Chloride abstraction from the group 9 metal bis(N-heterocyclic carbene) complexes M(NHC)(2)(H)(2)Cl [M = Rh, Ir; NHC = IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene or IMes = N,N'-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] leads to the formation of highly reactive cationic species capable of the dehydrogenation of saturated CC and BN linkages. Thus, the reaction of Ir(IPr)(2)(H)(2)Cl (1) with Na[BAr(f)(4)] in fluorobenzene generates [Ir(IPr)(2)(H)(2)](+)[BAr(f)(4)](-) (4) in which the iridium center is stabilized by a pair of agostic interactions utilizing the methyl groups of the isopropyl substituents. After a prolonged reaction period C-H activation occurs, ultimately leading to the dehydrogenation of one of the carbene (i)Pr substituents and the formation of [Ir(IPr)(IPr'')(H)(2)](+)[BAr(f)(4)](-) (5), featuring the mixed NHC/alkene donor IPr'' ligand. By contrast, the related IMes complexes M(IMes)(2)(H)(2)Cl (M = Rh, Ir), which feature carbene substituents lacking beta-hydrogens, react with Na[BAr(f)(4)] in fluorobenzene to give rare examples of NaCl inclusion compounds, viz., [M(IMes)(2)(H)(2)Cl(Na)](+)[BAr(f)(4)](-) (M = Rh, 6; M = Ir, 7). Intercalation of the sodium cation between the mesityl aromatic rings of the two NHC donors has been demonstrated by crystallographic studies of 7. Synthetically, 6 and 7 represent convenient yet highly reactive sources of the putative 14-electron [M(NHC)(2)(H)(2)](+) cations, readily eliminating NaCl in the presence of potential donors. Thus 7 can be employed in the synthesis of the dinitrogen complexes [Ir(IMes)(2)(N(2))(2)](+)[BAr(f)(4)](-) (8a) and [Ir(IMes)(2)(N(2))THF](+)[BAr(f)(4)](-) (8b) (albeit with additional loss of H(2)) by stirring in toluene under a dinitrogen atmosphere and recrystallization from the appropriate solvent system. The interactions of 6 and 7 with primary, secondary, and tertiary amineboranes have also been investigated. Although reaction with the latter class of reagent simply leads to coordination of the amineborane at the metal center via two M-H-B bridges {and formation, for example, of the 18-electron species [M(IMes)(2)(H)(2)(mu-H)(2)B(H).NMe(3)](+)[BAr(f)(4)](-) (M = Rh, 9; M = Ir, 10)}, the corresponding reactions with systems containing N-H bonds proceed via dehydrogenation of the BN moiety to give complexes containing unsaturated aminoborane ligands. Thus, for example, 6 catalyzes the dehydrogenation of R(2)NH x BH(3) (R = (i)Pr, Cy) in fluorobenzene solution (100% conversion over 6 h at 2 mol % loading) to give R(2)NBH(2); the organometallic complex isolated at the end of the catalytic run in each case is shown to be [Rh(IMes)(2)(H)(2)(mu-H)(2)BNR(2)](+)[BAr(f)(4)](-) (R = (i)Pr, 11; R = Cy, 12). In contrast to isoelectronic alkene donors, the aminoborane ligand in these complexes (and in the corresponding iridium compounds 13 and 14) can be shown by crystallographic methods to bind in end-on fashion via a bis(sigma-borane) motif. Similar dehydrogenation chemistry is applicable to the primary amineborane (t)BuNH(2) x ...

The chemistry of the Group 13 metals is dominated by the +1 and +3 oxidation states, and simple monomeric M(II) species are typically short-lived, highly reactive species. Here we report the first thermally robust monomeric MX2 radicals of gallium, indium and thallium. By making use of sterically demanding boryl substituents, compounds of the type M(II)(boryl)2 (M = Ga, In, Tl) can be synthesized. These decompose above 130 °C and are amenable to structural characterization in the solid state by X-ray crystallography. Electron paramagnetic resonance and computational studies reveal a dominant metal-centred character for all three radicals (>70% spin density at the metal). M(II) species have been invoked as key short-lived intermediates in well-known electron-transfer processes; consistently, the chemical behaviour of these novel isolated species reveals facile one-electron shuttling processes at the metal centre.

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The structures of the molecules methylamine-borane, MeH(2)N.BH(3), and dimethylamine-borane, Me(2)HN.BH(3), have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations. The crystal structures have also been determined for methylamine-, dimethylamine-, and trimethylamine-borane, Me(n)H(3-n)N.BH(3) (n = 1-3); these are noteworthy for what they reveal about the intermolecular interactions and, particularly, the N-H...H-B dihydrogen bonding in the cases where n = 1 or 2. Hence, structures are now known for all the members of the ammonia- and amine-borane series Me(n)H(3-n)N.BH(3) (n = 0-3) in both the gas and solid phases. The structural variations and energetics of formation of the gaseous adducts are discussed in relation to the basicity of the Me(n)H(3-n)N fragment. The relative importance of secondary interactions in the solid adducts with n = 0-3 has been assessed by the semi-classical density sums (SCDS-PIXEL) approach.