Unsymmetrical tren-based ligands: Synthesis and reactivity of rhenium complexes

Article abstract of DOI:10.1021/ic025572u

Reaction of bis(2-aminoethyl)(3-aminopropyl)amine with C₆F₆ and K₂CO₃ in DMSO yields unsymmetrical {(C₆F₅)HNCH₂CH₂}₂ NCH₂CH₂CH₂NH(C₆F₅) ([N₃N]H₃). The tetraamine acts as a tridentate ligand in complexes of the type H[N₃N]Re(O)X (X = Cl 1, Br 2) prepared by reacting Re(O)x₃(PPh₃)₂ with [N₃N]H₃ and an excess of NEt₃ in THF. Addition of 1 equiv of TaCH(CMe₂Ph)Br₃(THF)₂ to 1 gives the dimeric compound H [N₃N]ClReOReBrCl-[N₃N]H (3) in quantitative yield that contains a Re(V)=O-Re(IV) core with uncoordinated aminopropyl groups in each ligand. Addition of 2 equiv of TaCH(CMe₂Ph)Cl₃(THF)₂ to 1 leads to the chloro complex [N₃N]ReCl (4) with all three amido groups coordinated to the metal, whereas by addition of 2 equiv of TaCH(CMe₂Ph)Br₃(THF)₂ to 2 the dibromo species H[N₃N]ReBr₂ (5) with one uncoordinated amino group is isolated. Reduction of 4 under an atmosphere of dinitrogen with sodium amalgam gives the dinitrogen complex [N₃N]Re(N₂) (6). Single-crystal X-ray structure determinations have been carried out on complexes 1, 3, 5, and 6.

Full text of DOI:10.1021/ic025572u

Inorg. Chem. 2002, 41, 3513−3520
Unsymmetrical Tren-Based Ligands: Synthesis and Reactivity of
Rhenium Complexes
Nadia C. Mo1sch-Zanetti,* Sinje Ko1pke, Regine Herbst-Irmer, and Manuel Hewitt
Institut fu¨r Anorganischen Chemie der Georg-August-UniVersita¨t Go¨ttingen, Tammannstrasse 4,
37077 Go¨ttingen, Germany
Received March 6, 2002
Reaction of bis(2-aminoethyl)(3-aminopropyl)amine with C F and K CO in DMSO yields unsymmetrical
6
6
2
3
{(C F )HNCH CH }2NCH CH CH NH(C F ) ([N N]H ). The tetraamine acts as a tridentate ligand in complexes of
6
5
2
2
2
2
2
6
5
3
3
the type H[N N]Re(O)X (X ) Cl 1, Br 2) prepared by reacting Re(O)X (PPh3)2 with [N N]H and an excess of NEt3
3
3
3
3
in THF. Addition of 1 equiv of TaCH(CMe2Ph)Br3(THF)2 to 1 gives the dimeric compound H[N N]ClReOReBrCl-
3
[N N]H (3) in quantitative yield that contains a Re(V)dOsRe(IV) core with uncoordinated aminopropyl groups in
3
each ligand. Addition of 2 equiv of TaCH(CMe2Ph)Cl3(THF)2 to 1 leads to the chloro complex [N N]ReCl (4) with
3
all three amido groups coordinated to the metal, whereas by addition of 2 equiv of TaCH(CMe2Ph)Br3(THF)2 to 2
the dibromo species H[N N]ReBr2 (5) with one uncoordinated amino group is isolated. Reduction of 4 under an
3
atmosphere of dinitrogen with sodium amalgam gives the dinitrogen complex [N N]Re(N ) (6). Single-crystal X-ray
3
2
structure determinations have been carried out on complexes 1, 3, 5, and 6.
Introduction
dehydrogenation of alkyl compounds or by C,C-bond cleav-
age of cyclic alkyls,25-27 as well as the preparation of terminal
phosphido and arsenido compounds.28-30 One of the major
reasons for the reactivity found is the symmetry and energy
of the three frontier metal orbitals (one σ and two π), an
ideal arrangement for the formation of metal ligand triple
bonds. A second requirement for the stabilization of such
Sterically hindered triamidoamine ligands with a C3
symmetrical tren-based backbone (tris(2-aminoethyl)amine,
tren) have been shown to coordinate to a variety of transition
metals stabilizing unusual complexes thereby allowing
exceptional reactivities.1-47 Prominent examples include the
activation of dinitrogen,18-24 alkylidyne formation by R,R-
(17) Schrock, R. R.; Rosenberger, C.; Seidel, S. W.; Shih, K.-Y.; Davis,
W. M.; Odom, A. L. J. Organomet. Chem. 2001, 617, 495.
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8804.
(19) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem.
Soc. 1994, 116, 4382.
(20) Neuner, B.; Schrock, R. R. Organometallics 1996, 15, 5.
(21) O’Donoghue, M. B.; Zanetti, N. C.; Davis, W. M.; Schrock, R. R. J.
Am. Chem. Soc. 1997, 119, 2753.
(22) Roussel, P.; Scott, P. J. Am. Chem. Soc. 1998, 120, 1070.
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Soc. 1995, 117, 6609.
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O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J. Am. Chem. Soc.
1997, 119, 11876.
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Engl. 1995, 34, 2044.
* To whom correspondence should be addressed. E-mail: nmoesch@
gwdg.de. Phone: +551 39 19405. Fax: +551 39 33 73.
(1) Verkade, J. G. Acc. Chem. Res. 1993, 26, 483.
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1998, 17, 4077.
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10.1021/ic025572u CCC: $22.00 © 2002 American Chemical Society
Published on Web 06/05/2002
Inorganic Chemistry, Vol. 41, No. 13, 2002 3513

Mo1sch-Zanetti et al.
Re(O)X3(PPh3)2 (X ) Cl, Br)50 and TaCH(CMe2Ph)X3(THF)2 (X
) Cl, Br)51 were prepared by published methods. Diethylenetri-
amine, phthalic anhydride and N-(3-bromopropyl)phthalimide were
purchased from commercial sources and used as received. NMR
spectra were recorded with Bruker Avance 200 and Bruker Avance
500 spectrometers at ∼22 °C. Chemical shifts were referenced to
compounds is the three sterically demanding groups attached
to the amido substituents. While most research focused on
ligands containing SiMe3 groups, chemists have been inge-
nious in synthesizing tren ligands with other substituents such
as Me,31,32 Et,33 iPr,34-37 SiMe2tBu,18,22,38-42 C6F5,19,20,43-45
and very recently also Ar (e.g., Ar ) 3,5-Me2C6H3 or 3,5-
Ph2C6H3).23,24,46,47 In comparison, almost no research was
directed toward the influence of the tren backbone. This is
surprising, because the coordination chemistry of the un-
substituted, unsymmetrical tren homologues such as bis(2-
aminoethyl)(3-aminopropyl)amine (baep) or (2-aminoethyl)-
bis(3-aminopropyl)amine (abap) with late transition metals
has been thoroughly investigated.48,49 In these systems, the
insertion of additional CH2 groups has profound structural
as well as chemical consequences. In addition, such ligands
are thought to model the active site of metalloenzymes. By
the controlled variation of the ligand geometry, the elucida-
tion of principles governing biological reactions might be
possible.
Here, we report the synthesis of a C6F5 substituted
unsymmetrical triamidoamine ligand along with the prepara-
tion of two rhenium(V) oxo compounds 1 and 2, of which
1 is crystallographically characterized. Furthermore, we have
studied their stepwise reduction by preparing several Re-
(IV) and Re(III) species. The molecular structures of µ-oxo
bridged, mixed-valent dirhenium compound 3, mononuclear
Re(IV) dibromide 5, and Re(III) dinitrogen complex 6 are
reported. The data are compared with previously prepared
tren-based symmetrical rhenium complexes.11,20
the following standards: 1H and 13C NMR, Si(CH3)4 at 0 ppm; 19
F
NMR, C6F6 at 0 ppm. IR samples were prepared as mineral oil
mull, taken between KBr plates on a Bio-Rad FTS7 spectrometer.
Mass spectra were recorded on a Finnigan MAT 8200 or MAT 95
spectrometer. Elemental analysis were performed on a Heraeus
CHN-O-RAPID analyzer in our institute.
Synthesis of Bis(2-aminoethyl)(3-aminopropyl)amine (baep).
To 47.4 g (0.32 mol) of hot phthalic anhydride (∼180 °C) was
added 18.0 g (0.17 mol) of diethylenetriamine by syringe. Elimina-
tion of water was immediately apparent. The melt was stirred for
2 h, cooled to room temperature, ground to a powder, and
recrystallized from hot DMSO yielding 50.0 g (87%) of the
diphthalimide as slightly yellow microcrystals. They were mixed
with 43.1 g (0.16 mol) of N-(3-bromopropyl)phthalimide and heated
under stirring to ∼180 °C for 2 h resulting in a light brown melt.
Cooling to room temperature afforded a brown glassy material,
which was ground to a powder. This yellow material was suspended
in 600 mL of 10 M HCl(aq), stirred under reflux overnight, and
cooled to 0 ˚C, and the thus formed phthalic acid was removed by
filtration. After addition of 40 g of NaOH, the filtrate was
concentrated to a minimum to give an oily mixture of sodium
phthalate, NaOH, H2NCH2CH2OH, and the product. The volatile
materials were separated from the solid residues by distillation, and
subsequent fractional distillation at 95 °C and 0.01 bar gave the
pure tetraamine baep as a colorless liquid (11.2 g, 44%). Analytical
data are identical to previously reported values.52
Synthesis of [N3N]H3. To a solution of 2.78 g (17.3 mmol) of
baep in 20 mL of DMSO were added 11.7 g (62.9 mmol) of C6F6
and 8.3 g (60.1 mmol) of K2CO3. The resulting white suspension
was stirred at 70 °C for 24 h. After cooling to room temperature
and hydrolysis with 150 mL of H2O, the product was extracted
with 3 × 50 mL of CHCl3 and dried over MgSO4. The solvent
was removed under reduced pressure. The brown residue was
extracted with 200 mL of Et2O and filtered over basic alumina.
Evaporation of the solvent gave 11.0 g (94.8%) of the ligand [N3N]-
H3 as a orange oil, which was used without further purification.
1H NMR (CDCl3): δ 4.05 (br s, 2 H, NH), 3.68 (br s, 1 H, NH),
3.37 (m, 6 H, C6F5NHCH2), 2.71 (t, 4 H, J ) 6 Hz, C6F5-
NHCH2CH2N), 2.61 (t, 2 H, J ) 7 Hz, C6F5NHCH2CH2CH2N),
1.73 (quint, 2 H, J ) 7 Hz, C6F5NHCH2CH2CH2N). 13C NMR
Experimental Section
General Remarks. All manipulations were performed under a
nitrogen atmosphere using standard Schlenk technique or a vacuum
atmosphere drybox. The solvents were dried by standard methods.
(31) Plass, W.; Verkade, J. G. J. Am. Chem. Soc. 1992, 114, 2275.
(32) Plass, W.; Verkade, J. G. Inorg. Chem. 1993, 32, 3762.
(33) Schubart, M.; O’Dwyer, L. O.; Gade, L. H.; Li, W.-S.; McPartlin, M.
Inorg. Chem. 1994, 33, 3893.
(34) Duan, Z.; Verkade, J. G. Inorg. Chem. 1995, 34, 5477.
(35) Duan, Z.; Verkade, J. G. Inorg. Chem. 1996, 35, 5325.
(36) Scheer, M.; Mu¨ller, J.; Baum, G.; Haser, M. Chem. Commun. 1998,
2505.
(37) Scheer, M.; Mu¨ller, J.; Schiffer, M.; Baum, G.; Winter, R. Chem.s
Eur. J. 2000, 6, 1252.
(38) Boaretto, R.; Roussel, P.; Kingsley, A. J.; Munslow, I. J.; Sanders, C.
J.; Alcock, N. W.; Scott, P. Chem. Commun. 1999, 1701.
(39) Boaretto, R.; Roussel, P.; Alcock, N. W.; Kingsley, A. J.; Munslow,
I. J.; Sanders, C. J.; Scott, P. J. Organomet. Chem. 1999, 591, 174.
(40) Morton, C.; Alcock, N. W.; Lees, M. R.; Munslow, I. J.; Sanders, C.
J.; Scott, P. J. Am. Chem. Soc. 1999, 121, 11255.
(41) Morton, C.; Munslow, I. J.; Sanders, C. J.; Alcock, N. W.; Scott, P.
Organometallics 1999, 18, 4608.
(42) Roussel, P.; Alcock, N. W.; Boaretto, R.; Kingsley, A. J.; Munslow,
I. J.; Sanders, C. J.; Scott, P. Inorg. Chem. 1999, 38, 3651.
(43) Nomura, K.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1996, 35,
3695.
(44) Rosenberger, C.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1997,
36, 123.
(45) Seidel, S. W.; Schrock, R. R.; Davis, W. M. Organometallics 1998,
17, 1058.
(46) Greco, G. E.; Popa, A. I.; Schrock, R. R. Organometallics 1998, 17,
5591.
(47) Morton, C.; Gillespie, K. M.; Sanders, C. J.; Scott, P. J. Organomet.
Chem. 2000, 606, 141.
(CDCl3): δ 138.10 (Cortho and Cmeta, 1JCF ) 239 Hz), 133.56 (Cpara
1JCF ) 243 Hz), 123.85 (Cipso, CNHCH2CH2N), 123.72 (Cipso
,
,
CNHCH2CH2CH2N), 53.97 (NHCH2CH2N), 51.40 (NHCH2-
CH2CH2N), 44.55 (NHCH2CH2CH2N), 43.58 (NHCH2CH2N),
28.24 (NHCH2CH2CH2N). 19F NMR (CDCl3): 1.67 (m, 6 F, Fpara),
-2.52 (m, 6 F, Fmeta), -9.75 (m, 3 F, Fortho).
Synthesis of H[N3N]Re(O)Cl (1). To a suspension of 0.81 g
(0.97 mmol) of Re(O)Cl3(PPh3)2 in THF (50 mL) was added a
solution of 0.64 g (0.97 mmol) of [N3N]H3 and 2 mL (excess) of
NEt3 in THF (20 mL) at room temperature. The dark mixture was
stirred for 5 h, evaporated to 10 mL, cooled to -10 °C, and filtered
through Celite. The solvent was removed under reduced pressure,
and the solid was washed with Et2O (3 × 20 mL) to remove PPh3
(48) Dittler-Klingemann, A. M.; Orvig, C.; Hahn, F. E.; Thaler, F.; Hubbard,
C. D.; van Eldik, R.; Schindler, S.; Fa´bian, I. Inorg. Chem. 1996, 35,
7798.
(50) Parshall, G. W. Inorg. Synth. 1977, 17, 110.
(51) Rupprecht, G. A.; Messerle, L. W.; Fellmann, J. D.; Schrock, R. R. J.
Am. Chem. Soc. 1980, 102, 6236.
(49) Ochs, C.; Hahn, F. E.; Lu¨gger, T. Eur. J. Inorg. Chem. 2001, 1279.
(52) Dittler-Klingemann, A. M.; Hahn, F. E. Inorg. Chem. 1996, 35, 1996.
3514 Inorganic Chemistry, Vol. 41, No. 13, 2002

Unsymmetrical Tren-Based Ligands
and a brown unidentified impurity resulting in a light green powder.
Recrystallization from hot CH3CN gave 0.65 g (75%) of H[N3N]-
Re(O)Cl as green crystals suitable for X-ray analysis. Mp 185 °C.
1H NMR (THF-d8): δ 5.41 (br s, 1 H, NH), 4.17 (m, 2 H), 3.77
(m, 2 H), 3.47 (m, 6 H), 3.27 (m, 2 H), 2.25 (m, 2 H, NHCH2CH2-
CH2N). 13C NMR (THF-d8): δ 142.75-135.13 (m, ArF), 134.35
(ReNCipso), 131.12 (HNCpara, 1JF ) 242 Hz), 122.75 (m, HNCipso),
66.83 (ReNCH2), 62.34 (HNCH2CH2CH2), 58.26 (ReNCH2CH2),
41.44 (NHCH2), 23.69 (CH2CH2CH2). 19F NMR (THF-d8): δ 14.78
(m, 4 H, ReNC6Fortho), 2.89 (m, 2 F, HNC6Fmeta), 1.03 (t, 2 F, 3JFF
) 21 Hz, HNC6Fortho), -2.1 to -2.9 (m, 6 F, ReNC6Fpara and
and 0.70 g (1.01 mmol) of TaCH(CPhMe2)Br3(THF)2. Yield: 0.21
g (47%). MS(EI): m/z (%) 921 (M+ - HBr). Anal. Calcd for
C25H15N4Br2F15Re: C, 29.95; H, 1.56; N, 5.59. Found: C, 30.18;
H, 1.56; N, 5.57.
Synthesis of [N3N]Re(N2) (6). To a mixture of 0.24 g (0.23
mmol) of 4 and 0.064 g Na (3.01 g of 0.28% Na/Hg) was added
30 mL of precooled THF (-20 °C), and the mixture was stirred
for 1 h resulting in a deep red suspension. The mixture was allowed
to warm to room temperature and stirred for an additional hour
during which the color changed gradually to orange. The suspension
was filtered over Celite, and the solvent was removed under reduced
pressure. The orange solid was extracted with toluene and filtered
and the volume reduced to 5 mL and cooled to -25 °C affording
0.1 g (42%) of the orange product. Crystals suitable for X-ray
analysis were obtained from a layered mixture of CH2Cl2/hexane.
1H NMR (C6D6): δ 3.63 (m, 2 H), 3.10 (m, 4 H), 1.99 (m, 4 H),
1.75 (m, 2 H), 1.36 (m, 2 H). 13C NMR (C6D6): δ 143.4 (CAr),
141.4 (CAr), 139.6 (CAr), 138.8 (CAr), 137.6 (CAr), 136.7 (CAr), 133.3
(CAr), 61.3 (CH2CH2CH2NAr), 60.9 (CH2CH2NAr), 59.1 (CH2CH2-
NAr), 55.7 (CH2CH2CH2NAr), 28.2 (CH2CH2CH2NAr). 19F NMR
(C6D6): δ 11.4-10.8 (m, 4 F, CH2CH2NCFortho and CH2CH2CH2-
NCFortho), 9.85-9.40 (m, 2 F, CH2CH2NCFortho), 2.12 (t, 2 F, 3JFF
3
4
ReNC6Fmeta), -11.28 (tt, 1 F, JFF ) 22 Hz, JFF ) 7 Hz,
HNC6Fpara). IR (cm-1): 3352 (NH), 911 (ReO). Anal. Calcd for
C25H15N4ClF15ORe: C, 33.59; H, 1.69; N, 6.27. Found: C, 33.34;
H, 1.80; N, 6.15.
Synthesis of H[N3N]Re(O)Br (2). The compound was prepared
analogously to 1 employing 0.79 g (1.14 mmol) of Re(O)Br3(PPh3)2,
0.79 g (1.20 mmol) of [N3N]H3, and 1 mL (excess) NEt3. Yield:
1
0.63 g (59%). H NMR (THF-d8): δ 5.46 (br s, 1 H, NH), 4.20
(m, 2 H), 3.73 (m, 2 H), 3.55-3.32 (m, 6 H), 3.22 (m, 2 H), 2.24
(m, 2 H, NHCH2CH2CH2N). 13C NMR (THF-d8): δ 146.08-137.19
(m, ArF), 133.65 (HNCpara, 1JF ) 242 Hz), 125.28 (t, 3JF ) 12 Hz,
HNCipso), 69.69 (ReNCH2), 65.06 (HNCH2CH2CH2), 60.56
(ReNCH2CH2), 43.97 (NHCH2), 26.17 (CH2CH2CH2). 19F NMR
(THF-d8): δ 15.08 (m, 4 H, ReNC6Fortho), 2.90 (d, 2 F, HNC6Fmeta),
3
) 22 Hz, CH2CH2NCFpara), 1.32 (t, 1 F, JFF ) 22 Hz, CH2CH2-
CH2NCFpara), -1.04 to -1.48 (m, 6 F, CH2CH2NCFmeta and CH2-
CH2CH2NCFmeta). IR (cm-1): 2010 (NtN). Anal. Calcd for
C25H14F15N6Re: C, 34.53; H, 1.62; N, 9.66. Found: C, 34.66; H,
1.70; N, 9.46.
3
3
1.12 (t, 2 F, JFF ) 21 Hz, HNC6Fortho), -2.26 (t, 2 F, JFF ) 20
Hz, ReNC6Fpara), -2.60 (m, 4 F, ReNC6Fmeta), -11.31 (t, 1 F, 3JFF
) 21 Hz, HNC6Fpara). IR (cm-1): 3353 (NH), 911 (ReO). Anal.
Calcd for C25H15N4BrF15ORe: C, 31.99; H, 1.61; N, 5.97; Br, 8.51.
Found: C, 31.73; H, 1.78; N, 5.77; Br, 8.54.
Crystal Structure Analysis. The crystals were mounted on a
glass fiber in a rapidly cooled perfluoropolyether.53 Diffraction data
were collected on a Stoe-Siemens-Huber four-circle diffractometer
coupled to a Siemens CCD area detector with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å) at 133 K, performing æ-
and ω-scans. The structures were solved by direct methods using
SHELXS-9754 and refined against F2 on all data by full-matrix least-
squares with SHELXL-97.55 All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms bound to carbon atoms were
included in the model at geometrically calculated positions and
refined using a riding model, while all hydrogen atoms bound to
nitrogen atoms were refined using distance restraints. Some of the
CH2Cl2 molecules in 3 are disordered about two positions. They
were refined with distance restraints and restraints for the anisotropic
displacement parameters.
Synthesis of H[N3N]ClReOReBrCl[N3N]H (3). To a cooled
(-20 °C) green suspension of 1 (1.08 g, 1.21 mmol) in toluene
(15 mL) was slowly added by cannula a solution of 0.84 g (1.2
mmol, 1 equiv) of TaCH(CPhMe2)Br3(THF)2 in toluene (15 mL).
The reaction color turned gradually darker, and the product
precipitated as fine needles, which were filtered at low temperature.
Drying in vacuo gave 1.06 g (95%) of the product as deep blue
powder. Crystals suitable for X-ray analysis were obtained by
recrystallization from a mixture of CH2Cl2 and hexane at -20 °C
giving almost black crystals. MS(EI): m/z (%) 921 (100, [N3N]-
ReBr+); 894 (20, [N3N]Re(O)Cl); 877 (80, [N3N]ReCl). Anal. Calcd
for C50H30N8BrCl2F30ORe2‚2toluene: C, 37.75; H, 2.28; N, 5.50.
Found: C, 37.97; H, 2.31; N, 5.45.
Results
Synthesis of [N3N]ReCl (4). To a cooled (-20 °C) green
suspension of 1 (1.10 g, 1.23 mmol) in toluene (15 mL) was slowly
added by cannula a solution of 1.46 g (2.59 mmol, 2.1 equiv) of
TaCH(CPhMe2)Cl3(THF)2 in toluene (15 mL). The reaction color
turned darker, and initially dark green-blue needles precipitated.
After addition of the tantalum reagent, the reaction mixture was
stirred at room temperature for 2 h during which the precipitate
disappeared and a clear orange-brown solution was formed. The
solvent was removed under reduced pressure to a volume of 5 mL
and stored at -20 °C. The yellow microcrystals were filtered and
washed with a minimum amount of cold toluene and dried under
reduced pressure. Yield: 0.75 g, (70%). Mp 292 °C (dec). MS-
(EI): m/z 877 (M+). 19F NMR (C6D6): δ 34.80 (br s, 2 F), 21.13
(br s, 2 F), 16.46 (br s, 2 F), 13.05 (br s, 2 F), 9.23 (br s, 2 F), 8.06
(s, 1 F), 7.11 (s, 2 F), 4.65 (br s, 2 F) Anal. Calcd for C25H14N4-
ClF15Re: C, 34.24; H, 1.61; N, 6.39. Found: C, 34.27; H, 1.69;
N, 6.30. An attempted X-ray crystal structure analysis confirms
the connectivity.
Synthesis of the Ligand. The parent amine (baep) was
synthesized according to a modified method published for
the ligand (2-aminoethyl)bis(3-aminopropyl)amine (abap) as
shown in Scheme 1.56-58 The tetraamine was isolated in 44%
overall yield as a colorless oil (bp 95 °C, 0.01 bar). The
synthesis of baep has been published before employing a
fundamentally different method by reduction of the corre-
sponding trinitrile (overall yield 37%).52 Introduction of the
three C6F5 groups was performed according to a published
procedure for the analogous symmetrical ligand by nucleo-
(53) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615.
(54) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(55) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1997.
(56) Fanshawe, R. L.; Blackman, A. G. Inorg. Chem. 1994, 34, 421.
(57) Streater, M.; Taylor, P. D.; Hider, R. C.; Porter, J. J. Med. Chem.
1990, 33, 1749.
Synthesis of H[N3N]ReBr2 (5). The compound was prepared
in a fashion analogous to 4 employing 0.43 g (0.45 mmol) of 2
(58) Geue, R. J.; Sargeson, A. M.; Wijesekera, R. Aust. J. Chem. 1993,
46, 1021.
Inorganic Chemistry, Vol. 41, No. 13, 2002 3515

Mo1sch-Zanetti et al.
Scheme 1. Synthesis of Ligand [N3N]H3
Figure 1. ORTEP plot of [N3N]Re(O)Cl (1).
An X-ray study of 1 confirmed the tridentate coordination
of the ligand. An ORTEP plot of the structure is shown in
Figure 1. Table 1 contains crystallographic data, while Table
2 contains selected bond lengths and angles. Compound 1
crystallizes in the space group P1h with one molecule of
noncoordinating acetonitrile. The geometry at the metal
center is distorted trigonal bipyramidal with two nitrogen
atoms and one oxygen atom in the equatorial plane and with
the chlorine being trans to the apical nitrogen. Presumably
because of the large electron density of the oxo ligand, the
N4-Re1-Cl1 angle with 159.59(5)° significantly deviates
from linearity. Interestingly, the conformation of the free
aminopropyl substituent allows no interaction with the metal
or the oxygen atom. However, an intermolecular hydrogen
bond is formed between N3 and O1 of the next unit cell
leading to the formation of chains (N3-H3 0.825(2) Å,
H3‚‚‚O1 2.286(2) Å, N3‚‚‚O1 3.087(3) Å, N3-H3‚‚‚O1 164-
(3)°).
This situation is presumably analogous to the compound
involving the C3 symmetrical ligand, but a comparison is
not possible as no X-ray crystal structure was reported.
However, a recently reported rhenium complex displays a
similar structure to 1 except for the free amino arm at the
apical nitrogen, for which a methyl group has been intro-
duced ([{(C6F5)NCH2CH2}2NMe]Re(O)Cl).60 Both structures
show the same coordination at the metal center with very
similar bond lengths and angles.
Reaction with 1 equiv of a Tantalum Alkylidene
Reagent. The exchange of the oxo ligand by halides in 1
and 2, respectively, was realized by the reaction with a
tantalum alkylidene compound Ta(CHR)X3(THF)2 (X ) Cl,
Br).51 This unusual reaction has previously been employed
in the symmetrical system.20 As attempts to replace the oxo
functionality by more convenient methods failed, such as
refluxing in the presence of PPh3 or reduction with Na/Hg,
we proceeded accordingly: by the addition of 1 equiv of
TaCH(CPhMe2)Br3(THF)2 to 1 at -20 °C in toluene, the
deep blue colored compound H[N3N]ClReOReBrCl[N3N]H
(3) precipitated as shown in Scheme 3 in quantitative yield.
Scheme 2. Synthesis of Complexes 1 and 2
philic substitution by the amine on hexafluorobenzene giving
{(C6F5)HNCH2CH2}2NCH2CH2CH2NH(C6F5) ([N3N]H3) in
high yield.19 The orange oil obtained after evaporation of
solvents was generally used without further purification.
Synthesis of Rhenium Oxo Halides. The triaminoamine
ligand [N3N]H3 reacted with Re(O)X3(PPh3)2 (X ) Cl, Br)50
in the presence of a slight excess of NEt3 in THF at room
temperature yielding dark brown reaction mixtures within 2
h. After filtration, the solvent was removed under reduced
pressure to give dark residues that contain, aside from the
product, triphenylphosphine and unidentified impurities. The
latter two were removed by extraction with Et2O yielding
the 90% pure products. Recrystallization from hot acetonitrile
gave the rhenium oxo halides [HN3N]Re(O)X (1, X ) Cl;
2, X ) Br) as green crystalline solids. The compounds are
highly soluble in most common polar solvents such as THF,
acetonitrile, or CH2Cl2, but not Et2O. NMR spectra show
signals indicating the ligand to coordinate in the fashion
shown in Scheme 2. Both ethylene substituted amido groups
are bound to the metal center while the larger aminopropyl
substituent is not, indicated by the broad NH resonance at
1
5.4-5.6 ppm in the H NMR spectrum as well as the NH
stretch at approximately 3350 cm-1 in the IR spectrum. The
Re-O frequency is assignable to the signal at 911 cm-1 by
comparison with the spectrum of the monochloride [N3N]-
ReCl (vide infra) that lies in the normal range for this
moiety.59
(59) Adam, D. M. Metal-Ligand and Related Vibrations; Edward Arnold
(60) Cochran, F. V.; Bonitatebus, P. J., Jr.; Schrock, R. R. Organometallics
2000, 19, 2414.
Ltd.: London, 1967.
3516 Inorganic Chemistry, Vol. 41, No. 13, 2002

Unsymmetrical Tren-Based Ligands
Table 1. Crystallographic Details of the Structures
1
3
5
6
empirical formula
fw
space group
a, Å
b, Å
C25H15ClF15N4ORe‚CH3CN
935.11
P1h
7.912(2)
14.281(3)
14.801(3)
72.20(3)
74.91(3)
89.59(3)
C50H30BrCl2F30N8ORe2‚6CH2Cl2
C25H15Br2F15N4Re
1002.43
P1h
C25H14F15N6Re
869.62
P1h
2361.59
P1h
13.316(2)
17.316(2)
18.332(2)
76.00(2)
81.54(2)
68.25(2)
3801.7(8)
2
2.063
4.319
0.5 × 0.3 × 0.1
1.84-27.56
102817
13.797(2)
13.959(2)
15.722(2)
80.86(2)
86.87(2)
77.18(2)
2914.4(7)
4
2.285
7.034
0.5 × 0.3 × 0.2
2.15-27.85
43858
9.409(2)
11.554(2)
13.180(3)
91.66(3)
93.04(3)
109.18(3)
1349.7(5)
2
2.140
4.636
0.2 × 0.1 × 0.1
1.87-27.93
22326
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
1532.6(6)
2
2.026
F
calcd, Mg m-3
µ, mm-1
4.176
cryst size, mm3
θ range, deg
0.2 × 0.2 × 0.1
2.44-28.28
11982
no. reflns collected
no. independent
7583 (0.0239)
17483 (0.0658)
13657 (0.0731)
6343 (0.0399)
reflns (Rint
no. data
)
7583
17483
13657
6343
no. params
no. restraints
GOF
457
1
1103
320
1.135
0.0421 (0.0815)
854
1
425
0
1.061
0.0189 (0.0474)
1.035
0.0488 (0.1151)
1.131
0.0261 (0.0611)
final R1 indicesa
[I > 2σ(I)] (wR2)
R1 indices, all data
(wR2)
0.0204 (0.0482)
0.0531 (0.0849)
0.0742 (0.1263)
0.0285 (0.0619)
extinction coeff
largest diff peak
0.00208(19)
0.497 and -0.595
0.00035(6)
2.147 and -2.173
0.00133(11)
3.172 and -2.809
0.0022(3)
1.336 and -0.912
and hole (e Å-3
)
2
2
2 2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR1 ) [∑w(|Fo | - |Fc |)2/∑|Fo | ]1/2
.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 1
conclusion that more than one [N3N] ligand is involved and
that the compound contains uncoordinated NHC6F5 groups
because of a signal at δ -8.7 ppm. This is consistent with
the finding that the IR spectrum shows a NH stretch at 3381
cm-1, whereas no classical RedO stretch is detectable in
the usual 900-1000 cm-1 range. The mass spectrum shows
m/z peaks corresponding to H[N3N]Re(O)Cl (894), [N3N]-
ReBr (921), and [N3N]ReCl (877).
Re1-O1
Re1-N1
Re1-N4
1.6991(2)
1.9544(2)
2.1473(2)
Re1-Cl1
Re1-N2
2.3536(9)
1.9454(2)
N4-Re1-Cl1
N1-Re1-O1
N1-Re1-N4
N2-Re1-N4
O1-Re1-N4
159.59(5)
121.17(8)
80.21(7)
79.49(8)
98.13(8)
N1-Re1-N2
N2-Re1-O1
N1-Re1-Cl1
N2-Re1-Cl1
O1-Re1-Cl1
117.87(8)
119.50(8)
89.22(6)
90.33(7)
102.28(6)
Crystallization of 3 in a mixture of CH2Cl2 and hexane
over several days at -20 °C yielded dark crystals that were
suitable for X-ray crystal structure analysis. An ORTEP plot
is shown in Figure 2, while selected bond lengths and angles
are listed in Table 3. The crystal structure analysis revealed
a dinuclear species with a RedOsRe core and mixed-valent
rhenium centers. The structure is best described as a rhenium-
Scheme 3. Synthesis of Complex 3
The interpretation of NMR spectra (in CD2Cl2) proved to
be challenging because of the presence of a paramagnetic
center in combination with an apparently complex structural
situation. This is a general problem in the unsymmetrical
Re(IV) systems described here that hampered the investiga-
tion in solution, and therefore, all the compounds described
so far were characterized by X-ray crystal structure analysis.
Multiple signals in the 19F NMR spectrum of 3 also did not
give insight into structural features. However, it allowed the
Figure 2. ORTEP plot of H[N3N]ClReOReBrCl[N3N]H (3).
Inorganic Chemistry, Vol. 41, No. 13, 2002 3517

Mo1sch-Zanetti et al.
Table 3. Selected Bond Lengths (Å) and Angles (deg) of 3
The structure of 3 is quite unusual, because a Cambridge
structural database search revealed only few Re(IV) species
containing Re-O-Re units with a single µ-oxo bridge. One
of these compounds, [L2Re2Cl4(µ-O)][ZnCl4]61 (L ) N-
methylated 1,4,7-triazacyclononane) is centrosymmetric with
an inversion center on the (µ-O) atom showing a strictly
linear Re-O-Re linkage, whereas [L2Re2Me2(O)2(µ-O)]62
(L ) η2-2-butyne) and [Cp2Re2Br2(µ-O)][BF4]263 involve bent
groups due to metal-metal bond interaction. The Re-O
bond distance in [L2Re2Cl4(µ-O)][ZnCl4] is 1.878(1) Å
indicating single bonds with considerable double bond
character. This value is between Re1-O2 and Re2-O2
distances in 3 pointing to the different bonding situation.
The bonding is therefore best described as a donor-acceptor
interaction between the lone pair of the oxo ligand and the
Re(IV) center.
Re1-N20
Re1-O2
Re1-Cl1
Re2-O2
Re2-N40
Re2-Cl2
1.931(4)
2.038(3)
2.3800(1)
1.756(3)
1.932(4)
2.3863(1)
Re1-N10
Re1-N31
Re1-Br1
Re2-N(50)
Re(2)-N(61)
1.936(4)
2.192(4)
2.5688(6)
1.919(4)
2.144(4)
N20-Re1-N10
N10-Re1-O2
N10-Re1-N31
N20-Re1-Cl1
O2-Re1-Cl1
N20-Re1-Br1
O2-Re1-Br1
Cl1-Re1-Br1
O2-Re2-N40
O2-Re2-N61
N40-Re2-N61
N50-Re2-Cl2
N61-Re2-Cl2
101.80(2)
N20-Re1-O2
N20-Re1-N31
O2-Re1-N31
N10-Re1-Cl1
N31-Re1-Cl1
N10-Re1-Br1
N31-Re1-Br1
O2-Re2-N50
N50-Re2-N40
N50-Re2-N61
O2-Re2-Cl2
N40-Re2-Cl2
Re2-O2-Re1
87.32(1)
81.18(2)
92.73(1)
95.04(1)
171.77(1)
89.27(1)
95.48(1)
120.33(2)
115.57(2)
80.31(2)
99.99(1)
90.03(1)
170.77(2)
167.88(2)
80.96(2)
92.68(1)
92.45(9)
167.70(1)
80.99(9)
91.65(4)
122.80(2)
97.87(1)
79.95(2)
90.94(1)
162.13(1)
Reaction with 2 equiv of the Tantalum Reagent. The
addition of 2 equiv of TaCH(CPhMe2)Cl3(THF)2 to 1 gave
paramagnetic compound 4 in good yield as shown in Scheme
4. We propose complex 4 to be the species with all three
amido substituents coordinated to the metal center, which
has also been found in the symmetric analogue.11 The 19F
NMR spectrum shows eight broad signals between δ 5 and
35 ppm consistent with a species with a mirror plane between
the two aminoethyl groups. Elemental analysis gave correct
values for complex 4. In addition, an attempted crystal
structure analysis unambiguously confirmed the connectivity,
but the structure was severely disordered about three posi-
(IV) species that is coordinated by the oxo group of an
additional molecule of 1. The Re2 center with the formal
oxidation state V is five-coordinate in a distorted trigonal-
bipyramidal geometry, whereas the Re1 center with the
oxidation state IV displays a distorted six-coordinated
octahedron. In both ligands, the propylamino groups are not
in coordinating contact to any metal. Intermolecular hydrogen
bonds are formed between N30 and Br1 (N30-H30 0.74(4)
Å, H30‚‚‚Br1 2.86(5) Å, N30‚‚‚Br1 3.513(5) Å, N30s
H30‚‚‚Br1 148(5)°) leading to dimers. Additionally, weak
intramolecular hydrogen bonds between N60 and Br1 are
observed (N60sH60 0.74(4) Å, H60‚‚‚Br1 3.23(5) Å,
N60‚‚‚Br1 3.906(5) Å, N60sH60‚‚‚Br1 152(7)°).
The Re1-O2-Re2 bond angle slightly deviates from
linearity (170.8(2)°) with two significantly different Re-O
bond distances (Re2-O2 1.756(3) and Re1-O2 2.038(3) Å)
indicating a double bond character for Re2-O2 and a
coordinating bond for Re1-O2. The Re2-O2 bond length
in 3 is elongated in comparison to 1 (from 1.6991(2)° to
1.753(3)°), presumably because of the coordination to Re1.
The Re1-O2 bond length is in the normal range for a Re-O
single bond.59 The amido ligands are coordinated in a way
that the two apical nitrogen atoms are in transoid position
to each other and trans to the chlorine atoms. The N-Re-N
angle is smaller at the higher coordinated Re1 in comparison
to the Re2 center (N10-Re1-N20 101.8(2)°, N40-Re1-
N50 115.6(2)°). The bromide is located in cis position to
the chloride ligand.
1
tions, each with an occupancy of /3 pretending the 3-fold
axis of the C3 symmetrical tren ligand. The disorder can be
modeled, but of course, all bond lengths and angles are not
precise enough to be discussed.
As shown in Scheme 4, by the analogous reaction
employing 2 and 2 equiv of TaCH(CPhMe2)Br3(THF)2, red-
brown H[N3N]ReBr2 (5) could be isolated. Recrystallization
from a mixture of CH2Cl2 and hexane at room temperature
gave red crystals suitable for an X-ray analysis that confirmed
the formation of the dibromide (5). This is in contrast to the
formation of 4, where the final product is isolated after
elimination of HCl. Possibly, differences in the stability of
the Re-Br versus the Re-Cl bond prevent such a reactivity
in 5 and/or the increased steric requirement of the bromide
ligand impedes the coordination of the bulky NC6F5 sub-
stituent.
Scheme 4. Synthesis of Complexes 4 and 5
3518 Inorganic Chemistry, Vol. 41, No. 13, 2002

Unsymmetrical Tren-Based Ligands
Figure 4. ORTEP plot of [N3N]Re(N2) (6).
Scheme 5. Synthesis of Complex 6
Figure 3. ORTEP plot of H[N3N]ReBr2 (5).
Table 4. Selected Bond Lengths (Å) and Angles (deg) of 5
Re1-N20
Re1-N1
Re1-Br1
Re2-N60
Re2-Br4
1.891(6)
2.168(6)
2.5143(9)
1.910(6)
2.4166(8)
Re1-N10
Re1-Br2
Re2-N50
Re2-N2
Re2-Br3
1.904(6)
2.4203(8)
1.895(6)
2.162(6)
2.5165(9)
N20-Re1-N10
N10-Re1-N1
N10-Re1-Br2
N20-Re1-Br1
N1-Re1-Br1
N50-Re2-N60
N60-Re2-N2
N60-Re2-Br4
N50-Re2-Br3
N2-Re2-Br3
112.7(3)
81.0(2)
N20-Re1-N1
N20-Re1-Br2
N1-Re1-Br2
N10-Re1-Br1
Br2-Re1-Br1
N50-Re2-N2
N50-Re2-Br4
N2-Re2-Br4
N60-Re2-Br3
Br4-Re2-Br3
81.9(2)
127.87(2)
94.53(2)
94.51(2)
93.59(3)
80.7(2)
116.09(2)
95.71(2)
94.73(2)
92.32(3)
118.06(2)
93.69(2)
171.84(2)
116.1(2)
80.9(2)
126.27(2)
95.29(2)
171.95(2)
Å, Re1sN2 1.945(2) Å). Five-coordinate rhenium(IV)
species are rare.64,65 Like other d3 ions, the rhenium(IV) ion
normally adopts an octahedral geometry, as in the case of
compound 3, where the metal center is six-coordinate. It is
therefore surprising that the aminopropyl group of the ligand
does not bind to the metal. An intermolecular hydrogen bond
is observed between N70 and Br1 connecting the two
independent molecules to form a dimer (N70sH70 0.76(7)
Å, H70‚‚‚Br1 2.91(7) Å, N70‚‚‚Br1 3.666(7) Å, N70s
H70‚‚‚Br1 172(8)°), while the other NH group only forms a
weak intramolecular hydrogen bond to F31 (N30sH30 0.76-
(7) Å, H30‚‚‚F31 2.30(9) Å, N30‚‚‚F31 2.689(9) Å, N30s
H30‚‚‚F31 113(8)°).
Reduction of [N3N]ReCl under Dinitrogen. The reduc-
tion of 4 under an atmosphere of dinitrogen with Na/Hg gave
[N3N]Re(N2) (6) in good yield (Scheme 5). The reaction time
of 2 h should not be exceeded; otherwise, the yields decrease
significantly as side reactions start to compete. Other
reduction methods were not successful. The orange complex
is soluble in most common organic solvents. NMR and IR
spectroscopy are consistent with the structure shown in
Scheme 5, and the data are similar to the reported sym-
metrical one.11
N1-C5-C6-C7
C5-C6-C7-N30
-178.0(6)
168.7(6)
N2-C44-C45-C46
C44-C45-C46-N70
164.7(6)
-65.8(8)
An ORTEP plot of the structure is given in Figure 3;
selected bond lengths and angles are given in Table 4. The
unit cell contains two independent molecules, which differ
only in the conformation of the free aminopropyl group. The
bond distances and angles at the Re(IV) center are in both
molecules almost identical; therefore, the following discus-
sion only deals with molecule 1. The geometry is distorted
trigonal bipyramidal with the two coordinated amido sub-
stituents and one bromide ligand in the equatorial positions.
As expected according to VSEPR, the Re1sBr1 bond length
(2.5143(9) Å) in the axial position is slightly longer compared
to Re1sBr2 (2.4203(8) Å). The geometry is comparable to
that of 1 with the exception that the RedO double bond leads
to a more pronounced distortion from a perfect trigonal
bipyramid. For example, the N1sRe1sBr1 angle in 5 with
171.8(2)° is almost linear whereas the corresponding angle
in 1 is 159.59(5)°. Surprisingly, the equatorial Re(IV)sN
bonds (Re1sN10 1.904(6) Å, Re1sN20 1.891(6) Å) are
shorter than the Re(V)sN bonds in 1 (Re1sN1 1.954(2)
The end-on coordination of the N2 molecule to the
diamagnetic Re(III) center was confirmed by X-ray crystal-
lography. Figure 4 shows an ORTEP plot of the complex,
and bond lengths and angles are given in Table 5. The NtN
bond length is 1.087(4) Å, corresponding to a normal value
(61) Bo¨hm, G.; Wieghardt, K.; Nuber, B.; Weiss, J. Inorg. Chem. 1991,
30, 3464.
(62) Herrmann, W. A.; Felixberger, J. K.; Kuchler, J. G.; Herdtweck, E.
Z. Naturforsch., B: Chem Sci. 1990, 45, 876.
(63) Carfagna, C.; Carr, N.; Deeth, R. J.; Dossett, S. J.; Green, M.; Mahon,
M. F.; Vaughan, C. J. Chem. Soc., Dalton Trans. 1996, 415.
(64) Hambley, T. W.; Knott, R. K.; Jackson, T. W.; Kojima, M.; Lambrecht,
R. M. Acta Crystallogr., Sect. C 1995, 51, 203.
(65) Masood, M. A.; Sullivan, B. P.; Hodgson, D. J. Inorg. Chem. 1999,
38, 5425.
Inorganic Chemistry, Vol. 41, No. 13, 2002 3519

Mo1sch-Zanetti et al.
Table 5. Selected Bond Lengths (Å) and Angles (deg) of 6
bridged dinuclear tantalum compounds with other ligands
have been structurally characterized.67-69 After separation
of the products, NMR spectra of the remaining reaction
mixtures are complex but show no alkylidene signals.
Therefore, we assume that the electrons necessary for the
formation of the reduced Re(IV) complex stem from dimer-
ization of the alkylidene group.
N100-N101
Re1-N1
Re1-N3
1.087(4)
1.929(3)
1.943(3)
Re1-N101
Re1-N2
Re1-N4
1.943(3)
1.941(3)
2.178(3)
N100-N101-Re1
N1-Re1-N2
177.7(3)
114.60(1)
123.87(1)
81.11(1)
94.73(1)
95.06(1)
N101-Re1-N4
N1-Re1-N3
N1-Re1-N4
N3-Re1-N4
N3-Re1-N101
173.81(1)
120.12(1)
82.55(1)
94.00(1)
92.18(1)
N2-Re1-N3
N2-Re-N4
N1-Re1-N101
N2-Re1-N101
The systematic study on complexes with the unsubstituted
symmetrical and unsymmetrical tren-type ligands has shown
the significant influence of the size of the chelate rings
toward the basicity of the ligand as well as the geometry of
the complexes.48,49 With this in mind, we set our goal to
influence the geometry and thereby provoke unusual reac-
tivities in rhenium complexes that contain triamidoamine
ligands having symmetries other than trigonal. The introduc-
tion of an additional CH2 group in the ligand either leads to
complexes with a six-membered chelate ring or to tri- instead
of tetradentate coordination of the ligand. This variability
of the ligand system caused by the decreased stability of the
larger chelate ring allows the isolation of unusual intermedi-
ates not traceable with the symmetrical ligand. However,
once the ligand coordinates in a tetradentate manner, the
complexes show minute differences in comparison to the
symmetrical one. This is interesting in the view that such
ligands are thought to model the nitrogen-rich active site of
metalloenzymes. The investigation of controlled changes in
the ligand geometry thereby retaining the donor atom set
might eventually prove useful in the understanding of
principles governing the activation of biological substrates.
for a triple bond. The geometry at the metal center is trigonal
bipyramidal with a slightly smaller N1-Re1-N2 angle
(114.6(1)°) than the other two trigonal angles (120.1(1)°,
123.9(1)°). As expected, the six-membered metallacycle
formed by the coordinated amidopropyl group has a larger
NsResN angle (N3sRe1sN4 94.0(1)° compared to N1s
Re1sN4 82.55(1)° and N2sRe1sN4 81.11(1)°) as well as
a larger ResNsC angle (129.(1)° compared to 118.7(2)°
and 116.4(2)°), leading to a tilting of the C6F5 ring toward
the metal center. The thus imposed steric effect on the apical
ligand is apparently small as there is almost no tilting of the
N2 molecule between the two other C6F5 groups (N4sRe1s
N101 173.8(1)° and Re1sN101sN100 177.7(3)°).
Discussion
The here described system allows significant insights into
the unusual reaction of the tantalum alkylidene reagent with
the metal oxide. Such reactions have previously been shown
to transfer entire alkylidene groups by metathesis with a
metal oxide.66 Here, this reaction does not take place, but
rather, a halogen atom is transferred. The choice of two
different halogen precursors (rhenium chloride and tantalum
bromide) in the reaction forming 3 allows the conclusion
that only one halogen atom is transferred forming intermedi-
ates of the type H[N3N]ReX2. Depending on the nature of
the X ligand, these dihalogenides eliminate HX which is
obvious by a slow gas evolution thereby forming the
monohalogenides [N3N]ReX. The nature of the tantalum
species formed is unclear; however, the stoichiometry of the
reactions (1 equiv of the Ta reagent for 3 and 2 equiv for 4
and 5) points to the formation of a Ta-O-Ta species. Oxo-
Acknowledgment. Generous support by the Swiss Na-
tional Foundation and Prof. H. W. Roesky is gratefully
acknowledged.
Supporting Information Available: X-ray crystallographic files
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC025572U
(67) Chisholm, M. H.; Huffman, J. C.; Tan, L.-S. Inorg. Chem. 1981, 20,
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(68) Jernakoff, P.; de Meric de Bellefon, C.; Geoffrey, G. L.; Rheingold,
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Lehmann, C.; Walawalkar, M. G.; Murugavel, R.; Schmidt, H.-G.;
Noltemeyer, M. Organometallics 1999, 18, 832.
(66) LaPointe, A. M.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc.
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3520 Inorganic Chemistry, Vol. 41, No. 13, 2002