Preparation and characterization of macrocyclic dinickel complexes coligated by monoalkyl- and dialkylcarbamates

Article abstract of DOI:10.1016/j.ica.2008.03.016

The dinuclear nickel(II) complex [Ni₂L(Cl)]⁺ (1), where (L)^2- represents a 24-membered binucleating hexamine-dithiophenolate ligand, reacts readily with primary and secondary amines RR′NH in the presence of CO₂

Full text of DOI:10.1016/j.ica.2008.03.016

Inorganica Chimica Acta 362 (2009) 793–798
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Preparation and characterization of macrocyclic dinickel complexes coligated
by monoalkyl- and dialkylcarbamates
*
Vasile Lozan, Joscha Holldorf, Berthold Kersting
Institut für Anorganische Chemie, Universität Leipzig, Johannisallee 29, D-04103 Leipzig, Germany
a r t i c l e i n f o
a b s t r a c t
The dinuclear nickel(II) complex [Ni2L(Cl)]+ (1), where (L)2ꢀ represents a 24-membered binucleating hex-
amine-dithiophenolate ligand, reacts readily with primary and secondary amines RR0NH in the presence
of CO2 (1 bar) to give dinuclear monoalkyl- and dialkylcarbamate complexes [Ni2L(O2CNRR0)]+ (R = H,
R0 = CH2Ph (2), R = H, R0 = n-Bu (3), R = H, R0 = n-Oct (4), R = H, R0 = CH2CH2OH (5), R = R0 = Et (6), and
R = R0 = CH2CH2OH (7)). Complexes 2–7 can also be prepared by the reaction of 1 with CO2(air)/amine.
The carbamate complexes are hydrolyzed in methanolic solution to give the known alkylcarbonate com-
plex [Ni2L(O2COMe)]+ (8). These conversions are less rapid than the transesterification reactions of 8, due
to a less electron-demanding carboxyl C(carbamate) atom. All new complexes were either isolated as per-
chlorate or tetraphenylborate salts and fully characterized by elemental analysis, UV/Vis, and IR spectros-
copy. The structures of 2[BPh4] and 7[BPh4] have also been determined by X-ray crystallography. They
confirm the presence of l1,3-bridging alkylcarbamate units in the products.
Article history:
Received 30 November 2007
Received in revised form 3 March 2008
Accepted 5 March 2008
Available online 18 March 2008
Dedicated to Professor Dr. Bernhard Lippert
with appreciation for his friendship
Keywords:
Binucleating ligands
Nickel complexes
Coordination chemistry
Carbamate complexes
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
[27–30] or formate complexes [Ni2L(HCO2)]+, respectively (Scheme
1) [20]. In view of the biological, technological and environmental
The chemistry of carbamic acid H2NCO2H [1] and its organo
derivatives R2NCO2H [2] has been extensively investigated in re-
cent years [3], owing to their relevance in biological systems
[4,5], their technological importance [6–8], and their occurrence
in interstellar space [9]. Carbamate ligands have also been widely
used for the preparation of transition metal complexes [10,11],
and some carbamate complexes have found applications as inter-
mediates in organic synthesis [12–16]. We therefore extended
our studies to such systems.
importance of such reactions, we decided to explore the possibility
of fixing CO2 in the form of carbamate complexes. Our first at-
tempts afforded a series of dinuclear Ni carbamate complexes of
the type [Ni2L(O2CNRR0)]+. Their preparation, reactivity, spectro-
scopic properties and X-ray crystal structures are reported here.
To our knowledge, dinuclear nickel amine-thiophenolate coligated
by alkyl- or dialkylcarbamates are without precedence in the
literature.
In previous papers, we reported a series of coordinatively unsat-
urated [M2L(L0)]+ complexes of first row transition metal ions
supported by the binucleating hexaaza-dithiophenolate ligand
L2ꢀ (Scheme 1). The dinuclear [M2L(L0)]+ complexes have a rich
coordination chemistry since their active coordination site is acces-
sible for a large variety of coligands (L0) such as Clꢀ [17], OHꢀ [18],
2. Experimental
2.1. General methods and instrumentation
Complex [Ni2L(Cl)][ClO4] (1[ClO4]) was prepared according to
the literature procedure [17]. All other compounds were pur-
chased. Melting points were determined with a Waters VG-ZAB-
HSQ instrument in open glass capillaries and are uncorrected,
infrared spectra were recorded on a Bruker Vector27 FT-IR-spec-
trometer. Electronic absorption spectra were taken on a JASCO
V670 UV/Vis/near spectrometer. Elemental analyses were carried
out with a VARIO EL – elemental analyzer.
ꢀ
ꢀ
ꢀ
NO2ꢀ, NO3ꢀ, N3 [19], BH4 [20], ClO4 [21], and various carboxyl-
ates [22–26]. The hydroxo- and boranato-bridged dinickel com-
plexes are unique in the sense that they readily fix carbon
dioxide from air in the form of methylcarbonate [Ni2L(MeOCO2)]+
CAUTION! Perchlorate salts are potentially explosive. Only
small quantities should be prepared and handled with appropriate
care.
* Corresponding author. Tel.: +49 341 9736143; fax: +49 341 973 6199.
E-mail address: b.kersting@uni-leipzig.de (B. Kersting).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.03.016

794
V. Lozan et al. / Inorganica Chimica Acta 362 (2009) 793–798
2.4. Synthesis of [Ni2L(l-O2CNHnC4H9)][ClO4] (3[ClO4])
t
Bu
+
This compound was prepared in analogy to 2[ClO4]. Yield:
157 mg (78%). M.p.: >317 °C (decomp.). IR (KBr): m/cmꢀ1 3550 (w,
m[NH]), 3459 (m), 2958 (s), 2928 (w), 2899 (w), 2863 (s), 1592 (s,
mas[RNHCO2ꢀ]), 1485 (m), 1462 (s), 1392 (m), 1361 (m), 1349
(w), 1334 (w, ms[RNHCO2ꢀ]), 1311 (w), 1292 (w), 1263 (m), 1233
(m), 1202 (w), 1170 (m), 1152 (m), 1096 (vs, m3[ClO4ꢀ]), 1040 (s),
1002 (w), 983 (w), 931 (w), 913 (w), 881 (w), 825 (m), 818 (m),
808 (w), 791 (w), 751 (w), 624 (s, m4[ClO4ꢀ]), 563 (w), 541 (w),
H3C
CH3
N
N
N
N
S
L'
S
H3C
N
M
M
N CH3
CH3
H3C
535 (w), 492 (w), 416 (w). UV/Vis (MeCN): kmax/nm (e/Mꢀ1 cmꢀ1
)
[M2L(L')]+
656 (46), 1135 (88). Elemental Anal. Calc. for C43H74ClN7Ni2O6S2
(1002.06): C, 51.54; H, 7.44; N, 9.78; S, 6.40. Found: C, 51.32; H,
7.22; N, 9.82; S, 6.32%.
t
Bu
CO2
[Ni2L(OH)]+
[Ni2L(BH4)]+
[Ni2L(MeOCO2)]+
[Ni2L(HCO2)]+
(1)
(2)
CH3OH
CO2
2.5. Synthesis of [Ni2L(l-O2CNHnC8H17)][ClO4] (4[ClO4])
CH3CN
This compound was prepared in analogy to 2[ClO4]. Yield:
165 mg (78%). M.p.: 318 °C (decomp.). IR (KBr): m/cmꢀ1 3538 (m,
m[NH]), 2957 (s), 2926 (s), 2858 (s), 1593 (s, mas[RNHCO2ꢀ]), 1486
(s), 1460 (s), 1392 (m), 1362 (m), 1347 (w), 1336 (w), 1312 (m),
1293 (w), 1264 (m), 1233 (m), 1203 (w), 1170 (m), 1153 (m),
1095 (vs, m3[ClO4ꢀ]), 1040 (s), 1002 (w), 982 (w), 931 (w), 913
(w), 881 (w), 825 (m), 818 (m), 808 (w), 791 (w), 751 (m), 627
(s, m4[ClO4ꢀ]), 563 (w), 541 (w), 535 (w), 492 (w), 416 (w). UV/
Vis (MeCN): kmax/nm (e/Mꢀ1 cmꢀ1) = 656 (45), 1132 (103). Elemen-
tal Anal. Calc. for C47H82ClN7Ni2O6S2 (1058.17): C, 53.35; H, 7.81; N,
9.27; S, 6.06. Found: C, 53.22; H, 7.65; N, 9.30; S, 5.82%.
Scheme 1. Structures of dinuclear metal complexes [M2L(L0)]n+ supported by the
hexaaza-dithiophenolate ligand (L)2ꢀ (L0 = coligand) and CO2 fixation by [Ni2L(OH)]+
(Eq. 1) and [Ni2L(BH4)]+ (Eq. 2).
2.2. Synthesis of [Ni2L(l-O2CNHCH2Ph)][ClO4] (2[ClO4])
A solution of 1[ClO4] (184 mg, 0.200 mmol) and benzylamine
(107 mg, 1.00 mmol) in acetonitrile (40 mL) was stirred for 1 day
under a CO2 atmosphere (1 bar). To the resulting pale-green solu-
tion was added a solution of LiClO4 ꢁ 3H2O (321 mg, 2.00 mmol)
in ethanol (20 mL). The solution was quickly concentrated in vacuo
to ꢂ20 mL. The resulting green solid was filtered, washed with cold
ethanol, and dried in air. The crude product was purified by recrys-
tallization from acetonitrile/ethanol. Yield: 168 mg (81%). M.p.:
326–327 °C (decomp.). IR (KBr): m/cmꢀ1 3546 (m, m[NH]), 3456
(m), 2962 (s), 2867 (s), 1597 (s, mas[RNHCO2ꢀ]), 1459 (s), 1392
(m), 1363 (m), 1342 (m, ms[RNHCO2ꢀ]), 1306 (m), 1263 (w), 1233
(w), 1202 (w), 1170 (w), 1153 (m), 1094 (vs m3[l-ClO4ꢀ]), 1040
(s), 1001 (w), 982 (w), 931 (w), 913 (w), 881 (w), 826 (m), 818
(m), 808 (w), 791 (w), 751 (w), 702 (w), 624 (s, m4[l-ClO4ꢀ]), 563
(w), 535 (w), 492 (w), 416 (w). UV/Vis (MeCN): kmax/nm (e/
2.6. Synthesis of [Ni2L(l-O2CNEt2)][ClO4] (5[ClO4])
A solution of [Ni2L(Cl)]ClO4 (184 mg, 0.200 mmol) and diethyl-
amine (731 mg, 10 mmol) in acetonitrile (40 mL) was stirred under
an atmosphere of CO2 for 2 days, during which time the color of the
solution turned from yellow to green. A solution of LiClO4 ꢁ 3H2O
(320 mg, 2.00 mmol) in ethanol (20 mL) was added, and the clear
solution concentrated to ca. 20 mL to produce a green solid that
was filtered, washed with cold ethanol and dried in air. Yield:
164 mg (82%). M.p.: 309–310 °C (decomp.). IR (KBr): m/cmꢀ1 3430
(br m), 2962 (s), 2926 (w), 2900 (w), 2867 (s), 2805 (w), 1637
(w), 1559 (s, mas[R2NCO2ꢀ]), 1481 (s), 1460 (vs), 1423 (m), 1395
(w), 1374 (vw), 1363 (w), 1309 (s), 1264 (w), 1233 (w), 1202
(w), 1170 (vw), 1152 (m), 1120 (w), 1109 (w), 1081 (vs,
m3[ClO4ꢀ]), 1040 (m), 1003 (w), 982 (w), 931 (m), 913 (m), 880
(m), 826 (m), 818 (m), 808 (w), 788 (w), 752 (w), 625 (m,
m4[ClO4ꢀ]), 564 (w), 535 (w), 492 (w), 415 (w). UV/Vis (MeCN):
kmax/nm (e/Mꢀ1 cmꢀ1) = 273 (20829), 305 (15337), 327 (12958),
659 (10), 1138 (75). Elemental Anal. Calc. for C43H74ClN7Ni2O6S2
(1002.06): C, 51.54; H, 7.44; N, 9.78; S, 6.40. Found: C, 51.39; H,
7.37; N, 9.81; S, 6.22%.
M
ꢀ1 cmꢀ1) 270 (17394), 304 (15547), 326 (13044), 658 (42),
1136 (65). Elemental Anal. Calc. for C46H72ClN7Ni2O6S2 (1036.08):
C, 53.33; H, 7.00; N, 9.46; S, 6.19. Found: C, 53.12; H, 7.22; N,
9.58; S, 6.08%.
2.3. Synthesis of [LNi2(l-O2CNHCH2Ph)][BPh4] (2[BPh4])
A
solution of NaBPh4 (342 mg, 1.00 mmol) in methanol
(50 mL) was added to solution of 2[ClO4] (104 mg,
a
0.100 mmol) in methanol (40 mL). The resulting green product
was quickly filtered, washed with ethanol and dried in air to
give 111 mg (88%) of 2[BPh4] as a green, air-stable, microcrystal-
line powder. M.p.: 305–306 °C (decomp.). IR (KBr): m/cmꢀ1 3546
(w), 3459 (m), 3055 (m), 3031 (m), 2962 (s), 2864 (s), 1598 (s,
mas[RNHCO2ꢀ]), 1479 (s), 1458 (s), 1381 (m), 1362 (m), 1331
(m), 1304 (m), 1263 (m), 1231 (m), 1200 (w), 1168 (w), 1151
(m), 1077 (s), 1066 (s), 1040 (s), 999 (w), 982 (w), 929 (w),
911 (m), 881 (m), 843 (m), 825 (s), 807 (w), 791 (w), 749
(w), 732 (s, m[BPh4ꢀ]), 702 (s, m[BPh4ꢀ]), 629 (m), 611 (s), 582
2.7. Synthesis of [Ni2L(l-O2CNEt2)][BPh4] (5[BPh4])
The preparation of this compound was similar to that used for
2[BPh4]. Yield: 111 mg (91%). M.p.: 288–289 °C (decomp.). IR
(KBr): m/cmꢀ1 3441 (m), 3059 (m), 3032 (m), 2963 (s), 2866 (s),
1634 (w), 1580 (w), 1555 (s, mas[R2NCO2ꢀ]), 1481 (s), 1459 (vs),
1421 (s), 1394 (m), 1375 (w), 1362 (m), 1309 (s), 1265 (m), 1232
(m), 1201 (w), 1170 (w), 1152 (m), 1078 (s), 1058 (m), 1041 (m),
1001 (w), 981 (w), 930 (m), 911 (m), 881 (m), 825 (m), 817 (m),
807 (m), 788 (w), 732 (s, m[BPh4ꢀ]), 704 (s, m[BPh4ꢀ]), 629 (m),
612 (m), 563 (w), 534 (w), 468 (w), 415 (w). UV/Vis (MeCN):
kmax/nm (e/Mꢀ1 cmꢀ1) = 304 (14889), 327 (12659), 657 (21),
1137 (69). Elemental Anal. Calc. for C67H94BN7Ni2O2S2 (1221.84):
C, 65.86; H, 7.75; N, 8.02; S, 5.25. Found: C, 65.62; H, 7.74; N,
7.60; S, 5.58%.
(w), 562 (w), 534 (w), 469 (w), 415 (w). UV/Vis (MeCN): kmax
/
nm (e/Mꢀ1 cmꢀ1) 266 (19140), 304 (15208), 327 (13054), 657
(32), 1136 (69). Elemental Anal. Calc. for C70H92BN7Ni2O2S2
(1255.85): C, 66.95; H, 7.38; N, 7.81; S, 5.11. Found: C, 66.30;
H, 7.60; N, 7.82; S, 5.26%.

V. Lozan et al. / Inorganica Chimica Acta 362 (2009) 793–798
795
2.8. Synthesis of [Ni2L(l-O2CNHCH2CH2OH)][ClO4] (6[ClO4])
carried out with the perchlorate complexes in neat methanol at
62 °C. In a typical experiment, a solution of the carbamate complex
(ca. 80 mg) in methanol (ꢂ100 mL) was refluxed under argon.
Samples (ca. 10 mL) of the reaction mixture were removed at reg-
ular intervals, taken to dryness, and then analyzed by IR spectros-
copy. The relative amounts of precursors and products could be
quantified by visual inspection of the intensity of the characteristic
stretching frequencies (mas[RR0NCO ꢀ] for 2–7, mas[CH3OCO ꢀ] for
This compound was prepared in analogy to 2[ClO4]. Yield:
171 mg (86%). M.p.: 320–312 °C (decomp.). IR (KBr): m/
cmꢀ1 = 3530 (w, m[NH]), 3389 (s br, m[NH]), 2960 (s), 2868 (s),
1593 (s, mas[RNHCO2ꢀ]), 1484 (s), 1461 (w), 1393 (m), 1363 (m),
1315 (m), 1264 (m), 1233 (m), 1202 (w), 1170 (w), 1153 (m),
1099 (vs, m3[ClO4ꢀ]), 1079 (s), 1059 (s), 1041 (s), 1002 (w), 983
(w), 931 (m), 913 (m), 881 (m), 826 (s), 808 (m), 792 (w), 752
(w), 624 (s, m4[ClO4ꢀ]), 564 (w), 537 (w), 494 (w), 416 (w). UV/
Vis (CH3CN): kmax/nm (e/Mꢀ1 cmꢀ1) 270 (16907), 304 (14975),
326 (12776), 657 (28), 1136 (63). Elemental Anal. Calc. for
C41H70ClN7Ni2O7S2 (990.01): C, 49.74; H, 7.13; N, 9.90; S, 6.48.
Found: C, 49.48; H, 7.31; N, 10.12; S, 6.17%.
2
2
8).
2.13. Collection and reduction of X-ray data
Single crystals of 2[BPh4] ꢁ 0.75MeCN ꢁ 0.25H2O and 7[BPh4] ꢁ
0.5MeCN were grown by recrystallization from acetonitrile. The
data sets were collected at 213(2) K using a STOE IPDS-2T diffrac-
tometer and graphite monochromated Mo Ka radiation
(0.71073 Å). The intensity data were processed with the program
STOE X-AREA. Structures were solved by direct methods [31] and re-
fined by full-matrix least-squares on the basis of all data against
F2 using SHELXL-97 [32]. PLATON was used to search for higher symme-
try [33]. H atoms were placed at calculated positions and refined as
riding atoms with isotropic displacement parameters. All non-
hydrogen atoms were refined anisotropically. Selected crystallo-
graphic data are summarized in Table 1.
In the crystal structure of 2[BPh4] ꢁ 0.75MeOH ꢁ 0.25H2O one sol-
vent site was found to be occupied partially by MeCN and H2O sol-
vate molecules. The hydrogen atoms H(7) bonded to the benzylic
nitrogen atom N(7) was located unambiguously from final Fourier
maps. Water hydrogen atoms were not included in the refinement.
In 7[BPh4]2 ꢁ 0.5MeCN two tert-butyl groups were found to be rota-
tionally disordered. The disorder was refined with restrained C–C
and Cꢁ ꢁ ꢁC distances and fixed occupancy factors of 0.50 applying
the SADI-instructions implemented in the SHELXL program suite.
One of the two hydroxyethyl groups in molecule B was also found
to be disordered over two sites with occupancy factors of 0.50 each.
Drawings were produced with ORTEP 3 for Windows [34].
2.9. Synthesis of [Ni2L(l-O2CNHCH2CH2OH)][BPh4] (6[BPh4])
This compound was prepared in a manner identical to that used
for 2[BPh4]. Yield: 112 mg (93%). M.p.: 296–297 °C (decomp.). IR
(KBr): m/cmꢀ1 3532 (s), 3441 (s), 3054 (m), 3032 (m), 2963 (s),
2868 (s), 2806 (w), 1948 (w), 1817 (w), 1590 (s, mas[RNHCO2ꢀ]),
1483 (s), 1460 (s), 1427 (m), 1392 (m), 1361 (m), 1316 (m), 1264
(m), 1234 (w), 1201 (w), 1153 (w), 1133 (w), 1111 (w), 1078 (s),
1057 (s), 1041 (s), 1000 (w), 983 (w), 930 (w), 912 (w), 884 (w),
843 (m), 825 (w), 808 (w), 792 (w), 735 (s, m[BPh4ꢀ]), 705 (s,
m[BPh4ꢀ]), 656 (w), 630 (m), 613 (m), 562 (w), 535 (w), 493 (w),
470 (w), 415 (w). UV/Vis (CH3CN): kmax/nm (e/Mꢀ1 cmꢀ1) = 266
(21170), 304 (15869), 326 (13530), 657 (35), 1136 (71). Elemental
Anal. Calc. for C65H90BN7Ni2O3S2 (1209.78): C, 64.53; H, 7.50; N,
8.10; S, 5.30. Found: C, 64.43; H, 7.69; N, 7.83; S, 4.82%.
2.10. Synthesis of [Ni2L(l-O2CN(CH2CH2OH)2)][ClO4] (7[ClO4])
This compound was prepared in analogy to 2[ClO4]. Yield:
158 mg (76%). M.p.: 295–296 °C (decomp.). IR (KBr): m/
cmꢀ1 = 3442 (s), 2955 (s), 2869 (s), 2023 (w), 1634 (w), 1564 (s,
mas[R2NCO2ꢀ]), 1461 (s), 1414 (m), 1397 (m), 1363 (m), 1310 (m),
1264 (m), 1233 (m), 1202 (w), 1170 (w), 1153 (m), 1119 (s),
1099 (vs, m3[ClO4ꢀ]), 1079 (s), 1059 (s), 1041 (s), 1002 (w), 983
(w), 930 (w), 913 (m), 881 (m), 826 (m), 808 (w), 790 (w), 753
(w), 670 (w), 626 (vs, m4[ClO4ꢀ]), 564 (w), 536 (w), 494 (w), 416
(w). UV/Vis (CH3CN): kmax/nm (e/Mꢀ1 cmꢀ1) = 270 (16578), 306
(14929), 328 (12721), 660 (31), 1134 (70). Elemental Anal. Calc.
for C43H74ClN7Ni2O8S2 (1034.06): C, 49.94; H, 7.21; N, 9.48; S,
6.20. Found: C, 49.73; H, 7.39; N, 9.68; S, 5.92%.
Table 1
Crystallographic data for 2[BPh4] ꢁ 0.75MeCN ꢁ 0.25H2O and 7[BPh4] ꢁ 0.5MeCN
Compound
Formula
Mr [g/mol]
Space group
a (Å)
b (Å)
c (Å)
a (°)
b (°)
2[BPh4] ꢁ 0.75MeCN ꢁ 0.25H2O 7[BPh4] ꢁ 0.5MeCN
C71.50H94.75BN7.75Ni2O2.25S2
1291.15
C68H95.50BN7.50Ni2O4S2
1274.37
ꢀ
P1
P21/c
13.7854(4)
15.6450(5)
16.0833(5)
87.920(3)
84.536(2)
72.500(2)
3293.05(18)
2
15.563(5)
31.695(11)
27.595(11)
90.00
105.962(7)
90.00
2.11. Synthesis of [Ni2L(l-O2CN(CH2CH2OH)2)][BPh4] (7[BPh4])
This compound was prepared in a manner identical to that used
for 2[BPh4]. Yield 116 mg (93%). M.p.: 266–267 °C (decomp.). IR
(KBr): m/cmꢀ1 = 3443 (s), 3055 (m), 3035 (m), 2998 (m), 2963 (s),
2868 (s), 2806 (w), 1945 (w), 1633 (w), 1566 (s, mas[R2NCO2ꢀ]),
1480 (s), 1460 (s), 1420 (m), 1396 (m), 1363 (m), 1309 (m), 1264
(m), 1233 (w), 1201 (m), 1170 (w), 1152 (w), 1077 (s), 1058 (s),
1040 (s), 982 (w), 930 (w), 912 (w), 882 (w), 844 (w), 826 (m),
790 (w), 748 (m), 734 (s, m[BPh4ꢀ]), 706 (s, m[BPh4ꢀ]), 670 (w),
629 (m), 613 (m), 563 (w), 537 (w), 494 (w), 469 (w), 416 (w).
c (°)
V (Å3)
13087(8)
8
Z
Dcalc. (g/cm3)
1.302
1.294
Crystal size (mm3)
0.20 ꢃ 0.20 ꢃ 0.20
0.30 ꢃ 0.30 ꢃ 0.10
l(Mo Ka) (mmꢀ1
h Limits (°)
)
0.687
0.693
3.47–28.00
36032
1.00–29.07
40320
Measured reflections
Independent reflections
Observed reflectionsa
Number of parameters
15865
28420
UV/Vis (CH3CN): kmax/nm (e/Mꢀ1 cmꢀ1
) 266 (18258), 306
13219
4546
(13948), 328 (11887), 657 (32), 1133 (62). Elemental Anal. Calc.
for C67H94BN7Ni2O4S2 ꢁ 2H2O (1289.87): C, 62.39; H, 7.66; N,
7.60; S, 4.97. Found: C, 62.16; H, 7.60; N, 7.33; S, 4.62%.
794
1537
b
R1 (R1 all data)
0.0488 (0.0580)
0.1463 (0.1529)
0.981/–1.236
0.0857 (0.3913)
0.1706 (0.2642)
0.766/–0.831
c
wR2 (wR2 all data)
Maximum, minimum
peaks (e/Å3)
2.12. Reactivity studies
a
Observation criterion: I P 2r(I).
P
P
b
c
R1
=
kFoj ꢀ jFck/ jFoj.
n
P
2
o
1=2
Solubility considerations and the slow rate of the reactions at
ambient temperature dictated that all alcoholysis reactions were
P
2
wR2
¼
½wðF2o ꢀ Fc2Þ ꢄ= ½wðF2oÞ ꢄ
.

796
V. Lozan et al. / Inorganica Chimica Acta 362 (2009) 793–798
3. Results and discussion
OH
NH2
3.1. Synthesis and characterization of compounds
O
HN
Complex [Ni2L(Cl)]ClO4 1 was found to react smoothly with a
variety of amine/CO2 systems (RNH2, R = Bz; n-Bu, n-Oct; R2NH,
R = Et; CO2 (1 bar)) in acetonitrile over reaction times of several
hours to give the green cationic carbamate complexes 2–5. The
complexes could be isolated from the reaction mixtures upon addi-
tion of an excess of LiClO4 ꢁ 3H2O in 70–80% yields (Scheme 2). The
same products can also be obtained upon exposure of the reaction
solutions to air in similar yields, but these reactions proceed much
less rapidly (typically 3–4 days). All carbamate complexes are air-
stable solids that are readily soluble in a variety of common organ-
ic solvents such as dimethylformamide, acetonitrile, and dichloro-
methane, but insoluble in water. In alcoholic solutions alcoholysis
occurs (see below).
Previous work in this laboratory has demonstrated that alco-
holic solutions of 1 fix carbon dioxide from air in the form of alkyl-
carbonate complexes [27,28]. This prompted us to examine
reactions of 1 with aminoalcohols/CO2 and to determine which of
the two possible products – alkylcarbonate or alkylcarbamate
complex – would form (Scheme 3).
O
Ni
O
Ni
O
Ni
O
Ni
alkylcarbonate
complex
alkylcarbamate
complex
Scheme 3. Alkylcarbonate and alkylcarbamate complexes.
R
R'
CH3
N
O
CH3OH (exc.)
O
O
O
O
+
HNRR'
Ni
Ni
Ni
Ni
[LNi2(O2COMe)]+
2-7
8
Scheme 4. Alcoholysis of alkylcarbamate complexes 2–7.
We chose to examine the reactions of 1 with ethanolamine and
diethanolamine. Again, under ambient conditions both carbon-
ation reactions (CO2(1 bar) or CO2(air)) proceeded smoothly pro-
ducing green solutions, from which green crystals of
[Ni2L(O2CNCH2CH2OH)]ClO4 (6) and [Ni2L(O2CN(CH2CH2OH)2)]-
ClO4 (7) were obtained in analytically pure form after addition of
LiClO4, subsequent work-up and recrystallization.
Crystals of the perchlorate salts of 2–7 were not suitable for X-
ray crystallographic analysis, therefore selected complexes were
transformed into tetraphenylborate salts by salt metathesis reac-
tions with NaBPh4. These salts exhibited better crystallinity. It
has thus been possible to determine the solid state structures of
2[BPh4] and 7[BPh4] by X-ray crystallography. This confirmed
unambiguously the formulation of the products as carbamate com-
plexes as represented in Scheme 2. Thus, carbonation reactions of 1
with amines/CO2 or aminoalcohols/CO2 in acetonitrile proceed
with strict ‘‘carbamate” selectivity.
Finally, we considered it worthwhile to probe whether the car-
bamate complexes 2–7 would undergo alcoholysis reactions with
solvent molecules (Scheme 4) [35]. Indeed when the carbamate
complexes are stirred in methanol at ambient temperature a slow
conversion to the known methylcarbonate complex 8 takes place
(ca. 10% conversion after 1 week by IR spectroscopy). When heated
to reflux the reactions complete within a period of 3–5 days. The
alkylcarbamate complexes 2–7 differ in this respect from the alkyl-
carbonate complexes of L2ꢀ such as 8. These hydrolyse much more
rapidly (100% conversion at ambient temperature within less than
24 h). This is indicative of extensive electron delocalisation of the
nitrogen lone pair into the carboxyl group such that the carbamate
is less susceptible for nucleophilic attack by the solvent than the
alkycarbonate. It is supported by the crystal structure described
below.
All compounds gave satisfactory elemental analyses and were
characterized by IR and UV/Vis spectroscopy, and compounds
2[BPh4] and 7[BPh4] also by X-ray structure analysis. Characteriza-
tion data for 8 were reported in previous work [27,28]. UV/Vis
spectra of 2–7 in acetonitrile are marked by two weak absorption
bands above 500 nm typical of octahedral Ni2+ (d8, S = 1) ions
(Table 2). Values below 500 nm are either associated with p–p
transitions within the ligand or with RSꢀ ? Ni2+ ligand-to-metal
charge transfer transitions. The values for the two d–d transitions
closely compare with those of the acetato-bridged complex [Ni2-
L(OAc)]+ (9, [27,28]) as one might expect from the similar N3S2O
coordination environments.
One prominent vibration band is seen in the IR (Table 2), as in
other carbamato-bridged complexes [36]. This band is associated
with the antisymmetric (mas(O2CNR2)) stretching modes of the
carbamato ligands. The symmetric stretching modes (ms(O2CNR2))
could not be located, but are expected to lie in the 1400–
1300 cmꢀ1 region. Note that the antisymmetric stretching vibra-
tion for the monoalkyl carbamate complexes 2–4 and 6 appear at
somewhat higher energies than those of the dialkyl carbamate
complexes 5 and 7. The observed values are significantly different
RR'NH, CO2 (1 bar)
CH3CN
[Ni2LCl]+
[Ni2L(O2CNRR')]+
or
1
Table 2
2-7
RR'NH, CO2 (air)
Selected spectroscopic data for Ni2 carbamate, alkyl carbonate and carboxylate
CH3CN
a
complexes supported by (L2ꢀ
)
UV/Vis (kmax/nm) mas(R-CO2ꢀÞ m(NH) Reference
R
R'
t
Bu
R
R
'
t
Bu
N
2 [Ni2L(O2CNHBz)]+
658
1136
1135
1132
1138
1136
1134
1108
1134
1597
1592
1593
1559
1593
1564
1635
1588
3546
3550
3538
–
This work
This work
This work
This work
This work
This work
[27,28]
2 H
3 H
4 H
5 Et
6 H
CH2Ph
3 [Ni2L(O2CNHn-Bu)]+
4 [Ni2L(O2CNHn-Oct)]+
5 [Ni2L(O2CNEt2)]+
656
656
659
657
O
n
n
C4H9
C8H17
N
N
O
N
Ni
N
Et
6 [Ni2L(O2CNHC2H4OH)]+
3530
–
Ni
N
N
S
S
CH2CH2OH
7 [Ni2L(O2CN(C2H4OH)2)]+ 660
7 CH2CH2OH CH2CH2OH
8 [Ni2L(O2COMe)]+
9 [Ni2L(OAc)]+
650
649
[27,28]
a
Scheme 2. Synthesis of carbamate complexes 2–7.
Data refer to the perchlorate salts.

V. Lozan et al. / Inorganica Chimica Acta 362 (2009) 793–798
797
Fig. 2. Structure of one of the two independent cations 7 in crystals of 7[BPh4] -
0.5MeCN with thermal ellipsoids drawn at the 30% probability level. Hydrogen
atoms, except H(3b) and H(4a), are omitted for reasons of clarity. Only one orien-
tation of the disordered tert-butyl group is shown.
Fig. 1. Structure of cation 2 in crystals of 2[BPh4] ꢁ 0.75MeCN ꢁ 0.25H2O with ther-
mal ellipsoids drawn at 50% probability. Hydrogen atoms, except H(7), are omitted
for reasons of clarity.
features as far as bond lengths and angles around the Ni atoms
are concerned. The average Ni–N, Ni–S, and Ni–O distances are
2.233(2), 2.466(6) and 1.997(2) Å, respectively. Similar values were
observed in [LNi2(O2COMe)]+ [27,28], and related carboxylato-
bridged Ni2 complexes of L2ꢀ [26] (c.f. Table 3).
from the corresponding antisymmetric (mas(O2COR)) stretching
mode of the alkylcarbonate complex 8. For 2–4, the N–Hamide
stretching vibration appears as a weak sharp band at ca. 3550–
3535 cmꢀ1, indicating that the carbamate moiety is not involved
in hydrogen bonding interactions. This is confirmed by X-ray
crystallography.
The structure of 2[BPh4] confirms the presence of the carbamate
complex 2. Fig. 1 provides an ORTEP representation of the cation 2,
Table 3 lists selected bond lengths and angles. The divalent Ni ions
are bridged by the benzylcarbamato ligand in a l1,3-bridging mode,
resulting in a Niꢁ ꢁ ꢁNi distance of 3.483(1) Å. The carbamate nitro-
gen is essentially planar, indicative of extensive delocalization of
the nitrogen lone pair into the carboxyl group. The C–O bonds
are practically identical and the O2C–N bond is of length
1.367(3) Å, which is a typical value [2,16]. Note that the O2CNH
group forms no hydrogen bonds, as already established by IR spec-
troscopy. This unique situation could arise from the steric protec-
tion offered by the supporting ligand (L2ꢀ). There are no unusual
Green crystals of 7[BPh4] ꢁ 0.5MeCN are monoclinic P21/c. There
are two crystallographically independent but chemically almost
identical molecules (labelled A and B) in the asymmetric unit.
Fig. 2 shows the bis(2-hydroxyethyl)carbamate ligand to be coordi-
nated to the [Ni2L]2+ unit in a manner identical to the situation
found in 2. Thus, both NiII ions are six-coordinate with three N
and two S atoms from L2ꢀ and one O atom of a l1,3-bridging carba-
mate group. The carbamate group is again planar, but the C–N dis-
tance is by ca. 0.08 Å longer than in 2. The Ni–O, Ni–S, and Ni–N
distances are unexceptional and are very close to the correspond-
ing distances in 2. The hydroxyethyl units link adjacent complexes
via intermolecular hydrogen bonding interactions (d(OHꢁ ꢁ ꢁO) =
2.542 and 2.917 Å). Overall, the two structures clearly show that
the [Ni2L]2+ units can expand their binding pockets sufficiently to
accommodate l1,3-bridging carbamate ligands.
Table 3
4. Concluding remarks
Selected bond lengths [Å] in complexes 2, 7, 8 and 9
2
7a
8
9
A series of novel dinuclear nickel(II) carbamate complexes
supported by a hexaamine-dithiophenolate ligand have been syn-
thesized and characterized, namely [Ni2L(O2CNHBz)]+ (2), [Ni2-
L(O2CNHn-Bu)]+ (3), [Ni2L(O2CNHn-Oct)]+ (4), [Ni2L(O2CNEt2)]+
(5), [Ni2L(O2CNHCH2CH2OH)]+ (6), and [Ni2L(O2CN(CH2CH2OH)2]+
(7)). The carbonation reactions of 1 with ambidentate aminoalco-
hols proceed with ‘‘carbamate” selectivity. The crystal structures
of 2[BPh4] and 7[BPh4] confirm the presence of l1,3-bridging carba-
mate units showing that the [Ni2L]2+ units can expand their bind-
ing pockets sufficiently to accommodate carbamate ligands. All
carbamate complexes are hydrolyzed in methanol. These conver-
sions are much slower than the transesterification reaction of the
methyl carbonate complex 8, due to the more extensive electron
delocalisation of the nitrogen lone pair into the carboxyl group. Fu-
ture work is focused on the hydrogenation of the carbamate moi-
ety in the pocket of the complexes.
M(1)–O(1)
M(1)–N(1)
M(1)–N(2)
M(1)–N(3)
M(1)–S(1)
M(1)–S(2)
M(2)–O(2)
M(2)–N(4)
M(2)–N(5)
M(2)–N(6)
M(2)–S(1)
M(2)–S(2)
M–Nb
1.990(2)
2.287(2)
2.136(2)
2.266(2)
2.4597(6)
2.4802(6)
2.003(2)
2.335(2)
2.156(2)
2.218(2)
2.4572(6)
2.4681(6)
2.233(2)
1.997(2)
2.466(6)
3.472(1)
1.264(3)
1.255(3)
1.367(3)c
1.990(8) [2.030(8)]
2.208(9) [2.295(11)]
2.123(11) [2.162(11)]
2.330(10) [2.252(11)]
2.480(4) [2.444(4)]
2.468(3) [2.474(4)]
2.014(8) [1.992(8)]
2.207(10) [2.337(10)]
2.130(10) [2.136(11)]
2.327(10) [2.223(10)]
2.439(4) [2.464(4)]
2.496(4) [2.444(4)]
2.221(10) [2.234(10)]
2.002(8) [2.011(8)]
2.471(4) [2.457(4)]
3.453(1) [3.452(1)]
1.258(14) [1.218(14)]
1.244(14) [1.267(15)]
1.430(15) [1.435(15)]c
2.021(2)
2.240(3)
2.139(3)
2.278(3)
2.453(1)
2.479(1)
2.003(2)
2.300(3)
2.151(3)
2.227(3)
2.457(1)
2.486(1)
2.223(3)
2.012(2)
2.469(1)
3.491(1)
1.250(4)
1.237(4)
1.361(4)d
1.998(2)
2.281(2)
2.152(2)
2.251(2)
2.4929(9)
2.448(1)
2.008(2)
2.244(2)
2.158(2)
2.295(2)
2.493(1)
2.4500(9)
2.230(2)
2.003(2)
2.471(1)
3.483(1)
1.249(3)
1.252(3)
1.509(4)e
M–Ob
M–Sb
Mꢁ ꢁ ꢁM
C(39)–O(1)
C(39)–O(2)
C(39)–X
a
There are two crystallographically independent molecules
asymmetric unit. Values in square-brackets refer to molecule B.
A
and B in the
5. Supplementary material
b
Average values.
X = N.
X = O.
X = C.
c
CCDC 668900 and 668901 contain the supplementary crystallo-
graphic data for 2[ClO4]2 ꢁ 0.75MeCN ꢁ 0.25H2O and 7[BPh4] ꢁ
0.5MeCN. These data can be obtained free of charge from The
d
e

798
V. Lozan et al. / Inorganica Chimica Acta 362 (2009) 793–798
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Acknowledgements
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