Synthesis and structural characterization of a series of group 11 2,2-Dialkyl-1,3-dicyclohexylguanidinate complexes

Article abstract of DOI:10.1071/CH14134

The addition of either lithium dimethylamide or lithium diethylamide to a tetrahydrofuran (THF) solution of 1,3-dicyclohexylcarbodiimide yielded THF adducts of lithium 2,2-dimethyl-1,3-dicyclohexylguandidinate (1) and lithium 2,2-diethyl-1,3-dicyclohexylguandidinate (2), respectively. One equivalent of either 1 or 2 was subsequently reacted with one equivalent of Group 11 halide (CuCl, AgBr, and AuCl) to generate oligonuclear complexes with the general formula {M[CyNC(NR2)NCy]}n where M, R, and n are respectively Cu, CH3, 2 (3); Cu, CH2CH3, 2 (4); Ag, CH3, 3 (5); Ag, CH2CH3, 3 (6); Au, CH3, 2 (7); and Au, CH2CH3, 2 (8). Compounds 1-8 were characterized by single-crystal X-ray diffraction. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, Fourier transform infrared spectroscopy, and 1H, 13C, and 7Li NMR studies. The unique structural aspects of this family of Group 11 complexes are highlighted. CSIRO 2014.

Full text of DOI:10.1071/CH14134

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1021–1029
Full Paper
http://dx.doi.org/10.1071/CH14134
Synthesis and Structural Characterization of a Series
of Group 11 2,2-Dialkyl-1,3-dicyclohexylguanidinate
Complexes
A
A
A B
,
Sonya K. Adas, Jesus A. Ocana, and Scott D. Bunge
A
Kent State University, Department of Chemistry and Biochemistry,
Kent OH 44242, USA.
B
Corresponding author. Email: sbunge@kent.edu
The addition of either lithium dimethylamide or lithium diethylamide to a tetrahydrofuran (THF) solution of 1,3-
dicyclohexylcarbodiimide yielded THF adducts of lithium 2,2-dimethyl-1,3-dicyclohexylguandidinate (1) and lithium
2,2-diethyl-1,3-dicyclohexylguandidinate (2), respectively. One equivalent of either 1 or 2 was subsequently reacted with
one equivalent of Group 11 halide (CuCl, AgBr, and AuCl) to generate oligonuclear complexes with the general formula
{M[CyNC(NR2)NCy]}n where M, R, and n are respectively Cu, CH3, 2 (3); Cu, CH2CH3, 2 (4); Ag, CH3, 3 (5); Ag,
CH2CH3, 3 (6); Au, CH3, 2 (7); and Au, CH2CH3, 2 (8). Compounds 1–8 were characterized by single-crystal X-ray
diffraction. The bulk powders for all complexes were found to be in agreement with the crystal structures based on
elemental analyses, Fourier transform infrared spectroscopy, and 1H, 13C, and 7Li NMR studies. The unique structural
aspects of this family of Group 11 complexes are highlighted.
Manuscript received: 11 March 2014.
Manuscript accepted: 16 April 2014.
Published online: 4 June 2014.
Introduction
diffraction. The bulk powders for all complexes were in agree-
ment with the crystal structures based on elemental analyses,
Fourier transform infrared (FTIR) spectroscopy, and 1H and
13C NMR studies.
The use of the mono-anionic guanidinate ligand set has had a
renaissance in the field of inorganic chemistry.[1–15] Guanidi-
nates have developed into a versatile class of both N-donor and
N,N0-donor ligands owing to the zwitterionic resonance of the
‘CN3’ core. The dynamic resonance of the guanidinate anion
facilitates delocalization of the negative charge on the coordi-
nating N atom.[16] This resonance, coupled with steric and
electronic tuning of the substituents, imparts the versatility
necessary to readily coordinate hard and soft Lewis acids.[9–12]
This degree of electronic stabilization is not obtained by using
classic amido ligands such as NPh2, NEt2, and NMe2.[17]
Owing to the unique nature of these ligands, multinuclear
Group 11 guanidinate compounds have become well repre-
sented in the literature. These complexes have been studied
for their potential to have closed shell d10–d10 metal interac-
tions, as reagents for atomic layer deposition, and for their
luminescent properties.[18–24]
One of the underlying themes of our research has involved the
development of 1,1,3,3-tetraalkylguanidinate (TAG) ligands (L3,
Fig. 1).[25–31] Our focus has been to use the N-donor to generate
well-defined low-coordinate complexes. Using Group 11 metals,
this ligand set resulted in the formation of novel hexanuclear, [Cu
(m-TAG)]6 and tetranuclear {M2(m-TAG)[m-N(SiMe3)2]}2 (M¼
Cu, Ag, and Au) structural motifs. Herein, we describe an
extension of this work to the synthesis and characterization of
Li, Cu, Ag, and Au complexes containing the 1,3-dicyclohexyl-
2,2-dialkylguanidinate ligand CyNC(NR2)NCy (L1, Fig. 1).
Compounds 1–8 were characterized by single-crystal X-ray
Experimental
Materials and Physical Measurements
All syntheses were handled with rigorous exclusion of air and
water using standard glove box techniques. All anhydrous sol-
vents were stored under argon and used as received in sure seal
bottles. The following chemicals were used as received from
commercial suppliers: lithium dimethylamide, lithium diethy-
lamide, CuCl, AgBr, AuCl, and 1,2-dicyclohexylcarbodiimide.
CuCl was purchased from a commercial supplier and purified
using standard methods before use. {Cu[CyNC(NMe2)NCy]}2
(3) was synthesized according to a modified literature proce-
dure.[32] FTIR data were obtained on a Bruker Tensor 27 spec-
trometer using KBr under an atmosphere of flowing nitrogen.
Melting points of the samples were determined in sealed cap-
illary tubes under an atmosphere of argon using an Electro-
thermal Mel-Temp apparatus and are uncorrected. Elemental
analysis was performed on a Perkin–Elmer 2400 Series 2 CHN-
S/O Elemental Analyzer. All NMR samples were prepared from
dried crystalline materials that were handled and stored under an
argon atmosphere and re-dissolved in [D8]toluene or [D6]ben-
zene. All solution spectra were obtained on a Bruker DRX 400
spectrometer at 400.1, 155.5, and 100.6 MHz for 1H, 7 Li, and
13C experiments, respectively.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

1022
S. K. Adas, J. A. Ocana, and S. D. Bunge
R
N
RЈ
RЉ
RЉ
(w). dH ([D8]toluene) 2.98 (2H, m, NCH), 2.62 (6H, s, N
(CH3)2), 2.04–1.00 (20H, m, Cy). dC ([D8]toluene) 172.2
(NCN), 68.5 (N(CH3)2), 58.1, 41.7, 39.8, 29.3 (Cy). Anal. Calc.
for C30H56Cu2N6: C 57.39, H 8.99, N 13.38. Found: C 57.52,
H 9.27, N 13.39 %.
N
N
R
N
RЈ
C
C
C
R
N
N
N
N
RЈ
N
Ϫ
Ϫ
Ϫ
L1
L2
L3
{Cu[CyNC(NEt2)NCy]}2 (4)
Fig. 1. Structures of mono-anionic guanidinate ligands. R ¼ silyl;
R0 ¼ alkyl; R00 ¼ aryl.
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide
(1.04 g, 5.0 mmol) was added dropwise to a 10 mL THF solution
of LiN(CH2CH3)2 (0.26 g, 5.0 mmol). CuCl (0.50 g, 5.0 mmol)
was ground to a fine powder then added dry to the mixture and
the reaction was stirred for 1 h with the exclusion of light. The
reaction generated a dark orange solution that was centrifuged
(1000 g, 258C, 5 min) then concentrated. The solution yielded
colourless crystals at ꢀ358C (0.41 g, 0.60 mmol, 24 %), mp
1298C (dec.). nmax (KBr)/cmꢀ1 2927 (s), 2852 (s), 1536 (s),
1449 (m), 1400 (w), 1364 (w), 1340 (w), 1282 (w), 1143 (w),
1089 (w), 1030 (w), 889 (w), 804 (w), 616 (w), 446 (m). dH ([D6]
benzene) 3.60ꢀ3.57 (4H, m, N(CH2CH3)2), 3.25–3.09 (2H, m,
NCH), 1.96–1.34 (20H, m, Cy), 1.23–1.01 (6H, t, J 8.8, N
(CH2CH3)2). dC ([D6]benzene) 172.6 (NCN), 67.5 (N
(CH2CH3)2), 58.3, 52.6, 45.6, 41.7, 39.8, 37.5, 35.5, 29.3,
27.7, 27.1 (Cy), 13.5, 12.1 (N(CH2CH3)2). Anal. Calc. for
C34H64Cu2N6: C 59.70, H 9.43, N 12.29. Found: C 60.22, H
10.13, N 13.45 %.
{Li[CyNC(NMe2)NCy](THF)}2 (1)
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide
(0.36 g, 1.7 mmol) was added dropwise to a 10 mL THF solution
of LiN(CH3)2 (0.088 g, 1.7 mmol). The reaction was stirred for
1 h. The reaction yielded a pale yellow solution, which was
concentrated. The solution yielded colourless crystals at ꢀ358C
(0.41 g, 1.2 mmol, 72 %), mp 1088C. nmax (KBr)/cmꢀ1 2979 (s),
2923 (s), 2848 (s), 2778 (m), 1637 (m), 1505 (s), 1446 (s), 1355
(s), 1312 (m), 1274 (w), 1251 (m), 1235 (m), 1180 (w), 1156
(m), 1121 (m), 1107 (m), 1061 (s), 1027 (w), 1002 (m), 916 (m),
902 (m), 888 (m), 843 (w), 804 (w), 782 (w), 764 (w), 675 (w),
629 (w), 546 (w), 499 (w), 462 (w), 427 (w). dH ([D6]benzene)
3.58 (THF), 3.41 (2H, m, NCH), 2.74 (6H, s, N(CH3)2), 2.20–
1.20 (20H, m, Cy), 1.49 (THF). dC ([D6]benzene) 166.1
(NCN2), 68.2 (N(CH3)2), 66.3 (THF), 55.2, 44.3, 37.7, 27.6
(Cy), 26.3 (THF). dLi ([D6]benzene) 2.1. Anal. Calc. for
C38H72Li2N6O2: C 69.27, H 11.01, N 12.75. Found: C 68.32,
H 10.26, N 14.96 %.
{Ag[CyNC(NMe2)NCy]}3 (5)
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide
(1.0 g, 5.0 mmol) was added dropwise to a 10 mL THF solution
of LiN(CH3)2 (0.26 g, 5.0 mmol). AgBr (0.95 g, 5.0 mmol) was
then added to the mixture and the reaction was stirred for 1 h in
the exclusion of light. The solution generated an off-white
precipitate as the desired product. The powder was re-dissolved
in toluene and crystallized at ꢀ358C to generate the final product
(0.32 g, 0.90 mmol, 18 %), mp 1108C (dec.). nmax (KBr)/cmꢀ1
2985 (w), 2921 (s), 2849 (s), 2790 (m), 2664 (w), 1496 (s), 1445
(s), 1387 (s), 1355 (m), 1342 (m), 1315 (w), 1277 (w), 1255 (m),
1230 (m), 1182 (w), 1150 (w), 1125 (m), 1088 (w), 1068 (m),
1016 (m), 961 (w), 920 (w), 906 (w), 887 (m), 846 (w), 810 (w),
784 (w), 699 (w), 637 (w), 551 (w), 454 (w), 429 (w). dH ([D8]
toluene) 3.12 (2H, m, NCH), 2.694 (6H, s, N(CH3)2), 2.0–1.0
(20H, m, Cy). dC ([D8]toluene) 169.6 (NCN), 67.9 (N(CH3)2),
57.6, 41.1, 39.5, 26.8 (Cy). Anal. Calc. for C45H84Ag3N9: C
50.29, H 7.88, N 11.73. Found: C 47.96, H 7.61, N 10.86 %.
{Li[CyNC(NEt2)NCy](THF)}2ꢁ2(THF) (2)
A 5 mL THF solution of dicyclohexylcarbodiimide (1.0 g,
5.0 mmol) was added dropwise to a 10 mL THF solution of LiN
(CH2CH3)2 (1.4 g, 5.0 mmol). The reaction was stirred for 1 h.
The reaction yielded a pale yellow solution, which was centri-
fuged (1000 g, 258C, 5 min) then concentrated. The solution
yielded colourless crystals at ꢀ358C (1.24 g, 4.3 mmol, 87 %),
mp 688C. nmax (KBr)/cmꢀ1 2926 (s), 2852 (s), 2721 (s), 2665
(w), 2360 (w), 1636 (s), 1506 (s), 1449 (s), 1365 (s), 1339 (s),
1286 (m), 1257 (m), 1239 (m), 1211 (m), 1181 (w), 1143 (m),
1121 (w), 1071 (s), 1032 (w), 987 (w), 901 (w), 888 (w). dH
([D6]benzene) 3.61 (2H, m, NCH2CH3)2), 3.59 (THF), 3.26–
3.17 (4H, q, N(CH2CH3)2), 3.13–3.105 (2H, m, NCH), 1.93–
1.34 (20H, m, Cy), 1.71 (THF), 1.13–1.09 (6H, t, N(CH2CH3)2).
dC ([D8]benzene) 157.7 (NCN), 68.2 (N(CH2CH3)2), 53.9,
43.6, 36.2, 35.2, 26.9, 26.3, 26.1 (Cy), 25.8 (THF), 13.3,
12.9 (N(CH2CH3)2). dLi ([D6]benzene) 2.1. Anal. Calc. for
C42H80Li2N6O2: C 70.05, H 11.28, N 11.75. Found: C 69.76,
H 11.24, N 12.75 %.
{Ag[CyNC(NEt2)NCy]}3ꢁ(THF) (6)
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide
(1.0 g, 5.0 mmol) was added dropwise to a 10 mL THF solution
of LiN(CH2CH3)2 (0.39 g, 5.0 mmol). AgBr (0.95 g, 5.0 mmol)
was ground to a fine powder then added dry to the mixture and
the reaction was stirred for 1 h in the exclusion of light. The
reaction generated a dark grey solution. THF was removed to
yield a white powder. The powder was re-dissolved in toluene
and crystallized at ꢀ358C to generate the final product (0.48 g,
0.41 mmol, 8.3 %). nmax (KBr)/cmꢀ1 2925 (s), 2851 (s), 2721
(m), 1635 (s), 1505 (s), 1449 (m), 1359 (m), 1339 (m), 1288 (m),
1239 (w), 1211 (w), 1143 (w), 1122 (w), 1072 (m), 998 (w), 888
(m), 804 (w), 630 (w), 498 (w), 472 (w). dH ([D6]benzene) 3.62–
3.55 (4H, m, N(CH2CH3)2), 3.24–3.10 (2H, m, NCH), 2.11–1.39
(20H, m, Cy), 1.17–1.13 (6H, t, J 7.05, N(CH2CH3)2). dC ([D6]
benzene) 170.4 (NCN), 68.2 (N(CH2CH3)2), 57.4, 53.9, 44.52,
43.6, 37.7, 36.2, 35.7, 27.7, 27.0, 26.1 (Cy), 14.8, 13.3
{Cu[CyNC(NMe2)NCy]}2 (3)
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide
(1.0 g, 5.0 mmol) was added dropwise to a 10 mL THF solution
of LiN(CH3)2 (0.26 g, 5.0 mmol). CuCl (0.50 g, 5.0 mmol) was
then added to the mixture and the reaction was stirred for 1 h
with the exclusion of light. The solution generated an off-white
precipitate as the desired product. The powder was re-dissolved
in toluene and crystallized at ꢀ358C to give the final product
(0.50 g, 1.6 mmol, 32 %). nmax (KBr)/cmꢀ1 3001 (w), 2921 (s),
2848 (s), 2790 (m), 1504 (s), 1470 (s), 1387 (s), 1356 (m), 1341
(m), 1272 (w), 1252 (m), 1228 (m), 1181 (w), 1128 (m), 1110
(w), 1174 (m), 1118 (m), 964 (w), 920 (w), 907 (w), 887 (m), 844
(w), 814 (w), 790 (w), 740 (w), 710 (w), 656 (w), 509 (w), 458

Group 11 Guanidinate Clusters
1023
(N(CH2CH3)2). Anal. Calc. for C51H96CAg3N9: C 52.85,
H 8.35, N 10.88. Found: C 52.08, H 8.66, N 10.89 %.
N2-cooled N2 stream on a Bruker AXS diffractometer. The
radiation used was graphite monochromatized MoKa (l
˚
0.7107A). The lattice parameters were optimized from a least-
{Au[CyNC(NMe2)NCy]}2 (7)
squares calculation on carefully centred reflections. Lattice
determination, data collection, structure refinement, scaling,
and data reduction were carried out using APEX2 (version
2014–1.1) software package.
A 5 mL THF solution of 1,2-dicyclohexylcarbodiimide (1.0g,
5.0 mmol) was added dropwise to a 10 mL THF solution of
LiN(CH3)2 (0.26 g, 5.0 mmol). AuCl (0.40 g, 1.7 mmol) was then
added to the mixture and the reaction was stirred for 1 h with the
exclusion of light. The solution generated a dark precipitate,
which was centrifuged (1000 g, 258C, 5 min) off. The remaining
solution was allowed to crystallize by slow evaporation to
generate the final product (0.34 g, 0.70 mmol, 44 %), mp 638C
(dec.). nmax (KBr)/cmꢀ1 2999 (w), 2924 (s), 2849 (s), 2790 (m),
1635 (s), 1579 (s), 1505 (s), 1465 (s), 1386 (s), 1358(m), 1342
(m), 1247 (s), 1225 (m), 1183 (w), 1131 (m), 1105 (w), 1072 (w),
1023 (w), 978 (w), 956 (w), 921 (w), 910 (w), 889 (m), 846 (w),
810 (w), 793 (w), 736 (w), 711 (w), 696 (w), 648 (w), 627 (w),
590 (w), 560 (w), 509 (w), 461 (w), 436 (w). dH ([D8]toluene)
3.25 (2H, m, NCH), 2.70, 2.50 (6 H, d, N(CH3)2), 1.9–1.0 (20H,
m, Cy). dC ([D8]toluene) 171.4 (NCN), 68.2 (N(CH3)2), 59.7,
41.4, 40.3, 39.0 (Cy). Anal. Calc. for C30H56Au2N6: C 40.18,
H 6.52, N 9.37. Found: C 41.29, H 6.90, N 9.32 %.
Each structure was solved using direct methods. This proce-
dure yielded Ag, Au, Cu, or Li atom along with several O, N, and
C atoms. Subsequent Fourier synthesis yielded the remaining
atom positions. The hydrogen atoms were fixed in positions of
ideal geometry and refined using the XSHELL software. These
hydrogen atoms had their isotropic temperature factors fixed at
either 1.2 or 1.5 times of the equivalent isotropic U of the C
atoms to which they were bonded. The final refinement of each
compound included anisotropic thermal parameters on all non-
hydrogen atoms.
Computational Details
Becke’s gradient-corrected exchange and LYP correlation
functional and its hybrid which form the B3 LYP level of the-
ory[33,34] was employed along with the Wachters[35] and Hay[36]
LANL2DZ basis set for molecular orbital and natural bond
orbital (NBO)[37] calculations. All molecular orbital calcula-
tions were done with the Spartan’04 package[38] and the coor-
dinates for the atoms in each structure were taken from the
crystallographic data. NBO analysis was conducted using the
Gaussian 98 package.[39,40]
{Au[CyNC(NEt2)NCy]}2ꢁ(THF) (8)
Compound 2 (1.2 g, 1.7 mmol) was dissolved in 10 mL of
THF and cooled to ꢀ348C. AuCl (0.40 g, 1.7 mmol) was then
added and the reaction was stirred for 1 h with the exclusion of
light. The solution generated a small amount of dark precipitate,
which was centrifuged (1000 g, 258C, 5 min) off. The remaining
solution was re-crystallized by slow evaporation to generate the
final product (0.57 g, 0.60 mmol, 35 %), mp 788C (dec.). nmax
(KBr)/cmꢀ1 2927 (s), 2852 (m), 2720 (m), 1636 (s), 1577 (w),
1449 (m), 1400 (m), 1363 (s), 1340 (m), 1307 (w), 1282 (s), 1258
(w), 1240 (w), 1207 (w), 1143 (w), 1090 (w), 1072 (w), 1045
(w), 889 (w). dH ([D6]benzene) 3.70–3.25 (6H, m, N(CH2CH3)2
and NCH), 1.25–1.22 (6H, t, J 7.0, N(CH2CH3)2), 2.02–0.97
(20H, m, Cy). dC ([D6]benzene) 153.7 (NCN), 68.2
(N(CH2CH3)2), 56.7, 53.9, 43.6, 36.3, 35.3, 34.8, 26.9, 26.4,
26.1 (Cy), 13.3 (N(CH2CH3)2). Anal. Calc. for C34H64Au2N6: C
42.95, H 6.78, N 8.84. Found: C 42.17, H 6.65, N 7.92 %.
Results and Discussion
Synthesis
Lithium 2,2-dialkyl-1,3-dicyclohexylguanidinate may be
straightforwardly generated via the reaction between lithium
dialkylamide and 1,2-dicyclohexylcarbodiimide. This ligand
has been successfully employed to facilitate the isolation of
monomeric early transition metal complexes e.g. {[s : Z1 : Z5-
(OCH2)(Me2NCH2)C2B9H9]Ti[Z3-CyNC(NMe2)NCy]}, {Ta
(NMe2)4[CyNC(NMe2)NCy]}, and Zr {Zr[CyNC(NiPr2)NCy]
Cl3}.[41–50] Herein, we report the use of this approach to cleanly
generate {Li[CyNC(NR2)NCy](THF)}2 where NR2 ¼ NMe2 (1)
and NEt2 (2) (Scheme 1). Compounds 1 and 2 were subsequently
reacted with MX (MX ¼ CuCl, AgBr, and AuCl) to form the
corresponding guanidinate complex {M[CyNC(NR2)NCy]}n
where M, R, and n are respectively Cu, CH3, 2 (3); Cu, CH2CH3,
2 (4); Ag, CH3, 3 (5); Ag, CH2CH3, 3 (6); Au, CH3, 2 (7); and
Au, CH2CH3, 2 (8). The synthesis of compounds 3–8 is shown in
X-Ray Structural Studies
X-ray crystallography was performed by mounting each col-
ourless crystal sample 1–8 onto a thin glass fibre from a pool of
FluorolubeTM and immediately placing it under a liquid
(a)
2
ϩ
2 LiNR2
N
C
N
{Li[CyNC(NR2)NCy](THF)}2
THF
(1) NR2 ϭ NMe2
(2) NR2 ϭ NEt2
(b)
n MX
n LiNR
ϩ
N
C
N
n
{M[CyNC(NR2)NCy]}n
2
THF
Ϫn LiX
(3) MX ϭ CuCl, n ϭ 2, NR2 ϭ NMe2
(4) MX ϭ CuCl, n ϭ 2, NR2 ϭ NEt2
(5) MX ϭ AgBr, n ϭ 3, NR2 ϭ NMe2
(6) MX ϭ AgBr, n ϭ 3, NR2 ϭ NEt2
(7) MX ϭ AuCl, n ϭ 2, NR2 ϭ NMe2
(8) MX ϭ AuCl, n ϭ 2, NR2 ϭ NEt2
Scheme 1. Synthesis of (a) 1–2 and (b) 2–4.

1024
S. K. Adas, J. A. Ocana, and S. D. Bunge
Scheme 1. Owing to the photosensitivity of the Group 11
complexes, the reactions are shielded from light throughout the
course of the synthesis. In each of these reactions, reduction to
elemental metal is observed and the insoluble precipitate is
removed from solution via centrifugation before concentration.
The reaction mixture is concentrated and cooled to ꢀ358C to
facilitate isolation of 1–8 as colourless crystals. For elemen-
tal analysis, re-crystallization was additionally performed by
re-dissolving the isolated solid in a THF/hexanes (1 : 1) mixture
and then cooling the sample to ꢀ358C for 24 h. Photosensitivity
precluded obtaining satisfactory elemental analysis for several
samples. Dry crystals of 1–8 are stable under argon at ꢀ358C in
the absence of light for several months.
Figs S1–S4 (Supplementary Material). The data collection
parameters are presented in Tables 1 and 2, and selected inter-
atomic distances and angles are includedwith the plots in Table 3.
Structural descriptions of the complexes are presented in the
N(2A)
N(3A)
N(1A)
Spectroscopic Studies
Cu(1A)
Cu(1)
Crystals of 1–8 were dried under vacuum to obtain a bulk
powder for use in subsequent studies. FTIR spectroscopic
studies revealed the absence of a characteristic n¼C¼N stretch
(2117 cmꢀ1) and the presence of a C¼N stretch typical of L1
guanidinates (1496 to 1474 cmꢀ1).[51] Compounds 1–8 were
moderately soluble in [D6]benzene and [D8]toluene, and
revealed expected resonances in the 1H and 13C NMR spectra. In
particular, all of the spectra show low-field resonances in the 13C
NMR analysis that are characteristic of guanidinates
(,160 ppm). Inherent asymmetry within the [CyNC(NEt2)
NCy] ligated complexes (2, 4, 6, and 8) results in multiple
resonances in the 13C NMR spectra assignable to the cyclohexyl
N(3)
N(1)
N(2)
7
Fig. 3. Thermal ellipsoid plot of 4. Ellipsoids are drawn at the 30 % level.
H atoms have been omitted for clarity. The additional ‘A’ letters in the atom
labels indicate that these atoms are at (–x þ 1, –y, –z). Selected inter-atomic
and ethyl substituents. Additionally, the Li NMR spectra for
compounds 1 and 2 reveal a single peak at 2.1 ppm.
˚
distances (A) and angles (8): Cu(1)–N(3A) 1.870(6), Cu(1)–N(1) 1.875(6),
Structural Description
˚
Cu(2)–N(3) 1.870(6), Cu(2)–N(1A) 1.875(6) A, N(3A)–Cu(1)–N(1) 173.2
All eight complexes were characterized by X-ray crystallogra-
phy. Thermal ellipsoid plots of 1–8 are shown in Figs 2–5 and
(3), N(3)–Cu(2)–N(6) 173.2(3)8.
N(1A)
N(3A)
N(8)
N(7)
N(9)
N(2A)
O(1A)
Ag(3)
Ag(1)
Li(1)
N(1)
Li(1A)
N(6)
O(1)
N(2)
N(2)
Ag(2)
N(3)
N(3)
N(4)
N(5)
N(1)
Fig. 2. Thermal ellipsoid plot of 1. Ellipsoids are drawn at the 30 % level. H
atoms have been omitted for clarity. The additional ‘A’ letters in the atom
labels indicate that these atoms are at (–x þ 1, –y, –z). Selected inter-atomic
Fig. 4. Thermal ellipsoid plot of 5. Ellipsoids are drawn at the 30 % level.
˚
H atoms have been omitted for clarity. Selected inter-atomic distances (A)
˚
distances (A) and angles (8):Li(1)–O(1)1.942(3), Li(1)–N(3)1.991(3), Li(1)–
and angles (8): Ag(1)–N(1) 2.096(8), Ag(1)–N(9) 2.109(9), Ag(2)–N(4)
2.100(9), Ag(2)–N(3) 2.121(8), Ag(3)–N(6) 2.093(9), Ag(3)–N(7) 2.095
˚
N(2A) 2.066(3), Li(1)–N(2) 2.184(3)A, O(1)–Li(1)–N(3) 115.74(15), O(1)–
˚
(9) A, N(1)–Ag(1)–N(9) 169.5(3), N(4)–Ag(2)–N(3) 163.2(3), N(6)–Ag(3)–
Li(1)–N(2A) 110.04(14), N(3)–Li(1)–N(2A) 129.52(16), O(1)–Li(1)–N(2)
118.82(15), N(3)–Li(1)–N(2) 66.14(10), N(2A)–Li(1)–N(2) 108.74(13)8.
N(7) 162.3(4)8.

Group 11 Guanidinate Clusters
1025
following paragraphs. Owing to the similarity, when appropriate,
a general description of the complexes is provided. Table 3 lists
selected inter-atomic distance and angles for structurally char-
acterized Group 11L1 and L2 guanidinate complexes.
{Li[CyNC(NMe2)NCy](THF)}2 (1) and {Li[CyNC(NEt2)
NCy](THF)}2 (2)
Thermal ellipsoid plots of 1 and 2 are given in Figs 2 and S1.
Both 1 and 2 are centrosymmetric dimers that adopt a ‘ladder’
structure similar to that of previously reported solvated lithium
dialkyl-1,3-dialkylguanidinate complexes i.e. {Li[iPrNC(NiPr2)
NiPr](THF)}2, {Li[CyNC(NCH2CH2CH2CH2)2)NCy](THF)}2,
and {Li[CyNC(NiPr2)NCy](Et2O)}2.[52–54] In 1 and 2, each
lithium metal has a coordination number of four where Li(1)
is coordinated to one terminal THF molecule (Li(1)–O(1) 1.942
N(2)
˚
˚
(3) A in 1 and 1.928(7) A in 2). Each Li is connected to an
adjacent Li by two bridging N atoms (Li(1)–N(3) 1.991(3), Li
N(3)
N(1)
˚
(1)–N(2) 2.184(3) A in 1 and Li(1)–N(2) 1.991(7), Li(1)–N(1)
˚
2.282(8) A in 2). The Li coordination sphere is completed by
further coordination to an additional N atom from the guanidi-
˚
˚
nate (Li(1)–N(2A) 2.066(3) A in 1 and Li(1)–N(1) 2.050(7) A in
2). The Li–O(THF) bond lengths are in agreement with the
Au(2)
Au(1)
˚
average value of 1.94(6) A from the Cambridge Structural
Database.[55,56] Li–N(3)–C(1)–N(2) in 1 and Li–N(2)–C(11)–
N(1) in 2 form a nearly planar four-membered ring with
˚
˚
maximum deviations of 0.131 A and 0.122 A, respectively, on
either side of the planar central Li2N2 ring. These central and
side planes form dihedral angles of 51.388 and 52.258 in 1 and 2,
respectively. Owing to the symmetry of the molecule, the planes
of the guanidinate CN3 structure are parallel and deviate by
N(6)
N(4)
N(5)
˚
˚
0.278 A and 0.374 A. However, the CN3 plane in 1 and 2 deviate
only by 4.318 and 5.748, respectively, from the base of the
pyramidal structure. To quantify the four-coordinate geometry
around the metal centre, the t4 parameter[57] was calculated
from the two largest angles in 1 (N(3)–Li(1)–N(2A) 129.58 and
N(2)–Li(1)–O(1) 118.88) and 2 (N(2)–Li(1)–N(1A) 129.08 and
N(1)–Li(1)–O(1) 118.88). The geometry around the metal centre
Fig. 5. Thermal ellipsoid plot of 7. Ellipsoids are drawn at the 30 % level.
˚
H atoms have been omitted for clarity. Selected inter-atomic distances (A)
and angles (8): Au(1)–N(6) 2.025(9), Au(1)–N(1) 2.048(10), Au(2)–N(4)
˚
2.028(9), Au(2)–N(3) 2.044(9) A, N(6)–Au(1)–N(1) 167.7(3), N(4)–Au(2)–
N(3) 166.8(4)8.
Table 1. Data collection parameters for 1–4
Compound
1
2
3
4
Chemical formula
Formula weight
T [K]
C38H72Li2N6O2
658.9
C50H96Li2N6O4
859.20
C30H56Cu2N6
658.9
C34H64Cu2N6
683.99
189(2)
189(2)
160(2)
180(2)
Space group
Monoclinic
P2(1)/c
Monoclinic
P2(1)/c
Triclinic
Monoclinic
P2(1)/c
Pı
¯
Size [mm]
˚
a [A]
˚
b [A]
0.38 ꢂ 0.31 ꢂ 0.23 0.10 ꢂ 0.10 ꢂ 0.10 0.20 ꢂ 0.19 ꢂ 0.12 0.35 ꢂ 0.30 ꢂ 0.20
10.9032(16)
18.073(3)
13.442(4)
18.884(6)
11.606(4)
10.4108(16)
11.3907(15)
16.049(3)
97.117(3)
107.487(2)
112.556(4)
1613.4(4)
2
13.397(13)
7.098(8)
˚
c [A]
10.6721(17)
22.211(18)
a [8]
b [8]
g [8]
103.214(4)
113.617(4)
119.27(5)
3
˚
V [A ]
2047.2(5)
2
2699.4(15)
4
1842(3)
2
Z
Dc [Mg mꢀ3
]
1.069
0.880
1.292
1.233
Reflections collected (unique) 16199 (3617)
18952 (4767)
0.796 (237)
0.233
13151 (5720)
0.759 (347)
0.357
14095 (3263)
0.853 (192)
0.438
GOF (parameters)
ꢀ3
0.856 (219)
0.286
˚
Drmax [e A
Tmin/Tmax
]
0.894/0.985
0.065
0.824/0.993
0.053
0.558/0.855
1.346
0.680/0.796
1.184
m(MoKa) [mmꢀ1
]
RA1 [%] (all data)
wRB2 [%] (all data)
4.82 (6.66)
8.69 (22.95)
3.21 (4.54)
6.57 (17.40)
13.94 (15.94)
20.04 (25.11)
9.41 (10.86)
14.44 (21.06)
AR1 ¼ S(||Fo| ꢀ |Fc||)/S|Fo| ꢂ 100 %.
BwR2 ¼ [Sw(Fo2 ꢀ Fc2)2/S(w|Fo|2)2]1/2 ꢂ 100 %.

1026
S. K. Adas, J. A. Ocana, and S. D. Bunge
Table 2. Data collection parameters for 5–8
Compound
5
6
7
8
Chemical formula
Formula weight
T [K]
C49H92Ag3N9O
1146.92
C51H96Ag3N9
1158.98
C30H56Au2N6
894.74
C38H56Au2N6O
1022.94
160(2)
189(2)
189(2)
189(2)
Space group
Monoclinic
P2(1)/n
Triclinic
Triclinic
Tetragonal
ꢀ
P4b2
Pı
¯
Pı
¯
Size [mm]
˚
a [A]
˚
b [A]
0.29 ꢂ 0.15 ꢂ 0.12 0.30 ꢂ 0.20 ꢂ 0.20 0.20 ꢂ 0.19 ꢂ 0.14 0.10 ꢂ 0.08 ꢂ 0.05
13.663(8)
17.927(10)
22.310(13)
12.986(4)
14.266(4)
17.000(5)
95.134(5)
95.318(4)
114.367(4)
2828.0(13)
2
10.4435(3)
11.5080(3)
16.0854(4)
97.535(2)
106.587(2)
112.530(2)
1646.98(8)
2
16.622(2)
16.622(2)
7.6463(14)
˚
c [A]
a [8]
b [8]
g [8]
99.680(10)
3
˚
V [A ]
5387(5)
4
2112.5(7)
2
Z
Dc [Mg mꢀ3
]
1.414
1.363
1.804
1.608
Reflections collected (unique) 28356 (9505)
22579 (9993)
0.903 (574)
0.667
39364 (5838)
0.846 (347)
1.123
1947 (1569)
0.992 (98)
0.865
GOF (parameters)
ꢀ3
0.946 (565)
0.656
˚
Drmax [e A
Tmin/Tmax
]
0.286/0.877
1.122
0.683/0.814
1.068
0.268/0.368
8.925
0.737/0.877
6.971
m(MoKa) [mmꢀ1
]
RA1 [%] (all data)
wRB2 [%] (all data)
6.94 (18.60)
6.00 (11.68)
3.79 (7.49)
4.55 (6.58)
11.13 (15.17)
14.30 (18.58)
10.06 (13.51)
13.14 (14.26)
AR1 ¼ S(||Fo| ꢀ |Fc||)/S|Fo| ꢂ 100 %.
BwR2 ¼ [Sw(Fo2 ꢀ Fc2)2/S(w|Fo|2)2]1/2 ꢂ 100 %.
Table 3. Structurally characterized Group 11 L1 and L2 guanidinate complexes
Complex
Reference
˚
M–N [A]
˚
MꢁꢁꢁM [A]
N–M–N [8]
Cu
{Cu[iPrNC(NMe2)NiPr]}2
{Cu[iPrNC(NHiPr)NiPr]}2
{Cu[CyNC(NEt2)NCy]}2 (4)
{Cu[CyNC(NMe2)NCy]}2 (3)
{Cu{CyNC(NMe2)NCy]}2
[61]
[61]
A
1.88
1.88
1.87
1.88
1.88
1.86
1.90
2.42
2.43
2.43
2.44
2.44
2.45
2.40
174.75
173.71
173.23
170.33
170.56
175.98
176.8
A
[32]
[58]
[65]
[Cu2(hpp)2]
i
{Cu[(C6H3 Pr2-2,6)NC(NCy2)N(C6H3 Pr2-2,6)]}2
i
Ag
[20]
A
[Ag4(hpp)4]
2.08
2.10
2.10
2.86
3.04
3.04
172.1
165.0
164.9
{Ag[CyNC(NMe2)NCy]}3 (5)
{Ag[CyNC(NEt2)NCy]}3 (6)
A
Au
[20]
[18]
A
[Au2(hpp)2Cl2]
2.04
2.04
2.03
2.04
2.02
2.48
2.66
2.66
2.67
2.92
169.4
170.7
165.8
166.3
173.7
{Au[iPrNC(NMe2)NiPr]}2
{Au[CyNC(NEt2)NCy]}2 (8)
{Au[CyNC(NMe2)NCy]}2 (7)
[Au4(hpp)4]
A
[22]
AThis work.
closely resembles a distorted trigonal pyramidal (C3v) geometry
with a t4 value[57] of 0.79 for both 1 and 2.
3 and 4, each complex contains two Cu atoms bridged by two
guanidinate ligands in a m, Z1 : Z1-fashion. The average Cu–N
distance is 1.877 A in 3 and 1.872 A in 4, similar to that observed
in analogous compounds copper guanidinates (Table 3).[18,58]
˚
˚
{Cu[CyNC(NMe2)NCy]}2 (3) and
{Cu[CyNC(NEt2)NCy]}2 (4)
˚
˚
Cu–Cu distances for 3 and 4 are 2.437 A and 2.438 A, respec-
tively. These fall within the range of general Cu–Cu distances
with bridging ligands, and are much shorter than the Cu–Cu
distance in metallic copper.[59] The N–Cu–N angles in 3 and 4
Thermal ellipsoid plots of 4 and 3 are given in Figs 3 and S2,
respectively. The structure of 3 has been previously reported and
it is metrically similar to the previous data acquired (Table 3). In

Group 11 Guanidinate Clusters
1027
are 170.338 and 173.238, respectively, and deviate from linearity
and analogous compounds in the literature.[18,60] This is attrib-
uted to the added steric strain from the cyclohexyl groups,
generating a decrease in the Cu–Cu separation. Density func-
tional theory (DFT) calculations are used to investigate any Cu–
Cu interactions owing to this decrease in linearity and the short
Cu–Cu distance.[60–62] Both 3 and 4 support the delocalization
of the imine bond across the two coordinating nitrogen atoms,
and 8 and the previous report is a slight decrease in the N–Au–N
angle; attributable to an increase in steric congestion contributed
by the cyclohexyl substituents relative to the isopropyl groups in
the previous report.
Guanidinate Resonance
The resonance structure of the L1 TAG anion facilitates delocal-
ization of the negative charge on the Nimino atom. A convenient
method to assess the extent of delocalization within the ‘–n¼C–
N–’ component of the guanidinate ligand is the via evaluation of
theDCN parameter:DCN ¼ d(C–N)ꢀ d(C¼N).[63] TheDCN values
˚
resulting in C–N distances ranging from 1.334 to 1.343 A. This
is further supported by the co-planarity of the N–C–N backbone,
whereby in each case an angle close to 1208 was observed.
Torsion angles of 48.018 for 3 and 34.848 for 4 are observed for
the plane of one N–C–N of the guanidinate to the plane of the
other. The significant difference in the torsion angle may be
attributed to steric repulsions between the ethyl groups and the
peripheral cyclohexyl rings. The small values of these torsion
angles is a further indication that electron delocalization is
present within the guanidinate ligands.
˚
˚
range from 0 A in a fully delocalized system to up to ,0.10A in a
fully localized system. The DCN values for complexes 1–8 were
˚
calculated from crystallographic data: 1 (0.026A), 2 (0.055A), 3
˚
˚
(0.009 and 0 A), 4 (0.003A), 5 (0.030, 0.024, and 0.012 A), 6
˚
˚
˚
˚
˚
(0.012, 0.004, and 0.001A), 7 (0.009A), and 8 (0A). From these
values, it can be determined that a slight localization of charge
existswithinthe amidine moietyfor the Licomplexes 1 and 2, and
in the trinuclear Ag complex 5. For complexes 3–4 and 6–8, there
is significant delocalization across the N–C–N unit.
{Ag[CyNC(NMe2)NCy]}3 (5) and {Ag[CyNC(NEt2)
NCy]}3 (6)
To further examine the potential zwitterionic resonance of
the 2-dialkyl-1,3-dicyclohexylguanidinate, it is useful to also
define a DC0 N value, determined as the difference between the
average value of the C–Namidine bond length and the C–Namide
distance.[64] A positive DC0 N value would indicate contribution
from a resonance form where the maximum negative charge is
located on the coordinating N-donors. The calculated DC0 N
values for complexes 1–8 are all negative, ranging from
Thermal ellipsoid plots of 5 and 6 are given in Figs 4 and S3,
respectively. Each complex forms a trimeric cluster. In the
structures, each guanidinate ligand bridges two silver atoms
together in a Z1 : Z1-fashion, enclosing three metal centres,
similar to the silver amidinate trimer [Ag(N,N0-diisopropylace-
tamidinate)][360] and the silver guanidinate trimer {Ag[iPrNC
(NMe2)NiPr]}3.[18] The centre of the structures consists of three
Ag atoms that are arranged in a triangular fashion with Ag–Ag
˚
˚
ꢀ0.0405 A in 7 to ꢀ0.106 A in 5. The negative value indicates
a small degree of zwitterionic resonance, and is consistent with
guanidinate coordination to metals with small coordination
spheres (Li) and to electron-rich metals (Cu, Ag, and Au).
Overall, there was no distinct trend in the negative DC0 N values
that could be attributed to the different metal or NR2 substituent.
˚
distances of 2.994, 2.940, and 3.177 A in 5, and 2.995, 2.988,
˚
and 3.172 A in 6, and AgꢁꢁꢁAgꢁꢁꢁAg angles in the range of 578 to
658 in each complex. The cluster contains Ag–N bonds ranging
˚
˚
from 2.093 to 2.120 A in 5, and from 2.075 to 2.108 A in 6. The
smaller Ag–N distance in 6 is tentatively attributed to the
increase in steric repulsions from the presence of the bulkier
ethyl substituents. These angles and distances are in agreement
with similar complexes in the literature.[18,60] Two ligands
coordinate to each Ag metal centre in a linear fashion, with an
average N–Ag–N bond angle of 1658 in both 5 and 6. The
guanidinate ligands are twisted across the molecule owing to
steric interactions. As such, the planes of each form 60, 67, and
858 angles to one another in 5, and 68, 71, and 828 angles to one
another in 6. Also, the guanidinates produce 40, 48, and 498
torsion angles with respect to the plane of the Ag metal centres in
5, and 40, 50, and 538 torsion angles in 6.
DFT Calculations
To investigate any possible d10–d10 metallophilic interactions, a
theoretical inquiry (Fig. S5) of {Cu[CyNC(NEt2)NCy]}2 (4) and
{Ag[CyNC(NEt2)NCy]}3 (6) was performed.[38] Using the atom
coordinates for 4 and 6 garnered from the single crystal X-ray
diffraction investigation, the molecular orbitals for 4 and 6 were
calculated at the B3 LYP/LANL2DZ[33–36] level of theory. The
orbitals are depicted in Fig. S5 (Supplementary Material). For
each structure, localized d-atomic orbitals (AOs), instead of
delocalized electron density between the metal atoms, are
observed, suggesting negligible M–M interaction. To further
evaluate the bonding, the natural bond orbital (NBO) analy-
sis[37,39,40] at the B3 LYP/LANL2DZ[33–36] level of theory was
performed for 4 and 6.
According to the NBO analysis, the Cu atoms in 4 have
4s0.73d9.5 valence atomic occupations and an effective atomic
charge of þ0.72 e, whereas the coordinating N atoms each have
2s1.42p4.4 atomic occupation and an effective atomic charge of
ꢀ0.79 e. Each Cu–N bond showed an average of 89 % nitrogen
character (25 % s-character and 75 % p-character) and 11 %
copper character (78 % s-character and 22 % p-character). The
{Au[CyNC(NMe2)NCy]}2 (7) and {Au[CyNC(NMe2)
NCy]}2 (8)
Thermal ellipsoid plots of 7 and 8 are given in Figs 5 and S4,
respectively. In each structure, the two Au atoms are bound by
two guanidinate molecules. Each ligand contributes a coordinat-
ed nitrogen to each metal centre, where the average Au–N bond
˚
length is 2.03 A. The Au metal centres both hold nearly linear
coordination sites with angles of 1678. This conformation allows
˚
the Au metal centres to be separated by a distance of 2.6 A. The
cyclohexyl groups are staggered between the two ligands thus
resulting in a torsion angle of 36.08, where the distance between
the two Au centres bisects this torsion angle. The plane of the
amino substituent has a torsionangle of ,36.08 with respect to its
corresponding guanidinate backbone. Each compound has met-
rical parameters similar to those of the previously reported {Au
[iPrNC(NMe2)NiPr]}2 (Table 3). A notable difference between 7
hybridization for each Cu–N bond is 0.33(sd0.3)Cu þ 0.95(sp3.0
)
N, displaying the expected sp3 hybridization on the N atoms.
These results are analogous to those found for the copper dimer,
Cu2(hpp)2 (hpp [L2] ¼ 1,3,4,6,7,8-hexahydro-2H-pyrimido
[1,2-a]pyrimidinato), in which the NBO analysis exhibited a
4s0.63d9.8 configuration for the Cu atoms, indicating that the Cu

1028
S. K. Adas, J. A. Ocana, and S. D. Bunge
atoms have nearly occupied 3d-AOs and are partially reduced by
the electron donating effect of the N atom.[58]
[2] W. Schneider, A. Bauer, A. Schier, H. Schmidbaur, Chem. Ber. 1997,
130, 1417. doi:10.1002/CBER.19971301010
[3] N. Kuhn, R. Fawzi, M. Steimann, J. Wiethoff, Z. Anorg. Allg. Chem.
1997, 623, 554. doi:10.1002/ZAAC.19976230186
[4] N. De Vries, C. E. Costello, A. G. Jones, A. Davison, Inorg. Chem.
1990, 29, 1348. doi:10.1021/IC00332A012
[5] M. A. Paver, D. S. Wright, D. Stalke, Angew. Chem. Int. Ed. Engl.
1993, 32, 428. doi:10.1002/ANIE.199304281
[6] W. Clegg, R. Snaith, H. M. M. Shearer, K. Wade, G. Whitehead,
J. Chem. Soc., Dalton Trans. 1983, 1309. doi:10.1039/DT9830001309
[7] W. Clegg, R. E. Mulvey, R. Snaith, G. E. Toogood, K. Wade, J. Chem.
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[8] A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A.
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[10] P. J. Bailey, S. Pace, Coord. Chem. Rev. 2001, 214, 91. doi:10.1016/
S0010-8545(00)00389-1
For complex 6, the three Ag atoms have an average of
5s0.534d9.82 valence atomic occupation and an effective atomic
charge of þ0.63e, and the N atoms have 2s1.312p4.38 atomic
occupations and an effective atomic charge of ꢀ0.73 e. Examina-
tion of the atomic occupation of Ag indicates that the 4d-AOs are
almost completely occupied and thus the net bonding effect from
molecular orbitals (MOs) composed of 4d-AOs is not significant.
TheaveragehybridizationforeachAg–Nbondshows0.31(sd0.10
)
Ag þ 0.95(sp3.51)N, exhibiting sp3 hybridization of the N atoms.
Each Ag–N bond showed an average of 90% N character (22 %
s-character and 78% p-character), with the difference being Ag
character (90 % s-character and 10 % p-character).
Overall, the results of the NBO analysis are consistent with
the calculated molecular orbitals. The short Cu and Ag inter-
atomic distances are attributed to the coordination of the
guanidinate ligands and not due to significant M–M interactions.
Furthermore, the results and conclusions drawn for the Cu
bonding in 4 are consistent with studies conducted on the
structurally and electronically similar Cu guanidinate complex,
[Cu2(hpp)2].[58]
[11] A. R. Cowley, A. J. Downs, H. J. Himmel, S. Marchant, S. Parsons,
J. A. Yeoman, Dalton Trans. 2005, 1591. doi:10.1039/B501818H
[12] M. P. Coles, Dalton Trans. 2006, 985. doi:10.1039/B515490A
[13] F. T. Edelmann, in Recent Progress in the Chemistry of Metal
Amidinates, Guanidinates: Syntheses, Catalysis, Materials (Eds
A. F. Hill, M. J. Fink) 2013, Vol. 61, pp. 55–374 (Elsevier Academic
Press Inc: San Diego, CA).
Conclusion
[14] M. P. Coles, Chem. Commun. 2009, 3659. doi:10.1039/B901940E
[15] F. T. Edelmann, in Advances in the Coordination Chemistry of
Amidinate, Guanidinate Ligands (Eds A. F. Hill, M. J. Fink) 2008,
Vol. 57, p. 183–352 (Elsevier Academic Press Inc: San Diego, CA).
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[17] R. Kempe, Angew. Chem. Int. Ed. 2000, 39, 468. doi:10.1002/(SICI)
1521-3773(20000204)39:3,468::AID-ANIE468.3.0.CO;2-G
[18] T. J. J. Whitehorne, J. P. Coyle, A. Mahmood, W. H. Monillas, G. P. A.
Yap, S. T. Barry, Eur. J. Inorg. Chem. 2011, 3240. doi:10.1002/EJIC.
201100262
Overall, in this work, 2,2-dialkyl-1,3-dicyclohexylguanidinate
was shown to be a useful ligand for the isolation of a family of
eight Li, Cu, Ag, and Au guanidinate complexes. This synthetic
and structural investigation contributes to the growing field of
L1-type guanidinate chemistry and further adds to the limited
number of examples of stable Lewis base-free complexes con-
taining Group 11 nitrogen bonds. Altering the steric bulk of the
dialkyl group (NMe2 versus NEt2) did not alter the nuclearity of
the Cu, Ag, and Au systems. However, the diakyl group does
have an effect on the resulting M–N and M–M inter-atomic
distances; for the Cu and Au systems, the NEt2 substituent was
found to generate compounds with shorter M–N and M–M inter-
atomic distances. Theoretical investigations of the Cu and Ag
systems indicate a negligible M–M bonding contribution to the
short inter-atomic distances. The synthesis of additional gua-
nidinate clusters is currently under investigation.
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Supplementary Material
Plots for 2, 3, 6, and 8, molecular orbital diagrams and Cartesian
coordinates are available on the Journal’s website. Crystallo-
graphic data for the structures have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication Nos. CCDC 988466 for 1, CCDC 988467 for 2,
CCDC 988468 for 3, CCDC 988469 for 4, CCDC 988470 for 5,
CCDC 988471 for 6, CCDC 988472 for 7, and CCDC 988644
for 8. Copies of the data can be obtained on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; fax: þ44(0)
1223 336 033; email: deposit@ccdc.cam.ac.uk.
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Acknowledgements
The authors acknowledge Kent State University and the National Science
Foundation through the Ohio Consortium for Undergraduate Research:
Research Experiences to Enhance Learning (REEL) Award No. 0532250.
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