Preparation, structure, and reactivity of dipalladium(I) complexes containing the carbanion 2-C6F4PPh2: Coexistence of distinct, noninterconverting head-to-head [dipalladium(0/II)] and head-to-tail [dipalladium(I)] species

Article abstract of DOI:10.1021/om300525p

Comproportionation of trans-[Pd(κ²-2-C₆F ₄PPh₂)₂] with [PdL₄] (L = PPh ₃, AsPh₃) gives metal-metal-bonded dipalladium(I) complexes [Pd₂^I(μ-2-C₆F₄PPh ₂)₂(L)₂] [L = PPh₃ (5), AsPh ₃ (6)] in which the bridging ligands adopt a head-to-tail arrangement. The corresponding diplatinum(I) complex [Pt₂ ^I(μ-2-C₆F₄PPh₂) ₂(PPh₃)₂] (9) is obtained similarly from [Pt(κ²-2-C₆F₄PPh₂) ₂] and [Pt(PPh₃)₃]. The separations between the metal atoms in the dipalladium(I) complexes [2.5740(3) A (5), 2.5511(3) A (6)] are slightly less than that in the diplatinum(I) complex 9 [2.61179(15) A]. The axial triphenylarsine ligands of 6 are replaced by tert-butyl isocyanide to give the dipalladium(I) complex [Pd₂ ^I(μ-2-C₆F₄PPh₂) ₂(CN^tBu)₂] (7). However, treatment of trans-[Pd(κ²-2-C₆F₄PPh₂) ₂] with [Pd(CN^tBu)₂], generated in situ from a mixture of tert-butyl isocyanide and [Pd(η⁵-Cp) (η³-allyl)], gives a formally mixed-valent palladium(0)- palladium(II) complex [Pd₂^0/II(μ-2-C₆F ₄PPh₂)₂(CN^tBu)₂] (8), in which the bridging ligands are arranged head-to-head. In contrast, comproportionation of [Pt(κ²-2-C₆F ₄PPh₂)₂] with [Pt₃(CN ^tBu)₆] gives the diplatinum(I) complex [Pt ₂^I(μ-2-C₆F₄PPh₂) ₂(CN^tBu)₂] (10) analogous to 7; there was no evidence for the formation of a dinuclear mixed-valent species. Although complexes 7 and 8 are isomers, with similar Pd-Pd separations [2.5803(4) A (7), 2.5580(2) A (8)], they do not interconvert in solution. The diplatinum(I) complex 9 undergoes oxidative addition with iodine to give an A-frame cation, [Pt₂(μ-I)(μ-2-C₆F ₄PPh₂)₂(PPh₃)₂] ⁺, isolated as its PF₆^- salt (11). In contrast, the dipalladium(I) complex 5 eliminates one of the PPh₃ ligands when it undergoes oxidative addition with halogens and with methyl iodide, the products being A-frame dipalladium(II) complexes [Pd₂X(μ-Y)(μ- 2-C₆F₄PPh₂)₂(PPh₃)] [X = Y = I (12), Cl (13); X = Me, Y = I (14)]. The metal-metal distances in 11-14 [2.9478(5) A (11), 2.8078(7) A (12), 2.8241(3) A (13), and 2.8013(5) A (14)] are ca. 0.3 A greater than in their dimetal(I) precursors, consistent with a weaker metal-metal interaction in the dimetal(II) complexes. Unexpectedly, reaction of 5 with iodobenzene gives a mononuclear palladium(II) complex, cis-[Pd(κ²C,P-2-C₆F ₄PPh₂)(κC-2-C₆F₄PPh ₂)(PPh₃)] (15). This is suggested to be formed by a sequence of (a) oxidative addition of iodobenzene to 5 to give a σ-phenyl complex analogous to the σ-methyl complex 14, (b) a change in the binding mode of one of the 2-C₆F₄PPh₂ ligands from μ- to κ²-, and (c) reductive elimination of tetraphenylphosphonium iodide and loss of Pd(0).

Full text of DOI:10.1021/om300525p

Article
pubs.acs.org/Organometallics
Preparation, Structure, and Reactivity of Dipalladium(I) Complexes
Containing the Carbanion 2‑C6F4PPh2: Coexistence of Distinct,
Noninterconverting Head-to-Head [Dipalladium(0/II)] and Head-to-
Tail [Dipalladium(I)] Species
Suresh K. Bhargava,*,† Steven H. Priver,† Anthony C. Willis,‡ and Martin A. Bennett*,‡
́
†School of Applied Sciences (Applied Chemistry), RMIT University, GPO Box 2476 V, Melbourne, Victoria 3001, Australia
‡Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
S
* Supporting Information
ABSTRACT: Comproportionation of trans-[Pd(κ2-2-
C6F4PPh2)2] with [PdL4] (L = PPh3, AsPh3) gives metal−
I
metal-bonded dipalladium(I) complexes [Pd2 (μ-2-
C6F4PPh2)2(L)2] [L = PPh3 (5), AsPh3 (6)] in which the
bridging ligands adopt a head-to-tail arrangement. The
I
corresponding diplatinum(I) complex [Pt2 (μ-2-
C6F4PPh2)2(PPh3)2] (9) is obtained similarly from [Pt(κ2-2-
C6F4PPh2)2] and [Pt(PPh3)3]. The separations between the metal atoms in the dipalladium(I) complexes [2.5740(3) Å (5),
2.5511(3) Å (6)] are slightly less than that in the diplatinum(I) complex 9 [2.61179(15) Å]. The axial triphenylarsine ligands of
I
6 are replaced by tert-butyl isocyanide to give the dipalladium(I) complex [Pd2 (μ-2-C6F4PPh2)2(CNtBu)2] (7). However,
treatment of trans-[Pd(κ2-2-C6F4PPh2)2] with [Pd(CNtBu)2], generated in situ from a mixture of tert-butyl isocyanide and
[Pd(η5-Cp)(η3-allyl)], gives a formally mixed-valent palladium(0)−palladium(II) complex [Pd20/II(μ-2-C6F4PPh2)2(CNtBu)2]
(8), in which the bridging ligands are arranged head-to-head. In contrast, comproportionation of [Pt(κ2-2-C6F4PPh2)2] with
I
[Pt3(CNtBu)6] gives the diplatinum(I) complex [Pt2 (μ-2-C6F4PPh2)2(CNtBu)2] (10) analogous to 7; there was no evidence for
the formation of a dinuclear mixed-valent species. Although complexes 7 and 8 are isomers, with similar Pd−Pd separations
[2.5803(4) Å (7), 2.5580(2) Å (8)], they do not interconvert in solution. The diplatinum(I) complex 9 undergoes oxidative
addition with iodine to give an A-frame cation, [Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2]+, isolated as its PF6− salt (11). In contrast, the
dipalladium(I) complex 5 eliminates one of the PPh3 ligands when it undergoes oxidative addition with halogens and with methyl
iodide, the products being A-frame dipalladium(II) complexes [Pd2X(μ-Y)(μ-2-C6F4PPh2)2(PPh3)] [X = Y = I (12), Cl (13); X
= Me, Y = I (14)]. The metal−metal distances in 11−14 [2.9478(5) Å (11), 2.8078(7) Å (12), 2.8241(3) Å (13), and 2.8013(5)
Å (14)] are ca. 0.3 Å greater than in their dimetal(I) precursors, consistent with a weaker metal−metal interaction in the
dimetal(II) complexes. Unexpectedly, reaction of 5 with iodobenzene gives a mononuclear palladium(II) complex, cis-[Pd(κ2C,P-
2-C6F4PPh2)(κC-2-C6F4PPh2)(PPh3)] (15). This is suggested to be formed by a sequence of (a) oxidative addition of
iodobenzene to 5 to give a σ-phenyl complex analogous to the σ-methyl complex 14, (b) a change in the binding mode of one of
the 2-C6F4PPh2 ligands from μ- to κ2-, and (c) reductive elimination of tetraphenylphosphonium iodide and loss of Pd(0).
For example, the mononuclear platinum(II) complexes cis-
[Pt(κ2C,P-5-R-2-C6H3PPh2)2] [R = H (1a), Me (1b)] dimerize
on heating to diplatinum(II) complexes 2a and 2b (Scheme
1),5,6 and the tetrapalladium(II) complex [Pd4(μ-Br)4(μ-2-
C6H4PPh2)4] (3) reacts with moderately bulky tertiary
phosphines to give monomeric species [PdBr(κ2C,P-
C6H4PPh2)(L)] (L = PPh3, PCy3) (Scheme 2).7,8
Comproportionation of the platinum(II) complex 1a or 1b
with [Pt(PPh3)3] affords diplatinum(I) complexes [Pt2(μ-5-R-
2-C6H3PPh2)2(PPh3)2] [R = H (3a), Me (3b)], in which the
carbanions bridge, in a head-to-tail (HT) arrangement, a pair of
covalently bound platinum(I) (5d9) atoms (Scheme 3).5,6
Efforts to extend these studies to the corresponding
INTRODUCTION
■
The ortho-C−H activation of triphenylphosphine is a well-
established route to cyclometalated complexes of the d-block
elements, although methods based on transmetalation from
reagents such as 2-LiC6H4PPh2 and on oxidative addition of 2-
BrC6H4PPh2 have also found application.1 Most of the resulting
complexes are mononuclear and contain the four-membered
ring M(κ2C,P-2-C6H4PPh2); however, there are cases where, in
the reaction product, the carbanion functions as a bridging,
bidentate ligand. Examples are [Rh2(MeCO2H)2(μ-
O2CMe)2(μ-2-C6H4PPh2)2], which is isolated from the
reaction of dirhodium(II) tetraacetate with PPh3 in glacial
acetic acid,2 and [Pt2(μ-PPh2)(μ-2-C6H4PPh2)(PPh3)2], which
is one of the products of thermal decomposition of
platinum(0)-triphenylphosphine complexes.3,4 Interconversion
between the two binding modes has also been demonstrated.
Received: June 12, 2012
Published: August 1, 2012
© 2012 American Chemical Society
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reaction of 4 with PPh3 and [Pd(η5-Cp)(η3-allyl)] at low
temperature. Complexes 5 and 6 gave satisfactory elemental
analyses, and their ESI mass spectra each showed a peak
corresponding to the [M]+ ion. The Raman spectra of both
compounds displayed a strong band at ca. 130 cm−1, assigned
to ν(Pd−Pd), the value being similar to those reported for the
bis(diphenylphosphino)methane (dppm)-bridged dipalladium-
(I) complexes [Pd2X2(μ-dppm)2] (X = Cl, 152 cm−1; X = Br,
120 cm−1).11 The 31P NMR spectrum of 5 contained two
resonances at δ −19.3 and 8.4, corresponding to the
phosphorus nuclei in the bridging and axial ligands,
respectively; that of 6 showed only one broad resonance at δ
−17.6, assigned to the bridging 2-C6F4PPh2 groups. The 19F
NMR spectra of 5 and 6 showed the expected four resonances,
at ca. δ −105, −130, −153, and −163 ppm relative to CFCl3.
By analogy with the previously reported spectra of 2-C6F4PPh2
complexes of Pd and Pt,9 we assign these to F6 (ortho to Pd−
C), F3 (ortho to PPh2), and F5 and F4 (para to Pd−C),
respectively (numbering shown in Scheme 4). The structures
proposed for 5 and 6 have been confirmed by X-ray
crystallography (see later).
Scheme 1
Scheme 2
Scheme 3
Attempts to produce heterobimetallic complexes by
comproportionation of [Pt(κ2-2-C6F4PPh2)2] with [Pd-
(PPh3)4], or of complex 4 with [Pt(PPh3)3], were unsuccessful.
When a solution of complex 6 was treated with two
equivalents of tert-butyl isocyanide, the axial triphenylarsine
ligands were displaced to give the dipalladium(I) complex
[Pd2 (μ-2-C6F4PPh2)2(CNtBu)2] (7) (Scheme 4), which was
I
isolated as a yellow solid in 91% yield. Surprisingly, when a
solution of trans-[Pd(κ2-2-C6F4PPh2)2] (4) was treated
t
sequentially with BuNC and [Pd(η5-Cp)(η3-allyl)], providing
[Pd(CNtBu)2] in situ,12 the product isolated was not 7 but the
isomeric, pale yellow, mixed-valent complex [Pd20/II(μ-2-
C6F4PPh2)2(CNtBu)2] (8), in which, as shown by X-ray
crystallography (see later), the bridging 2-C6F4PPh2 groups are
arranged head-to-head (HH) (Scheme 5). In addition to the
dipalladium(I) complexes have been frustrated by our inability
thus far to make the palladium(II) analogues of 1a and 1b.
Nevertheless, we have made a stable ortho-palladated complex,
trans-[Pd(κ2C,P-2-C6F4PPh2)2] (4),9 thus exemplifying the
stabilization of transition metal−aryl bonds (especially those
of palladium)10 brought about by the substitution of hydrogen
by fluorine in the aromatic ring. We show here that complex 4
is a suitable precursor to ortho-metalated dipalladium(I) species
and compare some of their chemistry with that of the
corresponding diplatinum(I) compound.
Scheme 5
RESULTS
■
Dipalladium(I) Complexes. Comproportionation of trans-
[Pd(κ2-2-C6F4PPh2)2] (4) with [Pd(PPh3)4] at room temper-
ature, or with [Pd(AsPh3)4] at 60 °C, gave the dipalladium(I)
I
complexes [Pd2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (5), AsPh3
(6)] as orange and yellow solids, respectively, in 80−95% yield
(Scheme 4). Complex 5 could also be prepared from the
Scheme 4
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1
t
expected aromatic multiplets, the H NMR spectrum of 7
shows a singlet at δ 0.56 due to the equivalent protons of the
tBuNC ligands, whereas the spectrum of 8 contains a pair of
singlets of equal intensity at δ 0.45 and 0.63, demonstrating the
inequivalence of the tBuNC ligands in 8. The 19F NMR spectra
of 7 and 8 are similar to those of 4−6, although the resonances
due to the ortho-fluorine atoms (F6) are shifted from ca. δ −105
to −109 in the case of 7 and −113 in the case of 8, possibly
because F6 resides in the shielding zone of the NC groups.
The 31P NMR spectra of 7 and 8 each show a broad singlet at
ca. δ −14, consistent with the presence of equivalent μ-2-
C6F4PPh2 groups, and the ESI mass spectra both have a parent-
ion peak at m/z 1046. The IR spectrum of 7 in a KBr disk
shows a strong ν(NC) band at 2164 cm−1, whereas the
spectrum of 8 in Nujol shows two such bands, at 2159 and
2187 cm−1, again consistent with the presence of inequivalent
tBuNC groups. There was no evidence from the 31P NMR
spectra for interconversion of these HH and HT isomers in air-
and moisture-free dichloromethane at room temperature;
decomposition occurred on heating.
C6F4PPh2)2(L)2] [L = PPh3 (5), AsPh3(6), BuNC (7)],
[Pd20/II(μ-2-C6F4PPh2)2(CNtBu)2] (8), and [Pt2 (μ-2-
C6F4PPh2)2(L)2] [L = PPh3 (9), BuNC (10)]. The crystals
of 5 and 6 were isomorphous with that of 9 (monoclinic, P21/
n). The molecular structures of 7−9 are shown in Figures 1−3,
respectively; selected bond distances and angles for 5−7, 9, and
10 are collected in Table 1, and selected bond distances and
angles for 8 are shown in the caption to Figure 2.
I
t
To enable direct comparison between analogous 4d9−4d9
and 5d9−5d9 systems, we prepared the diplatinum(I) analogues
I
of complexes 5 and 7, [Pt2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3
(9), BuNC (10)], by the comproportionation of [Pt(κ2-2-
t
C6F4PPh2)2] with [Pt(PPh3)3] and [Pt3(CNtBu)6], respec-
tively. The ESI mass spectra of 9 and 10 each showed a peak
corresponding to [M + H]+, and the Raman spectrum of 9
displayed a strong band at 126 cm−1 assignable to ν(Pt−Pt), cf.,
150 cm−1 in [Pt2Cl2(μ-dppm)2],13 157 cm−1 in [Pt2Cl(CO)(μ-
dppm)2]PF6,14 and 165 cm−1 in [Pt2(CO)6]2+;15 the
corresponding band in 10 was not observed. The 31P NMR
spectrum of 9 contained a pair of resonances at δ −8.2 and 24.4
due to the phosphorus nuclei in the 2-C6F4PPh2 (PA) and axial
PPh3 (PB) ligands, respectively, together with complex platinum
satellites. Simulation of the AA′BB′XX′ spin system (ignoring
19F coupling) enabled extraction of the P−P and Pt−P coupling
constants (see Experimental Section), which are, in general,
similar to those for complexes 3a and 3b.5,6 One notable
I
Figure 1. Molecular structure of [Pd2 (μ-2-C6F4PPh2)2(CNtBu)2] (7)
with selected atom labeling. Ellipsoids show 30% probability levels,
and asterisks denote atoms generated by symmetry. Hydrogen atoms
have been omitted for clarity.
1
difference appears in the values of JPtP (JAX), which are 2369
Hz for 9, 1937 Hz for 3a, and 1918 Hz for 3b, the larger value
for 9 being consistent with the lower NMR trans influence of
the perfluoroaryl group.16 In addition, the magnitude of the
coupling constant between the phosphorus nuclei of the
bridging groups (JAA′) appears to be close to zero in 9, in
contrast to ca. 55 Hz in 3a and 3b. The 31P NMR spectrum of
10 showed a broad singlet at δ −7.4. Simulation of the AA′XX′
spin system gave 195Pt coupling constants of 2330 Hz (JAX) and
156 Hz (JAX′), which are comparable to the corresponding
values in 9 (2369 and 133 Hz, respectively). As was observed in
9, the magnitude of the coupling between the two phosphorus
nuclei in 10 appears to be close to zero; however, both spectra
are complicated by unresolved 19F coupling to PA, which may
lead to errors in the estimated values of JAA′
.
Figure 2. Molecular structure of [Pd20/II(μ-2-C6F4PPh2)2(CNtBu)2]
(8) with selected atom labeling. Ellipsoids show 30% probability levels,
and asterisks denote atoms generated by symmetry. Hydrogen atoms
have been omitted for clarity. Selected bond distances (Å) and angles
(deg): Pd(1)−Pd(2) 2.5580(2), Pd(1)−P(1) 2.3013(5), Pd(1)−C(1)
2.057(3), Pd(2)−C(2) 1.993(3), Pd(2)−C(12) 2.076(2), Pd(2)−
Pd(1)−P(1) 76.461(13), P(1)−Pd(1)−C(1) 108.15(19), P(1)−
Pd(1)−P(1*) 152.92(3), Pd(2)−Pd(1)−C(1) 175.2(2), Pd(1)−
Pd(2)−C(12) 87.08(5), C(2)−Pd(2)−C(12) 93.0(4), C(12)−
Pd(2)−C(12*) 174.17(11), Pd(1)−Pd(2)−C(2) 175.6(5).
The 19F NMR spectra of 9 and 10 are similar to those of the
dipalladium(I) complexes 6 and 7, the resonance due to F6 at
ca. δ −105 being accompanied by 195Pt satellites [3JPtF = 267 Hz
(9), 262 Hz (10)]. The magnitudes of these coupling constants
3
are comparable with the values of JPtF in cis-[Pt(C6F5)2(L)2]
[L2 = 2PPh3 (315 Hz),17 dppe (309 Hz)18].
X-ray Structures of the Dipalladium(I), Palladium(0)−
Palladium(II), and Diplatinum(I) Complexes. Single-crystal
X-ray structural analyses have been carried out on [Pd2 (μ-2-
I
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Table 1. Selected Bond Distances (Å) and Angles (deg) for
I
[Pd2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (5), AsPh3t(6), tBuNC
I
(7)], [Pt2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (9), BuNC
(10)], [Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2][PF6] (11), and
[Pd2Y(μ-X)(μ-2-C6F4PPh2)2(PPh3)] [X = Y = I (12), Cl
(13); X = I, Y = Me (14)]
I
Figure 3. Molecular structure of [Pt2 (μ-2-C6F4PPh2)2(PPh3)2] (9)
with selected atom labeling. Ellipsoids show 30% probability levels,
and hydrogen atoms have been omitted for clarity.
The structures of 5−7, 9, and 10 resemble those of the
corresponding diplatinum(I) complexes of μ-2-C6H4PPh2 (3a)
and μ-5-Me-2-C6H3PPh2 (3b)5,6 and consist of two directly
bonded metal atoms bridged by the carbanions in a head-to-tail
arrangement. Distorted planar coordination about the metal
atoms is completed by the axial ligands (PPh3 for 5 and 9,
t
AsPh3 for 6 and BuNC for 7 and 10) that are trans to the
metal−metal bond, the L−M−M−L units being close to linear.
The Pt−Pt bond length in 10 [2.5941(2) Å] is slightly shorter
than that in 9 [2.61179(5) Å], consistent with the higher trans
influence of the P-donor ligand, and is comparable to those in
3a and 3b [2.630(1), 2.61762(16) Å], respectively. The Pd−Pd
distances are ca. 0.04 Å less than these and increase in the order
t
L = AsPh3 (6) < PPh3 (5) < BuNC (7), which does not
correspond with the order of increasing trans influence of these
ligands. A noteworthy feature is that both the M−P and M−C
bond lengths in the diplatinum(I) complex 9 are less than those
in its dipalladium(I) analogue 5, by ca. 0.03−0.05 Å (M−P)
and ca. 0.01 Å (M−C). A similar trend is observed for the M−P
distances in the divalent metal complexes cis-
[MMe2(PMePh2)2] (M = Pt, Pd), whereas the M−C distances
show the opposite trend.19,20 In the tBuNC complexes, the M−
P bond lengths in 10 are ca. 0.02 Å shorter than those in its
palladium analogue 7; the M−C bond lengths are comparable.
The X-ray structural analysis of complex 8 confirms the
conclusion drawn from NMR and IR spectra that the μ-2-
C6F4PPh2 groups are arranged head-to-head. Selected bond
distances and angles are given in the caption to Figure 2. As is
t
true also for complex 7, the methyl groups of the BuNC
ligands are disordered, and only one location for these groups is
shown. The Pd···Pd separation in 8 [2.5580(2) Å] is slightly
less than that in 7, whereas the Pd−P distance in 8 is about 0.03
Å greater than that in 7; the Pd−C(aryl) distances are equal.
a
b
c
M = Pt, X = PPh3, Y = I. M = Pd, X = Y = I. M = Pd, X = Y = Cl,
d
one of the two independent molecules in the asymmetric unit. M =
Pd, X = I, Y = Me.
t
The Pd−C bond lengths to the axial BuNC ligands are
significantly different [Pd(1)−C(1) = 2.057(3) Å, Pd(2)−C(2)
= 1.993(3) Å], the shorter distance being to the formally
divalent metal atom. The corresponding bond length in 7 is
midway between these values. Moreover, whereas the
coordination geometry about Pd(2) is close to planar, as
expected [C(12)−Pd(2)−C(12*) = 174°, Pd(1)−Pd(2)−C(2)
= 176°], that about Pd(1) is markedly distorted from planarity
[P(1)−Pd(1)−P(1*) = 153°, Pd(2)−Pd(1)−C(1) = 175°].
This distortion may reflect the attempt of the d10 metal center
to achieve its favored trigonal-planar coordination, as observed,
for example, in [Pt(PPh3)3],21−23 this tendency being opposed
by the presence of the adjacent metal atom and its associated
ligands.
Reactions. 1. Diplatinum(I). Like its μ-2-C6H4PPh2 and μ-
5-Me-2-C6H3PPh2 analogues,5,6 the diplatinum(I) complex 9
underwent oxidative addition with iodine to give the expected
A-frame cation [Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2]+, isolated as
−
its PF6 salt (11) (Scheme 6). The 31P NMR spectrum of 11
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In contrast with the diplatinum(I) complex [Pt2{μ-2-
C6H4P(Ph)CH2CH2PPh2}2],26 complex 9 did not react with
an excess of methyl iodide, probably because the nucleophilicity
of the dimetal unit is reduced by the electron-withdrawing
fluoro substituents in the bridging group.
Scheme 6
I
2. Dipalladium(I). The complex [Pd2 (μ-2-
C6F4PPh2)2(PPh3)2] (5) reacted immediately with one
equivalent of iodine to give a neutral, orange, microcrystalline,
iodo-bridged dipalladium(II) complex, [Pd2I(μ-I)(μ-2-
C6F4PPh2)2(PPh3)] (12), which was isolated in ca. 90%
yield; the corresponding reaction of 5 with one equivalent of
iodobenzene dichloride gave the yellow chloro analogue
[Pd2Cl(μ-Cl)(μ-2-C6F4PPh2)2(PPh3)] (13). There was no
evidence in either case for the formation of the dipalladium
analogue of the diplatinum(II) cation 11. Complex 5 also
underwent oxidative addition with methyl iodide to give the
neutral iodo-bridged complex [Pd2Me(μ-I)(μ-2-
C6F4PPh2)2(PPh3)] (14) containing a terminal methyl group,
together with [Ph3MeP]I, which was identified by 31P NMR
spectroscopy and mass spectrometry. These reactions are
summarized in Scheme 7.
shows a pair of broad, unresolved multiplets at δ 4.4 and 10.3,
flanked by 195Pt satellites, due to the bridging 2-C6F4PPh2 (PA)
and axial PPh3 (PB) ligands, respectively. The derived coupling
constants (see Experimental Section) are generally similar to
those of the corresponding μ-2-C6H4PPh2 and μ-5-Me-2-
C6H3PPh2 compounds, although some of the coupling
constants could not be determined because of unresolved 19F
coupling. The bridging iodide ligand between the two platinum
atoms causes a large increase in the magnitude of JBX (X =
195Pt) from 2001 Hz in 9 to 4645 Hz, cf. values of ca. 5080 Hz
in [Pt2(μ-I)(μ-5-R-2-C6H3PPh2)2]+ (R = H, Me)5,6 and 4265
Hz in [Pt2(μ-S)(μ-I)(PPh3)4]+;24 disruption of the Pt−Pt bond
is also responsible for the reduction of the long-range JBX′
coupling from 904 to 128 Hz. The 19F NMR spectrum of 11,
like that of its precursor 9, shows the expected four resonances
arising from the equivalent 2-C6F4PPh2 groups, and the Raman
spectrum contains a strong band at 154 cm−1 assignable to
ν(Pt−I).25 The molecular structure of the cation of 11 is shown
in Figure 4; selected metrical data are listed in Table 1. The
Scheme 7
The ESI mass spectra of 12 and 13 show peaks due to [M +
Na]+, while that of 14 has peaks assignable to [M − I]+ and [M
− Me]+. The 31P NMR spectrum of 12 shows three, equally
intense signals (multiplets, due to P−F coupling), at δ 35.5, due
to coordinated PPh3, and at δ 7.1 and 4.2, due to the
inequivalent 31P nuclei of the bridging 2-C6F4PPh2 groups. In
the case of 13, the 31P signals of 2-C6F4PPh2 accidentally
coincide at δ 4.6 in C6D6, but appear as well-separated
multiplets in CD2Cl2 (δ 4.4 and 3.3). The corresponding
resonances for 14 in C6D6 are at δ 29.4 (PPh3) and at 18.0 and
11.3 (2-C6F4PPh2). The 19F NMR spectra of 12−14 each
contain eight multiplets in the usual region, confirming the
inequivalence of the 2-C6F4PPh2 groups. In the 1H NMR
spectrum of 14 the Pd−Me resonance appears at δ 1.82 as a
doublet of doublets with separations of 2.7 and 7.5 Hz,
presumably arising from 31P and 19F coupling. The Raman
spectrum of 13 shows a strong ν(Pd−Cl) band at 340 cm−1,
typical for Cl trans to Cl in planar palladium(II) complexes;
there are also bands at 287 and 258 cm−1, which can be
assigned to the ν(Pd−Cl) vibrations of an unsymmetrical Pd−
Cl−Pd bridge. The Raman spectrum of 12 contains two strong
bands at 136 and 142 cm−1 assignable to ν(Pd−I), while 14
shows just one such band at 154 cm−1. Similar bands have been
observed in the Raman spectra of trans-[PdI2(PEt3)2] (140
cm−1)27 and [Bu4N]2[Pd2I6] (143 cm−1).28
Figure 4. Molecular structure of [Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2]-
[PF6] (11) with selected atom labeling. Ellipsoids show 30%
probability levels. Hydrogen atoms, PF6 counterion, and solvent of
crystallization have been omitted for clarity. The crystals of 11 were
twinned, arising from a 180° rotation about the (001) reciprocal axis,
and the twin elements were refined to 0.815(1):0.185(1).
−
iodide ligand bridges the two platinum atoms almost
symmetrically, with Pt−I distances of 2.7115(7) and
2.7035(7) Å and a narrow Pt−I−Pt angle of 66°. Consistent
with indications from the NMR data of a weakening of the Pt−
Pt interaction, the Pt···Pt separation of 2.9478(5) Å is
significantly greater than that of 9.
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Article
The molecular structures of 12−14, determined by single-
crystal X-ray analysis, confirm the conclusions drawn from the
spectroscopic data. The structure of 12 is shown in Figure 5,
Scheme 8
Figure 5. Molecular structure of [Pd2I(μ-I)(μ-2-C6F4PPh2)2(PPh3)]
(12) with selected atom labeling. Ellipsoids show 30% probability
levels. Hydrogen atoms and solvent of crystallization have been
omitted for clarity.
and selected metrical data for 12−14 are listed in Table 1. All
three compounds have typical A-frame structures with bridging
halogen atoms; 12 and 13 also have terminal halogen atoms,
while 14 has an η1-methyl group in place of the axial PPh3 of
the precursor 5. As expected, the Pd···Pd separations in 12−14
(ca. 2.81 Å) exceed that in 5 [2.5740(3) Å]. In 12 and 13, the
Pd−halide bridge distance trans to the terminal halide
[2.6529(7) Å in 12, 2.3507(6) Å in 13] is significantly less
than that trans to PPh3 [2.7090(6) Å in 12, 2.4261(6) Å in 13],
consistent with the relative trans influences of the halide ions
and PPh3; both are greater than the corresponding terminal
Pd−halide distances [2.5995(7) Å in 12, 2.3201(7) Å in 13].
Similarly, in 14, the Pd−I (bridge) distance trans to Me
[2.7386(5) Å] exceeds that trans to PPh3 [2.7101(5) Å], and
although the trend is consistent with the relative trans
influences of I− and Me−, the difference is unexpectedly
small. Moreover, the observed Pd−C distance in 14 [2.162(4)
Å] is significantly outside the range of 2.02−2.09 Å found for
Pd−C (Me or Et) bond lengths trans to a variety of ligands.29
These observations indicate that partial isomorphous replace-
ment of methyl by iodine may have occurred during
crystallization.34
Although complex 5 reacted with iodobenzene, the product,
isolated in 58% yield, was not the hoped-for phenyl analogue of
12, but rather a colorless, monomeric palladium(II) complex,
cis-[Pd(κ2C,P-2-C6F4PPh2)(κC-2-C6F4PPh2)(PPh3)] (15)
(Scheme 8). The only other product, tentatively identified by
31P NMR spectroscopy, was [Ph4P]+, arising from quaterniza-
tion of the released Ph3P by iodobenzene. The 31P NMR
spectrum of 15 contains three resonances of equal intensity at δ
19.2, −2.8, and −65.1, each broadened by poorly resolved 19F
and 31P coupling; the peaks are assigned to coordinated PPh3,
noncoordinated PPh2, and κ2-C,P-2-C6F4PPh2, respectively.
The molecular structure of 15, which is shown in Figure 6,
together with selected bond distances and angles, confirms the
conclusions drawn from the spectroscopic data and shows the
Figure 6. Molecular structure of cis-[Pd(κ2-C,P-2-C6F4PPh2)(κC-2-
C6F4PPh2)(PPh3)] (15) with selected atom labeling. Ellipsoids show
30% probability levels, and hydrogen atoms have been omitted for
clarity. Selected bond distances (Å) and angles (deg): Pd(1)−P(1)
2.3506(6), Pd(1)−P(3) 2.3385(5), Pd(1)−C(2) 2.069(2), Pd(1)−
C(32) 2.038(2), P(1)−Pd(1)−C(2) 69.34(6), P(1)−Pd(1)−P(3)
104.722(19), P(3)−Pd(1)−C(32) 93.72(6), C(2)−Pd(1)−C(32)
92.22(8), P(1)−Pd(1)−C(32) 161.55(6), P(3)−Pd(1)−C(2)
172.63(6).
two phosphorus atoms to be mutually cis. The bite angle of the
chelate group [69.34(6)°] is typical of ortho-metalated
triarylphosphines.1
Attempts to generate 15 by heating complex 4 with an excess
of PPh3 were unsuccessful. Evidently the fluorine substituents
strengthen the binding of the whole chelate ring, not just the
metal−carbon σ-bonds, since [Pt(κ2-2-C6H4PPh2)2] readily
undergoes stepwise opening of its chelate rings with tertiary
phosphines.35 Complex 15 was shown spectroscopically to be
formed when [Pd2Cl4(PPh3)2] was treated with two equivalents
of 2-LiC6F4PPh2, but the reaction was not clean and other
unidentified products were present.
DISCUSSION
■
I
The complexes [Pd2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (5),
AsPh3 (6), tBuNC (7)] join an extensive class of dipalladium(I)
complexes in which one or two ligands, either anionic or
neutral, bridge the two 4d9 metal centers. Anionic bridging
ligands that have been used include halide, η3-allyl, η3-
cyclopentadienyl, dialkyl- or diaryl-phosphido, and alkyl- or
aryl-thiolato; neutral ligands include carbon monoxide, arenes,
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Scheme 9
dienes, 1,1-bis(diphenylphosphino)methane, Ph2PCH2PPh2
(dppm), 1,1-bis(diphenylphosphino)amine, Ph2PNHPPh2 and
2-(diphenylphosphino)pyridine, (2-C5H4N)PPh2 2-
Ph2Ppy.36−40 Dipalladium(I) species continue to be of interest
because of their possible role in the catalysis of numerous C−C
and C−N bond-forming reactions by palladium compounds.41
An unusual feature of our complexes is the presence of a Pd−
C(aryl) bond as part of the bridging ligand. Indeed, the only
extensive series of dipalladium(I) complexes containing any
small molecules to [Pd2(μ-dppm)3]47 and [M2X2(μ-dppm)2]
(M = Pd, Pt).35,36,38,49,50 However, oxidative additions to 5 are
accompanied by loss of one of the axial ligands to give neutral
adducts, a reaction that does not occur in the addition of
halogens to the diplatinum(I) analogues 3a, 3b, and 9.
Palladium(II) complexes are, in general, more labile than
their platinum(II) counterparts, and the trend obviously
continues in the dimetal(I) series. The unexpected formation
of cis-[Pd(κ2C,P-2-C6F4PPh2)(κC-2-C6F4PPh2)(PPh3)] (15)
from the reaction of iodobenzene with complex 5 can be
accounted for by the sequence shown in Scheme 9. In the first
step, iodobenzene adds oxidatively to the Pd−Pd center, with
loss of one PPh3, to form a μ-iodo(phenyl) species 16
analogous to the methyl complex 14. In the second step, the
metal−carbon σ-bond of one of the μ-2-C6F4PPh2 ligands
migrates to the adjacent metal atom [i.e., from Pd(2) to Pd(1)
in Scheme 9], thus generating κ2-2-C6F4PPh2 on Pd(1) and
cleaving the Pd(1)−I bond. At this stage, PPh3 can reassociate
with Pd(2). A similar migration has been invoked as the first
step of the rearrangement of the homovalent dihalodigold(II)
complexes [Au2X2(μ-2-C6F4PPh2)2] (X = halide) to their
heterovalent gold(I)−gold(III) isomers [XAuI(μ-2-Ph2PC6F4)-
AuIIIX(κ2C,P-2-C6F4PPh2)].51 The sequence is completed by
cleavage of the Pd(2)−P bond from the remaining μ-2-
C6F4PPh2 ligand, giving 15, and elimination of [Ph4P]I from
Pd(2). Since the formation of metallic palladium is not
observed, the fate of Pd(2) is unclear; however, in general
agreement with the proposed course of the reaction, it has been
reported that [PdI(Ph)(PPh3)2] eliminates [Ph4P]I on
heating52 and that the quaternization of PPh3 by aryl bromides
is catalyzed by [Pd(OAc)2] in DMF,53 a reaction that probably
involves Pd(0).
́ ́
metal−aryl carbon σ-bonds, prepared by Uson, Fornies
, et al.,10
are of the types [Pd2(Ar)X(μ-dppm)2] (Ar = C6F5, X = Cl, Br,
I, NCO, C6F5; Ar = C6Cl5, X = Cl, C6F5) and [Pd2(Ar)X{μ-
(Ph2P)2NH}2]; like our compounds, they are probably
stabilized by the electron-withdrawing substituents in the aryl
groups. Stille et al.42 have generated and characterized the
thermally unstable methyldipalladium(I) compounds
[Pd2(Me)Cl(μ-dppm)2] and [Pd2Me2(μ-dppm)2] at −78 °C.
So far as we know, the only example of a dipalladium(I)
complex in which a Pd−C σ-bond forms part of the bridging
ligand is [Pd2(L)2(μ-dppm){μ-C,P-Ph2PCHP(O)PPh2}],
where the axial ligand L is 2,6-xylyl isocyanide; it results from
the deprotonation and subsequent aerial oxidation of the salt
[Pd2(L)2(μ-dppm)2][PF6]2.43
The method of comproportionation between the palladium-
(II) precursor 4 and the palladium(0) complexes [PdL4] (L =
PPh3, AsPh3) to give 5 and 6 follows a strategy that has been
widely applied to the synthesis of dipalladium(I) com-
plexes.35,38,44 However, in the case of L = BuNC, attempted
t
comproportionation gives complex 8, in which the 2-C6F4PPh2
ligands bridge head-to-head rather than head-to-tail. 8 can be
described as a heterovalent Pd(II)−Pd(0), 4d8−4d10, complex
in which a lone pair of electrons is donated from Pd(0) to
Pd(II), although the electron distribution in the Pd···Pd
interaction is unlikely to be as extreme as implied by this
description. The Pd···Pd separations in 7 and 8 are not very
different. The presence of HT and HH isomers of dipalladium-
(I) and diplatinum(I) complexes containing unsymmetrical
bridging ligands such as Ph2AsCH2PPh2,45 Ph2Ppy,46,47 and
Ph2PCH2SMe48 is well established. Both isomers retain the +1
oxidation state for the metal atoms. Although the HT isomers
in these cases appear to be thermodynamically favored, the HT
Pd(I)−Pd(I) isomer 7 and the HH Pd(II)−Pd(0) isomer 8 do
not interconvert in solution. The factors that control the
formation of 8 in the attempted comproportionation, and the
question whether HH isomers are intermediates in the
comproportionations leading to 5 and 6, remain to be
investigated.
Finally, we note that the work reported here extends the
series of dinuclear palladium complexes containing bridging 2-
C6R4PPh2 ligands so that it now spans the oxidation states
Pd(I)−Pd(I) (4d9−4d9) (R = F), Pd(II)−Pd(II) (4d8−4d8) (R
= H, F),7−9 and Pd(III)−Pd(III) (4d7−4d7) (R = H).54
EXPERIMENTAL SECTION
■
General Comments. Toluene, diethyl ether, dichloromethane,
and n-hexane were dried by the use of a standard column drying
system. The complexes [M(κ2-2-C6F4PPh2)2] (M = Pt, Pd),9
[Pt(PPh3)3],55 [Pd(PPh3)4],56 [Pd(AsPh3)4],57 and [Pd(η5-Cp)(η3-
allyl)]58 were prepared by literature methods. [Pt3(CNtBu)6] was
prepared by a reported method59 using [Pt(norbornene)3]60,61 instead
of [Pt(1,5-cyclooctadiene)2]; all other reagents were commercially
1
available and used as received. H (300 MHz), 19F (282 MHz), and
31P (121 MHz) NMR spectra were measured as C6D6 solutions, unless
otherwise stated, on a Bruker Avance 300 spectrometer at room
temperature. NMR spectral simulations were made by use of the
gNMR program.62 Raman spectra were obtained on a Perkin-Elmer
The formation of A-frame complexes by oxidative addition of
halogens or methyl iodide to complex 5 is clearly analogous to
the formation of similar species by the oxidative addition of
5567
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I
t
Table 2. Crystal and Refinement Data for [Pd2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (5), AsPh3 (6), BuNC (7)], [Pd20/II(μ-2-
C6F4PPh2)2(CNtBu)2] (8), [Pt2 (μ-2-C6F4PPh2)2(L)2] [L = PPh3 (9), BuNC (10)], [Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2][PF6]
(11), [Pd2I(μ-I)(μ-2-C6F4PPh2)2(PPh3)] (12), [Pd2Cl(μ-Cl)(μ-2-C6F4PPh2)2(PPh3)] (13), [Pd2Me(μ-I)(μ-2-
C6F4PPh2)2(PPh3)] (14), and [Pd(κ2-C,P-2-C6F4PPh2)(κC-2-C6F4PPh2)(PPh3)] (15)
I
t
5
6
7
8
formula
fw
C72H50F8P4Pd2
1403.87
C72H50As2F8P2Pd2
1491.76
C46H38F8N2P2Pd2·3C6H6
1279.89
C46H38F8N2P2Pd2
1045.55
cryst syst
space group
cryst color, habit
a (Å)
monoclinic
P21/n
monoclinic
P21/n
orthorhombic
Pbcn
tetragonal
P41212
brown, needle
12.9954(1)
22.8850(2)
20.2845(2)
orange, block
13.1071(2)
23.2833(2)
20.0903(3)
yellow, needle
19.7128(3)
pale yellow, block
12.2048(2)
12.2048(2)
30.1528(4)
b (Å)
21.4914(3)
c (Å)
13.9542(2)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
93.0380(6)
93.2236(6)
6024.13(9)
6121.39(14)
5911.78(15)
4491.47(12)
4
4
4
4
Dcalc (g cm−3
)
1.548
1.619
1.438
1.546
cryst dimens
0.40 × 0.09 × 0.05
0.77
0.16 × 0.07 × 0.05
1.78
0.28 × 0.08 × 0.07
0.73
0.35 × 0.30 × 0.30
0.94
μ (mm−1
)
no. indep reflns (Rint)
13794 (0.060)
14113 (0.097)
9981 [I > 2σ(I)]
775
6771 (0.064)
4207 [I > 2σ(I)]
380
6518 (0.039)
5518 [I > 2σ(I)]
327
no. obsd reflns
9166 [I > 2σ(I)]
no. params refined
775
R
0.026
0.075
0.96
0.042
0.027
0.020
Rw
0.076
0.128
0.054
GOF
ρmax/ρmin (e Å−3
0.96
0.94
0.91
)
0.71/−0.82
9
1.30/−1.23
10
0.65/−0.85
11
0.45/−0.42
12
formula
fw
C72H50F8P4Pt2
C46H38N2F8P2Pt2
C72H50F8IP4Pt2PF6·2CH2Cl2
2022.98
triclinic
2(C54H35F8I2P3Pd2)·C5H12·C6H6
2941.04
1581.25
1222.90
cryst syst
space group
cryst color, habit
a (Å)
monoclinic
P21/n
monoclinic
P21/c
orthorhombic
P212121
P1
̅
yellow, needle
12.9761(1)
22.8436(2)
20.3033(1)
colorless, needle
15.1933(7)
16.7722(8)
17.8033(8)
yellow, plate
12.8010(2)
14.8766(3)
20.1361(4)
106.5093(10)
93.0296(12)
105.5032(10)
3508.17(12)
2
orange, plate
11.3916(2)
b (Å)
21.7240(4)
c (Å)
44.4879(8)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
92.9339(4)
109.5320(10)
6010.42(8)
4275.7(3)
11009.5(3)
4
4
4
Dcalc (g cm−3
)
1.747
1.900
1.915
1.774
cryst dimens
0.42 × 0.14 × 0.12
4.83
0.20 × 0.06 × 0.06
6.68
0.29 × 0.22 × 0.02
4.77
0.42 × 0.08 × 0.08
1.93
μ (mm−1
)
no. indep reflns (Rint)
17572 (0.051)
14 066 [I > 2σ(I)]
775
93407 (0.079)
18 795 [I > 2σ(I)]
547
16027 (0.076)
13 226 [I > 2σ(I)]
902
19318 (0.048)
16 087 [I > 2σ(I)]
1297
no. obsd reflns
no. params refined
R
0.023
0.038
0.058
0.029
Rw
0.062
0.069
0.112
0.094
GOF
ρmax/ρmin (e Å−3
0.77
0.97
0.98
0.77
)
2.09/−1.38
1.55/−1.43
13
2.18/−1.82
14
0.83/−0.77
15
formula
fw
C54H35Cl2F8P3Pd2
1212.43
C55H38F8IP3Pd2·C6H6
1361.63
C54H35F8P3Pd
1035.18
cryst syst
orthorhombic
Pca21
monoclinic
P21/a
monoclinic
P21/a
space group
cryst color, habit
a (Å)
colorless, block
17.0645(6)
16.4054(6)
16.9043(6)
orange, plate
18.0043(4)
17.8269(5)
18.8760(5)
colorless, plate
11.3738(1)
12.0304(1)
12.0304(1)
b (Å)
c (Å)
α (deg)
5568
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Organometallics
Article
Table 2. continued
13
14
15
β (deg)
γ (deg)
V (Å3)
Z
94.7219(17)
98.3916(5)
4732.4(3)
6037.9(3)
4443.46(7)
4
4
4
Dcalc (g cm−3
)
1.702
1.498
1.547
cryst dimens
0.08 × 0.06 × 0.04
1.05
0.30 × 0.24 × 0.07
1.25
0.26 × 0.14 × 0.05
0.60
μ (mm−1
)
no. indep reflns (Rint)
56899 (0.037)
15617 [I > 2σ(I)]
622
13915 (0.090)
7677 [I > 2σ(I)]
676
10183 (0.054)
8133 [I > 2σ(I)]
760
no. obsd reflns
no. params refined
R
0.031
0.044
0.031
Rw
0.064
0.112
0.069
GOF
ρmax/ρmin (e Å−3
1.017
0.83
0.97
)
0.75/−0.39
2.03/−1.99
0.59/−0.55
Raman Station 400F spectrometer as solids in open glass capillaries,
and infrared spectra on a Perkin-Elmer Spectrum 2000 FT
spectrometer as KBr discs or Nujol mulls. Electrospray mass spectra
were measured on an HP 5970 MSD spectrometer, and elemental
analyses were carried out by the Microanalytical Unit at the Research
School of Chemistry, ANU.
solution was evaporated. The resulting orange precipitate was isolated
by filtration, washed with MeOH, and dried in vacuo (320 mg, 78%).
Spectral data were identical to those of (a) above.
I
[Pd2 (μ-2-C6F4PPh2)2(AsPh3)2] (6). To a mixture of trans-[Pd(κ2-2-
C6F4PPh2)2] (200 mg, 0.26 mmol) and [Pd(AsPh3)4] (344 mg, 0.26
mmol) was added toluene (40 mL) under an argon atmosphere, and
the yellow suspension was heated to 60 °C for 2 h. The solution was
allowed to cool and filtered through Celite, and the solvent was
removed in vacuo. The orange residue was dissolved in CH2Cl2,
MeOH was added, and the volume of the solution was reduced. The
yellow precipitate was isolated, washed with MeOH, and dried in vacuo
(370 mg, 96%). 1H NMR: δ 6.4−8.2 (m, 50H, aromatic). 31P NMR: δ
−17.6 (br s). 19F NMR: δ −105.5 (m), −129.8 (m), −153.2 (m),
−162.6 (m). Raman (cm−1): 131, ν(Pd−Pd). ESI-MS (m/z): 1492
[M]+. Anal. Calcd for C72H50As2F8P2Pd2: C 57.97; H 3.38; F 10.19.
Found: C 57.95; H 3.55; F 10.24.
X-ray Crystallography. Crystals of 5, 9, 12, 14, and 15 suitable
for X-ray crystallography were obtained from benzene/pentane, 6 and
7 from benzene/hexane, 8, 11, and 13 from dichloromethane/
methanol, and 10 from benzene. The crystals were coated in viscous
oil and mounted on fine-drawn capillaries. Crystal data and details of
data collection are given in Table 2. Data for complexes 10 and 13
were collected at 150 K on a D8 Bruker diffractometer equipped with
an APEX2 area detector using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å) from a 1 μS microsource. Geometric and
intensity data were collected using SMART software.63 The data were
processed using SAINT,64 and corrections for absorption were applied
using SADABS.65 The structures were solved by direct methods and
refined with full-matrix least-squares methods on F2 using the SHELX-
TL package.66 Data for the remaining complexes were collected at 200
K on a Nonius-Kappa CCD diffractometer using graphite-mono-
chromated Mo Kα radiation (λ = 0.71073 Å). Data were measured by
use of COLLECT.67 The intensities of reflections were extracted, and
the data were reduced by use of the computer programs Denzo and
Scalepack.68 The crystal structures were solved by direct methods69
and refined by use of the program CRYSTALS.70 Neutral atom
scattering factors,71 the values of Δf′ and Δf″, and mass attenuation
coefficients72 were taken from standard compilations.
I
[Pd2 (μ-2-C6F4PPh2)2(CNtBu)2] (7). To a solution of 6 (100 mg, 0.07
mmol) in CH2Cl2 (4 mL) was added tBuNC (17 μL, 0.14 mmol). The
color immediately faded from orange to yellow, and after the solution
had been stirred for 10 min, hexane was added. The volume of the
solution was reduced in vacuo, causing a yellow solid to precipitate.
This was isolated by filtration, washed with hexane, and dried in vacuo
1
t
(64 mg, 91%). H NMR: δ 0.56 (s, 18H, Bu), 6.8−7.9 (m, 20H,
aromatic). 31P NMR: δ −14.3 (br s). 19F NMR: δ −109.1 (m), −130.2
(m), −155.4 (m), −162.2 (m). IR (KBr, cm−1): 2164, ν(NC).
Raman (cm−1): 129, ν(Pd−Pd). ESI-MS (m/z): 1046 [M]+, 1063 [M
+ O + H]+. Anal. Calcd for C46H38F8N2P2Pd2: C 52.84; H 3.66; N
2.68; F 14.54. Found: C 52.72; H 4.00; N 2.79; F 14.50.
[Pd20/II(μ-2-C6F4PPh2)2(CNtBu)2] (8). To a solution of trans-[Pd(κ2-
2-C6F4PPh2)2] (200 mg, 0.26 mmol) in toluene (20 mL) was added
tBuNC (60 μL, 0.53 mmol) under argon. The colorless solution was
cooled to −78 °C, and [Pd(η5-Cp)(η3-allyl)] (55 mg, 0.26 mmol) was
added. The mixture was stirred at −78 °C for several hours, then
allowed to warm to room temperature overnight. The solvent was
removed in vacuo, and the residue was dissolved in CH2Cl2. After the
solution had been filtered through Celite, MeOH was added to the
filtrate and the volume of the solution was reduced in vacuo. The pale
yellow solid that precipitated was isolated, washed with MeOH, and
I
Preparations. [Pd2 (μ-2-C6F4PPh2)2(PPh3)2] (5). (a) To a mixture
of trans-[Pd(κ2-2-C6F4PPh2)2] (200 mg, 0.26 mmol) and [Pd(PPh3)4]
(299 mg, 0.26 mmol) was added toluene (20 mL) under an argon
atmosphere, and the orange-red solution was stirred at room
temperature overnight. The solution was filtered through Celite, and
the filtrate was evaporated to dryness. The orange-red residue was
dissolved in CH2Cl2, MeOH was added, and the volume of the
solution was reduced in vacuo. The resulting orange precipitate was
isolated by filtration, washed with MeOH, and dried in vacuo (320 mg,
1
83%). H NMR: δ 6.4−8.2 (m, 50H, aromatic). 31P NMR: δ 8.4 (s),
−19.3 (br s). 19F NMR: δ −105.1 (m), −128.9 (m), −153.1 (m),
−162.9 (m). Raman (cm−1): 135, ν(Pd−Pd). ESI-MS (m/z): 1404
[M]+. Anal. Calcd for C72H50F8P4Pd2: C 61.60; H 3.59; F 10.83.
Found: C 61.51; H 3.53; F 10.40.
1
t
dried in vacuo (195 mg, 72%). H NMR: δ 0.45 (s, 9H, Bu), 0.63 (s,
9H, tBu), 6.9−7.1 (m, 6H, aromatic), 7.2−7.3 (m, 6H, aromatic), 7.5−
7.6 (m, 4H, aromatic), 8.3−8.4 (m, 4H, aromatic). 31P NMR: δ −13.6
(br s). 19F NMR: δ −113.5 (m), −130.9 (m), −156.2 (m), −162.7
(m). IR (cm−1): 2159, 2187 (Nujol); 2161, 2188 (KBr), ν(NC).
Raman (cm−1): 128, ν(Pd−Pd). ESI-MS (m/z): 1046 [M]+, 1079 [M
+ 2O + H]+. Anal. Calcd for C46H38F8N2P2Pd2: C 52.84; H 3.66; N
2.68; F 14.54. Found: C 52.68; H 3.68; N 2.59; F 14.26.
(b) To a solution of trans-[Pd(κ2-2-C6F4PPh2)2] (225 mg, 0.29
mmol) in toluene (20 mL) was added PPh3 (153 mg, 0.58 mmol)
under argon. The colorless solution was cooled to −78 °C, and solid
[Pd(η5-Cp)(η3-allyl)] (62 mg, 0.29 mmol) was added. The mixture
was stirred at −78 °C for several hours, then allowed to warm to room
temperature overnight. The dark orange-brown solution was
evaporated to dryness, and the residue was dissolved in CH2Cl2 and
filtered through Celite. MeOH was added to the filtrate, and the
I
[Pt2 (μ-2-C6F4PPh2)2(PPh3)2] (9). A mixture of [Pt(κ2-2-C6F4PPh2)2]
(140 mg, 0.16 mmol) and [Pt(PPh3)3] (150 mg, 0.16 mmol) was
suspended in toluene (10 mL) under an argon atmosphere, and the
yellow mixture was refluxed overnight. After being cooled to room
5569
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Organometallics
Article
temperature, the solution was evaporated and EtOH was added. The
resulting orange solid was isolated and dissolved in CH2Cl2, and
MeOH was added. The solution was again evaporated in vacuo to give
a yellow solid, which was washed with MeOH and dried in vacuo (110
mg, 44%). 1H NMR: δ 0.38 (s, 2H, H2O), 6.0−8.0 (m, 50H,
aromatics). 31P NMR: δ −8.2 (PA, m), 24.4 (PB, m, JAA′ 0 Hz, JAB 15
Hz, JAB′ 15 Hz, JAX 2369 Hz, JAX′ 133 Hz, JBB′ 208 Hz, JBX 2001 Hz, JBX′
904 Hz). 19F NMR: δ −105.1 (m, JPtF 267 Hz), −129.0 (m), −153.4
(m), −163.0 (m). Raman (cm−1): 126, ν(Pt−Pt). ESI-MS (m/z):
1581 [M + H]+. Anal. Calcd for C72H50F8P4Pt2·2H2O: C 53.47; H
3.37; P 7.66. Found: C 53.21; H 3.34; P 7.86.
3.3 (m). 19F NMR (CD2Cl2): δ −107.7 (m), −114.2 (m), −121.5
(m), −123.0 (m), −150.2 (m), −152.0 (m), −159.6 (m), −160.9 (m).
Raman (cm−1): 287, 340, ν(Pd−Cl). ESI-MS (m/z): 1235 [M + Na]+.
Anal. Calcd for C54H35Cl2F8P3Pd2·0.7Et2O: C 53.96; H 3.35; Cl 5.61;
F 12.02. Found: C 54.21; H 3.41; Cl 5.62; F 12.17.
[Pd2Me(μ-I)(μ-2-C6F4PPh2)2(PPh3)] (14). To an orange solution of 5
(100 mg, 0.07 mmol) in CH2Cl2 (5 mL) was added MeI (1 mL), and
the mixture was stirred at room temperature overnight. After
evaporation of the orange solution to dryness, the residue was
suspended in toluene, and the mixture was passed down a short silica
column. The eluent was evaporated to dryness, and the residue was
recrystallized from CH2Cl2/hexane to give a golden-orange solid (70
mg, 81%). 1H NMR: δ 1.82 (dd, J 2.7, 7.5 Hz, 3H, CH3), 6.3−7.2 (m,
25H, aromatic), 7.5−8.1 (m, 8H, aromatic), 8.3−8.4 (m, 2H,
aromatic). 31P NMR: δ 29.4 (tm, J 26.5 Hz), 18.0 (m), 11.3 (m).
19F NMR: δ −106.4 (m), −107.6 (m), −121.6 (m), −122.2 (m),
−149.0 (m), −151.7 (m), −161.0 (m), −161.8 (m). Raman (cm−1):
154, ν(Pd−I). ESI-MS (m/z): 1156 [M − I]+, 1268 [M − Me]+. Anal.
Calcd for C55H38F8IP3Pd2: C 51.47; H 2.98; F 11.84; I 9.89. Found: C
51.25; H 3.23; F 11.54; I 10.04. A portion of the toluene-insoluble
material was carefully removed from the top of the column. The
spectroscopic properties of the solid residue were consistent with the
presence of [Ph3MeP]I. 31P NMR (CH2Cl2/C6D6): δ 21.9 [cf. δ 22.2
(CDCl3)73]. ESI-MS (m/z): 277 [M − I]+.
I
[Pt2 (μ-2-C6F4PPh2)2(CNtBu)2] (10). A mixture of [Pt(κ2-2-
C6F4PPh2)2] (105 mg, 0.12 mmol) and [Pt3(CNtBu)6] (44 mg, 0.04
mmol) was dissolved in toluene (20 mL) under an argon atmosphere,
and the orange solution was stirred at room temperature overnight.
The resulting pale yellow solution was evaporated to dryness, and the
residue was recrystallized from CH2Cl2/MeOH. The pale yellow solid
1
that precipitated was isolated and dried in vacuo (143 mg, 96%). H
NMR: δ 0.54 (s, 18H, tBu), 6.8−8.0 (m, 20H, aromatics). 31P NMR: δ
−7.4 (br s, JAX 2330 Hz, JAX′ 156, JXX′ ∼2360 Hz). 19F NMR: δ −109.7
(m, JPtF 262 Hz), −130.1 (m), −154.9 (m, JPtF 109 Hz), −161.6 (m).
ESI-MS (m/z): 1223 [M + H]+. Anal. Calcd for C46H38N2F8P2Pt2: C
45.18; H 3.13; N 2.29, F 12.43. Found: C 45.08; H 3.15; N 2.22; F
12.30.
[Pt2(μ-I)(μ-2-C6F4PPh2)2(PPh3)2]PF6 (11). To a solution of 9 (110
mg, 0.07 mmol) in CH2Cl2 (5 mL) was added I2 (18 mg, 0.07 mmol)
in CH2Cl2 (5 mL). After stirring for 10 min, KPF6 (100 mg, 0.54
mmol) in acetone (10 mL) was added, and the solution was
evaporated to dryness. The residue was taken up in CH2Cl2 and
filtered through Celite, and the filtrate treated with a solution of KPF6
(100 mg, 0.54 mmol) in acetone (10 mL). The mixture was again
evaporated to dryness, taken up in CH2Cl2, and filtered through Celite.
Hexane was added to the filtrate, and the volume of the solution was
reduced in vacuo. The yellow solid that precipitated was isolated,
cis-[Pd(κ2-C,P-2-C6F4PPh2)(κC-2-C6F4PPh2)(PPh3)] (15). To an
orange solution of 5 (150 mg, 0.11 mmol) in CH2Cl2 (10 mL) was
added PhI (1 mL), and the mixture was stirred at room temperature in
the dark for 6 h. The yellow solution was evaporated to dryness, and
the residue, after trituration with MeCN (3 × 5 mL), gave a colorless
solid. This was dissolved in CH2Cl2, MeCN was added, and the
solution was evaporated. The colorless solid that precipitated was
isolated by filtration, washed with MeCN, and dried in vacuo (64 mg,
1
58%). H NMR: δ 6.6 (t, J 1.1 Hz, 2H, aromatic), 7.0−7.5 (m, 33H,
aromatic). 31P NMR: δ 19.2 (br d, J ∼13 Hz), −2.8 (br t, J ∼21 Hz),
−65.1 (m). 19F NMR: δ −114.4 (m), −125.3 (m), −126.0 (m),
−135.6 (m), −150.6 (m), −156.4 (m), −160.4 (m), −162.4 (m). ESI-
MS (m/z): 1035 [M + H]+. Anal. Calcd for C54H35F8P3Pd: C 62.65; H
3.41; F 14.68. Found: C 62.70; H 3.53; F 14.72. The 31P NMR
spectrum of an aliquot of the crude reaction mixture before workup
(CH2Cl2/C6D6) showed the expected resonances due to 15, together
with a peak at δ −71.2 and several peaks in the range δ 20−27; an
intense singlet resonance at δ 23.4 was consistent with the formation
of [Ph4P]I [cf. δ 23.5 (CDCl3)73].
1
washed with hexane, and dried in vacuo (120 mg, 93%). H NMR
(CD2Cl2): δ 6.7−8.0 (m, 50H, aromatic). 31P NMR (CD2Cl2): δ 10.3
(br s, JPtP 128, 4645 Hz), 4.4 (br s, JPtP 1972 Hz), −144.5 (sept, JPF 710
Hz). 19F NMR (CD2Cl2): δ −73.6 (d, JPF 710 Hz), −102.8 (m, JPtF
195 Hz), −120.2 (m), −150.7 (m), −159.3 (m). Raman (cm−1): 154,
ν(Pt−I). ESI-MS (m/z): 1707 [M − PF6]+. Anal. Calcd for
C72H50F14IP5Pt2: C 46.67; H 2.72; F 14.35; I 6.85. Found: C 47.18;
H 3.01; F 14.79; I 6.77.
[Pd2I(μ-I)(μ-2-C6F4PPh2)2(PPh3)] (12). To an orange solution of 5
(100 mg, 0.07 mmol) in CH2Cl2 (5 mL) was added a solution of I2
(18 mg, 0.07 mmol) in CH2Cl2 (5 mL). The mixture was stirred for 10
min and evaporated to dryness in vacuo. The residue was dissolved in
toluene, and the solution was passed down a short silica column. The
eluent was evaporated to dryness, and the residue, suspended in Et2O
(10 mL), was stirred rapidly for 1 h. The orange solid was filtered off,
washed with Et2O, and dried in vacuo (90 mg, 91%). 1H NMR: δ 1.12
(t, J 6.9 Hz, 6H, CH3), 3.26 (q, J 6.9 Hz, 4H, CH2), 6.2−6.4 (m, 4H,
aromatic), 6.6−6.8 (m, 10H, aromatic), 6.9−7.1 (m, 11H, aromatic),
7.5−8.0 (m, 8H, aromatic), 8.3−8.4 (m, 2H, aromatic). 31P NMR: δ
33.5 (apparent td, J 6.0, 6.0, 27.2 Hz), 7.1 (m), 4.2 (m). 19F NMR: δ
−102.2 (m), −107.1 (m), −120.6 (m), −123.5 (m), −148.5 (m),
−152.1 (m), −159.9 (m), −160.0 (m). Raman (cm−1): 136, 142,
ν(Pd−I). ESI-MS (m/z): 1419 [M + Na]+. Anal. Calcd for
C54H35F8I2P3Pd2·0.7Et2O: C 47.14; H 2.92; F 10.50; I 17.54.
Found: C 47.17; H 2.96; F 10.55; I 17.34.
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic data in CIF format for complexes 5−15.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: bennett@rsc.anu.edu.au (M.A.B.); suresh.bhargava@
rmit.edu.au (S.K.B.).
Notes
The authors declare no competing financial interest.
[Pd2Cl(μ-Cl)(μ-2-C6F4PPh2)2(PPh3)] (13). This complex was made
analogously to 12 above by treatment of 5 (109 mg, 0.07 mmol) in
CH2Cl2 (5 mL) with PhICl2 (20 mg, 0.07 mmol) in CH2Cl2 (5 mL).
REFERENCES
■
1
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5570
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(29) For example: [PdMe2(TMEDA)] [2.026(3) Å],30 trans-
[Pd(Me)(OPh)(PMe3)2·PhOH] [2.039(4), 2.044(5) Å],31 trans-
[Pd(Me)(OCO2H)(PEt3)2] [2.05(2) Å],32 trans-[Pd(Et)Br(PMe3)2]
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