Synthesis and catalytic application of palladium imidazol(in)ium-2-dithiocarboxylate complexes.

The palladium(II) dimer, Pd(C,N-C(6)H(4)CH(2)NMe(2))Cl reacts with two equivalents of the NHC·CS(2) zwitterionic ligands [NHC = IPr (1,3-diisopropylimidazol-2-ylidene), ICy (1,3-dicyclohexylimidazol-2-ylidene), IMes (1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), IDip (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene)] in the presence of NH(4)PF(6), to yield the cationic products Pd(C,N-C(6)H(4)CH(2)NMe(2))(S(2)C·NHC). In a similar fashion, the compounds Pd(C,N-bzq)(S(2)C·NHC) (bzq = benzo[h]quinolinyl, NHC = ICy, IMes, IDip) are obtained from the corresponding dimer Pd(C,N-bzq)Cl. The bis(phosphine) compounds Pd(S(2)C·NHC)(PPh(3))(2) (NHC = ICy, IMes, IDip, SIMes) are obtained on treatment of [PdCl(2)(PPh(3))(2)] with NHC·CS(2) zwitterions in the presence of NH(4)PF(6). The reaction of [PdCl(2)(dppf)] with IMes·CS(2) and NH(4)PF(6) provides the complex Pd(S(2)C·IMes)(dppf). The complexes Pd(S(2)C·NHC)(PPh(3))(2)(2) (NHC = IMes, IDip) were active pre-catalysts (1 mol% loading) for the conversion of benzo[h]quinoline to 10-methoxybenzo[h]quinoline in the presence of PhI(OAc)(2) and methanol. The intermediacy of Pd(C,N-bzq)(S(2)C·NHC) was supported by the high yield of 10-methoxybenzo[h]quinoline using Pd(C,N-bzq)(S(2)C·IDip) to promote the same reaction. Small amounts of 2,10-dimethoxybenzo[h]quinoline were also isolated from these reactions. Using Pd(C,N-bzq)(S(2)C·IDip) and N-chlorosuccinimide as the oxidant led to the formation of 10-chlorobenzo[h]quinoline in moderate yield from benzo[h]quinoline. The molecular structures of Pd(S(2)C·IMes)(PPh(3))(2)(2) and Pd(S(2)C·IMes)(dppf)(2) were determined crystallographically.