Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

Abstract

Complexation of tetrakis(μ2-N,N'-diphenylformamidinato-N,N')-di-rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using (1)H, (13)C and (15)N NMR, (13)C and (15)N cross polarisation-magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T1 , and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan-1-amine), pentanenitrile, and (1-isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan-2-amine and 1-azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of (1)H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters.

Synthesis and Structural Characterization of a Series of One-Dimensional Heteronuclear Dirhodium-Silver Coordination Polymers

“…As the axial positions of the [Rh 2 (μ-O 2 CR) 4 ] (R = alkyl or aryl) are usually occupied, a great amount of molecular complexes of the type [Rh 2 (μ-O 2 CR) 4 L x ] (L = monodentate donor ligand; x = 1, 2) have been described [1,2,3,20,21,22]. Nevertheless, the Rh 2 4+ unit presents in the tetracarboxylatodirhodium(II) complexes has been used to achieve a large number of coordination polymers.…”

Linear One-Dimensional Coordination Polymers Constructed by Dirhodium Paddlewheel and Tetracyanido-Metallate Building Blocks

“…The ground state electron configuration for most of these complexes is σ 2 π 4 δ 2 δ* 2 π* 4 for a diamagnetic Rh 2 4+ unit, which, therefore, displays a single metal-metal bond order [1,2]. Many dirhodium molecular complexes have been reported owing to the facility of the rhodium ions to coordinate monodentate donor ligands at the axial positions of the paddlewheel structure [1,2,[14][15][16][17]. Moreover, dirhodium units have been used to form one-dimensional coordination compounds using bridging ligands between the dimetallic cores [18][19][20][21].…”

Heteronuclear Dirhodium-Gold Anionic Complexes: Polymeric Chains and Discrete Units

“…The structural diversity found in many of this kind of complexes must be also highlighted [ 12 , 20 , 21 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. The axial sites of the paddlewheel structure are easily occupied by monodentate ligands, which has allowed the preparation of a large number of molecular compounds [ 1 , 2 , 34 , 35 , 36 , 37 ]. One-dimensional polymers [ 1 , 2 , 38 , 39 , 40 , 41 ] can be obtained by means of bridging ligands between the dirhodium(II) cores.…”