Table 4 Selected bond lengths (A) and angles (◦) for
˚
or Ir), where the P-donor might act as a label for distinguishing
between the two ends of the binuclear unit. However, these
reactions resulted in unexpected and unusual products as a result
of triazenide-bridge cleavage.
The addition of two equivalents of I2 to [(OC)(Ph3P)Rh(l-p-
MeC6H4NNNC6H4Me-p)2Ir(CO)2] 3 in CH2Cl2 gave a brown-
green solution, showing IR carbonyl bands at 2093s, br and
1711w cm−1, from which a yellow powder, 7, and dark red crystals,
8 [m(CO) = 2084 cm−1], were isolated and separated by hand.
(Yields of 60 and 84% respectively were calculated on the basis of
the stoichiometry shown in eqn (1).)
[I(OC){RNNN(R)C(O)}Ir(l-I)2Ir{C(O)N(R)NNR}(CO)I]
7
(R
=
C6H4Me-p)a
Ir(1)–C(1)
Ir(1)–C(2)
Ir(1)–N(3)
Ir(1)–I(2)
Ir(1)–I(1)
Ir(1)–I(1A)
1.901(7)
1.980(6)
2.071(5)
2.656(1)
2.679(1)
2.838(1)
O(1)–C(1)
O(2)–C(2)
N(1)–C(2)
N(1)–N(2)
N(2)–N(3)
1.097(7)
1.193(6)
1.461(7)
1.331(6)
1.283(6)
C(1)–Ir(1)–C(2)
C(1)–Ir(1)–N(3)
C(2)–Ir(1)–N(3)
C(1)–Ir(1)–I(2)
C(2)–Ir(1)–I(2)
N(3)–Ir(1)–I(2)
C(1)–Ir(1)–I(1)
C(2)–Ir(1)–I(1)
N(3)–Ir(1)–I(1)
I(2)–Ir(1)–I(1)
C(1)–Ir(1)–I(1A)
C(2)–Ir(1)–I(1A)
91.7(2)
171.6(2)
80.0(2)
88.3(2)
91.6(2)
90.3(1)
92.9(2)
89.2(2)
88.6(1)
178.6(1)
89.4(2)
175.1(2)
N(3)–Ir(1)–I(1A)
I(2)–Ir(1)–I(1A)
I(1)–Ir(1)–I(1A)
Ir(1)–I(1)–Ir(1A)
N(2)–N(1)–C(2)
N(1)–N(2)–N(3)
N(2)–N(3)–Ir(1)
O(1)–C(1)–Ir(1)
O(2)–C(2)–Ir(1)
O(2)–C(2)–N(1)
N(1)–C(2)–Ir(1)
99.0(1)
93.3(1)
85.9(1)
94.1(1)
2[(OC)(Ph3P)Rh(l-RNNNR)2Ir(CO)2] + 2I2
= [I(OC)]RNNN(R)C(O)]Ir(l-I)2Ir[C(O)N(R)NNR](CO)I]
119.8(4)
115.2(5)
115.5(4)
177.3(6)
132.2(5)
118.6(5)
109.2(4)
+ 2[Rh(RNNNR)I2(CO)(PPh3)]
(1)
The yellow compound, 7, the elemental analysis (Table 1)
of which was consistent with the formula [Ir2I4(CO)4(p-
MeC6H4NNNC6H4Me-p)2], showed only one terminal carbonyl
band in the IR spectrum which, at 2095 cm−1, implied oxidation of
the original Ir(I) centre of 3. However, a second band was observed
at 1711 cm−1 in the region associated with a ketonic or a bridging
CO. The 1H NMR spectrum of 7 showed resonances at d 2.37 and
2.48 suggesting methyl groups in two different environments. In
the absence of further spectroscopic data by which 7 might be fully
identified the crystal structure was determined.
a The molecule lies on a crystallographic inversion centre. Atoms gen-
erated by symmetry share the same label as the original atoms but are
distinguished by an ‘A’ suffix.
The two iodine atoms in the central Ir2(l-I)2 unit asymmetrically
bridge the two iridium centres, with Ir(1)–I(1) [2.679(1) A], trans
to the terminal iodide, I(2), shorter than Ir(1)–I(1A) [2.838(1) A],
trans to C(2) of the chelating ligand C(O)N(R)NNR. The terminal
˚
˚
The structural analysis showed 7 to be the dimeric di-
iridium complex [I(OC){RNNN(R)C(O)}Ir(l-I)2Ir{C(O)N(R)-
NNR}(CO)I] (R = C6H4Me-p) (Fig. 3); selected bond lengths
and angles are given in Table 4.
˚
Ir(1)–I(2) distance [2.656(1) A] is shorter than those involving the
bridging iodines.
˚
In the Ir{C(O)N(R)NNR} ring, N(1)–N(2) [1.331(6) A] is
˚
longer than N(2)–N(3) [1.283(6) A]. Thus, N(1)–N(2) and N(2)–
Each iridium atom has an octahedral coordination sphere,
involving three iodine atoms (two bridging and one terminal) in a
mer arrangement, a terminal carbonyl group and the N and C(O)
atoms of the chelating ligand C(O)N(R)NNR (R = C6H4Me-p),
formed by CO insertion into a metal–nitrogen bond, the terminal
carbonyl ligand is trans to the N atom of this chelating ligand.
The presence of the amide carbonyl accounts for the IR band at
1711 cm−1, and the asymmetry of the chelating ligand gives rise
to the two different methyl resonances in the 1H NMR spectrum.
N(3) are assigned as single and double bonds respectively. The
C(2)–N(1) distance in the Ir{C(O)N(R)NNR} ring [1.461(7)
10
˚
˚
A] is typical of a C–N single bond (1.469 A). Such an
M{C(O)N(R)NNR} ring system, formed by carbonyl insertion
into a metal–triazenide bond, has been reported previously,
e.g. in [Rh{C(O)N(Me)NNMe}Cl2(PPh3)2] (R = Me)11 and
[Ir{C(O)N(R)NNRꢀ}(CO)2(PPh3)] (R, Rꢀ = Me, C6H4Me-p)12 but
not previously structurally characterised.
Elemental analysis (Table 1), mass spectrometry (a parent
ion at m/z = 870) and IR spectroscopy [m(CO) = 2084 cm−1]
suggested that the red crystalline complex 8 was monomeric [Rh(p-
MeC6H4NNNC6H4Me-p)I2(CO)(PPh3)]. The 1H NMR spectrum
showed two methyl resonances, at d 2.33 and 2.39, indicating the
two methyl groups to be in different environments, but which of
the several possible geometric isomeric structures was adopted was
only determined by X-ray crystallography.
The structure of 8 is shown in Fig. 4 and selected bond
lengths and angles are given in Table 5. The rhodium atom is
octahedral with one chelating triazenide ligand, two cis iodides,
one carbonyl and one PPh3 ligand. The Rh(1)–I(1) bond trans
˚
to PPh3 [2.701(1) A] is longer than the Rh(1)–I(2) bond trans
˚
to N [2.678(1) A] as PPh3 has a greater trans influence than the
−
˚
triazenide ligand. The Rh(1)–N(1) bond [2.050(5) A], trans to I ,
˚
is shorter than Rh(1)–N(3) [2.097(5) A], trans to CO, as CO has
Fig.
3
The molecular structure of [I(OC){RNNN(R)C(O)}-
a greater trans influence than I−. This, in turn, appears to lead to
a small difference in the N–N distances in the chelating triazenide
ligand [i.e. N(1)–N(2) = 1.307(6), N(2)–N(3) = 1.336(6)]. In
chelated triazenide complexes where the terminal nitrogen bonds
Ir(l-I)2Ir{C(O)N(R)NNR}(CO)I] 7 (R = C6H4Me-p). Hydrogen atoms
have been omitted for clarity. The molecule lies on a crystallographic
inversion centre, so the unnumbered atoms are symmetry equivalents of
the numbered atoms.
This journal is
The Royal Society of Chemistry 2007
Dalton Trans., 2007, 1325–1333 | 1329
©
Adams, Christopher J.
