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.