Steric Crowding and Redox Reactivity in Platinum(II) and Platinum(IV) Complexes Containing Substituted 1,10-Phenanthrolines

Abstract

The effect of the phenanthroline substituents on the structure and reactivity of platinum(II) and platinum(IV) complexes has been investigated. The X-ray crystal structures of the compounds [PtI(2)(4,7-Ph(2)phen)].CHCl(3) (1dz.CHCl(3)), [PtI(4)(4,7-Ph(2)phen)].CHCl(3) (2dz.CHCl(3)), [PtI(2)(2,9-Me(2)-4,7-Ph(2)phen)] (1fz), and [PtI(4)(2,9-Me(2)-4,7-Ph(2)phen)].I(2) (2fz.I(2)) have shown that complexes 1fz and 2fz, containing ortho-substituted phenanthrolines, exhibit a remarkable displacement of the equatorial iodine atoms from the N-Pt-N' plane (average 0.477(2) and 0.199(2) Å, respectively), a bending of the phenanthroline [angle between outer rings of 19.9(7) and 14.2(7) degrees, respectively] and a rotation of the N-C-C'-N' plane with respect to the N-Pt-N' plane [32.3(10) and 26.5(9) degrees, respectively]. Comparison between the structures of 1fz and 2fz, both having the phenanthroline with methyl substituents in the ortho position, indicates that, in the latter case, because of the presence of the two axial iodine ligands, the displacements of the ligands from the equatorial plane are smaller and find a compensation in a narrowing of the I(1)-Pt-I(1') angle (5 degrees ) and a lengthening of the Pt-N bonds (0.07 Å). The electrochemical behavior of the four-coordinate platinum(II) complexes shows that compounds possessing regular planar geometry have access to the one-electron reduced species, whereas those with distorted coordination geometry are irreversibly reduced by collapsing of the complex geometry. This is in sharp contrast with the behavior of related nickel complexes for which the pseudo-tetrahedral coordination imposed by bulky 2,9-substituents of phenanthroline stabilizes the nickel(I) species. Spectroscopic results allow us to assign a significant Pt(I) character to [1d](-) monoanions. The electrogenerated, plus one electron, complexes are not indefinitely stable and, because of conjugation with the phen ligand, progressively restore the Pt(II) oxidation state by transferring the electron to the peripheral organic ligand. The latter process can involve multiple electron additions in the macroelectrolysis time scale. The related platinum(IV) complexes [PtX(4)(L)] undergo irreversible two-electron reduction accompanied by fast release of the axial ligands and formation of the corresponding platinum(II) species.

Platinum-based inhibitors of amyloid-β as therapeutic agents for Alzheimer's disease

“…23. Peptides were obtained from AusPep and from the W. M. Keck Laboratory (Yale University, New Haven, CT).…”

1H, 13C, 195Pt and 15N NMR structural correlations in Pd(II) and Pt(II) chloride complexes with various alkyl and aryl derivatives of 2,2′‐bipyridine and 1,10‐phenanthroline

“…In this work we present the 1 H, 13 C, 15 N and 195 Pt NMR spectra of analogous Pd(II) and Pt(II) chloride complexes with some other alkyl and aryl derivatives of bpy and phen (LL): 6,6 -dimethyl-bpy (6,6 -dmbpy), 5,5 -dimethyl-bpy (5,5 -dmbpy), 4,4 -di-tert-butylbpy (4,4 -dbbpy), 2,9-dimethyl-phen (2,9-dmphen), 2,9-dimethyl-4,7-diphenyl-phen (2,9-dm-4,7-dpphen), 3,4,7,8-tetramethyl-phen (3,4,7,8- . Some of them were already studied by 1 H and/or 13 C NMR (1a, [10,11] 2a, [2] 3a, [12 -15] 4a, [16,17] 5a, [18] 1b, [10] 2b, [19] 3b, [1,20 -26] 4b, [17,27,28] 5b, [28] 6b [22,28] ) (Table S1, Supporting Information); however, no systematic comparison of their 1H coord and 13C coord coordination shifts ( coord = δ complex − δ ligand ) was performed. The 15 N and 195 Pt NMR spectra of the title complexes were never reported (although the former were published for the related organometallics: [Pd(2,9-dmphen )(bis(anisylimino)acenapthene)(CH 3 …”

“…[17,28,38] It was enhanced by the introduction of π -bonded alkenes, as exemplified by [Pd(2,9-dmphen)(alkene)X 2 ](X 2 = Cl 2 , ClBr, Br 2 , I 2 ; alkene being CH 2 CH 2 , CH 2 CHCH 3 : CH 3 coord = 0.49-0.65 ppm), [17] [Pt (2,9- = 0.37-0.79 ppm) [17,28,38 -40] and [Pt(2,9-dm-4,7-dpphen)(CH 2 CH 2 )X 2 ] (X = Cl, Br, I: CH 3 coord = 0.46-0.52 ppm), [28] whereas the influence of alkynes was variable, as illustrated by [Pt(2,9-dmphen)(alkyne)X 2 ] (X = Br, I; alkyne being CH CH, CH CCH 3 , CH 3 C CCH 3 , CH CCH 2 CH 2 CH 3 , CH CC 6 H 5 , CH 3 C CC 6 H 5 , C 6 H 5 C CC 6 H 5 : CH 3 coord = 0.08-0.82 ppm). [39] Such dependencies indicate that anisotropic phenomena, resulting from the presence of multiple bonds and affecting the 1 H shielding constants, must also be taken into account.…”

A Molecular Tool for Measuring the Electron‐Acceptor Ability of Ligands from Crystallographic Data

“…The complexes with L ϭ DMSO (2e) and DMS (2f) were synthesized according to a procedure reported previously. [8] Crystals of the compounds suitable for X-ray structure determinations were obtained from solutions of the platinum complexes in chloroform. Diethyl ether was gently stratified upon the above solutions in order to induce crystallization.…”

“…[8] [e] Experimental values. [5] [f] R ϭ H in the theoretical and C 3 H 7 (n-propyl) in the X-ray investigation.…”