Reactions of 'GaI' with organometallic transition metal halides

Article abstract of DOI:10.1016/j.ica.2007.02.037

Two approaches towards the synthesis of phosphine ligated half-sandwich complexes [(η^x-C_xH_x)M(PR₃)₂GaI₂]_n containing diiodogallyl ligands have been investigated. Insertion of 'GaI' into the Mo-I bond of (η⁷-C₇H₇)Mo(CO)₂I has been shown to yield the crystallographically characterized dimeric complex [(η⁷-C₇H₇)Mo(CO)₂GaI₂]₂ (2). Attempts to substitute the carbonyl ligands by the phosphine ligand dppe [dppe = bis(diphenylphosphino)ethane] have been shown instead to yield the sparingly soluble complex [(η⁷-C₇H₇)Mo(CO)₂GaI₂]₂(μ-dppe) (3) in which the phosphine bridges two [(η⁷-C₇H₇)Mo(CO)₂GaI₂] units via a pair of P → Ga donor/acceptor bonds. By contrast, attempts to insert 'GaI' directly into the metal-halogen bond of phosphine ligated complexes such as (η⁵-C₅H₅)Ru(PPh₃)₂Cl or (η⁵-C₅H₅)Ru(dppe)Cl have been shown to result in the formation of the tetraiodogallate species(η⁵-C₅H₅)Ru(PPh₃)₂(μ-I)GaI₃ (5) and [(η⁵-C₅H₅)Ru(dppe)]⁺[GaI₄]^- (7).

Full text of DOI:10.1016/j.ica.2007.02.037

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 449–456
www.elsevier.com/locate/ica
Reactions of ‘GaI’ with organometallic transition metal halides
a
b
a,
*
Natalie D. Coombs , Andreas Stasch , Simon Aldridge
a
Inorganic Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
b
School of Chemistry, Monash University, P.O. Box 23, Victoria 3800, Australia
Received 29 January 2007; accepted 25 February 2007
Available online 12 March 2007
Dedicated to Professor Tony Downs in recognition of his numerous contributions to main group chemistry, not least to the chemistry of gallium.
Abstract
Two approaches towards the synthesis of phosphine ligated half-sandwich complexes [(gx-CxHx)M(PR3)2GaI2]n containing diiodo-
gallyl ligands have been investigated. Insertion of ‘GaI’ into the Mo–I bond of (g7-C7H7)Mo(CO)2I has been shown to yield the crys-
tallographically characterized dimeric complex [(g7-C7H7)Mo(CO)2GaI2]2 (2). Attempts to substitute the carbonyl ligands by
the phosphine ligand dppe [dppe = bis(diphenylphosphino)ethane] have been shown instead to yield the sparingly soluble complex
[(g7-C7H7)Mo(CO)2GaI2]2(l-dppe) (3) in which the phosphine bridges two [(g7-C7H7)Mo(CO)2GaI2] units via a pair of P ! Ga
donor/acceptor bonds. By contrast, attempts to insert ‘GaI’ directly into the metal-halogen bond of phosphine ligated complexes such
as (g5-C5H5)Ru(PPh3)2Cl or (g5-C5H5)Ru(dppe)Cl have been shown to result in the formation of the tetraiodogallate species
(g5-C5H5)Ru(PPh3)2(l-I)GaI3 (5) and [(g5-C5H5)Ru(dppe)]+[GaI4]ꢀ (7).
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Gallium; Insertion; Substitution; Phosphine ligands; Ruthenium; Molybdenum
1. Introduction
Within this area we have been interested in synthesizing
cationic two coordinate diyl species [LnM(ER)]+ (for
E = B, Ga or In) [3–5]. DFT calculations have revealed
that the positive charge is located primarily on the group
13 centre in such systems, resulting in a significant
M ! E back-bonding component and M@E multiple bond
character [6]. From a synthetic point of view we have pre-
viously demonstrated that halide abstraction chemistry is a
viable route to cationic metal complexes featuringþgroup 1ꢀ3
ligands {e.g. ½ðg5-C5Me5ÞFeðCOÞ2ꢁð@BMesÞꢁ ½BAr4f ꢁ
and ½ðg5-C5H5ÞFeðCOÞ ð@BNCy2Þꢁþ½BArf ꢁꢀ, Arf = C6H3-
Investigation of the chemistry of transition metal com-
plexes featuring low coordinate group 13 ligands has been
the main focus of considerable recent research interest [1].
In particular, the nature of the interaction between the
ligand and the transition metal centre in diyl systems
[LnM(ER)] (E = B-Tl) has been the subject of considerable
debate [2]. The bonding descriptions proposed for
complexes such as (CO)4Fe(GaAr) [Ar = C6H3(2,4,6-iPr3-
C6H2)2-2,6] featuring either multiple bonds (i.e. LnM@ER
or LnM„ER) or simple donor–acceptor interactions (i.e.,
LnM ER) reflect not only the fundamental questions
of structure and bonding posed by such systems but also
the scarcity of structural data available.
2
4
(CF3)2-3,5} [3,4]. In recent work we have sought to extend
this approach to the heavier group 13 elements, in particu-
lar with a view to exploring the structural and reaction
chemistry of cationic two-coordinate gallanediyl complexes
[5]. Of particular interest in this respect are electron-rich
transition metal fragments (LnM) bearing ancillary phos-
phine ligands which would be expected to offer not only
enhanced steric shielding, but also increased p back-
bonding to the cationic gallium centre formed on halide
*
Corresponding author. Tel.: +44 (01865) 285201; fax: +44 (01865)
272690.
E-mail address: simon.aldridge@chem.ox.ac.uk (S. Aldridge).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.02.037

450
N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
Route 1
ηx-CxHx
ηx-CxHx
I
'GaI'
M
hal
M
Ga
insertion
OC
OC
OC
hal
OC
n
CxHx = C5H5, C7H7
hal = halogen
2 PR3 / -2CO
substitution
ηx-CxHx
ηx-CxHx
+
ηx-CxHx
ηx-CxHx
I
hal
[RnE]-
substitution
-I-
'GaI'
M
hal
M
Ga
M
Ga
M
Ga ERn
insertion
abstraction
R3P
R3P
R3P
R3P
R3P
hal
ERn
R3P
R3P
R3P
Route 2
Scheme 1. Strategies for the generation of cationic systems containing group 13 donor ligands utilizing GaI in the synthesis of key precursors.
abstraction. Central to this approach is ready access to a
range of halo-substituted precursors featuring three-coor-
dinate gallium centres and bearing ancillary phosphine
ligands at the metal centre (see Scheme 1).
Plus FT-NMR spectrometer; residual signals of solvent
1
were used for reference for H and 13C NMR, while 31P
NMR spectra was referenced with respect to 85% H3PO4.
Infrared were measured on a Nicolet 500 FT-IR spectrom-
eter. Mass spectra were measured by the EPSRC National
Mass Spectrometry Service Centre, University of Wales
Swansea. The presence of solvent molecules in the crystal-
line lattices of compounds 3, 5 and 7 precluded reproduc-
ible elemental microanalyses.
Abbreviations: s, singlet; d, doublet; t, triplet; q, quartet;
m, multiplet; b, broad; st, strong; md, medium; w, weak;
sh, shoulder.
We have previously demonstrated for iron-containing
systems that clean substitution of the carbonyl ligands in
the complex [(g5-C5Me5)Fe(CO)2GaI2]2 is possible; pro-
longed photolysis in the presence of dppe [dppe =
1,2-bis(diphenylphosphino)ethane] yields (g5-C5Me5)-
Fe(dppe)GaI2 in which the phosphine ligand binds to the
iron centre in a chelating fashion [7]. Herein we report
attemptstodeveloproutestorelatedrutheniumandmolybde-
num complexes. During the course of this study two parallel
synthetic approaches to these phosphine-containing halogal-
lyl species have been examined: (i) a two-step process involv-
ing initial insertion of ‘GaI’ into the metal–halogen bond of a
metal carbonyl complex followed by substitution of the CO
ligands at the metal centre by phosphines; and (ii) direct inser-
tion of ‘GaI’ into the metal–halogen bond of a metal complex
featuring ancillary phosphine ligands (Scheme 1).
2.2. Syntheses
2.2.1. [(g7-C7H7)Mo(CO)2GaI2]2 (2)
To a suspension of ‘GaI’ prepared by sonicating gallium
(1.057 g, 15.16 mmol) and I2 (1.925 g, 7.58 mmol) in tolu-
ene (50 cm3) for 16 h at 30 ꢁC was added a solution of 1
(2.003 g, 5.41 mmol) in toluene (100 cm3). The reaction
mixture was stirred at 20 ꢁC for 72 h leading to the forma-
tion of a red solution and dark purple precipitate. The pre-
cipitate was isolated, recrystallized from dichloromethane
(300 cm3) by cooling to ꢀ30 ꢁC, isolated by filtration and
dried in vacuo. Crystals suitable for X-ray diffraction were
obtained at ꢀ30 ꢁC from a concentrated solution in dichlo-
romethane. Yield: 1.108 g 36%. 1H NMR (300 MHz,
CD2Cl2): dH 5.60 (s, 14H, CH of g7-C7H7). 13C NMR
(76 MHz, CD2Cl2): dC 93.5 (CH of g7-C7H7), carbonyl
carbons not observed. IR (thin film CD2Cl2, cmꢀ1): mCO
2001 st, 1952 st. Mass spec. (CI ꢀve): m/z (%) 694.6 (3)
[(g7-C7H7)Mo(CO)2GaI3]ꢀ, 567.7 (2) [(g7-C7H7)Mo-
(CO)2GaI2]ꢀ; (EI): m/z (%) 567.7 (1) [(g7-C7H7)Mo(CO)2-
GaI2]+, 539.7 (1) [(g7-C7H7)Mo(CO)GaI2]+, 511.7 (2)
[(g7-C7H7)MoGaI2]+. Exact mass (CI -ve): Calc. for [(g7-
C7H7)Mo(CO)GaI2]ꢀ 539.6902; measd. 539.6902. Elemen-
tal Anal. Calc. for C18H14Ga2I4Mo2O4: C, 19.08; H, 1.25.
Measd.: C, 18.99; H, 1.11.
2. Experimental
2.1. General
All manipulations were carried out under a nitrogen or
argon atmosphere using standard Schlenk line or dry box
techniques. Solvents were pre-dried over sodium wire
(hexanes, toluene) or molecular sieves (dichloromethane)
and purged with nitrogen prior to distillation. Hexanes
(potassium), toluene (sodium), and dichloromethane
(calcium hydride) were then distilled from the appropriate
drying agent before use. Dichloromethane-d2 (Goss) was
degassed and dried over molecular sieves prior to use.
Starting materials, ‘GaI’ [8], (g7-C7H7)Mo(CO)2I (1) [9],
(g5-C5H5)Ru(PPh3)2Cl (4) [10] and (g5-C5H5)Ru(dppe)Cl
(6) [11] were prepared by literature routes. NMR spectra
were measured on a Bruker AM-400 or Jeol Eclipse 300

N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
451
2.2.2. [(g7-C7H7)Mo(CO)2GaI2]2(l-dppe) (3)
2.2.3. (g5-C5H5)Ru(PPh3)2(l-I)GaI3 (5)
A solution of dppe (0.779 g, 1.96 mmol) in toluene
(150 cm3) was added to a solution of 2 (1.108 g, 0.98 mmol)
in toluene (150 cm3) at 20 ꢁC with the immediate formation
of a light red precipitate. The precipitate was extracted into
dichloromethane (500 cm3; sparingly soluble) and filtered;
the resulting dark orange solution was concentrated in
vacuo, and a red solid obtained by cooling to ꢀ30 ꢁC. Crys-
tals suitable for X-ray diffraction were obtained from the
To a suspension of ‘GaI’ [prepared as described above
from gallium (0.272 g, 3.901 mmol) and I2 (0.499 g,
1.966 mmol)] was added
a solution of 4 (0.939 g,
1.293 mmol) in toluene (100 cm3). The reaction mixture
stirred at 20 ꢁC for 16 h. with the formation of an orange
solution and orange precipitate. The solid was recrystal-
lized from dichloromethane by cooling to ꢀ30 ꢁC. Crystals
suitable for X-ray diffraction were obtained at ꢀ30 ꢁC from
a concentrated solution in dichloromethane. Yield: 0.682 g
42%. 1H NMR (300 MHz, CD2Cl2): dH 4.61 (5H, s, CH of
g5-C5H5), 7.09 (12H, aromatic CH of PPh3), 7.27 (12H,
aromatic CH of PPh3), 7.39 (6H, aromatic CH of PPh3).
13C NMR (76 MHz, CD2Cl2): dC 80.2 (CH of g5-C5H5),
128.3 (aromatic CH of PPh3), 129.9 (aromatic CH of
PPh3), 133.8 (aromatic CH of PPh3), 137.5 (aromatic
ipso-C of PPh3). 31P NMR (122 MHz, CD2Cl2): dP 35.
Mass spec. (EI): m/z (%) 556.2 (2) [(g5-C5H5)Ru(PPh3)I]+,
449.7 (30) [GaI3]+, 322.8 (35) [GaI2]+.
1
concentrated solution at ꢀ30 ꢁC. Yield: 0.383 g 26%. H
NMR (300 MHz, CD2Cl2): dH 2.55 (m, 2H, CH2 of dppe),
2.92 (m, 2H, CH2 of dppe), 5.18 (s, 7H, g7-C7H7), 7.23 (m,
8H, aromatic CH of dppe), 7.49 (m, 8H, aromatic CH of
dppe), 7.62 (m, 4H, aromatic CH of dppe). 31P NMR
(122 MHz, CD2Cl2): dP ꢀ28 (broad). IR (thin film CD2Cl2,
cmꢀ1): mCO 1982 st, 1928 st. Mass spec. (EI): m/z (%) 712.0
(5) [(g7-C7H7)Mo(CO)2Ga(dppe)]+. The extremely low sol-
ubility of 3 in compatible solvents precluded the measure-
ment of reliable 13C NMR spectra.
Table 1
Crystallographic data for 2, 3, 5, 7, and 8
2
3 Æ 2.5(CH2Cl2)
5 Æ 0.5(C7H8)
7 Æ 2(CH2Cl2)
8
Empirical formula
CCDC reference
Formula weight
Temperature (K)
Crystal system
Space group
C
18H14Ga2I4Mo2O4 C46.50H43Cl5Ga2I4O4Mo2P2 C44.50H39GaI4P2Ru C33H33Cl4GaI4P2Ru C62H58Ga2I8P4Ru2
634453
1133.21
150(2)
634454
1743.92
150(2)
634455
1314.09
150(2)
634456
1311.72
150(2)
634457
2283.74
150(2)
triclinic
triclinic
monoclinic
C2/c
monoclinic
P21/n
monoclinic
P21/n
ꢀ
ꢀ
P1
P1
Unit cell dimensions
˚
a (A)
7.8446(16)
9.0483(18)
18.888(4)
90.52(3)
10.385(2)
16.850(3)
17.935(4)
65.63(3)
82.01(3)
86.40(3)
2830.9(10)
2, 2.046
3.887
22.862(5)
13.190(3)
29.374(6)
90
102.71(3)
90
8641(3)
8, 2.020
3.936
16.088(3)
15.257(3)
17.437(4)
90
98.82
90
4229.5(15)
4, 2.060
4.265
13.126(3)
17.613(4)
14.962(3)
90
100.64(3)
90
3399.4(12)
2, 2.231
4.984
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
93.93(3)
105.31(3)
1289.6(4)
2, 2.918
7.827
1024
3
˚
Volume (A )
Z, Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F000
)
1654
4984
2464
2128
Crystal size (mm)
h Range for data collection (ꢁ)
0.25 · 0.10 · 0.05
2.98–26.00
0.18 · 0.15 · 0.11
3.00–26.00
0.10 · 0.10 · 0.06
2.94–24.99
0.35 · 0.30 · 0.20
2.92–30.00
0.15 · 0.10 · 0.08
2.99–25.00
Index ranges
h
ꢀ9 to 9
ꢀ12 to 12
ꢀ20 to 20
ꢀ21 to 21
20483
ꢀ26 to 26
ꢀ15 to 15
ꢀ34 to 34
13338
ꢀ22 to 22
ꢀ21 to 21
ꢀ24 to 24
23357
ꢀ15 to 15
ꢀ20 to 20
ꢀ17 to 17
11181
k
ꢀ11 to 11
ꢀ22 to 23
8896
l
Reflections collected
Independent reflections [Rint
]
4947 [0.0327]
97.3
11030 [0.0374]
99.2
7447 [0.0433]
97.7
12261 [0.0212]
99.3
5940 [0.0425]
99.2
Completeness to hmaximum (%)
Absorption correction
Maximum and minimum
transmission
SORTAV
SORTAV
SORTAV
SORTAV
SORTAV
0.778, 0.521
0.659, 0.504
0.867, 0.644
0.475, 0.310
0.856, 0.713
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
4947/0/271
1.030
11030/48/645
1.012
R1 = 0.0424, wR2 = 0.0919 R1 = 0.0604,
wR2 = 0.1438
R1 = 0.0609, wR2 = 0.0998 R1 = 0.0909,
wR2 = 0.1587
1.569 and ꢀ0.920
7447/11/469
1.080
12261/0/406
1.016
5940/0/394
1.029
R1 = 0.0309,
wR2 = 0.0645
R1 = 0.0400,
wR2 = 0.0683
0.747 and ꢀ1.175
R1 = 0.0380,
wR2 = 0.032
R1 = 0.0508,
wR2 = 0.082
1.695 and ꢀ2.277
R1 = 0.0692,
wR2 = 0.1671
R1 = 0.1011,
wR2 = 0.1845
1.612 and ꢀ1.499
R indices (all data)
Largest difference in peak and
1.313 and ꢀ2.670
ꢀ3
˚
hole (e A
)

452
N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
2.2.4. [(g5-C5H5)Ru(dppe)]+[GaI4]ꢀ (7)
CIF. The disordered GaI4 unit in 8 was modelled with
two positions for each atom with half occupancy; I(5) sits
on a centre of inversion.
To a suspension of ‘GaI’ (prepared as described above
from gallium (0.581 g, 8.33 mmol) and I2 (1.057 g,
4.17 mmol)) was added a solution of 6 (0.499 g, 0.83 mmol)
in toluene (80 cm3). The reaction mixture was stirred at
room temperature for 72 h with the formation of a pale
yellow solution and yellow precipitate. The solution was
filtered, concentrated in vacuo, and a yellow solid was
obtained by cooling to ꢀ30 ꢁC. Crystals suitable for
X-ray diffraction were obtained by layering a toluene solu-
tion with hexanes and cooling to ꢀ30 ꢁC. Yield: 0.121 g
13%.1H NMR (300 MHz, CD2Cl2): dH 2.51 (2H, m, CH2
of dppe), 2.59 (2H, m, CH2 of dppe), 4.86 (5H, s, CH of
g5-C5H5), 7.16 (8H, aromatic CH of Ph), 7.28 (8H, aro-
matic CH of Ph), 7.69 (4H, aromatic CH of Ph). 13C
NMR (76 MHz, CD2Cl2): dC 21.2 (CH2 of dppe), 79.7
(CH of g5-C5H5), 128.8 (aromatic CH of Ph), 129.9
(aromatic CH of Ph), 130.7 (aromatic CH of Ph), 134.1
(aromatic ipso-C of Ph). 31P NMR (122 MHz, CD2Cl2):
dP 76. Mass spec (EI): m/z (%) 761.0 (2) [(g5-C5H5)Ru-
(dppe)GaI]+, 692.1 (64) [(g5-C5H5)Ru(dppe)I]+, 565.2
(100) [(g5-C5H5)Ru(dppe)]+. Exact mass (EI): calcd. for
[(g5-C5H5)Ru(dppe)GaI]+ 760.9089; measd. 760.9089. A
small amount (<5 mg) of a dark orange crystalline material
was also obtained from the layering the structure was
solved by X-ray diffraction to be the isomeric product
[(g5-C5H5)Ru(GaI4)(l-dppe)]2 (8).
3. Results and discussion
Two possible synthetic pathways towards systems of the
type [(gx-CxHx)M(PR3)2GaI2]n have been investigated dur-
ing this study (Scheme 1). Route 1 involves a two-step syn-
thesis via insertion of ‘GaI’ into the metal–halogen bond of
a metal carbonyl precursor followed by substitution of the
CO ligands by phosphines. Following this strategy, reaction
of (g7-C7H7)Mo(CO)2I with ‘GaI’ proceeds as expected
with insertion of ‘GaI’ into the Mo–I bond yielding the
desired complex [(g7-C7H7)Mo(CO)2GaI2]2 in modest
(36%) yield after recrystallization from dichloromethane
(Scheme 2).
NMR data for 2 are consistent with a formulation con-
taining a single environment for the C7H7 ring protons;
additionally, mass spectrometry data provides evidence
for a GaI2-containing species. However, as with related
iron-containing systems, definitive identification of a
metal–gallium bond and of the state of aggregation of
the diiodogallyl complex were reliant on crystallographic
methods (Fig. 1). The molecular structure of 2 features
dimeric [(g7-C7H7)Mo(CO)2GaI2]2 units in which each
(g7-C7H7)Mo(CO)2GaI2 fragment is linked to the other
through the bridging iodine ligands of the Ga(l-I)2Ga core.
The coordination geometry about each gallium centre is
somewhat distorted from tetrahedral, featuring Mo–Ga–I
angles of 125.9(4)ꢁ, 120.0(3)ꢁ and 116.9(3)ꢁ, and I–Ga–I
angles of 98.2(3)ꢁ, 98.6(4)ꢁ and 89.7(3)ꢁ. The narrower I–
Ga–I angle of ca. 90ꢁ associated with the bridging iodine
atoms finds precedent in the structures of related systems
{e.g. 92.01(2)ꢁ in [(g5-C5Me5)Fe(CO)2GaI2]2} [13]. The
2.3. Crystallographic method
Data was collected on an Enraf Nonius Kappa CCD
diffractometer equipped with a Mo Ka radiation source
˚
(k = 0.71073 A). Data collection and cell refinement were
carried out using DENZO and COLLECT, and structure solu-
tion and refinement (by full-matrix least-squares) using
SHELXS-97 and SHELXL-97, respectively [12]. Empirical
absorption corrections were carried out using SORTAV [12].
Details of the data collection, structure solution and refine-
ment for 2, 3, 5, 7 and 8 can be found in Table 1; relevant
bond lengths and angles are included in the figure captions.
Complete details of all structures have been deposited with
the CCDC (reference numbers as listed in Table 1) and are
included in the supporting information. The disordered sol-
vent molecules in the asymmetric units of 3 and 5 (two and
a half molecules of dichloromethane, and half a molecule
of toluene, respectively) were modelled as described in the
˚
Mo–Ga bond length of 2.577(1) A is unremarkable, being
similar to those reported for the complexes (g5-C5H4Me)-
Mo(CO)3GaI2 Æ Et2O and cis-(Cp*Ga)2Mo(CO)4 [2.582(2)
˚
and 2.554(1) A, respectively] [8,14].
The determination of the molecular structure of 2 con-
firms that insertion of ‘GaI’ is indeed a feasible pathway
for synthesizing gallium-containing transition metal car-
bonyl complexes. Similar chemistry has also been reported
by Green et al. in the synthesis of the closely related com-
plex (g7-C7H7)Mo(CO)2GaI2 Æ thf, which was character-
1
ized by H NMR [8]. In order to complete the two-step
CO
I
I
Ph
CO
Ph
Ga Mo
I
P
(i)
(ii)
Mo
P
Mo
Ga
Mo
Ga
I
I
OC
OC
I
Ph
OC
Ph
I
OC
OC
OC
2
1
2
3
Scheme 2. Synthesis of [(g7-C7H7)Mo(CO)2GaI2]2 (2) and its subsequent reactivity towards dppe. Reagents and conditions: (i) ‘GaI’ (2.8 equiv.), toluene,
20 ꢁC, 72 h, 36% isolated yield; (ii) dppe (2 equiv.), toluene, 20 ꢁC, 10 min., 26% isolated yield.

N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
453
Fig. 1. Structure of [(g7-C7H7)Mo(CO)2GaI2]2 (2) with hydrogen atoms omitted for clarity and ORTEP ellipsoids set at 50% probability level. Relevant
˚
bond lengths (A) and angles (ꢁ): Mo(1)–Ga(1) 2.577(1), Mo(1)–C(8) 2.010(6), Mo(1)–centroid 1.651(6), Ga(1)–I(1) 2.619(1), Ga(1)–I(2) 2.764(1), Ga(1)–
I(20) 2.807(1), Mo(1)–Ga(1)–I(1) 125.9(4), Mo(1)–Ga(1)–I(2) 120.0(1), Mo(1)–Ga(1)–I(20) 116.9(1), I(1)–Ga(1)–I(2) 98.2(1), I(1)–Ga(1)–I(20) 98.6(1), I(2)–
0
Ga(1)–I(20) 89.7(1). Symmetry transformations used to generate equivalent atoms: : ꢀx + 2, ꢀy + 1, ꢀz.
synthesis of [(g7-C7H7)M(PR3)2GaI2]n, 2 was further
reacted with the potentially chelating phosphine ligand
dppe; photolytically or thermally initiated substitution
reactions of (g7-C7H7)M(CO)2X with phosphines have
been amply demonstrated in the literature [15]. However,
on addition of dppe to 2 at room temperature, an immedi-
ate reaction resulted in the formation of a red precipitate,
which was subsequently determined crystallographically
to be the dinuclear species [(g7-C7H7)Mo(CO)2GaI2]2(l-
dppe) (3) (Scheme 2). Previous work with related iron-con-
taining systems is consistent with initial formation of
R3P ! Ga(III) adducts, but has shown that subsequent
photolysis can lead to migration of the phosphine donor
from gallium to the transition metal upon loss of CO [7].
Attempts to photolytically induce an analogous phosphine
migration for 3 were frustrated by its very sparing solubil-
ity in compatible organic solvents. Additionally, thermo-
lysis of 3 invariably resulted in decomposition. Attempts
to ameliorate these problems, e.g. by the use of other phos-
phine donors are currently ongoing.
1H and 31P NMR data for 3 are consistent with a gal-
lium-bound phosphine containing species [broad resonance
at dP ꢀ28 c.f. ꢀ41 for the analogous phosphorus centre in
Cp*Fe(CO)(l-dppe)GaI2]. Additionally, the presence of
strong infra-red bands at 1982 and 1928 cmꢀ1 implies
retention of the Mo(CO)2 fragment within the complex,
and therefore that phosphine substitution has not occurred
at the molybdenum centre. These spectroscopic inferences
were confirmed by X-ray diffraction which revealed the
structure of
3
as [(g7-C7H7)Mo(CO)2GaI2]2(l-dppe)
(Fig. 2). The molecular structure of 3 features dppe acting
as a bridging ligand between two (g7-C7H7)Mo(CO)2GaI2
units; the 1:2 dppe:Mo ratio in the product (c.f. the 2:1
reaction stoichiometry) is presumably driven by the insolu-
bility of 3. The coordination geometry about the gallium
centres is distorted tetrahedral with Mo–Ga–I angles of
Fig. 2. Structure of [(g7-C7H7)Mo(CO)2GaI2]2l-dppe (3) with hydrogen atoms and solvent molecules omitted for clarity and ORTEP ellipsoids set at 50%
˚
probability level. Relevant bond lengths (A) and angles (ꢁ): Mo(1)–Ga(1) 2.577(1), Mo(1)–C(1) 1.997(5), Mo(1)–centroid 1.660(5), Ga(1)–I(1) 2.632(1),
Ga(1)–I(2) 2.650(1), Ga(1)–P(1) 2.467(2), Mo(1)–Ga(1)–I(1) 118.2(1), Mo(1)–Ga(1)–I(2) 122.4(1), Mo(1)–Ga(1)–P(1) 119.8(1), I(1)–Ga(1)–I(2) 100.7(1),
I(1)–Ga(1)–P(1) 97.9(1), I(2)–Ga(1)–P(1) 92.3(1).

454
N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
118.21(3)ꢁ and 122.39(3)ꢁ and significantly narrower P–
Ga–I angles of 92.3(4)ꢁ and 97.9(5)ꢁ. The Mo–Ga bond
˚
length of 2.581(1) A is not significantly different that found
in 2.
An alternative synthetic approach to systems of the type
[(gx-CxHx)M(PR3)2GaI2]n was also examined (Scheme 1);
route 2 involves direct insertion of ‘GaI’ into the metal
halogen bond of a phosphine-ligated complex. On paper
this route is advantageous in that it involves a single step
synthesis from readily available starting materials of the
type (g5-C5H5)Ru(PR3)2hal. From the outset, relatively
forcing conditions were employed (e.g. the use of a large
excess of ‘GaI’), since preliminary studies indicated that
the use of fewer equivalents of ‘GaI’ at room temperature
merely resulted in halide substitution reactions to give
(g5-C5H5)Ru(PR3)2I [16]. The reactions of both (g5-
C5H5)Ru(PPh3)2Cl (4, Scheme 3) and (g5-C5H5)Ru-
(dppe)Cl (6, Scheme 4) with ‘GaI’ (4–10 equiv.) appear
from 31P NMR monitoring to follow a similar course. In
each case one major product is formed which can be crys-
tallized from the reaction supernatant by layering with hex-
anes and storage at ꢀ30 ꢁC.
Fig. 3. Structure of (g5-C5H5)Ru(PPh3)2(l-I)GaI3 (5) with hydrogen
atoms and solvent molecule omitted for clarity and ORTEP ellipsoids set
˚
at 50% probability level. Relevant bond lengths (A) and angles (ꢁ): Ru(1)–
P(1) 2.345(4), Ru(1)–centroid 1.849(3), Ru(1)–I(1) 2.742(2), Ga(1)–I(1)
2.603(2), Ga(1)–I(2) 2.513(2), Ga(1)–I(3) 2.533(2), Ga(1)–I(4) 2.528(2),
P(1)–Ru(1)–P(2) 102.6(2), Ru(1)–I(1)–Ga(1) 112.0(1), I(1)–Ga(1)–I(2)
103.7(1), I(1)–Ga(1)–I(3) 108.4(1), I(1)–Ga(1)–I(4) 111.6(1), I(2)–Ga(1)–
I(3) 112.9(1), I(2)–Ga(1)–I(4) 111.4(1), I(3)–Ga(1)–I(4) 108.8(1).
In each case the 31P NMR spectrum of the product is
consistent with retention of the Ru(PR3)2 moiety, however
mass spectrometry data are consistent with ready fragmen-
tation into GaIn and (g5-C5H5)Ru(phosphine)nI containing
units. In the reaction of 4 with ‘GaI’ (4 equiv.), the product
isolated in modest (42%) yield was subsequently shown
crystallographically to be (g5-C5H5)Ru(PPh3)2(l-I)GaI3
(5, Fig. 3). The molecular structure reveals a bis(phos-
phine) half sandwich complex containing a tetraiodogallate
fragment coordinated to the ruthenium centre via a single
bridging iodine atom. To our knowledge 5 represents the
first example of a transition metal complex containing a
coordinated [GaI4]ꢀ ligand. Alternatively, 5 can be thought
of as a Lewis acid/base adduct between (g5-C5H5)Ru-
(PPh3)2I and GaI3. The coordination geometry about the
gallium centre is approximately tetrahedral with I–Ga–I
bond angles of 103.7(1)ꢁ, 111.6(1)ꢁ, and 108.4(1)ꢁ. As
expected the Ga–I bond associated with the bridging unit
˚
[2.603(2) A] is considerably longer than the terminal Ga–I
˚
linkages [2.513(2), 2.533(2) and 2.528(2) A]. Interestingly,
the major product isolated from the reaction of 6 with
‘GaI’ (10 equiv.), despite having an analogous composition
to 5, [i.e. (g5-C5H5)Ru(dppe)(GaI4)], has been shown
crystallographically to consist of discrete [(g5-C5H5)-
Ru(dppe)]+ and [GaI4]ꢀ ions (7, Fig. 4). The shortest
I
Ga
I
(i)
(ii)
Ru
Ru
Cl
I
Ru
I
I
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
˚
4
5
Ruꢂ ꢂ ꢂI contact [5.535 A] is comfortably outside the sum
of the respective Van der Waals radii [17], and contrasts
Scheme 3. Synthesis of (g5-C5H5)Ru(PPh3)2(l-I)GaI3 (5) from (g5-C5H5)-
Ru(PPh3)2Cl. Reagents and conditions: (i) ‘GaI’ (2 equiv.), toluene, 20 ꢁC,
4 h, 67% isolated yield; (ii) ‘GaI’ (4 equiv.), toluene, 20 ꢁC, 16 h, 42%
isolated yield.
˚
with the Ru–I distance of 2.742(2) A found for 5. In com-
mon with the related system [(g5-C5Me5)Ru(PMeiPr2)2]+
[18], the trigonal planar geometry at the metal defined by
the two phosphorus atoms and the cyclopentadienyl
centroid [sum of the angles at ruthenium = 358.8ꢁ for 7]
implies negligible secondary interactions (for example of
ligand C–H bonds) with the 16-electron cationic ruthenium
centre. The difference in coordinating ability for the tetrai-
odogallate ion with respect to the metal centres in 5 and 7
can conceivably be rationalized on the basis of reduced
electrophilicity for the ruthenium centre found in conjunc-
tion with the more strongly r basic dppe ligand.
+ [GaI4]-
(i)
Ru
Cl
Ru
Ph2P
Ph2P
PPh2
PPh2
7
6
A second product was also crystallized from the (g5-
C5H5)Ru(dppe)Cl/‘GaI’ reaction mixture in very low yield
which has been shown crystallographically to be an isomer
Scheme 4. Synthesis of [(g5-C5H5)Ru(dppe)]+[GaI4]ꢀ (7) from (g5-
C5H5)Ru(dppe)Cl. Reagents and conditions: (i) ‘GaI’ (10 equiv.), toluene,
20 ꢁC, 72 h, 13% isolated yield.

N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
455
of 7 i.e. [(g5-C5H5)Ru(GaI4)(l-dppe)]2 (8, Fig. 5). Intrigu-
ingly the molecular structure of 8 reveals not only bridging
(rather than chelating) dppe ligands, but also an g1-coordi-
nated [GaI4]ꢀ moiety with Ru–I [2.714(10) A] and Ga–I
˚
˚
[2.612(9) A] contacts for the bridging unit which are closely
reminiscent of those found for 5. The origins of 8 are not
entirely clear – it could be that a mixture of products is
formed in the reaction of (g5-C5H5)Ru(dppe)Cl (6) with
excess ‘GaI,’ or that the starting material 6 is contaminated
with a trace of [(g5-C5H5)RuCl(l-dppe)]2. This dimeric
species is known to be a minor product formed in the
synthesis of 6 from (g5-C5H5)Ru(PPh3)2Cl and dppe (as
was employed herein) [19], although no trace was detected
in the 31P NMR spectrum of the starting material. Conceiv-
ably however, given the minute amounts of 8 which are
formed, the presence of a trace quantity of [(g5-C5H5)-
RuCl(l-dppe)]2 impurity cannot be ruled out. Finally, the
structures determined crystallographically for the isomeric
species 7 and 8 point to a relatively small energetic differ-
ence between coordinating and non-coordinating modes
of the [GaI4]ꢀ anion.
Fig. 4. Structure of [(g5-C5H5)Ru(dppe)]+[GaI4]ꢀ (7) with hydrogen
atoms and solvent molecules omitted for clarity and ORTEP ellipsoids set
˚
at 50% probability level. Relevant bond lengths (A) and angles (ꢁ): Ru(1)–
P(1) 2.286(1), Ru(1)–centroid 1.855(6), Ga(1)–I(1) 2.545(1), Ga(1)–I(2)
2.543(1), Ga(1)–I(3) 2.554(1), Ga(1)–I(4) 2.539(1), P(1)–Ru(1)–P(2)
86.5(1), I(1)–Ga(1)–I(2) 108.6(1), I(1)–Ga(1)–I(3) 109.1(1), I(1)–Ga(1)–
I(4) 109.0(1), I(2)–Ga(1)–I(3) 109.8(1), I(2)–Ga(1)–I(4) 110.2(1), I(3)–
Ga(1)–I(4) 110.2(1).
4. Conclusions
In conclusion, it has been shown that insertion of ‘GaI’
into the metal halogen bond of a half-sandwich metal car-
bonyl complex is a viable synthetic route for the generation
of Mo–Ga bonds. However, in the case of [(g7-C7H7)Mo-
(CO)2GaI2]2 (2) it was found that further reaction of this
complex with dppe does not proceed via the desired car-
bonyl ligand substitution process, instead forming [(g7-
C7H7)Mo(CO)2GaI2]2(l-dppe) (3). The isolation of 3 is
rationalized by the Lewis acidity of the diiodogallyl centres
and its very low solubility, which mitigates against further
reaction in solution (as has been observed for related iron
systems). By contrast, attempted ‘GaI’ insertions involving
the metal–halogen bonds of complexes bearing ancillary
phosphine ligands do not yield Ru–Ga containing prod-
ucts. Instead complexes containing the tetraiodogallate(III)
anion/ligand are isolated. The compound formulated as
‘GaI’ is known to undergo disproportionation reactions
in the presence of phosphine donors [8b], and a possible
explanation for the formation of Ga(III) species from the
reactions of (g5-C5H5)Ru(PPh3)2Cl and (g5-C5H5)Ru(dp-
pe)Cl with ‘GaI’ involves disproportionation to Ga(III)
and gallium metal mediated by reversible dissociation of
the ruthenium-bound phosphine ligands.
Appendix A. Supplementary material
Fig. 5. Structure of [(g5-C5H5)Ru(GaI4)(l-dppe)]2 (8) with hydrogen
atoms omitted for clarity and ORTEP ellipsoids set at 50% probability
˚
CCDC 634453, 634454, 634455, 634456 and 634457 con-
tain the supplementary crystallographic data for 2, 3, 5, 7
and 8. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from
the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
level. Relevant bond lengths (A) and angles (ꢁ): Ru(1)–P(1) 2.338(3),
Ru(1)–centroid 1.850(10), Ru(1)–I(1a) 2.748(9), Ga(1a)–I(1a) 2.590(8),
Ga(1a)–I(2a) 2.532(4), Ga(1a)–I(3a) 2.523(4), Ga(1a)–I(4) 2.462(4), P(1)–
Ru(1)–P(2) 98.0(1), Ru(1)–I(1a)–Ga(1a) 124.9(4), I(1a)–Ga(1a)–I(2a)
117.3(3), I(1a)–Ga(1a)–I(3a) 99.0(2), I(1a)–Ga(1a)–I(4) 109.0(2), I(2a)–
Ga(1a)–I(3a) 114.7(2), I(2a)–Ga(1a)–I(4) 106.0(1), I(3a)–Ga(1a)–I(4)
0
110.8(1). Symmetry transformations used to generate equivalent atoms: :
ꢀx + 2, ꢀy + 2, ꢀz + 1.

456
N.D. Coombs et al. / Inorganica Chimica Acta 361 (2008) 449–456
´
(b) N.R. Bunn, S. Aldridge, D.L. Kays (nee Coombs), N.D. Coombs,
A. Rossin, D.J. Willock, C. Jones, L.-L. Ooi, Organometallics 24
(2005) 5891.
data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2007.02.037.
[6] S. Aldridge, A. Rossin, D.L. Coombs, D.J. Willock, Dalton Trans.
(2004) 2649.
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