Reactions of alkynes with phosphido niobocenes: A combined experimental and theoretical study

Article abstract of DOI:10.1039/b918298e

The reactions of phosphido complexes [Nb(η⁵-C ₅H₄SiMe₃)₂(L)(PPh₂)] [L = CO (1), CNxylyl (2), CNCy (3)] with alkynes have been carried out. The new diphenylphosphinoalkenyl niobocene complexes [Nb(η⁵-C ₅H₄SiMe₃)₂(η¹-C- C(CO₂CH₃)C(R)PPh₂)(CO)] [R = H (4), CH ₃ (5)] and [Nb(η⁵-C₅H₄SiMe ₃)₂(η¹-C-C(CO₂R)C(CO ₂R)PPh₂)(CO)] [R = CH₃, (6), R = ^tBu, (7)] were successfully synthesized by the reaction of 1 with methyl propiolate (HCCCO₂CH₃) or methyl 2-butynoate (CH₃CCCO₂CH₃) and dimethyl 2-butynedioate [(CH₃ O₂C)CC(CO₂CH₃)] or di(tert-butyl) 2-butynedioate [(^tBuO₂C)CC(CO ₂^tBu)], respectively. However, reaction was not observed with more electron-rich alkynes. Complex 2 reacted with methyl propiolate, methyl 2-butynoate (MeCCCO₂Me) or di(tert-butyl) 2-butynedioate to give surprising new heteroniobacycle complexes [Nb(η⁵-C ₅H₄SiMe₃)₂(η¹-C- C(NXylyl)C(R¹)C(R²)PPh₂-κ¹-P)] [R¹ = H, R² = CO₂Me (8); R¹ = Me, R² = CO₂Me (9); R¹ = CO₂ ^tBu, R² = CO₂^tBu (10)]. Finally, the phosphido complexes 2 and 3 reacted with phenylacetylene (PhCCH) to give new diphenylphosphinoalkenyl niobocene derivatives [Nb(η⁵-C ₅H₄SiMe₃)₂(η¹-C- C(C₆H₅)C(H)PPh₂)(CNR)] [R = xylyl (11), Cy (12)]. All of these compounds were characterized by NMR spectroscopy and the molecular structure of 8 was determined by single-crystal X-ray diffraction studies. Theoretical studies were also carried out by means of density functional theory (DFT) calculations on the insertions of alkynes into the Nb-P bond in the phosphido niobocenes.

Full text of DOI:10.1039/b918298e

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PAPER
www.rsc.org/dalton | Dalton Transactions
Reactions of alkynes with phosphido niobocenes: a combined experimental
and theoretical study†
Antonio Antin˜olo,*a Santiago Garc´ıa-Yuste,a Isabel Lopez Solera,a Antonio Otero,*a Juan Carlos
Pe´rez-Flores,a Rebeca Reguillo-Carmona,a Elena Villasen˜or,a Eva Santos,b Erik Zuidemab and Carles Bo*b,c
Received 4th September 2009, Accepted 2nd November 2009
First published as an Advance Article on the web 11th January 2010
DOI: 10.1039/b918298e
5
The reactions of phosphido complexes [Nb(h -C5H4SiMe3)2(L)(PPh2)] [L = CO (1), CNxylyl (2), CNCy
(3)] with alkynes have been carried out. The new diphenylphosphinoalkenyl niobocene complexes
5
1
=
[Nb(h -C5H4SiMe3)2(h -C–C(CO2CH3) C(R)PPh2)(CO)] [R = H (4), CH3 (5)] and
5
1
t
=
[Nb(h -C5H4SiMe3)2(h -C–C(CO2R) C(CO2R)PPh2)(CO)] [R = CH3, (6), R = Bu, (7)] were
≡
successfully synthesized by the reaction of 1 with methyl propiolate (HC CCO2CH3) or methyl
≡
≡
2-butynoate (CH3C CCO2CH3) and dimethyl 2-butynedioate [(CH3 O2C)C C(CO2CH3)] or
di(tert-butyl) 2-butynedioate [( BuO2C)C C(CO2 Bu)], respectively. However, reaction was not
observed with more electron-rich alkynes. Complex 2 reacted with methyl propiolate, methyl
t
t
≡
≡
2-butynoate (MeC CCO2Me) or di(tert-butyl) 2-butynedioate to give surprising new heteroniobacycle
5
1
1
2
1
1
2
=
=
complexes [Nb(h -C5H4SiMe3)2(h -C–C( NXylyl)C(R ) C(R )PPh2-k -P)] [R = H, R = CO2Me (8);
R1 = Me, R2 = CO2Me (9); R1 = CO2 Bu, R2 = CO2 Bu (10)]. Finally, the phosphido complexes 2 and
t
t
≡
3 reacted with phenylacetylene (PhC CH) to give new diphenylphosphinoalkenyl niobocene
5
1
=
derivatives [Nb(h -C5H4SiMe3)2(h -C–C(C6H5) C(H)PPh2)(CNR)] [R = xylyl (11), Cy (12)]. All of
these compounds were characterized by NMR spectroscopy and the molecular structure of 8 was
determined by single-crystal X-ray diffraction studies. Theoretical studies were also carried out by
means of density functional theory (DFT) calculations on the insertions of alkynes into the Nb–P bond
in the phosphido niobocenes.
to C–P bond formation in the preparation of functionalized
phosphines.6
Introduction
Early transition metal phosphido complexes can be considered as
metallophosphines, and several studies on the synthesis and reac-
tivity of these systems have been reported,1 most of which concern
group 4 metal complexes. However, examples of this kind of group
5 metal complex still remain scarce.2 Among these compounds,
Additionally, functionalized phosphines bearing a multiple
carbon–carbon bond-containing moiety display versatile be-
haviour as ligands in coordination chemistry and have been rea-
sonably well explored in the past. For example, alkenylphosphines7
have a large number of representative examples in late transition
metal complexes.
In previous years we have studied the insertion of unsaturated
molecules such as alkynes,8 alkenes,9 carbon monoxide,10 and
isocyanides11 into the Nb–H or Nb–C bonds of niobocene com-
plexes. More recently, we have studied3,4 the insertion processes
of unsaturated molecules such as carbon disulfide into the Nb–P
bond.
Following our efforts in this field, we have recently found
an unexpected type of reactivity between electron-poor alkynes
and phosphido niobocene complexes that contain an isocyanide
ancillary ligand. In this process a cycloaddition reaction gave rise
to novel five-membered heteroniobacycles. Our initial results in
this area have been communicated.12 We wish to report here the
complete set of results found on the reactivity of phosphido com-
plexes 1, 2 and 3 toward alkynes, namely polarized alkynes such as
methyl propiolate, methyl 2-butynoate and phenylacetylene, and
electron-poor alkynes such as dimethyl 2-butynedioate and di(tert-
butyl) 2-butynedioate. In these reactions two classes of complexes,
namely phosphinoalkenyl niobocenes and heteroniobacycles, were
isolated depending on the nature of the ancillary ligand, i.e. carbon
monoxide versus alkyl or aryl isocyanides. In order to elucidate the
5
the phosphido complexes [Nb(h -C5H4SiMe3)2(L)(PPh2)], L = CO
(1),3 CNxylyl (2), CNCy (3),4a have proven to be suitable precursors
for the synthesis of new niobocene complexes with phosphorus-
containing functionalized ligands.
Furthermore, transition metal-catalyzed addition of
a
heteroatom-containing moiety to a carbon–carbon unsaturated
bond is one of the most straightforward ways to form carbon–
heteroatombonds infunctionalized compounds, and this synthetic
methodology has numerous applications in organic synthesis and
industrial processes.5
The addition of phosphines to double or triple carbon–carbon
bonds represents a convenient and atom-economic approach
aDepartment of Inorganic Chemistry, University of Castilla-La Mancha,
Ciudad Real, Spain. E-mail: antonio.otero@uclm.es; Fax: +34 926 295318;
Tel: +34 926 295300
bInstitute of Chemical Research of Catalonia (ICIQ), Avda dels Pa¨ısos
Catalans 16, 43007, Tarragona, Spain
cDepartment de Qu´ımica Fisica i Inorga`nica, Universitat Rovira i Virgili,
Marcel l´ı Domingo s/n, 43007, Tarragona, Spain
† CCDC reference number 294817. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b918298e
1962 | Dalton Trans., 2010, 39, 1962–1971
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possible reasons for the different behaviours observed, a series of
electronic structure calculations at the density functional theory
(DFT) level are also presented.
of the coupling constant are lower than 10 Hz in both cases,
which is consistent with a gem relative phosphorus–hydrogen or
phosphorus–methyl disposition,13 i.e. isomer I or III in Scheme 1.
These structures correspond to the (Z)- or (E)-stereochemistry for
the alkenyl group, respectively.
Results and discussion
1
13C{ H}-NMR and 13C-NMR spectroscopy, involving g-HSQC
Insertion reactions of phosphidocarbonyl-niobocene with alkynes
and g-HMBC techniques, allowed the assignment of the reso-
nances of the different carbon atoms of the phosphinoalkenyl moi-
ety. The 13C-NMR spectrum of 4 contains a doublet of doublets at
5
The new diphenylphosphinoalkenyl niobocene complexes [Nb(h -
1
=
C5H4SiMe3)2(h -C–C(CO2CH3) C(R)PPh2)(CO)] [R = H (4),
141.7 ppm (dd, 1JCH = 132.2 Hz, 1JCP = 31.7 Hz) corresponding
CH3 (5)] were successfully synthesized by the reaction of 1
1
to the olefinic carbon atoms, C CH, while the 13C{ H}-NMR
=
≡
with methyl propiolate (HC CCO2CH3) or methyl 2-butynoate
spectra of 4 and 5 contain doublet signals corresponding to the
olefinic carbon atom bonded to the phosphorus. This signal is
at d = 149.4 ppm (1JCP = 25.4 Hz) for complex 5. Additionally,
in these spectra the quaternary carbon of the carboxylate moiety
exhibits a doublet at 168.5 ppm (3JCP = 25.8 Hz) in 4 and at
167.1 ppm (3JCP = 34.7 Hz) in 5.
≡
(CH3C CCO2CH3) and were isolated as brownish-red air-
sensitive solids (see eqn (1)).
{[Nb](PPh2 )}+ RC ≡CCO2CH3
(1)
[Nb]={Nb(h5-C5H4SiMe3)2(CO)}
→
{[Nb](h1-C-C(CO2CH3) = C(R)PPh2 )}
R = H(4),CH3 (5)
(1)
In NMR spectroscopy the value of the vicinal coupling constant
of the alkenyl protons with the carbonyl carbon atom of the
a-carbon has been used as a useful tool to establish (E)- or (Z)-
stereochemistry for the alkenyl group (Scheme 2).8b In complex
In the insertion reaction of alkynes into s M–P bonds one
would expect several isomers to be formed as a consequence of the
stereochemistry of the process (see Scheme 1).
3
4, the coupling constant JCH of 6.7 Hz is consistent with a cis-
disposition of the a-ester and the alkenyl proton in the (Z)-isomer.
Scheme 2
Scheme 1
1
Furthermore, the 13C{ H}-NMR spectra of complexes 4 and 5
Isomers I and II correspond to the syn addition of the Nb–P
bond to the alkyne, whereas III and IV are the products of the anti
addition reaction.
Complexes 4 and 5 were isolated as single products that are
air-sensitive solids and can be considered as key intermediates
(and model systems) for the metal-catalyzed hydrophosphination
of alkynes to produce vinylphosphines.5 These compounds were
fully characterized by elemental analysis, IR spectroscopy and
multinuclear NMR spectroscopy in solution.
provide evidence for the expected Cs symmetry of the niobocene
moiety. The spectra show a single signal for the carbon atoms of
the SiMe3 groups and five signals for the cyclopentadienyl units.
The quaternary carbon atom of the carbonyl ancillary ligand is
observed as a broad singlet at ca. 289 ppm.
The spectroscopic data are in agreement with pseudo-
tetrahedral geometry where the diphenylphosphinoalkenyl ligand
is coordinated, in a h -C manner, to the metal centre. The data also
1
support a Z configuration for the carbon-carbon double bond, as
The IR spectra of complexes 4 and 5 contain the characteristic
shown in Fig. 1.
-1
≡
band due to the carbonyl ligand n(C O) at ca. 1910 cm , which
As described for the preparation of complexes
5, complex reacts with dimethyl 2-butynedioate or
di(tert-butyl) 2-butynedioate to give the new diphenylphos-
4 and
is a typical value for niobium(III) metallocenes,3,4 and two bands
1
at ca. 1720 and 1670 cm-1 corresponding to n(COO) and n(C C)
=
5
1
of the carboxylate and olefinic groups, respectively.
phinoalkenyl niobocene complexes [Nb(h -C5H4SiMe3)2(h -C–
The 31P{ H}-NMR spectra show single broad signal for each
1
t
=
C(CO2R) C(CO2R)PPh2)(CO)] [R = CH3, (6), R = Bu, (7)] as
complex, at 82.4 ppm for 4 and 93.1 ppm for 5. These resonances
were shifted downfield with respect to those of the phosphido
ligand in complex 1. This change is consistent with the expected
decrease in electron density on the phosphorus atom.
brownish-red air-sensitive solids (eqn (2)). Complex 6 was isolated
as a mixture of Z/E isomers in a 1 : 2 ratio, 6a and 6b, but these
compounds could not be separated.
{[Nb](PPh2 )}+ RO2CC ≡CCO2R
[Nb]={Nb(h5-C5H4SiMe3)2(CO)}(1)
→
{[Nb](h1-C-C(CO2R) = C(CO2R)PPh2 )}
The 1H-NMR spectra of both complexes contain a single
signal for the methyl groups of the SiMe3 and four multiplets
corresponding to the cyclopentadienyl protons, which adopt an
ABCD spin system. The 1H-NMR spectra of 4 and 5 also contain
doublets at 7.60 ppm (2JHP = 5.1 Hz) and 1.85 ppm (3JHP = 6.8 Hz)
R = CH3(6a), (6b)
R = t Bu (7)
(2)
Complexes 6a, 6b and 7 were characterized by elemental
analysis, IR spectroscopy and multinuclear NMR spectroscopy
in solution.
=
corresponding to the olefinic hydrogen of the C CH and the
=
methyl groups of the C CMe moieties, respectively. The values
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©

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Fig. 2 Proposed structure for complexes 6 and 7.
also considered. An unexpected type of reactivity was found in that
cycloaddition processes took place to give novel five-membered
heteroniobacycles.
Fig. 1 Proposed structure for complexes 4 and 5.
5
1
In fact, the novel heterometallacycles [Nb(h -C5H4SiMe3)2(h -
The IR spectra of complexes 6 and 7 contain the characteristic
1
2
1
1
C–C( Nxylyl)C(R ) C(R )PPh2-k -P)] [R = H, R2 =CO2Me
band due to the carbonyl ligand n(C O) at ca. 1912 cm-1 and two
=
=
≡
(8); R1 = Me, R2 = CO2Me (9); R1 = CO2 Bu, R2 = CO2 Bu
(10)] were prepared in a one-pot [3 + 2] cycloaddition reaction
from 2 and the appropriate alkyne (eqn (3)). These complexes
were isolated as air-sensitive red solids. Complexes 8 and 9 were
very stable but complex 10 decomposed rapidly in solution.
t
t
bands at ca. 1720 cm-1 and ca. 1660 cm-1 corresponding to the
=
n(COO) of the carboxylate groups and the n(C C) of the olefinic
groups, respectively.
The 31P{ H}-NMR spectrum of 7 shows a single broad signal
1
at 88.1 ppm. Furthermore, two broad singlets are observed in the
spectrum of 6, one for each isomer, 6a and 6b, at 79.5 ppm for the
minor component and at 94.0 ppm for the major component.
The 1H-NMR spectrum of 6 contains four singlets, at 3.00 ppm,
corresponding to the methyl units of the non-equivalent carboxy-
late groups, a finding consistent with the presence of two isomers,
1
(3)
6a and 6b, in a 1 : 2 ratio. The H-NMR spectrum of 7 shows
two resonances for the two non-equivalent tert-butyl units of the
carboxylate groups. The 1H-NMR spectra of both complexes also
contain the characteristic resonances of an ABCD spin system for
the cyclopentadienyl groups.
The preparation and characterization of complexes 8 and 9 were
reported previously.12 Examples of heterometallacycles of late-
middle transition metals from cycloaddition processes involving
alkynes are known.14
Complexes 8–10 were characterized by IR and NMR spec-
troscopy in solution and an X-ray crystallographic analysis of
8 was carried out on a suitable single crystal.
1
The 13C{ H}-NMR spectra of 6 and 7 are both consistent with
the observations outlined above. Isomers 6a and 6b decompose
in solution and, as a result, 13C-NMR spectroscopy, g-HSQC and
g-HMBC techniques were only used for the assignment of the
signals corresponding to the phosphinoalkenyl moiety of 7. The
spectrum of 7 contains two doublets corresponding to the qua-
X-Ray diffraction study of [Nb(g5-C5H4SiMe3)2(g1-
1
=
=
C–C( Nxylyl)C(CH) C(CO2Me)PPh2-j -P)] (8)
ternary carbons of the carboxylate moieties at 166.8 ppm (2JCP
24.0 Hz), consistent with a gem disposition of one carboxylate unit
with respect to the PPh2 fragment, and at 168.8 ppm (3JCP
=
A microcrystalline sample of 8, which was suitable for X-ray
diffraction studies, was obtained by crystallization from toluene.
An ORTEP diagram is depicted in Fig. 3. Selected bond distances
and angles are listed in Table 1. To the best of our knowledge,
the molecular structure of complex 8 represents the first example
in the literature, characterized by X-ray diffraction, with a five-
membered unsaturated heteroniobacycle.15
=
31.6 Hz), due to the second carboxylate group in a trans disposition
with respect to the PPh2 fragment in the (Z) isomer.
The spectroscopic data are in agreement with a pseudo-
tetrahedral geometry in which the diphenylphosphinoalkenyl
1
ligand is coordinated in a h -C manner to the metal, with a Z
The structure of complex 8 contains discrete molecules stabi-
lized by disordered solvent molecules. The Nb atom is bonded to
configuration in 6 and a mixture of E/Z configurations in 7 for
the carbon–carbon double bond (see Fig. 2).
A reaction did not occur when 1 was treated with more electron-
rich alkynes.
5
two cyclopentadienyl rings in a h mode, to the phosphorus atom
from the diphenylphosphine group and to the carbon atom of the
iminoacyl moiety in a pseudotetrahedral geometry typical of bent-
metallocene. The Nb1–P1 and Nb1–C1 bonds form the basis for a
five-membered chelate ring together the former alkyne moiety. The
five-membered chelate ring is slightly puckered, with the niobium
Insertion reactions of phosphidoisocyanide-niobocenes with alkynes
The reactivity of the phosphidoisocyanide-niobocene complex
2 towards polarized alkynes, namely methyl propiolate and
methyl 2-butynoate, as well as electron-poor alkynes, namely
dimethyl 2-butynedioate and di(tert-butyl) 2-butynedioate, were
˚
atom 0.607(6) A out of the mean plane passing through the P1,
C1, C2 and C3 atoms. The dihedral angle between planes Nb(1)–
P(1)–C(2) and Nb(1)–C(1)–C(3)–C(2) is 18.2(2)◦. The C1–C3 and
1964 | Dalton Trans., 2010, 39, 1962–1971
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Table 1 Selected bond lengths and angles for 8 determined by X-ray and DFT-based methods
Bond angles/◦
˚
Bond lengths/A
X-ray
DFT
X-ray
DFT
C(4)–O(2)
Cp(1)–Nb(1)
Cp(2)–Nb(1)
Nb(1)–C(1)
C(1)–N(1)
Nb(1)–P(1)
P(1)–C(2)
C(2)–C(3)
C(3)–C(1)
C(4)–O(1)
1.334(5)
2.050
2.059
2.305(4)
1.292(5)
2.515(1)
1.820(4)
1.340(6)
1.510(5)
1.193(6)
1.364 (1.364)
2.082 (2.099)
2.102 (2.084)
2.362 (2.344)
1.298 (1.289)
2.475 (2.464)
1.826 (1.827)
1.350 (1.352)
1.517 (1.528)
1.218 (1.219)
Dihedral angleb
16.8
140.5
-5.6 (-5.26)
141.5 (140.6)
133.4 (118.5)
127.4 (128.7)
107.3 (107.1)
76.0 (76.0)
117.0 (118.5)
123.4 (121.1)
114.9 (116.1)
124.1 (124.1)
Cent(1)–Nb(1)–Cent(2)a
Nb(1)–C(1)–N(1)
C(1)–N(1)–C(51)
Nb(1)–P(1)–C(2)
C(1)–Nb(1)–P(1)
Nb(1)–C(1)–C(3)
C(1)–C(3)–C(2)
C(3)–C(2)–P(1)
123.1(3)
128.6(3)
103.74(13)
76.07(10)
117.0(3)
121.7(4)
116.6(3)
124.5(4)
O(1)–C(4)–O(2)
a Cp(1) is constituted by C(12)–C(16) atoms. Cent(1) is the centroid of the Cp(1) ring. Cp(2) is constituted by C(21)–C(25) atoms. Cent(2) is the centroid
of the Cp(2) ring. b Dihedral angle formed by the plane defined by P(1)–C(2)–Nb(1) and the plane containing Nb(1)–C(1)–C(3)–C(2) atoms of the
metallacycle.
rings, i.e. the endo disposition, and the other with an opposite
orientation, i.e. the exo disposition (see Scheme 3). The ORTEP
diagram shows an exo disposition, probably due to a sterically
hindered disposition for the metallacycle.
Scheme 3 Possible endo and exo dispositions of the iminoacyl fragment.
Fig. 3 ORTEP diagram of 8 with 40% probability ellipsoids. Hydrogen
atoms and solvent molecules have been omitted for clarity.
The spectroscopic data for these complexes are consistent with
the formation of a heteroniobacycle moiety.
The IR spectra contain the characteristic bands due to the
˚
C2–C3 bond lengths of 1.515(5) and 1.340(6) A, respectively,
=
=
indicate that there is no charge delocalization in this ring.
The distances between the metal atom and the centroids of
iminoacyl n(C N) and olefinic n(C C) groups at ca. 1590 and
ca. 1505 cm-1, respectively. Additionally, the IR spectra exhibit a
band at 1718 cm-1 corresponding to n(COO) of the carboxylate
group.
˚
the Cp rings are 2.050 and 2.059 A and the angle Cent(1)–
Nb(1)–Cent(2) is 140.5◦ [Cent(1) and Cent(2) are the centroids
of C(12)–C(16) and C(21)–C(25), respectively]. These values are
typical of bent niobocene derivatives.3,4 The Nb(1)–C(1) distance
The 31P{ H}-NMR spectra show a single broad signal at ca.
1
90.0 ppm for the phosphorus of the diphenylphosphine group
present in the heterometallacycle. This signal is shifted downfield
with respect to that in the phosphido ligand in complex 2, which
is consistent with the expected decrease in electron density on the
phosphorus atom. The chemical shift is similar to those previously
found for other related heterometallacycles.14c
˚
of 2.305(4) A is slightly longer than those found in other
niobium iminoacyl derivatives.16 The Nb(1)–P(1) bond distance
˚
of 2.515(1) A is very similar to those found in other niobocene
systems.3,4
It is worth noting the relative disposition of the Cp¢ ligands
(Cp¢ = C5H4SiMe3) with respect to one other. The orientation
of these ligands is intermediate between eclipsed and staggered,
with the two SiMe3 groups in cis positions [Si(1)–Cent(1)–Cent(2)–
Si(2) angle of 102.2◦]. This arrangement is probably due to steric
hindrance between the SiMe3 groups situated in this region and
the bulky phenyl substituents on the phosphorus atom.
The xylyl fragment of the iminoacyl group can adopt two
possible dispositions with respect to the niobocene moiety—
one with the xylyl group oriented towards the cyclopentadienyl
As far as the complexes 4 and 5 are concerned, the most
interesting signal in the 1H-NMR spectra of 8 and 9 corresponds
=
to the olefinic substituent of the C CR moiety, which appears as
a doublet at 7.62 ppm (2JHP = 2.4 Hz) for the hydrogen atom in 8
and as a doublet at 1.91 ppm (3JHP = 6.6 Hz) for the methyl group
in 9. The values of the coupling constants are less than 10 Hz in
both cases and this is consistent with a gem relative phosphorus-
hydrogen/methyl disposition.13 The 1H-NMR spectrum of 10
shows two resonances at 1.02 and 1.46 ppm for the hydrogen
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atoms of the tert-butyl groups, which shows that these are not
equivalent.
The 1H-NMR spectra also contain a singlet for the methyl
groups of the SiMe3 and four multiplets corresponding to the
cyclopentadienyl units, in accordance with an ABCD spin system
in molecules with Cs symmetry.
consistent with the expected decrease in electron density on the
phosphorus atom.
The H-NMR spectra contain doublets corresponding to the
1
=
olefinic hydrogen of the C CH moiety and these are at d 7.18 ppm
(2JHP = 4.0 Hz) for 11 and at 7.17 ppm (2JHP = 6.2 Hz) for 12.
The values of the coupling constants, which are less than 10 Hz in
both cases, are consistent with a gem relative phosphorus-hydrogen
disposition.13 The 1H-NMR spectra also contain a single signal for
the methyl groups of the SiMe3 and four multiplets corresponding
to the cyclopentadienyl units.
13C-NMR spectroscopy involving g-HSQC and g-HMBC tech-
niques allowed the assignment of the resonances of the different
carbon atoms of the heteroniobacycle, particularly the olefinic
and iminoacyl carbon atoms (see Experimental) for complexes 8
and 9. It was mentioned above that complex 10 decomposes in
solution and, as a result, it was not possible to record the 13C-
NMR spectrum of this compound.
The spectroscopic data discussed above are consistent with a
pseudo-tetrahedral geometry for complexes 8–10, as shown in
Fig. 4.
1
13C{ H}-NMR and 13C-NMR spectra, g-HSQC and g-HMBC
techniques were used for the assignment of the signals correspond-
ing to the phosphinoalkenyl moiety for complexes 11 and 12.
The spectra each contain a doublet corresponding to the olefinic
carbon atom bonded to the phosphorus and these appear at
138.7 ppm (1JCP = 33.9 Hz) for 11 and at 175.8 ppm (1JCP
=
27.4 Hz) for 12. The quaternary carbon atom of the isocyanide
ligand gave a broad single signal at 225.3 ppm for 11 and at
219.3 ppm for 12.
The spectroscopic data are consistent with a pseudo-tetrahedral
geometry with the diphenylphosphinoalkenyl ligand coordinated,
1
in a h -C manner, to the metal and a Z configuration for the
carbon–carbon double bond, as shown in Fig. 5.
Fig. 4 Proposed structure for complexes 8–10.
≡
Complexes 2 and 3 react with phenylacetylene, PhC CH,
in contrast to complex 1, to give the new diphenylphos-
5
1
Fig. 5 Proposed structure for complexes 11 and 12.
phinoalkenyl niobocene derivatives [Nb(h -C5H4SiMe3)2(h -C–
=
C(C6H5) C(H)PPh2)(CNR)] [R = xylyl (11), Cy (12)] as
brownish-green solids (see eqn (4)).
Theoretical study and mechanistic proposals for alkyne insertion
{[Nb](PPh2 )(CNR)}+ HC ≡CPh
[Nb]={Nb(h5-C5H4SiMe3)2}
→
{[Nb](h1-C-C(Ph) = C(H)PPh2 )(CNR)}
R = Xylyl (11), Cy (12)
It has been shown in detail that the phosphido-niobocene com-
plexes 1–3 give very different products when they react with
polarized, electron-poor or electron-rich alkynes in insertion
processes. This behaviour may be influenced by the different
electronic environments of the niobocene molecules, which in
turn depend on the ancillary ligand contained in the molecule
(either CO or CN–R). With the aim of providing an insight
into the reaction mechanism and finding an explanation for the
distinct reactivity, models of 1 and 2 were studied by means of a
DFT-based method (see Experimental for details). The molecular
structure was slightly simplified by considering cyclopentadienyl
ligands instead of [C5H4SiMe3] and a PH2 moiety instead of the
diphenylphosphido system used in the experiments. The CNxylyl
group was also simplified by employing a CNPh ligand. It can
(4)
These complexes were characterized by elemental analysis and
by IR and NMR spectroscopy.
The IR spectra of these complexes contain the band due to the
n(C N) of the isocyanide ligand at 2039 and 2015 cm-1 for 11 and
≡
=
12, respectively. The band corresponding to n(C C) of the double
bond of the phosphinoalkenyl ligand is observed at ca. 1560 cm-1.
1
The 31P{ H}-NMR spectra of these complexes show a single
broad signal at 71.0 ppm for 11 and at 76.3 ppm for 12. These
resonances were shifted downfield with respect to those of the
phosphido ligands in complexes 2 and 3, and this behaviour is
1966 | Dalton Trans., 2010, 39, 1962–1971
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be seen from the results in Table 1 that the structure of complex
8 was fairly well reproduced at this level of theory. The most
striking difference between the X-ray data and the computed
structure was found in the disposition of the phenyl fragment
of the iminoacyl unit relative to the niobocene moiety. The lack
of steric hindrance imposed by the SiMe3 substituents in the
cyclopentadienyl ligands and the two methyls in the xylyl group
make the endo disposition more stable than the exo one by 5.2 kcal
mol-1. Note that the geometrical parameters in Table 1 are very
similar for both isomers, although the difference in stability is not
small.
In agreement with the results from the theoretical study, the
formation of complexes 4–10 can be understood in terms of the
mechanism depicted in Scheme 4.
The first step involves a (1,2) insertion of the alkyne into the
Nb–P bond to give a phosphinoalkenyl species, which are the final
products (complexes 4–7) in the insertion processes of 1 and in the
≡
reactions of 2 and 3 with PhC CH.
In the second step, which occurs in the reaction of 2 with
both polarized and electron-poor alkynes, it is proposed that
a new intermediate is formed by a (1,1) migratory insertion of
the isocyanide ligand into the Nb–C bond, which subsequently
undergoes ring closure by coordination of the phosphine group.
The behaviour of isocyanide towards metal-carbon bonds in
alkyl transition metal complexes is well documented and inser-
tion reactions are usually observed.17 The insertion reaction of
the xylylisocyanide into the Nb–C bond has previously been
reported by our group11 and is consistent with the weaker
strength of the Nb–CNxylyl bond compared with the Nb–CO
bond.
We subsequently studied the insertion mechanism of alkynes
into the Nb–P bond followed by migration of the ancillary ligand
into the Nb–C bond to give the final heteroniobacycle. In order to
achieve this goal we considered models of complexes 1 and 2, as
≡
described above, and the polarized alkyne HC CCO2Me. Firstly,
the whole reaction energy profile was characterized with acetylene.
The relative energies of all the intermediates and transition states
for the migration of the ancillary ligand are collected in Fig. 6.
Concluding remarks
In conclusion, we have succeeded in the synthesis of unprecedented
heterometallacyclic niobium complexes through an insertion
reaction between a phosphido/xylylisocyanide derivative 2 and
polarized and electron-deficient alkynes. These results open up a
different way to prepare new types of heteroniobacycles. Secondly,
when the auxiliary ligand CO or CNCy is present only the
formation of phosphinoalkenyl complexes takes place, as it did
when phenylacetylene was used. Furthermore, these complexes
represent stable intermediates in the hydrophosphination of
alkynes. A theoretical study confirmed the differences in reactivity
between 1–3 and the alkynes used.
Experimental
Fig. 6 Reaction energy profile of the intermediates in the reaction of
≡
model phosphido-niobocene complexes 1 and 2 with HC CCO2Me. In
All reactions were carried out using standard Schlenk tech-
niques. Oxygen and water were excluded through the use of
vacuum lines supplied with purified N2. Toluene was distilled
from sodium. Hexane was distilled from sodium/potassium
alloy. Diethyl ether and THF were distilled from sodium
red L = CO, 1. In violet L = CNxylyl, 2. (All values in kcal mol-1).
According to these results, the first step of the reaction involves
insertion of the alkyne into the Nb–P bond of both phosphido-
niobocene complexes to give a phosphinoalkenyl intermediate II.
This step is equally exothermic for both complexes (-22.1 and
-24.3 kcal mol-1). Several attempts to characterize a transition
state for this step were unsuccessful, but since our goal was to
study the different behaviour of CO and CN–R ligands in the
migration into the Nb–C bond, we focused our efforts on the next
steps in the process. A transition state structure, TSII-III, was
fully characterized for the subsequent insertion of the ancillary
ligand into the Nb–C bond. The differences in the energy barriers
between the models of 1 and 2 were small, but the insertion was
clearly favoured thermodynamically in the case of the isocyanide
(-34.6 kcal mol-1) more than in the carbonyl system (-20.1 kcal
mol-1). In order to reach the final product V, a reorganization
is required that involves decoordination of the carbonyl oxygen
atom and subsequent coordination of the phosphine to the metal.
This step is computed to be energetically costly but is equally so
for both systems.
benzophenone. All solvents were deoxygenated prior to use.
5
[Nb(h -C5H4SiMe3)2(PPh2)(L)] [L
=
CO (1), CNxylyl (2),
CNCy (3)] were prepared as described in the literature.3,4
The commercially available compounds like methyl propio-
≡
≡
late (HC CCO2CH3), methyl 2-butynoate (CH3C CCO2CH3),
≡
dimethyl 2-butynedioate [(CH3O2C)C C(CO2CH3)], di(tert-
t
t
≡
butyl) 2-butynedioate [( BuO2C)C C(CO2 Bu)] and phenylacety-
≡
lene (PhC CH) were used as received from Aldrich. Deuterated
˚
solvents were dried over 4 A molecular sieves and degassed prior
to use. H, 13C and 31P NMR spectra were recorded on a Varian
1
Inova 500 MHz spectrometer at room temperature unless stated
1
otherwise. H, 13C and 31P NMR chemical shifts (d values) are
given in ppm relative to the solvent signal (1H, 13C) or standard
resonances (31P, external 85% H3PO4). IR spectra were recorded
on a Perkin Elmer 883 spectrophotometer as Nujol mulls on CsI
windows. Microanalyses were carried out with a Perkin-Elmer
2400 microanalyzer.
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Scheme 4 Mechanistic proposal for the formation of complexes 4–12.
4.86, 5.06 (2 H, m, complex signal, C5H4SiMe3), 6.88–7.25 (m,
Preparations
2
=
10 H, PPh2), 7.60 (1 H, d, JHP = 5.13, HC C). dC (125 MHz;
13
1
5
=
C{ H}-NMR, C6D6) -0.1 (SiMe3), 51.4 (C CCO2CH3), 96.4
=
[Nb(g -C5H4SiMe3)2(C(CO2CH3) C(R)PPh2)(CO)], R = H (4),
(C1, C5H4SiMe3), 90.7, 94.0, 101.8, 104.0 (C2–5, exact assignment
not possible, C5H4SiMe3), 129.8–136.7 (PPh2), 141.7 (d, JCP
CH3 (5)
1
=
3
=
=
To a solution of 1 (0.28 g, 0.46 mmol and 0.42 g, 0.68 mmol)
in THF (30 mL) was added the stoichiometric amount of methyl
31.6, HC C), 168.5 (d, JCP = 25.7, C CCO2CH3), 170.2 (d,
JCP = 29.4, C CCO2CH3), 290.9 (CO). dC (125 MHz; 13C-NMR,
2
=
-3
1
1
≡
=
propiolate (HC CCO2CH3) (0.04 g, r = 0.945 g cm , 0.46 mmol)
C6D6) 141.7 (dd, JCH = 132.2, JCP = 31.6, HC C), 168.5 (dm,
JCP = 25.7, 3JCH = 6.70, 3JCH = 4.1, C CCO2CH3); dP (202 MHz;
3
≡
=
for 4 or methyl 2-butynoate (CH3C CCO2CH3) (0.07 g, r =
1
0.981 g cm-3, 0.68 mmol) for 5 at RT. The mixture was stirred
31P{ H}-NMR, C6D6) 82.4 (s).
for 15 min. The solvent was evaporated under vacuum to dryness.
(5): (0.37 g, 85%) Found: C 60.23, H 6.35. Calcd for
5
The new diphenylphosphinoalkenyl niobocene complexes [Nb(h -
C34H42NbO3PSi2: C 60.16, H 6.01%; nmax(Nujol/polyethylene)/
1
-1
=
=
C5H4SiMe3)2(h -C–C(CO2CH3) C(R)PPh2)(CO)], R = H (4),
cm , 1916 (CO), 1724 (COO), 1684 (C C). dH (500 MHz; C6D6)
3
=
CH3 (5), were isolated as brown and green solids that were soluble
in THF and toluene but insoluble in diethyl ether and hexane. The
solids were washed with hexane (2 ¥ 10 mL) at 0 ◦C.
0.16 (s, 18 H, SiMe3), 1.85 (3 H, d, JHP = 6.8, CH3C C), 3.47
=
(3 H, s, C CCO2CH3), 4.34, 4.85, 4.88, 5.31(2 H, m, complex
signal, C5H4SiMe3), 6.93–7.44 (10 H, m, PPh2). 13C{ H}-NMR
1
=
=
(4): (0.24 g, 80%) Found: C 59.74, H 6.01. Calcd for
(C6D6) 0.1 (SiMe3), 17.6 (CH3C C), 51.4 (C CCO2CH3), 96.7,
C33H40NbO3PSi2: C 59.63, H 6.07%; nmax(Nujol/polyethylene)/
(C1, C5H4SiMe3), 91.0, 93.7, 99.9, 104.7 (C2–5, exact assignment
-1
=
=
cm , 1910 (CO), 1717 (COO), 1653 (C C); dH (500 MHz; C6D6)
not possible, C5H4SiMe3), 127.7–135.4 (Ph), 149.4 (d, CH3C C,
1
3
=
=
0.16 (18 H, s, SiMe3), 3.47 (3 H, s, C CCO2CH3), 4.24, 4.83,
JCP = 25.4), 167.1 (d, C CCO2CH3, JCP = 34.2), 169.4
1968 | Dalton Trans., 2010, 39, 1962–1971
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2
1
(C CCO2CH3, JCP = 26.8), 289.3 (CO). dC (125 MHz; 13C-NMR,
C–C( Nxylyl)C(CO2Me) C(H)PPh2-k -P)] (8) was soluble in
THF and toluene but insoluble in diethyl ether. This compound
decomposed after s short period of time in solution.
=
=
=
3
3
=
C6D6) 167.1 (dm, C CCO2CH3, JCP = 34.2, JCH = 6.63 Hz,
JCH = 4.4), 169.4 (dm, C CCO2CH3, JCP = 26.8, 3JCMe = 4.8),
4
2
=
289.3 (CO). 3dP (202 MHz; 31P{ H}-NMR, C6D6) 93.1 (s).
(8): (0.24 g, 80%) Found: C 64.00, H 6.43, N 1.85.
Calcd for C41H49NNbO2PSi2: C 64.13, H 6.43, N 1.82%.
max(Nujol/polyethylene)/cm , 1718 (COO), 1630 (C N), 1583
(C C). dH (500 MHz; C6D6) 0.22 (18 H, s, SiMe3), 2.32 (6 H, s,
CH3, CNxylyl), 3.07 (3 H, s, C CCO2CH3), 4.42, 5.38 (m, 2
H complex signal, C5H4SiMe3), 4.74 (m, 4 H complex signal,
1
-1
=
n
5
=
[Nb(g -C5H4SiMe3)2(C(CO2R) C(CO2R)PPh2)(CO)] R = CH3
=
t
(6), R = Bu (7)
=
To a solution of 1 (0.37 g, 0.56 mmol) in THF (30 mL),
cooled to -78 ◦C for the synthesis of 6 and at RT for 7, was
C5H4SiMe3), 6.91–7.52 (m, 13 H, Ph), 7.62 (1 H, d, JHP = 2.4,
2
1
HC C). dC (125 MHz; 13C{ H}-NMR, C6D6) 0.4 (SiMe3), 20.0
=
added the stoichiometric amount of dimethyl 2-butynedioate
-3
1
≡
=
[(CH3O2C)C C(CO2CH3)] (0.08 g, r = 1.156 g cm , 0.56 mmol)
(CH3, CNxylyl), 51.2 (C CCO2CH3), 98.3 (C , C5H4SiMe3), 87.1,
95.5, 98.2, 106.5 (C2–5, exact assignment not possible, C5H4SiMe3),
t
t
≡
for 6, or di(tert-butyl) 2-butynedioate [( BuCO2)C C(CO2 Bu)]
(0.15 g, 0.68 mmol) for 7. The mixture was stirred for 2 h
at low temperature for 6 and 15 min at RT for 7. After this
time, the solvent was evaporated to dryness under vacuum.
1
=
121.4–153 (C6H5), 141.0 (d, HC C, JCP = 28.73 Hz), 167.9 (d,
2
3
=
=
JCP = 28.3, C CCO2CH3), 170.3 (d, JCP = 23.5, C CCO2CH3),
220.0 (C N). dP (202 MHz; 31P{ H}-NMR, C6D6) 82.4 (s).
1
=
5
The new diphenylphosphinoalkenyl niobocene complexes [Nb(h -
(9): (0.26 g, 85%) Found: C 64.27, H 6.24, N 1.94.
1
=
C5H4SiMe3)2(h -C–C(CO2R) C(CO2R)PPh2)(CO)] [R = CH3,
Calcd for C42H51NNbO2PSi2: C 64.51, H 6.57, N 1.79%
max(Nujol/polyethylene)/cm-1 1718 (COO), 1617 (C N), 1588
(C C). dH (500 MHz; C6D6) 0.15 (18 H, s, SiMe3), 1.91 (3 H,
t
=
(6), R = Bu, (7)] were washed twice with hexane (10 mL) at
n
◦
=
0 C. Complex 6 was isolated as a mixture of Z/E isomers in a
3
=
1 : 2 ratio, 6a and 6b, which could not be separated. (6): (0.32 g,
80%) Found: C 57.94, H 5.97. Calcd for C35H42NbO5PSi2 C 58.16,
H 5.86%; nmax(Nujol/polyethylene)/cm-1, 1914 (br, CO), 1726 (br,
d, JHP = 6.6, CH3C CCO2CH3), 2.33 (6 H, s, CH3, CNXylyl),
=
3.02 (3 H, s, C CCO2CH3), 4.59, 4.70, 4.79, 5.33 (2 H, m, each
complex signal, C5H4SiMe3), 6.97–7.58 (13 H, m, Ph), 7.62 (1
COO), 1671 (C C). dH (500 MHz; C6D6) Major isomer: 0.12 (18
H, d, JHP = 2.4, HC C). dC (125 MHz; 13C{ H}-NMR, C6D6)
2
1
=
=
=
H, s, SiMe3), 3.14, (3 H, s, CO2CH3), 3.40 (3 H, s, CO2CH3),
4.41, 4.82, 5.02, 5.41 (2 H, m, complex signal, C5H4SiMe3), 7.26–
7.93 (10 H, m, PPh2), Minor isomer: 0.14 (18 H, s, SiMe3), 2.67(3
H, s, CO2CH3), 3.51 (3 H, s, CO2CH3), 5.33, 5.53, 5.64, 5.75 (2
H, m, complex signal, C5H4SiMe3), 6.91–7.59 (10 H, m, PPh2),
0.4 (SiMe3), 20.0 (CH3, CNXylyl), 30.0 (CH3C CCO2CH3), 51.3
1
=
(C CCO2CH3), 98.4 (C , C5H4SiMe3), 87.0, 95.6, 98.3, 106.5
(C2–5, exact assignment not possible, C5H4SiMe3), 121.5–153.3
1
2
=
(C6H5), 141.1 (d, CH3C C, JCP = 29.4), 167.9 (d, JCP
=
3
=
=
26.1, C CCO2CH3), 170.3 (d, JCP = 23.7, C CCO2CH3), 219.9
1
1
dC (125 MHz; 13C{ H}-NMR, C6D6) For both isomers -0.2,
(C N). dP (202 MHz; 31P{ H}-NMR, C6D6) 101.1 (PPh2).
=
0.2 (SiMe3), 47.9, 51.0, 51.6 (CO2CH3), 91.0–104.3 (C1-5, exact
assignment not possible, C5H4SiMe3), 129.0–135.3 (Ph), 149.1,
(10): (0.30 g, 85%) Found: C 64.54, H 66.72, N 1.61.
Calcd for C49H63NNbO4PSi2: C 64.67, H 6.98, N 1.54%
max(Nujol/polyethylene)/cm-1 1718 (COO), 1590 (C N), 1505
=
=
149.5 (C C), 166.9, 167.3, 169.0, 169.3 (CO2CH3)). dP (202 MHz;
n
31P{ H}-NMR, C6D6) major isomer: 93.9 (s), minor isomer:
(C C). dH (500 MHz; C6D6) 0.04 (18 H, s, SiMe3), 1.02 (9 H, s,
CO2But), 1.46 (9 H, s, CO2But), 2.36 (6 H, s, CH3, CNxylyl), 4.47,
5.07 (2 H, m, each complex signal, C5H4SiMe3), 4.64 (4 H, m,
1
=
79.5 (s).
(7): (0.36 g, 80%) Found: C 61.19, H 6.58. Calcd for
C41H54NbO5PSi2 C 61.03, H 6.75%; nmax(Nujol/polyethylene)/
C5H4SiMe3), 6.97–7.77 (13 H, m, Ph). dP (202 MHz; 31P{ H}-
1
-1
=
cm , 1910 (CO), 1717 (COO), 1653 (C C). dH (500 MHz; C6D6)
NMR, C6D6) 92.0 (s).
0.13 (18 H, s, SiMe3), 1.15 (9 H, s, CO2But), 1.54, (9H, s, CO2But)
4.34, 4.72, 4.99, 5.26 (2 H, m, complex signal, C5H4SiMe3), 6.90–
5
1
=
[Nb(g -C5H4SiMe3)2(g -C–C(C6H5) C(H)PPh2)(CNR)] R =
7.61 (10 H, m, PPh2), dC (125 MHz; 13C{ H}-NMR, C6D6) 0.0
1
xylyl (11), Cy (12)
(SiMe3), 27.7, 28.3 (CO2But), 97.6 (C1, C5H4SiMe3), 94.0, 97.2,
102.8, 104.4 (C2–5, exact assignment not possible, C5H4SiMe3),
To a solution of 2 (0.45 g, 0.62 mmol) or 3 (0.35 g, 0.50 mmol)
in anhydrous THF (30 mL) was added a stoichiometric amount
of phenylacetylene (0.06 g, r = 0.930 g mL-1, 0.62 mmol) at RT.
The mixture was stirred for 30 min for 9 and 2 h for 10, and
the solvent was evaporated to dryness under vacuum. The brown-
green solids were washed with hexane (2 ¥ 10 mL) at 0 ◦C to yield
1
t
=
125.5–144.4 (Ph), 135.9 (d, JCP = 34.1, C C(CO2Bu )PPh2),
166.8 (d, 2JCP = 24.0, C C(CO2Bu )PPh2), 166.8 (d, JCP = 31.6,
t
3
=
t
t
=
=
([Nb](Bu O2C)C C), 168.8 ([Nb](Bu O2C)C C), 289.0 (CO). dP
1
(202 MHz; 31P{ H}-NMR, C6D6) 88.1 (s).
5
the new diphenylphosphinoalkenyl niobocene complexes [Nb(h -
5
1
1
2
1
=
=
[Nb(g -C5H4SiMe3)2(g -C–C( Nxylyl)C(R ) C(R )PPh2-j -P)];
1
=
C5H4SiMe3)2(h -C–C(C6H5) C(H)PPh2)(CNR)] R = xylyl (11),
R1 = H; R2 = CO2Me (8); R1 = Me; R2 = CO2Me (9). R1 =
Cy (12) as brownish-green solids in ca. 85% yield.
CO2 Bu, R2 = CO2 Bu (10)
t
t
(11): (0.41 g, 85%) Found: C 68.56, H 6.37, N 1.72. Calcd
To a solution of 2 (0.27 g, 0.39 mmol) in THF (30 mL),
for C45H51NNbPSi2: C 68.77, H 6.54, N 1.78%; nmax(Nujol/
polyethylene)/cm , 2039 (C N), 1557 (C C). dH (500 MHz;
C6D6) 0.19 (18 H, s, SiMe3), 2.16 (6 H, s, CH3 CNxylyl), 4.67,
cooled to 0 ◦C, was added the stoichiometric amount of
-1
≡
=
t
t
≡
di(tert-butyl) 2-butynedioate, [( BuCO2)C C(CO2 Bu)], (0.09 g,
0.39 mmol). The mixture was stirred for 10 min and the
solvent was evaporated to dryness under vacuum. The result-
4.79, 4.85, 5.17 (2 H, m, complex signal, C5H4SiMe3), 6.61–7.60
2
=
(18 H, m, Ph) 7.18 (1 H, d, JHP = 4.0, HC C). dC (125 MHz;
1
ing brown solid was washed with hexane (2 ¥ 10 mL) at
13C{ H}-NMR, C6D6) 0.9 (SiMe3), 20.8 (CH3, CNxylyl), 88.9,
◦
5
1
0
C. The heteroniobacycle derivative [Nb(h -C5H4SiMe3)2(h -
93.9, 99.5, 104.3 (C2–5, exact assignment not possible, C5H4SiMe3),
Dalton Trans., 2010, 39, 1962–1971 | 1969
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2
1
=
=
137.6 (d, JCP = 34.9, PhC C), 138.7 (d, C CH, JCP = 33.9),
Computational details
123.3–154.0 (Ph), 225.3 (C N). dC (125 MHz; 13C-NMR, C6D6)
≡
1
1
The geometries of all the structures were fully optimized using
the Amsterdam Density Functional (ADF v2005.01) program
package,21 in which the numerical integration scheme was devel-
oped by te Velde et al.22 and analytical energy first derivatives by
Versluis and Ziegler.23 The BP86 exchange–correlation functional
was used, which is a combination of the local VWN for correlation,
the non-local exchange potential by Becke,24 and the non-local
Perdew’s correlation potential.25 Scalar relativistic effects were
introduced using the ZORA26 approach and frozen cores (1 s
for C, N and O, up to 2p for P, and up to 3d for Nb). Valence
electrons were treated with triple-x plus polarization Slater basis
sets on all atoms as provided in the ADF library. For the
minima and for transition states, both geometry optimization and
numerical energy second derivatives were carried out with the
general integration parameter set to 6.
=
138.7 (dm, JCP = 33.9, JCH = 12.0, C CH), dP (202 MHz;
31P{ H}-NMR, C6D6) 71.0 (s).
1
(12): (0.32 g, 85%) Found: C 67.51, H 6.87, N 1.79.
Calcd for C43H53NNbPSi2:
max(Nujol/polyethylene)/cm , 2015 (C N), 1662 (C C). dH
C
67.60,
H
6.99,
N 1.83%;
-1
≡
=
n
(500 MHz; C6D6) 0.25 (s, 18 H, SiMe3), 0.85–1.84 (10 H, m,
CNCy), 3.52 (m, H1, Cy), 4.52, 5.10 (2 H, m, complex signal,
C5H4SiMe3), 4.81 (4 H, m, complex signal, C5H4SiMe3), 6.87–7.54
2
=
(10 H, m, Ph), 7.17 (d, 1 H, JHP = 6.2, HC C). dC (125 MHz;
13C{ H}-NMR, C6D6), 0.8 (SiMe3), 27.0, 34.6, 35.2 (Cy), 88.8 (C1,
1
Cy), 89.3, 89.4, 99.2, 100.9 (C2–5, exact assignment not possible,
C5H4SiMe3), 96.0 (C1, C5H4SiMe3), 126.3–135.0 (Ph), 142.0 (d,
2
1
=
=
=
JCP = 18.2 PhC C), 175.8 (d, JCP = 27.3, C CH), 219.3 (C N).
dP (202 MHz; 31P{ H}-NMR, C6D6), 76.3 (s).
1
Crystallography
Acknowledgements
Data for complex 8 were collected on aBruker X8APPEX II CCD-
based diffractometer, equipped with a graphite-monochromated
The authors gratefully acknowledge financial support from the
Ministerio de Ciencia e Innovacio´n (MICINN), Spain (grants
CTQ2006-11845/BQU and CTQ2008-06549-C02-02/BQU, Con-
solider Ingenio 2010 ORFEO CSD-2007-00006 and CSD2006-
0003), UE Action COST CM0802 and the Junta de Comunidades
de Castilla-La Mancha (grant no. PCI08-0010, PCIO8-0032).
˚
Mo-Ka radiation source (l = 0.71073 A). The crystal data,
data collection, structural solution, and refinement parameters
are summarized in Table 2. Data were integrated using SAINT18
and an absorption correction was performed with the program
SADABS.19 The structure was solved by direct methods using
SHELXTL,20 and refined by full-matrix least-squares methods
based on F2. All non-hydrogen atoms were refined with anisotropic
thermal parameters. Toluene groups were located in disordered
positions. Hydrogen atoms were placed using a “riding model”
and included in the refinement at calculated positions.
References
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Table 2 Crystal data for complex 8
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Formula
FW
T/K
C41H49NNbO2PSi2·1.5(C6H5Me)
904.56
100(2)
Crystal system
Space group
Triclinic
¯
P1
10.7939(5)
12.2093(6)
19.3334(9)
93.144(3)
102.049(3)
108.324(3)
2345.4(2)
2
1.281
0.382
951
0.352 ¥ 0.153 ¥ 0.117
1.09 to 25.90
-13 ≤ h ≤ 11,
-14 ≤ k ≤ 14
-23 ≤ l ≤ 23
25 036
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
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1, p 385; (b) H. R. Hudson. In The Chemistry of Organophosphorus
Compounds, ed. F. R. Hartley, Wiley, Chichester, 1990; vol. 1, p 173.
Z
D
calcd/g cm-3
m/mm-1
F(000)
=
7 For representative examples of complexes with R2PCH CH2, see the
Crystal dimensions/mm
q range/◦
following: [M] = [Cr] and [Mo] (a) P. G. Edwards, J. S. Fleming, S. S.
Liyanage, S. J. Coles and M. B. Hursthouse, J. Chem. Soc., Dalton
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hkl ranges
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
R indices (all data)
9067 [Rint = 0.0637]
9067/0/586
0.653
R1 = 0.0494, wR2 = 0.1338
R1 = 0.0771, wR2 = 0.1792
0.902 and -0.945
=
complexes with R2PCH2CH CH2, see the following: [M] = [Cr] and
[Mo], see ref. [7a][W]; (e) X. Morise, M. L. H. Green, P. C. McGowan
and S. J. Simpson, J. Chem. Soc., Dalton Trans., 1994, 871; [Pd]:; (f) S. J.
Coles, P. Faulds, M. B. Hursthouse, D. G. Kelly, G. C. Ranger, A. J.
Toner and N. M. Walker, J. Organomet. Chem., 1999, 586, 234For
Largest diffraction peak and
-3
˚
hole/e A
=
examples of complexes with R2PCH2CH2CH CH2, see the following:
1970 | Dalton Trans., 2010, 39, 1962–1971
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The Royal Society of Chemistry 2010
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This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 1962–1971 | 1971
©