Reactivity of cationic decamethylmetallocene complexes towards ketones

Article abstract of DOI:10.1016/j.jorganchem.2011.02.023

Reaction of decamethylmetallocene cations [Cp₂M]⁺ (M = Sc, Ti, V) with acetone and benzophenone resulted in the formation of the corresponding acetone adducts [Cp₂M(OCMe₂) _n]⁺ (M = Sc, n = 2; M = Ti, n = 1; M = V, n = 1) and benzophenone adducts [Cp₂M(OCPh)]⁺. The stoichiometry of these adducts is determined by both the electronic configuration of the metal center as well as steric pressure imparted by the large Cp-ligands. In addition, the M-O-C angle is controlled by the number of free valence orbitals of the Cp₂M unit.

Full text of DOI:10.1016/j.jorganchem.2011.02.023

Journal of Organometallic Chemistry 696 (2011) 1920e1924
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Reactivity of cationic decamethylmetallocene complexes towards ketones
,
b
,
a
a
Marco W. Bouwkamp a , Peter H.M. Budzelaar
, Auke Meetsma , Bart Hessen
*
**
a Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands
b Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
a r t i c l e i n f o
a b s t r a c t
Reaction of decamethylmetallocene cations [Cp*2M]þ (M ¼ Sc, Ti, V) with acetone and benzophenone
resulted in the formation of the corresponding acetone adducts [Cp*2M(OCMe2)n]þ (M ¼ Sc, n ¼ 2;
M ¼ Ti, n ¼ 1; M ¼ V, n ¼ 1) and benzophenone adducts [Cp*2M(OCPh)]þ. The stoichiometry of these
adducts is determined by both the electronic configuration of the metal center as well as steric pressure
imparted by the large Cp*-ligands. In addition, the MeOeC angle is controlled by the number of free
valence orbitals of the Cp*2M unit.
Article history:
Received 25 June 2010
Received in revised form
12 February 2011
Accepted 18 February 2011
Keywords:
Metallocenes
Ó 2011 Elsevier B.V. All rights reserved.
Ketone ligands
Coordination modes
1. Introduction
standard Schlenk, vacuum line, and glovebox techniques. Reagents
were purchased from commercial suppliers and used as received,
Early transition metal complexes play an important role in the
(selective) transformation of ketones [1], such as the reduction [2],
hydrosilylation [3], olefination [4], the addition of metal-alkyl
fragments [5], the Aldol condensation [6] and the reductive cou-
pling to form diols (pinacol coupling) [7]. It is expected that the
initial step in these transformations is the coordination of the
substrate via oxygen. It is known, that ketones can bind to early
transition metals in different ways, depending on the metal center,
unless stated otherwise. THF-d8 and cyclohexane were dried over
Na/K alloy prior to use and THF was dried by percolation over
columns of aluminum oxide, BASF R3-11 supported Cu oxygen
scavenger, and mol. sieves (4 Å). [Cp*2M][BPh4] (M ¼ Sc, Ti, V) were
prepared according to literature procedures [11]. 1H NMR spectra
were recorded on a Varian Gemini 200 spectrometer. Chemical
shifts are reported in ppm and referenced to residual solvent
resonances. IR spectra of KBr pellets of the samples were recorded
on a Mattson 4020 Galaxy FT-IR spectrophotometer. Despite many
attempts we were not able to obtain satisfactory elemental analysis
data because of low, but reproducible, carbon values. This is
a common observation for organometallic complexes with a high
carbon content and is associated with the formation of inert carbide
species [11]. In all cases, V2O5 was added to the samples to reduce
the formation of such species.
ranging from
complexes [7b,9] and dimeric structures [10].
kO-bound adducts [8], to side-on bound h
2-ketone
We have been interested in the coordination chemistry of
cationic decamethylmetallocene cations of trivalent metal centers
[11]. Here we describe the reactivity of [Cp*2M][BPh4] (M ¼ Sc, Ti, V)
with acetone and benzophenone to probe the influence of the
electronic structure of the metallocene fragment on the coordina-
tion mode of the ketone ligand.
2.2. Preparation of [Cp*2M(OCMe2)n][BPh4] (M ¼ Sc, n ¼ 2; M ¼ Ti,
n ¼ 1; M ¼ V, n ¼ 1)
2. Experimental section
2.1. Materials and methods
Metallocene cations [Cp*2M][BPh4] were dissolved in 1,2-
difluorobenzene. To the resulting solutions a small excess of
acetone was added. Recrystallization from 1,2-difluorobenzene/
cyclohexane resulted in small amounts of single crystals of the
corresponding acetone adducts. No attempts were made to opti-
mize the yields. [Cp*2Sc(OCMe2)2][BPh4]: 1H NMR (THF-d8, RT,
All reactions and manipulations of air and moisture sensitive
compounds were performed under a nitrogen atmosphere using
* Corresponding author. Tel.: þ31 50 3634432; fax: þ31 50 3634315.
** Corresponding author. Tel.: þ 1 204 474 8796; fax: þ1 204 474 7608.
E-mail addresses: M.W.Bouwkamp@rug.nl (M.W. Bouwkamp), budzelaa@cc.
umanitoba.ca (P.H.M. Budzelaar).
200 MHz)
d 7.31 (br, Dn1/2 15 Hz, BPh4), 6.87 (t, 7.2 Hz, BPh4), 6.72
(t, 7.2 Hz, BPh4), 2.38 (br, Dn1/2 15 Hz, OCMe2), 1.79 (s, Cp*) ppm.
[Cp*2Ti(OCMe2)][BPh4]: IR (KBr pellet) 3051(s), 3031(s), 2996(s),
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.02.023

M.W. Bouwkamp et al. / Journal of Organometallic Chemistry 696 (2011) 1920e1924
1921
Scheme 1. Synthesis of acetone adducts 2aec and benzophenone adducts 3aec.
2980(s), 2963(s), 2902(s), 2859(m), 1665(s), 1579(m), 1478(s), 1426
(s), 1378(s), 1355(m), 1264(w), 1254(m), 1181(w), 1143(m), 1065(m),
1029(m), 1019(m), 909(w), 859(w), 844(m), 802(w), 734(s), 705(s),
624(w), 606(s), 533(w), 482(w), 461(m), 414(w) cmꢀ1. [Cp*2V
(OCMe2)][BPh4]: IR (KBr pellet) 3025(s), 3031(m), 2997(m), 2982
(m), 2963(m), 2920(s), 2851(w), 1744(w), 1672(s), 1582(m), 1479(s),
1448(w), 1426(s), 1381(m), 1356(w), 1321(m), 1281(m), 1262(s),
1183(w), 1151(w), 1128(w), 1068(s), 1019(s), 887(w), 844(w), 801
(m), 733(s), 706(s), 663(w), 639(w), 606(m), 527(w), 466(w), 414
[12] SMART APEX CCD diffractometer. The final unit cell was
identified, the structure was solved by Patterson methods and
extension of the model was accomplished by direct methods
applied to difference structure factors using the program DIRDIF
[13]. The positional and anisotropic displacement parameters for
the non-hydrogen atoms were refined. A subsequent difference
Fourier synthesis of 2aec resulted in the location of all the
hydrogen atoms, which coordinates and isotropic displacement
parameters were refined.
(w) cmꢀ1
.
In the case of the benzophenone adducts, refinement was
complicated by disorder problems. In the case of compound 3a one
of the co-crystallized mono-fluorobenzene solvent molecules was
disordered over a rotation of 120ꢁ. The electron density of the
F-atom appeared to be spread out, indicating rotational disorder. A
disorder model (50:50 for F:H on both positions: bonded to C41 and
C43) was used in the final refinement. The hydrogen atoms were
included in the final refinement riding on their carrier atoms with
their positions calculated by using sp2 or sp3 hybridization at the
C-atom as appropriate with Uiso ¼ c ꢂ Uequiv of their parent atom,
where c ¼ 1.2 for the aromatic/non-methyl hydrogen atoms and
c ¼ 1.5 for the methyl hydrogen atoms and where values Uequiv are
related to the atoms to which the hydrogen atoms are bonded. The
methyl groups were refined as rigid groups, which were allowed to
rotate free. In 3b both difluorobenzene solvent molecules were
rotational disordered by 60ꢁ and 120ꢁ. The atoms connected to C31
and C33 of one fluorobenzene molecule and to C41, C42, C43 and
C44 of the other have a site occupancy factor of 0.5 (meaning in the
average disorder 0.5 F and 0.5 H is bonded to each involved carbon).
The hydrogen atoms were included in the final refinement riding
on their carrier atoms similar to 3a. In compound 3c unrealistic
displacement parameters were observed suggesting some degree
of dynamic disorder, which is in line with the weak scattering
power of the crystals investigated (dynamic means that the
smeared electron density is due to fluctuations of the atomic
positions within each unit cell). This dynamic behavior is especially
seen in the positions concerning the cyclohexane molecule, which
is located over an inversion center. The hydrogen atoms were
included similar to compounds 3a.
2.3. Preparation of [Cp*2M(OCPh2)][BPh4] (M ¼ Sc, Ti, V)
Metallocene cations [Cp*2M][BPh4] were dissolved in fluo-
robenzene (M ¼ Sc) or 1,2-difluorobenzene (M ¼ Ti, V). To the
resulting solutions a small excess of benzophenone was added.
Recrystallization by slow diffusion of cyclohexane into these solu-
tions resultedinsmall amountsofsinglecrystals of thecorresponding
benzophenone adducts. No attempts were made to optimize the
yields. [Cp*2Sc(OCPh2)][BPh4]: 1H NMR (THF-d8, RT, 200 MHz)
d 7.76
(d, 6.8 Hz, OCPh2), 7.63 (d, 7.4 Hz, OCPh2), 7.51 (t, 7.4 Hz, OCPh2), 7.3
(br, BPh4), 6.84(t, 7.6Hz, BPh4), 6.69(t, 6.9 Hz, BPh4),1.91 (s, Cp*) ppm.
IR (KBr pellet) 3054(s), 3032(s), 3000(s), 2998(s), 2947(s), 2908(s),
2898(s), 2872(s), 2859(s),1656(w),1605(s),1585(s),1554(s),1480(w),
1447(m), 1425(w), 1381(w), 1324(s), 1292(s), 1280(m), 1182(w), 1159
(w),1064(w), 1029(w), 999(w), 940(w), 921(w), 842(w), 808(w), 770
(w), 734(m), 703(w), 635(m), 614(w), 471(w) cmꢀ1. [Cp*2Ti(OCPh2)]
[BPh4]: IR (KBr pellet) 3054(s), 3000(s), 2982(s), 2920(s), 2908(s),
2850(s),1657(w),1618(w),1581(m),1544(m),1505(m),1482(w),1446
(m), 1526(m), 1380(w), 1327(m), 1289(w), 1266(m), 1203(w), 1182
(w), 1152(w), 1100(w), 1065(m), 1023(m), 999(w), 942(w), 925(w),
842(w), 807(w), 748(m), 733(m), 703(s), 636(w), 612(w), 566(w), 546
(w), 450(w), 413(w) cmꢀ1
.
2.4. Crystal data
Crystals with suitable dimensions were mounted on top of
a glass fiber, by using glovebox techniques and aligned on a Bruker
Fig. 1. ORTEP representation of the cation of 2aec showing 50% probability ellipsoids. The anions are omitted for clarity.

1922
M.W. Bouwkamp et al. / Journal of Organometallic Chemistry 696 (2011) 1920e1924
Table 1
Compound 3a: C69H70BF2OSc, FW ¼ 1009.08, monoclinic, space
group P21/c, a ¼ 9.9383(8), b ¼ 31.438(3), c ¼ 18.118(2) Å,
Selected bond distances (Å) and angles (ꢁ) of the cations of 2aec.
b
¼ 103.005(2)ꢁ, V ¼ 5515.6(9) Å3, Z ¼ 4, dcalc ¼ 1.215 g/cm3,
m(Mo-
2a
2b
2c
K
a
) ¼ 1.84 cmꢀ1, T ¼ 100(1) K,
q
range: 2.20ꢁe27.32ꢁ. wR
M(1)eCp*(1)a
M(1)eCp*(2)b
M(1)eO(n1)c
O(n1)eC(m1)d
2.1895
2.0285
1.9566
1.9710
2.0584(13)
1.225(2)
(F2) ¼ 0.1501 (reflections: 9726, parameters: 686). R(F) for Fo > 4.0
(Fo) ¼ 0.0667, weighing (a, b) ¼ 0.0362, 1.0517.
s
2.0429
2.1380(12)
1.2248(19)
2.0056(10)
1.2330(17)
Compound 3b: C69H68BF4OTi, FW ¼ 1047.97, monoclinic, space
group P21/c, a ¼ 9.9560(8), b ¼ 31.273(3), c ¼ 18.379(2) Å,
Cp*(1)eM(1)eCp*(2)
M(1)eO(n1)eC(m1)
O(n1)eM(1)eO(n1a)
S{angles M(1)}e
139.71
146.24
148.67
141.66(13)
b
¼ 103.463(2)ꢁ, V ¼ 5565.1(9) Å3, Z ¼ 4, dcalc ¼ 1.251 g/cm3,
m(Mo-
176.46(11)
91.50(5)
173.47(9)
Ka
) ¼ 2.11 cmꢀ1, T ¼ 100(1) K,
q
range: 2.24ꢁe25.03ꢁ. wR
(F2) ¼ 0.1957 (reflections: 9797, parameters: 722). R(F) for Fo > 4.0
(Fo) ¼ 0.0711, weighing (a, b) ¼ 0.0793, 3.1460.
s
359.98
359.35
359.9(3)
S{angles C(m1)}f
359.9(3)
89.11
360.0(2)
:(Cp*2M, MO2)g
Compound 3c: C123H131B2FO2V2, FW ¼ 1783.90, triclinic, space
a
Cp*(1) is the centroid of the C(11)eC(15) ring (M ¼ Sc, V) or C(1)eC(5) ring
group P-1, a ¼ 10.4140(8), b ¼ 20.749(2), c ¼ 23.141(2) Å,
a
¼ 85.066
(M ¼ Ti).
(2)ꢁ,
b
¼ 81.545(2)ꢁ,
g
¼ 88.534(2)ꢁ, V ¼ 4929.3(7) Å3, Z ¼ 2,
b
Cp*(2) is the centroid of the C(11)eC(15) ring (M ¼ Ti) or C(111)eC(115) ring
(M ¼ V).
dcalc ¼ 1.202 g/cm3,
m
(Mo-K
a
) ¼ 2.44 cmꢀ1, T ¼ 100(1) K,
q range:
M ¼ Sc, V: n ¼ 1; M ¼ Ti, n ¼ 0.
2.23ꢁe19.5ꢁ. wR(F2) ¼ 0.1681 (reflections: 17180, parameters:
c
d
e
f
M ¼ Sc: m ¼ 11; M ¼ Ti: m ¼ 2; M ¼ V: m ¼ 12.
1191). R(F) for Fo > 4.0
s(Fo) ¼ 0.0691, weighing (a, b) ¼ 0.0598, 0.0.
S{angles M(1)} is defined as the sum of the angles around M(1).
S{angles C(m1)} is defined as the sum of the angles around C(m1).
:(Cp*2M, MO2) is defined as the angle between the Cp*(1)eM(1)eCp*(1a) and
g
2.5. DFT calculations
O(11)eM(1)eM(11a) plane.
All calculations were carried out with the Turbomole program
[14a,b] coupled to the PQS Baker optimizer [15]. Geometries were
fully optimized at the bp86 [16]/RIDFT [17] level using the Turbo-
mole SV(P) basisset [14c,d] on all atoms (small-core pseudopotential
[14c,e] on Sc, Ti and V). The energies are relative to the base-free
metallocene cations and do not include zero-point energies or
thermal corrections. Furthermore, the anions have been omitted.
Final refinement on F2 carried out by full-matrix least-squares
techniques. The final difference Fourier map was essentially
featureless: no significant peaks having chemical meaning above
the general background were observed. The positional and aniso-
tropic displacement parameters for the non-hydrogen atoms and
isotropic displacement parameters for hydrogen atoms were
refined on F2 with full-matrix least-squares procedures minimizing
P
h½wðjðF02Þ ꢀ kðFc2ÞjÞ2ꢃ, where w ¼ 1=½s2ðF02Þþ
3. Results and discussion
the function Q ¼
ðaPÞ2 þ bPꢃ, P ¼ ½maxðF2; 0Þ þ 2Fc2ꢃ=3, Fo and Fc are the observed
and calculated structure0factor amplitudes, respectively; ultimately
the suggested a and b were used in the final refinement.
3.1. Synthesis
The addition of an excess of acetone to 1,2-difluorobenzene
solutions of decamethylmetallocene complexes [Cp*2M][BPh4]
(M ¼ Sc: 1a, Ti: 1b, V: 1c) resulted in formation of the corre-
sponding acetone adducts (2aec, Scheme 1). The stoichiometry
observed in these adducts is the same as found for the corre-
sponding THF adducts we reported earlier [11]. Thus, in case of
scandium a bis-acetone adduct is formed, whereas one molecule of
acetone is bound in the case of titanium and vanadium. The anal-
ogous reaction of the base-free decamethylmetallocene cations
with benzophenone resulted in the formation of the mono-
benzophenone adducts, [Cp*2M(OCPh2)][BPh4] (2aec, Scheme 1).
Compound 2a: C50H62BO2Sc, FW ¼ 750.81, monoclinic, space
group C2/c, a ¼ 20.539(1), b ¼ 28.090(2), c ¼ 15.3825(9) Å,
b
¼ 104.467(1)ꢁ, V ¼ 8593.4(9) Å3, Z ¼ 8, dcalc ¼ 1.161 g/cm3,
m(Mo-
Ka
) ¼ 2.09 cmꢀ1, T ¼ 100(1) K,
q
range: 2.40ꢁe27.50ꢁ. wR
(F2) ¼ 0.1118 (reflections: 9831, parameters: 736). R(F) for Fo > 4.0
(Fo) ¼ 0.0425, weighting (a, b) ¼ 0.0567, 2.69.
s
Compound 2b: C47H56BOTi, FW ¼ 695.64, monoclinic, space
group P21/n, a ¼ 10.3560(5), b ¼ 32.500(2), c ¼ 11.8554(5) Å,
b
¼ 92.960(1)ꢁ, V ¼ 3984.8(4) Å3, Z ¼ 4, dcalc ¼ 1.160 g/cm3,
m(Mo-
Ka
) ¼ 2.48 cmꢀ1, T ¼ 100(1) K,
q
range: 2.33ꢁe29.72ꢁ. wR
(F2) ¼ 0.1163 (reflections: 10568, parameters: 675). R(F) for Fo > 4.0
s
(Fo) ¼ 0.0449, weighing (a, b) ¼ 0.060, 1.538.
Compound 2c: C47H56BOV, FW ¼ 698.67, monoclinic, space
3.2. Structure
group P21/c, a ¼ 10.2905(6), b ¼ 19.707(1), c ¼ 19.210(1) Å,
b
¼ 96.4870(10)ꢁ, V ¼ 3870.7(4) Å3, Z ¼ 4, dcalc ¼ 1.199 g/cm3,
m(Mo-
Acetone adducts 2aec were studied using single-crystal X-ray
diffraction. The asymmetric unit of [Cp*2Sc(OCMe2)2][BPh4] consists
of two crystallographically independent, but geometrically indis-
tinguishable scandocene cations, each situated on a crystallographic
Ka
) ¼ 2.91 cmꢀ1, T ¼ 100(1) K,
q
range: 2.24ꢁe29.75ꢁ. wR
(F2) ¼ 0.1363 (reflections: 10083, parameters: 675). R(F) for Fo > 4.0
s
(Fo) ¼ 0.0497, weighing (a, b) ¼ 0.0805, 1.0278.
Fig. 2. Space filling models of the front view of [Cp*2Sc(THF)2]þ (left) and the cation of 2a (right).

M.W. Bouwkamp et al. / Journal of Organometallic Chemistry 696 (2011) 1920e1924
1923
Fig. 3. ORTEP representation of the cation of 3aec showing 50% probability ellipsoids. The anions are omitted for clarity.
Table 2
Selected bond distances (Å) and angles (ꢁ) of the cations of 3aec.
1.218(3) and1.221(3) Å [18]) and is in the range of other
k
O-acetone
adducts (1.212e1.269 Å) [8]. The most interesting structural feature
of these acetone adducts is the MeOeC bond angles. In the case of 2a
and 2b this angle is close to linear (176.46(11) and 173.47(9) deg
respectively), whereas the corresponding angle in 2c is significantly
smaller (141.66(13)ꢁ). This suggests a correlation between the
number of free valence orbitals on the metal and the MeOeC bond
angles (linear vs. bent). In the case of complexes where the acetone
ligand can donate more than one pair of electrons to the metal center
(2a, b and 3a, b) a linear MeOeC angle is observed. For compound
2c, where only one free valence orbital is available for the interaction
with ketone, a bent coordination mode is observed. This hypothesis
is supported by observations made in the structure of the titanocene
cation [Cp2Ti(OCMe2)(THF)][Zn(B10H12)2] [8a] and the Zwitterionic
3a
3b
3c
M(1)eCp*(1)a
2.1325
2.1368
2.039
2.0400
1.9725
1.980
M(1)eCp*(2)b
M(1)eO(11)
O(11)eC(121)
Cp*(1)eM(1)eCp*(2)
M(1)eO(11)eC(121)
S{angles M(1)}c
S{angles C(121)}d
2.051(2)
1.256(4)
145.52(7)
174.4(2)
360.00
1.988(3)
1.259(5)
144.25(8)
174.1(3)
360.00
1.820(3)
1.359(5)
140.92(8)
176.9(3)
360.00
360.1(5)
360.0(6)
360.0(7)
a
Cp*(1) is the centroid of the C(11)eC(15) ring.
Cp*(2) is the centroid of the C(111)eC(115) ring.
S{angles M(1)} is defined as the sum of the angles around M(1).
S{angles C(121)} is defined as the sum of the angles around C(121).
b
c
d
[CpB(C6F5)2(C6F5-kF)]CpTi(OCMe2) [8e]. In these complexes, one
molecule of acetone and one additional donor ligand is bound to the
metal center. Consequently, there is one valence orbital available for
the interaction with the acetone ligand, similar to 2c, thus bent
MeOeC bond angles are observed (140.7 and 143.2(2) deg,
respectively).
C2-axis, and of one [BPh4] anion. ORTEP representations of the
cations of 2aec are depicted in Fig. 1 (Table 1 consists of selected
bond distances and angles). The geometry of the acetone adducts
closely resembles that of the corresponding THF adducts [11]. The
Cp*-M-Cp* angles are slightly larger (acetone adducts: M ¼ Sc,
139.71ꢁ; M ¼ Ti, 146.24ꢁ; M ¼ V, 148.67ꢁ; THF adducts: M ¼ Sc,
137.21ꢁ; M ¼ Ti,142.11ꢁ; M ¼ V 146.51ꢁ) and the OeMeO angle in 2a
(91.50(4) deg) is virtually identical to that in [Cp*2Sc(THF)2][BPh4]
(91.59(5)ꢁ). The Cp*-M and the MeO bond distances in 2aec are
shorter than the corresponding distances in the THF adducts. This
might be a result of the fact that in the acetone molecule the methyl
ORTEP representations of the benzophenone adducts 3aec can
be found in Fig. 3 (Table 2 for selected bond distances and angles).
Compounds 3a and 3b are isomorphous, and have virtually iden-
tical geometries, taking into account the difference in ionic radius
of Sc3þ and Ti3þ [19]. The MeO bond distance in benzophenone
adduct [Cp*2Ti(OCPh2)]þ is similar to that in the corresponding
acetone adduct 2b (1.988(3) vs. 2.0056(10) Å). This distance in 3a is
significantly shorter than that in the bis-acetone adduct of scan-
dium (2.051(2) vs. 2.1380(12) Å), in response to the lower coordi-
nation number of the metal in 3a. The MeOeC angles in 3a, b are
comparable to that in the corresponding acetone adducts, i.e. close
to linear. The [Cp*2V(OCPh2)] cation also adopts a bent metallocene
geometry with a linear VeOeC bond angle of 176.9(3)ꢁ, instead of
a bent VeOeC angle as observed in the analogous acetone adduct
2c (141.66(13)ꢁ). Unfortunately, we are uncomfortable in discussing
the bond distances in the molecule as we have observed some
groups are more distant from the metal compared to the a-methy-
lene moieties of the THF ligand. Therefore, the acetone ligands are
less affected by steric bulk imparted by the large Cp*-ligands (Fig. 2).
The TieO bond distance in 2a is shorter compared to that in [Cp2Ti
(OCMe2)(THF)]þ [8a], as expected considering the lower coordina-
tion number of the metal center in 2a. The VeO bond distance in 2c
of 2.0584(13) Å is smaller than that in [Cp2V(OCMe2)]þ (2.081(4) Å)
[8b]. The C]O bond distance of the acetone molecule is virtually
unaffected by the coordination to the transition metal ions (M ¼ Sc:
1.2248(19); M ¼ Ti: 1.2330(17); M ¼ V: 1.225(2) Å; free acetone:
Table 3
Calculated binding energies (kcal/mol) for the acetone and benzophenone ligands including MeO bond distances and MeOeC bond anglesa.
½aꢃ
Erel kcal/mol
MeO (Å) calcd
X-ray
2.08
CeO (Å) calcd
X-ray
1.22
MeOeC (ꢁ) calcd
X-ray
136.8
[Cp2Sc(OCMe2)]þ
[Cp2Sc(OCMe2)2]þ
[Cp2Ti(OCMe2)]þ
[Cp2V(OCMe2)]þ
[Cp2Sc(OCPh2)]þ
[Cp2Ti(OCPh2)]þ
[Cp2V(OCPh2)]þ
ꢀ42.73
ꢀ70.04
ꢀ42.04
ꢀ37.20
ꢀ48.49
ꢀ47.73
ꢀ40.95
2.10
2.16, 2.15
2.03
2.09
2.06
1.25
1.24, 1.24
1.25
1.25
1.27
178.5
159.1, 164.0
178.9
142.6
178.0
2.00
2.03
1.27
1.26
178.8
177.5
[Cp*2Sc(OCMe2)]þ
[Cp*2Sc(OCMe2)2]þ
[Cp*2Ti(OCMe2)]þ
[Cp*2V(OCMe2)]þ
[Cp*2Sc(OCPh2)]þ
[Cp*2Ti(OCPh2)]þ
[Cp*2V(OCPh2)]þ
ꢀ34.04
ꢀ52.40
ꢀ32.29
ꢀ22.94
ꢀ36.84
ꢀ34.76
ꢀ23.81
2.10
2.15, 2.15
2.03
2.08
2.08
1.25
1.24, 1.24
1.25
1.24
1.27
178.2
177.9, 177.6
176.0
151.8
179.3
2.14
2.01
2.06
2.05
1.99
1.82
1.22
1.23
1.23
1.26
1.26
1.36
176.5
173.5
141.7
174.4
174.1
176.9
2.01
2.06
1.27
1.26
178.1
178.9
Binding energy listed are relative to [Cp*2M]þ
.
a

1924
M.W. Bouwkamp et al. / Journal of Organometallic Chemistry 696 (2011) 1920e1924
(c) R.L. Halterman, T. Ramsey, Z. Chen, J. Org. Chem. 59 (1994) 2642;
(d) J.Y. Yun, S.L. Buchwald, J. Am. Chem. Soc. 121 (1999) 5640.
[4] (a) N.A. Petasis, E.I. Bzowej, J. Am. Chem. Soc. 112 (1990) 6392;
(b) S.H. Pine, G.S. Shen, H. Huang, Synthesis (1991) 165;
(c) N.A. Petasis, E.I. Bzowej, J. Org. Chem. 57 (1992) 1327.
[5] B. Klei, J.H. Teuben, H.J.J. De Liefde Meijer, Chem. Soc. Chem. Commun. (1981)
342.
[6] T. Nakano, T. Migita, Chem. Lett. (1993) 2157.
[7] (a) J.C. Huffman, K.G. Moloy, J.A. Marsella, K.G. Caulton, J. Am. Chem. Soc. 102
(1980) 3009;
unrealistic CeC bond distances in the structure of 3c: the C-Ph bond
distances observed are 1.58e1.60 Å (1.47 Å for compounds 3a, b).
3.3. Computational studies
To probe the preferred binding modes of acetone and benzo-
phenone to these trivalent decamethylmetallocene cations, both
the acetone and the benzophenone adducts were studied using
RIDFT calculations (see Experimental Section for more information
on the calculations, and Table 3 for energies). In addition to the
[Cp*2M] ketone adducts, also the corresponding [Cp2M] complexes
were considered. The optimized geometries are in general very
similar to the X-ray data. The relative energies associated with the
binding of acetone vs. benzophenone are very similar, especially in
case of the [Cp*2M] cations. Furthermore, the calculations corrob-
orate the observation that the coordination of a second molecule of
acetone is favored in case of 2a. The binding energies in the scan-
docene and titanocene cations are virtually identical, whereas
those in the vanadocene cations are considerable smaller.
(b) E. Klei, J.H. Telgen, J.H. Teuben, J. Organomet. Chem. 209 (1981) 297;
(c) L. Giannini, A. Caselli, E. Solari, C. Floriani, A. Chiesi-Villa, C. Rizzoli, N. Re,
A. Sgamellotti, J. Am. Chem. Soc. 119 (1997) 9709;
(d) O.V. Ozerov, S. Parkin, C.P. Brock, F.T. Ladipo, Organometallics 19 (2000)
4187;
(e) J.V. Kingston, O.V. Ozerov, S. Parkin, C.P. Brock, F.T. Lapido, J. Am. Chem.
Soc. 124 (2002) 12217;
(f) J.V. Kingston, V. Sarveswaran, S. Parkin, F.T. Ladipo, Organometallics 22
(2003) 136.
[8] (a) R. Allmann, V. Bätzel, R. Pfeil, G. Schmid, Z. Naturforsch. 31b (1976) 1329;
(b) S. Gambarotta, M. Pasquali, C. Floriani, A.C. Villa, C. Guastini, Inorg. Chem.
20 (1981) 1173;
(c) Y. Sun, W.E. Piers, G.P.A. Yap, Organometallics 16 (1997) 2509;
(d) W. Spaether, K. Klass, G. Erker, F. Zippel, R. Fröhlich, Chem. Eur. J. 4 (1998)
1411;
(e) V.V. Burlakov, P. Arndt, W. Baumann, A. Spannenberg, U. Rosenthal,
A.V. Letov, K.A. Lyssenko, A.A. Korlyukov, L.I. Strunkina, M.K. Minacheva,
V.B. Shur, Organometallics 20 (2001) 4072;
4. Conclusions
(f) W.J. Evans, C.H. Fujimoto, M.A. Johnston, J.W. Ziller, Organometallics 21
(2002) 1825.
[9] (a) J.E. Hill, P.E. Fanwick, I.P. Rothwell, Organometallics 11 (1992) 1771;
(b) N. Peulecke, A. Ohff, A. Tillack, W. Baumann, R. Kempe, V.V. Burlakov,
U. Rosenthal, Organometallics 15 (1996) 1340;
(c) B. Castenello, A. Zanotti-Gerosa, E. Solari, C. Floriani, A. Chiesi-Villa,
C. Rizzoli, Organometallics 15 (1996) 4898.
[10] (a) G. Erker, U. Dorf, P. Czisch, J.L. Petersen, Organometallics 5 (1986) 668;
(b) S. Stella, C. Floriani, Chem. Commun. (1986) 1053;
(c) B. Hessen, J. Blenkers, J.H. Teuben, G. Helgesson, S. Jagner, Organometallics
8 (1989) 2809;
The reaction of the decamethylmetallocene cations [Cp*2M]
[BPh4] (M ¼ Sc, Ti, V) with ketones resulted in the formation of the
corresponding kO-ketone adducts. The stoichiometry of the reac-
tions is dependent on both electronic and steric factors. For
acetone, complexes with the same stoichiometry were obtained as
the corresponding THF adducts. In case of the larger benzophenone
ligand, mono-benzophenone adducts were isolated, exclusively. In
the absence of overruling steric effects, the MeOeC angle in these
ketone adducts is dependent on the number of free valence orbitals
in the base-free metallocene cations. A bent coordination of the
ketone is observed in case of complexes with one free valence
orbital (M ¼ V), whereas linear structures are observed when the
ketone can donate more than one pair of electrons to the metal
center (M ¼ Sc, Ti). In the benzophenone adduct [Cp*2V(OCPh2)]þ,
a close to linear MeOeC angle was observed as well. This is most
likely the result of the increased size of the benzophenone ligand
compared to the acetone ligand. The acetone and benzophenone
ligands in the other complexes seem virtually unaffected by the
binding to the metallocene cations.
(d) R.W. Waymouth, K.S. Potter, W.P. Schaefer, R.H. Grubbs, Organometallics
9 (1990) 2843;
(e) U. Blaschke, G. Erker, M. Nissinen, E. Wegelius, R. Frohlich, Organometallics
18 (1999) 1224;
(f) O. Tardif, Z. Hou, M. Nishiura, T. Koizumi, Y. Wakatsuki, Organometallics 20
(2001) 4565.
[11] (a) M.W. Bouwkamp, J. de Wolf, I. del Hierro Morales, J. Gercama, A. Meetsma,
S.I. Troyanov, B. Hessen, J.H. Teuben, J. Am. Chem. Soc. 124 (2002) 12956;
(b) M.W. Bouwkamp, P.H.M. Budzelaar, J. Gercama, I. del Hierro Morales, J. de
Wolf, A. Meetsma, S.I. Troyanov, J.H. Teuben, B. Hessen, J. Am. Chem. Soc. 127
(2005) 14310.
[12] SMART, SAINT, SADABS, Xprep and SHELXL/NT. Smart Apex Software Refer-
ence Manuals. Bruker AXS Inc., Madison, Wisconsin, USA, 2000.
[13] P.T. Beurskens, G. Beurskens, R. de Gelder, S. García-Granda, R.O. Gould,
R. Israël, J.M.M. Smits, The DIRDIF-99 Program System. University of Nijme-
gen, The Netherlands, 1999.
[14] (a) R. Ahlrichs, M. Bär, H.-P. Baron, R. Bauernschmitt, S. Böcker, M. Ehrig,
K. Eichkorn, S. Elliott, F. Furche, F. Haase, M. Häser, C. Hättig, H. Horn, C. Huber,
U. Huniar, M. Kattannek, A. Köhn, C. Kölmel, M. Kollwitz, K. May,
C. Ochsenfeld, H. Öhm, A. Schäfer, U. Schneider, O. Treutler, K. Tsereteli,
B. Unterreiner, M. von Arnim, F. Weigend, P. Weis, H. Weiss, Turbomole
Version 5. Theoretical Chemistry Group, University of Karlsruhe, January
2002;
Acknowledgments
This investigation was supported by The Netherlands Organi-
zation for Scientific Research.
(b) O. Treutler, R.J. Ahlrichs, Chem. Phys. 102 (1995) 346;
(c) Turbomole basisset library, Turbomole Version 5, see Reference [1].
(d) A. Schäfer, H. Horn, R.J. Ahlrichs, Chem. Phys. 97 (1992) 2571;
(e) C. Andrae, U. Häussermann, M. Dolg, H. Stoll, H. Preuss, Theor. Chim. Acta
77 (1990) 123.
Appendix A. Supplementary material
CCDC 775892e775898 contain the supplementary crystallo-
graphic data for the X-ray structures in this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[15] (a) PQS Version 2.4. Parallel Quantum Solutions, Fayetteville, Arkansas, USA,
2001, (the Baker optimizer is available separately from PQS upon request);
(b) J.J. Baker, Comput. Chem. 7 (1986) 385.
[16] (a) A.D. Becke, Phys. Rev. 38A (1988) 3089;
(b) J.P. Perdew, Phys. Rev. 33B (1986) 8822.
References
[17] K. Eichkorn, F. Weigend, O. Treutler, R.J. Ahlrichs, Theor. Chem. Acc. 97 (1997)
119.
[18] The crystallization behavior of acetone is dependent on pressure and
temperature. The value reported here is that of the structure determined at
atmospheric pressures and 110K, the conditions most similar to the X-ray
analysis performed on compounds D.R. Allen, S.J. Clark, R.M. Ibberson,
S. Parsons, C.R. Pulham, L. Sawyer, Chem. Commun. (1999) 751 2aec.
[19] R.D. Shannon, Acta Crystallogr. A32 (1976) 751.
[1] N.A. Petasis, Y.-H. Hu, Curr. Org. Chem. 1 (1997) 249.
[2] (a) F. Sato, T. Jinbo, M. Sato, Tetrahedron Lett. 21 (1980) 2171;
(b) M.C. Barden, J.J. Schwartz, Org. Chem. 60 (1995) 5963.
[3] (a) T. Nakano, Y. Nagai, Chem. Lett. (1988) 481;
(b) M.B. Carter, B. Schiøtt, A. Gutiérrez, S.L. Buchwald, J. Am. Chem. Soc. 116
(1994) 11667;