Halide abstraction as a route to cationic transition-metal complexes containing two-coordinate gallium and indium ligand systems

Article abstract of DOI:10.1021/om0506318

Halide abstraction chemistry offers a viable synthetic route to the cationic two-coordinate complexes [{Cp*Fe(CO)₂} ₂(μ-E)]⁺ (7, E = Ga; 8, E = In) featuring linear bridging gallium or indium atoms. Structural, spectroscopic, and computational studies undertaken on 7 are consistent with appreciable Fe-Ga π-bonding character; in contrast, the indium-bridged complex 8 is shown to feature a much smaller π component to the metal-ligand interaction. Analogous reactions utilizing the supermesityl-substituted gallyl or indyl precursors of the type (η⁵-C₅R₅)Fe(CO)₂E(Mes*)X, on the other hand, lead to the synthesis of halide-bridged species of the type [{(η⁵-C₅R₅)Fe(CO)₂E(Mes*)} ₂(μ-X)]⁺, presumably by trapping of the highly electrophilic putative cationic diyl complex [(η⁵-C ₅R₅)Fe(CO)₂E(Mes*)]⁺.

Full text of DOI:10.1021/om0506318

Organometallics 2005, 24, 5891-5900
5891
Halide Abstraction as a Route to Cationic
Transition-Metal Complexes Containing Two-Coordinate
Gallium and Indium Ligand Systems
Natalie R. Bunn, Simon Aldridge,* Deborah L. Kays,† Natalie D. Coombs,
Andrea Rossin, David J. Willock, Joanna K. Day, Cameron Jones, and
Li-ling Ooi
Centre for Fundamental and Applied Main Group Chemistry, School of Chemistry,
Cardiff University, Main Building, Park Place, Cardiff, U.K. CF10 3AT
Received July 26, 2005
Halide abstraction chemistry offers a viable synthetic route to the cationic two-coordinate
complexes [{Cp*Fe(CO)2}2(µ-E)]+ (7, E ) Ga; 8, E ) In) featuring linear bridging gallium or
indium atoms. Structural, spectroscopic, and computational studies undertaken on 7 are
consistent with appreciable Fe-Ga π-bonding character; in contrast, the indium-bridged
complex 8 is shown to feature a much smaller π component to the metal-ligand interaction.
Analogous reactions utilizing the supermesityl-substituted gallyl or indyl precursors of the
type (η5-C5R5)Fe(CO)2E(Mes*)X, on the other hand, lead to the synthesis of halide-bridged
species of the type [{(η5-C5R5)Fe(CO)2E(Mes*)}2(µ-X)]+, presumably by trapping of the highly
electrophilic putative cationic diyl complex [(η5-C5R5)Fe(CO)2E(Mes*)]+.
Scheme 1. Halide Abstraction Methodology for
Cationic Transition-Metal Complexes Containing
Two-Coordinate Group 13 Ligands (E ) Group 13
Element; R ) Bulky Substituent; X ) Halide; L )
Generic Ligand Coordinated to Transition Metal
M)
Introduction
Compounds offering the potential for multiple bond-
ing involving the heavier group 13 elements have
attracted considerable attention in recent years, with
studies reporting examples of both homo- and hetero-
nuclear multiple bonds having appeared in the litera-
ture.1 Within this sphere, the transition-metal diyl
complexes LnM(EX) have been the subject of consider-
able debate,2,3 primarily concerning the nature of the
interaction between the group 13 and transition-metal
centers. The description of superficially similar com-
plexes as being bound via multiple bonds (e.g. LnMd
EX or LnMtEX) or via donor/acceptor interactions
(LnMrEX) reflects not only the fundamental questions
of structure and bonding posed by such systems but also
the lack of definitive experimental verification of po-
tential bonding models.4
* To whom correspondence should be addressed, E-mail:
AldridgeS@cardiff.ac.uk. Tel: (029) 20875495. Fax: (029) 20874030.
Web: www.cf.ac.uk/chemy/cfamgc.
In an attempt to broaden the scope of synthetic
methodologies available for unsaturated group 13 sys-
tems, we have been examining the use of halide ab-
straction chemistry to generate cationic derivatives
(Scheme 1).5 A series of preliminary computational
analyses has suggested that the positive charge in
cationic terminal diyl species, [LnM(EX)]+, resides pri-
marily at the group 13 center (e.g. Mulliken charges of
+0.438, +0.680, and +0.309 for [Cp*Fe(CO)2E(Mes)]+;
E ) B, Al, Ga) and that MfE back-bonding may
† Ne´e Coombs.
(1) For selected recent examples see: (a) Mork, B. V.; Tilley, T. D.
Angew. Chem., Int. Ed. 2003, 42, 357. (b) Wright, R. J.; Phillips, A.
D.; Allen, T. L.; Fink, W. H.; Power, P. P. J. Am. Chem. Soc. 2003,
125, 1694. (c) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P.
P. J. Am. Chem. Soc. 2003, 125, 2667. (d) Power, P. P. Chem. Commun.
2003, 2091. (e) Filippou, A. C.; Weidemann, N.; Schnakenburg, G.;
Rohde, H.; Philippopoulos, A. I. Angew. Chem., Int. Ed. 2004, 43, 6521.
(f) Sekiguchi, A.; Kinjo, R.; Ichinohe, M. Science 2004, 305, 1755. (g)
Power, P. P. J. Organomet. Chem. 2004, 689, 3904. (h) Cowley, A. H.
J. Organomet. Chem. 2004, 689, 3866. (i) Zhu, H.; Chai, J.; Chan-
drasekhar, V.; Roesky, H.; Magull, J.; Vidovic, D.; Schmidt, H.-G.;
Noltemeyer, M.; Power, P. P.; Merrill, W. A. J. Am. Chem. Soc. 2004,
126, 9472. (j) Wang, Y.; Quillian, B.; Yang, X.-J.; Wei, P.; Chen, Z.;
Wannere, C. W.; Schleyer, P. v. R.; Robinson, G. H. J. Am. Chem. Soc.
2005, 127, 7672. (k) Vidovic, D.; Moore, J. A.; Jones, J. N.; Cowley, A.
H. J. Am. Chem. Soc. 2005, 127, 4566.
(2) For recent examples of diyl coordination chemistry see: (a)
Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am.
Chem. Soc. 2003, 125, 2667. (b) Yang, X.-J.; Quillian, B.; Wang, Y.;
Wei, P.; Robinson, G. H. Organometallics 2004, 23, 5119. (c) Uhl, W.;
El-Hamdan, A, Petz, W.; Geiseler, G.; Harms, K. Z. Naturforsch., B
2004, 59, 789. (d) Braunschweig, H.; Radacki, K.; Rais, D.; Seeler, F.;
Uttinger, K. J. Am. Chem. Soc. 2005, 127, 1386. (e) Cokoja, M.; Gemel,
C.; Steinke, T.; Schro¨der, F.; Fischer, R. A. Dalton Trans. 2005, 44. (f)
Steinke, T.; Gemel, C.; Cokoja, M.; Winter, M.; Fischer, R. A. Dalton
Trans. 2005, 552.
(3) For recent reviews of diyl chemistry see: (a) Fischer, R. A., Weiss,
J. Angew. Chem., Int. Ed. 1999, 38, 2830. (b) Linti, G, Schno¨ckel, H.
Coord. Chem. Rev. 2000, 206-207, 285. (c) Schebaum, L. O.; Jutzi, P.
ACS Symp. Ser. 2002, 822, 16. (d) Gemel, C.; Steinke, T.; Cokoja, M.;
Kempter, A.; Fischer, R. A. Eur. J. Inorg. Chem. 2004, 4161. (e) Cowley,
A. H. J. Organomet. Chem. 2004, 689, 3866. (f) Braunschweig, H. Adv.
Organomet. Chem. 2004, 51, 163. (g) Aldridge, S.; Coombs, D. L. Coord.
Chem. Rev. 2004, 248, 535.
(4) See, for example: (a) Su, J.; Li, X.-W.; Crittendon, R. C.;
Campana, C. F.; Robinson, G. H. Organometallics 1997, 16, 4511. (b)
Cotton, F. A.; Feng, X. Organometallics 1998, 17, 128.
(5) (a) Coombs, D. L.; Aldridge, S.; Jones, C.; Willock, D. J. J. Am.
Chem. Soc. 2003, 125, 6356. (b) Coombs, D. L.; Aldridge, S.; Rossin,
A.; Jones, C.; Willock, D. J. Organometallics 2004, 23, 2911.
10.1021/om0506318 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/26/2005

5892 Organometallics, Vol. 24, No. 24, 2005
Bunn et al.
measured for each compound either pressed into a disk with
excess dry KBr or as a solution in the appropriate solvent, on
a Nicolet 500 FT-IR spectrometer. Mass spectra were mea-
sured by the EPSRC National Mass Spectrometry Service
Centre, University of Wales, Swansea, Wales. Perfluorotribu-
tylamine was used as the standard for high-resolution EI mass
spectra. Despite repeated attempts, satisfactory elementary
microanalyses for the new cationic gallium and indium com-
plexes were frustrated by their extreme air and moisture
sensitivity. Characterization of the new compounds is therefore
based upon multinuclear NMR, IR, and mass spectrometry
data (including accurate mass measurement), supplemented
by single-crystal X-ray diffraction studies in the cases of 7, 8,
10, and 14. In all cases the purity of the bulk material was
established by multinuclear NMR to be >95% (see the Sup-
porting Information). Abbreviations: br ) broad, s ) singlet,
q ) quartet, m ) multiplet.
Chart 1. Cationic Trimetallic Systems Featuring
Naked Group 13 Atoms as Bridging Ligands (E )
Group 13 Element; L ) Generic Ligand
Coordinated to Transition Metal M)
contribute appreciably to the overall metal-ligand
interaction (e.g., a 38% π contribution to the FeB
bonding density in [Cp*Fe(CO)2B(Mes)]+).6 Hence, the
FedB double bond in [Cp*Fe(CO)2B(Mes)]+ can be
described simplistically as being comprised of BfFe
σ-donor and FefB π-acceptor components. Recently we
have been seeking to extend this synthetic approach
from boron to the heavier group 13 elements and from
isolated metal-ligand bonds (i.e. I) to delocalized tri-
metallic systems featuring naked group 13 atoms as
ligands (i.e. II; Chart 1).7
Herein we report an extended investigation into the
use of halide abstraction chemistry in heavier group 13
systems, leading to the synthesis of cationic derivatives
containing gallium and indium donors. This has allowed
for comparative spectroscopic, structural, and compu-
tational probes of M-E bond character as a function of
the element E, thereby probing the controversial subject
of multiple bonding involving the heavier group 13
elements. In addition, preliminary studies of the fun-
damental reactivity of the trimetallic systems [LnM(µ-
E)MLn]+ (E ) Ga, In) are reported.
(ii) Syntheses. [{Cp*Fe(CO)2}2(µ-Ga)][BArf4] (7). To a
suspension of Na[BArf4] (0.067 g, 0.075 mmol) in dichlo-
romethane (10 mL) at -78 °C was added a solution of 4 (0.045
g, 0.075 mmol) in dichloromethane (10 mL), and the reaction
mixture was warmed to 20 °C over 30 min. Further stirring
for 20 min, filtration, and removal of volatiles in vacuo yielded
7 as a golden yellow powder (0.050 g, 46%). X-ray-quality
crystals were grown by layering a dichloromethane solution
with hexanes at -30 °C. 1H NMR (300 MHz, CD2Cl2): δ 1.93
(s, 30H, Cp*), 7.54 (s, 4H, para CH of BArf4-), 7.70 (s, 8H, ortho
CH of BArf4-). 13C NMR (76 MHz, CD2Cl2): δ 10.3 (CH3 of Cp*),
97.5 (quaternary of Cp*), 117.5 (para CH of BArf4-), 122.8 (q,
1JCF ) 273 Hz, CF3 of BArf4-), 128.8 (q, 2JCF ) 34 Hz, meta C
1
of BArf4-), 134.8 (ortho CH of BArf4-), 160.8 (q, JCB) 53 Hz,
ipso C of BArf4-), 211.4 (CO). 19F NMR (283 MHz, CD2Cl2): δ
-62.8 (CF3). 11B NMR (96 MHz, CD2Cl2): δ -7.6 (BArf4-). IR
(CH2Cl2): ν(CO) 2016, 1994, 1963 cm-1. MS: ES-, m/z 863
(100%) [BArf4]-; ES+, m/z 563 (5%) [M]+, correct isotope
distribution for 2 Fe and 1 Ga atoms. Exact mass: calcd for
[M]+ 563.0093, found 563.0092.
[{Cp*Fe(CO)2}2(µ-In)][BArf4] (8). To a suspension of Na-
[BArf4] (0.057 g, 0.064 mmol) in dichloromethane (4 mL) at
-78 °C was added a solution of 5 (0.044 g, 0.064 mmol) in
dichloromethane (4 mL), and the reaction mixture was warmed
to 20 °C over 30 min. Further stirring for 90 min, filtration,
and layering with hexanes and storage at -30 °C yielded 8 as
orange crystals suitable for X-ray diffraction (0.060 g, 64%).
1H NMR (400 MHz, CD2Cl2): δ 1.85 (s, 30H, Cp*), 7.44 (s, 4H,
para CH of BArf4-), 7.64 (s, 8H, ortho CH of BArf4-). 13C NMR
(76 MHz, CD2Cl2): δ 10.4 (CH3 of Cp*), 96.5 (quaternary of
Cp*), 117.8 (para CH of BArf4-), 124.6 (q, 1JCF ) 272 Hz, CF3
Experimental Section
(i) General Considerations. All manipulations were car-
ried out under a nitrogen or argon atmosphere using standard
Schlenk line or drybox techniques. Solvents were predried over
sodium wire (hexanes, toluene, thf) or molecular sieves (dichlo-
romethane) and purged with nitrogen prior to distillation from
the appropriate drying agent (hexanes, potassium; toluene and
thf, sodium; dichloromethane, CaH2). Benzene-d6 and dichlo-
romethane-d2 (both Goss) were degassed and dried over the
appropriate drying agent (potassium or molecular sieves) prior
to use. Na[BPh4], [nBu4N]I, and [PPN]Cl were dried in vacuo
prior to use; the compounds (η5-C5R5)Fe(CO)2E(Mes*)X (Mes*
2
of BArf4-), 128.9 (q, JCF ) 35 Hz, meta C of BArf4-), 134.8
(ortho CH of BArf4-), 161.8 (q, 1JCB ) 50 Hz, ipso C of BArf4-),
211.9 (CO). 19F NMR (283 MHz, CD2Cl2): δ -62.7 (CF3). 11B
NMR (96 MHz, CD2Cl2): δ -7.6 (BArf4-). IR (CD2Cl2): ν(CO)
2005, 1983, 1951 cm-1. MS: ES-, m/z 863 (100%) [BArf4]-;
ES+, m/z 609 (6%) [M]+, correct isotope distribution for 2 Fe
and 1 In atoms, significant fragment ions at m/z 581 (weak)
[M - CO]+, 553 (5%) [M - 2CO]+. Exact mass: calcd for [M]+
608.9876, found 608.9884.
t
) supermesityl ) C6H2 Bu3-2,4,6; 1, E ) Ga, R ) H, X ) Cl;
2, E ) Ga, R ) Me, X ) Cl; 3, E ) In, R ) H, X ) Br), [Cp*Fe-
(CO)2]2EX (4, E ) Ga, X ) Cl; 5, E ) In, X ) Br; 6, E ) In, X
) I), and Na[BArf4] (Arf ) C6H3(CF3)2-3,5) were prepared by
literature methods.8,9
NMR spectra were measured on a Bruker AM-400 or JEOL
300 Eclipse Plus FT-NMR spectrometer. Residual signals of
the solvent were used for reference for 1H and 13C NMR, while
a sealed tube containing a solution of [nBu4N][B3H8] in CDCl3
was used as an external reference for 11B NMR and CFCl3 was
used as a reference for 19F NMR. Infrared spectra were
Reaction of [Cp*Fe(CO)2]2InI (6) with Na[BArf4]: Iso-
lation of [{Cp*Fe(CO)2}2(µ-I)][BArf4] (9). To a suspension
of Na[BArf4] (0.111 g, 0.13 mmol) in dichloromethane (6 mL)
at -78 °C was added a solution of 6 (0.092 g, 0.13 mmol) in
dichloromethane (8 mL), and the reaction mixture was warmed
to 20 °C over 30 min. Further stirring for 3 h, filtration, and
layering with hexanes yielded orange crystals of 9 (0.028 g,
15%). 1H NMR (400 MHz, CD2Cl2): δ 1.84 (s, 30H, Cp*), 7.48
(s, 4H, para CH of BArf4-), 7.64 (s, 8H, ortho CH of BArf4-).
13C NMR (76 MHz, CD2Cl2): δ 10.4 (CH3 of Cp*), 96.1
(6) Aldridge, S.; Rossin, A.; Coombs, D. L.; Willock, D. J. Dalton
Trans. 2004, 2649.
(7) For a preliminary report of part of this work see: Bunn, N. R.;
Aldridge, S.; Coombs, D. L.; Rossin, A.; Willock, D. J.; Jones, C. Ooi.,
L.-L. Chem. Commun. 2004, 1732.
1
(quaternary of Cp*), 117.5 (para CH of BArf4-), 124.6 (q, JCF
(8) Bunn, N. R.; Aldridge, S.; Kays, D. L.; Coombs, N. D.; Day, J.
K.; Ooi, L.-L., Coles, S. J.; Hursthouse, M. B. Organometallics 2005,
24, 5879.
2
) 274 Hz, CF3 of BArf4-), 128.9 (q, JCF ) 31 Hz, meta C of
1
BArf4-), 134.8 (ortho CH of BArf4-), 161.8 (q, JCB ) 49 Hz,
(9) Reger, D. L.; Wright, T. D.; Little, C. A.; Lamba, J. J. S.; Smith,
M. D. Inorg. Chem. 2001, 40, 3810.
ipso C of BArf4-), 212.8 (CO). 19F NMR (283 MHz, CD2Cl2): δ

Two-Coordinate Ga and In Ligand Systems
Organometallics, Vol. 24, No. 24, 2005 5893
-62.8 (CF3). 11B NMR (96 MHz, CD2Cl2): δ -7.6. IR (CH2-
Cl2): ν(CO) 2003, 1984, 1952 cm-1. MS: ES-, 863 (100%)
[BArf4]-; ES+, 621 (50%) [M]+, correct isotope distribution for
2 Fe and 1 I atoms, significant fragment ions at m/z 593 (weak)
[M - CO]+, 565 (20%) [M - 2CO]+, 537 (45%) [M - 3CO]+,
509 (5%) [M - 4CO]+. Exact mass: calcd for [M]+ 620.9882,
found 620.9872.
of ortho tBu), 34.7 (quaternary of para tBu), 38.5 (quaternary
t
of ortho Bu), 95.5 (quaternary of Cp*), 117.5 (para CH of
1
BArf4-), 123.4 (meta CH of Mes*), 124.6 (q, JCF ) 272 Hz,
CF3 of BArf4-), 128.9 (q, 2JCF ) 31 Hz, meta C of BArf4-), 134.9
(ortho CH of BArf4-), 137.9 (ipso C of Mes*), 151.6 (para C of
Mes*), 155.4 (ortho C of Mes*), 161.8 (q, 1JCB ) 50 Hz, ipso C
of BArf4-), 214.5 (CO). 11B NMR (96 MHz, CD2Cl2): δ -7.6
(BArf4-). 19F NMR (283 MHz, CD2Cl2): δ -62.8 (CF3). ν(CO)
1996, 1986, 1954, 1932 cm-1. MS (EI): m/z 1131.1 (weak) [M
- CO]+, correct isotope distribution for 2 Fe, 2Ga and 1 Cl
atoms, significant fragment ions at m/z 723.0 (25%) [Cp*Fe-
(CO)2GaArf2Cl - 2CO]+, 650.1 (100%) [BArf3]+, 631.1 (80%)
[BArf3 - F]+.
Reaction of [Cp*Fe(CO)2]2InI (6) with Na[BPh4]. To a
suspension of Na[BPh4] (0.074 g, 0.22 mmol) in dichlo-
romethane (10 mL) at -78 °C was added a solution of 6 (0.080
g, 0.11 mmol) in dichloromethane (10 mL), and the reaction
mixture was warmed slowly to 20 °C. Monitoring the reaction
mixture by IR spectroscopy over a period of 72 h led to the
gradual disappearance of the peaks due to the starting
material (1969, 1957, and 1922 cm-1) and the growth of bands
at 2016, 1995, 1970, and 1940 cm-1. Monitoring by 11B NMR
spectroscopy also revealed the growth of a strong broad signal
at δB 67.0. Filtration of the supernatant solution, removal of
volatiles in vacuo, and recrystallization from hexanes at -30
°C led to the formation of crops of colorless and dark red
microcrystalline material, which were identified as BPh3 (δB
67.0) and a mixture of Cp*Fe(CO)2I (ν(CO) 2016 and 1970
cm-1) and Cp*Fe(CO)2Ph (ν(CO) 1995 and 1940 cm-1), respec-
tively, by comparison of multinuclear NMR, IR, and mass
spectrometric data with those reported previously.10 A similar
procedure was adopted to monitor the reaction of [Cp*Fe-
(CO)2]2GaCl (4) with Na[BPh4]; in this case both BPh3 and
Cp*Fe(CO)2Ph were isolated and identified by comparison with
literature data.10
1
Data for 12 are as follows. H NMR (300 MHz, CD2Cl2): δ
1.18 (s, 18H, para tBu), 1.32 (s, 36H, ortho tBu), 4.81 (s, 10H,
Cp), 7.29 (s, 4H, aryl CH of Mes*), 7.37 (s, 4H, para CH of
BArf4-), 7.57 (s, 8H, ortho CH of BArf4-). 13C NMR (76 MHz,
t
t
CD2Cl2): δ 31.0 (CH3 of para Bu), 33.6 (CH3 of ortho Bu),
34.9 (quaternary of para tBu), 37.7 (quaternary of ortho tBu),
82.5 (Cp), 117.4 (para CH of BArf4-), 122.2 (meta CH of Mes*),
123.5 (q, JCF ) 273 Hz, CF3 of BArf4-), 128.7 (q, JCF ) 29
1
2
Hz, meta C of BArf4-), 134.8 (ortho CH of BArf4-), 151.2 (para
1
C of Mes*), 155.3 (ortho C of Mes*), 161.5 (q, JCB ) 49 Hz,
ipso C of BArf4-), 212.4 (CO), ipso carbon of Mes* not detected.
11B NMR (96 MHz, CD2Cl2): δ -7.6 (BArf4-). 19F NMR (283
MHz, CD2Cl2): δF -62.7 (CF3). IR (CD2Cl2): ν(CO) 2013, 1977,
1968 cm-1. MS (EI): m/z 1140.8 (5%) [M - Me]+, correct
isotope distribution for 2 Fe, 2 In, and 1 Br atoms, significant
fragment ions at m/z 1127.8 [M - 2CO]+, 650 (100%) [BArf3]+,
631 (80%) [BArf3 - F]+.
Reactions of (η5-C5R5)Fe(CO)2E(Mes*)X (1, R ) H, E )
Ga, X ) Cl; 2, R ) Me, E ) Ga, X ) Cl; 3, R ) H, E ) In,
X ) Br) with Na[BArf4]: Syntheses of [{(η5-C5R5)Fe-
(CO)2E(Mes*)}2(µ-X)][BArf4] (10, R ) H, E ) Ga, X ) Cl;
11, R ) Me, E ) Ga, X ) Cl; 12, R ) H, E ) In, X ) Br).
The three reactions were carried out in a similar manner,
exemplified for 1. To a suspension of Na[BArf4] (0.042 g, 0.047
mmol) in dichloromethane-d2 (1 mL) at -78 °C was added
dropwise a solution of CpFe(CO)2Ga(Mes*)Cl (1; 0.025 g, 0.047
mmol) in dichloromethane-d2 (5 mL), and the reaction mixture
was warmed to 20 °C over 30 min. At this point, the reaction
was judged to be complete by 1H NMR spectroscopy; filtration
and layering with hexanes led to the isolation of 10 as crystals
suitable for X-ray diffraction (yield: 0.021 g, 24%). 11 and 12
were isolated as pale yellow microcrystalline materials in
yields of 31 and 28%, respectively.
Reaction of 7 with [PPN]Cl: Synthesis of [Cp*Fe-
(CO)2]2GaCl (4). To a solution of [PPN]Cl (0.020 mg, 0.035
mmol) in dichloromethane-d2 (1 mL) was added a solution of
7 (0.050 g, 0.035 mmol) in dichloromethane-d2 (3 mL) at room
temperature. The reaction mixture was sonicated for 1 h, after
which time 1H NMR spectroscopy revealed complete conversion
to 4 (quantitative conversion by NMR). Further comparison
of multinuclear NMR and IR data (for the isolated compound)
with those obtained for an authentic sample of 4 confirmed
the identity of 4 as the sole organometallic product.7,8
Reaction of 8 with [nBu4N]I: Synthesis of [Cp*Fe-
(CO)2]2InI (6). To a solution of [nBu4N]I (0.010 g, 0.03 mmol)
in dichloromethane-d2 (1 mL) was added a solution of 8 (0.021
g, 0.01 mmol) in dichloromethane-d2 (2 mL) at room temper-
ature. The reaction mixture was sonicated for 1 h, after which
time 1H NMR spectroscopy revealed complete conversion to 6
(quantitative conversion by NMR). Further comparison of
multinuclear NMR and IR data (for the isolated compound)
with those obtained for an authentic sample confirmed the
identity of 6 as the sole organometallic product.8
1
Data for 10 are as follows. H NMR (300 MHz, CD2Cl2): δ
t
t
1.25 (s, 9H, para Bu), 1.46 (s, 18H, ortho Bu), 4.88 (s, Cp),
7.34 (s, 2H, aryl CH of Mes*), 7.55 (s, 4H, para CH of BArf4-),
7.71 (s, 8H, ortho CH of BArf4-). 13C NMR (76 MHz, CD2Cl2):
δ 30.9 (CH3 of para tBu), 34.0 (CH3 of ortho tBu), 34.7
(quaternary of para tBu), 38.2 (quaternary of ortho tBu), 83.5
(Cp), 117.4 (para CH of BArf4-), 119.4 (meta CH of Mes*), 122.9
(q, 1JCF ) 273 Hz, CF3 of BArf4-), 128.8 (q, 2JCF ) 31 Hz, meta
C of BArf4-), 134.9 (ortho CH of BArf4), 154.9 (para C of Mes*),
155.0 (ortho C of Mes*), 212.7 (CO), ipso carbons undetected.
11B NMR (96 MHz, CD2Cl2): δ -7.6 (BArf4-). 19F NMR (283
MHz, CD2Cl2): δ -62.7 (CF3). IR (CD2Cl2): ν(CO) 2016, 2002,
1972, 1954 cm-1. MS (EI): m/z 963.7 (5%) [M - 2CO]+, correct
isotope distribution for 2 Fe, 2Ga and 1 Cl atoms, significant
fragment ions at m/z 527.1 (5%) [CpFe(CO)2Ga(Mes*)Cl]+,
491.1 (20%) [CpFe(CO)2Ga(Mes*)]+.
Reactions of 7 and 8 with thf: Syntheses of [{Cp*Fe-
(CO)2}2{µ-E(thf)}][BArf4] (13, E ) Ga; 14, E ) In). The two
reactions were carried out in a similar manner, exemplified
for 7. To a solution of 7 in dichloromethane (12 mL), prepared
in situ from Na[BArf4] (0.059 g, 0.067 mmol) and [Cp*Fe-
(CO)2]2GaCl (4; 0.040 g, 0.067 mmol) at -78 °C, was added
thf (2 mL), and the reaction mixture warmed to 20 °C over 30
min. After the mixture was stirred for a further 1 h at 20 °C,
the reaction was judged to be complete by IR spectroscopy;
filtration and cooling to -30 °C led to the isolation of [{Cp*Fe-
(CO)2}2{µ-Ga(thf)}][BArf4] (13) as a pale yellow microcrystal-
line solid (yield: 0.035 g, 35%). 14 was isolated in a similar
manner as single crystals suitable for X-ray diffraction (0.030
g, 41%).
1
Data for 11 are as follows. H NMR (400 MHz, CD2Cl2): δ
1.25 (s, 18H, para tBu), 1.42 (s, 36H, ortho tBu), 1.76 (s, 30H,
Cp*), 7.30 (s, 4H, aryl CH of Mes*), 7.50 (s, 4H, para CH of
BArf4-), 7.66 (s, 8H, ortho CH of BArf4-). 13C NMR (76 MHz,
CD2Cl2): δ 10.0 (CH3 of Cp*), 30.9 (CH3 of para tBu), 33.9 (CH3
1
Data for 13 are as follows. H NMR (400 MHz, CD2Cl2): δ
1.80 (br m, 4H, CH2 of thf), 1.86 (s, 30H, Cp*), 3.65 (br m, 4H,
CH2 of thf), 7.48 (s, 4H, para CH of BArf4-), 7.65 (s, 8H, ortho
CH of BArf4-). 13C NMR (76 MHz, CD2Cl2): δ 10.2 (CH3 of Cp*),
25.5 (CH2 of thf), 69.0 (CH2 of thf), 97.4 (quaternary of Cp*),
(10) (a) Akita, M.; Terada, M.; Tanaka, M.; Morooka, Y. J. Orga-
nomet. Chem. 1996, 510, 255. (b) Odom, J. D.; Moore, T. F.; Goetze,
R.; No¨th, H.; Wrackmeyer, B. J. Organomet. Chem. 1979, 173, 15. (c)
Jacobsen, S. E.; Wojcicki, A. J. Am. Chem. Soc. 1973, 95, 6962.
1
117.6 (para CH of BArf4-), 122.8 (q, JCF ) 273 Hz, CF3 of
BArf4-), 129.1 (q, 2JCF ) 34 Hz, meta C of BArf4-), 134.9 (ortho

5894 Organometallics, Vol. 24, No. 24, 2005
Bunn et al.
Table 1. Details of Data Collection, Structure Solution, and Refinement for Compounds 8, 10, and 14
8
10
14
empirical formula
formula wt
temp (K)
C
56H42BF24Fe2InO4
C82H80BClF24Fe2Ga2O4
C60H50BF24Fe2InO5
1554.33
1472.23
150(2)
276094
0.71073
triclinic
P1h
1882.86
150(2)
276095
0.71073
triclinic
P1h
150(2)
CCDC deposit no.
wavelength (Å)
cryst syst
space group
unit cell dimens
a (Å)
276096
0.71073
orthorhombic
P212121
14.533(1)
14.644(1)
16.268(1)
65.829(3)
68.927(3)
74.823(3)
2920.5(4)
1.674
13.744(3)
14.521(3)
21.345(4)
99.44(3)
97.12(3)
95.59(3)
4139.6(14)
1.511
16.0540(3)
b (Å)
16.2940(3)
c (Å)
24.2520(6)
R (deg)
90
â (deg)
90
γ (deg)
90
V (Å3)
6343.9(2)
calcd density (Mg m-3
Z
)
1.617
2
2
4
abs coeff (mm-1
)
1.003
1.122
0.929
F(000)
1464
1912
3088
cryst size (mm3)
0.05 × 0.28 × 0.35
0.15 × 0.20 × 0.25
0.10 × 0.15 × 0.23
θ range (deg)
3.53-26.37
1.50-26.03
3.55-26.37
index ranges
h
-17 to +18
-16 to +16
-20 to +20
k
-16 to +18
-17 to +17
-20 to +20
l
-16 to +20
-26 to +26
-29 to +30
no. of rflns collected
no. of indep rflns
completeness to θmax (%)
abs cor
28 114
52 550
26 498
9917 (R(int) ) 0.1035)
86.9
15 346 (R(int) ) 0.0668)
94.0
12 739 (R(int) ) 0.0692)
99.5
semiempirical from equivs
0.952 and 0.720
Sortav
semiempirical from equivs
0.913 and 0.815
max and min transmissn
refinement method
0.879 and 0.780
full-matrix least squares (F2)
15346/18/1090
1.023
no. of data/restraints/params
9917/30/788
1.019
12739/150/857
1.023
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
R1 ) 0.0944, wR2 ) 0.1918
R1 ) 0.1812, wR2 ) 0.2314
1.828 and -1.026
R1 ) 0.0512, wR2 ) 0.1059
R1 ) 0.0807, wR2 ) 0.1175
0.723 and -0.557
R1 ) 0.0821, wR2 ) 0.1815
R1 ) 0.1226, wR2 ) 0.2068
1.154 and -1.007
largest diff. peak and hole (e Å-3
)
1
CH of BArf4-), 160.8 (q, JCB) 53 Hz, ipso C of BArf4-), 211.6
(CO). 11B NMR (96 MHz, CD2Cl2): δ -7.6 (BArf4-). 19F NMR
(283 MHz, CD2Cl2): δ - 62.8 (CF3). IR (CH2Cl2/thf): ν(CO)
1978, 1962, 1927 cm-1. MS: ES+, m/z 635.7 (weak) [M]+,
correct isotope distribution for 2Fe and 1 Ga atoms, significant
fragment ions at m/z 563 (45%) [M - thf]+, 535 (10%) [M -
thf - CO]+, 507 (5%) [M - thf - 2CO]+. Exact mass: calcd for
[M - thf]+ 563.0093, found 563.0095.
structure of which was communicated previously,7 the details
of each data collection, structure solution, and refinement can
be found in Table 1. Relevant bond lengths and angles are
included in the figure captions, and complete details of each
structure have been deposited with the CCDC (numbers as
listed in Table 1). In addition, complete details for each
structure (including CIF files) have been included in the
Supporting Information. The quality of the diffraction data for
compound 8 is less than optimal, although the final structure
(R1 ) 9.44%) is sufficient to corroborate the inferences made
on the basis of spectroscopic measurements and to confirm the
linear, two-coordinate geometry at indium.
The computational approaches utilized both for geometry
optimization processes and for the calculation of σ and π
contributions to bonding densities were as reported previously
for analogous investigations of transition-metal diyl and boryl
complexes.6,12
1
Data for 14 are as follows. H NMR (400 MHz, CD2Cl2): δ
1.69 (br m, 4H, CH2 of thf), 1.86 (s, 30H, Cp*), 3.63 (br m, 4H,
CH2 of thf), 7.48 (s, 4H, para CH of BArf4-), 7.64 (s, 8H, ortho
CH of BArf4-). 13C NMR (76 MHz, CD2Cl2): δ 10.5 (CH3 of Cp*),
27.3 (CH2 of thf), 59.1 (CH2 of thf), 96.5 (quaternary of Cp*),
117.4 (para CH of BArf4-), 124.6 (q, JCF ) 273 Hz, CF3 of
1
BArf4-), 128.9 (q, 2JCF ) 34 Hz, meta C of BArf4-), 134.8 (ortho
CH of BArf4-), ipso C of BArf4 and CO signals not observed.
-
IR (thf): ν(CO) 1974, 1958, 1922 cm-1. MS (EI): m/z 609.0
(75%) [M - thf]+, correct isotope distribution for 2 Fe and 1
In atoms. Exact mass: calcd for [M - thf]+ 608.9876, found
608.9874.
Results and Discussion
(iii) Crystallographic and Computational Methods.
Data for compounds 7, 8, 10, and 14 were collected on an
Enraf-Nonius Kappa CCD diffractometer; data collection and
cell refinement were carried out using DENZO and COLLECT
and structure solution and refinement using SIR-92, SHELXS-
97, and SHELXL-97; absorption corrections were performed
using SORTAV.11 With the exception of compound 7, the
(i) Synthetic and Reaction Chemistry of Cat-
ionic Derivatives. Halide abstraction chemistry has
been examined for a range of three-coordinate halogal-
lium and -indium substrates (Chart 2), with a view to
probing this route for the synthesis of cationic diyl and
metalladiyl complexes. The success of this methodology
in delivering tractable cationic derivatives containing
gallium or indium donors can readily be demonstrated
but is dependent both on the nature of the precursor
complex and on the halide abstraction agent. Thus,
Na[BArf4] reacts readily with the three-coordinate bridg-
(11) (a) Otwinowski, Z.; Minor, W. In Methods in Enzymology;
Carter, C. W., Sweet, R. M., Eds.; Academic Press: New York, 1996;
Vol. 276, p 307. (b) COLLECT: Data Collection Software; Nonius BV,
Delft, The Netherlands, 1999. (c) SIR-92: Altomare, A.; Cascarano,
G.; Giacovazzo, C.; Guagliardi, A. J. Appl. Crystallogr. 1993, 26, 343.
(d) Sheldrick, G. M. SHELX97: Programs for Crystal Structure
Analysis (Release 97-2); University of Go¨ttingen, Go¨ttingen, Germany,
1998. (e) SORTAV: Blessing, R. H. Acta Crystallogr. Sect. A 1995, 51,
33.
(12) Dickinson, A. A.; Willock, D. J.; Calder, R. J.; Aldridge, S.
Organometallics 2002, 21, 1146.

Two-Coordinate Ga and In Ligand Systems
Organometallics, Vol. 24, No. 24, 2005 5895
Chart 2 Precursor Systems for Halide Abstraction
Chemistry Examined in This Study
Scheme 3. Halide Abstraction from Asymmetric
(Supermesityl)halogallyl and -indyl Complexes:
Syntheses of Halide-Bridged Dinuclear Species
Scheme 2. Halide Abstraction Generating
Cationic Trimetallic Systems
(compared to [BArf4]-). Thus, here too the presence of
both BPh3 and Cp*Fe(CO)2Ph among the reaction
products is indicative of abstraction of a phenyl group
from the tetraphenylborate counterion.13 Similar reac-
tivity has been observed previously with highly elec-
trophilic group 13 complexes of iron.5 Consequently,
Na[BArf4] has generally been preferred for halide ab-
straction chemistry, with reactions employing sources
of the similarly weakly coordinating [CB11H6Br6]- anion
typically proceding at a significantly slower rate.
Similar abstraction methodology can be applied to the
(aryl)halogallyl and -indyl precursors 1-3. Given the
success of this approach in the synthesis of a cationic
aryl-substituted boranediyl complex featuring an iso-
lated FedB double bond,5 we were encouraged to
examine the corresponding reactivity of analogous gal-
lium and indium precursors. Complexes 1-3, containing
the extremely bulky supermesityl substituent, are
readily accessible either by direct reaction of [(η5-C5R5)-
Fe(CO)2]- with Mes*EX2 or (in the case of gallium) via
a two-step process involving insertion of “GaI” into a
M-X bond, followed by gallium-centered substitution
(e.g. by Li[Mes*]) in the intermediate dihalogallyl
[LnMGa(I)X]2.7,8
The reactions of Cp-substituted complexes 1 and 3
with Na[BArf]4 proceed in a very similar fashion.
Irrespective of reaction stoichiometry, time scale, or
order of reagent addition, reaction of 1 with Na[BArf4]
in dichloromethane yields the chloride-bridged dinuclear
species [{CpFe(CO)2Ga(Mes*)}2(µ-Cl)]+[BArf4]- (10;
Scheme 3). 10 presumably results from trapping of the
highly electrophilic first-formed intermediate species
[CpFe(CO)2Ga(Mes*)]+ by a second equivalent of the
chlorogallyl starting material 1. The formulation of 10
is implied by 1H NMR monitoring of the reaction in
dichloromethane-d2, which reveals a 2:1 ratio of Cp* and
[BArf4]- moieties. In addition, IR data shows the
expected shifts to higher wavenumber in the carbonyl
stretching bands (2016, 2002, 1972, 1954 vs 1999, 1952
cm-1 for 10 and 1, respectively), and the structure of
10 was subsequently confirmed crystallographically. In
a similar fashion, the reaction of the analogous bro-
moindyl complex CpFe(CO)2In(Mes*)Br (3) with Na-
[BArf4] generates [{CpFe(CO)2In(Mes*)}2(µ-Br)]+[BArf4]-
ing halogallane- and haloindanediyl complexes [Cp*Fe-
(CO)2]2EX (4, E ) Ga, X ) Cl; 5, E ) In, X ) Br; 6, E )
In, X ) I). In the cases of 4 and 5 this reaction proceeds
in dichloromethane over a period of ca. 2 h to give the
expected cationic complexes [{Cp*Fe(CO)2}2(µ-E)]+ (7,
E ) Ga; 8, E ) In) and sodium chloride/iodide (Scheme
2). The composition of the product in each case is
implied by 1H NMR and IR monitoring of the reaction,
the former being consistent with a 2:1 ratio of Cp* and
[BArf4]- components and the latter revealing the shifts
to higher wavenumber expected on formation of a
cationic complex (2016, 1994, 1963 vs 1960, 1925, 1910
cm-1 for 7 and 4, respectively; 2005, 1983, 1951 vs 1979,
1946, 1925 cm-1 for 8 and 5, respectively). In both cases,
the structures of 7 and 8 have been confirmed crystal-
lographically and are consistent with base-free cationic
two-coordinate group 13 systems (vide infra).
In the case of the reaction of the iodo-substituted
indanediyl precursor 6, an entirely different cationic
organometallic product is isolated. Whereas abstraction
chemistry with bromoindanediyl 5 proceeds as expected
(to give 8), the corresponding reaction with 6 leads to
the formation of [{Cp*Fe(CO)2}2(µ-I)]+[BArf4]- (9) in
15% isolated yield. 9 has been characterized by multi-
nuclear NMR, IR, and mass spectrometry (including
exact mass determination), and although the precise
mechanism for its formation is not clear, indium metal
is deposited during the reaction, and IR monitoring
reveals that Cp*Fe(CO)2I is an intermediate on the
overall reaction pathway. In addition to the nature of
the halide substituent, the identity of the abstraction
agent is also vital to the course of subsequent reaction
chemistry. Thus, the reaction of [Cp*Fe(CO)2]2GaCl (4)
with Na[BPh4] leads to the formation of Cp*Fe(CO)2Ph
and BPh3. Similarly, the course of the reaction of
[Cp*Fe(CO)2]2InI (6) with Na[BPh4] is also consistent
with the more reactive nature of the [BPh4]- anion
(13) Choukroun, R.; Douziech, B.; Pan, C.; Dahan, F.; Cassoux, P.
Organometallics 1995, 14, 4471.

5896 Organometallics, Vol. 24, No. 24, 2005
Bunn et al.
Scheme 5. Reversible Addition of
Scheme 4. Reaction of Cationic Trimetallic
Systems 7 and 8 with Sources of Halide Ions
Tetrahydrofuran to the Group 13 Center in 7 or 8
(12), which has been characterized by multinuclear
NMR, IR, and mass spectrometry and which, by analogy
with 10, would be expected to have an In-Br-In
bridged structure formed by trapping of the putative
[CpFe(CO)2In(Mes*)]+ by a further 1 equiv of 3.
X ) Cl; 6, E ) In, X ) I) in a fashion similar to the
boron-centered halide addition chemistry observed for
[Cp*Fe(CO)2B(Mes)]+. However, whereas the latter
compound is sufficiently Lewis acidic to abstract fluoride
from [BF4]- and generate Cp*Fe(CO)2B(Mes)F,5b the
gallium-centered cation 7, for example, is unreactive
toward sources of [BF4]- under similar conditions.
The reactivity of 7 and 8 toward neutral two-electron
donors is also reflective of moderate Lewis acid char-
acter. Thus, in the presence of tetrahydrofuran, both
cationic trimetallic species coordinate a single molecule
of thf to generate the 1:1 adducts [{Cp*Fe(CO)2}2{µ-
E(thf)}]+[BArf]- (13, E ) Ga; 14, E ) In; Scheme 5),
which can be isolated as pale yellow solids. In each case
the 1:1 stoichiometry is implied by integration of the
1H NMR signals due to thf and Cp* moieties, and
coordination of the oxygen donor at the group 13 center
is consistent with the significant shifts to lower wave-
number in the CO stretching bands (1978, 1962, 1927
and 2016, 1994, 1963 cm-1 for 13 and 7, respectively;
1974, 1958, 1922 and 2005, 1983, 1951 cm-1 for 14 and
8, respectively). Furthermore, in the case of 14, the
structure of the adduct has been confirmed crystallo-
graphically (vide infra).
The isolation of the Lewis base stabilized derivatives
13 and 14 contrasts markedly with the behavior of the
cationic boranediyl complex [Cp*Fe(CO)2B(Mes)]+, which
reacts rapidly in the presence of neutral two-electron
donors with rupture of the metal-group 13 linkage.5b
Interestingly, the coordination of the thf donor in 13 and
14 appears to be reversible. Thus, upon prolonged
exposure to continuous vacuum (10-4 Torr), spectro-
scopic data for both compounds are consistent with loss
of coordinated thf. Monitoring of this process by IR and
1H NMR spectroscopy reveals that, in the case of 13, a
mixture of the donor-stabilized complex and the “naked”
two-coordinate species 7 is obtained. In the case of 14
complete loss of thf is observed over a period of 6 h,
leading to the regeneration of [{Cp*Fe(CO)2}2(µ-In)]+-
[BArf4]- (8). Such behavior is consistent with a relatively
weak Lewis acid/base interaction in each case, with the
apparently greater ease of removal of the indium-bound
thf ligand being consistent with previous reports of the
Given the extremely facile trapping of the putative
diyl complexes [CpFe(CO)2E(Mes*)]+ implied by the
formation of 10 and 12, a potential route to tractable
mononuclear cationic systems involves the use of more
sterically bulky and/or more electron releasing substit-
uents at the metal center. The reactivity of Cp*Fe-
(CO)2Ga(Mes*)Cl (2) toward Na[BArf4] was therefore
investigated. Despite the increased steric requirements
of the Cp* ligand, however, the product isolated from
this reaction (under a range of different conditions) is
the analogous dinuclear compound [{Cp*Fe(CO)2Ga-
(Mes*)}2(µ-Cl)]+[BArf4]- (11). 11 has been characterized
by multinuclear NMR, IR, and mass spectrometry, with
the similarity in the pattern of carbonyl stretches
compared to that of 10 (1996, 1986, 1954, 1932 vs 2016,
2002, 1972, 1954 cm-1 for 11 and 10, respectively) and
the 2:1 integrated ratio of the Cp* and [BArf4]- signals
in the 1H NMR spectrum providing compelling evidence
for a chloride-bridged structure analogous to 10.
The fundamental reactivity of group 13 diyl and
related complexes remains an area which has received
relatively little attention,3f,g despite obvious parallels
with carbenes, silylenes, and their heavier homo-
logues,14 and the range of interesting and useful reac-
tivity in which these group 14 systems have been
implicated. Initial studies of the reactivity of the
prototype cationic boranediyl system [Cp*Fe(CO)2B-
(Mes)]+ imply dominant electrophilic character, with
anionic and/or neutral nucleophiles displaying a mixture
of boron- and iron-centered reactivity.5 A preliminary
survey of the reactivities of two-coordinate metalladiyls
7 and 8 toward neutral and anionic two-electron donors
implies that the group 13 center in each is somewhat
less electrophilic than that in [Cp*Fe(CO)2B(Mes)]+.
Both 7 and 8 react rapidly with sources of halide ions
in dichloromethane solution (Scheme 4) to generate the
(structurally characterized) bridging halogallane- and
haloindanediyl complexes [Cp*Fe(CO)2]2EX (4, E ) Ga,
(14) See, for example: (a) Nugent, W. A.; Mayer, J. M. Metal Ligand
Multiple Bonds; Wiley-Interscience: New York, 1988. (b) Glaser, P.
B.; Wanandi, P. W.; Tilley, T. D. Organometallics 2004, 23, 693 and
references therein. For a review of related germylene and stannylene
chemistry, see: (c) Petz, W. Chem. Rev. 1986, 86, 1019.

Two-Coordinate Ga and In Ligand Systems
Organometallics, Vol. 24, No. 24, 2005 5897
near-linear coordination geometry at the group 13
center (176.01(4)°),17 in marked contrast to the bent
frameworks typically found for base-stabilized ana-
logues such as [{CpFe(CO)2}2{µ-Ga(bipy)}]+ and [Cp*Fe-
(CO)2]{µ-Ga(bipy)}[Fe(CO)4] (132.81(5) and 136.68(2)°,
respectively).17,21
Of significant interest are the Fe-E bond lengths for
7 and 8 (2.266(1), 2.272(1) and 2.460(2), 2.469(2) Å,
respectively). These can be compared to the analogous
bond lengths found for the bridging halogallane- and
haloindanediyl precursors [Cp*Fe(CO)2]2EX (2.352(1)
and 2.513(3), 2.509(3) Å for 4 (E ) Ga, X ) Cl) and 5 (E
) In, X ) Br), respectively7,8) and for three- or four-
coordinate base-stabilized cationic systems (e.g. 2.397(2),
2.404(1) and 2.494(2), 2.498(2) Å for [{CpFe(CO)2}2{µ-
Ga(bipy)}]+ and [{Cp*Fe(CO)2}2{µ-In(thf)}]+, respec-
tively (vide infra)).21 In the case of gallium compound
7, the shortening with respect to the single bonds found
in 4 (ca. 3.5%) places the Fe-Ga distance in the region
of values previously reported for two-coordinate gallium-
containing systems.4,17 Thus, the Fe-Ga bond lengths
reported for [Cp*Fe(dppe)](µ-Ga)[Fe(CO)4] are 2.248(1)
and 2.293(1) Å,17 with the former distance (for the
Cp*Fe(dppe)Ga unit) being described as indicative of
“significantly unsaturated character”. Clearly the Fe-
Ga bond shortening observed on halide abstraction from
4 (to give 7) is consistent with both steric and electronic
factors: i.e., with a reduction in the coordination number
at gallium and/or with an increase in the extent of
FefGa back-bonding. The extent of bond shortening
accompanying the halide abstraction process is signifi-
cantly less in the case of indium complex 8 (<2% with
respect to 6). This observation is also consistent with
both underlying steric and electronic factors: i.e., both
the extent of FefE back-bonding and the relief of steric
strain are likely to be less pronounced in the case of 8,
due to the longer Fe-E linkages. A further point of
interest concerning the structures of cations 7 and 8 is
the relative alignment of the two [Cp*Fe(CO)2] frag-
ments. In each case the Cp* centroid-Fe(1)-Fe(2)-Cp*
centroid torsion angle is close to 90° (e.g. 84.6(1)° for
7). Given the presence of two formally vacant mutually
perpendicular p orbitals at the group 13 center, such
an alignment allows in principle for optimal π back-
bonding from the HOMO of each of the two [Cp*Fe-
(CO)2]+ fragments.22
Figure 1. Structure of the cationic component of [{Cp*Fe-
(CO)2}2(µ-In)]+[BArf4]- (8). Hydrogen atoms have been
omitted for clarity and ORTEP ellipsoids set at the 50%
probability level. Important bond lengths (Å) and angles
(deg): Fe(1)-In(1) ) 2.460(2), Fe(2)-In(1) ) 2.469(2),
Fe(1)-Cp* centroid ) 1.725(10), Fe(1)-C(1) ) 1.757(13);
Fe(1)-In(1)-Fe(2) ) 175.32(6), Cp* centroid-Fe(1)-Fe(2)-
Cp* centroid ) 86.8(3).
thermodynamics of oxygen donor coordination to gal-
lium- and indium-based Lewis acids.15
(ii) Spectroscopic, Structural and Computa-
tional Studies. Single-crystal X-ray diffraction studies
were undertaken on compounds 7, 8, 10, and 14. With
the exception of compound 7, the structure of which has
been communicated previously,7 details of the data
collection, structure solution, and refinement param-
eters for each compound are given in Table 1; relevant
bond lengths and angles are included in the figure
captions. Complete details of all structures are given
in the Supporting Information and have been deposited
with the Cambridge Structural Database.
Compounds 7 and 8 (Figure 1 and Table 1) represent
extremely rare examples of structurally characterized
species containing two-coordinate cationic gallium or
indium centers. Previously reported examples typically
feature extremely bulky hydrocarbyl substituents (e.g.
[Ar2Ga]+),16 and 7 and 8 represent the first examples
containing metal-group 13 element bonds. In each case
the geometry of the cationic component features a linear
trimetallic unit (e.g. Fe(1)-Ga(1)-Fe(2) ) 178.99(2)°
for 7) in which the central group 13 atom engages in no
significant intra- or intermolecular secondary interac-
tions, for example with the [BArf4]- anion. To our
knowledge, the only other example of an isolated transi-
tion-metal complex featuring a “naked” bridging gallium
or indium center is the neutral species [Cp*Fe(dppe)]-
(µ-Ga)[Fe(CO)4], reported by Ueno and co-workers in
2003.17-20 Like 7 and 8, this complex also features a
Of significant interest from a comparative viewpoint
are the metalloheterocumulene complexes of the type
[(η5-C5R5)Mn(CO)2]2(µ-E) (E ) Ge, Sn), reported by a
number of groups, including those of Hu¨ttner and
Herrman.23 Indeed, the Ge and Sn compounds of this
type, which have been described as featuring MndE
double bonds, are formally isoelectronic with the cationic
components of 7 and 8, respectively. Furthermore, the
structural parameters for the crystallographically char-
acterized species [Cp*Mn(CO)2]2(µ-Ge) are remarkably
(15) See, for example: (a) Tuck, D. G. In Chemistry of Aluminium,
Gallium, Indium and Thallium; Downs, A. J., Ed.; Blackie Academic
and Professional: London, 1993; Chapter 8. (b) Greenwood, N. N.;
Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, U.K.,
1984; Chapter 7.
(16) (a) Hausen, H. D.; Mertz, K.; Weidlein, J.; Schwarz, W. J.
Organomet. Chem. 1975, 93, 291. (b) Gahlmann, F.; Neumuller, B. Z.
Anorg. Allg. Chem. 1994, 620, 847. (c) Wehmschulte, R. J.; Steele, J.
M.; Young, J. D.; Khan, M. A. J. Am. Chem. Soc. 2003, 125, 1470.
(17) Ueno, K.; Watanabe, T.; Tobita, H.; Ogino, H. Organometallics
2003, 22, 4375.
(20) For cationic compounds containing two-coordinate thallium see,
for example: (a) Balch, A. L.; Nagle, J. K.; Olmstead, M. M.; Reedy,
P. E. J. Am. Chem. Soc. 1987, 109, 4123. (b) Jeffery, J. C.; Jelliss, P.
A.; Liao, Y.-H.; Stone, F. G. A. J. Organomet. Chem. 1998, 551, 27. (c)
Catalano, V. J.; Bennett, B. L.; Kar, H. M.; Noll, B. C. J. Am. Chem.
Soc. 1999, 121, 10235. (d) Catalano, V. J.; Bennett, B. L.; Yson, R. L.;
Noll, B. C. J. Am. Chem. Soc. 2000, 122, 10056.
(18) For an example of a metal cluster containing near linear
M-Ga-M units, see: Scheer, M.; Kaupp, M.; Virovets, A. V.; Konchen-
ko, S. N. Angew. Chem., Int. Ed. 2003, 42, 5083.
(21) Ueno, K, Watanabe, T, Ogino, H. Organometallics 2000, 19,
5679.
(19) For a related boron-containing system, see: Braunschweig, H.;
Radacki, K.; Scheschkewitz, D.; Whittell, G. R. Angew. Chem., Int. Ed.
2005, 44, 1658.
(22) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. J. Am.
Chem. Soc. 1979, 101, 585.

5898 Organometallics, Vol. 24, No. 24, 2005
Bunn et al.
) 1.78 kcal mol-1 between rotamers, corresponding to
torsion angles of 161.8 and 82.4°). σ and π contributions
to the overall Fe-In bonding density have therefore
been calculated for both of these conformations.
Table 2. Calculated and Crystallographically
Determined Structural Parameters for the
Cationic Components of
[{Cp*Fe(CO)2}2(µ-E)]+[BArf4]- (7, E ) Ga; 8, E ) In)
A bond population analysis for [{Cp*Fe(CO)2}2Ga]+
carried out using a widely precedented method reveals
a 61:38 σ:π breakdown of the covalent Fe-Ga interac-
tion,6,12 which can be put in context by comparison with
a ratio of 86:14 for the formal Fe-Ga single bond in the
model compound CpFe(CO)2GaCl2.6,25 Using the same
approach, corresponding values of 62:38 have been
calculated for the iron to boron linkage in [Cp*Fe(CO)2-
(BMes)]+. Further evidence for a significant Fe-Ga π
component in [{Cp*Fe(CO)2}2Ga]+ is provided by the
orbitals HOMO-3 to HOMO-6, each of which features
in-phase contributions from gallium- and iron-centered
π symmetry orbitals (Ga 4px and 4py; Fe 3dxz and 3dyz).
Similar analyses for the indium-centered cation [{Cp*Fe-
(CO)2}2In]+ are consistent with a significantly smaller
π contribution to the metal-group 13 element bond.
Thus, the σ:π breakdown in this case is 74:26 (for both
conformations corresponding to torsion angles of 82.4
and 161.8°); these values can be compared to an 11%
calculated π contribution for the formal Fe-In single
bond in the model compound CpFe(CO)2InCl2.25 The
significantly smaller π contribution for E ) In than for
E ) Ga is as expected on the well-precedented basis of
diminished π orbital overlap for the heavier main-group
elements.26 In addition, although the barrier to rotation
about the Fe-In-Fe axis is not a direct measure of π
bond strength (rather the difference in π contributions
between 0 and 90° orientations), the relatively flat
potential function for rotation about his bond is consis-
tent with the similar (and relatively low) π contributions
calculated for both conformations.
Fe-E-Fe Ct-Fe-Fe-Ct σ:π
Erel
angle
(deg)
torsion
break- (kcal
a
compd Fe-E dist (Å)
angle (deg)
down mol-1
)
7 (exptl) 2.266(1),
178.99(2)
84.6(1)
2.272(1)
7 (calcd) 2.338, 2.337 177.93
86.5
86.8(3)
61:38
74:26
0
0
8 (exptl) 2.460(2),
175.32(6)
2.469(2)
8 (calcd) 2.463,2.463 179.40
8 (calcd) 2.469, 2.469 179.87
161.8
82.8
74:26 +1.78
a Calculated energy relative to minimum energy conformation.
similar to those for 7 (d(Mn-Ge) ) 2.18(2) Å; Mn-
Ge-Mn ) 179(1)°; centroid-Mn-Mn-centroid torsion
angle 83(3)°).23b
In an attempt to determine whether these structural
observations (i.e. the shortening in Fe-E bond lengths
on halide abstraction, the orthogonal alignment of
[Cp*Fe(CO)2]+ fragments, and the close relationship of
the structures of [Cp*Mn(CO)2]2(µ-Ge) and 7) are related
to any Fe-E multiple-bond character, and to relate any
trends in bonding to the nature of the group 13 element
E, DFT analyses were carried out on compounds 7 and
8 using methods described previously.6,12
DFT calculations were carried out at the BLYP/TZP
level, and salient parameters relating to the fully
optimized geometries of [{Cp*Fe(CO)2}2E]+ (E ) Ga, In)
are detailed in Table 2. In the case of [{Cp*Fe-
(CO)2}2Ga]+, the agreement between calculated and
experimentally derived geometric parameters is very
good, with the near-linear Fe-Ga-Fe trimetallic frame-
work and near-orthogonal alignment of the [Cp*Fe-
(CO)2] fragments being accurately reproduced compu-
tationally. The 2-3% overestimate in the calculated
Fe-Ga bond lengths mirrors that found for related diyl
systems and has been ascribed to solid-state effects,
leading to the shortening of donor/acceptor bonds ac-
companied by a general overestimate in bond lengths
by generalized gradient approximation (GGA) meth-
ods.6,12,24 In the case of [{Cp*Fe(CO)2}2In]+, the mini-
mum energy conformation calculated by DFT corre-
sponds to a centroid-Fe-Fe-centroid torsion angle of
161.8°, in contrast to the experimentally determined
value of 86.3(3)°. Closer inspection, however, reveals
that there is a very shallow potential energy surface for
rotation about this axis (see the Supporting Information
for a complete rotational profile) and that the energy
difference between the minimum energy conformer and
that corresponding to the approximately orthogonal
alignment found in the solid state is very small (e.g. ∆E
An X-ray diffraction study has also been carried out
on the thf-stabilized complex [{Cp*Fe(CO)2}2{µ-In-
(thf)}]+[BArf4]- (14), with the results being displayed
in Figure 2 and Table 1. This is consistent with the 1:1
stoichiometry and indium-coordinated thf donor implied
by spectroscopic data. The indium center is trigonal
planar (sum of angles at indium 360.0(3)°), and the
approximately orthogonal alignment of Fe2In and OC2
planes (torsion Fe(1)-In(1)-O(5)-C(57) ) 80.0(4)°) is
presumably enforced on steric grounds. As expected,
given the relatively small π component determined for
the Fe-In bonds in base-free 8, there is only a relatively
minor lengthening of these linkages on coordination of
the thf molecule (2.498(2), 2.494(2) vs 2.460(2), 2.469(2)
Å for 14 and 8, respectively). 14 represents only the
second structurally characterized cationic three-coordi-
nate indium species and the first containing bonds to a
transition metal,27 although related N-donor-stabilized
gallium complexes of the type [(LnM)2GaD2]+ have
previously been reported.21,28 The Fe-In-Fe angle
(156.72(6)°) is somewhat wider than that found in
[{CpFe(CO)2}2{µ-Ga(bipy)}]+, presumably reflecting not
only the longer Fe-E bonds for E ) In but also the lower
coordination number at the group 13 center in 14 (i.e.
(23) For examples of metalloheterocumulene complexes of the type
LnMdEdMLn (E ) Ge, Sn), see: (a) Ga¨de, W.; Weiss, E. J. Organomet.
Chem. 1981, 213, 451. (b) Korp, J. D.; Bernai, I.; Horlein, R.; Serrano,
R.; Herrmann, W. A. Chem. Ber. 1985, 118, 340. (c) Herrman, W. A.;
Kneuper, H. J.; Herdtweck, E. Chem. Ber. 1989, 122, 437. (d) Ettel,
F.; Hu¨ttner, G.; Imhof, W. J. Organomet. Chem. 1990, 397, 299. (e)
Ettel, F.; Hu¨ttner, G.; Zsolnai, L.; Emmerich, C. J. Organomet. Chem.
1991, 414, 71.
(24) See, for example: (a) McCullough, E. A., Jr.; Apra`, E.; Nichols,
J. J. Phys. Chem. A 1997, 101, 2502. (b) MacDonald, C. A. B.; Cowley,
A. H. J. Am. Chem. Soc. 1999, 121, 12113. (c) Uddin, J.; Boehme, C.;
Frenking, G. Organometallics 2000, 19, 571. (d) Giju, K. T.; Bickel-
haupt, M.; Frenking, G. Inorg. Chem. 2000, 39, 4776. (e) Uddin, J.
Frenking, G. J. Am. Chem. Soc. 2001, 123, 1683.
(25) Dickinson, A. A. Ph.D. Thesis, Cardiff University, 2003.
(26) See, for example, Massey, A. G. Main Group Chemistry;
Wiley: London, 2000; pp 51-59.
(27) Delpech, F.; Guzei, I. A.; Jordan, R. F. Organometallics 2002,
21, 1167.
(28) Ueno, K.; Watanabe, T.; Ogino, H. Appl. Organomet. Chem.
2003, 17, 403.

Two-Coordinate Ga and In Ligand Systems
Organometallics, Vol. 24, No. 24, 2005 5899
Figure 3. Structure of the cationic component of [{CpFe-
(CO)2Ga(Mes*)}2(µ-Cl)]+[BArf4]- (10). Hydrogen atoms and
tBu methyl groups have been omitted for clarity and
ORTEP ellipsoids set at the 50% probability level. Impor-
tant bond lengths (Å) and angles (deg): Fe(1)-Ga(1) )
2.333(1), Fe(2)-Ga(2) ) 2.328(1), Fe(1)-Cp* centroid )
1.724(4), Fe(1)-C(1) ) 1.755(4), Ga(1)-Cl(1) ) 2.552(1),
Ga(2)-Cl(1) ) 2.476(1); Fe(1)-Ga(1)-C(8) ) 149.07(8),
Fe(2)-Ga(2)-C(33) ) 150.50(9), Ga(1)-Cl(1)-Ga(2) )
142.16(3).
Figure 2. Structure of the cationic component of [{Cp*Fe-
(CO)2}2{µ-In(thf)}]+[BArf4]- (14). Hydrogen atoms have
been omitted for clarity and ORTEP ellipsoids set at the
50% probability level. Important bond lengths (Å) and
angles (deg): Fe(1)-In(1) ) 2.498(2), Fe(2)-In(1) ) 2.494(2),
Fe(1)-Cp* centroid ) 1.729(12), Fe(1)-C(23) ) 1.748(13);
Fe(1)-In(1)-Fe(2) ) 156.72(6), Fe(1)-In(1)-O(5) ) 100.1(3),
Fe(2)-In(1)-O(5) ) 103.2(3), Fe(1)-In(1)-O(5)-C(57) )
80.0(4).
3 vs 4).21 Furthermore, this angle is significantly wider
than that found in the charge-neutral bridging haloin-
danediyl complexes [Cp*Fe(CO)2]2InX (141.46(1), 141.98-
(2)° for 5 (E ) Br) and 6 (E ) I), respectively), despite
the greater steric demands of thf (cf. Br- or I-).7,8 This
phenomenon has previously been observed for a range
of group 13 adducts. Thus, for example, the Cl-Ga-Cl
angles in GaCl3‚thf (113.07° (mean)) are significantly
wider than those in the corresponding Cl- adduct
(109.5° (mean)).29
An X-ray diffraction study has also confirmed the
chloride-bridged structure of [{CpFe(CO)2Ga(Mes*)}2-
(µ-Cl)]+[BArf4]- (10; see Figure 3 and Table 1). The
synthesis of 10 is viewed as being due to the trapping
of the putative cationic gallanediyl [CpFe(CO)2Ga-
(Mes*)]+ by a second equivalent of the precursor CpFe-
(CO)2Ga(Mes*)Cl (1). Thus, the structure of 10 can be
viewed as a base-stabilized gallanediyl complex, in
which the gallium-coordinated donor is the bridging
chloride ligand. In common with other base-stabilized
diyl complexes, the metal-group 13 distance is more
akin to that expected for related single bonds rather
than for unsaturated species (e.g. 2.333(1), 2,328(1) and
2.346(1) Å for 10 and 1, respectively).7,8 By comparison,
an Fe-Ga distance of 2.416(3) Å has been reported by
Fischer and co-workers for base-stabilized (OC)4FeGaMe-
(tmpa) (tmpa ) Me2NCH2CH2CH2NMe2), compared
with 2.225(1) Å for two-coordinate (OC)4FeGaAr (Ar )
2,6-(2,4,6-iPr3C6H2)2C6H3).4,30 In contrast, the structural
effects of the abstraction and Ga-Cl-Ga bridge forma-
tion processes are much more pronounced on the Ga-
Cl bonds and on the Fe-Ga-Cipso angles. Thus, the
bridging nature of the remaining chloride substituent
is reflected in markedly longer Ga-Cl bond lengths
(2.476(1), 2.552(1) and 2.272(1) Å for 10 and 1, respec-
tively), which in turn allows for significant opening out
of the Fe-Ga-Cipso angle (149.07(8), 150.50(9) and
139.18(10)° for 10 and 1, respectively).
Conclusions
Halide abstraction chemistry has been demonstrated
to offer a viable synthetic route to cationic two-
coordinate complexes featuring the heavier group 13
elements gallium and indium as donor atoms. Thus, the
linear trimetallic species [{Cp*Fe(CO)2}2(µ-E)]+ (7, E )
Ga; 8, E ) In) featuring naked bridging gallium or
indium atoms can be synthesized by the reaction of the
corresponding chloro- or bromo-substituted bridging diyl
complexes with Na[BArf]4. Analogous reactions utilizing
the supermesityl-substituted gallyl or indyl precursors
of the type (η5-C5R5)Fe(CO)2E(Mes*)X, on the other
hand, lead to the synthesis of halide-bridged species of
the type [{(η5-C5R5)Fe(CO)2E(Mes*)}2(µ-X)]+, presum-
ably by trapping of the highly electrophilic putative
cationic diyl complex [(η5-C5R5)Fe(CO)2E(Mes*)]+. Ongo-
ing further attempts to modify these systems, e.g. by
the introduction of bulky, strongly σ-basic phosphine
ligands at the group 8 metal center, are aimed at the
isolation of such cationic gallane- and indanediyl sys-
tems.
Preliminary studies have shown complexes 7 and 8
to be reactive toward both anionic and neutral nucleo-
philes, although the reversible coordination of thf is
indicative of surprisingly weak Lewis acidic behavior.
Structural, spectroscopic, and computational studies
performed for 7 are consistent with appreciable Fe-Ga
π-bonding character, as proposed for the only other
previously reported example of a trimetallic system
featuring a naked bridging gallium atom. The analogous
(29) (a) Schmidbaur, H.; Thewalt, U.; Zafiropoulous, T. Organome-
tallics 1983, 2, 1550. (b) Scholz, S.; Lerner, H.-W.; Bolte M. Acta
Crystallogr., Sect. E 2002, 58, m586.
(30) Fo¨lsing, H.; Segnitz, O.; Bossek, U.; Merz, K.; Winter, M.;
Fischer, R. A. J. Organomet. Chem. 2000, 606, 132.

5900 Organometallics, Vol. 24, No. 24, 2005
Bunn et al.
Supporting Information Available: Complete details of
the crystal structures of compounds 7, 8, 10, and 14, details
of the DFT derived (fully optimized) geometries of the cations
[{Cp*Fe(CO)2}2E]+ (E ) Ga, In), and NMR spectra for all
compounds (as evidence for bulk purity). This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystal data for 7, 8, 10, and 14 have also been deposited with
the Cambridge Structural Database.
indium-bridged complex 8, in contrast, is shown both
by structural and quantum chemistry methods to fea-
ture a much smaller π component to the metal-ligand
interaction.
Acknowledgment. We acknowledge the support of
the EPSRC for funding this project and the EPSRC
National Mass Spectrometry Service Centre, University
of Wales, Swansea, Wales.
OM0506318