Rhenium complexes with 2-(diphenylphosphinomethyl)aniline: Formation of a cyclic, trinuclear oxorhenium(V) core

Article abstract of DOI:10.1021/ic101792j

Reactions of 2-(diphenylphosphinomethyl)aniline, H₂L ², with (NBu₄)[ReOCl₄] yield different oxo rhenium(V) complexes depending on the conditions applied. This comprises monomeric compounds such as [ReOCl₃

Full text of DOI:10.1021/ic101792j

10694 Inorg. Chem. 2010, 49, 10694–10701
DOI: 10.1021/ic101792j
Rhenium Complexes with 2-(Diphenylphosphinomethyl)aniline: Formation of a
Cyclic, Trinuclear Oxorhenium(V) Core
Jennifer Schroer, Stefan Wagner, and Ulrich Abram*
€
Institute of Chemistry and Biochemistry, Freie Universitat Berlin, Fabeckstrasse 34-36, D-14195 Berlin, Germany
Received September 1, 2010
Reactions of 2-(diphenylphosphinomethyl)aniline, H2L2, with (NBu4)[ReOCl4] yield different oxo rhenium(V) complexes
depending on the conditions applied. This comprises monomeric compounds such as [ReOCl3(H2L2)] (1),
[ReOCl2(OMe)(H2L2)] (2), or [ReO2(H2L2)2]Cl (5) as well as the dimeric μ-oxo complex [{ReOCl2(H2L2)}2]O] (3) and
the oxo-bridged trimer [{ReOCl(H2L2)}O]3 (4). The latter compound represents the first example of a hitherto unknown
trinuclear, cyclic oxo(V) core. [{ReOCl(H2L2)}O]3 contains a tensed 6-membered metallacycle, which readily undergoes
rearrangements and reactions with additional ligands. Compounds of the compositions 5and [ReO2(H2L2)(H2L1)]Cl (6) were
isolated either from the decomposition of 4 in CH2Cl2/n-pentane or from reactions with 2-(diphenylphosphino)aniline, H2L1.
Chart 1. Selected Rhenium and Technetium Complexes with H2L1 16-19
Introduction
Phosphines bearing o-amino moieties are versatile ligands,
which form stable complexes with a variety of transition
metals.1-21 Considerable time was spent on studies with
*To whom correspondence should be addressed. Phone: (#49) 30
83854002. Fax: (#49) 30 83852676. E-mail: abram@chemie.fu-berlin.de.
(1) Ansell, C. W. G.; McPartlin, M.; Tasker, P. A.; Cooper, M. K.;
Duckworth, P. A. Inorg. Chim. Acta 1983, 76, L135.
(2) Wang, H.-Y.; Jin, G.-X. Eur. J. Inorg. Chem. 2005, 1665.
(3) Dahlenburg, L.; Herbst, K.; Zahl, A. J. Organomet. Chem. 2000, 616, 19.
(o-aminophenyl) diphenyl phosphine, H2L1, which has hard
and soft donor atoms and is able to stabilize metals in different
(4) Ainscough, E. W. J. Organomet. Chem. 1994, 468, 229.
(5) Dahlenburg, L.; Herbst, K.; Berke, H. J. Organomet. Chem. 2000, 585, 225.
€
(6) Klein, H.-F.; Beck, R.; Florke, U.; Haupt, H.-J. Eur. J. Inorg. Chem.
oxidation states. The coordination behavior toward Re and
Tc has been extensively studied revealing a high flexibility of
the ligand.15-20 Reactions starting from MO4- (M=Re, Tc)
or other common oxorhenium(V) or oxotechnetium(V) pre-
cursors such as [MOCl4]- (M=Re, Tc) or [ReOCl3(PPh3)2]
give neutral oxo complexes of the composition [MO(HL1)2X]
(M=Re, Tc; X=halide, hydroxo, alkoxo or carboxylic
ligands),16 neutral or cationic homoleptic [TcIII(HL1)3] or
[TcIII(H2L1)(HL1)2] complexes with single-deprotonated amine-
phosphines,19 or even phenylimido species as a result of a
complete deprotonation of the amino group and replacement
of the oxo ligand,17,18 depending on the reaction conditions
applied (Chart 1).
2003, 240.
(7) Fernandez, E. J.; Gil, M.; Olmos, M. E.; Crespo, O.; Laguna, A.;
Jones, P. G. Inorg. Chem. 2001, 40, 3018.
(8) Farnetti, E.; Nardin, G.; Graziani, M. J. Organomet. Chem. 1991, 417, 163.
(9) Fester, V. D.; Houghton, P. J.; Main, L.; Nicholson, B. K. Polyhedron
2007, 26, 430.
(10) Reddy, K. R.; Tsai, W.-W.; Surekha, K.; Lee, G.-H.; Peng, S.-M.;
Chen, J.-T.; Liu, S.-T. J. Chem. Soc., Dalton Trans. 2002, 1776.
(11) Cooper, M. K.; Downes, J. M.; Goodwin, H. J.; McPartlin, M. Inorg.
Chim. Acta 1983, 76, L157.
(12) Organ, G. J.; Cooper, M. K.; Henrick, K.; McPartlin, M. J. Chem.
Soc., Dalton Trans. 1984, 2377.
(13) Papathanasiou, P.; Salem, G.; Waring, P.; Willis, A. C. J. Chem. Soc.,
Dalton Trans. 1997, 3435.
(14) Dahlenburg, L.; Herbst, K.; Liehr, G. Acta Crystallogr. 1997, C53, 1545.
(15) Bolzati, C.; Tisato, F.; Refosco, F.; Bandoli, G.; Dolmella, A. Inorg.
Chem. 1996, 35, 6221.
(16) Refosco, F.; Tisato, F.; Bandoli, G.; Bolzati, C.; Dolmella, A.;
Moresco, A.; Nicolini, M. J. Chem. Soc., Dalton Trans. 1993, 605.
(17) Ahmet, M. T.; Coutinho, B.; Dilworth, J. R.; Miller, J. R.; Parrott,
S. J.; Zheng, Y.; Harman, M.; Hursthouse, M. B.; Malik, A. J. Chem. Soc.,
Dalton Trans. 1995, 3041.
As a part of our systematic work in the synthesis of
multidentate ligands for rhenium and technetium as founda-
tion for the development of metal-based bioconjugates with the
radioactive nuclides 99mTc, 186Re and 188Re,22-25 the present
(18) Refosco, F.; Tisato, F.; Moresco, A.; Bandoli, G. J. Chem. Soc.,
Dalton Trans. 1995, 3475.
(19) Refosco, F.; Bolzati, C.; Moresco, A.; Bandoli, G.; Dolmella, A.;
Mazzi, U.; Nicolini, M. J. Chem. Soc., Dalton Trans. 1991, 3043.
(20) Refosco, F.; Bolzati, C.; Tisato, F.; Bandoli, G. J. Chem. Soc., Dalton
Trans. 1998, 923.
(21) Andrieu, J.; Camus, J.-M.; Richard, P.; Poli, R.; Gonsalvi, L.; Vizza,
F.; Peruzzini, M. Eur. J. Inorg. Chem. 2006, 51.
(22) Barandov, A.; Abram, U. Inorg. Chem. 2009, 48, 8072.
(23) Schroer, J.; Abram, U. Polyhedron 2009, 28, 2277.
r
pubs.acs.org/IC
Published on Web 10/21/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10695
Scheme 1. Synthesis of H2L2
2
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) in [ReOCl3(H2L )] (1) and
[ReOCl2(OMe)(H2L2)] (2)
1
2
Re1-O10
Re1-Cl1
1.672(7)
2.394(2)
2.317(3)
2.451(2)
1.69(2)
2.468(3)
2.363(4)
1.84(2)
Re1-Cl2
Re1-Cl3/O2
Re1-P1
2.440(2)
2.441(3)
2.21(2)
87.3(3)
172.2(5)
Re1-N1
2.173(8)
88.0(2)
P1-Re1-N1
O10-Re1-Cl3/O2
164.3(3)
Hydrogen Bonds in Complex 1a
d (D-H) d (H A) d (D A) — (D-H A)
3 3 3
3 3 3
3 3
N1-H1A Cl3#
0.90
0.90
2.57
2.50
3.354(9)
3.281(9)
145.6
146.1
3 3 3
Figure 1. Molecular structure of the complex 1. Hydrogen atoms at
carbon atoms are omitted for clarity.
N1-H1B Cl1#
3 3 3
a Symmetry transformations used to generate equivalent atoms: # -xþ 1,
-y þ 1, -z þ 1.
m/z = 292 is assigned to [M þ H]þ. The route used for the
synthesis of H2L2 can readily be modified and may give
access to tri- or tetradentate phosphines with PNN or
PNNN donor sets.
work describes the synthesis of the novel phosphine amine
2-(diphenylphosphinomethyl)aniline (H2L2) and syntheses
and structures of several of its oxorhenium(V) complexes.
We prepared this phosphine as a building block for the synthe-
sis of ligands with higher denticity, but as foundation for these
ongoing studies, knowledge about its basic complex formation
behavior is required. With respect to the higher steric flexibility
(by insertion of a CH2 building block) and its expected higher
basicity, some differences are expected between the coordina-
tion behavior of the diarylalkylphosphine H2L2 and the
triarylphosphine H2L1.
Treatment of (NBu4)[ReOCl4] with 1 equiv of H2L2 in
CH2Cl2 or acetonitrile results in the formation of a green
solid of the composition [ReOCl3(H2L2)] (1). The IR spec-
trum shows bands at 3224 and 3190 cm-1, which are due to
the NH vibrations of the protonated ligand. A very strong
band at 987 cm-1 is assigned to the RedO vibration. The
structure of 1 is confirmed by X-ray diffraction on green
single crystals, which were obtained from overlayering an
acetonitrile solution of the complex with toluene. The mo-
lecular structure of 1 is shown in Figure 1. Table 1 contains
selected bond lengths and angles. The coordination sphere of
the Re atom can be best described as a distorted octahedron.
Results and Discussion
Unlike a previous synthesis,26 H2L2 was prepared from
N-tert-butylcarbonate(BOC)-protected o-toluidine,27 by lithia-
tion of the methyl group and subsequent reaction with
PPh2Cl (Scheme 1). After deprotection with trifluoroacetic
acid (TFA), the compound H2L2 is obtained as a colorless
solid in an overall yield of about 60%. The 31P resonance of
the phosphine appears at -22.49 ppm. The 1H NMR
spectrum shows a singlet at 2.74 ppm for the methylene
group and multiplets for the aromatic protons in the region of
6.51-7.71 ppm. The deprotection of the amino group can
clearly be seen in the IR spectrum by the absence of a
carbonyl band. Furthermore there are two bands at 3406
and 3330 cm-1, which can be assigned to the NH2 group.
In the ESIþ mass spectrum of the compound, one peak at
˚
The RedO bond of 1.672(7) A is in the expected range for a
rhenium-oxygen double bond.28 H2L2 coordinates, as ex-
pectedon the basis of the spectroscopic results, as a bidentate,
neutral ligand. The NH hydrogen atoms are involved in
hydrogen bonds to the chloro ligands of adjacent molecules.
Details are shown in Figure S1b as Supporting Information.
The coordination sphere of the rhenium atom in 1 is com-
pleted by three chloro ligands. While the Re1-Cl1 and
Re1-Cl2 bonds are in the expected range of Re-Cl bonds,
˚
the Re1-Cl3 bond of 2.451(2) A is slightly elongated as a
consequence of the structural trans influence of the multiple
bonded oxo ligand. The obvious weakening of this bond has
consequences for the reactivity of 1.
(24) Nguyen, H. H.; Grewe, J.; Schroer, J.; Kuhn, B.; Abram, U. Inorg.
Chem. 2008, 47, 5136.
(25) Nguyen, H. H.; Jegathesh, J. J.; da S. Maia, P. I.; Deflon, V. M.;
Gust, R.; Bergemann, S.; Abram, U. Inorg. Chem. 2009, 48, 9356.
(26) Kellner, K.; Rothe, S.; Steyer, E.-M.; Tzschach, A. Phosphorus,
Sulfur Silicon Relat. Elem. 1980, 8, 269.
(28) Abram, U. In Rhenium, Comprehensive Coordination Chemistry II;
McCleverty, J. A., Meyer, T. J., Eds.; Elsevier: Amsterdam, The Netherlands,
2004; p 271.
(27) Chankeshwara, S. V.; Chakraborti, A. K. Org. Lett. 2006, 8, 3259.

10696 Inorganic Chemistry, Vol. 49, No. 22, 2010
Schroer et al.
In solution, the complex is not stable, which can be seen
from the 31P-{1H} NMR spectra, which are obtained after
dissolution of the crystalline compound. They reveal several
resonances depending on the solvent used. They all appear in
the range between -11.97 and 34.62 ppm and can be assigned
to coordinated phosphine. No evidence was found for
uncoordinated H2L2. Two products of such ongoing reac-
tions in acetonitrile and methanol could be isolated in
crystalline form (vide infra), but it is most probable that also
the formation of coordination isomers plays a role in such
solutions. A similar isomerization was found previously
for oxorhenium(V) complexes with H2L1.16 First struc-
tural evidence for the nature of the formed complexes
after dissolution in methanol was found in the ESIþ MS
spectrum of 1, which was measured in methanol solu-
tion. It gives evidence for a species of the composition
[ReOCl(MeO)(H2L2)]þ.
the oxo ligand and is a common feature in ReO complexes.28
An X-ray crystal structure determination confirms the spec-
troscopic results. The molecular structure of 2 is depicted in
Figure 2, and selected bond lengths and angles are compared
to the values in 1 in Table 1. While the Re1-O10 bond length
remains almost unchanged upon the replacement of Cl- by
MeO-, the Re-O bond to the methanolate ligand is remark-
ably short, and some double-bond character is indicated also
for this bond. Such a situation is not without precedent
and has been observed for a number of oxorhenium(V)
complexes with other co-ligands.28 The bonding situation
of the chelating aminophosphine remains almost unin-
fluenced by the Cl-/MeO- ligand exchange. NMR spec-
tra of 2 of sufficient quality could not be obtained because
of the low solubility of this compound in methanol, and
rapid ongoing reactions in solvents such as CH2Cl2 or
acetonitrile.
The lability of the chloro ligand trans to the oxo oxygen
atom is not surprising and leads to a ready exchange of this
ligand. Consequently, the reaction of (NBu4)[ReOCl4] with 1
equiv of H2L2 in MeOH gives a pale violet precipitate of the
composition [ReOCl2(OMe)(H2L2)] (2), which can directly
be isolated from the reaction mixture. The same compound is
obtained when 1 is dissolved in methanol at room tempera-
ture. The IR spectrum of 2 reveals NH bands in the range
between 3139 and 3286 cm-1, which indicates that the ligand
is still protonated. The RedO vibration is bathochromically
shifted by almost 60 cm-1 with respect to [ReOCl3(H2L2)]
and appears at 929 cm-1. Such a bathochromic shift is
consistent with a coordination of a methoxo group trans to
Dissolution of 1 or 2 in acetonitrile results in blue-green
solutions, from which turquoise crystals can be isolated after
keeping the solutions for 2 weeks at 4 ꢀC. The IR spectrum of
this compound contains a strong band at 671 cm-1 and a
medium band at 975 cm-1, which can be assigned to the
Re-O vibration of a μ-oxo dimer and the RedO vibration.28
Together with bands at 3278 and 3182 cm-1, which have been
assigned to NH vibrations of the non-deprotonated H2L2
ligand, the formation of a dimeric compound of the tentative
composition [{ReOCl2(H2L2)}2O] (3) is strongly suggested
(Scheme 2). This is supported by the mass and NMR spectra
of the product. The ESIþ MS spectrum contains peaks for the
fragments assigned to [M - Cl]þ and [M - 2Cl þ H]þ. In the
31P-{1H} NMR one peak at -0.35 ppm can be assigned to
coordinated phosphorus atoms. The 1H NMR clearly shows
two multiplets at 4.75 and 4.96 ppm for the two methylene
groups and two multiplets at 8.90 and 9.24 ppm for the amino
functions.
An X-ray structure determination confirms the formation
of a μ-oxo bridged Re dimer. The compound crystallizes in
the triclinic space group P1 with 2 co-crystallized molecules
of acetonitrile per asymmetric unit. The molecular structure
is depicted in Figure 3, and selected bond lengths and angles
˚
can be found in Table 2. The bond lengths of 1.684(3) A and
˚
1.699(3) A for Re1-O10 and Re2-O20 are in the expected
range for Re oxo bonds. The monomeric building blocks of
the compound can be best described as distorted octahedra
with the oxo bridge trans to the terminal oxo ligands. The
equatorial positions are occupied each by one H2L2 and two
chloro ligands. The Re1-O12-Re2 angle of 167.33(13)ꢀ
significantly deviates from the common linear arrangement
Figure 2. Molecular structure of complex 2. Hydrogen atoms at carbon
atoms are omitted for clarity.
Scheme 2. Reactions of (NBu4)[ReOCl4] with H2L2 without Addition of a Supporting Base

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10697
Scheme 3. Oxorhenium(V) Cores
Scheme 4. Synthesis of the Trimeric Complex [{ReOCl(H2L2)}O]3 (4)
Figure 3. Molecular structure of 3. Hydrogen atoms at carbon atoms
are omitted for clarity.
2
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) in [{ReOCl2(H2L )}2O] (3)
Re1-O10
Re1-P1
Re1-N1
Re1-Cl1
Re1-Cl2
Re1-O12
1.684(3)
2.424(2)
2.212(4)
2.471(2)
2.349(2)
1.936(3)
Re2-O20
Re2-P2
Re2-N2
Re2-Cl3
Re2-Cl4
Re2-O12
1.699(3)
2.423(2)
2.214(4)
2.459(2)
2.341(2)
1.914(3)
compensation. Generally, the occupation of the equatorial
coordination sphere with neutral ligands will prefer [ReO2]þ
centers (see also the formation of [ReO2(H2L2)2]þ vide infra),
whereas ligands with two or more negative charges, will pref-
erably be coordinated to the [ReO]3þ core.28 Consequently in
the case of complex 3 (one neutral H2L2 ligand, two Cl-), a
central {ReO(OH)}2þ unit is preferred, which condenses to the
dimeric {OdRe-O-RedO}4þ core. This allows maximum
charge compensation by partial transfer of electron density
from the terminal oxo ligands to the bridging unit. Commonly
(as in the present example) the formation of a central
{Re2O3}4þ unit is irreversible, and only in some exceptional
cases has the cleavage of the Re-O-Re backbone of this core
been used to prepare monomeric species, as in the synthesis of
[ReO(OEt)Cl2(py)2] from [Re2O3Cl4(py)4].32
O10-Re1-O12
Re1-O12-Re2
P2-Re2-N2
167.3(2)
166.4(2)
87.8(1)
O20-Re2-O12
P1-Re1-N1
165.8(2)
87.3(1)
Hydrogen Bonds
d (D-H) d (H A) d (D A) — (D-H A)
3 3 3
3 3 3
3 3
N1-H1A N99
0.90
0.90
0.90
0.90
2.70
2.35
2.32
2.33
3.384(4)
3.232(4)
3.141(7)
3.223(4)
132.8
168.6
152.3
171.5
3 3 3
N1-H1B Cl3
3 3 3
N2-H2A N99
3 3 3
N2-H2B Cl1
3 3 3
for μ-oxo bridges in Re oxo complexes.28-30 Such a slightly
bent arrangement of the commonly linear {OdRe-O-Red
O}4þ core is not without precedent.31 In the case of complex 3,
it is evident that the distortions are due to hydrogen bonds,
which are established between N1 and Cl3 as well as N2 and
Cl1. Additional hydrogen bonds are found between the nitro-
gen atoms of the coordinated H2L2 and the solvent acetonitrile
(see Figure 3).
The formation of the dimeric, almost linear {OdRe-O-
RedO}4þ core results from the replacement of the axial Cl-
ligand in compound 1 by H2O and subsequent deprotonation
of the water ligand. Such a behavior is frequently observed in
oxorhenium(V) compounds, and species with {ReO}3þ, {ReO-
(OH2)}3þ, {ReO(OH)}2þ, and {ReO2}þ cores are observed
(Scheme 3). Depending on the net charge of the ligands applied,
the different central units are formed for optimal charge
The novel amine phosphine H2L2 acts in all rhenium(V)
complexes described above as a neutral bidentate ligand. This
is a clear contrast to the behavior of 2-(diphenylphosphino)-
aniline, H2L1, which readily deprotonates and forms amido
chelates or imido complexes (cf. Chart 1). Even the addition of
a supporting base such as NEt3 does not result in deprotonation
of H2L2, but in the removal of chloro ligands and the formation
of a trimeric compound with a hitherto unprecedented
oxorhenium(V) core (Scheme 4).
The reaction of (NBu4)[ReOCl4] with 1 equiv of H2L2 and
3 drops of NEt3 in CH2Cl2 results in the formation of a red com-
pound of the composition [{ReOCl(H2L2)}O]3 (4). Single-
crystals of the compound were obtained by careful overlayering
of a CH2Cl2 solution of the complex with n-pentane, and an
X-ray structure determination confirms the trimeric structure of
the complex. Figure 4a shows the molecular structure of the
compound, and Table 3 summarizes selected bond lengths and
angles.
(29) (a) Patsis, G.; Pirmettis, I.; Tsoukalas, C.; Pelecanou, M.; Raptopoulou,
C. P.; Terzis, A.; Papadopoulos, M.; Chiotellis, E. Inorg. Chim. Acta 2003, 342,
272.
(30) Nguyen, H. H.; Abram, U. Inorg. Chem. 2007, 46, 5310.
(31) (a) Pillai, M. R. A.; Barnes, C. L.; Schlemper, E. O. Polyhedron 1994,
13, 701. (b) Pietzsch, H.-J.; Spies, H.; Leibnitz, P.; Reck, G. Polyhedron 1995, 14,
1849.
(32) Johnson, N. P.; Taha, F. I. M.; Wilkinson, G. J. Chem. Soc. 1964,
2614.

10698 Inorganic Chemistry, Vol. 49, No. 22, 2010
Schroer et al.
Scheme 5. Reactions of the Trimeric Complex [{ReOCl(H2L2)}O]3 (4)
co-crystallizes together with CH2Cl2 in large channels
along the crystallographic b axis (see Figure S 4b in
Supporting Information).
The single crystals of [{ReOCl(H2L2)}O]3 2 CH2Cl2
3
3
2 H2O are only stable when they are covered with the CH2Cl2/
pentane mixture from which they are grown. The X-ray struc-
ture determination was performed in a capillary, since the single
crystals decomposed even at temperatures < -100 ꢀC.
Removal of the solvent results in immediate collapse of the
single crystals and formation of a reddish powder, which
rapidly undergoes an irreversible decomposition under forma-
tion of an unattractive, dark oil. This also prevents further
spectroscopic characterization.
In the reaction mixture, compound 4 is stable for several
hours at room temperature. Prolonged standing, however,
results in a color change from red to yellow, and a yellow
precipitate is slowly formed. From the IR and NMR spectro-
scopic analyses of this solid, the formation of [ReO2(H2L2)2]Cl
(5) is strongly suggested, and was finally confirmed by an X-ray
crystal structure determination of the product. Thus, com-
pound 4 undergoes a slow decomposition, from which the
dioxo rhenium(V) core results (see also Schemes 3 and 5).
Perrhenate is the second product of this decomposition and has
been identified in the residue by IR spectroscopy.
Figure 4. (a) Structure of the complex 4. Hydrogen atoms are omitted
for clarity. (b) Hydrogen bonds, which stabilize the trimeric arrangement.
2
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) in ReOCl(H2L )}O]3 (4)
Re1-O10
Re2-O20
Re3-O30
Re1-O2
1.740(9)
1.700(9)
1.659(8)
2.133(8)
2.107(7)
150.7(5)
138.7(4)
Re1-O3
1.817(8)
1.884(8)
2.050(8)
1.952(8)
160.1(4)
Re2-O1
Re2-O3
Re3-O1
Re3-O2
Re2-O1-Re3
Re1-O3-Re2
Re3-O2-Re1
H Bonds
d (D-H) d (H A) d (D A) — (D-H A)
3 3 3
3 3 3
3 3
Compound 5 can also be prepared directly by treatment of
(NBu4)[ReOCl4] with 2 equiv of H2L2 and 3 drops of triethyl-
amine in CH2Cl2. Pale yellow crystals deposit from the clear
brown reaction solution after reducing the solvent and over-
layering with methanol. The IR spectrum reveals a weak band at
3232 cm-1, which can be assigned to the amino function of the
ligands. A very strong band at 806 cm-1 can be assigned to a
{ReO2}þ core.15 The 31P-{1H} NMR spectrum of 5 presents a
single resonance at 19.91 ppm, which proves the coordination of
N1-H1D Cl2
0.90
0.90
0.90
2.47
2.42
2.28
3.33(1)
3.32(2)
3.14(2)
158.7
174.7
159.8
3 3 3
N2-H2C Cl3
3 3 3
N2-H2D O14
3 3 3
The monomeric building blocks contain octahedrally
coordinated rhenium atoms with the chelate-bonded H2L2
and a chloro ligand in cis position to a terminal oxo ligand.
The remaining two coordination positions are occupied by
the oxo bridges in a way that the oxygen atoms trans to the
terminal oxo ligands are bonded trans to the phosphorus
atoms of the adjacent unit. This finally gives a trimeric
structure which has to the best of our knowledge no
precedent in chemistry of group 7 elements. The resulting
oxo bridges are bent with angles between 138 and 160ꢀ.
They are stabilized by hydrogen bonds (Figure 4b), which
are established between the nitrogen atoms of H2L2 and
the chloro ligands of the neighboring unit. Additional
hydrogen bonds are formed with solvent water, which
1
two equivalent phosphorus atoms. The H NMR spectrum
shows two multiplets for the methylene groups at 4.12 and
4.27 ppm, which indicates inequivalence of the protons. Two
doublets at 3.15 ppm can clearly be assigned to the NH2
groups of two coordinated ligands because they disappear
after the addition of D2O. The ESIþ MS spectrum confirms
the existence of a dioxorhenium(V) species with two H2L2
ligands with a peak at m/z = 801.18, which corresponds to
the complex cation.

Article
Compound 5 crystallizes from a mixture of CH2Cl2 and
Inorganic Chemistry, Vol. 49, No. 22, 2010 10699
The inherent instability of the trimeric compound 4, which
finally results in the decomposition described above and the
formation of compound 5 and perrhenate, can be applied in
the synthesis of mixed-ligand complexes.
MeOH in the triclinic space group P1 with two independent
[ReO2(H2L2)2]þ cations, two chloride counterions, and 3/2
methanol molecules per asymmetric unit. The molecular
structure of one of the complex cations and the hydrogen
bonds, which are established to the corresponding chloride
anion, are shown in Figure 5. Selected bond lengths and
angles are given in Table 4. The rhenium atom is octahedrally
coordinated with two oxo ligands in trans positions to
each other. The neutral chelating ligands coordinate in cis
arrangement with respect to their nitrogen and phosphorus
This is demonstrated with a reaction that has been per-
formed between 4 and 2-(diphenylphosphino)aniline, H2L1.
Two compounds, [ReO2(H2L2)2]Cl (5) and [ReO2(H2L2)
(H2L1)]Cl (6), could be isolated from such reactions in
crystalline form, but more (non-isolatable) products are
contained in the CH2Cl2/n-pentane reaction mixture as could
be seen from the 31P NMR spectrum of the solution, for
example, the bis-chelate [ReOCl(HL1)2] with two 31P NMR
doublets at 18.51 and 6.73 ppm. The reaction mixture also
contains considerable amounts of perrhenate, which could be
isolated upon concentration as tetrabutylammonium salt.
Compound 5 crystallizes as a CH2Cl2 solvate as described
above (yield about 5%) and co-crystallized with compound 6
(overall yield 36%). Interestingly, H2L1 is not deprotonated
in compound 6. Figure 6 depicts the molecular structure of
the mixed-chelate complex 6, and Table 5 summarizes se-
lected bond lengths and angles of this compound. The values
for the co-crystallized complex 5 are given in Table 4 together
with those of the methanol solvate.
˚
atoms. The RedO bonds of the dioxo core of 1.743(5) A or
˚
1.777(5) A are slightly longer than those in the corresponding
monooxo rhenium(V) complexes 1 and 2, which is a common
feature of oxorhenium complexes and has also been observed in
related complexes with the ligand H2L1.15,28 With bond lengths
˚
˚
of 2.252(6) A and 2.241(5) A, the rhenium-nitrogen bonds
can be regarded as single bonds. Hydrogen bonds between the
coordinated amine groups and the Cl- counterions are estab-
lished in the solid state structure of the compound (Figure 5).
The Re atom in compound 6 has expectedly a distorted
octahedral coordination environment. The axial positions
are occupied by the dioxo core, whereas equatorially one
Figure 5. Molecular structure of the complex 5. Hydrogen atoms at
carbon atoms are omitted for clarity.
Figure 6. Molecular structure of complex 6. Hydrogen atoms at carbon
atoms are omitted for clarity.
2
a
˚
Table 4. Selected Bond Lengths (A) and Angles (deg) in [ReO2(H2L )2]Cl
Re11-O101
Re11-O201
Re11-N11
Re11-N21
Re11-P11
Re11-P21
1.743(5)/1.780(5), (1.746(6))
1.776(5)/1.745(5), (1.773(6))
2.253(6)/2.258(6), (2.239(6))
2.239(5)/2.246(5), (2.246(7))
2.424(2)/2.414(2), (2.413(2))
2.409(29/2.404(2), (2.422(2))
O101-Re11-O201
P11-Re11-P21
N11-Re11-N21
P11-Re11-N11
P21-Re11-N21
175.3(2)/175.2(2), (174.9(3))
101.52(6)/100.39(6), (100.96(7))
85.5(2)/86.0(2), (87.3(3))
85.9(2)/85.9(2), (85.7(2))
87.0(2)/87.6(2), (86.3(2))
Hydrogen Bondsb
H bonds
d (D-H)
d (H A)
3 3 3
d (D A)
3 3 3
— (D-H A)
3 3 3
N11-H11A Cl11
0.90
0.90
0.90
0.90
2.46/2.46, (2.32)
2.34/2.36, (2.48)
1.95/1.94, (1.91#)
2.39/2.42, (2.50)
3.356(6)/3.358(6) (3.201(7))
3.227(6)/3.241(6), (3.375(7))
2.826(7)/2.818(7) (2.791(9)#)
3.246(6)/3.256(6) (3.345(7))
176.3/177.5, (164.9)
166.7/165.7, (174.5)
163.9/166.4, (166.4#)
159.4/154.0, (157.1)
3 3 3
N11-H11B Cl12
3 3 3
N21-H21A O102
3 3 3
N21-H21B Cl11
3 3 3
a The values given are for two crystallograpically independent molecules in [ReO2(H2L2)2]Cl (5) 0.75 MeOH. The values in parentheses refer to the
same complex co-crystallized with complex 6. b Symmetry transformations used to generate equivalent atoms: # -x þ 1, y, z.

10700 Inorganic Chemistry, Vol. 49, No. 22, 2010
Schroer et al.
2
1
˚
Table 5. Selected Bond Lengths (A) and Angles (deg) in [ReO2(H2L )(H2L )]Cl (6)
and freshly distilled prior to use unless otherwise stated.
(NBu4)[ReOCl4] was prepared by a published method.33
N-BOC protected o-toluidine was synthesized by a standard
procedure.25
Re2-O102
Re2-O202
Re2-N12
Re2-N22
Re2-P12
Re2-P22
1.775(6)
1.762(6)
2.204(6)
2.245(6)
2.420(2)
2.454(2)
O102-Re2-O202
P12-Re2-P22
N12-Re2-N22
N12-Re2-P12
N22-Re2-P22
176.3(3)
107.71(8)
87.3(2)
Physical Measurements. Infrared spectra were measured as
KBr pellets on a Shimadzu FTIR-spectrometer between 400 and
4000 cm-1. Electrospray Ionization (ESI) mass spectra were mea-
sured with an Agilent 6210 ESI-TOF. All MS results are given in the
form: m/z, assignment. EI mass spectra were recorded with a MAT
711, Varian MAT, Bremen, the electron energy was set to 80 eV.
Elemental analysis of carbon, hydrogen, nitrogen, and sulfur were
determined using a Heraeus vario EL elemental analyzer. Some
values of the elemental analyses of the rhenium complexes signifi-
cantly differ from the calculated values. This seems to be a
systematic problem probably caused by some hydride and/or
carbide formation during the combustion process and does not
refer to impure samples. Reference samples have been checked
by high resolution mass spectrometry. NMR-spectra were taken
with a JEOL 400 MHz multinuclear spectrometer.
H2L2BOC. N-BOC protected o-toluidine (5.0 g, 24 mmol)
was dissolved in 60 mL of dry tetrahydrofuran (THF) under an
atmosphere of argon and cooled to -60 ꢀC. tert-Butyllithium
(1.5 M, 35 mL, 53 mmol) was added dropwise over a period of
30 min. The reaction mixture was stirred for 3 h and allowed to
warm to room temperature. After this time, it was cooled again
to -50 ꢀC, and Ph2PCl (4.0 mL, 22 mmol) was added slowly
under stirring. Stirring was continued for 4 h, during which the
mixture was slowly warmed to room temperature. After addi-
tion of 100 mL of a saturated NaCl solution, the color imme-
diately turned from orange to pale yellow. The organic phase
was washed three times with each 50 mL of a NaCl solution and
dried over MgSO4. Finally the solvent was removed under
vacuum, and the resulting solid was washed with ethanol to
yield the product as a colorless precipitate.
Yield: 68% (5.85 g). Anal. Calcd for C24H26NO2P: C, 73.64; H,
6.69; N, 3.57%. Found: C, 73.29; H, 6.38; N, 3.31%. IR (ν in cm-1):
3371 st (N-H), 3070 m (CHPh), 2977 m (CHmethylene), 1735 s
(CdO). 1H NMR (CDCl3, δ, ppm): 1.42 (s, 9 H, CH3), 3.61 (s, 2 H,
CH2), 7.00-7.50 (m, 14 H, Ph). 31P-{1H} NMR (CDCl3, δ, ppm):
-18.36, ESIþ MS (m/z): 392 [M þ H]þ, 414 [M þ Na]þ.
H2L2. H2L2BOC (5.03 g, 12.8 mmol) was dissolved in 20 mL
of a 1:1 mixture of CH2Cl2/trifluoroacetic acid and stirred for
2 h. After this time, the solution was neutralized with a solution
of NaOH. The organic phase was once washed with a solution of
NaCl and dried over MgSO4. The solvent was removed under
reduced pressure to yield H2L2 as a colorless solid, which was
stored under nitrogen.
80.3(2)
85.0(2)
Hydrogen Bondsa
d (D-H) d (H A) d (D A) — (D-H A)
3 3 3
3 3 3
3 3 3
172.7
N12-H12A O201#
0.90
0.90
0.90
0.90
1.87
2.63
2.37
2.41
2.763(9)
3.376(7)
3.268(7)
3.282(7)
3 3 3
N12-H12B O201#
141.0
175.0
162.0
3 3 3
N22-H22C Cl2#
3 3 3
N22-H22D Cl1#
3 3 3
a Symmetry transformations used to generate equivalent atoms:
# x - 1, y, z.
molecule H2L1 and one molecule H2L2 are coordinated. The
phosphorus atoms are arranged in cis position to each other.
˚
˚
The RedO bonds of 1.775(5) A or 1.762(6) A are slightly
elongated in comparison to the rhenium monooxo core in
compound 1, but are in the normal range for a dioxo
core.16,28 Significant differences are found for the Re-N
bonds to the neutral phosphineamine ligands on the cationic
mixed-ligand complex under study (2.204(6) for H2L2 and
1
1
˚
2.245(6) A for H2L ) and the neutral [ReOCl(HL )2] complex
˚
(1.990(8) and 2.003(8) A), which contains two deprotonated
chelating ligands.16 This clearly reflects the protonation/
deprotonation pattern in both complexes.
Hydrogen bonds are established between the amino func-
tions and two chloride counterions, as well as to oxo ligands
of adjacent complex molecules.
Conclusions
The novel phosphinoaniline H2L2 readily forms oxorhe-
nium(V) complexes with different cores. In all cases the ligand
remains doubly protonated, which is unexpected with respect to
the behavior of (o-aminophenyl)diphenylphosphine, H2L1,
which readily deprotonates during reactions with the same
oxorhenium(V) starting material. One of the driving forces
for the different reactivity may be the opportunity of a better
electron delocalization in the five-membered chelate rings with
{HL1}- compared with the six-membered rings of the H2L2
complexes which contain CH2 units interrupting a possible
π-conjugation. Another structure-determining influence might
be given by charge compensation and hydrogen bonding, as can
be seen by the fully protonated H2L1 ligand in the mixed-ligand
complex [ReO2(H2L1)(H2L2)]Cl (6), where the positive charge
of the complex is obviously better compensated by hydrogen
bonding of the Cl- counterion than by an oxo/chloro rhenium-
(V) complex with a deprotonated (o-aminophenyl)diphenyl-
phosphine ligand.
Yield: 85% (3.2 g). Anal. Calcd for C19H18NP: C, 78.33; H,
6.23; N, 4.81%. Found: C, 78.29; H, 5.95; N, 4.49%. IR (ν in
1
cm-1): 3406 m (N-H), 3330 m (N-H). H NMR (DMSO, δ,
ppm): 2.74 (s, 2 H, CH2), 6.51-7.71 (m, 14 H, Ph). 31P-{1H}
NMR (CDCl3, δ, ppm): -22.49, ESIþ MS (m/z): 292 [M þ H]þ.
[ReOCl3(H2L2)] (1). (a) H2L2 (29 mg, 0.1 mmol) was added to
a solution of (NBu4)[ReOCl4] (58 mg, 0.1 mmol) in 3 mL of
CH2Cl2. The mixture was stirred for 4 h and kept overnight at
room temperature. A pale green solid precipitated from the red-
brown mother liquor. The product was filtered off and washed
with small amounts of CH2Cl2. Yield: 48% (29 mg).
Addition of a supporting base to reaction mixtures between
H2L2 and (NBu4)[ReOCl4] does not result in deprotonation of
the aminophosphine, but in the formation of a rhenium(V) com-
plex with a hitherto unprecedented trimeric oxorhenium core.
(b) (NBu4)[ReOCl4] (58 mg, 0.1 mmol) was dissolved in 3 mL
of acetonitrile, and H2L2 (29 mg, 0.1 mmol) was added together with
p-toluene sulfonic acid (19 mg, 0.1 mmol), which gave a green
solution. The mixture was stirred for 3 h at room temperature.
Finally, the mixture was overlayered with toluene and kept quiet for
slow diffusion of the solvents. The product was obtained as green
crystals. Yield: 42% (25 mg). More product could be recovered as a
pale green powder after concentration of the mother liquor.
Elemental analysis: Calcd for C19H18Cl3NOReP: C, 38.04; H,
3.02; N, 2.33%. Found: C, 38.42; H, 2.87; N, 2.38%. IR (ν in cm-1):
3224 m (N-H), 3190 m (N-H), 3124 m (N-H), 987 s (RedO).
Experimental Section
Materials. All reagents used in this study were reagent grade
and used without further purification. Solvents were dried
(33) Alberto, R.; Schibli, R.; Egli, A.; Schubiger, P. A.; Herrmann, W. A.;
Artus, G.; Abram, U.; Kaden, T. A. J. Organomet. Chem. 1995, 217, 492.

Article
Inorganic Chemistry, Vol. 49, No. 22, 2010 10701
Table 6. X-ray Structure Data Collection and Refinement Parameters
[{ReOCl(H2L2)-
O}3] 2 CH2Cl2
2 H2O
[ReO2(H2L2)(H2L1)]Cl
3
[ReOCl3-
(H2L2)]
[ReOCl3(OMe)-
(H2L2)]
[{ReOCl2(H2L2)}2O]
2 CH3CN
[ReO2(H2L2)2]-
Cl 0.75 MeOH
[ReO2(H2L2)2]Cl
2.5 CH2Cl2
3
3
3
3
3
formula
C19H18Cl3-
NOPRe
599.86
C20H21Cl2-
NO2PRe
595.45
monoclinic
12.769(2)
9.536(1)
16.646(2)
90
92.77(1)
90
2024.5(52)
P21/c
4
1.954
6.361
10775
4389
245
0.0517/0.1141
0.857
C
42H42Cl4-
C59H58Cl7-
N3O8P3Re3
1836.74
C38.75H39Cl-
N2O2.75P2Re
860.31
C
77.5H75Cl7-
N4O4P4Re2
N4O3P2Re2
1226.94
triclinic
11.685(1)
13.807(1)
14.876(1)
98.07(1)
108.25(1)
91.41(1)
2250.7(3)
P1
2
1.810
5.724
25302
12017
504
0.0308/0.0732
1.055
Mw
crystal system
1870.85
triclinic
15.047(2)
15.087(2)
20.609(2)
84.05(1)
77.87(1)
61.74(1)
4028.8(9)
P1
2
1.542
3.362
34643
17415
899
0.0594/0.1672
0.961
triclinic
9.448(1)
9.913(1)
13.075(1)
101.64(1)
103.78(1)
114.20(1)
1021.0(2)
P1
2
1.951
6.430
11171
triclinic
13.532(2)
16.606(2)
17.555(2)
75.36(1)
76.15(1)
79.55(1)
3675.0(8)
P1
2
1.638
5.293
21289
triclinic
11.836(1)
12.563(1)
27.119(2)
93.56(1)
95.41(1)
109.07(1)
3775.7(5)
P1
4
1.513
3.411
40424
˚
a/ A
˚
b/ A
˚
c/ A
R/ deg
β/ deg
γ/ deg
3
˚
V/ A
space group
Z
Dcalc./g cm-3
μ/mm-1
no. of reflections
no. of independent
no. parameters
R1/wR2
5438
236
0.0524/0.1491
1.129
15925
791
0.0666/0.1554
0.850
20155
885
0.0590/0.1452
0.932
GOF
ESIþ MS (m/z): 528.03 [M - HCl - Cl]þ, 560.06 [M - HCl - Cl þ
MeOH]þ, MS (EI): m/z 526.7 [M - 2 HCl]þ, 562.7 [M - HCl]þ.
[ReOCl2(H2L2)(OMe)] (2). H2L2 (29 mg, 0.1 mmol) was
added to a solution of (NBu4)[ReOCl4] (58 mg, 0.1 mmol) in
7 mL of MeOH and stirred for 4 h at room temperature. Then,
the reaction mixture was kept overnight at 4 ꢀC. During this
time, pale violet crystals precipitated.
Yield: 54% (32 mg). Elemental analysis: Calcd for C20H19Cl2-
NO2ReP: C, 40.34; H, 3.55; N, 2.35%. Found: C, 40.17; H, 3.39;
N, 2.27%. IR (ν in cm-1): 3286 m (N-H), 3217 m (NH), 3139 m
(NH), 929 s (RedO). MS (EI): m/z 426.9 [M - HCl, - CH3OH]þ,
562.9 [M - CH3OH]þ.
(58 mg, 0.1 mmol) in 2 mL of CH2Cl2. Finally, three drops of
triethylamine were added, which resulted in an immediate
change of the color to brown. The solution was stirred for 3 h
at room temperature, and MeOH (3 mL) was added. Pale yellow
crystals appeared during slow evaporation of the solvent. The
product was washed with diethylether and dried in air.
Yield: 62% (54 mg). Elemental analysis: Calcd for C38H36-
ClN2O2ReP2: C, 54.57; H, 4.34; N, 3.35%. Found: C, 54.21; H,
3.68; N, 3.07%. IR (ν in cm-1): 3232 w (N-H), 806 s (OdRedO).
1H NMR (DMSO, δ, ppm): 3.15 (2d, 4 H, NH2), 4.12 (m, 2H,
CH2), 4.27 (m, 2H, CH2), 6.76-7.48 (m, 28 H, Ph). 31P-{1H} NMR
(CDCl3, δ, ppm): 19.91, ESIþ MS (m/z): 801 [M - Cl]þ.
[ReO2(H2L2)(H2L1)]Cl [ReO2(H2L2)2]Cl 2.5 CH2Cl2. A so-
[(ReOCl2(H2L2))2O] (3). [ReOCl3(H2L2)] (1) (45 mg, 0.08
mmol) was dissolved in acetonitrile. The product was obtained
as blue crystals upon slow evaporation of the solvent.
Yield: 55% (26 mg). Elemental analysis: Calcd for C38H36-
Cl4N2O3Re2P2: C, 39.87; H, 3.17; N, 2.45%. Found: C, 39.96; H,
2.93; N, 2.48%. IR (ν in cm-1): 3278 w (N-H), 3182 w (N-H),
975 m (RedO), 671 vst (Re-O-Re). 1H NMR (CDCl3, δ, ppm):
4.75 (m, 2 H, CH2), 4.96 (m, 2H, CH2), 6.99-7.87 (m, 28 H,
Ph), 8.90 (d, 2 H, NH2), 9.24 (d, 2 H, NH2) . 31P-{1H} NMR
(CDCl3, δ, ppm): -0.35. ESIþ MS (m/z): 1073 [M - 2Cl þ H]þ,
1109 [M - Cl ]þ.
3
3
lution of (NBu4)[ReOCl4] (58 mg, 0.1 mmol) and 3 drops of
NEt3 were added to H2L2 (29 mg, 0.1 mmol) in 3 mL of CH2Cl2.
The mixture was stirred for 15 min at room temperature and then
overlayered with n-pentane. Red crystals were obtained by slow
diffusion of the solvents. H2L1 (27 mg, 0.1 mmol) was added to this
reaction mixture. After 1 day, the red crystals had disappeared, and
yellow crystals of [ReO2(H2L2)(H2L1)]Cl [ReO2(H2L2)2]Cl 2.5
3
3
CH2Cl2 deposited at the glass walls.
Estimated yield: about 5 mg (<10%). 31P-{1H} NMR (CDCl3,
δ, ppm): -5.50, 0.27, ESIþ MS (m/z): 787 [ReO2(H2L2)(H2L1)]þ.
X-ray Crystallography. The intensities for the X-ray determi-
nations were collected on a STOE IPDS 2T instrument with Mo
[(ReOCl(H2L2))3O3] (4). A solution of (NBu4)[ReOCl4] (58
mg, 0.1 mmol) and 3 drops of NEt3 were added to H2L2 (29 mg,
0.1 mmol) in 3 mL of CH2Cl2. The color of the solution imme-
diately turned to red. The mixture was stirred for 15 min at room
temperature and then overlayered with n-pentane. Red crystals
were obtained by slow diffusion of the solvents. The crystals are
extremely unstable without the solvent and were prepared for
the X-ray measurement at -80 ꢀC with a small amount of
solution in a capillary.
˚
KR radiation (λ = 0.71073 A) at 200 K. Standard procedures
were applied for data reduction and absorption correction.
Structure solution and refinement were performed with
SHELXS-97 and SHELXL-97 embedded in the WINGX
system.34,35 Hydrogen atom positions were calculated for ide-
alized positions and treated with the “riding model” option of
SHELXL. More details on data collections and structure calcu-
lations are contained in Table 6. Ellipsoid plots of all structures
are shown in the Supporting Information.
Estimated yield: 60%. Elemental analysis as well as more
spectroscopic studies could not be performed because of the
rapid decomposition of the complex.
Supporting Information Available: Crystallographic data in
CIF format; further details are given in Figures S1-S6 and
Tables S1-S6. This material is available free of charge via the
Internet at http://pubs.acs.org.
[ReO2(H2L2)2]Cl (5). (a) By decomposition of (4): H2L2
(27 mg, 0.1 mmol) was added to the reaction mixture described
above for the synthesis of 4 containing the red crystals of this
complex. After standing one day at room temperature, the red
crystals disappeared, and yellow (compound 5) and colorless
crystals ((NBu4)Cl) were obtained.
(34) Sheldrick, G. M. SHELXS-97 and SHELXL-97, programs for the
€
solution and refinement of crystal structures; University of Gottingen:
(b) H2L2 (59 mg, 0.2 mmol) was dissolved in 3 mL of CH2Cl2
and dropwise added to a stirred solution of (NBu4)[ReOCl4]
€
Gottingen, Germany, 1997.
(35) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.