Bis[dirhodium(II)] complexes with a Rh (ì-Cl) core: preparation and
4
4
characterization‡
,
Zhiyong Yang, Hiroki Oki, Masahiro Ebihara and Takashi Kawamura* †
Department of Chemistry, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193,
Japan
CH Cl –PhCN with hexane resulted in axial ligand exchange
2
2
n
The reaction of [Rh (O CPr ) ] or [Rh (mhp) ] (Hmhp = 2-
and gave small brown single crystals of (hh,hh)-[Rh (mhp) Cl -
2
2
4
2
4
4 4 4
hydroxy-6-methylpyridine) with a trialkylchlorosilane followed
(PhCN) ] 3 which were of moderate quality for X-ray study.
2
n
by crystallization from a nitrile unexpectedly gave [Rh (O -
When [Rh (O CPr ) ] was refluxed with (CH ) SiCl in CH CN
4
2
2
2
4
3
3
3
n
CPr ) Cl (CH CN) ] 1 or an isomer of [Rh (mhp) Cl (PhCN) ]
until complete consumption of the starting dirhodium com-
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3
4
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4
2
both with a ‘twisted-cage’ Rh (µ-Cl) core, which were studied
plex had occurred (TLC), only a mononuclear rhodium()
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5
by X-ray crystallography, cyclic voltammetry and UV/VIS
spectroscopy; 1 catalyzed the hydrogenation of acrylic acid
in water.
complex, mer-[Rh(CH CN) Cl ], was isolated.
3
3
3
The crystal structures of 1§ and 3¶ are shown in Figs. 1 and 2,
II
II
respectively. The two Rh –Rh units of these Rh (µ-Cl) com-
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4
plexes, each of which contains two bridging carboxylato or
II
II
mhp ligands spanning a Rh ᎐Rh bond, are linked together
II
II
by four µ-Cl ligands. The two Rh ᎐Rh bonds are arranged
perpendicularly when viewed along the centers of the Rh᎐Rh
The chloro ligand is interesting because it is substitutionally
labile, co-ordinates in both terminal and bridging fashion and
has metal–ligand σ- and π-type electronic interactions. When
the ligand is bridging it may induce metal–metal indirect
electronic interactions through its orbital(s). We have unexpect-
edly isolated bis[dirhodium()] complexes supported by four
chloro bridges in low to moderate yields in trials aimed at sub-
n
stituting the bridging ligands of [Rh (O CPr ) ] or [Rh (mhp) ]
2
2
4
2
4
(
Hmhp = 2-hydroxy-6-methylpyridine) with chloro ligands.
Stimulated by the work of Cotton and co-workers in preparing
Rh (O CCH ) Cl (L᎐L)] and [Rh Cl (L᎐L) ] (L᎐L denotes a
[
2
2
3
2
2
2
4
2
diphosphine) by the reaction of [Rh (O CCH ) ] with (CH ) -
2
2
3
4
3 3
n
SiCl in the presence of L᎐L we treated [Rh (O CPr ) ] or
2
2
4
[
Rh (mhp) ] with trialkylchlorosilane. Since complexes with
2 4
an M (µ-X) (X = halogen) skeleton similar to that found in
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n
[
Rh (O CPr )Cl (CH CN) ] and [Rh (mhp) Cl (PhCN) ] have
been known to us only in the chemistry of Mo with a limited
number of compounds, we report here the preparation, crystal
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2
4
4
3
4
4
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4
III
2
2
structures and properties of the current Rh (µ-Cl) complexes
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4
as a preliminary communication.
n
3
Axial-ligand free [Rh (O CPr ) ] (2.22 g, 4.0 mmol) was
7
2
2
4
Fig. 1 An ORTEP view of the non-hydrogen atoms of [Rh (O -
4 2
n
3
3
heated with (C H ) SiCl (3.0 cm , 18 mmol) in toluene (70 cm )
CPr ) Cl (CH CN) ] 1. Thermal ellipsoids are drawn at the 50% level.
4 4 3 4
The C(6) ellipsoid shows one of the two disordered methyl carbon
atoms of the butyrato ligand. The geometry belongs to the S point
group. Selected bond lengths (Å) and angles (Њ): Rh(1)᎐Rh(1Ј)
.5552(9), Rh(1)᎐Cl(1) 2.330(2), Rh(1)᎐Cl(1Љ) 2.317(2), Rh(1)᎐O(1)
.029(5), Rh(1)᎐O(2Ј) 2.033(5), Rh(1)᎐N(1) 2.272(6); Rh(1Ј)᎐Rh(1)᎐
Cl(1) 99.72(4), Rh(1Ј)᎐Rh(1)᎐Cl(1Љ) 96.69(4), Rh(1)᎐Cl(1)᎐Rh(1*)
107.36(6), Cl(1)᎐Rh(1)᎐Cl(1Љ) 87.81(3)
2
5
3
at reflux under Ar for 20 h to give a brown precipitate. After
collection the precipitate was stirred with 40 mL of CH CN to
give a yellow-green powder of [Rh (O CPr ) Cl (CH CN) ] 1
in 35% yield. The reaction of trans-(hh,tt)-[Rh (mhp) ] (where
hh,tt represents head-to-head, tail-to-tail) with (CH ) SiCl in
toluene at reflux gave a brown precipitate, which was loaded
4
3
n
4
2
4
4
3
4
2
2
2
4
4
3
3
onto a silica-gel column and eluted with a CH Cl –CH CN
2
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3
mixture (4:1 v/v) to give (hh,hh)-[Rh (mhp) Cl (CH CN) ] [2;
4
4
4
3
2
§
(Found: C, 26.80; H, 3.63; Cl, 13.29; N, 5.13. C H Cl N O Rh
24 40 4 4 8 4
see Fig. 2 in the following paragraph for the arrangement of
the mhp bridging ligands in the ‘(hh,hh)-isomer’] in 8% yield
as the second band (yellow). Although we could obtain only
poor-quality single crystals of 2, layering and solution of 2 in
requires C, 27.04; H, 3.78; Cl, 13.30; N, 5.26%). Crystal data for com-
plex 1: M = 1066.04, tetragonal, space group I4 (no. 82), a = 10.512(2),
c = 15.660(2) Å, U = 1730.4(6) Å , Z = 2, µ = 22.27 cm , T = Ϫ80 ЊC.
Solved by direct methods (SHELXS 86 ). R = 0.023, R
S = 1.25 for 962 unique reflections.
¯
3
Ϫ1
6
= 0.031 and
w
¶
Crystal data for complex 3: C H Cl N O Rh , M = 1192.16, mono-
38 34 4 6 4 4
†
‡
E-Mail: kawamura@apchem.gifu-u.ac.jp
clinic, space group C2/c (no. 15), a = 12.405(4), b = 24.119(4),
3
Ϫ1
Supplementary data available: UV/VIS absorption spectra of
c = 14.405(3) Å, β = 112.49(2)Њ, U = 3982(1) Å , Z = 4, µ = 19.42 cm
,
n
6
[
Rh (O CPr ) Cl (CH CN) ] in CH CN, CH CN–CH Cl and CH Cl
T = Ϫ80 ЊC. Solved by direct methods (SHELXS 86 ). R = 0.069,
4
2
4
4
3
4
3
3
2
2
2
2
n
and electronic spectra of [Rh (O CPr ) Cl L ] (L = CH CN or H O).
R = 0.070 and S = 1.36 for 1157 unique reflections. Owing to weak
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2
w
For direct electronic access see http://www.rsc.org/suppdata/dt/1998/
277/, otherwise available from BLDSC (No. SUP 57 397, 3 pp.) or the
RSC Library. See Instructions for Authors, 1998, Issue 1 (http://
www.rsc.org/dalton).
diffraction due to the small size of the crystal, the deduced geometric
parameters are not of high quality, but the chemical structure is reliable,
CCDC reference number 186/1039. See http://www.rsc.org/suppdata/
dt/1998/2277/ for crystallographic files in .cif format.
2
J. Chem. Soc., Dalton Trans., 1998, Pages 2277–2278
2277
Yang, Zhiyong
