A polycyclic tetra(tertiary phosphine) cage ligand has been synthesised by the spontaneous intramlecular cyclisation of 1,2-phenylenebis[di(4-pentyl)phosphine with 1,2-phenylenebis(phosphine) on copper(I). The mixed-ligand copper complex was generated in acetonitrile by mixing together the corresponding homoleptic complexes and the progress of the redistribution of the ligands was monitored by electrospray mass spectrometry. The copper(I) complex of the cage phosphine has been characterised by 31P{1H} and 63Cu NMR spectroscopy and X-ray crystallography. Current work is concerned with the synthesis of related complexes with use of Grubbs’ catalysts and appropriate homoleptic copper(I) complexes of 1,2-phenylenebis(dialkenylphosphines).