David A. Addy

AND/NOT Sensing of Fluoride and Cyanide Ions by Ferrocene-Derivatised Lewis Acids

A simple two-component sensor system was developed, featuring the strongly Lewis acidic (but air-stable) FcRBMes2 (1: FcR=(η5-C5H4)Fe(η5-C5R5), R=H, Me; Mes=2,4,6-Me3C6H2), which can be shown to bind both fluoride AND cyanide in solution (but not other anions), and the weaker boronic ester Lewis acid FcRB(OR)2 (2: (OR)2=R,R-OC(H)PhC(H)PhO), which signals the presence of fluoride but NOT cyanide in solution. By coupling the electrochemical shifts with a suitable redox-active tetrazolium dye, a colorimetric AND/NOT sensor system for fluoride and cyanide ions can be developed

Borane to boryl hydride to borylene dihydride: explicit demonstration of boron-to-metal α-hydride migration in aminoborane activation.

The sequence of fundamental steps implicit in the conversion of a dihydroborane to a metal borylene complex have been elucidated for an [Ir(PMe(3))(3)] system. B-H oxidative addition has been applied for the first time to an aminodihydroborane, H(2)BNR(2), leading to the generation of a rare example of a primary boryl complex, L(n)(H)M{B(H)NR(2)}; subsequent conversion to a borylene dihydride proceeds via a novel B-to-M α-hydride migration. The latter step is unprecedented for group 13 ligand systems, and is remarkable in offering α- substituent migration from a Lewis acidic center as a route to a two-coordinate ligand system.

Generation of cationic two-coordinate group-13 ligand systems by spontaneous halide ejection: remarkably nucleophile-resistant (dimethylamino)borylene complexes.

Spontaneous ejection of chloride from a three-coordinate boron Lewis acid can be effected by employing very electron rich metal substituents and leads to the formation of a sterically unprotected terminal (dimethylamino)borylene complex that has a short metal-boron bond and remarkable resistance to attack by nucleophilic and protic reagents.

Extending the Chain: Synthetic, Structural, and Reaction Chemistry of a BN Allenylidene Analogue†

α versus γ: [CpFe(CO)(PCy3)(BNCMes2)]+, synthesized by halide abstraction, represents the first example of a BN allenylidene analogue, and features an unsaturated MBNC π system. Although DFT calculations show significant LUMO amplitude at the γ (carbon) position, primary reactivity towards nucleophiles occurs at the sterically less hindered α (boron) center.

Synthesis and Reactivity of Half-Sandwich Ruthenium κ2-Aminoborane Complexes

Cationic half-sandwich ruthenium complexes featuring κ2-bound aminoborane ligands can readily be accessed from 16-electron precursors via chloride abstraction in the presence of H2BNR2 (R = iPr, Cy). Complexes [Cp*Ru(L)(κ2-H2BNR2)][BArf4] (2a: R = iPr, L = PCy3; 2b: R = iPr, L = PPh3; 2c: R = iPr, L = 1,3-bis-(2,4,6-trimethylphenyl)-imidazol-2-ylidene; 3a: R = Cy, L = PCy3; Arf = C6H3(CF3)2‐3,5) were isolated in yields of ~60 %, and characterised in the solid state by X-ray crystallography (for 2a, 2c, and 3a). Low-field 11B NMR shifts for the coordinated aminoborane fragment, together with short Ru⋯B contacts (of the order of 1.97 A) imply a relatively tightly bound borane ligand, a finding which is given further credence by the results of density functional theory studies (e.g. bond dissociation energies in the range 24 kcal mol–1; 1 kcal mol–1 = 4.186 kJ mol–1). In terms of reactivity, κ2 systems of this type, while potentially offering a versatile route to asymmetric κ1 systems, in fact undergo borane extrusion even in the presence of a single equivalent of added ligand.

CCDC 744802: Experimental Crystal Structure Determination

Related Article: A.E.J.Broomsgrove, D.A.Addy, A.Di Paolo, I.R.Morgan, C.Bresner, V.Chislett, I.A.Fallis, A.L.Thompson, D.Vidovic, S.Aldridge|2010|Inorg.Chem.|49|157|doi:10.1021/ic901673u