Stereoselectivity for S-bridged polynuclear transition metal complexes formed by aggregation of octahedral complexes to square-planar palladium(II)

Novel pentanuclear complexes, [Pd{Pd(aet)}{(M(aet)(2)}{M(aet)(3)}(2)](4+) (M = Rh (1); Ir (2); aet = 2-aminoethanethiolate) and [Pd-2{Pd(aet)(2)}{Co(aet)(3)}(2)](4+), were prepared by the reactions of fac(S)-[M '(aet)(3)] (M ' = M, Co) with Na-2[PdCl4]. Molecular structures for 1, 2 and 4 were determined by X-ray diffraction. In 1 and 2, two Pd atoms forming the parallel planes are spanned by the aggregation of two octahedral fac(S)-[M(aet)(3)] units and cis(N)-[M(S)(2)(aet)(2)] unit. In these complexes, one of the aet ligands in the starting fac(S)-[M(aet)(3)] transfers from the M (= Rh, Ir) atom to the Pd one. Two Pd atoms in 4 are bridged by two fac(S)-[Co(aet)(3)] units and cis(S)-[Pd(aet)(2)] unit. In this complex, two aet ligands transfer to the Pd one. The methylation reaction for one non-bridging S atom in 1 gave the corresponding complex [Pd{Pd(aet)}{Rh(aet)(smaet}{Rh(aet)(3)}(2)](5+) (3; smaet = S-methyl-2-aminoethanethiolate), whose structure was also determined by X-ray diffraction. For all of the complexes, the chiral configurations are selectively regulated owing to the octahedral units (Delta or Lambda) and the bridging sulfur atoms (R or S), and they are characterized on the basis of the electronic absorption, circular dichroism (CD) and C-13 NMR spectral behavior. The binding modes of the octahedral units in 1, 2, and 4 are also discussed in relation to their stereochemical behavior.