Chelating or bridging Pd(ii) and Pt(ii) metalloligands from the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New heterometallic Pd(ii)/Pt(ii) and Pt(ii)/Au(i) complexes

Article abstract of DOI:10.1039/c0dt01782e

The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine Ph₂PNHCNNCHS (2) with [PdCl₂(NCPh)₂] in the presence of NEt₃ gives the neutral, P,N-chelated complex cis-[Pd(Ph₂PNCNNCHS)₂] ([Pd(2_-H)₂], 3b), which is analogous to the Pt(ii) analogue cis-[Pt(Ph₂PNCNNCHS)₂] ([Pt(2_-H) ₂], 3a) reported previously. These complexes function as chelating metalloligands when further coordinated to a metal through each of the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes cis-[Pt(Ph₂PNCNNCHS) ₂PdCl₂] ([Pt(2_-H)₂·PdCl ₂], 4a) and cis-[Pd(Ph₂PNCNNCHS)₂PtCl ₂] ([Pd(2_-H)₂·PtCl₂], 4b) were obtained by reaction with [PdCl₂(NCPh)₂] and [PtCl₂(NCPh)₂], respectively. In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the platinum/digold complex cis-[Pt{Ph₂PN(AuCl)CNNCHS}₂] ([Pt(2_-H)₂(AuCl)₂], 5). For comparison, reaction of 4a with HBF₄ yielded cis-[Pt(Ph₂PNHCNNCHS) ₂PdCl₂](BF₄)₂ ([H ₂4a](BF₄)₂, 6), in which the chelated PdCl ₂ moiety is retained. Complexes 3b, 4a·CH₂Cl ₂, 4b·0.5C₇H₈, 5·4CHCl ₃ and 6 have been structurally characterized by X-ray diffraction. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c0dt01782e

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PAPER
Chelating or bridging Pd(II) and Pt(II) metalloligands from the functional
phosphine ligand N-(diphenylphosphino)-1,3,4-thiadiazol-2-amine. New
heterometallic Pd(II)/Pt(II) and Pt(II)/Au(I) complexes†
Shuanming Zhang, Roberto Pattacini and Pierre Braunstein*
Received 16th December 2010, Accepted 9th March 2011
DOI: 10.1039/c0dt01782e
The reaction of two equivalents of the functional phosphine ligand N-(diphenylphosphino)-
1,3,4-thiadiazol-2-amine Ph2PNHC NNCHS (2) with [PdCl2(NCPh)2] in the presence of NEt3 gives
the neutral, P,N-chelated complex cis-[Pd(Ph2PN CNN CHS)2] ([Pd(2-H)2], 3b), which is analogous
to the Pt(II) analogue cis-[Pt (Ph2PN CNN CHS)2] ([Pt(2-H)2], 3a) reported previously. These
complexes function as chelating metalloligands when further coordinated to a metal through each of
the CH-N atoms. In the resulting complexes, each endo-cyclic N donor of the thiadiazole rings is
bonded to a different metal centre. Thus, the heterodinuclear palladium/platinum complexes
cis-[Pt(Ph2PN CNN CHS)2PdCl2] ([Pt(2-H)2·PdCl2], 4a) and cis-[Pd(Ph2PN CNN CHS)2PtCl2]
([Pd(2-H)2·PtCl2], 4b) were obtained by reaction with [PdCl2(NCPh)2] and [PtCl2(NCPh)2], respectively.
In contrast, reaction of 3a with [AuCl(tht)] occurred instead at the P-bound N atom, and afforded the
platinum/digold complex cis-[Pt{Ph2PN(AuCl) CNN CHS}2] ([Pt(2-H)2(AuCl)2], 5). For
comparison, reaction of 4a with HBF4 yielded cis-[Pt(Ph2PNH CNN CHS)2PdCl2](BF4)2
([H24a](BF4)2, 6), in which the chelated PdCl2 moiety is retained. Complexes 3b, 4a·CH2Cl2,
4b·0.5C7H8, 5·4CHCl3 and 6 have been structurally characterized by X-ray diffraction.
mentation into the corresponding mononuclear square planar
Introduction
Ni(II) complexes [NiCl2(L)] (Scheme 1).4 Interestingly, recrys-
The synthesis of phosphines containing in addition a nitrogen
tallization of the latter from CH2Cl2–pentane regenerates the
donor function (P,N ligands) and their transition metal complexes
tetranuclear complex.
has become increasingly attractive in the last few years owing
to their intrinsic properties, considerable structural diversity and
broad range of applications.1 We are interested in oxazoline-
and thiazoline-based phosphine systems, such as (2-oxazoline-
2-ylmethyl)diphenylphosphine (Lox) and (2-thiazoline-2-ylmethyl)
diphenylphosphine (Lth),2 which have been successfully applied in
several catalytic processes, like some of their derivatives.3
Scheme 1
For comparative purposes, we replaced the PCH2 group of
With both Lox and Lth, unprecedented tetranuclear complexes
Lth with the isoelectronic PNH group and began to examine
[NiCl2(L)]4·2CH2Cl2 have been structurally characterized, which,
the coordination properties of N-(diphenylphosphino)-thiazolin-
2-amine Ph2PNHC NCH2CH2S (1) (Scheme 2).5 Complexes
in the solid state, undergo an irreversible pressure-induced frag-
with ligand 1 have shown a higher sensitivity towards hydrolysis
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177
CNRS), Universite´ de Strasbourg, 4 Rue Blaise Pascal, F-67081, Stras-
bourg, France. E-mail: braunstein@unistra.fr; Fax: +33 (0)3 68 85 13 22;
Tel: +33 (0)3 68 85 13 08
† CCDC reference numbers 801707–801711. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt01782e
or alcoholysis of the P–N bond compared to the P–C bond of
Lth. However, facile deprotonation in the a-position to the P atom
leads to 3 electron donor P,N-chelates with enhanced chemical
persistency compared to their precursors. Thus, reaction of 1 with
[PtCl2(NCPh)2] in the presence of NEt3 gives the neutral complex
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purified by taking advantage of its poor solubility in MeCN and
it was characterized by X-ray diffraction (Fig. 1).
Scheme 2
cis-[Pt(Ph2PN CNCH2CH2S)2] (cis-[Pt(1-H)2]) (Scheme 2). This
complex is luminescent and showed an interesting solvent-induced
emission enhancement in the solid state when exposed to alcohols,
which interact by H-bonding with the P–N nitrogen atoms.6
Reactions of cis-[Pt(1-H)2] with the organic electrophile
EtN
C S
and the monovalent cations Cu+, Ag+ and
Au+, as inorganic electrophiles, occurred at one or both
electron-rich P-bound N atoms, respectively. With the latter
reagents, the complexes isolated were polymeric in the case of
7
[Cu{Pt(1-H)2}(PF6)]• and [Ag{Pt(1-H)2}(OTf)]•, or molecular
in the case of [Pt(1-H)2AuCl] and [Pt(1-H)2(AuCl)2]. When the
thiazoline ring in cis-[Pt(1-H)2] was replaced with aromatic thiazole,
thiadiazole or benzothiazole, the corresponding metalloligands
qualitatively showed slower reactions towards d10 cations, and the
resulting heterometallic complexes were found to be less stable.6
Since the P-bound N atoms in cis-[Pt(1-H)2] represented the
dominating reaction sites towards electrophiles so far, we wished
to introduce an additional function to expand the coordina-
tion properties of such metalloligands. We shall see that re-
placing ligand 1 with N-(diphenylphosphino)-1,3,4-thiadiazol-
2-amine (2) resulted in the new P,N-chelated complex cis-
[Pd(Ph2PN CNN CHS)2] (cis-[Pd(2-H)2], 3b), which should
behave as a N,N-chelating metalloligand (Scheme 3), owing
to the favourable position of the additional, non coordinated
CH-nitrogen atom of each of the thiadiazole rings and the
Fig. 1 An ORTEP view of the molecular structure of compound 3b.
Hydrogen atoms and solvent molecules omitted for clarity. Ellipsoids
include 30% of the electron density. Only one of the two independent
˚
molecules is shown (A). Selected distances (A) and angles (deg), molecule
A: P1–Pd1 2.2675(12), P2–Pd1 2.2626(11), N2–Pd1 2.081(3), N5–Pd1
2.083(3), N1–P1 1.660(4), N4–P2 1.662(4), N2–N3 1.370(4), N5–N6
1.384(4), C1–N1 1.305(5), C1–N2 1.351(5), C15–N4 1.324(5), C15–N5
1.345(5), C2–N3 1.271(5), C16–N6 1.277(6); P2–Pd1–P1 102.44(4),
N5–Pd1–P2 79.52(9), N2–Pd1–P1 79.52(10), N2–Pd1–N5 98.53(13).
2
suitable orientation of their lone pairs. This would lead to a k -
In the molecular structure of 3b, two almost identical de-
protonated ligands, 2-H, chelate the metal centre through their
phosphorus atoms P1 and P2, and the sp2-hybridized nitrogen
atoms N2 and N5, respectively. This structure is analogous to that
of the related Pt(II) bischelated complex [Pt(2-H)2] (3a).6 The bonds
N1–C1/N4–C15 and C1–N2/C15–N5 are longer than a double
bond and shorter than a single bond, respectively, indicating
electronic delocalization over the NCN system (for convenience,
we represent the N1–C1 and N4–C15 bonds by formal double
bonds in the schemes).
P,N-chelating/m-N,N-bridging mode for ligand 2-H. A similar
behaviour should be anticipated for its Pt(II) analogue cis-
[Pt(Ph2PN CNN CHS)2] (cis-[Pt(2-H)2], 3a).6 Although doubly
bridged thiadiazole dinuclear compounds have already been
reported in the 1970s,8 to the best of our knowledge only a
few heterometallic complexes have been characterized.9 Herein,
we examine the reactivity of this N,N function and report new
heterometallic complexes in which the thiadiazole moieties form
a double bridge.
1
In solution, the 31P{ H} NMR spectrum of 3b shows a singlet
at 90.9 ppm, whereas the 1H NMR spectrum shows a complicated
filled-in doublet signal for the protons H2 and H16, bound
to C2 and C16, respectively, which consists of five peaks. This
multiplet could be simulated by considering two 5 + 6J(H,P) values
of 3.6 Hz and 1.4 Hz for the coupling between H2,P1 and H2,P2,
respectively, and a small 2J(P,P) cis-coupling of 0.7 Hz. A similar
situation will be encountered below with 4a (Fig. 6).
Scheme 3
The coordination chemistry of systems in which two pyrazolyl
groups are linked by a spacer X (Scheme 4) through one nitrogen
atom of each pyrazole ring and behave as N,N chelates have
been much studied.10 Such ligands usually readily react with Pd(II)
or Pt(II) precursors to give [Pd(N,N)Cl2] or [Pt(N,N)Cl2] chelate
complexes (Scheme 4).11
Results and discussion
The Pd(II) complex cis-[Pd(Ph2PN CNN CHS)2] (cis-
[Pd(2-H)2], 3b) has been obtained by
a 2 : 1 reaction of
Ph2PNHC NNCHS (2)6 with [PdCl2(NCPh)2] in the presence
of NEt3 at room temperature (Scheme 3). Complex 3b was easily
Complexes 3a and 3b were reacted with [PdCl2(NCPh)2]
and [PtCl2(NCPh)2] in
a
toluene–CH2Cl2 mixture under
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In the molecular structure of the bimetallic complex 4a in
4a·CH2Cl2, the metalloligand 3a chelates the Pd(II) centre through
N3 and N6, which are in a mutual cis arrangement. Although
the Pt(II) centre is not located on a symmetry element, the two
chelating moieties have very similar bonding characteristics. Both
metals feature a slightly distorted square planar environment. The
N1–C1 and C1–N2 (likewise the N4–C15 and C15–N5) bond
lengths are not significantly different from the corresponding
bonds in the parent complex 3a. However, a major difference
between them stems from the orientations of the chelating ligands.
In 3a, the complex shows a planar structure (excluding the
phenyls), whereas in 4a, the mean planes formed by C1, N2, N3,
C2, S1 and C15, N5, N6, C16, S2 form an angle of 33.3(1)◦.
The resulting orientation of the lone pairs at N3 and N6 and the
non-coplanarity of the PdCl2 group with the Pt mean that the
coordination plane [angle between the Pt1, P1, P2, N2, N5 and
Pd1, N3, N6, Cl1, Cl2 planes: 38.21(6)◦] allows a minimization of
the steric repulsions between the chlorides and the neighbouring
Scheme 4 X = organic or organometallic group, M = Pd(II) or Pt(II).
reflux to give the heterobimetallic Pt(II)/Pd(II) complexes
cis-[Pt(Ph2PN CNN CHS)2PdCl2]
([Pt(2-H)2·PdCl2],
4a)
(Scheme 5, Fig. 2) and cis-[Pd(Ph2PN CNN CHS)2PtCl2]
([Pd(2-H)2·PtCl2], 4b) (Scheme 5, Fig. 4), respectively.
˚
CH groups (Fig. 3). The N3 ◊ ◊ ◊ N6 separation of 3.006(5) A is
˚
comparable to that in the parent complex 3a [3.011(4) A and
3.057(4), two crystallographically independent molecules were
present].6
Scheme 5
Fig. 3 An ORTEP side view of the molecular structure of 4a in 4a·CH2Cl2.
Hydrogen atoms, phenyls and solvent molecules have been omitted for
clarity, except for the H atoms in proximity to the two chlorides. Ellipsoids
include 40% of the electron density.
The structure of 4b is analogous to that of 4a, the Pt(II) and
Pd(II) centres having exchanged positions (Fig. 4). The angles of
32.8(4)◦ between the planes of the two thiadiazole rings and of
36.3(2)◦ between the Pd1, P1, P2, N2, N5 and Pt1, N3, N6, Cl1,
Cl2 planes are only slightly smaller than in 4a. The N3–N6 distance
˚
of 3.058(5) A in 3b is only slightly longer than that in 4b [2.999(9)
˚
A]. The similarities between the two structures reflect the similar
˚
covalent radii of the two metal centres, that of Pt (1.36 A) being
12
˚
only slightly smaller than that of Pd (1.39 A).
Fig.
2 An ORTEP view of the molecular structure of 4a in
Pairs of molecules of 4b are disposed centrosymmetrically to
form pseudo-dimers through multiple non-classical H-bonds13
between the two coordinated chlorides and the thiadiazole protons
(Fig. 5).
In view of the surprisingly severe thermal conditions required
for the synthesis of 4a and 4b, when considering the usually facile
substitution reactions of [MCl2(NCPh)2] (M = Pd, Pt), and the
lack of reaction at room temperature of 3a with [Pd(NCMe)4]2+ or
[Cu(NCMe)4]+ in CH2Cl2, it is reasonable to suggest that the nature
of the spacer X (Scheme 4) significantly influences the reactivity
4a·CH2Cl2. Hydrogen atoms and solvent molecules have been omit-
ted for clarity. Ellipsoids include 40% of the electron density. Se-
˚
lected distances (A) and angles (deg): P1–Pt1 2.2512(11), P2–Pt1
2.2469(11), N5–Pt1 2.072(3), N2–Pt1 2.065(3), N3–Pd1 2.056(3), N6–Pd1
2.040(3), Pd1–Cl1 2.2754(11), Pd1–Cl2 2.2779(11), N1–P1 1.671(4),
N4–P2 1.676(4), N2–N3 1.383(5), N5–N6 1.371(5), C1–N1 1.297(6),
C1–N2 1.359(5), C15–N4 1.291(5), C15–N5 1.371(5), C2–N3 1.292(5),
C16–N6 1.298(6); P2–Pt1–P1 103.46(4), N5–Pt1–P2 79.84(10), N2–Pt1–P1
80.25(10),N2–Pt1–N5 96.27(14), N6–Pd1–N3 94.43(13), N3–Pd1–Cl1
88.52(10), N6–Pd1–Cl2 88.07(10), Cl1–Pd1–Cl2 89.03(4).
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to accommodate the second metal between these donor atoms.
Thus, the high kinetic barrier to N,N-chelation of 3a,b results
from the necessary folding of their structure to allow coordination
of a metal centre to N3 and N6.
In solution, the two heterobimetallic complexes show NMR
spectra that are fully consistent with their solid state structure. In
1
the 31P{ H} NMR spectrum of 4a, the phosphorus nuclei resonate
at 62.8 ppm, and show 195Pt satellites with a 1J(31P,195Pt) coupling
constant of 3420 Hz, consistent with the trans influence exerted
1
by the N atoms.6,14 The pattern of the H NMR resonance for
the H2 and H16 protons is a filled-in doublet at 8.92 ppm (Fig.
6), significantly low-field shifted when compared to that of 3a
(8.26 ppm),6 as a result of the proximity of the PdCl2 group.
A similar trend is observed for 4b, whose H2 and H16 protons
1
resonate at 8.83 ppm (8.11 ppm in 3b). The 31P{ H} singlets of
4a (62.8 ppm) and 4b (84.7 ppm) are slightly deshielded, by a
similar value, when compared to those of the precursor complexes
3a (69.6 ppm) and 3b (90.9 ppm).
Fig.
4
An ORTEP view of the molecular structure of com-
pound 4b in 4b·0.5C7H8. Hydrogen atoms and solvent molecules
have been omitted for clarity. Ellipsoids include 40% of the elec-
˚
tron density. Selected distances (A) and angles (deg): P1–Pd1
2.2639(19), P2–Pd1 2.267(2), N5–Pd1 2.068(5), N2–Pd1 2.079(6),
N3–Pt1 2.045(6), N6–Pt1 2.036(6), Pt1–Cl1 2.278(2), Pt1–Cl2 2.2900(18),
N1–P1 1.662(6), N4–P2 1.666(6), N2–N3 1.379(7), N5–N6 1.352(7),
C1–N1 1.311(8), C1–N2 1.345(9), C15–N4 1.315(9), C15–N5 1.355(10),
C2–N3 1.281(9), C16–N6 1.280(9); P2–Pd1–P1 103.42(7), N5–Pd1–P2
80.72(18), N2–Pd1–P1 80.91(16),N2–Pd1–N5 94.7(2), N6–Pt1–N3
94.7(2), N3–Pt1–Cl1 88.82(18), N6-Pt1-Cl2 88.46(16), Cl1-Pt1-Cl2
88.19(7).
1
Fig. 6 Experimental (top) and simulated (bottom) H NMR spectra of
4a in the region of the resonance of protons H2 and H16 centered at
8.92 ppm.
Although diazole and thiadiazole doubly bridged dinuclear
compounds are fairly common, no example of structurally char-
acterized heterometallic palladium–platinum complexes appears
to have been reported in the literature.15 Only one example was
found, in which a diazole ligand bridges these two metals .16
Since complex 4a could, in principle, still be used as a
bimetalloligand (via the P–N and/or the S donors), we attempted
to coordinate a third metal, by reacting 4a with [AuCl(tht)]
(tht = tetrahydrothiophene). Although the latter readily reacted
with the nitrogen atoms in the a-position to phosphorus, ex-
pulsion of the PdCl2 moiety from the complex, in the form of
[PdCl2(tht)2], was concomitantly observed with the formation
of cis-[Pt{Ph2PN(AuCl) CNN CHS}2] ([Pt(2-H)2·(AuCl)2], 5)
(Fig. 7, Scheme 6).
Fig. 5 A diagram of the solid-state structure of 4b in 4b·0.5C7H8 showing
the pseudo-dimers formed by multiple non-classical H-bonds. Hydrogen
atoms and solvent molecules have been omitted for clarity, except for the
H atoms of the thiadiazole rings. Contacts between these atoms and the
coordinated chlorides are depicted as dashed lines (H ◊ ◊ ◊ Cl distances £
˚
2.9 A).
of the uncoordinated N–N atoms of 3a,b and thus the propensity
of these metalloligands to function as N,N-chelates toward Pd(II)
and Pt(II) precursors. This is most probably related to the rigidity
of the [Pt(P,N)2] and [Pd(P,N)2] moieties in 3a and 3b and to the
steric hindrance generated by the C16–H and C2–H protons. The
similarities between the N ◊ ◊ ◊ N separations in 3a/4a and 3b/4b
suggest that a significant increase in this separation is not required
Unlike 4a, complex 5 is not stable in solution and releases
metallic gold with reformation of 3a. Complex 5 was also prepared
by direct reaction of [AuCl(tht)] with 3a. Reactions of 3a or 3b with
[AuCl(tht)] never allowed characterization of a complex showing
coordination of the sulfur atom to gold, which suggests that this
sulfur would be a weaker donor than that of tht, consistent with
the aromaticity of the thiadiazole ring.
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˚
Table 1 A comparison of selected bond distances (A) between complexes
3a, 4a and 6, together with a common atom numbering scheme
Complex 3a
M = nothing
Complex 4a
M = PdCl2
Complex 6
M = PdCl2
Pt1–P1
Pt1–P2
Pt1–N2
Pt1–N5
P1–N1
2.2560(9)
2.2502(8)
2.076(3)
2.078(3)
1.661(3)
1.672(3)
—
—
—
—
1.311(5)
1.310(5)
1.365(4)
1.352(4)
1.380(4)
1.371(4)
2.2512(11)
2.2469(11)
2.065(3)
2.072(3)
1.671(4)
1.676(4)
2.056(3)
2.040(3)
2.2754(11)
2.2779(11)
1.297(6)
1.291(5)
1.359(5)
1.371(5)
1.383(5)
1.371(5)
2.241(3)
2.230(3)
2.074(3)
2.063(9)
1.724(4)
1.708(4)
2.056(9)
2.051(10)
2.272(3)
2.288(3)
1.315(14)
1.305(15)
1.352(14)
1.323(14)
1.370(13)
1.376(13)
P2–N4
Fig.
7
An ORTEP view of the molecular structure of 5 in
Pd1–N3
Pd1–N6
Pd1–Cl1
Pd1–Cl2
C1–N1
C15–N4
C1–N2
C15–N5
N2–N3
N5–N6
5·4CHCl3. Hydrogen atoms and solvent molecules have been omit-
ted for clarity. Ellipsoids include 40% of the electron density. Se-
˚
lected distances (A) and angles (deg): Pt1–P1 2.2383(16), Pt1–P2
2.2469(15), Pt1–N5 2.063(5), Pt1–N2 2.070(5), Au1–N1 2.014(5), Au1–Cl1
2.2431(19), Au2–N4 2.014(5), Au2–Cl2 2.2394(16), P1–N1 1.700(5),
P2–N4 1.707(5), N1–C1 1.339(9), N2–C1 1.353(8), N2–N3 1.382(8),
N3–C2 1.275(9), S1–C1 1.708(6), S1–C2 1.743(9), N4–C15 1.337(8),
N5–C15 1.342(8), N5–N6 1.387(7), N6–C16 1.292(8), S2–C15 1.720(6),
S2–C16 1.746(7); P1–Pt1–P2 99.33(6), N5–Pt1–N2 98.4(2), N2–Pt1–P1
81.13(15), N5–Pt1–P2 81.11(14), N1–Au1–Cl1 177.08(17), N4–Au2–Cl2
178.38(15).
distances in 3a (Table 1), the N1–C1 and C1–N2 distances, and
the related N4–C15 and C15–N5, are slightly longer and shorter,
respectively. This may indicate a more delocalized N···C···N p-
system. Related Pd–Au complexes have been prepared by reaction
of a cyclometallated phosphinoenolate or phosphinoiminolate
Pd(II) complex, respectively, with a Au(I) reagent which binds to
the carbon or nitrogen atom, respectively, in a-position to the
phosphorus donor (Scheme 7).17,18
Scheme 7
˚
The lengths of the Au–Cl [2.2431(19) and 2.2394(16) A] and Au–
˚
N [2.014(5) A] bonds compare well with those reported for anal-
ogous phosphino-thiazoline Pt(II)/Au(I) bimetallic complexes.6
Excluding the phenyl groups, the complex shows a planar structure
˚
(maximum deviation from the mean plane: 0.089(9) A for C2),
contrasting with 4a.
Despite the instability of 5, we were able to record NMR data. Its
1
31P{ H} NMR spectrum consists of a singlet at 77.5 ppm, slightly
deshielded when compared to that of 3a, whereas, the diagnostic
H2 and H16 protons undergo a low-field shift (from 8.26 to 8.47
ppm), suggesting a rather pronounced electronic communication
between the P-nitrogen atoms and the C2 and C16 carbons.
We first hypothesized that the AuCl coordination-induced
expulsion of the PdCl2 fragment could stem from electronic
factors, the electron density at N3 and N6 being reduced upon
coordination of N1 and N4 to an electrophile. However, when 4a
was reacted in an NMR tube with two equivalents of tht, the ligand
associated with the Au(I) reagent, the mononuclear Pt complex
Scheme 6
In the molecular structure of 5 in 5·4CHCl3, 3a acts as a
bidentate bridging metalloligand, coordinating two AuCl units
through N1 and N4. The bond lengths around Pt are analogous
to those found in 4a. Compared to the corresponding bond
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1
3a formed within a few minutes (with 31P{ H} monitoring). This
was rather surprising, since a formally bisimine chelating ligand,
such as in 4a, was thought to be more efficient towards Pd(II)
than the labile tht. Formation of 3a from 4a and tht suggests
that steric factors play an important role in this reaction, and
that the tension of the metalloligand 3a within 4a (exemplified
by its bent arrangement) could labilize the structure, promoting
the expulsion of PdCl2. On the other hand, upon incorporation
of the AuCl fragments, the system seems to lose stability since, as
mentioned above, complex 5 is an unstable product. With the aim
to introduce a PdCl2 moiety into 5 by formation of an N,N-chelate,
5 was reacted with [PdCl2(cod)], rather than [PdCl2(NCPh)2]
because the liberated cod would be easier to remove from the
reaction mixture than benzonitrile, thus preventing the type of
competition reactions encountered in the Au/tht system. However,
our attempts failed, owing to the high kinetic barrier to the N,N-
chelation of 5, similar to that of 3a (see above), which requires
the use of thermal conditions incompatible with the instability
of 5.
To confirm that cis-[Pt(Ph2PN CNN CHS)2PdCl2] (4a) is
still an electron-rich species, we reacted it with HBF4·Et2O, both
in solution and in the solid state. This resulted in a rapid and clean
double protonation of the P-bound nitrogen atoms and the form-
ation of very stable cis-[Pt(Ph2PNH CNN CHS)2 PdCl2](BF4)2
(4a·2HBF4, 6, Fig. 8, Scheme 8), which retains the PdCl2 group.
In view of the isolobal analogy between the proton and a
[R3P–Au]+ cation,19 this indicates that the use of 4a as metal-
loligand for the formation of trimetallic, tetranuclear complexes
should, in principle, be possible but intrinsic difficulties remain to
be overcome.
Scheme 8 The localization of the NH C double bonds has a formal
character.
In the molecular structure of 6, the N atoms are all engaged
as donors. Metalloligand 3a chelates a PdCl2 unit as in 4a and
is doubly protonated on both P-bound nitrogen atoms. These
NH functions are involved in H-bonds with the neighbouring
-
BF4 counter ions. Protonation on N1 and N4 results in longer
P–N distances than in its parent complex 4a, suggesting that
their lone pair in 4a is partly engaged in this bond. The Pt–P
and Pd–Cl distances remain similar. Other distances cannot be
reliably compared, due to the relatively high standard deviations
for the bond lengths in 6. Selected bond distances are compared in
Table 1.
Conclusion
The multidentate, functional phosphine ligand 2 has proven to be
efficient in coordination chemistry and owing to the presence of
a P-bound NH group, it readily forms in the presence of NEt3, a
stable bischelated palladium(II) complex 3b, in which 2 has been
deprotonated at the N atom. In both 3b and its previously reported
Pt(II) analogue 3a, the cis-arrangement around the d8 metal centres
provides a potentially N,N-chelating system involving the CH–N
nitrogen of each of the thiadiazole ring. This has been exploited
with Pd(II) and Pt(II) precursors to form the heterobimetallic
complexes 4a and 4b, respectively, in which ligand 2 behaves as
an anionic, formally 6e- donor. Attempts to increase the ligand
donicity and prepare tetranuclear, trimetallic Pd(II)/Pt(II)/Au(I)
complexes failed, since 4a and 4b were found to be labile when
exposed to tht, which is the ligand associated with the Au(I)
reagent. This resulted in the loss of the MCl2 moiety. However, 4a
was successfully protonated to give a stable cationic Pt(II)/Pd(II)
complex, suggesting that 2 could indeed be used as an anionic
ligand, formally donating 8e-.
Experimental section
General considerations
All manipulations were carried out under an inert argon atmo-
sphere, using standard Schlenk line conditions and dried and
Fig. 8 An ORTEP view of the molecular structure of 6. Solvent
molecules and hydrogen atoms, except those bound to N1 and N4, have
been omitted for clarity. Ellipsoids include 40% of the electron density.
1
freshly distilled solvents. Unless otherwise stated, the 1H, 13C{ H}
1
and31P{ H} NMR spectra were recorded on a Bruker Avance 300
˚
Selected bond distances (A) and angles (deg): P1–Pt1 2.241(3), P2–Pt1
instrument at 300.13, 75.47, and 121.49 MHz, respectively, using
TMS or H3PO4 (85% in D2O) as the external standards, with down-
field shifts reported as positive. All NMR spectra were measured
at 298 K, unless otherwise specified. The assignment of the signals
was made by 1H, 1H-COSY, and 1H, 13C-HMQC, 13C-HSQC
experiments. Elemental C, H, and N analyses were performed by
the Service de Microanalyses, Universite´ de Strasbourg (France).
2.230(3), N5–Pt1 2.063(9), N2–Pt1 2.074(3), N3–Pd1 2.056(9), N6–Pd1
2.051(10), Pd1–Cl1 2.272(3), Pd1–Cl2 2.288(3), N1–P1 1.724(4), N4–P2
1.708(4), N2–N3 1.370(13), N5–N6 1.376(13), C1–N1 1.315(14), C1–N2
1.352(14), C15–N4 1.305(15), C15–N5 1.323(14), C2–N3 1.273(15),
C16–N6 1.265(15); P2–Pt1–P1 99.61(12), N5–Pt1–P2 82.6(3), N2–Pt1–P1
81.2(3), N2–Pt1–N5 96.3(4), N6–Pd1–N3 94.0(4), N3–Pd1–Cl1 88.1(3),
N6–Pd1–Cl2 88.8(3), Cl1–Pd1–Cl2 89.27(12).
5716 | Dalton Trans., 2011, 40, 5711–5719
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Ligand 26 and the complexes [PtCl2(NCPh)2], [PdCl2(NCPh)2],20
[AuCl(tht)] (tht = tetrahydrothiophene)21 and 3a6 were prepared
according to literature procedures. Ph2PCl and NEt3 were freshly
distilled before use. Other chemicals were commercially available
and were used as received.
quantitative formation of 5 was spectroscopically observed. Al-
though a gold mirror progressively formed, few crystals suitable for
X-ray analysis were obtained by layering the CDCl3 solution with
Et2O. A direct synthesis of this complex is detailed below, see (b).
1H NMR (CDCl3): d = 7.15–7.55 (m, 20H, Ph), 8.47 (m simulated
as a AA’XX’ spin system, 2H, 5 + 6J(H,P) = 4.5 Hz, 2J(P,P) = 5.2 Hz,
1
N
CH); 31P{ H} NMR (CDCl3): d = 77.5 (s, with Pt satellites,
Preparation and spectroscopic data for 3b
1J(P,Pt) = 3328 Hz); 13C{ H} NMR (CDCl3): d = 128–133 (m, Ph),
1
To a stirred solution of [PdCl2(NCPh)2] (0.200 g, 0.52 mmol)
in MeCN (100 mL), NEt3 (0.500 mL, 3.59 mmol) and solid
2 (0.300 g, 1.05 mmol) were added. Stirring was continued for
1 h and Et3N·HCl was removed by filtration. The volatiles were
removed under reduced pressure and the white powder obtained
was washed with MeCN (3 ¥ 10 mL). Drying under reduced
pressure gave pure 3b as a white powder. Yield: 0.327 g, 93%.
1H NMR (CD2Cl2): d = 7.13–7.39 (m, 20H, Ph), 8.11 (filled-in
doublet simulated as AA’XX’ spin system, 2H, 5 + 6J(H,P) = 3.6
142.7 (br, N CH), 187.6 (s, N–C N).
(b) Solid [AuCl(tht)] (0.064 g, 0.200 mmol) was added to a
solution of complex 3a (0.076 g, 0.100 mmol) in CH2Cl2 (10 mL).
The resulting reaction mixture was stirred for 5 min and then
precipitated with pentane (100 mL). The solid was collected by
filtration and washed with pentane (2 ¥ 10 mL). Evaporation of
the volatiles afforded 5 as a white powder. Yield: 0.122 g, 89%.
Anal. calcd for 5: C 27.37, H 1.81, N 6.84. Found: C, 29.50, H,
2.02, N 6.10.
1
and 1.4 Hz, 2J(P,P) = 0.7 Hz, N CH); 31P{ H} NMR (CD2Cl2):
1
d = 90.9 (s); 13C{ H} NMR (CD2Cl2): d = 128.2–132.5 (m, Ph),
Preparation and spectroscopic data for 6
4
139.2 (br, N CH, J(CP) = 6.4 Hz), 184.5 (N–C N, indirect
observation by HMBC). Anal. calcd for 3b: C 49.82, H 3.29, N
12.45. Found: C 49.61, H 3.40, N 12.57.
(a) In a 5 mm NMR tube, a solution of HBF4·Et2O (0.006 g,
0.037 mmol) was added to a CDCl3 solution (0.5 mL) of 4a
(0.016 g, 0.017 mmol). After 10 min, the NMR signals of 4a have
disappeared and a precipitate formed. The volatiles were removed
under reduced pressure and CD3CN was added, which dissolved
the precipitate. Complex 6 was observed spectroscopically and
suitable crystals for X-ray diffraction were obtained by layering
diethyl ether onto this saturated solution of complex 6 in CD3CN.
1H NMR (CD3CN): d = 7.34–7.63 (m simulated as a AA’XX’
Preparation and spectroscopic data for 4a
Solid [PdCl2(NCPh)2] (0.061 g, 0.157 mmol) was added to a
solution of complex 3a (0.120 g, 0.157 mmol) in a mixture of
CH2Cl2 (20 mL)/toluene (60 mL). The resulting slurry was stirred
under reflux for 3 h. The solution was cooled to room temperature,
the volatiles were removed under reduced pressure and the residue
was washed with CH2Cl2 (3 ¥ 10 mL), and evaporation of the
volatiles gave compound 4a as an orange powder. Yield: 0.130 g,
88%. The product can be recrystallized by layering toluene onto a
saturated solution of complex 4a in CH2Cl2. 1H NMR (CD2Cl2):
d = 7.19–7.45 (m, 20H, Ph), 8.92 (filled-in doublet simulated as a
spin system, 20H, Ph), 9.02 (m, 2H, 5 + 6J(H,P) = 1.8 and 1.9 Hz,
1
N
CH); 31P{ H} NMR (CD3CN): d = 67.1 (s, with Pt satellites,
1J(31P,195Pt) = 3415 Hz).
(b) A solution of HBF4·Et2O (0.035 g, 0.216 mmol) was added to
a stirred solution of 4a (0.100 g, 0.106 mmol) in CH2Cl2 (10 mL).
Stirring was continued for 10 min, the volatiles were removed
under vacuum and the residue was washed with diethyl ether (2 ¥
10 mL). The resulting residue was dissolved in a minimum amount
of acetonitrile and the solution was layered with diethyl ether,
giving yellow microcrystals of 6 (Yield: 0.087 g, 73%). Anal. Calcd
for 6: C 30.12, H 2.17, N 7.53. Found: C 29.71, H 2.35, N 7.75.
2
AA‘XX’ spin system, 2H, 5 + 6J(H,P) = 3.6 and 1.9 Hz, J(P,P) =
1
0.8 Hz, N CH); 31P{ H} NMR (CD2Cl2): d = 62.8 (s, with Pt
1
1
satellites, J(31P,195Pt) = 3420 Hz); 13C{ H} NMR (CD2Cl2): d =
128.1–132.4 (m, Ph), 151.5 (br, N CH), 183.2 (N–C N, indirect
observation by HMBC). Anal. calcd for 4a·CH2Cl2: C 33.95, H
2.36, N 8.19. Found: C 34.22, H 2.30, N 7.87.
Crystal structure determinations
Preparation and spectroscopic data for 4b
Suitable crystals for the X-ray analysis of all compounds were
obtained as described above. The intensity data were collected on
a Kappa CCD diffractometer22 (graphite monochromated Mo-
The procedure described for complex 4a was also applied to the
synthesis of 4b, by using [PtCl2(NCPh)2] (0.100 g, 0.212 mmol) and
3b (0.143 g, 0.212 mmol). Yield: 0. 170 g, 85%. 1H NMR (CDCl3):
d = 7.12–7.37 (m, 20H, Ph), 8.83 (filled-in doublet simulated as a
˚
Ka radiation, l = 0.71073 A) at 173(2) K. Crystallographic and
2
AA’XX’ spin system, 2H, 5 + 6J(H,P) = 3.4 and 1.4 Hz, J(P,P) =
experimental details for the structures are summarized in Table
2. The structures were solved by direct methods (SHELXS-97)
and refined by full-matrix least-squares procedures (based on
F2, SHELXL-97)23 with anisotropic thermal parameters for all
the non-hydrogen atoms. The hydrogen atoms were introduced
into the geometrically calculated positions (SHELXS-97 proce-
dures) and refined riding on the corresponding parent atoms. In
4b·0.5C7H8, a molecule of toluene was found disordered over
two positions around the symmetry centre. It was refined with
restrained anisotropic parameters. In 5·4CHCl3, a chloroform
molecule was found disordered in two positions with no atom
in common and with equal occupancy factors. The disorder was
1
1
0.4 Hz, N CH); 31P{ H} NMR (CDCl3): d = 84.7 (s); 13C{ H}
NMR (CDCl3): d = 128.1–132.4 (m, Ph), 149.4 (br, N CH),
178.8 (N–C N, indirect observation by HMBC). Anal. calcd for
4b·1.5CH2Cl2: C 33.16, H 2.36, N 7.87. Found: C 33.18, H 2.67,
N 7.79.
Observation and crystallization of 5
(a) In a 1 cm diameter NMR tube, solid complex 4a (0.050 g,
0.053 mmol) was dissolved in CDCl3 (5 mL). Solid [AuCl(tht)]
(0.033 g, 0.106 mmol) was added to this solution. After 10 min,
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Table 2 X-ray data collection and refinement parameters
3b
4a·CH2Cl2
4b·0.5C7H8
5·4CHCl3
6
Chemical formula
C28H22N6P2PdS2
C28H22Cl2N6P2PdPtS2·
CH2Cl2
1025.89
Monoclinic
10.2464(4)
19.2382(8)
19.7126(6)
90.00
120.504(2)
90.00
3348.0(2)
173(2)
P21/c
4
5.283
31 573
9783
0.0576
0.0392
0.0711
C28H22Cl2N6P2PdPtS2·
0.5(C7H8)
987.03
Triclinic
9.9144(3)
13.1141(3)
13.9616(3)
111.536(1)
102.871(1)
91.897(1)
C28H22Au2Cl2N6P2PtS2·
4(CHCl3)
1705.97
C28H24Cl2N6P2PdPtS2·
2(BF4)
Formula mass
Crystal system
674.98
Triclinic
1116.60
Monoclinic
14.5753(8)
13.1508(8)
21.3008(9)
90.00
92.351(3)
90.00
4079.4(4)
173(2)
P21/c
4
4.244
7937
7937
0.0000
0.0670
0.1725
0.1094
0.1905
1.024
Triclinic
˚
a/A
11.3926(4)
14.0042(4)
18.9125(8)
99.963(2)
91.366(2)
109.306(2)
2794.08(17)
173(2)
10.9741(5)
13.6758(9)
17.5503(9)
89.302(5)
73.211(5)
80.247(2)
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
1632.85(7)
173(2)
2483.3(2)
T/K
173(2)
¯
¯
¯
Space group
Z
P1
P1
P1
4
2
2
m/mm-1
0.959
11 343
11 343
0.0533
0.0441
0.0907
0.0835
0.1062
1.026
5.254
11 407
7496
0.0376
0.0482
0.0967
0.0942
0.1148
1.022
9.638
28 663
14 475
0.0570
0.0472
0.1036
0.0800
0.1179
0.999
Measd. Refl.
Indep. refl.
Rint
R1 (I > 2s(I))
wR(F2) (I > 2s(I))
R1 (all data)
wR(F2) (all data)
S on F2
0.0746
0.0802
0.986
modelled unrestrained. The crystals of 6 were of poor quality and
visibly twinned. In addition, badly disordered solvent molecules
were found. Attempts to determine these atomic positions failed.
A PLATON–SQUEEZE procedure was then applied.24 The
2 (a) R. Pattacini, G. Margraf, A. Messaoudi, N. Oberbeckmann-Winter
and P. Braunstein, Inorg. Chem., 2008, 47, 9886; (b) S. Jie, M. Agostinho,
A. Kermagoret, C. S. J. Cazin and P. Braunstein, Dalton Trans.,
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Mantovani, Dalton Trans., 2003, 1601; (d) P. Braunstein, G. Clerc and
X. Morise, New J. Chem., 2003, 27, 68; (e) P. Braunstein, F. Naud and
S. J. Rettig, New J. Chem., 2001, 25, 32; (f) P. Braunstein, C. Graiff, F.
Naud, A. Pfaltz and A. Tiripicchio, Inorg. Chem., 2000, 39, 4468; (g) P.
Braunstein, M. D. Fryzuk, M. Le Dall, F. Naud, S. J. Rettig and F.
Speiser, J. Chem. Soc., Dalton Trans., 2000, 1067.
3 (a) L. Mantilli, D. Ge´rard, S. Torche, C. Besnard and C. Mazet, Chem.–
Eur. J., 2010, 16, 12736; (b) P. Chavez, I. G. Rios, A. Kermagoret, R.
Pattacini, A. Meli, C. Bianchini, G. Giambastiani and P. Braunstein,
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A. Pfaltz, Angew. Chem., Int. Ed., 2007, 46, 8274; (d) F. Speiser, P.
Braunstein and L. Saussine, Organometallics, 2004, 23, 2633; (e) F.
Speiser, P. Braunstein, L. Saussine and R. Welter, Organometallics,
2004, 23, 2613; (f) P. Braunstein, F. Naud, C. Graiff and A. Tiripicchio,
Chem. Commun., 2000, 897; (g) G. C. Lloyd-Jones and A. Pfaltz, Z.
Naturforsch., B: J. Chem. Sci., 1995, 50, 361; (h) J. Sprinz and G.
Helmchen, Tetrahedron Lett., 1993, 34, 1769.
3
˚
estimation of the missing electron count was 379 in 651 A . This
is consistent with 2 Et2O molecules per asymmetric unit. The
procedure resulted in improved refinement parameters. One of the
BF4 anions was disordered as well. Attempts to model the disorder
failed. This anion was then refined with restrained anisotropic
parameters, B–F distances and F–B–F angles. CCDC 801707 (3b),
801708 (4a·CH2Cl2), 801709 (4b·0.5C7H8), 810710 (5·4CHCl3),
801711 (6) contain the supplementary crystallographic data for
this paper, see ESI.†
Acknowledgements
The work was supported by the CNRS, the Ministe`re de
l’Enseignement Supe´rieur et de la Recherche, and the Agence
Nationale de la Recherche (ANR-06-BLAN 410). We thank
Lionel Allouche for NMR experiments.
4 A. Kermagoret, R. Pattacini, P. Chavez Vasquez, G. Rogez, R. Welter
and P. Braunstein, Angew. Chem., Int. Ed., 2007, 46, 6438.
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Commun., 2006, 3098.
6 R. Pattacini, C. Giansante, P. Ceroni, M. Maestri and P. Braunstein,
Chem.–Eur. J., 2007, 13, 10117.
7 S. Zhang, R. Pattacini and P. Braunstein, Organometallics, 2010, 29,
6660.
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