Synthesis, characterization and Schlenk equilibrium studies of methylmagnesium compounds with O- and N-donor ligands - The unexpected behavior of [MgMeBr(pmdta)] (pmdta = N,N,N′,N″,N″- pentamethyldiethylenetriamine)

Article abstract of DOI:10.1016/j.jorganchem.2004.10.058

MgMe₂ (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex [{MgMe ₂(thf)}₂(μ-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt₃, and tmeda (N,N,N′,N′-tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt₃ (6); tmeda (7)) were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8) were obtained. Reactions of MgMeBr with pmdta (N,N,N′,N″,N″-pentamethyldiethylenetriamine) in thf resulted in formation of [MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta)·MgBr₂(pmdta) (10) and [{MgMe₂(pmdta)} ₇{MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe₂(pmdta)] (12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by microanalysis and ¹H and ¹³C NMR spectroscopy. The coordination-induced shifts of the ¹H and ¹³C nuclei of the ligands are small; the largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The single-crystal X-ray diffraction analyses of [MgMe₂(pmdta)] (12) and [MgBr ₂(pmdta)] (13) showed them to be monomeric with five-coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent ¹H NMR spectroscopic measurements (from 27 to -80°C) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); diglyme (5); NEt ₃ (6); tmeda (7)) in thf-d₈ solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted to the dimethylmagnesium/dibromomagnesium species. Furthermore, at -80°C the dimethylmagnesium compounds are predominant in the solutions of Grignard compounds 4-6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d₈ revealed no dismutation into [MgMe₂(pmdta)] (12) and [MgBr₂(pmdta)] (13) even up to -100°C. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of [MgMeBr(pmdta)] (9c), [MgMe₂(pmdta)] (12c), and [MgBr₂(pmdta)] (13c) were calculated on the DFT level of theory. The calculated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium constant of the Schlenk equilibrium (2 9c ? 12c + 13c) was calculated to be K _gas = 2.0 × 10^-3 (298 K) in the gas phase. Considering the solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were calculated to be K_thf = 1.2 × 10^-3 and K_ether = 3.2 × 10^-3 (298 K), respectively.

Full text of DOI:10.1016/j.jorganchem.2004.10.058

Journal of Organometallic Chemistry 690 (2005) 1178–1191
www.elsevier.com/locate/jorganchem
Synthesis, characterization and Schlenk equilibrium studies of
methylmagnesium compounds with O- and N-donor ligands –
the unexpected behavior of [MgMeBr(pmdta)]
0
00
00
(
pmdta = N,N,N ,N ,N -pentamethyldiethylenetriamine)
a
b
b
a
Rushdi I. Yousef , Bernhard Walfort , Tobias R u¨ ffer , Christoph Wagner ,
a
Harry Schmidt , Renate Herzog , Dirk Steinborn
a
a,
*
a
Institut f u¨ r Anorganische Chemie, Martin-Luther-Universit a¨ t Halle-Wittenberg, Kurt-Mothes-Straße 2, 06120 Halle/Saale, Germany
b
Institut f u¨ r Chemie, Technische Universit a¨ t Chemnitz, Straße der Nationen 62, 09107 Chemnitz, Germany
Received 23 September 2004; accepted 28 October 2004
Available online 7 February 2005
Abstract
MgMe (1) was found to react with 1,4-diazabicyclo[2.2.2]octane (dabco) in tetrahydrofuran (thf) yielding a binuclear complex
2
[
{MgMe
tmeda (N,N,N ,N -tetramethylethylenediamine) in etheral solvents compounds MgMeBr(L), (L = diglyme (5); NEt
2
(thf)}
0
2
(l-dabco)] (2). Furthermore, from reactions of MgMeBr with diglyme (diethylene glycol dimethyl ether), NEt
3
, and
(6); tmeda (7))
0
3
were obtained as highly air- and moisture-sensitive white powders. From a thf solution of 7 crystals of [MgMeBr(thf)(tmeda)] (8)
0
00
00
were obtained. Reactions of MgMeBr with pmdta (N,N,N ,N ,N -pentamethyldiethylenetriamine) in thf resulted in formation of
MgMeBr(pmdta)] (9) in nearly quantitative yield. On the other hand, the same reaction in diethyl ether gave MgMeBr(pmdta) Æ
MgBr (pmdta) (10) and [{MgMe (pmdta)} {MgMeBr(pmdta)}] (11) in 24% and 2% yield, respectively, as well as [MgMe (pmdta)]
12) as colorless needle-like crystals in about 26% yield. The synthesized methylmagnesium compounds were characterized by micro-
[
2
2
7
2
(
1
13
1
13
analysis and H and C NMR spectroscopy. The coordination-induced shifts of the H and C nuclei of the ligands are small; the
largest ones were found in the tmeda and pmdta complexes. Single-crystal X-ray diffraction analyses revealed in 2 a tetrahedral
environment of the Mg atoms with a bridging dabco ligand and in 8 a trigonal-bipyramidal coordination of the Mg atom. The sin-
2 2
gle-crystal X-ray diffraction analyses of [MgMe (pmdta)] (12) and [MgBr (pmdta)] (13) showed them to be monomeric with five-
coordinate Mg atoms. The square-pyramidal coordination polyhedra are built up of three N and two C atoms in 12 and three
N and two Br atoms in 13. The apical positions are occupied by methyl and bromo ligands, respectively. Temperature-dependent
1
H NMR spectroscopic measurements (from 27 to ꢀ80 ꢀC) of methylmagnesium bromide complexes MgMeBr(L) (L = thf (4); dig-
3 8
lyme (5); NEt (6); tmeda (7)) in thf-d solutions indicated that the deeper the temperature the more the Schlenk equilibria are shifted
to the dimethylmagnesium/dibromomagnesium species. Furthermore, at ꢀ80 ꢀC the dimethylmagnesium compounds are predom-
inant in the solutions of Grignard compounds 4–6 whereas in the case of the tmeda complex7 the equilibrium constant was roughly
estimated to be 0.25. In contrast, [MgMeBr(pmdta)] (9) in thf-d
MgBr
(pmdta)] (13) even up to ꢀ100 ꢀC. In accordance with this unexpected behavior, 1:1 mixtures of 12 and 13 were found to
react in thf at room temperature yielding quantitatively the corresponding Grignard compound 9. Moreover, the structures of
MgMeBr(pmdta)] (9c), [MgMe (pmdta)] (12c), and [MgBr (pmdta)] (13c) were calculated on the DFT level of theory. The calcu-
lated structures 12c and 13c are in a good agreement with the experimentally observed structures 12 and 13. The equilibrium con-
8 2
revealed no dismutation into [MgMe (pmdta)] (12) and
[
2
[
2
2
ꢀ
3
stant of the Schlenk equilibrium (2 9c ꢀ 12c + 13c) was calculated to be Kgas = 2.0 · 10 (298 K) in the gas phase. Considering the
*
Corresponding author. Tel.: +49 345 55 25620; fax: +49 345 552 7028.
E-mail address: steinborn@chemie.uni-halle.de (D. Steinborn).
0
022-328X/$ - see front matter ꢁ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.10.058

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1179
solvent effects of both thf and diethyl ether using a polarized continuum model (PCM) the corresponding equilibrium constants were
ꢀ3
ꢀ3
calculated to be Kthf = 1.2 · 10 and Kether = 3.2 · 10 (298 K), respectively.
2004 Elsevier B.V. All rights reserved.
ꢁ
0
00
00
Keywords: Methylmagnesium bromide; Dimethylmagnesium; Grignard compounds; Pmdta (N,N,N ,N ,N -pentamethyldiethylenetriamine);
Schlenk equilibrium; DFT calculations
1
. Introduction
most widely used route to MgR is the exchange reac-
2
tion between excess magnesium metal and organomer-
cury compounds [12]. The high toxicity of
organomercurials is a severe drawback of this method.
The real composition of organomagnesium reagents
(especially Grignard compounds I) both in solution
and in the solid state is far more complex than it is ex-
pressed by such simple formula like I and II [4]. Rela-
tively few information on their solid-state structures
[13–15] has been known because in most cases reagents
I and II were used in situ. Thus, even with the most sim-
ple organo ligand, i.e. the methyl group, only one ‘‘clas-
For 100 years organomagnesium compounds have
been the most important reagents in organic and orga-
nometallic synthesis [1–3]. Probably most widely used
are Grignard compounds MgRX(L) (I, R = alkyl, aryl;
X = halide) and diorganomagnesium compounds
MgR (L) (II). Their structures and their reactivities
2
are strongly dependent on the co-ligands L and on the
solvents [4]. In 1929, Schlenk and Schlenk Jr. [5] found
that the addition of dioxane to etheral solutions of Grig-
nard compounds MgRX (X = halide, R = alkyl, aryl) re-
sults in precipitation of magnesium halides. This
observation gave proof for the dynamic behavior of
Grignard compounds, which is known today as the
Schlenk equilibrium. A simple representation of the
equilibrium is given in Scheme 1 showing the ‘‘basic’’
Schlenk equilibrium (a) as well as (schematically) the
formation of homo-oligomers (b/c) and the hetero-dimer
sical’’
characterized, namely [MgMeBr(thf) ] having a trigo-
Grignard
compound
was
structurally
3
nal-bipyramidal monomeric structure [16]. Further-
more, a tetranuclear complex [Mg Me (l -Cl) (thf) ]
4
2
2
6
6
that can be considered as a [MgCl (thf) ] adduct of
2
2
[MgMeCl(thf)] [17] and a trinuclear magnesium amide
cluster [MgI(thf) ][(MgI) (l -Me){SiMe(Nt-Bu) }(thf)]
5
3
2
3
(
d). Positions of all these equilibria are dependent on the
[18] having the building block IMg(l-Me)MgI have
been structurally characterized.
nature of X and R, the concentration, and the tempera-
ture. Furthermore, they are critically dependent on the
solvent with the generalization that in better coordinat-
ing solvents the monomeric species predominate and the
position of the Schlenk equilibrium a tends to be shifted
to the dismutation products [6,7]. In the last years high-
level ab initio molecular orbital and density-functional
studies provided further insight into the solvation effects
on the Schlenk equilibrium [8–11].
Several routes to organomagnesium compounds were
reported. The most important ones are the direct oxida-
tive addition of an organic halide to magnesium metal,
exchange reactions (metal–hydrogen exchange, metal–
halogen exchange), and the addition of a Grignard re-
agent to an unsaturated bond (carbomagnesiation)
In this work, we describe reactions of MgMe and
2
MgMeBr with different O- and N-donors being mono-
dentate (thf, NEt ), chelating and bridging biden-
3
0
0
tate (N,N,N ,N -tetramethylethylenediamine, tmeda;
1,4-diazabicyclo[2.2.2]octane, dabco), and tridentate
0
(diethylene glycol dimethyl ether, diglyme; N,N,N ,
00
00
N ,N -pentamethyldiethylenetriamine, pmdta) ligands.
Thereby, some novel methylmagnesium complexes were
synthesized, isolated in the solid state, and characterized
1
by means of microanalysis, NMR spectroscopy ( H,
1
C), and partially also by single-crystal X-ray diffrac-
3
tion analysis. Furthermore, we studied Schlenk equilib-
ria of some of these Grignard compounds (MgMeBr(L),
L = thf, NEt , diglyme, tmeda, pmdta) in thf solution as
3
1
[
6,7]. The addition of 1,4-dioxane to an etheral Grignard
based on H NMR measurements showing that in the
solution, followed by removal of the precipitated diox-
ane complex of the magnesium dihalide is a common
procedure for obtaining MgR [5] although the latter
case of the pmdta complex the equilibrium lies com-
pletely on the side of [MgMeBr(pmdta)]. Further insight
into this unexpected behavior was obtained from DFT
calculations.
2
usually contains some residual halogen [3,6]. The second
Scheme 1. Schlenk equilibrium (a) and formation of associated species (b–d). For simplicity, solvent molecules are excluded.

1180
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
2
. Results and discussion
MgMeBr(diglyme) (5) in 57% yield (Scheme 3). Reac-
tion of MgMeBr with a threefold excess of triethylamine
2
.1. Syntheses
in diethyl ether followed by addition of n-hexane re-
sulted in the formation of MgMeBr(NEt ) (6) as a white
highly air- and moisture-sensitive powder in nearly
3
Unsolvated dimethylmagnesium (1) was obtained by
0
0
the well known ‘‘dioxane route’’ [5] from reaction of
MgMeBr with 1,4-dioxane in diethyl ether as colorless
crystals in 29% yield. The bromine content was deter-
mined to be less than 0.2%. Reaction of 1,4-diazabicy-
clo[2.2.2]octane (dabco) with a twofold excess of 1 in
tetrahydrofuran and then cooling down to ꢀ40 ꢀC re-
sulted in the formation of [{MgMe (thf)} (l-dabco)]
quantitative yield (Scheme 3). Addition of N,N,N ,N -
tetramethylethylenediamine (tmeda) to a diethyl ether
solution of MgMeBr in an equimolar ratio proved to
be strongly exothermic and resulted in precipitation of
MgMeBr(tmeda) (7) also as a white powder in nearly
quantitative yield. From a thf solution of 7 well shaped
colorless crystals were crystallized at ꢀ40 ꢀC; single-
crystal X-ray diffraction analysis revealed the formation
of a thf adduct [MgMeBr(thf)(tmeda)] (8). Drying these
crystals in vacuo at room temperature for 1/2 h resulted
in removing the thf molecule yielding again 7. The over-
all composition for compounds 5–7 was deduced from
microanalysis and NMR measurements.
2
2
(2), a binuclear complex with dabco acting as a bridging
ligand. Complex 2 was obtained in 84% yield as color-
less highly air- and moisture-sensitive crystals (Scheme
2
characterized by microanalysis, NMR spectroscopy,
and complex 2 also by single-crystal X-ray diffraction
analysis.
Evaporating the solvent from the solution of com-
mercial MgMeBr (3 M in Et O) at low pressure and dry-
ing the residue in vacuo for 1 h resulted in formation of
a compound having the composition MgMeBr(Et O)
). Both dimethylmagnesium compounds 1 and 2 were
Reaction of MgMeBr with an equimolar amount of
0
00
00
N,N,N ,N ,N -pentamethyldiethylenetriamine (pmdta)
in tetrahydrofuran at room temperature revealed a clear
solution. Cooling down to ꢀ40 ꢀC provided a white
powdery precipitate of [MgMeBr(pmdta)] (9) in nearly
quantitative yield. On the other hand, the addition of
pmdta to a diethyl ether solution of MgMeBr, instead
of a thf solution, resulted in exothermic formation of a
white powder having the composition MgMeBr(pmd-
2
2
(
3). Dissolving 3 in thf provided the substitution of
diethyl ether by thf. Evaporating the solvents in vacuo
and drying the residue at 50 ꢀC gave a white powder
of the composition MgMeBr(thf) (4). Compounds 3
and 4 were isolated in quantitative yields (Scheme 3).
Equimolar amounts of MgMeBr and diglyme were
reacted in thf solution. After stirring overnight the clear
solution was cooled down to ꢀ80 ꢀC to form a small
quantity of crystals of the composition [MgBr (thf) ].
ta) Æ MgBr (pmdta) (10). After filtering off 10, n-hexane
2
was added to the filtrate to precipitate a small amount
of white powder [{MgMe (pmdta)} {MgMeBr(pmd-
2
7
ta)}] (11). After filtration, concentrating the filtrate in
vacuo again and cooling down to ꢀ40 ꢀC gave rise to
2
4
After filtering off these crystals, the filtrate was concen-
trated in vacuo to form a white precipitate of
formation of big colorless needles of [MgMe (pmdta)]
2
(12). Referring to the total magnesium content, precipi-
tates 10, 11, and 12 were isolated in 24%, 2%, and 26%
yields, respectively. The latter represents 52% of the the-
oretical yield of [MgMe (pmdta)] (Scheme 4).
2
The constitutions of precipitates 10 and 11 were de-
duced by microanalysis. Several parallel experiments
afforded reproducible analytical results for both 10
and 11. Furthermore, after filtering off compound 10,
2 2
Scheme 2. Synthesis of [{MgMe (thf)} (l-dabco)] (2).
2 3
Scheme 3. Syntheses of MgMeBr(L) (L = Et O (3); thf (4); diglyme (5); NEt (6); tmeda (7)) and [MgMeBr(thf)(tmeda)] (8).

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1181
2
Scheme 4. Reactions of MgMeBr with pmdta in thf and in Et O.
the filtrate was cooled down to 5 ꢀC to give colorless
well-shaped crystals. The X-ray structure analysis of
these crystals proved to be 11 Æ 2Et O in full agreement
2
C7
with the analytical results. The constitution of 12 was
confirmed by NMR spectroscopy and single-crystal X-
ray diffraction analysis. In most cases, 12 proved to be
free of bromide. In few cases, some bromide traces were
detected, thus 12 was recrystallized again from diethyl
ether to provide completely bromide-free dimethylmag-
nesium pmdta complex.
O
Mg´
N
C9
N´
C2
Mg
C1
C8
The complex [MgMe (pmdta)] (12) was indepen-
2
dently obtained by the reaction of MgMe with pmdta
2
C9a
in diethyl ether [19]. For this synthesis halide-free
MgMe was used as a starting material that is difficult
C9b
2
N
C8b
C8a
to be synthesized in the ‘‘dioxane route’’ [3,6]. More-
over, the alternative transmetalation route using Mg
and HgMe should be excluded due to the extraordi-
Mg
Mg´
C7a
2
C7b
narily high toxicity of the latter. Consequently, the route
to 12, as discussed in this paper, starting from easily
accessible and less expensive MgMeBr and pmdta may
Fig. 1. Molecular structure of [{MgMe
2
2
(thf)} (l-dabco)] (2) (top) and
disorder of the bridging dabco ligand (bottom). The two disordered
positions are termed ‘‘a’’ and ‘‘b’’, atoms generated by a C axis are
2
be superior to the ‘‘classical’’ route from MgMe and
2
marked with an asterisk. Selected bond lengths ( A˚ ) and angles (ꢀ): Mg–
C1 2.127(4), Mg–C2 2.133(4), Mg–O 2.071(3), Mg–N 2.208(3); C1–
pmdta.
Mg–C2 130.4(2), C1–Mg–O 105.2(2), C1–Mg–N 107.0(1), C2–Mg–O
1
06.4(2), C2–Mg–N 105.9(2), O–Mg–N 97.0(1).
2
.2. Structures
Single crystals of compound 2 were found to be built
up from binuclear molecules without unusual intermo-
lecular contacts (shortest distance between non-hydro-
bridging dabco ligands are rare. Apart from 2, only
two structures were reported in literature, namely
[(MMe ) (l-dabco)] (M = Al, Ga) [20].
Crystals of [MgMeBr(thf)(tmeda)] (8) contain iso-
lated molecules without unusual intermolecular contacts
(shortest distance between non-hydrogen atoms is >3.7
3
2
˚
gen atoms is >3.5 A). The molecular structure of
[
{MgMe (thf)} (l-dabco)] (2) is shown in Fig. 1 with se-
2 2
lected bond lengths and angles in the figure caption. The
carbon atoms of the dabco ligand are disordered over
two equally occupied positions amounting to an overall
˚
A). The molecular structure is shown in Fig. 2 with se-
lected bond lengths and angles in the figure caption.
The atoms of the thf ligand show a disorder over two
equally occupied positions. Furthermore, the methyl
and the bromo ligands are mutually disordered with
an occupancy ratio of 0.64/0.36. Magnesium is coordi-
nated in a trigonal bipyramide by carbon, bromine,
oxygen, and two nitrogen atoms. As usual for trigo-
nal-bipyramidal structures [21], the more electronegative
ligands (thf, one N of tmeda) occupy the apical posi-
tions. The angle O–Mg–N2 is 166.5(5)ꢀ/161.9(6)ꢀ. Sum
‘
‘rotation’’ of dabco around the Nꢁ ꢁ ꢁN axis by about
4
imposed C symmetry. The magnesium atoms are tetra-
5ꢀ. The binuclear complex exhibits crystallographically
2
hedrally coordinated; the donor set is made up of one
nitrogen, one oxygen, and two carbon atoms. The angle
C1–Mg–C2 (130.4(2)ꢀ) is widened up at the expense of
the O–Mg–N angle (97.0(1)ꢀ); all other angles are close
to the tetrahedral standard (105.2(2)–107.0(1)ꢀ). Note-
worthy, binuclear main-group metal complexes with

1182
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
mutual disorder between the methyl group and the bro-
mine is described in the Section 3.3. Due to that, the
numerical values given in the figure caption must not
be overestimated.
N1
The pmdta complexes [MgMe (pmdta)] (12) and
2
O
Mg
[MgBr (pmdta)] (13) crystallize also in the monoclinic
2
N2
C1
space group P2 /c with two crystallographically inde-
1
pendent molecules in the asymmetric unit. The struc-
tures of these molecules are very similar, one of them
is shown in Figs. 4 and 5 with selected bond lengths
and angles in the figure captions. Viebrock and Weiss
Br
Fig. 2. Molecular structure of [MgMeBr(thf)(tmeda)] (8). Only one of
disordered positions of Br/C1 and of thf atoms is shown (see Section
˚
[19] prepared complex 12 from MgMe2 and pmdta.
They found essentially the same structure.
3
.3). Selected bond lengths (A) and angles (ꢀ) (for disordered positions
In both complexes the magnesium atoms are five-
coordinated by three nitrogen and two carbon atoms
in 12 and three nitrogen and two bromine atoms in 13.
The coordination polyhedra can be regarded as dis-
torted square pyramides where the apical positions are
occupied by a methyl ligand (C1) and a bromo ligand
both values are given separated by a slash; in the case of Br/C1
disorder values of the major occupied positions are given first): Mg–C1
2.25(1)/2.27(1), Mg–Br 2.485(1)/2.434(2), Mg–O 2.204(9)/2.22(1), Mg–
N1 2.246(2), Mg–N2 2.334(3); N2–Mg–O 166.5(5)/161.9(6), C1–Mg–
Br 126.0(4)/117.3(5), C1–Mg–N1 127.4(4)/111.9(5), N1–Mg–Br
106.57(7)/130.68(9).
(Br1), respectively. The bond lengths of the apical li-
of angles of the equatorial ligands (Br, C1, N1) is 360.0ꢀ/
59.9ꢀ. A trigonal-bipyramidal geometry is an exception
from the tendency to form a tetrahedral structure in nor-
mal Grignard reagents [15]. This may be due to the small
size of the methyl group and the electronegativity of the
bromo ligand. The only reported structure of a methyl-
gands are significantly shorter than those of the corre-
sponding basal ligands. Thus, the differences in the
Mg–C and Mg–Br bond lengths amount to 0.036/0.016
3
˚
and 0.061/0.089 A, respectively. The apical ligands
include angles with the basal ones in 12 between
99.4(2)–114.5(2)ꢀ/100.4(1)–115.8(1)ꢀ and in 13 between
99.4(2)–113.2(2)ꢀ/98.7(2)–110.3(2)ꢀ.
magnesium bromide, namely [MgMeBr(thf) ], shows
3
also a disorder of the methyl and bromo ligands [16].
The Mg atom in this complex has a trigonal-bipyrami-
dal coordination with two thf ligands in apical positions.
2.3. NMR spectroscopic measurements
1
13
1
Furthermore, the Mg–C bonds in complex 2 (C.N. 4;
2
The H and C resonances as well as the J(C,H)
coupling constants of methyl groups in the dimethyl-
magnesium and Grignard compounds described before
˚
.127(4)/2.133(4) A) are found to be shorter than those
˚
in complex 8 (C.N. 5; 2.25(1)/2.27(1) A) being consistent
with Gutmannꢀs bond-length variation rules [22].
in thf-d solutions are given in Table 1. The coordina-
8
[
Et O) crystallizes in the monoclinic space group
{MgMe (pmdta)} {MgMeBr(pmdta)}] Æ 2Et O (11 Æ
tion-induced shift differences Dd and Dd for hydrogen
and carbon atoms of the ligands and the corresponding
1
changes of J(C,H) coupling constants are given in Ta-
2
7
2
H
C
2
P2 /c. The asymmetric unit contains two molecules of
2
1
[
tively, and a half molecule of Et O, see Fig. 3. The
MgMe (pmdta)] and [MgMe1.75Br0.25(pmdta)], respec-
ble 2. As shown in the synthesis of MgMeBr(thf) (4),
the diethyl ether molecule in MgMeBr(Et O) (3) is
2
2
2
C3
N3
C4
Mg2
C2
N6
N2
C1 (0.75)
Mg1
N4
N5
N1
Br (0.25)
Fig. 3. Molecular structure of [{MgMe
2
7 2 2
(pmdta)} {MgMeBr(pmdta)}] Æ 2Et O (11 Æ 2Et O). Hydrogen atoms and solvent molecules were omitted for
˚
clarity. In parentheses site occupancies of disordered atoms are given. Selected bond lengths (A) and angles (ꢀ): Mg1–C1 2.238(6), Mg1–C2 2.161(2),
Mg1–Br 2.580(2), Mg2–C3 2.256(2), Mg2–C4 2.247(2); C1–Mg1–C2 113.6(2), Br–Mg1–C2 111.7(1), C3–Mg2–C4 114.99(7).

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1183
cleaved off in thf (see Section 2.1). In accord with this
observation, the NMR spectra of compounds 3 and 4
in thf are identical. The same holds for the triethylamine
adduct 6. The NMR data (Table 1) and the negligible
coordination-induced shifts (Table 2) indicate that even
N2
N3
N1
C1
NEt may be substituted by a thf molecule in excess thf.
3
Mg1
The resonances for methyl H and C atoms were high-
field shifted and were found between ꢀ1.67 and ꢀ1.80
ppm (d ) and ꢀ13.2 and ꢀ16.9 ppm (d ). Such high-
H
C
C2
(pmdta)] (12); displacement
ellipsoids at 30% probability. One of the two crystallographically
field shifts can be rationalized in terms of the polarity
of Mg–CH bonds [23]. The coupling constants
3
Fig. 4. Molecular structure of [MgMe
2
1
J(C,H) for the compounds shown in Table 1 were
˚
independent molecules is shown. Selected bond lengths (A) and angles
found to be within the range from 104.6 to 106.7 Hz
revealing no significant dependence on the nature of
coordinated ligands. These relatively low values reflect
high s-electron densities in the Li–C bonds being consis-
tent with the high electropositive character of Li and
with Bentꢀs rules [24].
(ꢀ) (values for the two crystallographically independent molecules are
given separated by a slash): Mg1–C1 2.162(3)/2.186(2), Mg1–C2
2
2
.198(3)/2.202(2), Mg1–N1 2.347(2)/2.350(2), Mg1–N2 2.424(2)/
.391(2), Mg1–N3 2.357(2)/2.358(2); C1–Mg1–C2 114.5(2)/115.8(1),
C1–Mg1–N1 106.7(2)/106.6(1), C1–Mg1–N2 99.4(2)/100.4(1), C1–
Mg1–N3 108.5(2)/108.12(9), N1–Mg1–N3 136.07(8)/137.42(7).
Some general trends for proton and carbon chemical
shifts could be deduced according to the nature of the
ligand. Although the differences are small, the methyl
protons of MgMeBr(L) resonate at slightly lower field
for L = N-donor compared with L = O-donor, in con-
trast to dimethylmagnesium compounds where the
opposite was found. On the other hand, the methyl-car-
bon resonances of complexes having chelating N-donor
ligands are low-field shifted for both Grignard com-
pounds and dimethylmagnesiums. Furthermore, methyl
N2
Br1
N1
N3
Mg1
protons and carbon atoms in MgMe (L) compounds
2
resonate at higher field compared with MgMeBr(L) (1
versus 4 and 12 versus 9).
Br2
The coordination-induced shifts DdH and Dd for H
C
and C atoms of the ligands as well as the differences in
1
J(C,H) coupling constants are relatively small in all
2
Fig. 5. Molecular structure of [MgBr (pmdta)] (13); displacement
ellipsoids at 30% probability. One of the two crystallographically
˚
independent molecules is shown. Selected bond lengths (A) and angles
compounds under investigation (Table 2). In general,
the same was found for these ligands in organolithium
compounds [25]. Furthermore, the figures in Table 2
show that the strongest coordinating ligands (tmeda
and pmdta) give rise to the highest induced shifts (Dd).
(ꢀ) (values for the two crystallographically independent molecules are
given separated by a slash): Mg1–Br1 2.501(2)/2.482(2), Mg1–Br2
2
2
1
9
1
.562(2)/2.571(2), Mg1–N1 2.205(6)/2.208(6), Mg1–N2 2.297(6)/
.310(6), Mg1–N3 2.224(5)/2.231(5); Br1–Mg1–Br2 103.02(7)/
04.43(9), Br1–Mg1–N1 107.3(2)/110.3(2), Br1–Mg1–N2 99.4(2)/
8.7(2), Br1–Mg1–N3 113.2(2)/108.1(2), N1–Mg1–N3 136.7(2)/
37.9(2).
2.4. Schlenk equilibria in methylmagnesium bromide
complexes
Table 1
1
Methylmagnesium bromide complexes MgMeBr(L)
(L = thf (4); diglyme (5); NEt (6); tmeda (7); pmdta
13
1
The H and C resonances (d in ppm) as well as J(C,H) coupling
constants (J in Hz) of methyl groups in methylmagnesium compounds
3
(9)) as well as the dimethylmagnesium compounds
MgMe (1) and [MgMe (pmdta)] (12) in thf-d solutions
at room temperature revealed sharp singlets for the
1–7, 9, 12 in thf-d
8
(concentration: 0.04 M, 27 ꢀC)
2
2
8
1
Compound
d
H
d
C
J(C,H)
1
methyl resonances in both H and C NMR spectra.
13
MgMeBr(Et O) (3)
MgMeBr(thf) (4)
MgMeBr(diglyme) (5)
2
ꢀ1.71
ꢀ1.70
ꢀ1.71
ꢀ1.71
ꢀ1.67
ꢀ1.67
ꢀ1.77
ꢀ1.77
ꢀ1.80
ꢀ16.4
ꢀ16.3
ꢀ16.0
ꢀ16.5
ꢀ15.5
ꢀ13.2
ꢀ16.9
ꢀ16.8
ꢀ14.1
106.3
106.6
106.4
105.4
106.7
106.0
105.7
105.6
104.6
1
Down to ꢀ80 ꢀC, H NMR spectrum of MgMe (1) in
2
thf-d (0.04 mol/l) did show neither signal splitting nor
8
MgMeBr(NEt
MgMeBr(tmeda) (7)
MgMeBr(pmdta)] (9)
MgMe (1)
{MgMe (thf)}
MgMe (pmdta)] (12)
3
) (6)
broadening. This is fully consistent with the proposed
monomeric constitution of MgMe in thf solution at
[
2
2
room temperature [26,27]. In contrast, MgMe in diethyl
2
[
[
2
2
(l-dabco)] (2)
ether is known to be associated via methyl bridges, thus
showing at ꢀ80 ꢀC two separated signals due to different
2

1184
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
Table 2
(ꢀ1.83 ppm) was attributed to MgMe monomer and
2
1
13
1
The differences of H and C resonances (Dd in ppm) and of J(C,H)
coupling constants (DJ in Hz) for coordinated ligands in methylmag-
nesium compounds 2, 5–7, 9, 12 and corresponding free ligands in thf-
a smaller one (ꢀ1.70 ppm) to terminal sites in associated
species [27]. Thus, our investigations gave evidence that
MgMe in thf remains to be monomeric even at ꢀ80 ꢀC
d
8
at 27 ꢀC
2
a
1
a
at a concentration of 0.04 mol/l.
To gain an insight into the dynamic behavior of
Compound
Ligand
Dd
H
C
Dd (D J(C,H))
5
diglyme
CH
CH
3
+0.05
+0.08
+0.7 (+0.8)
ꢀ0.4 (+1.7)
ꢀ0.4 (+1.2)
[MgMeBr(tmeda)] (7), the dependence of the methyl
proton resonance on concentration as well as on temper-
2
+
0.08
ature was investigated in thf-d (Fig. 6). The spectra of 7
8
6
NEt
3
CH
CH
3
ꢀ0.01
ꢀ0.01
ꢀ0.1 (+0.2)
(concentrations 0.04–0.25 mol/l) revealed that the shift
2
0.0 (0.0)
of the methyl protons is not markedly dependent on
concentration. On the other hand, lowering the temper-
ature of the solution resulted via line broadening into
signal splitting; at ꢀ60 ꢀC and below two sharp signals
were observed.
2
7
dabco
tmeda
CH
2
+0.02
ꢀ0.2 (0.0)
+0.8 (+1.3)
CH
CH
3
+0.17
+0.17
2
ꢀ1.2 (+2.9)
+1.9 (+3.7)
+0.6 (+6.7)
9
pmdta
pmdta
CH
3
N
+0.16
+0.23
1
(
CH
3
)
2
N
N
The temperature dependence of H NMR spectra
for MgMeBr(thf) (4), MgMeBr(diglyme) (5), and
MgMeBr(NEt ) (6) in thf-d solutions is shown in Fig.
12
CH
3
N
+0.10
+0.05
+0.3 (+2.6)
+1.5 (+3.8)
1
(
3
CH )
2
3
8
a
1
1
Dd = dcoord.-lig. ꢀ dfree-lig.. D J(C,H) = J(C,H)coord.-lig. ꢀ J(C,H)free-lig.
.
7. As for 7, at ꢀ60 ꢀC and below two sharp singlet res-
1
onances were observed. Comparison with the H NMR
spectra of MgMe (1) at temperatures down to ꢀ80 ꢀC
2
methyl groups (terminal, bridging) [28]. But also in con-
centrated thf solutions of MgMe (0.86 mol/l) signal
splitting was observed at ꢀ76 ꢀC. A major signal
(see Fig. 7(d)) makes clear that the high-field shifted sig-
nal has to be assigned to dimethylmagnesium and the
low-field shifted signal to methylmagnesium bromide.
This order can be attributed to the deshielding caused
by the electronegative bromo ligand, but the reverse or-
der was also observed [6]. Inspection of the ratio of
intensities showed that the lower the temperature the
more the Schlenk equilibrium (Scheme 5, L = thf (4);
diglyme (5); NEt (6); tmeda (7)) is shifted to MgMe /
2
3
2
MgBr . At ꢀ80 ꢀC the equilibrium constant for the tme-
2
da complex 7 can be roughly estimated to be approxi-
mately 0.25. On the other hand, in complexes 4–6 the
dimethylmagnesium species are predominant; equilib-
rium constants were estimated to be about 5 to 10 at
ꢀ
80 ꢀC. As discussed in Section 2.3, the triethylamine li-
gand in 6 may be substituted by thf in excess thf solvent.
1
In sharp contrast to the H NMR spectra of 4–7,
1
Fig. 6. Low-temperature H NMR spectra of methyl protons for
an unexpected behavior of the pmdta complex
[MgMeBr(pmdta)] (9) was observed (Fig. 8). Cooling
[
8
MgMeBr(tmeda)] (7) in thf-d (concentration dependence: 0.04 M,
left; 0.12 M, middle; 0.25 M, right).
1
Fig. 7. Low-temperature H NMR spectra of methyl protons for (a) MgMeBr(diglyme) (5), (b) MgMeBr(NEt
3
) (6), (c) MgMeBr(thf) (4), and (d)
2 8
MgMe (1) in thf-d (concentration: 0.04 M).

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1185
(
(
12c), [MgBr (pmdta)] (13c), and [MgMeBr(pmdta)]
2
9c) are shown in Fig. 9, selected bond lengths and an-
Scheme 5. Schlenk equilibrium (L = thf, diglyme, NEt
3
, tmeda,
gles are given in Table 3. Calculated structures
MgMe (pmdta)] (12c) and [MgBr (pmdta)] (13c) are
pmdta).
[
2
2
consistent with the experimentally found structures 12
and 13, respectively. Although there are some deviations
in bond lenghts and angles, all important structural fea-
tures are correctly reflected in the calculated structures.
The two structures are best described as square pyrami-
des with apical methyl and bromo ligand, respectively;
there are severe distortions from trigonal bipyramides
as shown by the angles N1–Mg–N3 137.0ꢀ for 12c and
1
40.3ꢀ for 13c (to be expected 180ꢀ in undistorted trigo-
nal bipyramides). The Mg–L bonds are considerably
ap
˚
shorter than the Mg–Leq bonds by 0.011 A for L = Me
˚
and 0.064 A for L = Br. The angles between these two
ligands are 121.4ꢀ (12c) and 109.8ꢀ (13c). As for the
experimentally found structures 12 and 13 the more elec-
tronegative bromo ligands in 13c give rise to shorter
Mg–N bonds than in 12c. Furthermore, the Mg–N
bonds of the two terminal N atoms of the pmdta ligands
1
Fig. 8. Low-temperature H NMR spectra of methyl protons for
[
2 8
MgMeBr(pmdta)] (9) (left) and [MgMe (pmdta)] (12) (right) in thf-d
(concentration: 0.04 M).
˚
˚
are shorter by 0.069 A (12c) and 0.100 A (13c) than that
of the middle N atom.
thf-d solutions of 9 from room temperature down to
8
ꢀ
100 ꢀC did not result in signal splitting but only in a
slight high-field shift of the signal by about 0.1 ppm.
An analogous structure was calculated for the Grig-
nard type compound [MgMeBr(pmdta)] (9c), see Fig.
9 and Table 3. Experimental data for the structure of
‘‘pure’’ [MgMeBr(pmdta)] are not available. The only
available compound is [{MgMe (pmdta)} {Mg-
Furthermore, as for [MgMe (pmdta)] (12) a slight line
2
broadening was observed at ꢀ100 ꢀC, which may be
attributed to changes in solvent viscosity and to decreased
quadrupolar relaxation time at lower temperatures
2
7
MeBr(pmdta)}] Æ 2Et O (11 Æ 2Et O) (Fig. 3) where the
2
2
[
29].
MgBr (pmdta)] (13) proved to be sparingly soluble
in thf. But it was found to be dissolved immediately in
structure of the [MgMeBr(pmdta)] molecule is close to
the calculated structure 9c. In complex 9c the apical po-
sition of the distorted square pyramide is occupied by
the more electronegative bromo ligand. Compared with
the ‘‘symmetrically’’ substituted dimethyl- and dibromo
compound 12c and 13c, respectively, the Mg–C bond is
[
2
the presence of one equivalent of [MgMe (pmdta)]
2
(
ing quantitatively [MgMeBr(pmdta)] (9). In accordance
1
with this observation, H NMR investigations of the
12), which indicates a complete reaction with 12 yield-
˚
found to be shorter by 0.031 A and the Mg–Br bond
˚
longer by 0.061 A. The Mg–N bond lengths in the Grig-
reaction mixture of 12 and 13 exhibited only one sharp
signal for methyl protons of 9 at ꢀ1.68 ppm. To prove
definetely that this is not a time averaged signal of
nard compound 9c are shorter than those in the di-
methyl compound 12c but longer than those in the
magnesium dibromide complex 13c.
The energy for the disproportionation of the Grig-
nard compound
9/12 due to fast exchange reactions, more than one equiv-
alent of [MgMe (pmdta)] (12) was reacted with 9. Con-
2
sequently, two signals were observed namely one at
ꢀ
1.68 ppm for [MgMeBr(pmdta)] (9) and another one
2
½MgMeBrðpmdtaÞꢂ ꢀ ½MgMe ðpmdtaÞꢂ
2
12c
at ꢀ1.81 ppm for the surplus [MgMe (pmdta)] (12).
2
9c
Thus, it was clearly shown that the position of the
Schlenk equilibrium (Scheme 5, L = pmdta) in thf – even
at room temperature – lies completely on the side of the
Grignard reagent.
þ ½MgBr ðpmdtaÞꢂ
2
13c
was shown to be 4.86 kcal/mol at 0 K and 4.11 kcal/mol
when the zero-point vibrational eneriges were taken into
consideration. At 298 K the free reaction enthalpy was
2
.5. Quantum chemical calculations
1
calculated to be DGgas = 3.69 kcal/mol corresponding
ꢀ3
to an equilibrium constant Kgas = 2.0 · 10 . In order
To gain an insight into the position of the Schlenk
equilibrium of methylmagnesium bromide in the pres-
ence of the pmdta ligand, quantum chemical calcula-
tions on the DFT level of theory were performed. The
1
Values calculated in the gas phase as well as in tetrahydrofuran
and diethyl ether solution are marked by indices ‘‘gas’’, ‘‘thf’’, and
‘‘ether’’, respectively.
gas-phase optimized structures of [MgMe (pmdta)]
2

1186
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
C1
Br1
N2
N2
N1
N1
Mg
Mg
N3
N3
C2
C2
9c
12c
Br1
N2
N1
Mg
N3
Br2
13c
2 2
Fig. 9. Calculated structures of [MgMeBr(pmdta)] (9c), [MgMe (pmdta)] (12c), and [MgBr (pmdta)] (13c) along with their numbering schemes.
Table 3
Selected bond lengths (A) and angles (ꢀ) for calculated complexes [MgLap
˚
L
eq(pmdta)] (Lap/Leq = Br/Me (9c); Me/Me (12c); Br/Br (13c))
[MgMe (pmdta)] (12c) [MgBr (pmdta)] (13c)
[MgMeBr(pmdta)] (9c)
2
2
(
L
ap/Leq = Br1/C2H
3
)
(Lap/Leq = C1H
3
3
/C2H )
(Lap/Leq = Br1/Br2)
Mg–Lap
Mg–Leq
Mg–N1
Mg–N2
Mg–N3
2.617
2.145
2.354
2.406
2.354
2.165
2.176
2.426
2.495
2.426
2.556
2.620
2.255
2.355
2.255
N1–Mg–N3
144.5
115.6
102.8
95.8
137.0
121.4
106.1
97.5
140.3
109.8
107.8
96.7
L
L
L
L
ap–Mg–Leq
ap–Mg–N1
ap–Mg–N2
ap–Mg–N3
102.8
106.2
107.8
to consider the solvent effects the Tomasiꢀs polarized
continuum model (PCM) was applied [30]. In tetrahy-
drofuran the free enthalpies of solvation at 298 K were
calculated to be ꢀ3.27 kcal/mol for the Grignard com-
pound 9c, ꢀ6.24 kcal/mol for 13c and ꢀ0.01 kcal/mol
for the dimethylmagnesium compound 12c. This means
that the order of solvation is MgBr > MgRBr > MgR ,
The free enthalpies of solvation in diethyl ether were
calculated to be ꢀ2.89 kcal/mol for [MgMeBr(pmdta)]
(9c), ꢀ6.06 kcal/mol for [MgBr (pmdta)] (13c) and
2
ꢀ0.01 kcal/mol for [MgMe (pmdta)] (12c). As expected
2
(cf. the dielectric constants e/e = 4.3, Et O; e/e = 7.6,
0
2
0
thf) they are very similar to those obtained for tetrahy-
drofuran. Thus, the influence of diethyl ether on the po-
2
2
which
meets
the
expectations.
Due
to
sition of the Schlenk equilibrium is small (DG
= 3.40
ether
ꢀ
3
DGsolv(13c) ꢃ 2DGsolv(9c) and DGsolv(12c) ꢃ 0 the influ-
ence of thf on the position of the Schlenk equilibrium
is small: DGthf was calculated at 298 K to be 3.98 kcal/
mol corresponding to an equilibrium constant
Kthf = 1.2 · 10 . Thus, the quantum chemical calcula-
tions show clearly that in thf the Grignard compound
kcal/mol, Kether = 3.2 · 10 ). Hence it follows that the
synthesis of [MgMe (pmdta)] (12) directly from
2
MgMeBr and pmdta in diethyl ether/n-hexane as de-
scribed in Section 2.1 is based on the shift of the Schlenk
equilibrium caused by the precipitation of sparingly sol-
uble compounds. Thus, the dimer MgMeBr(pmd-
ꢀ3
[
1
MgMeBr(pmdta)] (9c) does not disproportionate into
2c and 13c for thermodynamic reasons, which is fully
consistent with the experimental findings.
ta) Æ MgBr (pmdta) (10) precipitates when pmdta is
2
added to an etheral solution of MgMeBr. Furthermore,
the desired complex [MgMe (pmdta)] (12) was found to
2

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1187
1
1
precipitate by adding n-hexane to the etheral reaction
mixture.
In summary, some novel methylmagnesium com-
pounds were synthesized via ligand-substitution reac-
tions. Diethyl ether is only weakly coordinated to
magnesium and was substituted by stronger basic
J(C,H) = 131.0 Hz, CH ). Dabco: H NMR: d 2.65 (s,
2
13 1
CH2). C NMR: d 48.7 (t, J(C,H) = 138.2 Hz, CH ).
Tmeda: H NMR: d 2.15 (s, 12H, CH ), 2.31 (s, 4H,
CH2). C NMR: d 46.2 (q, J(C,H) = 131.8 Hz, CH ),
58.9 (t, J(C,H) = 131.5 Hz, CH ). Pmdta: H NMR: d
2
1
3
1
3
1
3
1
1
2
2.15 (s, 3H, CH N), 2.20 (s, 12H, (CH ) N), 2.31/2.42
2
3
3 2
3
monodentate (thf, NEt ) as well as chelating bidentate
3
( J(H,H) = ꢀ4.20/ꢀ3.54 Hz, J(H,H) = 8.42/5.42 Hz,
1
3
(
tmeda) and tridentate ligands (diglyme, pmdta). Note-
4H/4H, CH ) [32].
2
C
NMR:
d
1
42.3 (q,
1
worthy, the reaction of MgMeBr with pmdta proved
to be strongly solvent dependent yielding in tetrahydro-
furan [MgMeBr(pmdta)] (9) and in diethyl ether/n-hex-
J(C,H) = 132.1 Hz, CH N), 45.2 (q, J(C,H) = 130.3
3
1
Hz, (CH ) N), 56.4/57.9 (t/t, J(C,H) = 131.7/131.2 Hz,
3
2
2 · CH2).
ane [MgMe (pmdta)] (12). Thus, a way was found to
2
synthesize the dimethylmagnesium pmdta complex 12
from easily accessible reagents (MgMeBr/pmdta). Fur-
thermore, studies of the Schlenk equilibrium of
MgMeBr exhibited that it is shifted in the presence of
the strongly coordinating and chelating pmdta ligand
completely towards the Grignard reagent in thf and in
diethyl ether solutions. The pronounced influence of
the pmdta ligand on the position of the Schlenk equilib-
rium opens up new possibilities to study reactivities and
mechanisms of Grignard reagents.
3.2. Syntheses
3.2.1. MgMe (1)
2
To a solution of MgMeBr (83.7 mmol) in diethyl
ether (60 ml), 1,4-dioxane (8.26 g, 93.7 mmol) was added
dropwise at 0 ꢀC. Immediately, a white precipitate was
formed and then the solution was stirred for 4 d before
filtration. The filtrate was cooled down to ꢀ40 ꢀC to
provide after 1 d colorless rectangular-shaped crystals,
which were filtered off and dried in vacuo for 1/2 h to
give 1. Yield: 0.65 g (29%). Anal. Calc. for C H Mg
2
6
(
54.37): C, 44.18; H, 11.12; Br, 0.00. Found: C, 42.77;
1
3
. Experimental
H, 10.89; Br, <0.2%. H NMR (500 MHz, thf-d ): d
8
13
ꢀ
1.81 (s, CH Mg). C NMR (125 MHz, thf-d ): d
3 8
1 1
3
.1. General comments
ꢀ16.9 (q, J(C,H) = 105.7 Hz, CH Mg). H NMR
3
(500 MHz, thf-d ), temperature dependence of d(CH );
8
3
All reactions and manipulations were carried out un-
concentration 0.04 mol/l: ꢀ1.772 (27 ꢀC), ꢀ1.791 (ꢀ20
ꢀC), ꢀ1.803 (ꢀ40 ꢀC), ꢀ1.818 (ꢀ60 ꢀC), ꢀ1.844 (ꢀ80
ꢀC).
der purified argon using standard Schlenk techniques
and a glove box from Fa. MB Braun, respectively.
Thf-d , diglyme, triethylamine, n-hexane, tmeda, and
8
pmdta were dried with LiAlH . Diethyl ether, 1,4-diox-
4
3.2.2. [{MgMe (thf)} (l-dabco)] (2)
2
2
ane, and thf were distilled from sodium benzophenone
ketyl. Dabco and MgMeBr (3 M in Et O) are commer-
To a solution of MgMe (1) (0.27 g, 5.0 mmol) in thf
2
(10 ml), dabco (0.30 g, 2.7 mmol) was added and stirred
for 1 h to give a clear yellowish solution. This solution
was cooled down to ꢀ40 ꢀC for 3 d to form colorless
sticky crystals of 2, whose structure was determined by
single-crystal X-ray diffraction. When these crystals
were filtered off and dried in vacuo for 1/2 h, a white pre-
cipitate was formed. Yield: 0.77 g (84%). Anal. Calc. for
C H Mg O N (365.13): C, 59.21; H, 11.04; N, 7.67.
2
1
cially available from Merck and Fluka, respectively. H
13
and C NMR spectra were recorded on Varian Unity
00, VXR 400, and Gemini 200 spectrometers. Protio
5
impurities and C resonances of thf-d were used as
1
3
8
internal standards. Microanalyses (C, H, N) were per-
formed by the University of Halle microanalytical labo-
ratory using a CHNS-932 (LECO) and Vario EL
1
8
40
2
2
2
1
(
elementar Analysensysteme) elemental analyzers,
Found: C, 58.56; H, 11.20; N, 7.85%. H NMR (400
MHz, thf-d ): d ꢀ1.77 (s, 12H, CH Mg), 1.78 (m, 8H,
respectively. Bromine contents were determined by mer-
curimetric titration method [31].
8
3
CH CH O), 2.67 (s, 12H, CH N), 3.62 (m, 8H,
2
2
2
1
13
CH O). C NMR (125 MHz, thf-d ): d ꢀ16.8 (q,
For comparison H NMR (400 MHz, 7.0 ll in 0.7 ml
2
8
1
3
1
1
J(C,H) = 105.6 Hz, CH Mg), 26.4 (t, J(C,H) = 131.6
thf-d ) and C NMR (125 MHz, 40.0 ll in 0.7 ml thf-
8
3
1
d ) spectra of free O- and N-donor ligands were mea-
8
Hz, CH CH O), 48.5 (t, J(C,H) = 138.2 Hz, CH N),
2 2 2
1
1
68.2 (t, J(C,H) = 143.5 Hz, CH O).
sured. Diglyme: H NMR: d 3.28 (s, 6H, CH ), 3.44/
3
2
2
3
3
.53 ( J(H,H) = ꢀ6.07 Hz/ꢀ4.10 Hz, J(H,H) = 12.3/
1
3
1
1
2.3 Hz, 4H/4H, CH ) [32]. C NMR: d 58.4 (q,
3.2.3. MgMeBr(L), L = (Et O, (3); thf, (4))
2
2
1
J(C,H) = 140.1 Hz, CH ), 71.4 (t, J(C,H) = 140.1 Hz,
From a solution of MgMeBr (15.5 mmol) in diethyl
ether (5 ml) the solvent was removed and the residue
was dried in vacuo at RT for 1 h to give a white powder
3
1
CH OCH ), 72.9 (t, J(C,H) = 139.9 Hz, CH OCH ).
2
2
2
3
1
3
NEt3: H NMR: d 0.97 (t, J(H,H) = 7.06 Hz, 9H,
3
CH ), 2.44 (q, J(H,H) = 7.12 Hz, 6H, CH ).
13
1
C
of 3. Yield: 2.9 g (97%). H NMR (200 MHz, thf-d ): d
3
2
8
1
3
NMR: d 12.7 (q, J(C,H) = 124.8 Hz, CH ), 47.3 (t,
ꢀ1.71 (s, 3H, CH Mg), 1.10 (t, J(H,H) = 6.96 Hz, 6H,
3
3

1188
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
3
CH CH O), 3.38 (q,
3
J(H,H) = 7.00 Hz, 4H,
N, 6.35. Found: C, 37.33; H, 8.28; Br, 36.36; N, 6.08%.
1
2
1
3
CH CH O). C NMR (125 MHz, thf-d ): d ꢀ16.4 (q,
H NMR (400 MHz, thf-d ): d ꢀ1.72 (s, 3H, CH Mg),
3
2
8
8
3
1
1
J(C,H) = 106.3 Hz, CH Mg), 15.7 (q, J(C,H) = 125.6
3
0.96 (t, J(H,H) = 7.11 Hz, 9H, CH CH N), 2.43 (q,
3
3 2
1
H CH O), 66.3 (t, J(C,H) = 139.1 Hz,
3
13
Hz,
CH CH O).
C
J(H,H) = 7.11 Hz, 6H, CH N). C NMR (125 MHz,
2
3
2
1
thf-d ): d ꢀ16.5 (q, J(C,H) = 105.4 Hz, CH Mg), 12.6
3
2
8
1
3
A sample of 3 (2.50 g, 12.9 mmol) was dissolved in thf
40 ml) and stirred for 1/2 h. The solvents were evapo-
(q,
1
J(C,H) = 125.0 Hz, CH CH N), 47.3 (t,
2
3
1
J(C,H) = 131.0 Hz, CH N). H NMR (500 MHz, thf-
(
2
rated in vacuo at RT. Then the residue was dried in va-
cuo at 50 ꢀC for 1 h to give a white powder 4. Yield: 2.4
g (97%). Anal. Calc. for C H BrMgO (191.35): C,
d ), temperature dependence of d(CH ); concentration
8
3
0.04 mol/l: ꢀ1.706 (27 ꢀC), ꢀ1.765 (ꢀ20 ꢀC), ꢀ1.750/
ꢀ1.800 (ꢀ40 ꢀC), ꢀ1.767/ꢀ1.817 (ꢀ60 ꢀC), ꢀ1.785/
ꢀ1.842 (ꢀ80 ꢀC).
5
11
3
1.38; H, 5.79; Br, 41.76. Found: C, 31.78; H, 5.37;
1
Br, 39.67%. H NMR (200 MHz, thf-d ): d ꢀ1.75 (s,
8
1
3
CH Mg). C NMR (125 MHz, thf-d ): d ꢀ16.3 (q,
3.2.6. MgMeBr(tmeda) (7) and
[MgMeBr(thf)(tmeda)] (8)
3
8
1
1
J(C,H) = 106.6 Hz, CH Mg). H NMR (500 MHz,
3
thf-d ), temperature dependence of d(CH ); concentra-
To a solution of MgMeBr (16.0 mmol) in diethyl
ether (25 ml), a solution of tmeda (2.08 g, 17.9 mmol)
in diethyl ether (3 ml) was added dropwise to give a
white precipitate of 7 in an exothermic process. The pre-
cipitate was filtered off, washed with diethyl ether (2 · 4
ml), and dried in vacuo for 1/2 h. Yield: 3.7 g (98%).
Anal. Calc. for C H BrMgN (235.45): C, 35.71; H,
8
3
tion 0.04 mol/l: ꢀ1.695 (27 ꢀC), ꢀ1.769 (ꢀ20 ꢀC),
ꢀ
ꢀ
1.748/ꢀ1.800 (ꢀ40 ꢀC), ꢀ1.767/ꢀ1.817 (ꢀ60 ꢀC),
1.786/ꢀ1.844 (ꢀ80 ꢀC).
3
.2.4. MgMeBr(diglyme) (5)
A solution of MgMeBr (18.6 mmol) in diethyl ether
7
19
2
(
6 ml) was concentrated in vacuo up to ca. 1 ml, and
subsequently thf (50 ml) was added. Diglyme (2.63 g,
9.6 mmol) was added dropwise and then the reaction
8.13; Br, 33.94; N, 11.90. Found: C, 35.13; H, 7.97;
1
Br, 35.54; N, 11.61%. H NMR (400 MHz, thf-d ): d
8
1
ꢀ1.67 (s, 3H, CH Mg), 2.32 (s, 12H, CH N), 2.48 (s,
3
3
1
3
mixture was stirred overnight at RT. The clear solution
was cooled down to ꢀ80 ꢀC for 1 d to form a small
quantity of colorless needles of [MgBr (thf) ], which
4H, CH N). C NMR (125 MHz, thf-d ): d ꢀ15.5 (q,
2
8
1
1
J(C,H) = 106.7 Hz, CH Mg), 47.0 (q, J(C,H) = 133.1
3
1
1
Hz, CH N), 57.7 (t, J(C,H) = 134.4 Hz, CH N). H
2
4
3
2
were filtered off and dried in vacuo for 1/2 h (Anal. Calc.
for C H Br MgO (472.54): C, 40.67; H, 6.83. Found:
NMR (500 MHz, thf-d ), temperature dependence of
8
d(CH ): concentration 0.04 mol/l: ꢀ1.668 (27 ꢀC),
1
6
32
2
4
1
3
13
C, 40.71; H, 6.53%. H and C NMR: no other than thf
signals). The filtrate was concentrated up to ca. 15 ml to
precipitate a white powder of 5, which was filtered off
and dried in vacuo for 1/2 h. Yield: 2.7 g (57%). Anal.
Calc. for C H BrMgO (253.42): C, 33.18; H, 6.76;
ꢀ1.690/ꢀ1.778 (ꢀ20 ꢀC), ꢀ1.702/ꢀ1.788 (ꢀ40 ꢀC),
ꢀ1.714/ꢀ1.800 (ꢀ60 ꢀC), ꢀ1.724/ꢀ1.812 (ꢀ80 ꢀC); con-
centration 0.12 mol/l: ꢀ1.677 (27 ꢀC), ꢀ1.705 (ꢀ20 ꢀC),
ꢀ1.698/ꢀ1.787 (ꢀ40 ꢀC), ꢀ1.710/ꢀ1.799 (ꢀ60 ꢀC),
ꢀ1.724/ꢀ1.814 (ꢀ80 ꢀC); concentration 0.25 mol/l:
ꢀ1.678 (27 ꢀC), ꢀ1.717 (ꢀ20 ꢀC), ꢀ1.701/ꢀ1.786 (ꢀ40
ꢀC), ꢀ1.712/ꢀ1.802 (ꢀ60 ꢀC), ꢀ1.727/ꢀ1.818 (ꢀ80 ꢀC).
A solution of 7 (50 mg) in thf (1 ml) was cooled down
to ꢀ40 ꢀC. After 3 d colorless crystals of 8 were formed,
which their structure was measured by single-crystal X-
ray diffraction analysis. When these crystals were iso-
7
17
3
1
Br, 31.53. Found: C, 33.35; H, 6.70; Br, 31.48%. H
NMR (400 MHz, thf-d ): d ꢀ1.73 (s, 3H, CH Mg),
8
3
2
3
.33 (s, 6H, CH O), 3.52/3.61 ( J(H,H) = ꢀ6.07/ꢀ4.14
3
3
Hz, J(H,H) = 11.03/11.26 Hz, 4H/4H, CH O) [32].
2
1
1
1
3
C
NMR (125 MHz, thf-d8):
J(C,H) = 106.4 Hz, H Mg),
J(C,H) = 140.9 Hz, CH O), 71.0 (t, J(C,H) = 141.8
d
ꢀ16.0 (q,
C
59.1 (q,
3
1
1
lated and dried in vacuo for 1/2 h they lost the thf ( H
13
and C NMR spectra are as described above for 7).
3
1
Hz, CH OCH ), 72.5 (t, J(C,H) = 141.1 Hz,
1
CH OCH ). H NMR (500 MHz, thf-d ), temperature
2
2
2
3
8
dependence of d(CH3); concentration 0.04 mol/l:
1.712 (27 ꢀC), ꢀ1.767 (ꢀ20 ꢀC), ꢀ1.754/ꢀ1.800 (ꢀ40
C), ꢀ1.766/ꢀ1.817 (ꢀ60 ꢀC), ꢀ1.784/ꢀ1.839 (ꢀ80 ꢀC).
3.2.7. [MgMeBr(pmdta)] (9)
ꢀ
A solution of MgMeBr (15.8 mmol) in diethyl ether
(5 ml) was concentrated in vacuo up to about 1 ml. Then
thf (50 ml) was added. After dropwise addition of pmdta
(2.91 g, 16.8 mmol), the solution was stirred overnight at
RT. When the clear solution was cooled down to ꢀ40 ꢀC
for 1 d, compound 9 was precipitated as a white powder,
which was filtered off and dried in vacuo for 1/2 h. Yield:
4.5 g (97%). Anal. Calc. for C H BrMgN (292.54): C,
ꢀ
3
.2.5. MgMeBr(NEt ) (6)
3
To a solution of MgMeBr (19.2 mmol) in diethyl
ether (30 ml), NEt (5.81 g, 57.4 mmol) was added drop-
3
wise with stirring. After 4 h the solution was concen-
trated in vacuo up to about 10 ml. Then n-hexane (30
ml) was added to precipitate a white powder of 6, which
was filtered off, washed with n-hexane (2 · 5 ml), and
dried in vacuo for 1/2 h. Yield: 4.1 g (97%). Anal. Calc.
for C H BrMgN (220.43): C, 38.14; H, 8.23; Br, 36.25;
1
0
26
3
41.06; H, 8.96; Br, 27.31; N, 14.36. Found: C, 41.01; H,
1
9.00; Br, 25.87; N, 14.23%. H NMR (500 MHz, thf-d ):
8
d ꢀ1.68 (s, 3H, CH Mg), 2.31 (s, 3H, CH N), 2.43 (s,
3
3
12H, (CH ) N), 2.54/2.70 (br/br, 4H/4H, 2 · CH N).
7
18
3 2
2

R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
1189
1
1
3
C
J(C,H) = 106.0 Hz, CH Mg), 44.2 (q, J(C,H) = 135.8
NMR (125 MHz, thf-d8):
d
ꢀ13.2 (q,
3.2.9. [MgBr (pmdta)] (13)
2
1
1,2-Dibromoethane (0.87 g, 4.64 mmol) in thf (36 ml)
was added dropwise to magnesium metal (0.21 g, 8.64
mmol) in thf (10 ml) and stirred overnight. The residual
metal was filtered off and to the clear filtrate pmdta (0.83
g, 4.79 mmol) was added dropwise to form immediately
a white precipitate of 13. This precipitate was filtered off,
washed with boiling thf (5 times), and dried in vacuo for
3
1
Hz, CH N), 45.8 (q, J(C,H) = 137.0 Hz, (CH ) N),
3
3 2
1
5
1
7.4/57.6 (t/t, J(C,H) = 134.0/133.7 Hz, 2 · CH N).
H NMR (500 MHz, thf-d ), temperature dependence
2
8
d(CH ); concentration 0.04 mol/l: ꢀ1.672 (27 ꢀC),
3
ꢀ
ꢀ
1.702 (ꢀ20 ꢀC), ꢀ1.712 (ꢀ40 ꢀC), ꢀ1.726 (ꢀ60 ꢀC),
1.741 (ꢀ80 ꢀC), ꢀ1.757 (ꢀ100 ꢀC).
8
h. Yield: 1.5 g (90%). Anal. Calc. for C H Br MgN
9 23 2 3
3
.2.8. [MgMe (pmdta)] (12)
2
(357.41): C, 30.24; H, 6.49; Br, 44.71; N, 11.76. Found:
C, 29.90; H, 6.42; Br, 44.28; N, 11.46%.
To a solution of MgMeBr (75.6 mmol) in diethyl
ether (90 ml), a solution of pmdta (14.97 g, 86.4 mmol)
in diethyl ether (20 ml) was added dropwise. Immedi-
3.3. Crystallographic studies
ately,
MgBr (pmdta) (10) was formed in an exothermic pro-
cess. After stirring for 5 h, the precipitate was filtered
off and dried in vacuo to give 10. The filtrate was con-
centrated in vacuo up to about 30–40 ml to form a small
amount of a precipitate, which was filtered off. n-Hexane
a
white precipitate of MgMeBr(pmdta) Æ
Single crystals which were suitable for X-ray diffrac-
tion measurements were obtained as follows: 2 (colorless
sticks, 0.7 · 0.4 · 0.3 mm) grown from thf solution at
ꢀ40 ꢀC; 8 (colorless blocks, 0.4 · 0.3 · 0.2 mm) grown
2
from thf solution at ꢀ40 ꢀC; 11 Æ 2Et O (colorless
2
(
itate [{MgMe (pmdta)} {MgMeBr(pmdta)}] (11),
60 ml) was added to the filtrate to form a white precip-
blocks, 0.2 · 0.3 · 0.4 mm) grown from Et O solution
2
at 5 ꢀC; 12 (colorless needles) from Et O/n-hexane solu-
2
7
2
which was filtered off. The resulted filtrate was concen-
trated in vacuo up to 50 ml and cooled down to ꢀ40
tion at ꢀ40 ꢀC; 13 (colorless needles) grown from thf
solution at room temperature. Intensity data were col-
lected on a Bruker Smart CCD (2, 8, 11 Æ 2Et O) and
ꢀ
C. After 1 d colorless needle-like crystals of 12 were
2
formed, which were filtered off, washed with cold n-hex-
ane, and dried in vacuo. Noteworthy, when the filtrate,
after isolating 10 and before adding n-hexane, was
cooled down to 5 ꢀC for 3 d, colorless crystals of
STOE imaging plate diffraction system (12, 13), respec-
˚
tively, with Mo-Ka radiation (0.71073 A, graphite
monochromator). A summary of crystallographic data,
data collection parameters, and refinement parameters
is given in Table 4. Absorption corrections were per-
formed for 2 (SADABS, multi-scan; Tmin/Tmax = 0.36/
1.00), 8 (SADABS, multi-scan; Tmin/Tmax = 0.88/1.00),
1
1 Æ 2Et O were obtained, whose structure was con-
2
firmed by single-crystal X-ray diffraction analysis.
MgMeBr(pmdta) Æ MgBr (pmdta) (10): Yield: 6.0 g
2
(
24%, referred to total Mg content). Anal. Calc. for
C H Br Mg N (649.95): C, 35.11; H, 7.60; Br,
11 Æ 2Et O (SADABS, multi-scan; Tmin/Tmax = 0.93/1.00),
2
and 13 (numerically; Tmin/Tmax = 0.25/0.65). The struc-
tures were solved by direct methods with SHELXS-97
and refined using full-matrix least-squares routines
1
9
49
3
2
6
3
6.88; N, 12.93. Found: C, 35.39; H, 7.65; Br, 36.81;
N, 12.83%.
{MgMe (pmdta)} {MgMeBr(pmdta)}] (11): Yield:
2
[
against F with SHELXL-97 [33]. Non-hydrogen atoms
0
2
7
0
for C H BrMg N (1886.25): C, 55.40; H, 12.24;
Br, 4.24; N, 17.82. Found: C, 55.40; H, 12.31; Br,
1
4
(
2
(
.35 g (2%, referred to total Mg content). Anal. Calc.
were refined with anisotropic (except for C1/C1 in 8)
and hydrogen atoms with isotropic displacement param-
eters. H atoms were added to the model in their calcu-
8
7
229
8
24
.20; N, 18.04%. H NMR (400 MHz, thf-d ): d ꢀ1.80
lated positions (riding model) (2, 8, 11 Æ 2Et O) and
8
2
s, 42H, (CH ) Mg), ꢀ1.68 (s, ca. 3H, CH MgBr),
found in the electron density maps (12, 13), respectively.
In 2 the carbon atoms of dabco ligand are disordered
over two positions that are equally occupied. In 8 bromo
and methyl ligands are disordered over two positions
with site occupancies 0.64/0.36, whereas atoms of thf li-
gand are disordered over two positions with equally
3
2
3
.27 (s, 24H, CH N), 2.32 (s, 96H, (CH ) N), 2.45/2.60
3 3 2
1
3
s/s, 32H/32H, CH N). C NMR (100 MHz, thf-d ): d
2 8
ꢀ
14.5 (s, (CH ) Mg), ꢀ13.6 (br, CH MgBr), 43.5 (s,
3
2
3
CH N), 46.4 (s, (CH ) N), 57.4/57.7 (s/s, CH N).
3 3 2 2
[
MgMe (pmdta)] (12): Yield: 4.52 g (26%, referred to
2
1
total Mg content). H NMR (400 MHz, thf-d ): d ꢀ1.81
occupied positions. In crystals of 11 Æ 2Et O the asym-
8
2
(
s, 6H, CH Mg), 2.25 (s, 15H, CH N), 2.46/2.57 (m/m,
3
metric unit contains two molecules of [MgMe (pmdta)]
2
3
1
3
4
H/4H, 2 · CH N). C NMR (125 MHz, thf-d ): d
and [MgMe1.75Br0.25(pmdta)], respectively, and a half
molecule of Et O. The site occupancies for C1H3/Br
2
8
1
14.1 (q, J(C,H) = 104.6 Hz, CH Mg), 42.6 (q,
ꢀ
3
2
1
1
J(C,H) = 134.7 Hz, CH N), 46.7 (q, J(C,H) = 134.1
were refined to be 0.72/0.28 and have been fixed at the
end of the refinement to 0.75/0.25. Furthermore, a
disordered diethyl ether molecule has been found with
site occupancies refined to 0.30/0.20. Thus the diethyl
ether molecule occupies only half of the ‘‘holes’’ in the
crystal.
3
1
1
Hz, (CH ) N), 57.6 (t, J(C,H) = 135.0 Hz, CH N). H
3
2
2
NMR (500 MHz, thf-d ), temperature dependence of
8
d(CH ); concentration 0.04 mol/l: ꢀ1.795 (27 ꢀC),
3
ꢀ
ꢀ
1.846 (ꢀ20 ꢀC), ꢀ1.867 (ꢀ40 ꢀC), ꢀ1.884 (ꢀ60 ꢀC),
1.901 (ꢀ80 ꢀC), ꢀ1.917 (ꢀ100 ꢀC).

1190
R.I. Yousef et al. / Journal of Organometallic Chemistry 690 (2005) 1178–1191
Table 4
2
Crystal data and structure refinement for 2, 8, 11 Æ 2Et O, 12 and 13
2
8
11 Æ 2Et
2
O
12
13
Empirical formula
Formula weight
T (K)
C
18
H
40Mg
2
2
N O
2
C
307.57
11
H
27BrMgN
2
O
C
23.75
H
62.25Br0.25Mg
2
N
6
O
0.50
C
227.68
11
H
29MgN
3
9 2 3
C H23Br MgN
365.14
183(2)
508.64
198(2)
357.43
220(2)
203(2)
Orthorhombic
Pbca
220(2)
Monoclinic
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
P2 /c
Monoclinic
P2 /c
1
1
P2 /c
1
˚
a (A)
23.799(3)
8.0779(8)
11.9984(12)
96.853(2)
2290.2(4)
4
11.1743(10)
12.1611(11)
22.832(2)
17.1465(6)
8.3947(3)
23.9605(9)
102.421(1)
3368.1(2)
4
8.588(2)
29.784(6)
12.511(3)
101.40(2)
3137(1)
8
8.486(1)
30.054(4)
12.357(2)
100.72(2)
3096.5(8)
8
˚
b (A)
˚
c (A)
b (ꢀ)
V (A )
˚
3
3102.7(5)
8
1.317
Z
3
q
calc (g/cm )
1.059
0.116
1.003
0.389
0.964
0.094
1024
1.533
5.255
1440
ꢀ1
l(Mo-Ka) (mm
F(000)
)
2.676
1296
808
1.72–26.43
10020
1134
1.74–26.02
39488
Scan range (ꢀ)
1.78–26.41
36260
2.15–26.07 2.16–26.04
22118 18857
5778 (0.0851) 6025 (0.0781)
Number of reflections collected
Number of independent reflections (Rint
Data/restraints/parameters
)
2516 (0.0710)
2347/38/139
1.029
3167 (0.0464)
3167/38/205
1.128
6632 (0.0347)
6632/151/358
1.040
5778/0/503
0.990
6025/0/456
1.065
2
Goodness-of-fit on F
R
R
1
2
, wR
, wR
1
2
[I > 2r(I)]
(all data)
0.0679, 0.1704
0.1131, 0.1945
0.344/ꢀ0.326
0.0400, 0.1052
0.0513, 0.1100
0.392/ꢀ0.421
0.0521, 0.1452
0.0665, 0.1566
0.512/ꢀ0.257
0.0471, 0.1090 0.0502, 0.1272
0.0878, 0.1246 0.0864, 0.1516
˚
Largest difference in peak/hole (e/A )
3
0.191/ꢀ0.189
0.774/ꢀ1.120
3
.4. Computational details
All DFT calculations were carried out by the GAUSS-
of charge on application to CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK [fax: (internat.) +44 1223
336 033; e-mail: deposit@ccdc.cam.ac.uk]. Tables of
Cartesian coordinates of atom positions calculated
for equilibrium structures 9c, 12c, and 13c. Supple-
mentary data associated with this article can be found,
in the online version at doi:10.1016/j.jorganchem.
2004.10.058.
IAN-98 program package [34] using the hybrid func-
tional B3LYP [35]. All systems have been fully
optimized without any symmetry restrictions using the
SDD basis set of atomic orbitals as implemented in
the GAUSSIAN-98 program. The resulting geometries
were characterized as equilibrium structures by the
analysis of the force constants of normal vibrations.
To model the solvent influence (thf, Et O) on the ener-
2
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