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Computational methods for contemporary carbene chemistry

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The use of computational methods in carbene chemistry has a long‐standing tradition. Indeed, the field has come a long way since the first ab initio calculations on methylene. Computations now routinely accompany most experimental studies, either to validate the obtained results or to help design appropriate experiments. Advances in computational carbene chemistry within the last decade are covered in this text, encompassing a plethora of studies on alkyl‐, aryl‐, halo‐, and heterocarbenes (N, P, O, S) as well as on persistent triplet carbenes. Moreover, the conceptual advancements in the fields of theoretical chemistry and computing technology have enabled researchers to conduct intricate ab initio studies. The application of leading‐edge theory to multireference problems, high‐accuracy thermochemical evaluations, atom tunneling, and the description of bonding is thoroughly reviewed. In addition, general recommendations for the choice of an appropriate method for a specific computational problem are given. Practitioners of the art are likely to discover new computational approaches in carbene chemistry applied to various examples from the current literature. © 2012 John Wiley & Sons, Ltd.

This article is categorized under:

  • Electronic Structure Theory > Ab Initio Electronic Structure Methods
Figure 1.

Left: Electronic configurations of methylene; right: qualitative Walsh diagram of methylene featuring its valence fragment orbitals.

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Figure 1.

Experimental parameters of triplet methylene (3B1; 1).61 Structural parameters computed at the AE‐CCSD(T)/cc‐pCVQZ level (AE, all‐electron) of theory are given in parentheses.

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Figure 2.

From left to right: [bis(diisopropylamino)phosphino]trimethylsilylcarbene (i), dimer of N,N′‐diphenylimidazolidin‐2‐ylidene (ii), N,N′‐diadamantylimidazol‐2‐ylidene (iii), 1,3,4‐triphenyl‐1,2,4‐triazol‐5‐ylidene (iv), 2,6‐dibromo‐4‐tert‐butyl‐2′,6′‐bis(trifluoromethyl)‐4′‐isopropyldiphenyl carbene (v), and silaethylidene (vi).

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Figure 2.

(a) p–π Interaction in norbornadienylidene and its rearrangement product from a [1,2]vinyl‐shift; (b) hypercoordinated carbene carbon in norbornenylidene; (c) pyramidal carbon in a foiled carbene; (d) hyperconjugative stabilization exceeds p–π interaction.

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Figure 3.

From left to right: ethylidene (vii), phenylmethylene (viii), dibromocarbene (ix), dichlorocarbene (x), (dimethylamino)trimethyl‐phosphoniumcarbene (xi), dimethoxycarbene (xii), 1,3‐dithian‐2‐ylidene (xiii), norbornenylidene (xiv), and cyclopropenylidene (xv).

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Figure 3.

(a) Mesomeric structures of propargylene; (b) reactivity of biradicaloid 1,3‐diphenyl‐propynylidene toward dioxygen; (c) reactivity of acetylenic penta‐2,4‐diyn‐1‐ylidene toward dioxygen; (d) photochemical rearrangements of 5‐methylhexa‐1,2,4‐triene‐1,4‐diyl.

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Figure 4.

The singlet stability–philicity correlation scheme of Mieusset and Brinker; computations were carried out at the B3LYP/6‐31G(d) level; carbenes marked with (#) have not yet been experimentally characterized.

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Figure 4.

(a) Solvolyses of 1‐noradamantylmethylenoxychlorocarbene and adamantyloxychlorocarbene both lead to the same adamantylchloride; (b) solvolyses of exo‐5‐norbornen‐2‐oxychlorocarbene and 3‐nortricyclyloxychlorocarbene both give mixed chlorides via the nortricyclyl cation.

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Figure 5.

Left: Structure of thiaminepyrophosphate (xvi); middle: a disilicon(0) species (xvii) stabilized by N‐heterocyclic carbene ligands; right: cleavage product (xviii) of xvii upon treatment with diborane, resulting in a hitherto unprecedented silylene/carbene species.

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Figure 5.

(a) Concerted versus stepwise mechanism of the dichlorocarbene addition to 1,2,2‐trimethylbicyclobutene yielding 1,1‐dichloro‐3,3,4‐trimethylpenta‐1,4‐diene; (b) novel heteroatom‐substituted fluorocarbenes; (c) carbon tunneling in the ring expansion of noradamantylchlorocarbene.

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Figure 6.

(a) Concerted rearrangement vs. fragmentation of N,N',N'‐triisopropyl‐N‐(piperidin‐1‐yl)diaminocarbene; (b) thermal and photochemical rearrangements of 3‐pyridazylcarbene.

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Figure 7.

(a, b) Reaction of chiral aldehydes with [bis(dimethylamino)phosphino](trimethylsilyl)carbene; (c) prototypical electrophilic and nucleophilic transition states for carbene additions to alkenes; (d) transition states for the addition of prototypical phosphinosilylcarbene to methyl acrylate at the M06–2X/6‐31+G(d) level of theory.

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Figure 8.

(a) Rearrangements of acetoxymethoxycarbene; (b) different decarbonylation pathways of methoxysilylcarbene; (c) stable conformation of bis(methoxycarbonyl)carbene.

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Figure 9.

(a) Rearrangement of dimethoxycarbene; (b) reactivity of singlet and triplet carbon toward water; (c) CH insertion in (o‐methoxyphenyl)hydroxycarbene.

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Figure 10.

(a) Reaction of thiophene with singlet carbon and consecutive rearrangements; (b) generation and intramolecular reactions of 1,3‐dithian‐2‐ylidene along with isodesmic equations; (c) generation of sulfaalkyne HOSCH in the matrix.

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Figure 11.

Hydrogen‐bonded complex of trifluoromethane with carbodiphosphorane and with imidazol‐2‐ylidene at the M06–2X/6‐311++G(d,p) level of theory (bond lengths in Å).

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Figure 12.

(a) Generation of 1,1‐dichlorosilaethylidene and silaethylidene; (b) electronic stabilization of prototypical triplet carbenes; (c) generation and reactions of tetramethylbisphosphonatocarbene.

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Figure 13.

(a) [1,2]H‐tunneling in hydroxymethylene to yield formaldehyde; (b) tunneling control in the H‐rearrangements of methylhydroxycarbene; (c) [1,2]H‐tunneling in phenylhydroxycarbene to yield benzaldehyde.

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Figure 14.

(a) Transformations of cyclopropylhydroxycarbene: [1,2]H‐tunneling and ring expansion; (b) [1,2]H‐tunneling in cyclopropylmethylcarbene and carbon tunneling in the ring expansion of cyclopropylmethylene; (c) isodesmic equations for the evaluation of hydroxycarbene stability.

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