(q5-Pentamethylcyclopentadienyl)cobalt Complexes 213

70. ( qS-PENTAMETHYLCYCLOPENTAD1ENYL)COBALT COMPLEXES

Submitted by STEVEN A. FRITH a d JOHN L SPENCER*$ Cbecked by W. E. GEIGER, Jr. and J. EDWIN?

Pen tamethylcyclopentadienyl complexes exhibit a chemistry complementary to that of the unsubstituted cyclopentadienyl analogs, with differences in behavior that may be ascribed to the greater bulk or the greater electron- releasing ability of the pentamethylcyclopentadienyl ligand. ’ The following syntheses lead to a group of complexes that have given access to rich areas of organocobalt chemistry. The syntheses have been designed such that later members of the group may be prepared without lengthy purification of the intermediates.

A. DICARBONYL($- PENTAMETHYLCY CLOPENTADIENYL)COBALT(I)

Co,(CO), + 2C,Me5H + C6H8 -P 2[Co(q5-C,Me5XCO),1

+ C6Hlo + 4CO

Originally [Co(q5-C,Me,)(CO),] was prepared’ by the photolysis of CO,(CO)~ and C5Me,H and subsequently’ by the reaction of Co,(CO), and C,Me,C(O)Me in refluxing cyclohexane. The method described here is a substantial modification of that used by Byers and Dah14 and gives excellent yields from both precursors.

Procedure

Caution. Both dicobalt octacarbonyl and carbon monoxide are poi- sonous and therefore the reaction should be carried out in a well-ventilated hood.

A 100-mL, two-necked, round-bottomed flask is fitted with a reflux condenser and a magnetic stirring bar. A T junction, placed on top of the

*Department of Inorganic Chemistry, University of Bristol, Bristol BS8 ITS, United

?Department of Chemistry, University of Vermont, Burlington, VT 05405. ?Present address: Department of Chemistry and Applied Chemistry, University of Salford,

Kingdom.

Salford M5 4WT, United Kingdom.

Inorganic Syntheses, Volume 28 Edited by Robert J. Angelici

Copyright © 1990 by Inorganic Syntheses, Inc.

214 Cyclopentadienyl Complexes

condenser, is connected to a supply of dry nitrogen and a mineral oil bubbler, and the flask is flushed for several minutes. Dry, deoxygenated dichlorometh- ane (50 mL), octacarbonyldicobalt(0) (6.0 g, 17.5 mmol), pentamethylcyclo- pentadiene* (3 g, 22.1 mmol) and 1,3-cyclohexadiene (2.5 mL) are added through the second neck, which is then closed with a stopper. The mixture is stirred and heated to maintain a very gentle reflux. After 45 min, a further 2.3 g (16.9 mmol) of pentamethylcyclopentadiene is added and heating is continued for another 1.75 h. The reaction may be conveniently monitored, using IR spectroscopy, by the appearance of vco bands at 1999 and 1935 cm-' (CH,Cl,). When reaction is complete, there may also be weak absorptions due to traces of Co,(CO),, (2065, 2055, and 1858cm-') or [Co(q3-C,H,)(CO),] [2047 and 1983 (sh) cm- '3.

The condenser is replaced with a stopcock adapter and the volatile components are evaporated at reduced pressure and ambient temperature. If the temperature is kept at or below 20°, the oily residue will crystallize spontaneously. This crude material may be used in the synthesis of [C012(qs- C,Me,)(CO)], or it may be purified as follows. Nitrogen is readmitted to the flask, the crude crystalline mass is dissolved in dry deoxygenated hexane (30mL), and the solution is applied to a column of alumina (Brockman, activity 11) (20 x 2.5 cm), previously prepared under nitrogen and washed with deoxygenated hexane (200mL). The product is eluted as an orange- brown band with hexane and collected under nitrogen. Evaporation of the solvent under reduced pressure yields deep-red crystals of [Co(qs- C,Me,)(CO),], 7.9 to 8.3 g [90-95% based on Co,(CO),]. Further purifica- tion may be effected by crystallization from hexane solution at low temper- atures or by sublimation (W, 0.01 torr).

Anal. Calcd. for C,,H,,O,Co: C, 57.61; H, 6.04. Found C, 57.51; H, 6.26 (mp 58", sealed tube).

Properties

Dicarbonyl(q5-pentamethylcyclopentadienyl)cobalt(I) is a deep red-brown crystalline solid that may be handled briefly in air but should be stored in an inert atmosphere. It dissolves readily in dry, deoxygenated organic solvents to give stable solutions but, in the presence of air or water, it slowly decomposes. The 'H NMR spectrum (CDClJ shows a sharp singlet at 6 1.98 ppm.

*Available from Strem. Chem., P.O. Box 212, Danvers, MA 01923 or Aldrich Chemical Co., 940 W. St. Paul Ave., Milwaukee, WI 53233.

(~5-Pentamethylcyclopentadienyl)cobalt Complexes 275

B. CARBONYLDIIODO- ( qS-PENTAMETHY LCY CLOPENTADIENYL)COBALT(III)

[Co(q5-C,Me,)(C0),] + I, -, [CoI,(qS-C,Me,)(CO)] + CO

The method described here is based on that of King and coworker^.^ Roe and Maitlis6 followed a similar procedure but used an alkane solvent.

Procedure

Caution. A large volume of carbon monoxide is released in a short time. The reaction should be carried out in a well-ventilated hood.

A 250-mL two-necked flask is fitted with a magnetic stirrer bar and a T piece connected to a nitrogen supply and a mineral oil bubbler. The flask is purged with nitrogen, and sodium4ry diethyl ether (150 mL) is added, followed by 8.9 g of iodine (35.0 mmol). The second neck is then closed with a rubber septum and a solution of [Co(qS-C,Me,)(CO),] (8.75 g, 35.0 mmol, or all of the crude material from the previous synthesis) in deoxygenated diethyl ether (20 mL) is added dropwise from a syringe to the rapidly stirred reaction mixture. Addition may be completed in 5-10 min. A black, crystalline precipitate forms rapidly with the evolution of carbon monoxide gas. Stirring is continued for another hour. The mixture is filtered in the air using a sintered-glass funnel and the crude product is washed with diethyl ether (three 20-mL portions) and dried in an oven at 80". The material so-formed is sufficiently pure for the preparation of [{CoI2(qS-C,Me,)},]. However, it may be purified by dissolution in a large volume of dichloromethane to give a deep purple solution, which is filtered through a glass sinter (porosity 3) and evaporated to small volume using a rotary evaporator. Lustrous black crystals of [CoI,(q5-C,Me,)(CO)] are filtered off and dried under vacuum. Yield: 15.0-15.8 g (90-95%).

Anal. Calcd. for C,,H,,OI,Co: C, 27.76; H, 3.18. Found: C, 27.70; H, 3.45.

Properties

Carbonyldiiodo(qS-pentamethylcyclopentadienyl)cobalt(III) is a black, crystalline, air-stable solid. It dissolves readily in polar solvents forming deep purple solutions but is virtually insoluble in diethyl ether, alkanes, and aromatic solvents. The 'H spectrum (CDCl,) shows a singlet at 6 2.20 ppm. The IR spectrum exhibits a single metal-carbonyl stretching band at

276 Cyclopentadienyl Complexes

2053 cm-' (CH,Cl,). Removal of the iodide ligands by Ag+ provides a facile route to cationic organometallic derivatives of Co(III).'

c. DI-~-IODO-BIS[IODO( $- PENTAMETHYLCYCLOPENTADIENYL)COBALT(IIQ]

A 2[CoI,(q5-C5Me5)(CO)] - [{COI,(~~-C,M~,)},] + 2CO

The method described here is based on that of Roe and Maitlk6 An analogous dichloro(tpethyltetramethylcyclopentadieny1) derivative, [(COC~,($-C,M~,E~)}~], has been prepared8 by the extraction of CoCl, from [Co,Cl,(qS-C,Me4Et),] in turn made from [Sn(n-Bu),(q'-C,Me,Et)] and CoCl,.

Procedure

Caution. The reaction releases toxic carbon monoxide and should be carried out in a well-ventilated hood.

A 250-mL, two-necked, round-bottomed flask is charged with 150 mL of dry n-octane and 15.5 g of powdered [CoI,(q5-C,Me,)(CO)] and equipped with a magnetic stirring bar, a nitrogen inlet, and a reflux condenser. The top of the condenser is connected to a mineral-oil bubbler venting into the hood. The rapidly stirred mixture is heated at reflux for 5 h under a slow N, purge. During the reaction, the microcrystalline suspension is converted to a suspension of lustrous, black crystals. After cooling to room temperature, the crude [{CoI,(qS-C,Me,)},] is collected in a sintered-glass filtration funnel, washed with pentane, and dried in an oven at 80". The product may be purified by dissolving it in a large volume of dichloromethane, filtering, and removing most of the solvent at reduced pressure on a rotary evaporator, or by using the continuous extraction apparatus shown in Fig. 1. The crude material is transferred to the paper thimble, a loose plug of glass wool is packed above it, and dry dichloromethane (120 mL), contained in the flask, is boiled at a sufficient rate that condensate drips into the thimble. This process may be run conveniently overnight. The flask is then detached and cooled to 0" for 3 h. The product, as lustrous, black crystals, is recovered by filtration and dried under vacuum (0.05 torr, 1 h). Yield 11.5 P. 4 further crop ( - 1.3 g) may be obtained by reducing the volume of the @;ate to 30mL, but this material should be checked by IR to ensure that it contains no [CoI,(q5- CsMe,)(CO)]. Total yield of [{Co12(q5-CsMe,)),] is 12.8 g (88%).

(q5-Pentatnethylcyclopentadienyl)cobalt Complexes 211

M i m l oil - - - N, bubbler r -

Soxhlet thimble

250 mL flask

Magnetic stirring bar

Fig. 1. Continuous extraction apparatus.

Anal. Calcd. for C,,H,,I,Co,: C, 26.81; H, 3.38. Found C, 26.71; H, 3.50.

Pro pert ies

Di-~-iodo-bis[iodo(~s--pentamethylcyclo~ntadienyl)cobalt(III)] is a black, crystalline, air-stable solid. It dissolves in polar solvents, forming dark green solutions, but is virtually insoluble in diethyl ether, alkanes, and aromatic solvents. The 'H NMR spectrum (CDCl,) exhibits a singlet at 6 1.80 ppm.

278 Cyclopentadienyl Complexes

D. BIS( q-ETHENE)( '1'- PENTAMETHYLCY CLOPENTADIENYL)COBALT(I)

Submitted by JULIAN C. NICHOLLS and JOHN L. SPENCER* Cbecked by JOHN R. SOWA, Jr. and ROBERT J. ANGELICIT

Green and Pardye prepared [Co(qS-C,Me4Et)(q2-C2H4),] by the sodium amalgam reduction of [(CoCl,(q5-C,Me4Et)},] under ethene (toluene, 1 lOOC). The pentamethylcyclopentadienyl complex described here offers several advantages: it is a crystalline solid rather than an oil; compounds derived from [Co(q5-C,Me5)(q-C2H4),] by displacement of ethylene are frequently solids also; and the 'HNMR is simpler. Frith and Spencerg prepared [CO(~~-C,M~,)(~-C,H,)~] from [{CoI2(qS-C,Me,)},] using Na/Hg amalgam as the reducing agent. The procedure described here uses activated zinc and is cleaner and more convenient although a longer reaction time is required.

Procedure

Caution. The large volumes of ethylene used in this synthesis are ajire hazard. The preparation should be carried out in a well-uentilated hood in the absence of naked James. Drying tetrahydrofuran is hazardous and should be carried out with due precaution.'O

A two-necked, round-bottomed flask is flushed with nitroger and charged with zinc dust (20 g). Dilute hydrochloric acid (25 mL of 2 M is added and allowed to react for 5 min, before being decanted. A solution of HgCl, (1.2 g) in 2 M HCl(25 mL) is added, allowed to react for 5 min, and then decanted. The activated zinc is washed with deionised water (2 x 25 mL), ethanol (2 x 25 mL), and diethyl ether (2 x 25 mL) and dried in vacuo 0.1 torr for 3 h at room temperature. The finely divided powder may form a solid mass on standing and should be used soon after preparation.

A 250-mL, two-necked, round-bottomed flask fitted with a magnetic stirrer is flushed with ethene and charged with 20 g of activated zinc and dry deoxygenated tetrahydrofuran (100 mL). The mixture is rapidly stirred under

*Department of Chemistry and Applied Chemistry, University of Salford, Salford M5 4WT,

TDepartment of Chemistry, Iowa State University, Ames, IA 5001 1. United Kingdom.

(q'-Pentamethylcyclopentadieny1)cobalt Complexes 279

a gentle flow of ethene as pure* solid [{CoI,(q5-C5Me5)>,] (lO.Og, 11.15 mmol) is added, and stirring is continued for 1.5 h, during which time the color of the solution changes from dark green to orange-brown.

A syringe is used to transfer the solution to a nitrogen-filled 250 mL, three- necked, round-bottomed flask connected by stopcock adapters to nitrogen and vacuum. Solvent is evaporated at reduced pressure and nitrogen is readmitted to the flask. The residue is dissolved in 40 mL of dry deoxygen- ated hexane and the solution transferred by a syringe to a N,-filled filtration apparatus containing a 1-cm pad of kieselguhr. The red-brown filtrate is reduced in volume to 20 mL by evaporation at reduced pressure, and the product is crystallized at - 78°C under nitrogen. The supernatant liquid is decanted with a syringe and the orange-brown crystals dried at 20"C, 0.05 torr for 1 h. A second crop of crystals may be obtained from the mother liquor by filtering, evaporating, and cooling as before. The combined yield is 3.9-4.5 g (70-85%).

Properties

Bis(~-ethene~~5-pentamethylcyclopentadienyl~obalt(I) is an orange-brown, volatile, crystalline solid. It may be handled briefly in air but if it is to be kept for long periods, it should be under an inert atmosphere at -20°C. It is soluble in organic solvents but the solutions decompose in the presence of air and water. In coordinating sol! ents decomposition occurs slowly. It is best therefore to allow it to react ix, alkane, diethyl ether, or aromatic solvents. The 'H NMR spectrum (C,D,) consists of a singlet at 6 1.43 [15H,C,Me5] and an CAB], pattern for the C2H, protons, dA 1.60, BB 0.86 ppm (IJ(AB) + J(AB')I 13 Hz). The IR spectrum (Nujol) has strong bands at 1197 and 1180cm-'.

References

1. (a) R. B. King, Coord. Chem. Rev., 20, 155 (1976); (b) P. M. Maitlis, Chem. SOC. Rev., 10, 1 (1981); (c) T. P. Wolczanski and J. E. Bercaw, Acc. Chem. Res., 13, 121 (1980); (d) J. M. Mannquez et al., Inorg. Synth., 21, 181 (1982).

2. R. B. King and M. B. Bisnette, J . Organomet. Chem., 8,287 (1967). 3. R. B. King and A. Efraty, J . Am. Chem. SOC., 94, 3773 (1972). 4. L. R. Byers and L. F. Dahl, Znorg. Chem., 19, 277 (1980). 5. R. B. King, A. Efraty, and W. M. Douglas, J . Organomet. Chem., 56, 345 (1973). 6. D. M. Roe and P. M. Maitlis, J . Chem. SOC. A, 1971, 3173. 7. G. Fairhurst and C. White, J . Chem. SOC. Dotton Trans., 1979, 1524, 1531.

*If any trace of [CoI,(q-C,Me,)(CO)] is present reduction will give the intense green compound [{Co(q-C,Me,)(p-CO)},], which will mask the progress of the reaction and may be difficult to separate later.

280 Cyclopentadienyl Complexes

8. M. L. H. Green and R. B. A. Pardy, J . Chem. SOC. Dalton Trans., 1979, 355. 9. S. A. Frith and J. L. Spencer, Inorg. Synth., 23, 15 (1985).

10. R. W. Parry, Inorg. Synth., 12, 317 (1970).

71. CYCLOPENTADIENYLBIS(TRIMETHYLPHOSPH1NE) A N D CYCLOPENTADIENYLBIS(TRIMETHYLPHOSPH1TE)

COMPLEXES OF Co A N D Rh

Submitted by H. WERNER,* R. FESER,* V. HARDER,* W. HOFMANN,* and H. NEUKOMM*

C k k e d by W. D. JONEst

The title complexes, CpM(PMe,), and CpM[P(OMt &J2, are electron-rich half-sandwich complexes that have been demonstrated to be valuable pre- cursors to a large number of organometallic derivatives.' They behave as Lewis bases and react with a wide variety of electrophiles E or EX to form new metal-element bonds. They have also been shown to be valuable starting materials for the syntheses of heterometallic di- and trinuclear complexes via their reactions with unsaturated transition metal compounds.' The only viable syntheses of these compounds now known are those reported here.

A. (#-CYCL0PENTADIENYL)BIS @RIMETHY LPHOSPHINE)RHODIUM(I)~

[(C8Hl,),RhCl], + 4PMe, + 2LiC,H, +

2Rh(q-C,H,)(PMe3), + 2LiC1+ 2C8H1,

Procedure

In a 125-mL Schlenk tube, equipped with a nitrogen inlet and a magnetic stirring bar, 3.7 g (5.1 5 mmol) [(C,H,,),RhCl], (Ref. 3) is dissolved in 40 mL of tetrahydrofuran (THF), freshly distilled over Na and benzophenone. The solution is treated dropwise with 2.1 mL (21.0 mmol) PMe, and then stirred for 1 h at room temperature. A 1.01-g (14.0-mmol) quantity of LiC5H5, freshly prepared from equimolar amounts of n-BuLi and C,H, in hexane: is added and the reaction mixture is stirred for 2 h at room temperature. The

Institut fiir Anorganische Chemie der Universitit, Am Hubland, D-8700 Wiirzburg, Federal

t Department of Chemistry, The University of Rochester, Rochester, NY 14627. Republic of Germany.