Tetraiododiborane(4) (B2 I4 ) is a Polymer Based on sp3 Boron in the Solid State.

Herein we present the first solid-state structures of tetraiododiborane(4) (B2 I4 ), which was long believed to exist in all phases as discrete molecules with planar, tricoordinate boron atoms, like the lighter tetrahalodiboranes(4) B2 F4 , B2 Cl4 , and B2 Br4 . Single-crystal X-ray diffraction, solid-state NMR, and IR measurements indicate that B2 I4 in fact exists as two different polymeric forms in the solid state, both of which feature boron atoms in tetrahedral environments. DFT calculations are used to simulate the IR spectra of the solution and solid-state structures, and these are compared with the experimental spectra.

Pseudodiborenes: hydride-bridged diboranes(5) as two-electron reductants of chalcogens.

The reactivity of two nucleophilic neutral sp2-sp3 diboranes towards chalcogens is presented herein. Both diboranes(5) serve as two-electron reductants, incorporating oxygen, sulfur and selenium atoms. Treatment with chalcogen sources results in the oxidative insertion of one chalcogen atom into the B-B single bond, while depending on the negative inductive effect of the chalcogen and the boron bound aryl substituent further N-heterocyclic carbene (NHC) ring expansion and hydride migration can occur. These reactions provide access to unprecedented six- or seven-membered heterocycles and help to illuminate the pseudo-multiple bonding character of hydrogen-bridged B-B single bonds.

Stable Lewis Base Adducts of Tetrahalodiboranes: Synthetic Methods and Structural Diversity.

A series of 22 new bis(phosphine), bis(carbene), and bis(isonitrile) tetrahalodiborane adducts has been synthesized, either by direct adduct formation with highly sensitive B2 X4 precursors (X=Cl, Br, I) or by ligand exchange at stable B2 X4 (SMe2 )2 precursors (X=Cl, Br) with labile dimethylsulfide ligands. The isolated compounds have been fully characterized using NMR spectroscopy, elemental analysis, and, for 20 of these compounds, single-crystal X-ray diffraction, revealing an unexpected variation in the bonding motifs. In addition to the classical B2 X4 L2 diborane(4) bis-adducts, certain more sterically demanding carbene ligands induce a halide displacement which led to the first halide-bridged monocationic diboron species, [B2 X3 L2 ]A (A=BCl4 , Br, I). Furthermore, low-temperature 1:1 reactions of B2 Cl4 with sterically demanding N-heterocyclic carbenes led to the formation of kinetically unstable mono-adducts, one of which was structurally characterized. A comparison of the NMR spectra and structural data of new and literature-known bis-adducts shows several trends pertaining to the nature of the halides and the stereoelectronic properties of the Lewis bases employed.

Phosphine-Stabilized Diiododiborenes: Isolable Diborenes with Six Labile Bonds.

The lability of B=B, B-P, and B-halide bonds is combined in the syntheses of the first diiododiborenes. In a series of reactivity tests, these diiododiborenes undergo cleavage of all six of their central bonds in different ways, leading to products of B=B hydrogenation and dihalogenation as well as halide exchange.

Oxidative addition of arsenic halides to platinum(0).

Reaction of AsCl3 with Pt(0) complexes [Pt(PCy3)2], [Pt(PCy3)(IMes)] and [Pt(IMes)2] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) resulted in oxidative addition of As-Cl bonds at the Pt centres to form complexes of the form trans-[PtCl(AsCl2)L2]. Two of these compounds were characterised by X-ray diffraction, making them the first structurally characterised examples of AsX2 ligands (X = halogen). AsBr3 also underwent oxidative addition to [Pt(PCy3)2], forming trans-[PtBr(AsBr2)(PCy3)2] in situ, as judged by 31P NMR spectroscopy. This reaction was unselective, yielding several products, of which a Pt3As2 cluster could be identified by single-crystal X-ray diffraction.

Reactivity of Tetrahalo- and Difluorodiboranes(4) toward Lewis Basic Platinum(0): Bis(boryl), Borylborato, and Doubly Boryl-Bridged Platinum Complexes.

The reaction of the tetrahalodiboranes(4) B2F4, B2Cl4, and B2Br4 with a Lewis basic platinum(0) complex led to the isolation of the cis-bis(difluoroboryl) complex cis-[(Cy3P)2Pt(BF2)2] (1) and the novel borylborato complexes trans-[(Cy3P)2Pt{B(X)-BX3}] (2, X = Cl; 3, X = Br), respectively. The trans influence of the borylborato group was found to be one of the strongest ever observed experimentally. Furthermore, the reactivity of little-explored diaryldifluorodiboranes(4) F2B-BMes2 and the new derivative F2B-BAn2 (An = 9-anthryl) toward a range of platinum(0) complexes was investigated. Reactions with relatively nonbulky platinum(0) complexes led to the formation of unsymmetrical cis-bis(boryl) complexes cis-[(R3P)2Pt(BF2)(BMes2)] (6, R = Me; 7, R = Et) as well as the first example of a fourfold-unsymmetrical bis(boryl) complex, [(Me3P)(Cy3P)Pt(BF2)(BMes2)] (12). The use of a more bulky Pt complex provided access to the unprecedented dinuclear bis(boryl) complexes [{( iPr3P)Pt}2(µ-BF2)(µ-BAr2)] (8, Ar = Mes; 9, Ar = An), which feature two different µ2-bridging boryl ligands.

Reactions of Digallanes with p- and d-Block Lewis Bases: Adducts, Bis(gallyl) Complexes, and Naked Ga+ as Ligand.

A range of double carbene adducts of digallanes(4) are prepared from an existing double digallane adduct, and their halides are subsequently exchanged, establishing the feasibility of both base and halide-exchange reactions from digallane adducts. Furthermore, a range of digallium species are treated with transition-metal Lewis bases, leading alternatively to oxidative addition products, species with monocoordinate Ga+ ligands, and an unusual ditopic metal-only Lewis pair (MOLP). These results underline the manifold and unpredictable chemistry of halogallane species with Lewis bases.

Transition-Metal π-Ligation of a Tetrahalodiborane.

The reaction of tetraiododiborane (B2 I4 ) with trans-[Pt(BI2 )I(PCy3 )2 ] gives rise to the diplatinum(II) complex [{(Cy3 P)(I2 B)Pt}2 (µ2 :η3 :η3 -B2 I4 )], which is supported by a bridging diboranyl dianion ligand [B2 I4 ]2- . This complex is the first transition-metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B2 X4 (X=halide) unit of any type to a metal center.

Simple solution-phase syntheses of tetrahalodiboranes(4) and their labile dimethylsulfide adducts.

Convenient solution-phase syntheses of tetrahalodiboranes(4) B2F4, B2Cl4 and B2I4 are presented herein from common precursor B2Br4. In addition, the dimethylsulfide adducts B2Cl4(SMe2)2 and B2Br4(SMe2)2 are conveniently prepared in one-step gram and multigram scale syntheses from the commercially-available starting material B2(NMe2)4. The results provide simple access to the full range of tetrahalodiboranes(4) for the exploration of their untapped synthetic potential.

Dynamic, Reversible Oxidative Addition of Highly Polar Bonds to a Transition Metal.

The combination of Pt0 complexes and indium trihalides leads to compounds that form equilibria in solution between their In-X oxidative addition (OA) products (PtII indyl complexes) and their metal-only Lewis pair (MOLP) isomers (LnPt→InX3). The position of the equilibria can be altered reversibly by changing the solvent, while the equilibria can be reversibly and irreversibly driven toward the MOLP products by addition of further donor ligands. The results mark the first observation of an equilibrium between MOLP and OA isomers, as well as the most polar bond ever observed to undergo reversible oxidative addition to a metal complex. In addition, we present the first structural characterization of MOLP and oxidative addition isomers of the same compound. The relative energies of the MOLP and OA isomers were calculated by DFT methods, and the possibility of solvent-mediated isomerization is discussed.