Joshua I. Bates

Enabling and Probing Oxidative Addition and Reductive Elimination at a Group 14 Metal Center: Cleavage and Functionalization of E–H Bonds by a Bis(boryl)stannylene

By employing strongly σ-donating boryl ancillary ligands, the oxidative addition of H2 to a single site Sn(II) system has been achieved for the first time, generating (boryl)2SnH2. Similar chemistry can also be achieved for protic and hydridic E-H bonds (N-H/O-H, Si-H/B-H, respectively). In the case of ammonia (and water, albeit more slowly), E-H oxidative addition can be shown to be followed by reductive elimination to give an N- (or O-)borylated product. Thus, in stoichiometric fashion, redox-based bond cleavage/formation is demonstrated for a single main group metal center at room temperature. From a mechanistic viewpoint, a two-step coordination/proton transfer process for N-H activation is shown to be viable through the isolation of species of the types Sn(boryl)2·NH3 and [Sn(boryl)2(NH2)](-) and their onward conversion to the formal oxidative addition product Sn(boryl)2(H)(NH2).

Formation of sub-valent carbenoid ligands by metal-mediated dehydrogenation chemistry: coordination and activation of H2Ga{(NDippCMe)2CH}

Reactions of the β-diketiminato (‘Nacnac’) stabilized gallium dihydride H2Ga{(NDippCMe)2CH} with a range of mono- and dinuclear metal carbonyl reagents are characterized by loss of dihydrogen and formation of donor/acceptor complexes featuring the Ga(I) carbenoid ligand : Ga{(NDippCMe)2CH}. Thus, far from simply mimicking the chemistry of the corresponding alane H2Al{(NDippCMe)2CH}, which yields κ1 and κ2 Al–H σ-complexes with similar reagents, the weaker nature of Ga–H bonds leads to extensive bond activation chemistry and enables an unprecedented dehydrogenative route to Ga(I) ligand systems. By consideration of the chemistry of dinuclear systems, two alternative pathways are revealed for this chemistry, with either H2 or M–H bonds acting as the ultimate hydrogen sink.

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.