Novel μ3-oxo complexes prepared from Cp*Zr(BH 3R)3 (R = H, CH3) and B(C6F 5)3 in diethyl ether

Article abstract of DOI:10.1039/b719863a

From the reactions of Cp*ZrCl₃ with 3 equiv. of LiBH ₃R (R = CH₃, Ph), the organotrihydroborate complexes, Cp*Zr(BH₃CH₃)₃, 1, and Cp*Zr(BH₃Ph)₃, 2, were isolated. One of the Zr-H-B bonding interactions in 2 could be described as an intermediate case between the bidentate and tridentate modes. Reactions of 1 and Cp*Zr(BH ₄)₃, 3, with Lewis acid B(C₆F₅) ₃ in diethyl ether produced the novel 14-electron ionic compounds [(μ₃-O)(μ₂-OC₂H₅) ₃{(Cp*Zr(OC₂H₅))₂(BCH ₃)}][HB(C₆F₅)₃], 4, and [(μ₃-O)(μ₂-OC₂H₅) ₃{(Cp*Zr(OC₂H₅))₂(BOC ₂H₅)}][HB(C₆F₅)₃], 5, respectively. These two unique compounds resulted from a sequential cleavage of Zr-H-B bonds of 1 and 3 and C-O bonds of ether followed by the formation of O-B bonds. The solid state single crystal X-ray analyses revealed that both compounds have similar structures. A μ₃-oxygen bridges two zirconiums and a boron atom. The latter three atoms are further connected by three μ₂-bridging ethoxy groups giving rise to three four-membered metallacycles within the structure of each cation.

Full text of DOI:10.1039/b719863a

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Novel l3-oxo complexes prepared from Cp*Zr(BH3R)3 (R = H, CH3) and
B(C6F5)3 in diethyl ether†
Fu-Chen Liu,*a Chien-Chan Yang,a Shou-Chon Chen,a Gene-Hsian Leeb and Shie-Ming Pengb
Received 3rd January 2008, Accepted 4th April 2008
First published as an Advance Article on the web 27th May 2008
DOI: 10.1039/b719863a
From the reactions of Cp*ZrCl3 with 3 equiv. of LiBH3R (R = CH3, Ph), the organotrihydroborate
complexes, Cp*Zr(BH3CH3)3, 1, and Cp*Zr(BH3Ph)3, 2, were isolated. One of the Zr–H–B bonding
interactions in 2 could be described as an intermediate case between the bidentate and tridentate
modes. Reactions of 1 and Cp*Zr(BH4)3, 3, with Lewis acid B(C6F5)3 in diethyl ether produced the
novel 14-electron ionic compounds [(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2(BCH3)}][HB(C6F5)3], 4, and
[(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2(BOC2H5)}][HB(C6F5)3], 5, respectively. These two unique
compounds resulted from a sequential cleavage of Zr–H–B bonds of 1 and 3 and C–O bonds of ether
followed by the formation of O–B bonds. The solid state single crystal X-ray analyses revealed that both
compounds have similar structures. A l3-oxygen bridges two zirconiums and a boron atom. The latter
three atoms are further connected by three l2-bridging ethoxy groups giving rise to three
four-membered metallacycles within the structure of each cation.
Introduction
Results and discussion
Group 4 transition metal hydroborate complexes are of interest
due to their fluxional behavior, the nature of the bonding
Formation and spectroscopic study of Cp*Zr(BH3CH3)3, 1,
Cp*Zr(BH3Ph)3, 2, [(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2-
(BCH3)}][HB(C6F5)3], 4, and [(l3-O)(l2-OC2H5)3{(Cp*Zr-
(OC2H5))2(BOC2H5)}][HB(C6F5)3], 5
interaction between the BH4 ligand and a metal,1,2 their ability
−
to function as reducing agents3 and precursors in the preparation
of hydride complexes4 as well as their applications in the chemical
vapour deposition (CVD) of ZrB2 and HfB2 films5 and in hydrob-
oration as catalysts.6 The terahydroborate zirconocene complexes
have been studied since the 1960’s.1 Recently the related Group
4 organohydroborate complexes have also been reported.7–13
Many zirconocene-based organohydroborate compounds have
been prepared and studied by Shore and co-workers7–10 as
well as by our group.12,13 These organohydroborate compounds
display interesting dynamic properties8 and bonding interactions
between the organohydroborate ligand and the metal.9 Compared
with the zirconocene compounds, the half-sandwich zirconocene
compounds possess a face that is more open to attack and has
more coordination sites available, which may result in interesting
bonding interactions and different chemical behavior. However,
the related organohydroborate complexes are not well studied. To
our knowledge, only a handful of examples of the half-sandwich
zirconocene hydroborate and organohydroborate complexes have
been reported.10,14,15 Thus, we are interested in exploration of the
half-zirconocene organohydroborate chemistry. Here we would
like to report the results of our recent study on the preparation of
the half-sandwich zirconocene organotrihydroborate compounds
and their reaction with a Lewis acid B(C6F5)3.
Compounds Cp*Zr(BH3CH3)3, 1, and Cp*Zr(BH3Ph)3, 2 were
prepared from the reaction of Cp*ZrCl3 with 3 equiv. of LiBH3R
(R = CH3, Ph) in diethyl ether, as shown in eqn (1).
(1)
Both compounds were crystallized from ether solution at
−35 ◦C. While compound 1 is very soluble in ether, compound
2 has a low solubility in this solvent. Their 11B NMR spectra
display a broad signal at −5.50 ppm for 1 and a broad quartet
(JB–H = 69 Hz) at −4.32 ppm for 2. These resonances are downfield
with respect to those of the free anions (LiBH3Ph: −26.5 ppm;
LiBH3CH3: −30.9 ppm).12,16 In the proton NMR spectra, the
BH hydrogens of 1 and 2 appear as broad quartets at 1.37 and
2.28 ppm, respectively.
Compounds [(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2(BCH3)}]-
[HB(C6F5)3], 4, and [(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2-
(BOC2H5)}][HB(C6F5)3], 5, were prepared from the reaction of
1 and Cp*Zr(BH4)3,15 3, respectively, with B(C6F5)3 in ether
according to eqn (2),
aDepartment of Chemistry, National Dong Hwa University, Hualien, 974,
Taiwan, ROC. E-mail: fcliu@mail.ndhu.edu.tw; Fax: +886 38633570;
Tel: +886 38633601
bDepartment of Chemistry, National Taiwan University, Taipei, 106, Taiwan,
ROC
† Electronic supplementary information (ESI) available: Crystallographic
data. CCDC reference numbers 672315–672319. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b719863a
(2)
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and isolated from a ether–hexane two-layered system. Crystals of
4 and 5 are only slightly soluble in ether while they decompose
in other commonly used solvents. In fact, decomposition of 4 is
so fast that its resonances could not be identified in the proton
NMR spectrum. Decomposition of 5 in d8-toluene is slower, and
by comparing the intensity of the signals of the time-elapsed
Molecular structures of 1, 2, 3, 4, and 5
The structure of Cp*Zr(BH4)3 (compound 3 first synthesized
by Wolczanski and Bercaw15) is included for comparison. The
molecular structures of 1–5 were determined by single-crystal X-
ray diffraction analysis. Crystallographic data and selected bond
distances and bond angles are given in Tables 1–4. The molecular
structures of 2, 4, and 5 are shown in Fig. 1–3. The molecular
structures of 1 and 3 are similar to that of 2 and they are included
in the ESI.†
1
spectra it was possible to identify its original H NMR signals.
Although four different bonding environments for an ethoxy
group can be found in 5, they cannot be distinguished in its
proton NMR spectrum, which displays only one set of signals
The coordination geometry of zirconium atoms in the molecular
structures of 1–3 can be described best as a distorted tetrahedron.
At the corners of each tetrahedron are the center of a Cp* ring
and three boron atoms connected to a zirconium atom through
bridging hydrogens. The metal–boron distance has been used as a
criterion for determining the bonding mode between the metal and
the hydroborate ligand.1,18 Hedberg et al. estimated the expected
for all of them. The CH2 protons appear at 3.19 ppm (q, JH–H
7.0 Hz) and the CH3 protons appear at 0.98 ppm (t, JH–H
=
=
7.0 Hz). In the 13C NMR the ethoxy methylene and methyl signals
appear at 65.55 and 14.61 ppm, respectively. The hydride signal
of the anion [HB(C6F5)3]− is not observed in the proton NMR
spectrum, possibly due to its broadness. The instance of terminal
and bridging alkoxide group proton chemical shifts being the
same has been observed previously.10,17 Two boron signals are
observed for each compound in a freshly prepared solution. A
doublet signal at −26 ppm (d, JB–H = 93 Hz) in each spectrum
is assigned to the anion [HB(C6F5)3]−. The cation boron signals
appear as singlets at 30.5 ppm for 4 and 17.6 ppm for 5. Unlike the
proton NMR spectra, the boron NMR spectra do not provide any
information with regard to the decomposition of these compounds
in solution. It is possible that decomposition occurs at the electron
deficient metal center, and the boron atom of the anion and the
four-coordinated boron atom of the cation are not affected at the
beginning of decomposition.
˚
Zr–B distances for a bidentate mode to be in the range 2.39–2.59 A
14
˚
and for a tridentate mode to be in the range 2.28–2.40 A. The
average Zr–B distances for 1–3 increase in the order 3 < 1 < 2,
which is consistent with the bulkiness of the fourth substituent
The reaction of Cp*Zr(BH3Ph)3 with B(C6F5)3 in diethyl ether
was also studied. The boron NMR spectrum of the product
mixture displayed three boron signals, with two major ones
appearing at 27.38 (s) and −26.19 ppm (d, JB–H = 91 Hz). This
result suggested the formation of a product similar to compound
4. However, we have not met with success in isolation of this
product.
Shore and co-workers10 have prepared compound [(l2-
OC2H5){CpZr(OC2H5)(OC4H10)}]2[HB(C6F5)3]2 from the reac-
tion of CpZr{BH2(C5H10)}3 with B(C6F5)3 in diethyl ether. For-
mation of 4 and 5 may follow a similar pathway producing an in-
termediate [(l2-OC2H5){Cp*Zr(OC2H5)(OC4H10)}]2[HB(C6F5)3]2,
which is an analog of Shore’s compound. It is possible that this
intermediate reacts further by coordination of a bridging oxygen to
BH3 formed in previous steps followed by a hydride transfer from
[HB(C6F5)3]− to the ethyl group giving rise to an intermediate [(l2-
OC2H5)(l2-OBH3){Cp*Zr(OC2H5)(OC4H10)}2][HB(C6F5)3]. Re-
peated attacks by the coordinated BH3 moiety on the ethyl
groups of coordinated ether molecules resulting in bond for-
mation between the oxygen and boron atoms will produce
[(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2(BH)}][HB(C6F5)3]. Reac-
tion of the last BH hydrogen of this intermediate with
ether will furnish final product 5. When the boron source
is (BH2CH3)2, which has only two BH hydrogens avail-
able, further reaction of the intermediate [(l2-OC2H5){Cp*Zr-
(OC2H5)(OC4H10)}]2[HB(C6F5)3]2 will produce compound 4. The
fact that these reactions do not stop at the formation of
[(l2-OC2H5){Cp*Zr(OC2H5)(OC4H10)}]2[HB(C6F5)3]2 may be at-
tributedtoa better electron donor abilityofthe Cp* ligand, and/or
the nature of the hydroboranes. Studies of the factors affecting the
formation of 4 and 5 are in progress.
Fig. 1 Molecular structure of Cp*Zr(BH3Ph)3, 2, showing 50% proba-
bility thermal ellipsoids.
Fig.
2
Molecular structure of the cation in [(l3-O)(l2-
OC2H5)3{(Cp*Zr(OC2H5))2(BCH3)}][HB(C6F5)3], 4, showing 30%
probability thermal ellipsoids.
3600 | Dalton Trans., 2007, 3599–3604
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Table 1 Crystal data and structure refinement for Cp*Zr(BH3CH3)3, 1, Cp*Zr(BH3Ph)3, 2, and Cp*Zr(BH4)3, 3
Empirical formula
M
C13H33B3Zr
313.04
150(2)
Tetragonal
P4(3)
7.8250(3)
7.8250(3)
28.7350(11)
C28H39B3Zr
499.24
150(2)
Monoclinic
P2(1)/n
8.8868(1)
14.7203(2)
20.4718(3)
C10H27B3Zr
270.97
150(1)
Triclinic
¯
P1
7.0619(8)
8.4186(9)
13.4982(15)
84.077(2)
88.589(2)
66.427(2)
731.47(14)
2
T/K
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
91.1669(5)
3
˚
V/A
1759.46(12)
4
1.182
2677.49(6)
4
1.238
Z
qcalcd/g cm−3
1.230
Crystal size/mm
0.30 × 0.30 × 0.30
Mo-Ka (0.71073)
2.60–27.50
−10 ≤ h ≤ 10
−10 ≤ k ≤ 10
−37 ≤ l ≤ 37
17156
4028
664
100.0
0.605
0.25 × 0.25 × 0.20
Mo-Ka (0.71073)
1.70–27.50
−11 ≤ h ≤ 11
−19 ≤ k ≤ 18
−26 ≤ l ≤ 26
20179
6152
1048
100.0
0.424
0.20 × 0.20 × 0.10
Mo-Ka (0.71073)
1.52–27.50
−9 ≤ h ≤ 9
−10 ≤ k ≤ 10
−17 ≤ l ≤ 17
9665
3345
284
99.7
0.717
˚
Radiation (k/A)
h limits/◦
Index ranges
Reflns collected
Unique reflns
F(000)
Completeness to h (%)
l/mm−1
Max., min. transm.
Data/restraints/params
R1a[I > 2.0r(I)]
wR2b(all data)
Rint
0.8394, 0.8394
4028/1/181
0.0257
0.0643
0.0366
0.940, 0.867
6152/0/326
0.0410
0.1152
0.0712
0.9318, 0.8699
3345/0/175
0.0364
0.0873
0.0351
GOF on F2
1.052
1.077
1.155
ꢀ
ꢀ
ꢀ
ꢀ
2
1/2
a R1 = ꢀFoꢀ − |Fcꢀ/ ꢀFo|. b wR2 = { w(Fo − Fc2)2/ w(Fo2)2}
.
Table 2 Crystal data and structure refinement for [(l3-O)(l2-
OC2H5)3{(Cp*Zr(OC2H5))2(BCH3)}][HB(C6F5)3], 4, and [(l3-O)(l2-
OC2H5)3{(Cp*Zr(OC2H5))2(BOC2H5)}][HB(C6F5)3], 5
Empirical formula
M
T/K
C49H59B2F15O6Zr2
1233.02
150(2)
C50H60B2F15O7Zr2
1262.04
295(2)
Crystal system
Space group
Monoclinic
P2(1)/c
Orthorhombic
P2(1)2(1)2(1)
14.6566(5)
18.0175(6)
20.3699(7)
˚
a/A
10.5767(5)
16.4862(8)
32.1655(17)
93.389(1)
5598.9(5)
4
˚
b/A
˚
c/A
b/◦
3
˚
V/A
5379.2(3)
4
1.558
Z
qcalcd/g cm−3
1.463
Crystal size/mm
0.50 × 0.32 × 0.20
Mo-Ka (0.71073)
1.27–27.50
−13 ≤ h ≤ 12
−21 ≤ k ≤ 17
−41 ≤ l ≤ 41
49575
12748
2504
99.2
0.466
0.36 × 0.30 × 0.25
Mo-Ka (0.71073)
1.51–27.49
−18 ≤ h ≤ 19
−23 ≤ k ≤ 23
−26 ≤ l ≤ 26
54149
12348
2564
100.0
0.488
˚
Radiation (k/A)
h limits/◦
Index ranges
Fig.
3
Molecular structure of the cation in [(l3-O)(l2-
Reflns collected
Unique reflns
F(000)
OC2H5)3{(Cp*Zr(OC2H5))2(BOC2H5)}][HB(C6F5)3], 5, showing 30%
probability thermal ellipsoids.
Completeness to h (%)
l/mm−1
Max., min. transm.
Data/restraints/params
R1a[I > 2.0r(I)]
wR2b(all data)
Rint
0.9126, 0.8005
12748/4/689
0.0695
0.2137
0.0591
0.8877, 0.8438
12348/2/704
0.0412
0.0899
0.0591
on the boron atom. The Zr–B distances and the hydrogen bridge
Zr–Hb bond distances of compounds 1 and 3 are in the range
˚
˚
2.366(3)–2.387(3) A and 2.02(3)–2.34(4) A, respectively. These
distances are consistent with those generally observed for the
tridentate bonding mode, namely, the Zr–B distances in the range
GOF on F2
1.089
1.029
ꢀ
ꢀ
ꢀ
ꢀ
˚
˚
a R1 = ꢀFoꢀ − |Fcꢀ/ ꢀFo|. b wR2 = { w(Fo − Fc2)2/ w(Fo2)2}
.
2
1/2
of 2.276(11)–2.403(29) A and the Zr–Hb bond distances in the
14,19
range of 2.04(5)–2.36(7) A.
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◦
˚
The Zr–B distances in 2 are 2.375(3), 2.389(3), and 2.413(4)
A. The two short Zr–B distances and their corresponding Zr–Hb
Table 3 Selected bond lengths (A) and angles ( ) for Cp*Zr(BH3CH3)3,
1, Cp*Zr(BH3Ph)3, 2, and Cp*Zr(BH4)3, 3
˚
distances are consistent with the tridentate bonding mode. The
1
2
3
˚
Zr–B distance of 2.413(4) A is longer than expected for a bond
distance characteristic of the tridentate mode. The corresponding
Zr–B
2.367(3)
2.374(3)
2.387(3)
2.02(4)
2.03(5)
2.04(4)
2.06(4)
2.10(4)
2.18(4)
2.29(4)
2.31(4)
2.33(3)
2.375(3)
2.389(3)
2.413(4)
2.04(3)
2.04(3)
2.05(3)
2.14(3)
2.15(3)
2.22(3)
2.26(3)
2.30(3)
2.366(3)
2.369(4)
2.378(4)
2.02(3)
2.03(3)
2.08(3)
2.09(4)
2.11(4)
2.13(3)
2.29(4)
2.33(3)
2.34(4)
˚
Zr–H distance of 2.475 A is significantly longer than the sum
˚
of the covalent radii of Zr and H atoms (1.91 A) and generally
Zr–Hb
observed Zr–Hb distances. However, it is shorter than a sum
20
˚
of the covalent radius of Zr (1.50 A) and the van der Waals
21
˚
radius of H (1.20 A). An additional piece of judgment in favor
of the tridentate bonding mode is the linearity of the Zr–B–C
angles. The corresponding Zr–B–C angle is 163.4(2)◦, which is 5◦
smaller than the smallest of Zr–B–C (Ht) angles in 1 and 3. Thus,
˚
the longest Zr–H distance of 2.475 A would suggest an agostic
Zr · · · H
2.475
interaction between Zr and H, and the coordination between the
Zr and this phenyltrihydroborate ligand could be described as an
intermediate between the bidentate and tridentate modes. This
deviation from the tridentate bonding mode can be accounted for
by steric reasons. It is worth noting that the average B–Hb and B–
B–Hb
1.06(4)
1.09(3)
1.14(4)
1.14(4)
1.17(4)
1.17(4)
1.21(4)
1.22(4)
1.29(3)
1.08(3)
1.09(3)
1.09(3)
1.09(3)
1.12(3)
1.14(3)
1.15(3)
1.18(2)
1.22(3)
1.02(3)
1.02(4)
1.05(4)
1.07(4)
1.08(4)
1.11(4)
1.12(4)
1.16(3)
1.20(4)
1.06(4)
1.09(4)
1.11(4)
168(2)
170(2)
171(2)
˚
Ht distances in 3 are about the same (1.09 A). This is in contrast
with an observation that for most tetrahydroborate compounds
the B–Hb distances are slightly longer than the B–Ht distances.1,22
Compounds 4 and 5 are ionic, with cation charges being
balanced by that of the [HB(C6F5)3]− anion. The molecular
structures of these cations are similar. A l3-oxygen bridges two
zirconiums and a boron atom, and these three atoms are further
connected through three l2-bridging ethoxy groups. Overall, there
are three four-membered metallacycles within the structure of each
cation. The bond angles in each of the four-membered rings in
both cations are also comparable. Except for those of Zr1–O4–B1
B–Ht
Zr–B–Rta
168.2(2)
172.3(2)
174.2(3)
163.4(2)
171.8(2)
174.9(2)
a Rt = C for 1 and 2, Rt = Ht for 3.
Table 4 Selected bond lengths (A) and angles (◦) for [(l3-O)(l2-OC2H5)3{(Cp*Zr(OC2H5))2(BCH3)}][HB(C6F5)3], 4, and [(l3-O)(l2-
OC2H5)3{(Cp*Zr(OC2H5))2(BOC2H5)}][HB(C6F5)3], 5
˚
4
5
4
5
Zr(1)–O(1)
Zr(1)–O(2)
Zr(1)–O(3)
Zr(1)–O(4)
Zr(2)–O(1)
Zr(2)–O(2)
Zr(2)–O(5)
Zr(2)–O(6)
Zr(1)–Zr(2)
O(2)–C(1)
2.147(3)
2.177(3)
1.908(4)
2.178(4)
2.121(3)
2.144(3)
2.174(4)
1.914(4)
3.3680(7)
1.474(7)
2.120(2)
2.149(2)
1.906(2)
2.194(2)
2.156(2)
2.161(2)
2.200(2)
1.908(2)
3.3608(4)
1.449(4)
O(3)–C(3)
O(4)–C(5)
O(5)–C(7)
O(6)–C(9)
O(7)–C(11)
O(1)–B(1)
O(4)–B(1)
O(5)–B(1)
O(7)–B(1)
B(1)–C(11)
1.428(7)
1.433(7)
1.427(7)
1.419(8)
1.407(5)
1.433(4)
1.450(4)
1.417(4)
1.431(4)
1.454(4)
1.521(4)
1.510(5)
1.407(4)
1.460(7)
1.532(8)
1.523(8)
1.578(9)
O(3)–Zr(1)–O(2)
O(3)–Zr(1)–O(4)
O(1)–Zr(1)–O(2)
O(1)–Zr(1)–O(4)
O(2)–Zr(1)–O(4)
O(1)–Zr(2)–O(2)
O(1)–Zr(2)–O(5)
O(2)–Zr(2)–O(5)
O(6)–Zr(2)–O(2)
O(6)–Zr(2)–O(5)
B(1)–O(1)–Zr(1)
B(1)–O(1)–Zr(2)
B(1)–O(4)–Zr(1)
B(1)–O(5)–Zr(2)
Zr(2)–O(1)–Zr(1)
C(1)–O(2)–Zr(1)
C(1)–O(2)–Zr(2)
90.82(15)
90.78(16)
70.91(13)
63.35(13)
113.20(13)
72.05(13)
63.23(14)
116.06(14)
91.83(17)
89.00(19)
100.8(3)
101.4(3)
97.1(3)
97.1(3)
104.18(15)
126.7(3)
91.40(10)
89.10(10)
71.16(8)
63.38(8)
120.85(9)
70.25(8)
C(3)–O(3)–Zr(1)
C(5)–O(4)–Zr(1)
C(7)–O(5)–Zr(2)
C(9)–O(6)–Zr(2)
Zr(2)–O(2)–Zr(1)
C(5)–O(4)–B(1)
C(7)–O(5)–B(1)
O(1)–B(1)–O(5)
O(1)–B(1)–O(4)
O(5)–B(1)–O(4)
O(1)–B(1)–C(11)
O(5)–B(1)–C(11)
O(4)–B(1)–C(11)
B(1)–O(7)–C(11)
O(7)–B(1)–O(1)
O(7)–B(1)–O(5)
O(7)–B(1)–O(4)
170.5(4)
138.9(4)
136.9(4)
175.1(6)
102.44(14)
121.5(5)
122.6(5)
98.0(4)
169.3(3)
132.5(2)
136.9(2)
164.1(3)
102.47(9)
122.5(3)
122.7(3)
99.8(3)
62.71(8)
110.01(9)
89.32(10)
93.06(10)
100.14(18)
100.5(2)
94.82(17)
96.76(18)
103.62(9)
119.0(2)
98.8(4)
99.3(3)
112.5(3)
110.3(5)
120.2(6)
113.4(5)
114.2(5)
117.3(3)
120.7(3)
108.8(3)
114.7(3)
117.4(3)
126.7(2)
3602 | Dalton Trans., 2007, 3599–3604
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(97.1(3) in 4, 94.82(17) in 5), O4–B1–O1 (98.8(4) in 4, 99.3(3) in
5), and O1–B1–O5 (98.0(4) in 4, 99.8(3) in 5), the difference for
each pair of angles is less than 1◦. Each zirconium atom in 4 and 5
is further coordinated to a Cp* ring and a terminal ethoxy group.
Thus, the coordination of each zirconium can be described best as
a distorted square pyramid with a Cp* ring occupying the apical
position and four oxygens occupying four distorted basal sites.
The boron atom is tetra-coordinated, in addition to three oxygens
it is either bonded to a methyl group in 4 or an additional ethoxy
group in 5.
X-Ray crystal structure determination
Suitable single crystals were mounted and sealed inside glass fibers
under nitrogen. Crystallographic data collections were carried out
on a Nonius KappaCCD diffractometer with graphite monochro-
mated Mo-Ka radiation (k = 0.71073 A) at 150(2) K and 295(2)
˚
K. Cell parameters were retrieved and refined using DENZO-
SMN27 software on all reflections. Data reduction was performed
with the DENZO-SMN27 software. An empirical absorption was
based on the symmetry-equivalent reflections and was applied to
the data using the SORTAV28 program. Structure analysis was
made using the SHELXTL program on a personal computer. The
structure was solved using the SHELXS-9729 program and refined
using the SHELXL-9730 program by full-matrix least-squares on
F2 values. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms attached to the borons were found from the
difference Fourier map and refined isotropically. Hydrogen atoms
attached to the carbons were fixed at calculated positions and
refined using a riding mode. Detailed crystal data are listed in
Tables 1 and 2.
˚
The terminal Zr–O bond distances are about 1.908 A in
˚
both compounds. This distance falls in the range 1.89–1.94 A
observed previously for the terminal Zr–O distances in zirconium
alkoxides.23,24 The corresponding Zr–O–C angles of 170.5(4),
175.1(6)◦ in 4 and 169.3(3), 164.1(3)◦ in 5 are consistent with a
strong O → Zr p-donation17 or an increased ionic character of
the Zr–O bond.20,25 The bridging Zr–O bond distances vary in
both cations. However, they increase in the order Zr–O1 < Zr–
O2 < Zr–O4, Zr–O5, and are longer than those of the terminal
Zr–O bonds. These bridging Zr–O bond distances fall in the range
˚
˚
2.121(3)–2.178(4) A in 4 and 2.120(2)–2.200(2) A in 5. They are
comparable with the bridging Zr–O distances in other zirconium
Preparation of Cp*Zr(BH3CH3)3 1
17,24,26
˚
alkoxides and zirconium oxides (2.098(8)–2.2215(2) A).
The
bonding environments of O4 and O5 in 4 and O5 in 5 are nearly
planar. The sums of angles around these oxygens are 357.5, 356.6,
and 356.4◦, respectively. Other bridging oxygens are nonplanar,
with the sums of the angles around O1 and O2 being 306.38 and
346.54◦ in 4, and 304.26 and 348.17◦ in 5.
In the drybox Cp*ZrCl3 (333.0 mg, 1.0 mmol) and LiBH3CH3
(111.0 mg, 3.1 mmol) were placed into a flask. The flask was
evacuated, and 20 mL of diethyl ether was condensed into it
at −78 ◦C. The system was warmed to room temperature and
stirred overnight. The LiCl thus formed was separated from
the solution by filtration. A white solid was obtained after
removal of the solvent from the filtrate. Colorless crystals of 1
(240.0 mg, 77% yield) were obtained after crystallization from
Et2O at −35 ◦C. IR(KBr, cm−1): 2980 m, 2939 s, 2904 m, 2854w,
2831w, 2238vw, 2169vw, 2065br, s, 1652vw, 1632vw, 1487w, 1461w,
1430 m, 1376w, 1308 s, 1227vs, 1104w, 1073w, 1020w, 962w, 805vw,
679vw and 667vw. 11B NMR (diethyl ether, d): −5.60 ppm (q, JB–H
69). 11B NMR (C6D6, d): −5.50 ppm (q, JB–H 69). 1H NMR (C6D6,
d): 1.84 (15H, s, Cp*), 1.37 (9H, br q, BH3) and 0.49 ppm (9H,
br q, JH–H 4.2, CH3,). Anal. Found: C, 49.81; H, 10.63. Calc. for
C13H33B3Zr: C, 49.88; H, 10.63%.
Conclusions
Novel l3-oxo compounds, 4 and 5, were isolated from the
reactions of half-sandwich zirconocene hydroborate compounds
with B(C6F5)3. Although C–O bond cleavage mediated by Group
4 metal complexes is not uncommon, it is the structure of these
compounds possessing three four-membered metallacycles that is
unique. It is possible that these l3-oxo compounds form as a result
of the sequential cleavage of Zr–H–B bonds and C–O bonds of
ether, and the formation of B–O bonds, albeit at this point it
could not be corroborated by observation of the corresponding
intermediates.
Preparation of of Cp*Zr(BH3Ph)3 2
Experimental section
A 50 mL flask was charged with 332.8 mg (1.0 mmol) of Cp*ZrCl3
and 294.0 mg (3.0 mmol) of LiBH3Ph. The flask was evacuated,
and about 15 mL of Et2O was condensed into it at −78 C. The
All manipulations were carried out on a standard high vacuum
line or in a drybox under an atmosphere of nitrogen. Diethyl
ether and hexane were dried over Na/benzophenone and were
freshly distilled prior to use. Cp*ZrCl3, LiBH4, and B(C6F5)3
were purchased from Strem Chemicals and used as received.
◦
system was warmed to room temperature and stirred for 12 h. The
LiCl was removed by filtration followed by solvent removal under
vacuum. The white solid left in the flask was dissolved in Et2O and
kept at −35 ◦C for crystallization furnishing 2 as colorless crystals
(290 mg, 58% yield). IR(KBr, cm−1): 3067vw, 3056vw, 3010vw,
2977vw, 2962vw, 2916vw, 2860vw, 2215br, vw, 2076br, m, 1944vw,
1490vw, 1483vw, 1432w, 1426vw, 1382w, 1364vw, 1341w, 1283s,
1265vs, 1160m, 1151m, 1125s, 1088w, 1054w, 1028m, 1000w,
983vw, 908vw, 804w, 793w, 739s, 733s, 698s, 670vw, 663vw, 574w
and 471vw. 11B NMR (C6D6, d): −4.32 ppm (br). 1H NMR
(C6D6, d): 7.56–7.09 (15H, m, Ph), 2.28 ppm (9H, br q, BH3)
and 1.84 (15H, s, Cp*). Anal. Found: C, 66.82; H, 7.83. Calc. for
C28H39B3Zr: C, 67.36; H, 7.87%.
LiBH3CH3,16 LiBH3Ph,16 and Cp*Zr(BH4)3 were prepared ac-
15
cording to literature methods. Elemental analyses were obtained
on a Hitachi 270–30 spectrometer. Proton spectra (d(TMS) =
0.00 ppm) were recorded either on a Bruker Avance DPX300
spectrometer operating at 300.132 MHz or Bruker Avance II
spectrometer operating at 400.130 MHz. 11B spectra (externally
referenced to BF3·OEt2 (d = 0.00 ppm)) were recorded on a Bruker
Avance DPX300 spectrometer operating at 96.294 MHz. Infrared
spectra were recorded on a Jasco FT/IR-460 Plus spectrometer
with 2 cm−1 resolution.
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Williams, Inorg. Chem., 1985, 24, 4316; J. E. Gozum, S. R. Wilson and
G. S. Girolami, J. Am. Chem. Soc., 1992, 114, 9483; J. E. Gozum and
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Preparation of [(l3-O)(l2-OC2H5)3{(Cp*Zr-
(OC2H5))2(BCH3)}][HB(C6F5)3] 4
In the drybox 156.0 mg (0.5 mmol) of Cp*Zr(BH3CH3)3 and
256.0 mg (0.5 mmol) of B(C6F5)3 were placed into a 50 mL
flask. The flask was degassed, and about 10 mL of diethyl ether
was transferred into it at −78 ◦C. The system was warmed
to room temperature and stirred overnight. After reducing the
volume of the clear solution to about 3 mL, it was transferred
into a tube and layered with hexane for crystallization. The title
compound was obtained as colorless crystals (140.0 mg, 45%
yield). IR(KBr, cm−1): 2980w, 2927w, 2870vw, 2403vw, 1636w,
1506m, 1465vs, 1380w, 1319vw, 1273m, 1250vw, 1119m, 1069m,
1036w, 970s, 931w, 878vw, 805vw, 764vw, 710vw, 667vw, 656vw,
599vw, 583vw, 564vw, 549vw and 461vw. 11B NMR (diethyl ether,
d): 30.64 (s) and −25.85 ppm (d, JB–H 93). 11B NMR (d8-THF, d):
30.46 (s) and −26.09 ppm (d, JB–H 93). Anal. Found: C, 47.32; H,
4.60. Calc. for C49H59B2F15O6Zr2: C, 47.73; H, 4.82%.
9 F.-C. Liu, J. Liu, E. A. Meyers and S. G. Shore, Inorg. Chem., 1998, 38,
2169; F.-C. Liu, J. Liu, E. A. Meyers and S. G. Shore, J. Am. Chem.
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M. Yousufuddin, R. Bau and G. Mclntyre, Inorg. Chem., 2005, 44,
2459.
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2002, 41, 5329.
11 P. Paetzold, L. Geret and R. Boese, J. Organomet. Chem., 1990, 385, 1;
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A. Zalkin, Inorg. Chem., 1983, 22, 2351.
Preparation of [(l3-O)(l2-OC2H5)3{(Cp*Zr-
(OC2H5))2(BOC2H5)}][HB(C6F5)3] 5
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15 P. T. Wolczanski and J. E. Bercaw, Organometallics, 1982, 1, 793.
16 B. Singaram, T. E. Cole and H. C. Brown, Organometallics, 1984, 3,
774.
17 B. A. Vaartstra, J. C. Huffman, P. S. Gradeff, L. G. Hubert-Pfalzgraf,
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18 N. Edelstein, Inorg. Chem., 1981, 20, 297; E. R. Bernstein, W. C.
Hamilton, T. A. Keiderling, S. J. LaPlaca, S. J. Lippard and J. J. Mayerle,
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21 J. Huheey, E. A. Keliter , and R. L. Keiter, Inorganic Chemistry, Harper
Collins, New York, 4th edn, 1993, Table 8.1, p. 292.
In the drybox 135.0 mg (0.5 mmol) of Cp*Zr(BH4)3 and 256.0 mg
(0.5 mmol) of B(C6F5)3 were placed into a 50 mL flask. The flask
was degassed, ◦and about 10 mL of diethyl ether was transferred
into it at −78 C. The system was warmed to room temperature
and stirred overnight. After reducing the volume of the clear
solution to about 3 mL, it was transferred into a tube and layered
with hexane for crystallization. The title compound was obtained
as colorless crystals (190.0 mg, 60% yield). IR(KBr, cm−1): 2985w,
2923w, 2879vw, 2404vw, 1648m, 1602vw, 1520m, 1508m, 1466vs,
1381m, 1349vw, 1322vw, 1274w, 1197w, 1160vw, 1106m, 1078m,
1025w, 972s, 879vw, 834vw, 787w, 762w, 743vw, 727vw, 688w,
674w, 663w, 622vw, 600vw, 567vw, 554vw and 471vw. 11B NMR
(diethyl ether, d): 17.62 (s) and −25.87 ppm (d, JB–H 93). 11B NMR
1
(d8-toluene, d): 17.63 (s) and −25.92 ppm (d, JB–H 94). H NMR
(d8-toluene, d): 3.19 (q, JH–H 7.0, CH2), 1.81 (s, Cp*) and 0.98
(t, JH–H 7.0, CH3). 13C NMR (d8-toluene, d): 122.0 (CCH3), 65.55
(CH2), 14.61 (CH3) and 10.69 ppm (CCH3). Anal. Found: C, 47.09;
H, 4.75. Calc. for C50H61B2F15O7Zr2: C, 47.55; H, 4.87%.
22 R. W. Broach, I.-S. Chuang, T. J. Marks and J. M. Williams, Inorg.
Chem., 1983, 22, 1081.
Acknowledgements
23 W. J. Evans, M. A. Ansari and J. W. Ziller, Inorg. Chem., 1999, 38, 1160.
24 Z. A. Starikova, E. P. Turevskaya, N. I. Kozlova, N. Y. Turova, D. V.
Berdyev and A. I. Yanovsky, Polyhedron, 1999, 18, 941.
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D. A. Rice and Y. Zubavichus, Polyhedron, 1998, 17, 2301.
27 Z. Otwinowsky and W. Minor, DENZO-SMN, Methods Enzymol.,
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This work was supported by the National Science Council of the
ROC through Grant NSC 95–2113-M-259–011.
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3604 | Dalton Trans., 2007, 3599–3604
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The Royal Society of Chemistry 2007
©