NMR spectroscopy and DFT calculations of a self-assembled arene ruthenium rectangle obtained from a combination of coordination and hydrogen bonds

The hydrogen-bonded arene ruthenium metalla-rectangle, [(p-cymene) 2Ru2(OOnOO)(UPy)2]24+ , obtained from 1-(4-oxo-6-undecyl-1,4-dihydropyrimidin-2-yl)-3-(pyridin-4- ylmethyl)urea (UPy) and the dinuclear arene ruthenium clip (p-cymene) 2Ru2(OOnOO)Cl2 (OOnOO = 2,5-dioxido-1,4- benzoquinonato), is investigated by means of solution-phase NMR spectroscopy. Rotating frame nuclear Overhauser effect measurements are used to probe the H- bond network that drives the UPy self-assembly as well as the full rectangular supramolecular system. An effective distance that takes into account both intra-and intermolecular polarization-transfer pathways is utilised for data analysis. The experimental findings are corroborated by DFT calculations of NMR parameters and internuclear distances, thus confirming the formation of a very stable tetranuclear metalla-assembly

Pyrazole and pyrazolyl copper and zinc complexes in ring opening polymerization of ε-caprolactone and D,L-lactide

M.Sc.Six pyrazole and pyrazolyl compounds, 3,5-dimethylpyrazole (L1), 3,5-diphenylpyrazole (L2), 3,5-di-tert-butylpyrazole (L3), bis(3,5-dimethylpyrazol-1-yl)methane (L4), bis(3,5-diphenylpyrazol-1-yl)methane (L5) and bis(1,2-bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L6), were reacted with Zn(II) and Cu(II) benzoates to form pyrazole and pyrazolyl metal benzoates. The complexes are [Zn(C6H5COO)2(L1)2] (1), [Zn(3,5-NO2-C6H3COO)2(L1)2] (2), [Zn(4-OH-C6H4COO)2(L1)2] (3), [Zn(2-Cl-C6H4COO)2(L1)2] (4), [Zn(C6H5COO)2(L2)2] (5), [Zn(3,5-NO2-C6H3COO)2(L2)2] (6), [Zn(4-OH-C6H4COO)2(L2)2] (7), [Zn(2-Cl-C6H4COO)2(L2)2] (8), [Zn(3,5-NO2-C6H3COO)2L4] (9), [Zn(4-OH-C6H4COO)2L6] (10), [Zn2(C6H5COO)4L6]n (11), [Zn(3,5-NO2-C6H3COO)2L6] (12), [Zn(2-Cl-C6H4COO)2L6] (13), [Cu(C6H5COO)2(L1)2] (14), [Cu(3,5-NO2-C6H3COO)2(L1)2] (15), [Cu(4-OH-C6H4COO)2(L1)2] (16), [Cu(2-Cl-C6H4COO)2(L1)2] (17), [Cu(C6H5COO)2(C6H5COOH)]2 (18), [Cu(2-Cl-C6H4COO)2(L3)2] (19), [Cu(C6H5COO)2L4] (20), [Cu(2-Cl-C6H4COO)2L4] (21), [Cu(C6H5COO)2DMSO]2 (22), [Cu(C6H5COO)2L6]2 (23), [Cu(2-Cl-C6H4COO)2L6]2n (24), [Cu(4-OH-C6H4COO)2L6]2(25) and [Cu(3,5-NO2-C6H3COO)2L6]n (26). The molecular structures of the Zn(II) and Cu(II) complexes 6, 9, 11, 14, 17-19, 22-26 were determined by X-ray diffraction studies that revealed four types of geometries adopted by these complexes: (i) 4-coordinate tetrahedral (6, 9, 14), (ii) 6-coordinate octahedral (17), (iii) paddle wheel (18, 19, 22, 23, 25) and (iv) polymeric structures (11, 24, 26). Catalysis studies performed with selected complexes (1-4, 9-17, 23-26) revealed that they initiate the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and D,L-lactide at elevated temperatures, and under solvent-free conditions and in toluene respectively. Polycaprolactone (PCL) and poly(D,L-lactide) (PLA) produced were of moderate molecular weights (858-4 757 Da for PCL and 602-3 185 Da for PLA) and polydispersity indices (1.36-2.16 for PCL and 1.42-2.35 for PLA). End group of the iv polymers, determined by MALDI-TOF MS, were benzoates, hydroxyl, methoxy groups and cyclic. From the 13C{1H} NMR spectra of polymers synthesized, the stereochemistry of PLA was predominantly isotactic

Pyrazole Supported Zinc(II) Benzoates as Catalysts for the Ring Opening Copolymerization of Cyclohexene Oxide and Carbon Dioxide

The bis(pyrazole)zinc(II) benzoate complexes bis(3,5-diphenylpyrazole)zinc(II) benzoate (1), bis(3,5-diphenylpyrazole)zinc(II) 3,5-dinitrobenzoate (2), bis(3,5-diphenylpyrazole)zinc(II) 4-hydroxybenzoate (3), and bis(3,5-di-tert-butylpyrazole)zinc(II) 2-chlorobenzoate (4) were synthesized from the reaction of 3,5-diphenylpyrazole (L1) or 3,5-di-tert-butylpyrazole (L2), zinc(II) acetate and the appropriate benzene carboxylic acid. The molecular structure of complex 2 confirmed that these zinc(II) benzoate complexes adopt a 4-coordinate tetrahedral geometry. All four complexes were screened as catalysts for the copolymerization of carbon dioxide (CO2) and cyclohexene oxide (CHO) and were found to be active for the formation of poly(cyclohexene carbonate) (PCHC) at CO2 pressures as low as 1.0 MPa under solvent-free conditions and without the use of a co-catalyst. At some reaction condition, most of the catalysts produced PCHC with high carbonate content of up to 98% and a good amount of cyclic cyclohexene carbonate (CCHC). The copolymers produced have low to moderate molecular weights (5200–12300 g/mol) and with polydispersity indices that vary from 1.19 to 2.50. Matrix Assisted Laser Desorption/Ionization-Time of Flight Mass Spectra (MALDI-TOF MS) of these copolymers showed they have benzoate and hydroxyl end groups