Synthesis and characterisation of magnesium complexes containing sterically demanding N,N′-bis(aryl)amidinate ligands

Article abstract of DOI:10.1039/c3dt53234h

Condensation reactions of carboxylic acids and anilines in the presence of polyphosphoric acid trimethylsilyl ester (PPSE) afforded a range of sterically demanding N,N′-bis(aryl)amidines, RN{C(R′)}N(H)R [R = Mes (Mes = 2,4,6-trimethylphenyl), R′ = Cy (Cy = cyclohexyl) L¹H; R = Dipp (Dipp = 2,6-diisopropylphenyl), R′ = Cy L²H; R = Mes, R′ = Ph L³H; R = Dipp, R′ = Ph L⁴H; R = Mes, R′ = Dmp (Dmp = 3,5-dimethylphenyl) L⁵H; R = Dipp, R′ = Dmp L ⁶H; R = Dmp, R′ = Cy L⁷H]. Amidines L ¹H-L⁷H have been characterised spectroscopically, and for L⁵H and L⁶H, by X-ray crystallography. Treatment of the amidines with di-n-butylmagnesium in THF solution afforded the monomeric magnesium bis(amidinates) [Mg(L¹)₂(THF)] 1, [Mg(L ²)₂] 2, [Mg(L³)₂(THF)] 3, [Mg(L ⁵)₂(THF)] 5, [Mg(L⁶)₂] 6, [Mg(L ⁷)₂] 7, and the magnesium mono(amidinate) complex [Mg(L⁴)(ⁿBu)] 4. These complexes have been characterised spectroscopically, with 1-3, 5 and 6 also being structurally authenticated. Comparison of the magnesium bis(amidinate) complexes reveals that the steric bulk of the amidinate ligand influences both the solid state structure and solution behaviour of these complexes.

Full text of DOI:10.1039/c3dt53234h

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Synthesis and characterisation of magnesium
complexes containing sterically demanding
Cite this: DOI: 10.1039/c3dt53234h
N,N’-bis(aryl)amidinate ligands†
Graeme J. Moxey,*‡ Fabrizio Ortu, Leon Goldney Sidley, Helen N. Strandberg,
Alexander J. Blake, William Lewis and Deborah L. Kays*
Condensation reactions of carboxylic acids and anilines in the presence of polyphosphoric acid trimethyl-
silyl ester (PPSE) afforded a range of sterically demanding N,N’-bis(aryl)amidines, RN{C(R’)}N(H)R [R = Mes
(Mes = 2,4,6-trimethylphenyl), R’ = Cy (Cy = cyclohexyl) L1H; R = Dipp (Dipp = 2,6-diisopropylphenyl),
R’ = Cy L2H; R = Mes, R’ = Ph L3H; R = Dipp, R’ = Ph L4H; R = Mes, R’ = Dmp (Dmp = 3,5-dimethylphenyl)
L5H; R = Dipp, R’ = Dmp L6H; R = Dmp, R’ = Cy L7H]. Amidines L1H–L7H have been characterised
spectroscopically, and for L5H and L6H, by X-ray crystallography. Treatment of the amidines with di-n-
butylmagnesium in THF solution afforded the monomeric magnesium bis(amidinates) [Mg(L1)2(THF)] 1,
[Mg(L2)2] 2, [Mg(L3)2(THF)] 3, [Mg(L5)2(THF)] 5, [Mg(L6)2] 6, [Mg(L7)2] 7, and the magnesium mono(amidi-
nate) complex [Mg(L4)(nBu)] 4. These complexes have been characterised spectroscopically, with 1–3, 5
and 6 also being structurally authenticated. Comparison of the magnesium bis(amidinate) complexes
reveals that the steric bulk of the amidinate ligand influences both the solid state structure and solution
behaviour of these complexes.
Received 15th November 2013,
Accepted 24th January 2014
DOI: 10.1039/c3dt53234h
www.rsc.org/dalton
ligand. This in turn can influence the structure and reactivity
Introduction
of the resulting metal amidinate complex. This effect has been
Amidinate ligands, [RN{C(R′)}NR]−, are readily accessible and demonstrated elegantly by Jordan, using mono(amidinate)
have been investigated in main group, transition metal and complexes of aluminium.9,10 Changing the amidinate carbon
t
rare earth chemistry.1–6 Amidinate ligands display a rich substituent from Me to Bu causes increased steric crowding
coordination chemistry, with both chelating and bridging around the Al centre, resulting in different synthetic outcomes
coordination modes reported.7 Metal amidinate complexes when the two aluminium amidinate complexes were treated
have found applications in many areas, including catalysis and with B(C6F5)3.10
materials science.8 The steric and electronic properties of ami-
In alkaline earth chemistry, bulky amidinate and the
dines can be readily tuned by changing the substituents at the closely related guanidinate ligands have been used to stabilise
nitrogen and carbon atoms of the ligand core, making amidi- complexes featuring hitherto unknown oxidation states and
nates an extremely versatile class of ligand, even more so than bonding modes, such as the Mg(I) species [LMg–MgL] (L =
the ubiquitous cyclopentadienyls.7 Studies have shown that as DippN{CN(iPr)2}NDipp),11 while less bulky amidinate ligands
the steric bulk of the three substituents around the amidine have been employed in magnesium chemistry for the synthesis
backbone is increased, the NCN angle decreases, which conse- of volatile complexes for MOCVD and ALD processes.8,12 More
quently affects the coordination properties of the amidinate recently, magnesium complexes containing amidinate support-
ing ligands have been shown to promote the dimerisation of
benzaldehyde in the Tishchenko reaction.13
School of Chemistry, University of Nottingham, University Park, Nottingham NG7
Despite the significant research interest in magnesium ami-
2RD, UK. E-mail: Deborah.Kays@nottingham.ac.uk; Fax: +44 (0)115-9513555;
dinates, only a handful of magnesium complexes containing
Tel: +44 (0)115-9513461
N,N′-bis(aryl)amidinates have been structurally characterised.14
†Electronic supplementary information (ESI) available: Characterisation data for
amidines L2H and L4H, the molecular structures of L5H and L6H, calculation of
Monomeric, homoleptic complexes were obtained using ami-
the ΔCN parameter for 1–3, 5, 6, L5H and L6H. CCDC 951585–951591. For
dinate ligands with bulky substituents at the nitrogen and
ESI and crystallographic data in CIF or other electronic format see DOI:
carbon atoms, despite the presence of coordinating solvents in
10.1039/c3dt53234h
the reactions: [Mg(ArN{C(R)}NAr)2] [Ar = Dipp, R = p-Tol (p-
‡Current address: Research School of Chemistry, Australian National University,
Tol = 4-methylphenyl), Me].15 The related [Mg(ArN{C(R)}NAr)2]
Canberra, ACT 0200, Australia.
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t
(Ar = Mes, R = Bu), was prepared using hexane as the reaction
This conceptually simple condensation route to amidines
medium.16 When bulky substituents were only present at the was first reported in 1984,22,23 for amidines with substituents
nitrogen atoms (formamidinates), metallation reactions of low steric bulk, but has attracted little attention since.20,24
between di-n-butylmagnesium and formamidines yielded There are two generally employed synthetic routes to symmetri-
monomeric solvated magnesium complexes, viz. [Mg(ArN- cal N,N′-bis(aryl)amidines;25 (i) treatment of a lithium alkyl or
{C(H)}NAr)2(solv)n] [Ar = p-Tol, solv = THF, n = 2; solv = DME, aryl with a diarylcarbodiimide, which yields an intermediate
n = 1; solv = TMEDA, n = 1] (DME = 1,2-dimethoxyethane, lithium amidinate species and is subsequently quenched to
TMEDA = N,N,N′,N′-tetramethylethylenediamine).17 These struc- form the amidine, and (ii) treatment of an acyl chloride with
tures contrast the dinuclear species such as [Mg2(iPrN{C(Me)}- an amine affording the corresponding amide, which is then
NiPr)4],12 which are afforded when amidinate ligands contain- dehydrated to give an imidoyl chloride intermediate; sub-
ing less bulky substituents are used. The structures of these sequent reaction with an amine affords the amidine. The main
complexes demonstrate the interplay between ligand bulk, disadvantage of these two routes is that each contains several
nuclearity and solvation in magnesium amidinates. A systema- synthetic steps, some involving the handling of air and moist-
tic study of the solution and solid state structures of mag- ure sensitive reagents. Furthermore, in route (i) the synthesis
nesium bis(amidinates) is therefore imperative, given the of diarylcarbodiimides typically involves the use of mercuric
renewed interest in alkaline earth chemistry18,19 and require- oxide,26 and consequently the reaction work-up involves hand-
ment to develop structure–activity relationships for potential ling toxic mercury residues, and in route (ii) thionyl chloride is
materials and catalysis applications.
often used as the dehydrating agent.27 The PPSE condensation
Herein we report the synthesis of a range of new sterically route to amidines circumvents these issues and has compar-
demanding N,N′-bis(aryl)amidines from the condensation able yields [L4H has been previously prepared using route (ii),
reactions of carboxylic acids and anilines in PPSE. We also with a 60% yield].21
report on a systematic investigation of the geometric ligand
Synthesis of magnesium amidinate complexes. Amidines
effects on the solution and solid state structures of magnesium L1H–L7H react smoothly with di-n-butylmagnesium in THF,
complexes containing bulky N,N′-bis(aryl)amidinate ligands. affording the monomeric magnesium bis(amidinate) com-
These complexes complement the handful of structurally plexes 1–3 and 5–7, and the magnesium mono(amidinate)
characterised magnesium bis(amidinate) complexes currently complex 4 (Scheme 2).
in the literature, facilitating a comprehensive view of mag-
nesium bis(amidinate) chemistry.
The isolation of a magnesium mono(amidinate) complex 4
was unexpected given that magnesium bis(amidinates) were
obtained from analogous reactions employing closely related
amidines. Attempts to isolate a magnesium bis(amidinate)
complex by altering reaction conditions proved unsuccessful,
consistently yielding 4, and/or an intractable mixture of pro-
ducts. Magnesium mono(amidinate) complexes have been pre-
viously reported, such as [Mg(iPr)(DippN{C(tBu)}NDipp)(OEt2)],
prepared by treating iPrMgCl with [Li(DippN{C(tBu)}NDipp)] in
diethyl ether.28
The influence of the steric bulk of the amidinate on the
structure of the resulting magnesium complex is evident in
comparing compounds 1, 3 and 5 with 2 and 6. The use of
amidinate ligands featuring mesityl substituents on the nitro-
gen atoms yielded magnesium species which also featured a
ligated THF molecule (1, 3 and 5), whereas for complexes 2
and 6, which contain amidinate ligands with bulkier Dipp
Results and discussion
Synthesis
Synthesis of N,N′-bis(aryl)amidines. Treatment of a carb-
oxylic acid with two equivalents of an aniline at 160 °C in
PPSE (prepared in situ from hexamethyldisiloxane and phos-
phorus pentoxide in refluxing dichloromethane), followed by
reaction work-up under basic conditions, afforded N,N′-bis-
(aryl)amidines L1H–L7H in good yields (Scheme 1). Amidines
L2H and L4H have been previously prepared using a similar
route.20,21 The amidines L1H–L7H were characterised by 1H
and 13C{1H} NMR spectroscopy, infrared spectroscopy, mass
spectrometry and elemental analysis. Amidines L5H and L6H
have also been characterised by X-ray crystallography (see the
ESI†).
Scheme 2 Synthesis of complexes 1–7. Reagents and conditions: (i)
0.5 nBu2Mg, THF, −78 °C → room temperature, – 2 nBuH. R = Mes, R’ =
Cy, n = 1, 1; R = Dipp, R’ = Cy, n = 0, 2; R = Mes, R’ = Ph, n = 1, 3; R =
Mes, R’ = Dmp, n = 1, 5; R = Dipp, R’ = Dmp, n = 0, 6; R = Dmp, R’ = Cy,
n = 0, 7. (ii) nBu2Mg, THF, −78 °C → room temperature – nBuH. R = Dipp,
R’ = Ph, 4.
Scheme 1 Synthesis of N,N’-bis(aryl)amidines L1H–L7H. Reagents and
conditions: PPSE, 160 °C, 16 hours. R = Mes, R’ = Cy L1H; R = Dipp, R’ =
Cy L2H; R = Mes, R’ = Ph L3H; R = Dipp, R’ = Ph L4H; R = Mes, R’ = Dmp
L5H; R = Dipp, R’ = Dmp L6H; R = Dmp, R’ = Cy L7H.
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substituents, the homoleptic magnesium complexes were centre. The steric bulk of the nitrogen-bound substituents
obtained. Homoleptic magnesium compounds containing all- influence the behaviour of the magnesium amidinates in solu-
nitrogen coordination spheres are of particular interest as pre- tion. The NMR spectra of 2 and 6 display four chemically
cursors for magnesium-doped semiconductors.12 Compounds inequivalent sets of isopropyl methyl groups and two isopropyl
1–7 have been characterised by spectroscopy, elemental ana- methine resonances, which can be attributed to extensive
lysis, and in the case of compounds 1–3, 5 and 6, by single steric crowding around the magnesium centre, giving rise to
crystal X-ray crystallography.
two distinct 2,6-diisopropylphenyl environments. Similar solu-
tion behaviour has been reported for other magnesium com-
plexes containing N,N′-bis(2,6-diisopropylphenyl)amidinate
ligands.15,28 In contrast, the NMR spectra of 1, 3 and 5 display
a single ligand environment, in agreement with the solution
behaviour of [Mg(ArN{C(R)}NAr)2] (Ar = Mes, R = tBu).16
Spectroscopic characterisation
Spectroscopic data for L2H and L4H are in good agreement
with the reported data for these compounds.20,21 The infrared
spectra of the amidines L1H–L7H display an N–H stretching
frequency at ∼3350 cm−1 and CvN stretching frequencies
in the region of 1610–1640 cm−1. In the H NMR spectra, the
1
Crystallographic characterisation
N–H resonance is in the region of 5.5 ppm, and in the 13C{1H} Crystalline samples of 1–3, 5 and 6, suitable for X-ray structure
NMR spectra, the amidine backbone NCN resonance is in the determinations, were grown from hexane, hexane–THF, or
region of 150–160 ppm; in good agreement with reported N,N′- benzene-d6 (see Experimental section), while crystals of L5H
bis(aryl)amidines.20,21 Amidines often display several isomeric and L6H were grown from hexane–ethanol mixtures. Selected
and tautomeric forms, due to C–N bond rotation and CvN iso- bond lengths and angles for complexes 1–3, 5 and 6 are pre-
merisation (Eanti, Esyn, Zanti, Zsyn).25 The presence of at least two sented in Table 1, while Table 2 contains a summary of rele-
isomers is evident in the 1H and 13C{1H} NMR spectra of L1H– vant crystal data and refinement parameters. The structures
L7H, which is consistent with reported data for related are depicted in Fig. 1–5. Selected bond lengths (Å) and
amidines.16,29,30
angles (°) for L5H and L6H are presented in Fig. S1 and S2 in
The lack of a v(N–H) absorption in the infrared spectra and the ESI.†
1
the absence of a N–H resonance in the H NMR spectra indi-
In all complexes, the magnesium centre is bound to two
cates complete deprotonation of the amidines in bulk vacuum chelating amidinate ligands; this coordination is sup-
dried samples of the isolated magnesium complexes 1–7. plemented by a ligated THF molecule in compounds 1, 3 and
Strong peaks in the infrared spectra in the region of 5. Compounds 1, 3 and 5 are five-coordinate monomers, with
1640 cm−1 are attributed to v(C–N) stretching bands. There is a distorted square pyramidal geometry around the magnesium
downfield shift of the amidine backbone NCN resonance to centre with the THF ligand occupying the apical position. In
170–180 ppm in the 13C{1H} NMR spectra of these complexes contrast, complexes 2 and 6 are four-coordinate monomers,
compared to the free amidine values. In contrast to the ami- with the magnesium centre adopting a distorted tetrahedral
dines L1H–L7H, the NMR spectra of 1–7 indicate the presence geometry. Broadly, the two N–C(backbone) distances in the
of a single isomer, plausibly Eanti, which is consistent with the amidinate ligands are the same, indicating ligand charge de-
deprotonation and coordination of the amidine to a metal localisation over the amidinate NCN backbone (refer to the
Table 1 Selected bond lengths (Å) and angles (°) for compounds 1–3, 5 and 6
1 C(n) = C(26)
2 C(n) = C(32)
3 C(n) = C(26)
5 C(n) = C(28)
6 C(n) = C(34)
Mg(1)–N(1)
Mg(1)–N(2)
Mg(1)–N(3)
Mg(1)–N(4)
Mg(1)–O(1)
N(1)–C(1)
N(2)–C(1)
N(3)–C(n)
2.2166(19)
2.099(2)
2.146(2)
2.091(2)
2.0832(17)
1.326(3)
1.342(3)
1.329(3)
1.350(3)
63.39(7)
170.83(8)
110.81(8)
114.21(8)
130.90(8)
63.40(7)
94.91(7)
114.63(8)
94.06(7)
114.45(7)
112.6(2)
112.46(19)
2.0798(18)
2.0523(18)
2.0649(18)
2.0694(19)
2.1081(10)
2.1209(10)
2.1291(11)
2.1048(11)
2.0568(9)
1.3305(15)
1.3341(15)
1.3307(16)
1.3360(16)
64.07(4)
111.95(4)
136.85(4)
168.20(4)
110.57(4)
63.98(4)
111.06(4)
96.00(4)
95.78(4)
112.09(4)
114.67(10)
114.51(10)
2.1488(15)
2.0883(15)
2.0964(15)
2.1435(15)
2.0626(13)
1.331(2)
1.338(2)
1.336(2)
1.335(2)
63.71(5)
109.42(6)
166.56(6)
129.58(6)
110.65(6)
63.80(5)
2.059(3)
2.050(3)
2.045(3)
2.067(3)
1.328(3)
1.342(3)
1.345(3)
1.337(3)
65.04(7)
126.28(8)
154.46(8)
141.96(8)
122.12(8)
65.45(7)
1.338(5)
1.335(5)
1.342(5)
1.331(5)
66.17(12)
131.57(13)
147.01(14)
134.07(14)
125.61(13)
66.22(12)
N(4)–C(n)
N(1)–Mg(1)–N(2)
N(1)–Mg(1)–N(3)
N(1)–Mg(1)–N(4)
N(2)–Mg(1)–N(3)
N(2)–Mg(1)–N(4)
N(3)–Mg(1)–N(4)
N(1)–Mg(1)–O(1)
N(2)–Mg(1)–O(1)
N(3)–Mg(1)–O(1)
N(4)–Mg(1)–O(1)
N(1)–C(1)–N(2)
N(3)–C(n)–N(4)
95.55(5)
115.08(6)
115.31(6)
97.87(6)
113.88(14)
114.06(14)
112.60(18)
112.90(17)
114.1(3)
114.3(3)
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Table 2 Crystallographic data for the X-ray structure determinations of 1–3, 5, 6, L5H and L6H
1·C6D6
60H74D6MgN4O
903.63
P21/n
12.3061(11)
21.499(2)
20.0063(18)
90
2·C6H14
3·C4H8O
5·C4H8O
6·C4H8O
L5H
L6H
Formula
FW
Space group
a [Å]
b [Å]
c [Å]
C
C68H104MgN4
1001.86
P21/c
12.3036(2)
24.7484(4)
20.4769(4)
90
C58H70MgN4O2
879.49
P21/c
12.57310(17)
29.1302(4)
15.8661(2)
90
C62H78MgN4O2
935.59
P21/n
16.6334(11)
12.9516(9)
26.3010(18)
90
C70H94MgN4O
1031.80
P21/c
18.2661(3)
18.2865(2)
19.1208(2)
90
C27H32N2
384.55
C2/c
27.7598(18)
8.4639(3)
23.1109(15)
90
C33H44N2
468.70
P21/n
11.5654(6)
16.5227(8)
16.1572(9)
90
α [°]
β [°]
92.042(5)
90
5289.8(8)
4
1.135
0.077
95.9387(17)
90
6201.64(19)
4
1.073
0.547
112.1894(16)
90
5380.72(12)
4
1.086
0.607
101.876(7)
90
5544.7(6)
4
1.121
0.616
103.6657(13)
90
6206.02(14)
4
1.104
0.578
125.776(10)
90
4405.4(4)
8
1.155
0.505
109.525(3)
90
2910.0(3)
4
1.070
0.061
γ [°]
Vol [Å3]
Z
Dcalc [g cm−3
]
μ [mm−1
F(000)
]
1952
2208
1896
2024
2248
1664
1024
No. of indep.
reflns (Rint
R1, wR2 (I > 2σ)
11 694 (0.0671)
12 380 (0.0434)
10 711 (0.0204)
11 162 (0.0447)
12 334 (0.0361)
4438 (0.0862)
0.0826, 0.2253
3803 (0.0970)
0.0877, 0.1695
)
0.0649, 0.1418
0.0723, 0.2013
0.0403, 0.1103
0.0522, 0.1376
0.0980, 0.2393
Fig. 1 Crystal structure of 1 with displacement ellipsoids set at 40%
probability. Hydrogen atoms and the lattice benzene-d6 molecule are
omitted for clarity.
Fig. 3 Crystal structure of 5 with displacement ellipsoids set at 40%
probability. Hydrogen atoms and the lattice THF molecule are omitted
for clarity.
Fig. 2 Crystal structure of 3 with displacement ellipsoids set at 40%
probability. Hydrogen atoms and the lattice THF molecule are omitted
for clarity.
Fig. 4 Crystal structure of 2 with displacement ellipsoids set at 40%
probability. Hydrogen atoms and the lattice hexane molecule are
omitted for clarity.
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Magnesium complexes of N,N′-bis(2,6-diisopropylphenyl)-
amidinate ligands. The Mg–N distances in the four-coordinate
compounds 2 and 6 (Fig. 4 and 5) range from 2.0523(18)–
2.0798(18) Å [average = 2.067(11) Å] in 2, and from 2.045(3)–
2.067(3) Å [average = 2.055(10) Å] in 6. These average values are
in good agreement with the average Mg–N distances in the two
crystallographically distinct molecules of [Mg(DippN{C(Me)}-
NDipp)2] (2.044 and 2.049
Å
respectively),28 as well as
the average Mg–N distance in the amidinate compound
[Mg(DippN{C(p-Tol)}NDipp)2] (2.058 Å).15 The N–C(back-
bone)–N angle of the amidinate ligands [112.60(18) and
112.90(17)° in 2, and 114.1(3) and 114.3(3)° in 6] are compar-
able with the analogous bite angles in 1 and 5 respectively,
indicating that the steric bulk of the backbone C substituent
of the amidinate ligand may have a greater influence on the
ligand backbone N–C–N than the substituent on the N atoms
of the amidinate, which is in agreement with Jordan’s
model.9,10 In 2 and 6, the two N–Mg–N–C(backbone) metalla-
cycle planes are near orthogonal [angle between metallacycle
least squares planes 61.65(9) in 2 and 76.58(16) in 6], presum-
ably to minimise steric repulsion between the 2,6-diisopropyl-
phenyl substituents. This ligand arrangement accounts for the
inequivalence of the isopropyl groups in the NMR spectra of 2
and 6.
The influence of the amidinate C backbone substituent on
the magnesium coordination environment is evident in com-
paring the square planar amidinate complex [Mg(DippN{C-
(p-Tol)}NDipp)2]15 with the distorted tetrahedral magnesium
environment in the closely related amidinate compounds 2
and 6 (Fig. 4 and 5). The coplanar NCNMg metallacycles in the
former compound were also attributed to preventing unfavour-
able interactions between diisopropylphenyl groups. Evidently,
very small changes in the steric demands of the amidinate
backbone C substituent can impart large structural variations.
In a similar vein to 1, the cyclohexyl backbone substituent in 2
is almost orthogonal to the N–Mg–N–C plane on each ligand
[angle between cyclohexyl and N–Mg–N–C(backbone) least
squares planes 96.96(11) and 85.45(11)°]. In 6, the less bulky
3,5-dimethylphenyl backbone substituent gives rise to a non-
orthogonal arrangement [54.79(15) and 46.69(14)° in 6].
Fig. 5 Crystal structure of 6 with displacement ellipsoids set at 40%
probability. Hydrogen atoms and the lattice THF molecule are omitted
for clarity.
ΔCN parameter calculations in the ESI†). The amidinate
ligands adopt an Eanti arrangement on coordination to the
magnesium centre, in contrast to the Zanti and Esyn structures
of L5H and L6H (ESI†).
Magnesium complexes of N,N′-bis(2,4,6-trimethylphenyl)-
amidinate ligands. Due to the collective presence of mesityl
substituents on the N atoms of the amidinate ligands in 1, 3
and 5 (Fig. 1–3), the average Mg–N bond lengths in all three
compounds are similar. The Mg–N bond distances range from
2.091(2)–2.2166(19)
Å [average = 2.14(6) Å], in 1, from
2.1048(11)–2.1291(11) Å [average = 2.116(11) Å] in 3, and
2.0883(15)–2.1488(15) Å [average = 2.12(3) Å] in 5. These
average Mg–N bond lengths are in good agreement with the
average Mg–N distances in the related five-coordinate mag-
nesium amidinate [Mg(CyN{C(Ph)}NSiMe3)2(OEt2)] (2.131 Å)31a
and guanidinate [Mg{iPr2NC(iPrN)2}2(THF)] (2.124 Å).31b
The Mg–O(THF) distances [2.0832(17) Å for 1, 2.0568(9) Å
for 3 and 2.0626(13) Å for 5] are shorter than the Mg–O(THF)
bond distance in [Mg(iPr2NC(iPrN)2)2(THF)] (2.098(9) Å).31
Although the steric bulk of the backbone C substituent on the
amidinate (cyclohexyl in 1, phenyl in 3, 3,5-dimethylphenyl in
5) has little effect on the average Mg–N bond lengths, it does
influence the N–C–N angle. The bulky cyclohexyl backbone
substituent in 1 results in more acute N–C–N angles [N(1)–
C(1)–N(2) 112.6(2)°; N(3)–C(26)–N(4) 112.46(19)°] compared
with the phenyl substituent in 3 [N(1)–C(1)–N(2) 114.67(10)°;
N(3)–C(26)–N(4) 114.51(10)°] and the 3,5-dimethylphenyl sub-
stituent in 5 [N(1)–C(1)–N(2) 113.88(14)°; N(3)–C(28)–N(4)
114.06(14)°]. This trend is further exemplified in the structure
of [Mg(MesN{C(tBu)}NMes)2];16 the bulky tert-butyl substi-
tuent on the amidine backbone gives rise to even more acute
N–C–N angles of 109.0(3) and 110.2(3)°. The cyclohexyl back-
bone substituent in 1 (Fig. 1) is almost orthogonal to the
NCNMg plane on each ligand [angle between cyclohexyl and
N–Mg–N–C(backbone) least squares planes 93.45(7) and
87.40(7)°]. On moving to a less bulky substituent, these angles
move away from orthogonality [54.54 and 44.22° in 3 (phenyl),
42.53(7) and 44.23(7)° in 5 (3.5-dimethylphenyl); Fig. 2 and 3].
Conclusions
A range of bulky N,N′-bis(aryl)amidines was synthesised from
the condensation reactions of carboxylic acids and anilines in
the presence of PPSE, establishing the utility of this synthetic
route to amidines of varying degrees of steric bulk. Treatment
of the amidines with di-n-butylmagnesium in THF afforded
mononuclear magnesium amidinates with concomitant for-
mation of butane. The steric bulk of the amidinate ligand was
found to influence both the solid state structure and solution
behaviour of the magnesium amidinates. The effect of the
amidinate ligand on the structure and properties of the result-
ing magnesium species is noteworthy, given the current
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interest in magnesium amidinate complexes as catalysts and The combined organic phases were dried over MgSO4 and the
molecular precursors for MOCVD and ALD processes.
solvent removed to yield the crude amidine. Crystallisation
from hot hexane (L1H, L2H), or hexane–ethanol (L3H–L7H),
afforded the pure amidines as colourless microcrystalline
solids.
Experimental section
General remarks
Data for MesN{C(Cy)}N(H)Mes (L1H). From cyclohexane-
carboxylic acid (0.96 g) and 2,4,6-trimethylaniline (2.03 g,
1
All magnesium compounds prepared herein are air- and moist-
ure-sensitive; therefore all reactions and manipulations were
performed using standard Schlenk line and glove box equip-
ment under an atmosphere of purified argon or dinitrogen.
Hexane and pentane were dried by passing through a column
of activated 4 Å molecular sieves. Dichloromethane was dis-
tilled over CaH2. THF was pre-dried over Na wire and freshly
distilled over sodium benzophenone ketyl under nitrogen. All
solvents were degassed in vacuo and stored over a potassium
mirror (hexane and pentane) or activated 3 Å molecular sieves
(THF and dichloromethane) prior to use. Benzene-d6 (Goss)
was dried over potassium and THF-d8 (Goss) was dried over
CaH2. Both were degassed with three freeze–pump–thaw cycles
prior to use. 1H and 13C{1H} NMR spectra were collected on
Bruker AV 400, DPX 400 or DPX 300 spectrometers. Chemical
shifts are quoted in ppm relative to TMS. Infrared spectra were
recorded as Nujol mulls sandwiched between KBr plates on a
Bruker Tensor 27 Fourier transform infrared spectrometer.
Mass spectra were measured by the departmental service at
the School of Chemistry, University of Nottingham. Elemental
analyses were performed by Mr Stephen Boyer at London
Metropolitan University. Amidines L2H and L4H have been pre-
viously prepared using a similar synthetic route,20,21 and L4H
has also been prepared via reaction of N-(2,6-diisopropyl-
phenyl)benzimidoyl chloride and 2,6-diisopropylaniline.21,29,32
Di-n-butylmagnesium was obtained from Aldrich as a 1.0 M
solution in heptane. The solvent was removed in vacuo and
nBu2Mg was stored as a solid in the glove box. All other reagents
were obtained from commercial sources and used as received.
Yields refer to purified products and are not optimised.
2.1 mL). Yield 1.81 g, 75%. H NMR (CDCl3, 298 K, 400 MHz):
δ 1.05–1.39 (m, 4H, Cy–CH2), 1.60–1.89 (m, 7H, Cy–CH2 + Cy–
CHN), 2.19 (s, 6H, CH3), 2.23 (s, 6H, CH3), 2.28 (s, 3H, CH3),
2.29 (s, 3H, CH3), 5.27 (s, 1H, NH), 6.87 (s, 2H, ArH), 6.90 (s,
2H, ArH). 13C{1H} NMR (CDCl3, 298 K, 100 MHz): δ 17.8 (CH3),
18.8 (CH3), 20.7 (CH3), 20.9 (CH3), 25.8 (Cy–CH2), 26.2 (Cy–
CH2), 31.2 (Cy–CH2), 39.6 (Cy–HCN), 128.8 (ArCH), 128.9
(ArCH), 129.1 (ArCH), 131.3 (ArC), 133.7 (ArC), 136.2 (ArC),
136.5 (ArC), 143.4 (ArC), 160.3 (CN2). Elemental analysis: calcd
for C25H34N2: C 82.82, H 9.45, N 7.73; found C 82.69, H 9.31, N
7.69. High res. mass spec. (ESI): calcd for C25H35N2 [M + H]+:
363.2795; measd 363.2804; calcd for C25H34N2Na [M + Na]+:
385.2614; measd 385.2602. IR (Nujol): ν = 3339 (m, NH), 1642
(s, CvN), 1336 (w), 1270 (m), 1232 (m), 1212 (w), 1151 (w),
1032 (w), 852 (m), 802 (w) cm−1
.
Data for DippN{C(Cy)}N(H)Dipp (L2H). From cyclohexane-
carboxylic acid (0.96 g) and 2,6-diisopropylaniline (2.66 g,
2.83 mL). Yield 2.18 g, 65%. Spectroscopic and analytical data
for L2H are listed in the ESI† and are in agreement with pre-
viously reported data.20
Data for MesN{C(Ph)}N(H)Mes (L3H). From benzoic acid
(0.92 g) and 2,4,6-trimethylaniline (2.03 g, 2.1 mL). Yield
1
1.82 g, 68%. H NMR (CDCl3, 298 K, 400 MHz): δ 2.12 (s, 6H,
CH3), 2.20 (s, 3H, CH3), 2.32 (s, 3H, CH3), 2.35 (s, 6H, CH3),
5.72 (s, 1H, NH), 6.74 (s, 2H, ArH), 6.97 (s, 2H, ArH), 7.21–7.32
(m, 3H, ArH), 7.49–7.52 (m, 2H, ArH). 13C{1H} NMR (CDCl3,
298 K, 100 MHz): δ 18.0 (CH3), 18.9 (CH3), 20.7 (CH3), 20.8
(CH3), 127.2 (ArCH), 128.2 (ArCH), 128.8 (ArC), 129.0 (ArCH),
129.2 (ArCH), 129.4 (ArCH), 132.0 (ArC), 134.5 (ArC), 134.6
(ArC), 135.5 (ArC), 136.1 (ArC), 143.3 (ArC), 154.3 (CN2).
Elemental analysis: calcd for C25H28N2: C 84.23, H 7.92, N
7.86; found C 84.11, H 8.05, N 7.72. High res. mass spec. (ESI):
General procedure for the synthesis of amidines L1H–L7H
The synthetic route is based on a modified literature pro- calcd for C25H29N2 [M + H]+: 357.2325; measd 357.2323. IR
cedure.22,23 A Schlenk flask was charged with phosphorus (Nujol): ν = 3358 (m, NH), 1632 (s, CvN), 1622 (s, CvN),
pentoxide (4.5 g, 31.7 mmol), hexamethyldisiloxane (15.3 g, 1495 (s), 1222 (w), 1212 (w), 1177 (w), 1093 (w), 1073 (w),
20 mL, 94.1 mmol) and dichloromethane (20 mL). The reac- 1028 (w), 892 (w), 852 (m), 808 (w), 768 (m), 698 (s) cm−1
.
tion mixture was heated to reflux for 45 minutes under nitro-
Data for DippN{C(Ph)}N(H)Dipp (L4H). From benzoic acid
gen, and then cooled to room temperature. All volatiles were (0.92 g) and 2,6-diisopropylaniline (2.66 g, 2.83 mL). Yield
removed in vacuo, affording a colourless, viscous syrup of 2.38 g, 72%. Spectroscopic and analytical data for L4H are
PPSE, which was used in situ for the subsequent reaction. The listed in the ESI† and are in agreement with previously
PPSE was heated to 160 °C, and the relevant carboxylic acid reported data.21
(7.5 mmol) and aniline (15 mmol) were then added to the
Data for MesN{C(Dmp)}N(H)Mes (L5H). From 3,5-dimethyl-
flask in quick succession under a flow of nitrogen. The con- benzoic acid (1.13 g) and 2,4,6-trimethylaniline (2.03 g,
1
denser was replaced on the flask and the reaction maintained 2.1 mL). Yield 2.02 g, 70%. H NMR (CDCl3, 298 K, 300 MHz):
at 160 °C. After 16 hours, the reaction mixture was poured hot δ 2.14 (s, 6H, CH3), 2.21 (s, 3H, CH3), 2.22 (s, 6H, CH3), 2.32 (s,
into a 1 M aqueous solution of NaOH, with vigorous stirring, 3H, CH3), 2.36 (s, 6H, CH3), 5.70 (s, 1H, NH), 6.74 (s, 2H, ArH),
affording an oily solid. The solid was extracted with dichloro- 6.95 (s, 1H, ArH), 6.97 (s, 2H, ArH), 7.01 (s, 2H, ArH). 13C{1H}
methane (3 × 50 mL), the organic layer was separated and the NMR (CDCl3, 298 K, 75 MHz): δ 18.0 (CH3), 18.4 (CH3), 19.0
aqueous phase was washed with dichloromethane (2 × 10 mL). (CH3), 20.8 (CH3), 21.3 (CH3), 125.6 (ArCH), 128.8 (ArCH),
Dalton Trans.
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129.1 (ArCH), 131.0 (ArCH), 131.2 (ArC), 134.7 (ArC), 135.3 stirred overnight. Volatiles were removed in vacuo and the oily
(ArC), 135.9 (ArC), 137.0 (ArC), 143.4 (ArC), 154.6 (CN2). residue was extracted with hexane (1, 2, 7), or a hexane–THF
Elemental analysis: calcd for C27H32N2: C 84.33, H 8.39, N mixture (3, 5, 6). The solution was filtered, concentrated to
7.28; found C 84.22, H 8.49, N 7.17. High res. mass spec. (ESI): ca. 5 mL and cooled to −30 °C affording colourless crystals
calcd for C27H33N2 [M + H]+: 385.2638; measd 385.2647; calcd suitable for X-ray crystallography after several days. Crystals of
for C27H32N2Na [M + Na]+: 407.2458; measd 407.2466. IR 1 were also obtained from benzene-d6. In the case of 4, after
(Nujol): ν = 3363 (w, NH), 1894 (w), 1621 (m, CvN), 1258 (m), removing the solvent, the residue was washed with pentane
1209 (w), 1111 (m), 845 (w), 760 (m), 617 (w) cm−1
Data for DippN{C(Dmp)}N(H)Dipp (L6H). From 3,5-
.
and dried to afford 4.
Data for [Mg(L1)2(THF)] (1). From 1.05 g of L1H. Yield
1
dimethylbenzoic acid (1.13 g) and 2,6-diisopropylaniline 0.97 g, 82%. H NMR (C6D6, 298 K, 300 MHz): δ 0.67–0.81 (m,
1
(2.66 g, 2.83 mL). Yield 2.39 g, 68%. H NMR (CDCl3, 298 K, 6H, Cy–CH2), 1.20–1.31 (m, 2H, Cy–CH2), 1.33–1.48 (m, 12H,
300 MHz): δ 0.95 (d, 6H, CH(CH3)2, J = 6.9 Hz), 1.02 (d, 6H, Cy–CH2 + THF–CH2), 1.92–1.97 (m, 4H, Cy–CH2), 2.33 (br s,
CH(CH3)2, J = 6.6 Hz), 1.28 (d, 6H, CH(CH3)2, J = 6.6 Hz), 1.40 36H, CH3), 2.45–2.60 (m, 2H, Cy–CHN), 3.73 (m, 4H, THF–
(d, 6H, CH(CH3)2, J = 6.9 Hz), 2.19 (s, 6H, CH3), 3.23 (sept, 2H, OCH2), 6.99 (s, 8H, ArH). 13C{1H} NMR (C6D6, 298 K, 75 MHz):
CH(CH3)2, J = 6.6 Hz), 3.32 (sept, 2H, CH(CH3)2, J = 6.9 Hz), δ 19.5 (CH3), 20.8 (CH3), 25.4 (THF–CH2), 26.0 (Cy–CH2), 27.8
5.68 (s, 1H, NH), 6.90 (s, 1H, ArH), 6.93–7.01 (m, 4H, ArH), (Cy–CH2), 29.4 (Cy–CH2), 43.2 (Cy–HCN), 68.9 (THF–OCH2),
7.11–7.17 (m, 2H, ArH), 7.23–7.25 (m, 2H, ArH). 13C{1H} NMR 128.6 (ArCH), 130.9 (ArC), 132.6 (ArC), 145.3 (ArC), 177.3 (CN2).
(CDCl3, 298 K, 75 MHz): δ 21.2 (CH(CH3)2), 22.4 (CH(CH3)2), Elemental analysis: calcd for C54H74MgN4O: C 79.14, H 9.10, N
22.7 (CH3), 24.5 (CH(CH3)2), 25.3 (CH(CH3)2), 28.3 (CH(CH3)2), 6.84; found C 79.06, H 9.01, N 6.88. IR (Nujol): ν = 1641 (w),
28.5 (CH(CH3)2), 123.2 (ArCH), 123.4 (ArCH), 123.5 (ArCH), 1608 (w), 1355 (m), 1311 (s), 1240 (s), 1209 (m), 1149 (m),
126.6 (ArCH), 127.4 (ArCH), 130.6 (ArCH), 134.0 (ArC), 134.7 1007 (m), 879 (m), 851 (m), 831 (s), 686 (w), 526 (w), 460 (w) cm−1
(ArC), 137.0 (ArC), 139.5 (ArC), 143.7 (ArC), 145.4 (ArC), 154.3
Data for [Mg(L2)2] (2). From 1.29 g of L2H. Yield 1.05 g,
.
(CN2). Elemental analysis: calcd for C33H44N2: C 84.56, H 9.46, 80%. 1H NMR (C6D6, 298 K, 300 MHz): δ 0.64 (d, 12H,
N 5.98; found C 84.62, H 9.38, N 5.95. High res. mass spec. CH(CH3)2, J = 6.6 Hz), 1.18–1.27 (m, 4H, Cy–CH2), 1.33 (d, 12H,
(ESI): calcd for C33H45N2 [M + H]+: 469.3577; measd 469.3588; CH(CH3)2, J = 6.6 Hz), 1.31–1.49 (m, 8H, Cy–CH2), 1.48 (d, 12H,
calcd for C33H44N2Na [M + Na]+: 491.3397; measd 491.3402. IR CH(CH3)2, J = 6.7 Hz), 1.54 (d, 12H, CH(CH3)2, J = 6.5 Hz),
(Nujol): ν = 3443 (w), 3370 (w, NH), 1786 (w), 1761 (w), 1625 (s, 1.88–1.92 (m, 8H, Cy–CH2), 2.45–2.58 (m, 2H, Cy–CHN), 3.43
CvN), 1599 (m), 1585 (m), 1355 (m), 1326 (w), 1257 (m), (sept, 4H, CH(CH3)2, J = 6.8 Hz), 3.82 (sept, 4H, CH(CH3)2, J =
1190 (w), 1176 (w), 1059 (m), 1042 (m), 949 (w), 934 (m), 858 (s), 6.6 Hz), 7.09 (s, 2H, ArH), 7.12 (s, 2H, ArH), 7.20 (s, 2H, ArH),
827 (m), 796 (s), 762 (s), 751 (m), 723 (s), 687 (m), 478 (m) cm−1
.
7.22 (s, 2H, ArH), 7.23 (s, 2H, ArH), 7.25 (s, 2H, ArH). 13C{1H}
Data for DmpN{C(Cy)}N(H)Dmp (L7H). From cyclohexane- NMR (C6D6, 298 K, 75 MHz): δ 22.9 (CH3), 22.9 (CH3), 23.5
carboxylic acid (0.96 g) and 3,5-dimethylaniline (1.82 g, (CH3), 25.4 (CH3), 25.7 (Cy–CH2), 26.1 (Cy–CH2), 26.2 (Cy–CH2),
1
1.87 mL). Yield 1.51 g, 60%. H NMR (C6D6, 298 K, 400 MHz): 28.3 (CH(CH3)2), 28.4 (CH(CH3)2), 29.6 (Cy–CH2), 30.0 (Cy–
δ 0.83–0.89 (m, 2H, Cy–CH2), 1.05–1.07 (m, 2H, Cy–CH2), CH2), 43.0 (Cy–HCN), 123.1 (ArCH), 123.2 (ArCH), 124.6
1.34–1.43 (m, 2H, Cy–CH2), 1.70–1.79 (m, 2H, Cy–CH2), (ArCH), 142.7 (ArC), 143.1 (ArC), 143.5 (ArC), 180.6 (CN2).
2.01–2.09 (m, 2H, Cy–CH2), 2.20 (s, 12H, CH3), 2.78–2.82 (m, Elemental analysis: calcd for C62H90MgN4: C 81.32, H 9.91,
1H, Cy–CHN), 5.90 (br, 1H, NH), 6.59–6.66 (br, 4H, ArH), 7.57 N 6.12; found C 81.28, H 10.00, N 6.17. IR (Nujol): ν = 1918
(br, 2H, ArH). 13C{1H} NMR (C6D6, 298 K, 100 MHz): δ 21.4 (w), 1854 (w), 1794 (w), 1636 (s), 1586 (s), 1315 (m), 1258 (s),
(CH3), 25.6 (Cy–CH2), 25.8 (Cy–CH2), 30.9 (Cy–CH2), 31.3 (Cy– 1176 (w), 1099 (w), 1045 (w), 1021 (w), 970 (m), 933 (m),
HCN), 117.4 (ArCH), 119.4 (ArCH), 123.6 (ArCH), 138.1 (ArC), 876 (m), 802 (s), 784 (s), 769 (w), 748 (m), 723 (w), 696 (m),
138.2 (ArC), 150.9 (CN2). Elemental analysis: calcd for 578 (s), 528 (s), 481 (s), 451 (m) cm−1
.
C23H30N2: C 82.59, H 9.04, N 8.37; found C 82.48, H 8.85, N
Data for [Mg(L3)2(THF)] (3). From 1.03 g of L3H. Yield
8.25. High res. mass spec. (ESI): calcd for C23H31N2 [M + H]+: 0.87 g, 75%. H NMR (C6D6, 298 K, 300 MHz): δ 1.28 (m, 4H,
335.2482; measd 335.2474; calcd for C23H30N2Na [M + Na]+: THF–CH2), 2.15 (s, 12H, CH3), 2.20 (s, 24H, CH3), 3.72 (m, 4H,
357.2301; measd 357.2299. IR (Nujol): ν = 3373 (s, NH), 1745 THF–OCH2), 6.65–6.73 (m, 6H, ArH), 6.75 (br s, 8H, ArH), 7.13
(w), 1714 (w), 1625 (s, CvN), 1613 (s, CvN), 1593 (s), 1320 (m, 2H, ArH), 7.67–7.70 (m, 2H, ArH). 13C{1H} NMR (CDCl3,
(m), 1284 (w), 1270 (w), 1253 (w), 1172 (w), 1153 (s), 1031 (s), 298 K, 75 MHz): δ 19.3 (CH3), 20.7 (CH3), 25.3 (THF–CH2), 69.3
970 (m), 947 (m), 908 (m), 837 (s), 755 (s), 715 (s), 685 (s), (THF–OCH2), 126.8 (ArCH), 128.7 (ArCH), 128.9 (ArCH), 132.1
1
591 (s) cm−1
.
(ArCH), 132.0 (ArC), 134.7 (ArC), 135.9 (ArC), 145.0 (ArC), 172.8
(CN2). Elemental analysis: calcd for C54H62MgN4O: C 80.33, H
7.74, N 6.94; found C 80.02, H 7.72, N 6.84. IR (Nujol): ν =
1699 (m), 1302 (w), 1261 (s), 1215 (m), 1092 (s), 1027 (s), 852
General procedure for the synthesis of magnesium amidinates
1–7
A solution of di-n-butylmagnesium (0.2 g, 1.4 mmol) in THF (m), 800 (s), 766 (w), 696 (m) cm−1
.
(20 mL) was added dropwise to a solution of amidine
Data for [Mg(L4)(nBu)] (4). From 1.27 g of L4H. Yield 0.33 g,
(2.8 mmol) in THF (20 mL) at −78 °C with stirring. The reac- 44%. 1H NMR (CDCl3, 298 K, 400 MHz): δ 0.66 (d, 6H,
tion mixture was slowly warmed to room temperature and CH(CH3)2, J = 6.3 Hz), 0.79 (d, 6H, CH(CH3)2, J = 6.3 Hz), 0.87
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n
n
(t, 3H, Bu–CH3, J = 7.1 Hz), 1.05–1.30 (m, 6H, Bu–CH2), 1.45 75 MHz): δ 19.5 (CH3), 20.8 (CH3), 26.0 (Cy–CH2), 27.8 (Cy–
(d, 6H, CH(CH3)2, J = 6.1 Hz), 1.60 (d, 6H, CH(CH3)2, J = CH2), 29.4 (Cy–CH2), 43.2 (Cy–HCN), 128.6 (ArCH), 130.9 (ArC),
6.3 Hz), 3.30 (m, 2H, CH(CH3)2), 3.95 (m, 2H, CH(CH3)2), 132.6 (ArC), 145.3 (ArC), 177.3 (CN2). Elemental analysis: calcd
6.58–6.62 (m, 1H, ArH), 6.65–6.69 (t, 2H, ArH, J = 7.4 Hz), 6.80 for C46H58MgN4: C 79.92, H 8.46, N 8.10; found C 79.83, H
(d, 2H, ArH, J = 7.3 Hz), 6.96–6.99 (t, 2H, ArH, J = 7.7 Hz), 7.11 8.38, N 8.03. IR (Nujol): ν = 2727 (w), 1625 (w), 1592 (s),
(d, 2H, ArH, J = 7.3 Hz), 7.19 (d, 2H, ArH, J = 7.2 Hz). 13C{1H} 1311 (s), 1284 (w), 1260 (m), 1235 (s), 1153 (m), 1094 (s),
NMR (CDCl3, 298 K, 100 MHz): δ 22.5 (nBu–CH3), 22.7 1023 (s), 885 (w), 842 (s), 800 (s), 699 (m), 686 (m), 604 (w) cm−1
(CH(CH3)2), 23.2 (CH(CH3)2), 24.0 (CH(CH3)2), 25.2
.
X-ray structure determinations
(CH(CH3)2), 28.3 (CH(CH3)2), 28.9 (CH(CH3)2), 34.1 (nBu–CH2),
34.2 (nBu–CH2), 123.0 (ArCH), 123.3 (ArCH), 123.6 (ArCH), Crystals of 1·C6D6, 2·C6H14, 3·C4H8O, 5·C4H8O, 6·C4H8O, L5H
124.4 (ArCH), 126.8 (ArCH), 129.0 (ArCH), 130.1 (ArCH), 131.9 and L6H were mounted on MicroMounts using YR-1800 per-
(ArC), 142.2–142.5 (br, ArC), 142.8 (ArC), 176.3 (CN2). Elemen- fluoropolyether oil (Lancaster) and cooled rapidly to 90 K in a
tal analysis: calcd for C35H48N2Mg: C 80.67, H 9.28, N 5.38; stream of cold nitrogen using an Oxford Cryosystems low-
found C 80.50, H 9.11, N 5.22. IR (Nujol): ν = 1623 (s), 1578 (s), temperature device. Diffraction data for 2·C6H14, 3·C4H8O,
1358 (m), 1318 (s), 1240 (s), 1185 (m), 1101 (s), 1055 (w), 1042 5·C4H8O, 6·C4H8O and L5H were collected on an Oxford
(w), 1027 (w), 964 (m), 934 (m), 918 (w), 802 (s), 785 (s), 767 (s), Diffraction SuperNova Atlas CCD diffractometer equipped with
697 (s), 522 (m) cm−1
.
a
mirror-monochromated Cu-Kα radiation source (λ
=
Data for [Mg(L5)2(THF)] (5). From 1.11 g of L5H. Yield 1.54184 Å), and for 1·C6D6 and L6H on a Bruker SMART APEX
1
0.98 g, 79%. H NMR (C6D6, 298 K, 300 MHz): δ 1.42 (m, 4H, CCD diffractometer equipped with graphite-monochromated
THF–CH2), 1.94 (s, 12H, CH3), 2.27 (s, 12H, CH3), 2.36 (s, 24H, Mo-Kα radiation (λ = 0.71073 Å). Intensities were integrated
CH3), 3.84 (m, 4H, THF–OCH2), 6.43 (s, 2H, ArH), 6.88 (s, 8H, from data recorded on 0.3° (APEX) or 1° (SuperNova) frames by
ArH), 6.93 (s, 4H, ArH). 13C{1H} NMR (C6D6, 298 K, 75 MHz): δ ω rotation. Semiempirical absorption corrections based on
19.2 (CH3), 20.7 (CH3), 21.0 (CH3), 25.4 (THF–CH2), 69.2 (THF– symmetry-equivalent and repeat reflections (APEX) or Gaussian
OCH2), 126.8 (ArCH), 128.6 (ArCH), 130.2 (ArC), 130.5 (ArCH), grid face-indexed absorption corrections with a beam profile
132.2 (ArC), 135.6 (ArC), 136.0 (ArC), 145.3 (ArC), 173.2 (CN2). correction (SuperNova) were applied. All non-H atoms were
Elemental analysis: calcd for C58H70MgN4O: C 80.67, H 8.17, N located using direct methods and difference Fourier syntheses.
6.49; found C 80.57, H 8.25, N 6.41. IR (Nujol): ν = 2725 (w), All non-H atoms were refined with anisotropic displacement
1759 (w), 1605 (m), 1307 (m), 1289 (w), 1261 (m), 1235 (m), parameters. Hydrogen atoms were constrained in calculated
1212 (m), 1124 (w), 1068 (w), 1030 (s), 968 (m), 868 (s), 858 (s), positions and refined with a riding model. Programs used
800 (s), 728 (s), 685 (s), 547 (m), 512 (s), 499 (m) cm−1
.
were CrysAlisPro33 and Bruker AXS SMART34 (control), Crys-
Data for [Mg(L6)2] (6). From 1.35 g of L6H. Yield 1.05 g, AlisPro33 and Bruker AXS SAINT34 (integration), and SHELXS,35
80%. 1H NMR (C4D8O, 298 K, 300 MHz): δ 0.42 (d, 12H, SHELXL35 and OLEX236 (structure solution and refinement
CH(CH3)2, J = 6.5 Hz), 0.74 (d, 12H, CH(CH3)2, J = 6.6 Hz), 1.19 and molecular graphics). Crystal data for 1·C6D6, 2·C6H14,
(d, 12H, CH(CH3)2, J = 6.8 Hz), 1.40 (d, 12H, CH(CH3)2, J = 6.5 3·C4H8O, 5·C4H8O, 6·C4H8O, L5H and L6H can be found in
Hz), 1.88 (s, 12H, CH3), 3.20 (sept, 4H, CH(CH3)2, J = 6.8 Hz), Table 2. CCDC 951585–951591 (for 1·C6D6, 2·C6H14, 3·C4H8O,
3.69 (sept, 4H, CH(CH3)2, J = 6.6 Hz), 6.46 (s, 2H, ArH), 6.56 (s, 5·C4H8O, 6·C4H8O, L5H and L6H) contain the supplementary
4H, ArH), 6.65–6.71 (m, 4H, ArH), 6.78–6.84 (m, 4H, ArH), data for these compounds. Variata: For 1, positional disorder
6.95–6.98 (m, 4H, ArH). 13C{1H} NMR (C4D8O, 298 K, 75 MHz): was identified for atoms C(3) and C(5): the occupancies of the
δ
18.1 (CH3), 20.5 (CH(CH3)2), 20.7 (CH(CH3)2), 21.7 two components [C(3)–C(3A) and C(5)–C(5A)] were refined
(CH(CH3)2), 23.2 (CH(CH3)2), 25.9 (CH(CH3)2), 26.4 competitively, converging at a ratio of 0.795(5) : 0.205(5). Pos-
(CH(CH3)2), 120.7 (ArCH), 121.0 (ArCH), 121.6 (ArCH), 125.8 itional disorder was identified for atoms C(28) and C(30): the
(ArCH), 126.6 (ArCH), 127.7 (ArC), 130.3 (ArC), 133.8 (ArC), occupancies of the two components [C(28)–C(28A) and C(30)–
140.4 (ArC), 140.6 (ArC), 141.2 (ArC), 174.3 (CN2). Elemental C(30A)] were refined competitively, converging at a ratio of
analysis: calcd for C66H86MgN4: C 82.60, H 9.03, N 5.84; found 0.885(5) : 0.115(5). Restraints were applied on the bond lengths
C 82.69, H 9.11, N 5.73. IR (Nujol): ν = 1917 (w), 1855 (w), 1794 of the cyclohexyl fragments C(27)–C(32) and C(2)–C(7). Sensi-
(w), 1636 (m), 1587 (m), 1579 (m), 1316 (m), 1269 (m), 1249 ble anisotropic parameters could not be refined for atoms
(w), 1214 (m), 1176 (m), 1158 (m), 1135 (m), 1103 (m), 1054 C(5A), C(28A) and C(30A), so these were refined isotropically.
(m), 1045 (m), 1022 (m), 969 (s), 933 (m), 910 (w), 895 (w), For 2, the anisotropic displacement parameters of atoms
877 (w), 834 (m), 803 (s), 783 (s), 768 (s), 748 (s), 610 (w), 578 C(14)–C(16) and C(17)–C(19) were restrained. The unit cell of 2
(s), 528 (s), 481 (s), 451 (s), 425 (s) cm−1
.
contains four hexane molecules which have been treated as a
Data for [Mg(L7)2] (7). From 0.97 g of L7H. Yield 0.48 g, diffuse contribution to the overall scattering without specific
48%. 1H NMR (C6D6, 298 K, 400 MHz): δ 0.84–0.89 (m, 4H, Cy– atom positions by PLATON SQUEEZE.37 For 3, hydrogens were
CH2), 1.04–1.07 (m, 4H, Cy–CH2), 1.34–1.48 (m, 4H, Cy–CH2), placed in calculated positions and refined using a riding
1.76–1.80 (m, 4H, Cy–CH2), 2.00–2.13 (m, 4H, Cy–CH2), 2.20 model. Methyl groups were refined as rigid rotors. Examin-
(br s, 24H, CH3), 2.78–2.84 (m, 2H, Cy–CHN), 6.62–6.65 (br s, ation of the difference map showed that three methyl groups
8H, ArH), 7.57 (br s, 4H, ArH). 13C{1H} NMR (C6D6, 298 K, [C(23), C(40) and C(49)] had alternative possible positions for
Dalton Trans.
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the hydrogens. These were placed in calculated positions with 14 Cambridge Structural Database version 5.34 (updates May
50 : 50 occupancy; the two positions were then allowed to
refine as rigid rotors. Following this two further methyls were
identified as split. These were placed in calculated positions;
however refinement showed that a 75 : 25 occupancy split was
more appropriate in this case. Again these groups were
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Acknowledgements
We thank the EPSRC (EP/G011850/1; PDRA GJM and for pro- 23 S. Ogata, A. Mochizuki, M. Kakimoto and Y. Imai, Bull.
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