Synthesis of neutral group 4 metal-carboryne complexes and their reactivity toward unsaturated molecules

Article abstract of DOI:10.1021/om400458r

A series of neutral group 4 metal-carboryne complexes of the general type [η²-R²C(NR¹)₂] ₂M(η²-C₂B₁₀H₁₀) were prepared via a salt metathesis reaction of [η²-R ²C(NR¹)₂]₂MCl₂ with Li₂C₂B₁₀H₁₀ (M = Ti, Zr, Hf; R ¹ = ⁱPr, cyclohexyl, R² = Me, ⁿBu, Ph) in high yields. Their structures were confirmed by single-crystal X-ray analyses. They reacted with ketone, nitrile, and heterocumulenes such as carbodiimide, isocyanate, thioisocyanate, carbon disulfide, and phenyl azide to give various monoinsertion products, in which the unsaturated bond inserted into one of the M-C_cage bonds, resulting in the formation of heterocycles. However, these metal-carboryne complexes did not show any reactivity toward pyridines, alkynes, and alkenes. The results clearly indicated that [η²-R²C(NR¹)₂] ₂M(η²-C₂B₁₀H₁₀) shared some common properties with Cp₂Zr(η²-C ₂B₁₀H₁₀) in reaction with heterocumulenes; on the other hand, they showed significant differences in reaction with pyridines, alkynes, and alkenes. These may be mainly ascribed to ligand steric effects.

Full text of DOI:10.1021/om400458r

Article
pubs.acs.org/Organometallics
Synthesis of Neutral Group 4 Metal−Carboryne Complexes and Their
Reactivity toward Unsaturated Molecules
Shikuo Ren,† Zaozao Qiu,‡ and Zuowei Xie*,†,‡,§
†Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China
‡Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 345 Lingling Road, Shanghai 200032, China
§State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin, China
S
* Supporting Information
ABSTRACT: A series of neutral group 4 metal−carboryne
complexes of the general type [η2-R2C(NR1)2]2M(η2-
C2B10H10) were prepared via a salt metathesis reaction of
[η2-R2C(NR1)2]2MCl2 with Li2C2B10H10 (M = Ti, Zr, Hf; R1 =
iPr, cyclohexyl, R2 = Me, nBu, Ph) in high yields. Their
structures were confirmed by single-crystal X-ray analyses.
They reacted with ketone, nitrile, and heterocumulenes such as carbodiimide, isocyanate, thioisocyanate, carbon disulfide, and
phenyl azide to give various monoinsertion products, in which the unsaturated bond inserted into one of the M−Ccage bonds,
resulting in the formation of heterocycles. However, these metal−carboryne complexes did not show any reactivity toward
pyridines, alkynes, and alkenes. The results clearly indicated that [η2-R2C(NR1)2]2M(η2-C2B10H10) shared some common
properties with Cp2Zr(η2-C2B10H10) in reaction with heterocumulenes; on the other hand, they showed significant differences in
reaction with pyridines, alkynes, and alkenes. These may be mainly ascribed to ligand steric effects.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
Carborynes (1,2-dehydro-o-carboranes) are reactive intermedi-
ates, which can undergo [4 + 2] addition, [2 + 2] addition, ene
reaction, and C−H bond insertion reactions.1 They can be
stabilized by transition metals to form metal−carboryne
complexes.2 The chemical properties of these complexes depend
upon the nature of the transition metals.3 For example, Ni-
carboryne can react with alkynes4 and alkenes5 to generate a
series of cycloaddition and coupling products in both
stoichimetric and catalytic manners, but does not show any
activity toward other polar unsaturated molecules. In contrast, in
situ generated zirconocene−carboryne Cp2Zr(η2-C2B10H10)
from Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 reacts readily with
alkynes,6 alkenes,7 pyridines,8 or polar unsaturated organic
substrates9 such as isonitrile, nitrile, and azide to give
monoinsertion products. However, many attempts to isolate
Cp2Zr(η2-C2B10H10) failed.
On the other hand, it is well documented that ligands play a
dominate role in both physical and chemical properties of a given
metal complex.10 We are interested in the ligand effects on the
chemical properties of Zr-carboryne complexes. Our previous
work focuses on the cyclopentadienyl ligand, and the proposed
intermediate Cp2Zr(η2-C2B10H10) is not isolable. To this end, we
have extended our research to structurally well-defined neutral
Zr-carboryne complexes and report herein the synthesis,
structure, and reactivity of a series of neutral group 4 metal−
carboryne complexes bearing amidinato ligands L, (η2-
C2B10H10)M(L)2. Similarities and differences between (η2-
C2B10H10)ZrCp2 and (η2-C2B10H10)Zr(L)2 in reactions with
unsaturated molecules are also discussed.
Synthesis. Salt metathesis between Li2C2B10H10 and metal
halides is a useful method for the preparation of metal−
carboryne complexes.11 The starting materials, diamidinato
group 4 metal dichloride complexes MCl2(L)2 (L = [η2-
R2C(NR1)2]), were prepared via reaction of MCl4 with 2 equiv
of lithium diamidinate that was generated in situ from the
corresponding carbodiimide and R2Li in ether (see Supporting
Information). Treatment of Li2C2B10H10 with 1 equiv of
MCl2(L)2 in toluene at 0 °C gave, after workup, group 4
metal−carboryne complexes (η2-C2B10H10)M(L)2 (M = Zr, R1 =
Cy, R2 = Me (2a);12 M = Zr, R1 = Cy, R2 = Ph (2b);12 M = Zr, R1
= Cy, R2 = nBu (2c); M = Ti, R1 = Cy, R2 = Ph (2d); M = Zr, R1 =
iPr, R2 = Me (2e); M = Zr, R1 = iPr, R2 = Ph (2f); M = Zr, R1 = iPr,
R2 = nBu (2g); M = Ti, R1 = iPr, R2 = nBu (2h); M = Hf, R1 = iPr,
R2 = nBu (2i)) as yellow or colorless crystals in 60−72% isolated
yields using the method developed in our laboratory (Scheme
1).12
Complexes 2a−i are very sensitive to moisture and air, though
very thermally stable. No decomposition is observed in refluxing
toluene for several days. They are soluble in toluene, pyridine,
and THF, but insoluble in diethyl ether and hexane.
Complexes 2a−i were fully characterized by various
spectroscopic techniques and elemental analyses. The 1H
NMR spectra, which displayed the signals of amidinato ligands
and broad peaks attributable to cage B−H, did not give much
Received: May 24, 2013
Published: July 25, 2013
© 2013 American Chemical Society
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Scheme 1. Preparation of Group 4 Metal−Carboryne
Complexes
Scheme 2. Reaction of Zr-Carboryne Complexes with Ketone
and Nitrile
Scheme 3. Reaction of Group 4 Metal−Carboryne Complexes
with Heterocumulenes
information on the solution structures. Their 13C NMR spectra
showed one peak in the region 101−116 ppm assignable to the
cage carbons and one resonance in the region 177−182 ppm
attributable to the quaternary carbon of the amidinato ligands, in
addition to the other alkyl or aryl resonances. Their 11B NMR
spectra displayed a 4:4:2 pattern spanning a range from −3.0 to
−16.0 ppm. The molecular structures of 2e, 2g, 2h, and 2i were
further confirmed by single-crystal X-ray analyses (vide infra).
Reactivity. The reactivity of the above group 4 metal−
carboryne complexes toward various kinds of unsaturated
molecules was examined. Complex 2b reacted with 1 equiv of
diphenyl ketone or cyclohexanone in toluene at room temper-
ature to give the monoinsertion products, five-membered
heterocycle [η2-CyNC(Ph)NCy]2Zr[σ:σ-{OC(Ph)2C2B10H10}]
(3b) or [η2-CyNC(Ph)NCy]2Zr[σ:σ-{OC[-(CH2)5-]-
C2B10H10}] (4b) in >87% isolated yield. Reaction of 2a with 1
equiv of PhCN in toluene at room temperature afforded [η2-
CyNC(Me)NCy]2Zr[σ:σ-{[NC(Ph)C2B10H10}] (5a) in 76%
yield (Scheme 2). They were inert toward an excess amount of
substrates, and no multi-insertion products were observed.
Reaction of 2b or 2i with 1 equiv of carbodiimide iPrNC
NPri in toluene at room temperature generated the mono-
insertion products [η2-CyNC(Ph)NCy]2M[σ:σ-{[iPrNC(
NPri)C2B10H10}] (M = Zr (6a), Hf (6i)) in >90% yields
(Scheme 3). Interaction of 2a with 1 equiv of PhNCO in toluene
at room temperature gave the CN insertion rather than the
CO insertion product, [η2-CyNC(Me)NCy]2Zr[σ:σ-
{[PhNC(O)C2B10H10}] (7a), in 93% yield. This is different
from the literature reports, in which the CO inserts into M−
C/M−N bonds.13 It was noted that 7a did not react further with
Reaction of 2i with an excessive amount of CS2 in refluxing
toluene in a closed vessel gave the monoinsertion product
[η2-iPrNC(Bun)NPri]2Hf[σ:σ-{[SC(S)C2B10H10}] (9i) in
60% yield, whereas no reaction was observed at room
temperature according to the 11B NMR spectrum (Scheme 3).
Reaction of 2c, 2f, or 2h with excessive PhN3 afforded the
monoinsertion products [η2-CyNC(nBu)NCy]2Zr[η2:σ-1-
PhNN-N-1,2-C2B10H10] (10c), [η2-iPrNC(Ph)NPri]2Zr-
[η2:σ-1-PhNN-N-1,2-C2B10H10] (10f), or [η2-iPrNC(nBu)-
n
PhNCO. Treatment of 2b or 2i with 1 equiv of BuNCS in
toluene at room temperature yielded again the CN insertion
products [η2-CyNC(Ph)NCy]2Zr[σ:σ-{[nBuNC(S)-
C2B10H10}] (8b) and [η2‑iPrNC(nBu)NiPr]2Hf[σ:σ-{[nBuNC-
(S)C2B10H10}] (8i) in ∼80% yields. These results may be
ascribed to the stability of the insertion products since the CO
or CS insertion species bearing an exocyclic imino group are
less stable than the CN insertion ones 7a, 8b, and 8i.
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for Metal−Carboryne Complexes 2
compd (M)
av M−Ccage
Ccage−Ccage
av M−N
Ccage−M−Ccage
av N−M−N
2e (Zr)
2g (Zr)
2h (Ti)
2i (Hf)
2.324(3)
2.271(2)
2.137(4)
2.258(2)
1.668(6)
1.685(4)
1.625(9)
1.696(6)
2.233(2)
2.201(1)
2.067(2)
2.187(2)
42.1(1)
43.6(1)
44.7(2)
44.1(2)
59.8(1)
60.3(1)
63.3(1)
60.7(1)
Figure 1. Molecular structures of (a) 2e and (b) 2h.
NPri]2Ti[η2:σ-1-PhNN-N-1,2-C2B10H10] (10h) in ∼80%
yields, which is similar to that of Cp2Zr(μ-Cl)(μ-C2B10H10)Li-
(OEt2)2.9
The insertion products 3−10 are moisture sensitive. They are
soluble in toluene, pyridine, and THF, but insoluble in diethyl
ether and hexane.
ligands, as π-coordination of alkenes/alkynes to group 4 metals
requires a larger vacant side.
Complexes 3−10 were fully characterized by 1H, 13C, and 11B
NMR and IR spectroscopy as well as elemental analyses. The 11B
NMR spectra showed different patterns from their parent metal−
carboryne complexes due to the changes in the molecular
symmetry of the insertion products. The characteristic cage
carbon atoms were observed in a range from 73.2 to 111.4 ppm as
two peaks, which were also very different from their parent
carboryne complexes.
The aforementioned results clearly show that the polar
unsaturated molecules can insert into the group 4 metal−
carbon(cage) bond in 2 to form the monoinsertion products
regardless of the nature of group 4 metals. No double insertion
products are observed even under forced reaction conditions in
the presence of an excess amount of substrates. Significantly
different from in situ generated Cp2Zr(η2-C2B10H10), these
amidinato-ligated neutral group 4 metal−carboryne complexes
show no reactivity toward internal alkynes, alkenes, and pyridine
derivatives even under forced reaction conditions, suggesting
that co-ligands play a crucial role in the chemical properties of
metal−carboryne complexes.
A question arises whether electronic or steric factors dominate
the differences in the above reactions. It is documented that Cp is
a 6e− donor, whereas amidinato anions are 4e− donors. The latter
ligands are expected to have polarized M−N bonds, leading to
more electrophilic metal centers. However, their group 4 metal
complexes [R1NC(R2)NR1]2MCl2 and [R1NC(R2)NR1]2MMe2
(M = Ti, Zr, and Hf; R1, R2 = alkyls) show lower catalytic
activities than the metallocene analogues Cp2MCl2/Cp2MMe2 in
ethylene polymerization. This unexpected result has been
ascribed to the larger steric effect of bis(amidinate) ligands
than that of biscyclopentadienyls.14 In this regard, the differences
in reactivities between (η2-C2B10H10)ZrCp2 and (η2-C2B10H10)-
Zr[R1NC(R2)NR1]2 may be best ascribed to steric effects of co-
Structure. Complexes 2e, 2g, 2h, and 2i were further
confirmed by single-crystal X-ray analyses. Their key structural
parameters are compiled in Table 1. They share a similar core
structure in which the group 4 metal atom is η2-bound to two
amidinato ligands and one carboryne moiety. An additional THF
coordination is observed in the solid-state structure of 2e. The
representative structures of 2e and 2h are shown in Figure 1. As
the recrystallization conditions for all complexes are identical, the
coordination of THF to the Zr atom in 2e might be simply
ascribed to the crystal packing requirements. On the other hand,
the structure of 2e could be viewed as a model complex of the
reaction intermediates for the insertion of unsaturated molecules
into the M−C bond in M-carboryne complexes.
The M−C(cage)/C(cage)−C(cage)/M−N distances and
C(cage)−M−C(cage)/N−M−N angles found in 2 (Table 1)
are similar to each other if the differences in ionic radii of group 4
metals are taken into consideration. These measured values are
very close to those reported for Zr-carboryne complexes.12
The molecular structures of monoinsertion products 3−9
contain a common structural motif of a five-membered
heterocycle and adopt a similar geometry, in which the group 4
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Figure 2. continued
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Figure 2. Molecular structures of (a) 3b, (b) 4b, (c) 5a, (d) 6b, (e) 6i, (f) 7a, (g) 8b, (h) 9i, and (i) 10f.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Monoinsertion Products
compd (M)
M−C(2)
C(1)−C(2)
C(1)−X(5)
Y(4)−X(5)
M−Y(4)
av M−Namidinato
C(2)−M−Y(4)
av Namidinato−M−Namidinato
3b (Zr)
4b (Zr)
5a (Zr)
6b (Zr)
6i (Hf)
7a (Zr)
8b (Zr)
9i (Hf)
10f (Zr)
2.371(6)
2.402(3)
2.413(4)
2.396(4)
2.349(4)
2.389(9)
2.383(7)
2.340(5)
2.506(3)
1.710(7)
1.711(5)
1.679(5)
1.695(6)
1.703(6)
1.658(12)
1.680(10)
1.669(6)
1.728(5)
1.595(7)
1.556(5)
1.508(6)
1.519(7)
1.534(6)
1.509(11)
1.522(10)
1.514(7)
1.449(4)
1.413(6)
1.421(4)
1.383(5)
1.389(6)
1.387(6)
1.380(11)
1.330(9)
1.725(6)
1.285(4)
1.954(3)
1.931(2)
2.089(3)
2.077(4)
2.099(4)
2.208(7)
2.383(7)
2.572(1)
2.137 (3)
2.223(5)
2.223(3)
2.220(5)
2.241(5)
2.208(4)
2.207(7)
2.207(7)
2.168(4)
2.218(3)
73.7(2)
74.1(1)
74.3(1)
72.7(2)
73.9(2)
74.3(3)
74.3(2)
77.4(1)
66.2(1)
60.0(2)
60.0(1)
59.8(1)
59.5(2)
60.5(1)
60.4(3)
60.9(3)
61.3(2)
60.3(1)
metal atom is η2-bound to two amidinato ligands and σ-bound to
one cage carbon atom and one heteroatom in a propeller-like
geometry, as shown in Figure 2. For complex 10f, an additional
intramolecular coordination of an exo-nitrogen atom to the Zr
atom at a distance of 2.330(3) Å is observed, which is similar to
that found in Cp2Zr[η2:σ-(PhNNN)(C2B10H10)].9 This extra
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CH2), 0.80 (t, J = 7.2 Hz, 6H, CH3). 13C{1H} NMR (benzene-d6): δ
182.0 (NCN), 104.2 (cage C), 57.8 (NCH), 35.3, 35.0, 29.4, 26.3, 26.2,
25.4, 23.2, 13.6 (CH2 and CH3). 11B{1H} NMR (benzene-d6): δ −0.1
(4B), −6.5 (4B), −14.2 (2B). IR (KBr, cm−1): ν 2564 (BH). Anal. Calcd
for C36H72B10N4Zr (2c): C, 56.87; H, 9.54; N, 7.37. Found: C, 56.74; H,
9.26; N, 7.28.
coordination bond leads to the elongated bond distances around
the Zr atom.
Table 2 lists the key structural parameters of 3−10. It is noted
that the five atoms of the heterocycle in these insertion products
are almost coplanar, with a sum of the five interior angles of ca.
537°. They have very comparable structural parameters around
the group 4 metals. The observed M−C(cage) and cage C−C
distances are longer than the corresponding values of their parent
complexes, but are similar to those found in group 4 metal−
carboranyl complexes.12,15
Preparation of [η2-CyNC(Ph)NCy]2Ti(η2-C2B10H10) (2d). This
complex was prepared as purple crystals from Li2C2B10H10 [prepared
in situ from o-C2B10H12 (0.72 g, 5.00 mmol) and nBuLi (6.3 mL, 10.00
mmol, 1.6 M in hexane)] and [η2-CyNC(Ph)NCy]2TiCl2 (3.43 g, 5.00
mmol) in toluene (40 mL) using the same procedure reported for 2c:
1
yield 2.73 g (72%). H NMR (benzene-d6): δ 7.28 (m, 2H), 7.08 (m,
8H), 3.48 (m, 4H, NCH), 2.04 (m, 4H), 1.90 (m, 4H), 1.59 (m, 16H),
1.37 (m, 4H), 0.99 (m, 12H) (Cy). 13C{1H} NMR (benzene-d6): δ
177.6 (NCN), 132.0, 129.9, 128.9, 127.3, 127.0 (phenyl C), 107.0 (cage
C), 61.4 (NCH), 34.8, 34.7, 26.2, 25.5 (CH2). 11B{1H} NMR (benzene-
d6): δ −2.4 (4B), −7.2 (4B), −14.9 (2B). IR (KBr, cm−1): ν 2568 (BH).
Anal. Calcd for C40H64B10N4Ti (2d): C, 63.47; H, 8.52; N, 7.40. Found:
C, 63.50; H, 8.60; N, 7.19.
CONCLUSION
■
A series of neutral group 4 metal−carboryne complexes were
synthesized via a salt metathesis reaction of (amidinato)2MCl2
with Li2C2B10H10. Single-crystal X-ray analyses show that they
have similar structures to η2-carboryne coordination regardless of
the metal size. They reacted with polar unsaturated molecules
such as ketone, nitrile, carbodiimide, isocyanate, thioisocyanate,
carbon disulfide, and azide to give monoinsertion products. No
double-insertion products were observed. However, they did not
show any activities toward pyridines, alkynes, and alkenes. These
results indicated that complexes 2 exhibited a similar reactivity
pattern to that of Cp2Zr(μ-Cl)(μ-C2B10H10)Li(OEt2)2 in
reaction with polar unsaturated molecules;9 on the other hand,
2 demonstrated significantly different properties from Cp2Zr(μ-
Cl)(μ-C2B10H10)Li(OEt2)2 in reaction with pyridines, alkenes,
and alkynes.6−8 These differences may be best ascribed to steric
effects imposed by amidonato ligands.
Preparation of [η2-iPrNC(Me)NPri]2Zr(η2-C2B10H10)(THF) (2e). This
complex was prepared as yellow crystals from Li2C2B10H10 [prepared in
n
situ from o-C2B10H12 (0.72 g, 5.00 mmol) and BuLi (6.3 mL, 10.00
mmol, 1.6 M in hexane)] and [η2-iPrNC(Me)NPri]2ZrCl2 (2.22 g, 5.00
mmol) in toluene (30 mL) using the same procedure reported for 2c:
yield 2.06 g (70%). 1H NMR (benzene-d6): δ 3.68 (m, 4H, THF), 3.49
(m, 4H, NCH), 1.46 (s, 6H, CH3), 1.37 (m, 4H, THF), 1.13 (d, J = 6.3
Hz, 12H, CH3), 1.00 (d, J = 6.6 Hz, 12H, CH3). 13C{1H} NMR
(benzene-d6): δ 177.3 (NCN), 104.2 (cage C), 71.6 (THF), 48.9
(NCH), 25.1, 24.5, 24.2, 12.9 (iPr + THF). 11B{1H} NMR (benzene-
d6): δ −1.4 (4B), −6.9 (4B), −13.8 (2B). IR (KBr, cm−1): ν 2556 (BH).
Anal. Calcd for C18H52B10N4Zr (2e − THF): C, 41.91; H, 8.60; N,
10.86. Found: C, 42.21; H, 8.82; N, 10.67.
Preparation of [η2-iPrNC(Ph)NPri]2Zr(η2-C2B10H10)(THF) (2f). This
complex was prepared as yellow crystals from Li2C2B10H10 [prepared in
EXPERIMENTAL SECTION
■
n
General Procedures. nBuLi was added under an atmosphere of dry
nitrogen with the rigid exclusion of air and moisture using standard
Schlenk techniques. Other experiments were performed in a glovebox.
All organic solvents were freshly distilled from sodium benzophenone
ketyl immediately prior to use. 1H NMR spectra were recorded on either
a Bruker DPX 300 spectrometer at 300 MHz or a Bruker DPX 400
spectrometer at 400 MHz. 13C{1H} NMR spectra were recorded on
either a Bruker DPX 300 spectrometer at 75 MHz or a Bruker DPX 400
spectrometer at 100 MHz. 11B{1H} NMR spectra were recorded on
either a Bruker DPX 300 spectrometer at 96 MHz or a Varian Inova 400
spectrometer at 128 MHz. All chemical shifts were reported in δ units
with reference to the residual protons and carbons of the deuterated
solvents for proton and carbon chemical shifts and to external BF3·OEt2
(0.00 ppm) for boron chemical shifts. Infrared spectra were obtained
from KBr pellets prepared in the glovebox on a Perkin-Elmer 1600
Fourier transform spectrometer. Elemental analyses were performed by
the Analytical Laboratory of the Shanghai Institute of Organic
Chemistry, CAS, China. Complexes 2a,12 2b,12 and [η2-R1NC(R2)-
NR1]2MCl2 were prepared according to literature methods16,17 or
modified methods. All other chemicals were purchased from either
Sigma-Aldrich or Acros Chemical Co. and used as received unless
otherwise specified.
situ from o-C2B10H12 (0.72 g, 5.00 mmol) and BuLi (6.3 mL, 10.00
mmol, 1.6 M in hexane)] and [η2-iPrNC(Ph)NPri]2ZrCl2 (2.85 g, 5.00
mmol) in toluene (30 mL) using the same procedure reported for 2c:
1
yield 3.24 g (91%). H NMR (benzene-d6): δ 7.29 (m, 2H), 7.17 (m,
8H) (phenyl H), 4.06 (m, 4H, THF), 3.56 (m, 4H, NCH), 1.54 (m, 4H,
THF), 1.23 (d, J = 6.6 Hz, 12H, CH3), 1.22 (d, J = 6.3 Hz, 12H, CH3).
13C{1H} NMR (benzene-d6): δ 178.7 (NCN), 133.0, 129.3, 129.1,
128.7, 126.2, 125.8 (phenyl C), 104.6 (cage C), 72.7 (THF), 50.5
(NCH), 25.2, 24.8 (iPr + THF). 11B{1H} NMR (benzene-d6): δ −0.7
(4B), −6.5 (4B), −13.9 (2B). IR (KBr, cm−1): ν 2567 (BH). Anal. Calcd
for C32H56B10N4OZr (2f): C, 53.97; H, 7.93; N, 7.87. Found: C, 53.66;
H, 7.93; N, 7.62.
Preparation of [η2-iPrNC(Bun)NPri]2Zr(η2-C2B10H10) (2g). This
complex was prepared as light yellow crystals from Li2C2B10H10
n
[prepared in situ from o-C2B10H12 (0.72 g, 5.00 mmol) and BuLi
( 6 . 3 m L , 1 0 . 0 0 m m o l , 1 . 6
M i n h e x a n e ) ] a n d
[η2‑iPrNC(Bun)NPri]2ZrCl2 (2.64 g, 5.00 mmol) in toluene (30 mL)
using the same procedure reported for 2c: yield 2.79 g (93%). 1H NMR
(benzene-d6): 3.47 (m, 4H, NCH), 2.01 (t, J = 8.1 Hz, 4H, CH2), 1.32
(m, 4H, CH2), 1.19 (d, J = 6.6 Hz, 12H, CH3), 1.13 (d, J = 6.3 Hz, 12H,
CH3), 1.11 (m, 4H, CH2), 0.77 (t, J = 7.2 Hz, 6H, CH3). 13C{1H} NMR
(benzene-d6): δ 181.7 (NCN), 103.8 (cage C), 48.7 (NCH), 29.1, 26.2,
25.2, 24.9, 23.3, 13.6 (CH2 and CH3). 11B{1H} NMR (benzene-d6): δ
−0.4 (4B), −6.8 (4B), −14.4 (2B). IR (KBr, cm−1): ν 2561 (BH). Anal.
Calcd for C24H56B10N4Zr (2g): C, 48.04; H, 9.41; N, 9.34. Found: C,
47.73; H, 9.00; N, 9.28.
Preparation of [η2-CyNC(Bun)NCy]2Zr(η2-C2B10H10) (2c). To a
stirring solution of o-C2B10H12 (0.72 g, 5.00 mmol) in diethyl ether
(30 mL) was slowly added nBuLi (6.3 mL, 10.00 mmol, 1.6 M in hexane)
at 0 °C, and the mixture was stirred at room temperature for 1 h. After
removal of the solvent under vacuum, the residue was suspended in
toluene (30 mL), to which was slowly added a toluene solution (20 mL)
of [η2-CyNC(Bun)NCy]2ZrCl2 (3.45 g, 5.00 mmol) at 0 °C. The
reaction mixture was then stirred at room temperature for 24 h. After
filtration, the precipitate was washed with hot toluene (3 × 10 mL).
Removal of the solvent from the combined toluene solutions gave a
crude product. Recrystallization from THF/hexane (30 mL, 1/5 in v/v)
Preparation of [η2-iPrNC(Bun)NPri]2Ti(η2-C2B10H10) (2h). This
complex was prepared as purple crystals from Li2C2B10H10 [prepared
in situ from o-C2B10H12 (0.72 g, 5.00 mmol) and nBuLi (6.3 mL, 10.00
mmol, 1.6 M in hexane)] and [η2-iPrNC(Bun)NPri]2TiCl2 (2.43 g, 5.00
mmol) in toluene (30 mL) using the same procedure reported for 2c:
yield 2.64 g (95%). 1H NMR (benzene-d6): δ 3.77 (m, 4H, NCH), 2.09
(m, 4H, CH2), 1.39 (m, 4H, CH2), 1.20 (d, J = 6.6 Hz, 12H, CH3), 1.16
(d, J = 6.6 Hz, 12H, CH3), 1.13 (m, 4H, CH2), 0.79 (t, J = 7.2 Hz, 6H,
CH3). 13C{1H} NMR (benzene-d6): δ 179.1 (NCN), 105.9 (cage C),
51.2 (NCH), 28.7, 27.4, 24.8, 24.5, 23.4, 13.6 (CH2 and CH3). 11B{1H}
1
at room temperature afforded 2c as yellow crystals (3.31 g, 87%). H
NMR (benzene-d6): δ 3.27 (m, 4H, NCH), 2.18 (m, 4H, CH2), 1.81 (m,
24H, CH2), 1.53 (m, 4H, CH2), 1.45 (m, 4H, CH2), 1.26 (m, 16H,
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NMR (benzene-d6): δ −2.7 (4B), −7.5 (4B), −15.2 (2B). IR (KBr,
cm−1): ν 2559 (BH). Anal. Calcd for C24H56B10N4Ti (2h): C, 51.78; H,
10.14; N, 10.06. Found: C, 52.24; H, 10.34; N, 10.06.
3H, CH3), 1.09 (m, 4H, CH2), 0.96 (m, 6H, CH2). 13C{1H} NMR
(pyridine-d5): δ 181.8, 180.0, 178.9 (NCN), 129.4, 129.3, 128.8, 128.5,
128.3, 126.5, 126.2, 125.9, 125.7, 122.9, 122.7, (phenyl C), 99.8, 80.7
(cage C), 59.1, 58.0, 57.3, (NCH), 46.3, 44.6, 36.7, 35.0, 34.8, 34.7, 34.4,
25.9, 25.3, 25.1, 24.9, 24.8, 24.3, 22.6, 21.6 (CH2 and CH3). 11B{1H}
NMR (pyridine-d5): δ −2.1 (3B), −6.7 (7B). IR (KBr, cm−1): ν 2582
(BH). Anal. Calcd for C49H82B10N6O0.5Zr (6b + 0.5 THF): C, 61.14; H,
8.59; N, 8.73. Found: C, 61.28; H, 8.92; N, 8.38.
Preparation of [η2-iPrNC(Bun)NPri]2Hf(η2-C2B10H10) (2i). This
complex was prepared as colorless crystals from Li2C2B10H10 [prepared
in situ from o-C2B10H12 (0.72 g, 5.00 mmol) and nBuLi (6.3 mL, 10.00
mmol, 1.6 M in hexane)] and [η2-iPrNC(Bun)NPri]2HfCl2 (3.08 g, 5.00
mmol) in toluene (40 mL) using the same procedure reported for 2c:
yield 2.85 g (83%). 1H NMR (benzene-d6): 3.67 (m, 4H, NCH), 2.05 (t,
J = 7.8 Hz, 4H, CH2), 1.34 (m, 4H, CH2), 1.20 (d, J = 6.3 Hz, 12H, CH3),
1.16 (d, J = 6.3 Hz, 12H, CH3), 1.11 (m, 4H, CH2), 0.78 (t, J = 7.2 Hz,
6H, CH3). 13C{1H} NMR (benzene-d6): δ 181.4 (NCN), 116.0 (cage
C), 48.5 (NCH), 29.1, 26.6, 25.1, 24.8, 23.3, 13.6 (CH2 and CH3).
11B{1H} NMR (benzene-d6): δ −0.8 (2B), −0.7 (2B), −7.5 (4B), −15.2
Preparation of [η2-iPrNC(nBu)NPri]2Hf[σ:σ:σ-{[iPrNC(NPri)-
C2B10H10}] (6i). This complex was prepared as a colorless solid from
2i (206 mg, 0.3 mmol) and N,N′-diisopropylcarbodiimide (76 mg, 0.6
mmol) in toluene (20 mL) using the same procedure reported for 3b:
yield 223 mg (91%). 1H NMR (benzene-d6): δ 4.91 (m, 1H), 4.39 (m,
1H), 4.22 (m, 1H) 3.69 (m, 2H), 3.54 (m, 1H) (NCH), 2.09 (m, 4H,
CH2), 1.83 (d, J = 8.4 Hz, 3H, CH3), 1.58 (d, J = 8.4 Hz, 6H, CH3), 1.40
(d, J = 8.4 Hz, 3H, CH3), 1.35 (d, J = 8.4 Hz, 3H, CH3), 1.31 (m, 8H,
CH2), 1.25 (m, 9H) (CH3), 1.17 (d, J = 8.4 Hz, 3H, CH3), 1.06 (d, J =
8.4 Hz, 3H, CH3), 0.90 (d, J = 8.4 Hz, 3H, CH3), 0.86 (d, J = 8.4 Hz, 3H,
CH3), 0.83 (m, 6H, CH3). 13C{1H} NMR (benzene-d6): δ 183.8, 181.6,
151.6 (NCN), 106.7, 81.6 (cage C), 49.0, 48.2, 47.7, 47.3, 46.7 (NCH),
29.2, 29.0, 28.7, 27.2, 27.1, 25.9, 25.4, 25.3, 25.0, 24.7, 24.6, 24.3, 23.6,
23.5, 23.4, 21.9, 13.6 (CH2 and CH3). 11B{1H} NMR (benzene-d6): δ
−2.09 (3B), −7.0 (3B), −10.0 (3B), −11.5 (1B). IR (KBr, cm−1): ν
2580, 2550 (BH). Anal. Calcd for C31H70B10HfN6 (6i): C, 45.77; H,
8.67; N, 10.33. Found: C, 45.77; H, 8.57; N, 10.16.
(2B). IR (KBr, cm−1): ν 2559 (BH). Anal. Calcd for C24H56B10N4Hf
(2i): C, 41.94; H, 8.21; N, 8.15. Found: C, 41.87; H, 8.30; N, 7.98.
Preparation of [η2-CyNC(Ph)NCy]2Zr[σ:σ:σ-{(Ph)2C(O)C2B10H10}]
(3b). To a stirring suspension of 2b (174 mg, 0.2 mmol) in toluene
(10 mL) at room temperature was added benzophenone (36 mg, 0.2
mmol), and the mixture was stirred at room temperature for 48 h. A clear
colorless solution was formed. After concentration of the solution to ca.
3 mL, the resulting solution stood at room temperature overnight to
yield 3b as colorless crystals (200 mg, 95%). 1H NMR (pyridine-d5): δ
8.31 (m, 4H), 7.65 (m, 6H), 7.55 (m, 2H), 7.49 (m, 4H), 7.42 (m, 2H),
7.31 (m, 2H) (phenyl H), 2.13 (m, 3H), 1.97 (m, 6H), 1.85 (m, 3H),
1.61 (m, 12H), 1.38 (m, 4H), 1.15 (m, 6H), 1.05 (m, 6H), 0.96 (m, 4H)
(Cy). 13C{1H} NMR (pyridine-d5): δ 182.5 (NCN), 129.3, 128.7, 128.3,
128.0, 127.2, 126.9, 126.8, 126.6, 125.9, 125.1, 122.3 (phenyl C), 107.7,
100.3 (cage C), 91.6 (C-O), 57.8 (NCH), 34.9, 25.1, 25.0, 24.8 (CH2).
11B{1H} NMR (pyridine-d5): δ −2.1 (4B), −7.5 (6B). IR (KBr, cm−1): ν
Preparation of [η2-CyNC(Me)NCy]2Zr[σ:σ:σ-{[PhN(CO)C2B10H10}]
(7a). This complex was prepared as colorless crystals from 2a (135
mg, 0.2 mmol) and PhNCO (24 mg, 0.2 mmol) in toluene (10 mL)
1
using the same procedure reported for 3b: yield 148 mg (93%). H
NMR (pyridine-d5): δ 7.43 (m, 2H), 7.33 (m, 2H), 7.25 (m, 1H)
(phenyl H), 4.10 (m, 2H, NCH), 3.59 (m, 2H, THF), 2.91 (m, 2H,
NCH), 2.30 (s, 3H), 2.27 (s, 3H) (CH3), 1.99 (m, 2H), 1.76 (m, 18H),
1.59 (m, 4H), 1.43 (m, 2H), 1.27 (m, 14H), 0.92 (m, 2H) (CH2+THF).
13C{1H} NMR (pyridine-d5): δ 183.5, 180.6, 171.8 (NCN and CO),
143.7, 128.0, 127.4, 125.7 (phenyl C), 88.6, 81.6 (cage C), 57.9, 56.0
(NCH), 35.5, 34.0, 32.8, 31.0, 25.7, 24.9, 15.1, 13.5 (CH2 and CH3).
11B{1H} NMR (pyridine-d5): δ −2.7 (4B), −6.9 (6B). IR (KBr, cm−1): ν
2563 (BH). Anal. Calcd for C61H90B10N4O3Zr (3b + 2THF): C, 64.79;
H, 7.59; N, 5.70. Found: C, 64.95; H, 7.12; N, 5.69.
Preparation of [η2-CyNC(Ph)NCy]2Zr[σ:σ:σ-{[-(CH2)5-]C(O)-
C2B10H10}] (4b). To a stirring suspension of 2b (174 mg, 0.20 mmol)
in toluene (10 mL) at room temperature was added cyclohexanone (20
mg, 0.20 mmol), and the mixture was stirred at room temperature for 48
h. A clear colorless solution was formed. After concentration of the
solution to ca. 3 mL, the resulting solution stood at room temperature
2596, 2564 (BH). Anal. Calcd for C37H65B10N5OZr (7a): C, 55.81; H,
8.23; N, 8.80. Found: C, 55.79; H, 8.29; N, 8.43.
1
overnight to yield 4b as colorless crystals (156 mg, 87%). H NMR
(pyridine-d5): δ 7.56 (m, 4H), 7.50 (m, 4H), 7.42 (m, 2H) (phenyl H),
3.36 (m, 2H, NCH), 2.99 (m, 2H, NCH), 2.42 (m, 2H, CH2), 1.99 (m,
4H, CH2), 1.72 (m, 24H, CH2), 1.46 (m, 6H, CH2), 1.06 (m, 14H,
CH2). 13C{1H} NMR (pyridine-d5): δ 181.2 (NCN), 132.1, 129.2,
128.3, 128.0, 127.4, 126.9, 125.9, 122.3 (phenyl C), 106.1, 100.7 (cage
C), 84.9 (C-O), 57.1 (NCH), 39.5, 34.9, 34.4, 25.3, 25.0, 22.6, 13.1
(CH2). 11B{1H} NMR (pyridine-d5): δ −5.5 (6B), −10.0 (4B). IR (KBr,
cm−1): ν 2570 (BH). Anal. Calcd for C46H74B10N4OZr (4b): C, 61.50;
H, 8.30; N, 6.24. Found: C, 61.38; H, 8.36; N, 6.03.
Preparation of [η2-CyNC(Ph)NCy]2Zr[σ:σ:σ-{[nBuNC(S)C2B10H10}]
(8b). This complex was prepared as yellow crystals from 2b (174 mg, 0.2
mmol) and nBuNCS (46 mg, 0.4 mmol) in toluene (10 mL) using the
same procedure reported for 3b. Recrystallization from a mixed solvent
of hexane and ether (1/2 in v/v) afforded 8b (144 mg, 79%). 1H NMR
(benzene-d6): δ 7.77 (d, J = 7.5 Hz, 1H), 7.30 (d, J = 7.5 Hz, 1H), 7.23
(m, 1H), 7.12 (m, 7H) (phenyl H), 4.83 (m, 1H), 4.24 (m, 1H), 4.01
(m, 1H), 3.30 (m, 1H) (NCH), 2.91 (m, 1H), 2.64 (m, 1H), 2.06 (m,
2H), 1.86 (m, 8H), 1.69 (m, 18H), 1.44 (m, 6H) (CH2), 1.04 (t, J = 7.2
Hz, 3H, CH3), 1.01 (m, 4H), 0.90 (m, 6H) (CH2). 13C{1H} NMR
(benzene-d6): δ 204.4, 186.1, 180.2 (NCN and CS), 133.0, 130.9, 130.2,
130.1, 129.8, 128.9, 126.5, 126.4, 126.3 (phenyl C), 95.4, 92.3 (cage C),
60.3, 59.1, 58.2, 58.1, 50.4 (NCH and NCH2), 44.3, 38.0, 36.9, 36.1,
35.8, 35.4, 35.3, 34.1, 33.8, 31.7, 31.5, 26.7, 26.5, 26.2, 25.8, 25.5, 25.3,
25.2, 21.4, 19.6, 14.5, 13.1 (CH2 and CH3). 11B{1H} NMR (benzene-
d6): δ −2.5 (4B), −6.8 (6B). IR (KBr, cm−1): ν 2563 (BH). Anal. Calcd
for C45H73B10N5SZr (8b): C, 59.04; H, 8.04; N, 7.65. Found: C, 59.07;
H, 7.98; N, 7.82.
Preparation of [η2-CyNC(Me)NCy]2Zr[σ:σ:σ-{[NC(Ph)C2B10H10}]
(5a). This complex was prepared as yellow crystals from 2a (270 mg, 0.4
mmol) and benzonitrile (51 mg, 0.5 mmol) in toluene (20 mL) using
1
the same procedure reported for 3b: yield 237 mg (76%). H NMR
(benzene-d6): δ 8.21 (m, 2H), 7.02 (m, 3H) (phenyl H), 3.31 (m, 4H,
NCH), 1.87 (m, 8H, CH2), 1.69 (s, 6H, CH3), 1.65 (m, 8H), 1.55 (m,
12H), 1.29 (m, 8H), 1.12 (m, 4H) (CH2). 13C{1H} NMR (benzene-d6):
δ 179.4 (NCN), 172.3 (CN), 135.4, 131.0, 129.8, 128.1 (phenyl C),
104.1, 99.2 (cage C), 56.9 (NCH), 35.1, 26.0, 13.8 (CH2). 11B{1H}
NMR (benzene-d6): δ −1.5 (3B), −5.0 (3B), −8.9 (4B). IR (KBr,
cm−1): ν 2585 (BH). Anal. Calcd for C37H65B10N5Zr (5): C, 57.03; H,
8.41; N, 8.99. Found: C, 56.91; H, 8.20; N, 9.01.
Preparation of [η2-iPrNC(Bun)NPri]2Hf[σ:σ:σ-{[nBuNC(S)-
C2B10H10}] (8i). This complex was prepared as a light yellow solid
from 2i (206 mg, 0.3 mmol) and nBuNCS (69 mg, 0.6 mmol) in toluene
(10 mL) using the same procedure reported for 3b: yield 209 mg (87%).
1H NMR (benzene-d6): δ 4.65 (m, 2H, NCH), 3.58 (m, 4H, NCH
+CH2), 2.10 (q, J = 7.2, 4H, CH2), 1.61 (m, 2H, CH), 1.41 (m, 6H), 1.18
(m, 19H), 0.98 (m, 6H), 0.87 (m, 12H) (CH2 and CH3). 13C{1H} NMR
(benzene-d6): δ 205.3, 187.8, 183.0 (NCN and CS), 102.7, 91.5 (cage
C), 51.0, 49.5, 48.2, 47.9, 47.6 (NCH and NCH2), 30.6, 29.7, 29.5, 28.2,
27.2, 26.8, 26.6, 25.1, 25.0, 24.5, 24.3, 24.0, 23.6, 23.4, 23.3, 21.2, 14.3,
13.6, 13.5 (CH2 and CH3). 11B{1H} NMR (benzene-d6): δ −3.3 (3B),
−7.0 (4B), −8.7 (2B), −12.8 (1B). IR (KBr, cm−1): ν 2594, 2564 (BH).
Preparation of [η2-CyNC(Ph)NCy]2Zr[σ:σ:σ-{[iPrNC(NiPr)-
C2B10H10}] (6b). This complex was prepared as colorless crystals from
2b (174 mg, 0.2 mmol) and N,N′-diisopropylcarbodiimide (25 mg, 0.2
mmol) in toluene (10 mL) using the same procedure reported for 3b:
yield 176 mg (95%). 1H NMR (pyridine-d5): δ 7.73 (m, 2H), 7.67 (m,
4H), 7.52 (m, 4H) (phenyl H), 4.82 (m, 2H, NCH), 3.77 (m, 2H,
THF), 3.35 (m, 2H, NCH), 2.99 (m, 2H, NCH), 2.45 (m, 2H, CH2),
2.15 (m, 2H, CH2), 2.05 (m, 8H, CH2), 1.95 (d, J = 6.0 Hz, 3H, CH3),
1.88 (d, J = 6.0 Hz, 3H, CH3), 1.79 (m, 12H, CH2), 1.63 (m, 2H, THF),
1.45 (m, 6H, CH2), 1.23 (d, J = 6.0 Hz, 3H, CH3), 1.20 (d, J = 6.0 Hz,
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Anal. Calcd for C45H73B10N5SZr (8i): C, 59.04; H, 8.04; N, 7.65. Found:
C, 59.07; H, 7.98; N, 7.82.
ASSOCIATED CONTENT
■
S
* Supporting Information
Preparation of [η2-iPrNC(Bun)NPri]2Hf[σ:σ:σ-{SC(S)C2B10H10}]
(9i). This complex was prepared as light purple crystals from 2i (206
mg, 0.3 mmol) and CS2 (76 mg, 1.0 mmol) in toluene (20 mL) in a
closed flask at 100 °C for 3 days using the same procedure reported for
3b: yield 137 mg (60%). 1H NMR (benzene-d6): δ 2.07 (m, 4H, CH2),
1.33 (m, 4H, CH2), 1.22 (q, J = 6.4, 12H, CH3), 1.16 (m, 6H, CH2), 1.04
(m, 10H, CH2), 0.79 (t, J = 7.2, 6H, CH3). 13C{1H} NMR (benzene-d6):
δ 185.2 (CS), 110.5, 99.5 (cage C), 48.6 (NCH), 28.9, 28.1, 25.0, 24.7,
23.4, 13.5 (CH2 and CH3). 11B{1H} NMR (benzene-d6): δ −1.2 (1B),
−3.4 (2B), −6.7 (4B), −8.7 (3B). IR (KBr, cm−1): ν 2564 (BH). Anal.
Calcd for C25H56B10HfN4S2 (9i): C, 39.33; H, 7.39; N, 7.34. Found: C,
39.53; H, 7.40; N, 6.97.
Synthesis and characterization of new complexes [η2-R2C-
(NR1)2]2MCl2, crystal data and details of data collection and
structure refinements, as well as crystallographic data in CIF
format for 1b, 1d, 1e, 1f, 1h, 2e, 2g, 2h, 2i, and 3−10. This
material is available free of charge via the Internet at http://pubs.
acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zxie@cuhk.edu.hk.
Preparation of [η2-CyNC(nBu)NCy]2Zr[σ:σ:σ-(PhN-NN)-C2B10H10}
(10c). This complex was prepared as yellow crystals from 2c (380 mg,
0.5 mmol) and PhN3 (179 mg, 1.5 mmol) in toluene (20 mL) using the
same procedure reported for 3b: yield 320 mg (76%). 1H NMR
(benzene-d6): δ 8.13 (d, J = 7.6 Hz, 2H), 7.19 (dd, J = 7.6 and 8.0 Hz,
2H), 6.92 (dd, J = 7.6 Hz, 1H) (phenyl H), 3.44 (m, 4H, NCH), 2.68
(m, 1H), 2.26 (m, 4H), 2.10 (m, 1H), 1.84 (m, 16H), 1.60 (m, 10H),
1.40 (m, 4H), 1.28 (m, 10H), 1.18 (m, 6H), 1.04 (m, 2H, CH2), 0.85 (t, J
= 7.2 Hz, 6H). 13C{1H} NMR (benzene-d6): δ 181.1, 180.0 (NCN),
143.6, 129.2, 127.5, 122.9 (phenyl C), 111.2, 108.2 (cage C), 58.3, 57.4,
57.2, 56.8 (NCH), 37.5, 36.8, 36.5, 35.9, 35.3, 34.9, 33.7, 33.6, 29.9, 28.9,
26.8, 26.6, 26.2, 26.1, 26.0, 25.9, 25.7, 25.4, 25.3, 23.6, 23.2 (CH2 and
CH3). 11B{1H} NMR (benzene-d6): δ −0.9 (2B), −6.0 (8B). IR (KBr,
cm−1): ν 2580 (BH). Anal. Calcd for C42H77B10N7Zr (10c): C, 57.36; H,
8.83; N, 11.15. Found: C, 57.61; H, 8.79; N, 11.32.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work described in this paper was supported by grants from
the Research Grants Council of the Hong Kong Special
Administration Region (Project No. CUHK7/CRF/12G and
404011), National Basic Research Program of China (973
Program, Grant No. 2012CB821600), and State Key Laboratory
of Elemento-Organic Chemistry, Nankai University (Project No.
0314).
REFERENCES
■
Preparation of [η2-iPrNC(Ph)NPri]2Zr[σ:σ:σ-(PhN-NN)-C2B10H10}
(10f). This complex was prepared as yellow crystals from 2f (357 mg, 0.5
mmol) and PhN3 (179 mg, 1.5 mmol) in toluene (20 mL) using the
same procedure reported for 3b: yield 338 mg (89%). 1H NMR
(benzene-d6): δ 8.26 (d, J = 8.1 Hz, 2H), 7.66 (brs, 1H), 7.38 (m, 12H)
(phenyl H), 3.56 (m, 1H), 3.45 (m, 1H), 3.29 (m, 2H), (NCH), 2.11 (s,
CH3 of toluene), 1.41 (m, 3H), 1.29 (m, 3H), 1.13 (d, J = 5.4 Hz, 12H,
CH3), 0.66 (m, 6H). 13C{1H} NMR (benzene-d6): δ 179.6, 177.9
(NCN), 143.4, 137.8, 132.5, 131.4, 129.5, 129.3, 129.2, 128.5, 127.5,
126.2, 125.6, 122.6 (phenyl C), 111.4, 108.5 (cage C), 49.8 (NCH),
26.1, 25.4, 25.0, 23.0, 21.4 (CH3). 11B{1H} NMR (benzene-d6): δ −1.0
(2B), −6.2 (8B). IR (KBr, cm−1): ν 2555 (BH). Anal. Calcd for
C41H61B10N7Zr (10f + toluene): C, 57.85; H, 7.22; N, 11.52. Found: C,
57.98; H, 7.27; N, 11.40.
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Preparation of [η2-iPrNC(Bun)NPri]2Ti[σ:σ:σ-(PhN-NN)-C2B10H10}
(10h). This complex was prepared as yellow crystals from 2h (279 mg,
0.5 mmol) and PhN3 (179 mg, 1.5 mmol) in toluene (20 mL) using the
same procedure reported for 3b: yield 301 mg (89%). 1H NMR
(benzene-d6): δ 8.30 (d, J = 7.6 Hz, 2H), 7.26 (dd, J = 7.6 and 8.1 Hz,
2H), 7.08 (dd, J = 7.6 Hz, 1H) (phenyl H), 3.76 (m, 2H), 3.68 (m, 2H)
(NCH), 2.05 (m, 4H, CH2), 1.42 (m, 4H, CH2), 1.25 (d, J = 6.6 Hz,
12H, CH3), 1.18 (d, J = 6.6 Hz, 12H, CH3), 1.12 (m, 4H, CH2), 0.76 (d, J
= 7.1 Hz, 6H, CH3). 13C{1H} NMR (benzene-d6): δ 179.5, 178.1
(NCN), 143.2, 130.5, 128.3, 125.0 (phenyl C), 110.8, 107.3 (cage C),
50.8 (NCH), 28.2, 27.0, 25.3, 25.0, 22.3, 15.1 (CH2 and CH3). 11B{1H}
NMR (benzene-d6): δ −1.6 (2B), −6.9 (8B). IR (KBr, cm−1): ν 2562
(BH). Anal. Calcd for C30H61B10N7Ti (10h): C, 53.32; H, 9.10; N,
14.51. Found: C, 53.58; H, 9.25; N, 14.33.
X-ray Structure Determination. All single crystals were immersed
in Paratone-N oil and sealed under nitrogen in thin-walled glass
capillaries. Data were collected at 293 K on a Bruker SMART 1000 CCD
diffractometer using Mo Kα radiation. An empirical absorption
correction was applied using the SADABS program.18 All structures
were solved by direct methods and subsequent Fourier difference
techniques and refined anisotropically for all non-hydrogen atoms by
full-matrix least-squares on F2 using the SHELXTL program package.19
All hydrogen atoms were geometrically fixed using the riding model.
Details of the crystal structures were included in the Supporting
Information.
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