Abstract
The new nitrosocarboranes [1-NO-2-R-1,2-closo-C2B10H10] [R = CH2Cl (1), CH3OCH2 (2) pMeC6H4
(3), SiMe3 (4) and SiMe2
tBu (5)] and [1-NO-7-Ph-1,7-closo-C2B10H10] (6) were
synthesised by reaction of the appropriate lithiocarborane in diethyl ether with NOCl in
petroleum ether followed by quenching the reaction with aqueous NaHCO3. These brightblue
compounds were characterised spectroscopically and, in several cases,
crystallographically including structural determinations of 2 and 6 using crystals grown in situ
on the diffractometer from liquid samples. In all cases the nitroso group bonds to the
carborane as a 1e substituent (bent C–N–O sequence) and has little or no influence on <δ
11B>,
the weighted average 11B chemical shift, relative to that in the parent (monosubstituted)
carborane. Mono- and dinitroso derivatives of 1,1′-bis(m-carborane), compounds 7 and 8
respectively, were similarly synthesised but attempts to prepare the mononitroso 1,1′-bis(ocarborane)
by the same protocol led only to the hydroxylamine species [1-(1′-1′,2′-closoC2B10H11)-2-N(H)OH-1,2-closo-C2B10H10]
(9); the desired compound [1-(1′-1′,2′-closoC2B10H11)-2-NO-1,2-closo-C2B10H10]
(10) was only realised by switching to a non-aqueous
work-up. The involvement of water in effecting the net reduction of the NO function in 10 to
N(H)OH in 9 was confirmed by a series of experiments involving [1-N(H)OH-2-Ph-1,2-
closo-C2B10H10] (11), [1-(1′-2′-D-1′,2′-closo-C2B10H10)-2-D-1,2-closo-C2B10H10] (12) and [1-
(1′-2′-D-1′,2′-closo-C2B10H10)-2-N(H)OH-1,2-closo-C2B10H10] (13). It is suggested that
during aqueous work-up a water molecule, H-bonded to the acidic C2′H of 10, is “delivered”
to the adjacent C2NO unit. The ability of the NO group in nitrosocarboranes to undergo
Diels-Alder cycloaddition reactions with cyclic 1,3-diene was established via the syntheses of
[1-(NOC10H14)-1,2-closo-C2B10H11] (14) and [1-(NOC6H8)-2-Ph-1,2-closo-C2B10H10] (15).
This strategy was then utilised to prepare derivatives of the elusive dinitroso compounds of
[1,2-closo-C2B10H12] and 1,1′-bis(o-carborane) leading to the sterically-crowded products
[1,2-(NOC6H8)2-1,2-closo-C2B10H10] (16, prepared as meso and racemic diastereoisomers),
[1-{1′-2′-(NOC6H8)-1′,2′-closo-C2B10H10}-2-(NOC6H8)-1,2-closo-C2B10H10] (17) and [1-(1′-
1′,2′-closo-C2B10H11)-2-(NOC6H8)-1,2-closo-C2B10H10] (18).
Original language | English |
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Pages (from-to) | 3635-3647 |
Number of pages | 13 |
Journal | Dalton Transactions |
Volume | 45 |
Issue number | 8 |
Early online date | 14 Jan 2016 |
DOIs | |
Publication status | Published - 28 Feb 2016 |