I54 Transition Metal Organometallic Compounds

warmed to room temperature, and the residual solvent is carefully pumped off with stirring. When all traces of solvent have been removed from the product, the extractor is opened in the glove box. The thimble and plug are removed, and the stub end of the side arm is scored and broken off. The bis(q"-cyclooctate- traene)uranium(IV) is scraped out through the resultant hole with a long-handled spatula. Yield 9.6 g (82%).

The bis(q"-cyclooctatetraene)uranium(IV) can be purified further by extraction with benzene or by sublimation at 140°/10" torr.

Properties

The green crystals of bis(q8-cyclooctatetraene)uranium(IV) are air and water sensitive and only slightly soluble in aromatic and polar organic solvents. The visible spectrum is characteristic. GkF: 615 (1850); 641 (890); 660 (600); and 680 nm (350 L/mole-cm). The IR spectrum shows only four strong bands at 3000,1430,900, and 741 ~ m - ' . ~

References

1. A. Streitwieser, Jr. and U. Mueller-Westerhoff, J. Am. Chem. SOC., 90, 7364 (1968). 2. A. Streitwieser, Jr. and C. A. Harmon, Inorg. Chem., 12, 1102 (1973). 3. K. 0. Hodgson, F. Mares, D. F. Starks, and A. Streitwieser, Jr., J. Am. Chem. Soc., 95,

8650 (1973). 4. A. Streitwieser, Jr., U. Mueller-Westerhoff, G. Sonnichsen, F. Mares, D. G. Monell,

K. 0. Hodgson, and C. A. Harmon, J. Am Chem SOC, 95, 8644 (1973). 5. D. F. Starks, Ph.D. Dissertation, University of California, Berkeley, 1974. 6. D. F. Starks and A. Streitwieser, Jr.,J. A m Chem. Soc., 95, 3423 (1973). 7. D. F. Shriver, The Manipulation of Air-Sensitive Compounds, McGraw-Hill Book Co.,

New York, 1969. 8. Inorg. Synth., 12, 317 (1970). 9. T. J. Katz,J. A m Chem. Soc.. 82, 3184 (1960).

10. J. A. Hermann and J. F. Suttle, Inorg. Synth., 5 , 143 (1957).

35. (q6 -ARENE)TRICARBONYLCHROMIUM COMPLEXES

Submitted by C. A. L. MAHAFFY* and P. L. PAUSON" Checked by M. D. RAUSCHt and W. LEE?

Most simple arenes react smoothly with Cr(C0)6 to give hexahapto complexes

*Deparement of Pure and Applied Chemistry, University of Strathclyde, Thomas Graham

?Department of Chemistry, University of Massachusetts, Amherst, MA 01002. Building, Cathedral Street, Glasgow, G1 EL.

35. (q6-.4rene) tricarbonylchromium Complexes 155

($-ArH)Cr(CO),. The reactions have been conducted under a wide variety of conditions,’ and the chief problems encountered arise from (a) the volatility of cr(co)6, (b) slowness of the reaction, and (c) difficulty in removing high-boiling solvents or excess arene from the product. Sublimation of Cr(CO)6 from the reaction vessel has been overcome by the use of rather complex apparatus,” but the following procedure shows this to be unnecessary. In inert solvents [decahydronaphthalene (decalin) has been widely used] , reaction is excessively slow. Donor solvents (D) lead to appreciably more rapid reaction, probably by way of intermediates Cr(CO),.,D, (where n = 1-3); but if the donor is too good (e.g., C6HsCN), it may compete, especially with the less reactive arenes (e.g., C6HSCN), leading to incomplete complex formation. Alkylpyridines have been re~ommended,~’~ but ethers have been much more widely used. Tetrahydro- furan (THF), a good donor, allows reaction to proceed cleanly’ but too slowly because of its low boiling point. Dibutyl ether also leads to rather slow reaction, probably because of its weak donor properties, whereas bis(2-methoxyethyl) ether (diglyme), which is better in t h i s respect, is relatively difficult to remove. The following procedure therefore uses a mixture of dibutyl ether with sufficient THF to “catalyze” the reaction and to wash back most of the Cr(C0)6 that sublimes into the condenser, but not enough to lower the boiling point too much.

A. ($-ANIS0LE)TRICARBONYLCHROMIUM

Procedure

.Caution. The reaction should be carried out in a well ventilated hood, as hexacarbonylchromium is toxic and carbon monoxide is evolved during the reaction. Both ether solvents peroxidize; they should be carefully freed from peroxide and dried (conveniently by distilling from lithium tetrahydridoalumi- nate or from sodium) before use. Benzene is toxic; contact with the liquid or vapor should be avoided.

In a 250-mL, round-bottomed flask fitted’with a gas inlet and a simple reflux condenser [not spiral or similar type from which subliming Cr(CO), is washed back less efficiently] are placed hexacarbonylchromium (4 g, 18 mmole), anisole (25 mL), dibutyl ether (120 mL) and tetrahydrofuran (10 mL). A bubbler is placed at the top of the condenser to prevent access of air. The apparatus is thoroughly purged with nitrogen. The nitrogen stream is stopped and the mixture is then heated at reflux for 24 hours (the checkers found stirring beneficial). The yellow solution is cooled and filtered through kieselguhr (diatomaceous earth) or a similar material (the checkers used Celite or, preferably, a small pad of anhydrous silica gel) on a sintered-glass filter, which is

156 Transition Metal Organometallic Compounds

then washed with a little additional solvent. The solvents are distilled off on a rotary evaporator from a water bath held at 60' (an oil pump may be required to remove the solvents completely); a deep-yellow oil remains to which dry lght petroleum ether (bp. 40-60') or hexane (20 mL) is added. Crystalline ($- aniso1e)tricarbonylchromium [4.1 g (92%), mp 83-84OI separates. A small amount of unreacted Cr(CO), may be recoverable from the condenser; the remainder distills off with the solvent. If a very pure product is required the compound may be recrystallized by dissolving it in benzene or in diethyl ether and adding light petroleum ether to give 3.53 g (80%), mp 84-85'; lit! mp 84-85'. Anal. Calcd. for CI0HBCrO4: C, 49.2; H, 3.3. Found: C, 49.5; H, 3.4.

Solutions of this compound and other arenetricarbonylchromiums can only be handled for very brief periods in air. The workup procedures are therefore best carried out in an inert atmosphere throughout, but they can be conducted in air if done rapidly and efficiently.

Properties

($-Aniso1e)tricarbonylchromium is a yellow crystalline solid. Its NMR spectrum' (CDC13 solution) shows a singlet at T 6.4 for the CH30 group and three well-resolved signals for the metal-bound ring at T 5.23 (lH, t) 4.97 (2H,d) and 4.6 (2H, t). Its solutions are air sensitive, forming greenish precipitates, but the pure solid is stable. However, refrigeration is recommended for prolonged storage.

B. OTHER ARENETRICARBONYLCHROMIUM COMPLEXES

The general applicability of the above method is illustrated by the examples in Table I. With the lowest boiling arenes, subliming cr(co)6 is completely washed back, and none is recovered at the end of the reaction. However, the reduced boiling point of the mixture necessitates a longer reaction time. For arenes of higher boiling points, it is preferable not to use a large excess, since it would be difficult to remove at the end of the reaction. This leads to a somewhat less complete reaction, but since much of the unchanged Cr(CO), is readily recovered from the condenser and the distillate, yields in the table are based on unrecovered carbonyl. The result with anisole when only a small excess is used is included for comparison. The arenes for which resuits are tabulated are liquids, but several solid arenes have been used similarly. Thus the checkers obtained an 8 1% yield of (tripheny1ene)tricarbonyl chromium using a 1 : 1 molar ratio of the hydrocarbon to Cr(CO),.

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158 Transition Metal Organometallic Compounds

Reactivity

The chemistry of arenetricarbonylchromium complexes has been extensively studied and reviewed.'0''' Compared to the uncomplexed arenes they show greatly enhanced reactivity towards nucleophiles."

References

1.

2.

3.

4. 5.

6. 7.

8.

9.

10.

11. 12.

Comprehensive references may be found in Cmelin 's Handbuch der anorganischen Chemie, Supplement to the 8th ed., Vol. 3, 1971, pp. 181-289). W. Strohmeier, Chem. Eer., 94, 2490 (19611, A. T. T. Hsieh, W. C. Matchan, H. van den Bergen, and B. B. West, Chem. and fnd. (London), 1974, 114. R. L. Pruett, J. E. Wyman, D. R. Rink, and L. Parts. U. S. Patent 3378569 (1968); Chem. Abstr., 69, 77512 (1968); U. S. Patent 3382263 (1968); Chem Abstr., 69,59376 (1968). M. D. Rausch, J. Org. Chem, 39, 1787 (1974). W. P. Anderson, N. Hsu, C. W. Stanger, and B. Munson, J. Organomet. B lem, 69, 249 (1974). W. R. Jackson, B. Nicholls, and M. C. Whiting, J. Chem SOC., 1960, 469. J. F. Bunnett and H. Hermann, J. Org. Chem 36, 4081 (1971); V. S. Khandkarova, S. P. Gubin, and B. A. Kvasov,J. Organomet. G e m , 23,509 (1970). W. McFarlane and S. 0. Grim, J. Organomet. Chem, 5,147 (1966); A. Mangini and F. Taddei,fnorg. a i m Acra., 2, 8 (1968). R. D. Fischer, Chem Ber., 93, 165 (1960); D. A. Brown and H. Sloan,J. Chem. Soc., 1963,4389; D. A. Brown and J. R. Raju,J. a e m . Soc., A, 1966,1617; D. M. Adams and A. Squire, J. Chem SOC., Dalton Trans.. 1974, 558. R. P. A. Sneeden, Organochromium Compounds, Academic Press Inc., New York, 1975. W. E. Silverthorn, Adv. Organomet. Chem, 13,47 (1975). M. F. Semmelhack, in New Applications of Organometallic Reagents in Organic Synthesis, D. Seyferth, ed., Elsevier Publishing Co., Amsterdam, 1976, p. 361.

36. PENTACARBONYLMANGANESE HALIDES

The pentacarbonylmanganese halides have been known for some time'" but are still the subject of intense interest. Numerous vibrational analyses h: qe been carried out: as well as synthetic and kinetic studies of carbonyl substitution reactions? Halide substitution, which requires elevated temperatures,' leads to charged species. Diazocyclopentadienes insert into the manganese-halogen bond!

The best method for preparation of pentacarbonylchloromanganese is the reaction of chlorine with dimanganese decacarbonyl in carbon tetrachloride solution. Earlier versions of this procedure' often give low yields; however, the present version is reliable and produces a good yield.