Electrophilic Methylation of Decaborane(14): Selective Synthesis of Tetramethylated and Heptamethylated Decaboranes and Their Conjugated Bases

Abstract

The paper reports specific syntheses of methylated decaborane( 14), nido-B 10 H 14 (1), derivatives. The reaction of 1 with an excess of neat MeI and AlCl 3 yields 1,2,3,4-Me 4 -nido-B 10 H 10 (2) essentially quantitatively when performed at room temperature. Heating the same mixture to 120 °C provides 1-I-2,3,4,5,7,8,10-Me 7 -nido-B 10 H 6 (3a). The formation of analogous 1-CF 3 SO 2 O-2,3,4,5,7,8,10-Me 7 -nido-B 10 H 6 (3b) is achieved by heating 1 or 2 with an excess of MeSO 3 CF 3 in the presence of a catalytic amount of HOSO 2 CF 3 to 120 °C. Compounds 2 and 3 can be deprotonated to yield the corresponding anions [1,2,3,4-Me 4 -nido-B 10 H 9 ] − (2 − ), [1-I-2,3,4,5,7,8,10-Me 7 -nido-B 10 H 5 ] − (3a − ), and [1-CF 3 SO 2 O-2,3,4,5,7,8,10-Me 7 -nido-B 10 H 5 ] − (3b − ). The structure of all the compounds isolated has been unambiguously confirmed by multinuclear ( 11 B and 1 H) NMR measurements, and the structures of 2 − , 3a, 3a − , and 3b have been established by X-ray diffraction analyses. The very high volatility of 2 has made it impossible to apply X-ray diffraction in this case; therefore, its structure has been derived computationally using the ab initio/GIAO/NMR tool. DFT-based computational protocols have also outlined the reason why it is impossible to obtain an octamethyl derivative of 1 experimentally.

Protonation of dppbz- and binap-ligated rhodathiaboranes yielding proton, hydride and hydrogen exchange

“…The bridging B6-O1 distance in the rhodathiaborane cage-triflate bond measures 1.514(5) Å, slightly exceeding the mean value of 1.469 Å observed across six triflate-ligated polyhedral boron-containing compounds deposited in the Cambridge Structural Database (CSD). [37] Conversely, the S-O1 length at 1.520(3) Å closely approximates the mean value of 1.524 Å for this B-O-S bridging linkage observed in substituted decaborane and carborane clusters analysed crystallographycally [49][50][51][52][54].The introduction of the CF3-SO3 group breaks the symmetry present in parent cluster 2 and the dppbz ligand tilts slightly in derivative 7 to mitigate steric hindrance from the triflate substituent.…”

Thiaborane Icosahedral Barrier Increased by the Functionalization of all Terminal Hydrogens in closo-1-SB11H11

“…Conceivably, those showing the resonances of B­(2,3,4,5,6,8,9,10,11) overlap and are deshielded with respect to those in closo- 1-SB 11 H 11 and, in the case of B(2–6), also with respect to 7,8,9,10,11,12-(CH 3 ) 6 - closo -1-SB 11 H 5 . This observation seems to be common in boron-cluster chemistry, in which CH 3 behaves as an electron acceptor. − Indeed, such an electron-withdrawing behavior leads to electron-density dilution, which is reflected in the prolongation of some of the bonds. For example, B2–B3 in 1 is optimized to be 1.907 Å, whereas the same bond in 7,8,9,10,11,12-(CH 3 ) 6 -1- closo -SB 11 H 5 has arrived at 1.881 Å at the same level of theory.…”

“…Consequently, the corresponding σ-hole magnitude of 31.0 kcal•mol −1 on the sulfur is more positive than that in closo-1-SB 11 H 11 , i.e., 28.2 kcal•mol −1 (ref 16) and in 12-Ph-closo-1-SB 11 H 10 (26.7 kcal•mol −1 ). 8 It is comparable to that in 12-Clcloso-1-SB 11 H 10 , with the latter having the σ-hole magnitude of 2) causes the methyl bonded to B (7) to leave. This, in turn, makes an iodine atom bond to the B7 vertex, which leads to the formation of 2,8,9,10,11,12-(CH 3 ) 6 -closo-1-SB 11 H 5 (see Figure 4).…”

“…Armed with the knowledge of the successful permethylation of the icosahedral parent boron hydride, we tried to apply a permethylate-like reaction to another parent building block of boron-cluster chemistry, again with both CH 3 I and CH 3 OTf, i.e., on decaborane (14), nido-B 10 H 14. 7 We realized that the electrophilic substitution of the upper B(6,9) vertices was impossible under such reaction conditions, as revealed by computing the corresponding electrostatic potentials of decaborane (14). 7 However, we obtained a heptamethyl derivative of decaborane (14) with either I or CF 3 OTf instead of CH 3 , bonded in position B (1).…”

“…7 We realized that the electrophilic substitution of the upper B(6,9) vertices was impossible under such reaction conditions, as revealed by computing the corresponding electrostatic potentials of decaborane (14). 7 However, we obtained a heptamethyl derivative of decaborane (14) with either I or CF 3 OTf instead of CH 3 , bonded in position B (1). Note that such a heptamethyl derivative can also be obtained from 1,2,3,4-(CH 3 ) 4 -nido-B 10 H 10 under identical electrophilic conditions.…”