Wesley J. Transue

A Molecular Precursor to Phosphaethyne and Its Application in Synthesis of the Aromatic 1,2,3,4-Phosphatriazolate Anion

Dibenzo-7-phosphanorbornadiene Ph3PC(H)PA (1, A = C14H10, anthracene) is reported here as a molecular precursor to phosphaethyne (HC≡P), produced together with anthracene and triphenylphosphine. HCP generated by thermolysis of 1 has been observed by molecular beam mass spectrometry, laser-induced fluorescence, microwave spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH(⧧) = 25.5 kcal/mol and ΔS(⧧) = -2.43 eu and is accompanied by formation of an orange insoluble precipitate. Results from computational studies of the mechanism of HCP generation are in good agreement with experimental data. This high-temperature method of HCP generation has pointed to new reaction chemistry with azide anion to produce the 1,2,3,4-phosphatriazolate anion, HCPN3(-), for which structural data have been obtained in a single-crystal X-ray diffraction study. Negative-ion photoelectron spectroscopy has shown the adiabatic detachment energy for this anion to be 3.555(10) eV. The aromaticity of HCPN3(-) has been assessed using nucleus-independent chemical shift, quantum theory of atoms in molecules, and natural bond orbital methods.

Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX– (E = As, P, and N; X = S and O) Anions

Three newly synthesized [Na+(221-Kryptofix)] salts containing AsCO-, PCO-, and PCS- anions were successfully electrosprayed into a vacuum, and these three ECX- anions were investigated by negative ion photoelectron spectroscopy (NIPES) along with high-resolution photoelectron imaging spectroscopy. For each ECX- anion, a well-resolved NIPE spectrum was obtained, in which every major peak is split into a doublet. The splittings are attributed to spin-orbit coupling (SOC) in the ECX• radicals. Vibrational progressions in the NIPE spectra of ECX- were assigned to the symmetric and the antisymmetric stretching modes in ECX• radicals. The electron affinities (EAs) and SO splittings of ECX• are determined from the NIPE spectra to be AsCO•: EA = 2.414 ± 0.002 eV, SO splitting = 988 cm-1; PCO•: EA = 2.670 ± 0.005 eV, SO splitting = 175 cm-1; PCS•: EA = 2.850 ± 0.005 eV, SO splitting = 300 cm-1. Calculations using the B3LYP, CASPT2, and CCSD(T) methods all predict linear geometries for both the anions and the neutral radicals. The calculated EAs and SO splittings for ECX• are in excellent agreement with the experimentally measured values. The simulated NIPE spectra, which are based on the calculated Franck-Condon factors, and the SO splittings nicely reproduce all of the observed spectral peaks, thus allowing unambiguous spectral assignments. The finding that PCS• has the greatest EA of the three triatomic molecules considered here is counterintuitive based upon simple electronegativity considerations, but this finding is understandable in terms of the movement of electron density from phosphorus in the HOMO of PCO- to sulfur in the HOMO of PCS-. Comparisons of the EAs of PCO• and PCS• with the previously measured EA values for NCO• and NCS• are made and discussed.

Mechanism and Scope of Phosphinidene Transfer from Dibenzo-7-phosphanorbornadiene Compounds

Dibenzo-7-phosphanorbornadiene compounds, RPA (A = C14H10 or anthracene), are investigated as phosphinidene sources upon thermally induced (70-90 °C) anthracene elimination. Analysis of substituent effects reveals that π-donating dialkylamide groups are paramount to successful phosphinidene transfer; poorer π-donors give reduced or no transfer. Substituent steric bulk is also implicated in successful transfer. Molecular beam mass spectrometry (MBMS) studies of each derivative reveal dialkylamide derivatives to be promising precursors for further gas-phase spectroscopic studies of phosphinidenes; in particular, we present evidence of direct detection of the dimethylamide derivative, [Me2N═P]. Kinetic investigations of iPr2NPA thermolysis in 1,3-cyclohexadiene and/or benzene-d6 are consistent with a model of unimolecular fragmentation to yield free phosphinidene [iPr2N═P] as a transient reactive intermediate. This conclusion is probed by density functional theory (DFT) calculations, which favored a mechanistic model featuring free singlet aminophosphinidenes. The breadth of phosphinidene acceptors is expanded to unsaturated substrates beyond 1,3-dienes to include olefins and alkynes; this provides a new synthetic route to valuable amino-substituted phosphiranes and phosphirenes, respectively. Stereoselective phosphinidene transfer to olefins is consistent with singlet phosphinidene reactivity by analogy with the Skell hypothesis for singlet carbene addition to olefins.

Phosphinidene Reactivity of a Transient Vanadium P≡N Complex

Toward the preparation of a coordination complex of the heterodiatomic molecule PN, P≡N-V(N[tBu]Ar)3 (1, Ar = 3,5-Me2C6H3), we report the use of ClPA (A = C14H10, anthracene) as a formal source of phosphorus(I) in its reaction with Na[NV(N[tBu]Ar)3] (Na[4]) to yield trimeric cyclo-triphosphane [PNV(N[tBu]Ar)3]3 (3) with a core composed exclusively of phosphorus and nitrogen. In the presence of NapS2 (peri-1,8-naphthalene disulfide), NapS2P-NV(N[tBu]Ar)3 (6) is instead generated in 80% yield, suggesting trapping of transient 1. Upon mild heating, 3 readily fragments into dimeric [PNV(N[tBu]Ar)3]2 (2), while in the presence of bis(trimethylsilyl)acetylene or cis-4-octene, the respective phosphirene (Ar[tBu]N)3VN-PC2(SiMe3)2 (7) or phosphirane (Ar[tBu]N)3VN-P(C8H16) (8) compounds are generated. Kinetic data were found to be consistent with unimolecular decay of 3, and [2+1]-cycloaddition with radical clocks ruled out a triplet intermediate, consistent with intermediate 1 reacting as a singlet phosphinidene. In addition, both 7 and 8 were shown to reversibly exchange cis-4-octene and bis(trimethylsilyl)acetylene, serving as formal sources of 1, a reactivity manifold traditionally reserved for transition metals.

Sulfur monoxide thermal release from an anthracene-based precursor, spectroscopic identification, and transfer reactivity

Significance The generation of highly reactive molecules under controlled conditions is desirable, as it allows exploration of synthetic chemistry and enables spectroscopic studies of such elusive species. We report here on the synthesis and reactivity of a precursor molecule that readily fragments with concomitant expulsion of dinitrogen and anthracene to release the highly reactive sulfur monoxide, a compound of interest for both synthetic chemists and astrochemists. Sulfur monoxide (SO) is a highly reactive molecule and thus, eludes bulk isolation. We report here on synthesis and reactivity of a molecular precursor for SO generation, namely 7-sulfinylamino-7-azadibenzonorbornadiene (1). This compound has been shown to fragment readily driven by dinitrogen expulsion and anthracene formation on heating in the solid state and in solution, releasing SO at mild temperatures (<100 °C). The generated SO was detected in the gas phase by MS and rotational spectroscopy. In solution, 1 allows for SO transfer to organic molecules as well as transition metal complexes.