Sterically controlled synthesis and nucleophilic substitution reactions of di- and trimeric n-heterocyclic phosphenium metal(0) halides

Article abstract of DOI:10.1002/ejic.201402137

The reaction of symmetrical bis(diazaphospholenyl) compounds with [MCl ₂(cod)] (M = Pd, Pt; cod = 1,5-cyclooctadiene) has been used to prepare N-heterocyclic phosphenium (NHP) metal(0) halides [M(NHP)Cl]_n with diverse N substituents.

Full text of DOI:10.1002/ejic.201402137

FULL PAPER
DOI:10.1002/ejic.201402137
Sterically Controlled Synthesis and Nucleophilic
Substitution Reactions of Di- and Trimeric N-Heterocyclic
Phosphenium Metal(0) Halides
Jan Nickolaus,[a] Johannes Bender,[a] Martin Nieger,[b] and
Dietrich Gudat*[a]
Keywords: P ligands / Bridging ligands / Aggregation / Cross coupling
The reaction of symmetrical bis(diazaphospholenyl) com-
pounds with [MCl2(cod)] (M = Pd, Pt; cod = 1,5-cycloocta-
diene) has been used to prepare N-heterocyclic phosphen-
ium (NHP) metal(0) halides [M(NHP)Cl]n with diverse N sub-
stituents. Characterisation by ESI-MS and NMR spec-
troscopy revealed that N-tBu- and N-aryl-substituted NHP
precursors yield trimeric (n = 3) and dimeric (n = 2) products,
respectively; the degree of aggregation is presumably con-
trolled by the different steric requirements of the NHP moi-
disturbed by crystallographic disorder. Studies of ligand sub-
stitution and redistribution processes revealed that the com-
plexes withstand exchange of the μ-bridging NHP units but
tolerate substitution of the terminal chlorido ligands by other
strong nucleophiles (SCN–, I–) with conservation of the oligo-
meric framework. Attempts to replace chlorido by thiolato
ligands led to the discovery of a reaction between a phos-
phenium metal thiolate [Pd(NHP)(SR)]3 and CH2Cl2 to give
a formaldehyde dithioacetal H2C(SR)2 (R = benzyl). This re-
ety. A single-crystal XRD study of a trimeric Pd complex con- action could be developed into a protocol for a C–S cross-
firmed the proposed constitution of the complexes with μ2-
bridging NHP and terminal chlorido ligands and allowed
their metrical parameters to be analysed for the first time un-
coupling reaction in the presence of a catalytic amount of the
phosphenium complex.
type carbene complexes (Ia; Scheme 1).[5,8] In contrast, the
bonding in complexes of the second type has been interpre-
ted in terms of the interaction of an anionic phosphide li-
gand with a divalent metal centre (Ib; Scheme 1), and the
dichotomy between the two types of complexes is assumed
to reflect a variable electron demand in the phosphenium
ligands, which has allowed one to establish an analogy with
the “non-innocent” behaviour of nitrosyl ligands.[6]
Introduction
Cyclic diaminophosphenium ions[1,2] (also known as N-
heterocyclic phosphenium ions, NHP) have a long history
in coordination chemistry because of their ability to act as
σ-donor/π-acceptor ligands in transition-metal com-
plexes.[3,4] A particularly interesting sub-class are complexes
with group 10 metal atoms (M = Ni, Pd, Pt) of the general
type [MX(NHP)(L)2] (I)[5,6] and [MX(NHP)]2 (II;[7,8] L =
phosphane, X = halide), which exhibit notable structural
diversity and raise some scientifically interesting electron-
counting difficulties (Scheme 1).[8] Thus, complexes I exist
as two structural varieties in which the phosphorus atom in
the NHP unit exists either in a trigonal-planar coordination
sphere with a short P–M bond or in a pyramidal coordina-
tion with a lengthened P–M bond. Structures of the first
type are considered to reflect the interaction of a cationic
phosphenium ligand with a zero-valent metal atom to form
a double bond in a bonding situation similar to Fischer-
[a] Institut für Anorganische Chemie, University of Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany
E-mail: gudat@iac.uni-stuttgart.de
http://www.iac.uni-stuttgart.de/arbeitskreise/akgudat
[b] Laboratory of Inorganic Chemistry, Department of Chemistry,
University of Helsinki,
Scheme 1. Structures of phosphenium complexes [MX(NHP)(L)2]
(I: R = aryl, X = halide, M = Pd, Pt, L = phosphane donor),
[MX(NHP)]2 (IIa: R = Dipp, M = Pd; IIb: R = Dipp, M = Pd;
IIc: R = Mes, M = Ni) and [PdCl{P(NR2)2}]3 (IIIa: R = Cy; IIIb:
R = iPr). Dipp = 2,6-iPr2C6H3.
P. O. Box 55 (A. I. Virtasen aukio 1), 00014 University of
Helsinki, Finland
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201402137.
Compounds II exhibit dimeric molecular structures held
together by asymmetrically μ2-bridging phosphenium li-
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gands (Scheme 1). Based on the analysis of spectroscopic
The palladium complexes 3 and 5 precipitated from the
data and the outcome of ligand displacement reactions, reaction mixture and were easily isolated after washing with
which showed that they can act as viable sources of zero- diethyl ether. The platinum complex 4 was obtained after
valent metal atoms, these species were addressed as metal(0) evaporation of the solvent and washing of the residue sev-
halides with cationic phosphenium ligands.[7] Nonetheless, eral times with diethyl ether, whereas complex 6 was gener-
complexes II still bear a close structural resemblance to the ated in a similar manner but could not be isolated in pure
trimers III, which were originally described on formal form as complete removal of all by-products proved unfeas-
grounds as triangulo clusters of bridging phosphido ligands ible. All four compounds are deep-red, air-stable solids that
and divalent metal centres.[9]
do not dissolve in ethers (traces of the platinum complexes
Bearing in mind that the acyclic diaminophosphenium are soluble in THF) or hydrocarbons but are fairly soluble
ions [P(NR2)2]+, which are formal constituents of III, are in dichloromethane. The products were unambiguously
much stronger electrophiles than the NHPs found in II, we identified from NMR and positive-mode ESI-MS data. The
were interested to establish whether the structural deviation mass spectra show dominant peaks of cations formed by
between the two types of complexes is caused by different cleavage of a chloride; the spectrum of 4 also exhibits the
electronic properties of the ligand fragments, or by other peak of a pseudo-molecular ion generated by attachment of
factors such as steric influences. In addition, we wondered Na+ to the intact complex. Analysis of nominal masses and
whether substitution of the halide functionalities in II could simulation of isotope patterns (see the Supporting Infor-
be used to access new multinuclear assemblies, or whether mation) confirmed that N-tert-butyl-substituted complexes
such attempts might, like reactions with phosphane do- 3 and 4 have a trimeric nature, whereas the N-aryl derivative
nors,[7] induce a breakdown of the oligomeric structures. To 5 is, like IIa,b, dimeric. The 31P and 1H NMR spectra show
address these questions, we synthesized an extended range signals of a single NHP unit and thus confirm a symmetric
of oligomeric NHP metal(0) halides of type II and studied molecular structure in which all the ligands are equivalent.
their reactivity towards suitable nucleophiles. The results, A different degree of aggregation of the Pt complexes 4 and
which are reported herein, give account of the successful 6 is directly visible from the dissimilar 195Pt satellite pat-
synthesis of trimeric NHP metal(0) halides, which are struc- terns in the 31P NMR spectra. The habit of the spectrum
tural analogues of III, an unprecedented crystal structure of 6 matches that of IIb,[7] and the satellite lines are readily
of one such derivative, and their stoichiometric and cata- attributable to A2X and A2X2 sub-spectra of P2(195Pt)1 and
lytic anion substitution reactions, which culminated in the P2(195Pt)2 isotopomers. The spectrum of 4, in contrast, exhi-
first catalytic application of a phosphenium metal halide in bits a complicated pattern that was decomposed by spectral
C–S cross-coupling reactions.
simulation into the AB2X, ABBЈXXЈ and AAЈAЈЈXXЈXЈЈ
sub-spectra expected for the P3(195Pt)n (A, B = 31P; X =
195Pt; n = 1–3) isotopomers of a trimer (Figure 1a). Com-
plementary splitting was also observed in the 195Pt NMR
spectrum (Figure 1b). Analysis of the multiplicities associ-
Results and Discussion
1
ated with the large J(31P,195Pt) couplings confirmed, as in
The synthesis of donor-free phosphenium metal(0) hal-
ides [MCl(NHP)]2 (IIa,b in Scheme 1) has previously been
described by several routes involving (1) the reaction of
[MCl2(cod)] (M = Pd, Pt) with a suitable diphosphane,
(2) the base-induced condensation of [MCl2(cod)] with a
secondary phosphane and (3) the reaction of [Pd2(dba)3]
(dba = dibenzylideneacetone) with an N-heterocyclic chlo-
rophosphane.[7] According to the first route, we treated
[MCl2(cod)] with the symmetrical diphosphanes 1 or 2 to
give the phosphenium complexes 3–6 and a stoichiometric
amount of N-heterocyclic chlorophosphanes 7 and 8,
respectively (Scheme 2).
IIb, the μ2-bridging coordination of the NHP ligands.
The 31P chemical shifts of 3–6 in general fall in the down-
field region (δ Ͼ 200 ppm), which is typical of the majority
of related phosphenium complexes[5–9] but not for IIb,
which exhibits a very unusual 31P chemical shift at δ =
26.9 ppm,[7] nearly 200 ppm lower than in the other com-
plexes. We attribute this amazing deviation to the rather
special electronic situation[7] that presumably makes this
compound an outlier. The finding that platinum complexes
4 and 6 display larger chemical shifts than their palladium
analogues 3 and 5 is likewise slightly unusual and contrasts
both common experience and the known trend for phos-
phane-stabilized Pd and Pt complexes of type I.[6] We there-
fore wish to refrain from a further interpretation of any
trends in chemical shifts, because a meaningful explanation
of the observed irregularities needs further studies that are
1
beyond the scope of this work. The value of J(31P,195Pt) in
4 (2304 Hz) is less than that in 6 (3954 Hz) and IIb
(5000 Hz), presumably as a consequence of the higher nu-
clearity of the complex.
The suggested structure of 3 was confirmed by a single-
crystal X-ray diffraction study of a THF solvate obtained
by slow crystallization from the reaction mixture. The com-
Scheme 2. Synthesis of donor-free phosphenium metal(0) halides
3–6 (3: R = tBu, M = Pd, n = 3; 4: R = tBu, M = Pt, n = 3; 5: R
= Dmp, M = Pd, n = 2; 6: R = Dmp, M = Pt, n = 2). Dmp = 2,6-
Me2C6H3; cod = cyclooctadiene).
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Figure 1. Experimental (blue traces) and simulated (red traces)
31P{1H} (top, the intense line of the parent isotopomer was cut off)
and 195Pt{1H} NMR spectra (bottom) of 4. The 31P NMR spec-
trum was simulated as a superposition of A3, AB2X, ABBЈXXЈ and
AAЈAЈЈXXЈXЈЈ sub-spectra and the 195Pt spectrum as a superposi-
tion of AB2X and ABBЈXXЈ sub-spectra, which were weighted ap-
propriately to reflect the different natural abundances of individual
isotopomers. Parameters used for simulation: δ31P = 281.5 ppm,
Figure 2. View of the molecular structure of 3 (top) and a reduced
plot displaying only atoms in the Pd3Cl3 core and diazaphosphol-
ene rings (bottom). Hydrogen atoms have been omitted for clarity.
Thermal ellipsoids are drawn at the 50% probability level. Selected
distances [Å]: Pd1–P1 2.2770(12), Pd1–P41 2.2901(12), Pd1–Cl1
2.4227(12), Pd1–Pd3 2.7464(5), Pd1–Pd2 2.7743(5), Pd2–P1
2.2893(12), Pd2–P21 2.2904(11), Pd2–Cl2 2.4044(11), Pd2–Pd3
2.7643(5), Pd3–P21 2.2622(12), Pd3–P41 2.2925(13), Pd3–Cl3
2.4156(11), P1–N5 1.669(4), P1–N2 1.682(4), N2–C3 1.407(6), C3–
C4 1.317(7), C4–N5 1.407(6), P21–N25 1.660(4), P21–N22
1.677(4), N22–C23 1.384(6), C23–C24 1.333(7), C24–N25 1.384(6),
P41–N45 1.673(4), P41–N42 1.676(4), N42–C43 1.379(6), C43–C44
1.328(7), C44–N45 1.388(6).
1
2
3
δ195Pt = –4505 ppm; JPtP = 2304 Hz, JPP = 490 Hz, JPtP
=
2
211 Hz, JPtPt = 129 Hz.
plex crystallizes in the orthorhombic space group P212121
and contains isolated molecules (Figure 2, top) that exhibit
a star-shaped structure similar to that of IIIb,[9] but lacks
the strong disorder that had prevented a detailed evaluation μ-bridging coordination, which contrasts the definitely un-
of the structural features of this species.
symmetrical binding mode in II.[7,8] Finally, the metal–
The core of each complex (Figure 2, bottom) consists of metal distances in 3 [2.746(1)–2.774(1) Å, average 2.762 Å]
a planar Pd3P3 unit (mean deviation from the least-squares are longer than in IIa [2.6410(2) Å[7]]. Even though these
plane 0.025 Å) in which the phosphorus atoms form a values are still in the range of Pd–Pd bonds in dimeric PdI
rather regular triangle and the metal atoms bisect the sides complexes (2.72Ϯ0.1 Å[11]), direct metal–metal bonding
of this triangle. The Pd–Cl bonds lie nearly in the core plane seems even less likely than in IIa.[7]
(angles with the least-squares plane are 2.7–6.8°). The metal
In summary, the molecular structure of 3 bears a close
atoms adopt a planar, distorted T-shaped coordination resemblance to those of the dimeric phosphenium metal(0)
sphere [the P–Pd–P units with angles between 164.0(1) and halide IIa and the triangulo cluster IIIb, but shows a nearly
165.7(1)° form the bar of the T]. The Pd–P distances symmetric μ-bridging coordination of the NHP units. The
[2.262(1)–2.293(1) Å, average 2.284 Å] are marginally observation that NHP units can stabilize both dinuclear
longer than in IIa [2.2738(4) and 2.2401(4) Å, average (IIa) and trinuclear (3) assemblies has led us to conclude
2.257 Å[7]]. The Pd–Cl distances [2.404(1)–2.423(1) Å, that the degree of aggregation in these complexes is not
average 2.414 Å] lie between the corresponding distance in determined by different electronic properties of the bridging
IIa [2.3361(4) Å[7]] and a Ib-type complex [2.4530(11) Å[6]]. diaminophosphanyl units but rather by steric influences: it
The diazaphospholene rings are planar (mean deviation seems that paddle-shaped N-aryl substituents (in II, 5 and
from the least-squares planes 0.010 Å) and perpendicular 6) favour the formation of dimers, whereas more globular
to the P3Pd3 plane (dihedral angles 86.9–88.9°). Intra-li- (and possibly sterically less-demanding) N-alkyl groups (in
gand bond lengths (cf. Figure 2) match the values in IIa[7] IIIb, 3 and 4) tolerate a higher degree of association.
and known chlorodiazaphospholenes and NHPs.[10] The ar-
rangement of NHP units in 3 comes close to a symmetrical with unlike NHP ligands stimulated us to explore the pros-
The coexistence of di- and trinuclear metal(0) halides
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pect of generating mixed species through intermolecular ex- stepwise manner. This was confirmed in a detailed study of
change processes. However, a 31P NMR spectroscopic a CH2Cl2 solution containing a mixture of chlorido com-
analysis of a CH2Cl2 solution containing equimolar plex 3 and iodido complex 9, which revealed that the start-
amounts of trinuclear 3 and dinuclear 5 revealed that even ing materials reacted eventually to form new products. Sim-
after a prolonged time (5 d) signals from the starting mate- ulation allowed us to interpret the observed spectral pattern
rials were exclusively observed. The failure to detect even (Figure 3) as a superposition of the A3 spin systems of the
trace amounts of reaction products suggested that cluster starting materials with two A2B spin systems, which we
interchange by the scrambling of μ-bridging ligands is ap- have assigned to trinuclear complexes with Cl2I and ClI2
parently not possible.
substitution patterns. The formation of new products is
Considering that the previously mentioned elongation of readily explained as resulting from stepwise halide transfer
Pd–Cl distances in 3 might imply a certain bond weakening, between the starting materials, and the failure to detect any
we believed that nucleophilic replacement of the terminal further intermediates suggests that the trinuclear structures
ligands should offer a more promising approach to cluster of the starting materials is conserved in all the reaction
modification. We therefore studied the behaviour of 3 steps. Even though the halide exchange may proceed by di-
towards suitable nucleophiles and found that the chloride rect interaction between trinuclear clusters, we cannot ex-
ions are indeed easily displaced by soft nucleophiles such as clude that it is promoted by trace amounts of halide impuri-
iodide or thiocyanate (Scheme 3).[12] No ligand substitution ties, and the apparent ligand redistribution is merely a spe-
but decomposition to give a black precipitate of palladium cial case of nucleophilic substitution.
and phosphenium triflate 11 (Scheme 3; identified by its
known chemical shift[10]) was observed upon treatment of
3 with excess trimethylsilyl triflate. We assume that this re-
action is likewise initiated by Cl/OTf exchange, but that a
hypothetical NHP palladium(0) triflate is unstable and de-
composes. This finding is in line with previous results,[5,13]
which indicated that the “push–pull” effect exerted by a
combined action of π-acceptor and strong σ-donor ligands
is essential for the stabilization of the zero-valent metal
atom in these complexes.
Figure 3. Experimental (blue trace) and simulated (red trace)
31P{1H} NMR spectra of a mixture of complexes [Pd3(NHP)3-
ClnI3–n] (n = 0–3; NHP = 1,3-di-tert-butyldiazaphospholenium) in
CH2Cl2. The spectra of the homoleptic complexes were simulated
Scheme 3. Substitution reactions of 3. Reagents and conditions:
as A3 (Cl3: δ = 250.4 ppm, molar fraction 0.28; I3: δ = 247.6 ppm,
(i) excess Me3SiI, THF, 2 h, –78 °C; (ii) excess NaSCN, THF, 1 h,
molar fraction 0.05) and those of heteroleptic complexes as AB2
room temp.; (iii) excess Me3SiOTf, room temp.
spin systems (Cl2I: δ = 250.3 and 248.9 ppm, J = 373.9 Hz, molar
fraction 0.44; ClI2: δ = 248.9 and 247.6 ppm, J = 359.9 Hz, molar
fraction 0.24).
Substitution products 9 and 10 were isolated after appro-
priate workup as red to purple air-stable solids that are
more soluble in THF than starting material 3. The identity
The successful synthesis of 10 stimulated us to investigate
of the complexes was confirmed, as before, by 31P NMR also the reactions of 3 with other sulfur nucleophiles. Treat-
and ESI-MS data (see the Exp. Sect.). Analysis of the MS ment of a THF solution of 3 with benzylthiol in the pres-
data indicated that the trinuclear assembly had in all cases ence of K2CO3 produced a purple precipitate clearly con-
remained intact. The IR spectrum of thiocyanato complex taining a mixture of the desired substitution product and
10 contains two bands at 2089 and 2106 cm–1, which have inorganic salts formed as by-products. Purification of the
been attributable to νCN stretching modes but did not allow solid material was prevented by its very low solubility in
clear discrimination between N- and S-bound ligands.[14]
A
most aprotic solvents and its chemical instability in DMSO
clear assignment was finally made on the basis of a prelimi- or protic media. The 31P NMR spectrum of a suspension in
nary single-crystal X-ray diffraction study. Even though the CH2Cl2 allowed us to identify the signal of the substitution
limited quality of the data (not deposited) impeded satisfac- product as a singlet with a chemical shift (δ = 255 ppm)
tory structure refinement, the data proved the presence of similar to that of 3 (δ = 250 ppm). Surprisingly, this solu-
a trinuclear complex with a shape similar to that of 3 and tion proved unstable, and the species initially present trans-
terminal S-thiocyanato ligands (see the Supporting Infor- muted slowly via spectroscopically detectable intermediates
mation).
into 3 (see the Supporting Information). These observations
led us to conclude that the reaction of 3 with benzylthiol
Monitoring of the progress of the halide exchange by 31
P
NMR spectroscopy permitted the detection of transient in- and K2CO3 affords thiolato complex 12, which then inter-
termediates and suggested that the reaction proceeds in a acts with CH2Cl2 to regenerate 3 by the stepwise substitu-
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tion of thiolato by chlorido ligands. The by-product of this ligands of 3 for thiolates led to the discovery of a catalytic
process was later identified as formaldehyde dithioacetal 13 cross-coupling reaction between dichloromethane and
(Scheme 4).
benzylthiol to give a formaldehyde dithioacetal under very
mild conditions. We are currently conducting a detailed
study to explore the use of phosphenium metal halides in
C–S cross-coupling reactions.
Experimental Section
General: All manipulations were carried out under dry argon using
standard vacuum-line techniques. Solvents were dried by using
standard procedures. NMR spectra were recorded with Bruker Av-
ance 400 (1H, 400.1 MHz; 13C, 100.6 MHz; 31P, 161.9 MHz; 195Pt,
86.7 MHz) and Avance 250 (1H, 250.1 MHz; 13C, 62.9 MHz; 31P,
101.2 MHz) NMR spectrometers at 303 K. Chemical shifts are ref-
Scheme 4. Mutual transformation between 3 and benzylthiolato
complex 12 and the mechanism proposed for the catalytic C–S
cross-coupling reaction between PhCH2SH and CH2Cl2. DCM =
CH2Cl2.
erenced to external TMS (1H, 13C), 85% H3PO4 (Ξ
=
40.480747 MHz, 31P) and 1.2 m Na2[PtCl6] (Ξ = 21.496784 MHz,
195Pt). Coupling constants are given as absolute values. Spectral
simulations were carried out by using the WinDaisy program,
which is part of the spectrometer software. (+)-ESI mass spectra
Combining the formation of 12 from 3 with the regenera-
tion of the starting material by reaction with CH2Cl2 forms
a cycle that should in principle allow catalytic base-induced were recorded in MeOH solutions with a Bruker Daltonics Micro-
TOF Q spectrometer. Elemental analyses were performed with a
Thermo Micro Cube CHN/S analyser. Melting points were deter-
mined in sealed capillaries with a Büchi B-545 melting-point appa-
ratus.
coupling of benzylthiol and dichloromethane at room tem-
perature. To verify this hypothesis, we studied the reaction
of CH2Cl2 with 2 equiv. of PhCH2SH and K2CO3 in anhy-
drous THF at ambient temperature. Whereas only traces of
the starting materials reacted in the absence of a catalyst,
the thiol was quantitatively consumed within 72 h when
5 mol-% of 3 were present. The bis(benzylthio)methane (13)
formed was isolated in 82% yield and identified by 1H
NMR spectroscopy. If one considers that dichloromethane
was employed as stoichiometric reactant rather than sol-
vent, the performance of this catalytic process can be con-
sidered to compare with that of other known cross-coupling
reactions between thiols and polyhaloalkanes, which are in-
duced by strong organic bases,[15] microwave irradiation[16]
or the action of catalytic amounts of rhodium complexes.[17]
Synthesis of Palladium Complexes 3 and 5: A solution of the appro-
[18]
priate diphosphane (1:[18] 199 mg, 0.50 mmol; 2:
295 mg,
0.50 mmol) and [PdCl2(cod)] (143 mg, 0.50 mmol) in anhydrous
THF (5 mL) was stirred at room temperature for 1 h. The solution
turned deep red. The precipitate formed was filtered off, washed
with diethyl ether (2ϫ 10 mL) and dried in vacuo. In the case of
3, prolonged storage of the filtrate produced a small batch of crys-
talline material that was suitable for single-crystal XRD analysis.
Complex 3: Yield: 153 mg (0.15 mmol, 90%), m.p. 306 °C (dec.).
1H NMR (CDCl3): δ = 7.14 (m, 6 H, CH-N), 1.65 (s, 54 H, CH3)
ppm. 13C{1H} NMR (CDCl3): δ = 124.9 (m, CH-N), 59.1 [s,
C(CH3)], 32.0 (m, CH3) ppm. 31P{1H} NMR (CDCl3): δ = 249.0
(s) ppm. MS [(+)-ESI]: m/z (%) = 987.06 (100) [M – Cl]+.
C30H60Cl3N6P3Pd3 (1023.39): calcd. C 35.21, H 5.91, N 8.21; found
C 34.57, H 6.10, N 7.92.
Conclusions
Complex 5: Yield: 153 mg (0.17 mmol, 70%), m.p. 306 °C (dec.).
1H NMR (CDCl3): δ = 7.60–6.90 (m, 12 H, C6H3), 6.84 (s, 4 H,
CH-N), 2.44 (s, 24 H, CH3) ppm. 13C{1H} NMR (CDCl3): δ =
135.9 (s), 134.8 (s), 128.7 (m), 127.2 (m, CH-N), 19.1 (s, CH3) ppm.
31P{1H} NMR (CDCl3): δ = 214.7 (s) ppm. MS [(+)-ESI]: m/z (%)
= 837.05 (100) [M – Cl – H2]+. C36H40Cl2N4P2Pd2 (874.43): calcd.
C 49.45, H 4.61, N 6.41; found C 49.03, H 4.62, N 6.22.
We have established that the reactions of bis(diazaphos-
pholenyl) compounds with [MCl2(cod)] (M = Pd, Pt) can
serve as a general synthetic route to both di- and trimeric
phosphenium metal(0) halides [MCl(NHP)]n (n = 2, 3) with
μ2-bridging N-heterocyclic phosphenium (NHP) ligands.
The degree of aggregation in the compounds studied seems
to be controlled by the steric bulk of the N substituents in
the NHP moiety. A single-crystal X-ray diffraction study of
a trimeric complex revealed that the NHP ligand exhibits
a more symmetrical μ-bridging coordination mode than in
previously reported[7] dimeric complexes. The oligomers re-
sist attempts to exchange the μ-bridging NHP ligands, but
replacement of the terminal chloride ions by other (pseudo)
halides is feasible and proceeds with conservation of the
oligomeric core. This behaviour contrasts the reactions of
IIa,b with neutral phosphanes, which proceed with rupture
of the oligomers to yield mononuclear, donor-stabilized
phosphenium metal chlorides or phosphane–metal(0) com-
Synthesis of Platinum Complexes 4 and 6: A solution of the appro-
priate diphosphane (1:[18] 199 mg, 0.50 mmol; 2:[18] 295 mg,
0.50 mmol) and [PtCl2(cod)] (187 mg, 0.50 mmol) in anhydrous
THF (10 mL) was stirred at room temperature for 4 h. The solution
turned deep red. The solvent was evaporated, and the remaining
red solid was washed with diethyl ether (5ϫ 5 mL) and then with
hexane (2ϫ 5 mL) and finally dried in vacuo.
Complex 4: Yield: 168 mg (0.13 mmol, 79%), m.p. Ͼ350 °C (dec.).
1H NMR (CDCl3): δ = 7.07 (m, 6 H, CH=N), 1.48 (s, 54 H, CH3)
ppm. 13C{1H} NMR (CDCl3): δ = 123.4 (m, CH-N), 58.2 [s,
C(CH3)], 31.6 (m, CH3) ppm. 31P{1H} NMR (CDCl3): δ = 281.5
(s; simulation of the 195Pt satellite spectrum gave: m, 2JPP = 490 Hz,
plexes, respectively.[7] An attempt to exchange the chlorido 1JPtP = 2304 Hz, JPtP = 211 Hz) ppm. 195Pt NMR (CDCl3): δ =
3
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1
3
2
–4505 (m, JPtP = 2304 Hz, JPtP = 211 Hz, JPtPt = 129 Hz) ppm. Crystallography: The crystal structure of 3 was determined with a
MS [(+)-ESI]: m/z (%) = 1311.21 (100) [M + Na]+, 1253.20 (25) Bruker Kappa APEXII Duo diffractometer at 110(2) K using Mo-
[M – Cl]+. C30H40Cl3N6P3Pt3 (1269.21): calcd. C 27.95, H 4.69, N
6.52; found C 28.13, H 4.80, N 6.51.
Kα radiation (λ = 0.71073 Å). The structure was solved by using
direct methods (SHELXS-97[19]) and refined by the full-matrix
least-squares method on F2 (SHELXL-97[19]). A numerical absorp-
tion correction was applied. Non-hydrogen atoms were refined an-
isotropically and hydrogen atoms with a riding model on F2. The
oxygen atom of one solvent molecule is disordered.
Complex 6: Complex 6 could not be obtained in pure form as quan-
titative separation of by-products formed during the reaction was
not possible. The complex was, however, unambiguously identified
1
by spectroscopic data. H NMR (CDCl3): δ = 7.16–6.76 (m, 12 H,
C30H60Cl3N6P3Pd3·2THF,
M =
1167.51 gmol–1, crystal size
C6H3), 6.70 (s, 4 H, CH=N), 2.20 (s, 24 H, CH3) ppm. 31P{1H}
0.32ϫ0.19ϫ0.17 mm, orthorhombic, space group P212121, a =
14.2069(7), b = 16.4980(8), c = 21.4425(12) Å, V = 5025.8(4) Å3, Z
= 4, ρ(calcd.) = 1.543 mgm3, F(000) = 2384, θmax = 27.5°, μ =
0.135 mm–1, 46529 reflections measured, 11511 unique reflections
(Rint = 0.035) for structure solution and refinement with 496 pa-
rameters and 31 restraints, max./min. transmission 0.882/0.667, R1
[for 9645 reflections with IϾ2σ(I)] = 0.035, wR2 = 0.067, GoF (on
F2) = 1.03, absolute structure parameter –0.05(2), largest diff. peak/
hole 0.672/–0.518 eÅ–3. CCDC-987716 contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
1
NMR (CDCl3): δ = 247.0 (s, JPtP = 3954 Hz) ppm. 195Pt NMR
1
(CDCl3): δ = –4369 (t, JPtP = 3969 Hz) ppm.
Synthesis of Complex 9: Me3SiI (22 mg, 0.11 mmol) was added
slowly through a syringe to a cooled (–78 °C) solution of complex
3 (37 mg, 36 μmol) in anhydrous THF (20 mL). The mixture was
stirred for 1 h and warmed to room temperature. The solvent was
then removed in vacuo, and the deep-red residue was washed hex-
ane (2ϫ 5 mL) and dried in vacuo to yield 42 mg (32 μmol, 90%)
of the product. M.p. 306 °C (dec.). 1H NMR (CDCl3): δ = 7.23 (br.
s, 6 H, CH=N), 1.60 (s, 54 H, CH3) ppm. 13C{1H} NMR (CDCl3):
δ = 125.9 (m, CH-N), 58.7 [s, C(CH3)], 31.0 (m, CH3) ppm.
31P{1H} NMR (CDCl3): δ = 247.9 (s) ppm. MS [(+)-ESI]: m/z (%)
= 1320.83 (100) [M + Na]+. C30H60I3N6P3Pd3 (1297.74): calcd. C
27.77, H 4.66, N 6.48; found C 26.87, H 4.82, N 6.89.
Supporting Information (see footnote on the first page of this arti-
cle): Molecular structure of the crystal of 10 and selected NMR
and MS data.
Synthesis of Complex 10: A solution of 3 (56 mg, 55 μmol) and
NaSCN (14 mg, 176 μmol) in anhydrous THF (10 mL) was stirred
at room temperature for 2 h. During this time the deep-red solution
turned pink. Undissolved solids were removed by filtration and the
filtrate concentrated to dryness. The solid residue was washed di-
ethyl ether (2ϫ 5 mL) and dried under reduced pressure to yield
51 mg (47 μmol, 85%) of the product. M.p. Ͼ350 °C (dec.). 1H
NMR (CDCl3): δ = 7.36 (m, 6 H, CH=N), 1.70 (s, 54 H, CH3)
ppm. 13C{1H} NMR (CDCl3): δ = 128.3 (m, CH-N), 124.2 (br.,
SCN), 60.1 [s, C(CH3)], 32.1 (m, CH3) ppm. 31P{1H} NMR
(CDCl3): δ = 243.3 (s) ppm. MS [(+)-ESI; solution in CHCl3/
MeCN, 1:3]: m/z (%) = 1033.0 (20) [M – SCN]+, 1114.0 (50) [M +
Acknowledgments
We thank the Academy of Finland for a Research Fellowship and
the Deutscher Akademischer Austauschdienst (DAAD) for finan-
cial support. We further thank J. Trinkner for measurement of mass
spectra and Dr. W. Frey (both from the Institute of Organic Chem-
istry, University of Stuttgart) for the collection of X-ray data.
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Na]+, 1195.0 (100) [M + Na + 2 MeCN]+. IR: ν 2106, 2089 (ν
)
˜
SCN
cm–1. C33H60N9P3Pd3S3 (1091.26): calcd. C 36.32, H 5.54, N 11.55;
found C 37.23, H 6.25, N 10.06.
Reaction of 3 with Benzylthiol: Complex 3 (153 mg, 0.15 mmol) and
K2CO3 (104 mg, 0.75 mmol) were suspended in anhydrous THF,
and benzylthiol (74 mg, 0.6 mmol) was added through a syringe.
The mixture changed colour from deep-red to purple and was
stirred for 2 h. The solid, deep-purple residue was removed by fil-
tration and washed with THF. Complex 12 was identified by 1H
and 31P NMR spectroscopic data; 13C NMR spectra were not avail-
able due to poor solubility. Attempts to separate this species from
the inorganic by-products by extraction or washing were unsuccess-
1
ful. H NMR (CDCl3): δ = 7.34–7.21 (m, 15 H, C6H5), 7.29 (m, 6
H, CH=N), 3.47 (s, 6 H, CH2S), 1.73 (s, 54 H, CH3) ppm. 31P{1H}
NMR (CDCl3): δ = 254.8 (s) ppm.
Bis(benzylthio)methane (13):
A mixture of K2CO3 (2.07 g,
15 mmol), dichloromethane (255 mg, 3.0 mmol) and benzylthiol
(745 mg, 6.0 mmol) was suspended in anhydrous THF (10 mL),
and a catalytic amount of 3 (153 mg, 0.15 mmol, 5 mol-%) was
added. The red solution turned purple. The mixture was stirred for
3 d during which time the solution turned red again. The solvent
was removed under reduced pressure and the remaining solid ex-
tracted with hexane (4ϫ 5 mL). Concentration of the combined
extracts gave 600 mg (2.5 mmol, 82%) of spectroscopically pure 13,
which was identified by 1H NMR spectroscopy. 1H NMR (CDCl3):
δ = 7.25–7.12 (m, 10 H, C6H5), 3.75 (s, 4 H, SCH2), 3.30 (s, 2 H,
SCH2S) ppm.
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[12] 31P NMR studies provided preliminary evidence that the
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Received: March 5, 2014
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Published Online: June 3, 2014
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim