Supramolecular structures by hydrogen bonding: The solid-state structure of tris[3-(3-dimethylamino-1-oxoprop-2-enyl)phenyl]phosphane oxide

Article abstract of DOI:10.1002/ejoc.200600847

Tris[3-(3-dimethylamino-1-oxoprop-2-enyl)phenyl]phosphane oxide, which can be synthesized quantitatively by oxidation of the corresponding phosphane, crystallizes in the trigonal space group R3. Because of the four different strong proton accepting sites

Full text of DOI:10.1002/ejoc.200600847

FULL PAPER
DOI: 10.1002/ejoc.200600847
Supramolecular Structures by Hydrogen Bonding: The Solid-State Structure of
Tris[3-(3-dimethylamino-1-oxoprop-2-enyl)phenyl]phosphane Oxide
Andreas Reis,[a] Yu Sun,[a] Gotthelf Wolmershäuser,[a] and Werner R. Thiel*[a]
Keywords: Solid-state structures / Hydrogen bonds / Phosphane oxides
Tris[3-(3-dimethylamino-1-oxoprop-2-enyl)phenyl]phosphane
oxide, which can be synthesized quantitatively by oxidation
of the corresponding phosphane, crystallizes in the trigonal
solid state, which results in the generation of two interpen-
etrating networks. In the cavities of the solid-state structure,
water and acetone are enclosed.
¯
space group R3. Because of the four different strong proton
accepting sites (1ϫP=O, 3ϫC=O), this molecule can form
P=O···H–O–H···O=P and C=O···H–C hydrogen bonds in the
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
by the elucidation of several solid-state structures.[4] The
Hydrogen bonds are of fundamental importance for the proton accepting power of the electron rich carbonyl group
world we are living in. This fact is mainly related to the of such compounds enables intermolecular C=O···H–C hy-
hydrogen bond strength (up to about 40 kJ/mol), which al- drogen bonding with the protons of the –CH=CH– frag-
lows reversible bond formation and cleavage under ambient ment or the NMe2 groups of a neighbouring molecule. In
conditions.[1] The resulting dynamics, especially in protic the present manuscript, we will show that the specific intro-
and/or polar solvents like water, enables a hydrogen bond- duction of multiple 3-dimethylaminoprop-2-en-1-one units
ing system, in contrast to a purely covalently bound struc- allows to design the solid-state structure of such systems.
ture, to adapt to the requirements of its environment.[2] This
reveals the relevance of hydrogen bonding in molecular one side chains at one central unit leads to chain-type hy-
biology and biochemistry. drogen bound aggregates, as realized, for example, in the
The introduction of two 3-dimethylaminoprop-2-en-1-
The secondary structures of proteins, for example, are solid-state structure of 2,6-bis(3-dimethylamino-1-oxoprop-
strongly determined by intramolecular hydrogen bonds 2-enyl)pyridine.[4b] By adding a third 3-dimethylaminoprop-
mainly performed between the proton donating and ac- 2-en-1-one function to one planar central unit, as it is real-
cepting sites of the amide units [-C(O)–NH-]. Here, the in- ized in 1,3,5-tris(3-dimethylamino-1-oxoprop-2-enyl)ben-
volvement of the N–H group as a proton donor in hydrogen zene, should thus make layer-type structures accessible.
bonding increases the hydrogen accepting feature of the car- Crystallization from wet acetone gives the trihydrate of this
bonyl moiety and vice versa. Removal of the proton of the compound wherein the water molecules act as proton do-
N–H group against a carbon substituent leaves a strong hy- nors and acceptors in the expected two-dimensional hydro-
drogen acceptor, which manifests itself in polar compounds gen bonded network. However, cocrystallization with larger
such as dmf, where the dimethylamino moiety enhances the proton donors like hydroquinone or 4,4Ј-dihydroxybiphenyl
electron density at the carbonyl oxygen atom. Introduction gives linear structures wherein only two of the three 3-di-
of a -CH=CH- fragment into the C–N bond results in vi- methylaminoprop-2-en-1-one side chains are engaged in hy-
nylogous 3-dimethylaminoprop-2-en-1-ones. Such mole- drogen bonding, presumably this is due to steric reasons.[4a]
cules, which are accessible in high yields by reacting an aryl By following something like a crystal engineering strategy,
methyl ketone with an activated dmf analogue have recently the steric problems can be overcome by changing the core
attracted our interest as precursors for the synthesis of pyr- from a planar 1,3,5-trisubstituded benzene into a pyramidal
azole- and pyrimidine-based ligands.[3] Additionally, 3-di- arrangement like it is, for example, realized in triarylphos-
methylaminoprop-2-en-1-ones are powerful proton ac- phanes.
cepting compounds, which we were able to prove spectro-
A similar strategy is realized in supramolecular coordina-
scopically and by quantum chemical calculations as well as tion chemistry where the thermodynamically reversible co-
ordination of transition metal building blocks to symmetri-
cally substituted donor ligands is used to build up oligonu-
clear aggregates of nanometer dimension.[5] M. Albrecht re-
cently highlighted the supramolecular chemistry of C3-sym-
metric ligands leading to C3-symmetric structures.[6]
[a] Fachbereich Chemie, Technische Universität Kaiserslautern,
Erwin-Schrödinger-Str., Geb. 54, 67663 Kaiserslautern,
Germany
Fax: +49-631-2054676
E-mail: thiel@chemie.uni-kl.de
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A. Reis, Y. Sun, G. Wolmershäuser, W. R. Thiel
FULL PAPER
thesized quantitatively by oxidation of the corresponding
phosphane by air. The phosphane is accessible following a
Results and Discussion
Our C3-symmetric target molecule tris[3-(3-dimethylamino- stepwise synthesis starting from 3-bromoacetophenone in
1-oxoprop-2-enyl)phenyl]phosphane oxide (1) can be syn- about 50% overall yield (Scheme 1).[3a]
Scheme 1. i) TsOH, HOCH2CH2OH, toluene, reflux; ii) Mg, thf, reflux; iii) PCl3, thf, reflux; iv) TsOH, H2O, thf, reflux; v) HC(OMe)2-
NMe2, reflux; vi) air, acetone, room temp.
Figure 1. P: orange, O: red, N: blue. Top: Molecular views of single molecules of 1 in the solid state (left, middle); hydrogen bonds
between two 3-dimethylamino-1-oxoprop-2-enyl side chains (right: disordered CH3 groups omitted for clarity). Selected bond lengths [Å]
and torsion angles [°]: P–O1 1.480(3), O2–C7 1.234(3), C7–C8 1.420(3), C8–C9 1.351(4), N–C9 1.320(3), O1–P–C1–C2 154.68(18), O2–
C7–C8–C9 –0.8(4), C7–C8–C9–N–179.6(3), C10–N–C9–C8–178.0(3), C9–N–C10–H10A 0.00. Hydrogen bond parameters [Å] and [°]:
C10–H10A 0.96, H10A···O2 2.35, C10···O2 3.277(4), C10–H10A···O2 161.00. Middle: Sketch of the two dimensional supramolecular
arrangement of 1 by hydrogen bonding; filled circles: P=O pointing up; open circles: P=O pointing down; dashed lines: hydrogen bonds.
Bottom: The two dimensional arrangement of 1 that results from intermolecular hydrogen bonding; views along the crystallographic c-
(left) and a axis (right).
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Solid-State Structure of a Supramolecular 2D Network
FULL PAPER
Compound 1 crystallizes under “transfer” of the sym- CH-unit of one of the terminal CH3 groups. Figure 1, top
metry of the molecule into the solid state in the trigonal right, gives a view on the 14-membered ring generated by
space group R3(No.148)[7] by slow diffusion of diethyl ether twofold C=O···H–C hydrogen bonding. These interactions
¯
into a concentrated solution of the compound in wet ace- enforce coplanarity of all atoms of the (O)C–C=C–N–CH
tone.[8] Figure 1 shows different aspects of the solid-state moieties (O2–C7–C8–C9–N–C10–H10A). However, be-
structure of 1. Up to now, crystallization of 1 could only cause the nitrogen atom of the dimethylamino group is
be performed successfully in this combination of solvents found in a slightly pyramidal environment, the terminal
because of the inclusion of water and acetone in its solid- CH3 groups, which are not included in hydrogen bonding,
state structure (see below). are found disordered in two positions (Figure 1, top, left
The aryl substituents of the triarylphosphane oxide cores and middle).
are arranged in a paddle wheel type structure (torsion angle
Hydrogen bonding under perpetuation of the C3 sym-
O1–P–C1–C2 154.68°), with the 3-dimethylamino-1-oxo- metry of the P(Ar)3 cores generates in the first step a two-
prop-2-enyl chains almost oriented to the interior of the dimensional network, wherein the P=O units, which are ori-
molecule’s cone (Figure 1, top, left and middle).[9] Looking ented parallel to the crystallographic c axis, are alternately
along the P–O axis of 1, which is one of the threefold axes pointing up and down (Figure 1, middle, bottom). As
of symmetry in the solid-state structure (Figure 1, top, left), shown, the resulting two-dimensional network contains
makes clear that the orientation of the carbonyl groups de- hexagonal pores along a crystallographic S6 axis. The layers
termines the docking of the neighbouring molecules. Be- above and below (layer 1 and –1) are linked through these
cause of steric reasons, there is only one proton donor site pores by hydrogen bonding between one P=O unit from
that is able to undergo C=O···H–C hydrogen bonding: a those layers and one molecule of water (half a molecule
Figure 2. P: orange, O: red, N: blue, water positions: yellow. Top left: molecular view of the linkage between layer 1 and layer –1 by
hydrogen bonding to disordered water molecules (yellow) through the pores of layer 0 (not shown); distances P=O···OH O: 2.95(2) and
2
2.83(2) [Å]. Top right: layer stacking that results in interconnection through “hexagonal” pores and formation of distorted hexagonal
bipyramidal cavities. Bottom left: side view of the distorted hexagonal bipyramidal cavity containing one molecule of acetone on disor-
dered positions (green: observed spots of enhanced electron density). Bottom right: top view (space filling) on one of those cavities
including disordered water positions (yellow, translucent).
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779

A. Reis, Y. Sun, G. Wolmershäuser, W. R. Thiel
FULL PAPER
per formula unit of 1), which results in two interpenetrating
hydrogen bound networks (network 1: odd numbered lay-
ers; network 2: even numbered layers, Figure 2, top right).
The water molecule is found disordered in six positions in
a chair like structure due to the symmetry of the location
(Figure 2, top left). The distance between the two water-
linked oxygen atoms of the phosphane oxides is 4.895 Å.
Additionally, neighbouring layers form a second, less po-
lar type of cavity, established by six [3-(3-dimethylamino-1-
oxoprop-2-enyl)phenyl] side chains. In this cavity, which can
be described by a distorted hexagonal bipyramid, one disor-
dered molecule of acetone is enclosed (half a molecule per
formula unit of 1, Figure 2, bottom). The P–P distance be-
tween the phosphorus centres on top and on bottom of
these cavities is 2.387 nm.
Conclusions
In the solid-state structure of 1, four different strong pro-
ton accepting sites are engaged in the formation of hydro-
gen bonds. The tetrahedral phosphane oxide centre gener-
ates an arrangement of the proton accepting sites, which is
comparable to certain building blocks frequently used in
supramolecular coordination chemistry. However, in our
case, the proton accepting sites are due to steric require-
ments oriented to the “outer” side of the molecule, which
results in the formation of a three dimensional hydrogen
bond based arrangement in the solid state.
Experimental Section
¯
The space group R3 is known from a series of solid-state
Tris[3-(3-dimethylamino-1-oxoprop-2-enyl)phenyl]phosphane[3a]
(5.76 g, 10.4 mmol) was dissolved in acetone (100 mL) and oxidized
by stirring the solution for 12 h under ambient conditions in the
air. The solvent was removed in vacuo to leave 1 as an orange-red
microcrystalline solid in almost quantitative yield (5.90 g). Product
structures of simple inorganic systems like dolomite,[10] per-
ovskites,[11] silicates,[12] metal halides and sulfates,[13] as well
as hexafluorometallates.[14] Additionally, a variety molecu-
lar inorganic and organic compounds crystallize in this
space group. Some of them, like TiCl3(NPPh3),[15] (PPh3)3- 1 was recrystallized by slow diffusion of diethyl ether into a satu-
1
[16]
or some spherands,[17] exhibit C3
rated solution of acetone. H NMR (400.13 MHz, CDCl3, 25 °C):
δ = 2.17 (s, 3 H, acetone), 2.44 (br., 1 H, H2O), 2.91, 3.16 (2ϫs,
Co–NϵN–Li(OEt2)3
symmetry in the single molecules as it is the case for 1.
However, they do not form hydrogen bond networks. On
the other hand, there is a series of nonsymmetrical com-
pounds or compounds with lower symmetry than C3, which
3
18 H, NMe2), 5.66 (d, JHH = 11.9 Hz, 3 H, =CHNMe2), 7.52 (dt,
4JPHm = 3.1 Hz, JHmHo
=
3JHmHp = 7.8 Hz, 3 H, H-meta), 7.65
3
(dd, 3JPHo = 11.9 Hz, 3 H, H-ortho), 7.93 [d, 3 H, C(O)CH=], 8.13
3
(d, 3 H, H-para), 8.23 (d, JPHoЈ = 12.6 Hz, 3 H, H-orthoЈ) ppm.
¯
also crystallize in the space group R3. In those cases, the
31P{1H} NMR (161.98 MHz, CDCl3, 25 °C): δ = 30.3 ppm.
C33H36N3O4P·(H2O)0.5·(C3H6O)0.5 (607.68): calcd. C 68.18, H 6.63,
N 6,91; found C 68.08, H 6.64, N 6.59.
solid states structures are mainly determined by hydrogen
bonding. Among them we have found two systems with in-
terpenetrating hydrogen bond networks: 1,4-(dihydroxy-
methyl)cubane[18] and the α-form of hydroquinone.[19] How-
ever, these compounds are too small and are not pre-
oriented to build up cavities for the inclusion of guest mole-
cules.
We are now able to start systematic crystal engineering
by the synthesis of a series of novel derivatives possessing
analogue structural motifs such as 1: replacement of the
phosphane oxide O=P group with another group that is
unable to undergo hydrogen bonding (e.g. R–Si) should
lead to systems without interpenetrating networks but still [3] a) Y. Sun, A. Hienzsch, J. Grasser, E. Herdtweck, W. R. Thiel,
with cavities for the inclusion of guest molecules. On the
other hand, we will extend the distance between the hydro-
gen bonding site and the central atom (here: P) to enlarge
the cavities for guest inclusion. Scheme 2 shows two exam-
ples.
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft for support of this
work.
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=
645.73; crystal system: trigonal; space group:
¯
R3(No.148); a = b: 13.6944(10), c: 31.725(3) [Å]; V: 5152.5(7)
[Å3]; Z: 6; ρcalcd.: 1.225; µ(Mo-Kα): 0.132 [mm–1]; F(000): 2004;
crystal size: 0.13·0.40·0.48 [mm3]; T: 293 [K]; λ: 0.71073 [Å];
Θmin–Θmax: 3.0–26.7 (°); h, k, l: –17/17, –17/17, –40/40; total
data: 14925; unique data: 2444; R(int): 0.062; observed data [I
Ͼ 2.0σ(I)]: 1196; Nref: 2444, Npar: 150; R: 0.0441; wR2: 0.1270;
Scheme 2.
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Solid-State Structure of a Supramolecular 2D Network
FULL PAPER
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Received: September 28, 2006
Published Online: December 7, 2006
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