Highly phosphorescent carbene-metal-carboranyl complexes of copper(I) and gold(I).

New phosphorescent "carbene-metal-carboranyl" (CMC) Cu(I) and Au(I) complexes based on the diamidocarbene (DAC) ligand show up to 68% photoluminescence quantum yield and microsecond range lifetimes. CMC organic light emitting diodes (OLEDs) emit sky-blue and warm white electroluminescence.

NHC-Stabilised Silyliumylidene Ions.

Donor-stabilised silyliumylidene ions, from the parent [R-Si:]+ , are a class of low-valent silicon species which have received increasing research interest in the last several years. This interest began in the fundamental synthesis and characterisation of these compounds, but has since started to include more investigation into their further reactivity after several stable NHC-stabilised silyliumylidene ions were reported. This personal account briefly discusses the history of the still-young field of silyliumylidene ions followed by a more detailed discussion of published work from our group on the further development of silyliumylidene chemistry over the last four years.

Further studies of the Enhanced Structural Carborane Effect: tricarbonylruthenium and related derivatives of benzocarborane, dihydrobenzocarborane and biphenylcarborane.

Detailed comparison of the molecular structures of [1,2-µ-(C4H4)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (1) and [1,2-µ-(C4H6)-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (2) reveals evidence for an Enhanced Structural Carborane Effect in 1 arising from the involvement of the cage pπ orbitals in the exopolyhedral ring to some degree. A minor co-product in the synthesis of 2 is [η-{1,2-µ-(C4H6)}-3,3-(CO)2-3,1,2-closo-RuC2B9H9] (3). Compounds 2 and 3 are readily interconverted, since heating 2 to reflux in THF or reaction with Me3NO affords 3 which readily reacts with CO to regenerate 2. The η-ene bonding in 3 is also displaced by PMe3, P(OMe)3 and t-BuNC to yield [1,2-µ-(C4H6)-3,3-(CO)2-3-PMe3-3,1,2-closo-RuC2B9H9] (4), [1,2-µ-(C4H6)-3,3-(CO)2-3-P(OMe)3-3,1,2-closo-RuC2B9H9] (5) and [1,2-µ-(C4H6)-3,3-(CO)2-3-t-BuNC-3,1,2-closo-RuC2B9H9] (6), respectively. Structural studies of 4-6, focussing on the Exopolyhedral Ligand Orientation of the {Ru(CO)2L} fragment relative to the C2B3 carborane face, are discussed in terms of the structural trans effects of PMe3, P(OMe)3 and t-BuNC relative to that of CO. An improved synthesis of [1,2-µ-(C6H4)2-1,2-closo-C2B10H10], "biphenylcarborane", is reported following which the first transition-metal derivatives of this species, [1,2-µ-(C6H4)2-3-Cp-3,1,2-closo-CoC2B9H9] (7) and [1,2-µ-(C6H4)2-3,3,3-(CO)3-3,1,2-closo-RuC2B9H9] (8), are prepared. Comparisons of the structures of 7 and 8 with the corresponding benzocarborane derivatives [1,2-µ-(C4H4)-3-Cp-3,1,2-closo-CoC2B9H9] and 1, respectively, suggest that Clar's rule for aromaticity can be applied to polycyclic aromatic hydrocarbons fused onto carborane cages.

Developing nitrosocarborane chemistry.

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 C­N­O 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).