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This work involves the synthesis and reactivity of pseudohalide-substituted boranes and borylenes. A series of compounds of the type (CAAC)BR2Y (CAAC = cyclic alkyl(amino)carbene; R = H, Br; Y = CN, NCS, PCO) were prepared first. The two-electron reduction of (CAAC)BBr2Y (Y = CN, NCS) in the presence of a second Lewis base L (L = N-heterocyclic carbene) resulted in the formation of the corresponding doubly Lewis base-stabilized pseudohaloborylenes (CAAC)(L)BY. These borylenes show versatile reactivity patterns, including their oxidation to the corresponding radical cations, coordination via the respective pseudohalide substituent to group 6 metal carbonyl complexes, as well as a boron-centered protonation with Brønsted acids to boronium cations. Reduction of (CAAC)BBr2(NCS) in the absence of a second donor ligand, led to the formation of boron-doped thiazolothiazoles via reductive dimerization of two isothiocyanatoborylenes. These B,N,S-heterocycles possess a low degree of aromaticity as well as interesting photophysical properties and can furthermore be protonated as well as hydroborated. Additionally, CAAC adducts of the parent boraphosphaketene (CAAC)BH2(PCO) could be prepared, which readily reacted with boroles [Ph4BR'] (R' = aryl) via decarbonylation in a ring expansion reaction. The obtained 1,2-phosphaborinines represent B,P-isosteres of benzene and consequently could be coordinated to metal carbonyl complexes of the chromium triade via η6-coordination, resulting in new half-sandwich complexes thereof.
The substitution of selected CC units by their isoelectronic and isosteric BN units in π−conjugated organic compounds (BN/CC isosterism), especially polycyclic aromatic hydrocarbons (PAHs), has emerged as a viable strategy to produce novel organic–inorganic hybrid materials with structural similarities to their all-carbon congeners, but in many cases with intriguing properties and functions.
In the first two chapters the synthesis and properties of novel BNB-doped phenalenyls, dithienoazadiborepins and dithienooxadiborepins are presented. The optoelectronic properties of these new building blocks can be effectively tuned by variation of the incorporated Ar (Mes, Tip, FMes) and R groups (H, Me, i-Pr, t-Bu, Ph). Theoretical investigations, including NICS (Nucleus Independent Chemical Shift) scans and AICD (Anisotropy of the Induced Current Density) calculations, have been performed which provide insight into their aromatic or antiaromatic character, respectively.
The incorporation of BP units, on the other hand, which are valence isoelectronic with BN and CC, into unsaturated organic compounds, has been scarcely studied, though the potential of the resulting BCP hybrid materials for electronic applications has been recognized quite recently. Main chain conjugated polymers featuring BP fragments in the backbone are unknown so far. The first molecular model compounds for a BP analogue of the conjugated polymer poly(p-phenylene vinylene) (PPV) are presented in chapter 3. Theoretical investigations revealed that the Mes* group to fully planarizes the phosphorus center, increasing the B=P double bond character and enabling conjugation over the BP unit. Different synthetic approaches to the molecular model compounds have been investigated and a viable synthetic strategy was found.