Investigation into the reactivity of oxoniobocene complexes [Cp*2Nb(=O)R] (Cp=η5-C5Me5; R=H, OH, OMe) towards heterocumulenes: Formation of carbamato and thiocarbamato complexes and catalytic cyclization of PhNC

Article abstract of DOI:10.1016/S0022-328X(01)01085-3

The reaction of [Cp*₂NbCl₂] (Cp=η⁵-C₅Me₅) with KOH or Ba(OH)₂·8H₂O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*₂Nb

Full text of DOI:10.1016/S0022-328X(01)01085-3

Journal of Organometallic Chemistry 634 (2001) 47–54
www.elsevier.com/locate/jorganchem
Investigation into the reactivity of oxoniobocene complexes
[Cp*Nb(ꢀO)R] (Cp*=h5-C5Me5; R=H, OH, OMe) towards
2
heterocumulenes: formation of carbamato and thiocarbamato
complexes and catalytic cyclization of PhNCO
Olivier Blacque b, Henri Brunner a, Marek M. Kubicki b, Jean-Claude Leblanc b,
Walter Meier a, Claude Moise b, Yves Mugnier b, Andre´ Sadorge b, Joachim Wachter a,*,
Manfred Zabel b
a Institut fu¨r Anorganische Chemie, Uni6ersita¨t Regensburg, D-93040 Regensburg, Germany
b Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, Uni6ersite´ de Bourgogne, F-21100 Dijon, France
Received 24 April 2001; accepted 10 June 2001
Abstract
The reaction of [Cp*NbCl2] (Cp*=h5-C5Me5) with KOH or Ba(OH)2·8H2O in THF was investigated under slightly modified
2
conditions. In addition to the known complex [Cp*Nb(ꢀO)H] (1), the new compound [Cp*Nb(ꢀO)OH] (2) was formed. The
2
2
reaction of 2 with PhNCS gave yellow [Cp*Nb(ꢀO){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*Nb(ꢀO){OC(O)NHPh}]
2
2
(4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show
that they contain either h1-S-thiocarbamato (3) or h1-O-carbamato ligand (4) along with a terminal NbꢀO group. The reaction
of 1 with one equivalent of PhNCO mainly gave orange [Cp*NbH{OC(O)NPh}] (5) along with some 4. The molecular structure
2
of 5 contains a niobocene unit comprising h2-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the
NbꢀO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess
PhNCO gave a mixture of heterocycles (PhNCO)2 (6) and (PhNCO)3 (7) in the approximate ratio 3:2. By contrast, the reaction
of [Cp*Nb(ꢀO)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7. © 2001 Published
2
by Elsevier Science B.V.
Keywords: Niobocene; Oxo ligands; Heterocumulenes; Cyclization
[1,4,5]. Recently, we have described oxo niobocene
1. Introduction
complexes of the type [Cp*Nb(ꢀO)R] (Cp*=h5-
2
C5Me5; RꢀH, OCH3), which have two different reaction
The transfer of an oxygen atom from a metal to an
sites [6]. In order to study the reactivity of the NbꢀO
organic molecule is a key step in many catalytic oxida-
and NbꢁX units towards heterocumulenes we investi-
tion reactions [1,2]. Metal oxo complexes play an im-
portant role in these reactions and sometimes
intermediate products may be isolated from such reac-
tions [3]. In this regard, metallacycles arising from
[2+2] cycloaddition reactions of MꢀO bonds with
unsaturated organic substrates are of continued interest
gated the reaction of [Cp*Nb(ꢀO)H] (1) with PhNCS
2
and PhNCO, respectively. During this study it turned
out that the preparation of 1 as described in Ref. [6]
needed to be revisited. Therefore, the reaction of
[Cp2*NbCl2] with KOH and Ba(OH)2·8H2O was rein-
vestigated, which led to the discovery of
[Cp2*Nb(ꢀO)OH] (2) as a further participant in the
reaction system. The results obtained from the reaction
of 1 and 2 with PhNCX (X=S, O) finally contribute to
the investigation of the catalytic cyclization of PhNCO
via a formal [2+2] cycloaddition.
* Corresponding author. Tel.: +49-941-9434419; fax: +49-941-
9434439.
E-mail address: joachim.wachter@chemie.uni-regensburg.de (J.
Wachter).
0022-328X/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0022-328X(01)01085-3

48
O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
1
2. Results
The H-NMR spectrum exhibits one singlet at l=1.93
for the C5Me5 groups, three multiplets for the C6H5
group, and one singlet at l=9.00 for the NH proton.
The integration of the signals is in agreement with the
proposed structure.
2.1. Rein6estigation of the reaction of [Cp*NbCl2] with
metal hydroxides
2
We have reported [6] that the reaction of [Cp*NbCl2]
2
with two equivalents of Ba(OH)2·8H2O in THF gives
[Cp2*Nb(O)H] (1), while in the analogous reaction with
(2)
KOH [Cp*Nb(O)Cl] is formed. Attempts to reproduce
2
the results obtained with Ba(OH)2·8H2O showed that 1
obviously contained a bright yellow compound 2. Then
we found that the formation of 2 is favored if the
reaction is carried out at 40 °C in a mixture of THF–
water 10:1 (Eq. (1)). After 20 h the ratio 2/1 is about
90:10. If, however, the reaction was stopped after the
green color of the starting material has disappeared
Although only twinned single crystals of complex 3
were available for an X-ray crystallographic study, the
molecular structure could be resolved unambiguously.
As a central feature 3 contains an oxo niobocene unit
to which a thiocarbamato ligand is coordinated via its
sulfur atom (Fig. 1). This ligand, including the phenyl
group, nearly forms a plane. The hydrogen atom fixed
at nitrogen was located directly from difference Fourier
synthesis. It is oriented towards the oxo ligand at Nb
and the order of the corresponding OꢁH distance of
(after 1–2 h), [Cp*Nb(O)Cl] was found.
2
(1)
,
2.084 A may indicate an intramolecular hydrogen bond
,
[7]. The distance C(21)ꢁN (1.358(4) A) is typical for
carbamato and thiocarbamato complexes (Table 1).
N-Monosubstituted thiocarbamato complexes seem
to be rare in the literature and the only structurally
characterized example is [Co(NH3)5-{h1-S-C(O)-
NHPh}][ClO4]2 [8] due to a Cambridge Data File re-
search. This compound is the result of a reaction of
[Co(NH3)5(OH)]2+ with PhNCO, for which a nucle-
ophilic attack of the Co(OH) oxygen at the electrophilic
carbon atom of PhNCS has been established, followed
by hydrogen migration to the N atom. The resulting
O-bonded complex rapidly isomerizes to the stable
S-bonded species.
Complex 2 was characterized by means of its FD
mass spectrum and elemental analyses. Its IR spectrum
shows a strong wNbꢀO absorption at 843 cm−1 along
with a weak and sharp wOH absorption at 3470 cm−1
.
1
The H-NMR spectrum in C6D6 exhibits one intense
singlet at l=1.77 and a weak resonance at l=2.11.
The latter is tentatively assigned to the NbꢁOH unit. It
1
is important to note that the H-NMR spectra alone
are not able to distinguish between
2
and
[Cp2*Nb(O)Cl], for both compounds exhibit identical
chemical shifts for the Cp* ligand.
The reaction of [Cp*NbCl2] with excess KOH in
2
The reaction of 2 with phenylisocyanate in THF at
room temperature gave the yellow complex
[Cp2*Nb(ꢀO){OC(O)NHPh}] (4) (Eq. (3)). The compo-
sition was confirmed by means of FD mass spectrum
and elemental analyses. The IR spectrum of 4 shows
boiling THF was described to form 1 in yields between
0 and 50% [6]. We now found that addition of H2O and
decrease of the reaction temperature to 20 °C gave 1 in
better reproducible yields around 40%. However, the
product still contains small amounts of 2 (B8%). The
difficulties in controlling the formation of 1 may be due
to the proposed reduction–protonation-mechanism of
the reaction of [Cp*NbCl2] with OH− [6]. The observed
2
influence of the cations may be explained by different
stabilization of intermediate products.
2.2. The reaction of [Cp*Nb(ꢀO)OH] (2) with PhNCS
2
and PhNCO
The reaction of 2 with an equimolar amount of
phenylisothiocyanate gave the yellow complex 3, which
turned out due to FD mass spectrum and elemental
analyses to have the composition [Cp*Nb(ꢀO){SC(O)-
2
NHPh}] (Eq. (2)). Although 2 still contained minor
amounts of 1 no by-products were isolated. The IR
spectrum of 3 shows characteristic absorptions at 3220
(wNH), 1635 and 1520 (wNHCO), and 860 (wNbꢀO) cm−1
.
Fig. 1. Molecular structure of [Cp*Nb(ꢀO){SC(O)NHPh}] (3).
2

O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
49
Table 1
may envisage an attack of the oxo ligand at the hetero-
cumulene carbon atom according to Scheme 1b. Such
an enhanced nucleophilicity of metallocene oxo ligands
,
Selected bond lengths (A) and angles (°) for [Cp*Nb(O)-
{SC(O)NHPh}] (3), [Cp*Nb(O){OC(O)NHPh}] (4) and [Cp*NbH-
{OC(O)NPh}] (5)
2
2
2
has been proposed for Cp*Zr(ꢀO)pyr [9] due to a
2
3
4
5
negative polarization of the oxygen atom within the
ZrꢀO bond.
Bond lengths
Nb(1)ꢁS(1)
2.525(1)
1.752(2)
2.3. The reaction of [Cp*Nb(ꢀO)R] (RꢀH, OMe) with
PhNCO
2
Nb(1)ꢁO(1)
Nb(1)ꢁO(3)
Nb(1)ꢁN(1)
Nb(1)ꢁC(1–5)mean
Nb(1)ꢁC(11–15)mean
S(1)ꢁC(21)
O(1)ꢁC(21)
O(2)ꢁC(21)
N(1)ꢁC(21)
N(1)ꢁC(22)
2.042(1)
1.757(2)
2.121(2)
2.162(2)
2.456(4)
2.441(4)
2.514(4)
2.518(4)
1.802(3)
2.503(3)
2.540(3)
The reaction of 1 with 1 equivalent of PhNCO gave
a mixture of several compounds, which could not be
separated by chromatographic methods. However, after
recrystallization orange prisms were obtained, contami-
nated by fine yellow and white needles. The orange
material was shown by means of FD mass spec-
troscopy, elemental analyses and X-ray crystallography
to have the composition [Cp*NbH{OC(O)NPh}] (5)
(Eq. (4)). The yellow needles are assigned to complex 4
by means of FD mass and H-NMR spectra. Complex
4 may arise from reaction of PhNCO with impurities of
2 in the starting material (see Eq. (1) and the related
discussion there). The white material is attributed to
triphenylisocyanurate 7 (see below). The content of
both side products in the reaction mixture is estimated
1.318(4)
1.231(3)
1.371(3)
1.425(3)
1.318(4)
1.206(4)
1.391(4)
1.412(4)
1.187(4)
1.358(4)
1.414(4)
Bond distances
S(1)ꢁNb(1)ꢁO(1)
O(1)ꢁNbꢁO(3)
Nb(1)ꢁS(1)ꢁC(21)
O(1)ꢁNbꢁN(1)
C(21)ꢁN(1)ꢁC(22)
S(1)ꢁC21)ꢁO(2)
S(1)ꢁC(21)ꢁN(1)
O(2)ꢁC(21)ꢁN(1)
94.8(1)
2
97.9(1)
125.7(2)
123.9(2)
113.7(1)
1
60.0(1)
122.6(2)
127.4(2)
118.9(3)
116.2(2)
124.9(3)
129.3(3)
1
by means of H-NMR spectra to 10–20%.
characteristic absorptions at 3290 (wNH), 1684 (wNHCO),
and 825 (wNbꢀO cm−1. Further strong absorptions at
1590, 1525, and 1495 cm−1 may be typical of the
carbamate skeleton. The 1H-NMR spectrum exhibits
one singlet at l=1.94 for the C5Me5 groups, three
multiplets for the C6H5 group, and one singlet at l=
7.23 for the NH proton. As in 3 the ratio of C5Me5–
C6H5 groups is equal to 2:1.
(4)
The IR spectrum of 5 exhibits a weak absorption at
1800 cm−1, which may be assigned to a wNbH fre-
quency, and strong absorptions at 1650, 1600 and 1500
1
cm−1, characteristic of a carbamato ligand. The H-
(3)
NMR spectrum contains besides aromatic multiplets
and a singlet for the C5Me5 group a slightly broadened
An X-ray crystallographic study of 4 reveals that its
molecular structure contains an oxo niobocene unit to
which a carbamato ligand is coordinated via its oxygen
atom (Fig. 2). Two types of NbꢁO distances are found
as expected for NbꢀO double and NbꢁO single bonds
[6] (Table 1). The other bonding parameters are close to
those in the related compound 3. Like the thiocarbam-
ato ligand in 3 the carbamato ligand is roughly copla-
nar with the NbꢀO moiety. The same orientation
towards the oxo ligand as in 3 is found for the NH
group. This means that both complexes 3 and 4 possess
similar conformations of the heteroatom chain.
As already mentioned for the reaction of 2 with
PhNCS (Eq. (2)), one may consider as a first step, a
nucleophilic attack of the OH ligand at the electrophilic
C atom of the heterocumulene (Scheme 1a), followed
by proton migration. The final step for the formation of
3 would be a rapid isomerization. Alternatively, one
Fig. 2. Molecular structure of [Cp*Nb(ꢀO){OC(O)NHPh}] (4). One
2
of the Cp* rings is disordered and occupies positions rotated by 21.5°.
The disorder degree is 50%.

50
O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
Scheme 1.
singlet at l=4.89, which may arise from the Nb
bonded hydride. The molecular structure of 5 shows a
niobocene unit comprising an N,O-coordinated carba-
mate ligand (Fig. 3). The coordination sphere of the Nb
center is completed by a hydride ligand. The oxygen
atom of the metallacycle occupies the central position
of the frontier plane bisecting the Cp* rings. Bond
distances and angles within the four-membered ring are
typical of a chelated h2-N,O-carbamato chelate [1,5,10].
A comparison of bond parameters of complexes 3–5
shows only small differences. The only striking trend is
a decrease of the CꢁN bond from 1.391(4) (5) to
The reaction of [Cp*Nb(O)OMe] [6] with three
2
equivalents of PhNCO gave a white precipitate, which
was identified as triphenylisocyanurate 7·THF (Eq. (5)).
After careful drying the solvent free compound gave
correct elemental analyses and a weak parent ion in the
1
EI mass spectrum. H-NMR and IR spectra are identi-
cal with those of known samples [12]. The crude mate-
rial only contains a small amount of (PhNCO)2, for in
the IR spectrum the intensity of its wCO frequency at
1760 cm−1 is very weak. The reaction also works with
catalytical amounts of [Cp*Nb(O)OMe]. Thus, in a
2
typical experiment 1 mol% of this complex is sufficient
to trimerize PhNCO in yields between 41 and 68% even
after 5 min at room temperature.
,
1.371(3) (4) and 1.358(4) (3) A (Table 1). This distance
has been ascribed to possess partial double bond char-
acter [1].
Formally, one may describe the formation of 5 as a
[2+2] cycloaddition. In fact, if one follows the ideas
given in Scheme 1, the absence of an acidic proton
provokes attack of the nucleophilic nitrogen at the
positively polarized metal center. Similar coupling reac-
tions are those of PhNCO with the MoꢀO bond of
[(C5H5)2MoO] [1] or with one of the ReꢀO bonds in
[Cp2*Re2O4] [5] and [Re(O)2I(PPh3)2] [10]. An analogous
cycloaddition at the TaꢀS bond of [(t-BuC5H4)2Ta(S)H]
has been reported for PhNCS [11].
(5)
If, in the reaction of [Cp*Nb(O)H] (1) an excess of
2
PhNCO (molar ratio 1:100) was employed, a white
crystalline material formed, which contains due to IR,
13C-NMR and mass spectra a mixture of (PhNCO)2 (6)
and triphenylisocyanurate (PhNCO)3 (7) (Eq. (5)). A
distinction between both heterocycles is possible by
means of IR and 13C-NMR spectra. Thus, the wCO
frequency at 1760 cm−1 is typical for the dimer [12],
whereas that of 7 appears at 1710 cm−1 [12,13]. No
13C-NMR spectrum has been reported thus far for
(PhNCO)2, the chemical shifts of 6 are quite close to
those of 7. An integration of the CꢀO resonances of the
recrystallized material allows to estimate the ratio (Ph-
NCO)2–(PhNCO)3 to ca. 60:40.
Fig. 3. Molecular structure of [Cp*NbH{OC(O)NPh}] (5).
2

O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
51
3. Conclusions
Due to 1H-NMR spectra, the product contains vari-
able, but small amounts (B8%) of [Cp*Nb(O)OH] (2).
2
Oxo niobocene complexes of the type [Cp*Nb(O)R]
The percentage of 2 depends on the concentration of
[Cp2*NbCl2] in the THF–H2O mixture and the reaction
time.
2
(R=H, OH, OMe) are versatile reagents for the trans-
formation of phenylisocyanate and phenylisothio-
cyanate into carbamato and thiocarbamato complexes
and heterocyclic organic products. Inspite of the rela-
tively poor selectivity it is obvious that there is an
influence of the functional groups R on nature and
distribution of the products. On the other hand, the Nb
hydride ligand, which may attack electrophilic carbon
atoms in unsaturated organic substrates [15,16], does
not participate in the reaction: no hint was detected for
the eventual formation of a corresponding N,O-coordi-
nated formamido complex.
The reaction of transition metal oxo complexes with
isocyanates has been intensively investigated in the past
with the aim to synthesize imido complexes [1,9,14]. A
particular role as intermediates in such reactions was
ascribed to the formation of N,O-carbamato chelates.
We have shown in this work that the reaction of
equivalent amounts of 1 and PhNCO produces the
stable complex 5 in a formal [2+2] cycloaddition reac-
tion (Eq. (4)).
4.2. Synthesis of [Cp*Nb(O)OH] (2)
2
A green suspension of 170 mg (0.39 mmol) of
[Cp2*NbCl2] and 220 mg (0.78 mmol) of Ba(OH)2·8H2O
in a mixture of 18 ml of THF and 1 ml of water was
stirred for 18 h at 40 °C. After evaporation of the
solvent the residue was extracted with 80 ml of pentane
and then recrystallized at −20 °C from n-hexane to
give 83 mg (54%) of bright yellow crystals of
[Cp2*Nb(O)OH] (2). The product contains up to 10% of
1
1 as determined for several experiments by H-NMR
spectroscopy.
2: Anal. Found: C, 60.12; H, 7.71. Calc. for
C20H31NbO2 (396.0): C, 60.61; H, 7.83%. FD-MS (from
1
toluene): 396.0. H-NMR (250 MHz, C6D6): l 1.77 (s,
30H), 2.11 (s, 1H). IR (KBr, cm−1): 3470 (m, wOH), 843
(vs, wNbꢀO).
With excess PhNCO complexes [Cp*Nb(O)R] (R=
2
H, OMe) form the organic heterocycles 6 and 7:
whereas R=H favors the formation of 6, with R=
OMe formation of the six-membered ring 7 is preferred.
As probable intermediates one may assume bipolar
intermediates the reactivity of which is directed by the
different NbꢁR functionalities. It may also be noted
that the cyclization of PhNCO seems to be a rapid
process, whereas complex 5 does not show any reactiv-
ity towards excess PhNCO.
4.3. Preparation of [Cp*Nb(ꢀO)(SC(O)NHPh)] (3)
2
A slight excess of phenylisothiocyanate (18 ml; 0.15
mmol) was added to a solution of 50 mg (0.13 mmol) of
[Cp*Nb(ꢀO)OH] in 5 ml of THF. After stirring for 16
2
h at room temperature (r.t.), the solvent was evapo-
rated and the yellow residue was washed with 5 ml of
pentane. Recrystallization of the crude material (42 mg)
from toluene–pentane gave yellow crystals (21 mg,
31%).
3: Anal. Found: C, 60.82; H, 6.77; N, 2.54. Calc. for
C27H36NNbO2S (531.6): C, 61.01; H, 6.83; N, 2.64%.
FD-MS (from toluene): 531.2. 1H-NMR (250 MHz,
CDCl3): l 1.93 (s, 30H, C5Me5), 6.97 (tt, 1H, C6H5),
7.23 (t, 2H, C6H5), 7.42 (dd, 2H, C6H5), 9.00 (s, 1H,
NH). {1H} 13C-NMR: (63 MHz, CDCl3): l 11.3
(C5Me5), 118.2 (C6H5), 121.0 (C5Me5), 122.6 (C6H5),
128.7 (C6H5), 139.4 (C6H5ipso), 167.2 (CꢀO). IR (KBr,
cm−1): 3220 (w, wNH), 1635 (s, wCO), 860 (m, wNbꢀO).
4. Experimental
All manipulations were carried out under nitrogen by
Schlenk techniques. The preparation of [Cp*NbCl2] is
reported in Ref. [17]. [Cp*2 Nb(O)OMe] was prepared
2
from [Cp*NbCl2] and NaOMe in MeOH [6].
2
4.1. Synthesis of [Cp*Nb(O)H] (1)
2
A green suspension of 1.12 g (2.58 mmol) of
[Cp2*NbCl2] and 1.50 g (26.7 mmol) of KOH in a
mixture of 180 ml of THF and 15 ml of water was
stirred for 20 h at 20 °C. After that time a nearly
colorless solution has formed. After evaporation of the
solvent the white residue was extracted several times
with pentane (100 ml altogether). After evaporation of
pentane recrystallization from 20 ml of n-hexane at
−20 °C gave 270–420 mg (31–48% yield) of a white
crystalline powder of 1. Spectroscopic and analytical
data of 1 are analogous to those reported elsewhere [6].
4.4. Preparation of [Cp*Nb(ꢀO){OC(O)NHPh}] (4)
2
The solution of 17 ml (0.16 mmol) of phenyliso-
cyanate and 60 mg (0.15 mmol) of [Cp*Nb(ꢀO)OH] (2)
2
in 5 ml of THF was stirred for 1 h at r.t. After
evaporation of the solvent the yellow residue was
washed with 5 ml of pentane. Recrystallization of the
crude material from toluene–pentane gave yellow
needles of [Cp*Nb(ꢀO)(OC(O)NHPh)] (4) (20 mg,
2
26%).

52
O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
Table 2
Crystallographic data for complexes 3–5
3
4
5
Formula
C27H36NNbO2S
531.6
C
515.2
27H36NNbO3
C27H36NNbO2
499.5
0.30×0.30×0.20
Orthorhombic
16.352(1)
Molecular weight
Crystal size (mm3)
Crystal system
0.18×0.03×0.03
Monoclinic
8.666(1)
16.798(1)
17.852(1)
101.78(1)
2544(1)
P21/n
4
1.39
Stoe IPDS
293
0.58
0.20×0.10×0.07
Monoclinic
9.4988(2)
9.8109(3)
26.383(1)
97.77(1)
2436.0(1)
P21/c (14)
4
,
a (A)
,
b (A)
15.758(1)
18.398(1)
,
c (A)
i (°)
3
,
V (A )
4740.6(2)
Pbcn (60)
8
1.40
Nonius KappaCCD
110
0.531
Space group
Z
Dcalc (g cm−3
Instrument
)
1.36
Nonius KappaCCD
110
0.517
Temperature (K)
v (mm−1
)
Scan range
Total reflections
2.7B[B25.9.0
13 580
2.16B[B28.64
6208
1.79B[B29.13
6348
Observed reflections (I\2.0|(I))
LS parameters
7624
290
2349
280
2296
284
Absorption correction
None
0.468/−0.319
0.042
None
0.50/−0.63
0.038
None
0.75/−0.54
0.040
Residual density (e A−3) max/min
,
R1
wR2
0.084
0.079
0.106
4: Anal. Found: C, 62.10; H, 7.20; N, 2.80. Calc. for
C27H36NNbO3 (515.5): C, 62.91; H, 7.04; N, 2.72%.
FD-MS (from THF): 515.2. 1H-NMR (250 MHz,
CDCl3): l 1.94 (s, 30H, C5Me5), 6.93 (t, 2H, C6H5),
7.23 (s, 1H, NH), 7.40 (m, 3H, C6H5). {1H}13C-NMR
(63 MHz, C6D6): l 10.7 (C5Me5), 117.7 (C6H5), 121.8
(C6H5), 122.0 (C5Me5), 129.2 (C6H5), 141.6 (C6H5ipso),
153.9 (CꢀO). IR (KBr, cm−1): 3290 (w, wNH), 1684 (m,
wCO), 825 (m, wNbꢀO).
4.6. Cyclization experiments of phenylisocyanate
A solution of 0.43 ml (3.95 mmol) of phenyliso-
cyanate and 16 mg (0.039 mmol) of [Cp*Nb(ꢀO)H] (1)
2
in 5 ml of THF was stirred for 1 h. After removal of the
solvent the crude material (0.38 g) was washed with 5
ml of pentane and recrystallized from THF–pentane.
The resulting white platelets, which contain (PhNCO)2
(6) and (PhNCO)3 (7) in an approximate ratio of 3:2,
were dried for 8 h in high vacuum.
4.5. Synthesis of [Cp*NbH{OC(O)NPh}] (5)
6: Anal. Found: C, 70.30; H, 4.31; N, 11.60. Calc. for
C14H10N2O2 (238.2): C, 70.58; H, 4.23; N, 11.76%.
2
1
The solution of 18 ml (0.16 mmol) of phenyliso-
EI-MS: 237.9. H-NMR (250 MHz, CDCl3): l 7.15–
cyanate and 50 mg (0.13 mmol) of [Cp*Nb(ꢀO)(H)] in
7.57 (m, C6H5). {1H}13C-NMR (63 MHz, CDCl3): l
116.7 (C6H5), 125.0 (C6H5), 129.5 (C6H5), 134.2
(C6H5ipso), 151.1 (CꢀO). IR (KBr, cm−1): 1780, 1760
(wCO).
2
5 ml of THF was stirred for 1 h at r.t. After evapora-
tion of the solvent the residue was washed with pentane
and dried to give 55 mg (84% yield) of an orange–yel-
low powder. Recrystallization from THF–pentane gave
orange prisms of 5 which are contaminated by yellow
needles. The latter consists of 4 due to mass spec-
If [Cp*Nb(ꢀO)OMe] was employed instead of 1 un-
2
der analogous conditions 0.23g (41% yield) of pure
(PhNCO)3·THF was obtained. Solvent free 7 was ob-
tained after drying for 8 h in high vacuum. The same
result has been obtained after a reaction time of 5 min.
7: Anal. Found: C, 70.37; H, 4.26; N, 11.72. Calc. for
C21H15N3O3 (357.5): C, 70.58; H, 4.23; N, 11.76%.
1
troscopy and H-NMR spectra.
5: Anal. Found: C, 64.58;H, 7.18; N, 3.04. Calc. for
C27H36NNbO2 (499.5): C, 64.92; H, 7.27; N, 2.80%.
FD-MS (from toluene): 499.1. 1H-NMR (250 MHz,
C6D6): l 1.57 (s, 30H, C5Me5), 4.89 (s, 1H, NbH), 6.97
(m, 1H, C6H5), 7.15 (m, 2H, C6H5), 7.40 (m, 2H, C6H5).
IR (KBr, cm−1): 1800 (w, wNbH), 1650 (vs, wCO), 1600,
1500 (s, wNCO).
1
EI-MS: 357.4. H-NMR (250 MHz, CDCl3): l 7.30–
7.55 (m, C6H5). {1H}13C-NMR (63 MHz, CDCl3): l
128.5 (C6H5), 129.37 (C6H5), 129.68 (C6H5), 133.7
(C6H5ipso), 148.7 (CꢀO). IR (KBr, cm−1): 1710 (wCO).

O. Blacque et al. / Journal of Organometallic Chemistry 634 (2001) 47–54
53
4.7. X-ray structure solution
two positions rotated by 21.5°. The geometrical centers
,
of C6–C10 and C6*–C10* exhibit a slippage of 0.17 A.
4.7.1. [Cp*Nb(ꢀO)(SC(O)NHPh)] (3)
Both cycles were constrained to perfect pentagonal
rings and refined with isotropic thermal parameters and
a multiplicity of 0.5. Other non-hydrogen atoms in this
structure were refined with anisotropic parameters. All
non-hydrogen atoms in the structure of 5 were refined
with anisotropic thermal parameters. All hydrogen
atoms (except the hydride in 5) in both structures were
included in calculated positions and refined in a riding
model with isotropic displacement coefficients. The nio-
bium hydride in 5 was located in a difference Fourier
map and freely refined with an isotropic temperature
factor.
2
The compound crystallized in thin yellow needles
with a size just suitable for X-ray structure analysis on
a STOE IPDS diffractometer. For a few crystals the
data for at least 180° in 8 were collected. The inspec-
tion of the reflections in reciprocal space (program part
RECIPE of STOE-IPDS software [18]) revealed, that all
crystals were twinned following the same law. The
crystals belong to the monoclinic crystal system and the
twin law is a twofold axis in [100] direction. The matrix
to transform one cell into the other is (1 0 0, 0 −1 0,
−0.8387 0 −1), the reciprocal lattices coincide almost
exactly when ꢀhꢀ=0 or 6 (a similar example is given in
Ref. [19]).
Further details for the structure refinements of com-
plexes 3–5 are listed in Table 2.
It was possible to solve the main part of the structure
from a data set of only one twin component. But
reliable results of a refinement in this case could only be
5. Supplementary material
obtained with the SHELXL97 program [20] and a HKLF
5
instruction thus including all available data and mark-
ing the reflections belonging to one of the two compo-
nents or to both. All reflections with undisturbed
intensities were collected by an integration in TWIN
modus of the STOE-IPDS software [18] with the two
orientation matrices for both components. From a sub-
sequent normal integration with only one orientation
matrix we extracted all reflections with intensity contri-
butions from both components. A modified program
from Ruck [21] looked with the known transformation
matrix for reflections with almost perfect coincidence,
added the corresponding F2(hkl)-values of the second
component and marked all these reflections to be used
with SHELXL97 and HKLF 5. All partially overlapped
reflections were discarded because the intensity of such
reflections could not be determined correctly.
Crystallographic data (excluding structure factors)
for the structural analyses have been deposited with the
Cambridge Crystallographic Data Centre, CCDC nos.
161795 (3), 161796 (5), 161797 (4). Copies of the data
can be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(Fax: +44-1223-336033; e-mail: deposit@ccdccam.
ac.uk; deposit@chemcrys. cam.ac.uk; www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
Parts of this work have been supported by the
Deutscher Akademischer Auslandsdienst (DAAD) and
the Ministe`re des Affaires Etrange`res (Procope
Program).
With this new data set, it was possible to locate the
remaining atoms from difference Fourier syntheses and
to refine the structure to absolutely reliable final
parameters. The refined fractional contribution of twin
component two was 0.3048.
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2
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54
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