TY - JOUR
T1 - Detection and characterization of mononuclear Pd(I) complexes supported by N2S2 and N4 tetradentate ligands
AU - Luo, Jia
AU - Tran, Giang N.
AU - Rath, Nigam P.
AU - Mirica, Liviu M.
N1 - Funding Information:
We thank the Department of Energy’s BES Catalysis Science Program (DE-SC0006862) for financial support. We also thank Drs. Jeffrey T. Miller and Ryan C. Nelson (Argonne National Lab) for assistance with obtaining the XAS data and Dr. Jason Schultz for assistance with the EPR measurements.
Funding Information:
H (300.121 MHz) NMR spectra were recorded on a Varian Mercury-300 spectrometer. Low-temperature (−20 °C) H (600 MHz) NMR spectra were recorded on a Varian Unity Inova-600 spectrometer. Chemical shifts are reported in ppm and referenced to residual solvent resonance peaks. Abbreviations for the multiplicity of NMR signals are s (singlet), d (doublet), t (triplet), q (quartet), sep (septet), m (multiplet), and br (broad). UV–vis spectra were recorded on a Varian Cary 50 Bio spectrophotometer. EPR spectra were recorded on a JEOL JES-FA X-band (9.2 GHz) EPR spectrometer in MeCN:PrCN (v:v = 1: 3) frozen glass at 77 K. Simulation of EPR spectra was performed by using WinEPR SimFonia v.1.25. Elemental analyses were performed by the Columbia Analytical Services Tucson Laboratory. ESI-MS experiments were performed on a Bruker Maxis QTOF mass spectrometer with an electron spray ionization source. ESI massspectrometry was provided by Washington University Mass Spectrometry Resource, a NIH Research Resource (Grant P41RR0954). 1 1
Publisher Copyright:
©
PY - 2020/11/2
Y1 - 2020/11/2
N2 - Palladium is a versatile transition metal used to catalyze a large number of chemical transformations, largely due to its ability to access various oxidation states (0, I, II, III, and IV). Among these oxidation states, Pd(I) is arguably the least studied, and while dinuclear Pd(I) complexes are more common, mononuclear Pd(I) species are very rare. Reported herein are spectroscopic studies of a series of Pd(I) intermediates generated by the chemical reduction at low temperatures of Pd(II) precursors supported by the tetradentate ligands 2,11-dithia[3.3](2,6)pyridinophane (N2S2) and N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4): [(N2S2)PdII(MeCN)]2(OTf)4 (1), [(N2S2)PdIIMe]2(OTf)2 (2), [(N2S2)PdIICl](OTf) (3), [(N2S2)PdIIX](OTf)2 (X = tBuNC 4, PPh3 5), [(N2S2)PdIIMe(PPh3)](OTf) (6), and [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9). In addition, a stable Pd(I) dinuclear species, [(N2S2)PdI(μ-tBuNC)]2(ClO4)2 (7), was isolated upon the electrochemical reduction of 4 and structurally characterized. Moreover, the (tBuN4)PdI intermediates, formed from the chemical reduction of [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9) complexes, were investigated by EPR spectroscopy, X-ray absorption spectroscopy (XAS), and DFT calculations and compared with the analogous (N2S2)PdI systems. Upon probing the stability of Pd(I) species under different ligand environments, it is apparent that the presence of soft ligands such as tBuNC and PPh3 significantly improves the stability of Pd(I) species, which should make the isolation of mononuclear Pd(I) species possible.
AB - Palladium is a versatile transition metal used to catalyze a large number of chemical transformations, largely due to its ability to access various oxidation states (0, I, II, III, and IV). Among these oxidation states, Pd(I) is arguably the least studied, and while dinuclear Pd(I) complexes are more common, mononuclear Pd(I) species are very rare. Reported herein are spectroscopic studies of a series of Pd(I) intermediates generated by the chemical reduction at low temperatures of Pd(II) precursors supported by the tetradentate ligands 2,11-dithia[3.3](2,6)pyridinophane (N2S2) and N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4): [(N2S2)PdII(MeCN)]2(OTf)4 (1), [(N2S2)PdIIMe]2(OTf)2 (2), [(N2S2)PdIICl](OTf) (3), [(N2S2)PdIIX](OTf)2 (X = tBuNC 4, PPh3 5), [(N2S2)PdIIMe(PPh3)](OTf) (6), and [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9). In addition, a stable Pd(I) dinuclear species, [(N2S2)PdI(μ-tBuNC)]2(ClO4)2 (7), was isolated upon the electrochemical reduction of 4 and structurally characterized. Moreover, the (tBuN4)PdI intermediates, formed from the chemical reduction of [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9) complexes, were investigated by EPR spectroscopy, X-ray absorption spectroscopy (XAS), and DFT calculations and compared with the analogous (N2S2)PdI systems. Upon probing the stability of Pd(I) species under different ligand environments, it is apparent that the presence of soft ligands such as tBuNC and PPh3 significantly improves the stability of Pd(I) species, which should make the isolation of mononuclear Pd(I) species possible.
UR - http://www.scopus.com/inward/record.url?scp=85094982909&partnerID=8YFLogxK
U2 - 10.1021/acs.inorgchem.0c01938
DO - 10.1021/acs.inorgchem.0c01938
M3 - Article
C2 - 33058678
AN - SCOPUS:85094982909
SN - 0020-1669
VL - 59
SP - 15659
EP - 15669
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 21
ER -