Convenient solution-phase syntheses of tetrahalodiboranes(4) and the dimethylsulfide adducts B2Cl4(SMe2)2 and B2Br4(SMe2)2 are presented.

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.

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 B2X4 precursors (X=Cl, Br, I) or by ligand exchange at stable B2X4(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 B2X4L2 diborane(4) bis‐adducts, certain more sterically demanding carbene ligands induce a halide displacement which led to the first halide‐bridged monocationic diboron species, [B2X3L2]A (A=BCl4, Br, I). Furthermore, low‐temperature 1:1 reactions of B2Cl4 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.

The reaction of tetraiododiborane (B I ) with trans-[Pt(BI )I(PCy ) ] gives rise to the diplatinum(II) complex [{(Cy P)(I B)Pt} (μ :η :η -B I )], which is supported by a bridging diboranyl dianion ligand [B I ] . This complex is the first transition-metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B X (X=halide) unit of any type to a metal center.

ABSTRACT:The combination of Pt 0 complexes and indium trihalides leads to compounds that form equilibria in solution between their In-X oxidative addition (OA) products (Pt II indyl complexes) and their metal-only Lewis pair (MOLP) isomers (L n Pt→InX 3 ). The position of the equilibria can be altered reversibly by changing the solvent, while the equilibria can be reversibly and irreversibly driven towards 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.

The reaction of the tetrahalodiboranes(4) BF, BCl, and BBr with a Lewis basic platinum(0) complex led to the isolation of the cis-bis(difluoroboryl) complex cis-[(CyP)Pt(BF)] (1) and the novel borylborato complexes trans-[(CyP)Pt{B(X)-BX}] (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) FB-BMes and the new derivative FB-BAn (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-[(RP)Pt(BF)(BMes)] (6, R = Me; 7, R = Et) as well as the first example of a fourfold-unsymmetrical bis(boryl) complex, [(MeP)(CyP)Pt(BF)(BMes)] (12). The use of a more bulky Pt complex provided access to the unprecedented dinuclear bis(boryl) complexes [{( iPrP)Pt}(μ-BF)(μ-BAr)] (8, Ar = Mes; 9, Ar = An), which feature two different μ-bridging boryl ligands.

Two neutral, hydride-bridged diboranes(5) were found to serve as two-electron reductants of chalcogens and thereby mimics of B–B multiply bound species.

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.