Diorganogallium β-diketonates and their lewis acid-base adducts. Crystal and molecular structures of Mes2Ga(hfac) and Me2Ga(hfac)·NC5H5

Article abstract of DOI:10.1021/om970988e

Compounds of the type R₂Ga(bdk) (R = Me, Et, Mes (mesityl); bdk = 2,4-pentanedionato (acac), 1,1,1-trifluoro-2,4-pentanedionato (tfac), 1,1,1,5,5,5-hexafluoro-2,4-penatedionato (hfac), 2,2,6,6-tetramethyl-3,5-heptanedionato (tmhd)) have been pr

Full text of DOI:10.1021/om970988e

Organometallics 1998, 17, 1101-1108
1101
Dior ga n oga lliu m â-Dik eton a tes a n d Th eir Lew is
Acid -Ba se Ad d u cts. Cr ysta l a n d Molecu la r Str u ctu r es
of Mes2Ga (h fa c) a n d Me2Ga (h fa c)‚NC5H5
O. T. Beachley, J r.,* J ames R. Gardinier, Melvyn Rowen Churchill,* and
Laurence M. Toomey
Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14260
Received November 12, 1997
Compounds of the type R2Ga(bdk) (R ) Me, Et, Mes (mesityl); bdk ) 2,4-pentanedionato
(acac), 1,1,1-trifluoro-2,4-pentanedionato (tfac), 1,1,1,5,5,5-hexafluoro-2,4-penatedionato
(hfac), 2,2,6,6-tetramethyl-3,5-heptanedionato (tmhd)) have been prepared by multiple routes,
including hydrocarbon elimination, metathesis, and ligand redistribution reactions, and fully
characterized by elemental analyses, cryoscopic molecular weight studies in benzene, and
IR and multinuclear NMR spectroscopic studies. An X-ray structural study of Mes2Ga-
(hfac) demonstrated four-coordinate gallium with σ bonds to the two mesityl rings and to
the two oxygen atoms of the â-diketonate ligand. The Lewis acidities of the diorganogallium
â-diketonate derivatives toward NMe3 and/or pyridine were also investigated. Two adducts,
Me2Ga(hfac)‚NMe and Me2Ga(hfac)‚py, were stable to dissociation at room temperature and
thus were fully characterized by elemental analysis, cryoscopic molecular weight studies in
benzene, vapor pressure-temperature studies, and IR and multinuclear NMR (including
variable temperature) spectroscopic studies. The compound Me2Ga(hfac)‚py was also
characterized by an X-ray structural study. The structure involved five-coordinate gallium
with one Ga-N, two (inequivalent) Ga-O, and two Ga-C bonds.
The incorporation of ligands with potential for the
intramolecular stabilization of group 13 compounds in
order to reduce their reactivity toward nucleophilic
reagents and ligand redistribution reactions is of current
interest.1 Therefore, an investigation of the chemistry
of organogallium compounds with â-diketonate ligands
which are uninegative, symmetrical and potentially
bidentate was initiated. Even though an extensive
literature exists on the chemistry of diorganoaluminum2
and diorganoindium3 â-diketonate derivatives, the cor-
responding gallium compounds have been little ex-
plored. Coates and Hayter4 reported in 1953 the
preparation of the first diorganogallium â-diketonate
derivative Me2Ga(acac) by a direct reaction between
trimethylgallium and acetylacetone, while the second
example, Et2Ga(acac),5 was not described until 1991.
Sato, Yamada, and Sugiura5 noted the increased air and
pyrolytic stability of Et2Ga(acac) as compared to tri-
ethylgallium. As the first part of our investigation into
the nature of gallium â-diketonate compounds, we
report on the preparation of a series of diorganogallium
â-diketonates by multiple types of reactions. These
compounds were used then to investigate the effects of
the â-diketonate ligand and of the organic groups bound
to gallium on their physical and chemical properties,
including Lewis acidity.
The twelve diorganogallium â-diketonate compounds
R2Ga(bdk) (R ) Me, Et, Mes; bdk ) hfac, tfac, acac,
tmhd) have been prepared in high yield by one or more
of three different types of synthetic reactions: elimina-
tion reactions, metathesis reactions and ligand redis-
tribution reactions. The elimination reaction (eq 1) was
GaR3 + H(bdk) f R2Ga(bdk) + RH
R2GaCl + Na(bdk) f R2Ga(bdk) + NaCl
2GaR3 + Ga(bdk)3 f 3R2Ga(bdk)
(1)
(2)
(3)
(1) (a) Fischer, R. A.; Mierh, A.; Ambacher, O.; Metzger, T.; Born,
E. J . Cryst. Growth 1997, 170, 139 and references therein. (b) J utzi,
P.; Dahlhaus, J .; Neumann, B.; Stammler, H.-G. Organometallics 1996,
15, 747. (c) Cowley, A. H.; King, C. S.; Decken, A. Organometallics
1995, 14, 20. (d) Schumann, H.; Hatrmann, U.; Wassermann, W.
Polyhedron 1990 9, 353.
(2) (a) Pasynkiewicz, S.; Dowbor, K. J . Organomet. Chem. 1972, 43,
75. (b) Kroll, W. R.; Kuntz, I.; Birnbaum, E. J . Organomet. Chem. 1971,
26, 313. (c) Kroll, W. R.; Naegele, W. J . Organomet. Chem. 1969, 19,
439. (d) Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1965, 4, 954. (e)
Lewinski, L. J .; Zachara, J .; J ustyniak, I. Organometallics 1997, 16,
4597.
(3) (a) Habeeb, J . J .; Tuck, D. G. J . Organomet. Chem. 1975, 101,
1. (b) Chung, H. L.; Tuck, D. G. Can. J . Chem. 1974, 52, 3944 and
references therein. (c) Clark, H. C.; Pickard, A. L. J . Organomet. Chem.
1967, 8, 427. (d) Coates, G. E.; Whitcombe, R. A. J . Chem. Soc. 1956,
3351.
the most desirable because nearly quantitative yields
of easily separable products were obtained in one
synthetic step from the readily available reagents.
Metathesis reactions (eq 2) were also used to synthesize
pure products in high yields. However, this reaction in
comparison with the elimination reaction suffers the
disadvantage that additional synthetic steps are re-
quired for the preparation of the reagents. A stoichio-
metric ligand redistribution reaction (eq 3) is the least
desirable. This method suffers the same type of disad-
(4) Coates, G. E.; Hayter, R. G. J . Chem. Soc. 1953, 2519.
(5) Sato, H.; Yamada, T.; Sugiura, H. J . Cryst. Growth 1991, 115,
241.
S0276-7333(97)00988-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 02/20/1998

1102 Organometallics, Vol. 17, No. 6, 1998
Beachley et al.
1.954(5) Å). The two bulky mesityl ligands are sepa-
rated by the expanded angle of C(11)-Ga(1)-C(21) )
131.5(8)° and are associated with the gallium-carbon
bond lengths Ga(1)-C(11) ) 1.971(13) Å and Ga(1)-
C(21) ) 1.943(10) Å (average 1.957 Å), a distance
comparable to that in GaMes3 (1.968(4) Å).7 Distances
within the metallacyclic ring are symmetrical, with
O(1)-C(2) ) 1.245(20) Å versus O(5)-C(4) ) 1.252(21)
Å and C(2)-C(3) ) 1.392(24) Å versus C(3)-C(4) )
1.422(23) Å. The C-CF3 bonds have values consistent
with their C(sp2)-C(sp3) nature (C(1)-C(2) ) 1.49(3) Å
and C(4)-C(5) ) 1.42(3) Å). The structure is marred
by extremely large “thermal vibration ellipsoids” for the
fluorine atoms. These large ellipsoids are consistent
with large librational motion or hindered rotation of the
CF3 groups about their C-CF3 bonds and give rise to
some artificially contracted C-F bond lengths (C-F )
1.18(3) - 1.30(3) Å as compared to the normal C(sp3)-F
distance of 1.333 ( 0.005 Å in polyfluorinated systems8).
Similar effects have been observed previously for mol-
ecules such as (η5-C5H5)Rh[η4-C6(CF3)6].9-11
F igu r e 1. Molecular geometry of Mes2Ga(hfac) (ORTEP2
diagram, 30% probability envelopes for thermal vibration
ellipsoids, with hydrogen atoms artificially reduced).
The physical and spectroscopic properties of all 12
diorganogallium â-diketonate compounds are consistent
with the presence of the bidentate ligand and four-
coordinate gallium. Cryoscopic molecular weight stud-
ies demonstrate the compounds to be monomeric in
benzene solution. The compounds are typically liquids
and can be distilled or sublimed quantitatively under
reduced pressure (10-4 mmHg) without decomposition
at about room temperature. The volatility was observed
to increase as the extent of fluorine sustitution on the
â-diketonate ligand increased. This same trend has
been observed for M(bdk)3 (M ) Al, Ga, In)12 and for
other metallic systems.13 None of the current com-
pounds are pyrophoric. The CdO stretching vibra-
tions14 for R2Ga(bdk) were observed in the range of
1643-1648 cm-1 for hfac compounds, 1575-1590 cm-1
for the acac compounds, and 1597-1599 cm-1 for tmhd
compounds. These bands are at significantly lower
energies than those found for the free ligands (1689
cm-1, H(hfac); 1728 cm-1, H(acac); 1720 cm-1, H(tmhd))
and are indicative of â-diketonate chelation to the metal
center. It should be noted, however, that such lowering
of the stretching frequencies for the metal derivatives
relative to the free ligand is not conclusive evidence for
carbonyl coordination to the metal center, as the CdO
stretching frequency for Me2Ga(tfac) was assigned to the
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for Mes2Ga (h fa c)
(a) Gallium-Ligand Bond Lengths
Ga(1)-O(1)
Ga(1)-O(5)
2.008(11)
2.009(11)
Ga(1)-C(11)
Ga(1)-C(21)
1.971(13)
1.943(10)
(b) Bond Lengths within Chelate Ring
O(1)-C(2)
O(5)-C(4)
1.245(20)
1.252(21)
C(2)-C(3)
C(3)-C(4)
1.392(24)
1.422(23)
(c) Bond Lengths Involving CF3 Groups
C(1)-F(1)
C(1)-F(2)
C(1)-F(3)
C(1)-C(2)
1.18(3)
1.21(3)
1.30(3)
1.49(3)
C(5)-F(4)
C(5)-F(5)
C(5)-F(6)
C(5)-C(4)
1.26(4)
1.26(3)
1.30(3)
1.42(3)
(d) Angles around Gallium
O(1)-Ga(1)-O(5)
88.7(4) O(5)-Ga(1)-C(11)
104.0(5)
109.1(5)
O(1)-Ga(1)-C(11) 111.4(5) O(5)-Ga(1)-C(21)
O(1)-Ga(1)-C(21) 103.8(6) C(11)-Ga(1)-C(21) 131.5(8)
vantage as the metathesis reaction. The reagent Ga-
(bdk)3 must be independently prepared before the
synthesis of R2Ga(bdk) can be attempted. When the
ligand redistribution reaction was used, the choice of
solvent was important to the success of the reaction. The
yield of Mes2Ga(hfac) was about 85% when Et2O was
used. In contrast, when the solvent was benzene, only
a 25% yield of product was isolated under the identical
reaction conditions of time and temperature.
very strong and relatively sharp band at 1620 cm-1
,
whereas the free ligand had a very strong and broad
An X-ray structural study of Mes2Ga(hfac) confirmed
the bidentate nature of the â-diketonate ligand bonded
to the gallium center. The molecular geometry and
labeling of atoms is shown in Figure 1. Interatomic
distances and angles are collected in Table 1. The
central gallium atom is in a very distorted tetrahedral
environment. The hexafluoroacetyl-acetonate moiety
behaves as a typical chelating ligand and is linked to
gallium by two equivalent bonds (Ga(1)-O(1) ) 2.008(11)
Å and Ga(1)-O(5) ) 2.009(11) Å) with a bite angle of
O(1)-Ga(1)-O(5) ) 88.7(4)°. These Ga-O bond lengths
are slightly longer than those found for Ga(hfac)3,6
which range from 1.942(5) to 1.971(5) Å (average
band centered around 1600 cm-1. The apparent differ-
(7) Beachley, O. T., J r.; Churchill, M. R.; Pazik, J . C.; Ziller, J . W.
Organometallics 1986, 5, 1814.
(8) Tables of Interatomic Distances and Configurations in Molecules
and Ions, Supplement 1956-1959; Spec. Publ. No. 18; The Chemical
Society: London, 1965.
(9) Churchill, M. R.; Mason, R. Proc. Chem. Soc., London 1963, 365.
(10) Churchill, M. R.; Mason, R. Proc. R. Soc., London 1966, A292,
61.
(11) Churchill, D. G.; Churchill, M. R.; Lake, C. H. J . Chem.
Crystallogr. 1994, 24, 711.
(12) Utsonomiya, K. Bull. Chem. Soc. J pn. 1971, 44, 2688.
(13) Mehrotra, R. C.; Bohra, R.; Gaur, D. P. Metal â-Diketonates and
Allied Derivatives; Academic Press: New York, 1978; pp 58-69.
(14) While the exact assignment of the highly mixed CdO and CdC
stretching frequencies has been the subject of much controversy (see
ref 7, pp 109-119, and: J oshi, K. C.; Pathak, V. N. Coord. Chem. Rev.
1977, 22, 37), the assignments used in this paper follow the convention
of: Behnke, G. T.; Nakamoto, K. Inorg. Chem. 1967, 6, 433.
(6) Ballarin, B.; Battiston, G. A.; Benetollo, F.; Gerbasi, R.; Porchia,
M.; Favretto, D.; Traldi, P. Inorg. Chim. Acta 1994, 217, 71.

Diorganogallium â-Diketonates
Organometallics, Vol. 17, No. 6, 1998 1103
ence in CdO stretching frequencies between Me2Ga-
(tfac) and other diorganogallium â-diketonates may be
attributed to the mixing of modes due to the asym-
metrical nature of the â-diketonate ligand. The room-
1
temperature H, 13C, and 19F NMR spectra of benzene
solutions of the diorganogallium â-diketonates are typi-
cal of compounds with chelated structures.
The potential of the diorganogallium â-diketonates
which were prepared in this study to react with the
Lewis base NMe3 was examined by tensimetric titra-
tions. The goals were to determine whether these four-
coordinate gallium compounds would exhibit Lewis
acidity and, if they were Lewis acids, to identify the site
of acidity and to elucidate the factors which appear to
control the relative Lewis acidities of the diorgano-
gallium â-diketonate derivatives. Lewis acidity was
observed and was found to be dependent upon the
â-diketonate and the organic ligands bound to the
gallium center. Only the fluorinated derivatives Me2-
Ga(hfac) and Me2Ga(tfac) in the series Me2Ga(bdk) (bdk
) hfac, tfac, acac, tmhd) reacted with NMe3 to form 1:1
Lewis adducts, and only Me2Ga(hfac)‚NMe3 was stable
to dissociation at room temperature. Furthermore, in
the series R2Ga(hfac) (R ) Me, Et, Mes) only the methyl
and ethyl derivatives formed 1:1 Lewis adducts accord-
ing to the tensimetric titration data but Et2Ga(hfac)‚
NMe3 was unstable with respect to dissociation of NMe3
at room temperature. The two adducts which were
isolated at room temperature, Me2Ga(hfac)‚py and
Me2Ga(hfac)‚NMe3, decompose at approximately 100 °C,
as indicated by the change in slope in their plots of vapor
pressure versus temperature and by the appearance of
an orange-brown liquid with a brown solid on the sides
of the tensimeter. Furthermore, thermal analysis of
Me2Ga(hfac)‚py by using a DSC operating at a heating
rate of 10 °C/min exhibited a sharp endotherm at 43.5
°C (mp 45.7-47.5 °C) and a broad endotherm with a
peak at 102.3 °C, an endotherm consistent with decom-
position. The nature of the decomposition was not
studied.
There are two possible sites for the coordination of a
Lewis base to a diorganogallium â-diketonate, either the
gallium atom or the carbonyl carbon of the ligand. Since
Me2Ga(hfac)‚NMe3 was not conducive to an X-ray
structural study in our laboratory because of its low
melting point (29.9-31.3 °C), the site of coordination of
an amine to Me2Ga(hfac) in the solid state was eluci-
dated by an X-ray structural study of Me2Ga(hfac)‚py
(mp 45.7-47.5 °C). The pyridine is bonded to the
gallium center. The molecular structure and labeling
of the atoms are shown in Figure 2. Interatomic
distances and angles are collected in Table 2. The
central gallium atom has an unusual sterochemistry,
as it is essentially a distorted trigonal bipyramid with
one very long (and presumably very weak) bond to
oxygen and four more normal bonds: one to oxygen, one
to nitrogen, and two to carbon atoms. Thus, the
hexafluoroacetylacetonate ligand is associated with very
asymmetric bonds to gallium with a Ga(1)-O(1) dis-
tance of 1.971(8) Å and another very long distance of
2.590(8) Å for Ga(1)‚‚‚O(2). The compound with five-
coordinate gallium atoms15 {Me2Ga[OCH(Me)2CH2-
F igu r e 2. Molecular geometry of Me2Ga(hfac)‚NC5H5
(ORTEP2 diagram, 30% probability envelopes for thermal
vibration ellipsoids, with hydrogen atoms artificially re-
duced).
NMe2]}2 has Ga-O distances of 1.919(2) Å (equatorial)
and 2.097(2) Å (axial). The Ga-O bond lengths in
oxygen adducts of triorganogallium compounds are
2.047 Å (average) for (Mes)3Ga‚OH2‚2THF,16 2.107(6)
Å for (o-MeC6H4)3Ga‚OEt2,17 and 2.069(7) Å for (C6H5-
CH2)3Ga‚THF.18 In contrast, the gallium-oxygen dis-
tance for the six-coordinate gallium compound Ga-
6
(hfac)3 is 1.954(5) Å, whereas for Mes2Ga(hfac) it is
2.009(11) Å. It may also be noted that the shorter
Ga(1)-O(1) bond length in Me2Ga(hfac)‚py is slightly
longer than the Ga-O average bond lengths found for
[(C5H5)2GaOEt]219 (1.906(3) Å), [Me2GaOH]420 (1.96 Å),
[tBu2GaOH]3,21 (1.957(5) Å), and [Mes2GaOH]2‚THF16
(1.949(2) Å). The remaining gallium-to-ligand bonds are
normal and internally consistent, viz., Ga(1)-N(1) )
2.128(9) Å and the Ga-CH3 linkages Ga(1)-C(21) )
1.986(13) Å and Ga(1)-C(22) ) 1.941(14) Å (average
Ga-CH3 ) 1.964 Å). This Ga-N distance is comparable
to that found for Ga(N3)3‚3py,22 where the average Ga-
N(py) distance is 2.131(4) Å. Bond lengths around the
six-membered Ga-O-C-C-C-O system are consistent
with some bond alternation, with Ga(1)-O(1) ) 1.971(8)
Å (short), O(1)-C(2) ) 1.287(15) Å (long), C(2)-C(3) )
1.346(16) Å (short), C(3)-C(4) ) 1.386(16) Å (long),
C(4)-O(2) ) 1.251(17) Å (short), and O(2)‚‚‚Ga(1) )
(16) Storre, J .; Klemp, A.; Roesky, H. W.; Schmidt, H.-G.; Noltem-
eyer, M.; Fleischer, R.; Stalke, D. J . Am. Chem. Soc. 1996, 118, 1380.
(17) Atwood, D. A.; Cowley, A. H.; J ones, R. A. J . Coord. Chem. 1992,
26, 69.
(18) Neumuller, B.; Gahlmann, F. Chem. Ber. 1993, 126, 1579.
(19) Cowley, A. H.; Mehrotra, S. K.; Atwood, J . L.; Hunter, W. E.
Organometallics 1985, 4, 1115.
(20) Smith, G. S.; Hoard, J . L. J . Am. Chem. Soc. 1959, 81, 3907.
(21) Atwood, D. A.; Cowley, A. H.; Harris, P. R.; J ones, R. A.
Organometallics 1993, 12, 24.
(15) Thiel, K.-H.; Hecht, E.; Gelbrich, T.; Du¨michen, U. J . J .
Organomet. Chem. 1977, 540, 89.
(22) Carmalt, C. J .; Cowley, A. H.; Culp, R. D.; J ones, R. A. J . Chem.
Soc., Chem. Commun. 1996, 1453.

1104 Organometallics, Vol. 17, No. 6, 1998
Beachley et al.
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
The infrared and NMR spectra of Me2Ga(hfac)‚NMe3
and Me2Ga(hfac)‚py are consistent with the hypothesis
that the Lewis base is bonded to gallium rather than to
a carbonyl carbon atom. If the observed bands at 1685
and 1683 cm-1 for Me2Ga(hfac)‚NMe3 and Me2Ga(hfac)‚
py, respectively, are assigned to the carbonyl stretching
frequencies,14 the adducts have stronger carbon-oxygen
bonds and weaker metal-carbonyl interactions than
does Me2Ga(hfac). The corresponding band for the
An gles (d eg) for Me2Ga (h fa c)‚NC5H5
(a) Gallium-Ligand Distances
Ga(1)-O(1)
Ga(1)‚‚‚O(2)
Ga(1)-N(11)
1.971(8)
2.590(8)
2.128(9)
Ga(1)-C(21)
Ga(1)-C(22)
1.986(13)
1.941(14)
(b) Bond Lengths within “Chelate” Ring
O(1)-C(2)
O(2)-C(4)
1.287(15)
1.251(17)
C(2)-C(3)
C(3)-C(4)
1.346(16)
1.386(16)
(c) Bond Lengths Involving CF3 Groups
parent compound Me2Ga(hfac) occurs at 1645 cm-1
,
C(1)-F(1)
C(1)-F(2)
C(1)-F(3)
C(1)-C(2)
1.311(18)
1.315(17)
1.288(17)
1.486(18)
C(5)-F(4)
C(5)-F(5)
C(5)-F(6)
C(5)-C(4)
1.302(24)
1.172(25)
1.177(27)
1.507(21)
whereas it is 1689 cm-1 for the free ligand H(hfac). The
NMR spectra of benzene solutions of the two adducts
suggest that the â-diketonate ligand and the amine
undergo very rapid exchange processes in solution, even
at -70 °C, the lowest temperature studied. The 13C
NMR spectrum at the normal operating temperature
of the instrument indicated only one type of carbonyl
carbon atom and one type of trifluoromethyl carbon
atom for each adduct, whereas the corresponding 19F
NMR spectra had only one apparent signal for the
trifluoromethyl groups of each compound. Similarily,
the room-temperature 1H NMR spectra of benzene
solutions of these compounds had one set of signals for
each compound, one for the unique hfac-H proton, one
for the CH3 group bonded to gallium, and only one signal
or set of signals attributable to the appropriate amine.
The line for the gallium methyl protons for a specific
adduct is at lower field than for Me2Ga(hfac), whereas
the line for the base protons is at higher field than for
the free base. The reverse situation is observed for
typical adducts.23 The gallium methyl lines of the
adduct are typically at higher field than for the free acid,
and amine protons for the adduct are at lower field than
for the free Lewis base. Variable-temperature 1H NMR
spectra of toluene solutions of Me2Ga(hfac)‚py and
Me2Ga(hfac)‚NMe3 over a temperature range of -70 to
+110 °C were also recorded. The spectra did not change
in appearance when compared with those observed at
the normal operating temperature of the instrument.
However, with increasing temperature, the amine reso-
nances moved downfield toward the chemical shift
observed for the free amine while the resonances for the
unique hfac proton and the Ga-CH3 protons moved
upfield toward the chemical shifts observed for a
benzene solution of Me2Ga(hfac). These observations
suggest that the gallium-nitrogen bonds of the adducts
are more dissociated at the higher temperatures, as
expected.
(d) Bond Lengths within Pyridine Ring
N(11)-C(12)
N(11)-C(16)
C(12)-C(13)
1.335(17)
1.297(16)
1.430(21)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
1.313(29)
1.380(26)
1.369(19)
(e) Angles around Gallium
O(1)-Ga(1)-N(11)
O(1)-Ga(1)-C(11)
85.8(3)
O(1)-Ga(1)-C(21)
112.2(5)
109.1(5)
109.9(5)
111.4(5) O(5)-Ga(1)-C(21)
N(11)-Ga(1)-C(21) 101.8(4) O(1)-Ga(1)-C(22)
N(11)-Ga(1)-C(22) 101.0(5) C(21)-Ga(1)-C(22) 133.0(6)
O(2)‚‚‚Ga(1)-O(1)
O(2)‚‚‚Ga(1)-C(21)
76.5(3)
84.8(5)
O(2)‚‚‚Ga(1)-N(11) 162.3(3)
O(2)‚‚‚Ga(1)-C(22)
85.8(5)
(f) Angles within the CF3COCHCOCF3 Ligand
Ga(1)-O(1)-C(2)
134.6(7) Ga(1)‚‚‚O(2)-C(4)
112.6(11) C(2)-C(1)-F(2)
103.5(12) C(2)-C(1)-F(3)
108.4(12) F(2)-C(1)-F(3)
109.2(10) O(1)-C(2)-C(3)
120.3(11) C(2)-C(3)-C(4)
127.2(11) O(2)-C(4)-C(5)
117.2(13) C(4)-C(5)-F(4)
116.0(16) F(4)-C(5)-F(5)
117.1(14) F(4)-C(5)-F(6)
120.7(8)
C(2)-C(1)-F(1)
F(1)-C(1)-F(2)
F(1)-C(1)-F(3)
O(1)-C(2)-C(1)
C(1)-C(2)-C(3)
O(2)-C(4)-C(3)
C(3)-C(4)-C(5)
C(4)-C(5)-F(5)
C(4)-C(5)-F(6)
111.0(11)
115.9(12)
104.5(11)
130.4(11)
123.3(11)
115.3(12)
109.0(18)
99.1(16)
97.8(17)
(g) Angles Involving the Pyridine Moiety
Ga(1)-N(11)-C(12) 120.4(8) Ga(1)-N(11)-C(16) 124.3(8)
C(12)-N(11)-C(16) 115.4(11) N(11)-C(12)-C(13) 121.8(14)
C(12)-C(13)-C(14) 120.1(17) C(13)-C(14)-C(15) 118.1(16)
C(14)-C(15)-C(16) 118.2(16) N(11)-C(16)-C(15) 126.3(13)
2.590(8) Å (long); unfortunately, differences between
C-O and C-C bonds are on the borderline of statistical
significance. Using the trigonal bipyramid description
for the coordination about Ga(1), the diaxial angle is
then O(2)‚‚‚Ga(1)-N(11) ) 162.3(3)° and the diequato-
rial angles are O(1)-Ga(1)-C(21) ) 112.2(5)°, O(1)-
Ga(1)-C(22) ) 109.9(5)°, and C(21)-Ga(1)-C(22) )
133.0(6)°. The CF3 centered on C(1) is well-behaved
with C(1)-F ) 1.288(17)-1.315(17) Å, whereas that
centered on C(5) shows once again the effects of libra-
tion and has some artifically reduced carbon-fluorine
distances (C(5)-F ) 1.172(25), 1.177(27), and 1.302(24)
Å).
Attempts to prepare MeGa(bdk)2 (bdk ) hfac, acac)
and MesGa(hfac)2 by elimination and ligand redistribu-
tion reactions were unsuccessful. The products were
mixtures of R2Ga(bdk) and Ga(bdk)3. Thus, these
observations are consistent with the chemistry observed
for the corresponding organoaluminum â-diketonate
compounds2 and might reflect the preferential coordina-
tion numbers of 4 and 6 rather than 5 for gallium and
aluminum.
The properties of the trimethylamine and pyridine
adducts of Me2Ga(hfac) in benzene solution were also
investigated in order to learn more the nature of
gallium-base interaction. The compound Me2Ga(hfac)‚
NMe3 was monomeric and was not dissociated in
benzene solution according to cryoscopic molecular
weight studies. There was no dependence of the ob-
served molecular weight on the concentration of the
solution. On the other hand, Me2Ga(hfac)‚py was
partially dissociated in solution. The observed molec-
ular weight was concentration-dependent. As the solu-
tion was diluted, the observed molecular weight de-
creased. Thus, pyridine would appear to be a weaker
Lewis base than is trimethylamine in benzene solution.
Exp er im en ta l Section
All compounds described in this investigation were manipu-
lated in a standard vacuum line or under a purified argon
atmosphere. The starting materials GaMe3 and GaEt3 were
(23) Beachley, O. T., J r.; Maloney, J . D. Organometallics 1997, 16,
4016.

Diorganogallium â-Diketonates
Organometallics, Vol. 17, No. 6, 1998 1105
purchased from Strem Chemical and vacuum distilled prior
to use. Trimesitylgallium(III) was prepared and purified
according to literature procedure.7 The starting material
GaCl3 was purchased from Strem Chemical and sublimed
under dynamic vacuum prior to each use. The â-diketones
were purchased from Aldrich Chemical Co., dried over K2CO3,
and vacuum-distilled prior to use. The sodium â-diketonates
were prepared according to literature procedures.24 Di-
methylgallium chloride25 and diethylgallium chloride26 were
prepared by stoichiometric ligand redistribution reactions in
pentane at room temperature and were purified by vacuum
sublimation at room temperature and by vacuum distillation
at 37 °C, respectively. The compound Ga(acac)3 was purchased
from Strem Chemicals and was used without further purifica-
tion. Tris(hexafluoroacetylacetonato)gallium(III) was pre-
pared by a metathesis reaction between GaCl3 and Na(hfac)
in a 1:3 mol ratio in pentane and was purified by room-
temperature sublimation under dynamic vacuum (10-4 mmHg).
The melting point and IR spectrum were in agreement with
published data.6 Pyridine and NMe3 were dried over KOH and
distilled prior to use. All solvents were dried by conventional
procedures. Infrared spectra of the compounds either as
liquids or as Nujol mulls of solids between CsI plates were
recorded by using a Perkin-Elmer Model 683 spectrometer.
Absorption intensities are reported with the abbreviations w
(weak), m (medium), s (strong), vs (very strong), and sh
(shoulder). Elemental analyses were performed by E+R
repeated fractional dynamic vacuum distillations by using -20
and -196 °C traps. The yellow crystalline solid which
remained in the -20 °C trap was further purified by vacuum
distillation at room temperature to yield Me2Ga(hfac) (2.22 g,
7.23 mmol, 91.6% yield based on Hhfac).
Syn th esis of R2Ga (h fa c) (R ) Me, Et) by Meta th esis
Rea ction s (Meth od B). The preparation of R2Ga(hfac) (R )
Me, Et) by metathesis reactions was accomplished by combin-
ing stoichiometric quantities of GaR2Cl and Na(hfac) in
pentane. In a typical experiment a Solv-Seal two-necked flask
was charged with the appropriate diorganogallium chloride
(3-7 mmol), was equipped with a magnetic stir bar and a
sidearm dumper containing a stoichiometric quantity of Na-
(hfac), and was connected to another Solv-Seal Schlenk flask
with a medium-porosity glass frit. Next, approximately 30 mL
of pentane was vacuum-distilled onto the diorganogallium
chloride at -196 °C. With the solution of R2GaCl at 0 °C,
Na(hfac) was added over a period of 20 min. After the reaction
mixture had been stirred at room temperature for 12 h, the
resulting yellow product was filtered. The diorganogallium
â-diketonate was separated from the solvent by fractional
distillations by using -20 and -196 °C baths as described
previously.
Syn th esis of R2Ga (bd k ) (R ) Me, bd k ) h fa c, a ca c; R)
Mes, bd k ) h fa c) by Liga n d Red istr ibu tion Rea ction s
(Meth od C). In a typical reaction, the reagents GaR3 and
Ga(bdk)3 were added to a reaction flask equipped with a
magnetic stir bar. Then, approximately 25 mL of solvent
(pentane for Me2Ga(hfac); Et2O for Me2Ga(acac)) was vacuum-
distilled into the flask. The reaction mixture was warmed to
room temperature, stirred, and subsequently heated in a 70
°C oil bath for 2 h. Then, the resulting clear solution was
stirred overnight at room temperature. In the case of Mes2-
Ga(hfac), an additional heating period of 3 h was required for
complete reaction. The solvent was removed while the reaction
mixture was held at -20 °C. Purification of the product was
achieved by either fractional vacuum distillation or vacuum
sublimation, as appropriate.
Ten sim etr ic Titr a tion s. The diorganogallium â-diketon-
ate derivatives which reacted with NMe3 were determined by
tensiometric titrations at 0 °C either as the neat species or as
toluene solutions (Mes2Ga(bdk), bdk ) hfac, acac, tmhd) as
described by Shriver and Drezdon.27b Those diorganogallium
â-diketonate derivatives which formed stoichiometric adducts
were subsequently prepared, isolated, and characterized.
P r ep a r a tion of Lew is Ad d u cts. A preweighed amount
(1-10 mmol) of R2Ga(hfac) (R ) Me, Et) was vacuum-distilled
into a flask at -196 °C which was connected by a glass elbow
to another Schlenk flask. After an excess of amine was added
by vacuum distillation, the reaction mixture was stirred for 1
h at room temperature. The excess amine was removed at 0
°C by vacuum distillation. The resulting product was then
purified at room temperature by either vacuum sublimation
(Me2Ga(hfac)‚NMe3, Me2Ga(hfac)‚py) or vacuum distillation
(Et2Ga(hfac)‚NMe3).
Deter m in a tion of Va p or P r essu r e a s a F u n ction of
Tem p er a tu r e. The vapor pressure of each diorganogallium
â-diketonate derivative was observed at room temperature and
above by using an immersible tensimeter that was connected
to the manometer on the vacuum line.27c Mercury heights
were measured by using a cathetometer which could be read
to (0.01 mmHg.
1
Microanalytical Laboratories, Inc., Corona, NY. The H NMR
(400 MHz) and 19F NMR (376.3 MHz) spectra were recorded
by using a Varian Unity-Inova 400 spectrometer. The 13C
NMR (75 MHz) spectra were recorded on a Varian Gemini 300
spectrometer. The 1H NMR (500 MHz) and 13C NMR (125.7
MHz) spectra were obtained by a Varian Unity-Inova 500
spectrometer. Proton chemical shifts are reported in δ (ppm)
units and are referenced to C6D5H at 7.15 ppm and SiMe4 at
0.00 ppm. Carbon chemical shifts are referenced to SiMe4 at
0.00 ppm and 13C impurities in C6D6 at 128.39 ppm. Fluorine
chemical shifts were referenced to CF3C6H5 at 0.00 ppm. The
following abbreviations are used to report the multiplicities
of lines: s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet). All samples for NMR spectroscopic studies were
contained in sealed tubes. Melting points were observed for
samples which were contained in sealed capillaries filled with
purified argon and are uncorrected. Molecular weights were
measured cryoscopically in benzene by using an instrument
similar to that described by Shriver and Drezdon.27a
Syn th esis of R2Ga (bd k ) by Elim in a tion Rea ction s
(Meth od A). The preparation of all diorganogallium â-dike-
tonate compounds by elimination reactions was accomplished
by combining stoichiometric quantities of GaR3 and the
â-diketone in pentane, essentially the same method reported
by Coates and Hayter4 except that solvent was used. In a
typical preparation, 0.823 g (7.23 mmol) of GaMe3 and 30 mL
of pentane were vacuum-distilled into a 250 mL round-
bottomed flask fitted with a stir bar and connected to a 100
mL Schlenk flask by a glass elbow. Then, 1.50 g (7.23 mmol)
of hfacH was added by vacuum distillation at -196 °C. As
the reaction mixture was slowly warmed to room temperature
with stirring, vigorous methane evolution occurred for about
10 min. The resulting yellow solution was stirred at room
temperature for 12 h to ensure complete reaction. The
methane and pentane were separated from the product by
vacuum distillation by holding the reaction flask at -20 °C
(alcohol/ice). Then, the product was isolated and purified by
Syn th etic Rea ction a n d P r od u ct Ch a r a cter iza tion
Da ta . Me2Ga (h fa c). Yield of product: method A, 91.6%;
method B, 73.6%; method C, 78.8%. Mp: yellow liquid at room
temperature; liquid easily supercooled; crystals formed by
maintaining pure compound at 0 °C for 2 h. Vp at 20 °C: 13.9
mmHg (log p ) -2155/T + 8.45, R2 ) 0.999). Cryoscopic
molecular weight, benzene solution, formula weight 306.84
(observed molality, observed mol wt, association): 0.0605, 274,
0.89; 0.0490, 261, 0.85; 0.0318, 266, 0.87. Anal. Calcd for
(24) Shin, H.-K.; Chi, K. M.; Farkas, J .; Hampden-Smith, M. J .;
Kodas, T. T.; Duesler, E. N. Inorg. Chem. 1992, 31, 424.
(25) Armer, B.; Schmidbaur, H. Chem. Ber. 1967, 100, 1521.
(26) Eisch, J . J . J . Am. Chem. Soc. 1962, 84, 3830.
(27) (a) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-
Sensitive Compounds; Wiley: New York, 1986. p 38. (b) Ibid., p 172.
(c) Ibid., p 175.

1106 Organometallics, Vol. 17, No. 6, 1998
Beachley et al.
C7H7F6GaO2: C, 27.40; H, 2.30. Found: C, 27.65; H, 2.43. 1H
NMR (C6D6): δ 5.80 (s, 0.7 H, H-hfac), -0.26 (Ga-CH3, 6H).
13C NMR (75.46 MHz, C6D6): δ 181.08 (q, J CO-F ) 37.7 Hz,
-CdO), 117.84 (q, J C-F ) 287 Hz, -CF3), 91.31 (s, dC-),
-6.17 (s, H3C-Ga). 19F NMR (C6D6): δ -14.38. IR (neat,
cm-1): 1735 (w), 1700 (w), 1652 (sh, s), 1645 (vs), 1615 (sh,
m), 1611 (m), 1562 (m), 1534 (m), 1500 (w), 1451 (vs), 1355
(w), 1332 (w), 1255 (vs). Vapor pressure vs temperature data
(1/T (×10-3) [log p]): 3.382 [1.161], 3.272 [1.446], 3.163 [1.678],
2.984 [2.045], 2.872 [2.291], 2.800 [2.439], 2.713 [2.622], 2.644
[2.78].
C6D6): δ 6.04 (s, 0.7 H, H-hfac), 1.68 (s, 9 H, NCH3), 1.14 (t,
J CH ) 8 Hz, 6 H, GaCH2CH3), 0.45 (t, J CH ) 8 Hz, 4 H, GaCH2-
2
CH3). 13C NMR (125.7 MHz, C6D6): δ 203.29 (q, J CF ) 36
Hz, CdO), 46.80 (s, NCH3), 9.84 (s, GaCH2CH3), 5.43 (s,
GaCH2CH3). IR (neat, cm-1): 1648 (s), 1613 (w), 1580 (w),
1565 (w), 1539 (w), 1477 (w), 1455 (m).
Mes2Ga (h fa c). Yield of product: method A, 65.7%; method
C, 87.3%. Bright yellow solid purified by recrystallization from
methylcyclohexane at -20 °C (crystallographic quality crys-
tals) or by vacuum sublimation at 60 °C. Mp: 91.1-93.4 °C.
Cryoscopic molecular weight, benzene solution, formula weight
515.14 (observed molality, observed mol wt, association):
0.0620, 601, 1.17; 0.0540, 570, 1.11; 0.0367, 561, 1.09. Anal.
Calcd for C23H23F6GaO2: C, 53.63; H, 4.50. Found: C, 53.81;
H, 4.51. 1H NMR (500 MHz, C6D6): δ 6.73 (s, 2H, Mes-H),
5.83 (s, 0.7 H, H-hfac), 2.38 (s, 12H, o-Mes-CH3), 2.10 (s, 6H,
Me2Ga(h fac)‚NMe3. Colorless crystalline solid. Mp: 29.9-
31.3 °C. Vp at 20 °C: 2.0 mmHg (log p ) -2281/T + 8.44, R2
) 0.978). Cryoscopic molecular weight, benzene solution,
formula weight 365.95 (observed molality, observed mol wt,
association): 0.0631, 348, 0.95; 0.0496, 343, 0.94; 0.0323, 344,
0.94. Anal. Calcd for C10H16F6GaNO2: C, 32.82; H, 4.41; N,
3.83. Found: C, 32.80; H, 4.52; N, 3.72. 1H NMR (500 MHz,
C6D6): δ 6.08 (s, 0.6 H, H-hfac), 1.62 (s, 9 H, NCH3), -0.16 (s,
2
p-Mes-CH3). 13C NMR (125.7 MHz, C6D6): δ 180.48 (q, J CF
) 36 Hz, CdO), 144.93 (s, Mes), 140.00 (s, Mes), 138.86 (s,
Mes), 128.89 (s, Mes), 117.70 (q, J CF ) 284 Hz, -CF3), 92.33
(s, dC-), 24.64 (s, o-Mes-CH3), 21.49 (s, p-Mes-CH3). 19F NMR
(C6D6): δ -14.36. IR (Nujol mull, cm-1): 1643 (m), 1609 (w),
1602 (w), 1562 (m), 1535 (w), 1458 (s), 1446 (sh, s), 1436 (sh,
m), 1365 (sh, m), 1356 (sh, w), 1340 (sh, w), 1287 (w).
6 H, Ga-CH3). 13C NMR (75 MHz, C6D6): δ 175.97 (q, 2J CF
)
34 Hz, CdO), 118.77 (q, J CF ) 288 Hz, -CF3), 90.41 (s, dC-),
46.46 (s, N-CH3), -7.073 (s, Ga-CH3). 19F NMR (C6D6): δ
-14.39. IR (Nujol mull, cm-1): 1685 (s), 1646 (m), 1605 (w),
1557 (s), 1529 (m), 1480 (s), 1447 (m), 1408 (w). Vapor
pressure vs temperature data (1/T (×10-3) [log p]): 3.66
[0.155], 3.31 [0.708], 3.27 [0.892], 3.1 [1.358], 3 [1.627], 2.92
[1.832], 2.83 [2.062], 2.74 [2.306], 2.7 [2.413], 2.61 [2.577], 2.54
[2.605], 2.45 [2.588].
Me2Ga (tfa c). Yield of product: method A, 93.4%. Colorless
liquid. Vp at 20 °C: 3.1 mmHg (log p ) -2172/T + 7.99, R2
) 0.997). Cryoscopic molecular weight, benzene solution,
formula weight 252.87 (observed molality, observed mol wt,
association): 0.0794, 238, 0.94; 0.0644, 234, 0.93; 0.0438, 232,
0.92. Anal. Calcd for C7H10F3GaO2: C, 33.25; H, 3.99.
Found: C, 33.20; H, 3.90. 1H NMR (500 MHz, C6D6): δ 5.35
(s, 0.5 H, H-hfac), 1.34 (s, 3 H, tfac-CH3), 0.42 (s, 6 H, Ga-
CH3). 13C NMR (125.7 MHz, C6D6): δ 202.90 (s, H3CCdO),
Me2Ga (h fa c)‚p y. Lilac colored solid before complete re-
moval of excess pyridine and colorless crystalline solid after
purification by room-temperature vacuum sublimation; iso-
lated in 85.6% yield. Mp: 45.7-47.5 °C. Vp at 20 °C: 0.4
mmHg (log p ) -2404/T + 8.41, R2 ) 0.976). Cryoscopic
molecular weight, benzene solution, formula weight 385.94
(observed molality, observed mol wt, association): 0.08342,
345, 0.89; 0.0703, 336, 0.87; 0.0528, 295, 0.76. Anal. Calcd
for C12H12F6GaNO2: C, 37.35; H, 3.13; N, 3.63. Found: C,
37.53; H, 3.07; N, 3.63. 1H NMR (500 MHz, C6D6): δ 8.13 (m,
py), 6.75 (m, py), 6.42 (m, py), 6.13 (s, 0.7 H, H-hfac), 0.09 (s,
6 H, Ga-CH3). 13C NMR (125.7 MHz, C6D6): δ 176.99 (q, 2J CF
) 35 Hz, CdO), 147.53 (s, py), 138.60 (s, py), 125.00 (s, py),
118.53 (q, J CF ) 286 Hz, -CF3), 90.81 (s, dC-), -4.14 (s, Ga-
CH3). 19F NMR (C6D6): δ -14.31. IR (Nujol mull, cm-1): 1740
(m, sh), 1683 (vs), 1656 (s, sh), 1610 (s), 1557 (s), 1533 (s), 1472
(vs, br), 1397 (m). Vapor pressure vs temperature data (1/T
(×10-3) [log p]): 3.4 [0.176], 3.37 [0.204], 3.27 [0.398], 3.19
[0.653], 3.13 [0.833], 3.08 [0.987], 3.02 [1.215], 2.97 [1.348],
2.87 [1.632], 2.86 [1.688], 2.8 [1.803], 2.75 [1.897], 2.68 [2.131],
2.61 [2.26], 2.51 [2.404], 2.5 [2.408], 2.44 [2.448], 2.41 [2.457],
2.34 [2.485].
Et2Ga (h fa c). Yield of product: method A, 94.9%; method
B, 85.5%. Brilliant yellow liquid purified by room-temperature
vacuum distillation. Vp at 20 °C: 2.2 mmHg. Cryoscopic
molecular weight, benzene solution, formula weight 334.90
(observed molality, observed mol wt, association): 0.0826, 330,
0.98; 0.0615, 328, 0.98; 0.0412, 326, 0.97. Anal. Calcd for
C9H11F6GaO2: C, 32.28; H, 3.31. Found: C, 32.30; H, 3.24.
1H NMR (500 MHz, C6D6): δ 5.86 (H-hfac, 0.7 H), 0.95 (t, J CH
) 8 Hz, GaCH2CH3), 0.42 (q, J CH ) 8 Hz, Ga-CH2). 13C NMR
(75 MHz, C6D6): δ 181.53 (q, J COF ) 36 Hz, -CdO), 117.90
(q, J CF ) 285 Hz, -CF3), 91.38 (s, dC-), 8.31 (s, GaCH2CH3),
5.55 (s, GaCH2CH3). 19F NMR (C6D6): δ -14.36. IR (neat,
cm-1): 1765 (w), 1648 (vs), 1615 (m), 1565 (m), 1538 (w), 1453
(s).
2
171.66 (q, J CF ) 34 Hz, -CdO), 121.49 (q, J CF ) 283 Hz,
-CF3), 96.59 (s, dC-), 28.46 (s, tfac-CH3), -6.14 (s, GaCH3).
IR (neat, cm-1): 1729 (w), 1620 (vs), 1527 (vs), 1442 (vs), 1365
(vs), 1300 (br, vs). Vapor pressure vs temperature data (1/T
(×10-3) [log p): 2.493 [2.603], 2.596 [2.377], 2.623 [2.215], 2.821
[1.895], 2.918 [1.667], 3.006 [1.459], 3.082 [1.26], 3.229 [0.973],
3.31 [0.82].
Me2Ga (a ca c). Yield of product: method A, 96.3%; method
C, 78.0%. Colorless solid. Mp: 20-22 °C (lit.4 mp 21.8-22.0
°C). Vp at 20 °C: 1.1 mmHg (lit4 mp 1.1 mmHg). Cryoscopic
molecular weight, benzene solution, formula weight 198.90
(observed molality, observed mol wt, association): 0.100, 186,
0.93; 0.0786, 179, 0.90; 0.0561, 174.46, 0.88. Anal. Calcd for
C7H13GaO2: C, 42.27; H, 6.59. Found: C, 42.49; H, 6.39. 1H
NMR (500 MHz, C6D6): δ 4.92 (H-acac, 0.7 H), 1.58 (s, 6 H,
acac-CH3), 0.03 (s, 6 H, Ga-CH3). 13C NMR (125.7 MHz,
C6D6): δ 193.33 (s, -CdO), 100.71 (s, dC-), 27.41 (s, acac-
CH3), -6.22 (s, Ga-CH3). IR (neat, cm-1): 1590 (vs), 1530
(s), 1430 (s), 1370 (vs).
Et2Ga (a ca c). Yield of product: method A, 89.2%. Colorless
liquid purified by vacuum distillation at 27 °C by using a short-
path distillation apparatus. Cryoscopic molecular weight,
benzene solution, formula weight 226.95 (observed molality,
observed mol wt, association): 0.0846, 219, 0.96; 0.0642, 215,
0.95; 0.0439, 211, 0.93. Anal. Calcd for C9H17GaO2: C, 47.63;
H, 7.55. Found: C, 47.52; H, 7.44. 1H NMR (500 MHz,
C6D6): δ 4.94 (H-acac, 0.7 H), 1.63 (s, 6H, acac-CH3), 1.28 (t,
J CH ) 8 Hz, 6H, Ga-CH2CH3), 0.69 (q, J CH ) 8 Hz, 4H, Ga-
CH2CH3). 13C NMR (125.7 MHz, C6D6): δ 193.75 (s, -CdO),
100.78 (s, dC-), 27.35 (s, acac-CH3), 9.74 (s, Ga-CH2CH3),
4.70 (s, Ga-CH2CH3). IR (neat, cm-1): 1587 (vs), 1525 (vs),
1417 (vs), 1370 (vs).
Et2Ga (h fa c)‚NMe3. Brilliant yellow liquid isolated in
73.7% yield by vacuum distillation at room temperature. Vp
at 20 °C: 1.5 mmHg. Cryoscopic molecular weight, benzene
solution, formula weight 394.01 (observed molality, observed
mol wt, association): 0.0822, 349, 0.89; 0.0670, 346, 0.88;
0.0466, 344, 0.87. Anal. Calcd for C12H20F6GaNO2: C, 36.58;
H, 5.12. Found: C, 36.60; H, 4.64. 1H NMR (500 MHz,
Mes2Ga (a ca c). Yield of product: method A, 89.3%. Color-
less solid. After the mesitylene was removed by holding the
sample at 45 °C while dynamically pumping on the sample
overnight, Mes2Ga(acac) was purified by recrystallization from
methylcyclohexane. Mp: 131.4 °C (onset of glass transition)
to 138.7 °C (melting to clear liquid). Cryoscopic molecular
weight, benzene solution, formula weight 407.20 (observed

Diorganogallium â-Diketonates
Organometallics, Vol. 17, No. 6, 1998 1107
Ta ble 3. Da ta for th e X-r a y Cr ysta llogr a p h ic
molality, observed mol wt, association): 0.0820, 382, 0.94;
Stu d ies of Mes2Ga (h fa c) a n d Me2Ga (h fa c)‚NC5H5
0.0647, 374, 0.92; 0.0397, 388, 0.95. Anal. Calcd for C23H29
-
GaO2: C, 67.84; H, 7.18. Found: C, 67.82; H, 7.35. 1H NMR
(400 MHz, C6D6): δ 6.86 (s, 4 H, Mes-H), 4.92 (s, 0.7 H,
H-acac), 2.60 (s, o-Mes-CH3), 2.18 (s, 6H, p-Mes-CH3), 1.52 (s,
6H, acac-CH3). 13C NMR (125.7 MHz, C6D6): δ 193.38 (s,
CdO), 145.17 (s, Mes), 142.15 (s, Mes), 138.31 (s, Mes), 128.46
(s, Mes), 101.43 (s, dC-), 27.50 (s, acac-CH3), 24.94 (s, ï-Mes-
CH3), 21.61 (p-Mes-CH3). IR (Nujol mull, cm-1): 1577 (s), 1530
(s), 1459 (s), 1399 (m), 1373 (m), 1362 (m, sh), 1355 (m), 1345
(m).
compd
Mes2Ga(hfac)
Me2Ga(hfac)‚
NC5H5
mol formula
cryst syst
space group
a, Å
C23H23F6GaO2
orthorhombic
Pna21 (No. 33)
8.167(2)
18.982(5)
15.345(4)
2378.9(10)
4
C12H12F6GaNO2
orthorhombic
Pbca (No. 61)
8.0160(13)
18.755(4)
21.591(4)
3246.1(11)
8
b, Å
c, Å
V, Å3
Z
mol wt
515.1
1.438
1.212
N/A
1048
5-45
-8 to 0
0-20
0-16
1833
1635
909
385.9
1.579
1.750
0.4536/0.5240
1536
Me2Ga (tm h d ). The colorless crystalline solid was isolated
by holding the reaction mixture at -20 °C (alcohol/ice) while
solvent was removed by vacuum distillation, and then the
product was purified by room-temperature vacuum sublima-
tion. Yield of product: method A, 95.9%. Mp: 24-25 °C. Vp
at 20 °C: 0.7 mmHg. Cryoscopic molecular weight, benzene
solution, formula weight 283.06 (observed molality, observed
mol wt, association): 0.0757, 288, 1.02; 0.0608, 280, 0.99,
0.0401, 271, 0.96. Anal. Calcd for C13H25GaO2: C, 55.16; H,
8.90. Found: C, 55.05; H, 8.86. 1H NMR (500 MHz, C6D6): δ
5.72 (s, 0.7 H, tmhd-H), 1.06 (s, 18 H, tmhd-CH3), 0.07 (s, 6
H, Ga-CH3). 13C NMR (125.7 MHz, C6D6): δ 203.70 (s,
-CdO), 91.32 (s, dC-), 41.65 (s, tmhd-CCH3), 28.33 (s, tmhd-
CCH3), -6.58 (s, Ga-CH3). IR (neat, cm-1): 1597 (m), 1571
(vs, sh), 1560 (vs, sh), 1554 (vs), 1538 (vs), 1501 (vs), 1459 (m),
1380 (vs), 1356 (vs).
D, g/cm3
µ(Mo KR), mm-1
T, max/min
F(000)
2θ range, deg
h
5-45
0-8
k
l
0-20
-23 to +23
no. of rflns collected
no. of indep rflns
no. of rflns above 6σ
absolute structure
weighting scheme, w-1
no. of params refined
4727
2132 (Rint ) 3.7%)
1002
N/A
η ) 0.2(2)
σ2(F) + 0.0017F2 σ2(F) + 0.0066F2
296
200
final R indices (all data), % R ) 8.78,
R ) 6.33,
Rw ) 7.03
R ) 4.44,
Rw ) 4.71
1.00
0.003, 0.001
5.5:1
Rw ) 9.34
R indices (6σ data), %
R ) 5.48,
Rw ) 6.53
Mes2Ga (tm h d ). Yield of product: method A, 75.5% based
upon GaMes3. The colorless solid was isolated after removing
other volatile products and solvent by vacuum distillation for
8 h while holding sample at 55 °C; then it was recrystallized
from methylcyclohexane at -30 °C. Mp: 152.0-155.4 °C
(glass transition), 160.5-165.2 °C (melting to clear liquid).
Cryoscopic molecular weight, benzene solution, formula weight
491.36 (observed molality, observed mol wt, association):
0.0780, 519, 1.06; 0.0573, 408, 0.83; 0.0381, 501, 1.02. Anal.
Calcd for C29H41GaO2: C, 70.89; H, 8.41. Found: C, 70.89;
H, 8.43. 1H NMR (500 MHz, C6D6): δ 6.85 (s, 4 H, Mes-H),
5.78 (s, 0.7 H, H-tmhd), 2.60 (s, 12H, o-Mes-CH3), 2.18 (s, 6H,
p-Mes-CH3), 1.02 (s, 18 H, tmhd-CH3). 13C NMR (125.7 MHz,
C6D6): δ 203.04 (s, CdO), 145.12 (s, Mes), 142.52(s, Mes),
138.21 (s, Mes), 128.44 (s, Mes), 92.18 (s, dC-), 41.69 (tmhd-
CCH3), 28.27 (s, tmhd-CCH3), 25.02 (s, o-Mes-CH3), 21.60 (p-
Mes-CH3). IR (Nujol mull, cm-1): 1599 (m), 1552 (vs), 1508
(s), 1460 (vs), 1400 (m), 1375 (s) 1353 (s).
goodness of fit
0.98
largest and mean ∆/σ
data-to-param ratio
largest diff peak, e Å-3
largest diff hole, e Å-3
0.075, 0.005
5.8:1
0.58
0.50
-0.41
-0.37
as unreacted Ga(acac)3 (1.360 g, 3.71 mmol; mp 197.0-199.5
°C (lit.12 mp 194 °C)). 1H NMR (500 MHz, C6D6): δ 5.17, 1.74.
Rea ction betw een Ga Mes3 a n d H(h fa c) in a 1:2 Mole
Ra tio (Nea t). Trimesitylgallium (0.816 g, 1.91 mmol) and
H(hfac) (0.808 g, 3.88 mmol) were combined in a Schlenk flask
to form a bright yellow reaction mixture, which was stirred
at room temperature for 12 h. Then, three products, a volatile
colorless liquid (0.394 g, 3.28 mmol of mesitylene), a volatile
colorless crystalline solid (0.429 g, 0.621 mmol of Ga(hfac)3,
mp 70.3-72.5 °C (lit.12 mp 68.5-70.0 °C), and a relatively less
volatile yellow solid (0.419 g, 0.815 mmol of Mes2Ga(hfac), mp
89.6-94.1 °C) were separated by either vacuum distillation
or sublimation, as appropriate, and identified by using the
vacuuum line to determine the vapor pressure and molecular
weight of the volatile liquid (mesitylene) and the melting points
to identify the gallium-containing solids.
Collection of X-r a y Diffr a ction Da ta . In each case
crystals were sealed into thin-walled glass capillaries under
an argon atmosphere inside a drybox kept under strictly
anaerobic and moisture-free conditions. The crystals were
inspected under a binocular polarizing microscope to ensure
that they were single; they were then centered accurately on
a Siemens R3m/V automated four-circle diffractometer. The
unit cell parameters and Laue symmetry were determined as
described previously.28 Intensity data (Mo KR, λ ) 0.710 730
Å) were collected at ambient temperatures (24-25 °C) with
graphite- monochromatized radiation. Data were corrected for
absorption and for Lorentz and polarization factors. Details
are provided in Table 3.
Rea ction betw een Ga Me3 a n d Ga (a ca c)3 in a 1:2 Mole
Ra tio. A Solv-Seal glass tube equipped with a magnetic stir
bar was charged with 2.025 g (5.516 mmol) of Ga(acac)3, 0.317
g (2.76 mmol) of GaMe3, and 20 mL of pentane. Then the
reaction mixture was heated with a 70 °C oil bath and stirred
for 20 h. However, the presence of a slightly soluble colorless
solid in the reaction mixture suggested that reaction was
incomplete. Thus, approximately 20 mL of Et2O was added
and the resulting solution was heated with a 70 °C oil bath
for 2 h. Vacuum distillation under dynamic vacuum with the
original flask held at -20 °C and with traps on the vacuum
line at -20 and -196 °C produced a mixture of a colorless
crystalline solid and a slightly yellow (almost colorless)
powdery solid in the Schlenk flask and a small amount of
colorless crystals in the -20 °C trap. The pentane and ether
collected in the -196 °C trap. The colorless crystals in the
Schlenk flask and in the -20 °C trap were transferred at room
temperature to a weighable tube on the vacuum line. The
melting point of the crystals (22-23 °C) and subsequent 1H
and 13C NMR spectra confirmed the presence of Me2Ga(acac)
(0.309 g, 1.55 mmol). 1H NMR (500 MHz, C6D6): δ 4.93 (s,
0.3H, acac-H), 1.58 (s, 6 H, acac-CH3), 0.03 (s, 6 H, Ga-CH3).
13C NMR (125.7 MHz, C6D6): δ 193.33 (CdO), 100.71 (dC-),
27.41 (acac-CH3), -6.22 (Ga-CH3). The powdery higher
melting solid remaining in the Schlenk flask was identified
(a ) Mes2Ga (CF 3COCHCOCF 3). The crystal had the di-
mensions 0.4 × 0.2 × 0.2 mm. The crystal belongs to the
orthorhombic system (mmm diffraction symmetry); the sys-
tematic absences (0kl for k + l ) 2n + 1, h0l for h ) 2n) are
consistent with either the centrosymmetric space group Pnam
(28) Churchill, M. R.; Lashewycz, R. A.; Rotella, F. J . Inorg. Chem.
1977, 16, 265.

1108 Organometallics, Vol. 17, No. 6, 1998
Beachley et al.
or the noncentrosymmetric space group Pna21. The successful
solution of the structure was carried out in the lower, acentric,
space group.
(b) Me2Ga (CF 3COCHCOCF 3)(p y). The crystal had the
dimensions 0.6 × 0.2 × 0.2 mm and belongs to the ortho-
rhombic crystal system. The systematic absences (0kl for k )
2n + 1, h0l for l ) 2n + 1, and hk0 for h ) 2n + 1) uniquely
define the centrosymmetric space group Pbca.
Deter m in a tion of th e Cr ysta l Str u ctu r es. All crystal-
lographic calculations were carried out on a VAXstation 3100
computer with use of the Siemens SHELXTL PLUS (Release
4.11 (VMS)) program package.29 The scattering factors used
were the analytical values for neutral atoms; these were
corrected for both components (∆f ′ and i∆f ′′) of anomalous
dispersion.30 The structures were solved by direct methods
and difference Fourier syntheses. All non-hydrogen atoms
were located, and their positional and anisotropic thermal
parameters were refined. Hydrogen atoms were included in
calculated positions based upon d(C-H) ) 0.96 Å and the
appropriate idealized trigonal or tetrahedral geometry.31 The
correctness of each structure was confirmed by means of a final
difference Fourier synthesis.
Ack n ow led gm en t. This work was supported in part
by the Office of Naval Research (O.T.B.). The upgrading
of the X-ray diffractometer was made possible by Grant
89-13733 from the Chemical Instrumentation Program
of the National Science Foundation.
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
positional parameters, interatomic distances and angles,
anisotropic thermal parameters, and calculated positions for
hydrogen atoms for each compound (7 pages). Ordering
information is given on any current masthead page.
(29) Sheldrick, G. M. SHELXTL PLUS, Release 4.11 (VMS); Siemens
Analytical Instrument Corp., Madison, WI, 1989.
OM970988E
(30) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, England, 1974; Vol. 4, pp 99-101, 149-150.
(31) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.