Synthesis, characterization and redox behaviour of mono- and dicarbonyl phosphane rhenium(I) complexes bearing N-, N,N- and N,O-type ligands

Article abstract of DOI:10.1002/ejic.200601026

New mono- and dicarbonyl phosphane Re^I complexes [ReCl(L) ₂(CO)(PPh₃)₂] {L = 3,5-Me₂-Hpz (3), quin (4)} and [Re(L)_n(CO)₂(PPh₃) ₂][BPh₄]_m

Full text of DOI:10.1002/ejic.200601026

FULL PAPER
DOI: 10.1002/ejic.200601026
Synthesis, Characterization and Redox Behaviour of Mono- and Dicarbonyl
Phosphane Rhenium(I) Complexes Bearing N-, N,N- and N,O-Type Ligands
Alexander M. Kirillov,[a] Matti Haukka,[b] M. Fátima C. Guedes da Silva,[a] and
Armando J. L. Pombeiro*[a]
Keywords: Carbonyl ligands / Electrochemistry / N ligands / Rhenium
New mono- and dicarbonyl phosphane ReI complexes
[ReCl(L)2(CO)(PPh3)2] {L = 3,5-Me2-Hpz (3), quin (4)} and
[Re(L)n(CO)2(PPh3)2][BPh4]m {L = pz/Hpz, n = 2, m = 0 (2); L
= 4,7-Ph2-phen, n = 1, m = 1 (5); L = 2-Me-dipic, n = 1, m = 0
(6)} were prepared by reaction of the dinitrogen ReI precursor
[ReCl(N2)(CO)2(PPh3)2] (1), in refluxing methanol or meth-
anol/benzene mixture, with 3,5-dimethylpyrazole (3,5-Me2-
Hpz), quinoline (quin), pyrazole (Hpz), 4,7-diphenyl-1,10-
phenanthroline (4,7-Ph2-phen) and dipicolinic acid (H2dipic),
respectively, with esterification of the latter in 6 to afford the
2-methoxycarbonyl-6-pyridinecarboxylate (2-Me-dipic) moi-
ety. Complexes 2–6 were characterized by IR spectroscopy,
1H-, 31P{1H}- and 13C{1H} NMR spectroscopy, FAB-MS, cyclic
voltammetry, elemental analyses and single-crystal X-ray
diffraction (for 2, 5 and 6) analyses which indicate mutually
trans triphenylphosphane ligands. The redox behaviour of
the obtained complexes in solution was studied, and the Le-
ver electrochemical ligand parameter EL was determined, for
the first time, for 4,7-Ph2-phen. Compounds 2–6 represent
the first examples of mono- and dicarbonyl Re complexes
bearing these types of ligands.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
gated only in a couple of cases; one instance involved its
reactions with some amino acids conjugated with 2-amino-
thiazole (L) to afford monocarbonyl ReII complexes of the
general formula [ReCl(L)(CO)(PPh3)2].[5c] The other case
led to the ReI dinitrogen compound [Re(pic)(N2)(CO)-
(PPh3)2] (pic = picolinate) by reaction of 1 with picolinic
acid (Hpic),[6a] thus initially extending to the low ReI oxi-
dation state (and to picolinate) our interest in higher-oxi-
dation-state rhenium complexes with N- or O-ligands,
namely some benzoyldiazenido-ReIII [6b] and oxo-ReV [6c]
compounds which were shown to act as catalysts for the
peroxidative oxidation[6b] or carboxylation[6c] of alkanes. To
further explore the use of 1 as a convenient precursor for
the synthesis of new ReI compounds with N-, N,N- or N,O-
ligands, we studied its reactions with various N-heterocycle
species, that is, pyrazole, 3,5-dimethylpyrazole, quinoline,
4,7-diphenyl-1,10-phenanthroline and dipicolinic acid
(Scheme 1), and we prepared and characterized a series of
derived mono- and dicarbonyl complexes. Although hetero-
cycle ligands of such types are rather simple and commonly
used in coordination chemistry, their complexes with the
monocarbonyl {Re(CO)} or dicarbonyl {Re(CO)2} core are
still very rare.[7] This contrasts with the tricarbonyl
{Re(CO)3} core, whose coordination chemistry was exten-
sively developed over the last two decades,[8] with applica-
tion in nuclear-medical research, in the preparation of pho-
toluminescent materials, in catalysis and in supramolecular
chemistry.[7a,9]
Introduction
Dinitrogen complexes of rhenium are an important class
of compounds within the low-oxidation-state coordination
chemistry of this metal, particularly because of their signifi-
cance in the field of nitrogen fixation and as versatile syn-
thons for a variety of new rhenium derivatives.[1,2] The la-
bility of the coordinated N2 in Re complexes allows its dis-
placement by a variety of small molecules (e.g., CO, H2,
CS2, NO, nitriles, oximes, alkynes, azides, cyanates, etc.)
and various P-, N-, O-, S- or mixed-donor ligands.[1,3]
In this respect, the bis(diphosphane) complex trans-
[ReCl(N2)(dppe)2] {dppe = 1,2-bis(diphenylphosphanyl)-
ethane} is the most studied member within the whole family
of Re dinitrogen complexes.[1b,1e,1g,3a,3e,4] A few studies have
been performed on the monophosphane analogues
[ReCl(N2)(L)4] (L = PMe2Ph or PMePh2),[1b,5a,5b] whereas
the reactivity of the related mixed N2/CO complex
[ReCl(N2)(CO)2(PPh3)2] (1) appears to have been investi-
[a] Centro de Química Estrutural, Complexo I, Instituto Superior
Técnico,
Av. Rovisco Pais, 1049–001 Lisbon, Portugal
Fax: +351-21-846-4455
E-mail: pombeiro@ist.utl.pt
[b] Department of Chemistry, University of Joensuu,
P.O. Box 111, 80101, Joensuu, Finland
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Rhenium(I) Complexes
FULL PAPER
phen)(CO)2(PPh3)2][BPh4] (5) (upon addition of Na[BPh4])
and the orange neutral complex [Re(2-Me-dipic)(CO)2-
(PPh3)2] (6), respectively. The complexes 2–6 were charac-
terized by IR spectroscopy, FAB-MS, 1H-, 31P{1H}- and
13C{1H} NMR spectroscopy, cyclic voltammetry, elemental
analyses and single-crystal X-ray diffraction (for 2, 5 and
6) structural analyses.
Complex 2 bears both one Hpz ligand and its anionic
1
conjugate base (pz–). However, the H- and 13C{1H} NMR
spectra show their magnetic equivalence as accounting for
a single set of resonances attributable to proton or carbon
1
atoms of both ligands. In the H NMR spectrum of 2, the
broad 1 H intensity NH signal at δ = 11.26 ppm is assigned
to N–H···N, although the upfield shift relative to uncoordi-
nated pyrazole [δ(NH) = 13.60 ppm, CCl4 (0.5 )][12] can-
not be directly related to the effects of the hydrogen bond
and/or of a dynamic proton exchange since in other ca-
ses[10a] they led to lowfield shifts. The solid-state IR spec-
trum of 2 exhibits an intense ν(NH) band with a maximum
at 3317 cm–1, whose broad character is indicative of hydro-
gen bonding.
Scheme 1.
In particular, despite the fact that a number of tricar-
bonyl Re complexes with these ligands were already
known,[10] to the best of our knowledge, there were no ex-
amples of mono- and dicarbonyl Re complexes comprising
pyrazole, 3,5-dimethylpyrazole or quinoline ligands, as well
as any phenanthroline or dipicolinate derivatives. The redox
properties of the synthesized complexes were also investi-
gated by cyclic voltammetry, and the value of the electro-
chemical Lever ligand parameter EL
the first time, for the 4,7-Ph2-phen ligand.
In contrast, both 3,5-Me2-Hpz ligands are neutral in
1
complex 3. Its H NMR spectrum shows a 2 H intensity
NH signal at δ = 11.06 ppm, which is also shifted upfield
relative to free 3,5-dimethylpyrazole [δ(NH) = 12.29 ppm,
CDCl3 (1.0 )],[12] while the IR spectrum of this compound
exhibits a ν(NH) band at 3222 cm–1.
[11]
was estimated, for
In complex 6 the dipicolinate ligand (2-Me-dipic) is bi-
dentate, exhibiting N,O-coordination and one free arm
whose esterification to give a methyl acetate moiety oc-
curred during the synthesis in methanol solution, conceiva-
bly being promoted by the ReI centre since the methyl ester
Results and Discussion
Synthesis and Spectroscopic Characterization
The reactions of the dinitrogen rhenium(I) complex was not detected in a blank experiment upon refluxing di-
[ReCl(N2)(CO)2(PPh3)2] (1) with the N-heterocycle ligands picolinic acid in methanol for several hours in the absence
of Scheme 1 in refluxing methanol or a methanol/benzene of a metal complex. The same type of esterification was
mixture led to the displacement of the N2/Cl– ligands, or of previously observed[6c] by us in the course of the synthesis
the N2 and one CO ligand in 1 (Scheme 2), thus allowing of ReV complexes such as [ReOCl2(2-Me-dipic)(PPh3)] and
the formation of the new mono- and dicarbonyl rhenium(I) [ReOCl{(OCH2CH2)N(CH2COO)(CH2COOCH3)}(PPh3)]
complexes [ReCl(L)2(CO)(PPh3)2] {L = 3,5-Me2-Hpz (3), derived from dipicolinic and N-(2-hydroxyethyl)iminodia-
quin (4)} and [Re(L)n(CO)2(PPh3)2][BPh4]m {L = pz/Hpz, n cetic acids, respectively. The presence of the methyl ester
= 2, m = 0 (2); L = 4,7-Ph2-phen, n = 1, m = 1 (5); L = group in 6 is corroborated by the detection of the corre-
1
2-Me-dipic (2-methoxycarbonyl-6-pyridinecarboxylate), n = sponding CH3 resonances in the H- (δ = 4.19 ppm) and
1, m = 0 (6)}, which were isolated as air-stable crystalline 13C{1H} (δ = 53.91 ppm) NMR spectra. Moreover, the IR
solids in 78–44% yields. Hence, the reaction of 1 with pyr- spectrum of 6 shows strong bands at 1740 and 1435 cm–1
azole (Hpz, Scheme 2, reaction 1) gave the pale-yellow di- associated with νas and νs vibrations, respectively, of the
carbonyl complex [Re(pz)(Hpz)(CO)2(PPh3)2] (2) with one COOMe fragment.
pyrazolate (pz–) ligand and one pyrazole (Hpz) ligand,
The 13C{1H} NMR spectra of the dicarbonyl complexes
formed upon N2 and HCl elimination, while the use of 3,5- exhibit two CO signals, lying in the δ range of ca. 203–
dimethylpyrazole (3,5-Me2-Hpz, reaction 2) led to the dis- 189 ppm for complexes 2 and 6, whereas in 5 they are signif-
placement of N2 and one CO ligand, yielding the yellow icantly shifted upfield to δ = 166.74 and 166.04 ppm. In the
monocarbonyl dipyrazole compound [ReCl(3,5-Me2-Hpz)2- monocarbonyl complex 3 the corresponding CO resonance
(CO)(PPh3)2] (3). The related deep-purple monocarbonyl is observed at δ = 197.80 ppm. The 31P{1H} NMR spectra
complex [ReCl(quin)2(CO)(PPh3)2] (4) was obtained by of all complexes 2–6 indicate the stereochemically favoured
treatment of the starting material 1 with an excess of quino- trans phosphane coordination in view of the single reso-
line (quin, Scheme 2, reaction 3). The reactions of 4,7-di- nance detected in the δ range of ca. 32–20 ppm (relative to
phenyl-1,10-phenanthroline (4,7-Ph2-phen) and dipicolinic external H3PO4), which is shifted downfield from that (δ =
(2,6-pyridinedicarboxylic) acid (H2dipic) with 1 (reactions –5.47 ppm) of free triphenylphosphane. These signals and
4, 5) led to the deep-red ionic Re compound [Re(4,7-Ph2- all other NMR resonances of complexes 2–6 are unexcep-
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Scheme 2. (1): + Hpz – N2 – HCl; (2): + 3,5-Me2-Hpz – N2 – CO; (3): + quin – N2 – CO; (4): + 4,7-Ph2-phen + Na[BPh4] – N2 – NaCl;
(5): + H2dipic – N2 – HCl.
tional and comparable to those found in related rhenium promotes the electron release from dπ orbitals of the metal
complexes.[6,10a,10e–g,13]
to the π*(CO) orbitals, as it also conceivably occurs in com-
The IR spectra of the dicarbonyl complexes 2, 5 and 6 plex 4. This is also assisted by the limited π-electron accept-
exhibit two strong ν(CO) bands in the 1929–1924 and 1853– ance of the two quinoline ligands in comparison with the
1841 cm–1 ranges, similar to those of the starting material 1 CO and N2 ligands in compound 1. The IR spectra of com-
(1921 and 1844 cm–1) and other dicarbonyl ReI complexes plexes 3–6 also show a set of bands due to the νas and νs
containing the cis-{Re(CO)2} moiety, for example, vibrations of CH groups in the typical 3060–3050 and
[Re(L)(CO)2(PPh3)2] {L
=
MeCOO or EtCOO;[14a] 3000–2925 cm–1 ranges, respectively. The characteristic
OC(NH2)S, OC(NHPh)S or OC(NHC6H4Me-4)S}[14b] and ν(PPh) bands due to the PPh3 ligands are observed at 747–
[Re(L)(CO)2(bipy)] {bipy = 2,2Ј-bipyridine, L = diethyl-2- 743 and 697–695 cm–1.
(N-p-tolylimino)-3-(hydroxymethylene)butane-1,2-dicarb-
The positive FAB-MS spectra of compounds 3–6 exhibit
oxylate}.[14c] An additional ν(CO) band is detected at the molecular ions [M]+ with the expected isotopic patterns
2032 cm–1 in the spectrum of 2, as observed with other rhe- at m/z values of 966, 1032, 1099 and 947, respectively, while
nium carbonyl complexes comprising pyrazole moieties.[14d] the protonated molecular ion [M + H]+ is detected at m/z
Two strong ν(CO) bands at 1922 and 1839 cm–1 are also = 903 in the spectrum of 2. Fragmentation pathways involve
shown by 3, whereas in complex 4 the ν(CO) band is de- the stepwise loss of CO, Cl and PPh3 ligands as well as of
tected at 1778 cm–1, being considerably shifted to a lower- N-, N,N- or N,O-moieties. A comparative analysis of peak
energy region more typical for a bridging carbonyl intensities concerned with typical fragmentations suggests
group.[14e] Nevertheless, we believe that compound 4 is mo- that in complexes 3–6 the elimination of one PPh3 ligand is
nonuclear and bears a terminal carbonyl ligand trans to the a favourable process, in agreement with the detection of
ligated Cl–, as formulated in Scheme 2. This is in agreement very intense signals assigned to the [M – PPh3] (in 3, 4),
with (i) an X-ray single-crystal diffraction analysis of 4 [M – PPh3 – 2CO] (in 5) and [M – PPh3 – CO] (in 6) frag-
which indicates its basic and mononuclear structure, with ments. In contrast, the release of one or two pyrazole li-
the trans-CO/Cl arrangement, although with a too-high er- gands is more favourable in 2 since a set of intense peaks
ror to be reported, as well as with (ii) a FAB-MS(+) analysis attributed to the [M – pz], [M – pz – CO], [M – pz – Hpz]
which clearly detects the molecular ion [ReCl(quin)2- and [M – pz – Hpz – CO] fragments is observed. The pres-
(CO)(PPh3)2]+ as the heaviest observed fragment (see later). ence of the [BPh4]– counterion in 5 is clearly confirmed by
A low IR ν(CO) value (ca. 1800 cm–1)[4e] was also found for the negative FAB-MS spectrum (the intense signal of the
the ReI monocarbonyl complex trans-[ReCl(CO)- [M]– molecular ion at m/z = 319 with the expected isotopic
(dppe)2] with the strong electron-donor chloro ligand which pattern) and by the IR spectrum. Also, elemental analyses
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Rhenium(I) Complexes
FULL PAPER
of all compounds are consistent with the proposed formula-
tions (Scheme 2) which are further confirmed by single-
crystal X-ray diffraction studies (for 2, 5 and 6).
X-ray Crystal Structures
The molecular structures of complexes 2, 5 and 6 are
shown in Figures 1, 2 and 3, respectively, and selected bond
lengths and angles are given in Table 1. All compounds
crystallize in the monoclinic crystal system (space group
P21/n) and exhibit a distorted octahedral coordination envi-
ronment about rhenium filled by the N-, N,N- or N,O-li-
gand(s), two triphenylphosphane groups and two carbonyl
groups.
Figure 2. An ORTEP representation of the cationic part of 5 with
ellipsoids shown at the 50% probability level. All hydrogen atoms
and the solvent molecule are omitted for clarity.
Figure 1. An ORTEP representation of 2 with ellipsoids shown at
the 50% probability level. Phenyl hydrogen atoms are omitted for
clarity.
The molecular structure of 2 (Figure 1) shows the pz–
and Hpz ligands trans to the carbonyl groups. The Re1–
C1 and Re1–C2 bond lengths of 1.920(4) and 1.893(4) Å,
respectively, are common for rhenium carbonyl com-
plexes,[10a,10d–g,15] while the carbonyl C1–O1 and C2–O2
distances of 1.141(5) and 1.162(5) Å, respectively, are com-
Figure 3. An ORTEP representation of 6 with ellipsoids shown at
the 50% probability level. Phenyl hydrogen atoms and the solvent
molecule are omitted for clarity.
parable to the CϵO bond of ca. 1.128 Å[16] in molecular H2···N4 intramolecular hydrogen bond with N2···N4 dis-
carbon monoxide. The binding of the Hpz/pz– ligands to tance of 2.627(5) Å [N2–H2 0.94(4) Å and H2···N4
rhenium is characterized by a slight difference between the 1.74(5) Å; N2–H2···N4 156(4)°], which connects two pyr-
Re1–N1 [2.219(3) Å] and Re1–N3 [2.176(3) Å] bond lengths azole groups forming the Re1–N1–N2···N4–N3 ring with
which agree with those reported for other rhenium carbonyl the N1–Re1–N3 angle of 89.22(12)°. Related features of the
complexes comprising pyrazole or hydrotris(pyrazolyl)- NH protons assignment and splitting, and the hydrogen-
borate [HB(pz)3]– derivatives, for example, [Re(pz)(Hpz)2- bonding interactions within the Hpz and pz– fragments
(CO)3],[10a] [Re{HB(pz)3}(CO)2L] (L = THF or PPh3)[15b] were observed in some Re, Ru, Co, Pd, Pt and Zn complex-
and [{Re(B(Hpz)3)(CO)2}2(N2)].[17] Although only one NH es.[10a] The triphenylphosphane groups are bound almost
proton is crystallographically localized at one of the pyr- linearly, and the Re–P distances range from 2.4251(10) to
azole moieties of 2, its assignment to the N2 atom is rather 2.4453(10) Å being comparable to those of compounds 5
formal and in reality it may be split between N2 and N4. and 6 and in accordance with those reported for other car-
This agrees with the observation of a rather short N2– bonyl rhenium complexes with trans PPh3 ligands.[14a,18]
Eur. J. Inorg. Chem. 2007, 1556–1565
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A. J. L. Pombeiro et al.
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Table 1. Selected bond lengths [Å] and angles [°] for compounds 2,
5 and 6.
The structure of 6 (Figure 3), with a chelating methyl-
dipicolinate ligand, is similar to that of 2 comprising the
pyrazolate/pyrazole ligands in the equatorial sites. In the
monoesterificated dipicolinate ligand, the nitrogen N1 is
trans to the C1–O1 carbonyl group and the carboxylate
oxygen O3 is trans to the C2–O2 ligand, forming a Re1–
N1–C3–C4–O3 chelate ring with a N1–Re1–O3 bite angle
of 74.51(16)° which is the most deviated angle from the ide-
alized 90° around the distorted octahedral geometry of the
Re1 centre. The bond lengths within the dipicolinate moiety
2
5·0.5CH2Cl2
6·EtOH
Re1–C1
Re1–C2
Re1–N1
Re1–N2
Re1–N3
Re1–O3
Re1–P1
Re1–P2
1.920(4)
1.893(4)
2.219(3)
–
2.176(3)
–
2.4251(10)
2.4453(10)
1.141(5)
1.162(5)
93.81(16)
85.54(13)
–
2.004(6)
2.042(7)
2.162(4)
2.147(4)
–
1.918(6)
1.887(7)
2.216(4)
–
–
–
2.176(4)
2.4273(13)
2.4246(13)
1.126(6)
1.167(7)
85.0(2)
172.8(2)
–
102.1(2)
–
176.63(18)
–
2.4434(12)
2.4439(13)
0.977(6)
0.860(6)
95.5(2)
168.77(17)
93.05(17)
95.7(2)
171.45(19)
–
C1–O1
C2–O2
in
6
are analogous to those of [ReBr{C5H3N-
and [ReOCl2(2-Me-di-
(COOEt)(COOMe)}(CO)3][10i]
C1–Re1–C2
C1–Re1–N1
C1–Re1–N2
C2–Re1–N1
C2–Re1–N2
C2–Re1–O3
N1–Re1–N2
N1–Re1–N3
N1–Re1–O3
C1–Re1–P1
C2–Re1–P1
C1–Re1–P2
C2–Re1–P2
N1–Re1–P1
N1–Re1–P2
P1–Re1–P2
Re1–C1–O1
Re1–C2–O2
pic)],[6c] although the latter contains a rather short Re–
Odipic bond [2.037(2) Å] relative to the corresponding Re1–
O3 distance of 2.176(4) Å in 6. The Re1–C1 [1.918(6) Å]
and Re1–C2 [1.887(7) Å] bonds as well as the C1–O1
[1.126(6) Å] and C2–O2 [1.167(7) Å] distances in 6 are stan-
dard and very close to those of 2 (Table 1) and other car-
bonyl rhenium complexes.[10a,10d–g,15] In the structure of
6·EtOH, O–H···O hydrogen-bonding interactions are ob-
served between the dipicolinate oxygen O4 and the hydroxy
group of the ethanol crystallization molecule [O99···O4
2.671(8) Å], as well as between two ethanol molecules from
adjacent units [O99···O99 2.869(2) Å].
176.20(14)
–
–
–
75.73(14)
–
–
89.22(12)
–
–
74.51(16)
89.19(14)
90.87(16)
89.18(14)
91.35(16)
90.37(11)
90.95(11)
177.13(5)
176.9(5)
176.1(5)
90.65(11)
84.02(12)
91.66(11)
91.69(12)
92.24(9)
92.07(9)
175.26(3)
176.6(3)
175.8(4)
89.78(14)
90.66(17)
88.90(14)
91.74(17)
89.94(10)
90.90(10)
177.36(4)
179.2(6)
178.2(8)
Electrochemical Studies
The major deviation from the octahedral geometry in 2
Complexes 2, 3, 5 and 6 exhibit, by cyclic voltammetry
concerns the C2–Re1–P1 angle of 84.02(12)°; the other at a Pt electrode in 0.2  [nBu4N][BF4]/CH2Cl2 solution, a
bond angles are relatively close to the idealized 90° and first single-electron reversible (or quasireversible) (for 2 and
I
ox
180°.
5) or irreversible (for 3 and 6) oxidation at E1/2 = 0.67
I
ox
Compound 5 is the first structurally characterized exam- (2) and 1.22 (5) V or Ep = 0.75 (3) and 0.87 (6) V vs.
ple with the 4,7-diphenyl-1,10-phenanthroline ligand within SCE (Table 2, Figure 4 for 5), assigned to the ReI Ǟ ReII
the large family of phenanthroline Re complexes. Its molec- oxidation, followed by a second reversible (for 2 and 3) or
ular structure comprises the [Re(4,7-Ph2-phen)(CO)2- irreversible (for 6) oxidation at close potentials (1.00 to
(PPh3)2]+ cation and the [BPh4]– anion, with the separation 1.15 V vs. SCE), most likely caused by the ReII Ǟ ReIII oxi-
between rhenium and boron centres being ca. 8.91 Å. The dation. A third irreversible oxidation wave is also observed
cationic part also contains two phosphane ligands in trans for compounds 2, 3 and 6 at a higher potential (ca. 1.34–
position, whereas the equatorial sites are occupied by the 1.43 V vs. SCE). Complex 4 could not be studied by cyclic
bidentate phenanthroline ligand and the two carbonyl voltammetry because of its instability in the solvent/electro-
groups (Figure 2). The octahedral environment around rhe- lyte medium.
nium is more distorted than that of complex 2, exhibiting
For the quasireversible waves, increasing the scan rate
a major deviation from an idealized geometry with a mini- from 0.2 to 0.5 or 1.0 Vs–1 usually led to an enhancement
mal N1–Re1–N2 angle of 75.73(14)°. The Re1–C1 and of the degree of reversibility. The oxidation potentials of
Re1–C2 bonds of 2.004(6) and 2.042(7) Å, respectively, are the neutral complexes 2, 3 and 6 are lower than the corre-
ox
lengthened by ca. 0.10–0.15 Å relative to the corresponding sponding potentials for the starting compound 1 (IE1/2
=
ox
distances in 2 and other complexes with a phenanthroline 0.94, IIEp = 1.79 V vs. SCE, measured[6a] under identical
moiety.[10d–g,15a] Such an elongation of the Re–C distances experimental conditions). This confirms the stronger elec-
is concomitant with the shortening of the C1–O1 and C2– tron-donor character of the N- and N,O-ligands in 2, 3 and
O2 bonds to 0.977(6) and 0.860(6) Å, respectively; the latter 6 relative to ligated Cl– + N2 or N2 + CO in 1, in agreement
distance is unusually short and this is not reflected in ν(CO) with the π-electron-acceptor character of N2 and CO. The
which is comparable to the other complexes. The phenan- highest oxidation potential is observed for [Re(4,7-Ph2-
ox
throline molecule is bound to the metal forming a N1–C13– phen)(CO)2(PPh3)2]+ in 5 (IE1/2 = 1.22 V vs. SCE) on ac-
C14–N2–Re1 chelate ring, and the Re1–N1 and Re1–N2 count of its positive charge.
bonds of 2.162(4) and 2.147(4) Å, respectively, lie in the
In addition, compounds 5 and 6 show (Table 2, Figure 4
range of ca. 2.14–2.22 Å reported for other phenanthroline for 5) one reversible reduction wave at an unusually high
red
Re complexes.[10d–g,15a]
potential (IE1/2
= –0.01 and –0.18 V vs. SCE, respec-
1560
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1556–1565

Rhenium(I) Complexes
FULL PAPER
Table 2. Cyclic voltammetric data for the ReI complexes.[a]
are expected to correspond to N,N(N,O)-ligand-centred re-
ductions, whereas the waves at more negative potentials can
be assigned to the ReI Ǟ Re0 reduction. Although our mea-
sured less-negative potentials are considerably higher than
most of those in the literature, they are comparable to, for
ox
ox
II
ox
ox
ox
red
II
red
IE1/2 (IEp
)
E
(IIEp
)
(
IIIEp
)
IE1/2
E
1/2
1/2
1[b]
2[c]
3[d]
5[f]
6
0.94
(1.79)
1.00
1.00
–
–
–
–
–
–
–
–
0.67
(1.41)
(1.34)
–
(0.75)[e]
1.22
red
–0.01
–0.18
–1.21
–0.57
example, E1/2 = –0.24 V vs. SCE reported for a ligand-
(1.15)[e]
(1.43)
centred process in [{Re(CO)3(CH3CN)}2(ppz)]2+ (ppz =
4Ј,7Ј-phenanthrolino-5Ј,6Ј:5,6-pyrazine).[20] However, one
should mention that the free 4,7-Ph2-phen species does not
show any waves in the window from –2.0 to +2.0 V vs. SCE.
The possible ligand-centred character of the Ired wave
(Figure 4) is also supported by the UV/Vis spectrum of 5
recorded in CH2Cl2 solution, which reveals the presence of
a rather broad and intense (ε ≈ 9200 Lmol–1 cm–1) band
with a maximum at ca. 400 nm, most likely related to a
metal-to-ligand charge-transfer (MLCT) process and in
agreement with reported data for ReI systems with polypyr-
idyl ligands.[7b,20–22] For example, MLCT bands with a
rather close absorption maximum and intensity have been
observed for [Re(bpy)(py)(CO)2{P(OEt)3}][PF6][7b] (bpy =
(0.87)
[a] Values given in VϮ0.02 vs. SCE (CH2Cl2/[nBu4N][BF4], v =
0.2 Vs–1, for further details see Exp. Sect.); E1/2 corresponds to
half-wave potential of reversible or quasireversible wave; peak po-
tentials (Ep) for irreversible waves are given in brackets. [b] Included
for comparison from ref.[6a] [c] Two new reduction waves at Ep
red
red
= –0.30 V and E1/2 = –0.79 V (not observed in initial oxidation
and reduction scans) appeared over time, conceivably caused by
red
decomposition products. [d] Two new reduction waves at E1/2
=
red
–0.21 V and E1/2 = –0.70 V (not observed in initial oxidation
and reduction scans) appeared over time, conceivably caused by
decomposition products. [e] This wave becomes quasireversible at
higher scan rates (v = 0.5 or 1.0 Vs–1). [f] An additional wave was
ox
observed at Ep = 0.97 V as a result of the oxidation of the coun-
terion [BPh4]–.
2,2Ј-bipyridine, py
=
pyridine) (λmax
=
397 nm),
[Re(bpy)(CO)2(PPh3)2][PF6][7b] (λmax = 401 nm), [Re{(CF3)2-
bpy}(CO)2{P(OEt)3}2][PF6][7b] {(CF3)2bpy = 4,4Ј-bis(tri-
fluoromethyl)bipyridine} (λmax = 404 nm) and [ReCl(bppz)-
(CO)3][20] {bppz = 2,3-bis(2-pyridyl)pyrazine} (λmax
=
417 nm).
The measured first oxidation potential (upon conversion
to the NHE scale) for the rhenium(I) complex [Re(4,7-Ph2-
ox
phen)(CO)2(PPh3)2]+ in 5 (IE1/2 = 1.22 V vs. SCE, i.e.,
1.22 + 0.245[11] = 1.47 V vs. NHE) was applied to calculate
the electrochemical Lever EL parameter[11,23] for the 4,7-
Ph2-phen ligand according to the Lever’s equation (1), valid
for octahedral complexes, where ∑EL is the sum of the EL
values for all the ligands, and SM and IM are standard pa-
rameters dependent on the metal redox couple, spin state
Figure 4. Cyclic voltammogram of [Re(4,7-Ph2-phen)(CO)2(PPh3)2]-
[BPh4] (5) (8.5ϫ10–4 molL–1), in 0.2  [nBu4N][BF4]/CH2Cl2, at a
Pt working electrode and at a scan rate of 0.2 Vs–1; * wave due to and stereochemistry.[11]
the oxidation of the counterion [BPh4]–.
E = SM(∑EL) + IM, V vs. NHE
(1)
=
tively), followed by a second quasireversible reduction wave
Thus, applying the corresponding SM = 0.76 and IM
II
red
at
E
= –1.21 (5) and –0.57 (6) V vs. SCE. The evi-
1/2
–0.95 V vs. NHE values for the ReII/I couple[11b] and the EL
values for the CO and PPh3 ligands (EL = 0.99 and 0.39 V
vs. NHE, respectively),[11a,23] we have estimated, for the first
time, the value of the electrochemical Lever ligand param-
eter, EL = 0.21 V vs. NHE, for each binding arm of the 4,7-
Ph2-phen ligand. This value is comparable to those pre-
viously established[11a,23] for monodentate 1,10-phenan-
throline (EL = 0.26 V vs. NHE) and 4,7-dimethyl-1,10-
phenanthroline (EL = 0.23 V vs. NHE) ligands.
dence for considering the wave at E1/2 = –0.01 V vs. SCE in
compound 5 as a reduction wave is apparent from its posi-
tion in the I (current) scale in the cyclic voltammogram
(Figure S1 in the Supporting Information). Further proof
is provided by controlled potential electrolysis (CPE) at a
potential slightly lower than that of Ired (i.e., at –0.30 V),
which led to a colour change of solution (i.e., from deep
brown to clear green), while neither alteration in colour was
detected nor charge was measured upon attempted CPE at
a potential above that of the same wave.
According to literature data for other ReI compounds
with aromatic N-heterocycle ligands[7b,19–22] (e.g.,
[{ReCl(CO)3}2(ddpq)] {ddpq = 6,7-dimethyl-2,3-bis(2-pyr-
Conclusions
This study shows that the mixed dinitrogen-dicarbonyl
idyl)quinoxaline}, [Re(bpa)(bqu)(CO)3]+ {bpa = 1,2-bis(4- complex [ReCl(N2)(CO)2(PPh3)2] (1) constitutes a conve-
pyridyl)ethane, bqu = 2,2Ј-biquinoline}, [Re(bpy)(4,4Ј- nient starting material for the synthesis of new low-oxi-
bpy)(CO)3]+ {bpy = 2,2Ј-bipyridine, 4,4Ј-bpy = 4,4Ј- dation-state Re complexes bearing N-, N,N- or N,O-ligands
bipyridine}, etc.),[19,20] the waves (one or two) observed at with unsaturated N-heterocycle groups coordinated to
less negative potentials (i.e., from –0.2 to –1.1 V vs. SCE) {Re(CO)} or {Re(CO)2} centres. It is thus possible to open
Eur. J. Inorg. Chem. 2007, 1556–1565
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1561

A. J. L. Pombeiro et al.
FULL PAPER
spectra were obtained with a Trio 2000 instrument by bombarding
3-nitrobenzyl alcohol (m-NBA) matrices of the samples with 8 keV
(ca. 1.18 1015 J) Xe atoms. Mass calibration for data system acqui-
sition was achieved using CsI. Infrared spectra (4000–400 cm–1)
were recorded with a Jasco FT/IR-430 instrument in KBr pellets.
1H-, 31P{1H}- and 13C{1H} NMR spectra were measured with a
Varian UNITY 300 spectrometer at ambient temp. The 31P chemi-
cal shifts are relative to external 85% H3PO4 aqueous solution.
UV/Vis spectra were recorded with a Jasco model 7800 UV/Vis
spectrophotometer.
a suitable entry to mono- and dicarbonyl Re complexes
with such types of ligands, allowing the extension to the
{Re(CO)n} (n = 1 or 2) centres of the rich coordination
chemistry that is being developed for complexes with the
tricarbonyl {Re(CO)3} site[8] which has found applications
in various fields such as nuclear medicine, pharmacology,
photoluminescent materials, supramolecular chemistry and
catalysis.[7a,9]
It is also necessary to mention that the axial bisphos-
phane trans-{Re(PPh3)2}+ core in complex 1 remains during
the substitution reactions which involve only the equatorial
N2/CO/Cl– ligands. The observed behaviour can be ac-
counted for by a combination of various factors, namely
the usual lability of the dinitrogen ligand (a rather weak σ-
electron donor),[24] the labilization of the chloro ligand
The electrochemical experiments were carried out with an EG&G
PAR 273A potentiostat/galvanostat connected to a personal com-
puter through a GPIB interface. Cyclic voltammetry (CV) studies
were undertaken in a two-compartment three-electrode cell, at
platinum-wire working electrode (d = 0.5 mm) and counter elec-
trodes, in 0.2  [nBu4N][BF4]/CH2Cl2 solution. A Luggin capillary
upon loss of N2 (a π-electron acceptor that, when trans to connected to a silver-wire pseudoreference electrode was used to
Cl–, enhances the electron release from the latter to the
control the working electrode potential. Controlled potential elec-
trolysis (CPE) experiments were carried out in electrolyte solutions
with the mentioned composition, in a two-compartment three-elec-
metal), the strong trans influence of the effective π-acceptor
CO ligands in trans position (with their resulting mutual
trode cell with platinum-gauze working electrode and counter elec-
labilization), the protic-acid character of the new ligand
trodes in compartments separated by a glass frit; a Luggin capil-
precursor and the chelating effect of a possible bidentate
lary, probing the working electrode, was connected to a silver-wire
new ligand.
pseudoreference electrode. The CPE experiments were monitored
regularly by cyclic voltammetry, thus assuring that no significant
potential drift occurred along the electrolyses. The oxidation poten-
tials of the complexes were measured by CV in the presence of
Hence, on reactions of 1 with acidic N-heterocycle li-
gands (pyrazole or dipicolinic acid, reactions 1 and 5,
respectively), N2 and Cl– are the replaced ligands (the sub-
stitution of the latter being assisted by protonation), ferrocene as the internal standard, and the redox potential values
are quoted relative to the SCE by using the [Fe(η5-C5H5)2]0/+
whereas the reactions of 1 with nonacidic and nonchelating
ox
(E1/2
= 0.525 V vs. SCE) redox couple in 0.2  CH2Cl2/
N-heterocycle ligands (3,5-dimethylpyrazole and quinoline,
reactions 2 and 3, respectively) occur by displacement of N2
and one CO ligand. Chelation of the new ligand(s) leads
to CO trans-to-cis isomerization with the formation of cis-
[Bu4N][BF4] solution.[25] The obtained potentials vs. SCE can be
converted into the NHE scale by addition of 0.245 V.[11]
[Re(pz)(Hpz)(CO)2(PPh3)2] (2):
A
mixture of
1
(50 mg,
dicarbonyl products (reactions 1, 4 and 5) from the trans- 0.060 mmol) and pyrazole (41 mg, 0.60 mmol) was refluxed in
MeOH (20 mL) for 2 d to produce a brown suspension. It was fil-
tered off, washed with MeOH (3ϫ10 mL), C6H6 (3ϫ5 mL) and
Et2O (3ϫ10 mL) and dried in vacuo to yield complex 2 as a pale-
yellow microcrystalline solid. Yield: 78% (42 mg), based on 1. Fur-
ther purification of 2 can be achieved by recrystallization from a
CH2Cl2/C6H6/EtOH mixture. C44H36N4O2P2Re (901.9): calcd. C
58.59, H 4.13, N 6.21; found C 58.27, H 4.21, N 5.89. FAB-MS(+):
m/z = 903 [M + H]+, 835 [M – pz]+, 807 [M – pz – CO]+, 778 [M –
Hpz – 2CO]+, 767 [M – pz – Hpz]+, 739 [M – pz – Hpz – CO]+,
709 [Re(PPh3)2 – 2H]+, 613 [M – PPh3 – CO + H]+, 449
dicarbonyl starting complex 1. However, cis- to trans-Cl/
CO isomerization can occur (reaction 3) with a nonchelat-
ing bulky ligand, resulting in a particularly favourable π-
donor/π-acceptor interaction between the former ligands
(compound 4).
The synthetic significance of those observations, namely
in terms of selectivity, deserves further exploration, by tak-
ing advantage of the versatile structural/electronic features
of the mixed N2/CO complex 1 as demonstrated in this
study.
[RePPh ]+. IR (KBr): ν = 3317 (s br) ν(NH), 3148 (w) ν (CH) and
˜
3
as
3055 (w) νs(CH), 2032 (m), 1924 (s) and 1841 (s) ν(CO), 743 (s)
1
and 697 (s) ν(PPh) cm–1. H NMR (CDCl3): δ = 11.26 (s br, 1 H,
NH), 7.81 [m, 2 H, pzH(3/5)], 7.68–7.50 (m, 12 H, PPh3), 7.45–
7.30 (m, 18 H, PPh3), 6.81 [d, J = 2.0 Hz, 2 H, pzH(3/5)], 5.88 [t,
J = 2.1 Hz, 2 H, pzH(4)] ppm. 13C{1H} NMR (CDCl3): δ = 202.86
and 202.04 (CO), 142.15 (pzC), 134.75–134.30 (m, PPh3), 133.91
(pzC), 129.77 (d, JCP = 9.4 Hz, PPh3), 128.70–128.35 (m, PPh3),
107.61 (pzC) ppm. 31P{1H} NMR (CDCl3): δ = 20.75 (s) ppm. X-
ray-quality crystals of 2 were grown by slow evaporation at 5 °C of
a CH2Cl2/C6H6/EtOH solution of 2.
Experimental Section
General Materials and Procedures
All synthetic work was performed under dinitrogen using standard
Schlenk techniques. The solvents were dried and degassed by stan-
dard methods. Potassium perrhenate (Merck), triphenylphosphane
(Aldrich), benzoylhydrazine (Aldrich), carbon monoxide (Air Prod-
ucts), pyrazole (Aldrich), 3,5-dimethylpyrazole (Aldrich), quinoline
(Merck), 4,7-diphenyl-1,10-phenanthroline (Aldrich), sodium tet-
raphenylborate (Aldrich) and 2,6-pyridinedicarboxylic acid (Ald-
rich) were obtained from commercial sources and used as received.
[ReCl(N2)(CO)2(PPh3)2] (1) was prepared by a published meth-
od.[1g]
[ReCl(3,5-Me2-Hpz)2(CO)(PPh3)2] (3): A mixture of 1 (50 mg,
0.060 mmol) and 3,5-dimethylpyrazole (58 mg, 0.60 mmol) was re-
fluxed in MeOH (20 mL) for 2.5 d to produce a brown-yellow
cloudy solution. The solid was filtered off, washed with MeOH
(3ϫ10 mL) and Et2O (3ϫ10 mL) and dried in vacuo to yield com-
plex 3 as a yellow microcrystalline solid. Further purification of 3
can be achieved by recrystallization from a C6H6/EtOH(MeOH)
C, H and N elemental analyses were carried out by the Microana-
lytical Service of the Instituto Superior Técnico. The FAB mass
1562
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1556–1565

Rhenium(I) Complexes
FULL PAPER
solution. Yield: 67% (39 mg), based on 1. C47H46ClN4OP2Re
(966.5): calcd. C 58.41, H 4.80, N 5.80; found C 58.08, H 4.56, N
5.50. FAB-MS(+): m/z = 966 [M]+, 834 [M – {3,5-Me2-Hpz} – Cl –
H]+, 802 [M – 2{3,5-Me2-Hpz} + CO]+, 774 [M – 2{3,5-Me2-
Hpz}]+, 746 [M – 2{3,5-Me2-Hpz} – CO]+, 739 [M – 2{3,5-Me2-
Hpz} – Cl]+, 704 [M – PPh3]+, 668 [M – PPh3 – Cl – H]+, 640 [M –
PPh3 – Cl – CO – H]+, 608 [M – PPh3 – {3,5-Me2-Hpz}]+, 580
[M – PPh3 – {3,5-Me2-Hpz} – CO]+, 531 [M – PPh3 – {3,5-Me2-
Hpz} – Ph]+, 512 [M – PPh3 – 2{3,5-Me2-Hpz}]+, 503 [M – PPh3 –
{3,5-Me2-Hpz} – CO – Ph]+, 484 [M – PPh3 – 2{3,5-Me2-Hpz} –
CO]+, 407 [M – 2PPh3 – Cl – 2H]+, 329 [M – PPh3 – 2{3,5-Me2-
133.24 (m), 130.97, 130.18 (d, JCP = 6.0 Hz), 129.32 (m), 126.62
(m), 126.09 (m) and 122.17 (PPh3 + BPh4 + phenC) ppm. 31P{1H}
NMR (CDCl3): δ = 22.51 (s) ppm. X-ray-quality crystals of
5·0.5CH2Cl2 were grown by slow evaporation of an EtOH/Me2CO/
CH2Cl2 solution of 5.
[Re(2-Me-dipic)(CO)2(PPh3)2] (6): To a solution of 1 (50 mg,
0.060 mmol) in MeOH (20 mL) and C6H6 (10 mL) was added an
excess of 2,6-pyridinedicarboxylic acid (108 mg, 0.60 mmol), and
the reaction mixture was refluxed for 1 d. The resulting deep-
orange clear solution was concentrated under reduced pressure to
give an orange oil which was treated with MeOH (15 mL). The
solid that separated out from the resulting solution was filtered off
and discarded. The filtrate was evaporated under reduced pressure
giving an orange oily solid to which Et2O (30 mL) was added to
form an orange precipitate. It was filtered off, washed with Et2O
(3ϫ10 mL) and dissolved on a filter in Me2CO (5 mL) to form a
deep-orange solution which was taken to dryness under reduced
pressure yielding an orange oil. Further addition of Et2O (30 mL)
led to the formation of a solid which was filtered off, washed with
Et2O (3ϫ10 mL) and dried in vacuo to give complex 6 as an
orange microcrystalline material. Yield: 44% (25 mg), based on 1.
C46H36NO6P2Re (946.9): calcd. C 58.35, H 3.83, N 1.48; found C
58.03, H 3.49, N 1.84. FAB-MS(+): m/z = 947 [M]+, 919
[M – CO]+, 767 [M – {2-Me-dipic}]+, 739 [M – {2-Me-dipic} –
CO]+, 657 [M – PPh3 – CO]+, 642 [M – PPh3 – CO – Me]+, 629
[M – PPh3 – 2CO]+, 614 [M – PPh3 – 2CO – Me]+, 505 [M – PPh3 –
Hpz} – CO – 2Ph – H]+. IR (KBr): ν = 3222 (s) ν(NH), 3059 (w)
˜
νas(CH), 3002 (w) and 2925 (w) νs(CH), 1922 (s) and 1839 (s)
ν(CO), 1571 (m) ν(C=N), 746 (m) and 695 (s) ν(PPh) cm–1. 1H
NMR (CDCl3): δ = 11.06 (s, 2 H, NH), 7.65–7.10 (m, 30 H, PPh3),
5.34 (s, 2 H, pzH), 1.76–1.56 (m, 12 H, pzCH3) ppm. 13C{1H}
NMR (CDCl3): δ = 197.80 (CO), 152.44 and 139.74 (pzC), 134.90–
134.20 (m, PPh3), 129.82 (s, PPh3), 128.60–128.30 (m, PPh3), 107.76
(pzC), 15.95 and 11.44 (pzCH3) ppm. 31P{1H} NMR (CDCl3): δ =
21.04 (s) ppm.
[ReCl(quin)2(CO)(PPh3)2] (4): Complex 1 (50 mg, 0.060 mmol) was
refluxed in a quinoline (0.50 mL) and methanol (20 mL) mixture
for 15 h to produce a deep-brown cloudy solution. The solid was
filtered off, washed with MeOH (5ϫ10 mL) and Et2O (3ϫ10 mL)
and dried in vacuo to yield complex 4 as a deep-purple microcrys-
talline solid. Yield: 70% (43 mg), based on 1. C55H44ClN2OP2Re
(1032.6): calcd. C 63.98, H 4.30, N 2.71; found C 63.66, H 4.63, N
2.72. FAB-MS(+): m/z = 1032 [M]+, 770 [M – PPh3]+, 641 [M –
{2-Me-dipic}]+, 447 [RePPh3 – 2H]+. IR (KBr): ν = 3058 (m)
˜
νas(CH), 2954 (w) νs(CH), 1929 (s) and 1853 (s) ν(CO), 1740 (s)
PPh3 – quin]+, 613 [M – PPh3 – quin – CO]+, 484 [M – PPh3
–
νas(COOMe), 1692 (s) νas(COO), 1482 (m) νs(COO), 1435 (s)
2quin – CO]+. IR (KBr): ν = 3051 (m) ν (CH), 3000 (w) ν (CH), νs(COOMe), 747 (s) and 696 (s) ν(PPh) cm–1. H NMR (CDCl3):
1
˜
as
s
1778 (s) ν(CO), 745 (s) and 695 (s) (PPh) cm–1. 1H NMR (CDCl3): δ = 8.59 (t, J = 7.9 Hz, 1 H, pyH), 8.49 (t, J = 7.8 Hz, 1 H, pyH),
δ = 7.71–7.40, 7.33–7.12 and 7.06–6.92 (m, 10 H + 18 H + 16 H, 8.30 (m, 1 H, pyH), 7.91–7.32 (m, 30 H, PPh3), 4.19 (s, 3 H, CH3)
PPh3 + quinH) ppm. 31P{1H} NMR (CDCl3): δ = 30.79 (s) ppm. ppm. 13C{1H} NMR (CDCl3): δ = 208.54 and 189.24 (CO), 166.31
No reliable 13C{1H} NMR spectrum could be accumulated because
of the gradual decomposition of 4 in CDCl3 or [D6]acetone. Single
crystals were grown by slow evaporation at 5 °C of a CH2Cl2/Me2-
CO(EtOH) solution of 4. The proposed formulation of 4 with the
trans-CO/Cl arrangement was also confirmed by a single-crystal X-
ray diffraction analysis, but with a rather high error due to a heavy
disorder.
(COO), 153.53 (COOMe), 140.27, 139.08, 132.37, 131.62 and
127.65 (pyC), 134.83 (d, JCP = 9.3 Hz), 134.42–134.26 (m), 130.25
and 129.63–128.30 (m, PPh3), 53.91 (CH3) ppm. 31P{1H} NMR
(CDCl3): δ = 31.96 (s) ppm. X-ray-quality crystals of 6·EtOH were
grown by slow evaporation at 5 °C of an EtOH/Me2CO or EtOH/
C6H6 solution of 6.
X-ray Crystal Structure Determinations: The X-ray diffraction data
[Re(4,7-Ph2-phen)(CO)2(PPh3)2][BPh4] (5): A mixture of 1 (50 mg, of 2, 5 and 6 were collected with a Nonius Kappa CCD dif-
0.060 mmol) and 4,7-diphenyl-1,10-phenanthroline (60 mg,
0.18 mmol) was refluxed in a MeOH (10 mL) and C6H6 (20 mL)
mixture overnight. The resulting deep-green clear solution was con-
centrated under reduced pressure to give a green oil which was
dissolved in EtOH (15 mL) and treated with an ethanol solution
(30 mL) of Na[BPh4] (205 mg, 0.60 mmol). The obtained deep-
green suspension was almost completely dissolved upon addition
of acetone (30 mL). The resulting green clear solution was filtered
and left to evaporate in air in a beaker at ambient temp. Deep-red
crystals formed in a few days from that green solution. They were
isolated by filtration, washed gently with Et2O, collected and dried
in vacuo to yield compound 5. Yield: 64% (54 mg), based on 1.
C86H66BN2O2P2Re (1418.4): calcd. C 72.82, H 4.69, N 1.97; found
C 72.47, H 4.86, N 2.25. FAB-MS(+): m/z = 1099 [M]+, 1071 [M –
CO]+, 837 [M – PPh3]+, 808 [M – PPh3 – CO – H]+, 781 [M –
PPh3 – 2CO]+, 767 [M – {4,7-Ph2-phen}]+, 739 [M – {4,7-Ph2-
phen} – CO]+, 703 [M – PPh3 – 2CO – Ph – H]+, 625 [M – PPh3 –
fractometer using Mo-Kα radiation. The Denzo-Scalepack[26] pro-
gram package was used for cell refinements and data reductions.
All structures were solved by direct methods using the SHELXS-
97,[27] SIR97[28] or SIR2002[29] programs with the WinGX[30] graph-
ical user interface. An empirical absorption correction was applied
to all data (Tmax/Tmin: 0.6242/0.5545, 0.8965/0.5149, 0.5172/0.7256
for 2, 5 and 6, respectively) using SORTAV[31] or XPREP in
SHELXTL v.6.14–1[32] program. Structural refinements were car-
ried out with SHELXL-97.[33] In 2 the NH hydrogen atom was
located from the difference Fourier map and refined isotropically.
In 5 one of the phenyl groups in 4,7-Ph2-phen is disordered over
two sites with occupancies 0.72 and 0.28. In these groups the aro-
matic rings were refined with fixed C–C distances of 1.39 Å. More-
over, the disordered CH2Cl2 solvent molecule was modelled by
placing the two chlorines over three sites with equal occupancies.
The solvent was partially lost from the structure, and all in all only
half a molecule of CH2Cl2 was introduced into the structure. Be-
cause of the disorder, CH2Cl2 was refined only isotropically and
the hydrogen atoms were omitted. In 6 the carbon atoms of the
2CO – 2Ph – 2H]+. FAB-MS(–): m/z = 319 [BPh ]–. IR (KBr): ν =
˜
4
3054 (m br) νas(CH), 2999 (w) and 2983 (w) νs(CH), 1927 (s) and
1852 (s) ν(CO), 744 (s) and 697 (s) (PPh) cm–1. 1H NMR (CDCl3): EtOH molecule are disordered over two sites with occupancies 0.55
δ = 7.90–6.40 (m, 66 H, PPh3 + BPh4 + phenH) ppm. 13C{1H}
NMR (CDCl3): δ = 166.04 and 164.74 (C=O), 140.15 (m), 137.08,
and 0.45. The OH hydrogen atom of EtOH was located from the
difference Fourier map but not refined (Uiso = 0.12). Other hydro-
Eur. J. Inorg. Chem. 2007, 1556–1565
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1563

A. J. L. Pombeiro et al.
FULL PAPER
Table 3. Crystal data and structure refinement details for complexes 2, 5 and 6.
2
5·0.5CH2Cl2
6·EtOH
Empirical formula
Formula weight
Temperature [K]
C44H37N4O2P2Re
901.92
120(2)
C86.5H67BClN2O2P2Re
1460.82
120(2)
C48H42NO7P2Re
992.97
120(2)
λ [Å]
Crystal system
Space group
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
0.71073
monoclinic
P21/n
a [Å]
b [Å]
c [Å]
α [°]
11.5079(2)
16.6886(3)
19.7901(3)
90
14.7466(3)
14.7938(2)
32.5113(6)
90
10.0823(2)
11.9229(2)
35.7524(7)
90
β [°]
99.4790(10)
90
3748.81(11)
4
1.598
3.371
97.335(8)
90
7034.6(2)
4
1.379
1.862
91.1040(10)
90
4297.01(14)
4
1.535
2.955
γ [°]
V [Å3]
Z
ρcalcd. [Mgm–3]
µ(Mo-Kα) [mm–1]
Number of collected reflections
Number of unique reflections
Rint
40567
8585
0.0584
0.0289, 0.0617
0.0490, 0.0864
1.127
72404
12266
0.0836
0.0430, 0.0926
0.0696, 0.1034
1.048
24191
7372
0.0586
0.0368, 0.0868
0.0525, 0.0947
1.063
[b]
Final R1,[a] wR2 (I Ն 2σ)
R1, wR2 (all data)
GOF on F2
Largest diff. peak and hole [eÅ–3]
0.844, –2.736
1.467, –0.965
1.560, –1.088
2
2 2
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [b] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
Lough, R. H. Morris, W. D. Harman, Inorg. Chem. 1997, 36,
3553.
gen atoms were placed in idealized positions and constrained to
ride on their parent atom. The crystallographic data are summa-
rized in Table 3.
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CCDC-623918 to -623920 (for 2, 5·0.5CH2Cl2 and 6·EtOH, respec-
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Supporting Information (see also the footnote on the first page of
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voltammogram of 5 initiated by the anodic and cathodic sweep.
[4]
Acknowledgments
This work has been partially supported by the Fundação para a
Ciência e a Tecnologia (FCT), Portugal and its POCI 2010 pro-
gramme (FEDER funded). A. M. K. is grateful to the FCT and
the POCTI and POCI programme for a fellowship (BD/6287/01).
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Received: October 31, 2006
Published Online: March 2, 2007
Eur. J. Inorg. Chem. 2007, 1556–1565
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1565