Reactions of 1,4-diazubutadienes with chloro-bridged palladium(II) and platinum(II) allyl derivatives
1981; Elsevier BV; Volume: 48; Linguagem: Inglês
10.1016/s0020-1693(00)90058-6
ISSN1873-3255
AutoresBruno Crociani, Tristano Boschi, Paolo Uguagliati,
Tópico(s)Synthesis and Reactivity of Heterocycles
ResumoThe 1,4-diazabutadienes (or α-diimines) RNC(R′)C(R″)NR, DAB, (R = p-C6H4OMe, R′ = R″ = H, DABI; R = p-C6H4OMe, R′ = H, R″ = Me, DABII; R = p-C6H4OMe, R′ = R″ = Me, DABIII; R = t-Bu, R′ = R″ = H, DABIV) react with the allylic compounds [PdCl(η3-2-Y-C3H4)]2 (Y = H: all; Y = Me: Meall) and [PtCl(C3H5)]4 in the presence of NaClO4 yielding the cationic complexes [M(η3-2-Y-C3H4)(DAB)]ClO4 (M = Pd, I; M = Pt, II). The 1H and 13C NMR spectra indicate a σ,σ′-N,N′ chelation of DAB. In the complexes with the asymmetric ligand DABII a fast syn-syn, anti-anti, exchange of the allylic protons occurs at room temperature in CDCl3. In acetonitrile a partial dissociation of DAB is observed, with the following order of stability constants; DABIII > DABI and Pt ⪢ Pd. In the absence of NaClO4, equilibria are established involving the starting reactant [PdCl(η3-Meall)]2, binuclear species {[PdCl(η3-Meall)]2(DAB)}, III (in which DAB acts as a bidentate bridging ligand) and ionic complexes [Pd(η3-Meall)(DAB)]+[PdCl2(η3-Meall)]−, IV. These equilibria were studied in various solvents by variable temperature 1H NMR spectra, electronic spectra, molecular weight and conductivity measurements. The complexes III can be isolated as solids and are the predominant species in concentrated solution only with DABI and DABIV, both having R′ = R″ = H. With DABIII, the predominant species in CDCl3 at −40 °C is a complex of type IV. A similar compound, [Pd(η3-Meall)(bipy)][PdCl2(η3-Meall)], is also obtained in the reaction with 2,2′-bipyridine.
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