The first structural evidence for the insertion of an unsubstituted lead into a carborane cage

Chemistry of C-Trimethylsilyl-Substituted Heterocarboranes. 25. Syntheses, Structures, and Reactivities of GeCl3-Substituted Half-Sandwich Germacarboranes, closo-1-Ge-2-(SiMe3)-3-(R)-5-(GeCl3)-2,3-C2B4H3 (R = SiMe3, Me, and H)

“…Figures 4 and 5 show that coordination of the capping germanium by either 2,2′-C 10 H 8 N 2 (VII) or 2,2′-C 8 H 6 N 4 (IX) disrupts the η 5 -bonding posture of the carboranes, leading to significantly distorted complexes. The Ge-(II)-C 2 B 3 bond distances in VII are Ge-C(11) ) 2.761-(6) Å; Ge-C(12) ) 2.806(6) Å; Ge-B(13) ) 2.443(7) Å; Ge-B(15) ) 2.407(7) Å; ) 2.173(7) Å and in IX are Ge(1,2)-C (11,21) ) 2.577, 2.455 Å; Ge(1,2)-C(12,22) ) 2.565, 2.443 Å; Ge(1,2)-B (13,23) ) 2.337, 2.284 Å; Ge (1,2)-B(15,25) ) 2.308, 2.303 Å; Ge (1,2)-B(14,24) ) 2.193, 2.200 Å. A comparison of these distances with the analogous Ge-C 2 B 3 distances in IV shows that the Ge-C(cage) distances increase by ∼0.5 Å in VII and ∼0.3 Å in IX, the Ge-B(basal) distances increase by ∼0.2 and ∼0.05 Å, while the Ge-B(unique) distances decrease slightly on complexation, by ∼0.07 Å in VII and ∼0.05 Å in IX.…”

“…All spectra show the appropriate resonances for the various groups present with the expected relative peak areas and are consistent with the structures proposed and with those shown in Figures 1-6. The 11 B NMR spectra of IV-VI, which are expected to be most sensitive to the nature of the capping metal group, all show an upfield resonance at δ -4.60 (IV), -3.45 (V), and -5.09 ppm (VI), due to the apical borons, with the resonances of the less-shielded facial borons being shifted downfield by 24-28 ppm (see Table 1). Table 1 also shows that coordination of the apical germanium by either the C 10 H 8 N 2 or C 8 H 6 N 4 base generally leads to upfield shifts of the apical boron resonances from 11.13 (for X) to 23.45 ppm (for VII), with the facial boron shifts being much lower (∼3-10 ppm).…”

“…However, it has been shown that factors other than gross electron density are also important in determining the shielding of the cage boron atoms in heterocarboranes. 40 Since the unsubstituted germacarborane analogues of IV-X have been prepared and their 11 B NMR spectra determined, the effects of GeCl 3 substitution on the NMR spectra can be assessed. Table 5 lists the 11 …”

“…[1][2][3][4][5][6] All elements in that group have been inserted into carborane cages, and a wealth of structural information is available on a number of half-sandwich, closo-carboranes of germanium, 7,8 tin, 9,10 and lead, 11 as well as the full-sandwich, commo-complexes of silicon, 12 † Dedicated with best wishes to Prof. Robert R. Holmes (University of Massachusetts) on the occasion of his 70th birthday. ‡ Camille and Henry Dreyfus Scholar.…”

14. Solute–solvent interactions mediated by main group element(lone-pair)···π(aryl) interactions

“…However, once again, there is a large void to accommodate one of the two benzene molecules co-crystallised with the lead compound via a Pb(II)···π(benzene) interaction [d = 3.77 Å and θ = 17.9°] (Figure 14.7b). The mononuclear structure of 2,3-bis(trimethylsilyl)-2,3-dicarba-1-plumba-closo-heptaborane(6) benzene solvate (12) [30] is isostructural with (8) (Figure 14.5b) [26]. Thus, the lead(II) centre is coordinated by a B 3 C 2 donor set, but the atoms comprising the cluster lie to one side of the molecule, enabling the formation of a Pb (Figure 14.7d).…”