Cationic Methallylnickel and (Meth)allylpalladium 2-Phosphinophenol Complexes:  Synthesis, Structural Aspects, and Use in Oligomerization of Ethylene

Reactions of methallylnickel bromide with 2-R<INF>2</INF>PC<INF>6</INF>H<INF>4</INF>OH <BO>1a</BO>,<BO>b</BO> (R = Ph, cHex) and AgSbF<INF>6</INF> furnish methallylnickel phosphinophenol hexafluoroantimonates <BO>2a</BO>,<BO>b</BO>, which are not very stable and decay in solution at room temperature within an hour (<BO>2a</BO>) or days (<BO>2b</BO>) to tetranuclear nickel complexes <BO>3a</BO>,<BO>b</BO>. The related cationic allylpalladium complex <BO>4a</BO> is more stable. A crystal structure analysis gives evidence of the monomeric nature, the typical η³-coordination of the allyl group, and the coordination of the phenolic hydroxyl group to palladium. In solution the OH group is uncoordinated and underlines the hemilabile character of the phosphinophenol ligands. The allylpalladium phosphinophenol tetrafluoroborate <BO>5a</BO>, stable as a solid, slowly decomposes in CDCl<INF>3</INF> solution to give a dinuclear complex <BO>6a</BO> and in THF/water as the solvent the palladium bis(phosphinophenolate) <BO>7a</BO>. Methallylpalladium phosphinophenol acetates <BO>8a</BO>,<BO>b</BO>, existing as phosphinophenolate acetic acid conjugates, are uncommonly stable and lose the acid on heating in a vacuum without cleavage of the methallyl group to give neutral methallylpalladium phosphinophenolates <BO>9a</BO>,<BO>b</BO>. The labile complexes <BO>2a</BO> and <BO>2b</BO> proved to be highly active single-component catalysts for the conversion of ethylene to isomer mixtures of butenes, hexenes, and lower amounts of higher olefins at ambient temperature. The C<INF>6</INF> fraction consists mainly of branched and internal olefins. <BO>5a</BO> is less active but converts ethylene on heating under pressure to a mixture of butenes and smaller amounts of hexenes, while <BO>8</BO> and <BO>9</BO> are inactive.