Rhenium(III) and rhenium(V) complexes that contain the (C6F5NCH2CH2)3N ligand

Article abstract of DOI:10.1021/om950581e

The reaction between [Et₄N]₂[ReOCl₅] and (C₆F₅NHCH₂CH₂)₃N in THF at room temperature in the presence of NEt₃ yielded air-stable emerald green diamagnetic [(

Full text of DOI:10.1021/om950581e

Organometallics 1996, 15, 5-6
5
Rh en iu m (III) a n d Rh en iu m (V) Com p lexes Th a t Con ta in
th e (C6F 5NCH2CH2)3N Liga n d
Brigitte Neuner and Richard R. Schrock*
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received J uly 26, 1995X
Summary: The reaction between [Et4N]2[ReOCl5] and
(C6F5NHCH2CH2)3N in THF at room temperature in the
presence of NEt3 yielded air-stable emerald green dia-
magnetic [(C6F5NCH2CH2)2NCH2CH2NHC6F5]Re(O)Cl
(1). The reaction between 1 and Ta(CH-t-Bu)(THF)2Br3
gave paramagnetic {[(C6F5NCH2CH2)3N]ReBr}Br (2).
Reduction of 2 by methyllithium under dinitrogen gave
diamagnetic [(C6F5NCH2CH2)3N]Re(N2), under carbon
monoxide gave [(C6F5NCH2CH2)3N]Re(CO), under di-
hydrogen gave [(C6F5NCH2CH2)3N]ReH2, and under
ethylene gave [(C6F5NCH2CH2)3N]Re(C2H4).
addition of D2O, although 1 is stable in air as a solid
and in a mixture of THF and water for at least 2 days.
Many attempts to remove HCl with a variety of bases
have not been successful. We speculate that 3-fold
symmetric, d2 [(C6F5NCH2CH2)3N]RedO would be a
high-energy species, since no π donation from the oxo
ligand into one of the three orbitals available in the
apical site (dxz, dyz, and a σ orbital along the RedO (z)
axis) is possible as a consequence of two d electrons
being present in the remaining π type orbital.
An attempt to exchange the oxo ligand4,5 in 1 with
6
the neopentylidene ligand in Ta(CH-t-Bu)(THF)2Br3
We recently reported the synthesis of tris(2-((pen-
tafluorophenyl)amino)ethyl)amine, (C6F5NHCH2CH2)3N,
and several molybdenum complexes containing its tri-
anion, including two that contain dinitrogen.1 The
complex that yielded structurally characterized diamag-
netic [(C6F5NCH2CH2)3N]MoNdNSi(i-Pr)3 upon treat-
ment with (i-Pr)3SiCl was proposed to be a sodium salt
of the d4 “Mo(II)” species, {[(C6F5NCH2CH2)3N]Mo(N2)}-,
or “[(C6F5NCH2CH2)3N]MoNdNNa”. Since we were not
able to confirm the nature of the sodium salt via an
X-ray study, we became interested in the possibility that
a neutral d4 Re(III) analog of {[(C6F5NCH2CH2)3N]-
Mo(N2)}- could be prepared. Therefore, we began to
search for entries into the chemistry of Re complexes
containing the (C6F5NCH2CH2)3N ligand. We report our
preliminary findings here.
gave olive green [(C6F5NCH2CH2)3N]ReBr2 (2; 60-85%
yield) instead. This reaction is formally an exchange of
the oxo ligand in 1 with Br2 on tantalum plus removal
of HCl from Re; no attempt to isolate and identify the
tantalum product (hypothetically “Ta(O)(CH2-t-Bu)BrCl-
(THF)x”) was made. The paramagnetism of 2 is consis-
tent with the ionic formulation, since the two d electrons
should then occupy the degenerate dxz/dyz orbital set.
The unexceptional structure of 2 has been confirmed in
an X-ray study,7 details of which will be published later.
An attempt to form a Re(V) methyl complex by
treating 2 with methyllithium under dinitrogen yielded
a sparingly soluble, diamagnetic, orange crystalline
complex with the formula [(C6F5NCH2CH2)3N]Re(N2) (3)
in good yield.8 Treatment of 2 with methyllithium
under 15N2 yielded the analogous complex [(C6F5NCH2-
CH2)3N]Re(15N2) (3-15N2). IR spectra of 3 (νNN 2004
The reaction between [Et4N]2[ReOCl5]2,3 and (C6F5-
NHCH2CH2)3N in THF at room temperature in the
presence of NEt3 gave emerald green diamagnetic 1 (eq
1). An attempted X-ray study confirmed the connectiv-
cm-1) and 3-15N2 (ν
1935 cm-1) are consistent with
N
15N15
(4) Recently it has been possible to exchange the oxo ligand in Os-
(VI) complexes with the neopentylidene ligand in Ta(V) complexes; see
ref 5.
(5) LaPointe, A. M.; Schrock, R. R.; Davis, W. M. J . Am. Chem. Soc.
1995, 117, 4802.
(6) Rupprecht, G. A.; Messerle, L. W.; Fellmann, J . D.; Schrock, R.
R. J . Am. Chem. Soc. 1980, 102, 6236.
(7) Reid, S. M., Davis, W. M. Unpublished results.
(8) An ether solution of methyllithium (0.357 mmol) was added to
a stirred solution of 2 (167 mg, 0.17 mmol) in 5 mL of THF under an
atmosphere of dinitrogen. The green-brown solution turned dark purple
immediately and then faded to orange-brown over a period of 1 h. The
solvent was evaporated in vacuo, and the oily orange residue was
dissolved in a minimum amount of methylene chloride. The extract
was filtered, pentane was added, and the mixture was cooled to -40
°C to yield orange cubes; yield 104 mg (0.12 mmol, 72%).
ity, but full solution and refinement were not successful.
(Details will be reported later.) NMR spectra of 1 are
entirely consistent with the mirror symmetry shown and
reveal a broad resonance for the NH proton between
2.15 and 4.70 ppm. The NH resonance disappears upon
X Abstract published in Advance ACS Abstracts, December 1, 1995.
(1) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J . Am. Chem.
Soc. 1994, 116, 4382.
(2) This compound was prepared in a manner analogous to that for
the known tetramethylammonium salt.3
(3) Grove, D. E.; Wilkinson, G. J . Chem. Soc. A 1966, 1224.
0276-7333/96/2315-0005$12.00/0 © 1996 American Chemical Society

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Organometallics, Vol. 15, No. 1, 1996
Communications
Sch em e 1. Red u ction s of 2 w ith Meth yllith iu m
for the hydrides, a possibly nonminimal value that
would favor 5 being a classical dihydride complex.10-12
On the other hand, the J HD coupling constant in 5-d 1
(15 Hz) is more consistent with 5 being a dihydrogen
complex (typically J HD ) 30 ( 4 Hz).10-12 Therefore,
at this stage we cannot state with certainty which
description, if either,13 is the most appropriate. Proton
NMR spectra of 6 in THF-d8 show a broad resonance
at 2.61 ppm, consistent with a intermediate rate of
“rotation” of the ethylene with respect to the (C6F5NCH2-
CH2)3N ligand. An X-ray study of 6 has shown it to
have the expected structure in which the ethylene lies
in the same plane as one of the Re-N bonds;7 details
will be published later.
The results presented here suggest that a variety of
Re(III)/Re(V) complexes that contain the [(C6F5NCH2-
CH2)3N] ligand should be accessible. Future efforts will
be directed toward synthesizing such species by more
direct methods and preparing analogous complexes that
contain other types of triamidoamine ligands, such as
an end-on mode of dinitrogen binding, as is the 15N
NMR spectrum of 3-15N2, which reveals two doublet
[(Me3SiNCH2CH2)3N]3- 14-21
.
1
resonances at 281.3 and 332.0 ppm with J NN ) 5.5 Hz.
Exposure of 3-15N2 to 14N2 (22 °C, 1 atm) does not lead
to exchange of 15N2 for 14N2. 3 also is formed upon
treating 2 with phenyl-, butyl-, or neopentyllithium
under dinitrogen. Attempts to synthesize 3 by reducing
2 with Zn dust or sodium amalgam under dinitrogen so
far have not been successful. Purple intermediates are
formed rapidly in all reactions involving lithium re-
agents, but attempts to identify any such intermediate
have been hampered by their extreme sensitivity to air
and moisture and their apparent paramagnetism (ac-
cording to NMR studies).
Ack n ow led gm en t. R.R.S. thanks the National In-
stitutes of Health (Grant No. GM 31978) for research
support, and B.N. thanks the Deutsches Forschungs-
gemeinschaft for partial support through a postdoctoral
fellowship.
Su p p or tin g In for m a tion Ava ila ble: Text giving experi-
mental details for the synthesis of compounds 1-6 (4 pages).
Ordering information is given on any current masthead page.
OM950581E
Addition of methyllithium to 2 under an atmosphere
of CO, dihydrogen, or ethylene led to the sparingly
soluble diamagnetic compounds 4, 5, and 6, respectively,
in good yields (Scheme 1).9 The IR spectrum of 4 has a
CO band at 1875 cm-1 that shifts to 1830 cm-1 in the
13CO analog. A sharp resonance for the hydrides in 5
is found at -0.89 ppm in the proton NMR spectrum in
CD2Cl2, but no peak could be located in the IR spectrum.
A T1 measurement at 21 °C yielded a value of 138 ms
(10) J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155.
(11) Crabtree, R. H.; Hamilton, D. G. Adv. Organomet. Chem. 1988,
28, 299.
(12) Heinekey, D. M.; Oldham, W. M., J r. Chem. Rev. 1993, 93, 913.
(13) Earl, K. A.; J ia, G.; Maltby, P. A.; Morris, R. H. J . Am. Chem.
Soc. 1991, 113, 3027.
(14) Verkade, J . G. Acc. Chem. Res. 1993, 26, 483.
(15) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Inorg. Chem.
1994, 33, 1448.
(16) Cummins, C. C.; Schrock, R. R. Inorg. Chem. 1994, 33, 395.
(17) Freundlich, J .; Schrock, R. R.; Cummins, C. C.; Davis, W. M.
J . Am. Chem. Soc. 1994, 116, 6476.
(9) A THF solution of 2 (10 mL of THF per 100 mg) and MeLi (in 10
mL of ether per 2.1 equiv) were separately degassed three times by
freeze-pump-thaw cycles. The reaction vessel was then filled with
the desired gas, and the solutions were combined. The rapidly formed
dark purple color that was generated in the case of 5 and 6 faded over
a period between 1 h and 3 days. The product was isolated in a manner
analogous to the isolation of 3.
(18) Shih, K.-Y.; Schrock, R. R.; Kempe, R. J . Am. Chem. Soc. 1994,
116, 8804.
(19) Shih, K.-Y.; Totland, K.; Seidel, S. W.; Schrock, R. R. J . Am.
Chem. Soc. 1994, 116, 12103.
(20) Duan, Z.; Verkade, J . G. Inorg. Chem. 1995, 34, 1576.
(21) Schrock, R. R.; Shih, K.-Y.; Dobbs, D.; Davis, W. M. J . Am.
Chem. Soc. 1995, 117, 6609.