Phosphinoalkyl nitriles as hemilabile ligands: New aspects in the homogeneous catalytic coupling of CO2 and 1,3-butadiene

‘In situ’ catalysts prepared from (η5-C5H5)Pd(η3-C3H5) 9 and phosphinoalkyl nitriles 10a–e of the general formula (iC3H7)2P(CH2)nCN have been used to catalyse the co-oligomerisation of 1,3-butadiene and carbon dioxide. The δ-lactone 2-ethylidene-6-heptene-5-olid 1 is formed, yielding up to 74%. Different solvent systems have been used of which pyridine provides the best result. The catalysis may also be performed without additional solvent. A minimum of five CH2 units (n = 5) within the ligand is necessary to produce 1 with a selectivity higher than 29% in a solvent-free reaction. Therefore, phosphinoalkyl nitriles of the type described here are acting as hemilabile ligands in the catalytic cycle.