Highly selective metal mediated ortho-alkylation of phenol. First platinum containing organometallic chromane analogues

Abstract

We were able, for the first time, to synthesize and characterize Pt derivatives with a structural shape similar to vitamin E, having a metalla-chromane core. The formation reaction mechanism includes an unexpected highly selective ortho aromatic electrophilic substitution on phenol, operated by [PtCl(eta(1)-C(2)H(4)OR)(N-N)], R = Me or Ph, and a final cyclization step. The X-ray structure of one of the new metalla-chromane complexes [Pt(EtPh)(phen)],1a, (EtPh = 2-(ethan-2'-yl-kC(1))-1-phenolato-k0(1), phen = 1,10-phenanthroline) is reported. Cytotoxicity and Pt uptake measurements, performed on HeLa cancer cells, show an interesting structure-activity correlation for the new metalla-chromane analogues 1a and [Pt(MeOEtPh)(phen)], 1b, (MeOEtPh = 2-(ethan-2'-yl-kC(1))-4-(methoxy)-1-phenolato-k0(1)), being the structurally closest to vitamin E and also the most active.

Insertion of alkynes into Pt–X bonds of square planar [PtX2(N^N)] (X = Cl, Br, I) complexes

“…43 Interestingly, the nucleophilic attack of X − on the π-bonded alkyne extends to halides the possibility of acting as nucleophiles toward unsaturated molecules π bonded to cationic complexes of platinum(II). [8][9][10][11]13,15,23,25,28,29,41,42 13 C} NMR data (δ, CDCl 3 ) for [PtX(η 1 -E-CHvCHX)(η 2 -CH 2 vCH 2 )(Me 2 phen)], X = Br, (7) and I, (12); syn and anti-[PtBr(η 1 -E-CHvCHBr)(η 2 -propene)(Me 2 phen)] (10); syn and anti-[PtBr(η 1 -E-CHvCHBr)(η 2 -cis-2-butene)(Me 2 phen)] (11); [PtBr(η 1 -E-CHvCHBr)(CuO)-(Me 2 phen)] ( evolve to square planar alkenyl complexes of the type [PtX(η 1 -E-CHvCHX)(Me 2 phen)] (X = Br, I). In the presence of excess acetylene, the square planar alkenyl complexes are in equilibrium with the pentacoordinate alkyne-alkenyl species [PtX-(η 1 -E-CHvCHX)(η 2 -CHuCH)(Me 2 phen)] (X = Br, I).…”

“…[PtI(η 1 -E-CHvCHI)(η 2 -CH 2 vCH 2 )(Me 2 phen)] (12). A solution of [PtI 2 (Me 2 phen)] (3) (50 mg, 0.075 mmol) in chloroform (10 cm 3 ) containing a large excess (thirty times) of tetra(n-Bu) ammonium iodide was saturated with acetylene gas and left standing at room temperature for 2.5 h under magnetic stirring.…”

“…The role of the metalto-olefin back donation in the stabilization of the metal-olefin bonding interaction was also supported by the enhanced stabilization of anionic square planar Pt(II) complexes bearing η 2 -olefins, with respect to neutral or cationic complexes, which instead exhibit reduced stability and increased reactivity. [11][12][13][14][15][16][17][18][19][20] In previous work we synthesized and characterized complexes with the Me 2 phen ligand, of the type [PtX 2 (Me 2 phen)] (X = halogen), 21 showing considerable distortions from the regular square planar arrangement and an unusual chemical and electrochemical behavior, with respect to analogous complexes in which the phenanthroline has no substituents in the 2,9 positions. 22 Because of steric interactions between ortho substituents of the phenanthroline and halogen ligands in cis positions, the square planar [PtX 2 (Me 2 phen)] complexes have a great tendency to add an external L ligand (L = CuO, PPh 3 , DMSO, DMS, py, n-PrNH 2 , alkene, alkyne) to give the corresponding addition product.…”

Hindrance, Donor Ability of Men∩NN Chelates and Overall Stability of Pentacoordinate [PtCl2(η2‐CH2=CH2)(Men∩NN)] Complexes as Observed by η2‐Olefin 1JPt,C Modulation: An NMR Study

“…These five-coordinate species of d 8 transition metals are of significant interest, because they are well known to play a fundamental role in reactions of ligand substitution, cis-trans isomerization, and a large variety of catalytic processes (isomerization, polymerization, etc. ); [17][18][19][21][22][23] moreover, they have also been proposed as protecting groups for the stabilization of unstable olefin derivatives.…”

Square‐Planar PtII versus Octahedral PtIV Halido Complexes: 195Pt NMR Explained by a Simple Empirical Approach

“…We recently reported the existence of specific linear relationships between the number and orientation of alkyl groups bonded to coordinated dinitrogen ligands and the observed 195 Pt NMR frequency for pentacoordinate and square‐planar Pt II species , . To better understand the relationship between the observed NMR chemical shifts and the molecular structures of platinum complexes, we studied the Pt II pentacoordinate complexes of the type [PtXY(η 2 ‐olefin)(N^N)] and [PtXY(η 2 ‐alkyne)(N^N)] (X,Y = Cl, Br, I; N^N = dinitrogen ligand). In particular, collection of the 1 H, 13 C, 15 N, and 195 Pt NMR spectroscopic data of the considered pentacoordinate complexes allowed the linear correlation of the chemical shift frequencies with both the spatial disposition of the observed nuclei and the ionic radii of the apical halido ligands (Figure , A) , .…”