Effects of electrochemical properties of ferrocenylpyrazolylnickel(ii) and palladium(ii) compounds on their catalytic activities in ethylene oligomerisation reactions.

Palladium complexes of ferrocenylpyrazolylpyridine and ferrocenylpyrazolylamine were synthesised and screened as pre-catalysts (1-4) for olefin polymerisation. The pre-catalysts 1-4 on activation with EtAlCl2 in the presence of ethylene with chlorobenzene or hexane as solvent were highly active with 1 being the most active, with an activity of 360 kg mol Pd-1 h-1. The major product from the reaction was 1-butene and high carbon content oligomers. The molecular weight (m/z) of the high carbon content oligomers is as high as 623.0. When toluene is used as solvent, the products obtained were ethyltoluene and butyltoluene and 1-butene. The electronic properties of the ligands (L1-L7) and complexes (1-10) were determined by cyclic voltammetry (CV) and molecular modelling. The CV results show that the ferrocenyl is easily oxidized upon the introduction of pyrazolyl derivatives, the process is quasi-reversible. However, complexation of the ligands with palladium or nickel results in difficulty in oxidizing the ferrocenyl moiety. This is an indication of the electrophilic nature of both the palladium and nickel centres. The mechanism of the oxidation was observed to be diffusion-controlled and is independent of scan rate. Molecular modelling experiments show that nickel and palladium complexes have lower HOMO-LUMO gaps and high global descriptors, an indication of a highly electrophilic metal centre. A plot of the electrophilicity indices of the pre-catalysts against yield of the oligomers show a linear correlation, an indication that the electrophilicity of the metal centre plays an important role in the activity of these pre-catalysts.

(3,5-Di-tert-butyl-2-eth-oxy-benzyl-idene)[2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)eth-yl]amine.

The angles within the benzene ring in the title compound, C(30)H(49)N(3)O, ranging from 116.34 (16) to 124.18 (16)°, reflect the presence of electron-donating and electron-withdrawing substituents. The angles at the two electron-donating tert-butyl substituents are smaller than 120°, at the electron-withdrawing eth-oxy substituent larger than 120°, and at the imine substituent equal to 119.59 (16)°. The latter does not reflect the electron-donating nature of the imine group due to the presence of other substituents.

Intramolecular hydrogen bonding in dichloridobis(3,5-di-tert-butyl-1H-pyrazole-κN2)cobalt(II) as a consequence of ligand steric bulk.

The title compound, [CoCl(2)(C(11)H(20)ClN(2))(2)], forms two intramolecular hydrogen bonds [graph set S(5)] between the N atoms of the pyrazole ligands and the chloride ligands. This hydrogen-bonding motif is uncommon among related compounds but occurs here because of the bulk of tert-butyl substituents on the pyrazole ligands which shield the central metal atom to a significantly larger extent than pyrazole ligands with smaller 3,5-substituents.

Constructor graph description of the hydrogen-bonding supramolecular assembly in two ionic compounds: 2-(pyrazol-1-yl)ethylammonium chloride and diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride.

Covalent bond tables are used to generate hydrogen-bond pattern designator symbols for the crystallographically characterized title compounds. 2-(Pyrazol-1-yl)ethylammonium chloride, C(5)H(10)N(3)(+).Cl(-), (I), has three unique, strong, charge-assisted hydrogen bonds of the types N-H...Cl and N-H...N that form unary through ternary levels of graph-set interactions. Diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride, [CoCl(2)(C(2)H(8)NO)(2)(H(2)O)(2)]Cl(2), (II), forms five unique charge-assisted hydrogen bonds of the types O-H...Cl and N-H...Cl. These form graph-set patterns up to the quinary level. The Co complex in (II) resides at a crystallographic inversion center; thus the number of hydrogen bonds to consider doubles due to their G-equivalence, and the handling of such a case is demonstrated.