Synthesis and reactivity of an 2-azabutadiene-based π-conjugated dithioether: Formation of a N,S-ligated molybdenum chelate complex and C,N,S-pincer complexes of palladium and platinum

Article abstract of DOI:10.1016/j.inoche.2005.03.016

Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1- diphenyl-2-azabuta-1,3-diene [Cl₂C=C(H)-N=CPh₂}] (1) affords the 2-azabutadiene derivative [(i-PrS)₂CC(H)-NCPh ₂] (2). Upon irradiation of Mo(CO)₆ in THF in the presence of 2, the chelate complex cis-[(OC)₄Mo{(i-PrS)₂C=C(H)-N= CPh₂}] (3) is obtained. Coordination on Mo occurs through the imine nitrogen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)₂CC(H)-NC(Ph)C₆H ₄)PtCl] (4b) have been determined by X-ray diffraction studies.

Full text of DOI:10.1016/j.inoche.2005.03.016

Inorganic Chemistry Communications 8 (2005) 610–613
www.elsevier.com/locate/inoche
Synthesis and reactivity of an 2-azabutadiene-based p-conjugated
dithioether: Formation of a N,S-ligated molybdenum chelate
complex and C,N,S-pincer complexes of palladium and platinum
a
Sandrine Jacquot-Rousseau , Abderrahim Khatyr , Gerard Schmitt
a
,a
*
´
,
a,
b
b
Michael Knorr *, Marek M. Kubicki , Olivier Blacque
a
´ ´ ´ ´
Laboratoire de Chimie des Materiaux et Interfaces, Universite de Franche-Comte, Faculte des Sciences et des Techniques,
16, Route de Gray, 25030 Besanc¸on Cedex, France
´
b
`
`
´
´
Laboratoire de Synthese et dÕElectrosynthese Organometalliques (UMR 5188), Universite de Bourgogne, Faculte des Sciences et des Techniques,
9, Av. A. Savary, 21000 Dijon Cedex, France
Received 9 March 2005; accepted 22 March 2005
Available online 23 May 2005
Abstract
Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl2C@C(H)–N@CPh2}] (1)
affords the 2-azabutadiene derivative [(i-PrS)2C@C(H)–N@CPh2] (2). Upon irradiation of Mo(CO)6 in THF in the presence of 2,
the chelate complex cis-[(OC)4Mo{(i-PrS)2C@C(H)–N@CPh2}] (3) is obtained. Coordination on Mo occurs through the imine nitro-
gen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or
Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)2C@C(H)–N@C(Ph)C6H4)PtCl] (4b) have been determined by X-ray
diffraction studies.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: 2-Azabutadiene; Dithioether; Chelate complex; Cyclometallation; Platinum; Palladium; Molybdenum
In a precedent paper, we have exploited the presence
of two reactive vinyl-chlorine bonds of [Cl2C@C(H)–
N@CPh2}] (1) [1] for oxidative addition reactions across
low-valent metal centers to synthesize r-alkenyl com-
plexes trans-[MCl{(C(Cl)@C(H)–N@CPh2)}(PPh3)2] (M =
Pd, Pt) and the l-vinylidene compound [(PPh3)ClPd
{l-(C@C(H)–N@CPh2)}PdCl(PPh3)2], ligated by a p-
conjugated organic array [2]. In the context of our
research on dithioether coordination chemistry [3–5],
we were interested in functionalisation of 1 by thioether
groups to assemble a polydentate ligand system possess-
ing both sulphur and nitrogen donor sites [6].
With this goal in mind, we reacted 1 with an excess of
thiolate in dry DMF. This led under mild conditions
exclusively to the dithioether derivative [(i-PrS)2C@
C(H)–N@CPh2] (2), consistent with formal substitution
of the two chloro-substituents by SRÀ on the vinylic
C(3) atom. After workup, 2 was isolated as stable yellow
crystalline solid with 55% yield.1 Note that the regiose-
lectivity of the nucleophilic attack of i-PrSÀ on C(3) con-
trasts with our finding that attack by sodium alkoxydes
1
Selected data for 2: IR(KBr): m(C@C) 1555, m(C@N) 1523 cmÀ1. 1H
NMR (acetone-d6): d 1.18 (d, 6H, 3J = 6,7 Hz, CH(CH3)2), 1.31 (d, 6H,
3J = 6.7 Hz, CH(CH3)2), 3.30 (sept, 1H, J = 6.7 Hz, CH(CH3)2), 3.91
3
*
(sept, 1H, J = 6.8 Hz, CH(CH3)2), 7.11 (s, 1H, Hvinyl), 7.15–7.80 (m,
10H, phenyl). Anal. Calcd. for C21H25NS2: C, 70.94; H, 7.09; N, 3.94.
Found: C, 70.71; H, 7.15; N, 3.70%.
Corresponding author. Tel.: +33 3 81 66 62 70; fax: +33 3 81 66
64 38.
E-mail address: michael.knorr@univ-fcomte.fr (M. Knorr).
1387-7003/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.03.016

S. Jacquot-Rousseau et al. / Inorganic Chemistry Communications 8 (2005) 610–613
611
Pri
S
H
N
H
N
Cl
Cl
2 NaSi-Pr
3
C
2
C
C
C
Ph
Ph
Ph
Ph
1
DMF
iPr
C
S
C
- 2 NaCl
1
2
Ph
Ph
O
O
C
C
N
C
h x ν
2
CO
OC
OC
OC
H
C
C
Mo
Mo
- CO
OC
THF
S
- THF
Pri
C
O
C
O
iPr
S
3
Scheme 1.
occurs at the more electrophilic C(2) atom [7] (see
Scheme 1).
˚
Fig. 1. View of the crystal structure of 2. Selected bond lengths [A] and
angles [°]: C(7)–S(2) 1.817(4), C(4)–S(1) 1.823(4), C(3)–S(1) 1.766(4),
C(3)–S(2) 1.752(4), C(3)–C(2) 1.337(5), N–C(2) 1.397(4), N–C(1)
1.288(4) and S(1)–C(3)–S(2) 119.9(3), C(2)–C(3)–S(1) 117.9(3), C(2)–
C(3)–S(2) 122.1(3), N–C(2)–C(3) 122.7(4), C(1)–N–C(2) 119.5(4),
N–C(1)–C(16) 124.6(4), N–C(1)–C(10) 117.9(4), C(16)–C(1)–C(10)
117.5(4).
As evidenced by an X-ray diffraction study, the tran-
soid conformation of the 2-azabutadiene chain of pre-
cursor 1 is also found in the solid-state structure of 2
(see Fig. 1). Compared with the C@C bond distance
found for 1, that of 2 is slightly elongated [1.319(3) vs.
˚
1.337(5) A], while the imine bond distances are almost
2
˚
the same (1.293(3) vs. 1.288(5) A) in both compounds.
One of the phenyl groups attached on C(1) is roughly
coplanar with the diene unit. However, the dihedral an-
gle between the C10–C15 ring in 2 with the C1–N–
C2–C3 chain is equal to 27.9(2)°, making so in doubt
the existence of a strong p-conjugation.
Me
H
H
Me
S
C
CH2Cl2
N
C
S
Cl2M(NCPh)2 + 2
- HCl
Upon irradiation of Mo(CO)6 in THF, first the ad-
duct [Mo(CO)5THF] was prepared in situ, then the irra-
diation was continued in the presence of 2 until complete
disappearance of the m(CO) vibrations due to [Mo
(CO)5THF]. After work-up, a red solid was isolated,
whose elemental analysis and IR data were consistent
with formation of a chelate complex cis-[(OC)4Mo
{(i-PrS)2C@C(H)–N@CPh2}] 3.3 Our suggestion of a
less strained five-membered S,N-chelation instead of a
strained S,S-chelation is furthermore corroborated by
the observation of three very distinct carbonyl reso-
nances in the 13C{1H} NMR spectrum at d 209.1,
216.2 and 223.2. Since one resonance corresponds to
two equivalent axial carbonyls, the quite diverging
chemical shifts of the two remaining equatorial carbo-
nyls is indicative for a dissymmetric S,N-chelation [8].
M
Me
-
2 benzonitrile
H
Me
4a, M = Pd 65% yield
4b, M = Pt 47% yield
Cl
Scheme 2.
The air-stable cyclometallated complexes C,N,S-
[(i-PrS)2C@C(H)–N@C(Ph)C6H4)MCl] (4a, M = Pd;
4b, M = Pt) were formed after stirring under reflux a
dichloromethane solution of [MCl2(NCPh)2] overnight
in the presence of 1.1 equiv. of 2 according to Scheme 2.4
In addition to a dative S (thioether) and N (imine)
bond, a covalent r–M–carbon bond has been formed
between the metal center and a phenyl group. This
orthometallation reaction with concomitant elimination
of HCl leads to a C,N,S-pincer coordination of the
2
Crystal data for 2: (293(2) K) C21H25NS2: Mr = 355.54, mono-
˚
clinic, P21/n, a = 11.192(3), b = 9.003(2), c = 20.434(4) A,
3
4
b = 93.75(2)°, V = 2054.5(8) A , l = 0.261 mmÀ1
,
Z = 4; Mo
K
Selected data for 4a: 1H NMR (CDCl3): d 1.39 (d, 6H, 3J = 6.7 Hz,
˚
a = 0.71073 A, Enraf–Nonius CAD4; structure refined by full-matrix
least-squares on observed F2 to give final indices R1 = 0.0489 and
CH(CH3)2), 1.65 (d, 6H, 3J = 6.8 Hz, CH(CH3)2), 3.69 (sept, 1H,
3J = 6.7 Hz, CH(CH3)2), 3.93 (sept, 1H, J = 6.8 Hz, CH(CH3)2), 6.84–
8.32 (m, 10H, phenyl + Hvinyl). Anal. Calcd. for C21H24 ClNPdS2: C,
50.81; H, 4.87; N, 2.82. Found: C, 50.42; H, 4.46; N, 2.53%. Selected
data for 4b: 1H NMR (CDCl3): d 1.28 (d, 6H, 3J = 6.2 Hz, CH(CH3)2),
1.61 (d, 6H, 3J = 5.9 Hz, CH(CH3)2), 3.40 (m, 1H, CH(CH3)2), 4.05
(m, 1 H, CH(CH3)2), 6.81–7.97 (m, 10H, phenyl + Hvinyl). Anal. Calcd
for C21H24ClNPtS2: C, 50.81; H, 4.87; N, 2.82. Found: C, 50.42; H,
4.46; N, 2.53%.
˚
wR2 = 0.1060; GOF = 1.112.
Selected data for 3: IR(CCl4): m(CO) 2017 m, 1896 s, 1861 s cmÀ1
3
.
1H NMR (acetone-d6): d 1.29 (d, 6H, 3J = 6.7 Hz, CH(CH3)2), 1.39 (d,
3
3
6H, J = 6.6 Hz, CH(CH3)2), 3.51 (sept, 1H, J = 6.7 Hz, CH(CH3)2),
3.91 (sept, 1H, J = 6.6 Hz, CH(CH3)2), 7.20–7.65 (m, 11H, phe-
nyl + Hvinyl). Anal. Calcd. for C25H29MoNS2: C, 50.23; H, 4.43; N,
2.48. Found: C, 53.18; H, 4.36; N, 2.52%.

612
S. Jacquot-Rousseau et al. / Inorganic Chemistry Communications 8 (2005) 610–613
these pincer complexes towards insertion reactions of
unsaturated organic molecules [12,13], their electronic
structures and their photophysical properties [14–22].
Appendix A. Supplementary data
Crystallographic data for the structural analyses of
compounds 2 and 4b have been deposited with the Cam-
bridge Crystallographic Data Centre (CCDC Nos.
265265 and 265266, respectively). Copies of this infor-
mation may be obtained free of charge from: The direc-
tor, CCDC, Union Road, Cambridge, CB2 IEZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk). The UV-vis spec-
tra of 1 and 2 can be found in the online version at
doi:10.1016/j.inoche.2005.03.016.
Fig. 2. View of the crystal structure of 4b. One of the two independent
molecules present in asymmetric unit is shown. Selected bond lengths
˚
[A] and angles [°]: Pt–Cl 2.3067(9), Pt–S(1) 2.3642(9), Pt–C(5) 2.002(3),
Pt–N 1.990(3), C(3)–S(1) 1.779(4), C(3)–S(2) 1.757(4), C(3)–C(2)
1.343(5), N–C(2) 1.400(4), N–C(1) 1.315(5) and N–Pt–Cl 177.03(9),
N–Pt–S(1) 85.77(9), S(1)–Pt–C(5) 166.6(1), N–Pt–C(5) 81.0(1), Cl–Pt–
S(1) 96.08(3), C(5)–Pt–Cl 97.2(1), N–C(2)–C(3) 120.7(3), C(1)–N–C(2)
124.3(3), S(2)–C(3)–S(1) 120.3(2).
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promising development in organometallic chemistry.
As shown in the case of the molybdenum complex 3, this
ligand system is prone to ligate to metal centers both via
the soft thioether function or the harder imine nitrogen.
The potential of this polydentate ligands to act as
C,N,S-pincer ligand after orthometallation reaction
with Pd(II) and Pt(II) has also been demonstrated. In
a forthcoming paper we will report on the reactivity of
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5
Crystal data for 4b (at 110(1) K) C21H24ClNPtS2: Mr = 585.07,
˚
ꢀ
triclinic, P1, a = 9.4840(2), b = 11.9340(3), c = 19.5280(6) A,
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3
˚
a = 96.695(1)°, b = 95.568(1)°, c = 99.445(1)°, V = 2150.1(1) A ,
Z = 4; Nonius Kappa CCD, Mo Ka = 0.71073 A, l = 6.850 mm
À1
˚
;
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final indices R1 = 0.0273 and wR2 = 0.0669, GOF = 1.005. There are
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