Functionalisation of the nido-dicarbaborate anion nido -7,8-C2B9H12− by hydride abstraction

• Precise hydride abstraction with acetone/AlCl3 in nido  -7,8-C2B9H12− is presented.
• This EINS-type substitution is a water-free alternative to existing methods.
• Hydride abstraction in nido  -7,8-C2B9H12− with tritylium tetrafluoroborate is shown.
• 10-L-nido-7,8-C2B9H11 (L = C5H5N, NEt3) is formed in higher yields than reported.
• Acidic electrophilic attack of MeCN and MeSCN in nido  -7,8-C2B9H12− is presented.

Substitution at the dicarbaborate anion nido  -7,8-C2B9H12− (1) with precise hydride abstraction leads to symmetric products 10-R-nido-7,8-C2B9H11, e.g., 10-[cyclo-(CH2)4O]-nido-7,8-C2B9H11 (2) and 10-[cyclo-(CH2)4S]-nido-7,8-C2B9H11 (3). However, this approach has been limited to acetaldehyde as hydride acceptor in an acidified, aqueous two-phase system. In expanding the concept of hydride abstraction, we have found that acetone, activated by AlCl3, is capable of accepting hydride with substitution of the symmetric B10 position in the presence of suitable donor molecules (Lewis bases). Thus, by employing a one-phase water-free system, 2 and 3 as well as moisture-sensitive 10-CH3CN-nido-7,8-C2B9H11 (4) were obtained in good to high yield. Reactions with 1 in neat acetone gave 10-HO-nido  -7,8-C2B9H11− (7). An alternative reagent for hydride abstraction in 1 is tritylium tetrafluoroborate (Ph3CBF4), which gave 10-Ph2S-nido-7,8-C2B9H11 (11) in the presence of Ph2S. The Ph2S moiety in 11 could easily be replaced by pyridine and triethylamine, giving 10-C5H5N-nido-7,8-C2B9H11 (12) and 10-Et3N-nido-7,8-C2B9H11 (13). Additionally, reactions of 1 with CF3SO3H in the presence of CH3CN or CH3SCN gave 9-CH3C(NH2)-nido-7,8-C2B9H11 (5) and 9-CH3SC(NH2)-nido-7,8-C2B9H11 (6) by electrophilic substitution.

Substitution at nido  -7,8-C2B9H12− (1) leads to symmetric products 10-R-nido-7,8-C2B9H11 (R = THF, THT, CH3CN, OH, Ph2S). Ph2S could easily be replaced by pyridine and triethylamine. Additionally, reactions of 1 with CF3SO3H in the presence of CH3CN or CH3SCN gave 9-CH3C(NH2)-nido-7,8-C2B9H11 and 9-CH3SC(NH2)-nido-7,8-C2B9H11 by electrophilic substitution.Figure optionsDownload as PowerPoint slide