Planar pentacoordinate carbons

Transition between [R]- and [S]-stereoisomers without bond breaking

“…[25][26][27][28][29][30][31][32][33][34] Several molecules consisting of planar hypercoordinate centers have also been reported. [35][36][37][38][39][40][41][42] Hoffmann and coworkers 5 in their seminal paper anticipated that realizing a stable planar tetracoordinate center would be "too much to hope" than to design one that "could serve as a thermally accessible transition state for a classical racemization experiment". The studies that followed have shown the reverse to be true where many stable planar structures have been found, but no example that met the original objective of achieving stereomutation of a tetrahedral center via a planar transition state has been identified.…”

From High-Energy C7H2 Isomers with A Planar Tetracoordinate Carbon Atom to An Experimentally Known Carbene

“…[18][19][20][21][22] Doped hydrocarbons or carbon clusters with lithium, 23 beryllium/boron, 24,25 boron, [26][27][28][29][30] nitrogen, 31 silicon, 32 phosphorus, 33,34 and late transition metals 35 with a ptC, ptB, ptN, ptSi, or ptP atom are also reported. It is worth to note here that planar penta, [36][37][38][39][40][41][42][43] hexa, [44][45][46][47][48] and hepta 49,50 coordinated carbon compounds are also actively pursued due to the potential implications of these molecules in making new materials. 51 In this work, we explored the dissociation pathways of three different isomers of C 7 H 2 , which contain a ptC atom.…”

Structure and Bonding in CE5− (E=Al–Tl) Clusters: Planar Tetracoordinate Carbon versus Pentacoordinate Carbon

“…Notably, all of the previous clusters, both CE 4 2− and CE 4 Li − , have 18‐valence electrons . This building rule has been exploited to propose, on paper, several planar hypercoordinate carbon atoms, such as CAl 5 + , which is the first cluster in which the global minimum structure possesses a planar pentacoordinate carbon atom . In contrast, the carbon atom in CAl 5 , with 19‐valence electrons, adopts a tetrahedral environment.…”

“…Planar tetracoordinate carbon (ptC) atoms are not just af igment of the chemist's imagination;t hey do exist in the gas phase and in the best cases also in bottles. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] One of the most representative systemso ft hese nonclassicalm olecules is CAl 4 2À . [20] It was detected in the gas phase throughp hotoelectron spectroscopy and structural assignment was achieved in combination with computations.…”

“…[24][25][26][27][28][29] This building rule has been exploited to propose, on paper, severalp lanar hypercoordinate carbon atoms, such as CAl 5 + , [30] which is the first cluster in which the global minimum structure possesses ap lanarp entacoordinate carbon atom. [10] In contrast, the carbon atom in CAl 5 ,w ith 19-valence electrons,a dopts at etrahedral environment. However,C Al 5 À ,a 20-valence electron system, again involves ap tC, [31] which could be described as af ragment CAl 4 2À interacting with an [a] E. Ravell, S. Jalife,J.…”