Diamidophosphine complexes of niobium(III) and (IV): Imide formation via ancillary ligand decomposition

Article abstract of DOI:10.1016/S0020-1693(02)01499-8

The diamidophosphine complexes of niobium ^CyPh[NPN]NbCl(DME) (2), ^CyPh[NPN]NbCl₂ (6), and ^PhPh[NPN]NbCl ₂ (9), where ^RR′[NPN]=RP(CH₂SiMe ₂NR′)₂ have been prepared, isolated and characterized. Generation of ^RR′[NPN]NbCl(DME) species competes with the production of (^RR′[NPN]NbCl) ₂(μ-N₂) and can be controlled with N₂ pressure. ^CyPh[NPN]NbCl₂ spontaneously decomposes into ^CyPh[NPN]NbCl(=NPh) (7), CyP(CH₂SiMe₂) ₂NPh (8), and a paramagnetic impurity. Compound 7 was characterized by an X-ray diffraction study and its structural features are discussed. The Nb-N_imido bond length is 1.789(2) A? with a Nb-N _imido-C bond angle of 167.9(2)° in a distorted square pyramidal structure. Reduction of ^PhPh[NPN]NbCl₂ (9), with KC ₈ produced ^PhPh[NPN]NbCl(=NPh), PhP(CH₂SiMe₂)₂NPh, and a paramagnetic impurity.

Full text of DOI:10.1016/S0020-1693(02)01499-8

Inorganica Chimica Acta 350 (2003) 293ꢁ298
/
www.elsevier.com/locate/ica
Diamidophosphine complexes of niobium(III) and (IV):
imide formation via ancillary ligand decomposition
Michael D. Fryzuk *, Michael P. Shaver, Brian O. Patrick
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1
Received 28 June 2002; accepted 23 September 2002
Dedicated to Dr. Pierre Braunstein for his important contributions to ligand design and coordination chemistry.
Abstract
The diamidophosphine complexes of niobium CyPh[NPN]NbCl(DME) (2), CyPh[NPN]NbCl2 (6), and PhPh[NPN]NbCl2 (9), where
RR?[NPN]ꢀRP(CH2SiMe2NR?)2 have been prepared, isolated and characterized. Generation of RR?[NPN]NbCl(DME) species
competes with the production of (RR?[NPN]NbCl)2(m-N2) and can be controlled with N2 pressure. CyPh[NPN]NbCl2 spontaneously
decomposes into CyPh[NPN]NbCl(Ä
NPh) (7), CyP(CH2SiMe2)2NPh (8), and a paramagnetic impurity. Compound 7 was
characterized by an X-ray diffraction study and its structural features are discussed. The NbÃ
with a NbÃNimido
C bond angle of 167.9(2)8 in a distorted square pyramidal structure. Reduction of PhPh[NPN]NbCl2 (9), with
KC8 produced PhPh[NPN]NbCl(Ä
NPh), PhP(CH2SiMe2)2NPh, and a paramagnetic impurity.
# 2002 Elsevier Science B.V. All rights reserved.
/
/
˚
Nimido bond length is 1.789(2) A
/
/
Ã
/
/
Keywords: Niobium; Diamidophosphine ligands; Imido; SiÃN bond cleavage; Reduction
/
1. Introduction
halides liberating the desired imido complex and HCl
[18]. In some cases, however, the tendency for niobium
and tantalum to form these stable imides dominates
expected or desired chemical outcomes. The reduction
of TaCl5 with LiBH4 in the presence of formamidinato
The unique properties of the metal-imide function-
ality have shown particular utility in the catalytic
metathesis of imines [1ꢁ8] and as supporting ligands
/
for many organic transformations including ring-open-
ing metathesis polymerization [9,10]. This ligand type
can provide a total of three bonds to a metal center,
stabilizing high oxidation states or facilitating further
reactivity [11,12]. Mono-imides of group 5 metals can be
prepared via a number of routes: through Wittig-like
reactions of Ta(CHtBu)Cl3(THF)2 with imines [13,14],
via reaction of silated alkylamines or arylamines with
MCl5 species [15,16] or reactions of hexamethyldisila-
zane with metal halides to afford silylimides [17].
Alternatively, imides can be afforded directly from
reaction of the requisite primary amines with metal
ligands affords TaÄ
[19]. As well, the decomposition of ansa-niobocene
amido complexes via photochemical SiÃN bond clea-
vage generates niobium imides [20].
Previous investigations into the reaction of the
diamidophosphine ligand where
PhPh[NPN]
PhPh[NPN]ꢀ
PhP(CH2SiMe2NPh)2 with NbCl3(DME)
/
NPh species via NÃ
/
C bond cleavage
/
/
afforded the dinitrogen complex (PhPh[NPN]NbCl)2(m-
N2) [21]. Further investigation of RR?[NPN] reactivity
with Nb(III) and Nb(IV) systems has shown that this
chemistry is complicated by the lability of the NÃ
/Si
linkage of the ancillary ligand. In this paper we report
the preparation of RR?[NPN]NbCl(DME) and investi-
gate the generation of RR?[NPN]NbCl(Ä
bimetallic decomposition process.
/NPh) from a
* Corresponding author. Fax: ꢂ
/
1-604-822 2847.
E-mail address: fryzuk@chem.ubc.ca (M.D. Fryzuk).
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01499-8

294
M.D. Fryzuk et al. / Inorganica Chimica Acta 350 (2003) 293ꢁ298
/
Cy-
solid from the yellow solution. The solid
Ph[NPN]Li2. (OEt2) was collected via filtration in 80%
2. Experimental
1
2.1. General procedures
yield (33.84 g). H NMR (C6D6, 25 8C, 500 MHz): d
0.45 (s, 12H, SiCH3), 0.58 (t, 6H, OCH2CH3), 0.95 (m,
Unless otherwise stated, all manipulations were
performed under an atmosphere of dry oxygen-free
dinitrogen by means of standard Schlenk or glovebox
techniques (Vacuum Atmospheres HE-553-2 glovebox
equipped with a MO-40-2H purification system and a
4H, PCH2Si), 0.3ꢁ
OCH2CH3), 6.48 (m, 2H, NPh p-H), 6.57 (m, 4H, NPh
o-H), 7.08 (m, 4H, NPh m-H). 31P{1H} NMR (C6D6,
/
1.5 (m, 11H, CyÃ
/
H), 2.94 (q, 4H,
7
25 8C, 500 MHz): d ꢃ
/
34.0 (s). Li NMR (C6D6, 25 8C,
500 MHz):d ꢃ
/
1.1 (s). Anal. Calc. for C28H47Li2-
ꢃ40 8C freezer). Hexanes and toluene were purchased
/
N2OPSi2: C, 63.61; H, 8.96; N, 5.30. Found: C, 63.75;
H, 9.04; N, 5.49%.
anhydrous from Aldrich and further dried by passage
through a tower of alumina and degassed by passage
through a tower of Q-5 catalyst under positive pressure
of nitrogen [22]. Anhydrous diethyl ether and THF were
stored over sieves and distilled from sodium benzophe-
none ketyl under argon. Nitrogen was dried and
deoxygenated by passage through a column containing
activated molecular sieves and MnO. Deuterated ben-
zene was dried by refluxing with molten potassium metal
in a sealed vessel under partial pressure, then trap-to-
trap distilled and freeze-pump-thaw-degassed three
times. Unless otherwise stated, 1H, 31P{1H}, and 7Li
NMR spectra were recorded on a Bruker AMX-500
2.3. Preparation of CyPh[NPN]NbCl(DME) (2)
A cooled solution (ꢃ
78 8C) of CyPh[NPN]Li2(OEt2)
/
(3.000 g, 5.674 mmol) in 50 ml of Et2O was added to a
slurry of NbCl3(DME) (1.642 g, 5.674 mmol) in 20 ml of
Et2O under one atmosphere of N2. The solution turned
red brown within a 30 min of reaching r.t. The solution
was evaporated to dryness, the remaining solid extracted
into 100 ml hexanes, and the solution filtered through
Celite. The solvent was removed and CyPh[NPN]-
1
1
instrument operating at 500.1 MHz for H spectra. H
NMR spectra were referenced to internal C6D5H (7.15
ppm), 31P{1H} NMR spectra to external P(OMe)3
(141.0 ppm with respect to 85% H3PO4 at 0.0 ppm)
and 7Li NMR spectra to a 0.3 M LiCl solution in
MeOH (0.00 ppm). Elemental analyses were performed
by Mr. P. Borda of this department; mass spectra were
recorded on a Kratos MS 50. Clusters assigned to
specific ions show appropriate isotopic distribution
patterns as calculated for the atoms present. Solid state
magnetic susceptibility measurements were taken on a
NbCl(DME) was isolated as a redꢁ
g, 3.69 mmol) in 65% yield. MS (EI): m/z 659 [Mꢂ,
CyPh[NPN]NbCl(DME)], 568 [MꢂꢃDME, CyPh[NPN]-
NbCl]. Anal. Calc. for C28H41ClN2NbO2PSi2: C, 51.49;
H, 6.33; N, 4.29. Found: C, 51.22; H, 6.27; N, 4.51%.
meff: 2.78 B.M.
The above reaction performed under 4 atm. of N2
resulted in the isolation of a brown solid identified as a
mixture of 2 and (CyPh[NPN]NbCl)(m-N2) (3). Attempts
to separate the products through recrystallization
proved unsuccessful. MS (EI): m/z 659 [Mꢂ,
Ph[NPN]NbCl(DME)], 582 [‘CyPh[NPN]NbClN’].
/brown solid (2.43
/
Cy-
JohnsonꢁMatthey MSB-1 Gouy balance at room tem-
/
perature (r.t.). The reagents PhNH2, ClSiMe2CH2Cl,
and CyPH2 were purchased from Aldrich and purified
by distillation [23]. Solutions of BunLi (1.6 M in
hexanes) were obtained from Acros Organics and used
as received. The compounds PhPh[NPN]Li2(THF)2 [21],
KC8 [24], NbCl3(DME) [25], and NbCl4(THF)2 [26]
were prepared by literature methods.
2.4. Reaction of PhPh[NPN]Li2(OEt2) with
NbCl3(DME)
A r.t. solution of PhPh[NPN]Li2(THF)2 (1.024 g, 1.727
mmol) in 50 ml of Et2O was added to a slurry of
NbCl3(DME) (0.50 g, 1.73 mmol) in 20 ml of Et2O
under a N2 atmosphere. The solution turned brown
within a few minutes of reaching r.t. The solution was
evaporated to dryness, the remaining solid was extracted
into 150 ml of toluene, and the solution was filtered
through Celite. The solvent was removed and the
remaining material isolated via filtration. A mixture of
PhPh[NPN]NbCl(DME) (4), and (PhPh[NPN]NbCl)2(m-
N2) (5), was isolated as a brown solid (0.678 g).
Separation of the mixture through recrystallization
proved unsuccessful. MS (EI): m/z 653 [Mꢂ,
PhPh[NPN]NbCl(DME)], 576 [‘PhPh[NPN]NbClN’].
2.2. Preparation of CyPh[NPN]Li2(OEt2) (1)
To a ꢃ78 8C solution of aniline (14.9 g, 0.16 mol) and
/
ClSiMe2CH2Cl (22.89 g, 0.16 mol) in 100 ml of Et2O
was slowly added BunLi (100 ml, 1.6 M in hexanes). The
resulting white suspension was stirred for 2 h at r.t., then
cooled again to ꢃ78 8C. To this mixture was added
/
CyPH2 (9.29 g, 0.08 mol) followed by dropwise addition
of BunLi (200 ml, 1.6 M in hexanes). The solution was
stirred for 2 h and then thoroughly dried in vacuo. The
remaining solids were extracted into 70 ml of toluene
and filtered through Celite. The solvent was removed
and 20 ml of hexanes was added, to precipitate a white

M.D. Fryzuk et al. / Inorganica Chimica Acta 350 (2003) 293ꢁ
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295
2.5. Preparation of CyPh[NPN]NbCl2 (6)
A cooled solution (ꢃ
78 8C) of CyPh[NPN]Li2(OEt2)
was removed giving a brown solid. Analysis of the
yellow solid indicated the production of PhPh[NPN]-
/
NbCl(Ä
/
NPh) (10), along with a paramagnetic impurity
(3.000 g, 5.674 mmol) in 50 ml of Et2O was added to a
slurry of NbCl4(THF)2 (2.150 g, 5.674 mmol) in 20 ml of
Et2O under one atmosphere of N2. The solution turned
golden yellow upon stirring for 1 h at r.t. The solution
was evaporated to dryness, the remaining solid extracted
into 100 ml toluene, and the solution filtered through
Celite. Addition of pentane precipitated a golden yellow
solid, CyPh[NPN]NbCl2 isolated in 79% yield (2.71 g,
4.48 mmol). MS (EI): m/z 603 [Mꢂ, CyPh[NPN]NbCl2].
Anal. Calc. for C24H31Cl2N2NbPSi2: C, 48.17; H, 5.22;
Cl, 11.85; N, 4.68. Found: C, 48.36; H, 5.11; N, 4.80%.
while the brown solid contained PhP(CH2SiMe2)2NPh
(11), along with a paramagnetic impurity. MS (EI)
yellow solid: m/z 653 [Mꢂ, PhPh[NPN]NbCl(Ä
/
NPh)].
MS (EI) brown solid: m/z 343 [Mꢂ, PhP(CH2Si-
Me2)2NPh].
2.8. Crystallography
Crystallographic data appears in Table 2 for 7. All
measurements were made on a Rigaku/ADSC CCD area
detector with graphite monochromated Mo KR radia-
tion. The data were processed [27] and corrected for
Lorentz and polarization effects. The structure was
solved by direct methods [28] and expanded by using
Fourier [29] techniques. All nonhydrogen atoms were
refined with anisotropic thermal parameters. Neutral
atom scattering factors and anomalous dispersion
corrections were taken from the International Tables
for X-ray Crystallography [30,31].
Recrystallization of CyPh[NPN]NbCl2 from
tolueneꢁhexanes solution resulted in the deposition of
yellow crystals containing CyPh[NPN]NbCl(Ä
NPh) (7),
a
/
/
leaving a brown supernatant solution behind containing
CyP(CH2SiMe2)2NPh (8), from which the solvent was
removed to give a brown solid. The two fractions both
contained a paramagnetic impurity and were analyzed
with mass spectrometry and the crystals analyzed by x-
ray diffraction. MS (EI) yellow crystals: m/z 659 [Mꢂ,
CyPh[NPN]NbCl(Ä
/
NPh)]. MS (EI) brown solid: m/z 349
[Mꢂ, CyP(CH2SiMe2)2NPh].
3. Results and discussion
2.6. Preparation of PhPh[NPN]NbCl2 (9)
The goal of this research was to prepare dinuclear
dinitrogen complexes of the formula (RR?[NPN]Nb-
A cooled solution (ꢃ
78 8C) of PhPh[NPN]Li2(THF)2
/
Cl)2(m-N2) (where Rꢀ
/
alkyl or aryl substituent at
(1.500 g, 2.530 mmol) in 50 ml of Et2O was added to a
slurry of NbCl4(THF)2 (0.959 g, 2.53 mmol) in 20 ml of
Et2O under one atmosphere of N2. The solution turned
yellow upon stirring for 5 min at r.t. The solution was
evaporated to dryness, the remaining solid extracted
into 100 ml toluene, and the solution filtered through
Celite. Addition of pentane precipitated a golden brown
solid, PhPh[NPN]NbCl2 isolated in 72% yield (1.090 g,
1.822 mmol). MS (EI): m/z 597 [Mꢂ, PhPh[NPN]NbCl2].
Anal. Calc. for C24H31Cl2N2NbPSi2: C, 48.17; H, 5.22;
N, 4.68. Found: C, 48.46; H, 5.35; N, 4.42%. meff: 1.86
B.M.
phosphorus and R?ꢀalkyl or aryl substituent at nitro-
/
gen) for a variety of different substituents on the
phosphine and at the amide. For example, the synthesis
of the ligand precursor CyPh[NPN]Li2(OEt2) (1), is
shown in Scheme 1. Reaction of cooled solutions (ꢃ
/
78 8C) of aniline and ClSiMe2CH2Cl with n-butyl
lithium followed by addition of a half equivalent of
cyclohexyl phosphine and 2 equiv. n-butyl lithium gave
the desired ligand precursor in a single step. Overall
reaction yields were much higher for this one-pot
reaction since it avoids isolation of the thermally
unstable silylamine intermediate that can decompose
upon purification by distillation. The ligand was isolated
as an ether adduct of the dilithium salt. Interestingly,
CyPh[NPN]Li2 was isolated as a monoether adduct,
unlike PhPh[NPN] which was found to contain two
coordinated THF molecules. The ligand was isolated
2.7. Reduction of PhPh[NPN]NbCl2 with KC8 under 4
atm. of N2
To a cooled Kontes flask containing PhPh[NPN]NbCl2
(0.500 g, 0.835 mmol) and KC8 (0.124 g, 0.919 mmol)
was added 50 ml Et2O at ꢃ
/
78 8C. The flask was then
cooled to the neck with liquid N2 (ꢃ
/
196 8C), charged
with 1 atm. N2, sealed and allowed to warm to r.t.
Within 2 h of warming to r.t. the solution turned golden
brown and a black solid was precipitated. The solution
was evaporated to dryness, the remaining solid extracted
into 100 ml toluene, and the solution filtered through
Celite. Addition of hexanes afforded a yellow solid and
a brown supernatant solution from which the solvent
Scheme 1.

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M.D. Fryzuk et al. / Inorganica Chimica Acta 350 (2003) 293ꢁ298
/
as CyPh[NPN]Li2(OEt2), a colorless solid identified by
1H, 31P{1H}, and 7Li{1H} NMR spectroscopies and
elemental analysis.
Treatment of a cooled solution of NbCl3(DME) with
CyPh[NPN]Li2(OEt2) did not give the desired dinitrogen
complex (CyPh[NPN]NbCl)2(m-N2) but instead gave a
redꢁ
brown, paramagnetic solid, CyPh[NPN]NbCl(DME)
/
(2) as confirmed by mass spectrometry and elemental
analysis. No dinitrogen containing species was observa-
ble by mass spectrometry. If, however, the reaction was
conducted under 4 atm. of N2, a mixture of products
was observed. The complex (CyPh[NPN]NbCl)2(m-N2)
(3), and 2 are generated as observed by mass spectro-
metry. Attempts to separate these products by crystal-
lization proved unsuccessful. This observed reactivity is
summarized in Scheme 2.
Scheme 3.
that 6 had decomposed to CyPh[NPN]NbCl(Ä
The low yield is attributed to decomposition via a
bimolecular mechanism.
The molecular structure of 7 is shown as an ORTEP
drawing in Fig. 1. Relevant bond lengths and angles are
listed in Tables 1 and 2, respectively, and crystal-
lographic data can be found in the Section 2. The
/NPh) (7).
Upon further investigation of the reaction of
PhPh[NPN]Li2(THF)2 with NbCl3(DME) it was seen
that this same complex reaction mixture is produced.
If the crude product from the reaction is analyzed by
mass spectrometry, both PhPh[NPN]NbCl(DME) (4),
and (PhPh[NPN]NbCl)2(m-N2) (5), are present. The
product distribution is strongly affected by temperature,
N2 concentration and reactant and solvent purity, but
under no conditions were either product produced
exclusively. Crystallization of either product from solu-
tion was problematic, as repetition of conditions could
not always produce crystals on a preparative scale.
In an attempt to find a high-yield reproducible
synthesis of 3 and 5, the reactivity of RR?[NPN] ligands
with NbCl4(THF)2 was investigated in hopes that the
resulting niobium(IV) complex, RR’[NPN]NbCl2, could
be reduced under N2 to afford the desired niobium(III)
derivatives free of DME. CyPh[NPN]NbCl2 (6), was
prepared by reacting CyPh[NPN]Li2(THF)2 with
Nb(1)Ã
/
N(3) bond length for the imido ligand is 1.789(2)
˚
1.76 A [12]. The
˚
A, slightly longer than the average of ꢀ
/
Nb(1)ÃN(3)ÃC(25) angle for the imido moiety is close
/
/
to linear, 167.9(2)8, but again deviates from the average
and is somewhat expected for the imido ligand in the
presence of amido ligands which may also act as p-
donors. The overall complex is distorted square pyr-
amidal with ligands cis to the amide pushed back from
the plane resulting in N(3)Ã
/
Nb(1)Ã
/
N(1), N(3)Ã
/
Nb(1)Ã
/
N(2) and N(3)Ã
/
Nb(1)Ã
/
Cl(1) angles being 100.04(9),
94.34(9) and 102.85(7)8, respectively.
Generation of imide 7 is reproducible and has been
confirmed by mass spectrometry. Analysis of the
crystals by NMR spectroscopy showed that a paramag-
netic impurity was present in the bulk sample. Multiple
recrystallizations did not result in analytically pure
material due to the high solubility in common saturated
organic solvents. Analysis of the brown filtrate after
solvent removal by mass spectrometry indicated the
generation of CyP(CH2SiMe2)2NPh (8), presumably
from ligand decomposition. Similar to 7, presence of a
paramagnetic impurity prevented analysis by NMR
NbCl4(THF)2 at ꢃ78 8C as shown in Scheme 3.
/
Compound 6 was isolated as a golden brown solid in
72% yield and characterized by mass spectrometry and
elemental analysis. Recrystallization from a layered
tolueneꢁ
/
hexanes solution at ꢃ35 8C gave irregular
/
yellow crystals and a deep brown solution. X-ray
analysis of the crystals, isolated in 39% yield, showed
Fig. 1. ORTEP drawing of CyPh[NPN]NbCl(Ä
NPh) (7). Thermal
/
ellipsoids are drawn to 30% probability level. Hydrogens, silyl methyls
and amido and phosphorus substituents other than the ipso carbons
are not shown for clarity.
Scheme 2.

M.D. Fryzuk et al. / Inorganica Chimica Acta 350 (2003) 293ꢁ
/298
297
Table 1
Selected bond distances (A) and angles (8) for CyPh[NPN]NbCl(Ä
NPh)
(7)
˚
/
Bond lengths
Nb(1)Ã
N(3)ÃC(25)
Nb(1)Ã
Nb(1)Ã
Nb(1)Ã
Nb(1)Ã
/
N(3)
1.789(2)
1.390(3)
2.5998(6)
2.047(2)
2.041(2)
2.7588(7)
/
/
Cl(1)
N(1)
N(2)
P(1)
/
/
/
Bond angles
Nb(1)ÃN(3)Ã
N(3)ÃNb(1)Ã
N(3)ÃNb(1)Ã
N(3)ÃNb(1)Ã
N(3)ÃNb(1)Ã
N(1)ÃNb(1)Ã
N(1)ÃNb(1)Ã
N(1)ÃNb(1)Ã
N(2)ÃNb(1)Ã
N(2)ÃNb(1)Ã
Cl(1)ÃNb(1)Ã
/
/
C(25)
Cl(1)
N(1)
N(2)
P(1)
167.9(2)
102.85(7)
100.04(9)
94.34(9)
172.60(7)
105.29(8)
155.95(6)
79.29(6)
158.57(6)
78.81(6)
84.46(2)
/
/
/
/
Scheme 4.
/
/
/
/
/
/
N(2)
Cl(1)
P(1)
paramagnetic impurity. Separation of 10 and 11 was
accomplished through washing with pentane, but the
paramagnetic impurity could not be separated from
either fraction. The presence of 10 and 11 was confirmed
reproducibly by mass spectrometry.
/
/
/
/
/
/Cl(1)
/
/P(1)
/
/P(1)
Generation of the imides 7 and 10 appears to be a
bimolecular process, as the products retain an intact
[NPN] ligand and gain a new imide functionality. A
proposed mechanism is shown in Scheme 5. While
Table 2
Crystallographic
data
and
details
of
refinement
for
CyPh[NPN]NbCl(NPh) (7)
breaking of SiÃ
imides, this reaction is interesting because the thermo-
Cl bonds, which
/
N bonds is a common route to group 5
Empirical formula
Formula weight
Crystal system
Space group
C30H42N3Si2PClNb
660.19
dynamically favorable SiÃ
/
O or SiÃ
/
drive preparative reactions, are not formed. Interest-
ingly, a similar transformation in which an unprece-
monoclinic
P21/n
˚
a (A)
12.7053(7)
17.6956(9)
14.8276(9)
104.540(3)
3226.9(3)
4
dented photochemical scission of a SiÃ/N bond on an
˚
b (A)
ansa-niobocene arm led to imide formation through a-
silicon abstraction has been previously reported [20]. In
our system, a similar transformation could be taking
place. If two RR?[NPN]NbCl2 moieties exchange amido
for chloro ligands, the photochemical scission of the
˚
c (A)
b (8)
3
V (A )
˚
Z
Dcalc (g cmꢃ3
)
1.359
6.03
m (Mo Ka) (cmꢃ1
T (K)
)
bridging amidoꢁ
products (i.e. the niobium imido complex, the [NP]
heterocycle, and NbCl3) directly. Conversely, if the SiÃ
bond breaking occurs is intramolecular,
/silicon bond would form the three
17391
/
2u Range (8)
Total reflections
Unique reflections
Parameters
55.7
/
29 601
7261
343
N
a
[NP]NbCl2(Ä/NPh) complex would form and imide
a
R1
0.054
0.077
1.15
a
Rw
Goodness-of-fit
a
R1ꢀ
/
ajjFojꢃ
/
jFcjj/ajFoj; Rw
ꢀ/
aw(jFo2jꢃ
/
jFc2j)2/awjFo2j2)1/2
.
spectroscopy. Decomposition of the [NPN] ligand to
form similar cyclic [NP] molecules has been observed
previously in our laboratory [32]. This reactivity is
summarized in Scheme 4.
The compound PhPh[NPN]NbCl2 (9), can be prepared
under the same conditions as 6. Mass spectrometry and
elemental analysis confirmed the generation of 9. While
9 does not seem to decompose in solution as quickly as
7, reduction with the intercalation compound potassium
graphite (KC8) resulted in the synthesis of PhPh[NPN]-
NbCl(Ä
/
NPh) (10), PhP(CH2SiMe2)2NPh (11), and a
Scheme 5.

298
M.D. Fryzuk et al. / Inorganica Chimica Acta 350 (2003) 293ꢁ298
/
transfer with another molecule of RR?[NPN]NbCl2
would give the observed products. The favorable
[8] R.L. Zuckerman, S.W. Krska, R.G. Bergman, J. Am. Chem. Soc.
122 (2000) 751.
[9] G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem. Int.
Ed. 38 (1999) 429.
[10] R.R. Schrock, Acc. Chem. Res. 23 (1990) 158.
formation of the NbÄ
/
NPh moiety as a stabilizing ligand
for high-oxidation state organometallics could drive this
reaction [12]. It is at this time unknown by what exact
mechanism this niobium imido complex forms. Future
work will be aimed at large substituents at N to reduce
the tendency for binuclear decomposition pathways.
[11] L.H. Gade, P. Mountford, Coord. Chem. Rev. 216ꢁ217 (2001)
/
65.
[12] D.E. Wigley, Prog. Inorg. Chem. 42 (1994) 239.
[13] S.M. Rocklage, R.R. Schrock, J. Am. Chem. Soc. 104 (1982)
3077.
[14] S.M. Rocklage, R.R. Schrock, J. Am. Chem. Soc. 102 (1980)
7808.
[15] Y.W. Chao, P.A. Wexler, D.E. Wigley, Inorg. Chem. 28 (1989)
3860.
4. Supplementary materials
[16] P.A. Bates, A.J. Nielson, J.M. Waters, Polyhedron 8 (1985) 1391.
[17] C.M. Jones, M.E. Lerchen, C.J. Church, B.M. Schomber, N.M.
Doherty, Inorg. Chem. 29 (1990) 3860.
Crystallographic data (excluding structure factors) for
CyPh[NPN]NbCl(Ä
/NPh) (7), have been deposited with
[18] A.V. Korolev, A.L. Rheingold, D.S. Williams, Inorg. Chem. 36
(1997) 2647.
the Cambridge Crystallographic Data Centre CCDC
No. 200906. Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12
[19] F.A. Cotton, J.H. Matonic, C.A. Murillo, X. Wang, Bull. Soc.
Chim. Fr. 133 (1996) 711.
Union Road, Cambridge, CB2 1Ez, UK (fax: ꢂ44-
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
/
[20] W.A. Herrmann, W. Baratta, J. Organomet. Chem. 506 (1996)
357.
[21] M.D. Fryzuk, S.A. Johnson, B.O. Patrick, A. Albinati, S.A.
Mason, T.F. Koetzle, J. Am. Chem. Soc. 123 (2001) 3960.
[22] A.B. Pangborn, M.A. Giardello, R.H. Grubbs, R.K. Rosen, F.J.
Timmers, Organometallics 15 (1996) 1518.
Acknowledgements
[23] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory
Chemicals, 3rd ed, ButterworthꢁHeinemann, London, 1994.
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[24] D.E. Berbreiter, J.M. Killough, J. Am. Chem. Soc. 100 (1978)
2126.
Funding for this research was provided by NSERC of
Canada in the form of a Research Grant to M.D.F. and
a postgraduate scholarship to M.P.S. and the Killam
Foundation for a postgraduate scholarship to M.P.S.
[25] E.J. Roskamp, S.F. Pedersen, J. Am. Chem. Soc. 109 (1987) 6551.
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