Ruthenium Complexes Containing “Noninnocent” o-Benzoquinone Diimine/
o-Phenylenediamide(2-) Ligands. Synthesis and Crystal Structure of the Nitrido-Bridged
Complex [{LRu(o-C
6
H
4
(NH)
2
)}
2
(μ-N)](PF
6
)
2
‚3CH
3
CN‚C
6
H
5
CH
3
Thomas Ju 1 stel,
†
Jesper Bendix,
†,‡
Nils Metzler-Nolte,
†
Thomas Weyhermu 1 ller,
†
Bernhard Nuber,
§
and Karl Wieghardt*
,†
Max-Planck-Institut fu ¨r Strahlenchemie, Stiftstrasse 34-36, D-45470 Mu ¨lheim an der Ruhr, Germany,
and Anorganisch-Chemisches Institut der Universita ¨t, Im Neuenheimer Feld 270,
D-69120 Heidelberg, Germany
ReceiVed July 8, 1997
X
Reaction of LRu
III
Cl
3
(L ) 1,4,7-trimethyl-1,4,7-triazacyclononane) with 1,2-phenylenediamine (opdaH
2
) in H
2
O
in the presence of air affords [LRu
II
(bqdi)(OH
2
)](PF
6
)(1), where (bqdi) represents the neutral ligand o-benzoquinone
diimine. From an alkaline methanol/water mixture of 1 was obtained the dinuclear species [{LRu
II
(bqdi)}
2
(µ-
H
3
O
2
)](PF
6
)
3
(1a). The coordinated water molecule in 1 is labile and can be readily substituted under appropriate
reaction conditions by acetonitrile, yielding [LRu
II
(bqdi)(CH
3
CN)](PF
6
)
2
(2), and by iodide and azide anions,
affording [LRu
II
(bqdi)I](PF
6
)‚0.5H
2
O(3) and [LRu(bqdi)(N
3
)](PF
6
)‚H
2
O(4), respectively. Heating of solid 4 in
vacuum at 160 °C generates N
2
and the dinuclear, nitrido-bridged complex [{LRu(o-C
6
H
4
(NH)
2
)}
2
(µ-N)](PF
6
)
2
(5). Complex 5 is a mixed-valent, paramagnetic species containing one unpaired electron per dinuclear unit
whereas complexes 1-4 are diamagnetic. The crystal structures of 1, 1a‚3CH
3
CN, 3, 4‚H
2
O, and 5‚3CH
3
CN‚0.5-
(toluene) have been determined by X-ray crystallography: 1 crystallizes in the monoclinic space group P2
1
/m, Z
) 2, with a ) 8.412(2) Å, b ) 15.562(3) Å, c ) 10.025 Å, and ) 109.89(2)°; 1a‚3CH
3
CN, in the monoclinic
space group C2/c, Z ) 4, with a ) 19.858(3) Å, b ) 15.483(2) Å, c ) 18.192(3) Å, and ) 95.95(2)°; 3, in the
orthorhombic space group Pnma, Z ) 4, with a ) 18.399(4) Å, b ) 9.287(2) Å, and c ) 12.052(2) Å, 4‚H
2
O,
in the monoclinic space group P2
1
/c, Z ) 4, with a ) 8.586(1) Å, b ) 15.617(3) Å, c ) 16.388(5) Å, and )
90.84(2)°; and 5‚3CH
3
CN‚0.5(toluene), in the monoclinic space group P2
1
/c, Z ) 4, with a ) 15.003(3) Å, b )
16.253(3) Å, c ) 21.196(4) Å, and ) 96.78(3)°. The structural data indicate that in complexes 1-4 the neutral
o-benzoquinone diimine ligand prevails. In contrast, in 5 this ligand has predominantly o-phenylenediamide
character, which would render 5 formally a mixed-valent Ru
IV
Ru
V
species. On the other hand, the Ru-N bond
lengths of the Ru-N-Ru moiety at 1.805(5) and 1.767(5) Å are significantly longer than those in other
crystallographically characterized Ru
IV
dNdRu
IV
units (1.72-1.74 Å). It appears that the C
6
H
4
(NH)
2
ligand in
5 is noninnocent and that formal oxidation state assignments to the ligands or metal centers are not possible.
Introduction
The dianionic form of doubly deprotonated o-phenylenedi-
amine is probably the archetype “noninnocent” ligand. Its
coordination chemistry has attracted the interest of chemists
because of the inherent problems associated with the assignment
of formal oxidation levels to the metal and the ligand itself in
a given transition metal complex.
1
In principle, the ligand can
bind as o-phenylenediamide(2-), o-benzosemiquinone diimide-
(1-), or neutral o-benzoquinone diimine to a transition metal
ion (Scheme 1). As Lever et al.
2
have stated, “the electron
distribution (in a coordination compound) will depend on the
extent of mixing between the metal and ligand orbitals, which,
in turn, is a function of the energies, symmetries, and overlap
of the valence metal and ligand orbitals.”
Conventional wisdom predicts then that the observed (mea-
sured) C-N and C-C bond lengths in a given complex
containing the coordinated C
6
H
4
(NH)
2
chelate should reflect its
oxidation level. Thus two short C-N bonds in conjunction with
two short conjugated and four longer C-C bonds in the ring
indicate (bqdi) character. In contrast, long C-N bonds and six
equivalent C-C bonds in ring are typical of the (opda)
2-
formulation.
Ruthenium(II) complexes containing a (bqdi) ligand have
been synthesized
3
and structurally characterized,
4
e.g. [Ru
II
-
†
Max-Planck-Institut.
‡
On leave from the University of Copenhagen.
§
Universita ¨t Heidelberg.
X
Abstract published in AdVance ACS Abstracts, December 15, 1997.
(1) See for example the discussion of the bonding in [Ni(C
6H4(NH)2)2]:
(a) Feigl, F.; Fu ¨rth, M. Monatsh. Chem. 1927, 48, 445. (b) Nyholm,
R. S. Chem. ReV. 1953, 53, 263. (c) Stiefel, E. I.; Waters, J. H.; Billig,
E.; Gray, H. B. J. Am. Chem. Soc. 1965, 87, 3016. (d) Balch, A. L.;
Holm, R. H. J. Am. Chem. Soc. 1966, 88, 5201. (e) Swartz Hall, G.;
Soderberg, R. H. Inorg. Chem. 1968, 7, 2300.
(2) Masui, H.; Lever, A. B. P.; Auburn, P. R. Inorg. Chem. 1991, 30,
2402.
(3) (a) Warren, L. F. Inorg. Chem. 1977, 16, 2814. (b) Pyle, A. M.; Barton,
J. K. Inorg. Chem. 1987, 26, 3820.
(4) Belser, P.; von Zelewsky, A.; Zehnder, M. Inorg. Chem. 1981, 20,
3098.
35 Inorg. Chem. 1998, 37, 35-43
S0020-1669(97)00850-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 01/12/1998