1-Phenyl-1,2-dicarba-closo-dodecaborane, 1-Ph-1,2-closo-C₂B₁₀H₁₁. Synthesis, Characterization, and Structure As Determined in the Gas Phase by Electron Diffraction, in the Crystalline Phase at 199 K by X-ray Diffraction, and by ab Initio Computations

Abstract

The compound 1-phenyl-1,2-dicarba-closo-dodecaborane(12), 1-C(6)H(5)-1,2-closo-C(2)B(10)H(11) (1), has been synthesized and characterized by a complete assignment of its (11)B NMR spectrum via (11)B{(1)H}/(11)B{(1)H} (COSY), (1)H{(11)B(selective)} and (1)H{(11)B}/(1)H{(11)B} (COSY) spectroscopy. An electron- and X-ray diffraction investigation of 1, complemented by ab initio calculations, has been undertaken. The gas-phase electron-diffraction (GED) data can be fitted by several models describing conformations which differ in the position of the phenyl ring with respect to the carborane cage. Local symmetries ofC(2)(v)() and D(6)(h)() for the 1,2-C(2)B(10) and C(6) moieties, respectively, were adopted in the GED model in order to simplify the problem. In addition, constraints among the close-lying C-C and B-B bonds were employed. However, even though such simplifications led to satisfactory refinements (R(G) = 0.069-0.071), a unique, definitive solution could not be gained. The (C-C)(mean), (C-B)(mean) and (B-B)(mean) bond lengths,r(a), are ca. 1.44, 1.72, and 1.78 Å, respectively. The C(6) hexagon, with r(a)(C-C) = ca. 1.394 Å, either eclipses the C(1)-C(2) vector (overall C(s)() symmetry) or more or less eclipses the C(1)-B(4) cluster bond (overall C(1) symmetry). In contrast, in the solid at 199 K, the ring lies at a position intermediate between the two GED positions, as determined by X-ray crystallography [C(8)H(16)B(10), monoclinic P2(1)/a: a = 12.047(3) Å, b = 18.627(4) Å, c = 12.332(5) Å, beta = 110.09(4) degrees, Z = 8]. The C-B distances span the range 1.681(6)-1.743(5) Å, and B-B lengths lie between 1.756(6) and 1.795(6) Å. A similar conformation was found for the theoretical (RHF/6-31G level) structure which was fully optimized in C(1) symmetry. The r(e) distances are consistent with the dimensions derived in the experimental studies. IGLO calculations of the (11)B chemical shifts, in addition to SCF single-point energies of the GED structures, further support these observations.

Sulfur, tin and gold derivatives of 1-(2′-pyridyl)-ortho-carborane, 1-R-2-X-1,2-C2B10H10(R = 2′-pyridyl, X = SH, SnMe3or AuPPh3)

“…24,25 This was further explored by ab initio RHF/6-31G* and MP2/6-31G* calculational studies on 1-phenylortho-carborane and other aryl-carboranes in order to probe the orientational preferences of aryl groups attached to the carbon atoms of ortho-carborane. 26,27 These calculations have indicated that, although the overall energy of an aryl-carborane may vary only slightly with the aryl group orientation, the latter does have a perceptible influence on the C(1)-C(2) bond distance, which is greatest when the aryl group is aligned perpendicular to the aryl C-C(1)-C(2) plane. This is because this orientation optimises transfer of electronic charge from the filled π orbitals of the aryl group into a cage LUMO that is σ-antibonding with respect to the cage bond C(1)-C(2).…”

C−C Bond Variation in the 1‐Phenyl‐o‐carborane: Steric versus Electronic Effects

“…According to the theoretical and experimental studies, the replacement of CH by a CPh group in the o ‐carborane has a small electronic influence on the cage, but results in significant steric changes in the molecule due to H ··· H contacts 1. It was found that in the isolated molecule 1 , there is an optimum value of the torsion angle θ [C(2)−C(1)−C(13)−C(14)], equal to 25°,9 defining the conformation of the ring with respect to the carborane cage (see Figure 1). Although the H ··· H contacts in all conformations are substantially shorter than the sum of the van der Waals radii the barrier to rotation of the phenyl ring according to the HF/6−31G* calculations is very small (2.1 kJ·mol −1 ).…”

Exploiting the Electronic Tuneability of Carboranes as Supports for Frustrated Lewis Pairs

“…Deuterated solvents were stored over 4 Å molecular sieves. [1-PPh 2 - closo -1,2-C 2 B 10 H 11 ] ( IVa ) [28], [1-P i Pr 2 - closo -1,2-C 2 B 10 H 11 ] ( IVb ) [29], [1-P t Bu 2 - closo -1,2-C 2 B 10 H 11 ] ( IVc ) [30], [9-PPh 2 - closo -1,7-C 2 B 10 H 11 ] ( V ) [13], [μ-2,2′-PPh-{1-(1′-1′,2′- closo -C 2 B 10 H 10 )-1,2- closo -C 2 B 10 H 10 }] ( IX ) [24], and [1-Ph- closo -1,2-C 2 B 10 H 11 ] [31,32] were prepared according to the literature. All other reagents were purchased from Sigma Aldrich Ltd. (Gillingham, UK), Fluorochem Ltd. (Hadfield, UK) or Alfa Aesar (Heysham, UK) and used without further purification.…”