Computations describe the dependence of the H2M=Si triplet electronic structure on the α-substituent. Whereas silylidenes H 2C=Si and H2Si=Si benefit from a π1p 1 triplet state, the electronegative nitrogen of HN=Si prefers an n1p1 triplet. CCSD(T) and B3LYP calculations predict R2Si=Si triplet silylenes are stabilized by π-donor/σ- acceptor R substituents which compensate for electron deficiency in the singly occupied π orbital of the π(1)p(1) triplet state. (NH2) 2Si=Si, (OH)2Si=Si, F2Si=Si, (NH 2)HSi=Si, and (OH)HSi=Si all are triplet ground states. In particular, (NH2)2Si=Si and (OH)2Si=Si have singlet-triplet energy gaps (ΔES-T = ET - E S) of -10.2 and -10.3 kcal/mol, respectively. More practical results are achieved via cyclization of (NH2)2Si=Si, which eliminates the probability of rearrangement. Unsaturation of the resulting cyclic structure to give (NHCHCHNH)Si=Si leads to a more favorable triplet silylene with a ΔES-T value of -19.6 kcal/mol. Similar to the common approach of bulky substitution in the synthesis of singlet Arduengo-type N-heterocyclic silylenes, triplet (NRCH2CH2NR)Si=Si and (NRCHCHNR)Si=Si could be experimentally achievable.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry