Nucleophilic addition of 1,3-dicarbonyl compounds as a route to functionalized cyclopalladated complexes with chelated 1,1-bis(diphenylphosphino)ethene

Abstract

Treatment of the chloride-bridged complex [Pd{2,4-(OMe)₂C₆H₂C(H)N(Cy)-C6,N}(μ-Cl)]₂ (1) with 1,1-bis(diphenylphosphino)ethene (vdpp) and NH₄PF₆ or NaClO₄ in 1∶2 molar ratio afforded the mononuclear cyclometallated palladium(II) complexes [Pd{2,4-(OMe₂)C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CCH₂-P,P′}](X) (2, X = PF₆; 3, X = ClO₄). The structure of 2 has been determined by X-ray diffraction analysis. Reaction of 2 with acetylacetone in the presence of anhydrous sodium carbonate yielded in high yield the addition product [Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CHCH₂CH(COMe)₂-P,P′}](PF₆) (4). The ³¹P-{¹H} NMR spectrum showed a greater ²J(PP) coupling constant than the one observed for the starting complex. Reaction of 2 with diethyl malonate afforded a 7∶3 mixture of the addition product [Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CHCH₂CH(COOEt)₂-P,P′}](PF₆) (5) and the starting complex. The desired addition compound could be isolated in pure form by treatment of 3 with diethyl malonate yielding [Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CHCH₂CH(COOEt)₂-P,P′}](ClO₄) (16). The reaction of 2 with asymmetric nucleophiles such as methyl acetoacetate, ethyl propionylacetate, ethyl acetoacetate, methyl 4-chloroacetoacetate, 1,1,1-trifluoroacetylacetone and thenoyltrifluoroacetone afforded the corresponding addition derivatives, [Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(PH₂P)₂CHCH₂CH(COR₁)(COR₂)-P,P′}](PF₆) (R₁ = Me, R₂ = OMe, 6; R₁ = Et, R₂ = OEt, 7; R₁ = Me, R₂ = OEt, 8; R₁ = CH₂Cl, R₂ = OMe, 9; R₁ = Me, R₂ = CF₃, 10; R₁ = CF₃, R₂ = 2-SC₄H₃, 11). The NMR spectra showed some resonances were duplicated, suggesting the existence of optical isomers, as a consequence of the existence of two chiral carbon atoms in the diphosphine moiety, (Ph₂P)₂C*HCH₂C*H(COR₁)(COR₂). The molecular structure of compound 7 has been determined by X-ray crystallography confirming the spectroscopic data. The crystal structure of 7 comprises equimolar amounts of the (C16R, C18S) and (C16S, C18R) enantiomers. Reaction of 2 with 1-(2-furyl)-1,3-butanedione, ethyl 2-methylacetoacetate, 3-chloroacetylacetone and methyl 2-chloroacetoacetate gave compounds [Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CHCH₂C(R₁)(COMe)(COR₂)-P,P′}](PF₆) (R₁ = H, R₂ = 2-OC₄H₃, 12; R₁ = Me, R₂ = OEt, 13; R₁ = Cl, R₂ = Me, 14; R₁ = Cl, R₂ = OMe, 15). The ²J(PP) coupling constants for 14 and 15 were smaller than in the other addition compounds due to the presence of the neighbouring chlorine atom. Treatment of 2 with 3-ethylacetylacetone or 2,2,6,6-tetramethyl-3,5-heptanedione did not give any addition product. However, reaction of 3 with 3-ethylacetylacetone yielded a mixture of 3/[Pd{2,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{(Ph₂P)₂CHCH₂C(Et)(COMe)₂-P,P′}](ClO₄) (17) in 1∶1 molar ratio.