Reversible intercyclobutadiene haptotropism in cyclopentadienylcobalt linear [4]phenylene

Transcription

1 Reversible intercyclobutadiene haptotropism in cyclopentadienylcobalt linear [4]phenylene Thomas A. Albright, Sander Oldenhof, Oluwakemi A. Oloba, Robin Padilla and K. Peter C. Vollhardt * Experimental Procedures Supporting Information 2,3,6,7-Tetraiodobiphenylene: To stirred Hg(O 2 CCF 3 ) 2 (9.98 g, 23.4 mmol) in dry CH 2 Cl 2 (200 ml) was added biphenylene (0.82 g, 5.39 mmol) in CH 2 Cl 2 (10 ml). The mixture was completely shielded from light and stirred at RT for 3 d. A saturated solution of CaCl 2 in MeOH (5.20 g in 45 ml) was added and stirring continued for 3 h. A slurry formed, from which the solvent was decanted, followed by addition of dry CH 2 Cl 2 (150 ml) and PyICl 1 (15.7 g, 6.50 mmol). The color changed from yellow-green to orange. After further stirring at RT for 42 h, the product was filtered off and the yellow solid washed with 1 M HCl (50 ml), H 2 O (50 ml), MeOH (50 ml), and CH 2 Cl 2 (50 ml) to give 2,3,6,7-tetraiodobiphenylene (1.09 g, 31%) as a bright yellow powder; m.p. >330 C (decomp), sub. p. 200 C (10 torr); 1 H NMR (400 MHz, CS 2 /C 6 D 6, 3:1): δ = 6.96 ppm (s); 13 C NMR (125 MHz, CS 2 /C 6 D 6, 3:1): δ = 150.5, 129.7, ppm; IR (KBr): ~ ν = 1403, 1218, 856, 801 cm 1 ; MS (70 ev): m/z (%): 656 (80) [M + ], 402 (100), 328 (24), 148 (32), 127 (17). Anal. calcd for C 12 H 4 I 4 : C, 21.98, H, 0.61; found: C, 22.48, H, H. A. Muathen, J. Chem. Res. (M), 1994, 2201.

2 2,3,6,7-Tetrakis(trimethylsilylethynyl)biphenylene: A Schlenk flask was charged with 2,3,6,7-tetraiodobiphenylene (100 mg, mmol), CuI (1.5 mg, mmol), Pd(PPh 3 ) 2 Cl 2 (5.6 mg, mmol) degassed benzene (5 ml), and NEt 3 (5mL) to furnish a yellow suspension. After the addition of degassed trimethylsilylacetylene (760 mg, 1.1 ml, 7.7 mmol), the mixture was stirred at RT for 48 h, the dark brown solution filtered through a plug of silica, and the filtrate concentrated and subjected to column chromatography (silica gel), eluting with hexane/et 2 O (20 : 1) to give 2,3,6,7- tetrakis(trimethylsilylethynyl)biphenylene (76 mg, 93%) as yellow crystals; m.p C (MeOH); 1 H NMR (400 MHz, CDCl 3 ) : δ = 6.74 (s, 4 H), 0.25 ppm (s, 36 H); 1 H NMR (300 MHz, C 6 D 6 ): δ = 6.40 (s, 4 H), 0.29 ppm (s, 36 H); 13 C NMR (50 MHz, C 6 D 6 ): δ = 148.6, 126.8, 103.6, 100.0, ppm; UV/Vis (CH 3 CN): λ max (lgε) = 265 (4.39), 290 (4.63), 303 (4.88), 385 (3.45), 404 nm (3.64); IR (KBr): ~ ν = 2960, 2155, 1300, 860, 840, 760 cm 1 ; MS (EI) m/z (%): 536 (M +, 21), 73 (100). Anal. calcd for C 32 H 40 Si 4 : C, 71.57; H, 7.51; found: C, 71.28; H, Linear [2,3,8,9-tetrakis(trimethylsilyl)[4]phenylene](cyclopentadienyl)cobalt (4): A Schlenk flask was charged with 2,3,6,7-tetrakis(trimethylsilylethynyl)biphenylene (300 mg, mmol), 18-crown-6 (70.5 mg, mmol), KF 2H 2 O (489 mg, 5.19 mmol), and dry, degassed THF (25 ml). After stirring at RT for 3 h, the deep green mixture was filtered through a plug of silica using degassed THF and concentrated to approximately 15 ml (keeping exposure to light to a minimum). CpCo(CO) 2 (180 mg, 133 μl, 1.01 mmol) was added and the solution syringed into a boiling solution of degassed THF (150 ml) and bis(trimethylsilyl)acetylene (23 ml) over a period of 5 h, while irradiating with a projector lamp. The deep red reaction mixture was boiled and irradiated for an additional 14 h, the volatiles removed in vacuo, and the resulting black solid subjected to air free column chromatography (neutral alumina, activity III), eluting with hexane. The

3 first dark red fraction gave 4 (200 mg, 50%) as an air-sensitive deep-red solid; 1 H NMR (500 MHz, C 6 D 6 ): δ = 7.45 (s, 4 H, H3), 6.72 (s, 4 H, H6), 4.60 (s, 5 H, H8), 0.33 ppm (s, 36 H, H1); 13 C NMR (150 MHz, C 6 D 6 ): δ = (C5 q ), (C2 q ), (C4 q ), (C3H), (C6H), 80.1 (C8H), 74.1 (C7 q ), 2.22 ppm (C1H 3 ); UV/Vis: (hexane): λ max (relative intensity) = 281 (0.40), 356 (0.80), 487 sh nm (0.07); MS (EI) m/z (%): 712 (M +, 10), 588 (30), 73 (100); HRMS (EI): calcd for C 41 H 49 CoSi 4 : ; found: Anal. calcd for C 32 H 40 Si 4 : C, 71.57; H, 7.51; found: C, 71.28; H, Linear [4]phenylene](cyclopentadienyl)cobalt (6): Under N 2, 4 (75 mg, mmol) in THF/DMSO (3 : 1; 8 ml) was added to KOt-Bu (175 mg, 1.56 mmol) in t-buoh (4 ml). The mixture was stirred at 85 C for 16 h, cooled to RT, charged with degassed hexane (4 ml), and washed with degassed H 2 O (3 x 5mL). Chromatography on an air free column of neutral alumina (activity III), eluting with toluene, provided 6 (31.2 mg, 70%) as an air-sensitive red solid; 1 H NMR (600 MHz, CS 2 /C 6 D 6, 3 : 1): δ = 6.78 (AA m, 4 H, H1), 6.73 (BB m, 4 H, H2), 6.52 (s, 4 H, H5), 4.39 ppm (s, 5 H, H7); 13 C NMR (150 MHz, C 6 D 6 ): δ = (C4 q ), (C3 q ), (C1H), (C5H), (C2H), 80.5 (C7H), 74.0 ppm (C6 q ); UV/Vis: (THF): λ max (relative intensity) = 303 (0.32), 337 (0.30), 350 (0.43), 386 (0.69), 512 (0.09), 548 nm (0.12); IR (neat) : ~ ν = 2957, 2924, 2853, 1661, 1632, 1459, 1418, 1380, 1284, 1261, 1106, 1024, 802, 745 cm 1 ; MS (EI) m/z (%): 424 (M +, 100), 363 (38), 300 (100), 150 (22). HRMS (EI): calcd for C 29 H 17 Co: ; found: Linear [4]phenylene: Complex 6 (13 mg, 0.03 mmol) in toluene (1 ml) was heated to 95 C for 90 h under a CO atmosphere. A precipitate formed that was triturated with a

4 few drops of degassed toluene to give highly insoluble linear [4]phenylene (9 mg, 100%): 1 H NMR (500 MHz, C 6 D 6 ): δ = 6.45 (AA m, 4 H, H1), 6.19 (BB m, 4 H, H2), 5.76 ppm (s, 4 H, H5); UV/Vis: (DMSO): λ max (relative intensity) = 302 (0.73), 314 (0.91), 458 (0.23), 487 nm (0.36); IR (film): 3069, 3045, 1645, 1436, 1409, 1277, 1180, 1148, 1105, 1077, 1013, 960, 916, 871, 849, 809, 744, 728 cm 1 ; MS (EI) m/z (%): 300 (M +, 100), 150 (16). HRMS (EI): calcd for C 24 H 12 : ; found: Linear [2,3,8,9-tetrakis(trimethylsilyl)[4]phenylene](cyclopentadienyl)cobalt (5): A sample of 4 in C 6 D 6 was irradiated in a Rayonet photochemical reactor fitted with 350 nm lamps for 3 h to reach the photostationary state of 5 : 4 = 2 : 1. Isomer 5: 1 H NMR (500 MHz, C 6 D 6 ): δ = 7.98 (s, 2 H, H12), 6.99 (s, 2 H, H3), 6.51 (s, 2 H, H9), 6.30 (s, 2 H, H6), 4.40 (s, 5 H, H15), 0.37 and 0.30 ppm (2 s, 36 H, H1 and H14); 13 C NMR (600 MHz, C 6 D 6 ): δ = (C5 q ), (C8 q ), (C4 q ), (C2 q ), (C7 q ), (C13 q ), (C12H), (C3H), and (C6/9 q ), 79.8 (C15H), 78.1 (C11 q ), 72.5 (C10 q ), 2.30 (C14H 3 ), 2.16 ppm (C1H 3 ); UV/Vis: (hexane): new λ max = 411 nm. Linear [4]phenylene](cyclopentadienyl)cobalt (7): A sample of 6 in THF-d 8 was irradiated in a Rayonet photochemical reactor fitted with 350 nm lamps for 3 h to reach the photostationary state of 7 : 6 = 2 : 1. Isomer 7: 1 H NMR (400 MHz, THF-d 8 ): δ = 7.32 (AA m, 2 H, H5), 6.93 (m, 4 H, H1 and H6), 6.49 (s, 2 H, H4), 6.44 (s, 2 H, H3), 6.41 (AA m, 2 H, H2), 4.38 ppm (s, 5 H, H7); 1 H NMR (600 MHz, CS 2 /C 6 D 6 ): δ = 7.16 (m, 2

5 H, H5), 6.57 (m, 4 H, H1 and H6), 6.37 (AA m, 2 H, H2), 6.32 (s, 2 H, H4), 6.20 (s, 2 H, H3), 4.27 ppm (s, 5 H, H7). Computational Details All calculations were performed using the GAUSSIAN03 2 program. GaussView and ChemCraft 4 were employed to input structures as well as view output results. Optimized geometries were obtained at the hybrid density functional theory (DFT) using Becke s three-parameter exchange-correlation functional 5 containing the non-local gradient correction of Lee, Yang, and Parr 6 (B3LYP). For optimization purposes, a standard basis 3-21G 7 was used for hydrogen and carbon atoms. For cobalt, the LANL2DZ 8 basis set was applied, with the outermost d function released, yielding a triple-zeta d basis, along with the effective core potentials (ECP) to describe the core electrons. For the single point energy calculations, the basis sets were increased to 6-31G 9 for hydrogen, 6-311G* 10 for carbon, and the modified LANL2DZ basis as described above for cobalt with an added f-orbital coefficient. 11 The potential energy surfaces were mapped through a scan calculation, a feature also available within the GAUSSIAN03 program. Transition state structures were obtained in three different steps: (i) determination of initial and final products or the minimum 2 Gaussian 03, Revision B.03, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc., Pittsburgh PA, A. D. Becke, J. Chem. Phys., 1993, 98, C. Lee, W. Yang and G. R. Parr, Phys. Rev. B, 1988, 37, J. S. Binkley, J. A. Pople and W. J. Hehre, J. Am. Chem. Soc., 1980, 102, 939 for hydrogen, and M. S. Gordon, J. S. Binkley, J. A. Pople, W. J. Pietro and W. J. Hehre, J. Am. Chem. Soc., 1983, 104, P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, W. J. Hehre, R. Ditchfield and J. A. Pople, J. Chem. Phys., 1972, 56, L. A. Curtiss, M. P. McGrath, J.-P. Blaudeau, N. E. Davis, R. C. Jr. Binning and L. Radom, J. Chem. Phys., 1995, 103, A. W. Ehlers, M. Böhme, S. Dapprich, A. Gobbi, A. Höllwarth, V. Jonas, K. F. Köhler, R. Stegmann, A. Veldkamp and G. Frenking, Chem. Phys. Lett., 1993, 208, 111.

6 closest to a TS, (ii) a linear QST2 12 search for an initial guess of a TS; and (iii) input of the results from (ii) into a QST3 search. Transition states and minima were confirmed by carrying out frequency calculations (using the same basis as that used for the optimizations). Cartesian Coordinates and total energies (from the large basis set) of the stationary points Structure a: QST is a synchronous transit approach to the quadratic region around the transition state structure. For details, see: (a) J. B. Foresman and A. Frisch in Exploring Chemistry with Electronic Structure Methods: A Guide to Using Gaussian, Gaussian, Inc., Pittsburgh, PA, USA, 1996; (b) H. B. Schlegel in Ab Initio Methods in Quantum Chemistry, Part I, Wiley, Chichester, 1987.

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8 E TOT = Structure b:

9 E TOT = Structure c:

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11 E TOT = Structure d:

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13 E TOT = Structure e:

14 E TOT = Structure f:

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16 E TOT = Structure g:

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18 E TOT =