title: Developing nitrosocarborane chemistry.
abstract: The new nitrosocarboranes [1-NO-2-R-1,2-closo-C2B10H10] [R = CH2Cl (1), CH3OCH2 (2) p-MeC6H4 (3), SiMe3 (4) and SiMe2tBu (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 bright-blue 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 <δ11B>, 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(o-carborane) by the same protocol led only to the hydroxylamine species [1-(1′-1′,2′-closo-C2B10H11)-2-N(H)OH-1,2-closo-C2B10H10] (9); the desired compound [1-(1′-1′,2′-closo-C2B10H11)-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-dienes 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).
authors.affiliation: Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. a.j.welch@hw.ac.uk.
authors.forename: Samuel L
authors.initials: SL
authors.lastname: Powley
authors.forename: Louise
authors.initials: L
authors.lastname: Schaefer
authors.forename: Wing Y
authors.initials: WY
authors.lastname: Man
authors.forename: David
authors.initials: D
authors.lastname: Ellis
authors.forename: Georgina M
authors.initials: GM
authors.lastname: Rosair
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Welch