New approach to the chemistry of technetium(V) and rhenium(V) phenylimido complexes: Novel [M(NPh)PNP]3+ metal fragments (M = Tc, Re; PNP = aminodiphosphine) suitable for the synthesis of stable mixed-ligand compounds

Article abstract of DOI:10.1021/ic048486y

Ligand-exchange reactions of the aminodiphosphine ligand bis[(2-diphenylphosphino)ethyl]amine hydrochloride (PNHP· HCl) with labile M(NPh)Cl₃(PPh₃)₂ precursors (M = Re, Tc) in the presence of triethylamine yield monocationic phenylimido mer,cis-[M(NPh)Cl₂(PNHP)]Cl (M = Re, 1; Tc, 2) intermediate complexes. X-ray analyses show that in both compounds the aminodiphosphine acts as a tridentate ligand dictating a mer,cis arrangement. Two chloride ligands, respectively in an equatorial and in the axial position trans to the linear M-NPh moiety, fill the remaining positions in a distorted-octahedral geometry. The chloride trans to the metal-imido core is labile, and is replaced by an alcoholate group, without affecting the original geometry, as established in mer,cis-[Re(NPh)(OEt)Cl(PNHP)]Cl 4. Otherwise, ligand-exchange reactions involving the aminodiphosphine bis[(2-diphenylphosphino)ethyl]methylamine (PNMeP), in which the central secondary amine has been replaced by a tertiary amine function, or its hydrochloride salt (PNMeP·HCl) give rise to three different species, depending on the experimental conditions: fac,cis-[Re(NPh)Cl₂(PNMeP)]Cl 3a, cis,fac-Re(NPh)Cl ₃(PNMeP)·HCl 3b, and mer,trans-[Re(NPh)Cl₂(PNMeP)] Cl 3c, which are characterized in solution by multinuclear NMR studies. The monodentate groups incorporated in these intermediate compounds, either halides and/or ethoxide, undergo substitution reactions with bidentate donor ligands such as catechol, ethylene glycol, and 1,2-aminophenol to afford stable mixed ligand complexes of the type [M(NPh)(O,O-cat)(PNP)]Cl [PNP = PNHP M = Re 5, Tc 6; PNP = PNMeP M = Re 7], [Re(NPh)(O,O-gly)(PNP)]Cl [PNP = PNHP 8, PNMeP 9] and [Re(NPh)(O,N-ap)(PNMeP)]Cl 10. X-ray diffraction analyses of the representative compounds 5 and 8 reveal that the aminodiphosphine switches from the meridional to the facial coordination mode placing the heteroatom of the diphosphine trans to the phenylimido unit and the bidentate ligand in the equatorial plane. Solution-state NMR studies suggest an analogous geometry for 6, 7, 9, and 10. Comparison with similar mixed ligand complexes including the terminal nitrido group is discussed.

Full text of DOI:10.1021/ic048486y

Inorg. Chem. 2005, 44, 4766−4776
New Approach to the Chemistry of Technetium(V) and Rhenium(V)
+
Phenylimido Complexes: Novel [M(NPh)PNP]3 Metal Fragments (M
Tc, Re; PNP Aminodiphosphine) Suitable for the Synthesis of Stable
Mixed-Ligand Compounds
)
)
Marina Porchia,*,† Francesco Tisato,*,† Fiorenzo Refosco,† Cristina Bolzati,† Mario Cavazza-Ceccato,‡
Giuliano Bandoli,‡ and Alessandro Dolmella‡
ICIS - C.N.R., Corso Stati Uniti, 4, 35127 PadoVa, Italy, and Department of Pharmaceutical
Sciences, UniVersity of PadoVa, Via Marzolo, 5, 35131 PadoVa, Italy
Received October 29, 2004
Ligand-exchange reactions of the aminodiphosphine ligand bis[(2-diphenylphosphino)ethyl]amine hydrochloride (PNHP
HCl) with labile M(NPh)Cl3(PPh3)2 precursors (M Re, Tc) in the presence of triethylamine yield monocationic
phenylimido mer,cis-[M(NPh)Cl2(PNHP)]Cl (M Re, 1; Tc, 2) intermediate complexes. X-ray analyses show that
in both compounds the aminodiphosphine acts as a tridentate ligand dictating a mer,cis arrangement. Two chloride
ligands, respectively in an equatorial and in the axial position trans to the linear M NPh moiety, fill the remaining
positions in a distorted-octahedral geometry. The chloride trans to the metal imido core is labile, and is replaced
‚
)
)
−
−
by an alcoholate group, without affecting the original geometry, as established in mer,cis-[Re(NPh)(OEt)Cl(PNHP)]-
Cl 4. Otherwise, ligand-exchange reactions involving the aminodiphosphine bis[(2-diphenylphosphino)ethyl]methylamine
(PNMeP), in which the central secondary amine has been replaced by a tertiary amine function, or its hydrochloride
salt (PNMeP
‚HCl) give rise to three different species, depending on the experimental conditions: fac,cis-[Re(NPh)-
Cl2(PNMeP)]Cl 3a, cis,fac-Re(NPh)Cl3(PNMeP)
‚
HCl 3b, and mer,trans-[Re(NPh)Cl2(PNMeP)]Cl 3c, which are
characterized in solution by multinuclear NMR studies. The monodentate groups incorporated in these intermediate
compounds, either halides and/or ethoxide, undergo substitution reactions with bidentate donor ligands such as
catechol, ethylene glycol, and 1,2-aminophenol to afford stable mixed ligand complexes of the type [M(NPh)(O,O-
cat)(PNP)]Cl [PNP
) PNHP M ) Re 5, Tc 6; PNP ) PNMeP M ) Re 7], [Re(NPh)(O,O-gly)(PNP)]Cl [PNP )
PNHP 8, PNMeP 9] and [Re(NPh)(O,N-ap)(PNMeP)]Cl 10. X-ray diffraction analyses of the representative compounds
5 and 8 reveal that the aminodiphosphine switches from the meridional to the facial coordination mode placing the
heteroatom of the diphosphine trans to the phenylimido unit and the bidentate ligand in the equatorial plane.
Solution-state NMR studies suggest an analogous geometry for 6, 7, 9, and 10. Comparison with similar mixed
ligand complexes including the terminal nitrido group is discussed.
Introduction
a particular metal core, stabilized by a suitable framework
of mono or polydentate ligands, whereas the coordination
sphere of the metal is completed by labile monodentate
ligands such as water molecules or halide groups. The latter
can be easily replaced by small chelating ligands, either
bidentate or tridentate, which in turn can be coupled to a
specific pharmacophore. The generality and the potentiality
of this synthetic approach is well described by two recent
prototypes, the tricarbonyl moiety, [TcI(CO)3]+,3 and the
“supernitrido” moiety [TcV(N)(PNP)]2+ (Scheme 1).4 Despite
The search for substitution-inert rhenium and technetium
compounds to be exploited as potential radiopharmaceuticals
recently led to the design of new molecules whose main
feature is the presence of both a stable building-block, which
includes the metal and suitable ancillary ligand(s), and a
coordinated chelating ligand eventually coupled to a bio-
molecule.1,2 The building-block comprises the metal ion, or
* To whom correspondence should be addressed. Phone: ++0498295958.
Fax: ++0498702911. E-mail: tisato@icis.cnr.it.
† ICIS - C.N.R.
(1) Jurisson, S.; Lydon, J. D. Chem. ReV. 1999, 99, 2205-2218.
(2) Liu, S.; Edwards, D. S. Chem. ReV. 1999, 99, 2235-2268.
‡ University of Padova.
4766 Inorganic Chemistry, Vol. 44, No. 13, 2005
10.1021/ic048486y CCC: $30.25
© 2005 American Chemical Society
Published on Web 05/25/2005

Technetium(V) and Rhenium(V) Phenylimido Complexes
metal fragment including the phenylimido core [Md NPh]3+
(M ) Tc, Re) for the following reasons. Despite several Tc-
imido complexes reported in the literature, the transfer of
this chemistry at non-carrier-added (nca) level, trying to
mimic the rich substitution reactivity exhibited by the oxo
core, has always met severe obstacles. So far, the 99mTc-
imido core has been claimed only among a series of cores
suitable for the development of new radiopharmaceuticals
in a patent report.11 As far as rhenium is concerned, a few
examples of nca 188Re species are reported as potential target-
specific radiopharmaceuticals. For instance, compounds of
general formula 188Re(NC6H4-X)Cl3(PPh3)2 contain a para-
substituted phenylimido ligand functionalized with a car-
boxylic group conjugated to various cholesterol derivatives12
or to a chlorambucil analogue.13 Further studies on the rhen-
ium phenylimido chemistry have been focused on the deriv-
atization of the phenylimido group only,14 or the replacement
of aryl for alkyl substituents at the imido unit.15,16 However,
these compounds are hydrolytically unstable under biological
conditions. In our opinion, this instability could arise from
the presence of several monodentate ligands in the coordina-
tion sphere. We thought, conversely, that the phenylimido
core would be stabilized by substitution of monodentate for
particular polydentate ligands. Taking into account that
imido-Tc and -Re derivatives strongly prefer the presence
of phosphine ligands (analogously to all other compounds
containing metal-nitrogen multiple bonds), we investigated
the possibility of introducing a aminodiphosphines (PNP)
in the phenylimido metal fragment [M(NPh)(PNP)]3+ using
a synthetic approach already successfully utilized in the case
of the “supernitrido” moiety.
Scheme 1
the striking differences in the main features of the synthons
(i.e., metal oxidation state and electronic configuration, type
of ancillary ligands, molecular weight and lipophilicity, etc.),
the ability to obtain stable mixed-ligands complexes confirms
the correctness of this design.
In more detail, in the case of [TcI(CO)3(OH2)3]+, the Tc-
(I) ion is stabilized by the carbonyl ligands arranged in a
facial fashion, thereby labilizing the trans positioned water
molecules, and making them susceptible for exchange with
a tridentate ligand such as histidine.5 Several biomolecules
including biotin, enkephalin, and vitamin B12 conjugates
have been inserted at the Nꢀ-position of the imidazolic
heterocycle of histidine6 providing further support of the
efficacy of the approach.
In the case of [TcV(N)(PNP)]2+, the distinctive [Tc(N)]2+
core is stabilized by a particular diphosphine ligand (having
a five-member spacer including the nitrogen atom of a
tertiary amine (PN(R)P)), adopting again a facial arrange-
ment. The equatorially and cis-positioned phosphorus donors
trans labilize the chloride groups in the intermediate species
Tc(N)(PNP)Cl2, making possible a straightforward formation
of mixed heterocomplexes of the type fac-[M(N)(PN(R)P)-
(X-Y)]+/0, where X-Y is a bidentate ligand like S,O-
cysteine or S,N-cysteine,7 and S,S-dithiolate.8 Representative
biomolecules such as 2-methoxyphenyl piperazines9 or
benzodiazepine analogues10 have been incorporated into the
cysteine framework giving stable metal conjugates.
In principle, in addition to the already investigated
[M(N)]2+ core, further moieties including metal nitrogen
multiple bonds, i.e., metal-imido, -hydrazido, and -dia-
zenido could be envisaged in order to exploit a synthetic
strategy comprising a substitution-inert metal fragment. Our
first effort in this direction was aimed at the study of a stable
In this study we report on a series of cationic complexes
of the type [M(NPh)X2(PNP)]+ (1-4), in which the relevant
aminodiphosphine predominantly adopts a meridional coor-
dination. In the case of rhenium, further substitution of
monodentate halide and/or ethoxide groups for bidentate
chelating ligand (H2L-L) yield dissymmetric mixed-ligand
complexes of the general formula fac-[Re(NPh)(L-L)-
(PNP)]+ (5-10), via rearrangement of the aminodiphosphine
into a facial configuration. Comparison of phenylimido [Re-
(NPh)(L-L)(PNP)]+ with previously synthesized nitrido
derivatives Re(N)(L-L)(PNP) is discussed.
(3) Alberto, R.; Schibli, R.; Waibel, R.; Abram, U.; Schubiger, A. P.
Coord. Chem. ReV. 1999, 190-192, 901-919 and references therein.
(4) Bolzati, C.; Boschi, A.; Uccelli, L.; Tisato, F.; Refosco, F.; Cagnolini,
A.; Duatti, A.; Prakash, S.; Bandoli, G.; Vittadini, A. J. Am. Chem.
Soc. 2002, 124, 11468-11479.
Experimental Section
Caution! 99Tc is a weak â-emitter (Eâ ) 0.292 MeV, t1/2 ) 2.12
× 105 years). All manipulations were carried out in laboratories
approved for low-level radioactivity using monitored hoods and
(5) Egli, A.; Alberto, R.; Tannahill, L.; Schibli, R.; Abram, U.; Schaffland,
R.; Tourwe, D.; Jeannin, K.; Iterbeke, K.; Schubiger, P. A. J. Nucl.
Med. 1999, 40, 1913-1917.
(6) Van Staveren, D. R.; Mundwiler, S.; Hoffmanns, U.; Pak, J. K.;
Spingler, B.; Metzler-Nolte, N.; Alberto, R. Org. Biomol. Chem. 2004,
2, 2593-2603.
(11) Archer, C. M.; Dilworth, J. R.; Jobanputra, P.; Thomson, R. M. Patent
n. WO 91/03262, 1991.
(7) Bolzati, C.; Benini, E.; Cazzola, E.; Jung, C.; Tisato, F.; Refosco, F.;
Spies, H.; Uccelli, L.; Duatti, A. Bioconjugate Chem. 2004, 15, 628-
637.
(12) Arterburn, J. B.; Hall, K. A.; Fogarty, I. M.; Goreham, D. M.; Bryan,
J. C.; Ott, K. C. Radiochim. Acta 1997, 79, 119-121.
(13) Arterburn, J. B.; Fogarty, I. M.; Hall, K. A.; Ott, K. C.; Bryan, J. C.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2877-2878.
(14) Arterburn, J. B.; Venketeswara Rao, K.; Goreham, D. M.; Valenzuela,
M. V.; Holguin, M. S.; Hall, K. A.; Ott, K. C.; Bryan, J. C.
Organometallics 2000, 19, 1789-1795.
(8) Boschi, A.; Bolzati, C.; Benini, E.; Malago`, E.; Uccelli, L.; Duatti,
A.; Piffanelli, A.; Refosco, F.; Tisato, F. Bioconjugate Chem. 2001,
12, 1035-1042.
(9) Bolzati, C.; Mahmood, A.; Malago`, E.; Uccelli, L.; Boschi, A.; Jones,
A. G.; Refosco, F.; Duatti, A.; Tisato F. Bioconjugate Chem. 2003,
14, 1231-1242.
(15) Chatt, J.; Dilworth, J. R.; Leigh, G. J. J. Chem. Soc. A 1970, 2239-
2243.
(10) Boschi, A.; Uccelli, L.; Duatti, A.; Bolzati, C.; Refosco, F.; Tisato,
F.; Romagnoli, R.; Baraldi, P.; Varani, K.; Borea, P. Bioconjugate
Chem. 2003, 14, 1279-1288.
(16) (a) Chatt, J.; Dosser, R. J.; King, F.; Leigh, G. J. J. Chem. Soc., Dalton
Trans. 1976, 2435-2440. (b) Ondraceck, A. L.; Fanwick, P. E.;
Walton, R. A. Inorg. Chim. Acta 1998, 278, 245-249.
Inorganic Chemistry, Vol. 44, No. 13, 2005 4767

Porchia et al.
gloveboxes. When handled in milligram amounts, 99Tc does not
present a serious health hazard because common laboratory
glassware provides adequate shielding. Bremsstrahlung is not a
significant problem due to the low energy of the â-particles.
However, normal radiation safety procedures must be used at all
times, especially with solid sample, to prevent contamination and
inhalation.
and dried in a vacuum pump. The oily residue was dissolved in
the minimum amount of dichloromethane, ethanol was added, and
the mixture was refrigerated overnight at 4 °C. A white precipitate
was formed which was filtered and dried under vacuum. Yield:
1
65%. H NMR (CDCl3, ppm): 7.40-7.20 (m, 20H, Harom), 2.95
(m, 4H, CH2-CH2), 2.68 (s, 3H, CH3), 2.42 (m, 4H, CH2-CH2).
31P{H} NMR (CDCl3, ppm): -20.0 (s). 13C{H}(CDCl3, ppm): 22.2
(d, 1JC-P ) 15 Hz, CH2-PPh2), 39.6 (s, N-CH3), 52.6 (d, 2JC-P
)
Materials. All solvents and commercially available substances
were of reagent grade and used without further purification.
Tetrahydrofuran was distilled under dinitrogen from the potassium
29 Hz, CH2-CH2-PPh2), aromatic C: 128.9(d, JC-P ) 7 Hz),
129.5, 130.7 and 132.7 (d, JC-P ) 19 Hz).
17
ketyl of benzophenone. The complexes Re(NPh)Cl3(PPh3)2 and
Synthesis of the Complexes. mer,cis-[Re(NPh)Cl2(PNHP)]Cl,
1. To a suspension of Re(NPh)Cl3(PPh3)2 (104 mg, 0.11 mmol) in
dichloromethane (15 mL) an excess of PNHP‚HCl (75 mg, 0.16
mmol) dissolved in dichloromethane (3 mL) with 50 µL of
triethylamine (0.38 mmol) was added dropwise. The reaction
mixture was refluxed for 2 h and then stirred overnight at room
temperature. The resulting solution was olive-green. The solvent
was removed and the green solid was washed with diethyl ether
and water, and dried under vacuum. The 31P NMR spectrum of
such solid in CDCl3 showed two peaks at 4.3 and 8.4 ppm, which
suggested the presence of two products. A pure product was
obtained from a 1:2 dichloromethane/n-hexane mixture. Grey-blue
crystals of 1 were obtained (final yield 50%). 1 is stable in air and
soluble in dichloromethane and chloroform, quite soluble in ethanol
and methanol, and insoluble in water, n-hexane, and diethyl ether.
Anal. calcd. for ReN2C34H34P2Cl3: C, 49.5; N, 3.4; H, 4.1. Found:
99Tc(NPh)Cl3(PPh3)218 were prepared according to literature meth-
ods.
Instrumentation. Elemental analyses were performed on a Carlo
Erba 1106 elemental analyzer. 1H, 13C, and 31P NMR spectra were
recorded on a Bruker AMX-300 instrument, using SiMe4 as internal
reference (1H, 13C) and 85% aqueous H3PO4 as external reference
(31P).
Synthesis of the Ligands. Bis[(2-diphenylphosphino)ethyl]amine
hydrochloride (PNHP‚HCl) was prepared according to the literature
method.19
Bis[(2-diphenylphosphino)ethyl]methylamine (PNMeP). Diphe-
nylphosphine (5.0 g, 26.9 mmol) was transferred into a two-necked
round-bottom flask containing tetrahydrofuran (50 mL) under
dinitrogen, and n-buthyllithium (2.5 M) in n-hexane (11 mL, 27
mmol) was slowly added to the solution giving rise to an orange
color. The mixture was cooled to -78 °C in an acetone/liquid
nitrogen slurry. N-Methylbis(2-chloroethyl)amine hydrochloride (2.6
g, 16.6 mmol), dissolved in tetrahydrofuran (50 mL), was neutral-
ized by adding n-buthyllithium (6 mL, 15.6 mmol) dropwise and
added to the reaction mixture using a pressure-equalizing funnel.
The addition was done quite rapidly to avoid decomposition of the
neutralized amine. The reaction mixture was allowed to warm to
room temperature, over a period of at least 2 h, and then stirred
overnight at room temperature. The resulting colorless solution was
cooled to 0 °C and degassed water (50 mL) was added dropwise.
The mixture was transferred into a separating funnel and treated
with freshly distilled (under dinitrogen) diethyl ether (2 × 50 mL).
The collected organic phases were rotoevaporated until an oil was
obtained, which, by treatment with degassed methanol, separated
a white solid. The product was recovered, washed with methanol,
and dried in a vacuum pump. Yield: 68%. In the case that no white
solid formed by addition of methanol, chromatographic purification
was necessary (silica gel column, chloroform/diethyl ether 1:1).
The desired product was eluted first and concentration of the first
fractions led to an oil, which was treated again following the above
procedure.1H NMR (CDCl3, ppm): 7.40-7.20 (m, 20H, Harom), 2.93
(m, 4H, CH2-CH2), 2.68 (s, 3H, CH3), 2.42 (m, 4H, CH2-CH2).
31P{H} NMR (CDCl3, ppm): -19.1. 13C{H}(CDCl3, ppm): 22.1
1
C, 50.9; N, 3.4; H, 5.1. H NMR (CDCl3, ppm): 10.06 (b, 1H,
NH), 8.07 (m, 4H, PPh2), 7.74 (d, 2H, o-NPh), 7.50 (m, 11H,
PPh2+ p-NPh), 7.02 (m, 6H, PPh2) 6.87 (t, 2H, m-NPh), 4.01 (bt,
2H, CH2), 3.39 (bm, 2H, CH2), 3.22 (bm, 4H, CH2). 31P{H} NMR
(CDCl3, ppm): 8.5 (s). 13C{H} NMR (CDCl3, ppm): 32.00 (d,
1JCP ) 30 Hz; >P-CH2-), 58.13 (s, -CH2-NH-). 12 aromatic
carbons: 125.5, 127.7, 128.1, 128.2, 128.5, 128.7, 129.6, 130.1,
131.0, 131.2, 133.2, 153.5 (s, ipso-CNPh).
mer,cis-[99Tc(NPh)Cl2(PNHP)]Cl, 2. To a solution of Tc(NPh)-
Cl3(PPh3)2 (45 mg, 0.05 mmol) in dichloromethane/methanol (5
mL/2 mL) a 1:1 equivalent of PNHP‚HCl (29 mg, 0.06 mmol) and
20 µL of triethylamine (0.15 mmol) was added under stirring. The
brown mixture turned brown-green in 2 min. After 3 h the solution
was taken to dryness with a flow of dinitrogen. The oily residue
was treated with diethyl ether and the resulting brown-green solid
was filtered. The crude solid was washed on the filter with acetone
(2 mL). The resulting light green solid was dried under dinitrogen
(yield 22 mg, 60%). The product is soluble in chlorinated solvents
and acetonitrile, slightly soluble in alcohols, insoluble in diethyl
ether. Crystals suitable for X-ray diffraction studies were collected
from a 1:1 dichloromethane/n-hexane mixture. Anal. Calcd. for
TcN2C34H34P2Cl3: C, 55.5; N, 3.8; H, 4.6. Found: C, 54.6; N, 3.6;
1
H, 4.8. H NMR (CDCl3, ppm): 9.70 (bs, 1H, NH), 8.06 (m, 6H,
(d, 1JC-P ) 15 Hz, CH2-PPh2), 39.6 (s, N-CH3), 52.4 (d, 2JC-P
)
PPh2+ o-NPh), 7.51 (m, 11H, PPh2 + p-NPh), 7.02 (m, 6H, PPh2),
6.86 (t, 2H, m-NPh), 3.97 (bt, 2H, CH2), 3.34 (bm, 6H, CH2). 31P-
{H} NMR (CDCl3, ppm): 31.6 (bs).
29 Hz, CH2-CH2-PPh2), aromatic C: 128.9(d, JC-P ) 7 Hz),
129.5, 130.5 and 132.7 (d, JC-P ) 19 Hz).
Bis[(2-diphenylphosphino)ethyl]methylamine hydrochloride
(PNMeP‚HCl). The synthesis procedure is analogous to that
reported above for PNMeP, but the workup of the product is
different. After the reaction quenching with degassed water and
extraction with n-hexane, hydrochloric acid (2 N, 50 mL) was added
under vigorous stirring. A milky oil was formed which was collected
fac,cis-[Re(NPh)Cl2(PNMeP)]Cl, 3a. To a suspension of Re-
(NPh)Cl3(PPh3)2 (145 mg, 0.16 mmol) in dichloromethane (15 mL)
a slight excess of PNMeP (86 mg, 0.17 mmol) was added. The
reaction mixture was refluxed for 24 h. The volume of the resulting
green-yellow solution was reduced to 3-4 mL and diethyl ether
(10 mL) was added. A TLC analysis of the precipitate showed a
mixture of different products, so separation by means of a
chromatographic column was performed (silica gel, chloroform/
ethanol 3:2). Two yellow fractions and a green fraction were
collected. The green product was identified as [Re(NPh)Cl2-
(PNMeP)]Cl (yield 47%). Anal. Calcd. for ReN2C35H36P2Cl3: C,
(17) La Monica, G.; Cenini, S. Inorg. Chim. Acta 1978, 29, 183-187.
(18) Nicholson, T.; Davison, A.; Jones, A. G. Inorg. Chim. Acta 1991,
187, 51-57.
(19) Wilson, M. E.; Nuzzo, R. G.; Whitesides G. M. J. Am. Chem. Soc.
1978, 100, 2269-2270.
4768 Inorganic Chemistry, Vol. 44, No. 13, 2005

Technetium(V) and Rhenium(V) Phenylimido Complexes
1
50.1; N, 3.3; H. 4.3. Found: C. 49.6; N, 3.3; H. 4.4. H NMR
3.2; H, 5.1. 31P {H} NMR (CDCl3, ppm) 19.52 (s). 13C{H} NMR
(CDCl3, ppm): 29.72 (d, JCP ) 32 Hz; >P-CH2-), 47.53 (s,
-CH2-NH-), 15 aromatic carbons: 115.4, 120.4, 122.3, 128.8,
128.9, 129.1, 129.3, 129.5, 130.8, 131.1, 131.3, 131.5, 131.7, 134.3,
160.9 (s, ipso-CNPh).
1
(CDCl3, ppm): 7.93 (t, 1H, p-NPh), 7.78 (d, 2H, o-NPh), 7.51-
7.31 (m, 12H, PPh2), 7.17(m, 8H, PPh2, 6.96 (m, 6H, PPh2 +
m-NPh), 4.08(m, 2H CH2), 3.45 (m, 2H CH2), and 2.95 (m, 4H
CH2), 2.61 (s, 3H, CH3). 31P{H} NMR (CDCl3, ppm): 19.9 (s).
cis,fac-Re(NPh)Cl3(PNMeP)‚HCl, 3b. In acetonitrile (15 mL),
Re(NPh)Cl3(PPh3)2 (100 mg, 0.11 mmol) and PNMeP‚HCl (86 mg,
0.17 mmol) were mixed. After refluxing for 15 min the reaction
mixture became clear light green, but with continued reflux a green
solid started to precipitate. After 4 h the mixture was allowed to
return to room temperature and filtered. The green powder was
washed with diethyl ether and resulted soluble in dichloromethane,
quite soluble in chloroform, and almost insoluble in diethyl ether
and benzene. NMR analysis evidenced the presence of two isomers
in solution (total yield 70%). Anal. calcd. for ReN2C35H37P2Cl4:
fac-[99Tc(NPh)(O,O-cat)(PNHP)]ClO4, 6. To a solution of 2
(26 mg, 0.04 mmol) in methanol (5 mL), catechol (5.2 mg, 0.047
mmol) and triethylamine (10 µL, 0.08 mmol) were added. The
mixture immediately turned deep purple. The solution was stirred
for 4 h at room temperature and then concentrated to 2 mL by a
dinitrogen flow. A drop of saturated NaClO4 solution in methanol
was added to the solution. After 1 day, dark-grey crystals were
formed; they were collected on a filter and washed with a 1 × 2
mL of methanol. Yield 63%. Anal. calcd. for TcN2C40H38O2P2-
ClO4: C, 57.3; N, 3.3; H, 4.6. Found: C, 57.0; N, 3.1; H, 4.8. 1H
NMR (CDCl3, ppm): 7.77 (m, 4H, NPh and PPh2), 7.49 (t, 3H,
NPh and PPh2), 7.37 (m, 4H, PPh2), 7.22 (m, 4H, PPh2), 7.14 (m,
2H, PPh2), 7.01 (m, 8H, NPh and PPh2), 6.81 (dd, 2H, catechol),
6.71 (dd, 2H, catechol), 3.5-2.7 (m, 8H, CH2CH2), 3.13 (bs, 1H,
NH). 31P{H} NMR (CDCl3, ppm) 46.5 (bs). 13C{H} NMR (CDCl3,
1
C, 48.0; N, 3.2; H, 4.3. Found: C, 47.7; N, 3.3; H, 4.1. H NMR
(CD2Cl2, ppm): 7.96 (m, 2H, PPh2), 7.85 (m, 2H, PPh2), 7.70 (m,
2H, PPh2 ), 7.55(m, 2H, PPh2), 7.45 (t, 1H, p-NPh), 7.37 (m, 4H,
PPh2), 7.21 (m, 4H, PPh2), 7.10 (m, 4H, PPh2 ), 6.73 (t, 2H,
m-NPh), 6.59 (d, 2H, o-NPh), 3.37 (m, 6H, CH2), 3.07 (m, 2H,
CH2), 2.99 (d, 1.5 H, CH3), 2.68 (d, 1.5H, CH3).31P{H} NMR (300
MHz,CD2Cl2, ppm): -25.1 (s); -26.9 (s).
mer,trans-[Re(NPh)Cl2(PNMeP)]Cl, 3c. Dissolution of cis,fac-
[Re(NPh)Cl3(PNMeP)]‚HCl 3b in dichloromethane in the presence
of triethylamine gave quantitatively the deprotonated species mer,-
trans-[Re(NPh)Cl2(PNMeP)]Cl. Compound 3c was identified in
1
ppm): 28.85 (d, JCP ) 29 Hz; >P-CH2-), 46.54 (s, -CH2-
NH-), 15 aromatic carbons: 114.9, 120.0, 124.0, 128.6, 128.8,
129.2, 129.4, 129.7, 130.5, 130.9, 131.1, 131.8, 134.1, 134.3, 159.7
(s, ipso-CNPh).
fac-[Re(NPh)(O,O-cat)(PNMeP)]Cl, 7. To a suspension of Re-
(NPh)Cl3(PPh3)2 (90 mg, 0.1 mmol) in dichloromethane (10 mL)
PNMeP (53 mg, 0.11 mmol) was added at room temperature. After
5 min, catechol (15 mg, 0.14 mmol) and 30 µL of triethylamine
(0.23 mmol) were added and the reaction mixture was refluxed for
30 min. The resulting solution was dark brown and was stirred at
room temperature for further 2 h. The solvent was removed under
vacuum and the brown residue was washed with diethyl ether. The
brown solid was purified by means of a SiO2 column using a
chloroform/methanol 85:15 mixture as eluant. Three main fractions
were separated: a dark brown, a green-yellow, and a red one (the
most intense). The last was identified as 7. Yield 30%. Anal. calcd.
for ReN2C41H40P2O2Cl: C, 56.2; N, 3.2; H, 4.6. Found: C, 56.5;
1
solution and not isolated. H NMR (CDCl3, ppm): 7.76 (m, 8H,
PPh2); 7.42 (t, 1H, p-NPh), 7.19 (m, PPh2, 12H), 6.71 (m, 4H,
NPh), 3.25 (m, 8H, CH2-CH2), 2.00 (s, 3H, N-CH3). 31P {H}
NMR (CDCl3, ppm): -24.4 (s).
mer,cis-[Re(NPh)(OEt)Cl(PNHP)]Cl, 4. To a suspension of Re-
(NPh)Cl3(PPh3)2 (52 mg, 0.06 mmol) in ethanol (15 mL), an excess
of PNHP‚HCl (43 mg, 0.089 mmol) dissolved in ethanol (3 mL)
with 25 µL of triethylamine (0.19 mmol) was added dropwise. The
reaction mixture was refluxed for 4 h giving a green-yellow solution.
The volume was reduced under a dinitrogen stream and diethyl
ether was added; after a few hours large bright blue crystals of 4
had formed. Yield: 40%. Anal. calcd. for ReN2C36H39P2Cl2O: C,
1
N, 3.3; H, 4.6. H NMR (CDCl3, ppm): 7.77 (m, 4H, NPh and
1
PPh2), 7.47 (m, 9H, NPh and PPh2), 7.05 (m, 12H, NPh and PPh2),
6.88 (2H, dd, cat), 6.71 (dd, 2H, cat), 3.73 (b, 4H, CH2CH2), 3.41-
(b, 2H, CH2CH2), 2.85 (b, 2H, CH2CH2), 2.1 (s, 3H, CH3).31P {H}
(CDCl3, ppm) ) 16.3 (s).
51.8; N, 3.4; H, 4.7. Found: C, 52.0; N, 3.2; H, 4.8. H NMR
(CDCl3, ppm): 9.59 (b, 1H, NH), 8.00 (m, 4H, PPh2), 7.53 (m,
13H, PPh2 + NPh), 7.07 (m, 6H, PPh2), 6.87(t, 2H, m-NPh), 3.99
(bt, 2H, CH2), 3.41(bm, 2H, CH2), 3.18 (bm, 4H, CH2), 2.64 (q,
2H, O-CH2-CH3), -0.13 (t, 3H, O-CH2-CH3). 31P{H} NMR
(CDCl3, ppm): -0.2 (s).
fac-[Re(NPh)(O,O-gly)(PNHP)]Cl, 8. To a bluish solution of
1 (40 mg, 0.05 mmol) in dichloromethane (15 mL) ethylene glycol
(30 µL, 0.54 mmol) and triethylamine (20 µL, 0.15 mmol) were
added at room temperature. The reaction mixture was refluxed for
1 h and then stirred at room temperature for 24 h. The solution
became gray. After removal of the solvent with a flow of dinitrogen,
the oily residue was treated with diethyl ether and the resulting
gray solid was filtered. The crude solid was purified by washing,
on the filter, with n-hexane and water. Gray crystals of [Re(NPh)-
(O,O-gly)(PNHP)]Cl, suitable also for X-ray analysis, were obtained
by crystallization from a dichloromethane/n-hexane solution. Yield
60%. Anal. calcd. for ReN2C36H38O2P2Cl‚2H2O: C, 50.8; N, 3.3;
fac-[Re(NPh)(O,O-cat)(PNHP)]Cl, 5. To a bluish solution of
1 (40 mg, 0.05 mmol) in dichloromethane (10 mL), catechol (5
mg, 0.045 mmol) and 20 µL of triethylamine (0.15 mmol) were
added at room temperature. The reaction mixture immediately
turned red. The solution was stirred overnight at room temperature.
Then the solvent was removed, the residue was treated with diethyl
ether, and the resulting red-brown solid was filtered and washed
several times with n-hexane, diethyl ether, and water. 5 was obtained
with a final yield of 53%. Anal. calcd. for ReN2C40H38O2P2Cl‚
2H2O: C, 53.5; N, 3.1; H, 4.7. Found: C, 53.8; N, 3.2; H, 4.6. 1H
NMR (CDCl3, ppm): 7.81 (m, 4H, NPh and PPh2), 7.46 (m, 7H,
NPh and PPh2), 7.20 (m, 4H, PPh2), 7.05 (m, 10H, NPh and
PPh2),6.94 (dd, 2H, catechol), 6.71 (dd, 2H, catechol), 3.68 (m,
6H, CH2CH2), 3.68 (bs, 1H, NH), 2.95 (m, 2H, CH2CH2).31P{H}
NMR (CDCl3, ppm) 19.5 (s). A stoichiometric amount of NBu4-
BF4 was added to a dichloromethane solution of 5 and by addition
of n-hexane a red-orange product quantitatively precipitated
characterized as [Re(NPh)(PNHP)(O,O-cat)]BF4. Anal. calcd. for
ReN2C40H38O2P2BF4: C, 52.6; N, 3.1; H, 4.2. Found: C, 52.9; N,
1
H, 5.0. Found: C, 50.6; N, 3.3; H, 5.2. H NMR (CDCl3, ppm):
7.74-6.91 (m, 25H, NPh and PPh2), 5.11 (bs, 1H, NH), 4.78 (d,
2H, OCH2CH2O), 4.60 (d, 2H, OCH2CH2O), 3.80 (m, 2H;
PCH2CH2N), 3.16 (m, 2H; PCH2CH2N), 3.06 (m, 2H; PCH2CH2N),
2.90 (m, 2H; PCH2CH2N).31P{H} NMR (CDCl3, ppm) 17.3. 13C-
1
{H} NMR (CDCl3, ppm): 28.78 (d, JCP ) 32 Hz; >P-CH2-),
47.70 (s, -CH2-NH-), 78.85 (s, O-CH2-), 122.24 (s, o-CNPh),
3
127.46 (s, p-CNPh) 128.64 (d, JCP ) 11 Hz; m-CPPhexo) 128.92 (d,
3JCP ) 10 Hz; m-CPPhendo) 129.37 (s, m-CNPh) 130.39 (s, p-CPPhendo
)
Inorganic Chemistry, Vol. 44, No. 13, 2005 4769

Porchia et al.
Table 1. X-ray Crystal Data, Data Collection Parameters, and Refinement Parameters of 1‚1/2CH2Cl2, 2‚1/2CH2Cl2, 4, 5‚2H2O, and 8‚2H2O
1‚1/2CH2Cl2
2‚1/2CH2Cl2
4
5‚2H2O
8‚2H2O
formula
C34H34Cl3N2P2Re‚
1/2CH2Cl2
867.58
monoclinic
P21/c
15.081(3)
12.146(2)
20.418(3)
C34H34Cl3N2P2T‚
1/2CH2Cl2
779.38
monoclinic
P21/c
15.106(3)
12.117(2)
20.481(4)
C36H39Cl2N2OP2Re
C40H42ClN2O4P2Re
C36H42ClN2O4P2Re
fw
834.73
triclinic
P1h
898.34
monoclinic
C2/c
34.801(7)
24.782(5)
10.671(2)
850.31
triclinic
P1h
cryst syst
space group
a, (Å)
b, (Å)
c, (Å)
R, (deg)
â, (deg)
γ, (deg)
V, (Å3)
Z
11.752(2)
12.519(3)
15.482(3)
75.97(3)
68.90(3)
64.96(3)
1914.4(7)
2
1.448
3.425
0.71073
0.042
0.100
12.733(3)
17.032(3)
18.806(4)
107.01(3)
90.85(3)
98.11(3)
3854(1)
4
1.465
3.343
0.71073
0.064
0.158
107.05(3)
107.25(3)
103.84(3)
3576(1)
4
3580(1)
4
8936(3)
8
F
calcd (g cm-3
)
1.612
3.814
0.71073
0.043
0.081
0.702
1.446
0.817
0.71073
0.058
0.156
0.879
1.335
2.887
0.71073
0.060
0.171
0.820
µ, mm-1
λ source (Å)
R(F)a [I > 2σ(I)]
Rw(F)b [I > 2σ(I)]
GOFc
0.886
0.822
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) {∑[w(|Fo | - |Fc |)2]/∑[w(|Fo |)2]}1/2
.
c GOF ) {∑[w(|Fo | - |Fc |)2]/(ndata - nvar)]}1/2
.
2
2
2
2
2
Scheme 2
130.84 (d, 2JCP ) 8 Hz; o-CPPhendo) 131.18 (s, p-CPPhexo) 132.89 (s,
ipso-CPPhendo) 133.58 (s, ipso-CPPheso) 134.21 (d, JCP ) 8 Hz;
2
o-CPPhexo) 158.07 (s, ipso-CNPh).
fac-[Re(NPh)(O,O-gly)(PNMeP)]Cl, 9. To a 20-mL solution
of 3a in acetonitrile (50 mg, 0.06 mmol) ethylene glycol (30 µL,
0.54 mmol) and triethylamine (20 µL, 0.15 mmol) were added.
The reaction mixture was refluxed for 24 h. After that the solvent
was evaporated and the dark green oily residue was dissolved in
dichloromethane. The excess of ethylene glycol was removed by
water extraction. The organic phase was dried and a green powder,
characterized as 9, was recovered (yield 43%). Anal. calcd. for
ReN2C37H40O2P2Cl: C, 53.6; N, 3.4; H, 4.9. Found: C, 53.9; N,
Structures were solved by Patterson syntheses and all nonhy-
drogen atoms were taken from a series of full-matrix least-squares
refinement cycles based on F2 with the program system SHELX-
TL,20 followed by difference Fourier syntheses. All nonhydrogen
atoms were refined with anisotropic thermal parameters, while
hydrogen atoms, except those of the CH2Cl2 and H2O of crystal-
lization, were placed at calculated positions and allowed to ride on
their corresponding carbon atoms with isotropic thermal parameters
1.2 times the value for Ueq of the bonding atom. Final difference
maps contained no features of chemical significance.
1
3.4; H, 4.7. H NMR (CDCl3, ppm): 7.48-6.98 (m, 25H, NPh
and PPh2); 4.91-4.76 (m, 4H, OCH2CH2O), 3.58 (m, 2H, CH2),
3.27 (m, 2H, CH2), 2.34 (s, 3H, N-CH3), 2.47 (m, 4H, CH2). 31P-
{H}NMR (CDCl3, ppm) 24.3 (s).
fac-[Re(NPh)(O,N-ap)(PNMeP)]Cl, 10. To a suspension of Re-
(NPh)Cl3(PPh3)2 (90 mg, 0.1 mmol) in dichloromethane (15 mL),
PNMeP (53 mg, 0.11 mmol) was added at room temperature. After
5 min 1,2 aminophenol (17 mg, 0.16 mmol) and 20 µL of
triethylamine were added and the reaction mixture was refluxed
and over 10 min the solution turned from green to dark brown.
Then it was refluxed for 30 min and stirred overnight at room
temperature. The solvent was removed and the residue was treated
with diethyl ether. The red-brown solid was filtered and redissolved
in dichloromethane. Elution from a silica column with chloroform/
methanol 85:15 separated a yellow uncharacterized byproduct and
the red fac-[Re(NPh)(O,N-ap)(PNMeP)]Cl. (Yield 38%). Anal.
calcd. for ReN3C42H40P2ClO: C, 56.9; N, 4.7; H, 4.5. Found: C,
Results
Synthesis. The aminodiphosphine ligand PNHP‚HCl was
prepared according to the literature,19 whereas PNMeP‚HCl
(see Scheme 2) was obtained by alkylation of diphenylphos-
phine lithium salt with the appropriate dihalide N-methyl-
bis(2-chloroethyl)amine hydrochloride.
In the case of PNMeP, better yields were achieved by
addition of a neutralized batch of N-methylbis(2-chloroethyl)-
amine hydrochloride at low temperature (-78 °C). Low
amounts of unidentified impurities or of amine decomposition
species may prevent the precipitation of the final product
from the reaction mixture, and purification via column
chromatography on silica was necessary to recover pure
PNMeP.
1
57.2; N, 4.5; H, 4.6. H NMR (CDCl3, ppm): 7.8-6.9 (m, 25H,
NPh and PPh2); 6.80 (1H, dd, O,N-ap), 6.55 (m, 3H, O,N-ap),
3.74-2.72 (b, 8H, PCH2CH2N), 2.0 (s, 3H, CH3).31P{H} (CDCl3,
ppm) ) 17.8 (d), 10.1 (d).
X-ray Structure Determinations and Refinements. For the five
complexes 1‚1/2CH2Cl2, 2‚1/2CH2Cl2, 4, 5‚2H2O, and 8‚2H2O
intensity data were obtained at room temperature on a Siemens
Nicolet R3m/V four-circle diffractometer using the ω - 2θ scan
technique with Mo KR radiation from a graphite monochromator.
Intensities were corrected for Lorentz and polarization effects.
Equivalent reflections were merged, and absorption corrections were
made using the ψ-scan method. Space groups, lattice parameters,
and other relevant information are given in Table 1.
Ligand-exchange reactions of PNHP‚HCl with M(NPh)-
Cl3(PPh3)2 precursors in dichloromethane solutions, in the
presence of triethylamine, gave the intermediate complexes
mer,cis-[M(NPh)Cl2(PNHP)]Cl, (M ) Re, 1; M ) Tc, 2) in
moderate yields. The reaction mixture, from which the
(20) Sheldrick, G. M. SHELXTL - NT V5.1. Program package for Crystal
Structure Refinement; Bruker AXS, Inc.: Madison, WI, 1999.
4770 Inorganic Chemistry, Vol. 44, No. 13, 2005

Technetium(V) and Rhenium(V) Phenylimido Complexes
Scheme 3
The diamagnetism shown by this class of mixed-ligand
complexes is in agreement with low-spin d2 distorted
octahedral geometries typical of M(V) species including a
phenylimido unit (vide infra, X-ray description). Thus, the
combination of proton and phosphorus NMR signals allows
a complete characterization of the complexes in solution. In
the case of technetium compounds 2 and 6 31P NMR signals
show broad profiles at ambient temperature. Such behavior
was previously attributed to the coupling of the 31P nuclei
with the quadrupolar 99Tc (I ) 9/2) center.23 In any case,
31P NMR is a powerful tool for a rapid evaluation of the
course of the reactions, as the signals of the various species
are spread over a wide range (roughly from -30 to +50
ppm, see Table 2), thus recognizing the presence of the
starting product, uncoordinated ligand, and compounds
formed. The characteristic singlet of magnetically equivalent
diphosphine phosphorus moves downfield from ca. -20 ppm
(uncoordinated P) to positive values (in the range 4-46
ppm), the only exception being complexes 3b and 3c, for
which a slightly upfield shift is observed (two singlets at
-25.1 and -26.9 ppm, respectively for the mixture syn or
anti 3b (see Scheme 3), and one singlet at -24.4 ppm for
3c). The presence of the dissymmetric aminophenolate ligand
in complex 10 removes the magnetic equivalence of the
diphosphine phosphorus giving rise to two doublets.
rhenium complex 1 was collected, showed the presence of a
persistent contaminant formulated as mer-[Re(NPh)(OH)-
Cl(PNHP)]Cl on the basis of NMR spectroscopy.21 Recrys-
tallization of 1 from dichloromethane/ethanol mixtures
afforded the ethoxide derivative mer-[Re(NPh)(OEt)Cl-
(PNHP)]Cl, 4. Obtaining both trans imido-hydroxo and trans
imido-ethoxo derivatives indicated that the halide group
located trans to the phenylimido unit in the intermediate
complex mer,cis-[Re(NPh)Cl2(PNHP)]Cl, is labile.
The substitution reactions with the tertiary aminodiphos-
phine PNMeP were less clean and reproducible. A mixture
of products was always detected in dichloromethane solu-
tions, from which the fac,cis-[Re(NPh)Cl2(PNMeP)]Cl, 3a
was isolated after purification via column chromatography.
By using the hydrochloride salt of PNMeP and without
addition of triethylamine, a mixture of syn- and anti-Re-
(NPh)Cl3(PNMeP)‚HCl, 3b, was collected from acetonitrile
solutions (Scheme 3). Addition of triethylamine to a dichlo-
romethane solution of 3b yielded quantitatively the mer,-
trans-[Re(NPh)Cl2(PNMeP)]Cl complex 3c.
In the proton spectra of all complexes, the signals due to
the phenyl rings of the diphosphine present a characteristic
pattern, depending on the geometry of the complex, and can
be considered a kind of fingerprint of different isomers. Mer,-
cis species (1, 2, and 4) show three distinct multiplets
(counting for 4H, 10H, and 6H, respectively), fac,cis species
(3a, 3b, and mixed complexes 5-10) exhibit a more
complicated pattern, whereas the mer,trans isomer 3c pro-
vides the simplest spectrum of the series with only two
multiplets (counting for 8 and 12 H). The bridging methylene
protons of the PNP backbone show a series of multiplets
spread over the 4.0-2.5 ppm region. In PNHP containing
complexes, no coupling of the N-H protons with either
methylene protons and/or phosphorus is detected, the signal
being a temperature-independent broad singlet (γ1/2 ) ca.
20 Hz) in the -50 to 50 °C range in chloroform-d solutions.
The >N-H signal in equatorially coordinated mer-com-
plexes (Table 3) experiences a significant downfield shift
(δ in the range 9.59-10.06 ppm) compared to the corre-
sponding signal in fac-complexes (δ in the range 3.13-5.11
ppm). In the latter the important shielding is likely provided
by electron density coming from the trans positioned
phenylimido group, and enhanced by π-contribution in
catecholate containing compounds.
Halides and/or ethoxide (or hydroxide) groups incorporated
in mer,cis-[M(NPh)Cl2(PNHP)]Cl, 1 and 2, mer-[Re(NPh)-
(OEt)Cl(PNHP)]Cl, 4, and mer-[Re(NPh)(OH)Cl(PNHP)]Cl
were readily substituted with di-negative bidentate ligands
(H2L-L) in dichloromethane solutions to afford stable mixed
ligand compounds of the type fac-[M(NPh)(L-L)(PNHP)]-
Cl, 5, 6, and 8. In contrast, mixed ligand complexes
incorporating the PNMeP ligand (7, 9, and 10) were obtained
only in poor yields (30-50%) starting from the intermediate
facial complex 3a. The yield of the latter could be improved
via a direct reaction starting from Re(NPh)Cl3(PPh3)2 with
sequential addition of PNMeP and H2L-L. Analogous
direct reaction was successfully utilized in the synthesis of
5 and 8.
Characterization. Complexes 1-10 have been character-
ized by (i) elemental analyses, which are in good agreement
with the proposed formulations (see Experimental Section),
(ii) multinuclear NMR spectroscopy, (iii) X-ray structure
analyses of selected compounds, and (iv) comparison with
strictly analogous nitrido-Re and -Tc species synthesized
previously.4,8,22
As a general feature, it is important to note that, due to
the greater acidity of Tc(V) compared to Re(V), both 31P
1
(21) 31P{H} NMR (CDCl3, 300 MHz) δ ppm 4.3. H NMR (CDCl3, 300
1
and H signals experience larger downfield shift in techne-
MHz) δ ppm: 7.95 (m, 4H, PPh2), 7.59 (m, 6H, PPh2 + NPh), 7.47
(m, 7H, PPh2 + NPh), 7.10 (m, 6H, PPh2 + NPh), 6.92 (t, 2H, NPh).
The OH signal is not detected. The formulation of the complex is
based on the strict similarity of the aromatic protons pattern with that
exhibited by the mer,cis-ethoxide analogue 4.
tium complexes.
13C{1H} spectra of uncoordinated aminodiphosphines
exhibit carbon-phosphorus couplings for both ethylene
(22) Bolzati, C.; Refosco, F.; Cagnolini, A.; Tisato, F.; Boschi, A.; Duatti,
A.; Uccelli, L.; Dolmella, A.; Marotta, E.; Tubaro, E. Eur. J. Inorg.
Chem. 2004, 1902-1913.
(23) Abram, U.; Lorenz, B.; Kaden, L.; Scheller, D. Polyhedron 1988, 7,
285-291.
Inorganic Chemistry, Vol. 44, No. 13, 2005 4771

Porchia et al.
Table 2. Comparison of 31P Chemical Shift of Reagents and Products of This Study
class of
compounds
31P chemical
shift (ppm)
31P chemical
shift (ppm)
compound
compound
ligands
precursors
PNHP
Re(NPh)Cl3(PPh3)2
Tc(NPh)Cl3(PPh3)2
Re(NPh)Cl(OEt)(PPh3)2
mer,cis-[Re(NPh)(OEt)Cl(PNHP)Cl 4
mer,cis-[Re(NPh)(OH)Cl(PNHP)Cl 1a
mer,cis-[Re(NPh)Cl2(PNHP)]Cl 1
mer,cis-[Tc(NPh)Cl2(PNHP)]Cl 2
[Re(NPh)(O,O-cat)(PNHP)]Cl 5
[Tc(NPh)(O,O-cat)(PNHP)]ClO4 6
[Re(NPh)(O,O-gly)(PNHP)]Cl 8
-20.3
-19.6
12.2
-9.9
-0.2
4.3
PNMeP
Re(NPh)Cl3(PPh3)2
-19.3
-19.6
Re(NPh)Cl(OEt)(PPh3)2
-9.9
19.9
-25.1; -26.9
-24.4
intermediates
fac,cis-[Re(NPh)Cl2(PNMeP)]Cl 3a
cis,fac-Re(NPh)Cl3(PNMeP)‚HCl 3b (syn and anti)
mer,trans-[Re(NPh)Cl2(PNMeP)]Cl 3c
8.3
31.6
19.5
46.5
17.3
mixed products
[Re(NPh)(O,O-cat)(PNMeP)]Cl 7
16.3
[Re(NPh)(O,O-gly)(PNMeP)]Cl 9
[Re(NPh)(O,N-ap)(PNMeP)]Cl 10
24.3
17.8; 10.1
Table 3. Summary of Selected Structural and NMR Data
compound RedNPh (Å)
Re(NPh)Cl3(pbo)a
H
orto-NPh (ppm)
>N-H (ppm)
ipso-CNPh
ref
1.698(9)
1.702(6)
1.72(1)
7.74
7.74
7.42
7.50
7.22
7.41
7.18
7.15
27
mer,cis-[Re(NPh)Cl2(PNHP)]Cl 1
fac-[Re(NPh)(O,O-gly)(PNHP)]Cl 8
fac-[Re(NPh)(O,O-cat)(PNHP)]Cl 5
Re(NPh)Cl3(PPh3)2
10.06
5.11
3.55
153.5
158.1
160.9
this work
this work
this work
29
1.72(1)
1.726(6)
1.731(9)
1.740(6)
1.743(5)
b
trans-[Re(NPh)(OH)(cyclam)](ClO4)2
26
25
c
trans-[Re(NPh)(bpy)2(OEt)](PF6)2
mer,cis-[Re(NPh)(OEt)Cl(PNHP)]Cl 4
9.59
153.8
this work
a pbo ) 2-(2-pyridyl)benzoxazole. b cyclam ) 1,4,8,11-tetraazacyclotetradecane. c bpy ) 2,2′-bipyridine.
bridging carbons and orto-, meta-, and ipso-phenyl ones, as
detailed in the Experimental Section. Upon coordination,
some of these couplings are burnt, presumably due to the
quadrupolar relaxation induced by the metal on neighboring
atoms, as assessed by the appearance of singlet signals for
H-N[CH2-CH2-P<]2 and for quaternary phenyl carbons.
1H-13C two-dimensional HMQC and HMBC experiments
on the representative fac-[Re(NPh)(O,O-gly)(PNHP)]Cl com-
plex allow the complete assignment of the signals including
the ipso-carbon of the phenylimido group. The latter is by
far the most downfield shifted signal in the carbon spectrum
and appears as a singlet. As reported in Table 3, this signal
falls in the 158-161 ppm region in fac-type complexes, and
it is slightly upfield shifted in mer-type ones.
The five complexes whose crystal structures are described
in this work (1‚1/2CH2Cl2, 2‚1/2CH2Cl2, 4, 5‚2H2O, and 8‚
2H2O) are all monocationic species containing the [M(NPh)-
Figure 1. ORTEP representation of mer,cis-[Tc(NPh)Cl2(PNHP)]Cl 2
showing 40% probability thermal ellipsoids. Hydrogen atoms and CH2Cl2
hemimolecule are omitted for clarity. The cation mer,cis-[Re(NPh)Cl2-
(PNHP)]+ 1 is isostructural with 2.
(PNHP)]3+ synthon (M ) Re in 1‚1/2CH2Cl2, 4, 5‚2H2O, and
8‚2H2O; M ) Tc in 2‚1/2CH2Cl2), where the aminodiphos-
phine acts as a tridentate ligand. In all the compounds, the
metal shows a somewhat distorted octahedral coordination
environment. The arrangement of the phosphorus atoms
around the core metal is such that the conformation of the
complexes 1‚1/2CH2Cl2, 2‚1/2CH2Cl2 and 4 (Figures 1 and
2) is mer,cis, while it is fac in 5‚2H2O and 8‚2H2O (Figures
3 and 4). 1‚1/2CH2Cl2 and 2‚1/2CH2Cl2 show isomorphous
structures and, as a consequence, the most relevant bond
distances and angles are virtually identical (Table 4).
Unlike the other molecules here reported, two distinct
crystallographic complexes have been found in the unit cell
of 8‚2H2O. The two items have different orientation in the
lattice, yet retain comparable bond distances and angles, with
the only change being the conformation assumed by the two
five-membered rings formed upon coordination by the neutral
aminodiphosphine ligand. These rings are found almost
invariably in the twist-enVelope (C2) conformation, but for
the second orientation of 8‚2H2O, in which one of the rings
assumes the enVelope (Cs) pucker. In all the structures, the
orientation of the phenylimido ligand is roughly orthogonal
to the equatorial mean plane, with the dihedral angles being
96.9° for 1‚1/2CH2Cl2, 96.4° for 2‚1/2CH2Cl2, 90.2° for 4,
79.0° for 5‚2H2O, and 78.6 and 84.6° for the two orientations
of 8‚2H2O.
In mer,cis complexes 1‚1/2CH2Cl2, 2‚1/2CH2Cl2, and 4, the
metal lies off the P2NCl mean plane toward N(1) by 0.18
Å; the displacement grows to 0.40 Å in the fac complexes
5‚2H2O and 8‚2H2O, where the equatorial plane is repre-
sented by the P2O2 donor set. The remaining two positions
in the coordination sphere of the mer,cis complexes are filled
4772 Inorganic Chemistry, Vol. 44, No. 13, 2005

Technetium(V) and Rhenium(V) Phenylimido Complexes
Figure 4. ORTEP representation of a cation in 8 showing 40% probability
thermal ellipsoids. Chloride counteranion, hydrogen atoms, and the two
water molecules are omitted for clarity.
Figure 2. ORTEP representation of the cation in 4 showing 40%
probability thermal ellipsoids. Hydrogen atoms are omitted for clarity.
in Table 4 indicate that fac complexes 5‚2H2O and 8‚2H2O
show some severe distortions in the coordination environment
of the metal. In fact, cis angles range from 76.4 to 110.9°,
whereas the trans angles go as low as 154.7°. In our opinion,
such values far from the ideality are due to the restraints
imposed by the contemporary presence of two chelate
ligands, both of them making, upon coordination, five-
membered rings of narrow “bite” angles (ca. 80°).
Relevant nonbonding interactions have been detected only
in mer,cis complexes. In 1‚1/2CH2Cl2 and 2‚1/ CH2Cl2 the H
atom of N(2) is hydrogen bonded to Cl(3), with bond
distances of 2.17 and 2.19 Å and pertinent angles of 161°;
in 4, the same H atom interacts with the Cl(2) atom, with a
bond distance of 2.22 Å and pertinent angle of 158°.
Discussion
Figure 3. ORTEP representation of the cation in 5 showing 40%
probability thermal ellipsoids. Chloride counteranion, hydrogen atoms, and
the two water molecules are omitted for clarity.
It is worth noting that the few examples of structurally
authenticated technetium phenylimido compounds reported
so far comprise only phosphine and halide ligands, as
illustrated by the Tc(NPh)Cl3(PPh3)2 starting material.17
Attempts to replace monodentate groups with tetradentate
ligands, trying to mimic the rich substitution chemistry
exhibited by oxo-containing precursors, have produced poor
results. This behavior is likely determined by the strong
preference for π-acceptor ligands exhibited by the [Tc-
(NPh)]3+ core, and the consequent reluctance to release
P-based donors such as triphenylphosphine. Instead, rhenium
phenylimido chemistry appears to be more flexible, and
examples of phosphine-free compounds are reported. These
species generally contain other π-acceptor ligands, including
nitrogen-based aromatic heterocycles.24-27 The crucial pres-
by a couple of chloride ligands, but for complex 4, where
an ethoxide group replaces one of such chlorides. The
substitution causes the Re-N(1) distance to grow to 1.743-
(5) Å (Table 4), due to the strong trans effect of the ethoxide
residue.
In the fac complexes 5‚2H2O and 8‚2H2O, the mean plane
of the O,O bidentate ligand is nearly perpendicular (77.4°)
to that of the phenylimido moiety. The latter is also almost
orthogonal to the glycolate ligand of 8‚2 H2O (79.4 and 84.2°
for the two orientations). Oppositely, the O,O bidentate mean
plane is more or less coplanar with the ReP2 plane, with the
dihedral angle being 16.7° in 5‚2H2O, and 15.4 and 16.3°
for the two orientations of 8‚2H2O. The Re-N(2) bond
distance in the fac molecules is more than 0.10 Å longer
than that in the mer,cis complexes. A contribution to crystal
stability in fac complexes is provided by π-π interaction
of two phenyl rings incorporated in cis-positioned phosphorus
donors (Figures 3 and 4). This feature had already been
observed in similar nitrido complexes.4 Structural data listed
(24) Masood, Md. A.; Sullivan, B. P.; Hodgson, D. J. Inorg. Chem. 1994,
33, 5360-5362.
(25) Bakir, M.; Paulson, S.; Goodson, P.; Sullivan, B. P. Inorg. Chem.
1992, 31, 1127-1129.
(26) Wang, Y.-P.; Che, C.-M.; Wong, K.-Y.; Peng, S.-M. Inorg. Chem.
1993, 32, 5827-5832.
(27) Gangopadhyay, J.; Sengupta, S.; Bhattacharyya, S.; Chakraborty, I.;
Chakravorty, A. Inorg. Chem. 2002, 41, 2616-2622.
Inorganic Chemistry, Vol. 44, No. 13, 2005 4773

Porchia et al.
Table 4. Selected Bond Distances (Å) and Bond Angles (deg) of 1‚1/2CH2Cl2, 2‚1/2CH2Cl2, 4, 5‚2H2O, and 8‚2H2O
1‚1/2CH2Cl2
2‚1/2CH2Cl2
4
5‚2H2O
8‚2H2O
Ma-P(1)
2.427(2)
2.422(2)
1.702(6)
2.169(5)
2.415(2)
2.379(2)
2.437(2)
2.424(2)
1.699(4)
2.148(4)
2.415(2)
2.413(2)
2.440(2)
2.456(2)
1.743(5)
2.161(5)
2.415(2)
2.422(4)
2.435(4)
1.72(1)
2.26(1)
2.448(3); 2.421(4)
2.423(3); 2.410(4)
1.70(1); 1.736(8)
2.293(9); 2.304(9)
M-P(2)
M-N(1)
M-N(2)
M-Cl(1)
M-Cl(2)
M-O(Et)
1.934(5)
M-O(1)
1.975(9)
2.061(8)
99.8(1)
1.996(7); 1.983(9)
1.984(7); 1.984(9)
101.9(1); 103.9(1)
M-O(2)
P(1)-M-P(2)
Cl(2)-M-N(1)
Cl(1)-M-N(2)
P(1)-M-N(2)
P(2)-M-N(2)
N(1)-M-O(1)
N(1)-M-O(2)
N(1)-M-O(Et)
N(1)-M-N(2)
P(1)-M-O(1)
P(2)-M-O(2)
O(1)-M-O(2)
162.3(1)
179.3(3)
169.2(2)
81.6(2)
162.0(1)
179.9(2)
170.0(1)
81.6(1)
162.9(1)
168.9(2)
81.4(2)
82.1(2)
79.0(4)
78.3(7)
110.9(4)
106.2(4)
76.4(2); 78.9(3)
77.0(3); 78.0(3)
106.6(4); 108.2(5)
110.6(4); 110.2(5)
82.1(2)
81.9(1)
178.6(2)
96.9(2)
97.5(3)
97.4(2)
168.0(5)
155.5(3)
157.4(3)
80.0(4)
165.5(4); 165.5(4)
154.7(2); 155.9(3)
156.3(3); 157.3(3)
80.1(3); 82.1(5)
a M ) Re; M ) Tc only for 2‚1/2CH2Cl2.
Scheme 4
Scheme 5
ence of π-acceptor ligands in the phenylimido coordination
sphere resembles the behavior of Tc- and Re-nitrido cores,
whereas the ability of coordinating nitrogen-based ligand in
octahedral geometries is similar to the behavior of the oxo-
core, thereby confirming the nature of the phenylimido unit
to be intermediate between oxo and nitrido groups.
With the aim at maintaining the essential contribution of
π-acceptor ligands in the metal phenylimido coordination
sphere, we thought to substitute monodentate with particular
polydentate ligands. Thus, aminodiphosphines PNHP and
PNMeP were used to replace triphenylphosphine in the
M(NPh)Cl3(PPh3)2 precursors. If we rule out the trans PhN-
M-P configuration, which has never been observed so far,
the molecular structure of the reaction products is comprised
among isomeric species (a), (b), and (c) depicted in Scheme
4. When the hydrochloric salt of PNMeP was utilized, an
additional neutral compound (d) was isolated.
Analyzing in detail the reactivity of rhenium complexes
(see Scheme 5), we observed that the stereochemistry of
intermediate compounds was determined by the nature of
the amine group inserted in the diphosphine backbone. A
secondary amine function (PNHP) promoted the formation
of the mer,cis isomer only, as established by the X-ray
structure of 1, whereas a tertiary amine group (PNMeP)
privileged the formation of the fac,cis form 3a, and, under
specific reaction conditions, of the mer,trans isomer 3c.
Similar arrangements of the aminodiphosphine were recently
observed in the corresponding nitrido complexes fac,cis-Tc-
(N)Cl2(PNHP) and mer,cis-Re(N)Cl2(PNMeP), and explained
in terms of different nucleophilicity of the amine group.28
Both mer,cis and fac,cis intermediate complexes 1 and 3a
underwent further substitution of cis positioned halides with
bidentate ligands, such as catechol, ethylene glycol, and 1,2-
aminophenol, to give mixed ligand complexes [Re(NPh)-
(L-L)(PNP)]+ (5, 7, 8, and 9), in which the aminodiphos-
phine were invariably facially arranged. Thus, an isomerization
of PNHP from the meridional into the facial form occurred
from 1 to 5, 6, and 8. A cis halide arrangement was found
to be an essential prerequisite for substitution, because the
trans halide alignment shown in the mer,trans species 3c gave
rise to negligible amounts of mixed complexes. Obtaining
stable fac-[Re(NPh)(L-L)(PNP)]+ mixed ligand complexes
again parallels the substitution chemistry exhibited by
aminodiphosphine containing nitrido complexes.4 A major
(28) Tisato, F.; Refosco, F.; Porchia, M.; Bolzati, C.; Dolmella, A.; Duatti,
A.; Boschi, A.; Jung, C. M.; Pietzsch, H.-J.; Kraus, W. Inorg. Chem.
2004, 43, 8617-8625.
4774 Inorganic Chemistry, Vol. 44, No. 13, 2005

Technetium(V) and Rhenium(V) Phenylimido Complexes
Table 5. Structural Data of Selected Nitrido and Phenylimido Technetium and Rhenium Complexesa
M-XN-trans
N-M-XN-trans (deg)
compound
M-Ncore (Å)
X ) N
X ) Cl
X ) N
X ) Cl
ref
fac-[Tc(N)(PNP)(L)]b,c
1.61
1.61
1.66
1.67
1.70
1.70
1.72
1.72
2.81
161.8
4
mer,cis-[Tc(N)Cl2(PNHP)]
2.65
170.2
28
22
4
this work
this work
this work
this work
fac-[Re(N)(dedc)(PNP)]Clb,d
fac,cis-Re(N)Cl2(PNP)b
2.73
2.64
164.4
164.2
mer,cis-[Tc(NPh)Cl2(PNHP)]Cl 2
mer,cis-[Re(NPh)Cl2(PNHP)]Cl 1
fac-[Re(NPh)(O,O-gly)(PNHP)]Cl 8
fac-[Re(NPh)(O,O-cat)(PNHP)]Cl 5
2.41
2.38
179.9
179.3
2.30
2.26
165.5
168.0
a Estimated average standard deviations of 0.01 Å for bond lengths and 0.4 deg for angles. b PNP ) bis[(2-diphenylphosphino)ethyl]methoxy-ethylamine.
c H2L ) S-methyl 2-methyldithiocar-bazate. d dedc ) diethyldithiocarbamate.
difference is constituted by the nature of the bidentate donor
atoms: the [Re(NPh)(PNP)]3+ moiety results best stabilized
by oxygen-based donors, whereas the nitrido moiety [Re-
(N)(PNP)]2+ prefers sulfur-based donors.
The coordination of an alkoxide residue trans to the phe-
nylimido group lengthens the Re-Nimido distance by ca. 0.04
Å, without affecting other parameters, whereas the coordina-
tion of trans N donors produces Re-Nimido distances in the
range 1.69-1.73 Å.
The analysis of NMR and structural data evidences a
correlation between the RedNPh bond length and the
Horto-NPh chemical shift of the phenylimido group. Table 3
comprises parameters of the complexes reported in this work
combined with those of some derivatives described in the
literature. A shortening of the metal nitrogen multiple bond
causes a decreasing of the electron density at the neighbor
phenylimido orto proton (downfield shift), irrespective of
the overall charge of the complex and nature of the
coordinating atom set. On this basis, qualitative speculations
on the RedNPh bond length may be envisaged from known
Horto chemical shifts. For example, if we consider the Horto
chemical shift of compounds 3a, 3b, and 3c (7.60, 6.59, and
6.73 ppm, respectively) such values could correspond to
RedNPh distances of ca. 1.71 Å for 3a and >1.75 Å for
3b and 3c.
Further comparison of selected structural data in similar
nitrido and phenylimido complexes synthesized in our
laboratory is shown in Table 5, which is organized according
to the increasing values of M-Ncore distances. In particular,
the data suggest that the lengthening of the M-Ncore distance
is matched by the shortening of the M-XN-trans bond, a result
in accordance with the expected trans labilizing effect
operated by the [M(N)]2+ and [M(NPh)]3+ cores. As a general
feature, the N-M-XN-trans angle widens as the M-Ncore
distance increases: fac arranged complexes (XN-trans ) N)
show narrower angles in the range 161.8-168.0°, while mer-
species (XN-trans ) Cl) show larger angles in the range
170.2-179.9°. The displacement of the metal from the mean
equatorial plane depends on the PNP assembly as well, being
0.39-0.43 Å in fac-species and 0.18-0.19 Å in mer-ones.
Comparison of the structural data of technetium and
rhenium phenylimido complexes described in this work and
in the literature16,24-26,29-39 (no substituted phenylimido or
alkylimido compounds are surveyed) reveals some common
features. The six reported technetium derivatives, which
include only phosphine and halide donors, exhibit Tc-Nimido
and Tc-Cltrans distances centered at 1.70 and 2.42 Å,
respectively, and nearly linear X-Tc-NPh units. Analogous
phosphine/halide rhenium complexes exhibit similar values.
As outlined in Scheme 5, syntheses of mixed-ligand
compounds can be performed using a one-step procedure at
room temperature. Since the nca synthesis of 188Re(NPh)-
Cl3(PPh3)2 is known from the literature,40 this method
might constitute a good start for the preparation of stable
188Re mixed-ligand complexes. Moreover, the incorpora-
tion of biologically active fragments onto para-substituted
phenylhydrazines, which is already a known technology,11,12
and the possibility to incorporate further functions onto the
1,2-ethylene glycol and catechol frameworks are the basis
for the design of target-specific rhenium radiopharma-
ceuticals.40
(29) Forsellini, E.; Casellato, U.; Graziani, R.; Carletti, M. C.; Magon, L.
Acta Crystallogr. 1984, C40, 1795-1797.
(30) Rochon, F. D.; Melanson, R.; Kong, P.-C. Inorg. Chem. 1995, 34,
2273-2277.
(31) Nicholson, T.; Davison, A.; Zubieta, J. A.; Chen, Q.; Jones, A. G.
Inorg. Chim. Acta 1995, 230, 205-208.
Conclusions
(32) Nicholson, T.; Storm, S. L.; Davis, W. M.; Davison, A.; Jones, A. G.
Inorg. Chim. Acta 1992, 196, 27-34.
Analogously to what was previously observed for nitrido
technetium and rhenium cores, phenylimido [M(NPh)]3+
groups also can be stabilized with suitable aminodiphos-
phines (PNP) leading to novel metal fragments of the type
fac- or mer-[M(NPh)(PNP)]3+. These complexes are useful
intermediates for the synthesis of a new class of dissym-
metric mixed-ligand fac-[M(NPh)(L-L)(PNP)]+ phenyl-
imido species.
(33) Lee, S. W.; Choi, N.-S. Acta Crystallogr. 1999, C55, 2018-2020.
(34) Clark, G. R., Nielson, A. J.; Rickard, C. E. F. Polyhedron 1988, 7,
117-128.
(35) Refosco, F.; Bolzati, C.; Tisato, F.; Bandoli, G. J. Chem. Soc., Dalton
Trans. 1998, 923-929.
(36) Bakir, M.; McKenzie, J. A. M.; Sullivan, B. P. Inorg. Chim. Acta
1997, 254, 9-17.
(37) Archer, C. M.; Dilworth, J. R.; Jobanputra, P.; Harman, M. E.;
Hursthouse, M. B.; Karaulov, A. Polyhedron 1991, 10, 1539-1543.
(38) 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, 3041-3048.
(39) Fung, W.-H.; Cheng, W.-C.; Peng, S.-M.; Che, C.-M. Polyhedron
1995, 14, 1791-1794.
(40) Lisic, E. C.; Mierzadeh, S.; Knapp, F. F., Jr. J. Labelled Compd.
Radiopharm. 1993, 33, 65-75.
Inorganic Chemistry, Vol. 44, No. 13, 2005 4775

Porchia et al.
refinement details, atomic coordinates, bond lengths and angles,
and anisotropic thermal parameters for complexes 1‚1/2CH2Cl2, 2‚
1/2CH2Cl2, 4, 5‚2H2O, and 8‚2H2O. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to Bracco Imaging,
Milano, Italy, for financial support of this study, and to A.
Moresco for elemental analyses.
Supporting Information Available: Crystallographic data in
CIF format, and tables of crystal data and structure solution and
IC048486Y
4776 Inorganic Chemistry, Vol. 44, No. 13, 2005