Towards design of the smallest planar tetracoordinate carbon and boron systems

Abstract

A series of cyclic hydrocarbons analogs where a carbon displays unusual planar tetracoordinate structure is proposed, employing hybrid density functional theory calculations using B3LYP functional and 6-311þG** basis set. Various strategies were employed to design the neutral planar tetracoordinate hydrocarbon analogs. The same strategy is employed for designing the planar tetracoordinate boron systems. The simplest neutral planar tetracoordinate hydrocarbons were proposed and the effect of substitution on their stability has been assessed. The aromatic stabilization is gauged with nucleus independent chemical shift calculations. The activation barriers for the ring opening reaction, the highest occupied molecular orbital and lowest unoccupied molecular orbitals gap and singlet-triplet energy difference were estimated to gauge the plausibility experimental realization.

CB7−: Experimental and Theoretical Evidence against Hypercoordinate Planar Carbon

“…Le Bel in 1874. However, after the proposal by Hoffmann and co-workers of tetracoordinate planar carbon in 1970, [1] extensive experimental and theoretical efforts were made to search for so-called anti-vant Hoff/ anti-Le Bel molecules (for recent reviews, see references [2][3][4]). In particular, the first experimental and theoretical realization of pentaatomic planar-coordinated carbon species in 1999 and 2000, [5][6][7][8] which confirmed earlier theoretical predictions, [9,10] has stimulated renewed interest in designing new tetracoordinate [11,12] and even hypercoordinate planar carbon molecules.…”

Perfect planar tetracoordinate carbon in neutral unsaturated hydrocarbon cages: A new strategy utilizing three‐dimensional electron delocalization

“…In fact, it has been pointed out that 1 is actually an energy minimum at MP2 but not at B3LYP/6-3111G (3df,2p) level. 16 At the B3LYP/6-3111G** level as calculated here, 1 has a 226i cm 21 imaginary frequency (see Table 1). At the same time, thanks to the bigger ring size in 7, the strain in 7 should be much less than in 3.…”

“…Info. ), the estimated strain energies for 1, 3, and 7 are 245, 315, and 264 kcal mol 21 , respectively, as shown in Table 2. The strain energy in 7 is a little higher than in 1, which may be due to the fact that unsaturated rings are involved in the cage structure of 7.…”

“…20 Basically, geometric structures were fully optimized at the B3LYP/6-3111G** level which has been applied to explore planar tetracoordinate 16,21 and other nonclassical carbon systems. 22,23 The stabilities of wavefunctions have been confirmed for the main compounds such as 1, 3, 7, and anions 4 22 and 5…”

Theoretical study on a family of organic molecules with planar tetracoordinate carbon

“…Similarly, the delocalized ptCcontaining molecules composed of C, B, H atoms were also extensively studied [14][15][16][17][18][19][20][21][22][23][24][25][26]. The smallest organic molecule C 3 B 2 H 4 with ptC, proposed by Minyaev et al [18], can be served as a basic block to build an extended system such as the stable beltlike compounds (C 3 B 2 ) n H 4 (n = 2-6) and tubular compounds (C 3 B 2 ) n [25,31].…”