The effect of substituents on the phenyl portion of the imido ligand on the structure and properties of molybdenum(VI) imido complexes

Article abstract of DOI:10.1021/ic025642x

Anilines with alkyl substituents on the phenyl ring (ArNH₂ = 2,4,6-trimethylaniline; 2,3-, 2,4-, 2,6-, and 3,4-dimethylaniline; and 2,6-diisopropylaniline) react with MoO(X)₂(dtc)₂ (X = Cl or Br; dtc = diethyldithiocarbamate) in methanol in the presence of 2 equiv of triethylamine to form ionic imido complexes of the type [MoNAr(dtc)₃]₂- [Mo₆O₁₉] or MoNAr(dtc)₃]₄[Mo₈O₂₆]. The same reaction in THF with butyllithium as base yields imido complexes of the type MoNAr(X)₂(dtc)₂. The structures of three ionic, five chloro, and two bromo complexes have been determined by X-ray crystallography. In all complexes, the molybenum center is a distorted pentagonal bipyramid. While the structures are similar, the angles of the imido linkages differ. The effect of the substituents on the phenyl ring of the imido ligand on the ⁹⁵Mo NMR chemical shifts was determined. The Mo nucleus becomes more deshielded with the substituents in the following order: 3,4-Me₂ < 2,3-Me₂ < 2,4-Me₂ < 2,6-Me₂ < 2,4,6-Me₃ < 2,6 isopropyl. Complexes with more deshielded ⁹⁵Mo centers tend to have angles of the imido linkage that are closer to 180°.

Full text of DOI:10.1021/ic025642x

Inorg. Chem. 2002, 41, 5954−5960
The Effect of Substituents on the Phenyl Portion of the Imido Ligand on
the Structure and Properties of Molybdenum(VI) Imido Complexes
,†
Martin Minelli,* My Le Hoang,† Michael Kraus,† Gena Kucera,† Jennifer Loertscher,† Mark Reynolds,†
Nathan Timm,† Michael Y. Chiang,‡ and Douglas Powell§
Departments of Chemistry, Grinnell College, Grinnell, Iowa 50112, Washington UniVersity,
One Brookings DriVe, St. Louis, Missouri 63130, National Sun Yat-Sen UniVersity,
70 Lein Hai Road, Kaoshiung 804, Taiwan, and UniVersity of WisconsinsMadison,
1101 UniVersity AVenue, Madison, Wisconsin 53706
Received April 10, 2002
Anilines with alkyl substituents on the phenyl ring (ArNH ) 2,4,6-trimethylaniline; 2,3-, 2,4-, 2,6-, and
2
3,4-dimethylaniline; and 2,6-diisopropylaniline) react with MoO(X)2(dtc)2 (X ) Cl or Br; dtc ) diethyldithiocarbamate)
in methanol in the presence of 2 equiv of triethylamine to form ionic imido complexes of the type [MoNAr(dtc)3]2-
[Mo6O ] or MoNAr(dtc)3]4[Mo8O ]. The same reaction in THF with butyllithium as base yields imido complexes of
19
26
the type MoNAr(X)2(dtc)2. The structures of three ionic, five chloro, and two bromo complexes have been determined
by X-ray crystallography. In all complexes, the molybenum center is a distorted pentagonal bipyramid. While the
structures are similar, the angles of the imido linkages differ. The effect of the substituents on the phenyl ring of
the imido ligand on the 95Mo NMR chemical shifts was determined. The Mo nucleus becomes more deshielded
with the substituents in the following order: 3,4-Me2 < 2,3-Me2 < 2,4-Me2 < 2,6-Me2 < 2,4,6-Me3 < 2,6 isopropyl.
Complexes with more deshielded 95Mo centers tend to have angles of the imido linkage that are closer to 180°.
Introduction
the imido ligand influences the properties of molybdenum-
(VI) imido complexes. We reported previously that the
reaction of 1,2-phenylenediamine with MoO(Cl)2(dtc)2
(dtc ) diethyldithiocarbamate) in methanol in the presence
of 2 equiv of triethylamine yields the imido complex
Mo(NC6H4(2-)NH2)Cl2(dtc)2.5 Although the structure of this
complex is almost identical to Mo(NC6H5)Cl2(dtc)2,6 the
angles of the imido linkages differ by 12° and the 95Mo NMR
chemical shifts are 91 ppm apart. Hogarth and co-workers
recently reported the synthesis of this type of complex with
para-substituted anilines.7 The varying properties of these
complexes depending on the substituents on the phenyl ring
of the imido ligand led us to study a number of complexes
with methyl and isopropyl substituents in different positions
on the phenyl ring to determine whether any systematic
trends are evident.
Molybdenum imido complexes have been studied widely1
because of their involvement in the activation of carbon-
hydrogen bonds,2 the oxidation, amination, and oxyamination
of unsaturated organic compounds3 and the catalysis of olefin
metathesis.4 The effect of slight modifications of the ligands
can be important in the design of such compounds. We report
here how a change of substituents on the phenyl group of
* Author to whom correspondence should be addressed. E-mail: minelli@
grinnell.edu.
† Grinnell College.
‡ Washington University and National Sun Yat-Sen University.
§ University of Wisconsin.
(1) Nugent, W. A.; Haymore, B. L. Coord. Chem. ReV. 1980, 31, 123
and references therein. Nugent, W. A.; Mayer, J. M. Metal Ligand
Multiple Bonds; John Wiley&Sons: New York, 1988. Wigley, D. E.
Prog. Inorg. Chem. 1994, 42, 239.
(2) (a) Cummins, C. C.; Baxter, M. S.; Wolczanski, J. J. Am. Chem. Soc.
1988, 110, 8731. (b) Walsh, P. J.; Hollander, F. J.; Bergmann, R. G.
J. Am. Chem. Soc. 1988, 110, 8729.
(3) Representative examples: (a) Schroder, M. Chem. ReV. 1980, 80, 187.
(b) Tokles, M.; Snyder, J. K. Tetrahredon Lett. 1986, 27, 3951. (c)
Patrick, D. W.; Truesdale, S. A.; Biller, S. A.; Sharpless, K. B. J.
Org. Chem. 1978, 43, 2628. (d) Herran, S. A.; Biller, S. A.; Sharpless,
K. B. J. Am. Chem. Soc. 1978, 100, 3596.
Experimental Section
All reactions were performed under an argon atmosphere using
standard Schlenk techniques unless otherwise noted. The solvents
(5) Minelli, M.; Carson, M. R.; Whisenhunt Jr., D. W.; Hubbard, J. L.
Inorg. Chem. 1990, 29, 442.
(4) Schrock, R. R.; Murdzek, J. S.; Bazan, G. C.; Robbins, J.; DiMare,
M.; O’Regan, M. J. Am. Chem. Soc. 1990, 112, 3875; Schrock, R. R.
NATO ASI Ser., Ser. C 1998, 506, 1.
(6) Maatta, E. A.; Haymore, B. L.; Wentworth, R. A. D. Inorg. Chem.
1980, 19, 1055.
(7) Hogarth, G.; Norman, T.; Redmond, S. P. Polyhedron 1999, 18, 1221.
5954 Inorganic Chemistry, Vol. 41, No. 23, 2002
10.1021/ic025642x CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/17/2002

Structure and Properties of Mo(VI) Imido Complexes
Table 1. Elemental Analyses of Complexes I-III
Table 2. Elemental Analyses of MoNAr(X)2(dtc)2 Complexes
V(2,4,6,Cl) V(2,3,Cl) VI(2,4,Cl)
% calcd % found % calcd % found % calcd % found
I(2,4,6)a
II(2,4)a
III(2,6)b
% calcd % found % calcd % found % calcd % found
C
H
N
29.00
4.17
5.65
28.67
3.98
5.29
28.60
4.10
5.73
29.10
4.13
5.72
25.11
3.57
5.10
25.41
3.54
5.18
C
38.0
5.0
7.0
38.2
5.1
7.1
37.0
5.0
7.2
38.8
5.5
6.7
37.0
5.0
7.2
36.3
5.0
7.1
H
N
Cl
12.0
11.8
12.0
11.8
12.0
12.0
a [III]4[Mo8O26]‚CH2Cl2. b [I or II]2[Mo6O19].
VII(2,6,Cl)
VIII(2,6,diiso,Cl)
were dried and distilled prior to use. MoO(Cl)2(dtc)2,8 MoO(Br)2-
(dtc)2,8 and [Mo(NC6H5)(dtc)3]BF49 were synthesized according to
literature methods. The ArNH2 ligands (2,4,6-trimethylaniline, 2,3-,
2,4-, 3,4-, and 2,6-dimethylaniline, 2,6-diisopropylaniline) and
butyllithium were purchased from Aldrich and used without further
purification. Triethylamine was dried over sodium and distilled prior
to use. The elemental analyses were carried out by Atlantic
Microlab, Inc., in Norcross, GA.
% calcd
% found
% calcd
% found
C
37.0
5.0
7.2
35.8
5.2
6.6
41.4
5.8
40.8
5.8
H
N
Cl
6.6
6.5
12.0
12.9
11.1
11.4
XI(2,4,6,Br)
XII(2,6,Br)
% calcd
% found
% calcd
% found
Preparation of [MoNAr(dtc)3]2[Mo6O19] or [MoNAr(dtc)3]4-
[Mo8O26]. MoO(Cl)2(dtc)2 (1.0 g; 2.1 mmol) was suspended in 20
mL of methanol to which 2.2 mmol of ligand, ArNH2, dissolved
in 10 mL of methanol, and 0.66 mL (5.0 mmol) triethylamine were
added. Upon addition of the triethylamine, the yellow solution
turned reddish-brown. The mixture was refluxed overnight and
filtered to remove any solids; the filtrate was then evaporated to
dryness. The crude green-brown residue was dissolved in CH2Cl2
and washed with water. Orange-brown crystals were grown by
adding a layer of hexane to the solution. The yields after
recrystallization ranged from 10% to 50%, based on the number
of molybdenum atoms per formula unit of product. The elemental
analyses for these complexes are listed in Table 1, and the 1H NMR
data are presented in Table 3.
Preparation of MoNAr(X)2(dtc)2 (X ) Cl or Br). MoO(Cl)2-
(dtc)2 (1.0 g; 2.1 mmol) or MoO(Br)2(dtc)2 (1.2 g, 2.1 mmol) was
dissolved in 20 mL of THF, and 2.2 mmol of ligand, ArNH2, plus
0.46 mL (5.0 mmol) of butyllithium were added. The yellow
solution turned brown after the addition of butyllithium. The
solution was refluxed for 4 h. The reaction mixture was filtered
and the filtrate evaporated to dryness. The resulting yellow solid
was dissolved in CH2Cl2, and a layer of hexane was added over
the solution. After several days, yellow crystals had formed, which
were filtered off and dried under vacuum. Yields of approximately
30% were obtained for the recrystallized product. The elemental
analyses for these complexes are listed in Table 2, and the 1H NMR
data are presented in Table 3.
C
33.4
4.1
6.2
33.2
4.3
6.0
33.2
4.3
6.2
33.2
4.3
6.1
H
N
Br
23.4
23.2
23.8
25.6
standards were used: nitromethane, neat (14N NMR); 2 M Na2-
MoO4 in D2O, basic (95Mo NMR).
X-ray Structure Determination. The crystallographic data for
all the new complexes are listed in Tables 4 and 5. All room
temperature samples were glued onto glass fibers for diffraction
analysis while all low-temperature samples were attached with
viscous oil and instant-frozen to the end of glass fibers instead.
Diffraction data were collected on various Siemens diffractometers
(R3m/V (compounds I, II, III), P4 (compounds IV, V, VI, VII,
XI, XII) or SMART/P4 (compound VIII)) using graphite-mono-
chromated Mo KR radiation (λ ) 0.71073 Å). Space group
determinations were first indicated by patterns of systematic
absences (P21/c and P2/n) or lacking any patterns (P1h) and
confirmed with successful structural refinements. Empirical absorp-
tion corrections and Lp (Lorentz and polarization) corrections were
applied onto the datasets. The structures were all solved by direct
methods and refined by full-matrix least-squares techniques mini-
mizing ∆f 2.11 Neutral atom scattering factors were taken from ref
12. All computations used the SHELXTL program package.11 All
non-hydrogen atoms were refined anisotropically, and all hydrogen
(10) I ) I(2,4,6): tris(diethyldithiocarbamato)((2,4,6-trimethylphenyl)-
imido)molybdenum(VI) cation. II ) II(2,4): tris(diethyldithiocarbam-
ato)((2,4-dimethylphenyl)imido)molybdenum(VI) cation. III ) III-
(2,6): tris(diethyldithiocarbamato)((2,6-dimethylphenyl)imido)molyb-
denum(VI) cation. IV ) IV(2,4,6,Cl): dichlorobis(diethyldithiocar-
bamato)((2,4,6-trimethylphenyl)imido)molybdenum(VI). V ) V-
(2,3,Cl): dichlorobis(diethyldithiocarbamato)((2,3-dimethylphenyl)-
imido)molybdenum(VI). VI ) VI(2,4,Cl): dichlorobis(diethyldithio-
carbamato)((2,4-dimethylphenyl)imido)molybdenum(VI). VII ) VII-
(2,6,Cl): dichlorobis(diethyldithiocarbamato)((2,6-dimethylphenyl)-
imido)molybdenum(VI). VIII ) VIII(2,6,diiso,Cl): dichlorobis(di-
ethyldithiocarbamato)((2,6-diisopropylphenyl)imido)molybdenum(VI).
IX ) IX(Cl): dichlorobis(diethyldithiocarbamato)((phenyl)imido)-
molybdenum(VI). X ) X(2,NH2): ((2-aminophenyl)imido)dichlorobis-
(diethyldithiocarbamato)molybdenum(VI). XI ) XI(2,4,6,Br): dibromo-
bis(diethyldithiocarbamato)((2,4,6-trimethylphenyl)imido)molybdenum(VI).
XII ) XII(2,6,Br): dibromobis(diethyldithiocarbamato)((2,6-dimeth-
ylphenyl)imido)molybdenum(VI).
(11) (a) Sheldrick, G. SHELXTL PLUS program package; Universitaet
Go¨ttingen: Go¨ttingen, West Germany, 1988. (b) SHELXTL Program
System, version 4.02; Siemens Analytical X-Ray Instruments: Madi-
son, WI, 1993. (c) SHELXTL Program System, version 5.03; Siemens
Analytical X-Ray Instruments: Madison, WI, 1995. For compounds
I, II, and III, analyses were done with (a); for compounds IV, V, VI,
VII, XI, and XII, with (b); compound VIII was analyzed with (c).
(12) International Tables for X-ray Crystallography; Kluwer: Boston, 1992;
Vol. C, Tables 6.1.1.4, 4.2.6.8, and 4.2.4.2.
For short and easy identification, the complexes will hereafter
be referred to with Roman numerals.10 In parentheses, the positions
of the methyl groups or other substitutents on the phenyl ring of
the imido ligand will be given. For substituents other than methyl
groups, diiso will be added for diisopropyl, and NH2 for the amine
group. For the halogen complexes, the halogen will be noted in
parentheses as well. For example, the cation [Mo(2,6-(CH3)2C6H3N)-
(dtc)3]+ will be abbreviated as III(2,6) and Mo(2,6-(CH3)2C6H3N)-
Cl2(dtc)2 as VII(2,6,Cl).
NMR Spectroscopy. The NMR spectra were measured on a
1
Bruker AC 300 MHz NMR spectrometer. For the H spectra a 5
mm dual 1H/13C probehead was used. 14N and 95Mo NMR spectra
were measured with a 10 mm broadband probehead (109Ag-31P)
1
with digital tuning. For the H NMR spectra the residual solvent
was used as an internal reference. For the other nuclei external
(8) Dirand, J.; Ricard, L.; Weiss, R. J. Chem. Soc., Dalton Trans. 1976,
278.
(9) Young, G. C.; Broomhead, J. A.; Boreham, C. J. J. Chem. Soc., Dalton
Trans. 1983, 2135.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5955

Minelli et al.
Table 3. 1H NMR Data (ppm)a
CH3(dtc)
CH2(dtc)
H (Ar)
CH3 (Ar)
I(2,4,6)
II(2,4)
1.31-1.47 (m, 18)
3.81-4.00 (m, 12)
6.85 (s, 2)
2.40 (s, 3)
2.57 (s, 6)
2.53 (s, 3)
2.45 (s, 3)
1.31-1.49 (m, 18)
3.80-4.03 (m, 12)
7.03 (s, 1)
7.07 (d, 1)
7.44 (d, 1)
6.70 (t, 1)
7.00 (d, 1)
7.07 (d, 1)
6.70 (s, 2)
III(2,6)
1.39-1.50 (m, 18)
3.75-4.04 (m, 12)
2.25 (s, 3)
2.62 (s, 3)
IV(2,4,6,Cl)
V(2,3,Cl)
1.32 (t, 12)
1.32 (t, 12)
1.30 (t, 12)
3.65-4.00 (m, 8)
3.65-4.00 (m, 8)
3.65-3.95 (m, 8)
2.30 (s, 3)
2.72 (s, 6)
2.20 (s, 3)
2.50 (s, 3)
2.35 (s, 3)
7.05 (d, 2)
7.50 (t, 1)
6.85 (s, 1)
7.55 (d, 1)
6.90 (d, 1)
6.88 (d, 2)
7.00 (t, 1)
7.13 (d, 2)
7.20 (t, 1)
6.65 (s, 2)
VI(2,4,Cl)
2.55 (s, 3)
2.72 (s, 6)
VII(2,6,Cl)
1.30 (t, 12)
1.39 (q, 12)
1.35 (t, 12)
1.35 (t, 12)
3.65-3.95 (m, 8)
3.74-4.35 (m, 8)
3.60-4.00 (m, 8)
3.60-4.00 (m, 8)
VIII(2,6,diiso,Cl)
XI(2,4,6,Br)
XII(2,6,Br)
1.27 (d, 12)
2.25 (s, 3)
2.65 (s, 6)
2.70 (s, 6)
6.82 (d, 2)
6.95 (t, 1)
a In CDCl3.
Table 4. Crystallographic Data for [MoNAr(dtc)3]2[Mo6O19] and [MoNAr(dtc)3]4[Mo8O24] Compounds
[I(2,4,6)]2[Mo6O19]
[II(2,4)]4[Mo8O26]
[III(2,6)]2[Mo6O19]
chem formula
fw
C48H82N8O19S12Mo8‚4CH2Cl2
2567.2
C92H156N16O26S24Mo12‚CH2Cl2
3908.0
C46H78N8O19S12Mo8
2199.4
space group
unit cell dimens
a, Å
b, Å
c, Å
â, deg
R, deg
γ, deg
vol, Å3
Z
P2/n (No. 13)
P1h (No. 2)
P21/c (No. 14)
15.279(4)
12.131(9)
24.748(10)
93.88(2)
16.073(3)
16.838(4)
16.948(4)
93.86(2)
108.55(2)
116.33(2)
3778.3(14)
1
10.377(4)
29.151(11)
12.696(5)
91.29(3)
4577(4)
2
3840(3)
2
T, °C
-100
0.71073
1.863
1.627
22
0.71073
1.718
22
λ, Å
0.71073
1.902
1.610
F
calcd, g/cm3
µ, mm-1
1.388
final R indices (obsd)
R, %
Rw, %
5.45
9.36
5.25
8.02
3.36
4.34
atoms were placed at their idealized positions for the last cycle of
least-squares refinement but not refined.
the aniline and 2 equiv of triethylamine, imido complexes
of the type [MoNAr(dtc)3]2[Mo6O19] or [MoNAr(dtc)3]4-
[Mo8O26] are formed. The structures of three of these
complexes, [III(2,4,6)]2[Mo6O19], [II(2,4)]4[Mo8O26], and
[III(2,6)]2[Mo6O19], were determined by X-ray crystal-
lography. The cations have distorted pentagonal-bipyramidal
molybdenum centers with five sulfur atoms in the equatorial
plane and the imido nitrogen and one sulfur in the axial
positions. There are no significant differences in the lengths
of the molybdenum imido bonds, Mo(4)-N(4) (1.74 Å). The
angles of the imido linkage range from 169° to 178°. The
axial Mo(4)-S(5) bond is slightly longer than the Mo-S
bonds in the equatorial positions. In the case of [II(2,4)]4-
[Mo8O26], all averaged distances obtained from two inde-
pendent cations are comparable to those of the corresponding
bond distances of the other two compounds. We have not
detected any systematic trends for the formation of the
[Mo6O19]2- or [Mo8O26]4- anions during these reactions, but
[Mo6O19]2- is the more commonly found anion.
Results
The ORTEP drawings of the cation III(2,6) and of VII-
(2,6,Cl) are shown in Figures 1 and 2. Figures 3 and 4 show
[II(2,4)]4[Mo8O26] and [III(2,6)]2[Mo6O19], respectively.
Selected bond lengths and bond angles for compounds I-XII
are listed in Tables 6 and 7. All atoms in Tables 6 and 7 are
numbered according to Figures 1 and 2. The14N and 95Mo
NMR chemical shifts of the compounds are listed in
Table 8.
Discussion
Synthesis and Structure. Depending on the reaction
conditions, MoO(X)2(dtc)2 (X ) Cl, Br) will form different
products when reacted with anilines that contain alkyl
subsitituents on the phenyl ring (Figure 5). When the
molybdenum starting material is refluxed in methanol with
5956 Inorganic Chemistry, Vol. 41, No. 23, 2002

Structure and Properties of Mo(VI) Imido Complexes
Table 5. Crystallographic Data for [MoNAr(X)2(dtc)2] Compoundsa
IV(2,4,6,Cl)
V(2,3,Cl)
VI(2,4,Cl)
VII(2,6,Cl)
chem formula
fw
C19H31N3S4Cl2Mo
596.55
C18H29N3S4Cl2Mo
582.52
C18H29N3S4Cl2Mo
582.52
C18H29Cl2N3S4Mo
582.5
space group
unit cell dimens
a, Å
b, Å
c, Å
â, deg
vol, Å3
Z
P21/c (No. 14)
P21/c (No. 14)
P21/c (No. 14)
P21/c (No. 14)
13.8410(10)
13.8499(7)
13.8845(12)
100.082(6)
2620.5(3)
4
12.843(2)
13.6179(12)
14.696(2)
100.382(13)
2528.2(5)
4
13.2424(11)
13.677(2)
14.615(2)
96.141(9)
2631.8(5)
4
7.741(2)
14.865(4)
24.845(9)
95.74(3)
2844.7(15)
4
T, °C
-160
-160
23
0.71073
1.470
23
0.71073
1.360
λ, Å
0.71073
1.512
0.71073
1.530
F
calcd, g/cm3
µ, mm-1
0.9038
0.9353
1.029
0.952
final R indices (obsd)
R, %
Rw, %
3.31
8.22
4.93
10.55
3.94
9.55
6.0
14.92
VIII(2,6, diiso,Cl)
XI(2,4,6,Br)
XII(2,6,Br)
chem formula
fw
C22H37Cl2N3S4Mo
638.63
C19H31Br2N3S4Mo
685.47
C18H29Br2N3S4Mo‚0.5(C6H6)
710.50
space group
unit cell dimens
a, Å
b, Å
c, Å
â, deg
R, deg
γ, deg
vol, Å3
Z
P21/c (No. 14)
P21/c (No. 14)
P1h (No. 2)
17.9468(2)
9.2198(2)
18.3413(2)
92.379(2)
88.920(9)°
85.898(9)
3032.24(8)
4
13.8497(13)
14.345(4)
14.330(3)
99.567(12)
10.1653(9)
10.6198(10)
13.8730(11)
74.744(7)
2807.4(9)
4
1441.2(2)
2
T, °C
-140
25
25
λ, Å
0.71073
1.399
0.71073
1.622
1.059
0.71073
1.637
1.085
F
calcd, g/cm3
µ, mm-1
0.900
final R indices (obsd)
R, %
Rw, %
2.10
5.26
5.49
12.27
3.95
10.17
a Crystallographic data for IX6 and X5 have been published previously.
Figure 1. ORTEP drawing of [Mo(2,6-(CH3)2C6H3N)(dtc)3]+, III(2,6).
Figure 2. ORTEP drawing of Mo(2,6-(CH3)2C6H3N)Cl2(dtc)2, VII-
(2,6,Cl).
To get more insight into the formation of these salts, the
reactions of MoO(Cl)2(dtc)2, MoO(Br)2(dtc)2, and MoO2-
(dtc)2, with 2,6-dimethylaniline were performed in evacuated
10 mm NMR tubes using one-tenth of the amounts described
in the Experimental Section. The progress of each reaction
was monitored by 95Mo and 14N NMR spectroscopy. In all
three cases, the first new peak to appear in the 95Mo NMR
spectrum was that of [MoO(dtc)3]+. After approximately 5
h, the peaks for the polymolybdate anion and the imido
cations could be detected. In a separate experiment, each
molybdenum starting material was mixed with triethylamine
in methanol without the aniline, and the cation [MoO(dtc)3]+
was also formed. In the 14N NMR spectrum, one broad peak
for 2,6-dimethylaniline and triethylamine around -330 ppm
was observed at the beginning; after several hours, the imido
Inorganic Chemistry, Vol. 41, No. 23, 2002 5957

Minelli et al.
Table 6. Selected Bond Lengths (Å) and Bond Angles (deg) for
[MoNAr(dtc)3]+
I(2,4,6)
II(2,4)
III(2,6)
Mo(4)-N4
Mo(4)-S1
Mo(4)-S2
Mo(4)-S3
Mo(4)-S4
Mo(4)-S5
Mo(4)-S6
N4-C16
1.737(8)
1.737(7)
1.726(8)
2.508(3)
2.520(2)
2.485(3)
2.486(4)
2.498(3)
2.511(2)
2.504(3)
2.485(2)
2.586(3)
2.587(3)
2.496(3)
2.489(3)
1.383(12)
1.369(14)
1.736(3)
2.481(3)
2.520(3)
2.499(3)
2.509(3)
2.581(3)
2.491(3)
1.369(13)
2.494(1)
2.519(1)
2.496(1)
2.505(2)
2.576(2)
2.493(1)
1.387(5)
C16-N4-Mo(4)
N4-Mo(4)-S6
N4-Mo(4)-S5
177.8(6)
98.4(2)
172.4(5)
170.5(6)
100.2(3)
93.3(3)
169.6(3)
162.8(3)
168.6(3)
93.9(1)
167.0(2)
162.3(1)
five new chloro complexes, IV(2,4,6,Cl), V(2,3,Cl), VI(2,4,-
Cl), VII(2,6,Cl), and VIII(2,6,diiso,Cl), and two new bromo
complexes, XI(2,4,6,Br) and XII(2,6,Br), were determined
by X-ray crystallography. The coordination sphere of the Mo
is distorted pentagonal-bipyramidal with four sulfurs and one
halogen in the equatorial positions and the imido nitrogen
and the second halogen along the axis. The length of the
molybdenum-imido nitrogen bonds for IV(2,4,6,Cl), V(2,-
3Cl), VI(2,4,Cl), VII(2,6,Cl) is the same (about 1.73 Å).
The axial Mo-Cl(2) bonds are longer than the equatorial
Mo-Cl(1) bonds due to the trans influence. The angles of
the imido linkages vary from 166° to 179°. The structures
of the bromo complexes are identical to the chloro com-
plexes. In each category (cations, chloro and bromo com-
plexes), the complex with methyl groups in the 2,4,6
positions has the angle of the imido linkage closest to 180°.
NMR. The cations and the halogen complexes can be
easily distinguished by their 1H NMR spectra (Table 3). The
methyl groups of the dithiocarbamate ligand in the cations
form a multiplet of overlapping triplets, while only one triplet
Figure 3. ORTEP drawing of [Mo(2,4-(CH3)2C6H3N)(dtc)3]4[Mo8O26],
[II(2,4)]4[Mo8O26].
1
is seen in the H spectrum of the halogen complexes. An
exception is VIII(2,6,diiso,Cl), which has two overlapping
methyl triplets, forming a quadruplet. This indicates that the
rotation of the ethyl groups of the dithiocarbamate ligand
about the N-C bond may be hindered by the isopropyl
substituents on the imido ligand.
Figure 4. ORTEP drawing of [Mo(2,6-(CH3)2C6H3N)(dtc)3]2[Mo6O19],
[III(2,6)]2[Mo6O19].
The formation of an imido complex can be easily
monitored by 14N NMR spectroscopy. A signal between -20
and +80 ppm indicates the presence of an imido nitrogen.
The starting materials, anilines and triethylamine, as men-
tioned above, appear around -330 ppm. The imido nitrogens
of I(2,4,6), II(2,4), and III(2,6) absorb around +10 ppm and
are more deshielded than the imido nitrogens in the halide
complexes, which are found around -10 ppm.
peak around +12 ppm could be detected. It is interesting to
note that under the same conditions the reaction of MoO-
(Cl)2(dtc)2 with 1,2-phenylenediamine produces the complex
MoNAr(Cl)2(dtc)2.5 This indicates that 2-aminoaniline reacts
faster than the anilines used here so that the imido complex
forms before the oxo cation [MoO(dtc)3]+.
When the reaction of MoO(X)2(dtc)2 with anilines contain-
ing alkyl subsitituents on the phenyl ring is performed in
THF with 2 equiv of butyllithium as base, imido complexes
of the type MoNAr(X)2(dtc)2 are formed. The structures of
In the 95Mo NMR spectrum, the [Mo6O19]2- cluster absorbs
at +125 ppm, the [Mo8O26]4- cluster at +20 ppm. The imido
cations are found below -200 ppm. Compared to the oxo
5958 Inorganic Chemistry, Vol. 41, No. 23, 2002

Structure and Properties of Mo(VI) Imido Complexes
Table 7. Selected Bond Lengths (Å) and Bond Angles (deg) for MoNAr(X)2(dtc)2
IV(2,4,6,Cl)
V(2,3,Cl)
VI(2,4,Cl)
VII(2,6,Cl)
Mo-N3
Mo-X1
Mo-X2
Mo-S1
Mo-S2
Mo-S3
Mo-S4
N3-C11
1.739(3)
1.735(4)
1.731(4)
2.4370(14)
2.502(2)
2.5013(14)
2.5295(14)
2.493(2)
1.734(5)
2.431(2)
2.525(2)
2.518(2)
2.493(2)
2.519(2)
2.493(2)
1.379(8)
2.4347(9)
2.5322(8)
2.5244(10)
2.4877(8)
2.4880(9)
2.5188(9)
1.383(4)
2.4288(13)
2.5020(3)
2.4990(14)
2.5217(14)
2.5027(13)
2.514(2)
2.515(2)
1.375(6)
1.364(12)
Mo-N3-C11
N3-Mo-X1
N3-Mo-X2
178.9(3)
93.35(10)
176.95(10)
166.4(7)
95.06(13)
175.54(13)
169.2(4)
94.64(14)
174.29(14)
177.7(4)
94.3(2)
177.6(2)
VIII(2,6,diiso,Cl)
IX(Cl)a
X(2,NH2,Cl)b
XI(2,4,6,Br)
XII(2,6,Br)
Mo-N3
1.7630(12)
2.4600(4)
2.5267((4)
2.5385(4)
2.5359(4)
2.5334((4)
2.5395(4)
1.401(2)
1.734
1.700
1.736(10)
2.5936(13)
2.710(2)
2.488(3)
2.521(3)
2.494(3)
2.524(3)
1.391(14)
1.738(5)
2.5946(8)
2.7012(8)
2.502(2)
2.517(2)
2.489(2)
2.524(2)
1.388(7)
Mo-X1
Mo-X2
Mo-S1
Mo-S2
Mo-S3
Mo-S4
N3-C11
2.469(1)
2.467(1)
2.512(1)
2.508(1)
2.499(1)
2.512(1)
1.377(6)
2.442(14)
2.497(12)
2.507(19)
2.516(24)
2.514(27)
2.515(6)
1.375(19)
Mo-N3-C11
N3-Mo-X1
N3-Mo-X2
173.83(11)
91.18(4)
176.13(4)
166.8(3)
88.6(1)
173.9(1)
178.0(11)
94.3(5)
177.8(5)
178.8(7)
92.8(2)
177.1(2)
173.5(4)
95.23(14)
176.07(14)
a Reference 6. b Reference 5.
Table 8. 95Mo and 14N NMR Data
The 95Mo NMR chemical shifts of the chloro complexes
are clearly influenced by the substituents on the benzene ring
of the imido ligands. IX(Cl), with no substituents, has the
most shielded molybdenum nucleus (-254 ppm). Methyl
groups in the 3,4 (-242 ppm) and 2,3 (-230 ppm) positions
cause a slight deshielding, methyl groups in the 2,4 (-211
ppm) position deshield more, and methyl groups in the 2,6
(-176 ppm) and 2,4,6 (-174 ppm) positions deshield most
among the methyl groups. Isopropyl substituents in the 2,6
(-163 ppm) positions deshield more than the methyl groups.
An amino group in the 2 position (-164 ppm) in X(2,NH2,-
Cl) has a similar effect. The same trends are found for the
cations and the bromo complexes. For [(η5-C5H5)(CO)3Mo-
(CH2C6H4R)], the effects of the substituents on the aryl ring
with σ-bonding to the molybdenum have been studied
earlier.14 Electron-donating substituents like methyl groups
cause shielding of the 95Mo nucleus in these Mo(II)
complexes, the opposite effect of what we observe for the
Mo(VI) imido complexes here. This is consistent with the
fact that molybdenum complexes in lower oxidation states
generally show opposite responses to changes in the ligand
field when compared to molybdenum complexes in the +VI
oxidation state, i.e., Mo(VI) complexes show a inverse
halogen dependence (chloro species more deshielded than
bromo species) while Mo(II) complexes show a normal
halogen dependence.13
δ
95Mo,
δ
14N
compd
I(2,4,6)
(ppm; LW, Hz)
(ppm; LW, Hz)
+125 (100)
-218 (500)
+20 (250)
+10 (450)
II(2,4)
III(2,6)
(2,3)
+11 (470)
+12 (400)
+12 (400)
-258 (600)
+123 (100)
-235 (400)
+123 (100)
-271 (650)
-174 (500)
-230 (500)
-211 (250)
-176 (500)
-242 (800)
-163 (500)
-254 (480)
-164 (400)
-129 (300)
-139 (350)
-196 (450)
-294 (450)
IV(2,4,6,Cl)
V(2,3,Cl)
VI(2,4,Cl)
VII(2,6,Cl)
(3,4,Cl)
VIII(2,6,diiso,Cl)
IX(Cl)
-2 (350)
-8 (300)
-11 (400)
-6 (300)
-21 (300)
-5 (300)
-14 (200)
-19 (360)
+2 (300)
-5 (250)
-11 (300)
-12 (300)
X(2NH2,Cl)
XI(2,4,6,Br)
XII(2,6,Br)
(2,3,Br)
[Mo(NC6H5)dtc3]+
complex, [MoO(dtc)3]+, the molybdenum nuclei in these
cations are shielded by about 300 ppm.13
The 95Mo NMR chemical shifts for the chloro compounds
range from -163 ppm for VIII(2,6,diiso,Cl) to -254 ppm
for IX(Cl); i.e., the molybdenum nuclei are less shielded
than in the cations. The Mo nuclei in the bromo complexes
are less shielded than the chloro complexes due to the inverse
halogen dependence which has generally been observed for
Mo(VI) complexes.13 The chemical shift difference between
MoO(Cl)2(dtc)2 and MoO(Br)2(dtc)2 is about 50 ppm, the
same order of magnitude as observed here for the imido
complexes.13
In Figure 6, the 95Mo NMR chemical shifts for the chloro
complexes (IV-X) are plotted versus the bond angles of
their imido linkages. The complexes with imido linkages
close to 180° have the least shielded molybdenum nuclei.
With the possible exception of VIII(2,6,diiso,Cl), where the
methyl protons of the dithiocarbamate ligand are not
(13) Minelli, M.; Enemark, J. H.; Brownlee, R. T. C.; O’Connor, M. J.;
(14) Brownlee, R. T. C.; Masters, A. F.; O’Connor, M. J.; Wedd, A. G.;
Wedd, A. G. Coord. Chem. ReV. 1985, 68, 169.
Kimlin, H. A.; Cotton, J. D. Org. Magn. Reson. 1982, 20, 73.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5959

Minelli et al.
Figure 5. Synthetic routes for the [MoNAr(dtc)3]2[Mo6O19] and MoNAr(X)2(dtc)2 complexes.
substituents on the phenyl ring yields ionic complexes of
the type [MoNAr(dtc)3]2[Mo6O19] and MoNAr(dtc)3]4-
[Mo8O26] or halogen complexes of the type MoNAr(X)2-
(dtc)2. The position of the alkyl groups on the aryl group of
the imido ligand influences the 95Mo NMR chemical shift
and the angle of the imido linkage. Alkyl groups in the 2,6
and 2,4,6 positions have the most deshielding effect on the
95Mo nucleus. The deshielded nuclei generally have bond
angles of the imido linkage that are close to 180°.
Figure 6. Angles of the imido linkages vs 95Mo NMR chemical shifts.
Acknowledgment. M.M. would like to thank the donors
of the Petroleum Research Fund, administered by the
American Chemical Society, the NSF-REU Program (Grants
CHE-9300596 and CHE-9619655), and Grinnell College for
the support of this research. D.P. acknowledges funds from
the NSF (Grants CHE-9105497 and CHE-9310428 and the
University of Wisconsin for the purchase of the X-ray
instrument and computers.
equivalent, steric hindrance due to the substituents on the
aromatic ring of the imido ligand does not seem to be a
determining factor for the angle of the imido linkage. All
chloro complexes have the same space group, P21/c, with
four molecules per unit cell, so packing does not seem to be
the main factor responsible for the difference in the bond
angles of the imido linkages, i.e., in these compounds the
angles of the solid structures correlate with the 95Mo NMR
chemical shifts in solution.
Supporting Information Available: Tables of crystallographic
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
Conclusions
Depending on the solvent and base used, the reaction of
MoO(X)2(dtc)2 compounds with anilines that contain alkyl
IC025642X
5960 Inorganic Chemistry, Vol. 41, No. 23, 2002