Generation And Photochemistry Of Transient Phosphorus-containing Small Molecules

As an important class of reaction intermediates,transient phosphorus-containing small molecules play key roles in synthetic chemistry,coordination chemistry,combustion chemistry and interstellar chemistry.Therefore,the generation,spectroscopic detection,and reaction mechanism research of these transient molecules are frontier topics in phosphorus chemistry.On account of the unique bonding characteristics of elemental phosphorus,this kind of species has the inherent nature of high reactivity,short lifetime,and facile polymerization which makes the production,spectroscopic detection,and related microscopic mechanism study rendering challenging.In this dissertation,we prepared and purified a series of metastable high-energy metastable phosphoryl diazide compounds RP(O)(N3)2(R=t-Bu,PhO,EtO)and CH3OP(S)(N3)2.Taking these compounds as precursors,we used high-vacuum flash pyrolysis(HVFP)and laser photolysis,novel transient phosphorus-containing small molecules ·OH …OP·,PhOPO,and CH3OPS were generated in situ from the corresponding precursor and directly detected by cryogenic matrix-isolation infrared spectroscopy.Combining isotope labeling experiments and high-level quantum chemical calculations,we comprehensively analyzed the decomposition mechanism of the azide precursor,experimental and theoretical studies have been carried out on the structure,conformation,spectroscopy and photochemistry of phosphorus-containing intermediates.The research content of this dissertation mainly includes the following three parts:1.Metaphosphorous acid(HOPO)was generated by HVFP of t-BuP(O)(N3)2 and EtOP(O)(N3)2,and its photochemical properties at 2.8 K low-temperature Ar-matrix were experimentally studied.The isomerization product HPO2 was obtained by 266 nm irradiation;the dissociation and recombination to a hydroxyl radical complex·OH…OP·(HRC)with triplet ground state from short-pulse 193 nm laser were also detected.The cryogenic matrix was programmed to 12.0 K and it was found that the radical complex could spontaneously convert to HOPO.Combined with D-and 18Oisotope labeling experiments,the kinetic process of this transformation and the kinetic isotope effect(KIE)was measured.In addition,that was involved in triplet·OH…OP· and its isomers were theoretically analyzed by natural bond orbital(NBO),atoms in molecules(AIM)and non-covalent interactions(NCI)theory,and the nature of hydrogen bonding in ·OH…OP· is also enclosed.2.The novel high-energy compound CH3OP(S)(N3)2 was synthesized and purified by the the cold trap vacuum line platform,and characterized by by NMR,matrix-isolation infrared,gas-phase infrared,Raman,and UV-Vis spectroscopy.CH3OPS has been generated in the gas phase through HVFP,and two kinds of conformational isomers of CH3OPS(cis and trans)were accurately detected by infrared spectroscopy.The tentative assignments of both cis-CH3OPS and trans-CH3OPS were supported by D-、13C-and 18O-isotope labeling experiments and high-level quantum chemical calculations.The conversion of cis-CH3OPS to trans-CH3OPS upon 365 nm UV-light irradiation could be detected.Upon 266 nm laser photolysis of the CH3OP(S)(N3)2,nitrene intermediate CH3OP(S)(N3)N was observed.Through further irradiation with 365 nm UV-light,the nitrene intermediate could further decompose to cis-CH3OPS or recombine with N2 to get CH3OPS(N3)2.The step-wise decomposition mechanism of CH3OP(S)(N3)2 is studied by the theoretical calculation of B3LYP/6-311++G(3df,3pd).3.The comprehensive spectroscopic characterization of PhOP(O)(N3)2 was supported by matrix-isolation infrared,Raman,UV-Vis,and NMR spectroscopy.The phosphinidene oxide cis-PhOPO and trans-PhOPO have been generated in the gas phase through HVFP of PhOP(O)(N3)2 at ca.1000 K.The conversion of cis-PhOPO to trans-PhOPO was induced by 266 nm laser irradiation,and reversibly rotamerization of trans-PhOPO to cis-PhOPO was detected upon 193 nm laser irradiation.In order to study the decomposition mechanism,photolysis experiments of PhOP(O)(N3)2 were carried out in the nitrogen matrix,and the depletion of precursor occurred first and the triplet nitrene intermediates PhOP(O)(N3)N were generated upon 266 nm laser irradiation,and trans-PhOPO was generated upon subsequently 365 nm irradiation as the single product.Moreover,the microscopic decomposition mechanism of PhOP(O)(N3)2 and conformational rotamerization in cis-and trans-PhOPO was analyzed by quantum chemical calculations.