832
Figure 3. ORTEP of the cationic complex in [Cp*Ir-
{BnSN=C(NMe2)S}]Br¢CH3CN ([8MeBn]Br¢CH3CN) (50%
probability level, H atoms omitted).
Figure 2. ORTEP of the cationic complex of [Cp*Ir{MeNS-
C(NEt2)S}]+ in a cocrystal of [5EtMe]I and [6Et]I (50%
probability level, H atoms omitted).
crystallized as a S-bridged dimer while it existed as a monomer
in solution,4 suggesting that the ³-donicity of bidentate
{SN=C(NR2)S}2¹ ligand is competitive with the nucleophilicity
of the coordinated S donor of the iminethiolate. Complex 3R
readily reacted with PPh3, and the Cp* resonance of the product
spectroscopic investigation revealed that this adduct [5RMe]+
was also thermally unstable and converted gradually to
[Cp*Ir(R2dtc)(PPh3)]+ ([6R]+) at room temperature. From the
reaction mixture of [4EtMe]I and PPh3, we could isolate orange
crystals, one of which was subjected to X-ray analysis.7 The
results indicated that it was a cocrystal of [5EtMe]I and [6Et]I in
an approximately 1:3 ratio.5 The molecular structure of cationic
complex, [5EtMe]+, is shown in Figure 2, which reveals the
1
in the H NMR spectrum was quantitatively shifted to ¤ ³ 1.5,
indicating the formation of a PPh3 adduct, [Cp*Ir{SN=
C(NR2)S}(PPh3)] (7R) (eq 3). Isolation of complex 7R was
attempted in vain, however the reaction products with MeI
([8RMe]I) or BnBr ([8RBn]Br) were isolated.5 The 1H NMR
spectroscopy suggested that alkylation occurred in a nearly
quantitative yield, and X-ray diffraction of [8MeBn]Br¢CH3CN7
revealed the product has a S-alkylated structure, [Cp*Ir{BnSN=
C(NMe2)S}(PPh3)]+ (Figure 3). Complexes [8RR¤]+ are stable
in air in the solid state and in solution, and are rare examples
¹
N-methylation of the bidentate ligand, {MeNSC(NEt2)S} . The
Ir1-N1 bond length is 2.205(11) ¡, which is extremely long
compared to those in the above-mentioned coordinatively
unsaturated complexes of 2Me and [4EtBn]Br. The Ir1-S2 bond,
2.343(3) ¡, is also longer by ca. 0.07 ¡ than those of 2Me and
[4EtBn]Br, but comparable to the Ir-S bonds of [Cp*IrIII-
(R2dtc)L] complexes (e.g., [6Et]I of the cocrystallized complex).
These elongations indicate that there is no more multiple-bond
character in the Ir-N and Ir-S coordination bond when PPh3 is
bound to the IrIII center. The coordination of PPh3 also makes the
S1-C11 bond remarkably longer to 1.875(11) ¡, as compared to
the S2-C11 bond (1.699(12) ¡), while the N1-S1 bond shortens
to 1.639(11) ¡ from the corresponding bond length (1.693(3) ¡)
in [4EtBn]Br. The bond angles around N1 are Ir1-N1-S1
116.4(5)°, Ir1-N1-C16 119.7(10)°, and S1-N1-C16 110.1(10)°,
which were indicative of the nonplanarity of the methyl(sulfa-
nyl)amido-N atom (Figure 2). This fact is in contrast to the
of complexes with
a
alkylsulfanyliminethiolate, {RSN=
¹
C(NR2)S} , as a chelate ligand.9
ð3Þ
The five-membered chelate ring in [8MeBn]Br¢CH3CN is
planar, and the chelate bite angle of S1-Ir1-S2 is 83.32(3)°. The
benzylated S atom gives typical tetrahedral bond angles: Ir-S1-
N1 109.9(1)°, Ir1-S1-C14 119.4(1)°, and N1-S1-C14 99.6(1)°.
The S1-N1 and N1-C11 bond lengths in [8MeBn]Br¢CH3CN are
1.674(3) and 1.281(4) ¡, indicating the single- and double-bond
characters of these bonds, respectively. The S2-C11 and N2-
C11 bonds are 1.775(3) and 1.372(4) ¡, respectively, and they
are remarkably elongated from those in the related R2dtc
complexes and in [5EtMe]I. These structural characteristics
are comparable to those in the S-bridged dimer structure of
[Cp*Ir{®-SN=C(NMe)2S}]2 (3Me)2.4 Consistent with the long
C-N(Me2) bond with single bond character, the 1H NMR
spectrum of [8MeBn]+ indicated the equivalency of two Me
¹
planar nature of {BnNSC(NEt2)S} in [4EtBn]Br and would
be related to diminution of the ³-donation from bidentate
¹
{R¤NSC(NR2)S} ligand.
The 1:3 occupancy ratio of [5EtMe]I and [6Et]I in the
isolated cocrystals was consistent with the molecular ratio
confirmed by 1H NMR spectroscopy. When this sample solution
in CD3CN stood at room temperature overnight, the resonances
due to [5EtMe]+ completely disappeared, and only the res-
onances of [6Et]+ were detected. Here, the most important
question related to this observation is what would be the product
from the released “MeN” group. The formation of methylene-
imine (CH2NH) complexes would be one of the possibilities,8
but we cannot give an explicit answer for this query at present,
and experiments in this line are now in progress.
¹
groups in the {BnSN=C(NMe2)S} ligand. In the structure of
[8MeBn]+ it is remarkable that the Ir and sulfane-S bond, Ir1-S1
2.3111(7) ¡, is apparently shorter than the Ir and thiolate-S
bond, Ir1-S2 2.3567(7) ¡.
In contrast to 2R, the thermally N,S-exchanged products of
3R were unreactive with MeI or BnBr; no spectral changes were
observed on addition of these reagents to a CD3CN solution
containing 3R. It has been reported previously that complex 3R
When the reaction solution containing complex 7Et was
exposed to air (eq 4) and treated with a methanolic solution of
K(CF3SO3), yellow block crystals of the oxidized product were
obtained after recrystallization from acetonitrile/diethyl ether.5
Chem. Lett. 2011, 40, 831-833
© 2011 The Chemical Society of Japan