Monocyclopentadienyl complexes of niobium, tantalum and tungsten containing heterodifunctional P,O ligands

Article abstract of DOI:10.1039/b202983a

The reactions of P,O type ligands with the half-sandwich complexes [(η-C₅R₅)MCl₄] (R₅ = H₅, Me₅, ⁱPrH₄; M = Nb, Ta, W) have been investigated. Monodentate P-adducts were obtained with the β-amidophosphine Ph₂PCH₂C(O)NPh₂, whereas in the case of the keto ligand Ph₂PCH₂C(O)Ph a spontaneous HCl elimination occurred to give direct access to the corresponding phosphinoenolate complexes. The crystal structures of [(η-C₅H₅)NbCl₃{PPh₂CH _---...C(_---...O)Ph}], [(η-C₅H₅)TaCl₃{PPh₂CH _---...C(_---...O)Ph}] and [η-C₅Me₅)TaCl₃{PPh₂CH _---...C(_---...O)Ph}] have been determined. Interestingly, the acetamido derived phosphine Ph₂PNHC(O)Me afforded O-adducts, which is an unusual bonding mode for a P,O ligand.

Full text of DOI:10.1039/b202983a

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Monocyclopentadienyl complexes of niobium, tantalum and tungsten
containing heterodifunctional P,O ligandsy
Xavier Morise,*a Malcolm L. H. Green,*b Pierre Braunstein,*a Leigh H. Reesb and Ino C. Veib
a
´
Laboratoire de Chimie de Coordination, UMR CNRS 7513, Universite Louis Pasteur, 4,
rue Blaise Pascal, 67070, Strasbourg Cedex, France. E-mail: morise@chimie.u-strasbg.fr,
braunst@chimie.u-strasbg.fr.
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford,
UK OX1 3QR. E-mail: Malcolm.Green@chemistry.oxford.ac.uk.
b
Received (in Montpellier, France) 21st March 2002, Accepted 27th May 2002
First published as an Advance Article on the web 13th September 2002
i
The reactions of P,O type ligands with the half-sandwich complexes [(Z-C5R5)MCl4] (R5 ¼ H5 , Me5 , PrH4 ;
M ¼ Nb, Ta, W) have been investigated. Monodentate P-adducts were obtained with the b-amidophosphine
Ph2PCH2C(O)NPh2 , whereas in the case of the keto ligand Ph2PCH2C(O)Ph a spontaneous HCl elimination
occurred to give direct access to the corresponding phosphinoenolate complexes. The crystal structures of
[(Z-C5H5)NbCl3{PPh2CHOC(OO)Ph}], [(Z-C5H5)TaCl3{PPh2CHOC(OO)Ph}] and [(Z-
C5Me5)TaCl3{PPh2CHOC(OO)Ph}] have been determined. Interestingly, the acetamido derived phosphine
Ph2PNHC(O)Me afforded O-adducts, which is an unusual bonding mode for a P,O ligand.
these complexes, the P,O ligands act either as P-monodentate
Introduction
phosphine or as a P,O-chelate, whereas O-monocoordination,
which may have been anticipated owing to the relatively hard
nature of molybdenum vs. late transition metals, was not
observed. Although ligands with carbonyl functions
(ketones,24–26 amides,27,28 acids/esters29,30) are known to coor-
dinate readily to groups 5 and 6 metals, there has been no
example reported, to the best of our knowledge, when a phos-
phine donor is also present in the ligand. This also applies to
somewhat related ligands, such as R2PNHP(O)R2 ,31 or even
Bifunctional P,O ligands, which combine a soft phosphine
moiety and a hard oxygen function, such as ester, amide or
ketone, remain the subject of numerous studies, owing to the
various properties and/or applications of their transition-
metal complexes.1–4 In metal complexes with these P,O
molecules both P-monocoordination and P,O chelation are
commonly found. The P,O chelate ligands give stable metal
complexes and due to the different properties of the P and O
ligand atoms they can strongly influence the stereoelectronic
properties at the metal centre.3 Furthermore, in late transition
metal complexes, the greater lability of the O-ligand atom
favours fluxional processes resulting from reversible O-atom
dissociation and recoordination.1–4 The O-atom dissociation
in these hemilabile ligands creates a vacant coordination site,
and conversely weak O-association can give rise to stabilisa-
tion of an otherwise coordinatively unsaturated species. For
this reason complexes with P,O ligands have been studied for
their catalytic properties,5–13 especially in reactions involving
the activation of small molecules.14–19
when the P atom is not available for coordination as in
32,33
We will present here a rare example of a
0
=
R3P NC(O)R .
P,O phosphine acting as a O-monodentate ligand in half-sand-
wich Nb, Ta and W complexes.
Anionic phosphino-enolates, formed from ketophosphines,
are also a well-developed group of P,O ligands.34–49 Interest
in this chemistry partly stems from the fact that nickel phos-
phino-enolate complexes catalyze the oligomerisation of ethy-
lene in a-olefins (Shell Higher Olefin Process).34,40,50,51
Substitutional modification of the phosphino-enolate ligands
can modify catalyst activity and the chain length distribu-
tion.49–52 Numerous phosphino-enolate complexes of group
8–10 metals have been synthesized and their reactivity stu-
died.35–39,41–46,49,53–58 For example, Rh(I) complexes in this
class are efficient catalysts for the transfer dehydrogenation
of alkanes to alkenes.59
As for their neutral counterparts, the early transition metal
chemitry of anionic P,O ligands has been little investigated.
The Z-arene-molybdenum complexes [(Z-C6H5R)Mo(Z-
C3H5){Ph2PXOC(OO)Ph-k2P,O}] or [(Z-C6H5R)Mo{Ph2P-
XOC(OO)Ph-k2P,O}2] (R ¼ H, Me; R0 ¼ Ph, NPh2 , Me;
X ¼ N, C) represent, to the best of our knowledge, rare exam-
ples of early transition metal complexes, containing a chelating
phosphinoenolate ligand.22,23 Very recently, Edwards et al.
reported the compound [(Z-C5H5)2Ti{OC(O)CH2PPh2}2], pre-
pared by treatment of [(Z-C5H5)2TiCl2] with the anion
Ph2PCH2C(O)Oꢀ.60 The titanocene and zirconocene com-
plexes of a camphor-derived phosphino-enolate have also been
In contrast to the wealth of late transition metal complexes
synthesized, which contain a b-keto-, ester- or amidophos-
phine ligand, there have been only a few studies on the early
transition-metal chemistry of these ligands and they have
mainly focused on molybdenum. Thus, the half-sandwich
complexes of the b-amidophosphine Ph2PCH2C(O)NPh2 1,
[(Z-C5H5)MoCl2{1-k2P,O}]
or
[(Z-C5Me5)MoCl2{1-
k2P,O}][BF4],20 and of the keto-functionalised N-pyrrolylphos-
phine Ph2PNHC4H3{C(O)Me}-2 (PpyrO), [(Z-C5H5)MoCl-
(CO)2{(PpyrO)-kP}]
and
[(Z-C5H5)Mo(CO)2{(PpyrO)-
k2P,O}][BF4],21 have been reported. More recently, we have
described the synthesis of Z-arene-molybdenum complexes,
such as [(Z-C6H5R)Mo(Z-C3H5){Ph2PXHC(O)R0-k2P,O}]-
[PF6] (R ¼ H, Me; R0 ¼ Ph, NPh2 , Me; X ¼ N, C).22,23 In
y Dedicated to Prof. P. Royo on the occasion of his 65th birthday,
with our warmest congratulations.
32
New J. Chem., 2003, 27, 32–38
DOI: 10.1039/b202983a
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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described.61 Further zirconocene phosphino-enolates derived
from the a-ketophosphine Ph2PC(O)R (R ¼ Me, Et) have
been prepared by Floriani et al.62,63
Here, we report the first investigations into the coordination
chemistry of P,O ligands, namely Ph2PCH2C(O)NPh2 1,
Ph2PCH2C(O)Ph 2 and Ph2PNHC(O)Me 3, with the half-
metallocene complexes [(Z-C5R5)MCl4]
4
(a: R5 ¼ H5 ,
M ¼ Nb; b: R5 ¼ H5 , M ¼ Ta; c: R5 ¼ Me5 , M ¼ Ta; d:
R5 ¼ iPrH4 , M ¼ W). The latter were chosen because they
represent versatile precursors for new materials, the design of
highly efficient catalysts for organic transformations and poly-
merization reactions64–68 or for W W triply bonded complexes
=
=
(4d),69 which have a remarkably rich chemistry.70 We will
show that under similar reaction conditions, the P,O ligands
1–3 lead to complexes in which they adopt either a P-mono-
dentate, an anionic P,O-chelating or, quite unexpectedly, a
neutral O-monodentate coordination mode.
Results and discussion
Half-sandwich complexes [(Z-C5R5)MCl4] 4a–d have Lewis
acid character and form mono-adducts [(Z-C5R5)MCl4(L)]
with neutral ligands such as L ¼ amines, phosphines or phos-
phites.71 Early studies led to the conclusion that adducts of
4a, [(Z-C5H5)NbCl4(L)] where L ¼ a tertiary phosphine or
phosphite, were labile in contrast to their tantalum analo-
gues.72–74 The niobium adducts [(Z-C5H4Me)NbCl4(L)]
(L ¼ PMe3 , PEt3 or P(OMe)3) slowly decompose in solu-
tion.75 Recently, Poli et al. showed that adducts of 4a with
PMenPh3ꢀn (n ¼ 3, 2 or 1) could be isolated provided that
no excess of the phosphine, which may cause reduction side-
Scheme 1 Reaction conditions: Room temperature; solvent: M ¼ Nb:
DME; M ¼ Ta: CH2Cl2 ; M ¼ W: THF (1), toluene (2) or CH2Cl2/
toluene 1:1 (3).
solution from which HCl fumes emanated (the acidic nature of
the gas was confirmed with pH-paper). After work up, brick-
red [(Z-C5H5)NbCl3{PPh2CHOC(OO)Ph}] 6a was isolated
(Scheme 1). The 1H NMR spectrum of 6a contains a sharp
singlet at d 6.95 (Cp) and a doublet at d 6.25 [J(P,H) ¼ 3.5
Hz], which is ascribed to the enolate proton. There were also
signals arising from the aromatic hydrogens. The 31P{1H}
NMR spectrum (CD2Cl2) shows a very broad hump at ca. d
36.5, as a result of the P–Nb coupling (w1/2 > 2500 Hz). In
the IR spectrum, a nCOC + nCOO vibration is observed at
1547 cmꢀ1 (vs 1670 cmꢀ1 for the nC vibration of uncoordi-
products, was present.76 The adducts of 4c, [(Z-C5H4 Pr)-
i
WCl4(L)] where L ¼ vinylPH2 , allylPH2 or PMe3 , are
stable.77,78
=
O
Formation of P-monoadducts
nated 2).35 This value lies within the range of those already
reported for the same phosphino-enolate moiety in other metal
complexes.35,37–39,41,43–46,49 The proposed structure of 6a was
confirmed by X-ray diffraction (vide infra). Note that 6a was
also obtained as the sole product when an excess of the keto-
phosphine ligand was used (2 to 4 mol. equiv.), no side-reac-
tion being observed.
Treatment of [(Z-C5H5)NbCl4] 4a with one mol. equiv. of 1
gave the P-monoadduct [(Z-C5H5)NbCl4{PPh2CH2C(O)-
NPh2}] 5a as a brown solid. The proposed structure is sup-
ported by the presence, in the 31P{1H} NMR spectrum
(CD2Cl2), of a very broad peak at ca. d 33.1 (w1/2 > 2500
Hz), owing to the quadrupolar broadening due to Nb (spin
9/2), and by the occurrence of a nC
vibration at 1658
Spontaneous elimination of HCl was also observed when 2
was reacted with 4b–d, thus leading to the formation of the
phosphino-enolate derivatives 6b–d, respectively (Scheme 1).
The spectroscopic data of the tantalum complex 6b mirror
those of 6a. In the case of the Cp* complex 6d, the 31P{1H}
resonance occurs at slightly higher field (d 31.3), whereas, in
the 1H NMR spectrum, the enolate and Z-C5Me5 protons
are observed at d 6.08 [J(P,H) ¼ 3.6 Hz] and 2.38 (singlet),
respectively. The paramagnetic complex 6c was characterized
by IR spectroscopy (nCOC + nCOO 1542 cmꢀ1), mass spectro-
scopy (m/z: 701 [M]) and elemental analysis. It was isolated
as a burgundy solid, whereas phosphine adducts of the type
=
O
cmꢀ1 in the IR spectrum, which indicates non-coordination
of the amide moiety (free ligand: 1657 cmꢀ1).42 In the 1H
NMR spectrum (CD2Cl2), the Z-C5H5 and PCH2 protons
are observed at
d 6.89 (singlet) and 3.88 (doublet,
2J(P,H) ¼ 7 Hz), respectively. The absence of coupling
between the 31P nucleus and the Cp protons was also noted
for [(Z-C5H5)NbCl4(PMenPh3ꢀn)] (n ¼ 3, 2 or 1).76 Complexes
i
[(Z-C5H5)TaCl4{PPh2CH2C(O)NPh2}] 5b and [(Z-C5H4 Pr)-
WCl4{PPh2CH2C(O)NPh2}] 5c were prepared from 4b,c and
1. The spectroscopic data of the tantalum complex 5b mirror
those of 5a. The paramagnetic tungsten complex 5c was char-
acterized by IR spectroscopy (nC 1662 cmꢀ1), mass spectro-
i
[(Z-C5H4 Pr)WCl4(PR3)] range from yellow ochre to
=
O
scopy (m/z: 793 [M ꢀ Cl]) and elemental analysis. Complexes
5a–c were stable in solution for several hours and in the solid
state for a few days, in the absence of oxygen. Contrary to the
situation reported for the Mo complexes mentioned in the
introduction,20,22,23 there was no observed tendency for chela-
tion for 1 in complexes 5a–c.
brown.77,78 The X-ray structures of the tantalum complexes
6b,d have been determined (vide infra).
To the best of our knowledge, such a spontaneous and facile
HCl elimination in the absence of base has not been described
for transition metal complexes containing 2 or any similar
ligands. Yet, thermal activation or treatment with I2 of Ru
clusters of the type [Ru3(CO)12ꢀnLn] (L ¼ 2, n ¼ 1–3) have
led to phosphino-enolate Ru complexes,43,44 whereas a Rh(III)
phosphino-enolate complex has been obtained by deprotona-
tion of a co-ordinated ketophosphine 2 by an excess of this
ligand present in the reaction mixture, the latter being a slow
process (ca. 1 week).48 Although the mechanism of the forma-
tion of 6 has not been established, we suggest, on the basis of
Formation of P,O-enolate complexes
Surprisingly, attempts to form the P-monodentate analogues
of 5a–c from [(Z-C5H5)NbCl4] 4a and the b-ketophosphine
Ph2PCH2C(O)Ph 2 failed. Instead, the reaction followed a dif-
ferent pathway, which resulted in the formation of a deep red
New J. Chem., 2003, 27, 32–38
33

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the formation of complexes 5, that P-coordination of 2 at the
metal centre occurs first. This would result in an enhanced
acidity of the PCH2 protons and thus favour HCl elimination.
This is consistent with our recent observation of an H/D
exchange involving the methylene protons of 2 in the Mo(II)
transition metal derivatives in which a neutral functionalized
phosphine is coordinated to the metal via the alternative donor
atom instead of the P atom. Precedents include N- and O-
adducts of MnI2 of 2-(diphenylphosphino)pyridine and 2,
respectively.80 In the case of phosphino-enolate zirconocene
and titanocene complexes, O-monocoordination of the anionic
P,O ligands results from the formation of a covalent M–O
bond.61–63 Previous investigations on the coordination proper-
ties of 3 concerned the synthesis of neutral and cationic Pd,79
Mo22 and Rh complexes,81 for which O-monocoordination
was never encountered. Comparative studies showed that 3 is
a better P,O-chelate than the keto- and amidophosphines 1
and 2, respectively.79
complexes [(Z-C6H5R)Mo(Z-C3H5){Ph2PCH2C(O)Ph}][PF6]
(R ¼ H, Me).23 The dehydrochlorination may also be facili-
tated by intra- and/or inter molecular Hꢁ ꢁ ꢁCl interactions
involving the methylene protons, a bonding situation which
has been encountered in the crystal structure of the Mo(II)
complex [(Z-C6H5Me)Mo(Z-C3H5)Cl{Ph2PCH2C(O)Ph}].23
The complexes 6 exhibit remarkable stability both in solu-
tion and in the solid state. In the latter case they can be kept
for weeks in the air. Note that when 6 was treated with an
excess of PMe3 , no opening or complete displacement of the
P,O chelate was observed. The straightforward formation of
these phosphino-enolate complexes, under the same reaction
conditions as those used for the preparation of 5a–c, empha-
sizes a marked difference of behaviour between the b -keto-
phosphine 2 and its b-amido counterpart 1. This is related to
the more acidic character of the CH2 protons in 2, owing to
the different electronic influence of its Ph substituent vs. the
NPh2 group in 1.
Crystal structures of 6a,b,d
Crystal data and data collection parameters are given in
Table 1. There are two crystallographically different but very
similar molecules in the asymmetric unit of 6b whose selected
bond lengths and angles are given in Table 2 together with
those of complexes 6a,d. ORTEP views of 6a, 6b and 6d are
pictured in Fig. 1, 2 and 3, respectively. If one considers the
Cp centroid of the cyclopentadienyl ligands as an apex of the
metal coordination polyhedron, then the three complexes exhi-
bit a distorted pseudooctahedral geometry, with the three
chlorine atoms and the oxygen atom lying in the equatorial
plane and the P atom trans to the cyclopentadienyl ring.82
The Cpcent–M–P(1) angles range from 175.76ꢂ (6a) to
178.48ꢂ (6d) and are slightly more obtuse than those found
Formation of O-monoadducts
The reaction of 4a–c with the acetamido-phosphine
Ph2PNHC(O)Me 3 led to the new complexes 7a–c in which
the P,O ligand is O-monocoordinated and this is an unsual
coordination mode for such a P,O ligand (Scheme 1). This pro-
=
in the ylide complex [(Z-C5Me5)TaCl4(CH2 PMePh2)]
(173ꢂ)83 or in [(Z-C5H5)NbCl4(PMePh2)] (174.6ꢂ),76 the only
phosphine adduct of [(Z-C5H5)NbCl4] that has been structu-
rally characterized to date. The chlorine and oxygen atoms
are bent away from the cyclopentadienyl ring towards the P
ligand. The molecular structures show M–Cl [2.3873(9)–
posed stucture is supported by the nC O vibration at 1646 cmꢀ1
=
(7a,b) or 1651 cmꢀ1 (7c), to be compared to 1715 cmꢀ1 for the
free ligand.79 The fact that the P atom does not coordinate to
the metal centre is suggested by the 31P{1H} NMR resonances
of 7a (d 33.1) and 7b (d 40.6), which occur in the same region
as that of 3 (d 31.1). These values suggest that the electronic
properties of the phosphorus centre are slightly more affected
by O-coordination of the ligand in the case of M ¼ Ta (7b)
than in the case of M ¼ Nb (7a). Furthermore, the slightly
broadened 31P singlet (w1/2 ¼ 65 Hz) observed for 7a contrasts
with the very broad signals (w1/2 > 2500 Hz) observed for 5a
2.446(1) A] bond lengths, Cpcent–M–Cl [103.35–105.28ꢂ] and
˚
Cl–M–Cl [87.08(4)–90.31(3)ꢂ cis; 150.95(3)–152.37(8)ꢂ trans]
bond angles which are consistent with those reported for
related structures.76,83–85 The M–O(1) bond lengths are similar
to those found in other transition metal complexes with the
same phosphino-enolate ligand35–39,41,43–46,49 or in [(Z-
85
1
˚
C5Me5)TaCl3{OC(SiMe3)NNCPh2}] [1.98(1) A]. In the case
˚
and 6a, in which the P atoms are coordinated to Nb. The H
NMR spectra of 7a,b show all the expected signals, including
those of the NH protons at ca. d 9 (free ligand: d 6.15).79 Com-
plexes 7 are stable for a few days in the solid state, in the
absence of air and moisture. They represent rare examples of
of [(Z-C5Me5)TaCl3{PPh2CHOC(OO)Ph}] 6d [2.024(2) A] it is
slightly longer than in the other complexes 6a,b [1.977(2)–
˚
1.983(3) A]. The M–P(1) bond lengths of ca. 2.66 A are shorter
˚
i
than those found in [(Z-C5H4Me)TaCl4{PH2(C6H2 Pr3)}]
Table 1 Selected crystallographic data for complexes 6a,b,d
6a
6b
6d
Formula
FW
Colour
C25H21Cl3OPNbꢁ0.5C7H8
C25H21Cl3OPTa
655.72
Yellow
C30H31Cl3OPTa
725.86
Yellow
613.75
Red
Crystal system
Space group
T/K
Monoclinic
P21/c
150(2)
Triclinic
¯
P1
150(2)
Trigonal
¯
R3
150(2)
˚
a/A
7.876(1)
26.392(1)
12.650(1)
90
8.4611(1)
16.6441(3)
16.8443(3)
92.6314(8)
99.3326(9)
94.1166(11)
2330.7
42.5519(5)
42.5519(5)
8.7407(5)
90
˚
b/A
˚
c/A
a/ꢂ
b/ꢂ
g/ꢂ
97.01(1)
90
90
120
3
˚
V/A
2609.8
4
0.851
13 706.1
18
3.945
Z
4
5.145
10 582
m/mmꢀ1
Unique reflections
Reflections
5001
6943
4100 with I > 3s(I)
0.0515
0.0543
8244 with I > 2s(I)
0.0314
0.0366
5794 with I > 3s(I)
0.0281
0.0298
R
Rw
34
New J. Chem., 2003, 27, 32–38

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ꢂ
˚
Table 2 Selected bond lengths (A) and angles ( ) for 6a, 6b (2 mole-
cules) and 6d; Cpcent refers to the computed cyclopentadienyl ring
centroids
6a
6b (molecule 1) 6b (molecule 2) 6d
M–P1
2.667(1)
2.132
2.670(1)
2.127
2.674(1)
2.142
2.6596(9)
2.168
Cpcent–M
M–Cl1
M–Cl2
2.4186(9)
2.4057(9)
2.446(1)
1.977(2)
1.779(4)
1.345(5)
1.346(4)
2.415(1)
2.4131(11)
2.422(1)
1.983(3)
1.779(5)
1.352(6)
1.349(5)
2.410(1)
2.402(1)
2.413(1)
1.982(3)
1.792(4)
1.342(6)
1.352(3)
2.4209(8)
2.3873(9)
2.3934(8)
2.023(2)
1.773(3)
1.349(5)
1.342(4)
M–Cl3
M–O1
P1–C1
C1–C2
C2–O1
Cpcent–M–P1
175.76
175.80
103.59
177.40
105.28
178.48
104.39
Cpcent–M–Cl1 104.02
Cpcent–M–Cl2 104.24
Cpcent–M–Cl3 103.44
Cpcent–M–O1 101.83
104.05
104.02
104.60
103.35
103.99
103.81
103.17
101.78
103.82
Cl1–M–Cl2
Cl1–M–Cl3
Cl1–M–O1
Cl2–M–Cl3
Cl2–M–O1
Cl3–M–O1
P1–M–O1
P1–C1–C2
C1–C2–O1
C2–O1–M
88.92(3)
88.25(4)
151.26(3)
85.21(9)
87.08(4)
153.56(8)
86.47(9)
74.10(8)
115.3(3)
121.5(4)
131.6(2)
87.41(4)
152.35(4)
85.50(9)
87.16(4)
152.76(9)
87.04(9)
74.23(8)
114.7(3)
122.3(4)
131.2(3)
89.49(3)
150.95(3)
82.04(7)
90.31(3)
152.12(7)
84.70(7)
74.83(7)
116.0(3)
122.6(3)
129.2(2)
152.37(3)
87.60(8)
87.26(3)
153.80(8)
83.921(8)
73.97(7)
115.4(3)
121.3(3)
131.8(2)
Fig. 2 Molecular structure of 6b. Only one of the two independent
molecules of the unit cell is shown. Hydrogen atoms, except H(11),
are omitted for clarity.
no phosphine adduct was isolated, instead HCl elimination
readily occurred giving the corresponding phosphino-enolate
complexes. To the best of our knowledge, such a facile forma-
tion of transition metal phosphino-enolate complexes, in the
absence of a base, has not been reported previously. The crys-
tal structures of the Nb and Ta complexes 6a,b,d have been
determined. The striking difference between 1 and 3 in bonding
cannot be of steric origin since P-coordination of 3 would have
led to a very similar steric situation at the metal centre. There-
fore, the bonding difference must be of electronic origin, which
has not been quantified at the moment and deserves further
investigations.
86
76
˚
˚
[2.710 A] or in [(Z-C5H5)NbCl4(PMePh2)] [2.7844(9) A]
and similar to those reported for [Nb(O)Cl3(PMe3)3]
[2.640(3) A].87 The other bond lengths and angles of the phos-
˚
phino-enolate and cyclopentadienyl ligands are within the
expected range.
Conclusion
We have described here the first investigations on the chemis-
try of half-sandwich complexes of the type [(Z-C5R5)MCl4]
(M ¼ Nb, Ta or W) with b-carbonylphosphines. Depending
on the nature of the P,O ligand three different coordination
modes have been observed. With Ph2PCH2C(O)NPh2 1 P-
monoadducts were obtained, whereas Ph2PNHC(O)Me 3 led
to O-monoadducts, which is an unsual coordination mode
for P,O ligands. The reactions with the b-ketophosphine
Ph2PCH2C(O)Ph 2 followed another pathway. In this case,
Experimental
Reagents and physical measurements
All manipulations of air- and/or moisture sensitive materials
were performed under an inert atmosphere of argon using
standard Schlenk line techniques, or in an inert atmosphere
dry box containing dinitrogen. Solvents were dried over
the appropriate drying agent and distilled under nitrogen.
Fig. 1 Molecular structure of 6a. Hydrogen atoms, except H(11),
and the solvent molecule (toluene) are omitted for clarity.
Fig. 3 Molecular structure of 6d. Hydrogen atoms, except H(11), are
omitted for clarity.
New J. Chem., 2003, 27, 32–38
35

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Deuterated solvents were dried over the appropriate drying
agent and vacuum distilled prior to use. The compounds [(Z-
C5H5)NbCl4],75 [(Z-C5H5)TaCl4],75 [(Z-C5Me5)TaCl4],88 [(Z-
Anal. calc. for C25H21Cl3NbOP: C, 52.90; H, 3.72. Found:
C, 53.21; H, 3.82%.
X-Ray quality single crystals were grown by slow diffusion
of Et2O into a toluene solution of 6a.
i
42
C5H4 Pr)WCl4],89 Ph2PCH2C(O)Ph,35 Ph2PCH2C(O)NPh2
and Ph2PNHC(O)Me79 were prepared according to previously
published methods. NMR spectra were recorded on a Varian
Mercury 300 (1H, 13C, and 31P at 300.17, 75.48 and 121.51
MHz, respectively) spectrometer. They were referenced intern-
ally using the residual protio solvent (1H) and solvent (13C)
resonances and measured relative to tetramethylsilane (1H
and 13C; d 0 ppm). 31P NMR was referenced externally to
85% H3PO4 (d 0 ppm). Elemental analyses were provided by
the microanalytical department, Inorganic Chemistry Labora-
tory, University of Oxford or by the Service de Microanalyses,
[(g-C5H5)TaCl3{PPh2CHOC(OO)Ph}] 6b. Solid [(Z-
C5H5)TaCl4] (0.400 g, 1.03 mmol) and Ph2PCH2C(O)Ph
(0.313 g, 1.03 mmol) were placed in a Schlenk flask and
CH2Cl2 (20 mL) was added at room temperature. The mixture
was stirred for 3 h, during which its colour changed from yel-
low to orange. The volatiles were then removed under reduced
pressure. The dark yellow residue was extracted with toluene
(15 mL) at 60 ꢂC. The resulting clear yellow solution was eva-
porated under reduced pressure affording 6b as a yellow pow-
1
´
Universite Louis Pasteur, Strasbourg. Infra-red spectra were
der (0.563 g, yield 83%). H NMR (CDCl3 , 300.18 MHz): d
2
recorded on a Perkin Elmer 1600 Series FTIR or a Bruker
IFS66 FTIR spectrometer. Mass spectra were recorded at
the Inorganic Chemistry Laboratory, on a Macromass LC
Tof spectrometer.
6.34 (d, 1H, JPH ¼ 3.0 Hz, PCH); 6.72 (s, 5H, Cp); 7.20–
7.91 (m, 15H, aromatics). 31P{1H} NMR (CDCl3 , 121.5
MHz): d 37.2. IR (Nujol): 1552 cmꢀ1 (nCOC + nCOO). Anal.
calc. for C25H21Cl3OPTa: C, 45.79; H, 3.63. Found: C,
46.01; H, 3.46%.
X-Ray quality single crystals were grown by slow diffusion
of petroleum ether (bp 40–60 ꢂC) into a CDCl3 solution of 6b.
Synthesis
[(g-C5H5)NbCl4{PPh2CH2C(O)NPh2}] 5a. Solid [(Z-
C5H5)NbCl4] (0.200 g, 0.66 mmol) and Ph2PCH2C(O)NPh2
(0.261 g, 0.66 mmol) were placed in a Schlenk flask and
DME (10 mL) was added. The solution was stirred for 3 h.
The volatiles were then removed under reduced pressure and
the residue washed with Et2O (10 mL) and pentane (10 mL).
Complex 5a was obtained as a pale brown air-sensitive solid
(0.417 g, yield 90%). 1H NMR (CD2Cl2 , 300.18 MHz): d
i
[(g-C5H4 Pr)WCl3{PPh2CHOC(OO)Ph}] 6c. Solid [(Z-
C5H4 Pr)WCl4] (0.600 g, 1.38 mmol) and Ph2PCH2C(O)Ph
i
(0.420 g, 1.38 mmol) were placed in a Schlenk flask and toluene
(15 mL) was added at room temperature. The mixture was stir-
red overnight, affording a claret solution. The volatiles were
then removed under reduced pressure and the residue was
washed with Et2O (15mL) and pentane (2 ꢃ 10 mL). It
afforded 6c as a purple solid, which was dried in vacuo (0.786
g, yield 81%). IR: 1539 cmꢀ1 (Nujol), 1542 cmꢀ1 (KBr)
(nCOC + nCOO). MS m/z: 701 (M+, showing the expected isoto-
pic pattern), 666 (M+ ꢀ Cl). Anal. calc. for C28H27Cl3OPW: C,
48.00; H, 3.88. Found: C, 47.83; H, 3.72%.
2
3.89 (d, 2H, JPH ¼ 7 Hz, PCH2); 6.90–7.79 (m, 25H, Cp
and aromatics). 31P{1H} NMR (CD2Cl2 , 121.5 MHz): d 33.1
(vbr, w1/2 > 2500 Hz). IR (CH2Cl2): 1658 cmꢀ1 (nC O). Anal.
calc. for C31H27Cl4NNbOP: C, 53.55; H, 3.91; N, 2.01. Found:
C, 53.81; H, 4.06; N, 1.95%.
=
[(g-C5H5)TaCl4{PPh2CH2C(O)NPh2}] 5b. This compound
was prepared in a similar manner to 5a from [(Z-C5H5)TaCl4]
(0.150 g, 0.38 mmol) and Ph2PCH2C(O)NPh2 (0.152 g, 0.38
mmol) in CH2Cl2 (10 mL). Complex 5b was obtained as a yel-
[(g-C5Me5)TaCl3{PPh2CHOC(OO)Ph}] 6d. This complex
was prepared in a similar manner to 6b from [(Z-C5Me5)TaCl4]
(0.400 g, 0.873 mmol) and Ph2PCH2C(O)Ph (0.266 g, 0.873
mmol). It was obtained as a yellow solid (0.544 g, yield
1
1
low solid (0.257 g, 85%). H NMR (CD2Cl2 , 300.18 MHz): d
86%). H NMR (CDCl3 , 300.18 MHz): d 2.38 (s, 15H, Me);
2
2
3.69 (d, 2H, JPH ¼ 5.5 Hz, PCH2); 6.77 (s, 5H, Cp); 6.95–
6.08 (d, 1H, JPH ¼ 3.6 Hz, PCH); 6.90–7.90 (m, 15H, aro-
7.97 (m, 20H, aromatics). 31P{1H} NMR (CD2Cl2 , 121.5
matics). 31P{1H} NMR (CDCl3 , 121.5 MHz): d 36.5 (vbr,
w1/2 > 2500 Hz). IR (Nujol): 1552 cmꢀ1 (nCOC + nCOO). Anal.
calc. for C30H31Cl3OPTa: C, 49.64; H, 4.30. Found: C, 49.87;
H, 4.18%.
MHz): d 27.9. IR (CH2Cl2): 1658 cmꢀ1 (nC O). Anal. calc.
for C31H27Cl4NOPTa: C, 47.54; H, 3.47; N, 1.79. Found: C,
47.69; H, 3.38; N, 1.92%.
=
X-Ray quality single crystals were grown by slow diffusion
of Et2O into a CDCl3 solution of 6d.
i
[(g-C5H4 Pr)WCl4{PPh2CH2C(O)NPh2}] 5c. This com-
pound was prepared in a similar manner to 5a from [(Z-
C5H4 Pr)WCl4] (0.600 g, 1.386 mmol) and Ph2PCH2C(O)NPh2
i
=
[(g-C5H5)NbCl4{O C(Me)NHPPh2}] 7a. This complex was
(0.548 g, 1.386 mmol) in THF (30 mL). Complex 5c was
obtained as a green-brown solid (0.845 g, 74%). IR (KBr):
prepared in a similar manner to 5a from [(Z-C5H5)NbCl4]
(0.500 g, 1.67 mmol) and Ph2PNHC(O)Me (0.354 g, 1.67
mmol) in DME (20 mL). It was obtained as an orange-pink
1662 cmꢀ1 (nC O). MS m/z: 793 (M+ ꢀ Cl showing the
=
expected isotopic pattern), 758 (M+ ꢀ 2Cl). Anal. calc. for
C34H33Cl4OPW: C, 49.30; H, 4.02; N, 1.69. Found: C, 48.87;
H, 4.27; N, 1.53%.
1
solid (0.751 g, yield 88%). H NMR (CD2Cl2 , 300.18 MHz):
d 2.16 (s, 3H, Me); 7.18 (s, 5H, Cp); 7.22–7.95 (m, 10H, aro-
matics); 9.64 (br s, 1H, NH). 31P{1H} NMR (CD2Cl2 , 121.5
MHz): d 33.1 (w1/2 ¼ 65 Hz). IR (CH2Cl2): 1646 cmꢀ1
[(g-C5H5)NbCl3{PPh2CHOC(OO)Ph}] 6a. Solid [(Z-
C5H5)NbCl4] (0.400 g, 1.33 mmol) and Ph2PCH2C(O)Ph
(0.405 g, 1.33 mmol) were placed in a Schlenk flask and
DME (30 mL) was added at ambient temperature. Rapidly,
the solution turned deep red, and HCl emanated from it.
The mixture was then stirred for 2 h and the volatiles were
removed under reduced pressure. The red-brown residue was
washed with Et2O (2 ꢃ 20 mL) and pentane (2 ꢃ 20 mL) and
dried in vacuo affording 6a as a red-brown solid (0.704 g, yield
93%). 1H NMR (CD2Cl2 , 300.18 MHz): d 6.25 (d, 1H,
2JPH ¼ 3.5 Hz, PCH); 6.95 (s, 5H, Cp); 7.24–7.88 (m, 15H,
aromatics). 31P{1H} NMR (CD2Cl2 , 121.5 MHz): d 36.5
(vbr, w1/2 > 2500 Hz). IR (Nujol): 1547 cmꢀ1 (nCOC + nCOO).
(nC O). Anal. calc. for C19H19Cl4NNbOP: C, 42.02; H, 3.53;
=
N, 2.58. Found: C, 42.26; H, 3.81; N, 2.61%.
=
[(g-C5H5)TaCl4{O C(Me)NHPPh2}] 7b. This complex was
prepared in a similar manner to 5b from [(Z-C5H5)TaCl4]
(0.150 g, 0.38 mmol) and Ph2PNHC(O)Me (0.080 g, 0.38
mmol) in CH2Cl2 (10 mL). It was obtained as a yellow-brown
1
solid (0.185 g, yield 80%). H NMR (CDCl3 , 300.18 MHz): d
2.61 (s, 3H, Me); 6.91 (s, 5H, Cp); 6.80–8.02 (m, 10H, aro-
matics); 8.85 (br s, 1H, NH). 31P{1H} NMR (CD2Cl2 , 121.5
MHz): d 40.6. IR (CDCl3): 1646 cmꢀ1 (nC O). Anal. calc. for
C19H19Cl4NOPTa: C, 36.16; H, 3.03; N, 2.22. Found: C,
36.28; H, 3.05; N, 2.26%.
=
36
New J. Chem., 2003, 27, 32–38

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i
[(g-C5H4 Pr)WCl4{O C(Me)NHPPh2}] 7c. This complex
=
15 J. I. Dulebohn, S. C. Haefner, K. A. Berglund and K. R. Dunbar,
Chem. Mater., 1992, 4, 506.
16 K. R. Dunbar, Comments Inorg. Chem., 1992, 13, 313.
was prepared in similar manner to 5c from [(Z-
a
i
C5H4 Pr)WCl4] (1.000 g, 2.30 mmol) and Ph2PNHC(O)Me
(0.490 g, 2.30 mmol) in a 1:1 CH2Cl2–toluene mixture (30
mL). It was obtained as a green-brown solid (1.212 g, yield
17 H. Werner, M. Schulz and B. Windmuller, Organometallics, 1995,
14, 3659.
¨
18 E. Lindner, B. Keppleler, H. A. Mayer, K. Gierling, R. Fawzi and
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19 H. Werner, J. Bank, B. Windmuller, O. Gevert and W.
¨
Wolfsberger, Helv. Chim. Acta, 2001, 84, 3163.
20 J.-M. Camus, D. Morales, J. Andrieu, P. Richard, R. Poli, P.
Braunstein and F. Naud, J. Chem. Soc., Dalton Trans., 2000,
2577.
81%). IR (Nujol): 1651 cmꢀ1 (nC O). MS m/z: 641 (M+ ꢀ Cl,
=
showing the expected isotopic pattern), 606 (M+ ꢀ 2Cl). Anal.
calc. for C22H25Cl4NOPW: C, 39.08; H, 3.73; N, 2.07. Found:
C, 38.70; H, 3.78; N, 2.03%.
21 C. D. Andrews, A. D. Burrows, J. M. Lynam, M. F. Mahon and
M. T. Palmer, New J. Chem., 2001, 25, 824.
Crystallography
22 N. G. Jones, M. L. H. Green, I. Vei, X. Morise and P. Braunstein,
J. Chem. Soc., Dalton Trans., 2002, 1487.
23 N. G. Jones, M. L. H. Green, I. C. Vei, L. H. Rees, S. I. Pascu, D.
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Data were collected on an Enraf-Nonius DIP2000 Image Plate
diffractometer (6a) and on an Enraf-Nonius KappaCCD dif-
fractometer (6b,d) (graphite-monochromated MoKa radiation
˚
l ¼ 0.71073 A). Intensity data were processed using the
DENZO-SMN package90 running on a Silicon Graphics Indy
computer. The structures were solved using the direct-methods
program SIR-92.91 Subsequent full-matrix least-squares refine-
ments were carried out using the SHELXL-9392 (6a) or the
CRYSTALS93 programs. The structure of 6b consists of two
‘‘pseudo-dimers’’ representing two slightly different mononuc-
lear complexes, referred to as molecules 1 and 2 in Table 2. All
non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were positioned geometrically after each cycle of refine-
ment. A 3-term Chebychev polynomial weighting scheme was
applied. Selected crystal data and refinement details are given
in Table 1.
CCDC reference numbers 190864–190866.
See http://www.rsc.org/suppdata/nj/b2/b202983a/ for
crystallographic data in CIF or other electronic format.
32 L. R. Falvello, M. M. Garcia, I. Lazaro, R. Navarro and E. P.
Urriolabeitia, New J. Chem., 1999, 227.
33 R. Navarro and E. P. Urriolabeitia, J. Chem. Soc., Dalton Trans.,
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34 W. Keim, A. Behr, B. Gruber, B. Hoffmann, F. H. Kowaldt,
Acknowledgements
U. Kurschner, B. Limba¨cker and F. P. Sistig, Organometallics,
¨
1986, 5, 2356 and references cited therein.
For providing financial support, we would like to thank the
Centre National de la Recherche Scientifique/Royal Society
cooperation programme (XM), the RSC for a travel grant
(XM, JGA No. 0103 306), the AG Leventis Foundation (IV)
and the EPSRC (LHR). We thank Dr. David Watkin and
Andrew Cowley (Crystallography Laboratory, Oxford) for
their generous assistance with the crystal structure determina-
tions.
35 S.-E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D.
Nobel, Inorg. Chem., 1986, 25, 3765.
36 F. Balegroune, P. Braunstein, D. Grandjean, D. Matt and D.
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37 S.-E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D.
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38 P. Braunstein, D. Matt, D. Nobel, F. Balegroune, S.-E. Bouaoud,
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39 P. Braunstein, T. M. Gomes-Carneiro, D. Matt, F. Balegroune
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40 W. Keim, Angew. Chem., Int. Ed. Engl., 1990, 29, 235.
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