COORDINATION DYNAMICS AND REACTIVITY OF PALLADIUM(II) COMPLEXES CONTAINING THE N-THIENYLIDENE-L D-METHIONINE METHYL-ESTER LIGAND/

Metathesis reactions of the N-thienylidene-L/D-methionine methyl ester ligand (th-metMe) with suitable palladium starting complexes afforded coordination complexes of the type PdX(2)(th-metMe), PdX(Me)(th-metMe ), and [Pd(Me)(th-metMe)(L '')](O3SCF3) (X = Cl, Br, I; and L '' = MeC N, pyridine, picoline, lutidine) which were studied by NMR with respec t to the fluxional behavior of the diastereomeric PdNS six-membered ri ng chelates. The structure of PdCl2(th-metMe) in the solid state (a = 13.318(5) Angstrom, b = 11.365(2) Angstrom, c = 13.579(5) Angstrom, be ta = 96.66(4)degrees) showed a square planar coordination complex in w hich the ligand is chelating via the imine nitrogen (Pd-N = 2.030(7) A ngstrom) and the methionine sulfur donor atom (Pd-S-1 = 2.283(2) Angst rom). The square planar geometry is completed by the chlorides (Pd-Cl- 1 = 2.275(3) Angstrom (trans to the imine nitrogen) and Pd-Cl-2 2.322( 2) Angstrom (trans to the sulfur donor)). The dimeric [PdCl(L')](2) co mplex (L' = anionic alpha-methoxycarbonyl, alpha-(2-thienylmethylidene )amine, alpha ''-(methylthio)ethane) was formed by C-H activation of t he chiral carbon atom of the alpha-amino acid moiety. The structure de termination (a = 8.1887(7) Angstrom, b = 20.507(2) Angstrom, c = 34.07 9(3) Angstrom, beta = 91.220(7)degrees) revealed two stretched out lig ands of which one is coordinating to Pd(1) via the methionine sulfur d onor (2.268(2) Angstrom) and sigma-bonded via the stereogenic chiral c arbon atom (2.068(6)) and to Pd(2) via the imine nitrogen (2.074(5) An gstrom). The second ligand coordinates to Pd(1) via the imine donor (2 .074(5) Angstrom) and to Pd(2) via the methionine sulfur (2.276(1)) an d the former stereogenic carbon atom (2.060(6)). Both square planar co ordination sites are occupied by the chlorides which are positioned tr ans to the carbon atom (2.390(2) and 2.414(2) Angstrom for Cl(1A) and Cl(2A)). Complexes of the type [PdX(C(O)Me)(th-metMe)] and [Pd(C(O)Me) (L '')(th-metMe)](O3SCF3) were obtained by reaction of CO with the cor responding methyl complexes. The rates of CO insertion into the methyl palladium bond were investigated, and it was found that the rate decre ases in the order [Pd(Me)(th-metMe)(CF3SO3)] > [Pd(Me)(I)(th-metMe)] > [Pd(Me)(Br)(th-metMe)] > [Pd(Me)(th-metMe)(MeCN)](CF3SO3) > [Pd(Me)(t h-metMe)(2,6-lutidine)](CF3SO3) > [Pd(Me)(Cl)(th-metMe)] > [Pd(Me)(th- metMe)(pyridine)](CF3SO3).