Cyclopentadiene elimination reaction as a route to bis(neopenty)gallium phosphides. Crystal and molecular structures of [(Me3CCH2)2GaPEt2]2 and [(Me3CCH2)2GaP(C6H 11)2]2

Article abstract of DOI:10.1021/om970090p

The compound (Me₃CCH₂)₂Ga(C₅H₅) has been observed to react at room temperature in pentane solution with HPEt₂ and H₂P(C₆H₁₁) to eliminate C₅H₆ and form [(Me₃CCH₂)₂-GaPEt₂]₂ and [(Me₃CCH₂)₂GaP(H)(C₆H ₁₁)]₂, respectively. The additional new compound [(Me₃CCH₂)₂GaP(C₆H ₁₁)₂]₂ was prepared by a metathetical reaction between Ga(CH₂CMe₃)₂-Cl and LiP(C₆H₁₁)₂ in diethyl ether. All three compounds were fully characterized in solution, whereas two of the three, [(Me₃CCH₂)₂GaPEt₂]₂ and [(Me₃CCH₂)₂GaP(C₆H ₁₁)₂]₂, were characterized by X-ray structural studies.

Full text of DOI:10.1021/om970090p

Organometallics 1997, 16, 3267-3272
3267
Cyclop en ta d ien e Elim in a tion Rea ction a s a Rou te to
Bis(n eop en tyl)ga lliu m P h osp h id es. Cr ysta l a n d
Molecu la r Str u ctu r es of [(Me3CCH2)2Ga P Et2]2 a n d
[(Me3CCH2)2Ga P (C6H11)2]2
O. T. Beachley, J r.,*,† J ohn P. Maloney,† and Robin D. Rogers‡
Departments of Chemistry, State University of New York at Buffalo, Buffalo, New York 14260,
and The University of Alabama, Tuscaloosa, Alabama 35487
Received February 6, 1997X
The compound (Me3CCH2)2Ga(C5H5) has been observed to react at room temperature in
pentane solution with HPEt2 and H2P(C6H11) to eliminate C5H6 and form [(Me3CCH2)2-
GaPEt2]2 and [(Me3CCH2)2GaP(H)(C6H11)]2, respectively. The additional new compound
[(Me3CCH2)2GaP(C6H11)2]2 was prepared by a metathetical reaction between Ga(CH2CMe3)2-
Cl and LiP(C6H11)2 in diethyl ether. All three compounds were fully characterized in solution,
whereas two of the three, [(Me3CCH2)2GaPEt2]2 and [(Me3CCH2)2GaP(C6H11)2]2, were
characterized by X-ray structural studies.
A major challenge for synthetic group 13 chemistry
is to discover new reactions for the preparation of
ultrapure precursors for electronic materials. Thus, the
simplest and most direct route which involves the most
limited number of synthetic steps from the fewest
reagents of high purity at the lowest possible reaction
temperature should minimize the introduction of im-
purities. Consequently, our research has been directed
toward the use of the hydrocarbon elimination reaction1
and the search for novel examples which occur at or
below room temperature. The cyclopentadiene elimina-
tion reaction (eq 1) between R2Ga(C5H5) (R ) Me,2 Et3)
and either amines, phosphines, or thiols is an example
of an elimination reaction which typically occurs at or
below room temperature. Our studies of these reac-
benzene to form equilibrium mixtures of R2Ga(C5H5),
RGa(C5H5)2 and GaR3 (eq 2). Thus, research projects
2R2Ga(C5H5) h RGa(C5H5)2 + GaR3
(2)
have been designed to attempt to learn more about the
reactivity patterns of the multiple gallium species which
are present in a solution and about the effects of the
organic substituents on gallium on the usefulness of the
cyclopentadiene elimination reaction for the preparation
of single-source precursors.
The cyclopentadienide group has been shown to be a
facile deprotonating group for phosphines when the
organogallium reagent was either Me2Ga(C5H5)2 or
Et2Ga(C5H5).3 In order to test whether the cyclo-
pentadienide ligand could be incorporated into a gallium
compound which had two bulky organic substituents,
(Me3CCH2)2Ga(C5H5) was prepared in situ and used to
study elimination reactions. The phosphide derivative
[(Me3CCH2)2GaPEt2]2 was prepared readily at room
temperature by combining Ga(CH2CMe3)3,6 Ga(C5H5)3,7
and HPEt2 in a 2:1:3 mol ratio, respectively, in pentane
(eq 3). After the phosphine was added to the solution
R2Ga(C5H5) + HER′2 f 1/2[R2GaER′2]2 + C5H6 (1)
tons2,3 suggested that the association of the initial group
13-15 monomeric product and/or removal of the cyclo-
pentadiene monomer by either dimerization or distil-
lation was necessary to minimize the occurrence of the
back-reaction for eq 1 and produce high yields of the
desired product. The study of the cyclopentadiene
elimination reaction is made more interesting with the
realization that even though R2Ga(C5H5) (R ) Me,4 Et5)
can be prepared by a stoichiometric ligand redistribution
reaction from GaR3 and Ga(C5H5)3, isolated by sublima-
tion, and fully characterized by elemental analyses and
X-ray structural studies, neither compound exists in
solution as a single compound. Both compounds under-
go ligand restribution reactions upon dissolution in
2Ga(CH2CMe3)3 + Ga(C5H5)3 + 3HPEt2 f
3(Me3CCH2)2GaPEt2 + 3C5H6 (3)
formed from the two gallium compounds, the resulting
solution was stirred for 18 h. All volatile components
were then removed by vacuum distillation. The product
was washed first with pentane at low temperature (-78
°C) and then purified by recrystallization to produce
(Me3CCH2)2GaPEt2 as a colorless crystalline solid in
45% yield. Even though the yield of (Me3CCH2)2GaPEt2
was only 45%, there was no evidence to suggest the
formation of any other gallium-phosphorus product. No
data suggested the elimination of neopentane with
formation of the unsymmetrically-substituted product
(Me3CCH2)(C5H5)GaPEt2. Thus, the very high solubility
† State University of New York at Buffalo.
‡ The University of Alabama.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) Beachley, O. T., J r.; Coates, G. E. J . Chem. Soc. 1965, 3241.
(2) Beachley, O. T., J r.; Royster, T. L., J r.; Arhar, J . R.; Rheingold,
A. L. Organometallics 1993, 12, 1976.
(3) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.; Lake,
C. H.; Toomey, L. M. Organometallics 1996, 15, 3653.
(4) Beachley, O. T., J r.; Royster, T. L., J r.; Arhar, J . R. J . Organomet.
Chem. 1992, 434, 11.
(5) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.; Lake,
C. H.; Krajkowski, L. M. Organometallics 1995, 14, 4402.
(6) Beachley, O. T., J r.; Pazik, J . P. Organometallics 1988, 7, 1516.
(7) Beachley, O. T., J r.; Getman, T. D.; Kirss, R. U.; Hallock,R. B.;
Hunter, W. E.; Atwood, J . L. Organometallics 1985, 4, 751.
S0276-7333(97)00090-3 CCC: $14.00 © 1997 American Chemical Society

3268 Organometallics, Vol. 16, No. 15, 1997
Beachley et al.
phosphorus substituents and intermolecular interac-
tions within the unit cell.8 Each gallium and each
phosphorus atom has a distorted tetrahedral coordina-
tion environment. The smallest angles in the molecule
are those between the atoms in the ring. The P-Ga-
P(a) angle is 80.47 (5)° and Ga-P-Ga(a) is 93.43 (6)°.
The angle between the two R-carbon atoms of the
neopentyl groups bonded to gallium C(1)-Ga-C(6) is
124.1(2)°. In constast, the angle between the two
R-carbon atoms of the ethyl groups on phosphorus
C(11)-P-C(13) is 103.7(2)°. The Ga-P bond distances,
2.450(1) and 2.452(1) Å, are comparable to the corre-
sponding distances of 2.479(3), 2.482 (3), 2.488 (3), and
2.512(3) Å observed for [(Me3CCH2)2GaPPh2]2.8 All
other distances and angles in [(Me3CCH2)2GaPEt2]2
appear normal.
Cryoscopic molecular weight and NMR spectral stud-
ies indicate that (Me3CCH2)2GaPEt2 exists as a dimer
in benzene solution. The combination of the absence of
a concentration dependence for the observed molecular
weight and the presence of only one line in the 31P NMR
spectrum at -50.1 ppm is consistent with the presence
of only one species in solution. The chemical shifts and
multiplicities of the lines which arise from the coupling
of proton(s) to the two phosphorus atoms in the 1H NMR
spectrum also support the presence of a dimer. Fur-
thermore, the spectrum of [(Me3CCH2)2GaPEt2]2 was
very similar to that observed for [(Me3CCH2)2InPEt2]2.9
The compound (Me3CCH2)2GaP(H)(C6H11) was also
prepared readily by a room temperature cyclopentadiene
elimination reaction by combining Ga(CH2CMe3)3,6
Ga(C5H5)3,7 and H2P(C6H11) in a 2:1:3 mol ratio, respec-
tively, in pentane (eq 4). There were no data to suggest
F igu r e 1. Molecular geometry of [(Me3CCH2)2GaPEt2]2.
ORTEP diagram for non-hydrogen atoms, with hydrogen
atoms arbitrarily reduced in size for clarity.
Ta ble 1. Im p or ta n t In ter a tom ic Dista n cesa (Å) a n d
An gles (d eg) for [(Me3CCH2)2Ga P Et2]2
Bond Distances (Å)
Ga-P
Ga-C(1)
P-C(11)
2.450(1)
1.998(5)
1.844(4)
Ga-P(a)
Ga-C(6)
P-C(13)
2.452(1)
2.006(4)
1.847(4)
Bond Angles (deg)
P-Ga-C(1)
100.5(1)
124.1(2)
114.4(1)
93.43(6)
107.6(1)
115.7(1)
122.9(3)
114.7(3)
P-Ga-C(6)
120.8(1)
80.47(5)
108.6(1)
122.5(1)
114.4(2)
103.7(2)
122.8(3)
115.6(3)
C(1)-Ga-C(6)
C(1)-Ga-P(a)
Ga-P-Ga(a)
C(13)-P-Ga(a)
Ga-P-C(13)
Ga-C(1)-C(2)
P-C(11)-C(12)
P-Ga-P(a)
C(6)-Ga-P(a)
C(11)-P-Ga(a)
Ga-P-C(11)
C(11)-P-C(13)
Ga-C(6)-C(7)
P-C(13)-C(14)
a
3
Symmetry code ) 2 - x, y,
/
- z.
2
of (Me3CCH2)2GaPEt2 in pentane, even at low temper-
ature (-78 °C), was probably responsible for the ob-
served low yield. Bis(neopentyl)gallium diethylphos-
phide was fully characterized by elemental analyses for
C and H, melting point, cryoscopic molecular weight
2Ga(CH2CMe3)3 + Ga(C5H5)3 + 3HP(H)(C6H11) f
3(Me3CCH2)2GaP(H)(C6H11) + 3C5H6 (4)
the formation of either neopentane or (Me3CCH2)(C5H5)-
GaP(H)(C6H11) from these reagents. The gallium phos-
phide product was isolated in approximately 70% yield
and was characterized by C and H elemental analyses,
melting point, and IR and 1H, 31P, and 13C NMR
spectroscopies. Additional characterization by cryo-
scopic molecular weight studies and X-ray structural
studies were unsuccessful. Even though cooling of the
dilute benzene solutions for cryoscopic molecular weight
studies lead to crystallization of the compound, crystals
suitable for an X-ray structural study could not be
obtained.
Extensive 31P, 13C, and 1H NMR spectral studies
suggest that (Me3CCH2)2GaP(H)(C6H11) exists in ben-
zene and toluene solutions as a dimer with the bulky
cyclohexyl groups oriented trans to each other in order
to minimize the steric effects between the cyclohexyl
groups. A more detailed examination of a model of this
molecule reveals that two different orientations of the
cyclohexyl group are possible if rotation of the cyclohexyl
group is restricted. These orientations are distin-
guished by the relationships between the hydrogen
bonded to the R-carbon atom of the cyclohexyl group and
the hydrogen bonded to phosphorus. These protons can
1
studies, infrared, H and 31P NMR spectroscopy, and
an X-ray structural study. All data are consistent with
the presence of only dimers [(Me3CCH2)2GaPEt2]2 in all
phases studied. The facile elimination of cyclopentadi-
ene between (Me3CCH2)2Ga(C5H5) and HPEt2 should be
compared with the observation that Ga(CH2CMe3)3 and
HPEt2 did not react to eliminate CMe4, even when a
benzene solution was heated at 70 °C for 3 weeks.
Dimeric units with the formula [(Me3CCH2)2GaPEt2]2
were identified by the X-ray structural study of the
crystalline product isolated from the reaction of
(Me3CCH2)2Ga(C5H5) with HPEt2. The solid state struc-
ture and labeling of the atoms in the molecule are shown
in Figure 1. Interatomic bond distances and angles are
listed in Tables 1. There were no abnormally close
contacts in the unit cell. The most noteworthy feature
about the structure is the buckled or butterfly-shaped
Ga2P2 ring. The only other symmetrically-substituted
gallium phosphorus compound with this type of struc-
ture is [(Me3CCH2)2GaPPh2]2.8 The dihedral or fold
angles for [(Me3CCH2)2GaPEt2]2, 153.9° about gallium
and 154.0° about phosphorus, are larger and closer to
planar than the corresponding dihedral angles for
[(Me3CCH2)2GaPPh2]2, 142.2° and 145.6°. The folding
of the four-membered ring has been suggested to result
from a variety of possible factors including steric
interactions between the neopentyl groups and/or the
(8) Banks, M. A.; Beachley, O. T., J r.; Buttrey, L. A.; Churchill, M.
R.; Fettinger, J . C. Organometallics 1991, 10, 1901.
(9) Beachley, O. T., J r.; Maloney, J . D.; Banks, M. A.; Rogers, R. D.
Organometallics 1995, 14, 3448.

Bis(neopentyl)gallium Phosphides
Organometallics, Vol. 16, No. 15, 1997 3269
be on the same side or on opposite sides and, thus, be
syn and anti to each other. The cyclohexyl group is
bonded to phosphorus, most likely through its equatorial
9
position as was observed for [(Me3CCH2)2InP(H)(C6H11)]3
and [(Me3CCH2)2GaP(C6H11)2]2. Thus, a given dimer
can have two pairs of syn protons, two pairs of anti
protons, or one pair of syn and one pair of anti protons.
These syn and anti protons are magnetically nonequiva-
lent and, in turn, make the phosphorus atoms and the
atoms in the cyclohexyl and neopentyl groups in the
molecule distinguishable by NMR spectroscopy. Thus,
the 31P{1H} NMR spectrum in C6D6 has two concentra-
tion-independent lines at -63.60 and -73.26 ppm (peak
heights of 17.5 and 20.6 units and with widths-at-half-
height of approximately eight and six units, respec-
tively). When phosphorus was coupled to the proton,
each line was a doublet of doublets. Thus, one line is
due to a phosphorus with syn protons, whereas the other
is for the phosphorus with anti protons. It is not
possible to assign a given line to a specific conformation
or molecular structure. An alternate interpretation of
the 31P NMR spectrum would assign these resonances
to cis and to trans geometrical isomers. However, other
NMR spectra do not support this hypothesis. Similarly,
an equilibrium between species of two different degrees
of association, such as monomer-dimer or dimer-
trimer, is also inconsistent with the data because the
spectrum was concentration independent. A variable-
temperature NMR experiment was used in an attempt
to confirm the hypothesis of syn and anti protons.
However, the 31P NMR spectrum at 100 °C, the highest
temperature used for the toluene solution, had only two
lines -64.1 and -73.3 ppm and was not significantly
different from the room temperature spectrum. Thus,
since neither the chemical shifts nor the intensities
changed significantly, 100 °C does not supply sufficient
energy to allow for free rotation of the P-C(C6H11) bonds
in this molecule. The 13C{1H} NMR spectrum in C6D6
has two sets of closely spaced lines and provides support
for the hypothesis of a trans isomer(s) with syn and anti
protons. The lines at 25.4 and 27.1 ppm of approxi-
mately equal intensity are assigned to magnetically
nonequivalent methylene carbon atoms in neopentyl
groups; the lines at 34.1 and 34.3 ppm are assigned to
the two different types of tertiary carbon atoms of the
neopentyl groups; the lines at 36.0 and 36.2 ppm are
assigned to the magnetically different types of tert-butyl
carbon atoms for the neopentyl groups; whereas the
eight lines between 31.0 and 32.7 ppm are assigned to
the carbon atoms of two magnetically nonequivalent
cyclohexyl groups. If cis and trans geometrical isomers
were present in almost equal concentrations, three sets
of 13C{1H} lines would be expected, one set for the trans
Figu r e 2. Molecular geometry of [(Me3CCH2)2GaP(C6H11)2]2
(molecule A). ORTEP diagram for non-hydrogen atoms.
Figu r e 3. Molecular geometry of [(Me3CCH2)2GaP(C6H11)2]2
(molecule B). ORTEP diagram for non-hydrogen atoms,
with hydrogen atoms omitted for clarity.
ether at 0 °C. The compound (Me3CCH2)2GaP(C6H11 2
)
was fully characterized by C and H elemental analyses,
melting point, cryoscopic molecular weight studies, IR
and 1H and 31P NMR spectroscopies, and an X-ray
structural study. All data are consistent with the
conclusion that dimers exist in all phases studied. The
cyclopentadiene elimination reaction was not investi-
gated as a potential route to (Me3CCH2)2GaP(C6H11)2.
Crystals of bis(neopentyl)gallium bis(cyclohexyl)phos-
phide consisted of discrete dimeric units with the
formula [(Me3CCH2)2GaP(C6H11)2]2. The unit cell con-
tained two very similar but different molecules (mol-
ecule A, Figure 2, and molecule B, Figure 3). Inter-
atomic bond distances and angles for each of these
molecules are collected in Table 2. There were no
abnormally close contacts in the unit cell. This struc-
tural determination suffered from high thermal motion
and disorder, which is consistent with the large steri-
cally bulky nature of the molecule. All 24 of the methyl
groups for the two unique molecules in the asymmetric
unit appear to be freely rotating or have multiple
orientations. It was not possible to resolve disordered
positions for these atoms. Thus, each methyl carbon
was refined with isotopic thermal parameters which
1
isomer and two sets for the cis isomer. The H NMR
spectrum had extensive overlapping of lines for the
neopentyl and cyclohexyl groups and, thus, was es-
sentially uninformative. However, two doublets of
doublets at 2.99 and 3.43 ppm for the hydrogen atoms
bonded to phosphorus were clearly discernable.
Even though the simple neopentane elimination reac-
tion between Ga(CH2CMe3)3 and HP(C6H11)2 in a ben-
zene solution at 70 °C cannot be used to prepare
(Me3CCH2)2GaP(C6H11)2, the compound was synthesized
in higher than 80% yield by a metathetical reaction
between Ga(CH2CMe3)2Cl6 and LiP(C6H11)2 in diethyl

3270 Organometallics, Vol. 16, No. 15, 1997
Beachley et al.
Ta ble 2. Im p or ta n t In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for [(Me3CCH2)2Ga P (C6H11)2]2
Ga(2)), one cyclohexyl group bonded to P(2) is disor-
dered. The carbon bonded to phosphorus (C(39)) and
one of the adjacent ring carbon atoms (C(44)) are
ordered and common to both orientations. The remain-
ing four carbon atoms (C(40)-C(43)) are disordered and
were resolved into two orientations at 50% occupancy
each.
Bond Distances (Å)-Molecule A
Ga(1)-P(1)
Ga(1)-C(1)
Ga(1)-C(6)
Ga(2)-P(2)
Ga(2)-C(16)
P(1)-C(27)
P(2)-C(39)
2.463(3)
2.02(3)
2.006(9)
2.460(3)
2.02(2)
1.88(1)
1.85(1)
Ga(1)-P(2)
Ga(1)-C(1)′
Ga(2)-P(1)
Ga(2)-C(11)
P(1)-C(21)
P(2)-C(33)
2.476(3)
2.07(3)
2.463(3)
2.02(1)
1.88(1)
1.89(1)
The cyclohexyl ring disorder in molecule A produces
two orientations, one of which is identical to the
conformation found in molecule B (Ga(3), Ga(4)) and one
of which is different. In molecule B and molecule A
containing C(40)-C(43), three of the cyclohexyl groups
(C(21), C(33), C(39); C(65), C(77), C(83)) are arranged
in a propeller-like fashion around the Ga2P2 ring. The
fourth cyclohexyl group in each molecule (C(27); C(71))
is twisted 90° relative to the other three. The uniquely
oriented cyclohexyl groups (C(27); C(71)) are bonded to
P(1) in molecule A and P(3) in molecule B and are
located such that the gallium atoms in the Ga2P2 ring
bend away from these groups.
Bond Distances (Å)-Molecule B
Ga(3)-P(3)
Ga(3)-C(45)
Ga(3)-C(50)
Ga(4)-P(4)
Ga(4)-C(55)′
P(3)-C(65)
P(4)-C(77)
2.465(3)
2.01(2)
2.07(1)
2.481(3)
2.12(2)
1.87(1)
1.89(1)
Ga(3)-P(4)
Ga(3)-C(45)′
Ga(4)-P(3)
Ga(4)-C(55)
Ga(4)-C(60)
P(3)-C(71)
P(4)-C(83)
2.463(3)
2.08(3)
2.481(3)
2.09(2)
2.01(2)
1.89(1)
1.86(1)
Bond Angles (deg)-Molecule A
84.3(1) P(1)-Ga(1)-C(1)
121.6(8) P(1)-Ga(1)-C(1)′
P(1)-Ga(1)-P(2)
P(2)-Ga(1)-C(1)
P(2)-Ga(1)-C(1)′
P(2)-Ga(1)-C(6)
C(1)′-Ga(1)-C(6)
P(1)-Ga(2)-C(11)
P(1)-Ga(2)-C(16)
99.6(9)
101.9(9)
117.2(4)
121.8(8)
84.6(1)
102.9(4)
123.6(5)
93.1(1)
91(1)
106.4(4) C(1)-Ga(1)-C(6)
138(1) P(1)-Ga(2)-P(2)
P(1)-Ga(1)-C(6)
The disordered positions of the cyclohexyl goup in
molecule A (C(40)′-C(43)′) produce a different orienta-
tion. The disordered cyclohexyl group in molecule A
(C(39)) is on the same side of the Ga2P2 ring as the
cyclohexyl group above which is twisted 90° relative to
the other three (C(27)). The effect of the disorder is such
that this cyclohexyl group is also twisted 90° relative
to the propeller-like orientations (C(21), C(33)). Thus,
in one conformation of molecule A, both cyclohexyl
groups, located in such a way that the gallium atoms
in the Ga2P2 ring bend away from them, are twisted 90°
relative to the remaining two rings.
101.8(3) P(2)-Ga(2)-C(11)
101.4(6) P(2)-Ga(2)-C(16)
C(11)-Ga(2)-C(16) 129.3(6) Ga(1)-P(1)-Ga(2)
Ga(1)-P(1)-C(21)
Ga(1)-P(1)-C(27)
C(21)-P(1)-C(27)
Ga(1)-P(2)-C(33)
Ga(1)-P(2)-C(39)
C(33)-P(2)-C(39)
Ga(1)-C(1)′-C(2)
110.1(4) Ga(2)-P(1)-C(21)
116.7(4) Ga(2)-P(1)-C(27)
105.7(6) Ga(1)-P(2)-Ga(2)
115.8(4) Ga(2)-P(2)-C(33)
116.0(4) Ga(2)-P(2)-C(39)
108.1(6) Ga(1)-C(1)-C(2)
109.2(3)
121.6(5)
92.8(1)
108.0(3)
115.4(5)
131(2)
119(2)
Ga(1)-C(6)-C(7)
124.1(9)
Ga(2)-C(11)-C(12) 124(1)
Ga(2)-C(16)-C(17) 133(2)
P(1)-C(27)-C(28)
P(1)-C(21)-C(22)
P(2)-C(39)-C(40)
P(2)-C(39)-C(40)′
109(1)
P(1)-C(27)-C(32)
114.0(8)
113.8(9)
115(1)
112.1(7) P(1)-C(21)-C(26)
126(1)
113(1)
P(2)-C(39)-C(44)
The presence of two unique molecules in the asym-
metric unit may be the result of the differences in
conformation found for the disordered models. Although
disorder and high thermal motion reduce the quality of
the structural results, the general features of the Ga2P2
ring and the orientations of the ligands about the ring
are quite evident. It is clear that the four-membered
Ga2P2 ring has a folded or butterfly-shaped ring similar
to that observed for [(Me3CCH2)2GaPEt2]2 and [(Me3-
CCH2)2GaPPh2]2.8 The dihedral or fold angles for the
four-membered rings for molecule A and B are different,
154.6° about gallium and 156.4° about phosphorus for
molecule A (Table 2) and 148.2° and 150.3°, respectively,
for molecule B. This observation might suggest that
crystal packing forces are more important than the
steric effects of the ligands in the molecule as a cause
for the folding of the four-membered ring. The con-
straints of the four-membered ring which reduce the
internal ring angles from the normal tetrahedral value
in turn increase the angles between the R-carbon atoms
of the neopentyl groups bound to gallium. Similar
observations have been made for the other two gallium-
phosphorus molecules which have butterfly-shaped
rings, [(Me3CCH2)2GaPEt2]2 and [(Me3CCH2)2GaPPh2]2.8
The Ga-P bond distances of 2.463(3) and 2.476(3) Å in
molecule A and 2.465(3) and 2.463(3) Å in molecule B
are within the the range of those observed for other
compounds with bulky substituents on phosphorus,
2.468(4)-2.483(5) Å in [(n-Bu2)2GaP(t-Bu)2]2,10 2.451(1)
Bond Angles (deg)-Molecule B
P(3)-Ga(3)-P(4)
84.3(1) P(3)-Ga(3)-C(45)
100.3(6)
97.8(8)
119.9(4)
118.0(6)
83.6(1)
95.5(7)
96.8(7)
120.8(5)
P(4)-Ga(3)-C(45)
P(4)-Ga(3)-C(45)′
P(4)-Ga(3)-C(50)
126.4(5) P(3)-Ga(3)--C(45)′
92.8(8) P(3)-Ga(3)-C(50)
104.1(4) C(45)-Ga(3)-C(50)
C(45)′-Ga(3)-C(50) 139.6(8) P(3)-Ga(4)-P(4)
P(3)-Ga(4)-C(55)
P(3)-Ga(4)-C(55)′
P(3)-Ga(4)-C(60)
123.6(7) P(4)-Ga(4)-C(55)
91.2(6) P(4)-Ga(4)-C(55)′
106.5(4) P(4)-Ga(4)-C(60)
C(55)-Ga(4)-C(60) 121.0(8) C(55)′-Ga(4)-C(60) 139.5(8)
Ga(3)-P(3)-Ga(4)
Ga(4)-P(3)-C(65)
Ga(4)-P(3)-C(71)
Ga(3)-P(4)-Ga(4)
Ga(4)-P(4)-C(77)
Ga(4)-P(4)-C(83)
Ga(3)-C(45)-C(46) 126(1)
Ga(3)-C(50)-C(51) 124(1)
Ga(4)-C(55)-C(56) 124(2)
91.8(1) Ga(3)-P(3)-C(65)
112.5(3) Ga(3)-P(3)-C(71)
119.6(5) C(65)-P(3)-C(71)
91.9(1) Ga(3)-P(4)-C(77)
111.2(3) Ga(3)-P(4)-C(83)
117.6(4) C(77)-P(4)-C(83)
109.5(4)
113.5(4)
108.7(6)
114.5(4)
108.8(4)
111.6(6)
Ga(3)-C(45)′-C(46) 112(1)
Ga(4)-C(60)-C(61)
Ga(4)-C(55)-C(59)
127(1)
158(2)
Ga(4)-C(55)′-C(56) 117(1)
P(3)-C(71)-C(72)
P(4)-C(77)-C(78)
P(4)-C(83)-C(84)
114.0(8) P(3)-C(71)-C(76)
108.3(8)
113.8(6)
115.8(9)
111.8(8) P(4)-C(77)-C(82)
115.5(7) P(4)-C(83)-C(88)
proved to be quite large. However, it was possible to
refine two alternate positions of 50% occupancy each
for three of the eight unique methylene carbon atoms
bonded to gallium. C(1), C(45), and C(55) were refined
in two orientations with the alternate orientation
designated with a prime (C(1)′, C(45)′, and C(55)′).
Although several of the other carbon atoms bonded to
gallium may also have been fractionally disordered, as
evidenced by elongated anisotropic thermal ellipsoids,
it was not possible to resolve the different positions.
The most interesting part of the disorder model
involves the cyclohexyl groups. In molecule A (Ga(1),
(10) Miller, J . E.; Kidd, K. B.; Cowley, A. H.; J ones, R. A.; Ekerdt,
J . G.; Gysling, H. J .; Wernberg, A. A.; Blanton, T. N Chem. Mater.
1990, 2, 589.

Bis(neopentyl)gallium Phosphides
Organometallics, Vol. 16, No. 15, 1997 3271
Å in [(t-Bu2)2GaP(H)(C5H9)2]2.11 Thus, the bulky cyclo-
hexyl groups which are bonded at their equatorial
positions do not appear to have any unusual effect on
the structure of the molecule.
resulting brown oil was recrystallized from pentane at -15
°C. The final product (Me3CCH2)2GaPEt2 (0.711 g, 2.36 mmol,
46% yield based on total mmol of gallium) was isolated as
colorless crystals. The high solubility of (Me3CCH2)2GaPEt2
in pentane served to lower the observed yield. The compound
(Me3CCH2)2GaPEt2 was also observed to sublime at 70 °C
under high vacuum. Mp: 101-103 °C. 1H NMR (C6D6): δ
1.00 (p, 3J PCCH ) 2J HCH ) 6.8 Hz, 3.1 H, -CH3), 1.06 (t, 3J PGaCH
) 3.4 Hz, 2.0 H, Ga-CH2-), 1.23 (s, 8.3 H, -CMe3), 1.73 (qt,
The compound [(Me3CCH2)2GaP(C6H11)2]2 has the
same degree of association in solution as it has in the
solid state. Cryoscopic molecular weight studies in
benzene lead to an observed degree of association of 2.1.
The absence of a concentration dependence for the data
further confirms the presence of only dimeric species
in solution. Thus, the presence of two bulky cyclohexyl
groups is insufficient for the length of the gallium-
phosphorus bond to destabilize the dimer in solution and
form monomers. The 31P{1H} NMR spectrum has only
one concentration-independent line at a chemical shift
of -15.43 ppm, a value which is very different than
those observed for [(Me3CCH2)2GaP(H)(C6H11)]2, -63.6
2
2J HCH ) 7.6 Hz, J PCH ) 2.3 Hz, 2.2 H, P-CH2-). 31P{1H}
NMR (C6D6): δ -50.08 (s). Anal. Calcd: C, 55.84; H, 10.71.
Found: C, 55.88; H, 10.80. Cryoscopic molecular weight,
benzene solution, fw 301.10 (observed molality, observed mol
wt, association): 0.08644, 617, 2.05; 0.0488, 618, 2.05; 0.0389,
621, 2.06. IR (Nujol mull, cm-1): 3175 (w), 2728 (w), 2700
(w), 1415 (m), 1233 (s), 1221 (s), 1128 (m), 1102 (m), 1099 (sh),
1035 (s), 1017 (sh), 1010 (s), 997 (s), 970 (m), 963 (m), 928 (m),
906 (m), 845 (w), 817 (vw), 752 (s), 743 (vs), 726 (vs), 719 (sh),
674 (vs), 600 (vs), 451 (vs), 395 (m), 328 (vw), 283 (m), 258
(m).
1
and -73.3 ppm. The H NMR spectrum is similar to
that observed for other gallium-phosphorus dimers and
Syn th esis of (Me3CCH2)2Ga P (H)(C6H11) by a Cyclop en -
ta d ien e Elim in a tion Rea ction . After a flask was charged
with 1.25 g (4.42 mmol) of Ga(CH2CMe3)3, 0.586 g (2.21 mmol)
of Ga(C5H5)3, and 20 mL of pentane, the resulting solution was
needs no further discussion.
Exp er im en ta l Section
stirred for 1 h. Then, a preweighed sample of H2P(C6H11
)
(0.771 g, 6.64 mmol) dissolved in 10 mL of pentane and
contained in a small tube was added to the flask. The reaction
mixture was stirred for 18 h at ambient temperature. After
the pentane was removed by vacuum distillation, the resulting
tan solid was washed with 10 mL of pentane at 0 °C to leave
a colorless solid, which was identified as (Me3CCH2)2GaP(H)-
(C6H11) (1.519 g, 4.643 mmol, 70.0% yield). This product was,
in turn, recrystallized from pentane at 0 °C. Mp: 204-210
°C. 1H NMR (C6D6, see Results and Discussion): δ 0.99-1.11
(mbr, C6H11), 1.13, 1.14, 1.18 (s, -CH2-), 1.24, 1.27 (s, CMe3),
1.32, 1.36 (s, C6H11), 1.42 (s, C6H11), 1.54, 1.58 (s, C6H11), 1.94
All compounds were extremely sensitive to oxygen and
moisture and were manipulated in a standard vacuum line or
in a purified argon atmosphere. The starting compounds
7
Ga(CH2CMe3)3,6 Ga(CH2CMe3)2Cl,6 and Ga(C5H5)3 were pre-
pared by literature methods. The phosphines were purchased
from Strem Chemicals, Inc. and were purified by vacuum
distillation before use. The reagent LiP(C6H11)2 was prepared
by deprotonating the parent phosphine with Li(n-Bu) in
hexane. Solvents were dried by conventional procedures.
Elememental analyses were performed by Schwarzkopf Mi-
croanalytical Laboratory, Woodside, NY, or by E+R Micro-
analytical Laboratory, Corona, NY. The 1H NMR spectra were
recorded either at 300 MHz by using a Varian Gemini-300
spectrometer or at 400 MHz by using a Varian VXR-400
spectrometer. Proton chemical shifts are reported in δ units
(ppm) and are referenced to SiMe4 at 0.00 and C6H6 at 7.15
ppm. The 31P NMR spectra were recorded at 161.9 MHz by
using the Varian VXR-400 specrometer and are referenced to
85% H3PO4 at 0.00 ppm. The 13C NMR spectra were recorded
at 75 MHz by using the Varian Gemini-300 spectrometer and
are referenced to benzene-d6 at 128.0 ppm. Standard ab-
breviations are used to report the multiplicites of the lines.
All samples for the NMR spectra were contained in flame-
sealed NMR tubes. Infrared spectra were recorded as Nujol
mulls between KBr plates with a Perkin-Elmer 683 spectrom-
eter. Absorption intensities are reported with standard ab-
breviations. Melting points were observed in sealed capillaries
and are uncorrected. Molecular weights were measured
cryscopically in benzene by using an instrument similar to that
described by Shriver and Drezdzon.12
1
(br, C6H11), 2.02, 2.06 (s, C6H11), 2.99 (dd, J PH ) 279 Hz,
1
3
3J HPGaP ) 10.4 Hz, P-H), 3.43 (dd, J PH ) 306 Hz, J HPGaP
)
9.6 Hz, P-H). 13C{1H} NMR (C6D6): δ 25.38 (s, -CH2), 27.08
(s, -CH2), 31.01, 31.18, 31.44, 31.48, 32.44, 32.47, 32.59, 32.67
(s, C6H11), 34.10 (s, -Me3), 34.30 (s, -Me3), 36.02 (s, -C-),
36.23 (s, -C-), 39.12 (t, J PC ) 7.5 Hz, P-C). 31P{1H} NMR
1
(C6D6): δ -63.60 (s, 1.0), -73.26 (s, 1.1). 31P NMR (C6D6): δ
1
3
1
-63.60 (dd, J PH ) 308 Hz, J PGaPH ) 9.4 Hz), -73.26 (dd, J PH
) 280 Hz, J PGaPH ) 10.6 Hz). 31P NMR (CD2Cl2): δ -63.73
3
(s, 1.0), -73.48 (s, 1.2). Anal. Calcd: C, 58.74; H, 10.61.
Found: C, 58.51; H, 10.59. IR (Nujol mull, cm-1): 2310 (w),
1354 (vs), 1340 (m), 1287 (w), 1262 (w), 1232 (m), 1224 (sh),
1170 (w), 1130 (m), 1114 (m), 1100 (m), 1068 (vw), 1039 (vw),
1012 (w), 996 (m), 888 (m), 880 (w), 820 (m), 805 (m), 742 (w),
712 (vs), 680 (w), 607 (m), 585 (sh), 456 (w), 446 (w), 350 (w),
290 (w).
Syn th esis of (Me3CCH2)2Ga P (C6H11
) by a Meta th esis
2
Rea ction . A side-arm dumper charged with 1.07 g (5.26
mmol) of LiP(C6H11)2 was attached to a flask which contained
1.30 g (5.26 mmol) of Ga(CH2CMe3)2Cl and 30 mL of Et2O.
After the solution of the gallium reagent was cooled to 0 °C,
the LiP(C6H11)2 was added. A colorless precipitate formed with
20 min. The ice bath was removed, and the mixture was
stirred for 18 h as it warmed to room temperature. After the
ether was separated by vacuum distillation, the product was
extracted four times with 30 mL of pentane each. A final
washing of the product with 10 mL of pentane at -78 °C left
1.82 g (4.44 mmol, 84.4% yield) of (Me3CCH2)2GaP(C6H11)2.
Crystals suitable for an X-ray structural study were grown
by the slow evaporation of a methylcyclohexane solution in
the drybox. Mp: 248-250 °C. 1H NMR (C6D6): δ 1.09-1.16
Syn th esis of (Me3CCH2)2Ga P Et2 by a Cyclop en ta d ien e
Elim in a tion Rea ction . The synthesis of (Me3CCH2)2GaPEt2
was also achieved by first reacting 0.970 g (3.42 mmol) of
Ga(CH2CMe3)3with 0.454 g (1.71 mmol) of Ga(C5H5)3 in 30 mL
of pentane. After this reaction mixture had stirred for 1 h at
room temperature, a solution of 0.463 g (5.14 mmol) of HPEt2
in pentane was added. This mixture was stirred for an
additional 18 h, and then all of the compounds volatile at room
temperature were removed by vacuum distillation. The
(11) Heaton, D. E.; J ones, R. A.; Kidd, K. B.; Cowley, A. H.; Nunn,
C. M. Polyhedron 1988, 7, 1901.
(12) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air
Sensitive Compounds; Wiley: New York, 1986; p 38.
(13) Sheldrick, G. M. SHELX76, a system of computer programs for
X-ray structure determination as locally modified; University of
Cambridge: Cambridge, England, 1976.
3
(br, 1.1 H, C6H11), 1.21 (t, J PGaCH ) 3.6 Hz, 2.0 H, -CH2-),
2
1.27 (s, 0.9 H, C6H11), 1.32 (s, 9.0 H, -CMe3), 1.62 (t, J HCH
)
10.5 Hz, 2.9 H, C6H11), 1.75 (d, 2J HCH ) 12.1 Hz, 2.0 H, C6H11),
2
2
2.14 (d, J HCH ) 12.1 Hz, 2.0 H, C6H11), 2.29 (t, J HCH ) 12.0
(14) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
Hz, 0.8 H, C6H11). 31P{1H} NMR (C6D6): δ -15.43 (s). Anal.

3272 Organometallics, Vol. 16, No. 15, 1997
Beachley et al.
Ta ble 3. Cr ysta l Da ta a n d Su m m a r y of In ten sity Da ta Collection a n d Str u ctu r e Refin em en t for
[(Me3CCH2)2Ga P Et2]2 a n d [(Me3CCH2)2Ga P (C6H11)2]2
[(Me3CCH2)2GaPEt2]2
[(Me3CCH2)2GaP(C6H11)2]2
mol form
color/shape
mol wt
cryst syst
space group
temp, °C
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
Å3
Ga2P2C28H64
colorless/parallelepiped
602.21
monoclinic
C2/c
20
16.524(2)
10.225(2)
20.677(4)
Ga2P2C44H88
colorless/parallelepiped
818.58
triclinic
P1h
20
15.280(2)
18.216(3)
19.046(7)
105.63(2)
102.54(2)
97.54(1)
4880.9
95.25(1)
3478.9
Z
4
1.15
17.4
4
1.11
12.5
D
µ
calcd, g cm-1
calcd, cm-1
diffractometer/scan
range of relative transmission factors, %
radiation, graphite monochromator
max cryst dimens, mm
no. of reflns measd
2θ range, deg
Enraf-Nonius CAD4/ω-2θ
94/100%
Mo KR (λ ) 0.710 73 Å)
Mo KR (λ ) 0.710 73 Å)
0.08 × 0.15 × 0.20
17 156
0.20 × 0.25 × 0.28
3349
2 e 2θ e 50
2 e 2θ e 50
+18,(21,(22
8503
range of h,k,l
+19,+12,(24 (except h + k ) 2n + 1)
no. of reflns obsd [Fo g 5σ(Fo)]
computer programs
structure solution
weights
GOF
2035
SHELX13
SHELXS14
SHELX13
SHELXS14
[σ(Fo)2]-1
[σ(Fo)2 + 0.0005Fo
0.71
]
2
-1
2.36
R ) ∑||Fo| - |Fc||/∑|Fo|
0.037
0.079
Rw
0.046
0.080
largest feature final diff map
0.3 e- Å-3
0.8 e- Å-3
Calcd: C, 64.56; H, 10.84. Found: C, 64.83; H, 10.79.
Cryoscopic molecular weight, benzene solution, fw 408 (ob-
served molality, observed mol wt, association): 0.0455, 863,
2.11; 0.0365, 868, 2.12; 0.0292, 857, 2.09. IR (Nujol mull,
cm-1): 2730 (w), 2700 (w), 2665 (w), 1352 (s), 1324 (m), 1292
(sh), 1287 (m), 1262 (m), 1254 (sh), 1236 (s), 1219 (s), 1192
(m), 1168 (m), 1130 (m), 1125 (m), 1106 (m), 1067 (w), 1042
(w), 1022 (sh), 1010 (m), 998 (s), 930 (w), 908 (m), 892 (sh),
882 (s), 847 (m), 842 (sh), 745 (m), 733 (m), 695 (vs), 664 (sh),
593 (s), 577 (sh), 509 (w), 487 (vw), 452 (m), 385 (w), 300 (w),
280 (w).
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t. (a ) [(Me3CCH2)2Ga P Et2]2. A transparent
single crystal of the compound was mounted in a thin-walled
glass capillary under Ar and transferred to the goniometer.
The space group was determined to be either the centric C2/c
or acentric Cc from the systematic absences. Subsequent
solution and refinement of the structure was carried out by
using the centric space group C2/c. A summary of the data
collection parameters is given in Table 3. Least-squares
refinement with isotropic thermal parameters led to R ) 0.072.
The geometrically constrained hydrogen atoms were placed in
calculated positions 0.95 Å from the bonded carbon atoms and
allowed to ride on that atom with B fixed at 5.5 Å2. The methyl
hydrogen atoms were included as a rigid group with rotational
freedom at the bonded carbon atom (C-H ) 0.95 Å, B ) 5.5
Å2). Refinement of non-hydrogen atoms with anisotropic
temperature factors led to the final values of R ) 0.037 and
Rw ) 0.046.
rotating, however, disorder at C(1) and at the cyclohexyl group
C(39)-C(44) in molecule A and at C(45), and C(59) in molecule
B was resolved. The disorder at C(1), C(45) and C(55) involves
fractional displacement of these CH2 groups, and C(1)′, C(45)′,
and C(55)′ were included at 50% occupancy. Any disorder in
the attached CMe3 groups was not resolvable. Conformational
disorder exists in the cyclohexyl group C(39)-C(44). Atoms
C(39) and C(44) are common to both orientations. C(40)-C(43)
were each resolved into two positions refined in alternate least-
squares cycles at 50% occupancy each. The conformation
without primes C(39)-C(44) results in molecules A and B
having essentially the same overall structure. In this orienta-
tion three of the cyclohexyl groups have the same general
orientation to the Ga2P2 ring, whereas one is twisted by
approximately 90°. In the disorder model containing C(39) and
C(40)′-C(43)′, two of the cyclohexyl groups are twisted.
Refinement of this structure in the acentric space group P1
was unsuccessful. The disorder was still apparent, and there
were high correlations between atoms that would be related
by the center of inversion in P1. Due to the high thermal
motion and disorder, the hydrogen atoms were not included
in the final refinement. Refinement of the non-hydrogen
atoms (except for the methyl groups) with anisotropic tem-
perature factors led to the final values R ) 0.079 and Rw
)
0.080.
Ack n ow led gm en t. This work was supported in part
by the Office of Naval Research.
(b ) [(Me3CCH2)2Ga P (C6H 11)2]2. The compound was
mounted in a thin-walled capillary under argon. The space
group was determined to be either the centric P1h or acentric
P1. Solution and refinement were successfully carried out in
P1h. A summary of data collection parameters is given in Table
3. After least-squares refinement with isotopic thermal pa-
rameters and no disorder led to R ) 0.111, it was obvious that
extremely high thermal motion was interferring with the
refinement of the structure. It was not possible to refine a
disorder model for the methyl groups which appear to be freely
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 and ORTEP diagrams of [(Me3CCH2)2GaPEt2]2
and [Ga(CH2CMe3)2P(C6H11)2]2 (25 pages). Ordering informa-
tion is given on any current masthead page.
OM970090P