Amine-oxide-mediated oxidative methanolysis of metal-metal bonds in [MM'(CO)10] (M = Mn, Re; M' = Re) and [Os3(CO)12]: Crystal structure of fac-[Re{OC(O)OMe}(CO)3(η2-dppf)]

Article abstract of DOI:10.1016/S0277-5387(00)00296-5

The reaction of 1,1'-bis(diphenylphosphino)ferrocene (dppf) with a mixture of [MnRe(CO)₁₀], MeOH and Me₃NO afforded the complexes fac-[MnH(CO)₃(η²-dppf)] and [Re₂(μ-OMe)₂(μ-dppf) (CO)₆]. In the one-pot reaction of [Re₂(CO)₁₀] with Me₃NO, MeOH and dppf, the major mononuclear Re species isolated was the CO₂-inserted complex fac-[Re{OC(O)OMe}(CO)₃(η²-dppf)], the crystal structure of which was determined. The coordination sphere of the rhenium atom is roughly octahedral, consisting of an oxygen atom from the methyl carbonate ligand, two phosphorus atoms from a chelating dppf ligand, and three carbon atoms from a facial arrangement of three terminally bonded carbonyls. Analogous Me₃NO-mediated methoxylation reactions involving [Os₃(CO)₁₂] were also investigated. With a [Me₃NO]:[Os₃(CO)₁₂] ratio of 2:1, the major product is [Os₃(CO)₁₀(μ-H)(μ-Ome)]. With three molar equivalents of Me₃NO, significant quantities of [Os₃(CO)₁₀(μ-OMe)₂] are also obtained. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(00)00296-5

www.elsevier.nl/locate/poly
Polyhedron 19 (2000) 641–647
Amine-oxide-mediated oxidative methanolysis of metal–metal bonds
in [MM9(CO)10] (MsMn, Re; M9sRe) and [Os3(CO)12]:
crystal structure of fac-[Re{OC(O)OMe}(CO)3(h2-dppf)]
b
b
b
b
Yaw-Kai Yan a, , Wendy Koh , Chenghua Jiang , Weng Kee Leong , T.S. Andy Hor
*
a Division of Chemistry, National Institute of Education, Nanyang Technological University, 469 Bukit Timah Road, Singapore 259756, Singapore
b Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260, Singapore
Received 20 October 1999; accepted 15 December 1999
Abstract
The reaction of 1,19-bis(diphenylphosphino)ferrocene (dppf) with a mixture of [MnRe(CO)10], MeOH and Me3NO afforded the
complexes fac-[MnH(CO)3(h2-dppf)] and [Re2(m-OMe)2(m-dppf)(CO)6]. In the one-pot reaction of [Re2(CO)10] with Me3NO, MeOH
and dppf, the major mononuclear Re species isolated was the CO2-inserted complex fac-[Re{OC(O)OMe}(CO)3(h2-dppf)], the crystal
structure of which was determined. The coordination sphere of the rhenium atom is roughly octahedral, consisting of an oxygen atom from
the methyl carbonate ligand, two phosphorus atoms from a chelating dppf ligand, and three carbon atoms from a facial arrangement of three
terminally bonded carbonyls. Analogous Me3NO-mediated methoxylation reactions involving [Os3(CO)12] were also investigated. With a
[Me3NO]:[Os3(CO)12] ratio of 2:1, the major product is [Os3(CO)10(m-H)(m-OMe)]. With three molar equivalents of Me3NO, significant
quantities of [Os3(CO)10(m-OMe)2] are also obtained.
q2000 Elsevier Science Ltd All rights reserved.
Keywords: Amine oxide; Methanolysis; Rhenium; Osmium; Carbonyl; Methylcarbonate
1. Introduction
Transition-metal carbonyl hydroxides and alkoxides have
been proposed as intermediates in a number of important
reactions, such as metal-catalysed hydrogenation of CO [1],
the water-gas shift reaction [2], and carboalkoxylation of
olefins [3]. They are also molecular models of silica-
Scheme 1.
rather drastic conditions, such as refluxing in methanolic
KOH [9].
anchored M(CO)n species, the only structural difference
between alkoxy and surfaced anchored complexes being that
the –OR group is replaced by an –OSi^ group [4].
At first, a mechanismfortheMe3NO-aidedoxidativemeth-
oxylation reaction in which the originally bonded Re atoms
in [Re2(CO)10] remain paired in the same molecule of the
product [Re2(m-OMe)2(m-PP)(CO)6](Scheme2)seemed
plausible [10]. We then extended our investigations to the
reaction of [Re2(CO)10] with Me3NO and phenol, which
yielded the complexes [Re3(m-H)(CO)14] and [Re2(m-
OPh)3(CO)6]y [11]. This suggested a mechanism involv-
ing the separation of the Re atoms of [Re2(CO)10] into
mononuclear hydrido and phenoxo species, followed by
dimerisation of the phenoxo species to form the
bis(phenoxo)-bridged intermediate [Re2(m-OPh)2(CO)8]
[11]. It seemed probable that the oxidative methoxylation
reaction also follows a similar pathway involving Re–Re
We have reported the facile synthesis of a series of dime-
thoxo-bridged complexes [Re2(m-OMe)2(m-PP)(CO)6]
(PPsdppf (1,19-bis(diphenylphosphino)ferrocene) or
Ph2P(CH2)nPPh2, ns1–4) by the addition of diphosphines
to a mixture obtained from the reaction of [Re2(CO)10] with
Me3NO in THF–MeOH mixture at room temperature
(Scheme 1) [5,6]. The facile rupture of the Re–Re bond
under such mild conditions is in sharp contrast to the general
observation that metal–metal bonds are quite resistant tother-
mal cleavage [7,8] and that Re–Re bond alcoholysisrequires
* Corresponding author. Tel.: q65-4605180; fax: q65-4698952; e-mail:
ykyan@nie.edu.sg
0277-5387/00/$ - see front matter q2000 Elsevier Science Ltd All rights reserved.
PII S0277-5387(00)00296-5
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Y.-K. Yan et al. / Polyhedron 19 (2000) 641–647
Scheme 2.
Scheme 3.
bond heterolysis, but we have not been able to observe any
rhenium hydrido species in this reaction. The reaction of
[Re2(CO)10] with Me3NO and methanol (without diphos-
phine) yields [Me3NH]q[Re3(m3-OMe)(m-OMe)(m-
OH)2(CO)9]y as the only isolable product [11].
These results confirm the occurrence of metal–metal bond
cleavage and the formation of metal hydride intermediates in
the reaction. The mechanism for the formation of [Re2(m-
OMe)2(m-dppf)(CO)6] from the reaction of dppf with
[Re2(CO)10], MeOH and Me3NO is therefore proposed as
shown in Scheme 3.
Interestingly, the complexes [Mn2(m-OMe)2(m-dppf)-
(CO)6] and [ReH(CO)3(h2-dppf)] are not observed as
products of the reaction, probably because these complexes
are unstable under the conditions of the reaction and isolation
of products. The complex [ReCl(CO)3(h2-dppf)] is likely
to be produced from the reaction of initially formed
[ReH(CO)3(h2-dppf)] with CH2Cl2 used during the isola-
tion of products by TLC [17]. We have also not been able
to synthesise [Mn2(m-OMe)2(m-dppf)(CO)6] via the reac-
tion of dppf with the mixture of [Mn2(CO)10], Me3NO and
MeOH.
In an effort to throw more light onto the mechanism of
Me3NO-aided oxidative methoxylation, we studied the reac-
tion of dppf with the mixture of [MnRe(CO)10], MeOH and
Me3NO. The products of this reaction should indicate
whether the Re and Mn atoms are separated during the reac-
tion. Formation of the homometallic complexes [Re2(m-
OMe)2(m-dppf)(CO)6] and/or [Mn2(m-OMe)2(m-dppf)-
(CO)6] would support the M–M bond heterolysis mecha-
nism. The results of this study are reported in this paper. We
also report a similar amine-oxide mediated methoxylation of
Os–Os bonds in the cluster [Os3(CO)12] to form [Os3(m-
H)(m-OMe)(CO)10] and [Os3(m-OMe)2(CO)10]. These
methoxo clusters were first reported in 1968 [12], but to date
no convenient one-pot synthesis giving high yields of these
clusters from [Os3(CO)12] has been reported [4,13–16].
2.2. One-pot reaction of [Re2(CO)10] with Me3NO, MeOH
and dppf
2. Results and discussion
In an attempt to trap the [Re(OMe)(CO)4] intermediate
in the reaction of [Re2(CO)10] with Me3NO and MeOH, the
one-pot reaction of [Re2(CO)10] with Me3NO, MeOH and
dppf has been carried out [11]. The major mononuclear Re
complex formed in this reaction (1) was mistakenly identi-
fied as the terminal methoxo complex fac-[Re(OMe)-
(CO)3(h2-dppf)] in Ref. [11]. We have subsequently
determined the crystal structure of 1 (see below), and iden-
2.1. Reaction of dppf with MnRe(CO)10, MeOH and Me3NO
The reaction of dppf with the mixture of [MnRe(CO)10],
MeOH and Me3NO afforded the complexes fac-[MnH-
(CO)3(h2-dppf)] (8%), [Re2(m-OMe)2(m-dppf)(CO)6]
(26%) and a trace amount of fac-[ReCl(CO)3(h2-dppf)].
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Y.-K. Yan et al. / Polyhedron 19 (2000) 641–647
643
tified it as the methyl carbonate complex fac-[Re-
{OC(O)OMe}(CO)3(h2-dppf)].
Complex 1 is most probably formed by the insertion of
CO2 into the intermediate complex fac-[Re(OMe)-
(CO)3(h2-dppf)] resulting from the reaction of dppf with
[Re(OMe)(CO)4]. The CO2 needed for the insertion reac-
tion is probably produced by the decarbonylation of
[Re2(CO)10] by Me3NO. The facile CO2-insertion reactions
of the complexes fac-[Re(OR)(CO)3(h2-PP)] (RsMe,
Et,
CF3CH2;
PPs1,2-bis(diphenylphosphino)ethane
(dppe), 1,3-bis(diphenylphosphino)propane) with atmos-
pheric CO2 has been reported [18].
2.3. Crystal structure of fac-[Re{OC(O)OMe}-
(CO)3(h2-dppf)] (1)
The crystal structure of 1 (Fig. 1) is similar to that of fac-
[Mn{OC(O)OMe}(CO)3(h2-dppe)] [18]. The coordina-
tion sphere of the rhenium atom is roughly octahedral,
consisting of an oxygen atom from the methyl carbonate
ligand (taken to occupy an axial position), two phosphorus
atoms from a chelating dppf ligand, and three carbon atoms
from a facial arrangement of three terminally bound carbon-
yls. The P–Re–P angle in 1 (Table 1) is larger than the P–
Mn–P angle in fac-[Mn{OC(O)OMe}(CO)3(h2-dppe)]
(84.1(1)8), probably owing to the greater steric demand of
dppf compared to dppe. The Re–CO(eq) distances (average
Fig. 1. Crystal structure of fac-[Re{OC(O)OMe}(CO)3(h2-dppf)] (1).
Hydrogen atoms are omitted for clarity.
Table 1
2
˚
Bond lengths (A) and angles (8) for fac-[Re{OC(O)OMe}(CO)3(h -
dppf)] (1)
Re(1)–P(1)
Re(1)–P(2)
Re(1)–O(1)
Re(1)–C(10)
Re(1)–C(20)
Re(1)–C(30)
C(10)–O(10)
2.508(2)
2.505(2)
2.150(4)
1.890(7)
1.946(7)
1.940(7)
1.154(8)
C(20)–O(20)
C(30)–O(30)
C(1)–O(1)
C(1)–O(2)
C(1)–O(3)
O(2)–C(2)
1.131(7)
1.138(7)
1.300(7)
1.244(8)
1.224(7)
1.438(8)
˚
1.943(7) A) are longer than the Re–CO(ax) distance
˚
(1.890(7) A). Correspondingly, the C–O bond length of the
˚
P(1)–Re(1)–P(2)
Re(1)–O(1)–C(1)
O(1)–C(1)–O(2)
96.18(5)
125.6(4)
112.3(5)
O(1)–C(1)–O(3)
C(1)–O(2)–C(2)
O(2)–C(1)–O(3)
124.1(7)
118.1(6)
123.6(7)
axial carbonyl (1.154(8) A) is longer than the lengths of
˚
1.131(7) and 1.138(7) A observed for the equatorial car-
bonyls. This can be attributed to the greater extent of M™CO
backbonding experienced by the axial carbonyl, which is
trans to the p-donating methyl carbonate ligand. The Re–
O(1) bond to the methyl carbonate ligand has a length of
steps are required starting from [Os3(CO)12], overall yields
are never more than 50%. More recently, the reaction of
methanol with the silica-anchored cluster [Os3(m-H)(m-
OSi^)(CO)10] (prepared by refluxing an n-octane solution
of [Os3(CO)12] with silica for 10 h) was reported to give
complex 2 in 52% yield (starting from [Os3(CO)12]) [4].
An alternative route involving the reaction of methanol with
[Os3(m-H)(m-OH)(CO)10] (prepared by heating a suspen-
sion of [Os3(m-H)(m-OSi^)(CO)10] in a water–toluene
mixture at 958C for 5 h) gives complex 2 in 82% overall
yield from [Os3(CO)12] [4]. Compared with the reported
syntheses of 2, the present method is much more attractive
since it is a high-yield one-pot synthesis over 4 h, starting
directly from [Os3(CO)12], underrelativelymildconditions.
When the molar ratio of Me3NO to [Os3(CO)12] is
increased to 3.3:1, the bis(methoxo) cluster [Os3(m-
OMe)2(CO)10] (3) is obtained in 11% yield, while complex
2 is obtained in 33% yield. The yield of 3 is increased to 17%
when 4.3 molar equivalents of amine oxide are used, while
the yield of 2 remains essentially unchanged. As far as we
are aware, the highest-yield synthesis for 3 reported thus far
involves direct reaction of [Os3(CO)12] with methanol at
1708C for 38 h in vacuo in a steel-lined autoclave, which
˚
2.150(4) A, which is comparable to the Re–O bond lengths
2
˚
of 2.150(4) A in fac-[Re(OPh)(CO)3(h -dppe)] [19],
˚
2.162(6) A (average) in [Re2(m-OMe)2(m-dppf)(CO)6]
˚
[5], and 2.143(8) A (average) in [Re2(m-OMe)2(m-
dppm)(CO)6] [6].
2.4. Reactions of [Os3(CO)12] with Me3NO and MeOH
Reaction of [Os3(CO)12] with Me3NO (1.2 molar equiv-
alents) in refluxing THF–methanol (7:1) mixture for 4 h
gave the complex [Os3(m-H)(m-OMe)(CO)10] (2) in 71%
yield. Increasing the amount of amine oxide (2.4 molar
equivalents) and methanol (THF:MeOH 4:1) did not signif-
icantly increase the yield of 2 (73%). The same cluster has
been prepared in 10% yield by direct reaction of
[Os3(CO)12] with methanol at 1708C for 38 h in vacuo in
a steel-lined autoclave [13]. It can also be prepared via
multi-step processes involving [Os3(CO)10(cyclohexa-
1,3-diene)] [14], [Os3(CO)10(cyclooctene)2] [15], [Os3-
(CO)10(CH3CN)2] [15], or [Os3(m-H)(m-NCHNMe2)-
(CO)10] [16] as intermediates. However, since three or four
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Y.-K. Yan et al. / Polyhedron 19 (2000) 641–647
gives 3 in 13% yield and 2 in 10% yield (see above) [13].
The present one-pot synthesis for 3 is comparatively more
convenient and gives a similar yield of the cluster.
1,19-binaphthyl) to give an 80% yield of the dihydroxo
complex [Ru3(m-OH)2(CO)8{m-(R)-BINAP}] [20].
Although the authors identified Me3NOP2H2O as the proba-
ble source of the hydroxo ligands, they did not propose any
mechanism for the formation of [Ru3(m-OH)2(CO)8{m-
(R)-BINAP}]. We believe that the mechanism is similar
to that proposed above for the formation of [Os3(m-
OMe)2(CO)10]. The complex [Ru3(m-OH)2(CO)10] is
probably formed, and is further decarbonylated by the excess
Me3NO present to give an unsaturated intermediate which
reacts with BINAP to form [Ru3(m-OH)2(CO)8{m-(R)-
BINAP}]. It is noteworthy that when dppm (bis-
(diphenylphosphino)methane) was added to the mixture
resulting from the reaction of [Os3(CO)12] with 4.3 molar
equivalents of Me3NO in THF–MeOH, a product tentatively
identified as [Os3(m-H)(m-OMe)(m-dppm)(CO)8] could
be isolated.
2.5. Proposed mechanism for the formation of clusters 2
and 3
A plausible mechanism for the formation of clusters 2 and
3 is given in Scheme 4. As in the proposed mechanism for
the formation of [Re2(m-OMe)2(m-dppf)(CO)6] from
[Re2(CO)10], the first step involves Me3NO-assisted substi-
tution of a CO ligand by methanol. Oxidative addition of
MeO–H across the M–M bond does not, however, result
in the formation of two separate mononuclear species
[OsH(CO)3] and [Os(OMe)(CO)3], since the two
[Os(CO)3] fragments are still bonded to the third osmium
atom, which keeps them in close proximity. The oxidative
addition reaction therefore results preferentially in the
hydrido- and methoxo-bridged cluster [Os3(m-H)(m-
OMe)(CO)10] (2), with three Os–Os bonds. The loss of the
second CO ligand which accompanies the oxidative addition
presumably does not require Me3NO, since there is no sig-
nificant difference in the yield of 2 whether 1.2 or 2.4 molar
equivalents of amine oxide is used.
The cluster [Os3(m-OMe)2(CO)10] (3) is probably
formed by the oxidative addition of methanol and elimination
of H2 from the disubstituted intermediate [Os3(CO)10-
(MeOH)2]. The formation of [Os3(CO)10(MeOH)2] from
[Os3(CO)11(MeOH)] probably requires Me3NO and is
slow compared to the conversion of [Os3(CO)11(MeOH)]
to [Os3(m-H)(m-OMe)(CO)10]. Hence cluster 3 is only
formed in significant quantities when excess amine oxide is
used. The higher concentration of Me3NO probably increases
the rate of formation of [Os3(CO)10(MeOH)2], enabling
this process to compete more effectively against the forma-
tion of [Os3(m-H)(m-OMe)(CO)10]. Cluster 3 is unlikely
to be formed from the secondary reaction of 2 with excess
methanol since 2 remains unchanged when refluxed in meth-
anol for 4 h.
So far, we have not observed products where two or more
Os–Os bonds have been methoxylated.
3. Summary and conclusions
The reaction of dppf with the mixture of MnRe(CO)10,
MeOH and Me3NO gives the complexes fac-[MnH(CO)3-
(h2-dppf)] and [Re2(m-OMe)2(m-dppf)(CO)6], confirm-
ing that mononuclear alkoxo and hydrido intermediates are
formed during the reaction. Reaction of [Os3(CO)12] with
Me3NO (1–2 molar equivalents) and methanol gives
[Os3(m-H)(m-OMe)(CO)10] in good yield. With 3 molar
equivalents of Me3NO, significant quantities of [Os3(m-
OMe)2(CO)10] are also obtained. No further methoxylation
of Os–Os bonds occurs when the [Me3NO]:[Os3(CO)12]
ratio is increased to 4:1.
4. Experimental
All reactions were performed under pure dry argon using
standard Schlenk techniques. Solvents used were of reagent
grade and were dried by published procedures and freshly
distilled under argon before use. Unless otherwise stated, all
reagents and starting materials used were of AR grade and
were obtained from commercial sourcesandusedassupplied.
Precoated silica plates of layer thickness 0.25 mm were
Interestingly, Deeming et al. reported that [Ru3(CO)12]
reacts with Me3NOP2H2O (5.8 molar equivalents) in the
presence of (R)-BINAP (2,29-bis(diphenylphosphino)-
1
obtained from Merck. H and 31P{1H} NMR spectra were
recorded at ca. 300 K on a Bruker ACF 300 MHz spectrom-
eter. 1H and 31P chemical shifts are quoted in ppm downfield
of tetramethylsilane and external 80% H3PO4, respectively.
Infrared spectra were recorded on either a Perkin Elmer 1600
or a Bio-Rad FTS165 FT-IR spectrophotometer. Elemental
analyses were performed by the Microanalytical Laboratory,
Department of Chemistry, National University of Singapore.
4.1. Preparation of [MnRe(CO)10]
The reported method [21,22] for the preparation of
[MnRe(CO)10] was used with slight modification. A
Scheme 4.
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Y.-K. Yan et al. / Polyhedron 19 (2000) 641–647
645
degassed solution of [Mn2(CO)10] (0.235 g, 0.60 mmol) in
4.3. Preparation of fac-[Re{OC(O)OMe}(CO)3(h2-dppf)]
(1)
freshly dried THF (10 cm3) was transferred into a Schlenk
flask (cooled in an ice bath) containing sodium amalgam
(3% Na by weight) (;1 g). The resultant suspension was
stirred under argon at 08C for 1 h, then at room temperature
for another 1 h. The solution was then filtered under argon
into a flask containing a stirred solution of [ReBr(CO)5]
(0.406 g, 1.0 mmol) in THF (10 cm3). Reaction was contin-
ued at room temperature under argon for 4 h. Solvent was
removed under reduced pressure and the resultant residue
was exposed in air for 1 week to oxidise any unreacted
[Mn2(CO)10]. The orange solid obtained was then sublimed
at 558C, 0.3 mmHg. The compound [MnRe(CO)10] was
obtained as an orange solid with a yield of 0.40 g (77% based
on Re).
A solution of Re2(CO)10 (0.151 g, 0.23 mmol) in THF
(20 cm3) was transferred into a stirred solution of
Me3NOP2H2O (0.062 g, 0.56 mmol) and dppf (0.128 g,
0.23 mmol) in a mixture of MeOH (10 cm3) and THF (20
cm3). The resultant solution was stirred under partial vacu-
um at room temperature for 4 h. The solvent was removed
under reduced pressure and the residue was redissolved in a
minimum amount of THF and chromatographed on silica
TLC plates (acetone:hexane 1:4). The complex fac-
[Re{OC(O)OMe}(CO)3(h2-dppf)] (1) was isolated from
the chrome-yellow band at Rfs0.23. Air-stable orange pris-
matic crystals of 1 were obtained by cooling a solution of 1
in benzene–hexane–MeOH mixture to y108C. Yield 0.016
g (4%). The crystals have the composition [Re{OC(O)-
OMe}(CO)3(h2-dppf)](C6H6)0.5. Anal. C42H34FeO6P2Re
(FW 938.7) requires: C, 53.7; H, 3.6; P, 6.5. Found: C, 53.8;
H, 3.7; P, 6.4%. nmax(CO) 2037vs, 1948m, 1899s (C6H6);
2033vs, 1951s, 1900s (acetone); 2029s, 1947s, 1895s cmy1
(KBr); n(C_O methyl carbonate ligand) 1678m cmy1
(KBr). dH (C6D6) 7.94–7.82 (m), 7.17–7.02 (m) (20H,
C6H5), 5.06 (s, 2H, CpH), 4.32 (s, 2H, CpH), 3.90 (s, 2H,
CpH), 3.81 (s, 2H, CpH), 3.59 (s, 3H, OCH3); dP (C6D6)
7.23 (s).
The purity of the [MnRe(CO)10] obtained was ascer-
tained by IR spectroscopy and elemental analysis.nmax(CO):
2054s, 2017 vs,1978s cmy1 (cyclohexane) (none of the IR
absorption peaks of [Mn2(CO)10] and [Re2(CO)10] were
detected). Anal. C10MnO10Re requires: C, 23.0. Found: C,
23.4%.
4.2. Reaction of dppf with [MnRe(CO)10], MeOH and
TMNO
4.4. Reaction of [Os3(CO)12] with MeOH and one molar
equivalent of Me3NO
The solution of Me3NOP2H2O (0.062 g, 0.56 mmol) in
THF–MeOH (1:1, 20 cm3) was transferred into a Schlenk
flask containing a stirred solution of [MnRe(CO)10] (0.120
g, 0.23 mmol) in THF (10 cm3) at room temperature. This
solution was stirred in vacuo for 4 h at room temperature.
Solid dppf (0.128 g, 0.23 mmol) was added and the orange
solution so formed was stirred in vacuo for 1 h. It was then
evaporated to half its volume and stirred for 3 h. The solvent
was then removed and the residue was redissolved in a min-
imum amount of CH2Cl2 and chromatographed on silicaTLC
plates (CH2Cl2:hexane 2:3). From the main bands the
complexes fac-[MnH(CO)3(h2-dppf)] (Rfs0.57) and
[Re2(m-OMe)2(m-dppf)(CO)6] (Rfs0.47) were isolated
with yields of 0.012 g (8%) and 0.035 g (26%), respectively.
A trace amount of fac-[ReCl(CO)3(h2-dppf)] (Rfs0.13)
was also isolated.
Tetrahydrofuran (60 cm3) and [Os3(CO)12] (0.0365 g,
0.040 mmol) were placed in a 250 ml three-neck round-
bottom flask fitted with a reflux condenser, an argon inlet,
and a 100 ml pressure-equalising dropping funnel. The reac-
tion mixture was stirred and heated to reflux (oil bath tem-
perature maintained at 808C). A solution of Me3NOP2H2O
(0.0052 g, 0.047 mmol) in THF–methanol (1:1) mixture
(20 cm3) was then added dropwise over an hour. The resul-
tant solution was refluxed for a further 3 h. The yellow solu-
tion obtained was then cooled to room temperature and
filtered through silica. The silica was washed with THF until
the washings were colourless. The combined filtrate and
washings was rotary evaporated to obtain an oily residue. The
residue was redissolved in a minimum amount of CH2Cl2 and
chromatographed on silica TLC plates, eluting with CH2Cl2–
hexane (5:95) mixture. A major yellow band (Rfs0.72)
was obtained and extracted with CH2Cl2 to give [Os3(m-
H)(m-OMe)(CO)10] (2). Yield 0.0251 g (71%). The iden-
The complex fac-[MnH(CO)3(h2-dppf)] was recrystal-
lised from CH2Cl2–MeOH mixture at 08C. Anal. Found: C,
63.5; H, 4.3; P, 8.8. C37H29O3P2FeMn (FW 694) requires:
C, 64.0; H, 4.2; P, 8.9%. nmax(CO): 1998s, 1920m(sh),
1903m (CHCl3); 1996s, 1917m(sh), 1903m (CH2Cl2);
1997s, 1922m(sh), 1906m cmy1 (THF). dH (CDCl3) 7.7–
7.4 (m) (20H, Ph), 4.38 (s, 2H, CpH), 4.29 (s, 2H, CpH),
4.18 (s, 2H, CpH), 4.08 (s, 2H, CpH), y6.18 (t, 1H,
hydride), J(P–Mn–H) 50 Hz; dp (CDCl3) 64.8. The complexes
[Re2(m-OMe)2(m-dppf)(CO)6] and fac-[ReCl(CO)3(h2-
dppf)] were identified by IR, 1H and 31P NMR spectroscopy
[5,23].
1
tity of this compound was confirmed by IR and H NMR
spectroscopy [12].
4.5. Reaction of [Os3(CO)12] with MeOH and two molar
equivalents of Me3NO
The procedure adopted was similar to that for the reaction
with one molar equivalent of Me3NO except for the relative
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646
Y.-K. Yan et al. / Polyhedron 19 (2000) 641–647
amounts of reagents used: [Os3(CO)12] 0.0352 g, 0.039
mmol; Me3NOP2H2O 0.0103 g, 0.093 mmol; dissolved in
THF–methanol (1:1) mixture (40 cm3). Yield of 2 was
0.0249 g (73%).
maximum 2u value of 55.08. A total of 9993 reflections were
measured, of which 8004 were unique (Rints0.034). The
number of data used for structure solution and refinementwas
5303 (I)2.0s(I)). Empirical c corrections were made; the
minimum and maximum transmission factors were 0.7130
and 0.9560 respectively. The structure was solved by direct
methods. All non-hydrogen atoms (except those of the dis-
ordered solvate molecule) were refined anisotropically by
the full-matrix least-squares method (on F2). Hydrogen
atoms were introduced in calculated positions and refined
isotropically (riding model) in the final cycles of least-
squares refinement. The disordered benzenesolvateislocated
about a crystallographic inversion centre. The unique half of
the benzene molecule was modelled isotropically in terms of
two overlapping C3 fragments of half occupancy each
(C(100)–C(300)) and (C(101)–C(301)), with the con-
4.6. Reaction of [Os3(CO)12] with MeOH and three molar
equivalents of Me3NO
The amounts of reagents used were as follows:
[Os3(CO)12] 0.0356 g, 0.039 mmol; Me3NOP2H2O 0.0143
g, 0.129 mmol; dissolved in THF–methanol (1:1) mixture
(60 cm3). TLC on silica plates (CH2Cl2:hexane 1:9) gave
two main yellow bands: 2 (Rfs0.87, 0.0173 g, 49%) and 3
[Os3(m-OMe)2(CO)10] (Rfs0.71, 0.0039 g, 11%). The
1
identity of compound 3 was confirmed by IR and H NMR
spectroscopy [12].
˚
straint C–Cs1.390"0.002 A. The C(100)∆C(300) and
4.7. Reaction of [Os3(CO)12] with MeOH and four molar
equivalents of Me3NO
C(101)∆C(301) distances were constrained to be
˚
2.400"0.002 A to fix the C–C–C angles at 1208. The last
least-squares cycle was calculated with 466 parameters
and 7950 reflections (all of the unique reflections except
very negative ones), and converged with R1 s
0.040 and wR2s0.080 (for reflections with I)2.0s(I))
The amounts of reagents used were as follows:
[Os3(CO)12] 0.0335 g, 0.037 mmol; Me3NOP2H2O 0.0178
g, 0.160 mmol; dissolved in THF–methanol (1:1) mixture
(80 cm3). Yields: 2 (0.0103 g, 32%); 3 (0.0056 g, 17%).
2
2
(R1 s 8NNFoNyNFcNN/8NFoN, wR2 s [8w(Fo yFc )2/
2
8w(Fo )2]1/2). The weighting function used was
2
2
2
4.8. Reaction of [Os3(CO)12] with MeOH, four molar
equivalents of Me3NO, and one equivalent of
bis(diphenylphosphino)methane (dppm)
wy1ss2(Fo )q(0.0400P)2, where Ps(Fo q2Fc )/3. In
y3
˚
the last difference map the deepest hole was y0.605 e A
,
and the highest peak was 0.677 e Ay3. Computations were
carried out on a Pentium PC using the SHELXTL PLUS
software package [24].
˚
The compounds [Os3(CO)12] (0.0556 g, 0.061 mmol),
Me3NOP2H2O (0.0294 g, 0.265 mmol, dissolved in THF–
methanol (1:1) mixture (80 cm3)) were allowed to react as
above. After 4 h, dppm (0.0243 g, 0.093 mmol) was added.
The solution was stirred for another 30 min, during which the
colour of the solution darkened somewhat. The solution was
filtered through silica and the filtrate was rotary evaporated
to obtain an oily residue. The residue wasdissolvedinCH2Cl2
and loaded onto a silica column. ElutionwithCH2Cl2–hexane
mixture (1:4) yielded a major yellow band which gave IR
Supplementary data
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK (fax: q44-1223-
336033; e-mail: deposit@ccdc.cam.ac.uk), CCDC no.
135934.
1
and H NMR spectra consistent with the formulation [Os3-
(m-H)(m-OMe)(m-dppm)(CO)8]. nmax(CO) 2086vw,
2074m, 2048w, 2038vw, 2003vs, 1990sh, 1941m cmy1
(hexane). dH (CDCl3) 7.3–7.5 (m) (20H, Ph), 3.4 (s) (3H,
OCH3), 3.1 (dt) (1H, CH2), 2.9 (dt) (1H, CH2), y11.2
(t) (1H, hydride), J(H–P) 12 Hz; dP (CDCl3) y8.4 (s).
Acknowledgements
Financial support by the National Institute of Education,
Singapore and the National University of Singapore (NUS)
is gratefully acknowledged. C.J. thanks NUS for the award
of a research scholarship.
4.9. X-ray crystallography of fac-[Re{OC(O)OMe}-
(CO)3(h2-dppf)] (1)
Data were collected on a crystal of dimensions
0.17=0.30=0.40 mm using a Siemens P4 diffractometer in
the u–2u mode, with graphite-monochromated Mo Ka
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