An Anthracene-based Precursor for Sulfur Monoxide Delivery: Thermal Release, Spectroscopic Identification and Transfer Reactivity Maximilian Joost, Matthew Nava, Wesley J. Transue, M. A. Martin-Drumel, Michael Mccarthy, David Patterson, Christopher C Cummins To cite this version: Maximilian Joost, Matthew Nava, Wesley J. Transue, M. A. Martin-Drumel, Michael Mccarthy, et al.. An Anthracene-based Precursor for Sulfur Monoxide Delivery: Thermal Release, Spectroscopic Identi- fication and Transfer Reactivity. Proceedings of the National Academy of Sciences of the United States of America , National Academy of Sciences, 2018, 115 (23), pp.5866-5871. 10.1073/pnas.1804035115. hal-02305406 HAL Id: hal-02305406 https://hal.archives-ouvertes.fr/hal-02305406 Submitted on 4 Oct 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. An Anthracene-based Precursor for Sulfur Monoxide Delivery: Thermal Release, Spectroscopic Identification and Transfer Reactivity Maximilian Joosta, Matthew Navaa, Wesley J. Transuea, Marie-Aline Martin-Drumelb, Michael C. McCarthyc, David Pattersond,e, and Christopher C. Cumminsa,1 aDepartment of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.; bInstitut des Sciences Moléculaires d’Orsay, CNRS, Bât. 210, Université Paris–Sud, 91405 Orsay, France.; cHarvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.; dDepartment of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138, USA.; eCurrent address: Department of Physics, University of California, Santa Barbara, Santa Barbara, CA 93106, USA. This manuscript was compiled on February 27, 2018 Sulfur monoxide (SO) is a highly reactive molecule and thus eludes O O bulk isolation. We report here on synthesis and reactivity of a S O S S S molecular precursor for SO generation, namely 7-sulfinylamino-7- S azadibenzonorbornadiene (1). This compound has been shown to N N fragment readily, driven by dinitrogen expulsion and anthracene for- mation upon heating in the solid state and in solution, releasing sul- A B C fur monoxide at mild temperatures (< 100 ◦C). The generated SO was (+31.8) (+1.9) (+36.4) detected in the gas phase by mass spectrometry and rotational spec- this work: troscopy. In solution, 1 allows for SO transfer to organic molecules O S S N as well as transition metal complexes. p-Tolyl S O N O N sulfur monoxide | molecular precursor | reactive species | species of MeO2C tBu Mes2P B(C6F5)2 t astrochemical interest | microwave spectroscopy MeO2C Bu D E 1 (-41.2) n contrast to the ubiquitous and well-studied chemistry of (-2.0) (+32.0) Iearth-abundant dioxygen,(1) the chemistry of its heavier, valence-isoelectronic analogue sulfur monoxide (SO) is hardly Fig. 1. Selection of previously reported compounds capable of SO transfer (A-E) and explored and has been relegated to a niche existence, which the anthracene-based sulfinylhydrazine 1 described herein. In parentheses: computed Gibbs free energies (in kcal·mol−1 at 298.15 K, at the B3LYP-D3BJ/Def2-TZVP level is certainly due to its high reactivity: SO is unstable under of theory) for singlet SO loss and formation of the respective coproducts. ambient conditions toward disproportionation to SO2 and elemental S,(2) and eludes bulk isolation. However, in space SO can accumulate, and has been found in the interstellar synthetic transfer has been amply capitalized on.(13, 14, 26– medium,(3, 4) as well as in our solar system,(5–7) which is 31) Against this backdrop and our reasoning that an additional important to note considering that both O and S are biogenic N2 unit should further increase the energy of the ground state elements.(8) of the precursor molecule, we envisioned our synthetic target, Fragmentation of suitable molecular precursors presents 7-sulfinylamino-7-azadibenzonorbornadiene, OSN2A (1), as a potential entrypoint to explore the synthetic chemistryDRAFT for promising for SO release, simultaneously with A and dinitro- such reactive species and opens new avenues for spectroscopic characterization.(9–16) In the case of SO, a limited num- ber of synthetic precursors have been reported which allow Significance Statement thermal transfer of SO (Fig.1): Well-investigated are the chemistry of episulfoxides (A),(17–20) a thiadiazepin S-oxide The generation of highly reactive molecules under controlled (B),(21) trisulfide oxides (C),(22, 23) thianorbornadiene-S- conditions is desirable as it allows to explore synthetic chem- oxides (D),(24) and N -sulfinylamine phosphinoborane adducts istry and enables spectroscopic studies of such elusive species. (E).(25) In explaining the SO-transfer reactions of some of We report here on the synthesis and reactivity of a precursor these substances, the intermediacy of free SO is assumed, molecule that readily fragments with concomitant expulsion of while for others the precursors fragment likely via associative dinitrogen and anthracene to release the highly reactive sul- mechanisms. fur monoxide (SO), a compound of interest for both synthetic Our group has a longstanding interest in small, chemists and astrochemists. reactive species such as P2,(9–11) AsP,(12) HCP,(13) M.J., M.N., W.J.T. and C.C.C. designed research; M.J., M.N., W.J.T., M.M.D. and D.P. performed phosphinidenes(14, 15) and dimethylgermylene,(16) generated research and analyzed data, M.J., M.N. and C.C.C. wrote the paper. by mild thermal activation of suitable precursors. The driving The authors declare no conflict of interest. force of anthracene (C14H10, A) expulsion for the release of highly reactive molecules and subsequent characterization and 1To whom correspondence should be addressed. E-mail: ccummins mit.edu www.pnas.org/cgi/doi/10.1073/pnas.XXXXXXXXXX PNAS | February 27, 2018 | vol. XXX | no. XX | 1–6 gen formation. To probe this hypothesis, we compared the computed Gibbs free energies (B3LYP-D3BJ/Def2-TZVP) for N1 S1 singlet SO release from A–E and 1 (Fig.1). Indeed, the for- O1 mation of singlet SO was predicted to be thermodynamically strongly favorable only in case of 1. N2 Free SO, amenable to spectroscopy, has been generated by C1 H1 electric discharge experiments of SO-containing gases (OCS, C8 SO2),(32) or using ethylene episulfoxide at high temperature (180 ◦C to 580 ◦C).(33) To the best of our knowledge, spectro- scopic observation of free SO provided by mild thermolysis of a well-defined, solid, and easy-to-handle precursor compound has not been achieved. With 1, we present now the synthesis of such a compound that fragments at ca. 95 ◦C in the solid state and allows for direct detection of sulfur monoxide in the gas phase. In addition, examples of SO transfer with this Fig. 2. Molecular structure of 1 in the solid state with thermal ellipsoids at the 50% reagent in solution to both organic molecules and transition probability level. Selected distances [Å] and angles [◦]: N1-N2 1.353(3), N1-S1 metal complexes are outlined. 1.544(2), S1-O1 1.466(2), O1-H1 2.432 (intramolecular), H1-O1 2.489 (intermolecu- lar), N2-N1-S1 125.9(2), N1-S1-O1 118.2(1), S1-O1-H1 100.0, C1-N2-C8 96.0(2). Results and Discussion The synthesis of 1 was achieved by reaction of Carpino’s hy- bimolecular reactivity and accordingly previous studies of drazine (7-amino-7-azadibenzonorbornadiene, H2N2A),(30) molecular precursors for SO in condensed media relied on with thionyl chloride in the presence of triethyl amine chemical trapping experiments and kinetic analysis to infer its (Scheme1).(34) intermediacy. Thermolysis in a gas infrared (IR) cell under static vacuum (ca. 50 mTorr) led to the identification of SO as the major S N 2 O H2N SOCl2, NEt3 gaseous product, in accord with loss of SO and subsequent N N Et2O disproportionation chemistry, but did not provide conclusive (83%) evidence for the intermediacy of SO (see SI). 1 For the detection of such short-lived species upon thermal decomposition of molecular precursors, molecular beam mass Scheme 1. Synthesis of 1. spectrometry (MBMS) has proven to be a valuable tool to analyze unstable gaseous products evolved from molecular Compound 1 was isolated as a pale-yellow solid in very precursors.(10, 13, 15) In case of thermolysis of 1 in the MBMS 1 good yield (83%). In solution (benzene-d6), the H NMR sample chamber, A,N2 and SO were observed (Fig.3). The chemical shift of the bridgehead protons at δ = 6.22 ppm, differing results of the MBMS and gas IR experiments can located 1.48 ppm downfield from that of H2N2A, is reflective be rationalized based upon differences in pressure when 1 of the strongly withdrawing effect of the sulfinyl group. Color- is thermolyzed and the large disparity in the rate of data less crystals grew from a concentrated toluene solution of 1 acquisition between the two methods (IR spectrum acquisition layered with diethyl ether at –35 ◦C, and were subjected to required several seconds). X-ray diffraction analysis. The metrical data of the NNSO chain of 1 in the solid state (Fig.2) compare well with the reported structures of sulfinyl hydrazines.(35–37) One bridge- 140 N + (28 m/z) head proton of the azanorbornadiene scaffold weakly interacts 2 SO+ (48 m/z) with the terminal oxygen atom, leading to a synperiplanarDRAFT120 + (178 m/z) i A NNSO arrangement as observed for Pr2N2SO.(36) A thermogravimetric analysis (TGA) was performed to 100 ◦ probe the potential release of SO.