1838 Table VI. Angles (+) &_tween the Principal Tensor Axes R3n and the Normal to the (201) Plane
~~
~
a
Corresponding to the largest mean square vibration.
GejFlz as a Mixed-Valence Compound. The subject of mixed-valence chemistry has been reviewed by Robin and Day, l6 who list few mixed-valence binary halides. The structure of Cr2F5 (CrF2.CrF3) is known,17 the environment around Cr” being distorted octahedral and around CrlI1 regular octahedral. No binary mixed-valence halides are given for the group IVb metals. Pb30416contains an octahedrally coordinated (16) M. B. Robin and P. Day, Aduan. Inorg. Chem. Radiochem., 10, 248 (1967). (17) H . Steinfink and J. H. Burns, Acfa Crystallogr., 17, 823 (1964).
PbIV atom and a PbII atom at the apex of a trigonal pyramid; the bonding in Pb304 has been discussed in covalent terms by Dickens. l8 Ge5FI2is colorless, showing no additional absorption in the visible region; this is normal when the two types of metal atom are in sites of different symmetry and ligand field strength. l 6 It is interesting to speculate on the possibility of preparing other members of the (GeF&. GeF4series. The compounds with x = 3 and x = 4 were prepared when the pressure of GeF4 was less than 1 atm. It may be possible to prepare the compounds with x = 1 or x = 2 by using pressures of GeF4 exceeding 1 atm, in a slightly modified reactor.’ It may also be possible to prepare compounds the type (GeF,),.MF, where M is Si, Sn, or Pb. Obviously, M could not be C since lack of available d subshells precludes occupation of an octahedral crystal site. It may also prove possible to prepare compounds of the type (M’F2),.M’’F4 where M’ is not Ge; however, for reasons listed elsewhere, this is unlikely. (18) B. Dickens, J . Inorg. Nucl. Chem., 27, 1509 (1965).
Molybdenocene and Tungstenocene. New “Carbene” Intermediates in Reactions with Hydrogen, Nitrogen, Carbon Monoxide, Olefins, and Acetylenes Joseph L. Thomas Contributionfrom the Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48104. Received September 8, 1972 Abstract: The generation and reactions of (C5H&Mo, [Ca(CH3),12Mo, and (CsHJ2W are described. Carbon monoxide and N2 complexes of the above metallocenes as well as dimethyl derivatives of molybdenocene and tungstenocene have been characterized. The role of 14- and 16-electron species in nitrogen reduction reactions is discussed. (CsH&Mo(C2H4),(C5H&Mo(CH3CCCH3),(C5H&Mo(CH2CHCHCH2),(C5H&Mo(CF3CCCF3), and some similar complexes of tungstenocene have been prepared. Metallocyclopropaneand metallocyclopropene structures are proposed for the olefin and acetylene complexes. respectively. Hydrolysis of some of these complexes resulted in reduction of the complexed hydrocarbon. Similarities to nitrogenase are noted. A systematic and (C5Hs)tWto carbenes was undertaken and revealed an comparison of the reaction chemistry of (C5H5)%Mo unprecedented parallelism of reactivities and product stabilities.
I
nterest in the preparation of molybdenocene and Thus, while chromocene is stable and readily prepared,5 tungstenocene resulted from a search for isolatable neither molybdenocene nor tungstenocene has ever been compounds that would coordinate and lead to reduction synthesized. A very inert bis(pentaphenylcyc1opentaof molecular nitrogen. Previous studies with titanodienyl)molybdenum(II) has been reported,6 and a few cene’ and other titanium species2 suggested that such a symmetrically bound olefin and acetylene complexes compound would be coordinatively unsaturated and have been prepared by insertion of the hydrocarbon into electron deficient. Molybdenocene and tungstenocene ( C ~ H & ) ~ M O Tungstenocene H~.~ has been postulated as satisfied these conditions. Interest in molybdenocene is an intermediate in the formation of aryl hydrides and especially high since molybdenum is one of the two ~~ some olefin complexes of that m e t a l l o ~ e n e . ~Recent metals known to be present in the nitrogenase e n ~ y m e . ~ investigations in these laboratories have led to the generWith the exception of group VIII, metallocenes of the ation of molybdenocene as a highly reactive species and second- and third-row transition metals are unknown. (1) J. E. Bercaw, R. H.Marvich, L. G. Bell, and H. H. Brintzinger, J . Amer. Chem. SOC.,94, 1219 (1972). (2) E. E. van Tamelen, R. B. Fechter, S . W. Schneller. G. Boche, R . H. Greeley, and B. Akermark, ibid., 91, 1551 (1969), and references
therein.
(3) J. R. Postgate, “The Chemistry and Biochemistry of Nitrogen Fixation,” Plenum Press, London, 1971, p 181. (4) R. B. King, “Transition-Metal Organometallic Chemistry,” Academic Press, New York, N. Y., 1969, p 18.
( 5 ) G. Wilkinson, F. A. Cotton, and J. M. Birmingham, J . I n o r g . Nucl. Chem., 2, 95 (1956). (6) W. Hubel and R. Merenyl, J . Organomefal. Chem., 2, 213 (1964). (7) A. Nakamura and S . Otsuka, J. Amer. Chem. SOC.,94, 1886 ( 1972).
(8) B. R. Francis, M. L. H. Green, and G. G. Roberts, Chem. Commun., 1290 (1971). (9) M. L. H. Green and P. R. Knowles, J . Chem. SOC. A , 1508 (1971).
Journal oj’the American Chemical Society 1 95:6 1 March 21, 1973
1839
t o the observation that tungstenocene demonstrated similar reactivity. lo
Results I. Generation and Reactions of (C5H5)*Mo and (C5H5)2W. I n an earlier report on the generation and reactions of molybdenocene, lo a polymeric species, [(CsH5)2M~]z,was briefly discussed. The suggested dimeric or polymeric structure containing regular (h5-C5H&Mo units is supported by recent evidence. The mass spectrum of [(C5Hs)zMo]zsuggests an apparent molecular weight of 460, corresponding to [(C,H5)2Mol2 (Table I). However, high source temperatures
Figure 1. Proposed structure for (CSHS)~MO~(CO)S. Table 11. Mass Spectrum of (C5Hj)4M03(C0)5 (Ionizing Voltage 30 eV)
Table I. Mass Spectrum of [(CSHJ~MO], (Ionizing Voltage 30 eV) Re1 intensity
mle
Ion
460 430 394 294 230 204 180-1 70 165
were required for obtaining this spectrum and may have caused decomposition of a higher polymer. The infrared spectrum of [(CjH&Mo], exhibits no absorptions in the region 2500-1 500 cm-l while strong absorptions have been observed in the region 1841-1905 cm-' for a variety of molybdenocene hydride compound^.^' l 1 The absence of such a Mo-H unit would preclude a bridging cyclopentadienyl structure similar to that of (C20H20)Nbz or (CzoHzo)Ta2. l2 At room temperature, [(C5H5)zMo]zis inert to 200 atm of hydrogen, nitrogen, or carbon monoxide. At elevated temperatures, reaction with hydrogen and carbon monoxide yields products containing regular (h5-C5HJ2Mounits.
+
200 a i m
[ ( C > H ~ ) Z M O IHz ~
+
+(CjHj)zMoH2 1100
(2OZ)
(1)
200 a t m
[(CSHS)ZMOI~CO +(C:Hj)4ModCO)j (95 %) 1103
Re1 intensity
700 451 442 414 386 3 58 330 293 249 230 202 165
12 9 3 6 9 6 36 57 26 9 100 27
Ion
of [(C5H&MoIz with gaseous HC1 yields (C5H&MoClZ as the major product.
+
[(CSH~)~MOIZ2HC1
*(CrHs)zMoCla + Hz
(3)
This reaction as well as reactions 1 and 2 demonstrate the possibility of producing (h5-CsHj)ZM~ species from [(C~H~)ZMO]~. Reduction of (C5H5),WC12 gives products exactly analogous to those obtained in the reduction of (C5H5)ZMoC12. (CjHj)2WC1z
+ Na/Hg
-
4
(c5H~hWH2
(CjHj)>W
(4)
[(CSHJ?Wl,
The physical and chemical properties and mass spectrum of [(C5H&W], are very similar to the molybdenum analog (see Table 111). Similar reductions carried out
(2)
(CjHj)dM~3(CO)jis an orange-yellow solid exhibiting a sharp singlet in its nmr at T 5.13 and carbonyl absorptions in the infrared region at 1990, 1963, 1900, and 1882 cm-I. The four carbonyl absorptions reflect the low symmetry of this complex, and their position suggests that no bridging carbonyls are present.13 The structure most consistent with these data is shown in Figure 1. The nmr singlet of (C5Hj)4M03(CO)5may mean that the absorptions of the cyclopentadienyl protons fortuitously coincide. l 4 All ions expected for the fragmentation of the molecule depicted in Figure 1 are contained in its mass spectrum (Table 11). Treatment (IO) J. L. Thomas and H. H. Britzinger, J . Amer. Chem. SOC., 94, 1386
mle
(1972).
(11) H . P. Fritz, Y . Hristidu, H. Hummel, and R. Schneider, Z . Naturforsch. B, 15, 419 (1960). (12) F. N. Tebbe and G. W. Parshall, J . Amer. Chem. Soc., 93, 3793
(1971). (13) Cyclopentadienylmolybdenum species with bridging carbonyl groups are currently unknown. (14) The nmr absorption of a freshly prepared sample of [(CjHj)Mo(CO)SIZcoincides exactly with that of (CsH.)aMoa(CO)j.
Table 111. Mass Spectrum of [(CjH&W], ~~
mle
Re1 intensity
Ion
630 602 578 565 552 540 316 288 158
in the presence of carbon monoxide yielded bis(cyc1opentadienyl)molybdenum(II) monocarbonyl, described in an earlier publication, lo and the tungsten analog. 357~
(C5Hj):MCl2 M = Mo or W
+
CO
+
(C,H,)AM(CO)
?;a/Hg
(5) [(C&)Plx
Thomas / Molybdenocene and Tungstenocene
1840
These monocarbonyls can be produced by using butyllithium as a reducing agent, but yields are diminished.
+
(C5Hs),MCl~ CO M = MoorW
methylzinc, orange-red (CSH~)~MO(CH,), and yellow ( C , H ~ ) Z W ( C Hwere ~ ) ~ obtained.
+
147,
+ LiC4H9 +(C6H&M(CO)
Treatment of (C6Hj)zMHz or [(C5H&MIZwith carbon monoxide does not generate the above monocarbonyls. Bis(cyclopentadienyl)tungsten(II) monocarbonyl exhibits a single sharp absorption in the infrared spectrum at 1864 cm-' and a sharp singlet in its nmr spectrum at T 5.63. Mass spectra are given in Table IV.
00
( C ~ H S ~ M C I ZZn(CHd2 +(CsHs)lM(CH3)2 M = Moor W
(6)
(8)
These compounds are very stable, sublimable solids which have only moderate sensitivity to the atmosphere. (CSHE,)~MO(CH~)~ exhibits two sharp singlets in its nmr spectrum at T 5.93 and 9.78 for the cyclopentadienyl and methyl peaks, respectively. The peaks integrate 10 :5.6. (C5H&W(CH3)2 has a similar spectrum with sharp singlets at T 5.80 and 9.63 which integrate 10 : 5 . 8 . The mass spectrum of (CjH5)2Mo(CH3)2is given in Table V.
Table IV. Mass Spectrum of (CsH&Mo(CO) and (CSH~)~W(CO) Re1
intenm/e
sity
Ion
258 230 204 202 178 165 115
25 100 31 30 11 2 10
(CsHs)zMo(CO)+ (CjHs)zMo+ (CsHs)MO+ (CsHs)MO+ (C&I~)MO+ (CsHs)Mo+ (CsHs)zMoZ+
Re1 intenmje sity 344 316 290 260 251 158
16 100 30 13 3 6
Table V. Mass Spectrum of ( C ~ H & M O ( C H ~ ) ~ Ion
mle
Re1 intensity
(CsHb)zW(CO)+ (CsHs)zW+ (CsHs)W+ (C&I.)W+ (CsHs)W+ (CsH&WZ+
260 245 243 230 204 202 178 165 121.5 115 100
44 58 13 100 15 10 13 10 10 10 12
One of the most interesting reactions of the proposed (C5H&Mo intermediate is its coordination to molecular nitrogen. If the sodium amalgam reduction of (C5H5)2MoClz is carried out under a high pressure of nitrogen, a nitrogen-containing complex is obtained that yields approximately 1 equiv of nitrogen per equivalent of molybdenum upon pumping under high vacuum at room temperature. atm
(C;Hd2MoC12
350 + NZ + NaIHg --+ [(CSHJZMON~L(7)
This complex is thermally very unstable, readily liberating nitrogen at room temperature and atmospheric pressure. While repeated experiments and comparison with blanks demonstrated conclusively that nitrogen was being coordinated in the molybdenocene system, the thermal instability frustrated all attempts to characterize this complex instrumentally. The structure of the compound is unknown at this time. It is important to note that acid hydrolysis of this nitrogen complex yielded no ammonia. Thus, while molybdenocene, a 16-electron species, does coordinate nitrogen, it apparently does not provide conditions sufficient for reduction of the nitrogen molecule. Similar nitrogen complexes of tungstenocene were generated, but no increased stability was noted, and chemical and physical behavior was essentially identical with that of the molybdenocene-nitrogen complex. Synthesis of (C5HS)2M~(CH3)2 and (CjH&W(CH3)z was undertaken in the hope that these alkyl species would be thermally unstable and provide a method of isolating (CjH&Mo or (C6H&W as was possible for titanocene. Treatment of (CsH5)zMoC12with stoichiometric amounts or large excesses of methyllithium at -78" in ether gave no products which could be identified as (C,H&MO(CH~)~.Upon warming to room temperature and removing the solvent, a yellow-brown, pyrophoric, involatile solid was obtained. When (CsH&MoC12 or (CjH&WClZ was treated with di-
Ion
The observation of an abundant parent ion in (C&)2M O ( C H ~is) in ~ sharp contrast to the total lack of such a This peak in the mass spectrum of (C5H5)2Ti(CH3)2.1B suggests a considerably decreased lability of the methyl groups as compared to the titanium analog. ( C ~ H & M O ( C H and ~ ) ~ (C jH j ) 2 W( CH 3)2 exhibit exceptional thermal stability for metal dialkyls. (C5H&Mo(CH3)z survives heating to 150" for 24 hr with no change in the nmr spectrum. This is in contrast to (CsH5)ZTi(CH3), which readily decomposes at room temperature.16 To date, no method of selective reduction or decomposition of these compounds to the free metallocene has been successful. 11. Preparation and Reactions of Transient Bis(pentamethylcyclopentadienyl)molybdenum(II) and Its Stable Dimer. In an attempt to stabilize and more adequately characterize the molybdenocene system, bis(pentamet hylcyclopen tadieny1)di hydri d om 01 y bden u m (IV) was prepared by the reduction of molybdenum pentachloride with sodium pentamethylcyclopentadienide and sodium borohydride. MoCls
+ 3NaC&(CH3);+ 2NaBH, 37c7,
--f
+ 5NaC1 + C d C H d j + BzHs
[CdCHdsl~MoHz
(9)
The orange product exhibited a strong infrared absorption at 1857 cm-' which is slightly higher than the hydride stretch of (CSH&MoH2 at 1847 cm-'.'' The nmr spectrum of [Cj(CH3)&MoHn contained two singlets at T 7.93 and 18.18 which integrated 15.1 : l . The absorption at T 18.18 is characteristic of hydride ligands coordinated to molybdenum7 and is near the literature (15) J. E. Bercaw and H. H. Brintzinger, J . Amer. Cfiem. Soc., 92, 6182 (1970). (16) I
