Synthesis and characterization of 3,3”-dihydroxy-[1,1’:4’,1”-terphenyl]-4,4”- dicarboxylic acid derivatives as precursors for functionalized Co-MOF-74-III materials

A series of new 4,4”-di[methoxyethoxymethoxy]-[1,1’:4’,1”-terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl] derivatives were synthesised as possible linkers for MOF-74-III derivatives. The following products were synthesised via Suzuki-Miyuara cross-coupling and characterized by a combination of FTIR and 1H NMR spectroscopy as well as MS spectrometry: 4,4”-di[methoxyethoxymethoxy]-2’,5’-dimethyl-[1,1’:4’,1”-terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl], (90 %); 4,4”-di[methoxyethoxymethoxy]-2’,5’-dihydroxy-[1,1’:4’,1”- terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl], (90 %); 4,4”-di[methoxyethoxymethoxy]- 2’,5’-bis-benzyloxy-[1,1’:4’,1”-terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl], (60 %) and 4,4”-di[methoxyethoxymethoxy]- 3’-[3-ferrocenylpropamide]-[1,1’:4’,1”-terphenyl]- 3,3”-di[methoxyethoxymethoxycarbonyl], (70 %). Novel methods were developed for the syntheses of these linkers, with a different structural orientation than these found in literature. A generalized method, using methoxyethoxymethoxychloride (MEMCl), was developed for the protection of the hydroxy- and carbonyl-functionalities on these ligands Two MOF-74-III derivatives, Co-MOF-74-III-Me, and Co-MOF-74-III-NHCOCH2CH2Fc were successful synthesised from the methylated and ferrocene-containing linkers respectively. Co-MOF-74-III-Me is mesoporous with a pore width of 32.6 Å. Co-MOF-74-III-Me and Co-MOF-74-III-NHCOCH2CH2Fc are both thermally stable up to 180°C. All the 4,4”-di[methoxyethoxymethoxy]-[1,1’:4’,1”-terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl] derivatives showed irreversible redox couples for the carbonyl functionalities of the MEM-groups (-1500 mV vs. FcH/FcH+). An additional redox couple (-2160 mV vs. FcH/FcH+) was found for the amide functionality of the 4,4”-di[methoxyethoxymethoxy]- 3’-[3- ferrocenylpropamide]-[1,1’:4’,1”-terphenyl]-3,3”-di[methoxyethoxymethoxycarbonyl] ligand. Solid state cyclic voltammetry of Co-MOF-74-III-NHCOCH2CH2Fc, showed a redox couple (17 mV vs. FcH/FcH+) for the ferrocenyl fragments on the linkers, detected because electron transfer through the mesoporous material was fast enough.