On the basis of different approaches for modifying α-diimine palladium catalysts, a series of methyl chloride palladium complexes with various α-diimine ligand backbones were synthesized and characterized. The corresponding cationic palladium complex chelating esters were further obtained by treatment of methyl chloride palladium complexes with methyl acrylate (MA). It was observed that decomposition of a cationic palladium complex chelating ester can occur to produce a new cationic palladium complex chelating two ligands and two counteranions, which provides a new pathway for deactivation of palladium catalysts and formation of palladium black by a fragmentation pattern with ester loss. These α-diimine palladium catalysts were employed in the homopolymerization of ethylene and copolymerization of ethylene and MA to evaluate substituent effects of the ligand backbone. A bulky camphyl α-diimine palladium catalyst was found to show better thermal stability and afford high-molecular-weight copolymer with higher incorporation of polar monomer. Longstanding living polymerization of ethylene was also achieved within 12 h using a bulky camphyl α-diimine palladium catalyst.
On
the basis of the steric effects of ligand, a series of imine–N-heterocyclic
carbene (NHC) ligands and their corresponding five-membered palladium
complexes with bulky substituents on both the imine and the NHC moieties
were synthesized and characterized. Transpalladation of silver carbene
complexes with (COD)PdCl2 and (COD)PdMeCl afforded the
palladium dichloride and methylpalladium complexes, respectively.
Bulky cationic palladium complexes were further obtained by treatment
of the methylpalladium complexes with sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate
(NaBAF) in CH3CN. Well-defined cationic palladium complexes
were confirmed by X-ray crystal diffraction to have trans forms. Palladium
dichloride complexes and methylpalladium complexes after activation
with MMAO show high activity for norbornene polymerization, whereas
cationic palladium complexes can polymerize norbornene alone without
any cocatalysts and exhibit a high thermostability. Norbornene polymerization
with the cationic palladium catalyst was proven to proceed through
a coordination–insertion mechanism by NMR studies. Analysis
of oligomers obtained by polymerizing the monomer in the presence
of H2 reveals the existence of a C7 linkage in the polynorbornene
(PNB) by σ-bond metathesis, which may be the reason for the
insolublity of polynorbornenes obtained by palladium catalysts.
I n t e r n a t i o n a l J o u r n a l o f O c e a n o g r a p h y a n d H y d r o b i o l o g y
AbstractThe method introduced in this study for future projection of coastline changes hits the vital need of communicating the potential climate change impact on the coast in the 21th century. A quantitative method called the Dynamic Equilibrium Shore Model (DESM) has been developed to hindcast historical sediment mass budgets and to reconstruct a paleo Digital Elevation Model (DEM). The forward mode of the DESM model relies on paleo-scenarios reconstructed by the DESM model assuming stationary wind-wave climate. A linear relationship between the sea level, coastline changes and sediment budget is formulated and proven by the least square regression method. In addition to its forward prediction of coastline changes, this linear relationship can also estimate the sediment budget by using the information on the coastline and relative sea level changes. Wind climate change is examined based on regional climate model data. Our projections for the end of the 21 st century suggest that the wind and wave climates in the southern Baltic Sea may not change compared to present conditions and that the investigated coastline along the Pomeranian Bay may retreat from 10 to 100 m depending on the location and on the sea level rise which was assumed to be in the range of 0.12 to 0.24 m.
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