A decade ago we initiated research, the goal of which was isolation of a stable carbene. Our success has helped to catalyze a resurgence of interest in readily available and easily handled carbenes. Research on stable (nucleophilic) carbenes is again a popular theme worldwide. Efforts in the general area of stable carbenes now focus not only on chemistry of the carbenes themselves but also on their applications to other chemical systems, where their chemical properties create technical opportunities that are unavailable with other functional groups. The quest for isolable carbenes is a long saga whose origin can be traced back to the first half of the 1800s. A recently published history of this quest provides an important backdrop for the research described in this Account.1 It is the intent of this Account to delineate the events and environment that led to the report from DuPont laboratories of the first isolation of a stable crystalline carbene. Getting Started

Looking for Stable Carbenes: The Difficulty in Starting Anew

Carbenes : Synthesis, properties, and organometallic chemistry

A spin correction procedure for unrestricted Hartree-Fock and Møller-Plesset wavefunctions for singlet diradicals and polyradicals

Pericyclic Reaction Transition States: Passions and Punctilios, 1935-1995

Multiconfiguration Self-Consistent Field and Multireference Configuration Interaction Methods and Applications

MCSCF/CI investigation of the low-lying potential energy surfaces of the formyloxyl radical, HCO2.cntdot.

The potential surfaces for the lowest singlet and triplet states of cyclobutadiene

Ab initio study of m-benzoquinodimethane

The transition states for single and double methylene group rotation on the singlet trimethylene potential surface have been located at the GVB/6-31G * level of theory, with one pair of electrons correlated. The preference for conrotatory double rotation over single rotation is found to be 0.97 kcal/mol at the GVB level, and is expected to increase slightly with inclusion of additional electron correlation, on the basis of SD-CI calculations on (0,0)- and (0,90)-trimethylene

Stereomutation of cyclopropane revisited. An ab initio investigation of the potential surface and calculation of secondary isotope effects

High level ab initio calculations find that nitrenes are more stable than carbenes, as indicated by the computed enthalpy differences of 25−26 kcal/mol between triplet phenylnitrene and the isomeric triplet pyridylcarbenes. More generally, the greater thermodynamic stability of nitrenes manifests itself in the finding that the N−H bond dissociation energies (BDEs) of aminyl radicals are approximately 20 kcal/mol lower than the C−H BDEs of analogous alkyl radicals. The greater thermodynamic stability of nitrenes, relative to carbenes, is attributed to the large amount of 2s character in the orbital that is occupied by the lone pair of electrons in nitrenes.

Weston Thatcher Borden

Papers

MCSCF/CI investigation of the low-lying potential energy surfaces of the formyloxyl radical, HCO2.cntdot.

The potential surfaces for the lowest singlet and triplet states of cyclobutadiene

Ab initio study of m-benzoquinodimethane

Stereomutation of cyclopropane revisited. An ab initio investigation of the potential surface and calculation of secondary isotope effects

Why Are Nitrenes More Stable than Carbenes? An Ab Initio Study