Synthesis of molybdenum(VI) monoimido alkyl and alkylidene complexes

Article abstract of DOI:10.1021/om0401408

In this paper we report the synthesis of several new Mo(NR)Cl ₄(THF) species (R = C₆F₅, 3,5-(CF ₃)₂C₆H₃, 1-adamantyl, CPh ₃, and 2,6-i-Pr₂C₆H₃) via the treatment of MoCl₄(THF)₂ with azides and their reactions with neopentyl reagents. Addition of Mo(NR)Cl₄(THF) complexes in toluene to a cold solution of NpMgCl in ether gave Mo(NR)Np₃Cl species (R = C₆F₅) 3,5-(CF₃)₂C ₆H₃) Ad, Ph₃C, and 2,6-i-Pr₂C ₆H₃ (Ar); Np = CH₂-t-Bu) in poor (35%) to modest (51%) yields. Heating Mo(NAr)Np₃Cl in C₆D ₆ to 50 °C results in α-hydrogen abstraction to give neopentane and a molecule whose NMR spectra are consistent with it being Mo(NAr)(CH-t-Bu)(CH₂-t-Bu)Cl; it decomposed bimolecularly upon attempted isolation. The other Mo(NR)Np₃Cl species were found to be more stable than Mo(NAr)Np₃Cl, but when they did decompose at elevated temperatures, no neopentylidene complex could be observed. Addition of neopentyllithium to Mo(NR)Np₃Cl species (R = Ar, CPh₃, or Ad) yielded Mo(NR)(CH-t-Bu)Np₂ species, the adamantylimido version of which is unstable toward bimolecular decomposition. Addition of neopentyllithium to Mo(NR)Np₃Cl complexes in which R = pentafluorophenyl or 3,5-trifluoromethylphenyl led to intractable mixtures. Addition of 1 equiv of 2,6-diisopropylphenol, 2,6-dimethylphenol, or 3,5-(2,4,6-i-Pr₃C₆H₂)₂C ₆H₃OH (HIPTOH) to Mo(NCPh₃)(CH-t-Bu)Np ₂ led to formation of Mo(NCPh₃)(CH-t-Bu)Np(OR) species, while treatment of Mo(NCPh₃)(CH-t-Bu)₂(CH ₂-t-Bu) with C₆F₅OH gave Mo(NCPh ₃)-Np₃(OC₆F₅). The three monophenoxide neopentylidene complexes showed poor to moderate metathesis activity for ring-closing a small selection of substrates. X-ray studies were completed for Mo[N-3,5-(CF₃)₂C₆H ₃]Cl₄(THF), Mo[N-3,5-(CF₃)₂C ₆H₃]Np₃Cl, Mo(NCPh₃)-Np ₃Cl, and Mo(NCPh₃)(CH-t-Bu)(CH₂-t-Bu)(OHIPT).

Full text of DOI:10.1021/om0401408

Organometallics 2005, 24, 1929-1937
1929
Synthesis of Molybdenum(VI) Monoimido Alkyl and
Alkylidene Complexes
Tatiana S. Pilyugina, Richard R. Schrock,* Adam S. Hock, and Peter Mu¨ller
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received December 21, 2004
In this paper we report the synthesis of several new Mo(NR)Cl4(THF) species (R ) C6F5,
3,5-(CF3)2C6H3, 1-adamantyl, CPh3, and 2,6-i-Pr2C6H3) via the treatment of MoCl4(THF)2
with azides and their reactions with neopentyl reagents. Addition of Mo(NR)Cl4(THF)
complexes in toluene to a cold solution of NpMgCl in ether gave Mo(NR)Np3Cl species (R )
C6F5, 3,5-(CF3)2C6H3, Ad, Ph3C, and 2,6-i-Pr2C6H3 (Ar); Np ) CH2-t-Bu) in poor (35%) to
modest (51%) yields. Heating Mo(NAr)Np3Cl in C6D6 to 50 °C results in R-hydrogen
abstraction to give neopentane and a molecule whose NMR spectra are consistent with it
being Mo(NAr)(CH-t-Bu)(CH2-t-Bu)Cl; it decomposed bimolecularly upon attempted isolation.
The other Mo(NR)Np3Cl species were found to be more stable than Mo(NAr)Np3Cl, but when
they did decompose at elevated temperatures, no neopentylidene complex could be ob-
served. Addition of neopentyllithium to Mo(NR)Np3Cl species (R ) Ar, CPh3, or Ad) yielded
Mo(NR)(CH-t-Bu)Np2 species, the adamantylimido version of which is unstable toward
bimolecular decomposition. Addition of neopentyllithium to Mo(NR)Np3Cl complexes in which
R ) pentafluorophenyl or 3,5-trifluoromethylphenyl led to intractable mixtures. Addition
of 1 equiv of 2,6-diisopropylphenol, 2,6-dimethylphenol, or 3,5-(2,4,6-i-Pr3C6H2)2C6H3OH
(HIPTOH) to Mo(NCPh3)(CH-t-Bu)Np2 led to formation of Mo(NCPh3)(CH-t-Bu)Np(OR)
species, while treatment of Mo(NCPh3)(CH-t-Bu)2(CH2-t-Bu) with C6F5OH gave Mo(NCPh3)-
Np3(OC6F5). The three monophenoxide neopentylidene complexes showed poor to moderate
metathesis activity for ring-closing a small selection of substrates. X-ray studies were
completed for Mo[N-3,5-(CF3)2C6H3]Cl4(THF), Mo[N-3,5-(CF3)2C6H3]Np3Cl, Mo(NCPh3)-
Np3Cl, and Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)(OHIPT).
Introduction
prepared in high yield by adding p-tolyl azide to MoCl4-
(THF)2 and was crystallographically characterized. A
dimeric version in which two imido nitrogens are linked
with a p-phenylene group, (THF)Cl4ModN-p-C6H4-Nd
MoCl4(THF), was prepared in an analogous manner.5
Mo(NCH2CHdCH2)Cl4(THF) was prepared in situ from
allyl azide and MoCl4(THF)2; it was not isolated or
characterized, but converted directly into a Mo(V)
bisphosphine derivative.6 All published imido tetrachlo-
rides are reduced readily by phosphines to yield Mo(V)
species, e.g., Mo(NAllyl)Cl3(PPh3)2.6
In this paper we report the synthesis of several new
Mo(NR)Cl4(THF) species and their reactions with neo-
pentyl reagents. The object is to explore the general
features of alkylation and R hydrogen abstraction in
Mo(VI) monoimido species, and in particular to prepare
new examples of Mo(NR)(CH-t-Bu)(OR′)(CH2-t-Bu) spe-
cies more simply and directly.
We recently reported complexes of the type M(NR)-
(CH-t-Bu)(OR′)(CH2-t-Bu) where M is Mo1 or W,2 R is
2,6-i-Pr2C6H3 (Ar) or 2,6-Me2C6H3 (Ar′), and OR′ is one
of several alkoxides or phenoxides. The molybdenum
complexes were prepared via a traditional route to
bisalkoxide metathesis catalysts3 that centers around
the reaction of Mo(NAr)2(CH2-t-Bu)2 with triflic acid
to yield Mo(NAr)(CH-t-Bu)(dme)(OTf)2. In contrast,
W(NAr)(CH-t-Bu)(CH2-t-Bu)2 could be prepared from
W(NAr)Cl4.2 M(NR)(CH-t-Bu)(OR′)(CH2-t-Bu) species
are being explored as olefin metathesis catalysts and
have also been found to decompose to give unusual
species of the type [M(NR)(OR′)(CH2-t-Bu)]2 that contain
unbridged MdM bonds.2
A potentially more direct route to Mo(NR)(CH-t-Bu)-
(OR′)(CH2-t-Bu) complexes would involve a synthesis
patterned after that for the W analogues, i.e., addition
of neopentyl groups to Mo(NR)Cl4(THF) complexes.
However, few examples of Mo(NR)Cl4 complexes have
appeared in the literature. The first, Mo(N-p-tolyl)Cl4-
(THF), was published in 1984 by Maata.4 It was
Results
Synthesis of Imido Tetrachloride Complexes. We
were interested in the possibility of preparing catalysts
* To whom correspondence should be addressed. E-mail: rrs@mit.edu.
(1) Sinha, A.; Schrock, R. R. Organometallics 2004, 23, 1643.
(2) Lopez, L. P. H.; Schrock, R. R. J. Am. Chem. Soc. 2004, 126,
9526.
(3) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare,
M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875.
(4) Chou, C. Y.; Huffman, J. C.; Maatta, E. A. J. Chem. Soc., Chem.
Commun. 1984, 1184.
(5) Maatta, E. A.; Devore, D. D. Angew. Chem., Int. Ed. Engl. 1988,
27, 569.
(6) Maatta, E. A.; Du, Y.; Rheingold, A. L. Chem. Commun. 1990,
756.
10.1021/om0401408 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/15/2005

1930 Organometallics, Vol. 24, No. 8, 2005
Pilyugina et al.
Table 1. Crystal Data and Structure Refinement for Mo[N-3,5-(CF3)2C6H3]Cl4(THF),
Mo[N-3,5-(CF3)2C6H3](CH2-t-Bu)3Cl, Mo[NC(C6H5)3](CH2-t-Bu)3Cl, and
Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)(OHIPT)a
empirical formula
fw
C12H11Cl4F6MoNO
536.96
C23H36ClF6MoN
571.92
C34H48ClMoN
602.12
C65H85MoNO
992.28
T (K)
193(2)
193(2)
193(2)
100(2)
cryst syst
space group
unit cell dimens (Å, deg)
triclinic
P1h
monoclinic
C2/c
17.3743(13)
9.8338(7)
32.380(2)
90
monoclinic
P2(1)/n
10.153(2)
18.451(4)
17.416(4)
90
monoclinic
P2(1)
10.212(6)
40.85(3)
13.861(9)
90
a ) 9.0151(8)
b ) 10.3616(9)
c ) 11.0455(10)
R ) 63.349(2)
â ) 86.872(2)
γ ) 88.901(2)
920.76(14)
2
103.7330(10)
90
103.55(3)
90
102.618(12)
90
volume (Å3)
5374.2(7)
8
3171.7(11)
4
5642(6)
Z
4
density (calcd; Mg/m3)
1.937
1.414
1.261
1.168
absorp coeff (mm-1
F(000)
)
1.351
0.639
0.519
0.273
524
2352
1272
2128
cryst size (mm)
θ range (deg)
index ranges
0.3 × 0.16 × 0.09
2.07 to 24.99
-10 e h e 9
-7 e k e 12
-13 e l e 12
5000
0.38 × 0.28 × 0.20
1.29 to 28.30
-22 e h e 23
-8 e k e 13
-32 e l e 42
16 562
0.25 × 0.20 × 0.20
1.63 to 26.44
-12 e h e 12
-23 e k e 23
-21 e l e 21
54 550
0.25 × 0.08 × 0.08
1.00 to 28.28
-13 e h e 13
-54 e k e 54
0 e l e 18
125 702
no. of reflns collected
no. of indep reflns [R(int)]
completeness (to θ ))
3233 [0.0233]
99.6% (24.99°)
3233/0/227
1.076
R1 ) 0.0360
wR2 ) 0.0883
R1 ) 0.0524
wR2 ) 0.0929
0.518 and -0.486
6297 [0.0153]
94.1% (28.30°)
6297/0/290
1.114
R1 ) 0.0309
wR2 ) 0.0755
R1 ) 0.0321
wR2 ) 0.0762
0.800 and -0.608
6532 [0.0300]
99.8% (26.44)
6532/0/334
1.097
R1 ) 0.0265
wR2 ) 0.0669
R1 ) 0.0313
wR2 ) 0.0706
0.816 and -0.257
27 827 [0.07980]
99.7% (28.28°)
27 827/1374/1247
1.091
R1 ) 0.0685
wR2 ) 0.1461
R1 ) 0.0875
wR2 ) 0.1562
1.268 and -1.101
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff. peak and hole (e Å-3
)
a In each case the wavelength was 0.71073 Å, the refinement method was full-matrix least-squares on F2, and the absorption correction
was semiempirical.
that contain an electron-withdrawing imido group and
therefore chose to attempt to prepare pentafluoro-
phenylimido and 3,5-bis(trifluoromethyl)phenylimido
Mo(NR)Cl4(THF) complexes. We also were interested
in preparing alkylimido complexes and, for this rea-
son, chose 1-adamantylimido (AdN) and tritylimido (tri-
phenylmethylimido). Finally, we chose to prepare
Mo(NAr)Cl4(THF) (Ar ) 2,6-i-Pr2C6H3), since molybde-
num alkylidene complexes that contain the NAr group
are the most numerous and stable.7,8
out in 1,2-dichloroethane or toluene. The lowest yield
was obtained for Mo(NAr)Cl4(THF), in which the imido
group is the most demanding sterically.
Pentafluorophenyl azide,9 3,5-bis(trifluoromethyl)-
phenyl azide,10 1-adamantyl azide,11 triphenylmethyl
azide,12 and 2,6-diisopropylphenyl azide13 were all pre-
pared readily in good yields by published methods or
slight variations thereof. Adamantyl azide and trityl
azide are white crystalline compounds; the others are
oils.
The azides react with MoCl4(THF)2 to give com-
plexes of the type Mo(NR)Cl4(THF) in good (66%) to
excellent (96%) yields (eq 1). Reactions can be carried
Single crystals of Mo[N-3,5-(CF3)2C6H3]Cl4(THF) were
grown from pentane, and an X-ray determination was
carried out (Tables 1 and 2). The structure of Mo[N-
3,5-(CF3)2C6H3]Cl4(THF) (Figure 1) is closely analogous
to that of Mo(N-p-tolyl)Cl4(THF).4 The Mo-N(1) dis-
tance (1.715(3) Å) and Mo-N(1)-C(1) angle (171.2(3)°)
are typical of imido complexes of Mo(IV). The chlorides
are all bent away from the imido group, as judged from
the N(1)-Mo-Cl angles, which vary from ∼92° to ∼98°.
The Mo-O(1) bond length (2.230(2) Å) is normal, even
though it is trans to the pseudo triply bound imido
ligand.
14
(7) Schrock, R. R. Chem. Rev. 2002, 102, 145.
(8) Schrock, R. R.; Hoveyda, A. H. Angew. Chem., Int. Ed. 2003, 42,
4592.
(9) Kanakarajan, K.; Haider, K.; Czarnik, A. W. Synthesis 1988, 7,
566.
Synthesis of Imido Trineopentyl Complexes.
Osborn reported in 1987 that Mo(N-t-Bu)(O)Cl2(MeCN)3
(10) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P.
Inorg. Chem. 2003, 125, 7354.
could be alkylated with MgNp2(dioxane) (Np
)
(11) Sasaki, T.; Eguchi, S.; Katada, T.; Hiroaki, O. J. Org. Chem.
1977, 42, 3741.
CH2-t-Bu) in diethyl ether to yield Mo(N-t-Bu)Np3Cl
in 35% yield as a colorless crystalline solid.15 On the
basis of proton NMR spectra he proposed that this
compound has a trigonal bipyramidal structure with the
(12) Franceschi, F.; Solari, E.; Floriani, C.; Rosi, M.; Chiesi-Villa,
A.; Rizzoli, C. Chem. Eur. J. 1999, 5, 708.
(13) Al-Benna, S.; Sarsfield, M. J.; Thornton-Pett, M.; Ormsby, D.
L.; Maddox, P. J.; Bres, P.; Bochman, M. J. Chem. Soc., Dalton Trans.
2000, 4247.
(14) Stoffelbach, F.; Saurenz, D.; Poli, R. Eur. J. Inorg. Chem. 2001,
2699.
(15) Ehrenfeld, D.; Kress, J.; Moore, B. D.; Osborn, J. A.; Schoettel,
G. J. Chem. Soc., Chem. Commun. 1987, 129.

Molybdenum(VI) Monoimido Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1931
Table 2. Selected Bond Lengths (Å) and Angles (deg) in Mo[N-3,5-(CF3)2C6H3]Cl4(THF),
Mo[N-3,5-(CF3)2C6H3](CH2-t-Bu)3Cl, and Mo(NCPh3)(CH2-t-Bu)3Cl
Mo[N-3,5-(CF3)2C6H3]Cl4(THF) Mo[N-3,5-(CF3)2C6H3]Np3Cl Mo(NCPh3)Np3Cl
Mo-N(1)
1.711(3)
Mo-N(1)
1.7471(17)
2.1473(19)
2.151(2)
2.1281(19)
2.3944(5)
90.24(8)
91.69(8)
93.06(8)
120.17(8)
120.34(7)
119.23(8)
177.39(6)
174.94(15)
87.55(6)
88.24(6)
89.24(6)
120.42(13)
121.25(14)
121.71(13)
Mo-N(1)
1.7509(15)
2.1507(18)
2.1430(19)
2.1475(18)
2.4268(7)
93.83(7)
Mo-Cl(1)
2.3271(12)
2.3137(11)
2.3311(11)
2.3459(11)
2.230(2)
Mo-C(10)
Mo-C(10)
Mo-Cl(2)
Mo-C(20)
Mo-C(20)
Mo-Cl(3)
Mo-C(30)
Mo-C(30)
Mo-Cl(4)
Mo-Cl(1)
Mo-Cl(1)
Mo-O(1)
N(1)-Mo-C(10)
N(1)-Mo-C(20)
N(1)-Mo-C(30)
C(10)-Mo-C(20)
C(10)-Mo-C(30)
C(20)-Mo-C(30)
N(1)-Mo-Cl(1)
C(1)-N(1)-Mo
C(10)-Mo-Cl(1)
C(20)-Mo-Cl(1)
C(30)-Mo-Cl(1)
C(11)-C(10)-Mo
C(21)-C(20)-Mo
C(31)-C(30)-Mo
N(1)-Mo-C(10)
N(1)-Mo-C(20)
N(1)-Mo-C(30)
C(10)-Mo-C(20)
C(10)-Mo-C(30)
C(20)-Mo-C(30)
N(1)-Mo-Cl(1)
C(40)-N(1)-Mo
C(10)-Mo-Cl(1)
C(20)-Mo-Cl(1)
C(30)-Mo-Cl(1)
C(11)-C(10)-Mo
C(21)-C(20)-Mo
C(31)-C(30)-Mo
N(1)-Mo-Cl(1)
N(1)-Mo-Cl(2)
N(1)-Mo-Cl(3)
N(1)-Mo-Cl(4)
N(1)-Mo-O(1)
C(1)-N(1)-Mo
O(1)-Mo-Cl(1)
O(1)-Mo-Cl(2)
O(1)-Mo-Cl(3)
O(1)-Mo-Cl(4)
Cl(2)-Mo-Cl(1)
Cl(2)-Mo-Cl(3)
Cl(2)-Mo-Cl(4)
Cl(1)-Mo-Cl(3)
Cl(1)-Mo-Cl(4)
Cl(3)-Mo-Cl(4)
95.39(12)
98.03(12)
95.69(12)
92.20(12)
176.09(13)
171.4(3)
94.03(7)
93.03(7)
117.89(7)
121.13(7)
119.80(7)
178.25(5)
178.16(12)
86.77(5)
84.51(7)
85.88(7)
84.39(7)
87.14(5)
85.26(5)
123.86(12)
121.10(12)
122.69(12)
83.89(7)
89.42(4)
89.73(4)
169.77(4)
168.89(4)
89.61(5)
89.26(4)
neopentyl groups in equatorial positions. We have found
that addition of Mo(NR)Cl4(THF) complexes in tol-
uene to a cold solution of NpMgCl in ether gave ana-
logous Mo(NR)Np3Cl species (R ) C6F5, 3,5-(CF3)2-
C6H3, Ad, Ph3C, and 2,6-i-Pr2C6H3) in poor (35%) to
modest (51%) yields (eq 2). NMR data at room temper-
ature are all in accord with 3-fold symmetric species.
Varying the order of addition, time, and tempera-
ture (down to -78 °C) so far has not led to an increase
in the yields. We suspect that a susceptibility of Mo
to reduction is limiting the yields under the condi-
tions and with the reagents employed so far. The
trineopentyl species tend to be quite soluble and there-
fore relatively difficult to crystallize, especially in small
quantities.
abstraction. The only notable feature of the structure
is a somewhat long Mo-Cl distance of 2.3944(5) Å that
Figure1. ThermalellipsoiddrawingofMo[N-3,5-(CF3)2C6H3]-
Cl4(THF).
An X-ray structural determination of Mo[N-3,5-
(CF3)2C6H3]Np3Cl (Tables 1 and 2) confirmed that it is
approximately a trigonal bipyramid with neopentyl
groups in equatorial positions (Figure 2). The neopentyl
groups are all turned in one direction with their â
carbon atoms approximately in the equatorial plane and
with Mo-CR-Câ angles of ∼121° and Mo-CR bond
distances of ∼2.13 Å. These Mo-CR-Câ angles and
Mo-CR bond distances are typical for neopentyl ligands
in Mo(VI) and W(VI) complexes. There is no evidence
that the neopentyl ligands are distorted for steric
reasons or that any R hydrogen is activated toward
Figure 2. Thermal ellipsoid drawing of Mo[N-3,5-
(CF3)2C6H3](CH2-t-Bu)3Cl.

1932 Organometallics, Vol. 24, No. 8, 2005
Table 3. Selected Bond Lengths (Å) and Angles (deg) in the Two Molecules of
Pilyugina et al.
Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)(OHIPT)
Mo(1)-N(1)
Mo(1)-C(171)
Mo(1)-O(1)
Mo(1)-C(161)
1.725(4)
1.886(5)
1.928(4)
2.154(5)
Mo(2)-N(2)
Mo(2)-C(271)
Mo(2)-O(2)
Mo(2)-C(261)
1.725(4)
1.855(5)
1.926(4)
2.107(6)
N(1)-Mo(1)-C(171)
N(1)-Mo(1)-O(1)
105.4(2)
123.97(15)
111.0(2)
105.0(2)
92.9(2)
113.9(2)
122.3(4)
146.9(4)
133.4(3)
164.1(3)
N(2)-Mo(2)-C(271)
N(2)-Mo(2)-O(2)
106.7(2)
125.29(16)
109.7(2)
107.7(2)
106.5(3)
99.4(2)
131.9(4)
148.5(4)
126.0(4)
161.2(3)
C(171)-Mo(1)-O(1)
N(1)-Mo(1)-C(161)
C(171)-Mo(1)-C(161)
O(1)-Mo(1)-C(161)
C(162)-C(161)-Mo(1)
C(172)-C(171)-Mo(1)
C(101)-O(1)-Mo(1)
C(140)-N(1)-Mo(1)
C(271)-Mo(2)-O(2)
N(2)-Mo(2)-C(261)
C(271)-Mo(2)-C(261)
O(2)-Mo(2)-C(261)
C(262)-C(261)-Mo(2)
C(272)-C(271)-Mo(2)
C(201)-O(2)-Mo(2)
C(240)-N(2)-Mo(2)
could be ascribed to the combined steric effect of the
three equatorial neopentyl groups on the apical chloride
ligand, plus the trans effect of the imido ligand.
not stable in solution at 22 °C, judging from the
appearance of olefinic resonances at 5.38 and 5.42 ppm,
which are characteristic of cis- and trans-(t-Bu)CHdCH-
(t-Bu), the product of bimolecular coupling of neopen-
tylidenes. Mo(NAd)(CH-t-Bu)Np2 prepared from Mo-
(NAd)(CH-t-Bu)(OTf)2(dme)16 on a multigram scale also
was found to be unstable at room temperature in
solution and could be isolated only as a partially
decomposed red oil. These results suggest that Mo(N-
t-Bu)(CH-t-Bu)Np215 also may not be completely stable
with respect to decomposition to give di-tert-butyleth-
ylene.
Addition of neopentyllithium to Mo(NR)Np3Cl com-
plexes in which R ) pentafluorophenyl or 3,5-trifluo-
romethylphenyl led to intractable mixtures.
Synthesis of Monoalkoxide Complexes. Addition
of 1 equiv of 2,6-diisopropylphenol or 2,6-dimethylphenol
to Mo(NCPh3)(CH-t-Bu)Np2 leads to formation of Mo-
(NCPh3)(CH-t-Bu)Np(OAryl) species as a consequence
of addition of the alcohol across a Mo-C single bond in
a manner similar to reactions reported for Mo(NAr)-
(CH-t-Bu)(CH2-t-Bu)21 (eq 3). The 2,6-dimethylphenox-
Synthesis of Imido Neopentylidene Complexes.
Heating Mo(NAr)Np3Cl in C6D6 to 50 °C results in
R-hydrogen abstraction to give neopentane and a mol-
ecule that we propose to be Mo(NAr)(CH-t-Bu)(CH2-t-
Bu)Cl. The decomposition takes place in a unimolecular
fashion in C6D6 with a rate constant of k50 ) 9.0 × 10-5
s-1 at an initial concentration of 0.1 M, and k50 ) 9.5 ×
10-5 s-1 at an initial concentration of 0.2 M. At 60 °C
k60 ) 3.0 × 10-4 s-1. This rate constant should be
compared with that found for decomposition of Mo(NAr)-
Np3(OC6F5) to Mo(NAr)(CH-t-Bu)(CH2-t-Bu)(OC6F5) in
C6D6 at 60 °C (1.0 × 10-4 s-1).1 A resonance for the
alkylidene proton in Mo(NAr)(CH-t-Bu)(CH2-t-Bu)Cl is
found at 11.70 ppm and for the alkylidene carbon atom
at 283 ppm (JCH ) 109 Hz). Unfortunately this species
is not stable toward bimolecular decomposition to yield
di-tert-butylethylene, and so far all attempts to isolate
it have failed. The nature of the metal-containing
decomposition product or products is not known. The
other Mo(NR)Np3Cl species were found to be more
stable than Mo(NAr)Np3Cl, but when they did decom-
pose (after several hours at 70 °C or higher tempera-
tures), no neopentylidene complex could be observed. If
neopentylidene complexes are formed, they presumably
decompose too readily under these conditions to be
observed.
Addition of neopentyllithium to Mo(NAr)Np3Cl at -30
°C led to formation of Mo(NAr)(CH-t-Bu)Np2 in 90%
yield (δ HR ) 9.50 in C6D6, δ CR ) 255 ppm in C6D6,
JCH ) 108 Hz). This compound is identical in all respects
to the relatively stable crystalline solid prepared by
alkylation of Mo(NAr)(CH-t-Bu)(OTf)2(dme).1 The low
JCH value is typical of imido alkylidenes that have a syn
orientation with respect to the imido group.7
Addition of neopentyllithium to Mo(NCPh3)Np3Cl led
to formation of Mo(NCPh3)(CH-t-Bu)Np2 as a pentane-
soluble ivory powder in 96% yield. The proton NMR
spectrum of Mo(NCPh3)(CH-t-Bu)Np2 in C6D6 shows the
neopentylidene HR resonance at 8.95 ppm and the CR
resonance at 250.1 ppm with JCH ) 109 Hz. It should
be noted that although Mo(N-t-Bu)(CH-t-Bu)Np2 could
be prepared in 75% yield, it could be isolated only as a
brown oil (δ HR ) 9.22, δ CR ) 249.5 in C6D6).15
ide derivative is a colorless powder, while the extremely
soluble 2,6-diisopropylphenoxide derivative could be
obtained only as a brown oil. Reaction of 1 equiv of
3,5-(2,4,6-i-Pr3C6H2)2C6H3OH (HIPTOH), which was
prepared in 75% yield from 3,5-(2,4,6-i-Pr3C6H2)2-
C6H3Br,17,18 with Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)2 gives
(16) Tsang, W. C. P.; Jernelius, J. A.; Cortez, A. G.; Weatherhead,
G. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 2003, 125,
2591.
(17) Gotteland, J.-P.; Halazy, S. Synlett. 1995, 931.
(18) Yandulov, D. V.; Schrock, R. R.; Rheingold, A. L.; Ceccarelli,
C.; Davis, W. M. Inorg. Chem. 2003, 125, 796.
Addition of neopentyllithium to Mo(NAd)Np3Cl led
to formation of what is believed to be Mo(NAd)(CH-t-
Bu)Np2 with δ HR ) 9.22 ppm in C6D6. This species is

Molybdenum(VI) Monoimido Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1933
A reaction between Mo(NCPh3)(CH-t-Bu)2(CH2-t-Bu)
and C6F5OH gives Mo(NCPh3)Np3(OC6F5) as an off-
white powder in 93% yield (eq 4). The difference in
behavior between the phenols described above and
pentafluorophenol in the manner in which they react
with a dineopentyl neopentylidene complex is analogous
to that reported for reactions of phenols and various
other alcohols with Mo(NAr)(CH-t-Bu)2(CH2-t-Bu);1 that
is, pentafluorophenol adds across the ModC bond
instead of the Mo-C bond. Mo(NCPh3)Np3(OC6F5) does
not undergo R-hydrogen abstraction upon heating in
C6D6 to 60 °C for 2 days. In contrast, when benzene-d6
solutions of Mo(NAr)Np3(OC6F5) are heated to 60 °C,
neopentane evolves smoothly and Mo(NAr)(CH-t-Bu)-
(CH2-t-Bu)(OC6F5) is formed in a unimolecular manner
with k ) 1.0 × 10-4 s-1.1 It is not clear whether the
more rapid decomposition of Mo(NAr)Np3(OC6F5) can
be ascribed to steric or electronic differences between
the imido groups, or both.
Figure 3. Thermal ellipsoid drawing of Mo(NCPh3)-
(CH2-t-Bu)3Cl.
The three monophenoxide neopentylidene complexes
showed poor to moderate metathesis activity for ring-
closing a small selection of substrates shown in Table
4.8 It is worth noting that in the case of Mo(NCPh3)-
(CH-t-Bu)Np(OAr′) and Mo(NCPh3)(CH-t-Bu)Np(OAr)
the majority of the initial species can be observed
throughout the reaction; that is, no alkylidene reso-
nance ascribed to an intermediate could be observed.
Mo(NCPh3)(CH-t-Bu)Np(OHIPT), on the other hand,
was completely consumed in the initial reaction with
an olefin. However, no intermediate alkylidene could be
observed in this case either. No improvement in the
metathesis conversions could be detected after the first
hour of the experiment. Therefore we suspect that
although the metal in Mo(NCPh3)(CH-t-Bu)Np(OHIPT)
is sterically more accessible toward olefin substrates,
for the same reason some intermediate alkylidenes,
especially Mo(NCPh3)(CH2)Np(OHIPT), are unstable
toward bimolecular decomposition, while in Mo(NCPh3)-
(CH-t-Bu)Np(OAr′) and Mo(NCPh3)(CH-t-Bu)Np(OAr)
the ortho methyl and isopropyl groups sterically prevent
ready reaction of the initial neopentylidene complex
with olefin substrate. Therefore only a small fraction
of any initial neopentylidene complex is consumed.
Attempted Synthesis of Tritylimido Neopentyl-
idene Bisalkoxide Complexes. We were interested
in whether Mo(NCPh3)(CH-t-Bu)(OR)2 catalysts could
be prepared via the “bistriflate” route,3 which currently
Figure 4. Thermal ellipsoid drawing of Mo(NCPh3)-
(CH-t-Bu)(CH2-t-Bu)(OHIPT).
Mo(NCPh3)(CH-t-Bu)Np(OHIPT) as a yellow-golden
powder in 95% yield.
The X-ray structure of Mo(NCPh3)(CH-t-Bu)(CH2-t-
Bu)(OHIPT) (Tables 1 and 3; Figure 4) shows it to be a
monomeric species with a syn neopentylidene ligand.
The two molecules in the unit cell are enantiomers in
terms of the arrangement of the four ligands around
the metal; only one of the two molecules (containing
Mo(2); Table 3) is shown in Figure 4. The bond lengths
and angles are typical of four-coordinate alkylidene
imido compounds, although this is actually the first
published structural determination of a compound of
this mononeopentyl monoalkoxide type.1 Several bond
lengths and angles differ significantly in the two
molecules, including (for example) the Mo-N-C angles
(164.1(3)° in Mo(1) and 161.2(3)° in Mo(2)). Both are at
the lower end of the range of angles typically found in
“linear” imido alkylidene complexes. Since several other
bond lengths and angles differ significantly from one
another in the two molecules (Table 3), we believe that
packing forces may play a significant role in determin-
ing the detailed structures of the two molecules of
Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)(OHIPT).

1934 Organometallics, Vol. 24, No. 8, 2005
Table 4. Catalytic Ring-Closing Metathesis Reactions
Pilyugina et al.
a Catalyst loading 5%, C6D6, rt. b The reactiom mixture was heated to 65 °C for 18 h after 12 h at rt.
is the only route to bisalkoxide complexes of this general
type. That would require the synthesis of Mo(NCPh3)2-
(DME)Cl2 and Mo(NCPh3)2(CH2-t-Bu)2 and reaction of
the latter with triflic acid to yield Mo(NCPh3)(CH-t-Bu)-
(OTf)2(DME). Mo(NCPh3)2(DME)Cl2 was prepared as
shown in eq 5 as a yellow powder in 66% yield.
Alkylation of Mo(NCPh3)2Cl2(DME) with 2 equiv of
PhMe2CCH2MgCl at -78 °C in ether gave Mo(NCPh3)2-
(CH2CMe2Ph)2 in 60% yield as yellow crystals. How-
ever, addition of 3 equiv of triflic acid to Mo(NCPh3)2-
(CH2CMe2Ph)2 yielded an orange oil whose 1H NMR
spectrum showed it to be a complex mixture of uniden-
tifiable species, only a minor component of which could
be the desired Mo(NCPh3)(CHCMe2Ph)(OTf)2(DME).
Varying the reaction conditions so far has not changed
the outcome of this reaction. We suspect that the trityl
group is cleaved from the imido nitrogen, although at
this stage we have no proof. In any case, we must turn
to alternative methods of preparing what we believe
should be relatively stable Mo(NCPh3)(CHCMe2Ph)-
(OR)2 complexes.
(CH-t-Bu)(OR)Np complexes, which are potentially valu-
able variations of known Mo(NAr)(CH-t-Bu)(OR)Np
complexes. We still consider syntheses of Mo(NR′)(CH-
t-Bu)(OR)2 species in which R′ is an alkyl group other
than adamantyl a worthwhile goal, although alternative
methods must be devised when R′ is a CPh3 group.
Experimental Section
General Details. All reactions were conducted in oven-
dried (135 °C) and flame-dried glassware under an inert
atmosphere of dry nitrogen employing standard Schlenk and
glovebox techniques. Toluene, diethyl ether, and THF were
degassed and then passed through a column of activated
alumina. DME was distilled from sodium/benzophenone under
nitrogen atmosphere. n-Pentane was washed with H2SO4 and
water, dried over CaCl2, degassed, and then passed through a
column of activated alumina. MoCl4(THF)2,14 C6F5N3,9 3,5-
(CF3)2C6H3N3,10 1-AdN3,11 Ph3CN3,12 and 3,5-(2,4,6,-i -Pr3C6H2)2-
C6H3Br18 were prepared according to literature procedures.
1H, 19F, and 13C NMR spectra were recorded on Varian
spectrometers. Chemical shifts in 1H and 13C NMR spectra are
reported in ppm from tetramethylsilane with the solvent as
an internal standard. 19F NMR spectra were referenced
externally using C6F6 as a standard. Elemental analyses were
performed by H. Kolbe Laboratories, Mu¨lheim an der Ruhr,
Germany.
2 Ph3CNH2 + NaMoO4 excess Me SiCl, Et N8
3
3
DME
Mo(NCPh3)2(DME)Cl2 (5)
2,6-i-Pr2C6H3N3.13 2,6-Diisopropyl aniline (8.81 g, 0.049
mol) was dissolved in a mixture of concentrated HCl and H2O
(10/30 mL) and 30 g of ice. The mixture was stirred vigorously
with a mechanical stirrer, and a solution of NaNO2 (3.80 g,
0.055 mol) in 20 mL of water was added slowly over a period
of 5 min. The mixture was stirred for 20 min, and then a
saturated solution of NaHCO3 (30 mL) was added. NaN3 (3.71
g, 0.057 mol) in 30 mL of water was added. After 30 min the
reaction mixture was warmed to room temperature and the
organic layer was extracted with diethyl ether (3 × 50 mL).
The ethereal fractions were combined and washed with a
saturated solution of NaHCO3 (50 mL) and water (2 × 50 mL)
and dried over MgSO4. The solvent was removed from the
ether solution in vacuo, and the oily residue was chromato-
graphed on silica gel with hexane as an eluent to yield the
Conclusions
A variety of Mo(NR)Cl4(THF) complexes can be pre-
pared readily from azides and MoCl4(THF)2. Alkylation
of Mo(NR)Cl4(THF) is a viable route to Mo(NR)(CH-t-
Bu)Np2 species when R is trityl or 2,6-diisopropylphenyl.
However, it is necessary to isolate intermediate Mo(NR)-
Np3Cl complexes, and these are formed in only modest
yield. The stability of Mo(NCPh3)(CH-t-Bu)Np2 com-
pared to Mo(NAd)(CH-t-Bu)Np2 suggests that the sta-
bility of ModNR complexes (where R contains a qua-
ternary carbon bound to Mo) will depend sensitively
upon the steric bulk of R. Mo(NCPh3)(CH-t-Bu)Np2
reacts cleanly with certain alcohols to yield Mo(NCPh3)-

Molybdenum(VI) Monoimido Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1935
product as a pale yellow, light-sensitive oil; yield 6.51 g (0.032
mol, 65%): 1H NMR (C6D6) δ (ppm) 7.07-6.94 (m, 3H), 3.33
(septet, JHH ) 6.9 Hz, 2H), 1.12 (d, JHH ) 6.9 Hz, 12H);
13C{1H} NMR (C6D6) δ (ppm) 143.31 (s, 2C), 135.52 (s, 1C),
127.02 (s, 1C), 124.14 (s, 1C), 29.01 (s, 1C), 23.73 (s, 2C); IR
(neat, KBr, cm-1) 2125 (azide). These NMR data match those
for the published material.13
C23H23NOCl4Mo: C, 48.70; H, 4.09; Cl, 25.00; N, 2.47. Found:
C, 48.86; H, 4.03; Cl, 24.82; N, 2.39.
Mo(NC6F5)(CH2-t-Bu)3Cl. A solution of t-BuCH2MgCl (25.0
mmol) in 20 mL of ether was cooled to -78 °C, and a solution
of Mo(NC6F5)Cl4(THF) (4.09 g, 8.3 mmol) in 20 mL of toluene
was added to it dropwise with stirring. The reaction mixture
was stirred at -78 °C for 20 min, then warmed to 20 °C and
stirred for 2 h. The solvents were removed in vacuo, the solid
residue was extracted with 70 mL of pentane, and the mixture
was filtered. The pentane was removed in vacuo to give the
pale yellow crystalline product; yield 1.84 g (3.7 mmol, 45%):
1H NMR (C6D6, ppm) δ 3.275 (s, 6H), 1.155 (s, 27H); 19F NMR
(C6D6, ppm) δ -141.27 (d, JFF ) 22.2 Hz, 2F), -151.55 (m, F),
-160.31 (m, 2F). Anal. Calcd for C21H33NClF5Mo: C, 47.96;
H, 6.33; N, 2.66; Cl, 6.74. Found: C, 47.81; H, 6.27; N, 2.56;
Cl, 6.63.
Mo(N[3,5-(CF3)2C6H3])(CH2-t-Bu)3Cl. A solution of t-BuCH2-
MgCl (37.4 mmol) in 25 mL of diethyl ether was cooled to -78
°C, and a solution of Mo(3,5-(CF3)2C6H3N)Cl4(THF) (7.13 g,
12.5 mmol) in 35 mL of ether was added to it dropwise while
the mixture was stirred. The reaction mixture was stirred at
-78 °C for 1 h, then it was warmed to 20 °C and stirred for 2
h. Ether was removed in vacuo, and the solid residue was
extracted with 400 mL of pentane for 2 h. The mixture was
filtered and pentane was removed from the filtrate in vacuo
to give the yellow crystalline product; yield 2.52 g (4.4 mmol,
35%): 1H NMR (C6D6, ppm) δ 8.16 (s, 2H), 7.52 (s, 1H), 3.09
(s, 6H), 1.05 (s, 27H); 19F NMR (C6D6, ppm) δ -62.49 (s, 6F);
13C NMR (C6D6, ppm) δ 154.3 (quintet, JCF ) 4 Hz), 133.3 (q,
JCF ) 34.6 Hz), 129.0 (s), 126.6 (s), 122.6 (q, JCF ) 274.1 Hz),
86.7 (s), 36.1 (s), 33.7 (s). Anal. Calcd for C23H36NClF6Mo: C,
48.30; H, 6.34; N, 2.45; Cl, 6.20. Found: C, 48.16; H, 6.29; N,
2.40; Cl, 6.30.
Mo(NC6F5)Cl4(THF). A 200 mL Schlenk vessel was loaded
with MoCl4(THF)2 (5.48 g, 14.3 mmol), pentafluorophenyl azide
(6.00 g, 28.7 mmol), and 50 mL of toluene. The reaction
mixture was heated to 50 °C and stirred under a flow of
dinitrogen for 30 h. The reaction mixture was filtered, and the
solvent was removed from the filtrate in vacuo to give a dark
red solid. The solid was washed with cold pentane and dried
to yield a red crystalline product; yield 6.16 g (12.0 mmol,
88%): 1H NMR (C6D6, ppm) δ 4.50 (m, 4H), 1.31 (m, 4H); 19F
NMR (C6D6, ppm) δ -151.84 (m, 2F), -160.81 (m, 1F), -162.37
(m, 2F). Anal. Calcd for C10H8NOCl4F5Mo: C, 24.47; H, 1.64;
N, 2.85; Cl, 28.99. Found: C, 24.51; H, 1.58; N, 2.79; Cl, 28.70.
Mo(N[3,5-(CF3)2C6H3])Cl4(THF). A 200 mL Schlenk vessel
was loaded with MoCl4(THF)2 (4.68 g, 12.3 mmol), 3,5-bis-
(trifluoromethyl)phenyl azide (3.75 g, 14.7 mmol), and 30 mL
of toluene. The reaction mixture was heated to 60 °C and
stirred under a flow of dinitrogen for 10 h. The reaction
mixture was filtered, and the solvent was removed in vacuo
to give a dark red solid. The solid was washed with cold
pentane and dried to yield a red crystalline product; yield 4.93
g (9.2 mmol, 75%): 1H NMR (C6D6, ppm) δ 7.77 (s, 2H), 7.10
(s, 1H), 4.49 (m, 4H), 1.32 (m, 4H); 19F NMR (C6D6, ppm) δ
-62.66 (s, 6F); 13C NMR (C6D6, ppm) δ 152.8 (s), 132.8 (q, JC-F
) 34.6 Hz), 129.9 (s), 127.4 (s), 122.6 (q, JC-F ) 274.1 Hz),
74.7 (s), 25.9 (s). Anal. Calcd for C12H11NOCl4F6Mo: C, 26.84;
H, 2.06; N, 2.61; Cl, 26.41. Found: C, 26.73; H, 2.11; N, 2.55;
Cl, 26.58.
Single crystals for the X-ray study were grown from a
Single crystals for the X-ray study were grown from a
pentane solution at -30 °C.
pentane solution at -30 °C.
Mo(NAd)(CH2-t-Bu)3Cl. A solution of t-BuCH2MgCl (4.00
mmol) in 15 mL of diethyl ether was cooled to -78 °C, and a
solution of Mo(NAd)Cl4(THF) (608 mg, 1.33 mmol) in 15 mL
of toluene was added to it dropwise with stirring. The reaction
mixture was warmed to 20 °C and stirred for 2 h. The solvents
were removed in vacuo, and the solid residue was extracted
with 100 mL of pentane. The mixture was filtered and the
pentane was removed in vacuo to give a brown crystalline
product; yield 193 mg (0.68 mmol, 51%): 1H NMR (C6D6, ppm)
δ 2.92 (s, 6H), 2.21 (d, JHH ) 2.8 Hz, 6H), 1.59 (s, 3H), 1.41 (br
s, 6H), 1.24 (s, 27H). Anal. Calcd for C25H48NClMo: C, 60.78;
H, 9.79; N, 2.84; Cl, 7.18. Found: C, 60.65; H, 9.85; N, 2.73;
Cl, 7.14.
Mo(NAr)(CH2-t-Bu)3Cl. Mo(NAr)Cl4(THF) (915 mg, 1.89
mmol) was dissolved in 10 mL of toluene. The solution was
cooled to -30 °C and added dropwise to a -30 °C solution of
t-BuCH2MgCl (5.66 mmol) in 5 mL of diethyl ether. The
mixture was stirred at room temperature for 18 h. The solvents
were removed in vacuo, and the resulting brown residue was
extracted with pentane. The mixture was filtered and the
solvent was removed in vacuo to give yellow powder; yield 414
mg (0.0796 mmol, 42%): 1H NMR (C6D6, ppm) δ 6.97 (s, 3H),
4.07 (septet, JHH ) 6.6 Hz, 2H), 3.04 (s, 6H), 1.25 (s, 27 H),
1.22 (d, JHH ) 6.6 Hz, 12H). Anal. Calcd for C27H50NClMo: C,
62.35; H, 9.69; Cl, 6.82; N, 2.69. Found: C, 62.31; H, 9.56; Cl,
6.74; N, 2.71.
Mo(NAd)Cl4(THF). A 300 mL Schlenk vessel was loaded
with MoCl4(THF)2 (7.52 g, 19.7 mmol), 1-adamantyl azide (3.49
g, 19.7 mmol), and 100 mL of toluene. The reaction mixture
was heated to 55 °C and stirred under a flow of nitrogen for
17 h. The reaction mixture was filtered, and the solvent was
removed under vacuum to give a dark red solid. The solid was
triturated with pentane for 10 h, and the mixture was filtered
and the red crystalline product thereby isolated; yield 8.34 g
(18.3 mol, 93%): 1H NMR (C6D6, ppm) δ 4.55 (br s, 4H), 2.25
(d, JHH ) 3 Hz, 6H), 1.74 (br s, 3H), 1.35 (br s, 4H), 1.14 (t,
JHH ) 3 Hz, 6H). Anal. Calcd for C14H23NOCl4Mo: C, 36.63;
H, 5.05; N, 3.05; Cl, 30.89. Found: C, 36.54; H, 5.12; N, 2.72;
Cl, 30.75.
Mo(NAr)Cl4(THF). ArN3 (3.35 g, 16.4 mmol) was added to
a suspension of MoCl4(THF)2 (6.28 g, 16.4 mmol) in 50 mL of
toluene, and the mixture was heated to 50 °C for 12 h under
a flow of dinitrogen. The dark red reaction mixture was then
cooled to room temperature and filtered, and the solvent was
removed from the filtrate under vacuum to give dark red solid.
The solid was stirred in pentane for 24 h, and the mixture
was filtered and the product dried to give a red powder (5.30
g, 10.9 mmol, 66%): 1H NMR (C6D6, ppm) δ 6.91 (d, JHH ) 7.6
Hz, 2H), 6.44 (t, JHH ) 7.6 Hz, 1H), 5.08 (septet, JHH ) 6.4
Hz, 2H), 4.53 (s, 4H), 1.23 (d, JHH ) 6.7 Hz, 16H). Anal. Calcd
for C16H25NOCl4Mo: C, 39.61; H, 5.19; Cl, 29.23; N, 2.89.
Found: C, 39.73; H, 5.25; Cl, 29.82; N, 2.84.
Mo(NCPh3)(CH2-t-Bu)3Cl. Mo(NCPh3)Cl4(THF) (13.6 g, 24
mmol) was dissolved in 50 mL of toluene. The solution was
cooled to -78 °C and added dropwise to a solution of t-BuCH2-
MgCl (77 mmol) in 100 mL of diethyl ether. The mixture was
stirred at room temperature for 3 h. The solvents were
removed in vacuo, and the resulting brown residue was
extracted with 400 mL of pentane. The extract was filtered,
and the solution was reduced in volume in vacuo to 100 mL
and left at -30 °C for 12 h. The first crop of off-white crystals
was collected, and the remaining solution was reduced in
Mo(NCPh3)Cl4(THF). Ph3CN3 (7.12 g, 25 mmol) was added
to a suspension of MoCl4(THF)2 (9.54 g, 25 mmol) in 100 mL
of toluene, and the mixture was stirred for 12 h at room
temperature under a flow of N2. The dark red reaction mixture
was filtered, and the solvent was removed in vacuo. The dark
red solid residue was triturated with pentane for 24 h, and
the product was filtered off and dried in vacuo; yield 13.69 g
(24 mmol, 96%): 1H NMR (C6D6, ppm) δ 7.75-7.72 (m, 6H),
7.17-7.00 (m, 9 H), 4.42 (s, 4H), 1.26 (s, 4H). Anal. Calcd for

1936 Organometallics, Vol. 24, No. 8, 2005
Pilyugina et al.
volume to 20 mL and left at -30 °C for 1 day. Three additional
crops were collected over a period of 3 days; yield 6.28 g (10
mmol, 42%): 1H NMR (C6D6, ppm) δ 7.44-7.41 (m, 6H),
7.16-7.05 (m, 9H), 3.12 (s, 6H), 1.03 (s, 27H). Anal. Calcd for
C34H48NClMo: C, 67.82; H, 8.03; Cl, 5.89; N, 2.33. Found: C,
68.48; H, 8.26; Cl, 5.69; N, 2.17.
washed with water (5 × 50 mL). The aqueous washes were
extracted with ether, and the ethereal fractions were combined
and dried with MgSO4. The solvents were removed in vacuo,
and the oily residue was transferred to a silica gel column and
eluted with hexanes, then a 5:1 hexanes/ether mixture and
then a 1:1 hexanes/ether mixture. The second collected fraction
upon solvent removal gave a white powder; yield 260 mg (0.52
mmol, 73%): 1H NMR (C6D6, ppm) δ 7.20 (s, 4H), 7.13 (s, 2H),
6.53 (s, 1H), 3.91 (s, 1H), 3.03 (septet, JHH ) 11.3 Hz, 4H),
2.87 (septet, JHH ) 11.1 Hz, 2H), 1.28 (d, JHH ) 11.3 Hz, 24H),
1.22 (septet, JHH ) 11.1 Hz, 12H).
Single crystals for the X-ray study were grown from a
pentane solution at -30 °C.
Mo(NAr)(CH-t-Bu)(CH2-t-Bu)2. Mo(NAr)(CH2-t-Bu)3Cl (465
mg, 0.89 mmol) and LiCH2-t-Bu (69.4 mg, 0.89 mmol) were
dissolved in 5 mL of pentane in separate vials, and each
solution was cooled to -30 °C. The solution of Mo(NAr)(CH2-
t-Bu)3Cl was added to the solution of LiCH2-t-Bu, and the
mixture was stirred at room temperature for 12 h. The LiCl
was removed by filtration. The filtrate was stirred with dry
activated charcoal and filtered, and the solvent was removed
to give a brown powder; yield 389 mg (0.80 mmol, 90%). The
NMR spectral data for this compound match those reported.1
Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)2. Mo(NCPh3)(CH2-t-Bu)3-
Cl (600 mg, 0.95 mmol) was dissolved in 6 mL of toluene, and
the solution was cooled to -30 °C. Solid LiCH2t-Bu (81.7 mg,
1.05 mmol) was added to the solution, and the reaction mixture
was stirred for 24 h at room temperature. Activated charcoal
was added to the reaction mixture, and the mixture was stirred
for 1 h. Toluene was removed in vacuo. The mixture was
redissolved in pentane, and the solution was filtered. The
pentane was removed in vacuo to yield an ivory powder; yield
539 mg (0.91 mmol, 96%): 1H NMR (C6D6, ppm) δ 8.95 (s, JCH
) 108.5 Hz, 1H), 7.61-7.58 (m, 6H), 7.15-7.02 (m, 9 H), 2.45
(d, JHH ) 11.7 Hz, 2H), 1.10 (s, 18H), 1.06 (s, 9H), 0.98 (d, JHH
) 11.7 Hz, 2H). Anal. Calcd for C34H47NMo: C, 72.19; H, 8.37;
N, 2.48. Found: C, 72.28; H, 8.24; N, 2.39.
Mo(NCPh3)(CH-t-Bu)Np(OAr). Mo(NCPh3)(CH-t-Bu)(CH2-
t-Bu)2 (228 mg, 0.38 mmol) was dissolved in 2 mL of pentane,
and 2,6-diisopropyl phenol (68.5 mg, 0.38 mmol) was added.
The solution was stirred for 24 h. Activated charcoal was
added, and the mixture was stirred for 1 h. The solution was
filtered, and the solvent was removed to give a brown oil; yield
235 mg (0.35 mmol, 92%): 1H NMR (C6D6, ppm) δ 11.81 (s,
1H), 7.53-7.50 (m, 6H), 7.14-6.93 (m, 12 H), 3.44 (quintet,
JHH ) 6.9 Hz, 2H), 2.82 (d, JHH ) 12.5 Hz, 1H), 2.29 (d, JHH
)
12.5 Hz, 1H), 1.19 (s, 9H), 1.19 (d, JHH ) 6.6 Hz, 12H), 1.10 (s,
9H); 13C NMR (C6D6, ppm) δ 278.38 (d, JCH ) 111.7 Hz). Anal.
Calcd for C41H53NOMo: C, 73.30; H, 7.95; N, 2.08. Found: C,
73.15; H, 7.90; N, 1.96.
Mo(NCPh3)(CH-t-Bu)Np(OAr′). Mo(NCPh3)(CH-t-Bu)-
(CH2-t-Bu)2 (486 mg, 0.76 mmol) was dissolved in 2 mL of
pentane, and 2,6-dimethyl phenol (92.5 mg, 0.82 mmol) was
added. The solution was stirred for 24 h. Activated charcoal
was added, and the mixture was stirred for 1 h. The solution
was filtered, and the solvent was removed in vacuo to give
the product as a yellow powder; yield 434 mg (0.71 mmol,
93%): 1H NMR (C6D6, ppm) δ 11.69 (s, 1H), 7.54-7.16 (m, 6H),
7.10-6.93 (m, 9H), 6.88-6.74 (m, 3H), 2.73 (d, JHH ) 12.4 Hz,
1H), 2.34 (d, JHH ) 12.4 Hz, 1H), 2.16 (s, 6H), 1.16 (s, 9H),
1.08 (s, 9H). 13C NMR (C6D6, ppm): δ 277.52 (d, JCH ) 109.4
Hz). Anal. Calcd for C37H45NOMo: C, 72.18; H, 7.37; N, 2.27.
Found: C, 72.06; H, 7.41; N, 2.19.
Mo(NCPh3)(CH-t-Bu)Np(OHIPT). Mo(NCPh3)(CH-t-Bu)-
(CH2-t-Bu)2 (159 mg, 0.32 mmol) was dissolved in 2 mL of
pentane, and 2 mL of ether and solid HIPTOH (189 mg, 0.32
mmol) was added. The solution was stirred for 24 h. Activated
charcoal was added, and the mixture was stirred for 1 h. The
solution was filtered and the solvent was removed to give the
product as a golden yellow powder; yield 299 mg (0.30 mmol,
95%): 1H NMR (C6D6, ppm) δ 11.45 (s, 1H), 7.57-7.42 (m, 8H),
7.32-6.90 (m, 13H), 6.72 (s, 1H), 3.08 (septet, JHH ) 11.3 Hz,
4H), 2.88 (septet, JHH ) 11.1 Hz, 2H), 2.53 (d, JHH ) 13 Hz,
1H), 2.26 (d, JHH ) 13 Hz, 1H), 1.30 (d, JHH ) 11.3 Hz, 24H),
1.22 (s, 9H), 1.19 (d, JHH ) 11.1 Hz, 12H), 1.03 (s, 9H); 13C
NMR (C6D6, ppm): δ 278.00 (d, JCH ) 112.8 Hz). Anal. Calcd
for C65H85NOMo: C, 78.67; H, 8.63; N, 1.41. Found: C, 78.58;
H, 8.57; N, 1.37.
Conversion of Mo(NAr)(CH2-t-Bu)3Cl to Mo(NAr)(CH-
t-Bu)(CH2-t-Bu)Cl. Mo(NAr)(CH2-t-Bu)3Cl (32.1 mg, 0.062
mmol) was dissolved in 0.6 mL of C6D6 in a J. Young tube to
give a 0.1 N solution, and the solution was heated to 50 °C for
8 h. The 1H NMR spectrum showed that Mo(NAr)(CH2-t-Bu)3-
Cl had been converted quantitatively to Mo(NAr)(CH-t-Bu)-
(CH2-t-Bu)Cl in a reaction that was unimolecular with k )
9.0 × 10-5 s1: 1H NMR (C6D6, ppm) δ 11.71 (s, JC-H ) 109 Hz,
1H), 6.97 (s, 3H), 3.82 (septet, JHH ) 6.9 Hz, 2H), 2.63 (d, JHH
) 13.2 Hz, 1H), 1.91 (d, JHH ) 13.2 Hz, 1H), 1.22 (s, 3H), 1.20
(s, 3H), 1.19 (s, 3H), 1.17 (s, 3H), 1.14 (s, 9H), 1.01 (s, 9H).
A 0.2 N solution of Mo(NAr)(CH2-t-Bu)3Cl (72.8 mg, 0.14
mmol) in 0.7 mL of C6D6 was heated to 50 °C for 8 h. The
reaction was unimolecular with k ) 9.5 × 10-5 s-1. At an initial
concentration of 0.1 M k50 ) 9.0 × 10-5 s-1
.
A 0.1 N solution of Mo(NAr)(CH2-t-Bu)3Cl (35 mg, 0.07
mmol) in 0.7 mL of C6D6 was heated to 60 °C for 4 h. The
reaction was unimolecular with k ) 3.0 × 10-4 s-1
.
Mo(NCPh3)Np3(OC6F5). Mo(NCPh3)(CH-t-Bu)(CH2-t-Bu)2
(244 mg, 0.41 mmol) was dissolved in 4 mL of benzene, and
solid C6F5OH (75.6 mg, 0.41 mmol) was added. The mixture
was stirred for 24 h, then benzene was removed and the solid
residue was redissolved in 5 mL of pentane and stirred with
dry activated charcoal for 1 h. The solution was filtered, and
the solvent was removed from the filtrate to give off-white
powder; yield 293 mg (0.38 mmol, 93%): 1H NMR (C6D6, ppm)
δ 7.50-7.47 (m, 6H), 7.17-7.06 (m, 9H), 2.76 (s, 6H), 0.93 (s,
27 H); 19F NMR (C6D6, ppm) δ -156.08 (m, 2F), -165.46 (m,
2F), -175.42 (m, 1F). Anal. Calcd for C41H56NOF5Mo: C, 63.97;
H, 7.33; N, 1.82. Found: C, 64.14; H, 7.24; N, 1.76.
Single crystals for the X-ray study were grown from a
pentane solution at -30 °C.
Mo(NCPh3)2Cl2(dme). Ph3CNH2 (11.53 g, 0.044 mol),
Na2MoO4 (4.53 g, 0.022 mol), Et3N (8.90 g, 12.3 mL, 0.088 mol),
and trimethylsilyl chloride (23.9 g, 27.9 mL, 0.22 mol) were
dissolved in 150 mL of dry DME. Upon stirring at 65 °C for
12 h the mixture became bright yellow. The solids were filtered
off and the solvent was removed from the filtrate in vacuo to
give a yellow powder. The yellow powder was triturated with
100 mL of pentane, filtered off, and dried in vacuo. The
pentane washes were reduced to 20 mL in volume in vacuo,
and an additional crop of the product was crystallized from
this solution; yield 11.27 g (0.015 mol, 66%): 1H NMR (C6D6,
ppm) δ 7.57-7.53 (m, 12H), 7.03-7.01 (m, 18H), 3.05 (s, 4H),
3.01 (s, 6H). Anal. Calcd for C42H40N2O2Cl2Mo: C, 65.37; H,
5.23; N, 3.63; Cl, 9.19. Found: C, 65.47; H, 5.20; N, 3.51; Cl,
9.23.
3,5-(2,4,6-i-Pr3C6H2)2C6H3OH (HIPTOH).17 Li-n-Bu (0.85
mmol) was added to a solution of 3,5-(2,4,6-i-Pr3C6H2)2-
C6H3Br (400 mg, 0.71 mmol) in 20 mL of dry THF that had
been cooled to -78 °C. In 15 min B(OMe)3 (0.24 mL, 2.13
mmol) was added to the mixture. The mixture was allowed to
warm to room temperature and was stirred for 2 h. Anhydrous
N-methylmorpholine N-oxide (250 mg, 2.13 mmol) was added
to the reaction mixture, and the mixture was refluxed for 5 h.
The mixture was diluted with 50 mL of diethyl ether and
Mo(NCPh3)2(CH2CMe3)2. A solution of Mo(Ph3CN)2Cl2-
(dme) (2.06 g, 3.63 mmol) dissolved in 30 mL of toluene was

Molybdenum(VI) Monoimido Alkyl Complexes
Organometallics, Vol. 24, No. 8, 2005 1937
cooled to -78 °C. A solution of (PhCMe2CH2)MgCl (7.25 mmol)
in 15 mL of ether was added dropwise to the reaction mixture.
The mixture was allowed to warm to room temperature and
was stirred for 12 h. The solvents were removed in vacuo, and
the solid residue was redissolved in 20 mL of toluene. After
addition of 4 mL of 1,4-dioxane the mixture was stirred for 1
h and the white precipitate was removed by filtration. The
solvents were removed in vacuo, and the solid was triturated
with pentane overnight. The product was filtered off, and the
pentane washes were reduced to 5 mL and left at -35 °C for
12 h. The material that crystallized from pentane was collected
and combined with the solid obtained from trituration to give
a tan powdery product; yield 1.84 g (2.1 mmol, 58%): 1H NMR
(C6D6, ppm) δ 7.26-7.12 (m, 16H), 7.10-7.01 (m, 24H), 2.13
(s, 4H), 1.34 (s, 12H). Anal. Calcd for C58H56N2Mo: C, 79.43;
H, 6.44; N, 3.19. Found: C, 79.57; H, 6.41; N, 3.11.
Representative Olefin Metathesis with Mo(NCPh3)-
(CH-t-Bu)Np(OR) Complexes. Diallyl ether (10.6 mg, 0.108
mmol) was dissolved in 1 mL of C6D6 in a 20 mL vial, and
Mo(NCPh3)(CH-t-Bu)Np(OHIPT) (5.4 mg, 5.5 × 10-3 mmol)
was added. The reaction mixture was stirred for 1 h and then
transferred to a J. Young tube. Conversion of the ring-closing
metathesis reaction with time was judged by analysis of the
1H NMR spectrum. The amine substrates shown in Table 4
were prepared as described in the literature.19
Crystallography. Low-temperature diffraction data were
collected on a Siemens Platform three-circle diffractom-
eter coupled to a Bruker-AXS Smart 1K CCD detector (for
the structures of Mo[N-3,5-(CF3)2C6H3](CH2-t-Bu)3Cl and
Mo(Ph3CN)(CH2-t-Bu)3Cl) or a Bruker-AXS Apex CCD de-
tector (for the structures of Mo[N-3,5-(CF3)2C6H3]Cl4(THF) and
Mo(NCPh3)(CH-t-Bu)Np(OHIPT)) with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å), performing phi and
omega scans. All four structures were solved by direct methods
using SHELXS20 and refined against F2 on all data by full-
matrix least squares with SHELXL-97 (Sheldrick, G. M.
SHELXL 97; Universita¨t Go¨ttingen: Go¨ttingen, Germany,
1997). All non-hydrogen atoms were refined anisotropically.
All hydrogen atoms were included in the model at geo-
metrically calculated positions and refined using a riding
model. The isotropic displacement parameters of the hydrogen
atoms were fixed to 1.2 times the U value of the atoms they
are linked to (1.5 times for methyl groups).
atic absences were found. However, a closer look suggested
the presence of both a 2-fold screw axis along b and a glide
plane, compatible only with the space group P21/c. Even though
all systematic absences were somewhat violated, a solution
could be found in this space group. The refinement, however,
was not stable, and practically all carbon atoms seemed to be
involved in disorders. The structure can also be solved in the
triclinic space group P1 with four crystallographically inde-
pendent molecules. Analysis of the coordinates in this solution
with the program PLATON21 resulted in 100% equivalence
with P21 and only 90% equivalence with P21/c. Therefore the
structure was solved and refined in the monoclinic space group
P21 with two crystallographically independent molecules in the
asymmetric unit. The two crystallographically independent
molecules are basically a pair of enantiomers. In addition to
the pseudo-inversion, the two molecules differ from one
another significantly in several bond lengths and angles,
thereby avoiding the higher symmetric space group P21/c. This
explains the problems described above. The structure was
refined as a recemic twin (twin law -1 0 0 0 -1 0 0 0 -1); the
twin ratio refined to 0.43(3). To break the parameter correla-
tion arising from the pseudo-symmetry, similarity restraints
as well as rigid bond restraints for anisotropic displacement
parameters were applied to all atoms. Three disordered i-Pr
groups were refined with the help of similarity restraints on
1-2 and 1-3 distances and constraining the anisotropic
displacement parameters of equivalent atoms to be identical.
The occupancies for the disordered components were refined
freely.
Acknowledgment. We thank the National Science
Foundation (CHE-0138495) for supporting this research,
and D. S. Laitar and Professor J. P. Sadighi for valuable
discussions.
Supporting Information Available: Experimental de-
tails, fully labeled thermal ellipsoid drawing, crystal data and
structure refinement, atomic coordinates, bond lengths and
angles, anisotropic displacement parameters, hydrogen coor-
dinates, isotropic displacement parameters, and torsion angles
for Mo[N-3,5-(CF3)2C6H3]Cl4(THF), Mo[N-3,5-(CF3)2C6H3](CH2-
t-Bu)3Cl, Mo(NCPh3)(CH2-t-Bu)3Cl, and Mo(NCPh3)(CH-t-Bu)-
(CH2-t-Bu)(OHIPT). This material is available free of charge
via the Internet at http://pubs.acs.org.
The space group determination for Mo(NCPh3)(CH-t-Bu)-
Np(OHIPT) was problematic. The data intensity statistics
suggests a non-centrosymmetric space group, and no system-
OM0401408
(19) Dolman, S. J.; Sattely, E. S.; Hoveyda, A. H.; Schrock, R. R. J.
Am. Chem. Soc. 2002, 124, 6991.
(20) Sheldrick, G. M. Acta Crystallogr. Sect. A 1990, 46, 467.
(21) Speck, A. L. J. Appl. Crystallogr. 2003, 36, 7.