Title
Linear Bidentate Ligands (L) with Two Terminal Pyridyl N-Donor Groups Forming Pt(II)LCl Complexes with Rare Eight-Membered Chelate Rings
Document Type
Article
Publication Date
10-15-2018
Abstract
NMR and X-ray diffraction studies were conducted on Pt(II)LCl complexes prepared with the new N-donor ligands N(SOR)Me dpa (R = Me, Tol; n = 2, 4). These ligands differ from N(H)dpa (di-2-picolylamine) in having the central N within a tertiary sulfonamide group instead of a secondary amine group and having Me groups at the 6,6'-positions ( n = 2) or 3,3',5,5'-positions ( n = 4) of the pyridyl rings. The N(SOR)3,3',5,5'-Medpa ligands are coordinated in a bidentate fashion in Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes, forming a rare eight-membered chelate ring. The sulfonamide N atom did not bind to Pt(II), consistent with indications in the literature that tertiary sulfonamides are unlikely to anchor two meridionally coordinated five-membered chelate rings in solutions of coordinating solvents. The N(SOR)6,6'-Medpa ligands coordinate in a monodentate fashion to form the binuclear complexes [ trans-Pt(DMSO)Cl]( N(SOR)6,6'-Medpa). The monodentate instead of bidentate N(SOR)6,6'-Medpa coordination is attributed to 6,6'-Me steric bulk. These binuclear complexes are indefinitely stable in DMF- d, but in DMSO- d the N(SOR)6,6'-Medpa ligands dissociate completely. In DMSO- d, the bidentate ligands in Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes also dissociate, but incompletely; these complexes provide rare examples of association-dissociation equilibria of N,N bidentate ligands in Pt(II) chemistry. Like typical cis-PtLCl complexes, the Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes undergo monosolvolysis in DMSO- d to form the [Pt( N(SOR)3,3',5,5'-Medpa)(DMSO- d)Cl] cations. However, unlike typical cis-PtLCl complexes, the Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes surprisingly do not react readily with the excellent N-donor bioligand guanosine. A comparison of the structural features of over 50 known relevant Pt(II) complexes having smaller chelate rings with those of the very few relevant Pt(II) complexes having eight-membered chelate rings indicates that the pyridyl rings in Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes are well positioned to form strong Pt-N bonds. Therefore, the dissociation of the bidentate ligand and the poor biomolecule reactivity of the Pt( N(SOR)3,3',5,5'-Medpa)Cl complexes arise from steric consequences imposed by the -CH-N(SOR)-CH- chain in the eight-membered chelate ring.
Publication Source (Journal or Book title)
Inorganic chemistry
First Page
12756
Last Page
12768
Recommended Citation
Ranasinghe, K., Marzilli, P. A., Pakhomova, S., & Marzilli, L. G. (2018). Linear Bidentate Ligands (L) with Two Terminal Pyridyl N-Donor Groups Forming Pt(II)LCl Complexes with Rare Eight-Membered Chelate Rings. Inorganic chemistry, 57 (20), 12756-12768. https://doi.org/10.1021/acs.inorgchem.8b01943