Metal phosphine complexes incorporating alkyl substituents with ethane and ethylene backbones

Abstract

Abstract The new chelating bis-phosphine ligands 1,2-bis(butylphenylphosphino)ethane (bppe) and cis-1,2-bis(butylphenylphosphino)ethylene (bppey) have been synthesised by (i) a one-pot synthesis from Ph2PBu and Li/dihalo alkyl, (ii) the reaction of 1,2-bis(diphenylphosphino)ethane (dppe) or cis-1,2- bis(diphenylphosphino)ethylene (dppey) and Li/n-BuCl and, (iii) in the case of bppe by sequential synthesis (all intermediates were isolated) from Ph2PBu via PhBuPLi and Ph2PH. bppe and bppey as well as the new lithium phosphide [(TMEDA)•LiPPh(Bu)]2 (17) were fully characterised by multinuclear NMR spectroscopy, mass spectrometry and, in the case of [(TMEDA)•LiPPh(Bu)]2 (17), by X-ray crystallography. Reaction of the bis-phosphines bppe and bppey with suitable metal precursors yielded the corresponding metal complexes: [PdCl2(bppe)] (18), [Pd(bppe)2](ClO4)2 (20), [(AuCl)2(bppe)] (21a), [(AuCl)2(bppey)] (21b), [Au(bppe)2]Cl (22a), [Au(bppey)2]Cl (22b), [(AgNO3)2(bppe)] (23) and [Au(bppe)2]ClO4 (24) in moderate to good yields. All were characterised by multinuclear NMR spectroscopy and mass spectrometry, while 18 and 20 were further characterised by X-ray crystallography. Preliminary stability tests showed, that of all new metal complexes only 18, 20 and 22a were adequately stable to justify further tests for anti-tumour activity. The cationic complexes 20 and 22a showed activity against HeLa cells while the neutral complex 18 was not active. A comparison with the previously investigated analogous dppe and dppey complexes revealed that 20 and 22a were found to be less active as a result of the replacement of a Ph groups with butyl groups in the phosphine ligand.