Phosphacarborane Chemistry: The 7,8,9,11-, 7,9,8,10- and 7,8,9,10-Isomers ofnido-P2C2B7H9—Diphosphadicarbaborane Analogues of 7,8,9,10-C4B7H11

Abstract

The reaction between the carborane arachno-4,6-C2B7H13 (1) and PCl3 in dichloromethane in the presence of a "proton sponge" (PS = 1,8-dimethylaminonaphthalene) resulted in the isolation of the eleven-vertex nido-diphosphadicarbaboranes 7,8,9,11-P2C2B7H, (2) and 3-Cl-7,8,11-P2C2B7H, (3-Cl-2) in yields of 54 and 7%, respectively. Replacement of the PS by NEt3 in the same reaction gave diphosphadicarbaboranes 2 and 3-CI-2 together with the isomeric species nido-7,9,8,10-P2C2B7H, (3) in yields of 28, 15 and 3%, respectively. The reaction between the isomeric carborane arachno-4,5-C2B7H13 (4) and PCl3 in dichloromethane in the presence of PS gave the asymmetrical isomer, nido-7,8,9,10-P2C2B7H, (5). along with the chloro derivatives 4-Cl-7,8,9,10-P2C2B7H8 (4-Cl-5) and 11-Cl-7,8,9,10-PC2B7,H8 (11-Cl-5) (yields of 21, 1 and 13%, respectively). The structures of the chlorinated derivatives 3-Cl2 and 11 -Cl-5 were determined by X-ray diffraction analysis. In addition, the structures of all compounds isolated were geometry-optimised and confirmed by comparison of experimental 11B chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/6-31G* method. The calculations also include the structure and 11B NMR shifts of the isomer nido-7,10,8,9-P2C2B7H9 (6) which has not yet been isolated.

Phosphacarborane Chemistry: The Synthesis of the Parent Phosphadicarbaboranesnido-7,8,9-PC2B8H11 and [nido-7,8,9-PC2B8H10]−, and Their 10-Cl Derivatives − Analogs of the Cyclopentadienide Anion

“…Interestingly, in the reaction corresponding to Equation (4), the Cl substituent enters a position not adjacent to the P vertex, as observed earlier in the case of the P 2 C 2 B 7 H 8 Cl derivatives. [7] Both 2 and 10-Cl-2 can easily be deprotonated by reactions with stoichiometric amounts of PS in CH 2 Cl 2 to give the crystalline salts PSH ϩ [nido-7,8,9-PC 2 B 8 H 10 ] Ϫ (compound PSH ϩ 2 ؊ ) and PSH ϩ [10-Cl-nido-7,8,9-PC 2 B 8 H 9 ] Ϫ (compound PSH ϩ 10-Cl-2 ؊ ) upon careful addition of pentane onto the surface of the solution. The deprotonation reaction thus generates a bare pentagonal face, a favorable feature for employing these anions as Cp analogs for metal complexation.…”

“…Indeed, the contiguous PϪCϪC string substitutes the analogous BϪBϪB string of the hypothetical [nido-B 11 H 11 ] 4Ϫ in its open pentagonal belt [RMP2(fc)/6-31G* natural population analysis (NPA) charge is Ϫ0.334, in contrast to Ϫ0.170 attributed to the B 5 girdle capped by B(1)]. [7] The experimental NMR spectra indicate a total lack of symmetry in all compounds and, consequently, their geometries were fully optimized (see Figure 3) without any symmetry constraints beginning at the SCF level with 3-21G and 6-31G* basis sets. Frequency calculations confirmed the structures to be minima on the corresponding 6-31G* potential energy hypersurfaces.…”

“…Such deviations from a regular pentagonal angle of 108°are by far the largest noticed so far in the family of heteroboranes that contain a third-row element. [7,10] In the case of the corresponding anions, 2 ؊ and 10-Cl-2 ؊ , these angles are opened by ca. 3.5°with respect to 2 and 10-Cl-2, but still deviate substantially from 108°.…”

“…[1] Recent efforts are dominated by successful attempts at the isolation of phoshacarborane analogues of tricarbollides (11-vertex nido-tricarbaboranes). [2] In this field of chemistry, one of our groups has recently reported preliminary results on the synthesis of the nido-phosphadicarbaboranes 7,8,11-PC 2 B 8 H 11 and [7,8,11-PC 2 B 8 H 10 ] Ϫ based on the reaction between [6,9-C 2 B 8 H 10 ] 2Ϫ and PCl 3 . [3] The first species is an analog of the neutral tricarbollide 7,8,9-C 3 B 8 H 12 and the second anion is analogous to [7,8,9-C 3 B 8 H 11 ] Ϫ .…”

“…[3] The first species is an analog of the neutral tricarbollide 7,8,9-C 3 B 8 H 12 and the second anion is analogous to [7,8,9-C 3 B 8 H 11 ] Ϫ . [4] Both anions, [7,8,11-PC 2 B 8 H 10 ] Ϫ and [7,8,9-C 3 B 8 H 11 ] Ϫ are also regarded [2] as perfect Cp analogs as they are monoanionic and contain an ab initio methods at a correlated level of theory [RMP2(fc)] using the 6-31G* basis set and their correctness was assessed by a comparison of the experimental 11 B NMR chemical shifts with those calculated by the GIAO-SCF/II//RMP2(fc)/ 6-31G* method. Moreover, the structure of 10-Cl-2 − was determined by an X-ray diffraction analysis.…”