Universität zu Köln

Jordan, Rose, Niazi, Maryam, Schaefer, Sascha, Kaim, Wolfgang and Klein, Axel ORCID: 0000-0003-0093-9619 (2022). Rhenium Tricarbonyl Complexes of Azodicarboxylate Ligands. Molecules, 27 (23). BASEL: MDPI. ISSN 1420-3049

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Abstract

The excellent pi-accepting azodicarboxylic esters adcOR (R = Et, iPr, tBu, Bn (CH2-C6H5) and Ph) and the piperidinyl amide derivative adcpip were used as bridging chelate ligands in dinuclear Re(CO)(3) complexes [{Re(CO)(3)Cl}(2)(mu-adcOR)] and [{Re(CO)(3)Cl}(2)(mu-adcpip)]. From the adcpip ligand the mononuclear derivatives [Re(CO)(3)Cl(adcpip)] and [Re(CO)(3)(PPh3)(mu-adcpip)]Cl were also obtained. Optimised geometries from density functional theory (DFT) calculations show syn and anti isomers for the dinuclear fac-Re(CO)(3) complexes at slightly different energies but they were not distinguishable from experimental IR or UV-Vis absorption spectroscopy. The electrochemistry of the adc complexes showed reduction potentials slightly below 0.0 V vs. the ferrocene/ferrocenium couple. Attempts to generate the radicals [{Re(CO)(3)Cl}(2)(mu-adcOR)](center dot-) failed as they are inherently unstable, losing very probably first the Cl- coligand and then rapidly cleaving one [Re(CO)(3)] fragment. Consequently, we found signals in EPR very probably due to mononuclear radical complexes [Re(CO)(3)(solv)(adc)](center dot). The underlying Cl--> solvent exchange was modelled for the mononuclear [Re(CO)(3)Cl(adcpip)] using DFT calculations and showed a markedly enhanced Re-Cl labilisation for the reduced compared with the neutral complex. Both the easy reduction with potentials ranging roughly from -0.2 to -0.1 V for the adc ligands and the low-energy NIR absorptions in the 700 to 850 nm range place the adc ligands with their lowest-lying pi* orbital being localised on the azo function, amongst comparable bridging chelate N<^>N coordinating ligands with low-lying pi* orbitals of central azo, tetrazine or pyrazine functions. Comparative (TD)DFT-calculations on the Re(CO)(3)Cl complexes of the adcpip ligand using the quite established basis set and functionals M06-2X/def2TZVP/LANL2DZ/CPCM(THF) and the more advanced TPSSh/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) for single-point calculations with BP86/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) optimised geometries showed a markedly better agreement of the latter with the experimental XRD, IR and UV-Vis absorption data.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Jordan, Rose UNSPECIFIED UNSPECIFIED UNSPECIFIED Niazi, Maryam UNSPECIFIED UNSPECIFIED UNSPECIFIED Schaefer, Sascha UNSPECIFIED UNSPECIFIED UNSPECIFIED Kaim, Wolfgang UNSPECIFIED UNSPECIFIED UNSPECIFIED Klein, Axel UNSPECIFIED orcid.org/0000-0003-0093-9619 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-665383
DOI:	10.3390/molecules27238159
Journal or Publication Title:	Molecules
Volume:	27
Number:	23
Date:	2022
Publisher:	MDPI
Place of Publication:	BASEL
ISSN:	1420-3049
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EFFECTIVE CORE POTENTIALS; TETRACARBONYL HALIDE DIMERS; TRANSITION-METAL-COMPLEXES; HETERODINUCLEAR COMPLEXES; MOLECULAR CALCULATIONS; EXCITED-STATES; OS3(CO)N(CH3OCONNCOOCH3) N; MULTIFREQUENCY EPR; BRIDGING LIGANDS; INFRARED-SPECTRA Multiple languages Biochemistry & Molecular Biology; Chemistry, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/66538