The synthesis and charactererization of the complexes [PdX 2(L)] and [PdX(Me)(L)] (XCl,Br,I;L S-methyl- D/ L-cysteine methyl ester (H[Me]cysMe- N, S (a), D/ L-methionine methyl ester ( HmetMe-N,S ( b) , 2-[ aminoemthyl]pyridine (Py 1-N,N′ ( c)) , 2-[2- amino-ethyl]pyridine (Py 2-N,N′ ( d)) have been reported. A single crystal X-ray determination of [ PdCl( Me)( H[ Me] cysMe- N, S)] ( 2a) showed chelated coordination of the NS ligand. The square planar surrounding is completed by the chloride and the methyl group, which is positioned cis to the sulfur atom. The crystal structure determination of [PdCl(Me)(HmetMe)- N, S)] ( 2) shows an analogous geometry with the HmetMe- NS ligand forming a six-membered chelate ring with palladium. Again the methyl group is cis to the sulfur atom. The structure of [PdCl(Me)(Py 2- N, N′)] ( 2d) shows the presence of an amine-pyridine ligand also forming a six-membered chelate ring with Pd(II), with the methyl group positioned cis to the amine group. The unexpectedly stable methypalladium complexes reacted with Co to give the corresponding acyl complexes. The structure of [PdCl(C(O)Me)(HmetMe- N, S)] ( 5) in the solid state shows the presence of a six-membered chelate ring. The acyl group is cis to the sulfur atom. The NS and the NN′ complexes ( 1a–4b) contain, also in solution, a chelating ligand L as demonstrated by NMR. The complexes [PdX(R)(L) (RMe, C(O)Me; L=HmetMe- N, S; H[Me]cys-N,S) exist in two diastereoisometric forms which differ by the position of the methyl substituent on the S atom and can be distinguished at low temperatures. The free energy values ( ΔG) of the interconversion varies between 49.5 and 62.1 kl mol −1. Reaction of [PdX(R)(L)](RMe, C(O)Me); L= HmetMe- N, S; H[Me]cysMe- N, S; Py 1- N, N′) with allenes afforded [Pd( ν 3-allyl)(L)]Cl. This insertion reaction is faster for the NS complexes containing the six-membered rings than for the five-membered NS containing complexes. The kinetics of the allene insertion show a two term rate law, k obs= k 1+ k 2[allene], and depend on the nature of both the ligand and the allene substrate; either an allene dependent ( k 2; for 2a+3- methyl-1,2- butadiene, 2b+3- methyl-1,2- butadiene and 2b+1,2- heptadiene ) of an allene independent ( k 1; for 2b+2,4- dimethyl-2,3- pentadiene ) pathway is the dominant one.