Synthesis and Conformational Behavior of Rhodium(I) Metallohosts Derived from Diphenylglycoluril

Article abstract of DOI:10.1021/jo9505583

The design and synthesis of molecules containing both a substrate-binding cavity and a nearby catalytically active metal center is a useful approach to the development of synthetic systems that function according to the principles of enzymes.To this end the receptor molecule 2a, derived from diphenylglycoluril, was functionalized with triaryl phosphite ligands to give the recoptor ligand 2d. exchange reactions of 2d with (diketonate)Rh(CO)2, (diketone = acetylacetone, dibenzoylmethane, or dipivaloylmethane) led to the formation of the metallohosts 3a-c, respectively.The properties and conformational behavior of these metal complexes were studied by NMR techniques.Reaction of compounds 3 with H2 in the presence of a small excess of additional triphenyl phosphite yields the rhodium(I) hydride complex 5.The metallohosts are capable of binding dihydroxybenzene guests in their cavities by hydrogen bonding and ?-? stacking interactions.On binding a substrate the conformational behavior of hosts 3a-c was affected considerably.

Full text of DOI:10.1021/jo9505583

J . Org. Chem. 1996, 61, 4739-4747
4739
Syn th esis a n d Con for m a tion a l Beh a vior of Rh od iu m (I)
Meta lloh osts Der ived fr om Dip h en ylglycolu r il
Hein K. A. C. Coolen,† Piet W. N. M. van Leeuwen,‡ and Roeland J . M. Nolte*,†
Department of Organic Chemistry, Nijmegen SON Research Center, Toernooiveld, 6525 ED Nijmegen,
The Netherlands, and Department of Chemical Engineering, J . H. van’t Hoff Instituut,
University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
Received March 23, 1995 (Revised Manuscript Received February 16, 1996X)
The design and synthesis of molecules containing both a substrate-binding cavity and a nearby
catalytically active metal center is a useful approach to the development of synthetic systems that
function according to the principles of enzymes. To this end the receptor molecule 2a , derived
from diphenylglycoluril, was functionalized with triaryl phosphite ligands to give the receptor ligand
2d . Exchange reactions of 2d with (diketonate)Rh(CO)2, (diketone ) acetylacetone, dibenzoyl-
methane, or dipivaloylmethane) led to the formation of the metallohosts 3a -c, respectively. The
properties and conformational behavior of these metal complexes were studied by NMR techniques.
Reaction of compounds 3 with H2 in the presence of a small excess of additional triphenyl phosphite
yields the rhodium(I) hydride complex 5. The metallohosts are capable of binding dihydroxybenzene
guests in their cavities by hydrogen bonding and π-π stacking interactions. On binding a substrate
the conformational behavior of hosts 3a -c was affected considerably.
In tr od u ction
hosts6 with metal centers have been described in the
literature., e.g. functionalized cyclodextrines,5a,7 capped
Current interest in the field of supramolecular chem-
istry is focused on the design of advanced molecular
devices and catalytic systems. As a result of built-in
ordering or information the system or device is intended
to perform certain actions, mostly based on and inspired
by biological processes. Macrocyclic rings and molecular
cages have been synthesized and explored for applica-
tions such as selective recognition,1 transport,2 switch-
ing,3 self-replication,4 and catalysis.1b,5 For a supramo-
lecular catalyst, a host is required that recognizes the
substrate selectively and contains a nearby catalytic
center that can convert the bound substrate, and finally,
the catalyst should be able to release the product and
have the property to be regenerated efficiently. Our
objective is to develop these systems by the design and
synthesis of molecules containing both a cavity and a
catalytically active metal center. Several examples of
porphyrins,6,8 and modified cyclophanes.1b
In this paper we decribe host molecules that are
provided with a nearby Rh(I)-triorganyl phosphite com-
plex. They are synthesized from the clip molecule 1a ,
which is derived from diphenylglycoluril.9 These metal-
lohosts are selective hydrogenation and isomerization
catalysts for dihydroxy-substituted allylarene substrates,
as will be described in a separate paper.10
Resu lts a n d Discu ssion
Design . The substrate-binding moiety of our metal-
lohosts is molecule 2a (R ) H), previously reported by
us.11 The central part of this molecule has the form of a
clip (see Figure 1).12 The two side walls of 1a are
connected by azatetrakis(ethylene glycol) chains, giving
the molecule the structure of a basket. The nitrogen
atoms in the rings can be used to functionalize the basket
with metal binding ligands, viz. by connecting them via
spacers. The form and the length of the spacers will
define the final flexibility and property of the system.
Since the rings of 2a contain many hard donor atoms we
decided to connect soft donor ligands to the nitrogen
atoms in order to be able to distinguish between the two
ligating moieties (Pearson’s HSAB theorem13). The che-
late effect is expected to be small because of the large
† Nijmegen SON Research Center.
‡ J . H. van’t Hoff Institute.
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) (a) Gokel, G. W. Crown Ethers and Cryptands; Royal Society of
Chemistry: Cambridge, U.K., 1991. (b) Diederich, F. Cyclophanes;
Royal Society of Chemistry: Cambridge, U.K., 1991. For other
examples, see: (c) Fan, E.; Vanarman, S. A.; Kincaid, S. Hamilton, A.
D. J . Am. Chem. Soc. 1993, 115, 369. (d) Yoon, S. S.; Still, W. C. Ibid.
1993, 115, 823. (d) Rebek, J ., J r.; Nemeth, D. Ibid. 1985, 107, 6738.
(e) Schmitchen, F. P. Tetrahedron Lett. 1989, 30, 4493. (f) Dougherty,
D. A.; Stauffer, D. A. Science 1990, 250, 1558.
(2) See for example: (a) Nijenhuis, W. F.; Buitenhuis, E. G.; de J ong,
F.; Sudho¨lter, E. J . R.; Reinhoudt, D. N. J . Am. Chem. Soc. 1991, 113,
7963. (b) Pregel, M. J .; J ullien, L.; Lehn, J .-M. Angew. Chem. 1992,
104, 1695. (c) Roks, M. F. M.; Nolte, R. J . M. Macromolecules 1992,
25, 5398. (d) van Straaten-Nijenhuis, W. F.; van Doorn, A. R.;
Reichwein, A. M.; de J ong, F.; Reinhoudt, D. N. J . Org. Chem. 1993,
58, 2265. (e) Rebek, J ., J r.; Askew, B.; Nemeth, D.; Parris, K. J . Am.
Chem. Soc. 1987, 109, 2432.
(3) See for example: (a) Beer, P. D. Chem. Soc. Rev. 1989, 18, 409.
(b) Shinkai, S. Pure Appl. Chem. 1987, 59, 425. (c) Sabbatini, N.;
Guardigli, M.; Lehn, J .-M. Coord. Chem. Rev. 1993, 123, 201. (d)
Cobben, P. L. H. M.; Egberink, R. J . M.; Bomer, J . G.; Bergveld, P.;
Verboom, W.; Reinhoudt, D. N. J . Am. Chem. Soc. 1992, 114, 10573.
(4) (a) Nowick, J . S.; Feng, Q.; Tjivikua, T.; Ballester, P.; Rebek, J .,
J r. J . Am. Chem. Soc. 1991, 113, 8831. (b) Park, T. K.; Feng, Q.; Rebek,
J ., J r. Ibid. 1992, 114, 4529.
(6) Meade T. J .; Busch, D. H. Prog. Inorg. Chem. 1985, 33, 59.
(7) (a) Breslow, R.; Overman, L. E. J . Am. Chem. Soc. 1970, 92, 1075.
(b) Komiyama, M.; Matsumoto, Y. Chem. Lett. 1989, 719.
(8) (a) Baldwin, J . E.; Perlmutter, P. Top. Curr. Chem. 1984, 121,
181. (b) Mansuy, D. Pure Appl. Chem. 1987, 59, 759. (c) Groves, J . T.;
Viski, P. J . Am. Chem. Soc. 1989, 111, 8537; J . Org. Chem. 1990, 55,
3628. (d) Collman, J . P.; Zhang, X.; Lee, V. J .; Brauman, J . I. J . Chem.
Soc., Chem. Commun. 1992, 1647.
(9) Smeets, J . W. H.; Sijbesma, R. P.; Niele, F. G. M.; Spek, A. L.;
Smeets, W. J . J .; Nolte, R. J . M. J . Am. Chem. Soc. 1987, 109, 928.
(10) Coolen, H. K. A. C.; Meeuwis, J . A. M.; van Leeuwen, P. W. N.
M.; Nolte, R. J . M. J . Am. Chem. Soc. 1995, 117, 11906.
(11) (a) Smeets, J . W. H.; Sijbesma, R. P.; van Dalen, L.; Spek, A.
L.; Smeets, W. J . J .; Nolte, R. J . M. J . Org. Chem. 1989, 54, 3710. (b)
Smeets, J . W. H.; Visser, H. C.; Kaats-Richters, V. E. M.; Nolte, R. J .
M. Recl. Trav. Chim. Pays-Bas 1990, 109, 147.
(5) See for example: (a) Tabushi, I. Acc. Chem. Res. 1982, 15, 66.
(b) Anslyn, E.; Breslow, R. J . Am. Chem. Soc. 1989, 111, 8931. (c) Kelly,
T. R.; Bridger, T. J .; Zhao, C J . Am. Chem. Soc. 1990, 112, 8024. (d)
Walter, C. J .; Anderson, H. L.; Sanders, J . K. M. J . Chem. Soc., Chem.
Commun. 1993, 458.
(12) Sijbesma, R. P.; Bosman, W. P.; Nolte, R. J . M. J . Chem. Soc.,
Chem. Commun. 1991, 885.
S0022-3263(95)00558-5 CCC: $12.00 © 1996 American Chemical Society

4740 J . Org. Chem., Vol. 61, No. 14, 1996
Coolen et al.
The 1H NMR spectrum of the protonated derivative
2c‚2HCl in DMSO-d6 revealed a complex pattern for the
protons of the benzyl spacers. This result suggests that
also in this molecule one of the benzyl groups is clamped
between the walls. In contrast to 2c the exchange now
is slow on the NMR time scale. This feature may be the
result of various hydrogen bonds present in the molecule
(see Figure 2b), viz. a bond between a quaternized amine
and an adjacent carbonyl moiety on one side of the
glycoluril unit, a bond between a phenolic hydroxyl
function and a protonated amine on the other side of the
molecule, in which the former is the H-bond acceptor and
the latter the H-bond donor, and a hydrogen bond
between the last-mentioned phenolic hydroxyl group and
a carbonyl moiety in which the phenol group is the donor.
In the IR spectrum of 2c‚2HCl the stretching frequencies
of the carbonyl functions of the glycoluril unit had shifted
to νCdO ) 1691 cm-1 and an intense broad OH signal was
observed in the region from 3000 to 3600 cm-1. More-
over, a weak broad signal at 1900 cm-1 was visible, which
can be attributed to the tN+sH vibrations. All these
observations are in line with the structure proposed in
Figure 2b.
F igu r e 1. X-ray structure of 1a (see ref 12).
distance between the two ligands of modified 2a . In order
to avoid displacement of the bound metal center by
exchange with other ligands, the applied metal complex
must not be kinetically too labile. The combination of
rhodium(I) and triaryl phosphite ligands was felt to meet
the above-mentioned criteria.
Reaction of 2c with diphenyl phosphochloridite in CH2-
Cl2 with Et3N as a base gave the corresponding bis(triaryl
phosphite) 2d (96%). The same result was obtained with
2c‚2HCl when an excess of Et3N was used. Compound
2d was fully characterized by elemental analysis and
spectroscopic methods.
Syn th esis. The synthesis of the ligand system is
outlined in Scheme 1. The starting compound is tetrapo-
dand 1b.14 Double ring closure of 1b with 2 equiv of
p-(methoxymethoxy)benzylamine under high dilution
conditions in acetonitrile with Na2CO3 as a base gave 2b
(62% after column chromatography). The p-hydroxyben-
zylamine was prepared from cyanophenol according to a
standard procedure (see the Experimental Section).
Quantitative removal of the p-methoxymethyl groups of
2b was achieved with concentrated hydrochloric acid to
give 2c‚2HCl (Chart 1). This compound can be depro-
tonated with a NaHCO3/NaOH buffer of pH ) 9.8, albeit
with loss of product. CPK models suggest that in
deprotonated 2c an intramolecular hydrogen bond can
be formed between a phenolic hydroxyl function and a
tertiary amine group (see Figure 2a). Evidence for such
a bond was found in the infrared spectrum of 2c in CDCl3,
which displayed a relatively sharp signal for a free
phenolic hydroxyl function (ν ) 3604 cm-1) as well as a
broad signal for a hydrogen bonded one (ν ) 3327 cm-1).15
The concentration was taken such (ca. 8 mM) that
intermolecular hydrogen bonding could be excluded. The
Rh (I)-Dik eton a te Com p lexes. The addition of an
equimolar amount of (acac)Rh(CO)2 (Hacac ) acetylac-
etone) to a solution of ligand 2d in CHCl3 led to the
substitution of the carbonyl ligands in the rhodium
complex and the formation of metallocage 3a . The 31P
NMR spectrum of 3a displayed a set of four resonances
which had different intensities (Figure 3a and Table 1).
Space-filling models suggest that these signals may be
attributed to four different conformations of 3a prescribed
by the square-planar coordination of the metal center in
combination with the rigidity of the spacers. The inter-
conversions of these conformers, which will be discussed
below, require considerable rearrangements in the mol-
ecule. These interconversions are slow processes, as was
demonstrated by 31P NOESY. Since no cross peaks were
observed with a mixing time of 1 s, the lifetime of a single
conformation is at least that period.
When more than 1 equiv of (acac)Rh(CO)2 was added
to 2d an additional doublet became visible in the 31P
NMR spectrum at δ ) 117.8 (J Rh-P ) 292 Hz). We assign
this signal to the dirhodium complex 4, which is analo-
gous to the complex (acac)RhCO[P(OPh)3].17 This sug-
gests that the chelating ability of ligand system 2d is
moderate. No polymeric structures were formed. Ap-
parently, compound 4 is free of strain as only one doublet
in the 31P NMR spectrum was observed.
The geometrical isomers of 3a can be divided into two
sets in which the diketonate ligand has either an upward
(U) or a downward (D) orientation with respect to the
substrate-binding moiety (see Figure 4). One of the
conformers of the U set, the U1 form, is flexible: the
rhodium complex is situated above the cavity and can
twist easily. The metal center in this conformation is
very mobile with regard to the host molecule. In this
form the cavity is best accessible for a guest molecule.
stretching frequencies of the carbonyl functions of the
16
glycoluril unit (νCdO ) 1716 and 1692 cm-1
)
remained
unaffected, indicating that these are not involved in the
hydrogen bonding process. The protons of the benzyl
1
spacers gave rise to only one AB pattern in the H NMR
spectrum. Moreover, these signals had shifted to higher
field as compared to the ortho- and meta-proton signals
of the reference compound HOC6H4CH2NH2. On the
basis of these data, we propose that one of the p-
hydroxybenzyl groups of 2c is clamped between the side
walls of the cleft, as is shown in Figure 2a, and that the
in-out movement of this group is a rapid process on the
NMR time scale.
(13) (a) Pearson, R. G. J . Am. Chem. Soc. 1963, 85, 3533. (b)
Hancock, R. D.; Martell, A. E. Chem. Rev. 1989, 89, 1875.
(14) Sijbesma, R. P.; Nolte, R. J . M. Recl. Trav. Chim. Pays-Bas
1993, 112, 643.
(15) Vinogradov, S. N.; Linnell, R. H. Hydrogen Bonding; Van
Nostrand Reinhold Co.: New York, 1971; Chapters 3 and 6.
(16) The ν˜ (CdO) of the free host molecule is split into at least two
bands, probably caused by coupling of the CdO vibration with the CsN
stretching vibration. See: Sijbesma, R. P. Ph.D. Thesis, University of
Nijmegen, 1992, and ref 13.
(17) (a) Trzeciak, A. M.; Ziołkowski, J . J . Inorg. Chim. Acta 1982,
64, L267. (b) van Eldik, R.; Aygen, S.; Kelm, H.; Trzeciak, A. M.;
Ziołkowski, J . J . Trans. Met. Chem. 1985, 10, 167.

Rh(I) Metallohosts Derived from Diphenylglycoluril
J . Org. Chem., Vol. 61, No. 14, 1996 4741
Sch em e 1a
a
(i) ClCH2OCH3, CH2Cl2/H2O/NaOH/PTC; (ii) AlH3, THF; (iii) p-CH3OCH2OC6H4CH2NH2, Na2CO3/NaI, MeCN; (iv) THF/i-PrOH/HCl;
(v) ClP(OPh)2/Et3N, CH2Cl2.
The other conformer of the U set, (U2 form), is character-
ized by the fact that one of the phenyl groups of the
triphenyl phosphite ligands is located in the cleft of the
host molecule.
NMR and 31P NMR signals and taking into account the
different intensities we were able to make the assigments
listed in Table 1. In addition the following comments
can be made.
The U conformers can be converted into D conformers
by a process in which two phenyl rings of a phosphite
ligand pass through the ring formed by the rhodium
center, the spacer arms, and the receptor molecule. In
fact, the U2 form can be regarded as an intermediate on
the route of U1 to these D conformers.
Once in a downward position the diketonate ligand can
have two orientations. The most compact structure is
obtained when this ligand is located in the cavity (D1
conformer), but this arrangement is only possible for
diketonate ligands with small substituents. As indicated
by CPK models, the sterically less hindered conformation
is D2, in which the diketonate ligand is situated next to
the cleft and the benzyl spacers are partly covering the
cavity.
In order to obtain more information about the confor-
mational behavior of the metallocage we also synthesized
complexes 3b,c using (dbm)Rh(CO)2 and (dpm)Rh(CO)2
as starting complexes (Hdbm ) dibenzoylmethane, Hdpm
) dipivaloylmethane). In contrast to 3a , compounds 3b,c
displayed only three resonances in their 31P NMR spectra
(Figure 3b,c and Table 1). The signal attributed to the
D1 conformer is absent because this geometric arrange-
ment is not possible as a result of the bulky substituent
on the diketone ligand.
Several AX patterns, originating from the methylene-
bridge protons between the glycoluril unit and the side
walls (Figure 5, e) were present in the 1H NMR spectrum.
It was not possible to assign them unequivocally to each
of the conformations. In all conformations the proton
signals of the aromatic walls (d) gave rise to a complex
pattern because of the interference by the aryl groups of
the phosphite ligands (Table 1).
The protons f in the crown ether rings in the U1
conformers were visible as a broad signal, reflecting the
fluxional movement of the metal complex parts.
The U2 conformers were identified by the fact that their
31P NMR resonances disappeared after addition of a
substrate molecule (vide infra).
The shoulder on the CH3 signal at δ ) 1.49, belonging
to the U1 conformer of 3a , was assigned to the methyl
groups of the acetylacetonate ligand of the D1 conformer.
Despite the fact that these methyl groups are located in
the cleft their shift is small as compared to that of the
methyl groups in the U1 conformation. The reason for
this may be that these groups are positioned just outside
the shielding zone of the side walls.11a Further support
for this assignment came from the binding experiments
(vide infra).
The D2 conformers were identified on the basis of
the methylene protons next to the nitrogen atoms in
the crown ether ring (Figure 5, protons f). These pro-
tons displayed an AA′BB′ pattern which is the result of
the asymmetric arrangement of the diketonate ligand.
The different conformations of 3a -c possess varying
1
degrees of symmetry. In the H NMR spectra of these
complexes specific signals can be found in which the
1
extent of symmetry is expressed. By correlating the H

4742 J . Org. Chem., Vol. 61, No. 14, 1996
Coolen et al.
Ch a r t 1
F igu r e 2. Proposed structures of 2c (a) and 2c‚2HCl (b).
sections in the molecule.21 As a result for a molecule with
ωτc > 1.2 both positive and negative NOEs may be
observed.
1
In Figure 6 the H NOESY spectrum of compound 3b
is shown. The spectra of 3a ,c displayed very similar
features. All of the NOEs originating from the host
molecule itself, e.g. between the geminal protons (e)
(Figure 5) of the bridging methylene groups (Figure 6,
a) and between the latter protons and the ortho protons
(g) (Figure 6, b), were negative, indicating that this part
of the molecule is rigid and tumbling slowly. Enhance-
ments coming from the diketonate ligand were either
positive or negative, depending on the conformation of
the entire molecule. The negative cross peaks were more
intense than the positive ones, in accordance with
theory.20 In the D2 conformation, the diketonate ligand
is in a more or less fixed position next to the cavity and
its movement is coupled to that of the framework of the
molecule. As a result, the interactions between the
protons i and h of the diketonate ligand give rise to
negative NOEs. On the contrary, in the U1 conformation
the metal complex part is rather mobile and its move-
ment is virtually independent of that of the host molecule,
resulting in positive NOEs between protons h and i
(Figure 6, c). The benzylic CH2 groups act as a pivot
point in the fluxional movement and therefore their
protons (b) displayed only weak negative NOEs with the
neighboring protons (a) (Figure 6, d) and with the
methylene protons (f).
In a control experiment we confirmed that the sign of
the NOE indeed depends on the mobility of the diketo-
nate ligand. The methyl protons of the acetylacetonate
ligand in (acac)Rh[P(OPh)3]2 generated a positive en-
hancement of 22% at the methynic proton (i). In 3a the
same protons gave a net negative NOE of 22%, which is
the sum of contributions from the U1 (positive enhance-
ment) and the D2 conformations (negative enhancement).
For the D2 conformation two different negative NOEs
between the aromatic wall protons (d) and the methylene
protons (c) were observed, viz. one originating from the
exposed d protons (sharp singlet in the 1H NMR spec-
trum) and one coming from the d protons that are cov-
ered by the metal complex part (complicated proton
signals in the 1H NMR spectrum) (Figure 6, e). This
observation is in line with the asymmetry of the D2
conformation. The positive NOE between the d and c
protons in the spectrum arises from contacts in the U1
conformation.
In the D2 conformations the rings containing the triph-
enyl phosphite ligands are rather constrained, which
causes the 31P signal to shift to higher fields (see Fig-
ure 3).18 The sharp singlets at δ ) 6.63 in the 1H
NMR spectra of the complexes were attributed to the
most exposed set of d protons in the D2 conformations
(the wall protons on the right-hand side of the complex
in Figure 4d).
To confirm the existence of different conformational
isomers and to support the assignment of the individual
signals we carried out 1H NOESY measurements. The
2D spectra of 3a -c revealed both positive and negative
cross peaks. The sign of the nuclear Overhauser en-
hancement is determined by the relaxation pathway.19
The transitions are stimulated by the fluctuating fields
induced by the rotation of the dipoles in solution and are
characterized by the correlation time τc. For common
organic compounds with low molecular weights in non-
viscous solvents τc is short, i.e. the tumbling rate 1/τc is
fast with respect to the spectrometer frequency (ω), so
that ωτc < 1.2. Under these conditions the NOEs are
positive. On the other hand, if ωτc > 1.2, the NOEs are
negative.20 For a rigid molecule one single correlation
time τc applies. When internal motion plays a role it is
possible to define effective correlation times τe < τc for
(18) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(19) (a) Derome, A. E. Modern NMR Techniques for Chemistry
Research; Pergamon Press Ltd.: Oxford, U.K., 1987. (b) Sanders, J .
K. M.; Hunter, B. K. Modern NMR Spectroscopy; Oxford University
Press: Oxford, U.K., 1987.
The factors that determine the preference for a certain
conformation are not fully understood yet. For all
(20) Ernst, R. R.; Bodenhausen, G.; Wokaun, A. Principles of NMR
in One and Two Dimensions; Clarendon Press: Oxford, U.K., 1987.
(21) Lipari, G.; Szabo, A. J . Am. Chem. Soc. 1982, 104, 4546.

Rh(I) Metallohosts Derived from Diphenylglycoluril
J . Org. Chem., Vol. 61, No. 14, 1996 4743
F igu r e 3. 31P{1H} NMR spectra of 3a (a), 3b (b), and 3c (c).
Ta ble 1. NMR Da ta of Com p ou n d s 3a -c
1H NMRb,c
compd
3a
conformer
U1
31P NMRa
H(d)
H(f)
H(i)
5.06
H(h)
1.49
121.2 [304]
2.88 (br)
6.67
6.65
6.63
U2
D1
121.4 [304]
121.3 [304]
-
-
-
-
-
{
6.62
6.56
-
D2
U1
120.2 [304]
120.5 [304]
2.7-2.85 (m)
2.84 (br)
5.07
6.55
1.51
7.53 (7)d
3b
3c
6.60
6.59
6.53
6.53
U2
120.7 [303]
-
-
-
{
{
D2
U1
119.1 [305]
121.0 [302]
2.6-2.8 (m)
2.88 (br)
6.49
5.57
7.53 (7)
0.86
6.67
6.63
6.58
U2
D2
121.2 [303]
119.6 [303]
-
-
-
2.68-2.83 (m)
5.57
0.84
a
b
δ in ppm [J Rh-P (Hz)] at 80 MHz, referenced to external OP(OMe)3 at 298 K in CDCl3. δ in ppm [J (Hz)] at 400 MHz, referenced to
internal TMS at 298 K in CDCl3. c Abbreviations used are d ) doublet, m ) multiplet, br ) broad; (-) no assignment could be made; the
d
protons are denoted as shown in Figure 5. Ortho protons of the phenyl rings of the dbm ligand.
compounds 3 the U2 and the D1 forms are minor
conformations. The more bulky metallohosts 3b,c tend
to prefer the D2 conformation, and at higher tempera-
tures, the U1 form is slightly preferred by all compounds.
An important factor is the amount of water present. This
water can be bound in the cavity of the metallohost and
can force the latter to adopt its most accessible conforma-
tion (U1).
In the case of compound 5 a complex set of signals was
visible in the 31P NMR spectrum. The pattern was
dependent on the amount of triphenyl phosphite present
in solution (Figure 7). In the case of an excess of P(OPh)3
also the signal of uncoordinated phosphites of 2d became
visible besides signals for free P(OPh)3 and 5 (Figure
7b,c). This suggests that in the presence of additional
P(OPh)3 the chelated form of 5 (Figure 8, 5a ) is in
equilibrium with a form (5b) in which one of the ligands
of the receptor molecule is replaced by a P(OPh)3 ligand.
Other structures can also be imagined, e.g. one in which
each of the phosphorus atoms of the ligand system is
coordinated to a different rhodium center (5c) or one in
which the rhodium center is chelated by two ligand
systems (5d ). These structures, however, are less likely
when equal amounts of ligand 2d and rhodium are
present. They may become important at lower or higher
ligand to rhodium ratios. A polymeric form is also
conceivable but entropically unfavorable, and not in
Rh (I)-Hyd r id e Com p lexes. Reaction of compounds
3 with H2 in the presence of a small excess of P(OPh)3 in
chloroform led to the formation of the hydride compound
5. This compound can be isolated by precipitation in
hexane but is not stable for long periods of time. In the
22
reference compound HRh[P(OPh)3]4 the Rh center is
tetrahedrally surrounded by the phosphites. The hydride
is positioned along one of the trigonal axes of the complex.
The four phosphites have the same chemical shift and
they couple strongly to each other. Hence they give rise
to a single resonance in the 31P NMR spectrum (J Rh-P
)
229 Hz). This virtual equivalence of the phosphorus
1
agreement with the fact that the signals in the H NMR
1
atoms is also expressed in the H NMR spectrum by the
spectrum are relatively sharp. We assign the complex
signal in the 31P NMR spectrum after isolation of the
metallohost to structure 5a . The complexity of the signal
may arise from a distortion of the tetrahedral arrange-
ment of the phosphites around the rhodium center, due
to the bulky ligand system. As compared to HRh-
appearence of a double quintet for the hydride signal
(J P-H ) 44 Hz, J Rh-H ) 3 Hz).22
(22) (a) Levison, J . J .; Robinson, S. D. J . Chem. Soc., Chem.
Commun. 1968, 1045. (b) Coolen, H. K. A. C.; Nolte, R. J . M.; van
Leeuwen, P. W. N. M. J . Organomet. Chem. 1995, 496, 159.

4744 J . Org. Chem., Vol. 61, No. 14, 1996
Coolen et al.
to a solution of 2d in chloroform, signals for 5, for the
uncoordinated phosphites of 2d , as well as for free
P(OPh)3 were clearly resolved in the 31P NMR spectrum.
By integration of these signals the equilibrium constant
for the process 5a + P(OPh)3 a 5b could be determined.
This constant amounted to Kab ) 0.034 M-1. This value
implies that in the presence of an extra 2 equiv of
P(OPh)3 still 94% of the rhodium is in the chelated form
5a . If only an additional 1 equiv of phosphite is present
this percentage is 97%. Apparently, in spite of the fact
that 2d has a large ring, the ligand exerts a substantial
chelate effect.
Bin d in g P r op er ties. Recent studies in our group
have shown that basket-shaped compounds of type 2 can
complex dihydroxybenzene guests.24 Binding occurs by
means of hydrogen bonds between the hydroxyl substit-
uents of the guest and the carbonyl functions of the
glycoluril unit and depending on the type of guest also
by hydrogen bonding with the crown ether fragments.
In addition to this the host-guest complex is stabilized
by π-stacking interactions between the benzene ring of
the guest and the aromatic side walls of the host. The
binding properties of the metallohosts were evaluated by
1H and 31P NMR spectroscopy monitoring the shifts and
intensities of appropriate signals of the host-guest
complex.
The addition of a substrate was found to affect the
conformational behavior of complexes 3a -c considerably
(Figure 10). In the presence of resorcinol, the signals for
the U2 conformation in the 31P NMR spectra disappeared
completely. Apparently, the substrate dispels the aro-
matic ring of the triphenyl phosphite ligand out of the
cleft. Furthermore, the binding of a substrate induced
a change of the D2 into the U1 conformation, probably
because the latter has a less strained cavity. After
approximately 2 equiv of substrate hardly any D2 con-
former was left. At that point the 31P signals of the U1
conformer had slightly shifted to lower field (∼0.1 ppm),
whereas the signals of the D2 conformer had strongly
shifted to higher field (∼0.4 ppm). For 3a addition of
resorcinol did not result in the instantaneous disappear-
ance of the 31P signal of the D1 conformation. In the
presence of approximately 0.5 equiv of resorcinol still
about 7% of the 31P NMR signal is due to the D1
conformer (Figure 10a). Only after 5 equiv of substrate
had been added did this signal weaken, indicating that
the compact D1 structure with the acetylacetone ligand
bent into the cavity is rather stable.
NMR titrations were used to determine the association
constant Ka for resorcinol in 3a -c. In order to avoid
complications due to D-U transitions the first points of
the titration curve ([host]/[guest] < 2) were not used to
calculate the Ka. The values found amounted to Ka )
3100 M-1 for 3a and Ka ) 2850 M-1 for 3b, in good
agreement with the values measured for the reference
compounds 1a and 2e (see Table 2).
It was not possible to manipulate solutions of the
hydride complex 5 to such an extent that association
constants for this complex could be determined quanti-
tatively. However, the observed shifts of mixtures of
resorcinol and 5 indicated that the Ka value is in the same
F igu r e 4. Schematic representations of the different confor-
mations of metallohost 3.
[P(OPh)3]4 this could lead to a considerable change in
the magnitude of the couplings between the different
phosphorus atoms and between the phosphorus atoms
and the rhodium center.23 In 5b , there is no need
for a distortion and the phosphorus atoms will give rise
to a single doublet, comparable to HRh[P(OPh)3]4. In
Figure 7b-d this doublet is superimposed on the signal
of 5a .
The signal in Figure 7a cannot be simulated to fit an
A2B2 pattern. Such a pattern would be expected if one
of the C2v symmetry planes of the basket of 5 laterally
bisects one of the Td symmetry planes of the metal
complex. Apparantly, the metal complex part is slightly
twisted with respect to the receptor molecule thereby
cancelling the symmetry in the system. As a result all
of the phosphorus atoms have become chemically and
magnetically unequivalent. When more than 2 equiv of
P(OPh)3 is added the fine structure of the 31P NMR signal
is lost probably as a result of broadening due to ligand
exchange. Additionally, the signal sharpens because
compound 5b becomes dominant (Figure 7c,d).
1
The signal of the hydride ligand in the high-field H
NMR spectrum of 5 was broadened, probably for two
reasons: (i) the nonequivalence of the phosphorus atoms
and (ii) the fact that the two pairs of faces of the rhodium
tetrahedron are unequal (the hydride ligand can point
toward the cavity or away from it). In Figure 9 this
hydride signal is shown for a solution of 5 containing
approximately an additional 4 equiv of P(OPh)3. The
sharp signals originating from structure 5b are super-
imposed on the broad signals of structure 5a .
Compound 5 could also be obtained by an exchange
reaction in which two of the P(OPh)3 ligands of HRh-
[P(OPh)3]4 are displaced by the phosphite ligands of 2d .
After addition of an equimolar amount of HRh[P(OPh)3]4
(23) Pregosin, P. S.; Kunz, R. W. 31P and 13C NMR of Transition
Metal Phosphine Complexes. (NMR, Basic Principles and Progress, part
16), 2nd ed.; Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer-Verlag:
Berlin, 1979.
(24) (a) Sijbesma, R. P.; Kentgens, A. P. M.; Nolte, R. J . M. J . Org.
Chem. 1991, 56, 3199. (b) Sijbesma, R. P.; Nolte, R. J . M. J . Org. Chem.
1991, 56, 3122.

Rh(I) Metallohosts Derived from Diphenylglycoluril
J . Org. Chem., Vol. 61, No. 14, 1996 4745
F igu r e 5. Numbering of H atoms used for the assignment of the 1H NMR signals.
tetrahedral arrangement of the phosphites around the
metal center.
Exp er im en ta l Section
Gen er a l P r oced u r es. Unless indicated otherwise, com-
mercial products were used as received. Hexane and toluene
were distilled under a nitrogen atmosphere from sodium ketyl.
Dichloromethane (CH2Cl2) and tetrahydrofuran (THF) were
distilled from lithium aluminium hydride (LiAlH4). Chloro-
form and chloroform-d1 were distilled from phosphorus pent-
oxide (P2O5). All solvents were stored on molecular sieves
under an inert atmosphere.
Cya n o-4-(m eth oxym eth oxy)ben zen e. This compound
was prepared according to a literature procedure:25 16 g (0.2
mmol) of chloromethyl methyl ether was added dropwise to a
vigorously stirred two-phase system consisting of 5.96 g (50
mmol) of 4-cyanophenol, 3 g (7.5 mmol) of Aliquat in 250 mL
of CH2Cl2, and 3 g (75 mmol) of sodium hydroxide in 100 mL
of water. After TLC (eluent: acetone-hexane ) 1:4 v/v) had
indicated the disappearance of the 4-cyanophenol, the layers
were separated and the water layer was extracted twice with
CH2Cl2. The combined organic layers were dried (MgSO4), and
the solvent was removed under reduced pressure. The product
was purified by column chromatography (silica, eluent: ac-
etone-hexane ) 1:4, v/v) to yield 4.23 g (52%) of a yellowish
oil that solidified on cooling: 1H NMR (90 MHz, CDCl3) δ 7.59
(d, J ) 9 Hz), 7.09 (d, J ) 9 Hz), 5.22 (s), 3.48 (s).
p-(Meth oxym eth oxy)ben zyla m in e. This compound was
prepared according to a literature procedure26 using 4.2 g (25.7
mmol) of cyano-4-(methoxymethoxy)benzene, 1.47 g (38.6
mmol) of LiAlH4, and 1.89 g (19.3 mmol) of sulfuric acid in 80
mL of THF; yield 3.2 g (75%) of product as a yellow oil; 1H
NMR (90 MHz, CDCl3) δ 7.23 (d, J ) 9 Hz), 7.00 (d, J ) 9
Hz), 5.16 (s), 3.80 (s), 3.47 (s), 1.66 (s).
5,7,12,13b,13c,14-Hexa h yd r o-1,4,8,11-tetr a k is[2-(2-ch lo-
r oet h oxy)et h oxy]-13b ,13c-d ip h en yl-6H ,13H -5a ,6a ,12a ,-
13a -t et r a a za b en z[5,6]a zu len o[2,1,8-ija ]b en z[f]a zu len e-
6,13-d ion e (1b). This compound was synthesized as described
in ref 14.
F igu r e 6. 1H-NOESY of compound 3b in CDCl3 (τm ) 0.8 s,
T ) 298 K). The enlargements of regions c and e are given
separately. The dashed lines indicate that the cross peaks are
negative. The splitting of the signals in region c is due to
coupling with an ortho proton.
range as for 3 (∼3000 M-1), assuming that the maximum
shift ∂max of the host-guest complex for 5 is appromately
the same as that for 3. After addition of resorcinol to a
solution of 5 in chloroform the signals in the 31P NMR
spectrum sharpened and the second-order effects disap-
peared. This suggests that the binding of the substrate
forces the system to adopt a more symmetrical geometry.
Possibly, the metal complex part is lifted a little with
respect to the receptor molecule, which restores the
2a ,8,9,12,13,14,15,17,18,25,26,29,30,31,32,34,35,38b -Oc-
t a d e c a h y d r o -2a ,38b -d ip h e n y l-13,30-b is [4-(m e t h o x y -
m eth oxy)p h en ylm eth yl]-1H,4H-6,37:20,23-d ieth en o-2,22:
(25) van Heerden, F. R.; van Zyl, J . J .; Rall, G. J . H.; Brandt, E. V.;
Roux, D. G. Tetrahedron Lett. 1978, 661.
(26) Yoon, N. M.; Brown, H. C. J . Am. Chem. Soc. 1968, 90, 2927.

4746 J . Org. Chem., Vol. 61, No. 14, 1996
Coolen et al.
F igu r e 7. 31P{1H} NMR spectra of compound 5 with different amounts of additional P(OPh)3 present: after isolation (no extra
triphenyl phosphite) (a) and with 2 equiv (b), with ca. 4 equiv (c), and with ca. 6 equiv (d) of extra P(OPh)3. The signal of free
P(OPh)3 is marked with an asterisk and that of an uncoordinated phosphite ligand of 2d with a triangle.
F igu r e 9. Hydride region of the 1H NMR spectrum of 5 in
the presence of approximately an additional 4 equiv of P(OPh)3.
The sharp signals of structure 5b are superimposed on the
broad signals of structure 5a .
F igu r e 8. Schematic representation of the different rhodium
6.62 (s), 5.51 (d, J ) 16 Hz), 5.45 (d, J ) 16 Hz), 4.7-3.2 (br);
hydride complexes derived from 2d .
IR (CsI) ν˜ (cm-1) ) 3448 (OH, br), 1691 (NC(O)N), 1131 (COC);
FAB-MS m/z 1089 ([2c + H]+), 545 (1/2[2c + 2H]+). Anal. Calcd
3,21-d im et h a n o-5H ,11H ,28H ,38H -7,10,16,19,24,27,33,36-
for C62H68N6O12‚3HCl‚H2O: C, 61.21; H, 6.05; N, 6.91.
Found: C, 61.99; H, 6.04; N, 6.80%.
octa oxa -2,3,4a ,13,30,38a -h exa a za cyclop en ta [cd ]cyclotet-
r a tr ia con t[g]a zu len e-1,4-d ion e (2b). This compound was
prepared according to a procedure developed in our labora-
tory14 using 5 g (5.1 mmol) of 1b, 2.52 g (15.2 mmol) of
p-(methoxymethoxy)benzylamine, 16.25 g of Na2CO3 (0.15
mol), and 50 g of NaI in 1.5 L of acetonitrile. The product
was purified by column chromatography using gradient elu-
tion (silica, eluent: CHCl3 with 1% Et3N and 0.5%-1%
methanol): yield 4.45 g (75%) of white 2b ; 1H NMR (90
MHz, CDCl3) δ 7.31(d, J ) 9 Hz), 7.11 (s), 6.98 (d, J ) 9 Hz),
6.74 (s), 5.69 (d, J ) 16 Hz), 5.18 (s) 4.26-3.57 (m), 2.89 (tr, J
) 6 Hz); FAB-MS m/z 1178 ([M + H]+). Anal. Calcd for
C66H76N6O14‚H2O: C, 66.32; H, 6.58; N, 7.03. Found: C, 66.56;
H, 6.26; N, 7.04%.
2a ,8,9,12,13,14,15,17,18,25,26,29,30,31,32,34,35,38b-Oc-
t a d e c a h y d r o -2a ,38b -d ip h e n y l-13,30-b is [(4-h y d r o x y -
p h e n yl)m e t h yl]-1H ,4H -6,37:20,23-d ie t h e n o-2,22:3,21-
dim eth an o-5H,11H,28H,38H-7,10,16,19,24,27,33,36-octaoxa-
2,3,4a ,13,30,38a -h e x a a za c y c lo p e n t a [cd ]c y c lo t e t r a -
tr ia con t[g]a zu len e-1,4-d ion e Dih yd r och lor id e [2c‚2HCl].
To a solution of 2.5 g (2.1 mmol) of compound 2b in a mixture
of 50 mL of THF and 50 mL of isopropyl alcohol was added
dropwise 10 mL of concentrated aqueous HCl (30%). After
being stirred for 3 h, the solution was evaporated to dryness,
and the resulting solid material was dried under high vacuum,
to give 2.45 g (100%) of white 2c‚2HCl: 1H NMR (100 MHz,
DMSO-d6) δ 10.4 (br), 7.56-7.43 (m), 7.15 (s), 6.97-6.60 (m),
The compound can be deprotonated to 2c with a NaHCO3/
NaOH buffer of pH ) 9.75 (2.1 g of NaHCO3 and 0.4 g of
NaOH in 600 mL of water): 1H NMR (400 MHz, CDCl3) δ
7.16-7.10 (m), 6.93 (d, J ) 7.5 Hz), 6.32 (s), 6.23 (d, J ) 7.5
Hz), 5.67 (d, J ) 16 Hz), 4.02-3.60 (m), 2.79 (s br); IR (CDCl3)
ν˜ (cm-1) ) 3604 (ArOH free), 3327 (ArOH bridged), 1716, 1692
(NC(O)N); FAB-MS m/z 1089 ([M + H]+). Anal. Calcd for
C62H68N6O12‚NaCl: C, 64.88; H, 5.97; N, 7.32. Found: C,
64.73; H, 6.05; N, 7.04%.
2a ,8,9,12,13,14,15,17,18,25,26,29,30,31,32,34,35,38b -Oc-
tadecah ydr o-2a,38b-diph en yl-13,30-bis[[4-(diph en ylph os-
p h ito)p h en yl]m eth yl]-1H,4H-6,37:20,23-d ieth en o-2,22:3,-
21-d im e t h a n o-5H ,11H ,28H ,38H -7,10,16,19,24,27,33,36-
oct a oxa -2,3,4a ,13,30,38a -h exa a za cyclop en t a [cd ]cyclo-
tetr a tr ia con t[g]a zu len e-1,4-d ion e (2d ). Under an inert
atmosphere 2.7 g (10.8 mmol) of diphenyl phosphochloridite
was slowly added to a solution containing 2.5 g (2.15 mmol) of
2c‚2HCl, 30 mL of CH2Cl2, and 2.1 mL (15.1 mmol) of Et3N.
The mixture was refluxed for 2.5 h with stirring. The reaction
volume was reduced to 5 mL and added dropwise to 150 mL
of dry hexane. The resulting precipitate was filtered off,
washed twice with hexane, and dried under vacuum. The solid
was dissolved in 100 mL of CH2Cl2 and washed 4× with a
NaHCO3/NaOH buffer (pH ) 9.5). The organic layer was dried
(MgSO4) and evaporated to dryness, and the resulting product

Rh(I) Metallohosts Derived from Diphenylglycoluril
J . Org. Chem., Vol. 61, No. 14, 1996 4747
F igu r e 10. 31P{1H} NMR spectra of 3a (a), 3b (b), and 3c (c) in the presence of approximately 0.5 equiv of resorcinol.
Ta ble 2. Associa tion Con sta n ts of Com p lexes betw een
Differ en t Hosts a n d Resor cin ol in CDCl3
of hexane. After filtration and drying under vacuum 201 mg
(85%) of 3a as a yellow solid was obtained: 31P NMR (80 MHz,
CDCl3) δ 121.4, 121.3, 121.2, 120.2 (d, J Rh-P ) 304 Hz) (see
text); 1H NMR (400 MHz, CDCl3) δ 7.33-7.01 (m), 6.67-6.56
(m), 5.67-5.61 (several d, J ) 16 Hz), 5.073 and 5.067 (2 s),
4.12-3.65 (m), 2.88 and 2.82-2.73 (br and m), 1.51 and 1.50
(2 s); IR (CsI) ν˜ (cm-1) ) 1715 (NC(O)N), 1580 (CC, diketone),
1197 (POPh); FAB-MS m/z 1723 (M+). Anal. Calcd for
C91H93N6O18P2Rh: C, 63.41; H, 5.44; N, 4.88. Found: C, 63.48;
H, 5.38; N, 4.87%.
host
Ka/M-1 a
ref
25a
25b
this work
this work
1a
2e
3a
3b
2600
2900
2850
3100
a
Estimated error: 10-15%.
Com p ou n d 3b. This compound was prepared in the same
way as 3a , using 195 mg (0.13 mmol) of ligand 2d and 49 mg
(0.13 mmol) of (dbm)Rh(CO)2: yield 200 mg (85%) of 3b as a
yellow solid; 31P NMR (80 MHz, CDCl3) δ 120.7, 120.5, 119.1
was dried under high vaccuum: yield 3.09 g (94%) of foamy
1
white 2d ; 31P NMR (80 MHz, CDCl3) δ 125.9; H NMR (400
MHz, CDCl3) δ 7.36-7.04 (m), 6.68 (s), 5.66 (d, J ) 16 Hz),
4.15-3.67 (m), 2.89 (tr, J ) 5.6 Hz); 13C NMR (100 MHz,
CDCl3) δ 157.5, 151.7, 129.6, 120.7, 124.2, 150.4, 134.0, 129.3,
119.1, 150.7, 128.6, 113.8, 130.2, 128.6-128.3, 85.1, 69.9, 69.6,
69.4, 59.1, 53.7, 36.9; IR (CsI) ν˜ (cm-1) ) 1712 (NC(O)N), 1197
(POPh), 504 (P(OR)3); FAB-MS m/z 1522 ([M + H]+). Anal.
Calcd for C86H86N6O16P2: C, 67.89; H, 5.70; N, 5.52. Found:
C, 67.47; H, 5.84; N, 5.29%.
1
(d, J Rh-P ) 304 Hz) (see text); H NMR (400 MHz, CDCl3) δ
7.89-6.92 (m), 6.78-6.51 (m), 6.55 and 6.49 (2 s), 5.63 and
5.62 (2 d, J ) 16 Hz), 4.07-3.64 (m br), 2.84 and 2.79-2.63
(br and m); IR (CsI) ν˜ (cm-1) ) 1712 (NC(O)N), 1591 (C-C,
diketone), 1194 (POPh), 592 (diketone). Anal. Calcd for
C101H97N6O18P2Rh: C, 65.65; H, 5.29; N, 4.55. Found: C,
65.80; H, 5.29; N, 4.40%.
R h od iu m Dica r b on yl Dib en zoylm et h a n oa t e [(d b m )-
Rh (CO)2]. This complex was prepared according to a modified
literature procedure:27 200 mg (0.76 mmol) of RhCl3‚3H2O and
0.5 g (2.23 mmol) of dibenzoylmethane in 4 mL of dimethyl-
formamide (DMF) was refluxed for 1 h. During that time the
solution became orange. After cooling, 10 mL of a 0.5 N
aqueous NaOH solution was added and the dark precipitate
was filtered off, subsequently washed with water, cold ethanol,
and cold ether, and dried. The product was extracted from
the solid material with hot hexane. After evaporation of the
solvent 142 mg (49%) of (dbm)Rh(CO)2 was obtained as orange
flakes: 1H NMR (90 MHz, CDCl3) δ 8.83-7.77 (m), 7.66-7.31
(m), 6.94 (s); IR (CsI) ν˜ (cm-1) ) 2963 (ArH), 2079, 2002
(RhCO), 1541 (CO diketonate), 519 (RhO). Anal. Calcd for
C17H11O4Rh: C, 53.43; H, 2.90. Found: C, 54.36; H, 2.98%.
Rh od iu m Dica r bon yl Dip iva loylm eth a n oa te [(d p m )-
Rh (CO)2]. This complex was prepared as described for (dbm)-
Rh(CO)2 using 200 mg (0.76 mmol) of RhCl3‚3H2O and 0.42 g
(2.28 mmol) of dipivaloylmethane in 4 mL of DMF: yield 196
mg (75%) of (dpm)Rh(CO)2 as flakes with characteristic red-
green dichroism; 1H NMR (90 MHz, CDCl3) δ 5.44 (s), 0.64
(s); IR (CsI) ν˜ (cm-1) ) 2067, 2011 (RhCO), 1548 (CO diketo-
nate), 1362 (C(CH3)3), 474 (RhO). Anal. Calcd for C13H19O4-
Rh: C, 45.63; H, 5.6. Found: C, 45.71; H, 5.56%.
Com p ou n d 3c. This compoud was prepared in the same
way as 3a using 180 mg (0.12 mmol) of ligand 2d and 40 mg
(0.12 mmol) of (dpm)Rh(CO)2: yield 200 mg (85%) of 3b as a
yellow solid; 31P NMR (80 MHz, CDCl3) δ 121.2, 121.0, 119.6
1
(d, J Rh-P ) 304 Hz) (see text); H NMR (400 MHz, CDCl3) δ
7.36-6.98 (m), 6.67-6.58 (m), 5.64 (d br, J ) 16 Hz), 4.12-
3.65 (m), 2.88 and 2.82-2.68 (br and m), 0.86 and 0.84 (2 s);
IR (CsI) ν˜ (cm-1) ) 1716 (NC(O)N), 1594 (C-C, diketone), 1359
(C(CH3)3), 1199 (POPh), 596 (diketone). Anal. Calcd for
C97H105N6O18P2Rh: C, 64.45; H, 5.85; N, 4.65. Found: C,
64.43; H, 5.85; N, 4.67%.
Com p lex 5. This compound was prepared by following the
same procedure as described for compound 3a . An extra
amount of 90 mg (0.29 mmol) of P(OPh)3 was added, and the
reaction mixture was stirred for 12 h under 10 atm of hydrogen
pressure. The complex was precipitated by first reducing the
solvent volume to 2 mL and subsequently adding the resulting
solution dropwise to 25 mL of hexane. Complex 5 could also
be prepared by the addition of 41 mg (30 mmol) of HRh-
[P(OPh)3]4 to a solution of 46 mg (30 mmol) of ligand 2d in
CHCl3: 31P{1H} NMR (80 MHz, CDCl3) δ 127.6 (d br, J Rh-P
)
1
229 Hz) (see Figure 7); H NMR (200 MHz, CDCl3) δ 7.6-6.4
(m), 5.63 (d br, J ) 16 Hz), 4.3-3.35 (m), 3.15-2.65 (br), -11.0
(qu br) (see Figure 9); due to its limited stability no satisfying
elemental analysis could be obtained for this product.
Com p ou n d 3a . To a solution of 200 mg (0.14 mmol) of
ligand 2d in 20 mL of CHCl3 was added 35.4 mg (0.14 mmol)
of (acac)Rh(CO)2. Argon was led through the solution for 15
min to remove the released carbon monoxide. The product was
precipitated by first reducing the solvent volume to 2 mL and
subsequently adding the resulting solution dropwise to 25 mL
Ack n ow led gm en t. This research was financed by
Shell Research BV. We would like to thank Dr. S.
Wymenga for helpful discussions and Mr. J . J oordens
and Mr. A. Swolfs for recording the 2D-NMR spectra.
(27) Varshavskii, Yu. S.; Cherkasova, T. G. Russ. J . Inorg. Chem.
1967, 12, 899.
J O9505583