Triazenide-bridged rhodium-palladium complexes: [I2Rh(-p- MeC6H4NNNC6H4Me-p) 2Pd(η3-C3H5)]-, a stable paramagnetic [RhPd]4+ species with a localised Rh(ii) centre

Article abstract of DOI:10.1039/b514513a

Deprotonation of mixtures of the triazene complexes [RhCl(CO) ₂(p-MeC₆H₄NNNHC₆H₄Me-p)] and [PdCl(η³-C₃H₅)(p-MeC₆H ₄NNNHC₆H₄Me-p)] or [PdCl₂(PPh ₃)(p-MeC₆H₄NNNHC₆H₄Me-p)] with NEt₃ gives the structurally characterised heterobinuclear triazenide-bridged species [(OC)₂Rh(-p-MeC₆H ₄NNNC₆H₄Me-p)₂PdLL′] {LL′ = η³-C₃H₅ 1 or Cl(PPh ₃) 2} which, in the presence of Me₃NO, react with [NBuⁿ₄]I, [NBuⁿ₄]Br, [PPN]Cl or [NBuⁿ₄]NCS to give [(OC)XRh(-p-MeC₆H ₄NNNC₆H₄Me-p)₂PdCl(PPh ₃)]^- (X = I 3^-, Br 4^-, Cl 5 ^- or NCS 6^-) and [NBuⁿ₄][(OC)XRh(-p- MeC₆H₄NNNC₆H₄Me-p) ₂Pd(η³-C₃H₅)], (X = I 7 ^- or Br 8^-). The allyl complexes 7^- and 8 ^- undergo one-electron oxidation to the corresponding unstable neutral complexes 7 and 8 but, in the presence of the appropriate halide, oxidative substitution results in the stable paramagnetic complexes [NBu ⁿ₄][X₂Rh(-p-MeC₆H ₄NNNC₆H₄Me-p)₂Pd(η³- C₃H₅)], (X = I 9^- or Br 10^-). X-Ray structural (9^-), DFT and EPR spectroscopic studies are consistent with the unpaired electron of 9^- and 10^- localised primarily on the Rh(ii) centre of the [RhPd]⁴⁺ core, which is susceptible to oxygen coordination at low temperature to give Rh(iii)-bound superoxide. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b514513a

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www.rsc.org/dalton | Dalton Transactions
Triazenide-bridged rhodium–palladium complexes:
[I2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g3-C3H5)]−, a stable
paramagnetic [RhPd]4+ species with a localised Rh(II) centre
Christopher J. Adams, R. Angharad Baber, Neil G. Connelly,* Phimphaka Harding, Owen D. Hayward,
Mathivathani Kandiah and A. Guy Orpen
Received 12th October 2005, Accepted 30th November 2005
First published as an Advance Article on the web 3rd January 2006
DOI: 10.1039/b514513a
Deprotonation of mixtures of the triazene complexes [RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)] and
3
[PdCl(g -C3H5)(p-MeC6H4NNNHC6H4Me-p)] or [PdCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)] with
NEt3 gives the structurally characterised heterobinuclear triazenide-bridged species [(OC)2Rh(l-p-
3
MeC6H4NNNC6H4Me-p)2PdLLꢀ] {LLꢀ = g -C3H5 1 or Cl(PPh3) 2} which, in the presence of Me3NO,
react with [NBun ]I, [NBun ]Br, [PPN]Cl or [NBun ]NCS to give [(OC)XRh(l-p-MeC6H4NNN-
4
4
4
C6H4Me-p)2PdCl(PPh3)]− (X = I 3−, Br 4−, Cl 5− or NCS 6−) and [NBun ][(OC)XRh(l-p-MeC6H4-
4
3
NNNC6H4Me-p)2Pd(g -C3H5)], (X = I 7− or Br 8−). The allyl complexes 7− and 8− undergo
one-electron oxidation to the corresponding unstable neutral complexes 7 and 8 but, in the presence
of the appropriate halide, oxidative substitution results in the stable paramagnetic complexes
3
[NBun ][X2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)], (X = I 9− or Br 10−). X-Ray structural (9−),
4
DFT and EPR spectroscopic studies are consistent with the unpaired electron of 9− and 10− localised
primarily on the Rh(II) centre of the [RhPd]4+ core, which is susceptible to oxygen coordination at low
temperature to give Rh(III)-bound superoxide.
3
MeC6H4NNNHC6H4Me-p)] and [PdCl(g -C3H5)(p-MeC6H4NN-
NHC6H4Me-p)] or [PdCl2(PPh3)(p-MeC6H4NNNHC6H4Me-p)]
in CH2Cl2.2 In the case of 1, small quantities of the symmetric
species [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Rh(CO)2] and
Introduction
We have recently reported the synthesis of paramagnetic hetero-
bimetallic triazenide-bridged complexes in which the distribution
of unpaired electron density within a rhodium–iridium bond is
controlled by the systematic variation of the ancillary ligands at
the two metal centres. For example, EPR spectroscopic studies
showed the unpaired electron of [(OC)(Ph3P)Rh(l-RNNNR)2-
Ir(CO)(PPh3)]+ or [(g ,g -cod)Rh(l-RNNNR)2Ir(CO)2]+ (R =
C6H4Me-p, cod = cycloocta-1,5-diene), although in the r* metal–
metal orbital in both cases, to be more associated with the
Ir (ca. 75%) and Rh centres (ca. 80%), respectively.1 Here we
describe novel triazenide-bridged rhodium–palladium complexes,
including the first examples of stable paramagnetic complexes
formally with the [RhPd]4+ core but with the unpaired electron
3
3
[(g -C3H5 )Pd(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5 )] were
separable by column chromatography.
Complexes 1 (orange) and 2 (orange–red) were characterised
by elemental analysis and IR (Table 1) and NMR spectroscopy
(Table 2). Both show two IR carbonyl bands of similar intensity,
separated by ca. 60 cm−1, suggesting the presence of a cis-Rh(CO)2
group.
2
2
The 1H NMR spectrum of 2 shows three resonances, in a 1 : 2 :
1 ratio, for the methyl groups of the bridging triazenide ligands;
two of the four methyl resonances expected for the asymmetric
structure are coincident. The 31P–{ H} NMR spectrum shows
1
2
effectively localised in the dz orbital of a Rh(II) centre prone to
oxygenation.
one singlet resonance, at d 17.16, in accord with the PPh3 ligand
attached to Pd. (Though no ligand exchange between the two
metal centres is observed in these cases, it is notable that deproto-
nation of a mixture of [RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)]
Results and discussion
2
2
2
2
and [IrCl((g ,g -cod)(p-MeC6H4NNNHC6H4Me-p)] gave [(g ,g -
The [RhPd]3+ complexes [(OC)2Rh(l-p-MeC6H4NNN-
C6H4Me-p)2PdLLꢀ] {LLꢀ = g3-C3H5 or Cl(PPh3)}
cod)Rh(l-p-MeC6H4NNNC6H4Me-p)2Ir(CO)2].1) The 13C–{ H}
1
NMR spectrum shows two doublets for the inequivalent Rh-
bound CO ligands, at d 185.18 and 187.30 [J(103Rh13C) 68].
The compounds [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd-
Two such doublets are also observed in the 13C–{ H} NMR
1
3
(g -C3H5)] 1 and [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdCl-
spectrum of 1 which are, however, a result of isomerism (not
observed for 2). Thus, the 1H NMR spectrum, invariant between
20 ◦C and −80 ◦C, shows the presence of two non-interconverting
isomers in solution, resulting from the orientation of the allyl
group (Scheme 1). Two AAꢀBBꢀX patterns are observed for the
allyl protons of the two isomers, 1a and 1b, in the ratio 7 : 2.
A particular set of signals could not be assigned to a particular
(PPh3)] 2 were prepared in good yield by adding NEt3 to a
mixture of the monodentate triazene complexes [RhCl(CO)2(p-
School of Chemistry, University of Bristol, Bristol, UK BS8 1TS.
E-mail: Neil.Connelly@bristol.ac.uk; Fax: +44 (0)117 929 0509; Tel: +44
(0)117 928 8162
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Table 1 Analytical and IR spectroscopic data for [L1L2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdL3L4]z
Analysis (%)a
IR/cm−1
L1L2
L3L4
z
Colour
Yield (%)
C
H
N
m(CO)b
3
1
(CO)2
(CO)2
(CO)I
(CO)Br
(CO)Cl
(CO)(NCS)
(CO)I
(CO)Br
I2
g -C3H5
0
0
Orange
Orange–red
Brown
Brown
Brown
Brown
Yellow
Yellow
Red–brown
Brown
85
65
59
68
84
68
82
62
67
70
52.4(52.5)
57.2(56.8)
53.3(53.6)d
57.2(57.9)
63.3(64.0)
59.9(59.4)
49.8(49.8)
54.8(54.9)
45.9(46.1)
50.1(49.9)
4.6(4.4)
4.4(4.6)
6.1(5.7)
6.0(6.1)
5.3(4.7)
6.2(6.0)
6.5(6.2)
6.7(6.6)
5.7(6.0)
7.2(6.8)
11.1(11.1)
8.0(8.3)
6.6(6.8)
7.7(7.5)
6.5(6.3)
8.7(8.7)
8.8(8.5)
9.0(9.0)
7.8(7.9)
8.3(8.6)
2071vs, 2009
2076vs, 2012
1951
1953
1954
1961
1944
1947
—
2
Cl(PPh3)
Cl(PPh3)
Cl(PPh3)
Cl(PPh3)
Cl(PPh3)
3
−1c
−1c
−1e
−1c
−1c
−1c
−1c
−1c
4
5
6
3
7
g -C3H5
3
8
g -C3H5
3
9
g -C3H5
3
10
Br2
g -C3H5
—
+
a Calculated values in parentheses. b Strong absorptions unless otherwise stated, vs = very strong. c Isolated as an [NBun
]
salt. d Sample analysed as a
4
1.0 CH2Cl2 solvate. e Isolated as a [PPN]+ salt.
Scheme 1 R = C6H4Me-p.
isomer but steric hindrance is likely to disfavour 1b, and 1a is
thought to be the major isomer in solution.
Crystals of 1 and 2·CH2Cl2 suitable for X-ray diffraction study
were grown by allowing a concentrated CH2C◦l2 solution of each
complex to diffuse slowly into MeOH at −20 C. The structures
of 1 and 2 are shown in Fig. 1 and 2 with bond lengths and angles
given in Table 3.
Fig. 2 The molecular structure of [(OC)2Rh(l-p-MeC6H4NNNC6H4-
Me-p)2PdCl(PPh3)] 2. Hydrogen atoms have been omitted for clarity.
3
atom to an g -allyl in 1 and one chloride and one PPh3 ligand
in 2, as deduced from the NMR spectra (see above). Of the two
possible isomers of 1 detected by NMR spectroscopy in solution,
the structure observed is that of 1a.
The ligand arrangement around the Rh atom is approximately
square planar in both cases although that around Pd in 1 is
somewhat distorted {X(a)–Pd(1)–N(6) ≈ X(b)–Pd(1)–N(3) ≈
150◦; X(a) and X(b) are the midpoints of the C–C bonds of the
allyl ligand} as a result of the small X(a)–Pd(1)–X(b) angle (35.3◦).
In both cases the metal centres adopt a face-to-face arrangement,
˚
with the Rh(1) · · · Pd(1) distance 2.834(1) and 2.830(1) A in 1 and
2 respectively. In 2 the Pd(1)–N(6) bond, trans to PPh3, is longer
Fig. 1 The molecular structure of [(OC)2Rh(l-p-MeC6H4NNNC6H4-
Me-p)2Pd(g -C3H5)] 1. Hydrogen atoms have been omitted for clarity.
than the Pd(1)–N(3) bond, trans to Cl− [i.e. 2.104(2) vs. 2.037(2)
3
−
˚
A]; PPh3 has a greater trans influence than Cl .
In both 1 and 2 each metal is bonded to one terminal N atom of
each of two triazenide ligands, giving a cis-MN2 unit; the rhodium
atoms are bonded to two cis carbonyl ligands, and the palladium
Complexes 1 and 2 (and others in this paper) have also been
studied by cyclic voltammetry at a platinum disk electrode in
CH2Cl2. Both undergo one reversible one-electron oxidation (at
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1
Table 2 Proton, 13C–{ H} and 31P NMR spectroscopic dataa for [L1L2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdL3L4]z
1
Complex
1H
13C–{ H}
31P
—
1 (isomer 1a) 7.90–6.95 (m, C6H4)b, 5.79 (m, 1H, allyl Hc), 186.24 [d, J(13C103Rh) 68, CO], 150.80 (C1),
3.81 (d, 1H, 3JHH 7, allyl Hb), 3.26 (d, 1H,
3JHH 12, allyl Ha), 2.20 (s br, 12H, CH3)
150.27 (C1), 150.25 (C1), 134.71 (C4), 134.65
(C4), 129.43 (C2), 129.34 (C2), 121.98 (C3),
121.65 (C3), 113.01 (s, CH2CHCH2), 56.72 (s,
CH2CHCH2), 20.87 (CH3)
1 (isomer 1b) 7.90–6.95 (m, C6H4)b, 5.56 (m, 1H, allyl Hc), 186.64 [d, J(13C103Rh) 68, CO], 116.22 (s,
—
3.99 (d, 1H, 3JHH 7, allyl Hb), 3.11 (d, 1H,
3JHH 12, allyl Ha), 2.22 (s br, 12H, CH3)
7.73 (d, 2H, 1JHH 9, C6H4), 7.70–7.57 {m,
8H, C6H4 and P(C6H5)3}, 7.49–7.40 {m,
5H, C6H4 and P(C6H5)3}, 7.37–7.27 {m,
CH2CHCH2), 56.16 (s, CH2CHCH2), 20.87
(CH3)
2
187.30 [d, J(13C103Rh) 68, CO], 185.18 [d,
J(13C103Rh) 68, CO], 149.20 [d, J(13C103Rh) 2,
C1], 148.73 (C1), 148.68 (C1), 146.91 [d,
17.16
6H, C6H4 and P(C6H5)3}, 7.17–7.09 (m, 4H, J(13C31P) 2, C1, P], 134.33 (C4), 134.20 (C4),
C6H4), 7.09–7.01 (m, 4H, C6H4), 6.58 (d,
2H, 1JHH 8, C6H4), 2.24 (s, 3H, CH3), 2.20
(s, 6H, CH3), 2.12 (s, 3H, CH3)
130.82 (C4, Ph), 123.12 (C3), 121.65 (C3),
121.45 (C3), 20.30 (CH3), 20.15 (CH3), 20.00
(CH3)
[NBun4]+3−
[NBun4]+4−
7.78–6.80 {m, C6H4 and P(C6H5)3}, 2.89 {t
br, N(CH2CH2CH2CH3)4}, 2.22, 2.21, 2.20,
2.17, 2.15, 2.07 (s, 2 : 1 : 1 : 2 : 1 : 1, CH3),
1.38 {m br, N(CH2CH2CH2CH3)4}, 0.84 {t
br, N(CH2CH2CH2CH3)4}
—
27.98, 27.94
27.31, 27.96
7.98–6.50 {m, C6H4 and P(C6H5)3}, 2.98 {t
br, N(CH2CH2CH2CH3)4}, 2.26, 2.24 2.23,
2.22, 2.19, 2.17, 2,15 (s, 1 : 2 : 1 : 1 : 1 : 1 : 1,
CH3), 1.42 {m br, N(CH2CH2CH2CH3)4},
0.88 {t br, N(CH2CH2CH2CH3)4}
—
[PPN]+5−
8.25–6.20 {m, 61H, C6H4, P(C6H5)3 and
N(PPh3)2}, 2.20 (s, 3H, CH3), 2.18 (s, 6H,
CH3), 2.15 (s, 3H, CH3)
185.10 [d, J(13C103Rh) 76, CO], 150.00–122.82
{C6H4, P(C6H5)3 and N(PPh3)2}, 20.54 (s,
CH3), 20.33 (s, CH3), 19.83 (s, CH3).
21.70 {N(PPh3)2}, 18.52 {P(C6H5)3}
[NBun4]+6−
7.97–7.91 (m, 4H, C6H4), 7.90–7.50 {m, 6H, 184.67 [d, J(13C103Rh) 68, CO], 150.05 (C1),
17.29
P(C6H5)3}, 7.48 (d, 2H, 1JHH 9, C6H4),
7.46–7.00 {m, 10H, C6H4 and P(C6H5)3},
6.99–6.86 {m, 7H, C6H4 and P(C6H5)3},
149.52 (C1), 148.30 (C1), 134.11 (C4), 134.03
(C4), 131.17 (C4, Ph), 130.83 (C4, Ph), 130.60
(C4, Ph), 127.53 (C2), 127.10 (C2), 127.03 (C2),
6.84 (d, 2H, 1JHH 9, C6H4), 6.54 (d, 2H, 1JHH 126.96 (C2), 126.91 (C2, Ph), 126.78 (C2, Ph),
9, C6H4), 3.01 {t br, 8H,
126.62 (C2, Ph), 122.08 (C3), 121.87 (C3),
121.56 (C3), 120.89 (C3), 24.04
N(CH2CH2CH2CH3)4}, 2.26 (s, 3H, CH3),
2.25 (s, 3H, CH3), 2.23 (s, 3H, CH3), 2.12 (s, {N(CH2CH2CH2CH3)4}, 20.23 (s, CH3), 20.18
3H, CH3), 1.49 {m br, 8H,
(s, CH3), 20.15 (s, CH3), 20.07 (s, CH3), 19.77
{N(CH2CH2CH2CH3)4}, 13.49
{N(CH2CH2CH2CH3)4}
N(CH2CH2CH2CH3)4}, 1.31 {m br, 8H,
N(CH2CH2CH2CH3)4}, 0.93 {t, 12H,
N(CH2CH2CH2CH3)4}
[NBun4]+7−
7.81 (d, 2H, 1JHH 9, C6H4), 7.61 (d, 2H, 1JHH 178.00 [d, J(13C103Rh) 68, CO], 152.64 (C1),
—
9, C6H4), 7.30–6.58 (m, 8H, C6H4), 5.43 (m, 152.22 (C1), 151.68 (C1), 151.09 (C1), 133.72
1H, allyl Hc), 4.16 (d, 1H, 3JHH 7, allyl Hb),
3.61 (d, 1H, 3JHH 12, allyl Ha), 2.67 {t br,
8H, N(CH2CH2CH2CH3)4}, 1.98 (s, 3H,
CH3), 1.96 (s, 3H, CH3), 1.94 (s, 3H, CH3),
1.92 (s, 3H, CH3), 1.40 {m br, 8H,
(C4), 133.66 (C4), 129.65 (C2), 129.58 (C2),
122.60 (C3), 122.55 (C3), 121.48 (C3), 120.80
(C3), 115.66 (s, CH2CHCH2), 58.86 (s,
CH2CHCH2), 58.86 (s, CH2CHCH2), 24.01
{N(CH2CH2CH2CH3)4}, 20.82 (s, CH3), 20.60
(s, CH3), 19.75 {N(CH2CH2CH2CH3)4}, 13.48
{N(CH2CH2CH2CH3)4}
N(CH2CH2CH2CH3)4}, 1.26 {m br, 8H,
N(CH2CH2CH2CH3)4}, 0.88 {t, 12H,
N(CH2CH2CH2CH3)4}
[NBun4]+8−
7.80 (d, 2H, 1JHH 9, C6H4), 7.58 (d, 2H, 1JHH 177.16 [d, J(13C103Rh) 68, CO], 152.61 (C1),
—
9, C6H4), 7.28–6.55 (m, 8H, C6H4), 5.40 (m, 152.59 (C1), 151.44 (C1), 151.00 (C1), 133.71
1H, allyl Hc), 4.10 (d, 1H, 3JHH 7, allyl Hb),
3.60 (d, 1H, 3JHH 12, allyl Ha), 2.66 {t br,
8H, N(CH2CH2CH2CH3)4}, 1.98 (s, 3H,
CH3), 1.97 (s, 3H, CH3), 1.95 (s, 3H, CH3),
1.93 (s, 3H, CH3), 1.39 {m br, 8H,
(C4), 133.65 (C4), 129.59 (C2), 129.57 (C2),
122.60 (C3), 122.54 (C3), 121.44 (C3), 120.78
(C3), 115.65 (s, CH2CHCH2), 58.85 (s,
CH2CHCH2), 58.83 (s, CH2CHCH2), 24.00
{N(CH2CH2CH2CH3)4}, 20.81 (s, CH3), 20.56
(s, CH3), 19.72{N(CH2CH2CH2CH3)4}, 13.47
{N(CH2CH2CH2CH3)4}
N(CH2CH2CH2CH3)4}, 1.26 {m br, 8H,
N(CH2CH2CH2CH3)4}, 0.87 {t, 12H,
N(CH2CH2CH2CH3)4}
a Chemical shift (d) in ppm, J values in Hz, spectra in CD2Cl2 at 20 ◦C unless stated otherwise, atom numbering for the NC6H4Me and allyl groups shown
below. b Overlapping triazenide signals for isomers 1a and 1b.
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◦
3
˚
Table 3 Selected bond lengths (A) and angles ( ) for [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] 1, [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-
p)2PdCl(PPh3)]·CH2Cl2, 2·CH2Cl2 and [NBun4][RhI2(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)]·0.19CH2Cl2 [NBun4]+ 9−·0.19CH2Cl2
3
1
2
9−
Pd(1)–Rh(1)
Pd(1)–N(3)
Pd(1)–N(6)
Pd(1)–C(3)
Pd(1)–C(4)
Pd(1)–C(5)
Pd(1)–X(a)a
Pd(1)–X(b)b
Pd(1)–P(1)
Pd(1)–Cl(1)
Rh(1)–N(1)
Rh(1)–N(4)
Rh(1)–C(1)
Rh(1)–C(2)
Rh(1)–I(1)
Rh(1)–I(2)
C(1)–O(1)
C(2)–O(2)
N(1)–N(2)
N(2)–N(3)
N(4)–N(5)
N(5)–N(6)
C(3)–C(4)
C(4)–C(5)
2.834(1)
2.103(3)
2.117(3)
2.116(5)
2.135(5)
2.118(5)
2.005
2.005
—
—
2.100(3)
2.076(3)
1.875(6)
1.887(5)
—
2.830(1)
2.037(2)
2.104(2)
—
—
—
2.840(1)
2.116(8))
2.100(7)
2.139(12)
2.090(14)
2.118(12)
2.018
2.003
—
—
—
—
2.299(1)
2.315(1)
2.126(3)
2.090(2)
1.858(4)
1.853(3)
—
2.052(8)
2.064(7)
—
—
2.593(1)
2.617(1)
—
—
—
1.132(7)
1.089(7)
1.294(4)
1.293(4)
1.297(4)
1.292(4)
1.411(9)
1.414(9)
1.145(4)
1.136(4)
1.307(3)
1.292(3)
1.305(3)
1.296(3)
—
—
1.300(10)
1.281(10)
1.305(10)
1.301(10)
1.26(2)
1.29(2)
—
X(a)–Pd(1)–X(b)
X(a)–Pd(1)–N(3)
X(b)–Pd(1)–N(3)
X(a)–Pd(1)–N(6)
X(b)–Pd(1)–N(6)
C(3)–Pd(1)–C(5)
N(6)–Pd(1)–C(3)
N(3)–Pd(1)–C(3)
N(6)–Pd(1)–C(5)
N(3)–Pd(1)–C(5)
X(a)–Pd(1)–Rh(1)
X(b)–Pd(1)–Rh(1)
N(3)–Pd(1)–P(1)
N(6)–Pd(1)–P(1)
N(3)–Pd(1)–Cl(1)
N(6)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Rh(1)
Cl(1)–Pd(1)–Rh(1)
N(3)–Pd(1)–N(6)
N(3)–Pd(1)–Rh(1)
N(6)–Pd(1)–Rh(1)
N(4)–Rh(1)–Pd(1)
N(1)–Rh(1)–Pd(1)
C(1)–Rh(1)–C(2)
C(1)–Rh(1)–N(4)
C(2)–Rh(1)–N(4)
C(1)–Rh(1)–N(1)
C(2)–Rh(1)–N(1)
N(1)–Rh(1)–N(4)
N(1)–Rh(1)–I(1)
N(1)–Rh(1)–I(2)
I(1)–Rh(1)–I(2)
35.3
117.2
151.4
150.3
115.7
70.1(2)
169.1(1)
101.0(2)
99.1(2)
170.8(2)
116.5
114.9
—
—
—
—
—
—
—
89.8(1)
81.8(1)
77.4(1)
82.5(1)
77.4(1)
89.1(2)
88.3(2)
177.0(2)
171.6(2)
95.1(2)
87.6(1)
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
92.9(1)
176.8(1)
174.1(1)
88.8(1)
91.3(1)
103.9(1)
98.5(1)
86.8(1)
84.6(1)
79.3(1)
82.3(1)
77.7(1)
90.0(2)
91.1(1)
170.2(1)
178.6(1)
90.9(1)
87.9(1)
—
—
—
—
—
—
—
103.1(1)
106.9(1)
118.4(2)
117.5(2)
179.2(4)
175.0(3)
—
34.6
113.7
148.3
153.2
118.7
68.4(6)
167.8(5)
96.9(5)
101.2(5)
164.8(5)
108.0
107.5
—
—
—
—
—
—
—
92.9(3)
84.4(2)
83.0(2)
—
—
—
—
—
87.9(3)
179.1(2)
88.4(2)
91.77(3)
97.80(3)
97.07(3)
91.9(2)
175.8(2)
—
I(1)–Rh(1)–Pd(1)
I(2)–Rh(1)–Pd(1)
N(4)–Rh(1)–I(1)
N(4)–Rh(1)–I(2)
C(1)–Rh(1)–Pd(1)
C(2)–Rh(1)–Pd(1)
N(1)–N(2)–N(3)
N(4)–N(5)–N(6)
Rh(1)–C(1)–O(1)
Rh(1)–C(2)–O(2)
C(3)–C(4)–C(5)
109.3(2)
96.8(2)
117.0(3)
116.7(3)
175.2(5)
174.8(6)
118.8(7)
—
118.7(8)
119.2(7)
—
—
139(2)
1752 | Dalton Trans., 2006, 1749–1757
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Table 3 (Contd.)
Torsion angles
N(1)–Rh(1) · · · Pd(1)–N(3)
N(4)–Rh(1) · · · Pd(1)–N(6)
C(1)–Rh(1) · · · Pd(1)–X(b)
C(2)–Rh(1) · · · Pd(1)–X(a)
C(1)–Rh(1) · · · Pd(1)–C(5)
C(2)–Rh(1) · · · Pd(1)–C(3)
C(2)–Rh(1) · · · Pd(1)–P(1)
C(1)–Rh(1) · · · Pd(1)–Cl(1)
20.8
18.4
8.7
43.5
7.3
26.3
—
—
12.7(1)
14.5(1)
—
—
—
—
17.2(1)
16.6(1)
8.4
1.8
—
—
—
—
—
—
a X(a) = midpoint of C(3)–C(4). b X(b) = midpoint of C(4)–C(5).
0.99 and 1.15 V, respectively) and a second irreversible process
with a peak potential, (Ep)ox (at a scan rate of 200 mV s−1), of
1.28 and 1.53 V. Complex 2 also shows an irreversible reduction
peak at ca. −1.3 V (the irreversibility possibly due to the loss
of chloride from the anion [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-
p)2PdCl(PPh3)]− 2−).
substitution of one carbonyl ligand of 1 by the halide results in a
marked shift of the oxidation wave to a more negative potential,
i.e. by ca. 1.0 V.
The low potentials for the oxidation of [(OC)XRh(l-p-
3
MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)]− (X = I 7− or Br 8−) sug-
gested that the formation of the neutral complexes [(OC)XRh(l-p-
3
MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] should be readily effected
The anions [(OC)XRh(l-p-MeC6H4NNNC6H4Me-p)2PdLLꢀ]−
{LLꢀ = Cl(PPh3) or g3-C3H5}
5
with mild chemical oxidants. Accordingly, addition of [Fe(g -
C5H5)2][PF6] to 7− or 8− in CH2Cl2 gave brown solutions with
m(CO) at ca. 2035 cm−1, the shifts of ca. 90 cm−1 to higher energy
consistent with one-electron oxidation.
The complexes [(OC)XRh(l-p-MeC6H4NNNC6H4Me-p)2PdCl-
(PPh3)]− (X = I 3−, Br 4−, Cl 5− or NCS 6−) were prepared
by reacting [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdCl(PPh3)]
2 in CH2Cl2 with [NBun ]I, [NBun ]Br, [PPN]Cl and [NBun ]NCS,
Although these paramagnetic complexes proved too reactive to
isolate, related but very stable [RhPd]4+ derivatives were prepared
via the oxidative substitution reactions of 7− and 8−. Thus, the
4
4
4
respectively, in the presence of Me3NO, and isolated in good
5
reaction of these anions with [Fe(g -C5H5)2][PF6] in the presence
yields as brown powders. The complexes [NBun ][(OC)XRh(l-p-
4
of the appropriate halide, or of 7− directly with iodine, gave
3
MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)], (X = I 7− or Br 8−) were
brown solutions from which the crystalline dihalide complexes
prepared similarly from 1, as yellow solids.
3
[NBun ][X2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] (X =
Complexes 3−–6− were characterised (as either [NBun ]+ or, in
4
4
I, [NBun ]+9− or Br, [NBun ]+10−) were isolated in ca. 70% yield.
the case of 5−, [PPN]+ salts) by elemental analysis and IR (Table 1)
and NMR (Table 2) spectroscopy. All of the anions show one
carbonyl band, in the range 1944–1962 cm−1, and complex 6−
shows bands at 2098 cm−1 [m(CN)] and at 794 cm−1 [m(CS)] for the
coordinated NCS ligand. The latter band, within the range 780–
860 cm−1, is consistent with an N-bonded rather than an S-bonded
(690–720 cm−1) thiocyanate.3
4
4
The anions 9− and 10− were characterised as their [NBun ]+ salts
4
by elemental analysis (Table 1) but their paramagnetism precluded
the acquisition of meaningful NMR spectra. Brown crystals
of [NBun ]+9− (as a partial CH2Cl2 solvate) suitable for X-ray
4
diffraction study were therefore grown by allowing a concentrated
CH2Cl2 solution of the complex to diffuse slowly into n-hexane at
−20 ◦C.
1
The H NMR spectra of complexes 3−–8− show resonances
The structure of the anion 9− is shown in Fig. 3 and selected
bond lengths and angles are given in Table 3. As in 1 and 2, the lig-
and arrangement around the Rh and Pd centres is approximately
square planar with, for example, N(3)–Pd(1)–N(6) = 92.9(3)◦,
between d 6.25 and 8.50 corresponding to the aromatic protons
of the diaryltriazenide and PPh3 ligands. Anions 6−–8− each show
four resonances for the triazenide methyl resonances, between d
1.50 and 2.50, as expected for the asymmetric unit (OC)XRh(l-
RNNNR)2Pd (X = halide, R = C6H4Me-p). (The anion 5− shows
N(1)–Rh(1)–N(4) = 87.9(3)◦, N(1)–Rh(1)–I(1)
=
179.1(2)◦
1
only three such resonances, in a 1 : 2 : 1 ratio.) The H NMR
spectra of the iodide and bromide complexes 3− and 4−, however,
show six and seven different Me signals respectively, with relative
1
intensities suggesting a 1 : 1 ratio of two isomers. The 31P–{ H}
NMR spectra also reveal the presence of the two isomers, as shown
by two singlets, at d 27.98 and 27.94 and at 27.31 and 27.96,
respectively. Isomers were not detected for 5− or 6−.
1
The 13C–{ H} NMR spectra of 5−–8− each show one doublet in
the range d 180.0–190.0 for the CO ligand {J(13C103Rh) ca. 70 Hz).
The cyclic voltammograms of 3−–5− were disappointingly ill-
defined, in either CH2Cl2 or MeCN and at platinum or glassy
carbon electrodes, although the thiocyanate complex 6− did show
an irreversible oxidation wave with (Ep)ox = 0.41 V. By contrast,
the allyl complexes 7− and 8− undergo reversible oxidation (at scan
rates greater than 200 mV s−1) at 0.04 and 0.06 V, respectively. Thus,
Fig. 3 The structure of the anion [I2Rh(l-p-MeC6H4NNNC6H4Me-p)2-
3
Pd(g -C3H5)]− 9−. Hydrogen atoms have been omitted for clarity.
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and N(4)–Rh(1)–I(2) = 175.8(2)◦; the Pd atom bonds to the allyl
ligand while the Rh atom and the two iodide ligands give a cis-RhI2
group. The two square planes are held in a face-to-face geometry
with the two planes more eclipsed in 9− than 1 {as shown by the
torsion angles N(1)–Rh(1) · · · Pd(1)–N(3) (8.4 and 20.8◦ for 9−
and 1, respectively) and N(4)–Rh(1) · · · Pd(1)–N(6) (1.8 and 18.4,
respectively)}.
unpaired electron spin density located on the rhodium atom, with
only approximately 10% on the palladium atom. In other words,
the SOMO is highly polarised towards the rhodium atom, i.e.
2
more like a localised dz orbital and only slightly antibonding with
respect to the metal–metal bond. Thus, oxidative replacement of
two CO ligands in 1 ([RhPd]3+) by two iodides in 9− ([RhPd]4+)
leads to localisation of unpaired electron density on the rhodium
atom and only a small difference in the Rh · · · Pd bond distances
of 1 and 9−. A more localised, formally Rh(II), centre in 9− is also
supported by the marked Rh–N bond length changes noted above,
cf. Pd–N which are essentially invariant (Table 3). Note that the
same change occurring on oxidation of 3−–8− would cause a large
decrease in backbonding to the carbonyl ligands, explaining the
large increase in m(CO) and the lability of the M–C(O) bond.
In order to understand further the processes leading to the
localisation of the SOMO on the rhodium atom of 9−, calculations
were carried out on the additional model complexes [(OC)2Rh-
Of most interest, however, is the Rh(1) · · · Pd(1) bond length of
3+
˚
2.840(1) A which is surprisingly similar to that in the [RhPd]
3
precursor [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)]
1 [2.834(1) A], especially given the marked shortening of
the Rh · · · Ir distance from 2.945(2) to 2.713(1) A on one-
˚
˚
electron oxidation of [(OC)(Ph3P)Rh(l-p-MeC6H4NNNC6H4Me-
p)2Ir(CO)(PPh3)].1 It is also noteworthy, in the context of the
DFT calculations described below, that the Rh–N bonds in 9−
are shorter than in 1 [i.e. 2.052(8) and 2.064(7) vs. 2.076(3) and
2.100(3)] whereas the Pd–N distances [2.100(7) and 2.116(8) vs.
2.103(3) and 2.117(3)] are essentially invariant.
3
3
(l-HNNNH)2Pd(g -C3H5)]+ and [(OC)IRh(l-HNNNH)2Pd(g -
In order to explain these structural findings, DFT calculations
C3H5)], possible intermediates in the ECC (Electrochemical–
3
3
were carried out on the model anion [I2Rh(l-HNNNH)2Pd(g -
Chemical–Chemical) conversion of [(OC)2Rh(l-HNNNH)2Pd(g -
3
3
C3H5)]− and neutral compound [(OC)2Rh(l-HNNNH)2Pd(g -
C3H5)] to [I2Rh(l-HNNNH)2Pd(g -C3H5)]− (Scheme 2). These
C3H5)] (and, for comparison, the cation [(OC)(H3P)Rh(l-
calculations show that in the [RhPd]4+ complexes, stepwise re-
placement of the carbonyl ligands by iodide ions results in the
unpaired electron spin density becoming increasingly localised on
the rhodium atom. Replacement of the p-acceptor CO ligands by
the p-donor iodides appears to destabilise the rhodium d-orbitals,
HNNNH)2Ir(CO)(PH3)]+).
3
The HOMO of the dicarbonyl [(OC)2Rh(l-HNNNH)2Pd(g -
C3H5)] (Fig. 4) is r* (i.e. the out-of-phase combination of the
2
two metal 4dz orbitals) and lies between the metal atoms (as
does the SOMO of [(OC)(H3P)Rh(l-PhNNNPh)2Ir(CO)(PH3)]+).
Half depopulation of this HOMO would therefore be expected
to lead to a significant shortening of the Rh · · · Pd bond dis-
tance, as found for [(OC)(Ph3P)Rh(l-p-MeC6H4NNNC6H4Me-
p)2Ir(CO)(PPh3)].1 However, the SOMO of the anion [I2Rh(l-
raising the energy of the dz orbital. Thus, it plays an increasing
2
2
role in the antibonding combination of the metal dz orbitals (the
SOMO) to the point where the SOMO is essentially nearly entirely
rhodium dz in nature and no longer metal–metal r*.
2
On the basis of the calculations described above, the EPR
spectra of 9− and 10− were expected to show strong hyperfine
coupling to the rhodium(II) atom. The spectra, recorded for the
pure crystalline dihalides in 1 : 1 CH2Cl2 : CH2ClCH2Cl or toluene
solution are, however, ill-defined. They are qualitatively similar
to each other but obviously dissimilar to those observed for
[Rh2]3+ 4 and [RhIr]3+ 1 complexes. In fact, in spite of the care taken
to exclude oxygen from the EPR samples the anisotropic spectra
are more similar to those of Rh(III) superoxide complexes.5,6 This
suggests that in solution complexes 9− and 10− are very susceptible
to oxygen binding, probably because the unpaired electron is
3
HNNNH)2Pd(g -C3H5)]− (Fig. 5) has approximately 90% of the
2
largely located in the dz orbital on the rhodium(II) atom.
Precedent for transient binding of dioxygen to a dinuclear
metal–metal bonded centre at low temperature is provided by
[Rh2(l-ap)4(CCH)] (ap = 2-anilinopyridinate) which displays
an anisotropic EPR spectrum at low temperature characteris-
tic of a superoxide complex (which is not detected at higher
temperatures).6 This complex is similar to 9− and 10− in having
a (formal) mixed-valence core (in this case RhIIRhIII) but with
a SOMO largely polarised towards the Rh(II) atom. Here, the
superoxide ligand must coordinate to this rhodium atom as the
other is coordinatively saturated (by axial coordination of the
acetylide ligand).
Fig. 4 Computed HOMO (94% probability level) for the model com-
pound [(OC)2Rh(l-HNNNH)2Pd(g -C3H5)].
3
Further support for this hypothesis is provided by DFT
calculations which show that the model complex [(O2)I2Rh(l-
3
HNNNH)2Pd(g -C3H5)]− has the unpaired electron density lo-
cated almost entirely in a p* O2 orbital (Fig. 6), i.e. it is
Fig. 5 Computed SOMO (94% probability level) for the model compound
3
[I2Rh(l-HNNNH)2Pd(g -C3H5)]−, showing the polarisation towards the
effectively a superoxide complex with a Rh(III)Pd(II) core. The cal-
3
rhodium atom.
culated O–O distance in [(O2)I2Rh(l-HNNNH)2Pd(g -C3H5)]− is
1754 | Dalton Trans., 2006, 1749–1757
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Scheme 2 (a) The ECC sequence converting 2 into 9−; the numbers give the calculated unpaired electron spin density on each metal atom in the [RhPd]4+
2
complexes. (b) Schematic MO diagrams showing how the r* SOMO of the binuclear complex becomes increasingly rhodium-based as the rhodium dz
orbital is raised in energy.
3
5
5
5
[{Pd(l-Cl)(g -C3H5)}2],10 [Fe(g -C5H5)2][PF6], [Fe(g -C5H5)(g -
C5H4COMe)][PF6],11 [PPN]Cl12 and p-MeC6H4NNNHC6H4Me-
p
13 were prepared by published methods. The salts [NBun ]X were
4
purchased from Aldrich (X = Br and I) or Fluka Chemicals
(X = NCS). 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
1
5ZDX FT spectrometer. H NMR spectra were recorded on a
Jeol GX270, GX 400 or k300 spectrometer with SiMe4 as an
internal standard. 31P and 13C NMR spectra were recorded on
a Jeol k300 spectrometer. X-band EPR spectra were recorded on
a Bruker ESP300 spectrometer equipped with a Bruker variable
temperature accessory and a Hewlett-Packard 5350B microwave
frequency counter. The field calibration was checked by measuring
the resonance of the diphenylpicrylhydrazyl (dpph) radical before
each series of spectra. Electrochemical studies were carried out
using an EG & G model 273A potentiostat linked to a computer
using EG & G Model 270 Research Electrochemistry software in
conjunction with a three-electrode cell. The auxiliary electrode was
a platinum wire and the working electrode a platinum or glassy
carbon disc. The reference was an aqueous saturated calomel
electrode separated from the test solution by a fine porosity frit
and an agar bridge saturated with KCl. Solutions were 5.0 × 10−4
or 1.0 × 10−3 mol dm−3 in the test compound and 0.1 mol dm−3 in
Fig. 6 Computed SOMO (94% probability level) for the model compound
3
[(O2)I2Rh(l-HNNNH)2Pd(g -C3H5)]− (viewed along the RhPd bond),
showing the unpaired electron density localised predominantly on the
superoxide ligand.
˚
1.28 A, which compares with the crystallographically determined
˚
distance of 1.306(5) A in the rhodium(III)-superoxide complex
[Rh(NCMe)(O2){meso-Me6-[14]aneN4}]2+.7
The calculated Rh · · · Pd bond distance in the model complex
3
[(O2)I2Rh(l-HNNNH)2Pd(g -C3H5)]− (2.91 A) is longer by only
˚
3
−
˚
˚
0.04 A than that of [I2Rh(l-HNNNH)2Pd(g -C3H5)] (2.87 A).
Thus, changing the SOMO from a rhodium-based orbital in
9− and 10− to an O–O p* orbital in the adduct has little
effect on the rhodium–palladium distance, once again supporting
the interpretation that the former has little metal–metal r*
antibonding character.
[NBun ][PF6] as the supporting electrolyte. The solvents used were
4
CH2Cl2 or MeCN. Under the conditions used, Eoꢀ for the one-
5
electron oxidation of [Fe(g -C5H5)2], added to the test solutions as
an internal calibrant, is 0.47 V in CH2Cl2.
Microanalyses were carried out by the staff of the Microanalyt-
ical Service of the School of Chemistry, University of Bristol.
Experimental
[(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g3-C3H5)] 1
The preparation, purification and reactions of the complexes
described were carried out under an atmosphere of dry dini-
trogen using dried, distilled and deoxygenated solvents; re-
actions were monitored by IR spectroscopy where necessary.
The compounds [{Rh(l-Cl)(CO)2}2],8 [{Pd(l-Cl)Cl(PPh3)}2],9
3
Method a. A mixture of [{Pd(l-Cl)(g -C3H5)}2] (0.201 g,
0.55 mmol) and p-MeC6H4NNNHC6H4Me-p (0.248 g, 1.10 mmol)
in CH2Cl2 (20 cm3) was stirred for 20 min to give [PdCl(g -C3H5)-
3
(p-MeC6H4NNNHC6H4Me-p)]. In a second flask, a mixture
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3
Table 4 Crystal and refinement data for [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] 1, [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdCl-
3
(PPh3)]·CH2Cl2 2·CH2Cl2 and [NBun4][RhI2(l-p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)]·0.19CH2Cl2 [NBun4]+9−·0.19CH2Cl2
Compound
1
2·CH2Cl2
[NBun4]+9−·0.19CH2Cl2
Formula
M
C33H33N6O2PdRh
754.96
C49H45Cl3N6O2PPdRh
1096.54
Triclinic
C47.19H69.37Cl0.37I2N7PdRh
1210.82
Crystal system
Space group (no.)
Monoclinic
P2/c (13)
17.962(3)
8.912(1)
26.282(6)
90
Monoclinic
P2/n (13)
16.035(2)
16.053(2)
20.138(2)
90
97.057(2)
90
173(2)
P-1 (2)
˚
a/A
12.316(2)
12.570(1)
17.359(2)
105.29(2)
104.37(2)
104.95(2)
293(2)
˚
b/A
˚
c/A
a/◦
b/◦
129.61(2)◦
90
c /◦
T/K
193(2)
3241.4(10)
4
3
˚
U/A
2355.9(5)
2
0.982
5144.6(9)
4
1.927
Z
l/mm−1
1.102
Reflections collected
Independent reflections (Rint
5127
4572 (0.0241)
0.0321, 0.0850
20155
10641 (0.0302)
0.0344, 0.0786
33507
11740 (0.1174)
0.0666, 0.1542
)
Final R indices [I > 2r(I)]: R1,wR2
was added [NBun ]I (0.052 g, 0.139 mmol) and Me3NO (15 mg
of [{Rh(l-Cl)(CO)2}2] (0.214 g, 0.55 mmol) and p-MeC6H4-
NNNHC6H4Me-p (0.248 g, 1.10 mmol) in CH2Cl2 (20 cm3) was
stirred to give [RhCl(CO)2(p-MeC6H4NNNHC6H4Me-p)]. The
two solutions were then mixed and stirred for 20 min before NEt3
(0.35 cm3, 2.44 mmol) was added. The red–orange solution was
stirred for a further 5 min then evaporated to low volume (ca.
5 cm3) before silica was added. The solvent was removed and the
resulting solid was placed on a silica–n-hexane chromatography
column. Elution with CH2Cl2–n-hexane (1 : 5) gave a yellow band
which was collected and evaporated to dryness to give the orange
product, yield 0.320 g (39%).
4
0.20 mmol). The yellow solution was stirred for 20 min then
filtered and concentrated in vacuo. n-Hexane (15 cm3) was added
and the solution was concentrated in vacuo (to ca. 3 cm3) to give
a yellow precipitate which was thoroughly washed with n-hexane
(2 × 20 cm3). The product was then purified using CH2Cl2–hexane
to give a yellow powder, yield 125 mg (82%).
The complexes [NBun ][(OC)XRh(l-p-MeC6H4NNNC6H4Me-
4
p)2PdCl(PPh3)] (X = Br [NBun ]+4− or NCS [NBun ]+6−), [PPN]-
4
4
[(OC)ClRh(l-p-MeC6H4NNNC6H4Me-p)2PdCl(PPh3)] [PPN]+5−
3
and [NBun ][(OC)BrRh(l-p-MeC6H4NNNC6H4Me-p)(g -C3H5)]
4
[NBun ]+8− were prepared similarly.
The complex [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdCl-
(PPh3)] 2 was prepared similarly but was eluted from an alumina–
n-hexane chromatography column using CH2Cl2–n-hexane (3 : 7).
The eluate was dried in vacuo to give the orange–red product.
4
[NBun ][I2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g3-C3H5)]
4
[NBun ]+9−
4
Method b. A solution of [RhCl(CO)2(p-MeC6H4NNNH-
3
Method a. To a yellow solution of [NBun ][(OC)IRh(l-
C6H4Me-p)] (0.211 g, 0.502 mmol) and [PdCl(g -C3H5)(p-
4
3
p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] [NBun ]+7− (0.091 g,
MeC6H4NNNHC6H4Me-p)] (0.205 g, 0.502 mmol) in CH2Cl2
(20 cm3) was stirred for 10 min and NEt3 (0.154 cm3, 1.104 mmol)
was then added. After 5 min, the orange–red mixture was
evaporated to a small volume in vacuo (ca. 5 cm3) before alumina
was added and the solvent removed. The resulting solid was
placed on a 25 cm long, alumina–n-hexane chromatography
column. Elution with CH2Cl2 : n-hexane (1 : 3) gave a red so-
lution of [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Rh(CO)2] and
4
0.085 mmol) in CH2Cl2 (10 cm3) was added [NBun ]I (0.030 g,
0.085 mmol). After stirring the mixture for 5 min, [Fe(g -
4
5
C5H5)2][PF6] (0.018 g, 0.085 mmol) was added. The brown solution
was stirred for 30 min, then filtered and concentrated in vacuo.
n-Hexane was added to precipitate a brown solid which was thor-
5
oughly washed with n-hexane to remove small quantities of [Fe(g -
C5H5)2]. The complex was purified by allowing a concentrated
CH2Cl2 solution to diffuse slowly into n-hexane to give red–brown
crystals, yield 68 mg (67%).
3
a yellow solution of [(g -C3H5)Pd(l-p-MeC6H4NNNC6H4Me-
3
p)2Pd(g -C3H5)] as minor products. Elution with CH2Cl2–n-
hexane (1 : 1) then gave an orange solution of [(OC)2Rh(l-p-
3
MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)] 2 as the major product.
Method b. To a yellow solution of [NBun ][(OC)IRh(l-
4
The volume of the orange solution was reduced in vacuo and the
precipitate formed was purified using CH2Cl2–n-hexane to give an
orange powder, yield 0.322 g (85%).
p-MeC6H4NNNC6H4Me-p)2Pd(g -C3H5)], [NBun ]+7− (0.091 g,
3
4
0.085 mmol) in CH2Cl2 (10 cm3) was added I2 (0.012 g,
0.085 mmol). The brown solution was stirred for 20 min and
then filtered and concentrated in vacuo. n-Hexane was added to
precipitate a brown solid which was purified using CH2Cl2–n-
hexane to give a red–brown powder, yield 64 mg (63%).
Complex 2 was prepared similarly.
[NBun ][(OC)IRh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g3-C3H5)]
4
[NBun ]+7−
4
The complex [NBun ][Br2Rh(l-p-MeC6H4NNNC6H4Me-p)2-
4
3
To an orange solution of [(OC)2Rh(l-p-MeC6H4NNNC6H4Me-
Pd(g -C3H5)], [NBun ]+10− was prepared by method (a), using
4
3
p)2Pd(g -C3H5)] 1 (0.105 g, 0.139 mmol) in CH2Cl2 (20 cm3)
[NBun ]Br, to give a brown powder.
4
1756 | Dalton Trans., 2006, 1749–1757
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
DFT calculations
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b514513a
The geometries of the model compounds were optimised as
unrestricted spin-doublets using B3LYP density functional theory
implemented by the programme Jaguar14 with the 6-31G* basis
set for non-metals and lacv3p for the metal atoms, providing the
spin density by atom.
Acknowledgements
We thank the EPSRC (R. A. B. and O. D. H.) and the Royal Thai
Government (P. K.) respectively for Postgraduate Scholarships.
Structure determinations of
[(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2Pd(g3-C3H5)] 1,
[(OC)2Rh(l-p-MeC6H4NNNC6H4Me-p)2PdCl(PPh3)]·CH2Cl2
References
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4
C3H5)]·0.19CH2Cl2 [NBun ]+9−·0.19CH2Cl2
4
Many of the details of the structure analyses of 1, 2·CH2Cl2 and
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4
were carried out by standard area detector methods.
In the structure of 9−, the central carbon atom C(4) of the allyl
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This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 1749–1757 | 1757
©