Synthesis and characterization of Pd(0) and Pt(0) metallocryptands encapsulating Tl+ ion

Article abstract of DOI:10.1021/ja001672s

Pt(0)/Pd(0) metallocryptates encapsulating Tl(I) have been constructed utilizing mixed phosphineimine ligands 2,9-bis(diphenylphosphino)-1,10-phenathroline, P₂phen, and 6,6′-bis(diphenylphosphino)-2,2′-bipyridine, P₂bpy. The red compounds [M₂Tl(P₂phen)₃](NO₃) (M = Pt, 1; M = Pd, 3) and [M₂Tl(P₂bpy)₃](NO₃) (M = Pt, 2; M = Pd, 4) have been isolated as air-stable crystalline solids. Complexes 1-4 exhibit single signals in their ²⁰⁵Tl NMR spectra that are well deshielded compared to the TlNO_3(aq) reference signal. Additionally, ¹⁹⁵Pt NMR spectra of complexes 1 and 2 exhibit a doublet of quartets pattern resulting from large one-bond couplings to both ³¹P and ²⁰⁵Tl. Characterization of 1-4 by single-crystal X-ray diffraction studies confirms the metallocryptand structure consisting of three phosphine-imine ligands in a D₃-symmetric cage with the Tl(I) ion in its center and the zero-valent Pt or Pd atoms on each end. Each Pd or Pt atom is coordinated to three phosphorus centers, forming approximately trigonal geometry. The Tl(I) ion is positioned away from the imine nitrogen atoms of the phosphine ligands by ～3.5 A. Further, the outer capping metals are distorted toward the central Tl(I) ion, indicating a strong interaction. The Pt-Tl and Pd-Tl separations are at ～2.8 A each, further manifesting the strength of the metallophilic attraction in these assemblies.

Full text of DOI:10.1021/ja001672s

10056
J. Am. Chem. Soc. 2000, 122, 10056-10062
Synthesis and Characterization of Pd(0) and Pt(0) Metallocryptands
Encapsulating Tl+ Ion
Vincent J. Catalano,*,† Byron L. Bennett,†,§ Renante L. Yson,† and Bruce C. Noll‡
Contribution from the Department of Chemistry, UniVersity of NeVada, Reno, NeVada 89557, and
Department of Chemistry and Biochemistry, UniVersity of Colorado, Boulder, Colorado 80309
ReceiVed May 15, 2000
Abstract: Pt(0)/Pd(0) metallocryptates encapsulating Tl(I) have been constructed utilizing mixed phosphine-
imine ligands 2,9-bis(diphenylphosphino)-1,10-phenathroline, P2phen, and 6,6′-bis(diphenylphosphino)-2,2′-
bipyridine, P2bpy. The red compounds [M2Tl(P2phen)3](NO3) (M ) Pt, 1; M ) Pd, 3) and [M2Tl(P2bpy)3](NO3)
(M ) Pt, 2; M ) Pd, 4) have been isolated as air-stable crystalline solids. Complexes 1-4 exhibit single
signals in their 205Tl NMR spectra that are well deshielded compared to the TlNO3(aq) reference signal.
Additionally, 195Pt NMR spectra of complexes 1 and 2 exhibit a doublet of quartets pattern resulting from
large one-bond couplings to both 31P and 205Tl. Characterization of 1-4 by single-crystal X-ray diffraction
studies confirms the metallocryptand structure consisting of three phosphine-imine ligands in a D3-symmetric
cage with the Tl(I) ion in its center and the zero-valent Pt or Pd atoms on each end. Each Pd or Pt atom is
coordinated to three phosphorus centers, forming approximately trigonal geometry. The Tl(I) ion is positioned
away from the imine nitrogen atoms of the phosphine ligands by ∼3.5 Å. Further, the outer capping metals
are distorted toward the central Tl(I) ion, indicating a strong interaction. The Pt-Tl and Pd-Tl separations
are at ∼2.8 Å each, further manifesting the strength of the metallophilic attraction in these assemblies.
Introduction
Chart 1
Metallocryptates are an emerging class of inorganic cage
complexes that are well-suited to encapsulate a variety of metal
ions.1,2,4 Unlike their purely organic counterparts, metallo-
cryptates are capable of binding metal ions either through strong
Lewis base interactions of the donor groups of the ligands or
through metallophilic interactions between the late transition
metal capping groups and the guest metal ion. In the absence
of attractive guest-ligand interactions, metallocryptates offer
a unique opportunity to explore the remaining metal-metal
interactions in a rigidly controlled environment.
Recently, we reported the syntheses of cationic Au(I)-based
metallocryptates,2 [Au2M(P2phen)3]3+ (M ) Na+ and Tl+; P2-
phen ) 2,9-bis(diphenylphosphino)-1,10-phenathroline,3 A in
Chart1). Each species contains Au centers in trigonal coordina-
tion environments, a D3-symmetrical cavity imposed by helical
phenanthroline subunits, long guest ion-imine distances, and
a nearly linear Au-M-Au core. In [Au2Tl(P2phen)3]3+, two
short Au(I)-Tl(I) distances of ∼2.9 Å are observed, indicative
of a strong interaction between these two closed-shell ions.
However, replacing the aurophilic Tl(I) ion with a Na+ ion
eliminates the metallophilic interaction, making this assembly
unstable, and the alkali metal readily dissociates. In contrast,
by employing the 2,9-bis(diphenylphosphino)-1,8-naphthyridine
ligand (dppn) which is capable of strong imine-Na+ interac-
tions, the assembly is maintained (B in Chart 1).4 In fact, Na+
is preferred over Tl(I) ion in this case.
This aurophilic and metallophilic behavior between formally
closed-shell ions and atoms has been invoked previously5 and
theoretically treated.6 There is a considerable attraction between
closed-shell species, and a large number of inorganic assemblies
based on this attraction have been reported.7 In many cases it
is difficult to separate purely metallophilic interactions from
secondary ligand interactions. However, metallocryptands, with
(5) (a) Ferna´ndez, E. J.; Lo´pez-de-Luzuriaga, J. M.; Monge, M.;
Rodr´ıguez, M. A.; Crespo, O.; Gimeno, M. C.; Laguna, A.; Jones, P. G.
Chem. Eur. J. 2000, 6, 636. (b) Pyykko¨, P.; Runeberg, N.; Mendizabal, F.
Chem. Eur. J. 1997, 3, 1451. (c) Pyykko¨, P.; Mendizabal, F. Inorg. Chem.
1998, 37, 3018. (d) Ferna´ndez, E. J.; Lo´pez-de-Luzuriaga, J. M.; Monge,
M.; Rodr´ıguez, M. A.; Crespo, O.; Gimeno, M. C.; Laguna, A.; Jones, P.
G. Inorg. Chem. 1998, 37, 6002. (e) Schmidbaur, H. Chem. Soc. ReV. 1995,
391.
* To whom correspondence should be addressed. E-mail: VJC@unr.edu.
Fax: (775) 784-6804.
† University of Nevada, Reno.
‡ University of Colorado, Boulder.
§ Current address: Department of Chemistry, University of Nevada, Las
Vegas, NV 89154.
(1) Uang, R.-H.; Chan, C.-K.; Peng, S.-M.; Che, C.-M. J. Chem. Soc.,
Chem. Commun. 1994, 2561.
(2) Catalano, V. J.; Bennett, B. B.; Kar, H. M.; Noll, B. C. J. Am. Chem.
Soc. 1999, 121, 10235.
(3) Ziessel, R. Tetrahedron Lett. 1989, 30, 463.
(4) Catalano, V. J.; Kar, H. M.; Bennett, B. L. Inorg. Chem. 2000, 39,
121.
(6) Pyykko¨, P. Chem. ReV. 1997, 97, 597.
(7) (a) Crespo, O.; Fernandez, E. J.; Jones, P. G.; Laguna, A.; Lopez-
de-Luzuriaga, J. M.; Mendia, A.; Monge, M.; Olmos, E. J. Chem. Soc.,
Chem. Commun. 1998, 2233. (b) Wang, S.; Garzo´n, G.; King, C.; Wang,
J.-C.; Fackler, J. P., Jr. Inorg. Chem. 1989, 28, 4623. (c) Wang, S.; Fackler,
J. P., Jr.; King, C.; Wang, J. C. J. Am. Chem. Soc. 1988, 110, 3308.
10.1021/ja001672s CCC: $19.00 © 2000 American Chemical Society
Published on Web 09/22/2000

Pd(0) and Pt(0) Metallocryptands Encapsulating Tl+ Ion
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10057
Scheme 1
Table 1. NMR Data for Complexes 1-4
observed
complex
31P{1H}δ 205Tl δ 195Pt δ couplings (Hz)
[Pt2Tl(P2phen)3](NO3), 1 +46.1a +1866b -4119c 1J(Tl-Pt) ) 5560
1J(Pt-P) ) 4436
[Pt2Tl(P2bpy)3](NO3), 2
+35.3a +2390b -4120c 1J(Tl-Pt) ) 6100
1J(Pt-P) ) 4332
[Pd2Tl(P2phen)3](NO3), 3 +27.1d +2022e
[Pd2Tl(P2bpy)3](NO3), 4
+21.6d +2636e
Figure 1. (A) 121.7-MHz 31P{1H} NMR spectrum of 1 in CD3CN at
a 121 MHz, 25 °C, CDCl3. b 288.8 MHz, 25 °C, DMSO, external
1
25 °C, showing coupling to 195Pt (I ) /2, 33% abundant) but not to
reference Tl(NO3)(aq)
c 107.0 MHz, 25 °C, DMSO/CDCl3, external
reference H2PtCl6(aq)
d 121 MHz, 25 °C, CDCl3/CD3CN. e 288.8 MHz,
25 °C, CD3CN, external reference Tl(NO3)(aq)
.
203Tl or 205Tl. (B) 288.8-MHz 205Tl NMR spectrum displaying the
anticipated five-line pattern for the statistical mixture of isotopomers
(outer two lines are obscured in the noise). A 1J(205Tl-Pt) coupling is
.
.
1
observed. (C) 107.0-MHz 195Pt NMR spectrum showing J(Pt-Tl) )
1
5560 and J(Pt-P) ) 4436 Hz.
their large cavities, provide a convenient means to study the
guest-metal attractions in the absence of guest-ligand interac-
tions. Herein we report the synthesis and characterization of
Pt(0)- and Pd(0)-based metallocryptands with encapsulated Tl(I)
ion.
of quartets, confirming coupling to three equivalent 31P nuclei
1
and a single Tl nucleus (195Pt 33.8% abundant, I ) /2; 203Tl
29.5% abundant, I ) 1/2; 205Tl 70.5% abundant, I ) 1/2). Because
of the large line widths and nearly identical gyromagnetic ratios,
the individual couplings to 203Tl and 205Tl could not be
differentiated. The 195Pt chemical shifts observed for 1 and 2
are typical of three-coordinate Pt(0) and slightly deshielded in
comparison to the Pt(PPh3)3 shift (-4583 ppm).10 The 31P{1H},
205Tl, and the 195Pt NMR spectra of 1 are shown in Figure 1.
The observation of sharp, single 31P{1H} resonances for
species 1-4 supports the highly symmetrical environment of
the metallocryptate complex (Table 1). The chemical shifts of
1-4 compare well with the related species Pd(PPh3)3 (22.6
ppm)10 and Pt(PPh3)3 (49.9 ppm).11 Additionally, the 31P{1H}
signals for 1 and 2 exhibit typical couplings to 195Pt as compared
to Pt(PPh3)3 (1J(Pt-P) ) 4455 Hz).10 Interestingly, no coupling
of 31P to Tl is observed (line width < 10 Hz) for 1-4. This is
Results
The metallocryptate complex [Pt2Tl(P2phen)3](NO3), 1, was
prepared by addition of Pt(dba)2 (dba ) dibenzylideneacetone)
to a dichloromethane solution of the P2phen ligand containing
excess TlNO3 (Scheme 1). Analogously, the Pd-containing
congener, [Pd2Tl(P2phen)3](NO3), 3, is synthesized using Pd2-
(dba)3‚CHCl3. Alternatively, utilization of 6,6′-bis(diphenylphos-
phino)-2,2′-bipyridine, P2bpy, in place of P2phen readily yields
[Pt2Tl(P2bpy)3](NO3), 2, and [Pd2Tl(P2bpy)3](NO3), 4. The
nitrate salts of 1-4 were isolated as red-orange solids. Ad-
8
ditionally, Pt(AsPh3)4 may be used in place of Pt(dba)2,
producing similar results. Compounds 1-4 are all moderately
soluble in dichloromethane, 1,2-dichloroethane, acetonitrile,
tetrahydrofuran, and acetone, moderately soluble in alcohols,
and practically insoluble in diethyl ether, benzene, or toluene.
Solutions are stable to air and moisture for several days.
Solution-state NMR spectroscopy supports the proposed
structural formulations of 1-4 (Table 1). 205Tl spectra of 1-4
display broad single resonances with chemical shifts well
downfield from typical thallium(I) signals.9 Complexes 1 and
2 exhibit nearly identical 195Pt spectra consisting of a doublet
2
in contrast to the 186 Hz J(P-Tl) observed in the analogous
[Au2Tl(P2phen)3]3+ complex.2
Proton NMR spectra further support the highly symmetrical
character of 1-4 by displaying single signals for the three
magnetically distinct phenanthroline and bipyridine protons.
These signals are only minimally shifted ((0.06 ppm) relative
to those of the respective uncoordinated ligands. However, two
sets of resonances corresponding to phenyl ring protons are
(8) Malatesta, L.; Cariello, C. J. Chem. Soc. 1958, 2323.
(9) Brevard, C.; Granger, P. Handbook of High-Resolution Multinuclear
NMR; Wiley-Interscience: New York, 1981.
(10) Mann, B. E.; Musco, A. J. Chem. Soc., Dalton Trans. 1975, 1673.
(11) Benn, R.; Buech, H. M.; Reinhardt, R. Magn. Reson. Chem. 1985,
23, 559.

10058 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Catalano et al.
Figure 3. Thermal ellipsoid plot of 2 with hydrogen atoms omitted
for clarity, emphasizing the two phenyl ring environments, parallel and
perpendicular to the metal-metal axis. Only the asymmetric unit and
the metals are numbered. The Tl atom resides on a three-, two-fold
crystallographic symmetry element.
Figure 2. X-ray structural drawing for the cation of 1 viewed looking
down the metal-metal axis. Hydrogen atoms and all but the ipso carbon
of the phenyl rings are omitted for clarity.
observed in the metallocryptates. Interpretation of the 31P-
selective and homonuclear decoupling experiments suggests that
two phenyl ring environments exist: one along the metal-metal
axis and one equatorial to this axis (vide supra). Variable-
temperature experiments in CD3CN up to 70 °C reveal no
exchange processes between the two ring environments. This
lack of interchange suggests that the helical nature of these
complexes is maintained in solution, as there is no evidence of
a trigonal twisting process that would interconvert the M and P
helices.
Complexes 1 and 3 were additionally characterized in the
gas phase by MALDI-TOF and FAB mass spectrometry
(nitrobenzyl alcohol matrix, Supporting Information). For such
large molecules there is remarkably little fragmentation. The
mass spectra for both compounds contain peaks assigned to the
molecular ion along with peaks corresponding to the loss of
one ligand followed by loss of Tl+ ion. Further, the most intense
peak in all of the spectra corresponds to the loss of one ligand
while the three-metal core is maintained. The composition of
this species is verified by its distinct isotopomer pattern.
In solution, the electronic absorption spectra of complexes
1-4 exhibit high-energy features (λ < 320 nm) corresponding
to π-π* transitions and a single broad intense feature near 450
nm (Experimental Section). No emission out to 800 nm was
observed for any the complexes reported here.
The electrochemical character of 1-4 was probed by cyclic
voltammetry in acetonitrile and dichloromethane. No reversible
oxidative features were observed for complexes 1-4; however,
reductive processes (quasi-reversible) were observed in the range
expected for ligand reductions between -1.0 and -1.6 V.12
Further, chemical oxidation with I2 and Br2 was equally
unsuccessful, producing only decomposition and phosphine
oxide. No reaction was observed for the addition of CH3I to 3
with either thermal initiation or photoinitiation. Moreover, the
outer metals are not available for further coordination, as no
reaction of 3 with triethyl phosphite, pyridine, acetonitrile, or
n-butyl isonitrile was noted.
Figure 4. X-ray structural drawing for the cation of 3 viewed end-on,
emphasizing the helical nature of the cation. Only the asymmetric unit
is numbered. The Tl atom resides on a crystallographic two-fold
symmetry element. Hydrogen atoms and all but the ipso carbon of the
phenyl rings are omitted for clarity.
Compounds 1 and 3 crystallize in the monoclinic space group
C2/c; however, in 3 only half of the cation is crystallographically
unique (related by a two-fold axis), while in 1 the entire cation
is crystallographically unique. Compounds 2 and 4 are iso-
structural and crystallize in the rhombohedral space group R3hc.
The trimetallic cores of molecules 1-4 are nearly linear, with
an average M-Tl-M angle of 174°. The metal-metal separa-
tions are short and reside near the sum of the covalent radii.
For 1 and 2, the Pt-Tl separations are nearly equal, with Pt(1)-
Tl(1) and Pt(2)-Tl(1) distances of 2.7907(9) and 2.7919(9) Å,
respectively, for 1 and a Pt(1)-Tl(1) distance of 2.7953(2) Å
for 2. Similarly, for 3 and 4 the Pd(1)-Tl(1) separations are
2.7914(6) and 2.7678(6) Å, respectively. The coordination
geometry about each Pt and Pd center is roughly trigonal, with
a slight displacement of Pt and Pd out of the trigonal plane
(0.3507 Å average) toward the Tl atom. In 2, the P-M-P angles
are equal at 117.68(1)°, and in 4 they are 117.44(2)°. In the
corresponding P2phen species, the angles are different, with
P(1)-Pd-P(3), P(1)-Pd-P(5), and P(3)-Pd-P(5) angles of
The solid-state structures of 1-4 were probed by single-
crystal X-ray diffraction, and thermal ellipsoid drawings are
provided in Figures 2-5, while selected bond distances and
angles are tabulated in Table 2. The cationic portions of the
molecules are remarkably similar within each ligand set.
(12) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271.

Pd(0) and Pt(0) Metallocryptands Encapsulating Tl+ Ion
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10059
Table 2. Bond Distances and Angles for 1-4
Distances (Å)
[Pt2Tl(P2phen)3]+, 1
[Pt2Tl(P2bpy)3]+, 2
Pt(1)-Tl(1)
Pt(2)-Tl(1)
Pt(1)‚‚‚Pt(2)
Pt(1)-P(1)
Pt(1)-P(3)
Pt(1)-P(5)
Pt(2)-P(2)
Pt(2)-P(4)
Pt(2)-P(6)
Tl(1)-N(1)
Tl(1)-N(2)
Tl(1)-N(3)
Tl(1)-N(4)
Tl(1)-N(5)
Tl(1)-N(6)
2.7907(9)
2.7919(9)
5.578(1)
2.269(5)
2.284(4)
2.279(4)
2.298(4)
2.277(4)
2.281(4)
3.60(2)
3.63(2)
3.39(2)
3.38(2)
3.69(2)
2.7953(2)
5.591(1)
2.312(1)
3.886(5)
3.73(2)
[Pd2Tl(P2phen)3]+, 3
[Pd2Tl(P2bpy)3]+, 4
Figure 5. Thermal ellipsoid drawing for the cation of 4 viewed end-
on, emphasizing the three-fold symmetry and the helical nature of the
cation. Hydrogen atoms and all but the ipso carbon of the phenyl rings
are omitted for clarity. Only the asymmetric unit is numbered. The Tl
atom resides on a three-, two-fold crystallographic symmetry element.
Pd(1)-Tl(1)
Pd(1)‚‚‚Pd(2)
Pd(1)-P(1)
Pd(1)-P(2)
Pd(1)-P(3)
Tl(1)-N(1)
Tl(1)-N(2)
Tl(1)-N(3)
2.7914(6)
5.503(2)
2.3254(2)
2.326(2)
2.310(2)
3.91(1)
2.7678(6)
5.536(2)
2.345(1)
3.89(2)
3.76(1)
3.19(1)
119.0(1), 124.5(1), and 111.4(1)° for 1 and 120.62(3), 122.40(7),
and 110.02(7)° for 2. These angles are similar to those found
in the structure of Pt(PPh3)3 that shows two angles of 122° and
one contracted to 115°.13 The deviation of trigonal planarity is
reflected in the obtuse P-M-Tl angles observed in 1 (97.86°
average) and 2 (98.83°) for the Pt complexes and in 3 (98.51°
average) and 4 (99.29°) for the Pd complexes.
As seen in Figures 2-5, all of the complexes are helical, but
as dictated by the crystallography the bulk material is racemic.
The helical nature of the cation is manifested in the phenan-
throline portions of 1 and 3 with the three “propeller blade”
features, affording an overall D3 symmetry. Cations 2 and 4
also exhibit D3 symmetry along with rotation around the 2-2′
carbon-carbon bonds of each bipyridine (dihedral angle ) 47°),
allowing the two sets of phosphorus atoms to achieve a
“staggered” configuration. Two separate orientations of the
phenyl rings attached to phosphorus atoms are evident. The
P-Cipso bond describes a vector for each phenyl ring environ-
ment: one is almost parallel to the metal-metal axis, while
the other is orthogonal.
Angles (deg)
1
2
Pt(1)-Tl(1)-Pt(2)
P(1)-Pt(1)-P(3)
P(1)-Pt(1)-P(5)
P(3)-Pt(1)-P(5)
P(2)-Pt(2)-P(4)
P(4)-Pt(2)-P(6)
P(2)-Pt(2)-P(6)
P(1)-Pt(1)-Tl(1)
P(3)-Pt(1)-Tl(1)
P(5)-Pt(1)-Tl(1)
P(2)-Pt(2)-Tl(1)
P(4)-Pt(2)-Tl(1)
P(6)-Pt(2)-Tl(1)
175.27(3)
119.00(16)
124.50(16)
111.40(16)
114.42(18)
119.97(17)
119.43(16)
97.90(13)
95.84(11)
98.67(11)
97.77(11)
95.99(12)
101.04(11)
180
117.685(14)
98.83(3)
3
4
Pd(1)-Tl(1)-Pd(2)
P(1)-Pd(1)-P(3)
P(1)-Pd(1)-P(2)
P(3)-Pd(1)-P(2)
P(1)-Pd(1)-Tl(1)
P(2)-Pd(1)-Tl(1)
P(3)-Pd(1)-Tl(1)
160.62(3)
120.63(7)
122.40(7)
110.02(7)
105.51(5)
93.88(5)
180
117.44(2)
99.29(4)
Discussion
96.16(5)
The compounds reported here represent new examples of a
growing class of inorganic cage complexes called metallo-
cryptands that, in the absence of strong guest-ligand attractions,
utilize strong metallophilic interactions to maintain their as-
sembly. This concept is exemplified by comparing the Au(I)-
dppn metallocryptates to the P2phen analogues. In the latter
complexes there are no Tl(I)-ligand interactions, and the Tl(I)
ion is held tightly solely by a strong bonding interaction with
the Au(I) ions. In contrast, the dppn metallocryptates possess
ligands that allow for attractive ligand-ion interactions and can
bind alkali metal ions that have little or no affinity for Au(I)
ion. Moreover, it was originally believed that a template
synthesis was necessary to form metallocryptates, and efforts
to prepare Au(I)-P2bpy cryptates were unsuccessful, presumably
because the flexibility or rotation around the 2-2′ C-C bond
precluded template formation. However, the successful synthesis
and characterization of 2 and 4 implies that ligand rigidity and
the template effect are not stringent requirements for metallo-
cryptate formation.
Compounds 1-4 are synthesized easily and are remarkably
air-stable. In contrast, M(PR3)314 and M2(dppm)315 (M ) Pt or
Pd) are air-sensitive both in solution and in the solid state. The
encapsulation of thallium has been confirmed by multiple
techniques including MALDI-TOF mass spectrometry, elemen-
tal analysis, and NMR spectroscopy. In the MALDI-TOF mass
spectra, several thallium-containing fragments were identified,
demonstrating the high stability of the metal-thallium bonds.
In solution, direct observation of 205Tl NMR signals coupled to
195Pt nuclei not only supports Tl ion encapsulation but also
indicates substantial interaction. As rationalized by Oro and co-
(13) Albano, V.; Bellon, P. L.; Scatturin, V. J. Chem. Soc., Chem.
Commun. 1966, 507.
(14) Kuran, W.; Musco, A. Inorg. Chim. Acta 1975, 12, 187.
(15) Caspa, J. V. J. Am. Chem. Soc. 1985, 107, 6718.

10060 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Catalano et al.
workers16 with theoretical support by Pyykko¨ et al.,17 extreme
deshielding of the Tl(I) nucleus may be the result of spin-
orbit effects dictated by the heavy atoms with which it interacts.
The lack of Tl coupling to 31P in 1-4 is puzzling, given the
observation of a 2J(P-Tl) of 186 Hz in the structurally similar
[Au2Tl(P2phen)3]3+ complex. Since a similar observation is
noted in the analogous [Pd2Pb(P2phen)3]2+ and [Pt2Pb(P2-
phen)3]2+ complexes,18 the effect must be related to the inclusion
of the zero-valent capping metals. The simplest explanation
suggests a diminution of s character in the M(0)-Tl bond in
1-4 compared to that in the Au(I) analogue. Simple relativistic
arguments19 suggest that Au(I) would have the smallest d-s
gap and hence greater d9s1 character than either Pt(0) or Pd(0).
This notion has been invoked to describe many of the unusual
observations noted in Au(I) chemistry.20 Moreover, using
calculations to describe the bonding of the trigonally coordinated
AuP2S complex, Fackler and co-workers21 noted a significant
decrease in the contribution of the Au 6s orbital in the (metal-
ligand bonding) HOMO, concurrent with an increase in the
LUMO as compared to the linear AuP2 system. Such a
contribution allows for a greater participation of the Au 6s orbital
for metal-metal bonding.
The electronic spectra of complexes 1-4 exhibit absorption
peaks below 320 nm that are tentatively assigned to ligand-
based processes. As expected, these red/orange complexes also
absorb in the visible region.22 The platinum complexes 1 and 2
absorb at lower energy (454 and 469 nm) than their palladium
analogues 3 and 4 (424 and 450 nm), reflecting a significant
difference in HOMO-LUMO gap as principal quantum number
is altered. The trend may be rationalized23 as an increase in
overlap and therefore a decreased HOMO-LUMO gap for the
Pt system, as exemplified by the simplified molecular orbital
diagram presented in Figure 6.
Figure 6. Simplified molecular orbital picture for two trigonally
coordinated d10 metal ions interacting with a Tl(I) center. Only the filled
dz and empty pz are considered on the d10 metal.
2
systems with Tl(I) ions. Pt(0)-Tl(I) separations ranging from
2.860(3) to 2.992(3) Å have been reported by Puddephatt and
co-workers25 in a cluster compound that contains Tl(I) bound
to the Pt30 triangular face. The metallocrypands described here
offer a relatively simple way to probe these metal-metal
interactions in the absence of restrictive ligand-Tl(I) ion
interactions. All of the four structures exhibit long N-Tl
separations, averaging greater than 3.5 Å. When compared with
sum of the covalent radii for Tl and N (2.23 Å), these separations
indicate little to no interaction. Furthermore, the N-Tl separa-
tion is longest for 2 and 4 (3.88 and 3.89 Å), where the pyridyl
rings twist, positioning the imine lone pairs without proper
directionality for interaction with the Tl atom. The most striking
features of 1-4 are their short metal-metal separations. All
four structures exhibit interatomic separations between the
formally closed-shell Pd(0)/Pt(0) atoms and Tl(I) ion which
almost match the sum of the appropriate covalent radii (Pt-Tl,
2.78 Å; Pd-Tl, 2.76 Å). The short M(0)-Tl(I) separations of
1-4 are close to the analogous separations (2.708(1) and
2.698(1) Å) in [Tl{Pt(C6F5)4}2]2-, which formally contains two
Pt(II) ions and a Tl(II) ion.26 In light of the molecular orbital
diagram of Figure 6, the metal core of this compound can be
viewed as having one fewer electron than 1 or 2 and thus an
increased bond order by one-half. The deformation of the Pt
and Pd centers toward Tl is another reflection of this strong
attraction. This “inward” puckering is noted even in the
isoelectronic and cationic Au(I) system, where the positive
charges might be expected to repel each other.
Unlike other trigonal Pt(0) and Pd(0) systems,22 the com-
pounds reported here are not intensely photoluminescent in the
visible portion of the electromagnetic spectrum. This is curious
when compared to the isoelectronic [Au2Tl(P2phen)3]3+ species,
which is highly emissive. These results are in line with the lack
of electrochemical redox behavior noted in 1-4 and the resulting
inertness of the three-metal assembly.
Although there are many examples describing the association
of Pt(II) centers with Tl(I),24 there are no examples of the
corresponding trigonally coordinated, zero-valent Pt or Pd
(16) Casado, M. A.; Perez-Torrente, J. J.; Lopez, J. A.; Ciriano, M. A.;
Lahoz, F. J.; Oro, L. A. Inorg. Chem. 1999, 38, 2482.
(17) Kaupp, M.; Malkina, O. L.; Malkin, V.; G.; Pyykko¨, P. Chem. Eur.
J. 1998, 4, 118.
(18) Catalano, V. J.; Bennett, B. L.; Noll, B. C. Chem. Commun. 2000,
1413.
(19) (a) Bardaji, M.; Laguna, A. J. Chem. Educ. 1999, 76, 201. (b)
Balasubramanian, K. RelatiVistic Effects in Chemistry, Part A; Wiley-
Interscience: New York, 1997.
(20) (a) Schmidbaur, H.; Graf, W.; Mu¨ller, G. Angew. Chem., Int. Ed.
Engl. 1988, 27, 417. (b) Go¨rling, A.; Ro¨sch, N.; Ellis, D. E.; Schmidbaur,
H. Inorg. Chem. 1991, 30, 3986. (c) Schmidbaur, H. Gold Bull. 1990, 23,
11.
The role of the Tl atom as a donor to the formally 16-electron
Pt(0) and Pd(0) centers may explain the relative inertness
observed for these metallocryptate species. The strength of this
interaction may be responsible for the substitutionally inert
character of the metallocryptate species. Formally, a saturated
18-electron Pt(0) or Pd(0) center would be less likely to undergo
oxidative processes or increase its coordination number.
Conclusion
(21) Assefa, Z.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem. 1994, 33,
2790.
Here, we have reported the synthesis and characterization of
a new series of metallocrypates that bind Tl(I) ion in the absence
of attractive ligand interactions through metallophilic connec-
tions. The cationic species 1-4 have been characterized by a
variety of methods and have considerable stability. From the
solid-state structural data it is apparent that interaction of the
(22) Harvey, P.; Gray, H. B. J. Am. Chem. Soc. 1988, 110, 2145.
(23) (a) Mann, K. R.; Grodon, J. G., II.; Gray, H. B. J. Am. Chem. Soc.
1975, 97, 3553. (b) Mann, K. R.; Lewis, N. S.; Williams, R. M.; Gray, H.
G.; Gordon, J. G., II. Inorg. Chem. 1978, 17, 828. (c) Balch, A. L.; Fossett,
L. A.; Olmstead, M. M.; Reedy, P. E., Jr. Organometallics 1986, 5, 1929.
(d) Clodfelter, S. A.; Doede, T. M.; Brennan, B. A.; Nagle, J. K.; Bender,
D. P.; Turner, W. A.; LaPunzina, P. M. J. Am. Chem. Soc. 1994, 116, 11379.
(24) (a) Balch, A. L.; Rowley, S. P. J. Am. Chem. Soc. 1990, 112, 6139.
(b) Balch, A. L.; Fung, E. Y.; Nagle, J. K.; Olmstead, M. M.; Rowley, S.
P. Inorg. Chem. 1993, 32, 3295. (c) Nagle, J. K.; Balch, A. L.; Olmstead,
M. M. J. Am. Chem. Soc. 1988, 110, 319. (d) Renn, O.; Lippert, B.;
Mutiainen, I. Inorg. Chim. Acta 1993, 208, 219.
(25) (a) Hao, L.; Vittal, J. J.; Puddephatt, R. J. Inorg. Chem. 1996, 35,
269. (b) Hao, L.; Xiao, J.; Vittal, J. J.; Puddephatt, R. J.; Manojlovic´-Muir,
L.; Muir, K.; Torai, A. A. Inorg. Chem. 1996, 35, 658.
(26) Uso´n, R.; Fornie´s, J.; Tomas, M.; Ga´rde, R. J. Am. Chem. Soc. 1995,
117, 1837.

Pd(0) and Pt(0) Metallocryptands Encapsulating Tl+ Ion
J. Am. Chem. Soc., Vol. 122, No. 41, 2000 10061
Cl2N7O3P6Pt2Tl), calcd: C, 54.8; H, 3.4; N, 4.1. Found: C, 55.38; H,
3.27; N, 3.85. 1H{31P} NMR (500 MHz (obs), 202 MHz (dec), CDCl3,
25 °C): δ ) 5.804 (t, J ) 7.5 Hz), 6.095 (t, J ) 7.5 Hz), 6.529 (d, J
) 7.5 Hz), 6.897 (t, J ) 7.5 Hz), 7.123 (d, J ) 6.0 Hz), 7.239 (t, J )
7.5 Hz), 7.393 (d, J ) 8.0 Hz), 7.771 (s), 7.971 (d, J ) 8.0 Hz). 31P-
{1H} NMR (121 MHz, CDCl3, 25 °C): δ 46.1 (s, 1J(Pt-P) ) 4436.6
Hz). 195Pt NMR (107.0 MHz, DMSO/CDCl3, external reference H2-
PtCl6 in D2O, 25 °C): δ ) -4119 (dq, 1J(P-Pt) ) 4436.6 Hz, 1J(205Tl-
Pt) ) 5560 Hz). 205Tl NMR (288.8 MHz, DMSO, external reference
metal atoms with one another is the dominant bonding interac-
tion within the metallocryptate cavity. The characterization of
complexes 1-4 supports the concept of “metallophilic” behavior
as a fundamental component of bonding in closed-shell systems.
These materials may ultimately serve as prototypical systems
for detection of closed-shell ions.
Experimental Section
1
Tl(NO3), 25 °C): δ ) 1865.9 (br m, J(205Tl-Pt) ) 5560 Hz). UV-
General. Solvents were distilled just prior to use from the appropriate
drying agents: CH2Cl2 (CaH2), THF (Na/benzophenone), and aceto-
nitrile (CaH2). Commercially available reagents included diphenylphos-
phine (Strem, 10% w/w in hexanes), Ph3As (Strem), dibenzylidene-
acetone (Aldrich), K2PtCl4 (Pressure Chemical), K2PdCl4 (Pressure
Chemical), Pb(NO3)2 (Strem), and TlNO3 (Strem). (Ph3As)4Pt, (dba)2Pt,27
Pd2(dba)3‚CHCl3,28 and P2bpy3,29 were prepared according to literature
procedures. P2phen was originally reported by Ziessel;3 however, slight
modifications were employed and are outlined below in detail. NMR
chemical shift reference materials used were the following: 205Tl,
TlNO3; 195Pt, H2PtCl6 in D2O; 31P, 85% H3PO4. 1H NMR spectra were
internally referenced to residual signal in CDCl3, CD3CN, CD3OD, and
DMSO-d6 (as received from Cambridge Isotope Labs). Cyclic volta-
metric experiments were carried out using a BAS CW50 instrument
with the following cell configuration: Pt or glassy carbon working
electrodes, Pt wire auxiliary electrode, Ag/AgCl reference in a modified
Lugin electrode. Solutions were prepared with 0.1 M TBAP as
electrolyte in nitrogen purged MeCN or CH2Cl2 and referenced to
internal Cp2Fe (+400 mV). Combustion analysis was carried out by
Desert Analytics, Tucson, AZ. UV-visible spectra were obtained using
a Hewlett-Packard 8453 diode array spectrometer (1-cm-path length
cells). Emission data were recorded using a PTI steady-state fluorom-
eter.
Preparation of 2,9-Bis(diphenylphosphino)-1,10-phenanthroline.
A 500-mL flask fitted with a high-efficiency coldfinger, a 125-mL
addition funnel, and a two-way gas inlet port was cooled to -78 °C
and 80 mL of NH3(l) condensed. Under a nitrogen counter flow, 0.096
g of Na(s) (4.192 mmol) was added. After 15 min, 0.784 g of HPPh2
(4.216 mmol) was added dropwise. After an additional 45 min at -78
°C, 0.500 g of 2,9-dichloro-1,10-phenanthroline30 (2.00 mmol) (in 60
mL of THF) was added dropwise over a 60-min period. Upon warming
to ambient temperature, the reaction was quenched with 5 mL of
methanol. Volatiles were then removed in vacuo. The residue was taken
up in 50 mL of CH2Cl2 and passed through a small pad of Celite. The
solvent was removed, and the crude product was crystallized from
ethanol, affording the ligand as a white solid, 0.603 g (1.100 mmol,
55%). 1H NMR (300 MHz, CDCl3, 25 °C): δ ) 8.027 (d, J ) 8.0 Hz,
2H), 7.712 (s, 2H), 7.652 (m, 8H), 7.393 (d, J ) 8.0 Hz, 2H), 7.304
(m, 12H). 13C{1H} NMR (75.5 MHz, CDCl3, 25 °C): δ ) 137.0, 135.1,
134.8, 134.5, 129.1, 128.7, 128.6, 127.4, 126.8, 126.5. 31P{1H} NMR
(121 MHz, CDCl3, external reference H3PO4): δ ) -2.7 (s).
Preparation of [Pt2Tl(P2phen)3](NO3), 1. A 500-mL round-
bottomed flask was charged with 0.100 g (0.1824 mmol) of 2,9-bis-
(diphenylphosphino)-1,10-phenanthroline dissolved in 20 mL of CH2Cl2.
Tl(NO3) (0.161 g, 0.606 mmol) dissolved in 45 mL of MeOH was
added slowly with swirling. After the mixture was stirred for 10 min,
a suspension of 0.172 g of Pt(Ph3As)4 (0.1216 mmol) in 1:1 MeOH-
CH2Cl2 (10 mL) was added, affording an orange-colored solution. After
the mixture was stirred an additional 60 min, volatiles were removed,
and the residue was dissolved in a minimum amount of MeCN. Flash
chromatography (alumina), eluting with MeCN affords, an orange solid
after MeCN removal. Precipitation of the orange solid by addition of
Et2O to a saturated CHCl3 solution affords 0.091 g (0.0395 mmol) of
1 as a red-orange solid (65%). Elemental analysis. 1‚CH2Cl2 (C109H80-
vis (CH2Cl2, 0.00869 mM), λ in nm (ꢀ in M-1 cm-1): 237 (103 410),
279 (89 208), 293* (64 030), 308* (40 772), 454 (26 476) [* denotes
shoulder].
Preparation of [Pt2Tl(P2bpy)3](NO3), 2. To a 250-mL Schlenk flask
charged with 0.5245 g of P2bpy (1.0 mmol) dissolved in 60.0 mL of
CH2Cl2 was added 0.1066 g of TlNO3 (0.40 mmol, 10-mL suspension
in MeOH). The mixture was stirred for several minutes and then
degassed. To this was added 0.2462 g of Pt(dba)2 (0.0371 mmol) as a
35-mL CH2Cl2 solution. The reaction was stirred for 30 min at room
temperature, after which it was brought to reflux for 12 h under nitrogen
atmosphere. The resulting mixture was passed through Celite, and the
solvents were removed. Flash chromatography (neutral alumina) eluting
with acetonitrile followed by precipitation with diethyl ether affords
1
0.0248 g (0.111 mmol, 60%) of a dark red solid. H{31P} NMR (500
MHz (obs), 202 MHz (dec), CDCl3, 25 °C): δ ) 6.205 (t, J ) 8.0
Hz), 6.535 (t, J ) 7.0 Hz), 6.693 (d, J ) 7.0 Hz), 6.817 (t, J ) 8.0
Hz), 7.076 (d, J ) 7.5 Hz), 7.139 (t, J ) 7.5 Hz), 7.173 (d, J ) 7.0
Hz), 7.602 (t, J ) 7.0 Hz), 7.727 (d, J ) 8.0 Hz). 31P{1H} NMR (121
MHz, CDCl3, 25 °C): δ ) 35.3 (s, 1J(Pt-P) ) 4332 Hz). 205Tl NMR
(288.8 MHz, DMSO, external reference Tl(NO3), 25 °C): δ ) 2389.5
(br m, 1J(205Tl-Pt) ) 6100 Hz). 195Pt NMR (107.0 MHz, DMSO/
CDCl3, external reference H2PtCl6 in D2O, 25 °C): δ ) -4120 (dq,
1J(P-Pt) ) 4379 Hz, 1J(Tl-Pt) ) 6100 Hz). UV-vis (CH2Cl2,
0.007404 mM), λ in nm (ꢀ in M-1 cm-1): 230 (91 501), 285 (50 703),
469 (20 071).
Preparation of [Pd2Tl(P2phen)3](NO3), 3. A 100-mL Schlenk flask
was charged with 0.200 g (0.3648 mmol) of 2,9-bis(diphenylphos-
phino)-1,10-phenanthroline dissolved in 10 mL of CH2Cl2. To this
solution was added 0.324 g (1.216 mmol) of TlNO3 dissolved in 5 mL
of 1:1 MeOH/DMSO with stirring. After 10 min the vessel was capped,
and the contents were subjected to two freeze-pump-thaw cycles and
moved to a glovebox. A suspension of 0.126 g of Pd2(dba)3‚CHCl3
(0.1216 mmol) in MeCN (10 mL) was added dropwise, affording an
orange solution. After the mixture was stirred an additional 30 min,
volatiles were removed and the residue was dissolved in a minimum
amount of MeCN. Flash chromatography (alumina) eluting with MeCN
affords an orange solid after MeCN removal. Removal of trace DMSO
is accomplished by precipitation of the orange solid by addition of Et2O
to a saturated CH2Cl2 solution, affording 0.164 g (0.0785 mmol) of 3
as an orange solid (64%). Elemental analysis. 3‚CH2Cl2 (C109H80-
Cl2N7O3P6Pd2Tl) calcd: C, 59.2; H, 3.6; N, 4.4. Found: C, 59.66; H,
3.43; N, 4.78. 1H{31P} NMR (500 MHz, CDCl3, 25 °C): δ ) 5.794 (t,
J ) 7.5 Hz), 6.127 (t, J ) 7.0 Hz), 6.529 (d, J ) 8.0 Hz), 6.881 (t, J
) 8.0 Hz), 7.105 (d, J ) 7.0 Hz), 7.220 (t, J ) 7.5 Hz), 7.375 (d, J )
8.0 Hz), 7.799 (s), 8.018 (d, J ) 8.0 Hz). 31P{1H} NMR (121 MHz,
MeCN/CDCl3, 25 °C): δ ) 27.12 (br). 205Tl NMR (288.9 MHz, MeCN,
external reference Tl(NO3), 25 °C): δ ) 2022.05 (br). UV-vis (CH2-
Cl2, 0.005176 mM), λ in nm (ꢀ in M-1 cm-1): 235 (190 586), 281
(167 519), 423 (46 731).
Preparation of [Pd2Tl(P2bpy)3](NO3), 4. P2bpy (0.1572 g, 0.3
mmol) was dissolved in 40.0 mL of CH2Cl2 and placed in a Schlenk
flask. To this was added 10 mL of a methanolic suspension of TlNO3
(0.0267 g, 0.1 mmol). The mixture was degassed and placed inside a
drybox. To this was added a 20-mL CH2Cl2 solution of Pd2dba3‚CHCl3
(0.1035 g, 0.1 mmol). The reaction was stirred for 30 min, during which
time the mixture turned dark. The mixture was passed through Celite,
and the solvents were evaporated using a rotary evaporator. Flash
chromatography (neutral alumina), eluting with acetonitrile followed
by precipitation with diethyl ether, affords 0.0123 g (0.060 mmol, 60%)
of a dark red solid. 31P{1H} NMR (121 MHz, MeCN/CDCl3, 25 °C):
δ ) 21.6 (br). 205Tl NMR (288.9 MHz, MeCN, external reference Tl-
(27) Cherwinski, W. J.; Johnson, B. F. G.; Lewis, J. J. Chem. Soc., Dalton
Trans. 1974, 1405.
(28) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers J. A. J.
Organomet. Chem. 1974, 65, 253.
(29) Newkome, G. R.; Hager, D. C. J. Org. Chem. 1978, 43, 947.
(30) (a) Halcrow B. E.; Kermack, W. O. J. Chem. Soc. 1946, 155. (b)
Ogawa, S.; Yamaguchi, T.; Gotoh, N. J. Chem. Soc., Perkin Trans. 1 1974,
976.

10062 J. Am. Chem. Soc., Vol. 122, No. 41, 2000
Catalano et al.
Table 3. Crystallographic Data for 1-4
1
2
3
4
formula
fw
a, Å
b, Å
c, Å
C
109.25H63Cl0.75N7O5P6Pt2Tl
C126H78N7O7P6Pt2Tl
2582.32
19.3694(1)
19.3694(1)
51.9258(2)
90
90
120
16871.20(14)
R3hc
6
C132H78N7O3P6Pd2Tl
2413.00
21.1124(8)
20.3657(8)
26.3042(10)
90
102.57
90
11039.1(7)
C2/c
4
C126H78N7O7P6Pd2Tl
2404.94
19.3452(2)
19.3452(2)
51.7853(8)
90
90
120
15785.2(2)
R3hc
6
2360.62
33.6379(5)
14.81300(10)
41.9035(6)
90
107.7430(10)
90
19886.4(4)
C2/c
8
R, deg
â, deg
γ, deg
V, Å3
space group
Z
D
calc, g/cm3
1.577
1.525
1.452
1.420
crystal size, mm
µ(Mo KR), mm-1
λ, Å
0.22 × 0.18 × 0.16
0.24 × 0.23 × 0.20
0.44 × 0.07 × 0.07
0.24 × 0.15 × 0.14
4.597
4.055
1.923
1.890
0.71073
138(2)
0.71073
138(2)
0.71073
138(2)
0.71073
138(2)
temp, K
transm factors
R1, wR2 (I > 2σ(I))
0.82-0.92
0.0642, 0.1339
0.51-0.44
0.0436, 0.1312
0.89-0.49
0.0669, 0.1820
0.80-0.68
0.0816, 0.2356
(NO3), 25 °C): δ ) 2636.7 (br). UV-vis (CH2Cl2, 0.00975 mM), λ in
nm (ꢀ in M-1 cm-1): 301* (67 900), 324 (73 465), 450 (16 653) (*
denotes shoulder).
direct methods. Complex 1 crystallizes in the monoclinic space group
C2/c, with the cation, a nitrate anion disordered over three positions,
one water, one methanol solvate, and one-quarter of a dichloromethane
which is partially disordered. There is no unusual contact between these
moieties. Compounds 2 and 4 are isostructural and crystallize in the
rhombohedral space group R3hc. The asymmetric unit of each contains
one-sixth of the cation and nitrate anion, two-thirds of a benzene, and
two-thirds of a water solvate. Compound 3 crystallizes in the monoclinic
space group C2/c, with one-half of the cation and anion in the
asymmetric unit along with one-half of a benzene solvate. The
refinement of these data was unremarkable. Simple models of the
disorder provided satisfactory refinements.
X-ray Crystallography. Crystals of 1-4 were grown by slow
diffusion of benzene or n-Bu2O into concentrated 1,2-dichloroethane
solutions. Suitable crystals were coated with light petroleum oil,
mounted on a glass fiber, and placed in the -135 °C nitrogen cold
stream of a Siemens SMART diffractometer. Unit cell parameters were
determined by least-squares analysis of 5332 reflections with 1.51-
θ-22.5° for 1, 8192 reflections with 1.45-θ-30.0° for 2, 8019
reflections with 1.50-θ-25.0° for 3, and 7529 reflections with 1.45-
θ-30.0° for 4. A total of 47 076 reflections were collected in the range
1.51 < θ < 22.50°, yielding 12 965 unique reflections (Rint ) 0.1533)
for 1, while a total of 12 495 reflections were collected in the range
1.45 < θ < 30°, yielding 5460 unique reflections (Rint ) 0.057) for 2.
A total of 34 122 reflections were collected in the range 1.50 < θ <
25.00°, yielding 9727 unique reflections (Rint ) 0.0934) for 3, while a
total of 49 051 reflections were collected in the range 1.45 < θ < 30°,
yielding 5473 unique reflections (Rint ) 0.069) for 4.
Acknowledgment is made to the National Science Founda-
tion (CHE-9624281), to the donors of the Petroleum Research
Fund, administered by the American Chemical Society, for their
generous financial support of this research, and to Mr. Lewis
Cary and to Prof. J. H. Nelson for their assistance with the NMR
spectroscopy.
The data were corrected for Lorentz and polarization effects. Crystal
data are given in Table 3. Scattering factors and corrections for
anomalous dispersion were taken from a standard source.31
Calculations were performed using the Siemens SHELXTL Version
5.10 system of programs refining on F2. The structures were solved by
Supporting Information Available: Complete table of
X-ray crystallographic data and mass spectra plots for 1 and 3
(PDF). X-ray crystallographic data, in CIF format, are also
available.This material is available free of charge via the Internet
at http://pubs.acs.org.
(31) International Tables for X-ray Crystallography: Kynoch Press:
Birmingham, England, 1974; Vol. 4.
JA001672S