M...HNR interactions in imino-bound diaryltriazene complexes: Structure and fluxionality

Article abstract of DOI:10.1039/b408410a

The nominally square-planar coordination of the d⁸ complexes [MClL¹L²(p-XC₆H₄NNNHC ₆H₄X-p)] (M = Rh, L¹ = L² = CO, X = H, Me, Et or F; M = Ir, L¹

Full text of DOI:10.1039/b408410a

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F U L L P A P E R
MHNR interactions in imino-bound diaryltriazene complexes:
structure and fluxionality
Christopher J. Adams, Kirsty M. Anderson, R. Angharad Baber, Neil G. Connelly,
Mathivathani Kandiah and A. Guy Orpen
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS.
E-mail: Neil.Connelly@bristol.ac.uk; Fax: +0117 929 0509; Tel: + 0117 928 8162
Received 3rd June 2004, Accepted 17th August 2004
First published as an Advance Article on the web 8th September 2004
The nominally square-planar coordination of the d8 complexes [MClL1L2(p-XC6H4NNNHC6H4X-p)] (M = Rh,
L1 = L2 = CO, X = H, Me, Et or F; M = Ir, L1 = L2 = CO, X = Me; M = Pd or Pt, L1 = Cl, L2 = PPh3, X = Me;
M = Pd, L1L2 = g3-C3H5, X = Me), with the triazene N-bonded via the imine group, is supplemented by an axial
MH–N interaction involving the terminal amino group.
triazene ligand is bonded to the metal through the imine N atom
(as shown by X-ray crystallography, see below).
Introduction
Our previous studies of the synthesis of redox-active, triazenide-
bridged binuclear complexes of Rh1 and Ir2 involved the deproto-
nation of metal triazene complexes preformed in situ. However,
in order to synthesise analogous heterobimetallic species3 it
proved advantageous to isolate the mononuclear triazene inter-
mediates before use. We therefore give details of the synthesis
and characterisation of square-planar triazene complexes of
Rh, Ir, Pd and Pt, their structural characterisation, which has
revealed an additional MH–N axial interaction, and vari-
able-temperature NMR spectroscopic studies which revealed a
fluxional process involving interchange of the two aryl groups,
R, of the triazene ligand RNNNHR.
The structures of 1, 2, 6 and 7
Crystals of 1, 2, 6 and 7 suitable for single crystal X-ray diffrac-
tion studies were obtained by allowing n-hexane to diffuse into
a concentrated CH2Cl2 solution of the complex at −20 °C. The
structures of 1, 2, 6 and 7 are shown in Figs. 1–4, respectively
and selected structural data are given in Tables 2–4. Only the
structure of 2 is discussed in detail, as a representative example,
but differences from the structures of 1, 6 and 7 are noted where
appropriate.
Results and discussion
The complexes [RhCl(CO)2(p-XC6H4NNNHC6H4X-p)] (X = H,
1; Me, 2; Et, 3; F, 4) (Table 1) were prepared by reacting [{Rh(l-
Cl)(CO)2}2] with the appropriate triazene in CH2Cl2. When
the reaction was complete, as shown by IR spectroscopy (ca.
10 min), the solution was filtered, evaporated to low volume
in vacuo, and then treated with n-hexane to give a yellow
precipitate of the product. The iridium analogue of 2, namely
[IrCl(CO)2(p-MeC6H4NNNHC6H4Me-p)] 5, was prepared as
before,2 by reacting [{Ir(l-Cl)(g4-cod)}2] (cod = cycloocta-
1,5-diene) with p-MeC6H4NNNHC6H4Me-p in CH2Cl2 to give
[IrCl(g4-cod)(p-MeC6H4NNNHC6H4Me-p)] and then passing
CO gas through the solution to displace cod.
The yellow complexes [PdCl(g3-C3H5)(p-MeC6H4NNNHC6-
H4Me-p)] 6, trans-[PtCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)]
7 and [PdCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 8 (the last
as a mixture of cis and trans isomers) were prepared similarly
by reacting p-MeC6H4NNNHC6H4Me-p with [{Pd(l-Cl)(g3-
C3H5)2}], [{Pt(l-Cl)Cl(PPh3)}2] and [{Pd(l-Cl)Cl(PPh3)}2],
respectively.
Compounds 1–8 were characterised by elemental analysis,
IR (Table 1) and NMR spectroscopy and, in the cases of 1,
2, 6 and 7, by X-ray crystallography. The IR spectra of the
carbonyl complexes 1–5 show two carbonyl bands in the region
2200–1900 cm−1 in agreement with the presence of a cis-M(CO)2
group (M = Rh or Ir). There is little if any dependence of m(CO)
on the substituent X of the aryl group C6H4X-p but the iridium
complex 5 shows carbonyl bands approximately 10–20 cm−1
lower in energy than those of the Rh complex 2, in accord with
the presence of the more electron rich iridium centre.
Fig. 1 The molecular structure of [RhCl(CO)2(PhNNNHPh)] 1.
The rhodium atom of 2 is bonded to two cis carbonyls, one
chloride and the nitrogen atom of the imine, rather than the
amine group, of the triazene ligand (Fig. 2). The metal is there-
fore effectively square planar. However, the triazene ligand is
orientated in such a way as to bring the amine hydrogen atom
H(3) close to the metal; the atoms Rh(1), N(1), N(2), N(3) and
H(3) are coplanar and this plane is nearly perpendicular (at an
angle of 81°) to the plane containing C(1), C(2), Cl(1) and N(1).
Thus, H(3) is positioned above the metal, with a Rh(1)H(3)
distance of 2.647 Å (cf. 2.624 Å in 1). This interaction
between Rh(1) and H(3) results in a weakened N–H bond, and
hence the energy of m(NH) is lower than in the free triazene
p-MeC6H4NNNHC6H4Me-p. The sole cause of the close
proximity of the hydrogen atom and the metal appears to be the
ligand geometry though the ligand is not especially distorted
Each of the triazene complexes 1–8 shows a m(NH) absorption
in the range 3080–3110 cm−1 (Table 1), cf. the free triazene
p-MeC6H4NNNHC6H4Me-p for which m(NH) = 3199 cm−1,
indicating a weakening of the N–H bond even though the
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9
3 3 5 3

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Table 1 Analytical and IR spectroscopic data for [MClL1L2(p-XC6H4NNNHC6H4X-p)]
Analysisa (%)
IR/cm−1
M
X
L1L2
Yield (%)
C
H
N
m(CO)b
m(NH)c
1
2
3
4
5
6
7
8
Rh
Rh
Rh
Rh
Ir
H
Me
Et
(CO)2
(CO)2
(CO)2
(CO)2
60
81
78
65
43.6 (43.3)
45.8 (46.0)
48.3 (48.1)
39.3 (39.4)
2.8 (2.9)
3.6 (3.6)
9.4 (9.3)
2.1 (1.7)
10.7 (11.6)
10.0 (9.8)
4.3 (4.4)
2095, 2025
2094, 2024
2094, 2024
2096, 2026
2083, 2005d
3086
3109
3108
3112
3078
3097
3099
3091
F
9.8 (9.5)
Me
Me
Me
Me
(CO)2
Pde
Pd
Pt
Cl(PPh3)
g3-C3H5
Cl(PPh3)
41
83
71
58.0 (58.0)
49.9 (50.0)
51.0 (51.1)
5.0 (5.0)
4.9 (4.9)
4.0 (3.7)
6.4 (6.2)
10.4 (10.3)
5.6 (5.6)
a Calculated values in parentheses. b Strong absorptions in CH2Cl2. c Weak absorptions in Nujol. d Data from ref. 2. e Sample analysed as a 0.5 n-hexane
solvate.
Table 2 Selected bond lengths (Å) and angles (°) for RhCl(CO)2-
(RNNNHR)] (R = Ph 1 or C6H4Me-p 2)
1
2
PhNNNHPha
Rh(1)–C(1)
Rh(1)–C(2)
Rh(1)–Cl(1)
Rh(1)–N(1)
Rh(1)H(3)
C(1)–O(1)
C(2)–O(2)
N(3)–H(3)
N(1)–N(2)
N(2)–N(3)
1.846(4)
1.854(3)
2.348(1)
2.097(2)
2.624
1.127(4)
1.125(4)
0.783
1.889(4)
1.873(4)
2.358(1)
2.098(2)
2.647
1.048(4)
1.123(4)
0.775
1.283(3)
1.306(3)
1.277(3)
1.311(3)
1.27
1.32
N(1)–Rh(1)–Cl(1)
C(1)–Rh(1)–Cl(1)
C(2)–Rh(1)–Cl(1)
C(1)–Rh(1)–N(1)
C(2)–Rh(1)–N(1)
O(1)–C(1)–Rh(1)
O(2)–C(2)–Rh(1)
Rh(1)–N(1)–N(2)
N(1)–N(2)–N(3)
N(3)–H(3)Rh(1)
89.9(6)
175.9(1)
87.3(1)
92.4(1)
176.5(1)
177.4(3)
177.8(3)
125.4(2)
116.2(2)
120.7
88.5(7)
177.8(1)
90.6(1)
90.5(1)
178.4(4)
179.5(4)
177.5(3)
125.6(2)
116.2(2)
124.0
115
Fig. 2 The molecular structure of [RhCl(CO)2(p-MeC6H4NNNHC6-
H4Me-p)] 2.
a Data from ref. 4.
Table 3 Selected bond lengths (Å) and angles (°) for [PdCl(g3-C3H5)(p-
MeC6H4NNNHC6H4Me-p)] 6
Pd(1)–Cl(1)
Pd(1)–C(15)
Pd(1)–C(16)
Pd(1)–C(17)
Pd(1)H(3)
Pd(1)–N(1)
C(15)–C(16)
C(16)–C(17)
N(1)–N(2)
2.373(1)
2.114(5)
2.056(6)
2.114(5)
2.718
2.102(4)
1.261(9)
1.257(10)
1.278(5)
1.305(5)
C(15)–Pd(1)–Cl
98.9(2)
133.6(2)
167.5(2)
69.1(2)
69.1(2)
99.7(2)
168.4(2)
116.3(3)
144.7(9)
127.8(3)
124.75
C(16)–Pd(1)–Cl(1)
C(17)–Pd(1)–Cl(1)
C(16)–Pd(1)–C(15)
C(17)–Pd(1)–C(15)
N(1)–Pd(1)–C(17)
N(1)–Pd(1)–C(15)
N(1)–N(2)–N(3)
C(15)–C(16)–C(17)
Pd(1)–N(1)–N(2)
N(3)–H(3)Pd(1)
N(2)–N(3)
sequence C(3)–N(1)–N(2)–N(3)–C(10) is almost planar with the
N(1)–N(2)–N(3) angle 116°. The imine and amine tolyl groups
are only slightly twisted with respect to this plane, by ca. 1 and
10°, respectively, bringing the ortho hydrogen atom of the imine
tolyl ring into close proximity to the rhodium atom (2.651 Å).
This interaction could be removed by twisting the tolyl group
from the plane of the triazene unit, which does not occur in the
solid state, but from the NMR spectroscopic data (see below)
there is free rotation around this bond in solution. A similar
situation is seen in the structure of 1, with a hydrogen–metal
distance of 2.662 Å.
Fig. 3 The molecular structure of [PdCl(g3-C3H5)(p-MeC6H4NNN-
HC6H4Me-p)] 6.
to maximise the interaction. In fact, the angle M–N(1)–N(2) is
greater than 120° in all four X-ray structures presented herein,
which actually moves H(3) away slightly from the metal centre.
The coordinated triazene ligand in 2 has a trans conforma-
tion about both the N(1)–N(2) and N(2)–N(3) bonds; the
Interestingly, for both 1 and 2, the bond distances N(1)–N(2)
and N(2)–N(3) are very similar to those of the free triazene
PhNNNHPh4 (Table 2). The former distance is shorter than
the latter indicating that bond N(1)–N(2) has somewhat greater
3 3 5 4
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9

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Table 4 Selected bond lengths (Å) and angles (°) for [PtCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p] 7a
Pt(1)–Cl(1)
Pt(1)–Cl(2)
Pt(1)–P(1)
Pt(1)H(3)
Pt(1)–N(1)
N(1)–N(2)
N(2)–N(3)
N(3)–H(3)
2.298(2)
2.293(2)
2.239(2)
2.598
2.115(5)
1.259(7)
1.306(7)
0.87
2.310(2)
2.300(2)
2.250(2)
2.680
2.107(5)
1.266(7)
1.305(8)
0.80
N(1)–Pt(1)–Cl(2)
N(1)–Pt(1)–Cl(1)
P(1)–Pt(1)–Cl(1)
P(1)–Pt(1)–Cl(2)
Cl(1)–Pt(1)–Cl(2)
N(1)–Pt(1)–P(1)
N(1)–N(2)–N(3)
Pt(1)–N(1)–N(2)
N(3)–H(3)Pt(1)
86.30(14)
89.37(15)
89.00(7)
95.22(7)
173.56(8)
177.97(15)
117.0(5)
124.0(4)
116.34
87.40(14)
87.69(14)
90.56(6)
94.44(6)
174.93(6)
175.09(16)
115.0(5)
128.3(4)
119.70
a There are two independent molecules in the asymmetric unit, and hence two possible values for each measurement.
Table 5 Intermolecular distances (Å) and angles (°) in the crystal
structures of 1, 2 and 6
1
2
6
CHCl
NHCl
2.899
2.629
2.908
2.629
2.828
2.780
C–HCl
N–HCl
129.85
148.93
144.79
153.19
146.89
153.83
Fig. 4 The molecular structure of one of the independent molecules
in the crystal structure of trans-[PtCl2(PPh3)(p-MeC6H4NNNHC6H4-
Me-p)] 7.
multiple bond character than N(2)–N(3). However, both
distances lie between the values expected for an NN double
bond (ca. 1.12 Å) or an N–N single bond (1.37 Å), suggesting
some delocalisation of p electrons along the N(1)–N(2)–N(3)
fragment.
The molecular structure of [PdCl(g3-C3H5)(p-MeC6H4NNN-
HC6H4Me-p)] 6 (Fig. 3) is also approximately square planar
with, for example, the angle N(1)–Pd(1)–Cl(1) = 92.5(1)°
(Table 3). The C(15)–C(16)–C(17) angle of the allyl ligand is
144.7(9)°, with the central carbon atom C(16) effectively in the
N(1)–Pd(1)–Cl(1) plane, and the two terminal atoms C(15) and
C(17) on one side of this plane.
Unlike in complexes 1 and 2, the triazene ligand p-
MeC6H4NNNHC6H4Me-p is not planar; the amine tolyl and
imine tolyl groups are twisted out of the N(1)–N(2)–N(3) plane
by ca. 5 and 35°, respectively, and the torsion angle between
the planes of the two tolyl groups is 21°. This has the effect of
increasing the distance of the ortho proton of the imine tolyl
group away from a site above the metal, unlike in 1 and 2. As in
1 and 2, however, the N(1)–N(2) and N(2)–N(3) bond lengths
for 6 are in agreement with some delocalisation along the
N(1)–N(2)–N(3) chain.
In crystals of 1, 2 and 6 there are significant interactions
between the Cl atom and both the N–H proton and an ortho-H
atom on the amine tolyl ring from an adjacent molecule. These
interactions lead to solid-state dimers, with similar inter-
molecular dimensions in all three cases (Table 5) and very similar
motifs in the cases of 2 and 6 (Fig. 5).
Fig. 5 Solid-state dimerisation of (a) 2 and (b) 6.
The average values of the angles Cl(1)–Pt–Cl(2), N(1)–Pt–P(1),
P(1)–Pt–Cl(2) and P–Pt–Cl(1) are 174.3(1), 176.5(2), 94.8(1)
and 89.8(1)°, respectively. As in 1 and 2, the Pt–N(1)–N(2)–
N(3)–H(3) plane is almost perpendicular to the square plane
about the metal, bringing the amine hydrogen atom H(3) in close
contact with the metal [PtH(3), average value = 2.639 Å].
The structure of 7 shows no dimerisation of the kind shown by
the structures of 1, 2 and 6; presumably the bulk of the PPh3
ligand is sufficient to prevent the close approach of adjacent
molecules.
The platinum atom of trans-[PtCl2(PPh3)(p-MeC6H4NNN-
HC6H4Me-p)] 7 (Fig. 4, Table 4) is also approximately square
planar, coordinated to one triazene, one PPh3 and two trans Cl
ligands; the asymmetric unit of the crystal structure contains
two independent molecules with a very similar conformation.
The structure of 7 can also be compared with that of a closely
related monodentate triazenide complex, namely square-planar
cis-[PtCl(PPh3)2(p-MeC6H4NNNHC6H4Me-p)] 9 in which the
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9
3 3 5 5

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Table 6 1H and 13C{1H} NMR spectroscopic data for trans-[PtCl2-
(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 7 at 20 °C in CD2Cl2a
Table 7 1H NMR spectroscopic data for [MCl(CO)2(RNNNHR)] in
CD2Cl2a
Complex
T/°C
Chemical shift/ppm
1
20
−80
20
11.55 (s, 1H, NH), 7.90 (s br, 2H, C6H5), 7.46–
7.35 (br, 6H, C6H5)
11.62 (s, 1H, NH), 7.95 (d, 2H, 1JHH 8, C6H5),
7.35 (m, 8H, C6H5)
1H
12.17 (s, 1H, NH), 8.12 (d, 2H, 1JHH 9, C6H4), 7.82–7.74
{m, 9H, P(C6H5)3}, 7.58–7.45 {m, 6H, P(C6H5)3}, 7.31
(d, 2H, 1JHH 9, C6H4), 7.29–7.24 (m, 4H, C6H4), 2.42
(s, 3H, CH3), 2.38 (s, 3H, CH3)
2
3
11.50 (s, 1H, NH), 7.95 (s br, 2H, C6H4), 7.39–
7.30 (br, 6H, C6H4), 2.39 (s, 6H, CH3)
11.51 (s, 1H, NH), 7.81 (d, 2H, 1JHH 9, C6H4),
7.26 (d, 2H, 1JHH 9, C6H4), 7.22 (d, 2H, 1JHH 9,
C6H4), 7.16 (d, 2H, 1JHH 9, C6H4), 2.34 (s, 3H,
CH3), 2.31 (s, 3H, CH3)
−80
13C{1H}
145.70 (C1), 139.04 (C1), 135.92 (C4), 135.82 (C4), 134.02
(C3, Ph), 133.88 (C3, Ph), 131.70 (C2), 129.95 (C2), 128.62
(C2, Ph), 128.47 (C2, Ph), 127.60 (C4, Ph), 126.75 (C4, Ph),
122.06 (C3), 115.97 (C3), 21.43 (CH3), 21.22 (CH3)
20
11.44 (s, 1H, NH), 7.80 (s br, 2H, C6H4), 7.34–
7.15 (br, 6H, C6H4), 2.60 (s, 4H, CH2CH3), 1.16
(s, 6H, CH2CH3)
a J values in Hz.
−80
11.53 (s, 1H, NH), 7.86 (d, 2H, 1JHH 8, C6H4),
7.28 (d, 2H, 1JHH 8, C6H4), 7.25 (d, 2H, 1JHH 9,
C6H4),7.17 (d, 2H, 1JHH 8, C6H4), 2.61 (m, 4H,
CH3), 1.72 (m, 6H, CH3)
Pt–N(1), Pt–Cl and Pt–P (PPh3 trans to Cl) bond lengths are
2.108(9), 2.353(7) and 2.11(2) Å, respectively,5 similar to those
of complex 7 (Table 4). However, while the N(1)–N(2) distance
is similar for 7 and 9 [1.262(7) and 1.26(3) Å, respectively],
the distance N(2)–N(3) [1.306(7) and 1.26(3) Å, respectively]
is longer for the former, reflecting the difference between the
amino and imino termini of the triazene and triazenide ligands,
respectively. Moreover, the Pt–P distance trans to the nitrogen
donor is shorter in 7 than in 9 [2.245(2) cf. 2.289(6) Å], perhaps
indicating a stronger trans influence for the anionic triazenide
ligand.
4
5
20
11.50 (s, 1H, NH), 7.95 (s, br, 2H, C6H4), 7.39–
7.30 (br, 6H, C6H4)
−80
11.65 (s, 1H, NH), 7.96 (dd, 2H, 1JHH 8, 2JHF 5,
C6H4), 7.36 (dd, 2H, 1JHH 8, 2JHF 5, C6H4), 7.15
1
2
(dd, 2H, JHH 8, JHF 8, C6H4), 7.06 (dd, 2H,
1JHH 8, 2JHF 8, C6H4)
20, −80
11.90 (s, 1H, NH), 7.89 (d, 2H, 1JHH 9, C6H4),
1
7.33 (d, 2H, JHH 9, C6H4), 7.30–7.21 (m, 4H,
C6H4), 2.40 (s, 3H, CH3), 2.38 (s, 3H, CH3)
a Chemical shifts (d) in ppm, J values in Hz.
NMR spectroscopy
involving exchange of the C6H4X-p groups of the triazene ligand.
The H NMR spectra of [RhCl(CO)2(p-XC6H4NNNHC6H4X-
1
At temperatures between 20 and −80 °C, the 1H NMR spectrum
of [PtCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 7 is invariant,
with resonances between 7.23 and 8.20 ppm for the aromatic
protons of the diaryltriazene and PPh3 ligands, two methyl
resonances at d 2.38 and 2.42 (Table 6), consistent with two
different methyl environments, and one triazene NH proton
signal at d 12.17. Similarly, there are two methyl resonances
in the 13C{1H} NMR spectrum, at d 21.43 and 21.22. The
31P{1H} NMR spectrum shows a single resonance at d 5.58,
p)] (X = H 1, Me 2, Et 3 and F 4) (Table 7) show the C6H4 and
NH protons of the triazene ligand between d 6.50–7.50 and
11.40–11.90, respectively. At room temperature, [RhCl(CO)2(p-
MeC6H4NNNHC6H4Me-p)] 2 shows two broad peaks, at d 7.80
and 7.37, one doublet at d 7.27 for the C6H4 groups, and one
singlet for the Me groups [Fig. 7(i)]. At −40 °C [Fig. 7(ii)], the
two broad peaks and the methyl singlet are partially resolved
into doublets, and at −80 °C [Fig. 7(iii)], two (AB)2 splitting
patterns are evident for the two C6H4 groups, centred at d 7.48
and 7.24, with two Me resonances, at d 2.31 and 2.34. Thus,
the rate of exchange of the C6H4X-p groups is slowed at low
temperature so that the amine and imine C6H4X-p groups are
distinguishable.
with platinum satellites, J(195Pt31P) 3597 Hz. This, and the H
NMR spectrum therefore indicate the presence of only the
trans isomer in solution (as shown by X-ray crystallography,
see above).
1
1
By contrast, the H NMR spectrum of 8, the Pd analogue
The fluxional process which leads to equivalent C6H4X-p
groups at higher temperatures may involve the formation of
[RhHCl(CO)2(RNNNR)] [(b) in Scheme 1], with equivalent
cis carbonyls cis to the hydride ligand, by oxidative addition
of the triazene to form a six-coordinate 18-electron triazenide
hydride complex. The X-ray structural study of 2 supports this
proposal, effectively showing the incipient formation of a Rh–H
bond (Fig. 2). Moreover, just such an oxidative addition reaction
occurs when [RhH(PPh3)4] reacts with PhNNNHPh to give the
stable triazenide complex [RhH2(PPh3)2(PhNNNPh)].6
of 7, shows cis and trans isomers in a 1:2 ratio (though it is
not known which isomer is the more abundant). Thus, as well
as several signals for the triazenide C6H4 protons between
6.9–8.0 ppm [Fig. 6(a)] there are four different Me singlets, in
a 1:1:2:2 ratio, at d 2.34, 2.28, 2.27 and 2.25 [Fig. 6(b)]. There
are also two NH proton signals, at d 11.63 and 11.45, and the
31P{1H} NMR spectrum shows two singlets, at d 28.29 and
27.21, also in a 1:2 ratio.
Unlike for 7 and 8, the variable temperature 1H NMR
spectra of complexes 1–4 and 6 show a fluxional process
Scheme 1 R = aryl.
At −80 °C, the 13C{1H} NMR spectra (Table 8) of 1–4 also
show inequivalent C6H4X-p groups. Moreover, in each case there
are two doublets for the CO ligands, in the range d 183.4–178.8
[J(13C103Rh) 68–72 Hz], in agreement with the cis-Rh(CO)2 unit
Fig. 6 1H NMR spectrum showing (a) the C6H4 and C6H5, and
(b) the Me resonances of a mixture of cis- and trans-[PdCl2(PPh3)(p-
MeC6H4NNNHC6H4Me-p)] 8, at 20 °C.
3 3 5 6
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9

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Table 8 13C{1H} NMR spectroscopic data for [MCl(CO)2(RNNNHR)]
in CD2Cl2 at −80 °Ca
Complex
Chemical shift/ppm
1
183.28 [d, J(13C103Rh) 68, CO], 178.96 [d, J(13C103Rh)
72, CO], 148.09 (C1), 138.33 (C1), 129.95 (C3), 129.42 (C3),
128.87 (C4), 126.06 (C4), 122.09 (C2), 116.47 (C2)
183.32 [d, J(13C103Rh) 68, CO], 179.04 [d, J(13C103Rh) 72,
CO], 145.83 (C1), 139.10 (C1), 135.98 (C4), 135.95 (C4),
130.42 (C3), 129.87 (C3), 121.74 (C2), 116.21 (C2), 21.33
(CH3), 21.15 (CH3)
2
3
4
183.16 [d, J(13C103Rh) 68, CO], 178.88 [d, J(13C103Rh)
72, CO], 146.25 (C1), 145.34 (C1), 142.41 (C4), 136.23 (C4),
129.31 (C2), 128.77 (C2), 121.80 (C3), 116.32 (C3), 28.66
(CH2), 28.50 (CH2), 15.95 (CH3), 15.87 (CH3)
183.31 [d, J(13C103Rh) 68, CO], 178.89 [d, J(13C103Rh)
72, CO], 163.79 (C1), 161.82 (C1), 160.50 (C2), 158.57 (C2),
144.41 (C3), 134.73 (C3), 123.79 [d, J(13C19F) 9, C4],
118.22 [d, J(13C19F) 8, C4]
5
171.55 (CO), 145.83 (C1), 139.22 (C1), 136.57 (C4),
135.62 (C4), 130.56 (C3), 129.97 (C3), 121.97 (C2), 116.36
(C2), 21.37 (CH3), 21.24 (CH3)
a J values in Hz.
Table 9 19F{1H} spectroscopic data for [RhCl(CO)2(p-FC6H4NNN-
HC6H4F-p)] 4 in CD2Cl2a
Complex
T/°C
Chemical shift/ppm
Fig. 7 1H NMR spectra of (a) the C6H4, and (b) the Me resonances
of [RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)] 2, at (i) 20 °C, (ii) −40 °C,
(iii) −80 °C.
4
20
−80
−112.9, −116.2
−112.3, −116.8 [each tt, J(19F1H) 5, 8]
a Chemical shifts (d) in ppm.
detected by IR spectroscopy and confirmed by X-ray crystallo-
graphy.
Replacing the Rh atom of 2 with Ir gives 5, the H NMR
observe inequivalent C6H4Me-p groups and an asymmetric
1
1
g3-C3H5 group in the H NMR spectrum (Table 10). At room
spectrum of which is temperature invariant. Thus, between
room temperature and −80 °C, two signals are observed for the
methyl groups, at d 2.34 and 2.32, and the NH proton is observed
at d 11.90. The reason for the different fluxional behaviour of 2
and 5 is not understood.
temperature, there is one signal at d 2.36 for the methyl protons
and two doublets at d 3.99 and 3.10 for the syn (Ha) and anti
(Hb) protons of the allyl ligand. The multiplet centred at d 5.48
corresponds to Hc [Fig. 9(i)]. This suggests the syn and anti
protons are equivalent due to a fluxional process which also
leads to equivalent C6H4Me-p groups at room temperature.
As for 2, this may involve the formation, by oxidative addi-
tion, of [PdHCl(g3-C3H5)(p-MeC6H4NNNC6H4Me-p)], similar
to the intermediate shown in Scheme 1, with chloride trans to
the hydride ligand. On cooling the solution to −70 °C, the Me
signal splits into two, at d 2.32 and 2.29, and the signals for the
allyl syn and anti protons split into four doublets at d 3.24, 3.47,
3.85 and 4.07 [Fig 9(ii)]. Similarly, the 13C{1H} NMR spectrum
at −80 °C (Table 11) shows two singlets, at d 21.13 and 21.28,
for the methyl carbon atoms and two, at d 61.53 and 64.15 and
115.18 for the terminal allyl carbon atoms.
The 19F NMR spectroscopic data for complex 4 at 20
and −80 °C are given in Table 9. The presence of two broad
signals at 20 °C [Fig 8(i)] suggests that this is not the limiting
high temperature spectrum. On lowering the temperature
to −80 °C, each of these signals becomes a triplet of triplets due
to coupling to the ortho- and meta-hydrogens of the C6H4F-p
groups [Fig. 8(ii)].
The fluxional process for [PdCl(g3-C3H5)(p-MeC6H4NNN-
HC6H4Me-p)] 6 can also be slowed sufficiently at −70 °C to
Experimental
The preparation, purification and reactions of the complexes
described were carried out under an atmosphere of dry dinitrogen
using dried, distilled and deoxygenated solvents; reactions were
monitored by IR spectroscopy where necessary. The com-
pounds [{Rh(l-Cl)(CO)2}2],7 [{M(l-Cl)Cl(PPh3)}2] (M = Pd8
Fig. 8 19F NMR spectra of [RhCl(CO)2(p-FC6H4NNNHC6H4F-p)]
4, at (i) 20 °C and (ii) −80 °C.
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9
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Table 10 1H NMR spectroscopic data for [PdCl(g3-C3H5)(p-MeC6H4-
NNNHC6H4Me-p)] 6 in CD2Cl2a
Table 11 13C{1H} NMR spectroscopic data for [PdCl(g3-C3H5)(p-
MeC6H4NNNHC6H4Me-p)] 6 in CD2Cl2 at −80 °C
T/°C
Chemical shift/ppm
20
11.51 (s, 1H, NH), 7.46 (s br, 2H, C6H4), 7.20 (d, 6H, C6H4),
5.48 (m, 1H, allyl, Hc), 3.99 (d, 2H, 3JHH 6, allyl, Ha), 3.10
(d, 2H, 3JHH 13, allyl, Hb), 2.36 (s, 6H, CH3)
−70
11.50 (s, 1H, NH), 7.46 (d, 2H, 1JHH 8, C6H4), 7.24
(d, 2H, 1JHH 8, C6H4), 7.07 (d, 2H, 1JHH 8, C6H4), 6.98
(d, 2H, 1JHH 8, C6H4), 5.62 (m, 1H, allyl, Hc), 4.07
(d, 1H, 3JHH 6, allyl, Ha), 3.85 (d, 1H, 3JHH 6, allyl, Ha), 3.47
(d, 1H, 3JHH 12, allyl, Hb), 3.24 (d, 1H, 3JHH 13, allyl, Hb),
2.32 (s, 3H, CH3), 2.29 (s, 3H, CH3)
Complex
Chemical shift/ppm
6
147.45 (C1), 137.92 (C1), 137.61 (C4), 134.27 (C3),
129.96 (C3), 129.38 (C2), 122.07 (C2), 116.53 (C2),
115.18 (s, CH2CHCH2), 64.15 (s, CH2CHCH2),
61.53 (s, CH2CHCH2), 21.28 (CH3), 21.13 (CH3)
a Chemical shifts (d) in ppm, J values in Hz. Allyl numbering as below
(L = p-MeC6H4NNNHC6H4Me-p).
Table 12 Crystal and refinement data for 1, 2, 6 and 7
Compound
1
2
6
7
Formula
M
C14H11ClN3O2Rh
391.62
C16H15ClN3O2Rh
419.67
C17H19ClN3Pd
408.21
C32H29Cl2N3PPt
753.54
Crystal system
Space group (no.)
a/Å
b/Å
c/Å
a/°
b/°
c/°
Monoclinic
C2/c (15)
17.165(3)
10.403(2)
16.633(3)
90
96.922(3)
90
173(2)
Triclinic
P1 (2)
Orthorhombic
Pbca (61)
17.355(3)
9.906(2)
19.753(3)
90
Monoclinic
P21 (14)
11.404(2)
16.906(4)
15.680(3)
90
90.428(13)
90
193(2)
9.202(3)
10.234(3)
10.509(3)
61.077(4)
84.978(5)
79.941(5)
173(2)
852.9(4)
2
1.169
90
90
T/K
173(2)
3395.9(10)
8
U/Å3
2948.4(7)
8
1.346
3020.2(10)
4
4.902
Z
l/mm−1
1.250
Reflections collected
Independent reflections (Rint)
Final R indices [I > 2r(I)]: R1, wR2
9302
3394 (0.0341)
0.0302, 0.0660
5468
3770 (0.0195)
0.0311, 0.0668
22655
3897 (0.0713)
0.0487, 0.1022
31862
13667 (0.0585)
0.0322, 0.0664
CH2Cl2 (20 cm3) was added p-MeC6H4NNNHC6H4Me-p
(0.12 g, 0.536 mmol). After 10 min the yellow solution was
filtered through Celite and the solvent evaporated to low volume
(ca. 5 cm3) in vacuo. n-Hexane (10 cm3) was added to precipitate
a yellow powder which was washed with n-hexane (2 × 20 cm3)
and dried in vacuo, yield 182 mg (81%).
The complexes [RhCl(CO)2(p-XC6H4NNNHC6H4X-p)] (X =
H 1, Et 3, F 4) were prepared similarly.
The complexes [PdCl(g3-C3H5)(p-MeC6H4NNNHC6H4Me-
p)] 6, trans-[PtCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 7 and
cis- and trans-[PdCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 8
were prepared similarly as yellow powders, on replacing [{Rh(l-
Cl)(CO)2}2] by [{Pd(l-Cl)(g3-C3H5)}2] [{Pt(l-Cl)Cl(PPh3)}2]
and [{Pd(l-Cl)Cl(PPh3)}2], respectively.
Fig. 9 1H NMR spectra of the g3-C3H5 resonances of [PdCl(g3-
C3H5)(p-MeC6H4NNNHC6H4Me-p)] 6, at (i) 20 °C, (ii) −70 °C. The
peak marked with an asterisk, *, is due to CD2Cl2.
Structure determinations of [RhCl(CO)2(PhNNNHPh)] 1,
[RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)] 2, [PdCl(g3-
C3H5)(p-MeC6H4NNNHC6H4Me-p)] 6, and trans-
[PtCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] 7
or Pt9), [{Pd(l-Cl)(g3-C3H5)}2],10 and p-XC6H4NNNHC6H4X-p
(X = H, Me, Et and F)11 were prepared by published methods.
New complexes were purified using a mixture of two solvents.
The impure solid was dissolved in the more polar solvent, the
resulting solution was filtered and then treated with the second
solvent, and the mixture reduced in volume in vacuo to induce
precipitation. IR spectra were recorded on a Nicolet 5ZDX FT
spectrometer. 1H NMR spectra were recorded on a Jeol GX270,
GX 400 or k300 spectrometers with SiMe4 as an internal
standard. 19F, 31P and 13C NMR spectra were recorded on a
Jeol k300 spectrometer. Microanalyses were carried out by the
staff of the Microanalytical Service of the School of Chemistry,
University of Bristol.
Many of the details of the structure analyses of 1, 2, 6 and 7
are listed in Table 12. All structure analyses were carried out by
standard low-temperature area detector methods.
CCDC reference numbers 240474–240477.
See http://www.rsc.org/suppdata/dt/b4/b408410a/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the University of Bristol and the EPSRC for Post-
graduate Scholarships (to K. M. A. and R. A. B., respectively).
References
Syntheses
1 See, for example: N. G. Connelly, G. Garcia, M. Gilbert and
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[RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)] 2. To a stirred
solution of [{Rh(l-Cl)(CO)2}2] (0.104 g, 0.268 mmol) in
3 3 5 8
D a l t o n T r a n s . , 2 0 0 4 , 3 3 5 3 – 3 3 5 9

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