Singlet–triplet gaps and insertion reactions of aminocyanocarbenes: A computational study of hydrogen cyanide covalent dimers

Abstract

AbstractSinglet–triplet gaps (S–T, ΔEST), structural parameters, intramolecular CH insertion reactions, intramolecular NH insertion reactions, intermolecular CH insertion reactions, and intramolecular 1,2‐rearrangements of aminocyanocarbenes (NCCNX2, X = H, CH3, CF3) have been studied using restricted and unrestricted CCD, CCSD, QCISD, B3LYP, and MP2 methods with the 6‐31G(d), 6‐311+G(d,p), cc‐pVDZ, and cc‐pVTZ basis sets. HCNH2, NCCNH2, NCCN(CH3)2, and NCCN(CF3)2 have singlet ground states. The ΔEST values for aminocyanocarbene, N,N‐(dimethylamino)cyanocarbene, and N,N‐(ditrifluoromethylamino)cyanocarbene are 29.34, 32.75, and 19.48 kcal/mol, respectively. Aminocyanocarbene, a hydrogen cyanide covalent dimer, is predicted to have higher energy than the dimer (Z)‐C‐cyanomethanimine which is lower in energy than the isomeric (E)‐C‐cyanomethanimine and N‐cyanomethanimine. The three‐centered transition state connecting singlet aminocyanocarbene with (Z)‐C‐cyanomethanimine is 55.7 kcal/mol higher in energy than the carbene and the transition state connecting the E and Z isomers of C‐cyanomethanimine is 29.54 kcal/mol higher in energy than the Z isomer. CCSD/cc‐pVDZ predicted the barrier for the intermolecular insertion of singlet aminocyanocarbene into a CH bond of methane to be 35.40 kcal/mol. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006