N-heterocyclic carbene and cyclic (alkyl)(amino)carbene complexes of molybdenum(<scp>iv</scp>) and tungsten(<scp>iv</scp>)

Luz, Christian; Glok, Eduard; Horrer, Günther; Radius, Udo

doi:10.1039/d2dt03409c

Cited by 6 publications

(4 citation statements)

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“…This series of complexes was accessed starting from a novel d 2 W(IV)-oxo complex 4 stabilized with two NHC ligands, namely, [WOCl 2 (IMes) 2 ], as illustrated in Scheme . The diamagnetic complex 4 forms in moderate yields either upon the reduction of WOCl 4 with KC 8 in the presence of 2 equiv of free carbene or upon substitution of phosphine ligands in [WOCl 2 (PPh 2 Me) 3 ] with 2 equiv of free carbene. , Complex 4 is among the rare low-valent tungsten NHC complexes and is the only NHC-stabilized W(IV)-oxo complex reported to date. The reaction of 4 with 2 equiv of methylenetriphenylphosphorane (Ph 3 PCH 2 ) results in a magenta-colored oxo-methylidyne complex 3 , namely, [WO(CH)Cl(IMes) 2 ], in moderate yields.…”

Section: Resultsmentioning

confidence: 98%

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues

Kakiuchi,

Docherty,

Berkson

et al. 2024

J. Am. Chem. Soc.

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Olefin metathesis has become an efficient tool in synthetic organic chemistry to build carbon−carbon bonds, thanks to the development of Grubbs-and Schrock-type catalysts. Olefin coordination, a key and often rate-determining elementary step for d 0 Schrock-type catalysts, has been rarely explored due to the lack of accessible relevant molecular analogues. Herein, we present a fully characterized surrogate of this key olefin-coordination intermediate, namely, a cationic d 0 tungsten oxo-methylidene complex bearing two N-heterocyclic carbene ligands�[WO(CH 2 )Cl(IMes) 2 ](OTf) (1) (IMes = 1,3-dimesitylimidazole-2-ylidene, OTf−triflate counteranion), resulting in a trigonal bipyramidal (TBP) geometry, along with its neutral octahedral analogue [WO(CH 2 )Cl 2 (IMes) 2 ] (2)�and an isostructural oxo-methylidyne derivative [WO(CH)Cl(IMes) 2 ] (3). The analysis of their solid-state 13 C and 183 W MAS NMR signatures, along with computed 17 O NMR parameters, helps to correlate their electronic structures with NMR patterns and evidences the importance of the competition among the three equatorial ligands in the TBP complexes. Anchored on experimentally obtained NMR parameters for 1, computational analysis of a series of olefin coordination intermediates highlights the interplay between σand π-donating ligands in modulating their stability and further paralleling their reactivity. NMR spectroscopy descriptors reveal the origin for the advantage of the dissymmetry in σ-donating abilities of ancillary ligands in Schrock-type catalysts: weak σ-donors avoid the orbital-competition with the oxo ligand upon formation of a TBP olefin-coordination intermediate, while stronger σ-donors compromise M�O triple bonding and thus render olefin coordination step energy demanding.

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Section: Resultsmentioning

confidence: 98%

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues

Kakiuchi,

Docherty,

Berkson

et al. 2024

J. Am. Chem. Soc.

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“…The diamagnetic complex 4 forms in moderate yields either upon reduction of WOCl4 with KC8 in the presence of two equivalents of free carbene, or upon substitution of phosphine ligands in [WOCl2(PPh2Me)3] with two equivalents of free carbene. [52][53] Complex 4 is among the rare low-valent tungsten NHC complexes 54 and is the only NHC-stabilized W(IV)oxo complex reported to date. The reaction of 4 with two equivalents of methylenetriphenylphosphorane (Ph3PCH2) results in a magenta-colored oxo-methylidyne complex 3, namely [WO(CH)Cl(IMes)2], in moderate yields.…”

Section: Synthesis and Characterizationmentioning

confidence: 99%

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogs

Kakiuchi,

Docherty,

Berkson

et al. 2024

Preprint

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Olefin metathesis has been established as an efficient tool to build carbon-carbon bonds, and its widespread applications in organic synthesis have been made possible by the development of efficient homogeneous catalysts – Grubbs and Schrock-type – that operate through the same intermediates and Chauvin mechanism. With d0 Schrock-type catalysts, the first elementary step, olefin-coordination, is often rate determining, but it been rarely explored due to the lack of accessible relevant molecular analogs. Here, we develop a surrogate of this key olefin-coordination intermediate, namely a cationic d0 tungsten oxo-methylidene complex bearing two N-heterocyclic carbene ligands, [WO(CH2)Cl(IMes)2](OTf) (1) (IMes = 1,3-dimesitylimidazole-2-ylidene; OTf – triflate counter-anion) resulting in a trigonal bipyramidal (TBP) geometry, along with its neutral octahedral analog [WO(CH2)Cl2(IMes)2] (2), and an isostructural oxo-methylidyne derivative [WO(CH)Cl(IMes)2] (3). These compounds were fully characterized by state-of-the-art methods, including single-crystal X-ray diffraction (scXRD) and multinuclear (1H, 13C, 183W) solution NMR spectroscopy. The analysis of their solid-state 13C and 183W MAS NMR signatures, along with computed 17O NMR parameters, helps to correlate their electronic structures with NMR patterns and evidences the importance of the competition between the three equatorial ligands in the TBP complexes. Further analysis validates the suitability of complex 1 as a surrogate molecule to interrogate the electronic structure of the key olefin coordination intermediate of the Chauvin cycle. Anchored on experimentally obtained NMR parameters for 1, computational analysis of a series of olefin coordination intermediates highlights the interplay between σ- and π-donating ligands in modulating the stability of TBP olefin-coordination intermediates, paralleling their reactivity. In this work, NMR spectroscopy descriptors reveal the origin for the advantage of the dissymmetry in σ-donating abilities of ancillary ligands in Schrock-type catalysts: weak σ-donors avoid the orbital-competition with the oxo ligand upon formation of a TBP olefin-coordination intermediate, while stronger σ-donors compromise M≡O triple bonding and thus render olefin coordination step energy expensive.

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“…Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany. E-mail: u.radius@uni-wuerzburg.de mium complexes substituted with di-and polydentate NHC ligands is rather rich 11g,14 and due to our earlier interests in 3d transition metal complexes of monodentate NHCs (metal = Ti, 15 V, 16 W 17 (5d), Fe, 18 Co, 19 Ni, 20 Cu 21 ) and cAACs [15][16][17]22 we focus herein on monodentate NHC ligated chromium complexes.…”

Section: Introductionmentioning

confidence: 99%

“…Compared to the rich chemistry of group 6 carbene complexes in oxidation state zero in general, the chemistry of intermediate and high oxidation state NHC half-sandwich complexes of chromium is still in its infancy. As the field of chromium complexes substituted with di- and polydentate NHC ligands is rather rich 11 g ,14 and due to our earlier interests in 3d transition metal complexes of monodentate NHCs (metal = Ti, 15 V, 16 W 17 (5d), Fe, 18 Co, 19 Ni, 20 Cu 21 ) and cAACs 15–17,22 we focus herein on monodentate NHC ligated chromium complexes.…”

Section: Introductionmentioning

confidence: 99%

N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(ii) and chromium(i)

Horrer,

Luff,

Radius

2023

Dalton Trans.

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N-heterocyclic carbene and cyclic (alkyl)(amino)carbene complexes of molybdenum(iv) and tungsten(iv)

Abstract: The synthesis and characterization of N heterocyclic carbene (NHC) and cyclic (alkyl)(amino)carbene (cAAC) complexes of molybdenum(IV) and tungsten(IV) chloride is reported. Reaction of two equivalents of the NHCs IMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene),...

Cited by 6 publications

References 122 publications

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogues

Origin of Reactivity Trends of an Elusive Metathesis Intermediate from NMR Chemical Shift Analysis of Surrogate Analogs

N-Heterocyclic carbene and cyclic (alkyl)(amino)carbene ligated half-sandwich complexes of chromium(ii) and chromium(i)

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