The trigonal-bipyramidal [ReOI2(PPh3)2] - The first monomeric oxorhenium(IV) complex with monodentate ligands only

Article abstract of DOI:10.1016/j.inoche.2016.04.031

The reaction of cis-[Re^VO₂I(PPh₃)₂] with 2-(3,5-dimethylpyrazol-1-yl)benzothiazole (dbt) in ethanol led to the isolation of the trigonal-bipyramidal oxorhenium(IV) complex trans-[ReOI₂(PPh₃

Full text of DOI:10.1016/j.inoche.2016.04.031

Inorganic Chemistry Communications 69 (2016) 45–46
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Short Communication
The trigonal-bipyramidal [ReOI (PPh ) ] — The first monomeric
2
3 2
oxorhenium(IV) complex with monodentate ligands only
Xandri Schoultz, Thomas I.A. Gerber ⁎, Richard Betz
Department of Chemistry, Nelson Mandela Metropolitan University, 6031 Port Elizabeth, South Africa
a r t i c l e i n f o
a b s t r a c t
V
Article history:
2 3 2
The reaction of cis-[Re O I(PPh ) ] with 2-(3,5-dimethylpyrazol-1-yl)benzothiazole (dbt) in ethanol led to the
Received 14 March 2016
Received in revised form 21 April 2016
Accepted 22 April 2016
2 3 2
isolation of the trigonal-bipyramidal oxorhenium(IV) complex trans-[ReOI (PPh ) ] (1). The complex is the
first example of a monomeric oxo complex of rhenium(IV). Complex 1 was characterized by FTIR, H NMR, mi-
croanalysis and single crystal X-ray diffraction.
1
Available online 23 April 2016
©
2016 Elsevier B.V. All rights reserved.
Keywords:
Oxorhenium(IV)
Iodide
Monomeric
Trigonal-bipyramid
The oxo group and halides are most commonly found as ligands in the
high oxidation state coordination chemistry of rhenium [1,2]. Normally
the choice of halide has been either a chloride or bromide, and iodide
has rarely been used as ligand. For example, the most common starting
(dbt) in ethanol [10]. The expectation was that coordination would
occur via the nitrogen atoms on the benzothiazole and pyrazole moieties
to form the trans-dioxorhenium(V) complex salt [ReO (dbt) ]I, as was
2 2
observed for other similar reactions with nitrogen-donor ligands [11].
Surprisingly, dbt did not coordinate to the metal, and the known
complexes for the synthesis of oxorhenium(V) complexes have been
−
trans-[ReOX
3
(PPh
3
)
2
] and [ReOX
4
]
(X = Cl, Br) [3]. Although
] are easily synthesized [4],
2 3 2
oxorhenium(V) compound [ReO(OEt)I (PPh ) ] [4] and oxorhenium(IV)
[
ReO(OEt)I (PPh
2
3
)
2
] and cis-[ReO
2
I(PPh
)
3 2
complex [ReOI (PPh ] (1) were isolated [12]. The product 1 is unusual
2
3 2
)
they are not commonly used as precursors. The chloro and bromo ana-
logue of the latter complex do not exist, implying that the coordination
chemistry of high oxidation state iodo-rhenium complexes may be differ-
since it is the first example of a monomeric monooxorhenium(IV)
complex.
In the IR spectrum of 1 the ν(Re_O) appears as a very strong peak at
−
1
1
ent to that of chloride/bromide. Indeed, using cis-[ReO
starting complex has led to some unusual and unexpected products,
quite different to those formed by trans-[ReOX (PPh ] as precursors [5].
2 3 2
I(PPh ) ] as
966 cm . The H NMR spectrum only contains the signals of the phenyl
protons of the PPh3 ligands, with no other signals that can be ascribed to
the protons of dbt. The complex is soluble, and gives orange solutions, in
polar organic solvents.
3
3 2
)
Oxorhenium(V) complexes acting as catalysts for various catalytic
processes commonly contain iodo as a ligand. For example, cis-
Fig. 1 shows an ORTEP illustration of 1, which is a five-coordinate
rhenium(IV) complex containing only monodentate ligands, i.e. two
triphenylphosphines, two iodos and an oxo group [13]. The complex
adopts a trigonal-bipyramidal (tbp) geometry with the phosphines in
the trans apical positions. The oxo oxygen and iodos form the trigonal
plane. The distortion from the tbp geometry is the result of the trans
2 3 2
[ReO I(PPh ) ] is active as a catalyst in the enantioselective reduction
3 2
of imines and hydrosilylation [6], and [(HBpz )ReO I] has been used
to activate C\\H bonds of alkyls/aryls [7].
To our knowledge, monomeric oxorhenium(IV) complexes contain-
ing only monodentate ligands have never been reported in the litera-
ture. Monomeric oxo complexes of rhenium(V) are well known, and
they have even been reported for rhenium(III) [for example
i
P(1)\\Re\\P(1 ) angle of 163.43(2)°, and the equatorial bond angles
i
I(1)\\Re\\I(1 ) [143.82(1)°] and O(1)\\Re\\(I) [108.09(1)°]. The two
−
ReOI(MeC`CMe)] [8] and rhenium(I) [ReO(MeC`CMe)] [9].
3
trans axial PPh groups are bent away from the oxo group
As part of our program on benzothiazole complexes of rhenium in var-
[O(1)\\Re\\P(1) = 98.29(1)°; I(1)\\Re\\P(1) = 87.58(2)°].
ious oxidation states, we have reacted cis-[ReO
tially bidentate N,N-donor 2-(3,5-dimethyl-pyrazol-1-yl)benzothiazole
2
I(PPh
3
)
2
] with the poten-
The Re_O bond length [1.688(3) Å] falls at the upper end of the
range of 1.66 (2)–1.69(2) Å observed for this bond in other similar neu-
tral monooxorhenium(V) complexes [14], and it shows considerable
triple bond character. The Re\\P bond lengths of 2.4547(7) Å are shorter
2 3 2
than in the five-coordinate cis-[ReO I(PPh ) ] [2.488(3) Å], while the
⁎
Corresponding author.
E-mail address: Thomas.gerber@nmmu.ac.za (T.I.A. Gerber).
Re\\I bonds [2.6951(3) Å] are longer [2.664(2) Å] [4].
http://dx.doi.org/10.1016/j.inoche.2016.04.031
387-7003/© 2016 Elsevier B.V. All rights reserved.
1

46
X. Schoultz et al. / Inorganic Chemistry Communications 69 (2016) 45–46
i
2 3 2
Fig. 1. ORTEP representation of trans-[ReOI (PPh ) ] (1). Selected bond lengths [Å]: Re \\ I 2.6951(3), Re \\ O 1.688(3), Re \\ P 2.4547(7); bond angles[°]: P(1) \\ Re \\ P(1 ) 163.43(2),
i
O(1) \\ Re \\ I(1) 108.09(1), O(1 )\\ Re \\ P(1) 98.29(1), I(1 )\\ Re \\ I(1 ) 143.82(1).
I.N. Booysen, M. Ismael, T.I.A. Gerber, M. Akerman, B. van Brecht, S. Afr. J. Chem. 65
2012) 174;
K.C. Potgieter, T.I.A. Gerber, R. Betz, L. Rhyman, P. Ramasami, Polyhedron 59 (2013) 91.
[6] J.J. Kennedy-Smith, K.A. Nolin, H.P. Gunterman, F.D. Toste, J. Am. Chem. Soc. 125
Compared to rhenium(III) or (V), complexes of rhenium(IV) are rare
in the literature. It is an inter-mediate oxidation state which can easily
(
be oxidized or reduced under mild conditions [15]. It was shown
−
(2003) 4056.
that perrhenate [ReO
4
] is a common byproduct in the synthesis of
[
[
7] S.N. Brown, A.W. Myers, J.R. Fulton, J.M. Mayer, Organometallics 17 (1998) 3364.
8] J.M. Mayer, D.L. Thorn, T.H. Tullip, J. Am. Chem. Soc. 107 (1985) 7454.
[9] T.R. Cundari, R.R. Conry, E. Spaltenstein, S.C. Critchlow, K.A. Hall, S.K. Tahmassebi,
J.M. Mayer, Organometallics 13 (1994) 322.
rhenium(IV) complexes from rhenium(V) precursors [16], so it is
likely that complex 1 originates from the disproportionation of
−
[
ReO(OEt)I
2
(PPh
3
)
2
] to 1 and ReO
4
. Interestingly, the reaction of
IV
[10] V.H. Arali, V.K. Revankar, V.B. Mahale, Transit. Met. Chem. 18 (1993) 158.
[ReO(OEt)Cl
2
(PPh
3
)
2
] with acetylacetone (Hacac) gave [Re Cl
2 2
(acac) ]
[
11] A. Bhattacharya, S. Majumder, J.P. Naskar, P. Mitra, S. Chowdhury, J. Coord. Chem. 67
2014) 1413;
as product [17].
(
M. Freni, D. Giusta, P. Romiti, G. Minghetti, Gazz. Chim. Ital. 99 (1969) 286;
J.C. Brewer, H.B. Gray, Inorg. Chem. 28 (1989) 3334;
J.H. Beard, J. Casey, R.K. Murmann, Inorg. Chem. 4 (1965) 797.
Acknowledgements
[
12] A mixture of cis-[ReO
2 3 2
I(PPh ) ] (100 mg, 115 μmol) and 2-(3,5-dimethyl-pyrazol-1-
yl)-benzothiazole (dbt) (53 mg, 231 μmol) was heated under reflux in 20 cm of
ethanol for four hours. After cooling to room temperature, the solution was filtered
3
This work was supported financially by the Nuclear Technologies in
Medicine and the Biosciences Initiative (NTeMBI), a national technology
platform developed and managed by the South African Nuclear Energy
Corporation and supported by the Department of Science and
Technology.
to produce [ReO(OEt)I
anol and dried under vacuum. Yield = 38 mg (32% based on Re), m.p. 173–175 °C.
Anal. Calcd. for C38 Re: C, 44.5; H, 3.4. Found: C, 44.7; H, 3.3%. IR (νmax/
2 3 2
(PPh ) ] as a green precipitate, which was washed with eth-
H
35
I
O
2 2
P
2
−
1
1
cm ): ν(Re_O) 943 m; δ(OCH
m, PPh ); 3.64 (q, 2H, OCH CH
2
) 906 s. H NMR (295 K, ppm, CDCl
3
): 7.32–7.82
(
3
2
3
); 1.17 (t, 3H, OCH CH ). The mother liquor was
2
3
left to evaporate at room temperature, and after 5 days orange-red crystals of 1
were harvested. These were washed with acetone and dried under vacuum.
Appendix A. Supplementary data
Yield = 14 mg (12% based on Re), m.p. 139–141 °C. Anal. Calcd. for C36
H I OP
30
2
2
Re:
C, 44.1; H, 3.1. Found: C, 44.6; H, 3.3%. IR (νmax/cm ): ν(Re_O) 966 s. H NMR
295 K, ppm, CDCl ): 7.32–7.72 (m, PPh ).
[13] Crystallographic data for C36 I OP Re (1): monoclinic; space group I2/a; a =
−
1
1
Supplementary data for 1 (CCDC 1449984) are available from the
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK on request. These data
can be obtained free of charge from the Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
(
3
3
H
30 2
2
3
c
15.755(1), b = 9.8578(6), c = 22.536(2) Å; V = 3394.9(4) Å ; Z = 4; D =
.918 g cm− ; μ = 5.519 mm ; data/parameters: 4248/191; S = 1.04; final R in-
3
−1
1
dices [I N 2σ(I)]: R1 = 0.0164, wR2 = 0.0411.
[
14] F.J. Femia, X. Chen, K.P. Maresca, J.W. Babich, J. Zubieta, Inorg. Chim. Acta 5 (2000)
210;
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