Gallium(III) halide complexes with phosphines, arsines and phosphine oxides - a comparative study

Article abstract of DOI:10.1016/j.poly.2007.05.008

The phosphine oxide complexes [GaX₃(Me₃PO)] and [(GaX₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] have been prepared and characterised by microanalysis, IR and multinuclear NMR (¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷¹Ga) spectroscopy. The structures of [GaCl₃(Me₃PO)], [(GaBr₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] and of the ionic product [GaI₂(Me₃PO)₂][GaI₄] have been determined and show that the Lewis acidity of the gallium halides towards phosphinoyl ligands diminishes as the halogen becomes heavier. The [GaX₃(Ph₃E)] (X = Cl, Br or I; E = P or As) and [(GaX₃)₂{μ-o-C₆H₄(CH₂PPh₂)₂}] (X = Br or I) have been prepared and their structural and spectroscopic properties compared with those of the phosphinoyl complexes. The results, and competitive solution NMR studies, show that Ga(III) binds the hard R₃PO in preference to the softer phosphine or arsine ligands. Hydrolysis of gallium(III) phosphines is shown to lead to [R₃PH][GaX₄], but in contrast to some other p-block halides, GaX₃ do not promote air-oxidation of R₃P to R₃PO.

Full text of DOI:10.1016/j.poly.2007.05.008

Polyhedron 26 (2007) 4147–4155
www.elsevier.com/locate/poly
Gallium(III) halide complexes with phosphines, arsines
and phosphine oxides – a comparative study
*
Fei Cheng, Hannah L. Codgbrook, Andrew L. Hector, William Levason, Gillian Reid ,
Michael Webster, Wenjian Zhang
School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK
Received 26 March 2007; accepted 4 May 2007
Available online 22 May 2007
Abstract
The phosphine oxide complexes [GaX3(Me3PO)] and [(GaX3)2{l-o-C6H4(CH2P(O)Ph2)2}] have been prepared and characterised by
microanalysis, IR and multinuclear NMR (1H, 13C{1H}, 31P{1H} and 71Ga) spectroscopy. The structures of [GaCl3(Me3PO)],
[(GaBr3)2{l-o-C6H4(CH2P(O)Ph2)2}] and of the ionic product [GaI2(Me3PO)2][GaI4] have been determined and show that the Lewis
acidity of the gallium halides towards phosphinoyl ligands diminishes as the halogen becomes heavier. The [GaX3(Ph3E)] (X = Cl, Br
or I; E = P or As) and [(GaX3)2{l-o-C6H4(CH2PPh2)2}] (X = Br or I) have been prepared and their structural and spectroscopic prop-
erties compared with those of the phosphinoyl complexes. The results, and competitive solution NMR studies, show that Ga(III) binds
the hard R3PO in preference to the softer phosphine or arsine ligands. Hydrolysis of gallium(III) phosphines is shown to lead to
[R3PH][GaX4], but in contrast to some other p-block halides, GaX3 do not promote air-oxidation of R3P to R3PO.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Gallium; Phosphine oxide; Phosphine; Phosphonium; NMR spectroscopy
1. Introduction
ligands. There are limited reports of gallium(III)
halide complexes of phosphorus or arsenic donor ligands
[17–27], and only one phosphine oxide complex,
[GaCl3(Ph3PO)], has been thoroughly characterised [28].
We have also explored whether gallium(III) promotes or
catalyses air-oxidation of R3P to R3PO as established pre-
viously for Sn(IV) and Bi(III) halides [29,30].
The heavier p-block metals and metalloids have a rich,
albeit poorly explored, coordination chemistry, which is
significantly different to that of the transition elements
[1,2]. The differences arise from the limited range of oxida-
tion states in the p-block and also from the different metal–
ligand bonding which utilises only s and p orbitals and
where necessary multicentre orbitals or M–X r* (X = hal-
ogen, etc.) as acceptor orbitals [3–5]. We have recently
explored the complexes of Sn(IV) [6–10], Bi(III) [11–13],
Tl(I) [14] and Sb(III) [11,15,16] with a variety of P, As, S,
Se and Te donor ligands. Here we report a comparative
structural and spectroscopic study of gallium(III) halide
complexes with soft P or As (R3E) and hard R3PO donor
2. Results and discussion
2.1. Ga(III) phosphine oxides
Reaction of the appropriate GaX3 (X = Cl, Br or I) with
Me3PO in a 1:1 mol. ratio in CH2Cl2 under anhydrous con-
ditions gave the white [GaX3(Me3PO)]. The diphosphine
dioxide complexes [(GaX3)2{l-o-C6H4(CH2P(O)Ph2)2}]
were obtained similarly using a 2:1 GaX3:o-C6H4(CH2P-
(O)Ph2)2 ratio. The isolated complexes are air-stable in
the solid state and easily soluble in a range of organic
*
Corresponding author. Tel.: +44 023 80593609; fax: +44 023
80593781.
E-mail address: gr@soton.ac.uk (G. Reid).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.05.008

4148
F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for [GaCl3(Me3PO)]
Ga1–O1
Ga1–Cl2
P1–O1
1.828(6)
2.161(2)
1.518(7)
Ga1–Cl1
Ga1–Cl3
2.162(2)
2.159(2)
O1–Ga1–Cl3
Cl3–Ga1–Cl2
Cl3–Ga1–Cl1
P1–O1–Ga1
108.9(3)
O1–Ga1–Cl2
O1–Ga1–Cl1
Cl2–Ga1–Cl1
106.5(2)
109.9(2)
110.52(12)
109.60(11)
111.28(10)
147.9(4)
solvents. Crystals of [GaCl3(Me3PO)] were obtained from
CH2Cl2–hexane and showed the expected pseudo-tetrahe-
˚
˚
dral structure (Table 1, Fig. 1). The d(P–O) (1.518(7) A)
is lengthened from the value in Me3PO itself (1.489(6) A)
˚
Fig. 1. View of the structure of [GaCl3(Me3PO)] with atom numbering
scheme adopted. Ellipsoids are drawn at the 50% probability level and H
atoms are omitted for clarity.
[31] and d(Ga–O) 1.828(6) A is similar to the value in
˚
[GaCl3(Ph3PO)] (1.818(10) A) [28], although in the latter
the phosphine oxide coordination is linear by symmetry
(although adp ellipsoids suggest some disorder [28]), com-
pared to the significantly bent geometry in the present com-
plex (angle Ga–O–P = 148ꢁ). The three [GaX3(Me3PO)]
complexes show strong m(P@O) stretches in the IR spectra
at ꢀ1100 cmꢁ1, lowered from 1166 cmꢁ1 in Me3PO, and
m(GaX) are typical of tetrahedral Ga(III) (Table 2, Section
different, but the other parameters seem unexceptional,
including the non-linear Ga–O–P angles of 148ꢁ and
153ꢁ. Spectroscopically the three [(GaX3)2{l-o-C6H4-
(CH2P(O)Ph2)2}] complexes show similar trends to those
with Me3PO described above, notably the significant fall
in m(PO) on coordination and the high frequency coordina-
tion shifts in d(31P) which vary with halogen Cl > Br > I
(Table 2). Curiously, we were unable to observe a 71Ga
NMR resonance for any of the diphosphine dioxide com-
plexes over the temperature range 295–180 K, presumably
due to the line broadening resulting from fast relaxation
of the quadrupolar gallium nucleus in these large and
asymmetric molecules.
1
6). In chlorocarbon solvents the H NMR spectra show
sharp doublets for the Me resonances, and the 31P{1H}
NMR spectra are sharp singlets with substantial high fre-
quency coordination shifts from Me3PO (d = 38). The
chemical shifts fall with halogen: d = 73.5 (Cl), 72.0 (Br),
70.5 (I), suggesting the Lewis acidity of the GaX3 also falls
in this order. All exhibit relatively sharp singlets in the 71Ga
NMR spectra1 at ambient temperatures (Table 2), which
will be discussed further below. Although the spectroscopic
data on [GaI3(Me3PO)] showed only the neutral species
present, a solution in CH2Cl2–hexane produced a small
number of colourless crystals which were shown to be the
ionic product, [GaI2(Me3PO)2][GaI4]. The structure is
shown in Fig. 2 (Table 3) and contains a tetrahedral
2.2. Gallium phosphine and arsine complexes
As indicated in Section 1, it is of interest to compare the
spectroscopic and structural consequences of changing the
hard R3PO donor for a soft R3P or R3As ligand. Initially
[GaX3(Me3P)] were prepared, but were found to be very
poorly soluble in solvents suitable for spectroscopic studies
(cf. Ref. [19]), and we have therefore used [GaX3(Ph3P)]
and [GaX3(Ph3As)] as comparator complexes (the R group
is expected to have a minimal effect on the trends). These
complexes have been reported previously and some data
presented [20–23,26]. The complexes were obtained in high
yield by reaction of the appropriate GaX3 and Ph3E in
anhydrous diethyl ether. X-ray crystal structures were
determined for [GaX3(Ph3P)] (X = Cl or Br) (Table 5, Figs.
4 and 5). There are two reports [20,21,26] of the crystal
structure of [GaI3(Ph3P)] both in the trigonal space group
[GaI4]ꢁ anion (d(Ga–I) = 2.548(2) A) and a pseudo-tetra-
˚
˚
hedral cation with d(Ga–O) = 1.854(8), 1.848(8) A and
˚
d(Ga–I) = 2.488(2), 2.500(2) A, with Ga–O–P angles of
136.8(6) and 140.6(6)ꢁ. The Ga–I distances are somewhat
shorter in the cation than the anion as expected, but the
˚
˚
notable difference is the longer d(Ga–O) (1.851 (av) A),
compared to the neutral [GaCl3(Me3PO)] (1.828 A)
(above). In spite of the crystallographic evidence for
[GaI2(Me3PO)2]+, [GaCl2(Me3PO)2]+ could not be pre-
pared from [GaCl3(Me3PO)], Me3PO and either FeCl3 or
SbCl5 (as chloride abstractors).
The structure of [(GaBr3)2{l-o-C6H4(CH2P(O)Ph2)2}]
(Table 4, Fig. 3) shows a bridging diphosphine dioxide
coordinated to two pseudo-tetrahedral gallium moieties,
which are staggered to minimise steric crowding. The
ꢀ
R3, but with one using hexagonal and the other rhombohe-
˚
dral basis vectors. The Ga–P (2.416(5), 2.413(4) A) and
˚
Ga–I (2.5212(9), 2.518(2) A) are in excellent agreement,
˚
as are the I–Ga–I (ca. 113.8ꢁ) and I–Ga–P (ca. 104.6ꢁ)
angles. [GaCl3(Ph3P)] and [GaBr3(Ph3P)] show the expected
pseudo-tetrahedral monomer geometry. The Ga–P dis-
tances increase along the series Cl (2.372(2)) ! Br
Ga–O distances 1.892(4) and 1.858(4) A are surprisingly
1
71Ga, I = 3/2, 39.9%, N = 30.49 MHz, Q = 0.112 · 10ꢁ28 m2; 69Ga,
I = 3/2, 60.1%, N = 24.00 MHz, Q = 0.178 · 10ꢁ28 m2 [32].
(2.385(1)) ! I (2.416(5) A) consistent with reduced Lewis
˚

F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
4149
Table 2
Selected spectroscopic data
acidity of the gallium as the halide becomes less electroneg-
ative, whilst the changes in Ga–X follow the changes in
covalent radii of X. The literature structure of [GaI3(-
Ph3As)] [20,21] is isomorphous with the Ph3P analogue
Complex
m(P@O)/
d(31P)a
d(71Ga)b
cmꢁ1
[GaCl3(Me3PO)]
[GaBr3(Me3PO)]
[GaI3(Me3PO)]
[GaCl3(Ph3PO)]c
[(GaCl3)2{l-o-
C6H4(CH2P(O)Ph2)2}]
[(GaBr3)2{l-o-
C6H4(CH2P(O)Ph2)2}]
[(GaI3)2{l-o-
1100
1095
1102
1144
73.5
72.0
70.5
45.9
52.5
230
106
˚
ꢀ
(R3) with a slightly shorter Ga–I (2.509(1) A) and with
˚
Ga–As = 2.490(1) A. We note that in the series containing
ꢁ242
the silyl phosphine, [GaX3{P(SiMe3)3}] (X = Cl, Br, I), [17]
the Ga–P distances decrease Cl ! Br ! I, which is the
reverse of that observed in organophosphine complexes.
The 31P{1H} NMR spectra of [GaX3(Ph3P)] are notable
in showing resolved 31P–69/71Ga couplings. [GaCl3(Ph3P)]
in CH2Cl2 solution shows no 31P{1H} NMR resonance at
room temperature, but a broad feature appears on cooling
the solution to 273 K, and at 183 K this has resolved into a
broad multiplet which approximates to two overlapping
quartets due to coupling to the I = 3/2 69Ga and 71Ga.
For [GaBr3(Ph3P)] the room temperature 31P{1H} NMR
resonance is an ill-defined multiplet, becomes a quartet at
273 K (although the lines are too broad to show resolved
couplings to the separate gallium isotopes). For
[GaI3(Ph3P)] two superimposed quartet couplings are
230
1088, 1070
n.o.
1091, 1080
1086, 1076
52.0
n.o.
n.o.
51.4
C6H4(CH2P(O)Ph2)2}]
[GaCl3(Ph3P)]
ꢁ5.5(m)
264
(d,
J = 721 Hz)
[GaBr3(Ph3P)]
[GaI3(Ph3P)]
ꢁ10.7(m) 152
(d,
J = 693 Hz)
ꢁ29.7(m) ꢁ151
(d,
J = 466 Hz)
264
132
ꢁ203
[GaCl3(Ph3As)]
[GaBr3(Ph3As)]
[GaI3(Ph3As)]
a
Relative to external 85% H3PO4, ligand shifts are Me3PO d = 38,
Table 4
o-C6H4(CH2P(O)Ph2)2 d = 30.8, PPh3 d = ꢁ6.
˚
Selected bond lengths (A) and angles (ꢁ) for [(GaBr3)2{l-o-C6H4-
b
Relative to [Ga(H2O)6]3+ in water at pH = 0, [GaCl4]ꢁ d = 251,
(CH2P(O)Ph2)2}]
[GaBr4]ꢁ d = 64, [GaI4]ꢁ d = ꢁ455.
c
Ga1–O1
Ga1–Br3
Ga2–O2
Ga2–Br4
P2–O2
1.892(4)
2.2952(8)
1.858(4)
2.2983(8)
1.520(4)
Ga1–Br1
Ga1–Br2
Ga2–Br5
Ga2–Br6
P1–O1
2.2669(9)
2.3133(8)
2.2853(9)
2.2990(8)
1.525(4)
Data from Ref. [28].
O1–Ga1–Br1
Br1–Ga1–Br3
Br1–Ga1–Br2
O2–Ga2–Br5
Br5–Ga2–Br4
Br5–Ga2–Br6
P1–O1–Ga1
109.11(11)
112.50(3)
113.99(3)
105.55(13)
113.41(3)
114.01(3)
148.3(2)
O1–Ga1–Br3
O1–Ga1–Br2
Br3–Ga1–Br2
O2–Ga2–Br4
O2–Ga2–Br6
Br4–Ga2–Br6
P2–O2–Ga2
106.88(10)
101.93(11)
111.62(3)
102.32(11)
107.24(12)
113.10(3)
153.9(2)
Fig. 2. View of the structure of the cation in [GaI2(Me3PO)2][GaI4] with
atom numbering scheme adopted. Ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity.
Table 3
˚
Selected bond lengths (A) and angles (ꢁ) for [GaI2(Me3PO)2][GaI4]
Ga1–O1
Ga1–I1
Ga2–I3
Ga2–I5
P1–O1
1.854(8)
Ga1–O2
Ga1–I2
Ga2–I4
Ga2–I6
P2–O2
1.846(8)
2.4997(17)
2.5472(16)
2.5461(15)
1.523(9)
2.4875(16)
2.5482(15)
2.5258(16)
1.525(8)
O2–Ga1–O1
O1–Ga1–I2
O1–Ga1–I1
Ga1–O1–P1
101.3(4)
106.7(3)
109.2(3)
136.8(6)
O2–Ga1–I2
O2–Ga1–I1
I2–Ga1–I1
Ga1–O2–P2
111.8(3)
109.8(3)
116.89(6)
140.6(6)
Fig. 3. View of the structure of [(GaBr3)2{o-C6H4(CH2P(O)Ph2)2}] with
the atom numbering scheme adopted. Ellipsoids are shown at the 50%
probability level and H atoms are omitted for clarity.

4150
F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
Table 5
˚
Selected bond lengths (A) and angles (ꢁ) for [GaX3(Ph3P)]
X = Cl
X = Br (Ga1)
X = Br (Ga2)a
Ga1–P1
Ga1–X1
Ga1–X2
Ga1–X3
2.3717(16)
2.1677(15)
2.1679(16)
2.1696(15)
2.3848(13)
2.3134(7)
2.3048(7)
2.3225(7)
2.3879(13)
2.3133(7)
2.3212(7)
2.3082(8)
X1–Ga1–P1
X2–Ga1–P1
X3–Ga1–P1
X1–Ga1–X2
X1–Ga1–X3
X2–Ga1–X3
104.17(6)
104.08(6)
111.46(6)
112.98(6)
112.40(6)
111.24(6)
105.83(4)
107.45(4)
107.50(4)
111.79(3)
114.27(3)
109.63(3)
106.71(4)
106.88(4)
105.93(4)
111.68(3)
112.39(3)
112.73(3)
˚
For comparison [GaI3(Ph3P)] has Ga–I = 2.5212(9) or 2.518(2) A (Refs.
˚
[26,20] respectively), Ga–P = 2.416(5) or 2.413(4) A and [GaI3(Ph3As)] has
˚
˚
Ga–I = 2.509(1) A and Ga–As = 2.490(1) A (Ref. [21]).
a
For the second molecule the data are for Ga2, P2, X4, X5 and X6.
Fig. 5. View of the structure of [GaBr3(Ph3P)] showing the atom
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity. The other molecule in the
asymmetric unit is very similar.
Fig. 4. View of the structure of [GaCl3(Ph3P)] showing the atom
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms are omitted for clarity.
clearly resolved at ambient temperatures; the lines sharpen
on cooling to 273 K (Fig. 6) and then broaden on further
cooling. The changes with halide and temperature reflect
the different electric field gradients in the three compounds
and how these affect the quadrupolar relaxation rates of
the gallium nuclei over this temperature range. The 71Ga
NMR spectra of all three compounds show clear doublet
Fig. 6. 31P{1H} NMR of [GaI3(Ph3P)] in CH2Cl2 at 273 K.
tion places the two GaI3 groups ‘anti’ to minimise steric
interactions (Ga1–P1ꢂ ꢂ ꢂP2–Ga2 = 161ꢁ). Spectroscopically
these complexes (Table 2) are similar to those of Ph3P, but
provide a useful comparison with the diphosphine dioxide
compounds described above.
1
couplings to 31P (Table 2) with J(31P-71Ga) falling from
Cl ! Br ! I.
The o-xylyl diphosphine o-C6H4(CH2PPh2)2 is some-
what pre-organised for chelation by the central o-pheny-
lene backbone, and functions as a chelate to many late
transition metals, despite forming a seven-membered ring
in the process [33]. However, on reaction with GaX3 it
behaves as a bridging bidentate, forming [(GaX3)2-
{o-C6H4(CH2PPh2)2}] as confirmed by the crystal structure
of the iodo-complex (Table 6, Fig. 7). The molecule has
approximate twofold symmetry and the ligand conforma-
3. Some comparisons of the effect of donor types on
gallium(III)
The spectroscopic and structural data set out in previous
sections clearly support the expected conclusion that Lewis
acidity decreases in the gallium(III) halides Cl > Br > I,

F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
4151
Table 6
with Bi and Sb halides [11,30]. In order to explore whether
[GaX3(Ph3P)] forms Ph3PO in chlorocarbon solvents, solu-
tions of all three complexes in anhydrous CH2Cl2 were
placed in 10 mm o.d. NMR tubes, the tubes filled with
dry O2 and the 31P{1H} NMR spectra monitored at regular
intervals over a three week period. The spectra showed no
evidence for phosphine oxide formation (although some
[R3PH][GaX4] were evident due to trace hydrolysis). We
conclude that, in marked contrast to the Group 15 MX3
and especially the Sn(IV) systems, gallium halides do not
promote phosphine oxidation under these conditions.
In rigorously anhydrous chlorocarbons (CH2Cl2 or
CHCl3 and their deuterated analogues), gallium(III) halide
phosphine and diphosphine complexes exhibit 31P{1H}
NMR spectra consistent with the presence of a single spe-
cies in each. In favourable cases with the (C3v) GaPX3
donor sets, 71Ga NMR spectra lead to the same conclu-
sions. However, even brief exposure of the solutions of
[GaX3(R3P)] to air resulted in the appearance of new reso-
nances. In the 31P{1H} NMR spectra the new features were
broad with ill-defined structure and typically to high fre-
quency of that of the gallium complex, and were assigned
to the corresponding phosphonium cations [R3PH]+ both
by comparison of their chemical shifts with literature val-
ues [35], and from the 1H-coupled 31P NMR spectra which
˚
Selected bond lengths (A) and angles (ꢁ) for [(GaI3)2{l-o-C6H4-
(CH2PPh2)2}]
Ga1–P1
Ga1–I1
Ga1–I2
Ga1–I3
2.3891(9)
2.5312(4)
2.5286(4)
2.5194(4)
Ga2–P2
Ga2–I4
Ga2–I5
Ga2–I6
2.3872(9)
2.5143(4)
2.5211(4)
2.5516(5)
P1–Ga1–I1
P1–Ga1–I2
P1–Ga1–I3
I1–Ga1–I2
I1–Ga1–I3
I2–Ga1–I3
111.78(2)
102.22(2)
105.87(2)
112.752(15)
111.335(15)
112.337(16)
P2–Ga2–I4
P2–Ga2–I5
P2–Ga2–I6
I4–Ga2–I5
I4–Ga2–I6
I5–Ga2–I6
109.57(2)
109.66(2)
99.97(2)
111.195(15)
115.297(15)
110.526(14)
1
showed doublets due to JPH (300–700 Hz).2 The 71Ga
spectra also showed resonances due to the corresponding
[GaX4]ꢁ anion at X = Cl: d = 251; X = Br: d = 64; X = I:
d = ꢁ455 [32]. All of the complexes we examined showed
a tendency to form phosphonium salts, although it is par-
ticularly evident with alkyl phosphines, probably because
these are the strongest proton bases [36].
Fig. 7. View of the structure of [(GaI3)2{o-C6H4(CH2PPh2)2}] showing
the atom numbering scheme adopted. Ellipsoids are drawn at the 50%
probability level and H atoms are omitted for clarity.
Addition of small amounts of water to the solutions
resulted in immediate and complete loss of the resonances
due to [GaX3(R3P)] and the only species evident in the
71Ga NMR spectra were the [GaX4]ꢁ anions. The forma-
tion of phosphonium salts was also observed in the gal-
lium–diphosphine complexes, and we note that Sigl et al.
[37] identified the hydrolysis product of [GaCl2-
{o-C6H4(PPh2)2}][GaCl4] as [o-C6H4(PPh2)(PPh2H)][GaCl4]
by an X-ray crystal structure.
Final confirmation of the identity of the hydrolysis
products comes from the crystal structure of [Me2PhPH]
[GaCl4] (Fig. 8). Colourless crystals of which were obtained
from a solution shown by NMR spectroscopy to contain
mainly [GaCl3(Me2PhP)], showing the ionic species crystal-
lise preferentially. [GaCl3(Ph3P)] is quantitatively con-
verted into [Ph3PH][GaCl4] by treatment with HCl gas in
CH2Cl2 solution, which provides the most convenient syn-
thesis for these phosphonium species.
towards both hard and soft donor ligands. The second
point to note is the trends in bond lengths about the gal-
˚
˚
lium centre with Ga–Cl (ꢀ2.15 A), Ga–Br (ꢀ2.3 A), Ga–I
˚
˚
˚
˚
(ꢀ2.5 A), Ga–O (ꢀ1.85 A), Ga–P (ꢀ2.4 A) and Ga–As
(ꢀ2.5 A). It is clear that the Ga–X and the Ga–O bond
˚
lengths are ca. 0.1 A shorter than the sum of the covalent
radii, [34] whilst the Ga–P(As) are rather longer than
expected, suggesting that the softer donors are more
weakly bound. Support for this came from in situ
31P{1H} NMR measurements (CH2Cl2 solution) which
showed that Me3PO displaced Ph3P or Ph3As (L) from
their [GaCl3L] complexes, but that [GaCl3(Me3PO)] was
unaffected by the presence of excess L.
The 71Ga NMR spectra show progressive low frequency
shifts with halide Cl ! Br ! I, but the trends with neutral
donor are more variable, giving evidence that several com-
peting factors are involved.
4. Studies on oxidation and hydrolysis of gallium
phosphines
In the presence of dioxygen, tin(IV) halides readily con-
vert phosphines to phosphine oxides [8,10,29] and similar
behaviour, although less thoroughly explored, is observed
2
The broad lines arise from incomplete decoupling of the P–H proton
under normal broad band decoupling settings.

4152
F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
1.09 mmol) and the reaction mixture was stirred under
N2 for ca. 2 h. The volatiles were then removed in vacuo
and the white solid rinsed with hexane and dried in
vacuo. Yield 0.26 g, 88%. Anal. Calc. for C3H9Cl3GaOP:
C, 13.4; H, 3.4. Found: C, 13.7; H, 3.4%. 1H NMR
2
(CDCl3, 298 K): d = 1.83 (d, Me, JPH = 12.8 Hz).
1
13C{1H} NMR (CDCl3): d = 17.1 (d, Me, JPC
=
70.6 Hz). 31P{1H} NMR (CDCl3): d = 73.5. 71Ga NMR
(CDCl3): d = 230. IR (Nujol): m = 1100 br s (P@O),
387, 358 (Ga–Cl) cmꢁ1
.
6.2. [GaBr3(Me3PO)]
Method as above, but using GaBr3. White solid (62%).
Fig. 8. View of the structure of the cation in [Me2PhPH][GaCl4] with
numbering scheme adopted. Ellipsoids are drawn at the 50% probability
level and H atoms (except that on P1) are omitted for clarity. Selected
Anal. Calc. for C3H9Br3GaOP: C, 9.0; H, 2.6. Found: C,
1
9.1; H, 2.0%. H NMR (CDCl3, 298 K): d = 1.85 (d, Me,
2JPH = 13.0 Hz). 13C{1H} NMR (CDCl3): d = 17.3 (d,
˚
bond lengths (A) and angles (ꢁ): P1–C1 1.788(4); P1–C2 1.784(3); P1–C3
1
Me, JPC = 70.2 Hz). 31P{1H} NMR (CDCl3): d = 72.0.
1.788(3); C–P1–C 110.08(16)–111.50(17); Ga1–Cl 2.1657(11)–2.1770(11).
71Ga NMR (CDCl3): d = 106. IR (Nujol): m = 1095 br s
(P@O), 283, 244 (Ga–Br) cmꢁ1
.
5. Conclusions
6.3. [GaI3(Me3PO)]
These results show that the Lewis acidity of GaX3
decreases as the halide becomes heavier and that the max-
imum coordination number at the gallium in these species
is four. With only one exception, all the complexes were
neutral with X3O or X3E (X = Cl, Br or I; E = P or As)
donor sets. Competitive NMR studies on the GaCl3 sys-
tems show that R3PO are preferred to R3E suggesting that
GaCl3 is quite a hard Lewis acid.
Method as above, but using GaI3. White solid (65%).
Anal. Calc. for C3H9GaI3OP Æ CH2Cl2: C, 7.6; H, 1.8.
Found: C, 7.4; H, 1.8%. 1H NMR (CDCl3, 298 K):
d = 1.85 (d, Me, 2JPH = 13.0 Hz). 13C{1H} NMR (CDCl3):
1
d = 17.0 (d, Me, JPC = 70.5 Hz). 31P{1H} NMR (CDCl3):
d = 70.5. 71Ga NMR (CDCl3): d = ꢁ242. IR (Nujol):
m = 1102 (P@O), 250 (Ga–I) cmꢁ1
.
6. Experimental
6.4. [(GaCl3)2{l-o-C6H4(CH2P(O)Ph2)2}]
All the reactions and manipulations were performed in an
inert atmosphere (N2) glovebox or using Schlenk techniques.
Diethyl ether and hexane were dried by distillation over
sodium/benzophenone and dichloromethane was dried by
distillation from CaH2. Infrared spectra were measured as
Nujol mulls between CsI plates on a Perkin–Elmer PE983
Method as above, but using a 2:1 GaCl3:diphosphine
ratio. White solid (89%). Anal. Calc. for C32H28Cl6Ga2O2-
P2 Æ 0.25CH2Cl2: C, 44.0; H, 3.3. Found: C, 44.1; H, 2.6%.
1H NMR (CDCl3, 298 K): d = 4.08 (d, CH2, 4H,
2JPH = 12.4 Hz), 6.51 (m, o-C6H4, 2H), 6.98 (m, o-C6H4,
2H), 7.50–7.78 (m, Ph, 20H). 13C{1H} NMR (CDCl3):
1
spectrometer. H NMR spectra were recorded in CDCl3
1
solution on a Bruker AV300, 31P{1H} and 71Ga NMR spec-
tra on a Bruker DPX400 and referenced to 85% H3PO4 and
[Ga(H2O)6]3+ respectively. Me3PO (Aldrich) was freshly
sublimed prior to use. o-C6H4(CH2P(O)Ph2)2 was obtained
as a white solid by stirring a CH2Cl2 solution of o-C6H4-
(CH2PPh2)2 in dry air with a catalytic amount of SnI4 [29]
followed by hydrolysis, extraction with CH2Cl2 and drying
d = 33.7 (d, CH2, JPC = 68.1 Hz), 124.3–135.4 (aromatic
C). 31P{1H} NMR (CDCl3): d = 52.5. 71Ga NMR
(CDCl3): not observed. IR (Nujol): m = 1088 br s, 1070 sh
(P@O), 397, 356 (Ga–Cl) cmꢁ1
.
6.5. [(GaBr3)2{l-o-C6H4(CH2P(O)Ph2)2}]
(MgSO4). 1H NMR (CDCl3): d = 3.90 (d, [4H], CH2, 2JPH
=
Method as above, but using a 2:1 GaBr3:diphosphine
ratio. White solid (94%). Anal. Calc. for C32H28Br6Ga2O2-
P2 Æ CH2Cl2: C, 32.8; H, 2.5. Found: C, 32.4; H, 2.1%.
1H NMR (CDCl3, 298 K): d = 4.11 (d, CH2, 4H,
2JPH = 12.3 Hz), 6.50 (m, o-C6H4, 2H), 6.95 (m, o-C6H4,
2H), 7.50–7.77 (m, Ph, 20H). 13C{1H} NMR (CDCl3):
13.0 Hz), 6.68 (m, [2H], o-C6H4), 6.78 (m, [2H], o-C6H4),
7.30–7.67 (m, [20H], Ph). 13C{1H} NMR (CDCl3): d = 35.9
(d, CH2, 1JPC = 66.4 Hz), 126.6–133.3 (aromatic C). 31P{1H}
NMR (CDCl3): 30.8. IR (Nujol): m = 1181 br s (P@O) cmꢁ1
.
1
6.1. [GaCl3(Me3PO)]
d = 34.1 (d, CH2, JPC = 68.0 Hz), 124.2–135.4 (aromatic
C). 31P{1H} NMR (CDCl3): d = 52.0. 71Ga NMR
(CDCl3): not observed. IR (Nujol): m = 1091 s, 1080 s
GaCl3 (0.19 g, 1.09 mmol) in CH2Cl2 (5 mL) was com-
bined with a CH2Cl2 solution (10 mL) of Me3PO (0.10 g,
(P@O), 296, 230 (Ga–Br) cmꢁ1
.

F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
4153
1
6.6. [(GaI3)2{l-o-C6H4(CH2P(O)Ph2)2}]
2.1. Found: C, 28.2; H, 1.9%. H NMR (CDCl3): 3.60 (d,
4H, CH2), 6.97–6.69 (m), 7.63–7.40 (m, aromatic H).
31P{1H} NMR (CDCl3): d = ꢁ33.7 (s). 71Ga NMR
Method as above, but using a 2:1 GaI3:diphosphine ratio.
White solid (65%). Anal. Calc. for C32H28Ga2I6O2P2: C,
(CDCl3): d = ꢁ146 (s). IR (Nujol): m = 234 m (Ga–I) cmꢁ1
.
1
27.3; H, 2.0. Found: C, 27.4; H, 1.7%. H NMR (CDCl3,
298 K): d = 4.15 (d, CH2, 4H, 2JPH = 12.6 Hz), 6.50 (m, o-
C6H4, 2H), 6.95 (m, o-C6H4, 2H), 7.50–7.80 (m, Ph, 20H).
13C{1H} NMR (CDCl3): d = 33.6 (d, CH2, 1JPC = 68.1 Hz),
124.1–135.3 (aromatic C). 31P{1H} NMR (CDCl3): d = 51.4.
71Ga NMR (CDCl3): not observed. IR (Nujol): m = 1086 s,
6.12. [GaCl3(Ph3As)]
A solution of Ph3As (0.220 g, 0.718 mmol) in diethyl
ether (10 mL) was added dropwise to a stirred solution of
GaCl3 (0.126 g, 0.718 mmol) in diethyl ether (5 mL). After
stirring at room temperature for 4 h, removal of Et2O gave
a white solid, which was dried in vacuo. (Yield 0.32 g, 92%).
71Ga NMR (CDCl3): d = 264 (s, W1/2 = 4000 Hz). IR
1076 s (P@O), 240 (Ga–I) cmꢁ1
.
6.7. [GaCl3(Ph3P)]
(Nujol): m = 392 s, 365 m (Ga–Cl) cmꢁ1
.
A solution of Ph3P (0.300 g, 1.14 mmol) in diethyl ether
(5 mL) was added dropwise to a stirred solution of GaCl3
(0.201 g, 1.14 mmol) in diethyl ether (4 mL). After stirring
at room temperature for 15 h, the resultant white precipitate
was filtered off, washed with diethyl ether (2 mL) and dried in
vacuo. Yield 0.32 g, 65%. Anal. Calc. for C18H15Cl3GaP: C,
6.13. [GaBr3(Ph3As)]
Prepared similarly to the chloro compound. White solid
(93%). 71Ga NMR (CDCl3): d = 132 (s, W1/2 = 3000 Hz).
IR (Nujol): m = 285 br s, 219 m (Ga–Br) cmꢁ1
.
1
49.3; H, 3.5. Found: C, 48.7; H, 3.8%. H NMR (CDCl3,
295 K): d 7.69–7.41 (m, Ph). 31P{1H} NMR (CDCl3):
295 K not observed; 273 K d = ꢁ5.4 (m). 71Ga NMR
(CDCl3): d = 264 (br d, J = 721 Hz). IR (Nujol): m = 387 s,
6.14. [GaI3(Ph3As)]
Prepared similarly to the chloro compound. White solid
347 m (Ga–Cl) cmꢁ1
.
(90%). 71Ga NMR (CDCl3): d = ꢁ203 (s, W1/2 = 2500 Hz).
IR (Nujol): m = 244 m (Ga–I) cmꢁ1
.
6.8. [GaBr3(Ph3P)]
6.15. [Me2PhPH][GaCl4]
Made similarly to the chloro compound. White solid
(64%). Anal. Calc. for C18H15Br3GaP: C, 37.8; H, 2.9.
Found: C, 38.1; H, 2.8%. 1H NMR (CDCl3, 295 K): d
7.81–7.38 (m, Ph). 31P{1H} NMR (CDCl3): d = ꢁ10.7.
71Ga NMR (CDCl3): d = 152 (d, J = 693 Hz). IR (Nujol):
Crystals of [PPhMe2H][GaCl4] were isolated from solu-
tions of the corresponding [GaCl3(Me2PhP)] in CH2Cl2
solution by vapour diffusion of n-hexane under nitrogen.
1
1H-coupled 31P NMR (CDCl3): d ꢁ0.47 (d, J = 511 Hz).
m = 289 s, 234 m (Ga–Br) cmꢁ1
.
71Ga NMR: d = +251 (s).
6.9. [GaI3(Ph3P)]
6.16. X-ray experimental
Made similarly to the chloro compound. White solid
(66%). Anal. Calc. for C18H15GaI3P: C, 30.3; H, 2.1.
Found: C, 30.5; H, 2.0%. 1H NMR (CDCl3, 295 K): d
7.81–7.38 (m, Ph). 31P{1H} NMR (CDCl3): d = ꢁ29.7.
71Ga NMR (CDCl3): d = ꢁ151 (d, J = 466 Hz). IR
Crystallographic parameters are given in Table 7. All
the crystals were grown from CH2Cl2 solutions of the com-
plexes by vapour diffusion of n-hexane under dinitrogen.
Data collections were carried out with a Bruker-Nonius
Kappa CCD diffractometer with graphite-monochromated
(Nujol): m = 241 m (Ga–I) cmꢁ1
.
Mo Ka radiation (k = 0.71073 A) and with the crystals
˚
held at 120 K in a nitrogen gas stream. The structure solu-
tions were straightforward [38–40] except as indicated
below with the hydrogen atoms being introduced into the
models in calculated positions with default C–H distances.
6.10. [(GaBr3)2{o-C6H4(CH2PPh2)2}]
Made similarly using a 2:1 Ga:ligand mol. ratio. White
˚
solid (76%). Anal. Calc. for C32H28Br6Ga2P2: C, 35.2; H,
The phosphonium H atom had P–H fixed at 1.40 A.
1
2.6. Found: C, 35.5; H, 2.5%. H NMR (CDCl3): 3.72 (d,
[GaCl3(Me3PO)] is reported in the space group Cc
although the ‘checkcif’ software raised the possibility of
missed symmetry. The Cc-C2/c problem is well known
[41,42], but with Z of 4 a C2/c solution would require the
molecule to have symmetry (or to be disordered). Attempts
to find a C2/c solution failed. [GaI2(Me3PO)2][GaI4]
belongs to one of the 11 pairs of enantiomorphous space
groups and the fit to the data was slightly improved by
the inclusion of a TWIN command. The data for
4H, CH2), 6.53–6.97 (m), 7.45–7.75 (m, aromatic H).
31P{1H} NMR (CDCl3): d = ꢁ14.2 (s). 71Ga NMR (CDCl3):
d = 156 (br). IR (Nujol): m = 281 s, 227 m (Ga–Br) cmꢁ1
.
6.11. [(GaI3)2{o-C6H4(CH2PPh2)2}]
Prepared similarly to the previous compound. White
solid (75%). Anal. Calc. for C32H28Ga2I6P2: C, 27.9; H,

4154
F. Cheng et al. / Polyhedron 26 (2007) 4147–4155
Table 7
Crystallographic dataa
Complex
[GaCl3(Me3PO)]
[GaI2(Me3PO)2]
[GaI4]
[(GaBr3)2
{o-C6H4(CH2P(O)
Ph2)2}]
[(GaI3)2
{o-C6H4-
(CH2PPh2)2}]
[Me2PhPH]
[GaCl4]
[GaCl3(Ph3P)]
C18H15Cl3GaP
[GaBr3-
(Ph3P)]
Formula
C3H9Cl3GaOP
C6H18Ga2I6O2P2
C32H28Br6Ga2O2P2
C32H28Ga2I6P2
C8H12Cl4GaP
C18H15Br3-
GaP
Formula weight
Crystal system
Space group
268.14
monoclinic
Cc (#9)
8.144(2)
10.216(3)
12.418(4)
90
105.577(15)
90
995.3(5)
4
1084.98
tetragonal
P43212 (#96)
12.259(2)
12.259(2)
32.976(9)
90
1125.38
triclinic
1375.32
monoclinic
P21/c (#14)
25.401(2)
8.1399(5)
20.094(2)
90
106.943(5)
90
3974.4(6)
4
350.67
438.34
571.72
monoclinic
P21/c (#14)
6.705(2)
12.499(4)
16.848(4)
90
99.352(16)
90
1393.3(6)
4
monoclinic
C2/c (#15)
16.155(2)
14.567(2)
15.924(2)
90
98.249(8)
90
3708.6(8)
8
monoclinic
P21/c (#14)
16.193(2)
14.3938(12)
17.779(2)
90
109.652(4)
90
3902.5(7)
8
ꢀ
P1 (#2)
˚
a (A)
8.8772(15)
13.6809(15)
16.2405(15)
67.503(7)
87.495(8)
87.788(7)
1820.0(4)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
3
˚
U (A )
4956.2(18)
8
Z
l(Mo Ka)
3.664
9.773
8.183
6.118
2.820
1.998
7.631
(mmꢁ1
)
Rint
Total number of
reflections
0.0604
4208
0.0801
37005
0.0730
36009
0.042
46651
0.0525
16050
0.163
53745
0.088
43220
Unique
reflections
Number of
parameters/
restraints
2047
86/2
5707
8378
9147
3184
4269
8934
164/13
397/0
379/0
129/0
208/0
415/0
Rb1 [Io > 2r(Io)]
R1 [all data]
wRb2 [Io > 2r(Io)]
wR2 [all data]
a
0.054
0.073
0.110
0.121
0.054
0.065
0.113
0.121
0.047
0.075
0.090
0.099
0.024
0.028
0.050
0.052
0.042
0.060
0.082
0.088
0.060
0.155
0.130
0.167
0.042
0.108
0.069
0.086
˚
Common items: temperature = 120 K; wavelength (Mo Ka) = 0.71073 A; h(max) = 27.5ꢁ.
P
P
P
P
b
R1 = iFoj ꢁ jFci/ jFoj. wR2 = [ w(F2o ꢁ Fc2)2/ wFo4]1/2
.
[GaCl3(Ph3P)] was collected in the triclinic system and
yielded a solution with Z = 4 in the space group P1.
References
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and given numbers 640911 (Cl/O), 640912 (I/O), 640913
(Br/O), 640914 (Cl/P), 640915 (Br/P), 640916 (I/P),
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These data can be obtained free of charge via http://
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Cambridge Crystallographic Data Centre, 12 Union Road,
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e-mail: deposit@ccdc.cam.ac.uk. Supplementary data asso-
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at doi:10.1016/j.poly.2007.05.008.

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