Trifunctional primary phosphines of the type 1,3,5-[PH2(CH2)n]3C6H3 (3b–d) were obtained via an Arbusov reaction between the 1,3,5-tris(bromoalkyl)benzenes 1b–d and P(OEt)3 followed by a reaction of the trisphosphonates 1,3,5-[(EtO)2P(O)(CH2)n]3C6H3 (2b–d) with LiAlH4. A straightforward conversion of these sensitive key phosphines 3b–d to the corresponding water-soluble ligands 1,3,5-tris[bis(hydroxymethyl)phosphinylalkyl]benzenes 4b–d and 1,3,5-tris[bis(2′-diethylphosphonatoethyl)phophinylalkyl]benzenes 5b–d was achieved by formylation with formaldehyde and hydrophosphonation with diethyl vinylphosphonate, respectively. A five component self-assembly consisting of three equivalents of the platinum(II) complex Cl2Pt(NCPh)2 and two equivalents of the ligands 5b–d under high dilution conditions resulted in the formation of the nanoscaled, water-soluble triplatinacyclophanes 6b–d in high yields. However, comparable reactions with the ligands 4b–d led only to polymeric materials, which are insoluble in all organic solvents and water. The structures of the metallacyclophanes 6b–d were elucidated by 31P{1H}-, 13C{1H}-, and 195Pt{1H}-NMR spectroscopic investigations.