Formation and reactions of P-amino substituted Li/Cl phosphinidenoid complexes

Abstract

In this PhD Thesis results on the synthesis of P-amino substituted Li/Cl phosphinidenoid complexes are presented, with a particular focus on their reactivity in polar and apolar solvents and characteristic trapping reactions were performed. Furthermore, their use in the synthesis of phosphaquinodi-methane complexes was experimentally and theoretically investigated, and redox properties of the obtained products were studied via cyclic voltammetry and DFT calculations examining their non-innocent character. <br /> The study started with the generation of novel P-amino substituted Li/Cl phosphinidenoid metal complexes (M = Cr, W, Fe; R = NPh₂, NCy₂), some of which were detected at VT-NMR measurements at -80 °C. The reactivity of these complexes in polar solvents (THF) towards MeOH and MeNH₂ was investigated and the corresponding EH-insertion products isolated. A significant change of the reactivity was observed in weakly polar solvents such as toluene showing the formation of a transient electrophilic phosphinidene complex (M = W; R = NCy₂) undergoing [2+1] cycloaddition with apolar terminal alkenes and tolane at low temperatures. Here, DFT calculations reveiled thermodynamic aspects of the chloride leaving ability of (isolated) phosphinidenoid complex anions and also showed a superior N-P lone pair donation in case of P-NCy₂ substitution (compared to NPh₂), thus providing superior stabilization of the transiently formed terminal phosphinidene complex. <br /> The second part describes the SET oxidation of Li/Cl phosphinidenoid complexes and the isolation of the key intermediates at low temperature, the heterocoupling products of transient radicals. Subsequent reactions with the strong base KHMDS led to the electrochemically interesting phosphaquinodimethanes complexes (M = Cr, W; R = CPh₃). These were investigated in detail via cyclo-voltammetry displaying a diffusion controlled one-electron-reduction which was also supported by chemical reduction and EPR measurements. DFT calculations on phosphaquinodimethane model compounds in various charged spin states disclosed e.g. an interesting distonic radical anion with a ligand centred radical.