title: Pt(II)-mediated nitrile-tetramethylguanidine coupling as a key step for a novel synthesis of 1,6-dihydro-1,3,5-dihydrotriazines.
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.
authors.affiliation: Saint Petersburg State University, 198504 Stary Petergof, Russian Federation, Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Avenida Rovisco Pais, 1049-01 Lisbon, Portugal.
authors.forename: Pavel V
authors.initials: PV
authors.lastname: Gushchin
authors.forename: Nadezhda A
authors.initials: NA
authors.lastname: Bokach
authors.forename: Konstantin V
authors.initials: KV
authors.lastname: Luzyanin
authors.forename: Alexey A
authors.initials: AA
authors.lastname: Nazarov
authors.forename: Matti
authors.initials: M
authors.lastname: Haukka
authors.forename: Vadim Yu
authors.initials: VY
authors.lastname: Kukushkin
mesh_terms: D018360:Crystallography, X-Ray; D006146:Guanidines / Q000737:chemistry*; D007097:Imines / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D009944:Organoplatinum Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D013237:Stereoisomerism; D014227:Triazines / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D006146:Guanidines; D007097:Imines; D008024:Ligands; D009570:Nitriles; D009944:Organoplatinum Compounds; D014227:Triazines; D010984:Platinum; C477069:1,1,3,3-tetramethylguanidine