Polymorphs, enantiomorphs, chirality and helicity in [Rh{N,O} (η4-cod)] complexes with {N,O} = salicylaldiminato Schiff base or aminocarboxylato ligands

Article abstract of DOI:10.1039/b820072f

The dimeric complex acetato(η⁴-cycloocta-1,5-diene) rhodium(i), [Rh(O₂CMe)(η⁴-cod)]₂ (cod = cycloocta-1,5-diene) reacts with N,O-chelating Schiff-base ligands or with N-phenylglycine to afford the diminato- or a

Full text of DOI:10.1039/b820072f

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Dalton
Transactions
An international journal of inorganic chemistry
www.rsc.org/dalton
Number 19 | 21 May 2009 | Pages 3617–3868
ISSN 1477-9226
PERSPECTIVE
HOT ARTICLE
Garralda
Janiak et al.
Aldehyde C–H activation with late
transition metal organometallic
compounds.Formation and reactivity of plexes with {N,O} = salicylaldiminato
Polymorphs,enantiomorphs,chirality
and helicity in [Rh{N,O}(η -cod)] com-
4
1477-9226(2009)19;1-Z
acyl hydrido complexes
Schiff base or aminocarboxylato ligands

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PAPER
www.rsc.org/dalton | Dalton Transactions
Polymorphs, enantiomorphs, chirality and helicity in [Rh{N,O}(g4-cod)]
complexes with {N,O} = salicylaldiminato Schiff base or
aminocarboxylato ligands†‡
Christoph Janiak,*a Anne-Christine Chamayou,a A. K. M. Royhan Uddin,b Mohammad Uddin,c Karl S. Hagenc
and Mohammed Enamullah*b
Received 10th November 2008, Accepted 16th December 2008
First published as an Advance Article on the web 6th February 2009
DOI: 10.1039/b820072f
4
4
The dimeric complex acetato(h -cycloocta-1,5-diene)rhodium(I), [Rh(O2CMe)(h -cod)]2 (cod =
cycloocta-1,5-diene) reacts with N,O-chelating Schiff-base ligands or with N-phenylglycine to afford the
4
4
diminato- or aminocarboxylato(h -cycloocta-1,5-diene)rhodium(I) complexes [{Rh(h -cod)}2-
4
4
(salen)] (1), [{Rh(h -cod)}2(salophen)] (2), [Rh((S)-N-phenylglycinato)(h -cod)] (3S), [Rh(rac-N-
4
4
phenylglycinato)(h -cod)] (3rac), [Rh((R)-N-(4-methoxphenyl)ethyl-2-oxo-1-naphthaldiminato)(h -
cod)] (4) and [Rh(N-(o-tolyl)-2-oxo-1-naphthaldiminato)(h -cod)] (5) [salen2- = N,N ¢-ethylene-
4
bis(salicylaldiminato), salophen2- = N,N ¢-(1,2-phenylene)-bis(salicylaldiminato)]. The complexes are
characterized by IR-, UV/Vis-, 1H/13C-NMR- and mass-spectroscopy. Complexes 1, 2, 4 and 5 contain
six-membered metallaaromatic Rh–(N–CCC–O)-chelate rings which accept C–H ◊ ◊ ◊ p contacts. The
crystal structure of 2 presents a polymorph (dimorph) (2a) to a previously reported structure (2b, CSD
refcode SCLIRB10). Polymorphic forms 2a and 2b are traced to a different interlocking of adjacent
dinuclear molecules with their corrugated van der Waals surface. The achiral N-phenylglycine ligand
4
gives a chiral N-phenylglycinato complex [Rh(O2C–CH2–NHPh)(h -cod)] (3) with the nitrogen atom
becoming the stereogenic center upon metal coordination. Complex 3 can crystallize as the
enantiomorph 3S in the tetragonal, chiral space group P41 in a spontaneous resolution of the racemic
mixture into homo-chiral helix-enantiomers due to inter-molecular N–H ◊ ◊ ◊ O hydrogen bonding which
connects only molecules of the same (S-) configuration into (right-handed or P-) 41-helical chains.
Variation of the crystallization conditions gives 3 as a racemic polymorphic 3rac. R- and S-complexes 3
assemble in the polymorph 3rac in parallel chains along the 21-axes through N–H ◊ ◊ ◊ O hydrogen
bonding. Again, only molecules of the same configuration are combined into a chain, albeit
neighboring chains have complexes of opposite configuration. The chiral enantiomeric
naphthaldiminato complex 4 displays a herring-bone arrangement. Achiral compound 5 crystallizes in
the non-centrosymmetric polar space group Cc where all molecules show the same orientation.
how and why compounds are packed in different forms. Polymor-
Introduction
phism is associated with differences in molecular conformation,
molecular orientation, crystal packing, solubility, color etc.8,9
Polymorphs provide information on conformational flexibility
and are the basis for ab initio crystal structure predictions.10 The
aggregation of flexible molecules depends on the compromise
between intra- and inter-molecular weak bonding interactions
in the crystal (external or extra-molecular interactions).11,12 The
transformation of different polymorphs may be triggered by
the external stresses8,13 and governed by the intra- and inter-
molecular forces in the solid state.14 Hence, there is a need for
an understanding of intermolecular interactions in the context
of crystal packing in view of the ongoing difficulty involved
in investigating and quantifying structural differences between
polymorphs.8,9
Polymorphism, the occurence of different crystal structures for
the same chemical entity,1 is of timely interest2–6 and of particular
practical importance in industrial processes. Different physical
properties of polymorphic forms can substantially alter the
viability and quality of a product.7 It is very complex to rationalize
aInstitut fu¨r Anorganische und Analytische Chemie, Universita¨t Freiburg,
Albertstr. 21, 79104, Freiburg, Germany. E-mail: janiak@uni-freiburg.de;
Fax: +49 761 2036147; Tel: +49 761 2036127
bDepartment of Chemistry, Jahangirnagar University, Dhaka, 1342,
Bangladesh. E-mail: enamullahju@yahoo.com; Fax: +880 2-7791068;
Tel: +880 2-7791399
cDepartment of Chemistry, Emory University, Atlanta, GA 30322, USA
† Dedicated to Prof. Ingo-Peter Lorenz on the occasion of his 65th
birthday.
Polymorphism of transition metal complexes is of increasing
4
interest.2,3 Polymorphs of h -cod and related Rh(I)-complexes in-
‡ Electronic supplementary information (ESI) available: Crystal pictures
of 3R/3S and 3rac, UV/Vis, IR, olefinic cod 1H NMR data, Rh–
cod distances, C–H ◊ ◊ ◊ p contacts (Table and Figures). CCDC reference
numbers 708787–708792. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/b820072f
4
4
clude [Rh(h -cod){N,N }]O3SCF3,15 [Rh(h -cod){P, P }]O3SCF3,16
4
[Rh(h -nor){P, P }]ClO4 (cod = 1,5-cyclooctadiene, nor = norbor-
nadiene)17 and
a temperature-induced phase transition in
3698 | Dalton Trans., 2009, 3698–3709
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4
[Rh(h -cod)(H2O)2)]O3SCF3.18 Polymorphs of Rh–Schiff base
complexes are [RhICl{N,N,N }]19 and [RhIII(ad){N,O,N,O}-
(py)].20
At the same time molecular chiral metal complexes are of
permanent interest.21 There are continuous developments of
optically active Schiff base (HSB*) ligands and their transi-
tion metal complexes for applications as chiral catalysts.22–26
Organometallic compounds with anionic Schiff base (SB*-)
6
ligands are the half-sandwich complexes [Ru(SB*)X(h -benzene)]
{SB* = (S)-N-1-phenylethylsalicylaldiminato; X = Cl, 4-/2-Me-
6
py, PPh3}, [M(SB*)X(h -arene)] (M = Ru(II), Os(II); X = Cl, I),27,28
6
[Ru(SB*)X(h -p-cymene)] (X = various monodentate ligands),29,30
4
and [Rh(SB*)(h -cod)] {SB* = (S)-(a)-(2-pyridyl)-salicylaldi-
minato,31 (R)-N-(1-aryl-ethyl)-salicylaldiminato32,33}. Chiral [Rh-
4
(SB*)(h -cod)] complexes with chiral Schiff bases, derived from
(S)-a-(2-pyridyl)ethylamine and benzaldehyde derivatives, have
been used successfully as enantioselective catalysts in the hydrosi-
lylation of acetophenone with diphenylsilane.31
4
Scheme
respectively.
1
Synthesis of [{Rh(h -cod)}2(salen/salophen)]
1 and 2,
The N,O-chelate type bidentate (HSB) and tetradentate (H2SB)
4
Schiff bases readily react with dinuclear [Rh(m-X)(h -cod)]2
4
(X = Cl, OMe, O2CMe) to give mononuclear [Rh(SB)(h -
4
cod)] (SB = salicylaldiminato) and dinuclear [{Rh(h -cod)}2(SB)]
{SB = bis(salicylaldiminato)} complexes, respectively.34–37 The
similar reactions with N,N-chelate type enantiopure Schiff bases
4
4
afford the mononuclear [Rh(diminato)(h -cod)] complexes.31,38,39
Scheme 2 Crystallization routes to the polymorphs of [{Rh(h -cod)}2-
(salophen)] 2 (PE = petroleum ether, bp 40–60 ◦C).
4
Prior to our work only one Rh(h -cod) structure with an N,O-
chelate ligand giving a six-membered Rh{N,O} chelate ring had
4
been known.35,40 We recently synthesised Rh(h -cod) complexes
containing chiral Schiff bases, chiral aminocarboxylato or chiral
amino alcohols as N,O-chelating ligands starting from dinuclear
4
[Rh(m-O2CMe)(h -cod)]2.32,41–43
In continuation, we describe here the syntheses and structures
4
of Rh(h -cod) complexes with the N,O-chelating ligands N,N ¢-
ethylene-bis(salicylaldiminato) (salen2-), N,N ¢-(1,2-phenylene)-
bis(salicylaldiminato) (salophen2-), N-phenylglycinato, (R)-N-
(4-methoxphenyl)ethyl-2-oxo-1-naphthaldiminato or N-(o-tolyl)-
2-oxo-1-naphthaldiminato which present polymorphs, enan-
4
tiomorphs with helical chains, chiral and acentric [Rh{N,O}(h -
cod)] complexes.
Results and discussion
Scheme 3 Synthesis and crystallization routes to the enantiomorphs and
the racemic mixture of 3 (PE = petroleum ether, bp 40–60 ◦C).
4
Dinuclear (acetato)(h -cycloocta-1,5-diene)rhodium(I), [Rh(m-
4
O2CMe)(h -cod)]2 reacts with the tetradentate Schiff bases N,N ¢-
ethylene-bis(salicylaldimine) (H2salen) and N,N ¢-(1,2-phenylene)-
reported by us.41 The orange needle crystal mixture (Fig. S1a in
ESI‡) of 3R and 3S was obtained by slowly adding 10 ml of PE
(bp 40–60 ◦C) on the top of a warm (40 ◦C) concentrated (to
60%) mixture of initially 5 ml of MeOH and 20 ml of toluene
(Scheme 3). When the crystallization conditions were changed to
adding 5 ml of PE (bp 40–60 ◦C) on top of a concentrated (to 50%)
mixture of initially 3 ml of MeOH and 7 ml of benzene red-brown
intergrown crystals of 3rac were obtained (Scheme 3, Fig. S1b‡).
These polymorphic crystals analyzed as the racemic mixture of 3
in a centrosymmetric space group.
bis◦(salicylaldimine) (H2salophen) in C6H6–MeOH (5 : 1, v/v) at
4
25 C to afford the dinuclear complexes [{Rh(h -cod)}2(salen)] (1)
4
and [{Rh(h -cod)}2(salophen)] (2), respectively (Scheme 1).
The structure of 2 revealed a case of polymorphism.35 Crys-
tallizat◦ion of 2 by gas phase diffusion of petroleum ether (bp
40–60 C) into a concentrated chloroform solution gave crystals
of the same orange-yellow color but of a different space group
(2◦a) as previously described35 and obtained from slow diffusion at
5 C of methanol into a concentrated dichloromethane solution
(2b) (Scheme 2).
4
Furthermore, [Rh(m-O2CMe)(h -cod)]2 reacts with the biden-
tate Schiff bases (R)-N-(4-methoxphenyl)ethyl-2-oxo-1-naphthal-
4
[Rh(m-O2CMe)(h -cod)]2 reacts with the amino acid N-
phenylglycine, (HO2C–CH2–NHPh) to mononuclear [Rh(O2C–
CH2–NHPh)(h -cod)] (3) (Scheme 3). The structure of enan-
tiomorph 3R from a spontaneous resolution has recently been
dimine or N-(o-tolyl)-2-oxo-1-naphthaldimine to mononuclear
4
4
[Rh(X-2-oxo-1-naphthaldiminato)(h -cod)] 4, {X = (R)-N-(4-
methoxphenyl)ethyl} and 5 {X = N-(o-tolyl)} (Scheme 4).
Dalton Trans., 2009, 3698–3709 | 3699
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[M3 - AA]+, [M2]+ and [M2 - AA]+ (AA = N-phenylglycinato)
possibly due to inter-molecular hydrogen bonding as shown in the
structure of 3 (see below).
Polarimetry
The polarimetric measurement of 4 in CHCl3 shows a rotation to
the right ([a]25 = +91◦, c = 0.92, at 598 nm), while the free Schiff
base turns left ([a]25 = -222◦, c = 0.52, at 598 nm).47
NMR spectroscopy
1
4
In H NMR the 1,5-cyclooctadiene in [Rh{N,O}(h -cod)] com-
plexes shows the signals as expected for the exo- and endo-
methylene protons as well as the olefin protons.32,33,41–44,48–50 The
exo-methylene protons show two multiplets at 1.6–1.8 ppm in
4
dinuclear [{Rh(h -cod)}2{N,O}] (1, 2) and one multiplet at 1.7–
4
2.0 ppm for the mononuclear [Rh{N,O}(h -cod)] (3–5). The endo-
methylene protons appear at 2.1–2.55 as two (1) or one multiplet
in 2–5. The multiplets for the olefinic protons are listed in
4
Table S3 in ESI‡ together with other related Rh{N,O}(h -cod)
complexes.
4
Scheme 4 Synthesis of [Rh(X-2-oxo-1-naphthaldiminato)(h -cod)] 4
and 5.
The different signals for exo- and endo-methylene protons
and the olefin protons are explained by the trans effects of the
co-ordinated N,O-chelate on proton resonances.32–35,41–44,46,48,49 In
UV/Vis
4
Rh(I)(h -cod)–Schiff base complexes two kinds of olefin proton
4
The Rh(h -cod)–Schiff base complexes show very similar elec-
tronic spectra, which mainly feature: (i) a very strong band
at higher energy (<360 nm), associated with the intra-ligand
resonances (two multiplets) arise from the two sets of two
equivalent protons trans to N and trans to O, respectively. The
occurrence of more than two multiplets for the olefin proton
resonances is explained due to the steric and magnetic anisotropy
4
p→p* transitions of the Schiff base imino group and the h -cod
effects in addition to this trans effect,32,48c as will be seen later in the
moiety and (ii) a strong broad band at 400–500 nm (lmax/emax
=
403 nm/8655 l mol-1 cm-1 for 1, 413 nm/8077 l mol-1 cm-1
for 2, 411 nm/13150 l mol-1 cm-1 for 4 and 416 nm/3828 l
mol-1 cm-1 for 5), assigned to the metal-to-ligand charge transfer
(MLCT) transitions between Rh(I) and the diminato ligand
13
=
C NMR studies. Complex 2 shows the CH N signal relatively
downfield (8.58 ppm) due to interactions with the neighboring
phenyl ring (cf . 7.57 ppm for 1).
4
In 13C NMR of [Rh{N,O}(h -cod)] complexes the cod methy-
4
(Schiff base anion). The CT transitions for the [Rh(h -cod)]
lene carbon atoms can give two singlets and the olefin carbon
give two doublets. The observations of two signal groups each
are explained by the trans effect of the coordinated N,O-chelate
on the carbons resonances.32,33,41–44,46,48,49 The doublets are due to
the coupling of the olefinic carbon with the rhodium atom. The
103Rh–13C(olefin) spin–spin coupling constants for trans to N (J =
12–13 Hz) and trans to O (J = 14–15 Hz) are in good agreement
moiety, which are observed at lmax = 356 nm in the starting
4
material, [Rh(O2CMe)(h -cod)]2, likely shift to the higher energy
and overlap with the very strong intra-ligand p→p* transitions,
4
and are not detectable in Rh(h -cod)–Schiff base/–amino acid
complexes (further details in Fig. S2 and Table S1 in ESI‡).27,32,41–45
4
Infrared spectroscopy
with those found for the related mono- and dinuclear (h -cod)Rh–
Schiff bases complexes (see Table S4 in ESI‡). Similarly, two broad
The complexes show two new bands (which are absent in the
free ligands) around 675–680 cm-1 and 459–465 cm-1 which are
assigned to nRh–N and nRh–O, respectively. Further, the nO–
H stretching band of the free Schiff bases, usually observed at
3250–3254 cm-1, disappears in the complexes, which indicates
dissociation of the protic hydrogen and formation of a bond
between Rh and the hydroxyl oxygen atom (for further details
see Table S2 in ESI‡).28,32,41–46
signals for methylene and olefin carbons each are found in a [Rh(o-
4
aminophenolato)(h -cod)] complex (Table S4‡).43 Yet, four singlets
and four doublets can be observed for the methylene and olefinic
carbon atoms in 2, 4 and 5 and other related complexes (Table S4‡).
The occurrence of four singlets and four doublets is explained by
steric and magnetic anisotropy effects in addition to this trans
effect.32,48c Two downfield doublets (84–86 ppm) are assigned to
the olefinic carbon resonances trans to N, the other two upfield
doublets (69–75 ppm) trans to O (see Table S4‡). Contrary to
Mass spectroscopy
4
these findings, [Rh(N-phenylglycinato)(h -cod)] (3) and Rh(amino
4
EI, CI or FAB mass spectra show the parent ion peaks [M]+ corre-
sponding to the formation of dinuclear 1 and 2 and mononuclear
3, 4 and 5. Further peaks present the species [M + H]+, [M -
cod]+, [Rh(cod)]+, Schiff base/deprotonated Schiff base or N-
phenylglycine. The FAB-MS of 3 includes ions such as [M4 - AA]+,
acetato)(h -cod) (see Tables S3, S4‡) show only one multiplet for
the olefin protons and one broad signal for the olefin carbon
atoms. This might be due to a ring opening of the five membered
N,O-chelate resulting in a rapid exchange on the NMR time
scale.
3700 | Dalton Trans., 2009, 3698–3709
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[{Rh(g4-cod)}2(salen)] 1 and [{Rh(g4-cod)}2(salophen)] 2 (with
◦
˚
Table 1 Selected bond lengths [A] and angles [ ] in 1 and 2
dimorphs 2a and 2b)
1
2
The molecular structures of the rhodium complexes 1 and
2 prove the N,O-chelation of the deprotonated N,N ¢-ethylene-
bis(salicylaldiminato) (salen2-) and N,N ¢-(1,2-phenylene)-bis(sali-
cylaldiminato) (salophen2-) Schiff base ligands, respectively, to
Rh1–O1
Rh1–N1
Rh1–C9
Rh1–C10
Rh1–C13
Rh1–C14
Rh2–O2
2.0299(18)
2.096(2)
2.109(3)
2.117(3)
2.135(3)
2.146(2)
2.0353(18)
2.093(2)
2.132(3)
2.140(3)
2.117(3)
2.138(3)
90.34(8)
89.49(8)
Rh1–O1
Rh1–N1
Rh1–C21
Rh1–C22
Rh1–C25
Rh1–C26
Rh2–O2
2.0316(15)
2.0859(16)
2.118(2)
2.133(2)
2.094(2)
2.119(2)
2.0311(14)
2.0805(17)
2.118(2)
2.097(2)
2.143(2)
2.121(2)
90.03(6)
89.83(6)
4
two Rh(h -cod) groups (Fig. 1 and Fig. 2). Bond lengths and
angles are as expected.29,32,35,41,48b,c Compound 1 is only the third
4
structurally authenticated example of Rh(h -cod) complexes with
Rh2–N2
Rh2–N2
six-membered Rh-N,O-chelate rings.32,35,40 The ethylene bridge
between the two salicylaldiminato moieties in 1 is in the s-trans
conformation. The two N–C–C planes form an angle of 156.4(3)◦.
The metallacycle Rh–(N–CCC–O) planes are tilted 83.3(1)◦ with
respect to each other in 1. The intermolecular packing in 1
shows a p ◊ ◊ ◊ p contact between the Rh2-metallacycles51–53 and
complementary C–H ◊ ◊ ◊ p contacts54 from salen-CH2 groups onto
the Rh2-metallacycle and the aromatic salicyl ring C3–8 (see
Table S5 and Fig. S3–S5 in ESI†). The p-stacking between the
parallel Rh2-metallacycle ring planes (symmetry relation 2 - x,
Rh2–C25
Rh2–C26
Rh2–C29
Rh2–C30
O1–Rh1–N1
O2–Rh2–N2
Rh2–C29
Rh2–C30
Rh2–C33
Rh2–C34
O1–Rh1–N1
O2–Rh2–N2
nitrogen or oxygen donor atoms and the ‘left’ and ‘right’ differen-
tiation as mirrored in the four olefinic 13C NMR resonances.
The crystal structure of 2 presents a polymorph (dimorph) (2a)
to a previously reported X-ray structure of the same compound
(2b, CSD refcode SCLIRB10, cf . Scheme 2).35 From an overlay of
the molecules of the dimorphs 2a and 2b in Fig. 3 there are slight
conformational differences in the interplanar angles (Table 2)
which goes together with a different packing arrangement.
˚
1 - y, 1 - z) exhibits a short centroid–centroid distance (3.86 A),
◦
˚
a small slippage of 1.62 A and a small slip angle of 25 . Masui
had suggested an active electron delocalization within a metal–N-
heterocyclic chelate ring in such a way that it could exhibit some
degree of “metalloaromaticity”.55,56 The packing index57 (“calc
void” with PLATON58) of 1 is 74.5%.
4
Fig. 1 Thermal ellipsoid plot for [{Rh(h -cod)}2(salen)] (1) at 50%
probability level; bond lengths and angles in Table 1.
Fig. 3 Overlay of the molecular structures of the dimorphs 2a (in red) and
2b (CSD refcode SCLIRB10, in green) by specifying the carbon atoms of
the central phenylene ring as pairs in the two structures (RMS = 0.0405).
51
The crystal packing of 2a does not have p ◊ ◊ ◊ p but one
C–H ◊ ◊ ◊ p interaction54 (see Table S5 and Fig. S6 in ESI‡). In the
packing of 2b there are still no p ◊ ◊ ◊ p but some weak C–H ◊ ◊ ◊ p
contacts from cod-CH2 groups onto the RhNC3O metallacycle
and the anellated salicyl ring of an adjacent molecule (see Table S5
and Fig. S7 in ESI‡). In the packing of both 2a and 2b we invoke
a different interlocking of adjacent dinuclear molecules with their
corrugated van der Waals surface.41 The Rh-metallacycles form an
opening or a cleft with the anellated salicyl rings in the dinuclear
molecule (Fig. 2). A motif found in the packing of 2a is a “cupping”
arrangement where the openings created by the anellated ring
planes of two inversion-symmetry related Rh2 molecules fit into
each other (Fig. 4).2 In the dimorph 2b each phenylene ring
interdigitates into the cleft formed by the salicyl–metallacycle ring
4
Fig. 2 Thermal ellipsoid plot for [{Rh(h -cod)}2(salophen)] (2) at 50%
probability level; bond lengths and angles in Table 1.
Both cod-ligands in each complex are slightly asymmetrically
bound (see Scheme S1 in ESI‡) which reflects the different trans
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4
◦
˚
Table 2 Intramolecular distances and angles in the [{Rh(h -cod)}2-
Table 3 Selected bond lengths [A] and angles [ ] in 3S, 3rac, 3R
(salophen)] complexes of the two polymorphs 2a and 2b
3S
3rac
3R41
2a (red)
2b (green) a,b
Rh–O1
Rh–N
Rh–C9
Rh–C10
Rh–C13
Rh–C14
O1–Rh–N
O1–Rh–C9
O1–Rh–C10
O1–Rh–C13
O1–Rh–C14
N–Rh–C9
N–Rh–C10
N–Rh–C13
N–Rh–C14
2.053(8)
2.075(1)
2.059(3)
˚
Rh ◊ ◊ ◊ Rh/A
4.905(1)
5.737(1)
2.151(9)
2.11(1)
2.12(1)
2.07(1)
2.09(1)
81.0(3)
90.8(4)
95.8(4)
160.2(4)
160.9(4)
157.9(3)
162.1(3)
94.5(4)
99.4(5)
2.145(2)
2.124(2)
2.099(2)
2.113(2)
2.104(2)
80.84(5)
95.53(7)
89.35(7)
157.81(7)
163.65(7)
161.85(9)
157.93(9)
99.58(7)
96.09(7)
2.145(3)
2.112(5)
2.131(4)
2.108(4)
2.125(4)
80.8(1)
90.8(2)
95.4(2)
160.6(2)
161.0(2)
158.7(2)
161.5(2)
95.6(2)
Acute interplanar angle between central phenylene
ring ◊ ◊ ◊ RhNC3O metallacycle/◦
Rh1
Rh2
73.25(9)
74.19(9)
86.5(4)
86.5(4) c
Acute interplanar angle between central phenylene
ring ◊ ◊ ◊ C6-salicyl ring/◦
Rh1
Rh2
69.2(1)
67.1(1)
84.2(5)
84.2(5) c
a Calculated from the deposited cif-file SCLIRB1035 with PLATON.58
b Corresponding colors in Fig 4. c The asymmetric unit in 2b consists of half
4
of [{Rh(h -cod)}2(salophen)]. The two halves of the dinuclear molecule in
2b are related by a two-fold rotation axis, located at the midpoints of two
99.1(2)
C–C bonds of the central phenylene ring.
4
Fig. 6 Thermal ellipsoid plot for [Rh(O2C–CH2–NHPh)(h -cod)] (3)
from the structure of 3rac (showing the R enantiomer in this racemic
structure). The numbering scheme in 3S is identical (except that this
polymorph contains only the S enantiomer); bond lengths and angles
in Table 3.
Fig. 4 Cupping motif in the packing of the dimorph structure of 2a
(hydrogen atoms omitted for clarity).
planes of the next molecule along the 21-screw axis parallel to c
in Pccn (Fig. 5). The packing index57,58 of polymorph 2a and 2b is
virtually identical with 72.5% and 72.2%, respectively.
The nitrogen atom of the prochiral N-phenylglycinato ligand
becomes a stereogenic center upon metal coordination, yielding
a racemic mixture of R- and S-configured complexes. From
the racemic mixture the complex with the R-configuration at
4
nitrogen [Rh((R)-O2C–CH2–NHPh)(h -cod)] (3R) crystallizes in
the tetragonal, chiral space group P43 under the appropriate
conditions (see Scheme 3). The crystal structure revealed a case of
a two-fold spontaneous resolution of a racemic complex mixture
into homo-chiral helix-enantiomers.41 The overall crystal ensemble
(Fig. S1a in ESI‡) is racemic which we prove here with the structure
of the S-configured enantiomorphic complex 3S in the tetragonal
space group P41. The chiral space groups P43 and P41 form an
enantiomorphous pair.61,62 It was not possible to visibly distinguish
the crystals with the R-and S-configuration (cf . Fig. S1a‡) so we
had to carry out full data set collections on various crystals to
determine the space group. By investigating six of the needle-
shaped crystals in Fig. S1a‡ four of them were found to contain
the R-configured complex in P43 and two of them contained the
S-configured complex in P41. The S-configured complexes in the
enantiomorph 3S assemble in a right-handed (or P) 41-helical
chain through N–H ◊ ◊ ◊ O hydrogen bonding from the stereogenic
amino group to a neighboring unligated carboxyl oxygen atom
(Fig. 7 and Fig. 8). Only molecules of the same S-configuration
are combined into a chain and neighboring chains are of the same
41 handedness.
Fig. 5 Interdigitating motif in the packing of the dimorph structure of
2b (hydrogen atoms omitted for clarity).
[Rh(O2C–CH2–NHPh)(g4-cod)] 3 (with polymorphs 3R,
3S and 3rac)
Complex 3 in the crystal structures of 3S and 3rac has
the prochiral phenylglycinato ligand coordinated with N,O-
4
chelate formation to the rhodium atom of the Rh(h -cod)
4
fragment (Fig. 6). Related Rh(h -cod) complexes with a five-
membered Rh-N,O-chelate ligand are structurally elucidated
with 8-hydroxyquinolinato,48a tryptophan benzyl ester,15 4-
methylpyridinium 2-pyridylcarbonylmethylide,59 1-(2¢-pyridyl)-
3-dimethylamino-2-propenone,60
imidazole-4,5-carboxylato,49a
An attempt was made to collect circular dichroism (CD)
spectra on a toluene solution of a single crystal with X-ray
orotato46a and 3-oxo-1-(pyridin-2-yl)prop-1-en-1-olato.48b
3702 | Dalton Trans., 2009, 3698–3709
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Fig. 7 Right-handed (P) 41-helical chain in 3S. Hydrogen bonding
Fig. 9 The interlocking of two neighboring right-handed (P) 41-helical
chains in 3S with their corrugated van der Waals surface; space-filling
representation of the chains, which are differentiated by light and dark
gray shading.
◦
interaction (dashed red line) [A, ]: N–H 0.9(1), H ◊ ◊ ◊ O3 2.0(1), N ◊ ◊ ◊ O3
2.90(1), N–H ◊ ◊ ◊ O3 170(10); symmetry transformations: 2 = 2 - x, 2 - y,
0.5 + z; 2¢ = 2 - x, 2 - y, -0.5 + z; 3 = 2 - y, x, 0.25 + z; 4 = y, 2 - x,
0.75 + z; 4¢ = y, 2 - x, -0.25 + z. Carbon atoms of the phenyl and cod
rings are depicted semi-transparent and C–H hydrogen atoms are omitted
for clarity.
˚
Fig. 10 Overlay of the molecular structures of the polymorphs 3rac (in
red) and 3R (CSD refcode DEGQUC,41 in green) by specifying the Rh, N
and (Rh–)O atom as pairs in the two structures (RMS = 0.00727).
Fig. 8 Right-handed 41-helical chain in 3S viewed along the chain
direction. Carbon atoms of the phenyl and cod rings are depicted
semi-transparent and C–H hydrogen atoms are omitted for clarity.
determined absolute R- or S-configuration at the nitrogen atom.
However, no useful CD spectra could be obtained either due
to the low absolute amount of a single crystal with its subse-
quent low concentration or because of a rapid racemization in
solution.
The homochirality, that is, the same handedness of the he-
lices and, thereby, the packing in a chiral space group can
only be due to the corrugated van der Waals surface of
the helix (Fig. 9). No noteworthy p–p-stacking or C–H ◊ ◊ ◊ p
interactions are found between the helices in 3S or 3R,41 despite
the presence of phenyl rings.
When the crystallization conditions for 3 were changed slightly
(cf. Scheme 3) a racemic mixture of R- and S-configured complexes
crystallizes in the monoclinic, centrosymmetric space group P21/c
as 3rac. Crystals of 3rac can be considered a polymorph to the
two enantiomorphs 3R and 3S. Bond lengths of 3 in the different
forms are identical within experimental error (3s) (Table 3) and
an overlay of R-complexes from 3R and 3rac in Fig. 10 reveals
only slight conformational differences.
Fig. 11 Hydrogen-bonded complexes in two parallel chains along the
21-axes, parallel to the b-axis in 3rac. Here, the lower chain contains only
R-configured, the upper chain only S-configured complexes. Hydrogen
◦
bonding interaction (dashed red line) [A, ]: N–H 0.82(2), H ◊ ◊ ◊ O2
˚
2.01(2), N ◊ ◊ ◊ O2 2.820(2), N–H ◊ ◊ ◊ O2 171(2); symmetry transformations:
2 = -x, -1/2 + y, 1/2 - z. C–H hydrogen atoms are omitted for clarity.
only molecules of the same configuration are combined into a
chain, albeit now neighboring chains have complexes of opposite
configuration. As in 3R or 3S no noteworthy p–p-stacking or
As before molecules in the polymorph 3rac assemble in
chains through N–H ◊ ◊ ◊ O hydrogen bonding (Fig. 11). Again,
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C–H ◊ ◊ ◊ p interactions are found between the chains. The packing
index57,58 of 71.3% in 3rac is slightly higher than in 3R or 3S with
68.7–69.8%.
[Rh(X-2-oxo-1-naphthaldiminato)(g4-cod)] 4, {X = (R)-N-
(4-methoxphenyl)ethyl} and 5 {X = N-(o-tolyl)}
Complexes 4 and 5 have the 2-oxo-1-naphthaldiminato ligand
coordinated with a six-membered Rh–N,O-chelate ring formation
4
and the rhodium-bound h -cod fragment (Fig. 12 and Fig. 13). The
intermolecular packing in 4 and 5 shows no p ◊ ◊ ◊ p contacts despite
the presence of an extended aromatic system in the naphthyl
ring.51–53 Only two or one C–H ◊ ◊ ◊ p contacts onto the RhNC3O
metallacycle can be noted54 in 4 or 5, respectively (see Table S5
and Fig. S8 and S9 in ESI‡). The crystal packing in 4 is a herring-
bone pattern (Fig. 14). Compound 5 crystallizes in the non-
centrosymmetric polar space group Cc. Accordingly, all molecules
show the same orientation, e.g. the naphthyl–Rh–cod axes or the
o-tolyl planes, respectively, are oriented parallel to each other, with
the naphthyl ring or the methyl group of the o-tolyl, respectively,
all pointing in the same direction (Fig. 15). The packing index57,58
is 68.7% for 4 and 69.8% for 5.
Fig. 13 Thermal ellipsoid plot (50% level) for 5; bond lengths and angles
in Table 4.
Fig. 14 Herring-bone motif in the packing of the chiral complex 4
(hydrogen atoms omitted for clarity).
Fig. 12 Thermal ellipsoid plot (50% level) for 4; bond lengths and angles
in Table 4.
◦
˚
Table 4 Selected bond lengths [A] and angles [ ] in 4 and 5
4
5
Rh–O(1)a
Rh–N
Rh–C21
Rh–C22
Rh–C25
Rh–C26
O(1)–Rh–N
O(1)–Rh–C21
O(1)–Rh–C22
O(1)–Rh–C25
O(1)–Rh–C26
N–Rh–C21
N–Rh–C22
N–Rh–C25
N–Rh–C26
2.0273(10)
2.0684(12)
2.1460(16)
2.1288(14)
2.1311(15)
2.1058(14)
89.16(5)
86.28(6)
86.92(6)
165.75(5)
153.14(6)
164.02(6)
156.97(5)
97.91(5)
2.033(5)
2.053(5)
2.138(7)
2.106(7)
2.131(6)
2.107(6)
88.52(19)
87.0(2)
Fig. 15 Polar packing in the structure of complex 5. The naphthyl–
Rh–cod axes lie approximately parallel to the (-5 0 4) lattice planes (in red)
and the naphthyl or cod groups, respectively point in the same direction.
Also, the o-tolyl planes lie parallel to the (4 0 2) lattice planes (in green)
and the methyl groups are oriented in the same direction.
89.0(2)
168.1(2)
151.8(2)
168.1(2)
153.2(3)
96.8(2)
Conclusions
4
95.38(6)
96.9(2)
The [Rh{N,O}(h -cod)] complexes with the salicylaldiminato
Schiff base ligands described here have an unpolar molecule
surface, such that their crystal packing can only be controlled
a O1 in 4, O in 5.
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by weak C–H ◊ ◊ ◊ p and van der Waals contacts. The salophen
complex 2 is then found in a second polymorph. The weak
interactions in the N-(o-tolyl)-2-oxo-1-naphthaldiminato complex
5 enable the molecules arranged in the same orientation to give
polar packing. Only the N-phenylglycinato complex [Rh(O2C–
(5 : 1, v/v) and the solution stirred for 5–6 h at room temperature.
The color soon changed from red-orange to bright-yellow. The
solvent was evaporated in vacuo, the residue dissolved in 10 ml
of C6H6–MeOH (5 : 1, v/v), the solution stirred for 30 min
and the solvent evaporated again. This procedure was repeated
three more times in order to remove the acetic acid. Finally,
the residue was dried in vacuo (0.1–0.2 mbar) at 60 ◦C to give
bright-yellow 1 (yield 145 mg, 84%). Single crystals suitable
for X-ray measurement were grown by gas phase diffusion of
petroleum ether (bp 40–60 ◦C) into a concentrated chloroform
solution of 1 within one week at 25 ◦C. IR (see ESI‡). UV/Vis
(see ESI‡). MS (FAB, +) [m/z (%)]: 689 (15) [M + H]+, 580
(100) [M - cod]+, 578 (25) [M - cod - H2]+, 461 (15) [M -
cod - C6H4(OH)(CN)]+, 391 (52) [(RhOC6H5)2 - H]+, 327 (45)
[Rh(cod)OC6H4(CN) - H2]+, 289 (35) [(RhOC6H5)2 - Rh]+, 267
(30) [H2Salen - H]+ and 207 (55) [Rh2 + H]+. 1H NMR (400 MHz,
CDCl3): d = 1.71 (m, 4H, CH2codexo), 1.81 (m, 4H, CH2codexo),
2.14 (m, 4H, CH2codendo), 2.36 (m, 4H, CH2codendo), 3.29 (s, 4H,
4
CH2–NHPh)(h -cod)], 3 has a hydrogen-bonding functionality
which leads to chain formation of homochiral molecules. In
between the chains only van der Waals interactions persist.
Subsequently, polymorphic forms of 3 crystallize with either
helical chains around a fourfold screw axis (41 or 43) or chains
along a twofold screw axis (21). The corrugated van der Waals
surface of the fourfold helical chains allows only for a homochiral
assembly so that spontaneous resolution occurs. R-Complexes of
3 crystallize in the chiral space group P43 and S complexes in P41
with the crystal ensemble being racemic. The 21 chains alternate
in R- and S-composition so that the structure 3rac contains the
racemic mixture within each crystal.
H
8,9), 3.58 (m, 4H, CHcod), 4.40 (m, 4H, CHcod), 6.32 (t, J =
Experimental section
7.0 Hz, 2H, H4,4¢), 6.70 (d, J = 8.5 Hz, 2H, H6,6¢), 6.81 (d, J =
7.6 Hz, 2H, H3,3¢), 7.15 (t, J = 7.0 Hz, 2H, H5,5¢) and 7.57 (s,
All reactions were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques. Solvents used were
dried and distilled under nitrogen prior to use: benzene and
petroleum ether (bp 40–60 ◦C) over Na metal; methanol over
CaO. IR spectra were recorded on a Bruker Optik IFS 25 spec-
trometer as KBr disks at ambient temperature. UV/Vis spectra
were obtained with a Shimadzu UV 3150 spectrophotometer
in C6H6 or CH2Cl2 at 25 ◦C. Elemental analyses were done
on a VarioEL from Elementaranalysensysteme GmbH. NMR
spectra were run on Bruker AC DPX 400 operating at 400 MHz
(1H) and 100 MHz (13C) at 25 ◦C with calibration against the
residual protonated solvent signal (CDCl3 1H NMR 7.26 ppm,
13C NMR 77.0 ppm; DMSO-d6 1H NMR 2.52 ppm). The NMR
grade solvents CDCl3 and DMSO-d6 were deoxygenated prior
to use. FAB-MS (positive mode): Finnigan MAT 8230 with data
system SS 300, matrix: m-nitrobenzyl alcohol. EI- and CI-MS:
Thermo-Finnigan TSQ 700, with NH3 as ionization gas for CI.
Polarimetric measurements were◦ carried with a Perkin-Elmer
241 instrument in CHCl3 at 25 C and the values of [a]25 were
determined according to the literature.27,32 The starting dinuclear
1
2H, H7,7¢). H NMR (400 MHz, DMSO-d6): d = 1.71 (m, 4H,
CH2codexo), 1.84 (m, 4H, CH2codexo), 2.09 (m, 4H, CH2codendo),
2.32 (m, 4H, CH2codendo), 3.41 (s, 4H, H8,9), 3.78 (m, 4H, CHcod),
4.28 (m, 4H, CHcod), 6.50 (t, J = 7.0 Hz, 2H, H4,4¢), 6.68 (d, J =
8.4 Hz, 2H, H6,6¢), 7.15 (d, J = 7.8 Hz, 2H, H3,3¢), 7.27 (t, J =
7.0 Hz, 2H, H5,5¢) and 8.00 (s, 2H, H7,7¢). 13C NMR (100 MHz,
CDCl3): d = 28.8, 31.7 (s, CH2cod), 60.9 (s, C8,8¢), 71.2 (d, JC-Rh
14.2 Hz, CHcod), 85.50 (d, JC-Rh = 11.9 Hz, CHcod), 114.5 (s,
3,3¢), 118.8 (s, C5,5¢), 121.3 (s, C1,1¢), 135.0 (s, C6,6¢), 135.4 (s, C4,4¢),
=
C
166.5 (s, C2,2¢) and 166.9 (s, C7,7¢). C32H38N2O2Rh2 (688.46) calcd
C 55.83, H 5.56, N 4.07; found C 55.85, H 5.55, N 3.73%.
4
4
[Rh(O2CMe)(h -cod)]2 complex was synthesized from [RhCl(h -
cod)]2 according to the literature.42,50,63 The crystallization of
3R and 3S has been described before.41 RhCl3·3H2O (Wako),
Na2CO3 (Lancaster), 1,5-cyclooctadiene (Wako) were used
as received. The Schiff bases (R)-N-(4-methoxyphenyl)ethyl-2-
hydroxy-1-naphthaldimine, N-(o-tolyl)-2-oxo-1-naphthaldimine,
N,N ¢-ethylene-bis(salicylaldimine) (H2salen) and N,N ¢-(1,2-
phenylene)-bis(salicylaldimine) (H2salophen) were synthesized
according to the literature.47 The enantiopure amine (R)-N-(4-
methoxyphenyl)ethylamine was used as received from BASF,
Ludwigshafen, Germany.
Bis(g4-cycloocta-1,5-diene)(l-N,N ¢-o-phenylene-
bis(salicylaldiminato)-j4N,O:N¢,O¢)dirhodium(I),
[{Rh(g4-cod)}2(salophen)] (2)
The same procedure was followed as for the synthesis of 1
using N,N ¢-(1,2-phenylene)-bis(salicylaldimine) (H2salophen) to
give orange-yellow 2 (yield 152 mg, 82%). Single crystals suitable
for X-ray measurement were obtained by gas phase diffusion of
petroleum ether (bp 40–60 ◦C) into a concentrated chloroform
solution of 2 within one week at 25 ◦C. IR (see ESI‡). UV/Vis (see
ESI‡). MS (FAB, +) [m/z (%)]: 737 (5) [M + H]+, 628 (25) [M -
cod]+, 486 (18) [M - cod2 - 2OH]+, 418 (25) [M - salophen - 2H2]+,
391 (100) [(RhOC6H5)2 - H]+, 307 (92) [Rh(cod)OC6H5 + H2 +
H]+, 289 (80) [(RhOC6H5)2 - Rh]+, 219 (65) [RhOC6H4(CN) -
Bis(g4-cycloocta-1,5-diene)(l-N,N ¢-1,2-diaminoethane-
bis(salicylaldiminato)-j4N,O:N¢,O¢)dirhodium(I),
[{Rh(g4-cod)}2(salen)] (1)
1
H2]+ and 207 (25) [Rh2 + H]+. H NMR (400 MHz, CDCl3): d
Equimolar amounts of N,N ¢-ethylene-bis(salicylaldimine)
(H2salen) (67.4 mg, 0.25 mmol) and [Rh(O2CMe)(h -cod)]2
(135.3 mg, 0.25 mmol) were dissolved in 10 ml of C6H6–MeOH
1.62 (m, 4H, CH2codexo), 1.79 (m, 4H, CH2codexo), 2.17 (m, 8H,
CH2codendo), 2.45 (m, 2H, CHcod), 3.53 (m, 2H, CHcod), 4.37
(m, 2H, CHcod), 4.54 (m, 2H, CHcod), 6.62 (t, J = 7.0 Hz, 2H,
4
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H
4,4¢), 6.81 (d, J = 8.5 Hz, 2H, H6,6¢), 7.01 (m, 2H, H3,3¢), 7.18 (m,
and the solvent evaporated again in vacuo. This procedure was
repeated three times, and finally the product was dried in vacuo
(0.1–0.2 mbar) at 40 ◦C to give yellow 4 (yield 165 mg, 85%).
Single crystals suitable for X-ray diffraction were grown by slow
diffusion of diethyl ether into a concentrated chloroform solution
of 4 after 3–4 d at room temperature. [a]25 (c = 0.92, CHCl3): +91◦
(578 nm). IR (see ESI‡). UV/Vis (see ESI‡). MS (EI, 70 eV)
[m/z (%)]: 515 (100) [M]+, 407 (60) [M - cod]+, 379 (10) [M -
cod - CO]+, 305 (6) [HSB]+, 238 (20) [Rh(cod) + CO - H]+, 218
(10) [Rh(C6H5CH3CN)]+, 211 (5) [Rh(cod)]+, 207 (10) [Rh(cod) -
2H2]+, 135 (10) [CH3CHC6H4OMe]+, 103 (8) [Rh]+, 77 (5) [C6H5]+
2H, H5,5¢), 7.33 (m, 2H, H10,10¢), 7.43 (d, J = 7.8 Hz, 2H, H9,9¢
)
and 8.58 (s, 2H, H7,7¢). 13C NMR (100 MHz, CDCl3): d 27.9, 29.5,
30.3, 32.6 (s, CH2cod), 69.7 (d, JC-Rh = 14.4 Hz, CHcod), 74.3 (d,
JC-Rh = 14.6 Hz, CHcod), 84.3 (d, JC-Rh = 11.8 Hz, CHcod), 85.8
(d, JC-Rh = 11.7 Hz, CHcod), 114.8 (s, C3,3¢), 119.1 (s, C5,5¢), 122.2 (s,
C
1,1¢), 124.2 (s, C9,9¢), 126.1 (s, C10,10¢), 135.5 (s, C6,6¢), 135.6 (s, C4,4¢),
143.7 (s, C8,8¢), 166.2 (s, C2,2¢) and 167.1 (s, C7,7¢). C36H38N2O2Rh2
(736.52) calcd C 58.71, H 5.20, N 3.80; found C 57.26, H 5.27, N
3.54%.
1
(HSB = free Schiff base = C20H19NO2). H NMR (200 MHz,
(g4-Cycloocta-1,5-diene)(rac-N-phenylglycinato-
CDCl3): d = 1.73 (d, JHH = 6.8 Hz, 3H, H13), 2.00 (m, 4H,
CH2codexo), 2.53 (m, 4H, CH2codendo), 3.82 (m, 3H, H20), 3.91
(m, 2H, CHcod), 4.43 (q, JHH = 6.8 Hz, 1H, H12), 4.61 (m, 2H,
CHcod), 6.91–7.03 (m, 2H, HAr), 7.13–7.17 (m, 1H, HAr), 7.23–
7.43 (m, 5H, HAr), 7.56–7.65 (m, 2H, HAr), 8.86 (d, JHH = 2.0 Hz,
1H, H11). 13C NMR (50 MHz, CDCl3): d = 22.7 (s, C13), 28.3,
28.9, 31.1, 31.8 (s, CH2cod), 54.9 (s, C12), 60.1 (s, C20), 71.1 (d,
JC-Rh = 14.3 Hz, CHcod), 73.3 (d, JC-Rh = 14.2 Hz, CHcod), 84.1
(d, JC-Rh = 11.65 Hz, CHcod), 84.7 (d, JC-Rh = 11.75 Hz, CHcod),
113.7 (s, C3,16,18), 118.3 (s, C1), 121.3 (s, C6), 124.6 (s, C5), 126.3
(s, C7), 126.7 (s, C8), 128.4 (s, C15,19), 128.5 (s, C10), 134.5 (s, C4),
134.8 (s, C14), 134.9 (s, C9), 157.6 (s, C2), 158.4 (s, C17), 165.4 (s,
C11). C28H30NO2Rh (515.46) calcd C 65.24, H 5.87, N 2.72; found:
C 64.91, H 5.96, N 2.50%.
j2N,O)rhodium(I), [Rh(N-phenylglycinato)(g4-cod)] (3rac)
Two equivalents of N-phenylglycine (70 mg, 0.46 mmol) were
dissolved in 3 ml of MeOH. This solution was poured into a
solution of [Rh(O2CMe)(h -cod)]2 (123 mg, 0.23 mmol) in 7 ml of
benzene and stirred for 8–10 h at room temperature. The volume
4
◦
was reduced to 50% in vacuo at 30 C, then 5 ml of PE (bp 40–
60 ◦C) was very slowly added on the top of this solution and the
combined solution was left standing for crystallization at room
temperature. Crystal formation started after 2 d and block-shaped
red-brown crystals, suitable for X-ray measurement, were obtained
after 5 d. The crystals were filtered off and washed 3 times with PE
(5 ml each). Finally, the crystals were dried in vacuo (0.1–0.2 mbar)
at 40 ◦C (yield 120 mg, 73%). IR (see ESI‡). MS (EI, 70 eV) [m/z
(%)]: 361 (4) [M + H]+, 359 (10) [M - H2]+, 317 (16) [M - CO2]+,
315 (35) [M - H2 - CO2]+, 285 (10) [M - Ph + H]+, 211 (13) [M –
AA - Rh(cod)]+, 208 (25) [Rh(cod) - H2 - H]+, 151 (14) [HAA]+,
106 (100) [cod - H2]+ and 77 (57) [Ph]+ (AA = N-phenylglycinato).
MS (FAB, +) [m/z (%)]: 1293 (2) [M4 - HAA]+, 1143 (4) [M4 -
(AA)2 - H]+, 933 (38) [M3 - AA]+, 722 (4) [M2]+, 572 (100) [M2 -
AA]+, 362 (48) [M + H]+, 360 (4) [M - H]+, 211 (4) [M - AA -
Rh(cod)]+. 1H NMR (CDCl3, 200 MHz): d = 1.70 (dd, J = 7.2 Hz,
4H, CH2codexo), 2.33 (m, 4H, CH2codendo), 3.83 (m, 4H, CHcod),
4.00 (m, 2H, CH2), 4.24 (m, 1H, NH), 7.12 (m, 2H, Ho-Ar), 7.30
(m, 3H, Hm,p-Ar). 1H NMR (DMSO-d6, 200 MHz): d = 1.63 (dd,
J = 8.05 Hz, 4H, CH2codexo), 2.23 (m, 4H, CH2codendo), 3.34 (s,
2H, CH2), 3.58 (m, 4H, CHcod), 3.61 (m, 1H, NH), 7.01 (d, J =
8.19 Hz, 2H, Ho-Ar), 7.32 (t, J = 7.9, 7.5 Hz, 3H, Hm,p-Ar). 13C
NMR (CDCl3, 50 MHz): d = 29.8 (s, CH2cod), 56.1 (s, CH2), 78.5
(br, CHcod), 119.6 (s, Co-Ar), 124.5 (s, Cp-Ar), 129.0 (s, Cm-Ar),
(g4-Cycloocta-1,5-diene){N-(o-tolyl)-2-oxo-1-naphthaldiminato-
j2N,O}rhodium(I) (5)
The procedure for the synthesis of 4 was followed using N-(o-tolyl)-
2-oxo-1-naphthaldimine to give yellow 5 (yield 130 mg, 77%).
Single crystals suitable for X-ray diffraction were grown by slow
diffusion of diethyl ether into a concentrated chloroform solution
of 5 after 3–4 d at room temperature. IR (see ESI‡). UV/Vis
(see ESI‡). MS (EI, 70 eV) [m/z (%)]: 471 (100) [M]+, 363 (11)
[M - cod]+, 335 (55) [M - C6H4(CH3)(NHCHO) - H]+, 260 (10)
[HSB - H]+, 218 (35) [HSB - CO2 + H]+, 211 (10) [Rh + cod]+,
208 (20) [Rh + cod - H2 - H]+, 103 (5) [Rh]+ (HSB = free Schiff
base = C18H15NO). MS (CI, NH3) [m/z (%)]: 472 (100) [M + H]+,
471 (12) [M]+, 262 (50) [HSB + H]+, 261 (10) [HSB]+, 108 (8)
-
145.4 (s, NC-Ar), 179.3 (s, CO2 ). 13C NMR (DMSO-d6, 50 MHz):
d = 30.1 (s, CH2cod), 56.3 (s, CH2), 78.2 (br, CHcod), 119.9 (s,
Co-Ar), 124.8 (s, Cp-Ar), 129.6 (s, Cm-Ar), 146.4 (s, NC-Ar), 179.6
-
(s, CO2 ). C16H20NO2Rh (361.25) calcd C 53.20, H 5.58, N 3.88;
found C 51.81, H 5.26, N 3.67%.
(g4-Cycloocta-1,5-diene){(R)-N-(4-methoxphenyl)ethyl-2-oxo-1-
naphthaldiminato-j2N,O}rhodium(I) (4)
1
Two equivalents of (R)-N-(4-methoxyphenyl)ethyl-2-hydroxy-1-
naphthaldimine (116 mg, 0.38 mmol) and one equivalent of
[Rh(O2CMe)(h -cod)]2 (102 mg, 0.19 mmol) were dissolved in
(C6H5CH2OH). H NMR (200 MHz, CDCl3): d = 1.76 (m, 4H,
CH2codexo), 2.31 (s, 3H, CH3), 2.35 (m, 4H, CH2codendo), 2.62 (m,
1H, CHcod), 3.32 (m, 1H, CHcod), 4.53 (m, 1H, CHcod), 4.59
4
10 ml of C6H6–MeOH (5 : 1, v/v). The color soon changed
from red-orange to bright-yellow. The solution was stirred for
5–6 h at room temperature and the solvent evaporated in vacuo
at 40 ◦C. The yellow product was then dissolved in 10 ml of
C6H6–MeOH (5 : 1, v/v), the solution stirred for another 30 min
(m, 1H, CHcod), 6.92 (d, JHH = 7.6 Hz, 1H, H3), 7.00 (d, JHH =
9.2 Hz, 1H, H6), 7.12 (m, 4H, H14–17), 7.21 (dd, JHH = 8.3 Hz,
JHH = 1.5 Hz, 1H, H7), 7.56 (dd, JHH = 8.0 Hz, JHH = 1.2 Hz, 1H,
H8), 7.64 (d, JHH = 9.2 Hz, 1H, H5), 7.73 (d, JHH = 8.4 Hz, 1H,
H4), 8.68 (d, JHH = 2.0 Hz, 1H, H11). 13C NMR (50 MHz, CDCl3):
3706 | Dalton Trans., 2009, 3698–3709
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
4
4
4
Table 5 Crystal data for [{Rh(h -cod)}2(salen)] (1), [{Rh(h -cod)}2(salophen)] (2), [Rh(S-N-phenylglycinato)(h -cod)] (3S), [Rh(rac-N-
4
phenylglycinato)(h -cod)] (3rac), 4 and 5
Compound
1
2
3S
3rac
4
5
Empirical formula
M/g mol-1
C32H38N2O2Rh2
688.46
C36H38N2O2Rh2
736.50
C16H20NO2Rh
361.24
C16H20NO2Rh
361.24
C28H30NO2Rh
515.44
C26H26NORh
471.39
Crystal size/mm
0.16 ¥ 0.12 ¥ 0.10 0.17 ¥ 0.15 ¥ 0.07 0.28 ¥ 0.12 ¥ 0.09 0.20 ¥ 0.16 ¥ 0.08 0.49 ¥ 0.21 ¥0.14
0.35 ¥ 0.26 ¥ 0.11
4.26–51.7
19; 14; 13
Monoclinic
Cc
16.254(3)
11.992(3)
10.771(2)
90
102.288(3)
90
2051.4(7)
4
2q range/◦
h; k; l range
4.02–60.02
16; 16; 17
Triclinic
¯
P1
11.578(1)
11.676(1)
12.500(1)
112.549(2)
115.690(2)
96.732(2)
1322.3(3)
2
3.46–60.06
14; 16; -17, 16
Triclinic
¯
P1
10.6521(8)
11.9883(8)
12.0891(9)
77.496(1)
89.989(1)
76.808(1)
1465.4(2)
2
4.28–51.96
11; 11; 19
Tetragonal
P41
9.5338(6)
9.5338(6)
16.209(2)
90
90
90
1473.3(2)
4
1.629
4.52–52.4
10; 13; 22
Monoclinic
P21/c
8.1730(1)
10.8373(2)
17.9416(3)
90
114.589(1)
90
1445.04(4)
4
3.54–56.8
12; 14; 30
Orthorhombic
P212121
9.1961(2)
11.0473(3)
22.9704(5)
90
90
90
2333.6(1)
4
1.467
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
D
calc/g cm-3
1.729
1.669
1.660
1.526
F(000)
700
1.282
0.8825/0.8212
20655 (0.0271)
7677
6836
343
1.445/–0.458
0.0326/0.0809
0.0373/0.0831
1.070
748
1.163
0.9923/0.8268
22946 (0.0277)
8494
7406
379
1.077/–0.394
0.0299/0.0735
0.0355/0.0765
1.045
0.0388/0.4090
—
736
1.160
0.9038/0.7335
4821 (0.0298)
2352
2258
184
0.940/–0.839
0.0464/0.1304
0.0520/0.1377
1.385
0.0000/10.3862
-0.01(10)
736
1.182
0.9155/0.7945
25789 (0.0283)
2900
2688
184
0.411/–0.338
0.0183/0.0474
0.0203/0.0485
1.061
0.0228/0.9439
—
1064
0.757
0.8982/0.7076
61679 (0.0225)
5854
5778
289
0.310/–0.399
0.0165/0.0442
0.0170/0.0449
1.088
0.0265/0.5149
-0.008(14)
968
0.850
0.9123/0.7553
7908 (0.0335)
3912
3200
263
1.616/–0.572
0.0425/0.0959
0.0609/0.1045
1.004
0.0604/0.0000
0.13(5)
m/mm-1
Max/min transmission
Reflect. collected (Rint
Independent reflections
Obs. reflect. [I > 2s(I)]
Parameters refined
)
a
-3
˚
Max./min. Dr /e A
R1/wR2 [I > 2s(I)] b
R1/wR2 (all reflect.) b
Goodness-of-fit on F2
c
Weighting scheme w; a/b d 0.0360/1.9483
Flack parameter e
—
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2
2
a Largest difference peak and hole. b R1 = [ (ꢀFo| - |Fcꢀ)/ |Fo|]; wR2 = [ [w(Fo - Fc2)2]/ [w(Fo2)2]]1/2
.
c Goodness-of-fit = [ [w(Fo - Fc2)2]/
(n - p)]1/2
.
d w = 1/[s (Fo2) + (aP)2 + bP] where P = (max(Fo or 0) + 2Fc2)/3. e Absolute structure parameter.68
2
2
d = 17.6 (s, C18), 27.9, 28.2, 30.3, 30.7 (s, CH2cod), 72.3 (d, JC-Rh
14.1 Hz, CHcod), 73.4 (d, JC-Rh = 14.1 Hz, CHcod), 83.2 (d, JC-Rh
=
=
13 for aliphatic CH, 23 for CH2, AFIX 33 or 137 for CH3) with
U
iso(H) = 1.2Ueq(CH, CH2) and Uiso(H) = 1.5Ueq(CH3). Details of
11.8 Hz, CHcod), 83.7 (d, JC-Rh = 12.2 Hz, CHcod), 117.9 (s, C1),
121.1 (s, C3), 122.5 (s, C17), 124.9 (s, C6), 125.1 (s, C7), 126.3 (s,
C8), 127.3 (s, C5,15,16), 128.0 (s, C10), 129.6 (s, C14), 130.0 (s, C13),
134.1 (s, C4), 134.6 (s, C9), 150.9 (s, C12), 157.5 (s, C2), 166.4 (s,
C11). C26H26NORh (471.36) calcd C 66.25, H 5.56, N 2.97; found
C 67.30, H 5.88, N 2.21%.
the X-ray structure determinations and refinements are provided in
Table 5. Graphics were drawn with DIAMOND (Version 3.1f).67
Computations on the supramolecular interactions were carried
out with PLATON for Windows.58 p-Stacking interactions can be
viewed as medium to weak if they exhibit rather long centroid–
˚
centroid distances (Cg ◊ ◊ ◊ Cg> 4.0 A) together with large slip
◦
˚
angles (b, g > 30 ) and vertical displacements (d > 2.0 A).
In comparison, strong p-stackings show rather short centroid–
centroid contacts (< 3.8 A), small slip angles (b, g < 25 ) and
X-Ray crystallography
◦
˚
˚
Data collection. Bruker AXS with CCD area-detector, tem-
perature 173(2) K for 1 and 2, 203(2) K for 3–564, Mo-Ka
vertical displacements (d < 1.5 A) which translate into a sizable
overlap of the aromatic planes.51–53 CCDC reference numbers
˚
radiation (l = 0.71073 A), graphite monochromator, w-scans.
780787–780792 for 1–5, respectively.
Data collection and cell refinement with SMART,65 data re-
duction with SAINT,64 experimental absorption correction with
SADABS.66
Acknowledgements
Structure analysis and refinement. The structures were solved
by direct methods (SHELXS-97),67 refinement was done by full-
matrix least squares on F2 using the SHELXL-97 program suite.66
All non-hydrogen positions were refined with anisotropic tem-
perature factors. Hydrogen atoms on nitrogen (–NH) were found
and refined in 3S and 3rac with Uiso(H) = 1.2Ueq(N). Hydrogen
We thank the Alexander-von-Humboldt Foundation (AvH),
Bonn, for a fellowship to M. Enamullah. We acknowledge the
financial support from the Ministry of Science and Information &
Communication Technology (MSICT), Project 2004/05, Dhaka,
Bangladesh and from DFG-grant Ja466/14-1. We thank Dr Klaus
Ditrich (ChiPros) at BASF, Ludwigshafen for providing (R)-N-(4-
methoxyphenyl)ethylamine. We wish to express our sincere thanks
to Dr Jean-Pierre Djukic, University Louis Pasteur, Strasbourg for
his kind assistance with the attempted CD spectral measurements.
˚
atoms on carbon were positioned geometrically (C–H = 0.94 A for
˚
˚
˚
aromatic CH, 0.99 A for aliphatic CH, 0.98 A for CH2, 0.97 A for
CH3) and refined using a riding model (AFIX 43 for aromatic CH,
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 3698–3709 | 3707
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