Formation of nickel-thiolate aggregates via reaction with CH 2Cl2

Article abstract of DOI:10.1039/b309523a

Reaction of the mononuclear nickel-thiolate complex [Ni(L ¹)(dppe)] with CH₂Cl₂ affords the novel pentanuclear complex [Ni₅Cl₂(L¹) ₄(dppe)₂], while [Ni(L¹)(

Full text of DOI:10.1039/b309523a

Formation of nickel-thiolate aggregates via reaction with CH2Cl2
Qiang Wang, Andrew C. Marr, Alexander J. Blake, Claire Wilson and Martin Schröder*
School of Chemistry, The University of Nottingham, Nottingham, UK NG7 2RD.
E-mail: M.Schroder@nottingham.ac.uk; Fax: + 44(0)115 9513563; Tel: + 44(0)115 9513490
Received (in Cambridge, UK) 8th August 2003, Accepted 18th September 2003
First published as an Advance Article on the web 20th October 2003
Reaction of the mononuclear nickel-thiolate complex
[Ni(L1)(dppe)] with CH2Cl2 affords the novel pentanuclear
complex [Ni5Cl2(L1)4(dppe)2], while [Ni(L1)(dcpe)] reacts
and the 31P{1H} NMR spectrum of the crystalline product
obtained by diffusion of Et2O vapour into a solution of
[Ni(L1)(dppe)] in CH2Cl2 over a period of 3 days showed in
CDCl3 solution a single resonance at 33.78 ppm, confirming the
equivalence of the terminal phosphine ligands. A single crystal
X-ray structural determination confirmed‡ the formation of a
with
CH2Cl2
to
give
the
binuclear
species
[Ni2Cl2(L2)(dcpe)2] in which two L1 units are linked by a
methylene group derived from CH2Cl2.
highly
unusual
pentanuclear
nickel(II
)
aggregate,
The study of nickel thiolates is frequently complicated by their
air sensitivity and a tendency to form polymetallic complexes
with bridging m-SR groups.1 Steric factors and/or thiolates
containing electron-withdrawing groups have been employed to
avoid and control such unwanted reactivity,2 while another
successful strategy for obtaining discrete complexes involves
the use of chelating dithiolate ligands with chelating phosphines
such as dppe or dcpe [dppe = 1,2-bis(diphenylphosphino)-
ethane, dcpe = 1,2-bis(dicyclohexylphosphino)ethane].3 Li-
gand-based reactivity of transition metal thiolates via alkyla-
tion, metalation, oxygenation, and adduct formation is well
documented,4 while methylation of the nickel-bound thiolates
by electrophiles such as MeI has been observed by Darensbourg
et al.5 Alkylation of ruthenium-bound thiolates has been
reported by Sellmann et al.6 and Grapperhaus et al.,4 and Jones
and co-workers7 have recently reported the alkylation of nickel-
bound sulfides by 1,2-dichloroethane. We report herein the first
example of reaction of nickel thiolate complexes with CH2Cl2,
and examine the influence of the electronic environment of the
nickel-thiolate moiety upon this reactivity.
As part of our wider project on the modelling of the active site
of [NiFe] hydrogenase,8 we have synthesized a series of nickel
thiolate–phosphine complexes with NiS2P2 co-ordination
spheres, and have investigated the reactivity of these complexes
as a function of variation of phosphine and/or thiolate ligands.
When [NiCl2(PP)] (PP = dppe, dcpe) is reacted with 2,4,6-tri-
isopropylthiophenol (HL3) or 2-mercaptomethyl-benzenethiol
(H2L4) in the presence of NaOMe in MeOH, via a modification
of the procedure reported by Bowmaker et al.,9 the correspond-
ing mononuclear nickel thiolate complexes [Ni(L3)2(PP)] and
[Ni(L4)(PP)] are obtained in good yields and have been fully
characterised.† These diamagnetic complexes are stable in
CH2Cl2 solution and their formulations have been confirmed by
X-ray crystallographic studies of single crystals grown from
CH2Cl2 solution. Reaction of 4,5-dimethyl-1,2-benzenedime-
thanethiol (H2L1) with [NiCl2(dppe)] via a procedure similar to
that described above,9 affords the mononuclear complex
[Ni(L1)(dppe)] (Scheme 1) which is stable in the solid state
under N2 or Ar. The formulation of the product as
[Ni(L1)(dppe)] was confirmed by FAB mass spectrometry,
NMR spectroscopy and elemental analysis.† The 31P{1H}
NMR spectrum of [Ni(L1)(dppe)] in CDCl3 solution shows a
single resonance at 55.30 ppm confirming that the two P centres
in the complex are, as expected, in identical environments about
a cis square-planar Ni(II) centre. However, unlike [Ni(L3)2(PP)]
and [Ni(L4)(PP)], [Ni(L1)(dppe)] is reactive in CH2Cl2 solution,
[Ni5Cl2(L1)4(dppe)2] 1 (Fig. 1, upper) [FAB MS: m/z 1910 (M–
Cl)+, 1875 (M–2Cl)+]. The complex 1 comprises three central
square-planar NiS4 units and two terminal square-planar P2NiS2
units arranged in a zig-zag pattern (Fig. 1, lower). Ni(1)
occupies a crystallographic inversion centre and the Ni5
complex therefore has imposed Ci symmetry. Each terminal
Ni(II) centre is further bound by a chloride ion derived from
CH2Cl2 and occupies the apical position of a square pyramid at
the Ni(II) centres. The angle between the least-squares mean
planes through P(1)–P(2)–Ni(3)–S(1)–S(2) and S(1)–S(2)–
Ni(2)–S(3)–S(4) is 65.32(2)°, while that between the S(1)–
S(2)–Ni(2)–S(3)–S(4) and S(3)–S(4)–Ni(1)–S(3A)–S(4A)
planes is 70.30(3)°. This brings the metals into fairly close
proximity with Ni(1)…Ni(2) = 2.7738(5) Å, Ni(2)…Ni(3) =
2.8552(6) Å. These Ni…Ni distances are comparable to the
mean value of 2.8345(1)Å in the thiolate-bridged penta-
nickel(II) complex [NEt4]2[Ni5(edt)4(dmit)2] (edt = ethane-
1,2-dithiolate; dmit = 2-thione-1,3-dithiole-4,5-dithiolate) re-
ported by Sheng et al.10 However, whereas the
Ni(1)…Ni(2)…Ni(3) angle of 176.30(2)° in 1 is close to
linearity, the corresponding angle in [NEt4]2[Ni5(edt)4(dmit)2]
is 102.83°.10 Thus, 1 represents, to the best of our knowledge,
the first example of a linear pentanuclear nickel cluster bridged
by thiolates.
Reaction of H2L1 with [NiCl2(dcpe)] affords [Ni(L1)(dcpe)]
(Scheme 1) as confirmed by FAB mass spectrometry, NMR
spectroscopy and elemental analysis.† The 31P{1H} NMR
spectrum of [Ni(L1)(dcpe)] in CDCl3 solution shows a single
resonance at 73.56 ppm confirming a cis square-planar
configuration at Ni(II). [Ni(L1)(dcpe)], however, reacts with
CH2Cl2/n-hexane stored at 210°C for 7 days to afford crystals
of the unexpected binuclear complex [Ni2Cl2(L2)(dcpe)] 2 (L2
= [bis-(4,5-dimethyl-1,2-benzenedimethanethiolato)methane])
(Fig. 2). The structure of 2 reveals that the cis thiolates in
[Ni(L1)(dcpe)] have been alkylated by CH2Cl2 to yield the
corresponding methylene-bridged dithoether/thiolate ligand
[L2]22 bound to Ni(II). C(61) lies on a crystallographic two-fold
axis, and the dinickel complex has imposed C2 symmetry. Thus,
a thiolate centre in each of two [Ni(L1)(dcpe)] moieties is
alkylated by reaction with one equivalent of CH2Cl2 with the
† Electronic supplementary information (ESI) available: syntheses and
characterisation of [Ni(L1)(dppe)], [Ni(L1)(dcpe)], [Ni(L3)2(PP)] and
[Ni(L4)(PP)], and crystallographic data for 1·4CH2Cl2 and 2·4CH2Cl2. See
http://www.rsc.org/suppdata/cc/b3/b309523a/
Scheme 1
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CHEM. COMMUN., 2003, 2776–2777
This journal is © The Royal Society of Chemistry 2003

without any breaking of Ni–S bonds. Thus, introduction of a
single chelate in L1, rather than a polychelate thiolate as in the
the Darensbourg system,13 reduces the stability of the [Ni(L1)]
chelate. This increased lability of the NiS2P2 complex in our
case opens up new pathways for manipulating reactivity at S-
centres involving the breaking of labile Ni–S bonds. In
[Ni(L1)(dppe)], the lability of dppe allows the formation of a
pentanuclear nickel species. However, when the electron-
donating power of the phosphine is increased by changing from
dppe to dcpe, the Ni–P bond cleavage is inhibited and CH2Cl2
is activated leading to the formation of two [NiClSP2] centres.
Intriguingly, the splitting of CH2Cl2 by concerted attack of a
Lewis acidic metal centre and basic sulfur reveals a direct
analogy with one of the proposed mechanisms for heterolytic
cleavage of dihydrogen by [NiFe] hydrogenase.8,14
We thank the BBSRC (UK) and the University of Notting-
ham for funding, and the CVCP (ORS Awards Scheme) for a
studentship to Q.W. We also thank the EPSRC for the provision
of a diffractometer and EPSRC National Service for mass
spectrometry at the University of Wales, Swansea for mass
spectra.
Notes and references
‡
Crystallographic data for 1· 4CH2Cl2: C92H96Cl2Ni5P4S8·4CH2Cl2, M
= 2286.20, triclinic, a = 11.0330(7), b = 13.1947(8), c = 19.0517(12) Å,
a = 89.446(2), b = 82.054(2), g = 66.885(2)°, U = 2523.3(5) Å3, T =
150(2) K, space group P1, Z = 1, m (Mo–Ka) = 1.454 mm21, 15902 data
¯
Fig. 1 (upper) Molecular structure of 1; (lower) diagram showing the zig-
zag structural pattern of 1. Selected bond lengths (Å) and angles (°): Ni(1)–
S(3) 2.1813(9), Ni(1)–S(4) 2.1922(9), Ni(2)–S(1) 2.1874(10), Ni(2)–S(2)
2.2031(10), Ni(2)–S(3) 2.1840(10), Ni(2)–S(4) 2.2000(10), Ni(3)–P(1)
2.1616(10), Ni(3)–P(2) 2.1687(10), Ni(3)–S(1) 2.2343(10), Ni(3)–S(2)
2.2300(10), Ni(3)–Cl(1) 2.6217(10), Ni(1)…Ni(2) 2.7738(5), Ni(2)…Ni(3)
2.8552(6), S(3)–Ni(1)–S(4) 75.95(3), S(1)–Ni(2)–S(3) 173.26(4), S(3)–
Ni(2)–S(4) 75.73(4), S(1)–Ni(2)–S(4) 98.38(4), S(3)–Ni(2)–S(2) 96.55(4),
S(1)–Ni(2)–S(2) 88.98(4), S(2)–Ni(2)–S(4) 170.62(4), Ni(1)–Ni(2)–Ni(3)
176.30(2), P(1)–Ni(3)–P(2) 84.16(4), P(1)–Ni(3)–S(2) 165.17(4), P(2)–
Ni(3)–S(2) 91.44(4), P(1)–Ni(3)–S(1) 93.83(4), P(2)–Ni(3)–S(1),
166.42(4), S(1)–Ni(3)–S(2) 87.13(4), P(1)–Ni(3)–Cl(1) 90.17(4), P(2)–
Ni(3)–Cl(1) 94.27(4), S(2)–Ni(3)–Cl(1) 104.30(4), S(1)–Ni(3)–Cl(1)
99.17(4).
collected, 11126 unique (Rint = 0.019). Final R1 [I > 2s(I)] = 0.0463, wR2
[all data] = 0.145.
Crystallographic data for 2·4CH2Cl2: C73H122Cl2Ni2P4S4·4CH2Cl2, M =
1779.85, monoclinic, a = 21.971(3), b = 17.011(2), c = 23.878(3) Å, b =
92.151(2)°, U = 8918(4) Å3, T = 150(2) K, space group C2/c, Z = 4, m
(Mo–Ka) = 0.926 mm21, 22072 data collected, 10528 unique (Rint
0.030). Final R1 [I > 2s(I)] = 0.0416, wR2 [all data] = 0.113.
=
CCDC reference numbers 217239–217240. See http://www.rsc.org/
suppdata/cc/b3/b309523a/ for crystallographic data in .cif format.
1 C. A. Grapperhaus and M. Y. Darensbourg, Acc. Chem. Res., 1998, 31,
451.
2 (a) M. A. Halcrow and G. Christou, Chem. Rev., 1994, 94, 2421 and
references therein (b) S. C. Shoner, M. M. Olmstead and J. A. Kovacs,
Inorg. Chem., 1994, 33, 7 and references therein.
3 M. Capdevila, P. González-Duarte, C. Foces-Foces, F. H. Cano and M.
Martinez-Ripoll, J. Chem. Soc., Dalton Trans., 1990, 143.
4 C. A. Grapperhaus, S. Poturovic and M. S. Mashuta, Inorg. Chem.,
2002, 41, 4309.
5 P. J. Farmer, J. H. Reibenspies, P. A. Lindahl and M. Y. Darensbourg,
J. Am. Chem. Soc., 1993, 115, 4665.
6 D. Sellmann, M. Waeber, H. Binder and R. Z. Boese, Naturforsch., B:
Chem. Sci., 1986, 41b, 1541.
7 S. S. Oster, R. J. Lachicotte and W. D. Jones, Inorg. Chim. Acta, 2002,
330, 118.
8 (a) A. Volbeda, M. H. Charon, C. Piras, E. C. Hatchikian, M. Frey and
J. C. Fontecilla-Camps, Nature, 1995, 373, 580; (b) A. Volbeda, E.
Garcia, C. Piras, A. L. deLacey, V. M. Fernandez, E. C. Hatchikian, M.
Frey and J. C. Fontecilla-Camps, J. Am. Chem. Soc., 1996, 118,
12989.
9 G. A. Bowmaker, P. D. W. Boyd and G. K. Campbell, Inorg. Chem.,
1982, 21, 2403.
10 T. Sheng, X. Wu, W. Zhang, Q. Wang, X. Gao and P. Lin, Chem.
Comm., 1998, 263.
11 (a) M. Zhou, C-F. Lam, K. F. Mok, P-H. Leung and T. S. Andy Hor, J.
Organomet. Chem., 1994, 476, C32; (b) C. Tejel, M. A. Ciriano, L. A.
Oro, A. Tiripicchio and F. Ugozzoli, Organometallics, 2001, 20,
1676.
12 B. S. Snyder, C. P. Rao and R. H. Holm, Aust. J. Chem., 1986, 39,
963.
13 J. A. Bellefeuille, C. A. Grapperhaus, A. Derecskei-Kovacs, J. H.
Reibenspies and M. Y. Darensbourg, Inorg. Chim. Acta, 2000, 300,
73.
14 (a) A. L. DeLacey, E. C. Hatchikian, A. Volbeda, M. Frey, J. C.
Fontecilla-Camps and V. M. Fernandez, J. Am. Chem. Soc., 1997, 119,
7181; (b) D. Sellmann, G. H. Rackelmann and F. W. Heinemann, Chem.
Eur. J., 1997, 3, 2071; (c) D. Sellmann, F. Geipel and M. Moll, Angew.
Chem., Int. Ed., 2000, 39, 561.
Fig. 2 Molecular structure of 2. Selected bond lengths (Å) and angles (°):
Ni–P(1) 2.1652(8), Ni–P(2) 2.1796(8), Ni–S(1) 2.2042(8), Ni–Cl
2.2170(8), S(2)–C(61) 1.803(3), P(1)–Ni–P(2) 88.65(3), P(1)–Ni–S(1)
88.40(3), P(2)–Ni–S(1) 175.66(3), P(1)–Ni–Cl 174.02(3), P(2)–Ni–Cl
85.45(3), S(1)–Ni–Cl 97.54(3), S(2)–C(61)–S(2A) 117.6(3).
two displaced chloride ions binding each to a Lewis acid Ni
centre11 to yield 2.
It should be noted that when a solution of [Ni(L1)(dcpe)] in
CH2Cl2 is stirred at room temperature for 7 days under nitrogen,
[NiCl2(dcpe)] is obtained. This confirms that the Ni–S bonds
are labile in solution12 leading to potential reaction with CH2Cl2
and abstraction of chloride by Ni(II). It is interesting to note that
Darensbourg et al.13 have observed that the reaction of square-
planar Ni(II)-dithiolate [NiS2N2] complexes with alkyl halides
typically leads to metal-bound dithioether complexes, either as
a square planar dication or a halide bound octahedral complex
CHEM. COMMUN., 2003, 2776–2777
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