Rhenium carbonyl complexes with monodentate-coordinated diphosphines: Activation of terminal phosphino groups towards amine-oxide oxidation

Article abstract of DOI:10.1016/j.jorganchem.2005.05.010

Terminal phosphino groups of [Re₂(CO)₉(η ¹-P-P)] (P-P = diphosphines) are activated towards oxidation by Me₃NO. The respective reactions of Me₃NO with [Re ₂(CO)₉{η¹-P(o-anisyl)₂(CH ₂)₃PPh₂}], [Re₂(CO) ₉{η¹-PPh₂(CH₂) ₃P(o-anisyl)₂}] and [Re₂(CO) ₉(η¹-trans-PPh₂CH=CHPPh₂)] were studied to investigate the mechanism of this oxidation. The results are consistent with an intramolecular pathway involving a cyclic intermediate, without exchange of the coordinated and terminal phosphino groups. A mechanism which involves an interaction of the terminal phosphino group with a carbonyl ligand is proposed. In sharp contrast to eq-[Re₂(CO) ₉(η¹-P-P)] (P-P = Ph₂P(CH₂) _nPPh₂, n = 1-6), eq-[Re₂(CO) ₉(η¹-trans-PPh₂CHCHPPh₂)] appears to be indefinitely stable towards equatorial → axial isomerization at room temperature, thus, allowing its crystal structure to be determined.

Full text of DOI:10.1016/j.jorganchem.2005.05.010

Journal of Organometallic Chemistry 690 (2005) 3765–3773
www.elsevier.com/locate/jorganchem
Rhenium carbonyl complexes with monodentate-coordinated
diphosphines: activation of terminal phosphino groups
towards amine-oxide oxidation
a
Wei Fan , Rui Zhang , Weng Kee Leong , Chit Kay Chu , Yaw Kai Yan
a
b
a
a,
*
a
Natural Sciences & Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk,
Singapore 637616, Republic of Singapore
b
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
Received 18 April 2005; received in revised form 9 May 2005; accepted 9 May 2005
Available online 21 June 2005
Abstract
Terminal phosphino groups of [Re2(CO)9(g1-P-P)] (P-P = diphosphines) are activated towards oxidation by Me3NO. The respec-
tive reactions of Me3NO with [Re2(CO)9{g1-P(o-anisyl)2(CH2)3PPh2}], [Re2(CO)9{g1-PPh2(CH2)3P(o-anisyl)2}] and [Re2(CO)9-
(g1-trans-PPh2CH@CHPPh2)] were studied to investigate the mechanism of this oxidation. The results are consistent with an
intramolecular pathway involving a cyclic intermediate, without exchange of the coordinated and terminal phosphino groups. A
mechanism which involves an interaction of the terminal phosphino group with a carbonyl ligand is proposed. In sharp contrast
to eq-[Re2(CO)9(g1-P-P)] (P-P = Ph2P(CH2)nPPh2, n = 1–6), eq-[Re2(CO)9(g1-trans-PPh2CH@CHPPh2)] appears to be indefinitely
stable towards equatorial ! axial isomerization at room temperature, thus, allowing its crystal structure to be determined.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Rhenium; Carbonyl; Monodentate diphosphines; Amine-oxide; Phosphine-oxide complexes; Equatorial isomer
1. Introduction
free diphosphines do not react with Me3NO under sim-
ilar conditions, the phosphine-oxide complexes could
not have been formed by a straightforward oxygen-
transfer from the amine-oxide to the uncoordinated
phosphino group.
A plausible mechanism for the formation of the phos-
phine-oxide complexes (Mechanism 1, Scheme 1)
involves the interaction of the uncoordinated phospho-
rus atom with the electron-deficient carbon atom of a
CO ligand. This reduces the electron density on phos-
phorus, facilitating nucleophilic attack by Me3NO. A
net electron flow from the electron-rich carbonyl oxygen
to the electron-deficient nitrogen then follows, resulting
in the formation of the phosphine-oxide complex and
trimethylamine. It is noteworthy that an intramolecular
P–CO interaction has been observed in the complex
[W(CO)5(g1-dppm)] (dppm = Ph2PCH2PPh2), in which
Reactions of the complexes [Re2(CO)9(g1-P-P)]
(P-P = Ph2P(CH2)nPPh2, n = 1–6) with Me3NO yield
the close-bridged complexes [Re2(CO)8(l-P-P)] and
phosphine-oxide complexes [Re2(CO)9{P-P(O)}] (Fig.
1) as major products [1]. Whilst the formation of
close-bridged products can be easily explained by
Me3NO-assisted decarbonylation followed by phos-
phine coordination, it is not clear how the phosphine-
oxide complexes are formed. This oxidation reaction
has been observed in the reaction of [Re2(CO)9(g1-
dppf)]
with Me3NO, but no mechanism was proposed [2]. Since
[dppf = 1,10-bis(diphenylphosphino)ferrocene]
*
Corresponding author. Tel.: +65 6 790 3821; fax: +65 6 896 9414.
E-mail address: ykyan@nie.edu.sg (Y.K. Yan).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.010

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W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
OC CO
CO
CO
CO
P
P
CO
OC
OC
Re
Re
P
P
O
OC
OC
Re
Re
CO
OC CO
CO
CO
OC
CO
close-bridged complex
phosphine-oxide complex
=
Ph2P(CH2)nPPh2, n = 1-6
P
P
Fig. 1. General structures of the close-bridged and phosphine-oxide complexes.
NMe3
NMe3
O
O
..
..
O
P
.
.
.
:P
O
.
C
P
C
P
(OC)4Re
Re(CO)4
(OC)4Re
Re(CO)4
(A)
with a pentacoordinate
phosphorus atom
= Ph2P(CH2)nPPh2, n = 1-6
P
P
O
P
..
O
+
C
P
:NMe3
(OC)4Re
Re(CO)4
Scheme 1.
the lone pair of the terminal phosphino group is ori-
ented towards one of the cis-CO groups (Pꢀ ꢀ ꢀC dis-
has been observed in [(OC)5WPPh2CH2CH(PPh2)2],
[(OC)5MPPh2CH2CH2{P(p-tolyl)2}] and [(OC)5M{P(p-
tolyl)2CH2CH2PPh2}] (M = Cr, Mo, W) [4,5].
tance = 3.5 A), and there is 13C (cis-CO)–31P (terminal)
˚
coupling [3]. Another possible mechanism (Mechanism
2, Scheme 2) involves nucleophilic attack of Me3NO
on the coordinated phosphorus atom, which is then dis-
placed by the terminal phosphino group. The coordi-
nated phosphorus is activated towards attack by the
amine-oxide since it is less electron-rich compared to
the uncoordinated phosphorus atom. Intramolecular ex-
change of coordinated and terminal phosphino groups
The above mechanisms were tested by studying the
reactions of Me3NO with the dirhenium nonacarbonyl
complexes of monodentate-coordinated trans-1,2-bis-
(diphenylphosphino)ethene (dppene) and 1-(di-o-anis-
ylphosphino)-3-(diphenylphosphino)propane (dadpp),
Ph2P(CH2)3P(o-anisyl)2. Mechanism 2 requires the
diphosphine to adopt a chelating conformation in tran-
sition-state B, which would not be possible for dppene.

W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
3767
Me
N
3
Me
N
3
Me
N
O
3
O
P
..
O
P
P
P
P
P
..
..
Re
Re
Re
(B)
CO
CO
OC
OC
Re
Re
P=O
P
Re(CO)5
Re
:NMe3
+
=
Ph2P(CH2)nPPh2, n = 1-6
P
P
Scheme 2.
Mechanism 1, on the other hand, requires the diphos-
phine to adopt an A-frame-like conformation, which is
possible for dppene [6]. Hence, if Mechanism 2 is cor-
rect, no phosphine-oxide complex would be observed
for dppene. In addition, Mechanism 2 would result in
the originally coordinated phosphino group being oxi-
dized, and the originally terminal phosphino group
coordinating to the metal, which would be observable
for the dadpp complexes [Re2(CO)9{g1-P(o-anisyl)2-
(CH2)3PPh2}] (1) and [Re2(CO)9{g1-PPh2(CH2)3P-
(o-anisyl)2}] (2). If Mechanism 1 is correct, however,
the originally terminal phosphino group would be the
one oxidized.
The reaction of [Re2(CO)9(g1-dppm)] with [ReO4]ꢁ
was also carried out to investigate the possible involve-
ment of [ReO4]ꢁ in the formation of the phosphine-
oxide complex. It has been reported that the reaction
of [Re2(CO)10] with a large excess of Me3NO (8.4·) in
THF for 24 h gives the perrhenate salt [Re(CO)3(ON-
Me3)3][ReO4] in 9% yield [7]. It is therefore possible that
the reaction of [Re2(CO)9(g1-P-P)] with Me3NO may
generate some [ReO4]ꢁ, which in turn oxidizes the termi-
nal phosphino group.
phines with [Re2(CO)10] and Me3NO. As in the analo-
gous reactions of Ph2P(CH2)nPPh2 (n = 1–6) [1],
mixtures of [Re2(CO)9(g1-P-P)] (monodentate com-
plexes) and [{Re2(CO)9}2(l-P-P)] (dimer complexes)
were formed.
For dadpp, two monodentate complexes, [Re2(CO)9-
{P(o-anisyl)2(CH2)3PPh2}] (1) and [Re2(CO)9{PPh2-
(CH2)3P(o-anisyl)2}] (2) were obtained. The 31P NMR
spectrum of 1 shows two equally intense singlets at
ꢁ8.3 and ꢁ17.5 ppm, respectively. The lower-field signal
could be assigned to the anisyl-bonded phosphorus
atom coordinated to the [Re2(CO)9] moiety, and the
higher-field signal can be assigned to the uncoordinated,
phenyl-bonded phosphorus atom [cf. dp (CDCl3, ppm)
for Ph2P(CH2)3PPh2 = ꢁ17.5; for PaPh2(CH2)3Pb(o-ani-
syl)2, Pa = ꢁ16.7, Pb = ꢁ37.1]. Complex 2 exhibits two
singlets (ꢁ11.7 and ꢁ35.8 ppm), corresponding to
the coordinated phenyl-bonded phosphorus and the
uncoordinated anisyl-bonded phosphorus atoms,
respectively. The dimer complex [Re2(CO)9{P(o-ani-
syl)2-(CH2)3PPh2}Re2(CO)9] (3) gives two signals [4.3
(PPh2) and ꢁ5.2 {P(anisyl)2} ppm] in its 31P NMR spec-
trum. It is evident that the 31P shift of the coordinated
Ph2P group in 2 is very different from that of the Ph2P
group in 3. This difference can be explained by the fact
that the Ph2P group is coordinated equatorially in 2,
but axially in 3 (the Re–Re bond being the molecular
axis). In general, the 31P resonance for the axial isomer
always occurs 10–20 ppm downfield of the equatorial
isomer for [Re2(CO)9(PR3)] complexes [8]. The anisyl-
bonded phosphorus atoms in 1 and 3 are both in the ax-
ial position, as indicated by their large coordination
shifts (dcoord ꢁ dfree = Dd) of +28.8 (for 1) and
2. Results and discussion
2.1. Synthesis and characterization of [Re2(CO)9-
(g1-P-P)] (P-P = dadpp, dppene)
The complexes [Re2(CO)9(g1-P-P)] (P-P = dadpp,
dppene) were synthesized by reactions of the diphos-

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W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
+31.9 ppm (for 3), cf. Dd = +22.9 ppm for ax-[Re2-
(CO)9(g1-dppf)] [2].
Conversion of eq-2 to its axial isomer occurs readily
in solution at room temperature. For example, after
incubating a CH2Cl2 solution of eq-2 at room tempera-
ture under nitrogen for a week, only ax-2 was detected
[dP = 4.5 and ꢁ35.8 ppm]. This isomerization could also
be accomplished in refluxing toluene within 10 min. The
fast equatorial–axial isomerization of 2, and the isola-
tion of the axial isomers of 1 and 3 are consistent with
the observation by others that monosubstitution of
[Re2(CO)10] with phosphines usually results in axially
substituted products [9].
Reaction of dppene with [Re2(CO)10] and Me3NO
gives the monodentate complex eq-[Re2(CO)9(g1-
dppene)] (4) and the dimer complex diax-[{Re2-
(CO)9}2(l-dppene)]. Interestingly, despite the bulkiness
of dppene, complex 4 appears to be indefinitely stable
as the equatorial isomer in solution at room tempera-
ture, and can only be converted into the axial isomer
by heating in toluene. This provided a unique opportu-
nity to grow single crystals of an equatorial [Re2-
(CO)9(g1-P-P)] complex for X-ray crystallography (see
below).
C223
C213
C113
C2
P2
C1
O25
O24
P1
O12
C123
C24
Re1
O21
Re2
O11
O23
C13
O13
O22
Fig. 2. Crystal structure of eq-[Re2(CO)9(g1-dppene)] (4)
2.2. Crystal structure of [Re2(CO)9(g1-dppene)] (4)
˚
The two Re octahedra in the molecule of 4 (Fig. 2)
are approximately staggered, being rotated from the
C(13)–C(22) eclipsed position by 49.2ꢁ. The presence
of the phosphine on the equatorial position probably
precludes an ideal staggered form.
being 4.262 A [P(2)ꢀ ꢀ ꢀC(24)]. These distances are larger
than the sum of van der Waals radii of the relevant ele-
ments. The lack of short Pꢀ ꢀ ꢀC contacts in the crystal of
4 does not, however, preclude Pꢀ ꢀ ꢀC interaction in short-
lived intermediates (e.g., intermediate A in Scheme 1) in
solution.
Viewed down the P(1)–Re(1) direction, the backbone
of the dppene ligand is rotated clockwise from the
eclipsed position with the Re–Re bond, giving a C(1)–
P(1)–Re(1)–Re(2) torsional angle of 26.2ꢁ. This rotation
directs C(1) close to the equatorial carbonyl group
[C(24)–O(24)] and causes this CO group to bend away
from the Re–Re bond. The C(1)ꢀ ꢀ ꢀC(24) distance is
The only reported structurally characterized equato-
rial [Re2(CO)9(PR3)] complex is eq-[Re2(CO)9(PPh2H)]
[10]. Compared with this compound, complex 4 is
clearly very strained. This is most evident from the
Re–Re–P angle [99.79(2)ꢁ], which is much larger
than the corresponding angle [91.77(8)ꢁ] of eq-[Re2-
(CO)9(PPh2H)], and the acute Re–Re–C(NR) angles of
equatorially coordinated isonitrile complexes [11,12].
˚
3.389 A, slightly less than twice the van der Waals radius
of carbon, and the Re(1)–Re(2)–C(24) angle [93.0(2)ꢁ] is
much larger than the Re–Re–C angles of the other equa-
torial carbonyl groups [average 83.6(2)ꢁ]. Despite the
short C(1)ꢀ ꢀ ꢀC(24) distance, there is no evidence for elec-
tronic interaction between the C@C bond of the diphos-
phine with the carbonyl group, the C(1)–C(2) bond
˚
The Re–P bond length of 4 [2.4887(9) A] is also longer
˚
than that in eq-[Re2(CO)9(PPh2H)][2.443(3) A]. The ste-
ric strain in 4 could also be partially responsible for the
˚
lengthening of the Re–Re bond [3.1077(2) A], compared
˚
to those in eq-[Re2(CO)9(PPh2H)] [3.0526(7) A] and
˚
˚
[Re2(CO)10] [3.041(1) A] [13].
length [1.334(5) A] being normal for a C–C double
˚
bond. There is also a very short contact of 3.291 A
between C(121) and C(14), the phenyl ring [C(121)–
C(126)] and the carbonyl group [C(14)–O(14)] being al-
most eclipsed. The C(121)–P(1)–Re(1)–C(14) torsional
angle is only 10.7ꢁ, compared with the C(111)–P(1)–
Re(1)–C(11) torsional angle of 34.1ꢁ.
2.3. Reactions of complexes 1 and 2 (axial isomers) with
Me3NO
As expected, a close-bridged complex and a phos-
phine-oxide complex were obtained from each of the
above reactions. The 31P NMR spectra of the two phos-
phine-oxide complexes, 5 and 6, each shows two equally
intense singlets. Complex 5 (dP ꢁ7.2 and 32.7 ppm), iso-
There are no short contacts between P(2) and any of
the carbonyl groups, the shortest Pꢀ ꢀ ꢀO distance being
˚
3.516 A [P(2)ꢀ ꢀ ꢀO(24)] and the shortest Pꢀ ꢀ ꢀC distance

W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
3769
lated from the reaction of 1 with Me3NO, is identified as
ax-[Re2(CO)9{P(o-anisyl)2(CH2)3P(O)Ph2}] (30% yield),
while complex 6 (dP 4.8 and 33.3 ppm), isolated from
the reaction of 2 with Me3NO, is identified as ax-[Re2-
(CO)9{PPh2(CH2)3P(O)(o-anisyl)2}] (27%). To confirm
these structural assignments, oxidation reactions of 1
and 2 by oxygen were also carried out. Exposure of a
CH2Cl2 solution of 1 to air for one week at room tem-
perature gave a product whose 31P shifts were identical
to those of 5. Similar treatment of 2 gave 6 as the sole
product. These observations clearly show that there is
no exchange between the coordinated and free phos-
phino groups in the reactions of 1 and 2 with Me3NO.
The close-bridged complexes isolated from the reac-
tions of 1 and 2 with Me3NO were identical and identi-
fied to be dieq-[Re2(CO)8(l-dadpp)]. The IR spectrum of
this complex in the carbonyl stretching region is similar
to that of dieq-[Re2(CO)8(l-dppp)] [1] [dppp =
Ph2P(CH2)3PPh2]. Its 31P NMR spectrum shows two
equally intense doublets (JP–P = 30 Hz) at ꢁ10.4 and
ꢁ20.2 ppm, respectively, the relatively large negative
dP values being consistent with the compound being a
[Re2(CO)8(l-P-P)] complex with a seven-membered
metallacycle (cf. dP = ꢁ17.5 ppm for dieq-[Re2(CO)8(l-
dppp)]) [1]. That the non-coupled phosphorus atoms in
free dadpp become coupled to each other in dieq-[Re2-
(CO)8(l-dadpp)] further confirms the close-bridged
structure of the latter. The formation of dieq-[Re2-
(CO)8(l-dadpp)] from ax-1 and -2 shows that
axial ! equatorial isomerization is possible.
The structure of 7 was deduced mainly from its 31P
NMR and mass spectra. There are two coupled dou-
blets (JP–P = 4.5 Hz) at 26.3 and ꢁ23.6 ppm, respec-
tively, in its 31P NMR spectrum. The signal at
26.3 ppm is most likely the resonance of the phos-
phoryl group, and the signal at ꢁ23.6 ppm can be as-
signed to the phosphino group. The very negative 31P
shift for the latter is also consistent with its being part
of a seven-membered metallacycle [1]. The FAB mass
spectrum of the complex shows its M+ ion at m/z
1008, together with a [M + H]+ peak at m/z 1009, with
overlapping isotope patterns. The IR spectrum of 7 is
consistent with its assigned structure, there being five
mCO absorptions, with the highest-energy absorption
(2091 cmꢁ1) occurring at a lower frequency than that
of eq-[Re2(CO)9{PPh2CH@CHP(O)Ph2}] (2104 cmꢁ1).
Complex 7 is most likely formed via Me3NO-assisted
decarbonylation of eq-[Re2(CO)9{PPh2CH@CHP(O)-
Ph2}], followed by coordination of the phosphoryl oxy-
gen to rhenium.
2.5. Mechanistic implications
The lack of exchange between the coordinated and
terminal phosphino groups of 1 and 2 and the forma-
tion of dppene-oxide complexes from 4 confirm that
Mechanism 2 is incorrect. Focusing on Mechanism 1,
it would appear from Scheme 1 that, for the axial iso-
mers of 1, 2 and 4 to react with Me3NO to form phos-
phine-oxide complexes, they must either isomerize back
to the equatorial isomers, or the terminal phosphino
group must interact with a CO ligand on the P-coordi-
nated rhenium (proximal CO) rather than one on the
adjacent Re atom. From the foregoing discussion, it
may be assumed that back-and-forth axial–equatorial
isomerization is much more facile for 1 and 2 than
for 4. Due to its flexible backbone, dadpp is also much
better able than dppene to bend to allow its uncoordi-
nated phosphino group to interact with a proximal CO
ligand. It is thus not surprising that the yields of phos-
phine-oxide complexes from ax-1 and -2 are much
higher than that from ax-4, and that better yields of
phosphine-oxide complexes are obtained from eq-4
than ax-4. Overall, the dependence of the yields on
chain flexibility and position of substitution is consis-
tent with an intramolecular pathway involving a cyclic
intermediate (Scheme 1).
2.4. Reaction of [Re2(CO)9(g1-dppene)] with Me3NO
Reaction of eq-[Re2(CO)9(g1-dppene)] with Me3NO
produces the phosphine-oxide complex eq-[Re2-
(CO)9{g1-PPh2CH@CHP(O)Ph2}] [dP 22.6(d) and
ꢁ5.9(d) ppm, JP–P = 36 Hz] in 14% yield and an unu-
sual complex, [Re2(CO)8(l-OPPh2CH@CHPPh2)] (7)
in 19% yield. The reaction of ax-[Re2(CO)9(g1-
dppene)] with Me3NO is much slower than that of
the equatorial isomer, and gives mainly the axially
substituted phosphine-oxide complex (dP 23.2 and
8.7 ppm, JP–P = 45 Hz) and an unidentified, unstable
complex.
Ph
Ph
H
P
Ph
2.6. Reaction of eq-[Re2(CO)9(g1-dppm)] with
perrhenate
C
C
O
Ph
P
H
OC
OC
CO
Like the reactions of 1, 2 and 4 with Me3NO, the
reaction of eq-[Re2(CO)9(g1-dppm)] with [NBu4][ReO4]
was carried out in THF under N2 at room temperature
for 4 h. Much unreacted eq-[Re2(CO)9(g1-dppm)] was
recovered, and a small amount of the equatorial
CO
Re
Re
OC
CO
CO
OC
7

3770
W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
phosphine-oxide complex, eq-[Re2(CO)9(dppmO)] (15%
yield based on the consumed starting material) was
formed. Free dppm does not react with [NBu4][ReO4]
under the same conditions.
tra were recorded at room temperature on a Bruker
DRX400 spectrometer at 162 MHz. The phosphorus
chemical shifts are quoted from the proton-decoupled
spectra, and are reported in ppm to the higher frequency
of external 85% H3PO4. Fast atom bombardment mass
spectra were recorded on a VG AutoSpecQ mass spec-
trometer using a 3-nitrobenzyl alcohol matrix. Elemen-
tal analyses were performed using a LECO CHNS-932
instrument.
The above results show that the perrhenate ion can
indeed oxidize (albeit very slowly) eq-[Re2(CO)9(g1-
dppm)] to the phosphine-oxide complex. However, since
the quantity of [ReO4]ꢁ formed in the Me3NO reactions
should be very small compared to that reported in [7],
given the stoichiometric amount of Me3NO used and
shorter reaction time, its role in the formation of the
phosphine-oxide complexes should be negligible. Fur-
thermore, the failure of [ReO4]ꢁ to oxidize free dppm
suggests that, even if [ReO4]ꢁ plays a significant part
in the formation of the phosphine-oxide complex, the
mechanism should also involve the rhenium carbonyl
units, and is not a direct oxygen-transfer between
[ReO4]ꢁ and the phosphino group.
4.2. Synthesis of [Re2(CO)9(g1-P-P)] (P-P = dadpp,
dppene)
Solid Me3NO Æ 2H2O (0.0511 g, 0.46 mmol) was
added to a continuously stirred solution of [Re2(CO)10]
(0.3132 g, 0.48 mmol) in 50 ml of THF at room tem-
perature. The yellow reaction mixture so formed was
stirred under reduced pressure. After all the Me3-
NO Æ 2H2O solid had dissolved, stirring was continued
for another 30 min, and half of the solvent was re-
moved under reduced pressure. The remaining solution
was stirred for a further 15 min before it was slowly
transferred to a stirred solution of the diphosphine
(0.44 mmol) in 24 ml of THF via a PTFE transfer tube.
The resultant yellow solution was stirred under nitro-
gen for 1 h. Half of the solvent was then removed
and stirring was continued for another 50 min, after
which the solution was evaporated to dryness to give
a yellow residue.
3. Conclusions
Terminal phosphino groups of [Re2(CO)9(g1-P-P)]
(P-P = diphosphines) are activated towards oxidation
by Me3NO. This oxidation yields [Re2(CO)9{P-P(O)}],
which is most likely formed via an intramolecular path-
way involving a cyclic intermediate. Exchange of coordi-
nated and terminal phosphino groups does not occur
during the reaction. A mechanism which involves an
interaction of the terminal phosphino group with a car-
bonyl ligand is proposed. Perrhenate does not play a sig-
nificant role in the formation of the phosphine-oxide
complexes. In sharp contrast to eq-[Re2(CO)9(g1-P-P)]
(P-P = Ph2P(CH2)nPPh2, n = 1–6), eq-[Re2(CO)9(g1-
trans-PPh2CH@CHPPh2)] appears to be indefinitely sta-
ble towards equatorial ! axial isomerization at room
temperature.
4.2.1. Workup procedure for P-P = dadpp
The yellow residue was redissolved in a minimum
quantity of CH2Cl2 and chromatographed on silica
TLC plates. Elution with CH2Cl2–hexane (1:4) followed
by recrystallization from CH2Cl2–MeOH yielded
0.050 g (9%) of [Re2(CO)9{P(o-anisyl)2(CH2)3PPh2}]
(Rf = 0.48), 1; 0.039 g (7%) of [Re2(CO)9{PPh2(CH2)3-
P(o-anisyl)2}] (Rf = 0.25), 2, and 0.040 g (10%) of [{Re2-
(CO)9}2(l-dadpp)] 3 (Rf = 0.52).
4. Experimental
[Re2(CO)9{P(o-anisyl)2(CH2)3PPh2}], 1 (Found: C,
39.9; H, 2.7. C38H30O11P2Re2 requires C, 39.6; H,
2.9%); mmax(CO) 2102m, 2032m, 1991s, 1956m, 1931m
cmꢁ1 (CH2Cl2); dp (CDCl3) ꢁ8.3 (s, Re–P), ꢁ17.5 (s,
free-P). [Re2(CO)9{PPh2(CH2)3P(o-anisyl)2}], 2 (Found:
C, 40.2; H, 2.7. C38H30O11P2Re2 requires C, 39.6; H,
2.9%); mmax(CO) 2104m, 2034m, 1994s, 1958m, 1939m
cmꢁ1 (CH2Cl2); dp (CDCl3) ꢁ11.7 (s, Re–P), ꢁ35.8 (s,
free-P). [{Re2(CO)9}2(l-dadpp)], 3 (Found: C, 31.5; H,
1.7. C47H30O20P2Re4 requires C, 31.4; H, 1.8%);
4.1. General
All reactions were routinely performed under pure
dry nitrogen using standard Schlenk techniques. All sol-
vents for the reactions were also vacuum degassed be-
fore use. The solvents were of reagent grade and were
freshly purified and dried by published procedures
[14]. Chemical reagents, unless otherwise stated, were
commercial products and were used without further
purification. Pre-coated silica TLC plates of layer thick-
ness 0.25 mm were purchased from Merck. The diphos-
phine Ph2P(CH2)3P(o-anisyl)2 (dadpp) was synthesized
by the method of Benn et al. [15]. Fourier-transform
infrared spectra were recorded with a Perkin–Elmer
1725X FT-IR Spectrometer. Phosphorus-31 NMR spec-
m
max(CO) 2104m, 2033m, 1994s, 1958m, 1933m cmꢁ1
(CH2Cl2); dp (CDCl3) 4.3 (s, Ph–P), ꢁ5.2 (s, anisyl-P).
4.2.2. Workup procedure for P-P = dppene
About 3 ml of CH2Cl2 was added to the yellow resi-
due. A suspension was obtained, which was centrifuged
to yield the light yellow [{Re2(CO)9}2(l-dppene)] (10%)

W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
3771
solid and a yellow supernatant. The yellow supernatant
was chromatographed on silica TLC plates. Elution
with CH2Cl2–hexane (1:3) followed by recrystallization
from CH2Cl2–MeOH yielded eq-[Re2(CO)9(g1-dppene)],
4 (15%).
4.3.3. eq-[Re2(CO)9(g1-dppene)], eq-4
Elution with ether–hexane (9:1) followed by recrys-
tallization from CH2Cl2–hexane yielded 0.0069 g
(19%)
of
[Re2(CO)8(O@PPh2CH@CHPPh2)],
7
(yellow, Rf = 0.71) and 0.0052 g (14%) of eq-[Re2-
eq-[Re2(CO)9(g1-dppene)], 4 (Found: C, 40.9; H, 2.1.
C35H22O9P2Re2 requires C, 41.2; H, 2.2%); mmax(CO)
2103m, 2036m, 1994s, 1959m, 1929m cmꢁ1 (CH2Cl2);
dp (CDCl3) ꢁ2.6 (d, Re–P), ꢁ7.1 (d, free-P),
JP–P = 8 Hz. The axial isomer was obtained by boiling
a solution of eq-4 in toluene for 10 min under N2. dp
(CDCl3) 7.3 (d, Re–P), ꢁ6.7 (d, free-P), JP–P = 10 Hz.
[{Re2(CO)9}2(l-dppene)] (Found: C, 32.1; H, 1.3.
C44H22O18P2Re4 requires C, 31.8; H, 1.3%); mmax(CO)
2104m, 2038m, 1994s, 1959m, 1938m cmꢁ1 (toluene);
dp (toluene-d8) 8.6 (s).
(CO)9{PPh2CH@CHP(O)Ph2}]
0.55).
(colourless,
Rf =
[Re2(CO)8(O@PPh2CH@CHPPh2)], 7 (Found: C,
39.8; H, 2.3. C34H22O9P2Re2 requires C, 40.4; H,
2.2%); mmax(CO) 2091m, 2052m, 1997s, 1963w, 1935w
cmꢁ1 (CH2Cl2); dp (CDCl3) 26.3 (d, O@P), ꢁ23.6 (d,
Re–P), JP–P = 4.5 Hz; FAB-MS: 1009 (60%, [M + H]+);
981 (10%, [M + H ꢁ CO]+); 953 (10%, [M + H ꢁ
2CO]+); 925 (40%, [M + H ꢁ 3CO]+); 897 (10%,
[M + H ꢁ 4CO]+); 869 (30%, [M + H ꢁ 5CO]+); 841
(10%, [M + H ꢁ 6CO]+); 813 (10%, [M + H ꢁ 7CO]+);
785 (20%, [M + H ꢁ 8CO]+) (masses quoted are those
of the [185Re–187Re] ions, which give the strongest peak
in each cluster; the relative intensities of the peaks in
each cluster are consistent with each cluster being an
overlap of the isotope patterns of the [M + H ꢁ nCO]+
and [M ꢁ nCO]+ ions).
4.3. Reactions of [Re2(CO)9(g1-P-P)] (P-P = dadpp,
dppene) with Me3NO
In
a
typical experiment, [Re2(CO)9(g1-P-P)]
(0.036 mmol) was dissolved in 5 ml of freshly distilled
and degassed THF. A 0.012 M solution of Me3NO Æ
2H2O in THF–MeOH (49:1) mixture (3 ml, 0.036
mmol of Me3NO) was then added dropwise under
nitrogen. The resultant solution was degassed again
and stirred under nitrogen for 4 h at room tempera-
ture. The solution was then evaporated to dryness
and the yellow residue was redissolved in a minimum
quantity of CH2Cl2 and chromatographed on silica
TLC plates.
eq-[Re2(CO)9{PPh2CH@CHP(O)Ph2}] (Found: C,
40.3; H, 2.0. C35H22O10P2Re2 requires C, 40.5; H,
2.1%); mmax(CO) 2104w, 2037m, 1995s, 1962m, 1931m
cmꢁ1 (CH2Cl2); dp (CDCl3) 22.6 (d, O@P), ꢁ5.9 (d,
Re–P), JP–P = 36 Hz.
4.3.4. ax-[Re2(CO)9(g1-dppene)], ax-4
Two main product bands were eluted by ether–hex-
ane (9:1). A colourless solid was recovered from the
band at Rf = 0.32 by recrystallization from CH2Cl2–
hexane, and was identified to be ax-[Re2(CO)9-
{PPh2CH@CHP(O)Ph2}] (0.0030 g, yield 8%). (Found:
C, 40.2; H, 2.1. C35H22O10P2Re2 requires C, 40.5; H,
2.1%); mmax(CO) 2106w, 2036m, 1997s, 1963m, 1939m
cmꢁ1 (CH2Cl2); dp (CDCl3) 23.2 (d, O@P), 8.7 (d,
Re–P), JP–P = 45 Hz.
4.3.1. [Re2(CO)9{P(o-anisyl)2(CH2)3PPh2}] (1)
Elution with acetone–hexane (1:3) followed by recrys-
tallization from CH2Cl2–hexane yielded [Re2(CO)8
(ldadpp)] (5%, Rf = 0.45) and [Re2(CO)9{P(o-ani-
syl)2(CH2)3P(O)Ph2}], 5 (30%, Rf = 0.35).
[Re2(CO)8(l-dadpp)] (Found: C, 41.3; H, 2.9.
C37H30O10P2Re2 requires C, 41.6; H, 2.8%); mmax(CO)
2067w, 2031m, 2011w, 1972s, 1947m, 1903s cmꢁ1
(CH2Cl2); dp (CDCl3) ꢁ10.4 (d, Ph–P), ꢁ20.2 (d, ani-
syl-P), JP–P = 30 Hz.
[Re2(CO)9{P(o-anisyl)2(CH2)3P(O)Ph2}], 5 (Found:
C, 40.8; H, 2.9. C38H30O12P2Re2 requires C, 41.0; H,
2.7%); mmax(CO) 2102w, 2031m, 1991s, 1953m, 1931m
cmꢁ1 (CH2Cl2); dp (CDCl3) 32.7 (s, P@O), ꢁ7.2 (s,
Re–P).
An unidentified, unstable yellow compound was
recovered from the band at Rf = 0.55.
mmax(CO)
2085m, 2044m, 1990s (sh), 1933w cmꢁ1 (CH2Cl2).
Unreacted ax-[Re2(CO)9(g1-dppene)] was observed
on the TLC plates.
4.4. Attempted reaction of free 1,4-bis(diphenyl-
phosphino)butane with Me3NO
The diphosphine (0.0307 g, 0.072 mmol) was dis-
solved in 10 ml of freshly distilled and degassed THF.
A 0.012 M solution of Me3NO Æ 2H2O in THF–MeOH
(49:1) mixture (6 ml, 0.072 mmol of Me3NO) was then
added under nitrogen. The resultant solution was de-
gassed again and stirred under nitrogen at room tem-
perature for 4 h. Analysis of the solution by TLC
(ether–hexane, 9:1) showed that no reaction had
occurred.
4.3.2. [Re2(CO)9{PPh2(CH2)3P(o-anisyl)2}] (2)
Elution with acetone–hexane (1:3) followed by
recrystallization from CH2Cl2–hexane yielded [Re2-
(CO)8(l-dadpp)] (20%) and [Re2(CO)9{PPh2(CH2)3-
P(O)(o-anisyl)2}], 6 (27%, Rf = 0.35) (Found: C, 40.9;
H, 2.9. C38H30O12P2Re2 requires C, 41.0; H, 2.7%);
m
max(CO) 2104w, 2033m, 1994s, 1958m, 1936m cmꢁ1
(CH2Cl2); dp (CDCl3) 33.3 (s, P@O), 4.8 (s, Re–P).

3772
W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
Table 2
4.5. Preparation of [NBu4][ReO4]
1
˚
Selected bond lengths (A) and angles (ꢁ) for eq-[Re2(CO)9(g -dppene)]
(4)
The compound Re2O7 (0.60 g, 1.2 mmol) was dis-
solved in 3 ml of 1 M aqueous NaOH solution (3 mmol
of NaOH). A solution of [NBu4]Br (1.9 g, 5.9 mmol) in a
minimum volume of water was then added dropwise
with stirring. The white precipitate obtained was filtered,
washed with deionized water, and dried under vacuum
to yield 0.8 g (70%) of [NBu4][ReO4].
Re(1)–Re(2)
Re(1)–P(1)
3.1077(2)
2.4887(9)
1.943(5)
1.980(5)
1.957(4)
1.993(5)
1.945(5)
Re(2)–C(22)
Re(2)–C(23)
Re(2)–C(24)
Re(2)–C(25)
P(1)–C(1)
1.998(5)
2.010(5)
2.006(5)
1.996(5)
1.812(4)
1.826(4)
1.334(5)
Re(1)–C(11)
Re(1)–C(12)
Re(1)–C(13)
Re(1)–C(14)
Re(2)–C(21)
P(2)–C(2)
C(1)–C(2)
C(11)–Re(1)–P(1)
C(12)–Re(1)–P(1)
C(13)–Re(1)–P(1)
C(14)–Re(1)–P(1)
P(1)–Re(1)–Re(2)
C(12)–Re(1)–Re(2)
C(13)–Re(1)–Re(2)
C(14)–Re(1)–Re(2)
C(2)–C(1)–P(1)
88.9(1)
86.8(1)
177.8(1)
91.0(1)
99.79(2)
83.1(1)
81.2(1)
84.2(1)
125.2(3)
126.0(3)
C(21)–Re(2)–C(24)
C(22)–Re(2)–C(24)
C(23)–Re(2)–C(24)
C(25)–Re(2)–C(24)
C(22)–Re(2)–Re(1)
C(23)–Re(2)–Re(1)
C(24)–Re(2)–Re(1)
C(25)–Re(2)–Re(1)
C(1)–P(1)–Re(1)
93.7(2)
175.3(2)
85.5(2)
91.4(2)
83.3(1)
86.5(1)
93.0(2)
83.6(1)
118.6(1)
4.6. Reaction of eq-[Re2(CO)9(g1-dppm)] with
[NBu4][ReO4]
The complex eq-[Re2(CO)9(g1-dppm)] (0.0363 g,
0.036 mmol), prepared as described in [1], was dissolved
in 5 ml of freshly distilled and degassed THF. Solid
[NBu4][ReO4] (0.0177 g, 0.036 mmol) was added under
nitrogen. The resultant solution was degassed and stir-
red under nitrogen for 4 h at room temperature. The
solution was then evaporated to dryness and the residue
redissolved in a minimum quantity of CH2Cl2 and chro-
matographed on silica TLC plates. Elution with ether–
hexane (9:1) followed by recrystallization from
CH2Cl2–hexane yielded 0.0039 g (15% yield based on
C(1)–C(2)–P(2)
the consumed starting material) of eq-[Re2(CO)9-
(dppmO)] (identified by its 31P NMR spectrum [1]).
Unreacted [Re2(CO)9(g1-dppm)] was also isolated (ca.
0.01 g, 0.01 mmol).
4.7. X-ray crystallography
Table 1
Crystallographic data for eq-[Re2(CO)9(g1-dppene)] (4)
Single crystals of 4 were grown from CH2Cl2–MeOH
at ca. 5 ꢁC. The crystal was mounted on a quartz fibre
for data-collection on a Bruker SMART CCD system,
using Mo Ka radiation, with 6s exposures. Data were
corrected for Lorentz and polarization effects with the
SMART suite of programs [16], and for absorption effects
with SADABS [17]. Structural solution and refinement
were carried out with the SHELXTL suite of programs
[18]. Final unit cell parameters were determined from
6934 reflections. The structure was solved by direct
methods. Hydrogen atoms were placed in idealized posi-
tions and refined as riding on their carrier atoms, with
the constraint Uiso(H) = 1.2Ueq(carrier). All non-hydro-
gen atoms were given anisotropic thermal parameters in
the final model. Crystallographic data are given in Table
1 and selected bond lengths and angles in Table 2.
Empirical formula
Formula weight
Temperature (K)
C35H22O9P2Re2
1020.87
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
C2/c
Crystal system
Space group
Unit cell dimensions
˚
a (A)
35.7794(3)
9.6654(2)
21.0640(3)
97.674(1)
7219.2(2)
8
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
Volume (A )
Z
Dcalc (Mg/m3)
1.879
6.841
3872
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
0.38 · 0.35 · 0.30
2.18–29.17
ꢁ48 6 h 6 46,
ꢁ13 6 k 6 11,
ꢁ28 6 l 6 26
22,822
h Range for data collection (ꢁ)
Index ranges
Reflections collected
Independent reflections (Rint
5. Supplementary material
)
8842 (0.0269)
90.5%
0.234 and 0.148
Completeness to theta = 29.17ꢁ
Maximum and minimum
transmission
Crystallographic data (excluding structure factors)
for the structure reported in this paper have been depos-
ited with the Cambridge Crystallographic Data Centre
as Supplementary Publication No. CCDC 268940. Cop-
ies of the data can be obtained free of charge on appli-
cation to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44 1223 336 033; e-mail: deposit@ccdc.
cam.ac.uk or http://www.ccdc.cam.ac.uk).
Refinement method
Full-matrix least-squares on F2
8842/0/433
1.112
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
R1 = 0.0288, wR2 = 0.0571
R1 = 0.0440, wR2 = 0.0624
0.854 and ꢁ1.071
Largest differential peak
ꢁ3
˚
and hole (e A
)

W. Fan et al. / Journal of Organometallic Chemistry 690 (2005) 3765–3773
3773
[6] R. Zhang, C.L. Kee, W.K. Leong, Y.K. Yan, J. Organomet.
Chem. 689 (2004) 2837.
Acknowledgements
[7] S.D. Christie, M.D. Clerk, M.J. Zaworotko, J. Crystallogr.
Spectrosc. Res. 23 (1993) 591.
We acknowledge the financial support (Grant No.
RP 15/95 YYK) of the National Institute of Education,
Nanyang Technological University (NTU). Wei Fan
and Rui Zhang are grateful to NTU for scholarship
awards.
[8] W.L. Ingham, A.E. Leins, N.J. Coville, S. Afr. J. Chem. 44 (1991)
6.
[9] G.W. Harris, J.C.A. Boeyens, N.J. Coville, J. Chem. Soc., Dalton
Trans. (1985) 2277.
[10] T.S.A. Hor, P.M.N. Low, Y.K. Yan, L.-K. Liu, Y.-S. Wen, J.
Organomet. Chem. 448 (1993) 131.
[11] G.W. Harris, J.C.A. Boeyens, N.J. Coville, Organometallics 4
(1985) 914.
References
[12] M.O. Albers, J.C.A. Boeyens, N.J. Coville, G.W. Harris, J.
Organomet. Chem. 260 (1984) 99.
[1] W. Fan, R. Zhang, W.K. Leong, Y.K. Yan, Inorg. Chim. Acta
357 (2004) 2441.
[13] M.R. Churchill, K.N. Amoh, H.J. Wasserman, Inorg. Chem. 20
(1981) 1609.
[2] T.S.A. Hor, H.S.O. Chan, K.-L. Tan, L.-T. Phang, Y.K. Yan,
L.-K. Liu, Y.-S. Wen, Polyhedron 10 (1991) 2437.
[14] A.J. Gordon, R.A. Ford, The Chemistꢀs Companion: a Handbook
of Practical Data, Techniques and References, Wiley-Interscience,
New York, 1972.
[3] J.W. Benson, R.L. Keiter, E.A. Keiter, A.L. Rheingold,
G.P.A. Yap, V.V. Mainz, Organometallics 17 (1998) 4275,
˚
The value of 3.5 A given in this reference is the distance
[15] F.R. Benn, J.C. Briggs, C.A. McAuliffe, J. Chem. Soc., Dalton
Trans. (1984) 293.
between the terminal phosphorus and the CO carbon to which
the phosphorus lone pair is directed. Data for this structure
(Refcode HAQNAO) from the Cambridge Crystallographic
Database (Version 5.26, November 2004) showed that another
[16] SMART Software Reference Manual, Version 4.0, Siemens Energy
& Automation, Inc., Analytical Instrumentation, Madison, WI,
1996.
˚
short P(terminal)ꢀ ꢀ ꢀC(cis-CO) contact of 3.42 A exists. Two
[17] G.M. Sheldrick, SADABS, a Software for Empirical Absorption
Correction, University of Gottingen, Gottingen, 1996.
other structures with short Pꢀ ꢀ ꢀC contacts were also found in
¨
¨
the CCD: [W(CO)4(CNCH2Ph)(g1-dppm)] (3.35 A, Refcode
[18] SHELXTL Reference Manual, Version 5.03, Siemens Energy &
Automation, Inc., Analytical Instrumentation, Madison, WI,
1996.
˚
1
˚
UNAPII) [19] and [Fe(CO)4(g -dppm)] (3.43 A, Refcode JOF-
JOD) [20].
[4] R.L. Keiter, E.A. Keiter, D.M. Olson, J.R. Bush, W. Lin, J.W.
Benson, Organometallics 13 (1994) 3752.
[5] R.L. Keiter, J.W. Benson, Z. Jia, E.A. Keiter, D.E. Brandt,
Organometallics 19 (2000) 4518.
[19] M. Knorr, I. Jourdain, D. Lentz, S. Willemsen, C. Strohmann, J.
Organomet. Chem. 684 (2003) 216.
[20] A.M.G. Dias Rodrigues, J.R. Lechat, R.H.P. Francisco, Acta
Crystallogr. C 48 (1992) 159.