Functionalized Bis(pentafluoroethyl)phosphanes: Improved Syntheses and Molecular Structures in the Gas Phase

摘要

(C_2F_5)_2PNEt_2 represents an excellent starting material for the selective synthesis of bis(pentafluoroethyl)phosphane derivatives. The moderately air-sensitive aminophosphane is accessible on a multi-gram scale by treating Cl_2PNEt_2 with C_2F_5Li. Treatment with gaseous HCl or HBr yielded the corresponding phosphane halides (C_2F_5)_2PCl and the so far unknown (C_2F_5)_2PBr in good yields. The hitherto unknown (C_2F_5)_2PF was obtained by treating (C_2F_5)_2PBr with excess antimony trifluoride. Treatment of (C_2F_5)_2PCl with Bu_3SnH led to the quantitative formation of (C_2F_5)_2PH. Deprotonation formally yielded the (C_2F_5)_2P~- anion in a form that was stabilized by coordination to mercury ions to form the complex [Hg{P(C_2F_5)_2}_2(dppe)]. An improved high-yielding synthesis of (C_2F_5)_2POH was achieved by treating (C_2F_5)_2PNEt_2 with p-toluenesulfonic acid. The gas-phase structures of (C_2F_5)_2- PH and (C_2F_5)_2POH were determined by electron diffraction. The vibrational corrections employed in the data analysis of the diffraction data were derived from molecular dynamics calculations. Both compounds exist in the gas phase mostly as C_1-symmetric cis,cis conformers with regard the orientation of the C_2F_5 groups relative to the functional groups H and OH. The presence of a second conformer at ambient temperature is likely in both cases. The refined amounts of dominant conformers are 94(6) and 85(6)%for (C_2F_5)_2PH and (C_2F_5)_2POH, respectively. The conformational behaviour was further explored by potential energy surface scans based on DFT calculations. Important experimental structural parameters for the most stable conformers are r_e(P-C)_(average) = 1.884(3) ? for (C_2F_5)_2PH and r_e(P-C)_(average) = 1.894(4) ? and re(P-O) = 1.582(3) ? for (C_2F_5)_2POH. The different coordination properties of (C_2F_5)_3P, (C_2F_5)_2POH, (CF_3)_3P and (CF_3)_2- POH were evaluated by complex formation with [Ni(CO)_4]: the maximum achievable number of CO ligands substituted by (C_2F_5)_3P is 1, by (C_2F_5)_2POH is 2, by (CF_3)_3P is 3 and by the smallest ligand (CF_3)_2POH is 4.