Different positions of the formally isolobal moieties H+ and (AuPPh3)+ in N-(5-methoxyquinolyl-8)-2,4,6-trinitroaniline and its auration product

Article abstract of DOI:10.1039/b102938j

It has been shown by an X-ray crystallographic analysis of N-(triphenylphosphinegold)-N-(5-methoxyquinolyl-8)-2,4,6-trinitroaniline 1 and quantum chemical calculations on N-(5-methoxyquinolyl-8)-2,4,6-trinitroaniline 2 that H⁺ and (AuPPh_3<

Full text of DOI:10.1039/b102938j

Different positions of the formally isolobal moieties H+ and (AuPPh3)+
in N-(5-methoxyquinolyl-8)-2,4,6-trinitroaniline and its auration
product
Lyudmila G. Kuz’mina,*a Alexander A. Bagatur’yants,b Andrei V. Churakova and Judith A. K.
Howardc
a Institute of General and Inorganic Chemistry, Russian Acad. Sci., Leninskii pr. 31, Moscow, 119991
Russia. E-mail: kuzmina@igic.ras.ru
b Center of Photochemistry, Russian Acad. Sci., Novator Str. 7a, Moscow, 117421 Russia.
E-mail: sasha@photonics.ru
c
Department of Chemistry, University of Durham, South Road, Durham, UK DH1 3LE.
E-mail: j.a.k.howard@durham.ac.uk
Received (in Cambridge, UK) 2nd April 2001, Accepted 20th June 2001
First published as an Advance Article on the web 11th July 2001
It has been shown by an X-ray crystallographic analysis of
N-(triphenylphosphinegold)-N-(5-methoxyquinolyl-8)-
2,4,6-trinitroaniline 1 and quantum chemical calculations on
N-(5-methoxyquinolyl-8)-2,4,6-trinitroaniline 2 that H+ and
(AuPPh3)+ sub-units in 1 and 2 occupy different positions at
the amine and quinoline nitrogen atoms, respectively.
Au…N(quinoline) secondary bond.6 The N(2)–Au(1)–P(1)
bond angle is equal to 168.4(2)° with the Au(1)–P(1) bond bent
away from N(1). In contrast to AuPPh3+ in 1, the proton in N-
substituted 2,4,6-trinitroanilines is always located at the amino
nitrogen atom. According to the CSD,2 the N(amino)–C(Ar)
bond length varies within 1.33–1.37 Å, the C(ipso)–C(ortho)
bond lengths range within 1.41–1.45 Å, and the other C–C
bonds in the aniline Ph ring lie within 1.37–1.39 Å. Thus, the
bonds C(ipso)–C(ortho) are longer than the others in the ring
and no bond length alternation is observed within the C(or-
tho)…C(para) fragment. The C(ortho)–C(ipso)–C(ortho) angle
varies within 112–115°.
This paper is part of our systematic investigations into the
structural chemistry of gold( ) compounds. It is well known that
I
the singly charged heavy-metal complex cation AuL+ (L =
neutral ligand) is isolobal with the cation HgR+ (R = acido
ligand). Both these metals commonly form 14-electron linear
complexes QAuL or QHgR (Q = organic ligand). In real
structures, the strict collinearity of metal bonds can be disturbed
because of weak interactions (secondary bonds) of the metal
with a heteroatom (X) involved in Q.1 Commonly, the HgR+
moiety behaves like a proton. Structures of chemically related
organic and organomercury compounds display high similarity
and secondary bonds M…X formed by Hg in QHgR are
analogous to hydrogen bonds H…X in the corresponding
organic compounds QH.2 In accordance with isolobal analogy,
it could be expected that the AuL+ moiety also behaves like a
proton; that is, in QAuL compounds, it forms a covalent bond
with the same atom as the proton in QH compounds.
The formation of the Au–N covalent bond with the quinoline
rather than amine nitrogen atom is the most interesting property
of molecule 1. This fact means that the formal zwitterionic bond
structure is characteristic of this molecule. As a result, a
To explore the limits of the analogy between the correspond-
ing isolobal particles AuL+, HgR+ and H+, we subjected
compound 2 to auration and investigated the structures of
compounds 1 and 2 (Scheme 1.)
The X-ray structure of complex 1 and selected geometric
parameters are shown in Fig. 1. The gold atom of the AuPPh3
moiety forms a chemical bond with the quinoline nitrogen N(2)
in 1. The Au(1) atom adopts a T-shaped coordination. Two
covalent bonds Au(1)–N(2) and Au(1)–P(1) are of normal
length [2.121(8) and 2.231(3) Å, respectively].3–6 The
Au(1)…N(1) distance [2.621(9) Å] corresponds to a secondary
bond.
A
similar distance [2.627(9) Å] was found in
8-mercaptoquinolinate) for the
(8-Squ)AuPPh3 (8-Squ
=
Fig. 1 Molecular structure of 1. Bond lengths (Å) and bond angles (°) are:
Au(1)–P(1) 2.231(3), Au(1)–N(2) 2.121(8), N(2)–Au(1)–P(1) 168.4(2),
Au(1)…N(1) 2.621(9), N(1)–Au(1)–N(2) 71.6(3), N(1)–Au(1)–P(1)
120.0(2), N(1)–C(1) 1.30(1), C(1)–C(2) 1.47(1), C(1)–C(6) 1.47(1), C(2)–
C(3) 1.36(1), C(6)–C(5) 1.35(1), C(3)–C(4) 1.38(1), C(4)–C(5) 1.39(1),
N(1)–C(7) 1.44(1), C(1)–N(1)–C(7) 120.5(8), N(2)–C(15) 1.36(1), N(2)–
C(14) 1.33(1), C(14)–N(2)–C(15) 121.4(8).
Scheme 1
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Chem. Commun., 2001, 1394–1395
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b102938j

significant redistribution of bond lengths in the trinitroaniline
moiety should be observed for molecule 1. Actually, in 1, the
N(1)–C(1) bond 1.30(1) Å is shorter, both the C(1)–C(2) and
C(1)–C(6) bonds 1.47(1) Å are longer, and the C(2)–C(1)–C(6)
angle is more strongly reduced [109.5(8)°] than the analogous
parameters in N-substituted 2,4,6-trinitroanilines. A pro-
nounced alternation of bond lengths corresponding to the para-
quinoid structure of the aniline sub-unit is observed; the C(2)–
C(3) and C(5)–C(6) bonds [1.36(1) and 1.35(1) Å] are
systematically shorter than the C(3)–C(4) and C(4)–C(5) bonds
[1.38(1) and 1.39(1) Å]. Apparently, because of the contribution
of the para-quinoid structure to the total molecular structure of
1, the colour of this compound is deeper (black) than those of N-
aryl-2,4,6-trinitroanilines (tones of red).†
particular ortho-nitro group is twisted from the C(1)…C(6)
plane by only 16.8°, whereas another ortho-nitro group is
twisted by 52.0°. In 2, these values are equal to 5.3 and
38.0°.
In 1, the C(1)–N(1)–C(7)/C(1)…C(6) dihedral angle is also
rather small (27.0°). The flattened conformation at the formally
double N(1)–C(1) bond is a result of a compromise between two
effects. One of these is conjugation between the formally double
N(1)–C(1) bond and the C(1)…C(6) benzene ring while the
other is steric interaction between two ring systems. There is no
weak interaction between Au(1) and the nearest ortho-nitro
group N(5)–O(5)–O(6). Because of steric interactions both
ortho-NO2 groups are strongly twisted from the C(1)…C(6)
plane by 43.4 and 38.1°.
On the other hand, the C(1)–N(1)–C(7)–C(8) torsion angle in
1 is 41.7° (cf. 49.8° in 3), indicating that there is no significant
conjugation between the amine nitrogen lone pair and the
quinoline moiety. The coordination of Au(1) with the aminoqui-
noline moiety causes only minor changes in the geometry of the
quinoline fragment. Only the endocyclic angle at N(2) increases
to 121.4(8)° vs. 117.0° in aminoquinolines and 117.7o in 2. Such
an increase in this angle is typical for N-protonated pyridines
(CSD).
The structure of 1 also contrasts with that of N-(5-methoxy-
quinolyl-8)-2,4,6-trinitroaniline 2. To provide an insight into
subtle geometric changes in the molecular skeleton caused by
substituting the proton for the AuPPh3 moiety, ab initio
quantum chemical calculations were performed for 2.
Geometry optimisation7 resulted in the structure shown in
Fig. 2. Molecule 2 exists in the same neutral form as all
substituted trinitroanilines.
The distribution of bond lengths in 2 agrees well with that
observed for N-(naphthyl)-2,4,6-trinitroaniline 3.8 However,
the general conformation of 2 differs significantly from that
found for 3. For instance, dihedral angles between the C(1)–
N(1)–C(7) fragment and C(1)…C(6) and C(7)…C(15) rings are
27.3 and 12.3° in 2, whereas these angles are of 17.4 and 49.8°,
respectively, in 3. The N–H group in 2 forms a bifurcated
hydrogen bond with the quinoline nitrogen (H…N 2.104 Å) and
one of the oxygen atoms of one ortho-nitro group (H…O 1.862
Å). Therefore, the geometry of 2 is somewhat flattened
compared to that of 3, where the N–H group forms only one
hydrogen bond with the oxygen of the ortho-nitro group. This
We wish to thank The Royal Society, the RFBR for financial
support (projects No. 99-03-33180 and 01-03-32474) and the
EPSRC for a Senior Research Fellowship (J. A. K. H.).
Notes and references
† Crystal data for 1: C34H25AuN5O7P, M = 843.53, triclinic, space group
¯
P1, a = 7.5814(2), b = 13.0849(4), c = 16.6256(4) Å, a = 74.433(1), b
= 77.980(1), g = 82.332(1)°, V = 1548.68(7) Å3, Z = 2, Dc = 1.809 g
cm23, m(Mo-Ka) = 4.861 mm21. A black needle-like crystal was covered
with perfluoropolyether oil and mounted on a Bruker SMART-CCD
diffractometer (w scan, 0.3° frame, 15 s per frame, 150 K). A total of 10117
reflections were collected in the q range 1.29–26.00° using Mo-Ka
radiation (l = 0.71073 Å). Of these, 6080 were considered unique (Rint
=
0.0689). A semi-empirical absorption correction was applied (min. and
max. transmissions are 0.74362 and 0.97352). The structure was solved by
direct methods and refined by full-matrix least squares based on F2 for all
data using SHELXL software. All non-hydrogen atoms were refined with
anisotropic displacement parameters. H atoms were placed geometrically at
the calculated positions and refined with the riding model. Final R1
=
0.0662 (5616 observed reflections) and R1 = 0.0989 (all data), number of
variables is 435, GOF = 1.127, Drmin,max = 21.455 and 1.757 e Å23
.
CCDC reference number 162720. See http://www.rsc.org/suppdata/cc/
b102938j/ for crystallographic data in CIF or other electronic format.
1 L. G. Kuz’mina, Russ. J. Coord. Chem., 1999, 25, 599.
2 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1.
3 A. V. Churakov, L. G. Kuz’mina and J. A. K. Howard, Acta Crystallogr.,
Sect. C, 1998, 54, 212.
4 A. V. Churakov, L. G. Kuz’mina, J. A. K. Howard and K. I. Grandberg,
Acta Crystallogr., Sect. C, 1998, 54, 54.
5 L. G. Kuz’mina, A. A. Bagatur’yants, J. A. K. Howard, K. I. Grandberg,
A. V. Karchava, E. S. Shubina, L. N. Saitkulova and E. V. Bakhmutova,
J. Organomet. Chem., 1998, 575, 39.
6 L. G. Kuz'mina, N. V. Dvortsova, O. Yu. Burtseva, M. A. Porai-Koshits,
E. I. Smyslova and K. I. Grandberg, Metalloorg. Khim., 1990, 3, 364.
7 The calculations were carried out using the MP2 method with the 3-21G*
basis sets. Full geometry optimisation was performed starting from two
initial geometries. In the first the quinoline fragment was considered as
coplanar to the amino group and the N(2)–O(1)–O(2) nitro group was
twisted by 60° from this plane. In the second this nitro group was
considered as coplanar to the amino group, whereas the quinoline
fragment was twisted by 60° from this plane. Both calculations converged
to the same flattened geometry.
Fig. 2 Structure of 2 on the basis of ab initio quantum chemical calculation
(MP2). Bond lengths (Å) and bond angles (°): N(1)–C(1) 1.374, C(1)–C(2)
1.426, C(1)–C(6) 1.436, C(2)–C(3) 1.390, C(6)–C(5) 1.388, C(3)–C(4),
1.388, C(4)–C(5) 1.388, N(1)–C(7) 1.405, C(1)–N(1)–C(7) 131.0, N(2)–
C(15) 1.386, N(2)–C(14) 1.347, C(14)–N(2)–C(15) 117.7.
8 G. V. Gridunova, V. N. Petrov, Yu. T. Struchkov, I. G. Il'ina and O. V.
Mikhalev, Kristallografiya., 1990, 35, 59.
Chem. Commun., 2001, 1394–1395
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