Structural diversity in the coordination of amidines and guanidines to monovalent metal halides

Article abstract of DOI:10.1039/b314707j

A series of structurally characterised, monovalent metal-halide complexes incorporating neutral amidine and guanidine ligands is reported. N,N′-diphenylbenzamidine reacted with copper(I) chloride to afford the bis-ligand complex [CuCl(PhC{NPh} {NHPh})₂]₂ (1), that exists as a chlorine bridged dimer in the solid state, with a non-symmetrical distribution of NH ... Cl interactions within the 'Cu₂Cl ₂' metallacycle. In contrast, only one equivalent of the guanidine, Me₂NC{N_iPr} {NH_iPr} (2), is coordinated in the copper(I) iodide complex [CuI(Me₂NC{NⁱPr}-{NH ⁱPr})]₂ (3), which was also isolated as the dimer with bridging halide atoms. The molecular structure of the bicyclic guanidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), is reported, revealing a hydrogen bridged dimer with extensive delocalisation throughout the ligand framework. Coordination of hppH to lithium chloride afforded the dimeric bis-ligand complex [LiCl(hppH)₂]₂ (4) in which each hppH molecule interacts with a different chlorine atom of the central 'Li ₂Cl₂' core of the molecule via NH ... Cl hydrogen bonding. In contrast the 2:1 ligand to metal complex is formed with silver(I) chloride to afford AgCl(hppH)₂ (5), a unique example of a monomeric, three-coordinate silver chloride supported by nitrogen-based ligands. The series of mixed ligand complexes [CuX(hppH)(PPh₃)]_n (6, X = Cl, n = 1; 7, X = Br, n = 2; 8 X = I, n = 2) have also been synthesised and structurally characterised, allowing comparisons of the relative coordinating behaviour of hppH and PPh₃ as neutral donors at copper(I) centres to be made.

Full text of DOI:10.1039/b314707j

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Structural diversity in the coordination of amidines and guanidines
to monovalent metal halides
Sarah H. Oakley, Delia B. Soria,† Martyn P. Coles* and Peter B. Hitchcock
Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton,
UK BN1 9QJ. E-mail: m.p.coles@sussex.ac.uk.; Fax: ϩ44 (0)1273 677196;
Tel: ϩ44 (0)1273 877339
Received 17th November 2003, Accepted 5th January 2004
First published as an Advance Article on the web 16th January 2004
A series of structurally characterised, monovalent metal-halide complexes incorporating neutral amidine and
guanidine ligands is reported. N,NЈ-diphenylbenzamidine reacted with copper() chloride to afford the bis-ligand
complex [CuCl(PhC{NPh}{NHPh})2]2 (1), that exists as a chlorine bridged dimer in the solid state, with a non-
symmetrical distribution of NH ؒ ؒ ؒ Cl interactions within the ‘Cu2Cl2’ metallacycle. In contrast, only one equivalent
of the guanidine, Me2NC{NiPr}{NHiPr} (2), is coordinated in the copper() iodide complex [CuI(Me2NC{NiPr}-
{NHiPr})]2 (3), which was also isolated as the dimer with bridging halide atoms. The molecular structure of the
bicyclic guanidine, 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH), is reported, revealing a hydrogen
bridged dimer with extensive delocalisation throughout the ligand framework. Coordination of hppH to lithium
chloride afforded the dimeric bis-ligand complex [LiCl(hppH)2]2 (4) in which each hppH molecule interacts with a
different chlorine atom of the central ‘Li2Cl2’ core of the molecule via NH ؒ ؒ ؒ Cl hydrogen bonding. In contrast the
2 : 1 ligand to metal complex is formed with silver() chloride to afford AgCl(hppH)2 (5), a unique example of a
monomeric, three-coordinate silver chloride supported by nitrogen-based ligands. The series of mixed ligand
complexes [CuX(hppH)(PPh3)]n (6, X = Cl, n = 1; 7, X = Br, n = 2; 8 X = I, n = 2) have also been synthesised and
structurally characterised, allowing comparisons of the relative coordinating behaviour of hppH and PPh3 as neutral
donors at copper() centres to be made.
maximise the possibility and degree of adduct formation, a
Introduction
procedure that was often employed which took advantage of
The application of neutral, N-based donor ligands in co-
the liquid state of many of the nitrogen donor species, was the
ordination chemistry is, perhaps, exemplified by the use of
pyridine and pyridine-based compounds, where many different
use of solvent-free conditions, where the metal salt was dis-
solved directly in the organic base and crystals were isolated
structural patterns are observed, depending upon the nature
from the resultant mixture. However, it was found that in
and extent of substitution of the C5N-ring. During the 1990s,
an extensive structural study was performed by White and co-
certain cases, even these conditions were insufficient to promote
formation of the desired adduct.
workers on these, and other group 15 element donor com-
Research in our laboratory has been concerned with the
pounds (e.g. phosphines, arsines, stibines), spanning many of
synthesis of a number of transition metal complexes incorpor-
the ‘closed shell’ metal ions of the periodic table.1 Of particular
ating neutral guanidines, R2NC{NRЈ}{NHRЈ}, and their
relevance to the study presented in this work, research was con-
corresponding anions, [R2NC{NRЈ}2]Ϫ, as N-based ligands.2–5
ducted into the nature of the complexes formed with the group
Whilst application of the latter class of negatively charged
1 and group 11 metals, employing a range of N-based ligands,
guanidinates has become more widespread in coordination
typified by the examples illustrated in Fig. 1. In order to
chemistry, the use of the former as neutral donors has not, to
date, received similar attention.6 We have previously found,
however, that the combination of a donor-imine functionality
and an NH group within the bicyclic guanidine 1,3,4,6,7,8-
hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH, Fig. 1), per-
mitted the facile coordination of this compound to copper()
halides.4 The solid-state structure of the resultant CuX(hppH)2
compounds indicated a three-coordinate copper with intra-
molecular hydrogen bonds between the NH and halide atoms
for the chloride and bromide species. We wish to present here
our results from a further study into the coordinating potential
of this versatile class of neutral ligand, and identify a number
of different structural motifs with monovalent lithium, copper
and silver halides, allowing detailed comparisons to be made
with the solid-state structures of related Lewis-base adducts.
Experimental
Fig. 1 Examples of nitrogen-based donor ligands typically used in
coordination chemistry studies at monovalent metal halides.
General experimental procedures
All manipulations were carried out under dry nitrogen using
standard Schlenk-line and cannula techniques, or in a con-
ventional nitrogen-filled glovebox. Solvents were dried over
appropriate drying agent and degassed prior to use. N,NЈ-di-
† Member of research Career of CONICET, Consejo Nacional de
Investigaciones Científicas y Técnicas, on leave from CEQUINOR,
Departamento de Química, Facultad de Ciencias Exactas, Universidad
Nacional de La Plata, C.C. 962, 1900 La Plata, R. Argentina.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
537

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phenylbenzamidine (Lancaster), hppH (Fluka), diisopropyl-
carbodiimide (Aldrich), lithium dimethylamide (Aldrich),
copper() chloride (Aldrich), copper() bromide (Aldrich),
copper() iodide (Fluka), silver() chloride (Aldrich) and lithium
chloride, anhydrous (Acros) were purchased from commercial
sources and used as received. PPh3 (Aldrich) was recrystallised
from Et2O.
NMR (CDCl3, 298 K): δ 3.54 (br, sept, 2H, CHMe2), 3.01
(s, 6H, NMe2), 1.22 (br, d, 12H, CHMe2), NH not observed. 13
C
NMR (CDCl3, 298 K): δ 161.3 (CN3), 50.5 (CHMe2), 47.1
(CHMe2), 40.3 (NMe2), 26.8 (CHMe2), 24.1 (CHMe2). IR
(Nujol mull, cmϪ1): 3374s (N–H), 1592s (C᎐N), 1260m, 1125m,
᎐
1094m, 1037m, 936m, 800s, 591m.
Elemental analyses were performed by S. Boyer at London
Metropolitan University. NMR spectra were recorded using
a Bruker Avance DPX 300 MHz spectrometer at 300 (1H),
75 (13C{1H}) and 121 (31P{1H}) MHz. Proton and carbon
chemical shifts were referenced internally to residual solvent
resonances; phosphorus chemical shifts were referenced to an
external 85% aqueous solution of H3PO4; lithium chemical
shifts were referenced to an external aqueous solution of LiCl.
Coupling constants (J) are quoted in Hz.
[LiCl(hppH)2]2 (4). A solution of hppH (1.00 g, 7.18 mmol)
in THF (25 mL) was added dropwise to a slurry of LiCl (0.15 g,
3.59 mmol) in THF (20 mL) and the mixture was stirred
under ambient conditions for 18 h. The solution was warmed
(ca. 50 ЊC) and filtered before cooling to Ϫ30 ЊC, affording 4 as
colourless crystals. Yield 0.73 g (63%).
Anal. Calc. for C14H26N6ClLi: C, 52.4; H, 8.2; N, 26.2%.
1
Found: C, 50.0; H, 8.5; N, 24.0%. H NMR (C6D6, 298 K):
δ 7.21 (s, 1H, NH), 3.21 (m, 4H, CH2), 2.47 (m, 4H, CH2), 1.44
(M, 4H, CH2). 13C NMR (C6D6, 298 K): δ 152.7 (CN3), 47.9
(CH2), 41.2 (CH2), 43.2 (CH2). 7Li NMR (C6D6, 298 K): δ 2.01.
Mass spectrum (EIϩ, m/z): 138 [hpp Ϫ H]ϩ. IR (Nujol mull,
[CuCl(PhC{NPh}{NHPh})2]2 (1). A solution of PhC{NPh}-
{NHPh} (1.00 g, 3.67 mmol) in THF (25 mL) was added drop-
wise to a slurry of CuCl (0.18 g, 1.86 mmol) in THF (20 mL),
resulting in immediate colour change to red–brown. On com-
plete addition, most of the CuCl had dissolved, affording a
slightly cloudy orange–yellow solution, which was stirred at
room temperature for 18 h. The solution was filtered and
the volatiles removed in vacuo to afford a dark yellow foam.
Crystallisation from Et2O at Ϫ30 ЊC resulted in formation of 1
as yellow crystals. Yield 0.73 g (60%).
Anal. Calc. for C38H32N4ClCu: C, 70.9; H, 5.0; N, 8.7%.
Found: C, 71.0; H, 5.0; N, 8.8%. 1H NMR (C6D6, 298 K): δ 6.90
(br, C6H5), 6.70 (br, C6H5), NH not observed. 13C NMR (C6D6,
298 K): δ 130.1 (CH), 129.5 (br, CH), 128.6 (br, CH), 128.3
(CH), 123.8 (br, CH). Mass spectrum (EIϩ, m/z): 180 [PhC-
{NPh}]ϩ, 272 [PhC{NPh}{NHPh}]ϩ. IR (Nujol mull, cmϪ1):
cmϪ1) 3299s (N–H), 1636s (C᎐N), 1520s (C–N), 1316m, 1249m,
᎐
1187m, 1110m, 1020m, 932w, 626m, 514w, 455m, 406m, 376m.
AgCl(hppH)2 (5). A solution of hppH (1.60 g, 11.50 mmol) in
THF (30 mL) was added to a slurry of silver chloride (0.85 g,
5.93 mmol) also in THF (30 mL) at room temperature with the
exclusion of light. The solution was stirred in the dark for 48 h,
after which time a small quantity of a pale pink precipitate
was observed. The reaction was filtered and the volatiles were
removed to afford crude AgCl(hppH)2 as a pale pink solid.
Analytically pure samples of 5 were obtained as colourless
crystals by recrystallisation from toluene at 0 ЊC. Yield 1.50 g,
60%.
Anal. Calc. for C14H26N6AgCl: C, 39.8; H, 6.2; N, 19.1%.
1
3191 (N–H), 1609s (C᎐N), 1582 (C–N), 1491m, 1239w, 1212m,
Found: C, 39.9; H, 6.3; N, 19.4%. H NMR (C6D6, 298 K):
᎐
3
1170w, 1155w, 1123m, 1025w, 975w, 922m, 898w, 888w, 791m,
769m, 754m, 731m, 706m, 692s, 643w, 621m, 530m, 501m,
460w, 405w, 388w.
δ 7.77 (br, s, 1H, NH), 3.21 (t, JHH = 5.6, 4H, CH2), 2.43
3
(t, JHH = 6.1, 4H, CH2), 1.36 (m, 4H, CH2). 13C NMR (C6D6,
298 K): δ 153.9 (CN3), 48.1 (CH2), 44.0 (CH2), 23.3 (CH2). IR
(Nujol mull, cmϪ1): 3270w (N–H), 1599m (C᎐N), 1537m,
᎐
Me2NC{NiPr}{NHiPr} (2). A slurry of lithium dimethyl-
amide (5.00 g, 98.0 mmol) in Et2O (100 mL) was cooled to 0 ЊC
and a solution of diisopropylcarbodiimide (12.40 g, 98.0 mmol)
in Et2O (50 mL) was added dropwise via cannula. The mixture
was allowed to warm to room temperature to afford a cloudy
yellow solution that was stirred for a further 14 h under ambi-
ent conditions. Degassed water (1.8 mL, 100 mmol) was sub-
sequently added dropwise via syringe causing the formation of
a clear yellow solution and a white precipitate. The mixture was
filtered through Celite and the volatiles were removed to afford
a pale yellow liquid that was used without further purification.
Yield 11.75 g, 70%.
1315m, 1295m, 1261m, 1184m, 1102w, 1068m, 1018m, 802m,
569w, 515w, 450w.
CuCl(hppH)(PPh3) (6). A solution of PPh3 (1.33 g, 5.05
mmol) and hppH (0.70 g, 5.05 mmol) in THF (25 mL) was
added dropwise to a slurry of CuCl (0.50 g, 5.05 mmol). The
CuCl gradually dissolved during the addition. The mixture
was stirred for 24 h at room temperature then warmed gently
(ca. 50 ЊC), filtered and cooled slowly to ambient temperature
affording pale green crystals of analytically pure 6. Yield 1.83 g,
72%.
Anal. Calc. for C25H28N3ClCuP: C, 60.0; H, 5.6; N, 8.4%.
Found C, 59.8; H, 5.6; N, 8.6%. 1H NMR (C6D6, 298 K): δ 8.44
(br, s, 1H, NH), 7.74 (m, 6H, o-C6H5), 7.02 (m, 9H, m- and
3
1H NMR (CDCl3, 298 K): δ 3.37 (sept, JHH = 6.4, 1H,
3
CHMe2), 3.25 (sept, JHH = 6.3, 1H, CHMe2), 2.67 (s, 6H,
3
3
3
NMe2), 1.03 (d, JHH = 6.3, 6H, CHMe2), 1.02 (d, JHH = 6.3,
6H, CHMe2), NH not observed. 13C NMR (CDCl3, 298 K):
δ 155.8 (CN3), 47.3 (CHMe2), 45.9 (CHMe2), 39.0 (NMe2),
25.1 (CHMe2), 23.6 (CHMe2).
p-C6H5), 2.93 (br, s, 4H, CH2), 2.28 (t, JHH = 6.1, 4H, CH2),
1.17 (m, 4H, CH2). 13C NMR (C6D6, 298 K): δ 154.4 (CN3),
134.6 (d, JPH = 45.8, C6H5), 134.4 (d, JPH = 15.4, C6H5), 129.7 (s,
C6H5), 128.8 (d, JPH = 9.2), 47.6 (2 coincident CH2 peaks), 22.6
(CH2). 31P NMR (C6D6, 298 K) δ Ϫ6.4. Mass spectrum (EIϩ,
m/z): 499 [M]ϩ, 464 [M Ϫ Cl]ϩ. IR (Nujol mull, cmϪ1): 3269s
[CuI(Me2NC{NiPr}{NHiPr})]2 (3). A solution of 2 (0.45 g,
2.63 mmol) in MeCN (20 mL) was added dropwise via cannula
to a slurry of CuI (0.25 g, 1.31 mmol) in MeCN (20 mL). The
CuI gradually dissolved during the course of the addition. The
mixture was allowed to stir under ambient conditions for 24 h,
after which time the solution was gently heated (ca. 40 ЊC) to
redissolve precipitated product and filtered to remove any in-
soluble material. Slow cooling to room temperature afforded
pale brown crystals of analytically pure 3. Yield 0.52 g, 62%.
Anal. Calc. for C18H42N6Cu2I2: C, 29.88; H, 5.85; N, 11.62%.
(N–H), 1593s (C᎐N), 1548m, 1434m, 1417m, 1313m, 1260m,
᎐
1092s, 1025m, 799m, 751m, 693m, 519m, 501m.
[CuBr(hppH)(PPh3)]2 (7). Compound 7 was prepared using
the procedure described for 6, using PPh3 (0.91 g, 3.49 mmol),
hppH (0.48 g, 3.49 mmol) and CuBr (0.50 g, 3.49 mmol). The
compound was crystallised from THF, affording analytically
pure, pale green crystals of 7. Yield 1.26 g, 66%.
Anal. Calc. for C50H56N6Br2Cu2P: C, 55.1; H, 5.2; N, 7.7%.
Found C, 55.3; H, 5.1; N, 7.6%. 1H NMR (C6D6, 298 K): δ 8.01
(br, s, 1H, NH), 7.74 (m, 6H, o-C6H5), 7.02 (m, 9H, m- and
1
Found C, 30.14; H, 5.68; N, 11.72%. H NMR (C6D6, 298 K):
δ 3.34 (br, sept, 2H, CHMe2), 2.65 (s, 6H, NMe2), 1.41 (br, d,
1
3
6H, CHMe2), 0.72 (br, d, 6H, CHMe2), NH not observed. H
p-C6H5), 2.92 (br, s, 4H, CH2), 2.26 (t, JHH = 6.1, 4H, CH2),
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
538

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Table 1 Crystal structure and refinement data for 1, 3, 4 and hppH
1
3
4
hppH
Formula
Formula weight
C76H64Cl2Cu2N8
1287.33
C18H42Cu2I2N6
723.46
C28H52Cl2Li2N12
641.60
C7H13N3
139.20
T /K
λ/Å
173(2)
0.71073
173(2)
0.71073
173(2)
0.71073
173(2)
0.71073
Crystal size/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
0.2 × 0.2 × 0.1
Triclinic
P1 (no. 2)
10.7522(4)
11.9924(6)
13.9711(8)
112.261(2)
107.954(3)
92.424(3)
1559.9(1)
1
1.37
0.82
0.3 × 0.2 × 0.1
Triclinic
P1 (no. 2)
8.2768(2)
8.8985(2)
10.8561(3)
107.040(1)
95.260(1)
112.759(1)
685.61(3)
1
1.75
0.3 × 0.2 × 0.1
Monoclinic
P21/c (no. 14)
8.8979(7)
19.2720(19)
10.7363(8)
90
113.465(5)
90
1688.8(2)
2
0.4 × 0.3 × 0.3
Orthorhombic
Pbca (no. 61)
8.5628(2)
14.8659(3)
11.6451(2)
90
¯
¯
90
90
γ/Њ
V/Å3
1482.35(5)
8
1.25
Z
Dc/Mg mϪ3
1.26
0.23
µ/mmϪ1
3.82
0.08
θ Range for data collection/Њ
Reflections collected
Independent reflections
Reflections with I > 2σ(I )
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2σ(I )]
R Indices (all data)
Largest diff. peak and hole/e ÅϪ3
3.73–27.84
12659
7363 [Rint = 0.055]
5217
7363/0/405
1.042
R1 = 0.051, wR2 = 0.110
R1 = 0.084, wR2 = 0.123
0.60 and Ϫ0.567
3.87–30.05
6652
3871 [Rint = 0.048]
3643
3871/0/132
1.179
R1 = 0.033, wR2 = 0.084
R1 = 0.035, wR2 = 0.085
1.27 and Ϫ0.98
3.79–25.02
8057
2934 [Rint = 0.051]
2242
2934/0/277
1.094
R1 = 0.061, wR2 = 0.136
R1 = 0.084, wR2 = 0.146
0.76 and Ϫ0.29
4.03–25.01
14208
1298 [Rint = 0.055]
1148
1298/0/110
1.046
R1 = 0.049, wR2 = 0.131
R1 = 0.055, wR2 = 0.136
0.30 and Ϫ0.27
1.15 (m, 4H, CH2). 13C NMR (C6D6, 298 K): δ 154.4 (CN3),
134.5 (d, JPH = 25.9, C6H5), 134.4 (d, JPH = 15.1, C6H5), 129.7 (s,
C6H5), 128.8 (d, JPH = 9.2, C6H5), 47.6 (2 coincident CH2
peaks), 22.6 (CH2). 31P NMR (C6D6, 298 K) δ Ϫ6.7. Mass
spectrum (EIϩ, m/z): 262 [PPh3]ϩ. IR (Nujol mull, cmϪ1): 3282s
hppH: The C(6) atom is disordered over two positions, with
occupancies 0.71 and 0.29. The H(N) atom is disordered over
the two nitrogens, both with occupancy 0.5.
[LiCl(hppH)2]2 (4): H atoms on N(1) and N(4) refined; all
others in riding mode.
(N–H), 1615s (C᎐N), 1525m, 1315m, 1261m, 1180m, 1093m
1025m, 803m, 742m, 695m, 522m, 504m, 487w.
AgCl(hppH)2 (5): The data were collected at 253 K as upon
cooling to 173 K, the crystal undergoes a phase change,
seriously affecting the quality of the data (the crystal is
observed to go opaque). The C(3) atom is disordered over two
positions, with occupancies 0.74 and 0.26. H atoms on nitrogen
were refined; all others in riding mode.
᎐
[CuI(hppH)(PPh3)]2 (8). Compound 8 was prepared using the
procedure described for 6, using PPh3 (0.69 g, 2.63 mmol),
hppH (0.37g, 2.63 mmol) and CuI (0.50 g, 2.63 mmol). The
compound was crystallised from THF, affording analytically
pure, pale brown crystals of 8. Yield 1.10 g, 70%.
CuCl(hppH)(PPh3) (6): H atom on N(2) refined; all others in
riding mode.
Anal. Calc. for C50H56N6Cu2I2P: C, 50.7; H, 3.1; N, 7.1%.
Found C, 50.7; H, 3.1; N, 7.0%. 1H NMR (C6D6, 298 K): δ 7.74
(m, 6H, o-C6H5), 7.02 (m, 9H, m- and p-C6H5), 2.93 (br, s, 4H,
[CuBr(hppH)(PPh3)]2 (7): H atom on N(3) refined; all others
in riding mode.
[CuI(hppH)(PPh3)]2 (8): Isomorphous with the bromide.
3
CH2), 2.25 (t, JHH = 6.1, 4H, CH2), 1.16 (m, 4H, CH2). 13C
H atom on N(3) refined; all others in riding mode.
NMR (C6D6, 298 K): δ 153.7 (CN3), 134.7 (d, JPH = 24.3,
C6H5), 134.5 (d, JPH = 14.9, C6H5), 129.6 (s, C6H5), 128.7 (d,
JPH = 9.0, C6H5), 47.6 (2 coincident CH2 peaks), 22.6 (CH2).
31P NMR (C6D6, 298 K) δ Ϫ7.2. Mass spectrum (EIϩ, m/z): 329
[1/2M Ϫ PPh3]ϩ. IR (Nujol mull, cmϪ1): 3290s (N–H), 1610s
Results and discussion
Our initial investigation of the coordinating behaviour of ami-
dines and guanidines at monovalent metal centres concerned
the addition of two molar equivalents of N,NЈ-diphenylbenz-
amidine to a slurry of copper() chloride in THF, following a
protocol that had previously proved successful in our labor-
atory for the synthesis of [CuX(hppH)2].4 On addition, the
immediate formation of red colour was observed, and during
the course of the addition, it was noted that the CuCl gradually
dissolved to afford a clear, orange–yellow solution. Attempted
recrystallisation from the reaction solvent or toluene failed due
to the high solubility of the compound, which was subsequently
found to be insoluble in pentane. Addition of diethylether to
the dark yellow foam formed upon removal of the volatiles,
however, formed a brown oil which slowly dissolved (ca. 1 h)
and, on stirring for a further 4 h, precipitated a yellow crystal-
(C᎐N), 1526m, 1315m, 261m, 1183m, 1093m 1025m, 799m,
᎐
755m, 695m, 522m, 504m, 486w.
Crystallography
Details of the crystal data, intensity collection and refinement
for complexes 1, 3, 4 and hppH are listed in Table 1, and for
complexes 5–8 in Table 2. Crystals were covered in an inert oil
and suitable single crystals were selected under a microscope
and mounted on a Kappa CCD diffractometer. The structures
were refined with SHELXL-97.7 Compounds 1, 3, 4, 7 and 8
all have crystallographically imposed inversion symmetry;
additional features of note are described below.
CCDC reference numbers 224306–224313.
See http://www.rsc.org/suppdata/dt/b3/b314707j/ for crystal-
lographic data in CIF or other electronic format.
1
line solid 1. H and 13C NMR spectra are non-informative in
this instance, showing a number of broad resonances in the
aromatic region of the spectrum, and no resonance corre-
sponding to the NH atom was observed in the proton NMR
spectrum. The IR spectrum shows absorptions at 3191 and
[CuCl(PhC{NPh}{NHPh})2]2 (1): H(N) atoms freely refined;
all others in riding mode.
[CuI(Me2NC{NiPr}{NHiPr})]2 (3): H atom on N(3) refined;
all others in riding mode.
1609 cmϪ1, attributed to ν(N–H) and ν(C᎐N) respectively, and
᎐
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
539

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Table 2 Crystal structure and refinement data for 5, 6, 7 and 8
5
6
7
8
Formula
Formula weight
C14H26AgClN6
421.73
C25H28ClCuN3P
500.46
C50H56Br2Cu2N6P2
1089.85
C50H56Cu2I2N6P2
1183.83
T /K
λ/Å
253(2)
0.71073
173(2)
0.71073
223(2)
0.71073
223(2)
0.71073
Crystal size/mm
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
0.30 × 0.30 × 0.20
Monoclinic
P21/c (no. 14)
7.4791(1)
14.4246(2)
16.1899(3)
90
0.30 × 0.30 × 0.30
Monoclinic
P21/n (no. 14)
9.3552(1)
16.3599(3)
15.2723(2)
90
0.30 × 0.20 × 0.20
Triclinic
P1 (no. 2)
0.20 × 0.10 × 0.10
Triclinic
P1 (no. 2)
¯
¯
9.6014(2)
9.6964(2)
11.2158(2)
12.0457(2)
74.402(1)
11.2108(2)
12.2893(2)
74.032(1)
βЊ
97.165(1)
90
1732.98(5)
4
1.62
1.32
90.656(1)
90
2337.27(6)
4
1.42
1.14
73.373(1)
89.615(1)
1193.69(4)
1
1.52
72.476(1)
89.277(1)
1221.15(4)
1
1.61
γ/Њ
V/Å3
Z
Dc/Mg mϪ3
µ/mmϪ1
2.67
2.24
θ Range for data collection/Њ
Reflections collected
Independent reflections
Reflections with I > 2 σ(I )
Data/restraints/parameters
Goodness-of-fit on F 2
Final R indices [I > 2σ(I )]
R Indices (all data)
Largest diff. peak and hole/e ÅϪ3
3.77–25.02
17656
3020 [Rint = 0.041]
2702
3020/0/217
1.004
R1 = 0.033, wR2 = 0.084
R1 = 0.038, wR2 = 0.088
0.68 and Ϫ0.91
3.97–27.88
21620
5515 [Rint = 0.044]
4591
5515/0/284
1.015
R1 = 0.032, wR2 = 0.069
R1 = 0.044, wR2 = 0.074
0.29 and Ϫ0.37
3.72–27.88
15808
5659 [Rint = 0.039]
4793
5659/0/284
1.045
R1 = 0.032, wR2 = 0.067
R1 = 0.043, wR2 = 0.072
0.58 and Ϫ0.43
3.71–27.89
12510
5758 [Rint = 0.035]
5282
5758/0/284
1.063
R1 = 0.025, wR2 = 0.058
R1 = 0.028, wR2 = 0.060
0.42 and Ϫ0.73
Table 3 Selected bond lengths (Å) and angles (Њ) for 1
combustion analysis is consistent with the bis-ligand complex
[CuCl(PhC{NPh}{NHPh})2]n.
Cu–N(1)
Cu–Cl
C(1)–N(1)
C(20)–N(3)
H(2a)ؒ ؒ ؒCl
2.050(2)
2.4900(8)
1.302(3)
1.302(3)
2.42
Cu–N(3)
Cu–ClЈ
C(1)–N(2)
C(20)–N(4)
H(4a)ؒ ؒ ؒCl
2.063(2)
2.3217(7)
1.348(4)
1.372(3)
2.56
To determine the nuclearity of 1, in addition to the bonding
mode adopted by this ligand at the copper centre, X-ray diffrac-
tion analysis was performed. The molecular structure is illus-
trated in Fig. 2(a), crystal data are summarised in Table 1 and
selected bond lengths and angles in Table 3.
N(1)–Cu–N(3)
N(3)–Cu–ClЈ
N(3)–Cu–Cl
Cu–Cl–CuЈ
105.88(9)
113.04(6)
100.34(7)
69.88(2)
N(1)–Cu–ClЈ
N(1)–Cu–Cl
Cl–Cu–ClЈ
115.06(6)
111.38(6)
110.12(2)
Symmetry operation: Ј Ϫx, Ϫy, Ϫz.
Compound 1 forms a µ,µ-dichlorobridged dimer, with two
Nimine-bound amidine ligands, generating a distorted tetra-
hedral geometry at copper with angles in the range 115.06(6)–
100.34(7)Њ. Similar halide-bridged dimeric structures have been
reported for bis-pyridine adducts of copper() chloride.8 The
copper–nitrogen distances [2.050(2) and 2.063(2) Å] are longer
than in the related guanidine adduct CuCl(hppH)2 [1.962(2)
and 1.966(2) Å],4 which may be a simple consequence of the
increased coordination number at the copper() centre in 1.
Investigation of the carbon–nitrogen bond distances within
the framework of amidine and guanidine ligands has been used
as a diagnostic tool when considering the distribution of π-elec-
tron density throughout the core of the ligand.9 A particularly
informative parameter that has been used when discussing the
extent of delocalisation across the amidine unit is the ∆CN
value,10 defined as d(C–Nsingle) Ϫ d(C᎐Ndouble). Predicted values
᎐
fall in the range 0 Å for a fully delocalised system to ∼ 0.14 Å for
localised single and double bonds at an sp2-hybridised carbon.11
Care should be exercised when discussing this parameter how-
ever as research in our laboratory has shown that this value can
vary from as much as 0.008 to 0.108 Å in closely related linked-
bis(N,NЈ-dialkylamidines).12 The ∆CN values for each of the
amidine ligands within compound 1 are significantly different
from each other [0.070 and 0.046 Å], with similar differences
observed in the related cobalt adduct, CoCl2(PhC{NPh}-
{NHPh})2 [0.054 and 0.033 Å].13 The former value is approx-
imately midway between the values predicted for isolated C–N
Fig. 2 (a) Molecular structure of [CuCl(PhC{NPh}{NHPh})2]2 (1)
with thermal ellipsoids drawn at the 30% probability level. Hydrogen
atoms except NH atoms omitted. (b) Core of 1 showing two H-bonding
interactions to secondary chlorine atoms.
single and C᎐N double bonds, while the latter is closer to the
᎐
∆
CN
values for the free ligand, which exists as a hydrogen
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
540

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Table 4 Selected bond lengths (Å) and angles (Њ) for 3
bonded dimer with one N–H ؒ ؒ ؒ N interaction [0.056 and
0.058 Å].14 The nitrogen-phenyl substituents are distributed
in an Eanti configuration about the amidine unit (Scheme 1),15
shifting from the Esyn arrangement in the neutral ligand. This
minimises steric interactions and allows stabilisation from
intramolecular hydrogen bonding to occur (vide infra).
Cu–N(1)
Cu–IЈ
C(1)–N(2)
1.993(2)
2.6434(4)
1.383(3)
Cu–I
C(1)–N(1)
C(1)–N(3)
2.5469(4)
1.304(3)
1.375(3)
I–Cu–IЈ
N(1)–Cu–IЈ
121.378(12)
110.78(7)
N(1)–Cu–I
Cu–I–CuЈ
127.82(7)
58.622(12)
Symmetry operation: Ј Ϫx, Ϫy, Ϫz.
Initial attempts at coordinating 2 to copper() chloride were
frustrated by the oily nature of the products, greatly compli-
cating attempted purification. However, a crystalline solid (3)
was isolated from the 2 : 1 reaction between 2 and CuI, allowing
further characterisation to be performed. The 1H NMR in C6D6
indicated broad resonances corresponding to the expected
ligand signals, with separation of the isopropyl –CH3 signals
into two distinct doublets. In CDCl3, these doublets resonances
are coincident, suggesting the presence of fluxionality within
the molecule. In contrast to the expected bis-ligand complex
analogous to 1, combustion analysis indicated that only one
ligand was present per ‘CuI’ unit, giving the formula [CuI-
(Me2NC{NiPr}{NHiPr})]n. To establish the nature of the
ligand bonding in 3, X-ray structural analysis was performed.
The molecular structure of 3 is illustrated in Fig. 3, crystal data
are summarised in Table 1 and selected bond lengths and angles
in Table 4.
Scheme 1 Isomeric and tautomeric forms of the amidine unit.
The amidine ligands within 1 are orientated such that
each amine-hydrogen atom is in close contact with one of the
chlorine atoms, with NH ؒ ؒ ؒ Cl distances of 2.42 and 2.56 Å
(Fig. 2(b)). Considering the significant asymmetry present
within the ‘Cu2Cl2’ core of the dimer [Cu–Cl 2.4900(8) Å;
Cu–ClЈ 2.3217(7) Å], it is reasonable to consider the shorter
copper–chlorine distance to ClЈ as being a primary interaction,
and the other metal–halide bond to Cl as representing a
secondary weaker interaction (Scheme 2). Using this model,
both of the hydrogen bonding interactions are with the second-
ary chloride and therefore may represent a significant contri-
bution to the stabilisation of the observed dimeric structure in
the solid-state.
Fig. 3 Molecular structure of [CuI(Me2NC{NiPr}{NHiPr})]2 (3) with
thermal ellipsoids drawn at the 30% probability level.
Scheme 2 Schematic representation of the hydrogen bonding within
the metallacyclic cores of dimeric 1 and 4.
Compound 3 also crystallises as the µ,µ-dihalobridged dimer,
with a single ligand coordinated to each copper (cf. compound
1), giving an overall molecular formula of [CuI(Me2NC-
{NiPr}{NHiPr})]2. As expected, the ligand is coordinated
through the Nimine atom, to afford a distorted trigonal planar
metal (Σangles = 359.97Њ) with angles in the range 110.78(7) to
127.82(7)Њ. Similar mono-ligand complexes with a central
‘Cu2I2’ core have been reported for the bulky N-based donors
tetramethylpiperidine,19 lutidine,20 and 1,2,3,4,5,6,7,8-octa-
hydroacridine.21 The internal angles in the metallacycle of 3 are
121.378(12) and 58.622(12)Њ at copper and iodine, respectively,
with unsymmetrical copper–iodine bond lengths of 2.5469(4)
and 2.6434(4) Å. The resultant I ؒ ؒ ؒ I distance [4.526 Å] is
relatively long in comparison with the aforementioned dimers,
being significantly greater than sum of the van der Waals
radii [4.30 Å]. The Cu ؒ ؒ ؒ Cu separation of 2.542 Å may be
considered as a close non-bonded interaction, although the
distance is slightly longer than in the previously reported [hpp]Ϫ
bridged dimer [2.4527(10) Å].22
Whilst a number of adducts of amidines at metal centres
have been reported,16 extension to neutral guanidines has to
date not been investigated to a comparable degree.6 Notable
exceptions include adducts of the neutral palladium() and
cobalt() dichlorides, and the cationic silver() triflate.17,18 We
have investigated the neutral bicyclic guanidine, hppH, as a
ligand at copper() centres, demonstrating that different co-
ordination modes are possible in the solid state.3,4 As part of
our interest in the application of such species as catalysts in
the polymerisation of olefins,4 we have investigated the co-
ordination of the acyclic guanidine, Me2NC{NiPr}{NHiPr}
(2), at copper() halide centres. The guanidine is synthesised by
quenching the intermediate lithium salt ‘[Me2NC{NiPr}2]LiЈ,
generated from the reaction of lithium dimethylamide with
diisopropylcarbodiimide, with a stoichiometric amount of
water. For the purposes of this study, no further purification
was necessary.
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
541

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Table 5 Selected bond lengths (Å) and angles (Њ) for hppH
Table 6 Selected bond lengths (Å) and angles (Њ) 4
C(1)–N(1)
C(1)–N(3)
H(1) ؒ ؒ ؒ N(3Ј)
1.328(2)
1.331(2)
2.08
C(1)–N(2)
H(3Ј) ؒ ؒ ؒ N(1)
1.367(3)
2.09
Li–Cl
Li–N(2)
C(1)–N(1)
C(1)–N(3)
C(8)–N(5)
H(1)ؒ ؒ ؒCl
2.398(5)
2.028(5)
1.377(3)
1.369(3)
1.295(4)
2.45
Li–ClЈ
Li–N(5)
C(1)–N(2)
C(8)–N(4)
C(8)–N(6)
H(4)ؒ ؒ ؒClЈ
2.416(5)
2.037(6)
1.293(3)
1.366(4)
1.377(4)
2.47
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
C(1)–N(2)–C(5)
121.19(15)
120.89(14)
122.29(14)
N(1)–C(1)–N(3)
C(1)–N(2)–C(4)
C(4)–N(2)–C(5)
117.90(14)
122.15(13)
115.47(13)
N(2)–Li–N(5)
N(2)–Li–ClЈ
N(5)–Li–ClЈ
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
N(4)–C(8)–N(6)
102.9(2)
114.9(2)
110.0(2)
117.0(2)
126.2(2)
116.5(2)
N(2)–Li–Cl
N(5)–Li–Cl
Cl–Li–ClЈ
N(1)–C(1)–N(3)
N(4)–C(8)–N(5)
N(5)–C(8)–N(6)
109.7(2)
119.3(2)
100.7(2)
116.7(2)
117.8(3)
125.7(2)
The C(6) atom is disordered over two positions (occupancies 0.71 and
0.29); the N(H) atom is disordered over the two nitrogens occupancies
0.5 : 0.5).
The ligand substituents are located in a Zanti arrangement
about the amidine unit (Scheme 1), precluding any hydrogen
bonding interactions with the halogen atom. The ∆CN value
[0.071 Å] is typical for segregated single and double bonds
within an amidine unit, with virtually no delocalisation of the
amide lone-pair into the core reflected by the relatively large
angle between the ‘–NMe2’ group and the ‘CN2’ moiety [40.0Њ]
and long carbon–nitrogen bond [1.383(3) Å].
Despite the application of the bicyclic guanidine hppH
as a source of both anionic2,9,23 and neutral3,4 ligand, and sub-
sequent interest in the distribution of π-electron density
throughout the framework, the crystal structure of the neutral
compound has not been reported.24 A sample of commercial
hppH was therefore recrystallised from THF and the crystals
examined by X-ray diffraction. The molecular structure is illus-
trated in Fig. 4(a), crystal data are summarised in Table 1 and
selected bond lengths and angles in Table 5.
Symmetry operation: Ј Ϫx, Ϫy ϩ 1, Ϫz
of the molecule. The NH atom is disordered over two positions
(occupancy 0.5 : 0.5) and, as a consequence, the carbon–
nitrogen distances within the amidine moiety [1.328(2) and
1.331(2) Å] are commensurate with a delocalised bonding situ-
ation with an insignificant ∆CN value. As is often the case with
this bicyclic framework, disorder is observed in one of the
β-methylene units (labeling with respect to CN2) where the C(6)
carbon atom is located above and below the plane defined by
the ‘CN3’ core of the molecule (Fig. 4(b)). The relative occu-
pancies in this case are 0.71 and 0.29 with the predominant
structure consisting of an ‘up-down’ arrangement of the C(6)
and C(3) β-methylene units, respectively.
Having previously demonstrated that hppH is an effective
ligand at copper() centres,2,4 we were interested in investigating
its potential to function as a neutral ligand at alternative metals.
It was noted as part of White’s previously mentioned study on
adduct formation that substituted pyridine complexes of the
lithium halides LiX (X = Cl, Br or I) often formed analogous
structures to those observed in the copper() complexes. For
example, when L = 3,5-Me2-py or 4-tBu-py, the halides of both
copper() and lithium form tris-ligand complexes [MXL3],
whilst the ortho-methyl substituted base L = 2-Me-py adopts
the dihalobridged dimer structures, [L2MX2ML2], in the solid
state.25,26 We therefore decided to investigate the solid state
structure of the hppH adduct of lithium chloride, and compare
it with the copper() complex, CuCl(hppH)2.
The bis-ligand complex, [LiCl(hppH)2]n (4) was generated
from the reaction of two equivalents of the guanidine with LiCl
in THF at room temperature. The ν(C᎐N) stretch in the IR
᎐
spectrum (1636 cmϪ1) is virtually unchanged when compared
with the non-coordinated hppH value (1641 cmϪ1), and the
mass spectrum was similarly uninformative, with the highest
molecular weight fragment (m/z = 138) only indicating the
presence of the ligand. Combustion analysis was consistently
inaccurate for the predicted bis-ligand complex [LiCl(hppH)2]n
which we attribute to the presence of a small amount of hydrox-
ide contamination of the ‘anhydrous’ LiCl starting material,
where it has previously been noted that absolute dryness of the
starting material is not easily attained.26 To unambiguously
determine the molecular structure of 4, an X-ray diffraction
study was performed on representative crystals. The structure is
illustrated in Fig. 5(a), crystal data are summarised in Table 1
and selected bond lengths and angles in Table 6.
In contrast to the molecular structure of the copper() chlor-
ide adduct of hppH, which is monomeric with a trigonal-planar
metal centre, compound 4 exists as the µ,µ-dichlorobridged
dimer, with each lithium atom coordinated by two Nimine bound
hppH ligands in a distorted tetrahedral geometry [angles in
the range 100.7(2)–119.3(2)Њ]. The carbon–nitrogen distances
within the ligand framework indicate a tendency towards local-
ised single and double bonds, with ∆CN values of 0.085 Å and
0.068, considerably larger than in the corresponding Cu()
monomer [0.029 and 0.043 Å]. The C–Namide bond lengths
[1.369(3) and 1.377(4) Å] are also shorter than predicted for
Fig. 4 (a) Dimeric structure of hppH. Thermal ellipsoids drawn at the
30% probability level. (b) Disorder present in the C(6) β-methylene
group of hppH, with the major ‘up–down’ isomer illustrated by filled
bonds.
hppH crystallises as the hydrogen bridged dimer with two
NH ؒ ؒ ؒ N interactions [2.08 and 2.09 Å], similar to the
reported structures of the neutral amidine MeC{NAr}{NHAr}
(Ar = 2,6-iPr2C6H3).15 Such an interaction is attainable due to
the enforced Eanti configuration of the nitrogen substituents
arising from their incorporation within the bicyclic framework
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
542

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Table 7 Selected bond lengths (Å) and angles (Њ) 5
Ag–Cl
Ag–N(4)
C(1)–N(2)
C(8)–N(4)
C(8)–N(6)
H(5n) ؒ ؒ ؒ Cl
2.550(1)
2.191(3)
1.348(4)
1.306(4)
1.360(4)
2.80
Ag–N(1)
2.197(3)
1.303(4)
1.356(4)
1.353(4)
2.71
C(1)–N(1)
C(1)–N(3)
C(8)–N(5)
H(2n) ؒ ؒ ؒ Cl
N(1)–Ag–N(4)
N(4)–Ag–Cl
N(1)–C(1)–N(3)
N(4)–C(8)–N(5)
N(5)–C(8)–N(6)
128.25(9)
115.81(7)
124.4(3)
118.1(3)
117.5(3)
N(1)–Ag–Cl
115.55(7)
118.6(3)
117.0(3)
124.4(3)
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
N(4)–C(8)–N(6)
intramolecular NH ؒ ؒ ؒ Cl interactions that favour formation
of monomeric copper() halides4 we decided to investigate the
formation of hppH adducts at silver() chloride.
Addition of two equivalents of a THF solution of hppH to a
slurry of AgCl also in THF resulted in gradual dissolution of
the solid over a 48 h period, during which time light was
excluded from the reaction. A pale pink solid was isolated from
the reaction upon removal of the volatiles and crystallisation
from toluene afforded colourless crystals. Combustion analysis
was consistent with formation of the bis-ligand complex
[AgCl(hppH)2]n (5), although mass spectrometry was once
1
again uninformative. H NMR data indicated a symmetrical
environment for the bicyclic guanidine with a low field reson-
ance at δ 7.77 assigned to the ligand NH proton. To determine
the degree (if any) of oligomerisation within 5 the X-ray dif-
fraction study was performed on representative crystals. The
molecular structure is illustrated in Fig. 6, crystal data are
summarised in Table 2 and selected bond lengths and angles in
Table 7.
Fig. 5 (a) Molecular structure of [LiCl(hppH)2]2 (4) with thermal
ellipsoids drawn at the 30% probability level. Hydrogen atoms
excluding NH omitted. (b) Core of
interactions to both primary and secondary chlorine atoms.
4 illustrating H-bonding
single C(sp2)–N distance ca. 1.42 Å,11 indicating some delocal-
isation of the nitrogen lone pair into the ligand π-system.
In contrast to the central metallacycle within compound 1,
the ‘Li2Cl2’ core of 4 forms a much more symmetrical structure
with Li–Cl and Li–ClЈ distances of 2.398(5) and 2.416(5) Å,
respectively. A plausible explanation for the observed similarity
in bond length becomes apparent upon consideration of the
NH ؒ ؒ ؒ Cl hydrogen bonding interactions, where it is found
that in contrast to 1, each ligand of the metal centre is hydro-
gen-bonded to a different chloride ion with distances of 2.45
and 2.47 Å (Fig. 5(b) and Scheme 2). Thus we can consider any
stabilisation from NH ؒ ؒ ؒ Cl interactions as being approx-
imately equal to the ‘primary’ and “secondary’ chlorides, with
the resultant structure of 4 containing an effectively sym-
metrical metallacyclic core.
Fig.
6
Molecular structure of AgCl(hppH)2 (5) with thermal
ellipsoids drawn at the 30% probability level.
Despite a wealth of information concerning the diversity of
solid-state structures adopted by copper() halides incorpor-
ating unidentate N-donor ligands, extension to the heavier
silver() congeners is somewhat restricted. It is reported that,
even upon recrystallisation from the neat base, only well formed
crystals of non-complexed AgCl are isolated when 2- or
4-methylpyridine is employed,27 and, whilst under similar
experimental conditions evidence exists for adduct formation
with piperidine, morpholine and triethylamine, only quinoline
afforded crystals suitable for an X-ray diffraction study, reveal-
ing the 1 : 1 complex.28 The only structurally characterised
example of a 2 : 1 ligand to silver chloride complex, to date, is
the bis-piperidine adduct which forms an infinite one-dimen-
sional –Cl–Ag–Cl–Ag– polymer chain with four-coordinate
silver centres.29 The related cationic silver triflate complex,
[Ag(PhHC{NPh}{NHPh})2]ϩ[SO3CF3]Ϫ, should also be noted,
consisting of a well separated ion pair with a linear co-
ordination geometry at silver.18 In light of the stabilising
Compound 5 is isostructural to the copper() complex, and
exists as a monomeric, trigonal-planar [Σangles = 359.61Њ] silver()
chloride unit supported by two Nimine bound hppH ligands. This
structure represents the first example of a three-coordinate
silver() centre supported by nitrogen-based ligands, and is a
likely consequence of the intramolecular NH ؒ ؒ ؒ Cl stabilis-
ation [H(2n) ؒ ؒ ؒ Cl 2.71 Å; H(5n) ؒ ؒ ؒ Cl 2.80 Å] resulting in a
‘pseudo-chelating’ bonding mode for the ligand with inter-
actions at both the metal and the halide atoms. The carbon–
nitrogen bond lengths within the guanidine core are similar to
related complexes in which the ligand is acting as an Nimine
donor with ∆CN values of 0.045 and 0.047 Å indicating partial
retention of the single and double bonds. The Ag–N distances
[2.197(3) and 2.191(3) Å] in 5 are significantly shorter than
in the aforementioned bis(piperidine) complex [2.385(8) and
2.347(11) Å],29 a likely consequence of the reduced co-
ordination geometry at the metal in 5.
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543

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Table 8 Activation parameters for the fluxional process involving the
The Ag–Cl distance in 5 [2.550(1) Å] is comparable to that in
the recently reported bis(triphenylphosphine) complex [2.539
Å],30 but significantly longer than in the corresponding bis(tri-
cyclohexylphosphine) complex [2.489(1) Å].31 This suggests
similar electronic donor properties from both the hppH and
PPh3 ligands, although it is difficult to make direct comparisons
due to differences in the steric demands of the two ligand
classes (vide infra). For example, the greater the Ag–X bond
length, the closer this may be considered to an ionic bonding
situation, where the extreme case corresponds to the ion-pair,
[AgL2]ϩ[Cl]Ϫ, consisting of a linear L–Ag–L unit. However,
comparison of this angle (θ) in the three-coordinate silver
complexes above shows by far the largest P–Ag–P angle in
the triphenylphosphine complex [137.17Њ] with indistinguish-
able values for the tricyclohexylphosphine [128.29(3)Њ] and
5 [128.25(9)Њ]. It is also likely that intramolecular H-bonding
in 5 will influence both the Ag–Cl distance and the L–Ag–L
angle.
hppH ligand
Compound
∆G‡ a/kJ molϪ1
CuCl(hppH)2
CuBr(hppH)2
CuI(hppH)2
CuCl(hppH)(PPh3)
[CuBr(hppH)(PPh3)]2
[CuI(hppH)(PPh3)]2
45.8 0.2
47.2 0.4
44.9 0.4
50.2 0.5
51.6 0.4
49.4 0.2
a Values calculated from variable temperature 1H NMR spectroscopy at
500 MHz in d8-toluene.
lographic studies were undertaken on compounds 6–8; the
molecular structures of 6 and 8 are illustrated in Figs. 7 and 8,
crystal data are summarised in Table 2 and selected bond
lengths and angles in Tables 9–11.
Our initial interest in hppH bound copper() complexes
focused on the application of such species as catalysts for the
atom transfer radical polymerisation (ATRP) of methacryl-
ates.4 We demonstrated (by variable temperature NMR studies)
that, for the precursor bis-ligand halide complexes, a fluxional
process existed in solution likely involving decoordination of
the guanidine from the ‘CuX’ fragment, and that this was a
lower energy process than in Cu() bipy and pyridine imine
systems.32 We reasoned that by substituting one of the hppH
ligands with a second ligand providing a greater electron-with-
drawing effect or binding through an element with π-acceptor
properties, a more electron deficient metal would result leading
to an increased interaction of the Nimine lone pair and hence a
stronger N–Cu interaction. As phosphines have been exten-
sively used as neutral donors at copper() centres, we decided to
focus initially on targeting the mixed ligand complexes [CuX-
(hppH)(PPh3)]n. In addition, the synthesis of a coherent series
of complexes will allow a more meaningful delineation of
the relative influences of the steric and electronic factors
contributing to the bonding of hppH compared with PPh3.
The mixed ligand complexes [CuX(hppH)(PPh3)]n (6, X = Cl,
n =1; 7, X = Br, n = 2; 8 X = I, n = 2) were synthesised directly by
the addition of a 1 : 1 mixture of hppH and PPh3 in THF, to a
slurry of CuX also in THF. The resultant complexes 6–8 are
soluble in this solvent so that on complete addition, a clear
solution is obtained. Crystallisation by slow cooling of a
warmed, saturated solution to room temperature afforded the
desired complex as off-white crystals in good (66–72%) yields.
Spectroscopic (1H, 13C, 31P NMR; IR) data were consistent with
the incorporation of one guanidine and one phosphine per
‘CuX’ unit, and mass spectral analysis of 6 indicated a molecu-
lar ion peak corresponding to the monomeric unit [m/z 499].
In each of the compounds 6–8, three resonances attributable
to the guanidine methylene groups are observed in the room
Fig. 7 Molecular structure of CuCl(hppH)(PPh3) (6) with thermal
ellipsoids drawn at the 30% probability level. Hydrogen atoms except
NH omitted.
1
temperature H NMR spectra, suggesting a similar fluxional
process to that observed in the bis(hppH) adducts.4 This was
examined by variable temperature NMR experiments, the
results of which are presented in Table 8. It is clear from these
data that a higher energy barrier to the observed fluxional pro-
cess is evident in the mixed ligand complexes compared with the
CuX(hppH)2 species, with values an average of 4.4 kJ molϪ1
greater. This is in agreement with the supposition that ligand
decoordination must occur in order to render the methylene
units equivalent on each ring of the bicyclic guanidine, with a
stronger Nimine
Cu interaction observed upon replacement of
Fig. 8 Molecular structure of [CuI(hppH)(PPh3)]2 (8) with thermal
ellipsoids drawn at the 30% probability level. Hydrogen atoms except
NH omitted.
the second hppH with a less basic PPh3. Comparison of the
different values within the two series of compounds reveals a
similar trend in each, with a significantly higher value observed
for the bromide. Presumably in this case the correct balance of
steric and electronic factors are present to favour coordination
of the guanidine and enhance intramolecular stabilisation. In
order to further understand these observations, X-ray crystal-
In agreement with spectroscopic data, compounds 6–8 each
exist as the mixed ligand compounds [CuX(hppH)(PPh3)]n. The
chloride forms a monomeric, distorted trigonal planar copper
centre (n = 1) while the bromide and iodide are isomorphous
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
544

View Article Online
and consist of a dimeric structure (n = 2) with distorted tetra-
hedral metal atoms. Compound 6 is therefore most closely
related to the bis(hppH) analogue, with the Σangles at Cu = 360Њ
and an intramolecular NH ؒ ؒ ؒ Cl interaction [2.47 Å]. The
carbon–nitrogen distances within 6 again reveal a relatively low
102.20(5)Њ, respectively, with NH ؒ ؒ ؒ X distances of 2.67 Å (7)
and 2.83 Å (8). Using the same argument presented above, the
hydrogen bonds in 7 and 8 may be considered as being to the
primary halide in each case. Slightly larger ∆CN values [7, 0.058
Å; 8, 0.048 Å] imply a greater degree of localisation within the
guanidine compared with the monomeric chloride, 6.
∆
value [0.028 Å] suggesting a degree of delocalisation.
CN
Compounds 7 and 8 each contain distorted tetrahedral coppers
with angles in the range 115.42(6)–101.70(5)Њ and 116.96(5)–
Synthesis of 6–8 allows us to assess the different properties of
hppH as a ligand compared to PPh3, through comparison of
bond lengths and angles with the previously reported CuX-
(PPh3)2 and CuX(hppH)2 compounds (Table 12). The most
valid series is comprised of the chlorides as each of the com-
pounds crystallises as the monomeric species in the solid state.
The bis(triphenylphosphine) adduct has been reported as both
the hemi-THF solvate (entry 3),33 and the hemi-benzene solvate
(entry 4);34 the structures are essentially identical and will be
discussed together. It is also noted that the compound also
crystallises as the µ,µЈ-dichlorobridged dimer, with one mole-
cule of acetone.35
On sequential replacement of an hppH ligand by PPh3 we
can see a notable shortening of the Cu–Cl bond distance from
approximately 2.40 to 2.21 Å, consistent with an increased
withdrawal of electron density from the metal by the phosphine
(in agreement with the solution state behaviour, vide supra).
However we do not observe a similar reduction of the Cu–N
distances (entries 1 and 2) which may reflect steric interactions
between the donor ligands in the solid-state, substantiated
by comparison of the mixed ligand compound with the
bis(phosphine) adducts, where introduction of a second PPh3
group greatly increases both of the Cu–P distances. Steric inter-
actions are also presumed to be the cause of the variation
in L1–Cu–L2 angles (θ) which is largest for the bis(guanidine)
derivative.
Further comparisons are complicated by the dimeric nature
of compounds 7 and 8 and the accompanying change from
trigonal to tetrahedral geometry; however both of the end
members of the series for the bromides are monomeric (entries
6 and 8).36 A similar shortening of the Cu–Br distance is evident
on replacing the guanidines with phosphines, and comparable
θ-values to the chlorides are noted. Comparing analogous
compounds 7 and 8 we observe an increase in both the Cu–N
and Cu–P distances when replacing the bromide with an iodide,
reflecting the increased electron density at the metal.
In summary, X-ray diffraction studies of a number of mono-
valent halides of copper, lithium and silver incorporating neu-
tral amidines and guanidines are presented, demonstrating a
wide diversity in the types of structure adopted in the solid-
state. Examples of monomeric (trigonal planar) and dimeric
(tetrahedral) metal centres are reported, incorporating one or
two donor ligands. The presence of different patterns of intra-
molecular NH ؒ ؒ ؒ X (X = halogen) stabilisation are noted, and
synthesis of the series of compounds [CuX(hppH)(PPh3)]n has
permitted a brief discussion of the relative donor properties of
the two ligands to be carried out.
Table 9 Selected bond lengths (Å) and angles (Њ) for 6
Cu–N(1)
Cu–Cl
C(1)–N(2)
H(2) ؒ ؒ ؒ Cl
1.9722(15)
2.2718(5)
1.351(3)
2.47
Cu–P
C(1)–N(1)
C(1)–N(3)
2.2018(5)
1.323(2)
1.355(2)
P–Cu–N(1)
122.85(5)
116.02(5)
123.55(17)
115.30(6)
117.29(6)
102.52(8)
P–Cu–Cl
121.115(19)
118.52(16)
117.87(17)
113.25(6)
101.99(8)
104.68(8)
N(1)–Cu–Cl
N(1)–C(1)–N(3)
C(8)–P–Cu
C(20)–P–Cu
C(8)–P–C(20)
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
C(14)–P–Cu
C(8)–P–C(14)
C(14)–P–C(20)
Table 10 Selected bond lengths (Å) and angles (Њ) 7
Cu–N(1)
Cu–Br
C(1)–N(1)
C(1)–N(3)
2.0179(19)
2.5807(4)
1.305(3)
Cu–P
Cu–BrЈ
C(1)–N(2)
H(3) ؒ ؒ ؒ BrЈ
2.2111(6)
2.5272(3)
1.359(3)
2.67
1.363(3)
P–Cu–N(1)
P–Cu–BrЈ
115.42(6)
113.367(19)
113.69(5)
125.1(2)
P–Cu–Br
N(1)–Cu–Br
Br–Cu–BrЈ
N(1)–C(1)–N(3)
C(8)–P–Cu
C(20)–P–Cu
C(8)–P–C(20)
106.136(18)
101.70(5)
104.868(11)
118.0(2)
115.39(7)
110.82(7)
102.11(10)
N(1)–Cu–BrЈ
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
C(14)–P–Cu
C(8)–P–C(14)
C(14)–P–C(20)
116.8(2)
118.44(8)
105.74(10)
102.38(10)
Symmetry operation: Ј Ϫx, Ϫy, Ϫz.
Table 11 Selected bond lengths (Å) and angles (Њ) for 8
Cu–N(1)
Cu–I
C(1)–N(1)
C(1)–N(3)
2.0282(17)
2.7248(3)
1.310(3)
Cu–P
Cu–IЈ
C(1)–N(2)
H(3) ؒ ؒ ؒ IЈ
2.2377(5)
2.6791(3)
1.364(3)
2.83
1.358(3)
P–Cu–N(1)
P–Cu–IЈ
N(1)–Cu–IЈ
N(1)–C(1)–N(2)
N(2)–C(1)–N(3)
C(14)–P–Cu
C(8)–P–C(14)
C(14)–P–C(20)
113.85(5)
109.021(16)
116.96(5)
124.81(19)
116.64(19)
119.60(7)
105.16(9)
102.81(10)
P–Cu–I
N(1)–Cu–I
I–Cu–IЈ
N(1)–C(1)–N(3)
C(8)–P–Cu
C(20)–P–Cu
C(8)–P–C(20)
105.548(15)
102.20(5)
108.285(9)
118.47(18)
114.51(7)
110.55(6)
102.25(9)
Symmetry operation: Ј Ϫx, Ϫy, Ϫz.
Table 12 Metrical parameters for the series of compounds [CuX{L1}{L2}]n (X = Cl, Br, I; L1 and L2 = hppH or PPh3; n = 1 or 2; θ = L1–Cu–L2 angle)
Entry
L1
L2
X
n
Cu–L1/Å
Cu–L2/Å
Cu–X/Å
Cu–XЈ/Å
θ/Њ
Ref.
1
2
3
4
5
6
7
8
9
hppH
PPh3
PPh3
PPh3
PPh3
hppH
PPh3
PPh3
hppH
PPh3
PPh3
hppH
hppH
PPh3
PPh3
PPh3
hppH
hppH
PPh3
hppH
hppH
PPh3
Cl
Cl
Cl
Cl
Cl
Br
Br
Br
I
1
1
1.962(2)
2.2018(5)
2.2564(9)
2.272(2)
2.279
1.962(3)
2.2111(6)
2.282(3)
–
1.966(2)
1.9722(15)
2.2676(9)
2.260(2)
2.295
1.962(3)
2.0179(19)
2.263(3)
–
2.3977(8)
2.2718(5)
2.214(1)
2.208(2)
2.401
2.5611(5)
2.5807(4)
2.346(2)
–
–
–
–
–
130.37(9)
122.85(5)
125.55(4)
125.48(7)
116.49
130.49(10)
115.42(6)
126.0(1)
–
4
This work
33
34
35
1a
1b
2c
1
2.403
–
2.5272(3)
–
4
2
This work
36
4
This work
34
1d
1
–
10
11
I
I
2
1
2.2377(5)
2.273(2)
2.282(17)
2.273(2)
2.7248(3)
2.524(2)
2.6791(3)
–
113.85(5)
126.9(1)
a (THF)0.5 solvate. b (C6H6)0.5 solvate. c (acetone) solvate. d (C6H6)0.5 solvate.
D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
545

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Acknowledgement
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We thank the University of Sussex for financial support, and
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D a l t o n T r a n s . , 2 0 0 4 , 5 3 7 – 5 4 6
546