Neutral and cationic organometallic aluminium and indium complexes of mono-pendant arm triazacyclononane ligands

Article abstract of DOI:10.1039/b007323g

Organometallic monomeric and dimeric, neutral and cationic, κ²- and κ⁴-coordinated mono-pendant arm triazacyclononane complexes of aluminium and indium have been prepared, along with three new mono-pendant arm triazacyclononane ligand precursors HL⁴, HL⁵ and HL⁶ (HL⁴ = 1-(2-hydroxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane; HL⁵ = 1-(2-hydroxy-2-methylethyl)-4,7-dimethyl-1,4,7-triazacyclononane; HL⁶ = 1-(2-hydroxy-2,2-diphenylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of HL⁴ or HL⁵ with AlMe₃ or AlMe₃·py gives the μ-alkoxide bridged dimeric complexes [Al₂(κ²-L⁴)₂Me⁴] and [Al₂(κ²-L⁵)₂Me₄]. Reaction of HL⁴ with two equivalents of AlMe₃ gives the monomeric compound [Al(κ²-L⁴·AlMe₃)Me₂] which can also be prepared by treating [Al₂(κ²-L⁴)₂Me⁴] with two equivalents of AlMe₃. Reaction of HL² with AlMe₃·py gives [Al(κ²-L²)Me₂], whereas AlMe₃ reacts with one or two equivalents of HL¹ to give exclusively [Al(κ²-L¹)₂Me] which contains two κ²-L¹ ligands (HL¹ = 1-(2-hydroxy-3,5-dimethylbenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane; L² = 1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of AlMe₃ with HL⁶ gives low yields of the monomeric derivative [Al(κ²-L⁶)Me₂]. The κ²-coordination mode of the triazacyclononane ligands in all these compounds is unique in the chemisty of these ligands. The crystal structures of four of them are discussed. Methyl group abstraction from [Al(κ²-L⁴·AlMe₃)Me₂] or [Al(κ²-L²)Me₂] using B(C₆F₅)₃ gives the κ⁴-coordinated cationic derivatives [Al(κ⁴-L²)Me][MeB(C₆F₅)₃ ] and [Al(κ⁴-L⁴·AlMe₃)Me][MeB(C₆ F₅)₃], and the latter undergoes reaction with pyridine or MeCN to form [Al(κ⁴-L⁴)Me][MeB(C₆F₅)₃ ]. The cationic centres in the last three compounds are unreactive to unsaturated substrates and aprotic Lewis bases. Reaction of In(CH₂Ph)₃ with HL¹ or HL² affords the four-coordinate complexes [In(κ²-L¹)(CH₂Ph)₂] and [In(κ²-L²)(CH₂Ph)₂] in which the L^1,2 ligand is κ² bound to In. With the sterically less demanding HL³ [1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-dimethyl-1,4,7-triazacyclononane], however, the six-coordinate complex [In(κ⁴-L³)(CH₂Ph)₂] is formed. The compound [In(κ²-L²)(CH₂Ph)₂] reacts with B(C₆F₅)₃ to form [In(κ⁴-L²)(CH₂Ph)][(PhCH₂)B(C ₆F₅)₃].

Full text of DOI:10.1039/b007323g

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Neutral and cationic organometallic aluminium and indium
complexes of mono-pendant arm triazacyclononane ligands
David A. Robson,a Sergei Y. Bylikin,a Martine Cantuel,a Nigel A. H. Male,a Leigh H. Rees,a
Philip Mountford*a and Martin Schröderb
a Inorganic Chemistry Laboratory, South Parks Road, Oxford, UK OX1 3QR
b School of Chemistry, University of Nottingham, University Park, Nottingham, UK NG7 2RD
Received 11th September 2000, Accepted 13th October 2000
First published as an Advance Article on the web 21st December 2000
Organometallic monomeric and dimeric, neutral and cationic, κ2- and κ4-coordinated mono-pendant arm triaza-
cyclononane complexes of aluminium and indium have been prepared, along with three new mono-pendant arm
triazacyclononane ligand precursors HL4, HL5 and HL6 (HL4 = 1-(2-hydroxy-2-methylethyl)-4,7-diisopropyl-1,4,7-
triazacyclononane; HL5 = 1-(2-hydroxy-2-methylethyl)-4,7-dimethyl-1,4,7-triazacyclononane; HL6 = 1-(2-hydroxy-
2,2-diphenylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of HL4 or HL5 with AlMe3 or AlMe3ؒpy
gives the µ-alkoxide bridged dimeric complexes [Al2(κ2-L4)2Me4] and [Al2(κ2-L5)2Me4]. Reaction of HL4 with two
equivalents of AlMe3 gives the monomeric compound [Al(κ2-L4ؒAlMe3)Me2] which can also be prepared by treating
[Al2(κ2-L4)2Me4] with two equivalents of AlMe3. Reaction of HL2 with AlMe3ؒpy gives [Al(κ2-L2)Me2], whereas
AlMe3 reacts with one or two equivalents of HL1 to give exclusively [Al(κ2-L1)2Me] which contains two κ2-L1 ligands
(HL1 = 1-(2-hydroxy-3,5-dimethylbenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane; L2 = 1-(3,5-di-tert-butyl-2-
hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of AlMe3 with HL6 gives low yields of the
monomeric derivative [Al(κ2-L6)Me2]. The κ2-coordination mode of the triazacyclononane ligands in all these
compounds is unique in the chemisty of these ligands. The crystal structures of four of them are discussed. Methyl
group abstraction from [Al(κ2-L4ؒAlMe3)Me2] or [Al(κ2-L2)Me2] using B(C6F5)3 gives the κ4-coordinated cationic
derivatives [Al(κ4-L2)Me][MeB(C6F5)3] and [Al(κ4-L4ؒAlMe3)Me][MeB(C6F5)3], and the latter undergoes reaction
with pyridine or MeCN to form [Al(κ4-L4)Me][MeB(C6F5)3]. The cationic centres in the last three compounds are
unreactive to unsaturated substrates and aprotic Lewis bases. Reaction of In(CH2Ph)3 with HL1 or HL2 affords the
four-coordinate complexes [In(κ2-L1)(CH2Ph)2] and [In(κ2-L2)(CH2Ph)2] in which the L1,2 ligand is κ2 bound to In.
With the sterically less demanding HL3 [1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-dimethyl-1,4,7-triazacyclononane],
however, the six-coordinate complex [In(κ4-L3)(CH2Ph)2] is formed. The compound [In(κ2-L2)(CH2Ph)2] reacts with
B(C6F5)3 to form [In(κ4-L2)(CH2Ph)][(PhCH2)B(C6F5)3].
were carried out under an atmosphere of dinitrogen using
Schlenk-line or dry-box techniques. All protio-solvents and
Introduction
The 1,4,7-triazacyclononane ligands R3[9]aneN3 (R typically
commercially available reagents were pre-dried over activated
= H or alkyl) and their N-functionalised derivatives with one,
molecular sieves and refluxed over an appropriate drying
two or three pendant arms (terminated with neutral or anionic
agent under an atmosphere of dinitrogen and collected by
donor groups) are well established, effective and important
distillation. NMR solvents for air- and/or moisture-sensitive
ligands in metal coordination chemistry, and there is an exten-
compounds were dried over freshly ground calcium hydride
sive literature associated with them.1–3 This interest stems from
the well defined environments that these face-capping ligands
at rt (CD2Cl2), molten potassium (C6D6) or molten sodium
(C6D5CD3), distilled under reduced pressure and stored under
and their functionalised derivatives can provide and the
N2 in J. Young ampoules. NMR samples of air- and moisture-
subsequent opportunities for complex synthesis and reactivity
sensitive compounds were prepared in the dry-box in 5 mm
studies that this presents. However, apart from our own recent
Wilmad tubes, equipped with a Young’s Teflon valve.
work on aluminium systems,4 there has been only one other
1H and 13C NMR spectra were recorded on Varian Unity
report (without structural authentication) of a mono-pendant
Plus 500 or Varian Mercury Vx300 spectrometers and refer-
arm triazacyclononane complex of a Group 13 metal.5
A
enced internally to residual protio-solvent (1H) or solvent (13C)
resonances. Chemical shifts are reported relative to tetra-
methylsilane (δ 0) in δ (ppm) and coupling constants in
Hertz. 19F NMR Spectra were recorded on a Varian Mercury
Vx300 spectrometer and referenced to external CF3Cl. Assign-
ments were supported by DEPT-135 and DEPT-90, homo-
and hetero-nuclear, one- and two-dimensional experiments as
appropriate. Mass spectra were recorded on an AEI MS902,
Micromass LC Tof ESI or Micromass Autospec 500 mass
spectrometer. Elemental analyses were carried out by the
analysis laboratory of this department.
number of derivatives with tris-pendant arm homologues
have, however, been described.6–9 We report herein novel
neutral and cationic organo-aluminium and -indium com-
plexes of mono-pendant arm triazacyclononanes, including
the first structurally authenticated examples of complexes
having a triazacyclononane ligand coordinated through only
one nitrogen. Part of work has been communicated.4
Experimental
General methods and instrumentation
Where appropriate, NMR assignments are quoted with
reference to the general labelling scheme illustrated below.
All manipulations of air- and/or moisture-sensitive compounds
DOI: 10.1039/b007323g
J. Chem. Soc., Dalton Trans., 2001, 157–169
This journal is © The Royal Society of Chemistry 2001
157

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500 MHz, 298 K): δ 7.76 (m, 4H, o-H of C6H5), 7.18 (m, 4H,
m-H of C6H5, 7.03 (m, 2H, p-H of C6H5), 6.79 (s, 1H, OH),
3.38 (s, 2H, NCH2C(Ph)2OH), 2.65 (sept, J = 6.5, 2 H,
NCHMe2), 2.60 (m, 4 H, NCH2), 2.32 (s, 4 H, NCH2), 2.24 (m,
4 H, NCH2) and 0.85 (d, 12 H, J = 6.5 Hz, CHMe2). 13C -{1H}
NMR (C6D6, 125.7 MHz, 298 K): δ 148.8 (1-C of C6H5), 128.1,
126.7 and 126.4 (2-, 3-, and 4-C of C6H5), 77.1 (NCH2C-
(Ph)2OH), 70.4 (NCH2C(Ph)2OH), 60.8 (NCH2CH2N), 54.4
(CHMe2), 54.0, 53.2 (2 × NCH2CH2N) and 18.4 (CHMe2).
APCI-MS: m/z = 410, [M ϩ H]ϩ. Found (calculated for
C26H39N3O): C, 75.85 (76.22); H, 9.29 (9.61); N, 10.27 (10.26)%.
Preparations
HPri2[9]aneN3,10 HMe2[9]aneN3,11 HL1 1,12 HL2 2,12 HL3 3,13
2,2-diphenyloxirane,14 In(CH2Ph)3,15 and AlMe3ؒMeCN16 were
prepared according to literature methods. Propylene oxide was
purchased from Sigma-Aldrich and dried over freshly ground
calcium hydride under an atmosphere of dinitrogen and
collected by distillation. AlMe3 was purchased from Sigma-
Aldrich and used as received. AlMe3ؒpy17 was prepared by
dropwise addition of a pentane solution of pyridine to AlMe3
also diluted in pentane.
[Al2(ꢀ2-L4)2Me4] 7. The ligand precursor HL4 (0.57 g, 2.09
mmol) was diluted in hexanes (25 cm3) and a hexane (15 cm3)
solution of AlMe3 (0.15 g, 2.1 mmol) added dropwise.
The resulting colourless solution was allowed to stir at rt for
2 h before all volatiles were removed under reduced pressure
affording a white solid. The solid was dissolved in pentane, the
solution concentrated and placed at Ϫ30 ЊC overnight. White
crystalline needles of the product were collected. Yield: 0.21 g
(30%). 1H NMR (C6D5CD3, 500.0 MHz, 223 K): δ 4.66 (app. t,
J = 14, 2H, CHaHbCH2N), 4.00 (m, 4H, NCH2C(H)Me and
NCHmHnCH2N), 3.28 (app. t, J = 14, 1H, NCH2CHoHpN),
3.09 (m, 2H, CHMe2), 2.60–2.20 (m, 18H, NCHaHbCH2N,
NCHwHxCH2N, NCH2CHcHdN, NCH2CHoHpN, NCHmHn-
CH2N, CHMe2 and NCH2C(H)Me), 1.79 (d, J = 12, 2H,
NCH2CHcHdN), 1.64 (m, 4H, NCH2CHyHzN), 1.32 (d, J = 5.5,
6H, NCH2C(H)Me), 0.98 (d, J = 6.5 Hz, 6H, CHMe2), 0.79
and 0.66 (2 × overlapping d, 12H, 4 × CHMe2), Ϫ0.28, Ϫ0.35
(2 × s, 4 × 3H, 4 × AlMe). 13C-{1H} NMR (C6D5CD3, 125.7
MHz, 223 K): δ 62.1 (NCH2C(H)Me), 59.8 (NCH2C(H)Me),
56.2 (CHMe2), 55.4 (NCCH2CDH2N), 55.2 (CHMe2), 54.0
(NCH2CH2N), 53.8 (NCCH2CDH2N), 49.9 (NCAH2CBH2N),
48.8 (NCH2CH2N), 46.1 (NCAH2CBH2N), 22.9 (CHMe2),
22.5 (NCH2C(H)Me), 15.8, 12.9 (4 × CHMe2), Ϫ6.4, Ϫ6.8 (4 ×
AlMe). EI-MS: m/z = 327, [½M]ϩ; and 312, [(½M) Ϫ Me]ϩ.
Found (calculated for C17H38AlN3O): C, 60.3 (62.3); H, 11.9
(11.7); N, 12.6 (12.8)%. Despite repeated attempts, a satis-
factory %C analysis could not be obtained for this compound.
1-(2-Hydroxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triaza-
cyclononane (HL4, 4). HPri2[9]aneN3 (2.0 g, 9.4 mmol) was
diluted in EtOH (30 cm3) and an EtOH (10 cm3) solution of
propylene oxide (1.3 cm3, 18.7 mmol) added dropwise at 0 ЊC.
The resulting solution was allowed to stir for 4 d at rt before all
volatiles were removed in vacuo affording a pale yellow oil. The
product was purified by distillation using Kügelröhr apparatus
(90 ЊC, 0.04 Torr) to afford a colourless oil. Yield: 2.1 g (93%).
1H NMR (C6D6, 500.0 MHz, 298 K): δ 5.54 (br s, 1 H, OH),
3.86 (m, 1 H, NCH2C(H)MeOH), 2.63 (sept, J = 6.0, 2 H,
NCHMe2), 2.60–2.40 (m, 12 H, NCH2CH2N), 2.32 (m, 2 H,
NCH2C(H)MeOH), 1.19 (d, J = 6.0,
3 H, NCH2C(H)-
MeOH) and 0.90 (apparent triplet, apparent J = 7.0 Hz,
12 H, CHMe2). 13C-{1H} NMR (C6D6, 125.7 MHz, 298 K):
δ 66.5 (NCH2C(H)MeOH), 65.5 (NCH2C(H)MeOH), 58.6,
54.6 (NCH2CH2N), 54.5 (CHMe2), 52.3 (NCH2CH2N), 20.3
(NCH2C(H)MeOH), 18.5 and 18.2 (2 × CHMe2). APCI-MS
(Atmospheric Pressure Chemical Ionisation-Mass Spectro-
scopy): m/z = 272, [M ϩ H]ϩ. Found (calculated for
C15H33N3O): C, 66.0 (66.3); H, 12.6 (12.3); N, 15.4 (15.5)%.
[Al2(ꢀ2-L5)2Me4] 8. The ligand precursor HL5 (0.50 g,
2.3 mmol) was diluted in hexanes (20 cm3) and a hexane (20 cm3)
solution of AlMe3ؒpy (0.35 g, 2.3 mmol) added dropwise. The
colourless solution was allowed to stir at rt for 2 h before all
volatiles were removed under reduced pressure. The resulting
white solid was dissolved in the minimum volume of pentane
and placed at 4 ЊC for 2 d. White crystals of the product were
collected. Yield: 0.38 g (61%). 1H NMR (C6D5CD3, 500.0 MHz,
203 K): δ 4.64 (app. t, J = 14, 2H, NCHaHbCH2N), 3.91 (app t,
J = 14, 2H, NCHmHnCH2N), 3.90 (m, 2H, NCH2C(H)Me),
3.39 (app t, J = 14, 2H, NCH2CHoHpN), 2.49 (d, J = 14, 2H,
NCHaHbCH2N), 2.43–2.31 (m, 8H, NCHmHnCH2N, NCH2-
CHcHdN and NCHwHxCH2N), 2.30 (d, 2H, NCH2C(H)Me),
2.28 (s, 6H, NMe), 2.27–2.05 (m, 8H, NCH2C(H)Me and
NCHwHxCH2N), 2.0 (m, 6H, NCH2CHoHpN and NCH2-
CHyHzN), 1.94 (s, 6H, NMe), 1.5 (d, J = 14, 2H, NCH2CHc-
HdN), 1.24 (d, J = 5.5 Hz, 6H, NCH2C(H)Me), Ϫ0.25, Ϫ0.35
(2 × s, 4 × 3 H, 4 × AlMe). 13C-{1H} NMR (C6D5CD3, 125.7
MHz, 203 K): δ 61.9 (NCH2C(H)Me), 60.8 (NCH2CH2N),
59.1 (NCH2CH2N), 58.3 (NCH2C(H)Me), 58.2 (NCH2CD-
H2N), 54.6 (NCH2CBH2N), 53.4 (NCCH2CH2N), 49.0 (NMe),
48.4 (NMe), 45.8 (NCAH2CH2N), 22.1 (NCH2C(H)Me), Ϫ6.6,
Ϫ6.7 (4 × AlMe). EI-MS: m/z = 256, [(½M) Ϫ Me]ϩ. Found
(calculated for C13H30AlN3O): C, 55.0 (57.5); H, 11.1 (11.2);
N, 15.2 (15.5)%. Despite repeated attempts, a satisfactory %C
analysis could not be obtained for this compound.
1-(2-Hydroxy-2-methylethyl)-4,7-dimethyl-1,4,7-triazacyclo-
nonane (HL5, 5). HMe2[9]aneN3 (0.75 g, 4.8 mmol) was diluted
in EtOH (20 cm3) and an EtOH (20 cm3) solution of propylene
oxide (0.67 cm3, 9.5 mmol) added dropwise at 0 ЊC. The colour-
less solution was allowed to warm to rt and stirred for 20 h
before all volatiles were removed under reduced pressure. The
resulting pale yellow oil was purified by distillation using a
Kügelröhr apparatus (73–77 ЊC, 0.1 Torr) to give a colourless
1
oil. Yield: 0.69 g (67%). H NMR (C6D6, 300 MHz, 298 K):
δ 5.47 (br s, 1H, OH), 3.82 (m, 1H, NCH2C(H)MeOH),
2.58–2.45 (m, 12 H, NCH2CH2N), 2.33–2.25 (m, 2 H, NCH2-
C(H)MeOH), 2.19 (s, 6 H, NMe) and 1.17 (d, 3H, J = 6.3 Hz,
NCH2C(H)MeOH). 13C-{1H} NMR (C6D6, 75.5 MHz, 298 K):
δ 66.4 (NCH2C(H)MeOH), 65.6 (NCH2C(H)MeOH), 59.1,
58.4 and 56.8 (3 × NCH2CH2N), 46.3 (NMe) and 20.3 (NCH2-
C(H)MeOH). HRMS: Found m/z = 216.206, calculated for
C11H26N3O 216.207.
1-(2-Hydroxy-2,2-diphenylethyl)-4,7-diisopropyl-1,4,7-triaza-
cyclononane (HL6, 6). HPri2[9]aneN3 (2.00 g, 9.37 mmol) was
diluted in EtOH (30 cm3) and an EtOH (20 cm3) solution of
2,2-diphenyloxirane (3.68 g, 18.7 mmol) added dropwise. The
colourless solution was allowed to stir at rt for 10 d before the
solvent was removed under reduced pressure. The product was
isolated by fractional distillation using Kügelröhr apparatus.
The second fraction, a thick colourless oil, was collected (228–
232 ЊC, 0.05 Torr) and subsequently crystallised on standing
[Al(ꢀ2-L4ؒAlMe3)Me2] 9. The ligand precursor HL4 (1.35 g,
5.0 mmol) was diluted in hexanes (30 cm3) and a hexane
(20 cm3) solution of AlMe3 (0.72 g, 10.0 mmol) added dropwise.
1
to yield a white solid. Yield: 2.76 g (72%). H NMR (C6D6,
158
J. Chem. Soc., Dalton Trans., 2001, 157–169

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The resulting cloudy white solution was allowed to stir for 2 h
before all volatiles were removed under reduced pressure. The
resulting white solid was recrystallised from a saturated pentane
solution at Ϫ30 ЊC. Colourless crystals of the product were
stir for 2 h at rt. All volatiles were then removed under reduced
pressure affording an off-white solid which was washed with
cold hexanes (2 × 20 cm3). Further crops of product were
obtained from placing the washings at Ϫ30 ЊC. Yield: 0.90 g
1
1
collected. Yield: 1.4 g (71%). H NMR (CD2Cl2, 500.0 MHz,
(35%). H NMR (C6D5CD3, 500.0 MHz, 213 K): δ 7.00 and
213 K): δ 4.81 (app t, J = 13, 1 H, NCHaHbCH2N), 4.57 (app t,
J = 13, 1 H, NCHmHnCH2N)), 4.16 (m, 1 H, NCH2C(H)Me),
3.10 (m, 1 H, NCH2C(H)Me), 3.00–2.83 (m, 3 H, NCH2CH2N
and CHMe2), 2.83–2.79 (m, 2 H, NCH2CHcHdN and NCH2-
CHoHpN), 2.71 (app. t, J = 13, NCH2CHcHdN and NCH2-
CH2N), 2.55 (d, J = 13, 1H, NCH2C(H)Me), 2.51 (d, J = 13, 1
H, NCHaHbCH2N), 2.43 (app. t, J = 14, 2 H, NCHmHnCH2N),
1.90 (app. quin, J = 14, 2 H, NCH2CHoHpN and NCH2CH2N),
1.30 (d, J = 6.5, 3 H, NCH2C(H)Me), 0.97, 0.95, 0.93, 0.87, 0.79
(overlapping 4 × d and m, J = 6.5 Hz, 13 H, 4 × CHMe2 and
NCH2CHcHdN), Ϫ0.73, Ϫ0.85 (2 × s, 2 × 3 H, 2 × AlMe) and
Ϫ1.07 (s, 9H, AlMe3). 13C-{1H} NMR (CD2Cl2, 125.7 MHz,
213 K): δ 66.3 (NCH2C(H)Me), 58.3 (NCH2C(H)Me), 56.1,
55.1 (2 × CHMe2), 54.6 (NCH2CBH2N), 53.6 (NCH2CDH2N),
53.3 (NCCH2CH2N), 48.9 (NCH2CH2N), 46.1 (NCAH2CH2N),
21.7, 20.0, 15.6, 13.2 (4 × CHMe2), 20.9 (NCH2C(H)Me), Ϫ6.8
(AlMe3), Ϫ8.5, Ϫ10.8 (2 × AlMe). Found (calculated for
C20H47Al2N3O): C, 59.7 (60.1); H, 11.9 (11.9); N, 10.3 (10.5)%.
6.72 (s, 4 H, C6H2Me2), 4.65 (app. t, J = 13, 2 H, NCHaHb-
CH2N), 4.36 (d, J = 13, 2 H, ArCH2), 4.30 (app. t, J = 13, 2 H,
NCHmHnCH2N), 3.65 (m, 4 H, NCH2CHoHpN and NCHmHn-
CH2N), 3.32 (d, J = 13, 2 H, ArCH2), 3.20 (m, 2 H, CHMe2),
2.95 (t, J = 13, 2 H, NCH2CHcHdN), 2.82 (m, 2 H, CHMe2),
2.67 (d, J = 13, 2 H, CH2CHoHpN), 2.55 (d, J = 13, 2 H,
NCHaHbCH2N), 2.44, 2.31 (2 × s, 12 H, C6H2Me2), 2.30 (m,
4 H, NCH2CH2N), 1.83 (d, J = 13, 2 H, NCH2CHcHdN), 1.65
(m, 4 H, NCH2CH2N), 0.93, 0.86, 0.76, 0.69 (4 × d, J = 6 Hz,
24 H, 4 × CHMe2) and Ϫ0.05 (s, 3 H, AlMe). 13C-{1H} NMR
(C6D5CD3, 125.7 MHz, 213 K): δ 157.0 , 137.5 and 131.6 (Cq
of Ar), 128.4 and 126.2 (CH of Ar), 122.4 (Cq of Ar), 58.7
(ArCH2), 56.5 (NCH2CDH2N), 56.4 (CHMe2), 55.0 (over-
lapping CHMe2 and NCCH2CH2N), 54.3 (NCH2CH2N), 51.3
(NCH2CBH2N), 49.5 (NCH2CH2N), 46.4 (NCAH2CH2N), 23.2
(CHMe2), 21.0, 19.2 (2 × C6H2Me2), 16.4 , 12.5 (2 × CHMe2)
and Ϫ7.9 (AlMe). EI-MS: m/z = 388, [M Ϫ L1 Ϫ Me]ϩ. Found
(calculated for C43H75AlN6O2): C, 70.0 (70.2); H, 10.5 (10.3);
N, 11.4 (11.4)%.
NMR tube scale synthesis of [Al(ꢀ2-L4ؒAlMe3)Me2] 9 from
[Al2(ꢀ2-L4)2Me4] 7. Compound 7 (0.01 g, 0.052 mmol) was dis-
solved in C6D6 (500 µl) and placed in an NMR tube equipped
with a Young’s Teflon valve. Trimethylaluminium (3 µl, 0.104
mmol) was added via microsyringe and the resulting colour-
[Al(ꢀ2-L6)Me2] 12. The ligand precursor HL6 (1.0 g, 2.45
mmol) was dissolved in hexanes (30 cm3) and to this stirring
solution AlMe3 (0.17 g, 2.45 mmol) in hexanes (20 cm3) added
dropwise. The solution was allowed to stir for 3 h before all
volatiles were removed under reduced pressure. The solution
was concentrated and placed at Ϫ30 ЊC affording a white
crystalline solid. This was filtered off and the mother liquors
evaporated to dryness. A further crop of compound 12 was
obtained by high vacuum tube sublimation (180 ЊC, 6 × 10Ϫ6
mbar). Combined yield: 0.16 g (15%). 1H NMR (CD2Cl2, 500.0
MHz, 213 K): δ 7.66, 7.50, 7.26, 7.11 (4 × m, 10 H, C6H5), 4.62
(app. t, J = 13, 1 H, NCHaHbCH2N), 4.42 (app. t, J = 13, 1 H,
NCHmHnCH2N), 4.18 and 3.20 (d, J = 13, 2 H, NCH2CPh2),
2.87 (overlapping 3 × m, 3 H, 2 × CHMe2 and NCH2CHcHdN),
2.65 (overlapping m, 3 H, NCH2CH2N and NCH2CHcHdN),
2.56 (app. t, J = 13 Hz, 1 H, NCH2CHoHpN), 2.39 (d, J = 13,
1 H, NCHaHbCH2N), 2.13 (d, J = 13, 1 H, NCHmHnCH2N),
1.82 and 1.75 (2 × app. t, J = 13, 2 H, NCH2CH2N), 1.57 (d,
J = 13, 1 H, NCH2CHoHpN), 0.88 (overlapping 3 × d, 9 H,
3 × CHMe2), 0.75 (d, J = 6.5 Hz, 3 H, CHMe2), Ϫ0.8, Ϫ1.02
(2 × s, 2 × 3 H, AlMe). 13C-{1H} NMR (CD2Cl2, 125.7 MHz,
213 K): δ 151.5 and 149.3 (1-C of C6H5), 127.9, 127.7 (2 × 2-C
of C6H5), 125.9, 125.8 (2 × 4-C of C6H5), 124.7 and 124.4
(2 × 3-C of C6H5), 76.2 (NCH2CPh2), 63.3 (NCH2CPh2),
56.2 and 55.1 (2 × CHMe2), 55.0 (NCH2CBH2N), 54.4 (NCH2-
CDH2N), 53.4 (NCCH2CH2N), 49.3 and 48.0 (NCH2CH2N),
47.0, (NCAH2CH2N), 21.4, 19.1, 16.6 and 13.6 (4 × CHMe2)
and Ϫ10.7 (AlMe). EI-MS: m/z = 450 [M Ϫ Me]ϩ. Found
(calculated for C28H44AlN3O): C, 72.2 (71.3); H, 9.6 (9.5); N,
9.0 (9.0)%.
1
less solution shaken. H NMR analysis showed quantitative
formation of 9.
NMR tube scale synthesis of [Al2(ꢀ2-L4)2Me4] 7 from [Al-
(ꢀ2-L4ؒAlMe3)Me2] 9. Compound 9 (0.01 g, 0.027 mmol) was
dissolved in C6D6 (500 µl) and placed in an NMR tube
equipped with a Young’s Teflon valve. Pyridine (2.2 µl, 0.027
mmol) was added via a microsyringe and the resulting colour-
1
less solution shaken. H NMR analysis revealed quantitative
formation of 7 and AlMe3ؒpy.
[Al(ꢀ2-L2)Me2] 10. The ligand precursor HL2 (0.5 g, 1.2
mmol) was dissolved in hexanes (30 cm3) and a hexane (20 cm3)
solution of AlMe3ؒpy (0.086 g, 1.2 mmol) added dropwise.
The resulting colourless solution was allowed to stir at rt for 2 h
then concentrated and placed at Ϫ30 ЊC for 3 d affording the
1
product as colourless crystals. Yield: 0.34 g (57%). H NMR
(C6D5CD3, 500.0 MHz, 213 K): δ 7.57 and 6.99 (s, 2H,
C6H2But2), 4.40 (app. t, J = 13, 1 H, NCHaHbCH2N), 4.05 (app.
t, J = 13, 1 H, NCH2CHmHnN), 3.86, 3.23 (2 × d, J = 13, 2 × 1
H, ArCH2), 3.02 (app. t, J = 13, 1 H, NCH2CHoHpN), 2.87 (m,
1 H, CHMe2), 2.85 (app. t, J = 13, 1 H, NCH2CHcHdN), 2.68
(m, 1 H, CHMe2), 2.35 (d, J = 13, 1 H, NCHaHbCH2N), 2.26
(d, J = 13, 1 H, NCH2CHoHpN), 2.20 (m, 3 H, NCH2CH2N and
NCHmHnCH2N), 1.78 and 1.47 (s, 18 H, But), 1.45 (m, 2 H,
NCH2CH2N), 1.36 (d, J = 13, 1 H, NCH2CHcHdN), 0.93
(d, J = 7, 3H, CHMe2), 0.81 (overlapping 2 × d, 6 H, CHMe2),
0.61 (d, J = 7 Hz, 3 H, CHMe2), Ϫ0.23, Ϫ0.26 (2 × s, 2 × 3 H,
2 × AlMe). 13C-{1H} NMR (C6D5CD3, 125.7 MHz, 213 K):
δ 157.5, 138.2 and 137.5 (Cq of Ar), 124.9 and 124.3 (CH of
Ar), 120.3 (Cq of Ar), 58.3 (ArCH2), 56.8, 55.5 (2 × CHMe2),
55.4 (NCH2CH2N), 55.0 (NCH2CDH2N), 53.6 (NCCH2CH2N),
49.0 (NCH2CH2N), 48.6 (NCH2CBH2N), 46.1 (NCAH2CH2N),
35.6, 34.5 (2 × CMe3), 32.2, 29.9 (2 × CMe3), 22.4, 19.2, 17.7,
13.2 (4 × CHMe2) and Ϫ9.4 (AlMe). Found (calculated for
C29H54AlN3O): C, 71.1 (71.4); H, 11.1 (11.2); N, 8.4 (8.6)%.
[Al(ꢀ4-L2)Me][MeB(C6F5)3] 13. [Al(κ2-L2)Me2] 10 (0.34 g,
0.71 mmol) was dissolved in CH2Cl2 (20 cm3) and a CH2Cl2 (15
cm3) solution of B(C6F5)3 (0.36 g, 0.71 mmol) added dropwise.
The colourless solution was stirred for 30 min at rt before the
solvent was removed under reduced pressure. The product was
collected as a white solid. Yield: 0.67 g (96%). 1H NMR
(CD2Cl2, 500.0 MHz, 298 K): δ 7.35, 6.91 (2 × d, J = 2.5, 2 × 1
H, C6H2But2), 4.00 (s, 2H, ArCH2), 3.64 (m, 2 H, CHMe2), 3.05,
2.96, 2.82 and 2.74 (m, 12 H, NCH2CH2N), 1.37, 1.23 (2 × s,
2 × 9 H, 2 × But), 1.25, 1.19 (2 × d, J = 6.5 Hz, 2 × CHMe2),
0.44 (br s, 3H, MeB(C6F5)) and Ϫ0.28 (s, 3H, AlMe). 13C -{1H}
NMR (CD2Cl2, 125.7 MHz, 298 K): δ 156.4 (Cq of Ar), 148.6
[Al(ꢀ2-L1)2Me] 11. AlMe3 (0.23 g, 3.1 mmol) was diluted in
hexanes (20 cm3) and was added to HL1 (2.17 g, 6.2 mmol) in
hexanes (35 cm3). The resulting cloudy solution was allowed to
1
(d, JCF = 233, o-C of C6F5), 140.6 (Cq of Ar), 137.9 (d,
J. Chem. Soc., Dalton Trans., 2001, 157–169
159

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1
1JCF = 238, p-C of C6F5), 137.6 (Cq of Ar), 136.7 (d, JCF
=
3H, Me2CH). EI-MS: m/z = 552, [M Ϫ CH2Ph]ϩ; and 461,
233, m-C of C6F5), 126.0 and 124.6 (CH of Ar), 118.5 (Cq
of Ar), 64.2 (CH2Ar), 57.8 (CHMe2), 43.8, 49.5 and 47.3
(NCH2CH2N), 35.1 and 34.4 (CMe3), 31.6 and 30.5 (CMe3),
19.7 and 16.9 (CHMe2), 10.3 (BMe) and Ϫ4.3 (AlMe). 19F
NMR (CD2Cl2, 282 MHz, 298 K): δ Ϫ133.6 (d, JCF = 20, o-F
of C6F5), Ϫ165.2 (t, JCF = 20, p-F of C6F5) and Ϫ167.9
(m, JCF = 20 Hz, m-F of C6F5). Found (calculated for
C47H54AlBF15N3O): C 55.7 (56.4), H 5.1 (5.4), B 0.9 (1.1), N 4.2
(4.0)%.
[M Ϫ 2(CH2Ph)]ϩ. Found (calculated for C35H50InN3O): C,
65.0 (65.3); H, 7.9 (7.8); N, 6.1 (6.5)%.
[In(ꢀ2-L2)(CH2Ph)2] 17. In(CH2Ph)3 (0.39 g, 1 mmol) was
dissolved in benzene (15 cm3) and a solution of HL2 (0.43 g,
1 mmol) in benzene (15 cm3) added dropwise over 2 h. The
mixture was stirred at rt for 24 h. The volatiles were removed
under reduced pressure and the residue dried in vacuo for
24 h to give the product as a white solid. Yield: 0.52 g (71%).
1H NMR (CDCl3, 300.1 MHz, 248 K): δ 7.71 (s, 1H, C6H2),
6.9–7.3 (m, 11H, C6H5 ϩ C6H2), 4.12 (broad m, 1H, N(CH2)2-
N), 3.95 (broad d, J = 12.6, 1H, NCH2C6H2), 3.41 (broad d,
J = 12.6, 1H, NCH2C6H2), 3.12 (broad m, 2H, N(CH2)2N),
1.94 (s, 9H, Me3CC6H2), 1.55 (s, 9H, Me3CC6H2), 1.5–2.8
(broad m, 15H, N(CH2)2N ϩ CH2Ph ϩ Me2CH), 0.91 (broad
d, J = 6.0, 3H, Me2CH), 0.81 (broad m, 6H, Me2CH) and
0.60 (broad d, J = 6.0 Hz, 3H, Me2CH). EI-MS: m/z = 636,
[M Ϫ (CH2Ph)]ϩ; and 545, [M Ϫ 2(CH2Ph)]ϩ. Found (cal-
culated for C41H62InN3O): C, 67.1 (67.7); H, 8.3 (8.6); N, 5.5
(5.8)%.
1
1
1
[Al(ꢀ4-L4ؒAlMe3)Me][MeB(C6F5)3] 14. [Al(κ2-L4ؒAlMe3)Me2]
9 (0.5 g, 1.25 mmol) was dissolved in CH2Cl2 (25 cm3) and
a CH2Cl2 (15 cm3) solution of B(C6F5)3 (0.36 g, 0.71 mmol)
added dropwise. The resulting solution was allowed to stir at
rt for 30 min before the solvent was removed under reduced
pressure. The product was collected as a white solid. Yield: 0.96
1
g (84%). H NMR (CD2Cl2, 300.0 MHz, 298 K): δ 4.12 (m,
1H, NCH2CH(Me)), 3.76 and 3.40 (sept, J = 11, 1H, CHMe2),
3.4–2.6 (m, 15 H, NCH2CH2N and NCH2CH(Me)), 1.38
(d, J = 9, 3H, NCH2CH(Me)), 1.31 (overlapping 3 × d, 3 × 3 H,
3 × CHMe2), 1.18 (d, J = 11 Hz, 3 H, CHMe2), 0.47 (br s, 3 H,
MeB(C6F5)3), Ϫ0.32 (s, 3 H, AlMe) and Ϫ0.84 (s, 9 H, AlMe3).
13C-{1H} NMR (CD2Cl2, 75.5 MHz, 298 K): δ 148.4 (d,
[In(ꢀ4-L3)(CH2Ph)2] 18. In(CH2Ph)3 (0.76 g, 2 mmol) was
dissolved in benzene (30 cm3) and a solution of HL3 (0.75 g,
2 mmol) in benzene (15 cm3) added dropwise over 3 h. The
mixture was stirred at rt for 16 h. The solution was filtered
and all volatiles were removed under reduced pressure. The
resulting white solid was washed with pentane (2 × 20 cm3)
1JCF = 240, o-C of C6F5), 137.8 (d, JCF = 243, p-C of C6F5),
1
1
136.6 (d, JCF = 246 Hz, m-C of C6F5), 66.6 (NCH2C(H)CH3),
66.0 (NCH2C(H)CH3), 58.6, 57.8, 52.6, 52.0, 46.3 and 41.7
(NCH2CH2N), 22.5 (NCH2C(H)CH3), 19.7, 17.0 and 14.6
(CHMe2), 10.6 (BMe), Ϫ4.0 (AlMe3) and Ϫ4.7 (AlMe). 19F
NMR (CD2Cl2, 282 MHz, 298 K): δ Ϫ133.4 (d, JCF = 20,
o-F of C6F5), Ϫ164.9 (t, JCF = 20, p-F of C6F5) and Ϫ167.6
(m, JCF = 20 Hz, m-F of C6F5). Found (calculated for C38-
H47Al2BF15N3O) C 49.4 (50.0), H 5.0 (5.2), B 0.7 (1.2), N 4.6
(4.6)%.
1
and dried in vacuo. Yield: 1.06 g (78%). H NMR (C6D6, 500
1
MHz, 298 K): δ 7.62 (d, J = 2.5, 1H, C6H2But2), 7.22–7.00
(m, 7H, InCH2C6H5), 6.93 (m, 2H, InCH2C6H5), 6.87 (d,
J = 2.5, 1H, C6H2But2), 6.81 (m, 1H, InCH2C6H5), 4.40
(d, J = 12, 1H, CH2Ar), 2.75 (d, J = 12, 1H, CH2Ar), 2.69
(d, J = 10, 1H, InCH2Ph), 2.43 (m, 1H, NCH2CH2N), 2.31
(m, 5H, NCH2CH2N), 2.25 (d, J = 10, 1H, InCH2Ph), 2.20
(d, J = 10 Hz, 1H, InCH2Ph), 2.08 (s, 3H, NMe), 1.84 (s,
9H, C(Me3), 1.78 (m, 4H, NMe and InCH2Ph), 1.62 (m, 2H,
0.48, NCH2CH2N), 1.44 (s, 9H, CMe3), 1.35–1.20 (m, 2H,
NCH2CH2N), 1.15 (m, 1H, NCH2CH2N) and 1.05 (m, 1H,
NCH2CH2N). 13C -{1H} NMR (C6D6, 75.5 MHz, 298 K):
δ 165.1 (2-C of C6H2But2), 149.8 (1-C of C6H2But2), 138.0 (3-C
of C6H2But2), 133.5 (1-C of C6H5), 128.5, 128.4, 128.3, 128.2,
127.8, 127.6, 126.7, 125.9 and 124.0 (C6H5), 121.1 and 120.9
(4,6-C of C6H2But2), 120.6 (C6H5), 120.0 (5-C of C6H2But2),
64.9 (CH2Ar), 55.9, 55.7, 54.2, 50.3 and 50.2 (NCH2CH2N),
48.2 (NMe), 47.8 (NCH2CH2N), 47.6 (NMe), 35.8 and 34.0
(CMe3), 32.3 and 30.3 (CMe3), 28.5 and 27.5 (CH2Ph). Found
(calculated for C37H58InN3O): C, 66.4 (66.2); H, 8.1 (8.2); N,
5.5 (6.2)%.
1
1
NMR tube scale synthesis of [Al(ꢀ4-L4)Me][MeB(C6F5)3] 15.
Compound 14 (0.01 g, 0.011 mmol) was dissolved in CH2Cl2
(500 µl) and added to an NMR tube equipped with a Young’s
Teflon tap. Pyridine (1.8 µl, 0.022 mmol) was added via
microsyringe and the resulting colourless solution shaken.
All volatiles were removed under reduced pressure overnight
and the residue was dissolved in CD2Cl2 (500 µl). 1H and
19F NMR analysis was conducted on the product. Attempts to
prepare analytically pure samples of 15 on a preparative scale
were unsuccessful. 1H NMR (CD2Cl2, 300.0 MHz, 298 K):
δ 3.81 (m, 1H, NCH2CH(Me)), 3.41 (m, 2H, 2 × CHMe2), 3.30–
3.10 (m, 4H, NCH2CH2N), 3.09–3.02 (m, 2H, NCH2CH2N),
3.00 (dd, 1H, NCH2CH(Me)), 2.98–2.80 (m, 4H, NCH2CH2N),
2.78–2.45 (m, 6H, NCH2CH2N), 2.12 (dd, 1H, NCH2CH(Me)),
1.39, 1.33, 1.20 and 1.15 (d, J = 7, 12H, 4 × CHMe), 1.09 (d,
J = 6 Hz, 3H, NCH2CH(Me)), 0.47 (br s, 3H, BMe) and Ϫ0.72
(s, 3H, AlMe). 19F NMR (CD2Cl2, 282 MHz, 298 K): δ Ϫ133.6
[In(ꢀ4-L2)(CH2Ph)][(PhCH2)B(C6F5)3] 19. [In(κ2-L2)(CH2-
Ph)2] 17 (0.14 g, 0.192 mmol) was dissolved in benzene (8 cm3)
and a solution of B(C6F5)3 (0.099 g, 0.192 mmol) in benzene
(8 cm3) added dropwise over 20 min. The mixture was stirred at
rt for 3 h. The volatiles were removed under reduced pressure,
the residue was washed with pentane (10 cm3) and dried in
vacuo for 24 h to afford the product as a white solid. Yield 0.19
1
1
(d, JCF = 20, o-F of C6F5), Ϫ165.6 (t, JCF = 20, p-F of C6F5)
and Ϫ168.2 (m, 1JCF = 20 Hz, m-F of C6F5).
[In(ꢀ2-L1)(CH2Ph)2] 16. In(CH2Ph)3 (0.39 g, 1 mmol) was
dissolved in benzene (25 cm3) and a solution of HL1 (0.35 g,
1 mmol) in benzene (25 cm3) added dropwise over 20 min. The
mixture was stirred at rt for 24 h. The volatiles were removed
under reduced pressure. The residue was washed with pentane
(2 × 20 cm3) and dried in vacuo for 24 h to give the product as
1
g (78%). H NMR (C6D6, 300.1 MHz, 298 K): δ 7.61 (s, 1 H,
C6H2But2), 7.05–7.25 (m, 6 H, InCH2C6H5 and BCH2C6H5),
6.9–7.0 (m, 4 H, InCH2C6H5, BCH2C6H5 and C6H2But2),
6.81 (m, 1 H, InCH2C6H5 or BCH2C6H5), 3.35 (br. s, 2 H,
BCH2C6H5), 3.24 (broad s, 2 H, ArCH2), 2.64 (m, 2 H, CH-
Me2), 2.38 (s, 2 H, InCH2Ph), 2.1–2.3 (m, 2 H, NCH2CH2N),
2.03 (m, 4 H, NCH2CH2N), 1.89 (overlapping m, 4 H, NCH2-
CH2N), 1.6–1.8 (overlapping m, 2 H, NCH2CH2N), 1.57, 1.39
(2 × s, 2 × 9 H, 2 × But), 0.48, 0.24 (2 × d, J = 6.5, 2 × 6 H,
2 × CHMe2). 19F NMR (C6D6, 300 MHz, 298 K): δ Ϫ136.0
(d, J = 23.6, o-F of C6F5), Ϫ168.7 (t, J = 21.3, p-F of C6F5)
and Ϫ171.8 (t, J = 21.3 Hz, m-F of C6F5). ES-MS: m/z = 636
a white solid. Yield: 0.47 g (73%). H NMR (toluene-d8, 300
1
MHz, 248 K): δ 6.7–7.5 (m, 12H, C6H5 and C6H2), 4.14 (broad
m, 1H, N(CH2)2N), 3.91 (broad d, J = 12.4, 1H, NCH2C6H2),
3.39 (broad d, J = 12.4, 1H, NCH2C6H2), 2.98 (broad m,
2H, N(CH2)2N), 2.71 (s, 3H, Me2C6H2), 2.39 (s, 3H, Me2C6H2),
1.9–2.7 (broad m, 11H, N(CH2)2N ϩ CH2Ph ϩ Me2CH), 1.69
(broad d, 2H, N(CH2)2N), 1.39 (broad d, 2H, N(CH2)2N), 0.65–
0.85 (broad m, 9H, Me2CH) and 0.60 (broad d, J = 6.1 Hz,
160
J. Chem. Soc., Dalton Trans., 2001, 157–169

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Table 1 X-Ray data collection and processing parameters for [Al2(κ2-L5)2Me4] 8 and [Al(κ2-L4ؒAlMe3)Me2] 9
8
9
Formula
Formula weight
C26H60Al2N6O2
542.76
C20H47Al2N3O
399.57
Crystal system
Space group
Orthorhombic
Pbcn
Triclinic
P1
¯
a/Å
b/Å
c/Å
α/Њ
22.345(1)
139720(4)
10.6340(3)
—
—
—
3319.9
7.6670(6)
11.4630(15)
15.1650(13)
70.965(5)
88.397(5)
78.458(6)
1233.4
β/Њ
γ/Њ
V/Å3
Z
4
2
µ(Mo-Kα)/mmϪ1
Total reflections
Observed reflections
Final R, Rw (I > 3σ(I))
Final R, wR2 (all data)
Final R, wR2 (I > 2σ(I))
0.110
18308
1731 (I > 3σ(I))
0.054, 0.066
—
—
0.131
3762
3296 (I > 2σ(I))
—
0.0485, 0.131
0.0409, 0.118
[M]ϩ. Found (calculated for C59H62BF15InN3O): C, 56.9 (57.2);
H, 5.3 (5.0); N, 3.3 (3.4)%.
previously to attach one or more 2-hydroxyalkyl side
chains to triazacyclononane rings.24,25 The 2-hydroxypropyl
derivatives 4 and 5 are colourless oils whereas the diphenyl
substituted analogue 6 forms a white, semi-crystalline solid
on standing.
Crystal structure determinations of [Al2(ꢀ2-L5)2Me4] 8 and
[Al(ꢀ2-L4ؒAlMe3)Me2] 9
Structure determinations of compounds 7 and 10 have been
communicated previously.4 Crystal data collection and pro-
cessing parameters for 8 and 9 are given in Table 1. Crystals
were immersed in a film of perfluoropolyether oil on a glass
fibre and transferred to an Enraf-Nonius DIP2000 image
plate diffractometer equipped with an Oxford Cryosystems
low-temperature device.18 Data were collected at 150 K using
Mo-Kα radiation; equivalent reflections were merged and the
images processed with the DENZO and SCALEPACK pro-
grams.19 Corrections for Lorentz-polarisation effects and
absorption were performed and the structures solved by direct
methods. Subsequent Fourier difference syntheses revealed
the positions of all other non-hydrogen atoms, and hydrogen
atoms were included in calculated positions. Examination
of the refined extinction parameters and agreement analyses
suggested that no extinction correction was required. Crystal-
lographic calculations were performed using SIR 92,20
CRYSTALS-PC,21 SHELXS 96,22 and SHELXL 93.23
CCDC reference number 186/2230.
See http://www.rsc.org/suppdata/dt/b0/b007323g/ for crystal-
lographic files in .cif format.
There is considerable literature precedent for the synthesis
of hydroxy- or phenoxy-aluminium compounds from the
corresponding alcohol or phenol and an aluminium tri-
alkyl derivative.26–28 The compounds HL1–6 1–6 were therefore
selected as starting materials and the reactions between them
and either AlMe3 or AlMe3ؒpy17 are summarised in Scheme 1.
Full characterising data for these, and all the new compounds,
are given in the Experimental section.
Results and discussion
Ligand precursors
The ligand precursors used in this work are shown below.
The 2-hydroxybenzyl derivatives HL1 1, HL2 2 and HL3
3
were prepared according to literature procedures.12,13 The
2-hydroxyethyl N-substituted compounds HL4 4, HL5 5 and
HL6 6 have not been described previously. They were prepared
from either HMe2[9]aneN310 or HPri2[9]aneN311 and the appro-
priate mono- or di-substituted oxirane in good yield as shown
in eqn (1). Analogous ring-opening procedures have been used
Dimeric complexes of aluminium
Reaction between AlMe3 or AlMe3ؒpy and one equivalent of
the 2-hydroxypropyl functionalised triazacyclononanes HL4 4
or HL5 5 in hexanes at room temperature afforded the white,
crystalline products [Al2(κ2-L4)2Me4] 7 and [Al2(κ2-L5)2Me4]
8 in 30 and 61% isolated yield, respectively. The single
crystal structures of both compounds have been determined
and views of the molecular structures are given in Figs. 1
and 2. Data collection parameters for 8 are listed in Table 1
and selected bond lengths and angles for 7 and 8 are sum-
marised in Tables 2 and 3. Both compounds exist as binuclear
µ-alkoxy-bridged compounds in the solid state. Crystals of
7 contain one complete molecule in each asymmetric unit
whereas molecules of 8 lie across crystallographic two-fold
(1)
J. Chem. Soc., Dalton Trans., 2001, 157–169
161

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Table 2 Selected bond distances (Å) and angles (Њ) for [Al2(κ2-L4)2-
Me4] 74
Table 3 Selected bond distances (Å) and angles (Њ) for [Al2(κ2-L5)2Me4]
8. Atoms carrying the suffix “B” are related to their counterparts by the
symmetry operator [2 Ϫ x, y, ½ Ϫ z]
Al(1)–O(13)
Al(1)–O(28)
Al(1)–C(15)
Al(1)–C(14)
Al(1)–N(1)
1.849(3)
1.935(3)
1.972(5)
1.977(5)
2.245(4)
Al(2)–O(28)
Al(2)–O(13)
Al(2)–C(29)
Al(2)–C(30)
Al(2)–N(16)
1.845(3)
1.946(3)
1.966(5)
1.983(5)
2.265(4)
Al(1)–O(1)
Al(1)–O(1B)
Al(1)–N(3)
1.851(2)
1.944(3)
2.306(3)
Al(1)–C(11)
Al(1)–C(12)
1.993(4)
1.984(4)
N(3)–Al(1)–O(1)
N(3)–Al(1)–O(1B)
O(1)–Al(1)–O(1B)
N(3)–Al(1)–C(11)
O(1)–Al(1)–C(11)
O(1B)–Al(1)–C(11)
N(3)–Al(1)–C(12)
C(32)–O(1)–Al(1)
78.6(1)
151.0(1)
74.8(1)
94.0(1)
128.9(1)
93.8(1)
96.9(1)
123.9(2)
O(1)–Al(1)–C(12)
O(1B)–Al(1)–C(12) 103.7(1)
C(11)–Al(1)–C(12) 118.9(2)
Al(1)–N(3)–C(2)
Al(1)–N(3)–C(4)
Al(1)–N(3)–C(31)
Al(1)–O(1)–Al(1B) 104.7(1)
C(32)–O(1)–Al(1B) 129.7(2)
112.2(1)
O(13)–Al(1)–O(28)
O(13)–Al(1)–C(15)
O(28)–Al(1)–C(15)
O(13)–Al(1)–C(14)
O(28)–Al(1)–C(14)
C(15)–Al(1)–C(14)
O(13)–Al(1)–N(1)
O(28)–Al(1)–N(1)
C(15)–Al(1)–N(1)
C(14)–Al(1)–N(1)
C(10)–N(1)–Al(1)
C(9)–N(1)–Al(1)
C(2)–N(1)–Al(1)
Al(1)–O(13)–Al(2)
C(11)–O(13)–Al(1)
C(11)–O(13)–Al(2)
74.56(14)
112.2(2)
104.5(2)
127.9(2)
92.1(2)
120.0(2)
79.05(15)
151.0(2)
96.5(2)
O(28)–Al(2)–O(13)
O(28)–Al(2)–C(29)
O(13)–Al(2)–C(29)
O(28)–Al(2)–C(30)
O(13)–Al(2)–C(30)
C(29)–Al(2)–C(30)
O(28)–Al(2)–N(16)
O(13)–Al(2)–N(16)
C(29)–Al(2)–N(16)
C(30)–Al(2)–N(16)
C(25)–N(16)–Al(2)
C(24)–N(16)–Al(2)
C(17)–N(16)–Al(2)
Al(1)–O(28)–Al(2)
C(26)–O(28)–Al(1)
C(26)–O(28)–Al(2)
74.36(14)
113.7(2)
103.2(2)
128.4(2)
93.5(2)
117.9(2)
79.12(15)
151.33(15)
97.2(2)
94.5(2)
99.5(3)
107.5(3)
117.0(3)
104.7(2)
129.7(3)
123.3(3)
106.6(2)
118.0(2)
99.3(2)
amidal coordination environment. In each case the two methyl
groups and one of the bridging oxygens form the equatorial
donors; the axial sites are occupied by a single nitrogen of the
κ2 coordinated triazacyclic ligand and the second bridging
oxygen atom. The Al–O distances to the bridging alkoxide
moieties are inequivalent, the oxygen binding most tightly
to the aluminium to which the N of the same L4,5 ligand is
bonded. The Al–Me, Al–N and Al–µ-O distances in 7 and 8 are
comparable to previously reported values in related binuclear
systems.29 The compounds contain two chiral centres (not
resolved in the racemic ligand precursors HL4 and HL5),
namely the CH2C(H)MeO carbons of the pendant arms. As
94.7(2)
100.3(3)
106.2(3)
116.9(3)
104.1(2)
123.9(3)
130.6(3)
rotation axes and only one half of each moleule is crystal-
lographically independent.
Each of the aluminium centres in [Al2(κ2-L4)2Me4] 7 and
[Al2(κ2-L5)2Me4] 8 possesses an approximately trigonal bipyr-
Scheme 1 Reagents and conditions: (i) HL1 (2 equivalents), hexane, rt, 2 h, 35%; (ii) HL2, hexane, rt, 2 h, 57%; (iii) HL4 or HL5, hexane, rt, 2 h, 30
(7) or 61% (8); (iv) 0.5 HL4, hexane, rt, 2 h, 71%; (v) HL6, hexane, rt, 3 h, 15%; (vi) 2 AlMe3, C6D6, rt, 5 min, > 95%; (vii) py, C6D6, rt, 5 min, > 95%.
162
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Fig. 1 Displacement ellipsoid (35%) plot of [Al2(κ2-L4)2Me4] 7 with
H atoms omitted.
Fig. 3 Variable temperature 500.0 MHz 1H NMR spectra of [Al2-
(κ2-L5)2Me4] 8 in C6D5CD3.
Al(1) ؒ ؒ ؒ Al(2)–C(29) 18.3Њ and C(14)–Al(1) ؒ ؒ ؒ Al(2)–C(30)
59.8Њ. These differences are attributed to the greater steric
crowding around C(11), C(11B) versus that for C(12), C(12B)
in 8 (and around the corresponding carbons in 7).
While the kind of binuclear, five-coordinate motif found
for compounds 7 and 8 is structurally well established in
aluminium chemistry,29 the unique feature of these compounds
is the κ2 coordination mode of the L4 and L5 ligands that bind
through only one of the triazacyclononane nitrogens. There
is no structural precedent for any pendant arm functionalised
triazacyclononane ligand binding through fewer than all three
ring nitrogens. Triazacyclononanes without pendant arms
have been observed to bind in a κ2 mode (i.e. through two
ring nitrogens) to transition metals with a d8 electronic con-
figuration.30,31 This is presumed to arise from strong ligand field
effects in these square planar complexes. Aluminium com-
plexes of triazacyclononanes with three pendant anionic donor
arms have been described.8,32 These possess κ6-bound ligands in
which all three triazacyclic nitrogens are bound to the metal
centre. The κ2 coordination of the mono pendant arm macro-
cycles described here is presumably a function of the small
radius of aluminium and the good σ-donor ability of the metal-
bound methyl groups.
A solution molecular weight measurement for compound 7
(found: 657, calculated for dimeric 7: 655 g molϪ1) confirms that
the dimeric structures are maintained in the solution phase. The
1H and 13C NMR data for 7 and 8 are temperature-dependent
and show that these compounds are fluxional in solution. The
data for the ring N-methylated homologue 8 are the easiest to
interpret and we will discuss in detail only these. Those for 7 are
1
analogous but, for example, the H spectra feature additional
Fig. 2 Displacement ellipsoid (20%) plot of [Al2(κ2-L5)2Me4] 8 with
H atoms omitted. Atoms carrying the suffix “B” are related to their
counterparts by the symmetry operator [2 Ϫ x, y, ½ Ϫ z]. (a) Viewed
approximately perpendicular to the Al2O2 planes. (b) Viewed along the
Al(1) ؒ ؒ ؒ Al(1B) vector.
doublets and septets for the four methyl groups and two
methine hydrogens of the inequivalent, diastereotopic ring
N-isopropyl groups. Selected 500 MHz 1H spectra of [Al2-
(κ2-L5)2Me4] 8 in toluene-d8 between Ϫ70 and 21 ЊC are shown
in Fig. 3.
the axial view of 8 in Fig. 2(b) illustrates, the CH2C(H)MeO
methyl groups (C(33) and C(33B)) are both oriented “up”
towards the AlMe carbons C(12) and C(12B) and away from
the two triazacyclononane rings. As is apparent from the
structures of 7 and 8, the molecules form exclusively R,R (and
S,S) enantiomers and there is no evidence in the solid state or
solution (see below) for a second distinguishable product
corresponding to the R,S or S,R diastereoisomers. Presumably
this arises from the need to minimise steric interactions in the
binuclear products. The axial view in Fig. 2(b) also emphasises
the different Me–Al ؒ ؒ ؒ Al–Me torsion angles: C(12)–
Al(1) ؒ ؒ ؒ Al(1B)–C(12B) 16.7Њ and C(11)–Al(1) ؒ ؒ ؒ Al(1B)–
C(11B) 60.1Њ; the corresponding values for 7 are C(15)–
The slow exchange limit is reached at Ϫ70 ЊC and the
spectrum is consistent with the solid state structure (Fig. 2a
and 2b). The two singlets between δ ca. 0 and Ϫ0.5 are
attributed to the inequivalent AlMe groups, the doublet at
δ 1.24 is assigned to the CH2C(H)MeO methyl group of
the pendant arm and couples to the CH2C(H)MeO methine
hydrogen that appears at δ ca. 3.9 (overlapping with a triaza-
cyclononane ring CH2 signal). The two singlets at δ 1.94 and
2.28 are assigned to the two inequivalent macrocycle NMe
groups. The remaining multiplets all arise from the macrocycle
ring and arm diastereotopic methylene hydrogens, all of which
are inequivalent. The 13C NMR spectrum of compound 8 at
this temperature shows the expected 13 different carbon atom
J. Chem. Soc., Dalton Trans., 2001, 157–169
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Fig. 4 Proposed mechanism for the fluxional process in [Al2(κ2-L4)2Me4] 7 and [Al2(κ2-L5)2Me4] 8.
environments. It has been possible through the use of 1- and 2-
kinetic data from the NMe resonances in either the 1H or
dimensional shift correlation and NOE (Nuclear Overhauser
Effect) NMR spectroscopy to make a partial assignment of the
macrocycle ring methylene hydrogens. Details are given in the
Experimental section. Of particular interest are the apparent
triplets (each of intensity 2 H per dimer) at δ 4.64 and 3.91
(overlapping with the signal from CH2C(H)MeO mentioned
above). These are not mutually coupled and each is assigned to
one of the two methylene hydrogens either side of the Al-bound
N atom (i.e. one is attached to C(2) and one to C(4) in Fig. 2).
Such low-field shifts of triazacyclononane methylene reson-
ances are not encountered in the κ4-coordinated ligands (the
typical shift range being δ ca. 2 to < 4) and appear to be charac-
teristic of all the κ2-bound pendant arm macrocycles described
herein.
13C spectra of 7 (or the NPri signals of 8) due to overlapping
resonances, and so the following discussion of the exchange
mechanisms in 7 and 8 is only a qualitative one based on the
general appearance of the spectra. However, the interpretation
is underpinned by detailed and quantitative NMR studies by
Oliver and co-workers of a series of related fluxional systems
[Al2(µ-“O-N”)2Me4] where “O-N” denotes an optically active
amino-alkoxide ligand.34
The spectra in Fig. 3 can be interpreted with the aid of
Fig. 4. The overall dynamic processes probably proceed via
the binuclear species denoted 7* or 8* which possess four-
coordinate aluminium centres and κ1-coordinated L4,5 ligands.
Oliver and co-workers have eliminated the possibility of mono-
nuclear intermediates (favouring binuclear intermediates
analogous to 7* or 8*) in their related systems on the basis of
detailed kinetic data. Furthermore, binuclear, four-coordinate
complexes related to 7* and 8* (i.e. with a pendant donor
group) have often been proposed to be in equilibrium with their
binuclear, five-coordinate counterparts.34–37 As shown in Fig. 4,
for exchange of the two inequivalent AlMe groups to occur the
macrocycle nitrogen must detach from one Al atom and (via
a rotation about the O–C(H)Me single bond) then coordinate
to the other. Thus the AlMe groups that were originally closest
to the macrocyclic moiety (e.g. C(11), C(11B) in Fig. 2a) are
The 1H NMR spectra in Fig. 3 clearly change with increasing
temperature. The macrocycle NMe groups and pairs of
methylene H atoms undergo mutual site exchange. Thus at
21 ЊC the NMe groups appear as a singlet at δ 2.14 (intensity
12 H per dimer) while the unusually shifted apparent triplets at
δ 4.64 and 3.91 at Ϫ70 ЊC give rise to an averaged apparent
triplet at δ 4.17 (intensity 4 H per dimer) at 21 ЊC. The
CH2C(H)MeO (δ 3.93) and CH2C(H)MeO (doublet, δ 1.24)
resonances of the pendant arm do not significantly change with
temperature. The two AlMe signals at Ϫ70 ЊC coalesce to a
1
singlet at δ Ϫ0.47 (intensity 12 H per dimer). These H NMR
now furthest away, and vice versa. The estimated ∆G‡ values
Tc
spectral changes are paralleled in the 13C spectra. For example,
at 21 ЊC there are three macrocyclic ring CH2 carbon signals
(instead of the six observed at Ϫ70 ЊC) and one NMe and AlMe
of 52.1–54.0 1 kJ molϪ1 for AlMe group exchanges in 7 and
8 are consistent with the values reported by Oliver and co-
workers for the exchange processes in their [Al2(µ-“O-N”)2Me4]
systems. However, careful examination of molecular models
and the solid state structures in Figs. 1 and 2 shows that this
simple decoordination–rotation–recoordination process cannot
alone account for the observed mutual exchange of the macro-
cyclic NR (R = Me or Pri) groups. To exchange these two
groups (and to account for all the pairwise ring methylene
proton and carbon exchange processes in 7 and 8) requires a
rotation about the Nmacrocycle–CH2C(H)MeO (i.e. C(31)–N(3) in
Fig. 2) bond and subsequent inversion at the Nmacrocycle atom.
1
signal. The H and 13C NMR spectra of compound 7 show
analogous features.
We have estimated ∆GTc values (Gibbs free energy of
‡
activation at the coalescence temperature, Tc) for the AlMe
1
group exchange processes in compounds 7 and 8 from the H
NMR coalescence points (Tc = 261 and 255 K, respectively).33
For 7 ∆G‡261K is 54.0 1 kJ molϪ1 and for 8 the corresponding
∆G‡255K is 52.1 1 kJ molϪ1. The values are comparable within
experimental error. Unfortunately we cannot reliably extract
164
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Table 4 Selected bond distances (Å) and angles (Њ) for [Al(κ2-L4ؒ
AlMe3)Me2] 9
Al(1)–O(13)
Al(1)–C(15)
Al(1)–C(14)
Al(1)–N(1)
1.7959(11)
1.917(2)
1.931(2)
Al(2)–O(13)
Al(2)–C(18)
Al(2)–C(17)
Al(2)–C(16)
1.8671(12)
1.932(2)
1.940(2)
1.953(2)
1.9819(14)
O(13)–Al(1)–C(15) 111.25(8)
O(13)–Al(1)–C(14) 116.15(7)
C(15)–Al(1)–C(14) 118.83(9)
O(13)–Al(2)–C(18) 101.56(7)
O(13)–Al(2)–C(17) 111.46(7)
C(18)–Al(2)–C(17) 109.64(10)
O(13)–Al(2)–C(16) 103.58(7)
C(18)–Al(2)–C(16) 118.06(9)
C(17)–Al(2)–C(16) 111.84(9)
C(11)–O(13)–Al(1) 113.03(10)
C(11)–O(13)–Al(2) 121.71(10)
O(13)–Al(1)–N(1)
C(15)–Al(1)–N(1)
C(14)–Al(1)–N(1)
C(10)–N(1)–Al(1)
C(9)–N(1)–Al(1)
C(2)–N(1)–Al(1)
87.76(5)
108.78(8)
109.43(8)
97.58(10)
116.03(10)
108.87(10)
Al(1)–O(13)–Al(2)
121.72(6)
These variations in Al–C distances reflect the different co-
ordination numbers in 7 and 9. The Al–Nmacrocycle distance of
1.9819(14) Å in 9 is considerably shorter than those found in
five-coordinate 7 and 8 (2.245(4)–2.306(3) Å), again presumably
because of the different coordination numbers. The geometry
of compound 9 is similar to that of Barron’s [Al{OCH2CH2-
NMe2ؒAl(But)3}Me2].35a A number of other related compounds
with an AlMe3 unit bound to the anionic donor of a chelating,
bidentate ligand have crystallographically been charac-
terised.35b–d There is no evidence from NMR tube scale
reactions for the coordination of AlMe3 to either of the
“free” triazacyclonane nitrogens. A solution molecular weight
measurement for 9 (found 430; calculated for monomeric 9
400 g molϪ1) confirms that the monomeric structure is main-
tained in solution. Reaction of 9 with pyridine in C6D6 showed
quantitative formation of 7 and AlMe3ؒpy.17
Fig. 5 Displacement ellipsoid (40%) plot of [Al(κ2-L4ؒAlMe3)Me2] 9
with H atoms omitted.
Only this process can account for the apparent C2 symmetry of
the R2[9]aneN3 moiety sub-spectra of 7 and 8 at ambient
temperatures.
It is apparent (at least qualititatively) from Fig. 3 that the
AlMe group exchange in compounds 7 and 8 and the exchange
processes for the macrocyclic CH2 and NMe groups are not
kinetically degenerate. Thus the initial rates of broadening
of the AlMe and NMe signals (which are directly related to
the exchange rate constants33,38) are evidently different, with
the NMe signals broadening more quickly. This suggests
that the macrocycles in the intermediates 7* and 8* can
undergo the pairwise methylene and methyl group exchange
processes described above and then recoordinate at the same
aluminium centre to reform 7 and 8 without AlMe group
exchange.
The room temperature 1H and 13C NMR data for compound
9 are consistent with the solid state structure, although some of
1
the H ring methylene resonances are slightly broad, possibly
due to conformational flexing of the macrocyclic moiety. At
1
Ϫ60 ЊC all of the H resonances are very sharp. Three singlets
at δ Ϫ0.73 (intensity 3 H), Ϫ0.85 (3 H) and Ϫ1.07 (9 H) are
assigned to the two inequivalent AlMe2 and the three AlMe3
methyl groups, respectively. Rotation around the O(13)–Al(2)
bond is apparently rapid even at Ϫ60 ЊC. In addition to signals
for two inequivalent, diastereotopic N-isopropyl groups,
macrocyclic ring methylene and pendant arm resonances in the
δ ca. 0.8 to 4.2 region, there are also two apparent triplets
(intensity 1 H each) at δ 4.81 and 4.57. These are each assigned
to one of the two ring methylene hydrogens either side of the
coordinated N donor and, as for 7, appear to be characteristic
of the κ2 coordination of L4. There is neither evidence in the
NMR spectra for AlMe2 methyl group exchange, nor for
exchange between macrocycle NPri groups.
Monomeric four- and five-coordinate complexes of aluminium
The syntheses of monomeric aluminium complexes are also
summarised in Scheme 1. NMR tube scale reactions of [Al2-
(κ2-L4,5)2Me4] 7,8 in benzene with AlMe3 gave a clean reaction
to form [Al(κ2-L4ؒAlMe3)Me2] 9 in the case of 8, but no clean
product could be obtained from 7. Barron and co-workers
have recently reported the analogous reaction of dimeric [Al2-
(µ-OCH2CH2NMe2)2Me4] with Al(But)3 to form the monomeric
derivative [Al{OCH2CH2NMe2ؒAl(But)3}Me2] which has the
Al(But)3 bound to the anionic oxygen donor.35a The new com-
pound 9 was synthesized on a preparative scale by the reaction
of HL4 4 with two equivalents of AlMe3 in hexanes. Recrystal-
lisation from pentane afforded diffraction-quality crystals in
71% isolated yield. The structure of 9 has been determined; the
molecular structure is shown in Fig. 5 and selected bond lengths
and angles are listed in Table 4.
The formation of monomeric [Al(κ2-L4ؒAlMe3)Me2] 9 on
coordination of AlMe3 to the aryl oxide oxygen is attributable
to increased steric demands at the metal centre. Another poten-
tial way to achieve this is by use of the phenolic ligand
precursors HL1 1, HL2 2 or HL3 3 that feature methyl or tert-
butyl substituents, respectively, ortho to the oxygen donor. The
reactions of 1 and 2 with AlMe3ؒpy or AlMe3 are summarised
in Scheme 1; reactions with HL3 3 gave complex mixtures.
Reaction of HL2 with AlMe3ؒpy in hexanes followed by
cooling to Ϫ30 ЊC afforded diffraction quality crystals of
colourless [Al(κ2-L2)Me2] 10 in 57% isolated yield. The struc-
ture has been determined; selected bond lengths and angles are
listed in Table 5 and a view of the molecular structure is given
in Fig. 6. Molecules of [Al(κ2-L2)Me2] 10 are mononuclear
in the solid state and feature an approximately tetrahedral
aluminium with a κ2-coordinated L2 ligand and two methyl
groups. The Al–O distance of 1.759(4) Å is slightly shorter than
that of 1.7959(11) Å in four-coordinate 9 while the Al–N and
Al–Me distances are somewhat longer. The distances and angles
[Al(κ2-L4ؒAlMe3)Me2] 9 possesses an L4 ligand that is κ2-
coordinated to a AlMe2 unit displaying approximately tetra-
hedral coordination. The anionic O-donor of L4 is datively
bonded to an AlMe3 molecule that also has approximately
tetrahedral geometry. The Al(1)–O(13) bond length is some-
what shorter than Al(2)–O(13) in keeping with this description.
The Al(1)–Cmethyl distances in 9 are only slightly shorter
(av. 1.924 Å) than the Al(2)–Cmethyl values (av. 1.942 Å), but are
considerably contracted in comparison to those in the dimeric,
five-coordinate compound [Al2(κ2-L4)2Me4] 7 (av. 1.975 Å).
J. Chem. Soc., Dalton Trans., 2001, 157–169
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Table 5 Selected bond distances (Å) and angles (Њ) for [Al(κ2-L2)Me2]
10
Al(1)–O(17)
Al(1)–C(19)
1.759(4)
1.953(5)
Al(1)–C(18)
Al(1)–N(1)
1.965(5)
2.011(4)
O(17)–Al(1)–C(19)
O(17)–Al(1)–C(18)
C(19)–Al(1)–C(18)
C(16)–O(17)–Al(1)
C(2)–N(1)–Al(1)
110.7(2)
111.4(2)
119.8(2)
131.2(3)
112.7(3)
C(19)–Al(1)–N(1)
C(18)–Al(1)–N(1)
O(17)–Al(1)–N(1)
C(9)–N(1)–Al(1)
C(10)–N(1)–Al(1)
110.0(2)
107.0(2)
95.0(2)
108.4(3)
103.8(3)
1H NMR spectrum are diagnostic of a κ2 coordination mode
for the L1 ligand. The most likely structure based on the NMR
data has the square based pyramidal geometry (C2 symmetry)
shown in Scheme 1. The proposed structure and aluminium
coordination sphere of 11 is reminiscent of that previously
reported for N2O2-donor Schiff base complexes [Al(N2O2
donor)Me].39–41 The formation of only [Al(κ2-L1)2Me] 11 in
the 1:1 reaction of HL1 with AlMe3 (as opposed to the target
[Al(κ2-L1)Me2] complex) suggests that the expected inter-
mediate [Al(κ2-L1)Me2] (i.e. analogous to the isolated com-
pound 10) can either react rapidly with further HL1 forming 11
and CH4, or disproportionate to form 11 and AlMe3. Either
way, it is likely that it is the diminished steric demands of the L1
ligand (in comparison with those of the tert-butyl substituted
homologue L2) that facilitate formation of 11.
The results obtained so far show the importance of the steric
demands of the pendant arm in the ligands L1–L5. We were
therefore interested to examine the reaction of the 2,2-
diphenylethyl substituted ligand precursor HL6 with AlMe3.
It was expected that the presence of the two bulky phenyl sub-
stituents in the pendant arm of L6 would lead to monomeric
products analogous to 9 and 10. Reaction of HL6 6 with AlMe3
in hexanes afforded a mixture of products from which [Al-
(κ2-L6)Me2] 12 could be isolated in 15% yield by a combination
of fractional crystallisation and high vacuum sublimation. The
NMR spectra of 12 at 213 K show signals two inequivalent
AlMe groups; these coalesce on warming of the sample
(Tc = 255 K, ∆G‡255 = 52.6 1.2 kJ molϪ1). The remainder of
Fig. 6 Displacement ellipsoid (40%) plot of [Al(κ2-L2)Me2] 10 with
H atoms omitted.
within the Pri2[9]aneN3 moiety are comparable to those in 7–9
and the Pri2[9]aneN3 ring is folded somewhat to one side of
the complex. A solution molecular weight measurement for 10
(found 524, calculated for monomeric 10 575 g molϪ1) confirms
that the monomeric structure is maintained in solution.
At room temperature the 1H and 13C NMR spectra of
compound 10 are very broad and clearly indicative of one or
more fluxional processes. At low temperature the spectra are
fully consistent with the solid state structure. On warming
the sample, the two individual AlMe resonances coalesce
(∆G‡256K = 54.7 1.2 kJ molϪ1), and signals of the CH2Pri2-
[9]aneN3 moiety (but not those of the C6H2But ring) broaden
and undergo pairwise exchange of the type described above for
7 and 8. To account for all of these processes, a mechanism
involving the decoordination of N(1) (see Fig. 6), inversion at
N(1) as well as rotation around the N(1)–C(10) and Al(1)–O(17)
bonds is required. Finally, recoordination of N(1) effectively
gives inversion of configuration at Al(1) and exchanges the
relative positions of C(18) and C(19). These processes are
analogous to those proposed in Fig. 4 for 7 and 8 and are in line
with the ∆G‡256K value of 54.7 1.2 kJ molϪ1. It is not entirely
clear, however, why the compounds [Al(κ2-L4ؒAlMe3)Me2] 9
and [Al(κ2-L2)Me2] 10 differ so much with regard to their
degrees of fluxionality on the NMR timescale. Possibly the 3,5-
di-tert-butylphenoxy derived ligand of 10 is a more sterically
demanding than L4ؒAlMe3 in 9, thus aiding decoordination of
the triazacyclic nitrogen.
1
the H NMR spectra are consistent with the κ2 coordination
proposed for 12 in Scheme 1. Attempts to obtain reproducible
or reliable solution molecular weight measurements of 12 were
unsuccessful. The highest observed fragment in the electron
impact mass spectrum showed an envelope at m/z = 450, corre-
sponding to the monomeric fragment {[Al(κ2-L6)Me2] Ϫ Me}ϩ.
However, this observation could equally be consistent with a
dimeric ground state structure that has undergone symmetrical
cleavage prior to loss of a methyl radical. Nevertheless,
on balance, we favour the formulation of 12 as a monomer
analogous to 9 and 10 on the basis of the steric crowding
imposed by the two phenyl substituents adjacent to the alkoxide
donor atom.
Cationic complexes of aluminium
There is considerable current interest in well defined, cationic
organoaluminium compounds.39,42–52 We were interested to
make cationic derivatives of the new compounds in Scheme 1 in
order to explore their structures and reactivity. Jordan, Gibson
and Lappert have shown that the Lewis acid B(C6F5)3 (along
with related reagents) can be used to generate alkyl aluminium
cations from dialkyl precursors.52,43–47,50 The reactions of [Al-
(κ2-L2)Me2] 10 and [Al(κ2-L4ؒAlMe3)Me2] 9 with B(C6F5)3 are
summarised in Scheme 2. Reactions of 7, 8 or 11 with either
B(C6F5)3 or [Ph3C][B(C6F5)4] produced intractable mixtures.
Reaction of [Al(κ2-L2)Me2] 10 with B(C6F5)3 in CH2Cl2
afforded [Al(κ4-L2)Me][MeB(C6F5)3] 13 as a white solid in 96%
Reaction of the less sterically demanding ligand HL1 1 with
AlMe3 in a 1:1 molar ratio gave very poor yields of the bis-
(pendant arm ligand) complex [Al(κ2-L1)2Me] 11 (Scheme 1).
It was not possible to prepare monosubstituted products
analogous to [Al(κ2-L2)Me2] 10. Better yields of 11 were
obtained by reaction of two equivalents of HL1 with one of
AlMe3. We were not able to obtain diffraction-quality crystals
of 11 but a monomeric, five-coordinate structure is assigned
on the basis of a solution molecular weight measurement
(found 701, calculated for monomeric 11 736 g molϪ1). The
NMR spectra of 11 show only one L1 ligand environment at all
accessible temperatures (overall ratio of L1 :Me signals being
2:1). Resonances at δ 4.65 and 4.30 in the 500.0 MHz, 213 K
1
yield. The H NMR spectrum of the [Al(κ4-L2)Me]+ cation in
13 is substantially different from that of 10. A broad singlet
(intensity 3 H) at δ 0.44 is attributed to the free [MeB(C6F5)3]Ϫ
166
J. Chem. Soc., Dalton Trans., 2001, 157–169

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δ Ϫ0.32 (intensity 3 H) and Ϫ0.84 (intensity 9 H) and these
are assigned to single AlMe and AlMe3 groups of a [Al-
(κ4-L4ؒAlMe3)Me]ϩ cation (Scheme 2). The remaining signals
are attributed to a non-Cs symmetrical κ4-L4 ligand (to which
the AlMe3 is coordinated) on the NMR timescale. This is
indicated by, for example, the presence of two septets and four
independent doublets for the chemically distinct ring isopropyl
methine and methyl groups, respectively. The lower NMR
symmetry of the pendant arm ligand in [Al(κ4-L4ؒAlMe3)Me]ϩ
is consistent with the proposed structure in Scheme 2,
since flexing of the CH2CH(Me)O(AlMe3) pendant arm would
not, in this case, be expected to exchange the ring H and
C atoms.
We have investigated the NMR tube scale reactions of [Al(κ4-
L2)Me][MeB(C6F5)3] 13 and [Al(κ4-L4ؒAlMe3)Me][MeB(C6F5)3]
14 towards the following representative range of substrates:
᎐
benzophenone, acetone, propylene oxide, ethene, Me SiC᎐CH,
᎐
3
᎐
PhC᎐CH, pyridine and MeCN. Compound 13 is unreactive
᎐
towards any of them, and 14 does not react with benzophenone
᎐
or RC᎐CH. Reaction of 14 with pyridine and MeCN affords
᎐
AlMe3ؒL (L = py or MeCN)16,17 and a new complex tentatively
identified as {[Al(κ4-L4)Me][MeB(C6F5)3]} 15. Repeated
attempts to isolate analytically pure samples of 15 on a pre-
parative scale were unsuccessful and it has been characterised
by 1H NMR spectroscopy only. The BMe resonance of the
[MeB(C6F5)3]Ϫ appears at δ 0.47 indicating that the anion
does not interact significantly with [Al(κ4-L4)Me]+ in solution.
The cation shows a single AlMe resonance (intensity 3 H)
at δ Ϫ0.72 which is shifted somewhat upfield from the corre-
sponding signal (δ Ϫ0.32) of [Al(κ4-L4ؒAlMe3)Me]ϩ. The κ4-L4
resonances are sharp at room temperature and reveal a non-Cs
symmetrical environment. Thus the two isopropyl groups give
rise to two septets (overlapping) and four distinct doublets
for the methine and methyl groups, respectively. There are no
macrocyclic ring methylene resonances at shifts higher than
δ 3.3 consistent with the κ4-coordination mode illustrated
in Scheme 2. Addition of pyridine or MeCN to samples of 15
gives no adduct formation (i.e. only signals for free pyridine or
MeCN and [Al(κ4-L4)Me]+ are observed). This behaviour is
analogous to that of 13.
Apart from the reactions with pyridine and MeCN, com-
pound 14 also undergoes reactions with acetone and propylene
oxide. However, in both instances the disappearance of signals
for the [Al(κ4-L4ؒAlMe3)Me]ϩ cation of 14 is accompanied
by the appearance of signals for the [Al(κ4-L4)Me]ϩ cation
of 15. These do not change further with time or excess
reagent. It is proposed that only the AlMe3 fragment of the
[Al(κ4-L4ؒAlMe3)Me]ϩ cation undergoes reactions with added
substrates, while the “core” [Al(κ4-L4)Me]ϩ cation (like its aryl
oxide analogue, [Al(κ4-L2)Me]ϩ) is unreactive. The absence of
any reactivity associated with the cationic centres in 13 to 15
demonstrates the very effective shielding provided by the κ4-L2,4
ligands.
Scheme 2 Reagents and conditions: (i) B(C6F5)3, CH2Cl2, rt, 30 min,
>95%; (ii) B(C6F5)3, CH2Cl2, rt, 30 min, 84%; (iii) py (2 equivalents),
CH2Cl2, rt, 5 min, >95%.
anion,53 there being no evidence for significant AlؒؒؒMeB-
(C6F5)3 interactions of the kind recently reported by Coles and
Jordan.43 The AlMe resonance for [Al(κ4-L2)Me]+ appears at
δ Ϫ0.28, but the most significant features are those associated
with the macrocyclic ligand itself. The 1H resonances for L2 are
consistent with Cs symmetry such that there is only a singlet for
the two ArCH2N methylene protons of the pendant arm, and
only one set of resonances (one multiplet and two doublets)
for the diastereotopic isopropyl groups. Most significantly,
all of the triazacyclic NCH2CH2N resonances appear in the
δ 3.05 to 2.74 range (i.e. not at δ > ca. 4 that would indicate
a κ2-coordinated L2 ligand). We propose that the cation in 13
therefore possesses a fac-coordinated triazacyclonane ring.
These data are consistent with the trigonal bipyramidal,
five-coordinate [Al(κ4-L2)Me]+ cation shown in Scheme 2. The
NMR spectra for the cation broaden on cooling to Ϫ80 ЊC,
but no slow exchange limiting spectrum could be obtained.
We propose that the implied low activation energy, fluxional
process involves conformational flexing of the pendant arm
that would be expected to lie either side of the molecular plane
containing the Al, Me and aryl oxide O atoms. We have not
been able to obtain crystals of 13, but Tolman and co-workers
have reported the crystal structures of trigonal bipyramidal
complexes [M(L2)X] and [M(L1)X]+ (M = Cu or Zn; X = Cl or
MeCN) that have the same geometry as that proposed here
(with the pendant arm folded to one side of the approximate
molecular mirror plane). Moreover, the diamagnetic complexes
Neutral and cationic complexes of indium
A number of indium complexes of non-pendant arm or
tris(pendant arm) triazacyclononanes have been reported pre-
viously,6,8,9,54 but no organometallic derivatives of these ligands
have been described. In very recent work,55 we have prepared
and structurally characterised the mono-pendant arm tri-
azacyclononane complex [In(κ4-L2)Cl2]. Reactions of this with
alkylating reagents are unsuccessful and so we sought other
routes to dialkyl complexes with a view to preparing the
corresponding cations. Organoindium cations are com-
paratively rare.42,56 The syntheses and proposed structures of
the new neutral and cationic indium complexes are shown in
Scheme 3.
1
give H NMR spectra that are consistent with Cs symmetrical
structures on the NMR timescale.12
Reaction of [Al(κ2-L4ؒAlMe3)Me2] 9 with B(C6F5)3 in CH2Cl2
gives [Al(κ4-L4ؒAlMe3)Me][MeB(C6F5)3] 14 as a white solid
1
in 84% yield. The H NMR spectrum shows a broad singlet at
δ ca. 0.47 again consistent with a free [MeB(C6F5)3]Ϫ anion.
Reaction of HL1 1 or HL2 2 with In(CH2Ph)3 in benzene
at room temperature for 24 h affords the four-coordinate
In addition, there are two aluminium methyl resonances at
J. Chem. Soc., Dalton Trans., 2001, 157–169
167

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Conclusion
We have described the first neutral and organometallic mono-
pendant arm triazacyclononane complexes of aluminium
and indium. All of the neutral aluminium complexes, and
two of the indium derivatives, feature an unprecedented κ2
coordination mode for the ligands, with the macrocycle being
bound to the metal through one nitrogen only. Reaction of
certain aluminium and indium dialkyl complexes with B(C6F5)3
gives monoalkyl, cationic derivatives, all of which possess κ4-
coordinated L1 or L2 ligands. These complexes are unreactive at
the cationic metal centres.
Acknowledgements
This work was supported by grants from the EPSRC, Lever-
hulme Trust and Royal Society. We acknowledge the use of the
EPSRC Chemical Database Service at Daresbury Laboratory.
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