Preparation of novel titanium complexes bearing o-phosphinophenol ligands

Article abstract of DOI:10.1021/om950352s

The preparation of novel titanium complexes bearing o-phosphinophenol ligands is reported. The feature of this ligand system is that its electronic and steric properties can be independently tuned. The complexes were found to be fluxional by ¹H

Full text of DOI:10.1021/om950352s

472
Organometallics 1996, 15, 472-475
P r ep a r a tion of Novel Tita n iu m Com p lexes Bea r in g
o-P h osp h in op h en ol Liga n d s
Christopher A. Willoughby, Ronald R. Duff, J r., William M. Davis, and
Stephen L. Buchwald*
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received May 15, 1995X
Sch em e 1. Syn th esis of Cp Ti(Cl)2(o-P P O)
Summary: The preparation of novel titanium complexes
bearing o-phosphinophenol ligands is reported. The
feature of this ligand system is that its electronic and
steric properties can be independently tuned. The com-
Com p lexes
1
plexes were found to be fluxional by H NMR analysis
at low temperature. An X-ray structural analysis showed
that in the solid state the molecule is chiral at the metal
center. These complexes were shown to be effective
catalysts for olefin hydrogenation and imine hydro-
silylation.
titanium,6,7 the phosphinophenol ligand could act as a
six electron, monoanionic ligand. An additional feature
of the o-phosphinophenol ligand is that by changing the
substituents on phosphorus the electronic properties can
be easily varied without affecting steric properties of
the metal complex. In addition the steric environment
imposed by these ligands can also be modified. For
example by placement of two different substituents on
phosphorus the potential for a chiral ligand array exists.
This paper reports the preparation and properties of
novel titanium complexes bearing o-phosphinophenol
ligands.8
In tr od u ction
The cyclopentadienyl ligand is one of the most widely
used ligands in organometallic chemistry.1 The applica-
tion of bis(cyclopentadienyl) complexes of the group 4
transition metals to organic synthesis have been exten-
sively studied.2 We have previously reported the de-
velopment of a bis(cyclopentadienyl)titanium complex
that functions as a catalyst for the hydrogneation of
imines.3 For many reactions of transition metal com-
plexes, ligand electronic effects can dramatically change
the reactivity and/or selectivity.4 One of the limitations
of the cyclopentadienyl ligand is that its electronic
properties are not easily modified without significantly
changing the steric environment. We therefore sought
to develop an electronically tunable ligand system in
order to probe the electronic effects in the titanium-
catalyzed reduction of organic substrates. To accom-
plish this goal we required a ligand that has similar
electronic properties as a cyclopentadienyl ligand but
allows a systematic variation of its electron-donating
ability. The o-phosphinophenol5 ligands appear to meet
the desired criteria. Since titanium oxygen bonds are
known to posses double-bond character, when bound to
Resu lts a n d Discu ssion
Syn th esis. The ligands were prepared in a one pot
procedure by the reaction of 2-bromo-6-tert-butylphenol
with sodium hydride in ether, followed by metal-
halogen exchange with n-butyllithium to generate the
dianion. Quenching this dianion with the requisite
diarylchlorophosphine afforded the desired ligands in
78% and 26% yields for 1a ,b, respectively, after chro-
matography.
Reaction of 1a or 1b with n-butyllithium in THF
followed by slow addition of the anion to a THF solution
of CpTiCl3 (Scheme 1)9 afforded the desired titanium
complexes in 45-63% isolated yields after recrystalli-
zation from toluene or toluene/hexane.
X Abstract published in Advance ACS Abstracts, November 1, 1995.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley CA, 1987.
(2) Broene, R. D.; Buchwald, S. L. Science 1993, 261, 1696.
(3) (a) Willoughby, C. A.; Buchwald, S. L. J . Am. Chem. Soc. 1992,
114, 7562. (b) Willoughby, C. A.; Buchwald, S. L. J . Org. Chem. 1993,
58, 7627. (c) Viso, A.; Lee, N. L.; Buchwald, S. L. J . Am. Chem. Soc.
1994, 116, 9373. (d) Willoughby, C. A.; Buchwald, S. L. J . Am. Chem.
Soc., 1994, 116, 8952. (e) Willoughby, C. A.; Buchwald, S. L. J . Am.
Chem. Soc. 1994, 116, 11703.
(4) (a) Lorkovic, I. M.; Wrighton, M. S.; Davis, W. M. J . Am. Chem.
Soc. 1994, 116, 6220. (b) Casalnuovo, A. L.; RajanBabu, T. V.; Ayers,
T. A.; Warren, T. H. J . Am. Chem. Soc. 1994, 116, 9869. (c) Shih, K.-
Y.; Totland, K.; Seidel, S. W.; Schrock, R. R. J . Am. Chem. Soc. 1994,
116, 12103.
(5) For examples of metal complexes bearing o-phosphinophenol
ligands see: (a) Landvatter, E. F.; Rauchfuss, T. B. Organometallics
1982, 1, 506. (b) Canestrari, M.; Chaudret, B.; Dahan, F.; Huang, Y.-
S.; Poilblanc, R. J . Chem. Soc., Dalton Trans. 1990, 1179. (c) Empsall,
H. D.; Shaw, B. L.; Turtle, J . Chem. Soc., Dalton Trans. 1976, 1500.
(d) Empsall, H. D.; Hyde, E. M.; Shaw, B. L. J . Chem. Soc., Dalton
Trans. 1975, 1690. (e) Rauchfuss, T. B. Inorg. Chem. 1977, 16, 2966.
(6) Huffman, J . C.; Moloy, K. G.; Marsella, J . A.; Caulton, K. G. J .
Am. Chem. Soc. 1980, 102, 3009.
(7) For some leading references on titanium aryloxide complexes
see: (a) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059. (b)
Hill, J . E.; Balaich, G.; Fanwick, P. E.; Rothwell, I. P. Organometallics
1993, 12, 2911. (c) Hill, J . E.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1992, 11, 1771. (d) Duff, A. W.; Kamarudin, R. A.;
Lappert, M. F.; Norton, R. J . J . Chem. Soc., Dalton Trans. 1986, 489.
(8) While this work was in progress
a report on the related
(2-hydroxyethyl)phosphine complexes of titanium appeared; cf.: van
Doorn, J . A.; van der Heijden, H.; Opren, A. G. Organometallics 1994,
13, 4271.
(9) For a discussion of CpTiCl2X complexes see: Wailes, P. C.;
Coutts, R. S. P.; Weigold, H. Organometallic Chemistry of Titanium,
Zirconium and Hafnium; Academic Press: New York, 1974; pp 30-
50.
(10) Clearfield, A.; Warner, D. K.; Saldarriaga-Molina, C. H.; Ropal,
R.; Bernal, I. Can. J . Chem. 1975, 53, 1622.
0276-7333/96/2315-0472$12.00/0 © 1996 American Chemical Society

Notes
Organometallics, Vol. 15, No. 1, 1996 473
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p lex 2a
Bond Distances
Ti-Cl(1)
Ti-Cl(2)
Ti-P
2.333(3)
2.340(2)
2.624(3)
1.860(5)
P-C(6)
O-C(1)
Cp-Ti
1.794(7)
1.367(8)
2.13(2)
Ti-O
Bond Angles
Cl(1)-Ti-Cl(2)
Cl(1)-Ti-P
Cl(1)-Ti-O
Cl(2)-Ti-P
Cl(2)-Ti-O
89.14(9)
142.09(9)
89.2(2)
78.77(8)
129.7(2)
P-Ti-O
72.4(2)
97.2(2)
134.9(4)
116.6(6)
111.8(5)
Ti-P-C(6)
Ti-O-C(1)
O-C(1)-C(6)
P-C(6)-C(1)
Ta ble 2. Red u ction P oten tia ls of Tita n iu m
Com p lexes
complex
Ered vs SCE (V)
-0.69 ((0.02)
tBu
F igu r e 1. ORTEP diagram of complex 2a .
CpTiCl2
O
The complexes are orange moisture sensitive crystal-
line solids. They are very soluble in halogenated
solvents such as methylene chloride and slightly soluble
in ethereal solvents. The compounds exhibit limited
tBu
Cp2TiCl2
-0.80012
-0.79 ((0.02)
-0.78 ((0.02)
2a
2b
1
solubility in toluene or benzene. The H NMR spectra
of 2 (C6D6, rt) display a doublet for the Cp hydrogens
adopts a distorted square based pyramidal coordination
geometry. The cyclopentadienyl ligand occupies the
apical positon with the two chlorines, the oxygen, and
the phosphorus atoms making up the base of the
pyramid. In this geometry the molecule is chiral with
the two phenyl groups on the phosphorus being dia-
stereotopic. Both of the Ti-Cl bond lengths of 2.333(3)
and 2.340(2) Å are in good agreement with those of
Cp2TiCl2.10 The Cl(1)-Ti-Cl(2) angles of 89.14(9)°,
however, is smaller than that for Cp2TiCl2 which is
94.4°. The Ti-O bond length is 1.860(5) Å which is
consistent with some degree of π bonding being present.6,7
The Ti-O bond in [CpTiCl2]O is 1.74 Å,9 while that in
Cp2Ti(Cl)OEt is 1.855(2) Å.6 The Ti-O-Cl(1) angle is
134.9(4)° and also indicates the presence of a π interac-
tion between titanium and oxygen. The Ti-P distance
of 2.624(3) Å is in good agreement with known Ti-P
distances.11 The Ti-P-C(6) angle is 97.2(2)°. Some
strain in the ligand framework is evident from the
O-C(1)-C(6) and the P-C(6)-C(1) angles (116.6(6) and
111.8(5)°, respectively) as these angles are significantly
smaller than the expected value of 120°.
Cyclic Volta m m etr y. Titanium compounds gener-
ally exhibit reversible redox behavior between the +3
and +4 oxidation states. For titanocene dichloride
electrochemical measurements have shown that there
is a reversible redox wave that appears at -0.800 V (vs
SCE).12 With this in mind the reduction potential of
complexes 2 serve as a useful probe of the electron-
donating capabilities of the o-phosphinophenol ligands.
Thus the reduction potentials were measured by cyclic
voltammetry for complexes 2 and some other related
titanium complexes. The results are shown in Table 2.
Complexes 2a ,b exhibited reversible redox waves at
potentials of -0.79 ((0.02) V and -0.78 ((0.02) V (vs
SCE). In comparison the CpTiCl2(O-2,6-ditBuC6H3)
complex has a reduction potential of -0.69 ((0.02) V.
These results show that, as anticipated, 2a ,b are more
(2a , δ 6.18 ppm, J HP ) 2.7 Hz; 2b, δ 6.20 ppm, J HP
)
2.4 Hz) which indicates that the phosphorus is coordi-
nated to titanium. Additionally the chemical shifts in
the 31P NMR spectra (2a , δ 28.4 ppm; 2b, δ 27.6 ppm)
are consistent with a triarylphosphine bound to a metal
center. By 1H NMR the two aryl groups bound to
phosphorus are equivalent at room temperature. The
protons on the two unsubstituted phenyl groups ortho
to phosphorus (in complex 2a ) appear as a multiplet at
7.66 ppm integrating for 4 hydrogens. For complex 2b
the para methyl groups appear as a singlet at δ 1.91
ppm. The signals for the ortho and meta protons of the
two equivalent aryl groups are split into doublets by
coupling to phosphorus.
Since the solid-state structure indicates inequivalence
of the two aromatic groups (vide infra), the molecule
must be fluxional at room temperature. In order to
support this hypothesis, a solution of 2a in toluene-d8
1
was examined by variable-temperature H NMR spec-
troscopy. When the spectrum was acquired at temper-
atures above -30 °C, an apparent triplet at 7.60 ppm
integrating for 4 hydrogens is observed. These are the
hydrogens on the two unsubstituted phenyl groups ortho
to the phosphorus. Upon cooling the sample to -35 °C
this signal begins to broaden and at -40 °C is observed
as a broad singlet. At -50 °C the signal begins to
sharpen into two triplets. When the sample is cooled
to -60 °C, complete resolution is observed; the two
triplets appear at 7.61 and 7.54 ppm, and each signal
integrates to two hydrogens. These data are most
consistent with the suppositon that, of the two possible
coordination geometries for a 5 coordinate complex
(trigonal bipyramidal and square based pyramidal), the
molecule is square pyramidal in solution. At temper-
atures above -40 °C the two nonequivalent phenyl
groups are exchanging rapidly on the NMR time scale.
X-r a y Str u ctu r e. Crystals of 2a suitable for single-
crystal X-ray analysis were isolated by slow cooling of
a saturated hot toluene solution. The ORTEP diagram
is shown in Figure 1, and selected bond distances and
angles are listed in Table 1. The crystals are triclinic
in the P1 space group. In the solid state the molecule
(11) (a) Samuel, E.; Mu, Y.; Harrod, J . F.; Dromzee, Y.; J eannin, Y.
J . Am. Chem. Soc. 1990, 112, 3435. (b) Berry, D. H.; Procopio, L. J .;
Carrol, P. J . Organometallics 1988, 7, 570.
(12) Bajgur, C. S.; Tikkanen, W. R.; Petersen, J . L. Inorg. Chem.
1985, 24, 2539.

474 Organometallics, Vol. 15, No. 1, 1996
Notes
box under nitrogen. Hydrogenation reactions were conducted
in a Fisher-Porter bottle (purchased from Aerosol Lab Equip-
ment, Walton, NY) with Ultra High Purity hydrogen (grade
5). Nuclear magnetic resonance (NMR) spectra were recorded
on a Varian Unity-300, Varian XL-300, or Bruker AC-250
Fourier transform spectrometer. Variable-temperature NMR
experiments were conducted using a Varian VXR-500 spec-
trometer. Elemental analyses were performed by E & R
Microanalytical Laboratories (Corona, NY). Tetrahydrofuran
(THF) and ether were dried and deoxygenated by refluxing
and distilling from sodium/benzophenone ketyl under an argon
atmosphere. All reagents are commercially available and were
used as received unless otherwise stated.
Sch em e 2. Ca ta lytic Activity of Com p lex 2a
2-Br om o-6-ter t-bu tylp h en ol. The method of Pearson14
was used to prepare 2-bromo-6-tert-butylphenol from 2-tert-
butylphenol. The product was purified by column chromatog-
raphy (silica, hexane) to give a colorless oil (61% yield). 1H
NMR (300 MHz, CDCl3, TMS): δ 7.34-7.31 (m, 1H), 7.22-
7.19 (d, 1H, J ) 7.8 Hz), 6.75-6.70 (t, 1H, J ) 7.7 Hz), 5.79
(s, 1H), 1.39 (s, 9H).
electron rich than the related CpTiCl2(OAr) complex.
The potentials of 2a ,b are comparable to that of
Cp2TiCl2 at -0.800 V indicating that these ligands are
electronically similar to the cyclopentadienyl ligand.
However these measurements of the reduction potential
are not sensitive enough to determine the subtle elec-
tronic differences between 2a ,b.
Ca ta lytic Stu d ies. A brief investigation of the
catalytic activity of complex 2a was also conducted. The
results are shown in Scheme 2. Treatment of complex
2a with n-butyllithium under a hydrogen atomosphere
resulted in the formation of an active olefin hydrogena-
tion catalyst. Hydrogenation of 1-octene proceeded
under mild conditions (rt, 20 psig H2) to give a mixture
of octane and an unidentified octene isomer in a 90:5
ratio, respectively. Hydrogenation of an imine, however,
was not successful with this complex. At 80 psig and
65 °C no reduction of N-benzylidenemethylamine was
observed. Hydrosilylation of this imine was affected
using 2a . Treatment of 2a with n-butyllithium in THF
followed by addition of phenylsilane afforded an active
hydrosilylation catalyst which converted the starting
imine completely to product13 in 54 h at 65 °C; no side
products were observed in this reaction.
2-(Dip h en ylp h osp h in o)-6-ter t-bu tylp h en ol, 1a . A dry
Schlenk flask under argon was charged with NaH (0.4 g, 16.5
mmol) and 60 mL of ether. The suspension was cooled to 0
°C, and 2-bromo-6-tert-butylphenol (3.4 g, 15 mmol) was added
dropwise via syringe. The mixture was allowed to stir for 3
h, and n-butyllithium (9.5 mL, 1.74 M in hexanes, 16.5 mmol)
was added. After the mixture was stirred for 1 h, Ph2PCl was
added and the reaction mixture was warmed to room temper-
ature and stirred for 16 h. Ether (100 mL) and saturated
NH4Cl (100 mL) were added, and the layers were separated.
The organic portion was dried over MgSO4 and concentrated
to give the crude product. Column chromatography (silica,
100:1 hexane:EtOAc) afforded 3.92 g (78% yield) of the product
as a viscous oil. 1H NMR (300 MHz, CDCl3, TMS): δ 7.35-
7.32 (m, 11H, 6.98-6.95 (d, 1H, J HP ) 11.3 Hz), 6.87-6.80
(m, 2H), 1.40 (s, 9H). 13C NMR (75 MHz, CDCl3) δ 158.3 (d,
J CP ) 19 Hz), 136.2, 135.0, 133.3 (d, J CP ) 18.7 Hz), 132.4,
128.9, 128.8, 128.5 (d, J CP ) 6.6 Hz), 120.9, 120.3, 34.8, 29.6.
31P NMR (121 MHz, CDCl3, 85% H3PO4): δ -31.3; HRMS: calc
334.1486, found 334.1488.
2-[B i s (4-m e t h y lp h e n y l)p h o s p h i n o ]-6-t er t -b u t y l-
p h en ol, 1b. This was prepared as above from 2-bromo-6-tert-
butylphenol and bis(4-methylphenyl)chlorophosphine.4b
Yield: 26%. 1H NMR (300 MHz, CDCl3, TMS): δ 7.31-7.28
(d, 1H, J ) 7.8 Hz), 7.24-7.17 (m, 8H), 6.97-6.91 (d, 1H, J HP
) 11.2 Hz), 6.90-6.78 (m, 2H), 2.36 (s, 6H), 1.40 (s, 9H). 31P
NMR (121 MHz, CDCl3, 85% H3PO4): δ -32.7; HRMS: calc.
362.1799, found 362.1801.
Con clu sion s
Two novel titanium complexes bearing the phos-
phinophenol ligand system have been prepared and
studied. Electrochemical measurements indicate that
the ligands are similar to the cyclopentadienyl ligand
in their electron-donating properties. By the changing
of substituents on phosphorus, the o-phosphinophenol
ligands can be tailored both electronically and sterically
making the o-phosphinophenol ligands well suited for
further detailed reaction studies. A preliminary inves-
tigation of the catalytic activity of complex 2a indicated
that it is effective for the hydrogenation of an olefin and
the hydrosilylation of an imine. However the reaction
rates are rather slow. The reaction chemistry of these
new titanium complexes remains largely unexplored; we
are continuing to develop and study these and other
novel titanium complexes for catalytic and stoichio-
metric transformations.
P r ep a r a tion of Cyclop en ta d ien yltita n iu m Com p lexes.
2a . A dry Schlenk flask under an argon atmosphere was
charged with 1a (1.33 g, 4 mmol) and THF (20 mL). A solution
of n-butyllithium (2.4 mL, 1.74 M in hexanes, 4.2 mmol) was
added, and the mixture was allowed to stir for 1 h. The
resulting solution was then added via cannula to a solution of
CpTiCl3 (0.877g, 4 mmol) in THF (20 mL) over a period of 10
min. The deep red solution was stirred overnight (12 h), and
the solvent was removed in vacuo to give an orange solid.
Toluene (40 mL) was added, and the mixture was heated to
100 °C and then filtered via cannula while hot. Slow cooling
of the filtrate to -20 °C afforded orange crystals which were
isolated by decanting the supernatant and washing with
hexane. Removal of the residual solvents in vacuo afforded
1.3 g (63% yield) of the desired complex. 1H NMR (300 MHz,
CDCl3, TMS): δ 7.72-7.62 (m, 4H), 7.2-7.18 (d, 1H, J ) 7.5
Hz), 7.0-6.9 (m, 7H), 6.67-6.60 (t, 1H, J ) 7.5 Hz), 6.18 (d,
J HP ) 2.7 Hz), 1.55 (s, 9H). 31P NMR (121 MHz, C6D6, 85%
H3PO4): δ 28.4. 13C NMR (75 MHz, CD2Cl2): δ 171.3 (d, J CP
) 27.5 Hz), 138.6 (d, J CP ) 3.8 Hz), 132.6 (d, J CP ) 9.8 Hz),
131.4, 131.1 (d, J CP ) 11.3 Hz), 129.5 (d, J CP ) 9 Hz), 129.3,
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were conducted
under an atmosphere of prepurified argon or hydrogen using
standard Schlenk and glovebox techniques. Handling of
complexes 2 was conducted in a Vacuum Atmospheres glove-
(13) The initial product is assumed to be the silyl amine. However,
the Si-N bond is very labile and is immediately hydrolyzed upon
exposure to ambient atmosphere.
(14) Pearson, D. E.; Wysong, R. D.; Breder, C. V. J . Org. Chem. 1967,
32, 2358.

Notes
Organometallics, Vol. 15, No. 1, 1996 475
Ta ble 3. Cr ysta l Da ta for Com p ou n d 2a
128.5, 125.6, 122.4 (d, J CP ) 6 Hz), 121.5, 35.4, 29.7. Anal.
Calc for C27H27Cl2OPTi: C, 62.69; H, 5.26. Found: C, 62.94;
H, 5.37.
empirical formula
C27H27OPCl2Ti
517.295
fw
2b. A dry Schlenk flask under an argon atmosphere was
cryst color, habit
cryst dimens
cryst system
lattice params
orange, prismatic
0.050 × 0.100 × 0.300 mm
triclinic
charged with 1b (1.4 g, 3.8 mmol) and THF (20 mL).
A
solution of n-butyllithium (2.5 mL, 1.60 M in hexanes, 4.1
mmol) was added, and the mixture was allowed to stir for 1
h. The resulting solution was then added via cannula to a
solution of CpTiCl3 (0.847 g, 3.8 mmol) in THF (20 mL) over
a ) 10.009(3) Å
b ) 14.590(4) Å
c ) 9.889(3) Å
R ) 92.95(3)°
â ) 98.56(3)°
γ ) 77.72(2)°
V ) 1395.0(8) Å3
P1
a
period of 10 min. The deep red solution was stirred
overnight (12 h), and the solvent was removed in vacuo to give
an orange solid. Toluene (25 mL) and hexane (20 mL) were
added, and the mixture was heated to 80 °C and filtered via
cannula while hot. The filtrate was slowly cooled to -20 °C
to give orange crystals. The crystals were washed with hexane
and dried in vacuo to afford 0.54 g of product. The supernatant
was concentrated and the resulting solid recrystallized in a
similar manner to give an additional 0.4 g of product. Yield:
0.94 g (45%). 1H NMR (300 MHz, CDCl3, TMS): δ 7.68-7.62
(m, 4H), 7.22-7.20 (d, 1H, J ) 7.8 Hz), 7.12-7.09 (m, 1H),
6.81-6.78 (m, 4H), 6.68-6.63 (t, 1H, J ) 7.8 Hz), 6.20 (d, J HP
) 2.4 Hz), 1.91 (s, 6H), 1.55 (s, 9H). 31P NMR (121 MHz, C6D6,
85% H3PO4): δ 27.6. 13C NMR (75 MHz, CD2Cl2): δ 171.1 (d,
space group
Z value
Dcalc
diffractometer
radiation
temp
2
1.341 g/cm3
Rigaku AFC6R
Mo KR (0.710 69 Å)
195 K
take-off angle
scan rate
scan width
2θmax
6.0°
8.0°/min (in ω)
(1.15 + 0.3 tan æ)°
0.0°
no. of reflcns measd
tot. 4016
unique 3709
Lorentz-polarization
abs (0.86-1.19)
2117
334
0.052
corrs
J CP ) 27.2 Hz), 142.0, 138.5 (d, J CP ) 4.5 Hz), 132.5 (d, J CP
)
9.5 Hz), 130.9 (d, J CP ) 14 Hz), 130.2 (d, J CP ) 9.9 Hz), 129.3,
128.5, 125.8, 122.3 (d, J CP ) 5.3 Hz), 121.5, 35.3, 29.7, 21.6.
Anal. Calc for C29H31Cl2OPTi: C, 63.87; H, 5.73. Found: C,
63.92; H, 5.96.
no. of obsd reflcns
no. of variables
R
Rw
0.057
Cp TiCl2(O-2,6-d itBu C6H3). A dry Schlenk flask under
argon was changed with 2,6-di-tert-butylphenol (0.825 g, 4
mmol) and THF (15 mL). A solution of n-butyllithium (2.5
mL, 4 mmol, 1.6 M in hexanes) was added, and the reaction
mixture was stirred for 30 min. The resulting solution was
transferred via cannula to a solution of CpTiCl3 (0.877 g, 4
mmol) in THF (15 mL). The mixture turned deep red and was
allowed to stir at room temperature for 8 h. The solvent was
removed in vacuo, and the resulting orange solid was extracted
with hot hexane (60 mL). Cooling to -20 °C afforded 0.80 g
of orange crystals (51% yield). 1H NMR (250 MHz, C6C6): δ
7.2-7.25 (d, 2H, J ) 6.8 Hz), 6.88-6.79 (dd, 1H, J ) 6.8 Hz),
6.08 (s, 5H), 1.43 (s, 18 H).
X-r a y Str u ctu r e Deter m in a tion of 2a . The X-ray struc-
ture determination of complex 2a was conducted using a
Rigaku-AFC6R diffractometer at 195 K. A total of 4016
reflections were collected. The crystals are triclinic, space
group P1, with a ) 10.009 Å, b ) 14.590 Å, c ) 9.889 Å, R )
92.95°, â ) 98.56°, and γ ) 77.72°. An empirical absorption
correction, using the DIFABS15 program, was applied. Aniso-
tropic refinement was conducted using direct methods.16 The
final cycle was based on 2117 reflections and converged with
an agreement factor of R ) 0.052. Crystal data are shown in
Table 3.
max shift/error in final cycle
1.51
Ether (10 mL) and 1-octene (314 µL, 2 mmol) were added. A
solution of n-butyllithium (123 µL, 1.63 M in hexanes, 0.2
mmol) was added, and the mixture turned a dark brown color.
The vessel was charged to 20 psig, and the reaction mixture
was stirred at room temperature for 5 h. At this point GC/
MS analysis showed no 1-octene remaining. Two new products
were present in a 90:5 ratio. These were identified by GC/
MS; the major product was octane (MW ) 114), and the minor
product was an octene isomer (MW ) 112).
Hyd r osilyla tion of N-Ben zylid en em eth yla m in e w ith
2a . A dry Schlenk flask under argon was charged with 2a
(52 mg, 0.1 mmol) and THF (5 mL). The solution was cooled
to 0 °C, and a solution of n-butyllithium (123 µL, 1.63 M in
hexanes, 0.2 mmol) was added. After 1 min phenylsilane (271
µL, 2.2 mmol) was added followed by N-benzylidinemethyl-
amine (250 µL, 2.0 mmol). The mixture was heated in an oil
bath at 65 °C for 54 h. At this point GC analysis showed that
no imine remained. The only product detected was N-
methylbenzylamine.13
Cyclic Volta m m etr y. In a glovebox the titanium complex,
Bu4NPF6, and ferrocene were dissolved in THF (5 mL). The
measurements were conducted using a Pine RDE4 potentiostat
with a glassy carbon working electrode, a Pt counter electrode,
and a Ag reference electrode. The potential was scanned at a
rate of 100 mV/s, and the voltammograms were recorded using
a Kipp & Zonen BD90 X-Y recorder. The potentials were
corrected vs the Cp2Fe/Cp2Fe+ couple (+0.51 V vs SCE):
Cp2TiCl2O(2,6-tBu6H3), -0.69 ((0.02) V; 2a , -0.79 ((0.02) V;
2b, -0.78 ((0.02) V.
Ack n ow led gm en t. This research was supported by
the National Institutes of Health (Grant GM 46059), to
whom we are grateful. S.L.B. acknowledges additional
support as a support as a Camille & Henry Dreyfus
Teacher-Scholar. C.A.W. acknowledges support as an
ACS Organic Division Predoctoral Fellow (sponsored by
the Monsanto Co.). R.R.D. acknowledges support from
the National Science Foundation. We thank Professor
Mark S. Wrighton for use of the electrochemical equip-
ment.
Hyd r ogen a tion of 1-Octen e w ith 2a . A dry Fisher-Porter
bottle under nitrogen was charged with 2a (52 mg, 0.1 mmol),
and the vessel was evacuated and filled with hydrogen (3×).
(15) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(16) (a) Calbrese, J . C. PHASE-Patterson Heavy Atom Solution
Extractor. Ph.D. Thesis, University of WisconsinsMadison, 1972. (b)
Beurskens, P. T. DIRDIF-Direct Methods for Difference Structures-
an automatic procedure for phase extension and refinement of differ-
ence structure factors. Technical Report, 1984/1 Crystallography
Laboratory, Toernooiveld, 6525 Ed Nijmegen, The Netherlands.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and thermal parameters, U values, and complete bond dis-
tances and angles for complex 2a (21 pages). Ordering
information is given on any current masthead page.
OM950352S