Synthesis, characterization and X-ray crystal structures of polyether and ethylene bridged bis(azolyl) platinum(II) complexes

Abstract

The preparation of platinum(II) complexes of the types [PtCl 2 {Y(CH 2 CH 2 O) x CH 2 CH 2 Y}] (Y: imidazol-1-yl, im; pyrazol-1-yl, pz or benzimidazol-1-yl, bim) and [PtI 2 {im(CH 2 CH 2 O) x CH 2 CH 2 im}] with varying ligand backbone length (x between 0 and 3) is described. A new bis(pyrazol-1-yl) polyether compound, pz(CH 2 CH 2 O) 2 CH 2 -CH 2 pz, is reported. Spectroscopic characterization of the complexes is discussed. Two crystal structures of the general formula [PtCl 2 {im(CH 2 CH 2 O) x CH 2 CH 2 im}] (x is 1 or 3) are also reported.Abbreviations bim Benzimidazol-1-yl im Imidazol-1-yl pz Pyrazol-1-yl

Linear Bidentate Ligands (L) with Two Terminal Pyridyl N-Donor Groups Forming Pt(II)LCl2 Complexes with Rare Eight-Membered Chelate Rings

“…This angle, defined as the Pt–N–centroid angle (N = N1 or N3, centroid = aromatic ring center) should approach ∼180°. The Pt–N–centroid angle ranges from 164–180° for known Pt­(II) complexes of imidazolyl or pyridyl ligands bound in a monodentate, bidentate, or tridentate fashion. − ,− This angle averages 174.5° for 5 (Table ), which is similar to the value for monodentate ligands (176.7°; see the Supporting Information); this is another indication that the pyridyl rings in 5 are well-positioned to form a strong Pt–N bond.…”

“…The N1–Pt–N3 bite angle of 5 (87.98°) is at the high end of the range reported for Pt­(II) complexes with mono- or bidentate-coordinated ligands terminated by pyridyl or imidazolyl rings (78–91°). − The bite angles of known Pt complexes having eight-membered chelate rings (average 89.5°) are higher than for Pt complexes with smaller chelate rings − but are quite close to those for monodentate complexes (average 89.4°) − (Figure ). We attribute this finding to the greater spatial freedom provided by the larger chelate ring; this freedom allows the N-donor rings to be located in the same relative position as monodentate ligands.…”

“…Most examples have very closely related bidentate ligand derivatives with Pt­(II) bound to the pyridyl N of a fused bicyclic 7-azaindol-1-yl group. ,, Only one Pt­(II) complex contains a linear ligand terminated with two simple aromatic rings (pyridyl). Other complexes commonly have macrocyclic N-donor (mostly sp 3 ) ligands bound in a bidentate mode. , In the CCDC database we found only three Pt­(II) complexes with an eight-membered chelate ring that contain two aromatic-ring nitrogens (pyridyl/imidazolyl) and two halides as the other ligating atoms; − however, at the time of our analysis there were 7, 17, and 108 complexes having seven-, six-, and five-membered chelate rings, respectively. − Structural data for 53 complexes (all of the complexes containing eight-, seven-, and six-membered chelate rings plus 26 randomly chosen complexes of five-membered chelate rings) were utilized in the following comparison with the structural data for 5 and 6 .…”

“…The two pyridyl rings in 5 and 6 are only slightly tilted, with dihedral angles ranging from 77° to 87° (Table ); thus, the eight-membered ring allows the pyridyl rings to be oriented roughly perpendicular to the coordination plane. In contrast, other known bifunctional Pt­(II) complexes with a bidentate ligand terminated by pyridyl or imidazolyl rings [with the remaining coordination site(s) occupied by halide(s)] and forming five-, six-, or seven-membered chelate rings − have relatively smaller average dihedral angles (Figure ). However, the three known Pt­(II) complexes with eight-membered chelate rings − used in the plot have large dihedral angles (73–89°), values close to the dihedral angles observed in the complexes reported here (Figure ).…”

“…Previous studies have shown that N (H)­dpa (Figure ) and related ligands readily form [Pt­(L tri )­Cl] + complexes. , However, the new N (SO 2 R)­Me n dpa ligands form Pt­(II) complexes with bidentate N (SO 2 R)­Me n dpa ligands having an eight-membered chelate ring, in which the tertiary sulfonamide nitrogen is not bound to Pt­(II) but serves as an atom in the −CH 2 –N­(SO 2 R)–CH 2 – chain of the chelate ring. Structural characterizations of Pt­(II) complexes with bidentate ligands having eight-membered chelate rings such as those found here are very few in number compared with bifunctional Pt­(II) complexes with smaller five-, six-, or seven-membered chelate rings of bidentate pyridyl/imidazolyl ligands − or with two pyridyl/imidazolyl monodentate ligands. − The rarity and unusual properties of the new bifunctional Pt­(II) compounds with a large eight-membered chelate ring described herein led us to compare their structural features with those of related bifunctional Pt­(II) complexes. The relevance of binding at G residues in DNA by anticancer-active Pt­(II) compounds ,,,, has led to many studies of adduct formation of guanine derivatives ( G ).…”