Directed reactivity at a vanadium(II) thiolate center: Synthesis and structure of a novel vanadium thiolate complex and its reaction product with azobenzene

Article abstract of DOI:10.1039/a804231d

The vanadium(II) thiolate complex [V(tmeda)(DCTP)₂] [DCTP = 2,6-dichlorothiophenolate; tmeda = N,N,N′,N′tetramethylethylenediamine] is obtained by the reaction of 2 equiv. of LiDCTP with [VCl₂(tmeda)₂] and reacts with azobenzene to yield the imido-containing complex [V(tmeda)(DCTP)₂(≡NPh)].

Full text of DOI:10.1039/a804231d

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Directed reactivity at a vanadium(II) thiolate center: synthesis and structure of
a novel vanadium thiolate complex and its reaction product with azobenzene
John A. Davis, Christopher P. Davie, David B. Sable and William H. Armstrong*†
Department of Chemistry, Eugene F. Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts, 02167-3860, USA
The vanadium(II) thiolate complex [V(tmeda)(DCTP)2]
[DCTP = 2,6-dichlorothiophenolate; tmeda = N,N,NA,NA-
tetramethylethylenediamine] is obtained by the reaction of 2
equiv. of LiDCTP with [VCl2(tmeda)2] and reacts with
azobenzene to yield the imido-containing complex [V(tme-
da)(DCTP)2(·NPh)].
graphically characterized vanadium(II) thiolates are still quite
uncommon.5 The structure of 1 reveals as well the presence of
two dative, aryl–halide bonds. The observed V–Cl distances
[2.515(2) Å, 2.510(2) Å] are well within the sum of radii of the
atoms (3.131 Å),6 and there is a slight lengthening of the Cl–C
bond [1.758(9) Å] relative to the bond for the non-coordinated
chlorine [1.727(9) Å]. While the ability of DCTP2 to act as a
bidentate ligand through sulfur and chlorine is unknown in the
literature, such dative bonds with other halides are not
unprecedented,7 including one at a vanadium center.8 The
Low-valent vanadium thiolate complexes are of interest due in
part to their potential relevance to the functioning of the
alternative nitrogenase cofactor,1 and to their presumed re-
activity toward small reducible molecules in general. Recently,
Coucouvanis and coworkers have shown that vanadium in a
sulfur- and nitrogen-containing environment can catalyze the
reduction of hydrazine to ammonia.2 We have had considerable
interest in lower-valent vanadium chalcogenide complexes,
particularly with respect to their reactivity toward small
molecules.3 Herein we report the synthesis and structural
occurrence of such potentially labile bonds at a vanadium(II
)
center, and particularly at an electron-rich vanadium(II) thiolate
center, gives hope that these might be sites for reactivity.
These hopes were realized in the reaction that yields complex
2, [V(tmeda)(DCTP)2(·NPh)]. Complex 2, whose ORTEP is
shown in Fig. 2,¶ is obtained from the reaction of 1 with 0.5
equiv. of azobenzene.∑ The azobenzene is cleaved to give one
phenylimido group per vanadium, with concomitant dissocia-
tion of one of the chlorine dative bonds of 1. The other dative
chlorine bond is now located trans to the imido group, and the
V–Cl bond distance is, as expected from the strongly electron
donating nature of the imido functionality, significantly length-
ened relative to that seen in 1 [2.671(3) vs. 2.510(2) Å].
Structurally, 2 is quite similar to other vanadium(IV) and
characterization of a novel and rare mononuclear vanadium(II
)
thiolate complex containing labile coordination sites. We also
provide an initial report on its reactivity with a substrate of
relevance to dinitrogen reduction.
Complex 1, [V(tmeda)(DCTP)2] (DCTP = 2,6-dichloro-
thiophenolate; tmeda
mine), is formed from the reaction of 2 equiv. of the lithium salt
=
N,N,NA,NA-tetramethylethylenedia-
of 2,6-dichlorothiophenol (LiDCTP)‡ with
1
equiv. of
vanadium(
) arylimido complexes,9 with the short V–N
V
[VCl2(tmeda)2].§4 The crystal structure of 1 is shown in Fig. 1.¶
Bond distances and angles for 1 are consistent with those
observed for other complexes of this sort, though crystallo-
distance [1.670(7) Å] and nearly linear V–N–C angle
[171.2(7)°] indicating a V·NAr bonding moiety.9 Other
distances are as expected, though again it should be noted that
Cl(2)
Cl(4)
Cl(3)
S(1)
S(2)
N(2)
Cl(1)
N(2)
V(1)
S(1)
V(1)
N(3)
Cl(3)
N(1)
N(1)
C(1)
Cl(1)
Cl(2)
S(2)
Cl(4)
Fig. 1 ORTEP of [V(tmeda)(DCTP)2], 1, showing the 30% probability
thermal ellipsoids and atom labelling scheme. Hydrogen atoms are omitted
for clarity. Selected bond distances (Å) and angles (°) are as follows:
V(1)–S(1) 2.468(2), V(1)–S(2) 2.464(2), V(1)–Cl(1) 2.515(2), V(1)–Cl(3)
2.510(2), V(1)–N(1) 2.206(6), V(1)–N(2) 2.220(7), S(1)–V(1)–S(2)
165.19(7), Cl(1)–V(1)–Cl(3) 92.84(6).
Fig. 2 ORTEP of [V(tmeda)(DCTP)2(·NPh)], 2, showing the 30%
probability thermal ellipsoids and atom labelling scheme. Hydrogen atoms
are omitted for clarity. Selected bond distances (Å) and angles (°) are as
follows: V(1)–N(1) 1.670(7), V(1)–S(1) 2.465(3), V(1)–S(2) 2.434(3),
V(1)–Cl(3) 2.671(3), V(1)–N(2) 2.245(8), V(1)–N(3) 2.243(7), V(1)–N(1)–
C(1) 171.2(7).
Chem. Commun., 1998
1649

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refluxed and became dark brown and homogeneous over 2 h. The solution
was filtered, concentrated and cooled, affording brown crystals in 65%
yield. Analysis was satisfactory. EPR (X-band, THF, 77 K): g = 2.0, 8
lines.
very few vanadium(IV) imido complexes have been structurally
characterized.10 Perhaps more interestingly, of those that have,
none have been prepared from reduction of a diazo moiety. In
fact, of all reported vanadium imido complexes, only one other
is formed as the result of the reductive cleavage of a dinitrogen
analogue.11
Compound 1 has also shown reactivity with many other small
molecules such as tert-butyl isocyanide, 1,2-diphenylhydrazine
and organic aldehydes. Elucidation of other reaction products
and details of the reactivity of related compounds will be
reported elsewhere. Further development of chemistry at other
low-valent vanadium thiolate centers is under way.
For funding this work we thank the National Science
Foundation (Grant CHE-8857455). We also thank the National
Institutes of Health (Grant 1 S10 RR09008) and Boston College
for providing funds for the purchase of a Siemens SMART
single crystal X-ray diffractometer.
1 R. R. Eady, in Advances in Inorganic Chemistry, ed. A. G. Sykes,
Academic, San Diego, 1991, vol. 36, pp. 77–101 and references
therein.
2 S. M. Malinak, K. D. Demadis and D. Coucouvanis, J. Am. Chem. Soc.,
1995, 117, 3126.
3 W. C. A. Wilisch, M. J. Scott and W. H. Armstrong, Inorg. Chem., 1988,
27, 4333; C. R. Randall and W. H. Armstrong, J. Chem. Soc., Chem.
Commun., 1988, 986; L. Gelmini and W. H. Armstrong, J. Chem. Soc.,
Chem. Commun., 1989, 1904; M. J. Scott, W. C. A. Wilisch and W. H.
Armstrong, J. Am. Chem. Soc., 1990, 112, 2429; D. B. Sable and W. H.
Armstrong, Inorg. Chem., 1992, 31, 161; H. H. Murray, S. G. Novick,
W. H. Armstrong and C. S. Day, J. Cluster Sci., 1993, 4, 439; P. J.
Bonitatebus, Jr., S. K. Mandal and W. H. Armstrong, Chem. Commun.,
1998, 939.
4 J. J. H. Edema, S. Gambarotta, A. Meetsma, A. L. Spek and N.
Veldman, Inorg. Chem., 1991, 30, 2062.
Notes and References
5 D. W. Stephan and T. T. Nadasdi, Coord. Chem. Rev., 1996, 147, 147;
[V(pyt)3]2: G. Henkel, B. Krebs and W. Schmidt, Angew. Chem., Int.
Ed. Engl., 1992, 31, 1366; [V(tmeda)(pyt)2]: J. G. Reynolds, S. C.
Sendlinger, A. M. Murray, J. C. Huffman and G. Christou, Angew.
Chem., Int. Ed. Engl., 1992, 31, 1253; J. G. Reynolds, S. C. Sendlinger,
A. M. Murray, J. C. Huffman and G. Christou, Inorg. Chem., 1995, 34,
5745; [V(tmeda)(‘S4’)]: W. Tsagkalidis, D. Rodewald and D. Rehder,
J. Chem. Soc., Chem. Commun., 1995, 165.
6 Values for Cl (van der Waals) and V (atomic) taken from J. Emsley, The
Elements, Oxford University Press, Oxford, 1991, pp. 50, 210.
7 R. M. Catala, D. Cruz-Garritz, P. Sosa, P. Terreros, H. Torrens, A. Hills,
D. L. Hughes and R. L. Richards, J. Organomet. Chem., 1989, 359, 219;
R. M. Catala, D. Cruz-Garritz, A. Hills, D. L. Hughes, R. L. Richards,
P. Sosa and H. Torrens, J. Chem. Soc., Chem. Commun., 1987, 261;
Y. A. Simonov, A. A. Dvorkin, G. S. Matuzenko, M. A. Yampol’skaya,
T. S. Gifeisman, N. V. Berbeleu and T. I. Malinovskii, Koord. Khim.,
1984, 10, 1247; Y. A. Simonov, G. S. Matuzenko, M. M. Botoshanskii,
M. A. Yampol’skaya, N. V. Gerbeleu and T. I Malinovskii, Zh. Neorg.
Khim., 1982, 27, 407; M. J. Burk, R. H. Crabtree and E. M. Holt,
J. Organomet. Chem., 1988, 341, 495; J. M. Casas, L. R. Falvello, J.
Fornie´s and A. Martín, Inorg. Chem., 1996, 35, 56.
8 V. C. Gibson, C. Redshaw, L. J. Sequeira, K. B. Dillon, W. Clegg and
M. R. J. Elsegood, Chem. Commun., 1996, 2151.
9 D. E. Wigley, Prog. Inorg. Chem., 1995, 42, 239, and references therein;
W. A. Nugent and J. M. Mayer, Metal Ligand Multiple Bonds, John
Wiley and Sons, New York, 1988.
10 N. Wiberg, H.-W. Häring and U. Schubert, Inorg. Chem., 1978, 17,
1880; F. Preuss, H. Becker, J. Kaub and W. A. Sheldrick, Z.
Naturforsch., B: Anorg. Chem. Org. Chem., 1988, 43, 1195; S.
Gambarotta, A. Chiesi-Villa and C. Guastini, J. Organomet. Chem.,
1984, 270, C49; J. H. Osborne, A. L. Rheingold and W. C. Trogler,
J. Am. Chem. Soc., 1985, 107, 7945.
11 For compound [V(·NPh)Cl(µ-Cl)]2, M. Mazzanti, M. Khadkhodayan
and W. H. Armstrong, Abstracts of the 203rd National Meeting, ACS,
INOR No. 461, San Francisco, CA, 1992.
† E-mail: william.armstrong@bc.edu
‡ In a typical preparation, 5.372 g (30.00 mmol) of 2,6-dichlorothiophenol
(Lancaster) were added to 20 ml of toluene. 18.75 ml (30.00 mmol) of 1.6
M
n-butyllithium (Aldrich, in hexanes) were added over 0.5 h to the thiol
solution with vigorous stirring. The resulting white precipitate was washed
with hexane and dried, affording an approximately quantitative yield.
§ In a typical preparation, 1.00 g (2.82 mmol) of [VCl2(tmeda)2]4 was
dissolved in 20 ml of THF. Then 1.04 g (5.65 mmol) of LiDCTP were added
at once with stirring. The light blue solution turned homogeneous and
emerald green. Over 0.2 h a light green precipitate of [V(tmeda)(DCTP)2]
appeared. The precipitate was filtered off, washed with diethyl ether and
dried in vacuo to give analytically pure product in 68% yield. The yield
could be improved by treating the remaining filtrate with pentane. The green
precipitate was filtered off and rinsed with 5 ml of diethyl ether and then 5
ml of THF. The combined solids then afforded an 82% yield. Elemental
analysis was satisfactory. EPR (X-band, CH2Cl2, 77 K): g
multiline.
= 5.33,
¶ Crystal data for 1: a single crystal was mounted under the cold stream
(290 °C) of a Siemens SMART system. An initial collection of 60 frames
of data yielded the crystal system (hexagonal) and unit cell [a = 7.6735(1),
c = 65.3685(2) Å]. 20749 reflections were collected, of which 5003 were
unique. The space group (P61, Z = 6) was chosen by systematic absences
and successful refinement of the structure. No absorption correction was
used. The structure was solved using SHELX 5.0 using anisotropic thermal
parameters for all non-hydrogen atoms to values of R1 = 7.35%, wR2
=
15.7% for I > 2s(I). For 2·thf: a single crystal was mounted under the cold
stream (290 °C) of a Siemens SMART system. An initial collection of 60
frames of data yielded the crystal system (orthorhombic) and unit cell [a =
13.621(4), b = 15.254(4), c = 30.410(7) Å]. 17675 reflections were
collected, of which 10152 were unique. The space group (P212121, Z = 2)
was chosen by systematic absences and successful refinement of the
structure. No absorption correction was used. The structure was solved
using SHELX 5.0 using anisotropic thermal parameters for all non-
hydrogen atoms to values of R1 = 8.40%, wR2 = 13.72% for I > 2s(I).
CCDC 182/902.
∑ In a typical preparation, 0.25 g (0.478 mmol) of 1 was suspended with
stirring in 20 ml of THF. Addition of 0.044 g (0.239 mmol) of azobenzene
(Aldrich) yielded a yellow–green heterogeneous mixture which was then
Received in Bloomington, IN, USA, 5th January 1998; revised manuscript
received 27th May 1998; 8/04231D
1650
Chem. Commun., 1998