η2-iminoacyl and η2-acyl monocyclopentadienyl tantalum complexes bearing oxo and oxo-borane ligands

Article abstract of DOI:10.1002/ejic.200500643

Alkyl-chloro ligand exchange by the reaction of [TaCp*R ₂{O·B(C₆F₅)₃}] (R = CH ₂Ph, Me) with Ph₃CCl gave the monoalkyl compounds [TaCp*RCl{O·B(C₆F₅)₃}] (R = CH₂Ph, Me). Insertion of CNAr (Ar = 2,6-Me₂C ₆H₃) and CO into a Ta-C bond of the mono- and dialkyl complexes gave the iminoacyl compounds [TaCp·X{η²-C(R)= NAr}{O·B-(C₆F₅)₃}] (X = R = CH ₂Ph, Me; X = Cl, R = CH₂Ph) and the acyl compounds [TaCp*X{η²-C(R)=O}{O·B(C₆F ₅)₃}] (X = R = CH₂Ph, Me; X = Cl, R = CH ₂Ph), respectively. The related chloro compound [TaCp*Cl{η²-C(Me)=NAr}{O·B(C₆F₅) ₃}] was isolated from the reaction of the oxo derivative [TaCp*Cl{η²-C(Me)=NAr}(O)] with the Lewis acid B(C ₆F₅)₃. Addition of CNAr or pyridine to [TaCp*(CH₂Ph){η²-C(CH₂Ph)=NAr} {O·B(C₆F₅)₃}] afforded the borane-free complex [TaCp*(CH₂Ph){η²-C(CH ₂Ph)=NAr}(O)] and the acid-base adduct L·B(C₆F ₅)₃ (L = py, CNAr). The molecular structures of [TaCp*Cl{η²-C(Me)=NAr}{O·B(C₆F ₅)₃}] and [TaCp*(CH₂Ph) {η²-C(CH₂Ph)=O}{O·B(C₆F ₅)₃}] were obtained from X-ray diffraction studies. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200500643

FULL PAPER
DOI: 10.1002/ejic.200500643
η2-Iminoacyl and η2-Acyl Monocyclopentadienyl Tantalum Complexes Bearing
Oxo and Oxo-Borane Ligands
Javier Sánchez-Nieves,[a] Pascual Royo,*[a] and Marta E. G. Mosquera[a][‡]
Dedicated to J. Antonio Abad, an excellent scientist and friend
Keywords: Tantalum / Oxo ligands / Insertion reactions / Isocyanide / Carbon monoxide
Alkyl-chloro ligand exchange by the reaction of
[TaCp*R2{O·B(C6F5)3}] (R = CH2Ph, Me) with Ph3CCl gave
[TaCp*Cl{η2-C(Me)=NAr}(O)] with the Lewis acid B(C6F5)3.
Addition of CNAr or pyridine to [TaCp*(CH2Ph){η2-
C(CH2Ph)=NAr}{O·B(C6F5)3}] afforded the borane-free com-
plex [TaCp*(CH2Ph){η2-C(CH2Ph)=NAr}(O)] and the acid-
base adduct L·B(C6F5)3 (L = py, CNAr). The molecular struc-
the monoalkyl compounds [TaCp*RCl{O·B(C6F5)3}] (R
=
CH2Ph, Me). Insertion of CNAr (Ar = 2,6-Me2C6H3) and CO
into a Ta–C bond of the mono- and dialkyl complexes gave
the iminoacyl compounds [TaCp*X{η2-C(R)=NAr}{O·B-
(C6F5)3}] (X = R = CH2Ph, Me; X = Cl, R = CH2Ph) and the
acyl compounds [TaCp*X{η2-C(R)=O}{O·B(C6F5)3}] (X = R =
CH2Ph, Me; X = Cl, R = CH2Ph), respectively. The related
chloro compound [TaCp*Cl{η2-C(Me)=NAr}{O·B(C6F5)3}]
was isolated from the reaction of the oxo derivative
tures
of
[TaCp*Cl{η2-C(Me)=NAr}{O·B(C6F5)3}]
and
were ob-
[TaCp*(CH2Ph){η2-C(CH2Ph)=O}{O·B(C6F5)3}]
tained from X-ray diffraction studies.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
the imine-η2-iminoacyl derivatives [TaCp*(NtBu)X{η2-
C[C(Me)=NR]=NR}].[20] With regard to the CO insertion
reactions, double migration of the alkyl group [process (a)]
was observed for [TaCp*Cl2Me2],[10] whereas the coupling
of the acyl groups [process (b)] occurred for
[TaCp*Me2(NR)] (R = 2,6-Me2C6H3) to give the dinuclear
compound [TaCp*(NR)Me]2{µ-η2-OC(Me)=C(Me)O},[10]
and ligand exchange [process (c)] for complexes
[TaCp*ClMe(NR)] (R = 2,6-Me2C6H3,[10] tBu)[11] led to the
oxo compounds [TaCp*Cl(O){η2-C(Me)=NR}]. Further-
more, the η2-(methyl)acyl complexes remained elusive and
were only detected as intermediates by NMR spectroscopy,
whereas the related η2-iminoacyl complexes are stable.
It was observed that for monocyclopentadienyl imido
tantalum derivatives addition of a second CNR molecule
into the iminoacyl compounds [TaCp*(NR)X{η2-
C(Me)=NR}] (R = 2,6-Me2C6H3, tBu; X = Cl, Me) re-
sulted in differing behaviours depending on the R group
of the imido ligand. No reaction was found for R = 2,6-
Me2C6H3,[10] whereas a second insertion occurred for R =
tBu.[20] Conversely, the imido complexes [TaCp*MeX(NR)]
(R = 2,6-Me2C6H3, tBu; X = Cl, Me) reacted with CO to
give the dinuclear compound [TaCp*(NR)Me]2{µ-η2-OC-
(Me)=C(Me)O} for X = Me[10] and one of the few mononu-
clear derivatives [TaCp*Cl(O){η2-C(Me)=NR}] containing
a terminal tantalum-oxo double bond for X = Cl.[10,11]
The versatility and potential applications of all these re-
sults determined by the R and X substituents of the imido
Introduction
The formation of C–C bonds through insertion of isocy-
anides (CNR) and carbon monoxide (CO) into M–C bonds
is well-documented, and this reaction initially affords imi-
noacyl and acyl complexes, respectively.[1] For a given metal
atom, the stability and further evolution of these com-
pounds are determined by the nature of the ancillary li-
gands. Many reaction pathways may follow to give a broad
variety of products:[1] (a) migratory insertion of a second
alkyl or aryl group to give η2-imine or η2-ketene com-
plexes;[2–5] (b) intra- or intermolecular coupling of imi-
noacyl or acyl units affording diaza- or dioxobutene com-
plexes;[6,7] (c) transfer of the NR or O moieties to the metal
centre;[8–11] (d) insertion of a second CNR[12–16] or CO[17]
molecule into the new M–C bond formed after the first in-
sertion process and (e) hydrogen migration.[18,19]
We reported the results of our studies on the insertion
reactions of CNR into the Ta–C(methyl) bond of monocy-
clopentadienyl complexes of the type [TaCp*ClxMe4–x
for which processes (a) and (c) were observed. Similar
reactions with imido compounds of the type
[TaCp*MeX(NtBu)] (X = Cl, Me, OR, NHtBu) gave
[8–10]
]
[a] Departamento de Química Inorgánica, Universidad de Alcalá,
Campus Universitario,
28871 Alcalá de Henares, Madrid, Spain
Fax: +34-91-885-4683
E-mail: pascual.royo@uah.es
[‡] X-ray diffraction studies.
Eur. J. Inorg. Chem. 2006, 127–132
© 2006 Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim
127

J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
complexes [TaCp*MeX(NR)] led us to extend our studies These pale yellow complexes are air and thermally stable in
to similar insertion reactions of CNR and CO into the Ta– solution. The 13C NMR resonance at ca. δ = 240 ppm is
alkyl bonds of the related oxo-borane compounds the most apparent spectroscopic feature and confirms the
[TaCp*X2{O·B(C6F5)3}] that have recently been isolated.[21] presence of the η2-iminoacyl ligand in complexes 2.
We previously reported[10] on the isolation of the related
oxo complex [TaCp*Cl{η2-C(Me)=NAr}(O)] from the re-
Results and Discussion
action of the monomethyl compound [TaCp*ClMe(NAr)]
with CO through a process that involved insertion of CO
into the Ta–Me bond and further rearrangement of the η2-
acyl intermediate with intramolecular oxo-imido exchange.
Since the starting oxo-borane chloro-methyl complex could
not be isolated, thus preventing access to the oxo-borane
compound [TaCp*Cl{η2-C(Me)=NAr}{O·B(C6F5)3}] (2d)
by insertion of CNAr into the Ta–C bond of the corre-
sponding alkyl-chloro compound, we tried to obtain this
compound by an alternative route. With this aim, we inves-
tigated the reaction of the oxo iminoacyl compound
[TaCp*Cl{η2-C(Me)=NAr}(O)] with B(C6F5)3, which af-
forded 2d in high yield. The formation of 2d was confirmed
by 13C and 19F NMR spectroscopy. The 13C NMR spec-
trum shows the resonance corresponding to the Csp2 atom
of the η2-iminoacyl ligand (δ = 240.1 ppm) to be slightly
low-field shifted with respect to that of the starting com-
pound [TaCp*Cl{η2-C(Me)=NAr}(O)] (δ = 236.8 ppm). An
The
monoalkyl
oxo-borane
compounds
[TaCp*RCl{O·B(C6F5)3}] (R = CH2Ph 1c, Me 1d) were
synthesised by an alkyl-chloro metathesis reaction of
[TaCp*R2{O·B(C6F5)3}] (R = CH2Ph 1a, Me 1b) with
one equiv. of Ph3CCl as chlorinating agent (Scheme 1). The
reaction for 1c proceeded smoothly at room temperature to
give a pale yellow solid in good yield, whereas complex 1d
could not be isolated in the solid state. The formation of 1d
was demonstrated on a small scale by 1H NMR spec-
troscopy with a C6D6 solution of 1b that was treated with
Ph3CCl and heated to 40 °C. All attempts made to obtain
the monomethyl complex through alkylation of
[TaCp*Cl2{O·B(C6F5)3}] and redistribution reactions
between [TaCp*Cl2{O·B(C6F5)3}] and [TaCp*Me2{O·B-
(C6F5)3}] failed. The 11B and 19F NMR spectra of com-
plexes 1c and 1d are consistent with the presence of a tetra-
coordinate boron atom,[21–31] and the 1H NMR spectra
with the monosubstitution of only one of the alkyl ligands.
1
analogous behaviour was observed in the H NMR spec-
trum for the methyl-iminoacyl group, which was shifted
from δ = 2.65 ppm in [TaCp*Cl{η2-C(Me)=NAr}(O)] to δ
= 2.94 ppm in 2d.
The molecular structure of compound [TaCp*Cl{η2-
C(Me)=NAr}{O·B(C6F5)3}] (Ar = 2,6-Me2C6H3) (2d) was
obtained by X-ray diffraction studies. Figure 1 depicts an
ORTEP drawing of 2d with selected bond lengths and
angles. Compound 2d exhibits the typical geometry known
for group 5 half-sandwich iminoacyl compounds with a tet-
rahedral coordination environment around the tantalum
atom. Considering the centroid of the Cp* ring and the
midpoint of the C(10)–N bond as coordination sites, the
other two positions are occupied by the chloro and oxo li-
gands. The N atom of the η2-iminoacyl group is located in
a trans position with respect to the oxo ligand, as in analo-
gous half-sandwich imido complexes and in [TaCp*Cl{η2-
C(Me)=NAr}(O)]. Furthermore, the oxygen atom is at-
tached to the boron atom of the B(C6F5)3 group.
All the values of the bond lengths and angles of com-
pound 2d are very close to the corresponding bond lengths
and angles found for the parent compound [TaCp*Cl{η2-
C(Me)=NAr}(O)][10] except for the Ta–O bond, which is
longer in [TaCp*Cl{η2-C(Me)=NAr}(O)] [1.731(7) Å] than
in 2d [1.809(5) Å] as a consequence of the coordination of
the oxygen atom to the B(C6F5)3 ligand.[21,23–28,30,31] The
Scheme 1.
The alkyl complexes [TaCp*R2{O·B(C6F5)3}] (R = linear Ta–O–B angle [174.4(6)°] and the B–O bond length
CH2Ph 1a, Me 1b) and [TaCp*(CH2Ph)Cl{O·B(C6F5)3}] [1.52(1) Å] are typical of oxo-borane compounds.[21–31] The
(1c) immediately reacted at room temperature with Ta–O bond in 2d is longer than that in the oxo-borane com-
one equiv. of the isocyanide CNAr (Ar = 2,6-Me2C6H3) pound [TaCp*Cl2{O·B(C6F5)3}][21] [1.784(2) Å]. This bond
to give the corresponding η2-iminoacyl compounds length is similar to the lower end of the range of Ta–O bond
[TaCp*X{η2-C(R)=NAr}{O·B(C6F5)3}] (X = R = CH2Ph lengths for compounds with Ta–O–Ta bridges (1.82–2.10 Å)
[32–35]
2a, Me 2b; X = Cl, R = CH2Ph 2c) in high yields by inser-
and with terminal Ta–OH bonds (1.85–1.97 Å).[36–38]
tion of the isocyanide ligand into a Ta–C bond (Scheme 1). However, the single bond Ta–O distances are ca. 2.18 Å,
128
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 127–132

η2-Iminoacyl and η2-Acyl Monocyclopentadienyl Tantalum Complexes
FULL PAPER
Figure 1. ORTEP diagram of the X-ray structure of compound 2d.
Thermal ellipsoids are drawn at the 50% level, and hydrogen atoms
and C6F5 groups have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Ta–O 1.809(5), Ta–N 2.127(7), Ta–C(10)
2.120(9), Ta–Cl 2.392(2), B–O 1.525(11), N–C(10) 1.26(1), N–Ta–
C(10) 34.5(3), C(10)–N–Ta 72.4(5), N–C(10)–Ta 73.1(5), B–O–Ta
174.4(6).
Figure 2. ORTEP diagram of the X-ray structure of compound 3a.
Thermal ellipsoids are drawn at the 50% level, and hydrogen atoms
and C6F5 groups have been omitted for clarity. Selected bond
lengths [Å] and angles [°]: Ta–O(1) 1.816(2), Ta–O(2) 2.110(3), Ta–
C(1) 2.229(4), Ta–C(2) 2.011(3), B–O(1) 1.512(4), O(2)–C(2)
1.209(4), O(2)–Ta–C(2) 34.02(12), C(2)–O(2)–Ta 68.5(2), O(2)–
C(2)–Ta 77.5(2), B–O(1)–Ta 173.02(19).
and thus a bond order of two should be considered for the
Ta–O bond in 2d.
sponding bond in compound 3a [2.110(3) Å], because of the
different trans effect and higher donor capacity of the imido
ligand.
The reaction of the dialkyl [TaCp*R2{O·B(C6F5)3}] (R
= CH2Ph 1a, Me 1b) and the monobenzyl [TaCp*(CH2Ph)-
Cl{O·B(C6F5)3}] (1c) complexes with CO in toluene gave
the η2-acyl compounds [TaCp*X{η2-C(R)=O}{O·B-
(C6F5)3}] (X = R = CH2Ph 3a, Me 3b; X = Cl, R = CH2Ph
3c) after ca. 24 h at room temperature in moderate yields
(Scheme 1). These pale yellow compounds were air and
thermally stable below 120 °C for several hours. The 13C
NMR spectra showed a resonance at ca. δ = 305 ppm corre-
sponding to the Csp2 atom of the η2-acyl fragment. The
slowness of the insertion reactions of CO is in contrast with
the rapid transformations observed for complexes 1 with
isocyanide and the behaviour observed[10,11] for the reac-
tions of the imido compounds [TaCp*MeX(NR)] (R = 2,6-
Me2C6H3, tBu; X = Cl, Me) with CO. This difference may
be attributed to the lower oxophilicity of the tantalum atom
in compounds 1 that is caused by the presence of the oxo
ligand.
The insertion of a second CNAr or CO molecule into
these new acyl and iminoacyl oxo-borane complexes was
not observed, in contrast with the behaviour observed for
the analogous tert-butyl imido complexes.[20] Rather, all
complexes 2–3 released the acid-base adduct L·B(C6F5)3 (L
= py, CNAr) in the presence of donor ligands such as isocy-
anide or pyridine.[41] Only in the case of compound 2a were
we able to isolate the borane-free 18-electron compound
[TaCp*(CH2Ph){η2-C(CH2Ph)=NAr}(O)] (4a), with a ter-
minal oxo-tantalum bond. The remaining oxo-borane com-
plexes decomposed under similar conditions. The 13C NMR
spectrum of the new oxo iminoacyl compound 4a showed
the η2-iminoacyl Csp2 resonance at δ = 240.3 ppm. A com-
parison of this 13C resonance and that assigned to the CH2–
1
iminoacyl group in the H NMR spectrum with the corre-
sponding resonances in the parent compound 2a, showed
a behaviour that is opposite to that observed for 2d and
[TaCp*Cl{η2-C(Me)=NAr}(O)].
The X-ray structure of compound 3a is shown in Fig-
ure 2. The environment around the Ta atom is analogous
to that described for compound 2d (see above) with the oxy-
gen atom of the acyl group located trans to the oxo-borane
ligand, as expected. The Ta–O(1) bond length of 1.816(2) Å
is similar to that observed for compound 2d, and the O(1)–
B bond length [1.512(4) Å] and Ta–O(1)–B angle [173.0(2)°]
Conclusions
The dialkyl oxo-borane compounds [TaCp*R2{O·B-
have values that are normally seen for these types of com- (C6F5)3}] can be transformed into the monoalkyl deriva-
pounds.[21–31]
tives [TaCp*RX{O·B(C6F5)3}] by alkyl-chloro exchange
The whole set of angles and bond lengths of the [Ta-(η2- with Ph3CCl. All of these complexes reacted with one mole-
acyl)] group is in line with compounds of this type[1] and cule of isocyanide or carbon monoxide to give the η2-imi-
is similar to those found in the other two tantalum-acyl noacyl or η2-acyl compounds, respectively. No further in-
complexes for which X-ray structures are known, sertion processes have been observed. This behaviour is
[TaCp*Me{η2-C(CH2CMe2Ph)=O}{N(2,6-Me2C6H3)}][39] analogous to that observed for the imido compounds
and [TaCp*Cl3{η2-C(CH2CMe3)=O}].[40] However, in the [TaCp*MeX(NR)] (R = 2,6-Me2C6H3; X = Cl, Me), al-
particular case of the isostructural imido derivative though in the oxo-borane compounds the insertion of CO
[TaCp*Me{η2-C(CH2CMe2Ph)=O}{N(2,6-Me2C6H3)}], the gave stable η2-acyl derivatives because of the presence of a
Ta–O bond [2.21(1) Å] is slightly longer than the corre- Ta–O multiple bond, which prevents further rearrangement.
Eur. J. Inorg. Chem. 2006, 127–132
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129

J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
FULL PAPER
N 1.28. 1H NMR: δ = 0.79 (s, 3 H, Ta–Me), 1.48 (s, 3 H, Me2C6H3),
1.69 (s, 3 H, Me2C6H3), 1.95 (s, 15 H, C5Me5), 2.72 (s, 3 H, C–
Me), 7.06 (m, 2 H, Me2C6H3), 7.13 (m, 1 H, Me2C6H3) ppm. 13C
NMR{1H}: δ = 11.0 (C5Me5), 17.2 (Me2C6H3), 18.6 (Me2C6H3),
20.0 (Ta–Me), 31.6 (C–Me), 118.7 (C5Me5), 127.6–148.8 (Me2C6H3
and C6F5), 238.3 (Ta–C=N) ppm. 19F NMR: δ = –131.7 (o-C6F5),
Experimental Section
All manipulations were carried out under argon, and solvents were
distilled from appropriate drying agents. NMR spectra were re-
corded at 300.13 (1H NMR), 188.31 (19F NMR), 75.47 (13C NMR)
and 128.38 Hz (11B NMR) at room temperature with a Varian
Unity 300 (1H, 13C, 19F) or Bruker Advance 400 (11B NMR) instru-
ment. Chemical shifts (δ, CDCl3) are given in ppm, relative to in-
ternal TMS (1H and 13C NMR), and external CFCl3 (19F NMR)
and BF3·OEt2 (11B NMR). Elemental analyses were performed
–158.4 (p-C F ), –163.8 (m-C F ) ppm. IR (KBr): ν = 1629
˜
6
5
6 5
(C=N) cm–1.
[TaCp*Cl{η2-C(CH2Ph)=NAr}{O·B(C6F5)3}] (Ar = 2,6-Me2C6H3)
(2c): The procedure used for 2a, but starting from
[TaCp*Cl(CH2Ph){O·B(C6F5)3}] (1c) (0.50 g, 0.52 mmol) and
CNAr (0.072 g, 0.55 mmol), gave 2c (0.51 g, 89%).
C44H31BClF15NOTa (1101.91): calcd. C 47.96, H 2.84, N 1.27;
with
a
Perkin–Elmer
240C
instrument.
Compounds
[TaCp*Me4],[42] [TaCp*(CH2Ph)2{O·B(C6F5)3}],[21] [TaCp*Me2-
{O·B(C6F5)3}],[21] [TaCp*Cl{η2-C(Me)=NAr}(O)][10] and B-
(C6F5)3
(C6F5)3
[43]
were prepared by literature methods, and H2O·B-
was prepared from H2O and B(C6F5)3 in toluene at
found 47.00, H 2.75, N 1.24. 1H NMR: δ = 1.55 (s, 3 H, Me2C6H3),
[44]
2
1.64 (s, 3 H, Me2C6H3), 2.09 (s, 15 H, C5Me5), 4.59 (d, JH,H
=
room temperature and used in situ without further purification.
2
18.5 Hz, 1 H, C–CH2Ph), 4.72 (d, JH,H = 18.5 Hz, 1 H, C–
CH2Ph), 6.76–7.06 (m, 8 H, C6H3 and C6H5) ppm. 13C NMR{1H}:
δ = 11.4 (C5Me5), 17.8 (Me2C6H3), 21.4 (Me2C6H3), 43.3 (C–
CH2Ph), 123.2 (C5Me5), 125.3–149.2 (C6H5, Me2C6H3 and C6F5),
236.7 (Ta–C=N) ppm. 19F NMR: δ = –130.6 (o-C6F5), –157.9 (p-
[TaCp*Cl(CH2Ph){O·B(C6F5)3}] (1c): A suspension of Ph3CCl
(0.14 g, 0.50 mmol) and [TaCp*(CH2Ph)2{O·B(C6F5)3}] (1a)
(0.50 g, 0.49 mmol) in toluene (5 mL) was stirred overnight at room
temperature, with a colour change from yellow to brown. Later, all
volatile components were removed under vacuum until the volume
was ca. 1 mL, leaving a dark oil that was washed with hexane
C F ), –163.4 (m-C F ) ppm. IR (KBr): ν = 1644 (C=N) cm–1.
˜
6
5
6 5
[TaCp*Cl{η2-C(Me)=NAr}{O·B(C6F5)3}] (Ar = 2,6-Me2C6H3) (2d):
A solution of [TaCp*Cl{η2-C(Me)=NAr}(O)] (0.25 g, 0.49 mmol)
and B(C6F5)3 (0.28 g, 0.51 mmol) in toluene (5 mL) was stirred at
room temperature for 1 h. Later, the solution was filtered, layered
with hexane (5 mL) and cooled to –10 °C, obtaining 2d as yellow
crystals (0.40 g, 74%). C38H27BClF15NOTa·(C7H8)2 (1210.09):
(2×10 mL) to yield 1c as
a brownish solid (0.36 g, 76%).
C35H22BClF15OTa (970.75): calcd. C 43.31, H 2.28; found C 42.99,
H 2.25. 1H NMR: δ = 2.14 (s, 15 H, C5Me5), 2.52 (d, JH,H
=
2
14.0 Hz, 1 H, CH2Ph), 2.80 (d, 2JH,H = 14.0 Hz, 1 H, CH2Ph), 6.74
(m, 2 H, C6H5), 7.02 (m, 3 H, C6H5) ppm. 11B NMR: δ = 0.10
[O·B(C6F5)3] ppm; 13C NMR{1H}:
δ = 11.5 (C5Me5), 82.3
1
(CH2Ph), 125.7 (C5Me5), 127.1 (C6H5), 128.2 (C6H5),128.3 (C6H5),
131.4 (C6H5), 135.0 (C6F5), 138.3 (C6F5), 145.9 (C6F5), 149.1
(C6F5) ppm; 19F NMR: δ = –132.9 (o-C6F5), –157.7 (p-C6F5),
–163.3 (m-C6F5) ppm.
calcd. C 51.61, H 3.58, N 1.16; found C 51.01, H 3.22, N 1.19. H
NMR: δ = 1.62 (s, 3 H, Me2C6H3), 1.91 (s, 3 H, Me2C6H3), 2.18
(s, 15 H, C5Me5), 2.94 (s, 3 H, C–Me), 7.13 (m, 2 H, Me2C6H3),
7.20 (m, 1 H, Me2C6H3) ppm. 13C NMR{1H}: δ = 11.5 (C5Me5),
17.6 (Me2C6H3), 19.2 (C–Me), 21.1 (Me2C6H3), 113.3 (C5Me5),
128.7–149.4 (Me2C6H3 and C6F5), 240.1 (Ta–C=N) ppm. 19F
NMR: δ = –131.5 (o-C6F5), –158.4 (p-C6F5), –164.0 (m-C6F5) ppm.
[TaCp*ClMe{O·B(C6F5)3}] (1d): A solution of Ph3CCl (0.080 g,
0.028 mmol) and [TaCp*Me2{O·B(C6F5)3}] (1d) (0.025 g,
0.028 mmol) in C6D6 was heated at 45 °C for 18 h. Total transfor-
IR (KBr): ν = 1638 (C=N) cm–1.
˜
1
mation of 1b to 1d was then observed. H NMR (C6D6): δ = 1.26
(s, 3 H, Ta–Me), 2.13 (s, 15 H, C5Me5) ppm. 11B NMR (C6D6): δ
= 0.05 [O·B(C6F5)3] ppm. 19F NMR (C6D6): δ = –133.0 (o-C6F5),
–157.2 (p-C6F5), –163.3 (m-C6F5) ppm.
[TaCp*(CH2Ph){η2-C(CH2Ph)=O}{O·B(C6F5)3}] (3a): A flask con-
taining a solution of [TaCp*(CH2Ph)2{O·B(C6F5)3}] (1a) (0.50 g,
0.49 mmol) in toluene (10 mL) was charged with CO, and the mix-
ture was stirred for 24 h at room temperature. The solution was
then filtered, all volatile components were removed under vacuum
to leave ca. 4 mL of solution and the solution was layered with
hexane (4 mL) and cooled to –10 °C to give 3a as yellow crystals
(0.39 g, 70%). C43H29BF15O2Ta·C7H8 (1146.56): calcd. C 52.38, H
[TaCp*(CH2Ph){η2-C(CH2Ph)=NAr}{O·B(C6F5)3}] (Ar
= 2,6-
Me2C6H3) (2a): A solution of [TaCp*(CH2Ph)2{O·B(C6F5)3}] (1a)
(0.50 g, 0.49 mmol) in toluene (5 mL) was treated with CNAr
(0.065 g, 0.50 mmol), and the mixture was stirred for 1 h at room
temperature. All volatile components were removed under vacuum,
and the remaining solid was washed with hexane (2×10 mL) to
give 2a as a white solid (0.49 g, 87%). C51H38BF15NOTa (1157.59):
1
3.25; found C 52.43, H 3.17. H NMR: δ = 1.88 (s, 15 H, C5Me5),
2
2
2.54 (d, JH,H = 12.1 Hz, 1 H, Ta–CH2Ph), 2.70 (d, JH,H
=
2
1
12.1 Hz, 1 H, Ta–CH2Ph), 4.59 (d, JH,H = 19.4 Hz, 1 H, C–
CH2Ph), 4.88 (d, JH,H = 19.4 Hz, 1 H, C–CH2Ph), 6.70–6.90 (m,
calcd. C 52.91, H 3.31, N 1.21; found C 52.67, H 3.21, N 1.09. H
2
NMR: δ = 1.34 (s, 3 H, Me2C6H3), 1.41 (s, 3 H, Me2C6H3), 1.93
6 H, C6H5), 7.20–7.45 (m, 4 H, C6H5) ppm. 13C NMR{1H}: δ =
10.8 (C5Me5), 49.2 (C–CH2Ph), 60.0 (Ta–CH2Ph), 120.0 (C5Me5),
123.5–148.9 (C6H5 and C6F5), 306.9 (Ta–C=O) ppm. 19F NMR: δ
= –133.0 (o-C6F5), –157.7 (p-C6F5), –163.4 (m-C6F5) ppm. IR
2
(s, 15 H, C5Me5), 2.78 (d, JH,H = 12.5 Hz, 1 H, Ta–CH2Ph), 2.93
2
2
(d, JH,H = 12.5 Hz, 1 H, Ta–CH2Ph), 4.46 (d, JH,H = 17.4 Hz, 1
2
H, C–CH2Ph), 4.56 (d, JH,H = 17.4 Hz, 1 H, C–CH2Ph), 6.47–
7.03 (m, 13 H, C6H3 and C6H5) ppm. 13C NMR{1H}: δ = 11.1
(C5Me5), 17.6 (Me2C6H3), 18.8 (Me2C6H3), 42.2 (C–CH2Ph), 54.8
(Ta–CH2Ph), 120.1 (C5Me5), 123.5–149.2 (C6H5, Me2C6H3 and
C6F5), 237.7 (Ta–C=N) ppm. 19F NMR: δ = –130.7 (o-C6F5),
(KBr): ν = 1643 (C=O) cm–1.
˜
[TaCp*Me{η2-C(Me)=O}{O·B(C6F5)3}] (3b): The procedure used
for 3a, but starting from [TaCp*Me2{O·B(C6F5)3}] (1b) (0.50 g,
0.57 mmol) and CO, gave 3b as a white solid (0.41 g, 80%).
C31H21BF15O2Ta (902.23): calcd. C 41.27, H 2.35; found C 40.87,
H 2.30. 1H NMR: δ = 0.81 (s, 3 H, Ta–Me), 1.90 (s, 15 H, C5Me5),
3.23 (s, 3 H, C–Me) ppm. 13C NMR{1H}: δ = 10.6 (C5Me5), 28.7
–158.3 (p-C F ), –163.8 (m-C F ) ppm. IR (KBr): ν = 1601
˜
6
5
6 5
(C=N) cm–1.
[TaCp*Me{η2-C(Me)=NAr}{O·B(C6F5)3}] (Ar
(2b): The procedure used for 2a, but starting from
=
2,6-Me2C6H3)
[TaCp*Me2{O·B(C6F5)3}] (1b) (0.50 g, 0.57 mmol) and CNAr (Ta–Me), 37.6 (C–Me), 119.4 (C5Me5), 134.3–149.8 (C6F5), 313.8
(0.079 g, 0.060 mmol), gave 2b (0.52 g, 91%). C39H30BF15NOTa
(1005.41): calcd. C 46.59, H 3.09, N 1.39; found C 46.40, H 3.00,
(Ta–C=O) ppm. 19F NMR: δ = –133.2 (o-C6F5), –157.7 (p-C6F5),
–163.4 (m-C F ). IR (KBr): ν = 1644 (C=O) cm–1.
˜
6
5
130
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 127–132

η2-Iminoacyl and η2-Acyl Monocyclopentadienyl Tantalum Complexes
[TaCp*Cl{η2-C(CH2Ph)=O}{O·B(C6F5)3}] (3c): The procedure lised with every molecule of 2d; both solvent molecules were found
FULL PAPER
used for 3a, but starting from [TaCp*Cl(CH2Ph){O·B(C6F5)3}] (1c)
(0.50 g, 0.52 mmol) and CO, gave 3c as a yellowish solid (0.40 g,
78%). C36H22BClF15O2Ta (998.76): calcd. C 43.29, H 2.22; found
C 43.17, H 2.24. 1H NMR: δ = 2.05 (s, 15 H, C5Me5), 4.41 (d,
in the difference Fourier map but one of them was very disordered
and it was not possible to get a chemically sensible model for it, so
the Squeeze procedure[45] was used to remove its contribution to
the structural factors. In 3a some restraints on the solvent molecule
were applied. Crystal data for both compounds are given in
2
2JH,H = 19.0 Hz, 1 H, C–CH2Ph), 4.91 (d, JH,H = 19.0 Hz, 1 H,
C–CH2Ph), 7.05–7.40 (m, 5 H, C6H5) ppm. 13C NMR{1H}: δ = Table 1. CCDC-272817 (for 2d) and CCDC-272818 (for 3a) contain
10.5 (C5Me5), 49.2 (C–CH2Ph), 123.7 (C5Me5), 127.8–130.0
(C6H5), 135.8, 138.3, 139.2, 141.7, 146.8 and 150.1 (C6F5), 310.5
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
(Ta–C=O) ppm. 19F NMR: δ = –132.5 (o-C6F5), –156.9 (p-C6F5), graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
–162.9 (m-C F ) ppm. IR (KBr): ν = 1658 (C=O) cm–1.
˜
6
5
[TaCp*(CH2Ph){η2-C(CH2Ph)=NAr}(O)] (Ar = 2,6- Me2C6H3)
Acknowledgments
(4a):
A
solution of [TaCp*(CH2Ph){η2-C(CH2Ph)=NAr}-
{O·B(C6F5)3}] (2a) (0.25 g, 0.22 mmol) in toluene (5 mL) was
treated with pyridine (0.026 g, 0.33 mmol), and the mixture was
stirred for 2 h at room temperature. All volatile components were
removed under vacuum until ca. 1 mL remained, and hexane
(10 mL) was added to precipitate a white solid that was washed
with a hexane/toluene mixture (2×10 mL, 9:1) to give 4a (0.10 g,
72%). C33H38NOTa (645.62): calcd. C 61.39, H 5.93, N 2.17; found
We gratefully acknowledge the Ministerio de Educación y Ciencia
(project MAT2004–02614) and DGUI-Comunidad de Madrid
(project GR/MAT/0622/2004) (Spain) for financial support.
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1
C 61.00, H 5.83, N 2.21. H NMR: δ = 1.25 (s, 3 H, Me2C6H3),
1.72 (d, 2JH,H = 11.9 Hz, 1 H, Ta–CH2Ph), 1.80 (s, 3 H, Me2C6H3),
2
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39.3 (C–CH2Ph), 48.8 (Ta–CH2Ph), 121.1 (C5Me5), 126.1–149.8
(C H and Me C H ), 240.3 (Ta–C=N) ppm. IR (KBr): ν = 1631
˜
6
5
2
6
3
(C=N) cm–1.
Crystal Structure Determination for 2d and 3a: Selected crystals
were covered with perfluoropolyether oil and mounted on a Nonius
KAPPA-CCD single crystal diffractometer. The crystal structure
was solved by direct methods and refined using full-matrix least-
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Table 1. Crystallographic data for compounds 2d and 3a.
Compound
2d
3a
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Empirical formula
Formula mass
λ [Å]
Crystal system
Space group
T [K]
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å3]
Z
Calcd. density [mgm–3
Absorption coefficient [mm–1
θ range [°]
Reflections collected/unique reflections 13375/8067
R(int.)
Data/restraints/parameters
GOF
Final R indices
[I Ͼ 2σ(I)]
Largest diff. peak/hole [eÅ–3
C52H43BClF15NOTa C50H37BF15O2Ta
1210.08
0.71069
triclinic
1146.56
0.71069
triclinic
¯
P1
¯
P1
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200(2)
150(2)
9.565(1)
13.7547(3)
19.545(3)
77.483(7)
79.50(1)
71.389(4)
2361.1(5)
2
12.739(2)
13.171(2)
15.104(2)
88.20(1)
82.58(2)
63.20(1)
2242.1(6)
2
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]
1.572
1.698
]
2.478
2.555
3.52–27.50
3.61–27.50
19150/10201
0.0228
0.0863
8067/3/586
1.101
10201/239/622
1.042
R1 = 0.0575
wR2 = 0.1211
1.596/–1.899
R1 = 0.0292
wR2 = 0.0678
1.303/–1.364
]
Eur. J. Inorg. Chem. 2006, 127–132
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
131

J. Sánchez-Nieves, P. Royo, M. E. G. Mosquera
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Received: July 19, 2005
Published Online: November 11, 2005
132
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Eur. J. Inorg. Chem. 2006, 127–132