N1-Coordination in palladium(II) and platinum(II) complexes with 9-methylhypoxanthine: Crystal structures and theoretical calculations

Article abstract of DOI:10.1039/b915427b

The synthesis of the new palladium and platinum complexes with 9-methylhypoxanthine (9-mhypH) of the type [M(dmba)(L)(9-mhypH-N7)]ClO ₄ [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl; M = Pd or Pt; L = DMSO, PPh₃ or PTA (PTA = 1

Full text of DOI:10.1039/b915427b

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www.rsc.org/dalton | Dalton Transactions
N1-Coordination in palladium(II) and platinum(II) complexes with
9-methylhypoxanthine: crystal structures and theoretical calculations†
Jose´ Ruiz,*a Natalia Cutillas,a Mar´ıa Dolores Villa,a Gregorio Lo´pez,a Arturo Espinosab and Delia Bautistac
Received 29th July 2009, Accepted 9th September 2009
First published as an Advance Article on the web 26th September 2009
DOI: 10.1039/b915427b
The synthesis of the new palladium and platinum complexes with 9-methylhypoxanthine (9-mhypH) of
the type [M(dmba)(L)(9-mhypH-N7)]ClO4 [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl;
M = Pd or Pt; L = DMSO, PPh3 or PTA (PTA = 1,3,5-Triaza-7-phosphaadamantane)] is reported.
Pd(II) and Pt(II) complexes with the anion of 9-mhypH of the type [M(dmba)(L)(9-mhyp-N1)] [L =
PPh3 or PTA] have also been prepared. The crystal structures of [Pt(dmba)(PPh3)(9-mhypH-N7)]ClO4
and [Pt(dmba)(PPh3)(9-mhyp-N1)] have been established by X-ray diffraction. The last complex is the
first structurally authenticated example of N1 coordination of 9-methylhypoxanthine to platinum.
DFT-based calculations at the BP86/def2TZVP level predict a most favourable interaction (both
kinetically and thermodynamically) of the metal(II) centre with N7 in the neutral ligand 9-mhypH, but
with N1 in the deprotonated ligand 9-mhyp- in agreement with the experimentally observed preference
in neutral conditions or upon basic treatment, respectively.
Introduction
The discovery of the anticarcinogenic activity of cis-[PtCl2(NH3)2]
(cisplatin) by B. Rosenberg in 1969 has led to research interests
being focused on the interactions of Pt compounds with nucleic
acids and their constituents.1–3 From a chemical point of view,
considerable effort has been paid to the various binding modes.4
Selective coordination to a nucleobase is influenced by structural
and electronic factors arising from the nucleobase and the complex
itself.5–9 It is well known that hypoxanthine (Chart 1) is a naturally
occurring purine derivative that occasionally can be found as a
constituent of nucleic acids where it is present in the anticodon of
tRNA in the form of its nucleotide inosine.10
Chart 1
The synthesis of the antitumor drug cisplatin derivative contain-
ing the purine model nucleobase cis-[Pt(NH3)2(9-madeH-N6)(9-
mhypH-N7)]2+ (9-mhypH = 9-methylhypoxanthine, 9-madeH =
9-methyladenine)11 and the cationic tetrakis(nucleobase)12 com-
plex [Pt(9-mhypH-N7)4]2+ has been reported. The compounds
trans-[(NH3)2Pt(9-mhypH-N7)2]2+ and trans-[(CH3NH2)2Pt(1-
MeC-N3)(9-mhypH-N7)]2+ (1-MeC = 1-methylcytosine) have also
been previously prepared.13
In this article we describe the synthesis of mononuclear
palladium and platinum complexes of the type [M(dmba)(L)-
(9-mhypH-N7)]ClO4 [dmba = N,C-chelating 2-(dimethylamino-
methyl)phenyl; M = Pd or Pt; L = DMSO, PPh3 or PTA (PTA =
1,3,5-Triaza-7-phosphaadamantane)] and [M(dmba)(L)(9-mhyp-
N1)] [M = Pd or Pt; L = PPh3 or PTA]. [Pt(dmba)(PPh3)(9-
mhyp-N1)] is the first structurally authenticated example of N1
coordination of 9-methylhypoxanthine according to a search of
the Cambridge Structure Database (CSD).14 The experimentally
observed preference for the coordination to the metal(II) centre
using the N7 atom as donor in neutral conditions and N1 upon
basic treatment has been studied by means of computational
calculations.
aDepartamento de Qu´ımica Inorga´nica, Facultad de Qu´ımica, Universidad de
Murcia, 30071, Murcia, Spain. E-mail: jruiz@um.es; Fax: +34 868 884148;
Tel: +34 868 887455
bDepartamento de Qu´ımica Orga´nica, Facultad de Qu´ımica, Universidad
de Murcia, 30071, Murcia, Spain. E-mail: artuesp@um.es; Fax: +34 868
884149; Tel: +34 968367489
cUniversidad de Murcia, SAI, 30071, Murcia, Spain. E-mail: dbc@um.es;
Fax: +34 968 367302; Tel: +34 868 88 4165
Results and discussion
Complexes [M(dmba)(L)(9-mhypH)]ClO4
† Electronic supplementary information (ESI) available: Selected geomet-
rical parameters for experimental and calculated structures of 2 and
6. Figures with the calculated structures of 2calc and 6calc. Cartesian
coordinates and energies for all calculated species. HSAB-derived global
and group parameters for the reaction of 9-mhypH derivatives with the Pt
atom in [Pt(PPh3)(dmab)]+. CCDC reference numbers 742533 & 742534.
For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/b915427b
The dmba complexes 1–4 have been prepared from the correspond-
ing chlorometal complex [M(dmba)(L)Cl] (M = Pd or Pt).15,16 Af-
ter precipitationofAgClbyaddition of AgClO4 ina 1:1 molar ratio
in acetone, the solvent complexes [M(dmba)(L)(Me2CO)]ClO4
(M = Pd or Pt), generated in situ, react with 1 equiv of 9-mhypH
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to give the cationic complexes [M(dmba)(L)(9-mhypH)]ClO4
(1–4) (Scheme 1). Complexes 1–4 are white, air stable solids that
decompose on heating above 200 ◦C in a dynamic N2 atmosphere.
NMR, electrospray ionization (ESI) mass spectrometry, and ele-
mental analysis were used to characterize 1–4. ESI mass spectra of
1–4 show peaks with a recognisable isotope pattern corresponding
to [Pt(dmba)(L)(9-mhypH)]+ (L = DMSO, PPh3 or PTA). Their
acetone solutions show conductance values corresponding to
1:1 electrolytes (KM in the range 135–145 S cm2 mol-1),17 which
indicates the presence of the neutral ligand HmtpO in these
complexes. An IR band is observed at ca. 1095 which is assigned
to the n3 mode of free perchlorate (Td symmetry). The observation
of an additional band at ca. 623 cm-1 for the n4 mode confirms
the presence of free perchlorate.18 The IR spectra also show a very
strong band at ca. 1705 cm-1 assigned to the n(CO) of the neutral
9-mhypH (1680 cm-1 for the free ligand). COSY and NOESY
experiments were used for the assignment. The 1H NMR spectra
of complexes 1–4 are consistent with the N7 metal coordination
of the 9-methylhypoxanthine. Thus H8 exhibits a noe effect with
NMe2 protons of dmba and H2 shows a noe effect with the NH
of 9-mhypH. In complexes 1, 2 and 4 the phosphine-trans-to-
NMe2 ligand arrangement in the starting products15,16 is preserved,
after chlorine abstraction and 9-mhypH coordination, as can be
Fig. 1 ORTEP representation (50% probability) of 2. Selected bond
˚
lengths (A) and angles (deg): Pt(1)–C(11) = 2.016(2), Pt(1)–N(7) =
2.1253(18), Pt(1)–N(10) = 2.1390(17), Pt(1)–P(1) = 2.2333(5), C(11)–
Pt(1)–N(10)
=
81.46(8), C(1)–Pt(1)–N(7)
=
172.66(7), N(7)–
Pt(1)–N(10) = 92.67(7), C(11)–Pt(1)–P(1) = 94.34(6), P(1)–Pt(1)–N(7) =
91.64(5), N(10)–Pt(1)–P(1) = 175.46(5).
1
inferred by H NMR from the small, but significant, coupling
bridging three complex cations through N–H ◊ ◊ ◊ O and C–H ◊ ◊ ◊ O
bonds in which the NH, CH3, CH2 and CH groups are involved.
Furthermore, there is an intramolecular interaction by phenyl-9-
constant 4JP-H (2.5 Hz) of the CH2N or the NMe2 protons of dmba
with the phosphorus atom.19 Platinum satellites are observed as
shoulders in several of the resonances of complexes 2–4 (I = 1/2,
natural abundance 33.8). It is also noteworthy that the proton
resonance of H2 of the coordinated 9-mehypH of complexes 3
and 4 is duplicated, which could be as a consequence of the
slightly different chemical environment of the nucleus caused by
two possible orientations in DMF-d7 solution.
22
˚
mhypH p-stacking (centroid–centroid distance: 3.487 A). There
is also an intermolecular stacking interaction between 9-mhypH
pairs yielding a centrosymmetric dimer arrangement (Fig. 2), and
an intermolecular stacking interaction between phenyl pairs is
˚
also present (centroid–centroid distance: 3.780 A). Intermolecular
aromatic CH/p interactions9,23–25 are also found.
Scheme 1
Crystal structure of 2. The structure of 2 consists of mononu-
clear [Pt(dmba)(PPh3)(9-mhypH-N7)]+ cations and perchlorate
anions. The cation of 2 is depicted in Fig. 1. The angles around
platinum deviate from 90◦ due to the bite of the cyclometallated
ligand, the C(1)–Pt(1)–N(1) angle of 81.46(8)◦ being within the
normal range for such complexes.9,19 The PPh3 ligand is trans
to the nitrogen donor, displaying no tendency to occupy the
position trans to the s-bound orthoplatinated aryl group.20 The
cyclometallated ring is puckered with the nitrogen atom signifi-
cantly out of the plane defined by the platinum and carbon atoms,
a feature which is quite commonly observed in cyclometallated
dmba complexes.7,9,21 In the crystal, the perchlorate anion is
Fig. 2 Relevant p-stacking interactions in complex 2.
Complexes [M(dmba)(L)(9-mhyp-N1)]
The reaction in dichloromethane at room temperature of the
26
hydroxopalladium complex [Pd(dmba)(m-OH)]2 with PPh3 and
9-mhypH in the molar ratio 1:2:2 leads to the formation of
the mononuclear palladium complex [Pd(dmba)(PPh3)(9-mhyp-
N1)] (5) (Scheme 2). The platinum analogous complexes have
been prepared from the corresponding chloro platinum complex
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Scheme 2
Fig.
3
ORTEP representation (50% probability) of 6. Selected
˚
bond lengths (A) and angles (deg): Pt(1)–C(11)
Pt(1)–N(1)
2.2148(9), C(11)–Pt(1)–N(10)
171.76(13), N(10)–Pt(1)–N(1) = 90.25(11), C(11)–Pt(1)–P(1) = 94.94(11),
P(1)–Pt(1)–N(1) = 93.18(8), N(10)–Pt(1)–P(1) = 174.42(8).
=
2.017(3),
=
2.108(3), Pt(1)–N(10)
=
2.138(3), Pt(1)–P(1)
=
[Pt(dmba)(L)Cl] (L = PPh3 or PTA)16 (Scheme 2). After pre-
cipitation of AgCl by addition of AgClO4 in a 1:1 molar ratio
in acetone, the solvent complexes [Pt(dmba)(L)(Me2CO)]ClO4
generated in situ react with 1 equiv of both 9-mhypH and
[NBu4]OH to give the neutral complexes [Pt(dmba)(L)(9-mhyp-
N1)] (L = PPh3 or PTA; 6 and 7).
=
81.76(13), C(11)–Pt(1)–N(1)
=
Complexes 5–7 are white and air-stable solids. Their acetone
solutions show no conductance values which indicates the presence
of the anionic ligand 9-mhyp in these complexes. The structure
was assigned also on the basis of microanalytical, IR and 1H and
31P NMR data. The n(CO) band of the IR spectra of complexes
5–7 is observed at 1630 cm-1, which is a significant difference
when comparing with the values (over 1705 cm-1) observed for
1
complexes 1–4, containing the neutral 9-mhypH ligand. The H
NMR spectra of complexes 5–7 show that both the N-methyl
and the CH2 group of the dmba are diastereotopic, two separate
signals being observed for the former and an AB quartet for the
later (some broadening being observed for complex 5). Therefore
there is no plane of symmetry in the metal coordination plane. The
assignment of the H8 and H2 signals in complexes 5–7 was made
by NOESY. The inversion in the chemical shifts of these signals
compared with the corresponding values observed in complexes
1–4 is in agreement with the literature values of cis-[Pt(NH3)2(9-
mhyp-N1)(9-made-N6)]n+, where the N1-coordination of 9-mhyp
has been suggested.3 The X-ray crystal structure of complex 6
(vide infra) supports this assigment.
Crystal Structure of 6. The structure of 6 is shown in Fig. 3.
This is the first structurally authenticated example of N1 coor-
dination of 9-methylhypoxanthine to platinum according to a
search of the Cambridge Structure Database (CSD).14 Thus, in
the previously reported27 related complex trans-[PtCl(NH3)2(9-
mhyp)]·2H2O the metal coordinates to N7 of the 9-mhyp. The
packing of complex 6 is stabilized predominantly by hydrogen
bonding giving centrosymmetric or head-to-tail dimer arrange-
ments (see the ESI†), the C(6)O group of the nucleobase being
also involved (Fig. 4). Intermolecular contacts23–25 C–H ◊ ◊ ◊ p9-mhyp
(Fig. 5) and C–H ◊ ◊ ◊ pPh are also observed. Stacking of the
hypoxanthine bases does not seem to play an important role in
stabilizing the crystal packing of 6. It has been suggested that
deprotonation of the N1H site leads to an increase in the electron
Fig. 4 Intermolecular C–H ◊ ◊ ◊ O interactions in 6.
density in the heterocyclic ring and probably causes repulsion
between the base moieties.28
Theoretical calculations
Binding of the aforementioned 9-methylhypoxanthine (9-mhypH)
to the metallic Pt centre in either neutral or basic media has also
been studied by quantum chemical calculations. The experimen-
tally observed preference for the coordination to the metal(II)
centre using the N7 atom as donor in neutral conditions and N1
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pairs are HOMO-4 (HOMO has p symmetry, whereas HOMO-1,
HOMO-2 and HOMO-3 are perchlorate-centered), HOMO-5
and HOMO-8 (Fig. 7a), all of them displaying higher quadratic
coefficients31 on N7 than on N3 (0.021/0.008, 0.207/0.178 and
0.072/0.044, respectively). In the case of the anionic ligand
9-mhyp- (Fig. 7b) HOMO-1 and HOMO-2 are mainly located on
N1 (calculated coefficients ratio N1/N3/N7: 0.150/0.041/0.038
and 0.264/0.117/0.017, respectively), whereas in HOMO-4 the
contribution of N7 (0.079/0.098/0.241) predominates and N3
only dominates in HOMO-6 (0.041/0.202/0.162). These relative
sequences of MO are almost invariant as they are essentially
kept on using other different types of hybrid exchange–correlation
functionals such as LSDA.
Fig. 5 Intermolecular C–H ◊ ◊ ◊ p interactions in 6.
upon basic treatment requires some detailed analysis. Assuming
the limitations of the working level of theory, e.g. structures being
optimized in the gas phase, in neutral medium the perchlorate
counteranion acts as H-bond acceptor towards the amide-like NH
˚
group at position 1 of the ligand (dH ◊ ◊ ◊ O = 1.821 A), supplemented
˚
by a second weaker interaction (dH ◊ ◊ ◊ O = 2.244 A) (Fig. 6). This
feature prevents the action of N1 as donor and increases slightly
the electron density at N3 with respect to that in the parent
neutral ligand 9-mhypH.28 Pure electrostatic arguments based,
for instance, on atomic natural charges29 would lead to a wrong
prediction, as N3 (-0.495 au) is expected to behave as more basic
than N7 (-0.392 au). Mulliken charges vary similarly (-0.309 and
-0.211 au for N3 and N7, respectively). Finally, steric crowding
at N3, due to the proximity of the methyl substituent on N9,
could be invoked in order to explain qualitatively the observed
regioselectivity. In basic conditions the formal negative charge
corresponding to the deprotonated ligand 9-mhypH- is spread
mainly on N3 (qN = -0.572 au) ≥ N1 (qN = -0.545 au) ꢀ N7 (qN =
-0.412 au). Owing to steric reasons N1 could be selected as the
best donor candidate, in agreement with the experimental results.
-
Fig. 7 Calculated (method C) MO diagram for (a) 9-mhypH·ClO4
(perchlorate anions omitted for clarity) and (b) 9-mhyp-. Energies (au)
relative to the HOMO. Perchlorate-centered MO are displayed in gray.
Nevertheless, during the last two decades many important con-
cepts and parameters related to chemical reactivity have been ratio-
nalized within the framework of DFT.32 The DFT formulation33
of the HSAB principle states that the most favourable situation
occurs when the reactants have equal softness, provided that the
charge reshuffling step can be neglected. The best suited local
reactivity index for studying regioselectivity34 is local softness s(r),
easily obtained from the Fukui function f (r), defined by Parr and
Yang,35 and the global softness S = (∂N/∂m)v(r), which describes
the ability of the molecule to take or lose electrons in response to a
change in the chemical potential, m. Therefore s(r) describes both
the charge transfer between the reactants and how the charge
is redistributed within the reactants themselves. A local HSAB
principle can then be devised as follows: a regioisomer is favored
when the new bond is formed between atoms of equal softness.
In other words, the preferred regioisomer in the reaction between
atom k in molecule A and molecule B will be formed on reaction at
atom l that minimizes the quadratic difference in local condensed-
to-atom softness function36 D(s2)kl = (sAk - sBl)2. For situations in
which condensed local softness was found inadequate to provide
the correct intermolecular reactivity trends, the group softness37
descriptor, s(k)g, has been highlighted, which is obtained after
Fig. 6 Calculated (method B) structures for ligands 9-mhypH·ClO4- (left)
and 9-mhyp- (right).
The preference among several donor atoms to interact with
an acidic centre can also be qualitatively analysed in the context
of Pearson’s hard–soft acid–base (HSAB) principle.30 Besides the
steric contribution that systematically unfavours binding through
N3, the relatively soft Pt(II) centre will preferably interact with the
softer donor centre, which is that with highest energy content for its
basic electron lone pair. Using method C as the computation level,
-
in 9-mhypH·ClO4 the uppermost MO containing nitrogen lone
9640 | Dalton Trans., 2009, 9637–9644
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Table 1 Relevant HSAB-related calculated (method B) parametersa
the complexation seems to be thermodynamically controlled
as only the relative complex energy sequence agrees with the
experimentally observed N1-complexation. This could tentatively
point to a possible occurrence of such N1-coordination types in
other not sterically hindered and relatively soft metal centres.
In spite of the fact that intermolecular interactions were not
taken into account, at the highest level of theory (method B)
both calculated structures [Pt(dmba)(PPh3)](9-mhypH·ClO4) and
[Pt(dmba)(PPh3)](9-mhyp) very nicely agree with those experimen-
tally obtained by single-crystal X-ray diffraction analysis (see the
ESI†).
for the reaction of N-donor atoms in L’H, L¢H·ClO4 and L¢- with
-
[Pt(dmba)(Ph3P)]+ and relative energies (method A) for the resulting
products (L¢H = 9-mhypH)
b
c
c
D(s2)kl
DXkl
Erel
L¢H
N3
N7
N3
N7
N1
N3
N7
0.58
0.35
0.95
0.71
0.44
0.55
0.40
3.8
2.9
11.4
6.7
20.0
29.5
11.5
55.9
0.0
10.4
0.0
0.0
67.6
29.7
-
L¢H·ClO4
L¢-
a Derived from Mulliken charges. b Group property. c kJ mol-1.
Experimental
Instrumental measurements
summing the condensed local softness over all of the n neighboring
atoms attached to the reactive site k. Finally, in the very first step
of the bond-forming interaction between atoms k and l, charge is
transferred within them, equalizes the electron chemical potential
and induces a variation of the grand potential DX of the system.
The contribution due to the interaction of atoms k and l is DXkl =
The CHN analyses were performed with a Carlo Erba model
EA 1108 microanalyzer. Decomposition temperatures were de-
termined with a SDT 2960 simu◦ltaneous DSC-TGA from TA
instruments at a heating rate of 5 C min-1 and the solid samples
under nitrogen flow (100 mL min-1). The 1H and 31P NMR spectra
were recorded on Bruker AC 300E, Bruker AC 400E or Bruker AV
600 spectrometers, using SiMe4 and H3PO4 as standards. Infrared
spectra were recorded on a Perkin-Elmer 1430 spectrophotometer
using Nujol mulls between polyethylene sheets. All ESI spectra
were recorded in positive mode and performed on a LC-MS
Agilent VL system.
–1 (mA - mB)2sAksBl/(sAk+ sBl). Table 1 collects the values for both
2
parameters D(s2)kl and DXkl computed for the nucleophilic attack
-
of all possible donor atoms in each case, 9-mhypH·ClO4 or
9-mhyp- (the case of 9-mhypH is also included for comparison),
to the Pt(II) centre in an hypothetical tricoordinated electrophilic
[Pt(dmba)(PPh3)]+ species38 (Fig. 8).
Materials
The starting complexes [M(dmba)Cl(L))] (M = Pd or Pt; L = PPh3,
PTA or DMSO),15,16 and [Pd(dmba)(m-OH)]2,26 were prepared by
procedures described elsewhere. Solvents were dried by the usual
methods.
Warning!. Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Only small amounts of material
should be prepared, and these should be handled with great
caution.
Preparation of complexes
[M(dmba)(PPh3)(9-mhypH)]ClO4 [M = Pd (1), Pt (2)]. To a
solution of [M(dmba)(Cl)(PPh3)] (0.185 mmol) in CH2Cl2 (20 ml)
was added AgClO4 (38.4 mg, 0.185 mmol). AgCl immediately
formed. The resulting suspension was stirred for 1 h and then
Fig. 8 Calculated (method B) structure (see text) for the electrophilic
fragment [Pt(PPh3)(dmba)]+.
R
filtered through a short pad of Celiteꢀ. To the filtrate was then
added 9-mhypH (27.8 mg, 0.185 mmol). The solution was stirred
for 5 h (complex 1) or 20 h (complex 2), and then the solvent
was partially evaporated under vacuum and hexane added to
precipitate a white solid, which was collected by filtration and
air-dried. 1: Yield: 94 mg (68%). Calcd. for C33H33ClN5O5PPd: C
52.7, H 4.4, N 9.3. Found: C 52.3, H, 4.5, N 9.0. Mp: 201 ◦C
(dec). IR (Nujol, cm-1): 3180 n(NH); 1704 n(CO); ClO4, 1094,
-
For 9-mhypH·ClO4 the lowest interaction values—most
favourable interactions—are observed for the imidazole-like N7
atom (the same holds for 9-mhypH) that, in addition, gives rise
to the most stable product (Table 1). The large thermochemical
instability arising from complexation through N3 in 9-mhypH,
-
notably decreases in 9-mhypH·ClO4 due to intramolecular hy-
1
drogen bond formation. In the case of 9-mhyp- a new donor atom
N1 is now available. Here also the most unfavourable interaction
(kinetic) parameters and most unstable (thermodynamic) complex
formation corresponds to binding through N3. Nevertheless,
discrimination between N1 and N7 is not properly predicted
using HSAB-derived interaction parameters. On the contrary,
622. H NMR (CDCl3): d 10.26 (s, 1H, NH of 9-mhypH), 8.08
(s, 1H, H8 of 9-mhypH), 7.95 (s, 1H, H2 of 9-mhypH), 7.61 (m,
6H, PPh3), 7.28 (m, 9H, PPh3), 6.97 (d, 1H, C6H4, JHH = 6.9
Hz), 6.82 (m, 1H, C6H4), 6.34 (m, 2H, C6H4), 4.22 (brm, 1H,
NCH2 of dmba), 4.00 (brm, 1H, NCH2 of dmba), 3.60 (brs, 3H,
Me of 9-mhypH), 2.64 (brs, 3H, NMe2 of dmba), 2.52 (brs, 3H,
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NMe2 of dmba). 31P NMR (CDCl3): d(H3PO4) 42.6 (s). ESI+ mass
spectra (CH3CN): m/z +651.8 ([Pd(dmba)(PPh3)(9-mhypH]+ -1,
12%); +501.3 ([Pd(dmba)(PPh3)]+ -2, 100%). 2: Yield: 132 mg
(85%). Calcd. for C33H33ClN5O5PPt: C 47.1, H 4.0, N 8.3. Found:
crystals of complex 4, which were collected by filtration and air-
dried. Yield: 99 mg (70%). Calcd. for C21H30ClN8O5PPt: C 34.3, H
4.1, N 15.2. Found: C 34.8, H, 4.1, N 16.4. Mp: 262 ◦C (dec). IR
(Nujol, cm-1): 3147 n(NH); 1700 n(CO); ClO4, 1097, 623. 1H NMR
(DMF-d7): d 12.91 (s, 2H, NH of 9-mhypH), 8.94 (s, 2H, H8 of 9-
mhypH), 8.46 (s, H, H2 of 9-mhypH), 8.45 (s, H, H2 of 9-mhypH),
7.60 (m, 2H, C6H4, Pt satellites are observed as shoulders), 7.15
(m, 2H, C6H4), 7.04 (m, 4H, C6H4), 4.54 (d, 6H, NCH2N of PTA,
JHH = 12.8 Hz), 4.46 (d, 6H, NCH2N of PTA, JHH = 12.8 Hz), 4.20
(d, 6H, NCH2P of PTA, JHH = 15.9 Hz), 4.12 (d, 6H, NCH2P of
PTA, JHH = 15.9 Hz), 4.02 (d, 4H, NCH2 of dmba, JHP = 2.6 Hz),
◦
C 47.2, H, 4.1, N 8.5. Mp: 292 C (dec). IR (Nujol, cm-1): 3188
n(NH); 1708 n(CO); ClO4, 1100, 624. 1H NMR (CDCl3): d 10.48
(s, 1H, NH of 9-mhypH), 8.06 (s, 1H, H8 of 9-mhypH), 7.95
(s, 1H, H2 of 9-mhypH), 7.64 (m, 6H, PPh3, Pt satellites are
observed as shoulders), 7.20 (m, 9H, PPh3), 7.01 (d, 1H, C6H4,
JHH = 6.9 Hz), 6.83 (m, 1H, aromatic of dmba), 6.40 (dd, 1H,
JHH = 7.3 Hz, JHP = 2.4 Hz, aromatic of dmba, Pt satellites are
observed as shoulders), 6.35 (m, 2H, aromatic of dmba), 4.19 (dd,
1H, NCH2 of dmba, JHH = 13.0 Hz, JHP = 1.5 Hz, Pt satellites
4.00 (s, 6H, Me of 9-mhypH), 2.50 (d, 6H, NMe2 of dmba, JHP
=
2.6 Hz, Pt satellites are observed as shoulders), 2.45 (d, 6H, NMe2
of dmba, JHP = 2.6 Hz, Pt satellites are observed as shoulders).
31P NMR (DMF-d7): d(H3PO4) -64.87 (s, JPPt = 3669 Hz).
ESI+ mass spectra (CH3CN): m/z +635.8 ([Pt(dmba)(PTA)(9-
mhypH)]+, 100%); +485.7 ([Pt(dmba)(PTA)]+, 45%).
are observed as shoulders), 4.05 (dd, 1H, NCH2 of dmba, JHH
=
13.0 Hz, JHP = 2.8 Hz, Pt satellites are observed as shoulders),
3.63 (s, 3H, Me of 9-mhypH), 2.75 (d, 3H, NMe2 of dmba,
JHP = 2.4 Hz, Pt satellites are observed as shoulders), 2.66 (d,
3H, NMe2 of dmba, JHP = 2.7 Hz, Pt satellites are observed as
shoulders). 31P NMR (CDCl3): d(H3PO4) 20.3 (s, JPPt = 4171 Hz).
ESI+ mass spectra (CH3CN): m/z +740.9 ([Pt(dmba)(PPh3)(9-
mhypH)]+, 100%), +591.1 ([Pt(dmba)(PPh3)]+, 61%).
Preparation of complex [Pd(dmba)(PPh3)(9-mhyp)] (5). To a
solution of [Pd(dmba)(m-OH)]2 (100 mg, 0.195 mmol) in CH2Cl2
(20 ml) was added PPh3 (102.4 mg, 0.390 mmol) and 9-mhypH
(58.61 mg, 0.390 mmol). The solution was stirred for 6 h at room
temperature, and then the solvent was concentrated to dryness
under reduced pressure. Addition of ether yielded a white solid,
which was collected by filtration and air-dried. Yield: 201 mg
(79%). Calcd. for C33H32N5OPPd: C 60.8, H 5.0, N 10.7. Found:
C 60.7, H, 5.0, N 10.5. Mp: 241 ◦C (dec). IR (Nujol, cm-1): 1632
n(CO). 1H NMR (CDCl3) at 0 ◦C: d 7.68 (m, 6H, PPh3), 7.63 (s,
1H, H2 of 9-mhypH), 7.44 (s, 1H, H8 of 9-mhypH), 7.24 (m, 9H,
PPh3), 7.03 (d, 1H, C6H4, JHH = 7.2 Hz), 6.86 (m, 1H, C6H4),
6.40 (m, 2H, C6H4), 4.23 (d, 1H, NCH2 of dmba, JHH = 12.9 Hz),
3.99 (dd, 1H, NCH2 of dmba, JHH = 12.9 Hz, JHP = 2.4 Hz,),
3.58 (s, 3H, Me of 9-mhypH), 2.80 (brs, 3H, NMe2 of dmba),
2.56 (brs, 3H, NMe2 of dmba). 31P NMR (CDCl3): d(H3PO4) 43.4
(s). ESI+ mass spectra (CH3CN): m/z +652.1 ([Pd(dmba)(PTA)(9-
mhypH)]+, 5%); +502.4 ([Pd(dmba)(PTA)]+, 47%).
Preparation of complex
[Pt(dmba)(DMSO)(9-mhypH)]ClO4 (3). To a solution of
[Pt(dmba)(Cl)(DMSO)] (100 mg, 0.226 mmol) in acetone (20 ml)
was added AgClO4 (46.9 mg, 0.226 mmol). AgCl immediately
formed. The resulting suspension was stirred for 1 h and then
R
filtered through a short pad of Celiteꢀ. To the filtrate was then
added 9-mhypH (33.9 mg, 0.226 mmol). The solution was stirred
for 20 h, and then the solvent was concentrated to dryness under
reduced pressure. Addition of ether yielded a white solid, which
was collected by filtration and air-dried. Yield: 117 mg (79%).
Calcd. for C17H24ClN5O6SPt: C 31.1, H 3.7, N 10.7, S, 4.9. Found:
C 31.2, H, 3.5, N 10.4, S, 5.0. Mp: 257 ◦C (dec). IR (Nujol, cm-1):
3180 n(NH); 1704 n(CO); ClO4, 1096, 624.1H NMR (DMF-d7):
d 13.03 (brs, 2H, NH of 9-mhypH), 9.17 (s, 2H, H8 of 9-mhypH),
8.48 (1H, H2 of 9-mhypH), 8.47 (1H, H2 of 9-mhypH), 7.86 (m,
2H, C6H4), 7.17 (d, 2H, aromatic of dmba, JHH = 7.2 Hz), 7.09 (m,
2H, aromatic of dmba, Pt satellites are observed as shoulders), 7.02
Preparation of complexes
[Pt(dmba)(L)(9-mhyp)] [L = PPh3 (6), PTA (7)]. To a solution
of [Pt(dmba)(Cl)(L)] (0.159 mmol) in acetone (20 ml) was added
AgClO4 (33.0 mg, 0.159 mmol). AgCl immediately formed. The
resulting suspension was stirred for 1 h and then filtered through
(m, 2H, aromatic of dmba), 4.22 (d, 2H, NCH2 of dmba, JHH
=
14.0 Hz, Pt satellites are observed as shoulders), 4.05 (d, 2H, NCH2
of dmba, JHH = 14.0 Hz), 4.01 (s, 6H, Me of 9-mhypH), 3.35 (s,
6H, DMSO, Pt satellites are observed as shoulders), 3.11 (s, 6H,
DMSO, JHH = 53.8 Hz), 2.63 (s, 6H, NMe2 of dmba, Pt satellites
are observed as shoulders), 2.48 (s, 6H, NMe2 of dmba). ESI+ mass
spectra (CH3CN): m/z +556.9 ([Pt(dmba)(DMSO)(9-mhypH)]+,
12%); +406.5.1 ([Pt(dmba)(DMSO)]+, 100%).
R
a short pad of Celiteꢀ. To the filtrate was then added a
solution containing 20% [NBu4]OH(aq) (208 mL, 0.159 mmol) and
9-mhypH (23.9 mg, 0.159 mmol). After stirring at room tempera-
ture for 10 h, the solvent was partially eliminated under reduced
pressure to yield a white precipitate. The solid was collected
by filtration and air-dried. 6: Yield: 93 mg (75%). Calcd. for
C33H32N5OPP◦t: C 53.5, H 4.4, N 9.5. Found: C 53.6, H, 4.4, N
1
9.2. Mp: 320 C (dec). IR (Nujol, cm-1): 1634 n(CO). H NMR
Preparation of complex
(DMF-d7) at room temperature: d 7.71 (m, 6H, PPh3), 7.70 (s,
1H, H2 of 9-mhyp), 7.42 (s, 1H, H8 of 9-mhyp), 7.21 (m, 9H,
PPh3), 7.04 (d, 1H, C6H4, JHH = 7.4 Hz), 6.85 (m, 1H, aromatic
of dmba), 6.51 (dd, 1H, JHH = 7.4 Hz, JHP = 2.5 Hz, aromatic
of dmba), 6.39 (m, 1H, aromatic of dmba), 4.23 (d, 1H, NCH2
[Pt(dmba)(PTA)(9-mhypH)]ClO4 (4). To
a
solution of
[Pt(dmba)(Cl)(PTA)] (100 mg, 0.192 mmol) in acetone (20 ml)
was added AgClO4 (39.7 mg, 0.192 mmol). AgCl immediately
formed. The resulting suspension was stirred for 1 h and then
R
filtered through a short pad of Celiteꢀ. To the filtrate was then
of dmba, JHH = 13.4 Hz), 3.96 (dd, 1H, NCH2 of dmba, JHH
=
added 9-mhypH (28.76 mg, 0.191 mmol). After stirring at room
temperature for 20 h a small amount of white solid was removed by
filtration. The filtrate was concentrated under vacuum affording
13.4 Hz, JHP = 3.6 Hz, Pt satellites are observed as shoulders),
3.56 (s, 3H, Me of 9-mhyp), 2.94 (d, 3H, NMe2 of dmba, JHP
=
2.4 Hz), 2.64 (d, 3H, NMe2 of dmba, JHP = 2.6 Hz). 31P NMR
9642 | Dalton Trans., 2009, 9637–9644
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(DMF-d7): d(H3PO4) 20.8 (s, JPPt = 4279 Hz). ESI+ mass spectra
(CH3CN): m/z +740.2 ([Pt(dmba)(PPh3)(9-mhyp)]+, 22%); +591.4
([Pt(dmba)(PPh3)]+ + 1, 100%). 7: Yield: 76 mg (65%). Calcd. for
C21H29N48OPPt: C 39.7, H 4.6, N 17.6. Found: C 39.4, H, 4.8, N
17.8. Mp: 305 ◦C (dec). IR (Nujol, cm-1): 1632 n(CO). 1H NMR
(DMF-d7) at room temperature: d 8.13 (s, 1H, H2 of 9-mhyp),
7.91 (s, 1H, H8 of 9-mhyp), 7.60 (m, 1H, C6H4, Pt satellites are
observed as shoulders), 7.16 (m, 1H, C6H4), 7.00 (m, 2H, C6H4 Pt
satellites are observed as shoulders), 4.58 (d, 3H, NCH2N of PTA,
JHH = 12.9 Hz), 4.48 (d, 3H, NCH2N of PTA, JHH = 12.9 Hz),
4.24 (d, 3H, NCH2P of PTA, JHH = 15 Hz), 4.19 (d, 3H, NCH2P
of PTA, JHH = 15 Hz), 4.12 (d, 2H, NCH2 of dmba, JHH = 13.7
Hz), 3.94 (dd, 2H, NCH2 of dmba, JHH = 13.7 Hz, JHP = 3.3 Hz),
3.79 (s, 3H, Me of 9-mhyp), 2.61 (d, 3H, NMe2 of dmba, JHP = 1.9
Hz), 2.53 (d, 3H, NMe2 of dmba, JHP = 2.4 Hz, JHPt = 37.5 Hz).
31P NMR (DMF-d7): d(H3PO4) -64.8 (s, JPPt = 3802 Hz). ESI+
mass spectra (CH3CN): m/z +636.2 ([Pt(dmba)(PTA)(9-mhyp)]+
+1, 12%); +486.4 ([Pt(dmba)(PTA)]+ + 1, 10%).
monochromated Mo Ka radiation in w scan mode. Absorption
corrections were applied on the basis of multi-scans. All structures
were solved by direct methods using SHELX-9739 and refined
anisotropically on F2. The NH hydrogen atoms were found and
refined with Uiso(H) = 1.2Ueq(N). Hydrogen atoms for aromatic
CH, aliphatic CH, CH2 and methyl groups were positioned
˚
˚
geometrically (C–H = = 0.98 A for CH2, C–H = 0.97 A for CH3)
and refined using a riding model (AFIX 43 for aromatic CH,
AFIX 13 for aliphatic CH, AFIX 23 for CH2, AFIX 137 for CH3),
with Uiso(H) = 1.2Ueq(CH, CH2) and Uiso(H) = 1.5Ueq(CH3).
Computational details
The reliably accurate description of weak interactions like those
between ligands and heavy metals generally requires a treatment
of electron correlation. Density functional theory (DFT)40 has
proved quite useful in this regard offering an electron correlation
correction frequently comparable to the second-order Møller–
Plesset theory (MP2) or in certain cases, and for certain purposes,
even superior to MP2, but at considerably lower computational
cost.41 Calculated geometries at the DFT level were fully optimized
in the gas-phase with tight convergence criteria using the Gaussian
03 package,42 employing the BP86 functional. The 6-31G** basis
set was used in the optimizations for all atoms and adding diffuse
functions on N, O and P atoms (denoted as aug6-31G**), as well
as the Stutgart relativistic small-core basis set with effective core
potential (StRSCecp) for Pt (method A). Thereafter only the most
stable complexes as well as the individual formal components
X-Ray crystal structure analysis
Suitable crystals from
2
and
6
were grown from
dichloromethane/hexane. The crystal and molecular structures
of the compounds 2 and 6 have been determined by X-ray
diffraction studies (Table 2). Compounds 2 and 6 were measured
on a Bruker Smart Apex diffractometer. Data were collected using
Table 2 Crystal structure determination details
9-mhypH, 9-mhypH·ClO4 , 9-mhyp- and [Pt(PPh3)(dmba)]+ were
-
refined using the same functional and the most extensive
def2TZVP basis set for all atoms, with effective core potential for
Pt (method B), that was used as the standard level of theory unless
otherwise stated. From these gas-phase optimized geometries
all reported data were obtained by means of single-point (SP)
calculations at the same level. Energy values are uncorrected for
the zero-point vibrational energy. Natural charges were obtained
from the Natural Bond Orbital (NBO) population analysis. The
MO isosurfaces and energies displayed in Fig. 7 were computed at
the B3LYP/def2TZVP level (method C).
Compound
2
6
Empirical formula
fw (g mol-1)
C33H33ClN5O5PPt
841.15
triclinic
C33H32N5OPPt
740.70
triclinic
Cryst system
˚
a (A)
8.8061(4)
9.5922(5)
19.6841(11)
94.609(2)
100.862(2)
102.408(2)
1582.07(14)
100(2)
P-1
2
1.766
4.620
8.4884(4)
10.0705(5)
17.4286(8)
103.460(2)
94.548(2)
90.602(2)
4653.8(4)
100(2)
P-1
2
1.704
4.951
˚
b (A)
˚
c (A)
a (deg)
b (deg)
g (deg)
3
˚
V (A )
Temp (K)
Space group
Z
Acknowledgements
Dcalc (Mg m-3)
m (mm-1)
This work was supported by the Ministerio de Educacion y
Ciencia of Spain and FEDER (Project CTQ2008-02178/BQU)
and Fundacio´n Se´neca-CARM (Project 08666/PI/08). A.E.
would like to acknowledge financial support from MICINN-
Spain, Project CTQ2008-01402 and Fundacio´n Se´neca (Project
04509/GERM/06).
F(000)
832
732
Crystal size (mm)
2q range (◦)
h; k; l (range)
0.31 ¥ 0.24 ¥ 0.17
2.12 -26.37
-10 ≤ h ≤ 10
-11 ≤ k ≤ 11
-24 ≤ l ≤ 24
0.5072/0.3285
17320
6396
0.0140
0/422
1.083
0.13 ¥ 0.07 ¥ 0.05
2.08 -27.09
-10 ≤ h ≤ 10
-12 ≤ k ≤ 12
-22 ≤ l ≤ 21
0.6888/0.4884
16441
6233
0.0281
0/373
1.098
Max./min. transmission
Reflect. collcd [I > 2s(I)]
Independent reflections
R(int)
Notes and references
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Restraints/parameters
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R1/wR2 (all reflect.)c
0.0158/0.0392
0.0162/0.0394
0.873/-0.793
0.0280/0.0620
0.0301/0.628
1.625/-1.565
d
-3
˚
Max./min. Dr /e A
ꢀ
ꢀ
2
a Goodness-of-fit = [ [w(Fo - Fc2)2]/(n - p)]1/2
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b R1 =
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ꢀ
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|Fcꢁ/ |Fo|, wR2 = [ [w(Fo - Fc2)2]/ w(Fo2)2]1/2
;
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2
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program; d Largest difference peak and hole.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 9637–9644 | 9643
©

View Article Online
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9644 | Dalton Trans., 2009, 9637–9644
This journal is
The Royal Society of Chemistry 2009
©