Synthesis, characterisation and molecular structure of Re(III) 2-oxacyclocarbenes stabilised by a benzoyldiazenido ligand

Article abstract of DOI:10.1039/b315693a

A family of new Fischer-type rhenium(III) benzoyldiazenido-2-oxacyclocarbenes of formula [(ReCl₂{η¹-N₂C(O)-Ph} {=C(CH₂)_nCH(R)O}(PPh₃)₂][n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me (5)] have been prepared by reaction of [ReCl₂{η²-N₂C(Ph)O} (PPh₃)₂] (1) with ω-alkynols, such as 3-butyn-1-ol, 4-pentyn-1-ol, 4-pentyn-2-ol, 5-hexyn-2-ol in refluxing THF. The correct formulation of the carbene derivatives 2-5 has been unambiguously determined in solution by NMR analysis and confirmed for compounds 2-4 by X-ray diffraction methods in the solid state. All complexes are octahedral with the benzoyldiazenido ligand, Re{N₂C(O)Ph}, adopting a single bent conformation. The coordination basal plane is completed by an oxacyclocarbene ligand and two chlorine atoms. Two triphenylphosphines in trans positions with respect to each other complete the octahedral geometry around rhenium. The reactivity of 1 towards different alkynes and alkenes including propargyl- and allylamine has been also studied. With propargyl amine, monosubstituted or bisubstituted complexes, [(ReCl₂ {η¹-N₂C(O)Ph} {η¹-NH₂-CH₂C≡CH}_n (PPh₃)_3-n][n = 1 (6); n = 2 (7)], have been isolated depending on the reaction conditions. In contrast, the reaction with allylamine gave only the disubstituted complex [(ReCl₂{η¹- N₂C(O)Ph}{η¹-NH₂CH₂ CH=CH₂}₂(PPh₃)] (8). The molecular structure of the monosubstituted adduct 6 has been confirmed by X-ray analysis in the solid state.

Full text of DOI:10.1039/b315693a

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Synthesis, characterisation and molecular structure of Re(III)
2-oxacyclocarbenes stabilised by a benzoyldiazenido ligand
Lorenza Marvelli,*a Nicoletta Mantovani,a Andrea Marchi,a Roberto Rossi,*a
Michele Brugnati,a Maurizio Peruzzini,*b Pierluigi Barbaro,b Isaac de los Riosc
and Valerio Bertolasid
a Laboratorio di Chimica Nucleare ed Inorganica, Dipartimento di Chimica,
Università di Ferrara, Via L. Borsari 46, 44100, Ferrara, Italy
b Istituto di Chimica dei Composti OrganoMetallici, ICCOM CNR, Via Madonna del Piano,
snc, Area di Ricerca del CNR, 50019, Sesto Fiorentino, Italy
c Departamiento de Ciencia de los Materiales e Ing. Met. y Quimica Inorganica,
Facultad de Ciencias, Universidad de Cadiz, Apartado 40, Puerto Real, 11510, Spain
d Centro di Strutturistica Diffrattometrica, Dipartimento di Chimica, Università di Ferrara,
Via L. Borsari 46, 4100 Ferrara, Italy
Received 3rd December 2003, Accepted 13th January 2004
First published as an Advance Article on the web 5th February 2004
A family of new Fischer-type rhenium() benzoyldiazenido-2-oxacyclocarbenes of formula [(ReCl2{η1-N2C(O)-
Ph}{᎐C(CH ) CH(R)O}(PPh ) ] [n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me (5)] have been prepared by
᎐
2
n
3 2
reaction of [ReCl2{η2-N2C(Ph)O}(PPh3)2] (1) with ω-alkynols, such as 3-butyn-1-ol, 4-pentyn-1-ol, 4-pentyn-2-ol,
5-hexyn-2-ol in refluxing THF. The correct formulation of the carbene derivatives 2-5 has been unambiguously
determined in solution by NMR analysis and confirmed for compounds 2–4 by X-ray diffraction methods in the
solid state. All complexes are octahedral with the benzoyldiazenido ligand, Re{N2C(O)Ph}, adopting a “single bent”
conformation. The coordination basal plane is completed by an oxacyclocarbene ligand and two chlorine atoms.
Two triphenylphosphines in trans positions with respect to each other complete the octahedral geometry around
rhenium. The reactivity of 1 towards different alkynes and alkenes including propargyl- and allylamine has been
also studied. With propargyl amine, monosubstituted or bisubstituted complexes, [(ReCl2{η1-N2C(O)Ph}{η1-NH2-
᎐
CH C᎐CH} (PPh )3Ϫn] [n = 1 (6); n = 2 (7)], have been isolated depending on the reaction conditions. In contrast, the
᎐
2
n
3
reaction with allylamine gave only the disubstituted complex [(ReCl {η1-N C(O)Ph}{η1-NH CH CH᎐CH } (PPh )]
᎐
2
2
2
2
2
2
3
(8). The molecular structure of the monosubstituted adduct 6 has been confirmed by X-ray analysis in the solid state.
study the reactivity of the benzoylhydrazido rhenium()
Introduction
complex [ReCl2{η2-N,O-N2C(Ph)O}(PPh3)2] (1) towards
Fischer-type oxacyclocarbenes are a well known class of
organometallic compounds which generally are obtained from
ω-alkynols. Complex 1 is a versatile species for encompassing
the two-step reduction, Re()
Re()
Re(), involving a
the reaction of a variety of ω-alkynols with coordinatively
unsaturated transition-metal ligand fragments.1 Although most
of these complexes contain metals of the chromium1,2 and iron
triad,1,3 particularly ruthenium,4 it has been seldom shown that
oxacyclocarbenes may also be stabilised through coordination
to manganese5 and rhenium.6 In particular, we have previously
reported that the Dötz protocol for the synthesis of oxacyclo-
carbenes ligands may be successfully applied to the rhenium()
complex [(triphos)(CO)2Re(OTf )], which easily loses the
weakly coordinated triflate ligand to generate the [(triphos)-
Re(CO)2]ϩ synthon (triphos = MeC(CH2PPh2)3).7 The reaction
of [(triphos)(CO)2Re(OTf )] with different ω-alkynols is a
straightforward process affording in excellent yield a variety
of 2-oxacyclocarbene derivatives of formula [(triphos)(CO)2-
total of four electrons as was originally demonstrated by Chatt
et al. (Scheme 1).10
Re{᎐C(CH ) CH(R)O}]ϩ (n = 2, 3, 4; R = H, Me).8,9 In these
᎐
2
n
complexes the stabilisation of the oxacyclocarbene moiety
is certainly favoured by the presence of the sterically demand-
ing tripodal triphosphine, which provides the appropriate
protective environment to accommodate the oxacyclocarbene
ligand. The electron richness of the rhenium() centre may
also contribute to stabilise this relatively unusual organo-
metallic ligand. In this respect, it is worth mentioning that
most of the known 2-oxacyclocarbenes, including those of
chromium() or ruthenium(), share with rhenium() the d6
electronic-configuration. In order to verify if other ligands,
less sterically demanding than triphos, may provide a suitable
environment to stabilise rhenium() oxacyclocarbenes and
investigate whether rhenium complexes in higher oxidation
states may still form these type of carbenes, we have begun to
Scheme 1
To better account for this redox process, it should be noted
that the benzoylhydrazido ligand in 1 behaves as a hemilabile
ligand allowing opening of the chelating ring upon reaction
with a variety of nucleophiles. As a result, organodiazenido
compounds of formula [ReCl2L{η1-N-N2C(O)Ph}(PPh3)2] (L =
neutral monodentate ligand such as PR3, CO or pyridine) have
been readily obtained (A).11 A further two-electron reduction is
generally feasible when the nucleophilic attack is carried out in
MeOH. In the latter case, the reduction process is accompanied
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
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by the breakdown of the benzoylhydrazido moiety by releasing
of methyl benzoate and hydrochloric acid whereas a side-on
dinitrogen ligand is left on the rhenium to form [ReCl2(N2)-
(L2)(PPh3)2] complexes (B).10
In this paper we show that rhenium() oxacyclocarbene
complexes may be synthesised starting from 1 and provide
details on the synthesis, the NMR spectroscopic behaviour and
the structural characterisation of [ReCl2{η1-N-N2C(O)Ph}-
ence of the benzoyl group.11a,12 The latter is partially super-
imposed to an additional medium intensity band between 1220
and 1250 cmϪ1 ascribable to the ν(COC) absorption of the
oxacyclic carbene ligand.8,9 The NMR analysis of 2–5 in
CDCl3, show typical diamagnetic spectra confirming the
presence of 2-oxacyclocarbene ligands. Unexpectedly, each
NMR spectra are complicated by the occurrence of a dynamic
equilibrium between two isomeric species which affects the
solution behaviour of all of the oxacyclocarbene complexes
here described (see below, NMR section). Particularly inform-
ative for validating the presence of a carbene ligand in either
isomers is the typical low-field triplet resonance occurring at
ca. 300 ppm (JCP ca. 8 Hz) in the 13C{1H} NMR.8 Attempts to
separate the two isomers by TLC chromatography on either
alumina or silica using different combinations of eluents
(n-hexane, CH2Cl2, CHCl3, CH3CN) failed likely as a conse-
quence of very similar Rf values.
In situ NMR monitoring of the reaction between 1 and
typical alkynols, such as 3-butyn-1-ol and ( )-5-hexyn-2-ol,
was attempted to clarify the mechanism leading to the 2-oxa-
cyclocarbenes 2–5. In contrast to our expectation, monitoring
the alkynol addition to a cooled, deoxygenated, CD2Cl2
solution of 1 in a 5-mm NMR tube, does not provide any
mechanistic information because of the complete lack of
reactivity up to ca. 0 ЊC. At this temperature, a fast and
unselective process takes place resulting in the rapid and simul-
taneous formation of a pair of isomers for both the ω-alkynols
used for the NMR experiment. On the other hand, the absence
of any intermediate does not represent a serious opposition to
the hypothesis that the usual mechanism, which is generally
assumed to drive the formation of 2-oxacyclocarbene species,
is also responsible for the formation of 2–5 from 1 and the
alkynol. The only necessary prerequisite is that a coordination
vacancy is easily provided by rhenium and this is in fact the case
for the present benzoylhydrazido complexes, which upon
decoordination of the oxygen linkage, may readily generate an
empty coordination site available to accommodate the alkynol
molecule. From now on, the well-known sequential cascade
entailing π-alkyne to hydroxyvinylidene tautomerization
followed by intramolecular nucleophilic attack of the OH end
to the electron deficient Cα carbon, may account well for the
2-oxacyclocarbene formation (Scheme 3).8,13
{᎐C(CH ) CH(R)O}(PPh ) ] [n = 1, R = H (2), R = Me (3);
᎐
2
3 2
n = 2, R =nH (4), R = Me (5)] complexes. The reaction of 1 with
different alkynes and alkenes is also briefly discussed.
Results and discussion
Synthesis and characterisation of 2-oxacyclocarbene complexes
Reaction of a slight excess of the appropriate ω-alkynol,
᎐
HC᎐C(CH ) CH(R)OH (n = 1, 2; R = H, Me), with 1 in THF
᎐
2
n
under reflux, affords, after η2-N,O- to η1-N-coordination
slippage of the organodiazenido ligand, the 2-oxacyclocarbene
rhenium
complexes
[ReCl {η1-N-N C(O)Ph}{᎐C(CH ) -
᎐
2 2 2 n
CH(R)O}(PPh3)2] [n = 1, R = H (2), R = Me (3); n = 2, R = H (4),
R = Me (5)] in fairly good yield (Scheme 2). Compounds 2–5
are obtained irrespectively of the reaction solvent (benzene,
CH2Cl2, CHCl3) and the reaction conditions (temperature and
ratio between 1 and the ω-alkynol). Particularly, the presence of
methanol, which is known to promote the elimination of
methyl benzoate from benzoylhydrazido complexes, resulting
in a metal coordinated dinitrogen species, does not affect the
outcome of the reaction.10
Scheme 2
Complexes 2–5 are orange, air-stable crystalline materials,
which may be recrystallised in the air from CH2Cl2–EtOH
mixtures. They have been characterised by elemental analyses
and chemico-physical measurements including IR and NMR
(1H, 31P{1H}, 13C{1H}) spectroscopy. Table 1 summarises
selected NMR data (see below) while IR data, other chemico-
physical properties and elemental analysis are gathered in
the Experimental section. In addition, the solid-state structure
of 2–4 has been determined by X-ray diffraction methods
(see below).
Scheme 3
Dynamic NMR properties of complexes 2–5
The solution behaviour of complexes 2–5 was examined in
1
detail by NMR spectroscopy. H, 31P{1H} and 13C{1H} NMR
A remarkable structural feature shared by all the com-
plexes 2–5 is the presence of a 2-oxacyclocarbene ligand cis
disposed to a N-bonded benzoyldiazenido ligand which forms
after oxygen detachment from rhenium and opening of the
five-membered ring in 1. In keeping with this structural
rearrangement, inspection of the IR spectra of 2–5 shows two
medium-to-strong intensity bands in the range 1648–1663 and
1537–1551 cmϪ1 assigned to ν(C᎐O) and ν(N᎐N) absorptions,
spectra of complexes 2–5 were recorded at 294 K in both
C2D2Cl4 and CDCl3 solutions. All resonances were unequiv-
ocally attributed on the basis of conventional 1D spectra,
homo- (1H{1H}) and heteronuclear (1H{31P}) decoupling NMR
experiments, 2D 1H COSY, 1H–13C correlations and 1H
NOESY/ROESY spectra. The labelling scheme adopted for
complexes 2–5 is shown in Fig. 1. As mentioned above, the
NMR spectra show that at room temperature solutions of all
complexes exist as a mixture of two isomers (A, major; B,
᎐
᎐
respectively. These bands are typical of metal complexes bear-
ing the η1-N-N2C(O)Ph organodiazenido moiety, while a
medium-intensity band around 1240 cmϪ1 indicates the pres-
1
minor; molar ratio, based on H NMR integration, ca. 2.1 : 1
for 2, 3.4 : 1 for 3, 1.1 : 1 for 4, 2.0 : 1 for 5).
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
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Table 1 Selected 1H, 31P{1H} and 13C{1H} NMR spectral data for the complexes 2–5
Complex
1Ha (δ, ppm; J, Hz)
31P{1H}b (δ, ppm; J, Hz)
13C{1H}c (δ, ppm; J, Hz)
2
Isomer Ad
0.67, 2H, qnt, 3JHH = 8.0, H4α
2.11, 2H, t, 3JHH = 7.9, H3α
4.42, 2H, t, 3JHH = 8.0, H5α
7.24, 2H, m, m-COPh
7.42, 1H, m, p-COPh
7.53, 2H, m, o-COPh
s, 0.44, 2P
298.07, t, 2JCP = 7.6, C2
52.24, C3
20.51, C4
84.43, C5
168.27, t, 4JCP = 3.5, CO
Isomer Bd
0.92, 2H, qnt, 3JHH = 8.0, H4α
3.28, 2H, t, 3JHH = 7.9, H3α
3.88, 2H, t, 3JHH = 7.7, H5α
7.30,f 2H, m, m-COPh
s, 0.80, 2P
291.24, t, 2JCP = 7.6, C2
169.34, t, 4JCP = 3.8, CO,
57.19, C3
21.43, C4
7.50, 1H, m, p-COPh
81.85, C5
7.64, 2H, m, o-COPh
3
Isomer Ad
0.23, 1H, dq, 2JHH = 12.0, 3JHH5 = 9.5, H4α
0.53, 2JPP = 264.5, P1,e
296.76, t, 2JCP = 8.6, C2
52.74, C3
28.54, C4
1.09, 1H, dddd, 3JHH = 7.4, H4β
0.19, P2
e
5
1.27, 3H, d, Me
1.63, 1H, dtt, 3JHH = 10.0, 4JHP = 1.8, H3β
2.89, 1H, dddd, 2JHH = 20.3, 3JHαHα = 9.5,
3JHαHβ = 1.8, 4JHP = 1.0, H3α
91.26, C5
20.70, Me
t, 167.23, 4JCP = 3.1, CO
4.51, 1H, ddq, 3JHH = 6.3, H5α
Me
7.27, 2H, m, m-COPh
7.46, 1H, m, p-COPh
7.56, 2H, m, o-COPh
Isomer Bd
0.53, 1H, dddd, 2JHH = 12.0, 3JHH = 10.1, H4α
1.31, 2JPP = 270.6, P1,e
290.42, t, 2JCP = 8.1, C2
58.58, C3
29.34, C4
5
e
1.05, 3H, d, Me
0.04, P2
1.30,f 1H, 3JHH = 7.4, H4β
5
3.06, 1H, dddt, 3JHβHα = 10.4, 3JHβHβ = 9.2,
91.00, C5
4JHP = 1.6, H3β
19.62, Me
3.67, 1H, dddd, 2JHH = 19.6, 3JHαHα = 8.7,
3JHαHβ = 2.2, 4JHP = 1.0, H3α
168.12, t, 4JCP = 3.0, CO
3.88, 1H, ddq, 3JHH = 6.4, H5α
Me
7.32,f 2H
7.51, 1H, m, p-COPh
7.68, 2H, m, o-COPh
4
Isomer A
3.33, 1H, t, 3JHH = 6.4, H3α
0.87, 2H, qnt, 3JHH = 6.7 H4α
0.95, 2H, qnt, 3JHH = 6.3, H5α
3.83, 2H, t, 3JHH = 5.7, H6α
7.55, 2H, m, o-COPh
s, 0.55, 2P
302.21, t, 2JCP = 8.3, C2
50.88, C3
17.38, C4
20.80, C5
73.38, C6
7.48, 2H, m, m-COPh
7.31, 1H, m, p-COPh
167.92, t, 4JCP = 2.8, CO
Isomer B
2.51, 2H, t, 3JHH = 6.5, H3α
0.49, 2H, qnt, 3JHH = 6.5, H4α
1.00, 2H, qnt, 3JHH = 6.4, H5α
4.27, 2H, t, 3JHH = 5.9, H6α
7.55–7.30, m, 5H COPhg
s, 0.07 (2P)
296.82, t, 2JCP = 8.3, C2
44.89, C3
16.54, C4
21.09, C5
73.87, C6
167.11, t, 4JCP = 2.9, CO
5
Isomer A
2.12, 1H, dt, 2JHH = 19.4, 3JHH = 6.2, H3α
2.89, 1H, dt, 2JHH = 19.6, 3JHH = 7.0, H3β
0.57,f 1H, H4α
1.31,2JPPc, =d 268.5, P1
302.85, t, 2JCP = 7.0, C2
43.80, C3
17.07, C4
28.47, C5
81.09, C6
0.12, P2
0.57,f 1H, H4β
1.36,f 1H, 3JHH = 2.9, H5α
6
0.47,f, 1H, 3JHH = 10.6, H5β
21.38, Me
6
4.04, 1H, ddq, 3JHH = 6.3, H6α
167.13, t, 4JCP = 3.1, CO
Me
1.30, 3H, d, Me
7.56, 2H, m, o-COPh
7.27, 2H, m, m-COPh
7.46, 1H, m, p-COPh
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Table 1 (Contd.)
Complex
1Ha (δ, ppm; J, Hz)
31P{1H}b (δ, ppm; J, Hz)
13C{1H}c (δ, ppm; J, Hz)
Isomer B
2.86,f 1H, q, JHH = 6.1, H3α
3.67, 1H, q, JHH = 6.1, H3β
1.12, 1H, m, H4α
1.42, 2JPP = 270.1, P1
1.32, P2
297.71, t, 2JCP = 8.3, C2
49.97, C3
17.45, C4
0.87, 1H, m, H4β
27.77, C5
79.80, C6
1.34,f 1H, 3JHH = 2.9, H5α
6
0.45,f 1H, 3JHH = 10.1, H5β
20.65, Me
3.30, 1H, ddq, 63JHH = 6.3, H6α
167.94, t, 4JCP = 3.1, CO
Me
1.16, 3H, d, Me
7.68, 2H, m, o-COPh
7.32,f 2H, m-COPh
7.51, 1H, m, p-COPh
a 400.132 MHz, C2D2Cl4, 294 K. b 202.46 MHz, C2D2Cl4, 294 K. c 125.76 MHz, C2D2Cl4, 294 K. Chemical shifts in ppm, coupling constants (J )
in Hz. Legend: m, multiplet; d, doublet; t, triplet; q, quartet; qnt, quintet; the label α denotes the opposite side of the oxacarbene plane with respect to
the methyl group; the label β refers to same side. d CDCl3. e AB spin system. f Partially overlapped with other resonances. g Masked by the
corresponding resonances of isomer A.
Fig. 1 Sketch of the complexes 2–5 showing the numbering scheme
adopted for NMR assignments.
Both isomers of complexes 2 and 4 show a single set of
resonances for both of the phosphorus nuclei and the methyl-
enic protons of the oxacarbene. The chemical equivalence of
these nuclei indicates that a time-averaged symmetry element is
present in the complexes on the NMR time scale. The only
symmetry element consistent with the solid-state structure,
and accounting for the observed NMR behaviour, is the
coordination plane of the metal atom containing the chloride
ligands and encompassing the oxametallacycle pseudo-plane as
well the organodiazenido plane.
In contrast with 2 and 4, NMR spectroscopy shows that
complexes 3 and 5 do not adopt a similar symmetry likely as a
Fig. 2 Section of the 1H NOESY spectrum of 2 (CDCl3, 294 K,
400.13 MHz, τm = 0.65 s). Positive phased (exchange) cross-peaks are
represented by filled circles, negative phased (NOE) cross-peaks are
represented by empty circles.
consequence of the methyl substituent residing on the oxa-
cyclocarbene ring. In keeping with the lack of a symmetry
plane, the 31P{1H} NMR spectra of 3 and 5 display a tightly
coupled AB spin system for each isomer, while a diastereotopic
pair of methylenic resonances are observed for the oxametalla-
1
2
cycle protons in the H NMR spectra. JPP coupling constants
range from 264.5 to 270.6 Hz, thus confirming a trans arrange-
ment of the two triphenylphosphine ligands in all compounds.14
1H NOESY spectroscopy shows that the A and B isomers
attain a slow exchange motional regime in complexes 2–5. This
1
is clearly shown by the H NOESY spectra of 2–5 in which a
B
selective MeA ↔ MeB, H3αA ↔ H3αB, H3βA ↔ H3βB, H4αA ↔ H4α
,
A
H4β ↔ H4βB, etc. exchange pattern is observed. The labels α
and β were used to define the protons on the opposite side and
on the same side as the methyl group with respect to the oxa-
cyclocarbene plane. A section of the 1H NOESY spectrum of 2
showing relevant cross-peaks is reported in Fig. 2 as an example.
Analogous results were obtained by 1H ROESY spectroscopy.
The dynamic process responsible for this exchange equi-
librium can be attributed to the existence of an isomerism
involving the benzoylhydrazido group, similar to the well
known amide isomerization.15 A sketch of the two possible
geometric isomers is reported in Fig. 3. At first glance, the
alternative mechanism accounting for the isomerization in
Fig. 3 Sketch of the geometric isomers of complexes 2–5.
Consistently with the observed 1H NOE interaction, the
minor isomer B can be identified as the species destabilised by
strong steric repulsions between the oxacyclocarbene and
the organodiazenido groups (see Fig. 3). The measurement
of activation parameters for the exchange process in
complexes 2–5 are currently in progress on the basis of variable-
temperature 31P{1H} NMR spectra and will be published in
due course.
2–5 via restricted rotation around the Re᎐C bond can be ruled
᎐
out as very high energy barriers have been previously reported
for this motion in comparable systems.8,16
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
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Structure and bonding of the oxacyclocarbene complexes
A relevant problem in all the compounds containing benzoyl-
hydrazido ligands is the correct evaluation of the formal
oxidation state of the metal centre. A perusal of the available
literature on this class of compounds shows that the assignment
of the metal oxidation state in complexes containing the
organodiazenido ligand is not trivial. This group may exhibit
different coordination modes entailing both linear vs. bent
disposition of the –NNR unit as well as η1- vs. η2-hapticity
when the residue R is bearing additional donor atoms.17 Since
crystallographic data have been largely used to assess the
metal-oxidation state in this class of compounds,18,19 it was
decided to undertake a in-depth crystallographic study on the
present family of rhenium 2-oxacyclocarbenes. Additionally,
the collection of the X-ray data could be helpful to verify
whether the occurrence of the solution equilibrium for the
complexes 2–4 has an effect in the corresponding solid state
structure.
X-Ray crystal structure analysis of the 2-oxacyclocarbene
complexes 2, 3 and 4
ORTEP drawings showing the molecular structures of these
complexes are given in Figs. 4–7. Pertinent crystallographic data
are summarised in Table 2 while selected bond lengths and
angles are listed in Table 3.
Fig. 4 An ORTEP view of complex 2 showing thermal ellipsoids at
30% probability.
Crystals of 2 and 4 contain a solvent molecule of CH2Cl2
interspersed in the lattice per octahedral complex. For complex
3, two type of crystals, namely 3a and 3b, were found within the
same crystallization bulk. They are polymorphic crystals differ-
ing mainly by the colour, orange for 3a and yellow for 3b, and
by the presence of a solvent molecule of ethanol in 3b. In all
derivatives studied by crystallographic methods, the rhenium
atom has an octahedral environment with similar arrangements
of the ligand set. The two triphenylphosphines are in trans
position to each other and the basal plane is perpendicular to
the P–Re–P vector and occupied by two cis chlorine atoms, the
cyclic oxacarbene (2-oxacyclopentylidene in 2, 2-oxa-3-methyl-
cyclopentylidene in 3a and 3b, and 2-oxacyclohexylidene in 4)
and the monodentate organodiazenido(Ϫ) moiety. The short
reported for other rhenium organodiazenido complexes.20–27
The organodiazenido group is roughly planar and, for steric
reasons, form angles of about 40Њ [39.4(1), 40.0(1), 39.3(1) and
39.9(1)Њ for 2, 3a, 3b and 4, respectively] with the mean basal
plane passing through the Re, Cl1, Cl2, N1 and C8 atoms. The
distances between Re and C8 of the oxacarbene rings are in the
range of 1.990(4)–2.021(5) Å and well correspond to double
bond distances Re᎐C as found in several rhenium carbenes
᎐
authenticated by X-ray methods.8,9,28,29 All the complexes show
systematic lengthening of the Re–Cl1 distance with respect to
the Re–Cl2 distance. Taking into account the average value
for Re–Cl bond distance of 2.360(8) Å, determined from
15 structural determinations of [ReCl6]2Ϫ complex ions,30 the
crystallographically meaningful difference affecting the distri-
bution of the presently determined Re–Cl bond distances
[Re–Cl1 from 2.506(2) to 2.516(1) Å and Re–Cl2 from 2.422(1)
to 2.435(1) Å] can be accounted for in terms of a greater trans
effect exerted by the cyclic oxacarbene group with respect to the
organodiazenido moiety.
Re᎐N1 [ranging from 1.751(3) to 1.769(4) Å] and N1᎐N2 dis-
᎐
᎐
tances [in the range 1.222(6)–1.246(4) Å] as well as the linearity
of Re᎐N1᎐N2 triatomic array [making angles from 170.3(5)
᎐
᎐
to 174.4(3)Њ] are indicative of two adjacent Re᎐N᎐N double
᎐
᎐
bonds. The structural data are in perfect agreement with those
Fig. 5 ORTEP views of complexes 3a (left) and 3b (right) showing thermal ellipsoids at 30% probability. In compound 3a, the C9(H)C12(H2)
moiety of the 2-oxa-3-methylcyclopentylidene ring, refined with two independent orientations, is shown only in one position for sake of clarity.
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
717

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Table 2 Crystal data for complexes 2–4 and 6
2
3a
3b
4
6
Formula
C47H41Cl2N2O2P2Reؒ
CH2Cl2
1069.78
Monoclinic
P21/n
11.4338(2)
25.3055(7)
16.0016(4)
100.177(1)
4557.0(2)
4
1.559
295
30.12
2.6–28
10669
0.072
C48H43Cl2N2O2P2Re C48H43Cl2N2O2P2Reؒ C48H43Cl2N2O2P2Reؒ
C46H40Cl2N3OP2Re.ؒ
CH2Cl2
1054.78
Orthorhombic
Pbcn
33.3037(1)
11.0025(3)
24.7218(5)
90
9058.7(3)
8
1.547
295
30.28
C2H5OH
1044.95
Monoclinic
P21/c
18.5316(3)
11.9170(2)
20.5233(4)
91.718(1)
4530.3(1)
4
CH2Cl2
1083.81
Monoclinic
P21/n
11.5556(2)
25.2193(6)
16.0768(2)
101.176(1)
4596.5(2)
4
M
999.88
Monoclinic
P21/n
16.0911(2)
15.0661(2)
19.1572(3)
110.089(1)
4361.7(1)
4
System
Space group
a/Å
b/Å
c/Å
β/Њ
U/Å3
Z
Dc/g cmϪ3
T /K
1.521
295
1.532
295
1.566
295
µ/cmϪ1
Range θ/Њ
Unique reflns.
Rint
30.23
3.5–28
29.15
3.6–28
29.87
2.4–28
2.7–28
10554
0.087
10503
0.041
10891
0.047
10977
0.067
Observed reflns. [I > 2σ(I )] 7836
8175
0.0354
0.0857
1.119
8375
0.0505
0.1235
1.151
9096
0.0464
0.0981
1.158
7866
0.0491
0.1146
1.169
R (Obs. reflns.)
wR (All reflns.)
S
0.0441
0.0971
1.104
1.437, Ϫ1.108
∆ρmax, ∆ρmin/e Å Ϫ3
1.583, Ϫ1.163
1.441, Ϫ1.449
1.545, Ϫ1.172
1.469, Ϫ0.951
Fig. 6 An ORTEP view of complex 4 showing thermal ellipsoids at
30% probability. The C10(H2)C11(H2) moiety of the 2-oxacyclo-
hexylidene ring, refined with two independent orientations, is shown
only in one position for sake of clarity.
Fig. 7 An ORTEP view of complex 6 showing thermal ellipsoids at
30% probability.
The Re–P distances of the two trans triphenylphosphine
ligands are in the range 2.484(1)–2.500(1) Å and are in agree-
ment with other Re–P distances in rhenium() octahedral
complexes.31
Re()-d4 complexes and has been interpreted either as a
consequence of more or less severe distortions in solution of
the octahedral symmetry11a,19 or as a consequence of significant
π-electron-transfer from ligand electrons to the t2g orbitals of
the metal ion.33,36,37
From inspection of the X-ray data and in agreement with the
bent coordination mode displayed by the organodiazenido
ligand, it seems plausible to assign a formal Re() oxidation
state to the presented cyclic carbene complexes. Similar assign-
ment was proposed by Chatt and Harman for related com-
plexes11a,32 and has been recently supported by X-ray studies
carried out on some rhenium and technetium organodiazenido
species.22,29,33 In agreement with the presence of a rhenium()
center, magnetic susceptibility measurements on 2 suggest the
presence of two unpaired electrons with a µeff of 2.40 µB, at
21 ЊC. Similar values have been reported for other 5d4 octa-
hedral rhenium() systems.34 At first glance, the paramagnetic
solid state behaviour of 2 does not agree with the solution
NMR spectra which are typical of diamagnetic complexes and
consist of 1H, 13C and 31P NMR spectra with narrow lines with
chemical shifts within normal values.35 However, this somewhat
surprising behaviour has some precedents in the literature of
Reaction of 1 with other alkenes and alkynes
The successful reaction of 1 with ω-alkynols prompted us to
preliminarily explore its reactivity with unsaturated hydro-
carbons such as alkenes and alkynes. Selected substrates to
᎐
investigate this chemistry were propargylic alcohols [HC᎐CR -
᎐
2
(OH), R = Me, Ph], mono- and di-substituted alkenes and
alkynes [styrene, stilbene, RC᎐CRЈ (R = H; RЈ = Me, Ph; R =
᎐
RЈ = Ph)], and unsaturated amines such as propargylamine,
᎐
HC᎐CCH NH , and allylamine, H C᎐CHCH NH . Irrespect-
᎐
᎐
2
2
2
2
2
ively, of the unsaturated substrate used, no reaction was
obtained even under harsh reaction conditions (prolonged
reflux in THF) and the starting material was recovered at the
end of each reaction test. Only when propargylamine was
reacted with 1, a reaction took place with formation of a
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
718

View Article Online
Table 3 Selected bond distances (Å) and angles (Њ) for complexes 2–4
Table 4 Selected bond distances (Å) and angles (Њ) for complex 6
2
3a
3b
4
Re1–P1
Re1–P2
Re1–Cl1
Re1–Cl2
Re1–N1
Re1–N3
2.459(1)
2.460(1)
2.424(1)
2.416(2)
1.742(4)
2.222(4)
N1–N2
N2–C1
C1–O1
N3–C8
C8–C9
C9–C10
1.260(6)
1.388(7)
1.227(8)
1.485(8)
1.489(8)
1.163(9)
Re1–P1
Re1–P2
Re1–Cl1
Re1–Cl2
Re1–N1
Re1–C8
N1–N2
N2–C1
C1–O1
2.494(1)
2.486(1)
2.509(1)
2.422(1)
1.752(4)
1.993(5)
1.242(6)
1.419(7)
1.204(7)
1.331(6)
1.512(9)
2.500(1)
2.484(1)
2.506(1)
2.435(1)
1.751(3)
1.990(4)
1.246(4)
1.399(5)
1.209(5)
1.326(5)
1.514(6)
2.492(1)
2.493(2)
2.507(2)
2.434(2)
1.755(5)
2.004(6)
1.233(7)
1.414(9)
1.224(9)
1.338(8)
1.470(9)
2.493(1)
2.484(1)
2.516(1)
2.425(1)
1.769(4)
2.021(5)
1.222(6)
1.406(7)
1.208(6)
1.325(6)
P1–Re1–P2
P1–Re1–Cl1
P1–Re1–Cl2
P1–Re1–N1
P1–Re1–N3
P2–Re1–Cl1
P2–Re1–Cl2
P2–Re1–N1
P2–Re1–N3
174.42(4)
87.67(5)
87.69(4)
92.3(2)
Cl1–Re1–Cl2
Cl1–Re1–N1
Cl1–Re1–N3
Cl2–Re1–N3
N1–Re1–N3
Re1–N1–N2
Re1–N3–C8
93.21(5)
96.1(1)
179.0(1)
85.9(1)
84.8(2)
177.0(4)
125.8(3)
91.9(1)
C8–O2
C8–C11
C8–C12
90.13(5)
87.31(5)
93.0(2)
1.489(8)
90.2(1)
P1–Re1–P2
P1–Re1–Cl1
P1–Re1–Cl2
P1–Re1–N1
P1–Re1–C8
P2–Re1–Cl1
P2–Re1–Cl2
P2–Re1–N1
P2–Re1–C8
Cl1–Re1–Cl2
Cl1–Re1–N1
Cl1–Re1–C8
Cl2–Re1–N1
Cl2–Re1–C8
N1–Re1–C8
Re1–N1–N2
Re1–C8–O2
Re1–C8–C11
Re1–C8–C12
N1–N2–C1
174.01(5)
90.43(4)
85.06(5)
91.7(1)
176.77(4)
87.47(4)
89.96(4)
89.0(1)
178.88(5)
89.38(5)
86.37(5)
90.3(2)
174.20(4)
89.32(4)
85.88(5)
91.0(1)
are collected in Table 2. An ORTEP drawing is showing in
Fig. 7 with selected bond distance and angles reported in Table
4. Crystals of 6 contain a solvent molecule of CH2Cl2 per
octahedral complex which behaves as a genuine Re() deriv-
ative quite similar to complexes 2–4 described above, except for
the propargylic amine ligand instead of a cyclic oxacarbene.
The diazenido group displays comparable metrical properties
93.5(2)
94.7(1)
93.2(2)
94.3(2)
85.73(4)
90.12(5)
93.1(1)
89.9(2)
86.89(5)
93.4(1)
89.62(4)
91.37(4)
89.8(1)
88.3(1)
88.32(4)
93.1(1)
174.6(1)
178.1(1)
86.7(1)
89.95(5)
92.72(5)
90.6(2)
87.4(2)
87.60(6)
92.3(1)
174.6(2)
176.7(2)
87.9(2)
86.12(4)
90.26(5)
92.7(1)
90.0(2)
86.34(5)
92.8(1)
174.1(2)
176.8(1)
89.2(2)
91.9(2)
171.7(4)
117.5(4)
with those previously observed for complexes 2–4, that is: Re᎐
N1 and N1᎐N2 distances of 1.742(4) and 1.260(6) Å, respect-
᎐
173.3(2)
176.8(1)
88.0(2)
᎐
ively. In addition, its mean plane is rotated by an angle of
34.6(1)Њ with respect to the mean plane passing through the Re,
N1, N3, Cl1 and Cl2 atoms. The Re–N3 (amine) bond length of
2.222(4) Å is typical for a single bond distance between Re and
an amine nitrogen, while the short Re–Cl distances, 2.424(1)
and 2.416(1) Å, indicate that both the propargylamino and
benzoyldiazenido ligands exert a similar small trans effect on
Cl atoms. The Re–P separations of the two mutually trans tri-
phenylphosphine groups are very similar [2.459(1)–2.460(1) Å]
and are in agreement with Re–P bond lengths found in the
other four crystallographically studied rhenium() oxacyclo-
carbene octahedral complexes.31
92.0(2)
91.9(2)
92.3(2)
172.4(4)
121.3(4)
130.4(4)
174.4(3)
121.4(3)
130.8(3)
170.3(5)
121.5(4)
131.3(4)
125.9(4)
121.0(5)
120.7(4)
119.5(3)
119.4(5)
As a final comment to this chemistry, it is notable that in
complexes 6 and 7, propargylamine coordinates to rhenium
via the nitrogen atom, rather than with the alkyne triple bond.
This behaviour does not appear surprising in view of the lack
of reactivity of 1 with terminal alkynes and of the preference to
coordinate via the N-donor atom shown by unsaturated amines
towards rhenium.38 In keeping with this result, it is found that
treatment of 1 with CH ᎐CHCH NH in refluxing THF
᎐
2
2
2
provides the coordinated N-allylamine complex [(ReCl2-
{η1-NH CH CH᎐CH } (η1-NNC(O)Ph)(PPh )] (8) as a brown
᎐
2
2
2
2
3
microcrystalline product obtained in low yield. The form-
ulation of 8 as a bis-amino adduct derives from IR and NMR
spectroscopy. Particularly, 1H,1H-2D NMR-COSY spectra
helped to ascertain the presence of two cis coordinating
inequivalent amines.
Scheme 4
mixture of the mono- and bi-substituted complexes [(ReCl2{η1-
NH CH C᎐CH} (η -NNC(O)Ph)(PPh ) ] (n = 1 (6); n = 2 (7))
1
᎐
᎐
2
2
n
3 2
Finally, it is worth stressing that the chemical inertness
shown by 1 towards terminal alkynes does not parallel the
general reactivity shown by rhenium() complexes.28 These
latter, in fact, readily react with HCCR and propargylic alcohols
to form stable vinylidene and allenylidene complexes, respect-
ively.28 This behaviour, although not representing any definitive
proof, further supports the assigned ϩIII oxidation state of
rhenium in these organodiazenido derivatives. The reduced
electron density at the d4-metal centre, could be reasonably
invoked to account for a better stabilization of carbenes in
contrast to the more π-acid vinylidene ligands.
(Scheme 4). The composition of this mixture strictly depends
on the stoichiometry between the amine and 1. Particularly,
when a tenfold excess of the amine was used, the yield of 7
increased by 70%, while, the monosubstituted derivative 6 was
obtained as the main product only when a stoichiometric
quantity of amine was added. Nonetheless, also in the 1 : 1
reaction, a variable amount of 7 (<10%) was observed by in situ
NMR experiments. Fractional crystallization of mixtures
enriched in each of the two amino-derivatives provided a good
method to obtain a pure sample of each compound, albeit in
moderate yield (<30% of pure compound).
Complexes 6 and 7 show elemental analysis, IR and NMR
spectral data consistent with the assigned structures (see
Experimental section). Slow crystallization from a dilute
CH2Cl2–EtOH solution of a 9 : 1 mixture of 6 and 7 separated
brownish microcrystals of 6 which were analytically pure and
suitable for X-ray diffraction analysis. Crystallographic details
Conclusions
A series of rhenium() benzoyldiazenido-2-oxacyclocarbene
complexes,namely[(ReCl {η1-N C(O)Ph}{᎐C(CH ) CH(R)O}-
᎐
2
2
2 n
(PPh3)2] [n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
719

View Article Online
(5)] have been synthesised. IR and NMR spectroscopy as well
as single crystal X-ray studies, have shown that these complexes,
representing the first documented examples of rhenium()
oxacyclocarbene species, exhibit in both solid state and solution
an octahedral geometry with a bent η1-N-benzoyldiazenido
ligand cis oriented with respect to the oxacyclocarbene unit.
Irrespectively of the oxacylocarbene ring size and sub-
stituents, the NMR analysis indicates the existence of an
unprecedented dynamic behaviour where the two inter-
converting species probably exchange via an amide-like
isomerization process involving the benzoyldiazenido moiety.
(60 mL) containing an excess of PPh3 (4.7 g, 19.9 mmol) and
7 mL of concentrated HCl solution (84.5 mol). The emerald
green solution was stirred at room temperature in the air for
30 min during which time 1 separated out as an emerald green
powder. The solution was filtered out and the solid was washed
with diethyl ether and dried under vacuum. Yield 84% (Found:
C, 56.52; H, 3.90; N, 2.99. C43H35Cl2N2OP2Re requires C, 56.41;
H, 3.86; N, 3.06%).
[ReCl (ꢀ1-N-NNC(O)Ph){᎐C(CH ) O}(PPh ) ] (2). A double
᎐
2
2
3
3 2
᎐
proportion of 3-butyn-1-ol, HC᎐C(CH ) OH (33 µL, 0.44
᎐
2
2
mmol) was added via a syringe to a suspension of 1 (200 mg,
0.22 mmol) in THF (20 mL) and the temperature was slowly
raised to the boiling point. After 3 h refluxing, the deep orange
solution was concentrated under nitrogen to half volume.
Addition of diethyl ether (3 mL) gave pale orange microcrystals
of 2, which were filtered off, washed with ethanol and diethyl
ether and dried under vacuum. The crude solid was recrystal-
lized from CH2Cl2–EtOH (1 : 2 v/v, 10 mL) to yield orange
crystals suitable for X-ray diffraction analysis. Yield 85%
(Found: C, 57.33; H, 4.24; N, 2.85. C47H41Cl2N2O2P2Re
Experimental
General procedures
All reactions and manipulations were routinely performed
under a dry nitrogen atmosphere by using standard Schlenk-
tube techniques. Tetrahydrofuran (THF) was freshly distilled
over LiAlH4, n-hexane was stored over molecular sieves and
purged with nitrogen prior to use, dichloromethane and meth-
anol were purified by distillation over CaH2 before use. All the
other chemicals were reagent grade and unless otherwise stated
were used as received from commercial suppliers without
further purification. The purity of all alkynols (Aldrich) was
requires C, 57.39; H, 4.19; N, 2.83%); νmax/cmϪ1 1650 (CO)benzoyl
,
1539 (N᎐N)hydrazido, 1231 (COCring, benzoyl); UV-VIS (CH2Cl2)
᎐
λmax1 = 287 nm (ε = 2099 MϪ1 cmϪ1), λmax2 = 367 (522.4); FABϩ-
MS: m/z 589 (PPh3Re(C5H6O)Cl2ϩ), 554 (PPh3Re(C5H6O)Clϩ),
484 (PPh3ReClϩ), 405 (PPh2ReClϩ), 329 (PPhReClϩ).
1
checked by H NMR spectroscopy and, when necessary, they
were distilled under inert atmosphere prior to use. IR spectra
were obtained in KBr using a Nicolet 510P FT-IR (4000–200
cmϪ1) spectrophotometer. UV-Vis spectra were recorded with
a LAMBQ 40 UV-VIS, Perkin–Elmer spectrophotometer.
31P{1H} NMR spectra were recorded on Bruker AC200, Varian
VXR300, or Bruker Avance DRX-400 spectrometers operating
at 81.01, 121.42 and 161.98 MHz, respectively. Chemical shifts
are relative to external 85% H3PO4 with downfield values
reported as positive. 1H and 13C{1H} NMR spectra were
recorded on the same instruments operating at 200.13, 299.94
and 400.13 MHz (1H) and 50.32, 75.42 or 100.61 MHz (13C),
respectively. Chemical shifts are relative to tetramethylsilane as
external reference or calibrated against the residual solvent
resonance (1H) or the deuterated solvent multiplet (13C). 13C-
135 DEPT experiments were run on the Bruker AC200
spectrometer. Variable-temperature experiments were measured
on the Bruker Avance DRX-400 spectrometer equipped with a
variable-temperature control unit accurate to 0.1 ЊC. The
[ReCl (ꢀ1-N-NNC(O)Ph){᎐C(CH ) CH(Me)O}(PPh ) ] (3).
The methyl-substituted oxacyclocarbene complex 3, was
᎐
2
2
2
3 2
prepared as described above for 2 using ( )-4-pentyn-2-ol,
᎐
HC᎐CCH CH(OH)CH (21 µL, 0.25 mmol) instead of
᎐
2
3
3-butyn-1-ol. Work-up as above, gave 3, as orange micro-
crystals. Yield 83% (Found: C, 57.75; H, 4.38; N,
2.81. C48H43Cl2N2O2P2Re requires C, 57.72; H, 4.34; N, 2.80%);
νmax/cmϪ1 1663 (CO)benzoyl, 1551 (N᎐N)hydrazido, 1232 (COCring ϩ
᎐
COPh).
[ReCl (ꢀ1-N-NNC(O)Ph){᎐C(CH ) O}(PPh ) ] (4). The
᎐
2
2
4
3 2
oxacyclocarbene complex 4, was obtained as described
above for 2 using 4-pentyn-1-ol (24 µL, 0.25 mmol) in place of
3-butyn-1-ol. Usual work-up gave 4 as pale orange crystals.
Yield 86% (Found: C, 57.81; H, 4.37; N, 2.79. C48H43Cl2N2O2-
P2Re requires C, 57.72; H, 4.34; N, 2.80%); νmax/cmϪ1 1648
(CO)benzoyl, 1537 (N᎐N)hydrazido, 1246 (COCring), 1222 (COPh).
᎐
1
assignments of the signals resulted from 1D spectra, H{31P}
[ReCl (ꢀ1-N-NNC(O)Ph){᎐C(CH ) CH(Me)O}(PPh ) ] (5).
1
1
᎐
2
2
3
3 2
heteronuclear decoupling experiments, H COSY, H-NOESY,
1H-ROESY and proton detected 1H,13C and 1H,31P correlations
using degassed nonspinning samples. 2D NMR spectra were
recorded on the Bruker Avance DRX-400 instrument using
pulse sequences suitable for phase-sensitive representations
using TPPI. The 1H,13C and 1H,31P correlations39 were recorded
using an HMQC sequence with decoupling during acquisition.
᎐
Replacing 3-butyn-1-ol with ( )-5-hexyn-2-ol, HC᎐CCH -
᎐
2
CH2CH(Me)OH (48 µL, 0.25 mmol) in the above procedure
gave orange microcrystals of 5. Yield 80% (Found: C, 58.16; H,
4.50; N, 2.71. C49H45Cl2N2O2P2Re requires C, 58.11; H, 4.48; N,
2.76%); νmax/cmϪ1 1650 (CO)benzoyl, 1542 (N᎐N)hydrazido, 1242
᎐
(COCring), 1222 (COPh).
1
Standard pulse sequences were used for the H-NOESY40 and
In situ NMR monitoring of the reactions between 1 and
3-butyn-1-ol or ( )-5-hexyn-2-ol. One equivalent of the
appropriate alkynol (0.03 mmol of 3-butyn-1-ol or ( )-5-
hexyn-2-ol) was added via syringe to a deoxygenated CD2Cl2
(0.8 mL) solution of 1 (25.0 mg, 0.03 mmol) in a 5 mm NMR,
cooled at Ϫ78 ЊC with acetone/dry ice bath.
1H-ROESY41 experiments with a 650 ms mixing time and 500
ms spin-lock time, respectively. Elemental analyses (C, H, N)
were performed using a Carlo Erba model 1110 elemental
analyser. MS-FAB spectra were acquired with a Hewlett-Pack-
ard MS ENGINE HP 5989A mass spectrometer (8 kV, 10 µA,
probe temperature 50 ЊC), using nitrobenzyl alcohol as matrix.
Electronic absorption spectra were obtained on a Perkin-Elmer
Lambda 40 spectrophotometer. Magnetic measurements were
carried out in the solid state with a magnetic susceptibility
balance, MSB-AUTO, Sherwood Scientific Ltd, and in solution
by the method of Evans in CHCl3 purged with nitrogen.35
The tube was flame-sealed under nitrogen at Ϫ78 ЊC and
introduced into the NMR probe of the spectrometer pre-cooled
to Ϫ50 ЊC. The progress of the reaction was followed by record-
1
ing 31P{1H} and H NMR spectra at different temperatures.
No reaction occurred until the temperature was raised to about
0 ЊC. At this temperature 1 slowly converts to the oxacyclo-
carbene derivatives 2 or 4, respectively, without any evidence for
the formation of intermediate species.
Synthesis of the complexes
[(ReCl2(ꢀ2-N,O-NNC(O)Ph)(PPh3)2] (1). Complex 1 was
prepared using a modification of the original method.10b,11a,12
Solid benzoylhydrazine (2.9 g, 21.3 mmol) was added to a
stirred suspension of KReO4 (1.0 g, 3.4 mmol) in ethanol
1
1
᎐
[ReCl (ꢀ -N-NNC(O)Ph){ꢀ -N-NH CH C᎐CH}(PPh ) ] (6).
᎐
2
2
2
3 2
To a suspension of 1 (200 mg, 0.22 mmol) in THF (30 mL), one
᎐
equivalent of propargylamine, HC᎐C(CH )NH (15.2 µL) was
᎐
2
2
D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
720

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added via micro-syringe. The resulting deep orange solution
was stirred and heated under reflux for 5 h. Concentration of
the solution under nitrogen to ca. 10 mL and addition of
diethyl ether (20 mL) gave a mixture of 6 and 7 (9 : 1) as a
brownish green powder. The yield, based on rhenium, was 70%.
Recrystallisation of the crude product from CH2Cl2–EtOH
(1 : 2 v/v, 10 mL) gave a small crop of analytically pure
brownish-green crystals of 6 suitable for X-ray analysis. Yield
30%, based on 1 (Found: C, 57.52; H, 4.40; N, 4.29.
C46H40Cl2N3OP2Re requires C, 56.98; H, 4.16; N, 4.33%);
on their carrier atoms. In compound 3a the C9(H)–C12(H2)
moiety of the 2-oxa-3-methylcyclopentylidene ring was found
disordered. This fragment was refined with two independent
orientations with multiplicity of 0.6 and 0.4, respectively.
In compound 4 the C10(H2) and C11(H2) atoms of the
2-oxacyclohexylidene six-membered ring were found disordered
and refined isotropically with two independent orientations
with multiplicity of 0.6 and 0.4, respectively. The crystal data
and refinement parameters are summarized in Table 2. Selected
interatomic distances and angles are given in Tables 3 and 4.
The program used and sources of scattering factors are given in
ref. 42.
νmax/cmϪ1 3404 (NH2), 1654 (CO)benzoyl, 1434 (N᎐N)hydraz, 1305,
᎐
᎐
1252 (COPh); δH (CDCl ), 2.14 (2H, m, –NH CH C᎐CH), 3.75
(1H, m, –NH CH C᎐CH ), 4.15 (2H, m, –NH CH C᎐CH),
᎐
3
2
2
ORTEP43 views of the five complexes are shown in Figs. 4–7.
The crystals 2, 4 and 6 contain a solvent molecule of CH2Cl2
per octahedral complex, while 3b contain a solvent molecule of
ethanol. The crystals 3a and 3b were found within the same
crystallization bulk. They are polymorphic crystals differing
mainly in their color, orange for 3a and yellow for 3b, and by
the presence of a solvent molecule of ethanol in 3b.
CCDC reference numbers 225817–225821.
See http://www.rsc.org/suppdata/dt/b3/b315693a/ for crystal-
lographic data in CIF or other electronic format.
᎐
᎐
᎐
᎐
2
2
2
2
7.2–7.9 (35H, m, Ph); δP (CDCl3) 1.24 (d, JPP 20.3 Hz), 10.10
(d, JPP 20.3 Hz).
1
1
᎐
[ReCl (ꢀ -N-NNC(O)Ph){ꢀ -N-NH CH C᎐CH} (PPh ) ] (7).
᎐
2
2
2
2
3 2
᎐
Addition of tenfold excess of HC᎐C(CH )NH (2.16 mmol)
᎐
2
2
following the procedure described above and similar work-up,
gave a mixture of 7 and 6 (9 : 1) as a brownish-green powder.
Total yield based on rhenium, 62%. An analytically pure
sample of
7 was obtained upon recrystallization from
CH2Cl2–EtOH (1 : 2 v/v, 10 mL) as described above (yield 28%
based on 1) (Found: C, 49.18; H, 4.12; N, 7.24. C31H30Cl2N4-
OPRe requires C, 48.83; H, 3.96; N, 7.34%); νmax/cmϪ1 3300
(NH2), 3260 (NH2), 1658 (CO)benzoyl, 1618 (CO)benzoyl, 1433
Acknowledgements
We are grateful to Dr S. Roma for technical assistance,
Mr M. Fratta (University of Ferrara) for elemental analyses
and Mr F. Cecconi (ICCOM CNR, Firenze) for magnetic
measurements in the solid state. Thanks are given to MURST
(Rome) and NATO (project PST.CLG.978521) for supporting
this research activity and to the EC (IHP Program) for an
access grant to the “Plataforma Solar de Almería” (Almería,
Spain).
(N᎐N)hydrazido, 1305, 1252 (COPh); δH (CDCl3), 3.80 (1H, m,
᎐
᎐
᎐
–NH CH C᎐CH ), 4.17 (4H, br t, J 7.5, –NH CH C᎐CH),
7.15 (4H, m, –NH CH C᎐CH), 7.2–7.8 (20H, m, Ph);
᎐
᎐
2
2
HH
2
2
᎐
᎐
2
2
δP (CDCl3) 7.04 (s); δC (CDCl3), 187.18 (s, –N2C(O)Ph), 98.92
᎐
᎐
(s, –NH CH C᎐CH)
85.20 (s, –NH CH C᎐CH)
,
᎐
᎐
2
2
trans to Cl,
2
2
trans to PPh3
᎐
73.92 (s, –NH CH C᎐CH)
, 61.95 (s, –NH2CH2-
᎐
2
2
trans to Cl
᎐
᎐
C᎐ CH)
, 40.14 (s, –NH CH C᎐CH)
Cl, 29.90
᎐
᎐
trans to PPh3
2
2
trans to
᎐
(s, –NH CH C᎐CH)trans to PPh , 6.4–7.6 (30H, m, Ph).
᎐
2
2
3
[ReCl (ꢀ1-N-NNC(O)Ph){ꢀ1-N-NH CH CH᎐CH } (PPh ) ]
References
᎐
2
2
2
2
2
3 2
(8). Addition of a stoichiometric amount of H C᎐CHCH NH
᎐
2
2
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(17 µL) to a suspension of 1 (200 mg, 0.22 mmol) in THF
(30 mL) and work-up as described above for 6, yielded a brown
powdered material in 66% yield. 31P{1H} NMR analysis of the
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᎐
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᎐
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HHtrans
–NH CH CH᎐CCH ), 5.17 (1H, d, 3J
10.8, –NH CH CH᎐
᎐
2 2
᎐
2
2
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᎐
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D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
721

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D a l t o n T r a n s . , 2 0 0 4 , 7 1 3 – 7 2 2
722