J . Am. Chem. SOC.1986, 108, 2547-2552
2547
Complexes of Iron and Cobalt Containing Coordinated Molecular Dihydrogen: Infrared Evidence for H2) and Co( CO),( NO)( H2) in Liquefied Xenon Fe( CO)( Solution Gerard E. Gadd,? Rita K. Upmacis, Martyn Poliakoff,* and James J. Turner* Contribution from the Department of Chemistry, University of Nottingham, Nottingham NG7 2RD, England. Received October 28, 1985
Abstract: Fe(CO)(NO),(H,) and Co(CO),(NO)(H,) were generated by UV photolysis of Fe(CO),(NO), and CO(CO)~(NO) dissolved in liquefied xenon at -104 OC and under 10-20 atm of pressure of H2 or D2.Coordinated molecular dihydrogen and dideuterium were identified by u(H-H) (-3000 cm-') and v(D-D) (-2200 cm-I) IR bands. Lower frequency IR bands associated with coordinated H2 and D, are also reported. Both compounds decayed with pseudo-first-order kinetics in t t 1 2 -20-30 min at -104 OC when the H, or D, was vented from the IR cell. Extensive additional IR data (available as supplementary material) are given for Fe(CO),(NO),, Fe(CO)(NO),(H2), and H2 and D2dissolved in liquefied xenon.'*
There is considerable interest in how molecular hydrogen, HZ, reacts with coordinatively unsaturated transition-metal centers. Until recently, such reactions were generally presumed to involve (1) the initial, albeit transient coordination of molecular dihydrogen to form an unstable complex and (2) the subsequent dissociation of the H-H bond to form stable dihydride compounds. This view has been somewhat changed by the isolation' of the first stable dihydrogen complexes, M(CO),(PR,),(H,) (M = Mo or W, R = cy or i-Pr). Since then, there has been spectroscopic identification of several complexes:-5 most rather less stable than the first, but all containing coordinated dihydrogen. It is now important to ask what factors determine the relative stabilities of molecular dihydrogen compounds and metal dihydrides. In what circumstances can dihydrogen be coordinated by a metal center without cleavage of the H-H bond? All the dihydrogen complexes reported so far1-5s25have involved metals with d4-d6 configuration. In this paper, however, we present detailed IR evidence for the formation, in liquid xenon solution, of two complexes, Fe(CO)(N0),(H2) and Co(CO),(NO)(H,), both of which have nominal d'O configurations. Liquid xenon (LXe) has proved itself to be a very useful solvent for characterizing reactive and unstable transition-metal complexes.6 In particular, it provides a simple and general route to dihydrogen compound^.^?^ and photolysis of metal carbonyl in the presence of H2. M(CO),
+ H2
uv
M(CO),,(H2)
+ CO
This route has been used to generate the complexes MfCO),(H2) (M = Cr, Mo, and W), where the coordinated H2, HD, or D2 could be identified by I R s p e c t r o ~ c o p y . ~ * ~ In this paper, (i) we show how I R spectra in the u(C-0) and v(N-0) regions can be used to monitor the generation of Co(C0)2(N0)(H,) and Fe(CO)(N0),(H2) in liquid xenon, (ii) we use diagnostic v(H-H) bands, -3000 cm-', and their D2analogues, 2200 cm-l, to confirm the presence of coordinated dihydrogen in both compounds, (iii) we demonstrate that IR bands below 1500 cm-' also provide evidence for the coordination of H2and D2, (iv) we examine the thermal stability and decay of the two compounds, and (v) in the Discussion we summarize the evidence for the formation of Fe(CO)(N0},(H2) and Co(CO),(NO)(H,) and briefly discuss the bonding between H2and the metal centers in these complexes.
Experimental Section The liquid Xe cell, originally designed by Maier et al., has been described in detail previously.* It has 2.7-cm path length and 8.5-mL 'Present address: Department of Chemistry, University of California, Berkeley, CA 94720.
volume. Liquid Xe has a number of advantages over solid matrices which have also been for the generation of dihydrogen complexes: (i) much larger quantities of compound can be generated because of the greater path length in liquids and weak IR bands are more easily observed;2(ii) the reactant gases can be rapidly (300 cm-I) IR bands of Fe(C-
O),(NO), (Table VI) and Fe(CO)(N0)*(H2) (Table VII), and IR bands of H2 (Table VIII) and D2 (Table IX) dissolved in liquid Xe18 (7 pages). Ordering information is given on any current masthead page.
Microwave Spectra, Electric Dipole Moment, and Molecular Structure of cis,trans-1,2,3-Trifluorocyclopropane R. N. Beauchamp, J. W. Agopovich,' and C. W. Gillies* Contribution from the Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 121 80. Received August 22, 1985
Abstract: The microwave spectra of the normal, monodeuterated, dideuterated, and carbon- 13 isotopic species of cispans1,2,3-trifluorocyclopropaneand cis,rrans-l,2,3-trifluorocyclopropaned3have been investigated and assigned in the region 26.5-40.0 GHz. The spectral assignments have yielded data sufficient for the complete determination of the molecular geometry in both the normal and trideuterated isotopic species frameworks. The partial r, parameters in the normal isotopic species framework are T ( C ~ , ~=C 1.478 ~ ) (10) A, r(CIC2)= 1.500 (3) A, r(C1,2H) = 1.076 (6) A, r(C3H)= 1.085 (16) A, r(Cl,2F) = 1.367 (8) A, r(C3F)= 1.387 (8) %I, B(HCl,2F) = 109.4 (8)', and B(HC3F) = 114.7 (lS)', where atom C3 lies in the ac symmetry plane of the molecule. All the ring bonds in the cis,trans isomer have shortened relative to cyclopropane, with the greater reduction occurring in the two equivalent trans ring bonds. The C-F bond distances are found to be inequivalent, with the longer C-F bond occurring in the HCF moiety exclusively trans to neighboring HCF groups. These results are interpreted in the context of several theoretical studies that predict the effect of fluorine substitution on the geometries of substituted cyclopropanes and oxiranes.
A number of e ~ p e r i m e n t a l and ~ - ~ theoreticaI8-l2 studies have been undertaken to elucidate the effect of fluorine substitution on the geometries of fluorinated cyclopropanes and oxiranes. A portion of the theoretical work suggests that the ring bond changes observed in 1 ,l-difluorocyclopropane*and cis,&- 1,2,3-trifluorocyclopropane4 and the contraction of the C1-C2bond in 1,I ,2,2tetrafluorocy~lopropane~ relative t o cyclopropane may be rationalized by fluorine-induced charge redistribution in occupied molecular orbitals (MOs) and the resultant forces acting on the ring nuclei.8 Several of the studies9J0 further suggest that the greater stability in the trans isomer of the cis- and trans-1,2difluorocy~lopropanes'~ and the shorter C-C bond distance in the trans isomer of the cis- and tranS-l,2-difl~orooxiranes~~~ may derive from greater conjugative d e ~ t a b i l i z a t i o n in ' ~ the ~ ~ ~corresponding cis forms. In the present study, the microwave investigation of various isotopic species of cis,trans-trifluorocy~lopropane~~~~~ (Figure 1)
has yielded data sufficient for the complete determination of the molecular geometry of the compound in each of two different frameworks. Coordinates have been calculated in a number of ways and the results intercompared to establish the reliability of the parameters resulting.I8 Trends in the experimentally determined ring geometries of the l ,2-difluorocy~lopropanes'~~~~ and 1 , 2 - d i f l ~ o r o o x i r a n e have s ~ ~ ~been identified and related to the observed ring geometry in cis,trans- 1,2,3-trifluorocyclopropane in a manner consistent with available theory. Substituent orientation has been examined in several ring systems and the observations correlated with substituent orientation in cis,trans1,2,3-trifluorocyclopropane to provide insight into angular effects observed in that species.
Experimental Section Synthesis. (1) C,HFC2HFC,FH. The normal isotopic species of cis,trans-l,2,3-trifluorocyclopropane was synthesized by ozonolysis of 3 mmol of rrans-1,2-difluoroethyleneat -95 OC in 3 mL of CF,CI, as
described oreviouslv.17,21 ( I ) Present address: The Charles Stark Draper Laboratory, Inc., Cam-
bridge, MA 02139. (2) Perretta, A. T.; Laurie, V. W. J . Chem. Phys. 1975, 62, 2469-2473. (3) Laurie, V. W.; Stigliani, W. M. Mol. Spectrosc. Symp., 30rh 1975, TF5. (4) Gillies, C. W. J . Mol. Spectrosc. 1976, 59, 482-492. (5) Gillies, C. W. J . Mol. Specrrosc. 1978, 71, 85-100. (6) LaBrecque, G.; Gillies, C. W.; Raw, T.T.; Agopovich, J. W. J . Am. Chem. Soc. 1984. 106, 6171-6175, (7) Agopovich, J. W.; Alexander, J.; Gillies, C. W.; Raw, T. T. J . Am. Chem. SOC.1984, 106, 2250-2254. (8) Deakyne, C. A.; Allen, L. C.; Craig, N. C. J . Am. Chem. SOC.1977, 99, 3895-3903. (9) Deakyne, C. A.; Cravero, J. P.; Hobson, W. S. J . Phys. Chem. 1984, 88, 5975-5981. (IO) Skancke, A,; Boggs, J. E. J . Am. Chem. SOC.1979,101,4063-4067. (11) Cremer, D.; Kraka, E. J. Am. Chem. SOC.1985, 107, 3800-3810,
381 1-3819. (12) Durmaz, S.; Kollmar, H. J . Am. Chem. SOC.1980,102,6942-6945. Cuellar, E.; Hendricksen, D. E.; (13) Craig, N. C.; Hu Chao, T.-N.; Koepke, J. W. J . Phys. Chem. 1975, 79, 2270-2282. (14) Bingham, R. C. J . Am. Chem. SOC.1976, 98, 535-540. Stewart, G. H.;Smith, R.P. Proc. Narl. Acad. Sci. U.S.A. (15) Eyring, H.; 1958, 44, 259-260. (16) Agopovich, J. W.; Gillies, C. W. Mol. Spectrosc. Symp., 37th 1982,
RB7. Beauchamp, R. N.; Agopovich, J. W.; Gillies, C. W. Mol. Spectrosc. Symp., 39rh 1984, WF10.
(2) C,DFC2DFC3FD. The d , isotopic species was synthesized by ozonolysis of 0.75 mmol of trans-1,2-difluoroethylene-d2at -95 OC in 2 mL of CF3C1. (3) trans-C1DFC2HFC3FHand trans-ClDFC2HFC3FD. These isotopic species were synthesized by ozonizing an equimolar mixture of 1.6 mmol of trans-1,2-difluoroethylene-d,and -d2 a t -95 "C in 2 mL of CF3CI. (4) cis-C,HFC2HFC3FDand cis-C,DFC,DFC,FH. These isotopic
.
(17) Agopovich, J. W. Ph.D. Thesis, Rensselaer Polytechnic Institute, Troy, NY, 1982. (18) Schwendeman, R. H. "Critical Evaluation of Chemical and Physical Structural Information"; National Academy of Sciences: Washington, DC, 1974; pp 94-115. Harmony, M. D.; Laurie, V. W.; Kuczkowski, R. L.; Schwendeman, R. H.; Ramsay, D. A,; Lovas, F. J.; Lafferty, W. J.; Maki, A. G. J . Phys. Chem. Re$ Data 1979.8, 619-626. (19) Craig, N.; Gillies, C. W.; Justnes, H.; Sengupta, S. Mol. Spectrosc. Symp., 39th 1984, WF9. Justnes, H.; Zozom, J.; Gillies, C. W.; Sengupta, S. K.; Craig, N. C. J . Am. Chem. SOC.,in press. (20) Craig, N.; Gillies, C. W.; Justnes, H.; Sengupta, S . Mol. Specrrosc. Symp., 39rh 1984, WF8. Craig, N.; Gillies, C. W.; Justnes, H.; Sengupta, S . .IAm. . Chem. SOC.,in press. (21) Agopovich, J . W.; Gillies, C. W. J . Am. Chem. SOC.1982, 104, 813-817.
0002-7863/86/ 1508-2552%01.50/0 0 1986 American Chemical Society
