Diphenylphosphino(phenyl pyridin-2-yl methylene)amine palladium(II) complexes: Chemoselective alkene hydrocarboxylation initiators

The heteroditopic, P–N-chelating ligand diphenylphosphino(phenyl pyridin-2-yl methylene)amine (1) has been synthesised via a simple ‘one-pot’ procedure and its donor characteristics assessed. The neutral [MX(Y)(1-κ2-P–N)] (3, M = Rh, X = Cl, Y = CO; 4, M = Pd, X = Y = Cl; 5, M = Pd, X = Cl, Y = Me; 6, M = Pt, X = Y = Cl; 7, M = Pt, X = Cl, Y = Me; 8, M = Pt, X = Y = Me) and cationic [Pd(Me)(MeCN)(1-κ2-P–N)][Z] (9, Z = B{3,5-(CF3)2-C6H3}4; 10, Z = PF6) complexes of 1 have been prepared and characterised. The solid-state structures of complexes 3, 4, 6 and 7 have been established by X-ray crystallography. Reactions of [PdCl(Me)(1-κ2-P–N)] towards CO and tBuNC have been investigated, affording the corresponding η1-acyl (12) and -iminoacyl (14) complexes, respectively. Similar insertion chemistry is observed for the cationic derivative 9. Treatment of the acyl complex 12 with ethene at elevated pressure establishes an equilibrium between the starting material and the product resulting from insertion, 13. Under catalytic conditions, combination of palladium(II) with 1 in MeOH affords a selective initiator for the formation of 4-oxo-hexanoic acid methyl ester (15) from CO/ethene (38 bar, 90 °C).

Graphical abstractThe P–N ligand diphenylphosphino(phenyl pyridin-2-yl methylene)amine has been synthesised via a simple ‘one-pot’ procedure, and been shown to form chelate complexes with a range of group 9 and 10 metal-containing fragments. In methanol, a combination of this ligand with sources of Pd(II) generates, exclusively, 4-oxo-hexanoic acid methyl ester from CO/ethene (38 bar, 90 °C).Figure optionsDownload full-size imageDownload as PowerPoint slide