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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 demonstrate 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.
Im Rahmen dieser Arbeit war es möglich, diverse Lewis-Basen für deren Einsatz zur Stabilisierung niedervalenter Borverbindungen zu testen. Dabei wurden neuartige Mono- und Diboran(4)-Addukte mit mesoionischen Carbenen, Phosphanen und Alkyl-verbrückten Carbenen synthetisiert, charakterisiert und deren Reduktionsverhalten getestet. Des Weiteren konnte gezeigt werden, dass elektronenreiche Bis(amidinato)- und Bis(guanidinato)silylene eine diverse Vielfalt an Reaktionstypen induzieren und dabei zu Redox-Reaktionen und Ligandenübertrag neigen.
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 spectroscopic, (C,H,N)- elemental and, for 20 of these compounds, X-ray crystallographic analysis, revealing an unexpected variation in the bonding motifs. Besides the classical B2X4L2 diborane(6) adducts, some of the more sterically demanding carbene ligands induce a halide displacement leading 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 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.
2,2′-Bipyridyl is shown to spontaneously abstract a borylene fragment (R–B:) from various hypovalent boron compounds. This process is a redox reaction in which the bipyridine is reduced and becomes a dianionic substituent bound to boron through its two nitrogen atoms. Various transition metal–borylene complexes and diboranes, as a well as a diborene, take part in this reaction. In the latter case, our results show an intriguing example of the homolytic cleavage of a B═B double bond.