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

Abstract

A lantern-type dinuclear complex cis-[Rh2(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-[Rh2(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-[Rh2(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)2·0.5C6H6 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.