Solvent effects on coordination chemistry - stepwise synthesis and structural properties of monometallic palladium(II) complexes and bimetallic palladium(II)/platinum(II) complexes

Stepwise syntheses of monometallic palladium(II) and bimetallic palladium(II)/platinum(II) complexes were carried out in order to measure the metallophilicity of potential, tetradentate bis(alkylthio)ylidenem.alonato ligands. The reaction of [Pd](SO₄) ([Pd] = (Me₄en)Pd; Me₄en = N,N,N′ ,N′-tetramethylethylenediamine) with Ba[L] {L: bis(methylthio)methylenepropanedioato (1); bis(ethylthio) methylenepropanedioato (2); l,3-dithiapan-2-ylidene-malonato (3)} produced. [[Pd]-O, O′-L]. Successive reactions of [[Pd]-O,O′-L] with {M}(NO₃)₂ ([M) = (en)M; en = ethylenediamine; M = Pd ^II, Pt^II), followed by anion exchange with PF ₆^-, yielded bananashaped bimetallic http://bimetallic complexes [[Pd]-O,O′-L-S,S′-{M}](PF₆)₂. In case of [[Pd]-O,O′-1], the bis(alkylthio)methylene group of 1 was bent strikingly from, the palladium, square plane (dihedral angle = 78.26°), in contrast to the cases of [[Pd]-O,O′-3] (120.84°) and [[Pd]-O,O′-L-S,S′-{M}](PF₆)₂ (101.75-103.54°). [[Pd]-O,O′-L] (L = 1, 2) in Me₂SO existed as a mixture of [[Pd]-O,O′-L] and [(Me₄en-N)(Me ₂SO-S)-Pd-O,O′-L] in a mol ratio of 1:1. For the labile species, a linkage isomeric equilibrium, between [[Pd]-O₁O′-L] and [[Pd]-O,S-L] in D₂O was observed. [[Pd]-O,O′-3] and [[Pd]-O,O′-L-S,S′-{M}](PF₆)₂, however, were found to be inert in Me₂SO or D₂O. Such notably different solution behavior possibly can be explained by the steric hindrance occurring via the dihedral angles between the palladium, square plane and the ylldene moiety. Variabletemperature ¹H NMR spectra of the banana-shaped bimetallic complexes [[Pd]-O,O′-L-S,S′-{M}](PF₆) ₂ in CD₃CN solution revealed that the amine proton resonances are sensitive to the fluxional motion of the remote bis(alkylthio)ylidene groups, suggesting the occurrence of interconversion between the two "bent-up" and "bent-down" forms