Carbene Transfer Reactions from Chromium(0) to Gold(I): Synthesis and Reactivity of New Fischer-Type Gold(I) Alkenyl Carbene Complexes

Fañanás‐Mastral, Martín; Aznar, Fernando

doi:10.1021/om801146z

Cited by 85 publications

(40 citation statements)

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“…[5] The 13 C{ 1 H} NMR spectrum underlines the distinct difference of the iminio ylide-type N-heterocyclic carbene ligand with a chemical shift of d = 185.1 ppm, and the carbene ligand with a signal at d = 321.3 ppm (Figure 3). It is even more deshielded than the gold-carbene signal of Aznar at d = 281.5 ppm, [4] of Widenhoefer at d = 303.9 ppm, [5] and of Fürstner at d = 284.5 ppm (Figure 1, second to fourth structure). [6] In the crystal structure, the ortho methyl groups of the mesityl substituents are pairwise diastereotopic.…”

Section: Methodsmentioning

confidence: 95%

“…A controversy has emerged about the electronic character as either carbene-like with significant gold-to-carbon back-bonding [3] or carbenium-like with marginal back-bonding. [4] However, structurally [3][4][5][6] or spectroscopically [7][8][9] characterized goldcarbene complexes that have been reported are comprised either of iminio ylide-type or oxonio ylide-type ligands ( Figure 1). The synthesis of non-heteroatom-stabilized gold carbenes has been rated as a formidable challenge: "Backdonation of electron density from gold to the vacant carbene p-orbital" … "alone is evidently too small to impart finite lifetimes onto such species."…”

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confidence: 99%

“…The gold bistriflimide 1 releases a 12-valence-electron gold cation that coordinates dimesityldiazomethane and Figure 1. Structurally characterized gold-carbene complexes with prevailing iminio ylide (left), [2a, 3] oxonio ylide (center left and center right), [4,5] and phenylogous oxonio ylide ligand character (right). [6] Scheme 1.…”

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Isolation of a Non‐Heteroatom‐Stabilized Gold–Carbene Complex

et al. 2014

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Gold-carbene complexes are essential intermediates in many gold-catalyzed organic-synthetic transformations. While gold-carbene complexes with direct, vinylogous, or phenylogous heteroatom substitution have been synthesized and characterized, the observation in the condensed phase of electronically non-stabilized gold-carbenes has so far remained elusive. The sterically extremely shielded, emerald-green complex [IPr**Au=CMes2](+)[NTf2](-) has now been synthesized, isolated, and fully characterized. Its absorption maximum at 642 nm, in contrast to 528 nm of the red-purple carbocation [Mes2CH](+), clearly demonstrates that gold is more than just a "soft proton".

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Section: Methodsmentioning

confidence: 95%

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Isolation of a Non‐Heteroatom‐Stabilized Gold–Carbene Complex

et al. 2014

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“…[6] [*] M. Sc Entsprechend der Regel von Bent [18] führen die elektronegativeren Stickstoffatome im IPr**-Steuerliganden und die grçßeren Au-C-N-Winkel zu einem hçheren s-Orbitalanteil in der Au-C(IPr**)-s-Bindung als in der Au-CMes 2 -s-Bindung. Es ist sogar stärker entschirmt als die Goldcarbensignale von Aznar bei d = 281.5 ppm, [4] von Widenhoefer bei d = 303.9 ppm [5] und von Fürstner bei d = 284.5 ppm (Abbildung 1, zweite bis vierte Struktur). [19] Wir führen die beobachtete Überkompensation auf einen signifikanten, aber nicht überwiegenden Au=CMes 2 -Doppelbindungscharakter zurück.…”

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Isolierung eines nicht‐Heteroatom‐stabilisierten Goldcarbens

et al. 2014

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Goldcarben-Komplexe sind essentielle Intermediate in vielen Gold-katalysierten synthetischen Transformationen. Während Goldcarbene mit direkter, vinyloger oder phenyloger Heteroatomstabilisierung schon synthetisiert und charakterisiert worden sind, waren elektronisch nichtstabilisierte Goldcarbene bislang schwer zu beobachten. Wir haben nun einen sterisch extrem abgeschirmten, smaragdgrünen Komplex [IPr**Au = CMes 2 ] + [NTf 2 ] À synthetisiert, isoliert und vollständig charakterisiert. Sein Absorptionsmaximum bei 642 nm, im Vergleich zu 528 nm des rotpurpurnen Carbokations [Mes 2 CH] + , zeigt klar, dass Gold mehr ist als nur ein "weiches Proton".

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“…(iii) Synthesis using a carbene transfer agent Silver carbene complexes are the most commonly used carbene transfer complexes [ 83 ]. Other carbene transfer agents include lithium adducts [ 56 ], potassium complexes [ 53 ], molybdenum carbene complexes [ 83 , 84 ] or chromium carbene complexes [ 85 ].…”

Section: Synthesis Of Transition Metal Complexes Of Nhcmentioning

confidence: 99%

The Nature of N‐Heterocyclic Carbenes

Kühl

2010

Functionalised N‐Heterocyclic Carbene Complexes

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There are essentially three different types of transition metal carbene complexes featuring three different types of carbene ligands. They have all been named after their fi rst discoverers: Fischer carbenes [ 27 -29 ], Schrock carbenes [ 30 , 31 ] and Wanzlick -Arduengo carbenes (see Figure 1.1 ). The latter, also known as N -heterocyclic carbenes (NHC), should actually be named after three people: Ö fele [ 2 ] and Wanzlick [ 3 ], who independently synthesised their fi rst transition metal complexes in 1968, and Arduengo [ 1 ] who reported the fi rst free and stable NHC in 1991. Fischer carbene complexes have an electrophilic carbene carbon atom [ 32 ] that can be attacked by a Lewis base. The Schrock carbene complex has a reversed reactivity. The Schrock carbene complex is usually employed in olefi n metathesis (Grubbs ' catalyst) or as an alternative to phosphorus ylides in the Wittig reaction [ 33 ].The NHC are different from both other types. They form transition metal complexes that are essentially inert, although exceptions are known. Their exceptional stability derives from their intrinsic stabilisation from the N -C p π -p π bonding interaction of the nitrogen atoms fl anking the carbene carbon atom. The p orbital of the carbon is thus partially fi lled and no longer available for nucleophilic attack. Also, it does not have a lone pair of its own with which it could possibly engage in a nucleophilic interaction of its own. Hence, it remains unreactive taking the middle ground between the opposing reactivities of Fischer and Schrock carbenes. It is this apparent lack of reactivity that meant that the transition metal NHC complexes received little attention in their early history. Functionalised N-Heterocyclic Carbene ComplexesOlaf Kühl

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Carbene Transfer Reactions from Chromium(0) to Gold(I): Synthesis and Reactivity of New Fischer-Type Gold(I) Alkenyl Carbene Complexes

Cited by 85 publications

References 45 publications

Isolation of a Non‐Heteroatom‐Stabilized Gold–Carbene Complex

Isolation of a Non‐Heteroatom‐Stabilized Gold–Carbene Complex

Isolierung eines nicht‐Heteroatom‐stabilisierten Goldcarbens

The Nature of N‐Heterocyclic Carbenes

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