Synthesis and Characterisation of Alkylated Isocyanate Derivatives of [Pt2(µ-S)2(Pph3)4]

The highly nucleophilic bridging sulfide centers in bis(μ-sulfido)tetrakis(triphenylphosphine) diplatinum(II), [Pt2(µ-S)2(PPh3)4] enables the incorporation of any organic functionality (R) through facile monoalkylation to form cationic complex [Pt2(µ-S)(µ-SR)(PPh3)4]+. The organic electrophiles; N,N’-(2-dichloroethyl) piperazine-4-carboxi-amine, N-(2-chloroethyl) morpholine-4-carboxi-amine, and N-(2-chloroethyl)-1-methylpiperazine-4-carboxi-amine derived from isocyanate were synthesised by the reactions of piperazine, morpholine and methyl piperazine respectively with 2-chloroethyl isocyanate in diethyl ether. This potentially formed highly functionalised organic electrophiles N-(2-chloroethyl) morpholine-4-carboxi-amine, and N-(2-chloroethyl)-1-methylpiperazine-4-carboxi-amine was incorporated into [Pt2(µ-S)2(PPh3)4] in methanol to yield the corresponding monoalkylated derivatives [Pt2(μ-S)(μ-SCH2CH2NHC(O)N(CH2CH2)2O)(PPh3)4]+ and [Pt2(μ-S)(μ-SCH2CH2NHC(O)N(CH2CH2)2N CH3)(PPh3)4]+. The reaction of [Pt2(μ-S)2(PPh3)4] with the functionalised dialkylating agent ClCH2CH2NHC(O)N(CH2CH2)2NC(O)HNCH2CH2Cl proceeded in two stages in a 2:1 mole ratio. The first stage is the monoalkylation of [Pt2(μ-S)2(PPh3)4] to give the monocation [Pt2(μ-S)(μ-SCH2CH2NHC(O)N(CH2CH2)2NC(O)HNCH2CH2Cl)(PPh3)4]+. The monoalkylated derivative provided the enabling condition for a second intermolecular nucleophilic attack by another molecule of [Pt2(μ-S)2(PPh3)4] yielding the bridging Pt4 aggregate spanned by SCH2CH2NHC(O)N(CH2CH2)2NC(O)HNCH2CH2S. The resulting products was isolated as the tetraphenyl borate (BPh4-) salts and characterized by Electrospray Ionization Mass Spectrometry (ESI-MS), FT-IR, 1H, 13C and 31P {H} NMR.