The variable binding modes of phenylbis(pyrid-2-ylmethyl)phosphane and Bis(pyrid-2-ylmethyl) Phenylphosphonite with AgI and CuI

Article abstract of DOI:10.1002/ejic.200900296

A series of new bridging phosphane and phosphonite structures forming three and six-membered rings with the metal centers were synthesized and characterized. The resulting compounds of phenylbis(pyrid-2-ylmethyl)phosphane (1) with the silver(I) salts of trifluoroacetate (tfa-), tetrafluoroborate (BF₄^-), and triluoromethanesulfonate (Ofa^-) and copper tetrakis(acetonitrile) hexafluorophosphate (PF₆^-) shows the flexibility of the ligand by displaying different coordination modes associated with the electronic and structural characteristics of the corresponding anion. Accordingly, ligand 1 in these complexes displays two different: binding modes. With Agtfa and AgBF₄ compounds 3 and 4 are obtained where the ligand chelates to two silver atoms that exhibit normal Ag-Ag contacts in the range of 2.9 A, When AgOTf or Cu(NCCH₃) ₄PF₆ are used, one molecule of 1 bridges the metal centers through a phosphorus atom while another is terminally bound. This induces short M-M distances of 2.6871 and 2.568 A for 5 and 6, respectively. Similarly, the coordination behavior of the heterofunctional bis(pyrid-2-ylmethyl) phenylphosphonite ligand (2) is reported with Cu(NCCHa)₄PF ₆ (7) and AgBF₄ (8) to form, two novel discrete molecules, In these complexes 2 coordinates through the P and N atoms, with the difference that in 7 the O atom of one of the carbinol arms is also bound to the Cu, Elemental analysis, variable-temperature multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and low-temperature luminescence studies were carried out to fully characterize the compounds.

Full text of DOI:10.1002/ejic.200900296

FULL PAPER
DOI: 10.1002/ejic.200900296
The Variable Binding Modes of Phenylbis(pyrid-2-ylmethyl)phosphane and
Bis(pyrid-2-ylmethyl) Phenylphosphonite with AgI and CuI
Fernando Hung-Low,[a] Amanda Renz,[a] and Kevin K. Klausmeyer*[a]
Keywords: N,P ligands / Silver / Metal-metal interactions / Coordination modes
A series of new bridging phosphane and phosphonite struc-
tures forming three- and six-membered rings with the metal
centers were synthesized and characterized. The resulting
compounds of phenylbis(pyrid-2-ylmethyl)phosphane (1)
with the silver(I) salts of trifluoroacetate (tfa–), tetrafluorobo-
rate (BF4–), and trifluoromethanesulfonate (OTf–), and copper
tetrakis(acetonitrile) hexafluorophosphate (PF6–) shows the
flexibility of the ligand by displaying different coordination
metal centers through a phosphorus atom while another is
terminally bound. This induces short M–M distances of
2.6871 and 2.568 Å for 5 and 6, respectively. Similarly, the
coordination behavior of the heterofunctional bis(pyrid-2-yl-
methyl) phenylphosphonite ligand (2) is reported with
Cu(NCCH3)4PF6 (7) and AgBF4 (8) to form two novel discrete
molecules. In these complexes 2 coordinates through the P
and N atoms, with the difference that in 7 the O atom of
modes associated with the electronic and structural charac- one of the carbinol arms is also bound to the Cu. Elemental
teristics of the corresponding anion. Accordingly, ligand 1 in
these complexes displays two different binding modes. With
Agtfa and AgBF4 compounds 3 and 4 are obtained where the
ligand chelates to two silver atoms that exhibit normal
Ag–Ag contacts in the range of 2.9 Å. When AgOTf or
Cu(NCCH3)4PF6 are used, one molecule of 1 bridges the
analysis, variable-temperature multinuclear NMR spec-
troscopy, single-crystal X-ray diffraction, and low-tempera-
ture luminescence studies were carried out to fully character-
ize the compounds.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
harder functionality[14,15] were synthesized and their coordi-
nation ability toward AgI and CuI salts was studied. Several
Introduction
The coordination chemistry of bifunctional pyridyl- reports show 1 acting as a face capping ligand in octahedral
phosphane ligands has been explored for many years. A metal complexes, as well as being a ligand suitable for use
wide variety of ligands containing a pyridyl functionality in catalysis.[6,16,17] The flexible nature of the ligand implies
in conjuction with phosphorus in the form of phosphanes, the possibility of additional coordination modes, for in-
phosphinites, phosphonites, phosphates and phosphazoles stance with metals that require angles larger than the 90°
have been synthesized and studied.[1–4] Complexes synthe- of the octahedral environment. The close proximity of the
sized with these ligands have exhibited catalytic[1,5–7] and binding functionalities can lead to the ligand bridging ac-
luminescence properties, as well as being useful in the con- ross two metal centers when chelation becomes difficult.
struction of extended structures.[8–11]
Tertiary phosphanes which bridge two metal centers are a
We have mainly been interested in synthesizing pyridyl- relatively recent discovery. Examples have been reported for
containing phosphinites and phosphonites where the pyr- several late transition metals including PtII, PdII,[18–20]
idyl is attached at either the 3- or 4-position which pre- RhI,[21,22] CuI,[23,24] and most recently AgI.[25,26] In the case
cludes the formation of discrete chelating structures.[8,10,12] of Cu and Ag a very sterically constrained phosphazole was
More recently we have begun studies on deriviates that are used as the bridging ligand. On the other hand, 2 (see
attached to the phosphorus in the 2 position.[11,13] Accord- Scheme 2) has been recently described[6] and the catalytic
ingly, the flexible tritopic ligands phenylbis(pyrid-2-ylme- ability of its Ni+2 complex to oligomerize ethylene was
thyl)phosphane (1) and bis(pyrid-2-ylmethyl) phenylphos- studied. X-ray data for metal complexes of this ligand have
phonite (2), also known as hemilabile ligands because of yet to be reported. The X-ray structure of complexes of 2
the presence of a soft phosphane moiety combined with a would prove informative since the added chain length im-
parted by the OCH2 linker could allow for additional coor-
dination varieties.
In this paper we demonstrate how with the very flexible
[a] Department of Chemistry and Biochemistry, Baylor University,
ligand 1 different conformations can be achieved support-
ing Ag–Ag and Cu–Cu interactions (Scheme 1). Also
shown is that with the larger 2 (Scheme 2) the added O
functionality leads to an unusual N–O chelate to CuI.
Waco, TX 76798, USA
Fax: +1-254-710-4272
E-mail: Kevin_Klausmeyer@baylor.edu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.200900296.
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Eur. J. Inorg. Chem. 2009, 2994–3002

Variable Binding Modes of Hemilabile P Ligands with Ag and Cu
rivative.[27] Ligand 2 is considerably more sensitive than its
singly substituted counterpart, decomposing more readily
in solution at room temperature. The purified compound is
a pale yellow oil that readily oxidizes and hydrolyzes in air,
and decomposes when exposed to heat or light. The ligand
can be preserved under inert atmosphere and at –35 °C for
a period of only three days, upon which time hexane extrac-
tions are required to separate 2 from its decomposition
1
products. H and 31P NMR spectra of 1 and 2 in CDCl3
and CD3CN respectively, verify the formation of the li-
gands, with phosphorus singlets at –13.73 for 1 and
160.06 ppm for 2, which are in the region expected for phos-
phane and phosphonite ligands.
Scheme 1. Reaction of AgX with 1 and observed binding modes of
the ligand.
The compounds 3–8 were synthesized by direct reaction
in a 1:1 ratio of the corresponding ligand with the appropri-
–
ate silver(I) salt (tfa–, BF4 , or OTf–) or [Cu(CH3CN)4][PF6]
under ambient conditions. The complexes of 1 were shown
to be stable at room temperature, surviving exposure to air
with little sign of decomposition, provided the complexes
are shielded from light. The Cu compound 6, has proved to
be the most stable among these, as it can be indefinitely
stored in air at room temperature. Compounds of ligand 2
decompose very quickly even under inert conditions in a
period of two or three days, and more rapidly in solution.
Decomposition of the silver complexes is characterized by
a change to a brown color from the initial white solids, and
the Cu compound 7 from white to a green or blue solid,
which is indicative of oxidation of the copper centers. The
range of structural motifs observed in crystal structures 3,
4, 5, and 8 is demonstrative of the ease with which the sil-
ver(I) cation varies its coordination sphere to accept the
number of donors required of it. This coordinative property
allows for a better study of the functionality characteristics
of the ligands as they exhibit different coordination modes
throughout the metal complexes. Coordination numbers
from 3 to 5 are seen in the silver(I) compounds, while the
copper(I) complexes are 4- and 5-coordinate. This versatil-
ity in coordination gives rise to several distorted geometries
such as T-shaped (4), tetrahedral (3, 5, 7, and 8), capped
tetrahedral (5), and trigonal bipyramidal (4). The different
Scheme 2. Binding modes of ligand 2 (M = Ag+ or Cu+).
Results and Discussion
Synthesis
Phosphane 1 was synthesized with modifications of a coordination modes reported for the compounds of 1 are
previously reported procedure[16] where the percent yield of affected by the counterion’s extent of interaction with the
the ligand was improved by using temperatures of –41 and metal center. All of the compounds presented here were de-
–84 °C during the reaction. Two crucial steps of the reac- termined to be dimeric in the crystalline state with 1:1 li-
tion were identified to be responsible for the formation of gand to metal ratios. Ligand 2 binds in a similar way to Ag
several unidentified phosphane oxide byproducts, as well as and Cu, but with the added interaction of the O with the
the overall yield of the final compound. Special care must metal in the Cu complex to achieve a tetrahedral geometry.
be taken during the formation of the (pyridylmethyl)lithium Counterion effects are not observed in the coordination of 2
and its addition to the phosphorus halide as high tempera- to silver, as a reaction with Agtfa formed a crystal structure
tures and rapid addition rates result in poor yield and pu- analogous to that reported for 8. All metal complexes re-
rity of the ligand. Additionally, hexane extractions of the ported herein were characterized by X-ray diffraction,
crude product allowed isolation of the ligand as a white NMR spectroscopy, fluorescence, and elemental analysis,
powder with Ͼ98% purity, as opposed to the creamy yellow except for compound 8, where its instability at room tem-
oil previously reported.[6,16] Pure 1 is thermally stable, and perature gives inconsistent elemental analysis results. Ac-
can be preserved for a period up to 6 months under an inert cordingly, formation of 8 was also confirmed by HRMS
atmosphere. Phenylphosphonite 2 is made by a procedure results. For all of the compounds reported here attempts
similar to that reported for the synthesis of bis(pyrid-3-yl- were made to alter the ligand to metal ratio, in each case
methyl) phenylphosphonite,[9] and the singly substituted de- the 1:1 ratio was obtained upon crystallization.
Eur. J. Inorg. Chem. 2009, 2994–3002
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F. Hung-Low, A. Renz, K. K. Klausmeyer
FULL PAPER
Description of the Crystal Structures
The equimolar reaction of 1 with Agtfa gives complex 3
as shown in Figure 1. The X-ray diffraction study shows
an inversion center relating the two halves of the complex.
Compound 3 displays a symmetric bridging interaction of
the ligands to the metal centers, resulting in a distorted tet-
rahedral geometry for the silver, with the angles ranging
between 79.7(2)° to 117.2(5)°. The Ag–Ag distance is
2.9499(4) Å and the Ag1–N2 distance is 2.786(2) Å, well
beyond normal bonding distance. In this case the strongly
binding of the tfa anion completes the coordination sphere
such that the binding of the additional pyridine is unfa-
vored due to the steric demands of chelation. There is also
likely a stabilizing effect from the Ag–Ag interaction which
also allows the pyridyl to remain free.
Figure 2. Thermal ellipsoid plot (50% level) of the cationic portion
of 4 with an atomic numbering scheme. Hydrogen atoms have been
removed for clarity.
Table 1. Selected bond lengths and angles for compounds 3–5.
3
Ag(1)–N(1)
Ag(1)–O(1)
2.275(2)
2.4091(19)
Ag(1)–P(1)
Ag(1)–Ag(1)#1
2.3960(7)
2.9499(4)
N(1)–Ag(1)–P(1)
P(1)–Ag(1)–O(1)
P(1)–Ag(1)–Ag(1)#1
145.25(6)
116.35(5)
79.716(17)
N(1)–Ag(1)–O(1)
N(1)–Ag(1)–Ag(1)#1 99.70(5)
O(1)–Ag(1)–Ag(1)#1 117.15(5)
95.06(7)
4
Ag(1)–N(3)
Ag(1)–Ag(2)
Ag(2)–N(1)
Ag(2)–P(2)
2.160(3)
2.9922(4)
2.411(3)
2.4613(9)
Ag(1)–N(2)
Ag(2)–N(4)
Ag(2)–P(1)
2.164(3)
2.395(3)
2.4589(9)
N(3)–Ag(1)–N(2)
N(2)–Ag(1)–Ag(2)
N(4)–Ag(2)–P(1)
N(4)–Ag(2)–P(2)
P(1)–Ag(2)–P(2)
N(1)–Ag(2)–Ag(1)
P(2)–Ag(2)–Ag(1)
168.86(10)
83.18(7)
114.32(7)
77.68(7)
154.54(3)
116.80(7)
76.35(2)
N(3)–Ag(1)–Ag(2)
N(4)–Ag(2)–N(1)
N(1)–Ag(2)–P(1)
N(1)–Ag(2)–P(2)
N(4)–Ag(2)–Ag(1)
P(1)–Ag(2)–Ag(1)
86.11(7)
122.94(10)
76.84(7)
116.71(7)
120.25(7)
78.26(2)
Figure 1. Thermal ellipsoid plot of 3 with an atomic numbering
scheme. Ellipsoids are shown at the 50% level. Hydrogen atoms
and a CH2Cl2 solvent molecule have been removed for clarity.
5
Ag(1)–N(1)
Ag(1)–N(4)
Ag(1)–Ag(2)
Ag(2)–N(2)
Ag(2)–P(1)
2.251(5)
2.533(5)
2.6871(6)
2.277(5)
2.5681(14)
Ag(1)–P(2)
Ag(1)–P(1)
Ag(2)–N(3)
Ag(2)–O(1)
2.4096(14)
2.5947(14)
2.260(5)
The X-ray crystal structure of compound 4, which results
from the equimolar reaction of 1 with AgBF4, shows an
unsymmetrical binding of the ligand. The phosphorus of
both ligands as well as a pyridyl arm chelate to the same
silver (Ag2) resulting in a distorted trigonal bipyramidal
geometry [P1–Ag2–P2 154.54(3)°], as shown in Figure 2.
Ag1 has only two pyridyl moieties ligated, giving a slightly
distorted T-shaped geometry, where the angles are N3–
Ag1–Ag2 86.11(7)°, N2–Ag1–Ag2 83.18(7)° and N3–Ag1–
N2 168.86(10)°.
The metal–metal distance in 4 is found to be 2.9922(4) Å,
which is in the typical range for Ag–Ag distances. The Ag–
P bonds also display typical values for both compounds 3
and 4, while the Ag1–N bonds for 4 are noticeably short-
ened ≈ 2.160 Å, due to the low coordination number
(Table 1).
2.555(4)
N(1)–Ag(1)–P(2)
P(2)–Ag(1)–N(4)
P(2)–Ag(1)–P(1)
N(1)–Ag(1)–Ag(2)
N(4)–Ag(1)–Ag(2)
N(3)–Ag(2)–N(2)
N(2)–Ag(2)–O(1)
N(2)–Ag(2)–P(1)
N(3)–Ag(2)–Ag(1)
O(1)–Ag(2)–Ag(1)
131.09(12)
77.06(12)
147.42(5)
138.70(12)
108.26(11)
108.36(16)
111.35(15)
80.97(12)
102.18(11)
90.23(10)
N(1)–Ag(1)–N(4)
N(1)–Ag(1)–P(1)
N(4)–Ag(1)–P(1)
P(2)–Ag(1)–Ag(2)
P(1)–Ag(1)–Ag(2)
N(3)–Ag(2)–O(1)
N(3)–Ag(2)–P(1)
O(1)–Ag(2)–P(1)
N(2)–Ag(2)–Ag(1)
P(1)–Ag(2)–Ag(1)
90.78(17)
80.69(12)
114.42(12)
89.50(4)
58.15(3)
96.75(15)
145.84(12)
110.58(10)
139.56(11)
59.12(3)
from the other ligand is bound terminally. The metal–metal
The reaction of 1 with AgOTf (1:1 ratio) in CH2Cl2 at distance in 5, 2.6871(6) Å, is found to be among the short-
room temperature gives the compound whose crystal struc- est reported, for example the bis{µ2-2-[bis(trimethylsilyl)-
ture is shown in Figure 3, in which the two metal centers methyl]pyridyl}disilver(I) (2.654 Å),[28] the bis[(µ2-1,3-di-
are bridged by a phosphorus from one ligand while the P phenyltriazenido-N,NЈ)silver] (2.669 Å)[29] and the bis[µ2-
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Eur. J. Inorg. Chem. 2009, 2994–3002

Variable Binding Modes of Hemilabile P Ligands with Ag and Cu
N,NЈ-bis(trimethylsilyl)benzenediamidinato-N,NЈ]disilver
(2.665 Å).[30] The Ag1–P1 and Ag2–P1 bonds are nearly
identical, differing by only 0.027 Å. Both Ag1 and Ag2 are
pentacoordinate with the environment about Ag1 being
AgP2N2 and the environment about Ag2 being AgPN2O
due to the coordinating triflate. The pyridyl rings of the
bridging phosphane ligand approach a coplanar conforma-
tion, as evidenced by the P1–C1–C2–N1 and the P1–C7–
C8–N2 torsion angles of 36.1(5)° and 33.5(5)° respectively.
The comparable torsion angles for the P2 ligand are 70.9(5)
and 50.9(6)°. P2 is 3.592(1) Å from Ag2, and the Ag1–P2
bond is typical at 2.410(11) Å, as is the pyridyl–Ag distance
between N2–Ag2, 2.257(5) Å. The pyridyl–Ag distance be-
tween N1–Ag1 displays an unusually long bond of
2.538(4) Å; this could be attributed to the orientation of
the pyridyl ring which does not point directly at the Ag
emphasizing the steric stress in the complex.
Figure 4. Thermal ellipsoid plot (50% level) of the cationic portion
of 6 with an atomic numbering scheme. Hydrogen atoms and the
–
two PF6 anions have been removed for clarity.
2.568 Å,[23] the phosphole is a more rigid ligand hence the
bridging interaction is likely promoted more by the con-
strained geometry of the ligand. It should be noted that the
Cu1–P2 and Cu2–P2 interactions are not symmetric, as in
5, differing by 0.243 Å (Table 2). The Cu1 atom has a dis-
torted capped tetrahedral geometry due to the bridging in-
teraction that distorts the symmetry of the angles, ranging
from 53.28(2)° to 131.23(16)°. Cu2 has a distorted tetrahe-
dral geometry due to both the chelating behavior of one of
the ligands and the bridging interaction presented through
P2, ranging the angles from 53.28(5)° to 159.20(17)°. The
terminally bound ligand shows a close pyridyl π separation
of 3.653 Å and an angle of 17.22(26)°. This favorable π-
stacking interaction may help account for the close proxim-
ity of Cu1 to Cu2, allowing for the opposing phosphane
to undergo the 3-centered bridge. The P1–Cu2 distance is
3.376(5) Å, well beyond bonding distance. The Cu1–P2
bond is typical at 2.254(2) Å, as are the pyridyl–Cu dis-
tances of 2.092(6) and 1.949(5) Å for N2–Cu1 and N1–Cu2,
respectively.
Figure 3. Thermal ellipsoid plot (50% level) of the cationic portion
of 5 with an atomic numbering scheme. Hydrogen atoms, one tri-
flate anion and one solvent CH2Cl2 molecule have been removed
for clarity.
The crystal structure of compound 7 contains two cop-
pers and two molecules of ligand 2. The ligand bridges the
An X-ray diffraction study revealed that the CuI complex two copper centers to create a symmetric and discrete mole-
6, obtained from
1 and an equimolar amount of cule (Figure 5). The Cu environment is a distorted tetrahe-
[Cu(CH3CN)4][PF6], has the structure shown in the Fig- dron. In order to achieve this geometry, the O atom from
ure 4, in which the two metal centers are bridged by a phos- one of the carbinol arms is ligated to the Cu. This unusual
phane donor, and the second ligand is a terminal bound bonding sequence between the metal center and the ligand
bridging ligand, very similar to 5.
has been previously reported with Fe,[31] Ru,[32,33] Sn,[34]
The different metal coordination environments in the Li,[35] Na[36–38] and K.[39] Each of the previously reported
crystal structure of 6 once again show the ability of the structures had smaller, symmetric ligands, and none of
ligand to coordinate either terminally (P1), or bridging them were di- or tritopic. The Cu1–O4 bond has a distance
(P2). The conformation of the ligand in this complex seems of 2.399(2) Å, and there is no Cu–Cu interaction, the dis-
to be quite sensitive to the affinity of CuI to achieve tetrahe- tance being 3.820 Å. The hexagonal ring at the center of
dral angles, where geometric effects contribute either to the structure created by the P–O–Cu progression is oriented in
bridging or terminal bond interactions. The metal–metal a chair conformation. A reaction mixture of a 2:3 metal to
distance in 6 [2.488 (12) Å] is the shortest reported for a ligand ratio produced only crystals of 7.
copper complex bridged by phosphane. The first Cu···Cu-
The X-ray crystal structure of compound 8 reveals a
bridged phosphane compound was reported with the 2,5- slightly alternate conformation of the ligand. The two nitro-
di(pyrid-2-yl)phosphole and a metal–metal distance of gens are seen chelating the Ag center, while the phosphorus
Eur. J. Inorg. Chem. 2009, 2994–3002
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2997

F. Hung-Low, A. Renz, K. K. Klausmeyer
FULL PAPER
Table 2. Selected bond lengths and angles for 6–8.
2.317 to 2.346 Å and fall within reported values. The pack-
ing structure of compound 8 shows long range interactions
holding the BF4 anion in place by CH–F and Ag–F interac-
tions with distances of 2.258 and 2.727 Å respectively.
6
Cu(1)–N(3)
Cu(1)–P(1)
Cu(1)–P(2)
Cu(2)–N(4)
1.994(5)
2.254(2)
2.497(2)
2.030(5)
Cu(1)–N(2)
Cu(1)–Cu(2)
Cu(2)–N(1)
Cu(2)–P(2)
2.092(6)
2.4882(12)
1.949(5)
2.235(2)
N(3)–Cu(1)–N(2)
N(2)–Cu(1)–P(1)
N(2)–Cu(1)–Cu(2)
N(3)–Cu(1)–P(2)
P(1)–Cu(1)–P(2)
N(1)–Cu(2)–N(4)
N(4)–Cu(2)–P(2)
N(4)–Cu(2)–Cu(1)
110.4(2)
N(3)–Cu(1)–P(1)
N(3)–Cu(1)–Cu(2) 134.34(16)
P(1)–Cu(1)–Cu(2) 89.97(6)
N(2)–Cu(1)–P(2)
Cu(2)–Cu(1)–P(2) 53.28(5)
N(1)–Cu(2)–P(2) 159.20(17)
N(1)–Cu(2)–Cu(1) 96.93(16)
126.96(16)
85.30(16)
96.95(15)
81.56(17)
126.02(7)
112.8(2)
131.23(16)
87.58(17)
149.28(17)
7
Cu(1)–N(3)
Cu(1)–P(2)
Cu(2)–N(2)
Cu(2)–P(1)
2.020(3)
2.1549(9)
2.029(3)
2.1594(9)
Cu(1)–N(4)
Cu(1)–O(4)
Cu(2)–N(1)
Cu(2)–O(1)
2.027(3)
2.399(2)
2.033(3)
2.413(2)
N(3)–Cu(1)–N(4)
N(4)–Cu(1)–P(2)
N(4)–Cu(1)–O(4)
N(2)–Cu(2)–N(1)
N(1)–Cu(2)–P(1)
N(1)–Cu(2)–O(1)
105.73(11)
129.64(8)
74.94(10)
104.81(11)
128.30(8)
74.41(10)
N(3)–Cu(1)–P(2)
N(3)–Cu(1)–O(4) 99.70(10)
P(2)–Cu(1)–O(4)
N(2)–Cu(2)–P(1)
N(2)–Cu(2)–O(1) 97.33(9)
P(1)–Cu(2)–O(1) 107.25(6)
122.71(9)
Figure 6. Thermal ellipsoid plot (50% level) of the cationic portion
of 8 with an atomic numbering scheme. Hydrogen atoms, the two
106.93(6)
125.40(8)
–
BF4 anions and one solvent CH2Cl2 molecule have been removed
for clarity.
8
Ag(1)–N(1)
NMR Spectroscopy
Ag(1)–N(2)
Ag(1)–P(1)
2.317(3)
2.3460(10)
2.336(3)
1
The H and 31P NMR spectra of all compounds were
N(2)–Ag(1)–N(1) 86.47(12)
N(1)–Ag(1)–P(1) 137.28(8)
N(2)–Ag(1)–P(1)
135.90(9)
collected in different solvents due to the solubility of each
compound. The H NMR spectra of compounds 3–6 are,
1
as expected, generally similar, as well as between 7 and 8.
31P NMR spectra were recorded at room and low tempera-
tures to observe the dissociation of the M–P bonds, the la-
bility of the M–P bond even at low temperatures precluded
observation of the coupling of the two isotopes of Ag to P.
The room temperature 31P NMR spectra of both 3 and 4
showed a defined phosphorus resonance at δ = 8.7 and
9.9 ppm respectively. Upon cooling to –45 °C, the signal for
3 begins to show coupling with Ag, giving a resonance at δ
= 11.2 ppm, while 4 shows similar behavior at δ = 11.2 ppm.
At room temperature the 31P NMR spectrum of 5 shows
again a broad phosphorus signal at δ = 11.8 ppm, which
indicates that in solution the P is not bridging the Ag
atoms, and may instead be chelating the metal centers.
Upon cooling to –45 °C, this broad signal splits into an
unsymmetrical resonance at δ = 12.0 ppm indicating that in
solution the structure likely is different than that reported
by X-ray diffraction. Possibly, even at low temperatures the
P1–Ag2 interaction is dissociated thus resulting in a confor-
mation similar to that reported for 3, which explains the
similar spectra observed for 3 and 5. The 31P spectrum of
6 shows a broad phosphorus resonance at δ = –15.5 ppm,
Figure 5. Thermal ellipsoid plot (50% level) of the cationic portion
of 7 with an atomic numbering scheme. Hydrogen atoms and the
–
two PF6 anions have been removed for clarity.
bridges to the opposing Ag producing a discrete dimer (Fig- indicating fluxional Cu–P bonding in solution. Upon cool-
ure 6). The trigonal planar environments of the metal cen- ing to –45 °C this broad signal splits into two singlets at
ters exhibit angles ranging from 86.47° to 137.28°. The –31.2 and –2.2 ppm, resulting from two separate phospho-
varying of the metal from Cu to Ag eliminated the strong rus environments present at low temperature, corresponding
tetrahedral affinity resulting in both Ag atoms being three- to the terminal and bound bridging phosphorus, respec-
coordinate. The Ag–N and Ag–P distances range from tively. As a result, the low-temperature 31P NMR of 6
2998
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Variable Binding Modes of Hemilabile P Ligands with Ag and Cu
agrees with the crystal structure reported for the com- 2 is also shown to be versatile as it is seen to act as a triden-
pound. The 31P NMR spectra of 7 and 8 show analogous tate and tetradentate ligand, forming a stable six-member
signals, as expected, with a singlet at δ = 134.9 and ring with the metal centers.
142.2 ppm respectively, as the crystal structures display a
Future work in our group encompasses the design and
similar structural motif. The variable temperature 31P NMR synthesis of more hemilable pyridyl-containing phosphanes
also showed singlet signals for both complexes, indicative and phosphinites. Additionally, we are also actively pursu-
of a fast equilibrium even at low temperatures.
ing the oxidation of ligand 1 to its oxide derivatives, as the
incorporation of one or more oxygen moieties, combined
with the demonstrated flexibility of the ligand, can exhibit
an interesting coordinative behaviour to different transition
metals and lanthanide starting materials.
Photoluminescence
Photoluminescence experiments were conducted on com-
plexes 3–8. The low-temperature solution luminescence
spectra were collected to give a general representation of
what the solid state spectra would be (Figure S1). The re-
semblance of the excitation spectra of compounds 3–6 with
that of free 1 suggests that the luminescent behavior of
these complexes is initiated by a ligand-based absorption,
which then decays by means of ligand-to-metal charge
transfer. A clear dependence is observed between the inten-
sities in which energy is absorbed, and the type of coordina-
tion metal–ligand encountered in the complex. Excitation
maxima of all compounds are presented in Table 3 along
with the local emission maxima. The emission spectra of
the various compounds cover a range of the spectrum with
local maxima spanning approximately 100 nm. Analyzing
only the spectra of the three silver–ligand compounds, we
find that the order in intensities increase in the following
sequence: [AgBF4(1)]2 Ͼ [Agtfa(1)]2 Ͼ [AgOTf(1)]2. The lu-
minescence properties of the compounds of ligand 2 (7 and
8) were also tested, however, their rapid decomposition un-
der ambient conditions precluded the collection of the spec-
tra, even when the corresponding solutions were prepared
under inert atmosphere.
Experimental Section
General Remarks: All experiments were carried out under a nitro-
gen atmosphere, using a Schlenk line and standard Schlenk tech-
niques. Glassware was dried at 120 °C for several hours prior to
use. Solvents were distilled under nitrogen from the appropriate
drying agent immediately before use. 1H and 31P NMR spectrum
were recorded at 499.78 and 202.32 MHz respectively, on a Varian
500 MHz spectrometer. Fluorescence spectra were recorded on an
Instruments S. A. Inc. model Fluoromax-2 spectrometer using
band pathways of 2.5 nm for both excitation and emission and are
presented uncorrected. Elemental analyses were performed by At-
lantic Microlabs Inc., Norcross, Georgia. High resolution mass
spectra (HRMS) were obtained in the Baylor University Mass
Spectrometry Core Facility on a Thermo Scientific LTQ Orbitrap
Discovery using +ESI.
Materials: Dichlorophenylphosphane was purchased from Aldrich
Chemical and used as received. Triethylamine was purchased from
Aldrich and was purged with nitrogen before use. 2-pyridylcarbinol
was purchased from Alfa Aesar and used as received. Silver salts
were purchased from Strem Chemicals Inc. and stored in an inert-
atmosphere glovebox. [Cu(CH3CN)4][PF6] was prepared according
to published procedures.[40]
Table 3. Luminescence spectroscopic data for compounds 3–6 at
77 K and 1ϫ10–4  in CH3CN.
General Synthesis: General procedures for the synthesis of com-
pounds 3–8 involve the addition of a 5 mL solution of the corre-
sponding ligand 1 or 2 in either CH3CN or CH2Cl2, to a stirred
solution of the appropriate salt in 5 mL of solvent. The mixtures
were then allowed to stir for 10 min and then dried in vacuo to
leave white or off-white powders. The flasks containing the silver
compounds were shielded from light with aluminum foil to prevent
photodecomposition. Colorless blocks of the four silver com-
pounds were obtained by slow diffusion of hexane into a CH2Cl2
solution of 3, 4, 5, and 7 at 5 °C. Crystals of compounds 6 and 8
were grown by layering ether over acetonitrile solutions at 5 °C.
The amounts of reagents used, yields, and spectroscopic data are
presented below as well as any modifications to the general syn-
thetic procedure. Percent yields are based upon the amount of the
corresponding silver or copper salt used.
Compound
Excitation λmax /nm
Emission λmax /nm
3
4
5
6
315
301
314
327
441, 455, 466
462
438
473, 491, 500, 512
Conclusions
Herein we have demonstrated that several coordination
environments and coordination numbers can be formed
with AgI and CuI salts, being controlled either by variations
in counterion or coordinative ability of the ligand. The
series 3–5 displays the flexibility of 1 to bind to AgI. In
each case the preferred chelating angle is greater than 90°
for which the ligand is ideally suited. This results in both
bridging and chelating by the ligand to two metal centers.
In addition, a very flexible tertiary phosphane is shown
with two AgI centers forming a very short argentophilic in-
teraction. A similar result is obtained by reaction of 1 with
Cu(NCCH3)4PF6, as the ligand bridges and chelates two
Phenylbis(pyrid-2-ylmethyl)phosphane (1): This compound was syn-
thesized by addition of n-butyllithium (17 mmol, 5.86 mL, 2.9  in
hexane) over a period of 10 min to 2-picoline (17 mmol, 1.67 mL)
in dry THF (20 mL) at –41 °C. The mixture was stirred for 1 h,
then added to a solution of dichlorophenylphosphane (3.0 g,
17 mmol) in dry THF (20 mL) at –84 °C over a period of 30 min.
Degassed water (25 mL) was then added over 10 min and the mix-
ture stirred for 30 min. The product was obtained by first extracting
with 0.3  HCl(aq), then neutralizing with aqueous NaHCO3 solu-
tion, and a final extraction with dichloromethane. The solvent and
coppers and induces a short cuprophilic interaction. Ligand any unreacted 2-picoline were removed under vacuum (oil pump)
Eur. J. Inorg. Chem. 2009, 2994–3002
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2999

F. Hung-Low, A. Renz, K. K. Klausmeyer
FULL PAPER
resulting in a yellow oil. The yield of crude product was 81%. Puri-
fication of the product was carried out by several extractions with
hexane which resulted in a white solid in 70% yield based on 2-
0.396 mmol) in CH3CN (5 mL). Solvent was removed in vacuo to
obtain an off-white powder. This was then re-dissolved in a small
amount of CH2Cl2 and precipitated with hexane, repeating until
compound 4 was obtained as a white powder upon drying in 51%
(0.180 g, 0.202 mmol) yield. 1H NMR (CDCl3, 298 K): δ = 4.35
(m, 8 H, CH2), 7.58 (m, 14 H, aromatic), 7.98 (m, 8 H, aromatic),
8.60 (d, 4 H, aromatic) ppm. 31P NMR [(CD3)2CO, 298 K]: δ = 9.9,
s; [(CD3)2CO, 231 K]: δ = 11.2 (d) ppm. C37H36Ag2B2Cl2F8N4P2
(1058.91): calcd. C 41.97, H 3.43, N 5.29; found C 42.21, H 3.48,
N 5.47.
1
picoline. H NMR (CD3Cl, 298 K): δ = 3.41 (q, 4 H, CH2), 7.02
(m, 4 H, aromatic), 7.33 (m, 3 H, aromatic), 7.49 (m, 4 H, aro-
matic), 8.52 (m, 2 H, aromatic) ppm. 31P NMR (CDCl3, 298 K): δ
= –13.7 (s) ppm.
Bis(pyrid-2-ylmethyl) Phenylphosphonite (2): In a nitrogen-purged
addition funnel, 1.39 mL of degassed triethylamine (10 mmol) was
added via syringe to a stirred solution of pyridine-2-methanol
(1.09 g, 10 mmol) in toluene (20 mL) at room temperature. The
solution was cooled to 0 °C and shielded from light with aluminum
foil. A solution of dichlorophenylphosphane (0.896 g, 5 mmol) in
toluene (20 mL) was then added dropwise over 10 min. The solu-
tion was stirred for 1 h, and warmed to room temperature, followed
by stirring for an additional 30 min. The resultant mixture was fil-
tered through Celite. The triethylammonium chloride salt was
washed with an additional 5 mL of cold toluene, and the solvent
was removed from the yellow liquid at reduced pressure to leave a
yellow oil. The oil was then extracted with 100 mL of hexane to
leave 2 as a pale yellow oil in 84% yield (1.36 g, 4.36 mmol). 1H
NMR (CH3CN, 298 K): δ = 5.01 (m, 4 H, CH2), 7.09 (t, 3 H,
aromatic), 7.66 (m, 7 H, aromatic), 8.43 (d, 3 H, aromatic) ppm.
31P NMR (CD3CN, 298 K): δ = 160.1 (s) ppm.
Synthesis of [AgOTf(1)]2 (5): To a stirred solution of AgOTf
(0.109 g, 0.399 mmol) in CH3CN (5 mL) was added 1 (0.116 g,
0.399 mmol) in CH3CN (5 mL). The compound was re-crystallized
upon drying in 49% (0.210 g, 0.194 mmol) yield. 1H NMR (CDCl3,
298 K): δ = 4.31 (m, 8 H, CH2), 7.32 (m, 6 H, aromatic), 7.49 (m,
8 H, aromatic), 7.85 (t, 4 H, aromatic), 7.96 (m, 4 H, aromatic),
8.45 (d, 4 H, aromatic) ppm. 31P NMR [(CD3)2CO, 298 K]: δ =
11.8, s; [(CD3)2CO, 298 K]: δ = 12.1, t ppm. C39H36Ag2Cl2F6-
N4O6P2S2 (1169.39): calcd. C 39.58, H 3.07, N 5.23; found C 40.13,
H 3.16, N 4.91.
Synthesis of [CuPF6(1)]2 (6): A solution of 1 (0.116 g, 0.399 mmol)
in CH3CN (5 mL) was added to [Cu(CH3CN)4][PF6] (0.149 g,
0.399 mmol) dissolved in CH3CN (5 mL). Compound 6 was ob-
tained as
a white powder upon drying in 85% (0.170 g,
Synthesis of [Agtfa(1)]2 (3): This reaction used
1
(0.116 g,
0.170 mmol) yield. 1H NMR (CDCl3, 298 K): δ = 3.83 (m, 4 H,
CH2), 7.47 (m, 11 H, aromatic), 8.21 (m, 2 H, aromatic) ppm. 31P
NMR [(CD3)2CO, 298 K]: δ = –15.5, s; [(CD3)2CO, 228 K]: δ =
–31.2 (s, br), –2.2 (s) ppm. C36H34Cu2F12N4P4 (1001.65): calcd. C
43.17, H 3.42, N 5.59; found C 43.12, H 3.31, N 5.62.
0.398 mmol) in CH3CN (5 mL) added to a stirred solution of Agtfa
(0.880 g, 0.398 mmol) in CH3CN (5 mL) to leave a fluffy off-white
solid. The compound was re-crystallized upon drying in 48%
(0.190 g, 0.185 mmol) yield. 1H NMR (CDCl3, 298 K): δ = 4.05
(m, 8 H, CH2), 7.31 (m, 14 H, aromatic), 7.68 (m, 4 H, aromatic),
7.85 (m, 4 H, aromatic), 8.47 (d, 4 H, aromatic) ppm. 31P NMR
[(CD3)2CO, 298 K]: δ = 8.7, s; [(CD3)2CO, 238 K]: δ = 11.2, t ppm.
C41H36Ag2Cl2F6N4O4P2 (1111.54): calcd. C 44.31, H 3.26, N 5.04;
found C 43.82, H 3.33, N 4.84.
Synthesis of [CuPF6(2)]2 (7): To a stirred solution of [Cu(CH3CN)4]-
[PF6] (0.111 g, 0.297 mmol) in CH2Cl2 (5 mL), was added to 2
(0.097 g, 0.299 mmol) in CH2Cl2 (5 mL). This solution was stirred
for 5 min, and then 45 mL of ether were added. Upon stirring for
10 min a white precipitate formed. The colorless solvent was re-
moved via cannula, and the residual solvent was removed in vacuo
to leave a white solid, 7, in 81% (0.278 g, 0.358 mmol) yield. 1H
Synthesis of [AgBF4(1)]2 (4): The reaction was done in a 1:1 ratio
of 1 (0.117 g, 0.396 mmol) in CH3CN (5 mL) to AgBF4 (0.077 g,
Table 4. Crystallographic data for compounds 3–5.
3
4
5
Empirical formula
Formula mass
C42H38Ag2Cl4F4N4O4P2
1196.24
C36H34Ag2B2F8N4P2
973.97
C39H36Ag2Cl2F6N4O6P2S2
1183.42
a /Å
b /Å
c /Å
α /°
9.9151(8)
10.5773(9)
11.8770(10)
81.442(4)
79.351(4)
75.428(4)
1177.90(17)
1
10.4667(8)
13.3392(8)
14.1342(11)
102.466(2)
104.341(2)
93.595(2)
1852.7(2)
2
9.7199(7)
13.9612(10)
16.5420(11)
79.481(3)
80.510(3)
82.583(3)
2165.5(3)
2
β /°
γ /°
V /Å3
Z
Crystal system
Space group
T /K
triclinic
P1
110(2)
1.686
1.195
triclinic
P1
110(2)
1.746
1.218
triclinic
P1
110(2)
1.815
1.276
¯
¯
¯
Dcalcd. /gcm–3
µ /mm–1
2θmax. /°
Reflections measured
Reflections used (Rint
Restraints/parameters
R1 [IϾ2σ(I)]
wR2 [IϾ2σ(I)]
R(Fo2) (all data)
Rw(Fo2) (all data)
GOF on F2
26.37
23421
25.00
17285
25.00
37239
)
4759 (0.0290)
0/289
0.0307
0.0800
0.0331
0.0816
1.036
7388 (0.0350)
0/487
0.0353
0.0742
0.0506
0.0824
1.017
7565 (0.0423)
0/568
0.0525
0.1517
0.0592
0.1593
1.010
3000
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2994–3002

Variable Binding Modes of Hemilabile P Ligands with Ag and Cu
Table 5. Crystallographic data for compounds 6 through 8.
6
7
8
Empirical formula
Formula mass
a /Å
b /Å
c /Å
α /°
β /°
C36H34Cu2F12N4P4
1001.63
9.559(19)
25.281(5)
16.763(3)
90
101.892(6)
90
3962.8(13)
4
C37H36Cl2Cu2F12N4O4P4
1150.56
C38H38Ag2B2Cl4F8N4O4P2
1207.82
9.5811(13)
16.958(2)
13.9024(18)
90
101.357(6)
90
2214.6(5)
2
11.8810(7)
15.0617(9)
16.3276(10)
67.705(3)
74.534(3)
68.830(3)
2492.3(3)
2
γ /°
V /Å3
Z
Crystal system
Space group
T /K
monoclinic
P21/n
110(2)
1.679
1.326
triclinic
P1
110(2)
1.533
1.174
monoclinic
P21/n
110(2)
1.811
1.278
¯
Dcalcd. /gcm–3
µ /mm–1
2θmax. /°
Reflections measured
Reflections used (Rint
Restraints/parameters
R1 [IϾ2σ(I)]
wR2 [IϾ2σ(I)]
R(Fo2) (all data)
Rw(Fo2) (all data)
GOF on F2
25.00
22722
8017 (0.1376)
0/523
0.0756
0.0906
0.1860
0.1154
1.002
26.53
74451
26.51
24112
4545 (0.0278)
0/289
0.0386
0.1129
0.0420
0.1167
1.055
)
10282 (0.0312)
0/587
0.0556
0.1422
0.0672
0.1490
1.063
NMR (CD3CN, 298 K): δ = 5.04 (d, 4 H, CH2), 7.35 (d, 9 H,
aromatic), 7.41 (s, 2 H, aromatic), 8.22 (s, 2 H, aromatic) ppm. 31
Acknowledgments
P
NMR (CD3CN, 298 K): δ = 134.9 (s, br); (CD3CN, 225 K): δ =
130.3 (s) ppm. C36H34Cu2N4O4P2 (775.73): calcd. C 40.58, H 3.22,
N 5.26; found C 40.85, H 3.13, N 5.36.
This research was supported by funds provided by grant from the
Robert A. Welch Foundation (AA-1508). The Bruker X8 APEX
diffractometer was purchased with funds received from the
National Science Foundation Major Research Instrumentation
Synthesis of [AgBF4(2)]2 (8): To a stirred solution of AgBF4
(0.0577 g, 0.300 mmol) in CH3CN (5 mL) was added 2 (0.099 g, Program Grant CHE-0321214
0.306 mmol) in CH3CN (5 mL). The resulting solution was allowed
to stir for 15 min and then dried in vacuo to leave a pale yellow
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Eur. J. Inorg. Chem. 2009, 2994–3002
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3001

F. Hung-Low, A. Renz, K. K. Klausmeyer
FULL PAPER
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Received: March 30, 2009
Published Online: May 26, 2009
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