Nucleophilic substitution reactions at planar tetra-coordinate bis-cationic-platinum(II)complexes.Kinetics of displacement of pyridine from {Pt[2,6-bis(methylthiomethyl)pyridine](py)}~(2+),(Pt[bis(2-pyridylmethyl)aminel(py)}~(2+)and {Pt[bis(2-(pyridy

摘要

The kinetics of nucleophilic substitution of pyridine in bis-cationic [Pt(L)(py)]~(2+)complexes(L=SNS,NNN,NSN)[SNS=bis(methylthiomethyl)pyridine,NNN=bis(2-pyridylmethyl)amine,NSN=bis(2-pyridylmethyl)sulphide] by a series of nucleophiles(Cl~-,Br~-,I~-,N_3~-,(C_2H_5)_2S,NH_3,thiourea(tu),NO_2~-,C_5H(10)NH,SeCN~-,SCN~-,CN~-when L=SNS;Cl~-,Br~-,I~-,N_3~-,(C_2H_5)_2S,SCN~-,NH_3,NO_2~-when L=NNN;Br~-,N_3~-,NO_2~-,NH_3,C_5H_(10)NH when L=NSN)have been measured in MeOH at 25 deg C,mu=0.1 mol dm~3(LiClO_4 or LiCF_3SO_3).The logarithms of the second-order rate constants calculated at mu=0,log kappa_2 deg,do not follow the dependence upon the n_(Pt)deg scale.In particular,the reactivity of the biphilic reagents tu,SeCN~-,SCN~-and,to a lesser extent,NO_2~-,towards these doubly charged substrates is largely lower than expected on the basis of the n_(Pt)deg scale.There are good linear relationships between log kappa_2 deg for the bis-cationic substrate [Pt(SNS)(py)]~(2+),chosen as the standard,and log kappa_2 deg for the same reactions with [Pt(NNN)(py)]~(2+),[Pt(NSN)(py)]~(2+)and other double charged complexes previously studied.A new wide nucleophilicity scale based on [Pt(SNS)(py)]~(2+),that is appropriate to all the bis-cationic substrates,is here proposed.