Versatile nuclephilic Michael addition to chelated (Ph2P)2CCH2 (vdpp) in Schiff base cyclometallated palladium(II) compounds: C–C, C–O and C–N bond formation, dinuclear palladacycles and geometrical isomerism

Treatment of the mononuclear complex [Pd{2,4-(MeO2)C6H2C(H)N(Cy)-C6,N}{(Ph2P)2CCH2-P,P′}][PF6] (1) with methyl 2-oxocyclopentanecarboxilate, α-acetylbutyrolactone or methyl phenylsulfonylacetate in the presence of anhydrous sodium carbonate yielded the addition products [Pd{2,4-(MeO)2C6H2C(H)N(Cy)-C6,N}{(Ph2P)2CHCH2C(R1)(R2)-P,P′}][PF6] (R1 = COOCH3, R2 = COCH2CH2CH2, 2; R1 = COCH3, R2 = COOCH2CH2, 3; R1 = COOCH3, R2 = SO2Ph, 4) in high yield. The existence of two chiral carbon atoms in the diphosphine moiety produces the existence of optical isomers. Reaction of 1 with acetone and potassium tert-butoxide afforded complex [Pd{2,4-(Me)2C6H2C(H)N(Cy)-C6,N}{(Ph2P)2CHCH2CH2COCH3-P,P′}][PF6] (5), via C–C bond formation. Complex 1 reacts in methanol and in ethanol to give the corresponding addition products [Pd{2,4-(MeO)2C6H2C(H)NCy-C6,N}{(Ph2P)2CHCH2OR-P,P′}][PF6] (R = CH3, 6; R = CH2CH3, 7), via C–O bond formation. Treatment of complex 1 with cyclohexylamine or dimethylhidrazine gives place to [Pd{2,4-(MeO)2C6H2C(H)N(Cy)-C6,N}{(Ph2P)2CHCH2N(H)R–P,P′}][PF6] (R = C6H11, 8; R = N(CH3)2, 9), via C–N formation. The crystal structure of 7 has been determined by X-ray crystallography and comprises equimolar amounts of the (C16R) and (C16S) enantiomers. Reaction of compound 1 with dl-alanine or dl-metionine and anhydrous sodium carbonate yields [Pd{2,4-(MeO)2C6H2C(H)N(Cy)-C6,N}{(Ph2P)2CHCH2NHCH(R1)(R2)-P,P′}][PF6] (R1 = CH3, R2 = COOH, 10; R1 = CH2CH2SCH3, R2 = COOH, 11). Treatment of complex 1 with piperazine give rise to the dinuclear compound [{Pd[2,4-(MeO)2C6H2C(H)N(Cy)-C6,N]}2{(Ph2P)2CHCH2N(CH2CH2)2NCH2CH(PPh2)2-P,P,P′,P′}][PF6]212, in which each N–H bond of the piperazine has been added to the vinylidene bond of one vdpp ligand.

Graphical abstractChelated (Ph2P)2CCH2 (vdpp) in Schiff base palladacycles is activated towards Michael addition to give compounds with new C–C, C–O and C–N bonds.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Activation of (Ph2P)2CCH2 (vdpp) towards Michael addition reactions. ► Geometrical isomerism in the addition products of (Ph2P)2CCH2 (vdpp). ► Double addition of a cyclic diamine.