such it has some biological relevance.11 Although we achieved
only limited characterisation of 1, it seems clear that 1 contains
a LOH ligand coordinated in a similar fashion as in 5 (Fig. 2).
The reaction appears to be copper-specific, in that 3–5 do not
decompose in this way. It does not require O2, and it is effected
by Cu() as well as by Cu(). We have been unable to obtain any
other mechanistic data relating to the transformation. However,
there is literature precedent for one mechanism of N-deoxygen-
ation of a Cu-bound substrate, namely O-atom transfer from a
Cu() complex of the substrate to another acceptor, followed by
an intramolecular electron transfer to yield a Cu() complex of
the final product.12 It is unclear what the O-atom acceptor
could be in this reaction, however, while such a mechanism
would also require pre-reduction of 1 to a Cu() species before
the O-atom transfer step.
Fig. 2 View of the [CoCl2LOH] molecule in the crystal structure of 5.
For clarity, all C-bound H atoms have been omitted. Thermal ellipsoids
are at the 50% probability level. Selected bond lengths (Å) and angles
(Њ): Co(1)–N(2) 2.0982(12), Co(1)–N(6) 2.1751(13), Co(1)–N(14)
2.1731(12), Co(1)–Cl(19) 2.2999(4), Co(1)–Cl(20) 2.3435(4); N(2)–
Co(1)–N(6) 91.01(5), N(2)–Co(1)–N(14) 90.93(5), N(2)–Co(1)–Cl(20)
113.54(3), N(2)–Co(1)–Cl(21) 121.78(3), N(6)–Co(1)–N(14) 176.61(5),
N(6)–Co(1)–Cl(20) 87.55(3), N(6)–Co(1)–Cl(21) 93.30(3), N(14)–
Co(1)–Cl(20) 89.13(3), N(14)–Co(1)–Cl(21) 88.04(3), Cl(20)–Co(1)–
Cl(21) 124.640(15).
The authors acknowledge financial support by the Royal
Society (M. A. H., M. P.), the Indian National Academy of
Sciences (M. P.), the EPSRC, Bharathidasan University and the
University of Leeds.
Notes and references
in ca. 80% purity, together with one or more unidentified con-
taminents. Hence, coordination of LOH to Cu() results in its
metal-promoted reduction to LH. Very similar dark green or
brown product mixtures, containing LH, are obtained when
decomposing 1 in MeCN in air or under N2, and when reacting
LOH with [Cu(NCMe)4]BF4 in MeCN in air or under N2.
Finally, LOH is recovered unchanged when washed with aque-
ous ammonia, showing that the transformation is copper-
effected.
‡ Crystal data for 2. C14H17Cl2CuN3, Mr = 361.75, monoclinic, P21/c,
a = 28.1563(4), b = 7.7451(2), c = 14.2271(2) Å, β = 104.4294(5)Њ,
V = 3004.69(7) Å3, Z = 8, µ(Mo-Kα) = 1.802 mmϪ1, T = 150(2) K; 45081
measured reflections, 5887 independent, Rint = 0.107; R(F) = 0.068,
wR(F 2) = 0.166. CCDC reference number 202131.
Crystal data for 5. C14H17Cl2CoN3O, Mr = 373.14, monoclinic, P21/c,
a = 7.3446(1), b = 15.4679(2), c = 15.2653(2) Å, β = 118.1960(5)Њ,
V = 1528.43(3) Å3, Z = 4, µ(Mo-Kα) = 1.473 mmϪ1, T = 150(2) K; 29114
measured reflections, 3483 independent, Rint = 0.070; R(F) = 0.027,
wR(F 2) = 0.071. CCDC reference number 218093.
Crystals of 2 were small, and had a high mosaicity of 0.60 (a strongly
diffracting crystal would give a mosaicity of ca. 0.45 under our condi-
tions). The asymmetric unit of 2 contains two molecules of the complex
lying on general positions, while 5 contains a single molecule per
asymmetric unit. No disorder was detected during refinement of either
structure. All non-H atoms were modeled anisotropically, and no
restraints were applied. All C- and (in 2) N-bound H atoms were placed
in calculated positions and refined using a riding model. The hydroxyl
H atom in 5 was located in the Fourier difference map and allowed to
refine freely.
In order to gain more insight into this reaction, the complex-
ation of LOH with ZnCl2, NiCl2 and CoCl2 was examined. All of
these salts yield crystalline compounds of formula [MCl2LOH
]
(M = Zn, 3; M = Ni, 4; M = Co, 5) from MeOH solution, in up
to 56% yield. Importantly, 3–5 are indefinitely stable under
ambient conditions in solution and the solid state. The d–d
spectra of 4 and 5 in CH2Cl2 (ESI†). resemble those of
[MCl2LH] (M = Ni,4 Co9), which have been previously proposed
to adopt trigonal bipyramidal stereochemistries. The similarity
of the spectra of 4 and 5 to those of their LH-containing con-
geners strongly suggests that the hydroxyl group of LOH does
not interact directly with the coordinated metal centre in these
compounds. This is borne out by the crystal structure of 5 (see
later). The 1H NMR spectra of 3–5 in CD2Cl2 all show a single
C2 or m-symmetric LOH environment (ESI†). Importantly, for
the paramagnetic compounds 4 and 5, eight contact-shifted
peaks of approximately equal integral are observed. That is the
number of C-bound H environments expected if the CH2
groups in the ligand are diastereotopic. This demonstrates that
the LOH ligand remains tridentate in this solvent.
graphic data in CIF or other electronic format.
1 A. G. Blackman and W. B. Tolman, Struct. Bonding (Berlin), 2000,
97, 179.
2 C. He, A. M. Barrios, D. Lee, J. Kuzelka, R. M. Davydov and
S. J. Lippard, J. Am. Chem. Soc., 2000, 122, 12683.
3 E. Uhlig, B. Borek and H. Glänzer, Z. Anorg. Allg. Chem., 1966, 348,
189.
4 S. M. Nelson and J. Rodgers, Inorg. Chem., 1967, 6, 1390.
5 J. K. Romary, R. D. Zachariasen, J. D. Barger and H. Schiesser,
J. Chem. Soc. C, 1968, 2884; H. J. Hoorn, P. de Joode, W. L. Driessen
and J. Reedijk, Recl. Trav. Chim. Pays-Bas, 1996, 115, 191.
6 L. Bauer, A. Shoeb and V. C. Agwada, J. Org. Chem., 1962, 27, 3153;
A. A. R. Sayigh, H. Ulrich and M. Green, J. Org. Chem., 1964, 29,
2042.
To compare the metal-binding modes of LH and LOH, single
crystal X-ray analyses of 2 and 5 were undertaken.‡ Both com-
pounds show mononuclear, five-coordinate metal centres with
MCl2N3 (M = Cu or Co) donor sets (Fig. 2). The bond angles at
the metal ions in the two structures show some differences,
however. The τ indices for the two independent molecules in the
structure of 2 are 0.53 and 0.46, showing that this compound
adopts a geometry that is intermediate between a square-
pyramid (τ = 0) and a trigonal bipyramid (τ = 1).10 This irregu-
lar five-coordinate geometry is consistent with the very rhombic
g-values, with g3 ≈ 2.00, shown by solid 2 (and 1).8 In contrast,
the Co ion in 5 exhibits τ = 0.91, showing that this has a
more regular trigonal bipyramidal structure (Fig. 1).10 Despite
these differences, it is clear that LOH and LH coordinate to the
metal ions in 2 and 5 in the same way. Taken together, the EPR
and structural data from 1, 2 and 5 strongly imply that the
coordination geometries of 1 and 2 will be very similar.
7 C. A. VanOrman, K. V. Reddy, L. M. Sayre and F. L. Urbach,
Polyhedron, 2001, 20, 541.
8 C. L. Foster, C. A. Kilner, M. Thornton-Pett and M. A. Halcrow,
Polyhedron, 2002, 21, 1031, and references therein.
9 D. P. Madden and S. M. Nelson, J. Chem. Soc. A, 1968, 2342.
10 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C.
Verschoor, J. Chem. Soc., Dalton Trans., 1984, 1349.
11 S. Suzuki, K. Kataoka and K. Yamaguchi, Acc. Chem. Res., 2000,
33, 728.
12 See, e.g.: J. A. Halfen, S. Mahapatra, E. C. Wilkinson, A. J. Gegen-
bach, V. G. Young, Jr., L. Que, Jr. and W. B. Tolman, J. Am. Chem.
Soc., 1996, 118, 763; L. Casella, O. Carugo, M. Gullotti, S. Doldi
and M. Frassoni, Inorg. Chem., 1996, 35, 1101; J. L. Schneider, S. M.
Carrier, C. E. Ruggiero, V. G. Young, Jr. and W. B. Tolman, J. Am.
Chem. Soc., 1998, 120, 11408; E. Monzani, G. J. A. A. Koolhaus,
A. Spandre, E. Leggieri, L. Casella, M. Gullotti, G. Nardin, L. Ran-
daccio, M. Fontani, P. Zanello and J. Reedijk, J. Biol. Inorg. Chem.,
2000, 5, 251.
The decomposition of 1 is an unusual example of an
N-deoxygenation reaction effected by copper centre, and as
D a l t o n T r a n s . , 2 0 0 3 , 4 2 2 4 – 4 2 2 5
4225