Replacement of N-heterocyclic carbenes by N-heterocyclic silylenes at a Pd(0) center: Experiment and theory

Zeller, Alexander; Bielert, Frank; Haerter, P.; Herrmann, Wolfgang A.; Straßner, Thomas

doi:10.1016/j.jorganchem.2005.03.061

Cited by 27 publications

(9 citation statements)

References 43 publications

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“…[17] Although numerous theoretical studies of NHC complexes have been published, [15p, 54] theoretical work on the heavier analogues is rather scarce. [55] To the best of our knowledge, the present work is the first detailed study of the structures and bonding situations of the complexes [TM]-NHE. Figure 3 shows the optimized geometries of the complexes [(CO) 5 W-(NHE)] (W-2 E) and the free ligands 2 E. The equilibrium structures of W-2 C, W-2 Si, and W-2 Ge have the NHE ligands bonded head-on to the tungsten atom.…”

Section: Resultsmentioning

confidence: 94%

Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Nhung

Frenking

2012

Chemistry A European J

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Quantum chemical calculations at the BP86/TZVPP//BP86/SVP level are performed for the tetrylone complexes [W(CO)(5) -E(PPh(3))(2)] (W-1 E) and the tetrylene complexes [W(CO)(5)-NHE] (W-2 E) with E=C-Pb. The bonding is analyzed using charge and energy decomposition methods. The carbone ligand C(PPh(3) ) is bonded head-on to the metal in W-1 C, but the tetrylone ligands E(PPh(3))(2) are bonded side-on in the heavier homologues W-1 Si to W-1 Pb. The W-E bond dissociation energies (BDEs) increase from the lighter to the heavier homologues (W-1 C: D(e) =25.1 kcal mol(-1); W-1 Pb: D(e) =44.6 kcal mol(-1)). The W(CO)(5) ←C(PPh(3))(2) donation in W-1 C comes from the σ lone-pair orbital of C(PPh(3))(2), whereas the W(CO)(5) ←E(PPh(3))(2) donation in the side-on bonded complexes with E=Si-Pb arises from the π lone-pair orbital of E(PPh(3))(2) (the HOMO of the free ligand). The π-HOMO energy level rises continuously for the heavier homologues, and the hybridization has greater p character, making the heavier tetrylones stronger donors than the lighter systems, because tetrylones have two lone-pair orbitals available for donation. Energy decomposition analysis (EDA) in conjunction with natural orbital for chemical valence (NOCV) suggests that the W-E BDE trend in W-1 E comes from the increase in W(CO)(5) ←E(PPh(3))(2) donation and from stronger electrostatic attraction, and that the E(PPh(3))(2) ligands are strong σ-donors and weak π-donors. The NHE ligands in the W-2 E complexes are bonded end-on for E=C, Si, and Ge, but side-on for E=Sn and Pb. The W-E BDE trend is opposite to that of the W-1 E complexes. The NHE ligands are strong σ-donors and weak π-acceptors. The observed trend arises because the hybridization of the donor orbital at atom E in W-2 E has much greater s character than that in W-1 E, and even increases for heavier atoms, because the tetrylenes have only one lone-pair orbital available for donation. In addition, the W-E bonds of the heavier systems W-2 E are strongly polarized toward atom E, so the electrostatic attraction with the tungsten atom is weak. The BDEs calculated for the W-E bonds in W-1 E, W-2 E and the less bulky tetrylone complexes [W(CO)(5) -E(PH(3))(2)] (W-3 E) show that the effect of bulky ligands may obscure the intrinsic W-E bond strength.

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Section: Resultsmentioning

confidence: 94%

Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Nhung

Frenking

2012

Chemistry A European J

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“…Formation of carbene species 11 may be hypothesized through dissociation of the NHC ligand from the reduced palladium complex or from the initial M(NHC)X 2 L complex. The possibility of M–NHC bond dissociation in Pd II and Pd 0 complexes has been supported both by experiments and by calculations. ,, Given that the carbene species 11 are accessible, the azolium salt formation should be an easy option due to the reaction with HX (i.e., with [Et 3 NH] + X – formed in the previous step).…”

Section: Resultsmentioning

confidence: 99%

Fast and Slow Release of Catalytically Active Species in Metal/NHC Systems Induced by Aliphatic Amines

et al. 2018

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The behavior of ubiquitously used nickel, palladium, and platinum complexes containing N-heterocyclic carbene ligands was studied in solution in the presence of aliphatic amines. Transformation of M(NHC)X 2 L complexes readily occurred according to the following reactions: (i) release of the NHC ligand in the form of azolium salt and formation of metal clusters or nanoparticles and (ii) isomerization of mono-NHC complexes M(NHC)X 2 L to bis-NHC derivatives M(NHC) 2 X 2 . Facile cleavage of the M−NHC bond was observed and provided the possibility for fast release of catalytically active NHC-free metal species. Bis-NHC metal complexes M(NHC) 2 X 2 were found to be significantly more stable and represented a molecular reservoir of catalytically active species. Slow decomposition of the bis-NHC complexes by removal of the NHC ligands (also in the form of azolium salts) occurred, generating metal clusters or nanoparticles. The observed combination of dual fast-and slow-release channels is an intrinsic latent opportunity of M/NHC complexes, which balances the activity and durability of a catalytic system. The fast release of catalytically active species from M(NHC)X 2 L complexes can rapidly initiate catalytic transformation, while the slow release of catalytically active species from M(NHC) 2 X 2 complexes can compensate for degradation of catalytically active species and help to maintain a reliable amount of catalyst. The study clearly shows an outstanding potential of dynamic catalytic systems, where the key roles are played by the lability of the M−NHC framework rather than its stability.

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“…An abundance of synthetic routes enabling access to NHSi complexes now exist, mostly involving ligand elimination reactions (CO, thf, cod (1,5-cycloocta-1,3-diene), PPh 3 , PEt 3 , or even N-heterocyclic carbenes) from suitable transition metal precursors upon reaction with “free” NHSis . We recently showed that a PMe 3 elimination strategy can even enable facile entry to novel titanium NHSis complexes of the type [(C 5 H 5 ) 2 Ti(←:SiXL) 2 ] (L = PhC( t BuN) 2 , X = Cl, CH 3 , H), representing the first examples of group IV NHSi complexes …”

Section: Introductionmentioning

confidence: 99%

Electron-Rich N-Heterocyclic Silylene (NHSi)–Iron Complexes: Synthesis, Structures, and Catalytic Ability of an Isolable Hydridosilylene–Iron Complex

et al. 2013

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The first electron-rich N-heterocyclic silylene (NHSi)-iron(0) complexes are reported. The synthesis of the starting complex is accomplished by reaction of the electron-rich Fe(0) precursor [(dmpe)2Fe(PMe3)] 1 (dmpe =1,2-bis(dimethylphosphino)ethane) with the N-heterocyclic chlorosilylene LSiCl (L = PhC(N(t)Bu)2) 2 to give, via Me3P elimination, the corresponding iron complex [(dmpe)2Fe(←:Si(Cl)L)] 3. Reaction of in situ generated 3 with MeLi afforded [(dmpe)2Fe(←:Si(Me)L)] 4 under salt metathesis reaction, while its reaction with Li[BHEt3] yielded [(dmpe)2Fe(←:Si(H)L)] 5, a rare example of an isolable Si(II) hydride complex and the first such example for iron. All complexes were fully characterized by spectroscopic means and by single-crystal X-ray diffraction analyses. DFT calculations further characterizing the bonding situation between the Si(II) and Fe(0) centers were also carried out, whereby multiple bonding character is detected in all cases (Wiberg Bond Index >1). For the first time, the catalytic activity of a Si(II) hydride complex was investigated. Complex 5 was used as a precatalyst for the hydrosilylation of a variety of ketones in the presence of (EtO)3SiH as a hydridosilane source. In most cases excellent conversions to the corresponding alcohols were obtained after workup. The reaction pathway presumably involves a ketone-assisted 1,2-hydride transfer from the Si(II) to Fe(0) center, as a key elementary step, resulting in a betaine-like silyliumylidene intermediate. The appearance of the latter intermediate is supported by DFT calculations, and a mechanistic proposal for the catalytic process is presented.

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Replacement of N-heterocyclic carbenes by N-heterocyclic silylenes at a Pd(0) center: Experiment and theory

Cited by 27 publications

References 43 publications

Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Fast and Slow Release of Catalytically Active Species in Metal/NHC Systems Induced by Aliphatic Amines

Electron-Rich N-Heterocyclic Silylene (NHSi)–Iron Complexes: Synthesis, Structures, and Catalytic Ability of an Isolable Hydridosilylene–Iron Complex

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Replacement of N-heterocyclic carbenes by N-heterocyclic silylenes at a Pd(0) center: Experiment and theory

Cited by 27 publications

References 43 publications

Transition‐Metal Complexes of Tetrylones [(CO)5W‐E(PPh3)2] and Tetrylenes [(CO)5W‐NHE] (E=C–Pb): A Theoretical Study

Transition‐Metal Complexes of Tetrylones [(CO)5W‐E(PPh3)2] and Tetrylenes [(CO)5W‐NHE] (E=C–Pb): A Theoretical Study

Fast and Slow Release of Catalytically Active Species in Metal/NHC Systems Induced by Aliphatic Amines

Electron-Rich N-Heterocyclic Silylene (NHSi)–Iron Complexes: Synthesis, Structures, and Catalytic Ability of an Isolable Hydridosilylene–Iron Complex

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Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study

Transition‐Metal Complexes of Tetrylones [(CO)₅W‐E(PPh₃)₂] and Tetrylenes [(CO)₅W‐NHE] (E=C–Pb): A Theoretical Study