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Home , Singlet oxygen, Sulfur monoxide

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

Maximilian Joosta, Matthew Navaa, Wesley J. Transuea, Marie-Aline Martin-Drumelb, Michael C. McCarthyc, David Pattersond,1, and Christopher C. Cumminsa,2

aDepartment of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139; bInstitut des Sciences Moleculaires´ d’Orsay, CNRS, Universite´ Paris–Sud, Universite´ Paris-Saclay, 91405 Orsay, France; cHarvard-Smithsonian Center for Astrophysics, Atomic and Molecular Physics Division, Cambridge, MA 02138; and dDepartment of Physics, Harvard University, Cambridge, MA 02138

Contributed by Christopher C. Cummins, April 19, 2018 (sent for review March 8, 2018); reviewed by Norman C. Craig and Douglas W. Stephan)

Sulfur monoxide (SO) is a highly reactive and thus, Free SO, amenable to , has been generated by eludes bulk isolation. We report here on synthesis and reactiv- electric discharge experiments of SO-containing gases (OCS, ity of a molecular precursor for SO generation, namely 7-sulfin- SO2) (32) or using episulfoxide at high temperature ylamino-7-azadibenzonorbornadiene (1). This compound has (180 ◦C to 580 ◦C) (33). To the best of our knowledge, spec- been shown to fragment readily driven by dinitrogen expulsion troscopic observation of free SO provided by mild thermolysis and anthracene formation on heating in the solid state and in of a well-defined, solid, and easy-to-handle precursor compound solution, releasing SO at mild temperatures (<100 ◦C). The gen- has not been achieved. With 1, we present now the synthesis of erated SO was detected in the gas phase by MS and rotational such a compound that fragments at approximately 95 ◦C in the spectroscopy. In solution, 1 allows for SO transfer to organic solid state and allows for direct detection of SO in the gas phase. as well as transition metal complexes. In addition, examples of SO transfer with this reagent in solu- tion to both organic molecules and transition metal complexes microwave spectroscopy | reactive intermediate | molecular precursor | are outlined. | Results and Discussion 1 n contrast to the ubiquitous and well-studied chemistry of The synthesis of was achieved by reaction of Carpino’s A Iearth-abundant dioxygen (1), the chemistry of its heavier, hydrazine (7-amino-7-azadibenzonorbornadiene, H2N2 ) (30) valence-isoelectronic analogue sulfur monoxide (SO) is hardly with thionyl chloride in the presence of triethyl amine (Scheme explored and has been relegated to a niche existence, which is 1) (34). Compound 1 was isolated as a pale yellow solid in very good certainly due to its high reactivity: SO is unstable under ambient 1 yield (83%). In solution (-d6), the H NMR chemical conditions toward disproportionation to SO2 and elemental S (2) δ and eludes bulk isolation. However, in space, SO can accumulate shift of the bridgehead protons at = 6.22 ppm, located 1.48 ppm A and has been found in the (3, 4) as well as in downfield from that of H2N2 , is reflective of the strongly with- our solar system (5–7), which is important to note considering drawing effect of the sulfinyl group. Colorless crystals grew from a concentrated toluene solution of 1 layered with diethyl ether that both O and S are biogenic elements (8). ◦ Fragmentation of suitable molecular precursors presents a at −35 C and were subjected to X-ray diffraction analysis. potential entry point to explore the synthetic chemistry for such reactive species and opens new avenues for spectroscopic charac- Significance terization (9–16). In the case of SO, a limited number of synthetic precursors have been reported that allow thermal transfer of SO The generation of highly reactive molecules under controlled (Fig. 1): well-investigated are the chemistries of episulfoxides (A) conditions is desirable, as it allows exploration of synthetic (17–20), a thiadiazepin S- (B) (21), trisulfide (C) (22, chemistry and enables spectroscopic studies of such elusive 23), thianorbornadiene-S-oxides (D) (24), and N-sulfinylamine species. We report here on the synthesis and reactivity of a phosphinoborane adducts (E) (25). In explaining the SO transfer precursor molecule that readily fragments with concomitant reactions of some of these substances, the intermediacy of free expulsion of dinitrogen and anthracene to release the highly SO is assumed, while for others, the precursors fragment likely reactive sulfur monoxide, a compound of interest for both via associative mechanisms. synthetic chemists and astrochemists. Our group has a longstanding interest in small reactive species, such as P2 (9–11), AsP (12), HCP (13), phosphinidenes Author contributions: M.J., M.N., W.J.T., and C.C.C. designed research; M.J., M.N., W.J.T., (14, 15), and dimethylgermylene (16), generated by mild ther- M.-A.M.-D., M.C.M., and D.P. performed research; M.J., M.N., W.J.T., M.-A.M.-D., M.C.M., mal activation of suitable precursors. The driving force of and D.P. analyzed data; and M.J., M.N., W.J.T. and C.C.C. wrote the paper. anthracene (C14H10, A) expulsion for the release of highly Reviewers: N.C.C., Oberlin College; and D.W.S., University of Toronto. reactive molecules and subsequent characterization and syn- The authors declare no conflict of interest. thetic transfer has been amply capitalized on (13, 14, 26–31). Published under the PNAS license. Against this backdrop and our reasoning that an additional N2 Data deposition: The crystallography, atomic coordinates, and structure factors have unit should further increase the energy of the ground state been deposited in the Cambridge Structural Database to www.ccdc.cam.ac.uk/Solutions/ of the precursor molecule, we envisioned our synthetic tar- CSDSystem/Pages/CSD.aspx (accession nos. 1567576 and 1567577). 1 get, 7-sulfinylamino-7-azadibenzonorbornadiene, OSN2A (1), as Present address: Department of Physics, University of California, Santa Barbara, CA promising for SO release simultaneously with A and dinitrogen 93106. formation. To probe this hypothesis, we compared the computed 2 To whom correspondence should be addressed. Email: [email protected]. Gibbs free energies for singlet SO release from A–E and 1 (Fig. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. 1). Indeed, the formation of singlet SO was predicted to be 1073/pnas.1804035115/-/DCSupplemental. thermodynamically strongly favorable only in case of 1. Published online May 17, 2018.

5866–5871 | PNAS | June 5, 2018 | vol. 115 | no. 23 www.pnas.org/cgi/doi/10.1073/pnas.1804035115 Downloaded by guest on September 23, 2021 Downloaded by guest on September 23, 2021 eopsto fmlclrpeusr,mlclrba MS beam molecular precursors, molecular of decomposition Appendix). conclusive (SI SO provide of not intermediacy the did for it evidence dispro- however, SO subsequent and chemistry; of SO of portionation identification loss with the accord in to product gaseous led mtorr) 50 mately intermediacy. trapping its chemical infer on to pre- analysis relied kinetic media molecular and condensed experiments of in SO studies for previous cursors accordingly, bimolecular minimize and to vacuum reactivity, high in observed and generated the in culminating media self-reaction SO condensed rapid of its in formation to difficult due phase is of gas SO the observation of and spectroscopic Detection sought. direct was experiment, SO TGA the Appendix). with (SI released were respectively) %, wt 19 and (11 0w a bevd uprigtento htN that notion the supporting 95 observed, At was SO. % wt of 30 release potential the edn oasneilnrNS ragmn sosre for observed as arrangement NNSO synperiplanar atom, i a sulfinyl azanorbor- to terminal of the the leading with of structures interacts proton weakly reported scaffold bridgehead nadiene the of One with (35–37). chain well hydrazines NNSO compare the 2) of (Fig. data metrical The the of formation parentheses. and in B3LYP-D3BJ loss shown SO are the singlet coproducts for using respective set) performed basis Def2-TZVP were and calculations functional theory functional sity os tal. et Joost kilocalories· (in energies free Gibbs Computed (A–E fer 1. Fig. Pr o h eeto fsc hr-ie pce nthermal on species short-lived such of detection the For (approxi- vacuum static under cell IR gas a in Thermolysis only typically is SO self-reaction, for propensity the to Due from SO of evolution the confirm to Eager hrorvmti nlss(G)wspromdt probe to performed was (TGA) analysis thermogravimetric A 2 N 2 n h nhaeebsdsulfinylhydrazine anthracene-based the and ) eeto fpeiul eotdcmonscpbeo Otrans- SO of capable compounds reported previously of Selection O(36). SO A D 2 2SO 2S S n oyufie (Eq. polysulfides and 2 O 2 cee1. Scheme O 2

SO + → S SO 2 O → 2 2 S + ytei of Synthesis E SO B 3 2 S + ◦ ,ams oseetof event loss mass a C, 2 8 39): 38, (2, 1) 2 O. 1. −1 1 t281 ;teden- the K; 298.15 at ntesldstate solid the in 1 1 ecie herein. described 2 naccordance in stemajor the as C 2 n SO and [1] h w ehd I pcrmaqiiinrqie several required acquisition between spectrum acquisition data (IR of methods rate seconds). the two when in rational- pressure disparity be the large can in the experiments differences IR and on gas based and of MBMS ized the thermolysis of unsta- of results (10, analyze case precursors to molecular In chamber, tool from valuable 15). evolved a 13, products be gaseous to ble proven has (MBMS) 2.432 O1-H1 96.0(2). 1.466(2), C1-N2-C8 angles 100.0, S1-O1 S1-O1-H1 N1-S1-O1 and 118.2(1), 125.9(2), 1.544(2), N2-N1-S1 (angstroms) (intermolecular), N1-S1 2.489 distances H1-O1 (intramolecular), Selected 1.353(3), level. N1-N2 probability (degrees): 50% the at 2. Fig. oeua tutr of structure Molecular N A, 2 n Owr bevd(i.3.Tediffering The 3). (Fig. observed were SO and , PNAS i.3. Fig. | 1 ue5 2018 5, June ntesldsaewt hra ellipsoids thermal with state solid the in BSof MBMS 1 1. | nteMM sample MBMS the in o.115 vol. 1 sthermolyzed is | o 23 no. | 5867

CHEMISTRY Fig. 4. Microwave spectrum of the compounds released during the thermal heating of 1. Transitions belonging to 1, SO2, SO, and S2O are indicated in green, orange, blue, and pink, respectively, and the black portions depict baseline and a few unassigned lines. The spectrum showing the SO transition was the result of a deeper integration, and an additional spectrum was recorded in the same conditions but under the influence of an external magnetic field (red) to confirm the open shell of the carrier of the lines assigned to SO. In presence of the magnetic field, lines of SO are not visible (as expected for a species with unpaired electrons in a 3Σ ground electronic state), while the transitions of 1 (closed shell) are unaffected.

The direct observation of SO via MS encouraged us to attempt 42,591.23 MHz is out of range of the microwave instrument used its characterization by microwave spectroscopy as well. The rota- (12,000–17,500 MHz) (46). The observation of open shell and tional transitions of SO have been previously studied in detail for closed shell singlet electronic states of SO should be feasible ground electronic as well as the first excited state (40, 41). Com- pound 1 was thermolyzed in a specially constructed solid sample holder directed at the entrance of a buffer-gas cell (42). Gases evolved from 1 during heating enter the buffer-gas cell, where they collide with gaseous helium at approximately 10 K. The collisions of the evolved gases with the helium rapidly cool the molecules, which results in the rotational and vibrational cool- ing of the sample, simplifying their rotational spectra but also inhibiting bimolecular reactivity. After introduction and cooling of the fragment molecules, a microwave spectrum of the mixture was recorded (Fig. 4). Next to characteristic transitions corresponding to S2O (21,2 ← 30,3; 13,258.94 MHz) (43) and SO2 (11,1 ← 20,2; 3 − 12,256.58 MHz) (44), Σ SO (12 ← 11; 13,043.7 MHz) (40) was 3 − detected. As for O2, the triplet ( Σ ) is the lowest-energy config- uration for SO, with the closed shell (1∆) and open shell (1Σ+) singlets lying 18.2 kcal·mol−1 (1 kcal = 4.18 kJ) and 30.1 ·mol−1 above the ground state, respectively (45). The transition for 3Σ− SO was split due to Earth’s magnetic field and disappeared out of the spectral window in the presence of a strong external mag- Fig. 5. Computed mechanism for the fragmentation of 1 as revealed netic field. We are unable to verify the presence of the closed by quantum chemical calculations carried out using the RI-B2PLYP-D3(BJ) shell singlet SO, because the lowest-frequency transition at density functional and the Def2-TZVP basis set.

5868 | www.pnas.org/cgi/doi/10.1073/pnas.1804035115 Joost et al. Downloaded by guest on September 23, 2021 Downloaded by guest on September 23, 2021 n ftescn – od hsi ieydet h NNSO the to due N–S likely the is of This bond. breaking collapsed C–N structure with second the way the products: asynchronous of final and concerted, stationary the further a to no in route revealed state en C–N transition points the this energy of minimum across The breaking moiety. path the sulfinylamino the to to opposed corresponding bond A state set. transition and gle SO basis singlet Def2-TZVP of loss N the concerted with RI-B2PLYP- and fragmentation the single-step functional using density out carried D3(BJ) were calculations from chemical evolved are gases critical what how to illustrate are also conditions but thermolysis used the the techniques in the of differences nature The tary of Appendix ). thermolysis (SI of phase products gas observed the in of and structure of from state the geometry recovered that imply the those ture on and experimen- based constants the calculations rotational between obtained differences small tally Resonance The Double (50). Microwave of Automated technique the spectrum of rotational variant pure a using The phase. gas the of (49). holder sample the of walls colli- heated for the SO the an singlet to of However, relaxation propensity sional Appendix). the (SI is phase complication gas reasonable additional apparatus a the assuming our in ms velocity 2–3 with SO of molecular time detection Singlet 13.6 flight 48). for approximate calculated an (47, long-lived with value; respectively sufficiently (exp. (calculated), thus ms ms is 450 7 deter- and were approximately species ms) be these of to lifetimes mined radiative the principle: in 25 benzene, eq), 70 (10 benzene, eq), (5 1,3-cyclohexadiene 70 benzene, 2. Scheme os tal. et Joost 2 ocmeto h hroyi ehns of mechanism thermolysis the on comment To transitions rotational the identify to able were we addition, In 1 rmteatrcn ltomwsfud etrn sin- a featuring found, was platform anthracene the from tef hc atal rnfre ihu rgetto into fragmentation without transferred partially which itself, cee3. Scheme rnfro Ofrom SO of Transfer ◦ ,2 qatttv) (ii (quantitative); h 24 C, rnfro Ofrom SO of Transfer ◦ ,1 (55%). h 16 C, 3 Σ − (i 1: pnsaewt hr ois uhas such bodies, third with state 3,5-di-tert ) 1 M na) 80 (neat), DMB ) ◦ snal dnia ntesolid the in identical nearly is 1 ,2 5%;(iv (59%); h 24 C, orteimcomplexes. to 1 ihih h complemen- the highlight 1 btl12qioe( eq), (1 -butyl-1,2-quinone ntecytlstruc- crystal the in ◦ ,1 6%;(iii (60%); h 16 C, 1 norbornadiene ) a analyzed was quantum 1, 1. ) rdcino ufr h oepoutosral by to with due observable likely product was yellow sole spectroscopy to The colorless sulfur. from of change production color a by visually for- the state: singlet its in the released of be of mation indeed case may In SO state. process, transition the bonds of two in which fragmentation reformed at and constric- atom(s) coarctate broken The the are cycle. at located constricted is a cyclic point tion of a topology in with transition-state occur rearrangements a bonds bond describe of processes coarctate forming coarctate a manner, and as breaking reactions, pericyclic concerted classified for While the be (52). Herges by may defined as process reaction fragmentation bonds of sur- this making energy and in potential breaking quasisimultaneous the This on (51). minimum face a being not intermediate fti in a ufiin ola ofraino 7-oxo-7- of formation to using reactions unsuccessful: olefins was other to to or transfer sufficient SO locked Thermal (23). was (59%) the thianorbornene to to this SO due of of Likely transfer successful. cisoid Similarly, (60%). was observed 1,3-cyclohexadiene was product 80 fer at reaction the decomposi- performing to of led of Heating (DMB) tion 2,3-dimethyl-1,3-butadiene 55). of 54, eq) 21–24, (5 (18, 1,3- to (53). 70 sulfite known to corresponding as Compound h the to such 24 quantitatively 2). trapping, for (Scheme 3,5-di-tert-butyl-1,2-quinone SO with olefins for suitable and compounds quinones focused organic We on used. were first partners reaction representative various of value calculated of barrier kcal·mol activation an cor- to barrier responded This spectroscopy. ultraviolet–visible by determined d of reactivity the explored we 5). (Fig. material starting the to respect with H ovn oeuehv enoitdfrcaiy eetddistances Selected Ru1-N 1.503(2), clarity. S1-O1 118.17(11). for 2.0282(8), Ru1-S1-O1 (average); Ru1-S1 omitted sepa- 2.044 (degrees): been and angles cocrystallized have and cation one (angstroms) molecule as well solvent SO-coordinated as THF cation level. tris(1,2-dimethoxyethane) probability sodium rate 50% the at 6. Fig. 6 eea Orlaigpeusr r aal fS addition SO of capable are precursors SO-releasing Several from transfer SO of possibility the assess To state, solid the in thermolysis on release SO of evidence With nasae ueldt t eopsto,wihwsindicated was which decomposition, its to led tube sealed a in k obs ofraino h obebn,js vfl excess fivefold a just bond, double the of conformation oeua tutr of structure Molecular 1 −1 oiefrain oee,when However, formation. thiophene-S-oxide without (2.743 = N A, codn oteErn qain iia othe to similar equation, Eyring the to according 2 n ige Oi aoe by favored is SO singlet and , ohNaosaecacaeaos nthis In atoms. coarctate are atoms N both 1, hsrato bydafis-re aelaw rate first-order a obeyed reaction This A. ∆G ± PNAS 0.436) calc ‡ (80 | 2 1 ue5 2018 5, June ntesldsaewt hra ellipsoids thermal with state solid the in × ◦ nslto.Heating solution. in ◦ C) nna M,ti Otrans- SO this DMB, neat in C 10 33kcal·mol 23.3 = −4 ∆ s −1 | G o.115 vol. ‡ t80 at (80 sibn,styrene, cis-stilbene, 04kcal·mol −40.4 1 1 ◦ C) oa acceptor, an to iha excess an with ◦ | ◦ 1 −1 nTFas THF in C 1 oconvert to C o 23 no. 26.55(11) = a heated was nbenzene- in . 1 NMR H | 5869 −1

CHEMISTRY or phenyl in excess did not provide the respective SO due to the electron-rich porphyrinogen ligand. Coor- addition products. Contrasting reactivity of 1 toward norbor- dination of the sodium cations to the oxygen atom of ligated SO nadiene yielded the corresponding thiirane (55%): addition of may enhance this effect. SO occurred at 25 ◦C (16 h), well below the temperature We did not observe selective reaction of 1 with N-heterocyclic required for fragmentation of 1, and thus, it does not involve carbenes to give the corresponding sulfines. However, heating a t free SO but rather, proceeds via an associative mechanism. mixture of 1 and a (PPh3 or P Bu3) in benzene gave The SO transfer from 1 to transition metal complexes also about equimolar mixtures of the respective phosphine oxides and occurs through an associative mechanism (Scheme 3). Stirring phosphine sulfides via formal splitting of SO (25). ∗ ∗ 5 a solution of 1 and [RuCl(Cp )(PCy3)] (Cp = η -C5Me5) in THF at 25 ◦C for 30 min led to a gradual color change Conclusion from blue to red–brown. After removal of A, the known SO We have shown here a well-controlled synthetic route to SO ∗ ruthenium complex [RuCl(Cp )(SO)(PCy3)] was isolated (82%) by thermal decomposition of 1. Taking reactivity, computational (56, 57). Compound 1 also reacted with the anionic ruthenium studies, and spectroscopic detection of 3Σ− SO into considera- 1 3 − complex [Na(DME)3]2 [Ru(N4Me8)] (H4N4Me8 = octamethyl- tion, it is believed that 1 generates ∆ SO on thermolysis. Σ porphyrinogen) (58) to give [Na(DME)3][Ru(N4Me8)(SO)] (2), SO is detected by microwave spectroscopy, possibly originating obtained in 51% yield after removal of anthracene and selective from a small amount of 1∆ SO that has had enough time to crystallization as a brown–orange solid. phosphoresce into the lower-energy triplet ground state. Regard- Cooling a solution of this compound in THF and DME to less of the spin state of the SO evolved from 1, this study firmly −35 ◦C yielded dark orange crystalline blocks. An X-ray diffrac- establishes that SO is in fact released from the molecular pre- tion analysis revealed a dimeric structure, with sodium ions cursor, illustrating the power of synthesis in combination with 2− bridging two units of the [Ru(N4Me8)(SO)] platform (Fig. 6). spectroscopy to shed on reactive intermediates of general These units feature the ruthenium center in a square-pyramidal importance. environment, in which the SO ligand occupies the apical posi- tion. The Ru–S bond [2.0282(8) A]˚ is slightly shorter and the S–O Methods bond [1.503(2) A]˚ is slightly longer than in a related Ru(II)-SO Experimental and computational details and crystallographic information ˚ are included in SI Appendix. Computed atomic coordinates are included in complex [2.0563(11) and 1.447(3) A, respectively] (59). Termi- Datasets S1–S4. nal SO transition metal complexes generally show a strong SO −1 stretch around 1,046–1,126 cm (55, 56, 59, 60). Analysis of ACKNOWLEDGMENTS. We thank Prof. Robert Field (Massachusetts Institute the IR spectrum of 2 revealed a band at 1,021 cm−1 assigned of Technology) for inspiring discussions. This material is based on research supported by National Science Foundation (NSF) Grant CHE-1664799. M.J. to the SO stretching vibration. Both this notable red shift with thanks the Alexander von Humboldt Foundation for a Feodor Lynen regard to values for related compounds as well as the metrical Postdoctoral Fellowship. D.P. acknowledges support from NSF Instrument data for 2 are in accord with strong backbonding from Ru to the Development for Biological Research Program NSF Award 134076–5101408.

1. Wiberg E, Wiberg N, Holleman AF (2001) (Academic, San Diego). 21. Chow YL, Tam JNS, Blier JE, Szmant HH (1970) Mechanism of sulphur monoxide 2. Herron JT, Huie RE (1980) Rate constants at 298 K for the reactions SO+SO+M→ extrusion. J Chem Soc D, 1604–1605. (SO) 2+M and SO+(SO)2 →SO2+S2O. Chem Phys Lett 76:322–324. 22. Grainger RS, Procopio A, Steed JW (2001) A novel recyclable sulfur monoxide transfer 3. Gottlieb CA, Gottlieb EW, Litvak MM, Ball JA, Penfield H (1978) Observations of reagent. Org Lett 3:3565–3568. interstellar sulfur monoxide. Astrophys J 219:77–94. 23. Grainger RS, Patel B, Kariuki BM, Male L, Spencer N (2011) Sulfur monoxide transfer 4. Sakai N, et al. (2014) Change in the chemical composition of infalling gas forming a from peri-substituted trisulfide-2-oxides to dienes: Substituent effects, mechanistic disk around a protostar. Nature 507:78–80. studies and application in thiophene synthesis. J Am Chem Soc 133:5843–5852. 5. Na CY, Esposito LW, Skinner TE (1990) International Ultraviolet Explorer observation 24. Nakayama J, Tajima Y, Xue-hua P, Sugihara Y (2007) [1 + 2] Cycloadditions of sulfur of SO2 and SO. J Geophys Res 95:7485–7491. monoxide (SO) to and alkynes and [1 + 4] cycloadditions to dienes (polyenes). 6. Russell CT, Kivelson MG (2000) Detection of SO in ’s Exosphere. Science 287:1998– Generation and reactions of singlet SO? J Am Chem Soc 129:7250–7251. 1999. 25. Longobardi LE, Wolter V, Stephan DW (2015) Frustrated Lewis pair activation of an 7. Boissier J, et al. (2007) Interferometric imaging of the sulfur-bearing molecules H2S, N-sulfinylamine: A source of sulfur monoxide. Angew Chem Int Ed 54:809–812. SO, and CS in comet C/1995 O1 (Hale-Bopp). Astron Astrophys 475:1131–1144. 26. Corey EJ, Mock WL (1962) Chemistry of diimide. III. transfer to multiple 8. National Research Council (1990) The Search for ’s Origins: Progress and Future bonds by dissociation of the diimide-anthracene adduct, anthracene-9,10-biimine. J Directions in Planetary and Chemical Evolution (National Academies, Am Chem Soc 84:685–686. Washington, DC), pp 21–55. 27. Wasserman HH, Scheffer JR (1967) reactions from photoperoxides. J 9. Piro NA, Figueroa JS, McKellar JT, Cummins CC (2006) Triple-bond reactivity of Am Chem Soc 89:3073–3075. diphosphorus molecules. Science 313:1276–1279. 28. Baldwin JE, Lopez RCG (1982) The generation and trapping of thiobenzaldehyde and 10. Velian A, et al. (2014) A retro Diels–Alder route to diphosphorus chemistry: Molecu- thioacetaldehyde. J Chem Soc Chem Commun 1029–1030. lar precursor synthesis, kinetics of P2 transfer to 1,3-dienes, and detection of P2 by 29. Appler H, Gross LW, Mayer B, Neumann WP (1985) Die chemie der schweren carben- molecular beam mass spectrometry. J Am Chem Soc 136:13586–13589. analogen R2M, M = Si, Ge, Sn. J Organomet Chem 291:9–23. 11. Velian A, Cummins CC (2015) Synthesis and characterization of P2N3-: An aromatic 30. Carpino LA, et al. (1988) Synthesis, characterization, and thermolysis of 7-Amino-7- ion composed of and . Science 348:1001–1004. azabenzonorbornadienes. J Org Chem 53:2565–2572. 12. Spinney HA, Piro NA, Cummins CC (2009) Triple-bond reactivity of an AsP com- 31. Courtemanche MA, Transue WJ, Cummins CC (2016) Phosphinidene reactivity of a plex intermediate: Synthesis stemming from molecular , As4. J Am Chem Soc transient P≡N complex. J Am Chem Soc 138:16220–16223. 131:16233–16243. 32. Sanz ME, McCarthy MC, Thaddeus P (2003) Rotational transitions of SO, SiO, and 13. Transue WJ, et al. (2016) A molecular precursor to phosphaethyne and its applica- SiS excited by a discharge in a Supersonic molecular beam: Vibrational tempera- tion in synthesis of the aromatic 1,2,3,4-phosphatriazolate anion. J Am Chem Soc tures, Dunham coefficients, Born–Oppenheimer breakdown, and hyperfine structure. 138:6731–6734. J Chem Phys 119:11715–11727. 14. Velian A, Cummins CC (2012) Facile synthesis of Dibenzo-7λ3-phosphanorbornadiene 33. Saito S (1969) Detection of sulfur monoxide in the pyrolysis of ethylene episulfoxide derivatives using anthracene. J Am Chem Soc 134:13978–13981. by microwave spectroscopy. Bull Chem Soc Jpn 42:667–670. 15. Transue WJ, et al. (2017) On the mechanism and scope of phosphinidene transfer from 34. Michaelis A (1889) Uber¨ anorganische derivate des phenylhydrazins. Ber Dtsch Chem Dibenzo-7-phosphanorbornadiene compounds. J Am Chem Soc 139:10822–10831. Ges 22:2228–2233. 16. Velian A, Transue WJ, Cummins CC (2015) Synthesis, characterization, and thermolysis 35. Gieren A, Dederer B (1977) X-ray structure analysis of N-phenyl-N0-sulfinyl-hydrazine. of Dibenzo-7-dimethylgermanorbornadiene. Organometallics 34:4644–4646. Angew Chem Int Ed 16:179–180. 17. Hartzell GE, Paige JN (1966) Ethylene episulfoxide. J Am Chem Soc 88:2616–2617. 36. Cerioni G, Piras P, Marongiu G, Macciantelli D, Lunazzi L (1981) Conformational 18. Dodson RM, Sauers RF (1967) Sulphur monoxide: Reaction with dienes. Chem studies by dynamic nuclear magnetic resonance spectroscopy. Part 21. Structure, Commun, 1189–1190. conformation, and stereodynamics of sulphinylhydrazines. J Chem Soc Perkin Trans 19. Abu-Yousef IA, Harpp DN (1995) A useful precursor for sulfur monoxide transfer. 2:1449–1453. Tetrahedron Lett 36:201–204. 37. Schanda F, Gieren A, Filhol A (1984) Refinement of the structure of N-phenyl-N0- 20. Abu-Yousef IA, Harpp DN (1997) Effective precursors for sulfur monoxide formation. sulfinylhydrazine, C6H6N2OS, at 120(1) K with neutron data. Acta Crystallogr Sect C J Org Chem 62:8366–8371. Cryst Struct Commun 40:306–308.

5870 | www.pnas.org/cgi/doi/10.1073/pnas.1804035115 Joost et al. Downloaded by guest on September 23, 2021 Downloaded by guest on September 23, 2021 7 id ,Fn H itrR ae 18)Rdaielftm n unhn of quenching and lifetime Radiative (1983) F Zabel R, Winter EH, Fink J, Wildt 47. M b The 46. (1968) R Colin 45. 4 lebokA,DmnsA(96 emnefc nSO in effect Zeeman (1976) A Dymanus AW, Ellenbroek 44. 8 lt ,Mra M eeihf D esB,BekrR 18)Cluaino spin- of Calculation (1984) RJ Buenker BA, Hess SD, Peyerimhoff CM, Marian R, Klotz 48. S of spectroscopy Rotational (2006) via beams al. molecular et and S, atomic Thorwirth Intense 43. (2009) JM structure Doyle J, rotational Rasmussen and D, Patterson spectrum microwave 42. The (1976) FC Lucia equi- . De SO WW, the Clark of major 41. spectrum the Microwave as (1967) identification Y Morino Its E, I. Hirota monoxide. T, Disulfur Amano (1956) 40. RJ Myers DJ, Meschi (S 39. monoxide disulfur Reversible (2004) al. et J, Nakayama 38. os tal. et Joost oeua pcrsoy DS sflto o srnmr n spectroscopists. and astronomers for tool Struct Mol useful A CDMS: Spectroscopy, Molecular SO(b spectroscopy. stpmr,adtesbmliee-aespectrum. sub-millimeter-wave the and isotopomers, obde aitv rniin sn orltdwvfntos ieie fb of Lifetimes wavefunctions: correlated a using transitions radiative forbidden cooling. buffer-gas neon 342. the of hyperfine magnetic and constant coupling constants. structure quadrupole electric distance, S-O librium monoxide.” “sulfur Schenk’s in constituent S (SO of Disproportionation reaction. Alder 1 le S,Schl HSP, uller ∆ ¨ 2 n eciiiso 2 n S3. and S2O of reactivities and ) 1 ttsi O in States Σ 1 + ∆ ,υ 742:215–227. and 0 0). = hmPy Lett Phys Chem 2 drF ttk ,WneisrG(05 h oon aaaefor Database Cologne The (2005) G Winnewisser J, Stutzki F, oder 3 ¨ S , Σ hmPhys Chem 2 1 hsScJpn Soc Phys J lcrncsae fslu monoxide. sulfur of states Electronic n SO. and Σ + –X e Phys J New 3 Σ hmPhys Chem 80:167–175. 42:303–306. − adsse fSO. of system band 22:399–412. 11:055018. mCe Soc Chem Am J 2 89:223–236. otihoOoe(S trithio- to O mCe Soc Chem Am J 126:9085–9093. a Phys J Can o Struct Mol J 2 :Vbainlsatellites, Vibrational O: 2 78:6220–6223. o Spectrosc Mol J yba ae Zeeman maser beam by 2 )frigretro-Diels- O)-forming 3 46:1539–1546. n ufrdioxide sulfur and ) 795:219–229. 60:332– 1 Σ 33 + S J , 0 cekW,Lise ,Brck 18)Saiiaino ufrmnxd by monoxide sulfur of Stabilization (1984) C Burschka J, Leissner WA, Schenk N(SPR 60. with complexes Ruthenium (2000) al. et WH, chemistry Leung Redox nitrides: Ruthenium 59. (2001) C Floriani R, Scopelliti E, Solari molecules: L, sulfur-containing Bonomo small 58. of chemistry coordination The (2011) WA Schwefel- Schenk des 57. Ruthenium-Halbsandwichkomplexe Chirale (1989) U Karl WA, mit Schenk Bis(triphenylphosphan)-Komplexe (1992) 56. IP Lorenz A, Neher O, thiirane the Heyke of Kom- Stereochemistry 55. chemistry. seinen monoxide Sulfur aus (1973) DM Schwefelmonoxid Lemal P, von Chao Freisetzung 54. (1987) J Leißner WA, Schenk 53. rules. Stereochemical reactions: pseudocoarctate and Coarctate (2015) R Herges 52. nitric of Reactions (1996) M Neurock A, Citra GD, Brabson (2016) P, Hassanzadeh KN L, Andrews Crabtree BA, 51. McGuire D, Patterson MC, episulfoxide McCarthy ethylene MA, of pyrolysis Martin-Drumel the in 50. monoxide sulfur of Detection (1969) S Saito 49. oriaint rniinmetals. transition to coordination 423–430. Trans, Dalton Soc, group. Ru–Nitrido the of photolability and perspective. personal A Schwefeldioxids. und monoxids Schwefeloxid-Liganden. reaction. oxide-diene [1]. plexverbindungen Chem calculations theory functional density SNO and and SNO, spectra for identify species. sulfur to with oxide tool A spectroscopy: resonance compounds. chemical characterize double microwave Automated spectroscopy. microwave by 80:11869–11876. + SO n NOi oi . solid in SNNO and SSNO, , mCe Soc Chem Am J aufrc hmSci Chem B Naturforsch Z atnTrans Dalton nr lgChem Allg Anorg Z PNAS ulCe o Jpn Soc Chem Bull aufrc hmSci Chem B Naturforsch Z | ne hmItEd Int Chem Angew hmPhys Chem J ue5 2018 5, June 40:1209–1219. 95:920–922. ne hmItEd Int Chem Angew 608:23–27. 42:667–670. 144:124202. 42:799–800. hsChem Phys J | o.115 vol. 23:806–807. 44:988–989. 2 ) 2 - 100:8273–8279. R=P rPr or Ph = (R 40:2529–2531. | o 23 no. i ). | Chem J Org J 5871

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