Organometallics 1995, 14,5068-5072
5068
Synthesis and Characterization of CO2-Bridged Bimetallic Compounds Derived from a Rhenium Metallocarboxylate. Correlation of IR Spectral Data with Coordination Geometry and Bonding Type Dorothy H. Gibson,* Jaime 0. Franco, Jayesh M. Mehta, Mark S. Mashuta, and John F. Richardson Department of Chemistry and Center for Chemical Catalysis, University of Louisville, Louisville, Kentucky 40292 Received June 5, 1995@ The synthesis and characterization of CO2-bridged complexes, Cp*Re(CO)(NO)(C02)M(3, M = Re(C0)5; 5, M = Mo(C0)zCp; 7, M = W(CO)&p; 8, M = W(CO)2Cp) are described. Compound 5 has been structurally characterized. The geometry about the molybdenum atom in 5 is square-based pyramidal. All compounds have been characterized by DRIFTS IR spectral data, These data, together with DRIFTS and structural data from other symmetrical p2-q3-C02complexes characterized recently, show that the coordination geometry a t the metal center which anchors the carboxyl oxygens determines the position of the Yasym band of the Cog ligand. The position of the vSymband in these compounds varies only slightly and is determined by the metallocarboxylate group.
Introduction Complexes having C02 ligands bridged between two transition-metal centers provide homogeneous models for intermediates in the catalytic furation of carbon dioxide. Indeed, such bifunctional coordination has been suggested to be necessary for C 0 2 activation.2 Methods for the synthesis of the bridged complexes have generally involved displacement of a weakly coordinated ligand from one metal center by a nucleophilic metallocarboxylate group. These methods might include the displacement of a weakly bound ethylene ligand from the coordination sphere of a metal cation. However, our @Abstractpublished in Advance ACS Abstracts, October 1, 1995. (1)(a) Audett, J. D.; Collins, T. J.; Santarsiero, B. D.; Spies, G. H. J . A m . Chem. SOC.1982,104,7352. (b) Tso, C. T.; Cutler, A. R. J . A m . Chem. SOC.1986,108,6069. (c) Gibson, D. H.; Ong, T.-S. J. Am. Chem. SOC.1987,109,7191.(d) Senn, D. R.; Gladysz, J . A.; Emerson, K.; Larsen, R. D. Inorg. Chem. 1987,26,2737. (e) Bennett, M. A.; Robertson, G. B.; Rokicki, A,; Wickramasinghe, W. A. J. A m . Chem. SOC.1988,110,7098. (0 Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L. J . Chem. Soc., Chem. Commun. 1989, 1287. (g) Pilato, R. S.; Housmekerides, C. E.; Jernakoff, P.; Rubin, D.; Geoffroy, G. L.; Rheingold, A.L. Organometallics 1990,9,2333.(h) Field, J. S.; Haines, R. J . ; Sundermeyer, J.; Woolam, S. F. J . Chem. Soc., Chem. Commun. 1990, 985. (i) Gibson, D. H.; Richardson, J . F.; Ong, T.-S. Acta Crystallogr. 1991,C47,259. 6 ) Torreson, I.; Michelin, R. A.; Marsella, A,; Zanardo, A,; Pinna, F.; Strukul, G. Organometallics 1991,10,623. (k) Vites, J . C.; Steffey, B. D.; Giuseppetti-Dery, M. E.; Cutler, A. R. Organometallics 1991,10,2827. (1) Gibson, D. H.; Ong, T.-S.; Ye, M. Organometallics 1991,10,1811.(m) Gibson, D. H.; Ye, M.; Richardson, J . F. J . A m . Chem. SOC.1992,114, 9716. (n)Szalda, D.J.; Chou, M. H.; Fujita, E.; Creutz, C. Znorg. Chem. 1992,31,4712.( 0 ) Field, J. S.; Haines, R. J.; Sundermeyer, J.; Woolam, S. F. J . Chem. SOC.,Dalton Trans. 1993,2735. (p) Gibson, D. H.; Richardson, J. F.; Mbadike, 0. P.; Acta Crystallogr. 1993,B49,784. (9)Pinkes, J. R.; Cutler, A. R. Inorg. Chem. 1994,33,759. (r) Gibson, D. H.; Mehta, J . M.; Ye, M.; Richardson, J. F.; Mashuta, M. S. Organometallics 1994,13,1070.(s) Yang, Y.-L.; Chen, J.-D.; Liu, Y.-C.; Chen, M.-C.; Wang, Y. J . Organomet. Chem. 1994,467,C8. (t)Pinkes, J. R.; Steffey, B. D.; Vites, J. C.; Cutler, A. R. Organometallics 1994,13,21. (u) Gibson, D. H.; Ye, M.; Richardson, J. F.; Mashuta, M. S.Organometallics 1994,13,4559. (v) Gibson, D.H.; Ye, M.; Sleadd, B. A.; Mehta, J. M.; Mbadike, 0. P.; Richardson, J. F.; Mashuta, M. S. Organometallics 1995,14,1242.(w) Gibson, D. H.; Mehta, J . M.; Sleadd, B. A,; Mashuta, M. S.; Richardson, J . F., Organometallics, in press. (2) (a) Fachinetti, G.; Floriani, C.; Zanazzi, P. F. J . A m . Chem. SOC. 1978,100,7405. (b) Gambarotta, S.;Arena, F.: Floriani, C.: Zanazzi, P. F. J . A m . Chem. SOC.1982,104,5082.
previous investigations, with an iron metallocarboxylate, afforded carboxyethylene-bridged compounds as a result of nucleophilic additions to the ethylene ligand^.^ We now report the reactions of two systems which readily lose coordinated ethylene to provide CO2-bridged compounds and the structural characterization of one of these products. Also, we provide further evidence, based on data from these and related new compounds, that the position of the IR vasymbands in symmetrically bonded ~2-)1~-CO2 compounds is controlled by the coordination geometry at the metal center which binds the carboxyl oxygen^.^ Such data are expected to be useful in identifying active metal-bound COz-containing species in catalytic processes.
Results and Discussion Synthesis of Cot-BridgedCompounds. We have used the reactions of the metallocarboxylic acid Cp*Re(CO)(NO)COOH(1;Cp* = r5-C5Me5)with other metal complexes having weakly coordinated ligands to generate COz-bridged complexes previously.lr,v,w Reaction of 1 with Re(C0)5(C2H4)+BF4- W5 in the presence of sodium carbonate afforded a product which has been formulated as the p2-)12-C02compound 3, as illustrated in eq 1. The product has been characterized through Cp*Re(CO)(NO)COOH 1
+
Na,CO,
Re(CO),(C2H4)+BF42
Cp*Re(CO)(NO)(CO,)Re(CO), (1) 3 elemental analysis and spectral properties. The forma(3)Gibson, D. H.; Franco, J. 0.;Harris, M. T.; Ong, T.-S. Organometallics 1992,11, 1993. (4)A preliminary account of some of this work was presented a t the Third International Conference on Carbon Dioxide Utilization in Norman, OK, on May 1, 1995. (5)Raab, K.;Olgemoeller, B.; Schloter, K.; Beck, W. J . Organomet. Chem. 1981,214,81.
0276-7333/95/2314-5068$09.00IQ 0 1995 American Chemical Society
Organometallics, Vol. 14, No. 11, 1995 5069
C02-Bridged Bimetallic Compounds
tion of the pz-$ type of bridging COZligand in this case contrasts sharply with our previous results involving the reaction of 1 with cis-Re(C0)4(PPh3)(F-BF3), which led directly to the bridged complex with p2-v3 bonding of the C02 1igand.l' Furthermore, 3 is not converted t o the p2-v3 type of product by solution thermolysis (3 h at room temperature in CDzClz or 45 min in toluene-& at 57 "C) of the compound or by attempted thermolysis in the solid state (30 min at 105 "C); degradation results instead. Reaction of 1 with C~MO(CO)~(CZH~)+BF~(4, Cp = 95-C5H5),6at room temperature and in the presence of sodium carbonate, afforded a product which has been identified as the CO2-bridged compound 5 with p~12-q~ bonding of the COz ligand as illustrated in eq 2. ComCp*Re(CO)(NO)COOH
1
Figure 1. ORTEP drawing of 5 with thermal ellipsoids shown at the 50% probability level. Table 1. Summary of Crystallographic Data for 5
+ Na2C0,
CpMo(CO),(C2H4)+BF4-__+ 4
Cp*Re(CO)(NO)(CO,)Mo(CO),Cp (2) 5
pound 5 has been characterized by elemental analysis, spectral data, and an X-ray structure determination (see below). Conversion of the presumed intermediate pzv2-C0z compound to the ~ 2 - form 7 ~ occurs readily even under the mild conditions used for this reaction; we have not tried to probe for this intermediate under lower temperature conditions. The reasons COz-bridged compounds 3 and 5 are formed instead of the carboxyethylene-bridged compounds are not understood at present. It is hoped that further investigations of the reactions will clarify these differences. In order to be able t o compare its spectral data with those for 5, we decided to try to prepare the tungsten analog by the type of route we had used previously to prepare the dirhenium ~ z - ~ ~ - C bridged O Z comp1ex:l' by reaction of the metal carbonyl complex CpW(CO)3(F-BF3) (6)7with the acid 1. However, the properties of the resulting product were clearly in agreement with those expected for a p ~ - 9 ~ - C 0complex 2 instead (see the Experimental Section and discussion of spectral data below). This compound, 7, afforded the desired p2-v3COZ complex (8)after mild thermolysis in the solid state. Compounds 7 and 8 were characterized by elemental analyses and spectral data. Structural Characterization of 5. The solid-state structure of 5 was established by X-ray crystallography and shows the geometry about the molybdenum atom t o be a distorted square-based pyramid with the cyclopentadienyl group at the apex; the geometry a t this center is unique in comparison to the other symmetrical p2-$-COz transition-metal complexes which we have characterized previously.lr~U~W The ORTEP diagram for 5 is shown in Figure 1. The crystallographic data for 5 are summarized in Table 1. Atomic positional parameters for 5 are shown in Table 2, and selected bond distances and angles are shown in Table 3. The structural data indicate highly symmetrical bonding about the bridging COz ligand. The C-0 bond lengths ( 6 )Cousins, M.;
C(1la
Green, M. L. H. J . Chem. SOC.1963,889. (7)Appel, M.; Schloter, K.; Heidrich, J.; Beck, W. J . Organomet. Chem. 1987,322,7 7 .
formula Cryst SySt space group
a,A
b, A C, A P, deg
v, A3
Z Dc,dcm3 cryst dimens, mm cryst descripn p(Mo Ka), cm-l ab8 cor transmission factors: midmax radiation ( I , A) diffractometer monochromator temp, "C scan range scan speed, deglmin max 28, deg no. of unique rflns collected no. of rflns included (I, > 3dZ,)) no. of params computer hardware computer software ext coeff agreement factors" R Rw function minimized GOF weighting scheme high peak in final diff map, e
ClsHzoMoNO6Re monoclinic P2 1lc 13.794(3) 10.683(2) 14.425(3) 94.80(2) 2118.2(7) 4 2.008 0.43 x 0.33 x 0.15 magenta prism 63.36 q scans 0.5811.00 Mo Ka (0.710 73) Enraf-Nonius CAD4 graphite cryst 22w 0.80 + 0.35 tan e 1-5 46.0 3126 2151 264 Silicon Graphics Iris Indigo teXsan 9.23 x lo-* 0.035 0.035 ZW(lF0l - I F C I Y
1.60 [u~(F,)I-~ 0.70
' R = XllFnI - l ~ c l l E l ~Rnwl ~= [ L W ' o I - l F c 1 ) z E ~ ~ 0 2 1 " 2 ~ in 5 are 1.26(1) and 1.29(1) 8,and the 0-Mo bond
lengths are 2.149(7) and 2.158(7) A. IR Spectral Data. Over the past several years, we have developed a base of infrared data, collected by the DRIFTS technique8(diffise reflectance infrared Fourier transform spectroscopy)which has been correlated with structural data on the Con-bridged comple~es.~ All compounds of the pzq2 type show the v a s p and vSymCOz bands near 1500 and 1140 cm-1, respectively. Thus, 3 shows these bands at 1514 and 1182 cm-I and 7 shows the bands at 1541 and 1100 cm-'. Compounds of the symmetrical p2-v3-C02 type show the vsymband in the region 1240-1290 cm-l. However, the higher frequency, vasymband varies over a larger range. Data for nine compounds of this type, six of which have been structurally characterized, are summarized in Table 4. (8) Griffiths, P. W.; de Haseth, J. A. Fourier Transform Infrared Spectroscopy; Wiley: New York, 1986; Chapter 5. (9) A fuller discussion of these relationships is contained in ref lv.
5070 Organometallics, Vol. 14, No. 11, 1995
Gibson et al.
Table 2. Atomic Positional Parameters for 6 atom
Y
z
0.19796(4) -0.1160(1) -0.0461(7) 0.0727(7) 0.1769(9) 0.4099(9) -0.3399(10) -0.135(1) 0.325(1) 0.0619(10) 0.1838(10) 0.111(3) 0.072(2) 0.237(4) 0.185(4) 0.297(3) 0.294(3) 0.204(4) 0.247(3) 0.088(2) 0.110(3) -0.054(2) 0.006(2) 0.197(3) 0.285(3) 0.428(2) 0.447(3) 0.236(3) 0.316(2) -0.035(3) 0.018(2) -0.255(1) -0.126(1) -0.098(4) -0.09(1) -0.052(9) -0.028(3) -0.114(3) -0.167(7) -0.27(1) -0.231(3) -0.230(3) -0.206(9)
0.28365(3) 0.22682(7) 0.2160(6) 0.2687(6) 0.1149(6) 0.2083(7) 0.3318(8) 0.4112(8) 0.2368(7) 0.2505(8) 0.1787(7) 0.431(2) 0.417(2) 0.440(2) 0.441(2) 0.405(2) 0.427(2) 0.380(2) 0.390(2) 0.390(2) 0.383(2) 0.435(2) 0.463(2) 0.483(2) 0.488(2) 0.450(2) 0.418(2) 0.348(2) 0.372(1) 0.372(2) 0.355(2) 0.291(1) 0.341(1) 0.156(2) 0.135(9) 0.089(6) 0.096(2) 0.063(1) 0.062(5) 0.119(9) 0.097(2) 0.149(2) 0.165(6)
X
0.15409(4) 0.37557(8) 0.2290(5) 0.3446(5) 0.0192(7) 0.2701(7) 0.2955(10) 0.4983(9) 0.2276(9) 0.2537(8) 0.0749(7) 0.178(2) 0.149(3) 0.186(3) 0.204(2) 0.099(3) 0.139(2) 0.034(2) 0.046(2) 0.080(3) 0.047(2) 0.194(2) 0.245(2) 0.307(2) 0.288(2) 0.160(2) O.lOO(2) -0.074(2) -0.051(2) 0.022(2) -0.030(2) 0.325(1) 0.453(1) 0.519(2) 0.486(7) 0.406(6) 0.450(3) 0.383(2) 0.339(5) 0.40(1) 0.401(4) 0.478(2) 0.516(5)
+
Be,," A' 4.06(1) 4.51(3) 5.1(2) 5.0(2) 7.5(3) 7.9(3) 10.6(4) 11.6(4) 6.5(3) 3.7(3) 3.3(3) 2.7(5) 3.0(6) 4.3(7) 3.8(7) 5.4(8) 2.7(5) 5.0(9) 2.6(6) 3.2(6) 3.2(7) 4.8(6) 5.5(6) 6.3(6) 6.9(7) 4.8(6) 7.7(8) 8.5(8) 3.7(5) 6.1(7) 4.9(6) 6.8(4) 7.1(5) 8.7(10) 5.7(10) 3(1) 8(1) 6.4(8) 4(1) 8.8(6) 8.0(10) 7.2(10) 4(1)
+
a Be, = 8/3x2(Ull(aa*)2 U~z(bb*)~U ~ ~ ( C C + *2Ulzaa*bb* )~ cos y + 2U13aa*cc* cos p + 2U23bb*cc* cos a).
Table 3. Selected Bond Distances Angles (den) for 5 C(1)-0(1) C(1)-0(2) Re-C(l)
(A) and Bond
Bond Distances 1.29(1) O(l)-Mo 1.26(1) 0(2)-M0 2.08(1)
Bond Angles O(l)-C(l)-0(2) 112.8(10) O(l)-Mo-C(14) 0(1)-M0-0(2) 59.2(3) 0(2)-Mo-C(15) C(14)-Mo-C(15) 74.7(7)
2.149(7) 2.158(7)
85.9(5) 8535)
The IR spectral bands have been assigned only after comparisons with numerous model compounds containing one or the other of the two metal fragments represented in the structure. Also, as noted previously,lW the bands for CO2 in the zirconium complexes (entries 4-7 in Table 4) are analogous to those in Ti and Zr complexes characterized by Cutler,lkfor which labeling experiments were used t o assist in band assignments. The two characteristic bands for coordinated C02 are well defined in DRIFTS spectral data. For example, Figure 2 shows the spectral region from 1600 to 1000 cm-l for compounds 5, 7,and 8 and the related acid 1. AS expected, the vasym and Ysym bands for 8 are closely similar to those for 6. Six of the compounds shown in Table 4 are derived from the same rhenium metallo-
carboxylate; note that the position of the vasym band varies by more than 100 cm-l while the vsp band varies by only 10 cm-l. Interestingly, the latter band remains in nearly the same place even though the atomic weight of the metal center which anchors the carboxylate oxygens more than doubles in going from Zr to Re. However, comparisons of the Yasym bands show that there are clearly three groups of compounds represented in Table 4: (a) those which have an octahedral Re center bound t o the carboxyl oxygens (entries 1-31, (b) those which have the carboxyl oxygens bound t o an edgecapped tetrahedral Zr center (entries 4-7), and (c) those which have the oxygens bound to square-based pyramidal Mo or W centers (entries 8 and 9). It is apparent from the positions of the Vasym bands that the new Mo and W complexes 5 and 8 (entries 8 and 9 in the table) are unique. And, clearly, it is the coordination geometry a t this center which controls the position of the Yasym band. Relationships between structure and reactivity of the coordinated C02 in these compounds are being probed. Experimental Section General Data. Reactions and manipulations were carried out under a n atmosphere of prepurified nitrogen in Schlenkware or in a Vacuum Atmospheres glovebox (with Dri-Train). All glassware was dried in the oven before use. Reagent grade dichloromethane was used as received. Benzene, toluene, and hexane were dried over concentrated sulfuric acid and fractionally distilled before use. Solvents used in the glovebox were distilled under nitrogen from P205: methylene chloride, acetone, pentane, hexane, benzene, and toluene. Acetone& and benzene-ds were obtained from Aldrich; dichloromethane-d2 was obtained from Cambridge Isotope Laboratories or Aldrich. Cp*Re(CO)(NO)COOH,lrRe(C0)5(C2HJCBF4-,5 C ~ M O ( C O ) ~ ( C ~ H ~ )CpW(C0)3CH3,10 +BF~-,~ and CpW(C0)3(F-BF3I7 were prepared as described previously. Spectral data were obtained on the following instruments: FTNMR, Bruker A M X - B O O ; FT-IR, Mattson Galaxy Series 5000. Diffuse-reflectance FT-IR data were obtained on the Mattson instrument with a DRIFTS accessory (Spectra Tech, Inc., Barnes Analytical Division) as KC1 dispersions and at 1cm-l resolution. 'H and I3C NMR chemical shifts were referenced to residual protons in the deuterated solvents. Melting points were obtained on a Thomas-Hoover capillary melting point apparatus and are uncorrected. Elemental analyses were performed by Midwest Microlab, Indianapolis, IN. Cp*Re(CO)(NO)(COz)Re(CO)~ (3). In a glovebox, (co)5Re(CHz=CHz)+BFd- (0.25 g, 0.57 mmol) was dissolved in 10 mL of acetone at 0 "C; to the solution was added solid Na2C03 (excess). Solid Cp*Re(CO)(NO)COOH(0.25 g, 0.59 mmol) was then added, and the mixture was stirred at this temperature for 1 h. The mixture was filtered through Celite, and the filtrate was evaporated to dryness. The residue was extracted with ether (3 x 10 mL), and the combined extracts were filtered through Celite. The filtrate was evaporated to dryness, and the residue was dried under vacuum, giving an orange solid: 0.35 g (82% yield); mp 132 "C dec. Anal. Calcd for C17H15N09Re: C, 27.23; H, 2.02. Found: C, 27.56; H, 2.21. IR (CHzC12): Y C O 2138 (w), 2028 (vs), 1970 (s, br) cm-'; YNO 1690 (m, br) cm-'. DRIFTS (KCl): voco 1514 (w), 1182 (m) cm-'. 'H NMR (CDzClz, -10 "C): 6 2.09 (s, CpMe5). 13CNMR (CD2C12, -10 "C): 6 210.61 (s, CO), 192.72 (s, C o d , 183.49 (s, CO), 182.84(s, CO), 104.46 (s, CpMed, 10.48 (s, CpMed. Cp*Re(CO)(NO)(COz)Mo(CO)&p (5). Cp*Re(CO)(NO)COOH (0.20 g, 0.47 mmol) was dissolved in 15 mL of acetone, (10)King, R. B. Organometallic Syntheses; Academic Press: New York, 1965;p 145.
Organometallics, Vol. 14,No.11, 1995 5071
COz-Bridged Bimetallic Compounds
Table 4. Dependence of Carboxylate vasW on Coordination Geometry symmetrical pZ-y3complex M=C
entry no.
IR (cm-l)a
MI
CpFe(CO)(PPh3)(C02)Re(C0)3[P(OEt)31b Cp*Re(CO)(NO)(COz)Re(CO)3(PPh3T Cp*Re(CO)(NO)(COz)Re(CO)z(PPh~hd
1 2 3 4 5 6 7 8 9 a
