Synthesis and structural diversity of mono-, di- and trinuclear complexes with N,N′-bis[(2-diphenylphosphanyl)phenyl]formamidine

Article abstract of DOI:10.1002/ejic.201100492

The synthesis, characterization, and coordination chemistry of a series of mono-, di-, and trinuclear homo-/heterometallic complexes with the dinucleating ligand, N,N′-bis[(2-diphenyl-phosphanyl)phenyl]formamidine (pnnp)1 are reported. Treatment of (pnnp)

Full text of DOI:10.1002/ejic.201100492

FULL PAPER
DOI: 10.1002/ejic.201100492
Synthesis and Structural Diversity of Mono-, Di- and Trinuclear Complexes
with N,NЈ-Bis[(2-diphenylphosphanyl)phenyl]formamidine
Kyung-sun Son,[a] David M. Pearson,[a] Sang-Jin Jeon,[b] and Robert M. Waymouth*[a]
Keywords: Heterometallic complexes / Coordination chemistry / N,P ligands / Metal–metal interactions
The synthesis, characterization, and coordination chemistry
of a series of mono-, di-, and trinuclear homo-/heterometallic
complexes with the dinucleating ligand, N,NЈ-bis[(2-di-
(pnnp)FeCl2 (7), respectively. The dinuclear (pnnp)-
PdMe(μ-Cl)NiCl (3) and (pnnp)NiCl(μ-X)NiCl (X = Cl or OH)
(4) complexes adopt A-frame structures with two square-
phenyl-phosphanyl)phenyl]formamidine (pnnp)[1] are re- planar d8 metal complexes hinged by the bridging ligand;
ported. Treatment of (pnnp)PdMe (1) with NiCl2(dme) forms
the heterobimetallic (pnnp)PdMe(μ-Cl)NiCl (3) complex,
the angles between the square planes correlate to the coval-
ent radii, in which the smaller homo-bimetallic Ni complex
adopts a more coplanar arrangement of the two Ni square
planes. The heterometallic trinuclear complex (pnnp)Pd(Me)
CuPd(Me)(pnnp)·PF6 (8) adopts an unusual structure around
the Cu center, suggestive of a weak d8–d10 interaction be-
tween the Pd and Cu atoms. All complexes have been char-
acterized by NMR spectroscopy, elemental analysis, and X-
ray crystallography, and their structural diversity is dis-
cussed.
–
whereas reaction of 1 with Cu(CH3CN)4+PF6 yields the
Pd···Cu···Pd heterometallic trinuclear complex (pnnp)Pd-
(Me)CuPd(Me)(pnnp)·PF6 (8). The reaction of pnnp with
NiCl2(dme) (dme = 1,2-dimethoxyethane) produces the Ni
dimer [(pnnp)NiCl(μ-Cl)]2 (5) or the dinuclear (pnnp)-
NiCl(μ-X)NiCl (X = Cl or OH) (4) complexes, depending
upon the stoichiometry. The reaction of pnnp with CoII or FeII
ions leads to the monometallic complexes (pnnp)CoCl2 (6) or
metal complexes in a stepwise fashion, enabling the synthe-
sis of heterometallic multinuclear complexes. As a part of
our ongoing investigation into potential bimetallic olefin
polymerization catalysts,[2f,2j,2k] we have expanded the coor-
dination chemistry of this ligand to a family of various
metal complexes of Pd, Ni, Fe, Co, and Cu. Herein, we
report the synthesis, characterization and crystal structures
of homo-/heterometallic mono-, di-, and trinuclear com-
plexes and describe the versatility of the pnnp ligand featur-
ing various coordination modes for the transition metals.
Introduction
The placement of two metal centers in close proximity
by an appropriate ligand can allow for cooperative effects,
both improving their efficiency and selectivity in catalysis
and promoting reactions that are not possible using a single
metal center.[1–2] A variety of bridging ligands, such as
bis(diphenylphosphanyl)methane, (diphenylphosphanyl)-
pyridine, and various P2N2-type ligands have been devel-
oped extensively over the past decades.[3,4] In an effort to
design novel bimetallic complexes, we recently explored a
class of dinucleating N-heterocyclic carbene ligands
spanned by pyrazoles (CNNC) and reported corresponding
bimetallic complexes.[5] As an extension of these efforts, our
attention was drawn to the N,NЈ-bis[(2-diphenylphos-
Results and Discussion
Treatment of the pnnp ligand with one equivalent of
phanyl)phenyl]formamidine (pnnp) ligand recently dis- (tmeda)PdMe2 (tmeda
= tetramethylethyldiamine), as
closed by Tsukada for dinuclear Pt2, Pd2, and PtPd com- shown by Tsukuda, generates a stable square-planar (pnnp)
plexes.[1] Tsukada has investigated these complexes for a PdMe complex 1, a useful synthon for generating dinuclear
variety of organic transformations including arylation of (pnnp)PdXMY2 complexes using a step-by-step reaction
alkynes and alkyne/alkene coupling reactions.[2m,6] An ap- protocol.[1] Addition of THF to a 1:1 mixture of (pnnp)
pealing feature of this ligand is the ability to introduce PdMe (1) and NiCl2(dme) (dme
= 1,2-dimethoxy-
ethane) yielded the dark purple mixed-metal PdNi com-
pound (3) (Scheme 1). Complex 3 was isolated as a purple
solid in 98% yield. This bimetallic complex crystallized as
prismatic crystals by vapor diffusion of pentane into a
dichloromethane solution. The molecular structure is
shown in Figure 1. The Pd ion is coordinated in a square-
planar fashion by a P and a N atom of the chelating ligand,
a methyl group, and a Cl atom that bridges to the nickel
[a] Department of Chemistry, Stanford University,
Stanford, CA 94305, USA
Fax: +1-650-725-0259
E-mail: waymouth@stanford.edu
[b] Petrochemicals and Polymers R&D, LG Chem. Ltd.,
Daejeon, Korea
Supporting information Supporting: information for this article
is available on the WWW under http://dx.doi.org/10.1002/
ejic.201100492 or from the author.
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Complexes with N,NЈ-Bis[(2-diphenylphosphanyl)phenyl]formamidine
center. The methyl group is located trans to the N atom; 2.9655(10) Å lies outside the sum of the covalent radii for
the coordinating P and N atoms are necessarily in a cis- these elements (approx. 2.63 Å).[8] Therefore, any direct in-
geometry. The Ni atom is also coordinated in a square- teraction between the Pd and Ni centers is likely weak.
planar geometry by the other N and P atoms of the ligand
To investigate the influence of the metal radii on the co-
and two Cl atoms, one of which forms the bridge (see Fig- ordination geometry of these ligands, we prepared the cor-
ure 1). The τ4 values {a measure of the coordination about responding Ni complexes 4 and 5 (Scheme 2). The addition
a four-coordinate atom, given by τ4 = [360 – (β + α)]/141}[7] of a THF solution of a 1:1 mixture of the pnnp ligand and
for the Pd and the Ni ions are 0.026 and 0.116, respectively, KOtBu to two equivalents of NiCl2(dme) yielded the dinu-
indicating square planar geometries. As observed for the clear NiNi complex (4), which crystallized as red plate-like
Pd2 complex,[1] the solid structure of the PdNi complex 3 crystals by vapor diffusion of diethyl ether into a dichloro-
1
features an A-frame structure with the bridging Cl at the methane solution. The H NMR spectrum of 4 was consis-
apex, where the angles of the two square planes are almost tent with a symmetrical dinuclear Ni complex, however, the
perpendicular to one another [angle formed by the mean micro-analytical data and X-ray analysis revealed that 4 was
planes is 89.07(10)°, see Table 1]. Whereas the Pd and the comprised of a 1:1 mixture of the bridging chloride 4a and
Ni ions are in close proximity, the Pd···Ni distance the bridging hydroxide 4b. As the hydroxide-containing
complex co-crystallizes with that of the chloride, we were
unable to separate the two. We have not yet definitively as-
signed the source of hydroxide in the formation of 4, but
adventitious water in the KOtBu is a likely source. Efforts
to reproduce the synthesis of 4 yielded a similar mixture of
4a and 4b. The Ni centers are each coordinated in a square-
planar geometry by a P and a N atom of the ligand. Com-
pleting the coordination sphere is a terminal Cl and a bridg-
Scheme 1. Synthesis of heterodinuclear complex 3.
Figure 1. Molecular structure of 3 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths [Å] and angles [°]; see Table 1.
Scheme 2. Synthesis of dinickel complexes 4 and 5.
Table 1. Selected bond lengths [Å] and bond angles [°] for dinuclear complexes 2–4.
2a[1] (PdPd)
3 (PdNi)
4 (NiNi)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–Cl(1)
Pd(1)–Cl(2)
Pd(2)–N(2)
Pd(2)–P(2)
Pd(2)–Cl(1)
2.04(1)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–Cl(1)
Pd(1)–C(2)
Ni(1)–N(2)
Ni(1)–P(2)
Ni(1)–Cl(1)
2.122(5)
Ni(1)–N(1)
Ni(1)–P(1)
Ni(1)–Cl(3)
Ni(1)–Cl(1)
Ni(2)–N(2)
Ni(2)–P(2)
Ni(2)–Cl(3)
Ni(1)–O(1)
Ni(2)–O(1)
Ni(2)–Cl(2)
N(1)–C(1)
N(2)–C(1)
1.921(3)
2.1217(11)
2.142(3)
2.1647(13)
1.911(3)
2.1348(12)
2.102(3)
1.859(9)
1.874(9)
2.1643(14)
1.328(5)
1.327(5)
2.200(4)
2.405(4)
2.285(5)
2.05(1)
2.189(4)
2.398(4)
2.1750(18)
2.3928(18)
2.055(6)
1.977(5)
2.1318(18)
2.3077(17)
Pd(2)–Cl(3)
N(1)–C(1)
N(2)–C(1)
Pd(1)···Pd(2)
Pd(1)–Cl(1)–Pd(2)
N(1)–C(1)–N(2)
2.276(5)
1.32(2)
1.31(2)
3.24
84.8(1)
130(1)
Ni(1)–Cl(2)
N(1)–C(1)
N(2)–C(1)
Pd(1)···Ni(1)
Pd(1)–Cl(1)–Ni(1)
N(1)–C(1)–N(2)
2.133(2)
1.312(8)
1.327(8)
2.9655(10)
78.21(6)
124.6(6)
Ni(1)–Cl(3)–Ni(2)
N(1)–C(1)–N(2)
Ni(1)–O(1)–Ni(2)
116.0
130.6
147.5
Angles formed by two square planes
78.67
89.07(10)
22.88(10)
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K.-s. Son, D. M. Pearson, S.-J. Jeon, R. M. Waymouth
FULL PAPER
ing Cl 4a or OH 4b (Figure 2). The Ni–O and Ni–Cl bond
lengths are in the expected ranges for such bonds (see
Table 1). Interestingly, the angle formed by the two Ni-con-
taining square planes, 22.88(10)°, is considerably less than
those of the analogous Pd homodimer 2a (78.67°) and PdNi
heterodimer 3 (89.07°) (see Table 1). This more planar ar-
rangement is presumably due to the smaller covalent radii
of the Ni ion relative to Pd,[1] reflecting that small variation
within these complexes can lead to large structural differ-
ences in the solid state.
Figure 3. Molecular structure of 5 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms and solvate molecules have
been omitted for clarity. Selected bond lengths [Å] and angles [°]:
Ni(1)–N(1), 2.1161(16); Ni(1)–Cl(1), 2.4524(7); Ni(1)–Cl(2),
2.2450(7); Ni(1)–P(1), 2.2893(6); Ni(1)–Cl(1A), 2.3258(6); N(1)–
C(1), 1.299(2); N(2)–C(1), 1.340(2); Ni(1)–Cl(1)–Ni(1A),
95.641(18); Cl(1)–Ni(1)–Cl(1A), 84.359(18); N(1)–C(1)–N(2),
125.59(17).
Figure 2. Molecular structure of 4 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths [Å] and angles [°]; see Table 1.
around the Cu ion (Figure 4) features an unusual butterfly
structure in which the two approximately square planar Pd
centers are hinged by a CuI ion coordinated in a linear N–
Cu–N arrangement from the amidine nitrogen atoms de-
rived from two pnnp ligands. The Pd centers are ligated by
two trans-phosphane moities derived from two pnnp li-
gands, an amidine nitrogen, and a terminal methyl group,
but are distorted from a square-planar geometry, as evi-
denced by the P(1)–Pd(1)–P(3) and P(2)–Pd(2)–P(4) angles
of 152.98(4)° and 153.79(4)°, respectively [the τ4 values for
the Pd(1) and Pd(2) square planes are 0.29 and 0.26, respec-
tively]. This distortion may be a consequence of a weak
On the other hand, the bridging chloride dimer 5 was
generated as a dark yellow solid in 94% yield by addition
of a THF solution of NiCl2(dme) to an equimolar amount
of the pnnp ligand. The complex crystallized as yellow, pris-
matic crystals from a dichloromethane/hexane solution.
The dimeric nature of 5 in the solid state was established
by X-ray crystallography, revealing that the asymmetric unit
consists of one Ni center coordinated by one P and one N
(imide) atom of the ligand and two Cl atoms (Figure 3).
Expansion of the asymmetric unit through the inversion
center at [0, 0, 0] shows that the Ni ion is coordinated in a
distorted square-pyramidal fashion by two bridging Cl
atoms, one non-bridging Cl as well as N and P atoms. The
P atom occupies the apical position of the square pyramid.
The τ5 value for the Ni center is 0.47 [given by τ5 = (β –
α)/60], indicating that the geometry is intermediate between
full square pyramidal (τ5 = 0) and trigonal bipyramidal (τ5
= 1).[9] The bridging chlorine Cl(1), has a slightly asymmet-
ric bonding to the Ni centers, as reflected by the two Ni–
Cl distances [2.3258(6) and 2.4524(7) Å]. The disposition of
the uncoordinated amidine nitrogen N(2) and the N(2)···
Cl(2) distance of 2.38(2) Å are suggestive of an intramolec-
ular H-bond from N(2)–H to the non-bridging chlorine
Cl(2).
Pd and Cu complexes exhibit a rich chemistry in a vari-
ety of oxidation reactions,[2e,10] and weak “metallophilic
bonds” (d8–d10 bonds) have been observed between the Pt
group and the coinage metals.[11] To investigate the coordi-
nation chemistry of bimetallic PdCu complexes, an equi-
Scheme 3. Synthesis of mixed-metal trinuclear complex 8.
Table 2. Selected bond lengths [Å] and bond angles [°] for 8.
+
–
Pd(1)···Cu(1)
Pd(1)–C(3)
Pd(1)–N(1)
Pd(1)–P(1)
Pd(1)–P(3)
Cu(1)–N(2)
P(1)–Pd(1)–P(3)
2.8291(5)
2.075(4)
2.180(3)
2.2372(10)
2.3683(10)
1.880(3)
Pd(2)···Cu(1)
Pd(2)–C(4)
Pd(2)–N(4)
Pd(2)–P(2)
Pd(2)–P(4)
Cu(1)–N(3)
P(2)–Pd(2)–P(4)
N(3)–Cu(1)–N(2)
2.8016(5)
2.068(4)
2.156(3)
2.3405(10)
2.2641(10)
1.868(3)
153.79(4)
179.07(14)
molar mixture of (pnnp)PdMe (1) and Cu(NCCH3)4 PF6
was dissolved in acetonitrile (Scheme 3). Crystallization of
the resulting yellow complex from dichloromethane/diethyl
ether yielded block-like crystals of the mixed-metal trinu-
clear complex 8, instead of the expected heterometallic di-
nuclear complex. Selected bond lengths and angles for 8
can be found in Table 2. The coordination geometry of 8
152.98(4)
Pd(2)–Cu(1)–Pd(1) 111.832(18)
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Complexes with N,NЈ-Bis[(2-diphenylphosphanyl)phenyl]formamidine
d8–d10 interaction between the Pd and Cu centers. The The hydrogen on the amide nitrogen N(2) forms an intra-
Cu···Pd(1,2) distances of 2.8291(5) and 2.8016(5) Å, respec- molecular H-bond to one of the Cl atoms [N(2)···
tively, fall outside the sum of the covalent radii (approx. Cl(1) distance: 3.2676(19) Å, see Table 3].
2.71 Å)[8] but are comparable to the bond lengths observed
for heterodinuclear PtII···CuI [distance: 2.7368(4) Å], and
PdII···AuI [distance: 2.954(1) Å] complexes of [MЈMЈЈ(μ-
dcpm)2(CN)2]+ {dcpm
=
bis(dicyclohexylphosphanyl)-
methane}, for which a d8–d10 interaction was proposed.[12]
Figure 5. Molecular structure of 6 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths [Å] and angles [°]; see Table 3.
Table 3. Selected bond lengths [Å] and bond angles [°] for com-
plexes 6 and 7.
6
7
Co(1)–N(1)
Co(1)–P(1)
Co(1)–Cl(1)
Co(1)–Cl(2)
N(1)–C(1)
N(2)–C(1)
N(2)···Cl(2)
2.029(2)
2.3587(7)
2.2232(7)
2.2262(7)
1.306(3)
1.333(3)
3.241(2)
Fe(1)–N(1)
Fe(1)–P(1)
Fe(1)–Cl(1)
Fe(1)–Cl(2)
N(1)–C(1)
N(2)–C(1)
N(2)···Cl(1)
2.1046(17)
2.4189(7)
2.2357(7)
2.2345(8)
1.302(2)
Figure 4. Molecular structure of 8 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms, counterions, solvent mole-
cules, and phenyl groups attached to carbons 21, 31, 51, 61, 81, 91,
111, and 121 have been omitted for clarity. Selected bond lengths
[Å] and angles [°]; see Table 2.
1.334(3)
3.2676(19)
Cl(1)–Co(1)–Cl(2) 115.00(3)
N(1)–C(1)–N(2) 121.4(2)
Cl(1)–Fe(1)–Cl(2) 121.30(3)
N(1)–C(1)–N(2) 121.54(18)
Further exploration into the coordination chemistry out-
side of Group 10 was also carried out with Co- and Fe-
containing complexes. The monometallic cobalt compound
(6) was prepared by reacting an equimolar quantity of pnnp
with CoCl2 in THF (Scheme 4). The product was obtained
as a green solid in 89% isolated yield. The Co complex
crystallizes as turquoise rod-like crystals from a dichloro-
methane/diethyl ether solution. The Co ion is coordinated
in a distorted tetrahedral fashion by two Cl atoms, and one
N and one P atom of the ligand (Figure 5). The τ4 value
for this complex is 0.86.[9] The non-coordinating N atom is
protonated and forms an intramolecular H-bond to one of
the Cl atoms [N(2)···Cl(2) distance: 3.241(2) Å, see Table 3].
The second P atom of the ligand does not have any interac-
tions with nearby atoms or molecules. It is also possible to
synthesize the iron analogue of 6; complex 7 was prepared
by reacting an equimolar quantity of pnnp with FeCl2 in
THF (Scheme 4). The product was obtained as a yellow
solid in 87% yield and single crystals of the Fe complex
suitable for X-ray studies were obtained as colorless colum-
nar crystals from a dichloromethane/diethyl ether solution.
The iron is coordinated in a distorted tetrahedral fashion
by one N and one P atom of the ligand and two Cl atoms
(Figure 6) with the τ4 value of 0.82.[9] The bond lengths
about the Fe center reflect its distorted nature (see Table 3).
Figure 6. Molecular structure of 7 represented by thermal ellipsoids
at 50% probability. Hydrogen atoms have been omitted for clarity.
Selected bond lengths [Å] and angles [°]; see Table 3.
Conclusion
A series of homo-/heterometallic mono-, di-, and trinu-
clear complexes involving mid and late metals supported by
the pnnp ligand was prepared as summarized in Scheme 5.
The ability of this ligand to stabilize mononuclear metal
species enables the facile synthesis of multinuclear struc-
tures by the stepwise introduction of different metal precur-
sors. The heterometallic dinuclear PdNi complex adopts A-
frame structures, whereas the homo-dinuclear Ni complex
exhibits a more coplanar arrangement of the two Ni-con-
taining square planes, reflecting the influence of the coval-
ent radii of metal centers. The mixed-metal trinuclear com-
plex 8 adopts the rare coordination geometry of the butter-
fly structure around Cu, probably as a consequence of a
weak d8–d10 interaction between the Pd and Cu ions. All
the complexes have been characterized by NMR spec-
Scheme 4. Synthesis of mononuclear complexes 6 and 7.
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K.-s. Son, D. M. Pearson, S.-J. Jeon, R. M. Waymouth
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Scheme 5. Versatility of the pnnp ligand to chelate with various transition metals.
The reaction mixture was stirred for 15 min until no more solids
were observed. The solvent was removed in vacuo, the residual sol-
ids were dissolved in CH2Cl2, filtered through celite, and the filtrate
was dried in vacuo to give a deep wine-colored powder (yield
216 mg, 92%). 1H NMR (600 MHz, –20 °C, CD2Cl2): δ = 6.87–
7.98 (m, 29 H, Ph and amidine CH). 31P{1H} NMR (162 MHz,
25 °C, CD2Cl2): δ = 26.4. As discussed in the X-ray crystal struc-
ture analysis section, this compound was found to be a 50:50 mix-
ture of (pnnp)NiCl(μ-Cl)NiCl and (pnnp)NiCl(μ-OH)NiCl by the
elemental analysis. a 50:50 mixture of (pnnp)NiCl(μ-Cl)NiCl and
(pnnp)NiCl(μ-OH)NiCl: calcd. C 57.11, H 3.82, N 3.60; found C
57.11, H 3.82, N 3.60.
troscopy, elemental analysis, and X-ray crystallography. Re-
activity investigations on multinuclear complexes are now
underway.
Experimental Section
General: Unless otherwise stated, all manipulations were carried
out under a nitrogen atmosphere using standard Schlenk-line tech-
niques or in an inert atmosphere glove box. Solvents were pur-
chased from Sigma–Aldrich or Fisher Chemical and dried before
use. All metal precursors were purchased from Strem Chemicals
and used as received. CD2Cl2 was purchased from Cambridge Iso-
topes. CH2Cl2 was dried with CaH2, vacuum transferred, and
stored under a nitrogen atmosphere. THF was dried with sodium/
benzophenone, vacuum transferred, and stored under a nitrogen
atmosphere. N,NЈ-Bis[(2-diphenylphosphanyl)phenyl]formamidine
(pnnp) and 1 were prepared as previously reported.[1] All NMR
spectra were acquired on Inova 500 MHz or 600 MHz spectrome-
[(pnnp)NiCl(μ-Cl)]2 (5): A THF (5 mL) solution of the pnnp ligand
(56.5 mg, 0.1 mmol) was added to a THF (5 mL) solution of
NiCl2(dme) (22 mg, 0.1 mmol). NiCl2(dme) was consumed com-
pletely within 20 min while a rapid color change from green to dark
red was observed. The solvent was removed in vacuo to give a dark
yellow powder (yield 65 mg, 94%); in solution the complex is dark
1
red. H NMR (500 MHz, 25 °C, CD2Cl2): δ = 6.33 (s, 2 H, NH),
1
ters. H NMR spectra are referenced to the residual solvent peak.
7.21–7.72 (m, 56 H, Ph), 8.02 (s, 2 H, amidine CH) ppm. 31P{1H}
NMR (162 MHz, 25 °C, CDCl3): δ = 3.18, 5.4, 20.2, 22.5 ppm.
[(pnnp)NiCl(μ-Cl)]2·CH2Cl2: calcd. C 61.22, H 4.11, N 3.81; found
C 60.89, H 4.39, N 3.74.
31P NMR spectra are referenced to phosphoric acid in D2O.
(pnnp)PdMe(μ-Cl)NiCl (3): A mixture of (pnnp)PdMe (1, 37 mg,
0.0546 mmol) and NiCl2(dme) (12 mg, 0.0546 mmol) was dissolved
in THF (4 mL) and stirred for 15 min. A rapid color change from
yellow to dark purple was observed. The reaction mixture was
dried in vacuo to give a dark purple powder of 3 (yield 44 mg,
(pnnp)CoCl2 (6): A THF (5 mL) solution of pnnp ligand (56.4 mg,
0.1 mmol) and CoCl2 (13 mg, 0.1 mmol) was stirred for 2 h. A
color change was observed from dark blue to a red-wine color in
10 min. After 2 h, the reaction mixture was dried in vacuo to give
1
98%). H NMR (500 MHz, 25 °C, CD2Cl2): δ = 1.49 (s, 3 H, Pd
CH3), 6.29 (d, J = 7.5 Hz, 1 H, Ph), 6.66 (t, J = 7.5 Hz, 2 H, Ph),
7.03 (t, J = 7.5 Hz, 1 H, Ph), 7.22 (t, J = 7.5 Hz, 1 H, Ph), 7.27
(m, 1 H, Ph), 7.35–7.59 (m, 13 H, Ph), 7.78 (d, J = 7.5 Hz, 1 H,
amidine CH), 7.97–8.07 (m, 9 H, Ph) ppm. 31P{1H} NMR
(162 MHz, 25 °C, CD2Cl2): δ = 25.7, 40.0 ppm. (pnnp)PdMe(μ-Cl)
NiCl·0.25CH2Cl2: calcd. C 54.96, H 3.92, N 3.35; found C 55.11,
H 4.15, N 3.14.
a
paramagnetic green powder (yield 62 mg, 89%). (pnnp)-
CoCl2·0.5CH2Cl2: calcd. C 61.12, H 4.24, N 3.80; found C 60.97,
H 4.37, N 3.74.
(pnnp)FeCl2 (7): A THF (5 mL) solution of pnnp ligand (56.4 mg,
0.1 mmol) and FeCl2 (12.6 mg, 0.1 mmol) was stirred for 1.5 h. The
FeCl2 was completely consumed in 10 min. The resulting yellow
solution was dried in vacuo to give a paramagnetic yellow powder
(yield 60 mg, 87%). (pnnp)FeCl2·0.5CH2Cl2: calcd. C 61.38, H
4.26, N 3.82; found C 61.11, H 4.12, N 3.72.
(pnnp)NiCl(μ-X)NiCl (X = Cl or OH in 1:1 ratio) (4): THF (8 mL)
was added to a vial containing KOtBu (33.7 mg, 0.3 mmol) and the
pnnp ligand (169 mg, 0.3 mmol) and stirred. A color change from
white to pale yellow was observed immediately. After 10 min, the
(pnnp)Pd(Me)CuPd(Me)(pnnp)·PF6 (8):
pale yellow solution was added to NiCl2(dme) (132 mg, 0.6 mmol). PdMe (1, 34 mg, 0.050 mmol) and Cu(CH3CN)4 PF6 (19 mg,
A mixture of (pnnp)-
+
–
4260
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Eur. J. Inorg. Chem. 2011, 4256–4261

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0.050 mmol) was dissolved in acetonitrile (10 mL) and stirred for
10 min, the color of the mixture turned yellow. The volatiles were
removed in vacuo from the resulting solution and the residue was
washed with diethyl ether. The yellow powder remaining was dried
in vacuo (yield 26 mg, 66%). 1H NMR (500 MHz, 25 °C, CD2Cl2):
δ = 0.50 (t, J = 6 Hz, 6 H, Pd CH3), 6.47–7.64 (m, 56 H, Ph),
8.34 (2 H, amidine CH) ppm. 31P{1H} = NMR (162 MHz, 25 °C,
CD2Cl2): δ = –144.4, 4.3, 6.8, 27.5, 30.0 ppm. (pnnp)Pd(Me)-
CuPd(Me)(pnnp)·PF6·1.2CH2Cl2: calcd. C 55.18, H 3.98, N 3.33;
found C 54.98, H 3.81, N 3.46.
CCDC-825816 (for 3), -825817 (for 4), -825818 (for 5), -825819
(for 6), -825820 (for 7), -825821 (for 8) contain 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.
Supporting Information (see footnote on the first page of this arti-
1
cle): Crystallographic data of 3–8, H NMR spectra of 3–6 and 8,
31P NMR spectra of 4, 5, and 8.
Acknowledgments
This material is based upon work supported by the National Sci-
ence Foundation (NSF), grant number NSF-CHE-0910729. K.-
s. S. acknowledges an Evelyn Laing McBain graduate fellowship
and D. M. P. a Stanford Graduate Fellowship. The single-crystal
X-ray diffraction data in this work were recorded on an instrument
supported by the National Science Foundation, Major Research
Instrumentation (MRI) Program (grant number CHE-0521569).
Samples for synchrotron crystallographic analysis were submitted
through the SCrALS (Service Crystallography at Advanced Light
Source) program. Crystallographic data were collected at Beamline
11.3.1 at the Advanced Light Source (ALS), Lawrence Berkeley
National Laboratory. The ALS is supported by the U.S. Dept. of
Energy, Office of Energy Sciences under contract DE-AC02-
05CH11231.
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Received: May 13, 2011
Published Online: August 9, 2011
Eur. J. Inorg. Chem. 2011, 4256–4261
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