P oceedings 2020, 62, 13; doi:10.3390/p oceedings2020062013 www.mdpi.com/jou nal/p oceedings
P oceedings
Syn hesis and X- ay Di ac ion S udy o
hiosemica bazone Palladacycles wi h dppm †
Ma cos Rúa-Suei o *, Paula Munin-C uz, F ancisco Reigosa, José M. Vila and Juan M. O iguei a
1 Depa men o Ino ganic Chemis y, Facul y o Chemis y, Uni e si y o San iago de Compos ela,
A da. das Ciencias s/n, 15782 San iago de Compos ela, Spain; paula.muni[email p o ec ed] (P.M.-C.);
ancisco. eigo[email p o ec ed] (F.R.); josemanuel. [email p o ec ed]s (J.M.V.); juanm.o iguei [email protected] (J.M.O.)
* Co espondence: ma cos. ua.suei [email protected]
† P esen ed a he 2nd In e na ional Elec onic Con e ence on C ys als, 10–20 No embe 2020; A ailable
online: h ps://iocc_2020.sci o um.ne /.
Published: 22 Janua y 2021
Abs ac : Cyclome alla ed compounds ha e been ex ensi ely s udied, in pa icula hose wi h
palladium and pla inum. This is because o hei possible applica ions in medicinal chemis y, as
an icance o an imic obial agen s; in some cases, wi h simila esul s as cispla in, ca bopla in o
oxalipla in. Wha is also ema kable is hei use as homogeneous ca alys s, o example, in c oss
coupling eac ions such as Suzuki–Miyau a o Mizo oki–Heck. He ein, we epo he syn hesis o
di e en hiosemica bazone ligands, which will be eac ed wi h a palladium o pla inum sal , o gi e
he co esponding cyclome alla ed compounds; in addi ion, hei eac i i y wi h
bis(diphenylphosphino)me hane (dppm) will be s udied. Cha ac e iza ion has been ca ied ou by
elemen al analysis, IR spec oscopy, 1H and 31P NMR spec oscopy. Addi ionally, 1c has been
s udied by X- ay di ac ion.
Keywo ds: cyclome alla ion; hiosemica bazone; palladium; pla inum; X- ay di ac ion
1. In oduc ion
Palladium and pla inum cyclome alla ed compounds ha e been s udied due o hei in e es ing
applica ions in se e al chemical ields.
On he one hand, hey a e use ul in syn he ic o ganic chemis y, as ca alys s in many eac ions
wi h o ma ion o C–C and C–N bonds [1–6].
On he o he hand, hei cy o oxic ac i i y has been conside ed in biological assays [7–11],
showing in some cases signi ican esul s in his ield.
The e a e many cha ac e iza ion echniques ha could be used o his kind o complex.
P obably he mos p ecise one is single c ys al X-Ray di ac ion, which in his esea ch wo k is gi en
o compound 1c.
2. Expe imen al
2.1. Ligands
The ligands we e syn hesized acco ding o Scheme 1. Fi s , he hiosemica bazide and
hyd ochlo ic acid (0.4 cm3) we e added in wa e (20 cm3). A e comple e solubiliza ion, he
co esponding amoun o ke one (shown in Table 1) was added. The mix u e was s i ed a oom
empe a u e o 8 h, a e which a whi e solid appea ed, ha was il e ed, washed wi h wa e and
d ied unde acuum.
P oceedings 2020, 62, 13 2 o 8
Scheme 1. Syn hesis o hiosemica bazone ligands.
Table 1. Quan i ies o eagen s added.
Ligand R
Thiosemica bazide (mg)
Ke one (mg) Yield (%)
1a
H
250 412 90
2a
Me
250 357 98
3a
E
250 315 88
2.2. Cyclome alla ed Compounds
Cyclome alla ion was ca ied ou ollowing Scheme 2. K2MCl4 (M = Pd, P ) was added in 6 cm3
o wa e . A e o al solubiliza ion, he co esponding amoun o each hiosemica bazone ligand
(shown in Table 2) was added in e hanol (25 cm3). The mix u e was s i ed a oom empe a u e o
24 h. A suspension o med, ha was cen i uga ed and he solid was d ied unde acuum.
Scheme 2. Syn hesis o cyclome alla ed compounds.
Table 2. Quan i ies o eagen s added.
Compound R M
K2MCl4 (mg)
Thiosemica bazone (mg) Yield (%)
1b
H
Pd
200 164 71
2b
Me
Pd
200 174 78
3b
E
Pd
200 185 86
4b
H
P
150
80.7
85
5b
Me
P
150
85.8
85
6b
E
P
150
90.8
86
2.3. Reac i i y wi h dppm
Compounds 1c–6c we e syn hesized ollowing Scheme 3. The cyclome alla ed compounds and
he co esponding amoun o bis(diphenylphosphino)me hane (dppm) (shown in Table 3) we e
P oceedings 2020, 62, 13 3 o 8
added unde ni ogen in 15 cm3 o oxygen- ee ace one. A e s i ing a 50 °C o 24 h, a solid was
ob ained, ha was cen i uga ed and d ied unde acuum.
Scheme 3. Reac ions wi h dppm.
Table 3. Quan i ies o eagen s added.
Compound
R M
Me allacycle (mg)
dppm (mg)
Yield (%)
1c
H
Pd
35
41.0
60
2c
Me
Pd
35
39.3
75
3c
E
Pd
35
37.8
72
4c
H
P
35
32.3
64
5c
Me
P
35
31.3
59
6c
E
P
35
30.2
61
3. Resul s and Discussion
All he compounds we e cha ac e ized by IR spec oscopy, 1H and 31P NMR spec oscopy. In
addi ion, compound 1c was cha ac e ized by single c ys al X- ay di ac ion.
3.1. IR Spec oscopy
IR spec oscopy cha ac e iza ion da a o he hiosemica bazone ligands and cyclome alla ed
compounds a e shown in Table 4. The dep o ona ion and he loss o he C=S double bond cha ac e
a e equi ed o cyclome alla ion o occu .
Table 4. IR spec oscopy cha ac e iza ion.
Compound
R
M
ν(N-H) ν(C=S)
1a
H
-
3154/3243/3375 826
2a
Me
-
3193/3366 836
3a E
-
3201/3299 829
1b
H
Pd
3159/3292
-
2b
Me Pd
3353
-
3b E
Pd
3341
-
4b
H
P
3215/3320
-
5b
Me
P
3286
-
6b E
P
3303
-
3.2. 1H NMR Spec oscopy
The compa ison o he spec a (in Figu e 1) o he hiosemica bazone ligands and
cyclome alla ed compounds shows he disappea ance o he o ho a oma ic p o on esonance and he
hyd azinic p o on esonance in ag eemen wi h cyclome alla ion.
P oceedings 2020, 62, 13 4 o 8
Mo eo e , a oma ic signals change hei mul iplici y upon o ma ion o he Pd–C bond.
Figu e 1. 1H NMR s acked spec um (400 MHz, DMSO-d6) o compounds 2a and 2b.
A e eac ion wi h dppm, he spec a did no show e y signi ican changes, as shown in Figu e 2.
The only ema kable change is he high ield shi o he H5 p o on signal, caused by he phenyl ings
o he diphosphine, which p oduces s ong shielding in ha posi ion.
Figu e 2. 1H NMR spec um o compound 3c in CDCl3.
P oceedings 2020, 62, 13 5 o 8
3.3. 31P-{1H} NMR spec oscopy
The 31P NMR spec um gi es in o ma ion abou he coo dina i e beha io o he phosphine
ligand.
In his case, he spec a show wo double s, one o each o he wo inequi alen 31P nuclei.
Sa elli es due o 195P –31P coupling we e obse ed o 4c–6c (see Figu e 3).
Figu e 3. 31P-{1H} NMR o compound 5c in ace one-d6.
3.4. Single C ys al X- ay Di ac ion
Single c ys als o compound 1c we e ob ained by slow e apo a ion o an ace one solu ion.
Compound 1c c ys allizes in he monoclinic sys em, C2/c space g oup. The esolu ion o he
molecula s uc u e con i ms he spec oscopic da a. The molecula s uc u e o 1c is shown in Figu e 4
and selec ed bond dis ances (Å) and angles (°) a e shown in Table 5.
(a) (b)
P oceedings 2020, 62, 13 6 o 8
(c)
Figu e 4. (a) Molecula s uc u e o compound 1b. Hyd ogen a oms ha e been omi ed o cla i y. (b)
Bond dis ances (Å) and angles (°) a ound he palladium cen e . (c) In amolecula π–π s acking
in e ac ion in 1c.
Complex 1c (shown in Table 5) p esen s a mononuclea s uc u e, wi h sligh ly dis o ed squa e-
plana geome y a ound he palladium cen e , su ounded by he o ho ca bon a om o he phenyl
ing (C1), he iminic ni ogen (N1), he sul u (S1) and one phospho us a om (P1). Selec ed bonds
dis ances and angles a e p esen ed in Table 5. The sum o angles abou palladium a om is
app oxima ely 360˚. Pd1-N1 2.029(3) Å, Pd1-C1 2.048(3) Å and Pd1-S1 2.3351(13) Å bond dis ances
a e wi hin he expec ed ange, and hey a e in ag eemen wi h simila s uc u es p e iously p esen ed
by us [12–14].
Table 5. Selec ed bonds (Å) and angles (°) o compound 1c.
Pd(1)-N(1) 2.029(3) S(1)-C(9) 1.762(3)
Pd(1)-C(1) 2.048(3)
N(1)-C(7)
1.305(4)
Pd(1)-P(1)
2.2504(8) N(1)-N(2)
1.379(4)
Pd(1)-S(1)
2.3351(13)
N(2)-C(9)
1.305(4)
N(1)-Pd(1)-C(1) 81.22(12) N(1)-Pd(1)-S(1)
82.70(8)
N(1)-Pd(1)-P(1) 177.18(8)
C(1)-Pd(1)-S(1) 163.87(10)
C(1)-Pd(1)-P(1)
97.52(10) P(1)-Pd(1)-S(1)
98.60(4)
In amolecula π–π s acking in e ac ions we e obse ed be ween wo phenyl ings, one om
each phospho us a om (see Figu e 4c).
The dis ance be ween he wo cen oids is 4.163 Å, and he angle be ween he ing planes is 3.43°.
In addi ion, in e molecula hyd ogen bond in e ac ions we e obse ed be ween he hyd azinic
ni ogen and he hioamidic ni ogen. The hyd ogen bond dis ances we e 2.127 Å, as shown in Figu e 5.
P oceedings 2020, 62, 13 7 o 8
Figu e 5. In e molecula hyd ogen bonding in e ac ion in 1c.
4. Conclusions
• Coo dina ion o he me al cen e occu s in he hiol o m o he hiosemica bazone ligand, as
shown by IR spec oscopy.
• 1H NMR spec oscopy con i ms cyclome alla ion, wi h he hiosemica bazone ligand as
iden a e [C, N, S].
• The cyclome alla ed compounds show a e anuclea s uc u e, wi h wo ypes o bonds be ween
palladium and sul u : Pd-Schela e and Pd-Sb idging.
• Reac ion wi h dppm gene a es mononuclea compounds wi h one ee phospho us a om.
• Single c ys al X- ay di ac ion s udy o compound 1c shows he p oposed s uc u e,
wi h he
pallada ed hiosemica bazone ligand and dppm as a monoden a e ligand.
Funding: F ancisco Reigosa wan s o hank he Spanish Go e nmen (AEI) o hei inancial suppo h ough
an FPU g an (numbe 13/05014). The au ho s hank unding om Xun a de Galicia (Galicia, Spain) unde he
G upos de Re e encia p og am (GRC 2019/014).
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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Publishe ’s No e: MDPI s ays neu al wi h ega d o ju isdic ional claims in published maps and ins i u ional
a ilia ions.
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