Versatile nuclephilic Michael addition to chelated (Ph2P)2C=CH2 (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)(2)C=CH2-P,P')] [PF6] (1) with methyl 2-oxocyclopentanecarboxilate, alpha-acetylbutyrolactone or methyl phenyl-sulfonylacetate in the presence of anhydrous sodium carbonate yielded the addition products [Pd{2,4(MeO)(2)C6H2C(H)=N(Cy)-C6,N}{(Ph2P)(2)CHCH2C(R-1)(R-2)-PP'}][PF6] (R-1 = COOCH3, R-2 = COCH2CH2CH2, 2; R-1 = COCH3, R-2 = COOCH2CH2, R-1 = COOCH3, R-2 = 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)(2)C6H2C(H)=N(Cy)-C6,N} {(Ph2P)(2)CHCH2CH2COCH3-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)(2)C6H2C(H)=NCy-C6,N} {(Ph2P)(2)CHCH2OR-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)(2)C6H2C(H)=N(Cy)-C6,N} {(Ph2P)(2)CHCH2N(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)(2)C6H2C(H)=N(Cy)-C6,N}{(Ph2P)(2)CHCH2NHCH(R-1)(R-2)-P,P'}] [PF6] (R-1 = CH3, R-2 = COOH, 10; R-1 = CH2CH2SCH3, R-2 = COOH, 11). Treatment of complex 1 with piperazine give rise to the dinuclear compound [{Pd[2,4-(MeO)(2)C6H2C(H)=N(Cy)C6,N]}(2){(Ph2P)(2)CHCH2N(CH2CH2)(2)NCH2CH(PPh2)(2)-P,P,P',P'}][PF6](2) 12, in which each N-H bond of the piperazine has been added to the vinylidene bond of one vdpp ligand. (C) 2012 Elsevier B.V. All rights reserved.