Adducts of Rhodium(II) Acetate and Rhodium(II) Pivalate with 1,8-Diazabicyclo[5.4.0]undec-7-ene

In this article, we describe the synthesis of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) adducts of rhodium(II) carboxylate complexes, [Rh-2(mu-O2CCR3)(4)(DBU)(2)] (R = H (1), Me (2)). The DBU ligand is coordinated to the axial site in both adducts via the imido-nitrogen atom, and single-crystal X-ray diffraction analysis of 1 and 2 revealed structurally similar attributes between the compounds. The Rh-Rh bond distance is 2.4108(3) angstrom for 1 and 2.4143(2) angstrom for 2. The Rh-N distance is 2.2681(3) angstrom for compound 1 and 2.2587(10) angstrom for compound 2. Compound 1, however, crystallized with solvent molecules in its unit cell, and Hirshfeld surface analysis showed intermolecular C-H center dot center dot center dot O interactions between oxygen atoms of [Rh-2(mu-O2CCH3)(4)] and the hydrogen of the chloroform solvent among other intermolecular close-contact interactions. The crystal structure of compound 2 was found to be devoid of solvent and showed weak intramolecular C-H center dot center dot center dot O interactions from the DBU axial ligand to the oxygens of the bridging acetates. Otherwise, Hirshfeld analysis showed that 2 was dominated by H center dot center dot center dot H interactions. UV-vis spectroscopy of both adducts was also conducted in different solvents to examine shifts attributed to the pi*(Rh-2) to sigma*(Rh-2) band.

Automated summary

This article describes the synthesis and structural characterization of rhodium(II) carboxylate complexes, including two DBU adducts with similar attributes revealed by single-crystal X-ray diffraction analysis. Compound 1 crystallized with solvent molecules showing intermolecular interactions, while compound 2 lacked solvent and exhibited weak intramolecular interactions. UV-vis spectroscopy was conducted on both adducts in various solvents to study band shifts.