New studies on the reactivity of hydride-containing niobocene complexes towards insertion and protonation processes

Article abstract of DOI:10.1002/1099-0682(200007)2000:7<1437::AID-EJIC1437>3.0.CO;2-J

The trihydride complex [Nb(η⁵-C₅H₄SiMe₃)₂(H)₃] (1) reacts with diphenylphosphane to afford the monohydride [Nb(η⁵- C₅H₄SiMe₃)₂(H)(PHPh₂)] (3). The synthesis of complex 3 has also been achieved from the initial formation of the phosphonium salt [Nb(η5- C₅H₄SiMe₃)₂(H)₂(PHPh₂)]Cl (2) by reaction of the trihydride complex [Nb(η⁵-C₅H₄SiMe₃)₂(H)₃] (1) with chlorodiphenylphosphane, followed by deprotonation of this salt in aqueous NaOH. Protonation of complex 3 at low temperature with a slight excess of CF₃COOH or CF₃COOD leads to the η²- dihydrogen complex [Nb(η⁵-C₅H₄SiMe₃)₂(η²-H₂)(PHPh₂)]CF₃CO₂ (4) or its monodeuterated isotopomer [Nb(η⁵-C₅H₄SiMe₃)₂(η²- HD)(PHPh₂)]CF₃CO₂ (5). When the temperature is increased to room temperature, complexes 4 and 5 transform into the transoid dihydrides [Nb(η⁵-C₅H₄SiMe₃)₂(H)₂(PHPh₂)]CF₃CO₂ (6) and [Nb(η⁵- C₅H₄SiMe₃)₂(H)₂(PDPh₂)]CF₃CO₂ (7), respectively. Complex 3 undergoes an insertion of CS₂ into the niobium-hydrogen bond to give the η¹- dithioformato complex [Nb(η⁵-C₅H₄SiMe₃)₂(PHPh₂)(η¹-S-S(S)CH)] (8). This complex could be detected by NMR spectroscopy but could not be isolated due to rapid conversion into the η²-dithioformato complex [Nb(η⁵- C₅H₄SiMe₃)₂(η²-S,S-SSCH)] (9) by loss of the phosphane molecule. Complex 3 also reacts with CO₂ to give the η²-formato complex [Nb(η⁵- C₅H₄SiMe₃)₂(η²-O,O-OOCH)](10); in this case the η¹-formato complex could not be detected. The reagent ClPPh₂ very smoothly inserts into the Nb- H bond of the complexes [Nb(n⁵-C₅H₄SiMe₃)₂(H)(L)] [L = PHPh₂, CN(xylyl), CO; xylyl = 2,6-dimethylphenyl], yielding the new ionic complexes [Nb(η⁵-C₅H₄SiMe₃)₂(PHPh₂)(L)]C1 [L = PHPh₂ (11), CN(xylyl) (12), CO (13)]. All the complexes described have been characterized by analytical and spectroscopic methods.

Full text of DOI:10.1002/1099-0682(200007)2000:7<1437::AID-EJIC1437>3.0.CO;2-J

FULL PAPER
New Studies on the Reactivity of Hydride-Containing Niobocene Complexes
Towards Insertion and Protonation Processes
[a]
[a]
[a]
´
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Antonio Antinolo,* Fernando Carrillo-Hermosilla, Juan Fernandez-Baeza,
[a]
[a]
[a]
[a]
´
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Santiago Garcıa-Yuste, Antonio Otero,* Javier Sanchez-Prada, and Elena Villasenor
Keywords: Niobium / Metallocenes / Hydrides / Dihydrogen / Protonations / Insertions
The trihydride complex [Nb(η5-C5H4SiMe3)2(H)3] (1) reacts
with diphenylphosphane to afford the monohydride [Nb(η5- η1-dithioformato complex [Nb(η5-C5H4SiMe3)2(PHPh2)(η1-S-
insertion of CS2 into the niobium−hydrogen bond to give the
C5H4SiMe3)2(H)(PHPh2)] (3). The synthesis of complex 3 has
S(S)CH)] (8). This complex could be detected by NMR spec-
also been achieved from the initial formation of the phos-
troscopy but could not be isolated due to rapid conversion
phonium salt [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]Cl (2) by reac- into the η2-dithioformato complex [Nb(η5-C5H4SiMe3)2(η2-
tion of the trihydride complex [Nb(η5-C5H4SiMe3)2(H)3] (1)
with chlorodiphenylphosphane, followed by deprotonation of
this salt in aqueous NaOH. Protonation of complex 3 at low
temperature with a slight excess of CF3COOH or CF3COOD
leads to the η2-dihydrogen complex [Nb(η5-C5H4SiMe3)2(η2-
H2)(PHPh2)]CF3CO2 (4) or its monodeuterated isotopomer
[Nb(η5-C5H4SiMe3)2(η2-HD)(PHPh2)]CF3CO2 (5). When the
temperature is increased to room temperature, complexes 4
and 5 transform into the transoid dihydrides [Nb(η5-C5H4Si-
S,S-SSCH)] (9) by loss of the phosphane molecule. Complex
3 also reacts with CO2 to give the η2-formato complex
[Nb(η5-C5H4SiMe3)2(η2-O,O-OOCH)] (10); in this case the
η1-formato complex could not be detected. The reagent
ClPPh2 very smoothly inserts into the Nb−H bond of the com-
plexes [Nb(η5-C5H4SiMe3)2(H)(L)] [L = PHPh2, CN(xylyl),
CO; xylyl = 2,6-dimethylphenyl], yielding the new ionic com-
plexes [Nb(η5-C5H4SiMe3)2(PHPh2)(L)]Cl [L = PHPh2 (11),
CN(xylyl) (12), CO (13)]. All the complexes described have
Me3)2(H)2(PHPh2)]CF3CO2 (6) and [Nb(η5-C5H4SiMe3)2(H)2- been characterized by analytical and spectroscopic methods.
(PDPh2)]CF3CO2 (7), respectively. Complex 3 undergoes an
Introduction
Me3)2(H)(PHPh2)] (3) by thermal reaction of [Nb(η5-
C5H4SiMe3)2H3] (1) with PHPh2. In addition, and in keep-
ing with our interest in dihydrogen complexes,[6,7] we report
here the results for the low temperature protonation of the
new monohydride complex [Nb(η5-C5H4SiMe3)2(H)-
(PHPh2)] (3) and, for the first time, the deprotonation reac-
tion of the cationic species obtained in this kind of reaction
when the temperature is increased to room temperature.
Finally, the insertion of unsaturated molecules into the
metalϪhydride bond is considered as a fundamental chem-
ical step in several catalytic cycles and frequently leads to
reactive intermediates.[8] In connection with our recent
studies of metal-promoted activation of unsaturated molec-
ules such as heterocumulenes,[9] carbon disulfide,[10] carbon
dioxide,[11] and activated alkynes,[12] we also decided to ex-
plore the reactivity of the new hydride phosphanyl complex
3 with carbon disulfide and carbon dioxide. These reactions
have permitted the isolation of dithioformato- and formato-
derivatives as well as the insertion of ClPPh2 into the
NbϪH bond of the monohydride derivatives [Nb(η5-
C5H4SiMe3)2(H)(L)] [L ϭ PHPh2, CN(2,6-Me2C6H3), CO],
and this has allowed us to prepare new cationic NbIII spe-
cies.
Hydride complexes of transition metals represent one of
the most important classes of compounds due to their
chemical reactivity and importance in catalysis.[1] Further-
more, the chemistry of phosphorus-substituted early trans-
ition metal complexes has also recently received a great deal
of attention.[2] Several groups[3,4] have found that the trihyd-
rides [Cp2MH3] (M ϭ Nb, Ta) react with chlorophosphanes
PR2Cl to afford the phosphonium salts [Cp2MH2-
(PR2H)]Cl. Depending on the metal (Nb or Ta) and on the
nature of the phosphane substituent, deprotonation of these
salts leads to hydride(phosphane) [Cp2MH(PR2H)] or hy-
dride(phosphide) [Cp2MH2(PPh2)] metalloligands. As part
of a study of the electronic and steric influence of trimethyl-
silyl-substituted cyclopentadienyl ligands on the properties
of niobocene complexes, we have studied the reaction of the
trihydride niobocene complex [Nb(η5-C5H4SiMe3)2H3][5]
with ClPPh2 and the subsequent deprotonation of the phos-
phonium salt obtained. We have previously prepared[6] the
hydride(phosphane) niobocene complexes [Nb(η5-C5H4Si-
Me3)2(H)(PR3)] by heating the trihydride complex [Nb(η5-
C5H4SiMe3)2H3] (1) in the presence of the corresponding
phosphane PR3. We have now used this method to synthes-
ize the monohydride phosphane complex [Nb(η5-C5H4Si-
Results and Discussion
Reaction of [Nb(η5-C5H4SiMe3)2(H)3] With ClPPh2
The reaction of [Nb(η5-C5H4SiMe3)2(H)3] (1) with
ClPPh2 proceeds smoothly to give quantitatively the ionic
[a]
´
´
´
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Departamento de Quımica Inorganica, Organica y Bioquımica,
´
Facultad de Quımicas, Universidad de Castilla-La Mancha,
Campus Universitario, 13071-Ciudad Real, Spain
Fax: (internat.) ϩ 34-926/295-318
E-mail: aotero@qino-cr.uclm.es
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ1948/00/0707Ϫ1437 $ 17.50ϩ.50/0
1437

A. Antin˜olo et al.
FULL PAPER
complex [Nb(η5-C5H4SiMe3)2(H)2(PHPh2]Cl (2) as de-
picted in Equation (1).
Complex 2 immediately precipitates as grey voluminous
flakes after mixing Et2O solutions of [Nb(η5-C5H4Si-
Me3)2(H)3] (1) and ClPPh2 at room temperature. Even at
low temperature (253 K) the rate of the reaction is very fast.
The low solubility of complex 2 in hydrocarbons, ethers and
aromatic solvents means that the product can be isolated
very easily in an analytically pure form. However, it is suffi-
ciently soluble in acetone to allow its NMR spectrum to be
recorded. The ionic nature of complex 2 was confirmed by
Scheme 1. Formation of 3 by reaction of 2 with NaOH
measurement of the molar conductivity (ΛM ϭ 135 reaction was carried out in a two-phase system (water/tolu-
Ω
Ϫ1molϪ1), which is in agreement with a 1:1 electrolyte.[13] ene), which enabled easy extraction and isolation of the
Complex 2 was formed in high yield and was characterized product as a red oily material. The characterization of com-
by 1H and 31P NMR and IR spectroscopy. In the 1H NMR plex 3 was performed by NMR and IR spectroscopy. The
spectrum ([D6]acetone) only the symmetric isomer [Nb(η5- 1H NMR spectrum shows a high-field resonance at δ ϭ
C5H4SiMe3)2(H)2(PHPh2)]Cl was observed. The cyclo- Ϫ7.37 for the hydride ligand, which appears as a doublet
pentadienyl rings are equivalent and give rise to two broad (2JHP ϭ 29.30 Hz), whereas the PϪH resonance appears as
resonances (see Experimental Section) for an A2B2 spin sys- a doublet at δ ϭ 6.90 (1JHP ϭ 332 Hz). Three multiplets
1
tem in the H NMR spectrum, which indicates a symmet- can also be observed that integrate for 4, 2 and 2 protons,
rical disposition at the niobium centre with a rapid rotation respectively, and correspond to an AAЈBBЈ spin system.
1
of the phosphane moiety around the NbϪP bond. The H These signals are due to the cyclopentadienyl rings and are
NMR spectrum also shows a resonance due to the hydride in accordance with an asymmetrical environment for the
ligands at δ ϭ Ϫ2.16 and this value is similar to those re- niobium centre (see Experimental Section). Finally, the IR
ported for the equivalent hydride ligands in [Nb(η5-C5H4Si- spectrum shows two bands at ca. 1643 and 2281 cmϪ1
,
[6a]
Me3)2(H)2(L)]PF6
[L ϭ P(OR)3, PMe2Ph] and [M(η5- which correspond to ν(NbϪH) and ν(PϪH), respectively,
C5H5)2(H)2(PR3)]ϩ.[14] The hydride ligands are equivalent and confirm the existence of the coordinated phosphane
and show a single resonance that appears as a doublet due molecule.
to coupling with the phosphorus atom (2JHP ϭ 78.2 Hz).
The reaction of [Nb(η5-C5H4SiMe3)2(H)3] (1) with
The signal for the hydrogen atom of the PϪH group ap- ClPPh2 can be rationalized in terms of an insertion of the
3
pears as a doublet at δ ϭ 6.67 (1JHP ϭ 283 Hz). The JHH chlorophosphane into the NbϪH bond, followed by elim-
value could not be observed due to the broadness of the ination of the chloride ion and rearrangement of the molec-
signals. The 31P NMR spectrum shows a broad doublet at ule as shown in Scheme 2. The nature of the insertion pro-
δ ϭ 20 that corresponds to a second-order spin system due cess can be considered as an interaction of the empty d-
1
2
to the couplings JHP and JHP. The IR spectrum shows a orbitals on the phosphorous with the NbϪH σ-bond, a
ν(PϪH) band at ca. 2293 cmϪ1, which confirms the exist- situation that means a pentavalent phosphorus structure
ence of the coordinated phosphane molecule, and also a should be initially formed.
ν(NbϪH) band of medium intensity at ca. 1703 cmϪ1 (see
Deprotonation of 2 should initially occur at the more lab-
Experimental Section).
ile hydrogen atom, which is, according to the spectroscopic
A characteristic feature of complex 2 is the existence of data, the PϪH proton. This implies that deprotonation of
two acidic centres: the PϪH and the NbϪH bonds. The 2 should initially produce a dihydride(phosphide) complex.
reaction between complex 2 and an aqueous solution of However, such a complex could not be detected and prob-
NaOH in toluene affords only the hydride(phosphane) com- ably transforms rapidly into complex 3 through a hydride
plex 3 in good yield (75%); the corresponding phosphido shift into the vacant d-orbital at phosphorus (see
complex could not be observed (Scheme 1).
Scheme 3).
The tantalum phosphido complex Cp2TaH2(PPh2) has
Further experiments, which are described later in this pa-
been isolated by Nikonov et al. while the homologous ni- per, allowed us to confirm unequivocally that depro-
obium compound Cp2NbH2(PPh2) was not observed.[3] The tonation occurs at the PϪH bond. This is not unexpected
1438
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443

Hydride-Containing Niobocene Complexes
FULL PAPER
The reaction is similar to that previously reported[6a,7,10]
for the preparation of several families of niobocene com-
plexes [Nb(η5-C5H4SiMe3)2(H)(L)] (L ϭ π-acid ligand).
Complex 3 was isolated as a spectroscopically pure, air-
sensitive red oily material and the spectroscopic data are in
agreement with those recorded for the complex isolated by
the first method described in this paper. This one-step syn-
thesis gives a better yield (90%) and represents a cleaner
way of preparing complex 3.
Scheme 2. Proposed reaction pathway for the formation of 2
Protonation Reaction of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)]
(3)
Complex 3 was easily protonated with CF3COOH at low
temperature to give the corresponding cisoid dihydrogen-
containing complex 4 according to Equation (3).
When CF3COOD is used, the monodeuterated complex
5 is obtained [Equation (4)]:
Scheme 3. Proposed reaction pathway for the deprotonation of 2
as the PϪH bond is kinetically more labile than the
NbϪH bond.
Reaction of [Nb(η5-C5H4SiMe3)2(H)3] With PHPh2
These processes were carried out by adding a slight excess
We also prepared complex 3 in an alternative manner by of CF3COOH/D to a solution of complex 2 in [D6]acetone
reaction of [Nb(η5-C5H4SiMe3)2(H)3] with PHPh2. In fact, in an NMR tube at 183 K.
1
[Nb(η5-C5H4SiMe3)2(H)3] (1) reacts slowly (3 hours) with
The H NMR spectrum of 4 at low temperature shows a
PHPh2 in THF at ca. 70 °C to afford the complex [Nb(η5- dihydrogen resonance at ca. δ ϭ Ϫ4.57 that appears as a
C5H4SiMe3)2(H)(PHPh2)] (3). The initial step should be the doublet due to the H-P coupling (JHP ϭ 19.7 Hz). The sig-
formation of the coordinatively unsaturated 16-electron nal broadens at very low temperature but does not show
species [Nb(η5-C5H4SiMe3)2(H)] by thermolytic loss of H2, decoalescence. The high-field H{31P} NMR spectrum of 5
1
followed by coordination of the phosphane ligand [Equa- at 183 K shows two triplets (1:1:1) at ca. δ ϭ Ϫ4.7 due to
tion (2)].
the existence of two different rotamers; endo 5a and exo 5b
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443
1439

A. Antin˜olo et al.
FULL PAPER
to Crabtree’s proposal, the HϪH distance rHϪH in the co-
ordinated H2 ligand can be determined from the T1 meas-
urements. The observed relaxation, Robs, for 4 is the sum of
that due to the HϪH dipoleϪdipole interaction (RHϪH
)
and that due to all other effects (RO), which can be estim-
ated using the observed relaxation for 3 [Robs (3)], as a reas-
onable indication of the niobium and solvent contributions.
From this equation we calculated RHϪH ϭ 52.68 (µsϪ1).
Figure 1. Rotation process of the HD coordinated molecule
Using the Morris approximation,[16] we found that rHϪH
ϭ
ϭ
˚
˚
1.16 A assuming rapid rotation of dihydrogen and rHϪH
(Figure 1). Both isomers show a similar JHD coupling of
ca. 18.20 Hz.
These rotamers exist due to the fact that the rotation of
the coordinated HD molecule is frozen on the NMR time
scale at this temperature.[6a,7]
When the temperature is raised, the rotamers endo H 5a
and exo H 5b interconvert by rotation of the HD molecule.
Coalescence is reached at 225 K, and at this temperature it
is not possible to distinguish between the two isomers. At
263 K a single resonance (1:1:1 triplet) is observed at ca.
δ ϭ Ϫ4.70 for the HD fragment (Figure 2).
0.92 A assuming a slow rotation. These values are in agree-
ment with the JHϪD value measured for complex 5 and in-
dicate significant stretching of the coordinated HϪH bond.
Similar results were found for the related compounds
[Nb(η5-C5H4SiMe3)2(η2-HD)(L)]ϩ [L ϭ P(OEt)3, PMe2-
Ph].[6a]
After low-temperature protonation the temperature was
raised to room temperature and 4 and 5 transformed into
the transoid isomers [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]-
CF3CO2 (6) and [Nb(η5-C5H4SiMe3)2(H)2(PDPh2)]-
CF3CO2 (7), respectively, through an irreversible process.
Complex 6 shows similar spectroscopic data to complex 2,
with the counterion being the only difference between the
two. Complex 7 also shows very similar spectroscopic data
and these are in agreement with a symmetrical disposition
of the niobium centre, showing an A2B2 spin system in the
1H NMR spectrum for the cyclopentadienyl ligands. Thus,
1
the H{31P} NMR spectrum shows a singlet resonance at
δ ϭ Ϫ1.76 due to the hydride ligands; no resonance due to
a possible PH moiety is observed. Moreover, the 31P NMR
spectrum shows a 1:1:1 triplet resonance due to coupling
with the deuterium atom (1JPD ϭ 34 Hz). This signal al-
lowed us to confirm the existence of the PϪD bond for
complex 7.
The formation of complexes 6 and 7 could be considered
to be the result of an oxidative addition of a coordinated
dihydrogen molecule to give a cisoid dihydride derivative
that transforms rapidly into the transoid isomer. According
to the results obtained, the cisoidϪtransoid isomerization
may involve the phosphorus atom, as shown in Scheme 4.
Figure 2. High-field 1H{31P} NMR spectrum (300 MHz) of 5 at
variable temperature; the point denotes the presence of residual
complex 4
This phenomenon allowed the estimation of the free en-
ergy of activation of the internal rotation at the coalescence
temperature (∆G϶ ഠ 10.43 kcal/mol K). Similar values have
been observed previously for the related complexes [Nb(η5-
C5H4SiMe3)2(η2-HD)(PMe2Ph)]ϩ (∆G‡ ഠ 11 kcal/mol
K)[6a] and [Nb(η5-C5H4SiMe3)2(η2-HD)(CNR)]ϩ (∆G‡
ഠ
8Ϫ9 kcal/mol K).[7] As a consequence of this high barrier,
rotation of the HD molecule can be blocked on the NMR
time scale. The value of the JHD coupling constant
(18.2 Hz) verifies the presence of an HϪD bond and is
strong evidence for the presence of a dihydrogen complex.[7]
Moreover, the observation of low longitudinal-relaxation
times, T1, is very useful in providing evidence for the exist-
ence of a dihydrogen ligand. The T1 values of the dihydro-
gen nuclei of 4, T1(H2), and the hydride ligand of complex
3, T1(H), were determined using the method described by
Crabtree et al.[15] The T1 minima were found to be 15.8 ms
at 215 K for 4 and 95 ms at 186 K for complex 3. According Scheme 4. Proposed reaction pathway for the formation of 7
1440 Eur. J. Inorg. Chem. 2000, 1437Ϫ1443

Hydride-Containing Niobocene Complexes
FULL PAPER
1
Isomerization of 5 may proceed by attack of the NbϪD
The most significant H NMR spectroscopic data for 8
bond at an empty d-orbital of the phosphorus atom. At the is the resonance at δ ϭ 12.33, which corresponds to the
same time the PϪH bond interacts with the niobium centre, CϪH group and appears as a doublet (4JPH ϭ 2 Hz). This
thus making possible the rearrangement of the molecule to coupling constant confirms the presence of the coordinated
give the transoid derivative 7.
phosphane. In addition, the 1H NMR spectrum shows four
When the reaction between 3 and CF3COOH/D in acet- multiplets for the cyclopentadienyl rings in accordance with
one is performed on a Schlenk-tube scale, the only isolated an asymmetrical environment for the niobium centre.
products are the transoid dihydrides 6 and 7. The low solu-
The reaction of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3)
bility of these complexes in hydrocarbons, ethers and aro- with CO2 in THF under 2.5 atm. of CO2 results in the
matic solvents enabled very easy isolation of the products formation of the η2-formato complex [Nb(η5-
as colourless, analytically pure solids.
C5H4SiMe3)2(η2-O,O-OOCH)] (10) (Scheme 5) as a brown,
The similarity between complexes 6 and 7 and the phos- air-sensitive oily product after appropriate workup. Com-
phonium salt 2, which was obtained by the reaction be- plex 10 was previously prepared by some of us using differ-
tween trihydride 1 and ClPPh2, led us to study their behavi- ent methods.[11] We have been unable to detect the η1-for-
our towards deprotonation reactions. Both complexes react mato complex due to the difficulties involved in carrying
with aqueous sodium hydroxide in toluene to give the previ- out test reactions on an NMR-tube scale. The spectroscopic
ously characterized hydridophosphane 3. This observation data of 10 agree with those previously described.[11]
confirms that deprotonation of complexes 2, 6 and 7 occurs
Reactivity of [Nb(η5-C5H4SiMe3)2(H)(L)] (L ؍ PHPh2,
at the PϪH(PϪD) bond, as discussed above.
CN(xylyl), CO) Towards ClPPh2
Reaction of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3) with CX2
(X ؍ S, O)
ClPPh2 very smoothly inserts into the NbϪH bond of
[Nb(η5-C5H4SiMe3)2(H)(L)] [L ϭ PHPh2, CN(xylyl), CO]
to give the ionic phosphanyl complexes [Nb(η5-C5H4Si-
Me3)2(PHPh2)(L)]Cl [L ϭ PHPh2 (11), CN(xylyl) (12), CO
(13)] (Scheme 6). These reactions can be rationalized in
terms of an electrophilic attack of the phosphorus atom
(which contains empty d orbitals) at the NbϪH bond, for-
ming a three-centre transition state that evolves with elim-
ination of chloride.
Insertion of CS2 into the NbϪH bond of [Nb(η5-C5H4Si-
Me3)2(H)(PHPh2)] results in the formation of an η1-dithi-
oformato intermediate [Nb(η5-C5H4SiMe3)2(PHPh2)(η1-S-
S(S)CH)] (8), which could not be isolated but could be de-
tected by 1H NMR spectroscopy. This complex rapidly
evolves by an elimination of phosphane (due to a substitu-
tion reaction of phosphane by the noncoordinated sulfur
atom) to give an η2-dithioformato complex [Nb(η5-
C5H4SiMe3)2(η2-S,S-SSCH)] (9) (Scheme 5). This complex
was isolated as an air-sensitive orange solid and was previ-
ously isolated and characterized by some of us.[10]
This behaviour has previously been found in the reactions
of some complexes of the type [Nb(η5-C5H4SiMe3)2(H)(L)]
with CS2.[10]
Complexes 11Ϫ13 were formed in high yield (ഠ 85%)
as red solids after precipitation from Et2O. The H NMR
spectrum of 11 reveals the equivalence of the cyclo-
pentadienyl rings, with two pseudotriplets observed at δ ϭ
5.36 and δ ϭ 5.50. In contrast, an asymmetrical environ-
ment for the niobium centre is observed for complexes 12
1
Scheme 5. Proposed reaction pathway for the formation of 9 and 10
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443
Scheme 6. Insertion process of ClPPh2 into an NbϪH bond
1441

A. Antin˜olo et al.
FULL PAPER
1
(C5H4, C1), 91.2 (C5H4), 89.1 (C5H4), 88.7 (C5H4), 83.4 (C5H4),
134.3 (s, Ph, C1), 133.3 (Ph), 129.0 (Ph), 128.3 (Ph). Ϫ 31P NMR
(300 MHz, C6D6): δ ϭ Ϫ38.20 (d, JPH ϭ 322 Hz, PϪH).
and 13. In addition, the H NMR spectra of 11Ϫ13 show
a doublet resonance for the PϪH moiety (1JPH ഠ 370 Hz).
The IR spectra of 11Ϫ13 reveal the absence of an ν(NbϪH)
1
band and the existence of ν(PϪH) at ca. 2280 cmϪ1
.
Protonation of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3): Either
CF3COOH or CF3COOD was added to a [D6]acetone solution of
[Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3) in a 5 mm NMR tube at
183 K, to give either the dihydrogen complex [Nb(η5-
C5H4SiMe3)2(η2-H2)(PHPh2)]CF3CO2 (4) or its isotopomer
[Nb(η5-C5H4SiMe3)2(η2-HD)(PHPh2)]CF3CO2 (5).
In conclusion, several aspects of the reactivity of hydride-
containing niobocene species have been considered in the
work described here. In particular, the reactions of ClPPh2
towards hydride-niobocene complexes [Nb(η5-C5H4Si-
Me3)2(H)3] (1) and [Nb(η5-C5H4SiMe3)2(H)(L)] occur
through insertion of chlorophosphane into an NbϪH
bond. Furthermore, the protonation reaction of 3 at low
temperature gives an η2-dihydrogen complex, which evolves
at high temperature to the corresponding transoid dihydride
species. Further work in this field is in progress.
Preparation of [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]CF3CO2 (6) and
[Nb(η5-C5H4SiMe3)2(H)2(PDPh2)]CF3CO2 (7): To a solution of
[Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3) (0.30 g, 0.55 mmol) in 30 mL
of THF at 183 K was added CF3COOH or CF3COOD (42 µL,
0.55 mmol) by syringe. The solution was allowed to reach room
temperature and stirred for 2 h. The resulting solution was evapor-
ated to dryness. Complexes 6 and 7 were obtained as colourless
solids after precipitation with Et2O (yield: 80%).
Experimental Section
Preparation of [Nb(η5-C5H4SiMe3)2(η2-S,S-SSCH)] (9): To a solu-
tion of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3) (0.30 g, 0.55 mmol) in
THF (40 mL) was added CS2 (93.1 µL, 0.55 mmol) and the reac-
tion mixture was stirred for 1 h. The resulting solution was evapor-
ated to dryness to give a red oily material. Complex 9 was isolated
as an orange solid after precipitation from hexane (yield: 95%). Ϫ
1H NMR (300 MHz, CDCl3): δ ϭ 0.22 (s, 18 H, SiMe3), 5.05 (4
H, C5H4), 5.44 (4 H, C5H4), 4.17 (s, 1 H, SSCH). Ϫ 13C{1H} NMR
(300 MHz, CDCl3): δ ϭ 0.5 (SiMe3), 98.6 (C5H4, C1), 103.6 (C5H4),
106.9 (C5H4), 120.0 (SCHS). Ϫ C17H27NbS2Si2 (444.12): calcd. C
45.95, H 6.08; found C, 45.81, H 5.96.
General Remarks: All operations were performed under an inert
atmosphere using standard vacuum line (Schlenk) techniques. Solv-
ents were purified by distillation from the appropriate drying agents
before use. NMR spectra were obtained on a Varian Unity FT-300
and Varian Gemini FT-200 instruments. IR spectra were recorded
on a PerkinϪElmer PE 883 IR spectrophotometer. Elemental ana-
lyses were performed on a PerkinϪElmer 2400 microanalyzer.
[Nb(η5-C5H4SiMe3)2(H)3] was prepared as described previously.[5]
Preparation of [Nb(η5-C5H4SiMe3)2(H)2(PHPh2)]Cl (2): [Nb(η5-
C5H4SiMe3)2(H)3] (1) (0.30 g, 0.80 mmol) was dissolved in 40 mL
of Et2O to form a tan solution. To this solution was added ClPPh2
(180 µL, 1 mmol). A colourless precipitate formed immediately.
When sedimentation was complete, the colourless solution was fil-
tered and the residue washed twice with 10 mL of Et2O and dried
in vacuo. Complex 2 was isolated as a grey solid (yield: 90%). Ϫ
IR (KBr): ν(NbϪH) ϭ 1703 cmϪ1; ν(PϪH) ϭ 2293 cmϪ1. Ϫ 1H NMR
(300 MHz, CDCl3): δ ϭ 0.08 (s, 18 H, SiMe3), 4.76 (m, 4 H, C5H4),
Preparation of [Nb(η5-C5H4SiMe3)2(η2-O,O-OOCH)] (10): A THF
solution of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3) (0.30 g,
0.55 mmol) was saturated with CO2 (2.5 atm.) in a FischerϪPorter
bottle for 8 h at room temperature. The solution became increas-
ingly dark and a brown solution was finally obtained and then
evaporated to dryness. Complex 10 was obtained as an oily brown
material (yield: 90%). Ϫ IR (Nujol): νasym (CO2Ϫ) ϭ 1638 cmϪ1
;
νsym (CO2Ϫ) ϭ 1545 cmϪ1. Ϫ 1H NMR (300 MHz, C6D6): δ ϭ
Ϫ0.04 (s, 18 H, SiMe3), 4.14 (m, 4 H, C5H4), 5.68 (m, 4 H, C5H4),
7.47 (s, 1 H, O2CH). 13C{1H} NMR (300 MHz, C6D6): δ ϭ 0.1
(SiMe3), 107.8 (C5H4, C1), 105.0 (C5H4), 108.1 (C5H4), 184.3
(O2CH).
1
5.86 (m, 4 H, C5H4), 6.67 (d, JPH ϭ 283 Hz, 1 H, PϪH), Ϫ2.16
(d, 2JPH ϭ 78.20 Hz, 2 H, NbϪH), 7.33Ϫ7.45 (m, Ph). Ϫ 13C NMR
(300 MHz, CDCl3): δ ϭ Ϫ0.2 (SiMe3), 98.0 (C5H4, C1), 99.9
(C5H4), 97.2 (C5H4), 131.9 (s, Ph, C1), 130.9 (Ph), 128.9 (Ph). Ϫ
31P NMR (300 MHz, CDCl3): δ ϭ 20.00 (d, 1JPH ϭ 283 Hz, PϪH).
Ϫ C28H39ClNbPSi2 (590.45): calcd. C 56.86, H 6.60; found C 56.20,
H 6.45.
Preparation of [Nb(η5-C5H4SiMe3)2(PHPh2)(L)]Cl [L ؍ PHPh2
(11), CN(xylyl) (12), CO (13)]: To a solution of [Nb(η5-C5H4Si-
Me3)2(H)(L)] [L ϭ PHPh2, CN(xylyl), CO] (0.55 mmol) in 40 mL
of Et2O was added ClPPh2 (125 µL, 0.70 mmol) by syringe. A red-
orange precipitate formed immediately. When sedimentation was
complete the solution was filtered and the residue washed twice
with 20 mL of Et2O and dried in vacuo. Complexes 11, 12 and 13
Preparation of [Nb(η5-C5H4SiMe3)2(H)(PHPh2)] (3): (a) [Nb(η5-
C5H4SiMe3)2(H)3] (1) (0.30 g, 0.80 mmol) was dissolved in 40 mL
of THF to form a tan solution. To this solution was added PHPh2
(0.14 mL, 0.80 mmol) by syringe. The mixture was stirred at 343 K
for 4 h. The resulting red solution was evaporated to dryness. Com-
plex 3 was isolated as a red oily material after maintaining it under
vacuum for a lengthy period (yield: 95%). Ϫ (b) [Nb(η5-C5H4Si-
Me3)2(H)2(PHPh2)]Cl (2) (0.30 g, 0.51 mmol) in 30 mL of toluene
was treated with an excess (4 mL) of 0.5  aqueous NaOH. The
mixture was vigorously stirred. Within 1 h the precipitate had dis-
solved and the organic phase turned dark red. The toluene solution
was filtered and evaporated to dryness. Complex 3 was obtained as
were obtained as orange or red solids. Ϫ 11: IR (KBr): ν(PϪH)
ϭ
2297 cmϪ1. Ϫ H NMR (300 MHz, [D6]acetone): δ ϭ 0.05 (s, 18
H, SiMe3), 5.36 (m, 4 H, C5H4), 5.50 (m, 4 H, C5H4), 7.87 (d,
1JHP ϭ 362 Hz, 1 H, PϪH), 7.35Ϫ7.60 (m, Ph), 8.12 [s, 2 H, Hpara
(Ph)]. Ϫ 13C NMR (300 MHz, [D6]acetone): δ ϭ 0.1 (SiMe3), 102.9
(C5H4, C1), 92.5 (C5H4), 103.7 (C5H4), 135.7 (Ph, C1), 133.0 (Ph),
129.0 (Ph), 128.3 (Ph). Ϫ 31P NMR (300 MHz, [D6]acetone): δ ϭ
1
1
32.00 (d, JHP ϭ 362 Hz, PϪH). Ϫ C40H48ClNbP2Si2 (774.45):
a red oily material (yield: 75%). Ϫ IR (CsI): ν(NbϪH) ϭ 1643 cmϪ1
;
calcd. C 61.98, H 6.20; found C 62.10, H 6.18.
ν(PϪH) ϭ 2281 cmϪ1. Ϫ H NMR (300 MHz, C6D6): δ ϭ 0.26 (s,
1
18 H, SiMe3), 3.63 (pst, 2 H, C5H4), 4.03 (pst, 2 H, C5H4), 4.72
12: IR (KBr): ν(PϪH) ϭ 2280 cmϪ1; ν(CNAr) ϭ 2058 cmϪ1. Ϫ 1H
1
(m, 4 H, C5H4), 6.90 (d, JPH ϭ 322 Hz, 1 H, PϪH), Ϫ7.37 (d, NMR (300 MHz, [D6]acetone): δ ϭ 0.17 (s, 18 H, SiMe3), 5.36 (m,
2JPH ϭ 29.30 Hz, 2 H, NbϪH), 7.36Ϫ7.71 (m, Ph), 8.12 [s, 2 H,
Hpara (Ph)]. Ϫ 13C NMR (300 MHz, C6D6): δ ϭ 0.9 (SiMe3), 90.6 H, C5H4), 8.70 (d, 1JHP ϭ 387 Hz, 1 H, PϪH), 7.35Ϫ7.90 (m, Ph),
2 H, C5H4), 5.55 (m, 2 H, C5H4), 5.65 (m, 2 H, C5H4), 6.11 (m, 2
1442
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443

Hydride-Containing Niobocene Complexes
FULL PAPER
[4] [4a]
2.31 [CN(2,6-Me2C6H3)]. Ϫ 13C NMR (300 MHz, [D6]acetone):
δ ϭ 0.1 (SiMe3), 100.2 (C5H4, C1), 92.3 (C5H4), 100.0 (C5H4), 100.8
(C5H4), 102.4 (C5H4), 132.5 (Ph, C1), 133.0 (Ph), 129.0 (Ph), 127.6
(Ph), 19.4 [CN(2,6-Me2C6H3)], 248.0 [CN(2,6-Me2C6H3)]. Ϫ 31P
NMR (300 MHz, [D6]acetone): δ ϭ 38.50 (d, JHP ϭ 387 Hz,
PϪH). Ϫ C37H46NNbPSi2 (684.00): C 66.86, H 6.93; found C
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C5H4), 5.82 (m, 2 H, C5H4), 5.93 (m, 2 H, C5H4), 6.03 (m, 2 H,
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Yuste, A. Otero, S. Camanyes, F. Maseras, M. Moreno, A.
8.12 [s, 2 H, Hpara (Ph)]. Ϫ 13C NMR (300 MHz, [D6]acetone): δ ϭ
Ϫ0.5 (SiMe3), 102.9 (C5H4, C1), 97.0 (C5H4), 98.1 (C5H4), 100.6
(C5H4), 101.8 (C5H4), 131.5 (Ph, C1), 131.0 (Ph), 129.5 (Ph), 128.0
(Ph), 250 (CO). Ϫ 31P NMR (300 MHz, [D6]acetone): δ ϭ 38.00
(d, 1JHP ϭ 381 Hz, PϪH). Ϫ C29H37NbOPSi2 (581.16): C 62.03, H
6.60; found C 61.82, H 6.68.
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Received January 26, 2000
[I00027]
Eur. J. Inorg. Chem. 2000, 1437Ϫ1443
1443