Abstract
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)ylidenemalonato ligands. The reaction of Pd ([Pd] = (Me~4~en)Pd; Me~4~en = N,N,N′,N′‐tetramethylethylenediamine) with Ba[L] {L: bis(methylthio)methylenepropanedioato (1); bis(ethylthio)methylenepropanedioato (2); 1,3‐dithiapan‐2‐ylidene‐malonato (3)} produced [[Pd]‐O,O′‐L]. Successive reactions of [[Pd]‐O,O′‐L] with {M}(NO~3~)~2~ ({M} = (en)M; en = ethylenediamine; M = Pd^II^, Pt^II^), followed by anion exchange with PF~6~^–^, yielded banana‐shaped bimetallic complexes [Pd]‐O,O′‐L‐S,S′‐{M}~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}~2~ (101.75–103.54°). [[Pd]‐O,O′‐L] (L = 1, 2) in Me~2~SO existed as a mixture of [[Pd]‐O,O′‐L] and [(Me~4~en‐N)(Me~2~SO‐S)‐Pd‐O,O′‐L] in a mol ratio of 1:1. For the labile species, a linkage isomeric equilibrium between [[Pd]‐O,O′‐L] and [[Pd]‐O,S‐L] in D~2~O was observed. [[Pd]‐O,O′‐3] and [Pd]‐O,O′‐L‐S,S′‐{M}~2~, however, were found to be inert in Me~2~SO or D~2~O. 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 ylidene moiety. Variable‐temperature ^1^H NMR spectra of the banana‐shaped bimetallic complexes [Pd]‐O,O′‐L‐S,S′‐{M}~2~ in CD~3~CN 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.