Intramolecular hydrogen bonding controls 1,3-N,S- vs. 1,5-S,S′- coordination in NiII complexes of N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)2

Article abstract of DOI:10.1039/c0dt01382j

Reaction of the deprotonated N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)₂ (R = Ph, HL^I; 2-MeC₆H ₄-, HL^II; 2,6-Me₂C₆H₃-, HL^III; 2,4,6-Me₃C<

Full text of DOI:10.1039/c0dt01382j

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PAPER
Intramolecular hydrogen bonding controls 1,3-N,S- vs. 1,5-S,S¢-coordination
in NiII complexes of N-thiophosphorylated thioureas
RNHC(S)NHP(S)(OiPr)2†
Maria G. Babashkina,*a,b Damir A. Safin,a,b Michael Bolte,c Monika Srebro,d Mariusz Mitoraj,d Andre´ Uthe,b
Axel Klein*b and Martin Ko¨ckerlinga
Received 13th October 2010, Accepted 13th December 2010
DOI: 10.1039/c0dt01382j
Reaction of the deprotonated N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)2 (R = Ph, HLI;
2-MeC6H4–, HLII; 2,6-Me2C6H3–, HLIII; 2,4,6-Me3C6H2–, HLIV; Me–, HLV) with NiII leads to
complexes of the formula [NiLI–V2]. The molecular structures of the thioureas HLII–V and the complexes
[NiLII–V2] in the solid were elucidated by single-crystal X-ray diffraction analysis. In the complexes, the
metal is found to be in a square planar trans-N2S2 ([NiLII–IV2]) environment formed by the C S sulfur
atoms and the P–N nitrogen atoms, or in a square planar trans-S2S¢2 ([NiLV2]) environment formed by
the C S and P S sulfur atoms of two deprotonated ligands. DFT calculations confirmed that the
[Ni(LII–IV-N,S)2] isomers are more stable (by 16–21 kcal mol-1) than the corresponding [Ni(LII–IV-S,S¢)2]
conformers. The main reason for higher stability of the 1,3-N,S vs. 1,5-S,S¢ isomers is the formation of
intramolecular N–H ◊ ◊ ◊ S P hydrogen bonds. In solution the complexes [Ni(LII–V-N,S)2] have an
exclusive 1,3-N,S coordination, while the compound [Ni(LI-N,S)2] exhibits two isomers in the 1H and
31P NMR spectra. The major species is assigned to the 1,3-N,S coordinated isomer, while the minor
(~25%) signals are due to the 1,5-S,S¢ isomer. UV-Vis spectroscopic results are in line with this. The
electrochemical measurements reveal reversible one-electron reduction and irreversible oxidations, both
assigned to ligand-centred processes.
electrodes,4–7 extractants8–10 and masking reagents in analytical
Introduction
chemistry.11
Polyfunctional ligands, able to achieve different coordination
In previous contributions we have studied the struc-
tures of NiII complexes with N-phosphoryl-N¢-(R)-thioureas
modes with metal cations, are of great interest since they are widely
used as selective complexing and analytical reagents.1 In particular,
phosphorylated thioamides and thioureas have attracted the
attention of researchers in the last two decades due to their ability
RNHC(S)NHP(O)(OiPr)2 (HZ) ligands, and found that the
square planar complexes [NiZ2] exhibit either a 1,3-N,S- or a 1,5-
O,S coordination mode (Scheme 1, A and B). It was established
to form stable chelate complexes with Ib, IIb, and VIIIb group
that intramolecular hydrogen bonds N–H ◊ ◊ ◊ O P are a necessary
condition for the formation of 1,3-N,S-isomers for R = Ph;12 R = p-
transition metal cations. Such compounds exhibit a number of very
interesting properties for their application as antiviral drugs,2 their
use in stationary phases for GLC,3 as components of ion-selective
MeOC6H4, p-BrC6H4, tBu, cyclo-C6H11;13 iPr;14 1-Ad15 (Scheme 1,
A), while 1,5-O,S coordination takes place when H-bonding in the
coordinated anionic ligands is not possible (R = Et2N, morpholin-
N-yl13) (Scheme 1, B). It can be concluded from this that the
aInstitut fu¨r Chemie, Anorganische Festko¨rperchemie, Albert-Einstein-
Str., 3a, D-18059, Rostock, Germany. E-mail: maria.babashkina@ksu.ru;
Fax: +49 381 4986390; Tel: +49 381 4986381
C
S group represents the strongest ligand, and that the 1,5-O,S
bInstitut fu¨r Anorganische Chemie, Universita¨t zu Ko¨ln, Greinstrasse 6, D-
50939, Ko¨ln, Germany. E-mail: axel-klein@uni-koeln.de; Fax: +49 221
4705196; Tel: +49 221 4702913
coordination is slightly more stable than the 1,3-N,S coordination,
probably due to the unfavourable four-ring chelate of the latter.
However, the energy difference between 1,3-N,S- and 1,5-O,S
coordination is small, and 1,3-N,S is observed in cases where
the formation of N–H ◊ ◊ ◊ O P hydrogen bridges adds to the total
energy (or blocks the 1,5-O,S coordination) (Scheme 1, A and B).
Moreover, N-phosphorylated thioamides RC(S)NHP(O)(OiPr)2
(R = p-BrC6H4;16 Ph17) form distorted octahedral complexes with
NiII, where two deprotonated ligands are coordinated through
the sulfur and oxygen atoms of the C S and P O groups,
cInstitut fu¨r Anorganische Chemie J.-W.-Goethe-Universita¨t, Frank-
furt/Main, Germany
dDepartment of Theoretical Chemistry, Faculty of Chemistry, Jagiellonian
University, R. Ingardena 3, 30-060, Cracow, Poland
† Electronic supplementary information (ESI) available: Figs. S1–S4.
CCDC reference numbers 736205 (HLII), 721784 (HLIII), 736206 (HLIV),
736207 (HLV), 736208 ([NiLII2]), 721785 ([NiLIII2]), 736209 ([NiLIV2]) and
736210 ([NiLV2]). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0dt01382j
3142 | Dalton Trans., 2011, 40, 3142–3153
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structures of the complexes, we carried out DFT calculations on
the structures, focusing on the energy difference between [Ni(LII–V
-
N,S)2] and [Ni(LII–V-S,S¢)2] conformers. Finally, we investigated
the structures of the complexes in solutions by multinuclear NMR
and UV-Vis absorption spectroscopy. The latter method, in com-
bination with electrochemical investigations (cyclic voltammetry)
should also allow us to shed light on the electronic properties of
these complexes. Very preliminary results of these investigations
have been presented previously, including a comparison with the
complex [NiZI2] (HZI = PhNHC(S)NHP(O)(OiPr)2).12
Results and discussion
Scheme 1
The N-(thio)phosphorylated thioureas HLI–V and HZI were
synthesised by reacting the corresponding amine with the
respectively, and two neutral forms of the ligands are bonded
through the oxygen atoms of the P O groups (Scheme 1, C).
Thus, there is a strong influence of the nature of the substituents
and donor atoms on the coordination mode of N-phosphorylated
thioureas and thioamides towards NiII.
In the case of the corresponding thioanalogues, N-
thiophosphorylated thioamides RC(S)NHP(S)(OiPr)2 and
thioureas RR¢NC(S)NHP(S)(OiPr)2, containing two donor sulfur
atoms of the thiocarbonyl and thiophosphoryl groups, a great
number of complexes of the VIIIb group metal cations CoII, NiII,
PdII and PtII exhibit also exclusively the 1,5-S,S¢ coordination
mode in the solid state.18–20 It was assumed that the superior
bond strength of both M–S bonds over the M–N bond will not
allow a change in the coordination mode in these complexes
through formation of N–H ◊ ◊ ◊ S P bridges, steric interaction of
the substituents or other factors.18,20
25–27
isothiocyanate (iPrO)2P(S)NCS (HLI–V
)
or (iPrO)2P(O)NCS
(HZ1)12,28,29 as recently described (Scheme 2). The complexes
[NiLI–V2] and [NiZI2] were prepared by the following procedure:
the corresponding ligand was deprotonated in situ using KOH,
followed by reaction with NiCl2 (Schemes 3 and 4).12,20,23,24 The
compounds obtained are crystalline solids, which are soluble in
most polar solvents.
It is important to note that the situation for the coordination
of NiII to N-thiophosphorylated thioamides and thioureas is
further complicated by the possibility to form tetrahedrally
configured complexes, as recently described for the complex
[Ni{Me2NC(S)NP(S)(OiPr)2}2], which in polar solvents exhibits
spectral features for a tetrahedral complex (colour, paramag-
netism), while in non-polar solvents and in the solid the complex
has a trans square planar geometry. Both configurations exhibit
clearly a 1,5-S,S¢ coordination.21,22
Scheme 2
Recently we were able to report the first example of a 1,3-N,S
coordination of the deprotonated chelate backbone in the square
planar NiII complex [Ni{2-Py(6-Me)NHC(S)NP(S)(OiPr)2}2]. No
crystal structure has been obtained so far, but from spectroscopic
results it is clear that the 2-pyridyl functions are additionally
coordinating in this octahedral complex.23
To get
a comprehensive picture, we started a study
Scheme 3
of complexes using various N-thiophosphorylated thioureas
RHNC(S)NHP(S)(OiPr)2, all comprising the possibility of in-
tramolecular N–H ◊ ◊ ◊ S P hydrogen bridges and various ste-
rically bulky residues (R = Ph, HLI; 2-MeC6H4–, HLII; 2,6-
Me2C6H3–, HLIII; 2,4,6-Me3C6H2–, HLIV; Me–, HLV). As a
preliminary result, we reported success in inducing the formation
of a 1,3-N,S coordination mode in the trans square planar NiII
complex [NiLIII2] (R = 2,6-Me2C6H3–).24 This contrasted to the
1
For the characterisation of the complexes in solution H and
31P NMR spectra were recorded. An initial inspection reveals that
the NMR spectra of [NiLII–V2] are all quite similar. For [NiLI2]
more than one set of signals was observed. The 31P NMR signal of
[NiLII–V2] in CDCl3 appears as a broad singlet or triplet at d = 53.7–
54.3 ppm, and a shift, relative to that of the parent ligands HLII (d =
52.7 ppm), HLIII (d = 52.8 ppm), HLIV (d = 52.9 ppm) and HLV (d =
57.5 ppm), is observed, confirming the deprotonated form of the
ligand.18,30 The signal is considerably high-field shifted in DMF-d7
and was found as a broad singlet at 44.8–47.9 ppm. The 1H NMR
spectra of HLII–V and [NiLII–V2] in CDCl3 contain a single set of
signals for the iPr, Me and aryl protons. The aromatic ring proton
previously published complexes [NiLI2] (R = Ph)20 and [NiLVI
]
2
(R = tBu)19 exhibiting 1,5-S,S¢ coordination. In this contribution
we now report the synthesis and crystal structure of the N-
thiophosphorylated thioureas HLI–V and their NiII complexes
[NiL2I–V]. In order to obtain a complete picture of the molecular
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the paramagnetic central ion and the phosphorus atoms.16,20 In
1
contrast to this H NMR signals were observed for [NiZI2] in
DMF-d7 (Fig. 1) which can be explained by the fact that such
pseudocontact interactions are practically absent in the case
of protons for which dipole–dipole interactions dominate. The
1
signals a and b in the H NMR spectrum of [NiZI2] in DMF-d7
correspond to the CH3 protons of the iPr group, while the signal
d is attributed to the OCH protons (Fig. 1). Signals for the C6H5
protons were found as a multiplet (e) and singlet (f). The latter
signal is considerably low-field shifted. Furthermore, the signal of
the NH protons were observed at extremely high-field region (dH
=
4.79 ppm, c). Thus, NMR spectra of [NiZI2] in DMF-d7 indicate
paramagnetic species, which are presumably either octahedral (in
[Ni(DMF)2ZI2]) or tetrahedral (in [NiZI2]tetr) geometries. On the
basis of NMR spectra the two possibilities cannot be validated.
Unfortunately, it is also not possible to state whether the ligand ZI
in [Ni(DMF)2ZI2] or [NiZI2]tetr is 1,3-N,S or 1,5-O,S coordinated
in DMF solution.
Scheme 4
signals in the complexes [NiLII–IV2] are at 6.89–7.83 ppm and shifted
high-field relative to those in HLII–IV. In the H NMR spectra of
1
HLII–V the signal for the NHP proton is at 6.99–7.65 ppm, while
this signal is absent in the spectra of [NiLII–V2], confirming the
anionic form of the ligand in the complexes. Signals for the arylNH
protons in the spectra of HLII–IV and [NiLII–IV2] are at 9.22–9.36
and 10.21–10.67 ppm, respectively. The MeNH proton signal in
the spectrum of [NiLV2] is at 9.00 ppm. These signals are low-field
shifted, presumably due to the formation of hydrogen bonds of
1
the type arylN–H ◊ ◊ ◊ S P. The H NMR spectra of [NiLII–V2] in
DMF-d7 are similar to those observed in CDCl3. However, it is
noteworthy that the signal for the arylNH proton in the spectra
of [NiLII–IV2] was observed at 9.43–9.73 ppm, while the signal for
the MeNH proton in the spectrum of [NiLV2] was found at about
8.00 ppm.
The 31P NMR spectrum of [NiLI2] in CDCl3 is more complicated
and contains two signals, a multiplet at 49.1–52.1 ppm and a broad
singlet at 52.9 ppm. The same was previously observed in the
spectra of [NiLI2] in CD2Cl2 by Brusko et al.20 The high-field signal
was referred to the trans-boat–boat 1,5-S,S¢ coordination mode of
the deprotonated ligand, while the low-field signal was referred to
the cis-boat–boat 1,5-S,S¢ coordination mode. However, herein
we suggest that the high-field signal corresponds to the 1,5-
S,S¢ coordination, while the second signal is typical of the 1,3-
N,S coordination of the deprotonated N-thiophosphorylated
thioureas (see Experimental section and description above). The
31P NMR spectrum of [NiLI2] in DMF-d7 contains exclusively a
broad singlet at 48.5 ppm and in the same region as it was observed
Fig. 1 1H NMR spectrum of [NiZI2] in DMF-d7. Signals of the solvent
are marked by asterisks.
Crystals of HLII–V and [NiLII–V2] were obtained by slow evapora-
tion of the solvent from CH2Cl2–n-hexane solution. The molecular
structures of HLII–V and [NiLII–V2] are shown in Figs. 2–5 and in
the ESI (Figs. S1–S4†), while the crystal and structure refinement
data are given in the Experimental section.
1
in the spectra of [NiLII–V2]. The H NMR spectrum of [NiLI2] in
CDCl3 also contains two sets of signals which are obviously due
to the presence of two types of coordination, while there is only
one set of signals in the spectrum of the compound measured in
DMF-d7. The major species (ca. 75%) exhibits e.g. a broad singlet
signal at 5 ppm for the isopropyl CH protons, while the signal for
the minor species (ca. 25%) is high-field shifted. In line with the
results from 31P NMR spectra, we assign the major species to the
1,3-N,S and the minor species to the 1,5-S,S¢ isomers. In DMF-d7
the corresponding signal is resolved to a septet and the spectrum
represents exclusively the 1,3-N,S isomer.
The compounds HLII–V and [NiLII–V2] crystallise in the space
¯
group P1. The parameters of the C S, C–N, P–N and P
S
bonds for HLII–V (Table 1) are in the typical range for N-
thiophosphorylated thiourea derivatives.18,30
The S–C–N–P backbone in HLII–V has an E conformation (Figs.
2 and 3). The crystal structures of all thioureas are stabilised by
an intramolecular hydrogen bond of the type N(2)–H(2) ◊ ◊ ◊ O(2)–
P(1) (HLII) or N(2)–H(2) ◊ ◊ ◊ S P(1) (HLIII–V) (Table 2). There are
intermolecular hydrogen bonds of the type N(1)–H(1) ◊ ◊ ◊ S#1 C#1
in the crystals of HLII–V (Table 2), which are formed between the S
atoms of the C S groups and the H atoms of the PNH fragment
of two molecules. As a result of the intermolecular interactions, a
centrosymmetric dimer is formed.
1
The 31P and H NMR spectra of [NiZI2] in CDCl3 are similar
to those described by Sokolov et al.12 and uniquely testify the
formation of the 1,3-N,S coordination mode of the deprotonated
ligand in the structure of [NiZI2].12,13,18 In DMF-d7 no signals were
observed in the 31P NMR spectrum of [NiZI2]. This is probably
due to strong contact or pseudocontact interactions between
The complexes [NiLII–V2] crystallize in centrosymmetric struc-
tures. The NiII ion is coordinated in a square-planar fashion
3144 | Dalton Trans., 2011, 40, 3142–3153
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◦
II–V
Table 1 Selected bond lengths (A), and bond angles ( ) for HL and [NiLII–V
]
˚
24
24
HLII
HLIII
HLIV
HLV
[NiLII
]
[NiLIII
]
[NiLIV
]
[NiLV
]
2
2
2
2
C
P
P–N
S
S
1.669(2)
1.9102(7)
1.678(2)
1.381(2)
1.334(2)
1.6800(13)
1.9195(5)
1.6839(11)
1.375(2)
1.672(2)
1.9296(6)
1.671(2)
1.382(2)
1.338(2)
1.680(2)
1.9169(5)
1.6748(13)
1.377(2)
1.325(2)
1.725(2)
1.9423(7)
1.647(2)
1.351(3)
1.324(3)
1.908(2)
2.2217(6)
1.724(2)
1.811(2), 2.220(5)
1.642(2)
1.343(3)
1.319(3)
1.911(2)
2.2195(6)
1.717(2)
1.9447(7)
1.652(2)
1.344(3)
1.330(3)
1.916(2)
2.2178(6)
1.754(2)
1.9992(9)
1.598(2)
1.313(3)
1.336(3)
C–N(P)
C–N(C)
Ni–N
Ni–S(C)
Ni–S(P)
S–C–N(C)
S–C–N(P)
N–C–N
N–P–S
1.332(2)
2.2213(7)
2.2126(9),
113.83(16)
129.21(16)
116.96(19)
115.87(8)
125.20(15)
122.53(14)
120.66(13)
116.81(16)
109.94(6)
122.68(10)
119.92(10)
117.40(11)
115.03(4)
132.05(9)
123.12(13)
120.52(13)
116.36(15)
116.29(6)
122.92(12)
119.76(11)
117.32(14)
115.86(5)
127.06(15)
108.49(14)
124.45(17)
117.15(7)
130.86(14)
74.28(5)
77.89(7)
99.31(12)
129.17(10)
124.22(18)
109.39(17)
126.4(2)
109.76(13), 118.90(11)
128.34(18)
74.51(6)
77.31(8)
98.54(14)
132.56(12)
123.88(16)
110.03(14)
126.07(19)
115.97(6)
128.80(14)
74.62(5)
77.23(7)
97.88(13)
133.32(10)
C–N–P
130.23(14)
128.89(12)
128.21(11)
N–Ni–Sendo
Ni–S–C
Ni–N–C
Ni–N–P
Ni–S–P
S–Ni–Sendo
117.81(8)
102.04(4)
98.52(3)
◦
II–V
Table 2 Selected hydrogen bond lengths (A) and angles ( ) for HL and [NiLII–V
]
˚
D–H ◊ ◊ ◊ A
d(D–H)
d(H ◊ ◊ ◊ A)
d(D ◊ ◊ ◊ A)
∠(DHA)
HLIIa
HLIII
HLIV
N(1)–H(1) ◊ ◊ ◊ S(2)#1
N(2)–H(2) ◊ ◊ ◊ O(2)
N(1)–H(1) ◊ ◊ ◊ S(1)#1
N(2)–H(2) ◊ ◊ ◊ S(2)
N(1)–H(1) ◊ ◊ ◊ S(2)#1
N(2)–H(2) ◊ ◊ ◊ S(1)
N(1)–H(1) ◊ ◊ ◊ S(2)#1
N(2)–H(2) ◊ ◊ ◊ S(1)
N(2)–H(2) ◊ ◊ ◊ S(2)
N(2)–H(2) ◊ ◊ ◊ S(2)
N(2)–H(2) ◊ ◊ ◊ S(2¢)
N(2)–H(2) ◊ ◊ ◊ S(1)
N(2)–H(2) ◊ ◊ ◊ S(2)#2
0.80(2)
0.81(3)
0.88(2)
0.85(2)
0.84(2)
0.81(2)
0.78(2)
0.84(2)
0.896(10)
0.80(3)
0.80(3)
0.88(3)
0.88(3)
2.57(2)
2.66(3)
2.47(2)
2.47(2)
2.56(2)
2.63(2)
2.59(2)
2.63(2)
2.33(2)
2.48(3)
2.49(3)
2.39(3)
2.80(3)
3.3545(17)
3.153(2)
167.6(19)
121(2)
b
c
24
3.3291(12)
3.2202(12)
3.3878(16)
3.3414(16)
3.3656(14)
3.3341(15)
3.1571(17)
3.177(2)
165.9(16)
148.5(16)
170.0(19)
147.8(18)
172.4(19)
141.6(19)
153(2)
146(3)
145(3)
145(2)
156(3)
d
HLV
[NiLII
]
]
e
2
[NiLIII
f
24
2
3.178(3)
3.152(2)
3.628(2)
[NiLIV
[NiLV
]
2
g
]
2
a Symmetry transformations used to generate equivalent atoms: #1 -x + 1, -y + 1, -z + 2. b Symmetry transformations used to generate equivalent
atoms: #1 -x + 1, -y + 2, -z + 1. c Symmetry transformations used to generate equivalent atoms: #1 -x, 2 - y, 1 - z. d Symmetry transformations used
to generate equivalent atoms: #1 -x + 2, -y + 1, -z. e Symmetry transformations used to generate equivalent atoms: -x + 1, -y + 1, -z + 2. f Symmetry
transformations used to generate equivalent atoms: -x + 1, -y, -z + 1. g Symmetry transformations used to generate equivalent atoms: -x + 2, -y + 1, -z
+ 2; #2 -x + 2, -y + 2, -z + 2.
Fig. 3 View of the hydrogen bonded dimer of HLV. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms not involved in
H-bonding are omitted for clarity.
Fig. 2 View of the hydrogen-bonded dimer of HLIV. Thermal ellipsoids
are drawn at the 50% probability level. Hydrogen atoms not involved in
H-bonding are omitted for clarity. The structures of HLII,III are similar to
HLIV and given in the ESI (Figs. S1 and S2).
the complex [NiLV2] have an asymmetric boat form. The values
of the intracyclic S–Ni–N angles in the four-membered rings of
[NiLII–IV2] fall in the range of 74–75◦, while the intracyclic S–
Ni–S angle in [NiLV2] is about 99◦. Inspection of the C S and
P–N bond lengths of [NiLII–IV2] indicates that these bonds are best
described as single bonds, while the P S distance indicates the
with the ligands arranged in a trans-configuration (Fig. 4 and
5). The four-membered Ni–S–C–N metallocycles are planar in
[NiLII–IV2]. The six-membered Ni–S–C–N–P–S metallocycles in
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Fig. 4 Molecular structure of [NiLIV2]. Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms not involved in H-bonding are
omitted for clarity. The structures of [NiLII,III2] are similar to [NiLIV2] and
given in the ESI (Figs. S3 and S4).
Fig. 5 View of two complex units of [NiLV2] connected by hydrogen
bonds. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms not involved in H-bonding are omitted for clarity.
presence of a double bond (Table 1).18,30 In comparison with the
parent ligand HLV lengthening of the C S and shortening of the
C–N bonds are observed upon the [NiLV2] complex formation.
The same change, but to a smaller degree, has been observed for
the P–N and P S bonds. The arylNH protons in [NiLII–IV2] are
[Ni(LII–V-S,S¢)2] exhibiting the following conformations: (i) cis-
1,3-N,S, (ii) cis-1,5-S,S¢, (iii) trans-1,3-N,S, and (iv) trans-1,5-
S,S¢. All structures with cis-configuration appeared to be less
stable than those corresponding to the trans-isomers. In Fig. 6
the relative energetic stability of trans-1,3-N,S vs. trans-1,5-S,S¢
isomers are presented, showing that in each case the coordination
in a 1,3-N,S-fashion is preferred (by 16–21 kcal mol-1, depending
on the system) over the 1,5-S,S¢ conformation. Also, the results
clearly show an important role of the methyl substituent on
the phenyl ring in the stabilisation of the 1,3-N,S conformers
with the highest stabilisation observed for the trimethylphenyl
derivative. The results for the complexes [Ni(LII–IV-N,S)2] are in
line with the observed molecular structures from XRD of the
compounds obtained from reaction of the deprotonated ligands
HLII–IV with NiII. However, while the energy difference between
the two isomers is largest for [NiLV2] the 1,5-S,S¢ isomer has
been crystallised. Here it is important to note that the DFT
involved in intramolecular hydrogen bonds of the N–H ◊ ◊ ◊ S
P
type (Table 2). Due to their formation, a flat syn,syn-conformation
of the N–C–N–P–S unit is favoured (Fig. 4). The MeNH protons
in [NiLV2] are involved in intermolecular hydrogen bonds of the
type N–H ◊ ◊ ◊ S C (Table 2) which leads to the formation of a
polymeric chain in the crystal (Fig. 5). A closer inspection of
the crystal structures revealed further H ◊ ◊ ◊ X hydrogen bridges;
however, based on established criteria31 we consider them not to
be determining the crystal or molecular structures.
In order to study the relative energy of the possible isomers
[Ni(LII–V-N,S)2] vs. [Ni(LII–V-S,S¢)2] DFT/LanL2DZ calculations
were performed at the B3LYP level, as implemented in the
Gaussian 09 package.32 We found true minima on the potential
energy surface (PES) for the complexes [Ni(LII–V-N,S)2] and
Fig. 6 Relative energies of the [Ni(LII–V-N,S)2] vs. [Ni(LII–V-S,S¢)2] isomers from DFT/LanL2DZ calculations; relative energy values DE in kcal mol-1.
3146 | Dalton Trans., 2011, 40, 3142–3153 This journal is The Royal Society of Chemistry 2011
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calculations refer to the complex unit (with no surrounding),
while stability in the crystal includes further energy increments
as intermolecular hydrogen bonds and packing. Indeed, since
Very obviously the aryl substituent contributes to this by electron
donation, which is in line with the calculated series (o-Tol < Xyl
< Mes) for the relative energies.
The same qualitative picture of intramolecular hydrogen bond-
ing emerges for the remaining systems, i.e. [NiLII2] and [NiLIV2].
It is noteworthy that such a qualitative mechanism is similar to
other types of hydrogen bonds studied previously by one of us.34
In summary, this means that efficient delocalisation of bonding
the complex units of [NiLV2] exhibit intermolecular N–H ◊ ◊ ◊ S
C
hydrogen bonds while the remaining systems [NiLII–IV2] lack any
such interactions, the energetically slightly disfavoured 1,5-S,S¢-
isomer might have a greater tendency to crystallise. The same
probably holds also for the recently reported derivative [NiL0 ]
2
(HL0 = H2NC(S)NHP(S)(OiPr)2),22 and the herein-reported com-
plex [NiLI2] (R = Ph)20 which both have been found in the 1,5-S,S¢
isomeric form in their crystal structures.
electrons into the C(aryl)–N–H unit stabilises the N–H ◊ ◊ ◊ S
P
hydrogen bonding and as a consequence the 1,3-N,S conformers.
This is in line with the effect of the increasing number of methyl
substituents on the phenyl ring increasing the stability of the 1,3-
N,S over the 1,5-S,S¢ isomer.
Accordingly, in order to obtain a more realistic picture of the
total energy of [Ni(LV-N,S)2] vs. [Ni(LV-S,S¢)2] in the crystal, pe-
riodic DFT calculations are ongoing using the BAND program,33
which is suitable for the study of bulk crystals, polymers, surfaces,
etc. The comprehensive theoretical analysis of the total energy of
the crystals [Ni(LII–IV-N,S)2] vs. [Ni(LII–IV-S,S¢)2] will be the subject
of an upcoming paper.
In order to gain further insight into the character of NH ◊ ◊ ◊ S
P
interaction, the ETS-NOCV35 bonding analysis was performed
using the ADF program, version 2009.01.36 The main advantage
of ETS-NOCV scheme is that it provides both a qualitative
and a quantitative picture of chemical bond formation within
one common theoretical framework. The qualitative picture of
bonding originates from the depiction of deformation density
contributions (Drk) that characterize specific bonding channels
(s, p, etc.):
From the results of the DFT calculations, we conclude that the
main factor responsible for higher stability of the [Ni(LII–IV-N,S)2]
isomers vs. [Ni(LII–IV-S,S¢)2] is the presence of intramolecular
hydrogen interaction in the former case. In order to shed some
light on the mechanism of such intramolecular interactions in
the [Ni(LII–IV-N,S)2] isomers, the deformation density isosurface
was plotted in one of the N–P S planes (those located on the
right-hand side of the metal centre; for an example see Fig. 7).
We used the convention that red shows charge depletion, whereas
blue shows charge accumulation upon bond formation. It can be
seen that the intramolecular N–H ◊ ◊ ◊ S P interaction (Fig. 7) is
based on electron density from the lone electron pair of the S atom
into the empty s*(N–H) orbital. Such an electron density transfer
M / 2
M / 2
Dr(r) =
v k (j−k +jk ) =
Drk
∑
∑
k =1
k =1
where vk are eigenvalues corresponding to the pairs of Natural
Orbitals for Chemical Valence (NOCVs) (j-k, jk); M stands
for the number of basis functions. In the ETS-NOCV scheme
a quantitative picture of bonding is obtained by providing the
energies [DEorb(k)] associated with each charge flow-channel (Drk):
˚
leads to weakening of the N–H bond (by 0.15 A), as compared to
M / 2
v k −F−k ,−k + FTS
a non-hydrogen bonding, isolated NHC6H3(Me)2 unit.
TS
⎡
⎤
DEorb
=
DEorb (k ) =
k ,k
⎢
⎣
⎥
⎦
∑
∑
k
k =1
where FTk,Sk are diagonal Kohn–Sham matrix elements defined over
NOCV with respect to the transition state (TS) density (at the
midpoint between density of the molecule and the sum of fragment
densities). It was shown that ETS-NOCV is especially useful when
describing a bonding between molecular fragments.35 Therefore, in
order to obtain information on the intramolecular N–H ◊ ◊ ◊ S
P
interaction, the bonding between the NHC6H3(Me)2 moiety and
the remaining Ni-containing fragment was performed; see Fig.
8a. For both fragments doublet spin states with opposite spin
polarizations were considered.
As can be seen from Fig. 8b, the two deformation density
contributions, Dr1 and Dr2, constitute the bonding between the
NHC6H3(Me)2 unit and the rest of the complex. The first dominant
component, Dr1, with the corresponding energy, DEorb(1) =
-472.8 kcal mol-1, clearly exhibits the formation of a strong
covalent N–C bond polarized towards the more electronegative
nitrogen atom. The contours of Dr2 depict an intramolecular
hydrogen bonding (i.e. an accumulation of electron density in
the bonding region) of the N–H ◊ ◊ ◊ S P unit, together with the
charge depletion from both lone electron pairs of the sulfur atom
and the N–H bond. Clearly, such a bonding is supported by the
delocalization of electrons into the empty p*(N–C) and s*(N–H)
states. The energy corresponding to Dr2 amounts to DEorb(2) =
-17.2 kcal mol-1. In line with the energetic strength of N–C
Fig. 7 Total deformation density isosurface (0.001 a.u.) plotted in one
of the planes defined by the N–P S group for the complex [NiLIII
]
–
2
ꢀ
(deformation density is calculated as Dr(r) = rmol(r) – ri(r), where rmol
density of molecule, ri – densities of spherically symmetric atoms). Dr < 0 –
red colour (charge depletion), Dr > 0 – blue colour (charge accumulation).
Additionally, electron density is shifted from the occupied N–
H orbital into a region which is bonding in view of the H ◊ ◊ ◊ S
interaction and also to the vicinity of the sulfur atom (see Fig. 7).
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UV absorptions of the nickel complexes can be assigned to
corresponding intraligand transitions (p–p* or n–p* type). The
different behaviour of the complex [NiLI2] might be explained by
the presence of the 1,5-S,S¢ isomer in the reaction product for
this derivative (as evidenced from NMR measurements) while for
the other complexes exclusively the 1,3-N,S isomer was present.
In contrast to this, the spectrum of the complex [NiLV2] (R =
Me) deviates only marginally from those of the aryl derivatives
[NiLII–IV2], which provides strong evidence that in solution the
same isomeric form (1,3-N,S) is present, in line with the DFT
calculations.
In the visible region essentially two absorption bands were
observed, one ranging from 509 (R = Mes) to 541 (R = Ph), and
another being rather invariant at 640 nm. From the rather low
intensities (70–190 M-1 cm-1) of the two long-wavelength bands we
assigned them to ligand field (d–d) transitions. For a square planar
1
1
1
3d8 system three bands [1A1g → B1g (dx → dxy), A1g → B3g (dxz
2
2
–y
→ dxy), and 1A1g → B1g (dz → dxy); assuming the orbital ordering:
1
2
20,22,30,40,41
2
2
2
dxy > dx
> dyz > dxz > dz ] are expected;
however,
–y
comparison with spectra of related complexes suggests that the
third band is hidden under the tail of the intense intraligand bands.
Fig. 8 Fragmentation used in the bonding analysis (panel a). In panel
b the dominant contours of deformation density contributions Dr1, Dr2
together with the corresponding energies, DEorb(1), DEorb(2), are presented
for the complex [NiLIII2].
2
2
It is thus interesting to note, that the transition dx → dxy strongly
–y
depends on the substituent R, while the transition (dxz → dxy) is
completely invariant. If we have a closer look at the impact of
the variation of R then we find a series of decreasing energy for
2
2
the dx
→ dxy transition along the series R = Mes > Xyl > Me
and H ◊ ◊ ◊ S components are calculated bond-order indices of the
Nalewajski–Mrozek method.37,38 These values are 1.39 for the N–C
bond and 0.11 for the H ◊ ◊ ◊ S intramolecular interaction.
–y
> Tol > Ph, which meets almost the corresponding series for the
p–p* band at around 310 nm (Me > Mes > Xyl > Tol > Ph). The
spectra recorded on selected samples [NiLI,V2] in DMF are very
similar to those obtained in CH2Cl2, only for [NiLI2] the UV band
at 324 nm is much weaker than expected.
The complexes [NiLI–V2] were obtained as violet or greenish-
blue microcrystals. Dissolving these crystals in CH2Cl2 leads to
greenish-blue solutions, while DMF solutions are dark green. The
UV-Vis absorption spectra of [NiLII–V2] in CH2Cl2 and DMF are
very similar (Table 3). In the UV region two intense bands are
discernible, one lying invariantly at 227 nm, the other around
305 nm. For [NiLI2] very similar absorption bands were observed;
however, their energies (267 nm and 320 nm) deviate markedly
from those of the other derivatives [NiLII–V2]. Furthermore, for
the complexes [NiLII–V2] the band at about 305 nm tails down to
about 400 nm, showing one or two further shoulders. They are
absent for [NiLI2]. Absorption bands for the free and protonated
ligands RC(S)NHP(X)(OiPr)2 (X = O, S) are rather high in
The assumption that the complexes [NiLII–V2] are exclusively
1,3-N,S configured, while solutions of [NiLI2] contain both 1,3-
N,S as well as 1,5-S,S¢ isomers are strongly supported by the
absorption spectrum of the recently reported R = H derivative
[NiL0 ] (HL0 = H2NC(S)NHP(S)(OiPr)2) (Table 3). Crystals of the
2
1,5-S,S¢-coordinated compound were dissolved in CH2Cl2 and
the absorption spectrum showed two intense bands at 248 nm
(e = 32894 M-1 cm-1) and 261 nm (sh, 18301 M-1 cm-1) in the UV
region, as well as two bands at 533 nm (268 M-1 cm-1) and 669
nm (228 M-1 cm-1) accompanied by a shoulder at 446 nm (1623
M-1 cm-1). Although the overall spectra features are very similar,
the marked differences, e.g. for the two observable d–d bands,
make us confident that the HL0 derivative represents an exclusive
abs
energy (lmax < 250 nm) while the absorption bands of KLI–V
were observed in the range 291–304 nm (e = 179–195 M-1 cm-1)
and have been assigned to intraligand transitions.39 Thus, the
Table 3 Selected UV-Vis absorption data for nickel complexesa
Compound
l1 (e)
l2 (e)
Solvent
[NiLI2]
267 (20660)
232sh (40050)
225 (34580)
227 (37870)
227 (51730)
248 (32890)
241 (15100)
275 (20290)
320 (21670)
310 (43640)
305 (32510)
305 (21460)
294 (33420)
261sh (18300)
302 (24570)
284sh (2780)
296 (17980)
541 (190)
524 (178)
513 (117)
509 (93)
519 (103)
533 (268)
478 (100)
545 (146)
552 (111)
671 (202)
435 (95)
640 (180)
638 (150)
640 (91)
641 (68)
639 (88)
669 (228)
613 (62)
640 (158)
634 (113)
724 (277)
518 (33)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMF
[NiLII
]
337sh (24090)
332sh (14560)
334sh (9670)
325sh (12110)
2
[NiLIII
[NiLIV
[NiLV
]
2
2
]
]
380sh (4320)
412sh (1390)
2
[NiL0 ] b
2
[NiZI2]
335sh (7440)
324 (2240)
339sh (8570)
[NiLI2]
[NiLV
]
—
—
DMF
Acetone
DMF
c
2
[NiL0 ] b
—
796 (158)
639 (12)
c
c
2
[NiZI2]
—
288 (39240)
785 (14)
c
a Absorption maxima l in nm and extinction coefficients e in M-1 cm-1. b From ref. 22, (HL0 = H2NC(S)NHP(S)(OiPr)2). c Obscured by solvent absorption.
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1,5-S,S¢ configuration also in solution. Further support comes
from the absorption spectroscopy of the complex [NiZI2] having
an established 1,3-N,S conformation, which is very similar to those
of the complexes [NiLII–V2]. The presence of the two isomers (in
variable ratios) might also explain the discrepancy of our data for
[NiLI2] with previous work.20
In contrast to the behaviour of the thiophosphoryl (P S)
complexes [NiLI–V2], solutions of the phosphoryl (P O) derivative
[NiZI2] in CH2Cl2 or DMF differ markedly in colour. Dissolving
the blue crystals of [NiZI2] in CH2Cl2 leads to a violet solution.
The spectrum of [NiZI2] in CH2Cl2 exhibits two intense bands
with maxima at 241 and 302 nm, and a less intense shoulder at
335 nm (Fig. 9). Besides, there are two weak bands at 478 and
613 nm. The assignment of all these bands is identical to the
spectra of the complexes [NiLI–V2]. The comparison of the spectra
obtained for the thiophosphoryl (P S) derivatives with those of
the phosphoryl (P O) complex reveals only slight variations in
energy for the strong UV-absorption (especially the 302 nm band),
while both lowest d–d bands lie markedly higher in energy (478
and 613 nm) in line with a stronger ligand field.
(277 M-1 cm-1) and 796 (158 M-1 cm-1) nm. We assign this band
3
to the 3T1(F) → T1(P) transition of this tetrahedrally configured
complex.22
It is noteworthy that the absorption spectra of the complexes
exhibit weak and insignificant temperature (5–35 ◦C) and concen-
tration (10-4–10-3 M) dependences both in CH2Cl2 and DMF.
The electrochemistry of the complexes [NiLI–V2] was measured in
comparison with the complex [NiZI2] using cyclic voltammetry. At
a first glance, the cyclic voltammograms of the complexes [NiLI–V
]
2
are quite similar, regardless of the solvent (CH2Cl2 vs. DMF)
(Fig. 11, Table 4). An initial reversible one-electron reduction at
around -1.5 V is followed by a number of further irreversible
reduction steps. The potentials for the first reduction are more or
less independent from the solvent and also essentially the same for
[NiLI–IV2] while the potentials for [NiLV2] are markedly increased.
A closer inspection of Fig. 11 reveals that the cathodic wave is
somewhat broadened in CH2Cl2 compared to the measurements in
DMF while the corresponding anodic wave exhibits the expected
shape for an unhindered electron transfer. On the oxidative side
several irreversible waves were observed, revealing a marked
dependence on the solvent. The first oxidation wave occurs at
around +0.7 V in CH2Cl2 solution (Ox1) followed by a second at
around +1.1 V (Ox2). Measurements in DMF reveal oxidation
processes having very similar potentials (Ox3), however at far
lower potentials at around -0.1 V (Ox1). At around 0.4 V (Ox2)
there are seemingly additional oxidation waves. The situation is
additionally complicated by the fact that some of these anodic
waves appear only after cathodic pre-treatment (see Table 4).
Unfortunately, the irreversible nature of all the oxidation processes
precludes the quantitative comparison of potentials within the
series of complexes. The complex [NiZI2] behaves very differently;
Fig. 9 UV-Vis absorption spectrum of [NiZI2] in CH2Cl2.
DMF solutions of [NiZI2] are orange in colour, and the UV-
Vis spectrum (Fig. 10) is characterised by an intense band in the
UV at 288 nm assigned to an intraligand transition and several
weak bands in the range 400–800 nm (Fig. 10). A closer inspection
reveals an absorption maximum with the long-wavelength band at
785 nm (e 15 M-1 cm-1). The number of bands and the extremely
low intensity is a strong indication for octahedral NiII species, while
thed–dbands ofcomplexes with tetrahedralgeometryusually have
higher e values.42,43 The octahedral geometry of the complex [NiZI2]
in DMF is again supported by comparison with the electronic
absorption spectrum of [NiL0 ] in acetone, which is characterised
2
by a broad band with three maximum at 671 (202 M-1 cm-1), 724
Fig. 11 Cyclic voltammograms of [NiLII2] in nBu4NPF6/CH2Cl2 (top) or
nBu4NPF6/DMF (bottom) solution at ambient temperature; potentials
vs. ferrocene/ferrocenium.
Fig. 10 UV-Vis absorption spectrum of [NiZI2] in DMF.
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Table 4 Selected electrochemical data for nickel complexesa
Compound
Epa (Ox3)
Epa (Ox2)
Epa (Ox1)
Epa (Red1)
Epc (Red1)
E1/2 (Red1) (DEpp
)
Solvent
[NiLI2]
1.02
1.05
1.18
1.22
1.17
1.21
0.39
0.45
0.32d
0.34d
0.40
0.18
0.74
0.65
0.70
0.71
0.78
0.77
-1.33
-1.45
-1.47
-1.50
-1.49
—
-1.27
-1.32
-1.38
-1.40
-1.41
—
-1.42
-1.57
-1.58
-1.61
-1.60
-2.08
-1.34
-1.40
-1.46
-1.48
-1.48
-1.96
-1.38 (100)
-1.51 (115)
-1.53 (105)
-1.56 (110)
-1.55 (112)
—
-1.31 (71)
-1.36 (77)
-1.42 (81)
-1.44 (75)
-1.44 (72)
—
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMF
DMF
DMF
DMF
DMF
[NiLII
]
2
[NiLIII
[NiLIV
[NiLV
]
2
]
2
]
2
[NiZI2]
[NiLI2]
0.64
0.66
0.76
0.74
0.78
-0.07b
-0.06
-0.05b
-0.07b
-0.14c
-0.13b
[NiLII
]
2
2
[NiLIII
[NiLIV
[NiLV
]
]
2
]
2
[NiZI2]
—
DMF
e
a From cyclic voltammetry in 0.1 M nBu4NPF6/solvent solutions at 100 mV s-1 scan rate. Potentials in V vs. FeCp2+/0. Half-wave potentials E1/2 for
reversible processes, peak potential differences DEpp = Epa – Epc in mV in parentheses (the value for ferrocene was 68 mV), cathodic peak potentials Epc
and anodic peak potentials Epa.
b Smaller than Ox2 and Ox3; gets larger on reverse scan out of the cathodic range. c Appears only on reverse scan out of
the cathodic range. d Smaller than Ox3; gets larger on reverse scan out of the cathodic range. e Not detected.
both oxidation and reduction waves are completely irreversible.
Conclusions
While the two oxidation potentials lie in the same range as the
complexes of the S,S¢ ligands (LI–IV2)- the first reduction potential
of the complex containing the O,S-bound ligand (ZI)- lies beyond
-2 V (Table 4).
In
summary,
the
N-thiophosphorylated
thioureas
RNHC(S)NHP(S)(OiPr)2 (R
=
2-MeC6H4–, 2,4-Me2C6H3–,
2,4,6-Me3C6H2–, Me–), and their NiII complexes have been
synthesised. The complexes [NiLII–IV2] are the first examples of NiII
containing asymmetric RC(S)NHP(S)R¢2 ligands coordinating the
metal in a 1,3-N,S fashion in the crystal, while for the derivatives
Since such complexes were investigated for the first time, we
can only speculate on the origin of the observed electrochemical
phenomena. The marked differences between the complexes
[NiLI–V2] and [NiZI2] and also the trend of facilitated reduction
[NiLV2] and [NiL0 ] 1,5-S,S¢ coordination has been found.
2
DFT-based calculations show that the [Ni(LII–IV-N,S)2] isomers
are more stable (by 16–21 kcal mol-1) than the corresponding
[Ni(LII–IV-S,S¢)2] conformers. We believe that the main reason of
along the series [NiLI2] > [NiLII2] > [NiLIII2] > [NiLIV2] = [NiLV
]
2
makes a ligand-centred initial reduction quite plausible. The strong
solvent dependence on the oxidation might be interpreted in terms
of different isomers being (potentially) present (or produced)
in solutions of differing polarity. Although from NMR and
absorption spectroscopy there is no evidence for other isomers
than the 1,3-N,S coordinated forms, DMF might facilitate the
conversion to other isomers by interacting with (and weakening
of) the H bridges. If such an isomer exhibits a lower oxidation
potential than the 1,3-N,S form, it might be (electro-catalytically)
formed during the oxidation process, provided that the conversion
is fast enough. The latter might be the reason for the different be-
haviour in DMF vs. CH2Cl2 solutions. Such an electron-transfer-
catalysed isomerisation44 could explain the puzzling oxidative
electrochemistry. Given this, the oxidation is attributed also to
a ligand-centred process, since the observed vast difference in
oxidation potentials by 0.7 to 0.8 V for the assumed isomers is too
large to be attributed to a nickel-centred oxidation NiII/NiIII. For
the higher stability of the [Ni(LII–IV-N,S)2] isomers vs. [Ni(LII–IV
-
P
S,S¢)2] lies in the formation of intramolecular N–H ◊ ◊ ◊ S
hydrogen bonds. The deformation density maps revealed the
presence of such an interaction, which includes the transfer of
electron density from the lone electron pair of the S atom into
the empty s*(N–H) orbital and from the occupied N–H orbital
into a bonding H ◊ ◊ ◊ S region and the vicinity of the sulfur
atom. This latter shift is strengthened alongside with increasing
electron-donating capacity of the R group (o-Tol < Xyl < Mes).
Thus, the previously reported crystal structures of the deriva-
tives containing R = H, Me or Ph, showing the complex units in a
1,5-S,S¢ conformation, probably do not represent the most stable
isomeric forms but were obtained due to superior crystallisation
properties of the 1,5-S,S¢ form over the 1,3-N,S isomers. The
thermodynamic stability of the 1,3-N,S coordination of the
investigated complexes is also evident from their behaviour in
solution. Only for the complex [NiLI2] evidence for the 1,5-
S,S¢ coordination was found in 1H and 31P NMR spectra (as
a minor species along with the 1,3-N,S isomer) and UV-Vis
spectra. In contrast to this, in solutions of the methyl-substituted
derivative [NiLV2], which crystallises in the 1,5-S,S¢ isomeric form,
spectroscopic evidence (NMR, UV-Vis) for only the 1,3-N,S
isomer is found. Electrochemical measurements in the rather non-
polar solvent CH2Cl2 reveal the electronic properties only for the
1,3-N,S coordinated state, while measurements in DMF solution
give evidence for other isomers, formed upon electron-transfer-
catalysed conversion during electrochemical oxidation. From the
combination of absorption spectroscopy and electrochemistry the
comparison, in the absorption spectra of the two complexes [NiL0 ]
2
and [NiLV2] the change from 1,3-N,S (HLV; R = Me) to 1,5-S,S¢
(HL0; R = H) coordination is paralleled by a decrease in absorption
energy by about 700 cm-1 or 0.1 eV. The assumption of a ligand-
based oxidation is also in line with the absorption spectroscopy,
which gave no evidence for a metal-to-ligand or ligand-to-metal
charge transfer. Instead, rather low-energy intraligand transitions
were observed alongside with low-lying d–d transitions. Detailed
electrochemical (low temperatures) and spectroelectrochemical
(stability and spectroscopy of the reduced and oxidised states)
experiments, combined with quantum-chemical calculations (TD-
DFT) should allow a more profound assignment of the redox
behaviour. Such experiments are on our agenda for the near future.
3150 | Dalton Trans., 2011, 40, 3142–3153
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3
3
frontier orbitals of these complexes were preliminarily assigned
both to be ligand-centred. Support for this assignment comes
also from comparison with the phosphoryl derivative [NiZI2]. This
assignment will be further investigated in the future.
4.89 (d. sept, JPOCH = 10.6 Hz, JH,H = 6.2 Hz, 2H, OCH, iPr),
6.99–7.65 (m, overlapping with the solvent signal, C6H3 + PNH),
9.36 (s, 1H, NH) ppm. 31P NMR (CDCl3): d = 52.7 (q, JPOCH
=
3
10.5 Hz, 2JPNH = 9.3 Hz) ppm. Calc. for C14H23N2O2PS2 (346.44):
C, 48.54; H, 6.69; N, 8.09. Found: C, 48.46; H, 6.74; N, 8.05%.
Experimental
HLIII. Yield: 1.73 g (96%). M.p. 149 ◦C. 1H NMR (CDCl3): d =
1.41 (d, 3JH,H = 6.2 Hz, 6H, CH3, iPr), 1.45 (d, 3JH,H = 6.2 Hz, 6H,
CH3, iPr), 2.33 (s, 6H, CH3, Me), 4.92 (d. sept, 3JPOCH = 10.4 Hz,
3JH,H = 6.2 Hz, 2H, OCH, iPr), 7.07–7.38 (m, overlapping with the
solvent signal, C6H3 + PNH), 9.32 (s, 1H, NH) ppm. 31P NMR
(CDCl3): d = 52.8 (q, 3JPOCH = 10.4 Hz, 2JPNH = 9.2 Hz) ppm. Calc.
for C15H25N2O2PS2 (360.47): C, 49.98; H, 6.99; N, 7.77. Found: C,
49.82; H, 7.06; N, 7.69%.
General procedures
NMR spectra were obtained on a Bruker Avance 300 MHz
◦
spectrometer at 25 C. H and 31P NMR spectra were recorded
at 299.948, and 121.420 MHz, respectively. Chemical shifts are
reported with reference to SiMe4 (1H) and 85% H3PO4 (31P).
Elemental analyses were performed on a CHNS HEKAtech
EuroEA 3000 analyzer. UV-Vis/NIR absorption spectra in 10-4–
10-3 M solutions in CH2Cl2 or DMF were recorded on Varian
Cary 05E or Cary50 Scan spectrophotometers at 5–35 ◦C. Cyclic
voltammetry was carried out at 100 mV s-1 scan rate in 0.1 M
nBu4NPF6 solutions using a three-electrode configuration (glassy
carbon electrode, Pt counter electrode, Ag/AgCl reference) and
a Autolab PG STAT 30 potentiostat and function generator. The
ferrocene/ferrocenium couple served as internal standard.
1
◦
1
HLIV. Yield: 1.58 g (84%). M.p. 130 C. H NMR (CDCl3):
d = 1.38 (d, 3JH,H = 6.1 Hz, 6H, CH3, iPr), 1.42 (d, 3JH,H = 6.3 Hz,
6H, CH3, iPr), 2.27 (s, 6H, CH3, Me), 2.30 (s, 3H, CH3, Me), 4.892
(d. sept, 3JPOCH = 10.4 Hz, 3JH,H = 6.1 Hz, 2H, OCH, iPr), 6.94 (s,
2H, C6H2), 7.30 (d, 2JPNH = 8.8 Hz, 1H, PNH), 9.22 (s, 1H, NH)
3
2
ppm. 31P NMR (CDCl3): d = 52.9 (q, JPOCH = 10.2 Hz, JPNH
=
9.0 Hz) ppm. Calc. for C16H27N2O2PS2 (374.50): C, 51.32; H, 7.27;
N, 7.48. Found: C, 51.23; H, 7.15; N, 7.52%.
Synthesis of HLI, HLV, HZI, [NiLI2] and [NiZI2]
Synthesis of [NiLII–V
]
The N-(thio)phosphorylated thioureas HLI,25,26 HLV,27 HZI,12,28,29
and the complexes [NiLI2]20 and [NiZI2]12 were prepared as
described previously.
2
A suspension of HLII–V (3 mmol, 1.04, 1.08, 1.13 or 0.81 g) in
aqueous EtOH (10 mL) was mixed with an aqueous EtOH solution
of KOH (3.3 mmol, 0.18 g). An aqueous EtOH (10 mL) solution
of NiCl2 (1.9 mmol, 0.25 g) was added dropwise with vigorous
stirring to the resulting potassium salt. The mixture was stirred
at room temperature for a further 3 h and left overnight. The
resulting complex was extracted with CH2Cl2, washed with water
and dried with anhydrous MgSO4. The solvent was then removed
in vacuo. Violet [NiLII–IV2] or greenish-blue [NiLV2] crystals were
isolated by recrystallisation from a 1 : 5 mixture of CH2Cl2 and
n-hexane.
[NiLI2]. 1H NMR (CDCl3): d = 1.20–1.84 (m, 24H, CH3, iPr),
4.68 and 4.98 (br. s, 4H, OCH, iPr), 6.95–7.64 (m, overlapping
1
with the solvent signal, C6H5), 11.12 (br. s, 2H, NH) ppm. H
NMR (DMF-d7): d = 1.41 (d, 3JH,H = 6.1 Hz, 12H, CH3, iPr), 1.51
(d, 3JH,H = 6.1 Hz, 12H, CH3, iPr), 5.07 (d. sept, 3JPOCH = 10.3 Hz,
3JH,H = 6.0 Hz, 4H, OCH, iPr), 7.07 (t, 3JH,H = 7.3 Hz, 2H, p-C6H5),
7.34 (t, 3JH,H = 7.8 Hz, 4H, m-C6H5), 7.66 (d, 3JH,H = 7.9 Hz, 4H,
4
o-C6H5), 10.18 (d, JPNCNH = 6.7 Hz, 2H, NH) ppm. 31P NMR
(CDCl3): d = 49.1–52.1 (m, 3P), 52.9 (br. s, 1P) ppm. 31P NMR
(DMF-d7): d = 48.5 (br. s) ppm.
[NiLII2]. Yield: 1.02 g (91%). M.p. 96 ◦C. 1H NMR (CDCl3):
d = 1.19–1.84 (m, 24H, CH3, iPr), 2.17–2.41 (m, 6H, CH3, Me),
4.53–5.12 (m, 4H, OCH, iPr), 6.91–7.83 (m, 6H, C6H3), 10.67 (br.
s, 2H, NH) ppm. 1H NMR (DMF-d7): d = 1.42 (d, 3JH,H = 6.1 Hz,
12H, CH3, iPr), 1.45 (d, 3JH,H = 6.1 Hz, 12H, CH3, iPr), 2.35 (s, 6H,
CH3, Me), 4.96 (br. s, 4H, OCH, iPr), 7.14–7.45 (m, 6H, C6H3),
9.73 (d, 4JPNCNH = 7.8 Hz, 2H, NH) ppm. 31P NMR (CDCl3): d =
53.7 (br. s) ppm. 31P NMR (DMF-d7): d = 47.8 (br. s) ppm. Calc.
for C28H44N4NiO4P2S4 (749.56): C, 44.87; H, 5.92; N, 7.47. Found:
C, 45.03; H, 5.86; N, 7.50%.
3
[NiZI2]. 1H NMR (CDCl3): d = 1.37 (t, JH,H = 6.2 Hz, 12H,
3
CH3, iPr), 1.66 (t, JH,H = 6.1 Hz, 12H, CH3, iPr), 4.65 (d. sept,
3JPOCH = 7.4 Hz, 3JH,H = 6.2 Hz, 4H, OCH, iPr), 7.15–7.23 (m, 2H,
p-C6H5), 7.30–7.38 (m, 4H, m-C6H5), 7.39–7.45 (m, 4H, o-C6H5),
1
10.56 (s, 2H, NH) ppm. H NMR (DMF-d7): d = 1.01–2.58 (m,
24H, CH3, iPr), 4.79 (br. s, 2H, NH), 5.31 (br. s, 4H, OCH, iPr),
6.91–7.94 (m, 6H, p-C6H5 + m-C6H5), 8.64 (br. s, 4H, o-C6H5)
3
ppm. 31P NMR (CDCl3): d = 1.3 (t, JPOCH = 7.4 Hz) ppm. 31P
NMR (DMF-d7): no signals.
Synthesis of HLII–IV
[NiLIII2]. Yield: 0.98 g (84%). M.p. 106 ◦C. 1H NMR (CDCl3):
d = 1.29 (d, 3JH,H = 5.9 Hz, 12H, CH3, iPr), 1.73 (d, 3JH,H = 6.1 Hz,
12H, CH3, iPr), 2.32 (s, 12H, CH3, Me), 4.59–4.79 (m, 4H, OCH,
iPr), 6.96–7.24 (m, 6H, C6H3), 10.41 (s, 2H, NH) ppm. 1H NMR
A solution of 2-methylaniline, 2,6-dimethylaniline or 2,4,6-
trimethylaniline (5 mmol, 0.54, 0.61 or 0.68 g) in anhydrous
CH2Cl2 (15 mL) was treated with vigorous stirring with a solution
of (iPrO)2P(S)NCS (6 mmol, 1.43 g) in the same solvent. The
mixture was stirred for 1 h. The solvent was removed in a vacuum,
and the product was purified by recrystallisation from a 1 : 5 (v/v)
mixture of CH2Cl2 and n-hexane.
3
(DMF-d7): d = 1.35 (d, JH,H = 6.0 Hz, 12H, CH3, iPr), 1.39 (d,
3JH,H = 6.2 Hz, 12H, CH3, iPr), 2.27 (s, 12H, CH3, Me), 4.88 (d.
3
3
sept, JPOCH = 10.2 Hz, JH,H = 6.2 Hz, 4H, OCH, iPr), 7.11–7.27
(m, 6H, C6H3), 9.53 (d, 4JPNCNH = 8.1 Hz, 2H, NH) ppm. 31P NMR
(CDCl3): d = 54.2 (br. s) ppm. 31P NMR (DMF-d7): d = 47.5 (br.
s) ppm. Calc. for C30H48N4NiO4P2S4 (777.61): C, 46.34; H, 6.22;
N, 7.20. Found: C, 46.52; H, 6.17; N, 7.26%.
HLII. Yield: 1.59 g (92%). M.p. 86 ◦C. 1H NMR (CDCl3): d =
3
1.40 (t, JH,H = 6.1 Hz, 12H, CH3, iPr), 2.33 (s, 3H, CH3, Me),
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Dalton Trans., 2011, 40, 3142–3153 | 3151
©

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[NiLIV2]. Yield: 0.96 g (79%). M.p. 93 ◦C. 1H NMR (CDCl3):
d = 1.28 (s, 12H, CH3, iPr), 1.71 (s, 12H, CH3, iPr), 2.26 (br. s,
18H, CH3, Me), 4.42–5.01 (m, 4H, OCH, iPr), 6.89 (br. s, 4H,
C6H2), 10.21 (s, 2H, NH) ppm. 1H NMR (DMF-d7): d = 1.35 (d,
3JH,H = 6.2 Hz, 12H, CH3, iPr), 1.39 (d, 3JH,H = 6.2 Hz, 12H, CH3,
iPr), 2.12–2.46 (m, 18H, CH3, Me), 4.89 (d. sept, 3JPOCH = 10.2 Hz,
3JH,H = 6.1 Hz, 4H, OCH, iPr), 6.85–7.07 (m, 4H, C6H2), 9.43
(d, 4JPNCNH = 7.9 Hz, 2H, NH) ppm. 31P NMR (CDCl3): d = 54.3
(br. s) ppm. 31P NMR (DMF-d7): d = 47.9 (br. s) ppm. Calc. for
C32H52N4NiO4P2S4 (805.67): C, 47.71; H, 6.51; N, 6.95. Found: C,
47.99; H, 6.46; N, 7.01%.
Crystal data for HLIV. C16H27N2O2PS2, Mr = 374.49 g mol-1,
¯
triclinic, space group P1, a = 9.6196(9), b = 10.0482(8)◦, c =
˚
10.6353(10) A, a = 82.561(7), b = 88.528(7), g = 75.021(7) , V =
3
-3
-1
˚
984.68(15) A , Z = 2, r = 1.263 g cm , m(Mo-Ka) = 0.361 mm ,
reflections: 9742 collected, 3666 unique, Rint = 0.041, R1(all) =
0.0388, wR2(all) = 0.0841.
Crystal data for HLV. C8H19N2O2PS2, Mr = 270.34 g mol-1,
¯
triclinic, space group P1, a = 7.4084(7), b = 9.7510(8), c = 10.2595(9)
◦
3
˚
˚
A, a = 80.832(7), b = 76.351(7), g = 70.632(7) , V = 676.79(10) A ,
Z = 2, r = 1.327 g cm-3, m(Mo-Ka) = 0.497 mm-1, reflections: 5904
collected, 2507 unique, Rint = 0.0311, R1(all) = 0.0311, wR2(all) =
0.0776.
[NiLV2]. Yield: 0.79 g (88%). M.p. 124 ◦C. 1H NMR (CDCl3):
d = 1.31 (d, 3JH,H = 6.0 Hz, 12H, CH3, iPr), 1.66 (d, 3JH,H = 6.0 Hz,
12H, CH3, iPr), 2.83 (d, 3JH,H = 4.8 Hz, 6H, CH3, Me), 4.61 (d. sept,
Crystal data for [NiL2II]. C28H44N4NiO4P2S4, Mr = 749.56 g
-1
¯
mol , triclinic, space group P1, a = 8.3222(8), b = 9.3599(10), c =
3
3JPOCH = 10.6 Hz, JH,H = 6.0 Hz, 4H, OCH, iPr), 9.00 (br. s, 2H,
◦
˚
12.9907(13) A, a = 103.075(8), b = 105.168(8), g = 106.810(8) , V =
NH) ppm. 1H NMR (DMF-d7): d = 1.46 (d, 3JH,H = 6.0 Hz, 12H,
CH3, iPr), 1.55 (d, 3JH,H = 6.2 Hz, 12H, CH3, iPr), 2.98 (overlapping
with the solvent signal, CH3, Me), 4.98 (d. sept, 3JPOCH = 9.7 Hz,
3
-3
-1
˚
883.60(15) A , Z = 1, r = 1.409 g cm , m(Mo-Ka) = 0.914 mm ,
reflections: 7372 collected, 3270 unique, Rint = 0.0489, R1(all) =
0.0415, wR2(all) = 0.0992.
3JH,H = 6.2 Hz, 4H, OCH, iPr), 7.92–8.06 (m, 2H, NH) ppm. 31
P
NMR (CDCl3): d = 54.2 (t, JPOCH = 10.1 Hz) ppm. 31P NMR
(DMF-d7): d = 44.8 (br. s) ppm. Calc. for C16H36N4NiO4P2S4
(597.36): C, 32.17; H, 6.07; N, 9.38. Found: C, 32.28; H, 6.01;
N, 9.43%.
3
III 13
Crystal data for [NiL2
] . C30H48N4NiO4P2S4, Mr = 771.61 g
-1
¯
mol , triclinic, space group P1, a = 10.3417(10), b = 10.4409(1◦0), c =
˚
10.6637(10) A, a = 116.961(7), b = 92.299(8), g = 106.498(8) , V =
3
-3
-1
˚
964.63(16) A , Z = 1, r = 1.339 g cm , m(Mo-Ka) = 0.840 mm ,
reflections: 9493 collected, 3597 unique, Rint = 0.043, R1(all) =
0.0514, wR2(all) = 0.0966.
DFT calculations
Crystal data for [NiL2IV]. C32H52N4NiO4P2S4, Mr = 805.67 g
We have applied in DFT-based geometry optimizations the hybrid
exchange–correlation functional B3LYP45 and the LanL2DZ basis
set by Wadt and Hay,46 as implemented in the Gaussian 09
package.32 Deformation density map as well as deformation
density contributions of the ETS-NOCV method were plotted
based on an ADF-GUI interface.47
-1
¯
mol , triclinic, space group P1, a = 9.2223(5), b = 10.4480(6), c =
◦
˚
˚
11.6919(7) A, a = 97.788(5), b = 102.023(5), g = 111.808(4) , V =
3
-3
-1
994.49(10) A , Z = 1, r = 1.345 g cm , m(Mo-Ka) = 0.817 mm ,
reflections: 15144 collected, 4039 unique, Rint = 0.0537, R1(all) =
0.0399, wR2(all) = 0.0888.
Crystal data for [NiL2V]. C16H36N4NiO4P2S4, Mr = 587.38 g
mol , triclinic, space group P1, a = 8.7500(17), b = 8.8100(18),
X-Ray crystallography
-1
¯
◦
˚
c = 9.6200(19) A, a = 93.60(3), b = 90.68(3), g = 111.40(3) , V =
The X-ray data were collected on a STOE IPDS-II diffractometer
with graphite-monochromatised Mo-Ka radiation generated by
a fine-focus X-ray tube operated at 50 kV and 40 mA. The
reflections of the images were indexed, integrated and scaled using
the X-Area data reduction package.48 Data were corrected for
absorption using the PLATON program.49 The structures were
solved by direct methods using the SHELXS-97 program50 and
refined first isotropically and then anisotropically using SHELXL-
97.50 Hydrogen atoms were revealed from Dr maps and those
bonded to C were refined using appropriate riding models. H
atoms bonded to N were freely refined. Figures were generated
using the program Mercury.51
3
-3
-1
˚
688.6(2) A , Z = 1, r = 1.441 g cm , m(Mo-Ka) = 1.152 mm ,
reflections: 7919 collected, 2564 unique, Rint = 0.0478, R1(all) =
0.0367, wR2(all) = 0.0722.
CCDC 736205 (HLII), 721784 (HLIII), 736206 (HLIV), 736207
(HLV), 736208 ([NiLII2]), 721785 ([NiLIII2]), 736209 ([NiLIV2])
and 736210 ([NiLV2]) contain the supplementary crystallographic
data.†
Acknowledgements
Mariusz Mitoraj greatly acknowledges the financial supports from
the Foundation for Polish Science (“START” scholarship) as
well as from Polish Ministry of Science and Higher Education
(“Outstanding Young Researchers” scholarship). We are grateful
to ACK CYFRONET - Krakow and to the Laboratory of Parallel
Computing of the Institute of Computer Science AGH for the
computer time.
Crystal data for HLII. C14H23N2O2PS2, Mr = 346.43 g mol-1,
monoclinic, space group P21/n, a = 9.9075(7), b = 15.1449(7), c =
◦
3
˚
˚
12.9257(8) A, b = 111.187(5) , V = 1808.38(19) A , Z = 4, r = 1.272
g cm-3, m(Mo-Ka) = 0.388 mm-1, reflections: 9964 collected, 3372
unique, Rint = 0.0455, R1(all) = 0.0434, wR2(all) = 0.0871.
Crystal data for HLIII
.
C15H25N2O2PS2, Mr = 360.46 g mol-1,
13
¯
triclinic, space group P1, a = 10.1225(6), b = 10.4047(7◦), c =
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