Platinum(II) phosphine and orotate complexes with aminopyridine co-ligands, and their molecular recognition via hydrogen bonding

The new complexes [Pt(dppp)(py)(2)][OTf](2), 1, [Pt(dppp)(2-ap)(2)][OTf](2) , 2, [(dppp)Pt(mu -OH){mu -NH(C5H3N)NH2}Pt(dppp)][OTf](2), 3 (py=pyridine, 2-ap=2-aminopyridine, NH(C5H3N)NH2=2,6-diaminopyridine anion, dppp = 1,3-bi s(diphenylphosphino)propane, OTf=O3SCF3) have been prepared via reactions b etween [Pt(dppp)(OTf)(2)] and pyridine, 2-aminopyridine or 2,6-diaminopyrid ine (2,6-dap) respectively. The amines exhibit a range of co-ordination mod es. Pyridine and 2-aminopyridine co-ordinate to platinum through endo-nitro gen atoms in complexes 1 and 2, the latter existing as a pair of rotomers d ue to the steric hindrance introduced by the 2-substituent. However, 2,6-di aminopyridine co-ordinates to platinum through the exo-nitrogen of one amin o group, to give the unusual mu -amido complex 3. Reaction of the known oro tate chelate complex [Pt(PEt3)(2)(N,O-HL)] [HL=orotate, the dianion of 2,6- dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid (orotic acid)] with 2, 6-dap gave [Pt(PEt3)(2)(2,6-dap)(N-HL)] 4, which contains an unconventional monodentate orotate ligand. In this co-ordination mode the orotate retains an ADA hydrogen bonding site and was found to co-crystallise with 2,6-dap via complementary ADA:DAD triple hydrogen bonds to give [Pt(PEt3)(2)(N-HL)( 2,6-dap)].2,6-dap, 5. Complex 5 exhibits a helical chain structure of assoc iated [1+1] adducts in the solid state.