'Electronic bending' of imido ligands and the effect on the coordination mode of a tridentate ancillary ligand

Article abstract of DOI:10.1016/j.poly.2007.02.008

The five-coordinate mixed-imido complex [Mo(Nt-Bu)(NC₆F₅)(L)] (1) can be prepared in high yield via treatment of [Mo(Nt-Bu)(NC₆F₅)(Ot-Bu)₂] with LH₂, where LH₂ is 2,6-bis(2-hydroxy-2,2-diphenylethyl)pyridine. Contrastingly, the reaction of [Mo(NAd)(NC₆F₅)(Ot-Bu)₂] (Ad = adamantyl, C₆H₁₀) with LH₂ gave [Mo(NAd)₂(L)] (2) via an imido-exchange reaction. Complex 2 can also be synthesised via treatment of in situ generated [Mo(NAd)₂(Ot-Bu)₂] with LH₂; the latter method also results in trace amounts of the five-coordinate complex [MoCl(NAd)₂(L_dehyd)] (3) (L_dehyd = 2-(2-hydroxy-2,2-diphenylethenyl)pyridine). The structures of 1-3 have been determined by X-ray crystallographic study. In each complex, the geometry at the metal is distorted trigonal bipyramidal with the pyridinediolate ligand adopting an 'aea' bonding arrangement in 1 and an 'eee' arrangement in 2. The angle associated with the imido moiety also varies, with the greatest deviations found in 1 and 3, indeed, the pentafluoroimido ligand in 1 has one of the largest deviations from linearity for an M-N-C angle recorded to-date [135.98(16)°]. This has been rationalised on the basis of an electronic effect rather than intramolecular steric interactions or crystal packing forces.

Full text of DOI:10.1016/j.poly.2007.02.008

Polyhedron 26 (2007) 3161–3167
www.elsevier.com/locate/poly
‘Electronic bending’ of imido ligands and the effect on the
coordination mode of a tridentate ancillary ligand
a
b,
c
d
Vernon C. Gibson , Carl Redshaw *, William Clegg , Mark R.J. Elsegood
a
Department of Chemistry, Imperial College, South Kensington, London SW7 2AY, UK
School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK
b
c
School of Natural Sciences, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK
d
Chemistry Department, Loughborough University, Loughborough LE11 3TU, UK
Received 4 January 2007; accepted 15 February 2007
Available online 20 February 2007
Abstract
The five-coordinate mixed-imido complex [Mo(Nt-Bu)(NC6F5)(L)] (1) can be prepared in high yield via treatment of [Mo(Nt-
Bu)(NC6F5)(Ot-Bu)2] with LH2, where LH2 is 2,6-bis(2-hydroxy-2,2-diphenylethyl)pyridine. Contrastingly, the reaction of [Mo(N-
Ad)(NC6F5)(Ot-Bu)2] (Ad = adamantyl, C6H10) with LH2 gave [Mo(NAd)2(L)] (2) via an imido-exchange reaction. Complex 2 can also
be synthesised via treatment of in situ generated [Mo(NAd)2(Ot-Bu)2] with LH2; the latter method also results in trace amounts of the
five-coordinate complex [MoCl(NAd)2(Ldehyd)] (3) (Ldehyd = 2-(2-hydroxy-2,2-diphenylethenyl)pyridine). The structures of 1–3 have
been determined by X-ray crystallographic study. In each complex, the geometry at the metal is distorted trigonal bipyramidal with
the pyridinediolate ligand adopting an ‘aea’ bonding arrangement in 1 and an ‘eee’ arrangement in 2. The angle associated with the imido
moiety also varies, with the greatest deviations found in 1 and 3, indeed, the pentafluoroimido ligand in 1 has one of the largest deviations
from linearity for an M–N–C angle recorded to-date [135.98(16)ꢀ]. This has been rationalised on the basis of an electronic effect rather
than intramolecular steric interactions or crystal packing forces.
ꢁ 2007 Elsevier Ltd. All rights reserved.
Keywords: Molybdenum; Imido; Crystal structures
1. Introduction
noted [4]. Contrastingly, there are few examples of bent
imido groups (III), although a number of chelate species
are known where the restricted imido bond angle is a func-
tion of the bite angle of the ligand [5]. In the case of III, the
lone pair resides on the sp2-hybridised nitrogen atom and
the metal imido group can be described as possessing dou-
ble-bond character (2 electron donor).
The organoimido function has featured heavily in coor-
dination chemistry over the last three decades [1]. Interest
in bis(imido) complexes of group VI in-particular contin-
ues, primarily because of their use as precursors to useful
catalytic systems [2]. The vast majority of terminal orga-
noimido (NR, R = alkyl or aryl) groups in the literature
are sp-hybridised at nitrogen and hence triple-bond in nat-
ure (four electron donors). The softness of the M–N–C
angle has been noted previously with angles in the range
180–150ꢀ considered linear (I) [3]. An additional linear
form (II) with a formal M = N double bond has also been
M
N
R
M
N
M
N
R
R
*
Corresponding author.
I
II
III
E-mail address: Carl.Redshaw@uea.ac.uk (C. Redshaw).
0277-5387/$ - see front matter ꢁ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.02.008

3162
V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
The earliest structurally characterised example [Mo-
5-coordination geometry. Furthermore, would an imido
ligand with a strong electron-withdrawing substituent show
a preference for the equatorial site. We were also interested
to compare the effect of facial (eae) coordination of the
[O,N,O] ligand with meridional (eee) coordination, and
the effect this might have on the imido ligand bonding.
(NPh)2(S2CNEt2)2], a 20 electron complex, was found to
possess one bent [Mo–N–C = 139.4(4)ꢀ] and one linear
[Mo–N–C = 169.4(4)ꢀ] imido group at ꢀ80 ꢀC [6]; only
slight differences were observed in a later room temperature
study [7]. Interestingly, the related complexes [Mo-
(NAr)2(S2CNEt2)2] (Ar = 2-MeC6H4, 2,6-Me2C6H3, 2,6-i-
Pr2C6H3 and 2,6-Cl2C6H3) do not contain bent imido
groups, leading to the conclusion that the bending of the
imido ligand in this system is attributable to intramolecular
steric interactions and/or crystal packing forces [7]. Exam-
ples of bent imido ligands for other metals (see Table 1)
include the manganese complexes [Mn(Nt-Bu)3X]
(X = Cl, OC(O)Me, OC6F5 and SC6F5) for which the
Mn–N–C angles fall in the range 138.5(3)–144.6(3)ꢀ [8],
and the rhenium(VII) complex {[Re(Nt-Bu)2(g1-
C5H5)]2(l- C5H4)(l-O)} [9]. Recently, Odom et al. have
carried out a statistical analysis of bis(imido) group VI
complexes using data from the Cambridge Structural Data
Base, and presented the data in terms of the sum of the
imido angles [10]. The average sum of the imido angles
was found to be 328ꢀ (standard deviation 8ꢀ), whilst it
was also apparent that bending of the imido group was
no more prevalent for 6-coordinate complexes than for 4-
or 5-coordinate species.
In our previous studies on the 2,6-bis(2-hydroxy-2,2-
diphenylethyl)pyridine (LH2), IV, we have described the
synthesis and X-ray crystal structure of the five-coordinate
molybdenum (VI) compound [Mo(NAr)2(L)], where
Ar = N-2,6-i-Pr2C6H3 [3]. In this case the pyridinediolate
ligand adopts a ‘facial’, (eae) coordination mode1 leaving
one of the imido ligands to occupy an axial coordination
site within the trigonal bipyramidal structure, the other
imido group occupies an equatorial site. The structure of
this complex revealed a severe bending of the equatorial
imido ligand, [144.8(5)ꢀ] the axial imido group remaining
essentially linear [164.7(4)ꢀ]. In order to help understand
whether the bending was due to an electronic or steric
effect, the related alkylidene complex was prepared and
structurally characterised. Here, the alkylidene ligand was
found to preferentially occupy the equatorial site and is
of course necessarily bent due to the sp2-hybridised
alkylidene carbon centre. Indeed, it was thought likely that
the alkylidene ligand would prefer the equatorial site since
in that position there exists only one dp metal orbital
available for bonding to the p-ligand. Thus, the bending
of the imido group in this environment may be attributed
to an electronic explanation rather than due to steric effects
or crystal packing forces. In extending this work, we
wished to probe the effect of incorporating differing
imido ligands, especially those with different electronic
requirements, i.e. an electron-withdrawing substituent
and an electron-releasing substituent within this
Table 1
Bent imido groups
Compound
M–N–C
angle (ꢀ)
Metal
coordination
number
Reference
[11]
[CrO(Nt-Bu)(O(Ph2SiO)2)2]
145.6(6)
146.4(6)
146.2(3)
144.1(3)
4
[Cr(NAr)(O)(Ni–Pr2)(Ar)]
[Cr(O)(NSiMe3)(py)]2-
(l-OSiMe3)
4
5
[12]
[13]
[Mo(NPh)2(S2CNEt2)2]
139.4(4)
[141.4(5)]
169.4(4)
[170.9(6)]
144.8(5)
164.7(4)
135.98(16)
173.52(18)
148.6(3)
170.9(3)
138.5(3)
141.8(3)
140.6(3)
144.6(3)
140.1(5)
142.2(5)
141.9(2)
139.9(2)
140.7(2)
6
[6,7]
[Mo(NAr)2L]
5
5
5
4
[3]
[Mo(Nt-Bu)(NC6F5)L]
[Mo(NAd)2Cl(LHdehyd)]
[Mn(Nt-Bu)3Cl]
this work
this work
[8]
[Mn(Nt-Bu)3(OC(O)Me)]
[Mn(Nt-Bu)3(OC6F5)]
4
4
4
4
4
5
[8]
[8]
[8]
[8]
[8]
[10]
[Mn(Nt-Bu)3(NH2t-Bu)](PF6)a 141.0(6)
141.4(6)
146.5(6)
[Mn(Nt-Bu)3(NH2t-
Bu)](O3SCF3)a
135.8(6)
140.5(7)
136.2(4)
143.1(2)
142.0(2)
142.2(2)
146.1(10)
152.5(12)
173.4(11)
176.2(12)
142.4(22)
148.37
[Mn(Nt-Bu)3(SC6F5)]
{[Re(Nt-Bu)2(g1-C5H5)]2-
(l-C5H4)(l-O)}
[Re(Nt-Bu)3(mesityl)]
[MoCl(Nt-Bu)2(O–O)]b
[Re(Nt-Bu)3(NH2t-Bu)]-
(SO3CF3)
[Re4(Nt-Bu)8(l-O)2(l3-O)2-
(O3SCF3)4]
[Os(p-NC6H4NO2)2(TTP)]d
4
5
4
[14]
[15]
[16]
146.0(8)
139.8(7)c
143.9(6)
5
6
6
[17]
[18]
[19]
144.74
141.91
143.8(6)
141.3(6)
[Os(p-NC6H4NO2)2-
(4-Cl-TTP)]d
a
Severe disorder prevented an accurate structure determination.
(O–O) = ring-opened biaryl lactone.
Thought to be protonated.
b
c
1
We have opted not to use the terms fac and mer here, as IUPAC
d
TTP = tetratolylporphyrin.
usually reserves such descriptions for hexa-coordinate centres.

V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
3163
In this paper, we report the successful synthesis and struc-
tural characterisation of two complexes [Mo(Nt-
Bu)(NC6F5)(L)] (1) and [Mo(NAd)2(L)] (2), which possess
the desired facial and meridional coordination geometries,
respectively. The structure of the trace product [MoCl(-
NAd)2(Ldehyd)] (3) is also reported.
Few other studies of the tridentate ligand L have been
reported, examples include oxo, nitrido and imido com-
plexes of osmium [20], the dioxo complexes of molybde-
num reported by Holm [21], a titanium dichloride
complex [TiCl2L] [22] and the main-group complex
[SiMe2L] [23–25]. We have also recently reported the isod-
iazene complex [MoCl(O3SCF3)(NNPh2)L] which contains
a meridional ligand [26].
Fig. 1. The molecular structure of 1 with H-atoms omitted.
N
N
Ph
Ph
Ph
Ph
Ph
Ph
Table 2
Selected bond lengths (A) and angles (ꢀ) for 1
˚
OH
OH
HO
LH2 (IV)
Ph
LHdehyd (V)
Ph
Mo(1)–N(1) 1.7228(19)
Mo(1)–O(1) 1.9173(15)
Mo(1)–N(3) 2.3914(18)
Mo(1)–N(2) 1.8074(19)
Mo(1)–O(2) 1.9274(15)
N(1)–Mo(1)–N(2) 103.55(9)
N(2)–Mo(1)–O(1) 116.97(8)
N(2)–Mo(1)–O(2) 115.49(8)
Mo(1)–N(1)–C(1) 173.52(18)
N(1)–Mo(1)–O(1) 95.40(8)
N(1)–Mo(1)–O(2) 93.86(8)
O(1)–Mo(1)–O(2) 122.51(7)
Mo(1)–N(2)–C(5) 135.98(16)
2. Results and discussion
Starting materials of the form [Mo(NR0)(NR00)Cl2(dme)]
(R0 = t-Bu, R00 = C6F5; R0 = Ad, R00 = C6F5) have been
used previously for the synthesis of mixed-imido
compounds [27]. The five-coordinate complex [Mo(Nt-
Bu)(NC6F5)(L)] (1) can be prepared in multigram
quantities via treatment of [Mo(Nt-Bu)(NC6F5)(Ot-Bu)2]
(prepared in situ from [Mo(Nt-Bu)(NC6F5)2Cl2(dme)]
and LiOt-Bu) with LH2.
Crystals of 1 suitable for an X-ray determination were
grown from a saturated MeCN solution upon standing at
room temperature. The molecular structure is shown in
Fig. 1 and key bond lengths and angles are given in Table
2, crystal data are given in Table 3. The molecular structure
is best described as a distorted trigonal pyramid with the
pyridine of the diolate and the tert-butylimido groups
occupying axial sites, i.e. an ‘aea’ set.
the nitrogen and the ipso-carbon of the phenyl ring as evi-
˚
denced by the short C(5)–N(2) distance [1.379(3) A cf.
˚
1.449(3) A for C(1)–N(1)]. Table 1 contains literature
examples of ‘bent’ imido groups and reveals that for com-
plex 1 the imido group has one of the greatest deviations
from linearity observed to-date. The sum of the imido
angles for 1 = ca. 309.5(ꢀ), which is very close to that
observed for [Mo(NPh)2(S2CNEt2)2] [309ꢀ] – which is the
lowest ‘sum’ in the literature.
The five-coordinate complex [Mo(NAd)2(L)] (2) can be
prepared via treatment of [Mo(NAd)(NC6F5)(Ot-Bu)2]
(prepared in situ from [Mo(NAd)(NC6F5)Cl2(dme)] and
LiOt-Bu) with LH2 in refluxing toluene. The production
of complex 2 at elevated temperatures indicates that under
these conditions imido-ligand exchange occurs. Similar
imido ligand exchange has been observed for the four-coor-
dinate complexes [MoX2(Ot-Bu)2] (X = O or NR), the tet-
ratungstate [W4(Nt-Bu)4O4Cl10]2ꢀ and more recently for
the tert-butylimido titanium complex [Ti(Nt-Bu)Cl2(py)2]
[28–30]. It is also noteworthy that the bis(imido) complexes
[Mo(NR)2Cl2(dme)] (R = t-Bu, 2,6-C6H3-i-Pr2) and
[Mo(NAr)2(Ot-Bu)2] undergo metathesis with the imines
PhN = CH(t-Bu) or (n-Pr)N = CHPh [31]. Crystals of
2 Æ MeCN suitable for an X-ray determination were
obtained from a saturated MeCN solution upon prolonged
standing at ambient temperature. The molecular structure
is shown in Fig. 2a and b; key bond lengths and angles
The ‘aea’ arrangement of the pyridinediolate (L) is sim-
ilar to that observed in [Mo(NAr)2L] (Ar = N-2,6-i-
Pr2C6H3)2 and [OsNCl(L)] [20]. The structural parameters
associated with the two imido groups in 1 reflect their
differing electronic properties. The result is one linear
˚
[Mo(1)–N(1) = 1.7228(19) A,
tert-butylimido
ligand
Mo(1)–N(1)–C(1) = 173.52(18)ꢀ] and one bent pentafluor-
˚
ophenylimido group [Mo(1)–N(2) = 1.8074(19) A, Mo(1)–
N(2)–C(5) = 135.98(16)ꢀ]; a feature attributed to the more
electron-releasing nature of the tert-butylimido ligand. In
the bent ligand, there is also a diminished metal-nitrogen
p contribution due to the presence of p-bonding between

3164
V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
Table 3
Summary of crystal data and structure determination for compounds 1, 2 Æ MeCN and 3
Compound
1
2 Æ MeCN
3
Formula
M
C43H36F5N3O2Mo
817.69
C53H57N3O2Mo Æ C2H3N
905.01
C53H56ClN3OMo
882.40
Temperature (K)
Crystal size (mm)
Crystal colour, habit
Crystal system
Space group
160
160
160
0.42 · 0.17 · 0.11
yellow, block
monoclinic
P21/c
0.29 · 0.23 · 0.23
yellow, block
monoclinic
P21/c
0.25 · 0.18 · 0.16
yellow, block
monoclinic
P21/c
˚
a (A)
11.0769(5)
33.8115(16)
11.2651(5)
116.687(2)
3769.6(3)
4
25.762(11)
8.671(4)
21.877(11)
111.99(2)
4531(4)
12.4861(12)
18.1988(17)
19.0842(18)
99.806(2)
4273.2(7)
4
˚
b (A)
˚
c (A)
b (ꢀ)
3
˚
V (A )
Z
4
Dcalc (g cmꢀ3
l (mmꢀ1
h Range (ꢀ)
)
1.441
0.414
1.327
2.726
1.372
0.413
)
2.06–28.40
ꢀ14 to 8
ꢀ43 to 38
ꢀ14 to 14
23182
8566 {7205}
0.0297
0.0383
3.70–60.09
ꢀ28 to 28
ꢀ9 to 5
1.56–25.85
ꢀ15 to 12
ꢀ22 to 14
ꢀ21 to 22
18725
7387 {6108}
0.0494
0.0530
Maximum indices: h
k
l
ꢀ24 to 24
6721
Reflections measured
Unique reflections {observed F2 > 2r(F2)}
Rint
6721 {5814}
R [F2 > 2r(F2)]a
0.0615
0.1345
wR2 [all data]b
0.0766
0.1086
Number of refined parameters
Largest difference map features (e A
491
0.354, ꢀ0.590
560
1.631, ꢀ1.417
533
0.453, ꢀ0.693
ꢀ3
˚
)
P
P
a
R ¼ kF oj ꢀ jF ck= jF oj.
P
P
2
2
1=2
b
wR2 ¼ f ½wðF 2o ꢀ F c2Þ = ½wðF 2oÞ g
.
are given in Table 4 and crystal data appear in Table 3.
Each molecule of 2 crystallises with a molecule of MeCN.
The molecular structure is best described as a distorted tri-
gonal pyramid with the pyridine of the diolate and the two
imido groups in equatorial positions, i.e. ‘eee’ ligated L.
the partially dehydrated ligand V. The structure of 3 is
shown in Fig. 3, with selected bond lengths and angles
given in Table 5. There is approximate trigonal bipyrami-
dal geometry at the metal centre, with the pyridine of the
chelate and two imido ligands equatorial. As in 1, the
two imido ligands are quite different: Mo(1)–N(3)
1
The H NMR spectrum of 1 reveals an AB quartet at
˚
3.86 ppm for the ligand backbone methylene units consis-
tent with the diastereotopic proton environments in the
‘aea’ coordinated ligand. Contrastingly the room tempera-
1.724(3) A/Mo(1)–N(3)–C(44) 170.9(3)ꢀ versus Mo(1)–
˚
N(2) 1.745(3) A/Mo(1)–N(2)–C(34) 148.6(3)ꢀ; the latter is
now in the range associated with bent imido groups (sum
of angles = 319.5ꢀ). This bending could arise as a conse-
quence of steric interactions with the pendant alkenyl
arm of the chelate ligand. Pyridinediols have previously
been found to act as HCl receptors, and the structure of
the partially dehydrated ligand V Æ HCl (i.e., the HCl
adduct of LHdehyd) was shown to contain a Clꢀ ion hydro-
gen-bonded to a protonated pyridine nitrogen atom. Inter-
estingly, in order to achieve complete dehydration, neat
H3PO4 had to be used at elevated temperatures [32].
1
ture H NMR spectrum of 2 reveals a broadened singlet
consistent with the ‘eee’ coordination geometry.
Meridional arrangements for L have been observed
previously in the 6-coordinate complexes [Mo(O)2(L)-
(Me2SO)] and [Os(O)2(L)(H2Nt-Bu)] [20,21]. In 2, a non-
crystallographic 2-fold-axis bisects the N(1)–Mo–N(2)
angle between the imido groups and passes along the
Mo–N(3) bond of the pyridinediolate. The bond parame-
ters associated with the equatorial imido ligands are of par-
ticular interest to us here. The Mo–N distances are similar,
˚
viz Mo–N(1) = 1.710(5), Mo–N(2) = 1.727(4) A, whereas
3. Summary
the angles at the imido nitrogens are quite different,
168.8(4)ꢀ and 159.6(4)ꢀ (sum of angles = 328.4ꢀ), however,
both imido ligands are still considered to be ‘linear’.
Reaction of [Mo(NAd)2(Ot-Bu)2] (prepared in situ from
[Mo(NAd)2Cl2(dme)] and LiOt-Bu) with LH2 led to com-
plex 2 together with trace amounts of yellow plate-like
crystals, which were shown by X-ray diffraction to be the
complex [MoCl(NAd)2(LHdehyd)] (3), where LHdehyd is
We have described the synthesis and characterisation of
two bis(imido)molybdenum complexes that differ in the
coordination geometry of a tridentate [O,N,O] ligand:
one of the complexes also has two electronically differing
imido substituents. In this case the imido ligands with an
electron-releasing tertiary-butyl substituent occupies the
axial site within the trigonal bipyrimidal coordination

V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
3165
a
Fig. 3. The molecular structure of 3 with H-atoms omitted.
b
Table 5
Selected bond lengths (A) and angles (ꢀ) for 3
˚
Mo(1)–N(1) 2.366(3)
Mo(1)–O(1) 1.962(2)
Mo(1)–N(3) 1.724(3)
Mo(1)–N(2) 1.745(3)
Mo(1)–Cl(1) 2.4196(11)
N(1)–Mo(1)–N(2) 104.62(12)
N(2)–Mo(1)–O(1) 97.16(12)
N(3)–Mo(1)–O(1) 100.77(12)
N(3)–Mo(1)–Cl(1) 90.59(11)
Mo(1)–N(2)–C(34) 148.6(3)
N(1)–Mo(1)–O(1) 76.25(10)
N(1)–Mo(1)–N(3) 147.41(13)
N(3)–Mo(1)–N(2) 107.93(14)
N(2)–Mo(1)–Cl(1) 108.03(10)
Mo(1)–N(3)–C(44) 170.9(3)
the observation that for electronically similar imido groups
in identical coordination environments, especially when
placed in direct competition for the available metal dp
orbitals, an imido bend angle in the range 150–180ꢀ is
anticipated. The M–N–C angle then appears to be dictated
by intramolecular steric effects and crystal packing forces, a
consequence of a relatively shallow potential energy well
for M–N–C bending when the two imido groups are in
chemically equivalent sites and therefore in direct competi-
tion for the available metal p-orbitals.
Fig. 2. (a,b) Two views of the molecular structure of 2 with H-atoms and
MeCN of crystallisation omitted.
Table 4
˚
Selected bond lengths (A) and angles (ꢀ) for 2
Mo–N(1) 1.710(5)
Mo–O(1) 1.995(3)
Mo–N(3) 2.299(4)
Mo–N(2) 1.727(4)
Mo–O(2) 2.020(4)
N(1)–Mo–N(2) 111.8(2)
N(2)–Mo–O(1) 95.99(18)
N(2)–Mo–O(2) 100.05(18)
Mo–N(1)–C(1) 168.8(4)
N(1)–Mo–O(1) 101.22(18)
N(1)–Mo–O(2) 94.99(19)
O(1)–Mo–O(2) 151.05(14)
Mo–N(2)–C(11) 159.6(4)
4. Experimental
4.1. General
geometry, the electron-withdrawing pentafluorophenyl
imido group, the equatorial site. This would appear to be
a favourable arrangement allowing the tertiary-butylimido
group to maximise its p-donor group capacity through the
formation of two p bonds. In the equatorial position, there
is only a single dp metal orbital available to overlap with
the imido nitrogen p orbital thereby restricting the imido
group to a single p-bond. A consequence of this is a for-
mally sp2-hybridised nitrogen and an accordingly bent
imido ligand. The structure of 2 lends further support to
All manipulations were carried out under an atmosphere
of nitrogen using standard Schlenk and cannula techniques
or in a conventional nitrogen-filled glove-box. Solvents
were refluxed over an appropriate drying agent, and dis-
tilled and degassed prior to use. Elemental analyses were
performed by the microanalytical services of the Depart-
ment of Chemistry at Durham and of Imperial College.
NMR spectra were recorded on a Varian VXR 400S spec-
trometer at 400.0 MHz (1H), and 376.3 MHz (19F) at
298 K; chemical shifts are referenced to the residual protio

3166
V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
impurity of the deuterated solvent; IR spectra (nujol mulls,
CsI windows), Perkin–Elmer 577 and 457 grating spectro-
photometers. [Mo(Nt-Bu)(NC6F5)Cl2(dme)], [Mo(NAd)-
(NC6F5)Cl2(dme)], [Mo(NAd)2Cl2(dme)] and LH2 were
prepared by the literature methods [27,21]. All other chem-
icals were obtained commercially and used as received
unless stated otherwise.
1267w, 1233m, 1181w, 1122m, 1095m, 1053s, 1027m,
950m, 907w, 821w, 779m, 735w, 701s, 666s, 598s. 1H
NMR (CD3CN) d: 7.83–7.01 (several m, 23H, arylH),
6.50 (d, 1H, CH), 4.09 (bs, 2H, CH2), 1.97 (m, 18H,
AdH), 1.65 (m, 12H, AdH).
4.5. X-ray crystallography
4.2. Preparation of [Mo(Nt-Bu)(NC6F5)L] (1)
Crystallographic data and details of the data collection
procedures and structure refinement for structures 1, 2
and 3 are presented in Table 3.
To [Mo(Nt-Bu)(NC6F5)(Ot-Bu)2] [prepared in situ from
[Mo(Nt-Bu)(NC6F5)Cl2(dme)] (1.50 g, 2.98 mmol) and
LiOt-Bu (0.48 g, 6.00 mmol)] in ca. 50 cm3 diethyl ether
was added LH2 (1.37 g, 2.91 mmol). After stirring for
5–10 min, the volatiles were removed in vacuo. Toluene
(ca. 40 cm3) was added and the system was refluxed for
12 h. On cooling, volatiles were removed in vacuo and
the residue was extracted with hot MeCN (40 cm3). On
standing at room temperature large yellow prisms of 1
formed. Yield: 1.90 g, 80%. Anal. Calc. for
MoF5O2N3C43H36 requires C, 63.2; H, 4.4; N, 5.1. Found:
C, 63.4; H, 4.4; N, 5.0%. IR: 1600w, 1575w, 1494m, 1343m,
1312m, 1292m, 1261s, 1239m, 1211m, 1189m, 1093s, 1060s,
1023s, 977m, 960m, 947m, 916m, 892m, 875m, 801s, 770m,
753m, 733m, 724m, 701m, 658w, 638w, 619w, 607w, 600w,
592w, 565w, 512w, 497w, 484w, 452w, 427w, 417w, 404w.
1H NMR (CDCl3): d 7.46–6.74 (several m, 23H, arylH),
3.86 (ABq, 4H, CH2), 1.12 (s, 9H, C(CH3)3). 19F NMR
Data for 1 and 3 were collected on a Bruker AXS
SMART 1K CCD area detector diffractometer using
graphite monochromated Mo Ka radiation (k =
˚
0.71073 A) and narrow frames (0.3ꢀ in x). Corrections
were applied for Lorentz-polarisation effects and semi-
empirically for absorption based on symmetry equivalent
and repeated data. Programs used were Bruker AXS
SMART (machine control) and SAINT (frame integration)
[33]. Data for 2 were collected on a Stoe-Siemens diffrac-
tometer with x/h scans and on-line profile fitting [34] with
all machine-control calculations performed using Stoe
DIF4 software and with graphite monochromated Cu Ka
˚
radiation (k = 1.54184 A). Corrections were applied for
Lorentz-polarisation effects and semi-empirically for
absorption using W-scans. The structures were solved by
direct methods for 1 and 3, (Patterson synthesis for 2)
and refined by full-matrix least-squares on all data using
F2 values. All non-H atoms were refined anisotropically,
H atoms, initially located in difference maps, were included
using a riding model with Uiso equal to 1.2 times that of the
carrier atom (1.5 times for methyl H). The program
SHELXTL [35] was used for crystal structure solution and
refinement and molecular graphics.
3
(CDCl3): d ꢀ152.00 (m, 2F, o-F), ꢀ165.36 (tm,* 2F, JFF
4
*
18 Hz, JFF 3Hz, m-F), ꢀ167.44 (m, 1F, p-F). triplet of
multiplets.
4.3. Preparation of [Mo(NAd)2L] (2)
As for 1, using [Mo(NAd)(NC6F5)Cl2(dme)] (2.00 g,
3.42 mmol) and LiOt-Bu (0.54 g, 6.75 mmol) and LH2
(1.60 g, 3.39 mmol) affording 2 Æ MeCN as golden-yellow
prisms. Yield: 1.37 g, 89%. Anal. Calc. for MoO2N3-
C53H55 Æ CH3CN (sample dried for 12 h in vacuo) requires
C, 73.2; H, 6.5; N, 6.2. Found: C, 73.7; H, 6.5; N, 6.1%. IR:
2359m, 2342m, 1737w, 1705w, 1654w, 1602w, 1580w,
1560w, 1500s, 1308w, 1242m, 1182w, 1119w, 1096w,
1062m, 1044s, 1027s, 984w, 963w, 924w, 890w, 812w,
5. Supplementary material
CCDC 147054, 147055 and 147056 contain the supple-
mentary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.
ac.uk/conts/retrieving.html, or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
1
784m, 752w, 701s, 606s. H NMR (Acetone-d6) d: 7.65–
7.16 (several m, 23H, arylH), 4.08 (bs, 4H, CH2), 1.98
(m, 6H, CHad), 1.57 (m, 12H, CH2ad), 1.56 (m, 12H,
CH2ad).
Acknowledgements
The Engineering and Physical Sciences Research Coun-
cil and The University of East Anglia are thanked for
financial support.
4.4. Preparation of [MoCl(NAd)2(Ldehyd)] (3)
As for 1, but using [Mo(NAd)2Cl2(dme)] (0.93 g,
1.69 mmol) and LiOt-Bu (0.26 g, 3.25 mmol) with LH2
(0.80 g, 1.70 mmol) affording on recrystallisation from
hot acetonitrile 2 (0.61 g, 80%) and 3 (0.11 g, 15% based
on Mo). For 3, Anal. Calc. for MoClON2C43H40 requires
C, 70.5; H, 5.5; N, 3.8. Found: C, 69.4; H, 5.7; N, 3.8%.
IR: 2359m, 2325m, 1654w, 1603m, 1568w, 1491m, 1302w,
References
[1] (a) W.A. Nugent, B.L. Haymore, Coord. Chem. Rev. 31 (1980) 123;
(b) W.A. Nugent, J.M. Mayer, Metal-Ligand Multiple Bonds, Wiley-
Interscience, New York, 1988;
(c) D.E. Wigley, Prog. Inorg. Chem. 42 (1994) 239;

V.C. Gibson et al. / Polyhedron 26 (2007) 3161–3167
3167
(d) P.R. Sharp, Comm. Inorg. Chem. 21 (1999) 85;
(e) P.R. Sharp, J. Chem. Soc., Dalton Trans. (2000) 2647;
(f) R.A. Eikey, M.M. Abu-Omar, Coord. Chem. Rev. 243 (2003) 83;
(g) W.-H. Leung, Eur. J. Inorg. Chem. (2003) 583;
(h) U. Radius, Z. Anorg. Allg. Chem. 630 (2004) 957.
[2] (a) See for example R.R. Schrock, J. Mol. Cat. A: Chem. 213 (2004)
21;
(b) V.R. Jensen, K.J. BØrve, Chem. Commun. (2002) 542.
[3] V.C. Gibson, E.L. Marshall, C. Redshaw, W. Clegg, M.R.J.
Elsegood, J. Chem. Soc., Dalton Trans (1996) 4197.
[4] G. Parkin, A. van Asselt, D.J. Leahy, L.R. Whinnery, N.G. Hua,
R.W. Quan, L.M. Henling, W.P. Schaefer, B.D. Santarsiero, J.E.
Bercaw, Inorg. Chem. 31 (1992) 82.
[10] J.T. Ciszewski, J.F. Harrison, A.L. Odom, Inorg. Chem. 43 (2004)
3605.
[11] L. King, M. Motevalli, A.C. Sullivan, J. Chem. Soc., Dalton Trans.
(1999) 3225.
[12] E.W. Jandeiu, P. Legzdins, W.S. McNeil, B.O. Patrick, K.M. Smith,
Chem. Commun. (2000) 1809.
[13] H.-W. Lam, G. Wilkinson, B. Hussain-Bates, M.B. Hursthouse,
J. Chem. Soc., Dalton Trans. (1993) 1477.
[14] A. Gutierrez, G. Wilkinson, B. Hussain-Bates, M.B. Hursthouse,
Polyhedron 9 (1990) 2081.
[15] J. Sundermeyer, K. Weber, H. Werner, N. Mahr, G. Bringmann, O.
Schupp, J. Organomet. Chem. 444 (1993) C37.
[16] V. Saboonchian, A.A. Danopoulos, A. Gutierrez, G. Wilkinson, D.J.
Williams, Polyhedron 10 (1991) 2241.
[5] (a) O.D. Sloan, P. Thornton, Polyhedron 7 (1988) 329;
(b) M. Minelli, M.R. Carson, D.W. Whisenhunt Jr., W. Imhof, G.
Huttner, Inorg. Chem. 29 (1990) 4801;
[17] H.-W. Lam, G. Wilkinson, D.J. Williams, Polyhedron 10 (1991)
2647.
(c) W.A. Hermann, D.W. Marz, E. Herdtweck, Z. Naturforsch Teil B
46 (1991) 747;
[18] J.A. Smieja, K.M. Omberg, G.L. Breneman, Inorg. Chem. 33 (1994)
614.
(d) M. Minelli, R.L. Kuhlman, S.J. Schaffer, M.Y. Chiang, Inorg.
Chem. 31 (1992) 3891;
[19] J.A. Smieja, K. Shirzad, M. Roy, K. Kittilstved, B. Twamley, Inorg.
Chim. Acta 335 (2002) 141.
(e) S.D. Gray, D.P. Smith, M.A. Bruck, D.E. Wigley, J. Am. Chem.
Soc. 114 (1992) 5462;
[20] Z-Y. Li, W-Y. Yu, C-M. Che, C-K. Poon, R-J. Wang, T.C.W. Mak,
J. Chem. Soc., Dalton Trans (1996) 4197.
(f) M.T. Ahmet, B. Coutinho, J.R. Dilworth, J.R. Miller, S.J. Parrott,
Y. Zheng, M. Harman, M.B. Hursthouse, A. Malik, J. Chem. Soc.,
Dalton Trans. (1995) 3041;
[21] J.M. Berg, R.H. Holm, J. Am. Chem. Soc. 107 (1985) 917.
[22] H. Mack, M.S. Eisen, J. Chem. Soc., Dalton Trans. (1998) 917.
´
´
[23] E. Gomez, V. Santes, V. de la Luz, N. Farfan, J. Organomet. Chem.
(g) F. Refosco, F. Tisato, A. Moreesco, G. Bandoli, J. Chem. Soc.,
Dalton Trans. (1995) 3475;
(h) R.R. Schrock, S.W. Seidel, N.C. Moesch-Zanetti, D.A. Dobbs,
K.-Y. Shih, W.M. Davis, Organometallics 16 (1997) 5195;
(i) T.I. Gountchev, T.D. Tilley, J. Am. Chem. Soc. 119 (1997)
12831;
(j) R.R. Schrock, S.W. Seidel, N.C. Mosch-Zanetti, D.A. Dobbs,
K.Y. Shih, W.M. Davis, Organometallics 16 (1997) 5195;
(k) S. Cai, R.R. Schrock, R.R. Kempe, W.M. Davis, Polyhedron 17
(1998) 747;
590 (1999) 237.
[24] T.K. Prakasha, A. Chandrasekaran, R.O. Day, R.R. Holmes, Inorg.
Chem. 35 (1996) 4342.
[25] J.J.H. Edema, R. Libbers, A. Ridder, R.M. Kellogg, A.L. Spek, J.
Organomet. Chem. 464 (1994) 127.
[26] J.R. Dilworth, V.C. Gibson, N. Davies, C. Redshaw, A.J.P. White,
D.J. Williams, J. Chem. Soc., Dalton Trans. (1999) 2695.
[27] R.C.B. Copley, P.W. Dyer, V.C. Gibson, J.A.K. Howard, E.D.
Marshall, W. Wang, B. Whittle, Polyhedron 15 (1996) 3001.
[28] M. Jolly, J.P. Mitchell, V.C. Gibson, J. Chem. Soc., Dalton Trans
(1992) 1331.
(l) U. Siemeling, T. Turk, W.W. Schoeller, C. Redshaw, V.C. Gibson,
¨
Inorg. Chem. 37 (1998) 4738;
(m) V.C. Gibson, C. Redshaw, W. Clegg, M.R.J. Elsegood, Inorg.
Chem. Comm. 4 (2001) 95.
[29] W. Clegg, R.J. Errington, C. Redshaw, D.C.R. Hockless, J. Chem.
Soc., Dalton Trans (1993) 1965.
[30] A.J. Blake, P.E. Collier, S.C. Dunn, W.-S. Li, P. Mountford, O.V.
Shishkin, J. Chem. Soc., Dalton Trans (1997) 1549.
[31] G.K. Cantrell, T.Y. Meyer, J. Chem. Soc., Chem. Commun. (1997)
1551.
[32] J.H. Edema, R.J. Libbers, A.M. Ridder, R.M. Kellog, F. van Bolhuis,
H. Kooijman, A.L. Spek, J. Chem. Soc., Chem. Commun. (1993) 625.
[33] SMART and SAINT software for CCD diffractometers, Bruker AXS Inc.
Madison, WI, 1994.
[34] W. Clegg, Acta. Crystallogr., Sect A 37 (1981) 22.
[35] G.M. Sheldrick, SHELXTL Manual, Version 5, Bruker AXS Inc.,
Madison, WI, USA, 1994.
[6] B.L. Haymore, E.A. Maatta, R.A.D. Wentworth, J. Am. Chem. Soc.
101 (1979) 2063.
[7] P. Barrie, T.A. Coffey, G.D. Forster, G. Hogarth, J. Chem. Soc.,
Dalton Trans. (1999) 4519.
[8] (a) A.A. Danopoulos, G. Wilkinson, T. Sweet, M.B. Hursthouse,
Chem. Commun. (1993) 495;
(b) A.A. Danopoulos, G. Wilkinson, T. Sweet, M.B. Hursthouse, J.
Chem. Soc., Dalton Trans. (1994) 1037.
[9] A.A. Danopoulos, G. Wilkinson, D.J. Williams, Chem. Commun.
(1991) 181.