Structure of trans-diisothiocyanato(ethoxo)oxo-bis(triphenylphosphine)rhenium(V) complex

Article abstract of DOI:10.1016/S0020-1693(00)00057-8

The title compound consists of [ReO(NCS)₂(OEt)(PPh₃)₂] units in which the rhenium(V) center shows a slightly distorted octahedral coordination. The two N-coordinated NCS^- groups are trans to each other, as the Re=O and the Re-OEt units. The Re=O and Re-OEt bond lengths [1.682(10) and 1.871(10) ?, respectively] and the geometry about the ethoxide oxygen atom indicate that in both cases M-O ligation has a considerable degree of multiple bond. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(00)00057-8

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Inorganica Chimica Acta 304 (2000) 114–117
Note
Structure of trans-diisothiocyanato(ethoxo)oxo-bis(triphenyl-
phosphine)rhenium(V) complex
Raffaele Battistuzzi *, Monica Saladini
Department of Chemistry, Uni6ersity of Modena and Reggio Emilia, 41100 Modena, Italy
Received 2 November 1999; accepted 29 December 1999
Abstract
The title compound consists of [ReO(NCS)2(OEt)(PPh3)2] units in which the rhenium(V) center shows a slightly distorted
octahedral coordination. The two N-coordinated NCS− groups are trans to each other, as the ReꢀO and the ReꢁOEt units. The
,
ReꢀO and ReꢁOEt bond lengths [1.682(10) and 1.871(10) A, respectively] and the geometry about the ethoxide oxygen atom
indicate that in both cases MꢁO ligation has a considerable degree of multiple bond. © 2000 Elsevier Science S.A. All rights
reserved.
Keywords: Crystal structures; Rhenium complexes; Oxo–ethoxo complexes; Isothiocyanato complexes
1. Introduction
ous report [15]. trans-[ReOI2(OEt)(PPh3)2] (500 mg,
0.487 mmol) were suspended in 25 ml of absolute
ethanol and 79 mg (0.975 mmol) of NaSCN dissolved
in 10 ml of absolute ethanol were added with stirring.
The mixture was heated under reflux for 1 h. Upon
cooling at room temperature (r.t.) the grey–brown
microcrystalline product was filtered, washed with
EtOH and dried in vacuo. On standing at r.t., the
mother liquor afforded, after 10–15 days, a further
amount of the compound as grey–brown crystals suit-
able for X-ray diffraction analysis. Anal. Calc. for
C40H35N2O2P2S2Re: C,54.0; H, 4.0; N, 3.2; S, 7.2.
Found: C, 54.0; H,4.0; N, 3.1; S, 7.1%.
Analogously to the corresponding trans-[ReOX2-
(OEt)(PPh3)2] halo-complexes (X=Cl, Br, I) of rheni-
um(V) [1–10], the title compound may be a versatile
starting material for the synthesis, by ligand exchange,
of new coordination compounds of the metal in its
higher oxidation states. Here, we describe the X-ray
crystal structure of title compound, in order to deter-
mine the thiocyanate bonding mode (N- or S-) and to
ascertain if the thiocyanato compound occurs in the
same isomeric form as the chloro-, bromo- and iodo-
analogues [11–14].
Selected IR bands (cm−1): was(CN) 2096vs, 2064vs;
w(PꢁC) 1433vs, 1094vs; w(CꢁO)OEt 1065s, w(ReꢀO) 952s;
2. Experimental
l(OꢁC2H5) 912s; w(CS) 847s; l(NCS) 470m cm−1
.
Analyses and physical measurements. Elemental
analysis (C, H, N, S) was performed using a C. Erba
1106 Elemental Analyzer. IR spectra were recorded in
KBr pellets (4000–400 cm−1) on a Perkin–Elmer 1600
Series FTIR spectrophotometer. Conductivity measure-
2.1. Synthesis
The preparation of the trans-[ReO(NCS)2-
(OEt)(PPh3)2] was performed along the lines of a previ-
ments were performed on a freshly prepared 10−3
M
solution in CH2Cl2 at 25°C with a Jenway 4020 conduc-
tivity meter.
* Corresponding author. Tel.: +39-59-378 428; fax: +39-59-373
543.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(00)00057-8

R. Battistuzzi, M. Saladini / Inorganica Chimica Acta 304 (2000) 114–117
115
served (I\2|(I)). All data were corrected for Lorenz
and polarization effects and an absorption correction
based on c scan [16] was applied [Tmin (Tmax) 0.86
(0.96)]. The Patterson method was applied for the
structure solution. Re, N, S and P atoms were refined
anisotropically while phenyl rings were constrained at
ideal geometry and refined isotropically owing to disor-
der problems. Hydrogen atoms were calculated at ideal
positions and introduced in the structure factor calcula-
tions as fixed contributors. The R factor based on F
was 0.062 while the wR (GOF on F2 1.087) was 0.133
with w=1/[Fo2+(0.0682P)2] where P=(Fo2+2Fc2)/3.
The largest features in a final difference map were
2.2. X-ray crystal data
Data collection was obtained using a grey–brown
crystal of C40H35N2O2P2S2Re (Mw 887.99) of dimen-
sion 0.3×0.25×0.3 mm at 25°C on an automatic
CAD4 diffractometer (Enraf Nonius). Mo Ka (u=
,
0.71073 A) radiation was used throughout the experi-
ment. Cell parameters were determined from 25 high
angle setting: a=9.400(2), b=9.871(3), c=20.688(6)
,
A; h=87.46(2), i=82.32(2), k=87.82(2)°; V=
3
1898.4(9) A ; Dm (Dcalc)=1.50 (1.55) g cm−3; v(Mo
,
Ka)=3.43 mm−1; space group P1; Z=2. 6788 reflec-
(
tions were collected, h −11 to 11, k −11 to 11, l 0 to
24, with v scan technique from which 3079 were ob-
0.982–2.012 A−3. All calculations were carried out on
,
a personal computer using SHELX76 [17], SHELX93 [18]
and ORTEP [19] programs. Final fractional atomic coor-
dinates are reported as supplementary material.
3. Results and discussion
3.1. General
The air-stable [ReO(NCS)2(OEt)(PPh3)2] compound,
which behaves as non-electrolyte in CH2Cl2 solution, is
readily soluble also in acetone, benzene and chloro-
form, whereas it is only slightly soluble in hot ethanol.
The IR spectra, show that the majority of the bands of
the compound in the mid-IR range, arise from PPh3
and that metal–phosphorus bonding induces only small
shifts in the bands of the free ligand [20,21]. However,
the spectrum is characterized by an intense w(ReꢀO)
peak at 952 cm−1 and by thiocyanate absorption
modes. In line with the reported X-ray molecular struc-
ture, the very strong antisymmetric CꢀN stretching
frequencies at 2096 and 2064 cm−1 and the medium
peaks due to w(CS) 847 cm−1 and l(NCS) at 470
cm−1, occur in the range observed for N-bonded
NCS− moieties [22,23] in other rhenium–isothio-
cyanato complexes [24–27]. The splitting of was(CN)
mode is related to the significant differences in the
Fig. 1. ORTEP view (50% ellipsoids) of transꢁ[ReO(NCS)2-
(OEt)(PPh3)2] moiety with atom numbering scheme.
Table 1
,
Selected bond lengths (A) and bond angles (°)
ReꢁO(1)
ReꢁO(2)
ReꢁN(2)
ReꢁN(1)
ReꢁP(1)
1.682(10)
1.871(10)
2.046(12)
2.079(12)
2.512(4)
2.520(4)
1.45(2)
N(2)ꢁC(2)
C(2)ꢁS(2)
P(1)ꢁC(3)
P(1)ꢁC(9)
P(1)ꢁC(15)
P(2)ꢁC(33)
P(2)ꢁC(27)
P(2)ꢁC(21)
1.16(2)
1.56(2)
1.806(7)
1.811(7)
1.814(7)
1.792(12)
1.809(10)
1.823(8)
,
ReꢁN(1) and ReꢁN(2) bond distances (0.033 A) and
angles (3.5°) between the bent ReꢁN(2)ꢀC(2) and
ReꢁN(1)ꢀC(1) units. In addition, as expected for com-
plexes containing RꢁO− alkoxo ligands, the strong
bands at 1065 and 912 cm−1, which are indeed in the
spectrum of [ReO(NCS)3(PPh3)2] complex, may be as-
signed to w(CꢁO−) and l(−OꢁC2H5) modes, respec-
tively, in agreement with literature data [15,28–30].
ReꢁP(2)
O(2)ꢁC(39)
S(1)ꢁC(1)
C(1)ꢁN(1)
1.61(2)
1.14(2)
O(1)ꢁReꢁO(2)
O(1)ꢁReꢁN(2)
O(2)ꢁReꢁN(2)
O(1)ꢁReꢁN(1)
O(2)ꢁReꢁN(1)
N(2)ꢁReꢁN(1)
O(1)ꢁReꢁP(1)
O(2)ꢁReꢁP(1)
N(2)ꢁReꢁP(1)
ReꢁN(2)ꢁC(2)
172.8(5)
93.4(5)
93.6(5)
87.9(5)
85.0(4)
178.6(5)
93.3(4)
85.9(3)
86.1(3)
168(2)
N(1)ꢁReꢁP(1)
O(1)ꢁReꢁP(2)
O(2)ꢁReꢁP(2)
N(2)ꢁReꢁP(2)
N(1)ꢁReꢁP(2)
P(1)ꢁReꢁP(2)
N(1)ꢁC(1)ꢁS(1)
N(2)ꢁC(2)ꢁS(2)
ReꢁN(1)ꢁC(1)
93.6(3)
94.5(4)
86.6(3)
91.5(3)
88.5(3)
172.0(1)
176(2)
3.2. Crystallography
A perspective drawing of the structure of the trans-
[ReO(NCS)2(OEt)(PPh3)2] compound is given in Fig. 1.
and selected bond lengths and angles are listed in Table
1. The rhenium(V) atom is six-coordinated in an octa-
177(2)
164.5(14)

116
R. Battistuzzi, M. Saladini / Inorganica Chimica Acta 304 (2000) 114–117
,
hedral environment with a trans arrangement of the
oxo and ethoxo ligands. Two P atoms of triphenylphos-
phine and two nitrogen atoms of the isothiocyanate
groups act as equatorial ligands. The two bulky
triphenylphosphine ligands are in trans position, this
way minimising the intramolecular contacts among the
phenyl rings and stabilising the crystal structure. The
trans position to the O(oxo) is occupied by the O atom
of the EtO− ligand as in analogous trans-
[ReOX2(OEt)(PPh3)2] (X=Cl, Br, I) [11–14] halo-com-
plexes, in line with the mutual ligand influence observed
in monomeric heteroligand octahedral rhenium(V)
mono–oxo complexes with acido-ligands (EtO−,
MeO−, OH−) with p-donor properties [14]. The redis-
tribution of the dp–pp interaction along the axial
OꢀReꢁOR coordinate and the formation of linear
pseudo-dioxo O···Re···O− group, typical of the metals
with a d2 configuration, is usually accompanied by a
shortening of the ReꢁO(alkoxo) bond. On the contrary,
the length of the Re–O(oxo) bond is rather insensitive
to both the character of the trans partner (neutral or
acidic ligand) and the formal multiplicity of the
ReꢁO(oxo) bond [31]. In the present compound the
ReꢁN bond distances of 2.046(12) and 2.079(12) A,
show a small lengthening if compared with the mean
,
value of 2.02 A found in other equatorially coordinated
isothiocyanate groups [24–26,34–36]. These groups are
linear with NꢁCꢁS angles of 177(2) and 176.9(14)°,
while there seems to be some bending at the nitrogen
atoms since the ReꢁNꢁC bond angles are of 164.9(13)
and 168.0(14)°. This bending could be explained in
terms of packing requirements and steric interactions
,
because the CꢁN [1.14(3), 1.16(2) A] and the CꢁS
[1.61(2), 1.56(2) A] bond lengths are consistent with a
,
sp hybridization of the N atom [34].
4. Supplementary material
Observed and calculated structure factors, atomic
positional parameters, anisotropic thermal parameters
for non hydrogen atoms, hydrogen atom parameters,
complete bond distances and angles, are supplied as
supplementary material (pp. 38). The supplementary
material is available from the authors on request.
,
ReꢁO(oxo) bond distance of 1.682(10) A falls in the
,
range 1.639–1.76 A [2,13,14,31], which is typical of
Acknowledgements
complexes of rhenium(V) having a [ReO]3+ core.
Therefore the ReꢁO(oxo) bond distance suggests a con-
siderable degree of triple bond character due to O“Re
p bonding, whereas the length of the ReꢁO(ethoxo)
We are grateful to the Centro Interdipartimetale
Grandi Strumenti (CIGS) of the University of Modena
and Reggio Emilia, which supplied the diffractometer,
and the Ministero dell’Universita` e della Ricerca Scien-
tifica e Tecnologica (MURST, Cofinanziamento) for
financial support.
,
bond (1.871 A) and ReꢁO(2)ꢁC(39) angle (146.2(11)°)
indicate an appreciable double bond character [32,33].
In the mono–oxo complexes the equatorial ligands
are normally displaced ‘downward’ toward the trans
partner of the oxo ligand, thus diminishing the repul-
sion of their bonding electrons with those of the Re ꢀ O
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