Assembly of Mo/Ti µ-Oxo Complexes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10187
filtrate still contained a significant amount of (MeO)(N)Mo{[µ-O]Ti-
(NRAr)3}2 but further isolation proved difficult. Pure samples of
(MeO)(N)Mo{[µ-O]Ti(NRAr)3}2 may be crystallized by slow evapora-
tion from Et2O to form orange parallelepipeds. 1H NMR (300 MHz,
CDCl3, 25 °C): δ ) 6.74 (s, 6H, para C6H3Me2), δ ) 5.9 (s, 12H,
ortho C6H3Me2), δ ) 4.68 (s, 3H, OCH3) δ ) 2.20 (s, 36H, meta
C6H3Me2), δ ) 1.25 (s, 18H, C(CD3)2CH3). 1H NMR (300 MHz, C6D6,
25 °C): δ ) 6.76 (s, 6H, para C6H3Me2), δ ) 6.2 (s, 12H, ortho C6H3-
Me2), δ ) 4.61 (s, 3H, OCH3) δ ) 2.24 (s, 36H, meta C6H3Me2), δ )
1.53 (s, 18H, C(CD3)2CH3). 13C{1H} NMR (75 MHz, CDCl3, 25 °C):
δ ) 152.75 (aryl ipso), δ ) 136.16 (aryl meta), δ ) 127.58 (aryl ortho),
δ ) 125.89 (aryl para), δ ) 60.36 (NC(CD3)2(CH3)), δ ) 56.51
(OCH3), δ ) 31.00 (NC(CD3)2(CH3)), δ ) 21.71 (NAr(CH3)2). Anal.
Calcd for C73H75D36MoTi2N7O3: C, 64.34; H, 8.17; N, 7.20. Found:
C, 63.11; H, 8.34; N, 6.95.
Note: 1H NMR analysis of the fine light brown powder initially
filtered away indicated the presence of the anilinium salt [H(Me)NRAr]-
[I]. This salt was prepared independently through treatment of HNRAr
with neat MeI. 1H NMR (300 MHz, CDCl3, 25 °C): δ ) 10.95 (s
(br), 1H, HN), δ ) 7.37 (s, 1H, para C6H3Me2), δ ) 7.05 (s, 2H,
ortho C6H3Me2), δ ) 3.102 (d, 3H, NCH3), δ ) 2.31 (s, 6H, meta
C6H3Me2), δ ) 1.51 (s, 3H, C(CD3)2CH3).
7.05 (m, 18H, para,meta C6H5), δ ) 6.26 (d, 12H, ortho C6H5), δ )
1.15 (s, 54H, C(CH3)3. 1H NMR (300 MHz, C6D6, 25 °C): δ ) 7.12
(m, 18H, meta C6H5), δ ) 7.03 (t, 6H, para C6H5), δ ) 6.49 (d, 12H,
ortho C6H5), δ ) 1.43 (s, 54H, C(CH3)3. 13C{1H} NMR (75 MHz,
CDCl3, 25 °C): δ ) 152.01 (aryl ipso), δ ) 127.63 (aryl meta), δ )
129.31 (aryl ortho), δ ) 125.23 (aryl para), δ ) 62.20 (NC(CH3)3), δ
) 30.97 (NC(CH3)3). Anal. Calcd for C60H84MoTi2N6O4: C, 62.90;
H, 7.39; N, 7.34. Found: C, 63.00; H, 7.32; N, 7.15.
X-ray Structure of O2Mo{[µ-O]Ti(tBuNPh)3}2. Crystal structure
data for C60H84MoN6O4Ti2: orange plate, 0.65 × 0.35 × 0.05 mm,
monoclinic, a ) 18.0093(13) Å, b ) 18.6394(14) Å, c ) 18.9783(14)
Å, â ) 112.5350(10)°, V ) 5884.3(8) Å3, Z ) 4, space group P21/n,
u ) 0.524 mm-1, Fcalc ) 1.293 g/cm3, F(000) ) 2416. Data collection
on a Siemens Platform goniometer with a CCD detector at 193(2) K
using Mo KR radiation [λ ) 0.710 73 Å] (-20 e h e 18, -16 e k e
20, -14 e l e 21). Total data 8680 (3545 unique, Rint ) 0.0605).
Data were corrected for Lorentz polarization and absorption (Tmax, Tmin
,
1.0000 and 0.9334 respectively). Structure solved by direct methods
(SHELXTL V5.0, Sheldrick, G. M. and Siemens Industrial Automaion,
Inc. 1995) in conjunction with standard difference Fourier techniques.
Least-squares refinement based upon F2 converged with final residu-
als: R1 ) 0.0827, wR2 ) 0.1497, and GOF ) 1.235 based upon I >
2σ(I). Residual electron density, +0.326 and -0.324 e Å-3
.
Spectroscopic Study of (MeO)(15N)Mo{[µ-O]Ti(NRAr)3}2 and
(H313CO)(15N)Mo{[µ-O]Ti(NRAr)3}2. Mo(15N)(OtBu)[OTi(NRAr)3]2
(75 mg, 0.53 mmol) was stirred in MeI (2 mL) for 13 h and worked
up as described above for (MeO)(N)Mo{[µ-O]Ti(NRAr)3}2. 1H NMR
(300 MHz, C6D6, 25 °C) indicated no splitting of the resonance at δ )
4.61 ppm, consistent with an O-bound methyl group rather than an
N-bound methyl group. As it was difficult to definitively assign the
methyl resonance in the 13C NMR spectrum, a sample was prepared
using 13CH3I. 13C{1H} NMR (75 MHz, CDCl3, 25 °C) revealed an
enhanced methyl resonance exhibiting no 15N coupling at δ ) 56.45.
The gated-decoupled spectrum showed a quartet for this resonance (JCH
Attempted Reaction of O2Mo{[µ-O]Ti(tBuNPh)3}2 with Ti-
(tBuNPh)3. Ti(tBuNPh)3 (21.3 mg, 0.0432 mmol) in C6D6 (0.5 mL)
was added to O2Mo{[µ-O]Ti(tBuNPh)3}2 (49.5 mg, 0.0432 mmol) in
C6D6 (0.5 mL). None of the starting O2Mo{[µ-O]Ti(tBuNPh)3}2 was
consumed, even with gentle heating at 50 °C for 1 h, as indicated by
1H NMR. This was confirmed by intergration against an internal
standard (hexamethylbenzene).
Attempted Deoxygenation of O2Mo{[µ-O]Ti(tBuNPh)3}2 with
PEt3. O2Mo{[µ-O]Ti(tBuNPh)3}2 (70 mg, 0.0611 mmol) was dissolved
in 5 mL of a 1:1 solution of benzene/PEt3 (by volume). There was no
indication of deoxygenation after 1 week at 70 °C as ascertained by
removal of volatile material in Vacuo and subsequent 1H NMR analysis
of the residue. Similar results were obtained using P(OEt)3 in place
of PEt3 in an otherwise identical experiment.
1
) 140 Hz), consistent with the H NMR (300 MHz, CDCl3, 25 °C)
spectrum of this sample which showed a doublet at δ ) 4.69p (JCH
)
135 Hz). These data strongly support our assignment of an O-bound
methyl group.
Attempted Deoxygenation of O2Mo{[µ-O]Ti(tBuNPh)3}2 with
Mo(NRAr)3. One equivalent of Mo(NRAr)3 (15.4 mg, 0.0239 mmol)
in C6D6 (0.5 mL) was added to O2Mo{[µ-O]Ti(tBuNPh)3}2 (27.4 mg,
Attempted X-ray Structure of (MeO)(N)Mo{[µ-O]Ti(NRAr)3}2.
Further confirmation of the proposed O-CH3 connectivity was sought
by an X-ray diffraction study of an orange crystal of (MeO)(N)Mo-
{[µ-O]Ti(NRAr)3}2. Though the presence of the two titanoxo moieties
was confirmed, a disorder problem prevented the assignment of the
methyl linkage (i.e., CH3-O-Mo versus CH3-NdMo).
2
0.0239 mmol) in C6D6 (0.5 mL). The reaction was monitored by H
NMR. No diminishment of intensity of the Mo(NRAr)3 64 ppm signal
was noted after 1 h at 55 °C.
Attempted Deoxygenation of O2Mo{[µ-O]Ti(tBuNPh)3}2 with
(THF)V(Mes)3. One equivalent of V(Mes)3(THF) (12 mg, 0.025
mmol) was added as a blue solid to O2Mo{[µ-O]Ti(tBuNPh)3}2 (28.6
mg, 0.025 mmol) in toluene (2 mL). After 9 h at 70 °C, it appeared
that some of the starting O2Mo{[µ-O]Ti(tBuNPh)3}2 had been consumed
(1H NMR). However, no OV(Mes)3 was observed and isolation of a
Mo/Ti product was not attempted.
Synthesis of O2Mo{[µ-O]Ti(tBuNPh)3}2. MoO2(OtBu)2 was pre-
pared by the (slightly modified) method91,92 of Chisholm and co-
workers: Mo(OtBu)6 (471 mg, 0.747 mmol) was dissolved in Et2O
(10 mL) under N2 in a Schlenk vessel fitted with a septum. Dry oxygen
(40 mL, 1 atm, 1.63 mmol) was added via syringe, and the orange
reaction mixture was stirred at 25 °C. After 15 min, another 10 mL of
O2 was added to ensure complete consumption of Mo2(OtBu)6, as
suggested by the production of a yellow solution lacking any orange
tint. Volatile material was removed in Vacuo, and the yellow oil was
Attempted Reaction of O2Mo{[µ-O]Ti(tBuNPh)3}2 with Ethylene.
O2Mo{[µ-O]Ti(tBuNPh)3}2 (40 mg, 0.035 mmol) in C6D6 (2.5 mL) was
stirred under an atmosphere of ethylene at 70 °C for 1 week. No
reaction was observed as ascertained by removal of volatile material
t
triturated once with toluene in order to remove any residual BuOH.
The yellow oil thereby obtained was used without further purification
1
in preparing O2Mo{[µ-O]Ti(tBuNPh)3}2 as follows.
in Vacuo and subsequent H NMR analysis of the residue.
Attempted Reaction of O2Mo{[µ-O]Ti(tBuNPh)3}2 with Ph2SiH2.
One equivalent of Ph2SiH2 (15 mg, 0.0169 mmol) in C6D6 (0.5 mL)
was added to O2Mo{[µ-O]Ti(tBuNPh)3}2 (19.3 mg, 0.0169 mmol) in
C6D6 (0.5 mL). There was no reaction after 3 days at 70 °C, as
A green solution of Ti(tBuNPh)3 (706 mg, 1.43 mmol) in benzene
(15 mL) was added via pipet to a stirring solution of freshly prepared,
yellow MoO2(OtBu)2 (197 mg, 0.717 mmol) in benzene (1.3 mL). The
murky reaction mixture adopted a brown color after the addition was
complete. The solution was transferred to a 100 mL glass vessel with
a Teflon needle plug and was stirred at 65 °C for 17 h, by which time
the solution had turned reddish-orange in color. Volatile material was
removed in Vacuo, and the residue was triturated with pentane (1 × 5
mL) affording a reddish-orange solid. This solid was transferred to a
sintered glass frit and washed with cold pentane (3 × 5 mL) until a
fine, bright orange powder (440 mg) remained on the frit. This powder,
when pure, has very low solubility in pentane. A second crop of 40
mg was attained by slow cooling of the combined washings at -35
°C, affording 480 mg (58.5%) of O2Mo{[µ-O]Ti(tBuNPh)3}2 overall.
This powder was spectroscopically pure. The product can be recrystal-
lized efficiently by vapor diffusion of hexane into a THF solution to
form red-orange crystals. 1H NMR (300 MHz, CDCl3, 25 °C): δ )
1
indicated by H NMR.
Synthesis of (iPrO)3V[µ-O]Ti(NRAr)3. A -35 °C solution of Ti-
(NRAr)3 (399.6 mg, 672 µmol) in ether (10 mL) was added dropwise
via pipet to a thawing solution of OV(OiPr)3 (164.0 mg, 672 µmol) in
ether (5 mL). The reaction mixture warmed to 30 °C and was stirred
for 3 h. Removal of all volatile material in vacuo left a yellow-green
solid. Three recrystallizations (ether, -35 °C) yielded pure (iPrO)3V-
1
[µ-O]Ti(NRAr)3 (434.7 mg, 518 µmol, 77%). Mp: 154-156 °C. H
NMR (300 MHz, C6D6, 25 °C): δ ) 6.76 (s, 3H, para ArH, ∆ν1/2
)
10 Hz), 6.11 (bs, ∆ν1/2 ) 77 Hz, 6H, ortho ArH), 4.15 (s, ∆ν1/2 ) 203
Hz, 27H, OCH(CH3)2), 2.23 (s, ∆ν1/2 ) 12 Hz, 18H, meta ArCH3),
∼2.2 (vbs, 9H, NCCH3), no signal corresponding to OCH(CH3)2 was
located. 2H NMR (300 MHz, ether, 25 °C): δ ) 2.29 (∆ν1/2 ) 10
Peters, Jonas C.
