Nickel mediated sulfur-selenium and sulfur-sulfur bond formation

Article abstract of DOI:10.1039/a903973b

Electrophilic addition of the PhSeCl to a nickel dithiolate yields S,S'- bis(phenylselenenyl-N,N'-bis(mercaptoethyl)-1,5-diazacyclooctane nickel(II) dichloride and a dimeric, intermolecular bis-disulfide which results from ligand oxidation.

Full text of DOI:10.1039/a903973b

Nickel mediated sulfur–selenium and sulfur–sulfur bond formation
Chia-Huei Lai, Joseph H. Reibenspies and Marcetta Y. Darensbourg*
Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA.
E-mail: marcetta@mail.chem.tamu.edu
Received (in Bloomington, IN, USA) 18th May 1999, Revised manuscript received 4th August 1999,
Accepted 22nd October 1999
Electrophilic addition of the PhSeCl to a nickel dithiolate
yields
1,5-diazacyclooctane nickel(II) dichloride and a dimeric,
intermolecular bis-disulfide which results from ligand
oxidation.
was green and the minor, dark red–brown.6 The mixture was
S,SA-bis(phenylselenenyl-N,NA-bis(mercaptoethyl)-
separated by extraction with CH2Cl2 into which the former
dissolved. The latter dark solid 3 was identified as a salt of a
trimetallic cation2 (Scheme 1). The green material crystallized
in two forms, compounds 1 and 2, which were characterized by
X-ray crystallography. When dissolved in MeOH under Ar, the
isolated and purified compound 1, rapidly disproportionated,
producing a mixture of 2, 3 and diphenyl diselenide (as
determined by 1H NMR).
The molecular structures of 1 and 2 are shown in Figs. 1 and
2. Complex 1 contains a pseudo-octahedral nickel in N2S2Cl2
coordination; the average deviation in the NiN2S2 best plane is
0.096 Å. The axial chlorides are bent away from the daco
framework with a Cl–Ni–Cl angle of 159.07(14)°. As is usual
for six-coordinate Ni complexes containing the diazacy-
clooctane moiety,7 the fused nickel diazacyclohexane rings
adopt chair/chair configurations with the pendant ethylene
linkages (NCH2CH2S) staggered with respect to each other,
across the N2S2Ni plane.
Another open, N2S2 tetradentate, six-coordinate complex
based on Ni-1,8 the dibenzyl dibromide complex 4, is compared
to that of 1 in Table 1. Notably, in compound 4 the benzyl
groups are on the same side of the N2S2 planes, while the
phenylselenolate groups of complex 1 are in transoid positions.
For both complexes the S–Ni–S angles are ca. 10° greater than
that of the parent Ni-1, corresponding to larger S···S distances
(as contrasted to 3.04 Å in Ni-1).7a The Se–Sav distance of
2.202(4) Å agrees well with that of Se-bound (CO)5Cr(PhS-
SePh) ([Se–S = 2.226(6) Å]4 and the sum of covalent radii of
2.21 Å for a Se–S single bond.9 The Ph(PhSe)S?Ni dative
bond presumably relaxes the typical 90° torsion angle in REEAR
dichalcogenides which minimizes lone-pair repulsion. In fact
the C–S–Se–CPh torsion angles are 73 and 82°.
To extend the well known S-based nucleophilicity of [N,NA-
bis(mercaptoethyl)-1,5-diazacyclooctane]nickel(II),
(bme–
daco)Ni or Ni-1,1 especially with regard to developing reactive
ligand functionalities, we explored the reactivity of Ni-1 with
PhSeCl, Scheme 1. The desired nickel-bound selenosulfide 1, a
moiety which should be capable of subsequent oxidative
addition to low-valent metals and thus of potential usefulness to
the preparation of heterobimetallics, was obtained (Scheme 1).
In addition the intermolecular bis-disulfide of H2bme–daco 2
was also isolated and characterized. The latter represents the
product of ligand oxidation proposed in one-electron oxidative
processes of Ni-1,2 concomitantly releasing Ni2+ which is
rapidly scavenged by Ni-1, producing the stable trimetallic
species. Its existence supports our supposition that the mono-
meric intramolecular disulfide of the bme–daco ligand is
sterically prohibited, accounting for much of the well behaved
S-oxygenation chemistry displayed by the ligand.3
A combination of solution conductivity and electrochemical
measurements, when compared with previous detailed studies
Scheme 1 Synthetic scheme of the reaction of Ni-1 and PhSeCl.
Compound 1 is, to our knowledge, the only example of a
structurally characterized mixed RS–SeRA ligand which is S-
bound to a transition metal. Our literature and data base searches
find only one other structurally characterized mixed dichalcoge-
nide, a low yield byproduct of an organometallic reaction which
is Se-bound, (PhSSePh)Cr(CO)5.4 An interesting bioinorganic
reaction of selenocysteine–S-dithiolene coupling at the mo-
lybdenum site of Desulfovibrio desulfuricans ATCC 27774
formate dehydrogenase (FDH) has implied both Se and S
binding at Mo.5 The following report is a designed mixed
dichalcogenide synthesis, doubtlessly made possible by the well
known ability of nickel to facilitate the nucleophilicity of
thiolate-S as well as to bind charge-neutralized sulfur, stabiliz-
ing the RS–SeRA toward disproportionation.
On mixing MeCN solutions of orange PhSeCl with purple
Ni-1, two different precipitates developed; a major component
Fig. 1 ORTEP drawing (50% probability ellipsoids) of complex 1. Metric
data are given in Table 1.
Chem. Commun., 1999, 2473–2474
This journal is © The Royal Society of Chemistry 1999
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We gratefully acknowledge financial support from the
National Science Foundation (CHE-9812355 for this work, and
CHE 85-13273 for the X-ray diffractometer and crystallo-
graphic computing system, and CHE-8912763 for the EPR
spectrometer) and contributions from the R. A. Welch Founda-
tion. We thank Dr Guang Ming Li for 77Se NMR spectra
measurements.
Notes and references
† Syntheses: 1 and 2: At 0 °C, 2 equiv. of PhSeCl (0.150 g, 0.8 mmol) added
to a 15 mL CH3CN solution of Ni-1 (0.116 g, 4.0 mmol) produced a green
precipitate and a red–brown solid. The resulting mixture was stirred for 30
min, and the solvent was removed in vacuo. Extraction of the residue with
20 mL of CH2Cl2 gave a deep green solution. Slow evaporation yielded dark
green crystals of 1 and blue–green crystals of 2 in 55 and 3% yield,
respectively. 1: Anal. Calc. (Found) for C22H30N2S2NiCl2Se2: C, 39.20
(39.90); H, 4.49 (4.59); N, 4.16 (4.19)%. UV–VIS(MeOH) lmax/nm (e/M21
cm21): 236(3232), 270(937), 316 (272), 338 (145). MS: +ESI; m/z (%
intensity); 639 (20), 545 (29), 547 (29), 447 (9), 290 (10). 77Se NMR
(CH2Cl2): d 2372. 2: Anal. Calc. (Found) for C20H42N4S4NiCl4: C, 36.00
(36.08); H, 6.34 (5.98)%. MS: +ESI; m/z (% intensity); 594 (6), 466 (49),
250 (21), 233 (96), 146 (100).
‡ Crystal data: 1: C22H30N2S2NiCl2Se2, M = 674.13, triclinic, space group
PI, a = 7.714(2), b = 8.031(3), c = 22.728(7) Å, a = 81.31, b = 85.50,
Fig. 2 ORTEP drawing (50% probability ellipsoids) of complex 2. Selected
distances (Å) and angles (°): S(3)–S(3A) 2.048(7), S(3)–C(11) 1.786(13),
S(4)–S(4A) 2.023(6), S(4)–C(20) 1.845(11), av. Ni–Cl 2.272(4); av. Cl–
Ni–Cl 107.1(2), C(11)–S(3)–S(3A) 104.0(4), C(20)–S(4)–S(4A) 102.7(4).
¯
g = 65.610(10)°, U = 1267.4(7) Å3, Z = 2, Dc = 1.766 g cm23. X-Ray
crystallographic data were obtained on a Siemens R3m/V single crystal X-
ray diffractometer using Mo-Ka (l = 0.71073 Å) radiation and equipped
with a Siemens LT-2 cryostat. A single crystal was mounted on a glass fiber
with epoxy cement at 193(2) K. Structures were solved by direct methods.
The elbow carbons C4, C7, C9 and C10 were found to be disordered and
were modelled accordingly. Anisotropic refinement for all non-hydrogen
Table 1 Metrical structural data and electrochemical data
atoms was by full-matrix least squares with R
= 0.0861 and Rw =
0.2187.
2: C20H42Cl4N4NiS4, M = 667.33, orthorhombic, space group Fdd2, a =
27.396(6), b = 18.885(4), c = 22.838(5) Å, U = 11816(4) Å3, Z = 16, Dc =
1.501 g cm23. X-Ray crystallographic data were obtained on a Siemens
R3m/V single crystal X-ray diffractometer using Cu-Ka (l = 1.54178 Å)
radiation and equipped with a Siemens LT-2 cryostat. The structures were
solved by direct methods. Anisotropic refinement for all non-hydrogen
atoms was by full-matrix least squares with R = 0.0569 and Rw = 0.1461.
A single crystal was mounted on a glass fiber with epoxy cement at room
temperature. CCDC 182/1466.
Ni–Sav/Å
Ni–Nav/Å
S···S/Å
X–Ni–X/°
S–Ni–S/°
Ni–S–Se(C)av/°
Reduction potential (NiII/I)/V
2.560(4)
2.120(11)
3.95
159.07(14)
100.91(12)
109.71(13)
20.38, 20.86
2.493(1)
2.118(3)
3.767
162.01(2)
98.14(3)
114.91(14)
20.67
1 H2bme–daco = N,NA-bis(mercaptoethyl)-1,5-diazacyclooctane; D. K.
Mills, J. H. Reibenspies and M. Y. Darensbourg, Inorg. Chem., 1990,
of analogues of compound 4 and similar derivatives,7,8,10 led to
the conclusion expressed in Scheme 2. The NiII/I couple at
20.38 V is the most positive observed thus far in a wide range
of Ni-1 thioether dicationic derivatives suggesting that the
addition of two SePh+ groups to the thiolate S achieves a charge
neutralization better than that of any carbon-based electrophile.
The selenosulfide derivative is less stable to reduction,
consistent with weaker S–Se bonds at reduced nickel as
compared to S–C bonds.11 It is also consistent with the observed
loss of the Se–S interaction in the reduction of the MoVI-
selenosulfide site of FDHH.5 A complicated anodic region of the
cyclic voltammogram was not resolved as to ligand or metal-
based oxidation.10,12
29, 4364.
2 P. J. Farmer, T Solouki, D. K. Mills, T. Soma, D. H. Russell, J. H.
Reibenspies and M. Y. Darensbourg, J. Am. Chem. Soc., 1992, 114,
4601.
3 C. A. Crapperhaus and M. Y. Darensbourg, Acc. Chem. Res., 1998, 31,
451.
4 D. Neugebauer and U. Schubert, J. Organomet. Chem., 1983, 256,
43.
5 G. N. George, C. Costa, J. J. G. Moura and I. Moura, J. Am. Chem. Soc.,
1999, 121, 2625.
6 The dark red–brown precipitate was characterized by spectroscopy as
bis{N,NA-bis(mercaptoethyl)-1,5-diazacyclooctane]nickel(II)}nickel(II
)
tetrachloronickelate: UV–VIS(MeOH): lmax/nm (e/M21 cm21): 408
(3033), 486 (1316), 548 (850). Anal. Calc. (Found) for
C20H40N4S4Ni4Cl4: C, 28.55 (29.55); H, 4.79 (4.63)%. MS: +ESI; m/z
(% intensity) 319 (85), 70 (100), 42 (82), 23 (39).
7 (a) M. Y. Darensbourg, I. Font, D. K. Mills, M. Pala and J. H.
Reibenspies, Inorg. Chem., 1992, 31, 4965; (b) D. C. Goodman, T.
Tuntulani, P. J. Farmer, M. Y. Darensbourg and J. H. Reibenspies,
Angew. Chem., Int. Ed. Engl., 1993, 32, 116.
8 R. M. Buonomo, J. H. Reibenspies and M. Y. Darensbourg, Chem. Ber.,
1996, 129, 779.
9 N. J. Brondmo, S. Esperas and S. Husebye, Acta Chem. Scand., Ser. A,
1975, 29, 93.
Scheme 2 The combined results of solution conductivity measurements and
electrochemical studies.
10 P. J. Farmer, J. H. Reibenspies, P. A. Lindahl and M. Y. Darensbourg,
J. Am. Chem. Soc., 1993, 115, 4665.
11 T. L. Cottrell, The Strengths of Chemical Bonds, Academic Press Inc.
Publishers, New York, 1958.
12 M. Kumar, R. O. Day, G. J. Colpas and M. J. Maroney. J. Am. Chem.
Soc., 1989, 111, 5974.
13 W. Tsagkalidis, D. Rodewald and D. Rehder, Inorg. Chem., 1995, 34,
1943.
The intermolecular disulfide 2 crystallizes in a dicationic
protonated form, with NiCl422 as counter ion. The bisdisulfide
attains a cage conformation (C2 symmetry) with a typical
disulfide S–S average distance (2.04 Å) and a large cross cage
S(3)...S(4) distance of 7.207 Å. A similar bisdisulfide was
isolated as a byproduct of a N2S2 ligating reaction of
VOCl2(thf)2.13 The H-bonding interaction linking the two N
atoms significantly shortens the N...N distance to 2.633 Å, in
contrast to Ni-1, 2.783 Å.
Communication 9/03973B
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Chem. Commun., 1999, 2473–2474