Gal : A versatile reagent for the synthetic chemist

Article abstract of DOI:10.1039/b501310k

The current renaissance in main group chemistry has been fuelled by the remarkable array of fundamentally interesting yet synthetically applicable low oxidation state p-block compounds that have appeared over the last decade. Their syntheses generally require the ready availability of low oxidation state element halide precursors. In the case of gallium this is provided by the simple to prepare reagent, GaF , which since it was first reported in 1990, has been utilised in areas as varied as organic synthesis and gallium cluster construction. This article tracks the history of this extraordinary material and highlights its synthetic diversity; hopefully allowing the reader to envisage its application to aspects of their own research fields. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b501310k

View Article Online / Journal Homepage / Table of Contents for this issue
P E R S P E C T I V E
“GaI”: A versatile reagent for the synthetic chemist
Robert J. Baker and Cameron Jones*
Centre for Fundamental and Applied Main Group Chemistry, School of Chemistry, Cardiff
University, P.O. Box 912, Park Place, Cardiff, UK CF10 3TB. E-mail: Jonesca6@cardiff.ac.uk
Received 26th January 2005, Accepted 28th February 2005
First published as an Advance Article on the web 9th March 2005
The current renaissance in main group chemistry has been
fuelled by the remarkable array of fundamentally interesting
yet synthetically applicable low oxidation state p-block
compounds that have appeared over the last decade. Their
syntheses generally require the ready availability of low
oxidation state element halide precursors. In the case of
gallium this is provided by the simple to prepare reagent,
“GaI”, which since it was first reported in 1990, has been
utilised in areas as varied as organic synthesis and gallium
cluster construction. This article tracks the history of this
extraordinary material and highlights its synthetic diversity;
hopefully allowing the reader to envisage its application to
aspects of their own research fields.
1
Introduction
The chemistry of gallium has been dominated by compounds
containing this element in the +3 oxidation state.1 The reason
for this lies partly with the general assumption that compounds
containing gallium in lower oxidation states, although accessible,
are inherently unstable and are really only “chemical curiosi-
ties”. This view neglects the enormous importance that both
indium(I) and thallium(I) compounds have had to areas ranging
from organic synthesis to materials chemistry.1 This is especially
so for the mono-halides of these metals which are thermally
stable, commercially available and make excellent synthetic
precursors to indium(I) and thallium(I) alkyls, aryls, amides etc.
The stability of these halides is derived from the so-called “inert
pair effect” and its various causes2 which can also be used to
explain the diminished stability of low oxidation state gallium
(and aluminium) halides. Despite this, a variety of sub-oxidation
state binary gallium halides are known, though their solid-
state architectures are not always as simple as their empirical
formulae might suggest. Examples here include “GaX2”, X =
Cl, Br or I, which have mixed valence structures in the solid
state, [GaI][GaIIIX4]. Intriguingly, however, their reactions with
Lewis bases (L) generally lead to “true” Ga(II) complexes which
contain metal–metal bonds, [(L)X2Ga-GaX2(L)].1
The only crystallographically authenticated gallium(I) halide
complexes have come from the group of Schno¨ckel who
have developed a specialised reactor for the high-temperature
generation of GaX and its subsequent co-condensation with
coordinating solvents. This yields “metastable”, oligomeric
complexes of the type, [{GaX(L)}n], X = Cl, Br or I; L =
ether, amine or phosphine.3 Even more impressively, the same
reactor has been utilised to generate a series of analogous
aluminium(I) halide complexes, e.g. [{AlBr(NEt3)}4]. In the past
decade Schno¨ckel and co-workers have proved the synthetic
worth of such complexes in the preparation of a remarkable
array of fascinating sub-valent metal halide, amide, phosphide,
silyl and alkyl cluster compounds, e.g. [Ga84{N(SiMe3)2}20]4−,
which in some cases challenge existing theories on metal–metal
bonding.4 In addition, these compounds have been employed
as precursors to oligomeric metal(I) alkyls and aryls (group 13
diyls), (MR)n,4c the monomeric units of which, e.g. :GaCp*,
are fast becoming important as ligands in organometallic
synthesis.5
Robert Baker was born in 1975 in Blaenavon, South Wales.
He completed his undergraduate degree at the University of
Warwick and carried out his PhD studies under the supervision
of Prof. P. G. Edwards at Cardiff University (1997–2000). He
then worked as a postdoctoral research fellow with Professor
Cameron Jones (2001–2005). In March 2005 he commenced an
Alexander von Humboldt Research Fellowship at the Technische
Universita¨t Mu¨nchen.
Cameron Jones was born in Perth, Australia in 1962. He completed
both his BSc (1982) and BSc (Hons.) (1984) degrees at the
University of Western Australia. From 1985–1987 he worked
as a Research Officer at the University Department of Surgery
at Royal Perth Hospital. His PhD degree (1989–1992) was
gained from Griffith University, Brisbane, under the supervision
of Professor Colin L. Raston. He then moved to a postdoctoral
research fellowship (1992–1994) at Sussex University under
the supervision of Professor John F. Nixon FRS. From 1994–
1998 he held a lectureship at The University of Wales, Swansea
before moving to a Readership in Inorganic Chemistry at Cardiff
University. He was promoted to a Personal Chair in Inorganic
Chemistry at Cardiff in 2002. Cameron was awarded the Royal
Society of Chemistry’s Main Group Chemistry Prize in 2004. He
is the current chairman of the Royal Society of Chemistry’s Main
Group Chemistry Interest Forum. His research interests include
the low oxidation state and hydrido chemistry of the heavier group
13 elements, and the low coordination chemistry of heavier group
15 elements. In these areas he has published more than 160 papers.
Despite the novelty and synthetic utility of “metastable”
gallium(I) (and aluminium(I)) halide complexes, the specialised
technology required to generate and manipulate these species is
not normally available to the preparative chemist. Fortunately,
in the case of gallium an alternative is offered from the reaction
of the metal with half an equivalent of diiodine in toluene.6 The
resultant green precipitate, “GaI”, is finding an ever increasing
number of applications in organic, inorganic and organometallic
syntheses, as summarised herein.
Cameron Jones and Robert J. Baker
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8
1 3 4 1
©

View Article Online
(III) iodide adducts and gallium metal (vide infra). It is relatively
easy to prepare on a multigram scale in a matter of hours using
commercially available ultrasonic baths. In addition, it can be
stored as a toluene suspension, or as a dry solid, for months
without decomposition of loss or activity. These properties make
it accessible to many preparative chemists who have used it as
source of Ga(I) in a variety of synthetic applications
2
Synthesis and characterisation of “GaI”
The first reported synthesis of GaI in 1955 by Corbett and
McMullan involved heating the elements under vacuum at 350–
◦
500 C for 3 days.7 The product of this reaction was washed
exhaustively with benzene to leave a solid of composition
GaI1.05 (mp 271 ◦C) which was analysed by X-ray powder
diffractometry. “GaI” was similarly prepared by Wilkinson and
Worral in 1975 who heated the elements in vacuo at 250 ◦C for
24 h.8 The product was shown to contain both Ga2I3 and Ga2I4
by Raman spectroscopy. Later, in 1982, Gerlach et al.9 revealed
that the powder diffraction pattern of Ga2I3 was identical to that
of “GaI” prepared by Corbett and McMullan. In addition, they
crystallographically characterised the dark yellow Ga2I3 (mp
263 ◦C) and found it to exist as a mixed valence salt in the solid
state, viz. [Ga]2[Ga2I6]. Moreover, they established that heating
iodine and gallium under vacuum did not lead to a more reduced
product than Ga2I3, all of which casts doubt on the original
formulation of “GaI”. In 1990 a new synthesis of “GaI” was
reported by Green et al.6 They carried out the ultrasonically
activated reaction of gallium metal and half an equivalent of
diiodine in toluene at >30 ◦C to give a pale green, insoluble
powder, “GaI”. The powder diffraction pattern of this material
did not match those of the previously reported “GaI” of Corbett
and McMullan or pure Ga2I3. It was, however, suggested that
this material could be similar to “GaI” prepared by Wilkinson
and Worral. This was later seemingly confirmed by Coban10 who
analysed Green’s “GaI” by Raman spectroscopy and found it to
consist of a mixture of gallium sub-iodides, predominated by
[Ga]2[Ga2I6].
3
Reactivity of “GaI”
3.1 Reactions with Lewis bases
The reactivity of “GaI” towards a variety of Lewis bases has been
explored in some detail. This always leads to disproportionation
reactions and the formation of Ga(II), Ga(III) or mixed valence
products with accompanying gallium metal deposition. For
example, reactions with monodentate amines, phosphines or
ethers normally yield Ga(II) halide complexes, 1, in good yield
(Scheme 1).6,11,12 It is noteworthy that this outcome contrasts
with Schno¨ckel’s aforementioned preparation of gallium(I)
halide complexes, [{GaX(L)}n], X = Cl, Br or I, from the co-
condensation of monodentate amines or phosphines with GaX.3
The facile nature of the synthesis of 1 affords them significant
synthetic potential in their own right. This is beginning to
be examined and has led to number of results including the
preparation of the first dialkylphosphide–gallium(II) complex,
2, via an unusual phosphine ligand deprotonation reaction.13
The reactions of monodentate Lewis bases with “GaI” do
not always lead to Ga(II) iodide complexes and can give Ga(III)
complexes, e.g. [GaI3(PPh3)],6 or mixed-valence species, e.g. 3.11
The latter complex contains two terminal Ga(II) fragments
covalently bonded to a Ga(I) centre. This can perhaps be
considered as an intermediate in the formation of [Ga2I4(PEt3)2]
This green powder is thermally stable, very air sensitive and
insoluble in non-coordinating solvents. In coordinating solvents
it decomposes via disproportionation to give gallium-(II) or -
Scheme 1 Reactions of Lewis bases with “GaI”.
1 3 4 2
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8

View Article Online
which was also isolated from the reaction mixture. Another
interesting result has come from the treatment of “GaI” with
an excess of SbPh3 which, in contrast to the formation of 1, gave
complex 4, presumably via a series of disproportionation and
Sb–C insertion reactions.14 The differences here result from the
relative weakness of the Sb–C bond and highlight the reducing
ability of “GaI”. N-Heterocyclic carbenes (NHCs) can be
thought of as highly nucleophilic Lewis bases which in the case
of :C{N(C6H3Pri2-2,6)C(H)}2, IPr, has been shown to react with
“GaI” to give the salt [IPrH][Ga2I5(IPr)], 5.12 The imidazolium
proton was presumably abstracted from the toluene solvent since
the reaction is reproducible under strictly anhydrous conditions.
The anion of this salt is of interest as it could have been
formed by displacement of one iodide ligand from the [Ga2I6]2−
dianion, which is thought to be a major component of “GaI”.
In comparison, the reaction of a similar NHC, :C{N(C6H2Me3-
2,4,6)C(H)}2, IMes, with InBr yielded the neutral In(II) complex,
[In2Br4(IMes)2] via a disproportionation process.15
Unlike reactions with monodentate Lewis bases, di- and
tridentate donors normally lead to Ga(III) products when treated
with “GaI”. Examples include the bipyridine (bipy), terpyridine
and bis(imino)pyridine complexes, 6–8, all of which were formed
in good yield.16 Although not strictly a tridentate ligand, the
triphosphabenzene, 1,3,5-P3C3But3, has been shown to react
with “GaI” to give the 1,3,5-triphosphacyclohexa-1,4-diene
complex, 9.17 It was proposed that in this transformation the
“GaI” acted as a reducing reagent to give an intermediate [4 +
1] cycloadduct, 10, which abstracted a proton from the toluene
solvent and concomitantly underwent a disproportionation
reaction with excess “GaI” to give the observed product.
own synthetic applications. In our laboratories18 and that of
Jutzi19 the reactions of diazabutadienes, {RN C(H)}2 (DAB)
=
with “GaI” have been examined. These lead to either Ga(II)
or Ga(III) complexes, 11 and 12 (Scheme 2), depending on the
nature of the DAB N-substituents. The mechanism of formation
of 12 is thought to involve a combination of one electron
DAB reduction and disproportionation reactions. In contrast,
the likely initial reduction product in the formation of 11, viz.
•
[•GaI{[N(But)C(H)]2 }], dimerises in preference to undergoing
a disproportionation reaction, probably because of its relatively
less bulky N-substituents. Related to this work is the reaction
of bis(2,6-diisopropylphenyl)acenaphthalene, Ar-BIAN, with
“GaI” which yields 13 in a moderate yield.16 These paramagnetic
species have all been characterised by EPR spectroscopy and
the hyperfine couplings displayed by each indicate that the
unpaired electron is primarily ligand based. In addition, several
of the complexes have been studied by ENDOR spectroscopy
in order to quantify the very small hyperfine couplings to the
hydrogen atoms of the ligand N-substituents.20 This has allowed
an accurate map of the unpaired electron distribution over the
molecules to be constructed.
An examination of the further chemistry of 1121 and 1218 has
given some interesting results. Most importantly, the reduction
of 12, R = C6H3Pri2-2,6 (Ar), with potassium metal gives good
yields of the anionic Ga(I) heterocycle, 14, which is valence
isoelectronic with the important N-heterocyclic carbene class
of ligand. This anion possesses a singlet lone pair at the gallium
centre and, as a result, its coordination chemistry has begun to be
examined. These studies are proving 14 to show close analogies
to NHCs, especially with regard to its strongly nucleophilic
nature and stabilising properties.22 Much of this work has been
recently reviewed.23
3.2 Use in heterocycle formation
“GaI” has been utilised in the preparation of another
closely related Ga(I) heterocycle, 15, which is formed in a salt
elimination reaction with [Li{[N(Ar)C(Me)]2CH}] (Li[nacnac])
in ca. 40% yield.24 A minor product in this reaction is
One of the more useful applications “GaI” has found is in the
synthesis of heterocycles containing gallium in either the +1, +2
or +3 oxidation state. Many of these have gone on to find their
Scheme 2 Use of “GaI” in heterocycle formation.
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8
1 3 4 3

View Article Online
“GaI” offers a valuable alternative to the preparative chemist.
For example, Jutzi et al. have shown that the known compounds
Cp*Ga and (C5Me4Et)Ga, 21, are formed in high yield by
treatment of “GaI” with the potassium salt of the substituted
cyclopentadienyl ligand.30 Considering the wide use of Cp*Ga
as a ligand in a variety of novel complex types,5 this represents
a significant advance over the previously reported and more
difficult routes to Cp*Ga. These involve either alkali metal
[GaI2{[N(Ar)C(Me)]2CH}] (ca. 25% yield) which was isolated by
fractional recrystallisation.25 Notably, this gallium(III) complex
can be reduced with potassium to give 15. As is the case with
anionic 14, the ligating properties of the neutral heterocycle, 15
(and its aluminium analogue), towards both main group and
transition metal fragments are being studied with fascinating
results.23
Related to the b-diketiminate ligand in 15 is the N-methyl-2-
(methylamino)troponiminate anion, [Me2ATI]−, the tin(II) salt
of which, [{Me2ATI}2Sn], undergoes a redox transmetallation
reaction with one equivalent of “GaI” to give the gallium(III)
complex, 16, and elemental tin (Scheme 2).26 No evidence was
found for the formation of the intended gallium(I) species
[{(Me)2ATI}Ga], presumably due to lack of steric protection
from the ligand.
Metathesis reactions between “GaI” and the tris(pyra-
zolyl)borate salts, [HB{C3N2(But)2-3,5}3][Na] ([TptBu]Na) or
[HB{C3N2(CF3)2-3,5}3][Ag] ([TpCF3]Ag) have been shown to give
the Ga(I) complexes, 1727 and 18,28 the former of which was
revealed to be monomeric by an X-ray crystallographic study.
In both reactions GaI3 complexes, viz. [(TptBu)Ga→GaI3] and
[(TpCF3)Ga→GaI3], were isolated as by-products. These presum-
ably arise from disproportionation of some of the “GaI” reactant
during the syntheses. Both complexes were structurally charac-
terised and found to contain rare examples of Ga(I)→Ga(III)
dative bonds. It is of note that upon coordination, the Ga–
31
reduction of Cp*GaI2 or salt elimination reactions between
Schno¨ckel’s metastable GaCl and Cp* metallates.4 Jutzi notes,
however, that in the preparation of Cp*Ga, benzyl-Cp* is
formed as a by-product, presumably via benzyl iodide resulting
from iodination of the toluene solvent in the synthesis of the
“GaI” reactant. It was revealed that this can be avoided if
benzene is used as a solvent in the initial synthesis of “GaI”.
Several other Ga(I) alkyls or aryls can be accessed by
employing salt elimination reactions with “GaI”. These in-
clude the tetrameric species, [{GaC(SiMe3)3}4],4 and the
dimeric gallium diyls, 22–24 (Ar* = C6H3(C6H2Pri3-2,4,6)2-
2,6; Arꢀ = C6H3(C6H3Pri2-2,6)2-2,6; Ar# = C6H3(C6H2Pri2But-
2,6,4)2-2,6.32,33 Also formed in the latter syntheses were the cor-
responding aryliododigallanes(4), 25–27. The crystal structure
of 23 showed the molecule to have a “trans-bent” geometry
˚
with a Ga–Ga bond length of 2.6268(7) A, i.e. at the upper
end of single bond interactions. This, along with cryoscopic
molecular weight determinations, UV/VIS spectroscopy and
further reactivity studies suggest that in solution 22–24 exist
as monomeric arylgallium(I) units. The relative weakness of
the solid state Ga–Ga interaction in neutral 23 has important
implications when it is considered that the doubly reduced form
of the analogous compound 22, viz. Na2[Ar*GaGaAr*], also
possesses a trans-bent structure but has a much shorter Ga–
˚
˚
N bond lengths in 17 [2.230(5) A] shortened by ca. 0.17 A
to 2.05(2) A (avg.) found in the complex [(TptBu)Ga→GaI3].
˚
This observation was explained by an increase in the formal
charge on the gallium(I) centre upon coordination, thus re-
sulting in a contraction of its covalent radius. The only other
heterocycle containing Ga–N bonds to be prepared from “GaI”
is the phosphoraneiminato complex, 19, which arose from a
redox reaction between the gallium reagent and Me3SiNPEt3.29
This was structurally characterised and found to contain a
centrosymmetric Ga2N2 ring with equal Ga–N bond lengths of
˚
Ga interaction of 2.319(3) A. This was controversially described
as a Ga–Ga triple bond by Robinson et al.,34 though a range
of subsequent theoretical studies have implied a bond order of
between 1 and 2.35 If the compound did have a triple bond, its
unreduced form, 22, should have a Ga–Ga distance indicative
of a double bond. This is highly unlikely given the weak Ga–Ga
interaction in 23.
˚
1.909(4) A.
3.3 Use in organogallium synthesis
One further novel synthetic use of “GaI” involves its
=
reaction with the phosphavinyl Grignard reagent, [CyP
One of the earliest uses of “GaI” was in the facile syntheses of a
variety of alkyl gallium diiodides, 20, via oxidative insertion reac-
tions with alkyl iodides (Scheme 3).6 Since that time the gallium
reagent has been used to prepare a range of organogallium-(I),
-(II) and -(III) compounds. In general, the lower oxidation state
species require kinetic stabilisation by incorporation of sterically
bulky ligands. Although these can sometimes be prepared by
reduction of organogallium(III) complexes, this route is often
either low yielding or technically difficult. In such instances
C(But)MgCl(OEt2)],36 Cy = cyclohexyl, to yield a terminal bis-
(phosphavinyl)gallium(III) complex, 28 (Scheme 3).37 The mech-
anism of this reaction was postulated as involving the initial
t
=
formation of a Ga(I) intermediate, [Ga{C(Bu ) PCy}], which
reacts with excess “GaI” to give the product via a series of
redistribution and disproportionation reactions. This outcome
is unusual in light of the fact that the closely related reaction of
2 equivalents of [CyP C(Bu )MgCl(OEt2)] with GaCl3 did not
t
=
Scheme 3 Use of “GaI” in the synthesis of organogallium compounds.
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8
1 3 4 4

View Article Online
Fig. 1 Examples of gallium containing clusters prepared using “GaI”.
pound [Ga10{Si(SiMe3)3}6] 30,40 was said to be reminiscent of
a conjuncto-polyhedral cluster and to fit Cotton’s definition of
a metal atom cluster.44 Also of note are [Ga22{Si(SiMe3)3}8],43
which had been previously prepared from metastable GaBr,45
and the “closo-silatetragallane” anion, 32, which theoretical
studies suggest has weak “equatorial” Ga–Ga interactions.42
Small variations in the electronics and steric bulk of the an-
ionic ligand in reactions with “GaI” can afford different cluster
products. Examples here include 34 and 35 which incorporate
the ligand [SiBut3]−. The presence of benzyl ligands in the latter
was said to arise from deprotonation of the toluene solvent
by the very basic silyl anion reactant.46 Other closely related
anions that have been reacted with “GaI” are [SiMe(SiMe3)2]−
and [Ge(SiMe3)3]− which have given rise to clusters such as 33,
36 and [Ga22{Ge(SiMe3)3}8].46,47
give the chloro analogue of 28, though this was implicated as
an intermediate in the formation of the observed phosphavinyl
coupled galladiphospabicyclo[1.1.1]pentane product, [ButC(l-
t
t
38
=
PCy)2{l-GaC(Bu ) PCy}CBu ].
3.4 Use in the synthesis of gallium cluster and related
compounds
Given the great success that Schno¨ckel has had using metastable
solutions of GaX in the preparation of an impressive range
of gallium clusters, it is not surprising that the more widely
accessible reagent, “GaI”, has also been exploited as a precursor
in this regard. Indeed, to date this has been the most versatile
synthetic use of the gallium reagent. Of the reactions described
in the literature, the majority involve salt eliminations involving
“GaI” and bulky silyl or germyl anions. Often, complex mixtures
of decomposition or disproportionation products arise from
these reactions. For example, treatment of “GaI” with LiGePh3
gives, amongst other products, the first linear trigallane anion,
[(Ph3Ge)3Ga–Ga–Ga(GePh3)3]−, which contains a naked central
gallium centre.39
As an illustration of the versatility of “GaI” in polyhedral
and sub-polyhedral cluster formation, its treatment with the
bulky [Si(SiMe3)3]− anion under various stoichiometries and
conditions has given a large number of interesting compounds,
most of which have been structurally characterised, e.g. 29–
33 (Fig. 1).40–43 Of these, [Ga9{Si(SiMe3)3}6]− 29, was the
first polyhedral gallium cluster with more metal atoms than
substituents.41 The structure consists of a pentagonal bipyra-
midal core with two of the equatorial edges bridged by a
Ga{Si(SiMe3)3} unit (i.e. eight framework electron pairs), as
predicted by Wade–Rudolph–Mingos rules. Similarly, com-
A small number of gallium cluster and cage compounds
have come from the treatment of “GaI” with reagents other
than silyl or germyl anions. For example, reaction with LiArꢀꢀ,
Arꢀꢀ = C6H3(C6H2Me3-2,4,6)2-2,6, yielded a paramagnetic clus-
ter, [Ga11Arꢀꢀ ], which incorporates seven gallium atoms that do
4
not carry any substituents.33 This result can be compared to
the analogous preparations of the dimeric gallium diyls, 22–
24, and suggests that in those compounds the greater steric
bulk of the terphenyl ligands is required to prevent dispropor-
tionation processes and cluster formation. The Arꢀꢀ ligand has
also been utilised to stabilise a Ga2Ge3 cluster, 37, from the
reaction of “GaI” with ArꢀꢀGeCl in which the gallium reagent
is acting as a reducing reagent.48 This is the first structurally
characterised example of a cluster with a Ga–Ge framework.
“GaI” has additionally been utilised as a reducing reagent (in
combination with Cp*Ga) in its reaction with [AuI(PPh3)].49
This afforded the unusual cluster, 38, which contains the first
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8
1 3 4 5

View Article Online
Scheme 4 Reactions of “GaI” with metal–halide and metal–metal bonds.
Scheme 5 The use of “GaI” as a reductant in C–C bond forming reactions.
structurally characterised Au–Ga bonds. Finally, it is worth
mentioning the preparation of a hydridogallanate cage complex,
[{KHGa(OBut)}2], from a redox disproportionation reaction of
“GaI” with KOBut.43
43.6 This is in contrast to reactions with the diiron precursors,
[{(C5R5)Fe(CO)2}2], R = H or Me, which give the salt, 44,52
and the diiodogallyl complex, 45, respectively.50 The presence
of water in the former reaction also led to an unusual partial
oxidative hydrolysis product, [{Cp(CO)2FeGa}6O4(OH)2I2].
3.5 Oxidative insertion of “GaI” into metal–halide and
metal–metal bonds
3.6 Use in C–C bond forming reactions
There have been several reports of the oxidative insertion of
“GaI” into either transition metal–halide or metal–metal bonds.
The former reactions generally lead to dihalogallyl–transition
metal complexes, e.g. 39–41 (Scheme 4).6,50 In some instances,
e.g. 39, these are obtainable from gallium(III) halide precursors51
but routes employing “GaI” are much more facile. The stepwise
nature of the pathway to 39 (n = 0) has recently been demon-
strated with the isolation of 42 which reacts with one equivalent
of “GaI” to give the final product.50 Dihalogallyl–transition
metal complexes have significant potential as precursors to a
variety of Ga–M bonded species, e.g. dialkylgallyl complexes, as
has been previously demonstrated.6
Perhaps one of the least explored uses of “GaI” is as a
reagent in organic synthesis. This is surprising considering the
emerging application of InI as a reducing reagent in C–C bond
forming procedures such as Barbier allylations and Reformatsky
reactions.53 The more reducing nature of “GaI” could well lead
to its chemoselective use in similar transformations. An indica-
tion of this has come from the treatment of “GaI” with the 1,3-
diyne, Me3SiC≡CC≡CSiMe3, which affords the unusual ene-
diyne–bis(gem-organodigallium(III)) complex as two isomeric
forms, 46 and 47 (Scheme 5).54 The crystal structures of both
show them to contain rare examples of a Ga(III)–p interactions,
and the first structurally characterised gem-organodigallium
fragments. The proposed mechanism for the formation of 46
and 47 involves a reduction of the diyne with “GaI” followed by
C–C coupling and disproportionation reactions. It is instructive
Insertion of “GaI” into metal–metal bonds gives
more variable results than reactions with metal halides.
For example, reaction with the dimolybdenum precursor,
[{(C5H4Me)Mo(CO)3}2], led to the expected trimetallic system,
1 3 4 6
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8

View Article Online
that the weaker reducing agent, InI, does not react with the
diyne.
7 J. D. Corbett and R. K. McMullan, J. Am. Chem. Soc., 1955, 77,
4217; see also: J. R. Chadwick, A. W. Atkinson and B. G. Huckstepp,
J. Inorg. Nucl. Chem., 1966, 28, 1021.
8 M. Wilkinson and I. J. Worrall, J. Organomet. Chem., 1975, 93, 39.
9 C. Gerlach, W. Ho¨nle and A. Simon, Z. Anorg. Allg. Chem., 1982,
486, 7.
In contrast to the reactions of either diazabutadienes or
bis(imino)pyridines with “GaI” (which gave 7, 11 and 12), the
=
treatment of the mono(imino)pyridines, RN C(H)Py (Py = 2-
pyridyl, R = C6H3Pri2-2,6 or But), with the gallium reagent led
to the coupled products, 48 and 49.16 As with the formation of
46 and 47, the reaction mechanism is thought to involve a com-
bination of imine reduction and disproportionation reactions to
yield the intermediates, [GaI2{RNC•(H)Py}], two equivalents
of which subsequently couple. The molecular structures of
48 and 49 confirmed the C–C bond formations and revealed
that both compounds exist as their meso-isomers. The most
unusual feature of these structures is that the newly formed
10 S. Coban, Diplomarbeit, Universita¨t Karlsruhe, 1999.
11 A. Schnepf, C. Doriat, E. Mo¨llhausen and H. Schno¨ckel, Chem.
Commun., 1997, 2111.
12 R. J. Baker, H. Bettentrup and C. Jones, Eur. J. Inorg. Chem., 2003,
2446.
13 R. J. Baker, H. Bettentrup and C. Jones, Inorg. Chem. Commun.,
2004, 7, 1289.
14 C. Jones, C. Schulten and A. Stasch, Main Group Met. Chem., in
press.
15 R. J. Baker, R. D. Farley, C. Jones, M. Kloth and D. M. Murphy,
Chem. Commun., 2002, 1196.
16 R. J. Baker, C. Jones, M. Kloth and D. P. Mills, New. J. Chem., 2004,
28, 207.
17 C. Jones and M. Waugh, Dalton Trans., 2004, 1971.
18 R. J. Baker, R. D. Farley, C. Jones, M. Kloth and D. M. Murphy,
J. Chem. Soc., Dalton Trans., 2002, 3844. For an alternative synthesis
of a related anionic Ga(I) heterocycle, see: E. S. Schmidt, A. Jockisch
and H. Schmidbaur, J. Am. Chem. Soc., 1999, 121, 9758; E. S.
Schmidt, A. Schier and H. Schmidbaur, J. Chem. Soc., Dalton Trans.,
2001, 121, 505.
C–C bonds are longer than normally expected for C(sp3)–
3
˚
C(sp ) interactions [viz. 1.603(5) and 1.581(7) A for 48 and
49, respectively]. In comparison, the related reactions of imino-
pyridines with the weaker reductant, InCl, were shown not
to proceed via C–C couplings and, instead, gave only InCl3
2
i
=
adducts, e.g. [InCl3{g -N(C6H3Pr 2-2,6) C(H)Py}(THF)], by
disproportionation processes.
19 T. Pott, P. Jutzi, W. Kaim, W. W. Schoeller, B. Neumann, A. Stamm-
ler, H.-G. Stammler and M. Wanner, Organometallics, 2002, 21,
3169.
20 R. J. Baker, R. D. Farley, C. Jones, D. P. Mills, M. Kloth and D. M.
Murphy, Chem. Eur. J., in press.
21 K. L. Antcliff, R. J. Baker, C. Jones, D. M. Murphy and R. P. Rose,
Inorg. Chem., in press.
22 (a) R. J. Baker, C. Jones and J. A. Platts, Dalton Trans., 2003, 3673;
(b) R. J. Baker, C. Jones and J. A. Platts, J. Am. Chem. Soc., 2003, 125,
10534; (c) R. J. Baker, C. Jones, M. Kloth and J. A. Platts, Angew.
Chem., Int. Ed., 2003, 43, 2660; (d) R. J. Baker, C. Jones, M. Kloth
and J. A. Platts, Organometallics, 2004, 23, 4811; (e) R. J. Baker, C.
Jones and D. M. Murphy, Chem. Commun., 2005, 1339.
23 R. J. Baker and C. Jones, Coord. Chem. Rev., in press.
24 N. J. Hardman, B. E. Eichler and P. P. Power, Chem. Commun., 2000,
1991.
25 M. Stender, B. E. Eichler, N. J. Hardman, P. P. Power, J. Prust, M.
Noltemeyer and H. W. Roesky, Inorg. Chem., 2001, 40, 2794.
26 H. V. R. Dias and W. Jin, Inorg. Chem., 1996, 35, 6546.
27 M. C. Kuchta, J. B. Bonanno and G. Parkin, J. Am. Chem. Soc., 1996,
118, 10914.
4
Conclusion and future directions
The study of compounds containing p-block elements in a low
oxidation state is one of the most rapidly expanding areas of
main group chemistry. The advancement of this field requires
the ready availability of low oxidation state element halide
precursors. In group 13 the “true” gallium(I) halide complexes
of Schno¨ckel have allowed major advances to be made by his
group, especially in cluster chemistry. However, the development
of a facile synthetic route to “GaI” by Green et al. in 1990 has
allowed many other synthetic chemists entry to the fascinating
discipline of low oxidation state gallium chemistry. This easy
to prepare and handle reagent is being employed for an ever
increasing number of synthetic tasks that are either difficult or
indeed impossible to carry out by other methods. Many of the
products of these syntheses have themselves proved invaluable
as precursors in a diversity of reactions. This will only increase
into the future. Perhaps the greatest potential “GaI” holds is
as a specialist reducing agent for organic transformations, an
area which has only just begun to be explored. In addition, it is
certain there would be no main group chemist who would not
relish the opportunity to explore the synthetic possibilities that
a readily accessible “Al(I) halide” reagent would offer. Whether
such a reagent will appear remains to be seen.
28 H. V. R. Dias and W. Jin, Inorg. Chem., 2000, 39, 815.
29 S. Anfang, J. Grebe, M. Mo¨hlen, B. Neumu¨ller, N. Faza, W. Massa,
J. Magull and K. Dehnicke, Z. Anorg. Allg. Chem., 1999, 625,
1395.
30 P. Jutzi and L. O. Schebaum, J. Organomet. Chem., 2002, 654,
176.
31 P. Jutzi, B. Neumann, L. O. Schebaum, A. Stammler and H.-G.
Stammler, Organometallics, 1999, 18, 4462.
32 N. J. Hardman, R. J. Wright, A. D. Phillips and P. P. Power, Angew.
Chem., Int. Ed., 2002, 41, 2843.
33 N. J. Hardman, R. J. Wright, A. D. Phillips and P. P. Power, J. Am.
Chem. Soc., 2003, 125, 2667.
34 J. Su, X.-W. Li, C. Crittendon and G. H. Robinson, J. Am. Chem.
Soc., 1998, 120, 3773.
Acknowledgements
We thank the EPSRC for funding the aspects of the work
reviewed here that were carried out at Cardiff.
35 R. Ponec, G. Yuzhakov, X. Girone´s and G. Frenking,
Organometallics, 2004, 123, 1790, and references therein.
36 D. E. Hibbs, C. Jones and A. F. Richards, J. Chem. Soc., Dalton
Trans., 1999, 3531.
References
1 Chemistry of Aluminium, Gallium, Indium and Thallium, ed.
A. J. Downs, Blackie Academic Press, Glasgow, 1993, ch. 1, 3, 5,
7 and 8.
2 K. G. G. Hopkins and P. G. Nelson, J. Chem. Soc., Dalton Trans.,
1984, 1393, and references therein.
3 C. Dohmeier, D. Loos and H.-G. Schno¨ckel, Angew. Chem., Int. Ed.
Engl., 1996, 35, 129, and references therein.
4 (a) A. Schnepf and H.-G. Schno¨ckel, Angew. Chem., Int. Ed., 2002,
41, 3533; (b) H.-G. Schno¨ckel and A. Schnepf, Adv. Organomet.
Chem., 2001, 47, 235; (c) G. Linti and H.-G. Schno¨ckel, Coord. Chem.
Rev., 2000, 206-207, 285, and references therein.
37 S. Aldridge, C. Jones, P. C. Junk, A. F. Richards and M. Waugh,
J. Organomet. Chem., 2003, 665, 127.
38 C. Jones and A. F. Richards, J. Organomet. Chem., 2001, 629,
109.
39 G. Linti, A. Rodig and W. Ko¨stler, Z. Anorg. Allg. Chem., 2001, 627,
1465.
40 M. Kehrwald, W. Ko¨stlel, A. Rodig, G. Linti, T. Blank and N. Wiberg,
Organometallics, 2001, 20, 860.
41 W. Ko¨stler and G. Linti, Angew. Chem., Int. Ed., 1997, 36, 2644.
42 G. Linti, W. Ko¨stler, H. Piotrowski and A. Rodig, Angew. Chem., Int.
Ed., 1998, 37, 2209.
5 (a) C. Gemel, T. Steinke, M. Cokoja, A. Kempter and R. A. Fischer,
Eur. J. Inorg. Chem., 2004, 4161; (b) R. A. Fischer and J. Weiss,
Angew. Chem., Int. Ed., 1999, 38, 2830, and references therein.
6 M. L. H. Green, P. Mountford, G. J. Smout and S. R. Speel,
Polyhedron, 1990, 9, 2763.
43 G. Linti, S. Coban, A. Rodig and N. Sandholzer, Z. Anorg. Allg.
Chem., 2003, 629, 1329.
44 F. A. Cotton, Rev. Chem. Soc., 1996, 389.
45 A. Schnepf, E. Weckert, G. Linti and H. Schno¨ckel, Angew. Chem.,
Int. Ed., 1999, 38, 3381.
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8
1 3 4 7

View Article Online
46 G. Linti, S. Coban and D. Dutta, Z. Anorg. Allg. Chem., 2004, 630,
319.
47 G. Linti and A. Rodig, Chem. Commun., 2000, 127.
48 A. F. Richards, M. Brynda and P. P. Power, Organometallics, 2004,
23, 4009.
49 U. Anandhi and P. R. Sharp, Angew. Chem., Int. Ed., 2004, 43, 6128.
50 N. R. Bunn, S. Aldridge, D. L. Kays, N. D. Coombs, L. L. Ooi, S. J.
Coles and M. B. Hursthouse, Organometallics, submitted.
51 A. S. Borovik, S. G. Bott and A. R. Barron, Organometallics, 1999,
18, 2668.
52 G. Linti, G. Li and H. Pritzkow, J. Organomet. Chem., 2001, 626,
82.
53 (a) B. C. Ranu, Eur. J. Org. Chem., 2000, 2347; (b) K. K. Chauhan
and C. G. Frost, J. Chem. Soc., Perkin Trans. 1, 2000, 3015, and
references therein.
54 R. J. Baker and C. Jones, Chem. Commun., 2003, 390.
1 3 4 8
D a l t o n T r a n s . , 2 0 0 5 , 1 3 4 1 – 1 3 4 8