Synthesis, characterisation and electrochemical behaviour of rhodium(III) complexes containing 1,2-naphthoquiaone-2-oxime and formation of imine complexes through N - O bond cleavage

Article abstract of DOI:10.1002/1099-0682(200102)2001:2<511::AID-EJIC511>3.0.CO;2-U

The new rhodium (II) complexes [Rh(η²-nqo)L₂Cl₂] (1a-1d) and [Rh(η²-nqo)₂LCl] (2b-2d) [1a, L = PPh₃; 1b,2b, L = pyridine (py); 1c,2c, L = 4-phenylpyridine (ppy); 1d,2d, L = 4-acetylpyridine

Full text of DOI:10.1002/1099-0682(200102)2001:2<511::AID-EJIC511>3.0.CO;2-U

FULL PAPER
Synthesis, Characterisation and Electrochemical Behaviour of Rhodium(III)
Complexes Containing 1,2-Naphthoquinone-2-oxime and Formation of Imine
Complexes through N؊O Bond Cleavage
Xiao-Xia Liu[a] and Wing-Tak Wong*[a]
Keywords: Rhodium / N ligands / Electrochemistry
The new rhodium(III) complexes [Rh(η2-nqo)L2Cl2] (1a−1d)
and [Rh(η2-nqo)2LCl] (2b−2d) [1a, L = PPh3; 1b,2b, L = pyrid-
ine (py); 1c,2c, L = 4-phenylpyridine (ppy); 1d,2d, L = 4-
acetylpyridine (apy)] have been prepared by treatment of the
reaction mixture of RhCl3·3H2O and 1,2-naphthoquinone-2-
to RhI, accompanied by the loss of the chloride ligands. The
1,2-naphthoquinone-2-imine (nqi) complexes [Rh(η2-
nqo)(η2-nqi)Cl2]·L (3b−3d) (3b, L = py; 3c, L = ppy; 3d, L =
apy), [Rh(η2-nqo)(η2-nqi)Cl2] (4) and [Rh(η2-nqo)2(nqi)Cl] (5)
were obtained by deoxygenation of the oxime group in
oxime (nqo) in ethanol by P or N donor ligands. Cyclic vol- which N−O bond cleavage is observed. The molecular struc-
tammetric studies show that the new complexes display an
irreversible metal-localised two-electron reduction from RhIII
tures of 1a, 2b, 4 and 5 were established by single crystal X-
ray analyses.
Results and Discussion
Introduction
Synthesis and Characterisation of Rhodium(III) Complexes
[Rh(η2-nqo)L2Cl2] (1a؊1d) and [Rh(η2-nqo)2LCl] (2b؊2d)
Rhodium(III) complexes containing chloride ligands
have attracted much attention. They have been shown to
be active in processes such as the photochemical[1] and the
electrochemical[2Ϫ5] reduction of protons or water to dihy-
drogen, the electrocatalytic hydrogenation of organics,[2Ϫ4]
and the electrochemical regeneration of NADH from
NADϩ.[6,7] Most of the complexes mentioned above con-
tain 2,2-bipyridine type ligands. 1,2-Naphthoquinone-
monooximes are another kind of donor ligand with a π-
accepting ability.[8,9] In ruthenium 1,2-naphthoquinone-1-
oxime complexes, the MLCT from ruthenium(II) to the li-
gand occurs with comparatively low energy.[10] The exist-
ence and the number of this ligand in 2,2-bipyridine-con-
taining ruthenium complexes influence the electrochemical
property of the metal centre.[11] Metal complexes containing
1,2-naphthoquinone-monooximes are of interest as they are
widely used for analytical purposes[12,13] and are potentially
useful for the preparation of a wide variety of organic
compounds.[14Ϫ17] However, most of the studies have been
concerned with first-row transition metals.[14Ϫ20] Reports
dealing with these ligands involving complexes of second-
row transition metals are very limited.[9,11,21,22] As a con-
tinuation of our studies on 1,2-naphthoquinone-monoox-
ime complexes of second row transition metals,[10,23Ϫ25] we
herein present the formation of a series of chloro rhodiu-
m(III) complexes containing 1,2-naphthoquinone-2-oxime
(abbreviated as nqoH).
The new rhodium(III) complexes [Rh(η2-nqo)L2Cl2]
(1aϪ1d) and [Rh(η2-nqo)2LCl] (2bϪ2d) [1a, L ϭ PPh3;
1b,2b, L ϭ pyridine (py); 1c,2c, L ϭ 4-phenylpyridine (ppy);
1d,2d, L ϭ 4-acetylpyridine (apy)] were synthesised by the
treatment of a reaction mixture of RhCl3·3H2O and 1,2-
naphthoquinone-2-oxime in refluxing ethanol with PPh3,
pyridine, 4-phenylpyridine or 4-acetylpyridine (Scheme 1).
Characterisation of the new complexes by spectroscopic
methods (1H NMR, FAB MS) reveals that 1aϪ1d contain
one nqo and two P or N donor ligands coordinated to the
metal centre (Table 1). In order to establish the molecular
structure of complex 1a, a single-crystal X-ray diffraction
analysis was carried out. The molecular structure of 1a is
depicted in Figure 1, while bond lengths and angles are
available in the Supporting Information. The molecule of
1a contains a pseudo octahedrally coordinated rhodium
centre. The nqo ligand coordinates to the metal centre
through its oximato N and naphthoquinonic O atoms to
form a five-membered metallocyclic ring [O(1)ϪRhϪN(1)
81.3(2)°]. This coordination mode is very common for 1,2-
naphthoquinone-monooxime ligands.[9,10,16,19Ϫ25] The mo-
lecule also contains two chloride atoms [Cl(1) and Cl(2)],
which are trans to the oximato N and naphthoquinonic O
atoms,
respectively
([N(1)ϪRhϪCl(1)
170.8(1)°],
[O(1)ϪRhϪCl(2) 176.5(1)°]), forming an equatorial plane
with the nqo ligand. The two phosphane ligands occupy the
perpendicular positions to complete the six coordination
configuration of the Rh metal centre ([P(1)ϪRhϪP(2)
[a]
Department of Chemistry, The University of Hong Kong,
˚
178.32(5)°]). The mean RhϪP distance is 2.3945(1)A, which
Pokfulam Road, Hong Kong
is similar to other Rh complexes with phosphane coor-
Fax: (internat.) ϩ852-2547-2933, or -2857-1586
E-mail: wtwong@hkucc.hku.hk
dinated
to
their
metal centre, such
as
in
Supporting information for this article is available on the
WWW under http://www.wiley-vch.de/home/eurjic or from the
author.
[Rh(Hdmg)(bdio)(PEt3)]ϩ[Rh(Hdmg)2Cl2]Ϫ·H2O (dmg ϭ
dimethylglyoximato; bdio ϭ 2,3-butanedione 2-imino 3-oxi-
Eur. J. Inorg. Chem. 2001, 511Ϫ520
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0202Ϫ0511 $ 17.50ϩ.50/0
511

X.-X. Liu, W.-T. Wong
FULL PAPER
Scheme 1. Reaction of RhCl3·3H2O with nqoH followed by treatment with the pyridyl ligand
mato), where the corresponding bond length is complexes
˚
such
as
[Rh(Hdmg)(bdio)(PEt3)]ϩ[Rh-
Ϫ
[26]
2.3817(8)A.[26] In the 1H NMR spectra of the pyridine com- (Hdmg)2Cl2] ·H2O [2.3320(9) A].
The nqo ligands of
˚
plexes 1bϪ1d, the chemical shifts of the nqo proton signals 2bϪ2d exist in a similar chemical environment, since they
1
are very similar to those in 1a, showing that the nqo ligands display very similar chemical shifts in their H NMR spec-
have very similar chemical environments. Thus, complexes tra. The spatial arrangement of the ligands in complexes
1bϪ1d are proposed to have similar molecular structures to 2bϪ2d should be the same. The asymmetry of the nqo ligands
1a, with the bidentate nqo ligand and the two chloride gives rise to the possibility for the presence of structural iso-
atoms occupying the equatorial plane, and the two pyridyl mers other than 2bϪ2d; in fact, we observe some other minor
ligands occupying the perpendicular sites.
bands in the reaction mixture from TLC. Unfortunately, we
Characterisation of complexes 2bϪ2d by spectroscopic could not isolate or characterise these compounds.
methods (Table 1) reveals that they contain two nqo li-
gands, one pyridyl ligand and one chloride atom. A single
Electrochemistry of Complexes 1a؊1d and 2b؊2d
crystal X-ray analysis was conducted on 2b. The molecular
Cyclic voltammetry of complexes 1aϪ1d and 2bϪ2d was
structure of [Rh(η2-nqo)2(py)Cl] (2b) is depicted in Fig- performed at a standard scan rate of 100 mV sϪ1 in CH2Cl2/
ure 2, while the bond parameters can be obtained from the 0.1  tetrabutylammonium hexafluorophosphate (TBAH).
Supporting Information. A distorted octahedral coordina- The redox potentials are listed in Table 2 and the represent-
tion of the rhodium metal centre is observed. The nqo li- ative cyclic voltammogram of 1a is shown in Figure 3.
gands chelate to the metal centre in a similar way as in 1a
The electrochemical behaviour of [Rh(η2-nqo)(PPh3)2Cl2]
[O(1)ϪRhϪN(1) ϭ 81.3(2)° and O(3)ϪRhϪN(2) 81.8(2)°]. (1a) resembles that of other chloro rhodium(III) complexes
[2,27]
The oximato N and the naphthoquinonic O atoms adopt a with 2,2Ј-bipyridyl ligands, such as [RhL(P)2(Cl)2]ϩ
mutually cis geometry as in the ruthenium 1,2-naphthoqui- and [RhL2(Cl)2]ϩ,[3,28,29] and some complexes containing π-
none-2-oxime complexes cis,cis-[Ru(η2-nqo)2L1L2] (L1, coordinated ligands [Rh(C5Me5)LCl]ϩ (P ϭ PPh2Et or
L2 ϭ CO or pyridyl ligands).[10,24] Pyridine is coordinated PPh3; L ϭ 2,2-bipyridyl ligands).[1,4Ϫ6,30Ϫ32] This behaviour
to the Rh centre through its N atom and is trans to the is characterised by an irreversible, metal-localised two-elec-
oximato
N
of an nqo ligand, as in cis,cis-[Ru(η2- tron reduction at peak potential Ec1, which is associated
nqo)2(CO)L] (L ϭ pyridyl ligands).[10,24] The chloride atom with the loss of the two chloride ligands (EC mechanism)
is trans to the naphthoquinonic O atom of another nqo yielding the RhI complex [Scheme 2, Equation (1)]. A con-
˚
ligand, with a RhϪCl bond length of 2.332(2)A. This is trolled-potential electrolysis at a potential slightly negative
consistent with the RhϪCl distance in other rhodium to this wave, consumes two electrons per molecule of com-
512
Eur. J. Inorg. Chem. 2001, 511Ϫ520

Rhodium(III) Complexes Containing 1,2-Naphthoquinone-2-oxime
FULL PAPER
Table 1. Spectroscopic data for compounds 1a؊1d, 2b؊2d, 3b؊3d and 4؊7
Complex 1H NMR spectra (δ, J/Hz)
31P NMR spectra
(δ, J/Hz)
Mass spectra[a]
(m/z)
1a
1b
1c
1d
8.01 (d, J ϭ 7.9, 1 H, H1), 7.72Ϫ7.66 (m, phenyl, 12 H), 7.52 (m, 1 H, H3),
7.37 (m, 1 H, H4), 7.35 (m, 1 H, H2), 7.30Ϫ7.25 (m, 6 H, phenyl),
7.22Ϫ7.17 (m, 12 H, phenyl), 6.48 (d, J ϭ 9.5, 1 H, H5), 6.32
(d, J ϭ 9.5, 1 H, H6)[b]
18.26
834 (870)[c]
[d, J(Rh,P) ϭ 90.7]
8.99 (m, 2 H, H7), 8.80 (m, 2 H, H7Ј), 8.64 (m, 1 H, H1), 7.98 (tt, J ϭ 7.6,
1.5, 1 H, H9), 7.90 (tt, J ϭ 7.6, 1.5, 1 H, H9Ј), 7.66 (m, 1 H, H3), 7.60
(m, 1 H, H4), 7.53 (m, 2 H, H8), 7.51 (m, 1 H, H2), 7.41 (m, 2 H, H8Ј),
7.40 (d, J ϭ 9.5, 1 H, H6), 6.94 (d, J ϭ 9.5, 1 H, H5)
Ϫ
Ϫ
Ϫ
504 (504)
9.04 (br.d, J ϭ 6.5, 2 H, H7), 8.84 (m, 2 H, H7Ј), 8.65 (d, J ϭ 7.7, 1 H, H1),
7.73 (m, 2 H, H8), 7.74Ϫ7.68 (m, 4 H, phenyl), 7.67 (m, 1 H, H3), 7.61
(m, 3 H, H4,8Ј), 7.58Ϫ7.54 (m, 6 H, phenyl), 7.53 (m, 1 H, H2), 7.42
(d, J ϭ 9.5, 1 H, H6), 6.95 (d, J ϭ 9.5, 1 H, H5)[b]
621 (656)[c]
552 (588)[c]
9.19 (br.d, J ϭ 6.6, 2 H, H7), 9.00 (m, 2 H, H7Ј), 8.61 (d, J ϭ 7.9, 1 H, H1),
7.95 (dd, J ϭ 5.2, 2 H, 1.5, H8), 7.82 (dd, J ϭ 5.4, 2 H, 1.5, H8Ј), 7.68
(m, 1 H, H3), 7.61 (br.d, J ϭ 7.2, 1 H, H4), 7.52 (m, 1 H, H2), 7.38
(d, J ϭ 9.5, 1 H, H6), 6.96 (d, J ϭ 9.5, 1 H, H5), 2.72 (s, 3 H, H9
or H9Ј), 2.70 (s, 3 H, H9Ј or H9)
2b
2c
8.99 (br.d, J ϭ 5.3, 2 H, H7), 8.75 (d, J ϭ 7.7, 1 H, H1), 8.42 (d, J ϭ 7.9,
1 H, H1Ј), 7.89 (m, 1 H, H9), 7.71 (m, 1 H, H3), 7.63 (m, 1 H, H3Ј), 7.62
(m, 1 H, H4), 7.56 (m, 2 H, H2,4Ј), 7.50 (m, 2 H, H8), 7.42 (m, 1 H, H2Ј),
7.33 (m, 1 H, H6Ј), 7.18 (d, J ϭ 9.5, 1 H, H6), 6.90 (d, J ϭ 9.5, 1 H, H5Ј),
6.89 (d, J ϭ 9.5, 1 H, H5)[b]
Ϫ
Ϫ
562 (562)
638 (638)
8.99 (br.d, J ϭ 6.6, 2 H, H7), 8.77 (d, J ϭ 8.0, 1 H, H1), 8.44 (d, J ϭ 7.8,
1 H, H1Ј), 7.71 (m, 1 H, H3), 7.67 (m, 2 H, H8), 7.63 (m, 1 H, H3Ј), 7.63Ϫ7.55
(m, 3 H, H4, 2H of phenyl), 7.58 (m, 1 H, H2), 7.52Ϫ7.49 (m, 4 H,
H4Ј, 3H of phenyl), 7.43 (m, 1 H, H2Ј), 7.35 (d, J ϭ 9.5, 1 H, H6Ј),
7.20 (d, J ϭ 9.5, 1 H, H6), 6.91 (d, J ϭ 9.5, 1 H, H5Ј), 6.89 (d, J ϭ
9.5, 1 H, H5)[b]
2d
3b
3c
9.20 (br.d, J ϭ 6.5, 2 H, H7), 8.73 (d, J ϭ 7.9, 1 H, H1), 8.41 (d, J ϭ 8.4,
1 H, H1Ј), 7.92 (dd, J ϭ 5.1, 1.7, 2 H, H8), 7.72 (m, 1 H, H3), 7.63
(m, 1 H, H3Ј), 7.62 (m, 1 H, H4), 7.57 (m, 1 H, H2), 7.56 (d, J ϭ 7.8, 1 H, H4Ј),
7.43 (m, 1 H, H2), 7.31 (d, J ϭ 9.5, 1 H, H6Ј), 7.18 (d, J ϭ 9.5, 1 H, H6), 6.91 (d,
J ϭ 9.5, 1 H, H5Ј), 6.89 (d, J ϭ 9.5, 1 H, H5), 2.64 (s, 3 H, H9)[b]
11.46 (br., 1 H, H7Ј), 9.13 (m, 2 H, H8), 8.64 (d, J ϭ 8.1, 1 H, H1), 8.24
(d, J ϭ 7.6, 1 H, H1Ј), 8.00 (t, J ϭ 7.6, 1 H, H10), 7.67 (m, 2 H, H3, 3Ј), 7.60
(m, 2 H, H9), 7.57 (m, 1 H, H4), 7.51 (m, 1 H, H2), 7.48 (m, 1 H, H2Ј), 7.39
(d, J ϭ 9.5, 1 H, H6), 7.32 (br.d, J ϭ 7.6, 1 H, H4Ј), 7.09 (br.d, J ϭ 10.2,
1 H, H6Ј), 6.96 (br.d, J ϭ 10.2, 1 H, H5Ј), 6.94 (d, J ϭ 9.5, 1 H, H5)
11.50 (br., 1 H, H7Ј), 9.13 (br.d, J ϭ 6.6, 2 H, H8), 8.66 (d, J ϭ 7.9, 1 H, H1),
8.25 (d, J ϭ 7.6, 1 H, H1Ј), 7.77 (br.d, J ϭ 6.6, 1 H, H9), 7.75Ϫ7.72 (m, 2 H, phenyl),
7.67 (m, H, H3Ј), 7.65 (m, 1 H, H3), 7.61 (br.d, J ϭ 7.1, 1 H, H4), 7.58Ϫ7.54
(m, 3 H, phenyl), 7.51 (m, 1 H, H2), 7.49 (m, 1 H, H2Ј), 7.40 (d, J ϭ 9.5, 1 H, H6),
7.32 (br.d, J ϭ 7.5, 1 H, H4Ј), 7.11 (br.d, J ϭ 10.2, 1 H, H6Ј), 7.03 (br.d, J ϭ 10.2,
1 H, H5Ј), 6.95 (d, J ϭ 9.5, 1 H, H5)[b]
Ϫ
Ϫ
Ϫ
568 (604)[c]
582 (582)
658 (658)
3d
11.40 (br., 1 H, H7Ј), 9.34 (br.d, J ϭ 6.5, 2 H, H8), 8.61 (d, J ϭ 7.9, 1 H, H1), 8.25
(d, J ϭ 7.8, 1 H, H1Ј), 7.99 (dd, J ϭ 5.2, 1.5, 1 H, H9), 7.68 (m, 1 H, H3Ј), 7.66
(m, 1 H, H3), 7.61 (br.d, J ϭ 7.1, 1 H, H4), 7.52 (m, 1 H, H2), 7.49 (m, 1 H, H2Ј),
7.38 (d, J ϭ 9.5, 1 H, H6), 7.33 (br.d, J ϭ 7.4, 1 H, H4Ј), 7.11 (dd, J ϭ 10.1, 1.3,
1 H, H6Ј), 6.98 (br.d, J ϭ 10.1, 1 H, H5Ј), 6.96 (d, J ϭ 9.5, 1 H, H5), 2.71 (s, 3 H,
H10)[b]
Ϫ
624 (624)
4
5
Ϫ
Ϫ
Ϫ
331 (503)[d]
639 (640)
10.30 (br., 1 H, H7ЈЈ), 8.82 (d, J ϭ 7.9, 2 H, H1,1Ј), 7.98 (d, J ϭ 7.4, 1 H, H1ЈЈ),
7.75 (br.d, J ϭ 10.1, 1 H, H5ЈЈ), 7.67 (m, 1 H, H3 or H3Ј), 7.65 (m, 1 H, H3Ј or H3),
7.60 (m, 1 H, H3ЈЈ), 7.57 (m, 2 H, H2,2Ј), 7.56 (br.d, J ϭ 7.2, 2 H, H4,4Ј), 7.39
(m, 1 H, H6ЈЈ), 7.37 (m, 1 H, H2ЈЈ), 7.34 (d, J ϭ 9.5, 2 H, H6,6Ј), 7.30 (br.d, J ϭ 7.7,
1 H, H4ЈЈ) 6.86 (d, J ϭ 9.5, 2 H, H5,5Ј
)
6
7
8.58 (d, J ϭ 8.0, 3 H, H1,1Ј,1ЈЈ), 7.69 (m, 3 H, H3,3Ј,3ЈЈ), 7.60 (br.d, J ϭ 7.4,
3 H, H4,4Ј,4ЈЈ), 7.49 (m, 3 H, H2,2Ј,2ЈЈ), 7.20 (d, J ϭ 9.5, 3 H, H6,6Ј,6ЈЈ), 6.92
Ϫ
Ϫ
620 (619)[e]
620 (619)[e]
(d, J ϭ 9.5, 3 H, H5,5Ј,5ЈЈ [b]
)
8.59 (d, J ϭ 8.0, 1 H, H1), 8.50 (d, J ϭ 8.0, 2 H, H1Ј,1ЈЈ), 7.70Ϫ7.64 (m, 3 H,
H3,3Ј,3ЈЈ), 7.60Ϫ7.57 (m, 3 H, H4,4Ј,4ЈЈ), 7.51Ϫ7.45 (m, 3 H, H2,2Ј,2ЈЈ), 7.27 (m, 1 H,
H6 or H6Ј or H6ЈЈ), 7.25 (m, 1 H, H6 or H6ЈЈ), 7.20 (d, J ϭ 9.5, 1 H, H6, or H6Ј
or H6ЈЈ), 6.95 (d, J ϭ 9.5, 1 H, H5Ј or H5ЈЈ), 6.93 (d, J ϭ 9.5, 2 H, H5,5Јor5ЈЈ [b]
)
[a]
[b]
[c]
Calculated values in parentheses. Ϫ By 1H,1H COSY NMR spectroscopy. Ϫ Only [M Ϫ Cl]ϩ is observed. Ϫ [d] Only [M Ϫ nqo]ϩ
[e]
is observed. Ϫ By ESI MS.
plex and leads to a purple-coloured solution. We failed to The reverse process, the reoxidation of the RhI complex, is
isolate the purple product as it was not stable enough under also a two-electron step (Ea1), with subsequent completion
our experimental conditions. The colour of the solution of the coordination sphere of the d6 metal centre by addi-
slowly changed to red on removing the applied potential. tion of the chloride ligands [Equation (2)].
Eur. J. Inorg. Chem. 2001, 511Ϫ520
513

X.-X. Liu, W.-T. Wong
FULL PAPER
The RhI complex can be further reduced at a more nega-
tive potential with an apparently reversible (Ec2, Ea2) single-
electron step. The 2,2-bipyridyl complexes displayed similar
reversible redox couples, which have been attributed to the
reduction of the pyridyl ligand, leading to the coordinated
radical anion L·Ϫ. Lund reported the cyclic voltammetric
study of fluorenone oxime (F1ϭNOH), which displayed a
nearly reversible reduction at Ϫ1.67 V vs. SCE to its radical
anion F1ϭNOH·Ϫ.[33] The reduction of the oxime group in
a copper(II) complex [Cu(H2L)(H2O)2]Cl2 [L is a tripodal
ligand containing an oxime group, such as N,N-(2-hydroxy-
acetophenyl)-(3-butane-2-oxime)-NЈ-(2-hydroxyaceto-
phenyl)-1,2-diaminoethane] appeared around Ϫ1.5 V vs.
SCE.[34] Similarly, the one-electron reduction of our nqo
complex 1a is oximato-ligand centred [Equation (3)] and
leads to the radical anion. Compared with the free ligand
(Table 2), the coordinated nqo is more difficult to reduce
due to the π back-donation from the metal centre to the
ligand.[30,35] This reduction process for complexes 1bϪ1d
appears at a more negative potential than that of 1a. As the
phosphane is a π-acceptor ligand, the degree of metal-to-
nqo-ligand electron shift is smaller in 1a than in 1bϪ1d.
This ligand-based reduction in complexes 1bϪ1d is irrevers-
ible, and the reoxidation peak of RhI to RhIII is not de-
tected. In complexes 2bϪ2d, apart from the irreversible
metal-centred processes, two quasi-reversible one-electron
reductions of the nqo ligands (Ec2 for one nqo and Ec3 for
another) at less-negative potentials are observed. Since
there are two nqo ligands in each of the 2bϪ2d complexes,
Figure 1. The molecular structure of [Rh(η2-nqo)(PPh3)2Cl2] (1a)
with the atom numbering scheme
Figure 2. The molecular structure of [Rh(η2-nqo)2(py)Cl] (2b) with the atom numbering scheme
514
Eur. J. Inorg. Chem. 2001, 511Ϫ520

Rhodium(III) Complexes Containing 1,2-Naphthoquinone-2-oxime
FULL PAPER
Table 2. Electrochemical data for the free ligand nqoH and complexes 1aϪ1d and 2bϪ2d
[a]
Compound
Ec1
Ea1
Ec2
Ea2
Ea2ϪEc2
Ec3
Ea3
Ea3ϪEc3
nqoH
1a
Ϫ
Ϫ
0.14
Ϫ
Ϫ
Ϫ
Ϫ0.78
Ϫ0.75
Ϫ0.72
Ϫ1.08[b]
Ϫ1.61[c]
Ϫ1.81[b]
Ϫ1.83[b]
Ϫ1.81[b]
Ϫ1.26[d]
Ϫ1.31[d]
Ϫ1.23[d]
Ϫ0.87
Ϫ1.51
Ϫ
Ϫ
Ϫ
Ϫ1.15
Ϫ1.15
Ϫ1.12
0.21
0.10
Ϫ
Ϫ
Ϫ
0.11
0.16
0.11
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ1.23[b]
Ϫ1.12[b]
Ϫ1.18[b]
Ϫ1.19[b]
Ϫ1.09[b]
Ϫ1.14[b]
Ϫ1.11[b]
1b
1c
1d
Ϫ
Ϫ
Ϫ
2b
Ϫ1.43[d]
Ϫ1.52[d]
Ϫ1.49[d]
Ϫ1.31
Ϫ1.34
Ϫ1.32
0.12
0.18
0.17
2c
2d
[a]
[b]
Peak potentials in volts vs. Fc0/ϩobtained from cyclic voltammetry at 100 mV sϪ1 in CH2Cl2/0.1 mol dmϪ3 TBAH. Ϫ Irreversible.
[c]
[d]
Ϫ
Apparently reversible. Ϫ Quasi-reversible.
to elucidate the molecular structure. The molecular struc-
ture of 4 is shown in Figure 4, and the corresponding bond
parameters are available from the supplementary material.
The molecule contains two chloride atoms, one nqo ligand
and one oximato deoxygenated nqo ligand. There is no pyr-
idyl ligand. The central metal atom also adopts a distorted
octahedral coordination mode, as in 1a and 2b. The two
chloride atoms are trans to each other [Cl(1)ϪRhϪCl(2) ϭ
178.5(2)°] and the two naphthalene-derived rings occupy
the equatorial plane. The nqo and the nqo-derived ligands
adopt a chelate mode to the metal centre. The CϪO bond
˚
length O(3)ϪC(11) in the nqo-derived ligand is 1.24(2)A,
which is comparable with the corresponding bond length
˚
for the quinonic group [CϪO ϭ 1.247(5)A] in 3-hydroxy-2-
methyl-1,4-benzoquinone 4-oxime,[36] and is smaller than
˚
the corresponding one [O(1)ϪC(1) ϭ 1.32(1)A] for the nqo
Figure 3. Cyclic voltammogram of [Rh(η2-nqo)(PPh3)2Cl2] (1a) in
ligand in the same molecule. The CϪN bond length
([N(2)ϪC(20) ϭ 1.27(1) A]) is of a similar length to the
CH2Cl2 containing 0.1 mol dmϪ3 TBAH; scan rate, 100 mV sϪ1
˚
˚
imino
CϪN
bond
length
[1.294(5)A]
in
[Rh(Hdmg)(bdio)(PEt3)2]ϩ[Rh(Hdmg)2Cl2]Ϫ·H2O[26] and
also to that in [TcCl(dmg)2(bdio)BEt] [av. CϪN
ϭ
[37]
˚
1.29(1)A].
This bond length is shorter than the corres-
˚
ponding one [N(1)ϪC(10) ϭ 1.43(2)A] for the nqo ligand,
similar to the situation for the naphthoquinonic group.
Complex 4 can be obtained from all three orange-red com-
plexes 3bϪ3d (based on X-ray single crystal analyses and
FAB MS data) under very mild conditions (prolonged
standing in CHCl3 solution at room temperature for one
day or at Ϫ20 °C for a few days). In addition, the pyridyl
ligands in 3bϪ3d can be exchanged with one another, pro-
vided that an excess of the pyridyl ligand of the desired
complex is added (see below). We suggest that 3bϪ3d are
formed through interaction of the pyridyl ligands with part
of a surrounding ligand in 4. The nqo ligand is believed to
undergo NϪO bond cleavage of the oximato moiety to give
the 1,2-naphthoquinone-2-imino (nqi) ligand, and complex
4 can be formulated as [Rh(η2-nqo)(η2-nqi)Cl2]. Unfortu-
nately, due to the extremely low solubility of 4 in common
solvents, we failed to get satisfactory 1H NMR spectro-
scopic data. The MS data of 3bϪ3d conform to the stoichi-
ometry of a molecule containing two chloride atoms, one
nqo ligand, one nqi ligand and a pyridine or derived ligand.
These complexes can be formulated as [Rh(η2-nqo)(η2-
nqi)Cl2]·L (3b, L ϭ py; 3c, L ϭ ppy; 3d, L ϭ apy).
Scheme 2. Electrochemical reactions of [Rh(η2-nqo)(PPh3)2Cl2] 1a
the π back-donation from the metal centre to each nqo li-
gand will be less than that in complexes 1bϪ1d with only
one nqo ligand present.
Formation of 1,2-Naphthoquinone-2-imine Complexes
The orange-red complexes 3bϪ3d are also afforded in the
1
reactions with pyridyl ligands (Scheme 1). Their H NMR
spectra show the signals for the naphthalene ring and pyri-
dyl protons with an integration ratio of 2:1, and also a
broad peak near δ ϭ 11.4, assigned to the NH proton,
1
which disappears after D2O exchange. In the H,1H COSY
spectra of 3c and 3d, this peak is coupled with proton H6Јof
the nqo-derived ring. It can be assigned to the proton on
the imino N atom. Slow evaporation of a CHCl3 solution
of complexes 3bϪ3d gave a red crystalline product 4. An
X-ray diffraction analysis was carried out on a single crystal
Eur. J. Inorg. Chem. 2001, 511Ϫ520
515

X.-X. Liu, W.-T. Wong
FULL PAPER
Figure 4. The molecular structure of [Rh(η2-nqo)(η2-nqi)Cl2] (4) with the atom numbering scheme
Conversion Among 3b؊3d Through Pyridyl Ligand
Exchange
Figure 5, while the bond parameters are available from the
Supporting Information. The central metal atom adopts an
essentially octahedral geometry with three naphthalene-de-
rived rings and one chloride atom. Two of the naphthalene
rings are nqo ligands, which occupy the equatorial plane
and chelate to the Rh centre in a similar way to other nqoH
complexes[10,20,24] including 1a, 2b and 4. The oximato
groups, as well as the naphthoquinonic O atoms, adopt a
cis geometry relative to each other. This differs from our
previously determined ruthenium complex trans,trans-
[Ru{η2-(1-nqo)}2(PBu3)2] (1-nqo ϭ 1,2-naphthoquinone-1-
oximato), where both of the oximato N and the naphtho-
quinonic O atoms in the two equatorial 1-nqo ligands adopt
a mutual trans geometry.[10] One of the perpendicular posi-
tions in 5 is occupied by a chloride atom and the other by
an imino N atom of the 1,2-naphthoquinone-2-imino li-
gand, obtained through the deoxygenation of the oxime
group in 1,2-naphthoquinone-2-oxime. The naphthoqui-
nonic O atom of nqi is left pendant with a CϪO bond
Pyridyl ligand exchange of 3d by a tenfold excess of pyr-
idine or 4-phenylpyridine at 30 °C was conducted in CDCl3.
The reaction mixture was continuously monitored by H
NMR spectroscopy and a change in the spectrum observed
after 1 h. The proton resonances due to 3d gradually de-
crease, accompanied by an increase in the intensities of
other proton signals. The proton resonances of 3d com-
pletely disappear after one day. A single product 3b or 3c
is formed in the two reaction mixtures. The identity of 3b
1
1
and 3c are confirmed by both H NMR spectroscopy and
their chromatographic properties. Pyridyl ligand exchange
of 3b by a tenfold excess of 4-acetylpyridine similarly gives
3d after one day at 30 °C. No crystals of 4 are obtained
in these reaction mixtures, even when they stand at room
temperature for a long time. This ligand-exchange reaction
rate is found to be sensitive to the amount of pyridyl ligand
added. A substantial increase in the amount of ligand ad-
ded results in a faster ligand exchange. This result, along
with the isolation of 4 from the CHCl3 solution of 3b؊3d,
supports the hypothesis that 3b؊3d are adducts of 4 and
the corresponding pyridyl ligand through comparatively
loose interaction.
˚
length of 1.26(2)A, which is comparable with the corres-
˚
ponding ones in complex 4 [1.24(2)A] and 3-hydroxy-2-
Other Routes for N؊O Bond Cleavage of the Oxime
Group in 1,2-Naphthoquinone-2-oxime and the Formation
of Tris(1,2-naphthoquinone-2-oximato)rhodium(III)
Complexes
A low yield (10%) of the NϪO bond cleavage product
[Rh(η2-nqo)2(nqi)Cl] (5) was obtained from the reaction of
nqoH with [RhI(µ-Cl)(CO)2]2 in benzene. The reaction
also affords the tris(1,2-naphthoquinone-2-oximato)-
rhodium(III) complexes, fac-[Rh(η2-nqo)3] (6) in a 40%
yield and mer-[Rh(η2-nqo)3] (7) in a 10% yield (Scheme 3).
The molecular structure of complex 5 was confirmed by X-
ray single crystal analysis. The structure of 5 is shown in Scheme 3. Reaction of [RhI(µ-Cl)(CO)2]2 and nqoH
516 Eur. J. Inorg. Chem. 2001, 511Ϫ520

Rhodium(III) Complexes Containing 1,2-Naphthoquinone-2-oxime
FULL PAPER
Figure 5. The molecular structure of [Rh(η2-nqo)2(nqi)Cl] (5) with the atom numbering scheme
[36]
The 4-N-phenylimine was obtained on treatment with aniline.[17]
˚
methyl-1,4-benzoquinone-4-oxime [1.247(5)A].
CϪN bond length of the nqi ligand is [N(3)ϪC(30) ϭ Both indicated the formation of nitrene/quinone imine in-
˚
1.26(2)A], which is in good agreement with that in the im- termediates obtained through the deoxygenation of the oxi-
˚
ino group [N(2)ϪC(20) ϭ 1.27(1)A] in 4. The proton of the mato group of the ligand. Direct evidence for the imine
1
NH group appears as a broad peak at δ ϭ 10.30 in the H formation was given by the imine complexes [Fe(qoϪA)2]
NMR spectrum (Table 1) and also disappears after D2O ex- (where qoϪA
ϭ
4-phenylamino-1,2-naphthoquinone-
change. mono-imine) obtained through the interaction of pentacar-
Previously, there were two other reports on the reduction bonyl iron(0) with 1,2-naphthoquinone-mono-oxime in the
of the oxime group to imine in rhodium complexes.[26,38] In presence of aniline.[18] The reaction between [Cu{η2-(1-
both cases, NaBH4 was used as the reducing agent. nqo)}2] and aniline gave an imine complex, bis(4-phenylim-
[RhIII(Hdmg)(H2dmg)Cl2][26] was first reduced to the RhI ino-1,2-naphthoquinone-1-imino)bis(aniline)copper(II).[17]
complex and, upon addition of phosphanes of small size The mechanism for the formation of the nqi ligand in
and good donor ability, RhI was reoxidised to RhIII, accom- 3bϪ3d and 4 is not certain at this point; however, we believe
panied by the reduction of one of the equatorial oxime it occurs as a result of the modification of the coordinated
groups to imine. We have demonstrated a ruthenium car- nqo ligand as in the CuII analogue.[17]
bonyl-induced deoxygenation of 1,2-naphthoquinone-1-ox-
The molecular formulae of 6 and 7, as established by elec-
ime, leading to a coordinated 1,2-naphthoquinone-1-imine trospray ionisation (ESI) mass spectrometry, are consistent
intermediate.[23] The ruthenium cluster with naphthoqui- with the calculated experimental isotopic patterns for
none-imino ligands was obtained in low yield through the C30H18N3O6Rh, and reveal their isomeric nature. The iso-
following coupling reaction. The formation of 1,2-naphtho- merism of 6 and 7 was confirmed by 1H NMR spectroscopy
1
quinone-2-imine in complex 5 may be caused by the reduc- in CDCl3. Complex 6 gives rise to the same H NMR sig-
tion of the oxime group by RhI to imine, which is stabilised nals for the three ligands showing that it has a highly sym-
towards hydrolysis by coordination to the RhIII metal metrical fac geometry as in a very recently structurally char-
centre. However, in the reaction with RhCl3·3H2O as the acterised ruthenium 1-nqo analogue [Ru{η2-(1-nqo)}3]Ϫ, in
starting material and in the presence of pyridine-type li- which only one set of 1-nqo signals is present for the
gands, we have no reducing agent in the system. There are three ligands.[22] A nickel complex anion [Ni(4-Clqo)3]Ϫ
some other reports on the metal-induced deoxygenation of (4-Clqo
ϭ
4-chloro-1,2-benzoquninone-2-oximato)[39]
1,2-naphthoquinone-mono-oxime,[14Ϫ18] however, they are and a naturally occurring pigment ferroverdin[40] fac-
all concerned with first-row transition metals. Treatment of [FeII{4-[p-(CH2ϭCH)C6H4OC(ϭO)]-1,2-benzoquninone-2-
the 1,2-naphthoquinone-2-oxime copper(II) complex with oximato}3]Ϫ are other examples of fac geometry based on
PPh3 gave 2-amino-N4-(1-hydroxy-2-naphthyl)-1,4-naph- X-ray evidence. Although without X-ray analysis, the geo-
thoquinone 4-imine,[16] while 2-amino-1,4-naphthoquinone metry of [FeII(RQ)3]Ϫ (RQ ϭ 4-R-1,2-benzoquninone-2-ox-
Eur. J. Inorg. Chem. 2001, 511Ϫ520
517

X.-X. Liu, W.-T. Wong
FULL PAPER
imato, R ϭ Me, tBu, Cl, Br[41] and 3,4-benzo[42]) were also
deduced to be fac, since the three ligands in the molecule
are equivalent (shown by 1H NMR spectroscopy). The
three naphthalene rings of complex 7 give rise to different
1H NMR signals, although some of them merge together to
give intensified peaks. Thus, complex 7 is proposed to have
mer geometry as in [MnIIIL3] (L ϭ 4-chloro-1,2-benzoqui-
none-2-oximato)[43] and [NiIII(RQ)3] (RQ ϭ 4-R-1,2-benzo-
quninone-2-oximato, R ϭ Me, tBu and Cl).[44] However,
idine (apy), respectively, instead of PPh3. Upon TLC separation
with a solvent mixture of n-hexane/CH2Cl2 (1:5Ϫ1:6, v/v), the com-
plexes [Rh(η2-nqo)L2Cl2] (1b؊1d), [Rh(η2-nqo)2LCl] (2b؊2d) and
[Rh(η2-nqo)(η2-nqi)Cl2]·L (3b؊3d) (1b؊3b, L ϭ py; 1c؊3c, L ϭ
ppy; 1d؊3d, L ϭ apy) were isolated. Upon standing in a CHCl3
solution of 3b؊3d at room temperature for one day, red crystals of
[Rh(η2-nqo)(η2-nqi)Cl2] 4 were obtained. Red crystals of 2b were
grown by slow evaporation of n-hexane/CHCl3 solution at Ϫ20 °C.
1b: C20H16Cl2N3O2Rh (504.1805): calcd. C 47.6, H 3.2, N 8.3;
found C 47.8, H 3.1, N 8.1.
when [MnIIIL3] is electrochemically reduced to anionic 1c: C32H24Cl2N3O2Rh (656.3757): calcd. C 58.6, H 3.7, N 6.4;
[MnIIL3]Ϫ, it exists as a mixture of fac and mer isomers,
found C 58.3, H 3.9, N 6.3.
1d: C24H20Cl2N3O4Rh (588.2541): calcd. C 49.0, H 3.4, N 7.1;
both in solution (by 1H NMR spectroscopy) and in the
solid state (by X-ray analysis).[43] It was suggested that the
found C 48.7, H 3.2, N 7.3.
2b: C25H17ClN3O4Rh (561.7884): calcd. C 53.4, H 3.1, N 7.5; found
favourable mer geometry for neutral complexes is partially
C 53.5, H 2.9, N 7.2.
due to a steric factor, the pendant oximato oxygen atoms
2c: C31H21ClN3O4Rh (637.8860): calcd. C 58.4, H 3.3, N 6.6; found
are further apart than in the fac form. The origin of the
C 58.7, H 3.4, N 6.4.
2d: C27H19ClN3O5Rh (603.8252): calcd. C 53.7, H 3.2, N 7.0; found
C, 53.6, H 2.9, N 7.2.
fac form could be the effect of electrostatic stabilisation.[44]
Nevertheless, the complexes are neutral in our system, the
fac isomer is very favourable and there is no isomerisation
3b: C25H18Cl2N3O3Rh (582.2503): calcd. C 51.6, H 3.1, N 7.2;
observed after separation. This fac geometry is also fa- found C 51.8, H 2.9, N 7.5.
3c: C31H22Cl2N3O3Rh (658.3479): calcd. C 56.6, H 3.4, N 6.4;
found C 56.7, H 3.4, N 6.4.
3d: C27H20Cl2N3O4Rh (624.2871): calcd. C 51.9, H 3.2, N 6.7;
found C, 51.6, H 2.9, N 7.0.
4: C20H13Cl2N2O3Rh (503.1491): calcd. C 47.7, H 2.6, N 5.6; found
C 47.8, H 2.4, H 5.5.
voured in the tris(arylazooximato)rhodium(III) com-
plexes,[45] whereas the cobalt(III) analogues[46] exist exclus-
ively in the mer form. This was explained by an increase in
the facial area in going from the CoIII to the RhIII che-
late.[45]
Pyridyl Ligand Exchange of 3d and 3b: Complex 3d (6 mg,
0.01 mmol) and CDCl3 (1 cm3) were placed in an oven-dried NMR
tube. A tenfold excess of pyridine was added. After warming the
tube in a thermostat at 30 °C for 1 h, 1H NMR spectra were re-
corded at time intervals of 1 h until no 3d was detected. After 20 h,
Experimental Section
All manipulations were carried out under nitrogen with standard
Schlenk techniques. Chemicals were purchased from commercial
sources and used as received. Preparative thin-layer chromato-
graphic (TLC) plates were prepared from silica (Merck Kieselgel
1
all 3d had been converted into 3b according to the H NMR spec-
troscopic data. The single metal-containing product of 3b was ob-
tained by TLC separation with a solvent mixture of n-hexane/
CH2Cl2 (1:10, v/v) as the eluent.
1
60 GF254). Ϫ H NMR spectra were obtained on a Bruker DPX-
300 spectrometer using deuterated chloroform as the lock and ref-
erence. Ϫ Fast atom bombardment (FAB) mass spectra were re-
corded on a Finnigan MAT 95 mass spectrometer. Electrospray
ionisation quadropole ion trap mass spectra were obtained on a
Finnigan LCQTM LC/MSn system. Ϫ Electrochemical measure-
ments were conducted on a PAR 273A potentiostat in CH2Cl2 con-
taining 0.1 mol dmϪ3 n-tetrabutylammonium hexafluorophosphate
(TBAH), using a conventional argon gas sealed three-electrode cell.
The working electrode was a glassy carbon disc for cyclic voltam-
metry and a carbon plate for large-scale electrolysis. Potentials are
reported vs. ferrocene internal standard (Fc0/ϩ).
The single metal-containing products 3c and 3d were obtained by
a similar procedure of ligand exchange with 3d and 3b and 4-
phenylpyridine and 4-acetylpyridine, respectively.
Reaction Between [RhI(µ-Cl)(CO)2]2 and 1,2-Naphthoquinone-2-ox-
ime: [RhI(µ-Cl)(CO)2]2 (39 mg, 0.1 mmol) and 1,2-naphthoqui-
none-2-oxime (104 mg, 0.6 mmol) was dissolved in benzene
(50 mL) and stirred at room temperature for 3 h. The solvent was
removed from the dark red solution and the residue chromato-
graphed by TLC with n-hexane/CH2Cl2 (1:5, v/v) as the eluent.
Three red products were isolated as [Rh(η2-nqo)2(nqi)Cl] (5; 10%,
13 mg), fac-[Rh(η2-nqo)3] (6; 40% yield, 49 mg) and mer-[Rh(η2-
nqo)3] (7; 10% yield, 12 mg). Single crystals of 5 were grown by
slow evaporation of a n-hexane/CH2Cl2 solution at Ϫ20 °C.
5: C30H19ClN3O5Rh (639.86): calcd. C 56.3, H 3.0, N 6.6; found C
56.0, H 2.7, N 6.6.
Synthesis of [Rh(η2-nqo)(PPh3)2Cl2] (1a): Solid samples of
RhCl3·3H2O (53 mg, 0.2 mmol) and 1,2-naphthoquinone-2-oxime
(69 mg, 0.4 mmol) were dissolved in 100 mL ethanol and refluxed
for 2 h. PPh3 (105 mg, 0.4 mmol) in hot ethanol was then added
and the solution refluxed for another 10 h. The solvent was then
removed and the residue chromatographed by TLC, with a solvent
mixture of n-hexane/CH2Cl2 (1:4, v/v) as the eluent to afford the
complex [Rh(η2-nqo)(PPh3)2Cl2] (1a; 80%, 139 mg). Red crystals
of 1a were grown by slow evaporation of an n-hexane/CHCl3 solu-
tion at room temperature. C46H36Cl2NO2P2Rh (870.56): calcd. C
63.5, H 4.2, N 1.6; found C 63.2, H 4.5, N 1.5.).
6: C30H18N3O6Rh (619.40): calcd. C 58.2, H 2.9, N 6.8; found C
58.0, H 2.6, N 6.8.
7: C30H18N3O6Rh (619.40): calcd. C 58.2, H 2.9, N 6.8; found C
58.2, H 3.0, N 7.0.
Crystallography:
Synthesis of [Rh(η2-nqo)L2Cl2] (1b؊1d), [Rh(η2-nqo)2LCl] (2b؊2d),
Single crystals of 1a, 2b, 4 and 5 were obtained as described above.
[Rh(η2-nqo)(η2-nqi)Cl2]·L (3b؊3d) and the Formation of [Rh(η2- A crystal of 1a was mounted on a glass fibre by means of epoxy
nqo)(η2-nqi)Cl2] (4): A procedure analogous to the above was fol-
lowed, adding pyridine (py), 4-phenylpyridine (ppy) or 4-acetylpyr-
resin, while crystals of 2b, 4 and 5 were sealed in Lindemann glass
capillaries. Crystal intensity data were collected for 1a, 2b and 4 on
518
Eur. J. Inorg. Chem. 2001, 511Ϫ520

Rhodium(III) Complexes Containing 1,2-Naphthoquinone-2-oxime
FULL PAPER
Table 3. Crystal data and data collection parameters for compounds 1a, 2b, 4 and 5
1a
2b
4
5
Empirical formula
M
C46H36Cl2NO2P2Rh
870.55
C26H18Cl4N3O4Rh
681.16
C21H14Cl5N2O3Rh
622.52
Orange-red, block
0.24 ϫ 0.26 ϫ 0.31
Monoclinic
P21/n (no.14)
9.088(1)
17.651(1)
15.154(1)
Ϫ
106.22(2)
Ϫ
2334.1(4)
4
1.771
13.28
C34H27Cl9N3O5Rh
979.59
Crystal colour, habit
Crystal dimensions/mm
Crystal system
Space group
Red, block
0.12 ϫ 0.12 ϫ 0.17
Monoclinic
P21/n (no. 14)
11.506(1)
18.713(1)
19.574(1)
Ϫ
Red, block
Red, block
0.13 ϫ 0.12 ϫ 0.14
Monoclinic
P21/n (no.14)
11.883(1)
15.026(2)
22.833(1)
Ϫ
0.22 ϫ 0.16 ϫ 0.18
Triclinic
¯
P1(no.2)
˚
a/A
7.719(2)
12.881(2)
15.271(3)
111.636(3)
91.619(3)
98.801(3)
1388.8(4)
2
˚
b/A
˚
c/A
α/°
β/°
γ/°
106.62(2)
Ϫ
4038.5(6)
4
1.432
6.73
96.35(1)
Ϫ
3
˚
U/A
4051.9(6)
4
Z
Dc/g cmϪ3
1.629
10.35
1.606
µ(Mo-Kα)/cmϪ1
Reflections collected
Unique reflections
Observed reflectons [I Ͼ 1.5σ(I)]
R
10.56
38432
9355
5568
0.051
0.047
1.00
6236
5092
0.058
0.072
2.51
5405
2635
0.092
0.077
2.06
3295
1885
0.094
RЈ
0.098
Goodness of fit, S
2.14
[5]
S. Cosnier, A. Deronzier, N. Vlachopoulos, J. Chem. Soc.,
Chem. Commun. 1989, 1259Ϫ1261.
a Siemens Smart CCD and for 5 on a MAR research image-plate
scanner, using graphite-monochromated Mo-Kα radiation (λ ϭ
0.71073 A) for unit-cell determination and data collection. Intens-
[6]
[7]
[8]
[9]
S. Cosnier, H. Gunther, J. Electroanal. Chem. 1991, 315,
˚
307Ϫ312.
ity data were corrected for Lorentz and polarisation effects. An
approximation to absorption correction by inter-image scaling was
also applied. Summaries of the crystallographic data, structure so-
lution and refinement are given in Table 3. Scattering factors were
taken from part a in ref.[47] and anomalous dispersion effects were
included in Fc (part b). The structures were solved by direct
methods (SIR 92[48] for 1a, 4 and 5; SHELXS 86[49] for 2b). The
remaining non-hydrogen atoms were determined by subsequent
Fourier and Fourier-difference techniques. The structures were re-
fined by full-matrix least-squares analysis on F, with all non-hydro-
gen atoms refined anisotropically until convergence was reached.
The hydrogen atoms of the organic moieties were generated in their
R. Ruppert, S. Herrmann, E. Steckhan, Tetrahedron Lett. 1987,
28, 6583Ϫ6586.
B. Foretic, N. Burger, V. Hankonyi, Polyhedron 1995, 14,
605Ϫ609.
J. Charalambous, W. C. Stoten, K. Henrick, Polyhedron 1989,
8, 103Ϫ107.
X.-X. Liu, W.-T. Wong, Polyhedron 2000, 19, 7Ϫ21.
N. Ghatak, S. Bhattacharya, Transition Met. Chem. 1996, 21,
423Ϫ427.
O. K. Borggaard, H. E. M. Christensen, S. P. Lund, Analyst
1984, 109, 1179Ϫ1182.
O. K. Borggaard, H. E. M. Christensen, T. K. Nielsen, M.
Willems, Analyst 1982, 107, 1479Ϫ1483.
H. Barjesteh, E. G. Brain, J. Charalambous, P. Gaganatsou, T.
A. Thomas, J. Chem. Res. (S) 1995, 454Ϫ454.
A. McKillop, T. S. B. Sayer, J. Org. Chem. 1976, 41,
1079Ϫ1080.
R. G. Buckley, J. Charalambous, M. J. Kensett, M. McPartlin,
D. Mukerjee, E. G. Brain, J. M. Jenkins, J. Chem. Soc., Perkin
Trans. 1 1983, 693Ϫ697.
R. G. Buckley, J. Charalambous, E. G. Brain, J. Chem. Soc.,
Perkin Trans. 1 1982, 1075Ϫ1078.
J. Charalambous, L. I. B. Haines, J. S. Morgan, D. S. Peat, M.
J. M. Champbell, J. Bailey, Polyhedron 1987, 6, 1027Ϫ1032.
H. Saarinen, J. Korvenranta, Acta Chem. Scand. 1975, A29,
409Ϫ413.
J. Korvenranta, H. Saarinen, Acta Chem. Scand. 1975, A29,
861Ϫ865.
J. Charalambous, K. Henrick, Y. Musa, R. G. Rees, R. N.
Whiteley, Polyhedron 1987, 6, 1509Ϫ1512.
A. K. Das, A. Rueda, L. R. Falvello, S.Ϫ M. Peng, S. Bhattach-
arya, Inorg. Chem. 1999, 38, 4365Ϫ4368.
K. K.-H. Lee, W.-T. Wong, J. Chem. Soc., Dalton Trans.
1997, 2987Ϫ2995.
K. K.-H. Lee, W.-T. Wong, J. Organomet. Chem. 1997, 547,
329Ϫ335.
X.-X. Liu, W.-T. Wong, Inorg. Chim. Acta. 2000, 299, 16Ϫ27.
R. Dreos, G. Tauzher, S. Geremia, L. Randaccio, F. Asaro, G.
Pellizer, C. Tavagnacco, G. Costa, Inorg. Chem. 1994, 33,
5404Ϫ5410.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
˚
ideal positions (CϪH, 0.95A). They were included in the structure
factor calculations on a Silicon-Graphics computer using the pro-
gram package TEXSAN.[50]
Crystallographic data (excluding structure factors) for the struc-
tures 1a, 2b, 4 and 5 reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplement-
ary publication no. CCDC-144600 to -144603, respectively. Copies
of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [Fax: (internat.)
ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
Acknowledgments
We gratefully acknowledge financial support from the Hong Kong
Research Grants Council and the University of Hong Kong. X.-X.
Liu acknowledges the receipt of a demonstratorship administered
by the Department of Chemistry, University of Hong Kong.
[1]
[25]
[26]
U. Kolle, M. Grutzel, Angew. Chem. Int. Ed. Engl. 1987, 26,
567Ϫ570.
[2]
H. C.-Y. Bettega, J.-C. Moutet, S. Tingry, J. Electroanal. Chem.
1995, 391, 51Ϫ61.
[3]
[27]
[28]
I. M. F. De Oliveira, J.-C. Moutet, N. Vlachopoulos, J. Elec-
H. C.-Y. Bettega, J.-C. Moutet, J. Electroanal. Chem. 1994,
364, 271Ϫ275.
I. M. F. De Oliveira, J.-C. Moutet, J. Electroanal. Chem. 1993,
361, 203Ϫ210.
troanal. Chem. 1990, 291, 243Ϫ249.
[4]
C. Caix, S. Chardon-Noblat, A. Deronzier, J.-C. Moutet, S.
Tingry, J. Organomet. Chem. 1997, 540, 105Ϫ111.
Eur. J. Inorg. Chem. 2001, 511Ϫ520
519

X.-X. Liu, W.-T. Wong
FULL PAPER
[29]
[40]
[41]
[42]
[43]
G. Kew, K. DeArmond, K. Hanck, J. Phys. Chem. 1974, 78,
S. Candeloro, D. Grdenic, N. Taylor, B. Thompson, M. Viswa-
mitra, D. C. Hodgkin, Nature 1969, 224, 589Ϫ591.
P. Basu, S. B. Choudhury, S. Pal, A. Chakravorty, Inorg. Chem.
1989, 28, 2680Ϫ2686.
P. Basu, S. Pal, A. Chakravorty, J. Chem. Soc., Chem. Commun.
1989, 977Ϫ978.
P. Basu, A. Chakravorty, J. Chem. Soc., Chem. Commun.
1992, 809Ϫ810.
D. Ray, A. Chakravorty, Inorg. Chem. 1988, 27, 3292Ϫ3297.
K. C. Kalia, A. Chakravorty, Inorg. Chem. 1969, 8, 2586Ϫ2590.
K. C. Kalia, A. Chakravorty, Inorg. Chem. 1968, 7, 2016Ϫ2020.
D. T. Cromer, J. T. Waber, International Tables for X-ray Crys-
tallography, Kynoch Press, Birmingham, 1974, Vol. 4; (a) Table
2.2.B; (b) Table 2.3.1.
SIR 92, A. Altomare, M. C. Burla, M. Camalli, M. Cascarano,
C. Giacovazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr.
1994, 27, 435Ϫ442.
727Ϫ734.
[30]
M. Ladwig, W. Kaim, J. Organomet. Chem. 1991, 419,
233Ϫ243.
S. Chardon-Noblat, S. Cosnier, A. Deronzier, N. Vlachopoulos,
J. Electroanal. Chem. 1993, 352, 213Ϫ228.
U. Kolle, B.-S. Kang, P. Infelta, P. Comte, M. Gratzel, Chem.
Ber. 1989, 122, 1869Ϫ1880.
B. Soucaze-Guillous, H. Lund, Acta Chem. Scand. 1998, 52,
417Ϫ424.
S. Djebbar-Sid, O. Benali-Baitich, J. P. Deloume, Polyhedron
1997, 16, 2175Ϫ2182.
W. Kaim, R. Reinhardt, M. Sieger, Inorg. Chem. 1994, 33,
4453Ϫ4459.
P. C. Christidis, A. Dodd, N. D. Pathirana, J. Charalambous,
M. McPartlin, N. Talee, Acta Cryst. 1991, C47, 2640Ϫ2642.
K. E. Linder, D. P. Nowotnik, M. F. Malley, J. Z. Gougoutas,
A. D. Nunn, Inorg. Chim. Acta 1991, 190, 249Ϫ255.
[31]
[32]
[44]
[45]
[46]
[47]
[33]
[34]
[35]
[48]
[49]
[50]
[36]
G. M. Sheldrick, in Crystallographic Computing 3, G. M. Shel-
drick, C. Kruger, R. Goddard, Eds., Oxford University Press,
1985, 175Ϫ189.
[37]
[38]
D. Steinborn, M. Rausch, C. Bruhn, J. Organomet. Chem.
1998, 561, 191Ϫ197.
P. W. Carreck, J. Charalambous, M. J. Kensett, M. McPartlin,
R. Sims, Inorg. Nucl. Chem. Lett. 1974, 10, 749Ϫ751.
TEXSAN, Crystal Structure Analysis Package, Molecular
Structure Corporation, Houston, TX, 1985 and 1992.
Received May 24, 2000
[39]
[I00215]
520
Eur. J. Inorg. Chem. 2001, 511Ϫ520