Pt^II-Mediated Imine–Nitrile Coupling Leading to Symmetrical (1,3,5,7,9-Pentaazanona-1,3,6,8-tetraenato)Pt(II) Complexes Containing the Incorporated 1,3-Diiminoisoindoline Moiety

Abstract

Treatment of trans-[PtCl(2)(NCR)(2)] (1; R = Et (1a), Ph (1b)) with 1,3-diiminoisoindoline (2) gives access to the corresponding symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) complexes [PtCl{NH═C(R)N═C(C(6)H(4))NC═NC(R)═NH}] (3). The reactions of 1 with one equivalent of 1,1,3,3-tetramethylguanidine (4), 1,3-diphenylguanidine (6), or acetone oxime (8) leads to the formation of mixed asymmetrical Pt(II) complexes trans-[PtCl(2){NH═C(R)N═C(NMe(2))(2)}(NCR)] (5), [PtCl{NH═C(R)NC(NHPh)═NPh}(NCR)] (7), or trans-[PtCl(2){NH═C(Ph)ON═CMe(2)}(NCPh)] (9), respectively, as a result of nucleophilic addition to one of the nitrile ligands in 1. Treatment of 5, 7, and 9 with one equivalent of 2 leads to complexes 3. The complexes were characterized by IR, (1)H, (13)C{(1)H}, and (195)Pt NMR (for 3) spectroscopies, ESI(+)-MS, elemental analyses, and X-ray diffraction (for 3). Complex 3a has an asymmetric unit with five independent Pt molecules of the same chemical composition and two molecules of water, resulting in a total of 40 molecules of the complex and sixteen guest water molecules per unit cell. Theoretical calculations revealed that the most plausible mechanism of formation of complexes 3 includes stepwise nucleophilic addition of 2 to one of the nitrile ligands in 1, a first cyclization upon formation of the Pt-N bond and elimination of HCl, and a second nucleophilic addition/cyclization.

Metal-Mediated Addition of N-Nucleophiles to Isocyanides: Mechanistic Aspects

“…All attempts of its location led to TSs of the stepwise pathways discussed below. This result is different from that found previously for NA to nitriles N≡CR for which both 4-membered and 6-membered cyclic TSs of the concerted NA were located [ 105 ].…”

Platinum(II)‐Mediated Double Coupling of 2,3‐Diphenylmaleimidine with Nitrile Functionalities To Give Annulated Pentaazanonatetraenate (PANT) Systems

“…Such a tautomeric equilibrium was established for the related amidines, HN=C(R)-NHR′ # H 2 N-C(R)=NR′, by a series of chemical and physicochemical experiments, [40,41] and also for phthalimidine. [26] In accord with literature data, [42][43][44] the latter exists in tautomeric equilibrium between the amino and imino forms. Theoretical [43,44] and X-ray diffraction [42] studies indicate that the imino form possesses lower energy and is therefore expected to be the predominant in the solution, whereas the amino form is prevalent in the solid state because of the intermolecular hydrogen bond that is formed.…”

“…These compounds exhibit analogous structures, that is, the CN bonds in the PANT chelates display a low degree of delocalization. One should mention that these complexes are similar with the previously characterized (PANT)Pt II species [26,27] and all PANT complexes have the same sequence of single and double carbon-nitrogen bonds in the PANT conjugated π-system. However, these complexes may be aromatic, because, on the one hand, aromaticity was assumed for TAPD complexes, [5] and on the other hand, it was established for other platinum(II) complexes featuring two fused planar chelate rings.…”

“…The first approach was suggested by Lasri, Pombeiro, and co-workers, who reported two examples that include nucleophilic addition of phthalimidine to Pt II -bound propanenitrile and benzonitrile. [26] The second approach was developed by Cryder et al and involves a template reaction between heterocyclic imino esters with phthalonitrile at a Zn II center, giving octahedral complexes bearing two PANT species. [27] In both cases, the metal-mediated coupling of nitriles and NH nucleophiles leads to chelate ligands.…”

“…Moreover, the luminescence properties of PANT complexes have not been reported. Being inspired by an approach that utilizes metal-mediated nitrile-imidine (viz., diiminoisoindoline [26] ) coupling to afford PANT systems and, in addition, by the reported zinc(II)-mediated generation of [Zn(PANT) 2 ], [27] we conducted a study on platinum(II)-mediated double coupling of another imidine (abbreviated as Imd; the IUPAC name is 3,4-diphenyl-1H-pyrrole-2,5-diimine, whereas the trivial name, 2,3-diphenylmaleimidine, is by far more widely used [28][29][30] ) with both conventional nitriles NCR (R = Et, nPr, tBu, CH 2 Ph, Ph, p-CF 3 C 6 H 4 ) and push-pull nitriles such as dialkylcyanamides [31,32] NCNR 2 [R = NMe 2 , NEt 2 , N(CH 2 ) 5 ]. The reaction leading to PANT systems and the luminescence properties of the obtained species are discussed in this paper.…”