1. SPECTROSCOPY OF AND PHOTOINDUCED ELECTRON TRANSFER IN THE COMPLEXES OF C 2 H 4 WITH I AND I 2 Lisa George, Aimable Kalume, and Scott A. Reid Department of Chemistry, Marquette University, Milwaukee, WI 53233, USA 1

2. Background and literature review The Electron- Donor-Acceptor Complexes (EDA)of halogens with π-electron donors such as Ethylene are model systems to understand the mechanism of electrophilic addition and substitution reactions. Stereoselectivity of photoinitiated free radical addition reactions involving iodine and bromine to ethylene has received much attention. 1,2 Ihee and co-workers obtained evidence for the formation of symmetrically bridged C 2 H 4 ···I radical using time-resolved X-ray diffraction techniques. 3,4 We report the photoinduced electron transfer in the C 2 H 4 ···I 2 complex, leading to the formation of bridged intermediate C 2 H 4 ···I, trapped in Ne matrix and interrogated spectroscopically. 1: P. S. Skell et al, J. Am. Chem. Soc. 1964, 86, 2956. 2: G. Maier et al, Liebigs Annalen/Recueil, 1997, 317. 3: H. Ihee et al. Science, 2005, 309, 1223. 4: H. Ihee et al. J. Phys. Chem. A, 2012, 116, 2713. 2

3. Experimental and Computational Details C 2 H 4 /I 2 //Ne (1:2:1000) at 5K (Mixture of C 2 H 4 :Ne (1:1000) passing over I 2 held at 40°C) Pulsed deposition, 1ms pulse, 5hz, 1-2h deposition, IR and UV/Vis spectra Photolysis of C 2 H 4 ···I 2 at 240nm or 450nm, using Nd:YAG (Continuum NY- 61) pumped dye laser system (Lambda Physik Scanmate 2E). Photolysis of C 2 H 4 ···I at 355nm (Nd: YAG (Continuum Minilite) Geometry optimization: M062x, MP2(aug-cc-pVTZ, aug-cc-pVTZpp ) (Gaussian 09) Electronic absorption and oscillator strength: TD-DFT ( M06/ Sadlej-pVTZ) 3

4. UV/Vis spectrum of C 2 H 4 ···I 2 complex C 2 H 4 /I 2 //Ne (1:2:1000) matrix following pulsed deposition on a CaF 2 window at 5 K, together with TD-DFT predicted electronic absorptions of the ethylene-I 2 complex at the M06/Sadlej-pVTZ level. 4 247 450

5. UV spectrum of C 2 H 4 ···I 2 complex following photolysis at 240nm C 2 H 4 /I 2 //Ne (1:2:1000) matrix following pulsed deposition on a CaF 2 window at 5 K followed by photolysis at 240 nm, together with TD-DFT predicted electronic absorptions at M06/Sadlej-pVTZ. 5 366 450

6. Photolysis of C 2 H 4 ···I complex at 355nm 6 366 247

7. Infrared spectrum of C 2 H 4 ···I 2 complex following photolysis at 240nm 7 1145 953 1342 1442 1613 ʋ7 CH 2 wag ʋ3CH 2 deform. ʋ12 CH 2 deform. ʋ2 C-C stretch M06/Sadlej-pVTZ

8. Infrared spectrum of C 2 H 4 ···I complex following photolysis at 355nm 8

9. IR spectrum of C 2 H 4 ···I in Ne matrix following 450 nm Photolysis 9 1145 1210 1237 1438

10. Reaction path and mechanisms for the photolytic reaction of the C 2 H 4 …I 2 and C 2 H 4 …Br 2 Charge Transfer complex. Participation of bridged iodoethyl intermediate Participation of classical bromoethyl intermediate 10 240 nm, CT state of the complex 450 nm, the I 2 Chromophore 355 nm, CT state of the radical 266 nm, CT state λ > 300, the Br 2 Chromophore L. George, L. Wittmann, A. Kalume, and S. A. Reid, Photoinduced Electron Transfer in a prototypical Mulliken Donor-Acceptor Complex: C 2 H 4...Br 2 J. Phys. Chem. Lett. 2010, 1, 2618–2621 +

11. 11 + – _ _ + + + – * hν CT BET hν vis hν CT Photochemistry of the C 2 H 4 …I 2 and C 2 H 4 …Br 2 Charge Transfer complexes. + hν vis

12. IRC scan from symmetric bridged TS (at UM062x/aug-cc-pVTZ-pp level ), illustrating the concerted stereospecific addition 12

13. Optimized structures of the ethylene complexes with atomic and molecular iodine and bromine (M062x/aug-cc-pVTZpp). 13

14. 14 78 Scan for the C 2 H 4 I radical Fully relaxed scan of the C-C-I bond angle with the UM062x/aug-cc-pVTZpp method shows only one minimum which corresponds to the symmetrically bridged radical

15. Scan for the C 2 H 4 Br radical Fully relaxed scan along the C-C-Br and H-C-C-Br with DFT and MP2 method classical radical is the global minimum in both the methods.  The symmetricaly bridged radical is a local minimum at MP2  No experimental evidence for the bridged radical UB3LYP/aug-cc-pVDZ UMP2/aug-cc-pVDZ 15

16. Summary and Future directions Spectroscopic interrogation of symmetrically bridged radical complex C 2 H 4 …I by trapping in Ne matrix following photolysis of C 2 H 4 …I 2 charge-transfer complex. Irradiations into the CT band or the I 2 band, produced the C 2 H 4 ···I complex Photolysis of the C 2 H 4 ···I complex led to the formation of C 2 H 4 ···I 2, anti- and gauche-1,2 diiodoethane High level calculations were performed to confirm the structures of the radical intermediates in electrophilic addition of iodine and bromine to ethylene, C2H 4 …I (bridged) and C2H 4 …Br (classical). Examined the reaction path and identified a symmetric transition state leading to a concerted stereospecific addition. Experiments to understand the mechanisms in the case of C 2 H 4 ···ICl. 16

17.  Professor Scott. A. Reid Aimable Kalume Lloyd Muzangwa Silver Nyambo Brandon Uhler National Science Foundation and Petroleum Research Fund Acknowledgments

18. Infrared spectrum of C 2 H 4 ···I 2 complex following photolysis at 240nm

19. 19 Observed and predicted vertical transitions

20. Experimental and calculated vibrational frequencies of species 20 (intensity in km/mol)