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Borole-based half-sandwich complexes of germanium and tin
No full textThe synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described.The synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described. The 2,5-disilylborole substitution pattern allows their access via salt metathesis of the respective borole dianions.The synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described.The synthesis and initial observations regarding the reactivity of borole-based half-sandwich complexes with apical divalent group 14 elements germanium and tin are described. The 2,5-disilylborole substitution pattern allows their access via salt metathesis of the respective borole dianions
Electronic Push–Pull Modulation by Peripheral Substituents in Pentaaryl Boroles
No full textEstablishing access to a bulky tetraaryl dilithiobutadiene (Ph C)4 Li2 (Ph =3,5-tBu2 (C6 H3 )) allowed for the synthesis of five-membered heterocycles with incorporated main-group elements. Along with an amino borole, a set of substituted pentaaryl boroles (Ph C)4 BAr has been synthesized. The examination of their absorption spectra and computational studies by means of DFT granted insight into the influence of peripheral substituents on the electronic features of the parent pentaphenyl borole (PhC)4 BPh. Introduction of the more electron-rich Ph residue at the carbon atoms increases the HOMO energy, redshifting the visible π/π -absorption bands compared with the parent pentaphenyl borole. The influence on the frontier orbitals of three different boron-bound aryls with electronically modulating substituents in the remote 3,5-positions Ar=3,5-R2 -C6 H3 (R=Me, H, CF3 ) was studied. The substituents were found to increase (+I effect, Me) or decrease (-I effect, CF3 ) the LUMO energy, thus directly affecting the visible absorption spectra. This represents the first study on HOMO-LUMO-gap adjustments by a combined push-pull approach of a substituted pentaphenylborole
2,5-Bis-trimethylsilyl substituted boroles
No full textThis manuscript includes a comprehensive study of the synthesis and spectroscopic features of 2,5-disilyl boroles.This manuscript includes a comprehensive study of the synthesis and spectroscopic features of 2,5-disilyl boroles. Reacting boron trichloride BCl 3 with 2,3-Ph 2 -1,4-(SiMe 3 ) 2 -1,4-dilithiobuta-1,3-diene (Ph = 3,5- t -Bu 2 (C 6 H 3 )) allowed reliable access to 1-Chloro-2,5-(SiMe 3 ) 2 -3,4-(Ph ) 2 -borole in good yields (60%). Unlike 2,3,4,5-tetraphenyl haloboroles, this 2,5-bis-trimethylsilyl substituted chloroborole is thermally stable in solution to up to 130 °C. Metathesis reactions of the chloroborole with metal aryls or of the dilithiobutadiene with arylboron dihalides grant access to 1-Ar-2,5-(SiMe 3 ) 2 -3,4-(Ph ) 2 boroles (Ar = Ph, Mes, Ph , C 6 F 5 ). Unlike the generally intensely blue-green 2,3,4,5-tetraaryl boroles, brightly orange/red 2,5-bis-trimethylsilyl substituted boroles reveal blue-shifted π/π -transitions due to a lack of π-system interaction between borole and 2,5-bound aryls. Light is shed on the synthetic peculiarities for the synthesis of 2,5-disilyl-boroles. While direct treatment of the respective 1,1-dimethyl-stannole with ArBCl 2 via otherwise well-established B/Sn exchange reactions fails, the selectivity of reactions of 2,3-Ph 2 -1,4-(SiMe 3 ) 2 -1,4-dilithiobuta-1,3-diene with ArBCl 2 is solvent dependent and leads to rearranged 3-borolenes in hydrocarbons. Gutmann–Beckett analysis reveal reduced Lewis-acidity of disilylboroles compared to pentaphenyl borole
A Cationic NHC‐Supported Borole
No full textAbstract This work describes the synthesis and characterization of a highly reactive cationic borole. Halide abstraction with Li{Al[OC(CF3)3]4} from the NHC‐chloroborole adduct yields the first stable NHC‐supported 1‐(MeNHC)‐2,5‐(SiMe3)2‐3,4‐(Ph )2‐borole cation. Electronically, it features both a five‐membered cyclic conjugated 4 π‐electron system and a cationic charge and thus resembles the yet elusive cyclopentadienyl cation. The borole cation was characterized crystallographically, spectroscopically (NMR, UV/Vis), by cyclovoltammetry, microanalysis and mass‐spectrometry and its electronic structure was probed computationally. The cation reacts with tolane and reversibly binds carbon monoxide. Direct comparison with the structurally related, yet neutral, 1‐mesityl borole reveals strong Lewis acidity, reduced HOMO–LUMO gaps, and increased anti‐aromatic character.Think positive! Halide abstraction from an NHC‐adduct to a haloborole allowed for the synthesis of the first cationic borole featuring a three‐coordinate boron‐atom embedded in a cyclic 4π electron system. This cation reveals high boron‐centered Lewis‐acidity and a very small reduction potential. CO readily and reversibly binds to the boron‐center to form a rare carbonyl complex with considerably low stretching frequency that indicates backbonding. imageDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165
Linear and Bent Cp*2Si: Reversible Phase Transition of a Key Molecule
No full textThe solid-state structure of decamethylsilicocene Cp*2Si with a bent and a linear molecule in the same unit cell was so far considered an exception in relation to the structures of its all-bent heavier analogues Cp*2E with E=Ge, Sn, Pb. Here, we present the solution to this conundrum by reporting a low-temperature phase, where all three symmetrically independent molecules are present in a bent formation. This reversible enantiotropic phase transition occurs in the temperature range between 80 K and 130 K and provides a rationale for the unexpected linear molecule based in entropy beyond hand-waving explanations such as electronic reasons or packing effects
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No full textThe pentaaryl borole (Ph C)4 BXylF [Ph =3,5-tBu2 (C6 H3 ); XylF =3,5-(CF3 )2 (C6 H3 )] reacts with low-valent Group 13 precursors AlCp and GaCp by two divergent routes. In the case of [AlCp ]4 , the borole reacts as an oxidising agent and accepts two electrons. Structural, spectroscopic, and computational analysis of the resulting unprecedented neutral η5 -Cp ,η5 -[(Ph C)4 BXylF ] complex of AlIII revealed a strong, ionic bonding interaction. The formation of the heteroleptic borole-cyclopentadienyl "aluminocene" leads to significant changes in the 13 C NMR chemical shifts within the borole unit. In the case of the less-reductive GaCp , borole (Ph C)4 BXylF reacts as a Lewis acid to form a dynamic adduct with a dative 2-center-2-electron Ga-B bond. The Lewis adduct was also studied structurally, spectroscopically, and computationally.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165
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