Jan. 5 , 1954
CYCLOPENTADIENYL COMPOUNDS OF CHROMIUM, ~IOLYBDE AKD N UTUNGSTEN ~II 200 [CONTRIBUTION FROM THE
MALLINCKRODT LABORATORY, HARVARD UNIVERSITY]
Cyclopentadienyl Compounds of Chromium, Molybdenum and Tungsten BY GEOFFREY WILKINSON RECEIVED SEPTEMBER 2, 1953
A new preparative method for neutral bis-cyclopentadienyl compounds of the transition elements is the direct reaction of cyclopentadiene with the metal carbonyl. Bis-cyclopentadienylchromium( 11)is described. Cyclopentadienyl carbonyls of molybdenum and tungsten are described and a structure involving bridging carbon monoxide groups is suggested.
Bis-cyclopentadienyl compounds of various tran- has been attributed’ to the presence in the molecule sitional elements have been prepared by two meth- of two types of carbon monoxide groups, one nonods. Firstly, the reaction of cyclopentadienyl- bridging, the other in bridge positions between the magnesium halides with metal halides,’~~ or acetyl- metal atoms. The striking similarity of the ‘moacetonates2n3 leads to compounds of the type lybdenum and tungsten cyclopentadienyl carbonyls, particularly in view of the difference in their [(CsH5)2Mn]Xn2, where n = 2 to 5 is the oxidation state of the metal 111, and X is a halogen, e.g., stoichiometry, makes a similar interpretation for (C5H5)2Nir1, (C5H5)2Rh111Br,(C5H5)2TirVBr2,(C6- the existence of two C-0 frequencies in these H5)2NbVBr3; in the cases of FeCls and Ru(II1)- compounds difficult to accept. acetylacetonate, reduction to the neutral comThe structures of these cyclopentadienyl carbon. pound (CbH&M occurs. A modification of this yls are, perhaps, best formulated as “triple decker method is the reaction of hexaminenickel(I1) thio- sandwiches.” A cyclopentadienyl ring is bonded cyanate with cyclopentadienylpotassium in liquid to each metal atom and there are five and six ammonia solution to form (C6H5)2Ni.4 Secondly, bridging carbonyl groups in the molybdenum and the direct reaction of cyclopentadiene with an iron tungsten compounds, respectively. The molybdecatalyst a t 375’ forms (C5H5)2Fe5; no other appli- num compound, for example, is then formulated cations of this preparative method have been re- as bis-(cyclopentadieny1)-,u-pentacarbonmonoxideported. bi-molybdenum(1). The diamagnetism of the A third preparative method has been found in compounds can be accounted for. The cyclopentathe vapor phase reaction of cyclopentadiene with dienyl ring is taken to be bound to the metal by a metal carbonyls a t elevated temperatures. two electron delocalized bond resulting from the On passing chromium hexacarbonyl vapor and interaction of the unpaired a-electron of the cyclocyclopentadiene in nitrogen through a tube a t 280- pentadienyl radical with a d-electron of the neutral 340°, scarlet crystals of bis-cyclopentadienylchro- metal atom as in the bis-cyclopentadienyl commium(I1) are obtained in approximately 30% yield. pounds.8 Bonding of the cyclic carbon monoxide With molybdenum hexacarbonyl the main prod- system follows from the furnishing by this system uct of the reaction, which is obtained in about 30% of, on the average, three electrons to each metal yield a t temperatures above 240°, is a molybdenum atom, three of the d-orbitals of the metal being cyclopentadienyl carbonyl, C~H~MO(CO)&!~OC~&. used; the fifth d-orbital (or s-d hybrid orbital) is In the reaction of tungsten hexacarbonyl with cyclo- filled and not involved in bonding. With this arpentadiene a t temperatures above -280’ a cyclo- rangement, partial bonding between the carbon pentadienyl carbonyl, C5HsW(CO)8WCsH8, is ob- atoms of the carbon monoxide groups seems imtained. plied, and may provide an explanation for the obBoth of these cyclopentadienyl compounds are served C-0 frequencies. The fact that the sharp quite stable. Molecular weight determinations show band a t 1959 or 1960 cm.-’ is essentially unchanged them to be binuclear, and they are diamagnetic. in both compounds, and that this frequency is alThe infrared absorption spectra (Fig. 1) of the two most identical with the C-0 frequency in the hexacompounds are strikingly similar. Both show asingle carbonyls themselves, is consistent with the idea C-H stretching band, and have other bands in posi- that on the average, the electrons of only three of tions similar to those characteristic of bis-cyclopen- the carbon monoxide groups are being disturbed in tadienyl compounds.2a,6 In addition they have two bonding to the metal. The second, broader C-0 intense bands in the C-0 stretching region; for the band may arise from interactions between adjacent molybdenum compound there is a sharp band a t C-0 groups. 1960 em.-’ and a broader one of comparable intenX-Ray diffraction studiesg have confirmed the sity a t 1916 cm.-I, while for the tungsten compound stoichiometry of these compounds, and the results the analogous bands are a t 1959 and 1911 cm.-l, re- of a preliminary analysis for the molybdenum comspectively. I n the case of iron enneacarbonyl, pound are consistent with the structure suggested Fel(CO)p, the presence of two C-0 frequencies above. (1) T. J. Kealy and P. L. Pauson, Nafurc. 168, 1039 (1951). The carbonyl method is applicable to the prepa( 2 ) (a) G. Wilkinson, THISJOURNAL, 74, 6146 (1952); (b) 74, 6148 ration of neutral bis-cyclopentadienyl compounds of (1952). (3) G. Wilkinson, P. L. Pauson, J. M. Birmingham and F.A. Cotton, i b i d . , 7 6 , 1011 (1953). (4) E. 0.Fischer and R. Jira, 2. Naturforschuitg, 8b, 217 (1953). ( 5 ) S. A. Miller, J. A. Tebboth and J. F. Tremaine, J . Chem. SOC., 632 (1952). (6) E. R. Lippincott and R. D. Nelson, J . Chem. Phys., 21, 1307 (1933).
(7) Cf.R. K. Sheline and K. S. Pitzer, THIS JOURNAL, 72, 1107 (1950). (8) (a) W. E. Moffitt, Harvard University, in course of publication; (b) cf. also J. D. Dunitz and L. E. Orgel, Nature, 171, 121 (1863); H.H. Jaffe, J . Chem. Phys., 21, 156 (1953). (9) D. P. Shoemaker, Massachusetts Institute of Technology, private communication.
GEOFFREY WILKINSON
210
VOl. 76
W A V E N U M B E R S ird CM;'.
3000
5000
loo[#
,
r
I
8
~
~
2000
#
,
,
\
,
'
1
,
,
1500 8
8
1
,
,
I
,
,
,
1300
/ . ,
I100
I000
, ,,,, , , , ,
, I
300
, , ,
ROO
1 ' ' " ' ' ' 1 1
6 75
7GG "
I
'
'I
w
0
z
+a
t ul
z te
c
z
W 0 W ir
a
W A V E LENGTH
I N MICRONS,
Fig. 1.-Infrared absorption spectra: top, molybdenum cyclopentadienyl carboiiyl, full line 12.0 mg.,'l.5 g. KI, broken line 1.5 mg./cc. chloroform; bottom, tungsten cyclopentadienyl carbonyl, full line 19.0 nig./l.5 g. K I , broken line 2.1 mg. 'cc. chloroform. Band Double Beam Recording Spectrophotometer.
iron, cobalt and nickel using Fe(CO)s, C O ~ ( C O and ) ~ out t o 0.1 micron pressure, and then filled with specially Ni(CO)r, and is undoubtedly capable of further ex- purified nitrogen. [Seaford nitrogen, Air Reduction Sales, Inc., containing 0.002% water, 0.002% oxygen and 0.5% tension. hydrogen was purified by passage over reduced copper at 650' t o catalyze the combustion of oxygen; the treated g d S was dried by passage through flake potassium hydroxide. 1 Water, K = 0.72 X c.g.s.u., and bis-cyclopentadienylBis-cyclopentadienylchromium(11).-A slow stream of c.g.s.u.) which is pure nitrogen or argon is passed through a bubbler of cyclo- nickel(I1) ( ~ 2 : : ~=. 4-3318 X pentadiene a t room temperature, and then through a reac- known to follow Curie's law, were used as references. a t 298°K. was +3450 tion tube. The tube contains chromium hexacarbonyl (5- The molar susceptibility of (CSH6)
