Dichlorohis(~s-cyclopentadienyl)niobium(I V) 267

References and Notes

1. The checkers performed the synthesis on one-half scale. 2. E. 0. Fischer and S . Vigoureux, Chem. Ber., 91,2205 (1958). 3. G. Wilkinson, F. A. Cotton, and J. M. Birmingham, J . Inorg. Nucl. Chem., 2, 95 (1956). 4. F. H. Kohler, and W. Prossdorf, Z . Naturjorsch., 32 (B), 1026 (1977). 5. V. M. Hall, C. D. Schmulbach, and W. N. Soby, J . Organomet. Chem., 209.69 (1981); F. A.

Cotton, S. A. Duraj, M. W. Extine, G. E. Lewis, W. J. Roth, C. D. Schmulbach, and W. Schwotzer, J. Chem. Soc., Chem. Commun., 1983, 1377; R. J. Bouma, J. H. Teuben, W. R. Beukema, R. L. Bansemer, J. C. Huffman, and J. C. Caulton, Inorg. Chem., 23,2715 (1984).

6. Tetrahydrofuran (THF) is distilled over K-benzophenone ketyl. 7. To a 2-L Schlenk flask are added 1.2 L of dry degassed xylene under N,. Freshly cut pieces of

sodium metal (30-40 g) are immersed in the xylene. The Schlenk flask is then equipped with the vibromixer (Vibromixer Model El, by Chemap AG, Holzliwisenstr. 5, CH-8604 Volket- swil, Switzerland) as shown in Fig. 2. It is very important to align the vibrating rod properly and firmly adjust it to the correct height above the bottom of the Schlenk flask, as shown. The flask is then slowly heated in a 2 L heating mantle until the Na is completely molten, after which heating is stopped. The vibromixer is then switched on and the amplitude of vibration slowly increased to a maximum. The vibration is maintained at a maximum for about one minute until a fine Na sand is obtained. The vibromixer is then switched off and the heating mantle is removed being careful not to agitate the molten Na sand to prevent fusing. The mixture is then allowed to cool to room temperature and the vibromixer then removed and replaced with a stopper. The Na sand is filtered and dried under vacuum. The checkers used a commercial Na dispersion for the preparation of sodium cyclopentadienide. The oil was washed from this material with THF in a pressure filtration device, and the Na was washed from the filter into the reaction vessel with THF.

8. R. B. King and F. G. A. Stone, Inorg. Synth., 7,99 (1963). 9. Freshly cracked cyclopentadiene is collected in a dropping funnel with Dry Ice jacket.

10. A long strong spatula flattened, rounded, and hooked at one end: long enough to fit into the sublimator ( >, 50 cm), flat part 1-2 cm large.

68. DICHLOROBIS(+CYCLOPE"~L)NIOBIUM~

Submitted by C. R. LUCAS* Checked by J. A. LABINGERt and J. SCHWARTZt

The observation of catalytic behavior exhibited by lower-valent compounds of Group 5 elements'** makes it desirable to continue to expand our knowledge of the chemistry of these and neighboring elements. The organic chemistry of the early transition elements is relatively less explored in comparison with that of later members of the series. This situation has arisen

*Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland

?Department of Chemistry, Princeton University, Princeton, NJ 08540. A l B 3x7, Canada.

Inorganic Syntheses, Volume 28 Edited by Robert J. Angelici

Copyright © 1990 by Inorganic Syntheses, Inc.

268 Cyclopentadienyl Complexes

for a number of reasons, some at least of which are related to the lack of good preparative methods for starting materials. Preparations of dichlorobis(q- cyclopentadienyl)niobium3*4 are described in the literature, but give low yields and involve tedious procedures or the use of toxic thallium reagents. In contrast, the preparation reported below provides a relatively rapid route to good yields of a suitable starting material for the investigation of organo- niobium chemistry. For example, approximately 40 g of dichlorobis(q- cyclopentadieny1)niobium can be prepared in 1 day by this method.

NbCl, + 6NaC,H, - 5NaC1+ (CSH,),Nb + organic products

2(CSH,),Nb + 4HC1+ [O] 3 [ { (q-CsH,),NbC1},O]C1,* + 2C,H, 0,

5C1- + [{(q-C5H5),NbCl}20]2+ + SnC1; + 2H+ - 2(q-C5H,),NbC1, + SnClg- + H,O

Procedure

The reaction is carried out in a 3-L three-necked flask. Through the central neck, a mechanical stirrer is fitted, and through another is added the niobium pentachloride.7 To the third neck is attached a T piece, one side of which is connected to an inert-gas supply and the other to a bubbler.

Under an atmosphere of dry nitrogen, dry cyclopentadienylsodium $ (lOOg, 1.14mol) is prepared and suspended at room temperature in dry

*The ionic substances containing niobium(V) that exist in these red solutions have not all been identified. In addition to the ion indicated, species of the form [(q-C,H,),Nb(X)YI+ (X, Y = C1, Br, OH, or 0-) are probably present in an unknown equilibrium with each other.

t Niobium pentachloride is available commercially from Alfa Inorganics, Ltd. The checkers found that sublimation of the commercial material in U ~ C U O was necessary before use in the preparation.

t. White cyclopentadienylsodium can be prepared by cracking dicyclopentadiene (for details, see Organometallic Syntheses, J. J. Eisch and R. B. King (eds.), Vol. 1, pp. 64ff., Academic Press, New York, 1965) under an atmosphere of dry nitrogen directly into a suspension of sodium sand in dry tetrahydrofuran from which dissolved oxygen has been removed. The apparatus for this operation should be assembled so that the distillate of cyclopentadiene monomer is added directly under nitrogen to the sodium. The distillation should proceed at a rate of -3mLmin-' until almost all the sodium has dissolved. The bulk of volatile substances may then be removed in vacua on a hot-water bath to give a sticky white residue. Final removal of the last traces of tetrahydrofuran from this product is essential. This can be accomplished by heating the residue to loo" in u a m until no more liquid distils into a liquid- nitrogen trap. Breaking up large lumps assists solvent removal. Large batches (300 g) may require heating for up to 72 h.

Dichlorobis(r15-cyclopentodienyl)niobi~~ V) 269

benzene* (400 mL). With vigorous mechanical stirring, powdered niobium pentachloride (57 g, 0.21 mol) is added in small portions, with care being taken to prevent the reaction temperature from exceeding -70" after each addition. After 1 h the suspension has cooled to room temperature and is a uniform purple-brown color. It is stirred for another f h and then poured in air onto concentrated hydrochloric acid (1 L). The resulting mixture is heated gently (in the hood) with occasional swirling until all the benzene has been evaporated. To the boiling brown suspension, small quantities of bromine are then carefully added ( - 60 mL in all) until the solid phase no longer acts like a sticky lump (some scraping of the vessel walls may be necessary) but as a suspended powder.

Caution. Bromine attacks respiratory passages and should only be handled in an eficient hood.

Excess bromine is then boiled away. The hot red? liquid is decanted in air through a filter; extraction with hot concentrated hydrochloric acid and bromine is repeated until the extracts are nearly colorless. After about 10 extractions, the collected filtrates are brought to the boiling point to re- dissolve any precipitated matter, and they are placed under an inert atmosphere.$ To the hot solution is added under an inert atmosphere a hot solution of tin dichloride dihydrate (47.5 g, 0.21 mol) in concentrated (12 M) hydrochloric acid (200 mL), and the mixture is left standing overnight. The brown tabular crystals of dichlorobis(q-cyclopentadieny1)niobium are separ- ated by filtration, and the product is washed several times with water and once with acetone (50 mL) before being dried in uacuo. Yield is 45 g (75% based on NbC15).

Anal. Calcd. for C,,H,,Cl,Nb: C, 40.8; H, 3.4; C1,24.1; Nb, 31.6. Found: C, 40.8; H, 3.5; C1, 24.2; Nb, 31.3.

Properties

Crystals of the product obtained by this method may be weighed and handled in air although they should be stored and used in further reactions under an inert atmosphere. The compound is only very sparingly soluble in common organic solvents. It is paramagnetic and its electron spin resonance spectrum at room temperature and 77K has been rep~r ted .~ Its infrared spectrum

*Freshly distilled from calcium hydride and free from dissolved oxygen. tIf the cyclopentadienylsodium is not dry and white, the hydrochloric acid extracts will be

pink or yellow instead of red, and the major product of this preparation will be a white precipitate of Nb,O,.

$The checkers find that concentration of the extracts improves the yield.

270 Cyclopentodienyl Complexes

(Nujol) is 3090 (m), 101 1 (m), 822 (s), 725 (m), 308 (m), 290 (s), and 268 (s)cm-'.

References

1. F. N. Tebbe and G. W. Parshall, J. Am. Chem. SOC., 93, 3793 (1971). 2. M. D. Curtis, L. G. Bell, and W. M. Butler, Organometallics, 4, 701 (1985). 3. F. W. Siegert and H. J. de Liefde Meijer, J. Organomet. Chem., 23, 177 (1970). 4. W. E. Douglas and M. L. H. Green, J. Chem. SOC. Dalton Trans., 1972, 1796. 5. A. T. Casey and J. B. Raynor, J. Chem. SOC. Dalton Trans., 1983, 2057.

69. CHLORO( tf-CY CLOPENTADIENY L)BIS(TRIPHENYL PHOSPHINE)RUTHENIUM(I): RuCI(PPh,),( q5-C5H5)

Submitted by M. I. BRUCE,* C. HAMEISTER,* A. G. SWINGER,* and R. C. WALLIS*

Checked by S. D. ITTELt

The chemistry of RuCl(PPh,),(qS-C,H,) differs markedly from that of the corresponding dicarbonyl complex, RuCl(CO),(q5-C,H,).' The triphenyl- phosphine complex was first described by Gilbert and Wilkinson,, who obtained it from a 2-day reaction between RuCl,(PPh,), and cyclopenta- diene in benzene. An improved synthesis was described later,, from RuCl,(PPh,), and thallium(1) cyclopentadienide. Both reactions are difficult to employ if large amounts of this complex are required; the competing dimerization of RuCl,(PPh,), to [RuCl,(PPh,),], reduces yields in the first reaction, especially at temperatures above 20", while the bulk of the thallium compounds makes the second reaction less convenient. The present method employs a slight modification of the one-pot reaction described earlier.4

The most significant differences in the chemistries of RuC1(PPh,),(qs- C,H,) and RuCl(CO),(qS-C,H,) are the ready displacement of chloride from the former complex by neutral ligands, L, to form cationic complexes [RuL(PPh,),(q5-C5Hs)]+ 3, and exchange of one or both triphenylphos- phine ligands for other neutral ligands. The chloro complex is the precursor of choice for syntheses of related complexes containing other monodentate or chelating bidentate tertiary phosphines, including those with optically active

*Department of Physical and Inorganic Chemistry, University of Adelaide, Adelaide, South

?Central Research and Development Department, E. I. du Pont de Nemours & Co., Australia 5000.

Wilmington, DE 19898.