Synthesis, Reactivity and Application of λ3σ2-Phosphinines

Abstract

Additional donor-substituents on the aromatic phosphorus heterocycle significantly modify their stereo-electronic properties and their coordination abilities. This class of phosphinines shows a significantly enhanced basicity and nucleophilicity compared to the parent phosphinine C5H5P. Moreover, the electrophilic nature of the phosphorus atom in phosphinines allows a nucleophilic attack by organolithium compounds to form λ5-phosphinines. This leads to the possibility of introducing different substituents at the phosphorus atom of λ3-phosphinines. This dissertation describes the details exploration of the reactivity of functionalized phosphinines and first attempts to use phosphinines in more applied research fields. 1. Phosphinine borane adduct Upon reaction of 3,5-bis(SiMe3)phosphinine with B(C6F5)3, the first phosphinine borane adduct 6-1 was isolated and characterized. Interestingly, 6-1 turned out to be very reactive towards C-C multiple bonds. A zwitterionic alkenyl-phosphininium borate salt forms by insertion of phenylacetylene into the dative P-B bond of 6-1 and reacts further with a second equivalent of phenylacetylene to form 6-2. The first example of a dihydro-1-phosphabarrelene derivative 6-3 was formed by reacting 6-1 with styrene. The reaction of 6-1 with an ester proceeds instantaneously and forms a 1-R-phosphininium salt that further reacts with styrene or phenylacetylene to form a dihydro-1-R-phosphabarrelenium (6-4) and a 1-R-phosphabarrelenium salt 6-5, respectively. These results provide fascinating new perspectives for the future, particularly with respect to the activation of small molecules and the synthesis of adducts of phosphinines with other main group elements and main-group-based compounds. 2. Phosphinine selenides The phosphinine selenide (6-6) in the form of the cocrystalline adduct 6-7 with the organoiodine 1,4-TFDIB was structurally characterized by X-ray diffraction for the first time. The molecular structure of 6-7 in the solid state is mainly stabilized by several non-bonding interactions including π-π stacking, hydrogen bonding, F-F- and Se-I interactions. It demonstrates that phosphinine selenides can be used as a multifunctional molecules for crystal design. Furthermore, 6-6 can react with diiodine to form the adduct 6-8. The labile P=Se bond in 6-6 allows the formation of KSeCN 6-9 in the presence of KCN, which shows that 6-6 can act as an efficient selenium transfer reagent, 3. 3-N,N-dimethylaminophosphinine derivatives Novel 3-aminofunctionalized phosphinines were synthesized and characterized. The neutral 3-aminofunctionalized phosphinines show a classical σ-2e terminal coordination mode with CuBr·S(CH3)2. The pronated 3-aminofunctionalized phosphinine shows both the classical terminal 2e donation via the lone pair of the phosphorus atom and the uncommon μ2-bridging 2e-lone-pair donation to the CuI center when reacted with CuCl·S(CH3)2. Upon reaction with AuCl·S(CH3)2, the 3-aminofunctionalized phosphinines show an expected σ-2e terminal coordination mode. Moreover, in the presence of water and HCl, the phosphinine 6-10 undergoes a hitherto unknown, selective ring contraction to form a hydroxylphospholene oxide. DFT calculations and labelling experiments were performed to get insight into the reaction mechanism, 4. λ5-phosphinines A series of functionalized λ5-phosphinines were synthesized by combining four different synthetic methods to introduce different substituents at the 2-, 4- and 6-positions as well as the phosphorus atom of the phosphorus heterocycle. 5-22 is the first λ5-phosphinine with fluorescence emission that reaches the red region in solution. Furthermore, these λ5-phosphinines exhibit a colorful fluorescence emission (ranging from blue to deep red) when they were irradiated with UV light (Figure 6.6). By investigating the effects of the substituents at different positions of the phosphorus heterocycle, the luminescent properties of λ5-phosphinines were further clarified. These investigations provided a foundation for the design and synthesis of functionalized λ5-phosphinines for applications in optoelectronic devices in the future.