A Xanthene-based Ligand with Two Adjacent Malonate Binding Sites

The syntheses of two functionalized xanthenes are described which after deprotonation represent ligands for dinuclear metal complexes. For the previously prepared [Xanthdim]H2 – which after deprotonation leads to a ligand with two adjacent β -diiminato binding sites – a significantly improved synthetic procedure is described involving the Pd catalyzed coupling of two diethyl malonate moieties to the xanthene backbone. Deprotonation of the resulting compound [Xanthmal]H2 provides a ligand with two adjacent diethyl malonate functions. To demonstrate this, [Xanthmal]H2 was reacted exemplarily with two equivalents of LDA to obtain the lithium salt {Li2[Xanthmal]}2 (4) which can be treated with ZnBr2 to yield the zinc complex [Xanthmal]2Zn2 (5). Alternatively, 5 can be obtained directly from [Xanthmal]H2, when ZnEt2 is chosen as the metal precursor. The crystal structures of 4 and 5 are discussed. In summary, the results show that [Xanthmal]2− is a suitable ligand for the preparation of novel dinuclear metal complexes.