Supramolecular assemblies involving organometallic free acids

Article abstract of DOI:10.1021/om960361g

Reactions between W(η²-Ph₂C₂)Cl₄ and salicylic acid derivatives generate analytically pure free acids of formula W(η²-Ph₂C₂)Cl₃(Hsal-R) (1) in high yields (Hsal = a salicylate monoanion). The products exist as hydrogen-bonded dimers in the solid state. The acid functionality on one molecule hydrogen bonds to one of the cis-chloride ligands of an adjacent complex at a 3.03 A? distance. The more electron-rich tungsten center renders these acetylene complexes less acidic than their oxo and arylimido analogs. As a result, W(η²-Ph₂C₂)Cl₃-(Hsal) exhibits partial dimerization in solution and have relatively weak hydrogen bonds to nitrogen- and oxygen-containing organic molecules. Among a range of possible phenol-phenoxide complexes of the W(η²-Ph₂C₂)Cl₃ subunit, only the ether adduct of the catecholate, W(η²-Ph₂C₂)Cl₃(Hcat-OEt ₂) (2), has been isolated and structurally characterized. The weaker hydrogen bond strength of larger chelating bis(phenolates) evidently destabilize the phenol-phenoxide structures in favor of simple chelating bis(phenoxides). The salicylate free acids form various supramolecular complexes in solution and the solid state, including [W(η²-Ph₂C₂)Cl₃(Hsal)] ₄(18-Crown-6) (5), one of a family of tetranuclear systems organized around hydrogen bonding to an 18-crown-6 template. This structure is characterized by π-stacking of the Hsal ligands between confacial free acid complexes and the steric screening of the two non-hydrogen-bonded 18-crown-6 oxygens by pairs of antarafacial W(Ph₂C₂) units.

Full text of DOI:10.1021/om960361g

4872
Organometallics 1996, 15, 4872-4879
Su p r a m olecu la r Assem blies In volvin g Or ga n om eta llic
F r ee Acid s
Timothy E. Baroni,† J oseph A. Heppert,*,† Rolande R. Hodel,†
Richard P. Kingsborough,‡ Martha D. Morton,† Arnold L. Rheingold,*,§ and
Glenn P. A. Yap§
Department of Chemistry, University of Kansas, Lawrence, Kansas 66045, and Department of
Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716
Received May 14, 1996X
Reactions between W(η2-Ph2C2)Cl4 and salicylic acid derivatives generate analytically pure
free acids of formula W(η2-Ph2C2)Cl3(Hsal-R) (1) in high yields (Hsal ) a salicylate
monoanion). The products exist as hydrogen-bonded dimers in the solid state. The acid
functionality on one molecule hydrogen bonds to one of the cis-chloride ligands of an adjacent
complex at a 3.03 Å distance. The more electron-rich tungsten center renders these acetylene
complexes less acidic than their oxo and arylimido analogs. As a result, W(η2-Ph2C2)Cl3-
(Hsal) exhibits partial dimerization in solution and have relatively weak hydrogen bonds to
nitrogen- and oxygen-containing organic molecules. Among a range of possible phenol-
phenoxide complexes of the W(η2-Ph2C2)Cl3 subunit, only the ether adduct of the catecholate,
W(η2-Ph2C2)Cl3(Hcat···OEt2) (2), has been isolated and structurally characterized. The weaker
hydrogen bond strength of larger chelating bis(phenolates) evidently destabilize the phenol-
phenoxide structures in favor of simple chelating bis(phenoxides). The salicylate free acids
form various supramolecular complexes in solution and the solid state, including [W(η2-
Ph2C2)Cl3(Hsal)]4(18-crown-6) (5), one of a family of tetranuclear systems organized around
hydrogen bonding to an 18-crown-6 template. This structure is characterized by π-stacking
of the Hsal ligands between confacial free acid complexes and the steric screening of the
two non-hydrogen-bonded 18-crown-6 oxygens by pairs of antarafacial W(Ph2C2) units.
In tr od u ction
subunits.11-19 Supramolecular species containing hy-
drogen bonds have found a variety of applications in
biomimicry as receptors and switches and in materials
applications ranging from catalysis to photonic materi-
als.20,21 Recently, numerous structural and thermody-
namic studies have focused on transition metal com-
plexes containing both intramolecular and intermolecular
hydrogen-bonding interactions.22-26 Some projects have
sought to understand the kinetics and thermodynamics
From their inception, strategies for the assembly of
supramolecular molecules and materials have relied on
hydrogen-bonding interactions as critical organization
elements.1-7 The use of these functional groups as
building blocks follows naturally from the critical
structural and reactive role that they play in functional
biological supramolecular systems.8-10 Today, a broad
range of synthetic supramolecular species employ or-
ganizationally and chemically functional hydrogen bonds
that either have been introduced serendipidously or
have been carefully woven into the design of molecular
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* Authors to whom correspondence should be addressed.
† University of Kansas.
‡ NSF-URP student from the University of Arizona. Current ad-
dress: Department of Chemistry, University of Pennsylvania, Phila-
delphia, PA 19104.
§ University of Delaware.
X Abstract published in Advance ACS Abstracts, September 15, 1996.
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S0276-7333(96)00361-5 CCC: $12.00 © 1996 American Chemical Society

Assemblies Involving Organometallic Free Acids
Organometallics, Vol. 15, No. 22, 1996 4873
of hydrogen bonding between organic hydrogen bond
donors and the basic heteroatoms in the coordination
sphere of the complexes. Many investigations have
studied the interaction of hydrogen bonding functional-
ity in the metal coordination sphere with complemen-
tary sites on organic substrates and other coordination
complexes, employing the complexes as a type of simple
molecular receptor.23-25 An increasing number of re-
searchers have employed hydrogen-bonding metal
complexes as components of solid-phase materi-
als.11,12,26-28,30-34 Some initial studies have centered on
the structural chemistry of metal complexes bearing
hydrogen-bonding groups.26-34 These systems often
adopt organizational motifs homologous with the parent
organic functionality. More recently, investigators in-
tent on generating novel two- and three-dimensional
materials networks have employed hydrogen-bonding
complexes to address specific problems in molecular and
crystal engineering.35-39
tion of an uncommon class of d2 organometallic free
acids of tungsten, W(η2-Ph2C2)Cl3(Hsal-R) (1), where
Hsal-R is a substituted salicylate monoanion. We have
found that these complexes can adopt unusual struc-
tural motifs in the solid state and form polynuclear
aggregates with hydrogen bond acceptor molecules,
including some unusually weak Brønsted bases.
Resu lts a n d Discu ssion
Syn th esis of Sa licyla te Der iva tives of d 2 Tu n g-
sten Acetylen e Com p lexes. Reactions of substituted
salicylic acids (H2sal-R) with W(η2-Ph2C2)Cl444 in dichlo-
romethane result in deep red-orange solutions from
which high yields of red complexes of formula W(η2-
Ph2C2)Cl3(Hsal-R) (1) are isolated (eq 1). The products
Our interests in metal-mediated hydrogen-bonding
interactions began with the inadvertent discovery of
several members of a now extensive class of chelating
phenol-phenolate Brønstead acids of tungsten oxo and
arylimido complexes.40-43 It became clear that these
complexes were unique both in the accessability of a
broad range of isoelectronic, isostructural analogs of the
tungsten template and in the variability of the hydrogen
bond strength of the Brønstead acid. Our long term goal
in this project is to utilize the control of hydrogen bond
strength available in this class of molecules in the
rational assembly of inorganic/organic hybrid materials.
In the near term, understanding the structures and
association modes of the parent functionality and ex-
amining how systematic variations in the metal’s elec-
tronic environment influence the hydrogen-bonding
characteristics of the complexes is central to this objec-
tive. We report here the preparation and characteriza-
are modestly moisture sensitive, persisting on contact
with air in the solid state for up to several weeks and
for brief periods in solution. Although other examples
of organometallic early transition metal complexes
containing hydrogen-bonding ligands are known,45,46
these acetylene complexes are unusual, because the
tungsten is in a high formal oxidation state, the
hydrogen-bonding functionality possesses a low pKa, and
the organometallic functional group is prone to proto-
nolysis. d2 tungsten diphenylacetylene complexes hy-
drolyze to produce stilbenes in protic media.40,47 Mo-
lecular weights of the analytically pure free acids 1 in
benzene solution are determined (by the Signer method48)
to be between the mono- and dinuclear forms. This is
in sharp contrast to the oxo free acid analogs which exist
only as dimers in benzene solution.40 The d2 tungsten
centers of the alkyne complexes, which are more elec-
tron rich than those in isoelectronic do oxo complexes,
demand less electron density from the carboxylate
moiety. This results in reduced hydrogen bond strength
in the acid functionality. Both spectroscopic studies and
titrations of the isoelectronic tungsten salicylate com-
plexes suggest that the chemistry of the d2 tungsten
acetylene fragment is more similar to d0 tungsten
fragments bearing the stronger π-donor (2,6-dimethyl-
aryl)imido unit. This trend is not as evident in correla-
tions between aromatic substituent effects (Hammett
σ) of groups bound to the Hsal ligand and the carboxy-
late carbon chemical shift.49 Note that the oxo and
arylimido compounds have similar “F” values, thus
showing similar characteristics in their π-donating
ability (Figure 1). By comparison, the slope of the Ph2C2
complexes is greater due to the reduced electrophilicity
of the d2 tungsten center. This indicates that the
acetylene derivatives are more sensitive to negative
charge buildup at the acid group than analogous oxo
and arylimido complexes.
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Inorg. Chim. Acta. 1992, 202, 43.
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11, 4124.
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Inorg. Chem. 1994, 33, 845.
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1992, 114, 8719.
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A. L.; Yap, G. P. A. Manuscript submitted for publication. (b) Baroni,
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Manuscript in preparation.
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Int. Ed. Engl. 1983, 22, 1010.
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2119.
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J . B.; Richard,C. E. F.; Schwerdtfeger, P. Polyhedron 1992, 11, 1419.
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2039.
(43) Bell, A. J . Mol. Catal. 1991, 76, 165.

4874 Organometallics, Vol. 15, No. 22, 1996
Baroni et al.
F igu r e 1. Hammett plot of 13C NMR chemical shifts
of Hsal-R carboxylate groups in W(dO)Cl3(Hsal-R),
W(dNC6H3-2,6-Me2)Cl3(Hsal-R), and W(η2-Ph2C2)Cl3(Hsal-
R).
F igu r e 2. Ball and stick representation of the molecular
structure of [W(η2-Ph2C2)Cl3(Hsal-5-Cl)]2 (1b).
Attempts to isolate phenol-phenoxide chelates of the
d2 tungsten acetylene template analogous to those
observed for tungsten oxo and imido complexes are
complicated by the decreased electrophilicity of the
metal. Only W(η2-Ph2C2)Cl3(Hcat‚‚‚OEt2) (2) (Hcat )
[o-C6H4(OH)(O)]-) is readily isolated as a diethyl ether
adduct (eq 2). We have noted previously in the oxo and
Like other organic carboxylates,50-52 the spectroscopic
and chemical characteristics of interactions between the
tungsten free acids and hydrogen bond acceptor mol-
ecules (including ethers, amines, and aldehydes) indi-
cate that hydrogen bonding to 1 is weak, even in
nonpolar media. While NMR titrations of 1 with ether
and oxygen-containing acceptor molecules indicate that
Brønsted acid-base adducts are formed, it is difficult
to isolate such complexes from solvents other than the
neat acceptor molecule. Moreover, once ether adducts
are isolated, they are prone to ether loss even in the
solid state. The relatively strong self-association of the
free acids seems to detract from their ability to bind
some classical hydrogen bond acceptors.
This reduction in hydrogen-bonding aptitude can be
overcome by several strategies. The triethylammonium
salts W(η2-Ph2C2)Cl3(sal-R‚‚‚HNEt3) (4), which are pre-
sumably stabilized by the partial ionic character of the
O‚‚‚H-N interaction, are readily isolated as stoichio-
metric adducts (eq 4). These “salts” are highly soluble
imido cases that the strength of the hydrogen bond to
ether decreases as the ring size of the phenol-phenoxide
chelating ligand increases.40 This leaves complexes
with seven- or eight-membered chelate rings more prone
to eliminate HCl and produce W(dX)Cl2(O-Ar-O)(L)
derivatives.40,43 In tungsten acetylene complexes, this
effect is sufficiently pronounced that bis(phenols) larger
than the catechol only produce W(dX)Cl2(O-Ar-O)(L)
(3) species at ambient temperature (eq 3).
Although the origin of this difference in reactivity is
unclear, it may result from a combination of the
decreasing conformational compatibility of larger bis-
(phenols) with the tungsten coordination environment
and the increased trans-effect of the η2-Ph2C2 ligand.
The increasing trans-influence of the acetylene ligand
(O < NAr < Ph2C2) will result in greater lability of the
trans-phenol group. Since the larger ring size chelates
already exhibit reduced hydrogen bond strength, the
phenol functional group is protected neither by a strong
hydrogen bond to ether nor by tenacious coordination
to tungsten. These factors appear to greatly increase
the rate of proton transfer and HCl elimination from
complexes containing seven- and eight-membered phenol-
phenoxide chelates.
in benzene, toluene, dichloromethane, and chloroform,
indicating that ion pairing minimizes ionic character.
Still, the ammonium ions exchange rapidly in solution,
as indicated by the presence of broad trialkylammonium
proton resonances in 1H NMR spectra. More insipid
hydrogen bonds to organic ethers can be isolated even
from dilute solution, providing that higher molecular
weight poly(ether)s are employed. This strategy was
used in the preparation supramolecular complexes like
the [W(η2-Ph2C2)Cl3(Hsal)‚‚‚]4(18-crown-6) (5) complex,
whose structure is outlined below.
St r u ct u r es of R ep r esen t a t ive Br øn st ed Acid
Com p lexes. The structures of three Brønsted acidic
tungsten acetylene derivatives are shown in the ball and
stick models in Figures 2-4. Tables 1-3 contain the
(50) Conners, K. A. Binding Constants; J ohn Wiley and Sons: New
York, 1987.
(51) Grunwald, E.; Price, E. J . Am. Chem. Soc. 1964, 86, 2965.
(52) Deiter, D. F.; Novak, R. W. J . Am. Chem. Soc. 1970, 92, 1361.

Assemblies Involving Organometallic Free Acids
Organometallics, Vol. 15, No. 22, 1996 4875
Ta ble 1. P er tin en t Bon d Len gth s (Å) a n d An gles
(d eg) for [W(η2-C2P h 2)Cl3(Hsa l-5-Cl)]2
W-O(1)
2.211(6)
2.339(2)
2.391(3)
2.019(9)
1.313(10)
1.321(14)
W-O(3)
1.928(6)
2.352(3)
2.008(9)
1.233(12)
1.357(11)
80.5(2)
W-Cl(1)
W-Cl(3)
W-C(8)
W-Cl(2)
W-C(7)
O(1)-C(21)
O(3)-C(15)
O(1)-W-Cl(1)
O(2)-C(21)
C(7)-C(8)
O(1)-W-O(3)
O(3)-W-Cl(1)
O(3)-W-Cl(2)
O(1)-W-Cl(3)
Cl(1)-W-Cl(3)
O(1)-W-C(7)
Cl(1)-W-C(7)
Cl(3)-W-C(7)
O(3)-W-C(8)
Cl(2)-W-C(8)
C(7)-W-C(8)
W-O(3)-C(15)
W-C(7)-C(8)
W-C(8)-C(7)
81.5(2)
161.9(2)
85.9(2)
80.3(2)
87.4(1)
158.5(3)
113.1(3)
82.9(3)
111.8(3)
87.0(3)
38.3(4)
136.7(5)
71.3(5)
70.4(5)
O(1)-W-Cl(2)
Cl(1)-W-Cl(2)
O(3)-W-Cl(3)
Cl(2)-W-Cl(3)
O(3)-W-C(7)
Cl(2)-W-C(7)
O(1)-W-C(8)
Cl(1)-W-C(8)
Cl(3)-W-C(8)
W-O(1)-C(21)
W-C(7)-C(1)
O(1)-C(21)-O(2)
W-C(8)-C(9)
83.0(2)
90.7(1)
90.9(2)
163.3(1)
85.5(3)
113.1(3)
162.9(3)
856.7(3)
109.4(3)
130.5(5)
141.6(7)
119.6(8)
144.1(7)
Ta ble 2. P er tin en t Bon d Len gth s (Å) a n d An gles
(d eg) for W(η2-C2P h 2)Cl3(Hca t‚‚‚OEt2)
W-Cl(1)
W-Cl(3)
W-O(2)
2.363(3)
2.367(3)
1.942(7)
2.014(9)
1.315(15)
1.356(9)
W-Cl(2)
2.362(3)
2.240(7)
2.006(10)
1.349(10)
70.6(6)
W-O(1)
W-C(7)
W-C(8)
O(1)-C(15)
W-C(8)-C(7)
Cl(1)-W-Cl(3)
C(7)-C(8)
O(2)-C(20)
F igu r e 3. Ball and stick representation of the molecular
structure of [W(η2-Ph2C2)Cl3(Hcat‚‚‚OEt2) (2).
90.1(1)
Cl(1)-W-Cl(2)
Cl(2)-W-Cl(3)
Cl(2)-W-O(1)
Cl(1)-W-O(2)
Cl(3)-W-O(2)
Cl(1)-W-C(7)
Cl(3)-W-C(7)
O(2)-W-C(7)
Cl(2)-W-C(8)
O(1)-W-C(8)
C(7)-W-C(8)
W-O(2)-C(20)
W-C(7)-C(8)
163.7(1)
86.2(1)
84.1(2)
Cl(1)-W-O(1)
Cl(3)-W-O(1)
Cl(2)-W-O(2)
O(1)-W-O(2)
Cl(2)-W-C(7)
O(1)-W-C(7)
Cl(1)-W-C(8)
Cl(3)-W-C(8)
O(2)-W-C(8)
W-O(1)-C(15)
W-C(7)-C(6)
W-C(8)-C(14)
79.7(2)
83.6(2)
89.6(2)
75.9(3)
88.2(3)
156.4(4)
86.2(3)
87.6(3)
112.8(4)
111.9(5)
142.3(7)
144.8(7)
88.3(2)
159.4(2)
107.5(3)
118.1(3)
81.8(4)
109.5(3)
163.3(4)
38.2(4)
120.1(5)
71.3(6)
seem different from the related distances in 1b and 2,
but these bond lengths are also well within the range
observed for isoelectronic W(η2-R2C2) and Mo(η2-R2C2)
species.53-61 We might expect to see greater variations
in bonding between the acetylene and tungsten when
there are actual changes in the valence electron count
at tungsten. There is an apparent trend toward length-
ening of the CtC bonds in a pair of previously isolated
d3 and d4 phosphine-substituted tungsten acetylene
complexes, which could be explained by increasing back-
donation into the π* orbitals of the acetylene.62 But
even in this case, it is not clear that the observed CtC
distances are statistically different from those found in
d2 metal acetylene derivatives.
F igu r e 4. Ball and stick representation of the molecular
structure of [W(η2-Ph2C2)Cl3(Hsal)]4(18-crown-6) (5).
pertinent bond distances and angles for these com-
plexes. W(η2-Ph2C2)Cl3(Hsal-5-Cl) (1b ) and [W(η2-
Ph2C2)Cl3(Hsal)‚‚‚]4(18-crown-6) (5) have a common
chelating salicylate monoanion unit, while W(η2-Ph2C2)-
Cl3(Hcat‚‚‚OEt2) (2) contains the catecholate monoanion.
The core W(η2-Ph2C2) fragment shows similar structural
characteristics in all of these complexes. The W-CCtC
and CtC distances of 1b and 2 are very similar,
averaging 2.010(10) and 1.318(15) Å, respectively. These
distances are characteristic of the W(η2-Ph2C2)Cl4 pre-
cursor and other d2 tungsten and molybdenum acetylene
derivatives bearing halogen and aryloxide ligands.53-61
The W-CCtC and CtC bond lengths found in
5s2.031(24) and 1.238(31) Å, respectivelysinitially
(55) Stahl, K.; Weller, F.; Dernicke, K. Z. Anorg. Allg. Chem. 1986,
533, 73.
(56) Kersting, M.; El-Kohli, A.; Miller, U.; Dehnicke, K. Chem. Ber.
1989, 122, 279.
(57) Pauls, R.; Dehnicke, K.; Fenske, D. Chem. Ber. 1989, 122, 481.
(58) Fenske, D.; Baum, G.; Hafacher, P.; Dehnick, K. Anorg. Allg.
Chem. 1990, 585, 27.
(59) Dierkes, P.; Dehnicke, K.; Fenske, D. Z. Naturforsch. 1994, 49B,
1391.
(60) Kersting, M.; Dehnicke, K.; Fenske, D. J . Organomet. Chem.
1986, 309, 125.
(61) Kersting, M.; Dehnicke, K.; Fenske, D. J . Organomet. Chem.
1988, 346, 201.
(62) Nielson, A. J .; Boyd, P. D. W.; Clark, G. R.; Hunt, P. A.;
Hunsthouse, M. B.; Metson, J . B.; Richard, C. E. F.; Schwerdfeger, P.
A. J . Chem. Soc., Dalton Trans. 1995, 1153.
(53) Walborsky, E. C.; Wigley, D. E.; Rowland, E.; Dewan, J . C.;
Schrock, R. R. Inorg. Chem. 1987, 26, 1615.
(54) Kriley, C. E.; Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1993, 12, 2051.

4876 Organometallics, Vol. 15, No. 22, 1996
Baroni et al.
Ta ble 3. P er tin en t Bon d Len gth s (Å) a n d An gles
(d eg) for [W(η2-C2P h 2)Cl3(Hsa l)]4‚‚‚(18-cr ow n -6)
W(1)-Cl(1)
W(1)-Cl(3)
W(1)-O(3)
W(1)-C(2)
W(2)-Cl(5)
W(2)-O(5)
W(2)-C(4)
C(1)-C(2)
O(1)-C(37)
O(3)-C(36)
O(5)-C(67)
O(90)-C(90)
O(91)-C(92)
O(92)-C(94)
C(90)-C(95A)
C(93)-C(94)
2.382(9)
2.350(8)
1.920(17)
1.984(22)
2.331(7)
2.197(17)
2.073(23)
1.293(31)
1.335(39)
1.367(35)
1.288(30)
1.516(32)
1.443(36)
1.400(31)
1.594(43)
1.532(38)
W(2)-Cl(2)
W(1)-O(2)
W(1)-C(1)
W(2)-Cl(4)
W(2)-Cl(6)
W(2)-O(6)
W(2)-C(5)
C(4)-C(5)
O(2)-C(37)
O(4)-C(67)
O(6)-C(61)
O(90)-C(91)
O(91)-C(93)
O(92)-C(95)
C(91)-C(92)
C(95)-C(90A)
2.321(8)
2.166(19)
2.053(26)
2.359(7)
2.372(7)
1.895(18)
2.012(20)
1.238(36)
1.240(32)
1.261(28)
1.424(28)
1.392(34)
1.399(27)
1.378(38)
1.492(42)
1.594(43)
F igu r e 5. σ- and π-bonding scheme for a W(η2-Ph2C2)
fragment.
Cl(2)-W(1)-Cl(3)
Cl(2)-W(1)-O(2)
Cl(1)-W(1)-O(3)
Cl(3)-W(1)-O(3)
Cl(1)-W(1)-C(1)
Cl(3)-W(1)-C(1)
O(3)-W(1)-C(1)
Cl(2)-W(1)-C(2)
O(2)-W(1)-C(2)
C(1)-W(1)-C(2)
Cl(4)-W(2)-Cl(6)
Cl(4)-W(2)-O(5)
Cl(6)-W(2)-O(5)
Cl(5)-W(2)-O(6)
O(5)-W(2)-O(6)
Cl(5)-W(2)-C(4)
O(5)-W(2)-C(4)
Cl(4)-W(2)-C(5)
Cl(6)-W(2)-C(5)
O(6)-W(2)-C(5)
W(1)-O(2)-C(37)
W(2)-O(5)-C(67)
W(1)-C(1)-C(2)
C(2)-C(1)-C(16)
W(1)-C(2)-C(26)
O(2)-C(37)-C(35)
W(2)-C(4)-C(46)
W(2)-C(5)-C(4)
90.5(3) Cl(1)-W(1)-O(2)
82.0(5) Cl(3)-W(1)-O(2)
91.5(6) Cl(2)-W(1)-O(3)
86.2(6) O(2)-(1)-O(3)
80.5(5)
82.0(5)
163.4(6)
81.5(7)
111.0(7)
158.2(8)
109.1(6)
88.0(6)
110.0(9)
86.5(2)
92.3(3)
81.4(5)
88.6(5)
86.9(5)
114.2(7)
84.1(7)
108.9(9)
110.1(6)
163.5(8)
35.2(10)
132.0(19)
135.9(14)
139.0(21)
74.2(16)
138.0(23)
69.7(14)
144.9(25)
140.0(15)
82.8(8) Cl(2)-W(1)-C(1)
114.3(8) O(2)-W(1)-C(1)
85.1(9) Cl(1)-W(1)-C(2)
86.1(6) Cl(3)-W(1)-C(2)
164.3(7) O(3)-W(1)-C(2)
37.3(9) Cl(4)-W(2)-Cl(5)
161.7(2) Cl(5)-W(2)-Cl(6)
81.9(5) Cl(5)-W(2)-O(5)
79.9(5) Cl(4)-W(2)-O(6)
161.8(5) Cl(6)-W(2)-O(6)
80.6(7) Cl(4)-W(2)-C(4)
89.0(8) Cl(6)-W(2)-C(4)
160.9(9) O(6)-W(2)-C(4)
87.0(6) Cl(5)-W(2)-C(5)
110.5(6) O(5)-W(2)-C(5)
87.1(8) C(4)-W(2)-C(5)
127.8(18) W(1)-O(3)-C(36)
130.0(17) W(2)-O(6)-C(61)
68.5(14) W(1)-C(1)-C(16)
152.5(28) W(1)-C(2)-C(1)
147.6(16) C(1)-C(2)-C(26)
125.5(30) W(2)-C(4)-C(5)
145.1(21) C(5)-C(4)-C(46)
75.0(15) W(2)-C(5)-C(56)
F igu r e 6. Detailed bond distances in angstroms (Å) for
representative Hsal ligands.
F igu r e 7. Detailed bond distances in angstroms (Å) for
representative Hcat ligands.
coordination environment of the tungsten is a classic
example of a d0 octahedral complex that contains a
single strong trans influence ligand.41 The square plane
of the monoanionic ligands is bent an average of 9° away
from the acetylene ligand, while the W-OCOOH distance
of 2.211(6) Å illustrates the trans influence of the Ph2C2
group.
C(90)-O(90)-C(91) 109.8(19) C(92)-O(91)-C(93) 110.2(21)
C(94)-O(92)-C(95) 110.9(20) O(90)-C(90)-C(95A) 103.3(19)
O(90)-C(91)-C(92) 109.2(21) O(91)-C(92)-C(91) 108.9(27)
O(91)-C(93)-C(94) 108.5(21) O(92)-C(94)-C(93) 109.5(20)
O(92)-C(95)-C(90A) 111.7(22)
Considering the potential electronic and steric influ-
ence of the acetylene unit, the core chelate structures
of the Hsal and Hcat ligands are very similar in the
W(η2-R2C2)Cl3 subunit and analogous oxo and arylimido
complexes. Figures 6 and 7 compare the structures of
Hsal-R and Hcat ligands in a variety of tungsten
complexes.41,42 All of the Hsal-R and Hcat derivatives
have long W-OPh distances approximating 1.9 Å, char-
acteristic of scant π-bonding between tungsten and the
catecholate ligand. The three W-OCOOH distances are
also long, averaging 2.18(1) Å. Still, these distances are
significantly shorter than the trans W-OOH distances
2.29(1) Å observed in the Hcat structures in Figure 7.
The 0.11(1) Å difference between the trans W-OCOOH
and the trans W-OOH bond distance probably arises
from two sources. First, and most significantly, the
larger six-membered chelate of the Hsal ligand accom-
modates the coordination sphere of the tungsten better
than the five-membered chelate of the Hcat group.
Second, the sp2 hybridization of the carboxylate oxygen
probably contributes to a slightly shorter W-O distance
and a somewhat stronger W-O bond. All of the Hcat
There has been ongoing discussion in the literature
about the best bonding description for this class of
mononuclear d2 acetylene complexes.53,50,60-62 Some
authors have claimed that the structural parameters
of the tungsten derivatives provide little evidence for a
true tungstacyclopropene-like valence structure.53 Oth-
ers, citing the extreme downfield shift of the acetylenic
carbons, suggest that substantial positive charge resides
on the acetylene carbons.56 A more recent study likens
the electronic structure of the d2 acetylene complexes
to that of a system bearing a d0 tungsten arylimido
unit.62 This latter description,62 based on careful struc-
tural, XPS, and calculational studies, seems most
consistent with the observed chemistry of 1. It should
be noted, however, that the electronic structure of the
acetylene ligand need not completely adopt the charac-
ter of a stilbene dianion ([C2Ph2]2-) in order to mimic
the chemistry of an imido group. The most sensible
simple model for bonding in the W(η2-R2C2) unit is one
suggested by its 13C NMR spectrum: a four electron
donor acetylene ligand, which also acts as a two electron
π back-acceptor from an occupied tungsten d orbital
(Figure 5).63 Consistent with this description, the
(63) Templeton, J . L. Adv. Organomet. Chem. 1987, 29, 1.

Assemblies Involving Organometallic Free Acids
Organometallics, Vol. 15, No. 22, 1996 4877
Sch em e 1
Typically, in structures of non-hydrogen-bonded and
non-metal-coordinated 18-crown-6 molecules, dihedrals
are observed to be 60° around the C-C bonds and 180°
around the C-O bonds.73,74 This lends the macrocycle
its characteristic shape with the oxygen atoms oriented
toward the interior of the structure. This orientation
is largely maintained in the [W(η2-Ph2C2)Cl3(Hsal)‚‚‚]4-
(18-crown-6) complex, in which all of the atoms in the
18-crown-6 show a 0.248(40) Å RMS deviation from
planarity. Like the hydrogen bonds in hydrates, chlo-
roform, and chloroacetonitile adducts of 18-crown-
6,67,68,71,72 the hydrogen-bonding interactions in 5 are
not bifurcated but exhibit standard O‚‚‚O distances
averaging 2.51(1) Å. The hydrogen-bonding interactions
pull the ether oxygens slightly farther than normal out
of the interior of the ring, which may be responsible for
the slight observed increase in the O-C-C-O torsional
angles to 64.1° (average). The juxtaposed O(90), O(90′)
oxygens, which are free of hydrogen bonding, seem to
be protected from coordination to additional equivalents
of free acid by the steric demands of the proximate
tungsten centers. These oxygens come closest to the
achieving the gauche O-C-C-O dihedrals (62.2°)
expected for a noninteracting 18-crown-6 molecule. The
carboxylate moiety of the Hsal subunit π-stacks above
the aromatic ring of the Hsal subunit on the cofacial
tungsten complex with an inter-arene plane distance of
3.39(18) Å. This “sandwiches” the non-hydrogen-bonded
ether oxygens between adjacent W(η2-Ph2C2)Cl3(Hsal)
molecules, providing the steric protection noted above.
Similar steric congestion evidently also occurs in the d0
oxo and arylimido analogs, which are isolated with
identical tetranuclear stoichiometries.41
and Hsal chelates remain virtually planar. The car-
boxylate units of the salicylate ligands all exhibit a
localized valence bond structure, with the carbonyl
oxygen bound to tungsten. None of the hydrogen-
bonding interactions in 1b and 5 manifest substantial
carboxylate anion character, which may account for the
roughly similar electronic distributions of the carboxy-
late units. Ammonium salts of these complexes can
have much greater C-O bond delocalization in the acid
functionality.41
Complex 1b does not aggregate through a typical
hydrogen-bonded acid dimer structure in the solid state
but forms an enlarged ring in which the acid groups
hydrogen bond to chloride ligands that are cis to the
Hsal ligand on an adjacent molecule. The O-H‚‚‚Cl
distances are 3.03(2) Å, typical for solid-state O-H‚‚‚Cl
association.64,65 The trans-chloride ligand and the
5-chloro group play little role in the hydrogen bonding
scheme, being approximately 3.3 and 5.6 Å away from
the carboxylate oxygen, respectively. The “slippage” of
these hydrogen bonding interactions from the classic
acid dimer probably reflects both a reduction of electron
density at the coordinated carbonyl unit and the greater
steric congestion brought about by the neighboring
metal center. The only apparent driving force for
hydrogen bonding to the cis-chloride instead of the
trans-chloride ligand is the collapse of the hydrogen-
bonding ring into a more compact arrangement (Scheme
1). The hydrogen bonds are complemented by apparent
vander Waals contacts between two [W(η2-Ph2C2)Cl3-
(Hsal-5-Cl)]2 units in which the Hsal-5-Cl ligand on one
dimer stacks above the Hsal-5-Cl ligand of an adjacent
dimer at a distance of 3.77(10) Å. Hydrogen bonding
between the Hsal ligand and the 18-crown-6 molecule,
and between the Hcat ligand and ether in 5 and 2,
respectively, is characteristic of the bonds found in other
tungsten Brønsted acid adducts.22,23,28,41 Typical O‚‚‚O
distances found in these systems are 2.51(1) Å.
Con clu sion s. Approaches to constructing materials
with novel structural and chemical behavior can further
our understanding of basic concepts such as hydrogen
bonding. The organometallic free acids described in this
study provide an unusual opportunity for a detailed
study of how subtle steric and electronic perturbations
in ligand sets influence the reactivity and hydrogen
bonding ability of high oxidation state early transition
metal Brønsted acids. The study of these complexes
fosters the development of other applications intimately
related to hydrogen bonding, such as molecular recogni-
tion and the preparation of novel inorganic/organic
hybrid materials.
Exp er im en ta l Section
Gen er a l P r oced u r es a n d Ma ter ia ls. All experiments
were performed under a nitrogen atmosphere in a HE-553-2
Vacuum Atmospheres drybox or using standard Schlenk
techniques. Hexane and diethyl ether were purified by distil-
The ORTEP diagram of [W(η2-Ph2C2)Cl3(Hsal)‚‚‚]4(18-
crown-6) (5, Figure 4) is a representation of the most
remarkable of these supramolecular aggregates. The
18-crown-6 molecule adopts a typical crown conforma-
tion, in which the acid moieties of the Hsal ligands
hydrogen bond to four of the ether oxygens in a 1,4,-
10,13-substitution pattern. A large number of struc-
tures of the 18-crown-6 macrocycle exist, some of which
hydrogen bond to water and small organic molecules.66-72
(67) Mootz, D.; Albert, A.; Schaefgen, S.; Sta¨ber, D. J . Am. Chem.
Soc. 1994, 166, 12045.
(68) Strel’tsova, W. R.; Bel’skii, Y. K.; Nazarenko, A. Y.; Kranifovski,
O. T. Z. Obsh. Khim. 1992, 62, 598.
(69) Blaschette, A.; Safari, F.; Nagel, K.; J ones, P. G. Z. Naturforsch.
1993, 1355.
(70) Audet, P. J .; Savoie, R.; Simard, M. Can. J . Chem. 1990, 68,
2183.
(64) Hamilton, W. C. Hydrogen Bonding in Solids; W. A. Benjamin,
Inc.: New York, 1968.
(65) For a related hydrogen bond interaction involving N-H···Cl
bonds, see: Yap, G. P. A.; Rheingold, A. L.; Das, P.; Crabtree, R. H.
Inorg. Chem. 1995, 34, 3474.
(66) Watson, K. A.; Fortier, S.; Murchie, M. P.; Bovenkamp, J . W.;
Rodriguez, A.; Buchanan, G. W.; Ratcliffe, C. I. Can. J . Chem 1990,
68, 1201.
(71) J ones, P. G.; Hiemisch, O.; Blaschette, A. Z. Naturforsch. 1994,
852.
(72) Buchanan, G. W.; Rodrigue, A.; Bensimon, C.; Ratcliffe, C. I.
Can. J . Chem. 1992, 70, 1033.
(73) Miele, P.; Foulton, J .; Hovnanian, N.; Cot, L. Polyhedron 1993,
12, 267.
(74) Dunitz, J . D.; Dobler, M.; Seiler, P.; Phizackerley, R. P. Acta.
Crystallogr., Sect. B 1974, 30, 2733.

4878 Organometallics, Vol. 15, No. 22, 1996
Baroni et al.
lation from Na/benzophenone. Dichloromethane, acetonitrile,
and triethylamine were purified by distillation from CaH2,
followed by degassing with dry nitrogen. NMR solvents
(Cambridge Isotope Laboratories) were dried with 5 Å molec-
ular sieves and degassed with dry nitrogen. Celite was oven
dried for 48 h at 110 °C prior to use. Salicylic acid (H2sal,
Fisher), substituted salicylic acids (H2sal-R, Aldrich), and
diphenylacetylene (Ph2C2, Farchan) were used as received. 18-
Crown-6 was recrystallized from dry acetonitrile and vacuum
dried for 12 h (∼10-6 Torr, room temperature) prior to use.
W(η2-Ph2C2)Cl4 was synthesized from sublimed WCl6 and
Ph2C2 according to literature procedures.44
NMR spectra were recorded on Varian XL-300, GE QE-300,
or Bruker AM-500 spectrometers. 1H and 13C data are listed
in parts per million downfield from tetramethylsilane, with
data referenced by the residual solvent proton peak. Elemen-
tal analyses were performed by Desert Analytics (P.O. Box
41838, Tucson, AZ 85717).
suspended in toluene (10 mL). LiHedbp (0.502 g, 0.968 mmol
where edbp ) 2,2′-ethylenebis(4,6-di-tert-butylphenolate)) dis-
solved in ether (20 mL) was added via cannula. The reaction
was refluxed overnight, yielding a dark red solution and a light
colored precipitate. After filtration through Celite, and a
second filtration in ether/hexane solution, the filtrate volume
was reduced. Refrigeration at -20 °C yeilded a black micro-
crystalline solid of cis-W(η2-Ph2C2)Cl2(edbp)(OEt2) (3). Yield:
0.291 g (0.32 mmol, 33%). The product was prone to loss of
ether. NMR data (300 MHZ, CDCl3) are as follow. 1H: 8.30
(d, 4H, Ph2C2), 7.65 (t, 4H, Ph2C2), 7.56 (s, 1H, Ph2C2), 7.38 (s,
2H, edbp), 7.24 (s, 2H, edbp), 4.13 (q, 1H, CHCH3, edbp), 3.48
(q, 4H, OCH2CH3), 2.12 (d, 3H, CHCH3, edbp), 1.34 (s, 18H,
C(CH3)3), 1.03 (s, 18H,C(CH3)3). 13C: 227.62 (Ph2C2), 161.42,
150.14, 147.30, 142.94, 141.11, 135.95, 133.82, 132.76, 130.00,
128.84, 123.21, 122.53, 121.95, 120.73, 65.86 (CH3CH), 31.62
(C(CH3)3), 31.51 (C(CH3)3), 15.27 (CH3CH).
P r ep a r a tion of W(η2-P h 2C2)Cl3(Hsa l‚‚‚NEt3) (4a ). 1a
(0.899 g, 1.48 mmol) was placed into a 50 mL Schlenk flask
and slurried in 15 mL of benzene. Triethylamine (0.21 mL,
0.152 g, 1.50 mmol) was added by syringe over 5 min. The
solution darkened as the triethylamine was added and was
then allowed to stir for 30 min. The resulting orange-red
mixture was stripped to dryness, yielding a spongy mass that
dried further under high vacuum. Hexane (40 mL) was added
to the flask, and the solid mass was broken up with agitation.
The suspension was filtered, leaving orange-red microcrystals
that were washed with hexane (2 × 10 mL) and dried for 3 h
in vacuo. Yield: 0.943 g (1.33 mmol, 90%). NMR data (300
MHz, CDCl3) are as follow. 1H: 1.40 (9H, t), 3.35 (6H, m),
6.77 (H, d), 7.16 (H, t), 7.44 (H, t), 7.49 (2H, t, overlaps w/peak
at 7.44 ppm), 7.67 (4H, t), 8.15 (4H, d), 8.26 (H, d), 11.70 (H,
br s, -CO2H‚‚‚NEt3). 13C: 9.08 (N(CH2CH3)3), 46.03 (N(CH2-
CH3)3), 119.56, 120.68, 125.01, 128.85, 132.25, 132.31, 133.71,
134.08, 140.24, 162.70, 169.58, 244.95 (Ph2C2). Analytical data
are based on the formula C21H3NO3WCl3. Calc: 45.91, C; 4.28,
H; 1.98, N. Actual: 46.16, C; 4.13, H; 1.83, N.
P r ep a r a tion W(η2-P h 2C2)Cl3(Hsa l) (1a ). W(η2-Ph2C2)Cl4
(4.496 g, 8.92 mmol) was slurried in 25 mL of CH2Cl2 and 15
mL of hexane in a 50 mL Schlenk flask. To this reddish-purple
slurry, salicylic acid (1.231 g, 8.91 mmol) was added by
addition tube. The mixture immediately darkened to a deep
orange-red color. The flask was fitted with a condenser and
refluxed for 6 h. A brick red, microcrystalline powder pre-
cipitated and was harvested via filtration. The precipitate was
washed with hexane (2 × 15 mL) and dried for 8 h (∼10-6 Torr,
room temperature). Yield: 4.061g (75%). NMR data (CDCl3)
are as follow. 1H: 6.95 (1H, d, 3-position Hsal), 7.29 (1H, t,
4-position Hsal), 7.58 (2H, t, 4-position of Ph- in Ph2C2), 7.74
(5H, t, overlapping protons of 5-position on salicylate and
3-position of Ph- ring on the Ph2C2 ligand), 8.14 (4H, d, 2,
position of Ph- in Ph2C2), 8.27 (1H, d, 6-position Hsal). 13C:
112.47, 121.73, 125.11, 129.16, 132.47, 133.60, 134.49, 138.48,
138.93, 163.75, 165.64, 248.40 (Ph2C2). Analytical data are
based on the formula C21H15O3WCl3. Calc: 41.65, C; 2.50, H.
Actual: 41.51, C; 2.30, H.
P r ep a r a t ion of W(η2-P h 2C2)Cl3(H sa l-5-Cl) (1b ).
A
P r ep a r a tion of [W(η2-P h 2C2)Cl3(Hsa l)‚‚‚]4(18-cr ow n -6)
(5). This experiment was carried out in a fashion similar to
the synthesis of 1a or 1b with 18-crown-6 present. A 50 mL
Schlenk flask was charged with W(η2-Ph2C2)Cl4 (2.6760 g, 5.31
mmol) and a stir bar. In a separate flask, salicylic acid (0.7345
g, 5.32 mmol), 18-crown-6 (0.2393 g, 0.90 mmol), and ∼40 mL
of dichloromethane were combined. This solution was trans-
ferred, by cannula, to the Schlenk flask containing the solid
W(η2-Ph2C2)Cl4. Before all of the solution was transferred, all
of the tungsten-containing materials had dissolved. This red-
brown solution was stirred overnight and then filtered through
Celite. The volume of solution was reduced to ∼20 mL, and
then the flask was closed and cooled at -20 °C, yielding X-ray-
quality orange-red block crystals. The supernatant solution
yielded further crops of crystals after further reduction in
volume and layering with hexane. Yield: 2.175 g (3.42 mmol,
61%). NMR data (300 MHz, CDCl3) are as follow. 1H: 4.10
(24H, s), 6.86 (4H, d), 7.18 (4H, t), 7.56 and 7.62 (12H,
overlapping triplets), 7.72 (16H, t), 8.14 (16H, d), 8.25 (4H,
d), 11.8 (4H, broad s, -COOH‚‚‚OCH2-). 13C: 70.89, 113.37,
121.39, 125.15, 129.08, 132.57, 133.33, 134.42, 138.06, 138.67,
163.39, 171.58, 247.47 (Ph2C2). Analytical data are based on
weighed portion of W(η2-Ph2C2)Cl4 (0.7766 g, 1.54 mmol) and
a stir bar were placed in a 50 mL Schlenk flask and then
suspended in ∼30 mL of dichloromethane. 5-Chlorosalicylic
acid (0.2660 g, 1.54 mmol) was added by addition tube. Again,
the color of the solution changed to a deep red-orange. The
reaction was allowed to stir overnight and was then filtered
through Celite. The volume was reduced in vacuo to 10 mL
and then 5 mL of hexane was added. The solution was
warmed and allowed to stand overnight yielding reddish block
crystals suitable for X-ray analysis. Yield: 0.635 g (64%).
NMR data (300 MHZ, CDCl3) are as follow. 1H: 6.88 (H, d),
7.59 (2H, t), 7.64 (H, d), 7.67 (H, d), 7.74 (4H, t), 8.12 (4H, d),
8.21 (2H, d, J m ) 2.6Hz). 13C: 113.32, 123.47, 129.24, 130.07,
131.65, 133.83, 134.56, 138.42, 138.85, 162.60, 170.25, 249.77
(Ph2C2).
P r ep a r a tion of W(η2-P h 2C2)Cl3(Hca t···Et2O)] (2). Cat-
echol (0.218 g, 1.98 mmol) was dissolved in 20 mL of Et2O and
added to a solution of W(η2-Ph2C2)Cl4 (1.00 g, 1.98 mmol) in
15 mL of Et2O. The dark reddish-purple solution was stirred
overnight and then filtered through Celite. The resulting
solution was reduced in volume to ∼5 mL and cooled to -20
°C to afford purple block crystals suitable for X-ray analysis
(1.05 g, 1.61 mmol, 81%). NMR data (500 MHZ, CDCl3) are
as follow. 1H: 1.46 (6H, t, (CH3CH2)2O), 3.90 (4H, q,
(CH3CH2)2O), 6.99 (H, d), 7.07 (H, t), 7.12 (H, t), 7.27 (H, d),
7.59 (2H, t), 7.73 (4H, t), 8.24 (4H, d), 14.97 (H, broad s,
Hcat‚‚‚Et2O). 13C: 14.85, 67.44, 114.84, 118.50, 123.17, 126.29,
129.07, 133.44, 134.44, 138.11, 144.68, 156.12, 247.14 (η2-
Ph2C2). Analytical data are based on the formula C24H25O3-
WCl3‚1/3C4H10O. Calc: 44.98, C; 4.21, H. Actual: 45.45, C;
3.83, H.
the formula C96H84O18W4Cl12
tual: 43.17, C; 3.00, H.
. Calc: 42.92, C; 3.15, H. Ac-
Molecu lar Weigh ts of Fr ee Acids. The molecular weights
of the free acids in benzene solution were determined using a
modified Signer apparatus.48 The apparatus makes use of the
property of the change in vapor pressure of a solvent as a
function of concentration of solute (i.e. Raoult’s Law).
A
standard solution of triphenylmethane was placed in one side
of the apparatus and the complex solution placed in the other.
The apparatus was then sealed (using Kontes Teflon valves),
and the volume of each solution is measured. When the
volume of the two solutions stopped changing, the vapor
P r ep a r a tion of cis-W(η2-P h 2C2)Cl2(ed bp )(OEt2) (3). A
weighed portion of W(η2-Ph2C2)Cl4 (0.488 g, 0.968 mmol) and
a stir bar were placed in a 50 mL Schlenk flask and then

Assemblies Involving Organometallic Free Acids
Organometallics, Vol. 15, No. 22, 1996 4879
Ta ble 4. Cr ysta llogr a p h ic Da ta for 1b, 2, a n d 5
1b
2
5
(a) Crystal Parameters
formula
fw
C21H14Cl4O3W
640.0
C24H25Cl3O3W
651.6
C96H84Cl12O18W4
2686.5
cryst system
space group
a, Å
b, Å
c, Å
triclinic
P1h
monoclinic
P21/n
9.396(4)
24.849(6)
10.932(5)
triclinic
P1h
10.009(3)
10.725(3)
10.796(3)
105.70(2)
97.84(2)
92.02(2)
1102.0(2)
2
10.682(3)
12.201(3)
19.244(3)
81.70(3)
76.77(5)
85.66(3)
2416(6)
1
R, deg
â, deg
95.35(3)
γ, deg
V, Å3
2544(4)
4
Z
cryst dimens, mm
cryst color
D(calc), g cm3
Mo KR, cm-1
temp, K
T(max)/T(min)
0.40 × 0.40 × 0.30
0.38 × 0.42 × 0.46
0.32 × 0.34 × 0.36
red
black
black
1.928
57.45
228
0.62/0.41
1.701
48.78
296
0.88/0.62
1.892
51.55
296
0.57/0.32
(b) Data Collection
diffractometer
monochromator
radiation
2θ scan range, deg
rflns collcd
Siemens P4
graphite
Mo KR (λ ) 0.710 73 Å)
4-50
4688
4-48
3678
4-44
6120
indepd reflns
3011
4449
5905
indepd obsd reflcns F > nσ(Fo)
3011 (n ) 4)
3 stds/197 rflns
<1
2840 (n ) 4)
3 stds/197 rflns
1-2
3942 (n ) 4)
3 stds/197 rflns
<1
stds/reflcns
var in stds, %
(c) Refinementa
R(F), %
4.24 (4.98)b
5.20 (5.37)b
0.010
4.04 (7.75)
4.70 (5.68)
0.129
0.65
11.6
7.42 (11.00)
10.27 (11.86)
0.043
1.59
10.2
R(wF), %
∆σ(max)
∆(p), e Å-3
No/Nv
1.89
11.5
goodness of fit
1.21
1.00
1.18
a
b
Quantity minimized ) ∑w∆2; R ) ∑∆/∑(Fo); R(w) ) ∑∆w1/2/∑(Fow1/2), ∆ ) |(Fo - Fc)|. All data.
pressures were assumed to have equalized and the molecular
weight was calculated.
Patterson syntheses. All non-hydrogen atoms were refined
with anisotropic thermal parameters, except for the phenyl-
ring carbon atoms of 5 which were refined isotropically to
conserve data. Hydrogen atoms are treated as idealized
contributions. The nonrigidity of the loosely-bound crown
ether complex produces higher-than-usual thermal activity
that, in turn, creates diffuse diffraction. R factors and other
measures of structure quality compare favorably to those
commonly reported for similar compounds. All computations
used SHELXTL software (version 4.2, G. Sheldrick, Siemens
XRD, Madison, WI).
1H NMR Titr a tion of 1b w ith Tr ieth yla m in e in CDCl3.
A 4.35 mg amount of 1b was weighed directly into a calibrated
NMR tube, dissolved in CDCl3, and diluted to a total volume
of 750 µL. The tube was capped with a septum and secured
with Parafilm. Triethylamine (0.102 g) was placed into a 1
mL volumetric flask and was subsequently diluted to the mark
with CDCl3. This flask was also capped with a septum and
secured with Parafilm. Triethylamine solution (1 µL aliquots,
1.01 M) was added to the solution containing 1b (1.10 × 10-2
M) via microliter syringe and then allowed to equilibrate for
1 min. NMR spectra were recorded at 20 °C. At high
triethylamine concentrations, only one broad peak is observed,
attributed to fast exchange of the salt 4b with the free acid
1b remaining.
Ack n ow led gm en t. We gratefully acknowledge the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society, for support of this research. We
also thank Hercules Corp. for a generous gift of tungsten
compounds and a drybox in support of this work.
Cr ysta llogr a p h ic Str u ctu r e Deter m in a tion s. Crystal-
lographic data are collected in Table 4. Specimens of all three
compounds were mounted on glass fibers and characterized
photographically. Structures 1b and 5 showed no symmetry
greater than triclinic, and 2 was found to possess 2/m Laue
symmetry. For 1b and 5 an initial assumption of centrosym-
metry was supported by the results of the subsequent refine-
ment; for 2 the space group was uniquely determined by
systematic absences. Empirical corrections for absorption
were applied to the data. All structures were solved from
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and U values, interatomic distances, angles, and
anisotropic displacement coefficients and supplementary views
of inter-arene contacts (39 pages). Ordering information is
given on any current masthead page.
OM960361G