Substituted metal carbonyls. 26.1 One-step synthesis, structures, NMR, and dynamic laser-light scattering of Re2(μ-OMe)2[μ-Ph2P(CH2) nPPh2](CO)6 (n = 1-4)

Article abstract of DOI:10.1021/om9506779

Oxidative decarbonylation of Re₂(CO)₁₀ by Me₃NO in a mixture of THF and MeOH followed by addition of alkyl-chained diphosphine Ph₂P(CH₂)_nPPh₂ (PP) (n = 1-4) gives Re₂(μ-OMe)₂-(μ-PP)(CO)₆ in 34, 29, 28, and 10% yields, respectively. This methanolytic oxidation across the Re-Re bond provides a general and one-step route for the synthesis of these dirhenium hexacarbonyl complexes with diphosphine and methoxo bridges. The molecular structure of Re₂(μ-OMe)₂(μ-Ph₂PCH₂PPh ₂)(CO)₆ was determined by single-crystal X-ray diffraction analysis. It contains two fac-[Re(CO)₃] moieties bridged by dppm and two methoxo ligands. The {Re₂O₂} core is significantly more planar than that in the Fe(C₅H₄PPh₂)₂ analogue. That such a dinuclear core is maintained in spite of the different steric demands of the different bridging diphosphines illustrates the great geometric tolerance of the bridging methoxo groups. The fluxionality of the dppm, dppe, and dppp complexes has been studied and compared by molecular modeling and solution ¹H NMR spectroscopy. Dynamic laser-light scattering (DLS) shows that the dppe complex aggregates in CH₂Cl₂ to form small clusters with an average radius of ～370 nm. The use of a combination of DLS and NMR in organometallic chemistry is unprecedented.

Full text of DOI:10.1021/om9506779

Organometallics 1996, 15, 1369-1375
1369
Su bstitu ted Meta l Ca r bon yls. 26.1 On e-Step Syn th esis,
Str u ctu r es, NMR, a n d Dyn a m ic La ser -Ligh t Sca tter in g of
Re2(µ-OMe)2[µ-P h 2P (CH2)n P P h 2](CO)6 (n ) 1-4)
Pauline M. N. Low, Yuk Lin Yong, Yaw Kai Yan,† and T. S. Andy Hor*
Department of Chemistry, Faculty of Science, National University of Singapore,
Kent Ridge 119260, Singapore
Sik-Lok Lam, Kam Kwong Chan, Chi Wu, and Steve C. F. Au-Yeung*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong
Yuh-Sheng Wen and Ling-Kang Liu*
Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan
Received August 29, 1995X
Oxidative decarbonylation of Re2(CO)10 by Me3NO in a mixture of THF and MeOH followed
by addition of alkyl-chained diphosphine Ph2P(CH2)nPPh2 (PP) (n ) 1-4) gives Re2(µ-OMe)2-
(µ-PP)(CO)6 in 34, 29, 28, and 10% yields, respectively. This methanolytic oxidation across
the Re-Re bond provides a general and one-step route for the synthesis of these dirhenium
hexacarbonyl complexes with diphosphine and methoxo bridges. The molecular structure
of Re2(µ-OMe)2(µ-Ph2PCH2PPh2)(CO)6 was determined by single-crystal X-ray diffraction
analysis. It contains two fac-[Re(CO)3] moieties bridged by dppm and two methoxo ligands.
The {Re2O2} core is significantly more planar than that in the Fe(C5H4PPh2)2 analogue.
That such a dinuclear core is maintained in spite of the different steric demands of the
different bridging diphosphines illustrates the great geometric tolerance of the bridging
methoxo groups. The fluxionality of the dppm, dppe, and dppp complexes has been studied
1
and compared by molecular modeling and solution H NMR spectroscopy. Dynamic laser-
light scattering (DLS) shows that the dppe complex aggregates in CH2Cl2 to form small
clusters with an average radius of ∼370 nm. The use of a combination of DLS and NMR in
organometallic chemistry is unprecedented.
In tr od u ction
Diphosphine-substituted carbonyl complexes of rhe-
nium have attracted recent interest with regard to their
reactivities and electrochemical and photochemical
properties.2 We recently reported the facile synthesis
of the bis(methoxo) complex Re2(µ-OMe)2(µ-dppf)(CO)6
(1; dppf ) 1,1′-bis(diphenylphosphino)ferrocene) based
on a room temperature activation of a Re-Re bond in
Re2(CO)10 in methanol.3 The analogous dppm (Ph2-
PCH2PPh2) complex 2 had been previously reported as
a side product in the photolysis of Re2(CO)8(µ-dppm).4
Although the [Re2(µ-OMe)2] core does not appear to have
flexibility in adjusting its Re‚‚‚Re separation, it surpris-
ingly can accommodate a bridging phosphine such as
to support bridging diphosphines with both short and
extended backbones. In order to understand this be-
havior, and in view of the current significance of alkoxo
complexes of Re(I),7 we have extended this study to
other diphosphines. It is our aim to establish if this
Re-Re activation mechanism can provide a general
route to other methoxo carbonyl complexes and if the
different chain lengths of the phosphines would neces-
sitate any structural changes. Should a dinuclear frame
5
dppf or dppm,6 which differ in steric and conforma-
tional demands. It is rare for bridging methoxo ligands
* To whom correspondence should be addressed.
† Present address: Division of Chemistry, National Institute of
Education, 1025 Singapore.
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) Part 25 Fang, Z.-G.; Wen, Y.-S.; Wong, R. K. L.; Ng, S.-C.; Liu,
L.-K.; Hor, T. S. A. J . Cluster Sci. 1994, 5, 327-340.
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(3) Yan, Y. K.; Chan, H. S. O.; Hor, T. S. A.; Tan, K.-L.; Liu, L.-K.;
Wen, Y.-S. J . Chem. Soc., Dalton Trans. 1992, 423-426.
(4) Lee, K.-W.; Pennington, W. T.; Cordes, A. W.; Brown, T. L.
Organometallics 1984, 3, 404.
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1988, 86, 191-243.
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3993. Simpson, R. D.; Bergman, R. G. Organometallics 1992, 11, 4306-
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0276-7333/96/2315-1369$12.00/0 © 1996 American Chemical Society

1370 Organometallics, Vol. 15, No. 5, 1996
Low et al.
be maintained, the conformational differences of the
bridging diphosphines in relation to the methoxo bridges
would then be a subject of great interest. Apart from
our recent report of the solution dynamics of 1,8 we are
not aware of such a study in the literature. Such
dynamic studies could not be satisfactorily done without
structural data. In this context, we also report the
X-ray crystal structure of Re2(µ-OMe)2(µ-dppm)(CO)6
and its NMR behavior in solution. Although dppm and
dppf appear to share little similarities apart from being
difunctional phosphines, some of their dinuclear and
polynuclear complexes have common structural char-
acteristics.9 Comparisons of the structural data of 1 and
2 would give us the first insight into the different effects
of these two phosphines in identical bridging environ-
ments. On the basis of these structural data, we can
also carry out a molecular modeling study on the
fluxional behavior of these complexes in solution. In
the course of our study, some unusual features were
eties. Proton NMR resonances due to the bridging
methoxo protons lie in a narrow range 4.29-4.34 ppm,
which is in close agreement with those of the dppf
analogue (4.59 ppm). These data, supported further by
the characteristic low-field 13C NMR shifts of the
bridging methoxo carbon (72.55-73.27 ppm), suggest
that the title complexes are isostructural with the dppf
analogue. Molecular weight data are in general agree-
ment with a dinuclear structure. These give the first
indication that the synthetic route is applicable to all
the diphosphines used and that the dinuclear structure
is maintained regardless of the phosphine chain lengths.
A related terminal methoxo complex, Re(OMe)(η2-
dppe)(CO)3, prepared from the metathesis of fac-Re-
(OTs)(CO)3(dppe) with NaOMe, has been recently re-
ported.17 There is no evidence that a similar mono-
nuclear complex with a chelating diphosphine is formed
under our synthetic conditions. This can be ascribed
to different formation mechanisms for both syntheses.
There is evidence that the bis(methoxo)-bridged precur-
sor Re2(µ-OMe)2(CO)8 is formed in the activated mix-
1
observed in the H NMR spectrum of 3. We traced this
to an unexpected aggregation, which is revealed by
dynamic laser-light scattering (DLS). Similar applica-
tions of DLS in biomolecules,10 polymers,11 surface
films,12 optics,13 chromatography,14 and other fluids and
particles15 have attracted vigorous attention recently
but such study in organometallics is limited.
1
ture.18 The H NMR spectrum of this mixture shows
an intense resonance at 4.87 ppm, which may be
attributed to a methoxo bridge.19 This key intermediate
undergoes phosphine substitution to give the observed
products. Once these dirhenium complexes are formed,
they are stabilized by three bridging ligands and hence
show little tendency to dissociation. Addition of free
diphosphine has no effect on the complexes at room
temperature, i.e., they do not provide a synthetic pas-
sage to Re(OMe)(η2-PP)(CO)3.
Resu lts a n d Discu ssion
Oxidative decarbonylation of Re2(CO)10 at room tem-
perature by Me3NO in a THF/MeOH mixture gives an
“activated” mixture, which upon addition of free diphos-
phine (PP ) dppm (2), dppe (3), dppp (4), dppb (5))
results in Re2(µ-OMe)2(µ-PP)(CO)6 in 34, 29, 28, and
10% yields respectively.16 The IR spectra, which are in
excellent agreement with the spectrum of the dppf
analogue, are suggestive of fac-Re(I) tricarbonyl moi-
1
For unknown reasons, the spectroscopic (IR and H
NMR) data for 2 prepared by our method are slightly
different from those for the same complex4 from the
photolysis of Re2(µ-dppm)(CO)8.20 Formation of the
literature complex occurs via Re2(µ-H)(µ-OMe)(CO)6(µ-
dppm). There is no evidence that this hydride is
involved in the present synthesis. Notably, 3 (or its
precursor, Re2(µ-H)(µ-OMe)(CO)6(µ-dppe)) cannot be
obtained from Re2(CO)8(µ-dppe) under photolytic condi-
tions. Other diphosphine analogues have not been
reported. The method used here is hence a more
general route to prepare these bridging diphosphine
complexes.
The differences in the spectroscopic data for 2 ob-
tained by us and those reported are slight but disturb-
ing. They prompted us to investigate its solid-state
structure by X-ray crystallography. It confirms a
dimeric framework with dppm and two methoxo ligands
bridging two facial Re(I) tricarbonyl moieties (Figure
1). The methoxo methyls are pointing away from the
dppm group. Replacement of dppf (in 1) by dppm (in
2) induces some changes in the bonding characteristics
(8) Lam, S.-L.; Cui, Y.-X.; Au-Yeung, S. C. F.; Yan, Y.-K.; Hor, T. S.
A. Inorg. Chem. 1994, 33, 2407-2412.
(9) Neo, S. P.; Zhou, Z.-Y.; Mak, T. C. W.; Hor, T. S. A. Inorg. Chem.
1995, 34, 520-523. Neo, S.-P.; Hor, T. S. A.; Zhou, Z.-Y.; Mak, T. C.
W. J . Organomet. Chem. 1994, 464, 113-119.
(10) Wu, C. Macromolecules 1993, 26, 3821-3825. Wu, C. J . Polym.
Sci. B, Polym. Phys. 1994, 32, 803-810. Kadima, W.; Ogendal, L.;
Bauer, R.; Kaarsholm, N.; Brodersen, K.; Hansen, J . F.; Porting, P.
Biopolymers 1993, 33, 1643-1657. Komatsu, H.; Yoshii, K.; Ishimitsu,
S.; Okada, S.; Takahata, T. J . Chromatogr. 1993, 644, 17-24. Burne,
P. M.; Sellen, D. B. Biopolymers 1994, 34, 371-382. Watanabe, Y.;
Takagi, T. J . Chromatog. A 1993, 653, 241-246.
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Degroot, A. W.; Hamre, W. J . J . Chromatogr. 1993, 648, 33-39.
Sedlacek, J .; Vohlidal, J .; Grubisicgallot, Z. Makromol. Chem., Rapid
Commun. 1993, 14, 51-53. Hsu, C. H.; Peacock, P. M.; Flippen, R. B.;
Yue, J .; Epstein, A. J . Synth. Met. 1993, 60, 223-225. Kasparkova,
V.; Ommundsen, E. Polymer 1993, 34, 1765-1767. Grubisicgallot, Z.;
Gallot, Y.; Sedlacek, J . Macromol. Chem. Phys. 1994, 195, 781-791.
(12) Xu, R. L. Langmuir 1993, 9, 2955-2962. Yang, K.; Mirabelli,
E.; Wu, Z. C.; Schowalter, L. J . J . Vac. Sci. Tech. B 1993, 11, 1011-
1013. Smith, G. W.; Pidduck, A. J .; Whitehouse, C. R.; Glasper, J . L.;
Spowart, J . J . Cryst. Growth 1993, 127, 966-971.
(13) Celii, F. G.; Beam, E. A.; Filessesler, L. A.; Liu, H. Y.; Kao, Y.
C. Appl. Phys. Lett. 1993, 62, 2705-2707. Naqwi, A. A.; Durst, F. Appl.
Optics 1993, 32, 4003-4018.
(14) Mhatre, R.; Krull, I. S. Anal. Chem. 1993, 65, 283-286.
Aitzetmuller, K.; Gronheim, M. Fett Wiss. Technol. 1993, 95, 164-
168. Dayal, U.; Mehta, S. K. J . Liq. Chromatogr. 1994, 17, 303-316.
Mhatre, R.; Qian, R.; Krull, I. S.; Gadam, S.; Cramer, S. M. Chro-
matographia 1994, 38, 349-354. Meyer, E. M.; Vasconcellos, S. R. ACS
Symp. Ser. 1994, No. 548, 131-143.
(17) Mandal, S. K.; Ho, D. M.; Orchin, M. Inorg. Chem. 1991, 30,
2244-2248.
(18) Yan, Y. K. M.S. Thesis, National University of Singapore, 1992.
Hor, T. S. A.; Lam, C. F.; Yan, Y. K. Bull. Sing. Nat. Int. Chem. 1991,
19, 115-122.
(19) Although Re2(CO)8X2 (X ) halides) is well-established, there
has been no report of such a complex for X ) OMe. We are still trying
to isolate this proposed intermediate both from the reaction mixture
and by another independent synthetic route. Further results will be
reported in due course.
(15) Dishman, K. L.; Doolin, P. K.; Hoffman, J . F. Ind. Eng. Chem.
Res. 1993, 32, 1457-1463. Ochi, K.; Momose, M.; Kojima, K.; Lu, B.
C. Y. Can. J . Chem. Eng. 1993, 71, 982-985. Kriegs, H.; Schulz, R.;
Staude, W. Exp. Fluids 1993, 15, 240-246.
(16) These yields are generally modest, but the complexes isolated
are the principal products and the only ones isolable from the reaction
mixtures. Negligible Re2(CO)10 is apparent at the end of the reaction.
(20) Brown et al. reported a weak infrared band at 1893 cm-1 (2027s,
2010 m, 1924 m, 1893 w, 1885 (sh)). This band is the strongest band
in our spectrum. From the reported NMR data, the methylene protons
of dppm (3.71 ppm) are more deshielded compared to those of our
complex (3.14 ppm). These differences are, however, sufficiently minor
that both data sets could infer the structure proposed. Presumably
the differences, if any, are conformational in nature.

Substituted Metal Carbonyls
Organometallics, Vol. 15, No. 5, 1996 1371
F igu r e 1. ORTEP plot of the molecular structure of Re2(µ-
OMe)2[µ-Ph2PCH2PPh2](CO)6 (2) (50% probability ellip-
soids).
of the central {Re2O2} core. The Re-O bonds slightly
strengthen from 2.163(6) Å in 1 to 2.143(8) Å in 2
(mean). While the Re-O-Re angles remain fairly
constant (103.9(2)° in 1 and 104.7(3)° in 2 (mean)), the
O-Re-O angles open up (from 71.3(2)° in 1 to 74.8(3)°
in 2 (mean)), presumably as a result of the shorter
Re-O bonds. However, in supporting this {Re2O2} core,
which is found to be rigid in 1, the overhead bridgesdppf
or dppmsadjusts and adapts according to its own
geometric demands. In 1, the bulk of the dppf bridge
forces the centroids of the Cp‚‚‚Cp axis to twist signifi-
cantly with respect to the Re‚‚‚Re axis and the two Re-
(I) coordination planes to fold along the O‚‚‚O axis away
from the phosphine. These deformations are no longer
necessary in 2, as dppm is more suited as an overhead
bridge. Four effects are immediately obvious. (i) The
Re-P bonds strengthen significantly from 2.531(2) Å
in 1 to 2.482(4) Å in 2. (ii) In 1, the P‚‚‚P vector is
roughly parallel to the Re‚‚‚Re vector (dihedral angles
Re(2)‚‚‚Re(1)-P(1)‚‚‚P(2) ) Re(1)‚‚‚Re(2)-P(2)‚‚‚P(1) )
2.3(1)°); in 2, it is even more parallel (0.6(1)°). The
slight tilting of the P‚‚‚P axis allows more room for the
ferrocenyl moiety to fit into the [Re2(µ-OMe)2] pocket.
(iii) The folding of the {Re2O2} core is significantly less
pronounced in 2 ( Re-O‚‚‚O-Re ) 29.0(2)° in 1 and
9.4(3)° in 2; O-Re‚‚‚Re-O ) 38.5(3)° in 1 and 12.3-
(5)° in 2) (see Figure 2A). This freedom to fold provides
a leverage for the core to adapt to diphosphines of
different steric demands. The Re‚‚‚Re separation short-
ens from 3.4042(6) Å in 1 to 3.3917(7) Å in 2 as the
{Re2O2} core becomes more planar. (iv) As a result of
the opening up of the hinge angle of the Re-O‚‚‚O-Re
butterfly, the carbonyls trans to the phosphines no
longer have to bend away to avoid nonbonding contacts
(P-Re-C ) 167.1(3)° and Re-C-O ) 170.3(10)° in 1;
in 2 they are 178.3(4) and 176.6(14)°, respectively).
Equipped with the above structural data, we can
compare the solution dynamics of the title complexes.
Molecular models were constructed for 2-4 as shown
in Figure 2. Variable temperature 1H NMR experi-
ments were carried out for Re2(µ-OMe)(µ-PP)(CO)6 (PP
) dppm (2); dppe (3), dppp (4)) from 183 to 293 K
F igu r e 2. (A) Superimposed image of the crystal struc-
tures of Re2(µ-OMe)2(µ-PP)(CO)6 (PP ) dppf (1), and dppm
(2)). All phenyl rings are hidden. (B-D) Molecular-modeled
structures of the dppm, dppe, and dppp complexes, respec-
tively. The dppm complex is based on the single-crystal
X-ray structural data of this work. The structures of the
dppe and dppp complexes are proposed on the assumption
that the bridge fluxionality ceases.
confirmed that the diphosphine bridges of these com-
plexes undergo fluxional motion at room temperature.
The frozen configuration of 2 at 183 K, in which the
methylene bridge flips to one side of the Re2P2 plane,
possibly corresponds to the solid-state configuration. For
3, the ethylene bridge undergoes rapid fluxional motion
even at 183 K; the four ethylene protons are equivalent
in the temperature range studied. This implies the
symmetrical disposition of the ethylene bridge with
respect to the Re2P2 plane. In 4, the appearance of the
two inequivalent proton sets (Ha and Hb) at 183 K
directly confirms the fluxionality of the propylene
bridge. This complex is still nonrigid at 183 K. The
frozen structure is projected as shown in Figure 2D. In
our earlier study of the dppf complex,8 the fluxionality
of the dppf bridge was found to be controlled primarily
by the combined effects of torsional strains and the
interaction between the ferrocenyl C5 planes and phenyl
rings. For the present three complexes, the fluxionali-
ties for the conversion of the enantiomers are suggested
to be controlled by correlated bond rotation and torsional
motion.
1
Additional features are noted in the H NMR spectra
of 2 and 3. The methoxo peak in 2 is partially resolved
into two inequivalent groups at 183 K. With the
methylene bridge tilted to one side of the Re2P2 plane,
the two methoxo groups are differentiable (see Figure
2B) and two resonances begin to emerge at low tem-
perature. Interaction between a methylene proton (Ha)
1
(Figure 3). The assignment of the H NMR spectra is
given in the structures shown in Figure 2. The results

1372 Organometallics, Vol. 15, No. 5, 1996
Low et al.
F igu r e 4. Plots of the weight distribution fw(Rh) versus
the hydrodynamic radius Rh for the dppe complex after it
stood for 2.5 h in solution.
of the complex. One possibility which could account for
the anomalous NMR spectral feature is the formation
of clusters through association and/or aggregation. To
obtain an insight into this observed behavior, dynamic
DLS measurements (Appendix) of complexes 2-4 in
CH2Cl2 were carried out. In agreement with the NMR
data, there is no aggregate formation for 2 (dppm) but
there is a small tendency for 4 (dppp) to aggregate in
CH2Cl2. For 3 (dppe), the result conclusively confirms
the cluster formation on aggregation in dichloromethane.
By the end of the first 1 h of data collection, a broad
distribution of particles centered at Rh ∼1 nm is
detected. By the end of the 2.5 h period, aggregates are
formed with a particle size distribution centered at ∼370
nm. Since DLS is not very accurate in the size range
of 0.2-1 µm, especially when the sample is broadly
distributed, our DLS results showed only that there
exist some large aggregates in the solution. Figure 4
shows a differential weight distribution of the dppe
aggregates after 2.5 h. These results suggest that
aggregate formation which gives rise to differences in
the local environment is responsible for the broadening
F igu r e 3. H NMR spectra of Re2(µ-OMe)2(µ-PP)(CO)6 (PP
) dppm (A, B), dppe (C, D) and dppp (E, F) at 293 and 183
2
K. At 293 K, Ha and Hb are equivalent and the J P-H
a,b
values for the dppm and dppe complexes are determined
to be 11.4 and 7.8 Hz, respectively. For the dppp complex,
2
3J H-H and J P-H are determined to be 7.4 and 6.1 Hz,
respectively, at 293 K.
in the alkyl bridge and a methoxo proton (shown by the
broken lines connecting the proton pairs in Figure 2B)
consequently distinguishes it from the other methylene
proton (Hb). A similar methylene-methoxo interaction
is also expected in 3 (Figure 2C) and 4 (Figure 2D).
However, this interaction is stronger in 2 and 4 com-
pared to 3, as the closest contacts are determined to be
3.2 Å (2), 4.4 Å (3), and 3.3 Å (4). The methoxo protons
1
in the H NMR spectrum. The chemical origin of this
aggregation is unclear at present, but to our knowledge
this is the first experimental evidence for aggregation
of an organometallic complex in solution demonstrated
by a combination of DLS and NMR.21 Further work is
in progress to elucidate the species responsible for this
observed behavior.
The use of amine oxide in stoichiometric decarbony-
lation is well-known.22 It has also been reported
recently that Me3NO can induce disproportionation of
Re2(CO)10.23 The present synthesis, however, does not
require the stoichiometric presence of amine oxide. The
experimentally optimized Re2:Me3NO ratio of 1.0:2.4 is
significantly short of the theoretical ratio of 1:4. This
1
are not resolved in the H spectrum of 4. This can be
understood on the basis of the frozen structure (Figure
2D), in which a C2 axis is located along the central
methylene carbon and the center of the Re2O2 core. The
two methoxo groups are hence equivalent in this model.
Relatively normal phosphorus angles, Calkyl bridge-P-
Re, are obtained for 2 (∼113°) and 4 (∼118°). For 3, a
surprisingly high value for this angle (∼144°) suggests
large angular strain. It can be relieved if the staggered
conformation of the ethylene bridge is relaxed and/or
the folding of the {Re2O2} core is increased.
A second feature to be noted is the 1H NMR spectrum
of the methylene protons (δ(1H) 2.4 ppm) in the dppe
complex 3. It consists of a sharp doublet superimposed
on a broad peak with a half-height line width of 0.1 ppm.
There was no visible precipitation in the sample when
the NMR experiment was completed (minutes). On the
basis of the results of both 1H{31P} and 2D 1H-31P
COSY experiments, the presence of impurities or byprod-
ucts was ruled out. Molecular weight measurement of
a fresh solution (toluene) was also consistent with the
formulation of a dimeric complex. There is no chemical
evidence which could support the breakdown of the
{Re2O2} core to its monomeric form or polymerization
(21) One reviewer kindly drew our attention to the following
paper: Nelson, W. H.; Howard, W. F., J r.; Pecora, R. Inorg. Chem.
1982, 21, 1483. This work describes the use of depolarized Rayleigh
scattering in the study of Rayleigh intensity line shapes for SnBu2-
(dbzm)2 and Sn(Cyhex)(dbzm)2 (dbzm ) dibenzoylmethane). It gives
information on the structure and geometry of the complexes but bears
little relation to our work.
(22) Albers, M. O.; Coville, N. J . Coord. Chem. Rev. 1984, 53, 227-
259. Luh, T.-Y. Coord. Chem. Rev. 1984, 60, 255-276. Hor, T. S. A.;
Chan, H. S. O.; Tan, K. L.; Phang, L.-T.; Yan, Y. K.; Liu, L.-K.; Wen,
Y.-S. Polyhedron 1991, 10, 2437-2450. Hor, T. S. A.; Phang, L.-T. J .
Organomet. Chem. 1989, 373, 319-324. Hor, T. S. A. J . Organomet.
Chem. 1988, 340, 51-57. Hor, T. S. A.; bte Rus, S. R. J . Organomet.
Chem. 1988, 348, 343-347. Shen, J .-K.; Gao, Y.-C.; Shi, Q.-Z.; Basolo,
F. Coord. Chem. Rev. 1993, 128, 69-88 and references therein.
(23) Christie, S. D.; Clerk, M. D.; Zaworotko, M. J . J . Crystallogr.
Spectrosc. Res. 1993, 23, 591-594.

Substituted Metal Carbonyls
Organometallics, Vol. 15, No. 5, 1996 1373
on a Bruker AMX-500 spectrometer at 125.76 MHz. All IR
spectra were recorded in CHCl3 solution on an FT-IR Perkin-
Elmer 1600 spectrometer. Elemental analyses were performed
by the microanalytical laboratory of the Chemistry Depart-
ment at the National University of Singapore. Molecular
weight determination was carried out by vapor-pressure
osmometry in a Knauer-Dampfdruck osmometer by Galbraith
Laboratories, Inc., in Knoxville, TN, using toluene as solvent.
The presence of CH2Cl2 as a solvate molecule was confirmed
by NMR spectroscopy of the sample solutions in CDCl3.
Molecu la r Mod elin g Stu d ies. All molecular modeling
work was carried out on a Silicon Graphics Indigo II Extreme
workstation using the software SYBYL (version 6.04) licensed
from Tripos Associates Inc., St. Louis, MO. Single-crystal X-
ray data were used for the construction of the dppm and dppf
complexes in Figure 2. For the construction of the dppe and
dppp analogues, standard bond lengths and angles were used.
Typical bond lengths and the associated angles were used for
the C-H and C-P bonds. The Re-P distance of the dppm
complex was used to construct the dppe and dppp counter-
is not surprising, as nucleophilic substitution of carbonyl
can be induced by methoxo attack. Carbonyl labiliza-
tion can also be promoted by methoxycarbonyl24 forma-
tion (from direct attack of methoxide on the carbonyl
carbon25 ). When more Me3NO is added, or when the
mixture is doped with NEt3 in a hope to promote further
decarbonylation, the product yields are significantly
lower. We attribute this to the formation under these
conditions of the tribridged species [Re2(µ-OMe)3-
(CO)6]-,26 which does not easily undergo substitution
with the diphosphine to give the desired product.
The low yield of the dppb complex 5 is indicative of
the upper limit of the chain length of the diphosphine
which can be tolerated by the Re2(µ-OMe)2 core. In
agreement with this, the use of diphosphines with
longer chain length, namely, bis(diphenylphosphino)-
pentane and -hexane, failed to give any major charac-
terizable products. What seems surprising is that the
use of PPh3 in these syntheses gives no isolable products
except Re2(CO)10-n(PPhn) (n ) 1-3) in low yields. There
is no evidence for the formation of the expected product
Re2(µ-OMe)2(PPh3)2(CO)6. The importance of the bridg-
ing diphosphine in the stabilization of these methoxo-
bridged complexes is thus evident.
parts. Furthermore, it was assumed that (i) the Re
2O2 core of
the dppe and dppp complexes is similar to that of the dppm
complex and (ii) the ethylene and propylene bridges adopt the
staggered (thermodynamically more stable) conformation.
Support for the validity of these assumptions is derived from
1
the variable-temperature H NMR spectra for both dppe and
dppp complexes. A least-squares method was used to fit the
Re2O2 core of the dppm complex with that of the dppf analogue.
Dyn a m ic La ser -Ligh t Sca tter in g (DLS) In str u m en ta -
tion a n d Mea su r em en ts. For dynamic DLS measurements
of the dppe complex, the sample was prepared in CH2Cl2 at
the same concentration (5 mg/mL) at which the NMR spectrum
was recorded. It was then filtered through a Millipore 0.5 µm
LCR filter for dust removal. A commercial DLS spectrometer
(ALV-5000, Langen in Hessen, Germany) equipped with a fast
correlator card (minimum sample time is 12.5 ns) was used
for measurements. A Nd:YAG laser (ADLAS DPY 42511)
operated at 532 nm and 400 mW was used as the light source.
The primary beam was vertically polarized. Scattered inten-
sity was taken at 45° to the incident beam. With this DLS
spectrometer, we are able to determine the particle size down
to 1 nm. Details of the instrumentation employed in this study
have been published elsewhere.27 The correlation function was
accumulated until the difference between the measured and
calculated base lines was less than 0.1%. In this study, the
measured average line width Γ was linearly scaled by the
Con clu sion s
The Re2(µ-OMe)2(µ-PP)(CO)6 system proved to be a
good model for structural and solution dynamic com-
parisons for bridging diphosphines in a dinuclear frame.
The facile assembly and geometrical tolerance of the
Re2(µ-OMe)2 core are unexpected. This has encouraged
us to examine other related alkoxo systems; these
studies are presently in progress. What seems most
surprising is the aggregation phenomenon and its
verification by DLS. The potential of DLS in organo-
metallics is rich and awaits further exploitation. What
we reported here may not be a rare phenomenon, and
perhaps there should be reexamination of some of the
abnormal NMR peak broadenings in many literature
complexes in light of the present findings.
square of the scattering vector q, namely
Γ
q2, which
Exp er im en ta l Section
indicated that the relaxation is diffusive. To extract the
diffusion coefficient D (see Appendix), G(Γ) is calculated by
using the Laplace inversion program CONTIN.28 For readers
who are unfamiliar with the DLS technique, we have included
in the Appendix some detailed information. For the calcula-
tion of the hydrodynamic radius Rh in CH2Cl2, a value of 0.433
was used for the viscosity η.
Gen er a l Con sid er a tion s. All reactions were performed
under Ar using standard Schlenk techniques. Chemical
reagents were supplied from commercial sources and used
without further purification. Trimethylamine oxide (TMNO)
are used in its dihydrate form. Precoated silica plates of layer
thickness 0.25 mm were obtained from Merck or Baker.
Solvents used were reagent grade and were freshly distilled
under N2 before use. 1H NMR spectra were recorded on a
Bruker ARX-500 superconducting FT-NMR spectrometer op-
erating at a proton frequency of 500.13 MHz. All complexes
were dissolved in 0.5 mL of 99.6% CD2Cl2. The chemical shift
was referenced to the residual CH2Cl2 signal, which was set
at 5.3 ppm at room temperature. Variable-temperature NMR
measurements were made after the sample was equilibrated
for 1 h at 293, 253, 223, 203, 193, 188, and 183 K. 31P NMR
spectra were recorded on a Bruker ACF 300 MHz spectrometer
at 121.50 MHz. Chemical shifts are reported in ppm to a high
frequency of external H3PO4. 13C NMR spectra were recorded
Syn th esis. Re2(µ-OMe)2(µ-d p p m )(CO)6 (2). Separation
by TLC (CH2Cl2/hexane, 1:4) after reaction of TMNO·2H2O
(0.164 g, 1.47 mmol), Re2(CO)10 (0.400 g, 0.61 mmol) and dppm
(0.236 g, 0.61 mmol) gave fine white crystals of Re2(µ-OMe)2-
(µ-dppm)(CO)6 (mp 207-208 °C) as the main product after
recrystallization with CH2Cl2/hexane (0.205 g, 34%). IR:
v(CO) 2027 vs, 2013 s, 1927 m, 1912 m, 1895 vs cm-1 (toluene).
1H NMR: δ 7.36-7.19 (m, 20H, Ph), 4.32 (s, 6H, OMe), 3.14
2
(t, 2H, CH2, J P-H ) 11.3 Hz). 31P NMR δ 9.67 (s). 13C NMR:
δ 14.30 (t, CH2, J C-P ) 9.2 Hz), 74.83 (s, OMe), 128.71 (d, Ph,
C
meta, J C-P ) 9.5 Hz), 130.67 (s, Ph, Cpara), 132.40 (d, Ph, CH,
J C-P ) 48.0 Hz), 132.40 (d, Ph, Cortho, J C-P ) 11.4), 194.22 (d,
CO trans P, J C-P ) 83.3 Hz), 196.09 (s, CO cis P). Anal. Calcd
for C33H28O8P2Re2: C, 40.16; H, 2.86; P, 6.28. Found: C, 40.13;
H, 2.63; P, 6.38.
(24) Darensbourg, D. J . Adv. Organomet. Chem. 1982, 21, 113-150.
(25) Angelici, R. J . Acc. Chem. Res. 1972, 5, 335-341. Gross, D. C.;
Ford, P. C. J . Am. Chem. Soc. 1985, 107, 585-593. Trautman, R. J .;
Gross, D. C.; Ford, P. C. J . Am. Chem. Soc. 1985, 107, 2355-2362.
(26) Freni, M.; Romiti, P. Atti Accad. Naz. Lincei, Mem., Cl. Sci.
Fis., Mat. Nat., Rend. 1973, 55, 515. Ginsberg, A. P.; Hawkes, M. J . J .
Am. Chem. Soc. 1968, 90, 5930-5932.
R e2(µ-OMe)2(µ-d p p e)(CO)6‚CH2Cl2 (3). A solution of
(27) Wu, C.; Xia, K. Q. Rev. Sci. Instrum. 1994, 65, 587-590.
(28) Provencher, S. W. Biophys. J . 1976, 16, 29; J . Chem. Phys. 1976,
64, 2772-2777; Makromol. Chem. 1979, 180, 201.

1374 Organometallics, Vol. 15, No. 5, 1996
Low et al.
TMNO·2H2O (0.060 g, 0.54 mmol) in THF/MeOH (1:1; 20 cm3)
was transferred to a stirred solution of Re2(CO)10 (0.150 g, 0.23
mmol) in 20 cm3 of THF. The resultant yellow solution was
stirred in vacuo for 4 h at room temperature. Solid dppe (0.092
g, 0.23 mmol) was added. The reaction mixture was stirred
for 1 h in vacuo, after which half the volume of solvent was
removed and the solution was further stirred for 3 h under
Ar. The solution was evaporated to dryness and the residue
redissolved in the minimum amount CH2Cl2. Separation by
TLC using CH2Cl2/hexane (1:4) as eluent affords fine white
crystals of Re2(µ-OMe)2(CO)6(µ-dppe)·CH2Cl2 (mp 204-206 °C
dec) after recrystallization with CH2Cl2/hexane (0.067 g, 29%).
IR: v(CO) 2026 vs, 2010 s, 1925 m, 1903 vs (sh), 1890 vs (br)
Ta ble 1. Cr ysta llogr a p h ic Da ta for
[Re2(µ-OMe)2(µ-d p p m )(CO)6] (2)
chem formula: [Re2(µ-OMe)2(µ-Ph2PCH2PPh2)(CO)6]
fw: 986.93
space group: P41
a ) 16.686(1) Å
b ) 16.686(1) Å
c ) 12.547(1) Å
R ) 90°
â ) 90°
γ ) 90°
V ) 3493.3(3) Å3
Z ) 4
T ) 25 °C
cm-1
.
1H NMR (CDCl3) δ 7.47-7.50 (m, 20H, Ph), 5.30 (s, 2H,
λ ) 0.709 30 Å
Fcalcd ) 1.877 g cm-3
µ ) 7.15 mm-1
R(Fo)a ) 0.021
Rw(Fo)b ) 0.024
2
CH2Cl2), 4.29 (s, 6H, OMe), 2.47 (d, 4H, CH2, J P-H ) 7.8 Hz).
31P NMR: δ 15.24 (s). 13C NMR: δ 16.60 (d, CH2CH2, J C-P
21.4 Hz), 73.27 (s, OMe), 128.90 (s, Ph, Cmeta), 130.75 (s, Ph,
para), 132.48 (s, Ph, Cortho), 133.66 (d, Ph, C-P, J C-P ) 44.1
)
C
a
b
2
R ) ∑||Fo| -|Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
Hz), 193.82 (d, CO trans P, J C-P ) 83.2 Hz), 195.59 (s, CO
cis P). Mol wt: found, 1042; calcd, 1003. Anal. Calcd for
Ta ble 2. Selected F in a l F r a ction a l Coor d in a tes for
C
35H32Cl2P2O8Re2: C, 38.72; H, 2.97; P, 5.71. Found: C, 38.97;
[Re2(µ-OMe)2(CO)6(µ-d p p m )] (2)
H, 2.90; P, 6.43.
Re2(µ-OMe)2(µ-d p p p )(CO)6 (4). The dppp analogue was
prepared in the same manner from TMNO‚2H2O (0.125 g,
1.13 mmol), Re2(CO)10 (0.301 g, 0.46 mmol) and dppp (0.189
g, 0.46 mmol). Separation by TLC (CH2Cl2/hexane, 35:65) gave
Re2(µ-OMe)2(µ-dppp)(CO)6 as the main product after recrys-
tallization from a CH2Cl2/hexane mixture (0.133 g, 28%). IR:
atom
x
y
z
Re(1)
Re(2)
P(1)
P(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
0.03093(3)
0.14215(3)
0.14623(17)
0.2480(2)
-0.1116(7)
0.0034(6)
-0.0957(7)
0.0118(7)
0.2624(7)
0.1682(8)
0.0632(4)
0.1216(4)
-0.0562(8)
0.0161(7)
-0.0472(8)
0.0604(10)
0.2174(8)
0.1586(9)
-0.0011(9)
0.1195(9)
0.2432(6)
0.74524(3)
0.61457(3)
0.75811(17)
0.63550(18)
0.7359(8)
0.9260(6)
0.7296(8)
0.5928(8)
0.6396(7)
0.4339(6)
0.6205(4)
0.7390(4)
0.7365(8)
0.8576(8)
0.7377(9)
0.6021(9)
0.6275(7)
0.5035(8)
0.5626(8)
0.7929(8)
0.7330(6)
0.15514
0.30004(5)
0.03079(30)
0.16447(35)
0.3118(12)
0.1612(12)
-0.0175(10)
0.4712(10)
0.4808(8)
v(CO) 2026 vs, 2009 s, 1924 m, 1902 vs (sh), 1892 vs (br) cm-1
1H NMR: δ 7.41-7.50 (m, 20H, Ph), 4.34 (s, 6H, OMe), 2.35
.
2
3
(dt, 4Ha,b, J P-H ) 6.1 Hz, J H
) 7.4 Hz), 1.44 (m, 2Hc). 31P
H
a-
b
NMR δ 11.43 (s). 13C NMR: δ 18.44 (s, CHc), 21.18 (dd, CHa,b
J C-P ) 16.4 Hz, J C-P′ ) 4.4 Hz), 72.55 (s, OMe), 128.64 (d, Ph,
meta, J C-P ) 9.2 Hz), 130.37 (s, Ph, Cpara), 132.72 (d, Ph, Cortho
J C-P ) 10.2 Hz), 135.00 (d, Ph, C-P, J C-P ) 42.9 Hz), 193.96
(d, CO trans P, J C-P ) 81.3 Hz), 195.27 (d, CO cis P, J C-P
6.2 Hz). Mol wt: found, 1046; calcd, 1017. Anal. Calcd for
35H32P2O8Re2: C, 41.41; H, 3.18; P, 6.10. Found: C, 41.38;
,
0.3163(13)
0.1644(8)
0.2745(6)
C
,
0.2541(13)
0.1588(11)
0.0457(13)
0.4048(14)
0.4127(12)
0.3069(13)
0.1568(15)
0.3647(10)
0.0966(9)
)
C
H, 3.15; P, 6.22.
Re2(µ-OMe)2(µ-d p p b)(CO)6‚CH2Cl2 (5). Separation by
TLC (CH2Cl2/hexane, 1:1) from a mixture of TMNO‚2H2O
(0.125 g, 1.13 mmol), Re2(CO)10 (0.301 g, 0.46 mmol), and dppb
(0.197 g, 0.46 mmol) yielded Re2(µ-OMe)2(µ-dppb)(CO)6·1/2CH2-
Cl2 as the main isolable product (0.020 g, 10%). IR: v(CO)
C33H28O8P2Re2, Mr ) 986.93, tetragonal, a ) 16.686(1) Å, c )
12.547(1) Å, V ) 3493.3(3) Å3, Z ) 4, Dc ) 1.877 Mg m-3, F(000)
) 1879.47, µ(Mo KR) ) 7.15 mm-1, λ ) 0.709 30 Å. The space
group determined from the systematic absences, is P41. The
crystal dimensions are 0.16 × 0.19 × 0.38 mm. Cell dimen-
sions were obtained from 25 reflections with 2θ in the range
16.20-36.20°.
Da ta Collection a n d P r ocessin g. A Nonius diffractome-
ter in the θ-2θ mode, with graphite-monochromated Mo KR
radiation, was used. A total of 2599 reflections was measured,
of which 2407 were unique. Data were collected at 298 K to
a maximum 2θ value of 44.8°. The ranges of indices were h
0-17, k 0-17, and l 0-13. The diffraction intensities were
measured with background counts made for half the total scan
time on each side of the peak. Three standard reflections,
remeasured after every 1 h, showed no significant decrease
in intensity during the data collection. After corrections for
Lorentz-polarization and absorption effects (empirical ψ
corrections), 2056 data were used with I > 3.0σ(I). The
minimum and maximum transmission factors were 0.920 and
0.998.
2024 vs, 2007 s, 1921 m, 1896 vs (br) cm-1
.
1H NMR: δ 7.47-
7.38 (m, 20H, Ph), 5.30 (s, 1H, CH2Cl2), 4.25 (s, 6H, OMe),
3
2.52 (dt, 4Houter,
2J P-H ) 7.9 Hz, J H-H ) 6.9 Hz), 1.50 (m,
4Hinner). 31P NMR: δ 8.35 (s). Mol wt: found, 1383; calcd,
1032. Anal. Calcd for C36.5H35ClP2O8Re2: C, 40.91; H, 3.29;
P, 5.78. Found: C, 40.85; H, 3.17; P, 6.12.
Rea ction of Re2(CO)10 w ith P P h 3. Re2(CO)10 (0.271 g,
0.42 mmol) was mixed and reacted with PPh3 (0.213 g, 0.81
mmol) in a similar manner for ca. 18 h. Separation by TLC
(CH2Cl2/hexane, 1:4) yielded four products. In decreasing Rf
value, the first major band is unreacted PPh3. The second
band on recrystallization with CH2Cl2/hexane gave Re2(CO)9-
(PPh3) (0.016 g, 4%). IR: v(CO) 2105 w, 2033 w, 1995 vs, 1960
w, 1936 m cm-1 (CH2Cl2). 1H NMR: δ 7.42-7.47 (m, 15H,
Ph). 31P NMR δ 15.53 (s). Anal. Calcd for C27H15O9PRe2: C,
36.57; H, 1.70. Found: C, 36.53; H, 1.73. The third band is
Re2(CO)8(PPh3)2 (0.005 g, 1%). IR: v(CO) 2006 w, 1955 s cm-1
(CH2Cl2). 1H NMR δ 7.36-7.50 (m, 30H, Ph). 31P NMR: δ
17.61 (s). Anal. Calcd for C42H30O8P2Re2: C, 45.98; H, 2.75.
Found: C, 46.90; H, 2.59. The final band was Re2(CO)7(PPh3)3
(0.012 g, 2%). IR: v(CO) 2107 w, 2017 (sh) m, 2004 m, 1950
vs, 1906 m cm-1 (CH2Cl2); 1H NMR δ 7.16-7.47 (m, 30H, Ph),
7.62-7.70 (m, 15H, Ph). 31P NMR: δ 9.07 (s), 6.19 (s). Anal.
Calcd for C62.5H48.5O7P3Re2: C, 54.52; H, 3.55. Found: C,
55.78; H, 3.57.
Str u ctu r a l An a lysis a n d Refin em en t. The structure was
solved by direct methods and MULTAN.29 Refinement was
by full-matrix least-squares calculations with all non-hydrogen
atoms allowed anisotropic motion. All hydrogen atoms were
fixed as isotropic ellipsoids in the final cycles of least-squares
refinement. The last least-squares cycle was calculated with
Cr ysta l Str u ctu r e Deter m in a tion of [Re2(µ-OMe)2(µ-
d p p m )(CO)6] (2). Single colorless crystals suitable for an
X-ray diffraction study were grown from a sample solution in
a mixture of CH2Cl2/hexane at ∼-20 °C. Crystal data:
(29) Main, P.; Fiske, S. E.; Hull, S. L.; Germain, G.; Declerq, J . P.;
Woolfson, M. H. In MULTAN, a System of Computer Programs for
Crystal Structure Determination from X-ray Diffraction Data; Uni-
versities of York and Louvain, 1980.

Substituted Metal Carbonyls
Organometallics, Vol. 15, No. 5, 1996 1375
Ta ble 3. Selected bon d len gth s (Å) a n d An gles
(d eg) a n d Tor sion a l An gles (d eg) for
[Re2(µ-OMe)2(CO)6(µ-d p p m )] (2)
We appreciate assistance from Y. P. Leong in the
preparation of this paper.
Bond Distances
Ap p en d ix
Re(1)-P(1)
Re(1)-O(7)
Re(1)-O(8)
Re(1)-C(1)
Re(1)-C(2)
Re(1)-C(3)
Re(2)-P(2)
Re(2)-O(7)
Re(2)-O(8)
Re(2)-C(4)
Re(2)-C(5)
Re(1)···Re(2)
2.486(3)
2.154(7)
2.132(8)
1.917(16)
1.892(13)
1.897(15)
2.477(4)
2.154(9)
2.129(7)
1.905(17)
1.902(16)
3.3917(7)
Re(2)-C(6)
P(1)-C(9)
P(2)-C(9)
O(1)-C(1)
O(2)-C(2)
O(3)-C(3)
O(4)-C(4)
O(5)-C(5)
O(6)-C(6)
O(7)-C(7)
O(8)-C(8)
1.876(14)
1.864(11)
1.838(11)
1.175(19)
1.160(16)
1.142(19)
1.174(21)
1.156(19)
1.177(17)
1.446(14)
1.445(14)
In dynamic laser-light scattering (DLS), the intensity-
intensity time correlation function G(2)(t) in the self-
beating mode is measured which has the form
G(2)(t) ) A[1 + â|g(1)(t)| ]
where A is a measured base line; â is a parameter
depending on the coherence of the detection, t is the
delay time, and g(1)(t), the normalized first-order electric
field time correlation function. In general, g(1)(t) is
related to the line width distribution G(Γ) by
2
Bond Angles
P(1)-Re(1)-O(7)
P(1)-Re(1)-O(8)
85.64(22) O(7)-Re(2)-C(6)
99.8(5)
95.4(5)
96.1(4)
173.9(5)
88.4(7)
88.0(7)
89.0(6)
112.0(4)
114.3(3)
84.03(21) O(8)-Re(2)-C(4)
g(1)(t) ) ∫ G(Γ)e-Γt dΓ
P(1)-Re(1)-C(1) 178.4(4)
O(8)-Re(2)-C(5)
O(8)-Re(2)-C(6)
C(4)-Re(2)-C(5)
C(4)-Re(2)-C(6)
C(5)-Re(2)-C(6)
Re(1)-P(1)-C(9)
Re(2)-P(2)-C(9)
P(1)-Re(1)-C(2)
P(1)-Re(1)-C(3)
O(7)-Re(1)-O(8)
O(7)-Re(1)-C(1)
91.8(4)
94.8(4)
74.8(3)
94.7(5)
G(Γ) can be calculated from the measured G(2)(t) by a
Laplace inversion. For a diffusive relaxation, Γ is
further related to the translational diffusion coefficient
D of the particle by
O(7)-Re(1)-C(2) 171.7(4)
O(7)-Re(1)-C(3)
O(8)-Re(1)-C(1)
O(8)-Re(1)-C(2)
98.4(5)
94.6(5)
97.1(4)
Re(1)-O(7)-Re(2) 103.9(3)
Γ ) Dq2
Re(1)-O(7)-C(7)
Re(2)-O(7)-C(7)
117.1(8)
118.4(9)
O(8)-Re(1)-C(3) 173.2(5)
C(1)-Re(1)-C(2)
C(1)-Re(1)-C(3)
C(2)-Re(1)-C(3)
P(2)-Re(2)-O(7)
P(2)-Re(2)-O(8)
87.7(6)
86.7(6)
89.6(6)
Re(1)-O(8)-Re(2) 105.5(3)
where
Re(1)-O(8)-C(8)
Re(2)-O(8)-C(8)
120.2(7)
119.5(7)
175.5(13)
177.1(11)
176.4(13)
177.7(14)
176.5(11)
176.8(15)
116.3(6)
q ) (4πn/λ0) sin(θ/2)
83.53(23) Re(1)-C(1)-O(1)
82.77(21) Re(1)-C(2)-O(2)
is the scattering vector with n, λ0, and θ being the
refractive index of the solvent, the light wavelength, and
the scattering angle, respectively.
D can be further converted to the hydrodynamic
radius (1/Rh)-1, or simply Rh, by the Stokes-Einstein
equation:
P(2)-Re(2)-C(4) 178.2(4)
Re(1)-C(3)-O(3)
Re(2)-C(4)-O(4)
Re(2)-C(5)-O(5)
Re(2)-C(6)-O(6)
P(1)-C(9)-P(2)
P(2)-Re(2)-C(5)
P(2)-Re(2)-C(6)
O(7)-Re(2)-O(8)
O(7)-Re(2)-C(4)
91.4(4)
93.8(5)
74.8(3)
96.4(6)
O(7)-Re(2)-C(5) 170.1(4)
Dihedral Angles
Re(1)‚‚‚Re(2)-P(2)‚‚‚P(1) ) Re(2)‚‚‚Re(1)-P(1)‚‚‚P(2)
O(7)-Re(1)‚‚‚Re(2)-O(8)
2.3(1)
12.3(5)
9.4(3)
D ) kBT/6πηRh
Re(1)-O(7)‚‚‚O(8)-Re(2)
In this equation, kB is the Boltzmann constant, T is the
absolute temperature, and η is the solvent viscosity.
Therefore, G(Γ) can be converted into a hydrodynamic
radius distribution fz(Rh). The subscript z indicates that
this distribution is an intensity distribution. This can
then be further converted to the weight distribution fw-
(Rh), where fw(Rh) ) {fz(Rh)/Rh3}/Σ{fz(Rh)/Rh3}.
73 atoms, 406 parameters, and 2056 out of 2407 reflections
and converged with RF ) 0.021, R′ ) 0.024 (for all reflections,
R ) 0.036 and R' ) 0.025). The goodness of fit is 1.04.
Weights based on counting statistics were used. The weight
modifier was 0.000 100. The maximum shift/error ratio was
0.006. In the last difference map the deepest hole was -0.310
e Å-3, and the highest peak 0.470 e Å-3. Computations were
carried out on a Microvax 3600 computer with the NRCC
package. Final atomic coordinates and selected bond distances
and angles are listed in Tables 2 and 3, respectively.
Su p p or tin g In for m a tion Ava ila ble: Details of the X-ray
structural analysis for [Re2(µ-OMe)2(µ-dppm)(CO)6], including
tables of crystallographic data, refined atomic coordinates and
isotropic thermal parameters, anisotropic thermal parameters,
bond distances and angles, and torsion angles (10 pages).
Ordering information is given on any current masthead page.
Listings of structure factors (9 pages) can be obtained from
L.-K.L.
Ack n ow led gm en t. We acknowledge the National
University of Singapore (NUS) (Grant No. RP850030)
for financial support and technical assistance from the
Department of Chemistry, NUS. Scholarship awards
from NUS to P.M.N.L. and Y.K.Y. are acknowledged.
OM9506779