Gold(I) complexes with amine ligands. 3.1 Competition between
auriophilic and hydrogen bonding interactions in dimeric species
Peter G. Jones* and Birte Ahrens
Institut f ur Anorganische und Analytische Chemie, T echnical University of Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
L e t t e r
The gold(I) complexes (pip) Au`Cl~ and (Cy NH)AuCl (pip \ piperidine, Cy \ cyclohexyl) crystallise as loose
2
2
dimers; in the ionic species NwHÉ É ÉCl~ hydrogen bonding is the main secondary interaction, whereas in the
neutral complex the NwHÉ É ÉCl hydrogen bonding is weaker but is compensated by an auriophilic interaction.
Amine complexes of gold(I) have been little studied and are
generally regarded as relatively unstable (in the absence of sta-
bilising ligands as phosphines); this can be rationalized in
terms of incompatibility of the soft metal centre with the hard
nitrogen donor. Additional stabilisation may, however, be
provided by secondary interactions such as auriophilic inter-
actions (recognisable by formally non-bonded goldÈgold dis-
tances of ca. 2.7È3.4 Ó)2 or NwHÉ É ÉX hydrogen bonds.
from dichloromethaneÈlight petroleum. Crystals were
obtained by di†usion of light petroleum into dichloromethane
solution. NMR spectra were measured in CDCl solution,
3
with TMS as internal standard.¤
In (pip) Au`Cl~ (Fig. 1) an association of two cations and
2
two anions about a twofold axis is observed, in which chloride
anions accept two hydrogen bonds from the NwH groups
[NÉ É ÉCl~ 3.108(6), 3.122(7) Ó]. The AuÉ É ÉAu contact is long
[4.085(2) Ó] and can represent at best a very weak interaction;
this may be attributable to the positive charge associated with
the gold moieties. The NwAuwN axes are rotated with
respect to each other by 39.6(3)¡.
The stabilizing e†ect of hydrogen bonds was postulated for
the imine complex [Au(NHxCMe ) ](CF SO ),3 in which
2 2
3
3
the cationic gold moieties, despite disadvantageous electro-
static e†ects, form chains with short AuÉ É ÉAu distances
[3.1663(5), 3.1705(5) Ó], and the triÑate (triÑuoro-
methanesulfonate) anions are involved in NwHÉ É ÉO hydro-
gen bonds.
In the uncharged complex (Cy NH)AuCl dimers are also
2
observed (Fig. 2), but with inversion symmetry, making the
NwAuwCl axes antiparallel to each other. They have shorter
and presumably stronger AuÉ É ÉAu interactions [3.2676(14) Ó],
whereas the NÉ É ÉCl distances are longer at 3.391(8) Ó. Thus,
the reduction of charge of the gold species from ]1 to 0
makes the hydrogen bonding weaker, as expected, but the
auriophilic interactions stronger. It remains to be seen if this is
a general e†ect, but the same trend can also be recognised in
the neutral complex (pip)AuCl 7 [AuÉ É ÉAu 3.301(5), NÉ É ÉCl
3.346, 3.580 Ó], which forms loose tetramers with secondary
Stabilization through hydrogen bonding can also be
assumed for [Au(NH ) ]Br,4 in which pairs of ammineÈgold(I)
3 2
cations are linked through auriophilic interactions [AuÉ É ÉAu
3.414(1) Ó] with additional NwHÉ É ÉBr~ hydrogen bonds,
forming a layer structure.
In isocyanidegold(I) thiosalicylates,5 hydrogen bonding and
auriophilic interactions are observed, but the former does not
involve the donor atoms at gold; chains are built up via alter-
nating secondary bonding types.
We have begun a systematic study of gold(I) complexes with
aliphatic amine ligands, generally bearing an NwH function,
as a potential donor group for stabilizing hydrogen bonds. We
have not been able to obtain stable compounds with tertiary
amine ligands, and attribute this to the lack of hydrogen
bonds. Steric e†ects (“overcrowded nitrogenÏ) could represent
an alternative explanation (see below), but are difficult to
quantify; similar considerations apply, in the case of ionic
complexes, to Coulombic interactions.
¤ Bis(piperidine)gold(I) chloride. Yield 91%, dec. [ 86 ¡C. 1H NMR
(200.13 MHz, CDCl ): d 1.73 (m, 4 H, b-CH ), 3.25 (m, 4 H, a-CH ).
3
2
2
13C NMR (50.32 MHz, CDCl ) 23.41 (b-CH ), 26.52 (c-CH ), 53.50
3
2
2
(a-CH ). EI-MS, m/z 84 (100%, [M-Au-Cl-H]). Anal. calcd for
2
C
H
AuClN (402.72): C, 29.82; H, 5.51; N 6.96. Found: C, 29.34;
10 22
2
H, 5.35; N, 7.06%.
Chloro(dicyclohexylamine)gold(I). Yield 75%, dec. [ 114 ¡C. 1H
NMR (200.13 MHz, CDCl ) 1.26È1.84 (16 H, CH ), 2.12, 2.40 [m, 4
3
2
H, 2-, 2@-CH (eq.)], 2.99 (m, 2 H, CH). 13C NMR (50.32 MHz,
2
CDCl ) 25.05 (3-C), 35.50 (4-C), 34.82 (2-C) 58.73 (1-C). EI-MS,
We recently reported the structure of (pyrr) Au Cl 6
3
m/z \ 181 (16%, [M-Au-Cl]). IR (KBr) m(AuCl): 345 cm~1 (w). Anal.
4
3 3
(pyrr \ pyrrolidine), in which the AuÉ É ÉAu contacts were
rather long and thus presumably weak [3.2041(7), 3.5834(4)
Ó], whereas the hydrogen bonds were more signiÐcant
[NÉ É ÉCl~ 3.179, 3.284(6) Ó]. Here we report the structures of
two dimeric species, obtained from (tht)AuCl and the corre-
calcd for C
H
AuClN (413.74): C, 34.84; H, 5.60; N, 3.39. Found:
12 23
C, 34.86; H, 5.55; N, 3.34%.
X-Ray structure determinations. Data were measured using Mo-Ka
radiation. Absorption corrections were based on w-scans. Structures
were reÐned anisotropically on F2 using all reÑections (program
SHELXL-979). Hydrogen atoms were included using a riding model
except for those bonded to nitrogen, which were reÐned “freelyÏ with
sponding amine: (pip) Au`Cl~, previously synthesised by us,7
2
and (Cy NH)AuCl (pip \ piperidine, Cy \ cyclohexyl). These
restrained NwH bond lengths. Crystal data: (pip) Au`Cl~:
2
2
reveal an interesting balance between the two types of second-
C
H
AuClN , M \ 402.71, monoclinic, C2/c, a \ 21.346(5),
10 22
2
ary interaction.
b \ 6.480(2), c \ 19.630(5) Ó, b \ 111.54(3)¡, V \ 2525.8(13) Ó3,
Z \ 8, l \ 11.8 mm~1, T \ [130 ¡C, Stoe STADI-4 di†ractometer,
L Au`Cl~ with L \ piperidine and LAuCl with
2
3568 reÑections, 2228 unique, wR2 0.067, R1 0.030. (Cy NH)AuCl:
L \ dicyclohexylamine: (tht)AuCl (160 mg, 0.5 mmol) was dis-
2
C
H
AuClN,
M \ 413.73,
triclinic,
P([1),
a \ 8.306(3),
solved in neat amine (5 ml). The solution was stirred for 1 h
with exclusion of light at room temperature; a white precipi-
tate formed. Light petroleum was added and after cooling for
1 h at [18 ¡C the precipitate was Ðltered o† and recrystallized
12 23
b \ 8.978(2), c \ 10.132(3) Ó, a \ 68.24(2), b \ 85.17(3), c \ 77.71(3)¡,
V \ 685.7(3) Ó3, Z \ 2, l \ 10.9 mm~1, T \ [100 ¡C, Siemens P4
di†ractometer, 2399 reÑections, 2336 unique, wR2 0.088, R1 0.036.
CCDC reference number 440/051.
New J. Chem., 1998, Pages 1041È1042
1041