Pt^II-Mediated Nitrile−Tetramethylguanidine Coupling as a Key Step for a Novel Synthesis of 1,6-Dihydro-1,3,5-triazines

Abstract

The coupling between tetramethylguanidine, HN=C(NMe2)2, and coordinated organonitriles in the platinum(II) complexes cis/trans-[PtCl2(RCN)2] (R = Me, Et, Ph) proceeds rapidly under mild conditions to afford the diimino compounds containing two N-bound monodentate 1,3-diaza-1,3-diene ligands [PtCl2{NH=C(R)N=C(NMe2)2}2] (R = Et, trans-1; R = Ph, trans-2; R = Me, cis-3; R = Et, cis-4), and this reaction is the first observation of metal-mediated nucleophilic addition of a guanidine to ligated nitrile. Complexes 1-4 were characterized by elemental analyses (C, H, N), X-ray diffraction, FAB mass spectrometry, IR, and 1H and 13C{1H} NMR spectroscopies; assignment of signals from E/Z-forms of 1,3-diaza-1,3-diene ligands and verification of routes for their Z right harpoon over left harpoon E isomerization in solution were performed using 2D 1H,1H-COSY, 1H,13C-HETCOR, and 1D NOE NMR experiments. The newly formed and previously unknown 1,3-diaza-1,3-dienes NH=C(R)N=C(NMe2)2 were liberated from the platinum(II) complexes [PtCl2{NH=C(R)N=C(NMe2)2}2] (1-3) by substitution with 2 equiv of 1,2-bis-(diphenylphosphino)ethane (dppe) to give the uncomplexed HN=C(R)N=C(NMe2)2 species (5-7) in solution and the solid [Pt(dppe)2](Cl)2. The former were utilized in situ, after filtration of the latter, in the reaction with 1,3-di-p-tolylcarbodiimide, (p-tol)N=C=N(tol-p), in CDCl3 to generate (6E)-N,N-dimethyl-1-(4-methylphenyl)-6-[(4-methylphenyl)imino]-1,6-dihydro-1,3,5-triazin-2-amines) (8-10) due to the [4 + 2]-cycloaddition accompanying elimination of HNMe2. The formulation of 8-10 is based on ESI-MS, 1H, 13C{1H} NMR, and X-ray crystal structures determined for 9 and 10. The reaction of 1,3-diaza-1,3-dienes with 1,3-di-p-tolylcarbodiimide, described in this article, constitutes a novel synthetic approach to a useful class of heterocyclic species like 1,6-dihydro-1,3,5-triazines.

Phosphorescent PtII Systems Featuring Both 2,2′‐Dipyridylamine and 1,3,5‐Triazapentadiene Ligands

“…In addition to [4a,b](OTf) 2 and [3a,b,d](OTf), another major product formed in the reaction is probably diphenylcarbodiimide (PhN=C=NPh). [9,19] Similar reactions between carbodiimides and various N-donor nucleophiles have been reported previously.…”

“…In theory, the empty orbital is subject to coordination by electron donors in the solvent, which would induce dominant nonradiative deactivation pathways. [17][18][19] Furthermore, the short radiative lifetimes, in combination with the lack of vibronic progression in the emission spectra, manifests the T 1 -S 0 transition to be MLCT in nature mixed, in part, with π-π* character. Supporting evidence is provided by the strong emission acquired in the solid state for the studied complexes, for which Φ f was measured to be 0.23, 0.27, and 0.20 for [3a](OTf), [3b](OTf), and [3d](OTf), respectively ( Figure 3 and Table 1).…”

Optically Active Mixed Unsymmetric Imine Platinum(II) Complexes – Utilization of the Liberated Imines for Further Syntheses of Mixed Imine‐Diazadiene Complexes and of (E)‐Cyanoalkenes

“…The association of those reactions with the subsequent ligand liberation from the metal provides a facile metal‐mediated route to the syntheses of previously unknown optically active diimine compounds 8 , which are inaccessible directly by pure organic chemistry. They can thus be generated and used in situ,6a,6g namely for further coupling with the coordinated nitrile in 4 to give the new optically active, mixed unsymmetric imine‐diazadiene complexes [PtCl 2 {( R *)‐imine}{( R *)‐diazadiene}] 9 . In the case of the generated free diimino ester 8a (bearing an acidic α‐methylene group), its reaction with acyclic nitrones affords ( E )‐cyanoalkenes stereoselectively.…”

cis-Dichlorido(dimethyl sulfoxide-κS)(N,N,N′,N′-tetramethylguanidine-κN′′)platinum(II)

“…As a part of our ongoing investigations on structural features of platinum complexes with guanidines (Gushchin et al, 2007;Gushchin et al, 2008) a new compound, (I), having PtII-bound N,N,N′,N′-tetramethylguanidine, has been prepared and herein we report its X-ray crystal and molecular structures.…”