Bidentate guanidine ligands with ethylene spacer in copper-dioxygen chemistry: Structural characterization of bis(μ-hydroxo) dicopper complexes

Article abstract of DOI:10.1016/j.ica.2011.02.061

The syntheses of the aliphatic bidentate guanidine-amine-hybrid ligands DMEGdmae (L1), TMGdmae (L2), TMGdeae (L3) and DPipGdmae (L4) as well as the reaction of their Cu(I) complexes with molecular oxygen (monitored by UV-Vis spectroscopy) are reported. The molecular structures of 10 bis(μ-hydroxo) dicopper complexes based on these ligands are described. The solid state structures of [Cu₂(μ-OH)₂(DMEGdmae)₂]X ₂ (X^- = I^- (1), CF₃SO ₃^- (2), SbF₆^- (3), PF ₆^- (4)), [Cu₂(μ-OH)₂(TMGdmae) ₂]X₂ (X^- = I^- (5), CF ₃SO₃^- (6)), [Cu₂(μ-OH) ₂(TMGdeae)₂]Cu₂I₄ (7) and [Cu ₂(μ-OH)₂(DPipGdmae)₂]X₂ (X ^- = CF₃SO₃^- (8), SbF ₆^- (9), PF₆^- (10)) show a square-planar distorted coordination of the copper(II) ion. The bis(μ-hydroxo) dicopper complex 1 exhibits a Cu?Cu distance of 2.860(1) , which is one of the smallest observed for hydroxo-bridged copper compounds so far. The influence of the anion on the structure of the bis(μ-hydroxo) dicopper(II) unit is analyzed for the reported complexes and a literature overview with emphasis on the structural characteristics of the Cu₂O₂ moiety of bis(μ-hydroxo) dicopper(II) and bis(μ-oxo) dicopper(III) is given.

Full text of DOI:10.1016/j.ica.2011.02.061

Inorganica Chimica Acta 374 (2011) 546–557
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Bidentate guanidine ligands with ethylene spacer in copper-dioxygen
chemistry: Structural characterization of bis(l-hydroxo) dicopper complexes
a
a
a
b,
⇑
Roxana Haase , Tanja Beschnitt , Ulrich Flörke , Sonja Herres-Pawlis
a
Department Chemie, Fakultät für Naturwissenschaften, Universität Paderborn, Warburger Straße 100, 33098 Paderborn, Germany
Lehrstuhl für Anorganische Chemie II, Fakultät Chemie, Technische Universität Dortmund, Otto-Hahn-Str. 6, 44227 Dortmund, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 3 March 2011
The syntheses of the aliphatic bidentate guanidine–amine-hybrid ligands DMEGdmae (L1), TMGdmae
(
L2), TMGdeae (L3) and DPipGdmae (L4) as well as the reaction of their Cu(I) complexes with molecular
oxygen (monitored by UV–Vis spectroscopy) are reported. The molecular structures of 10 bis( -hydroxo)
l
Dedicated to Prof. W. Kaim
dicopper complexes based on these ligands are described. The solid state structures of [Cu
2
(
l
-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
OH)
2
(DMEGdmae)
2
]X
2
(X = I (1), CF
3
SO
3
(2), SbF
6
(3), PF
6
(4)), [Cu
-OH)
2
(
l
-OH)
2
(TMGdmae)
2
]X
2
(X = I
SO (8),
Keywords:
Guanidine ligands
O activation
2
Copper
Hydroxo-bridges
UV–Vis spectroscopy
X-ray diffraction
ꢀ
ꢀ
3ꢀ
(
5), CF
3
SO
3
(6)), [Cu
2
(
l
-OH) (TMGdeae)
2
2
]Cu (7) and [Cu
I
2 4
2
(
l
2
(DPipGdmae)
2
]X
2
(X = CF
3
ꢀ
ꢀ
SbF
6
(9), PF
6
(10)) show a square-planar distorted coordination of the copper(II) ion. The bis(l-
hydroxo) dicopper complex 1 exhibits a CuꢁꢁꢁCu distance of 2.860(1) Å, which is one of the smallest
observed for hydroxo-bridged copper compounds so far. The influence of the anion on the structure of
the bis(
l
-hydroxo) dicopper(II) unit is analyzed for the reported complexes and a literature overview
-hydroxo) dicopper(II) and
with emphasis on the structural characteristics of the Cu O2 moiety of bis(
2
l
bis(l-oxo) dicopper(III) is given.
Ó 2011 Elsevier B.V. All rights reserved.
1
. Introduction
The activation and transfer of molecular oxygen by copper
parent bisguanidine (Fig. 1b) and bisamine systems (Fig. 1c) has
shown that the improved accessibility of the active Cu center
is associated with an increase of the hydroxylation reactivity. For
this reason, additional guanidine–amine-hybrid ligands were
developed and the influence of the substituents on the formation
2 2
O
centers plays an important role in biological and technical oxida-
tion processes. Functional model complexes for the active site of
dioxygen binding and activating copper enzymes like tyrosinase
have been studied for more than 30 years and are primarily
aimed at the development of technically recoverable oxidation
catalysts. For such model complexes the ligand design is of vital
importance. On one hand the ligands should stabilize the reac-
2 2
and stability of the Cu O species was examined. With regard to
the ligand TMGdmap which possesses a propylene spacer, the
new hybrid ligands comprise an ethylene spacer between the
two N donor functions. Furthermore, the characterization of
2 2
the thermal decomposition products of the Cu O complexes
tive Cu
2
O
2
species, which are formed by the reaction of the cop-
provides additional information on the complexation properties
of the ligands.
per(I) complex with molecular oxygen. On the other hand they
may not shield the reaction center too much for external sub-
strates, so that the efficiency of oxygen transfer is not reduced
Herein, we report the synthesis and characterization of the
1
guanidine–amine-hybrid ligands N -(1,3-dimethylimidazolidin-
2
2
[
1–27].
Recently, we reported that guanidine–amine-hybrid ligands
2-yliden)-N ,N -dimethylethan-1,2-diamine (DMEGdmae, L1),
2-(2-(dimethylamino)ethyl)-1,1,3,3-tetramethylguanidine (TMGd-
1
proved to be particularly suited for the chemical modeling of
tyrosinase [25,27]. Besides the excellent donor properties of
the guanidine function, the main reason for this reactivity was
related to the open coordination space that is created by the
smaller amine function and facilitates the entry of a substrate
to the Cu
activity of the bis(
plex [Cu (TMGdmap)
mae, L2), [28,29] 2-(2-(diethylamino)ethyl)-1,1,3,3-tetramethyl-
1
2
guanidine (TMGdeae, L3) and N -(dipiperidin-1-ylmethylen)-N ,
2
N -dimethylethan-1,2-diamine (DPipGdmae, L4) (Scheme 1). After
synthesis of their copper(I) complexes, their reaction with O
was monitored by means of UV–Vis spectroscopy. Only in case
of L2, a bis( -oxo) dicopper complex could be detected. With
2
2
O
2
center. The superior biomimetic hydroxylation
-oxo)dicopper guanidine–amine-hybrid com-
-O) ][CF SO (Fig. 1a) compared to the
l
l
ligands L1, L2 and L4, several examples of bis(l-hydroxo) dicopper
2
2
(l
2
3
3 2
]
1
TMGdmae has been identified by Raczy n´ ska et al. using mass spectrometry in the
gas phase, but not isolated and was therefore not yet suitable for use in complex
chemistry.
⇑
Corresponding author.
E-mail address: sonja.herres-pawlis@tu-dortmund.de (S. Herres-Pawlis).
0
020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.061

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
547
2
+
2+
N
N
N
N
N
N
N
N
2
+
N
N
O
O
N
N
N
N
O
O
N
N
N
N
N
N
+
Cu
III
+III
Cu
+III
Cu
+III
Cu
+III
Cu
O
O
+III
Cu
N
N
N
N
-
-
-
2
CF SO
2 CF SO3
2 CF SO3
3
3
3
3
[
Cu (TMGdmap) (µ-O) ](CF SO )
[Cu (btmgp) (µ-O) ](CF SO )
[Cu (TMPD) (µ-O) ](CF SO )
2 2 2 3 3 2
2
2
2
3
3 2
2
2
2
3
3 2
a
b
c
Fig. 1. Bis(l-oxo) dicopper complex of (a) the guanidine–amine-hybrid ligand TMGdmap, (b) the bisguanidine ligand btmgp and (c) the bisamine ligand TMPD.
2
.1.2. 2-(2-(Dimethylamino)ethyl)-1,1,3,3-tetramethylguanidine
(TMGdmae, L2)
Used amine: 2-(Dimethylamino)ethylamine, used Vilsmeier salt:
N
N
N
N
N
N
N
N
0
0
N
N
N
N
N
N
N
N
N,N,N ,N -Tetramethylchloroformamidinium chloride, product:
1
yellow oil, yield: 90% (6.70 g, 36.0 mmol). H NMR (500 MHz, CDCl
5 °C, d [ppm]): 2.22 (s, 6H, CH ), 2.40–2.43 (m, 2H, CH ), 2.61 (s, 6H,
CH ), 2.70 (s, 6H, CH ), 3.20–3.23 (m, 2H, CH ). C NMR (125 MHz,
CDCl , 25 °C, d [ppm]): 38.8 (CH ), 39.6 (CH ), 46.0 (CH ) , 48.3
), 160.5 (CGua). EI-MS (m/z, (%)): 186.2 (10) [M ],
3
,
2
3
2
13
3
3
2
3
3
3
3
+
(
CH
2
), 62.3 (CH
42 (18) [M –N(CH
(16), 85 (100), 72 (28) [M –N@C(N(CH
CN(CH
2
DMEGdmae
TMGdmae
TMGdeae
DPipGdmae
+
+
1
8
3
)
2
], 128 (80) [M –H
2
CN(CH
3
)
2
], 112 (3), 97 (4),
L1
L2
L3
L4
+
6
3
)
2
)
2
], 58 (48)
~ [cm ]):
+
ꢀ1
Scheme 1. Synthesized guanidine–amine-hybrid ligands.
[H
937 m, 2883 m, 2813 m, 2789 m, 2765 m, 1622 vs (
m, 1454 m, 1404 vw, 1365 s, 1306 vw, 1236 w, 1132 m.
)
], 42(20). IR (film between NaCl plates,
m
2
3
2
2
m(C@N)), 1496
complexes could be isolated and structurally characterized.
2
.1.3. 2-(2-(Diethylamino)ethyl)-1,1,3,3-tetramethylguanidine
2
. Experimental
(
TMGdeae, L3)
Used amine: 2-(Diethylamino)ethylamine, used Vilsmeier salt:
2
.1. Synthesis and characterization of guanidine–amine-hybrid ligands
0
0
N,N,N ,N -Tetramethylchloroformamidinium chloride, product: yel-
1
3
low oil, yield: 88% (7.58 g, 35.4 mmol). H NMR (500 MHz, CDCl ,
3
To a solution of a primary amine (40 mmol) and triethylamine
2
5 °C, d [ppm]): 1.01 (t, 6H, CH
3
,
J = 7.18 Hz), 2.52–2.58 (m, 6H,
), 3.20–3.23 (m, 2H, CH ).
(
40 mmol) in 40 mL of dry MeCN a solution of the chloroformamid-
CH ), 2.64 (s, 6H, CH ), 2.72 (s, 6H, CH
2
3
3
2
1
3
inium chloride (40 mmol) in 40 mL of dry MeCN was added drop-
wise under vigorous stirring and ice cooling. After 3 h at reflux,
1
atile organics were removed under vacuum. For the deprotonation
of the formed guanidine hydrochloride 10 mL of 50% KOH solution
were added to the residue. Finally the free base was extracted into
C NMR (500 MHz, CDCl , 25 °C, d [ppm]): 11.8 (CH ), 38.8
3
3
(
CH
3
), 39.6 (CH
3
), 47.6 (CH
2
), 48.2 (CH
2
), 55.8 (CH
2
), 160.5 (Cgua).
+
+
0 mL of aquous NaOH (40 mmol, 1.6 g) were added, and the vol-
2 3
EI-MS (m/z (%)): 214.2 (33) [M ], 185 (14) [M –CH CH ], 143
26), 128 (90) [M –H
N@C(N(CH ) ) ], 86 (85) [H CN(CH CH ) ], 85 (100), 72
+
+
(
2 2 3 2
CN(CH CH ) ], 126 (63), 100 (35) [M –
+
3
2 2
2
2
3 2
+
+
(
30)[N(CH
2
CH
3
)
2
], 58 (31), 56 (21), 44 (24)[N(CH
3
)
2
], 42 (20). IR
~ [cm ]): 2968 s, 2931 s, 2871 s,
(C@N)), 1558 vw, 1539 vw, 1496 m,
452 m, 1404 w, 1365 s, 1292 w, 1236 w, 1203 w, 1174 vw, 1134
ꢀ1
MeCN (3 ꢂ 30 mL), dried under Na
2
SO
4
and after filtration the sol-
(film between NaCl plates, m
vent was evaporated under reduced pressure.
2
1
839 s, 2798 s, 1622 vs (m
m, 1065 m, 993 w, 914 w.
1
2
2
2
.1.1. N -(1,3-Dimethylimidazolidin-2-yliden)-N ,N -dimethylethan-
1
2
2
1
,2-diamine (DMEGdmae, L1)
2.1.4. N -(Dipiperidin-1-ylmethylen)-N ,N -dimethylethan-1,2-
diamine (DPipGdmae, L4)
Used amine: 2-(Dimethylamino)ethylamine, used Vilsmeier salt:
0
0
N,N,N ,N -Dimethylethylenechloroformamidinium chloride, prod-
uct: yellow oil, yield: 92% (6.78 g, 36.8 mmol). H NMR (500 MHz,
Used amine: 2-(Dimethylamino)ethylamine, used Vilsmeier
salt: Dipiperidin-1-yl-chloroformamidinium chloride, product:
yellow oil, yield: 88% (9.36 g, 35.2 mmol). H NMR (500 MHz,
1
1
CDCl
.60 (s, 6H, CH
NMR (125 MHz, CDCl
3
, 25 °C, d [ppm]): 2.09 (s, 6H, CH
), 2.96 (s, 4H, CH ), 3.30–3.33 (m, 2H, CH
, 25 °C, d [ppm]): 36.1 (CH ), 46.0 (CH
), 62.8 (CH ), 157.2 (Cgua). EI-MS (m/z, (%)): 184.2
CN(CH ], 114 (5), 98 (5), 85 (12), 70
], 56 (22), 42 (18). IR (film between NaCl
~ [cm ]): 2939 m, 2817 m, 2765 m, 1666 vs (
(C@N)), 1558
3
), 2.27–2.30 (m, 2H, CH
2
3
),
C
1
2
3
2
2
).
CDCl
2.33–2.36 (m, 2H, CH
4H, CH ), 3.13–3.16 (m, 2H, CH
25 °C, d [ppm]): 24.7 (CH ), 25.8 (CH
48.9 (CH ), 61.6 (CH ), 160.0 (CGua). EI-MS (m/z, (%)): 266.2 (12)
[M ], 208 (52) [M –H CN(CH ], 196 (75), 139 (12), 126 (69),
125 (97), 113 (48), 112 (93), 100 (58), 86 (38), 85 (84), 84 (100)
3
, 25 °C, d [ppm]):1.41–1.43 (m, 12H, CH
2
), 2.13 (s, 6H, CH
), 2.94–2.96 (m,
). C NMR (125 MHz, CDCl
), 45.8 (CH ), 47.2 (CH
3
),
3
3
3
), 46.2
2
), 2.88–2.91 (m, 4H, CH
2
1
3
(
CH2,), 49.2 (CH
2
2
2
2
3
,
2
),
+
+
(
10) [M ], 126 (100) [M –H
2
3
)
2
2
2
3
+
(
10), 58 (21) [H
2
CN(CH
3
)
2
2
2
ꢀ1
+
+
plates,
m
m
2
3 2
)
vw, 1541 vw, 1481 m, 1460 m, 1439 m, 1412 w, 1383 m, 1317 vw,
265 m, 1198 w, 1180 w, 1151 vw, 1119 vw, 1097 w, 1086 w, 1068
w, 1041 w, 1018 m, 987 w, 957 m, 928 vw, 914 vw.
+
+
1
[H10
C
5
N ], 83 (59), 72 (19) [H
4 2 3 2
C N(CH ) ], 70 (37), 69 (92), 56
ꢀ
1
(59), 42 (37), 41(74). IR (film between NaCl plates,
m
~ [cm ]):

5
48
R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
2
969 w, 2931 vs, 2850 s, 2815 m, 2765 w, 1646 m, 1616 vs
2.2.5. The complex salt 5, [Cu
2 2 2 2
(l-OH) (TMGdmae) ]I
(
1
1
m
(C@N)), 1558 vw, 1521 vw, 1506 vw, 1450 w, 1440 m, 1403 m,
371 m, 1347 w, 1324 vw, 1249 vs, 1213 s, 1182 w, 1155 w,
130 s.
Violet crystals, yield: 44%. EI-MS (m/z, (%)): 186 (57)
+
+
[TMGdmae ], 142 (65) [TMGdmae –N(CH
3
)
2
], 129 (64), 128 (93)
+
[TMGdmae –H
100), 72 (98) [H
(59), 44 (67) [N(CH
(OH)), 3001 vw, 2985 vw, 2935 w, 2891 w, 2810 vw, 1579 vs
(C@N)), 1533 s ( (C@N)), 1471 w, 1458 w, 1441 w, 1427 w,
2 3 2
CN(CH ) ], 112 (12), 100 (15), 97 (29), 86 (74), 85
+
+
(
4
C
2
N(CH
3
)
2
], 69 (72), 58 (91) [H
2
CN(CH
3
)
2
], 56
+
ꢀ1
2
.2. Synthesis and characterization of bis(
l
-hydroxo) dicopper
3
)
2
], 42(99). IR (KBr,
m
~ [cm ]): 3365 m (
m
guanidine–amine-hybrid complexes
(m
m
At first the copper(I) complexes were synthesised in situ by
reaction of 0.1 mmol of ligand with 0.1 mmol of the corresponding
copper(I) salt in 5 mL of MeCN at room temperature in a glove-box
1392 s, 1346 vw, 1331 vw, 1281 vw, 1254 vw, 1238 vw, 1159 w,
1138 vw, 1111 vw, 1084 vw, 1068 vw, 1043 vw, 1022 vw, 958
vw, 922 vw, 897 vw, 808 vw, 768 vw, 735 vw, 708 vw, 677 vw,
650 vw, 617 vw, 592 vw, 573 vw, 503 vw.
under nitrogen [25]. For the preparation of the bis(l-hydroxo)
dicopper complexes, 0.5 mL of this copper(I) solution was injected
into 10 mL of oxygenated THF or MeCN at 298 K. By vapor diffusion
of diethyl ether into this solution suitable crystals for X-ray diffrac-
tion can be obtained after a few weeks. Solvents were purified
according to the literature procedures and also kept under
nitrogen.
2.2.6. Complex salt 6, [Cu
2 2 2 3 3 2
(l-OH) (TMGdmae) ][(CF SO ) ]
Black crystals, yield: 55%. EI-MS (m/z, (%)): 186 (22)
+
+
[TMGdmae ], 142 (21) [TMGdmae –N(CH
3
)
2
], 139 (18), 128 (90)
+
[TMGdmae –H
86 (43), 85 (100), 72 (94) [H
2 3 2
CN(CH ) ], 126 (42), 116 (17), 115 (39), 97 (12),
+
4 2 3 2
C N(CH ) ], 71 (80), 69 (55), 58
+
+
(
94) [H
2
CN(CH
[cm ]): 3492 s (
vw, 1580 vs (
3 2
)
], 44 (77) [N(CH
(OH)), 3010 w, 2936 m, 2884 m, 2813 vw, 2787
(C@N)), 1467 s, 1453 s, 1430 s,
3 2
) ], 42 (81). IR (KBr, m
~
ꢀ
1
2
.2.1. Complex salt 1, [Cu
2
(l-OH)
2
(DMEGdmae)
]I
2 2
m
Violet crystals, yield: 37%. EI-MS (m/z, (%)): 184 (9) [DMEGd-
m(C@N)), 1538 vs (
m
+
+
mae ], 127 (48), 126 (100) [DMEGdmae –H
2
CN(CH
], 56 (43), 42 (31). IR (KBr,
~ [cm ]): 3404 m (
m(OH)), 2958 w, 2924 w, 2862 w, 1604 vs
3
)
2
], 114 (6),
1400 vs, 1334 m, 1275 vs, 1256 vs, 1220 vs, 1157 vs, 1111 w,
1080 m, 1070 w, 1026 vs, 958 m, 923 m, 897 m, 809 m, 768 m,
755 w, 729 vw, 706 vw, 622 vs, 593 w, 571 m, 516 vs.
+
8
2 3 2
5 (10), 70 (14), 58 (32) [H CN(CH )
ꢀ
1
m
(
1
1
m
(C@N)), 1504 m, 1473 w, 1429 w, 1400 w, 1581 vw, 1344 vw,
294 m, 1275 w, 1236 vw, 1201 vw, 1165 vw, 1124 vw, 1092 vw,
078 vw, 1036 vw, 1022 w, 980 vw, 953 vw, 916 vw, 883 vw, 849
2 2 2 2 4
2.2.7. Complex salt 7, [Cu (l-OH) (TMGdeae) ]Cu I
+
Black crystals, yield: 70%. EI-MS (m/z (%)): 214 (11) [TMGdeae ],
+
+
vw, 808 vw, 771 w, 733 vw, 700 vw, 669 vw, 650 vw, 606 vw, 567
vw.
143 (12), 128 (90) [M –H
N@C(N(CH
2
CN(CH
2
CH
3
)
2
], 126 (14), 100 (22) [M –
+
3
)
2
)
2
], 85 (100), 72 (63) [N(CH
2
CH
3
)
2
], 58 (28), 56
+
ꢀ1
(
(
(
18), 44 (34) [N(CH
m
3
)
2
], 42 (28). IR (KBr,
m
~ [cm ]): 3433 w
2
.2.2. Complex salt 2, [Cu
2
(l-OH) (DMEGdmae) ][(CF SO
2 2 3 3
2
) ]
(OH)), 3002 vw, 2975 m, 2939 m, 2879 m, 2805 vw, 1572 vs
(C@N)), 1532 vs ( (C@N)), 1459 s, 1440 s, 1427 s, 1361 m, 1347
Violet crystals, yield: 60%. EI-MS (m/z, (%)): 184 (6) [DMEGd-
m
m
+
+
mae ], 168 (13), 127 (30), 126 (100) [DMEGdmae –H
2
CN(CH
3
)
2
],
m, 1332 m, 1261 m, 1232 m, 1185 vw, 1165 m, 1147 m, 1115 w,
1080 m, 1063 m, 1052 m, 1003 m, 933 vw, 897 w, 838 vw, 792
m, 744 vw, 726 vw, 591 vw, 566 vw, 492 m.
+
1
7
(
12 (85) [DMEGdmae –H
0 (31), 58 (98) [H CN(CH
4 2 3 2
C N(CH ) ], 100 (75), 83 (16), 71 (39),
+
+
2
3
)
2
], 56 (66), 44 (71) [N(CH
~ [cm ]): 3433 m (
(OH)), 2963 vw, 2924 vw, 2886
vw, 2854 vw, 1610 s ( (C@N)), 1544 vw, 1509 vw, 1491 vw, 1468
3 2
) ], 42
ꢀ
1
78). IR (KBr,
m
m
m
2 2 2 3 3 2
2.2.8. Complex salt 8, [Cu (l-OH) (DPipGdmae) ][(CF SO ) ]
w, 1449 vw, 1430 vw, 1399 vw, 1383 vw, 1350 vw, 1274 s, 1261
s, 1224 vw, 1187 vw, 1149 m, 1098 w, 1075 vw, 1035 m, 955 vw,
Violet crystals, yield: 44%. EI-MS (m/z, (%)): 266 (4) [DPipGd-
+
+
mae ], 208 (45) [DPipGdmae –H
2 3 2
CN(CH ) ], 196 (18), 125 (100),
+
+
9
5
21 vw, 806 w, 782 vw, 753 vw, 724 vw, 708 w, 640 m, 572 vw,
17 w.
112 (19), 98 (13), 84 (96) [H10
C
5
N ], 72 (15) [H
C
4 2
N(CH
], 42 (38). IR (KBr,
(OH)), 2993 w, 2935 m, 2854 m, 1554 vs
(m(C@N)), 1500 s, 1444 m, 1408 vw, 1373 w, 1356 vw, 1336 w,
3 2
) ], 69
+
+
(34), 58 (50) [H
~ [cm ]): 3365 m (
2
CN(CH
3 2 3 2
) ], 44 (24) [N(CH )
ꢀ
1
m
m
2
.2.3. Complex salt 3, [Cu
2
(l-OH) (DMEGdmae) ][(SbF )
2 2 6 2
]
Violet crystals, yield: 73%. EI-MS (m/z, (%)): 184 (5) [DMEGd-
1284 vs, 1252 vs, 1223 m, 1190 vw, 1145 s, 1109 w, 1068 vw,
1028 vs, 987 vw, 955 w, 922 w, 854 w, 795 vw, 750 w, 636 s, 570
w, 514 m.
+
+
mae ], 127 (25), 126 (100) [DMEGdmae –H
2
CN(CH
3 2
) ], 114 (29),
+
1
(
(
00 (9), 85 (8), 82 (8), 72 (10), 70 (11), 58 (90) [H
2
CN(CH
)
3 2
], 56
~ [cm ]): 3618 m (
OH)), 3012 w, 2987 w, 2947 m, 2902 m, 2875 w, 2846 w, 2815
(C@N)), 1508 m, 1487 m, 1460 s, 1425 s,
398 s, 1383 w, 1342 m, 1292 vs, 1255 m, 1236 m, 1200 w, 1186
vw, 1138 vw, 1105 w, 1084 m, 1043 w, 1032 m, 1016 m, 978 w,
58 s, 918 m, 881 vw, 856 w, 814 w, 769 m, 731 m, 717 vw, 660
vs, 642 vs, 619 m, 607 m, 569 vw, 505 m.
+
ꢀ1
37), 44 (25) [N(CH
3
)
2
], 42 (52). IR (KBr,
m
m
2 2 2 6 2
2.2.9. Complex salt 9, [Cu (l-OH) (DPipGdmae) ][(SbF ) ]
vw, 2802 vw, 1612 s (
m
Violet crystals, yield: 35%. EI-MS (m/z, (%)): 266 (3) [DPipGd-
+
+
1
mae ], 208 (30) [DPipGdmae –H
2 3 2
CN(CH ) ], 195 (7), 194 (7), 180
(17), 178 (24), 167 (34), 160 (45), 159 (51), 138 (41), 125 (100),
+
+
9
112 (22), 98 (18), 84 (70) [H10
56 (20), 42 (18). IR (KBr,
vw, 2943 m, 2856 m, 1560 vs (
C
5
N ], 69 (15), 58 (14) [H
2
CN(CH
(OH)), 3010 vw, 2889
(C@N)), 1496 s, 1468 m, 1444 s,
3 2
) ],
ꢀ
1
m m
~ [cm ]): 3604 w (
m
2
.2.4. Complex salt 4, [Cu
2
(
l
-OH)
2
(DMEGdmae)
2
][(PF
6
)
2
]
1410 vw, 1373 m, 1356 w, 1336 m, 1273 m, 1252 s, 1227 w, 1190
vw, 1161 vw, 1136 m, 1109 w, 1036 w, 1016 w, 987 vw, 955 vw,
924 vw, 914 vw, 891 vw, 872 w, 854 m, 839 vw, 795 w, 748 w,
661 vs, 640 s, 569 vw, 515 w, 507 w.
Black crystals, yield: 67%. EI-MS (m/z, (%)): 184 (15) [DMEGd-
+
+
3 2
mae ], 140 (10) [DMEGdmae –N(CH ) ], 127 (79), 126 (100)
+
+
[
H
(
DMEGdmae –H
N(CH ], 107 (50), 100 (12), 98 (15), 85 (20), 82 (27), 70
54), 58 (93) [H
2 3 2
CN(CH ) ], 113 (54), 112 (53) [DMEGdmae –
C
4 2
3 2
)
+
+
2
CN(CH
3
)
2
], 56 (87), 44 (60) [N(CH
~ [cm ]): 3609 m (
(OH)), 3008 w, 2985 w, 2939 w,
(C@N)),
508 m, 1460 m, 1427 m, 1399 m, 1382 w, 1341 w, 1292 m, 1255
3
)
2
], 42 (90).
2.2.10. Complex salt 10, [Cu
2 2 2 6 2
(l-OH) (DPipGdmae) ][(PF ) ]
ꢀ
1
IR (KBr,
2
1
m
m
Violet crystals, yield: 45%. EI-MS (m/z, (%)): 266 (4) [DPipGd-
+
+
903 w, 2884 m, 2846 w, 2816 vw, 2800 vw, 1615 vs (
m
mae ], 208 (44) [DPipGdmae –H
2 3 2
CN(CH ) ], 196 (17), 125 (100),
+
112 (19), 107 (23), 98 (19), 84 (99) [H10
[H C N(CH ) ], 69 (35), 58 (82) [H CN(CH )
4 2 3 2 2 3 2
~ [cm ]): 3593 m (
IR (KBr, m m
1552 s (
C
5
N ], 72 (17)
], 42 (47), 41 (47).
(OH)), 2947 m, 2927 m, 2860 w,
m(C@N)), 1489 m, 1441 m, 1375 vw, 1356 vw, 1334 w,
+
+
w, 1236 w, 1198 vw, 1184 vw, 1137 vw, 1106 vw, 1084 w, 1043
vw, 1031 w, 1017 w, 978 vw, 960 m, 918 w, 840 vs, 770 w, 732
w, 648 vw, 607 vw, 558 s, 504 m.
ꢀ1

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
549
1
1
282 w, 1271 w, 1252 m, 1225 vw, 1190 vw, 1159 vw, 1130 vw,
105 vw, 1072 vw, 1038 vw, 1014 w, 953 w, 843 vs, 791 w, 752
3. Results and discussion
vw, 739 vw, 717 vw, 636 vw, 602 vw, 557 m, 519 vw.
3.1. Synthesis of the guanidine–amine-hybrid ligands
The preparation of guanidine–amine-hybrid ligands was carried
out according to the approved synthesis protocol of Kantlehner
et al. [32] by condensation of the chloroformamidinium chloride
(Vilsmeier salts) with primary aliphatic amines (Fig. 2). The re-
quired Vilsmeier salts are accessible in good yields from the appro-
priately substituted urea and phosgene. The ligands were obtained
after relatively short reaction times of 3–5 h in yields of 85–98%.
Ligand L2 has been identified previously in the gas phase by mass
spectrometry but not isolated [28,29]. The characterization of the
ligands was performed by NMR and IR spectroscopy as well as
EI-MS analysis.
2
.3. Measurements
Spectra were recorded with the following spectrometers: NMR:
BrukerAvance 500. The signals were calibrated to the residual sig-
nals of the deuterated solvent (d (CDCl ) = 7.26 ppm). IR: Nicolet
P510. MS (EI, 70 eV): Finnigan MAT 8200. UV–Vis: Perkin-Elmer
Lambda 45 with a low-temperature fiber-optic interface (Hellma;
H
3
1
mm) and a custom-designed Schlenk cell with compression
fittings.
2.4. X-ray structure analyses
3.2. Dioxygen activation by copper(I) guanidine–amine-hybrid
complexes
The X-ray intensities of the bis(l-hydroxo) dicopper complexes
were collected at 120 K on a Bruker-AXS Smart [30] APEX CCD-dif-
fractometer with graphite monochromated Mo radiation
k = 0.71073 Å). The structures were solved by direct and conven-
tional Fourier methods and refined on F by full-matrix least-
squares techniques using SHELXTL [31].
For investigation of the copper(I) guanidine–amine-hybrid com-
plexes of L1–L4 on their ability to activate oxygen the reaction of
K
a
(
2
the in situ prepared Cu(I) guanidine solutions with oxygen at
ꢀ ꢀ
1
95 K (THF, 1 atm O
2 6 3 3
, [Cu] = 2 mM, PF and CF SO ) was followed
by UV–Vis spectroscopy. The UV–Vis spectra of the formed bis(
l-
Selected crystallographic data of the compounds are summa-
rized in Table 1.
oxo) dicopper complexes are shown in Fig. 3. The oxygenated cop-
per complex of L2 has two intense charge transfer (CT) bands at
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
2
85 nm (
a shoulder at ꢄ450 nm (
in [Cu (TMGdmap) -O)
0, 385/18, 430/8) [25]. This supports its composition as an bis(
oxo) species. For the guanidine–amine-hybrid ligands L1, L3 and
L4, no Cu species could be observed in the reaction of the corre-
e
ꢃ 19 mM cm ) and 390 nm (
e
ꢃ 12 mM cm ) and
ꢀ1
ꢀ1
2.5. UV–Vis spectroscopy of the oxygenation of Cu(I) precursor
e
ꢃ 8 mM cm , Fig. 3) similar to those
ꢀ
1
ꢀ1
complexes
2
2
(l
2 3 3 2
](CF SO ) (k [nm]/e [mM cm ]: 297/
2
l-
Solutions for optical investigations were generally prepared
in situ by initially mixing equimolar amounts of a Cu(I) salt
Cu(MeCN) ](CF SO , [Cu(MeCN) ](SbF with the guanidine–
2 2
O
[
4
3
3
)
2
4
6
)
2
sponding Cu(I) precursor complexes with molecular oxygen, as the
resulting UV–Vis spectra showed no characteristic CT bands for a
amine-hybrid ligands L1–L4. Oxygenation proceeded by rapid
injection of a concentrated Cu(I) complex solution (2 mM) into
preoxygenated THF at 195 K.
Cu
2
O
2
species (Fig. 3). Change of counterion did not lead to better
species. Up to now, it is not clear why L1,
formation of any Cu
2 2
O
Table 1
Crystal data for compounds 1–10.
1
2
3
4
5
Empirical formula
Molecular mass
Crystal system
Space group
a (Å)
C
18
H
42Cu
2
I
2
N
8
O
2
C
20
H
42Cu
2
F
N
6 8
O
S
8 2
C
18
H
42Cu
2
F
12
8
N O
2
Sb
2
C
18
H
42Cu
2
F
12
8
N O
2
P
2
C
18
H
46Cu
2
I
2
N
8
O
2
783.48
monoclinic
P2 /n
8.776(1)
10.353(1)
16.235(2)
90
103.514(3)
90
1434.1(3)
2
827.82
triclinic
P1ꢀ
8.282(2)
9.110(2)
11.582(2)
88.721(4)
82.789(4)
69.471(4)
811.7(3)
1
1001.18
triclinic
P1ꢀ
8.7120(12)
9.3260(13)
11.0804(15)
88.254(3)
79.933(3)
67.579(2)
818.7(2)
1
819.62
triclinic
P1ꢀ
8.405(1)
9.043(1)
11.010(1)
88.392(2)
79.370(2)
69.756(2)
771.03(16)
1
787.51
monoclinic
P2 /n
8.5523(11)
16.8715(19)
10.5365(16)
90
93.515(3)
90
1517.5(3)
2
1
1
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
Z
R
1
[I > 2r
(I)]
R
1
= 0.0243,
R
1
= 0.0372,
R
1
= 0.0306,
R
1
= 0.0363,
1
R = 0.0378,
2
wR (all data)
wR
2
= 0.0621
wR
2
= 0.1017
wR
2
= 0.0818
wR
2
= 0.1004
2
wR = 0.0795
6
7
8
9
10
Empirical formula
Molecular mass
Crystal system
Space group
a (Å)
C
20
H
46Cu
831.85
monoclinic
P2 /n
2
F
6
N
8
O
S
8 2
C
22
H
54Cu
1224.49
monoclinic
P2 /c
4
I
N
4 8
O
2
C
32
H
62Cu
2
F
6
8
N O
S
8 2
C
30
H
62Cu
2
F
12
N
8
O
Sb
2 2
C
30
H
62Cu
983.9
monoclinic
P2 /c
2
F
N
12 8
O
2
P
2
992.08
triclinic
P1ꢀ
9.255(2)
10.756(2)
11.847(2)
66.623(4)
84.078(4)
81.285(4)
1068.8(4)
1
1165.46
triclinic
P1ꢀ
9.465(4)
10.797(5)
11.807(5)
66.249(6)
79.686(8)
77.721(8)
1073.3(8)
1
1
1
1
12.433(5)
9.330(3)
15.138(6)
90
103.262(7)
90
10.093(2)
17.394(3)
11.041(2)
90
100.162(3)
90
10.724(1)
9.360(1)
20.359(2)
90
90.635(2)
90
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
1709.2(11)
2
1907.9(5)
2
2043.5(4)
2
Z
R
1
[I > 2r
(I)]
R
1
= 0.0425,
R
1
= 0.0200,
R
1
= 0.0422,
R
1
= 0.0567,
R
1
= 0.0332,
2
wR (all data)
2
wR = 0.1046
2
wR = 0.0471
2
wR = 0.1156
2
wR = 0.1474
2
wR = 0.0880

5
50
R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
-
Cl
Cl
O
+
COCl2
+
3 4
2
1
NR R4
3
R RN
2
1
R RN
NR R
-
CO2
chloroformamidinium chloride
(Vilsmeier salt)
-
Cl
1
. NEt3
Cl
5
2 1
NR R6 2. NaOH, - [HNEt Cl]
R R N
+
H N
2
3
5
6
+
N
NR R
2
1
3
4
3. 50% KOH(aq), -H O, -KCl
2
R R N
NR R
4
3
R R N
Vilsmeier salt
amine
gunidine-amine-hybrid
Fig. 2. Synthesis of guanidine–amine-hybrid ligands.
2
98 K (Scheme 2a). They can be isolated in crystalline form by
gas phase diffusion of diethyl or diisopropyl ether. Due to the pre-
vious work of Schneider and Herres-Pawlis [16,33,34] on the
related bisguanidine complexes for the guanidine–amine-hybrid
systems a 1:1 mixture of bis(
per complex is expected as well. So far, for the guanidine–amine
hybrid ligands only the bis( -hydroxo)dicopper complex could
l-alkoxo) and bis(l-hydroxo)dicop-
l
be isolated and structurally characterized. An indication for the
simultaneous formation of the hydroxo and alkoxo form is the fact
that in some cases two different crystallization products could be
obtained. One example is the reaction of [Cu(DMEGdmae)I] with
O at 298 K, in which by gas-phase diffusion of diisopropyl blue
2
squares and violet needles could be isolated in a crystalline form.
But only the purple crystals could be characterized crystallograph-
ically and were identified as [Cu (DMEGdmae) (l-OH) ]I (1). The
2 2 2 2
blue crystals were not stable enough to be prepared for X-ray crys-
tallography. For this intramolecular monooxygenation reaction the
maximum yield for the bis(
The other possibility is the reaction of the Cu(I) precursor com-
plex with O in the presence of atmospheric moisture at 298 K in
THF leading to the bis( -hydroxo) dicopper complex in almost
quantitative yields (80–90%) (Scheme 2b). Apparently with this
type of reaction no formation of a bis( -alkoxo) species can be ob-
l-hydroxo) dicopper complex is 50%.
Fig. 3. UV–Vis spectra of the oxygenation products of the Cu(I) precursor
complexes of L1–L4.
2
l
2 2
L3 and L4 do not support Cu O species on the minute time scale. It
l
may be proposed that the ethylene spacer allows the competitive
formation of bis(chelate) copper species. To clarify this point, fur-
ther investigations such as stopped flow measurements are
planned. The occurring color change (yellow ? greenish blue) dur-
ing the reaction indicates that the resulting reaction products are
Cu(II) species. During the oxygenation of the Cu(I) precursor
complexes undefined reactions take place and for their determina-
tion crystallographic characterization of the Cu(I) precursor com-
plexes and the end products are required.
served. The reason for this is an intermolecular monooxygenation
reaction, in which THF acts as exogenous substrate. The oxidation
2 2
of THF to 2-hydroxytetrahydrofuran by Cu O species was already
18
described in the literature. On the basis of O-labeling experi-
ments it could be shown that the O atom in the 2-hydroxytetrahy-
2 2
drofuran originates from the Cu O species [35–38].
3.4. Crystal structures of bis(l-hydroxo) dicopper(II) guanidine–
amine-hybrid complexes
3
.3. Synthetic aspects of the bis(
l
-hydroxo)dicopper(II) guanidine–
3.4.1. Crystal structures of bis(
DMEG function
l-hydroxo) dicopper complexes with
amine-hybrid complexes
For the reaction of the guanidine–amine-hybrid ligand DMEGd-
mae (L1) with different Cu (I) salts (CuI, [Cu(MeCN) ]CF SO
[Cu(MeCN) ]SbF [Cu(MeCN) ]PF and subsequent reaction
with O the following bis( -hydroxo) dicopper complex could be
isolated in crystalline form: [Cu (DMEGdmae) -OH) ]I (1),
[Cu (DMEGdmae) -OH) ](CF SO (2), [Cu (DMEGdmae)
OH) ](SbF (3) and [Cu (DMEGdmae) -OH) ](PF (4). The
complex salt 1 crystallizes monoclinic in the space group P2 /n
and the complex salts 2–4 crystallize triclinic in the space group
Bis(
can be obtained on different synthesis routes. One synthetic possi-
bility is the thermal decomposition of Cu complexes to form
bis( -alkoxo) and bis( -hydroxo) complexes in a 1:1 ratio (Scheme
a). This decomposition reaction of bis( -oxo)dicopper(III) com-
plexes can be observed with UV–Vis spectroscopy (decrease of
the band at 400 nm, see also [25]) and can be seen visually on
the color changes from red to green, blue or purple. Monocrystal-
line products can be obtained by slow evaporation of the solvent
of the reaction mixture. The same products are obtained by reac-
l
-hydroxo)dicopper(II) guanidine–amine-hybrid complexes
4
3
3
,
4
6
,
4
6
)
2
O
2
2
l
l
l
2
2
(l
2 2
2
l
2
2
(l
2
3
3
)
2
2
2
(l-
2
6
)
2
2
2
(l
2
6 2
)
1
ꢀ
P1. All four compounds contain the complex cation [Cu
2
(DMEGd-
with different anions for charge compensation.
This series of bis( -hydroxo) dicopper complexes (1–4) allows to
2
+
2 2
mae) (l-OH) ]
tion of a in situ prepared Cu(I)-precursor solution with O
2
at
l

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
551
2+
2+
R
R N
R N NR2
2
2
N
R
R
H
O
CH2
R
R
N
N
N
N
N
N
O2
O
+II
+II
+II
Cu
+II
Cu
Cu
Cu
+
a)
1
95 K 298 K
or
O
H
O
NR2 NR2
N
N
N
R
H C
R
R
R
2
2
98 K
N
R N NR2
2
NR2
R
-
-
2
X
2 X
bis(µ-alkoxo) dicopper complex
N
bis(µ-hydroxo) dicopper complex
R
R
2+
+
R N NR2
2
R
R
Cu(I) salt
H
O
N
N
N
N
O , THF, H O
+II
+II
O
OH
b)
2
2
Cu
Cu
+
2
98 K
O
H
R
R
R N NR2
2
-
2
X
bis(µ-hydroxo) dicopper complex
2-hydroxytetrahydrofuran
Scheme 2. General reaction scheme for the synthesis of bis(l-hydroxo) dicopper(II) guanidine–amine-hybrid complexes.
investigate to which extent the structure of the complexes in the
crystal is influenced by the anions. The Cu(II) ions of the four com-
(ideal value 90°). The inverse rotation of the two CuN
against the central Cu
(3) and 7.7° (4) also leads to a minimal deviation from planarity
within the N CuO unit. This torsion is also reflected in the sum
2
planes
2 2
O plane about 11.9° (1), 4.1° (2), 5.7°
plexes are coordinated by a N
O
2 2
donor set in a distorted square-
core forms a rhomb
planar manner, in which the central Cu
2
O
2
2
2
with a central inversion center. The two chelating ligands are in
of the environment angles for the two copper ions, which is with
705.0° (1), 713.1° (2), 709.7° (3) and 710.1° (4) slightly reduced
from the ideal value of a square-planar geometry (720°). It is
anti position to each other. The molecular structure of the complex
2+
cation [Cu
2
(DMEGdmae)
2
(l
-OH)
2
]
is shown in Fig. 4 using the
0
example of 1, selected bond lengths and angles are summarized
in Table 2.
striking that the values of the Namine–Cu–O, O–Cu–O and Cu–
0
O–Cu angles in
1
(91.99(7)°/167.64(7)°, 84.49(7)° and
The bite angle N–Cu–N of the ligand DMEGdmae with an
average of 85.1° (85.35(8)° 1, 84.48(8)° 2, 85.3(6)° 3, 85.2(4)°
95.51(7)°) are significantly different from those of the complexes
2–4 (average 94.3°/173.2°, 81.7° and 98.3°). Due to the different
0
0
4) and the relatively sharp O–Cu–O bond angle with an average
Cu–O–Cu angles, the CuꢁꢁꢁCu distances of the four complexes
of 82.4° (84.49(7)° 1, 82.86(7)° 2, 80.1(6)° 3, 82.0(3)° 4) leads to
a slight distortion of the square-planar coordination geometry
also differ significantly from each other (see Table 2). Remark-
0
able is the short CuꢁꢁꢁCu distance of 2.860(1) Å in 1, which is
2 2 2
Fig. 4. Molecular structure of [Cu (DMEGdmae) (l-OH)
]2+ in crystals of 1 (left: frontal view, right: view with H bonds to iodine atoms).

5
52
R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
Table 2
Selected structural data of 1–4.
1
OH)
[Cu
2
(DMEGdmae)
2
(
l-
2 [Cu
2
(DMEGdmae)
SO
2
(l-
3 [Cu
2
(DMEGdmae)
2
(l
-
4 [Cu
2 2
(DMEGdmae) (l-
2
]I
2
OH) ](CF
2
3
3
)
2
OH) ](SbF
2
)
6 2
OH) ](PF )
2
6 2
Distances [Å]
0
CuꢁꢁꢁCu
2.860(1)
1.935(2)
1.928(2)
1.961(2)
2.031(2)
1.308(3)
1.345(3) 1.374(3)
2.909(1)
1.931(2)
1.949(2)
1.969(2)
2.068(2)
1.313(3)
2.944(4)
1.930(13)
1.914(12)
1.947(13)
2.034(15)
1.31(2)
2.912(2)
1.919(7)
1.940(8)
1.939(9)
2.045(9)
Cu–O
0
Cu–O
Cu–NImine,gua
Cu–NAmine
gua–NImine,gua
gua–NAmine,gua
C
C
1.308(13)
1.364(13) 1.372(13)
1.358(3) 1.387(3)
1.36(2)1.37(2)
Angles [°]
N–Cu–N
85.35(8)
84.48(8)
85.3(6)
85.2(4)
N
Imine,gua–Cu–O
98.25(7) 177.27(8)
91.99(7) 167.64(7)
84.49(7)
98.64(8) 177.25(8)
94.15(7) 175.69(7)
82.86(7)
99.8(6) 177.3(6)
94.6(5) 172.6(6)
80.1(6)
98.7(3) 178.9(3)
94.0(3) 171.3(3)
82.0(3)
NAmine–Cu–O
0
O–Cu–O
Cu–O–Cu
0
95.51(7)
97.14(7)
99.9(6)
98.0(3)
Structural parameter
0.96
0.96
0.96
0.96
(q)
Dihedral angle [°]
\
\
\
(CuN
2
, Cu
2
O
2
)
)
11.9(1)
40.4(1)
13.1(av)
4.1(1)
49.5(1)
16.1(av)
5.7(7)
45.9(5)
15.4(av)
7.7(3)
46.8(2)
16.1(av)
(Cgua
N
3
,CuN
2
(NAmine,gua
3 3
C ,CguaN )
significantly shorter than that in 2–4 and other bis(
dicopper complexes reported elsewhere [39–50]. Only three
l
-hydroxo)
described. The main structural data of the bis(l-hydroxo) dicopper
iPr
complex [Cu
2
(BL
)
2
(
l
4
-OH)
2
](PF
6
)
2
11 [39], [Cu
2
(Me
2
en)
2
(
l
-OH)
2
]
0
ꢀ
ꢀ
ꢀ
ꢀ
bis(
l
-hydroxo) species which have similar short CuꢁꢁꢁCu dis-
(X)
[42]), [Cu
OH) ](CF SO
[Cu (bipy)
2
ꢁnH
2
O (X /n = ClO
(DBED)
/2 12a [40], BF
](BF 13 [43], [Cu
(bpp)
4
/0 12b [41], Br /0 12c
cis
tances (2.847 [45], 2.871 [46], 2.892 Å [46]) as 1 have been de-
scribed so far, but in contrast to 1 these are stabilized by
aromatic ligand systems.
2
2
(l
-OH)
2
4
)
2
2 2
(d d) (l-
2
3
3
)
2
14 [44], [Cu
2
2
(
l
-OH)
2
](ClO
4
)
2
15 [45] and
ꢀ
ꢀ
ꢀ
2
2
(
l
-OH)
2
](X)
2
(X = ClO
4
16a [46], CF
3
SO
3
16b [47])
The differences in the geometric parameters of the complex
salts 1–4 can be explained by the position of the anions Y in the
crystal, because they form hydrogen bonds to the OH functions
of the complex cations (HꢁꢁꢁY distances: 2.698 (1), 2.768 (2),
are summarized in Table 3, the schematic structures of these com-
pounds are shown in Fig. 5.
A comparison of the structures 1–4 with the known compounds
shows a good agreement between the average Cu-O distances of
1–4 (1.922–1.940 Å) with 11, 15 and 16 (1.918–1.931 Å). The aver-
age Cu–O distances of 12, 13 and 14 (1.898–1.913 Å), however, are
slightly shorter, because they contain weaker N-donors. The
average Cu–N distance in 11 (1.933 Å) corresponds to that of the
Cu–Nimine,gua distances in 1–4 (1.939–1.969 Å), as the Nimine,gua
donor strength of the coordinating bis(imidazolin-2-imine) ligand
is comparable with that of the guanidine–amine-hybrid. The aver-
age Cu–N distances in 12–16 (1.990–2.034 Å) are due to the lower
donor strength of the coordinating ligands much longer and thus
match well with the longer Cu–NAmine distances in 1–4
2
.098 (3) and 2.204 Å (4)) and thereby easily influence the struc-
ture of bis(
l
-hydroxo) species. Here, it is remarkable that the com-
0
pound with the shortest H-bridge has the longest CuꢁꢁꢁCu distance
(
2.944(4) Å 3).
Another bis(l-hydroxo)dicopper complex with ethylene
bridged guanidine functions represents the complex [Cu
2
iPr
(
BL
based bisguanidine ligands. Besides this bis(
guanidine complex in the literature numerous bis(
)
2
(l-OH)
2
](PF
6
)
2
11 [39], which contains two imidazoline
-hydroxo) dicopper
-hydroxo)
l
l
species with ethylene bridged nitrogen chelate ligands have been
Table 3
Selected structural data of 11–21.
Complex
Distances [Å]
Angles [°]
Coordination geometryb
Ref.
CuꢁꢁꢁCu0
Cu–Oa
Cu–Na
N–Cu–N
O–Cu–O
0
0
Cu–O–Cu
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
1
3.049(1)
2.976(1)
2.996(1)
3.000(4)
2.972(1)
2.972(2)
2.847(1)
2.871(1)
2.920(1)
2.952(4)
3.014(1)
3.008(2)
3.032(1)
3.074(1)
2.938(1)
2.949(1)
1.931
1.913
1.911
1.902
1.908
1.898
1.926
1.918
1.927
1.929
1.944
1.944
1.944
1.935
1.942
1.932
1.933
2.034
2.010
2.030
2.009
2.024
2.008
1.990
1.996
2.013
2.014
1.987
1.987
1.975
2.037
2.034
84.52(8)
86.7(2)
87.28(7)
86.7(8)
75.72(8)
77.9(2)
104.28(8)
102.14
d.q.-p.
d.q.-p.
d.q.-p.
d.q.-p.
d.t.
d.q.-p.
d.q.-p.
d.q.-p.
d.q.-p.
d.t.
d.q.-p.
d.q.-p.
d.q.-p.
d.q.-p.
d.q.-p.
d.q.-p.
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[25]
[16]
[16]
[49]
[43]
[51]
2a
2b
2c
3
4
5
6a
6b
7
76.77(8)
75.92(17)
103.23(8)
104.08(17)
a
a
a
88.5
77.7
77.0
102.3
a
a
85.7
103.0(4)
a
a
a
80.5
84.6
95.4
81.58(11)
81.5(2)
83.06(14)
81.5(1)
96.94(15)
98.5(1)
a
a
90.5
79.5
99.2(10)
101.69(11)
101.4(2)
101.4(2)
105.22(11)
98.35(8)
99.63(9)
8
91.98(11)
94.0(2)
94.0(2)
96.02(11)
94.95(8)
95.07(11)
78.32(12)
78.6(2)
78.6(2)
74.78(11)
81.65(9)
80.50(9)
9a
9b
0
1a
1b
a
Average.
b
d.q.-p. = distorted square-planar, d. t. = distorted tetrahedral

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
553
0
0
(
2.031–2.068 Å). The O–Cu–O and Cu–O–Cu angle, as well as the
3.4.2. Crystal structures of bis(
TMG function
l
-hydroxo) dicopper(II) complexes with
0
CuꢁꢁꢁCu distances in 15 and 16 (81.5–84.6° and 95.4–98.5°,
2
.847–2.920 Å) are comparable with those in 1–4 (80.1–84.5°
The reaction of Cu (I) precursor complexes obtained by reaction
of TMGdmae (L2) and TMGdeae (L3) with CuI or [Cu(MeCN)
CF SO with molecular oxygen leads to the corresponding bis
-hydroxo) reaction products, which could be isolated as single
crystals with the composition [Cu (TMGdmae) -OH) ]I 5,
[Cu (TMGdmae) -OH) ](CF SO and [Cu (TMGdeae)
OH) ](Cu ) 7. The complex salts 5–7 crystallize monoclinic in the
space group P2 /n (5, 6) or P2 /c (7). The crystals of the three com-
pounds consist of the dinuclear complex cations [Cu (TMGd-
0
and 95.5–99.9°, 2.860–2.944 Å). The CuꢁꢁꢁCu distances in 11–14
4
]
(
2.972–3.049 Å), however, are significantly larger than that of the
3
3
guanidine–amine-hybrid complexes.
(l
Analogously to 1–4 the compounds 12c and 16a–b also repre-
2
2
(l
2 2
sent a series of bis(
l
-hydroxo) dicopper complexes that differ in
2
2
(l
2
3
3
)
2
6
2
2
(l-
composition only by the anions. However, 12a–c and 16a–b, show
only slight differences in the bond lengths and angles within a ser-
ies (see Table 3), so that the influence of the anions becomes only
slightly noticeable. Furthermore, it is striking that the Cu(II) ions in
1, 12 and 14–16 are surrounded in a distorted square-planar
manner as well as in 1–4, while the coordination geometry of the
Cu(II) ion in 13 is distorted tetrahedral. This for bis( -hydroxo)
dicopper complexes unusual tetrahedral coordination of Cu(II) ions
has been observed only for one other bis( -hydroxo) species
Cu (Sp) -OH) ](ClO 17 [48] so far, but this includes a propyl-
ene instead of an ethylene spacer (Fig. 5, Table 4).
2
2 4
I
1
1
2
2
+
2+
2
mae) (l
-OH)
2
]
( 5, 6) or [Cu
2
(TMGdeae)
2
(
l
-OH)
2
]
(7) and
anions (7).
2
ꢀ
1
charge-compensating iodide (5) triflate (6) or [Cu I ]
2 4
The Cu(II) ions in 5–7 are each four-coordinate with two coordina-
tion sites occupied by the two N-donor functions of the correspond-
ing guanidine–amine-hybrid ligands and two coordination sites
occupied by the bridging hydroxido ligands, so that each Cu(II) ion
l
l
[
2
2
(l
2
)
4 2
2 2
is bound in an approximately square-planar N O environment.
The central Cu
2
O
2
cores form a rhomb with a centric inversion
2+
2+
2+
H
O
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
H
O
N
H
O
Cu
Cu
N
N
N
N
N
N
N
N
O
H
Cu
Cu
N
Cu
Cu
O
H
O
H
CH Ph
PhCH2
2
-
ClO4
2
N
N
15
-
2
X
-
-
- (b))
1
9 (X : I (a), PF
-
6
2
PF
6
2+
H
O
1
1
N
N
N
2+
Cu
Cu
2+
H
O
O
H
N
H
O
N
N
N
N
N
N
N
N
Cu
Cu
Cu
Cu
O
H
-
2 X
O
H
-
-
-
1
6 (X : ClO (a), CF SO (b))
4
3
3
-
2
X
-
-
-
-
1
2 (X : ClO (a), BF (b), Br (c))
2+
4
4
H
O
-
PF6
2
N
N
N
2
0
2
+
Cu
Cu
H
O
O
H
N
H
H
H
2+
N
N
N
N
H
O
Cu
Cu
-
N
N
N
N
O
H
2 ClO4
H
Cu
Cu
17
O
H
-
2
BF
4
2+
13
-
2 X
N
N
H
O
- -
- (b))
1 (X : ClO (a), CF SO
4 3 3
2
N
N
N
H
O
2+
Cu
Cu
N N
N N
O
H
N
Cu
Cu
N
O
H
N
N
N
-
CuI32-
2
CF SO
3
3
14
18
Fig. 5. Schematic structures of the bis(l-hydroxo) dicopper complexes 11–21.

5
54
R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
Table 4
Selected structural data of 5–7.
5
[Cu
2
(TMGdmae)
2
(
l-OH)
2
]I
2
6 [Cu
2
(TMGdmae)
2
(
l-OH)
2 3
](CF SO
)
3 2
2 2 2 2 4
7 [Cu (TMGdeae) (l-OH) ](Cu I )
Distances [Å]
0
CuꢁꢁꢁCu
2.883(1)
1.932(2)
1.948(2)
1.949(3)
2.033(3)
1.311(4)
1.365(4)
2.901(1)
1.917(1)
1.936(1)
1.933(2)
2.037(2)
1.311(2)
1.355(3)
1.357(2)
2.944(1)
1.927(2)
1.967(2)
1.933(2)
2.071(2)
1.316(3)
1.364(3)
1.366(3)
Cu–O
0
Cu–O
Cu–NImine,gua
Cu–NAmine
gua–NImine,gua
gua–NAmine,gua
C
C
1
.368(4)
Angles [°]
N–Cu–N
84.90(11)
98.52(10)
85.27(7)
97.39(6)
178.16(6)
94.81(6)
171.63(6)
82.28(6)
97.72(6)
0.97
85.21(7)
96.71(7)
176.40(7)
96.83(7)
170.42(7)
81.77(7)
98.23(7)
0.96
NImine,gua–Cu–O
1
76.73(11)
93.00(10)
68.35(10)
NAmine–Cu–O
1
0
O–Cu–O
84.03(10)
95.97(10)
0.96
0
Cu–O–Cu
Structural parameter (q)
Dihedral angle [°]
\
\
\
(CuN
2
, Cu
2
O
2
)
11.7(1)
42.4(1)
35.9
8.0(1)
51.5(1)
34.4
10.3(1)
51.1(1)
34.9
(Cgua
N
3
,CuN )
2
(NAmine,gua
3 3
C ,CguaN )
Fig. 6. Molecular structure of [Cu
2
(TMGdmae)
2
(l
-OH)
2
]2+ (left) and [Cu ]2+ (right) in crystals of 5 and 7.
(TMGdeae) (l-OH)
2 2 2
center. Selected bond lengths and angles are given in Table 4, the
molecular structure of the complex cations of 5 and 6 (using the
example of 5) and of 7 in the crystal are shown in Fig. 6.
approximately the same length, in 6 (1.927 Å), however, they
are slightly shorter. The other bond lengths show no large differ-
ences (see Table 4). The dihedral angle for the torsion of the
An ideal square-planar coordination geometry of the Cu(II)
ions in 5–7 is not possible because of the N–Cu–N bite angle
of an average of 85.1° (84.90(11)° 5, 85.27(7)° 6, 85.21(7)° 7) im-
posed by the ligands and the relatively sharp O–Cu–O angle of
an average of 82.7° (84.03(10)° 5, 82.28(6)° 6, 81.77(7)° 7).
C
gua
N
3
against the CuN
2
plane, however, differs significantly
among the three complexes.
Furthermore for 5 and 6, that differ in composition only by the
anions, a slight influence of anions on the structure of the com-
plexes in the crystal can be observed, because they show signifi-
0
Due to the torsion of the two CuN
plane about 11.7° (5), 8.0° (6) and 10.3° (7) there is also a
slight deviation from planarity within the CuN unit, which is
2
planes against the central
cant differences in CuꢁꢁꢁCu (2.883 (1) 5 vs. 2.901(1) Å 6) and Cu–
2
Cu O
2
O distances (1.932(2)/1.948(2) 5 vs. 1.917(1)/1.936(1) Å 6) as well
as in the bond angles (see Table 4). The distances of the hydrogen
bonds HꢁꢁꢁY are 2.677 (5) and 2.063 Å (6), the compound with the
2 2
O
reflected in a slight distortion of the Cu(II) environment (angle
sum: 705.8° (5), 709.5° (6) and 707.3° (7), ideal value: 720°).
The average Cu–O bonds in 5 (1.940 Å) and 7 (1.947 Å) have
0
shorter H-bridge also exhibits the longer CuꢁꢁꢁCu distance
(2.901(1) Å 6). In the complex salt 7 also H-bonds to the anions

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
555
Table 5
angle (91.98(11)°), which is relatively similar to the ideal value of
the square-planar geometry (90°). But also in this case the very
sharp O–Cu–O bond angle of 78.32(12)° impedes a perfect
square-planar coordination geometry. In addition, the contraction
of the O–Cu–O angle in 18 due to the planarity of the central
Selected structural data of 8–10.
8
[Cu
2
9 [Cu
(DPipGdmae)
-OH)
(SbF
2
10 [Cu
(DPipGdmae)
-OH)
(PF
2
(
DPipGdmae)
-OH)
CF SO
2
2
2
(l
2
]
(l
2
]
(l
2
]
(
3
3
)
2
6
)
2
6
)
Cu
101.69(11)° vs. 95.97(10)° 5, 97.72(6)° 6, 98.23(7)° 7) and hence
an increase in the CuꢁꢁꢁCu distance (3.014(1) vs. 2.883(1) 5,
2.901(1) 6, 2.944 Å 7). Further bis( -hydroxo) dicopper complexes
with a propylene spacer (CH were described in the literature
only rarely. Similar complexes to 18 are the known bisguanidine
2 2
O units results in an expansion of the Cu–O–Cu angle
Distances [Å]
(
0
CuꢁꢁꢁCu
2.942(1)
1.911(2)
1.933(2)
1.937(2)
2.046(2)
1.325(3)
1.357(3)
2.952(2)
1.926(4)
1.938(4)
1.949(4)
2.038(4)
1.311(7)
1.352(7)
1.359(7)
2.921(2)
1.945(5)
1.907(5)
1.931(6)
2.041(6)
1.315(9)
1.364(9)
1.366(9)
Cu–O
0
l
Cu–O
Cu–NImine,gua
Cu–NAmine
2 3
)
C
C
gua–NImine,gua
gua–NAmine,gua
ꢀ
ꢀ
ꢀ
complexes [Cu
2
(btmgp)
p) -OH)
](ClO 17 [48] and the dimethylamino ethyl
2
(
l
2
-OH)
2
](X)
2
(X = I 19a, PF
6
19b)
[
[
16], [Cu
Cu (Sp)
2
(DPipG
-OH)
2
2
(l
](PF
6
)
2
20 [49], the sparteine complex
1
.364(3)
2
2
(
l
2
4 2
)
Angles [°]
N–Cu–N
ꢀ
ꢀ
pyridine complexes [Cu
2 2
(DMAEP) (l
-OH)
2
](X)
2
(X = ClO
4
21a
85.64(7)
99.49(7)
86.06(18)
99.37(18)
179.72(17)
94.20(17)
168.83(19)
80.38(19)
99.62(17)
0.97
85.4(2)
97.7(2)
177.7(2)
95.8(2)
168.7(2)
81.4(2)
98.6(2)
0.96
ꢀ
NImine,gua–Cu–O
[43], CF
3
SO
3
21b [51]). A comparison of the three structures 5–7
1
78.60(7)
95.03(7)
66.62(7)
with the known compounds 11–16 (see Fig. 5 and Table 3) shows
great similarities as the comparison of 1–4 with 11–16 (see above).
It is remarkable that the CuꢁꢁꢁCu distance correlates with the length
of the stabilizing hydrogen bonds which are formed between the
hydroxide O atoms and the counterions. Short HꢁꢁꢁO distances go
along with larger CuꢁꢁꢁCu distances. Especially in iodido stabilized
NAmine–Cu–O
1
0
O–Cu–O
Cu–O–Cu
Structural parameter (q)
80.11(7)
99.89(7)
0.97
0
Dihedral angle [°]
\
\
\
(CuN
(Cgua
(NAmine,gua
2
, Cu
2
O
2
)
12.8(1)
40.4(1)
32.3
9.9(2)
41.2(2)
38.2
11.4(4)
46.9(3)
34.1
bis(l-hydroxo) dicopper complexes (e.g. complexes 1 and 5), very
N
3
,CuN )
2
short CuꢁꢁꢁCu distances are found.
3 3
C ,CguaN )
3
.4.3. Crystal structures of bis(
DPipG function
The reaction of various Cu(I) precursor complexes [Cu
l-hydroxo) dicopper(II) complexes with
are present, but with HꢁꢁꢁY distances of 3.209 Å (7) they are much
longer, so their influence on the structure of the complex is negli-
gible. Compared with the corresponding complexes 1 and 2,
including a DMEG function, in particular the CuꢁꢁꢁCu distances
and the bond angles are in good agreement; but also between
m
(L)
leads
(DPipGdmae)
](SbF and
6 2
) 10. All three complex salts con-
n m
]Y
ꢀ
ꢀ
ꢀ ꢀ
(Y = CF
to the bis(
-OH) ](CF
[Cu (DPipGdmae)
tain the dinuclear complex cation [Cu
3
SO
3
, SbF
-hydroxo) dicopper complexes [Cu
SO 8, [Cu (DPipGdmae) -OH)
-OH) ](PF
6
, PF ) of DPipGdmae (L4) with O
6
2
l
3
2
2
(l
2
3
)
2
2
2
(l
2
6 2
) 9
2
–4 and 6–7 good agreements in bond lengths and angles can be
found.
Another bis(
complex with a TMG function, which was published by us recently,
is [Cu (TMGdmap) -OH) ](CuI ) 18 [25]. In contrast to 5–7, it
possesses a propylene-spacer, resulting in a significantly larger bite
2
2
(l
2
2+
2
2 2
(DPipGdmae) (l-OH) ]
l
-hydroxo) dicopper guanidine–amine-hybrid
with different anions for charge compensation. 8 and 9 crystallize
triclinic in the space group P1, 10 crystallizes monoclinic in space
group P2 /c. A summary of selected bond lengths and angles is gi-
1
ven in Table 5, the molecular structure of the complex cation
ꢀ
2
2
(l
2
3
Fig. 7. Molecular structure of [Cu
2
(DPipGdmae)
2
(
l-OH)
2
]2+ in crystals of 10 (left: frontal view, right: side view).

5
56
R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
Table 6
Extraction of the literature overview: ranges of bond lengths and angles in bis(
l
-oxo) and bis(
l
-hydroxo) dicopper complexes (key parameters are marked in bold).
Bis( -hydroxo) complexes of this work
Complex type
Ligand type
Bis(
l
-oxo) dicopper complexes
Bis( -hydroxo) dicopper complexes
l
l
Neutral
Anionic
Neutral
Anionic
Neutral
Cu–O (Å)
Cu–N (Å)
1.803–1.834
1.939–1.991
7.484–7.650
2.744–2.866
2.287–2.334
86.9–99.2
77.2–80.7
167.1–176.4
99.2–102.8
1.817–1.865
1.888–1.996
7.410–7.686
2.849–2.906
2.258–2.338
77.4–98.8
76.8–77.6
155.0–175.6
102.4–103.2
1.902–1.974
1.931–2.088
7.728–8.088
2.782–3.074
2.342–2.592
72.1–96.6
74.8–84.6
150.6–178.1
89.3–105.7
1.917–1.924
1.937–1.959
7.684–7.766
2.981–3.058
2.331–3.318
88.1–95.3
74.3–76.6
164.3–170.7
102.1–105.7
1.907–1.967
1.931–2.071
7.822–7.917
2.860–2.952
2.473–2.622
84.5–86.1
80.1–84.5
165.4–169.8
95.5–99.9
Sum2cuo+2CuN (Å)
CuꢁꢁꢁCu (Å)
OꢁꢁꢁO (Å)
N–Cu–N (°)
O–Cu–O (°)
sumNCuN,OCuO (°)
Cu–O–Cu
[
Cu
of 10.
In all three complex cations the Cu(II) ions are coordinated by a
donor set in a distorted square-planar manner, the chelating
ligands are in anti position to each other. The central Cu cores
2
(DPipGdmae)
2
(
l
-OH)
2
]2+ is shown in Fig. 7 using the example
ligands which results in longer Cu–O bonds for complexes with an-
ionic ligands. An analysis of the structural data of known bis(
oxo) and bis( -hydroxo) complexes is summarized in Table 6. This
l-
l
N
2
O
2
analysis shows that compounds with Cu–O, Cu–N and CuꢁꢁꢁCu dis-
2
O
2
tances in the range of 1.803–1.865, 1.888–1.996 and 2.744–2.906 Å
form a rhomb with a central inversion center. The average Cu–O
bond lengths in 8–10 (1.922 8, 1.932 9, 1.926 Å 10) show no large
are more likely to be bis(
pounds with Cu–O, Cu–N and CuꢁꢁꢁCu distances of 1.900–1.974,
1.931–2.088, 2.782–3.074 Å are more likely to be bis( -hydroxo)
dicopper complexes (see Supporting information, Tables A1–
-oxo) and bis( -hydro-
l-oxo) dicopper complexes, while com-
0
differences. The CuꢁꢁꢁCu distances in
8
(2.942(1) Å) and
9
l
0
(
2.952(2) Å) have approximately the same length, the CuꢁꢁꢁCu dis-
tance in 10 (2.921(2) Å), however, is slightly shorter. An ideal
square-planar coordination geometry of Cu(II) ions is not possible
due to the bite angle N–Cu–N with an average of 85.7° (85.64(7)° 8,
A16). The CuꢁꢁꢁCu distance ranges for bis(
l
l
xo) dicopper complexes with neutral ligands widely overlap and
cannot be used as single criterion for classification. For this reason,
8
6.06(18)° 9, 85.4(2)° 10) and the relatively sharp O–Cu–O bond
angle with an average of 80.6° (80.11(7)° 8, 80.38(18)° 9, 81.4(2)°
0), so that a slight distortion occurs. The torsion of the two
CuN planes against the central Cu plane of 12.8° (8), 9.9° (9)
and 11.4° (10) leads to a minimal deviation from planarity within
the N CuO unit. This is also reflected by the sum of environment
we calculated the sum of the bond lengths within the Cu
and the sum of the angles in this rhomb. By using the bond length
sum, it can be clearly distinguished between bis( -oxo) and bis(
hydroxo) dicopper complexes with neutral ligands: in bis( -oxo)
complexes, this sum ranges from 7.484 to 7.650 Å whereas bis(
2 2
O rhomb
1
l
l-
2
2
O
2
l
l-
2
2
hydroxo) complexes display a sum range from 7.728 to 8.088 Å.
angles of the Cu(II) ions, which are with 705.5° (8), 708.6° (9)
and 706.4° (10) slightly decreased compared with the ideal value
for a square-planar geometry (720°).
The complexes reported herein fit exactly in this range although
they differ in specific bond lengths or angles from other bis(
droxo) dicopper complexes.
l-hy-
All other bond lengths and angles of the three complexes show
no big differences and agree relatively well with the values in 1–7.
Hydrogen bonds between the anion to the proton of the OH ligands
are only in 9 (FꢁꢁꢁH = 2.097 Å) and 10 (FꢁꢁꢁH = 2.050 Å) present. A
significant influence of different anions can not be observed here.
An important feature of guanidines is the charge delocalization
4
. Conclusion
In this contribution, new bidentate guanidine–amine hybrid li-
gands are presented. Their copper (I) complexes react with dioxy-
gen, but only in case of L2, a defined Cu species could be
observed to be a bis( -oxo) dicopper species. Ethylene spacers in
guanidine–amine ligands seem not to be favorable for the forma-
tion of stable low-temperature Cu species. The subsequent
reactions allowed the isolation and structural characterization of
numerous bis( -hydroxo) dicopper(II) complexes. In all ten com-
2 2
O
within the CN
bond and the formal C–NR
uation of the elongation of the C@N double bond and the shorten-
ing of the C–NR bonds within the guanidine unit, the value was
introduced by Sundermeyer and co-workers [52]. It is calculated by
the formula = 2a/(b + c) wherein a is the C@N bond length and b
and c are the C–NR bond lengths. In the case of a C -symmetrical
3
unit. Hence, the lengths of the formal double C@N
l
2
single bonds are levelled. For the eval-
2 2
O
2
q
l
q
plexes, the copper(II) ion resides in a distorted square-planar envi-
ronment and the N donor ligands are arranged in anti position to
each other. The complex [Cu (DMEGdmae) (l-OH) ]I exhibits a
2 2 2 2
2
3
CN
parameter
3
unit
q
q
is equal to 1. In all complexes reported herein, the
ranges between 0.96 and 0.97 indicating a good delo-
CuꢁꢁꢁCu distance of 2.860(1) Å, which is one of the smallest ob-
served for hydroxo-bridged copper compounds so far. The CuꢁꢁꢁCu
distance correlates with the length of the stabilizing hydrogen
bonds which are formed between the hydroxide O atoms and the
counterions. Short HꢁꢁꢁO distances go along with larger CuꢁꢁꢁCu dis-
calization typical for copper(II) complexes.
3.5. Literature overview on structurally characterized bis(
l-oxo) and
bis( -hydroxo) dicopper(II) complexes
l
tances. Especially in bis(l-hydroxo) dicopper complexes with io-
Due to the structural characterization of complex 1 with the
very short CuꢁꢁꢁCu distance of 2.860(1) Å, the question arose which
dide as anion, short CuꢁꢁꢁCu distances are found.
In a literature overview of structurally characterized bis(l-oxo)
CuꢁꢁꢁCu distances still characterize a bis(
l-hydroxo) complex and if
and bis(l-hydroxo) dicopper complexes, the structural features of
there is a typical bond length range usable for identification of such
complexes. In some cases the H atoms cannot be located in the
complex structure and then, such a classification can be useful.
such complexes could be highlighted: the most important factors
are the type of ligand (anionic or neutral), the coordinative ability
of the charge compensating anion and the bite angle imposed by
the ligand. It is remarkable that the range of the CuꢁꢁꢁCu distance
Hence, we performed a CSD research on bis(
l-oxo) dicopper com-
plexes and bis( -hydroxo) dicopper(II) complexes with bidentate
l
in bis(l-oxo) and bis(l-hydroxo) dicopper complexes overlap to
ligands and differentiated them for the incorporated type of ligand.
a great extent, but by using the sum of the copper surrounding
Anionic ligands bind stronger to the copper centers as neutral
bond lengths, a classification is easily possible.

R. Haase et al. / Inorganica Chimica Acta 374 (2011) 546–557
557
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We gratefully acknowledge the financial support of the Fonds
der Chemischen Industrie and of the Deutsche Akademische
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Evonik Stiftung for granting a Ph.D. fellowship. S.H.-P. thanks Prof.
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