Tris(2,6-diisopropylphenolato)titanium(IV) dihydridodiorganylborates: Synthesis and structures

Article abstract of DOI:10.1002/ejic.201001108

The reactions of tris(2,6-diisopropylphenolato)titanium(IV) chloride with alkali-metal dihydridodiorganylborates M(H₂BR₂) (M = Li, K; R = Me, C₆H₁₁, CMe₃; BR₂ = BC₅H₁₀, BC₈H₁₄) led to the corresponding titanium dihydridodiorganylborates. However, in almost all cases byproducts such as (2,6-diisopropylphenolato)diorganylboranes, triorganylboranes, diorganylboranes, diborane and tetrakis(2,6- diisopropylphenolato)titanium(IV) were also generated. (2,6-iPr ₂C₆H₃O)₃Ti(H₂BR ₂) compounds also resulted from the interaction of methyltris(2,6-diisopropylphenolato)titanium, for example, with catecholborane. In addition to the formation of tris(2,6-diisopropylphenolato) catecholboratotitanium(IV), B-methylcatecholborane was also formed The reaction of potassium dihydro-9-cyclooctylborate with 2,6-bis(2,2-di-tert-butyl-2- hydroxyethyl)pyridinetitanium dichloride (LTiCl₂) led to the complex LTi(H₂BC₈H₁₄)₂. This compound showed no agostic C-H···Ti interaction in contrast to (2,6-iPr₂C₆H₃O)₃TiH ₂BC₈H₁₄ and the corresponding titanium dihydridobis(cyclohexyl)borate.

Full text of DOI:10.1002/ejic.201001108

FULL PAPER
DOI: 10.1002/ejic.201001108
Tris(2,6-diisopropylphenolato)titanium(IV) Dihydridodiorganylborates:
Synthesis and Structures[‡]
Jörg Knizek[a] and Heinrich Nöth*[a]
Dedicated to Professor Dr. S. G. Shore on the occasion of this 80th birthday
Keywords: Titanium / Boron / Borates / Structure elucidation / Agostic interactions
The reactions of tris(2,6-diisopropylphenolato)titanium(IV)
chloride with alkali-metal dihydridodiorganylborates
M(H2BR2) (M = Li, K; R = Me, C6H11, CMe3; BR2 = BC5H10
example, with catecholborane. In addition to the formation
of tris(2,6-diisopropylphenolato)catecholboratotitanium(IV),
B-methylcatecholborane was also formed The reaction of po-
,
BC8H14) led to the corresponding titanium dihydridodiorgan- tassium dihydro-9-cyclooctylborate with 2,6-bis(2,2-di-tert-
ylborates. However, in almost all cases byproducts such as
(2,6-diisopropylphenolato)diorganylboranes, triorganylbor-
anes, diorganylboranes, diborane and tetrakis(2,6-diiso-
propylphenolato)titanium(IV) were also generated. (2,6-
iPr2C6H3O)3Ti(H2BR2) compounds also resulted from the in-
teraction of methyltris(2,6-diisopropylphenolato)titanium, for
butyl-2-hydroxyethyl)pyridinetitanium dichloride (LTiCl2)
led to the complex LTi(H2BC8H14)2. This compound showed
no agostic C–H···Ti interaction in contrast to (2,6-iPr2C6H3O)3-
TiH2BC8H14 and the corresponding titanium dihydridobis-
(cyclohexyl)borate.
Introduction
Results
Synthesis and Structure of (2,6-iPr2C6H3O)3TiMe
The existence of titanium tetrakis(tetrahydrido)borate,
Ti(BH4)4, has so far not been proved. Attempts to synthe-
size it has led to green Ti(BH4)3,[2] which can be sublimed
in vacuo but decomposes above –30 °C. The thermal sta-
bility of titanium tetrahydridoborates can be greatly im-
proved by replacing the BH4 groups by other substituents.
For instance, the violet Cp2Ti(BH4) is stable up to 120 °C.[3]
Shore and co-workers have shown that bis(cyclopentadi-
enyl)titanium dihydridodiorganylborates are stable species
that are also characterized, depending on their structure, by
β-agostic C–H···Ti interactions.[4] The introduction of aryl–
O groups at the Ti atom allows not only the synthesis of
(2,6-iPr2C6H3O)2Ti(BH4)2 and (2,6-iPr2C6H3O)3Ti(BH4),
but also the hydride (2,6-iPr2C6H3O)3TiH, which can be
isolated as (2,6-iPr2C6H3O)3TiH·PMe3.[5] Moreover, if 6,6Ј-
di-tert-butyl-4,4Ј-dimethyl-2,2Ј-methylenebis(phenolate) is
used as the ligand L, the titanium(IV) bis(tetrahydrido)bor-
ate LTi(H3BH)2 can be isolated with μ3-BH4 groups.[6]
In this report we describe several (2,6-iPr2C6H3O)3Ti-
(H2BR2) compounds and their X-ray structures.
Steric shielding of the titanium centre in tris(phenolato)-
titanium(IV) compounds can be achieved by introducing
bulky organyl groups such as methyl,[7] tert-butyl,[8–10] iso-
propyl[11,12] or phenyl groups[7,13,14] into the 2,6-positions
of the phenolato ligand. In this study we chose tris(2,6-di-
isopropylphenolato)titanium(IV) chloride[5] (1), as the
starting material, which is readily available, as shown in
Equation (1). Compound 1 can be used for the preparation
of methyltris(2,6-diisopropylphenolato)titanium(IV) (2); see
Equation (2), which is a precursor of the methylhydridobor-
ate 4, as shown in Equation (4), whereas the reaction of 1
with LiBH2R2 should yield (2,6-iPr2C6H3O)3Ti(H2BR2) (3).
So far, only the structures of five alkyltris(organyloxo)tita-
nium compounds are known,[6,8,9] amongst them meth-
yltris(2,6-diphenylphenolato)titanium(IV)[8] and MeTi[N-
(SiMe3)2]3.[15]
The methyl derivative 2 is susceptible to hydrolysis and
photolytic decomposition. It turns black at room tempera-
ture within a few hours. NMR signals for the methyl group
bonded to the Ti atom are found at δH = 1.92 ppm and δC
= 54.5 ppm (Table 1). These atoms are better shielded than
[‡] Metal Tetrahydridoborates and Hydroboratometallates, 33.
Part 32: Ref.[1]
those of (Me2PCH2)2TiMe4 (δH
= 1.08 ppm, δC =
49.2 ppm).[16]
[a] Institut für Anorganische Chemie, Ludwig-Maximilians-
Universität München,
Single crystals of compound 2 grown from hexane at
–30 °C are orthorhombic with the space group Fdd2. The
molecular structure of 2 is depicted in Figure 1. Although
Butenandtstr. 5–13, 81377 München, Germany
Fax: +49-89-2180-77455
E-mail: H.Noeth@lrz.uni-muenchen.de
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Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
1
Table 1. H and 13C NMR signals for compounds 1 and 2 in C6D6 solution.
δ [ppm]
CHMe2
CHMe2
1.13 [d, J(1H,1H) = 3.43 [sept, J(1H,1H) =
6.8 Hz, 36 H] 6.8 Hz, 6 H]
m-H
p-H
TiMe
3
3
1H NMR (1)
6.98–7.07 [m, 9 H]
1H NMR (2)[a]
1.17 [d, J(1H,1H) = 3.60 [sept, J(1H,1H) =
7.08 [d, J(1H,1H) =
6.95 [t, J(1H,1H) = 1.92
3
3
3
3
6.8 Hz, 36 H]
6.8 Hz, 6 H]
7.4 Hz, 6 H]
7.2 Hz, 3 H]
CHMe2
CHMe2
m-Ph
p-Ph
o-Ph
i-Ph
13C NMR (1)
13C NMR (2)
23.06
23.31
27.52
27.88
123.01
123.16
123.76
123.38
137.4
137.4
163.06
161.08
[a] δC(MeTi) = 54.54 ppm.
all of the hydrogen atoms could be located in the difference nation sphere of Ti1 is a distorted tetrahedral with a ψ-C3
Fourier map, those in the Me groups did not refine well. axis through the Ti1 and C37 atoms. The O–Ti–O bond
Therefore they were included in the final refinement with angles range from 113.4(2) to 114.9(2)° and the Ti–O bond
fixed CH bond lengths riding on their C atoms. The coordi- lengths from 1.769(3) to 1.785(4) Å. A comparison of the
[5]
structures of 2 and (2,6-iPr2C6H3O)3TiBH4 shows that
the Me group needs less space than the BH4 group. For the
tetrahydroborate analogue of 2, the O–Ti–O bond angles
are on average 108.1° and the B–Ti–O bond angles are on
average 110.8°.[5] Their Ti–O bond lengths are identical to
those in the tetrahydroborate. The C–O–Ti bond angles are
in the range 171.4(4)–173.1(4)° for 2 and 171.2(5)–175.6(5)°
for the tetrahydroborate. This indicates that the oxygen
atoms can be considered as sp-hybridized, in accordance
with the short C–O bonds and the Ti–O bonds. The Ti–C
bond length in 2 is 2.074(7) Å, which is identical to that of
the Ti–C bond in (2,6-Ph2C6H3O)3TiMe.[8] However, its Ti–
C bond is significantly shorter than the Ti–C bond in
(iPr2C6H3O)3TiCMe3 [2.095(3) Å][5] or in [(Me3Si)2N]3-
TiMe [2.152(4) Å].[16] Clearly, the aryloxo groups shorten
the Ti–C bond lengths due to the electron-withdrawing ef-
fect of the O(sp)-hybridized atoms.[17]
Figure 1. Molecular structure of methyl[tris(diisopropylphenolato)]-
titanium(IV) (2). Thermal ellipsoids are drawn at the 50% prob-
ability level. CH hydrogen atoms have been omitted except for the
Me group. Bond lengths [Å] and bond angles [°]: Ti1–O1 1.769(3),
Ti1–O2 1.782(4), Ti1–O3 1.785(4), Ti1–C37 2.074(7), O1–C1
1.387(6), O2–C13 1.471(6), O3–C25 1.367(6), Ti1–C37 2.074(7);
Ti1···H37B 2.559; O1–Ti1–O2 114.5(2), O1–Ti1–O3 113.4(2), O2–
Ti1–O3 114.9(2), O1–Ti1–C37 103.6(2), O2–Ti1–C37 104.4(2), O3–
Ti1–C37 104.4(2), C1–O1–Ti1 171.3(4), C13–O2–Ti1 173.1(4),
C25–O3–Ti1 171.1(4), O1–C1–C2 117.3(5), O1–C1–C6 118.0(4),
C1–C2–C3 115.7(5), C6–C1–C2 124.8(5), C3–C4–C5 120.3(6), C1–
C6–C5 115.7(5), C5–C6–C10 123.0(5). Torsion angles [°]: Ti1–O1–
C1–C2 96.3, Ti1–O2–C13–C14 –38.8, Ti1–O2–C13–C18 143.0,
Ti1–O3–C25–C26 –113.7.
Reactions of Tris(2,6-diisopropylphenolato)titanium
Chloride with Alkali Metal Dihydridodiorganylborates
The reaction of 1 with lithium dimethyldihydridoborate
in diethyl ether was expected to produce the titanium di-
hydridodimethylborate 5; see Equation (5). Although com-
pound 5 was formed, as shown by a triplet in the 11B NMR
1
spectrum at δ = 5.6 ppm, J(1H,11B) = 56 Hz, it was only a
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J. Knizek, H. Nöth
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byproduct with a relative intensity of 4%. The main compo- Yellow crystals separated from the red filtrate at –30 °C,
nent in the solution turned out to be (2,6-diisopropylphen- which proved to be the titaniumtetrakis(phenolate) 8.[18]
olato)dimethyborane (6; δB = 56.3 ppm, relative intensity This shows that the dihydroborinate 10 disproportionates,
62%). A quartet at δB = 2.0 ppm [1J(1H,11B) = 64 Hz, 16% most likely according to Equation (8). However, we were
relative intensity] indicates the formation of (2,6- unable to isolate 10 by changing the solvent from pentane
iPr2C6H3O)3Ti(H3BMe) (7), which results partly from the to THF or diethyl ether, or the temperature from –78 to
presence of LiH3BMe as an impurity in the LiH2BMe2 –30 °C. The IR spectrum of the orange oily residue showed
used, but also as a result of ligand exchange according to strong IR stretching bands at 2017 and 2181 cm–1, which
Equation (6), which is supported by an NMR signal at δB are typical of a dihydridoborinate. This result contrasts the
= 86.9 ppm due to BMe3 (2%).
easy preparation and crystal structure determination of bis-
(cyclopentadienyl)zirconium(IV) dihydridoborinate.[4,19]
The reaction of 1 with [K(H2-9-BBN)][20] in hexane is
much less complicated. Yields of up to 70% of compound
11 (δB = 11.1 ppm) were obtained; see Equation (9). In ad-
dition, an 11B NMR signal at δ = 29.3 ppm was observed
resulting from dimeric 9-borabicyclononane 12; 17% inten-
sity, see also Equation (10). However, compound 9 could
not be isolated. An orange residue was isolated from the
filtrate, which on treatment with CH2Cl2 yielded colourless
crystals of 11·CH2Cl2. In the supernatant solution only sin-
2Li(H2BMe2) Ǟ Li(H3BMe) + (LiH + BMe3)
(6)
The weak 11B NMR signals at –27.5 (4%) and –17.4 ppm
(3%) are unresolved multiplets and could not be reliably
assigned. More importantly, single crystals of (iPr2C6H3O)4-
Ti (8) were isolated. This compound was characterized by
its unit cell constants.[18] Scheme 1 shows possible reaction
pathways.
Unexpected was the heterogeneous reaction of 1 with
K[H2B(C5H10)2][19,20] in pentane (T = –110 to 20 °C). This
reaction led to a single 11B NMR signal at 7.3 ppm, which
we assigned to compound 10; see Equation (7). The signal
appears to be a triplet, however, it was not well resolved.
1
gle sets of H and 13C NMR signals were observed, which
we assigned to the titanium species 11. This indicates that
there is unhindered rotation about the Ti–O and Ti–H–B
Scheme 1.
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Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
bonds at ambient temperature. A solution of 11 in deuter- two bands from BH2,symm and BH2,asymm, the observation
iotoluene also showed at –80 °C only one set of 1H and 13
C
of a single band is not unusual for bidentate bridging BH2
NMR signals. Similar NMR spectra were recorded for the units.[22] A weak band at 2708 cm–1 points to the presence
analogous [Cp2Zr(9-BBN)] complex.[19] The presence of BH of an agostic Ti···H–C bond and this structural unit was
bonds is also manifested by a strong IR band at 2033 cm–1. identified in its X-ray structure determination.
Compound 11·CH2Cl2 was also characterized by X-ray
crystallography.
All the tris(2,6-diisopropylphenolato)titanium dihydrodi-
organylborates that we have described so far are prone to
Compound 11 also resulted from the treatment of com- the formation of agostic β-Ti···C–H bonds.[23] To avoid such
pound 2 in diethyl ether with dimeric 9-borabicyclononane interactions we treated 1 with potassium dihydrido-di-tert-
[HBC8H14]2, (12); see Equation (11). This method was quite butylborate, as shown in Equation (14). In this case no β-
successful for the preparation of analogous zirconocene–9- Ti···C–H agostic bond was possible. Reaction (14), per-
BBN complexes.[19] The solution showed after 1 hour, in ad- formed in diethyl ether resulted in a single 11B NMR signal
dition to the 11B NMR signal for (H-9-BBN)2 at δB
=
at δ = 24.0 ppm for compound 17. Its H-coupled NMR
1
29.0 ppm, signals at δ = 88.9 (53% intensity) and 50.8 ppm spectrum shows significant line-broadening but no sharp
(29%) for 9-methyl-9-borabicyclcononane (13) and 9-(2,6- triplet. There was a second signal at δB = 81.6 ppm from
diisopropylphenolato)-9-borabicyclononane (14), respec- the borane (tBu)2BH,[21] which results from the decomposi-
1
tively; see Equations (11) and (12).[21] The relative inten- tion of compound 17. The H and 13C NNR spectra of 17
sities of the signals show that the formation of 13 occurs exhibit only single sets of signals. Its IR spectrum shows
more rapidly than the formation of the ester 14. Compound two separate stretching frequencies at 2087 cm–1 for
14 provided single crystals for an X-ray structure determi- νBH2,asym and at 2021 cm–1 for νBH2,sym. Orange single
nation. The expected titanium hydride 15 could not be iso- crystals of 17 were obtained from a concentrated hexane
lated.
solution.
The homogeneous reaction of 1 with lithium bis(cyclo-
No reaction was observed on treating 1 with lithium 2-
hexyl)dihydridoborate[20] in diethyl ether yielded the titani- dihydro-2-boratafluorene[20] in diethyl ether as expected for
um(IV) bis(cyclohexyl)dihydridoborate 16 within 4 hours a reaction according to Equation (15). However, when the
1
almost quantitatively; see Equation (13). H and 13C NMR ether was replaced by THF a 11B NMR signal at δ =
signals for compound 16 and one 11B NMR signal at δ = 7.6 ppm suggested the formation of the corresponding tita-
15.0 ppm were observed both at room temperature and at nium(IV) diorganyldihydridoborate. But this compound
–80 °C. Therefore there is free rotation of the C–O and Ti– could not be isolated because on work-up it decomposed to
H bonds. Also characteristic is the strong band at 2015 cm–1 give (2,6-iPr2C6H3O)4Ti. Similar behaviour was observed
for a B–H stretching vibration. Although one should expect for the reaction of 1 with lithium dibenzo-1-oxo-2,2-dihy-
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dridoborate.[20] Two 11B NMR signals were recorded. A
It has been reported that the reaction of Cp2TiMe2 with
weak signal at δB = –2.5 ppm shows the presence of the catecholborane yields methane and titanocene bis(catechol-
lithium compound and the strong signal at δB = 28.3 ppm atoborane).[24] Therefore we expected similar behaviour for
suggests the presence of the hydridoborate (2,6-iPr2C6H3O)3- the reaction of 2 with an excess of catecholborane in
Ti[HBOC12H10] but none of the expected compounds could pentane. A series of 11B NMR spectra were recorded by
be isolated.
increasing the temperature from –80 to 20 °C in 10 °C inter-
Table 2. Change of composition of the reaction products formed from (2,6-iPr2C6H3O)3TiMe and benzo[1,3,2]dioxaborolane in hexane.
T
δB [ppm],
δB(B2H6) [ppm],
δB(C6H4BO2BH) [ppm],
δB(C6H4OBTi) [ppm],
δB(C6H4O2BMe) [ppm],
[°C] intensity [%] intensity [%]
intensity [%]
intensity [%]
intensity [%]
–80 8.7, 10
–60 8.8, 11
–40 9.0, 11
–20 8.9, 13
16.8, 8
16.6, 9
27.2, 82
–
–
–
–
1
26.9 [d, J(11B1H) = 148 Hz], 80
16.8 [tt,1J(11B,1H) = 130 Hz], 6
27.1 [d, J(11B,1H) = 199 Hz], 65 22.0 (s), 10
33.6, 8
33.8, 8
33.9, 10
33.9, 12
1
16.8 [tt, J(11B,1H) = 120 Hz], 8
27.1 [d,1J(11B,1H) = 186 Hz], 62
21.5 (s), 10
21.8 (s), 13
1
1
0
9.3, 8
–
16.8, [tt, J(11B,1H) = 125 Hz], 8
27.3 [d,1J(11B,1H) = 195 Hz], 60
1
1
20
17.0 [tt, J(11B,1H) = 125 Hz], 8
27.5 [d, J(11B,1H) = 184 Hz], 61 21.9 (s), 19
Scheme 2.
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Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
vals. The changes in the 11B NMR spectra are shown in the signal at 16.7 ppm from B2H6.[21] Two new species ap-
Table 2. At –80 °C signals at 8.8, 16.7 and 27.2 ppm were peared at –50 °C. A resonance at δ = 21.9 ppm can be as-
observed in a ratio of 1:1:8. They showed no BH coupling. signed to (2,6-iPr2C6H3O)3Ti[H2BO2C6H4] (21; 8%) and
The signal at 27.2 ppm results from catecholborane 19 and the signal at δ = 33.6 ppm to B-methylcatecholborane
Scheme 3.
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(8%).[21] An increase to 20% at 20 °C was observed for the Ti···H37 distance of 2.30 Å, which is typical of an agostic
bis(catecholato)borate 22. The amount of diborane remains Ti···H–C interaction. The Ti1···C37 atom distance is
at 8%, but the amount of catecholborane decreases to 60%. 2.621(3) Å, in contrast to the Ti1···C41 distance of
At 20 °C the signal at 8.8 ppm had vanished. Scheme 2 de- 3.781(3) Å. The B···Ti distance in 11 is 2.212(2) Å and this
scribes the most likely steps in this reaction sequence.
corresponds to the B···Ti distance of 2.20(2) Å in the corre-
To prove that the titanium hydride (2,6-iPr2C6H3O)3TiH sponding tetrahydroborate[5] in which three Ti–H–B bridge
is an intermediate, we treated (2,6-iPr2C6H3O)3TiH(PMe3) bonds are present. In particular, the reduction of the Ti1–
with catecholborane and observed analogous behaviour to B1–C37 bond angle to 84.4° points to the presence of a β-
that of compound 2 [Equation (15)]. The spirocyle 22 agostic Ti···H–C interaction in the solid state, which could
showed an 11B NMR signal at δ = 24.5 ppm. The 1B NMR not be observed in the NMR spectra even at –80 °C.
1
1
signal at δ = 35.8 ppm [dq, J(P,B) = 58 Hz, J(11B,1H) =
[21]
96 Hz] is due to the phosphanylborane H3BPMe3 gener-
ated [Equation (15)]. We also checked for the formation of
22 from 1 by treating the latter with lithium bis(catechol-
ato)borate in diethyl ether; see Equation (16). The resulting
11B NMR spectrum shows a signal at δB = 14.1 ppm for the
Li compound and a signal at δ = 23.9 ppm for 22. The low-
field signal indicates that the latter contains a tricoordin-
ated and not tetracoordinated B atom.
Attempts to prepare a dihydridodiorganylborate of bis-
(tri-tert-butylmethanolato)titanium(IV)[20a] from [(tBu)3-
CO]2TiCl2 and Li[H2BC8H14] failed. The main product was,
as shown by 11B NMR spectroscopy, bis(9-borabicyclonon-
ane) with δB = 29.4 ppm. Therefore a larger ligand L had
to be chosen to stabilize a compound of type LTi-
(H2BC8H14)2. For this reason we prepared 2,6-[bis(2,2-di-
tert-butyl-2-hydroxyethyl)]pyridine (23) starting from lut-
idine (Scheme 3). Its reaction with TiCl4 yielded the penta-
coordinate dichlorotitanium complex 24. Treatment of 24
with K[H2BC8H14] in diethyl ether generated 25 (Scheme 3).
The 1H and 13C NMR spectra show different sets of signals
for the tert-butyl groups as well as for the diastereotopic
methylene protons. The 11B NMR signal at δ = 20.3 ppm is
Figure 2. Molecular structure of tris(2,6-diisopropylphenolato)tita-
nium(IV)-dihydrido-9-borabicyclononane (11·CH2Cl2). Only the Ti
complex is depicted. Thermal ellipsoids are drawn at the 25% prob-
ability level. CH hydrogen atoms have been omitted except for BH
and H37. Bond lengths [Å] and bond angles [°]: Ti1–O1 1.792(1),
Ti1–O2 1.806(2), Ti1–O3 1.802(2), Ti1–H1 1.85(2), Ti1–H2 1.86(3),
Ti1···H37 2.30(2), Ti1···B1 2.212(2), B1–C37 1.637(2), B1–C41
1.593(2), B1–H1 1.23(1), B1–H2 1.18(1); O1–Ti1–O2 107.01(7),
O1–Ti1–O3 106.53(7), O2–Ti1–O3 110.13(7), O1–Ti1–H1 93.3(7),
O2–Ti1–H1 146.6(8), O3–Ti1–H1 146.6(8), O1–Ti1–H2 92.2(7),
O2–Ti1–H2 93.8(8), O3–Ti1–H2 142.8(8), H1–Ti1–H2 58(1), H1–
B1–H2 97(2), H1–B1–C41 117(1), H2–B1–C41 116(1), Ti1–O1–C1
160.2(2), Ti1–O2–C13 161.4(2), Ti1–O3–C25 91.79(8), O1–C1–C2
118.2(2), O1–C1–O6 118.7(2), C1–C1–C6 123.1(2), C1–C6–C5
116.9(2), C1–C2–C3 116.8(2), C2–C3 C4 121.2(2), C3–C4–C5
120.3(2), C4–C5–C6 121.5(2). Torsion angles [°]: Ti1–O1–C1–C2
–89.8, Ti1–O2–C13–C14 152.0; Ti1–O3–C25–C26 44.9.
broad (h = 500 Hz) and the triplet structure is barely vis-
½
ible. However, the presence of BH2 groups is revealed by
two strong IR bands at 2078 and 2027 cm–1 with shoulders
at 2103 and 2056 cm–1, which indicates the bidentate func-
tion of the H2BC8H14 species. This was verified by the de-
termination of the crystal structure of 25.
The 9-BBN ester 14 crystallizes in the orthorhombic
space group Pnma. Its molecular structure is shown in Fig-
ure 3. There is a crystallographically determined mirror
X-ray Structure Determinations
Figure 2 shows the molecular structure of compound 11. plane through atoms B1, O1, C1, C5, C6 and C9. The B1–
It crystallizes from CH2Cl2 solution at –78 °C to give amber C bond lengths are 1.563(2) (to C1) and 1.560(2) Å (to C5),
crystals of 11·CH2Cl2 in the triclinic system, space group and the sum of the bond angles at B1 is 359.9°. The B1–
¯
P1. The most eye-catching structural feature is the asym- O1 bond length of 1.365 Å is typical of borinic esters
metric coordination of the 9-H2BBN ligand at the Ti centre. R2BOR.[21,25] However, the B1–O1–C1 bond angle is fairly
In spite of this, the Ti atom can still be regarded as being open at 127.1(1)° and the C1–B1–C5 plane is perpendicular
tetracoordinated to atoms B1, O1, O2 and O3 because the to the C7–C6–C7A plane of the aromatic ring.
average deviation from the tetrahedral angles is only 2°.
The orange prisms of the bis(cyclohexyl)dihydridoborate
¯
However, the atoms Ti1, H1, H2 and B1 are not arranged (16) are triclinic, space group P1, Z = 2. The most striking
in a plane; the interplanar angle H1–Ti1–H2/H1–B1–H2 is feature of its molecular structure is that one of the cyclo-
50°. In particular, the bending of the 9-H2BBN part against hexyl groups is involved in an agostic β-Ti···H–C interac-
the Ti–B–C plane leads to an Ti1–B1–C37 angle of 84.4(1)°, tion (Figure 4). This leads to a Ti···H distance of 2.26(2) Å,
in contrast to the Ti1–B1–C41 angle of 166.8(2)°. This in- whereas the two Ti1–H(B) bonds are, as expected, shorter
teraction positions H37 in an almost trans arrangement with 1.86(3) and 1.90(3) Å. A consequence of the Ti1···H–
with respect to the O1 atom (O1–Ti1–H37 170°) with a C interaction is that the atoms Ti1, B1, H1 and H2 do not
1894
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Eur. J. Inorg. Chem. 2011, 1888–1900

Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
tion. The B–C bond lengths are about 0.1 Å longer than in
11. An analysis of the Ti–H and B–H bond lengths indi-
cates that these show the beginnings of B–C bond cleavage
(Figure 4).
Figure 5 shows the molecular structure of compound 17.
¯
The orange crystals are triclinic, space group P1, Z = 4.
There are two independent molecules in the unit cell that
have similar structural data. If we neglect the H atoms
bonded to the boron atom then one can describe the coor-
dination sphere at the Ti atoms as distorted tetrahedral.
The O–Ti1–O bond angles are 107.5(1), 111.0(1) and
104.2(2)°, and for O–Ti2–O 106.3(1), 108.5(1) and
108.1(1)°. The B1–Ti1–O angles are 105.0(2), 118.9(2) and
110.5(2)°, which compare with 109.7(2), 113.1(2) and
111.0(2)° for B2–Ti2–O. The B–H bond lengths range from
1.13(4) to 1.27(4) Å, whereas the H–B–H bond angles are
narrow but equal for both molecules with 82(3)°. This is
counterbalanced by the two C–B–C bond angles of 123.9(6)
and 125.7(5)°, which differ due to the steric requirements
of the tert-butyl groups. Compared with compound 16, we
observe significantly longer B–C bonds for 17. Another
consequence is that the shortest distance of the C1 atom to
the closest H atom of the tert-butyl group is found in mole-
cule B1 (2.88 Å), but in molecule B2 the analogous distance
is 3.14 Å. This difference results from the different orienta-
tion of the phenoxy groups, which exerts different strains
on the tert-butyl groups. However, the four-membered rings
B1(B2)–H1–H2–Ti1 are planar, in contrast to those in 11
and 16.
Figure 3. The molecular structure of 9-(2,6-diisopropylphenolato)-
9-borabicyclononane (14). Thermal ellipsoids are drawn at the 25%
probability level. Hydrogen atoms have been omitted for the sake
of clarity. Selected bond lengths [Å] and bond angles [°]: B1–O1
1.365(2), O1–C6 1.395(2), B1–C1 1.563(2), B1–C5 1.560(2); O1–
B1–C1 127.1(1), O1–B1–C5 119.7(1), C1–B1–C5 113.1(1), B1–O1–
C6 124.6(1). Interplanar angles [°]: B1–O1–C6/C7–C6–C7A 90.0,
C1–B1–C5/C1–C2–C4–C5 56.9.
lie in a plane, as shown by the interplanar angle between
H1–Ti1–H2 and H1–B1–H2 of 50°. Moreover, the differ-
ence in angles Ti1–B1–C37 [82.5(1)°] and Ti1–B1–C41
[158.2(3)°] is a consequence of the Ti1···H37–C37 interac-
Figure 4. Molecular structure of tris(2,6-diisopropylphenolato)tita-
nium-dihydrido(dicyclohexyl)borate (16). Thermal ellipsoids are
drawn at the 25% probability level. All hydrogen atoms have been
omitted for the sake of clarity except for those at B1 and C37.
Bond lengths [Å] and bond angles [°]: Ti1–O1 1.819(92), Ti1–O2
Figure 5. Molecular structure of tris(2,6-diisopropylphenolato)tita-
1.796(2), Ti1–O3 1.794(2), C1–O1 1.376(3), C13–O2 1.370(3), C25– nium(IV)-dihydrido(di-tert-butyl)borate (17). Thermal ellipsoids
O3 1.371(3), Ti1–H1 1.90(3), Ti1–H2 1.86(3), Ti1···H37 2.26(3),
Ti1···B1 2.234(4), O1–C1 1.376(3), O2–C13 1.370(3), O3–C25
are drawn at the 25% probability level. All hydrogen atoms have
been omitted for the sake of clarity except for those at B1. Bond
1.371(3), B1–H1 1.18(3), B1–H2 1.10(3); O1–Ti1–O2 113.00(8), lengths [Å] and bond angles [°]: Ti1–O1 1.776(3), Ti1–O2 1.803(4),
O1–Ti1–O3 103.54(9), O2–Ti1–O3 105.22(9), O1–Ti1–H1 143.9(8), Ti1–O3 1.787(3), C1–O1 1.397(5), C13–O2 1.372(6), C25–O3
O1–Ti1–H2 139.9(9), O2–Ti1–H1 139.9(9), O2–Ti1–H2 95.0(9),
O3–Ti1–H1 96.4(9), O3–Ti1–H2 95.5(9), O1–Ti1–B1 110.7(1), O2–
Ti1–B1 112.2(1), O3–Ti1–B1 111.7(1), Ti1–C1–O1 140.6(2), Ti1–
1.401(5), B1–C37 1.625(8), C37–C38 1.535(8), C37–C39 1.521(7),
C37–C40 1.535(7), C41–C42 1.541(7), C41–C43 1.559(7), C41–C44
1.545(7), Ti1···B1 2.498, Ti1–H1 1.75, Ti1–H2 1.82, B1–H1 1.13(1),
O2–C13 170.0(2), Ti1–O3–C25 149.2(2), H1–B1–H2 9.5(2), H2– B1–H2 1.27(1); O1–Ti1–O2 107.5(1), O1–Ti1–O3 111.0(1), O2–
B1–C43 108(2), H1–B1–C45 114(1), H2–B1–C43 108(2), B1–H1– Ti1–O3 104.0(2), B1–Ti1–O1 94.6(2), B1–Ti1–O2 95.2(2), B1–Ti1–
Ti1 90(2), B1–H2–Ti1 56(2). Interplanar angles [°]: C37–B1–C43/
O3 110.5(2), Ti1–H1–B1 118.9, H2–B1–Ti1 106.7. Interplanar
H21–B1–H2 86.4, Ti1–O1–C2/C1 to C6 111, Ti1–O2–C13/C13 to angles [°]: Ti1–O1–C1/C1 to C6 36.1, Ti1–O2–C13/C13 to C18
C18 0.6, Ti1–O3–C2–C5/C15 to C30 67.1.
50.0, Ti1–O3–C25/C25 to C30 102.1.
Eur. J. Inorg. Chem. 2011, 1888–1900
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1895

J. Knizek, H. Nöth
FULL PAPER
Compound 25 crystallizes from hexane as amber mono- 1.77(2) Å, Ti1–H3 of 1.76(3) Å and Ti1–H4 of 1.93(2) Å.
clinic crystals, space group P21/n, Z = 4, after addition of This suggests that the H atoms at B1 form a double bridge
some toluene. The unit cell also shows the presence of tolu- with Ti, whereas H4 is only weakly coordinated to the Ti1
ene and hexane with site occupation factors of 0.7 for tolu- atom.
ene and of 0.4 for hexane. Figure 6 shows the molecular
structureofcompound25. Theligand2,6-[HOC(tBu)2CH2]2-
C5H3N (23) binds to the Ti centre through its two O atoms
[Ti–O 1.788 and 1.786(4) Å], whereas the Ti–N bond is
Discussion and Conclusion
rather long at 2.230(4) Å. Together with the two B atoms,
There are two important points to be considered in dis-
these atoms are arranged around the Ti atom in a distorted cussing the tris(organyloxo)titanium hydroborato com-
trigonal bipyramid. N1 and B1 occupy the trans positions plexes: 1) the geometries of the triphenolatotitanium part
and the other three atoms are placed in the equatorial plane and 2) the influence of the boranato groups at the Ti(OR)3
with bond angles of 123.3(2)° for O1–Ti1–O2, 115.2(2)° for fragment. In general, compounds of the type (RO)4Ti are
O1–Ti1–B2 and 117.0(2)° for O2–Ti1–B2. The equatorial monomeric, for example, (2,6-iPrC6H3O)4Ti,[18] (2-tBu-
plane is bent in the direction of the N atom, as shown by C6H4O)Ti,[9](2,3,5,6-Me4C6HO)4Ti[9]and[2,6-Me2C6H3O]4-
the angles of 95.2(2)° for B1–Ti1–O1 and of 101.7(2)° for Ti.[29,30] This also holds for several other triorganylphenol-
B1–Ti1–B2. In contrast to compound 11, the BH2Ti atoms atotitanium(IV)compounds,forexample,(2,4-tBu2C6H3O)3-
are arranged in a plane and there are no agostic C–H···Ti TiCl,[10] (3,5-tBu2C6H3O)3TiI,[31] tris(2,4-tBu2C6H4O)3-
interactions. On the other hand, the Ti1···B distances are TiCl,[10] (2-PhC6H4CO)3TiCl·OEt2[10] and (2,6-Ph2C6H3O)3-
identical, although one would expect a difference for apical TiCl.[14] In contrast, (iPr2C6H3O)3TiCl is dimeric,[31] as is
and equatorial sites. However, both are significantly longer (2,4-Me2C6H3O)3TiCl.[10] Amongst these species (2,4-tBu2-
than in (dmpe)Ti(BH4)3 [2.411(3)],[26] (Me3P)2Ti(BH4)3 C6H3O)TiCl shows the shortest Ti–O bond with 1.575 Å,
[2.40(1)][27] and Cp2TiBH4 [2.37(1) Å].[28] The compara- whereas the longest Ti–O bonds were determined for (3,5-
tively large deviations of the Ti1–H bond lengths are aston- tBu2C6H3O)3TiI.
ishing, as shown by Ti1–H1 of 1.83(2) Å, Ti1–H2 of
On the other hand, the Ti–O–C bond angles are largest
for (2,6-diphenylphenolato)titanium chloride with an
average of 164.7°, which is almost the same angle as found
for (2,6-iPr2C6H3O)4Ti (aver. 165.3°).[16] The longest Ti–O
bonds are observed for compound 17 (aver. 1.803 Å) and
the largest Ti–O–C bond angles for compound 2 (aver.
171.4°). One would expect that short Ti–O and C–O bonds
show more sp character, but there is no clear relationship
between the Ti1–O–C bond angles and the Ti–O or C–O
bond lengths. In fact, the observed C–O bonds correspond
to partial C–O double bond character, as also observed for
borinic esters.[25]
The Ti···B distances depend significantly on the organyl
substituents: the larger the steric requirement of the R
groups the longer the Ti···B distance. A comparison of
compound 11 with 25 demonstrates that the presence of
two H2-9-BBN units also leads to a considerable lengthen-
ing of the Ti···B distance. The longest Ti···B distance ob-
served so far was observed for (Me2PCH2CH2PMe2)Ti-
(BH4)2 with 2.534 Å.[26] This is of course also a conse-
quence of its +II oxidation state. The introduction of sub-
stituents like cyclopentadienyl at the Ti atoms leads to ther-
mal stabilization of, for example, Cp2TiBH4.[4,28] As shown
by us in 1995,[5] the introduction of sterically bulky bis- and
Figure 6. Molecular structure of compound 25. Thermal ellipsoids
are drawn at the 25% probability level. All hydrogen atoms have
been omitted for the sake of clarity except for those at B1. Bond
lengths [Å] and bond angles [°]: Ti1–O1 1.788(4), Ti1–O2 1.786(4),
Ti1–N1 2.230(4), Ti1···B1 2.452(7), Ti1···B2 2.454(7), O1–C10
1.440(7), O2–C8 1.430(6), N1–C2 1.358(7), N1–C6 1.363(7), C1–
C2 1.358(7), B1–C27 1.596(9), B1–C31 1.602(9), B2–C35 1.598(9),
B2–C39 1.610(9), B1–H1 1.22(6), B1–H2 1.24(6), B2–H3 1.12(6),
B2–H4 1.13(6), Ti1–H1 1.83(2), Ti1–H2 1.77(2), TI1–H3 1.76(3), tris(2,6-diorganylphenolato)titanium(IV) units allows the
Ti1–H4 1.93(2); O1–Ti1–O2 123.3(2), O1–Ti1–N1 84.0(2), O2–
synthesis of tetrahydridoborate complexes that are stable at
Ti1–N1 83.8(2), O1–Ti1–B1 94.6(2), O2–Ti1–B2 117.0(2), O2–Ti1–
ambient temperature.
B1 95.2(2), N1–Ti1–B1 177.5(2), N1–Ti1–B2 80.7(2), B1–Ti1–B2
101.7(2), C1–N1–C6 119.1(5), C2–N1–Ti1 120.2(4), C2–N1–Ti1
Studies by Shore and co-workers[4] revealed that
Cp2Ti(H2BR2), Cp*Ti(H2BC8H14)2 and similar compounds
show agostic Ti···H–C interactions. Such interactions have
now been proved for compounds 11 and 16, but not for 10.
Astonishingly, no agostic interaction was observed for 25.
This may be due to the different symmetry because the Ti
atom in compound 25 can be considered as pentacoordi-
120.2(4), C10–O1–Ti1 144.5(3), C8–O2–Ti1 145.3(3), O1–C10–C9
104.6(4), O1–C10–C11 107.0(4), O2–C8–C19 107.1(4), O2–C8–C7
117.4(5), Ti1–H1–B1 105.1, H2–Ti1–B1 108.3, H3–B2–Ti1 116.0,
H4–Ti1–B2 103.4, H1–B1–H2 89.1, H3–B2–H4 89.3, C27–B1–C31
106.4(5), C27–B2–C39 107.1(5). Interplanar angles [°]: C35–B2–
C39/C31–B1–C27 90.0, Ti1–N1–O1/C2–C9–C10 63.4, Ti1–N1–O2/
C6–C7–C9 60.3.
1896
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Eur. J. Inorg. Chem. 2011, 1888–1900

Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
a brownish colour after the Li compound had been added. The
solution was analysed by 11B NMR spectroscopy 30 min after the
nated to the 9-BBN groups in an apical and equatorial
manner in contrast to the tetracoordination in compounds
11 and 16.
We also observed that the reactions of (2,6-iPr2C6H3O)3-
TiCl with alkali-metal dihydridodiorganylborates often lead
not to reasonable amounts of (2,6-iPr2C6H3O)3TiH2BR2,
but rather to 2,6-iPr2C6H3OBR2, (HBR2)2, BR3 and B2H6
as well as (2,6-iPr2C6H3O)4Ti. This latter compound is
formed most likely via the intermediate (2,6-iPr2C6H3O3)3-
1
addition: δB = –30.2 [q, J(1H,11B) = 71 Hz, LiH3BMe, 5%], –27.5
(br., 4%), –22.0 [t, 1J(1H,11B) = 72 Hz, LiH2BMe2, 4%], –17.4 (br.,
3%), 2.0 [q, 1J(1H,11B) = 64 Hz, TiH3BMe, 16%], 5.6 [t, 1J(1H,11B)
= 56 Hz, TiH2BMe2, 4%], 56.3 (s, Me2BOAryl, 62%), 86.9 (BMe3,
2%). The diethyl ether was removed from the solution by distil-
lation and the orange-brown residue dissolved in pentane (50 mL).
Insoluble material was separated by filtration. The brown filtrate
was reduced to 20 mL and stored at –30 °C. Orange-yellow prisms
TiH, which could neither be isolated nor detected by NMR separated, which proved to be (iPr2C6H3O)4Ti by the determination
1
of its cell constants[18] as well by its H and 13C NMR spectra.
spectroscopy.
Compound 25 crystallizes from hexane after the addition
Reaction of Tris(2,6-diisopropylphenolato)titanium Chloride with Po-
of some toluene as amber monoclinic crystals, space group
P21/n, Z = 4. The unit cell also shows the presence of tolu-
ene and hexane with site occupation factors of 0.7 for tolu-
tassium Dihydridoborinate: K(H2BC5H10)[20] (630 mg, 1.86 mmol)
was dispersed in pentane (15 mL) at –110 °C. A solution of 1
(1.04 g, 1.69 mmol) in pentane (25 mL) was slowly added to the
ene and of 0.4 for hexane. Figure 6 shows its molecular suspension. The mixture was allowed to reach room temperature
over 3 h and stirring was continued for another 30 min. The re-
structure.
Our study demonstrates that most tris(2,6-diisopropyl-
phenolato)titanium dihydridodiorganylborates are difficult
to isolate and only a few species seem to be more stable
than (2,6-dimesitylphenolato)titanium species.
sulting 11B NMR spectrum showed the following signals: δB
=
1
–19.0 [t, J(1H,11B) = 70 Hz, KH2BC5H10], 7.3 ppm, (bad resolu-
tion of a multiplet, TiH BC H ). IR: ν = 2017 (br. s, νBH ), 2181
˜
2
5
10
2
(sh, νBH2) cm–1. Insoluble material was removed from the suspen-
sion and the solid was washed with pentane (10 mL); yield 440 mg
(excess KH2BC5H10·3THF and 370 mg KCl). The filtrate was con-
centrated to about 5 mL and stored at –30 °C. Within 3 weeks,
orange-yellow crystals separated, the cell constants of which
showed it to be (2,6-iPr2C6H3O)4Ti (8).[18] Total removal of the
solvent from the filtrate yielded an oil from which no other pure
compound could be isolated. Compound 10 could not be isolated.
Experimental Section
General: All experiments were performed under anhydrous condi-
tions using Schlenk techniques with either N2 or Ar as protecting
gas. The alkali metal organyl-hydridoborates were prepared accord-
ing to literature procedures.[20] Anhydrous solvents were prepared
by standard methods (LiAlH4, CaH2, P4O10). NMR: usually C6D6
solvent, SiMe4 as standard, JEOL GSX 270 and EX 400 spectrom-
eters. IR: Nicolet 520 spectrometer; in Nujol and/or Hostaflon. X-
ray diffraction: Siemens P4 diffractometer equipped with a scintil-
lation counter or an area detector, Mo-Kα radiation, LT2 low-tem-
perature device, graphite monochromator.
Tris(2,6-diisopropylphenolato)titanium Chloride (1):[5] 2,6-Diiso-
propylphenol (7.4 mL, 40 mmol) was dissolved in benzene (20 mL).
At ambient temperature this solution was added whilst stirring to
a solution of TiCl4 (13 mmol) in benzene (30 mL). A dark-red solu-
tion was generated. After the addition the mixture was kept at re-
flux until the gas evolution (HCl) had ceased. The benzene was
then removed by distillation and the remaining dark-orange-brown
residue was dried under high vacuum; yield 7.5 g (12.2 mmol,
94%), m.p. 115–120 °C. For NMR spectroscopic data, see Table 1.
Tris(2,6-diisopropylphenolato)titanium Dihydrido-9-boratabicyclo-
nonane (11): A solution of 1 (3.33 g, 5.41 mol) in hexane (40 mL)
was added to a suspension of K(H2BC8H14)[20] (1.01 g, 5.84 mmol)
in hexane (40 mL) whilst stirring. After stirring for 2 days, the in-
soluble product was separated by filtration. The 11B NMR spec-
trum of the solution showed two signals, one at δ = 11.1 ppm (main
signal) the other at δ = 29.3 ppm (dimeric H-9-BBN). The orange
filtrate was reduced in volume to a few mL. Storing this solution
for several days at –30 °C yielded 11. Recrystallisation from
CH2Cl2 produced crystals of 11·CH2Cl2. The CH2Cl2 was lost on
storing in vacuo. Yield of 11: 2.68 g (3.81 mmol, 70%), m.p. 130–
1
132 °C. H NMR (C6D6): δ = 1.07–1.15 (m, 2 H, C8H14), 1.23 [d,
3J(1H,1H)
= 6.8 Hz, 36 H, CHMe2], 1.32–2.01 (m, 12 H,
C8H14BH2), 3.87 [sept, J(1H,1H) = 6.8 Hz, 6 H, CH(CH3)2], 6.89
[t, 3J(1H,1H) = 7.4 Hz, 3 H, p-2,6-iPr], 7.00 [d, 3J(1H,1H) = 7.2 Hz,
6 H, m-2,6-iPr2] ppm. 13C NMR: δ = 23.79 (CH3), 24.49 (C8H14),
27.12 (CHMe2), 33.36 (C8H14), 123.61 (m-C), 123.65 (p-C), 137.62
(o-C), 162.68 (i-C) ppm. In [D8]toluene at –80 °C only a single set
of signals for the aliphatic C atoms were observed. 11B NMR: δ =
11.1 (br. m) ppm. C44H67BO3Ti (702.7): calcd. C 72.51, H 9.61;
found C 72.75, H 9.15.
3
Methyltris(2,6-diisopropylphenolato)titanium (2):
A solution of
LiMe (3.21 mL, 1.56 m) diluted with diethyl ether (40 mL) was
added to a stirred solution of 1 (5.01 mmol) in diethyl ether
(25 mL) at –78 °C within 1 h. The solution was then allowed to
reach ambient temperature and stirring was continued for a further
2 h. An olive-green solution formed. The solvent was then removed
in vacuo. The solid residue was treated with hexane (60 mL). After
filtration the filtrate was reduced in volume in vacuo to about
20 mL. Storing the solution at –30 °C yielded yellow prisms of 2
within a few days; yield 2.12 g (71%), m.p. 110–111 °C. C37H54O3Ti
(594.71): calcd. C 74.73, H 9.15; found C 74.15, H 9.14. For NMR
spectroscopic data, see Table 1.
Tris(2,6-diisopropylphenolato)titanium(IV) Dicyclohexyldihydrido-
borate (16):
A
solution of LiBH2(C6H11)2·THF[20] (1.95 g,
6.63 mmol) in diethyl ether (50 mL) was slowly added to a stirred
solution of 1 (3.68 g, 5.98 mmol) in diethyl ether (35 mL) at ambi-
ent temperature. LiCl precipitated. The solution turned orange. Af-
ter 4 h, the solvent was removed in vacuo and after filtration the
residue was treated with hexane (80 mL). Insoluble material was
removed by filtration. Then hexane (ca. 60 mL) was removed from
the clear orange filtrate in vacuo. The remaining solution was co-
oled to –30 °C. Within 2 days single crystals of 16 separated; yield
Reaction of Tris(2,6-diisopropylphenolato)titanium Chloride with
Lithium Dihydridodimethylborate: A solution of LiH2BMe2 (0.48 m
in THF, 12 mL) containing about 10% of LiH3BMe was added to
a stirred solution of 1 (3.06 g, 4.97 mmol) in diethyl ether (40 mL).
The solution first turned brown and then orange and again turned
1
3.73 g (4.91 mmol, 82%), m.p. 137–140 °C. H NMR (C6D6): δ =
1.15–1.73 (m, 22 H, C12H22), 1.25 [d, 3J(1H,1H) = 6.8 Hz, 36 H,
Eur. J. Inorg. Chem. 2011, 1888–1900
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1897

J. Knizek, H. Nöth
FULL PAPER
CH(CH3)2], 3.88 [sept, J(1H,1H) = 6.4 Hz, 6 H, CH(CH3)2], 6.88 and others. C44H71BO3Ti (706.73): calcd. C 74.78, H 10.63; found
3
[t, 3J(1H,1H) = 7.2 Hz, 3 H, p-H], 6.98 [d, 3J(1H,1H) = 7.4 Hz, 6
H, m-H] ppm. 13C NMR: δ = 23.94 [CH(CH3)2], 26.92 (p-C6H11),
27.13 [CH(CH3)2], 28.66 (m-C6H11), 32.06 (i-C6H11), 33.86 (o-
C6H11), 123.37 (m-C) 123.53, (p-C), 137.42 (o-C), 162.11 (i-C) ppm.
Even at –80 °C only single sets of signals for the aliphatic C atoms
of the borate ligand as well as for the aryloxy ligands were ob-
C 73.83, H 10.80.
2,6-Bis(2,2-di-tert-butyl-2-hydroxyethyl)pyridinetitanium(IV)
Di-
chloride (24): A solution of 2,6-bis(2,2-di-tert-butyl-2-hydroxy-
ethyl)pyridine (23; 4.84 g, 12.3 mmol) in toluene (100 mL) was
added to a stirred solution of TiCl4 (2.33 g, 12.3 mmol) in toluene
(40 mL). This resulted in the formation of an orange suspension.
HCl was released on heating the suspension at reflux. The now
clear yellow solution was set aside for 18 h. Then it was heated at
reflux for another 4 h. The volume of the solution was reduced to
about 20 mL in vacuo. Crystals of 24 separated at –30 °C, which
were isolated and dried in vacuo. From the filtrate another batch
of colourless crystals separated within 2 days. Total yield of 24:
3.9 g (69%), m.p. 265 °C (dec.). 1H NMR (CDCl3): δ = 1.11 (s,
1
served. 11B NMR: δ = 15.0 [t, J(1H,11B) = 65 Hz; only observed
by line-sharpening] ppm. IR (Hostaflon): ν = 2784 (w), 2733 (w),
˜
2708 (w), 2143 (m), 2015 (st, BH2), 1971 (m), 1916 (w), 1852
(vw) cm–1. C48H75BO3Ti (758.91): calcd. C 75.97, H 9.96; found C
76.01, H 9.54.
Tris(2,6-diisopropylphenolato)titanium(IV) Di-tert-butyldihydrido-
borate (17): A solution of 1 (3.42 g, 5.53 mmol) in diethyl ether
(40 mL) was dropped into a stirred solution of K(H2BtBu2)[20]
(1.43 g, 8.6 mmol) in diethyl ether (30 mL). After stirring the
orange-brown solution for 20 h the ether was removed from the
suspension in vacuo (1 Torr) and the solid residue suspended in
hexane (60 mL). After filtration the filtrate was reduced in volume
to about 20 mL. Orange prisms separated from the solution at
–30 °C within 3 d. Yield of 17: 3.42 g (68%), m.p. 132–134 °C (dec).
CMe3), 3.34 (s, CH2), 6.53 [d, J(1H,1H) = 7.81 Hz, 3-H, py], 7.93
3
3
[t, J(1H,1H) = 7.81 Hz, 4-H, py] ppm.
2,6-Bis(2,2-di-tert-butyl-2-hydroxyethyl)pyridinetitanium(IV) Bis-
(9,9-dihydro-9-borabicyclononane) (25): A diethyl ether solution
(30 mL) of Li(H2BC8H14)[19] (0.86 g, 4.64 mmol) was added to a
diethyl ether solution (26 mL) of compound 24 (1.06 g, 2.08 mmol)
within 10 min. A white suspension formed that slowly turned blue-
1H NMR (C6D6): δ = 1.23 [d, 3J(1H,1H) = 6.8 Hz, 36 H, CH- green. The ether was removed in vacuo and the residue was treated
(CH3)2], 1.49 [br. s., 18 H, C(CH3)3], 3.72 [sept, 3J(1H,1H) = 6.8 Hz,
with hexane (30 mL). After filtration a few drops of toluene were
3
6 H, CHMe2], 6.86 [t, J(1H,1H) = 7.2 Hz, 3 H, p-C6H3], 7.00 [d, added and the solution turned dark blue. Storing the solution at
3J(1H,1H) = 7.4 Hz, 6 H, m-C6H3] ppm. 13C NMR: δ = 23.82 –30 °C the filtrate turned amber and single crystals separated
[CH(Me3)2], 27.31 [CH(Me3)2], 34.84 (CMe3), 123.39 (m-C), 123.61 within 4 d; yield only about 12 well-shaped single crystals were iso-
(p-C), 137.49 (o-C), 162.32 (i-C) ppm. 11B NMR: δ = 24.0 (mul- lated besides microcrystalline 25 (700 mg), m.p. 132 °C (dec., black
tiplet not resolved), 81.6 (br., low intensity, Bu2BH) ppm. IR (Hos-
colour). 1H NMR (C6D6): δ = 0.89–1.97 (m, 9-BBN), 0.89 (s,
taflon): ν = 2087 (st, BH ), 2021 (st, BH ), 2180 (st, 10BH2) cm–1 CMe3), 2.11 (s), 2.18 [d, J(1H,1H) = 16.0 Hz], 3.96 [d, J(1H,1H)
2
2
˜
2
2
Table 3. Crystallographic data and data related to structure solution and refinement.
Compound
2
10
11
16
17
25
Formula
Mr
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C37H54O3Ti
594.70
0.2ϫ0.2ϫ0.3
orthorhombic
Fdd2
36.8369(6)
39.9611(2)
10.6105(2)
90
C20H31BO
298.26
0.4ϫ0.5ϫ0.6
orthorhombic
Pnma
12.841(3)
16.025(5)
8.782(2)
90.
90
90
1807.1(9)
4
1.096
C45H66BCl2H3O3Ti
787.61
C48H75BO3Ti
758.79
C44H71BO3Ti
706.72
C44H10B2N2O4Ti
738.12
0.2ϫ0.3ϫ0.4
monoclinic
P21/n
11.669(9)
18.707(13)
22.282(16)
90
100.37(2)
90
4784(6)
8
1.011
0.210
1603
0.2ϫ0.5ϫ0.6
triclinic
0.2ϫ0.2ϫ0.25
triclinic
0.3ϫ0.3ϫ0.4
triclinic
¯
¯
¯
P1
P1
P1
11.406(3)
12.898(3)
16.977(4)
86.570(6)
87.590(1)
66.496(3)
2285.9(9)
2
10.947(4)
11.591(4)
19.308(7)
85.07(1)
76.81(1)
68.44(2)
2218(1)
2
11.2670(2)
21.7485(5)
21.8012(5)
60.985(1)
75.42(1)
75.35(1)
4466.8(2)
4
90
90
γ [°]
V [Å3]
15619.1(4)
16
1.012
0.248
5152
Z
ρcalcd. [Mgm–3]
μ [mm–1]
F(000)
1.144
0.340
848
1.136
0.231
828
1.051
0.225
1544
0.064
656
Index range
–45ՅhՅ46
–50ՅkՅ46
–13ՅlՅ13
58.26
–15ՅhՅ15
–20ՅkՅ20
–11ՅlՅ11
54.88
–14ՅhՅ14
–14ՅkՅ16
–21ՅlՅ21
58.26
–13ՅhՅ13
–14ՅkՅ13
–24ՅlՅ24
58.84
–8ՅhՅ8
–27ՅkՅ27
–27ՅlՅ27
52.70
–15ՅhՅ15
–23ՅkՅ19
–28ՅlՅ28
58.12
2θ [°]
T [K]
183(2)
183(2)
193(2)
183(2)
203(2)
213(2)
Reflections collected
Reflections unique
Refl. observed (4σ)
Rint.
Number of variables
Weighting scheme[a] x/y
GOF
22290
7916
4321
0.0848
383
0.0867/47.78
1.129
8776
1953
1793
0.0418
174
12939
6950
5870
0.0375
493
0.0498/1.9403
1.059
12897
7097
5859
0.0342
502
22509
12076
6450
0.0894
931
0.0000/6.9493
1.188
23283
9894
4524
0.0883
500
0.0562/0.594
1.055
0.0000/2.5934
1.204
0.0822/21.5574
1.184
Final R (4σ)
0.0662
0.1603
0.491
0.0434
0.1112
0.278
0.0462
0.1144
0.676
0.0544
0.1056
0.284
0.0680
0.1233
0.355
0.0992
0.2523
1.185
Final wR2
Largest residual peak [eÅ–3]
[a] w–1 = σ2Fo + (xP)2 + yP; P = (Fo + 2Fc )/3.
2
2
2
1898
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Eur. J. Inorg. Chem. 2011, 1888–1900

Tris(diisopropylphenolato)titanium Dihydridodiorganylborates
= 15.4 Hz, CH2], 6.39 [d, 3J(1H,1H) = 7.85 Hz, 3-H, py], 6.79 [t,
3J(1H1H) = 7.75 Hz, 4-H, py] ppm. 13C NMR: δ = 30.23 (CMe3),
33.45 (CMe3), 24.12, 25.60, 31.20 (C8H14), 43.05, 44.81, 45.01
(CMe3, CH2), 97.57 (CO), 124.09 (C-3, py), 139.33 (C-4, py),
[2] a) H. R. Hoekstra, J. J. Katz, J. Am. Chem. Soc. 1949, 71,
2488–2492; b) B. D. James, M. G. H. Wallbridge, J. Inorg. Nucl.
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73, 371–383; d) V. V. Volkov, K. G. Myakishev, Sibirskii Khim.
Zh. 1992, 5, 105–108; e) V. Volkov, K. G. Myakishev, Isvest.
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160.61 (C-2, py) ppm. 11B NMR:
δ
=
20.3 (br.) ppm.
C41H75BNO2Ti (683.55): calcd. C 72.0, H 11.05, N 2.05; found C
69.12, H 10.51, N 1.89.
Reaction of Tris(2,6-diisopropylphenolato)titanium(IV) Chloride
with Lithium(H,H-9-borafluorenyl)·3THF:
A
suspension of
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Li(H2BC13H9)·3THF[20] (1.17 g, 3.02 mmol) in diethyl ether
(50 mL) was added to a solution of 1 (1.68 g, 2.73 mmol) in diethyl
ether (15 mL) at 0 °C. After stirring for 10 min, the residue in the
dropping funnel was added to the suspension by adding THF
(10 mL). This caused a change in colour from orange to orange-
red. The solution showed then an 11B NMR signal at –20.4 ppm [t,
1J(11B,1H) = 78 Hz, rel. intensity: 73%, C12H8BH2Li] and 7.6 ppm
[broad signal of C12H8BH2Ti(OAr)3, 27%)]. After stirring the solu-
tion for 18 h at ambient temperature the solvent was removed in
vacuo. The solid residue was treated with hexane (60 mL) and the
insoluble material removed by filtration. After 50% of the hexane
had been evaporated, the filtrate was cooled to –30 °C. Yellow crys-
tals separated which proved to be tetrakis(2,6-diisopropylphen-
olato)titanium by determining its cell constants.[18]
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Catecholborane: Compound 2 (30 mg) was dissolved in hexane
(2 mL) in an NMR tube. After cooling with liquid nitrogen, 10
drops of catecholborane were added. The NMR tube was then se-
aled in vacuo. 11B NMR spectra were recorded at various tempera-
tures beginning at –80 °C. The observed data are summarized in
Table 2. It can be seen that the main product is the B-methylcate-
cholborane (19; increase from 8 to 20% at higher temperature) as
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X-ray Structure Analysis: The air- and moisture-sensitive crystals
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[19]
CCDC-778514 (for 2), -778515 (for 14), -778516 (for 11), -778517
(for 16), -778518 (for 25) and -77519 (for 17) contain the supple-
mentary crystallographic data for 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.
[20]
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Acknowledgments
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We are indebted to Chemetall GmbH for financial support. We
also thank M. Kidik, P. Mayer and Mrs. D. Ewald for help in the
laboratory and for recording many spectra.
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J. Knizek, H. Nöth
FULL PAPER
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Received: October 18, 2010
Published Online: March 18, 2011
1900
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Eur. J. Inorg. Chem. 2011, 1888–1900