Extremely bulky amido and amidinato complexes of boron and aluminium halides: Synthesis and reduction studies

Article abstract of DOI:10.1071/CH13175

An extremely bulky secondary amine, HN(Ar?)(SiPr3i) HL? (Ar?≤C6H2{C(H)Ph2}2Pri-2,6,4) has been synthesised and deprotonated with KH in toluene, to afford the potassium amide [KL?(η6-toluene)], which was structurally authenticated. Reaction of this with BBr3 and AlBr3, reproducibly gave the crystallographically characterised amido bromo-borane, [L?B(H)Br], and aluminacycle, [AlBr2{2-C,N-N(H)(SiPr3i){C6H2[CPh2][C(H) Ph2]Pri-2,6,4}}], respectively, via ligand C-H activation processes. The known secondary amines, HN(Dip)(Mes) (HLMes) and HN(Dip)(Trip) (HLTrip) (Dip≤2,6-diisopropylphenyl, Mes≤mesityl, Trip≤2,4,6-triisopropylphenyl) , have been structurally characterised, and deprotonated to give the in situ generated lithium amides, [Li(LMes)] and [Li(LTrip)]. Reaction of these with BBr3 and AlBr3 has given the amido group 13 element halide complexes, [LMesBBr2] and [LAlBr2(THF)] (L≤LMes or LTrip), the crystal structures of all of which have been determined. Synthetic routes to two new bulky amidine pro-ligands, ArN≤C(But)-N(H)Ar, Ar≤C6H2{C(H)Ph2}2Me-2,6,4 (Piso*H) or C6H2Pr2i(CPh3)-2,6,4 (Piso″H), have been developed, and the compounds crystallographically characterised. Deprotonation of Piso″H gave the potassium amidinate, [K(Piso″)], which was reacted with BBr3 to give [(Piso″)BBr2]. Reaction of Piso″H with AlMe3 afforded [(Piso″)AlMe2], which, when treated with I2 yielded [(Piso″)AlI2], the crystal structure of which was determined. Reductions of all of the prepared amido and amidinato group 13 element(iii) halide complexes were attempted using a variety of reducing reagents, with a view to prepare boron(i) or aluminium(i) complexes. While these were not successful, this study does offer synthetic inorganic chemists a variety of new very bulky anionic N-donor ligands, and boron/aluminium halide complexes thereof, for use in their own research.

Full text of DOI:10.1071/CH13175

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2013, 66, 1144–1154
Full Paper
http://dx.doi.org/10.1071/CH13175
Extremely Bulky Amido and Amidinato Complexes of Boron
and Aluminium Halides: Synthesis and Reduction Studies
A
A
A
Edwin W.Y. Wong, Deepak Dange, Lea Fohlmeister,
A
A B
,
Terrance J. Hadlington, and Cameron Jones
A
School of Chemistry, PO Box 23, Monash University, Melbourne, Vic. 3800, Australia.
Corresponding author. Email: cameron.jones@monash.edu
B
An extremely bulky secondary amine, HN(Ary)(SiPr3i ) HLy (Ary ¼ C6H2{C(H)Ph2}2Pri-2,6,4) has been synthesised and
deprotonated with KH in toluene, to afford the potassium amide [KLy(Z6-toluene)], which was structurally authenticated.
Reaction of this with BBr3 and AlBr3, reproducibly gave the crystallographically characterised amido bromo-borane,
[LyB(H)Br], and aluminacycle, [AlBr2{k2-C,N-N(H)(SiPr3i ){C6H2[CPh2][C(H)Ph2]Pri-2,6,4}}], respectively, via ligand
C–H activation processes. The known secondary amines, HN(Dip)(Mes) (HLMes) and HN(Dip)(Trip) (HLTrip) (Dip ¼
2,6-diisopropylphenyl, Mes ¼ mesityl, Trip ¼ 2,4,6-triisopropylphenyl), have been structurally characterised, and depro-
tonated to give the in situ generated lithium amides, [Li(LMes)] and [Li(LTrip)]. Reaction of these with BBr3 and AlBr3 has
given the amido group 13 element halide complexes, [LMesBBr2] and [LAlBr2(THF)] (L ¼ LMes or LTrip), the crystal
structures of all of which have been determined. Synthetic routes to two new bulky amidine pro-ligands, ArN ¼ C(But)-
N(H)Ar, Ar ¼ C6H2{C(H)Ph2}2Me-2,6,4 (Piso*H) or C6H2Pri2(CPh3)-2,6,4 (Piso00H), have been developed, and the
compounds crystallographically characterised. Deprotonation of Piso00H gave the potassium amidinate, [K(Piso00)], which
was reacted with BBr3 to give [(Piso00)BBr2]. Reaction of Piso00H with AlMe3 afforded [(Piso00)AlMe2], which, when
treated with I2 yielded [(Piso00)AlI2], the crystal structure of which was determined. Reductions of all of the prepared amido
and amidinato group 13 element(III) halide complexes were attempted using a variety of reducing reagents, with a view to
prepare boron(I) or aluminium(I) complexes. While these were not successful, this study does offer synthetic inorganic
chemists a variety of new very bulky anionic N-donor ligands, and boron/aluminium halide complexes thereof, for use in
their own research.
Manuscript received: 13 April 2013.
Manuscript accepted: 7 May 2013.
Published online: 5 June 2013.
Introduction
made several contributions, which include the development of a
range of very hindered N,N0-chelating ligands, such as doubly
reduced 1,4-diazabutadienes,[3] amidinates,[4] and guanidi-
nates.[5] These have been enlisted in the preparation of a wide
spectrum of reactive low oxidation state main group com-
pounds, the most relevant of which to this study are the four-
membered group 13 metal(I) N-heterocyclic (NHC) carbene
analogues, 1 (Fig. 1).[6] More recently, we have turned our
attention to the synthesis of a new class of extremely bulky
monodentate amido ligand (e.g. -N(Ar*)(R), Ar* ¼ C6H2{C(H)
Ph2}2Me-2,6,4; R ¼ SiMe3, SiPh3, Ph, or mesityl (Mes)),[7]
which have the potential to stabilise low oxidation state main
group compounds with lower coordination numbers, and hence
higher reactivities, than their counterparts that incorporate bulky
chelating ligands (e.g. 1). This has, indeed, proved to be the case,
as we have recently shown that ligands such as -N(Ar*)(R) can
stabilise several one-and two-coordinategroup 14element(I orII)
compounds (e.g. the singly bonded digermyne [{(Me3Si)(Ar*)
NGe-}2]), examples of which are capable of activating H2 and
CO2, or polymerising alkenes, at well below 08C.[8] More
recently still, we have engaged extremely bulky amides in the
synthesis of an unprecedented series of one-coordinate group 13
metal(I) complexes, 2.[9]
The chemistry of low oxidation state/low coordination number
complexes of the s- and p-block elements has rapidly advanced
since the turn of the millennium.[1] In recent years it has been
realised that the properties and reactivity of such systems align
more closely with those of transition metal complexes, than with
those of ‘normal oxidation state’ main group compounds.[2] This
has led to the development of a variety of ‘transition metal-like’
synthetic applications for low oxidation state main group com-
pounds, the most studied of which are derived from the ability of
these complexes to facilely activate small molecules (e.g. H2,
CO2, NH3, C2H4 etc.) at, or below, ambient temperature. In this
respect, it has been predicted that cheap and typically non-toxic
main group compounds may soon find favour as viable alter-
natives to expensive, and often toxic, late transition metal
complexes in various synthetic and catalytic processes.[2]
Essentially all of the progress in this field has been facilitated
by the employment of sterically bulky ligands, which provide
kinetic protection to low oxidation main group complexes from
disproportionation processes and/or other decomposition path-
ways. While numerous ligand types have been utilised in this
domain, bulky aryl, alkyl, silyl, and anionic N-donor systems are
the most studied.[1,2] With regard to the latter, our group has
Journal compilation Ó CSIRO 2013
www.publish.csiro.au/journals/ajc

Bulky N-donor Ligands
1145
Pri
Ph Ph
Br
NCy2
Ph
Dip
Ph
Ph
Dip
N
N
B
M
N
Ph
M
N
H
BBr3
SiPri3
4
SiR3
1 M ϭ Ga or In
2 M ϭ Ga, In or Tl
R ϭ Me or Ph
[KL†(η6-toluene)
3
Pri
Fig. 1. Examples of guanidinato and amido group 13 metal(I) systems
(Dip ¼ 2,6-diisopropylphenyl, Cy ¼ cyclohexyl).
AlBr3
Ph
Ph
Br
Ph
Ph
Al
Despite the novelty of metal(I) complexes 1 and 2,
monomeric aluminium(I) and boron(I) analogues of these spe-
cies have proved elusive, despite considerable efforts from
several groups, including ours, to access them.[2a,10,11] If they
could be stabilised, they would undoubtedly be extremely
reactive compounds that would likely prove proficient in the
activation of small molecules, and related chemistry. It was the
aim of this study to develop new, extremely bulky amide and
amidinate ligands, and to use these for the stabilisation of low
coordinate aluminium(I) and boron(I) compounds. While the
latter goal has not so far been achieved, we report here high yield
syntheses of several novel anionic N-donor ligands, and their
use in the preparation of a series of boron(III) and aluminium(III)
halide complexes that should prove useful synthons for inor-
ganic chemists.
HN
SiPri3
Br
5
Scheme 1. Syntheses of 4 and 5.
coordination of the metal centre reduces its Lewis acidity.[9] It is
less clear how compound 4 is formed, although the fact that it
incorporates an intact Ly ligand possibly indicates that another
Ly is the source of the hydrogen at boron. That is, the reaction
may well proceed via a C–H activated product similar to 5,
which undergoes a KBr elimination reaction with a second
equivalent of 3, thereby yielding a very hindered bromo-borane.
This could eliminate an organic fragment(s) while delivering a
hydrogen atom to the boron centre. Although this is highly
speculative, the 1H NMR spectrum of the total reaction mixture
reveals it to contain ,50 % of 4, in addition to a complex
mixture of unidentified products, as might be expected if a
mechanism similar to this was in operation. Whatever the case,
the syntheses of 4 and 5 are very reproducible.
Results and Discussion
Bulky Amide Chemistry
Previously we have found that we could not stabilise boron(I) or
aluminium(I) complexes using the amide ligand, -N(Ar*)
(SiMe3), despite its considerable steric bulk.[9] Accordingly, our
initial strategy to achieve this goal here was to develop a sig-
nificantly bulkier, and more kinetically stabilising, amide. To
this end, the new secondary amine pro-ligand, HN(Ary)(SiPr3i )
HLy (Ary ¼ C6H2{C(H)Ph2}2Pri-2,6,4), was prepared in good
yield via a similar route to that used to synthesise HN(Ar*)
(SiMe3).[7b] That is, the bulky aniline, H2NAry, was deproto-
nated with LiBun to generate Li(H)NAry in situ, which was
subsequently quenched with Pri3SiCl to give the desired product.
This was readily deprotonated with KH in toluene, to afford a
good isolated yield of the crystalline potassium amide [KLy(Z6-
toluene)] 3. Surprisingly, reaction of 3 with BBr3 or AlBr3 in
toluene did not yield the expected amide products, [LyEBr2]
(E ¼ B or Al), but instead gave the related hydrido-bromo
borane complex, [LyBHBr] 4 (48 % yield), and a good yield
(71 %) of the unusual alumina-cycle 5, respectively (Scheme 1).
It cannot be sure how these compounds were formed,
although it seems likely that the mechanism that led to 5
involves the intramolecular migration of one of the benzhydryl
methine protons of the Ly ligand to its N-centre, with concomi-
tant alumination of the methine carbon. This could be facilitated
by a p-interaction of one or more of the phenyl groups of the
likely reaction intermediate, [LyAlBr2], with its Lewis acidic Al
centre (compare with the K-phenyl interactions in the solid state
structure of 3, see below). This would render the already acidic
benzhydryl protons even more acidic, thus promoting the
hydrogen migration. It is noteworthy that no similar hydrogen
migration was observed for the closely related amido aluminium
complex, [(Me3Si)(Ar*)NAlBr2(THF)], possibly because THF
All of the spectroscopic and analytical data for 4 and 5 are
fully consistent with their proposed formulations. Of note for 4
is its 11B{1H} NMR spectrum which exhibits a broad peak at
d ¼ 38.0 ppm, which is in the range normally observed for three-
coordinate bromo-boranes.[11] Moreover, the infrared spectrum
of the compound displays a B-H stretching band at n ¼ 2601 cmꢀ1
,
while an N-H absorption (n ¼ 3212 cmꢀ1) was observed in the
infrared spectrum of 5.
The X-ray crystal structures of 3–5 were determined and their
molecular structures are depicted in Fig. 2. Compound 3 is
monomeric and possesses a K centre that is coordinated by an
amido N-atom, while having approximately Z6-interactions
with a molecule of toluene and one benzhydryl phenyl group.
Another phenyl group from the other benzhydryl substituent
Z2-coordinates the potassium centre. A very similar toluene
capped monomeric structure has been reported for the related
compound, [KN(Ar*)(SiMe3)(Z6-toluene)].[9] Compound 4 is
also monomeric and exhibits a trigonal planar boron coordina-
˚
tion environment with a B-N distance (1.385(4) A) that is
slightly shorter than the mean for previously reported three-
[12]
˚
coordinate amido-bromo boranes (1.407(5) A).
Given that
the CSiNBBrH fragment of the compound is essentially planar,
it is likely that a degree of N-B p-bonding contributes to the
shortness of this bond. Surprisingly, 4 is the first structurally
authenticated compound of the type [R2NB(H)Br]. The struc-
ture of 5 confirms that one of the methine protons of the Ly
ligand has migrated to its N-centre, transforming it into an
amino-alkyl ligand, which chelates a distorted tetrahedral Al

1146
E. W. Y. Wong et al.
(a)
(b)
(c)
Fig. 2. ORTEP diagrams of (a) 3, (b) 4, and (c) 5 (25 % thermal ellipsoids; hydrogen atoms, except hydride and amino protons, omitted). Selected
˚
bond lengths (A) and angles (8) for 3: K(1)–N(1) 2.6779(14), K(1)–Ct(1) (Ct ¼ centroid)(1) 3.071(1), K(1)–Ct(2) 3.039(1), K(1)–C(24) 3.3097(17),
K(1)–C(29) 3.134(2), C(1)–N(1)–Si(1) 134.87(12). 4: N(1)–B(1) 1.385(4), Br(1)–B(1) 1.932(3), B(1)–H(1) 1.24(3), N(1)–B(1)–Br(1) 124.0(2),
N(1)–B(1)–H(1) 127.0(14), Br(1)–B(1)–H(1) 108.5(14), C(1)–N(1)–Si(1) 120.11(17). 5: Al(1)–N(1) 1.998(2), Al(1)–C(23) 2.011(3), Al(1)–Br(2)
2.3059(8), Br(1)–Al(1) 2.2959(8), Br(1)–Al(1)–Br(2) 103.52(3), N(1)–Al(1)–C(23) 91.17(9), C(1)–N(1)–Si(1) 117.51(15).
centre. The Al–C and Al–Br distances in the compound are in
the normal range,[12] while the dative N-Al bond is markedly
longer than the covalent Al–N interactions in the related system,
reducing
agent,
[{(MesNacnac)Mg}2]
(
MesNacnac ¼
[(MesNCMe)2CH]ꢀ),[13] gave no reaction, presumably because
of the considerable steric bulk of both reactants. Moreover, in an
attempt to directly prepare an AlI amide complex via a salt
elimination reaction, the potassium amide, 3, was treated with a
solution of aluminium(I) chloride, [{AlCl(THF)}n], prepared in
a specialist reactor by the method of Schno¨ckel.[9] Again, no
reaction was observed.
[9]
˚
[(Me3Si)(Ar*)NAlBr2(THF)] (1.806(3) A).
Although the expected potential precursors to group 13
element(I) compounds, [LyEBr2] (E ¼ B or Al), were not formed
in this study, it was thought that the reductions of 4 and 5 could
lead to interesting reduced species. Accordingly, compound 4
was treated with the NHC, IPriMe (:C{N(Pri)C(Me)}2), in the
hope that this might effect a dehydrobromination reaction and
the formation of the borylene, :BLy. However, instead, it gave an
intractable mixture of products. Similarly, reaction of 5 with an
excess of KC8 did not yield an AlI heterocycle, but instead gave
an unidentifiable mixture of products. Conversely, the
attempted reduction of 5 with the mild, soluble magnesium(I)
In order to circumvent the C–H activation problems incurred
while utilising the very bulky Ly amide ligand, it was decided to
attempt the preparation of amido boron and aluminium bromide
reduction precursor complexes incorporating sterically less
hindered amido ligands, and bearing less acidic methine
protons. In this respect, previous success has been had with
the stabilisation of a tetrahedral aluminium(I) amide cluster,

Bulky N-donor Ligands
1147
[{AlN(Dip)(SiMe3)}4], in which the amide ligand is substituted
with a 2,6,-diisopropyl (Dip) moiety.[14] This is closely related
to the Ary group, although is considerably less bulky. The
ligands chosen for the current study were the bulky bis(aryl)
molecular structures can be found in the Supplementary Mate-
rial. The amines were readily deprotonated by treatment with
LiBun in toluene, and the in situ generated lithium amides were
then added to toluene solutions of either BBr3 or AlBr3 in 1 : 1
stoichiometries. In the case of the BBr3 reactions, a good yield of
the amido-borane, [LMesBBr2] 6, was obtained upon work-up
(Scheme 2), although the corresponding complex, [LTripBBr2],
could not be recovered from the reaction with [LiLTrip]. Instead,
a complex mixture of unidentified products was generated. In
the case of the AlBr3 reactions, and in order to obtain crystalline
products, a small amount of THF was required to be added to the
reaction mixtures during work-up. This gave rise to low yields of
the amido-aluminium species, [LAlBr2(THF)] (L ¼ LMes 7 or
) ,
amines, -N(Dip)(Mes) (LMes and –N(Dip)(Trip) (LTrip
Trip ¼ 2,4,6-triisopropylphenyl), which unlike -N(Dip)(SiMe3),
do not possess labile N–Si linkages.
The pro-ligand secondary amines, HLMes and HLTrip, were
prepared by palladium catalysed cross-coupling reactions, as
described in the literature.[15] As their crystal structures have not
been previously reported, they were determined here, and their
L
Trip 8). The spectroscopic data for the three complexes are in
Br
[LiLMes
or [LiLTrip
]
BBr3
line with their proposed structures. This is perhaps best indicated
by the 11B or 27Al NMR spectra of the complexes which display
signals in the normal ranges for three-coordinate amido-boron
halide (6: d ¼ 30.1 ppm)[11] and four-coordinate aluminium
halide systems (7: d ¼ 93.5 ppm, 8: 94.5 ppm).[16] It is of further
note that the values for 7 and 8 are comparable to that reported
for the closely related complex, [(Me3Si)(Ar*)NAlBr2(THF)]
(d ¼ 97.4 ppm).[9]
N
B
]
Br
AlBr3,
THF
K,
trace O2 or H2O
THF
All complexes 6–8 were crystallographically characterised,
and the molecular structures of 6 and 8 can be found in Fig. 3.
Because the aluminium amides, 7 and 8, are essentially iso-
structural, the molecular structure of 7 has been included in the
Supplementary Material. The structure of 6 reveals a trigonal
Dip
Ar
7 Ar ϭ Mes
8 Ar ϭ Trip
˚
planar boron centre, with a B–N distance of 1.373(5) A. This is
short, and close to that in 4, [Ph2NBCl2] (1.3797(8) A),[17] and
[Me2NBCl2] (1.379(6) A),[18] all of which have been proposed
˚
˚
Scheme 2. Syntheses of 6–9 (Mes ¼ mesityl, Trip ¼ 2,4,6-
to exhibit a level of N-B p-bonding. The aluminium amide
complexes, 7 and 8, both adopt distorted tetrahedral geometries
triisopropylphenyl).
(a)
(b)
Br2
C1
Al1
Br1
N1
Br2
C13
C13
N1
O1
B1
C1
Br1
˚
Fig. 3. ORTEP diagrams of (a) 6 and (b) 8 (25 % thermal ellipsoids; hydrogen atoms omitted). Selected bond lengths (A) and angles (8) for 6: Br(1)–B(1)
1.937(4), Br(2)–B(1) 1.921(5), N(1)–B(1) 1.373(5), N(1)–B(1)–Br(2) 122.3(3), N(1)–B(1)–Br(1) 121.7(3), Br(2)–B(1)–Br(1) 115.9(2), C(1)–N(1)–C(13)
120.1(3). 8: Br(1)–Al(1) 2.3261(6), Br(2)–Al(1) 2.2789(6), Al(1)–N(1) 1.8142(15), Al(1)–O(1) 1.8634(13), Br(2)–Al(1)–Br(1) 105.60(2), N(1)–
Al(1)–O(1) 106.87(6), C(13)–N(1)–C(1) 114.74(13).

1148
E. W. Y. Wong et al.
˚
and their Al–N distances, 7: 1.8199(16) A and 8: 1.8142(15), are
Bulky Amidinate Chemistry
comparable to those in similar complexes, e.g. [(Dip)
[19]
All of the other
metrical parameters for the two complexes are unremarkable
and are within normal ranges.
As little success was had with the reduction of amido-boron or
aluminium dihalide species, it was decided to employ bulky
amidinate ligands in place of amides for the preparation of
suitable group 13 element(III) reduction precursor complexes.
The rationale here was that the chelating amidinate ligand
would provide more kinetic stabilisation than monomeric
amides, and might allow for the isolation of boron(I) and
aluminium(I) amidinate complexes upon reduction of the
element(III) precursor. We have attempted similar reductions
in the past utilising moderately bulky amidinate coordinated
precursor complexes, and while we have been able to access
low oxidation state products, e.g. amidinato AlII com-
plexes,[22] boron(I) and aluminium(I) products have remained
elusive. It seemed that these targets might be accessible if
more bulky, more kinetically stabilising amidinate ligands
were employed. One of the moderately bulky amidinates
we have widely utilised in the past is the Piso ligand,
[(Dip)2NCBut]ꢀ.[22,23] In the current study, we set out to
synthesise bulkier versions of Piso for the preparation of boron
and aluminium complexes.
Two new amidinine pro-ligands, ArN ¼ C(But)-N(H)Ar,
Ar ¼ Ar* (Piso*H) or C6H2Pri2(CPh3)-2,6,4 or Ar00 (Piso00H),
were prepared in moderate to good yields via a variation of one
reported preparation of PisoH.[24] That is, the imidoyl chlorides,
Cl(But)C ¼ NAr (prepared from the amides, ArN(H)C(¼ O)
But), were treated with a solution of in situ generated
LiN(H)Ar, followed by aqueous work-up. Both compounds
were spectroscopically characterised and their crystal structures
determined. Their solution state NMR spectroscopic data indi-
cate that they both exist in solution, predominantly as one of four
possible isomeric/tautomeric forms.[25] In the solid state,
Piso*H crystallises in the E-syn form as indicated by its
˚
{(Me3Si)2CH}NAlI2(THF)] (1.806(2) A).
Reduction reactions of 6–8 were explored using several
reagents. While no reaction was observed between 6 and either
KC8 or [{(MesNacnac)Mg}2], the bromo-borane did react with
potassium naphthalenide and potassium metal, producing com-
plex product mixtures in each case. The only product isolated
from these reactions was the unusual potassium azaborololate 9
(Scheme 2), a few crystals of which were obtained from the
reaction with potassium metal. Because of the very low yield of
this complex, no NMR spectroscopic data could be obtained for
it, although its structure was confirmed by X-ray crystallogra-
phy (see Supplementary Material). This shows it to be tetrameric
with a central K4O4 cube, each O centre of which is ligated by an
azaborole fragment. The complex likely results from a transient
borylene, :BLMes, which undergoes a C–H activation reaction at
an LMes methine centre, with a concomitant reaction with
adventitious moisture or oxygen to give 9. It is of note that
similar C–H activation processes for low-valent boron species
have been observed during the reduction of [(Me3Si)3CBCl2][20]
and [Pri2NBF2].[21]
Reduction reactions of aluminium complexes 7 and 8 proved
to be as challenging as the reduction of 6. Compound 7
appears to be unreactive towards both potassium naphthalenide
and potassium graphite, even after extended heating at 658C.
On the other hand, a reaction did occur between it and
[{(MesNacnac)Mg}2], although no reduction products could be
identified from the reaction. Complex 8 exhibited similar
reactivity towards reducing agents as did 7, and therefore its
reduction to aluminium(I) species was not further pursued.
C1
H1
N1
C6
C39
N2
Fig. 4. ORTEP diagram of Piso*H (25 % thermal ellipsoids; hydrogen atoms, except H(1), omitted). Selected bond
˚
lengths (A) and angles (8): N(1)–C(1) 1.375(3), N(2)–C(1) 1.280(3), N(2)–C(1)–N(1) 116.27(17), C(1)–N(1)–C(6)
123.51(16), C(1)–N(2)–C(39) 129.96(17).

Bulky N-donor Ligands
1149
molecular structure (Fig. 4), while that of Piso00H shows it to
exists in its Z-anti form (see Supplementary Material).
did not lead to the expected products, [(Piso*)EBr2] (E ¼ B or
Al), but instead gave complex reaction mixtures, the major
component of which was Piso*H in each case. In contrast,
treatment of BBr3 with one equivalent of [K(Piso00)] gave a
good isolated yield of [(Piso00)BBr2] 10 as an off-white solid
(Scheme 3). In contrast, no identifiable products were isolated
from the reactions of [K(Piso00)] with AlBr3 or, indeed, AlI3.
As a result, efforts were made to synthesise [(Piso00)AlI2]
via an alternate synthetic route. This involved the initial high
yield preparation of [(Piso00)AlMe2] 11 from the reaction of
Piso00H plus AlMe3 (Scheme 3). Treatment of this with two
equivalents of I2 afforded a high isolated yield of the expected
product, [(Piso00)AlI2] 12, as a colourless crystalline solid.
Unfortunately, all subsequent attempts to reduce 10 and 12 to
boron(I) and aluminium(I) heterocycles, similar to 1, using K(s),
KC8 or [{(MesNacnac)Mg}2] as reagents, led to intractable
product mixtures, or no reaction.
Despite their steric bulk, both Piso*H and Piso00H can be
deprotonated by reaction with KH or K{N(SiMe3)2} respectively,
1
although extended reaction times are required. The H NMR
spectra of the crude reaction products, [K(Piso*)] and
[K(Piso00)], exhibit only one set of resonances for their
N-substituents, which implies that their K-centres are N,N0-
chelated. The reaction of [K(Piso*)] with either BBr3 or AlBr3
But
ArЉ
ArЉ
N
N
BBr3
[K(PisoЉ)]
B
Br
Br
10
The NMR spectroscopic data for 10–12 are consistent with
their proposed formulations, and suggest they exist as four-
coordinate N,N0-chelated complexes in solution. Despite con-
siderable efforts, compounds 10 and 11 could not be obtained as
crystalline solids. However, the X-ray crystal structure of 12 was
determined (see Fig. 5), and this revealed the compound to be
monomeric, with a distorted tetrahedral aluminium centre, as is
the case for the closely related compound, [(Piso)AlI2].[23] The
ligand backbone C–N bond lengths are similar and imply
significant electronic delocalisation over the N2C fragment.
Both the Al–I and N–Al distances lie well within the reported
But
ArЉ
ArЉ
N
N
AlMe3
PisoЉH
Al
Me
Me
11
ranges,[12] and are close to those reported for [(Piso)AlI2],
I2
CPh3
[23]
˚
i.e. 2.460 A (mean) and 1.886 A (mean) respectively.
˚
But
ArЉ ϭ
Pri
Conclusion
Pri
ArЉ
A new extremely bulky amide ligand has been developed, and its
reactions with BBr3 and AlBr3 have reproducibly given ligand
C–H activation products, one of which represents the first
structurally characterised three-coordinate amido complex of
the B(H)Br fragment. Related reactions of two less bulky amides
with BBr3 and AlBr3 have given the expected amido-group 13
element(III) bromide products. In addition, two new extremely
ArЉ
N
N
I
Al
12
I
Scheme 3. Syntheses of 10–12.
C1
C37
C6
N2
N1
Al1
I2
I1
˚
Fig. 5. ORTEP diagram of 12 (25 % thermal ellipsoids; hydrogen atoms omitted). Selected bond lengths (A) and angles (8): I(1)–Al(1)
2.4600(16), Al(1)–N(1) 1.893(4), Al(1)–N(2) 1.894(4), Al(1)–I(2) 2.5024(14), N(1)–C(1) 1.341(5), C(1)–N(2) 1.354(5), N(1)–
Al(1)–N(2) 70.03(15), I(1)–Al(1)–I(2) 110.65(5), N(1)–C(1)–N(2) 107.5(3).

1150
E. W. Y. Wong et al.
bulky amidinate ligands have been synthesised and their use in
the preparation of amidinato group 13 element(III) halides
explored. This proved successful for one of the amidinate
ligands, for which complexes with the BBr2 and AlI2 fragments
were characterised. Reductions of all of the prepared amido and
amidinato group 13 element(III) halide complexes were
attempted using a variety of reducing reagents. While no boron(I)
or aluminium(I) complexes were forthcoming, the study does
offer synthetic inorganic chemists a variety of new, very bulky
anionic N-donor ligands, and boron/aluminium halide com-
plexes thereof, for use in their own research. In our group, we
continue to explore the possibility of stabilising monomeric,
one-coordinate, amido substituted borylene, :BL, and alumi-
nylene, :AlL, compounds.
(sept, 3JHH ¼ 6.8 Hz, 1H, Ary-CH(CH3)2), 6.29 (s, 2H, CHPh2),
6.96 (s, 2H, Ary-o-CH), 7.04–7.22 (m, 20H, Ar-H); 13C{1H}
NMR ([D6]benzene, 75.5 MHz) d 15.4 (SiPri3-CH(CH3)2), 19.6
(SiPri3-CH(CH3)2), 24.6 (Ary-CH(CH3)2), 34.2 (Ary-CH
(CH3)2), 52.3 (CHPh2), 127.1, 128.1, 129.1, 130.6, 141.3, 141.9,
143.8, 145.5 (Ar-C); 29Si NMR ([D6]benzene, 80.0 MHz) d
3.24; nmax(ATR)/cmꢀ1 3362 (w, NH), 2948 (br m), 2867 (m),
1598 (w), 1493 (m), 1443 (m), 890 (m), 759 (m), 699 (s); m/z
(ESI) 624.2 (28 %, MHþ); m/z (HR-MS ESI) 624.4016;
[MþH]þ requires 624.4025.
Preparation of [KLy(Z6-toluene)] (3)
A solution of HLy (1.50 g, 2.40 mmol) in THF (30 mL) was
added to a suspension of KH (0.25 g, 6.0 mmol) in THF (10 mL)
at 208C. The reaction mixture was then heated to 558C and
stirred for 12 h, whereupon volatiles were removed under vac-
uum. The resulting residue was extracted with toluene (40 mL)
and the extract filtered. The filtrate was concentrated to ,10 mL
and stored at ꢀ308C overnight to give colourless crystals of 3
Experimental
General Considerations
All manipulations were carried out using standard Schlenk and
glove box techniques under an atmosphere of high purity dini-
trogen. THF, toluene, and hexane were distilled over molten
potassium, while diethyl ether was distilled from Na/K alloy.
Dichloromethane was distilled over CaH2. Melting points were
determined in sealed glass capillaries under dinitrogen and are
uncorrected. Mass spectra were recorded at the EPSRC National
Mass Spectrometric Service at Swansea University. Micro-
analyses were carried out at London Metropolitan University.
Infrared (IR) spectra were recorded using either a Perkin–Elmer
RX1 Fourier transform infrared (FT-IR) spectrometer as Nujol
mulls between NaCl plates, or an Agilent Cary 630 attenuated
1
(1.56 g, 86 %). mp 190–1948C (dec); H NMR ([D6]benzene,
400 MHz, 296 K) d 1.10 (d, 3JHH ¼ 7.2 Hz, 6H, Ary-CH(CH3)2),
1.33 (d, JHH ¼ 7.2 Hz, 18H, SiPri3-CH(CH3)2), 1.50 (sept,
3
3JHH ¼ 7.6 Hz, 3H, SiPr3i -CH(CH3)2), 2.11 (s, 3H, toluene-
3
CH3), 2.65 (sept, J ¼ 6.8 Hz, 1H, Ary-CH(CH3)2), 6.59–7.41
(m, 27H, Ar-H); 13C{1H} NMR ([D6]benzene, 100 MHz,
296 K) d 19.0 (SiPr3i -CH(CH3)2), 21.3 (SiPri3-CH(CH3)2), 23.9
(Ary-CH(CH3)2), 33.6 (Ary-CH(CH3)2), 52.8 (CHPh2), 125.2,
125.9, 126.5, 127.4, 128.2, 128.5, 129.2, 130.0, 130.4, 130.8,
140.7, 144.9, 146.9, 151.1 (Ar-C); 29Si{1H} NMR ([D6]ben-
zene, 80 MHz, 296 K): no signal observed, even for a concen-
trated sample and long acquisition time; nmax(Nujol)/cmꢀ1
1629 (s), 1463 (s), 1377 (s), 1105 (m), 974 (w), 871 (s), 809 (s).
1
total reflectance (ATR) spectrometer. H and 13C{1H} NMR
spectra were recorded on either Bruker AvanceIII 400 or Varian
Inova 500 spectrometers and were referenced to the resonances
of the solvent used. The 29Si, 27Al, and 11B NMR spectra was
recorded on a Bruker AvanceIII 400 spectrometer and were
referenced to external SiMe4, 1 M aqueous [Al(OH2)6]3þ, or
[BF3(OEt2)] respectively. All NMR spectra were obtained at
Preparation of [LyB(H)Br] (4)
A solution of [KLy(Z6-toluene)] (0.50 g, 0.66 mmol) in toluene
(20 mL) was added to a solution of BBr3 (0.174 g, 0.69 mmol) in
toluene (10 mL) at ꢀ788C. The reaction mixture was warmed to
room temperature and stirred for 12 h. Volatiles were removed
under vacuum, the resultant solid was extracted with toluene
(40 mL), and the extract filtered. The filtrate was concentrated to
,10 mL and stored at ꢀ308C overnight to give colourless
crystals of 4 (0.23 g, 48 %). mp 142–1668C; (Found: C 73.9, H
7.5, N 2.0. C44H53BBrNSi requires C 73.9, H 7.5, N 2.0 %);
298 K, unless otherwise noted. HL , ,
Mes [15] HLTrip [15]
Ar*NH2,[26] and Ar00NH[227] were prepared by literature proce-
dures. AryNH2 was prepared by a procedure analogous to that
used in the preparation of Ar*NH2.[26] [K(Piso00)] was prepared
by treating Piso00H with one equivalent of [K{N(SiMe3)2}] in
toluene, followed by evaporation of volatiles, and washing the
residue with hexane. The crude product was used without further
purification. All other reagents were used as received.
3
1H NMR ([D6]benzene, 400 MHz, 296 K) d 0.98 (d, JHH
3
¼ 6.8 Hz, 6H, Ary-CH(CH3)2), 1.00 (d, JHH ¼ 7.6 Hz, 18H,
Preparation of HLy
SiPri3-CH(CH3)2), 1.28 (sept, JHH ¼ 7.6 Hz, 3H, SiPri3-CH
3
(CH3)2), 2.54 (sept, 3JHH ¼ 6.8 Hz, 1H, Ary-CH(CH3)2), 5.98 (s,
2H, CHPh2) 6.59–7.41 (m, 22H, Ar-H), no BH resonance
observed; 13C{1H} NMR ([D6]benzene, 100 MHz, 296 K) d
13.3 (SiPri3-CH(CH3)2), 19.4 (SiPr3i -CH(CH3)2), 23.7 (Ary-CH
(CH3)2), 33.5 (Ary-CH(CH3)2), 51.5 (CHPh2), 126.4, 126.6,
128.4, 129.7, 129.9, 130.8, 139.2, 144.8 (Ar-C); 11B{1H} NMR
([D6]benzene, 128 MHz, 296 K) d 38.0 (br s); 29Si{1H} NMR
([D6]benzene, 80 MHz, 296 K) d 16.1 (s); nmax(Nujol)/cmꢀ1
2601 (s, BH), 1599 (m), 1493 (m), 1076 (w), 1033 (w), 875 (s),
698 (s); m/z (EI) 672.2 (37 %, M-Priþ), 167 (100, CHPh2þ).
A solution of AryNH2 (10.0 g, 21.2 mmol) in THF (100 mL) was
cooled to ꢀ808C, and LiBun (14.6 mL, 1.6 M in hexane) was
added to it over 15 min. The resultant solution was warmed to
room temperature, and stirred for 1.5 h. Subsequently, Pri3SiCl
(5 mL, 23.3 mmol) was added to the solution at room tempera-
ture, then the reaction mixture was heated to 558C, and stirred
for 15 h. Solvents were subsequently removed under vacuum,
and the residue extracted into hot toluene (80 mL). The extract
was filtered and volatiles were removed from the filtrate under
vacuum. The orange, oily residue was washed with hexanes
(2 ꢁ 15 mL) to afford a colourless powder (9.83 g, 74 %). The
compound can be recrystallised by slow evaporation from a
diethyl ether solution. mp 178–1828C; 1H NMR ([D6]benzene,
Preparation of [AlI2{k2-C,N-N(H)(SiPr3i ){C6H2[CPh2]
[C(H)Ph2]Pri-2,6,4}}] (5)
A solution of [KLy(Z6-toluene)] (0.50 g, 0.66 mmol) in toluene
(20 mL) was added to a solution of AlBr3 (0.185 g, 0.69 mmol)
in toluene (10 mL) at ꢀ788C. The reaction mixture was warmed
3
500 MHz) d 0.92 (d, JHH ¼ 6.8 Hz, 6H, Ary-CH(CH3)2), 1.05
(d, JHH ¼ 6.8 Hz, 18H, SiPri3-CH(CH3)2), 1.32 (sept, JHH
¼
3
3
6.8 Hz, 3H, SiPri3-CH(CH3)2), 2.13 (s, 1H, NH), 2.47

Bulky N-donor Ligands
1151
to room temperature and stirred for 12 h. Volatiles were then
removed under vacuum, the resultant solid was extracted with
toluene (40 mL), and the extract filtered. The filtrate was con-
centrated to ,10 mL and stored at ꢀ308C overnight to give
colourless crystals of 5 (0.38 g, 71 %). mp: 154–1568C (dec);
(Found: C 65.2, H 6.4, N 1.8. C44H52AlBr2NSi requires C 65.3,
H 6.5, N 1.7 %); 1H NMR ([D6]benzene, 400 MHz, 296 K)
d 0.82–0.88 (overlapping d, 18H, SiPri3-CH(CH3)2), 0.98
3JHH ¼ 6.7 Hz, 2H, CH(CH3)2), 6.69 (s, 2H, Mes-ArH),
7.08–7.18 (m, 3H, Dip-Ar-H); 13C{1H} NMR ([D6]benzene,
100 MHz) d 20.6 (Mes-p-CH3), 22.6 (Mes-o-CH3), 24.6
(OCH2CH2), 25.6 (CH(CH3)2), 28.8 (CH(CH3)2), 74.8 (OCH2),
124.1, 125.7, 130.4, 133.0, 137.4, 145.2, 145.4, 146.5 (Ar-C);
27Al NMR ([D6]benzene, 104 MHz) d 93.5; nmax(Nujol)/cmꢀ1
1108 (m), 1031 (m), 982 (m), 948 (m), 909 (m), 855 (m),
826 (m), 798 (m), 750 (m); m/z (EI) 295.2 (100 %, LMesHþ).
3
(d, JHH ¼ 6.8 Hz, 6H, Ary-CH(CH3)2), 1.46 (br. sept,
3JHH ¼ 7.6 Hz, 3H, SiPr3i -CH(CH3)2), 2.36 (sept, 3JHH ¼ 6.8 Hz,
1H, Ary-CH(CH3)2), 4.69 (s, 1H, NH), 5.86 (s, 1H, CHPh2),
6.89–7.96 (m, 22H, Ar-H); 13C{1H} NMR ([D6]benzene,
100 MHz, 296 K) d 15.3 (br, SiPri3-CH(CH3)2), 19.1 (br, SiPri3-
CH(CH3)2), 23.8 (Ary-CH(CH3)2), 33.6 (Ary-CH(CH3)2), 52.2
(CHPh2), Al-C not observed, 124.4, 126.0, 127.2, 128.5, 128.8,
129.2, 129.4, 129.5, 129.7, 130.3, 132.7, 133.6, 136.7, 140.2,
142.8, 143.3, 146.5, 148.0 (Ar-C); 29Si{1H} NMR ([D6]ben-
zene, 80 MHz, 296 K) d 28.1 (s); 27Al NMR ([D6]benzene,
104.2 MHz, 296 K) signal not observed; nmax(Nujol)/cmꢀ1
1598 (s), 1494 (m), 1079 (w), 1029 (w), 804 (s), 699 (s); m/z (EI)
809.2 (3 %, Mþ), 467.2 (100, AryNH2þ), 167 (35, CHPhþ2 ).
Preparation of [LTripAlBr2(THF)] (8)
LiBun (1.67 M in hexanes, 0.83 mL, 1.4 mmol) was added to a
solution of HLTrip (0.500 g, 1.32 mmol) in THF (30 mL) at
ꢀ788C, and the solution was warmed to room temperature, then
stirred for 3.5 h. Volatiles were subsequently removed under
vacuum, and the residue dissolved in toluene (30 mL). The
resultant solution was then added to a solution of AlBr3 (0.351 g,
1.32 mmol) in toluene (25 mL) cooled to ꢀ788C. The reaction
mixture was warmed to room temperature, stirred overnight, and
then volatiles were removed under vacuum. The residue was
extracted with hexane and the extract was filtered. A few drops
of THF were added to the filtrate, and the filtrate was concen-
trated to the point where colourless crystals of 8 began to form.
After the crystallisation was complete, the mother liquor was
decanted and the crystals were washed with hexane and dried
under vacuum (0.23 g, 28 %). mp 105–1078C; (Found: C 58.2,
H 7.4, N 2.2. C31H48AlBr2NO requires C 58.4, H 7.6, N 2.2 %);
1H NMR ([D6]benzene, 400 MHz) d 0.92 (m, 4H, OCH2CH2),
1.13 (d, 3JHH ¼ 6.8 Hz, 12H, CH(CH3)2), 1.17 (d, 3JHH ¼ 6.8 Hz,
Preparation of [LMesBBr2] (6)
LiBun (1.6 M in hexanes, 2.9 mL, 4.6 mmol) was added to a
solution of HLMes (1.23 g, 4.17 mmol) in toluene (60 mL) at
ꢀ908C, and the reaction mixture was warmed to room temper-
ature, and stirred for 2 h. The resultant solution was then added
to a solution of BBr3 (4.6 mmol) in toluene (30 mL) at ꢀ908C.
The reaction mixture was warmed to room temperature, stirred
overnight, and then volatiles were removed under vacuum. The
residue was extracted with hexane and the extract was filtered to
give a pale yellow filtrate. The filtrate was concentrated and
cooled to ꢀ258C to give colourless crystals of 6 (1.02 g, 52 %).
mp 143–1458C; (Found: C 54.1, H 6.2, N 3.1. C21H28BBr2N
requires C 54.2, H 6.1, N 3.0 %); 1H NMR ([D8]toluene,
3
12H, CH(CH3)2), 1.21 (d, JHH ¼ 6.8 Hz, 6H, Trip-p-CH
(CH3)2), 2.76 (sept, 3JHH ¼ 6.8 Hz, 1H, Trip-p-CH(CH3)2), 3.54
(m, 4H, OCH2), 3.79 (m, 4H, CH(CH3)2), 6.99–7.09 (m, 5H,
ArH); 13C{1H} NMR ([D6]benzene, 100 MHz) d 24.3 (Trip-p-
CH(CH3)2), 24.6 (OCH2CH2), 25.6 (CH(CH3)2), 25.7 (CH
(CH3)2), 29.9 (CH(CH3)2), 30.0 (CH(CH3)2), 34.0 (Trip-p-CH
(CH3)2), 74.8 (OCH2), 123.8, 124.0, 126.2, 144.4, 145.0, 145.4,
145.6, 148.1 (Ar-C); 27Al NMR ([D6]benzene, 104 MHz)
d 94.5; nmax(Nujol)/cmꢀ1 1363 (m), 1094 (m), 1018 (m), 954
(m), 912 (m), 881 (m), 801 (m), 769 (m), 751 (m); m/z (EI) 379.3
(100 %, LTripHþ).
3
400 MHz, 373 K) d 0.87 (br d, JHH E7 Hz, 6H, CH(CH3)2),
3
1.28 (br d, JHH E7 Hz, 6H, CH(CH3)2), 2.01 (s, 3H, Mes-p-
CH3), 2.14 (s, 6H, Mes-o-CH3), 3.18 (br sept, 3JHH E7 Hz, 2H,
CH(CH3)2),6.63(s, 2H, Mes-ArH),6.99–7.06 (m, 3H,Dip-Ar-H).
N.B. the 1H and 13C{1H} NMR spectra for 6 acquired at 298 K
exhibited very broad signals, and could not be assigned with
confidence; 11B NMR ([D6]benzene, 128 MHz, 298K) d 30.1;
Preparation of [{KOB[k2-C,N-C6H3(NMes)(Pri)
(CMe2)-1,2,6]}4] (9)
n
max(Nujol)/cmꢀ1 1335 (m), 1095 (m), 1017 (m), 893 (m),
A solution of 6 (0.50 g, 1.08 mmol) in toluene (40 mL) was
stirred over a potassium mirror for 4 days and then the volatiles
were removed under vacuum. The residue was extracted with
warm hexane and the extract was filtered to give a yellow fil-
trate. The filtrate was concentrated and cooled to ꢀ258C to give
several small yellow crystals of 9. The amount of 9 obtained was
too low to obtain any meaningful spectroscopic data.
792 (m); m/z (EI) 465.1 (100 %, Mþ).
Preparation of [LMesAlBr2(THF)] (7)
LiBun (1.6 M in hexanes, 1.2 mL, 1.9 mmol) was added to a
solution of HLMes (0.500 g, 1.69 mmol) in toluene (80 mL) at
ꢀ808C, and the reaction mixture was warmed to room temper-
ature and stirred for 2.5 h. The resultant solution was then added
to a solution of AlBr3 (0.451 g, 1.69 mmol) in toluene (50 mL)
cooled to ꢀ908C. The reaction mixture was warmed to room
temperature, stirred overnight, and volatiles were then removed
under vacuum. The residue was extracted with hexane and the
extract was filtered. A few drops of THF were added to the
filtrate and then the filtrate was cooled to ꢀ258C to give col-
ourless crystals of 7, which were isolated and dried under vac-
uum (0.20 g, 21 %). mp 182–1848C; (Found: C 54.3, H 6.4,
Preparation of Ar*N(H)C(5 O)But
NEt3 (0.7 mL, 5.00 mmol) and pivaloyl chloride (0.6 mL,
4.90 mmol) were added to a solution of Ar*NH2 (2.04 g,
4.60 mmol) in CH2Cl2 (30 mL). After 3.5 h a white precipitate
was filtered off and washed with hexane. This was dried under
vacuum yielding Ar*N(H)C(¼ O)But as a white powder.
A second crop of product was isolated from the filtrate after
concentration under vacuum (2.16 g, 90 %). The compound
could be used for the preparation of Cl(But)C ¼ NAr* without
further purification. 1H NMR ([D6]benzene, 400 MHz, , 300 K)
d 0.95 (s, 9H, C(CH3)3), 1.81 (s, 3H, Ar-CH3), 5.88 (s, 2H,
CHPh2), 6.07 (s, 1H, NH), 6.81 (s, 2H, m-Ar*-H), 6.98–7.13
1
N 2.6. C25H36AlBr2NO requires C 54.3, H 6.6, N 2.5 %); H
NMR ([D6]benzene, 400 MHz) d 0.91 (m, 4H, OCH2CH2), 1.24
3
(d, JHH ¼ 6.7 Hz, 12H, CH(CH3)2), 2.08 (s, 3H, Mes-p-CH3),
2.34 (s, 6H, Mes-o-CH3), 3.53 (m, 4H, OCH2), 3.98 (sept,

1152
E. W. Y. Wong et al.
3
(m, 20H, Ar-H); 13C{1H} NMR (CDCl3, 100 MHz) d 21.8
(Ar-CH3), 27.3 (C(CH3)3), 39.1 (C(CH3)3), 52.4 (CHPh2),
126.5, 128.5, 128.6, 129.6, 131.5, 136.9, 141.9, 143.5 (Ar-C),
176.7 (NCO); m/z (HR-MS ESI) 524.2941; [MþH]þ requires
524.2953.
1H NMR (CDCl3, 500 MHz, 300 K) d 1.01 (d, JHH ¼ 6.8 Hz,
12H, CH(CH3)2), 1.33 (s, 9H, C(CH3)3), 2.92 (m, 2H, CH
(CH3)2), 6.81 (s, 1H, NH), 6.98 (s, 2H, m-Ar-H), 7.15–7.23
(m, 15H, Ar-H); 13C{1H} NMR (CDCl3, 100 MHz) d 23.5 (CH
(CH3)2), 27.9 (C(CH3)3), 28.9 (CH(CH3)2), 39.4 (C(CH3)3),
65.3 (CPh3), 125.9, 126.6, 127.5, 128.1, 131.3, 144.8, 146.1,
147.0 (Ar-C), 177.4 (NCO); m/z (HR-MS ESI) 504.3272;
[MþH]þ requires 504.3266.
Preparation of Cl(But)C 5 NAr*
PCl5 (1.20 g, 5.80 mmol) was added to a suspension of Ar*N(H)
C(¼ O)But (2.10 g, 4.00 mmol) in toluene (20 mL) at room
temperature. The reaction mixture was then heated at reflux for
40 h before volatiles were removed under vacuum. The resultant
orange solid was dried under reduced pressure (2.03 g, 93 %).
The compound could be used for the preparation of Piso*H
without further purification. 1H NMR ([D6]benzene, 400 MHz,
300 K) d 1.04 (s, 9H, C(CH3)3), 1.86 (s, 3H, Ar-CH3), 5.66
(s, 2H, CHPh2), 6.88 (s, 2H, m-Ar*-H), 6.99–7.25 (m, 20H,
Ar-H).
Preparation of Cl(But)C 5 NAr00
Method A: PCl5 (0.76 g, 3.60 mmol) was added to a suspension
of Ar00N(H)C(¼ O)But (1.74 g, 3.50 mmol) in toluene (20 mL) at
room temperature under a dry N2 atmosphere. After heating the
reaction mixture at reflux for 18 h, volatiles were removed
under vacuum, yielding Cl(But)C ¼ NAr00 as a light brown solid
(1.63 g, 89 %).
Method B: Ar00N(H)C(¼ O)But (6.70 g, 13.30 mmol) was
suspended in toluene (20 mL) and SOCl2 (3.0 mL, 41.4 mmol)
was added at room temperature under a dry N2 atmosphere. The
mixture was then heated to 1008C for 18 h yielding a brown oil.
Volatiles were removed under vacuum and 10 mL of toluene
was added to the mixture. Evaporation of the solvent and
subsequent drying of the resultant solid under vacuum for 2 h
afforded Cl(But)C ¼ NAr00 as a light brown solid (6.80 g, 98 %).
The compound could be used for the preparation of Piso00H
without further purification. 1H NMR (CDCl3, 400 MHz, 303 K)
Preparation of Piso*H
LiBun (1.6 M in hexanes, 2.2 mL, 3.52 mmol) was added to a
solution of Ar*NH2 (1.22 g, 2.80 mmol) in THF (60 mL) at
ꢀ808C. The reaction mixture was then slowly warmed to room
temperature. After 3 h the resultant solution was added to a
suspension of Cl(But)C ¼ NAr* (1.50 g, 2.80 mmol) in THF
(40 mL) at 208C. The mixture was subsequently heated at reflux
for 48 h, then cooled and concentrated to 20 mL. CH2Cl2
(60 mL) was added to the mixture, and the solution was washed
with water. The aqueous phase was extracted with CH2Cl2
(2 ꢁ 50 mL) and the combined organic layers were dried over
MgSO4 and evaporated to dryness. The residue was dissolved in
hot toluene and the extract cooled to 58C overnight. This yielded
a precipitate of Ar*N(H)C(¼ O)But, which was filtered off, and
volatiles then removed from the filtrate under vacuum.
Unreacted Ar*NH2 was removed from the residue by washing
with it with ethyl acetate, leaving Piso*H as a pale yellow
powder (1.30 g, 49 %). Single crystals suitable for X-ray
diffraction analysis were obtained by dissolving Piso*H in
1,2-dimethoxyethane and then slowly evaporating the solvent.
3
d 0.99 (virtual t, JHH ¼ 6.7 Hz, 12H, CH(CH3)2), 1.40 (s, 9H,
C(CH3)3), 2.66 (m, 2H, CH(CH3)2), 6.91 (s, 2H, m-Ar-H),
7.12–7.24 (m, 15H, Ar-H).
Preparation of Piso00H
LiBun (1.6 M in hexanes, 9.0 mL, 14.4 mmol) was added to a
solution of Ar00NH2 (5.50 g, 13.00 mmol) in a THF/toluene
mixture (30 mL/30 mL) at ꢀ108C. The reaction mixture was
then warmed to room temperature and stirred for 0.5 h.
A solution of Cl(But)C ¼ NAr00 (6.80 g, 13.00 mmol) in THF
(40 mL) was subsequently added to the mixture. The reaction
mixture was then heated to 708C for 18 h. After removing all
volatiles under vacuum, the resultant brown solid residue was
dissolved in CH2Cl2 (60 mL), washed with water (2 ꢁ 40 mL),
dried over MgSO4, and evaporated to dryness. The residue was
dissolved in hot hexane (50 mL) and the extract cooled to 58C
overnight, yielding colourless crystals of Piso00H (6.46 g, 55 %).
1
mp 288–3058C; H NMR ([D6]benzene, 400 MHz, 300 K) d
0.22 (s, 9H, C(CH3)3), 1.75 (s, 3H, Ar-CH3), 1.85 (s, 3H,
Ar-CH3), 4.58 (s, 1H, NH), 6.48 (s, 2H, CHPh2), 6.66 (s, 2H,
CHPh2), 6.85–7.74 (m, 44H, Ar-H); 13C{1H} NMR ([D6]ben-
zene, 100 MHz) d 21.0 (Ar-CH3), 21.4 (Ar-CH3), 29.8
(C(CH3)3), 40.2 (C(CH3)3), 51.1 (CHPh2), 53.1 (CHPh2), 125.8,
126.8, 126.9, 126.9, 127.9, 128.2, 128.5, 128.5, 128.7, 129.8,
129.9, 130.4, 131.0, 131.1, 131.7, 132.9, 135.9, 137.5, 141.6,
144.0, 144.2, 144.6, 147.4, 149.0 (Ar-C), 161.6 (NCN);
1
mp 204–2128C; H NMR (CDCl3, 400 MHz, 400 K) d 0.78
(br, 6H, CH(CH3)2), 1.06 (m, 18H, CH(CH3)2), 1.19 (s, 9H,
C(CH3)3), 2.98 (br, 2H, CH(CH3)2), 3.25 (m, 2H, CH(CH3)2),
5.30 (s, 1H, NH), 6.89 (br, 2H, m-Ar-H), 6.92 (s, 2H, m-Ar-H),
7.14–7.24 (m, 30H, Ar-H); 13C{1H} NMR (CDCl3, 100 MHz,
303 K) d 21.8 (CH(CH3)2), 24.2 (CH(CH3)2), 25.9 (CH(CH3)2),
26.0 (CH(CH3)2), 28.7 (C(CH3)3), 30.1 (CH(CH3)2), 31.4
(CH(CH3)2), 38.3 (C(CH3)3), 59.7 (CPh3), 65.3 (CPh3), 125.7,
126.0, 127.2, 127.5, 131.2, 131.4, 146.4, 147.7 (Ar-C), 161.6
(NCN); nmax(Nujol)/cmꢀ1 3338 (w), 1622 (s), 1598 (w), 1491
(w), 1035 (m), 871 (m), 748 (m), 733 (m), 700 (s); m/z (HR-MS
ESI) 905.5774; [MþH]þ requires 905.5774.
n
max(Nujol)/cmꢀ1 1642 (m), 1598 (w), 1491 (w), 1077 (w), 1029
(m), 804 (w), 701 (s); m/z (HR-MS ESI) 945.5149; [MþH]þ
requires 945.5148.
Preparation of Ar00N(H)C(5 O)But
NEt3 (2.20 mL, 15.70 mmol) and pivaloyl chloride (1.80 mL,
14.30 mmol) were added to a solution of Ar00NH2 (6.00 g,
14.30 mmol) in CH2Cl2 (80 mL). After 1 h a white precipitate
began to form. The reaction mixture was stirred for a further 5 h
and 100 mL of CH2Cl2 and 100 mL of water were added.
Subsequently, the organic layer was separated and washed with
water (40 mL), then dried over MgSO4. Volatiles were removed
under vacuum yielding Ar00N(H)C(¼ O)But as an off-white
powder (6.70 g, 93 %). The compound could be used for the
preparation of Cl(But)C ¼ NAr00 without further purification.
Preparation of [(Piso00)BBr2] (10)
A solution of [K(Piso00)] (1.00g, 1.06 mmol) in toluene (20 mL)
was added to a stirred solution of BBr3 (0.28 g, 1.11 mmol) in
toluene (5 mL) at ꢀ788C. The mixture was warmed to room
temperature, whereupon volatiles were removed under vacuum
to give 10 as an off-white solid (0.97 g, 82 %). mp 294–2968C

Bulky N-donor Ligands
1153
(dec.); 1H NMR ([D6]benzene, 400 MHz, 296 K) d 0.90 (s, 9H,
(SHELX97)[30] using all unique data. All non-hydrogen atoms
are anisotropic with hydrogen atoms included in calculated
positions (riding model), except the hydride ligand in 4, and the
amino protons of HLMes and HLTrip, the positional and isotropic
thermal parameters of which were freely refined. Crystallo-
graphic data (CIF files) for all structures have been deposited
with the Cambridge Crystallographic Data Centre (CCDC no.
933397–933408).
3
C(CH3)3), 1.09 (d, 12H, JHH ¼ 6.8 Hz, CH(CH3)2), 1.41
3
3
(d, 12H, JHH ¼ 6.8 Hz, CH(CH3)2), 3.82 (sept, 4H, JHH
¼
6.8 Hz, CH(CH3)2), 7.01–7.41 (m, 34H, Ar-H); 13C{1H} NMR
([D6]benzene, 100 MHz, 296 K) d 23.6 (C(CH3)3), 28.1 (CH
(CH3)2), 28.3 (CH(CH3)2), 29.2 (CH(CH3)2), 41.9 (br,
C(CH3)3), 65.6 (CPh3), 126.4, 127.8, 128.7, 130.6, 131.5, 146.6,
11
147.0, 147.3 (Ar-C), 182.0 (NCN); B NMR ([D6]benzene,
128 MHz, 296 K) d 0.04; nmax(Nujol)/cmꢀ1 1598 (m), 1377 (s),
1033 (m), 945 (s), 802 (w), 703 (s); m/z (EI) 904.6 (5 %,
Piso00Hþ).
Supplementary Material
Crystal data, details of data collections, and refinement for all
structures; ORTEP diagrams and selected metrical parameters
for 7, 9, HLMes, HLTrip, and Piso00H are available on the
Journal’s website.
Preparation of [(Piso00)AlMe2] (11)
To a solution of Piso00H (1.00 g, 1.10 mmol) in toluene (20 mL)
at ꢀ788C, was added AlMe3 (2 M in toluene, 0.58 mL). The
reaction mixture was warmed to ambient temperature, where-
upon volatiles were removed under vacuum and the residue was
washed with hexane (10 mL), leaving 11 as an off-white solid
(0.97 g, 88 % yield). mp 168–1708C (dec.); 1H NMR ([D6]
benzene, 400 MHz, 296 K) d–0.24 (s, 6H, Al(CH3)2), 0.99 (s,
9H, C(CH3)3), 1.15 (br d, 24H, 3JHH E7 Hz, CH(CH3)2), 3.58
Acknowledgement
We gratefully acknowledge financial support from the Australian Research
Council and the US Air Force Asian Office of Aerospace Research and
Development (grant FA2386–11–1-4110). The EPSRC Mass Spectrometry
Service, Swansea, is also thanked. Part of this research was undertaken on
the MX1 beamline at the Australian Synchrotron, Victoria, Australia.
3
(sept, 4H, JHH ¼ 6.9 Hz, CH(CH3)2), 7.00–7.40 (m, 34H,
Ar-H); 13C{1H} NMR ([D6]benzene, 100 MHz, 296 K) d–8.3
(Al(CH3)2), 22.5 (C(CH3)3), 27.0 (CH(CH3)2), 28.8
(CH(CH3)2), 29.6 (CH(CH3)2), 42.2 (C(CH3)3), 65.6 (CPh3),
126.3, 127.2, 128.2, 131.6, 137.2, 143.6, 144.2, 147.4 (Ar-C),
180.7 (NCN); 27Al NMR ([D6]benzene, 104.2 MHz, 296K): no
signal observed; nmax(Nujol)/cmꢀ1 1597 (m), 1377 (s), 1033
(m), 945 (s), 805 (m), 700 (s); m/z (EI) 904.5 (30 %, Piso00Hþ).
References
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To a solution of [(Piso00)AlMe2] (0.70 g, 0.78 mmol) in toluene
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C(CH3)3), 1.12 (d, 12H, JHH ¼ 6.8 Hz, CH(CH3)2), 1.29
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