O-chelating ligands

Catalysts based on nickel that dimerize or oligomerize a-olefins have been known for many years and are commercially valuable. The Shell higher olefin process (SHOP), for example, uses Ni(II) catalysts developed by Keim and coworkers such as 1.1 and 1.2 bearing P-O chelating ligands to oligomerize ethylene into higher olefins in the manufacture of surfactants, lubricants, and fine chemicals (Fig. 1) [9-11]. Late transition metals are more suited for the polymerization of... 

A numerous series of compounds containing a N,O-chelating ligand, namely the derivatives of anthranilic (157) and 3-amino-2-thiophenecarboxylic (158 and 159) acids, were prepared by the reactions of organohalogermanes with esters, amides or lithium derivatives of acids510-516. 

Derivatives with bidentate C,O-chelating ligands and related compounds... 

Habtemariam A, Melchart M, Fernandez R, Parsons S, Oswald IDH, Parkin A, Fabbiani FPA, Davidson JE, Dawson A, Aird RE, Jodrell DI, Sadler PJ (2006) Structure-activity relationships for cytotoxic ruthenium(II) arene complexes containing N, N-, N, O-, and O, O-chelating ligands. J Med Chem 49 6858-6868... 

Peacock AFA, Parsons S, Sadler PJ (2007) Tuning the hydrolytic aqueous chemistry of osmium arene complexes with N,O-chelating ligands to achieve cancer cell cytotoxicity. J Am Chem Soc 129 3348-3357... 

Fig. 29. A structural model of the steps involved in the in vitro uptake of iron by transferrins, shown for one lobe. ( ) Iron ( ) carbonate Y, Tyr ligands H, His ligand D, Asp ligand (O) chelate ligands. The positive charge at the anion site is due to the helix N-terminus and the Arg side chain. (Note that this is for the case in which Fe3+ is added as a chelate complex.)...

Based on Ziegler s work at the MPl fiir Kohlenforschung in Miilheim/Germany, Wilke and co-workers learned how to control the selectivity of nickel-catalyzed reaction by use of ligands. Keim, then at Shell at Emeryville, introduced P-O chelate ligands and carried out the basic research for the oligomerization process. The whole process was developed in a collaboration between Shell Development in the US and the Royal Shell Labs in Amsterdam/The Netherlands. Today there are two locations producing nearly 1 MMt of a-olefins per year. 

Another approach is to separate the products from the homogeneous catalyst using a two phase liquid system. For example, this method is used in the oligomerization step of the Shell Higher Olefins Process for the manufacture of linear a-olefins. A polar nickel catalyst containing a P-O chelate ligand is dissolved in a polar solvent e.g. 1,4-butanediol, which is immiscible with higher oc-olefins, and recovery of the catalyst is easily achieved by simple phase separation. 

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