Mono-, di- and trinuclear gold(I) complexes of new phosphino-substituted amides: initial steps to chlorogold(I)diphenylphosphino-terminated dendrimers

The amides MeNHCO-□-PPh₂ (□ CH₂ (2a); C₆H₄ (2b) have been prepared from methylamine and α-diphenylphosphinoacetic acid (1a) or p-diphenylphosphino-benzoic acid (1b), respectively, using EDC (N′-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride) as a coupling agent. The dendritic, multifunctional species MeN(CH₂CH₂CH₂NHCO□PPh₂)₂ (5a, 5b) and N(CH₂CH₂NHCOC₆H₄PPh₂)₃ (8) have been obtained following the same procedure. Treatment of the diphenylphosphino-terminated compounds with equivalent amounts of (dimethylsulfide)gold(I) chloride afforded the corresponding mono-, di- and trinuclear gold(I) complexes 3a,b, 6a,b and 9 with chain-end (diphenylphosphino)gold(I) chloride groups (-PPh₂AuCl) in excellent yields as stable colorless solids. X-ray structure analyses have been performed for MeNHCOC₆H₄PPh₂ (2b) (orthorhombic, space group Pna2₁), N(CH₂CH₂NHCOC₆H₄PPh₂)₃ (8) (triclinic, space group P1) and MeNHCOCH₂PPh₂AuCl (3a) (orthorhombic, space group P2₁2₁2₁). The conformation of the molecules and their packing can be rationalized on the basis of both inter- and intramolecular NH···O hydrogen bonds, which in this case exclude intermolecular Au^I···Au^I contacts between the MeNHCOCH₂PPh₂AuCl molecules.