J . Am. Chem. SOC.1990, 112, 4813-4821 Table IV. Comparison of the Wavenumbers,' cm-I, of v(C-0) bands, Their Relative Intensities: and Calculated C-MC Bond AnglesCfor (CJ-IH,)M(CO),LSpecies [L = H2, N2, and HSiEt,] (CnHm)M(C0)2 H2 N2 HSiEt, (CAHA)Fe(C0)2 2023.5 (1.0) 2016.3 (1.0) 2010 ( l . O ) d 1967.9 (1.22) 1967.0(1.25) 1950 ( l . O ) d
angle 95 f 2.5' 96 f 2.5' 90 f 3' (C5H5)Mn(C0)2 1992.1 (1.0) 1985.0 (1.0) 1978.3 (1.09)e 1932.7 (1.0) 1934.0(1.1) 1915.5 (I.O)c angle 90 f 2.5' 92 f 2.5' 87.5 f 2.5' (C,jH6)CT(C0)2 1947.7 (1.7) 1947.3 (1.43) 1921 (1.2)' 1895.7 (1.0) 1905.4 (1.0) 1821 (1.0)3 85 f 3' angle 75' (83 f 9)' 80 f 2.5' "Unless otherwise stated the IR data is for scXe at 25 OC from this work, f0.2 cm-I. *Intensity data in parentheses; the values used are the peak absorbance with the weaker of the two bands arbitrarily set to 1.0. In all cases, the symmetric v(C-0) stretch is the higher wavenumber band. The error in the intensity data is &IO%. 'For details of calculations see ref 49. dData from ref 8: methylcyclohexane, 100 K, f2 cm-I. #n-Heptane solution, 25 OC; as an indication of the solvent shift, the bands of (C5HS)Mn(CO), are shifted ca. 5 cm-' to lower wavenumber in this solvent than in scXe. /These bands have significantly different half-widths; 1947.7 is 3/4 the width of 1895.7. The angle in parentheses is calculated by using (I = absorbance X peak width). 'Data from ref 8: HSiEt3, 100 K,f 2 cm-'. "he wavenumber reported for this band seems anomalously low compared to data from our own work e.g., (C6Me6)Cr(Co)2(HsiEty), 1890 and 1841 cm-I, n-heptane -20 'C; (C6H6)Cr(C0)2(HSiEt~) in n-heptane at 4 0 'C 1931.3 and 1925.1 (two bands, partly resolved, intensity 1.0) and 1872.2 cm-l (intensity 1.2). The two bands have a combined width (FWHM) 1.4 times that of the lower frequency band. Thus, the angle calculated by using (I = absorbance X peak width) is 85.5'.
4813
for a particular ligand L, the C-M-C angle in (C,H,)M(CO),L decreases from Fe to Cr. This is consistent with crystallographic studiesS2on the unsubstituted (C,H,)M(CO), where a similar trend is found. The calculations also suggest that, for a given metal, the $-H, complex has a larger angle than the HSiEt, compound. However, the differences are small, and one is probably justified in concluding that steric effects play a relatively minor role in determining the geometry at the metal center in these compounds. Although the work described in this paper has been carried out in scXe (largely for spectroscopic reasons), less exotic supercritical fluids could also be used as solvents for such reactions. Preliminary experiments" indicate that the same compounds can be generated in supercritical C02 or ethane. Our experiments have taken advantage of just one specific property of supercritical fluids, their miscibility with Hzand N2. Work is now in progress in our laboratory applying some of the other unusual properties of supercritical fluids to organometallic chemistry.
Acknowledgment. We thank the SERC, EEC (Stimulation Contract No. SC1*OOO7), the BP Venture Research Unit, the donors of the Petroleum Research Fund, administered by the American Chemical Society, and IC1 Chemicals and Polymers Ltd for support. M.P. thanks the Nuffield Foundation for a Science Research Fellowship. We are grateful to Professor J. J. Turner, Dr. G. Davidson, M. T. Haward, M. Jobling, Dr. R. Whyman, J. M. Whalley, and D. R. Dye for their help and advice.
see Table IV. Although such calculations are difficult to verify
Schubert, U.; Miiller, J.; Alt, H. G.Organometallics 1987,6, 469. (52)The C-M-C angles obtained by X-ray crytallographyare as follows: (C,H,)Fe(CO)3 98.2' (Harvey, P. D.;Schaefer, W. P.; Gray, H. B.; Gilson, D. F. R.;Butler, I. S. Inorg. Chem. 1988,27, 57.). (CSHs)Mn(CO),91-94'
in detail, the values for the HSiEt, compounds of Mn and Cr are similar to the values found in the crystal structures of less labile silane complexes.5* In addition, the calculations indicate that,
Chem. 1972, 42,C102.). (53) Jobling, M.; Howdle, S. M.; Poliakoff, M. Unpublished results.
(51)
(Black, J. D.,Boylan, M.J.; Braterman, P.S. J . Chem. Soc., Dalron Tram. 1981,673.). (C6H6)Cr(CO),86.5-89O (Rees, B.;Coppens, P. J. Orgammer.
Synthesis and Structural Studies of Some New Rhenium Phosphine Heptahydride Complexes. Evidence for Classical Structures in Solution Xiao-Liang Luo* and Robert H. Crabtree* Contribution from the Department of Chemistry, Yale University, New Haven, Connecticut 0651 I. Received July 12, 1989 Abstract: A series of new rhenium phosphine heptahydride complexes ReH7Lz(L2 = a chelating bidentate phosphine) have been synthesized and characterized by IR and 'H, 31P,and I3C NMR spectroscopy. The hydride resonances of ReH7(dppf) (1, dppf = l,l'-bis(diphenylphosphino)ferrocene), ReH7(dppb) (2, dppb = 1,4bis(diphenylphaphino)butane), and ReH,((+)diop) (3, (+)-diop = (4S,SS)-4,5-bis((diphenylphosphino)methyl)-2,2-dimethyl-1,3-dioxolane) undergo decoalescence upon cooling. The low-temperature hydride patterns suggest classical 9-coordinate tricapped trigonal prismatic structures. Consistent with the classical structures, IH NMR spectra of deuterated ReH7Lzcomplexes show very small and temperature-independent upfield isotope shifts in the hydride region and nochange in 2JHp.Sequential treatment of 1,2, and 3 with NaH and Me2S04 in the presence of Ph3SiH leads to ReH6(SiPh3)Lz(L, = dppf, dppb, (+)-diop). Variable-temperature 'H NMR studies of these silyl derivatives provide further support for the classical formulation of their parent heptahydrides. Theoretical T,(min) values are calculated for some polyhydrides on the basis of different structural models and are compared with the experimental numbers. Precautions to be taken in interpreting T I data are discussed.
Transition-metal dihydrogen complexes1 have attracted much recent attention. Their structural characterization is a particularly challenging problem for which we have previously developed a solution 'H NMR TI method.2, The method is based on the fact ( I ) (a) Crabtree, R.H.; Hamilton, D.G. Adu. Orgammer. Chem. 1988, 28, 299. (b) Kubas, G.J. Acc. Chem. Res. 1988, 21, 120. (2)(a) Crabtree, R. H.; Lavin, M.J. Chem. Soc., C k m . Commun. 1985, 1661. (b) Crabtree, R.H.; Lavin, M.;Bonneviot. L. J. Am. Chem. Soc. 1986, 108.4032.
that the dipoledipole mechanism dominates spin-lattice relaxation in small diamagnetic molecules in which the protons are close together (I A). As shown by the calculations, the interpretation of TI data of fluxional polyhydride complexes is complicated by several factors. Tl(min) values in the range 55-100 ms at 250 MHz cannot always be taken as an indication of the presence of an $-H2 ligand. Several close nonbonding H-H contacts resulting from the high coordination number can also give low Tl(min) values. On the other hand, the calculations show that a genuinely nonclassical polyhydride may give a T,(min) value that is indistinguishable from the value expected for a classical structure if the q2-Hz ligand undergoes fast rotation and has a long H-H distance. Our results suggest that the structural assignments of fluxional polyhydrides that are based solely on TIvalues may need to be validated by other methods. In cases where the fluxionality of a polyhydride can be frozen out to give several well-separated hydride resonances, deuterium isotope effects on the hydride chemical shift and the 2JpHcoupling constant may help distinguish between classical and nonclassical structures.
Experimental Section General. All manipulations were performed under a dry N2 atmosphere by standard Schlenk techniques. Reagents were purchased from Aldrich Chemical Co. THF, Et20, and hexane were distilled from Na/PhzCO. CH2C12was distilled from CaH,. ReOC13(AsPh3)2was prepared according to the literature method.20 'H, I3C, and IlP N M R spectra were recorded on Bruker WM 250 and WM 500 spectrometers with CD2Clzas the solvent unless otherwise stated; 'H and "C chemical shifts are measured with reference to the residual solvent resonance; I'P chemical shifts are given in ppm downfield from external 85% H3P04.
Luo and Crabtree IR spectra were recorded on a Nicolet 5-SX FT-IR instrument. Microanalyses were carried out by the Desert Analytic Co. Oxotrichloro(I,l'-bis(dipbenylphosphino)ferrocene)rhenium(V). A mixture of AsOCI,(ASPh,), (1 .OOg, 1.09 mmol) and dppf (0.60 g, 1.09 mmol) in CH2CI2 (30 mL) was stirred at room temperature for I O h. The volume of the solution was reduced to I O mL in vacuo, and E t 2 0 (40 mL) was added. The greenish solid was filtered, washed with E t 2 0 (4 X 10 mL), and dried in vacuo. Yield: 0.91 g (97%). Anal. Calcd for C34H28C13FeOP2Re:C, 47.32; H, 3.27. Found: C, 47.09; H, 3.14. IR (Nujol): Y R 964~ cm-I. 'H NMR (298 K): 6 7.4-7.9 (c, 20 H, Ph), 5.31 (br s, 2 H, Cp), 4.78 (br t. 3.1 Hz, 2 H, Cp), 4.50 (br t, 3.0 Hz, 2 H, Cp), 4.39 (br s, 2 H, Cp). "P('H) NMR (298 K): 6 -26.2. Other cis-ReOCI3L2 complexes (L2 = (+)-diop, dppb, dppe', dppp, dppp', dpbz) were similarly prepared in 90-95% yields. Their analytical and spectroscopic data are reported in the supplementary material. Heptahydrido( 1,l'- bis(diphenylphosphino)fe~~~e)rhenium( MI) (1). LiA1H4 (0.28 g, 7.4 mmol) was added to a suspension of ReOC13(dppf) (0.80 g, 0.93 mmol) in E t 2 0 (60 mL). The mixture was stirred at room temperature for 2.5 h. The resulting yellowish suspension was filtered through Celite and the filtrate evaporated to dryness in vacuo. The residue was dissolved in T H F (25 mL), cooled to 0 "C, and hydrolyzed by dropwise addition of H 2 0 (0.6 mL) in 10 mL of THF. The mixture was dried with 5 g of anhydrous Na2S04and filtered through Celite. The yellow filtrate was concentrated to 5 mL in vacuo. Addition of hexane (40 mL) resulted in the precipitation of a pale-yellow solid that was filtered, washed with hexane (4 X 10 mL), and dried in vacuo. Yield: 0.42 g, 62%. Anal. Calcd for C34H35FeP2Re:C, 59.03; H, 5.10. Found: C, 58.62; H, 5.04. IR (Nujol): uRtH 2008, 1951, 1925 cm-I. 'H NMR (298 K): 6 7.3-7.7 (c, 20 H, Ph), 4.32 (pseudotriplet, 1.7 Hz, 4 H, Cp), 4.22 (pseudoquartet, 1.7 Hz, 4 H , Cp), -5.75 (t, 2 J p=~16.9 Hz, 7 H, Re-H). 'H NMR (183 K): 6 7.1-8.9 (c, 20 H, Ph), 4.66 (br s, 2 H, Cp), 4.24 (br S, 4 H, Cp), 3.54 (br S, 2 H, Cp), -3.89 (t, 'JpH = 32 Hz, 2 H, Re-H), -6.70 (br s, 5 H, Re-H). 'H NMR (CD2CI2/CFCI33:2 (v/v), 153 K): 6 6.9-9.0 (c, 20 H, Ph), 4.65 (br s, 2 H, Cp), 4.29 (br s, 2 H, Cp), 4.21 (br s, 2 H, Cp), 3.54 (br s, 2 H, Cp), -3.95 (br s, 2 H, Re-H), -6.57 (br s, 2 H, Re-H), -7.19 (br s, 3 H, Re-H). Selectively hydride-coupled "P NMR (298 K): 6 12.9 (octet, 2JHp = 16.4 Hz. "C('H1 NMR (298 K): 6 140.3 (c, CI of Ph), 134.4 (t, 'Jpc = 11.1 Hz, C2 of Ph), 130.0 (s, C4 of Ph), 127.9 (t, 'Jpc = 11.1 Hz, C3 of Ph), 78.6 (c, C I of Cp), 75.8 (t, 2Jpc = 9.3 Hz, C2 of Cp), 73.2 (t, ,JK = 7.4 Hz, c, of Cp). 2-7 were similarly prepared in 40-60% yields. The analytical and spectroscopic data for 4-7 are included in the supplementary material. The isotopomeric mixtures of 1-10 were prepared by treatment of ReOC13L2with 8 equiv of LiAID, followed by hydrolysis with H 2 0 / D 2 0 (1:l molar ratio). ReH,(dppb) (2). Anal. Calcd for C28HlJP2Re:C, 54.27; H, 5.69. Found: C, 54.63; H, 5.82. IR (Nujol): vRW" 1971, 1943, 1904 cm-'. 'H NMR (298 K): 6 7.4-7.7 (c, 20 H, Ph), 2.7 (c, 4 H, CH2P), 1.6-1.8 (c, 4 H, CH2CH2P), -6.18 (t, 2 J p H = 16.2 Hz, 7 H, Re-H). ' H N M R (CD2CI2/CFCI33:2 (v/v), 163 K): 6 7.4-7.7 (c, 20 H, Ph), 2.96 (br s, 2 H, CH2P), 2.36 (br s, 2 H, CH2P), 1.88 (c, 2 H, CH2CH2P), 1.46 (c, 2 H, CH,CH2P), -4.75 (br t, 2 J p H = 32 Hz, 2 H, Re-H), -7.04 (br S, 5 H, Re-H). )'P NMR (298 K): 6 11.4. l3C('HI NMR (298 K): 6 141.0 (c, C, of Ph), 132.9 (t, 2Jpc = 9.3 Hz, C2 of Ph), 129.8 (s, C4 of Ph), 128.3 (t, 'Jpc = 9.3 Hz, C3 of Ph), 31.1 (t, 'Jpc = 31.4 Hz, CH2P), 22.4 (t, 2Jpc = 7.4 Hz, CH2CH2P). ReH,((+)-diop) (3). Anal. Calcd for C31H3902P2Re: C, 53.82; H, 5.68. Found: C, 53.66; H, 5.75. 1R (Nujol): uRrH 1984, 1953, 1928 cm-I. 'H N M R (298 K): 6 7.3-7.9 (c, 20 H, Ph), 3.84 (c, 2 H, OCH), 3.68 (c, 2 H, CH2P), 2.61 (c, 2 H, CH2P), 1.27 (s, 6 H, Me), -6.1 1 (t, 'JpH = 16.2 Hz, 7 H, Re-H). ' H NMR (CD,CI2/CFCI, 3:2 (v/v), 153 K): 6 7.3-7.8 (c, 20 H, Ph), 3.70 (c, 2 H, OCH), 3.58 (c, 2 H, CHIP), 2.60 (e, 2 H, CHIP), 1.22 (s, 6 H, Me), -4.60 (br s, 2 H, Re-H), -6.97 (br s, 5 H, Re-H). I'P NMR (298 K): 6 0.9. ' C ( ' H }NMR (298 K): 6144.8(c,C1ofPh),135.1 (~,C~0fPh'),134.4(t,~Jpc=lI.l Hz,C2 of Ph), 131.0 (t, 2Jpc = 9.3 Hz, C2 of Ph'), 129.8 (s, C4 of Ph and Ph'), 128.7 (t, 3Jpc = 9.3 Hz, C3 of Ph), 128.4 (t, 'Jpc = 9.3 Hz, C3 of Ph'), 108.2 (s, Me2C), 78.5 (t, 2Jpc = 7.4 Hz, OCH), 39.7 (t. 'Jpc = 31.2 Hz, CH2P), 26.9 (s, Me). Re&(SiPh,)(dppf). NaH (60% dispersion in mineral oil, 52 mg, 1.3 mmol) was added to a T H F (10 mL) solution of ReH,(dppf) (100 mg, 0.13 mmol) and Ph3SiH (260 mg, 1.0 mmol). The mixture was heated at reflux for 5 min and then allowed to cool to room temperature. Me2S04(120 pL, 1.3 mmol) was added. After being stirred for 10 min, the suspension was filtered through Celite. The yellow filtrate was concentrate to 0.5 mL in vacuo. Addition of E t 2 0 (5 mL) and hexane (30 mL) precipitated a yellow solid, which was filtered, washed with hexane (3 X 10 mL), and dried in vacuo. Yield: 102 mg, 76%. Anal. Calcd for C52H49FeP2ReSi:C, 62.08; H, 4.91. Found: C, 61.65; H,
J . Am. Chem. SOC.1990, 112,4821-4830 4.82. IR (Nujol): vReH 2041, 1953, 1905 cm-I. 'H NMR (298 K): 8 7.1-7.5 (c, 35 H, Ph), 4.32 (s, 4 H, Cp), 4.26 (s, 4 H, Cp), -5.1 1 (t, 2 J p ~ = 16.2 Hz, 6 H, R t H ) . 'H NMR (213 K): 8 7.1-7.6 (c, 35 H, Ph), 4.27 (s, 4 H, Cp), 4.16 (br s, 4 H, Cp), -3.33 (t, 2JpH= 31.2 Hz, 2 H, R t H ) , -6.25 (d, 2JpH = 15.4 Hz, 4 H, R t H ) . 'H NMR (CD&I,/ CFCI, 3:2 (v/v), 173 K): 6 6.1-8.0 (c, 35 H, Ph), 4.72 (br s, 2 H, Cp), 4.29 (br S, 2 H, cp), 4.20 (br S, 2 H, cp), 3.58 (br S, 2 H, cp), -3.38 (br t, 2JpH= 31 Hz, 2 H, R t H ) , -6.20 (br s, 2 H, Re-H), -6.50 (br s, 2 H, R t H ) . Selectively hydride-coupled 31P NMR (298 K): 8 17.7 (heptet, 2JHp = 15.7 Hz). '3C('HJ NMR (298 K): 6 149.4 (s, C, of SiPh,). 139.8 (c, C, of PPh2), 136.4 (s, C,of SiPh3),134.1 (t, zJpc = 11.1 Hz, C2of PPh2), 130.0 (s, C, of PPh2), 127.9 (t, 3Jpc = 10.2 Hz, C3of PPh2). 127.3 (s, C4of SiPh3), 127.0 (s, C3of SiPh3).78.5 (c, C, of Cp),
4821
Hz, C2 of Cp), 73.2 (t, 3Jpc = 5.6 Hz, C3 of Cp). ReH,(SiPh3)(dppb) and ReH,(SiPh,){(+)-diop) were similarly prepared. Their analytical and spectroscopic data are included in the s u p plementary material. 75.7 (t, *Jpc = 9.3
Acknowledgment. We thank the National Science Foundation for support, Dr. Peter Demou for assistance, and Dr. Judith A. K.Howard for neutron diffraction data of ReH,(dppe).
supplementary Material Availabk Analytical and spectroscopic data for cis-ReOC13L2 ComPlexes, R e H h complexes 4-7, ReH,(SiPh,)(dppb), and ReH,(SiPh,){(+)-diop) (5 pages). Ordering information is given on any current masthead page.
Flexibility of the Zeolite RHO Framework. In Situ X-ray and Neutron Powder Structural Characterization of Divalent Cation-Exchanged Zeolite RHO D. R. Corbin,*.t L. Abrams,+G.A. Jones,? M. M. Eddy,$ W. T. A. Harrison,t G. D. Stucky,*and D. E. Cox5 Contribution from the Central Research and Development Department," E. I . du Pont de Nemours and Company, Inc., Experimental Station, P.O. Box 80262, Wilmington, Delaware 19880-0262, Department of Chemistry, University of California at Santa Barbara, Santa Barbara, California 93106, and Physics Department, Brookhaven National Laboratory, Long Island, Upton, New York 11973. Received May 1, 1989
Abstract: Zeolite RHO has an unusual three-dimensional monolayer surface with a topology that gives equal access to either side of the surface. In the absence of supporting structural subunits, e.g., smaller cages or channels, RHO exhibits atypical framework flexibility with large displacive rearrangements. These have been investigated by in situ X-ray powder diffraction studies of zeolite RHO exchanged with various divalent cations. The unit cell variation (e.g., Ca,H-RHO (400"C), a = 13.970 ( 5 ) A; Sr-RHO (250 "C), a = 14.045 (1) A; Ba-RHO (200 "C), a = 14.184 (2) A; Cd-RHO (350 "C), a = 14.488 (3) A; Na,Cs-RHO (25 "C), a = 15.031 (1) A) is a particularly sensitive function of cation and temperature. Rietveld analysis of neutron diffraction data was used to refine the structures of two samples, Ca,ND4-RH0 and Ca,D-RHO. Ca,D-RHO shows the largest reported deviation from Im3m symmetry (a = 13.9645 ( 7 ) A) for a RHO structure. The calcium atom is located in the center of the double 8-ring, distorting the framework to generate a tetrahedral environment. The in situ X-ray studies of zeolite RHO with both monvalent and divalent cations together with the Rietveld results for the extreme end member of this structural field confirm the largest displacive distortion observed for a molecular sieve framework with a unit cell volume increase of 25% when the calcium ions of Ca,H-RHO are replaced with hydrogen ions to give H-RHO.
Zeolites are crystalline aluminosilicate materials with open framework structures of molecular dimensions. The term 'open framework" indicates the presence of intracrystalline voids-that is, cages and channels or pore openings. It is the shape and size of these pore openings that give a zeolite its molecular sieving ability and hence shape and size selectivity when used as a catalyst, support, or absorbent. For many years, zeolite frameworks have been known to exhibit small distortions.' Recent studies have shown distortions resulting in a change of symmetry on sorption of different solventsh or as a function of temperature.2b The observed distortions and their effects on the pore openings are insignificant when compared to the flexiblity and distortions observed in the framework of zeolite RHO., The flexibility in zeolite R H O offers an oppotunity to introduce a high degree of catalytic selectivity by controlled cation siting a t reaction temperatures. Our studies of the selective synthesis of dimethylamine from methanol and ammonia over zeolite R H O showed it to exhibit a unique selectivity and activity compared to other small-pore zeolites.' This observation led us to further investigate the flexibility of this zeolite framework. 'E. I. du Pont de Nemours and Company, Inc. *University of California at Santa Barbara. 8 Brookhaven National Laboratory. 'Contribution No. 4930. 0002-7863/90/1512-4821%02.50/0
The framework of R H O (Figure 1) is composed of a bodycentered cubic arrangement of truncated cubo-octahedra or acages linked via double 8-rings. X-ray powder structural studies (1) Smith, J. V. J . Chem. Soc. 1964, 3759. (2) (a) Fyfe, C. A,; Kennedy, G. J.; De Schutter, C. T.; Kokotailo, G. T. J . Chem. Soc. 1984, 541-542. Fyfe, C. A.; Stobl, H.; Kokotailo, G. T.; Kennedy, G. J.; Barlow, G. F. J . Am. Chem. SOC.1988, I I O , 3373-3380. Schlenker, J. L.; Pluth, J. J.; Smith, J. V. Mater. Res. Bull. 1979, 14, 751 and references therein. (b) Bennett, J. M.;Blackwell, C. S.;Cox, D. E. In htrazeolite Chemistry; Stucky, G. D., Dwyer, F. G., Eds.; American Chemical Society: Washington, DC, 1983; Adv. Chem. Ser. 218 pp 143-158. Bennett, J. M.; Blackwell, C. S.; Cox, D. E. J. Phys. Chem. 1983, 87, 3783-3790. Hay, D. G.; Jaeger, H.; West. G. W. J. Phys. Chem. 1985,89, 1070-1072. (3) Natrolite, with a small kinetic channel diameter of 2.6 A that will admit molecules smaller than ammonia, also has large framework distortions. (See: Baur, W. H.; Fischer, R. X.;Shannon, R. D. In Innovation in Zeolite Materials Science; Grobet, P. J., et al., Eds; Elsevier Science: Amsterdam, 1988; pp 281-292.) (4) Keane, M.; Sonnichsen, G. C.; Abrams, L.; Corbin, D. R.; Gier, T. E.; Shannon. R. D. ADD^. Catal. 1987.32.361. Shannon, R. D.; Keane, M.,Jr.; Abrams, L.; Staldy', R. H.;Gier, T. E.; Corbin, D. R.; Sonnichsen, G. C. J . Catal. 1988,1/4,8-16. Shannon, R. D.; Keane, M..Jr.; Abrams, L.; Staley, R. H.; Gier, T. E.; Corbin, D. R.; Sonnichsen, G. C. J . Catal. 1988, 113, 367-382. Rergna, H. E.; Corbin, D. R.; Sonnichsen, G. C. U.S. Patent 4683334, 1987. Bergna, H. E.; Corbin, D. R.; Sonnichsen, G. C. US.Patent 4752596, 1988. Gier, T. E.; Shannon, R. D.; Sonnichsen, G. C.; Corbin, D. R.; Keane, M., Jr. US.Patent 4806689,1989. Abrams, L.; Corbin, D. R.; Shannon. R. D. US.Patent 4 814 503, 1989.
0 1990 American Chemical Societv
