Synthesis, Nujol matrix and solution photochemistry of M(CO)2[η5,η3-C5H 4-C(CH3)2-C5H6] (where M=Cr or Mo): Molecular structures

Article abstract of DOI:10.1016/S0022-328X(99)00118-7

Reaction of chromium or molybdenum carbonyl with 2,2-bis(cyclopentadienyl)propane yields mixtures of products including M₂(CO)₆[η⁵,η⁵-C ₅H₄-C(CH₃)₂-C₅H ₄], M₂(CO)₆[η⁵-C₅H ₄-C(CH₃)₂-C₅H₄] ₂, and the title compounds, M(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆], in which an η³-pentenyl group is tethered to the η⁵-cyclopentadienyl (Cp) group by a 2,2-propyl linkage. Although several isomers are possible for the cyclopentenyl groups, chromium and molybdenum appear to form only single, but unique isomers. Photolysis of M(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆], M=Cr or Mo, in Nujol glass at ca. 77 K has been found to be wavelength-dependent with low energy photolyses resulting in η³→η¹ transformations while higher energy photolyses result in loss of carbon monoxide. Solution photolysis of the molybdenum derivative with triphenylphosphine yields as a first product Mo(CO)₂[P(C₆H₅)₃][η ⁵,η¹-C₅H₄-C(CH₃) ₂-C₅H₆], which undergoes decomposition upon work-up to yield both starting material, and Mo(CO)[P(C₆H₅)₃][η⁵,η ³-C₅H₄-C(CH₃)₂-C ₅H₆]. The molecular structures of three compounds have been determined: Mo(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆]: monoclinic, P2₁/c, a=8.2767(4), b=19.875(1), c=7.960(1) A, β=96.720(6)°, V=1300.4(1) A³, Z=4, R(F)=2.82; Cr(CO)₂[η⁵,η³-C₅H ₄-C(CH₃)₂-C₅H₆]: monoclinic, P2₁/c, a=9.960(1), b=9.1015(6), c=13.997(1) A, β=92.460(9)°, V=1267.7(2) A³, Z=4, R(F)=4.67; Mo(CO)[P(C₆H₅)₃][η⁵,η ³-C₅H₄-C(CH₃)₂-C ₅H₆]: monoclinic, P2₁/c, a=7.939(1), b=22.381(3), c=15.050(2) A, β=103.55(1)°, V=2599.8(5) A³, Z=4, R(F)=4.01.

Full text of DOI:10.1016/S0022-328X(99)00118-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 583 (1999) 152–161
Synthesis, Nujol matrix and solution photochemistry of
M(CO)2[h5,h3-C5H4–C(CH3)2–C5H6] (where M=Cr or Mo):
molecular structures of Cr(CO)2[h5,h3-C5H4–C(CH3)2–C5H6],
Mo(CO)2[h5,h3-C5H4–C(CH3)2–C5H6], and
Mo(CO)[P(C6H5)3][h5,h3-C5H4–C(CH3)2–C5H6]ꢀ
Thomas E. Bitterwolf a,*, Abdelhimed A. Saygh a, J. Timothy Bays a,
Callie Ann Weiss a, W. Bruce Scallorn a, Joyce E. Shade b, Arnold L. Rheingold c,
Louise Liable-Sands c
a Department of Chemistry, Uni6ersity of Idaho, Moscow, ID 83844-2343, USA
b Department of Chemistry, US Na6al Academy, Annapolis, MD 21404, USA
c Department of Chemistry, Uni6ersity of Delaware, Newark, DE 19716, USA
Received in revised form 4 February 1999
Abstract
Reaction of chromium or molybdenum carbonyl with 2,2-bis(cyclopentadienyl)propane yields mixtures of products including
M2(CO)6[h5,h5-C5H4–C(CH3)2–C5H4], M2(CO)6[h5-C5H4–C(CH3)2–C5H4]2, and the title compounds, M(CO)2[h5,h3-C5H4–
C(CH3)2–C5H6], in which an h3-pentenyl group is tethered to the h5-cyclopentadienyl (Cp) group by a 2,2-propyl linkage.
Although several isomers are possible for the cyclopentenyl groups, chromium and molybdenum appear to form only single, but
unique isomers. Photolysis of M(CO)2[h5,h3-C5H4–C(CH3)2–C5H6], M=Cr or Mo, in Nujol glass at ca. 77 K has been found
to be wavelength-dependent with low energy photolyses resulting in h3“h1 transformations while higher energy photolyses result
in loss of carbon monoxide. Solution photolysis of the molybdenum derivative with triphenylphosphine yields as a first product
Mo(CO)2[P(C6H5)3][h5,h1-C5H4–C(CH3)2–C5H6], which undergoes decomposition upon work-up to yield both starting material,
and Mo(CO)[P(C6H5)3][h5,h3-C5H4–C(CH3)2–C5H6]. The molecular structures of three compounds have been determined:
5
3
,
Mo(CO)2[h ,h -C5H4–C(CH3)2–C5H6]: monoclinic, P21/c, a=8.2767(4), b=19.875(1), c=7.960(1) A, i=96.720(6)°, V=
3
5
3
,
1300.4(1) A , Z=4, R(F)=2.82; Cr(CO)2[h ,h -C5H4–C(CH3)2–C5H6]: monoclinic, P21/c, a=9.960(1), b=9.1015(6), c=
3
5
3
,
,
13.997(1) A, i=92.460(9)°, V=1267.7(2) A , Z=4, R(F)=4.67; Mo(CO)[P(C6H5)3][h ,h -C5H4–C(CH3)2–C5H6]: monoclinic,
3
,
,
P21/c, a=7.939(1), b=22.381(3), c=15.050(2) A, i=103.55(1)°, V=2599.8(5) A , Z=4, R(F)=4.01. © 1999 Published by
Elsevier Science S.A. All rights reserved.
Keywords: Organometallic photochemistry; Matrix photochemistry; Chromium allyl; Molybdenum allyl; Haptotropic rearrangement
We have recently reported the synthesis of
Ru(CO)2(h5,h1-C5H4–CR2–C5H5) [1] and have found
it to be a versatile reagent for the synthesis of hetero-
bimetallic compounds of ruthenium with the Group VI
metals, iron, nickel, manganese, and rhodium [2].
ꢀ Dedicated to our dear friend and colleague, Professor Alberto
Ceccon, on the occasion of his 65th birthday.
* Corresponding author. Tel.: +1-208-8856552; fax: +1-208-
8856173.
E-mail address: bitterte@uidaho.edu (T.E. Bitterwolf)
Green [3] has reported the synthesis of ZrCl(h5-
C5H5)[h5,h2-C5H4C(CH3)2C9H6] which has been shown
to react with ClM(CO)n, where M=Mn (n=5) and Rh
(n=2) to yield heterobimetallic compounds. In these
0022-328X/99/$ - see front matter © 1999 Published by Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00118-7

T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
153
cases a Cp or indenyl ring is loosely bound in the
monometallic compound making it available for reac-
tion with a second metal. Building upon this idea we
sought to prepare M(CO)3(h5,h1-C5H4–CR2–C5H5),
where M is a Group VI metal and R=H or CH3.
While these target molecules remain elusive, we have
isolated chromium and molybdenum derivatives of the
form M(CO)2(h5,h3-C5H4–CR2–C5H6) in which one
diene has been reduced to a trihapto allyl. In this paper
we describe the synthesis, characterization, and molecu-
lar structures of these new compounds, and examine
their photochemistry both in solution and in Nujol
matrices at ca. 77 K.
in a color change from red to yellow–orange. The IR
spectrum of the isolated material showed two terminal
carbonyl bands at 2052 and 1972 cm−1 virtually identi-
cal to those of (h5-C5H5)Mo(CO)3Cl. The 1H-NMR
spectrum contained resonances for a metal bound Cp
ring and a complex set of resonances consistent with an
unbound cyclopentadiene ring. Unfortunately it was
not possible to separate the isomers of this mixture
even through the use of medium pressure chromatogra-
phy on silica gel.
The available evidence suggests that a mixture of
isomers of Mo2(CO)6[h5-C5H4–C(CH3)2–C5H5] are
formed in the initial reaction. We are currently explor-
ing the possibility of deprotonating the cyclopentadiene
ring of these compounds or their methyl and chloride
derivatives to permit a second metal to be introduced.
The yellow solid I, was found to have two IR bands
in the terminal carbonyl region at 1956 and 1879 cm−1
(CH2Cl2) and 1967 and 1898 cm−1 (Nujol) in the
carbonyl stretching region. (h5-C5H5)Mo(CO)2(h3-
C5H7) has been reported to have carbonyl stretching
1. Results and discussion
1.1. Synthesis of M(CO)3(p5,p3-C5H4–CR2–C5H6)
By analogy with the previously reported synthesis of
Ru(CO)2(h5,h1-C5H4–CR2–C5H5) [1], Br2Mo(CO)4
was reacted with one equivalent of C(CH3)2(C5H4Na)2
in THF. Work-up of the reaction followed by chro-
matography yielded only the previously reported
Mo2(CO)6[h5,h5-C5H4–C(CH3)2–C5H4] [4] and [Mo-
(CO)3Br]2[h5,h5-C5H4–C(CH3)2–C5H4]. Repeating this
reaction with C(CH3)2(C5H4Tl)2 yielded similar results.
Reaction of the neutral ligand 2,2-bis(Cp)propane
(mixture of isomers) with Mo(CO)6 or Mo(CO)3-
(CH3CN)3 in refluxing xylene followed by work up and
chromatography yielded three bands, a clear yellow
band that gave a yellow crystalline solid I, a broad red
band that was shown by HPLC to consist of a number
of components, and Mo2(CO)6[h5,h5-C5H4–C(CH3)2–
C5H4].
1
bands at 1950 and 1880 cm−1 in alkanes [5]. H- and
13C-NMR spectra were consistent with the formulation
of the compound as Mo(CO)2[h5,h3-C5H4–C(CH3)2–
C5H6] in which the pendant cyclopentenyl group is
asymmetrically bound to the metal. 2-D COSY,
NOESY and H–C correlation spectra permitted assign-
ment of all resonances except for the ipso-carbons. The
numbering diagram for resonance assignments in I is
presented in Fig. 1.
The molecular structure of I was determined from
crystals grown by vapor diffusion methods and the
resultant structure is presented in Fig. 2. Crystallo-
graphic data are summarized in Table 1, while bond
length and bond angle data for I are presented in Table
2. All bond lengths and angles are within normal ranges
and there does not appear to be any significant strain
within the ring formed by the metal, h5-Cp and h3-cy-
clopentenyl groups. The bridge atom, C(11) is drawn
about 7.9° below the plane of the Cp ring.
The mixture of components making up the broad red
band had an IR spectrum consistent with the presence
1
of (C5H4R)2Mo2(CO)6 units. H- and 13C-NMR spectra
of this mixture were complex, but clearly indicated
C5H4R units and cyclopentadiene or cyclopentene
rings. No parent mass was observed in MS, but those
fragments observed were consistent with the proposed
formulation.
Reaction of the red mixture with K-Selectride yielded
a solution in which the (C5H4R)Mo(CO)3 anion was
identified by IR bands at 1895, 1790, 1746, and 1700
cm−1. Subsequent reaction of this anion mixture with
methyl iodide yielded a mixture whose IR bands at
2012 and 1924 cm−1 were consistent with the expected
(C5H4R)Mo(CO)3CH3 species, but whose NMR was
uninterpretable beyond the presence of a substituted
metal bound Cp group and a metal bound methyl
group.
Fig. 1. NMR numbering scheme for I, L=CO, and III, L=
Photolysis of the red mixture in chloroform resulted
P(C6H5)3.

154
T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
that the molecule have approximate Cs symmetry and
2-D spectra permitted most resonances to be assigned.
Neither the ipso-carbon, C-1, nor the allyl carbon, C-7,
could be assigned with confidence. The numbering
scheme for this molecule is presented in Fig. 3. It is
interesting to note that there is no spectral or chro-
matographic evidence of other isomers of II, thus the
reactions of molybdenum and chromium yield isomeri-
cally pure, but different products.
Crystals of II were grown by vapor diffusion and the
molecular structure was determined (see Fig. 4). As
anticipated, the molecule exhibits approximate Cs sym-
metry in which the allyl group is centered on the carbon
connecting the cyclopentenyl ring to the bridge. Bond
lengths and angles for II are presented in Table 3.
Although most bond lengths and angles in this
molecule are within normal ranges, the bond angle of
the bridge carbon, C(11)–C(6)–C(5) is compressed to
97.0(3)° compared to an angle of 108.0(4)° for the
comparable angle in I, indicating considerable strain at
this position in II. Additionally, C(6) is drawn about
23.2° below the plane of the Cp ring in order to
accommodate the bonding of the cyclopentenyl ring.
Strain is further reflected in the distortion of the cy-
clopentenyl ring, C(7)–C(11), from planarity by bend-
ing C(8) and C(9) away from the metal. The torsional
angle about the C(8)–C(9) bond is 1.3°. C(6) is folded
about 34.4° from the plane formed by C(7)–C(10).
Repeated attempts to prepare the tungsten analog of
I and II using both W(CO)6 and W(CO)3(CH3CN)3
were unsuccessful.
Fig. 2. Molecular structure of I.
Reaction of 2,2-bis(Cp)propane with Cr(CO)6 in
refluxing 10:1 butyl ether:THF for 48 h yielded, after
work-up and chromatography, a single yellow band
from which II was recovered as a crystalline solid. IR
spectra of the reaction mixture after 24 h provided
spectral evidence for the presence of (h5-
C5H4R)Cr(CO)3H species. Compound II was found to
have a pair of IR bands at 1929 and 1856 cm−1
(CH2Cl2) or 1940 and 1876 cm−1 (Nujol) in the termi-
nal
carbonyl
region.
The
compound
(h5-
C5H5)Cr(CO)2(h3-C5H7) is reported to have IR
stretching bands at 1942 and 1880 cm−1 in alkane
solvents [5]. The H- and 13C-NMR spectra required
1
Table 1
Crystallographic data for Mo(CO)2[h5,h3-C5H4–C(CH3)2–C5H6] (I) Cr(CO)2[h5,h3-C5H4–C(CH3)2–C5H6] (II) and Mo(CO)[P(C6H5)3][h5,h3-
C5H4–C(CH3)2–C5H6] (III)
I
II
III
Empirical formula
Formula weight
Crystal system
Space group
C15H16MoO2
324.22
Monoclinic
P21/c
C15H16CrO2
280.28
Monoclinic
P21/c
C32H31MoOP
558.48
Monoclinic
P21/c
,
a (A)
8.2767(4)
19.875(1)
7.960(1)
90
96.720(6)
90
9.960(1)
9.1015(6)
13.997(1)
90
92.460(9)
90
7.939(1)
22.381(3)
15.050(2)
90
103.55(1)
90
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
1300.4(1)
4
1267.7(2)
4
2599.8(5)
4
Z
Crystal color
Yellow block
1.656
9.99
298(2)
Mo–Ka (u=0.71073 A)
Yellow block
1.469
8.92
298(2)
Mo–Ka (u=0.71073 A)
Yellow block
1.427
5.89
298(2)
Mo–Ka (u=0.71073 A)
Dcalc. (g cm−3
)
v(Mo–Ka) (cm−1
Temperature (K)
Radiation
)
,
,
,
R(F) a (%)
2.82
6.97
4.67
13.08
4.01
7.29
R(wF2) a (%)
a Quantity minimized =R(wF2)=S[w(Fo2−Fc2)2]/S[(wF2o)2]0.5; R=SD/S(Fo), D=ꢀ(Fo−Fc)ꢀ.

T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
155
Table 2
5
3
,
Bond lengths (A) and bond angles (°) for Mo(CO)2[h ,h -C5H4–
C(CH3)2–C5H6] (I) and Mo(CO)[P(C6H5)3][h5,h3-C5H4–C(CH3)2–
C5H6] (III)
Atoms
I
Atoms
III
Bond lengths
C1–C2
C2–C3
C3–C4
C4–C5
1.410(6)
1.391(7)
1.405(6)
1.425(5)
1.412(5)
1.536(6)
1.534(5)
1.562(6)
1.493(6)
1.408(6)
1.399(6)
1.543(6)
2.324(4)
2.257(4)
2.290(4)
1.966(5)
1.990(5)
1.154(5)
1.153(5)
C11–C12
C12–C13
C13–C14
C14–C15
C11–C15
C15–C16
C5–C16
C1–C5
C1–C2
C2–C3
C3–C4
C4–C5
1.407(7)
1.402(8)
1.424(8)
1.424(7)
1.427(7)
1.516(7)
1.543(7)
1.546(7)
1.511(7)
1.410(7)
1.400(7)
1.532(7)
2.307(5)
2.236(5)
2.256(5)
C1–C5
C5–C11
C11–C10
C9–C10
C8–C9
C7–C8
C6–C7
C6–C10
Mo–C8
Mo–C7
Mo–C6
Mo–C12
Mo–C13
C12–O12
C13–O13
Mo–C2
Mo–C3
Mo–C4
Fig. 4. Molecular structure of II.
H2 to give M2(CO)6[h5,h5-C5H4–C(CH3)2–C5H4]. Re-
action of two molecules of M(CO)3H[h5,h5-C5H4–
C(CH3)2–C5H4] resulting in loss of H2 yields
M2(CO)6[h5-C5H4–C(CH3)2–C5H5]2, while a combina-
tion of hydride transfer and loss of CO results in the
formation of I and II. Wrighton has reported the
formation of (h5-C5H5)(h3-C5H7)M(CO)2, where M=
Cr and Mo, by photolysis of the respective metal
carbonyl with an excess of cyclopentadiene [5]. A metal
hydride was assumed to be an intermediate in this
process. The mechanism of the hydride transfer to the
cyclopentadiene ring in the formation of compounds I
and II is not known at this time and may involve
radical intermediates. It is interesting to note that al-
though several isomers of I and II are possible, we have
found no spectral or chromatographic evidence to sug-
Mo–C51
1.926(6)
C51–O51
Mo–P
1.172(6)
2.467(2)
Bond angles
C5–C11–C10
C10–C9–C8
C9–C8–C7
106.8(3)
104.7(4)
198.3(4)
105.7(4)
111.1(4)
100.5(3)
83.2(2)
C
15–C16–C5
105.8(4)
C5–C1–C2
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C1
104.2(4)
108.0(5)
105.6(5)
110.8(4)
101.7(4)
82.6(2)
C8–C7–C6
C7–C6–C10
C6–C9–C10
C12–Mo–C13
C8–Mo–C13
C6–Mo–C12
C
51–Mo–P
77.1(2)
88.8(2)
C2–Mo–P
C4–Mo–C51
80.77(14)
88.4(2)
It is likely that all compounds isolated from the
reaction of 2,2-bis(Cp)propane and chromium and
molybdenum carbonyls proceed through the intermedi-
acy of a set of isomers of the form M(CO)3H[h5-C5H4–
C(CH3)2–C5H5] as illustrated in Scheme 1. Reaction
with a second molecule of molybdenum carbonyl yields
[M(CO)3H]2[h5,h5-C5H4–C(CH3)2–C5H4] which loses
Table 3
5
3
,
Bond lengths (A) and bond angles (°) for Cr(CO)2[h ,h -C5H4–
C(CH3)2–C5H6] (II)
Atoms
II
Atoms
II
Bond lengths
C1–C2
C2–C3
C3–C4
C4–C5
C1–C5
C5–C6
C6–C11
C7–C11
C7–C8
1.422(6)
1.395(7)
1.404(6)
1.433(6)
1.417(6)
1.523(6)
1.520(6)
1.434(5)
1.513(6)
1.534(7)
C9–C10
C10–C11
Cr–C7
Cr–C10
Cr–C11
Cr–C12
Cr–C13
C12–O12
C13–O13
1.522(6)
1.422(6)
2.259(4)
2.238(4)
2.104(4)
1.826(5)
1.821(5)
1.156(5)
1.155(5)
C8–C9
Bond angles
C5–C6–C11
C11–C7–C8
C7–C8–C9
C8–C9–C10
C9–C10–C11
97.0(3)
108.8(4)
104.4(3)
103.1(3)
109.2(4)
C7–C11–C10
C7–Cr–C12
C10–Cr–C13
C12–Cr–C13
104.3(3)
75.1(2)
74.4(2)
84.3(2)
Fig. 3. NMR numbering scheme for II.

156
T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
Scheme 1.
gest that any other isomers are formed in these reac-
tions. The stereospecificity of these reactions may arise
from optimization of the stability of the final species.
growth of bands at 2132 (‘free’ CO), 1954, 1940, 1917,
1871, and 1608 cm−1. The band at 1608 cm−1 was
detected only in concentrated solutions. Continued
photolysis at 350BuB370 nm resulted in further de-
creases in bands of I, and decreases in the band at 1940
cm−1. Annealing this sample to 133 K (Fig. 5(d))
resulted in bands for ‘free’ CO and those at 1954 and
1871 cm−1 to decrease while bands of I and new bands
at 2024, 2017, and 1928 cm−1 appeared. In concen-
trated samples a band at 1603 cm−1 was also found to
grow in.
It appears that at least three photoproducts are gen-
erated during the photolysis of I and at least two new
species form upon annealing of the photoproducts.
Scheme 2 summarizes these observations and our anal-
ysis of the photochemical and thermal processes. Pho-
tolysis in the visible spectrum at 500970 nm results in
the formation of species IA with carbonyl bands at
1940 and 1874 cm−1 with no apparent loss of CO.
Opening of the h3-allyl ligand to an h1-allyl is the most
probable low energy process. The asymmetric substitu-
tion of the cyclopentenyl ring creates two unique hinge
points, C(6) and C(8), for the h1-allyl opening, al-
though an opening at C(6) would appear to yield the
least sterically hindered intermediate. An intermediate
opening at C(6) would also most easily account for the
1.2. Nujol matrix photochemistry of M(CO)3(p5,p3-
C5H4–CR2–C5H6), where M=Cr or Mo
Apparatus and procedures for Nujol matrix photo-
chemistry have been previously described [6].
The electronic spectrum of I isolated in Nujol at ca.
77 K showed a strong absorption at 355 and a weaker
feature at 420 nm. Photolysis at 500970 nm bleached
the band at 355 nm, while a new band appeared at ca.
310 nm. Subsequent photolysis at 350BuB370 nm
resulted in the formation of a new band at 340 nm.
The IR spectrum of I in a Nujol solution at ca. 77 K
(Fig. 5(a)) has bands at 1967 and 1898 cm−1 similar in
position to those of other compounds in the (h5-
C5H5)Mo(CO)2(h3-allyl) series. Photolysis at 500970
nm resulted in the growth of two new bands at 1940
and 1874 cm−1 and a decrease in the bands of I. It
should be noted that no bands for ‘free’ CO could be
observed in the spectrum of this sample. Annealing the
sample to 133 K resulted in a simple reversal of the
photolysis reaction. Photolysis of a second sample at
500970 nm as above, followed by an additional pho-
tolysis at 350BuB370 nm (Fig. 5(c)) resulted in the

T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
157
only arise when ‘free’ CO is present in the matrix, and
are very similar in position to those of (h5-
C5H5)Mo(CO)3CH3 in frozen Nujol (2023 and 1935
cm−1). We propose that the two sets of bands arise
from a pair of Mo(CO)3[h5,h1-C5H4–C(CH3)2–C5H5]
species, ID and IE, resulting from capture of CO by
either IA or IB.
conformation of the triphenylphosphine derivative, III,
to be described below.
Photolysis at 350BuB370 nm results in the appear-
ance of a new band at 1954 cm−1 and equivalent
growth of the band at 1871 cm−1 (which overlaps with
the lower energy band of the 1940 and 1874 cm−1
pair). We propose that these bands arise from the
second h1-allyl species IB, with a hinge opening at the
C(8) carbon.
The electronic spectrum for II isolated in a Nujol
matrix at ca. 77 K showed two weak absorption bands
at 340 and 430 nm in addition to the continuum cutoff
at about 280 nm. The IR spectrum of II in a Nujol
matrix at ca. 77 K (Fig. 6(a)) consists of two carbonyl
The unique band at 1917 cm−1 is assigned to the
carbonyl-loss species, IC, which forms only at high
energy. We cannot distinguish between a simple car-
bonyl-loss species and one in which a concurrent hy-
dride shift might form Mo(CO)H[h5,h4-C5H4–C-
(CH3)2–C5H5], although the fact that this species does
not appear to reverse upon annealing argues for the
formation of a stable, 18-electron species.
Annealing the photolyzed sample to 173 K results in
the decrease in bands associated with IA and IB, and
the growth of new bands at 2024, 2017, and 1928 cm−1
as well as those of starting material. These new bands
stretching bands at 1940 and 1876 cm−1
.
Irradiation of II in the Nujol matrix at low energies,
470BuB640 nm, corresponding to the bottom edge of
the 430 nm absorption feature resulted in a small
decrease in the bands of the starting material and
growth of two new bands at 1941 and 1878 cm−1
.
Annealing this sample to ca. 133 K resulted in complete
reversal with no new products being formed. Sequential
photolysis of a sample at 470BuB640 nm followed by
photolysis at 340BuB420 nm resulted in additional
growth of the bands at 1941 and 1878 cm−1 and the
appearance of small bands at 2132 and 1917 cm−1 (Fig.
6(b)). High energy photolysis, 260BuB420 nm, of a
second sample containing both II and the low energy
photoproduct resulted in a decrease of bands of both
sets of bands and growth of new bands at 2132, 1957,
1917, and 1883 cm−1 (Fig. 6(b)). The band at 2132
cm−1 is associated with ‘free’ carbon monoxide in the
matrix. In all experiments the band at 1917 cm−1 was
substantially more intense than those at 1957 and 1883
cm−1. Annealing these samples to ca. 133 K resulted in
only the first photoproduct reforming II.
The results of the several photochemical experiments
on II and our proposed assignments of the resultant
species are summarized in Scheme 3. Photolysis into the
two low lying absorption bands of II results in an
opening of the h3-allyl to an h1-allyl species, IIA,
similar to the transformation observed for I. Higher
energy photolysis gives rise to CO-loss to give the
species with a band at 1917 cm−1, IIB, that does not
reverse upon annealing, suggesting that CO-loss is ac-
companied by a hydride shift to the metal from the
cyclopentenyl ring to form an h4-cyclopentadiene ring
analogous to that proposed for I. IIC appears to be a
minor product forming simultaneously with IIB, and
may be a carbene/hydride arising from rearrangement
of the h1-allyl.
Fig. 5. IR spectra of Mo(CO)2[h5,h3-C5H4–C(CH3)2–C5H6] (I). (a)
Starting material. (b) Subtraction spectrum, 120 min irradiation
u=500970 nm minus (a). (c) Subtraction spectrum, 30 min irradia-
tion at 350BuB370 nm minus (a). (d) Subtraction spectrum, anneal
to 173 K minus 120 min photolysis at 350BuB370 nm. * This band
arises from a natural abundance of 13CO.
1.3. Solution photochemistry of
Mo(CO)2[p5,p3-C5H4–C(CH3)2–C5H6]
The observation of h1-allyl species in the matrix
photolysis of I, and their subsequent capture of CO to

158
T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
Scheme 2.
form a product assigned as Mo(CO)3[h5,h1-C5H4–
C(CH3)2–C5H6], suggested that it might be possible to
generate these photointermediates in solution and cap-
ture them with a phosphine ligand. The photolysis of I
in benzene solution with triphenylphosphine was fol-
lowed by IR. During the photolysis the bands due to
the starting material (1957 and 1876 cm−1) decreased
over a 50 min period while new bands at 1933 and 1852
cm−1 grew in. Bands at 1947 and 1871 cm−1 have been
reported for CH3Mo(CO)2(PPh3)(h5-C5H5) in cyclohex-
ane and indicated that the expected Mo(CO)2-
(PPh3)[h5,h1-C5H4–C(CH3)2–C5H6] product had been
formed [7]. Toward the end of the photolysis period a
low energy shoulder emerged at 1830 cm−1. After
removal of benzene by rotary evaporation from a warm
water bath, chromatographic purification of the reac-
tion mixture recovered starting material and a single
product, III, whose IR band at 1829 cm−1 suggested
that it was the material produced toward the end of the
photolysis. None of the initially formed phosphine ad-
dition product was isolated. Repeating the experiment
with HPLC monitoring confirmed that the major pho-
tolysis product disappeared during work-up with for-
mation of starting material and III.
1H- and 13C-NMR spectra of III confirmed the pres-
ence of a triphenylphosphine ligand as well as a single,
metal-bound carbonyl group. The proton and carbon
resonances of the Cp/allyl ligand were almost identical
in position and pattern to those of I requiring that III
be assigned the formula Mo(CO)(PPh3)[h5,h3-C5H4–
C(CH3)2–C5H6]. The numbering scheme for proton and
carbon resonances is identical to that for I.
Crystals grown by vapor diffusion were used to
determine the molecular structure of III, shown in Fig.

T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
159
We have carried out the analogous photolysis of
Mo(CO)2(h5-C5H5)(h3-C3H5) in the presence of
triphenylphosphine under similar conditions to those
described above and found no evidence for formation
of a phosphine containing product. This is consistent
with observations to be reported separately that
Mo(CO)2(h5-C5H5)(h1-C3H5) is only rarely observed
even at 77 K in a Nujol matrix. We believe that the
thermal relaxation h1“h3 is fast under solution condi-
tions precluding simple substitution by a ligand such as
triphenylphosphine.
7. Bond length and bond angle data are presented in
Table 2. As anticipated, the structure of III retains the
ring geometries of I with the triphenylphosphine group
adding to the metal on the side opposite to the allyl.
Introduction of a triphenylphosphine ligand into the
coordination sphere of the molybdenum has remark-
ably little effect on the geometry of the metal–Cp–cy-
clopentenyl unit. The reduced p-acid character of the
phosphine relative to CO is reflected in a slight reduc-
,
tion (ca. 0.02 A) of the Mo–C bond lengths for the
allyl unit, and a shortening of the Mo–CO bond length
(1.990(5) in I and 1.926(6) in III) and concomitant
lengthening of the C–O bond (1.153(5) in I and
1.172(6) in III). The bridge atom, C(16) is drawn about
6.8° below the plane of the Cp ring.
2. Experimental
All synthesis were carried out under an atmosphere
of dinitrogen using standard Schlenk techniques. All
purification chromatography was performed using
reagent grade solvents and neutral alumina provided by
CAMAG Inc. or silica gel (Fisher Scientific). All
preparative solvents were dried and distilled under
nitrogen.
The spectral and chromatographic evidence requires
that photolysis initially forms the expected phosphine
addition
product,
Mo(CO)2(PPh3)[h5,h1-C5H4–
C(CH3)2–C5H6], in which the allyl group has under-
gone an h3“h1 hinge opening, and that this material
decomposes during work-up by loss of either the CO or
PPh3 to give Mo(CO)(PPh3)[h5,h3-C5H4–C(CH3)2–
C5H6] or the starting material, respectively. Although
we cannot completely rule out the possibility that some
quantity of III is formed directly by CO loss, we believe
it is diagnostic that III is not observed until the later
stages of the photolysis or upon work-up.
1H-, 13C-, and 13P-NMR spectra were recorded on an
Bruker NR-300 spectrometer (University of Idaho) or a
QE300 NMR Spectrometer (US Naval Academy).
Chemical shifts were reported relative to TMS using
appropriate solvent resonances as internal standards.
IR spectra were obtained using a Perkin–Elmer Spec-
trum 1000 FT-IR spectrometer. Elemental analysis was
performed by Desert Analysis of Tucson, Arizona.
Metal carbonyls were purchased from Strem Chemi-
cals, Inc. and used as received. Bis(Cp)methane [8] and
2,2-bis(Cp)propane [9] were prepared by literature
methods.
2.1. Synthesis of Mo(CO)2[v-p5,p3:C5H4–C(CH3)2–
C5H6], I
2,2-Bis(Cp)propane (2.0 g, 11.5 mmol), and Mo(CO)6
(3.0 g, 11.5 mmol) were placed in a 500 ml Schlenk
flask under nitrogen. Air-free xylene, 250 ml, was added
to the flask and the reaction mixture was refluxed for 48
h. The red reaction mixture was stripped under vacuum
and the resulting dark red solid was chromatographed
on alumina with petroleum ether as an eluent. An
initial elution gave a yellow band which, after removal
of solvent, gave I as an orange–yellow solid: 0.99 g,
27% yield. m.p. (dec.) 104–107°C. IR (CH2Cl2) 1956
1
and 1879 cm−1. H-NMR: (l, CDCl3) 5.96 (m, 1H, Cp
H-5), 5.47 (m, 1H, Cp H-2), 5.04 (m, 2H, Cp H-3, H-4),
4.62 (m, 1H, allyl H-11), 4.09 (1H, m, allyl H-9), 3.68
(m, 1H, allyl H-10), 2.57 (d of d, 1H, J7a–8a=9.0,
Fig. 6. IR spectra of Cr(CO)2[h5,h3-C5H4–C(CH3)2–C5H6], II. (a)
Starting material. (b) Subtraction spectrum, 30 min irradiation at
340BuB420 nm following 30 min irradiation at u=500970 nm
minus (a). (c) Subtraction spectrum, 15 min irradiation at 225BuB
415 nm minus 60 min total irradiation at 340BuB570 nm. Note:
* Bands arise from a natural abundance of 13CO.
J
7a–11=2.9 Hz, H-7a) 2.44 (ddd, 1H, J8a–7a=9.0, J8a–
8s=13.6, J8a–9=2.27 Hz, H-8a), 2.06 (d, 1H, Cp,
8a–8s=13.6 Hz, H-8s), 1.34 (s, 3H, CH3-12), 0.94 (s,
3H, CH3-13). 13C-NMR: (l, CDCl3) 239.8 and 239.2
J

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T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
Scheme 3.
(2CO, Mo–CO), 129.1 (s, ipso-Cp, C-1), 99.7 (C-3),
92.0 (C-2), and 84.6 (C-5), 83.1 (C-10), 81.0 (C-4), 68.1
(C-11), 64.9 (C-7), 56.2 (C-9), 40.2 (C-6), 34.1 (C-8),
26.4 (CH3, C-12), 25.9 (CH3, C-13). Anal. Calc.
C15H16O2Mo: C, 55.57; H, 4.94. Found: C, 55.80; H,
4.67%.
produced II as an orange–yellow solid: 0.38 g, 10%
yield. M.p. (dec.) 208–210°C. IR (cm−1, CH2Cl2) 1928
and 1855.5. 1H-NMR: (l, CDCl3) 5.07 (t, 2H, Cp), 4.00
(t, 2H, Cp), 3.78 (br m, 2H, H-8, H-11), 2.11 (d of m,
2H, J=11.9 Hz, H-9a, H-10a), 1.45 (d of m, 2H,
2.2. Synthesis of Cr(CO)2[v-p5,p3-C5H4–C(CH3)2–
C5H6] (II)
2,2%-Bis-(Cp)propane (2.45 g, 14 mmol) and Cr(CO)6
(3 g, 14 mmol) were placed in a 500 ml Schlenk flask
under nitrogen. Air free solvent mixture of 10:1 butyl
ether:THF (250 ml) was added to the flask and the
reaction mixture was gently refluxed for 48 h. The
green–yellow reaction mixture was stripped under vac-
uum and the resulting dark green–yellow solid was
chromatographed under nitrogen atmosphere on alu-
mina with degassed petroleum ether as an eluent. A
yellow band was isolated which, after solvent removal,
Fig. 7. Molecular structure of III.

T.E. Bitterwolf et al. / Journal of Organometallic Chemistry 583 (1999) 152–161
161
J=11.9 Hz, H-9s, H-10s), 1.10 (s, CH3). 13C-NMR: (l,
CDCl3) 245.7 (2CO, Cr–CO), 91.8 (Cp), 81.3 (Cp), 68.4
(C-8, C-11), 29.7 (C-6), 28.7 (C-9, C-10), 23.5 (CH3).
C-1 and C-7 could not be assigned with confidence.
Anal. Calc. C15H16O2Cr: C, 64.28; H, 5.77. Found: C,
64.06; H, 5.47%.
allylic H-11), 3.05 (d, allylic H-9, JH–P=11.6 Hz), 3.00
(s, 1H, allylic H-10), 2.8 (d, 1H,, J7a–8a=10.1 Hz,
H-7a), 2.36 (dd, 1H, J8a–7a=10.1 Hz, J8a–8s=13.5 Hz,
H-8a), 1.30 (s, 3H, CH3 H-12), 0.98 (s, 3H, CH3 H-13)
13C-NMR: (l, CDCl3) 250.4 (d, JC–P=16.3 Hz, Mo–
CO), 137 (d, JC–P=35.9 Hz, ipso-Ph), 133 (d, JC–P
=
10.7 Hz, o-Ph), 129.2 (s, p-Ph) 127.8 (d, JC–P=7 Hz,
m-Ph), 127 (ipso-Cp, C-1) 98.3 (Cp C-3), 95.3 (Cp C-2),
84.0 (Cp C-5) 83.1 (C-10), 81.7 (Cp C-4), 66.6 (C-11),
64.4 (C-7), 58.4 (d, JC–P=5.0 Hz, C-9), 35.5 (C-6), 30.3
(C-8), 26.8 (C, CH3, C-12), 25.7 (C, CH3, C-13). 31P-
NMR: (l, CDCl3) 73.6 (Mo–PPh3). Anal. Calc.
C32H31OMoP: C, 68.81; H, 5.61; P, 5.54. Found: C,
68.54; H, 5.42; P, 5.79%.
2.3. Synthesis of Mo(CO)PPh3[v-p5,p3-C5H4–
C(CH3)2–C5H6] (III)
Compound I (0.68 g, 2.0 mmol) and triphenylphos-
phine (0.53 g, 2.0 mmol) were placed in a 400 ml quartz
irradiation vessel. Air-free redistilled benzene was
added and the solution was stirred under nitrogen. The
reaction cell was cooled by water and nitrogen was
bubbled through the cell. A medium pressure mercury
lamp was used for irradiation of the reactants. After 90
min of irradiation the color of the solution changed
from yellow to dark yellow. The photolysis was stopped
when IR spectra showed the absence of starting mate-
Acknowledgements
T.E.B. thanks Research Corporation for a generous
Research Opportunity Award for the purchase of an
FT-IR Spectrometer, and the State of Idaho for an
SBOE Research Grant. The University of Delaware
acknowledges the National Science Foundation for
their support of the CCD-based diffractometer (Grant-
CHE-9628768).
rial and the present of a stretching band at 1833 cm−1
.
The resultant mixture was stripped of benzene with a
rotary evaporator and the resulting solid was chro-
matographed on alumina. Initial elution with petroleum
ether removed unreacted phosphine. The main product
band was then chromatographed with a 90:10 mixture
of petroleum ether:methylene chloride. Upon elution
two yellow bands were collected. The first showed a
single IR stretching band at 1829 cm−1: 0.25 g, 22%
yield. The second band had IR bands of I and two new
stretching bands at 1928 and 1848 cm−1 which are
consistent with the second band being a mixture of
starting material and a species with two carbonyl
groups and a triphenylphosphine ligand. The solid from
the second band was taken up and rechromatographed
on silica gel with petroleum ether as an eluent. Two
yellow bands were isolated that were found to be I and
III. Repeated purification attempts failed to isolate the
simple addition product as a pure material. It appears
that this species decomposes into either I or III during
purification. III was isolated as yellow crystals, yield
22%. M.p. (dec.) 205–207°C. IR (cm−1, CH2Cl2) 1829.
1H-NMR: (l, CDCl3) 7.32 (br, 15H, triphenylphos-
phine H), 5.79 (s, 1H, Cp H-5), 5.02 (s, 1H, Cp H-2),
4.95 (s, 1H, Cp H-3), 4.74 (s, 1H, Cp H-4), 4.19 (s, 1H,
References
[1] T.E. Bitterwolf, M.B. Leonard, P.A. Horine, J.E. Shade, A.L.
Rheingold, D.J. Staley, G.P.A. Yap, J. Organomet. Chem. 512
(1996) 11.
[2] T.E. Bitterwolf, J.T. Bays, J.E. Shade, A.L. Rheingold, L. Liable-
Sands, J. Organomet. Chem. (1999) submitted for publication.
[3] (a) G.M. Diamond, M.L.H. Green, N.A. Popham, A.N.
Chernega, J. Chem. Soc. Chem. Commun. (1994) 727. (b) G.M.
Diamond, M.L.H. Green, P. Mountford, N.A. Popham, A.N.
Chernega, J. Chem. Soc. Chem. Commun. (1994) 103.
[4] T.E. Bitterwolf, A.L. Rheingold, Organometallics 10 (1991) 3856.
[5] W.C. Mills, M.S. Wrighton, J. Am. Chem. Soc. 101 (1979) 5832.
[6] T.E. Bitterwolf, K.A. Lott, A.J. Rest, J. Mascetti, J. Organomet.
Chem. 419 (1991) 113.
[7] J.W. Faller, A.S. Anderson, J. Am. Chem. Soc. 92 (1970) 5852.
[8] (a) H.E. Bryndza, R.G. Bergman, J. Am. Chem. Soc. 101 (1979)
4766. (b) H. Schaltegger, M. Neuenschwander, D. Meuche, Helv.
Chim. Acta 101 (1965) 955.
[9] I.E. Nifant’ev, V.L. Yarnikh, M.V. Borzov, B.A. Mazurchik,
V.A. Rozniatovskii, V.I. Mstislavskii, Yu.A. Ustynyuk,
Organometallics 10 (1991) 3739.
.