Organoplatinum Chemistry Related to Alkane Oxidation: The Effect of a Nitro Substituent in Ligands Having an Appended Phenol Group

The organoplatinum chemistry of the ligands 2-C5H4N-CH2-NH-C6H3-2-OH-5-X (L1, X = H; L3, X = NO2) and 2-C5H4N-CH=N-C6H3-2-OH-5-X (L2, X = H; L4, X = NO2), which contain an appended phenol substituent, is described. Comparisons are made between the ligands with amine or imine groups (L1, L3 vs. L2, L4) and ligands with X = H or NO2 (L1, L2 vs. L3, L4), and major differences are observed. Thus, on reaction with the cycloneophylplatinum(II) complex [{Pt(CH2CMe2C6H4)(μ-SMe2)}2], ligands L1, L2 and L4 give the corresponding platinum(II) complexes [Pt(CH2CMe2C6H4)(κ2-N,N′-L)], containing a Pt··HO hydrogen bond, whereas L3 gives a mixture of isomeric platinum(IV) hydride complexes [PtH(CH2CMe2C6H4)(κ3-N,N′,O-L3-H)], which are formed by oxidative addition of the phenol O-H bond and which react further with oxygen to give [Pt(OH)(CH2CMe2C6H4)(κ3-N,N′,O-L3-H)]. The differences in reactivity are proposed to be due to the greater acidity of the nitro-substituted phenol groups in L3 and L4 and to the greater ability of the deprotonated amine ligand L3 over L4 to stabilize platinum(IV) by adopting the fac-κ3-N,N′,O-L3-H coordination mode.