Synthesis of Catecholate Ligands with Phosphonate Anchoring Groups

By Seraya, Elaine; Luan, Zhongyue; Law, Matt & Heyduk, Alan F.
Published in Inorganic Chemistry NULL 2015

Abstract

New catecholate ligands containing protected phosphonate anchoring groups in the 4-position of the catecholate ring were synthesized. The catechol 4-diethoxyphosphorylbenzene-1,2-diol, (Etphoscat)H?, was prepared in three steps from pyrocatechol; whereas, the catechol 4-(diethoxyphosphorylmethyl)benzene-1,2-diol, (EtBnphoscat)H?, containing a methylene spacer between the catecholate ring and phosphonate anchor, was prepared from protocatechuic acid in six linear steps. Both catechol derivatives were further elaborated to their trimethylsilyl-protected counterparts to facilitate their binding to nanocrystalline metal oxides. Electronic spectroscopy and cyclic voltammetry were used to probe the electronic properties of the phosphonate-functionalized catecholates in charge-transfer complexes of the general formula (catecholate)Pd(pdi) (pdi = N,N′-bis(mesityl)phenanthrene-9,10-diimine). These studies show that attachment of the phosphonate anchor directly to the 4-position of the (Etphoscat)2- ligand significantly perturbs the donor ability of the catecholate ligand; however, incorporation of a single methylene spacer group in (EtBnphoscat)2- helps to isolate catecholate from the electron-withdrawing phosphonate group.

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