Isolation of Neutral Mononuclear Copper Complexes Stabilized by Two Cyclic (Alkyl)(amino)carbenes

Weinberger, David S.; Sk, Nurul Amin; Mondal, Kartik Chandra; Melaïmi, Mohand; Bertrand, Guy; Stückl, A. Claudia; Roesky, Herbert W.; Dittrich, Birger; Demeshko, Serhiy; Schwederski, Brigitte; Kaim, Wolfgang; Jerabek, Paul; Frenking, Gernot

doi:10.1021/ja502521b

Cited by 77 publications

(68 citation statements)

References 40 publications

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“…Such reduction steps lead to the formation of a d 10 closed‐shell gold(I) center with bound triazolylidene radicals. Thus, the formulation of the reduced forms of these gold complexes with MIC ligands are different from what has been recently reported for the reduced forms of gold and copper complexes with cyclic alkyl amino carbenes (CAAC) . In those cases, the reduced forms were formulated as gold(0) or copper(0) centers bound to a neutral CAAC ligand, which is a result of the gold(I) or copper(I) centers in those complexes being reduced as opposed to the carbene ligands.…”

Section: Resultsmentioning

confidence: 81%

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

et al. 2017

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Triazolylidenes are a prominent class of mesoionic carbenes (MICs) that are currently widely used in organometallic chemistry. Usually the metal complexes of such ligands are used as homogeneous catalysts even though they have vast potential in other branches of chemistry. We present here three related gold(I) complexes with MIC ligands: a neutral mononuclear chlorido complex [AuCl(MIC)], a cationic mononuclear complex containing two MIC ligands [Au(MIC)2]BF4, and a dicationic digold(I) complex containing two di‐MIC ligands [Au2(κ1,κ1,µ‐di‐MIC)2](BF4)2. The complexes were characterized by 1H and 13C{1H} NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The gold(I) centers are linearly coordinated through either one MIC‐C and chlorido donors or through two MIC‐C donors. The triazolylidenes display a delocalized bonding situation within the ring. Additionally, a short Au–Au distance of about 3 Å is observed for the digold(I) complex. All complexes display reduction steps in their cyclic voltammograms, and these are assigned to the reduction of the MIC ligands, as opposed to the generation of gold(0). The complexes emit at ca. 500 nm, with lifetimes of several microseconds in deoxygenated solutions; the emission intensity and lifetime are strongly decreased by the presence of oxygen, supporting the triplet origin of the emissive state. The present results display the utility of MIC ligands for generating electro‐ and photoactive molecules.

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Section: Resultsmentioning

confidence: 81%

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

et al. 2017

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“…The three (CAAC) 2 Mn/Cu/ Zn structures show linear coordination. [1,2,4] Structures with Mn, Ni, and Cu are toluene solvates, the Co structure is a THF hemisolvate, and for the Zn compound a desolvate was characterized. [1] The Co and Ni compounds show deviation from ideal linear coordination, [2,5] and they have attracted interest for their catalytic activity.…”

Section: Methodsmentioning

confidence: 99%

Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

et al. 2014

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Single-crystal X-ray diffraction (XRD) is often considered the gold standard in analytical chemistry, as it allows element identification as well as determination of atom connectivity and the solid-state structure of completely unknown samples. Element assignment is based on the number of electrons of an atom, so that a distinction of neighboring heavier elements in the periodic table by XRD is often difficult. A computationally efficient procedure for aspherical-atom least-squares refinement of conventional diffraction data of organometallic compounds is proposed. The iterative procedure is conceptually similar to Hirshfeld-atom refinement (Acta Crystallogr. Sect. A- 2008, 64, 383-393; IUCrJ. 2014, 1,61-79), but it relies on tabulated invariom scattering factors (Acta Crystallogr. Sect. B- 2013, 69, 91-104) and the Hansen/Coppens multipole model; disordered structures can be handled as well. Five linear-coordinate 3d metal complexes, for which the wrong element is found if standard independent-atom model scattering factors are relied upon, are studied, and it is shown that only aspherical-atom scattering factors allow a reliable assignment. The influence of anomalous dispersion in identifying the correct element is investigated and discussed.

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“…For the ionic ref 3 state, the (cAAC) 2 − "long-bond" density is seen (row 3, column 2, Table 4) to shift toward the positive charge of the Cu + . For the remaining NOCV deformation densities (corresponding to donation of cAAC lone pairs into the totally symmetric Cu 4s and 3d orbitals, column 3; donation from the π-symmetry Cu 3d into the cAAC π* orbitals, column 2 Obtained with Three Different Reference States a a The orbital interaction energies and eigenvalues are summed over both α and β spins (except for column 1, for which there is no β-spin).…”

Section: ■ Comparison With the Analysis Of Jrbf And The Importance Ofmentioning

confidence: 99%

“…A recent analysis of the bonding in these complexes using energy decomposition analysis−natural orbitals for chemical valence (EDA-NOCV) 4−8 and natural bond orbital (NBO) methods 9−15 prompted several claims from the authors that appear contrary to the empirical data and to previously published examinations of bonding at transition metals. Representative statements include "Metal-ligand interactions in [TM(cAAC) 2 ] involve the TM in the excited 2 P state," "cAAC ligands in TM(cAAC) 2 are stronger π-acceptors than σ donors!," "The TM(pπ) → (cAAC) 2 backdonation··· is not recognized by the calculation of the bonding orbitals by the NBO method because it is biased against mixing of n(p) functions for the TMs," and "The NBO picture of the C-TM-C bonding situation does not correctly represent the nature of the metal-ligand interaction in [TM(cAAC) 2 ]." 1 Because isolable, formally zerovalent molecular complexes of Cu, Ag, and Au are rare new additions to the literature, they arouse interest regarding the nature of their electronic structures.…”

Section: ■ Introductionmentioning

confidence: 99%

Bonding Analysis of TM(cAAC)₂ (TM = Cu, Ag, and Au) and the Importance of Reference State

2015

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A recent analysis of the bonding in transition metal (TM) complexes with cyclic aminoalkyl carbene (cAAC) ligands, TM(cAAC) 2 (TM = Cu, Ag, and Au), purports to show that metal−ligand bonding involves the TM in the excited 2 P state and that TM(pπ) → (cAAC) 2 backdonation is not properly recognized in NBO analysis because of biases against participation of np functions in transition metal bonding. The questions of TM np orbital involvement in bonding and the possible biases in the NBO occupancy-weighted symmetric orthogonalization procedure have been examined by performing NBO analyses in two ways:(1) single Lewis structure (loc) analysis with TM np orbitals treated as valence (NBO s ) or nonvalence (NBO x ) and (2) direct comparison of a two-configuration resonance model (res/NBO s ) treatment with a single configuration model using the expanded valency (loc/NBO x ) treatment. The principal bonding picture that emerges from NBO analysis features a TM cation with two "non-innocent" cAAC ligands that are each reduced by 0.5 electrons. The unpaired spin delocalizes over a π network spanning the two ligands, whether or not a TM cation is present. In the localized NBO framework, the unpaired spin primarily occupies a 1e π-type "long-bond" between the carbonic carbon centers, with secondary resonance delocalization over the TM npπ and the two Npπ orbitals. This description is consistent with all experimental data. Energy decomposition analysis−natural orbitals for chemical valence (EDA-NOCV) analysis of the Cu complex with different reference states reveals that the inferred nature of the bonding depends wholly on the choice of reference state. We show that the earlier selection of a neutral, excited 2 P Cu reference state virtually dictates the bonding description to feature an unphysical degree of TM(pπ) → (cAAC) 2 backdonation. ■ INTRODUCTIONIn recent publications, Jerabek, Roesky, Bertrand, Frenking (JRBF) and coauthors 1−3 demonstrate that cyclic aminoalkylcarbenes (cAACs) are capable of stabilizing coinage metals in the formal oxidation state zero, leading to crystallographically characterized structures for Cu and Au. The neutral coinage transition metals complexes [TM(cAAC) 2 ] (TM = Cu, Ag, and Au), which are generated by reduction of the [TM(cAAC) 2 ] + cations for TM = Cu,Au, exhibit interesting experimental and computational metrics, linear coordination geometries, EPR gvalues, and hyperfine couplings, indicating that the unpaired spin density is largely located on the carbene carbon atoms and that C-TM bond lengths that are slightly longer for the [TM(cAAC) 2 ] + cations than for the neutral complexes. A recent analysis of the bonding in these complexes using energy decomposition analysis−natural orbitals for chemical valence (EDA-NOCV) 4−8 and natural bond orbital (NBO) methods 9−15 prompted several claims from the authors that appear contrary to the empirical data and to previously published examinations of bonding at transition metals. Representative statements include "Metal-ligand interactions in [TM...

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Isolation of Neutral Mononuclear Copper Complexes Stabilized by Two Cyclic (Alkyl)(amino)carbenes

Cited by 77 publications

References 40 publications

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

Bonding Analysis of TM(cAAC)₂ (TM = Cu, Ag, and Au) and the Importance of Reference State

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Isolation of Neutral Mononuclear Copper Complexes Stabilized by Two Cyclic (Alkyl)(amino)carbenes

Cited by 77 publications

References 40 publications

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Structural, Electrochemical, and Photochemical Properties of Mono‐ and Digold(I) Complexes Containing Mesoionic Carbenes

Aspherical‐Atom Modeling of Coordination Compounds by Single‐Crystal X‐ray Diffraction Allows the Correct Metal Atom To Be Identified

Bonding Analysis of TM(cAAC)2 (TM = Cu, Ag, and Au) and the Importance of Reference State

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Bonding Analysis of TM(cAAC)₂ (TM = Cu, Ag, and Au) and the Importance of Reference State