Palladium and platinum compounds of the composition [MX(L)]X and [M(Me)(L)]X (M Pd, Pt; X Cl, Br, I, O 3SCF 3) have been prepared from the appropriate starting materials and the new ligands (L = N-[2-(diphenylphosphino)benzylidene]- L-methioninol (PNS-1), N-[2-(diphenylphosphino)benzylidene]-3-propylethylsulfide(PNS-2), N-{ N-[2-(diphenylphosphino)benzylidene]- D/ L-methio-nyl}- tert-butylamine (PNS-3), N-{ N-[2-(pyridine)methylidene]- D/ L-methionyl}- tert-butylamine (NN'S)). The single crystal X-ray determination of [PtI(PNS-3)]I ( 3cz) (triclinic, space group P 1 (No. 2) with a=10.5298(9), b=11.5584(8), c=14.545(2) A ̊ , α=77.368(8), β=84.453(9), γ=79.720(7)° , V=1696.5(3) →A 3, Z=2, R155, wR2=0.1195) showed terdentate coordination of the trifunctional PNS-3 ligand with a six-membered PN containing metallacycle and a six-membered NS containing metallacycle which is in a chair conformation. The square planar geometry is completed with an iodide atom, while the second iodide atom is non-coordinating. The methyl-palladium and -platinum complexes may occur in solution in various isomeric forms, as an equilibrium has been observed between the ionic [M(Me)( ν 3-PNS)X and the neutral [MX(Me)( ν 2-PNS)]. The η 3-PNS bonded complex may occur in two conformations, i.e. with the six-membered NS containing part of the ligand in either the chair or boat form. The methyl-palladium and -platinum complexes reacted slowly with CO to form corresponding acetyl complexes, with insertion rates which increased in the order Cl<BrI<O 3SCF 3 − and PNS-1<PNS-2<PNS-3<NN'S. Complexes [Pd( η 3-allyl)(PNS-3)]X (X = Cl, O 3SCF 3) with 2-methylallyl and 1,1,2-trimethylallyl groups have been prepared from the reaction of [PdCl( η 3-allyl)] 2 with PNS-3. Both the η 3-allyl and the unusual η 1-allyl species have been identified by 1H NMR and their dynamic properties have been investigated in CDCl 3.