Nitrosaminc/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) complexes and the formation of donor-appended DDQ chains in the solid state

Full text of DOI:10.1021/ja972254z

J. Am. Chem. Soc. 1997, 119, 11343-11344
11343
Scheme 1
Nitrosamine/2,3-Dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ) Complexes and the
Formation of Donor-Appended DDQ Chains in the
Solid State
Melinda L. Greer and Silas C. Blackstock*
Department of Chemistry
The UniVersity of Alabama
Tuscaloosa, Alabama 35487-0336
ReceiVed July 8, 1997
Supramolecular chemistry1 relies on associative functional
group interactions for molecular array formation. In molecular
solids, such interactions are the tools of crystal synthesis (or
engineering).2 As part of a program to uncover new modes of
organic donor-acceptor (DA) association3,4 for application to
crystal engineering, we have investigated the DA association
of nitrosamines and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) (eq 1).
isoindoline (TEMINO)/DDQ in CH2Cl2 yields ∆H° -4.8(2) kcal
mol-1 and ∆S° -11.9(10) eu. The more easily oxidized
nitrosamines yield the longer wavelength CT bands as ex-
pected.10
Cooling of red TEMINO/DDQ mixtures in CH2Cl2 affords
dichoric yellow/red crystals of 1:1 TEMINO/DDQ (1) whose
structure11 is composed of TEMINO-appended (DDQ)n chains
(Figure 1), as judged by close intermolecular contacts. Two
key interactions are apparent: DA “bonding” of TEMINO to
DDQ and carbonyl (CdO‚‚‚CdO) “bonding” between adjacent
DDQ molecules.
The 2.87 and 2.67 Å distances of TEMINO NdO atoms to
the DDQ carbonyl carbons are much shorter than the atomic
van der Waals radii sums (3.22 and 3.25 Å for C‚‚‚O and C‚‚‚N,
respectively).12 The nitrosamine/DDQ complex topology is that
expected for an n* donor/π* acceptor complexation. Relevant
(AM1-calculated) nitrosamine (Me2NNO) and DDQ frontier
molecular orbitals (FMOs) are shown in Figure 1.
The one-dimensionality of the TEMINO/DDQ array of 1
stems from (DDQ)n chain formation via 1,4′ CdO‚‚‚CdO
association at 2.75 Å.13 The topology of this interaction is that
of a π nucleophile/π* electrophile complex of carbonyl groups.14
Similar carbonyl bonding is found in the neat DDQ crystal
structure 2,15 as shown in Figure 2. However, in 2, the (DDQ)n
chains16 have a different (1,1′) regiochemistry than that observed
The low basicity and high oxidation potential (Epox 1.7-2.2
V vs SCE)5 of nitrosamines indicate that they are weak electron
donors, and, to the best of our knowledge, no nitrosamine DA
complexes have been previously reported, although some metal/
nitrosamine adducts are known.6 We nonetheless postulated
that nitrosamines, as NO n* donors, might bind to complemen-
tary strong π* acceptors such as DDQ (E°red 0.51 V vs SCE).
Confirmation of this postulate was afforded by the observance
of charge-transfer (CT) absorption bands for nitrosamine/DDQ
mixtures. Scheme 1 gives λCT values and selected Kf data
(determined by Benesi-Hildebrand analysis)7 for several nitros-
amine/DDQ complexes in CH2Cl2.8,9 Molar absorptivities for
these complexes are ∼2000 M-1 cm-1 near λm CT. The
temperature dependence of Kf for N-nitroso-1,1,3,3-tetramethyl-
(1) For recent reviews, see: (a) Lehn, J.-M. Supramolecular Chemis-
try: Concepts and PerspectiVes; VCH: Weinheim, 1995. (b) The Crystal
as a Supramolecular Entity. PerspectiVes in Supramolecular Chemistry;
Desiraju, G. R., Ed.; Wiley: New York, 1996.
(2) For reviews, see: (a) Desiraju, G. R. Crystal Engineering: The
Design of Organic Solids; Elsevier: Amsterdam, 1989. (b) Gavezzotti, A.
Acc. Chem. Res. 1994, 27, 309. (c) Reference 1b.
(3) (a) Blackstock, S. C.; Poehling, K.; Greer, M. L. J. Am. Chem. Soc.
1995, 117, 6617. (b) Greer, M. L.; Blackstock, S. C. J. Org. Chem. 1996,
61, 7895. (c) Greer, M. L.; McGee, B. J.; Rogers, R. D.; Blackstock, S. C.
Angew. Chem., Int. Ed. Engl. 1997, 36, 1864.
(4) For reviews of organic donor-acceptor chemistry, see: (a) Mulliken,
R. S.; Person, W. B. Molecular Complexes: A Lecture and Reprint Volume;
Wiley-Interscience: New York, 1969. (b) Hanna, M. W.; Lippert, J. L. In
Molecular Complexes; Foster, R., Ed.; Elek Science: London, 1973; Vol.
1, Chapter 1. (c) Bent, H. A. Chem. ReV. 1968, 68, 587.
(5) Sarker, H.; Greer, M. L.; Blackstock, S. C. J. Org. Chem. 1996, 61,
3177.
(6) (a) Yi, G.-B.; Khan, M. A.; Richter-Addo, G. B. J. Am. Chem. Soc.
1995, 117, 7850 and references therein. (b) For a bis(nitrosamine)/proton
complex, see: Keefer, L. K.; Hrabie, J. A.; Ohannesian, L.; Flippen-
Anderson, J. L.; George, C. J. Am. Chem. Soc. 1988, 110, 3701.
(7) Benesi, H. A.; Hildebrand, J. H. J. Am. Chem. Soc. 1949, 71, 2703.
Our analysis assumes 1:1 DA complexation. A Job plot of λCT for
[TEMINO] + [DDQ] ) 0.007 mM in CH2Cl2 gives a maximum at
[TEMINO] ) [DDQ], consistent with preferential 1:1 DA complexation
under these conditions.
(10) Epox for Me2NNO, i-Pr2NNO, TEMPNO, TEMINO, Nor2NNO, and
Ad2NNO are 2.13, 1.91, 1.82, 2.01, 1.87, and 1.45 V vs SCE, respectively,
at 200 mV s-1 scan rate in CH3CN (0.1 M n-Bu4NClO4) at 25 °C.
(11) X-ray diffraction data on a 0.10 × 0.18 × 0.38 mm red/yellow prism
of C20H16Cl2N4O3 (crystal 1) was collected at 173(2) K using a Siemons
SMART diffractometer (Mo KR monochromated radiation, λ ) 0.710 73
Å) equipped with a CCD area detector. Crystal 1 gave an orthorhombic
unit cell with a ) 9.3590(2), b ) 23.4163(3), and c ) 9.5319(3) Å; space
group Pna21, Z ) 4, cell volume ) 2088.95(8) Å3, and Dcalcd ) 1.371 g
cc-3. Data collection (ϑ 1.74-25.00°) gave 3522 unique observed reflections
(Rint 0.0614). The structure was solved by direct methods and refined on
F2 with non-hydrogen atoms allowed anisotropic thermal motion. Hydrogen
atoms were placed in geometrically calculated positions and allowed to
ride on their attached C atoms with Uiso(H) ) 1.2Ueq(C). Final refinement
cycles used 268 parameters and gave R1/wR2 (I > 2σI) 0.0588/0.0934, R1/
wR2 (all data) 0.1085/0.1142, and GOF ) 1.151.
(12) All DDQ ring carbons are inside of van der Waals distance of one
or the other NdO atoms. van der Waals radii are taken from Bondi, A. J.
Phys. Chem. 1964, 68, 441.
(13) Carbonyl self-complexation has been observed previously for other
systems, but its report is rare. For examples, see: (a) Chu, S. S. C.; Jeffrey,
G. A.; Sakurai, T. Acta Crystallogr. 1962 15, 661. (b) Bolton, W. Acta
Crystallogr. 1965, 18, 5.
(14) For a discussion of carbonyl π Lewis basicity, see: Corcoran, R.
C.; Ma, J. J. Am. Chem. Soc. 1992, 114, 4536.
(8) Nitrosamines were prepared as described in ref 5 except for
TEMINO9a which was made by NOCl nitrosation9b of tetramethylisoindoline9c
in ether/pyridine.
(9) (a) To¨njes, V. H.; Heidenbluth, K.; Scheffler, R. J. Prakt. Chem.
1964, 26, 218. (b) Back, T. G.; Barton, D. H. R. J. Chem. Soc., Perkin
Trans. 1 1977, 924. (c) Griffiths, P. G.; Moad, G.; Rizzardo, E.; Solomon,
D. H. Aust. J. Chem. 1983, 36, 397.
(15) Zanotti, G.; Bardi, R.; Del Pra, A. Acta Crystallogr. 1980, B36,
168. The presence of an intermolecular carbonyl-carbonyl close contact
was not mentioned by the authors but is apparent upon analysis of the crystal
packing.
(16) In addition, a similar close contact between the carbonyl oxygen
and the cyano-substituted ring carbon of DDQ (2.91 Å) is found.
S0002-7863(97)02254-3 CCC: $14.00 © 1997 American Chemical Society

11344 J. Am. Chem. Soc., Vol. 119, No. 46, 1997
Communications to the Editor
Figure 3. Orthogonal views of packing in TEMINO/DDQ composite
crystal 1.
as the sum of axial and lateral component dipoles. The axial
component (which is expected to be small) arises from
unidirectional nucleophile-electrophile connectivity along the
chain axis, while the lateral dipole component arises from an
all-syn intrachain DDQ stereochemistry. The basis for and
propensity of such syn stereochemistry is under further inves-
tigation. Interchain dipolar orientation determines the bulk
polarity of the crystal: crystal 2 is apolar (centrosymmetric)
and crystal 1 is polar (noncentrosymmetric). Figure 3 shows
the chain packing in crystal 1, in which axial chain dipoles
subtract and lateral chain dipoles add.
Figure 1. TEMINO/DDQ array of crystal 1 (top) and FMOs of
Me2NNO and DDQ (bottom).
In summary, the first DA-bonded nitrosamine/DDQ duplexes
and carbonyl-bonded (DDQ)n chains are reported. The topo-
logical specificity of these associative interactions is determined
within the TEMINO/DDQ composite crystal 1 and the neat
DDQ crystal 2. The former contains a novel 1D supramolecular
array, a donor-appended (DDQ)n chain, whose regiochemistry
appears to be influenced by the nitrosamine donor. The
stereochemical preference of syn alignment of DDQ molecules
within the DDQ chains of crystals 1 and 2 is noted and, in 1,
culminates in a net polarity of the lattice. Further work to
evaluate the theoretical basis of these interactions, their general
utility for crystal engineering, and their potential materials value
is underway.
Figure 2. DDQ packing in crystal 2.
in 1. We hypothesize that the 1,1′ (DDQ)n regiochemistry in 2
derives from cooperative carbonyl self-association, such that a
carbonyl undergoing nucleophilic “attack” becomes a better
nucleophile than a carbonyl not under attack; therefore, self-
promotion of 1,1′ (DDQ)n chain formation occurs. Accordingly,
we postulate that the 1,4′ (DDQ)n regiochemistry in 1 derives
from the influence of the TEMINO donor. For a donor-
appended DDQ, the two quinone carbonyl groups are presum-
ably electronically (and perhaps sterically) differentiated (so that
one is a better Lewis acid and the other a better Lewis base),
promoting 1,4′ (DDQ)n formation.
The supramolecular stereochemistry of the (DDQ)n chains
in 1 and 2 deserves mention. In 1 (and apparently also in 2,
although this structure was not solved by us), the DDQ chains
are composed of aligned DDQ components to render the strand
polar.17 For convenience, we may visualize the chain dipole
Warning! The strong toxicity of the materials used in this
work demands that they be handled, stored, and discarded with
due respect for the potential hazards involved.18
Acknowledgment. We thank the donors to the ACS Petroleum
Research Fund and the National Science Foundation for support of
this work. We are also very grateful to Robin Rogers and Lil Rogers
for assistance with the X-ray diffraction measurements reported.
Supporting Information Available: Spectroscopic data for the
solution nitrosamine/DDQ complexes and full crystal structure details
for 1 (10 pages). See any current masthead page for ordering and
Internet access instructions.
JA972254Z
(17) Disorder of the CN and Cl substituents of DDQ, which would render
the chain apolar, was looked for in difference density maps and was not
apparent.
(18) Pruessmann, R.; Stewart, B. W. In Chemical Carconogens, 2nd ed.;
Searle, C. E., Ed.; ACS Monograph 182; American Chemical Society:
Washington, DC, 1984; pp 643-828.