Synthesis of a series of ruthenium and rhodium complexes with tridentate pyridine-based ligands containing hydrogen bonding groups

Article abstract of DOI:10.1016/j.ica.2006.01.020

A series of ruthenium and rhodium complexes with a urea-disubstituted pyridine ligand are reported. The X-ray crystal structures of three of these species, RuCl₂(L¹)(PPh₃) (1), [Ru(MeCN)₂(L¹)(PPh₃)][BF₄]₂ (3) and Rh(CH₂Cl)Cl₂(L¹) (9) (where L¹ = N,N′-(2,2′-(1E,1′E)-(1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-ylidene)bis(ethane-2,1-diyl))diacetamide) have shown that the disubstituted pyridine acts as a tridentate ligand and its urea substituents engage in hydrogen bonding interactions with species coordinated to the metal centres. The reactivity of the ruthenium complexes towards coordination of other anions such as NCS^- has been investigated, as well as the oxidative-addition of alkyl chlorides to rhodium(I) centres (to yield species such as 9).

Full text of DOI:10.1016/j.ica.2006.01.020

Inorganica Chimica Acta 359 (2006) 3709–3722
www.elsevier.com/locate/ica
Synthesis of a series of ruthenium and rhodium complexes
with tridentate pyridine-based ligands containing hydrogen
bonding groups
a
a,b,c,
a
*, Andrew J.P. White
´
Hayley A. Burkill , Ramon Vilar
a
Department of Chemistry, Imperial College London, South Kensington, London SW7 2AZ, United Kingdom
Institute of Chemical Research of Catalonia (ICIQ), Avgda. Paı¨sos Catalanas 16, 43007 Tarragona, Spain
b
c
Institution of Research and Advanced Studies of Catalonia (ICREA), Barcelona, Spain
Received 23 November 2005; accepted 7 January 2006
Available online 28 February 2006
Dedicated to Prof. Mike Mingos in celebration of his major contributions to chemistry.
Abstract
A series of ruthenium and rhodium complexes with a urea–disubstituted pyridine ligand are reported. The X-ray crystal structures of
three of these species, RuCl2(L1)(PPh3) (1), [Ru(MeCN)2(L1)(PPh3)][BF4]2 (3) and Rh(CH2Cl)Cl2(L1) (9) (where L1 = N,N0-(2,20-
(1E,10E)-(1,10-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-ylidene)bis(ethane-2,1-diyl))diacetamide) have shown that the
disubstituted pyridine acts as a tridentate ligand and its urea substituents engage in hydrogen bonding interactions with species coordi-
nated to the metal centres. The reactivity of the ruthenium complexes towards coordination of other anions such as NCSꢀ has been
investigated, as well as the oxidative-addition of alkyl chlorides to rhodium(I) centres (to yield species such as 9).
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Rhodium compounds; Ruthenium compounds; Hydrogen bonding; X-ray crystal structures
1. Introduction
drase which uses zinc(II) centres and hydrogen bonding
groups to hydrolyse peptide bonds. The hydrogen bonding
interactions between metal complexes and substrates found
in enzymes have several functions including orientating the
substrates for optimal metal coordination, enhancing the
electrostatic interaction between the substrate and metal
ion and modulating the pKa at the active site.
Based on analogous principles to those employed by
metallo-enzymes, synthetic chemists have developed metal
complexes to study the role of hydrogen-bonding in the
activation of coordinated substrates. For example, Crab-
tree et al. have reported an unusual hydrogen-bonding
interaction present in an iridium complex with an amide
pendant group, leading to the activation of the Ir–H bond
for reactions such as isotope exchange, substitution and
cyclometallation [14,15]. A subsequent paper reported sim-
ilar interactions between the NH group of a 2-(aminophe-
nyl)pyridine group bound to the metal via the pyridine
Metal complexes with ligands containing hydrogen-
bonding groups are of increasing interest due to their poten-
tial applications in the design of molecular receptors [1–9]
and supramolecular catalysts [10–13]. In these systems the
metal centre provides unique structural, optical or catalytic
properties, while the hydrogen-bonding moieties can inter-
act via supramolecular forces with potential incoming
ligands modifying their reactivity or ‘‘sensing’’ their pres-
ence. The best examples of the important synergic role
played by metal coordination and hydrogen bonding for
the activation of substrates can be found in nature, namely
in metallo-enzymes. An examples of this is carbonic anhy-
*
Corresponding author. Tel.: +44 207594 1967; fax: +44 207594 1139.
E-mail address: r.vilar@imperial.ac.uk (R. Vilar).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.01.020

3710
H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
the carbon atoms are labelled with numbers (see Figs. 1
and 2). IR spectra were recorded on a Perkin–Elmer FT-
IR1720 Research Series Spectrometer using KBr discs over
the range 200–4000 cmꢀ1. Mass spectra were recorded at
Imperial College London by J. Barton using fast atom bom-
bardment methods on a VG AutoSpec-Q spectrometer. The
primary beam was 35 keV Cs+ and the matrix was 3-nitrob-
enzyl alcohol. Elemental analyses (C, H, N) were carried
out by S. Boyer at London Metropolitan University.
2.2. X-ray structure determination
Scheme 1. Synthesis of ligands L1 and L2.
Table 1 provides a summary of the crystallographic data
for compounds 1a, 1b, 3 and 9. Data were collected using
Oxford Diffraction PX Ultra (1a) and Siemens/Bruker P4
(1b, 3 and 9) diffractometers, and the structures were
refined based on F2 using the SHELXTL and SHELX-97 pro-
gram systems [20,21]. In the structures of 1a, 1b and 9, both
N–H protons were found from DF maps and refined sub-
nitrogen atom, and a hydride bound to the metal centre
[16]. Borovick on the other hand, has reported the activa-
tion of molecular oxygen by non-heme metal complexes
in which hydrogen bonds play an important role by inter-
acting with the coordinated O2 to be activated [17].
As part of our ongoing interest in developing metal-
complexes with hydrogen bonding units for sensing [2,6]
and catalysis [18], we have prepared several pyridine-based
ligands and studied their coordination chemistry [19].
Herein we report the preparation of L1 and L2 (see Scheme
1) and the synthesis of a series of ruthenium(II) and rho-
dium(I) complexes with these ligands.
˚
ject to an N–H distance constraint (0.90 A). In the struc-
ture of 3, whilst the N(11)–H proton was treated in this
fashion, the one on N(18) could not be located and so
was placed in an idealised position and refined with a riding
model with U = 1.5Ueq [N(18)]. CCDC 290189–290192
respectively.
The X-ray crystal structures of three of these complexes
have been obtained showing that the hydrogen bonding
groups (amide in L1 and urea in L2) can indeed interact
intramolecularly with molecules coordinated to the metal
centre. This could have some potential future applications
in the use of these complexes for catalysis.
2.3. Syntheses
2.3.1. N,N0-(2,20-(1E,10E)-(1,10-(pyridine-2,6-
diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-
ylidene)bis(ethane-2,1-diyl))diacetamide (L1)
The preparation of this ligand is based on a method pre-
viously reported by Martell et al. [22]. However, since the
full characterization of the compound was not reported
2. Experimental
2.1. General procedures
All reactions were carried out under an atmosphere of
dinitrogen using standard Schlenk line techniques unless
otherwise stated. Manipulations of air sensitive solids were
carried out in a glove box containing dinitrogen. Solvents
were dried using the appropriate drying agents, degassed
using purified, dry nitrogen and stored over molecular
sieves. Reactions involving silver compounds were carried
out with the exclusion of light. Commercially available
reagents (solids) were used as received without further puri-
fication unless otherwise stated, while liquid starting mate-
rials (including NMR solvents) were dried over molecular
sieves and degassed by freeze–pump–thaw prior to use
and subsequently stored under nitrogen. Nuclear magnetic
resonance spectra (1H, 31P{1H} and 13C{1H}) were
recorded on a JEOL JNM-EX270 (270.1, 109.38 and
67.94 MHz, respectively) or a Bruker AM-500 spectrome-
ter, with internal references of TMS, H2PO4 and TMS,
respectively. The labels of the NMR assignments are based
on those shown in the chemical structures of the ligands (see
below). The hydrogen atoms are labelled with letters while
Fig. 1. Numbering scheme for the NMR assignments of compounds
containing L1.
Fig. 2. Numbering scheme for the NMR assignments of compounds
containing L2.

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3711
Table 1
Crystal data, data collection and refinement parameters for compounds 1a, 1b, 3 and 9
Data
1a
1b
3
9
Formula
C35H40Cl2N5O2PRu
C35H40Cl2N5O2PRu [C39H46N7O2PRu](BF4)2 C18H27Cl3N5O2Rh
Solvent
2CHCl3
1004.40
1.75MeCN
1022.33
dark orange/red tablets
0.43 · 0.37 · 0.10
203
orthorhombic
Pbcn (no. 60)
16.585(5)
CH2Cl2
639.63
orange hexagonal needles
0.83 · 0.17 · 0.17
293
Formula weight
Colour, habit
Crystal size (mm)
Temperature (K)
Crystal system
Space group
765.66
v. dark orange/red needles deep red blocks
0.24 · 0.03 · 0.02
173
0.27 · 0.23 · 0.18
293
monoclinic
P21/c (no. 14)
15.2237(7)
9.9727(4)
22.9607(9)
92.670(3)
3482.1(3)
4
1.460
Cu Ka
5.802
142
orthorhombic
Pbca (no. 61)
12.6824(11)
18.6112(10)
37.519(5)
rhombohedral
ꢀ
R3 ðno. 148Þ
˚
a (A)
35.478(3)
˚
b (A)
21.164(3)
33.299(5)
˚
c (A)
11.619(2)
b (ꢁ)
3
˚
V (A )
8855.7(15)
8
1.507
Cu Ka
7.961
120
11688(4)
8
1.162
Mo Ka
0.358
45
12665(2)
18
1.510
Mo Ka
1.106
50
Z
Dc (g cmꢀ3
)
Radiation used
l (mmꢀ1
2hmax (ꢁ)
)
Number of unique reflections |Fo| > 4r(|Fo|)
Measured
6617
6549
7584
4555
Observed
6054
4149
3570
3133
Number of variables
R1, wR2
427
0.039, 0.094
463
0.059, 0.129
567
0.060, 0.117
332
0.051, 0.113
a
P
P
P
P
2
2
1=2
2
a
R1 ¼ jjF oj ꢀ jF cjj= jF oj; wR2 ¼ f ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF o2Þ ꢁg ; wꢀ1 ¼ r2ðF 2oÞ þ ðaPÞ þ bP.
3
in that paper, we provide it here. Yield 2.85 g, 70%. Ele-
mental analysis. Calc. for C17H25N5O2: C, 59.29; H, 7.06;
3JHH = 7.9 Hz), 8.11 (d, 2H, Hh, JHH = 7.67 Hz).
13C{1H} NMR dC (DMSO-d6): 166.57 (C3), 158.02 (C6),
155.43 (C8), 136.75 (C10), 121.00 (C9), 52.40 (C5), 40.37
(C4), 34.00 (C2), 15.56 (C7), 13.67 (C1). MS (FAB+) (m/
z): 390 {[M]+}.
N, 5.59. Found: C, 59.19; H, 7.13; N, 5.60%. IR (mmax
/
cmꢀ1, KBr): 3289 (N–H), 1650 (C@O), 1637 (C@N imine),
1
1562 (C@N pyridine). H NMR dH (CDCl3): 2.00 (s, 6H,
Ha), 2.40 (s, 6H, He), 3.62 (m, 8H, Hc, Hd), 6.09 (s (bd),
3
2H, Hb), 7.75 (t, 1H, Hg, JHH = 7.8 Hz), 8.09 (d, 2H,
2.3.3. RuCl2(L1)(PPh3) (1)
3
Hf, JHH = 7.9 Hz). 13C{1H} NMR dC (CDCl3): 170.37
To a mixture of L1 (1 g, 3.0 mmol) and RuCl2(PPh3)3
(2.97 g, 3.0 mmol) in a round-bottomed flask toluene
(50 ml) was added and the resulting brown suspension
refluxed under nitrogen with stirring for ca. 9 h. Upon
cooling, a dark brown-red solid precipitated from the solu-
tion. This was collected via filtration under nitrogen to
yield a red-brown solid which was dried under reduced
pressure and characterized as pure 1. Single crystals suit-
able for X-ray analysis were obtained from chloroform
and n-pentane. Yield 1.83 g, 80%. Elemental analysis. Calc.
for C35H40Cl2N5O2PRu: C, 54.91; H, 5.27; N, 9.15. Found:
C, 55.00; H, 5.34; N, 9.06%. IR (mmax/cmꢀ1, KBr): 3246
(N–H), 3053 (C–H), 2925, 1664 (C@O), 1649 (C@N imine),
1545 (C@N pyridine), 1434 (aryl, PPh3), 1365, 1287, 1093,
744, 699 (P-aryl, PPh3), 527. 1H NMR dH (CDCl3): 1.79 (s,
6H, He), 2.32 (s, 6H, Ha), 3.80 (m (bd), 4H, Hc, Hd), 4.04
(m, 2H, Hd), 4.26 (m, 2H, Hc), 6.83 (t, 2H, Hb), 7.13–
7.37 (m, 18H, aromatics). 13C{1H} NMR dC (CDCl3):
171.53 (C2), 170.63 (C5), 162.85 (C7), 131.13 (C9), 132.9–
128.0 (several signals corresponding to PPh3,
1JPC = 9.3 Hz), 123.61 (C8), 55.08 (C4), 39.60 (C3), 23.19
(C1), 15.68 (C6). 31P{1H} NMR dP (CDCl3): 35.9. MS
(FAB+) (m/z): 730 {M ꢀ Cl]+}, 468 {M ꢀ Cl ꢀ PPh3]+},
433 {[M ꢀ 2Cl ꢀ PPh3]+}.
(C2), 168.64 (C5), 155.77 (C7), 136.66 (C8), 121.29 (C9),
51.63 (C4), 40.41 (C3), 23.46 (C1), 14.48 (C6). MS
(FAB+) (m/z): 332 {[M]+}, 259 {[M ꢀ CH3CONHCH4]+}.
2.3.2. 1,10-(2,20-(1E,10E)-(1,10-(pyridine-2,6-
diyl)bis(ethan-1-yl-1-ylidene))bis(azan-1-yl-1-
ylidene)bis(ethane-2,1-diyl))bis(3-ethylurea) (L2)
2,6-Diacetylpyridine (1.918 g, 10 mmol) was dissolved in
the minimum amount of toluene and to this was added
H2NCH2CH2NH(@CO)NHEt (3.08 g, 20 mmol). The
resulting yellow solution was refluxed for ca. 2 h during
which time an off-white solid precipitated. After cooling,
the solid was collected by filtration and washed with diethyl
ether (3 · 25 ml), cold chloroform (3 · 25 ml) and diethyl
ether (3 · 25 ml), yielding an off-white solid. Yield
2.142 g, 55%. Elemental analysis. Calc. for: C19H31N7O2:
C, 58.59; H, 8.02; N, 25.17. Found: C, 58.39; H, 8.06; N,
25.13%. IR (mmax/cmꢀ1, KBr): 3327 (amide N–H), 2970
(C–H), 2928 (C–H), 2885 (C–H), 1629 (C@O and C@N
1
imine), 1579 (C@N pyridine). H NMR dH (DMSO-d6):
3
0.96 (t, 6H, Ha, JHH = 2.18 Hz), 2.34 (s, 6H, Hg), 2.99
(m, 4H, Hb), 3.34 (s (bd), He), 3.51 (t, 4H, Hf,
3JHH = 5.94 Hz), 5.91 (m, 4H, Hc, Hd), 7.87 (t, 1H, Hi,

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H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
2.3.4. RuCl2(L2)(PPh3) (2)
The solution was then filtered through a filter stick of celite
to remove AgCl, the volume reduced to ca. 3 ml under
reduced pressure and a dark brown solid was precipitated
with diethyl ether and characterized as 4. Yield 0.045 g,
75%. Elemental analysis. Calc. for [C41H52N9O2-
PRu][BF4]2: C, 48.83; H, 5.20; N, 12.50. Found: C, 48.73;
H, 5.09; N, 12.41%. IR (mmax/cmꢀ1, KBr): 3417 (amide
N–H), 2972 (C–H), 2933 (C–H), 2875 (C–H), 2360 (wk,
CN (CH3CN)), 1647 (bd, C@O), 1554 (C@N, imine and
pyridine), 1435 (aryl, PPh3), 1084 (BF4), 1036 (BF4), 750,
700, 530. 1H NMR dH (CD3CN): 1.06 (t, 6H, Ha,
3JHH = 7.1 Hz), 2.32 (s, 6H, Hg), 2.78 (s, 3H, CH3CN),
3.04 (m, 2H, Hb), 3.13 (m, 4H, Hf), 3.57 (m, 2H, Hb),
3.75 (m, 4H, He), 5.04, and 5.08 (dt, 4H, Hc, Hd,
3JHH = 5.6 Hz), 7.12–7.48 (m, 15H, PPh3), 7.76 (d, 2H,
Hh, JHH = 8.1 Hz), 7.93 (t, 1H, Hi, JHH = 8.1 Hz).
13C{1H} NMR dC (CD3CN): 177.14 (C3), 160.64 (C6),
158.97 (C8), 136.92 (CH3CN), 132.87–127.97 (PPh3,
1JPC = 10.7 Hz), 130.54 (C10), 127.51 (C9), 77.31–76.68
(CD3CN), 58.51 (C5), 39.75 (C4), 35.57 (C2), 16.66 (C7),
15.92 (C1), 5.10 (CH3CN). 31P{1H} NMR dP (CD3CN):
42.66. MS (FAB+) (m/z): 921, {[M–(BF4)]+}; 881,
{[M ꢀ (CH3CN) ꢀ (BF4)]+}; 752, {[M ꢀ (CH3CN)2 ꢀ
(BF4)2]+}; 491, {[M ꢀ (CH3CN)2 ꢀ (BF4)2 ꢀ (PPh3)]+}.
This complex was prepared and isolated by an analo-
gous procedure described for 1 using L2 (1.0 g, 2.57 mmol)
and RuCl2(PPh3)3 (2.52 g, 2.57 mmol). Yield 1.74 g, 82%.
Elemental analysis. Calc. for C37H46Cl2N7O2PRu: C,
53.95; H, 5.63; N, 11.90. Found: C, 54.13; H, 5.53; N,
12.14%. IR (mmax/cmꢀ1, KBr): 3057 (amide N–H), 2966
(C–H), 2927 (C–H), 2870 (C–H), 1687 (C@O), 1644
(C@N imine), 1562 (C@N pyridine), 1481, 1431 (aryl,
1
PPh3), 1247, 1092, 751, 699. H NMR dH (CDCl3): 1.00
3
(t, 6H, Ha, JHH = 8.8 Hz), 2.34 (s, 6H, Hg), 3.03 (m
(bd), 4H, Hb), 3.80 (m, 4H, He), 4.05 (m, 4H, Hf), 4.44
(s, (bd), 2H, Hc), 5.55 (m (bd), 2H,Hd), 7.15–7.69 (m,
20H, Hh, Hi, PPh3). 13C{1H} NMR dC (CDCl3): 171.60
(C3), 162.98 (C6), 158.33 (C8), 132.87–127.97 (PPh3,
1JPC = 9.2 Hz), 128.71 (C10), 123.37 (C9), 55.98 (C5),
40.16 (C4), 35.31 (C2), 15.64 (C7), 15.48 (C1). 31P{1H}
NMR dP (CDCl3): 36.24. MS (FAB+) (m/z): 762
{[LRuPPh3Cl]+}, 725 {[LRuPPh3]+}.
3
3
2.3.5. [Ru(L1)(PPh3)(CH3CN)2][BF4]2 (3)
To a solution of 1 (0.054 g, 0.07 mmol) in acetonitrile
(20 ml) AgBF4 (0.034 g, 0.16 mmol) was added as a solid
and the suspension stirred under nitrogen for ca. 30 min
with exclusion of light. The solution was then filtered
through a filter stick of dry celite to remove AgCl; the vol-
ume was then reduced under reduced pressure and a yel-
low-brown solid was obtained by precipitation with
diethyl ether and characterised as pure 3. The product
was further purified by recrystallisation from acetonitrile
and diethyl ether. Single crystals suitable for X-ray crystal-
lographic analysis were obtained from a mixture of aceto-
nitrile/diethyl ether. Yield 0.069 g, 96%. Elemental
analysis. Calc. for [C39H46N7O2PRu][BF4]2 Æ 1.75CH3CN:
C, 49.93; H, 11.99; N, 5.05. Found: C, 50.06; H, 11.82;
N, 4.96%. IR (mmax/cmꢀ1, KBr): 3412 (bd, N–H), 3061
(C–H), 2984 (C–H), 2288 (wk, CN (CH3CN)), 1659 (bd,
C@O stretch + C@N stretch imine), 1542 (bd, C@N pyri-
dine), 1435 (aryl, PPh3), 1061 (bd, BF4ꢀ), 750 (md), 701
(aryl, PPh3). 1H NMR dH (CD3CN): 1.90 (s, 6H, He),
2.33 (s, 6H, Ha), 2.79 (s, 3H, CH3CN), 3.04 (m, 2H, Hc),
3.55 (m, 2H, Hd), 3.85–3.66 (m, 2H, Hc, Hd), 6.55 (t, 2H,
Hb), 7.10–7.48 (m, 15H, PPh3), 7.77 (d, 2H, Hf,
2.3.7. Ru(L1)(PPh3)(NCS)2 (5)
To a solution of 1 (0.07 g, 0.091 mmol) in dichlorometh-
ane (20 ml) AgBF4 (0.036 g, 0.18 mmol) was added as a
solid and the solution stirred under nitrogen for ca.
30 min with exclusion of light. The solution was then fil-
tered through a filter stick of dry celite to remove AgCl,
and to the filtered solution was added KSCN (0.027 g,
0.27 mmol) as a solid. The solution was stirred for 3 days
under nitrogen, filtered and the volume reduced to 5 ml
under reduced pressure. Addition of diethyl ether precipi-
tated a red solid, which was washed with distilled water
(3 · 10 ml) to remove unreacted KSCN and dried under
reduced pressure. Yield 0.0741 g, 99%. Elemental analysis.
Calc. for [C37H49N7O2PS2Ru] Æ 0.5(CH2Cl2): C, 52.78; H,
4.84; N, 11.49. Found: C, 52.69; H, 4.26; N, 11.06%. IR
(mmax/cmꢀ1, KBr): 3413 (bd, N–H), 3058 (C–H), 2920 (C–
H), 2094 (CN), 1663 (bd, C@O), 1523 (C@N imine),
1433 (aryl, PPh3), 1281, 1090, 804 (CS), 700 (P-aryl,
3JHH = 8.0 Hz), 7.94 (t, 1H, Hg, JHH = 8.0 Hz). 13C{1H}
PPh3), 528. H NMR dH (CDCl3): 1.95 (s, 6H, He), 2.29
3
1
NMR dC (CD3CN): 176.61 (C2), 170.45 (C5), 159.66
(s, 6H, Ha), 3.41, 3.84 and 4.15 (each m, 8H, Hc, Hd),
6.61 (t (bd), 2H, Hb), 7.06–7.74 (m, 18H, PPh3, Hg, Hf).
13C{1H} NMR dC (CDCl3): 172.09 (C2), 171.62 (C5),
161.73 (C7), 141.62 (NCS), 131.23 (C9), 134.06–124.13
(C7),
136.07
(CH3CN),
132.90–128.85
(PPh3,
1JPC = 9.8 Hz), 129.62 (C9), 126.74 (C8), 56.52 (C4),
37.92 (C3), 22.09 (C1), 15.75 (C6), 4.52 (CH3CN).
31P{1H} NMR dP (CD3CN): 42.40. MS (FAB+) (m/z):
864, {[M ꢀ (BF4)]+}; 823, [M ꢀ (CH3CN) ꢀ (BF4)]+; 735,
1
(PPh3, JPC = 10.2 Hz), 124.13 (C8), 55.99 (C4), 39.66
(C3), 23.24 (C1), 15.42 (C6) (assignment of 13C{1H} signals
was confirmed by recorded 13C DEPT). 31P{1H} NMR dP
(CDCl3): 39.67. MS (FAB+) (m/z): 811, {[M]+}; 753,
{[M ꢀ (NCS)]+}; 491, {[M ꢀ (NCS) ꢀ PPh3]+}.
[M ꢀ (CH3CN) ꢀ 2(BF4)]+;
694,
[M ꢀ 2(CH3CN) ꢀ
2(BF4)]+; 433, [M ꢀ 2(CH3CN) ꢀ 2(BF4) ꢀ (PPh3)]+.
2.3.6. [Ru(L2)(PPh3)(CH3CN)2][BF4]2 (4)
To a solution of 2 (0.049 g, 0.06 mmol) in acetonitrile
(15 ml) AgBF4 (0.03 g, 0.15 mmol) was added as a solid
and the suspension stirred under nitrogen for ca. 72 h.
2.3.8. Ru(L2)(PPh3)(NCS)2 (6)
To a solution of 2 (0.051 g, 0.06 mmol) in dichlorometh-
ane (15 ml) AgBF4 (0.03 g, 0.156 mmol) was added as a

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3713
solid and the solution stirred under nitrogen for ca.
30 mins. The solution was then filtered through a filter stick
of celite to remove AgCl, and KSCN (0.018 g, 0.187 mmol)
was added as a solid. The solution was stirred under nitro-
gen for ca. 4 days during which time the solution became
redder in colour. The solution was then filtered to remove
excess KSCN and the volume reduced to ca. 3 ml under
reduced pressure. The reddish solid was obtained by pre-
cipitation with diethyl ether and washed with distilled
water (3 · 10 ml) until no further KSCN could be detected
by IR spectroscopy. Yield 0.08 g, 64%. Elemental analysis.
Calc. for [C39H46N9O2PRuS2]: C, 53.90; H, 5.34; N, 14.51.
Found: C, 53.86; H, 5.38; N, 14.59%. IR (mmax/cmꢀ1, KBr):
3404 (bd, N–H), 2970 (C–H), 2924 (C–H), 2094 (CN), 1643
(bd, C@O), 1549 (C@N imine), 1433 (aryl, PPh3), 1253,
carried out in a glove box due to the air-sensitivity of the
rhodium(I) complex. Elemental analysis. Calc. for
C19H31ClN7O2Rh: C, 43.23; H, 5.92; N, 18.57. Found: C,
42.94; H, 5.69; N, 18.32%. IR (mmax/cmꢀ1, KBr): 3353
(N–H), 2971 (C–H), 2935 (C–H), 2877 (C–H), 1641
(C@O and C@N (imine)), 1564 (C@N stretch (pyridine)),
1433, 1378, 1263, 1092, 614, 542. MS (FAB+) (m/z): 492,
{[M]+}.
2.3.11. Rh(CH2Cl)Cl2(L1) (9)
A small amount of complex 7 was dissolved in CH2Cl2
(10 ml) and the solution put into an autoclave anaerobi-
cally. The solution was pressurised with carbon dioxide
(12 atm) and left with no stirring for ca. 36 h. Upon
removal of the solution from the vessel a large number of
red-brown crystals suitable for X-ray crystallographic anal-
ysis were found. The same product was obtained when the
rhodium(I) complex 7 was dissolved in CH2Cl2 under
nitrogen and left stirring for 4 days. Elemental analysis.
Calc. for C18H27Cl3N5O2Rh Æ 0.75CH2Cl2: C, 36.42; H,
4.65; N, 11.32. Found: C, 36.63; H, 4.51; N, 11.48%. IR
(mmax/cmꢀ1, KBr): 3356 (N–H), 3065 (C–H), 2946, 1668
(C@O and C@N imine), 1578 (C@N stretch (pyridine)),
1
1091, 802 (CS), 748, 698 (P-aryl, PPh3), 528. H NMR
3
dH (CD2Cl2): 1.03 (t, 6H, Ha, JHH = 7.2 Hz), 2.30 (s,
6H, Hg), 3.10 (m (unresolved), 4H, Hb), 3.42, 3.72 and
4.07 (each m, 8H, He, Hf), 4.75 (s (bd), 2H, Hc), 5.18 (s
(bd), 2H, Hd), 7.10–7.39 (m, 15H, PPh3), 7.56 (d, 2H, Hh,
3
3JHH = 8.0 Hz), 7.71 (t, 1H, Hi, JHH = 8.0 Hz). 13C{1H}
NMR dC (CD2Cl2): 173.22 (C3), 161.89 (C6), 158.57
(C8), 141.36 (NCS), 132.17 (C10), 133.39–128.84 (PPh3,
1JPC = 8.1 Hz), 124.86 (C9), 57.40 (C5), 40.27 (C4), 35.47
(C2), 15.85 (C1 and C7). 31P{1H} NMR dP (CD2Cl2):
40.58. MS (FAB+) (m/z): 869, {[M]+}; 811, {[M ꢀ
(NCS)]+}; 549 {[M ꢀ (NCS) ꢀ (PPh3)]+}.
1
1516, 1426, 1374, 1275, 735, 674. H NMR dH (DMSO-
d6): 1.80 (s, 6H, He), 2.67 (s, 6H, Ha), 3.50 and 3.60 (each
m, 4H, Hc), 3.90 and 4.03 (m, 4H, Hd), 4.26 (d, 2H, Hh,
3
3JRh–H = 3.07 Hz), 7.79 (t, 2H, Hb, JHH = 5.7 Hz), 8.30–
8.39 (m, 3H, Hf, Hg). 13C{1H} NMR dC (DMSO-d6):
176.04 (C2), 169.84 (C5), 155.72 (C7), 138.68 (C9), 127.44
(C8), 53.23 (C4), 41.15 (C10), 37.99 (C5), 22.73 (C1),
16.01 (C6). MS (FAB+) (m/z): 518, {[M ꢀ Cl]+}; 504,
{[M ꢀ CH2Cl]+}; 434, {[M ꢀ CH2Cl ꢀ 2Cl]+}.
2.3.9. RhCl(L1) (7)
[Rh(COD)Cl]2 (0.099 g, 0.3 mmol) was dissolved in tol-
uene (20 ml) and to the resulting solution ligand L1
(0.073 g, 0.15 mmol) was added as a solid. The solution
was heated to reflux for 30 min, it was then allowed to cool
down to room temperature and a dark green solid precip-
itated. The air sensitive solid was washed with diethyl ether
(2 · 15 ml) and dried thoroughly under reduced pressure.
Elemental analysis. Calc. for C17H25ClN5O2Rh Æ
0.75CH2Cl2: C, 39.96; H, 5.01; N, 13.13. Found: C,
39.54; H, 5.01; N, 13.00%. IR (mmax/cmꢀ1, KBr): 3432
(bd, N–H), 3073 (C–H), 1640 (bd, C@O and C@N imine),
1549 (C@N pyridine), 1431, 1375, 1278, 1085. 1H NMR dH
(CD2Cl2): 1.81 (s, 6H, He), 2.54 (s, 6H, Ha), 3.65–4.35 (4
signals each m, 8H, Hc,d), 6.84, (t (bd, unresolved), 2H,
2.4. Rh(CH2Cl)Cl2(L2) (10)
Ligand L2 (0.071 g, 0.18 mmol) was dissolved in dichlo-
romethane (25 ml) and to this was added [Rh(COD)Cl]2
(0.045 g, 0.09 mmol) as a solid. The solution was heated
to reflux under nitrogen for 30 min, during which time no
clear colour change was observed. The solution was then
allowed to cool down to room temperature and was stirred
for a further 90 min, during which time its colour changed
from dark green to yellow and a yellow precipitate formed.
This solid was collected by filtration, washed with diethyl
ether (2 · 15 ml) and dried thoroughly under reduced pres-
sure. Yield 0.077 g, 70%. Elemental analysis. Calc. for
[C20H33Cl3N7O2Rh]: C, 37.58; H, 5.23; N, 14.96. Found:
C, 39.29; H, 5.34; N, 15.90%. IR (mmax/cmꢀ1, KBr): 3329
(N–H), 3068 (C–H), 2972 (C–H), 2929 (C–H), 2873
(C–H), 1649 (C@O and C@N (imine)), 1549 (C@N stretch
(pyridine)), 1490, 1425, 1275, 1149, 1090, 817, 669. 1H
3
Hb), 7.88 (d, 2H, Hf, JHH = 8.1 Hz), 8.18 (t, 1H, Hg,
3JHH = 8.1 Hz). MS (FAB+) (m/z): 469, {[M]+}; 434,
{[M ꢀ Cl]+}.
2.3.10. RhCl(L2) (8)
[Rh(COD)Cl]2 (0.052 g, 0.11 mmol) was dissolved in tol-
uene (10 ml), and added to a suspension of ligand L2
(0.0824 g, 0.21 mmol) in toluene (15 ml). The yellow sus-
pension was heated to reflux under argon for 30 min, dur-
ing which time the colour of the solution changed to dark
green. The solution was cooled down to room temperature
and a dark green solid precipitated. The air sensitive solid
was washed with diethyl ether (2 · 15 ml) and dried under a
vigorous stream of argon. All further manipulations were
3
NMR dH (CDCl3): 1.06 (t, 6H, Ha, JHH = 7.2 Hz), 2.62
(s, 6H, Hg), 3.11 (m (unresolved), 4H, Hb), 3.84, 4.09 and
4.30 (each m, 8H, He, Hf), 4.36 (d, 2H, Hj,
3JRh–H = 3.2 Hz), 5.62 (s (bd), 2H, Hd), 7.84 (d, 2H, Hh,
3
3JHH = 8.1 Hz), 8.14 (t, 1H, Hi, JHH = 8.1 Hz). 1H
3
NMR dH (DMSO-d6): 0.98 (t, 6H, Ha, JHH = 7.2 Hz),

3714
H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
2.61 (s, 6H, Hg), 2.99 (m (unresolved), 4H, Hb), 3.54,
3.70, 3.88 and 4.05 (each m, 8H, He, Hf), 4.24 (d, 2H, Hj,
3JRh–H = 3.2 Hz), 5.64 (t (bd), 2H, Hc), 6.24 (t (bd), 2H,
Hc), 8.34 (m (bd, unresolved), 3H, Hh, Hi). 13C{1H}
NMR dC (DMSO-d6): 175.04 (C3), 157.92 (C6), 155.85
(C8), 138.58 (C10), 127.07 (C9), 54.27 (C5), 40.86 (C11),
40.42–38.58 (C4 and DMSO-d6), 34.08 (C2), 15.69 (C7),
15.58 (C1). MS (FAB+) (m/z): 576, {[M ꢀ Cl]+}.
4H, Hb), 3.72, 4.05 and 4.18 (each m, 8H, He, Hf), 4.05
2
(d, 1H, Hl, JHH = 16.8 Hz), 4.51 (s (bd), 2H, Hc), 4.66
2
3
(dd, 1H, Hm, JHH = 9.9 Hz, JHH = 2.4 Hz), 5.31 (m
(unresolved), 1H, Hk), 5.69 (s (bd), 2H, Hd), 7.83 (d, 2H,
3
3
Hh, JHH = 8.1 Hz), 8.08 (t, 1H, Hi, JHH = 8.1 Hz).
13C{1H} NMR dC (CD2Cl2): 173.83 (C3), 158.50 (C6),
157.12 (C8), 143.21 (C12), 137.21 (C10), 126.12 (C9),
111.37 (C13), 55.71 (C5), 39.88 (C4), 35.53 (C2), 26.23
1
(C11, JRhC = 18 Hz), 16.59 (C7), 15.79 (C1). MS
2.4.1. Rh(CH2CH@CH2)Cl2(L1)(11)
(FAB+) (m/z): 603, {[M+]}; 568, {[M ꢀ Cl]+}, 527,
{[M ꢀ Cl ꢀ (CH2CHCH2)]+}; 492, {[M ꢀ 2(Cl) ꢀ (CH2-
CHCH2)+}.
Ligand L1 (0.076 g, 0.22 mmol) was dissolved in toluene
(15 ml) and to this was added [Rh(COD)Cl]2 (0.056 g,
0.11 mmol) as a solid, followed by allyl chloride (0.05 ml,
0.6 mmol) and the solution heated to reflux under nitrogen
for 30 min. During this time the colour of the solution
changed from dark green to orange. The solution was then
allowed to cool down to room temperature upon which a
bright orange solid precipitated. This solid was washed
with diethyl ether (2 · 15 ml) and dried thoroughly under
reduced pressure. Yield 0.038 g, 63%. Elemental analysis.
Calc. for C20H30Cl2N5O2Rh: C, 43.97; H, 5.54; N, 12.82.
2.5. Rh(CH2CN)Cl2(L1) (13)
Ligand L1 (0.075 g, 0.23 mmol) was dissolved in toluene
(15 ml) and to this was added [Rh(COD)Cl]2 (0.055 g,
0.12 mmol) as a solid and chloroacetonitrile (0.014 ml,
0.23 mmol). The solution was heated to reflux under nitro-
gen for 30 min, during which time a yellow precipitate
formed. The solution was then allowed to cool to room
temperature and the yellow product was collected by filtra-
tion. The solid was washed with diethyl ether (2 · 15 ml)
and dried thoroughly under reduced pressure. Yield
0.74 g, 60%. Elemental analysis. Calc. for C19H27-
Cl2N6O2Rh ꢀ 0.33(CH2Cl2): C, 40.48; H, 4.86; N, 14.65.
Found: C, 44.17; H, 4.37; N, 12.99%. IR (mmax/cmꢀ1
,
KBr): 3361 (N–H), 3059 (C–H), 2956 (C–H), 2924 (C–
H), 1655 (C@O and C@N (imine)), 1523 (C@N stretch
(pyridine)), 1427, 1373, 1281, 1107, 821, 586. 1H NMR
dH (CDCl3): 1.88 (s, 6H, He), 2.57 (s, 6H, Ha), 2.64 (dd,
3
3
2H, Hh, JHH = 8.62 Hz, JRh–H = 3.01 Hz), 3.91, 4.09
Found: C, 40.81; H, 4.44; N, 14.30%. IR (mmax/cmꢀ1
,
and 4.26, (each m (unresolved), 8H, Hc, Hd), 4.46 (d, 1H,
KBr): 3370 (N–H), 3288 (N–H), 3073 (C–H), 2948
(C–H), 2209 (CN), 1648 (C@O), 1543 (C@N (imine)),
1519 (C@N stretch (pyridine)), 1432, 1366, 1274, 1106,
2
2
Hj, JHH = 17.0 Hz), 4.67 (dd, 1H, Hk, JHH = 9.9 Hz,
3
3JHH = 2.2 Hz), 5.34 (m, 1H, Hi, JHH = 8.9 Hz), 7.26 (t
3
1
(bd), 2H, Hb), 7.85 (d, 2H, Hf, JHH = 8.0 Hz), 8.10 (t,
808, 746. H NMR dH (CDCl3): 1.62 (s, 6H, He), 2.10 (d,
3
3
1H, Hg, JHH = 8.0 Hz). 13C{1H} NMR dC (CDCl3):
2H, Hh, JRh–H = 3.46 Hz), 2.68 (s, 6H, Ha), 3.89, 4.05,
172.84 (C2), 170.88 (C5), 156.75 (C7), 142.66 (C11),
136.74 (C9), 125.67 (C8), 111.40 (C12), 53.79 (C4), 39.15
(C3), 26.95 (C10), 23.22 (C1), 16.36 (C6). MS (FAB+)
(m/z): 510, {[M]+}; 469, {[M ꢀ (CH2CHCH2) ꢀ Cl]+},
434, {[M ꢀ (CH2CHCH2) ꢀ 2(Cl)]+}.
4.14 and 4.31 (each m (unresolved), 8H, Hc, Hd), 6.72 (t
3
(bd), 2H, Hb), 7.98 (d, 2H, Hf, JHH = 8.2 Hz), 8.21 (t,
3
1H, Hg, JHH = 8.2 Hz). 13C{1H} NMR dC (CDCl3):
175.25 (C2), 170.91 (C5), 156.41 (C7), 138.35 (C9), 126.78
(C8), 124.05 (C11), 54.25 (C4), 39.09 (C3), 25.48 (C10),
23.19 (C1), 16.66 (C6). MS (FAB+) (m/z): 509, {[M]+}.
2.4.2. Rh(CH2CH@CH2)Cl2(L2) (12)
Ligand L2 (0.092 g, 0.23 mmol) was dissolved in toluene
(15 ml) and to this was added [Rh(COD)Cl]2 (0.058 g,
2.5.1. Rh(CH2CN)Cl2(L2) (14)
Ligand L2 (0.044 g, 0.11 mmol) was dissolved in toluene
(15 ml) and to this was added [Rh(COD)Cl]2 (0.028 g,
0.056 mmol) as a solid, followed by chloroacetonitrile
(0.0085 g, 0.12 mmol). The solution was heated to reflux
under nitrogen for 30 min, during which time an orange pre-
cipitate formed. The solution was then allowed to cool down
to room temperature and the resulting solid was collected by
filtration. The product was washed with diethyl ether
(2 · 15 ml) and dried thoroughly under reduced pressure.
Yield 0.057 g, 86%. Elemental analysis. Calc. for
[C21H33Cl2N8O2Rh] ꢀ 0.5(CH2Cl2): C, 39.99; H, 5.31; N,
0.12 mmol) as
a solid, followed by allyl chloride
(0.001 ml, 0.12 mmol). The solution was heated to reflux
under nitrogen for 30 min, during which time an orange
precipitate formed. The solution was then allowed to cool
down to room temperature and the orange solid was col-
lected by filtration. The solid was washed with diethyl ether
(2 · 15 ml) and dried thoroughly under reduced pressure.
Yield 0.066 g, 92%. Elemental analysis. Calc. for
[C22H36Cl2N7O2Rh]: C, 43.72; H, 6.00; N, 16.22. Found:
C, 43.66; H, 5.98; N, 16.11%. IR (mmax/cmꢀ1, KBr): 3346
(N–H), 3292 (N–H), 3066 (C–H), 2976 (C–H), 2935 (C–
H), 2875 (C–H), 1653 (C@O and C@N (imine)), 1549
(C@N stretch (pyridine)), 1500, 1425, 1273, 1252, 1151,
17.35. Found: C, 40.37; H, 5.00; N, 17.16%. IR (mmax
/
cmꢀ1, KBr): 3342 (N–H), 3078 (N–H), 2969 (C–H), 2933
(C–H), 2870 (C–H), 2202 (C„N), 1633 (C@O and C@N
(imine)), 1566 (C@N stretch (pyridine)), 1435, 1377, 1260,
1093, 812. 1H NMR dH (CDCl3): 1.07 (t, 6H, Ha,
1
1090, 810, 634. H NMR dH (CD2Cl2): 1.03 (t, 6H, Ha,
3JHH = 7.2 Hz), 2.56 (s, 6H, Hg), 2.63 (dd, 2H, Hj,
3
3
3JHH = 7.9 Hz, JRh–H = 2.9 Hz), 3.08 (m (unresolved),
3JHH = 7.2 Hz), 2.11 (d, 2H, Hj, JRh–H = 3.5 Hz), 2.69 (s,

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3715
6H, Hg), 3.11 (q, 4H, Hb, 3JHH = 7.0 Hz), 3.84, 4.07 and 4.32
(each m, 8H, He, Hf), 5.46 (s (bd), 2H, Hc), 7.95 (d, 2H, Hh,
3
1
3JHH = 8.0 Hz), 8.19 (t, 1H, Hi, JHH = 8.0 Hz). H NMR
3
dH (DMSO-d6): 0.98 (t, 6H, Ha, JHH = 7.0 Hz), 1.89 (d,
2H, Hj, 3JRh–H = 3.2 Hz), 2.66 (s, 6H, Hg), 3.00 (m (bd, unre-
solved), 4H, Hb), 3.56, 3.68, 3.89 and 4.08 (each m, 8H, He,
Hf), 5.64 (t (bd, unresolved), 2H, Hc), 6.21 (t (bd, unre-
solved), 2H, Hc), 8.39 (s (bd), 3H, Hh, Hi). 13C{1H} NMR
dC (DMSO-d6): 175.78 (C3), 157.97 (C6), 155.98 (C8),
138.78 (C10), 127.61 (C9), 124.92 (C12), 54.82 (C11,
1JRhC = 18 Hz), 54.43 (C5), 40.42–39.19 (C4 and DMSO-
d6), 34.08 (C2), 16.15 (C7), 15.59 (C1) MS (FAB+) (m/z):
603, {[M]+}; 567, {[M ꢀ Cl]+}; 527, {[M ꢀ Cl ꢀ
(CH2CN)]+}; 492, {[M ꢀ 2(Cl) ꢀ (CH2CN)]+}.
3. Results and discussion
3.1. Synthesis of hydrogen bonding pyridine-imine ligands L1
and L2
Ligands L1 and L2 were prepared by small modifications
of the procedure previously reported by Martell et al. (see
Scheme 1) [22]. 2,6-Diacetylpyridine was heated to reflux in
toluene with the corresponding substituted amine [in our
case N-acetyl-ethylenediamine for L1 and N-(2-amino-
ethyl)-N-ethylethene-1,1-diamine for L2] during 3 h. Upon
cooling the reaction mixture, the corresponding disubsti-
tuted pyridines (either L1 or L2) precipitate as white solids.
Both ligands were characterised by 1H and 13C NMR spec-
troscopy, FAB(+) mass spectrometry and IR spectroscopy.
Their formulations were confirmed by elemental analyses.
Scheme 2. Schematic representation of the reactions studied for the
ruthenium compounds.
and pyridine). The spectrum of complex 2 exhibits the N–H
stretch at 3057 cmꢀ1, the carbonyl stretch at 1687 cmꢀ1
,
with the imine and pyridine C@N bands occurring at
1644 and 1562 cmꢀ1. The elemental analyses of crystalline
and non-crystalline samples of both red-brown compounds
are consistent with the above formulation. The 1H and
13C{1H} NMR spectra of both complexes are consistent
with the proposed formulation.
3.2. Synthesis of cis-Ru(Ln)(PPh3)(Cl)2 and cis-
[Ru(Ln)(PPh3)(CH3CN)2][BF4]2
In order to unambiguously determine the structure of
these complexes and to establish whether the amide pro-
tons are involved in any hydrogen bonding interactions,
two different sets of single crystals of 1 suitable for X-ray
crystallographic analysis were obtained from dichloro-
methane/diethyl ether (crystals 1a) and chloroform/pen-
tane (1b). The solid state structure of 1a (Fig. 3) revealed
L1 coordinating to the ruthenium centre in the expected tri-
dentate N,N0,N0 0 fashion using the pyridyl and both of the
imino nitrogen atoms. The geometry at the ruthenium cen-
tre is distorted octahedral with cis angles in the range
79.10(10)–102.80(7)ꢁ (Table 2), the two most acute angles
being associated with the bites of the two five-membered
N,N0 chelate rings; the N(7)–Ru–N(14) trans angle is
158.16(10)ꢁ. The equatorial plane formed by the tridentate
bis(imino)pyridyl ligand and Cl(2) is noticeably distorted,
The two ruthenium complexes Ru(L1)Cl2(PPh3) (1) and
Ru(L2)Cl2(PPh3) (2) were prepared by the reaction of
RuCl2(PPh3)3 in toluene with the corresponding ligand
under reflux for approximately 9 h (see Scheme 2). Upon
cooling, a red-brown solid was obtained in each case, col-
lected by filtration and dried under reduced pressure to
yield pure samples of 1 and 2 in 80% and 82% yields,
respectively.
The 31P{1H} NMR spectra of the complexes show a sin-
glet at 35.9 ppm for 1 and 36.2 ppm for 2 which is consis-
tent with the proposed formulation (where only one
phosphine is coordinated to the metal centre). These chem-
ical shifts are within the range observed for other ruthe-
nium complexes containing a tridentate pyridine-diimine
ligand and triphenylphosphine. The highest molecular
weight peaks in the FAB(+) mass spectra of 1 and 2 are
those corresponding to the loss of one chloride from the
corresponding complex (at 730 and 762 a.m.u. for 1 and
2, respectively). The IR spectrum of 1 shows a broad band
centred at ca. 3246 cmꢀ1 (NH groups on L1), one strong
signal at 1664 (C@O of the amide), two peaks at 1649
and 1545 cmꢀ1 (assigned to the C@N groups of the imines
˚
Cl(2) lying ca. 0.38 A out of the {Ru,N(1),N(7),N(14)}
˚
plane (which is coplanar to within ca. 0.02 A) in the direc-
tion of Cl(1). The central pyridyl ring of the tridentate
ligand is inclined by ca. 9ꢁ to this plane. The N(1)/N(7)
five-membered chelate ring has an envelope geometry with
˚
the metal lying ca. 0.18 A out of the {N(1),C(2),C(7),N(7)}
˚
plane (which is coplanar to better than 0.01 A). The
N(1)/N(14) chelate ring, by contrast, is flat, all five atoms
˚
being coplanar to within ca. 0.01 A. As is usual for

3716
H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
˚
Fig. 3. The molecular structure of 1a. The geometries of the N–Hꢂ ꢂ ꢂX contacts [Nꢂ ꢂ ꢂX, Hꢂ ꢂ ꢂX (A), N–Hꢂ ꢂ ꢂX (ꢁ)] are (a) X = Cl, 3.293(3), 2.40, 176;
(b) X = O, 2.863(4), 1.96, 176.
Table 2
˚
Comparative selected bond lengths (A) and angles (ꢁ) for complexes 1a, 1b, 3 and 9
1aa
1ba
3b
9c
M–Ax(1)
M–Ax(2)
M–Eq
M–N(1)
M–N(7)
M–N(14)
N(1)–C(2)
C(2)–C(7)
C(7)–N(7)
N(1)–C(6)
C(6)–C(14)
C(14)–N(14)
2.4735(7)
2.4820(17)
2.086(6)
2.335(2)
2.069(6)
1.960(5)
2.096(6)
2.081(6)
1.356(10)
1.454(11)
1.300(10)
1.339(10)
1.459(11)
1.306(11)
2.514(2)
2.042(7)
2.378(2)
1.922(5)
2.059(5)
2.061(5)
1.341(8)
1.476(10)
1.295(9)
1.340(8)
1.483(10)
1.297(9)
2.3146(8)
2.4366(7)
1.932(2)
2.073(3)
2.084(3)
1.362(4)
1.475(5)
1.308(4)
1.359(4)
1.473(5)
1.310(4)
2.3193(17)
2.4609(16)
1.923(6)
2.100(5)
2.092(6)
1.365(10)
1.437(15)
1.303(12)
1.384(11)
1.454(12)
1.281(10)
Ax(1)–M–Ax(2)
Ax(1)–M–Eq
Ax(1)–M–N(1)
Ax(1)–M–N(7)
Ax(1)–M–N(14)
Ax(2)–M–Eq
Ax(2)–M–N(1)
Ax(2)–M–N(7)
Ax(2)–M–N(14)
Eq–M–N(1)
176.34(3)
178.67(7)
177.96(15)
85.6(2)
87.5(2)
88.5(2)
88.3(2)
95.27(17)
91.75(18)
89.44(18)
93.44(18)
172.2(2)
104.9(2)
97.6(2)
177.0(2)
90.61(6)
90.8(2)
90.6(2)
90.5(2)
88.4(2)
90.2(3)
92.4(2)
86.9(2)
178.5(2)
100.06(15)
100.5(2)
79.7(2)
79.8(2)
159.4(2)
87.06(3)
82.94(7)
86.82(7)
88.69(7)
95.72(3)
94.38(7)
90.24(7)
93.25(7)
169.71(7)
102.80(7)
98.30(7)
79.10(10)
79.14(10)
158.16(10)
87.83(6)
85.96(18)
88.37(18)
86.67(16)
93.00(6)
93.19(18)
92.46(18)
92.17(17)
173.72(18)
102.30(19)
99.90(17)
78.5(3)
Eq–M–N(7)
Eq–M–N(14)
N(1)–M–N(7)
N(1)–M–N(14)
N(7)–M–N(14)
a
78.6(2)
78.5(2)
156.9(2)
78.8(3)
157.0(2)
M = Ru, Ax(1) = Cl(1), Ax(2) = P, Eq = Cl(2).
M = Ru, Ax(1) = N(39), Ax(2) = P, Eq = N(42).
M = Rh, Ax(1) = Cl(1), Ax(2) = C(21), Eq = Cl(2).
b
c
2,6-bis(imino)pyridine complexes, the M–N bond to the
central pyridyl nitrogen is noticeably shorter [Ru–N(1)
1.932(2) A] than those to the imino nitrogens [Ru–N(7)
similar tridentate N,N0,N0 0 ligand backbone (2.406 and
2.422 A) [24,25]. The Ru–Cl distances are noticeably asym-
˚
˚
metric with that trans to the triphenylphosphine [Ru–Cl(1)
˚
˚
˚
˚
2.073(3) A, Ru–N(14) 2.084(3) A]. The Ru–Cl distances
are somewhat longer than typically seen at a six-coordinate
ruthenium centre [23], and in both of the examples with a
2.4735(7) A] being longer than that trans to pyridyl [Ru–Cl
2.4366(7) A] reflecting the stronger trans influence exerted
by the phosphine. The two –CH2–CH2–NH–C(@O)–Me

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3717
ligand side-arms adopt geometries that are approximately a
mirror image of each other as shown by the similarity of
the magnitudes, and the inversions of the signs, of the tor-
sion angles (see Scheme 3 and Table 3). Both of the amide
N–H protons are involved in intermolecular hydrogen
bonding interactions to a screw-related molecule, the
N(11) proton linking to the Cl(1) chloride of the adjacent
decided that prior to carrying out reactions it would be bet-
ter to remove the chlorides from the coordination sphere.
This would produce a cationic species with two vacant sites
for coordination. It was also rationalized that in the absence
of specific coordinating substrates, the de-halogenated com-
pounds would lead to the formation of complexes where the
carbonyl of the amide/urea groups could intramolecularly
coordinate in a hemilabile fashion. We have recently
reported that a similar system based on a monosubstituted
pyridine with a urea group, when coordinated to palla-
dium(II), indeed acts as a hemilabile ligand [18].
˚
˚
molecule [Nꢂ ꢂ ꢂCl 3.293(3) A, Hꢂ ꢂ ꢂCl 2.40 A, N–Hꢂ ꢂ ꢂCl
176ꢁ, interaction a in Fig. 3], and the N(18) proton to the
˚
˚
amide oxygen O(12) [Nꢂ ꢂ ꢂO 2.863(4) A, N–Hꢂ ꢂ ꢂO 1.96 A,
N–Hꢂ ꢂ ꢂO 176ꢁ, interaction b in Fig. 3], forming a chain
of molecules along the crystallographic b direction.
In order to isolate the species resulting from the de-halo-
genation of 1 and 2, the reactions between the complexes
and two equivalents of AgBF4 (added to remove the chlo-
rides as AgCl) were carried out in a coordinating solvent,
namely acetonitrile (see Scheme 2). The resulting com-
pounds were formulated as [Ru(L1)(CH3CN)2(PPh3)][BF4]
(3) and [Ru(L2)(CH3CN)2(PPh3)][BF4] (4), respectively on
the basis of spectroscopic, analytical and, in the case of
3, structural characterization. Particularly indicative of
the coordination of CH3CN to the ruthenium centre are
the characteristic C„N stretches at 2288 and 2360 cmꢀ1
in the IR spectra. The band for the BF4 group can also
be seen clearly in the spectra of the compounds (at ca.
Crystals of 1 grown from chloroform/pentane were shown
by X-ray analysis to be the chloroform solvate 1b (Fig. 4).
Interestingly, though the metal complex is chemically the
same as 1a, it adopts a noticeably different solid state struc-
ture. Most obviously, the –CH2–CH2–NH–C(@O)–Me
ligand side-arms adopt a very different conformation (Table
3) that allows for the formation of a pair of intramolecular
N–Hꢂ ꢂ ꢂCl hydrogen bonds between the amide N–H protons
and the axial chloride Cl(1) (interactions a and b in Fig. 4)
˚
with Nꢂ ꢂ ꢂCl, Hꢂ ꢂ ꢂCl (A) and N–Hꢂ ꢂ ꢂCl (ꢁ) geometries of
˚
˚
(a) 3.372(7), 2.74 A, 123ꢁ and (b) 3.314(7), 2.62 A, 135ꢁ. (In
1a the amide protons were both involved in intermolecular
interactions.) The geometry at the ruthenium centre is again
distorted octahedral with cis angles in the range 78.5(3)–
102.30(19)ꢁ and an N(7)–Ru–N(14) trans angle of 157.0(2)ꢁ
(Table 2). The equatorial coordination plane is flatter than
1
1084 cmꢀ1). The H NMR spectra of both 3 and 4 show
resonances for the methyl group of the coordinated
CH3CN molecules at 2.78 ppm (for both 3 and 4). The inte-
gration of these signals in comparison to those associated
to the corresponding ligand in 3 and 4 is consistent with
two molecules of CH3CN being coordinated to the ruthe-
nium centres. The coordination of the acetonitrile mole-
cules in these complexes was further confirmed by
13C{1H} NMR which clearly showed the signals for both
the carbon atoms of CH3CN (4.52 and 136.1 ppm for 3;
5.10 and 136.9 ppm for 4).
˚
˚
seen in 1a, Cl(2) lying only ca. 0.19 A (cf. 0.38 A in 1a) out
of the {Ru,N(1),N(7),N(14)} plane (which is coplanar to
˚
within ca. 0.04 A) in the direction of Cl(1); the pyridyl ring
is inclined by ca. 5ꢁ to this plane (cf. 9ꢁ in 1a). Both of the
five-membered N,N0 chelate rings are essentially flat, being
˚
coplanar to within ca. 0.01 and 0.02 A for the N(1)/N(7)
and N(1)/N(14) rings, respectively. The most noticeable dif-
ference in the coordination distances between the two struc-
tures (Table 2) is a marked lengthening of the Ru–Cl(2) bond
Single dark orange-red crystals of 3 suitable for X-ray
crystallographic analysis were obtained from a mixture of
acetonitrile and diethyl ether. The structure of this com-
pound (Fig. 5) is similar to that of 1a, the solvent-free
structure of the neutral bis-cis-chloride species. The torsion
angles for the –CH2–CH2–NH–C(@O)–Me ligand side-
arms are comparable to those seen for 1a (Table 3), and
the two amide N–H protons are again involved in intermo-
lecular interactions (rather than intramolecular interac-
tions as seen in 1b). Here in 3 they form N–Hꢂ ꢂ ꢂF
hydrogen bonds to the disordered BF4 anions (interactions
˚
in 1b cf. 1a [Ru–Cl(2) 2.4609(16) and 2.4366(7) A in 1b and
1a, respectively], though it is not immediately apparent why
this should be the case.
Once 1 and 2 were prepared and characterized it was of
interest to investigate their reactivity and whether the amide
and urea groups would interact with potential substrates.
Since these two complexes showed to be very stable, it was
˚
a and b in Fig. 5) with Nꢂ ꢂ ꢂF, Hꢂ ꢂ ꢂF (A) and N–Hꢂ ꢂ ꢂF (ꢁ)
˚
geometries of (a) 3.087(10), 2.19 A, 176ꢁ and (b) 2.94(3),
1
˚
2.32 A, 126ꢁ. The geometry at the metal centre is the
1
The N(18)–H proton in this structure could not be located from a DF
map and so was placed in an idealised position (see experimental text). The
BF4 anion to which this hydrogen apparently links is highly disordered,
three separate orientations having been identified. Though the contact
given has a longer Hꢂ ꢂ ꢂF distance and a smaller N–Hꢂ ꢂ ꢂF angle than
might be expected, it does represent the shortest contact to this amide
proton.
Scheme 3. Numbered schematic for the structural analysis of the ligand
side-arms in complexes 1a, 1b, 3 and 9.

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H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
Table 3
Comparative torsion angles (ꢁ) for the –CH2–CH2–NH–C(@O)–Me ligand side-arms in complexes 1a, 1b, 3 and 9a
1a
1b
3
9
N(7)
N(14)
N(7)
N(14)
N(7)
N(14)
89.1
N(7)
N(14)
C1–N2–C3–C4
N2–C3–C4–N5
C3–C4–N5–C6
C4–N5–C6–C7
a
ꢀ93.9
87.0
175.4
81.8
ꢀ108.6
63.0
95.0
175.6
99.6
ꢀ59.6
ꢀ82.6
176.0
ꢀ89.5
174.9
ꢀ80.7
173.0
ꢀ106.9
57.6
75.5
ꢀ176.8
107.8
ꢀ56.2
ꢀ89.2
176.5
ꢀ176.2
ꢀ79.8
ꢀ173.7
84.2
ꢀ179.1
175.8
ꢀ178.6
Columns headed ‘‘N(7)’’ refer to the side-arm linked to N(7), and likewise for the columns headed ‘‘N(14)’’. Atom numbering for torsion angles from
Scheme 3.
out of the equatorial coordination plane, N(42) lying ca.
˚
0.20 A out of the {Ru,N(1),N(7),N(14)} plane (which is
˚
coplanar to within ca. 0.03 A) in the direction of N(39);
the pyridyl ring is inclined by ca. 3ꢁ to this plane. The
two five-membered C2N2Ru chelate rings are essentially
flat, the maximum deviations from planarity being ca.
˚
0.02 and 0.01 A for the N(1)/N(7) and N(1)/N(14) rings,
respectively. Compared to the structures of the dichloro
species 1a and 1b, it is noticeable that here in 3 the Ru–
N(pyridyl) and Ru–P linkages are both lengthened [Ru–
˚
˚
N(1) 1.960(5) A cf. 1.932(2) and 1.923(6) A in 1a and 1b,
˚
respectively, and Ru–P 2.335(2) A cf. 2.3146(8) and
2.3193(17) A in 1a and 1b, respectively]. Since these link-
˚
ages are those trans to the MeCN/chloride ligands, these
lengthenings reflect the shorter Ru–N(MeCN) distances
˚
[2.086(6) and 2.069(6) A to N(39) and N(42), respectively]
cf. those to the chlorides in 1a and 1b [in the range.
˚
2.4366(7)–2.4820(17) A] (Table 2).
Fig. 4. The molecular structure of 1b. The geometries of the N–Hꢂ ꢂ ꢂCl
˚
3.3. Reactions of 3 and 4 with KSCN
contacts [Nꢂ ꢂ ꢂCl, Hꢂ ꢂ ꢂCl (A), N–Hꢂ ꢂ ꢂCl (ꢁ)] are (a) 3.372(7), 2.74, 128;
(b) 3.314(7), 2.62, 135.
Complexes Ru(L1)(NCS)2(PPh3) (5) and Ru(L2)(NCS)2
(PPh3) (6) were synthesised by addition of potassium thio-
cyanate to an acetonitrile solution of 3 and 4, respectively
(see Scheme 2). The products were isolated as red solids
by precipitation with diethyl ether and were purified by
washing with distilled water until no further KSCN could
be detected by IR spectroscopy. Both compounds were
fully characterised using spectroscopic and analytical
techniques.
The 31P{1H} NMR spectra of these compounds exhibit
one singlet each at 39.7 ppm (for 5) and 40.6 ppm (for 6).
1
The H NMR spectra of both complexes are very sharp
with well defined signals – in contrast to the broad spectra
obtained for 3 and 4. The spectrum of complex 5 exhibits
only one set of peaks for the two ligand pendant arms, indi-
cating that they are equivalent on the NMR timescale. The
two CH3 singlets appear at 1.95 ppm for the N@CCH3 pro-
tons and 2.29 ppm for the CH3(C@O)NH protons. The
two sets of CH2 protons on each arm appear as three mul-
tiplets, and the pyridine ring protons are partially masked
by the intense triphenylphosphine signal between 7.06
and 7.74 ppm. The two NH protons on the ligand arms
can be seen as one broad triplet at 6.61 ppm, suggesting
that the two ligand arms are equivalent on the NMR
Fig. 5. The molecular structure of the dication in 3. The geometries of the
˚
N–Hꢂ ꢂ ꢂF contacts [Nꢂ ꢂ ꢂF, Hꢂ ꢂ ꢂF (A), N–Hꢂ ꢂ ꢂCl (ꢁ)] are (a) 3.087(10),
2.19, 176; (b) 2.94(3), 2.32, 126.
expected distorted octahedral with cis angles in the range
78.5(2)–104.9(2)ꢁ with an N(7)–Ru–N(14) trans angle of
156.9(2)ꢁ (Table 2). The equatorial substituent is again bent

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3719
timescale. The chemical shift of these protons is very simi-
lar to that seen for the parent complex 1 (cf. 6.83 ppm)
compared to a value of 7.90 ppm for the acetonitrile com-
plex 3. The 1H NMR spectrum of 5 is also well defined. The
CH3 protons appear as a triplet at 1.03 ppm (CH3CH2NH)
and a sharp singlet at 2.30 ppm (N@CCH3), with the
CH2CH2 protons appearing as three multiplets at 3.42,
3.72 and 4.07 ppm. The pyridine protons for this complex
appear as a doublet and triplet at 7.56 and 7.71 ppm,
respectively. Two signals are present for the two NH pro-
tons, at 4.75 and 5.18 ppm, appearing as broad singlets.
In the 13C{1H} NMR spectra of 5 and 6 the expected
signals for triphenyl phosphine and the corresponding
ligand can be clearly assigned. The important feature in
the 13C{1H} NMR spectra of these complexes is the pres-
ence of peaks due to the bound NCS ligands at 141.6
and 141.4 ppm for 5 and 6, respectively.
The FAB(+) mass spectra of 5 and 6 both show the
same fragmentation patterns. The molecular ion peaks
can be seen at 811 and 869 a.m.u., respectively, followed
by a peak corresponding to loss of one NCS groups for
each complex at 753 and 811 a.m.u. and finally loss of
the triphenylphosphine ligand represented by a peak at
491 a.m.u. in the spectrum of 5 and 549 a.m.u. in that of 6.
The IR spectra of the two complexes both exhibit the
expected ligand bands, with C–H stretches being seen
between 3058 and 2920 cmꢀ1, the C@O bands occurring
at 1663 cmꢀ1 (for 5) and 1643 cmꢀ1 (for 6), and the imine
C@N at 1523 cmꢀ1 (for 5) and 1549 cmꢀ1 (for 6). The
bound NCS group can be identified by two bands corre-
sponding to the C„N and C–S stretches, occurring at
2094 and 804 cmꢀ1 for complex 5, and 2094 and 802 cmꢀ1
for complex 6. No bands due to BF4 stretches are seen
confirming the absence of a counter-ion for this neutral
complex. Elemental analyses of samples of both complexes
are also consistent with the proposed formulation.
The ruthenium thiocyanate complexes synthesised here
have been assigned the Ru–NCS bonding mode on the
basis of IR data. Two bands corresponding to the C„N
and C–S stretches, occurring at 2094 and 804 cmꢀ1 (for
5) and 2094 and 802 cmꢀ1 (for 6) can be seen in the IR
spectra. The band corresponding to the C–S stretch is
not obscured by any solvent or ligand bands in either spec-
trum and occurs at wavelengths lower than that for the free
SCNꢀ ion in both cases. The observed stretches compare
well with those in the N–bonded polypyridine ruthe-
nium(II) complexes synthesised by Nagao which were
found to be 2097 and 808 cmꢀ1 for mC–N and mC–S, respec-
tively [26].
3.4. Synthesis of Rh(Ln)Cl and study of its reactivity with
organic chlorides
The rhodium(I) complexes Rh(L1)Cl (7) and Rh(L2)Cl
(8) were synthesised from the reaction between the rho-
dium precursor [Rh(COD)Cl]2 and the corresponding
ligand (see Scheme 4) by refluxing in toluene for approxi-
mately 30 min. Upon cooling dark green solids precipitated
from solution and were collected by filtration, washed with
diethyl ether and dried under reduced pressure. These sol-
ids were spectroscopically and analytically characterized as
the rhodium(I) complexes 7 and 8.
The characterization of these complexes was not easy
since they are very air-sensitive changing colour rapidly
from dark green to mustard-yellow if traces of oxygen
are present. Furthermore – due to their insolubility in most
common solvents – NMR analysis also proved difficult. In
spite of these limitations, complex 7 was characterised by
1H NMR and IR spectroscopy, FAB(+) mass spectrometry
and elemental analysis. On the other hand, due to its very
limited solubility, complex 8 could only be characterized on
One important feature of complexes containing ambiden-
tate ligands such as thiocyanate is the mode of coordination
exhibited by the ligand. It has been noted by several authors
that the mode of coordination is strongly dependent on the
nature of the central metal and the surrounding ligands, as
well as other factors such as the spin state of the metal. For
example, the more linear N–bonded thiocyanate is generally
preferred over the sterically more demanding angular S–
bonded thiocyanate for complexes containing a bulky
ligands such as triphenylphosphine. The C–S stretching fre-
quency of ‘‘ionic’’ thiocyanate, such as that found in KNCS,
is known to occur at 749 cmꢀ1. This frequency is shifted to
higher wavenumbers (780–860 cm ꢀ1) in the spectra of
isothiocyanates (M–NCS), and to lower wavenumbers
(690–720 cmꢀ1) in the spectra of thiocyanates (M–SCN).
Consequently IR spectroscopy has proven to be a very useful
diagnostic tool, but it has a number of problems. The first is
that the lower wavenumber band occurring at wavelengths
of 690–860 cmꢀ1
, is often weak and is frequently
obscured by other bands, such as those of solvent and other
ligands.
Scheme 4. Schematic representation of the reactions studied for the
rhodium compounds.

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H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
the basis of IR spectroscopy, FAB(+) mass spectrometry
and elemental analysis.
1
The H NMR spectrum of 7 exhibits all the expected
ligand peaks. The CH2CH2 protons on the ligand arms
appear as four multiplets, integrating to a total of 8, but
cannot be individually assigned. The NH protons are visi-
ble and appear as a broad unresolved triplet at 6.61 ppm.
The FAB(+) mass spectra of the two compounds show lit-
tle fragmentation. The molecular ion peak is present in
both cases, appearing at 469 a.m.u. for complex 7 and
492 a.m.u. for 8. The only other fragmentation peak is
found in the spectrum of 7, and corresponds to the loss
of chloride (434 a.m.u.). There are no distinguishing fea-
tures in the IR spectra of these complexes. All stretches
for the ligand functional groups are present, the carbonyl
and C@N (imine) bands overlapping to give one broad
band in both cases (at ca. 1640 cmꢀ1). The pyridine C@N
band has a wavelength of 1564 cmꢀ1, while the aliphatic
Fig. 6. The molecular structure of 9. The geometries of the N–Hꢂ ꢂ ꢂCl
˚
contacts [Nꢂ ꢂ ꢂCl, Hꢂ ꢂ ꢂCl (A), N–Hꢂ ꢂ ꢂCl (ꢁ)] are (a) 3.457(7), 2.91, 121;
(b) 3.353(7), 2.63, 138.
complex 9 the geometry at the metal centre is again dis-
torted octahedral, with cis angles in the range 79.7(2)–
100.06(15)ꢁ and an N(7)–Ru–N(14) trans angle of
159.4(2)ꢁ (Table 2). Unlike the previous three structures,
however, here the equatorial coordination plane is almost
flat, {Rh,Cl(2),N(1),N(7),N(14)} being coplanar to within
C–H groups can be seen between 2971 and 2877 cmꢀ1
.
The elemental analyses for complexes 7 and 8 are consis-
tent with the proposed formulation.
Once compounds 7 and 8 were fully characterized, their
reactivity towards various gases was investigated. In partic-
ular, we had interest in studying whether 7 would react
with CO2 gas. This experiment was carried out by dissolv-
ing 7 (under N2) in CH2Cl2 and the solution was placed in
an autoclave with CO2 at 12 atm pressure. The reaction
mixture was left to stand overnight after which time it
was open to atmospheric pressure. From this reaction mix-
ture, small orange crystals had formed and where analysed
spectroscopically, analytically and by X-ray crystallogra-
phy. Instead of a product resulting from coordination to
CO2 to the metal centre, the crystalline solid obtained
was characterized as Rh(L1)(Cl)2(CH2Cl) (9) which forms
by the oxidative-addition of CH2Cl2 to the rhodium(I) cen-
tre (see Scheme 4).
There are a number of reports in the literature of the oxi-
dative addition of C–Cl bonds to rhodium(I) complexes con-
taining pyridyl-diimine ligands. For example, Vrieze et al.
reported in 1997 the reactions of rhodium(I) complexes with
various chlorinated compounds, namely dichloromethane,
chloroform and benzyl chloride. Hence, it is not surprising
that under the experimental conditions herein used, the sol-
vent oxidatively adds to the rhodium(I) complex 7.
˚
ca. 0.02 A; the pyridyl ring is inclined by only ca. 2ꢁ to this
plane. The two five-membered N,N0 chelate rings are also
˚
flat, being coplanar to within ca. 0.01 and 0.02 A for the
N(1)/N(7) and N(1)/N(14) rings, respectively. Whilst the
Rh–N distances are similar to the Ru–N distances seen in
1a (Table 2), it is noticeable that the Rh–Cl(1) bond is
˚
longer [2.514(2) A], and the Rh–Cl(2) bond shorter
˚
[2.378(2) A], than their counterparts in 1a and 1b (Table
2). This is due to a combination of the change in the metal
atom and its charge from Ru(II) to Rh(III) (which would be
expected to cause a general contraction of all of the M–X
bond lengths), and the change from neutral triphenylphos-
phine in 1a and 1b to formally mononegative chloromethyl
in the ‘‘lower’’ axial position in 9. Associated with this lat-
ter change is a ‘‘contraction’’ of the M–Ax(2) distance from
˚
2.3146(8) and 2.3193(17) A in 1a and 1b, respectively, to
˚
2.042(7) A in 9, causing a lengthening of the trans M–
Cl(1) distance. The Rh–Cl and Rh–CH2Cl distances seen
here are similar to those seen in the closely related
bis(imino)pyridyl complexes dichloro-(chloromethyl)-(pyr-
idine-2,6-bis(isopropyliminomethyl))-rhodium(III)
and
The single crystal X-ray structure of 9 revealed the unex-
pected presence of a chloromethyl unit in the ‘‘lower’’ axial
position (Fig. 6). Otherwise, this rhodium complex has a
geometry similar to that of 1b – the chloroform solvate
of the ruthenium triphenylphosphine species – the two –
CH2–CH2–NH–C(@O)–Me ligand side-arms adopting
conformations (Table 3) that allow for the formation of a
pair of intramolecular N–Hꢂ ꢂ ꢂCl hydrogen bonds between
the amide N–H protons and the axial chloride Cl(1) (inter-
dichloro-(chloromethyl)-(pyridine-2,6-bis(cyclohexylimino
methyl))-rhodium(III) [27].
The molecular structure established by X-ray is consis-
tent with the spectroscopic and analytical characterization
of the bulk of the sample. The 1H NMR spectra of 9
showed all the protons expected for the pyridine-based
ligand. Particularly indicative of the presence of CH2Cl
in the molecule is the signal at 4.26 ppm which is a doublet
due to the coupling to rhodium (2JRh–H = 3.1 Hz). The
13C{1H} NMR spectrum also shows all expected signals
associated to L1 carbon. The carbon atom of CH2Cl
directly bound to the metal centre appears at 41.2 ppm.
This signal should be a doublet due to coupling with the
˚
actions a and b in Fig. 6) with Nꢂ ꢂ ꢂCl, Hꢂ ꢂ ꢂCl (A) and N–
˚
Hꢂ ꢂ ꢂCl (ꢁ) geometries of (a) 3.457(7), 2.91 A, 121ꢁ and (b)
˚
3.353(7), 2.63 A, 138ꢁ. As was seen in the structures of
the ruthenium complexes 1a, 1b and 3, here in the rhodium

H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
3721
rhodium, but unfortunately the signal is slightly obscured
by the strong resonances of the DMSO-d6 and hence it is
not possible to provide a coupling constant. The chemical
shift, thought, is in the expected region of the spectrum
according to previously reported data for compound where
the Rh–CH2Cl moiety is present.
The FAB(+) mass spectrum of 9 shows a number of
peaks, the most intense of which is that at 518 a.m.u., cor-
responding to loss of one chloride atom from the complex.
Other fragmentation is evident, with a peak at 504 a.m.u.
representing loss of the CH2Cl group from the original
complex and a signal at 434 a.m.u. corresponding to loss
of CH2Cl as well as both chloride atoms.
Once complex 9 was fully characterized, an alternative
method for its synthesis was investigated to obtain the
complex in higher yields. The new synthetic method we
found allows to prepare the complex directly from
[Rh(COD)Cl]2 and ligand L1 by refluxing this mixture in
CH2Cl2 for 30 min and then stirring at room temperature
for a further 90 min. Compound 9 precipitates from the
solution as a yellow solid which, after washing with diethyl
ether and dried under reduced pressure give the pure prod-
uct in 70% yield. The characterization of the product
obtained by this method was identical to that one of the
complex formed in the autoclave.
in the chemical shifts (see Experimental Section for details).
The 13C{1H} NMR assignments for the spectra of the two
complexes are also consistent with the proposed formula-
tion. Signals from the bound aliphatic group appeared at
26.95 ppm (Rh–CH2), 142.66 ppm (CH) and 111.40
(@CH2) for complex 11 and 26.23 ppm (Rh–CH2),
143.21 ppm (CH) and 11.37 (@CH2) for complex 12.
The FAB(+) mass spectra of the two compounds exhibit
very similar fragmentation patterns. The molecular ion
peak is present in both cases, appearing at 510 and
603 a.m.u. for 11 and 12, respectively. The next peak in
the spectrum of 11 corresponds to loss of one chloride
(568 a.m.u.) but this is not seen for 12. The remaining frag-
mentation is the same for both rhodium oxidative addition
products, with peaks corresponding to loss of
CH2CH@CH2 and Cl (469 and 527 a.m.u.) followed by
loss of the second chloride (434 and 492 a.m.u.).
The oxidative addition reactions using chloroacetonit-
rile to yield Rh(L1)(Cl)2(CH2CN) (13) and Rh(L2)-
(Cl)2(CH2CN) (14) were carried in an identical way to
1
the reaction with allyl chloride discussed above. The H
NMR spectra of the two complexes recorded in CDCl3
show all the protons associated to the ligand, as well as
those of the CH2CN group coordinated to the metal.
The latter can be seen as a doublet at 2.10 ppm in the
spectrum of 13 and at 2.11 ppm in that of 13 (with
2JRhH = 3.5 Hz for both complexes). The 13C{1H} NMR
spectra also exhibit the expected signals for ligands L1
and L2, respectively. Indicative of the presence of the oxi-
dative addition product are the resonances for the two
carbon atoms of the bound CH2CN group which occur
at 25.48 ppm (CH2CN) and 124.05 ppm (CH2CN) in com-
plex 13, and 54.82 ppm (CH2CN) and 124.92 ppm
(CH2CN) in 14.
Once this synthetic methodology was established it was
of interest to investigate whether the same reaction would
take place using L2 instead of L1. The reaction was
repeated and, as expected, complex Rh(L2)(Cl)2(CH2Cl)
(10) was obtained in good yields. Both the 1H and
13C{1H} NMR spectra of this product are consistent with
the formulation showing all the resonances expected for
L2 plus those associated to the coordinated CH2Cl moiety
2
(dH = 4.24 ppm, JRhH = 3.2 Hz; dC = 40.86 ppm). The
FAB(+) mass spectrum shows a peak of high intensity at
576 a.m.u. assigned to the complex minus one chloride.
In order to investigate the generality of this reaction, the
oxidative-addition to other organic chlorides – namely allyl
chloride and chloroacetonitrile – was investigated. The
reactions between [Rh(COD)Cl]2, Ln (n = 1, 2) and the cor-
responding organic chloride were carried out yielding the
following products in good yields: Rh(L1)(Cl)2(CH2CH@
CH2) (11), Rh(L2)(Cl)2(CH2CH@CH2) (12), Rh(L1)(Cl)2-
(CH2CN) (13), Rh(L2)(Cl)2(CH2CN) (14) (see Scheme 3).
The compounds were characterized using spectroscopic
and analytical techniques.
The IR spectra of 13 and 14 exhibit all stretches which
would be expected due to the presence of the corresponding
pyridine-based ligands. In addition to this, both spectra
show the C„N stretch associated with the bound CH2CN
group, occurring at 2209 cmꢀ1 in the spectrum of 13 and at
2202 cmꢀ1 in that of 14 (shifted in comparison to the value
of 2251 cmꢀ1 in the uncoordinated ClCH2CN molecule).
The elemental analysis for both complexes is consistent
with the proposed formulation.
4. Conclusions
The protons of the CH2CH@CH2 group coordinated to
the metal centre are clearly identifiable in the H NMR
spectra of both complexes 11 and 12. In the case of 11,
the Rh-CH2 protons appear at 2.64 ppm as a doublet of
doublets. This multiplicity results from coupling to both
the rhodium metal and the CH proton of the allyl group,
A series of ruthenium and rhodium complexes with a
urea–disubstituted pyridine have been prepared. The
three X-ray crystal structures obtained have demon-
strated that in the solid state the urea substituents are
indeed engaged in hydrogen-bonding with species coordi-
nated to the metal centre. This is a first step towards the
possibility of using a combination of metal–ligand and
hydrogen-bonding interactions to modify the reactivity
of specific substrates. Investigations are currently under-
way to establish whether a change in reactivity is indeed
possible.
1
with coupling constants calculated to be 3.01 Hz (3JRhH
)
and 8.62 Hz (3JHH). The CH protons can be seen at
5.34 ppm, while the two @CH2 protons have chemical
shifts of 4.46 and 4.67 ppm. An analogous set of signals
is observed from complex 12 with only small variations

3722
H.A. Burkill et al. / Inorganica Chimica Acta 359 (2006) 3709–3722
[10] C.E. MacBeth, R. Gupta, K.R. Mitchell-Koch, V.G. Young Jr.,
Acknowledgements
G.H. Lushington, W.H. Thompson, M.P. Hendrich, A.S. Borovik, J.
Am. Chem. Soc. 126 (2004) 2556.
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We thank Imperial College London for a studentship
(H.A.B.) and Johnson-Matthey for a loan of ruthenium
salts.
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Appendix A. Supplementary data
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Crystallographic data have been deposited with the
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1a, 1b, 3 and 9. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.ica.2006.01.020.
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