Synthesis and characterisation of oxo- and phenylimido-rhenium(v) complexes containing bidentate phosphinoenolato ligands

Article abstract of DOI:10.1039/b106306p

Reacting 1-phenyl-2-(diphenylphosphino)ethanone (P₁～OH), 1-tert-butyl-2-(diphenylphosphino)ethanone (P₂～OH) and 1-phenyl-2-(diphenylphosphino)propanone (P₃～OH) with ReOCl₃(PPh₃)₂ and Re(NPh)Cl₃-(PPh₃)₂ in toluene and ethanol in the presence of NEt₃ yields complexes in which these ligands bind as monoanionic enolato chelating agents. Bromo and iodo analogues are prepared similarly. The reactions are solvent dependent. The disubstituted ReOCl(P～O)₂ compounds obtained in toluene adopt the 'twisted' cis-(P,P) octahedral structure. With Re(NPh)Cl₃-(PPh₃)₂, P₁～OH and P₂～OH give the corresponding Re(NPh)Cl(P～O)₂ compounds and the trans-(P,P)-trans-(Cl, Cl) isomer of monosubstituted Re(NPh)Cl₂(PPh₃)(P～O) as the major products, together with small amounts of 'twisted' trans-(P,P) Re(NPh)Cl(P～O)₂. The monosubstituted complex is the only species isolated with P₃～OH. The major structural difference between the two systems is the small stability gap between the cis- and the trans-(P,P) isomers of the imido complexes. In ethanol, unexpected cis-ethoxo-oxo complexes ReO(OEt)(P～O)₂ are isolated, resulting from stereoselective substitution of the halide in the 'twisted' cis-(P,P) octahedral complexes. The reactions with Re(NPh)Cl₃(PPh₃)₂ are less selective and give rise to mixtures of complexes. The trans-ethoxo-phenylimido compound Re(NPh)(OEt)(P₁～O)₂ is obtained in good yield. A crystallographic study reveals an unexpected 'equatorial' trans-(P,P) structure with the ethoxo ligand trans to the Re=NPh bond. ¹H NMR indicates that the ethoxo ligand acts as an electron reservoir in these complexes, since its protons are strongly deshielded in the cis-oxo-ethoxo species and strongly shielded in the trans-phenylimido-ethoxo complex.

Full text of DOI:10.1039/b106306p

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis and characterisation of oxo- and phenylimido-rhenium(V)
complexes containing bidentate phosphinoenolato ligands
Xavier Couillens,a Marie Gressier,a Reine Turpin,a Michèle Dartiguenave,*a Yvon Coulaisb
and André L. Beauchampc
a Laboratoire de Chimie Inorganique, UA 870, Université Paul Sabatier, 118 route de Narbonne,
31062 Toulouse, France. E-mail: dartigue@chimie.ups-tlse.fr
b Laboratoire Traceurs et Traitement d’Image, E.A. 3033, Université Paul Sabatier,
Faculté de Médecine Toulouse-Purpan, 133 route de Narbonne, 31062 Toulouse-Cedex, France
c Département de Chimie, Université de Montréal, C. P. 6128, Succ. Centre-ville, Montréal,
QC H3C 3J7, Canada
Received 16th July 2001, Accepted 25th January 2002
First published as an Advance Article on the web 22nd February 2002
Reacting 1-phenyl-2-(diphenylphosphino)ethanone (P1∼OH), 1-tert-butyl-2-(diphenylphosphino)ethanone (P2∼OH)
and 1-phenyl-2-(diphenylphosphino)propanone (P3∼OH) with ReOCl3(PPh3)2 and Re(NPh)Cl3(PPh3)2 in toluene
and ethanol in the presence of NEt3 yields complexes in which these ligands bind as monoanionic enolato chelating
agents. Bromo and iodo analogues are prepared similarly. The reactions are solvent dependent. The disubstituted
ReOCl(P∼O)2 compounds obtained in toluene adopt the ‘twisted’ cis-(P,P) octahedral structure. With Re(NPh)Cl3-
(PPh3)2, P1∼OH and P2∼OH give the corresponding Re(NPh)Cl(P∼O)2 compounds and the trans-(P,P)-trans-(Cl,Cl)
isomer of monosubstituted Re(NPh)Cl2(PPh3)(P∼O) as the major products, together with small amounts of ‘twisted’
trans-(P,P) Re(NPh)Cl(P∼O)2. The monosubstituted complex is the only species isolated with P3∼OH. The major
structural difference between the two systems is the small stability gap between the cis- and the trans-(P,P) isomers
of the imido complexes. In ethanol, unexpected cis-ethoxo-oxo complexes ReO(OEt)(P∼O)2 are isolated, resulting
from stereoselective substitution of the halide in the ‘twisted’ cis-(P,P) octahedral complexes. The reactions with
Re(NPh)Cl3(PPh3)2 are less selective and give rise to mixtures of complexes. The trans-ethoxo-phenylimido
compound Re(NPh)(OEt)(P1∼O)2 is obtained in good yield. A crystallographic study reveals an unexpected
‘equatorial’ trans-(P,P) structure with the ethoxo ligand trans to the Re᎐NPh bond. 1H NMR indicates that
᎐
the ethoxo ligand acts as an electron reservoir in these complexes, since its protons are strongly deshielded
in the cis-oxo-ethoxo species and strongly shielded in the trans-phenylimido-ethoxo complex.
tems giving stoichiometric and stereospecific reactions are
Introduction
actively desired.11,12
Over the recent years, we and others have been investigating the
Alkyl- and aryl-functionalised phosphinoketones belong to
reactions of bidentate phosphinophenols with Re() oxo, imido
the family of P∼O bifunctional ligands. In the field of organo-
metallic chemistry, they give rise to a variety of stable com-
and nitrido complexes and with various Re() precursors.1–10
The interest in these dissymmetric bidentate ligands originates
plexes, in which they are neutral and usually co-ordinated as a
in the presence of soft and hard donor atoms, which impart
monodentate phosphine or as a bidentate phosphinoketone.13–22
good co-ordinative capability toward metals in a variety of oxid-
Interestingly, phosphinoketones containing an acidic hydrogen
ation states and stereoelectronic control of the co-ordination
sphere of the metal. They react with the Re() complexes
ReOCl3(PPh3)2 and Re(NPh)Cl3(PPh3)2 by ligand exchange
processes, invariably behaving as bidentate four-electron donor
in the α position to the keto function can be converted into their
enol tautomer23 upon addition of a strong base, and the result-
ing enolate ions (Scheme 2) bind mainly in the monoanionic
anionic ligands and leading to species including trans O᎐Re–
᎐
O∼P and PhN᎐Re–O∼P moieties. The high stability of these
᎐
two units, due to electron delocalisation, is of particular signifi-
cance since it reduces the lability of the site trans to the multiple
bond and decreases significantly the number of geometric
isomers obtained. For instance, in the case ReYCl(P∼O)2 (Y =
O, NPh), the ‘twisted’ cis-(P,P) or trans-(P,P) isomers shown in
Scheme 1 are by far the major products. This point has crucial
implications in the area of radiopharmaceuticals, where sys-
Scheme 2
chelating P∼OϪ form. Several examples have been reported
for Ni,13,24 Co,16,17 Fe,18 Pt, Pd,13,15,25 Rh,21,22 and Ru.19,20,26 How-
ever, strong electrophilic alkali metals give only monodentate
O-bonded compounds,27 whereas a few cases of co-ordination
as a bridging bidentate anionic P∼C ligand have been achieved
with late transition-metal complexes when phosphinoester
ligands were used.28
The co-ordinative properties of Ph2PCH2C(O)Ph have been
tested already toward rhenium in low oxidation states. An
Scheme 1
914
J. Chem. Soc., Dalton Trans., 2002, 914–924
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b106306p

View Article Online
earlier work described the synthesis of Re() complexes with
the non-deprotonated phosphinoketone bonded as a unidentate
(P-bonded) or chelating (P,O-bonded) ligand, and a Re()
complex containing a chelating phosphinoenolate unit.29 We
reported previously the crystal structures of the Re() enol-
3.63. Found: C, 54.90; H, 3.60%. IR (KBr, cmϪ1): 971 ν(Re᎐O),
᎐
ؒ ؒ ؒ
ؒ ؒ ؒ
1537 ν(C
C
O). MS DCI/NH (m/z, %): 889 (100%) [M ϩ
–– ––
3
H]ϩ, 826 (20%) [M Ϫ Br ϩ NH4]ϩ.
cis-(P,P)-[ReOCl(P2∼O)2] (3). Same method as above for 2:
1.08 g (1.3 mmol) of ReOCl3(PPh3)2, 0.74 g (2.6 mmol) of
P2∼OH, 0.279 g (2.76 mmol) of NEt3, 50 mL of ethanol. Green
solid (yield 85%). Anal. calc. for C36H40ClO3P2Re: C, 53.76;
ate complexes ReOCl(Ph PCH᎐CO(Ph)) and ReN(PPh3)-
᎐
2
2
(Ph PCH᎐CO(Ph)) .30 However, no imido–Re complexes with
᎐
2
2
ligands of this type have yet been synthesised.
We describe here the reactions of three differently substi-
tuted diphenylphosphinoketones (Scheme 3) with ReO-
H, 5.01. Found: C, 53.95; H, 4.94%. IR (KBr, cmϪ1): 967 ν(Re᎐
᎐
ؒ ؒ ؒ
ؒ ؒ ؒ
O), 1535 ν(C
C
O). MS DCI/NH (m/z, %): 805 (100%)
–– ––
3
[M ϩ H]ϩ.
cis-(P,P)-[ReOBr(P2∼O)2] (4). Same method as 2: 0.498 g
(0.5 mmol) of ReOBr3(PPh3)2, 0.28 g (0.98 mmol) of P2∼OH,
0.142 g (1.40 mmol) of NEt3, 40 mL of ethanol. Green solid
(yield 91%). Anal. calc. for C36H40BrO3P2Re: C, 50.94; H, 4.75.
Found: C, 50.27; H, 4.55%. IR (KBr, cmϪ1): 968 ν(Re᎐O), 1534
᎐
ϩ
ؒ ؒ ؒ
ؒ ؒ ؒ
ν(C
C
O). MS DCI/NH (m/z, %): 849 (55%) [M ϩ H] .
–– ––
3
cis-(P,P)-[ReOI(P2∼O)2] (5). Same method as 2: 0.443 g
(0.40 mmol) of ReOI3(PPh3)2, 0.24 g (0.84 mmol) of P2∼OH,
0.094 g (0.93 mmol) of NEt3, 35 mL of ethanol. The green
complex was recrystallised from diethyl ether (yield 51%). Anal.
Scheme 3
Cl3(PPh3)2 and Re(NPh)Cl3(PPh3)2. This study was under-
taken to collect information on the structure and stability of
the new complexes and to evaluate the potential of these lig-
ands for the preparation of radiopharmaceuticals. The reac-
tions were run in toluene and in ethanol, in the presence of
the NEt3 base as proton quencher. The new oxo and phenyl-
imido reaction products were found to be solvent dependent.
Although monochloro species formed in toluene, ethanol gave
halo and ethoxo products. Furthermore, with the rhenium–
imido core, the stereochemistry of the resulting complexes
was found to be sensitive to the P∼O ligand used, and the
Re(NPh)(OEt)(P1∼O)2 compound isolated was shown by X-ray
diffraction to have an unexpected trans-(P,P) arrangement of
two phosphinoenolate chelate rings lying in the ‘equatorial’
plane.
calc. for C36H40IO3P2Re: C, 48.27; H, 4.50. Found: C, 47.98; H,
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
4.12%. IR (KBr, cm ): 968 ν(Re᎐O), 1532 ν(C
C
O). MS
–– ––
᎐
DCI/NH3 (m/z, %): 897 (100%) [M ϩ H]ϩ, 285 (7%) [P2∼OH ϩ
H]ϩ, 786 (3%) [M Ϫ I ϩ NH4]ϩ.
cis-(P,P)-[ReOCl(P3∼O)2] (6).
A mixture of 0.306 g
(0.37 mmol) of ReOCl3(PPh3)2, 0.234 g (0.74 mmol) of P3∼OH
and 0.306 g (0.37 mmol) of NEt3 in 40 mL of toluene was
refluxed for 4 h. The solvent was evaporated in vacuo, the dark-
green solid was redissolved in 20 mL of diethyl ether and pre-
cipitated with pentane (30 mL). The green solid was filtered off,
washed with pentane and dried in vacuo. Recrystallisation from
ethanol–pentane afforded green crystals (yield 49%). Anal. calc.
for C42H36ClO3P2Re: C, 57.79; H, 4.16. Found: C, 56.96; H,
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
3.67%. IR (KBr, cm ): 958 ν(Re᎐O), 1545 ν(C
C
O), 320
–– ––
᎐
ν(Re–Cl). MS DCI/NH3 (m/z, %): 873 (17%) [M ϩ H]ϩ, 854
(100%) [M Ϫ Cl ϩ NH4]ϩ, 837 (23%) [M Ϫ Cl ϩ H]ϩ, 890 (11%)
[M ϩ NH4]ϩ.
Experimental
All reactions were carried out under a nitrogen atmosphere
using standard Schlenk techniques. ReOX3(PPh3)2,31 Re(NPh)-
Cl3(PPh3)2,32 1-phenyl-2-(diphenylphosphino)ethanone (P1∼
OH),15 1-tert-butyl-2-(diphenylphosphino)ethanone (P2∼OH),19
1-phenyl-2-(diphenylphosphino)propanone (P3∼OH)19 and Re-
OCl(P1∼O)2 (1)30 were prepared as described in the literature.
The preparation of ReO(OEt)Cl2(PPh3)2 was adapted from the
literature by using NH4ReO4 (Strem Chemicals) as the starting
material.33 Infrared spectra (4000–400 cmϪ1) were recorded as
KBr pellets on a Vector 22 Bruker spectrophotometer. 1H
NMR spectra were obtained at room temperature on Bruker
AMX 400 and WM 250 instruments. The residual solvent sig-
nals (δ = 5.20 ppm for CD2Cl2 and 7.30 for CDCl3) were used as
internal standard and the chemical shifts are reported with
respect to Me4Si. For the 31P{1H} NMR spectra, the AC 200,
AMX 300 and ARX 400 instruments were used and the
external standard was H3PO4 (82% D2O, δ = 0.0 ppm).
Mass spectra were measured with a NERMAG R10–10
spectrometer. Elemental analyses were carried out at the
Laboratoire de Contrôle de l’École Nationale Supérieure de
Chimie de Toulouse.
cis-(P,P)-[ReO(OEt)(P1∼O)2] (7). To a brown suspension
of 0.202 g (0.24 mmol) of ReO(OEt)Cl2(PPh3)2 in 20 mL of
ethanol were added 0.219 g (0.72 mmol) of P1∼OH and 0.073 g
(0.72 mmol) of NEt3. The mixture was refluxed for 4 h, giving a
brown solution and a brown precipitate. The solution was
cooled to increased the amount of precipitate and the brown
solid was filtered off, washed with diethyl ether and dried in
vacuo (yield 40%). Anal. calc. for C42H37O4P2Re: C, 59.08; H,
4.37. Found: C, 58.80; H, 4.40. IR (KBr, cmϪ1): 965 ν(Re᎐O),
᎐
ؒ ؒ ؒ
ؒ ؒ ؒ
1527 ν(C
C
O). MS DCI/NH (m/z, %): 855 (100%)
–– ––
3
[M ϩ H]ϩ, 826 (34%) [M Ϫ EtOH ϩ NH4]ϩ, 809 (7%) [M Ϫ
EtOH ϩ H]ϩ.
cis-(P,P)-[ReO(OEt)(P2∼O)2] (8). A mixture of 0.202 g
(0.24 mmol) of ReO(OEt)Cl2(PPh3)2, 0.274 g (0.96 mmol) of
P2∼OH, and 0.101 g (1.00 mmol) of NEt3 in 20 mL of ethanol
was refluxed for 4 h, giving a brown solution. Evaporation of
the solvent in vacuo gave a solid residue, which was extracted
with a toluene–pentane mixture to eliminate the ammonium
salt. Filtration and evaporation of the solvent gave a brown
solid, which was recrystallised from acetonitrile (yield 40%).
Anal. calc. for C38H45O4P2Re: C, 56.07; H, 5.57. Found: C,
Syntheses
cis-(P,P)-[ReOBr(P1∼O)2] (2). To a green suspension of
0.50 g (0.52 mmol) of ReOBr3(PPh3)2 in 40 mL of ethanol were
added 0.32 g (1.06 mmol) of P1∼OH and 0.13 g (1.25 mmol)
of NEt3. Refluxing the mixture for 1.5 h gave a clear green
solution. Upon cooling, a green solid was deposited, which was
filtered off, washed with ethanol and diethyl ether, and dried in
vacuo (yield 50%). Anal. calc. for C40H32BrO3P2Re: C, 54.06; H,
56.24; H, 5.58%. IR (KBr, cmϪ1): 959 ν(Re᎐O), 1524
᎐
ϩ
ؒ ؒ ؒ
ؒ ؒ ؒ
ν(C
C
O). DCI/NH (m/z %): 815 (42%) [M ϩ H] , 786
–– ––
3
(100%) [M Ϫ EtOH ϩ NH4]ϩ, 769 (13%) [M Ϫ EtOH ϩ H]ϩ.
cis-(P,P)-[ReO(OEt)(P3∼O)2] (9). A mixture of 0.202 g
(0.24 mmol) of ReO(OEt)Cl2(PPh3)2, 0.160 g (0.50 mmol) of
J. Chem. Soc., Dalton Trans., 2002, 914–924
915

View Article Online
Table 1 Crystal data for compound 16
P3∼OH, and 0.050 g (0.50 mmol) of NEt3 in 30 mL of ethanol
was refluxed for 4 h. After cooling, a green solid was deposited,
which was filtered off, washed with ethanol and diethyl ether,
and dried in vacuo (yield 43%). Anal. calc. for C44H41O4P2Re: C,
59.85; H, 4.68. Found: C, 58.84; H, 4.01%. IR (KBr, cmϪ1): 959
Empirical formula
M
C48H42NO3P2ReؒCHCl3
1048.33
Crystal system
Space group
Triclinic
P1 (no. 2)
¯
ؒ ؒ ؒ
ؒ ؒ ؒ
ν(Re᎐O), 1545 ν(C
C
O). MS DCI/NH (m/z, %): 883 (24%)
–– ––
3
a/Å
b/Å
c/Å
α/Њ
12.027(3)
12.377(3)
17.916(3)
72.09(3)
80.05(2)
63.03(2)
2260.0(9)
2
᎐
[M ϩ H]ϩ, 854 (100%) [M Ϫ EtOH ϩ NH4]ϩ, 837 (19%)
[M Ϫ EtOH ϩ H]ϩ.
β/Њ
cis-(P,P)-[Re(NPh)Cl(P1∼O)2] (13). To a green suspension of
0.18 g (0.20 mmol) of Re(NPh)Cl3(PPh3)2 in toluene (20 mL)
were added 0.30 g (0.98 mmol) of P1∼OH and 0.10 g (1.00
mmol) of NEt3. The mixture was refluxed for 24 h, giving a
green solution from which a green solid was deposited upon
cooling. The solid was filtered off, washed with diethyl ether,
and dried in vacuo (yield 15%). Anal. calc. for C46H37ClO2-
γ/Њ
V/Å3
Z
T /ЊC
20
λ/Å
1.54178 (CuKα)
1.541
7.86
Dc/g cmϪ3
µ/mmϪ1
Crystal dimensions/mm
R1a [I > 2σ(I )]
wR2b [I > 2σ(I )]
Sc
0.74 × 0.34 × 0.11
0.0419
0.1186
P2NRe: C, 60.09; H, 4.06; N, 1.52. Found: C, 61.85; H, 4.39; N,
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
1.28%. IR (KBr, cm ): 1536 ν(C
C
O). DCI/NH (m/z, %):
–– ––
3
920 (100%) [M ϩ H]ϩ, 901 (14%) [M Ϫ HCl ϩ NH4]ϩ, 884 (4%)
[M Ϫ HCl ϩ H]ϩ.
1.118
a R1 = Σ(||Fo| Ϫ |Fc||/Σ(|Fo|). b wR2 = [Σ[w(Fo2 Ϫ Fc2)2]/Σ[w(Fo )2]]1/2
.
c S =
2
[Σ[w(Fo2 Ϫ Fc2)2]/(Nreflns Ϫ Nparams)]1/2
.
cis-(P,P)-[Re(NPh)Cl(P2∼O)2] (14). The procedure used for
13 was applied, with 0.208 g (0.23 mmol) of (ReNPh)-
Cl2(PPh3)2, 0.26 g (0.91 mmol) of P2∼OH and 0.094 g
(0.93 mmol) of NEt3 in 20 mL of toluene. The mixture was
refluxed for 1 day. The brown solution was reduced to half
volume. Adding pentane and cooling to 4 ЊC gave a brown-
violet solid, which was filtered off, washed with pentane, and
dried in vacuo (yield 30%). Anal. calc. for C42H45NO2P2ClRe: C,
atoms of the complex were readily located. The asymmetric
unit contained one severely disordered chloroform molecule.
Four sites with separations of 2.34–2.39 Å were found in the ∆F
map, consistent with fractional Cl atoms, but they could not be
assembled into sets of three sites for a chloroform unit. Thus,
in addition to positional disorder, the solvent showed high
thermal motion, probably rocking about a Cl–Cl vector, so that
two of the Cl sites of each fractional chloroform unit were
relatively well defined, whereas the third Cl and the C atoms
could not be distinguished from the general background. By
refining the Uiso and occupancy factors of these sites for a few
cycles, occupancies close to 0.50 were obtained. They were fixed
to 0.50 for the rest of the refinement. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were placed at
idealised positions and refined as riding atoms with C–H dis-
tances of 0.93 (sp2) or 0.96 Å (methyl). Their isotropic temper-
ature factors were adjusted to 20% (sp2) or 50% (methyl) above
the value for the supporting atom. The VOID routine of the
PLATON software37 was used to check that no holes remained
in the structure. Crystal data are collected in Table 1.
57.36; H, 5.16; N, 1.59. Found: C, 57.78; H, 5.38; N, 1.49%. IR
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
(KBr, cm ): 1527 (br) ν(C
C
O). MS DCI/NH (m/z, %):
–– ––
3
880 (100%) [M ϩ H]ϩ, 861 (25%) [M Ϫ HCl ϩ NH4]ϩ, 884 (5%)
[M Ϫ HCl ϩ H]ϩ.
trans-(P,P)-[Re(NPh)Cl(P2∼O)2] (15). The procedure used
for 13 was applied, with 0.208 g (0.23 mmol) of Re(NPh)-
Cl3(PPh3)2, 0.26 g (0.91 mmol) of P2∼OH, and 0.94 g (0.93
mmol) of NEt3 in 20 mL of ethanol. The mixture was refluxed
for 5 h. After cooling, the solution deposited a green solid,
which was filtered off, washed with pentane, and dried in vacuo
(yield 60%). Anal. calc. for C42H45NO2P2ClRe: C, 57.36; H,
5.16; N, 1.59. Found: C, 56.26; H, 5.15; N, 1.60%. IR (KBr,
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
cm ): 1536 ν(C
C
O). DCI/NH (m/z, %): 880 (100%)
–– ––
3
[M ϩ H]ϩ.
CCDC reference number 178319.
See http://www.rsc.org/suppdata/dt/b1/b106306p/ for crystal-
lographic data in CIF or other electronic format.
trans-(P,P)-[Re(NPh)(OEt)(P1∼O)2] (16). A mixture of 0.185
g (0.20 mmol) of Re(NPh)Cl3(PPh3)2, 0.30 g (0.98 mmol) of
P1∼OH, and 0.10 g (1.00 mmol) of NEt3 in 20 mL of ethanol
was refluxed for 16 h. Upon cooling a green solid was
deposited, which was filtered off, washed with diethyl ether and
dried in vacuo (yield 60%). Crystals suitable for X-ray work
were grown from chloroform. Anal. calc. for C48H42O3P2NRe:
Results
Synthesis of the cis-(P,P)-ReOX(P∼O)2 complexes (X ؍ Cl, Br,
I, OEt)
C, 62.06; H, 4.56; N, 1.51. Found: C, 62.00; H, 4.77; N, 1.48%.
The oxo Re() phosphinoenolato complexes were obtained
in good yield via ligand exchange of P∼OH with the halide
precursors ReOX3(PPh3)2 and ReO(OEt)Cl2(PPh3)2. Since the
nature of the complexes was found to depend on the sol-
vent polarity, the reactivity in toluene and in ethanol was
investigated.
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
IR (KBr, cm ): 1512 ν(C
C
O). MS DCI/NH (m/z, %):
–– ––
3
930 (7%) [M ϩ H]ϩ, 901 (100%) [M Ϫ EtOH ϩ NH4]ϩ, 884 (9%)
[M Ϫ EtOH ϩ H]ϩ.
Crystallographic measurements and structure determination for
16
Green crystals suitable for X-ray diffraction work appeared
overnight in an NMR tube containing a CDCl3 solution of 16.
A specimen was glued on to a glass fibre and mounted on an
Enraf-Nonius CAD-4 diffractometer. Low-angle spots in an
axial photograph led to a reduced triclinic cell,34 for which no
higher Laue symmetry was detected. A whole sphere of data
was collected, corrected for absorption and averaged to provide
the basic four-octant data set. The structure refined normally in
Reactions in toluene. Reacting two equivalents of the
diphenylphosphinoketones (P∼OH) with ReOX3(PPh3)2 (X =
Cl, Br, I) in refluxing toluene (110 ЊC) in the presence of
two equivalents of the NEt3 base produced quantitatively the
‘twisted’ cis-(P,P)-ReOX(P∼O)2 complexes (Scheme 4) as insol-
uble products. Since simultaneous precipitation of (HNEt3)Cl
occurred, recrystallisation from ethanol was needed to get pure
samples.
¯
the centric space group P1.
The compounds were characterised by elemental analysis,
whereas mass spectrometry (DCI/NH3) indicated mono-
meric molecular species. The [M ϩ H]ϩ parent ions give the
The structure was solved by the direct methods of SHELXS-
8635 and ∆F syntheses of SHELXL-93.36 The non-hydrogen
916
J. Chem. Soc., Dalton Trans., 2002, 914–924

View Article Online
Scheme 4
predominant peaks for 1–5, whereas the highest peaks for 6
correspond to [M Ϫ Cl ϩ H]ϩ and [M Ϫ Cl ϩ NH4]ϩ, which
indicates that the halogen is less strongly bonded in the latter
complex. In all cases, the ν(Re᎐O) stretch appears clearly in the
᎐
958–973 cmϪ1 range. Ligand co-ordination in the enol form is
ؒ ؒ ؒ
ؒ ؒ ؒ
confirmed by the presence of ν(C
C
O) bands in the 1530–
–– ––
1545 cmϪ1 range and the disappearance of the typical ν(C᎐O)
᎐
stretch of the free ligand in its keto form at ca. 1650 cmϪ1. A
small, but significant, decrease of ν(Re᎐O) in the series P ∼OϪ >
᎐
1
P2∼OϪ > P3∼OϪ suggests that the nucleophilic character of the
Fig. 1 2D 31P/1H NMR spectrum of ReOCl(P2∼O)2 (3) in CDCl3.
enol oxygen trans to the Re᎐O bond varies in the reverse order.38
᎐
The cis-(P,P) ‘twisted’ structure observed in the crystals of
130 is retained in solution for 1–6, as evidenced from NMR
spectroscopy. In all cases, the 31P{1H} spectra show resonances
for two non-equivalent enolato ligands. Both P donors must be
co-ordinated, since the signals have moved downfield consider-
phenyl group in 1 produces the expected deshielding of the
ethylenic protons (4.98/4.52 ppm for 3 versus 5.60/5.28 ppm
for 1).
Reactions in ethanol. When the above reactions with ReO-
Cl3(PPh3)2 were performed in refluxing ethanol (78 ЊC) for 2 h
in the presence of NEt3, besides ReOCl(P∼O)2 (1, 3, 6), a new
species appeared, which was shown to be the ‘twisted’ cis-(P,P)-
ReO(OEt)(P∼O)2 complex (7–9) (vide infra) in which the
Re–Cl bond has ethanolysed. The ratio of the two complexes
was ligand dependent: ReOCl(P∼O)2 was the major species for
P1∼O and P2∼O, but only the minor product for P3∼O, as
though ethanolysis occurred faster for the P3∼O complex. At
this stage, concentrating the solutions gave exclusively 1, 3, 6 as
microcrystalline solids.
ably upon co-ordination to the strongly acidic [Re᎐O]3ϩ core
᎐
and formation of the five-membered metallacycles.39,40 AX-type
2
spectra are observed, consisting of two doublets with JPP
values of ca. 11 Hz characteristic of two P atoms occupying cis
positions in octahedral Re() complexes1,3–11 (Table 2). Assign-
ing the individual doublets to Pax or Peq (Scheme 5) is not
In order to cast some light on the fact that ReO(OEt)(P3∼O)2
formed as the major species, the reaction between ReO-
Cl3(PPh3)2 and P3∼OH/NEt3 in refluxing ethanol was moni-
tored by 31P{1H} NMR (Fig. 2). ReO(OEt)(P3∼O)2 was
obtained as the only species after 1 h, showing complete
ethanolysis of the Re–Cl bond. After 4 h, the mixture consisted
of a ca. 1 : 3 ratio of the chloro (6) and ethoxo (9) compounds,
whereas heating for 11 extra hours produced the chloro com-
plex 6 as the only species. Therefore, 6 is the thermodynamic
complex, while 9 is the kinetic species. On the other hand, add-
ing HCl to an ethanol solution of 9 at room temperature for 2 h
produced 6 quantitatively.
Scheme 5
straightforward. Crystal structures of analogous Re() com-
plexes with P∼O ligands indicated that, in the absence of
particular steric effects, the Re–Peq bonds are generally shorter
than the Re–Pax bonds.1–3,8,30 On this basis, the downfield doub-
let was assigned to Peq and the upfield one to Pax in earlier
studies. This generalisation is assumed to hold here, although it
raises a problem for the related ethoxo complexes 7–9 to be
discussed below. No trans effect of the halide is detected (Table
2), since the Peq chemical shift is not halide sensitive, but a small
cis effect is observed on Pax, which may be steric in origin.
The presence of the two non-equivalent enolato P∼O ligands
This contrasts with the exchange reactions performed with
ReO(OEt)Cl2(PPh3)2. In these cases, complexes 7–9 were
obtained quantitatively (Scheme 6), and under all the experi-
1
is confirmed by H NMR spectroscopy. Compounds 1–5 show
signals for two ethylenic protons Hax and Heq in the range 4.1–
5.6 ppm, appearing as doublets due to coupling to the nearby
phosphorus atom (Scheme 5). These protons are assigned
individually from the 2D 31P/1H spectrum of 3 (Fig. 1), where
coupling is unambiguously found to occur between the low-
field Peq nucleus (16.1 ppm), the high-field ethylenic proton Heq
t
(4.52 ppm) and the low-field CH3 group of the Bu substituent
(1.39 ppm), on the one hand, and between the high-field Pax
(8.3 ppm), the low-field ethylenic Hax (4.98 ppm) and the high-
field Bu methyl group (0.64 ppm), on the other hand. These
Scheme 6
t
large chemical shift differences between the two ligands illus-
trate the importance of electron delocalisation in stabilising
these Re() complexes. For 6, the two methyl groups appear as
doublets near 1.8 ppm. Replacing the electron-releasing t-butyl
substituent on the enol carbon in 3 by an electron-withdrawing
mental variations applied, the ReOCl(P∼O)2 complexes never
formed. This suggests that HCl is an active species in this
process, since the acid formed is completely quenched as
(HNEt3)Cl in the present case, whereas 1 equivalent of HCl is
liberated when starting with ReOCl3(PPh3)2.
J. Chem. Soc., Dalton Trans., 2002, 914–924
917

View Article Online
Table 2 Selected spectroscopic properties of the complexes
31P{1H} NMR (ppm; Hz)a
1H NMR (ppm; Hz)a
H [or Me]
IR
Compound
Pax
Peq
2JPP
ν(Re᎐O)/cmϪ1
᎐
1
2
3
ReOCl(P1∼O)2
ReOBr(P1∼O)2
ReOCl(P2∼O)2
8.1
7.4
8.3
16.2
17.3
16.1
11.0
11.7
11.8
5.28 (d, 2JHP = 3.5); 5.60 (d, 2JHP = 4.9) [C᎐CH]
973
971
᎐
5.00 (d, 2JHP = 4.0); 5.35 (d, 2JHP = 4.9) [C᎐CH]
᎐
2
2
4.52 (d, JHP = 5.1); 4.98 (d, JHP = 6.2) [C᎐CH] 0.64 (s); 1.39 (s) 967
᎐
[t-Bu]
2
2
4
5
ReOBr(P2∼O)2
ReOI(P2∼O)2
7.1
5.6
16.5
16.1
11.8
11.8
4.39 (d, JHP = 5.3); 5.07 (d, JHP = 6.1) [C᎐CH] 0.66 (s); 1.40 (s) 968
᎐
[t-Bu]
4.14 (d, 2JHP = 4.0); 5.17 (d, 2JHP = 5.6 ) [C᎐CH] 0.61 (s); 1.38 (s) 968
᎐
[t-Bu]
6
7
ReOCl(P3∼O)2
ReO(OEt)(P1∼O)2
19.6
3.4
29.7
14.9
11.0
7.5
1.74 (d, 3JHP = 10.0); 1.80 (d, 3JHP = 10.0) [C᎐CMe]
958
5.22 (d, JHP = 4.4); 5.35 (d, JHP = 1.3) [C᎐CH] 5.38 (ABH3P, 965
᎐
2
2
᎐
2
3
4
2
m, JAB = 10.7; JAH = 6.9; JAP = 4.1); 5.45 (ABH3P, m, JAB
10.9; JBH = 6.9; JBP = 2.0) [ethoxo CH2] 1.25 (t, JHH = 6.9)
=
3
4
3
[ethoxo CH3]
2
4
2
8
9
ReO(OEt)(P2∼O)2
ReO(OEt)(P3∼O)2
5.0
16.1
22.5
8
4.68 (dd, JHP = 5.7; JHP = 0.5); 4.69 (d, JHP = 2.4) [C᎐CH] 959
᎐
3 4
0.56 (s); 1.36 (s) [t-Bu] 5.14 (qd, JHH = 7.0; JHP = 2.6) [ethoxo
CH2] 1.16 (t, 3JHH = 7) [ethoxo CH3]
3
3
17.2
8.0
1.67 (d, JPH = 10.0); 1.74 (d, JPH = 10.0) [C᎐CCH3] 5.30 959
᎐
3 4
(ABH3P, m, JAB = 11.0; JAH = 7.0; JAP = 1.8); 5.39 (ABH3P,
2
3
4
m, JAB = 11.0; JBH = 7.0; JBP = 3.7) [ethoxo CH2] 1.33 (t,
2JHH = 7.0) [ethoxo CH3]
10 Re(NPh)Cl2(PPh3)(P1∼O)
11 Re(NPh)Cl2(PPh3)(P2∼O)
12 Re(NPh)Cl2(PPh3)(P3∼O)
13 Re(NPh)Cl(P1∼O)2
(‘twisted’ cis-PP)
Ϫ5.7
Ϫ6.8
29.0
9.6
21.2
21.9
34.4
18.7
273
273
272
7.0
7.0
236
5.30 (d, 2JHP = 3.5); 5.38 (d, 2JHP = 4.4) [C᎐CH]
᎐
2
2
14 Re(NPh)Cl(P2∼O)2
14.9
14.2
3.6
19.0
28.4
4.56 (d, JHP = 5.2); 4.91 (d, JHP = 4.2) [C᎐CH] 0.83 (s); 1.40 (s)
᎐
(‘twisted’ cis-P,P)
[t-Bu]
2
4
2
4
15 Re(NPh)Cl(P2∼O)2
(‘twisted’ trans-P,P)
16 Re(NPh)(OEt)(P1∼O)2
4.49 (dd, JHP = 5.4, JHP = 1.0); 4.50 (dd, JHP = 2.4, JHP = 1.3)
[C᎐CH] 0.65 (s); 1.07 (s) [t-Bu]
᎐
5.40 (t, 2JHP = 4JHP = 1.2) [C᎐CH] 2.72 (ABH3P2, m, 2JAB = 11.2;
᎐
(‘equatorial’ trans-P,P)
3JAH = 7.0; 4JAP = 1.7); 2.95 (ABH3P2, m, 2JAB = 11.2; 3JBH = 7.0;
4JBP = 2.0) [ethoxo CH2] Ϫ0.14 (t, 2JHH = 7) [ethoxo CH3]
17 Re(NPh)(OEt)(P2∼O)2
(‘equatorial’ trans-P,P)
4.5
a In CDCl3. Multiplicity in parentheses: s = singlet; d = doublet; t = triplet; m = multiplets.
Compound 7 is stable under the conditions prevailing in the
mass spectrometer, since the [M ϩ H]ϩ parent peak is pre-
dominant. This is not the case for 8 and 9, whose main peaks
are [M Ϫ EtOH ϩ NH4]ϩ, thus indicating a decreased stability
protons agree with a cis-oxo-ethoxo structure, since these effects
are not found for the methylene protons in the related trans-
oxo-ethoxo cis-(P,P) complexes.8,42 Surprisingly, complex 8 gives
a single multiplet, as if HA and HB were equivalent. Since the
31P data indicate that 8 has the same structure as 7 and 9, the
equivalence of these protons likely results either from an acci-
dental chemical shift coincidence or some dynamic exchange
process. In the three compounds, the ethoxo CH2 protons are
coupled to a 31P nucleus, as noted for ReO(OEt)(Ph2PCH2-
C6H4O)2.8 The 2D 31P/1H NMR spectrum of 7 (Fig. 3) proves
that this coupling involves only the upfield 31P signal, which has
been assigned to the Pax donor sitting cis to the ethoxo group.
This is rather surprising, since the couplings observed so far
occurred with a trans P atom and we have no explanation at this
time for this different behaviour.
of the Re–OEt bond. The ν(Re᎐O) stretch is observed at 959–
᎐
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
965 cm , as expected, and the presence of the ν(C
C
O)
–– ––
stretches in the 1520–1550 cmϪ1 range confirms the co-
ordination of both ligands in their enolato form. The ethoxo
ligand is characterised by its strong ν(C–C–O) asymmetric
stretch at ca. 1050 cmϪ1.41 The ν(Re᎐O) frequency follows the
᎐
order P ∼O > P ∼O = P ∼O. With the P ∼O ligand, the ν(Re᎐O)
᎐
1
2
3
3
frequencies are identical for the chloro and ethoxo complexes,
whereas the frequency is ca. 8 cmϪ1 lower for the ethoxo com-
pounds of P1∼O and P2∼O, indicating that in these two cases the
Re᎐O bond gets weaker when Cl is regioselectively replaced by
᎐
OEt.
The ethoxo signals are significantly deshielded as compared
with those of various Re–oxo complexes containing a trans
Complexes 7–9 show AX-type 31P{1H} NMR spectra with
chemical shifts following the same trends as the halogen
O᎐Re–OEt unit with different types of chelating ligands
᎐
2
analogues (1–5) and JPP constant of ca. 8 Hz, consistent with
(Table 3). However, they compare well with those observed for
the cis-oxo-ethoxo ReO(OEt)(Ph2PCH2C6H4O)2 complex8 and
indicate a large ethoxo-to-rhenium electron transfer, thereby
decreasing the nucleophilicity of the ethoxo group, which thus
behaves like a chloro ligand.
the ‘twisted’ cis-(P,P) structure. The spectra of 7 and 8 exhibit
distinct signals for the ethylenic proton of the axial and
equatorial ligands, respectively, whereas two signals for methyl
substituents are similarly found for 9 (Table 2). The ethoxo
methyl protons give a triplet at ca. 1.25 ppm, whereas the dia-
stereotopic methylene protons produce a complex multiplet in
the 5.0–5.5 ppm range. For 7 and 9, this multiplet actually con-
sists of two overlapping HAHBH3P patterns, each due to the
non-equivalent methylene protons HA and HB coupling
together (ca. 11 Hz), with the methyl protons (ca. 7 Hz) and one
phosphorus atom (4JP–HA/HB 2–4 Hz). The presence of such pat-
terns and the significant downfield shifts experienced by these
Synthesis of cis- and trans-(P,P)-Re(NPh)X(P∼O)2 (X ؍ Cl,
OEt)
The solvent dependence noted above for the reactions of P∼OH
with the oxo precursor is also found to affect the reactivity of
Re(NPh)Cl3(PPh3)2. As generally observed, in the latter case,
the reactions are slower and less selective, higher ligand : Re
918
J. Chem. Soc., Dalton Trans., 2002, 914–924

View Article Online
figuration of the octahedral species was determined via the 2JPP
constant (Table 2).
Thus, refluxing a 4 : 4 : 1 ratio of P1∼OH, NEt3 and Re-
(NPh)Cl3(PPh3)2 in toluene for 4 h gave a clear green solution.
Concentration of this solution in vacuo produced a mixture
of compounds which was soluble in CDCl3 and analyzed by
31P{1H} NMR. The spectrum showed signals for PPh3 (Ϫ4
ppm), the free neutral ligand in its keto form (Ϫ16 ppm) and
two new complexes. The major product exhibited doublets at
9.6 and 18.7 ppm with a 2JPP constant of 7 Hz, consistent with
the ‘twisted’ cis-(P,P) disubstituted Re(NPh)Cl(P1∼O)2 com-
plex (13). The monosubstituted trans-(P,P)-Re(NPh)Cl2(PPh3)-
(P1∼O) species (10), showing doublets at Ϫ5.7 and 21.2 ppm
2
with a JPP constant of 273 Hz, formed in slightly smaller
amount. By increasing the reactant ratio to 5 : 5 : 1 and the
reaction time to 24 h, a green solid was precipitated, which was
found to be the pure cis-(P,P) complex 13.
P2∼OH was reacted under the same conditions for 4 h and the
reaction was followed as above. The monosubstituted trans-
(P,P) complex Re(NPh)Cl2(PPh3)(P2∼O) (11) (doublets at Ϫ6.8
2
and 21.9 ppm, JPP = 273 Hz) appeared as the major species,
whereas cis-(P,P)-Re(NPh)Cl(P2∼O)2 (14) (doublets at 14.9 and
2
19.0 ppm, JPP = 7 Hz) formed in smaller amount. Traces of
a third species, the ‘twisted’ trans-(P,P) complex Re(NPh)Cl-
(P2∼O)2 (15), were detected from the doublets at 14.2 and 28.4
ppm (2JPP = 236 Hz). Twenty-four hours later, the monosubsti-
tuted complex 11 had decreased significantly, while the cis-(P,P)
disubstituted compound 14 had become the major species.
The proportion of the trans-(P,P) isomer 15 had not changed.
Reducing the volume of the solution and adding pentane pre-
cipitated, as above, the ‘twisted’ cis-(P,P) compound 14 as a
brown-violet solid.
Refluxing P3∼OH for 4 h gave only the trans-(P,P) monosub-
Fig. 2 Monitoring the reaction of ReOCl3(PPh3)2 with P3∼OH and
NEt3 (complex : ligand molar ratio = 1 : 2) in ethanol by 31P{1H} NMR
(80.0 MHz). o = ReO(OEt)(P3∼O)2 (9), * = ReOCl(P3∼O)2 (6).
stituted complex Re(NPh)Cl2(PPh3)(P3∼O) (12), showing 31P
2
doublets at 29.0 and 34.4 ppm with a JPP constant of 272 Hz.
No new species appeared in the solution as heating was pursued.
Only the cis-(P,P)-Re(NPh)Cl(P∼O)2 complexes with P1∼O
(13) and P2∼O (14) were successfully isolated as powders stable
in air and in solution. No attempts were made to obtain the
monosubstituted complexes by using a lower ligand : metal
ratio. The formulas proposed for 13 and 14 are consistent with
the microanalyses and the mass spectra (DCI/NH3), whose
strongest features are the parent peaks [M ϩ H]ϩ. However,
small peaks are observed for [M Ϫ HCl ϩ H]ϩ and [M Ϫ HCl ϩ
NH4]ϩ, resulting from chloride loss, showing that the Re–Cl
bond is less stable here than it was in the Re᎐O analogues,
᎐
where such peaks were absent. As usual, no ν(Re᎐NPh) stretch
᎐
could be identified in the IR spectra, because these vibrations
overlap with ν(C–N) and ν(C–P) ligand modes. P∼O co-
ordination in the enolato form is evidenced from the strong and
Ϫ1
ؒ ؒ ؒ
ؒ ؒ ؒ
broad IR ν(C
C
O) stretch at 1536 cm for 13 and 1527
–– ––
1
cmϪ1 for 14. For both compounds, the H NMR spectrum
includes individual signals for the vinylic protons of the two
non-equivalent ligands (5.30/5.38 ppm for 13, 4.56/4.91 ppm for
14), which appear as doublets due to coupling with the nearby
phosphorus atom (Table 2). As noted for the related Re–oxo
complexes, the vinyl protons of P2∼O appear upfield from those
of P1∼O.
Fig. 3 2D 31P/1H NMR spectrum of ReO(OEt)(P1∼O)2 (7) in CDCl3.
Reactions in ethanol. Refluxing a 5 : 5 : 1 ratio of P1∼OH,
NEt3 and Re(NPh)Cl3(PPh3)2 in ethanol for 7 h precipitated
quantitatively a green solid analysing as Re(NPh)(OEt)(P1∼O)2
(16). Its 31P NMR spectrum in CDCl3 showed only one singlet
at 3.6 ppm, consistent with the high-symmetry structure shown
in Scheme 8. This complex is stable since the spectrum remained
unchanged after refluxing the mixture for 40 h.
When P2∼OH was reacted under the same conditions, the
31P{1H} spectrum of the solution showed evidence for two
complexes. The major species was the ‘twisted’ trans-(P,P)-
Re(NPh)Cl(P2∼O)2 complex (15), showing doublets at 14.2 and
ratios are needed for the substitution to go to completion, and
the influence of the ligand is more pronounced.
Reactions in toluene. Considering that the oxo complexes
were efficiently generated in toluene via ligand exchange, the
similar reactions starting from Re(NPh)Cl3(PPh3)2 and phos-
phinoenols in basic media was checked by 31P{1H} NMR. The
three main species detected (Scheme 7) gave characteristic
AX- or AB-type spectra, from which the cis- or trans-(P,P) con-
J. Chem. Soc., Dalton Trans., 2002, 914–924
919

View Article Online
Table 3 X-Ray and NMR data for the ethoxo co-ligand in Re() oxo and imido complexes
Compound
Structure
NMR data (ppm) CH3; CH2
X-Ray data
Ref.
[ReO(OEt)(P1∼O)2] (7)
[ReO(OEt)(P2∼O)2] (8)
[ReO(OEt)(P3∼O)2] (9)
[ReO(OEt)(P*∼O)2]a
[ReO(OEt)(cyclam)]2ϩ b
[ReO(OEt)Cl2(P∼N)c
[ReO(OEt)(dppd)]d
cis O–Re–OEt ‘twisted’ cis-P,P
cis O–Re–OEt ‘twisted’ cis-P,P
cis O–Re–OEt ‘twisted’ cis-P,P
cis O–Re–OEt ‘twisted’ cis-P,P
trans O–Re–OEt
trans O–Re–OEt ‘equatorial’ cis-P,P
trans O–Re–OEt ‘equatorial’ cis-P,P
trans O–Re–OEt ‘equatorial’ cis-P,P
1.25 (t); 5.38, 5.45 (m)
1.16 (t); 5.14 (qd)
1.33 (t); 5.30, 5.39 (m)
1.05 (t); 5.03, 5.56 (m)
1.17 (t); 3.68 (q)
0.49 (t); 2.93 (m)
0.15 (t); 2.56 (m)
This work
This work
This work
8
55
54
10,43
42
[ReO(OEt)(Hdpa)2]e
0.00 (t); 2.91 (m)
Re–O: 2.004(7) Å
Re–O–C: 124.6(6)Њ
Re–O: 1.880(9) Å
Re–O–C: 176.2(14)Њ
Re–O: 1.951(3) Å
Re–O–C: 135.0(3)Њ
Re–O: 2.003(8) Å (av.)
Re–O–C: 125(1)Њ (av.)
Re–O: 1.895(5) Å
Re–O–C: 147.5(6)Њ
[ReOI2(OEt)(PPh3)2]
trans O–Re–OEt ‘equatorial’ trans-P,P
trans N–Re–OEt ‘equatorial’ trans-P,P
trans N–Re–OEt ‘equatorial’ cis-P,P
trans N–Re–OEt
Ϫ0.26 (t); 1.51 (q)
Ϫ0.14 (t); 2.72, 2.95 (m)
0.30; 3.06 (q)
51
[Re(NPh)(OEt)(P1∼O)2] (16)
[Re(NPh)(OEt)(dppd)]d
[Re(NPh)(OEt)(bipy)2]2ϩ
This work
10,44
46
0.35; 3.25 (q)
a P*∼OH = 2-diphenylphosphino-4-methylphenol. b Cyclam = 1,4,8,11-tetraazacyclotetradecane. c P∼N = o-(diphenylphosphino)-N,NЈ-dimethyl-
aniline. d H2dppd = N,NЈ-bis[2-(diphenylphosphino)phenyl]propane-1,3-diamine. e H2dppa = (o-aminophenyl)diphenylphosphine.
Scheme 7
28.4 ppm with a 2JPP constant of 236 Hz. Re(NPh)(OEt)(P2∼O)2
(17), similar to 16, formed as a minor species, characterised
by a singlet at 4.5 ppm. Again, increased refluxing time had
no influence on the reaction. Concentration of the solution
produced only green crystals of pure 15.
P3∼OH reacted differently. The reaction mixture contained
only PPh3, free ligand and the monosubstituted trans-(P,P)-
Re(NPh)Cl2(PPh3)(P3∼O) compound (12) identified from its
doublets at 29.0 and 34.4 ppm with a 2JPP constant of 272 ppm.
This complex could not be precipitated. The formation of
ethoxo species was not observed.
with the P atoms being trans to one another. The ‘equatorial’
trans-(P,P) structure adopted by 16 is quite unusual, since all
‘equatorial’ alkoxo species reported so far for Re–oxo com-
plexes with P∼O and P∼N chelating ligands adopt the cis-
(P,P) configuration.42–44 Thus, the energy difference between the
cis-(P,P) and the trans-(P,P) configurations should be small.
The ethoxo group trans to the Re᎐NPh bond gives a methyl
᎐
triplet at Ϫ0.14 ppm, whereas the diastereotopic methylene pro-
tons give HAHBH3P2 multiplets at 2.72 and 2.95 ppm, respect-
ively, due to coupling with one another, the methyl protons and
two P nuclei. These 4JHP couplings of ∼2 Hz to two cis P atoms
are rather unusual for Re complexes. These signals have shifted
upfield with respect to free EtOH (1.2 CH3; 3.6 CH2), but they
remain in the range reported for groups trans to O᎐Re or PhN᎐
᎐
᎐
Re units (Table 3). These upfield shifts confirm that an import-
ant electron transfer occurs from the PhN group into its trans-
ethoxo ligand in accordance with the trans influence exerted by
the phenylimido group. It could also result in part from the
ethoxo group being located close to an enolate oxygen and
undergoing an H/O through-space interaction.
Scheme 8
Complex 16 was characterised as the ‘equatorial’ trans-(P,P)-
Re(NPh)(OEt)(P1∼O)2 isomer on the basis of elemental anal-
ysis, IR spectra, mass spectra, NMR data and crystal structure.
The ethoxo ligand was detected from its medium intensity
ν(O–C–C) IR stretching band at 1032 cmϪ1. Co-ordination of
P1∼O in its enolato form was confirmed by the absence of a
The ‘equatorial’ ethoxo compound (17) could not be
isolated with the P2∼O ligand, even though it was present in
solution. Instead, the trans-(P,P) monochloro complex (15) was
obtained.
It is noteworthy that the related chloro complex precipitated
as the cis-(P,P) isomer (14) in toluene. The trans-(P,P) species
obtained in ethanol appears to be the thermodynamic product,
poor solubility being probably responsible for isolating the
cis compound as the kinetic product from toluene. A subtle
difference in phosphorus binding between these two isomers
is revealed by the 31P NMR spectra. The Peq signal appears at
much lower field for the trans-(P,P) complex 15, thus indicating
a stronger Re–Peq bond than in the cis isomer.
ؒ ؒ ؒ
ؒ ؒ ؒ
ν(C᎐O) band and the presence of the ν(C
C
–– ––
O) stretch at
᎐
ca. 1512 cmϪ1. In the mass spectrum, the strongest feature is the
[M Ϫ EtOH ϩ NH4]ϩ peak (100%), the low intensity of the
parent peak [M ϩ H]ϩ (7%) being indicative of the low thermal
stability of the Re–OEt bond. The equivalence of the two
co-ordinated P∼O ligands is deduced from the 31P and 1H NMR
1
data (Table 2). The 31P spectrum exhibits only one singlet. H
NMR signals are found for all the ligand protons, but there are
only half as many as for the ‘twisted’ complexes. The two
equivalent vinyl protons give a triplet at 5.40 ppm, due to
virtual coupling with two phosphorus atoms, in agreement
Complex 15 was characterised by elemental analysis. The
highest peak in the mass spectra was that of the parent ion,
confirming that the stable Re–Cl bond had resisted alcoholysis.
ؒ ؒ ؒ
ؒ ؒ ؒ
The ν(C
C
–– ––
O) stretches for the enolato group appeared at
920
J. Chem. Soc., Dalton Trans., 2002, 914–924

View Article Online
1
1536 cmϪ1. The H NMR spectra confirmed the octahedral
Table 4 Selected bond lengths (Å) and angles (Њ) for 16
‘twisted’ trans-(P,P) structure indicated by 31P NMR (Table 2).
In 14, the vinyl proton of each ligand appears as a doublet
(4.56, 4.91 ppm) resulting from an intraligand 2JPH coupling of
ca. 5.5 Hz with the nearby phosphorus atom, no coupling being
detected with the other P atom. In contrast, for 16, these vinyl
protons are coupled with the two mutually trans P atoms, giving
HPaxPeq-type signals in both cases (Table 2).
Re–P1
Re–P2
Re–N
Re–O1
Re–O2
Re–O3
P1–C2
P1–C31
P1–C21
P2–C4
2.447(1)
2.420(1)
1.745(4)
2.076(3)
2.081(3)
1.951(3)
1.777(5)
1.819(5)
1.845(5)
1.736(5)
P2–C61
P2–C71
N–C11
O1–C1
O2–C3
O3–C5
C1–C2
C1–C41
C3–C4
C3–C81
C5–C6
1.805(5)
1.835(5)
1.378(6)
1.328(5)
1.323(5)
1.420(6)
1.341(7)
1.494(6)
1.362(7)
1.517(6)
1.498(9)
Crystal structure of Re(NPh)(OEt)(P1∼O)2 (16)
The crystal structure of 16 confirms that the stereochemistry of
the molecule is the same in solution and in the solid state.
ORTEP drawings are provided in Fig. 4 and 5. Selected bond
lengths and angles are listed in Table 4.
P1–Re–P2
P1–Re–N
P1–Re–O1
P1–Re–O2
P1–Re–O3
P2–Re–N
P2–Re–O1
P2–Re–O2
P2–Re–O3
N–Re–O1
N–Re–O2
N–Re–O3
O1–Re–O2
O1–Re–O3
O2–Re–O3
Re–P1–C2
Re–P1–C31
Re–P1–C21
C2–P1–C21
C2–P1–C31
175.61(3)
90.68(13)
80.62(9)
100.94(9)
88.86(11)
93.32(13)
97.25(9)
C21–P1–C31
Re–P2–C4
Re–P2–C61
Re–P2–C71
C4–P2–C61
C4–P2–C71
C61–P2–C71
Re–N–C11
Re–O1–C1
Re–O2–C3
Re–O3–C5
O3–C5–C6
O1–C1–C2
O1–C1–C41
C2–C1–C41
P1–C2–C1
O2–C3–C4
O2–C3–C81
C4–C3–C81
P2–C4–C3
103.0(2)
99.13(17)
118.86(16)
116.47(15)
108.4(3)
108.6(2)
104.8(2)
178.4(3)
119.6(3)
119.2(3)
135.0(3)
112.8(5)
125.8(4)
111.6(4)
122.6(4)
115.8(3)
124.7(4)
112.7(4)
122.5(4)
116.2(4)
80.47(9)
87.15(11)
94.47(15)
95.72(15)
179.38(14)
169.67(12)
85.86(13)
83.97(14)
98.09(16)
118.32(15)
119.16(15)
108.8(2)
109.0(2)
O2–N–O3 and Re–P1–P2–N–O3 planes, respectively), which
contrasts with the case of cis-(P,P)-Re(NPh)(OMe)(Hdpa)2,
[where HdpaϪ is the monoanion of (o-aminophenyl)diphenyl-
phosphine],44 in which the N-phenyl ring is rotated above the
chelate rings.
The axial Re–O3(ethoxo) bond [1.951(3) Å] is similar to
those found for alkoxo groups trans to the Re᎐NPh bond.44–50
Fig. 4 ORTEP drawing of 16. Ellipsoids correspond to 40% prob-
ability. Hydrogens are omitted for simplicity. In the ring-numbering
scheme, the last digit corresponds to the position around the ring,
starting with 1 for the ipso position.
᎐
Considering that distances of 2.04, 1.86 and 1.75 Å have been
proposed for typical single, double and triple bonds, respect-
ively,51 the Re–O3 distance indicates a significant double-bond
character. On the other hand, those with the P∼O ligands
[2.076(3) and 2.081(3) Å] correspond to typical single bonds.
Electron delocalisation in the co-ordinated enolate ligand is
evidenced from various structural features discussed earlier:14
the P–C bonds in the rings [1.777(5) and 1.736(5) Å] are much
shorter than those (ca. 1.83 Å) found for the same ligand
co-ordinated as the neutral keto form; multiple bond character
makes the C–C bonds [1.341(7) and 1.362(7) Å] shorter than
the single bonds in the keto form (ca. 1.51 Å); the opposite
effect is noted for the C–O bonds [mean 1.325(7) Å], which have
lost some double bond character compared with the keto form
(ca. 1.20 Å).
The departure from planarity in the P–C–C–O part of the
co-ordinated ligands, although significant, is not very large
(mean deviations from least-squares plane of 0.008 Å for O1–
C1–C2–P1 and 0.030 Å for O2–C3–C4–P2), but the Re atom
lies considerably out theses planes, the Re-to-plane distances
being 0.032 and 0.142 Å, respectively. It was noticed earlier30
that the phenyl substituent on the double bond tends to be
coplanar with the chelate ring, probably because this orient-
ation favours extended electron delocalisation. This holds true
here for one of the rings (dihedral angle of 11Њ for ring C81–86),
but the resulting stabilisation is probably not great since the
dihedral angle is ca. 40Њ for ring C41–46 in the other ligand.
The Re–O3–C5 bond angle of 135.0(3)Њ in the ethoxo group
lies in the normal range.44–54 Interestingly, the O3–C5 bond is
nearly coplanar with the Re–O1 bond [C5–O3–Re–O1 torsion
angle = 7.3(5)Њ] (Fig. 5). This orientation and the relatively large
angle at the ethoxo oxygen create favourable conditions for
The Re atom adopts a distorted octahedral co-ordination.
The two phosphinoenolate ligands lie the equatorial plane
(perpendicular to the Re᎐NPh multiple bond) with the P
᎐
donors trans to one another, whereas the sixth co-ordination
site is occupied by the oxygen of an ethoxo group.
The ‘pinched’ distortion in the octahedron is due to the small
O–Re–P bite angles (ca. 80.5Њ), similar to those found in 1 and
ReN(PPh3)(P1∼O)2,30 but a few degrees smaller than those
reported for various transition metals.14–17,21–23,25–28 Most of the
distortion is absorbed by the O1–Re–O2 angle [169.7(1)Њ], so
that the two other trans angles remain closer to ideality [N–Re–
O3 = 179.4(1)Њ and P1–Re–P2 = 175.6(3)Њ]. As usual, the equat-
orial ligands are displaced away from the Re᎐N multiple bond,
᎐
as evidenced from the N–Re–Leq angles ranging from 90.7 to
95.7Њ (mean 93.5Њ), whereas the O3–Re–Leq angles involving
the ethoxo oxygen lie in the 88.9–84.0Њ range (mean 86.5Њ).
As a result, the Re atom lies 0.135(1) Å away from the P2O2
‘equatorial’ plane, on the Re᎐N side.
᎐
The Re–P distances [2.447(1) and 2.420(1) Å] are normal,
similar to those observed in the related systems.1–3,8,30 The
geometry about the amide N atom is consistent with a triply-
bonded N–Ph group. The Re–N–C(Ph) unit is essentially linear
[178.4(3)Њ], whereas the Re–N and N–C distances of 1.745(4)
and 1.378(6) Å, respectively, correspond with the mean values
reported for phenylimido–alkoxo compounds.44–50 The phenyl
ring stands upright, roughly perpendicular to the equatorial
plane. The phenyl plane bisects the O1–Re–P2 and O2–Re–P1
angles (dihedral angle of 48.5 and 50.9Њ with the Re–O1–
J. Chem. Soc., Dalton Trans., 2002, 914–924
921

View Article Online
bonding interactions between the ethoxo π orbitals and the
empty dxz and dyz orbitals on rhenium. This point will be further
discussed below.
Scheme 9
density is delocalised in a different way: the complex reacts with
the electrophilic CoI2 to give the binuclear enolato-bridged
complex Ni(P1∼O)2CoI2.22
This same structure is retained in cis-(P,P)-ReO(OEt)(P1∼O)2,
as it was in cis-(P,P)-ReO(OEt)(P*∼O)2 (where P*∼OH =
2-diphenylphosphinomethyl-4-methylphenol),8 and these two
compounds belong to an unprecedented type of complexes
with an alkoxo group cis to the Re᎐O bond. So far, cis-(P,P)-
᎐
ReY(OR)L2 (Y = O, NPh; L = P∼N) have been observed only as
the ‘equatorial’ isomers, while the corresponding ‘twisted’ cis-
(P,P)-ReYClL2 complexes were obtained by addition of HCl,
thus indicating the preference of the OR group for the site trans
to the Re᎐Y bond and of the Cl ligand for a cis site.42 In the
᎐
present phosphinoenol complexes with the [Re᎐O]3ϩ core, the
᎐
Fig. 5 Simplified ORTEP view of 16 showing the location of the trans
stereochemistry is the same for the chloro and the ethoxo com-
plexes, that is, the OEt and the Cl ligands occupy the same
co-ordination site and the exchange reaction is stereoselective.
Furthermore, these compounds can be synthesised by reacting
the phosphinoenolate with ReO(OEt)Cl2(PPh3)2, whose trans-
OEt ligand. The atoms are numbered as in Fig. 4.
99mTc complexes
Preliminary results on the biodistribution of the neutral
complexes resulting from the co-ordination of P1∼OH to the
99mTc(), 99mTcO and 99mTcN centres, carried out by the pro-
cedures described elsewhere,12 indicated that the species are
taken up by the liver and the spleen due to their lipophilic
character, whereas the uptake in other organs is unimportant.
O᎐Re–OEt unit has to rearrange to position the ethoxo group
᎐
on a cis site. Therefore, it must be concluded that the cis-(P,P)
‘twisted’ structure is very stable and that the phosphinoenolate
oxygen competes efficiently with the OEt group for the position
trans to the Re᎐O bond.
᎐
In contrast with this simple chemistry, the [Re᎐NPh]3ϩ core
᎐
leads to monosubstituted Re(NPh)X2(PPh3)(P∼O) and two
disubstituted ‘twisted’ Re(NPh)X(P∼O)2 compounds. The first
species is an intermediate in which one PPh3 has been substi-
tuted and the P donors retain the mutually trans orientation of
the starting Re(NPh)Cl3(PPh3)2 compound. A Cl ligand is dis-
placed and ring closure positions the phosphinoenolate oxygen
trans to the Re᎐NPh bond. For the bulky P ∼OϪ ligand, the
Discussion
In the presence of NEt3 acting as base and proton quencher,
phosphinoketones give a new series of Re() oxo and imido
complexes in which they are bonded to the metal centre in their
enolate form via the enol oxygen and the phosphorus atoms. All
these compounds share as a common feature the presence of an
᎐
3
oxygen donor trans to the multiple Re᎐O or Re᎐NPh bond,
reaction stops at this stage.
᎐
᎐
which is a well-established trend in Re() chemistry.
The Re(NPh)Cl(P∼O)2 complexes previously obtained with
phosphinophenol usually adopted the ‘twisted’ trans-(P,P)
structure in the solid state and this may ascribed, at least in
part, to the steric effect from the imido phenyl substituent. With
the phosphinoenolates P1∼OϪ and P2∼OϪ, the toluene solutions
contained the cis-(P,P)-Re(NPh)Cl(P∼O)2 species as the main
product. In ethanol, however, the only Re(NPh)Cl(P∼O)2
species detected were of the trans-(P,P) form and this was the
major reaction product with P2∼OϪ. Therefore, even though
overall oxygen-to-metal π-bonding in the trans-(P,P) isomer is
probably less efficient since it takes place with the same d
orbital, the difference in thermodynamic stability between the
cis-(P,P) and the trans-(P,P) isomers seems to be small for the
Re–imido complexes: the balance between the electronic and
steric factors is apparently more subtle and the structure of the
complexes becomes solvent-dependent. Differences in the
bonding in these two isomers are revealed by their 31P NMR
spectra: downfield shifts indicate stronger Re–P bonds in the
trans-(P,P) complex, in agreement with the lower steric effects
of the ligands adopting the trans arrangement.
Full characterisation of these complexes allowed us to make
comparisons with the reactivity of the related phosphinophenol
ligand toward the [Re᎐O]3ϩ and [Re᎐NPh]3ϩ cores. The first
᎐
᎐
difference to be pointed out is the crucial role played by NEt3 in
the reactions involving phosphinoenols, since only a mixture of
complexes was isolated without this reagent. In contrast, with
phosphinophenol, NEt3 accelerated the process, but the reac-
tion occurred even in its absence. This agrees with the fact that
phenols are easier to deprotonate than enols. A second major
difference is the influence of the solvent. Phosphinophenol
affords halide complexes, while phosphinoenols in ethanol give
ethoxo compounds whose stability and structure depend on the
ligand and the Re᎐Y core.
᎐
The [Re᎐O]3ϩ core gives only disubstituted complexes, which
᎐
all show a cis-(P,P) ‘twisted’ octahedral configuration with the
two bidentate ligands located in mutually orthogonal planes.
Molecular orbital calculations carried out on P1∼OϪ indicate
that the HOMO is a bonding π orbital (similar to that of an
allylic system) highly localised on the enol oxygen atom.27 This
stereochemistry allows efficient electron delocalisation via π-
bonding interactions to take place, since electron density can
flow from the enol oxygens into the two empty rhenium dxz/dyz
The ethoxo compound Re(NPh)(OEt)(P1∼O)2 was the only
species precipitated from ethanol solutions. Its structure is
‘equatorial’ trans-(P,P). The site trans to the Re᎐NPh bond is
᎐
orbitals already involved in the Re᎐O π bonds (Scheme 9).
occupied by the ethoxo group and steric hindrance is minimised
by the phosphine groups adopting a trans arrangement. This
molecule is stable toward halide substitution, whereas the
᎐
It is noteworthy that in the electron-rich d8 Ni() complex
Ni(P1∼O)2, where these d orbitals are not empty, electron
922
J. Chem. Soc., Dalton Trans., 2002, 914–924

View Article Online
2 F. Loiseau, Y. Lucchese, M. Dartiguenave, F. Bélanger-Gariépy and
‘twisted’ cis-(P,P)-Re(NPh)Cl(P∼O)2 molecule does not ethan-
olyse. Interestingly, in the crystals of Re(NPh)(OEt)(P∼O)2,
the Re–OCH2 bond is nearly coplanar with the equatorial
Re–O(enolate) bonds. This orientation favours overall oxygen-
to-metal π-bonding, since the best ethoxo π orbital (p orbital
perpendicular to the Re–O–C plane, Scheme 10) interacts with
A. L. Beauchamp, Acta Crystallogr., Sect. C, 1996, 52, 1968.
3 C. Bolzati, F. Tisato, F. Refosco, G. Bandoli and A. Dolmella, Inorg.
Chem., 1996, 35, 6221.
4 C. Bolzati, F. Tisato, F. Refosco and G. Bandoli, Inorg. Chim. Acta,
1996, 247, 125.
5 C. Bolzati, F. Refosco, F. Tisato, G. Bandoli and A. Dolmella, Inorg.
Chim. Acta, 1992, 201, 7.
6 F. Loiseau, Y. Lucchese, M. Dartiguenave and Y. Coulais,
Polyhedron, 2000, 19, 1111.
7 F. Loiseau, F. Connac, Y. Lucchese, M. Dartiguenave, S. Fortin,
A. L. Beauchamp and Y. Coulais, Inorg. Chim. Acta, 2000, 306,
94.
8 F. Connac, Y. Lucchese, M. Gressier, M. Dartiguenave and A. L.
Beauchamp, Inorg. Chim. Acta, 2000, 304, 52.
Scheme 10
9 R. G. Carvell, R. W. Hilts, H. Luo and R. McDonald, Inorg. Chem.,
1999, 38, 897.
10 G. Bandoli, F. Tisato, F. Refosco and T. I. A. Gerber, Rev. Inorg.
Chem., 1999, 19, 187.
11 C. Bolzati, L. Ucelli, F. Refosco, F. Tisato, A. Duatti, M. Giganti
and A. Piffanelli, Nucl. Med. Biol., 1998, 25, 71.
12 X. Couillens, Synthèse et caractérisation de complexes de rhénium
et de technétium 99m à ligands phosphinoénolato et phosphino-
phénolato. Application en radiopharmacie, Thèse de l’Université
Paul Sabatier, 2001.
13 P. Braunstein, D. Matt, D. Nobel, F. Balegroune, S. E. Bouaoud,
D. Grandjean and J. Fischer, J. Chem. Soc., Dalton Trans., 1988, 353.
14 E. M. Georgiev, H. tom Dieck, G. Fendesak, G. Hahn, G. Petrov
and M. Kirilov, J. Chem. Soc., Dalton Trans., 1992, 1311.
15 S. E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D. Nobel,
Inorg. Chem., 1986, 25, 3765.
one of the dxz/dyz orbitals, while the other d orbital takes care of
the π interactions with the equatorial enolate oxygens.
The binding versatility of the ethoxo group plays a major
role in stabilising the novel ‘twisted’ cis-(P,P)-ReO(OEt)(P∼O)2
and ‘equatorial’ trans-(P,P)-Re(NPh)(OEt)(P∼O)2 complexes.
In an ethoxo group occupying a site cis to the Re᎐Y multiple
᎐
bond, one of the filled π orbitals can participate in π-
bonding, whereas the other is involved in a four-electron
destabilising interaction with the filled dxy orbital (Scheme
11).53 Large overall donation of the nucleophilic EtOϪ group
16 P. Braunstein, D. G. Kelly, A. Tiripicchio and F. Ugozzoli, Inorg.
Chem., 1993, 32, 4845.
17 P. Braunstein, D. G. Kelly, Y. Dusausoy, D. Bayeul, M. Lanfranchi
and A. Tiripicchio, Inorg. Chem., 1994, 33, 233.
Scheme 11
18 P. Braunstein, S. Coco Cea, A. DeCian and J. Fischer, Inorg. Chem.,
1992, 31, 4203.
19 B. Demerseman, B. Guilbert, C. Renouard, M. Gonzales and
P. Dixneuf, Organometallics, 1993, 12, 3906.
to the Re() centre and concomitant decrease of its nucleo-
philic character are consistent with the rather large down-
1
field H chemical shifts of the methylene protons with respect
to those of free ethanol. In contrast, an alkoxo ligand trans to
the multiple bond has two filled π orbitals suitably oriented
for donation into the dxz/dyz pair. If the EtOϪ group were
linearly co-ordinated, these would actually be pure p orbitals.
When the group is bent, one of these orbitals acquires sp2
character, but since the Re–O–C angle is large, π-bonding
ability is probably retained to a certain extent. At any rate, the
other π-bonding orbital of a bent alkoxo group remains fully
available and the orientation of the EtOϪ group in the crystal
structure of Re(NPh)(OEt)(P∼O)2 suggests that it plays a sig-
20 P. Braunstein, Y. Chauvin, J. Nähring, Y. Dusausoy, D. Bayeul,
A. Tiripicchio and F. Ugozzoli, J. Chem. Soc., Dalton Trans., 1995,
851.
21 P. Braunstein, Y. Chauvin, J. Nähring, A. DeCian, J. Fischer,
A. Titripicchio and F. Ugozzoli, Organometallics, 1996, 15, 5551.
22 P. Braunstein, Y. Chauvin, J. Nähring, A. DeCian and J. Fischer,
J. Chem. Soc., Dalton Trans., 1995, 863.
23 V. Grignard, G. Dupont and R. Locquin, Traité de Chimie
Organique, Masson, Paris, 1950, vol. 7, p. 744.
24 W. Keim, F. H. Kowaldt, R. Goddard and C. Krüger, Angew. Chem.,
Int. Ed. Engl., 1978, 17, 466.
25 S. Jacobson, N. J. Taylor and A. J. Carty, J. Chem. Soc., Chem.
Commun., 1974, 668; J. Andrieu, P. Braunstein and F. Naud,
J. Chem. Soc., Dalton Trans., 1996, 2903.
26 P. Braunstein, D. Matt and Y. Dusausoy, Inorg. Chem., 1983, 22,
2043; P. Braunstein, S. Coco Cea, M. Bruce, B. W. Skelton and
A. H. White, J. Organomet. Chem., 1992, 423, C38.
27 P. Veya, C. Floriani, A. Chiesi-Villa, C. Guastini, A. Deudieu,
F. Ingold and P. Braunstein, Organometallics, 1993, 12, 4359.
28 P. Braunstein, D. Matt, J. Fischer, L. Ricard and A. Mitschler, Nouv.
J. Chim., 1980, 4, 493.
1
nificant role in bonding. The upfield H NMR signal indicates
that this group remains relatively electron-rich, in agreement
with its own π-donating ability being counteracted by that of
the very electron-rich Re᎐NPh (or Re᎐O) bond. The ability of
᎐
᎐
OEtϪ to act as an electron reservoir and thus stabilise the
Re() complexes is fully apparent in Table 3, where a wide
range of O–C(R) distances and of Re–O–C(R) bond angles
are observed.
The three phosphinoenols studied here show no drastic
differences in reactivity, but the most sterically hindered P3∼O
ligand is the less reactive and gives the least stable complexes.
On the other hand, replacing Ph by tBu as the enol substituent
has no major effect.
29 P. Braunstein, L. Douce, F. Balegroune, D. Grandjean, D. Bayeul,
Y. Dusausoy and P. Zanello, New J. Chem., 1992, 16, 925.
30 F. Connac, Y. Lucchese, M. Dartiguenave and A. L. Beauchamp,
Inorg. Chem., 1997, 36, 256.
31 N. P. Johnson, C. J. L. Lock and G. Wilkinson, Inorg. Synth., 1967,
9, 145.
32 G. La Monica and S. Celini, Inorg. Chim. Acta, 1978, 29, 183.
33 N. P. Johnson, C. J. L. Lock and G. Wilkinson, J. Chem. Soc. A,
1964, 1054.
Acknowledgements
34 Enraf-Nonius CAD-4 Software, Version 5, Enraf-Nonius, Delft,
The Nederlands, 1989.
35 G. M. Sheldrick, SHELXS-86, Program for the Solution of
Crystal Structures, University of Göttingen, Göttingen, Germany,
1990.
36 G. M. Sheldrick, SHELXS-93, Program for the Refinement of
Crystal Structures, University of Göttingen, Göttingen, Germany,
1993.
We are grateful to the French Ministère de l’Education
Nationale, de la Recherche et de la Technologie and the Natural
Sciences and Engineering Research Council of Canada for
financial support. The authors wish to thank S. Richelme
for assistance in the mass spectrometry studies and F.
Bélanger-Gariépy in the X-ray diffraction study.
37 A. L. Spek, PLATON, Molecular Geometry Program (July 1995
version), University of Utrecht, Utrecht, The Nederlands, 1995.
38 J. Chatt and C. A. Rowe, J. Chem. Soc., 1962, 4019.
39 P. E. Garrou, Chem. Rev., 1981, 81, 229.
References
1 H. Luo, I. Setyawati, S. J. Rettig and C. Orvig, Inorg. Chem., 1995,
34, 2287.
40 C. A. Tolman, Chem. Rev., 1977, 77, 313.
J. Chem. Soc., Dalton Trans., 2002, 914–924
923

View Article Online
41 N. B. Colthup, L. H. Daly and S. E. Wiberley, Introduction to
Infrared and Raman Spectroscopy, Academic Press, San Diego,
3rd edn., 1990, p. 333.
42 F. Refosco, F. Tisato, G. Bandoli, C. Bolzati, A. Dolmella,
A. Moresco and M. Nicolini, J. Chem. Soc., Dalton Trans., 1993,
605.
48 Md. A. Masood, B. P. Sullivan and D. J. Hodgson, Inorg. Chem.,
1994, 33, 5360.
49 R. Hubener, U. Abram and J. Strahle, Acta Crystallogr., Sect. C,
1995, 51, 1284.
50 U. Wittern, J. Strahle and U. Abram, Z. Anorg. Allg. Chem., 1995,
621, 1338.
43 F. Tisato, F. Refosco, A. Moresco, G. Bandoli, A. Dolmella and
C. Bolzati, Inorg. Chem., 1995, 34, 1779.
44 F. Refosco, C. Bolzati, F. Tisato and G. Bandoli, J. Chem. Soc.,
Dalton Trans., 1998, 923.
45 V. Goeden and B. L. Haymore, Inorg. Chem., 1983, 22, 157.
46 M. Bakir and B. P. Sullivan, J. Chem. Soc., Dalton Trans., 1995,
1733; M. Bakir, S. Paulson, P. Goodson and B. P. Sullivan, Inorg.
Chem., 1992, 31, 1127.
47 M. T. Hamet, B. Coutinho, J. R. Dilworth, J. R. Miller, S. J. Parrot
and Y. Zhang, Polyhedron, 1996, 15, 2041.
51 G. F. Ciani, G. D’Alfonso, T. Romiti, A. Sironi and M. Freni, Inorg.
Chim. Acta, 1983, 72, 29.
52 J. Andrieu, P. Braunstein, M. Drillon, Y. Dusausoy, F. Ingold,
P. Rabu, A. Tiripicchio and F. Ugozzoli, Inorg. Chem., 1996, 35,
5986.
53 K. G. Caulton, New J. Chem., 1994, 18, 25.
54 F. Tisato, R. Refosco, C. Bolzati, A. Cagoli, S. Gatto and G.
Bandoli, J. Chem. Soc., Dalton Trans., 1997, 1421.
55 Y.-P. Wang, C.-M. Che, K.-Y. Wong and S.-M. Peng, Inorg Chem.,
1993, 32, 5827.
924
J. Chem. Soc., Dalton Trans., 2002, 914–924