Volume 19
Inorganic Chemistry
Number 3 March 1980
I
0 Copyright 1980 by the American Chemical Society
Contribution from the Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
Reactions of the Gaseous Hydrogen Halides with Dimers of Molybdenum(I1) and Tungsten(I1) Containing the Anion of 2-Hydroxy-6-methylpyridine DAVID DEMARCO, TAYSEER NIMRY, and RICHARD A. WALTON* Received September 14, 1979
Whereas the reaction of the molybdenum(I1) dimer Mo2(mhp), (where mhp represents the anion of 2-hydroxy-6methylpyridine) with a cesium halide and a hydrogen halide gas in refluxing methanol produces the cctahalodimolybdate(II) Cs4M02X8(X = C1 or Br), the related tungsten(I1) dimer is oxidized to Cs3W2X9.In the absence of CsX and in the presence of triethylphosphine, the Wz(mhp), complex is still oxidized, but in this case the green methanolysis products W2X4(OMe)*(MeOH), precipitate. The use of other alcohols as the reaction solvent shows that this is a convenient synthetic route to W-W bonded dimers of the type WzX4(OR),(ROH),. There is no evidence for the formation of the WzX:- anion from the reaction of W2(mhp), with HX in nonaqueous solvents.
Introduction The discovery by Cotton and co-workers',2 that tungsten hexacarbonyl is oxidatively decarbonylated by 2-hydroxy-6methylpyridine ( H m h p ) and 2,4-dimethyl-6-hydroxypyrimidine (Hdmhp) in refluxing diglyme to produce the metal-metal bonded dimers W2(mhp)4 and W2(dmhp)d is very important since it provides for the first time a direct and convenient entry into the chemistry of complexes containing tungsten-tungsten quadruple bonds. Such species have in the past been something of a rarity,3 the W2ClS4-anion, for example, having so far defied isolation in spite of the stability and ease of isolation of salts of the related molybdenum anion,
MO~C~~~-.~ Our interest in molecules such as W2(mhp)4 and W2(dmhp), stems from the possibility of using them as synthetic precursors to other tungsten dimers, particularly those which no longer contain a n intramolecular bridging ligand system (e.g., W2XS4-). Cotton et aL4have already demonstrated the synthetic utility of one of these dimers, namely, W2(mhp),, by converting it to W,(map),, a complex which contains the anion of 2-amino-6-methylpyridine (Hmap). Following our earlier investigation^^-^ into the reactivity of the dimeric metal acetates Mo2(02CCH3),, Re2(02CCH3),C12, and Rh2(02CCH3),toward the gaseous hydrogen halides, we became interested in exploring the related reactions of some suitable metal-metal bonded tungsten dimer. Although W2(02CCH3), has yet to be isolated and structurally characterized, the availability of complexes such as W2(mhp), now Cotton, F. A.; Fanwick, P. E.; Niswander, R. H.; Sekutowski, J. C. J . Am. Chem. Soc. 1978, 100, 4125. Cotton, F. A.; Niswander, R. H.; Sekutowski, J. C. Inorg. Chem. 1979, 18, 1152. Cotton, F. A. Acc. Chem. Res. 1978, 11, 224. Cotton, F. A.; Niswander, R. H.; Sekutowski, J. C. Inorg. Chern. 1978, 17, 3541. Glicksman, H. D.; Hamer, A. D.; Smith, T. J.; Walton, R. A. Inorg. Chem. 1976, 15, 2205. Glicksman, H. D., Walton, R. A. Inorg. Chem. 1978, 17, 200. Glicksman, H. D.; Walton, R. A. Inorg. Chem. 1978, 17, 3197. Glicksman, H. D.; Walton, R. A. Inorg. Chim. Acta 1979, 33, 255.
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provides us with the opportunity to study the reactivity of a complex containing the W +: core. The results of our studies into the reactions of W2(mhp), and its molybdenum analogue with the hydrogen halides in alcoholic media are now reported.
Experimental Section Starting Materials. The complexes Mo2(mhp), and W2(mhp), were prepared by the standard literature procedure.' 2-Hydroxy-6methylpyridine (Hmhp) and other reagents were obtained from commercial sources and were used as received. Diglyme was distilled over CaH, in a nitrogen atmosphere. All other solvents were dried over molecular sieves. Reaction Procedures. All reactions were carried out in a nitrogen atmosphere, and solvents were deoxygenated by purging with N2 gas prior to use. A. Reactions of Mo2(mhp)+ (i) Cs4MozCls. Finely ground Mo2(mhp), (0.65 g, 1.0 mmol) and CsCl (1.3 g, 7.7 mmol) were placed in a three-necked round-bottom flask which was then flushed with nitrogen for 30 min. A 25-mL sample of methanol was added, and the resulting suspension was refluxed while anhydrous HCl gas was bubbled through the reaction mixture. After 30 min, the reaction mixture was filtered and the resulting red solid (0.9 g) was washed with warm methanol and dried in vacuo; yield 84%. Anal. Calcd for C18Cs4M02:C1, 28.16. Found: C1, 27.99. (ii) Cs4M02Br8.This complex could be obtained in 66% yield by using a procedure similar to that described in section A(i). Anal. Calcd for Br8Cs4M02: Br, 46.91. Found: Br, 46.55. (iii) [Bu4NjzMo41i,. A mixture of finely ground Mo2(mhp), (0.9 g, 1.44 mmol) and Bu4NI (2.66 g, 7.2 mmol) was placed in a three-necked flask and flushed with nitrogen for 30 min. A 35-mL sample of tetrahydrofuran was added and the resulting mixture refluxed while anhydrous HI was bubbled through the solution. After 2.5 h, the reaction mixture was cooled and kept at 0 "C for 48 h. The resulting black crystals (0.57 g) were filtered off, washed with diethyl ether, and dried in vacuo; yield 38%. Anal. Calcd for C32H721,,M~2N2: C, 16.95; H, 3.17; I, 61.68. Found: C, 17.23; H, 3.39; I, 61.90. B. Reactions of W2(mhp)4. (i) Cs3W2Q-MeOH. With a procedure similar to that described in section A(& this green complex could be obtained in 8 1% yield. Anal. Calcd for CH4C19Cs30W2:C, 1.07; H, 0.36; C1, 28.55. Found: C, 1.07; H, 0.36; CI, 28.45. (ii) Cs3W2Br9.MeOH. The green complex of this stoichiometry was obtained in 46% yield by using a procedure analogous to section
0 1980 American Chemical Society
576 Inorganic Chemistry, Vol. 19, No. 3, 1980
DeMarco, Nimry, and Walton
A(i). Anal. Calcd for CH4Br9Cs30W2:Br, 47.3. Found: Br, 48.15. (iii) W,Q(OMe),(MeOH),. T h e reaction between W,(mhp), and HCI gas in refluxing methanol was carried out by using a procedure analogous to that used in section A ( i ) except that a quantity of triethylphosphine (0.5 mL) was added in place of t h e CsC1. The resulting bright green insoluble complex was obtained in 50% yield. Anal. Calcd for C6H2,C1406W2:C, 10.29; H, 3.14; C1, 20.26. Found: C, 10.60; H, 3.00; CI 20.93. (iv) W2Br,(OMe)2(MeOH)o The green complex approximating to this stoichiometry was obtained in 23% yield when a procedure analogous to that described in section B(iii) was followed. Anal. Calcd for CsH2,Br4O6W2:C, 8.21; H , 2.51; Br, 36.43. Found: C , 8.61; H , 2.36; Br 37.0. (v) W2C14(0Et)2(EtOH)4.Using a procedure similar to that described in section B(iii), but with ethanol as t h e reaction solvent, afforded this green complex in 53% yield. Anal. Calcd for C12C14H3406W2: C, 18.37; H, 4.33; CI, 18.10. Found: C, 18.58; H, 4.43; C1 18.12. Physical Measurements. Spectroscopic characterizations were carried out by using instrumentation described p r e v i o ~ s l ywith ~ ~ ~the exception of infrared spectra, which were obtained on a Digilab F t S 20B spectrometer.
sorption and vibrational spectral properties of these two complexes were in good agreement with literature data for these complex anions.I4-l6 Furthermore, their X-ray photoelectron spectra ( W 4f7j2binding energy of 32.8 eV in each case) are in accord with literature data for K3W2C19 and (B~qN)3W2Cl9.l 7 In an attempt to prevent the oxidation of WZ(mhp), to derivatives of the W26+core, this complex was reacted with a hydrogen halide gas in methanol or ethanol in the presence of triethylphosphine. Our hope was that the phosphine would immediately complex any tungsten(I1) halide intermediates which were formed and convert them to W2X4(PEt3),, the tungsten analogues of the well-known class of molybdenum dimers of this type.5J8J9 This strategy was unsuccessful as evidenced by our isolation of the green tungsten(II1) alkoxy species W2X4(OR)2(ROH)4. Complexes of this type had previously been prepared by Clark and WentworthZ0from reaction of the appropriate alcohol with ( ~ - B U , N ) ~ W ~ C ~ ~ . Accordingly, it seems likely that in the reaction of W2(mhp), with hydrogen halide, oxidation to tungsten(II1) occurs extremely rapidly, possibly through the oxidative addition of H X Results and Discussion across the tungsten-tungsten quadruple bondz1rather than the The reactions between mixtures of Moz(mhp),, cesium initial formation of simple halide substitution product conhalide, and gaseous HC1 and HBr in refluxing methanol taining the W+: core.23 provide a convenient route to the well-known salts Cs4MozX8 As it turns out, our synthesis of WzX4(0R)z(ROH)4conin yields in excess of 60%. The spectral properties of the stitutes a very convenient route to these complexes since this samples prepared in the present work compare favorably with procedure is easily extended to the previously unknown the published spectral To confirm further the bromide derivatives without changing the starting material. identity of these products, we converted both of them to We believe that the phosphine reagent which is added to the phosphine derivatives of the type Mo2X4(PR3), by reaction W,(mhp),/HX/ROH reaction mixture may promote the with triethylphosphine in refluxing methanol. The latter elimination of H X during the alcoholysis of the W-X bonds. complexes were characterized by a comparison of their infrared When it is excluded from’the reaction mixture, the tungand electronic absorption spectra with samples of these comsten(II1) alkoxides do not precipitate. plexes prepared from K4MozC18or P - M o X ~ . ~ The three complexes prepared in the present work, The retention of the Mo2,’ core in these reactions should W2C14(0R)2(ROH)4(R = Me or Et) and W2Br4(OMe)2be contrasted with the relative ease with which M O ~ ( O ~ C C H ~ ) (MeOH),, ~ had identical diffuse reflectance electronic abis oxidized under comparable reaction conditions.’ Thus in at 725-735 and 415-420 nm) which in sorption spectra (A, the presence of appropriate tetra-n-butylammonium halide, turn resembled the spectra of chloroform solutions of the complexes (n-Bu,N)MoOCl, and (n-Bu4N)Mo2Br6are W2C14(OR)2(ROH)4reported by Clark and Wentworth.20 isolated. Whether these differences reflect the greater senThe infrared spectra of the methoxy derivatives WzX4sitivity of Mo2(02CCH3), to adventitious oxygen or are a (OMe)2(MeOH)4were identical in the region 400Ck600 cm-’, consequence of different mechanisms for the displacement of and a molecular weight determination of a chloroform solution the bridging acetate and mhp ligands by halide ion is uncertain of W2C14(OEt),(EtOH), confirmed the dimeric nature of this a t present. complex (found, 778; calcd, 784). Our attempts to convert Mo2(mhp), to the analogous iodide The X-ray photoelectron spectra of these complexes reveal Cs4MoZI8failed. Only by changing to the tetra-n-butylammonium cation and by using tetrahydrofuran as the solvent thereby demonstrating that these products are free of any high did we isolate a pure product. This turned out to be the black oxidation state tungsten oxide contaminants. The W 4f5/2and crystalline cluster complex (~-Bu,N)~Mo,I,,,a species which 4f7j2energies occur a t 35.9-35.7 and 33.8-33.6 eV, respecwe had prepared’ previously from Mo2(OZCCH,), and which tively:, values which are somewhat higher than for the W2X9> had also been isolated independently by McCarley and coHayden, J. L.; Wentworth, R. A. D. J. A m . Chem. SOC.1968,90,5291. w o r k e r ~ . ~The ~ material prepared in the present investigation Saillant, R.; Hayden, J. L.; Wentworth, R. A. D. Inorg. Chem. 1967, had spectroscopic properties (including its ESR and X-ray 6 , 1497. R. J.; Risen, W. M., Jr. Inorg. Chem. 1972, 1 1 , 2796. Ziegler, Dhotoelectron sxctra) identical with those of authentic samples Ebner, J. R.; McFadden, D. L.; Tyler, D. R.; Walton, R. A. Inorg. bf ( ~ - B u ~ N ) ~ M o ~ I ~ , : ~ Chem. 1976, 15, 3014. Our ability to convert MoAmhp), into Cs4M02X8( x = c1 San Filippo, J., Jr. Inorg. Chem. 1972, 1 1 , 3140. A synthetic route to the tungsten(I1) complexes W2C14(PR3)4has reor Br) without any ensuing oxidafion of the metal dimer unit cently been devised through the thermal decomposition of WC12(PMe3)4. prompted us to attempt the conversion of W,(mhp), to See: Sharp, P. R.; Schrock, R. R. “Abstracts of Papers”, 178th Nacs4w2x8. Regrettably, the reactions involving mixtures of tional Meeting of the American Chemical Society, Washington, D.C., Sept 1979; American Chemical Society: Washington, D.C., 1979; W,(mhp),, cesium halide, and a hydrogen halide in methanol Abstract No. INOR 147. led to the rapid precipitation of the methanol solvate of Clark, P. W.; Wentworth, R. A. D. Inorg. Chem. 1969, 8, 1223. Cs3W2X9(X = C1 or Br) in good yield. The electronic abSuch a reaction could be similar to the oxidative addition of HX to the ~
~~~~
(9) Brant, P.; Walton, R. A. Inorg. Chem. 1978, 17, 2674. (IO) Ketteringham, A. P.; Oldham, C. J . Chem. SOC.,Dalton Trans. 1973, 1067. (11) Clark, R. J. H.; D’Urso, N. R. J . A m . Chem. SOC.1978, 100, 3088. (12) Bratton, W. K.; Cotton, F. A.; Debeau, M.; Walton, R. A. J . Coord. Chem. 1971, 1, 121. (13) Stensvad, S.; Helland, B. J.; Babich, M. W.; Jacobson, R. A,; McCarley, R. E. J . A m . Chem. SOC.1978, 100, 6252.
Mo-Mo quadruple bond of M O ~ ( O ~ C Cwhich H ~ ) ~occurs in aqueous media.22 Bino, A,; Cotton, F. A. Angew. Chem., Ini. Ed. Engl. 1979, 18, 332. While we have not yet established the nature of the reduction byproducts of these metal oxidations, we find no evidence for any gaseous products (including hydrogen). The C 1s energy of the methoxy and methanol carbon atoms of W2X4(0Me)z(MeOH)4is located at 285.5 f 0.1 eV. The full width at half-maximum (fwhm) values of the W 4f peaks are 1.4 i 0.1 eV.
Inorg. Chem. 1980, 19, 577-587
anions. The C12p binding-energy spectra of the two chloride complexes are each characterized by a very well-resolved C1 2P1/2,3/Z doublet (the c12P3 2 component is located at 198.2 eV for W2C14(OMe)2(MedH)4 and 197.9 eV for w2cl4(OEt),(EtOH),) which is a good indication that only a single type of chlorine environmentz5 is present within these complexes, This supports an alkoxy-bridged structure rather than (25) Walton, R. A. Coord. Chem. Reo. 1976,21, 63.
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a halogen-bridged structure for WzX4(0R)2(ROH)4. Acknowledgment. Support from the National Science Foundation (Grants CHE74-12788 and CHE79-09233) is gratefully acknowledged, Registry No. Moz(mhp),, 67634-80-4; W2(mhp),, 67634-84-8; Cs4M02C189 55937-61-6;CS4M02Br8, 41772-62-7; [Bu4N12M04111, 68024-65-7; Cs3W2Cl9, 23403-18-1; CsJW2Br9, 72332-25-3; WzC14(0Me)2(MeOH)4, 12552-15-7; WzBr4(OMe)2(MeOH)4, 72301-56-5; W2CI,(OEt)2(EtOH),, 72301-57-6.
Contribution from the Department of Chemistry, University of Natal, Pietermaritzburg, Republic of South Africa, and the Department of Inorganic and Analytical Chemistry, University of Pretoria, Pretoria, Republic of South Africa
Reactions of Metal Carbonyl Derivatives. 23.’ Donor Behavior of [FeP(C6H5)2(Co)2(r-C5H4R)] (R = H, CH3) toward Various Rhodium and Iridium Complexes and the Role of the Solvent in the Type of Product Formed. Reversible Uptake of Carbon Monoxide and Dihydrogen by the Nonclosed Trinuclear Species [M’{FeP(C6H5),(CO),( r-C5H4R)j2]+ (M’ = Rh, Ir)2 J. C. T. R. BURCKETT-ST. LAURENT,3aR. J. HAINES,*3a C. R. NOLTE,Sband N. D. C. T. STEEN3a Received July 13, 1979
The metal-containing phosphine [P(C&5)&fLn] (ML, = Fe(CO)z(?-C,H,R) (R = H or CHJ) reacts with various compounds of rhodium in alcohol, including [RhC13.3Hz0]and [(Rh(CsH12)C1]z], to produce in each case, when present in slight excess, having a nonclosed structure in which the iron a cationic species of stoichiometry [Rh(FeP(C6H5)z(CO)2(?-C5H4R))z]+, and rhodium atoms are bridged by a carbonyl as well as by a phosphino group. The iridium analogue is formed in the corresponding reaction involving [Ir(CsH,z)(solvent),]+but not [(Ir(CsH12)Cl)z]. Coordinating solvents such as tetrahydrofuran, acetone, diglyme, methanol, and acetonitrile react reversibly with these cationic species to afford products containing terminal carbonyls only. Controlled addition of P(OCH,),, P(C&)3, halide ions, or pseudohalide ions to [Rh(FeP(C,H,),(CO)z(~-C5H4R))2]+ leads to the formation of simple adducts of the parent compound, in which the bridged structure is retained, while treatment of [M’(FeP(C6H5)2(CO)z(?-C5H4R))z]+ (M’ = Rh, Ir) with carbon monoxide in dichloromethane or chloroform gives rise to a compound characterized as [M’(co)3{P(c6H5)2MLn)z]+.Whereas the carbonylation of [Rh(FeP(C6H5)2(CO)2(?-C5H4R))2]+ is reversible, that involving the iridium species is irreversible. Hydrogen also reacts although high pressures are required for the rhodium reaction. Treatment of with [M’(FeP(C6H5)z(CO)2(q-C5H4R))2]+ [(Rh(CO)zCl),] or [(Rh(CgHI2)Cl)z]with [P(C6H5)zMLn]in benzene affords neutral [Rh(CO)(P(C6H5)2MLn]zC1] which by treatment with silver ions. The iridium compound [Ircan be converted to [Rh(FeP(C6H5)z(CO)2(q-C5H4R)]z]+ (CO)(P(C6H,)2ML,)zCI] is obtained similarly from [(Ir(CSH1z)Cl)2].Reaction of [RhL’z(solvent),]+ or [Rh(C8H12)L’2] (L’ = P(OC6H&, P(CH3)*C6H5;2L’ = CsHlz or (C6H5)2PCzH4P(C6H5)2) with an equimolar amount of [P(C6H5)zMLn] which, similar to the trinuclear species, contains in alcohol gives a dinuclear product, [RhL’2(FeP(C6H5)z(CO)z(?-C5H5))]+, both a bridging carbonyl and a bridging phosphino group. The donor properties of [SR’ML,] (R’ = C2H5,r-C,H,, C&5) toward various rhodium derivatives are also described. +
Metal-cluster complexes are receiving much attention of late. This can be attributed to their potential as models for metal surfaces in heterogeneous catalysis4v5as well as to the highly fascinating and novel chemistry already discovered for a number of them.”12 Support for their utilization as models is provided by recent observations that certain metal-cluster derivatives are effective homogeneous catalysts for a number (1) Part 22: R. B. English, L. R. Nassimbeni, and R. J. Haines, J . Chem. SOC.,Dalton Trans., 1379 (1978). (2) Preliminary communications: (a) R. J. Haines, R. Mason, J. A. Zubieta, and C. R. Nolte, J. Chem. SOC.,Chem. Commun., 990 (1972); (b) R. J. Haines, J. C. T. R. Burckett-St. Laurent, and C. R. Nolte, J . Organomet. Chem., 104,C27 (1976). (3) (a) University of Natal. (b) University of Pretoria. (4) E. L. Muetterties, Bull. SOC.Chim. Belg., 84, 959 (1975). ( 5 ) E. L. Muetterties, Science, 196,839 (1977). (6) R. J. Haines, Chemsa, 2, 101 (1976). (7) See also ref 8-12 and references quoted therein. (8) E. G. Bryan, B. F. G. Johnson, J. W. Kelland, and J. Lewis, J . Chem. SOC.,Chem. Commun., 254 (1976). (9) J. B. Keister and J. R. Shapley, J. Am. Chem. SOC.,98,1056 (1976). 99,5225 (1977). (10) R. B. Calvert and J. R. Shapley, J . Am. Chem. SOC., (1 1) K. A. Azam, A. J. Deeming, R. E. Kimber, and P. R. Shukla, J. Chem. SOC.,Dalton Trans., 1853 (1976). (12) A. J. Deeming, J. Organomet. Chem., 128,63 (1977).
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of processes which, until these particular discoveries, could only be catalyzed by heterogeneous systems. For instance [Os3(CO),,] and [Ir4(CO)12]have been found to homogeneously catalyze the reduction of carbon monoxide by dihydrogen to methane,13 a reaction readily promoted by nickel surfaces14 and for which mononuclear homogeneous catalysts have thus far not been reported.I5 Furthermore ruthenium and mixed iron/ruthenium carbonyl clusters, in the presence of a base, (13) M. G. Thomas, B. F. Beier, and E. L. Muetterties, J. Am. Chem. SOC., 98,1296 (1976). (14) G. A. Mills and F. W. Steffgen, C a r d Reo., 8, 159 (1973). ( 15) Recent studie~’~~’’ have revealed that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadieny1)zirconium are capable of promoting the stoichiometric reduction of carbon monoxide by dihydrogen to methoxide but a dinuclear species [(Zr(?-C,(CHf)5]zH)zCHzO]has been proposed as an intermediate in this reaction. Significantly a compound analogous to this intermediate, viz., [{Zr(s-C,H,)zCl)zCHzO],has been shown to be roduced in the reaction of [Zr(tpC5H5)2HCI]with carbon monoxide.Ip (16) J. M. Manriquez, D. R. McAlister, R. D. Sanner, and J. E. Bercaw, J. Am. Chem. SOC.,98,6733 (1976). (17) J. M. Manriquez, D. R. McAlister, R. D. Sanner, and J. E. Bercaw, J. Am. Chem. Soc., 100, 2716 (1978). (18) G. Fachinetti, C. Floriani, A. Roselli, and S. Pucci, J. Chem. SOC., Chem. Commun., 269 (1978).
0 1980 American Chemical Society
