Synthetic approaches based on the direct borylation of ferrocene by BBr(3), followed by boryl substituent modification, or on the lithiation of ferrocene derivatives and subsequent quenching with the electrophile FBMes(2), have given access to a range of ferrocene derivatized Lewis acids with which to conduct a systematic study of fluoride and cyanide binding. In particular, the effects of borane electrophilicity, net charge, and ancillary ligand electronics/cooperativity on the binding affinities for these anions have been probed by a combination of NMR, IR, mass spectrometric, electrochemical, crystallographic, and UV-vis titration measurements. In this respect, modifications made at the para position of the boron-bound aromatic substituents exert a relatively minor influence on the binding constants for both fluoride and cyanide, as do the electronic properties of peripheral substituents at the 1'- position (even for cationic groups). By contrast, the influence of a CH(2)NMe(3)(+) substituent in the 2- position is found to be much more pronounced (by >3 orders of magnitude), reflecting, at least in part, the possibility in solution for an additional binding component utilizing the hydrogen bond donor capabilities of the methylene CH(2) group. While none of the systems examined in the current study display any great differentiation between the binding of F(-) and CN(-) (and indeed some, such as FcBMes(2), bind both anions with equal affinity within experimental error), much weaker boronic ester Lewis acids will bind fluoride (but give a negative response for cyanide). Thus, by the incorporation of an irreversible redox-matched organic dye, a two-component [BMes(2)/B(OR)(2)] dosimeter system can be developed capable of colorimetrically signaling the presence of fluoride and cyanide in organic solution by Boolean AND/NOT logic.

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 (see picture).

Reaction of 2,6-dimesityl pyridine (L(py)) with BBr(3) leads to the spontaneous formation of the trigonal dibromoborenium cation [L(py)·BBr(2)](+)via bromide ejection. Systematic structural and computational studies, and the reactivity displayed by a closely related N-heterocyclic carbene (NHC) donor, reveal the role played by arene-borane interactions in this chemistry. [L(py)·BBr(2)](+) features a structurally characterized (albeit weak) electrostatic interaction between the borane Lewis acid and flanking arene π systems.

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Aminoboranes, H(2)BNRR', represent the monomeric building blocks from which novel polymeric materials can be constructed via metal-mediated processes. The fundamental capabilities of these compounds to interact with metal centers have been probed through the coordination of H(2)BNCy(2) at 16-electron [CpRu(PR(3))(2)](+) fragments. In contrast to the side-on binding of isoelectronic alkene donors, an alternative mono(σ-BH) mode of aminoborane ligation is established for H(2)BNCy(2), with binding energies only ~8 kcal mol(-1) greater than those for analogous dinitrogen complexes. Variations in ground-state structure and exchange dynamics as a function of the phosphine ancillary ligand set are consistent with chemically significant back-bonding into an orbital of B-H σ* character.

Systems of the type [(p-cym)Ru(PR 3 )(H)-(H 2 BN i Pr 2 )] + (R = Cy, Ph) can be synthesized from (p-cym)Ru-(PR 3 )Cl 2 and H 2 BN i Pr 2 /Na[BAr f4 ] and are best formulated as (hydrido)ruthenium κ 1 -aminoborane complexes. VT-NMR measurements have been used to probe the σ-bond metathesis process leading to Ru−H/H−B exchange, yielding an activation barrier of ΔG ⧧ = 7.5 kcal mol −1 at 161 K. Moreover, in contrast to the case for related non-hydride-containing systems, reactivity toward alkenes constitutes a viable route to a metal borylene complex via sacrificial hydrogenation.

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.

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.