Steric Control between Neutral Metal-Only Lewis Pairs and Metal-Stabilized Gallenium and Gallinium Cations

Article abstract of DOI:10.1021/acs.organomet.6b00045

Reaction of a series of zerovalent Fe Lewis bases with Lewis acid GaCl₃ leads to both conventional, neutral metal-only Lewis pairs in the case of small metal complexes and cationic gallenium species in the case of larger metal bases. The results suggest the predominance of steric bulk in controlling the outcome of group 13 trihalide Lewis acid additions to metal bases.

Full text of DOI:10.1021/acs.organomet.6b00045

Article
pubs.acs.org/Organometallics
Steric Control between Neutral Metal-Only Lewis Pairs and Metal-
Stabilized Gallenium and Gallinium Cations
Holger Braunschweig,* Rian D. Dewhurst, and Christoph Schneider
Institut fur Anorganische Chemie, Julius-Maximilians-Universitat Wurzburg, Am Hubland, 97074 Wurzburg, Germany
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* Supporting Information
ABSTRACT: Reaction of a series of zerovalent Fe Lewis
bases with Lewis acid GaCl3 leads to both conventional,
neutral metal-only Lewis pairs in the case of small metal
complexes and cationic gallenium species in the case of larger
metal bases. The results suggest the predominance of steric
bulk in controlling the outcome of group 13 trihalide Lewis
acid additions to metal bases.
Ru0 complexes by comparisons of M−Ga bond distances, sums
of X−Ga−X angles, and computationally derived bond
dissociation energies. Lewis acid transfer experiments between
metal−ligand fragments (including strongly Lewis basic PtL2
complexes) enabled us to draw up experimental hierarchies of
Lewis basic precursors, which may be useful fundamental
information for future catalytic endeavors.
Recent work in our laboratories involving addition of gallium
halides to bulkier Fe0 complexes has shown new reactivity
patterns, leading to rare examples of compounds with
tricoordinate, cationic gallium centers and in one case a
dinuclear cationic complex wherein a GaCl2 fragment bridges
two iron centers. These results, described herein, suggest that
sterically bulky Lewis basic M0 complexes may induce the
disproportionation of GaCl3.
INTRODUCTION
■
The existenceand utilityof dative bonding between main-
group atoms is well-accepted in contemporary chemistry. In
contrast, dative bonding between metal atoms is much less
well-understood. The existence of dative bonds between metal
atoms dates back at least half a century: to our knowledge the
first mention of such an interaction is in a 1964 report from
Coffey, Lewis, and Nyholm,1 while the first structurally
authenticated M→M dative bond appears to be that in [(η5-
C5H5)(OC)2Co→HgCl2], as reported by Nowell and Russell in
1967.2 Despite this relatively early beginning, most so-called
metal-only Lewis pairs (MOLPs) reported in the intervening
years were prepared serendipitously and were often not
recognized as such. Our 2012 review on MOLPs was an
attempt to formalize the concept of metal−metal dative
bonding through the compilation of the scattered reports of
structurally characterized examples of these complexes.3
However, there are presumably many more complexes in the
literature that escaped our attention due to lack of structural
data or uncertain bonding situations. Since that time, work
from our group and those of Jones, Stasch, and Krossing have
expanded the field markedly,4 and the MOLP concept has since
been used as a basis for a description of oxidation states and
metal−metal dative bonds in a technical report published by
the International Union of Pure and Applied Chemistry
(IUPAC).5
When we began our work in this field, perhaps the most well-
studied subset of MOLPs was that featuring zerovalent group 8
donors (M0Ln, M = Fe, Ru, Os) and transition metal acceptors,
thanks to extensive work by the groups of Pomeroy, Mak, and
Dixneuf (and subsequently also Krossing).4l,6 However,
MOLPs featuring zerovalent group 8 donors and simple
main-group Lewis acids were at that time unknown. After our
discovery that gallium trihalides form stable Lewis adducts with
pentacoordinate Fe0 complexes, we began a systematic study of
MOLPs of the form [LnFe0/LnRu0→GaX3].7,8 Using a range of
different donor ligands bound to the group 8 metal centers, we
were able to establish trends in the Lewis basicity of Fe0 and
RESULTS AND DISCUSSION
■
Synthesis of MOLPs from Tri- and Tetracarbonyl Fe0
Complexes. In an attempt to increase the steric bulk at the
metal center of pentacoordinate Fe0 complexes, we turned to
the tetracarbonyl complexes [Fe(CO)4(PCy3)] (1a) and
[Fe(CO)4(IMes)] (1b; IMes = 1,3-dimesitylimidazol-2-yli-
dene).9 Treatment of solutions of 1a or 1b with an equimolar
amount of the Lewis acid GaCl3 led to isolation of the Lewis
adducts trans-[(Cy3P)(OC)4Fe→GaCl3] (1b; yield 83%) and
trans-[(IMes)(OC)4Fe→GaCl3] (2b; yield 93%) as white solids
in good yields (Figure 1). Both structures show only one
carbonyl stretching band in their IR spectra (1b: 2036 cm−1;
2b: 2062 cm−1), suggesting that the GaCl3 sits trans to the
phosphine or carbene ligand. Phosphine MOLP 1b additionally
shows a 31P NMR signal at δP 55.6, significantly upfield from
that of precursor 1a (δP 80.2). The apparently greater electron
density at the phosphorus atom of 1b over that of 1a is
somewhat surprising given the presence of a Lewis acidic GaCl3
Received: January 20, 2016
© XXXX American Chemical Society
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Figure 1. Synthesis of trans-[L(OC)4Fe→GaCl3] with L = PCy3 (1b)
or IMes (2b).
unit in trans position, even considering the strongly π-acidic
CO ligand present trans to the phosphine in 1a.
Single-crystal X-ray diffraction analysis of both adducts
confirmed the structures suggested by IR spectroscopy (Figure
2). However, the trans geometry of 1b and 2b contrasts with
the cis geometry observed in the less sterically bulky cis-
[(Me3P)(OC)4Fe→GaCl3]7 and cis-[(Me3P)(OC)4Ru→
GaCl3].8 The Fe−Ga bond distance of 1b (2.5072(5) Å) is
also slightly longer than that of the previously published
complex cis-[(Me3P)(OC)4Fe→GaCl3] (2.4844(3) Å), with
the alternative geometry.
In order to increase the steric bulk of the Lewis base slightly,
2a was photolyzed in the presence of one equivalent of PMe3 to
form the tricarbonyl complex [Fe(CO)3(IMes)(PMe3)] (3a;
see Supporting Information for more details). Adding the Lewis
acid GaCl3 to this complex led to spontaneous precipitation of
a white solid over 1 h. The 31P NMR spectrum of this solid
suggested the presence of two isomers of the MOLP mer-
[(IMes)(Me3P)(OC)3Fe→GaCl3] (3b,c) (Figure 3), with
signals at δP 8.5 and 13.5, as well as two sets of signals in the
1H NMR spectrum in a ratio of 1:0.7, respectively. Single-
crystal X-ray diffraction of the two different crystal forms
confirmed the presence of isomers in which the Ga atom (3b)
and the P atom (3c) are situated trans to the carbene ligand
(Figure 2). Variable-temperature NMR across the range −80 to
+70 °C showed no change in the relative intensities of the
signals, indicating no interconversion between the two formed
complexes. The Fe−Ga bond distances of 3b (2.4683(7) Å)
and 3c (2.4836(11) Å) are both shorter than that of 1b
(2.5072(5) Å) but closer to that of cis-[(Me3P)(OC)4Fe→
GaCl3] (2.4844(3) Å).7
Synthesis of Gallenium and Gallinium Salts Using
Sterically Bulky Fe0 Bases. In order to increase the steric
bulk of the iron Lewis bases further still, we turned to
tricarbonyl complexes with bulky donor ligands, namely, the
tricarbonyl complexes [Fe(CO)3(PCy3)2] (4a) and [Fe-
(CO)3(IMes)2] (5a).9 Treatment of a solution of 4a with
one equivalent of GaCl3 led to the observation of approximately
50% conversion to a new product (4b, Figure 4) by 31P NMR
(δP ∼63), in addition to unreacted starting material. Doubling
the amount of GaCl3 used led to complete conversion to 4b
and spontaneous precipitation of a white crystalline solid.
Infrared spectral data on a solution of 4b showed three CO
stretching bands (2065, 2009, 1971 cm−1), in accordance with a
mer tricarbonyl structure. Based on the need for two
equivalents of GaCl3 for complete conversion to 4b, and our
recent observation of halide abstraction from the MOLP
trans,mer-[(Me3P)2(OC)3Ru→GaCl3] by GaCl3,8 it was
assumed that the complex was a halide-bridged dimer of cation
trans,mer-[(Cy3P)2(OC)3Fe→GaCl2]+. However, a single-crys-
tal X-ray diffraction study showed the structure of 4b to be the
nondimeric salt trans,mer-[(Cy3P)2(OC)3Fe→GaCl2][GaCl4]
shown in Figure 5, with an effectively planar Fe-bound Ga
Figure 2. Crystallographically derived structures of MOLPs 1b, 2b, 3b,
and 3c. Thermal ellipsoids drawn at the 50% probability level.
Hydrogen atoms, solvent molecules, and some ellipsoids have been
omitted for clarity. Selected bond lengths [Å] and angles [deg] for 1b:
Fe1−P1 2.3343(8), Fe1−Ga1 2.5072(5); P1−Fe1−Ga1 174.57(3).
For 2b: Fe1−C5 2.026(2), Fe1−Ga1 2.5009(5); C5−Fe1−Ga1
175.09(6). For 3b: Fe1−P1 2.2858(6), Fe1−C4 2.056(2), Fe1−Ga1
2.4683(7); C4−Fe1−Ga1 176.59(5). For 3c: Fe1−P1 2.306(1), Fe1−
C4 2.038(4), Fe1−Ga1 2.484(1); C4−Fe1−Ga1 177.4(1).
Figure 3. Synthesis of the two geometrical isomers of mer-
[(IMes)(Me3P)(OC)3Fe→GaCl3] (3b,c).
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hindrance from the steric bulk of the PCy3 ligands.
Unsurprisingly, given the reduced coordination number at Ga
and the positive charge on the complex, the Fe−Ga distance in
4b (2.3694(5) Å) is significantly shorter than that of the
analogous PMe3 MOLP trans,mer-[(Me3P)2(OC)3Fe→GaCl3]
(2.4612(6) Å).7
Similarly to the case of 4b, addition of one equivalent of
GaCl3 to 5a led to spontaneous precipitation of a low yield of a
[GaCl4]− salt that showed three CO bands in its IR spectrum
(2025, 2006, 1974 cm−1) and one set of NHC signals in its 1H
NMR spectrum (5b, Figure 4); doubling the amount of added
GaCl3 increased the yield to 65%. A single-crystal X-ray
diffraction study confirmed the structure of 5b to be the
analogous nondimeric salt trans,mer-[(IMes)2(OC)3Fe→
GaCl2][GaCl4] with an effectively planar Fe-bound Ga atom
and orthogonally oriented IMes units. Salt 5b shows both a
completely different metal-center geometry and a significantly
shorter Fe−Ga distance (2.3590(8) Å) than its neutral
bis(carbene) MOLP analogue cis,mer-[(IMe)2(OC)3Fe→
GaCl3] (2.4443(4) Å), presumably a result of the larger
NHC ligands in the former. It should be noted that very few
examples of cationic, tricoordinate gallium compounds have
been reported,10 and of these only a handful exhibit planar,
rather than pyramidal, Ga atoms.
Figure 4. Synthesis of the salts trans,mer-[L2(OC)3Fe→GaCl2]-
[GaCl4] with L = PCy3 (4b) or IMes (5b).
The cations of 4b and 5b can be depicted in two resonance
forms as shown in Figure 4. The two resonance structures
represent (formal) extremes of the Fe−Ga bonding situation,
one a dative gallenium Fe(o)→Ga+ MOLP, the other a
covalent gallyl Fe(II)+−GaCl2 cation where the positive charge
resides on the iron center. However, in reality the bonding
situation presumably lies somewhere between these two
extremes. Readers are directed to a related discussion about
the notation and formalisms in metallaboratrane (M→B)
complexes in two letters to this journal by Hill and Parkin from
2006,11 as well as discussions of metal−metal dative bonds in
our Chemical Reviews article from 2012.3
A similar reactivity pattern was noticed when the diiron
complex [Fe2(μ-CO)(CO)4(μ-dcpm)2] was treated with two
equivalents of GaCl3. This reaction was envisaged as a possible
route to dinuclear bis(MOLP) complexes in which two
connected metal centers each donate to one Lewis acid unit.
Instead, this reaction led to the isolation of a good yield of the
[GaCl4]− salt 6b (92%, Figure 6) after recrystallization. The 31
P
Figure 5. Crystallographically derived structures of salts 4b, 5b, and
6b. Thermal ellipsoids drawn at the 50% probability level. Hydrogen
atoms, the counterions [GaCl4]−, solvent molecules, a second cation
(for 5b), and some ellipsoids of the ligands are omitted for clarity.
Selected bond length [Å] and angles [deg] for 4b: Fe1−Ga1
2.3694(5); C1−Fe1−Ga1 179.08(7), P1−Fe1−P2 173.51(2). For
5b: Fe1−Ga1 2.3590(8); C1−Fe1−C2 173.4(2), C3−Fe1−Ga1
166.1(1). For 6b: Fe1−Fe2 2.8692(7), Fe1−Ga1 2.4718(6), Fe2−
Ga1 2.4858(6), Fe1−C3 2.043(3), Fe2−C3 2.012(3), C1−Ga1
2.499(3), C5−Ga1 2.481(3); Fe1−Ga1−Fe2 70.72(2), Fe1−C3−
Fe2 90.1(1), C3−Fe1−Ga1 99.39(8), C3−Fe2−Ga1 99.81(8).
atom, indicating the absence of cation−cation interactions. The
inability of the cation of 4b to dimerize is presumably due to
Figure 6. Synthesis of the salt [(dcpm)2(OC)5Fe→(μ-GaCl2)]-
[GaCl4] (6b).
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phosphorus pentoxide (fluorobenzene, CH2Cl2) under argon and
stored over molecular sieves (4 Å). C6D6 and CD2Cl2 were degassed
by several freeze−pump−thaw cycles and stored over molecular sieves.
The NMR spectra were recorded on a Bruker AMX 400 (1H: 400.1
MHz, 13C: 100.6 MHz, 11B: 128.4 MHz, 31P: 162.0 MHz) and/or a
Bruker Avance 500 FT-NMR spectrometer (1H: 500.1 MHz, 13C:
125.8 MHz, 11B: 160.5 MHz, 31P: 202.5 MHz). Chemical shifts are
given in ppm and were referenced to external TMS (1H, 13C{1H}),
[BF3·OEt2] (11B{1H}) and 85% H3PO4 (31P{1H}), and coupling
constants are given in Hz. Elemental analyses were obtained from an
Elementar Vario MICRO cube instrument. Infrared spectra were
measured on a JASCO FT/IR-6200 type A spectrometer. The light
source for photochemical experiments was a Hg/Xe arc lamp (400−
550 W) equipped with IR filters, irradiating at 210−600 nm.
Trimethylphosphine,13 1,3-dimesitylimidazol-2-ylidene,14 tricyclohex-
ylphosphine,15 bis(dicyclohexylphosphino)methane (dcpm),16 [Fe-
(CO)4(PCy3)] (1a),9a [Fe(CO)4(IMes)] (2a),9b and [Fe-
(CO)3(IMes)2] (5a)9b were prepared according to literature
procedures. [Fe(CO)5] was purchased from Strem Chemicals, and
GaCl3 from Sigma-Aldrich; both were used without further
purification.
NMR spectrum of 6b shows one signal (δ 57.7) that is shifted
to higher field compared to that of 6a (δ 76.5, Table 1). The IR
Table 1. Fe−Ga Distances and 31P NMR Data of Published
Complexes and Those Prepared in This Work
complex
d(Fe−B) (Å)
2.547(1)
δ(31P)(ppm)
Pentacarbonyl MOLP
[(OC)5Fe→GaCl3]7
n.a.
Tetracarbonyl MOLPs
[(Me3P) (OC)4Fe→GaCl3]7
1b
2.4844(3)
2.5072(5)
2.5009(5)
9.75
55.6
n.a.
2b
Tricarbonyl MOLPs
a
3b
2.4683(7)
2.484(1)
8.5, 13.5
3c
Cationic Fe−Ga Complexes
4b
5b
6b
2.3694(5)
62.5
n.a.
2.3590(8)
2.4718(6), 2.4858(6)
57.7
Synthesis of [Fe(CO)3(IMes)(PMe3)] (3a). A solution of [Fe-
(CO)4(IMes)] (2a) (465 mg, 0.98 mmol) in 50 mL of benzene was
treated with an excess of PMe3 (0.31 mL, 224 mg, 2.95 mmol). The
solution was irradiated in front of a mercury lamp for 16 h. The
solvent was subsequently removed under vacuum, and the residue was
recrystallized in toluene at −30 °C to yield 3a (418 mg, 0.80 mmol,
81%) as a yellow crystalline solid. IR (CH2Cl2): 1852 (νCO) cm−1. 1H
a
The 31P NMR resonances of 3a,b could not be differentiated.
spectrum showed three carbonyl stretching bands (1980, 1947,
1785 cm−1), the lowest energy band of which presumably
corresponds to the bridging CO ligand. The crystallographically
determined molecular structure of 6b indicated the presence of
the dinuclear gallinium salt [Fe2(μ-CO)(CO)4(μ-dcpm)2(μ-
GaCl2)][GaCl4]. The complex showed a longer Fe−Fe distance
(2.8692(7) Å) than that of the dppm analogue of precursor 6a
(2.711(1) Å),12 reflective of a reduced Fe−Fe interaction upon
addition of the GaCl2 ligand. The Fe−Ga distances in 6b
(2.4718(6), 2.4858(6) Å) were also found to be significantly
longer than those of mononuclear cations 4b and 5b,
approaching those of the neutral MOLPs described above,
presumably a consequence of the increased coordination at
gallium. Weak interactions between the carbonyl carbon atoms
and the Fe-bound gallium atom are evident from the relatively
short Ga−C1/C5 distances (2.499(3), 2.481(3) Å). In contrast
to the above syntheses of gallenium salts 4b and 5b, the
selective formation of gallinium salt 6b cannot be solely
attributed to steric effects, since the presence of two Lewis-basic
metal centers in 6a leads to two (presumably stabilizing) Fe→
Ga interactions in the product 6b.
2
NMR (500.1 MHz, C6D6, 297 K): δ = 1.08 (d, JHP = 10 Hz, 9H,
CH3), 2.14 (s, 12H, CH3), 2.28 (s, 6H, CH3), 6.28 (s, 2H, CH), 6.88
(s, 4H, CH). 13C{1H} NMR (125.8 MHz, C6D6, 297 K): δ = 18.6 (s,
1
4C, CH3), 19.1 (d, JCP = 32 Hz, 9C, CH3), 21.2 (s, 2C, CH3), 123.4
4
(d, JCP = 3 Hz, 2C, CHImid), 129.5 (s, 4C, CH), 136.7 (s, 4C, Cq),
138.5 (s, 2C, Cq), 138.6 (s, 2C, Cq), 196.2 (d, 2JCP = 12 Hz, C, CImid),
2
218.3 (d, JCP = 32 Hz, 3C, CO). 31P{1H} NMR (202.5 MHz, C6D6,
297 K): δ = 45.9 (s). Anal. (%) Calcd for C27H33FeN2O3P: C 62.32; H
6.39; N 5.38. Found: C 62.48; H 6.26; N 5.38.
Synthesis of [Fe(CO)3(PCy3)2] (4a). The literature synthesis of
4a9a was altered slightly. A procedure similar to that used for the
preparation of 3a was applied by using [Fe(CO)5] (0.24 mL, 350 mg,
1.79 mmol) and PCy3 (1.10 g, 3.93 mmol) to provide 4a (970 mg,
1.43 mmol, 80%) as a white solid. IR (CH2Cl2): 1855 (νCO) cm−1. 1H
NMR (500.1 MHz, C6D6, 297 K): δ = 1.12−1.31 (m, 18H, Cy), 1.55−
1.62 (m, 6H, Cy), 1.71−1.84 (m, 24H, Cy), 2.26−2.35 (m, 18H, Cy).
13C{1H} NMR (125.8 MHz, C6D6, 297 K): δ = 27.0 (s, 6C, Cy), 28.4
(vt, N = |2JCP+4JCP| = 10 Hz, 12C, Cy), 30.6 (s, 12C, Cy), 39.4 (vt, N =
|1JCP+3JCP| = 20 Hz, 6C, Cy), 218.0 (t, 2JCP = 27 Hz, 3C, CO). 31P{1H}
NMR (202.5 MHz, C6D6, 297 K): δ = 86.1 (s). Anal. (%) Calcd for
C39H66FeO3P2: C 66.85; H 9.49. Found: C 67.00; H 9.38.
Similar to cations 4b and 5b, 6b can be depicted in a number
of different resonance forms, from the double-dative gallenium
Fe(0)/Fe(0)/Ga+ MOLP form depicted in Figure 6 to the
double-covalent gallate Fe(II)/Fe(II)/Ga−. The true bonding
situation lies presumably somewhere between these extremes.
Herein we have presented the outcomes of reactions of
gallium trichloride with a series of zerovalent iron complexes
with increasing steric bulk. When the electron density of the
metal complex is kept relatively constant but the steric bulk is
increased markedly, disproportionation of the GaCl3 occurs
(even when one equivalent is used), resulting in metal-
stabilized gallenium salts. A similar disproportionation reaction
is observed with a dinuclear iron(0) complex, in this case
providing a cationic complex with a bridging GaCl2 ligand.
Synthesis of [Fe2(CO)5(dcpm)2] (6a). A solution of [Fe(CO)5]
(0.5 mL, 725 mg, 3.70 mmol) in 70 mL of benzene was treated with
dcpm (1.51 g, 3.70 mmol). The solution was irradiated in front of a
mercury lamp for 8 d, and the resulting precipitate was filtered off. The
residue was dried under vacuum and recrystallized from toluene at
−30 °C to yield 6a (1.44 g, 1.31 mmol, 71%) as a light brown solid. IR
(CH2Cl2): 1687, 1853, 1930 (νCO) cm−1. 1H NMR (500.1 MHz,
C6D6, 297 K): δ = 1.25−1.35 (m, 8H, Cy), 1.38−1.52 (m, 16H, Cy),
1.66−1.79 (m, 24H, Cy), 1.90−1.99 (m, 16H, Cy), 2.03−2.09 (m, 4H,
CH2), 2.26−2.35 (m, 8H, Cy), 2.42−2.54 (m, 16H, Cy). 13C{1H}
NMR (125.8 MHz, C6D6, 297 K): δ = 22.4 (s, 2C, CH2), 26.7 (s, 8C,
Cy), 28.1 (s, 16C, Cy), 30.0 (m, 16C, Cy), 40.6 (m, 8C, Cy), 237.7−
238.3 (m, 5C, CO). 31P{1H} NMR (202.5 MHz, C6D6, 297 K): δ =
76.5 (s). Anal. (%) Calcd for C55H92Fe2O5P4: C 61.80; H 8.67. Found:
C 61.44; H 8.43.
Synthesis of [(Cy3P)(OC)4Fe→GaCl3] (1b). To a solution of
[Fe(CO)4(PCy3)] (1a) (50.0 mg, 0.12 mmol) in benzene (7 mL) was
added GaCl3 (19.6 mg, 0.12 mmol). The mixture was shaken and
allowed to stand for 1 h. The resulting precipitate was filtered off, and
the residue washed with benzene (3 × 5 mL) and pentane (3 × 5 mL).
The white solid was recrystallized from C6H5F at −30 °C to yield 1b
EXPERIMENTAL SECTION
■
General Information. All syntheses were performed under an
inert atmosphere of dry argon using standard Schlenk techniques or in
a glovebox (MBraun). Solvents were dried by distillation over
potassium (benzene, toluene), Na/K alloy (hexane, THF), or
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(57.2 mg, 0.09 mmol, 83%) as a white crystalline solid. IR (CH2Cl2):
2036 (νCO) cm−1. 1H NMR (500.1 MHz, CD2Cl2, 297 K): δ = 1.30−
1.40 (m, 12H, Cy), 1.49−1.56 (m, 6H, Cy), 1.80−1.97 (m, 12H, Cy),
2.21−2.23 (m, 3H, Cy). 13C{1H} NMR (125.8 MHz, CD2Cl2, 297 K):
δ = 26.1 (d, 4JCP = 2 Hz, 3C, Cy), 27.7 (d, 2JCP = 11 Hz, 6C, Cy), 29.9
(d, 3JCP = 3 Hz, 6C, Cy), 37.9 (d, 1JCP = 20 Hz, 3C, Cy), 205.7 (d, 2JCP
= 10 Hz, 4C, CO). 31P{1H} NMR (202.5 MHz, CD2Cl2, 297 K): δ =
55.6 (s). Anal. (%) Calcd for C22H33Cl3FeGaO4P: C 42.32; H 5.33.
Found: C 42.03; H 5.34.
Synthesis of [(IMes)(OC)4Fe→GaCl3] (2b). A procedure similar
to that used for the preparation of 1b was applied by using
[Fe(CO)4(IMes)] (2a) (30.0 mg, 0.06 mmol) and 1 equiv of GaCl3
(11.2 mg, 0.06 mmol) to provide 2b (38.4 mg, 0.059 mmol, 93%) after
recrystallization in CH2Cl2 at −30 °C as a white solid. IR (CH2Cl2):
2062 (νCO) cm−1. 1H NMR (500.1 MHz, CD2Cl2, 297 K): δ = 2.09 (s,
12H, CH3), 2.39 (s, 6H, CH3), 7.13 (s, 4H, CH), 7.41 (s, 2H, CHImid).
13C{1H} NMR (125.8 MHz, CD2Cl2, 297 K): δ = 17.2 (s, 3C, CH3),
20.9 (s, 2C, CH3), 127.3 (s, 2C, CHImid), 128.3 (s, 4C, CAr), 130.2 (s,
4C, CHAr), 135.4 (s, 2C, CAr), 141.9 (s, 2C, CAr), 173.1 (s, 1C, CImid),
202.9 (s, 4C, CO). Anal. (%) Calcd for C25H24Cl3FeGaN2O4.
(CH2Cl2)0.75: C 43.43; H 3.61; N 3.93. Found: C 43.27; H 3.68; N
3.90. One molecule of dichloromethane is observed in the crystal,
some of which presumably was removed when these crystals were
placed under high vacuum for elemental analysis measurement.
Synthesis of [(IMes)(Me3P)(OC)3Fe→GaCl3] (3b,c). A procedure
similar to that used for the preparation of 1b was applied by using
[Fe(CO)3(PMe3)(IMes)] (3a) (20.0 mg, 38.4 μmol) and 1 equiv of
GaCl3 (6.8 mg, 38.4 μmol) to provide 3b,c (18.3 mg, 26.3 μmol, 68%)
CH3), 129.20 (s, 8C, CHMes), 131.35 (s, 4C, CHImid), 135.12 (s, 8C,
Cq), 137.55 (s, 4C, Cq), 143.22 (s, 4C, Cq), 169.76 (s, 2C, CImid),
204.50 (s, 1C, CO), 205.39 (s, 2C, CO). Anal. (%) Calcd for
C45H48Cl6FeGa2N4O3: C 49.09, H 4.39, N 5.09. Found: C 49.42, H
4.46, N 5.42.
Synthesis of [(dcpm)2(OC)5Fe2(μ-GaCl2)][GaCl4] (6b). A
procedure similar to that used for the preparation of 1b was applied
by using [Fe2(μ-CO)(CO)5(μ-dcpm)2] (6a) (50.0 mg, 45.6 μmol)
and 2 equiv of GaCl3 (16.1 mg, 91.2 μmol) to provide 6b (60.5 mg,
42.2 μmol, 92%) as a red crystalline solid. IR (CH2Cl2): 1980, 1947,
1785 (νCO) cm−1. 1H NMR (500.1 MHz, CD2Cl2, 297 K): δ = 1.30−
1.60 (m, 42H, Cy), 1.75−2.17 (m, 38H, Cy), 2.22−2.39 (m, 8H, Cy),
2.41−2.55 (m, 4H, CH2). 13C{1H} NMR (125.8 MHz, CD2Cl2, 297
K): δ = 21.2 (s, 1C, CH2), 22.7 (s, 1C, CH2), 26.1 (d, 1JCP = 7 Hz, 8C,
Cy), 27.3 (s, 4C, Cy), 28.1 (s, 12C, Cy), 28.7 (m, 4C, Cy), 30.9 (s, 4C,
Cy), 31.3 (s, 4C, Cy), 32.2 (s, 4C, Cy), 39.9 (s, 4C, Cy), 44.1 (s, 4C,
Cy), 212.5 (br, 2C, CO) 214.5 (t, 2JCP = 7 Hz, 2C, CO), 259.6 (t, 2JCP
= 11 Hz, 1C, CO). 31P{1H} NMR (202.5 MHz, CD2Cl2, 297 K): δ =
57.7 (s). Anal. (%) Calcd for C55H92Cl6Fe2Ga2O5P4: C 46.49, H 6.53.
Found: C 46.51, H 6.46.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00045.
Experimental procedures (PDF)
Crystallographic data (ZIP)
as a colorless crystalline solid. IR (CH2Cl2): 2073, 2012, 1985 (νCO
)
1
2
cm−1. H NMR (500.1 MHz, CD2Cl2, 297 K): δ = 1.50 (d, JHP = 11
Hz, 9H, CH3), 1.55 (d, 2JHP = 11 Hz, 9H, CH3), [2.01 (s, 12H, CHAr),
2.35 (s, 6H, CHAr)], [2.34 (s, 12H, CHAr), 2.53 (s, 6H, CHAr)], 6.98
(br, 2H, CHAr), 7.04 (br, 4H, CHAr), 7.14 (s, 4H, CHAr), 7.27 (2H,
CHAr) (spectrum contained signals for both isomers). 13C{1H} NMR
AUTHOR INFORMATION
Corresponding Author
*E-mail: h.braunschweig@uni-wuerzburg.de.
■
1
(125.8 MHz, CD2Cl2, 297 K): δ = 18.55 (d, J = 34 Hz, 3C, CH3),
Notes
1
19.00 (s, 2C, CH3), 20.44 (d, J = 32 Hz, 3C, CH3), 20.71 (s, 2C,
The authors declare no competing financial interest.
CH3), 21.16 (s, 4C, CH3), 21.18 (s, 4C, CH3), 124.47 (d, 4JCP = 3 Hz,
2C, CHImid), 125.73 (s, 2C, CHImid), 127.23 (s, 4C, CH), 129.55 (s,
4C, CH), 130.67 (s, 4C, Cq), 136.24 (s, 4C, Cq), 136.71 (s, 4C, Cq),
138.60 (s, 4C, Cq), 140.92 (s, 2C, Cq), 141.41 (s, 2C, Cq), 179.29 (d,
2JCP = 13 Hz, C, CImid), 183.96 (d, 2JCP = 16 Hz, C, CImid), 207.98 (d,
2JCP = 32 Hz, 2C, CO), 208.07 (d, 2JCP = 19 Hz, 1C, CO), 208.34 (d,
ACKNOWLEDGMENTS
The authors gratefully acknowledge the Deutsche Forschungs-
gemeinschaft for financial support of this work.
■
2
2JCP = 25 Hz, 2C, CO), 209.23 (d, JCP = 23 Hz, 1C, CO) (spectrum
REFERENCES
■
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C27H33Cl3FeGaN2O3P: C 46.56, H 4.78, N 4.02. Found: C 46.38, H
4.70, N 3.69.
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(νCO) cm−1. H NMR (500.1 MHz, CD2Cl2, 297 K): δ = 1.38−1.44
(m, 18H, Cy), 1.65−1.67 (m, 12H, Cy), 1.83 (s, 6H, Cy), 1.99−2.03
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similar to that used for the preparation of 1b was applied by using
[Fe(CO)3(IMes)2] (5a) (30.0 mg, 40.1 μmol) and 2 equiv of GaCl3
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(125.8 MHz, CD2Cl2, 297 K): δ = 18.76 (s, 8C, CH3), 21.34 (s, 4C,
E
DOI: 10.1021/acs.organomet.6b00045
Organometallics XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.organomet.6b00045
Organometallics XXXX, XXX, XXX−XXX