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

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.