Synthesis and characterization of diametrically substituted tetra-O-n-butylcalix[4]arene ligands and their chelated complexes of titanium, molybdenum, and palladium

Article abstract of DOI:10.1021/ic020446b

The ligation properties of three new upper-rim-substituted calix[4]arene ligands, 5,17-bis(hydroxymethyl)-tetra-n-butoxycalix-[4]arene ((HOCH₂)₂-ⁿBu₄Clx, 7), 5,17-bis((diphenylphosphinito)methoxy)-tetra-n-butoxycalix[4]arene ((PPh₂OCH₂)₂ⁿBu₄Clx, 8), and 5,17-bis((diphenylphosphino)methyl)-tetra-n-butoxycalix[4]arene ((PPh₂CH₂)₂-ⁿBu₄Clx, 10) are reported herein. The newly prepared compounds differ from previously reported diametrically substituted calix[4]arene derivatives in that the lower-rim substituent was n-butyl. The presence of this lower-rim substituent did not reduce the inherent crystallinity of these complexes as purification of all materials occurred via simple crystallizations. The key precursor for the syntheses of 8 and 10 was 7, acquisition of which occurred in six steps starting from tetra- tert-butylcalix[4]arene, 1. Calix[4]arene derivatives include, tetra-n-butoxycalix[4]arene (ⁿBU₄Clx, 3), 5,11,17,23-tetrabromo-tetra-n-butoxycalix[4]-arene (Br₄-ⁿBu₄Clx, 4), 5,17-dibromo-tetra-n-butoxycalix[4]arene (Br₂-ⁿBu₄Clx, 5), 5,17-bis(formyl)-tetra-n-butoxycalix[4]-arene ((CHO)₂-ⁿBu₄Clx, 6), and 5,17-bis(chloromethyl)-tetra-n-butoxycalix[4]arene ((ClCH₂)₂-ⁿBu₄Clx, 9), all of which were synthesized using modifications of existing procedures. Characterization of all compounds occurred, when possible, using ¹H, ¹³C, and ³¹P NMR, elemental analyses, FAB-MS, ESI-MS, FT-IR, and X-ray crystallography. The solid-state structures of all calix[4]arene intermediates and ligands showed that the annulus adopted the pinched-cone conformation in which the average C(5) ... C(17) intraannular separation was 4.5 ± 0.4 A. Reaction of 7 with CpTiMe₃ yielded the cis-chelate, CpTi(Me)[(OCH₂)₂-ⁿBu₄Clx] (11), quantitatively. Data obtained using ESI-MS (positive-ion mode) confirmed the monomer formulation showed above, and ¹H NMR spectra provided sufficient information to deduce the nature of the Ti coordination sphere. Reaction of 8 with cis-Cl₂Pd(NCPh)₂ in refluxing benzene afforded cis-Cl₂Pd[(PPh₂ OCH₂)₂-ⁿBu₄Clx] (12) in good yields. The monomeric identity of this compound was verified by both X-ray crystallography and positive-ion ESI-MS. The cis-bidentate calix[4]arene ligand did not undergo any noticeable contortion upon chelation of the PdCl₂ fragment. Acidpromoted decomposition of 12 occurred in the presence of adventitious HCl and gaseous HCl, and the products of this decomposition were 9 and [μ₂-ClPd(PPh₂OH)(PPh₂O)]₂. In addition, chelates of 8 that contained Mo(CO)₃L (L = NCMe (14a), NCEt (14b), and CO (14c)) showed that the mode of coordination was relatively insensitive to the identity of the metal. X-ray crystallography afforded views of the solid-state structures of 14b,c and, like 12, showed that the Mo(CO)₃L fragment resided above the pinched-cone of the calix[4]arene. 1H NMR revealed that C-H/μ interactions existed between L (14a,b) and a phenyl ring of the coordinated phosphinite. Finally, the bis(diphenylphosphine)calix[4]arene ligand (10) readily coordinated the Mo(CO)₃L species, but the reaction did not go to completion, as evidenced by 1H NMR, even after a 5 day reaction time. Data suggest that the product is similar to that observed for 12 and 14, but the incomplete reaction complicated attempts to obtain pure material and prohibited definitive assignment of the coordination array.

Full text of DOI:10.1021/ic020446b

Inorg. Chem. 2002, 41, 5986−6000
Synthesis and Characterization of Diametrically Substituted
Tetra-O-n-butylcalix[4]arene Ligands and Their Chelated Complexes of
Titanium, Molybdenum, and Palladium
,†
Daniel R. Evans,* Mingsheng Huang,† James C. Fettinger,† and Tracie L. Williams‡
Department of Chemistry and Biochemistry, UniVersity of Maryland,
College Park, Maryland 20742, and U.S. Food and Drug Administration,
Center for Food Safety and Nutrition, College Park, Maryland 20741
Received July 9, 2002
The ligation properties of three new upper-rim-substituted calix[4]arene ligands, 5,17-bis(hydroxymethyl)-tetra-n-butoxycalix-
[4]arene ((HOCH ) -nBu4Clx, 7), 5,17-bis((diphenylphosphinito)methoxy)-tetra-n-butoxycalix[4]arene ((PPh2OCH ) -
2 2
2 2
nBu4Clx, 8), and 5,17-bis((diphenylphosphino)methyl)-tetra-n-butoxycalix[4]arene ((PPh2CH ) -nBu4Clx, 10) are reported
2 2
herein. The newly prepared compounds differ from previously reported diametrically substituted calix[4]arene derivatives
in that the lower-rim substituent was n-butyl. The presence of this lower-rim substituent did not reduce the inherent
crystallinity of these complexes as purification of all materials occurred via simple crystallizations. The key precursor for
the syntheses of 8 and 10 was 7, acquisition of which occurred in six steps starting from tetra-tert-butylcalix[4]arene, 1.
Calix[4]arene derivatives include, tetra-n-butoxycalix[4]arene (nBu4Clx, 3), 5,11,17,23-tetrabromo-tetra-n-butoxycalix[4]-
arene (Br4-nBu4Clx, 4), 5,17-dibromo-tetra-n-butoxycalix[4]arene (Br2-nBu4Clx, 5), 5,17-bis(formyl)-tetra-n-butoxycalix[4]-
arene ((CHO)2-nBu4Clx, 6), and 5,17-bis(chloromethyl)-tetra-n-butoxycalix[4]arene ((ClCH ) -nBu4Clx, 9), all of which were
2 2
synthesized using modifications of existing procedures. Characterization of all compounds occurred, when possible, using
1H, 13C, and 31P NMR, elemental analyses, FAB-MS, ESI-MS, FT-IR, and X-ray crystallography. The solid-state structures
of all calix[4]arene intermediates and ligands showed that the annulus adopted the pinched-cone conformation in which
the average C(5)‚‚‚C(17) intraannular separation was 4.5 ± 0.4 Å. Reaction of 7 with CpTiMe3 yielded the cis-chelate,
CpTi(Me)[(OCH ) -nBu4Clx] (11), quantitatively. Data obtained using ESI-MS (positive-ion mode) confirmed the monomer
2 2
formulation showed above, and 1H NMR spectra provided sufficient information to deduce the nature of the Ti coordination
sphere. Reaction of 8 with cis-Cl2Pd(NCPh)2 in refluxing benzene afforded cis-Cl2Pd[(PPh2OCH ) -nBu4Clx] (12) in good
2 2
yields. The monomeric identity of this compound was verified by both X-ray crystallography and positive-ion ESI-MS. The
cis-bidentate calix[4]arene ligand did not undergo any noticeable contortion upon chelation of the PdCl2 fragment. Acid-
promoted decomposition of 12 occurred in the presence of adventitious HCl and gaseous HCl, and the products of this
decomposition were 9 and [µ2-ClPd(PPh2OH)(PPh2O)]2. In addition, chelates of 8 that contained Mo(CO)3L (L ) NCMe
(14a), NCEt (14b), and CO (14c)) showed that the mode of coordination was relatively insensitive to the identity of the
metal. X-ray crystallography afforded views of the solid-state structures of 14b,c and, like 12, showed that the Mo(CO)3L
fragment resided above the pinched-cone of the calix[4]arene. 1H NMR revealed that C−H/π interactions existed between
L (14a,b) and a phenyl ring of the coordinated phosphinite. Finally, the bis(diphenylphosphine)calix[4]arene ligand (10)
readily coordinated the Mo(CO)3L species, but the reaction did not go to completion, as evidenced by 1H NMR, even
after a 5 day reaction time. Data suggest that the product is similar to that observed for 12 and 14, but the incomplete
reaction complicated attempts to obtain pure material and prohibited definitive assignment of the coordination array.
Introduction
1.1 This arrangement is attractive in that functionalization
of the lower-rim phenolic oxygens with alkyl chains, R >
nPr, enforces the cone-shaped structure of the molecule, while
Calix[4]arenes are host molecules that possess a tetragonal
array of phenolic rings joined by methylene linkers, Chart
* To whom correspondence should be addressed. E-mail: de44@
umail.umd.edu.
(1) (a) Gutsche, C. D. In Calixarenes, 1st ed.; The Royal Society of
Chemistry: Cambridge, U.K., 1989. (b) Gutsche, C. D. In Calixarenes
ReVisited, 1st ed.; The Royal Society of Chemistry: Cambridge, U.K.,
1998. (c) Gutsche, C. D. Aldrichim. Acta 1995, 28, 3-10.
† University of Maryland.
‡ U.S. Food and Drug Administration.
5986 Inorganic Chemistry, Vol. 41, No. 23, 2002
10.1021/ic020446b CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/15/2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
ligation in which monomers and dimers are possible.7 In the
case of the monomeric species (M ) Ru(II), Pt(II)), trans-
ligation resulted in a slight expansion of the cavity relative
to free ligand,7a,b but cis adducts (M ) Pd(II), Pt(II)) provided
a metal fragment that resided over a hydrophobic cleft, made
available by the splayed arenes.7b,c Species that possess a
single phosphine ligand (Y1 ) PPh2, Y2dH,8 Y2 ) H/Br7c)
coordinate either Rh(III) or Ru(II) in strikingly different
ways.7c,8 In the former case,8 the ligand directed the metal
fragment (Cp*Cl2Rh) away from the pinched-cone, but in
the latter, the (p-cymene)Cl2Ru arrangement resided above
the cavity in which encapsulation of the η6-p-cymene
occurred within the confines of the cavity.7c A variation of
the above-mentioned ligand is to include linkers (either Y
) -CH2PPh2 or Y ) -CH2OPR2) between the upper rim
of the cavity and the P-type ligand.9 Species that contain a
single methylene spacer (Y1 ) Y2 ) -CH2PPh2),9a,b do not
readily chelate metals above the open mouth of the cavity
but instead give rise to polymeric products. This is in contrast
to a calix[4]arene that contains the methyleneoxo (-CH2O-)
spacer.9a A single report described the coordination chemistry
Chart 1
the introduction of ligating elements, Y, on the upper-rim
provides an opportunity to introduce transition metals above
the annulus of the calix[4]arene.2 This aspect makes this class
of compounds particularly fascinating, as it is easy to
envision that this class of compounds could be used to (i)
create catalytic systems with greater selectivity,3 (ii) generate
small-molecule4 or anion sensors,5 (iii) serve as effective
cationic lanthanide extraction agents,6 and (iv) provide an
enthalpic trap that would promote the formation of alkane-
metal complexes. While examples ii and iii now exist, it is
still unclear whether these species will be able to affect
selectivity in catalytic processes or have a cavity large enough
to encapsulate alkanes. Considering the potential utility of
this class of ligands to a number of diverse areas in inorganic
chemistry, it is of importance to highlight some recently
recognized features and coordination properties.
The desire to exploit the presence of a hydrophobic pocket
in these types of molecules requires the recognition of a
potential drawbacksfunctionalization of the lower-rim oxy-
gens. This synthetic modification is a necessary prerequisite
as the parent calix[4]arenes, R ) H, are capable of adopting
three different conformations.1 Unfortunately, the process of
tetra-O-alkylation gives rise to a molecule that adopts a
pinched-cone conformation, in which there is a substantial
reduction of the effective volume of the cavity when
compared to the underivatized species. Synthetic strategies
are available that promote an enlargement of the size of the
cavity (cf. refs 4 and 5), but increasingly complicated routes
result in a reduction of the amount of material in hand.
Another challenging aspect is prediction of the mode of
coordination and the presence or absence of a hydrophobic
pocket. For example, calix[4]arene ligands (Y1 ) Y2 ) PPh2,
R ) nPr,7a,c R ) Bz7b) participate in either cis or trans metal
1
of this type of bidentate ligand, and H NMR provided
sufficient data to allow the authors to correctly deduce the
coordination geometry. At the onset of this work, the variety
of coordination modes was hard to predict, but with recent
reports and the data presented herein, a more lucid picture
is slowly emerging.
An understanding of how to introduce metals above an
opened cavity of the calix[4]arene molecule is crucial to one
aspect of our research program.10 This entails the utilization
of these basket-containing molecules to explore the final
frontier of coordination chemistry, i.e., the interactions that
occur between alkanes and metals. Our interest in this area
came from the fortuitous discovery of an alkane-metal
complex.11 This report showed that the host properties of a
porphyrin array served to encapsulate a heptane molecule
in the immediate vicinity of a coordinatively unsaturated
Fe(II) center. Complete characterization of this interaction
was fraught with difficulties, as the complex was insoluble
in hydrocarbon solvents, thereby prohibiting the possibility
of solution-phase NMR spectroscopic analysis. It seemed
logical to devise systems that contained a metal fragment in
close proximity to a cavity-containing molecule, with the
caveat that they possess solubility in hydrocarbon solvents.
(2) Wieser, C.; Dieleman, C. B.; Matt, D. Coord. Chem. ReV. 1997, 165,
93-161.
(3) (a) Shimizu, S.; Shirakawa, S.; Sasaki, Y.; Hirai, C. Angew. Chem.,
Int. Ed. 2000, 39, 1256-1259. (b) Cobley, C. J.; Ellis, D. D.; Orpen,
A. G.; Pring, P. G. J. Chem. Soc., Dalton Trans. 2000, 1109-1112.
(c) Parlevliet, F. J.; Kiener, C.; Fraanje, J.; Goubitz, K.; Lutz, M.;
Spek, A. L.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. J. Chem.
Soc., Dalton Trans. 2000, 1113-1122.
(7) (a) Wieser-Jeunesse, C.; Matt, D.; De Cian, A. Angew. Chem., Int.
Ed. 1998, 37, 2861-2864. (b) Takenaka, K.; Obora, Y.; Jiang, L. H.;
Tsuji, Y. Organometallics 2002, 21, 1158-1166. (c) Lejeune, M.;
Jeunesse, C.; Matt, D.; Kyritsakas, N.; Welter, R.; Kintzinger, J.-P. J.
Chem. Soc., Dalton Trans. 2002, 1642-1650.
(4) (a) Cameron, B. R.; Loeb, S. J. Chem. Commun. 1996, 2003-2004.
(b) Cameron, B. R.; Loeb, S. J.; Yap, G. P. A. Inorg. Chem. 1997,
36, 5498-5504.
(5) (a) Beer, P. D.; Hesek, D.; Kingston, J. E.; Smith, D. K.; Stokes, S.
E.; Drew, M. G. B. Organometallics 1995, 14, 3288-3295. (b)
Szemes, F.; Hesek, D.; Chen, Z.; Dent, S. W.; Drew, M. G. B.;
Goulden, A. J.; Graydon, A. R.; Grieve, A.; Mortimer, R. J.; Wear,
T.; Weightman, J. S.; Beer, P. D. Inorg. Chem. 1996, 35, 5868-5879.
(c) Beer, P. D.; Hesek, D.; Nam, K. C.; Drew, M. G. B. Organome-
tallics 1999, 18, 3933-3943.
(6) (a) Delmau, L. H.; Simon, N.; Schwing-Weill, M.-J.; Arnaud-Neu,
F.; Dozol, J.-F.; Eymard, S.; Tournois, B.; Bohmer, V.; Gruttner, C.;
Musigmann, C.; Tunayar, A. Chem. Commun. 1998, 1627-1628. (b)
Lambert, B.; Jacques, V.; Shivanyuk, A.; Matthews, S. E.; Tunayar,
A.; Baaden, M.; Wipff, G.; Bohmer, V.; Desreux, J. F. Inorg. Chem.
2000, 39, 2033-2041.
(8) (a) Vezina, M.; Gagnon, J.; Villeneuve, K.; Drouin, M.; Harvey, P.
D. Chem. Commun. 2000, 1073-1074. (b) Vezina, M.; Gagnon, J.;
Villeneuve, K.; Drouin, M.; Harvey, P. D. Organometallics 2001, 20,
273-281.
(9) (a) Bagatin, I. A.; Matt, D.; Thonnessen, H.; Jones, P. G. Inorg. Chem.
1999, 38, 1585-1591. (b) Fang, X.; Scott, B. L.; Watkin, J. G.; Carter,
C. A. G.; Kubas, G. J. Inorg. Chim. Acta 2001, 317, 276-281.
(10) (a) Evans, D. R.; Huang, M.; Seganish, W. M.; Fettinger, J. C.;
Williams, T. L. Organometallics 2002, 21, 893-900. (b) Evans, D.
R.; Huang, M.; Seganish, W. M.; Chege, E. W.; Fettinger, J. C.; Lam,
Y.-F.; Williams, T. L. Inorg. Chem. 2002, 41, 2633-2641.
(11) Evans, D. R.; Drovetskaya, T.; Bau, R.; Reed, C. A.; Boyd, P. W. D.
J. Am. Chem. Soc. 1997, 119, 3633-3643.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5987

Evans et al.
a
Scheme 1
modification resulted in the acquisition of kilogram quantities
of material in a 2-week period. Removal of the upper-rim
tert-butyl substituents to form Clx, 2, occurred using a
modification of a published procedure.13 Adoption of a
known synthetic step afforded tetra-O-alkylation of the phe-
nolic oxygens that provided nBu4-Clx, 3, in excellent yields.14
Preparation of the tetrabrominated calix[4]arene, Br4-nBu4-
Clx, 4, species proceeded at room temperature using NBS
and reagent grade acetone.15 A descriptive process served
as a guide for the preparation of the diametrically substituted
(C5 and C17, rings B and D, Scheme 1) derivatives 5 and
6.16 ThesyntheticschemepresentedforEtOEt4-Clxderivatives9a
afforded 7, 9, and 10, while synthesis of 8 occurred using
an adaptation of a method for the preparation of glucofura-
nose-phosphinite derivatives.17 All synthetic intermediates
were fully characterized, and the molecular structures for
all newly synthesized species, except 9, were accurately
determined. Synthetic and X-ray crystallographic details are
available in the Experimental Section and Supporting Infor-
mation, respectively. Acquisition of high-purity crystalline
material afforded elemental analyses in agreement with ex-
a Legend: (a) (2) 1 + AlCl3 (1:4.8), in toluene, 55 °C, 2 h; (b) (3) 2 +
(i) NaH (1:4), (ii) xs nBuBr, in DMF, 80 °C, 6 h; (c) (4) 3 + NBS (1:6:6),
acetone, 25 °C, 12 h; (d) (5) 4 (i) nBuLi (1:2.1), (ii) xs MeOH, in THF,
-78 °C; (e) (6) 5 + (i) nBuLi (1:2.1), (ii) DMF in THF, -78 °C; (f) (7) 6
+ LiAlH4 in Et2O, 25 °C; (g) (8) 7 + (i) pyridine (1:2.2), (ii) Ph2PCl (1:
2.0) in THF, rt, 12 h; (h) (9) 7 + SOCl2 (1:2.5) in CHCl3, 22 °C, 4 h; (i)
(10) 9 + LiPPh2 (1:2) in THF, -78 °C, 2 h.
Ideal candidates to explore with this goal in mind are the
metal chelates of 5,17-disubstituted-tetra-O-alkylated calix-
[4]arenes. The ultimate goal is to fit the cavities with metals
in which positions of coordinative unsaturation may be
directed toward the interior of the cavity. Ideally, the cavity
space will be large enough to encapsulate small alkanes but
small enough to exclude larger unwanted molecules.
In an attempt to enter this interesting area of research we
have devised a synthetic route, on the basis of existing
procedures, for the preparation of upper-rim-functionalized
calix[4]arenes capable of ligating metal centers with a
propensity to interact with alkanes. While it is difficult to
predict nature of metal ligation until it has been achieved,
results provided herein serve to confirm expectations that
P-type ligands, when separated from the cavity by a
-CH2O- linker, result in cis-chelates. Corroboration of this
statement occurred upon the synthesis and characterization
of three upper-rim-functionalized calix[4]arene-based ligands
that chelated metal fragments composed of Ti(IV), Pd(II),
and Mo(0).
1
pectations. The H and 13C NMR spectroscopic features of
all derivatives and ligands are in close agreement with pre-
viously reported tetra- and diametrically substituted R4-Clx
derivatives, with the only difference being due to the presence
of the O-n-butyl substituent. Crystallographically determined
structures of 3-8 and 10 showed that the calix[4]arene cavity
possessed the pinched-cone conformation in the solid-state;
see Discussion and the Supporting Information.
Metal Chelation with Bidentate Ligands. Bis(alkoxy)-
calix[4]arene Complexation. Due to the relative ease in
preparing 7, it served as a springboard for these complexation
studies. Alkoxy complexes of group 4 metals are readily
available;18 thus, we chose these metals to explore with this
system. For example, 7 reacted immediately with CpTiMe3
in toluene at room temperature to form 11 and methane, eq
1. Despite repeated attempts, this material failed to crystal-
Results and Discussion
Preparation and Characterization of Calix[4]arene
Ligand Precursors. Several synthetic strategies are presently
available for the preparation of diametrically substituted
calix[4]arenes.1b,3a,4,5,7,9 The selected pathway, Scheme 1,
showing an abbreviated numbering arrangement,1 resembles
that adopted by Matt et al.,9a with the exception that lower-
rim functionalization proceeded with n-butyl substituents.
Utilization of the n-butyl groups is advantageous in that they
provide additional solubility without a sacrificial loss of
crystallinity. Evidence to support this latter point comes from
the fact that purification of all synthetic intermediates and
ligands occurred via simple crystallizations.
The starting point for the synthesis of these ligands is
tBu4-Clx, 1. Preparation of this material from commercially
available 4-tert-butylphenol is straightforward using a known
method.12 The scale of this protocol was successfully
increased by a factor of 3 providing comparable yields. This
lize, and always existed as an off-white powder. Failure to
(13) Gutsche, C. D.; Levine, J. A.; Sujeeth, P. K. J. Org. Chem. 1985, 50,
5802-5806.
(14) Kenis, P. J. A.; Noordman, O. F. J.; Schonherr, H.; Kerver, E. G.;
Snellink-Ruel, B. H. M.; van Hummel, G. J.; Harkema, S.; van der
Vorst, C. P. J. M.; Hare, J.; Picken, S. J.; Engbersen, J. F. J.; van
Hulst, N. F.; Vancso, G. J.; Reinhoudt, D. N. Chem.sEur. J. 1998, 4,
1225-1234.
(15) Gutsche, C. D.; Pagoria, P. F. J. Org. Chem. 1985, 50, 5795-5802.
(16) Larsen, M.; Jorgensen, M. J. Org. Chem. 1996, 61, 6651-6655.
(17) Johnson, T. H.; Rangarajan, G. J. Org. Chem. 1980, 45, 62-65.
(12) Gutsche, C. D.; Iqbal, M. Org. Synth. 1990, 68, 234-236.
5988 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
obtain crystalline material, coupled with its inherent air-
sensitivity, resulted in variable microanalytical data. The
results obtained by ESI-MS (positive ion mode) confirmed
Bis(phosphinito) Complexation. The conversion of 7 to
8 provided ample quantities of the bis(phosphinite) ligand
which served as the ligand of choice for this study. The
complexation of 8 with cis-Cl2Pd(NCPh)2 occurred rapidly
(45 min) in refluxing benzene. Removal of the volatiles under
vacuum and subsequent workup gave rise to {cis-Cl2Pd-
[(PPh2OCH2)2-nBu4Clx]} (12) in 85% yield (eq 2). Charac-
+
its monomeric identity in solution (11 - CH3 , m/z 819.4115
amu). Due to the lack of crystallinity, an X-ray structure of
this complex was not possible, but analysis of the 1H NMR
spectrum provided ample clues as to the nature of the
coordination array. The 1H NMR spectrum of 11 is consistent
with bidentate ligation about the titanium atom where the
bis(alkoxy) ligation is cis, and the CH3 and Cp ligands reside
above different halves of the pinched-cone. 1H NMR showed
that the geometry of the coordination sphere gave rise to a
reduction of the overall molecular symmetry, as compared
to the free ligand. This is evident upon comparison of the
1H NMR spectra of 7 and 11 in C6D6, Figure S1 (Supporting
Information). Upon chelation, the hydrogens of the C(5) and
C(17) methylene substituents go from a singlet at 4.19
1
terization of 12 occurred spectroscopically by H, 13C, and
31P NMR, and elemental analysis of crystalline material was
in excellent agreement with theory. The monomeric nature
of 12 was established both in the solid state (X-ray
crystallography) and in solution (CH2Cl2, M+-ESI-MS; 12
- Cl+, m/z 1217 amu). (Solutions of 12 in CH2Cl2 with
added methanol showed, by ESI-MS, that aggregation
occurred at high concentrations; i.e., dimers, trimers, and
tetramers were present in the spectra but the signal intensities
of these aggregates were always minor and disappeared
completely upon dilution.) A complete discussion of the
NMR spectroscopic features of 12 appears after the descrip-
tion of the molecular structure.
2
ppm (7) to an AB quartet (4.89, 4.86 ppm, JAB ) 12.4
Hz) (11). Further inequivalence occurred for the bridging
calix[4]arene methylenes, ArCH2Ar, in which normal dou-
blets (AB spin system) for the axial and equatorial hydrogens
in 7 gave rise to two sets of doublets. The B and D ring
ArH resonances provided an informative glimpse of the
symmetry of the complex, as two doublets appeared at 6.45
and 6.41 ppm. The inequivalence of these resonances
suggests that the methyl and Cp ligands reside over different
halves of the pinched-cone. If the metal adopts a “twisted-
conformation” above the mouth of the pinched-cone,9a then
some dynamic exchange pathway must be present to account
for the observed spectroscopic features; see below. The Cp
H and Ti-CH3 resonances appeared at 6.03 and 0.8 ppm,
respectively.
Figure 1 contains two ORTEP (50% probability) repre-
sentations of 12, while Tables 1 and 2 contain selected
crystallographic data and metrical parameters, respectively.
The view from the side, Figure 1A, shows an abbreviated
numbering scheme where the alkyl carbon chains and
hydrogens were omitted for clarity. The view from the top,
Figure 1B, is somewhat congested but viewable upon
omission of the alkyl chains and phosphinitoaryl carbons;
several hydrogens (in their calculated positions) are shown.
The side view shows that the geometry of the palladium is
approximately square planar in which both phosphorus atoms
of the (PPh2OCH2)2-nBu4Clx ligand are cis with P-Pd-P
angle of 97.5°. The distances to Pd for both Cl (2.355(5) Å)
and P (2.249(6) Å) are remarkably similar to those reported
for cis-Cl2Pd(P(OMe)Ph2)2.20 The calix[4]arene adopted the
pinched-cone conformation as evidenced by the C(5)‚‚‚C(17)
distance of 4.27 Å. An even closer contact of 3.96 Å occurred
between the methylene carbons, C(45) and C(58). The view
from above, Figure 1B, reveals, ignoring the alkyl chains, a
C2-symmetry element that bisects that Cl-Pd-Cl vertex and
passes through the centroid of the calix[4]arene annulus. The
least-squares coordination plane is approximately orthogonal
to the plane defined by the four arene methylene bridges
(C(2), C(8), C(14), and C(20)) with a calculated angle of
Reaction of 7 with either TiCl4 or ZrCl4 was attempted,
but the results were not promising. The reaction of 7 with
either TiCl4 or ZrCl4 in THF/toluene solutions occurred in
the presence of 2 equiv of NEt3. The former reaction products
were too numerous to draw any conclusions, but it was
evident that metalation occurred due to the formation of the
+
HNEt3 salt. The reaction of 7 with ZrCl4 gave rise to a
deep purple solution, which upon filtration and sub-
sequent evaporation of the solvent gave a purple crystal-
line material. 1H NMR spectra of the product mixture
provided evidence to suggest that several decomposition
pathways of the calix[4]arene ligand were available. The
particular route of decomposition was not determined, but
detection of 6 by 1H NMR suggested that a â-elimi-
nation pathway was available for the Zr-bis(alkoxy)calix-
[4]arene complex. Another possibility is that cleavage of the
butoxy ether groups occurred under these conditions. A
recent study provided evidence, obtained by MALDI-
TOF-MS, which showed that diametrically substituted tetra-
O-propoxycalix[4]arenes, 5,17-R2-nPr4Clx, underwent cleav-
age of the propoxy ether groups in the presence of
ZrCl4.19
(18) Cotton, F. A.; Wilkinson, G. In AdVanced Inorganic Chemistry, 5th
ed.; John-Wiley & Sons: New York, 1988.
(19) Faldt, A.; Kregbs, F. C.; Jorgensen, M. Tetrahedron Lett. 2000, 41,
1241-1244.
(20) Powell, D. R.; Jacobson, R. A. Cryst. Struct. Commun. 1980, 9, 1023-
1027.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5989

Evans et al.
arene derivative, (η3-C4H7)Pd[5,17-(P(OEt)2OCH2)2-11,23-
tBu-EtOEt4Clx]+.9a In this report, the positioning of the
coordination plane relative to the annulus of the calix[4]arene
pinched-cone was inferred upon inspection of the 1H NMR
spectrum.
1
Unlike that observed in 11, the H NMR, in C6D6, of 12
did not exhibit an array of inequivalent hydrogens. The
hydrogens attached to the B and D rings, H4, H6, H16, and
H18, underwent an upfield shift of 0.8 ppm, which is a
characteristic signature of these species and is due to the
location of these atoms in close proximity to opposing arenes
in the pinched-cone conformation.21 Interestingly, all of the
hydrogens appear to be equivalent on the NMR time scale
as a single resonance was present, Figure S2. The observation
of a singlet for these hydrogens seems to contradict what
one might expect upon visualization of the molecular
structure of 12. Close inspection of the top view of 12 shows
that H4/H16 and H6/H18 are magnetically inequivalent. In
the absence of a dynamic exchange pathway, two singlets
should be present for these two sets of hydrogen atoms. The
appearance of a singlet indicates the presence of an exchange
process that serves to average these hydrogens on the NMR
time scale (400.132 MHz); see below.
The common practice of storing NMR solvents over
activated 4 Å molecular sieves served to complicate initial
solution characterization of 12. This complex was stable in
a number of freshly distilled anhydrous NMR solvents, C6D6,
C7D8, CD2Cl2, and CDCl3; however, decomposition of 12
to 9 and a sparingly soluble product occurred in solution
while using CDCl3 that was stored over activated molecular
sieves. X-ray crystallography provided the means to identify
the other product. Identification of this product [µ2-ClPd(PPh2-
OH)(PPh2O)]2, 13, and observation of 9 via 1H NMR showed
that 12 underwent scission of the -CH2-O bond in the
presence of HCl. The minimal stoichiometry for this reaction
appears in eq 3, in which the monomer, 12, while in the
presence of HCl, decomposed to 13 and 9. Confirmation of
this decomposition pathway occurred under controlled condi-
tions in which introduction of gaseous HCl to a solution of
12 resulted in the near quantitative recovery of 13. Charac-
terization of 13 occurred by 31P NMR, elemental analysis,
and X-ray crystallography, and identity of 9 was made
possible by comparison to authentic material. The 31P NMR
spectrum of 13 is nearly identical to that previously
reported,22 and the molecular structure (Figure S11) was
virtually indistinguishable from the published structure.23 This
substance crystallized in the crystallographic space group
P21/n, where 1.5 CHCl3’s were present in the lattice.
Chloroform solutions of 12 (ca. 5 mM), where the CHCl3
was stored for at least 1 day using zeolite material (activated
at 400 °C under vacuo), reproducibly showed complete
decomposition within a 24 h period according to eq 3.
Figure 1. ORTEP representation (50% probability) of cis-Cl2Pd[(PPh2-
OCH2)2-nBu4Clx], 12: (A) view from the side; (B) view from above.
Selected bond distances (Å) and bond angles (deg): Pd(1)-P(2) 2.2452-
(8), Pd(1)-P(1) 2.2533(8), Pd(1)-Cl(1) 2.3513(9), Pd(1)-Cl(2) 2.3583-
(8), P(2)-Pd(1)-P(1) 97.46(3), P(2)-Pd(1)-Cl(1) 86.95(3), P(1)-Pd(1)-
Cl(1) 175.03(3), P(2)-Pd(1)-Cl(2) 174.09(3), P(1)-Pd(1)-Cl(2) 88.44(3),
Cl(1)-Pd(1)-Cl(2) 87.14(3), C(5)‚‚‚C(17) 4.27. Intraannular distances:
C(5)‚‚‚C(11), 4.27 Å; C(11)‚‚‚C(23), 10.14 Å. Chloroform solvates, alkyl
chains, and hydrogens were omitted for clarity.
(21) Iwamoto, K.; Araki, K.; Shinkai, S. J. Org. Chem. 1991, 56, 4955-
4962.
(22) Wong, E. H.; Bradley, F. C. Inorg. Chem. 1981, 20, 2333-2335.
(23) Ghaffar, T.; Kieszkiewicz, A.; Nyburg, S. C.; Parkins, A. W. Acta
Crystallogr. C 1994, C50, 697-700.
90.3°. The mode of coordination observed in 12 is identical
to that described for a closely related cationic Pd-calix[4]-
5990 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
Table 1. Crystal Data and Structure Refinement for cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12, and Mo(CO)4[(PPh2OCH2)2-nBu4Clx], 14c
identificatn code
empirical formula
fw
cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12
C76H84O6P2Cl2Pd‚6CHCl3
1970.924
Mo(CO)4[(PPh2OCH2)2-nBu4Clx], 14c
C37H39O5PMo‚1/3C6H6
1311.35
T (°C)
-80
-100
wavelength (Å)
cryst system
space group
a (Å)
b (Å)
c (Å)
0.710 73
0.710 73
triclinic
P1h (No. 2)
trigonal
P3hc1 (No. 165)
26.166(9)
26.166(9)
17.935(11)
90
90
14.3690(11)
18.3194(14)
18.4160(14)
88.9780(10)
71.1410(10)
84.2300(10)
4563.6(6)
R (deg)
â (deg)
γ (deg)
120
10635(8)
V (Å3)
Z
2
3
F(calcd) (g/cm3)
1.434
0.870
1.089
1.277
0.29
1.013
µ (mm-1
)
goodness-of-fit on F2
final Ra indices [I> 2σ(I)]
Ra indices (all data)
R1 ) 0.0642, wR2 ) 0.1997
R1 ) 0.0795, wR2 ) 0.2116
R1 ) 0.0474, wR2 ) 0.1220
R1 ) 0.0645, wR2 ) 0.1437
2
2
2
a R ) Σ||Fo| - |Fc||/Σ|Fo|; wR2 ) {Σ[w(Fo - Fc )2]/Σ[w(Fo )2]}1/2
.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12, and
under gentle refluxing conditions within 3 h and yielded the
chelated complex in good yields, eq 4. Work up of the
residual solid resulted in the isolation of a pale-yellow
material with the formulation fac-(CO)3Mo(L)[(PPh2OCH2)-
nBu4Clx] (L ) NCCH3, 14a, L ) NCCH2CH3, 14b). Both
complexes were isolated upon rapid crystallization from
benzene solutions. This material was amenable to FT-IR
analysis, and elemental analyses provided excellent agree-
ment with theory. Unfortunately, both species were somewhat
unstable in solution, though freshly prepared solutions
provided ESI-MS analysis that confirmed the monomeric
identity in solution. This apparent solution instability ham-
pered attempts to obtain high-quality crystalline material, via
slow evaporation of solvent, suitable for X-ray analysis. For
example, solutions of 14a,b in benzene-d6 slowly decom-
posed over a 1-week period to unidentifiable material. Solid
samples of 14a,b were indefinitely stable at room temperature
and in the absence of air; however, upon heating under
reduced pressure at 175 °C, the pale-yellow solid turned
black. Analysis of the resultant material by 1H NMR revealed
a mixture of unidentifiable products, but most noticeable was
the loss of coordinated nitrile.
Mo(CO)4[(PPh2OCH2)2-nBu4Clx], 14c
cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12
Bond Lengths (Å)
Pd(1)-P(2)
Pd(1)-P(1)
Pd(1)-Cl(1)
Pd(1)-Cl(2)
P(1)-O(45)
2.2452(8)
2.2533(8)
2.3513(9)
2.3583(8)
1.610(2)
P(1)-C(46)
P(1)-C(52)
P(2)-O(58)
P(2)-C(65)
P(2)-C(59)
1.808(3)
1.816(3)
1.607(2)
1.808(3)
1.812(3)
Bond Angles (deg)
P(2)-Pd(1)-P(1)
P(2)-Pd(1)-Cl(1)
P(1)-Pd(1)-Cl(1)
97.46(3)
86.95(3)
175.03(3)
P(2)-Pd(1)-Cl(2)
P(1)-Pd(1)-Cl(2)
Cl(1)-Pd(1)-Cl(2)
174.09(3)
88.44(3)
87.14(3)
C‚‚‚C Intramolecular Distances
C(5)‚‚‚C(17)
C(11)‚‚‚C(23)
4.27
C(45)‚‚‚C(58)
C(26)‚‚‚C(28)
3.96
5.32
10.14
Mo(CO)4[(PPh2OCH2)2-nBu4Clx], 14c
Bond Lengths (Å)
Mo(1)-C(3)A
Mo(1)-C(3)
Mo(1)-C(5)A
Mo(1)-C(5)
2.013(5)
2.013(5)
2.032(5)
2.032(5)
Mo(1)-P(2)A
Mo(1)-P(2)
P(2)-O(19)
2.4910(13)
2.4910(13)
1.637(3)
Bond Angles (deg)
86.43(11) O(19)-P(2)-C(7)
C(5)A-Mo(1)-P(2)
C(5)-Mo(1)-P(2)
100.44(16)
86.22(11) O(19)-P(2)-Mo(1) 120.88(10)
P(2)A-Mo(1)-P(2) 100.42(5)
O(4)-C(3)-Mo(1)
174.9(4)
O(19)-P(2)-C(13)
98.27(16)
C‚‚‚C Intramolecular Distances
C(5)‚‚‚C(17)
C(11)‚‚‚C(23)
4.21
C(45)‚‚‚C(58)
C(26)‚‚‚C(28)
3.74
5.41
10.12
Solutions of 12 in CHCl3, where there was no exposure to
sieves, were stable over a 3-week period.
The 1H NMR spectra of both complexes are quite similar
and are reminiscent of that observed for 11, in which the
spatial orientation of the coordinated ligands gave rise to
several inequivalent calix[4]arene hydrogen resonances,
The bidentate ligand 8 readily reacted with Mo(CO)3-
(toluene) in the presence of either acetonitrile or propionitrile
Inorganic Chemistry, Vol. 41, No. 23, 2002 5991

Evans et al.
Figure S3. For example, the bridging ArCH2Ar methylene
resonances (AB spin system) appear as two sets of doublets,
and the hydrogens ortho to the C(5) and C(17) carbon atoms
appear as two doublets. Additional inequivalence is present
in the arene region in which two sets of doublets and triplets
are present for the hydrogens bound to the A and C rings.
The most notable difference between that observed for 14a,b
and 12 is the presence of a well-defined AB quartet (4.47,
2
1
4.37; JAB ) 12 Hz). Another interesting aspect of the H
NMR spectra of 14a,b to note is the upfield location of the
methyl and ethyl hydrogen resonances of the appropriate
nitrile ligands. In the case of 14a, a singlet at 0.14 ppm was
present, while for 14b a triplet and quartet appeared -0.16
and 0.71 ppm, respectively. (This corresponds to shifts of
about 2 ppm upfield from free ligand.) The initial expectation
was that the ligand was directed toward the interior of the
cavity, as examples exist in which metal-calix[4]arene
chelates were capable of encapsulating a variety of small
molecules.4,7a,c This scenario would require a meridonal
orientation of the CO ligands and trans ligation of the tethered
phosphinites. This formulation is inconsistent with the
FT-IR data; moreover, this arrangement did not exist in the
solid state as based on the acquisition of the somewhat poorly
defined molecular structure of 14b.
Figure 2. ORTEP representation (50% probability) of Mo(CO)4[(PPh2-
OCH2)2-nBu4Clx], 14c (including symmetry-equivalent atoms). Selected
distances (Å) and bond angles (deg): Mo(1)-P(2) 2.4910(13), Mo(1)-
C(3) 2.013(5), Mo(1)-C(5) 2.032(5), C(3)-O(4) 1.154(5), C(5)-O(6)
1.161(5), P(2)-Mo(1)-C(3) 170.43(12), P(2)-Mo(1)-C(5) 86.22(11),
P(2)-Mo(1)-C(3)A 88.61(12), C(3)-Mo(1)-C(5) 91.23(17), C(3)-
Mo(1)-C(3)A 82.6(2), C(5)-Mo(1)-C(5)A 168.5(2), C(5)‚‚‚C(17) 4.21.
Intraannular distances: C(5)‚‚‚C(17), 4.21 Å; C(11)‚‚‚C(23), 10.12 Å.
Benzene solvate, alkyl chains, and hydrogens were omitted for clarity.
As mentioned above, acquisition of high-quality crystals
for either 14a or 14b was not possible. Rapid recrystallization
of both yielded platelike microcrystals. The crystal quality
was poor, but 14b yielded diffraction-quality crystals,
wherein collection of a partial 2θ-data set provided an
opportunity to elucidate the gross features of the inner- and
outer-coordination sphere. The data, not shown, provide an
informative ORTEP representation, which can be found in
the Supporting Information (Figure S12). Like that observed
in 12, the bis(phosphinite) coordinates the molybdenum atom
in a cis fashion, which is twisted above the pinched-cone,
such that the original C2V symmetry of the metal-free ligand
is lost. The carbonyl ligands orient themselves facially in
the Mo coordination sphere leaving the CH3CH2CN ligand
bound to the Mo trans to a CO ligand. This picture shows
that the C-H/π interactions that must be present, to account
spectrum in the carbonyl region agrees with expectations.
As with the aforementioned complexes, ESI-MS provided
unambiguous evidence supporting the monomeric identity
1
of 14c in solution. The H NMR spectrum of 14c, in C6D6,
closely resembles that of 12. A singlet for the meta-
hydrogens of rings B and D appeared at 6.38 ppm, and only
two doublets were present for the ArCH2Ar axial and
equatorial hydrogen atoms, while the methylene hydrogens,
ArCH2OP-, sampled magnetically equivalent environments,
as deduced from the broadened singlet at 4.34 ppm. Inspec-
tion of the solid-state molecular structure of 14c would seem
to contradict the observed 1H spectroscopic properties.
Rationalization of these observables is possible if this system
is capable of undergoing dynamic exchange.
Figure 2 contains an ORTEP (50% probability) represen-
tation of the molecular structure of 14c, in which the alkyl
chains, hydrogens, and benzene solvate were omitted for
clarity. Tables 1 and 2 provide selected crystallographic and
metrical parameters for this complex. The material crystal-
lized in the space group P3hc1, where the Mo atom resided
in a special position. This presented a structure in which
exactly half of the molecule was crystallographically
unique. For the sake of uniformity, the depiction of 14c
shown in the figure contains the entire molecule and a num-
bering scheme consistent with the other structures reported
herein. As observed in 12, coordination of the metal frag-
ment by the two opposing phosphinite moieties gave rise to
a calix[4]arene structure best described as a “pinched-cone”.
This conformation resulted in an intraannular separation
(C(5)‚‚‚C(17)) of 4.21 Å and a C(45)‚‚‚C(58) through-space
1
for the anomalous H resonances, were due not to interac-
tion with the inner annulus of the calix[4]arene cavity but
with arene rings of the adjacent phosphinite ligand. The
CH3-Arcentroid distance observed in the solid state is 3.8 Å,
which is about 0.1 Å beyond the sum of the van der Waals
radii.24 Inspection of the complex using a molecular modeling
program showed that rotation of the propionitrile ligand about
the C-N-Mo axis places the methyl group as close as 3.1
Å. This close contact readily explains the nature of the
1
upfield H NMR shift.
Complex 14a readily underwent ligand substitution in the
presence of gaseous CO and yielded the tetrakis(carbonyl)
complex, 14c, in 98% isolated yield, eq 4. This complex,
unlike 14a,b, is quite stable in solution, and solid samples
were modestly air stable. The elemental analysis obtained
for this compound agrees well with theory, and the FT-IR
(24) Bondi, A. J. Phys. Chem. 1964, 68, 441-451.
5992 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
distance of 3.74 Å. Due to crystallographically imposed
symmetry, only one Mo-P bond is unique, and thus the
carbonyls cis and trans are unique as well. As such, quoted
distances and angles are not averages but the observed values.
The two phosphorus atoms are ligated to the molybdenum
(d(Mo-P2) ) 2.488(1) Å) in a cis manner, but the nature
of the calix[4]arene gives rise to an opened P-Mo-P angle
of 100.42(5)°. This angle is much larger than other d6-metal
systems that contain the cis-chelated dppe ligand.25 This is
clearly a testament to the flexibility of the calix[4]arene
macrocycle and is slightly larger than that observed in 12
(cf. 97.5°). The carbonyl trans to P2 gives normal Mo-C
and C-O distances of 2.013(5) and 1.154(5) Å, respectively.
As expected, the carbonyl cis to P2 gives an elongated
Mo-C distance of 2.032(5) Å, but the C-O distance of
1.161(5) Å is statistically indistinguishable from its neigh-
boring CO ligand. The coordination about the molybdenum
is best described as pseudooctahedral, but the symmetry at
the Mo is approximately C2V. This is supported by the four
CO stretches observed in the IR spectrum. While the
symmetry of the metal approximates C2V symmetry, the
orientation in the figure shows that the entire molecule has
5,17-(PPh2CH2)2-nPrClx appeared.9b These authors failed to
obtain chelated adducts with either (COD)PdMeCl or (COD)-
PtCl2 but, instead, isolated polymeric products. This observa-
tion was noted in an earlier study as well.9a In light of these
two studies, it is possible that chelation did not occur, and
the observed spectroscopic features of the isolated material
were that of a polymeric adduct.
Discussion
Solid-State Structures of Selected Tetra-O-alkylated
Calix[4]arenes. The literature is rife with examples that
suggest that the calix[4]arene cavities, when derivatized with
reactive metal centers, are analogous to the active sites of
metal-containing enzymes.26 The hydrophobic pocket avail-
able within the confines of the calix[4]arene annulus, in
practice, should provide additional stabilization for the
preassociation of hydrophobic substrates prior to the occur-
rence of metal-mediated transformations. This aspect alone
makes this class of host-guest molecules particularly at-
tractive as applied in the area of homogeneous catalysis, as
the presence of the cavity could provide added selectivity
or varying reactivity. In light of this attribute, it seems
important to highlight the observed solid-state parameters
gleaned from this study and provide comparisons with other
published calix[4]arene derivatives.
Table 3 contains data for tetra-O-alkylated calix[4]arenes
(R4Clx), with a few exceptions, showing the distances
between opposing arenes (as measured by the through-space
distances between C(5)‚‚‚C(17) and C(11)‚‚‚C(23)). The
listed entries (E) fit nicely into three categories: (i) tetra-
substitution at the upper rim (Y4-R4Clx, Y ) H, E2-E4, Y
) Br or NO2, E5-E7); (ii) di-5,17-substitution at the upper
rim (5,17-Y2-11,23-H2-R4Clx (E9-E25, E29) or 5,17-Y2-
11,23-tBu4-R4Clx (E26-E28)); (iii) structurally determined
metal chelates containing 5,17-calix[4]arene-containing ligands
(E30-E42).
1
approximate C2 symmetry. This would suggest that the H
NMR spectrum is indeed a time-averaged spectrum (room
temperature, 400.132 MHz), since the aforementioned reso-
nances appear to be magnetically equivalent.
At the onset of this work, it was conceivable that a
reduction in the linker from -CH2O- to -CH2- would
provide a bidentate ligand that would readily chelate the
metal center over an expanded cavity. Inspection of the
molecular structure of 10, Figure S10, shows that this ligand
set should be ideally suited to accomplish such a feat.
Unfortunately, the reaction of 10 with a stoichiometric
amount of Mo(CO)3(toluene), stirred in acetonitrile for 24 h
with gentle heating, did not go to completion. Analysis of
the isolated material by 1H NMR showed the reaction to be
incomplete; furthermore, neither longer reaction times (5 d)
nor purification provided material free of starting material.
It is believed that the material that formed was fac-(CO)3Mo-
(NCCH3)[(PPh2CH2)2-nBu4Clx], 15. 1H NMR spectra proved
difficult to interpret, but it was apparent that complexation
occurred and most noticeable was the presence of an upfield
singlet at -2.62 ppm. If the structure of 15 is similar to that
observed for 14b,c, then the anomalous shift would be
attributable to a C-H/π interaction perhaps with the arene
ring directly attached to P. 31P NMR showed two doublets
at 40.2 and 35.2 ppm (J ) 27 Hz). This would require the
molecular symmetry to be C1, and unlike that observed for
the other species reported herein, no operative dynamic
exchange pathway. Inspection of the IR data showed four
carbonyl stretches, which is consistent with cis-coordina-
tion by the 10. In the course of manuscript revision, another
article appeared in which the coordinative properties of
Given the data at hand, the first thing to recognize is the
presence or absence of a cavity. The phenolic oxygens of
the parent calix[4]arene cavities (1 and 2) participate in intra-
molecular hydrogen bonding, thereby enforcing the charac-
teristic C4V-symmetric cavity.1 In the case of the parent calix-
[4]arene, E1, the apparent symmetry is evident from the
(26) (a) Beer, P. D.; Drew, M. G. B.; Leeson, P. B.; Lyssenko, K.; Ogden,
M. I. J. Chem. Soc., Chem. Commun. 1995, 929-930. (b) Molenveld,
P.; Kapsabelis, S.; Engbersen, J. F. J.; Reinhoudt, D. N. J. Am. Chem.
Soc. 1997, 119, 2948-2949. (c) Blanchard, S.; Le Clainche, L.; Rager,
M.-N.; Chansou, B.; Tuchagues, J.-P.; Duprat, A. F.; Le Mest, Y.;
Reinaud, O. Angew. Chem., Int. Ed. 1998, 37, 2732-2735. (d)
Molenveld, P.; Engbersen, J. F. J.; Kooijman, H.; Spek, A. L.;
Reinhoudt, D. N. J. Am. Chem. Soc. 1998, 120, 6726-6737. (e) Xie,
D.; Gutsche, C. D. J. Org. Chem. 1998, 63, 9270-9278. (f) Blanchard,
S.; Rager, M.-N.; Duprat, A. F.; Reinaud, O. New J. Chem. 1998, 22,
1143-1146. (g) Molenveld, P.; Stikvoort, W. M. G.; Kooijman, H.;
Spek, A. L.; Engbersen, J. F. J.; Reinhoudt, D. N. J. Org. Chem. 1999,
64, 3896-3906. (h) Molendveld, P.; Engbersen, J. F. J.; Reinhoudt,
D. N. J. Org. Chem. 1999, 64, 6337-6341. (i) Rondelez, Y.; Seneque,
O.; Rager, M.-N.; Duprat, A. F.; Reinaud, O. Chem.sEur. J. 2000, 6,
4218-4226. (j) Clainche, L. L.; Giorgi, M.; Reinaud, O. Eur. J. Inorg.
Chem. 2000, 1931-1933. (k) Clainche, L. L.; Giorgi, M.; Reinaud,
O. Inorg. Chem. 2000, 39, 3436-3437. (l) Rondelez, Y.; Rager, M.-
N.; Duprat, A.; Reinaud, O. J. Am. Chem. Soc. 2002, 124, 1334-
1340. (m) Spencer, D. J. E.; Johnson, B. J.; Johnson, B. J.; Tolman,
W. B. Org. Lett. 2002, 4, 1391-1393.
(25) (a) Kubas, G. J.; Burns, C. J.; Eckert, J.; Johnson, S. W.; Larson, A.
C.; Vergamini, P. J.; Unkefer, C. J.; Khalsa, G. R. K.; Jackson, S. A.;
Eisenstein, O. J. Am. Chem. Soc. 1993, 115, 569-581. (b) Luo, X.
L.; Kubas, G. J.; Burns, C. J.; Eckert, J. Inorg. Chem. 1994, 33, 5219-
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K. W. J. Am. Chem. Soc. 1996, 118, 6782-6783.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5993

Evans et al.
Table 3. Pinched-Cone Arene-to-Arene Distances for Selected Calix[4]arenes
entry
compd
C(5)‚‚‚C(17) (Å)
C(11)‚‚‚C(23) (Å)
ref
1
2
3
4
5
6
7
8
9
Clxa
8.39
4.22
4.97
4.54
4.45(13)
5.08
4.64
4.04
10.061
10.11
9.97
9.96
10.10
4.96
4.95
5.36
4.37
9.8(1)
3.90
9.71
4.41
10.09
10.02
4.51
4.54
7.83
6.45
5.91
6.43
5.62
4.78
10.18
4.19
4.24
7.15
9.49
4.92
4.19
10.17
6.21
4.27
4.21
8.39
10.06
9.64
9.79
10.02(8)
9.96
27a
this work
28
29
this work
30
31
32
33
34
35
35
34
34
34
19
this work
7b
this work
this work
this work
this work
this work
this work
9b
32
9a
33
4b
7a
36b
7b
nBu4Clx, 3
(CH3SCH2CH2)4Clx
(CH2CH2OH)4Clx
Br4-nBu4Clx, 4b
Br4-nPr4Clx‚C60
c
(NO2)4-nPr4Clx
9.97
(NO2)2-nPr4Clx
10.11
4.958
4.35
4.61
4.41
4.11
9.64
9.52
9.48
tBu2-R4Clxd
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Ph2-nPr4Clx
Y2-nPr4-Clxe
Y2-nPr4-Clxf
(3-Br-Ph)2-nPr4Clx
1-Nap2-nPr4Clxg
Carb2-nPr4Clxh
Y2-nPr4Clxi
Br2-nBu4Clx, 5
9.92
Br2-Bz4Clxb
4.50(8)
10.12
4.94
9.88
3.78
(CHO)2-nBu4Clx, 6
(HOCH2)2-nBu4Clx, 7 (A)j
(HOCH2)2-nBu4Clx, 7 (B)j
(HOCH2)2-nBu4Clx, 7 (C)j
(PPh2OCH2)2-nBu4Clx, 8
(PPh2CH2)2-nBu4Clx, 10
(PPh2CH2)2-nPr4Clx
tBu4-nPr4Clx
4.20
10.11
10.13
7.79
9.21
9.32
9.19
9.63
9.89
4.06
9.96
10.36
8.97
6.20
9.60
10.17
4.18
9.21
10.14
10.12
5,17-(P(O)Ph2CH2)2-11,23-tBu2-nPr4Clxk
5,17-tBu2-11,23-cht2-R4Clxd,l
S2Clxm
Cl2Ru(CO)2[5,17-(PPh2)2-nPr4Clx]n
[Ag-nPr4Clx]OTfo
p
{trans-Cl2Pd[(PPh2)2-Bz4Clx]}2
cis-Cl2Pt[(PPh2)2-Bz4Clx]q
7b
5
5
5
8b
7c
7c
7c
5,17-(Cp′2)Co-O-5,O-17-Tos2Clx+ r
5,17-(Cp′CoCp)2-O-5,O-17-Tos2Clx2+ s
5,17-(Cp′FeCp)2-O-5,O-17-Tos2Clxs
Cp*Cl2Rh(5-(PPh2)-nPr4Clx]t
(η3-C4H7)Pd[(PPh2)2-nPr4Clx]
cis-Cl2Pt[(PPh2)2-nPr4Clx′]q,u
cis-Cl2(p-cymene)Ru[(PPh2)-nPr4Clx′]V
cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12
Mo(CO)4[(PPh2OCH2)2-nBu4Clx], 14c
this work
this work
c
a Acetone solvate outside of cavity. b Average value of two crystallographically unique molecules in the unit cell. C60 as cocrystallate. d R ) tert-
butyloxycarbonyl. e Y ) 2-(2-bromophenyl)ethenyl. f Y ) 2-(4-bromophenyl)ethenyl. g 1-Naphthalyl. h N-Carbazolyl. i Y ) fluorenyl. j Cystallographically
unique molecules in the unit cell. k R ) EtOEt. l cht ) cyclohepta-2,4,6-trienyl. m 5,17-(R,R′-m-Xylenedithioacetamide)-tetra-25,26,27,28-n-propoxycalix[4]arene
(S2Clx). n Phosphines, chlorides, and carbonyls are all trans, with the CO inside the pocket. o Ag(I) positioned at midpoint between line joining C(5) and
C(17). p Dimeric species. q Molecular structure showed Cl2Pt fragment over half of the annulus. r 5,17-Positions possess formamidocyclopentadienyl substituents,
NHC(O)C5H4, which when in pinched-cone conformation create a cobaltacenium complex. s Cp′ ) (C5H4)C(O)NH-. t Cp*RhCl2 fragment directed away
from the pinched-cone in the solid state. u Clx′ ) 5,17-Br2-11,23-(PPh2)2-nPr4Clx. V Clx′ ) 5,11,17-Br3-23-PPh2-nPr4Clx.
equivalent distances of 8.39 Å.27 These molecular dimensions
afford a cavity with an estimated van der Waals volume
(VvdW) of approximately 36-52 Å3.24 This cavity enforcing
interaction is lost upon tetra-O-alkylation, where the calix-
[4]arene cavity adopts a C2V-symmetric, or “pinched-cone”,
conformation. This is evident upon inspection of the values
in E2-E25, where the average pinched-arene distance is 4.5
( 0.4 Å7b,19,28-35 and the estimated VvdW is 8-20 Å3. It is
interesting to note that the sole purpose of tetra-O-alkylation
is to suppress the formation of intraannular conformations,
such as the partial-cone, 1,2- and 1,3-alternate structures,
and thereby retain the conelike shape of the calix[4]arene.1
Yet, it is obvious from the data that this modification clearly
reduces the effective volume of the cavity to a point where
it seems inaccurate to refer to these species as “bowl-shaped”
(31) Kenis, P. J. A.; Noordman, O. F. J.; Houbrechts, S.; van Hummel, G.
J.; Harkema, S.; van Veggel, F. C. J. M.; Clays, K.; Engbersen, J. F.
J.; Persoons, A.; van Hulst, N. F.; Reinhoudt, D. N. J. Am. Chem.
Soc. 1998, 120, 7875-7883.
(32) Verboom, W.; Struck, O.; Reinhoudt, D. N.; van Duynhoven, J. P.
M.; van Hummel, G. J.; Harkema, S.; Udachin, K. A.; Ripmeester, J.
A. Gazz. Chim. Ital. 1997, 127, 727-739.
(33) Orda-Zgadzaj, M.; Wendel, V.; Fehlinger, M.; Ziemer, B.; Abraham,
W. Eur. J. Org. Chem. 2001, 1549.
(34) Larsen, M.; Krebs, F. C.; Harrit, N.; Jorgensen, M. J. Chem. Soc.,
Perkin Trans. 2 1999, 1749-1757.
(35) Larsen, M.; Krebs, F. C.; Jorgensen, M.; Harrit, N. J. Org. Chem.
1998, 63, 4420-4424.
(27) (a) Ungaro, R.; Pochini, A.; Andreetti, G. D.; Sangermano, V. J. Chem.
Soc, Perkin Trans 2 1984, 1979-1985. (b) Harrowfield, J. M.; Ogden,
M. I.; Richmond, W. R.; Skelton, B. W.; White, A. H. J. Chem. Soc.,
Perkin Trans. 2 1993, 2183-2190. (c) Akdas, H.; Bringel, L.; Graf,
E.; Hosseini, M. W.; Mislin, G.; Pansanel, J.; De Cian, A.; Fisher, J.
Tetrahedron Lett. 1998, 39, 2311-2314.
(28) Yordanov, A. T.; Whittlesey, B. R.; Roundhill, D. M. Inorg. Chem.
1998, 37, 3526-3531.
(29) Moran, J. K.; Georgiev, E. M.; Yordanov, A. T.; Magu, J. T.;
Roundhill, D. M. J. Org. Chem. 1994, 59, 5990-5998.
(30) Barbour, L. J.; Orr, G. W.; Atwood, J. L. Chem. Commun. 1998,
1901-1902.
5994 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
1
derivatives, as the name implies the ability to contain.36 In
the absence of any other factors, see below, the calix[4]arene
species listed here that possess the “pinched-cone” confor-
mation but still may be called cavity-containing molecules
are found in E26-E29.4b,9,32,33 The increased arene-to-arene
separation for the first three must be due to the C(11) and
C(23) tert-butyl substituents, while the last one is brought
about by a spanning functionality that fixes the intraannular
separation.
but H NMR data confirmed the encapsulation of small
ligands, CH3CN and pyr, above the mouth of the cavity.
Matt et al., E30, reported a remarkable example of the
inclusion of a small ligand, CO, within the reduced confines
of the calix[4]arene.7a In this calix[4]arene complex, the
Ru(II) adopted an all-trans coordination sphere in which 5,-
17-bis(phosphines) provided a metal complex in which
entrapment of the coordinated carbonyl occurred. Given the
C(5)‚‚‚C(17) distance of 5.62 Å, this should be considered
a remarkable feat, as the CO-to-arene distance is 2.70 Å and
is well within the van der Waals radii of the observed
atoms.24 A third example in which metal complexation above
the mouth of the cavity occurred appears in E31.36b This
complex showed that the para-carbons of rings B and D
interact with Ag(I) in an η1-fashion. This mode of coor-
dination is now known to be somewhat common,37 but
the two-coordinate silver coordination sphere, with a
C(5)‚‚‚Ag(I)‚‚‚C(17) angle of 173°, makes this entity unique.
Tsuji et al. recently prepared Pd(II)- and Pt(II)-calix-
[4]arene analogues, E32 and E33, in which the same ligand
coordinated the metals in two strikingly different ways.7b In
the case of the complexes listed in E32 and E33, trans
ligation of the bis(phosphine) ligand to Pd(II) occurred for
the former, but cis-ligation to Pt(II) in the latter. Given the
fact that these disubstituted calix[4]arenes undergo the
aforementioned C2V-C2V interconversion,36 it becomes clear
why this ligand is capable of either chelation (E33) or
dimerization (E32). It would appear that the synthetic
conditions, and the nature of the metal, dictate the outcome
of coordination. Both complexes revealed a normal
C(5)‚‚‚C(17) distance, and the PtCl2 fragment resided on one
side of the cavity. The occupation of the Pt(II) coordination
array over a hydrophobic cleft would suggest that this
species, when appropriately derivatized, should be ideally
suited to participate in selective C-H activation. The
complexes prepared by Beer et al. are different from all other
entries, in that only two of the four phenolic oxygens were
functionalized, E35 and E36.5 Coupled with the presence of
bulky sandwich complexes, this arrangement afforded calix-
[4]arene derivatives with well-defined cavities as evidenced
by the larger than normal C(5)‚‚‚C(17) distances of about
8.1 Å. Indeed, these authors found that these molecules
served as anion receptors in which a change in potentials of
the electrochemically active species provided an opportunity
to sense different anions.
Since it is well-known that R4Clx species undergo a rapid
exchange between two C2V-symmetric species,36 i.e., one
conformer in which the C(5)‚‚‚C(17) separation is short and
another in which this distance is large, then it comes to no
surprise that these molecules crystallize in two conforma-
tional forms. For the sake of discussion, an “open” confor-
mation is one in which a C2V-symmetric calix[4]arene species
possesses a large C(5)‚‚‚C(17) distance and a “closed”
conformation will be used to denote a short arene-to-arene
separation. Given the limited data, E8, E17, and E19, it would
appear that when Y is small, the “closed” conformation is
preferred (E18 is an exception), and the converse is true when
Y is large, E9-E13 and E23. Disruption of this trend occurs
when the two substituents are capable of interacting with
one another. For example, complexes that possess the closed
conformation (E12-E16, E23, and E25) presumably adopt
this configuration due to the presence of either π-π
interactions (E14 and E15) or C-H/π interactions (E16, E24,
and E25) or some unforeseen crystal packing forces. In
addition, for the hydroxymethyl species (7, E20-E22),
intramolecular hydrogen bonding (O‚‚‚O separation of
2.75(3) Å) promoted the “closed” conformation, but inter-
molecular hydrogen bonding (with lattice solvent) gave rise
to the “open” conformation. These data clearly show that
the preferred solid-state conformation for unconstrained tetra-
O-alkylated calix[4]arenes is a pinched-cone. As such, metal
complexes should exhibit similar solid-state properties in
which the volume of the calix[4]arene cavity is significantly
diminished relative to the parent calix[4]arenes, E1.
Solid-State Structures of Selected Tetra-O-alkylated
Metal-Calix[4]arene Complexes. As mentioned in the
introductory remarks, the long-term goal is to situate reactive
metal fragments above the opened mouth of the calix[4]arene
such that the hydrophobic pocket can be used to promote
association of alkanes in close proximity to a reactive metal
center. To date, several examples exist in which positioning
of the metal above the binding-cleft occurred,4,7-9 and only
one of these investigators indicated that hydrocarbon activa-
tion is the thrust of future research.8 For example, Loeb et
al. were the first to prove that the cavity is large enough to
accommodate small ligands when a metal resides above the
mouth of the cavity.4 They employed the ligand, E29, which
is capable of undergoing cyclometalation with Pd(II) to form
a cationic R′(SCS)Pd-nPr4Clx adduct. This study did not
produce a molecular structure of the resultant complexes,
Harvey et al. prepared 5-PR2-nPr4Clx (R ) Ph, Pr)
i
derivatives capable of coordinating Rh(III) (E37).8 This was
a clever design in which a potential Rh(I) species might
undergo selective C-H activation with alkanes that could
undergo preassociation due to the positioning of the rhodium
(37) (a) Shelly, K.; Finster, D. C.; Lee, Y. J.; Scheidt, W. R.; Reed, C. A.
J. Am. Chem. Soc. 1985, 107, 5955-5959. (b) Xie, Z.; Wu, B.-M.;
Mak, T. C. W.; Manning, J.; Reed, C. A. J. Chem. Soc., Dalton Trans.
1997, 1213-1217. (c) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T.;
Maekawa, M.; Suenaga, Y.; Sugimoto, K.; Ino, I. J. Chem. Soc., Dalton
Trans. 1999, 373-378. (d) Batsanov, A. S.; Crabtree, S. P.; Howard,
J. A. K.; Lehmann, C. W.; Kilner, M. J. Organomet. Chem. 1998,
550, 59-61. (e) Tsang, C.-W.; Yang, Q.; Sze, E. T.-P.; Mak, T. C.
W.; Chan, D. T. W.; Xie, Z. Inorg. Chem. 2000, 39, 5851-5858.
(36) (a) Conner, M.; Janout, V.; Regen, S. L. J. Am. Chem. Soc. 1991,
113, 9670-9671. (b) Ikeda, A.; Tsuzuki, H.; Shinkai, S. J. Chem.
Soc., Perkin Trans. 2 1994, 2073-2080.
Inorganic Chemistry, Vol. 41, No. 23, 2002 5995

Evans et al.
fragment relative to the cavity. Inspection of the solid-state
structure showed that the reactive part of the rhodium
coordination sphere would appear to be directed away from
the mouth of the cavity. These authors discovered that a
dynamic exchange pathway could give rise to a conformer
which would position the more reactive part of the fragment
above the annulus, but inspection of the C(5)‚‚‚C(17) distance
(ca. 5 Å) shows that, rather than a cavity, a partial cleft would
be available to interact with alkanes prior to reaction with
the rhodium center.
Other attractive candidates occur in the examples provided
by Matt and Tsuji in which the PtCl2 fragment resides over
half of the cavity. While the binding pocket should really
only be classified as a binding-cleft, the availability of the
splayed arene could promote selectivity in alkane function-
alization. A deeper, more voluminous, binding pocket is
synthetically accessible upon the introduction of benzyl
substituents at the C(11) and C(23) positions.39 Harvey’s
system seems promising if, and only if, the reactive fragment
was found not only above the hydrophobic cleft but directed
toward it. The authors stated that the Rh(I) complex
undergoes C-H activation, and it will be interesting to see
if any selectivity occurs in this system. Inspection of the
molecular structures of 12 and 14c reveals that diametrically
functionalized species prepared herein render a metal coor-
dination sphere in which any subsequent reactivity would
occur directed away from the hydrophobic cleft. Even if a
rollover motion occurred, see below, the metal would be well
removed from the hydrophobic confines of the calix[4]arene.
One possibility that, to our knowledge, has not been tested
is to metalate the lower rim phenoxide atoms, thereby
enforcing an enlarged cavity, but then introduce traditional
P-ligands at the upper-rim positions. For example, Floriani,
and others, reported [M]O4Clx species that provide cavities
with an intraannular volume that approaches that of the C4V-
symmetric parent molecule. These complexes, (O)WO4Clx-
(OdC(CCH3)2),40 (cat′)WO4Clx,41 Cp*TaO4Clx,42 and (ArN)-
MoO4Clx(NCCH3),43 provide C(5)‚‚‚C(17) distances that
range from 7.3 to 8.3 Å. This enlarged cavity would then
require longer linkers that tether the ligand to the cavity,
e.g., either -CH2CH2- or -CH2O-, to promote chelation
above the mouth of the calix[4]arene. This seems to be
feasible but would be synthetically challenging, as it is
uncertain that the metals used to enforce the cavity would
survive the many steps required to achieve functionalization
along the upper rim. An alternative route would be to
introduce upper-rim substituents using the tetra-O-benzoy-
lated derivatives,1 where removal of the benzoyl groups
followed by formation of aryloxy-metal chelates would
afford a bidentate ligand with a well-defined cavity.
Finally, a recent report by Matt et al. revealed that
complexation of Pd, Pt, and Ru occurred using either di- or
monosubstituted calix[4]arenes, E38-E40.7c Both Pd and
Pt adducts closely resemble Tsuji’s complex, with close
C(5)‚‚‚C(17) contacts and the positioning of the metal
fragment over half of the pinched-cone. The Ru adduct, E40,
is remarkable in that the p-cymene ligand seemed to be
“encapsulated” within the enlarged annulus of the cavity (cf.
C(11)‚‚‚C(23) distance of 6.21 Å). This structure bears a
striking similarity to a calculated structure obtained for
Cp*Cl2Rh[5-(PPh2)-nPr4Clx].8b In the case of the complex
1
shown in E40, H NMR revealed that the encapsulation of
the p-cymene moiety was persistent in solution.
Given the complexes listed above, the structures reported
herein, and some selected literature examples (see below),
it is now clear that there are several ways of accomplishing
metal coordination over a calix[4]arene cavity. The factors
that dictate the mode of coordination, i.e., cis or trans, or
the formation of monomers, dimers, or polymeric species
are slowly becoming apparent. At present, only one report
exists in which a functionally modified calix[4]arene resulted
in metal chelation above an opened calix[4]arene hydropho-
bic pocket.4 All other variations seem to be complicated by
the conformational flexibility of these systems, such that the
metal actually resides over a hydrophobic cleft.7-9 It should
be clear that additional studies are necessary in order to
determine the precise ligand properties that will present a
metal-fragment above a well-defined cavity. This property
is crucial to the realization of our long-term goal of dis-
covering more examples of alkane-metal complexes. Of all
the published examples, Loeb’s ligand seems to be an
attractive candidate for such studies. This is especially true
when one considers the ability of R(PCP)IrI adducts to
undergo alkane activation.38 Conceivably, an Ir(I) adduct,
using this ligand, would provide the ideal system to affect
such transformations. The reactive part of the molecule would
be directed toward the interior of the cavity and, given the
size constraints, may serve to inhibit the process of olefin
isomerization which is known to occur in R(PCP)Ir catalytic
systems. Functionalization of the calix[4]arene with longer
alkyl chains, e.g., C6-C10, would increase the solubility in
alkane only solvent systems. Except for the two provided
reports,4 it is unclear if this investigator is interested in
pursuing this line of research.
Conformational Exchange Available to Metal-Calix-
[4]arene Chelates. The data reported herein would not be
complete without considering the possible dynamic exchange
that is available to these systems. The molecular structures
of cis-Cl2Pt[(PPh2)2-R4Clx]7b,c and (η3-C4H7)Pd[(PPh2)2-nPr4-
Clx]7c showed that the metal fragment resided over half of
the calix[4]arene, e.g., the A or C ring, though NMR data
suggested the presence of reflective elements present in the
molecule. Both authors independently proposed a dynamic
exchange pathway that rationalizes the observed NMR data
(39) Arduini, A.; Pochini, A.; Rizzi, A.; Sicuri, A. R.; Ugozzoli, F.; Ungaro,
R. Tetrahedron 1992, 48, 905-912.
(40) Corazza, F.; Floriani, Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1991,
30, 4465-4468.
(41) Vigalok, A.; Zhu, Z.; Swager, T. M. J. Am. Chem. Soc. 2001, 123,
7917-7918.
(42) Acho, J. A.; Doerrer, L. H.; Lippard, S. J. Inorg. Chem. 1995, 34,
2542-2556.
(38) (a) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J.
Am. Chem. Soc. 1999, 121, 4086-4087. (b) Liu, F.; Goldman, A. S.
Chem. Commun. 1999, 655-656.
(43) Gibson, V. C.; Redshaw, C.; Clegg, W.; Elsegood J. Chem. Soc., Chem.
Commun. 1995, 2371-2372.
5996 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
Scheme 2
large-scale preparation of the parent tert-butylcalix[4]arene
from 4-tert-butylphenol provided ample quantities of starting
material for the extended synthetic sequence used herein.
The choice of n-butyl lower-rim substituents provided
intermediates, ligands, and metal complexes that were, save
a few exceptions, readily crystalline and amenable to X-ray
crystallographic analysis. A comparison of the structures
reported herein, with previously published 5,17-diametrically
substituted calix[4]arenes, confirmed the configuration as a
pinched-cone.
by schematically showing that the metal may reside on either
side of the calix[4]arene by undergoing what Tsuji called a
“rollover motion”.7b An additional motion described by Tsuji
was called a “twist-motion”. This latter motion does not result
in the “flipping” of the PtCl2 fragment from half of the calix-
[4]arene to the other but appeared to be a process that resulted
in a contortion of the inner coordination sphere as a result
of partial rotation about the C-P bond.
The two ligands, 7 and 8, chelated Ti, Pd, and Mo de-
pending upon the nature of the ligand. Though not discussed,
chelates of Pt and W were realized, using ligand 8 and
conditions similar to that described for Pd and Mo, respec-
tively. All bidentate ligands coordinate the metal in a cis-
fashion. An alkoxy-based calix[4]arene, 7, effectively che-
lated the CpTi(Me) fragment. The isolated material was not
It seemed possible that some mode of exchange must occur
for the complexes prepared herein to account for the observed
room-temperature H NMR spectra. The diagnostic hydro-
1
readily crystalline, but the H NMR data showed that the
1
structure was consistent with chelation above the pinched-
cone in a twisted manner.
gens to note are the methylene hydrogens (I, ArCH2Ar) and
the meta-arene hydrogens (II, H4, H6, H16, and H18) of
rings B and D. Scheme 2 shows a partial representation of
two metal-calix[4]arene adducts (where the B and D rings
appear as rectangles with the carbons bearing the ligand
substituents labeled as C5 and C17) that undergo exchange
with one another by a simple rotation about the -CH2-
C(5/17) bonds. The complexes prepared in this study have
the following identities, using the formalism in Scheme 2:
11, M ) Ti, L ) -CH2O-, L1 ) CH3, L2 ) Cp; 12, M )
Pd, L ) -CH2OPPh2, L1 ) L2 ) nothing, Cls omitted for
clarity; 14a,b, M ) Mo, L ) -CH2OPPh2, L1 ) CO L2 )
NCR, COs omitted for clarity; 14c, L ) -CH2OPPh2, L1 )
A bis(diphenylphosphinito)calix[4]arene ligand, 8, afforded
chelates with Mo, W, Pd, and Pt using the appropriate starting
materials. The palladium adduct was thoroughly character-
ized using a battery of techniques and was found to be mono-
meric in which chelation occurred above the pinched-cone.
The solid-state structure confirmed the coordination mode
1
and coupled with the H NMR data revealed the presence
of a dynamic exchange pathway. This complex was found
to be susceptible to acid-promoted decomposition, in which
the products were [µ2-ClPd(PPh2OH)(PPh2O)]2 and 9.
As with the palladium complex, the molybdenum, for
14a-c, was situated above the “closed-mouth” of the calix-
1
L2 ) CO). The H NMR spectra of 11 and 14a,b gave rise
1
[4]arene cavity. H NMR of 14a,b revealed that C-H/π
interactions existed between the coordinated nitriles and some
part of the complex in solution, where the respective proton
resonances were shifted upfield by about 2 ppm, relative to
free nitrile. A partial solution of the molecular structure of
14b showed that the origin of this anomalous chemical shift
was due to an interaction that existed between the ligated
nitrile and a phenyl ring of the coordinated phosphinite. This
result should serve as a fair warning, however, as when there
are two types of arene rings present in the calix[4]arene
to similar patterns for the diagnostic hydrogens, while 12
and 14c yield common spectral characteristics. In the absence
of dynamic exchange, the C1-symmetric complexes, 11 and
14a,b, should yield four doublets each for the diagnostic
hydrogens of types I and II, while the C2-symmetric
complexes, 12 and 14c, should yield two doublets each for
the reporter hydrogens (I and II). Since this was not
observed, then the twisting motion shown in Scheme 2 served
to raise the average symmetry observed in solution to Cs,
for 11 and 14a,b, and to C2V, for 12 and 14c. Low-
temperature (-80 °C) 1H NMR for these complexes revealed
only slight broadening of the diagnostic hydrogen resonances.
This suggests that this exchange pathway is very rapid on
the NMR time scale (400.132 MHz). In light of the rate with
which this process occurs, it now seems prudent to suggest
that the inequivalence observed by Matt et al. for (η3-
C4H7)Pd[5,17-(P(OEt)2OCH2)2-11,23-tBu-EtOEt4Clx+ must
surely be due to the orientation of the η3-C4H7 ligand.9a This
supposition is bolstered by Tsuji’s data showing two distinct
orientations for an η3-C3H5 ligand in (η3-C3H5)Pd[(PPh2)2-
Bz4Clx]BF4.7b
1
derivative, observation of uncharacteristic H NMR shifts
cannot be readily attributed to interactions with the inner
walls of the cavity. An X-ray crystallographic study of the
Mo(CO)4-nBu4Clx, 14c, revealed that coordination to the
metal by the bidentate ligand occurs in a cis-fashion, where
the IR data supported the local C2V symmetry about the
molybdenum atom.
Preparation of the bis(diphenylphosphino)calix[4]arene
ligand, 10, occurred using known procedures, and its coor-
dinative properties were examined. Reaction with Mo(CO)3-
(toluene) in acetonitrile showed that coordination occurred,
but the reaction was incomplete. In light of Kubas’ work,
and the absence of a solid-state structure, it is impossible to
state conclusively whether chelated or polymeric adducts
formed under these reaction conditions.
Conclusions
This study presents the preparation of three new calix[4]-
arene ligands using a variety of literature protocols. The
A survey of the solid-state structures reported herein
Inorganic Chemistry, Vol. 41, No. 23, 2002 5997

Evans et al.
Experimental Section of the Supporting Information. All X-ray
crystallographic details are available in the Supporting Information.
5,17-Dihydroxo-25,26,27,28-tetra-n-butoxycalix[4]arene,
(HOCH2)2-nBu4Clx, 7.9a The preparation of this material was
achieved using a previously published procedure.9a X-ray-quality
crystals were obtained in a freezer upon slow evaporation of a
solution of 7 in diethyl ether/methanol. Great care was required to
mount the crystals as lattice solvent was immediately lost upon
showed that the pinched-cone conformation adopted by calix-
[4]arenes reduces the effective cavity volume to the point
that care should be taken when designating the molecules
as either “bowl-shaped” or “cavity-containing”. Inspection
of these structures showed that the 5,17-substituents prefer
a “closed” conformation when small or when there are
stabilizing factors present but adopt an “open” conformation
when sufficiently bulky. A brief review of the currently
available literature showed that the “closed” conformation
is present in cis-chelated metal complexes but that the trans
complexes gave rise to an expanded cavity. The only way
presently known to situate metals above a voluminous cavity
is to tether a rigid linker that constrains the calix[4]arene in
an opened conformation. The metal complexes reported
herein showed that there is binding of the metal fragment
above the pinched-cone, but the metal is too far removed
from the binding cleft to even suggest that the any participa-
tion in selective catalysis would occur. This is not true for
several other reported complexes, and it will be interesting
to see if any selectivity is possible for these systems.
Finally, the rationalization of the observed 1H NMR
spectroscopic features reported herein is possible when one
considers a simple twisting motion of the coordination sphere
above the pinched-cone of the calix[4]arene annulus. This
motion occurred by rotation about the -CH2-C(5/17) bonds
which raised the average symmetry of the complexes in
solution. Future work will continue with the aim of achieving
an organometallic species capable of binding alkanes that
reside within the interior of the cavity.
1
removal from the mother liquor. H NMR (δ, ppm; C6D6): 7.00
2
(d, 4H, ArH), 6.87 (t, 2H, ArH), 6.60 (s, 4H, ArH), 4.58 (d, JHH
) 13.2 Hz, 4H, ArCH2Ar), 4.19 (s, 4H, ArCH2OH), 4.08 and 3.77
3
2
(t, JHH ) 7.1 Hz, 8H, ArOCH2), 3.19 (d, JHH ) 13.2 Hz, 4H,
3
ArCH2Ar), 2.27 (br s, 2H, OH), 2.00 and 1.85 (quint, JHH ) 7.1
3
Hz, 8H, OCH2CH2Et), 1.47 and 1.34 (hex, JHH ) 7.1 Hz, 8H,
O(CH2)2CH2Me), 0.99 and 0.98 (t, 3JHH ) 7.1 Hz, 12H, CH3). 13
C
NMR (δ, ppm; CDCl3): 157.13, 155.49, 136.00, 134.32, 134.10,
128.68, 126.36, 122.13, 75.10, 74.83, 64.72, 32.47, 32.07, 31.01,
19.54, 19.18, 14.18, and 14.04. MS (FAB; m/z): MH+ ) 709.4.
Anal. Found for crystalline material: C, 76.27; H, 7.64. Calcd for
C46H60O6 (Mr ) 708.97): C, 77.93; H, 8.53. The results were
consistent with the presence of CH3OH in the lattice. Extended
heating under vacuo (110 °C, 48 h, 5 mTorr) resulted in a loss of
crystallinity but gave excellent agreement with theory.
5,17-Bis((diphenylphosphinito)methyl)-25,26,27,28-tetra-n-
butoxycalix[4]arene, (PPh2OCH2)2-nBu4Clx, 8.9a A 4.25 g (6.00
mmol) amount of 7 and 1.08 mL (13.35 mmol) of pyridine were
dissolved in 25 mL of THF in a 50 mL round-bottom flask. A
2.28 mL (12.06 mmol) volume of ClPPh2 was added slowly via a
syringe. The mixture was stirred at 22 °C for 12 h, and the white
precipitate formed was filtered out. The filtrate was evaporated to
dryness by vacuum. The resulting residue was recrystallized from
benzene, washed with 10 × 2 mL of Et2O, and then dried by
vacuum. A 67% yield (4.3 g) of colorless microcrystals of 8 was
obtained. X-ray-quality crystals were obtained upon slow evapora-
tion of a benzene solution of 8. Details of the crystallographic
Experimental Section
Unless otherwise noted, all reactions were carried out under an
atmosphere of helium, argon, or nitrogen. Solvents were ap-
propriately dried and degassed prior to use. ClPPh2 (95%) was
purchased from Aldrich and used without further purification.
Carbon monoxide was purchased from Scott Specialty Gases, Inc.
1
analysis are provided below. H NMR (δ, ppm; C6D6): 7.65 (m,
8H, PArH), 7.14-7.07 (m, 12 H, PArH), 6.94 (s, 4H), 6.59 (s,
3
2
6H), 4.74 (d, JHP ) 10.1 Hz, 4H, ArCH2OP), 4.53 (d, JHH
)
3
13.2 Hz, 4H, ArCH2Ar), 3.98 (t, JHH ) 7.1 Hz, 4H, ArOCH2),
45
Mo(CO)3(toluene)44 and cis-Cl2Pd(PhCN)2 were prepared as
3
2
3.79 (t, JHH ) 7.1 Hz, 4H, ArOCH2), 3.13 (d, JHH ) 13.2 Hz,
directed in the literature. IR spectra were obtained from a Nicolet
5DXC FTIR spectrophotometer. 1H, 13C, and 31P NMR spectra were
collected at operating frequencies of 400.132, 100.625, and 161.975
MHz, respectively, using a Bruker DRX-400 spectrometer. 1H and
13C NMR were referenced relative to internal TMS or solvent, and
31P NMR data were referenced to external H3PO4. Fast atom
bombardment (FAB) mass spectrometry was performed on a
VG7070E magnetic sector mass spectrometer. Midwest Microlab,
LLC (Indianapolis, IN), provided elemental analysis for the calix-
[4]arene derivatives (2-10), while all other species were analyzed
using Desert Analytics (Tucson, AZ). All solids were heated in a
vacuum oven at a temperature that ensured complete removal of
lattice solvents. Electrospray mass spectrometry was operated in
the positive-ion mode using a Micromass QTOF II (Beverly, MA).
Samples, in the appropriate solvent, were directly infused using a
syringe pump operating at 5 µL/min. High-resolution spectra were
recorded with poly-D-alanine as an internal molecular weight
standard. X-ray analyses were performed using a Bruker SMART
CCD system operating at -80 °C (vide infra). Synthetic procedures
and spectroscopic data for 1-6 and 9 are available in the
4H, ArCH2Ar), 1.94 (quint, 3JHH ) 7.1 Hz, 4H, OCH2CH2Et), 1.85
3
3
(quint, JHH ) 7.1 Hz, 4H, OCH2CH2Et), 1.41 (hex, JHH ) 7.1
Hz, 4H, O(CH2)2CH2Me), 1.35 (hex, JHH ) 7.1 Hz, 4H,
3
3
3
O(CH2)2CH2Me), 0.98 (t, JHH ) 7.1 Hz, 6H, CH3), 0.97 (t, JHH
) 7.1 Hz, 6H, CH3). 13C NMR (δ, ppm; C6D6): 157.2, 156.4, 143.1
(d, JCP ) 19 Hz), 136.0, 134.5, 132.8 (d, JCP ) 7.2 Hz), 130.9 (d,
JCP ) 21 Hz), 129.3, 128.6, 128.49, 128.47, 122.7. 31P NMR (δ,
ppm; C6D6): 113.8 (s). MS (FAB; m/z): MH+ ) 1077.5. Anal..
Found for crystalline material: C, 77.93; H, 7.37. Calcd for
C70H78O6P2 (Mr ) 1077.31): C, 78.04; H, 7.30.
5,17-Bis((diphenylphosphino)methyl)-25,26,27,28-tetra-n-
butoxycalix[4]arene, (PPh2CH2)2-nBu4Clx, 10.9a,b To a stirred
solution of Ph2PH (8.05 mmol) in 15 mL of dry THF at -78 °C
was added 5.04 mL of 1.6 M nBuLi/hexane solution (8.06 mmol).
The solution was stirred for 15 min at -78 °C and then transferred
via a cannula to a solution of 9 (4.02 mmol) in 20 mL of dry THF
at -78 °C. The mixture was stirred at -78 °C for 2 h and allowed
to slowly warm to room temperature. The solution was stirred at
room temperature for 12 h where the mixture was passed through
a bed of Celite and then washed with toluene. The combined
solution was reduced under vacuo. The oily residue was treated
with hexane. The resultant white powder was recrystallized from a
hexane solution at -30 °C. The colorless microcrystalline material
(44) Poli, R.; Krueger, S. T.; Mattamana, S. P. Inorg. Synth. 1998, 32,
200-201.
(45) Anderson, G. K.; Lin, M. Inorg. Synth. 1990, 28, 60-61.
5998 Inorganic Chemistry, Vol. 41, No. 23, 2002

Tetra-O-n-butylcalix[4]arenes and Their Complexes
formed was collected and vacuum-dried at 80 °C. This yielded 1.9
g of 10 in 45% yield. Crystals suitable for X-ray crystallographic
analysis were obtained upon slow evaporation of a solution of 10
in benzene. Details of the crystallographic analysis are provided in
the Supporting Information. 1H NMR (δ, ppm; in C6D6): 7.49 (m,
8H, PArH), 7.13 (m, 12H, PArH), 6.91 (s, 4H, ArH), 6.52 (t, 2H,
ArH), 6.35 (d, 4H, ArH), 4.51 (d, 2JHH ) 13.2 Hz, 4H, ArCH2Ar),
resolution ESI-MS (postive-ion mode, CH2Cl2): calcd for 12 -
Cl-, 1217.3997 amu; obsd, 1217.3973 amu (2.0 ppm). High-
resolution ESI-MS (negative-ion mode): calcd for 12 + Cl-,
1289.3378 amu; obsd, 1289.3362 amu (1.2 ppm). Crystalline
samples failed to give adequate elemental analysis results, presum-
ably due to the volatility of the CHCl3 in the lattice. Batches of
single crystals heated under vacuo (80 °C, 36 h, 5 mTorr) resulted
in a loss of crystallinity but provided agreement with theory. Anal.
Found: C, 67.18; H, 6.31. Calcd for C70H78O6P2Cl2Pd (Mr )
1254.63): C, 67.01; H, 6.27.
3
4.04 and 3.69 (t, JHH ) 7.1 Hz, 8H, ArOCH2), 3.34 (s, 4H,
2
ArCH2P), 3.10 (d, JHH ) 13.2 Hz, 4H, ArCH2Ar), 1.98 and 1.79
(m, 8H, OCH2CH2Et), 1.46 and 1.30 (m, 8H, O(CH2)2CH2Me), 0.95
(m, 12H, CH3). 31P NMR (δ, ppm; in C6D6): -9.92 (s). MS (FAB;
m/z): MH+ ) 1045.5. Anal. Found for crystalline material: C,
80.62; H, 7.58. Calcd for C70H78O4P2 (Mr ) 1045.31): C, 80.43;
H, 7.52.
Bis(µ-chloro)bis[hydrogenbis(diphenylphosphinito)(1-)-P,P′]-
dipalladium(II), µ-Cl2(PPh2OH)2(PPh2O)2Pd2, 13. A 0.100 g
amount of 12 (79.7 µmol) was dissolved in 10 mL of CH2Cl2 with
vigorous stirring. Anhydrous HCl was passed through the solution
for a period of 4 h. The solvent was removed under vacuo, and the
resultant residue was triturated with hexanes. The hexane precipitate
was collected by filtration and recrystallized from CHCl3/hexane
(7:3), where the solid was dried under vacuo providing an isolated
yield of 13 in 91%. 1H NMR (δ, ppm; in CDCl3): 8.03 (br s, 2H,
OH), 7.902 (m, 16H, m-H), 7.058 (m, p-H), 7.011 (m, o-H); both
resonances at 7.058 and 7.011 integrate to 24 H. 31P NMR (δ, ppm;
in CDCl3): 77.91 (s); cf. previously obtained value of 78.1 ppm
that was obtained in the same solvent.22 The hexane washes were
found to contain 9 and some trace unidentified products. Elemental
analysis was consistent with solid material containing 13‚CHCl3.
Anal. Calcd (found): C, 48.64 (48.74); H, 3.58 (3.60).
CpTiMe[(OCH2)2-25,26,27,28-tetra-n-butoxycalix[4]-
arene], CpTiMe[(OCH2)2-nBu4Clx], 11. A 79.0 mg (0.5 mmol)
amount of CpTiMe3 was added to a solution of 354.5 mg (0.5
mmol) of 7, in 5 mL of dry toluene. The solution was stirred at
room temperature for 30 min. The volatile solvents were removed
by vacuum. A pale yellow oil was produced, which when repeatedly
washed with hexanes, and dried under vacuo, yielded an off-white
1
3
powder in 97% yield. H NMR (δ, ppm; C6D6): 7.14 (d, JHH
)
3
7.6 Hz, 2H, A and C rings, meta-ArH), 7.13 (d, JHH ) 7.6 Hz,
2H, A and C rings, meta-ArH), 7.01 (t, 3JHH ) 7.6 Hz, 1H, A and
3
C rings, para-ArH), 6.95 (t, JHH ) 7.6 Hz, 1H, A and C rings,
para-ArH), 6.445 (d, 4JHH ) 2.2 Hz, 2H, B and D rings, m-ArH),
6.405 (d, 4JHH ) 2.2 Hz, B and D rings, m-ArH), 6.03 (s, 5H, CpH),
{fac-(CO)3Mo(NCCH3)[(PPh2OCH2)2-25,26,27,28-tetra-
n-butoxycalix[4]arene]}, fac-(CO)3Mo(NCCH3)[(PPh2OCH2)2-
nBu4Clx], 14a. A 1.08 g (1.00 mmol) amount of 8 and 0.272 g
(1.00 mmol) of Mo(CO)3(toluene) were dissolved in 40 mL of
MeCN in a 50 mL round-bottom flask. The mixture was gently
refluxed for 3 h. After cooling, the mixture was filtered, washed
with 2 × 1 mL of MeCN and 2 × 1 mL of Et2O, and dried by
vacuum. An 86% yield (1.1 g) of pale yellow crystals of 14a was
obtained. No crystals of X-ray quality were obtained despite
repeated attempts. IR (νCO, cm-1, KBr): 1942 (s), 1846 (s), 1832
2
2
4.90, 4.86 (AB-q, JAB ) 12.5 Hz, 4H, ArCH2OTi), 4.60 (d, JHH
2
) 13 Hz, 2H, ArCH2Ar), 4.57 (d, JHH ) 13 Hz, 2H, ArCH2Ar),
4.25 (t, 3JHH ) 7.2 Hz, 2H, ArOCH2), 4.22 (t, 3JHH ) 7.2 Hz, 2H,
3
2
ArOCH2), 3.63 (t, JHH ) 7.1 Hz, 4H, ArOCH2), 3.21 (d, JHH
)
13.2 Hz, 2H, ArCH2Ar), 3.16 (d, 2JHH ) 13.2 Hz, 2H, ArCH2Ar),
2.10 and 1.79 (m, 8H, OCH2CH2Et), 1.51 and 1.26 (m, 8H,
3
O(CH2)2CH2Me), 1.00 (t, JHH ) 7.1 Hz, 12H, CH3), 0.8 (s, 3H,
TiMe). High-resolution ESI-MS (positive-ion, CH2Cl2): calcd for
11 - CH3+, 819.4104 amu; obsd, 819.4115 amu (1.3 ppm). We
were unable to obtain satisfactory elemental analysis.
1
(s). H NMR (δ, ppm; CDCl3): 8.14 (m, 3H, ArH), 7.98 (m, 3H,
4
Ar-H), 7.30-6.99 (m, 20 H, PC6H5), 6.495 (d, JHH ) 1.5 Hz,
{cis-Cl2Pd[(PPh2OCH2)2-25,26,27,28-tetra-n-butoxycalix[4]-
arene]}, cis-Cl2Pd[(PPh2OCH2)2-nBu4Clx], 12. A 0.108 g (0.10
mmol) amount of 8 and 0.038 g (0.10 mmol) of Cl2Pd(PhCN)2
were dissolved in 5 mL of benzene in a 20 mL round-bottom flask.
The solution was gently refluxed for 45 min. After cooling, the
volatile solvents were removed by vacuum. The residue was
recrystallized from a solution mixture of 1:4 CH2Cl2/toluene. The
pale yellow crystals that formed were collected, washed with 4 ×
0.5 mL of hexane and 2 × 0.5 mL of Et2O, and dried by vacuum.
An 85% yield (0.11 g) of 12 was obtained. X-ray-quality crystals
were obtained upon slow evaporation of CHCl3/hexane solutions
of 12. Allowing the mother liquor to evaporate resulted in loss of
crystallinity and is a result of the large number of chloroform
4
2H, B and D rings, m-ArH), 6.459 (d, JHH ) 1.5 Hz, B and D
2
rings, m-ArH), 4.63 (d, JHH ) 13.4 Hz, 2H, ArCH2Ar), 4.595 (d,
2JHH ) 13.4 Hz, 2H, ArCH2Ar), 4.43 (AB q, 2JHH ) 11.1 Hz, 4H,
ArCH2OP), 4.25 (m, 4H, ArOCH2), 3.60 (m, 4H, ArOCH2), 3.181
(d, 2JHH ) 13.4 Hz, 2H, ArCH2Ar), 3.171 (d, 2JHH ) 13.4 Hz, 2H
ArCH2Ar), 2.04 (m, 4H, OCH2CH2Et), 1.75 (m, 4H, OCH2CH2-
Et), 1.54 (m, 4H, O(CH2)2CH2Me), 1.25 (m, 4H, 4H, O(CH2)2CH2-
Me), 0.98 (t, 3JHH ) 7.1 Hz, 6H, CH3), 0.96 (t, 3JHH ) 7.1 Hz, 6H,
CH3), 0.11 (s, 3H, CH3CN). 31P NMR (δ, ppm; C6D6): 145.2 (s).
High-resolution ESI-MS spectra of 14a resulted in a signal inten-
sity too low to observe in CH2Cl2. An adequate signal for (14a -
CH3CN + H+) was observed in CH2Cl2/MeOH (9:1) with an
observed mass of 1259.4271 amu (1.6 ppm). Platelike crystals (25
°C, 5 d, 5 mTorr) sealed in an ampule under nitrogen provided the
sample for elemental analysis. Anal. Found: C, 69.28; H, 6.26; N,
1.07. Calcd for C75H81NO9P2Mo (Mr ) 1298.33): C, 69.38; H,
6.29; N, 1.08.
1
solvates present in the lattice. H NMR (δ, ppm; C6D6): 8.29 (m,
6H), 7.25-7.09 (m, 20H), 6.04 (s, 4H, ArH), 4.49 (d, 2JHH ) 13.7
Hz, 4H, ArCH2Ar), 4.15 (m, 4H, ArOCH2), 4.0 (s, 4H, ArCH2-
OP), 3.53 (m, 4H, ArOCH2), 2.99 (d, 2JHH ) 13.7 Hz, 4H, ArCH2-
Ar), 1.93 (m, 4H, OCH2CH2Et), 1.70 (m, 4H, OCH2CH2Et), 1.50
(m, 4H, O(CH2)2CH2Me), 1.19 (m, 4H, 4H, O(CH2)2CH2Me), 0.94
{fac-(CO)3Mo(NCCH2CH3)[(PPh2OCH2)2-25,26,27,28-tetra-
n-butoxycalix[4]arene]},fac-(CO)3Mo(NCCH2CH3)[(PPh2OCH2)2-
nBu4Clx], 14b. A 0.54 g (0.50 mmol) amount of 8 and 0.14 g (0.50
mmol) of Mo(CO)3(toluene) were dissolved in 5 mL of EtCN in a
25 mL round-bottom flask. The mixture was stirred at 22 °C for
24 h. The pale yellow crystals that formed were collected, washed
with 2 × 1 mL of EtCN and 2 × 1 mL of Et2O, and vacuum-
dried. A 64% yield (0.42 g) of 14b was obtained. We were able to
3
3
(t, JHH ) 7.2 Hz, 6H, CH3), 0.93 (t, JHH ) 7.1 Hz, 6H, CH3),
0.11 (s, 3H, CH3CN). 13C NMR (δ, ppm; C6D6): calix-ArC, 158.2,
155.3, 137.1, 133.6, 133.2, 132.9, 129.1, 129.0, 128.22, 128.15,
125.3, 122.5; P-ArC, 133.5 (t, JCP ) 6.2 Hz), 132.9 (t, JCP ) 9.2
Hz), 131.8, 129.9 (t, JCP ) 4.1 Hz), 128.5 (t, JCP ) 5.1 Hz); calix-
ArCH2Ar, 74.7, 67.7; calix-ArO-nBu, 32.5, 32.4, 31.9, 31.3, 19.6,
19.0, 14.0, 13.8. 31P NMR (δ, ppm; C6D6): 112.48 (s). High-
Inorganic Chemistry, Vol. 41, No. 23, 2002 5999

Evans et al.
collect data on crystals of 14b, but the crystal quality was very
poor giving rise to an incomplete solution. The data obtained were
good enough to determine the coordination sphere about the
molybdenum; see Figure S12. IR (νCO, cm-1, KBr): 1943 (s), 1859
(s), 1833 (s). 1H NMR (δ, ppm; CDCl3): 8.15 (m, 3H, ArH), 8.00
(m, 3H, ArH), 7.30-7.00 (m, 20 H, PC6H5), 6.500 (d, 4JHH ) 1.6
210.3 (vt, JCP ) 11 Hz), 158.6, 155.1, 141.5 (vt, JCP ) 19 Hz),
137.7, 133.3, 131.7 (vt, JCP ) 5 Hz), 131.2 (vt, JCP ) 7 Hz), 130.2,
129.2, 128.7 (vt, JCP ) 5 Hz), 128.5, 124.6, 122.8, 75.11, 75.05
65.7, 32.9, 32.4, 31.6, 20.0, 19.4, 14.4, 14.2. 31P NMR (δ, ppm; in
C6D6): 145.2 (s). High-resolution ESI-MS of 14c experienced the
same problem as in 14a. There was an observed mass of 1287.4210
amu for (14c + H+) in CH2Cl2/MeOH (9:1) (0.6 ppm). Crystalline
material subjected to evacuation (70 °C, 3d, 5 mTorr) resulted in
the observed elemental analysis. Anal. Found: C, 69.41; H, 6.14.
Calcd for C74H78O10P2Mo (Mr ) 1285.29): C, 69.15; H, 6.12.
4
Hz, B and D ring m-ArH, 2H), 6.459 (d, JHH ) 1.6 Hz, B and D
ring m-ArH, 2H), 4.627 (d, 2JHH ) 13.7 Hz, ArCH2Ar, 2H), 4.595
2
2
(d, JHH ) 13.7 Hz, ArCH2Ar, 2H), 4.472, 4.372 (AB q, JHH
)
11.6 Hz, ArCH2OP, 4H), 4.24 (m, 4H, ArOCH2), 3.60 (m, 4H,
ArOCH2), 3.179 (d, 2JHH ) 13.7 Hz, ArCH2Ar, 2H), 3.163 (d, 2JHH
) 13.7 Hz, ArCH2Ar, 2H), 2.03 (m, 4H, OCH2CH2Et), 1.75 (m,
4H, OCH2CH2Et), 1.54 (m, 4H, O(CH2)2CH2Me), 1.25 (m, 4H,
fac-Tris(carbonyl)(NCCH3)[(PPh2CH2)2-nBu4Clx]molyb-
denum(0), fac-(CO)3Mo(NCCH3)[(PPh2CH2)2-nBu4Clx], 17. A
104.5 mg (0.10 mmol) amount of {(CH2PPh2)2-nBu4Clx}, 10, and
a 28.4 mg (0.10 mmol) amount of Mo(CO)3(toluene) were dissolved
in 15 mL of acetonitrile in a 50 mL round-bottom flask. The mixture
was heated to gentle reflux for 24 h. After cooling, the volatiles
were removed in a vacuum and the residue was extracted with Et2O.
The Et2O was removed under reduced pressure, and the residue
3
4H, O(CH2)2CH2Me), 0.97 (t, JHH ) 7.1 Hz, 6H, CH3), 0.96 (t,
3
3JHH ) 7.1 Hz, 6H, CH3), 0.72 (q, JHH ) 7.2 Hz, 2H, MeCH2-
CN), -0.15 (t, 3JHH ) 7.2 Hz, 3H, CH3CH2CN). 31P NMR (δ, ppm;
C6D6): 145.0 (s). High-resolution ESI-MS of 14b experienced the
same problem as in 14a. There was an observed mass of 1259.4276
amu for (14b -CH3CH2CN + H+) in CH2Cl2/MeOH (9:1) (1.8
ppm). Platelike crystals (25 °C, 5 d, 5 mTorr) sealed in an ampule
under nitrogen provided a sample for elemental analysis. Anal.
Found: C, 69.60; H, 6.40; N, 1.07. Calcd for C76H83NO9P2Mo (Mr
) 1312.36): C, 69.56; H, 6.38; N, 1.07.
1
was redissolved in benzene-d6. Analysis by H NMR showed the
reaction to be incomplete. The sample was returned to the flask
and, upon removal of volatiles, was resuspended in 15 mL of
acetonitrile, where the solution was refluxed for another 4 days.
1
Analysis by H NMR showed the reaction to be incomplete even
{Mo(CO)4[(PPh2OCH2)2-25,26,27,28-tetra-n-butoxycalix[4]-
arene]}, Mo(CO)4(PPh2OCH2)2-nBu4Clx), 14c. A 100.0 mg (0.077
mmol) amount of 14a was dissolved in 15 mL of benzene in a 50
mL round-bottom flask equipped with a sidearm. The solution was
purged slowly with CO at 22 °C for 20 h, and the volatile reagents/
solvents were removed by vacuum. A 98% yield (97 mg) of
colorless 14c was obtained. X-ray-quality crystals were grown from
solutions of benzene/methylene chloride by slow evaporation at
room temperature. Details of the crystallographic analysis are given
below. IR (νCO, cm-1, KBr): 2025 (w), 1931 (s), 1916 (s), 1905
after this extended period of time. IR (νCO, cm-1, KBr): cis 2039
(w), 1952 (m), 1896 (vs), 1869 (s); additional peak found in VCO
region 2001 (w). 31P NMR (δ, ppm; C6D6): 28.5 (d, J ) 28 Hz),
28.1 (d, J ) 28 Hz).
Acknowledgment is made for the financial support pro-
vided by the Research Corporation for a Research Innovation
Award, and through the Petroleum Research Fund, admin-
istered by the American Chemical Society.
1
(s). H NMR (δ, ppm; C6D6): 7.90 (m, 6H, ArH), 7.25-7.03 (m,
Supporting Information Available: Experimental details for
the synthesis of 1-6 and 9, comparison 1H NMR spectra of 7 and
11, 8 and 12, and 8, 14a, 14b, and 14c, ORTEP representations
for 3-8, 10, 13, and 14b, and complete crystallographic data
available as a CIF file. This material is available free of charge via
the Internet at http://pubs.acs.org.
2
20 H, PC6H5), 6.39 (s, 4H, ArH), 4.60 (d, JHH ) 15.3 Hz, 4H,
ArCH2Ar), 4.35 (s, 4H, ArCH2OP), 4.23 (m, 4H, ArOCH2), 3.60
2
(m, 4H, ArOCH2), 3.16 (d, JHH ) 15.3 Hz, 4H, ArCH2Ar), 2.04
(m, 4H, OCH2CH2Et), 1.76 (m, 4H, OCH2CH2Et), 1.55 (m, 4H,
O(CH2)2CH2Me), 1.25 (m, 4H, 4H, O(CH2)2CH2Me), 0.99 (t, 3JHH
3
) 7.1 Hz, 6H, CH3), 0.98 (t, JHH ) 7.1 Hz, 6H, CH3). 13C NMR
(δ, ppm; C6D6): 216.2 (low intensity, unable to resolve coupling),
IC020446B
6000 Inorganic Chemistry, Vol. 41, No. 23, 2002