β-Elimination and insertion of CNR in transient pentamethylcyclopentadienyl-imido-tantalum dialkyl complexes. X-ray structure of [TaCp*{N(2,6-Me2C6H3)}(CH 2=CH2)(PMe3)]

Article abstract of DOI:10.1016/S0022-328X(98)00570-1

The transient dialkyl complexes [TaCp*R₂(NAr)] (Cp* = C₅Me₅; R = Et, n-Pr; Ar = 2,6-Me₂C₆H₃), obtained by alkylation of [TaCp*Cl₂(NAr)] with two equiv. of RMgCl in diethylether a

Full text of DOI:10.1016/S0022-328X(98)00570-1

Journal of Organometallic Chemistry 563 (1998) 15–21
i-Elimination and insertion of CNR in transient
pentamethylcyclopentadienyl-imido-tantalum dialkyl complexes. X-ray
structure of [TaCp*{N(2,6-Me2C6H3)}(CH2ꢀCH2)(PMe3)]
Pascual Royo a,*, Javier Sa´nchez-Nieves a, Maria Angela Pellinghelli b, Antonio Tiripicchio b
a Departamento de Qu´ımica Inorga´nica, Facultad de Ciencias, Uni6ersidad de Alcala´, E-28871-Alcala´ de Henares, Spain
b Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, Uni6ersita` di Parma,
Centro di Studio per la Strutturistica Diffrattometrica del CNR, Viale delle Scienze, I-43100 Parma, Italy
Received 21 July 1997
Abstract
The transient dialkyl complexes [TaCp*R2(NAr)] (Cp*=C5Me5; R=Et, n-Pr; Ar=2,6-Me2C6H3), obtained by alkylation of
[TaCp*Cl2(NAr)] with two equiv. of RMgCl in diethylether at low temperature, react with one equiv. of PMe3 to give
[TaCp*(NAr)(CH2ꢀCHR)(PMe3)] (R=H1, Me2) after i-elimination and reductive elimination of alkane. When the same
alkylation is carried out and then one equiv. of CN(2,6-Me2C6H3) is added after heating to room temperature, the alkyl iminoacyl
insertion products [TaCp*R{p2-CRꢀN(Ar)}(NAr)] (R=Et3, n-Pr4) are obtained. However when alkylation with one equiv. of
MgClR (R=Et, n-Pr, i-Pr) is carried out at ambient temperature after the addition of CN(2,6-Me2C6H3), the chloro iminoacyl
complexes [TaCp*Cl{p2-CR=NAr)}(NAr)] (R=Et 5, n-Pr 6, i-Pr 7) are isolated. The structure of [TaCp*(NAr)(CH2ꢀCH2)
(PMe3)] (1) has been determined by X-ray diffraction methods. © 1998 Elsevier Science Ireland Ltd. All rights reserved.
Keywords: Alkyl; Imido; Iminoacyl; Pentamethylcyclopentadienyl; Tantalum
1. Introduction
complexes in high oxidation state [5]. Furthermore,
systems with neutral organic molecules coordinated to
the same metal center are useful as models for impor-
tant catalytic processes [6]. Related imido–alkene nio-
bium complexes and their -carbonyl and -acetylene
derivatives were isolated by Gibson [7]a using the same
i-hydride elimination and loss of alkane from diethyl
and di-n-propyl niobium intermediates, and similar
vanadium compounds have also been prepared by
Teuben [7]b reducing the dichloro complexes with mag-
nesium in the presence of the ligands.
We herein report the different behaviour observed
for the complex [TaCp*Cl2(NAr)] (Cp*=C5Me5, Ar=
2,6-Me2C6H3) in reactions with i-hydrogen containing
alkylmagnesium reagents in the absence and presence
of PMe3 and CN(2,6-Me2C6H3) and the X-ray structure
of the olefin phosphine complex [TaCp*(NAr)(CH2ꢀ
CH2)(PMe3)].
There is increasing interest in the study of group 5
metal complexes containing the half sandwich cyclopen-
tadienyl imido [M(p5-C5R5)(NR’)] fragment because
they offer the opportunity to make comparisons with
the isolobal dicyclopentadienyl group 4 metal fragment
[M(p5-C5R5)2] [1], which has been shown to have im-
portant applications in organic synthesis [2] and olefin
polymerization processes [3]. We have reported recently
[4] novel aspects of the chemistry of doubly SiMe2-
bridged dicyclopentadienylzirconium complexes with i-
hydrogen containing alkyl substituents and were
interested in isolating similar group 5 metal compounds
with the imido cyclopentadienyl fragment. The imido
group is a useful stabilizing ligand for transition metal
* Corresponding author. Tel.: +34
8854683; e-mail: proyo@inorg.alcala.es
1 8854765; fax: +34 1
0022-328X/98/$19.00 © 1998 Elsevier Science Ireland Ltd. All rights reserved.
PII S0022-328X(98)00570-1

16
P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
Table 1
2. Results and discussion
˚
Selected bond lengths (A) and angles (°) for complex 1
The alkylation of [TaCp*Cl2(NAr)] (Cp*=C5Me5,
Ar=2,6-Me2C6H3) with i-hydrogen containing alkyl-
magnesium reagents always led to unstable compounds
at room temperature. The addition of MgClR (R=Et,
n-Pr) to diethylether solutions of [TaCp*Cl2(NAr)] at
−78°C did not produce any observable transformation
but on heating the evolution of alkane was observed to
give a solution which after evaporation of the solvent
gave an intractable residue from which no identifiable
organometallic compound could be recovered.
Ta–CE(1)
Ta–M(1)
Ta–N
2.164(6)
2.119(8)
1.833(4)
2.545(2)
Ta–C(19)
Ta–C(20)
N–C(11)
2.231(8)
2.245(8)
1.376(6)
1.438(12)
Ta–P
C(19)–C(20)
CE(1)–Ta–M(1)
CE(1)–Ta–N
CE(1)–Ta–P
M(1)–Ta–N
113.3(3)
M(1)–Ta–P
N–Ta–P
Ta–N–C(11)
95.1(2)
88.9(1)
176.5(4)
133.6(2)
113.1(2)
104.2(3)
CE(1) is the centroid of the C(1)…C(5) cyclopentadienyl ring and
M(1) the midpoint of the double C(19)–C(20) bond.
When the same reaction was carried out in the
presence of one equiv. of PMe3, elimination of alkane
was similarly observed, leading to solutions which after
evaporation and recrystallization rendered the tantalu-
m(III) complexes [TaCp*(NAr)(CH2ꢀCHR)(PMe3)]
(R=H 1, Me 2) as yellow crystalline solids in 85%
yield. The olefin compounds [2,6] result from i-hydro-
gen activation with reductive elimination of alkane, to
give the olefin adducts stabilized as 18 electron com-
pounds by coordination of PMe3. Both complexes were
characterized by elemental analysis and NMR spec-
troscopy and the molecular structure of complex 1 was
determined by X-ray diffraction methods.
distances and angles are given in Table 1. The tantalum
is bound to a pentamethylcyclopentadienyl ring in a
slightly asymmetric p5-fashion; the Ta(1)–C distances
˚
range from 2.403(6) to 2.550(5) A), the distance be-
tween the metal and the centroid CE(1) of the ring
˚
being of 2.164(6) A. The Ta–CE(1) distance is close to
those found in comparable Ta complexes as
˚
TaCp*Cl2(NAr), 2.115(6) A [8](a), TaCp*Me(NAr)
˚
[NAr–CMeꢀCMe2], 2.179(7) A [8](b) and TaCp*Me-
(NAr)[p2-NArꢀC–CMe2–CMeꢀNAr], 2.155(11)
A
˚
[8](b), the shortest one is probably related to the pres-
ence of less hindered ligands.
The structure of complex 1 is shown in Fig. 1 to-
gether with the atomic labelling scheme. Selected bond
The Ta atom is bound also to one P atom from the
˚
PMe3 ligand [Ta–P=2.545(2) A], to the N atom from
˚
the phenylimido ligand [Ta–N=1.833(4) A] and to the
C(19) and C(20) atoms from the p2-coordinating
ethylene molecule [Ta–C(19) and Ta–C(20)=2.231(8)
˚
˚
and 2.245(8) A, respectively, Ta–M(1)=2.119(8) A,
M(1) is the midpoint of the C(19)–C(20) bond]. The
˚
olefinic C(19)–C(20) bond distance, 1.438(12) A is, as
expected, much longer than that corresponding to a
double bond, because of the p2-bonding to the metal.
The coordination geometry around the Ta atom can
be described as of three legged piano stool type or as
pseudotetrahedral if the centroid of the Cp* ring and
the midpoint of the C(19)–C(20) bond are considered
as occupying coordination sites. The complex is chiral
and in the crystals both enantiomers are present. The
˚
values of the Ta–N bond length, 1.833(4) A, and of the
Ta–N–C(11) angle, 176.5(4)°, are as expected for an
imido ligand and comparable with those found for the
same phenylimido ligand in TaCp*Cl2(NAr), 1.774(5)
˚
A and 169.9(5)° [8](a), in TaCp*Me(NAr)[NAr–CMeꢀ
˚
A and 168.0(4)° [8](b), and in
CMe2], 1.784(4)
TaCp*Me(NAr)[p2-NArꢀC–CMe2–CMeꢀNAr], 1.812
˚
(8) A and 171.1(8)° [8]b.
The 1H-NMR spectrum of complex 1 shows only one
resonance at l 2.41 for the two methyl groups of the
imido-aryl ligand in spite of their expected
diastereotopic character due to the presence of the
chiral metal center. Complex 2 with a similar structural
disposition as the niobium derivative [7]a could be
Fig. 1. Perspective view of the structure of the complex
[TaCp*{N(2,6-Me2C6H3)}(CH2ꢀCH2)(PMe3)] (1) with the atomic la-
belling scheme. The thermal ellipsoids are drawn at the 30% probabil-
ity level.

P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
17
Scheme 1.
expected to form four similar isomers, depending on the
endo or exo and syn or anti disposition of the methyl
group of the propene ligand. However only one of these
isomers was the major product (see Section 3) and a
protons of the metal-bonded alkyl groups appear as
two multiplets at l 0.74 (Et), 0.80 (n-Pr) and l 1.45
(Et), 1.41 (n-Pr) due to their coupling with the methyl
and methylene groups, respectively, whereas the imi-
noacyl carbon-bonded methylenic protons are observed
as two multiplets at l 2.47 (Et), 2.58 (n-Pr) and l 2.89
(Et), 3.01 (n-Pr). The methyl groups of the imidoaryl
ligand appear as one broad resonance at l 2.46 (Et),
2.47 (n-Pr) and those of the iminoacyl nitrogen-bonded
aryl are observed as two singlets at l 1.71 (Et), 1.76
(n-Pr) and l 1.88 (Et), 1.89 (n-Pr). The 13C-NMR
spectra of both complexes are also consistent with the
proposed structure. Formation of these alkyl iminoacyl
tantalum compounds demonstrates the presence of the
dialkyl complexes at room temperature, and therefore
indicates that alkylation of [TaCp*Cl2(NAr)] probably
takes place to give the monoalkylated derivative in a
first step, which is further transformed into the dialkyl
compound before total decomposition occurs in the
presence of phosphine.
1
second one (B20%) was observed by H-NMR spec-
troscopy after washing the resulting product with hex-
ane, although minor unrecoverable amounts of the
other isomers may also be present.
The presence of the bulkier pentamethylcyclopentadi-
enyl group and the different steric requirements of the
alkylimido and the trimethylphosphine ligands justify
the preferential formation of the major component.
To confirm the proposed intermediate formation of
the dialkyl complexes, we decided to study similar
reactions using 1 equiv. of CN(2-6-Me2C6H3) as the
free ligand, for which a simultaneous very rapid inser-
tion reaction into the tantalum–alkyl bonds could be
expected [9] (see Scheme 1). Addition of two equiv. of
the alkylating agent at −78°C to a toluene solution of
[TaCp*Cl2(NAr)] followed by heating at room tempera-
ture and then addition of one equiv. of the isocyanide
led to the iminoacyl derivatives [TaCp*R{p2-
CRꢀN(2,6-Me2C6H3)}{N(2,6-Me2C6H3)}] (R=Et 3, n-
Pr 4) which were isolated as pale yellow air sensitive
solids partially soluble in alkanes.
The coordination of the iminoacyl nitrogen to give
the 18 electron compounds is responsible of the stability
of the ethyl–tantalum complex, which does not decom-
pose through i-hydrogen elimination. Formulation of
complexes 3 and 4 is consistent with their analytical
composition and the behaviour observed by 1H and
13C-NMR spectroscopy. Both complexes contain a chi-
ral tantalum center which is responsible for the
diastereotopic behaviour observed in their 1H-NMR
spectra for the methylenic protons of the metal- and
iminoacyl carbon-bonded ethyl ligands and the two
methyl groups of the imido- and iminoacyl nitrogen-
bonded aryl groups (see Section 3). The methylenic
To confirm the first step formation of the monoalky-
lated compounds [TaCp*ClR(NAr)] we decided to
study the same reactions using one equiv. of the alky-
lating agent in the presence of the isocyanide in order
to produce the insertion reaction before the dialkyl
compounds could be formed. As shown in Scheme 2
addition of one equiv. of MgClR (R=Et, n-Pr, i-Pr)
under these conditions led to the chloro iminoacyl
derivatives
[TaCp*Cl{p2-CRꢀN(2,6-Me2C6H3)}–{N-
(2,6-Me2C6H3)}] (R=Et 5, n-Pr 6, i-Pr 7) isolated as
pale yellow solids, showing that insertion of the iso-
cyanide into the tantalum–alkyl bond of the monoalky-
lated compound formed in the first step is preferred to
i-hydrogen abstraction and to alkylation of the second
tantalum–chlorine bond. Complexes 5–7 were iden-
tified by their analytical composition and their formula-
tion was consistent with their observed NMR
behaviour. The methylenic protons of the alkyl group

18
P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
Scheme 2.
[ethyl (5); n-Pr (6)] bonded to the iminoacyl carbon, the
two methyl groups of the i-Pr (7) and the aryl imino
substituents show the diastereotopic character due to
the presence of the chiral metal center giving rise to
NMR behaviour similar to that discussed above for the
related alkyl complexes 3–4 (see Section 3).
ml) solutions of [Ta(p5-C5Me5)Cl2{N(2,6-Me2C6H3)}]
(0.25 g, 0.50 mmol) cooled to −78°C. After stirring for
0.5 h the solutions were warmed to room temperature
and stirred for 1 h. The resulting solutions were filtered
and the solvent was removed by evaporation in vacuo
leaving yellow oils which were crystallized from n-hex-
ane and identified as complexes 1 (0.23 g, 86%) and 2
(0.20 g, 73%).
1
3. Experimental section
Data for complex 1: H-NMR (300 MHz, l, ppm in
3
C6D6): 7.04 (d, 2H, JHH=7.3 Hz, m-Me2C6H3), 6.78
(t, 1H, 3JHH=7.3 Hz, p-Me2C6H3), 2.41 (s, 6H,
Me2C6H3), 1.77 (s, 15H, C5Me5), 1.07 (s, 9H, 2JHP=7.3
Hz, PMe3), −0.18, 0.82, 1.02 (m, 4H, C2H4). 13C-
All operations were carried out under a dry argon
atmosphere either in a vacuum atmosphere Dri-lab or
by standard Schlenck techniques. Hydrocarbon solvents
were dried and freshly distilled: n-hexane from sodium
potassium alloy, toluene from sodium and ether from
sodium–benzophenone. Reagent grade MgClR (R=
Et, n-Pr, i-Pr 2.0 M in THF, Aldrich), PMe3 (1.0 M in
toluene, Aldrich) and 2,6-Me2C6H3 (Fluka) were pur-
chased form commercial sources and were used without
NMR{1H} (75 MHz, l, ppm in C6D6): 156.0 (Cipso
–
Me2C6H3), 131.8–119.0 (Me2C6H3), 107.7 (C5Me5),
35.4 (Cendo
C2H4), 28.9 (Cexo C2H4), 19.8 (Me2C6H3),
16.2 (PMe3), 10.6 (C5Me5). MS (EI, 10 eV): m/e 539
([M+], 8), 511 (52), 435 (73), 121 (100). Anal. Calcd.
for C23H37NPTa: C, 51.20; H, 6.93; N, 2.60. Found: C,
51.00; H, 6.33; N, 2.46%.
further
purification.
The
starting
complex
1
TaCp*Cl2(NAr) [10] was prepared as described
previously.
Data for complex 2 (major isomer): H-NMR (300
MHz, l, ppm in C6D6): 7.11–6.84 (m, 3H, Me2C6H3),
3
Infrared spectra were recorded on a Perkin-Elmer
2.44 (s, 6H, Me2C6H3), 2.31 (dd, 3H, JH–H =1.6 Hz,
cis
3JH–H =6.8 Hz, MeCHꢀCH2), 1.72 (s, 15H, C5Me5),
1
583 spectrophotometer (4000–200 cm−1). H, 13C and
trans
1.12 (d, 9H, JHP=7.3 Hz, PMe3). Data for complex 2
31P-NMR spectra were recorded on a Varian Unity
VXR 300 MHz instrument, and chemical shifts were
2
(minor isomer): 1H-NMR (300 MHz, l, ppm in
1
measured relative to residual H and 13C resonances in
C6D6):7.10–6.70 (m, 3H, Me2C6H3), 2.37 (s, 6H,
2
the deuterated solvents C6D6 (l 7.15), CDCl3 (l 7.24)
and C6D6 (l 128), CDCl3 (l 77), respectively. Mass
spectra were recorded on an HP 5988 A instrument. C,
H and N analyses were carried out with a Perkin-Elmer
240C microanalyzer.
Me2C6H3), 1.81 (s, 15H, C5Me5), 1.14 (d, 9H, JHP
=
7.3 Hz, PMe3). The methine and methylene signals of
propene group are unresolved. Anal. Calcd. for
C24H39NPTa: C, 52.09; H, 7.12; N, 2.53. Found: C,
51.85; H, 6.93; N, 2.40%.
3.1. Synthesis of [Ta(p5-C5Me5){N(2,6-Me2C6H3)}
(CH2ꢀCHR)(PMe3)] (R=H 1, Me 2)
3.2. Synthesis of [Ta(p5-C5Me5)R{p2-CRꢀN(2,6-
Me2C6H3)}{N(2,6-Me2C6H3)}] (R=Et 3, n-Pr 4)
THF solution of MgClR (R=Et, n-Pr) (1.00 mmol)
THF solutions of MgClR (R=Et, n-Pr) (1.00 mmol)
and PMe3 (2.50 mmol) were added to diethylether (30
were added to toluene solutions (20 ml) of

P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
19
[Ta(p5-C5Me5)Cl2{N(2,6-Me2C6H3)}] (0.25 g, 0.50
mmol) cooled to −78°C. After stirring for 15 min,
CN(2,6-Me2C6H3) (0.07 mmol) dissolved in 20 ml of
toluene was added dropwise. The solutions were
warmed to room temperature and stirred for 1 h. The
resulting solutions were filtered and the solvent was
removed in vacuo. The residues were washed with
n-hexane (10 ml) and identified as complexes 3 (0.27 g,
89%) and 4 (0.29 g, 91%).
in toluene (15 ml) were added dropwise to a toluene
solution (20 ml) of
mixture of [Ta(p5-
a
C5Me5)Cl2{N(2,6-Me2C6H3)}] (0.25 g, 0.50 mmol) and
CN(2,6-Me2C6H3) (0.07 mmol). After stirring for 1 h at
room temperature the solutions were filtered and the
solvent was removed in vacuo. The residues were
washed with n-hexane (10 ml) and identified as com-
plexes 5 (0.27 g, 87%), 6 (0.28 g, 89%) and 7 (0.29 g,
93%).
1
Data for complex 3: H-NMR (300 MHz, l, ppm in
C6D6): 7.12–6.72 (m, 6H, Me2C6H3), 2.89 (m, 1H,
1
Data for complex 5: H-NMR (300 MHz, l, ppm in
C6D6): 7.11–6.65 (m, 6H, Me2C6H3), 2.78 (m, 1H,
p2-C(CH2CH3)ꢀNAr),
2.47
(m,
1H,
p2-
p2-C(CH2CH3)ꢀNAr),
2.55
(m,
1H,
p2-
C(CH2CH3)ꢀNAr), 2.46 (sbr, 6H, TaꢀN–Me2C6H3),
C(CH2CH3)ꢀNAr), 2.50 (sbr, 6H, TaꢀN–Me2C6H3),
3
1.91 (t, 3H, JHH=6.9 Hz, Ta–CH2CH3), 1.88 (s, 3H,
1.93 (s, 15H, C5Me5), 1.89 (s, 3H, p2-CRꢀNMe2C6H3),
p2-CRꢀNMe2C6H3), 1.83 (s, 15H, C5Me5), 1.71 (s, 3H,
p2-CRꢀNMe2C6H3), 1.45 (m, 1H, Ta–CH2CH3), 0.89
1.79 (s, 3H, p2-CRꢀNMe2C6H3), 0.76 (t, 3H, JHH
=
3
7.32 Hz, p2-C(CH2CH3)ꢀNAr). 13C-NMR{1H} (75
MHz, l, ppm in C6D6): 242.0 (p2-CRꢀNAr), 153.8–
119.3 (Me2C6H3), 115.6 (C5Me5), 29.9 (p2-
C(CH2CH3)ꢀNAr), 19.9 (TaꢀN–Me2C6H3), 18.7
(p2-CRꢀNMe2C6H3), 18.4 (p2-CRꢀNMe2C6H3), 11.3
(C5Me5), 9.2 (p2-C(CH2CH3)ꢀNAr). IR (KBr; w, cm−1):
1610 (s), 1327 (s), 982 (m), 356 (m), 306(m). MS (EI, 10
eV): m/e 630 ([M+], 39), 601 (64), 595 (11), 470 (58),
160 (100), 105 (39). Anal. Calcd for C29H38ClN2Ta: C,
55.20; H, 6.08; N, 4.44. Found: C, 54.95; H, 6.00; N,
4.30%.
3
(t, 3H, JHH=7.60 Hz, p2-C(CH2CH3)ꢀNAr), 0.74 (m,
1H, Ta–CH2CH3). 13C-NMR{1H} (75 MHz, l, ppm in
C6D6): 246.0 (p2-CRꢀNAr), 155.2–119.7 (Me2C6H3),
112.7 (C5Me5), 35.3 (Ta–CH2CH3), 25.5 (p2-
C(CH2CH3)ꢀNAr), 18.9 (Ta–CH2CH3), 18.7 (TaꢀN–
Me2C6H3),
18.6
(p2-CRꢀNMe2C6H3),
18.3
(p2-CRꢀNMe2C6H3), 11.1 (C5Me5), 10.1 (p2-
C(CH2CH3)ꢀNAr). IR (KBr; w, cm−1): 1631 (s), 1328
(s), 980 (m), 349 (m). MS (EI, 10 eV): m/e 624 ([M+],
26), 595 (100), 435 (20). Anal. Calcd. for C31H43N2Ta:
C, 59.60; H, 6.95; N, 4.49. Found: C, 59.30; H, 6.73; N,
4.36%.
1
Data for complex 6: H-NMR (300 MHz, l, ppm in
1
Data for complex 4: H-NMR (300 MHz, l, ppm in
C6D6): 7.10–6.65 (m, 6H, Me2C6H3), 2.86 (m, 1H,
p2-C(CH2CH2CH3)ꢀNAr),
2.75
(m,
1H,
p2-
C6D6): 7.10–6.65 (m, 6H, Me2C6H3), 3.01 (m, 1H,
p2-C(CH2CH2CH3)ꢀNAr),
2.58
(m,
1H,
p2-
C(CH2CH2CH3)ꢀNAr), 2.47 (sbr, 6H, TaꢀN-
Me2C6H3), 1.95 (s, 15H, C5Me5), 1.87 (s, 3H,
p2-CRꢀNMe2C6H3), 1.82 (s, 3H, p2-CRꢀNMe2C6H3),
1.32 (sbr, 2H, p2-C(CH2CH2CH3)ꢀNAr), 0.57 (t, 3H,
3JHH=7.32 Hz, p2-C(CH2CH2CH3)ꢀNAr). 13C-
NMR{1H} (75 MHz, l, ppm in C6D6): 241.0 (p2-
CRꢀNAr), 153.7–125.3 (Me2C6H3), 115.2 (C5Me5),
C(CH2CH2CH3)ꢀNAr), 2.47 (sbr, 6H, TaꢀN–
Me2C6H3), 1.89 (s, 3H, p2-CRꢀNMe2C6H3), 1.86 (s,
15H, C5Me5), 1.76 (s, 3H, p2-CRꢀNMe2C6H3), 1.41 (m,
1H, Ta–CH2CH2CH3), 1.20 (sbr, 4H, Ta–CH2CH2CH3
3
and p2-C(CH2CH2CH3)ꢀNAr), 1.15 (t, 3H, JHH=7.3
Hz,
Ta–CH2CH2CH3),
0.80
(m,
1H,
Ta–
CH2CH2CH3), 0.66 (t, 3H, 3JHH=7.29 Hz, p2-
C(CH2CH2CH3)ꢀNAr). 13C-NMR{1H} (75 MHz, l,
ppm in C6D6): 245.1 (p2-CR=NAr), 155.2–120.9
(Me2C6H3), 112.2 (C5Me5), 47.3 (Ta–CH2CH2CH3),
39.1
(p2-C(CH2CH2CH3)ꢀNAr),
19.9
(p2-
C(CH2CH2CH3)ꢀNAr), 19.1 (TaꢀN–Me2C6H3), 18.7
(p2-CRꢀNMe2C6H3), 18.4 (p2-CRꢀNMe2C6H3), 14.7
(p2-C(CH2CH2CH3)ꢀNAr), 11.3 (C5Me5). IR (KBr, w,
cm−1): 1628 (s), 1328 (s), 983 (m), 357 (m), 302 (m).
MS (EI, 10 eV): m/e 644 ([M+], 3), 601 (5), 470 (10),
174 (100), 105 (37). Anal. Calcd for C30H40ClN2Ta: C,
55.85; H, 6.23; N, 4.34. Found: C, 55.80; H, 6.13; N,
4.31%.
38.8
(p2-C(CH2CH2CH3)ꢀNAr),
25.2
(Ta–
CH2CH2CH3), 23.6 (p2-C(CH2CH2CH3)=NAr), 19.3
(Ta–CH2CH2CH3), 18.5 (TaꢀN–Me2C6H3), 18.7 (p2-
CRꢀNMe2C6H3), 18.4 (p2-CRꢀNMe2C6H3), 14.1 (p2-
C(CH2CH2CH3)ꢀNAr), 11.2 (C5Me5). IR (KBr, w,
cm−1): 1633 (s), 1326 (s), 981 (m), 347 (m). MS (EI, 10
eV): m/e 652 ([M+], 12), 609 (71), 174 (94), 105 (100).
Anal. Calcd for C33H47N2Ta: C, 60.72; H, 7.27; N,
4.29. Found: C, 60.55; H, 7.12; N, 4.06%.
1
Data for complex 7: H-NMR (300 MHz, l, ppm in
C6D6): 7.10–6.65 (m, 6H, Me2C6H3), 3.05 (m, 1H,
p2-C[CH(CH3)2]ꢀNAr), 2.50 (sbr, 6H, TaꢀN–
Me2C6H3), 1.96 (s, 15H, C5Me5), 1.95 (s, 3H, p2-
CRꢀNMe2C6H3), 1.80 (s, 3H, p2-CRꢀNMe2C6H3), 0.97
(d, 6H, 3JHH=7.32 Hz, p2-C[CH(CH3)2]ꢀNAr). 13C-
NMR{1H} (75 MHz, l, ppm in C6D6): 243.0 (p2-
CRꢀNAr), 153.6–125.9 (Me2C6H3), 115.8 (C5Me5),
36.4 (p2-C[CH(CH3)2]ꢀNAr), 19.9 (TaꢀN–Me2C6H3),
3.3. Synthesis of [Ta(p5-C5Me5)Cl{p2-CRꢀN(2,6-
Me2C6H3)}{N(2,6-Me2C6H3)}] (R=Et 5, n-Pr 6, i-Pr
7)
Solutions of MgClR (R=Et, n-Pr, i-Pr) (0.05 mmol)

20
P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
19.1 (p2-C[CH(CH3)2]ꢀNAr), 18.9 (p2-C[CH(CH3)2]ꢀ
NAr), 18.7 (p2-CRꢀNMe2C6H3), 18.3 (p2-CRꢀ
NMe2C6H3), 11.4 (C5Me5). IR (KBr, w, cm−1): 1631 (s),
1324 (s), 983 (m), 357 (m), 301 (m). MS (EI, 10 eV):
m/e 644 ([M+], 5), 601 (20), 470 (21), 174 (100), 105
(57). Anal. Calcd for C30H40ClN2Ta: C, 55.85; H, 6.26;
N, 4.34. Found: C, 55.72; H, 6.23; N, 4.26%.
Table 3
Atomic coordinates (×104) and equivalent isotropic displacement
2
4
˚
parameters (A ×10 ) for complex 1
x
y
z
Ua
Ta
532.2(3
3316.2(2)
2786(2)
2131.1(2) 389(1)
)
P
N
2061(2)
1920(6)
−1101(8)
−1313(8)
250(8)
3797(1)
494(5)
426(16)
523(21)
500(20)
532(23)
522(22)
508(22)
777(34)
735(30)
777(34)
840(38)
803(36)
432(19)
560(25)
692(30)
812(35)
686(28)
549(23)
762(36)
719(32)
684(29)
667(28)
724(31)
718(31)
759(32)
5011(4)
2218(6)
1176(6)
1016(6)
1975(6)
2708(6)
2555(8)
368(7)
−110(7)
2034(9)
3678(8)
6262(5)
7224(6)
8485(7)
8823(7)
7905(7)
6622(6)
6880(8)
5652(8)
3623(7)
3060(7)
4153(7)
2537(8)
1405(7)
2466(3)
406(4)
1009(4)
1357(4)
994(5)
381(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
3.4. X-ray data collection, structure determination and
refinement for complex 1.
1466(8)
601(8)
The crystallographic data of complex 1 are summa-
rized in Table 2. Data were collected at room tempera-
ture (22°C) on a Siemens AED diffractometer, using
the graphite-monochromated Mo–Kh radiation and the
q/2q scan type. One standard reflection was monitored
every 100 measurements; no significant decay was no-
ticed over the time of data collection. Intensities were
corrected for Lorentz and polarization effects. A cor-
rection for absorption was applied (maximum and min-
imum value for the transmission coefficient was 1.000
and 0.523 [11]).
−2533(10)
−2964(9)
543(11)
3255(10)
1305(11)
3005(7)
−286(6)
1192(6)
1874(6)
1071(7)
−294(6)
2772(4)
3297(5)
3623(6)
3446(6)
2955(6)
2610(5)
3483(7)
2085(6)
2235(7)
3126(6)
4820(5)
3882(6)
4398(5)
2506(9)
3592(11)
5180(12)
5689(9)
4623(8)
767(10)
5212(9)
The structure was solved by Patterson and Fourier
methods and refined by full-matrix least-squares first
with isotropic thermal parameters and then with an-
isotropic thermal parameters for all non-hydrogen
atoms. All hydrogen atoms were placed at their geo-
−1870(8)
−1310(8)
2587(11)
4111(9)
993(11)
a
˚
metrically calculated positions (C–H=0.96 A) and
Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
refined ‘riding’ on the corresponding parent atoms,
excepting those of the ethylene molecule which were
clearly found in the DF map and refined isotropically.
The final cycles of refinement were carried out on the
basis of 251 variables. A weighting scheme w=[|2Fo+
gF2o]−1 was used in the last cycles of refinement with
g=0.0004 at convergence. Final R and Rw values were
0.0386 and 0.0454, respectively. The analytical scatter-
ing factors, corrected for the real and imaginary parts
of anomalous dispersions, were taken from ref. [12]. All
calculations were carried out on the ENCORE 91 of
the ’Centro di Studio per la Strutturistica Diffrattomet-
rica‘‘ del C.N.R., Parma, using the SHELX-76 and
SHELXS-86 systems of crystallographic computer pro-
grams [13]. The final atomic coordinates for the non-
hydrogen atoms are given in Table 3. Additional data
(atomic coordinates of the hydrogen atoms, thermal
parameters) have been deposited at the Cambridge
Crystallographic Data Centre or are available from the
authors.
Table 2
Summary of crystallographic data for complex 1
Formula
Mol. wt.
C23H37NPTa
539.47
Crystal system
Space group
Triclinic
(
P1
˚
a, A
8.659(3)
10.807(4)
13.373(4)
94.06(2)
101.70(2)
107.23(2)
3 1158.9(7)
2
˚
b, A
˚
c, A
h, °
i, °
k, °
3
˚
V, A
Z
Dcalc, g cm−3
1.546
F(000)
540
Crystal size, mm
v (Mo–Kh), cm−1
q range, °
0.20×0.20×0.35
48.18
3–30
Acknowledgements
Unique total data
Unique observed data
6755
5175 [I\3|(I)]
The authors are grateful to DGICYT (Project PB-
9201178C) and Consiglio Nazionale delle Ricerche
(Rome) for financial supports. J.S.-N. acknowledges
MEC for a fellowship.
R=%ꢀDFꢀ/%ꢀFoꢀ
1
2
0.0386
0.0454
ꢁ
n
Rw= %w(DF)2/%wF2o

P. Royo et al. / Journal of Organometallic Chemistry 563 (1998) 15–21
[6] J.D. Burrington, R.K. Grasselli, Adv. Catal. 30 (1981) 133.
21
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