Phosphido-bridged Ta/Rh bimetallic complex: Synthesis, structure, and catalytic hydrosilylation of acetophenone

Article abstract of DOI:10.1039/c0dt00141d

Reaction of Cp₂TaH₃ (1) with ClPEt₂ gives the insertion product [Cp₂TaH₂(PHEt₂)]Cl (5), which upon deprotonation with LiN(SiMe₃)₂ affords the phosphido complex Cp

Full text of DOI:10.1039/c0dt00141d

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PAPER
www.rsc.org/dalton | Dalton Transactions
Phosphido-bridged Ta/Rh bimetallic complex: synthesis, structure, and
catalytic hydrosilylation of acetophenone†
a
a
b
c
Andrea E. Findlay, Somying Leelasubcharoen,‡ Lyudmila G. Kuzmina, Judith A. K. Howard and
a
Georgii I. Nikonov*
Received 15th March 2010, Accepted 10th May 2010
DOI: 10.1039/c0dt00141d
Reaction of Cp
deprotonation with LiN(SiMe
product. The latter transforms by a first-order reaction during the course of 3.5 days to the phosphine
complex Cp TaH(PHEt ) (7). Repetition of this insertion/deprotonation sequence gives the
Ta(PHEt ]Cl (8) and Cp Ta(PEt )(PHEt ) (9). Reaction of the latter with
in the presence of LiN(SiMe gives the bimetallic complex
) (10), which was studied by NMR and X-ray diffraction analysis.
2
TaH
3
(1) with ClPEt
2
gives the insertion product [Cp
2
TaH
2
(PHEt
2
)]Cl (5), which upon
3
)
2
affords the phosphido complex Cp
2
TaH
2
(PEt
2
) (6) as the kinetic
2
2
compounds [Cp
2
2
)
2
2
2
2
2
0.5[(m-Cl)Rh(h -C
2
H
4
)]
2
)
3 2
2
Cp
2
Ta(m-PEt
2
)
2
Rh(h -C
2
H
4
Complex 10 catalyses the hydrosilylation of acetophenone by PhMeSiH .
2
Introduction
Phosphine complexes of the late transition metals play a prominent
1
role in molecular catalysis. Phosphine ligands bind strongly to
metals and their electronic and steric properties can be easily
2
adjusted by varying the substituents at phosphorus atom. An-
other approach to a rational design of phosphine-based catalysts
is based on the substitution at the phosphorus atom by an
electron releasing organometallic group. Such a metalaphosphine
Scheme 1 Oxidative addition to a Group 5 early–late heterobimetallic
complex (ELHB).
d+
d-
ligand, L
n
M–PR possessing a highly polarized M –P bond
2
might be envisioned to be a better ligand to a catalytically active
late transition metal. Application of this idea to the Suzuki–
ELHB complexes have been known for decades, Group 5
3
7-10
phosphido-supported species are poorly studied,
little is known about their catalytic activity.
and very
Here we re-
10,11
Miyaura reaction catalysed by phosphido-bridged Re/Pd and
4
Ru/Pd complexes has been previously reported by Gladysz.
port the preparation of the precursor phosphide complex
Cp Ta(PEt )(PHEt ) and its application to the synthesis of the
In this context, the class of Group 5 metallocene-based bimetal-
lic bis(phosphido)-bridged complexes A (Scheme 1) is of interest
because they offer the advantage of an easily changeable oxidation
state of the Group 5 metal and the presence of an easily oxidizable
M–M¢ bond (where M is a Group 5 metal and M¢ is a late
transition metal centre). The M–M¢ bond can be sacrificed at the
oxidative addition stage of catalysis (Scheme 1), maintaining the
catalytically active late transition metal in a lower oxidation state
throughout the catalytic cycle, which will presumably facilitate
2
2
2
2
bimetallic complex Cp Ta(m-PEt ) Rh(m -C H ) (10). The X-ray
2
2
2
2
4
structure and catalytic hydrosilylation of acetophenone mediated
by complex 10 are also reported. Finally, we report a much
improved synthesis of the compound Cp TaH , which is a very
2
3
12
useful starting material in tantalocene chemistry.
Results and discussion
5
catalysis.
With these prerequisites in mind, we chose to synthesise and
Preparation of Cp
2
TaH (1)
3
study the catalytic activity of new early-late heterobimetallic
6
Our starting compound on the way to complex 10 was the tri-
hydride Cp TaH , whose one-pot synthesis is poorly reproducible
(
ELHB) complexes of the type Cp
2
2
2
n
Ta(m-PR ) ML . Although
2
3
13
and suffers from low yields (0–25%). Improved strategies are
based on the preparation and reduction of Cp TaCl , which
a
Chemistry Department, Brock University, 500 Glenridge Ave.,
St. Catharines, L2S 3A1, ON, Canada. E-mail: gnikonov@
brocku.casomying@kku.ac.th; Fax: (905) 6829020; Tel: (905) 6885550,
ext 3350
Institute of General and Inorganic Chemistry RAS, Leninskii Prosp. 31,
19991, Moscow, Russia. E-mail: kuzmina@igic.ras.ru; Tel: +7 4999521803
Chemistry Department, University of Durham, South Road, Durham, UK,
DH1 3LE. E-mail: j.a.k.howard@durham.ac.uk
CCDC reference number 770198. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt00141d
Current address: Department of Chemistry, Faculty of Science, Khon
Kaen University, Khon Kaen 40002 Thailand.
2
2
14
requires the use of toxic organotin reagents. We developed
a simple three-step synthesis of 1, each step of which goes
in high yield (Scheme 2). The reaction starts with making
b
t
15
1
( BuN=)TaCl
3
*py
2
by a literature procedure (90–99%) which is
c
then treated with two equivalents of CpNa to furnish the known
t
16
tantalocene Cp
treated with LiAlH
2
Ta(=NBu )Cl (90–96%). The latter compound is
†
4
in Et O affording, after quenching with water
2
and work-up, the target complex in 62% yield. Carrying out the
latter step in THF results in reduced yields (30%).
‡
9
264 | Dalton Trans., 2010, 39, 9264–9269
This journal is © The Royal Society of Chemistry 2010

Scheme 2 Improved three-step synthesis of Cp
Preparation of Cp Ta(PHEt )(PEt ) (9)
We have previously reported the preparation of the phos-
2 3
TaH .
2 2
Scheme 4 Preparation of complex Cp TaH(PHEt ) (7).
2
2
2
17b
to those reported for the related compound Cp
2
Ta(H)
2
(PPh ).
2
The formation of 6 is in accord with our earlier conclusion
that deprotonation of complexes 2 always affords the dihydride
phosphide derivatives 3 as kinetic products (Scheme 3), even when
the thermodynamic product is a hydride phosphine complex of
type 4.
phido phosphine complex Cp Nb(PHPh )(PPh ) by the inser-
tion/deprotonation method developed by us and by the group
2
2
2
17
1
8,19
of Mo ¨ı se.
This approach is based on the facile insertion of
M–H to give cationic
chlorophosphines into the M–H bond of L
n
+
17c
phosphine complexes [L
metallocene trihydrides, Cp
of the insertion products [Cp
dihydride phosphide derivative Cp
n
M(PHR
2
)] . In the case of Group 5
Indeed, complex 6 turned out to be metastable and it slowly
2
MH
3
(M = Nb, Ta) deprotonation
+
rearranges into the final phosphine hydride Cp
2
Ta(H)(PHEt ) (7).
2
2
M(H)
2
(PHR
2
)] (2) gives either the
17b
The rearrangement of 6 to 7 was followed by NMR spectroscopy.
Linearization in the coordinates [-ln(Xtot - X)/Xtot/]/t suggests
2
M(H)
2
(PR
2
)
(3, for M =
M(H)(PHR
and for M =
M(H)(PHR ) are
well suited for the second insertion of chlorophosphine to give
Ta and R = Ph) or the phosphine hydride Cp
4, for M = Nb, R = Me, Et, Bu, Ph;
Ta, R = Me ) (Scheme 3). Complexes Cp
2
2
)
20
1
7a,c
the occurrence of a first-order reaction (Fig. 1), which most likely
(
18a
proceeds as intramolecular phosphide insertion into the Ta–H
2
2
bond. The formation of the Ta(V) species Cp
2
Ta(H)
2
(PPh ) (3)
2
+
compared with the Nb(III) species Cp Nb(H)(PHPh
2
2
) reflects the
the cationic bis(phosphine) derivative [Cp
2
M(PHR ) ] , which
2
2
greater stability of the M–H bond in the third transition series
as opposed to that in the second series. In turn, the formation of
after deprotonation affords the target phosphido complexes
17c,18a
Cp
ClPR¢
species [Cp
2
M(PHR
2
)(PR
2
).
In contrast, Cp
2
Ta(H)
2
(PPh ) reacts with
2
the Ta(III) complex Cp
Cp Ta(H) (PPh ) (3) can be explained by the greater stability of
the dative bond Ta←PHEt compared with the Ta←PHPh bond
and the greater stability of the single bond Ta–PPh compared
2
Ta(H)(PHEt
2
) (7) versus the Ta(V) species
2
at the phosphido centre, affording the cationic diphosphine
1
+
2
Ta(H)
2
(h -PPh
2
PR¢ )] , which upon the reaction with
2
2
2
2
17b
a base regenerates the starting dihydride phosphido complex.
2
2
2
21
with the Ta–PEt bond.
2
Fig. 1 The kinetic graph for rearrangement of Cp
2
TaH
2
PEt
2
to
Cp TaH(PHEt ). X represents the amount of rearranged product and Xtot
2
2
represents the total amount of Ta complexes.
2 2
Scheme 3 Insertion/deprotonation route to complexes Cp M(H)(PHR ),
Cp M(H) (PR ), and Cp M(PHR )(PR ).
2
2
2
2
2
2
Preparation of the target phosphino phosphide complex
It has been shown previously that deprotonation of [Cp
2
-
-
Cp
Addition of ClPEt
precipitation of the bis(phosphine) derivative [Cp
8), which after deprotonation with LiN(SiMe
2
Ta(PHEt
2
)(PEt
2
) (9) was accomplished according to Scheme 5.
to the hydride Cp Ta(H)(PHEt ) (7) results in
Ta(PHEt ]Cl
affords the red
+
Ta(H)
PPh ) (3),
Cp Ta(H) (PHMe
derivative Cp
2
(PHPh
2
)] affords the dihydride phosphide Cp
2
Ta(H)
2
2
2
2
17b
(
[
2
whereas the closely related deprotonation of
2
)
2 2
+
2
2
2
)] results in the formation of the phosphine
(
)
3 2
18a
2
Ta(H)(PHMe ). In this study we discovered that
2
product 9. Compound 9 was characterized by NMR and IR
spectroscopy.
+
deprotonation of the tantalocene complex [Cp
2
Ta(H)
5), formed upon the reaction of trihydride Cp TaH
, unexpectedly affords the dihydride phosphido complex
(PEt ) (6), as the first product (Scheme 4). Complex
was characterised by NMR spectroscopy. In particular, the
2
(PHEt
2
)]
(
2
3
with
ClPEt
2
Cp
2
Ta(H)
2
2
6
1
H NMR spectrum displays a doublet for two Ta–H protons at
2
-
-
0.99 ppm ( J(P–H) = 51 Hz), coupled to the phosphide signal at
3
1
61.2 ppm in the P NMR. These structural features are similar
2 2 2
Scheme 5 Preparation of complex Cp Ta(PHEt )(PEt ) (9).
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9264–9269 | 9265

Preparation of bimetallic complex 10
Table 1 Catalytic hydrosilylation of acetophenone with 10
We have previously reported the preparation of bis(phosphido)
bridged Nb/Rh ELHB by a reaction of the anionic complex
Entry
1
Silane
PhSiH
Time
22 h
Yield (%)
-
9
3
PhSiH
PhSiH(OCH(Me)Ph)
2
OCH(Me)Ph: 50%
: 50%
[
Cp
2
Nb(PPh
2
)
2
] with Rh salts. Our initial attempts to prepare
2
-
the analogous anionic bis(phosphido) precursor [Cp
2
Ta(PEt ) ]
2
2
2
3
4
5
MePhSiH
Me PhSiH
Et SiH
(EtO) SiH
2
3 h 40 min
PhSiHMeOCH(Me)Ph
by treatment of 9 with BuLi resulted in decomposition. We
noticed that attempts at preparing the related neutral Mo complex
2
3 h
3 h
3 h
NR
NR
NR
3
3
Cp
2
Mo(PPh
2
2
) were also unsuccessful, which was then attributed
to repulsion between the phosphorus and metal centred lone
t
10
22
Cp(Cl)Nb(m-NBu )(m-PPh )RhCp (12) a much shorter Nb–Rh
pairs. However, in situ reaction of Cp
Rh(m-Cl)(C , and LiN(SiMe
complex Cp
1)). Complex 10 was isolated in the form of red crystals and
2
Ta(PHEt
in THF gives the target
) (10) in 49% isolated yield (eqn
2
)(PEt
2
), 0.5 equiv.
2
bond (2.6744(2)) was found. The Ta–P distances of 2.5629(8) and
2.5583(8) A˚ in 10 are close to the Nb–P bond lengths in 11 (2.555
˚
6) and 2.602(5) A), but are longer than the Nb–P bond in 12
2.4137(5) A). The Rh–P(1) and Rh–P(2) bond lengths in 10
are 2.2082(8) and 2.2174(8) A, again very close to values found
[
2
H
Ta(PEt
4
)
2
]
2
)
3 2
2
2
2
)
2
Rh(h -C
2
H
4
(
(
(
˚
characterized by NMR spectroscopy and X-ray analysis.
˚
˚
for 11 (2.209(5) and 2.118(6) A) and noticeably shorter than the
˚
Rh–P bond (2.3790(12) A) in 12. These trends indicate stronger
(
1)
bonding of two metal fragments in the imido-phosphido bridged
complex Cp(Cl)Nb(m-NBu )(m-PPh
t
2
)RhCp (12) compared with
the bis(phosphido) bridged complexes 10 and 11. The ethylene
1
˚
The H NMR spectrum of 10 showed the presence of coordi-
C–C bond of 1.419(5) A in 10 is elongated as compared with the
2
˚
nated ethylene (doublet at 3.16 ppm, JRh–H = 1.7 Hz) and the Cp
normal C=C double bond (1.34 A) suggesting a significant extent
signal at 4.37 ppm. Crystals suitable for X-ray diffraction study
of back-donation from the formally Rh(0) centre.
◦
were obtained from a solution in diethyl ether kept at -40 C.
The molecular structure of 10 is shown in Fig. 2. The tantalum
atom has a typical geometry for a disubstituted metallocene,
Catalytic studies
23
The ability of rhodium phosphine complexes to catalyze hy-
drosilylation reactions is well established.
usually mediated by Rh(I) complexes and proceed, after the Si–H
oxidative addition, via intermediate formation of Rh(III) species.
We reckoned that the bimetallic complex 10 featuring a formally
Rh(0) centre (see the canonical form A in Scheme 1) and an easily
oxidizable Ta–Rh bond could facilitate the Si–H oxidative addition
and presumably possess a superior catalytic activity.
whereas the rhodium centre is in a rare tri-coordinate ligand
25,26
◦
These reactions are
environment: the P1–Rh1–P2 bond angle is 117.25(3) and the
◦
phosphido–Rh1–X bond angles are 25 120.2 and 122.4 (X =
27
centre of the C–C bond). Both metals are linked by two bridging
phosphido ligands. Analogous structure has been previously
2
found for the Nb/Rh complex Cp¢
2
Nb(m-PPh
2
)
2
Rh(h -C
2
H )
4
9
(
11), whose metric parameters are very close to those of 10. The
short Ta–Rh distance of 2.8582(3) A indicates the presence of a
metal–metal bond (the sum of the metallic radii is 2.775 A).
˚
24
Hydrosilylation of acetophenone catalyzed by 10 (3% in ben-
zene) was studied. The course of the reaction was monitored
˚
˚
In 11, the Nb–Rh bond was marginally longer (2.869(2) A),
1
by H NMR spectroscopy by following the disappearance of
whereas in the related imido-phosphido bridged Nb/Rh complex
signals of the starting materials and appearance of new peaks
due to products. The results are presented in Table 1. A primary
silane (PhSiH ) exerts only sluggish hydrosilylation (entry 1),
3
affording a mixture of mono- and bis(hydrosilylation) products.
The latter observation suggests that the initially formed secondary
silane PhSiH
of PhSiH . And indeed, the secondary silane MePhSiH
about seven times greater activity than PhSiH (entry 2). However,
2
OCH(Me)Ph competes effectively with the excess
3
2
showed
3
trisubstituted silanes, including the tris(ethoxy)silane, were not
active under these conditions. For the previously studied bimetallic
t
complex Cp
2
Nb(=NBu )(m-PPh
2
)Rh(Cl)(COD) the order of ac-
was faster than
(2 h vs. 5 h, respectively). To our disappointment,
complex 10 happens to be less reactive in catalytic hydrosilylation
of acetophenone with MePhSiH than the phosphine-free Rh
(2 h at 3% load).
tivity was reverse: the hydrosilylation with PhSiH
3
10
with MePhSiH
2
2
complex [(m-Cl)RhCOD]
2
◦
Fig. 2 Selected bond distances ( A˚ ) and angles ( ) for compound
1
2
2
0: Ta1–Rh1 2.8582(3), Ta1–P1 2.5629(8), Ta1–P2 2.5583(8), Ta1–Cp1
.081, Ta1–Cp2 2.100, Rh1–P1 2.2082(8), Rh1–P2 2.2174(8), Rh1–C19
.124(3), Rh1–C20 2.128(3), P1–Ta1–P2 95.09(2), Ta1–P1–Rh1 73.18(2),
Conclusions
+
Deprotonation of the cationic complex [Cp
2
Ta(H
2
)(PEt
2
)] (5)
Rh1–P2–Ta1 73.13(2), P1–Rh1–P2 117.25(3). Hydrogen atoms are omitted
for clarity.
initially affords the dihydrido phosphide Cp
which slowly re-arrangers into the hydride-phosphine derivative
2
Ta(H
2
)(PEt ) (6)
2
9
266 | Dalton Trans., 2010, 39, 9264–9269
This journal is © The Royal Society of Chemistry 2010

-
1
-1
Cp
pare the phosphido-phosphine complex Cp
which was then employed as a metalaphosphine ligand to the
2
Ta(H)(PHEt
2
) (7). The latter compound was used to pre-
IR (nujol): nP–H = 2338 cm , nTa–H = 1771 cm . Anal. Calcd for
23ClTa: C, 38.33; H, 5.28. Found: C, 38.51; H, 5.37.
2
Ta(PEt )(PHEt ) (9)
2
2
14
C H
2
rhodium/olefin fragment Rh(h -C
bimetallic species Cp Ta(m-PPh
complex was found to catalyze the hydrosilylation of acetophe-
2
H
4
) in the preparation of the
Observation of Cp TaH (PEt ) (6)
2
2
2
2
2
2
)
2
Rh(h -C
2
H ) (10). The latter
4
A solution of LiN(SiMe
3
)
2
(0.134 g, 0.798 mmol) in 10 mL of
THF was added to a suspension of [Cp
2
TaH
2
(PHEt )]Cl (0.350 g,
2
none by PhMeSiH
studiedcomplexes Cp
Cl)RhCOD]
2
, but more sluggishly than the previously
t
0.798 mmol) in 15 mL of THF to give an orange mixture. Stirring
continued until all precipitate dissolved. THF was removed under
vacuum and the residue was extracted by 20 mL of toluene.
The solution was filtered through a microfiber glass filter and
the volatiles were removed under vacuum, leaving an orange
substance. NMR showed the presence of a mixture of 6 and
Nb(=NBu )(m-PPh
)Rh(Cl)(COD)and [(m-
2
2
2
.
Experimental
All manipulations were carried out, using conventional inert
atmosphere glove-box and Schlenk techniques. Solvents were
dried by Innovative Technology Grubbs-type columns. Unless
otherwise stated, the NMR parameters are those obtained with
Cp
2
TaH(PHEt
2
) (7) in the ratio 9 : 10. This mixture was dissolved
◦
in a minimum amount of pentane and cooled to -30 C to produce
a beige precipitate. Cold solution was decanted, and the residue
was washed twice by 5 mL of cold pentane and dried under
vacuum. The material thus obtained was used for the kinetic study
of the conversion of 6 to 7.
1
13
31
Bruker DPX-300 instrument ( H: 300 MHz; C: 75.5 MHz; P:
21.5 MHz) at room temperature and referenced to the residual
1
1
3
13
proton signal (or C nucleus in case of the C NMR) of the
solvent. Selected NMR parameters were obtained with Bruker
1
3
6
: H NMR (C
6
D
6
): d 4.69 (s, 10H, Cp), 1.82 (q, JH–H = 7.6 Hz,
3
3
4
-
H, CH
2
), 1.48 (dt, JH–H = 7.6 Hz, JP–H = 15.3 Hz, 6H, CH
3
),
).
1
31
Avance AV600 spectrometer ( H: 600 MHz; P: 243.0 MHz), as
specified in the text below. IR spectra were measured on ATI
Mattson FTIR spectrometer. Elemental analyses were carried out
2
31
0.99 ppm ( J(P–H) = 51 Hz). P NMR (C
6
6
D ): d -61.2 (s, PEt
2
Preparation of Cp
2
TaH(PHEt
2
) (7)
by the analytical laboratories of the University of Toronto and
t
McMaster University. H
2
NBu , pyridine, and silanes were pur-
A solution of LiN(SiMe ) (0.52 g, 3.08 mmol) in 40 mL of
3
2
chased from Sigma-Aldrich. [Rh(m-Cl)(C
2
15
H
and Cp
4
)]
2
was obtained from
THF was added to a suspension of [Cp TaH (PHEt )]Cl (1.35 g,
2
2
2
t
t
16
Strem. Complexes (Bu N=)Ta(Cl)
(Py)
Ta(=NBu )Cl
3
2
2
3.08 mmol) in 60 mL of THF. The initially white suspension
turned dark orange-red and most of the precipitate dissolved.
The mixture was left under stirring for 22 h and then filtered
through a microfiber glass filter to remove the precipitate. Volatiles
were removed under vacuum to yield 1.19 g of a reddish solid.
were prepared according to literature methods.
13,14
Improved synthesis of Cp
2
TaH (1)
3
1
3
00 mL of Et
2.6 mmol) and Cp
2
O was added to a mixture of LiAlH
4
(1.24 g,
This was purified further to remove any remaining LiN(SiMe
3 2
)
t
Ta(=NBu )Cl (3.39 g, 8.16 mmol). This brown
2
by dissolving the product in pentane and adding four drops of
degassed water. The mixture was vigorously stirred for 5 min,
then filtered through Celite and the Celite pad was washed with
mixture was left under stirring for 20 h. After this time, degassed
distilled water was added slowly to the mixture over the course
of 30 min. This caused the evolution of heat and the production
of hydrogen gas. The water addition was stopped when the brown
mixture turned white and the solid began to form slurry and stick
to the walls and bottom of the Schlenk tube. The slightly yellow
solution above the white slurry was decanted and the slurry was
3
0 mL of pentane. The solvent was removed from the filtrate
under vacuum to give a red solid. Yield of Cp TaH(PHEt ): 0.78 g
): d 5.14 (d, JP–H = 232.3 Hz,
H, P–H), 4.34 (bs, 10H, Cp), 1.37 (m, 2H, CH ), 1.14 (m, 2H,
2
2
1
1
(
1.94 mmol, 63%). H NMR (C
6
D
6
1
2
1
CH
2
), 0.95 (m, 6H, CH
3
), -9.46 (d, JP–H = 19.2 Hz, 1H, Ta–H).
thoroughly washed with 3 ¥ 10 mL of Et
removed under vacuum from combined fractions to yield a pale
2
O. The solvent was
13
1
C NMR (C
6
D
6
): d 78.3 (s, Cp), 24.2 (d, JP–C = 24.1 Hz, CH
2
),
).
2
31
1
1.7 (d, JP–C = 2.3 Hz, CH
3
). P NMR (C
6
6
D ): d 14.0 (s, PEt
2
1
yellow solid. Yield of Cp
2
TaH
): d 4.57 (s, 10, Cp), -1.63 (t, JH–H = 9.6 Hz, 1, TaH), -3.00
d, JH–H = 9.6 Hz, 2, TaH).
3
: 1.58 g (5.03 mmol, 62%). H NMR
-1
-1
IR (nujol): nP–H = 2338 cm , nTa–H = 1704 cm . Anal. Calc. for
2
(
(
C
6
D
6
C H
14
22TaP: C, 41.80; H, 5.51. Found: C, 41.57; H, 5.80.
2
Preparation of [Cp
2
Ta(PHEt ) ]Cl (8)
2
2
Preparation of [Cp
2
TaH
2
(PHEt )]Cl (5)
2
ClPEt
2
(0.20 ml, 1.61 mmol) was added to a 50 mL solution of
) (0.59 g, 1.46 mmol) in hexane. Immediately, an
To a solution of Cp
was added ClPEt (0.44 mL, 3.65 mmol) causing the formation of
a white voluminous precipitate. The mixture was stirred for 5 min
and then the Et O layer was filtered off. The white precipitate
was washed with 20 mL of Et O and the solution was once again
filtered off. The precipitate was dried under vacuum. Yield of
2
TaH
3
(1.15 g, 3.65 mmol) in 60 mL of Et
2
O
Cp TaH(PHEt
2
2
2
orange precipitate formed. It was stirredfor 5minandthen filtered.
The precipitate was washed with 10 mL of hexane and dried under
vacuum to give a light orange powder. Yield of [Cp
2
2
Ta(PHEt
): d 4.99 (t, 10H, Cp,
), 1.18 (m, 12H, CH ), 5.01 (q,
): d 5.0 (s, Cp),
2
)
2
]Cl:
1
2
0.732 g (1.39 mmol, 95%). H NMR (CDCl
3
3
J
P–H = 3.0 Hz), 1.86 (m, 8H, CH
2
3
1
1
13
[Cp
2
TaH
2
(PHEt
2
)]Cl: 1.47 g (3.36 mmol, 92%). H NMR (CDCl
3
):
2H, P–H, JP–H = 326.5 Hz). C NMR (CDCl
3
1
1
2
31
d 5.73 (bs, 10H, Cp), 4.98 (dm, 1H, P–H, JP–H = 351.7 Hz), 1.88
-0.7 (d, JP–C = 2.4 Hz, CH
2
), -1.4 (d, JP–C = 0.5 Hz, CH
3
). P
2
-1
-1
(
m, 4H, CH
2
), 1.19 (m, 6H, CH
3
), -1.47 (d, 2H, JP–H = 70.5 Hz).
NMR (CDCl
3
): d -2.0 (s, PEt). IR (nujol, cm ): vP–H = 2299 cm .
1
3
1
C NMR (CDCl
3
): d 91.8 (s, Cp), 21.0 (d, JP–C = 29.9 Hz, CH
2
),
Anal. Calc. for C18
H, 6.03.
H
32ClP Ta: C, 41.04; H, 6.12. Found: C, 40.74;
2
2
31
1
1.1 (d, JP–C = 5.8 Hz, CH
3
). P NMR (CDCl
3
): d -15.1 (s, PEt).
This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 9264–9269 | 9267

Preparation of Cp
2
Ta(PHEt
2
)(PEt
2
) (9)
Table 2 Crystal and structure refinement data for 10
To a suspension of [Cp
5
1
mixture turned dark red. It was stirred for 2 h and then the solvent
was removed under vacuum to give a dark red solid. Yield of
2
Ta(PHEt
0 mL of THF was added a solution of LiN(SiMe
.39 mmol) in 20 mL of THF. The precipitate dissolved and the
2
)
2
]Cl (0.37 g, 0.70 mmol) in
10
3 2
)
(0.23 g,
Empirical formula
Formula weight
Colour, habit
Crystal size/mm
Crystal system
Space group
20 34 2
C H P RhTa
620.27
Red, block
0.34 ¥ 0.26 ¥ 0.22
Triclinic
1
Cp
2
Ta(PHEt
2
)(PEt
2
): 0.21 g (0.43 mmol, 62%). H NMR (C
6
6
D ):
P1
1
d 4.47 (dq, 1H, JP–H = 309.1 Hz), 4.28 (bs, 10H, Cp), 1.60 (m,
Unit cell dimensions:
4
H, CH
2
), 1.43 (m, 6H, CH
). P NMR (C
3
), 1.50 (m, 4H, CH
2
), 0.83 (m, 6H,
): d 8.9 (d, JP–P = 17.0 Hz, PHEt ), -45.2
). Anal. Calc. for C18 Ta: C, 44.09;
˚
a/A
9.4251(6)
9.8107(6)
13.4457(8)
69.198(2)
72.757(2)
64.751(2)
1035.64(11)
2
1.989
0.623
604
Bruker SMART
123(2)
(0.71073) Mo-Ka
w
0.3
3
1
2
CH
3
2
6
D
6
2
b/A˚
c/A
˚
(
d, JP–P = 17.0 Hz, PEt
2
H
31
P
2
◦
a/
H, 6.37. Found: C, 44.41; H, 6.43.
◦
b/
◦
g /
2
3
Volume/A
˚
Synthesis of Cp
A solution of LiN(SiMe
2
Ta(l-PEt
2
)
2
Rh(g -C
2
4
H ) (10)
Z
Density (calculated), g cm-
3
3
)
2
(0.054 g, 0.323 mmol) in 5 mL of
Ta(PEt) (PHEt) (0.157 g,
(0.053 g, 0.159 mmol) in
0 mL of THF. After 30 min, THF was removed and the solid
Absorption coefficient, mm-
1
THF was added to a mixture of Cp
2
2
2
F(000)
0
.32 mmol) and [Rh(m-Cl)(C
2
H
4
)
]
2 2
Diffractometer
T/K
1
Radiation, (l/A
˚
),
was extracted with ether giving a dark red solution and a brown
solid. The solution was cooled to -20 C to produce red crystals
◦
Scan mode
Scan step (w)/
Time per step/s
◦
1
(
0.097 g, 49% yield). H NMR (300 MHz, C
6
D
6
, ppm): d 1.40 (dt,
),
), 4.37 (s, 10H, Cp). H NMR
15
3
2
◦
J
H–H = 7.5 Hz, JP–H = 14.0 Hz, 12H, Et), 2.00 (m, 8H, CH
2
Theta range for data collection/
Index ranges
1.64 to 29.95
-12 ≤ h ≤ 12
-12 ≤ k ≤ 13
2
1
3
.16 (d, JRh–H = 1.7 Hz, 4H, C
2
H
4
3
2
(600 MHz, C
6
D
5
CD
3
, ppm): d 1.43 (dt, JH–H = 7.4 Hz, JP–H =
-
18 ≤ l ≤ 18
3
2
3
1
3.9 Hz, 12H, Et), 1.92 (m, JH–H = 7.4 Hz, JP–H = 15.6 Hz, JRh–H
Reflections collected
Independent reflections
Absorption correction
Max. transmission
Min. Transmission
Refinement method
6867
3
2
~
2 Hz, 4H, CH
2
), 2.00 (m, JH–H = 7.4 Hz, JP–H = 14.3 Hz,
Rh–H ~ 2 Hz, 4H, CH ), 3.05 (bs, 4H, C ), 4.39 (s, 10H, Cp).
H NMR (300 MHz, THF-D
, ppm): 8 1.41 (dt, JH–H = 5.0 Hz,
Me), 2.30
), 4.88 (s, 10H, Cp). C NMR (75.5 MHz, C
), 31.7
), 88.8 (Cp). P NMR (121.5 MHz, C
4843 [R(int) = 0.0142]
3
Multi-scan
J
2
2
H
4
0.2258
0.3410
1
2
3
8
2
J
P–H = 13.8 Hz, 12H, Et), 1.99 (q, J = 5 Hz, 8H, CH
2
Full-matrix least-squares on F
(SHELXTL-Plus)
4843/0/217
1.034
1
3
(
bs, 4H, C
2
H
4
6
6
D ,
Data/restraints/parameters
Goodness-of-fit on F
Final R indices [I > 2s(I)]
R indices (all data)
ppm): d 13.1 (Me), 24.6 (dd, J = 3.4 Hz, J = 5.3 Hz, CH
2
2
3
1
(
d, JRh–C = 9.8 Hz, C
2
H
4
6
6
D ,
R
l
l
= 0.0215, wR
2
= 0.0541
1
31
ppm): d 167.3 (d, JP–Rh = 155.5 Hz, PEt
2
). P NMR (243.0 MHz,
). Anal. Calcd
RhTa: C, 38.73; H, 5.52. Found: C, 38.94; H, 5.75.
R
= 0.0230, wR
2
= 0.0547
Largest diff. peak and hole/e A
˚
-3
1.484 and -1.239
THF-D
for C20
8
, ppm): d 167.5 (d, 1.JP–Rh = 155.5 Hz, PEt
2
H
34
P
2
General procedure for hydrosilylation of PhC(O)CH
3
28
detector at 123 K. The crystallographic data and the character-
istics of structure solution and refinement are given in Table 2.
The structure factor amplitudes for all independent reflections
were obtained after the Lorentz and polarization corrections.
Complex 10 (0.002 g, 0.003 mmol, 3.0 mol%) was dissolved
in 0.6 mL of C . Silane was added [(OEt) SiH (30.0 ml,
SiH (13.0 ml, 0.105 mmol), MePhSiH (15.0 ml,
.109 mmol), Me PhSiH (17.0 ml, 0.111 mmol), and Et SiH
(12.0 ml,
.103 mmol). The reaction was monitored by H NMR spec-
troscopy by observing the disappearance of the starting materials
and appearance of products. There was no reaction of PhC(O)CH
with (OEt) SiH, Me PhSiH, or Et SiH in the presence of 1 in the
course of 3 h.
Hydrosilylation of PhC(O)CH
6
D
6
3
0
0
.164 mmol), Ph
3
2
29
The Bruker SAINT program was used for data reduction.
An absorption correction based on measurements of equivalent
2
3
(
0
17.0 ml, 0.106 mmol)] followed by PhC(O)CH
3
30
1
reflections was applied (SADABS). The structures were solved
3
1
by direct methods and refined by full-matrix least squares
2
2
2
procedures, using w(|F
o
| - |F |) as the refined function. All
c
3
non-hydrogen atoms were found from the difference electron
density map and refined with anisotropic thermal parameters,
whereas all hydrogen atoms were refined using the “riding”
model.
3
2
3
3
with PhSiH
3
. Reaction time:
2
5
2 h. Product: PhSiH
0%.
2
OCH(Me)Ph, 50%; PhSiH(OCH(Me)Ph) ,
2
Hydrosilylation of PhC(O)CH
3
with MePhSiH . Reaction time:
2
3
h 40 min. Product: PhSiHMeOCH(Me)Ph.
Acknowledgements
GIN thanks the Research Corporation for financial support
and the CFI/OIT for a generous equipment grant. LGK and
JAKH thank the Royal Society (London) for a Joint Research
Grant.
Crystal structure determination
A crystal of 10 was coated with polyperfluoro oil and mounted
on the Bruker Smart three-circle diffractometer with CCD area
9
268 | Dalton Trans., 2010, 39, 9264–9269
This journal is © The Royal Society of Chemistry 2010

Notes and references
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Dalton Trans., 2010, 39, 9264–9269 | 9269