Crystal and molecular structure of a tetracarbon carborane, (CH3)4C4B8H8, a new type of nido cage system

Chemistry ofC-Trimethylsilyl-Substituted Heterocarboranes. 26. Further Investigation of Oxidative Cage Closure, Cage Fusion, and Cage Isomerizations: Synthetic, Structural, and Bonding Studies on “Carbons Adjacent” and “Carbons Apart” Tetracarba-nido-dodecaborane(12) Derivatives

“…However, both the model compound ( XI ‘) and isomer GA show slightly longer middle carbon bond distances (in XI ‘ and GA the C(1,4)−C(2,3a) distances are 1.483 and 1.46 Å, respectively, compared to 1.511 and 1.53 Å for the C(2)−C(3a) distances). The C(1)−C(2)−C(3a) bond angle in XI is 107.9(4)°, which is similar to the value of 109.4(8)° reported for GA . In XII and isomer GB the carbon faces open up, with the distances between the two middle carbons being ∼2.9 Å, so that very little interaction between these two atoms would be expected (see Table and ref ).…”

“…As pointed out above, the “carbons adjacent” C 4 B 8 cages ( XI − XIII ) could only be obtained from the oxidative fusion reactions of the monoanion of I , [ nido -2-(SiMe 3 )-3-( n -Bu)-2,3-C 2 B 4 H 5 ] - , or the less sterically hindered [ nido -2-(SiMe 3 )-3-(Me)-2,3-C 2 B 4 H 4 ] 2- . The cage structures of XI and XII are essentially those reported by Grimes for (CH 3 ) 4 C 4 B 8 H 8 and (C 2 H 5 ) 4 C 4 B 8 H 8 , respectively. , This is not too surprising, since the synthesis of XI is similar to that used by Grimes in that both involve the reaction of the monoanion of a nido -2,3-C 2 B 4 carborane with an easily reduced divalent transition-metal halide. In Grimes' syntheses FeCl 2 was used, followed by air oxidation, while for XI and XII , the more easily reduced NiCl 2 was used , and no additional oxidant was needed.…”

“…Over 20 years ago, Grimes and co-workers reported the first metal-promoted oxidative face-to-face fusion reaction in the C 2 B 4 carborane system . In these reactions a transition metal sandwiched metallacarborane hydride of the type (R 2 C 2 B 4 H 4 ) 2 MH x (M = Fe ( x = 2), Co ( x = 1); R = CH 3 , C 2 H 5 , n -C 3 H 7 , CH 2 C 6 H 5 ) underwent mild air oxidation to produce 12-vertex tetracarbon carborane clusters with the general formula, R 4 C 4 B 8 H 8 . − The structures of the solid-state fusion products were found to be functions of the nature of R. When R = CH 3 , the C 4 B 8 cage had an distorted-icosahedral geometry in which all four carbon atoms were localized on the same side of the cluster face and linked to one another in a Z-shaped pattern (isomer GA), while when R = C 2 H 5 the carbon face was more open such that the middle carbon−carbon bond was broken (isomer GB); when R = C 3 H 7 , mixtures of both GA and GB structures were found in the solid products . The solution NMR spectra of these compounds showed equilibrium mixtures of both GA and GB structures .…”

Density functional theory study of twelve-atom germanium clusters: conflict between the Wade–Mingos rules and optimum vertex degrees

“…This D 2h structure (Fig. 5) has two square faces and 16 triangular faces and is closely related to a structure found experimentally 34 in stable isolable 12-vertex tetracarbon carboranes of the type R 4 C 4 B 8 H 8 . The structure 28-3 and the experimentally known R 4 C 4 B 8 H 8 structure are both derived from a regular icosahedron by the removal of two edges.…”

Supraicosahedral polyhedra in carboranes and metallacarboranes: The role of local vertex environments in determining polyhedral topology and the anomaly of 13-vertex closo polyhedra

“…solution based on NMR studies [42]. The favored structure in the solid state depends upon the alkyl substituents R. Thus the tetramethyl derivative (CH 3 ) 4 C 4 B 8 H 8 was found by X-ray diffraction [43] to have a solid state structure with two quadrilateral faces, 16 triangular faces, and 28 skeletal electrons (Fig. 7a), which can be derived from a closo-13-AEIVae henicosahedron with one quadrilateral face by removal of a degree 4 vertex to generate a second quadrilateral face.…”