Synthesis, structure, and properties of a lantern-type dinuclear rhodium(II) complex cis-[Rh2(4-Me-pf)2(O2CCMe3)2], 4-Me-pf- = N,N'-di-p-tolylformamidinate anion

A lantern-type dinuclear complex cis-[Rh-2(4-Me-pf)(2)(O2CCF3)(2)] (1) (4-Me-pf(-) = N,N'-di-p-tolylformamidinate anion) was reacted with an excess of pivalic acid in an aqueous NaOH solution with CHCl3/MeOH (1:3 vol./vol.) at room temperature for 24 h with stirring to give cis-[Rh-2(4-Me-pf)(2)(O2CCMe3)(2)] (2). A single crystal obtained by recrystallization of 1 from an acetonitrile solution was employed for X-ray crystal structure analysis. The analysis showed that the obtained complex was a cis-[Rh-2(4-Me-pf)(2)(O2CCMe3)(2)(MeCN)(2)] (2(MeCN)(2)) with a lantern-type dinuclear structure and a cis-(2:2) arrangement of the two formamidinato and two carboxylato ligands around the dirhodium(II) core, similar to the previously reported crystal structures for 1(H2O)(2)center dot 0.5C(6)H(6) and 1(MeCN)(2). Complex 2 showed absorption bands at 613, 506, 435, and 344 nm in MeCN, while complex 1 showed the bands at 516, 460, and 326 nm in MeCN. All the bands observed for 1 and 2 were reasonably assigned using time-dependent density functional theory calculation. Moreover, it was confirmed that the electron-donating t-butyl groups on the carboxylato bridges of 2 give rise to negative shifts in the redox potentials (E (1/2) = 0.32 and 1.22 V (vs. SCE) in CH2Cl2) for Rh-2(II,II)/Rh-2(II,III) and Rh-2(II,III)/Rh-2(III,III) processes relative to those of 1 (E (1/2) = 0.71 and 1.47 V (vs. SCE) in CH2Cl2) that has electron-withdrawing fluorine groups on the carboxylate bridges.