Solid-state and Computational Study of “Venus fly-trap” Geometric Parameters for 1,5-Cyclooctadiene in PdII and PtII β-Enaminonato Complexes

Article abstract of DOI:10.1002/zaac.201800097

The cod ligand (cis,cis-1,5-cyclooctadiene) can be superficially considered to mimic similarities in spatial behavior of a leaf of the Venus fly-trap (Dionaea muscipula). Thus, the synthesis of an unsymmetrical bidentate trans ligand (N,O-donor atoms) based on the β-enaminonate backbone is introduced to evaluate the electronic and steric influence on the structural behavior of the cod ligand when coordinated to a square planar transition metal. A range of platinum(II) / palladium(II) complexes of the type [M(cod)(N,O-Bid)]A (M = Pt^II, Pd^II; β-enaminonato ligand (N,O-Bid) = NH-acac, NMe-acac, NPh-acac; A = BF₄^–, PF₆^–) is reported. The complexes were fully characterized, including by detailed X-ray structural investigations. Theoretical calculations on the [M(cod)(N,O-Bid)]⁺ complexes for the complete nickel triad are also described and the structural behavior of the cod ligand critically evaluated. The influence of the variation of the β-enaminonato ligands on the coordination arrangement of the cod was investigated and found that no significant changes to the M–C and C=C bond lengths were observed. The Venus fly-trap jaw angle (ψ), however, varies by ca. 8° and the twist angle (τ) by ca. 10°, whereas the cod bite angle (χ), as well as the β-enaminonato ligand bite angle (N–M–O; θ) both remain virtually constant. Calculated spectroscopic tendencies within the Ni-triad are also included.

Full text of DOI:10.1002/zaac.201800097

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201800097
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Solid-state and Computational Study of “Venus fly-trap”
Geometric Parameters for 1,5-Cyclooctadiene in PdII and PtII
β-Enaminonato Complexes
Tania N. Hill[a] and Andreas Roodt*[a]
Dedicated to Prof Peter Comba on the Occasion of his 65th Birthday
Abstract. The cod ligand (cis,cis-1,5-cyclooctadiene) can be super- cal calculations on the [M(cod)(N,O-Bid)]+ complexes for the complete
ficially considered to mimic similarities in spatial behavior of a leaf nickel triad are also described and the structural behavior of the cod
of the Venus fly-trap (Dionaea muscipula). Thus, the synthesis of an ligand critically evaluated. The influence of the variation of the β-
unsymmetrical bidentate trans ligand (N,O-donor atoms) based on the
β-enaminonate backbone is introduced to evaluate the electronic and investigated and found that no significant changes to the M–C and
steric influence on the structural behavior of the cod ligand when coor- C=C bond lengths were observed. The Venus fly-trap jaw angle (ψ),
enaminonato ligands on the coordination arrangement of the cod was
dinated to a square planar transition metal. A range of platinum(II) / however, varies by ca. 8° and the twist angle (τ) by ca. 10°, whereas
palladium(II) complexes of the type [M(cod)(N,O-Bid)]A (M = PtII, the cod bite angle (χ), as well as the β-enaminonato ligand bite angle
PdII; β-enaminonato ligand (N,O-Bid) = NH-acac, NMe-acac, NPh-
acac; A = BF4 , PF6 ) is reported. The complexes were fully charac-
(N–M–O; θ) both remain virtually constant. Calculated spectroscopic
tendencies within the Ni-triad are also included.
–
–
terized, including by detailed X-ray structural investigations. Theoreti-
when one observes a 3D diagram of cyclooctadiene coordi-
nated to a transition metal it is clearly possible to visualize the
structure of the leaf of the Venus fly-trap plant, mimicking the
configuration of the cod.
Three parameters to describe the behavior of the cod ligand
as a “leaf” of the Venus fly-trap can thus be loosely defined,
namely the ψ or cod jaw angle, the χ or cod bite angle and the
twist angle or τ, as illustrated in Figure 1.[7] A fourth parameter
utilized but not illustrated since it is not formally part of the
“leaf” is the N–M–O bite angle of the β-enaminonato ligand
(θ), trans to the cyclooctadiene.
Introduction
The compound, cis,cis-1,5-cyclooctadiene (cod) is a cyclic
diolefin, which is often utilized as a precursor ligand in organic
type reactions, serving as a weak coordinating entity in organo-
metallic chemistry.[1] It is also an important substrate in indus-
trial reactions[2] and is utilized in a variety of chemical pro-
cesses from catalysis[3] to pharmaceuticals and model diolefin
complexes.[4] In some petrochemical processes diolefins can
also act as catalyst trapping agents/ inhibitors and thus quanti-
fication of aspects which defines its coordination to transition
metals are critically important.
The two most common conformers of cod are the boat and
chair configurations, and their well-known ability of coordinat-
ing with middle to late transition metals is broadly documen-
ted,[5] generally accompanied by the formation of halido com-
plexes. Cod also forms complexes with central metal atoms
bearing O,OЈ- and N,O-bidentate ligands, although only a few
of the latter have been synthesized and characterized.
In this paper we present low-temperature crystal structures
of several platinum(II) / palladium(II) cod β-enaminonato
complexes of the type [M(cod)(N,O-Bid)]A (M = PtII, PdII;
–
–
N,O-Bid = NH-acac, NMe-acac, NPh-acac; A = BF4 , PF6 ),
wherein we carefully examine the influence of the bidentate
ligand donor atoms on the pre-defined “Venus fly-trap” param-
eters. Furthermore, we present DFT calculations on the
[M(cod)(N,O-Bid)]+ complexes for the nickel triad, to further
the understanding of the coordination model of cod down the
series, and the electronic influence that the β-enaminonato li-
gand systems have on the distortion within the cod ligand. In
this regard we additionally opted to vary the counterion of
two complexes to evaluate the possible effect thereof. We thus
critically correlate the solid-state structural behavior of the cod
as defined by the Venus fly-trap parameters as a function of
the trans β-enaminonato ligand and expand it across the com-
plete Ni-triad using computational chemistry to observe and
attempt to account for the geometric changes observed.
It however further exhibits an additional interesting aspect,
i.e., to broadly structurally “mimic” the Venus fly-trap behav-
ior (Dionaea muscipula);[6] at least the jaw movement (not the
actual eating of insect subjects!) To clarify this statement:
* PhD. A. Roodt
[a] Department of Chemistry
University of the Free State
Bloemfontein 9300, South Africa
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201800097 or from the au-
thor.
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method for synthesizing β-enaminonato ligands involves the
condensation between either ammonia or a secondary amine
and a 1,3-diketone (Scheme 1). The β-enaminoketones 1–3
were prepared in high yields (ca. 70–90%) by the condensa-
tion of acetylacetone (pentane-2,4-dione, Hacac) with the re-
spective amine.
By using a modified synthetic procedure described by
White,[33] the palladium(II) and platinum(II) complexes 4–11
were synthesized utilizing either dichloro(1,5-cyclooctadiene)
palladium(II) or dichloro(1,5-cyclooctadiene)platinum(II) dis-
solved in dichloromethane, adding a silver salt to remove the
chloride ions via filtration, then followed by an equivalent of
a β-enaminonato ligand (1–3). The mixture was filtered, and
the product was precipitated by the addition of diethyl ether
(Scheme 1). The yield deviation of the β-enaminonato com-
plexes was found to be similar to the β-diketonato com-
–
plexes,[10] in that the tetrafluoroborate (BF4 ) complexes have
a marginally lower yield than their hexafluorophosphate
–
(PF6 ) counterparts. The variation is attributed to the increase
in stability and hydrogen bonding interactions of the coordinat-
ing anion (Figure S1, Supporting Information). Additionally,
the donor atom of the coordinating ligand plays a role, as men-
tioned in the hard and soft acid and base (HSAB) theory oxy-
gen is a hard base whilst palladium(II) / platinum(II) fall into
the soft acid category. With the introduction of a nitrogen do-
nor atom replacing one of the oxygen donors, the ligand takes
Figure 1. Definition of the three angles describing the arrangement of
the cod ligand: (a) ψ, opening of the Venus fly-trap “jaw”: dihedral on soft base characteristics. All the compounds were obtained
in reasonable yields, and characterized by IR, 1H and 13C
angle between the two planes through the alkane carbon fragments of
the cyclooctadiene moiety; (b) χ, the “bite” of the Venus fly-trap: dihe-
NMR spectroscopy and crystals suitable for X-ray crystallo-
dral angle between the two olefinic moiety-metal atom planes; (c) τ,
graphic analysis were obtained by dichloromethane / diethyl
ether vapor diffusion.
the twist angle: dihedral angle between the plane through the trans
bidentate ligand and the plane through the mid-points of the alkene
carbons of cod (illustrated by pink dummy atoms).
X-ray Structural Investigations
Results and Discussion
The central palladium and platinum metal atoms of com-
plexes 4, 6–11 are bonded by the nitrogen and oxygen atoms
of the β-enaminonato ligand and π-bonded by the two alkene
Synthesis
The starting compounds were synthesized by previously re- fragments of the cod ligand, resulting in a distorted square-
ported procedures. For dichlorido(1,5-cyclooctadiene)plati- planar coordination arrangement around the transition metal
num(II),[8] a solution containing potassium tetrachloridoplatin- atom. The cationic nature of the synthesized complexes and
ate in a mixture of water and propanol with an addition of an the resulting charge was balanced by the use of either tetra-
–
–
excess of cis,cis-1,5-cyclooctadiene (cod) followed by a cata- fluoroborate (BF4 ) or hexafluorophosphate (PF6 ) ions. The
lytic amount of tin chloride was stirred for several days and ions display classic tetrahedral and octahedral arrangements
allowed to evaporate to dryness. The [Pt(cod)Cl2] was sub- with a positional disorder only found for 4 and 9, whereas
sequently extracted with dichloromethane. For [Pd(cod)Cl2],[9] the remaining counterions were well behaved. The molecular
palladium dichloride was dissolved in concentrated hydrochlo- structures of four complexes are illustrated in Figure 2, with
ric acid and diluted with ethanol; after the addition of an equiv- selected bond lengths and angles reported in Table 1.
alent of cod, the mixture was filtered and dichlorido(1,5-cyclo-
octadiene)palladium(II) was obtained. The most general 5.36)
A search of the Cambridge structural database (CSD, ver
[11]
with a six-membered metal chelate ring using plati-
Scheme 1. Simplified reaction sequence for the synthesis of compounds 1–11.
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num and palladium as the central metal yielded 679 hits; of
these 174 were for platinum and the remaining 505 hits for
palladium. The majority of the structures were based on varia-
tions of Schiff base ligands. The average distances and angles
obtained for platinum(II) were Pt–N 1.997(30) Å, Pt–O
2.006(22) Å, and N–Pt–O angles of 92.931(1.787)° whilst, for
palladium(II) Pd–N 2.006(34) Å, Pd–O 2.012(38) Å, and N–
Pd–O of 92.039(1.758)° were found. In refining the search,
incorporating cod as an additional ligand to the six membered
chelate N,O-bidentate ligand previously searched, only two
structures were found and are reported by Boyer et al.;[12] both
structures comprise of a functionalized aminophenol ligand.
The β-enaminone ligands have as yet not been structurally
characterized with neither platinum nor palladium cod com-
plexes. However, a number of O,O-Bid (including β-diketon-
ato) complexes of platinum and palladium have been re-
ported.[11] Relevant selected solid-state data for the β-enami-
nonato complexes of PdII and PtII described in this study, are
summarized in Table 1. Before discussing this in detail how-
ever, the packing modes within these compounds are briefly
considered.
Hydrogen bond interactions for 4 and 6–11 are listed in
Tables S1 and S2 (Supporting Information), whereas represen-
tative illustrations of the hydrogen bonding for 4, 7, and 8
are given in Figure S1 (Supporting Information). Hydrogen
interactions are mostly observed between the fluorido moieties
of the counterions and the complexes themselves (Figure S1a
shows a classic example of a bifurcated hydrogen, H5). Metal
chelate ring···metal chelate ring interactions were observed for
4 and 6 with distances of 3.5513(1) Å and 3.5561(1) Å, with
symmetry operators of [2–x, 1 –y, 1 –z] and [1–x, –y, 1 –z]
respectively, illustrated in Figure 3a. Similarly, for 8, a metal
chelate ring hydrogen interaction was found with the methyl
hydrogen (H12C and H12A) of the β-enaminonato ligand with
distances of 2.9147(1) Å and 3.2013(1) Å and symmetry oper-
ators of [1–x, –1/2 + y, 3/2 –z] and [1/2 –x, –y, 1/2 + z], respec-
tively (Figure 3b).
Figure 2. Anisotropic displacement parameter plots (30% probability)
of 4, 6, 8, and 10 depicting the atomic numbering scheme; only se-
lected hydrogen atoms are shown.
Table 1. Selected crystallographic bond lengths /Å and angles /° for complexes 4, 6–11.
4
6
7
8
9
10
11
M–O1
M–N1
M–C1
M–C2
M–C5
M–C6
C1–C2
C5–C6
1.998(1)
1.972(2)
2.184(2)
2.210(2)
2.219(2)
2.226(2)
1.382(3)
1.374(3)
2.009(2)
1.978(3)
2.152(3)
2.168(3)
2.183(3)
2.187(3)
1.395(5)
1.396(5)
1.995(7)
1.996(6)
2.188(5)
2.188(5)
2.143(5)
2.143(5)
1.385(15)
1.385(15)
1.984(2)
2.035(2)
2.187(3)
2.180(3)
2.178(3)
2.161(3)
1.388(4)
1.396(4)
1.972(3)
2.047(3)
2.166(3)
2.166(3)
2.192(3)
2.192(3)
1.385(8)
1.396(7)
1.989(3)
2.033(4)
2.186(5)
2.196(5)
2.184(4)
2.171(4)
1.417(6)
1.403(6)
1.99(1)
2.07(1)
2.17(2)
2.19(2)
2.09(3)
2.17(2)
1.45(3)
1.42(3)
C1–M–C2
C5–M–C6
C1–M–C6
C2–M–C5
36.66(8)
36.00(8)
82.14(7)
81.79(8)
37.7(1)
37.2(1)
82.7(1)
82.1(1)
36.9(4)
36.9(4)
82.3(2)
82.3(2)
37.06(10)
37.52(11)
81.56(11)
81.67(10)
37.1(2)
37.7(2)
37.6(1)
80.8(2)
80.7(1)
38.7(9)
38.9(8)
80.9(9)
79.6(11)
37.0(2)
i)
i)
80.97(13)
θ (O1–M–N1)
χ (cod bite)
ψ (cod jaw)
τ (twist)
91.84(6)
86.4(1)
83.8(1)
3.3(1)
91.5(1)
87.2(2)
78.6(2)
3.8(2)
91.8(3)
87.8(2)
80.7(4)
0
92.12(8)
86.35(8)
78.5(1)
10.9(2)
92.28(14)
86.3(1)
81.4(2)
0
91.7(1)
85.3(2)
78.4(2)
3.6(2)
92.6(5)
86.1(9)
75.8(13)
5.3(6)
Symmetry operator: i) [x, –y, z].
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Figure 3. Molecular diagram of (a) compound 6, illustrating metal
chelate ring interactions by dashed bonds. Symmetry operator [1–x,
–y, 1 –z]; (b) compound 8, illustrating H···metal chelate ring interac-
tions by dashed bonds. Symmetry operators [1–x, –1/2 + y, 3/2 –z],
[1/2 –x, 1 –y, 1/2 + z]. Counter ions and hydrogen atoms are omitted
for clarity.
A clustered head-to-tail packing was observed for the iso-
morphous complexes of 4 and 6, whereas the isostructural
complexes of 7 and 9 were seen to have a classic head-to-tail
packing with a clear linear delineation (see Figure 4a and b,
respectively). The H···metal chelate ring interaction is also a
primary consequence for the clustered tail-to-tail packing
found in 8 (Figure 4c).
The remaining complexes showed head-to-tail packings: for
10 a zigzag in the overlying structure is observed, whereas 11
showed a more random arrangement viewed along the b axis
(Figure 4d and e). Naturally, the significant steric contribution
from the phenyl ring on the NPh-acac ligand is presumably
responsible for this latter packing mode (Figure 4e).
The solid-state data for the β-enaminonato complexes of
PdII and PtII agree well with each other, as manifested in the
general bonds and angles within the N,O-Bid ligand yielding
very similar bond lengths therein, as well as similar bonding
modes as defined by the O–M–N bite angles (θ) of around
91.5–92.6° (see Table 1). The influence of both the metal che-
late ring and the H···metal chelate ring interactions along with
the hydrogen bonding interactions of the counterions do not
significantly affect the Venus fly-trap angles. A minor increase
in the M–N bond lengths was observed as the electron donating
ability of the ligands was increased. As for M–O, C=C and
M–C bond lengths these did not show any appreciable changes
(Table 1).
Figure 4. Packing mode illustrations of (a) clustered head-to-tail for 4
and 6, (b) head-to-head for 7 and 9, (c) clustered tail-to-tail for 8, (d)
head-to-tail for 10, and (e) head-to-tail for 11. Counter-ions and
hydrogen atoms are omitted for clarity.
8° was thus observed with the more bulky N–Ph substituents
showing the smallest ψ (jaw) angle variation on the cod. The
cod bite angle χ, on the other hand also stays fairly constant
at around 86–87°. This is to be expected due to the lanthanide
contraction from the 4th to the 5th row transition series, yield-
ing very similar ion radii for the PdII and PtII. Thus, only the
It was envisaged that with the incorporation of the nitrogen
donor atom in the N,O-Bid ligand, the asymmetry of the coor-
dinating bidentate ligand will influence the Venus fly-trap
angles of the complexes. Thus, these parameters as defined in
Figure 1, using the solid-state data obtained from the crystallo-
graphic studies, and as illustrated in Figure 5 (data from
Table 1), shows emerging geometric tendencies within the cy-
clooctadiene ligand. Although the O–M–N bite angle (θ) stays
virtually constant, there is a systematic increase in the ψ (jaw)
from the N–Ph substituents (around 76–78°) to the mixed N–
Figure 5. Graph of the Venus fly-trap angles observed from single
crystal data for [M(cod)(N,O-Bid)]+ (M = Pd, Pt; N,O-Bid = NH-acac,
NMe-acac, NPh-acac). (a) θ (N–M–O enaminonato bite) (b) χ (cod
Me and N–H complexes of 79–84°. A total increase of ca. bite), and (c) ψ (cod jaw) (°) (see Table S3, Supporting Information).
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jaw angle, i.e., the opening/ closing of the “mouth” of the Computational Results
Venus fly-trap varies significantly, assumed indicative of the
electronic changes of the N-substituents H, Me, and Ph.
The fly-trap angles are predominantly defined on the core
coordination arrangement with a presumably small contri-
bution from the counterion. The latter was observed for the ψ
Geometry Optimization
Accurate relevant solid-state data for the isostructural com-
plexes of all the members is not available for comparison as
difficulties in isolating and crystallizing the complexes proved
quite a challenge; for the PdII but in particular with the NiII.
Therefore, DFT calculations were performed to compare the
arrangement with the obtained complexes 4, 6–11. The DFT
optimized structures are indicated by a "C" following the com-
plexes’ structure abbreviation. In addition, the complete nickel
triad was used for DFT studies to gain further insight into the
bonding nature of these complexes. An excellent correlation
between the computed structures and that of the experimental
structures was obtained as can be seen in Figure 6, which
presents selected HyperChem™ superimposed images of 4,
8, and 10 with the calculated [Pd(cod)(NH-acac)]+,
[Pt(cod)(NMe-acac)]+, and [Pt(cod)(NPh-acac)]+ moieties,
yielding r.m.s. values of only 0.07 Å, 0.13 Å and 0.02 Å.
The r.m.s. values for the remaining complexes 6, 7, and 11
with their respective calculated complexes were calculated as
0.13 Å, 0.16 Å, and 0.16 Å, respectively. Due to the disorder
for 9 (Figure S3, Supporting Information), two r.m.s. values
were calculated for the respective parts of the disorder namely
0.22 Å and 0.18 Å, the major difference in the overlay being
in the disordered carbon (C3) of the cod.
–
(jaw) angle in the complexes containing the BF4 ion to have
a slightly smaller value than those with the PF6– ions (Table 1)
as in 6 and 7 (NMe-acac) and 8 and 9 (NMe-acac), respec-
tively. However, the opposite holds true in 10 and 11, where
–
the PF6 salt exhibits the smallest ψ (jaw) angle.
These parameters within the complexes, including the twist
angle (τ), are further discussed under the computational study
following the incorporation of the DFT optimized data of the
complete Ni-triad.
Spectroscopy
The IR spectra of the compounds showed characteristic
bands at 635–664 cm–1 and 416–474 cm–1 assigned to
ν(Pt–O) + Δ(ring) (in-plane ring distortion) and ν(Pt–O), while
ν(Pt–[C=C]) were found at 521–557 cm–1. For the ν(Pt–O) the
effect of the counter ligand is inconsequential, however, the
change in the R group on the N atom leads to a downfield shift
of ca. 29 cm–1 as the electron donating ability of the R group
is increased.
In general, the optimized geometric parameters are in very
good agreement with the values based upon the X-ray crystal
structure data (see Figure 7 and Table 2), and the common
trends observed in the experimental data are reproduced in the
calculations. It should however be noted that the theoretical
calculations do not consider the effects of the chemical envi-
ronment for example intermolecular packing interactions. As a
result, the distances for the theoretical calculations are frac-
tionally longer (1–3%) than those observed for the X-ray crys-
tal structures.
The resonances of the methine hydrogen atoms of the cyclo-
octadiene demonstrated the classic triplet of 195Pt complexes,
and multiplets were observed for the 105Pd complexes. For the
β-enaminonato hydrogen (H10) an increase in the proton shift
from 5.33 ppm to 5.62 ppm was found consistent with the in-
crease electron with-drawing properties of the ligand. Along
with the vicinal coupling seen for both 4 and 5, resulting in
the splitting of the multiplets into a doublet of multiplets for
the olefinic hydrogens, the influence of the scalar hydrogen
H1
bond coupling (
J ) on 4 can be clearly seen by the in-
HF
The Venus fly-trap parameters were also obtained from the
DFT calculations, and these together with those obtained from
the solid-state crystallographic work are summarized in
Table 3.
creased splitting (Figure S2, Supporting Information, whereas
Figure S1a illustrates the hydrogen bonding of 4). The
13C{1H} NMR resonances (Experimental Section) are in ac-
cordance with the proposed structures.
Figure 6. HyperChem™ superimosed image of (a) 4 (black) vs. [Pd(cod)(NH-acac)]+ (calculated) (red) with an r.m.s. error of 0.07 Å, (b) 8
(black) vs. [Pt(cod)(NMe-acac)]+ (calculated) (red) with an r.m.s. error of 0.13 Å, and (c) 10 (black) vs. [Pt(cod)(NPh-acac)]+ (calculated) (red)
with an r.m.s. error of 0.02 Å. The counterions and hydrogen atoms of the X-ray crystal structures are omitted for clarity.
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the DFT results. Although a significant trend, it is unclear ex-
actly what the reason is, although it is known that nickel(II)
sometimes favors a tetrahedral arrangement and indications are
that the twist is more prominent therein. Changing the counter-
ion influences the distortion, but no discernible trend was ob-
served as alluded to above.
Encouraged by the trends observed from Figure 5, the indi-
vidual computational fly-trap parameters were next correlated
with that observed from the solid-state data (see Figure 8).
The increasing trend of the ψ (jaw) angle in Figure 8a is
somewhat maintained by the DFT results, albeit less pro-
nounced, for reasons not perfectly clear. Nevertheless, all be-
ing equal, it underlines the fact that the ψ angle of the cod as
defined, opens/ closes when electronic changes at the central
metal atom occurs.
The best agreement between the XRD and the computed
results is within the N–M–O bite angles, which are clearly very
good (Figure 8c). An interesting observation is the fact that the
cod bite angle (χ) seems to constantly follow a ca. 2° smaller
value for the DFT data compared to the crystallographic data
(see Figure 8b). A reason for this is potentially observable in
the four M–C bonds for the cod ligand. These are all ca. 0.02
to 0.06 Å longer than the corresponding crystallographic data
(Table 2), which might suggest that the DFT is not able in this
case to accurately model the distorted olefin interactions with
Figure 7. Graph of the twist angle τ (°): (a) computed values (open
symbols); compared to (b) crystallographically observed (filled sym-
bols); for [M(cod)(N,O-Bid)]+ (M = Ni, Pd, Pt; N,O-Bid = NH-acac,
NMe-acac, NPh-acac) (see Table S4, Supporting Information).
Next, the distortion from the square-planar arrangement was
probed by the twist angle τ (Figure 1c), i.e. the dihedral angle
between the planes defined by the metal atom and the mid-
points of the alkene carbons of the cod ring on the one hand,
and the metal atom and the O and N atoms of either the 4-
amino, 4-methylamino, and 4-anilinopent-3-en-onato ligand,
on the other. A general increasing trend is observed with 8
showing the largest distortion of 10.9(5)° (see Table 2). The
trend in the twist angle is illustrated in Figure 7, relating it to the central metal atoms; at least in these examples presented.
Table 2. Selected average crystallographic and DFT optimized bond lengths /Å and angles /° for complexes 4 and 6–11.
Bond/angle
Pd(cod)-(NH-acac)
Pt(cod)-(NH-acac)
Pt(cod)-(NMe-acac)
Pt(cod)-(NPh-acac)
XRD, 4
Calcd.
XRDavg, 6 and 7 Calcd.
XRD, 8 and 9
Calcd.
XRDavg, 10 and 11
Calcd.
M–O1
M–N1
M–C1
M–C2
M–C5
M–C6
C1–C2
C5–C6
1.998(1)
1.972(2)
2.184(2)
2.210(2)
2.219(2)
2.226(2)
1.382(3)
1.374(3)
2.024
2.012
2.266
2.242
2.309
2.279
1.385
1.377
2.002(4)
1.987(4)
2.180(4)
2.178(4)
2.163(4)
2.165(4)
1.390(10)
1.391(10)
2.033
2.013
2.215
2.201
2.261
2.241
1.402
1.391
1.978(3)
2.041(3)
2.177(3)
2.173(3)
2.185(3)
2.176(3)
1.387(6)
1.396(6)
2.024
2.069
2.233
2.211
2.260
2.244
1.400
1.393
1.990(2)
2.052(3)
2.178(3)
2.193(3)
2.137(4)
2.171(3)
1.434(5)
1.412(5)
2.030
2.070
2.234
2.218
2.263
2.243
1.399
1.393
O1–M–N1
C1–M–C2
C5–M–C6
C1–M–C6
C2–M–C5
91.84(6)
36.66(8)
36.00(8)
82.14(7)
81.79(8)
90.85
35.78
34.93
80.50
80.24
91.6(2)
37.3(3)
37.1(3)
82.5(2)
82.2(2)
90.41
37.01
36.00
81.00
80.80
92.21(5)
37.1(1)
37.3(2)
81.56(11)
81.37(10)
92.08
36.72
36.02
79.95
80.14
92.2(3)
38.2(6)
38.3(5)
80.9(5)
80.2(6)
91.78
36.64
36.01
80.15
79.94
Table 3. Venus Fly-trap parameters from crystallographic and DFT study.
Parameter
Pt-NPh- Pt-NPh-
Pt-NMe- Pt-NH- Pt-NH- Pt-NMe- Pt-NMe- Pd-NH- Pd-NMe-C Pd-NPh-C Ni-NMe-C Ni-NPh-C Ni-NH-C
b)
PF6
BF4
BF4
BF4
PF6
PF6
PF6
BF4
11
10
8
6
7
9b
9a
4
C1
C2
C3
C4
C5
χ, cod bitea)
χcc)
86.1
84.3
75.8
82.6
85.3
84.3
78.4
82.6
91.7
91.9
3.6
86.4
84.3
78.5
82.1
92.1
92.1
10.9
2.8
87.2
85.3
78.6
82.4
91.5
90.4
3.8
87.9
85.3
80.7
82.4
91.8
90.4
0
86.4
84.3
81.1
82.1
92.3
92.1
0
86.2
84.3
81.6
85.5
92.3
92.1
0
86.4
84.3
83.8
82.1
91.8
90.9
3.3
–
82.9
–
85.2
–
92.5
–
–
82.9
–
85.7
–
92.2
–
–
83.0
–
86.2
–
94.3
–
–
83.4
–
86.6
–
93.9
–
–
85.9
–
86.1
–
93.1
–
ψ, cod jawa)
ψcc
θ, N–M–O bitea) 92.6
θcc)
91.9
5.3
2.4
τ, twist anglea)
τcc)
2.4
1.5
1.5
2.8
2.8
1.8
3.4
4.5
4.9
9.6
3.8
a) e.s.d.’s for all XRD values ca 0.1–0.2 degrees. b) e.s.d.’s for 11 ca. 1 degree. c) Calculated values using cation only.
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unoccupied MOs, along with the differences in the respective
orbitals (Eg–1 ϵ Δ|HOMO-1| – |HOMO|; Eg ϵ Δ|HOMO| –
|LUMO|; Eg+1 ϵ Δ|LUMO| – |LUMO+1|) for the calculated
complexes of [M(cod)(N,O-Bid)]+ [M = NiII, PdII, PtII (group
10 metals) and N,O-Bid = NH-acac, NMe-acac, NPh-acac] are
presented in Figure 9.
In the HOMO-1 MOs of the NH-acac Ni-triad (Table S5,
Supporting Information), the p orbitals seen on the carbon ad-
jacent to the oxygen atoms of the NH-acac ligand, display an
in-phase overlap of the metal orbitals with the alkene p orbitals
of cod. For the HOMO MOs, π orbital delocalization on the
NH-acac ligand is observed for all computed structures. On
the other hand, for the LUMO MOs, dx2–y2 orbitals are ob-
served around the metal atoms, whereas for LUMO+1 MOs, a
dz2 orbital is clearly seen.
For the HOMO-1 MOs of the NMe-acac Ni-triad (Table S6,
Supporting Information), an interesting feature is the p orbitals
seen on the carbon adjacent to the oxygen atom of the NMe-
acac ligand, with an in-phase overlap of the metal orbitals with
the alkene p orbitals of the cyclooctadiene. This is continued
to a lesser extent in the HOMO MOs with the orbitals shifting
to the NMe-acac ligand, where the π delocalization on the
back-bone is clearly visible. The central metal atoms have dyz
orbitals, whereas the p orbital of the methyl carbon of the
NMe-acac ligand is seen. In the LUMO MOs, a dx2–y2 orbital
Figure 8. Graph of the Venus fly-trap angles (°) (a) ψ (cod jaw), (b)
χ (cod bite), (c) the θ (N–M–O enaminonato bite): computed values
(open symbols) vs. crystallographically observed (filled symbols) for is observed centered on the metals of the group. The LUMO+1
[M(cod)(N,O-Bid)]+ (M = Ni, Pd, Pt; N,O-Bid = NH-acac, NMe-acac,
NPh-acac) (see Table S4, Supporting Information).
MOs, tend to a dz2 orbital centered on the metal.
In the HOMO-1 MOs of the NPh-acac Ni-triad (Table S7,
Supporting Information), the π orbitals on the phenyl ring sys-
Orbitals
A visual representation of the nature of the bonding mode
is given through the use of the molecular orbitals (MOs). The
second-highest (HOMO-1) and highest (HOMO) occupied
tem are clearly observed. Similarly, for the HOMO MOs, π
orbital delocalization on the NPh-acac ligand is observed for
all computed structures, whereas for the LUMO MOs, dx2–y2
orbitals are observed around the central metal atoms and for
MOs and the lowest (LUMO) and second-lowest (LUMO+1) the LUMO+1 MOs, a dz2 orbital is seen, i.e., it is continued
Figure 9. Molecular orbitals of calculated structures [M(cod)(NH-acac)]+.
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Table 4. Molecular orbital energies (Hartree) and energy gaps (eV) of the [M(cod)(N,O-Bid)]+ (M = NiII, PdII, PtII and N,O-Bid = NH-acac,
NMe-acac, NPh-acac) calculated structures.
HOMO-1
HOMO
LUMO
LUMO+1
Eg–1
Eg
Eg+1
[M(cod)(NH-acac)]+
NiII
PdII
PtII
–0.40893
–0.40619
–0.40810
–0.35676
–0.35328
–0.35924
–0.23603
–0.22951
–0.19246
–0.18798
–0.18299
–0.18616
1.420
1.440
1.330
3.278
3.368
4.538
1.315
1.266
0.171
[M(cod)(NMe-acac)]+
NiII
PdII
PtII
–0.40565
–0.40513
–0.40713
–0.34794
–0.34509
–0.35095
–0.24074
–0.23256
–0.19542
–0.18502
–0.18095
–0.18401
1.570
1.634
1.529
2.917
3.062
4.232
1.516
1.404
0.310
[M(cod)(NPh-acac)]+
NiII
PdII
PtII
–0.36571
–0.36325
–0.36565
–0.34707
–0.34458
–0.35001
–0.23568
–0.22880
–0.19263
–0.17787
–0.17488
–0.17921
0.507
0.508
0.426
3.031
3.151
4.283
1.573
1.467
0.365
for all three ligand systems NH-acac, NMe-acac, and NPh-
acac throughout the Ni-triad.
Table 4 presents the molecular orbital energies and energy
gaps between the different corresponding MO levels in the
[M(cod)(N,O-Bid)]+ (M = NiII, PdII, PtII and N,O-Bid = NH-
acac, NMe-acac, NPh-acac) calculated structures. The trends
in particularly the energy gap (Eg) between the HOMO and
LUMO MOs follow the typical increase from NiII to PtII, with
PdII in between. Of interest is the fact that the NPh-acac com-
plex lies between that of the NH-acac on the one side and the
NMe-acac on the other.
Spectroscopy
In the spectra, which follow the peak assignments are de-
noted by the largest contributing vibration(s) to the band; the
reported calculated frequencies are unscaled. The data is illus-
trated in Figure 10, with selected values reported in Table 5.
For the [M(cod)(NH-acac)]+ complex, the band around
1610 cm–1 as seen in Figure 10a contains the ν(C=N),
ν(C=C)NH-acac, δ(CH), δ(NH), and γ(CH3) vibrational contri-
butions with the largest coming from ν(C=N). As can be seen
there is not a significant difference in the frequencies when
varying the metal atom for nickel, palladium, and platinum
respectively. For the [M(cod)(NMe-acac)]+ complex, the band
around 1600 cm–1 (Figure 10b) contains the ν(C=N),
ν(C=C)cod+NMe-acac, δ(CH)cod+NMe-acac, and γ(CH2) vibrations
Figure 10. Calculated IR spectra of (a) [Ni(cod)(NH-acac)]+ (blue),
with the largest fraction originating from ν(C=N). In Fig- [Pd(cod)(NH-acac)]+ (red), and [Pt(cod)(NH-acac)]+(green); (b)
[Ni(cod)(NMe-acac)]+ (blue), [Pd(cod)(NMe-acac)]+ (red), and
[Pt(cod)(NMe-acac)]+(green); (c) [Ni(cod)(NPh-acac)]+ (blue),
[Pd(cod)(NPh-acac)]+ (red), and [Pt(cod)(NPh-acac)]+(green). ν –
stretching, δ – in-plane bending and γ – out-of-plane bending.
ure 10c the data for the [M(cod)(NPh-acac)]+ complex is pre-
sented, where the band at 1590 cm–1 comprises ν(N=C),
ν(C=C)NPh-acac+cod, and δ(CH).
The ν(C=N) frequency for the complexes presented displays
a difference of ca. 10 cm–1 indicating that the changing of the affect the vibration in the back-bone of the β-enaminonato li-
R group attached to the nitrogen atom does not significantly gands. A contributing factor to this is the conjugation therein
Table 5. Selected IR data /cm–1 for the Group 10 metal (Ni-Triad) complexes.
[M(cod)(NH-acac)]+
[M(cod)(NMe-acac)]+
[M(cod)(NPh-acac)]+
Ni
Pd
Pt
Ni
Pd
Pt
Ni
Pd
Pt
v(C=N)
v(N–R)
1605
1480
1601
1480
1605
1483
1604
1399
1595
1401
1600
1402
1589
1514
1585
1514
1590
1516
a)
a) R = H, Me, Ph.
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tometer with a laser range of 4000–370 cm–1. Solid samples were pre-
pared as potassium bromide disks.
thus making the bonding character of the C–N, C–C, and C–
O very similar, as reflected in the bond lengths (Table 1 and
Table 2). It is interesting to note that a clearly defined band
was observed for [M(cod)(NPh-acac)]+ at 1401 cm–1 for this
conjugated vibration. The ν(N–R) frequency is related to the
inverse order of the electronegativity[13] (Ph, H, CH3), thus as
one decreases the electronegativity, the vibrational band shifts
up-field.
Computational Methods: The DFT (density functional theory) mo-
lecular orbital calculations were carried out using the Gaussian 03[14]
software suite. Becke’s three parameter hybrid (B3LYP),[15,16] ex-
change correlation functional was used. The basis set employed in
this study was 6-311++G(d,p)[17–19] for the main group elements and
LanL2DZ[20] for the middle to late transition metals. Vibrational fre-
quencies were calculated at the 6-311++G(d,p) level for the main
group elements and at the LanL2DZ level for the middle to late transi-
tion metals with minimum energies confirmed to have zero imaginary
frequencies. The frequencies were unscaled and used to compute the
zero-point vibrational energies. The calculated harmonic wavenumbers
were used in the analysis of the experimental IR spectra. DFT opti-
mized structures of compounds not having crystal structures, are indi-
cated by a “C” following the complexes’ structure abbreviation and
numbered C1–C6.
Conclusions
The synthesis, characterization, and low temperature X-ray
structures of six new β-enaminonato complexes of cis,cis-1,5-
cyclooctadiene with PdII and PtII are reported, wherein the
bonding arrangement of the cyclooctadiene ligand was criti-
cally evaluated based on different pre-defined parameters
mimicking the geometric behavior of a Venus fly-trap as
model.
A good correlation was found between the X-ray crystal
structures and that of the DFT computed compounds. The bite
(χ) and jaw (ψ) angles for both the solid-state crystal structures
and the computed structures are presented, leading to the con-
clusion that upon varying the central metal atom in identical
complexes down the nickel triad the jaw angle closes by ca.
8°. Further extended investigation into the Venus fly-trap
angles for various β-enaminonato ligands as well as other tran-
sition metals will be required to formulate a more complete
model of the bonding modes of cyclooctadiene.
X-ray Crystal Structure Determinations: Data collections
for [Pd(cod)(NH-acac)]BF4 (4), [Pt(cod)(NH-acac)]PF6 (7),
[Pt(cod)(NMe-acac)]BF4 (8), [Pt(cod)(NMe-acac)]PF6 (9), and
[Pt(cod)(NPh-acac)]PF6 (11) were obtained with a Bruker APEX II
4 K CCD diffractometer. The data for [Pt(cod)(NH-acac)]BF4 (6) and
[Pt(cod)(NPh-acac)]BF4 (10) were collected with an Oxford Diffrac-
tion Xcalibur 3 Crysalis CCD system.[21] All structures were collected
at 100(2) K using Mo-Kα radiation (0.71073 Å). Both systems were
equipped with a graphite-mono-chromatted Mo-Kα radiation, for the
Bruker system all the reflections were merged and integrated with
SAINT-PLUS[22] and corrected for Lorentz, polarization and absorp-
tion effects with SADABS,[23] whereas Crysalis RED[24] was used for
the Oxford system.
The molecular orbital diagrams show the influence of both
the p and d orbitals of the ligands as well as the central metal
atoms. The comparison of the HOMO-1, HOMO, LUMO, and
LUMO+1 MOs with those of the NH-acac, NMe-acac, and
NPh-acac group 10 metal (Ni-triad) complexes shows a
marked similarity. It is therefore concluded that the varying of
the R group attached to the nitrogen of the β-enaminonato li-
gands does not play as significant a role as originally pos-
tulated.
The infra-red spectra showed that the change in the central
metal atom exhibited not as a significant influence on the
ν(C=N) stretching frequency as anticipated, however the elec-
tronegativity of the group attached to the nitrogen does have
an influence on the ν(N–R) frequency.
Structures were solved by direct and conventional Patterson methods
using SHELX-97[25] as part of the WinGX[26] package, and anisotropic
refinement was performed on all non-hydrogen atoms by a full-matrix
least-squares method on F2. The positions of the hydrogen atoms were
calculated using a riding model to the adjacent carbon, unless other-
wise stipulated. Hydrogen interactions were calculated using the
PLATON[27–29] and PARST[30] programs. Molecular graphics were ob-
tained using DIAMOND,[31] while overlay illustrations were generated
using HyperChem™ 7.5.[32] Details of the crystal data, intensity mea-
surements and data processing are summarized in Table 6 for 4, 6–10,
whereas selected bond lengths and angles are given in Table 2. Se-
lected molecular structures with thermal ellipsoids (30%) along with
the general numbering scheme are presented in Figure 2; counterions
are omitted for clarity and only selected hydrogen atoms are shown.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1473585 (4), CCDC-1473590 (6), CCDC-1473595
(7), CCDC-1473596 (8), CCDC-1473604 (9), and CCDC-1473630
(10) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk)
Experimental Section
General: All reagents used for synthesis and characterization were of
analytical grade, purchased from Sigma-Aldrich, unless otherwise
stated. The metal complexes were purchased from Next Chimica
(South Africa). Reagents were used as received, without purification.
Spectroscopy Measurements: NMR spectra were recorded with a
Bruker Advance II 600 (1H: 600.28 MHz; 13C: 150.96 MHz), 1H NMR
spectra were referenced internally using residual protons in the deuter-
ated solvent (CDCl3: d 7.28; CD2Cl2: s 5.32). 13C NMR spectra were
similarly referenced internally to the solvent resonance (CDCl3:
t 77.36; CD2Cl2: m 53.8) with values reported relative to tetramethyl-
Synthesis of Dichlorido-1,5-cyclooctadieneplatinum(II): This was
used as starting material and was prepared by the previously published
method[8] by mixing of potassium tetrachloridoplatinate in water and
propanol with cis,cis-1,5-cyclooctadiene (cod). Dichlorido-1,5-cyclo-
octadienepalladium(II)[9] was prepared by dissolving palladium dichlo-
silane (d 0.0). Chemical shifts are reported in ppm. Infrared spectra ride in minimum of concentrated hydrochloric acid and diluting the
were recorded with a Bruker Tensor 27 Standard System spectropho- solution with ethanol. To this was added cod with rapid stirring.
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–
–
Table 6. Crystallographic data and refinement parameters for [M(cod)(LLЈ-Bid)]A (M = Pd, Pt, A = PF6 and BF4 , LLЈ-Bid = NH-acac, NMe-
acac, NPh-acac).
[Pd(cod)(NH-acac)]A
BF4 (4)
[Pt(cod)(NH-acac)]A
BF4 (6)
[Pt(cod)(NMe-acac)]A
[Pt(cod)(NPh-acac)]A
BF4 (10)
a)
PF6 (7)
BF4 (8)
PF6 (9)
Empirical formula
FW
Crystal system
Space group
a /Å
b /Å
c /Å
α /°
C
13H20BF4NOPd
C13H20BF4NOPt
488.20
monoclinic
P21/c
9.8588(2)
12.8652(2)
12.6969(3)
90
C13H20F6NOPPt
546.36
monoclinic
C2/m
26.8871(12)
7.1009(3)
8.7130(4)
90
C14H22BF4NOPt
502.23
orthorhombic
P212121
7.5277(2)
13.9653(4)
14.7872(4)
90
C14H22F6NOPPt
560.39
monoclinic
C2/m
26.5792(6)
7.19030(10)
9.3146(2)
90
C19H24BF4NOPt
564.29
monoclinic
P21/c
9.5952(7)
21.2609(16)
10.3336(6)
90
399.51
monoclinic
P21/c
9.8665(3)
12.7836(3)
12.7126(3)
90
β /°
110.851(1)
90
1498.42(7)
4
1.771
1.278
111.040(2)
90
1503.05(5)
4
2.157
9.375
105.305(3)
90
1604.51(12)
4
2.262
8.908
90
90
106.250(1)
90
1709.02(6)
4
2.178
8.366
117.664(5)
90
1867.1(2)
4
2.007
7.562
γ /°
V /Å3
1554.53(7)
4
2.146
9.068
960
Z
Dcalc /Mg·m–3
μ /mm–1
F(000)
800
928
1040
1072
1088
Crystal size /mm3
θ range /°
Index ranges
0.42ϫ0.19ϫ0.05
3.35 to 28.00
–13 Յ h Յ 12,
–16 Յ k Յ 16,
–16 Յ l Յ 16
17329
0.26ϫ0.15ϫ0.13 0.19ϫ0.17ϫ0.10 0.35ϫ0.15ϫ0.08 0.38ϫ0.13ϫ0.04 0.26ϫ0.23ϫ0.10
2.34 to 30.00
–13 Յ h Յ 9,
–17 Յ k Յ 18,
–16 Յ l Յ 17
13378
1.57 to 28.48
–35 Յ h Յ 35,
–9 Յ k Յ 9,
–11 Յ l Յ 11
18461
3.04 to 28.37
–6 Յ h Յ 9,
–18 Յ k Յ 18,
–19 Յ l Յ 19
28496
3.19 to 28.30
–35 Յ h Յ 35,
–6 Յ k Յ 9,
–12 Յ l Յ 12
14798
2.42 to 28.00
–12 Յ h Յ 12,
–27 Յ k Յ 28,
–8 Յ l Յ 13
14547
Reflections col-
lected
Independent reflec- 3611 [Rint = 0.0266]
tions
4374 [Rint
0.0226]
=
2167 [Rint
0.1076]
=
3853 [Rint
0.0403]
=
2296 [Rint
0.0413]
=
4398 [Rint = 0.0644]
Complete θ /°,%
Max/min. trans
Data/ restraints/ pa- 3611 / 0 / 215
28.00, 99.9
0.9389 / 0.6159
30.00, 100.0
0.3754 / 0.1942
4374 / 0 / 196
28.48, 98.9
0.4695 / 0.2824
2167 / 0 / 124
28.37, 99.4
0.5307 / 0.1435
3853 / 0 / 202
28.30, 99.7
0.7308 / 0.1432
2296 / 191 / 159
28.00, 97.7
0.5185 / 0.2438
4398 / 0 / 246
rameters
GoF on F2
1.068
1.003
1.252
1.044
1.042
0.991
Final R indices
[I Ͼ 2σ(I)]
R indices (all data) R1 = 0.0241,
wR2 = 0.0525
R1 = 0.0210,
wR2 = 0.0509
R1 = 0.0209,
wR2 = 0.0490
R1 = 0.0283,
wR2 = 0.0507
R1 = 0.0381
wR2 = 0.0787
R1 = 0.0410,
wR2 = 0.0802
R1 = 0.0148
R1 = 0.0205
R1 = 0.0332,
wR2 = 0.0805
R1 = 0.0389,
wR2 = 0.0823
3.323 and –2.601
R1 = 0.0154
R1 = 0.0226
Largest diff. peak/
0.507 and –0.450
2.427 and –0.952 1.440 and –1.925 0.912 and –0.713
0.621 and –0.966
hole /e·Å–3
a) Flack parameter = 0.006(5).
Synthesis of Ligands: 4-Aminopent-3-en-2-one [HNH-acac] (1): A 2.005 (s, 3 H, CH3), 2.113 (s, 3 H, CH3), 5.201 (s, 1 H, CH), 7.12 (d,
solution of acetylacetone (11 g, 0.11 mol), NH4OH (28% in H2O,
12.5 g, 0.1 mol) and 2 drops H2SO4 (conc.) in benzene (100 mL) was
refluxed overnight in a Dean Stark setup. The solution was filtered,
and the solvent removed on a rotary evaporator where upon the oil of
1 was allowed to stand overnight. Yield 9.7 g (89%). IR (KBr): ν˜ =
2 H, CH, J = 7.2 Hz), 7.203 (t, 1 H, CH, J = 7.2 Hz), 7.35 (t, 2 H,
CH, J = 7.2 Hz), 12.486 (s, 1 H, NH). 13C{1H} NMR (150.96 MHz,
CDCl3): δ = 20.15 (CH3), 29.49 (CH3), 97.91 (CH3), 125.07 (CH),
125.87 (CH), 129.4 (CH), 139.06 (CH), 160.56 (CNH), 196.45 (CO).
1
νC=O 1700, νN–H 3338 cm–1. H NMR (600.28 MHz, CDCl3): δ =
Synthesis of the Complexes: [Pd(cod)(NH-acac)]BF4 (4): Using a
modified synthetic procedure,[33] [Pd(cod)Cl2] (100 mg, 0.35 mmol)
was dissolved in DCM (5 mL). To this AgBF4 (136 mg, 0.7 mmol)
was added and the resulting solution was stirred for ca. 15 min. An
equivalent of 1 (31 μL, 0.35 mmol) was added and the mixture stirred
for a few min to allow the reaction to complete. The solution was
filtered and Et2O was added (ca. 20 mL) to the filtrate to precipitate
4. The resulting solution was again filtered and the precipitate washed
with Et2O (3ϫ3 mL) portions. Crystals suitable for X-ray diffraction
were obtained by DCM / Et2O vapor diffusion. Yield 36 mg (24%).
IR (KBr): ν˜ = νN–H 3314, νC=C 1589, νC=O 1708, νPd–O 717 and
476, νPd–[C=C] 522 cm–1. 1H NMR (600.28 MHz, CD2Cl2): δ =
2.086 (s, 3 H, CH3), 2.231 (s, 3 H, CH3), 2.681 (m, 4 H, CH2), 2.884
(m, 4 H, CH2), 5.216 (d, 1 H, CH, J = 2.4 Hz), 6.111 (m, 2 H, CH),
6.222 (m, 2 H, CH). 13C{1H} NMR (150.96 MHz, CD2Cl2): δ = 24.91
(CH3), 24.84 (CH3), 28.93 (CH2), 31.08 (CH2), 97.25 (CH), 110.76
(CH), 118.82 (CH), 166.24 (CN), 177.4 (CO).
1.911 (s, 3 H, CH3), 2.033 (s, 3 H, CH3), 5.032 (s, 1 H, CH), 9.701
(s, 1 H, NH). 13C{1H} NMR (150.96 MHz, CDCl3): δ = 22.56 (CH3),
29.53 (CH3), 96.08 (CH), 161.27 (CNH), 197.07 (CO).
4-(Methylamino)pent-3-en-2-one [HNMe-acac] (2): An analogous
method as described for 1 was used in the preparation of 2 replacing
NH4OH with H2NCH3 (40% in H2O, 7.76 g, 0.1 mol). Yield 8.9 g
(72%). 1H NMR (600.28 MHz, CDCl3): δ = 1.918 (s, 3 H, CH3),
1.970 (s, 3 H, CH3), 2.932 (d, 3 H, CH3, J = 4.8 Hz), 4.981 (s, 1 H,
CH), 10.699 (s, 1 H, NH) 13C{1H} NMR (150.96 MHz, CDCl3): δ =
18.97 (CH3), 28.95 (CH3), 29.77 (CH3), 95.43 (CH), 164.55 (CNH),
195.01 (CO).
4-Anilinopent-3-en-2-one [HNPh-acac] (3): An analogous method as
described for 1 was used in the preparation of 3 replacing NH4OH
with aniline (9.31 g, 0.1 mol). Yield 15.4 g (80%). IR (KBr): ν˜ =
1
νC=O 1606, νN–H 3050 cm–1. H NMR (600.28 MHz, CDCl3): δ =
Z. Anorg. Allg. Chem. 2018, 763–774
www.zaac.wiley-vch.de 772
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
[Pd(cod)(NH-acac)]PF6 (5): The compound was prepared in a similar 27 mmol). Crystals suitable for X-ray diffraction were obtained by
manner as described for 4, except AgPF6 (177 mg, 0.7 mmol) was used DCM / Et2O vapor diffusion. Yield 85 mg (55%). IR (KBr): ν˜ = νC=C
instead of AgBF4. Yield 32 mg (21%). IR (KBr): ν˜ = νN–H 3368,
νC=C 1582, νC=O 1699, νPd–O 692 and 474, νPd–[C=C] 557 cm–1.
1H NMR (600.28 MHz, CD2Cl2): δ = 2.097 (s, 3 H, CH3), 2.220 (s,
3 H, CH3), 2.698 (m, 4 H, CH2), 2.891 (m, 4 H, CH2), 5.239 (d, 1 H,
1518, νC=O 1566, νPt–O 659 and 474, νPt–[C=C] 522, νPt–N
1
548 cm–1. H NMR (600.28 MHz, CD2Cl2): δ = 1.806 (s, 3 H, CH3),
2.228 (s, 3 H, CH3), 2.392 (m, 4 H, CH2), 2.696 (m, 4 H, CH2), 4.712
(sep, 2 H, CH, J = 18.6 Hz, 8.4 Hz, 3 Hz), 5.619 (s, CH), 5.869 (sep,
CH, J = 2.4 Hz), 6.127 (m, 4 H, CH). 13C{1H} NMR (150.96 MHz, 2 H, CH, J = 15 Hz, 9 Hz, 2.4 Hz), 7.037 (d, 2 H, CH, J = 7.2 Hz),
CD2Cl2): δ = 24.93 (CH3), 25.15 (CH3), 28.97 (CH2), 31.05 (CH2), 7.34 (t, 1 H, CH, J = 7.8 Hz), 7.514 (t, 2 H, CH, J = 7.8 Hz). 13C{1H}
97.31 (CH), 110.76 (CH), 119.08 (CH), 166.36 (CN), 178.01 (CO).
NMR (150.96 MHz, CD2Cl2): δ = 24.9 (CH3), 25.43 (CH3), 28.03
(CH2), 30.77 (d, CH2, J = 25.6 Hz), 98.33 (CH), 101.45 (CH), 104.43
(CH), 146.91 (CN), 166.23 (CN), 177.35 (CO).
[Pt(cod)(NH-acac)]BF4 (6): An analogous method as described for 4
was used in the preparation of 6 replacing [Pd(cod)Cl2] with [Pt(cod)
Cl2] (100 mg, 27 mmol). Crystals suitable for X-ray diffraction were
obtained by DCM / Et2O vapor diffusion. Yield 55 mg (41%). IR
(KBr): ν˜ = νC=C 1539, νC=O 1587, νPt–O 664 and 470, νPt–[C=C]
[Pt(cod)(NPh-acac)]PF6 (11)[34]: The compound was prepared in a
similar manner as described for 10, replacing the AgBF4 with AgPF6
(135 mg, 27 mmol). Crystals suitable for X-ray diffraction were ob-
tained by DCM / Et2O vapor diffusion. Yield 132 mg (78%). IR
(KBr): ν˜ = νC=C 1519, νC=O 1563, νPt–O 658 and 473, νPt–[C=C]
1
521 cm–1. H NMR (600.28 MHz, CD2Cl2): δ = 2.136 (s, 3 H, CH3),
2.281 (s, 3 H, CH3), 2.508 (m, 4 H, CH2), 2.718 (m, 4 H, CH2), 5.428
(d, 1 H, CH, J = 2.4 Hz), 5.658 (dt, 4 H, CH, J = 3 Hz, 15.6 Hz),
9.212 (s, 1 H, NH). 13C{1H} NMR (150.96 MHz, CD2Cl2): δ = 25.55
(d, CH3, J = 7.5 Hz), 28.76 (CH3), 30.06 (CH2), 31.09 (CH2), 92.28
(CH), 100.01 (CH), 102.51 (CH), 166.48 (CN), 177.57 (CO).
1
557, νPt–N 525 cm–1. H NMR (600.28 MHz, CD2Cl2): δ = 1.804 (s,
2 H, CH3), 2.227 (s, 3 H, CH3), 2.387 (m, 4 H, CH2), 2.722 (m, 4 H,
CH2), 4.705 (sep, 2 H, CH, J = 20.4 Hz, 9 Hz, 2.4 Hz), 5.619 (s, 1 H,
CH), 5.866 (sep, 2 H, CH, J = 14.4 Hz, 9 Hz, 2.4 Hz), 7.03 (s, 2 H,
CH, J = 7.8 Hz), 7.34 (t, 1 H, CH, J = 7.2 Hz), 7.513 (t, 2 H, CH, J
= 7.8 Hz). 13C{1H} NMR (150.96 MHz, CD2Cl2): δ = 25.27 (CH3),
25.8 (CH3), 28.4 (CH2), 31.05 (CH2), 98.68 (CH), 101.83 (CH),
104.81 (CH), 125.51 (CH), 128.73 (CH), 130.25 (CH), 147.29 (CN),
166.62 (CN), 177.76 (CO).
[Pt(cod)(NH-acac)]PF6 (7): The compound was prepared in a similar
manner as described for 6, replacing the AgBF4 with AgPF6 (135 mg,
27 mmol). Crystals suitable for X-ray diffraction were obtained by
DCM / Et2O vapor diffusion. Yield 91 mg (60%). IR (KBr): ν˜ = νC=C
1539, νC=O 1587, νPt–O 664 and 471, νPt–[C=C] 557 cm–1. 1H NMR
(600.28 MHz, CD2Cl2): δ = 2.147 (2, 3 H, CH3), 2.269 (s, 3 H, CH3),
2.522 (m, 4 H, CH2), 2.725 (m, 4 H, CH2), 5.325 (d, 1 H, CH, J =
6.6 Hz), 5.627 (dt, 4 H, CH, J = 33 Hz, 57 Hz), 8.601 (s, 1 H, NH).
13C{1H} NMR (150.96 MHz, CD2Cl2): δ = 25.66 (d, CH3, J =
28.7 Hz), 28.76 (CH3), 29.95 (CH2), 31.04 (CH2), 92.21 (CH), 99.78
(d, CH, J = 83 Hz), 102.79 (CH), 166.51 (NH), 178.15 (CO).
Supporting Information (see footnote on the first page of this article):
Figures and Tables (21pp) are provided giving additional X-Ray re-
sults, Computed Orbitals as well as NMR and IR spectra.
Acknowledgements
[Pt(cod)(NMe-acac)]BF4 (8): Using the preparation method as de-
scribed for compound 6, ligand 1 was replaced with ligand 2 (31.9 μL,
27 mmol). Crystals suitable for X-ray diffraction were obtained by
DCM / Et2O vapor diffusion. Yield 96 mg (70%). IR (KBr): ν˜ = νC=C
1522, νC=O 1584, νPt–O 635 and 416, νPt–[C=C] 521, νPt–N
Financial assistance from the University of the Free State is gratefully
acknowledged. We thank Prof. Ola Wendt from the University of Lund,
Sweden for the use of their Oxford X-ray diffractometer. We also ex-
press our gratitude to SASOL, the South African National Research
Foundation (SA-NRF/THRIP), the Inkaba yeAfrica initiative, the UFS
Strategic Cluster Initiative (Materials and Nonosciences), the Swedish
International Development Co-operation Agency (SIDA), and the
Swiss NSF for financial support of this project. Part of this material is
based on work supported by the SA-NRF/ THRIP under grant number
GUN2068915 and GUN107802. Opinions, findings, conclusions or
recommendations expressed in this material are those of the authors
and do not necessarily reflect the views of the SA-NRF.
1
472 cm–1. H NMR (600.28 MHz, CD2Cl2): δ = 2.117 (s, 3 H, CH3),
2.228 (s, 3 H, CH3), 2.485 (m, 2 H, CH2), 2.607 (m, 2 H, CH2), 2.734
(m, 2 H, CH2), 2.890 (m, 2 H, CH2), 3.315 (t, 3 H, CH3, J = 12.6 Hz),
5.450 (s, 1 H, CH), 5.486 (sep 2 H, CH, J = 19.8 Hz, 7.8 Hz, 3 Hz),
5.791 (sep, 2 H, CH, J = 14.4 Hz, 9 Hz, 3 Hz). 13C{1H} NMR
(150.96 MHz, CD2Cl2): δ = 24.62 (CH3), 24.97 (CH3), 28.22 (CH2),
31.84 (CH2), 42.69 (CH), 97.32 (CH), 102.17 (CH), 104.83 (CH),
167.45 (CN), 174.94 (CO).
[Pt(cod)(NMe-acac)]PF6 (9): The compound was prepared in a sim-
ilar manner as described for 8, replacing the AgBF4 with AgPF6
(135 mg, 27 mmol). Crystals suitable for X-ray diffraction were ob-
tained by DCM / Et2O vapor diffusion. Yield 125 mg (82%). IR
(KBr): ν˜ = νC=C 1518, νC=O 1580, νPt–O 636 and 419, νPt–[C=C]
Keywords: Palladium; Platinum; Cyclooctadiene; X-ray crys-
tallography; Density functional calculations; Venus fly-trap
1
557, νPt–N 467 cm–1. H NMR (600.28 MHz, CD2Cl2): δ = 2.120 (s,
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www.zaac.wiley-vch.de 773
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
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Received: March 15, 2018
Z. Anorg. Allg. Chem. 2018, 763–774
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© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim