Synthesis, isomerism and supramolecular chemistry of diphenylmethanimine complexes of the coinage metals

Article abstract of DOI:10.1039/a604808k

The reactions of [AuCl(SMe₂)] or [AuBr(C₄H₈S)] with 1 equivalent of diphenylmethanimine led to the formation of the complexes [AuCl(Ph₂C=NH)] 1a, [Au(Ph₂C=NH)₂][AuCl₂] 1b and [Au(Ph₂C=NH)₂][AuBr₂] 2, respectively. Treatment of 1a, 1b with KI in the two-phase system dichloromethane-water induced a redox process to give Au⁰ and [Au(Ph₂C=NH)₂][I₃] 3. The same result was obtained when AuI and Ph₂C=NH were allowed to react under anhydrous and oxygen-free conditions. Copper(I) iodide reacted with an excess of Ph₂C=NH with formation of the complex [CuI(Ph₂C=NH)] 4. Bis(diphenylmethanimine) complexes of gold, [Au(Ph₂C=NH)₂]BF₄ 5, and silver, [Ag(Ph₂C=NH)₂]BF₄ 6, were prepared by the reaction of 2 equivalents of the ketimine and [Au(PhCN)₂]BF₄ or AgBF₄ in dichloromethane or tetrahydrofuran solutions, respectively. The crystal structures of the complexes 1a, 1b, 2, 3, 5 and 6 have been determined. The (Ph₂C=NH)AuCl units of compound 1a form infinite zigzag chains via weak Au ... Au contacts [3.3633(5) A]. In 1b two AuCl₂^- anions and two (Ph₂C=NH)₂Au⁺ cations form a tetranuclear Z-type unit with Au ... Au contacts of 3.1944(5) [Au(1) ... Au(2)], 3.604(1) [Au(1) ... Au(2′)] and 3.392(1)A [Au(1) ... Au(1′)]. The N-H ... Cl geometry suggests hydrogen bonding between the hydrogen and chlorine atoms of neighbouring ions. The bromine compound 2 is isostructural to the chloride 1b with slightly longer Au ... Au distances. Compound 3 shows bis(diphenylmethanimine)gold(I) cations and triiodide anions with no anomalies in the packing and in bond distances and angles. The geometry of the silver(I) and gold(I) complexes 5 and 6 are quite similar except for the observation that the Au-N bond is 0.11 A shorter than the Ag-N bond, which suggests that two-co-ordinate gold(I) is indeed smaller than two-co-ordinate silver(I) in systems with nitrogen-containing ligands, as previously observed for phosphine complexes.

Full text of DOI:10.1039/a604808k

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Synthesis, isomerism and supramolecular chemistry of
diphenylmethanimine complexes of the coinage metals
Wolfgang Schneider, Andreas Bauer and Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstrasse 4,
D-85747 Garching, Germany
The reactions of [AuCl(SMe2)] or [AuBr(C4H8S)] with 1 equivalent of diphenylmethanimine led to the formation
of the complexes [AuCl(Ph C᎐NH)] 1a, [Au(Ph C᎐NH) ][AuCl ] 1b and [Au(Ph C᎐NH) ][AuBr ] 2, respectively.
᎐
᎐
᎐
2
2
2
2
2
2
2
Treatment of 1a, 1b with KI in the two-phase system dichloromethane–water induced a redox process to give Au0
and [Au(Ph C᎐NH) ][I ] 3. The same result was obtained when AuI and Ph C᎐NH were allowed to react under
᎐
᎐
2
2
2
3
anhydrous and oxygen-free conditions. Copper() iodide reacted with an excess of Ph C᎐NH with formation of
᎐
2
the complex [CuI(Ph C᎐NH)] 4. Bis(diphenylmethanimine) complexes of gold, [Au(Ph C᎐NH) ]BF 5, and silver,
᎐
᎐
2
2
2
4
[Ag(Ph C᎐NH) ]BF 6, were prepared by the reaction of 2 equivalents of the ketimine and [Au(PhCN) ]BF or
᎐
2
2
4
2
4
AgBF4 in dichloromethane or tetrahydrofuran solutions, respectively. The crystal structures of the complexes 1a,
1b, 2, 3, 5 and 6 have been determined. The (Ph C᎐NH)AuCl units of compound 1a form infinite zigzag chains via
᎐
2
weak Au ؒ ؒ ؒ Au contacts [3.3633(5) Å]. In 1b two AuCl2Ϫ anions and two (Ph C᎐NH) Au+ cations form a
᎐
2
2
tetranuclear Z-type unit with Au ؒ ؒ ؒ Au contacts of 3.1944(5) [Au(1) ؒ ؒ ؒ Au(2)], 3.604(1) [Au(1) ؒ ؒ ؒ Au(2Ј)] and
3.392(1)Å [Au(1) ؒ ؒ ؒ Au(1Ј)]. The N᎐H ؒ ؒ ؒ Cl geometry suggests hydrogen bonding between the hydrogen and
chlorine atoms of neighbouring ions. The bromine compound 2 is isostructural to the chloride 1b with slightly
longer Au ؒ ؒ ؒ Au distances. Compound 3 shows bis(diphenylmethanimine)gold() cations and triiodide anions with
no anomalies in the packing and in bond distances and angles. The geometry of the silver() and gold() complexes
5 and 6 are quite similar except for the observation that the Au᎐N bond is 0.11 Å shorter than the Ag᎐N bond,
which suggests that two-co-ordinate gold() is indeed smaller than two-co-ordinate silver() in systems with
nitrogen-containing ligands, as previously observed for phosphine complexes.
Aldimines (A) and ketimines (B) have a long history in organic
chemistry as important derivatives of carbonyl compounds.
They have been widely used in organic synthesis and for the
identification of the parent compounds, e.g. in carbohydrate
chemistry. Their role as substrates or ligands in inorganic and
organometallic chemistry is still only poorly developed, how-
ever, except for a certain focus on the complexes of the coinage
metals (Cu, Ag and Au).
Previous work in this area arose from the use of copper salts
in the oxidative coupling of ammonia to produce hydrazine via
ketimine intermediates.1–4 The mechanism proposed for the
action of the copper salts in both the stoichiometric and cata-
lytic versions of this reaction included the formation of
ketimine complexes (C), but none of these intermediates has
been isolated and structurally characterized.
(SMe )], with equimolar quantities of Ph C᎐NH gives a colour-
less product [equation (1)]. This initial product, as well as
᎐
2
2
3[AuCl(SMe )] + 3Ph C᎐NH → [AuCl(Ph C᎐NH)] +
᎐
᎐
2
2
2
1a
[Au(Ph C᎐NH) ][AuCl ] + 3Me S (1)
᎐
2
2
2
2
1b
Our own recent studies in the co-ordination chemistry of
gold() with various nitrogen-containing ligands (amines,5–10
imines,11 carbodiimines,12 amides,13 phosphinimines,14,15 iso-
cyanides,16,17 etc.) led us to an investigation of the ligand
behaviour of aldimines and ketimines. The work initiated in this
context was also aimed at an improved understanding of the
intriguing supramolecular chemistry of coinage metal com-
pounds in general, and of gold() compounds in particular.18–21
Owing to the open co-ordination sphere at their nitrogen atoms,
aldimines and ketimines can be expected to function as excel-
lent donors in mono- and poly-nuclear complexes.
the material obtained after recrystallization, consists of roughly
equivalent amounts of two different types of crystals, which
can be separated under a microscope. The two separate forms
have the same analytical composition and are therefore isomers
{[AuCl(Ph C᎐NH)] 1a, m.p. 223 ЊC; [Au(Ph C᎐NH) ][AuCl ]
᎐
᎐
2
2
2
2
1b, m.p. 227 ЊC}.
Solutions of the mixture or of one of the components in
chloroform give almost identical NMR spectra, suggesting
rapid ligand exchange between the isomers. The IR spectra of
the crystals are slightly, but distinctly different, however, with
ν(N᎐H) and ν(C᎐N) stretching vibrations at 3249.9/3205.3 and
In this account we present our recent results on simple
᎐
1592.0/1598.9 cmϪ1 for 1a and 1b, respectively, as representative
examples. The data indicate that both compounds contain Au-
bonded Ph C᎐NH, but in different environments. Fast atom
mononuclear complexes of diphenylmethanimine Ph C᎐NH as
᎐
2
a ligand prototype with gold() and silver() salts. Unexpected
phenomena of isomerism and aggregation made this study a
much more interesting endeavour than originally expected.
᎐
2
bombardment (FAB) mass spectral studies gave a first clue as to
the identity of at least one of the isomers in that they showed,
amongst others, the cation [Au(Ph C᎐NH) ]+ and the anion
Preparative Results
(Diphenylmethanimine)gold(I) chloride and its ionic isomer
᎐
2
2
[AuCl2]Ϫ, which are proof of the presence of an ionic species
with these two components (1b). This result was later confirmed
in structural studies (below).
The reaction of (dimethyl sulfide)gold() chloride, [AuCl-
J. Chem. Soc., Dalton Trans., 1997, Pages 415–420
415

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solution, and the orange crystals produced from the reaction
mixture were not satisfactory for an X-ray study.
Bis(diphenylmethanimine)-gold(I) and -silver(I) tetrafluoroborate
Compounds 1b, 2 and 3 all contain the [Au(Ph C᎐NH) ]+
᎐
2
2
cation, together with the anions [AuCl2]Ϫ, [AuBr2]Ϫ and [I3]Ϫ,
respectively. In order to provide another set of related com-
pounds with ‘innocent’ counter ions instead of the ‘conspicu-
ous’ dihalogenogold() and triiodide anions, the pair of
tetrafluoroborates was prepared for silver() and gold(). The
reactions of 2 equivalents of Ph C᎐NH with either [Au(Ph-
᎐
2
CN)2]BF4 or AgBF4 give high yields of colourless crystalline
materials, which are readily identified as the 2:1 complexes
[Au(Ph C᎐NH) ]BF 5 and [Ag(Ph C᎐NH) ]BF 6, equations
᎐
᎐
2
2
4
2
2
4
(4) and (5). The solubility of the compounds is very limited even
[Au(PhCN) ]BF + 2Ph C᎐NH →
᎐
2
2
4
[Au(Ph C᎐NH) ]BF + 2PhCN (4)
᎐
2
2
4
5
Fig. 1 Infinite zigzag chains in [AuCl(Ph2C᎐NH)] 1a, formed via weak
AgBF + 2Ph C᎐NH → [Ag(Ph C᎐NH) ]BF
(5)
᎐
᎐
᎐
4
2
2
2
4
Au ؒ ؒ ؒ Au interactions and hydrogen bonds, (ORTEP,23 50% probability
ellipsoids phenyl hydrogen atoms omitted). Selected bond lengths (Å)
and angles (Њ): Au ؒ ؒ ؒ AuЈ 3.3633(5), Au᎐N 2.019(6), Au᎐Cl 2.250(2),
N᎐C 1.269(8), N᎐H 0.900, ClЈ ؒ ؒ ؒ H 2.570 and N ؒ ؒ ؒ ClЈ 3.470;
N᎐H ؒ ؒ ؒ ClЈ 140.7, N᎐Au᎐Cl 176.9(2), N᎐Au᎐AuЈ 88.8(2), N᎐Au᎐AuЉ
93.3(2), AuЈ᎐Au᎐AuЉ 107.17(2), Cl᎐Au᎐AuЈ 91.43(5), Cl᎐Au᎐AuЉ
89.60(4), C᎐N᎐Au 129.4(5), C᎐N᎐H 115.3(4) and Au᎐N᎐H 115.4(2)
6
in strongly polar solvents, which affects the quality of NMR
data.
Molecular and Supramolecular Structures
The compound [AuCl(Ph C᎐NH)] 1a crystallizes in the mono-
᎐
2
Bis(diphenylmethanimine)gold(I) dibromoaurate(I) and triiodide
clinic space group P21/c with Z = 4 formula units in the unit
cell. The monomeric units are paired up to give centrosym-
metric dimers with contacts Au ؒ ؒ ؒ AuЈ 3.3633(5) Å, which are
aggregated further into corrugated ribbons via equivalent con-
tacts [Au ؒ ؒ ؒ AuЈ, AuЉ 3.3633(5) Å] (Fig. 1). The folding of the
ribbon is characterized by the angle AuЈ᎐Au᎐AuЉ 107.17(2)Њ.
All N᎐Au᎐AuЈ(AuЉ) and Cl᎐Au᎐AuЈ(AuЉ) angles are close to
90Њ.
Treatment of (tetrahydrothiophene)gold() bromide, [AuBr-
(C H S)], with 1 equivalent of Ph C᎐NH affords a yellow solid
᎐
2
4
8
product [equation (2)], the IR spectra of which again indicate
2[AuBr(C H S)] + 2Ph C᎐NH →
᎐
2
4
8
[Au(Ph C᎐NH) ][AuBr ] + C H S (2)
᎐
2
2
2
4
8
2
This assembly is not without precedent in gold chemistry and
can be taken as just another example of auriophilicity-
determined supramolecular chemistry, albeit with rather weak
metal–metal interactions as judged from the rather long
Au ؒ ؒ ؒ Au separations. From close inspection of the details it
appears, however, that there may be support of the backbone
structure from weak N᎐H ؒ ؒ ؒ ClЈ hydrogen bonds with dimen-
sions N᎐H 0.900, H ؒ ؒ ؒ ClЈ 2.570, N ؒ ؒ ؒ ClЈ 3.470 Å and
N᎐H ؒ ؒ ؒ ClЈ 140.7Њ. The Au᎐N and Au᎐Cl distances show no
anomalies, and the co-ordination at the gold atom is close to
linear. The ketimine ligands have a standard geometry.
the presence of isomers [3230.8/3200.0 and 1585/1572 cmϪ1 for
ν(N᎐H) and ν(C᎐N), respectively]. Upon recrystallization only
᎐
one isomer could be obtained in the form of single crystals,
which was later identified as the ionic isomer [Au(Ph C᎐
᎐
2
NH)2][AuBr2] 2. Crystals of 2 are isomorphous to those of 1b.
All attempts to prepare a compound of composition
[AuI(Ph C᎐NH)] (or its ionic counterpart) either from AuI and
᎐
2
Ph C᎐NH or from 1a and KI met with failure. In all cases
᎐
2
deeply purple solutions were obtained, from which, surpris-
ingly, a triiodide [Au(Ph C᎐NH) ][I ] 3 could be crystallized, as
Crystals of the compounds [Au(Ph C᎐NH) ]+[AuX ]Ϫ
᎐
2
2
3
᎐
2
2
2
confirmed also by X-ray crystallography (below). In all pre-
parative experiments gold metal was produced as easily recog-
nized from a metal mirror at the wall of the reaction vessels,
equations (3a) and (3b). The IR spectra of the product confirm
(X = Cl 1b or Br 2) are isomorphous (monoclinic, space group
P21/n, Z = 4) and the molecular structures are very similar (Fig.
2). In the present description and discussion of the structures the
chloride complex 1b is considered as a representative example.
Compound 1b can be described as a tetranuclear unit (four
gold atoms) composed of two [AuCl2]Ϫ anions and two
3[AuCl(Ph C᎐NH)] + 3KI →
᎐
2
[Au(Ph C᎐NH) ]+ cations which is structurally based on a par-
[Au(Ph C᎐NH) ][I ] + 2Au + 3KCl (3a)
᎐
2
2
3
᎐
2
2
3
allelogram of gold atoms (with a crystallographic centre of
inversion at its centre, Fig. 2). This parallelogram has two short
and two large edges [Au(1) ؒ ؒ ؒ Au(2) 3.1944(5), Au(1) ؒ ؒ ؒ Au(2Ј)
3.604(1) Å] and a transannular contact Au(1) ؒ ؒ ؒ Au(1Ј) of
3.392(1) Å. If the longest of these metal–metal contacts
[Au(1) ؒ ؒ ؒ Au(2Ј)] is considered too large for gold–gold bonding,
the organization of the gold atoms can also be addressed as Z
type. Finally, simplifying further, if the medium contact
Au(1) ؒ ؒ ؒ Au(1Ј) is also considered as only very weak, the
assembly is an aggregate of two dinuclear units composed of
one anion and one cation. It is obvious that the aggregation of
the two components arises both from auriophilicity [Au(1) ؒ ؒ ؒ
Au(2)] and from N(1)᎐H(1) ؒ ؒ ؒ Cl(1)/N(2)᎐H(2) ؒ ؒ ؒ Cl(2) hydro-
3AuI + 2Ph C᎐NH → [Au(Ph C᎐NH) ][I ] + 2Au (3b)
᎐
᎐
2
2
2
3
the presence of only one isomer [e.g. 3249.9 and 1588.4 cmϪ1 for
ν(N᎐H) and ν(C᎐N), respectively]. It appears that the reactions
lead to a partial redox process to give gold metal and iodine, the
latter being taken up by IϪ to form the triiodide. Recent work by
Nakao and Sone22 supports this conclusion. This complication
was unexpected since most L᎐Au᎐X complexes show a more
uniform behaviour for X = Cl, Br or I.
᎐
Preliminary experiments with [CuI(Ph C᎐NH)] 4 also gave
unsatisfactory results. The product was found to be unstable in
᎐
2
416
J. Chem. Soc., Dalton Trans., 1997, Pages 415–420

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Fig. 3 Crystal structure of [Au(Ph2C᎐NH)2][I3] 3 (ORTEP, 50% prob-
᎐
ability ellipsoids, phenyl hydrogen atoms omitted). Two bis(diphenyl-
methanimine)gold() cations and one triiodide anion are shown.
Selected bond lengths (Å) and angles (Њ): Au᎐N 2.011(4), I(1)᎐I(2)
2.9111(4), N᎐C 1.290(6), NЈ᎐HЈ 0.900 and NЈ ؒ ؒ ؒ I(1) 3.681; NЈ᎐HЈ᎐I(1)
131.6, N᎐Au᎐NЈ 176.0(2), I(1)᎐I(2)᎐I(1Ј) 180.0, C᎐N᎐Au 130.4(3),
C᎐N᎐H 114.7(3) and Au᎐N᎐H 114.92(11)
Fig. 2 Tetranuclear unit of {[Au(Ph2C᎐NH)2][AuCl2]}2 in compound
᎐
1b (ORTEP, 50% probability ellipsoids, with exception of the phenyl
carbon atoms; phenyl hydrogen atoms omitted). Selected bond lengths
(Å) and angles (Њ): Au(1)᎐N(1) 1.995(7), Au(1)᎐N(2) 2.007(7),
Au(1) ؒ ؒ ؒ Au(2) 3.1944(5), Au(2)᎐Cl(1) 2.278(3), Au(2)᎐Cl(2) 2.269(2),
N(1)᎐C(1) 1.291(11), N(2)᎐C(2) 1.284(10), N(1)᎐H(1) 0.76(11),
N(2)᎐H(2) 0.75(10), H(1) ؒ ؒ ؒ Cl(1) 2.620, H(2) ؒ ؒ ؒ Cl(2) 2.686,
N(1) ؒ ؒ ؒ Cl(1) 3.377 and N(2) ؒ ؒ ؒ Cl(2) 3.433; N(1)᎐H(1) ؒ ؒ ؒ Cl(1) 134.1,
N(2)᎐H(2) ؒ ؒ ؒ Cl(2)143.8,N(1)᎐Au(1)᎐N(2)173.3(3),Cl(1)᎐Au(2)᎐Cl(2)
175.78(8), N(1)᎐Au(1)᎐Au(2) 87.0(2), N(2)᎐Au(1)᎐Au(2) 90.3(2),
Cl(1)᎐Au(2)᎐Au(1) 92.16(6), C(1)᎐N(1)᎐Au(1) 130.7(6), Au(1)᎐
N(1)᎐H(1) 113(8), C(2)᎐N(2)᎐Au(1) 130.1(6), Au(1)᎐N(2)᎐H(2) 119(8),
C(1)᎐N(1)᎐H(1) 117(8) and C(2)᎐N(2)᎐H(2) 111(8)
Fig. 4 Crystal structure of [Au(Ph2C᎐NH)2]BF4ؒCH2Cl2 5ؒCH2Cl2
᎐
(ORTEP, 50% probability ellipsoids, phenyl hydrogen atoms omitted).
Two bis(diphenylmethanimine)gold() cations and one tetrafluorobo-
rate anion are shown. Selected bond lengths (Å) and angles (Њ):
Au᎐N(1) 1.999(4), Au᎐N(2) 1.998(4), N(1)᎐C(1) 1.292(5), N(2)᎐C(2)
1.282(6), B᎐F(1) 1.335(7), B᎐F(2) 1.390(6), B᎐F(3) 1.362(7), B᎐F(4)
1.307(8), N(1)᎐H(1) 0.901, F(2) ؒ ؒ ؒ H(1) 2.112, N(2Ј)᎐H(2Ј) 0.900,
H(2Ј) ؒ ؒ ؒ F(2) 2.113 and N(2Ј) ؒ ؒ ؒ F(2) 3.013; N(1)᎐H(1) ؒ ؒ ؒ F(2) 176.1,
N(2Ј)᎐H(2Ј) ؒ ؒ ؒ F(2) 167.6, N(1)᎐Au᎐N(2) 178.4(2), C(1)᎐N(1)᎐Au
131.8(3), C(2)᎐N(2)᎐Au 134.1(3), C(1)᎐N(1)᎐H(1) 113.8(2), C(2)᎐
N(2)᎐H(2) 112.9(3), Au᎐N(1)᎐H(1) 114.37(11) and Au᎐N(2)᎐H(2)
112.97(10)
gen bonding, as already suggested for the extended structure of
1a (above).
The configuration of the anions and cations in compound 1b
is quasi-linear at the gold atoms, with two almost equivalent
Au᎐N and Au᎐Cl distances. It should be noted that these Au᎐N
distances (in a cation) are shorter than in the neutral molecule
1a, while the Au᎐Cl distances (in an anion) are longer than in
the neutral molecule. Angles N᎐Au᎐Au and Cl᎐Au᎐Au are all
close to rectangular as expected for auriophilic contacts.
The geometry of the bromine analogue 2 follows the same
structural principle. There is again a parallelogram of gold
atoms in a tetranuclear unit comprising two [AuBr2]Ϫ anions
anions, but the N᎐H ؒ ؒ ؒ I contacts (0.900/3.021 Å) are even
longer than in 2 and thus almost prohibitive for discrete
and two [Au(Ph C᎐NH) ]+ cations. ThecontactsAu(1) ؒ ؒ ؒ Au(2),
interactions.
᎐
2
2
Ϫ
Au(1) ؒ ؒ ؒ Au(2Ј) and Au(1) ؒ ؒ ؒ Au(1Ј) are 3.268(1), 3.597(1) and
3.552(1) Å long, respectively, suggesting again a Z-type bonding
to prevail. The individual cation/anion pair has the shortest
Au ؒ ؒ ؒ Au contact [Au(1) ؒ ؒ ؒ Au(2)] and its geometry is pre-
destined for hydrogen bonding, albeit this may be weak owing
to the larger separation of the N᎐H and Br components.
Crystals of [Au(Ph C᎐NH) ]+BF ؒCH2Cl2 5ؒCH2Cl2 are
᎐
2
2
4
monoclinic, space group P21/c, with Z = 4 formula units in the
unit cell. The lattice consists of tetrafluoroborate anions and
bis(ketimine)gold() cations which have no crystallographically
imposed symmetry. The geometry of the cation is close to that
of point group C2, however, and the dimensions are not
unusual. The conformation is different from that in compounds
1b, 2 and 3 in that the two ketimine double bonds can be taken
as single-trans to each other (Fig. 4), while they were single-cis
in 1b, 2 and 3. The tetrafluoroborate anions are engaged in
hydrogen bonding to the N᎐H groups of the cations, with two
contacts (F ؒ ؒ ؒ H᎐N) originating from the same fluorine atom
[F(2)]. Accordingly, the distance B᎐F(2) is longer than the
remaining three B᎐F bonds, but standard deviations are large
for these data. The N(1)᎐Au᎐N(2) unit is linear with two virtu-
Crystals of the compound [Au(Ph C᎐NH) ]+I Ϫ 3 are ortho-
᎐
2
3
rhombic, space group Pbcn, with Z =24 formula units in the unit
cell. The lattice contains cations with a crystallographic two-
fold axis passing through the gold atom. These cations are
chiral, and the enantiomers are related by a centre of inversion,
which is located at the central iodine atom of the triiodide
anions (Fig. 3). The anion is thus linear by symmetry and has
two equivalent I(1)[I(1Ј)]–I(2) distances. The cations are slightly
bent at Au [N᎐Au᎐NЈ 176.0(2)Њ] with equal Au᎐N distances.
These data are comparable to those of 1b and 2 which contain
the same cation, but as part of a tetranuclear aggregate. Inspec-
tion of Fig. 3 shows that the relative orientation of the ions
tempts one to suggest hydrogen bonding between cations and
ally identical Au᎐N bonds.
Ϫ
Crystals of [Ag(Ph C᎐NH) ]+BF 6 are monoclinic, space
᎐
2
2
4
group C2/c, with Z = 4 formula units in the unit cell. Contrary
to the asymmetrical structure of compound 5, a two-fold axis
J. Chem. Soc., Dalton Trans., 1997, Pages 415–420
417

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and solvents were distilled and kept under nitrogen. Instru-
ments: NMR, JEOL GX 400, SiMe4 as internal standard; IR,
Perkin-Elmer (type 1600 series FT-IR); mass spectra, Finnigan
MAT 90. Microanalyses were performed in-house by combus-
tion and atom absorption spectroscopy. Starting materials were
either commercially available or were prepared following litera-
ture procedures: Ph C᎐NH,25 [AuCl(SMe2)],26 [AuBr(C4H8S)]27
᎐
2
and [Au(PhCN)2]BF4.28
Preparations
(Diphenylmethanimine)gold(I) chloride 1a, 1b. To a solution
of [AuCl(SMe2)] (0.177 g, 0.60 mmol) in dichloromethane (10
cm3) was added diphenylmethanimine (101 µl, 0.60 mmol) at
room temperature. The solution immediately became pale yel-
low. After stirring for 3 h the product (0.166 g, 67% yield) was
precipitated by adding pentane. The light- and air-stable pow-
der was recrystallized from a dichloromethane–hexane mixture,
whereby two different types of crystals were obtained;
[AuCl(Ph C᎐NH)] 1a, m.p. 223 ЊC, and [Au(Ph C᎐NH) ]-
᎐
᎐
2
2
2
Fig. 5 Crystal structure of [Ag(Ph2C᎐NH)2]BF4 6 (ORTEP, 50%
᎐
[AuCl2] 1b, m.p. 227 ЊC (Found: C, 37.0; H, 2.9; N, 3.0.
C13H11AuClN 1a/1b requires C, 37.7; H, 2.7; N, 3.4%).
δH (CD3CN): 9.74 (1 H, br s, NH) and 8.88–8.45 (10 H, m, Ph).
probability ellipsoids, phenyl hydrogen atoms omitted). Two bis(diphe-
nylmethanimine)silver() cations and one tetrafluoroborate anion are
shown. Selected bond lengths (Å) and angles (Њ): Ag᎐N 2.113(2), N᎐C
1.2793(3), N᎐H 0.900, B᎐F(1) 1.382(4), B᎐F(2) 1.358(3), F(1) ؒ ؒ ؒ H
2.510 and F(1) ؒ ؒ ؒ N 3.286; F(1) ؒ ؒ ؒ H᎐N 144.7, NЈ᎐Ag᎐N 180.0,
C᎐N᎐Ag 131.9(2), C᎐N᎐H 114.2(2) and Ag᎐N᎐H 113.84(6)
FAB mass spectrum: cations, m/z 559, [Au(Ph C᎐NH) ]+, 31%;
᎐
2
2
anions, m/z 266.9, [AuCl2]Ϫ, 2.5%.
Bis(diphenylmethanimine)gold(I) dibromoaurate 2. To a solu-
tion of [AuBr(C4H8S)] (0.215 g, 0.59 mmol) in dichloromethane
(15 cm3) was added Ph C᎐NH (99 µl, 0.59 mmol) at room tem-
passes through the boron atom of the anion in 6, and the two
ligands of the cation (the C᎐N double bonds of which are in a
᎐
᎐
2
single-trans conformation) are also related by symmetry (Fig.
5). Hydrogen bonding between anions and cations occurs
through two of the four fluorine atoms [F(1), F(1Ј)], but is of
the same type as in 5.
Although taken from entirely different lattices (different
space groups, with and without crystal solvent), the cations of
compounds 5 and 6 are almost superimposible regarding the
general configuration and conformation, except for the differ-
ent Au/Ag᎐N bond lengths, which are Ag᎐N 2.113(2) Å in 6
and Au᎐N 1.9985 Å (average) in 5. This result confirms recent
findings24 that the covalent radius of two-co-ordinate AuI is
significantly smaller than the radius of two-co-ordinate AgI (by
ca. 6%).
perature. After 30 min the solvent was removed, the light yellow
residue was taken up in dichloromethane and the solution
layered with pentane. After 2 d colourless air-stable crystals
(0.212 g, 78% yield) were isolated, m.p. 219 ЊC (Found: C, 34.0;
H, 2.3; N, 2.9. C13H11AuBrN requires C, 34.1; H, 2.4; N, 3.1%).
δH (CDCl3): 9.21 (1 H, br s, NH) and 7.90–7.38 (10 H, m, Ph).
Bis(diphenylmethanimine)gold(I) triiodide 3. (a) To a solution
of compound 1 (0.178 g, 0.43 mmol) in dichloromethane (15
cm3) was added KI (0.072 g, 0.43 mmol) in water (5 cm3) at
room temperature and the two-phase mixture was stirred. Gold
metal (0.057 g) precipitated and the dichloromethane phase
became deep red-brown. The water was removed and the
dichloromethane phase was washed three times with small por-
tions of water. Then the solvent was removed in a vacuum and
the red-brown residue taken up with dry dichloromethane.
Upon layering this solution with pentane red-brown crystals
(0.102 g, 76% yield) were obtained.
Conclusion
The present work has shown that ketimines of the type
R C᎐NH are excellent ligands for salts of the two heavy coinage
᎐
2
metals AgI and AuI. For the prototype ligand Ph C᎐NH (L) it
(b) To a suspension of AuI (0.108 g, 0.33 mmol) in thf (10
᎐
2
cm3) was added Ph C᎐NH (56 µl, 0.33 mmol). After stirring for 3
᎐
2
could be demonstrated that both 1:1 and 2:1 complexes can
be obtained. The former can exist as neutral molecules L᎐Au᎐X
or as ionic isomers [ML2]+[MX2]Ϫ (X = Cl or Br) containing the
same cationic units as the 2:1 complexes [ML2]+YϪ (Y = BF4
or I3).
The structures of the neutral, cationic and anionic units
feature linearly two-co-ordinated metal atoms with the ligands
fixed to the metals through their planar three-co-ordinated
nitrogen atoms. These units can be aggregated to give dimers,
tetramers or polymers via auriophilic bonding between gold
atoms, supported by hydrogen bonding N᎐H ؒ ؒ ؒ X, Y.
In the [AuL2]+ cations the double bonds of the two ligands
can be present in single-trans or single-cis conformations
depending on the crystal environment. Comparison of analo-
gous complexes shows conclusively that in the present com-
pounds the covalent radius of gold() is smaller than that of
silver(), corroborating recent results for phosphine complexes.24
h the solution turned to deep red-brown and gold metal (0.032
g) precipitated. The solution was filtered, the thf was removed
in a vacuum and the red-brown residue crystallized (0.086 g,
82% yield) (see above). M.p. 162 ЊC (Found: C, 32.9; H, 2.0; N,
2.7. C26H22AuI3N2 requires C, 33.2; H, 2.4; N, 3.0%). νmax(KBr)/
cmϪ1 3250s (NH), 1588s (C᎐N). δ (CDCl ) 7.55–7.42 (br m, Ph);
᎐
H
3
NH not observed due to low solubility. FAB mass spectrum:
cations, m/z 182.2, [Ph C᎐NH ]+, 100; 559.4, [Au(Ph C᎐NH) ]+,
᎐
᎐
2
2
2
2
2%; anions, m/z 450.7, [AuI2]Ϫ, 100; 774.6, [Au2I3]Ϫ, 4.5%.
(Diphenylmethanimine)copper(I) iodide 4. To a suspension of
CuI (0.249 g, 1.31 mmol) in thf (10 cm3) was added Ph C᎐NH
᎐
2
(438 µl, 2.61 mmol) in one portion at room temperature. The CuI
dissolved and the solution became bright orange and was
stirred for 1 h. By layering a reduced volume of this reaction
mixture with pentane yellow-orange needles (0.362 g, 74% yield)
were obtained, m.p. 144 ЊC (Found: C, 42.1; H, 3.0; N, 3.7.
C13H11CuIN requires C, 42.0; H, 3.0; N, 3.8%). Solutions of the
compound in CHCl3 or thf are not stable and some CuI precipi-
tates. Therefore no NMR spectra could be recorded; νmax(KBr)/
Experimental
All experiments were carried out under an atmosphere of dry,
purified nitrogen. Glassware was dried and filled with nitrogen,
cmϪ1 3288s (NH) and 1590s (C᎐N).
᎐
418
J. Chem. Soc., Dalton Trans., 1997, Pages 415–420

View Article Online
Table 1 Crystallographic data for [AuCl(Ph2C᎐NH)] 1a, [Au(Ph2C᎐NH)2][AuCl2] 1b, [Au(Ph2C᎐NH)2][AuBr2] 2, [Au(Ph2C᎐NH)2][I3] 3,
᎐
᎐
᎐
᎐
[Au(Ph2C᎐NH)2]BF4ؒCH2Cl2 5ؒCH2Cl2 and [Ag(Ph2C᎐NH)2]BF4 6a
᎐
᎐
Compound
1a
1b
2
3
5ؒCH2Cl2
6
Empirical formula
M
Crystal system
Space group (no.)
Crystal size/mm
a/Å
C13H11AuClN
413.64
Monoclinic
P21/c (14)
C26H22Au2Cl2N2
827.29
Monoclinic
P21/n (14)
C26H22Au2Br2N2
916.21
Monoclinic
P21/n (14)
C26H22AuI3N2
940.12
Orthorhombic
Pbcn (60)
0.08 × 0.15 × 0.40
14.326(1)
10.227(1)
C27H24AuBCl2F4N2 C26H22AgBF4N2
731.16
Monoclinic
P21/c (14)
0.18 × 0.30 × 0.35
13.457(1)
14.933(1)
14.979(1)
115.98(1)
2705.9(4)
1.795
557.14
Monoclinic
C2/c (15)
0.09 × 0.16 × 0.46
18.349(1)
7.717(1)
16.785(1)
103.05(1)
2311.4(3)
1.601
0.20 × 0.30 × 0.45 0.10 × 0.15 × 0.65 0.09 × 0.12 × 0.45
9.935(1)
5.413(1)
22.980(2)
93.53(1)
1233.5(3)
2.227
768
121.1
Ϫ62
9.968(1)
12.725(1)
19.016(1)
94.69(1)
2402.4(5)
2.286
1536
124.3
Ϫ62
10.046(1)
12.918(1)
19.203(3)
92.53(1)
2489.6(5)
2.444
1680
150.0
Ϫ68
b/Å
c/Å
17.906(2)
β/Њ
U/Å3
2623.4(4)
2.380
1720
91.5
Dc/g cmϪ3
F(000)
1416
1120
µ(Mo-Kα)/cmϪ1
T/ ЊC
56.8
9.2
Ϫ62
Ϫ68
Ϫ68
Scan
ω
ω
ω–θ
ω
ω
ω
hkl Ranges
Ϫ12 to 12, 0–6,
Ϫ29 to 25
Ϫ12 to 12, 0–15,
0–23
Ϫ12 to 12,
0–16, 0–24
0–18, 0–13, 0–22
Ϫ16 to 14,
Ϫ18 to 0,
Ϫ18 to 18
4896
4892
4874
0.000
334
—, 24
0.5677, 0.9997
0.0284
Ϫ22 to 7,
0–9,
Ϫ20 to 20
3048
2115
2108
0.0137
156
—, 22
0.9039, 0.9985
0.0307
Measured reflections
Unique reflections
Used reflections
Rint
Refined parameters
H atoms (found/calc.)
Tmin, Tmax
3408
2589
2588
0.0296
146
4384
4212
4211
0.0300
296
4880
4692
4690
0.0161
289
—, 22
0.5316, 0.9940
0.0481
0.1109
2584
2580
2571
0.000
147
—, 22
0.5114, 0.9997
0.0251
0.0599
0.0275, 2.4193
—, 11
2, 20
0.5269, 0.9931
0.0346
0.0915
0.0640, 2.9925
0.5721, 0.9989
0.0363
0.0899
0.0587, 8.0508
R1 [Fo у 4σ(Fo)]
wR2 (used reflections)
a, b in weighting
scheme
0.0664
0.0323, 4.2403
0.0862
0.0458, 626.3666
0.0516, 45.3003
ρmax, ρminb/e ÅϪ3
+1.36, Ϫ2.25
+2.08, Ϫ2.08
+4.07, Ϫ3.30
+0.89, Ϫ1.39
+1.32, Ϫ0.79
+0.73, Ϫ0.38
¹
2 2

a
2
Details in
common: Z = 4; Enraf-Nonius CAD4 diffractometer; R1 = Σ( |F | Ϫ |F | )/Σ|F |; wR2 = Σw(Fo2 Ϫ Fc )2/Σ[w(Fo ) ]²;
| |
o c o
2
w = q/2σ2(Fo2) + (ap)2 + bp, where p = (Fo2 + 2Fc )/3. b Residual electron densities located at Au or Ag atoms.
Bis(diphenylmethanimine)gold(I) tetrafluoroborate 5. To a
Crystallography
solution of Ph C᎐NH (101 µl, 0.60 mmol) in dichloromethane
᎐
2
Suitable crystals of compounds 1a, 1b, 2, 3, 5 and 6 were sealed
into glass capillaries and used for measurement of precise cell
constants and intensity data collection. During data collection
three standard reflections were measured periodically as a gen-
eral check of crystal and instrument stability. No significant
changes were observed for all six compounds. Diffraction inten-
sities were corrected for Lorentz-polarization and absorption
effects (empirically). The structures were solved by direct
methods and refined by full-matrix least-squares calculations
against F 2.29 The thermal motion of all non-hydrogen atoms was
treated anisotropically. All hydrogen atoms were calculated in
idealized positions and allowed to ride on their corresponding
carbon or nitrogen atom. Their isotropic thermal parameters
were tied to that of the adjacent atom by a factor of 1.5. The
main experimental results are summarized in Table 1.
(10 cm3) was added slowly a solution of [Au(PhCN)2]BF4
(0.148 g, 0.30 mmol) in dichloromethane (5 cm3) at Ϫ78 ЊC.
After stirring for 30 min the solution was allowed to warm to
room temperature. The solvent was removed in a vacuum and
the colourless residue taken up again in dichloromethane,
filtered and the filtrate layered with pentane. After several days
colourless crystals of compound 5ؒCH2Cl2 (0.135 g, 61%) were
obtained, m.p. 238 ЊC (Found: C, 44.5; H, 3.3; N, 3.8. C27H24-
AuBCl2F4N2 requires C, 44.4; H, 3.3; N, 3.8%). δH [(CD3)2CD]
10.75 (1 H, br s, NH), 7.83–7.50 (10 H, m, Ph) and 5.61 (2 H, s,
CH Cl ); δ [(CD ) CO] 186.3 (s, C᎐N), 138.7 and 137.0 (s, ipso-
᎐
2
2
C
3 2
C), 130.8 and 129.6 (s, o-C), 130.2 and 129.9 (s, m-C), 134.5 and
133.5 (s, p-C). Mass spectrum: m/z 558.5, [Au(Ph C᎐NH) ]+,
᎐
2
2
100; and 377.5 [Au(Ph C᎐NH)]+, 23%.
᎐
2
Atomic coordinates, thermal parameters, and bond lengths
and angles have been deposited at the Cambridge Crystallo-
graphic Data Centre (CCDC). See Instructions for Authors,
J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the
CCDC for this material should quote the full literature citation
and the reference number 186/305.
Bis(diphenylmethanimine)silver(I) tetrafluoroborate 6. To a
solution of AgBF4 (0.290 g, 1.49 mmol) in tetrahydrofuran
(15 cm3) was added Ph C᎐NH (499 µl, 2.98 mmol) at room
᎐
2
temperature. Immediately a white solid precipitated and after
30 min the volume of the solvent was reduced to 3 cm3, the
off-white solid was filtered off, dried, and extracted with
dichloromethane (30 cm3). Upon layering this solution with
pentane colourless crystals (0.712 g, 85.9% yield) were obtained
(m.p. 246 ЊC). The crystals were only sparingly soluble in
acetone, tetrahydrofuran or dichloromethane (Found: C,
55.3; H, 3.9; N, 4.9. C26H22AgBF4N2 requires C, 56.1; H,
4.0; N, 5.0%). δH (CD2Cl2) 9.40 (1 H, br s, NH) and 7.60–7.34
Acknowledgements
This work was supported by Deutsche Forschungsgemeinschaft
and by Fonds der Chemischen Industrie. The authors are grate-
ful to J. Riede for establishing the X-ray data sets and to F. R.
Kreissl for the mass spectrometric measurements.
(10 H, m, Ph); δ (CD Cl ) 184.0 (s, C᎐N), 139.2 and 136.9
᎐
C
2
2
(br s, ipso-C), 133.0 and 132.5 (br s, p-C), 130.0–128.7 (br m,
o- and m-C). Mass spectrum: m/z 471.0 and 469.0, [Ag(Ph2-
C᎐NH) ]+, 56 and 60; 287.9 and 289.9, [Ag(Ph C᎐NH)]+, 100
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J. Chem. Soc., Dalton Trans., 1997, Pages 415–420