confidence: 98%

Mechanism of the Living Lactide Polymerization Mediated by Robust Zinc Guanidine Complexes

Börner

Vieira

Pawlis

et al. 2011

Chemistry A European J

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“…The Vilsmeier salts, N,N′-dimethylethylenechloroformamidinium chloride (DMEG) and N,N,N′,N′-tetramethylchloroformamidinium chloride (TMG), were synthesized as described in the literature [11,26]. The ligands DMEGpy and TMGpy were synthesized according to the protocol in the literature [27].…”

Section: Methodsmentioning

confidence: 99%

New Guanidine-Pyridine Copper Complexes and Their Application in ATRP

et al. 2014

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Abstract:The guanidine hybrid ligands, (tetramethylguanidine)methylenepyridine (TMGpy) and (dimethylethyleneguanidine)methylenepyridine (DMEGpy), were proven to be able to stabilize copper complexes active in the solvent-free polymerization of styrene at 110 °C using 1-phenylethylbromide as the initiator. The polymerization proceeded after first-order kinetics, and polystyrenes with polydispersities around 1.2 could be obtained. Using the ligand, DMEGpy, three new copper guanidine-pyridine complexes could be synthesized and structurally characterized. Their structural characteristics are discussed.

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“…These include those in which the pyridine and guanidine moieties are separated by a linker, several cobalt 21 and zinc 22 complexes that were studied for their potential in sensor technology and as lactide pyridine ring). Although the calculated barriers to the rotation are not high enough to completely restrict the C2-N1' rotation (36.9 and 45.7 kJ mol -1 ), the energetic difference between the anti and syn minima (34.0 kJ mol -1 ) suggests an almost quantitative preference for the syn conformation.…”

Section: Figurementioning

confidence: 99%

Pyridin-2-yl Guanidine Derivatives: Conformational Control Induced by Intramolecular Hydrogen-Bonding Interactions

et al. 2011

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The synthesis and conformational analysis of a series of pyridin-2-yl guanidine derivatives using NMR, X-ray crystallography and B3LYP/6-31+G** theoretical studies are reported. A remarkable difference was observed in the 1 H NMR spectra of the guanidinium salts compared with their N,N'-di-Boc protected and neutral analogues. This difference corresponds to a 180° change in the dihedral angle between the guanidine/ium moiety and the pyridine ring in the salts compared to the Boc protected derivatives; a conclusion which was supported by theoretical studies, X-ray data and NMR analysis. Moreover, our data sustains the existence of two intramolecular hydrogen bonding systems: (i) between the pyridine N1 atom and the guanidinium protons in the salts and (ii) within the tert-butyl carbamate groups of the Boc protected derivatives. To verify that the observed conformational control arises from these intramolecular interactions, a new series of N-Boc-N'-propyl substituted pyridin-2-yl guanidines was also prepared and studied.

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Synthesis and properties of guanidine-pyridine hybridligands and structural characterisation of their mono- and bis(chelated) cobalt complexes

Cited by 55 publications

References 21 publications

Mechanism of the Living Lactide Polymerization Mediated by Robust Zinc Guanidine Complexes

Mechanism of the Living Lactide Polymerization Mediated by Robust Zinc Guanidine Complexes

New Guanidine-Pyridine Copper Complexes and Their Application in ATRP

Pyridin-2-yl Guanidine Derivatives: Conformational Control Induced by Intramolecular Hydrogen-Bonding Interactions

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