Dialkyl(butadiene)cyclopentadienylmolybdenum(III) complexes. Synthesis, characterization, and reactivity

Article abstract of DOI:10.1021/om000329t

Treatment of CpMo(η⁴-diene)Cl₂ (diene = 1,3-butadiene, C₄H₆, 1′; isoprene, C₅H₈, 1″; 2,3-dimethyl-1,3-butadiene, C₆H₁₀, 1″) in diethyl ether at low temperature with 2 equiv of alkylmagnesium RMgX reagents affords the corresponding dialkyl complexes CpMo(η⁴-1,3-diene)R₂ (2, 2′, 2″, R = CH₃, a; CH₂Ph, b; CH₂SiMe₃, c). These species are isolable in moderate yields and have been fully characterized by EPR, elemental analyses, and cyclic voltammetry. They all show a reversible reduction process at relatively low potentials and an irreversible oxidation. The structure of 2″a was confirmed by single-crystal X-ray diffraction. The mixed complex CpMo(η⁴-C₄H₆)Cl(CH₃), 3, has also been obtained by selective monomethylation of 1. A slow ligand redistribution process occurs between equivalent amounts of 1 and 2a to afford 3 quantitatively. Compound 3 slowly decomposes by elimination of a CH₃ group, yielding compound [CpMo(η⁴-C₄H₆)Cl]₂, 4, which has been structurally characterized by X-ray crystallography. Arylation with PhMgBr or (C₆H₂Me₃-2,4,6)MgBr provides EPR evidence for formation of arylated Mo(III) products. However, the isolation and crystallographic characterization of [CpMo(η⁴-C₄H₄Me₂-2,3)Br_0.77Cl_0.23]₂, 4″, for the mesityl reaction indicates that halide exchange and electron transfer processes also take place competitively. Complex 2a does not react with Lewis bases such as phosphines or carbon monoxide nor with weak Bronsted acids (MeOH, H₂O, CH₃COOH, H₃PO₄, H₃O⁺). Protonolysis of the Mo-R bond could only be observed by interaction with HCl, HBF₄, and CF₃COOD, with formation of CH₄ or CH₃D. Compounds CpMo(η⁴-C₆H₁₀)(CH₃)(OCOCF₃), 5, and CpMo(η⁴-C₆H₁₀)(OCOCF₃)₂, 6, have been isolated from the reaction between 2″a and 1 or 2 equiv of CF₃COOD, respectively. Compound 6 has been structurally characterized by X-ray crystallography.

Full text of DOI:10.1021/om000329t

3842
Organometallics 2000, 19, 3842-3853
Dia lk yl(bu ta d ien e)cyclop en ta d ien ylm olybd en u m (III)
Com p lexes. Syn th esis, Ch a r a cter iza tion , a n d Rea ctivity
Erwan Le Grognec, Rinaldo Poli,* and Philippe Richard
Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, Faculte´ des Sciences
“Gabriel”, Universite´ de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France
Received April 18, 2000
Treatment of CpMo(η4-diene)Cl2 (diene ) 1,3-butadiene, C4H6, 1′; isoprene, C5H8, 1′′; 2,3-
dimethyl-1,3-butadiene, C6H10, 1′′) in diethyl ether at low temperature with 2 equiv of
alkylmagnesium RMgX reagents affords the corresponding dialkyl complexes CpMo(η4-1,3-
diene)R2 (2, 2′, 2′′, R ) CH3, a ; CH2Ph, b; CH2SiMe3, c). These species are isolable in moderate
yields and have been fully characterized by EPR, elemental analyses, and cyclic voltammetry.
They all show a reversible reduction process at relatively low potentials and an irreversible
oxidation. The structure of 2′′a was confirmed by single-crystal X-ray diffraction. The mixed
complex CpMo(η4-C4H6)Cl(CH3), 3, has also been obtained by selective monomethylation of
1. A slow ligand redistribution process occurs between equivalent amounts of 1 and 2a to
afford 3 quantitatively. Compound 3 slowly decomposes by elimination of a CH3 group,
yielding compound [CpMo(η4-C4H6)Cl]2, 4, which has been structurally characterized by X-ray
crystallography. Arylation with PhMgBr or (C6H2Me3-2,4,6)MgBr provides EPR evidence
for formation of arylated Mo(III) products. However, the isolation and crystallographic
characterization of [CpMo(η4-C4H4Me2-2,3)Br0.77Cl0.23]2, 4′′, for the mesityl reaction indicates
that halide exchange and electron transfer processes also take place competitively. Complex
2a does not react with Lewis bases such as phosphines or carbon monoxide nor with weak
Brønsted acids (MeOH, H2O, CH3COOH, H3PO4, H3O+). Protonolysis of the Mo-R bond could
only be observed by interaction with HCl, HBF4, and CF3COOD, with formation of CH4 or
CH3D. Compounds CpMo(η4-C6H10)(CH3)(OCOCF3), 5, and CpMo(η4-C6H10)(OCOCF3)2, 6,
have been isolated from the reaction between 2′′a and 1 or 2 equiv of CF3COOD, respectively.
Compound 6 has been structurally characterized by X-ray crystallography.
In tr od u ction
by class are Cp2MR2 (M ) Nb, Ta),7-9 [Cp2WR2]+,10-12
and CpCr(NO)(L)R.13,14
There has long been an interest in free radicals in
organometallic chemistry, because the presence of un-
paired electrons may open up new reactivity pathways
that are unavailable to the related and more frequently
studied diamagnetic analogues.1-5 In addition, funda-
mental reactions that are well established for diamag-
netic compounds are often found to be accelerated upon
transformation (e.g., by oxidation or reduction) to radical
species.6 A particularly interesting class of radical
compounds are those containing alkyl ligands, since
these are involved in most industrially relevant catalytic
processes. The conditions for the inertness of transition
metal alkyl compounds toward decomposition processes
(i.e., by R- or â-H elimination processes, reductive
elimination, etc.) are usually stricter in radical species.
A large variety of radical systems containing alkyl
ligands has, however, been described. Selected examples
As part of a systematic study of 17-electron mono-
cyclopentadienyl complexes of the general formula
CpMoL2X2 as starting materials or reactive intermedi-
ates for organometallic chemistry and catalysis, we
reported a few years ago15 the formation of a transient
paramagnetic dimethylmolybdenum(III) complex, CpMo-
(CH3)2(PMe3)2, by the low-temperature alkylation of the
dichloride precursor. This product was characterized in
situ by EPR spectroscopy but could not be isolated
because decomposition takes place at temperatures
greater than ca. -20 °C, with homolytic cleavage of one
Mo-CH3 bond. More recently, we have observed a
(7) Siegert, F. W.; De Liefde Meijer, H. J . J . Organomet. Chem. 1970,
23, 177-183.
(8) Elson, I. H.; Kochi, J . K.; Klabunde, U.; Manzer, L. E.; Parshall,
G. W.; Tebbe, F. N. J . Am. Chem. Soc. 1974, 96, 7374-7375.
(9) Manzer, L. Inorg. Chem. 1977, 16, 525-528.
(10) Cooper, N. J .; Green, M. L. H.; Mahtab, R. J . Chem. Soc., Dalton
Trans. 1979, 1557-1562.
* To whom correspondence should be addressed. Tel: +33-3-80-39-
68-81. Fax: +33-3-80-39-60-98. E-mail: Rinaldo.Poli@u-bourgogne.fr.
(1) Lappert, M. F.; Lednor, P. W. Adv. Organomet. Chem. 1976, 14,
345-399.
(2) Kochi, J . K. J . Organomet. Chem. 1986, 300, 139-166.
(3) Stiegman, A. E.; Tyler, D. R. Comments Inorg. Chem. 1986, 5,
215-245.
(4) Baird, M. C. Chem. Rev. 1988, 88, 1217-1227.
(5) Astruc, D. Chem. Rev. 1988, 88, 1189-1216.
(6) Organometallic Radical Processes; Trogler, W. C., Ed.; Elsevier:
Amsterdam, 1990; Vol. 22.
(11) Hayes, J . C.; Pearson, G. D. N.; Cooper, N. J . J . Am. Chem.
Soc. 1981, 103, 4648-4650.
(12) Asaro, M. F.; Cooper, S. R.; Cooper, N. J . J . Am. Chem. Soc.
1986, 108, 5187-5193.
(13) Legzdins, P.; Shaw, M. J . J . Am. Chem. Soc. 1994, 116, 7700-
7705.
(14) Legzdins, P.; Shaw, M. J .; Batchelor, R. J .; Einstein, F. W. B.
Organometallics 1995, 14, 4721-4723.
(15) Poli, R.; Krueger, S. T.; Abugideiri, F.; Haggerty, B. S.;
Rheingold, A. L. Organometallics 1991, 10, 3041-3046.
10.1021/om000329t CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/18/2000

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3843
Sch em e 1
similar instability for the methylation product of
CpMoCl2(MeSCH2CH2PPh2),16 and similar difficulties
were encountered by Fryzuk et al. in the alkylation of
[η5:P,P′-C5H3-1,3-(SiMe2CH2PiPr2)2]MoCl2.17 In parallel
studies, we have found a novel high-yield synthesis of
the previously known18 CpMo(η4-butadiene)Cl2 and have
started to investigate its reactivity.19 We now report
that the reaction of this compound and similar diene
derivatives with several alkylating reagents affords the
first isolable mononuclear alkyl complexes of Mo(III).
Somewhat unexpectedly, we find these products to be
chemically inert under a variety of conditions. A portion
of this work has been previously communicated.20
diene ligand preferentially adopts the supine (or endo)
conformation in this system.18 In this respect, it can be
noted that Davidson and co-workers have also reported
derivatives with 1,3-pentadiene but could not obtain
analogues with 1,3-cyclohexadiene.18 Compound 1′′
shows spectroscopic and electrochemical properties
analogous to those previously reported for 1 and 1′. The
cyclic voltammogram of 1′′ in THF shows a reversible
reduction wave at -1.24 V vs ferrocene (cf. -1.08 and
-1.20 V for 1 and 1′) and an irreversible oxidation at
0.66 V (cf. 0.75 V for 1′), while the EPR spectrum of 1′′
in THF shows a broad singlet at room temperature at
g ) 1.994. Upon cooling, a hyperfine splitting to the
external diene H atoms becomes visible, but unlike
compounds 1 and 1′, no distinction between the anti and
syn protons could be made.
Resu lts a n d Discu ssion
1. P r ep a r a tion of th e Dien e-Con ta in in g Dich lo-
r id e P r ecu r sor s. The butadiene and isoprene com-
pounds 1 and 1′ were first reported by Davidson et al.18
as the products of diene addition to a Mo(II) precursor,
which limits the yield to 50% at best. The diene complex
1 has been more recently synthesized in 90% yields by
addition of butadiene to CpMoCl2.21 By the same
procedure, we have now obtained 1′ and the previously
unreported 2,3-dimethylbutadiene analogue, 1′′, in iso-
lated yields greater than 70% (eq 1). No reaction takes
place between CpMoCl2 and cycloocta-1,3-diene or cy-
cloocta-1,5-diene under the same conditions. These
results may be rationalized by the steric repulsion
between the diene ligand and the Cp ring, because the
CpMoCl2 + diene f CpMoCl2(η4-diene)
(diene ) 1,3-butadiene, 1; isoprene, 1′;
(1)
2,3-dimethyl-1,3-butadiene, 1′′)
2. Alk yla tion s of Cp MoCl2(η4-d ien e). Treatment of
1, 1′, or 1′′ with 2.2 equiv of alkyl Grignard reagents in
a diethyl ether or THF suspension at -78 °C leads to
the formation of the corresponding dialkyl complexes
(see Scheme 1), which have been isolated as air- and
light-sensitive green solids. All these products, however,
are stable at room temperature as solids and in solution
under an inert atmosphere and in the dark. In addition,
compound 2a has been tested for thermal stability in
toluene and shows, remarkably, less than 50% decom-
position after 22 h heating at 70 °C, as monitored by
EPR spectroscopy. The thermal stability both as solids
and in solution critically depends on the absence of the
magnesium salt byproducts, which must therefore be
thoroughly eliminated. All these products are extremely
soluble in all common organic solvents. Any attempt to
crystallize compounds 2a , 2′a , 2b, and 2′′b from cold
concentrated solutions failed; however, they have been
(16) Morales, D.; Poli, R.; Richard, P.; Andrieu, J .; Collange, E. J .
Chem. Soc., Dalton Trans. 1999, 867-874.
(17) Fryzuk, M. D.; J afarpour, L.; Rettig, S. J . Organometallics 1999,
18, 4050-4058.
(18) Davidson, J . L.; Davidson, K.; Lindsell, W. E.; Murrall, N. W.;
Welch, A. J . J . Chem. Soc., Dalton Trans. 1986, 1677-1688.
(19) Poli, R.; Wang, L.-S. Coord. Chem. Rev. 1998, 178-179, 169-
189, and references therein.
(20) Le Grognec, E.; Poli, R.; Wang, L.-S. Inorg. Chem. Commun.
1999, 2, 95-96.
(21) Wang, L.-S.; Fettinger, J . C.; Poli, R. J . Am. Chem. Soc. 1997,
119, 4453-4464.

3844 Organometallics, Vol. 19, No. 19, 2000
Le Grognec et al.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 2′′a a
Mo-CNT(1)
Mo-CNT(2)
Mo-C(1)
Mo-C(2)
Mo-C(3)
Mo-C(4)
Mo-C(7)
Mo-C(8)
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
2.019(5)
1.925(3)
2.227(3)
2.362(2)
2.355(2)
2.219(3)
2.226(2)
2.224(3)
1.425(4)
1.397(4)
1.421(4)
Mo*-CNT(1*)
Mo*-CNT(2*)
Mo*-C(1*)
Mo*-C(2*)
Mo*-C(3*)
Mo*-C(4*)
Mo*-C(7*)
Mo*-C(8*)
C(1*)-C(2*)
C(2*)-C(3*)
C(3*)-C(4*)
2.021(4)
1.928(3)
2.235(3)
2.362(2)
2.355(2)
2.223(3)
2.233(2)
2.211(2)
1.428(3)
1.391(3)
1.431(4)
CNT(1)-Mo-CNT(2) 135.9(6) CNT(1*)-Mo*-CNT(2*) 136.3(5)
CNT(1)-Mo-C(7)
CNT(1)-Mo-C(8)
CNT(2)-Mo-C(7)
CNT(2)-Mo-C(8)
112.5(4) CNT(1*)-Mo*-C(7*)
112.6(3) CNT(1*)-Mo*-C(8*)
100.9(2) CNT(2*)-Mo*-C(7*)
101.1(2) CNT(2*)-Mo*-C(8*)
111.3(3)
112.9(3)
101.3(2)
100.8(2)
a
CNT(1) is the center of gravity of the cyclopentadienyl ring
[atoms C(9)-C(13)]. CNT(2) is the center of gravity of the
butadiene ligand [atoms C(1)-C(4)]. Starred atoms refer to the
second, independent molecule.
As previously discussed for compound 2a ,20 the spec-
tra of 2′a and 2′′a qualitatively exhibit an apparent
binomial undecet pattern, due to the unresolved cou-
pling (aH ca. 5.5 G) to 10 H atoms of three different
kinds: the six methyl hydrogens and the four (two syn
and two anti) external diene hydrogens. In accord with
this interpretation, the EPR resonance of the CD3
homologue 2a -d 6 is reduced to a broad quintet with
identical g, aMo, and aH values as 2a under similar
conditions. The individual coupling constants reported
in the Experimental Section derive from a standard
simulation and fitting of the experimental spectra on
the basis of the proposed spin system. The spectra of
the CH2Ph derivatives (2b and 2′′b) and CH2SiMe3
derivatives (2c and 2′′c) analogously show couplings to
the diene terminal H atoms and alkyl R-H atoms. In
these cases, the spectra are more complex because the
coupling constants to the different kinds of H atoms are
sufficiently distinct (see Figure 1).
The structure of compound 2′′a has been determined
by a single-crystal X-ray analysis. Two independent,
noninteracting, and essentially identical molecules are
contained in the asymmetric unit. Selected bond dis-
tances and angles for both molecules are collected and
compared in Table 1. A view of one of them is shown in
Figure 2. The geometry parallels that reported by
Davidson and co-workers for compound 1,18 including
the supine conformation adopted by the diene ligand.
The diene ligand has longer lateral C-C bonds with
respect to the internal one (averages are 1.426(4) and
1.394(4) Å over the two independent molecules), indicat-
ing significant back-bonding. These values are not too
different than those found for 1 (1.410(6) and 1.364(5)
Å, respectively).18 The values of d (average difference
between Mo-Clateral and Mo-Cinternal distances) and θ
(diene fold angle as defined by Yasuda and Nakamura)26
are -0.135 Å and 93.97° for one molecule and -0.129
Å and 93.64° for the other one. By comparison, the
corresponding values for compound 1 are -0.086 Å and
93.33°. These values indicate that the electronic distri-
bution in the Mo-diene bond is similar for compounds
1 and 2′′a . Thus, the compounds can more appropriately
F igu r e 1. Experimental (left) and simulated (right) EPR
spectra of compounds CpMo(R3)2(η4-CH2dCR1-CR2dCH2).
(a) 2b in pentane at -80 °C; (b) 2c in pentane at -80 °C.
recovered as analytically pure powders by evaporation
to dryness. In addition, the formulation of 2′′a was
confirmed by a single-crystal X-ray analysis (vide infra).
It is interesting to remark that the alkylation pro-
cesses occur cleanly, with no competitive nucleophilic
attack at the diene ligand nor SET processes. In
comparison, the Mo(III) complex [CpMo(η4-C4H6)(η3-
C3H5)]+ undergoes competitive nucleophilic attack and
one-electron reduction,22 while the Mo(II) complexes
[CpMo(η4-C4H6)2]+ and [CpMo(η4-diene)(CO)2]+ undergo
facile addition of the carbanion at a diene terminal
position.23-25 The arylation of 1 and 1′′ also provides
evidence of competitive metathesis and SET processes
(vide infra).
All dialkyl products exhibit a room-temperature EPR
signal around g ) 2.01 with molybdenum satelites (aMo
ca. 33 G) due to 95Mo (15.9%) and 97Mo (9.5%), both
having I ) 5/2. The spectra additionally show diagnostic
hyperfine couplings to the diene terminal H atoms and
to the alkyl R-H atoms. Like the previously described
compounds 1, 1′,18 and [CpMo(η4-C4H6)(η3-C3H5)]+,21 the
CpMo(III) diene complexes reported here do not show
hyperfine couplings to the diene internal H atoms nor
to the Cp H atoms in the EPR spectrum. The H
couplings may be observed in some cases for dilute
solutions at room temperature (2b, 2′′b, 2c, 2′′c),
whereas in all the other cases they are evident only at
low temperature. The spectra of complexes 2a and 2a -
d 6 are shown in the figure of the preliminary com-
munication.20 Compounds with identical alkyl ligands
and different substitution on the diene ligand show
similar spectra (e.g., 2a , 2′a , and 2′′a ). Representative
spectra for the bis(trimethylsilylmethyl) and dibenzyl
derivatives are shown in Figure 1.
(22) Poli, R.; Wang, L.-S. Polyhedron 1998, 17, 3689-3700.
(23) Faller, J . W.; Murray, H. H.; White, D. L.; Chao, K. H.
Organometallics 1983, 2, 400-409.
(24) Vong, W.-J .; Peng, S.-M.; Lin, W.-J .; Liu, R.-S. J . Am. Chem.
Soc. 1991, 113, 573-582.
(25) Wang, L.-S.; Fettinger, J . C.; Poli, R.; Meunier-Prest, R.
Organometallics 1998, 17, 2692-2701.
(26) Yasuda, H.; Nakamura, A. Angew. Chem., Int. Ed. Engl. 1987,
26, 723-742.

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3845
and investigated the product of monomethylation for
substrate 1, namely, compound 3; see Scheme 1. Treat-
ment of 1 with only 1 equiv of CH3MgBr in a THF or
toluene solution affords the expected monomethyl de-
rivative 3 as an analytically and spectroscopically pure
dark green powder. The EPR spectrum (shown in the
figure of the preliminary communication) has the quali-
tative appearance of a binomial octet because of unre-
solved coupling to the butadiene syn and anti external
H atoms. Both the g value and the aMo and aH coupling
constants are similar for 2a and 3. This feature,
therefore, does not allow us to rule out the presence of
minor amounts of each compound as a contaminant in
the other. The purity of both products, however, is
unambiguously shown by the electrochemical studies;
see next section. Other selective monoalkylation pro-
cesses of dichloride precursors have been previously
reported.42-44
3. Cyclic Volta m m etr ic Stu d ies of th e Alk ylm o-
lybd en u m (III) Der iva tives. All alkylmolybdenum(III)
derivatives have been investigated by cyclic voltamme-
try, since half-sandwich molybdenum(III) complexes
usually display an interesting redox behavior.45 All
compounds display a reversible reduction wave and an
irreversible oxidation process. The latter one was in-
vestigated in greater details for 2a , for which no return
wave could be observed even at scan rates up to 1000
V‚s-1 or at low temperatures (-30 °C) in different
solvents (THF, MeCN, or CH2Cl2). The important
results are collected in Table 3. It is immediately
apparent that the reduction potentials are much more
negative for the dialkyl complexes than for the dihalide
species. As could be predicted, the reversible reduction
wave for the mixed complex 3 is located halfway
between the potentials measured for the dichloro and
dimethyl species 1 and 2a . A similar situation was
reported for compounds Cp*M(NO)XY (M ) Mo, W; X,Y
) Cl, CH2CMe3).43 Therefore, cyclic voltammetry is the
best method to evaluate the presence of monoalkylated
species as a contaminant in the dialkylated products,
and vice versa. The observed negative shift is ap-
proximately 0.5 V per Cl/R substitution. Related sys-
tems where a process interconverting 18-electron and
17-electron species has been measured include [Cp2-
WX2]n+ (n ) 0, 1)12 and [CpCr(NO)(L)X]n- (n ) 0, 1),14,46
where the observed negative shifts per Cl/R substitution
F igu r e 2. ORTEP89 view of compound 2′′a with thermal
ellipsoids drawn at the 30% probability level.
Ta ble 2. Selected Mo(III)-C Bon d Dista n ces
Mo-C distance
compound
(Å)
ref
Mo2(CH2SiMe3)6
2.131
28
Mo2(CH2Ph)6
2.162(2)
2.167(7)
2.134(14)a
29
30
31
Mo2Me2(OtBu)4(py)2
Mo2(CH2SiMe3)4(OtBu)2
Mo2(CH2SiMe3)4(OC6H3Me2)2
Mo2(CH2Ph)2(OiPr)4(PMe3)
Mo2(CH2Ph)2(OiPr)4(dmpm)
Mo2Et2(NMe2)4
2.090(7), 2.112(6) 32
2.216(6)a
2.206(10)
2.164(7)a
2.19(1)a
33
33
34
35, 36
37
Mo2(CH2Ph)2(NMe2)4
Mo2(CH2CH2CH2CH2)(NMe2)4
2.168(4)
Mo2Et2(NMe2)2(CH3C6H4N3C6H4CH3)2 2.213(11)a
38
Mo2(CH2tBu)2(O2CCH3)4
2.192(2)
39
40
(iPrO)3MotMo(CH2Ph)2(OiPr)(PMe3) 2.22(1)
a
Average distance.
be described as Mo(III)-diene complexes rather than
as Mo(V) metallacyclopentene derivatives, although the
contribution of the metallacyclopentene form is certainly
not negligible. Most other crystallographically charac-
terized Mo(III)-alkyl derivatives are based on the triply
bonded Mo2X6 structural motif.27 The Mo-CH3 bond
length in compound 2′′a (average 2.224(9) Å over both
molecules) is at the longer limit of the range previously
established for these triply bonded molecules, as it
might be expected from the greater electronic and
coordinative saturation. Examples are shown in Table
2.
(33) Chisholm, M. H.; Folting, K.; Huffman, J . C.; Kramer, K. S.;
Tatz, R. J . Organometallics 1992, 11, 4029-4036.
(34) Chisholm, M. H.; Haitko, D. A.; Folting, K.; Huffman, J . C. J .
Am. Chem. Soc. 1981, 103, 4046-4053.
(35) Chetcuti, M. J .; Chisholm, M. H.; Folting, K.; Huffman, J . C.;
J anos, J . J . Am. Chem. Soc. 1982, 104, 4684-4686.
(36) Chetcuti, M. J .; Chisholm, M. H.; Folting, K.; Haitko, D. A.;
Huffman, J . C.; J anos, J . J . Am. Chem. Soc. 1983, 105, 1163-1170.
(37) Chetcuti, M. J .; Chisholm, M. H.; Chiu, H. T. Polyhedron 1985,
4, 1213-1217.
(38) Chetcuti, M. J .; Chisholm, M. H.; Folting, K.; Haitko, D. A.;
Huffman, J . C. J . Am. Chem. Soc. 1982, 104, 2138-2146.
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W. G.; Kober, E. M.; Lichtenberger, D. L.; Bursten, B. E. J . Am. Chem.
Soc. 1987, 109, 6796-6816.
(40) Chisholm, M. H.; Huffman, J . C.; J ., T. R. J . Am. Chem. Soc.
1984, 106, 5385-5386.
Since dialkylation reactions are known to occasionally
afford byproducts of monoalkylation, especially with the
bulkier alkylating agents,41 we deliberately synthesized
(27) Chisholm, M. H. Acc. Chem. Res. 1990, 23, 419-425.
(28) Huq, F.; Mowat, W.; Shortland, A.; Skapski, A. C.; Wilkinson,
G. J . Chem. Soc., Chem. Commun. 1971, 1079-1080.
(29) Beshouri, S. M.; Rothwell, I. P. Polyhedron 1986, 5, 1191-1195.
(30) Chisholm, M. H.; Huffman, J . C.; J ., T. R. J . Am. Chem. Soc.
1983, 105, 2075-2077.
(31) Chisholm, M. H.; Folting, K.; Huffman, J . C.; Rothwell, I. P.
Organometallics 1982, 1, 251-259.
(32) Coffindaffer, T. W.; Rothwell, I. P.; Huffmann, J . C. J . Chem.
Soc., Chem. Commun. 1983, 1249-1251.
(41) Aizenberg, M.; Turculet, L.; Davis, W. M.; Shattenmann, F.;
Schrock, R. R. Organometallics 1998, 17, 4795-4812.
(42) Fagan, P. J .; Manriquez, J . M.; Maata, E. A.; Seyam, A. M.;
Marks, T. J . J . Am. Chem. Soc. 1981, 103, 6650-6667.
(43) Debad, J . D.; Legzdins, P.; Rettig, S. J .; Veltheer, J . E.
Organometallics 1993, 12, 2714-2725.
(44) Foo, T.; Bergman, R. G. Organometallics 1992, 11, 1801-1810.
(45) Poli, R. J . Coord. Chem. B 1993, 29, 121-173.

3846 Organometallics, Vol. 19, No. 19, 2000
Le Grognec et al.
Ta ble 3. Cyclic Volta m m etr ic Da ta a t Room
Tem p er a tu r e in THF for All Com p ou n d sa
compound
E1/2 (MoII/MoIII) (V)
Ep,a (MoIII/MoIV)b (V)
1c
1′
-1.11
-1.19
-1.24
-2.09
-2.13
-2.14
-1.85
-1.85
-2.01
-2.07
-1.62
-1.61e
-1.00
0.73
0.75
0.66
1′′
2a
2′a
2′′a
2b
2′′b
2c
2′′c
3
-0.17
-0.18
-0.23
-0.38
-0.34
-0.26
-0.28
d
5
6
0.27
d
a
b
All potentials are relative to the ferrocene standard. Mea-
sured by using a scan rate of 200 mV s-1 for all compounds. c This
compound was also previously investigated by Davidson et al.18
(reversible reduction at -1.09 V in THF and -1.21 V in CH2Cl2;
d
irreversible oxidation at Ep,a ) +0.62 V in CH2Cl2). An oxidation
wave for this compound was not observed up to the discharge of
the solvent (ca. 1.5 V). e (ia/ic) < 1 (see text).
are ca. 350 mV (R ) Me) and 610 mV (R ) CH2SiMe3),
respectively. The irreversible oxidation process is also
significantly shifted toward negative potentials on going
from the dichloro to the dialkyl systems. Related
systems where the conversion between 17- and 16-
electron species has been observed, namely, [Cp2MX2]n+
(n ) 0, 1; M ) Ti, Zr)47-49 and [(C5R5)M(NO)X2]n- (n )
0, 1; R ) H, Me; M ) Mo, W),43,50,51 show again similar
negative shifts.
F igu r e 3. Cyclic voltammograms at different times of a
THF solution obtained by mixing equimolar amounts of
compounds 1 and 2a .
A comparison between members of homologous series
shows that greater substitution on the diene ligand
results in a small negative shift on both processes. For
compounds with the same diene and different alkyl
groups, the reduction potentials become less negative
in the order CH3 < CH2SiMe3 < CH2Ph, in agreement
with trends of the R-substituent electron-withdrawing
properties (H < SiMe3 < Ph). On the other hand, the
oxidation peak potential shifts in the opposite direction,
in contrast with the above effect. However, since these
oxidation processes are irreversible, the different ob-
served potentials must also depend on the relative rates
of the follow-up chemical processes.
4. Con p r op or tion a tion Rea ction of 1 a n d 2a . The
selective formation of the monoalkylated complex 3 by
methylation of 1 with 1 equiv of CH3MgBr could be
rationalized in two possible ways. The first alkylation
could proceed much more rapidly than the second one,
and/or compound 3 could be thermodynamically favored
relative to a 50:50 mixture of 1 and 2a . Note that the
greater solubility in THF of the monoalkylation product
3 with respect to the precursor 1 is a factor in favor of
a competitive second alkylation. The rationalization
based on thermodynamics was easily tested by monitor-
ing a solution obtained by mixing equivalent amounts
of the dichloro and dimethyl complexes; see eq 2.
4
CpMo(η4-C4H6)Cl2 CpMo(η -C4H6)(CH3)2
+
a
1
2a
2 CpMo(η4-C4H6)(CH3)Cl
(2)
3
As discussed above, the EPR signal of 3 has a g value
identical with that of 2a . Thus, the EPR monitoring
showed only the decrease of compound 1 and the
increase of a signal corresponding to the sum of 2a and
3. On the other hand, cyclic voltammetry permitted us
to follow the evolution of all three compounds indepen-
dently; see Figure 3. It can be noted that the reaction
is extremely slow and quantitative, a complete conver-
sion requiring several weeks at room temperature. The
slow rate of this ligand redistribution process also
indicates that the thermodynamic preference of 3 rela-
tive to a mixture of 1 and 2a is not a sufficient criterion
to rationalize the selectivity of the monoalkylation
process. A much slower second alkylation step relative
to the first one must also be invoked.
Reaction 2 is an example of the general ligand
redistribution process schematically described in eq 3,
for which many examples are known.52-54 Of particular
relevance here, because the metal and electronic con-
figuration are the same, is the equilibrium between
CpMo(PMe3)2Cl2 and CpMo(PMe3)2I2 on one side with
the mixed system CpMo(PMe3)2(Cl)(I) on the other
side.54 This equilibrium was found to lie in slight favor
(46) Legzdins, P.; McNeil, W. S.; Shaw, M. J . Organometallics 1994,
13, 562-568.
(47) Lappert, M. F.; Pickett, C. J .; Riley, P. I.; Yarrow, P. I. W. J .
Chem. Soc., Dalton Trans. 1981, 805-813.
(48) Chaloyard, A.; Dormond, A.; Tirouflet, J .; El Murr, N. J . Chem.
Soc., Chem. Commun. 1980, 214-216.
(49) Mugnier, Y.; Mo¨ıse, C.; Laviron, E. J . Organomet. Chem. 1981,
204, 61-66.
(52) Heaton, B. T. J . Chem. Soc., Chem. Commun. 1973, 931-932.
(53) Hunt, C. T.; Balch, A. L. Inorg. Chem. 1982, 21, 1641-1644.
(54) Linck, R. G.; Owens, B. E.; Poli, R.; Rheingold, A. L. Gazz. Chim.
Ital. 1991, 121, 163-168.
(50) Herring, F. G.; Legzdins, P.; Richter-Addo, G. B. Organome-
tallics 1989, 8, 1485-1493.
(51) Legzdins, P.; Veltheer, J . E. Acc. Chem. Res. 1993, 26, 41-48.

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3847
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d s 4 a n d 4′′a
Mo-CNT(1)
1.922(6)
Mo(1)-CNT(1)
Mo(2)-CNT(3)
Mo(1)-CNT(2)
Mo(2)-CNT(4)
Mo(1)-Br
1.945(3)
1.930(3)
1.949(2)
1.946(2)
2.6677(15)
2.6667(15)
2.572(13)
2.607(13)
2.4144(16)
2.2206(19)
2.4105(16)
2.2206(18)
1.402(4)
Mo-CNT(2)
1.911(10)
Mo-Cl
Mo-Cl#
2.5712(12)
2.5766(12)
Mo(2)-Br
Mo(1)-Cl
Mo(2)-Cl
Mo-C(6)
Mo-C(7)
Mo-C(8)
Mo-C(9)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
2.246(6)
2.308(7)
2.330(7)
2.242(7)
1.434(11)
1.367(11)
1.428(11)
Mo(1)-C(7)
Mo(1)-C(8)
Mo(2)-C(10)
Mo(2)-C(11)
C(7)-C(7)#
C(7)-C(8)
1.440(3)
1.403(4)
1.447(2)
C(10)-C(10)#
C(10)-C(11)
F igu r e 4. ORTEP89 view of compound 4 with thermal
ellipsoids drawn at the 30% probability level.
CNT(1)-Mo-CNT(2) 134.0(12) CNT(1)-Mo(1)-CNT(2) 132.2(3)
CNT(3)-Mo(2)-CNT(4) 131.6(3)
CNT(1)-Mo-Cl
CNT(1)-Mo-Cl#
CNT(2)-Mo-Cl
CNT(2)-Mo-Cl#
112.6(3) CNT(1)-Mo(1)-Br
111.9(4) CNT(1)-Mo(1)-Cl
102.9(5) CNT(2)-Mo(1)-Br
102.2(5) CNT(2)-Mo(1)-Cl
CNT(3)-Mo(2)-Br
112.1(2)
113.4(9)
104.5(1)
104.2(7)
113.3(2)
113.4(9)
103.8(1)
105.0(8)
101.95(4)
106.3(4)
78.02(7)
78.05(7)
74.3(6)
of the mixed chloroiodo system with respect to the
statistical distribution (K ) 12-15 in CH2Cl2 and 20-
28 in THF in the temperature range 22-35 °C, corre-
sponding to the experimental H° values of -0.7 and
-1.0 kcal/mol, respectively).54 The essential complete-
ness of reaction 2 means that this must be characterized
by an even greater exothermicity. For a reaction of this
kind, it can be safely assumed that the entropic and (PV)
contributions are negligible, thus G ≈ H ≈ E. Total
energy calculations for geometry optimized 1, 2a , and
3 by DFT/B3LYP methods afford an E value of -7.4
kcal/mol for the isodesmic reaction 2. From this value
and the above assumptions, the equilibrium constant
for reaction 2 is estimated as K ) 2.7 × 105, in
agreement with the observed complete conversion. A
similar redistribution process, also thermodynamically
favoring the mixed chloroalkyl species, is that involving
Cp*2MR2 and Cp*2MCl2 (M ) Th, U; R ) Me, CH2-
SiMe3).42
CNT(3)-Mo(2)-Cl
CNT(4)-Mo(2)-Br
CNT(4)-Mo(2)-Cl
100.45(5) Mo(1)-Br-Mo(2)
Mo(1)-Cl-Mo(2)
79.55(7) Br-Mo(1)-Br#
Br-Mo(2)-Br#
Mo-Cl-Mo#
Cl-Mo-Cl#
Cl-Mo(1)-Cl#
Cl-Mo(2)-Cl#
73.1(5)
a
CNT(n) is the center of gravity of the cyclopentadienyl ring
[for 4: n ) 1, atoms C(1)-C(5); for 4′′: n ) 1, atoms C(1), C(2),
C(3), C(3)#, C(2)#; n ) 3, atoms C(4), C(5), C(6), C(6)#, C(5)#] or
the butadiene ligand [for 4: n ) 2, atoms C(6)-C(9); for 4′′: n )
2, atoms C(7), C(7)#, C(8), C(8)#; n ) 4, atoms C(10), C(10)#, C(11),
C(11)#].
of Br (89%) and Cl (11%).21 The metals are separated
by the nonbonding distance of 3.96 Å (cf. 4.08 Å for the
Br0.89Cl0.11 analogue). The Mo-Cl distances are much
shorter than the Mo-X distances in the above-men-
tioned X analogue (2.6613(6) and 2.6570(6) Å), in
agreement with the different nature of the bridging
halide atom. The reasonable thermal ellipsoid of the
bridging Cl atom suggests that no significant composi-
tional disorder (e.g., with Br) is present in this case. All
other structural parameters are rather similar to the
compositionally disordered Br0.89Cl0.11 analogue, includ-
ing the previously defined26 ∆d and θ values, these being
-0.075 Å and 91.77° for compound 4. These values are
also similar to those reported above for compound 2′′a ,
indicating that both compounds adopt a similar Mo-
diene bonding situation.
The isolation of the reduced product 4 from a solution
originating from the monoalkylation of the dichloride
complex 1 might lead to the proposal of an alternative
formation mechanism, namely, direct reduction of 1 by
the methyl Grignard reagent (a well-known phenom-
enon). Indeed, compound 1 was reported to undergo a
reductive process by interaction with allylmagnesium
bromide.21 However, the product of this reduction was
found to be the above-mentioned [CpMo(η4-C4H6)(µ-
Br)0.89(µ-Cl)0.11]2 rather than the pure chloro species. The
reason for this result was traced to the relative prefer-
ence of the two acidic centers Mo(II) and Mg(II) for the
Lewis bases chloride and bromide, according to the
HSAB theory. Thus, the 16-electron product of reduc-
tion, CpMo(η4-C4H6)Cl, and MgClBr would exchange
halides to afford CpMo(η4-C4H6)Br and MgCl2 in an
X-M-X + Y-M-Y a 2 X-M-Y
(3)
The ligand redistribution process of eq 2 is much
slower than the Cl/I redistribution process mentioned
above, for which the equilibrium position was attained
within 48 h at room temperature. A possible reason for
this slower rate is the reduced ability of the methyl
groups to bridge two metals in a likely dinuclear
intermediate.
5. Decom p osition of 3 a n d Ar yla tion s of Cp -
MoCl2(η4-dien e). The di-µ-chlorodimolybdenum(II) com-
plex 4 crystallizes from a pentane solution of 3 upon
prolonged standing in laboratory roomlight at room
temperature. We believe that this conversion involves
the expulsion of methyl radicals (eq 4), by analogy with
the analogous process previously reported for CpMo-
(PMe3)2(CH3)2.15
4
f
2 CpMo(η -C4H6)(CH3)Cl
3
[CpMo(η4-C4H6)(µ-Cl)]2
+ 2 CH3° (4)
4
The structure of compound 4 is shown in Figure 4,
and selected bond distances and angles are collected in
Table 4. The basic geometry of the molecule is identical
with that previously established for the isomorphous
[CpMo(η4-C4H6)(µ-X)]2, X being a compositional disorder

3848 Organometallics, Vol. 19, No. 19, 2000
Le Grognec et al.
6. Ch em ica l Rea ctivity Stu d ies. 6.1. In er tn ess
tow a r d Lew is Ba ses. As stated above, the dialkyl
derivatives 2 are thermally stable in the solid state and
in solution, provided they are kept under an inert
atmosphere and in the dark. They could be kept
unaltered for several months when stored in flame-
sealed and aluminum foil-wrapped ampules under
argon at 4 °C. The exposure of pentane solutions of 2a
to the laboratory light induced a relative rapid decom-
position, with the formation of a black precipitate, which
does not dissolve in any common organic solvents. It is
possible that a light-induced methyl radical elimination
takes place as previously shown for the related CpMo-
(PMe3)2(CH3)2 species and as suggested above for com-
pound 3. If this is the case, the hypothetical CpMo(η4-
C4H6)(CH3) product would continue to decompose
because, contrary to CpMo(η4-C4H6)Cl, it is not able to
stabilize itself by dimerization. No diamagnetic product
of type CpMo(η4-C4H6)(CH3)(L) could be identified by
NMR (L ) PMe3, PEt3) or IR (L ) CO) spectroscopy
when the photodecomposition was carried out in the
presence of ligand L. As a matter of fact, the photode-
composition of 2a was retarded by the presence of L.
For instance, the half-life of 2a was 28 h in the presence
of a 3-fold excess of PMe3 at room temperature, as
compared with 10 h in the absence of the phosphine.
The only tentative rationalization that we are able to
offer is that the additional ligand somehow acts as a
quencher of the photodecomposition process.
F igu r e 5. ORTEP89 view of compound 4′′ with thermal
ellipsoids drawn at the 30% probability level. The bridging
atom X is a compositional disorder of Br (77%) and Cl
(23%). Only the major species (X ) Br) is shown for clarity.
equilibrium process. Now, the Grignard reagent em-
ployed to synthesize compound 3 was CH3MgBr, while
the X-ray analysis indicates that compound 4 is a pure
dichloro species. This means that compound 4 must
necessarily form only after removal of the magnesium
salts from the reaction mixture.
No increased loss of starting material (with respect
to control experiments carried out without the Lewis
basic reagent and in the absence of light) occurs upon
interaction of 2a with PEt3 at the reflux temperature
of THF or with CO at 65 °C and 600 psi. This behavior
is quite surprising because 17-electron organometallic
species are believed to establish rapid (electronically
favored, sterically disfavored) equilibria with formally
19-electron products of ligand addition,3,55,56 and be-
cause both alkyl-alkyl reductive elimination pro-
cesses57-61 and the insertion of CO into M-R bonds58,62-71
are known to be favored by an increase in metal
oxidation state. Since half-sandwich derivatives of Mo-
A competition between metathesis and reduction is
observed in arylation reactions of compounds 1 and 1′′.
The reactions between compounds 1 or 1′′ with PhLi,
PhMgI, or (C6H2Me3-2,4,6)MgBr lead to the formation
of solutions containing new EPR active Mo(III) deriva-
tives. These compounds, however, proved to be too
unstable to isolate as pure products. The EPR spectra
of these derivatives show as expected only an unresolved
binomial quintet pattern because of coupling with the
four terminal diene H atoms, since these derivatives
lack any R-H atom on the R3 substituent. The lack of
any signature in the EPR spectrum by the aryl substit-
uents does not unequivocally establish whether the
observed products are diaryl or mixed chloro-aryl spe-
cies. From the mesityl Grignard reaction, however,
(55) Ryan, O. B.; Tilset, M.; Parker, V. D. J . Am. Chem. Soc. 1990,
112, 2618-2626.
(56) Tyler, D. R. Acc. Chem. Res. 1991, 24, 325-331.
(57) Tsou, T. T.; Kochi, J . K. J . Am. Chem. Soc. 1978, 100, 1634-
1635.
crystals of compound [CpMo(η4-C4H4Me2-2,3)(µ-Br)0.77
-
(µ-Cl)0.23]2, 4′′, were recovered, documenting that a
reduction process takes place in this case as previously
observed for the allyl Grignard reaction.21 The structure
of 4′′, shown in Figure 5, is very similar to that of 4
and to that previously reported for compound [CpMo-
(η4-C4H6)(µ-Br)0.89(µ-Cl)0.11]2 (see relevant parameters in
Table 4). One minor difference, however, concerns the
intimate geometry of the Mo(η4-diene) moiety. A greater
tilting of the diene function is observed for 4′′, leading
to longer Mo-C bonds for the internal C atoms and
shorter ones for the external C atoms. This effect may
be attributable to a steric repulsion between the methyl
substituents at the diene 2 and 3 positions on one Mo
atom with the Cp ligand on the adjacent Mo atom,
rather than to a modification in the electronic structure
of the Mo-diene bond (i.e., degree of back-bonding). In
fact, the C-C bond alternation is similar in the two
compounds.
(58) Lau, W.; Huffman, J . C.; Kochi, J . K. Organometallics 1982, 1,
155-169.
(59) Pedersen, A.; Tilset, M. Organometallics 1993, 12, 56-64.
(60) Pedersen, A.; Tilset, M. Organometallics 1994, 13, 4887-4894.
(61) Fooladi, E.; Tilset, M. Inorg. Chem. 1997, 36, 6021-6027.
(62) Magnuson, R. H.; Zulu, S.; T'sai, W.-M.; Giering, W. P. J . Am.
Chem. Soc. 1980, 102, 6887-6888.
(63) Magnuson, R. H.; Meirowitz, R.; Zulu, S.; Giering, W. P. J . Am.
Chem. Soc. 1982, 104, 5790-5791.
(64) Magnuson, R. H.; Meierowitz, R.; Zulu, S. J .; Giering, W. P.
Organometallics 1983, 2, 460-462.
(65) Reger, D. L.; Mintz, E. Organometallics 1984, 3, 1759-1761.
(66) Bly, R. S.; Silverman, G. S.; Bly, R. K. Organometallics 1985,
4, 374-383.
(67) Reger, D. L.; Mintz, E.; Lebioda, L. J . Am. Chem. Soc. 1986,
108, 1940-1949.
(68) Golovin, M. N.; Meirowitz, R.; Rahman, M. M.; Liu, H. Y.; Prock,
A.; Giering, W. P. Organometallics 1987, 6, 2285-2289.
(69) Therien, M. J .; Trogler, W. C. J . Am. Chem. Soc. 1987, 109,
5127-5133.
(70) Reger, D. L.; Klaeren, S. A.; Babin, J . E.; Adams, R. D.
Organometallics 1988, 7, 181-189.
(71) Liu, H.-Y.; Golovin, N.; Fertal, D. A.; Tracey, A. A.; Eriks, K.;
Giering, W. P.; Prock, A. Organometallics 1989, 8, 1454-1458.

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3849
Sch em e 2
(II) have been shown to undergo CO insertion pro-
cesses,72,73 we were naturally expecting to observe a
reaction between CO and the formally Mo(III) dialkyl
derivatives reported here. However, despite the oxida-
tion state, the metal has a high electron density, as
demonstrated by the electrochemical studies described
above, which probably renders ligand coordination and
insertion/elimination processes thermodynamically and/
or kinetically less favorable. A paramagnetic alkyl
complex undergoing a CO insertion process is the 15-
electron Ti(III) system (η5-C5R′5)2Ti-R (R′ ) H, Me).74-76
The 17-electron complex CpCr(NO)(PPh3)(CH2SiMe3) is
equally unreactive toward CO, whereas the less steri-
cally hindered CpCr(NO)(pip)(CH2Ph) does react, but
an insertion process does not occur.14 In light of the
latter observation, steric hindrance toward the ligand
addition process to 2a may also be an important factor.
6.2. In er tn ess tow a r d Br øn sted Acid s. Reactivity
studies of 2a with Brønsted acids also reveal the
inertness of the Mo-CH3 bond toward heterolytic cleav-
age. EPR monitoring reveals that no reaction takes
place with the following acids, in order of increased
strength (all in THF solution): MeOH, H2O, CH3COOH,
H3PO4, and H3O+ (from aqueous HCl). On the other
hand, gaseous HCl in toluene converts 2a to the parent
dichloride compound 1 (eq 5). Heterolytic cleavage is
also observed upon interaction with excess HBF4 and
CF3COOD in C6D6. The formation in these reactions of
CH4 and CH3D, respectively, was evidenced by 1H NMR
spectroscopy.
is much faster than the second one (see Figure 5).
Analogously to the chloro system, the EPR signal of the
mixed methyl trifluoroacetato derivative (g ) 1.998) is
shifted to high g relative to the bis(trifluoroacetato)
analogue (g ) 1.982). The coupling pattern and H
hyperfine splittings for 5 parallel those of the corre-
sponding chloro analogue, namely, an apparent bino-
mial octet, while 6 exhibits an apparent quintet pattern.
Compounds 5 and 6, like all other CpMoIII(η4-diene)
derivatives described in this paper, exhibit a reduction
wave in the cyclic voltammogram. The E1/2 of this wave
is shifted positively relative to the dimethyl parent
system (see Table 3), each Me/O2CCF3 substitution
having quantitatively a similar effect as a Me/Cl sub-
stitution. It is curious that the reduction wave of 5 is
not fully reversible, the (ia/ic) increasing with increasing
scan speed (0.43, 0.50, 0.61, 0.65, and 0.68 at 200, 500,
1000, 2000, and 5000 mV/s, respectively), while the
reduction waves of 2′′a and 6 are fully reversible. In
the corresponding chloride series, the dichloro, methyl
chloro, and dimethyl complexes (1, 3, and 2a ) all show
reversible reduction processes.
Compound 6 could be obtained in the form of single
crystals, which were investigated by X-ray diffraction.
A view of the molecular structure is shown in Figure 6.
The most interesting feature is the monodentate coor-
dination for both trifluoroacetato ligands, confirming the
indications given by the IR spectrum. Selected bond
distances and angles are shown in Table 5. In compari-
son with the structure of compound 2′′a , both the
cyclopentadienyl ring and the diene ligand are closer
to the metal center in compound 6, as shown by the Mo-
CNT(1) and Mo-CNT(2) distances, respectively. A
greater effective positive charge on the metal center
resulting from the replacement of the two methyl groups
with the more electronegative trifluoroacetato ligands,
thereby reducing the metal radius, may be held respon-
sible for this difference. The diene relative arrangement
shows a larger fold angle θ (95.91°) and a larger
negative d (-0.155 Å) relative to compound 2′′a .
CpMo(η4-C4H6)(CH3)2
+ 2 HCl f
2a
CpMo(η4-C4H6)Cl2
+ 2 CH4 (5)
1
The CF3COOD reaction allowed the observation of an
EPR spectrum which is assigned to compound CpMo-
(η4-C4H6)(O2CCF3)2. This compound was not isolated.
However, the corresponding reaction of 2′′a with CF3-
COOD has allowed the isolation and full characteriza-
tion of a mixed methyl-trifluoroacetato derivative, 5,
and a bis(trifluoroacetato) derivative, 6, by the use of 1
or 2 equiv of the acid, respectively (Scheme 2). An EPR
monitoring of the reaction carried out with 2 equiv of
acid clearly indicates that the first protonolysis process
Con clu sion s
The alkylation of CpMo(η4-diene)Cl2 compounds has
permitted the isolation and characterization of the first
examples of stable radical complexes of Mo(III) contain-
ing alkyl ligands. The Mo-R bonds in these derivatives
are relatively robust, their homolytic cleavage being
observed only under photolytic activation at ambient
temperature or above. This is somewhat surprising,
because the corresponding decomposition in the related
CpMo(CH3)2(PMe3)2 compound occurs spontaneously
below room temperature.15 How the nature of the
neutral ligands (one diene vs two PMe3) affects the
(72) Butler, I. S.; Basolo, F.; Pearson, R. G. Inorg. Chem. 1967, 6,
2074-2079.
(73) Wax, M. J .; Bergman, R. G. J . Am. Chem. Soc. 1981, 103, 7028-
7030.
(74) Teuben, J . H.; de Boer, E. J . M.; Klazinga, A. H.; Klei, E. J .
Mol. Catal. 1981, 13, 107-114.
(75) de Boer, E. J . M.; de With, J . J . Organomet. Chem. 1987, 320,
289-293.
(76) Luinstra, G. A.; Ten Cate, L. C.; Heeres, H. J .; Pattiasina, J .
W.; Meetsma, A.; Teuben, J . H. Organometallics 1991, 10, 3227-3237.

3850 Organometallics, Vol. 19, No. 19, 2000
Le Grognec et al.
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 6
Mo-CNT(1)
Mo-CNT(2
Mo-O(1)
1.982(5)
1.918(5)
2.102(3)
2.092(3)
Mo-C(1)
Mo-C(2)
Mo-C(3)
Mo-C(4)
2.206(4)
2.370(4)
2.355(4)
2.209(4)
Mo-O(3)
CNT(1)-Mo-CNT(2) 133.2(7) CNT(2)-Mo-O(1) 98.7(3)
CNT(1)-Mo-O(1)
CNT(1)-Mo-O(3)
115.6(4) CNT(2)-Mo-O(3) 99.4(3)
117.0(4) O(1)-Mo-O(3) 78.84(11)
a
CNT(1) is the center of gravity of the cyclopentadienyl ring
[atoms C(7)-C(11)]. CNT(2) is the center of gravity of the
butadiene ligand [atoms C(1)-C(4)].
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions involving air- and
moisture-sensitive organometallic compounds were carried out
in a J acomex glovebox or by the use of standard Schlenck
techniques under an argon atmosphere. Toluene and diethyl
ether were purified by distillation under argon after drying
over sodium benzophenone ketyl. THF was dried over sodium
benzophenone ketyl and then over Na/K alloy. Pentane was
1
dried over sodium. H NMR measurements were carried out
on a Bruker AC200 spectrometer. The peak positions are
reported with positive shifts in ppm downfield of TMS as
calculated from the residual solvent peaks. The IR spectra
were recorded on a Bruker IFS 66V spectrophotometer with
NaCl optics. EPR measurements were carried out at the X
band microwave frequency on a Bruker ESP 300 spectrometer,
equipped with a ER 4111 VT unit. The spectrometer was
calibrated with DPPH (g )2.0037). EPR spectra simulations
and fittings were carried out with WinSim.77 Cyclic voltamo-
grams were recorded with an EG&G 362 potentiostat con-
nected to a Macintosh computer through MacLab hardware/
software. The electrochemical cell is a locally modified Schlenk
tube. The cell is fitted with a Pt counter electrode, a Ag/AgCl
reference electrode, and a Pt working electrode. Bu4NPF6 was
used as supporting electrolyte at a concentration of 0.1 M. All
potentials are reported vs the Cp2Fe/Cp2Fe+ couple, which was
introduced under argon into the cell at the end of each
measurement. All the voltammetric results obtained in this
study are collected in Table 3. Elemental analyses were
performed with a Fisons EA 1108 apparatus. Isoprene and 2,3-
dimethylbutadiene were purchased from Aldrich Chemical Co,
degassed, and stored on 4 Å molecular sieves before use. CH3-
MgBr (3.0 M in Et2O), CD3MgI (1 M in Et2O), (CH3)3SiCH2-
MgCl (1 M in Et2O), and (C6H2Me3-2,4,6)MgBr (1 M in THF)
were purchased from Aldrich Chemical Co. and used as
received. Diethyl ether solutions of PhLi, PhMgI, and PhCH2-
F igu r e 6. Room-temperature EPR spectra of a toluene
solution obtained by mixing compounds 2′′a and 2 equiv
of CF3COOD: (a) immediately; (b) after 50 min; (c) after
24 h.
MgBr78 and compounds {CpMoCl2}n and CpMo(η4-C4H6)Cl2
54
(1)21 were prepared as described in the literature.
Syn th esis of Cp Mo(η4-d ien e)Cl2. Dien e ) Isop r en e, 1′.
This synthetic procedure is an adaptation of that previously
reported for compound 1.21 {CpMoCl2}n (2.216 g; 9.55 mmol of
Mo) was suspended in 40 mL of THF. Isoprene (1.05 mL; 10.5
mmol) was added to the mixture via a syringe, followed by
heating to 70 °C for 4 h, yielding 1′ as a fine red-brown powder.
The suspension was concentrated to about half volume,
followed by addition of pentane (20 mL). Following filtration,
the solid was washed with pentane (2 × 10 mL) and dried
under vacuum. Yield: 2.222 g, 80%. EPR (THF, room tem-
perature): singlet, g ) 1.994 (cf. lit.18 1.995), aMo ) 37.7 G.
Anal. Calcd for C10H13Cl2Mo: C, 40,03; H, 4.37. Found: C,
40.11; H, 4.38.
F igu r e 7. ORTEP89 view of compound 6 with thermal
ellipsoids drawn at the 30% probability level.
stability and homolytic reactivity of these bonds is not
currently understood. Preliminary density functional
theory studies on CpMo(η4-diene)(CH3)2 and on the
model system CpMo(CH3)2(PH3)2 indicate that the
strength of the Mo-CH3 bond is not significantly altered
by the nature of the neutral ligands, suggesting that
the decomposition mechanism may be more complex
that a simple Mo-R bond homolysis. Further studies
both at the experimental and at the theoretical level
will be devoted to throwing light on this phenomenon.
We are also further pursuing reactivity studies of this
new class of alkyl derivatives.
Dien e ) 2,3-d im eth yl-1,3-bu ta d ien e, 1′′. A procedure
similar to that described above for 1′ yielded 4.512 g of 1′′ (72%)
(77) Duling, D. R. P.E.S.T., v. 0.96; National Institute of Environ-
mental Health Sciences: Research Triangle Park, NC, 1996.
(78) Vogel, A. Vogel’s Textbook of Practical Organic Chemistry, 4th
ed.; Longman: London, 1978; p 638.

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3851
from {CpMoCl2}n (4.715 g; 20.32 mmol of Mo) and 2,3-
dimethylbuta-1,3-diene (2.75 mL; 24 mmol) in 80 mL of THF.
EPR (THF, room temperature): singlet, g ) 1.994; aMo ) 37.7
G. Anal. Calcd for C11H15Cl2Mo: C, 42.07; H, 4.81. Found: C,
42.08; H, 4.41.
satellites; g ) 2.009; aMo ) 32.4 G; aH ) 6.3 G (2H); aH ) 5.2
G (2H); product of the 1′′-PhLi or PhMgBr reaction: apparent
quintet with Mo satellites; g ) 2.009; aMo ) 32.3 G; aH ) 6.3
G (2H); aH ) 5.1 G (2H); product of the 1′′-(C6H2Me3-2,4,6)-
MgBr reaction: apparent quintet with Mo satellites; g ) 2.010;
aMo ) 32.4 G; aH ) 6.1 G (2H); aH ) 5.2 G (2H). Crystallization
of the product of the 1′′/mesityl Grignard reaction by diffusion
of pentane into a concentrated THF solution at room temper-
ature provided crystals of compound 4′′.
Syn th esis of Cp Mo(η4-C4H6)ClMe, 3. To a stirred, brown
suspension of 1 (858 mg, 3 mmol) in THF (40 mL) at -80 °C
was added dropwise CH3MgCl in Et2O (1.1 mL, 3.0 M, 3.2
mmol) via a syringe. After the addition of the Grignard
reagent, the reaction mixture was stirred for 4 h while being
allowed to warm slowly to room temperature. During this time
a clear solid precipitated, while the red-brown solid dissolved
to afford a green solution. The solvent was removed in vacuo,
and the residue was extracted with pentane (60 mL). The
extract was filtered through Celite (1.5 × 2 cm). The pentane
was removed from the filtrate under reduced pressure to obtain
3 as a dark green powder. Yield: 550 mg, 69%. Anal. Calcd
for C10H14ClMo: C, 45.22; H, 5.31. Found: C, 45.22; H, 5.63.
EPR (toluene, room temperature): apparent octet with Mo
satellites, g ) 2.012; aMo ) 32.8 G; aH ) 6.4 G (2H); aH ) 5.4
G (3H); aH ) 4.5 G (2H).
Syn th esis of Cp Mo(η4-d ien e)R2. The synthesis of all the
dialkyl complexes was carried out under identical experimental
conditions. The preparation of CpMo(η4-C4H6)(CH3)2 (2a ) is
described below as a representative example. To a suspension
of 1 (534 mg, 1.86 mmol) in 30 cm3 of Et2O at -78 °C was
added 1.4 mL of MeMgBr in Et2O (3.0 M, 4.1 mmol; Grignard/
Mo ) 2.2). The resulting mixture was stirred while being
allowed to warm slowly to room temperature. During this time
a white solid precipitated, while the red-brown solid dissolved
to afford a green solution. The solvent was removed under
reduced pressure, and the residue was extracted with pentane
(2 × 20 mL). The extracts were combined and filtered through
a column of Celite (1.5 × 3 cm). The column was washed with
pentane until the washings were colorless. The solution was
evaporated under reduced pressure to dryness, yielding com-
pound 2a as a dark green powder. Yield: 232 mg, 51%. Anal.
Calcd for C11H17Mo: C: 53.88; H, 6.99. Found: C, 53,73; H,
7.34. EPR spectrum (toluene, -80 °C): apparent undecet with
Mo satellites; g ) 2.012; aMo ) 33.1 G; aH ) 6.0 G (2H); aH
5.4 (6H); aH ) 4.9 G (2H).
)
Com p ou n d 2a -d 6: 57% yield from 5.2 mmol of 1 and 2.2
equiv of CD3MgI. EPR (pentane, -113 °C): apparent broad
quintet with Mo satellites; g ) 2.012; aMo ) 33.3 G; aH ) 6.3
(2H); aH ) 4.7 G (2H); aD ) 0.41 G (6D).
Com p ou n d 2′a : 55% yield from 1.92 mmol of 1′ and 2.2
equiv of CH3MgBr. Anal. Calcd for C12H19Mo: C, 55.6; H, 7.39.
Found: C, 55.29; H, 7.50. EPR (pentane, -80 °C): apparent
undecet with Mo satellites; g ) 2.012; aMo ) 33.0 G; aH ) 6.3
G (2H); aH ) 5.2 G (6H); aH ) 5.7 (2H).
Com p ou n d 2′′a : 62% yield from 3.0 mmol of 1′′ and 2.2
equiv of CH3MgBr. Anal. Calcd for C13H21Mo: C, 57.14; H,
7.75. Found: C, 56.99; H, 7.75. EPR (pentane, -80 °C):
apparent undecet with molybdenum satellites; g ) 2.013; aMo
) 32.9 G; aH ) 6.6 G (2H); aH ) 5.5 G (6H); aH ) 5.3 G (2H).
Com p ou n d 2b: 51% yield from 1.8 mmol of 1 and 2.2 equiv
of PhCH2MgBr. Anal. Calcd for C23H25Mo: C, 69.52; H, 6.34.
Found: C, 69.47; H, 6.63. EPR (pentane, -80 °C): multiplet
with molybdenum satellites; g ) 2.012; aMo ) 33.5 G; aH ) 6.3
G (2H); aH ) 6.0 G (2H); aH ) 5.9 G (2H); aH ) 4.7 G (2H).
Com p ou n d 2′′b: 48% yield from 1.1 mmol of 1′′ and 2.2
equiv of PhCH2MgBr. Anal. Calcd for C25H29Mo: C, 70.58; H,
6.87. Found: C, 70.42; H, 7.12. EPR (pentane, -80 °C):
multiplet with molybdenum satellites; g ) 2.013; aMo ) 33.2
G; aH ) 6.0 G (2H); aH ) 5.9 G (2H); aH ) 5.7 G (2H); aH ) 5.4
G (2H).
In a separate preparative experiment, a concentrated pen-
tane solution of the product 3 was set for crystallization at
room temperature without protection from light. Single crys-
tals of compound 4 which were suitable for an X-ray analysis
formed over 1 week.
F or m a tion of 3 by Liga n d Red istr ibu tion fr om 1 a n d
2a . A solution of 2a (78 mg, 0.31 mmol) in 10 mL of THF was
cannulated onto a suspension of 1 (90 mg, 0.31 mmol) in 40
mL of THF at room temperature. The mixture was then
protected from light and stirred for 3 weeks. Aliquots from
this mixture were withdrawn from time to time by cannula
directly into an electrochemical cell which already contained
THF and supporting electrolyte for a monitoring of the reaction
by cyclic voltammetry (see Results section).
Attem p t To Rea ct Com p ou n d 2a w ith Lew is Ba ses. (a )
With CO. Compound 2a (187 mg, 0.76 mmol) was dissolved
in THF (80 mL). An initial EPR spectrum was recorded. The
solution was introduced into a 0.5 L Parr autoclave and
pressurized with CO (600 psi). The solution was stirred at room
temperature overnight. An aliquot the solution was withdrawn
and exhibited no change in color and intensity of the EPR
spectrum. No v(CdO) could be observed by IR. The autoclave
was then depressurized to 400 psi and warmed to 65 °C for 1
h (the pressure increased again to ca. 600 psi). No change in
the properties of the solution was again observed.
(b) With P Me3. Compound 2a (166 mg, 0.66 mmol) was
dissolved in THF (20 mL). PMe3 (1 M in THF, 0.8 mL, 0.8
mmol) was added by syringe, and the resulting solution was
stirred at room temperature for 24 h. The EPR spectrum
showed no decrease in intensity relative to the initial solution.
(c) With P Et3. Compound 2a (90 mg, 0.36 mmol) was
dissolved in THF (10 mL). PEt3 (1 M in THF, 0.5 mL, 0.5
mmol) was added by syringe, and the resulting solution was
heated to reflux under stirring for 24 h. The EPR spectrum
showed no decrease in intensity relative to the initial solution.
Rea ction of Com p lex 2a w ith Br øn sted Acid s. (a ) With
HBF 4. In a NMR tube, a solution of 2a (46 mg, 0.19 mmol) in
0.5 mL of C6D6 was prepared. HBF4‚OEt2 (54%, 24 µL, 0.17
mmol) was then added via a microsyringe. A dark precipitate
immediately formed while gas evolution was noted. The 1H
NMR spectrum revealed the formation of CH4 (δ ) 0.15 ppm),
while an EPR spectrum of the surpernatant solution was
featureless.
Com p ou n d 2c: 45% yield from 5.5 mmol of 1 and 2.2 equiv
of (CH3)3SiCH2MgCl. The compound was obtained as dark
green needles by cooling a pentane solution at -80 °C for 48
h. Anal. Calcd for C17H33Si2Mo: C, 52.41; H, 8.54. Found: C,
52.17; H, 8.56. EPR (pentane, -80 °C): multiplet with Mo
satellites; g ) 2.009; aMo ) 34.3 G; aH ) 6.5 G (2H); aH ) 6.0
G (2H); aH ) 4.4 G (2H); aH ) 3.5 G (2H).
Com p ou n d 2′′c: 44% yield from 1.5 mmol of 1′′ and 2.2
equiv of (CH3)3SiCH2MgCl. The compound was obtained as
dark green needles by cooling a pentane solution at -80 °C
for 48 h. Anal. Calcd for C19H37Si2Mo: C, 54.65; H, 8.93.
Found: C, 55.05; H, 9.09. EPR (pentane, -80 °C) multiplet
with Mo satellites; g ) 2.010; aMo ) 33.6 G; aH ) 6.4 G (2H);
aH ) 5.9 G (2H); aH ) 4.5 G (2H); aH ) 3.4 G (2H).
Ar yla tion Rea ction s. Reactions between compounds 1 and
1′′ and PhLi, PhMgBr, or (C6H2Me3-2,4,6)MgBr were carried
out under conditions similar to those described above for the
alkylation reactions. The resulting solutions are extremely
sensitive, and attempts to recover pure solid materials from
these solutions failed. EPR (pentane, -80 °C): product of the
1-PhLi or PhMgBr reaction: apparent quintet with Mo
(b) With CF 3COOD. In a NMR tube, a solution of 2a (10
mg, 0.04 mmol) in 0.5 mL of C6D6 was prepared. An excess
(20 µL, 0.26 mmol) of CF3COOD was then added via a

3852 Organometallics, Vol. 19, No. 19, 2000
Ta ble 6. Cr ysta l a n d Str u ctu r e Refin em en t Da ta
Le Grognec et al.
2′′a
4
4′′
6
formula
M
T; K
diffractometer
cryst syst
space group
a; Å
C
13H21Mo
C18H22Cl2Mo2
501.14
293(2)
CAD4
moniclinic
P21/c
10.636(1)
7.635(1)
11.912(1)
111.454(6)
900.3(2)
2
C22H30Br1.54Cl0.46Mo2
625.76
110(2)
Kappa CCD
orthorhombic
Pbcm
8.7030(2)
19.5210(3)
12.4410(3)
C15H15F6MoO4
469.21
293(2)
CAD4
orthorhombic
Pbca
14.566(1)
14.717(1)
16.700(1)
273.24
293(2)
CAD4
monoclinic
P21/c
15.092(1)
7.458(1)
22.186(2)
91.248(8)
2496.6(4)
8
b; Å
c; Å
â; deg
V; Å3
2113.62(8)
4
3579.9(4)
8
Z
F(000)
D
1128
1.454
496
1.849
1230.88
1.966
1864
1.741
calc; g/cm3
λ; Å
0.71073
1.013
0.71073
1.683
0.71073
4.16
0.71073
0.809
µ; mm-1
cryst size; mm3
sin(θ)/λ max; Å-1
index ranges
0.32 × 0.30 × 0.25
0.36 × 0.28 × 0.25
0.17 × 0.15 × 0.12
0.50 × 0.35 × 0.20
0.63
0.62
0.807
0.62
h: -18; 18
k: 0; 9
l: 0; 27
h: -13; 12
k: 0; 9
l: 0; 14
h: -14; 13
k: -30; 31
l: -20; 19
-7
SCALEPACK
29 175
h: -18; 0
k: -18; 0
l: -20; 0
decay; %
abs corr
12.5
2
psi-scan 85.9%-100%
4687
4561 [R(int))0.027]
4053
psi-scan 90.5%-99.6%
1914
1821 [R(int))0.038]
1639
psi-scan 96.1%-99.2%
3964
3633 [R(int))0.014]
2727
RC ) reflns collec
IRC ) unique RC
IRCGT ) IRC and [I>2σ(I)]
refinement method
no. of data/restr/params
R for IRCGT
4810 [R(int))0.034]
4230
full-matrix least squares on F2
4561/0/285
1821/0/106
4810/0/1753
R1a ) 0.029,
wR2b ) 0.0641
R1a ) 0.0368,
wR2b ) 0.0671
1.079
632/0/237
R1a ) 0.028,
wR2b) 0.073
R1a ) 0.033,
wR2b ) 0.075
1.063
R1a ) 0.046,
wR2b ) 0.135
R1a ) 0.053,
wR2b ) 0.140
1.115
R1a ) 0.042,
wR2b ) 0.113
R1a ) 0.065,
wR2b ) 0.130
1.033
R for IRC
goodness-of-fitc
largest ∆F; e Å-3
0.331 and -0.532
1.551 and -0.921
1.495 and -1.143
0.789 and -0.549
a
b
R1)∑(|Fo| - |Fc|)/∑|Fo|. wR2 ) [∑w(Fo2- Fc2)2/∑[w(Fo2)2]1/2 where w ) 1/[σ2(Fo2) + (uP)2 + vP] where P ) (Max(Fo2,0) + 2Fc2)/3, for
c
2′′a , u ) 0.0418 and v ) 0.98; for 4, u ) 0.0872 and v ) 2.11; for 4′′, u ) 0.03, v ) 2.35; and for 6, u ) 0.0739 and v ) 3.82. Goodness
of fit ) [∑w(Fo - Fc2)2/(No - Nv)]1/2
.
2
microsyringe. The color immediately changed from dark green
to yellow-brown. The 1H NMR spectrum revealed the formation
of CH3D (t, δ ) 0.14 ppm, 2J HD ) 0.2 Hz). No other resonances
were noticed except for those of the solvent. The EPR spectrum
of this solution showed a broad singlet (g ) 1.985; aMo ) 41
G). Identical results were obtained upon reacting compound
2′′a with CF3COOD under the same conditions.
(c) With HCl in THF . In a Schlenk tube, a solution of 2a
(17 mg, 0.07 mmol) in 10 mL of THF was prepared. Through
this solution was bubbled via a Pasteur pipet an excess amount
of gaseous HCl (generated in situ in a separate Schlenk tube
by adding a 37% HCl solution to P4O10). An immediate color
change from green to brown was observed. Bubbling was
stopped and the solution was stirred at room temperature for
4 h under the HCl-containing atmosphere. The combined EPR
and cyclic voltammetric analysis of the final solution showed
the conversion to compound 1.
(d ) With Oth er Br øn sted Acid s. Various THF solutions
of compound 2a were treated with excess amounts of other
acids (H2O, MeOH, CH3COOH, H3PO4, H3O+, the latter
corresponding to a ca. 1 M aqueous HCl solution) as described
in the previous two sections. EPR spectroscopic monitoring
over 1 h revealed no new signals and a reduction of EPR
intensity of the initial signal by less than 10% in all cases.
Syn th esis of Cp Mo(η4-C6H10)(CH3)(OCOCF 3), 5. One
equivalent (34 µL, 0.44 mmol) of CF3COOD was slowly added
by microsyringe to a vigorously stirred solution of 2′′a (122
mg, 0.44 mmol) in 10 mL of toluene. The green color turned
immediately yellow-brown. This solution was stirred for one
additional hour, and the solvent was removed in vacuo. A dark
yellow powder was obtained. The compound was recrystallized
by cooling a saturated pentane solution to -80 °C. Yield: 147
mg, 90%. Anal. Calcd for C14H18O2F3Mo: C, 45.30; H, 4.89.
Found: C, 45.14; H, 5.02. IR (Nujol mull, cm-1): 1685 [s, br,
v(CO)], 1190 [s, v(CO)], 1138 [s, v(CO)]. EPR (toluene, room
temperature): apparent octet with Mo satellites, g ) 1.998;
aMo ) 40.6 G; aH ) 7.0 G (2H); aH ) 5.6 G (2H); aH ) 5.4 G
(3H).
Syn th esis of Cp Mo(η4-C6H10)(OCOCF 3)2, 6. To a green
solution of 2′′a (143 mg, 0.52 mmol) in toluene (20 mL) was
added CF3COOD (88 µL, 1.15 mmol) via a microsyringe. The
evolution of gas could be observed, while the solution im-
mediately turned yellow-brown and then slowly yellow. After
stirring for 8 h at room temperature, the solvent was removed
in vacuo to yield a dark yellow powder, which was washed with
pentane. Yield: 212 mg, 87%. Anal. Calcd for C15H15O4F6Mo:
C, 38.40; H, 3.22 Found: C, 38.66; H, 3.23. IR (Nujol mull,
cm-1): 1700 [s, br., v(CO)], 1192 [s, v(CO)], 1143 [s, v(CO)].
EPR (toluene, room temperature): apparent quintet with Mo
satellites, g ) 1.982; aMo ) 40.6 G; aH ) 7.7 G (2H); aH ) 5.8
G (2H). A single crystal for the X-ray analysis was obtained
by slow diffusion of pentane into a THF solution at room
temperature.
X-r a y Cr ysta llogr a p h y. Crystal data and refinement
figures for all compounds are reported in Table 6.
(a ) Com p ou n d 2′′a . A dark green crystal (0.32 × 0.30 ×
0.25 mm3) was placed in a flame-sealed capillary under Ar and
mounted on an Enraf-Nonius CAD4 diffractometer. A total of
4687 reflections (of which 4561 were unique) were collected
at room temperature up to sin(θ)/λ ) 0.63 Å-1. The data were
corrected for Lorentz and polarization effects and for absorp-
tion (psi-scan method).79,80 A 12.5% decay was linearly cor-
rected. The structure was solved via a Patterson search
(79) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, A24, 351-359.
(80) Spek, A. L. Acta Crystallogr., Sect. A: Found. Crystallogr. 1990,
46, C34.

Dialkyl(butadiene)cyclopentadienylmolybdenum(III)
Organometallics, Vol. 19, No. 19, 2000 3853
program81 and refined (space group P21/c) with full-matrix
least-squares methods81 based on |F2|. All non-hydrogen atoms
were refined with anisotropic thermal parameters. Hydrogen
atoms of the cyclopentadienyl anion were included in their
calculated positions and refined with a riding model. The
methyl hydrogen atoms were located in the Fourier difference
map and refined, after idealization, as rigid rotating groups.
The hydrogen atoms attached to the butadiene ligand were
located in the Fourier difference map and were refined freely.
At the end of this refinement the agreement indices were wR2
) 0.0747 for all data and R1 ) 0.0276 for 4053 intensities with
I > 2σ(I). The final difference electron density is featureless:
with anisotropic thermal parameters. Hydrogen atoms of the
cyclopentadienyl anion were included in their calculated
positions and refined with a riding model. The methyl hydro-
gen atoms were located in the Fourier difference map and
refined, after idealization, as rigid rotating groups. The
hydrogen atoms attached to the butadiene ligand were located
in the Fourier difference map and were refined freely. At the
end of the refinement the thermal ellipsoids of the fluorine
atoms were quite large and indicated either a disorder on the
fluorine atom positions or very pronounced thermal librations.
Any attempt to impose a disorder model lowered the agree-
ment indices but did not lead to reasonable structural param-
eters. The final agreement indices were wR2 ) 0.113 for all
data and R1 ) 0.042 for 2727 intensities with I > 2σ(I). The
final difference electron density is featureless: ∆F ) 0.79 and
-0.55 e Å-3. Crystal data are reported in Table 6.
Com p u ta tion a l Deta ils. All electronic structure and ge-
ometry optimization calculations were performed using GAUSS-
IAN 9483 on an SGI Origin 200 workstation. The LanL2DZ
set was employed to perform geometry optimizations with a
density functional theory (DFT) approach. The B3LYP func-
tional (B3LYP ) the three-parameter form of the Becke, Lee,
Yang, and Parr functional)84 was employed. The LanL2DZ
basis set includes both Dunning and Hay’s D95 sets for H and
C85 and the relativistic core potential sets of Hay and Wadt
for the heavy atoms.86-88 Electrons outside the core were all
those for H and C, the 4s, 4p, 4d, and 5s electrons for Mo, and
the 3s and 3p electrons for Cl. The mean value of the first-
order electronic wave function, which is not an exact eigenstate
of S2 for unrestricted calculations on the triplet systems, was
considered suitable for the unambiguous identification of the
spin state. Spin contamination was carefully monitored, and
the value of S2 for the UB3LYP (UB3LYP ) unrestricted
B3LYP) calculations on the doublet CpMo(η4-C4H6)XY systems
at convergence (XY ) Cl2, 0.7655; ClMe, 0.7644; Me2, 0.7636)
indicated minor spin contamination.
∆F ) 0.33 and -0.53 e Å-3
.
(b) Com p ou n d 4. A brown crystal (0.36 × 0.28 × 0.25 mm3)
was mounted on an Enraf-Nonius CAD4 diffractometer. A total
of 1920 reflections (1827 unique) were collected up to sin(θ)/λ
) 0.62 Å-1. The data were corrected for Lorentz and polariza-
tion effects and for absorption (psi-scan method).79,80 The
structure was solved via a Patterson search program81 and
refined (space group P21/c) with full-matrix least-squares
methods based on |F2|. All non-hydrogen atoms were refined
with anisotropic thermal parameters. The cyclopentadienyl
ring was refined as a variable metric group. Except for the
CH2 hydrogen atoms of the butadiene ligand, which were
located on the difference Fourier map, all the hydrogen atoms
were included in their calculated positions. All H atoms were
refined with a riding model. The final agreement indices were
wR2 ) 0.140 for all data and R1 ) 0.046 for 1639 intensities
with I > 2σ(I). Final difference electron density: ∆F ) 1.0 and
-0.59 e Å-3
.
(c) Com p ou n d 4′′. A green crystal (0.17 × 0.15 × 0.12 mm3)
suitable for an X-ray analysis was mounted on an Enraf-
Nonius KappaCCD using Mo KR radiation, and 29 175 reflec-
tions (4810 unique) were collected up to sin(θ)/λ ) 0.807 at
110 K. Absorption correction was applied to the data during
integration by the SCALEPACK82 algorithm. The structure
was solved via a Patterson search program81 and refined (space
group Pbcm) with full-matrix least-squares methods based on
|F2|. Except for the chlorine atom, all non-hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms
were found by Fourier difference synthesis and freely refined
with isotropic temperature factors fixed to 1.3 times those of
the corresponding carbon atoms. The halide atom position was
found to be compositionally disordered. Two positions were
independently refined as Br and Cl with no constraints except
that the sof's were imposed as x and (1 - x), respectively, with
x refining to 0.77. The Cl atom was isotropically refined. The
Mo-X distances are consistent with a Mo-(µ-Br) and a Mo-
(µ-Cl). The final agreement indices were wR2 ) 0.0641 for all
data and R1 ) 0.0368 for 4230 intensities with I > 2σ(I). Final
Ack n ow led gm en t. This work was supported by the
Conseil Re´gional de Bourgogne and by the CNRS (Pro-
gramme Catalyse pour l’Industrie et l’Environnement).
E.L.G. thanks the MENRT for a doctoral fellowship.
Su p p or tin g In for m a tion Ava ila ble: A listing of posi-
tional coordinates, bond distances and angles, anisotropic
displacement parameters, and calculated H atom positions for
compounds 2′′a , 4, 4′′, and 6. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM000329T
difference electron density: ∆F ) 1.49 and -1.14 e Å-3
.
(d ) Com p ou n d 6. A dichroic green-yellow crystal (0.50 ×
0.35 × 0.20 mm3) was placed in a flame-sealed capillary under
Ar and mounted on an Enraf-Nonius CAD4 diffractometer. A
total of 3964 reflections (3633 unique) were collected at room
temperature up to sin(θ)/λ ) 0.62 Å-1. The data were corrected
for Lorentz and polarization effects and for absorption (psi-
scan method).79,80 A 7% decay was linearly corrected. The
structure was solved via a Patterson search program3 and
refined (space group Pbca) with full-matrix least-squares
methods81 based on |F2|. All non-hydrogen atoms were refined
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(89) J ohnson, C. K. ORTEP, Report ORNL-5138; Oak Ridge National
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(81) Sheldrick, G. M. SHELXS and SHELXL97; University of
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