Lewis acid-base studies of triorganogallium compounds with organophosphines

Article abstract of DOI:10.1021/om970296q

The relative Lewis acidities of the series of triorganogallium compounds GaR₃ (R = Me, Et, CH₂-CMe₃, CH₂SiMe₃, CH₂CMe₂Ph, C₆H₂Me₃) toward the common Lewis base HPPh₂ and the relative Lewis basicities of a series of organophosphines which incorporate an acidic hydrogen HPRR′ (PRR′ = PPh₂, P(C₆H₁₁)₂, PEt₂, P(H)(C₆H₁₁)) toward the common Lewis acid Ga(CH₂CMe₃)₃ have been investigated and compared. Cryoscopic molecular weight data permitted an evaluation of the equilibrium constant for the dissociation of each of the adducts. The ³¹P NMR spectral data, which were consistent with the molecular weight data, were also used to study the relative rates of hydrocarbon elimination reactions to form (R₂GaPRR′)₂.

Full text of DOI:10.1021/om970296q

4016
Organometallics 1997, 16, 4016-4019
Lew is Acid -Ba se Stu d ies of Tr ior ga n oga lliu m
Com p ou n d s w ith Or ga n op h osp h in es
O. T. Beachley, J r.,* and J ohn D. Maloney
Department of Chemistry, State University of New York at Buffalo,
Buffalo, New York 14260-3000
Received April 7, 1997X
Summary: The relative Lewis acidities of the series of
triorganogallium compounds GaR3 (R ) Me, Et, CH2-
CMe3, CH2SiMe3, CH2CMe2Ph, C6H2Me3) toward the
common Lewis base HPPh2 and the relative Lewis
basicities of a series of organophosphines which incor-
porate an acidic hydrogen HPRR′ (PRR′ ) PPh2,
P(C6H11)2, PEt2, P(H)(C6H11)) toward the common Lewis
acid Ga(CH2CMe3)3 have been investigated and com-
pared. Cryoscopic molecular weight data permitted an
evaluation of the equilibrium constant for the dissocia-
tion of each of the adducts. The 31P NMR spectral data,
which were consistent with the molecular weight data,
were also used to study the relative rates of hydrocarbon
elimination reactions to form (R2GaPRR′)2.
Lewis base HPPh2 have been compared by using cryo-
scopic molecular weight data and 31P NMR spectroscopy.
The cryoscopic molecular weight data for benzene solu-
tions permitted calculations of the equilibrium constant
for dissociation of the adduct (Kd, eq 1) (Table 1), and
R3Ga‚P(H)Ph2 h GaR3 + HPPh2
(1)
the percent dissociation of the adduct (R) as a function
of concentration, whereas 31P NMR spectral data (Table
2) were used to calculate changes in chemical shifts
between that observed for the solution which contained
the adduct and the solution of the pure phosphine (∆δ
) [δ(R3Ga‚P(H)Ph2 - δ(HPPh2)]) and in coupling con-
stants (1J PH) as a function of concentration. All data
confirm the existence of an equilibrium for each adduct
(eq 1) and are consistent with the following order of
Lewis acidity toward HPPh2: GaMe3 (strongest acid)
Even though adducts are fundamental to the chem-
istry of the group 13 elements, suprisingly few inves-
tigations have focused on the characterization of the
adducts of homoleptic triorganogallium compounds with
phosphorus bases in order to understand if these
compounds exist as single species in solution or whether
they are partially dissociated or even fully dissociated
in benzene solution. Only two of these types of adducts,1
(Me3CCH2)3Ga‚P(H)Ph2 and (Me3SiCH2)3Ga‚P(H)Ph2,
have been characterized in benzene solution by both
cryoscopic molecular weight and NMR spectroscopic
studies to our knowledge, and both were found to be
extensively dissociated in benzene solution. Of these
two Lewis acids, Ga(CH2CMe3)3 was the stronger acid
toward HPPh2. The adduct (Me3CCH2)3Ga‚P(H)Ph2
was a crystalline solid at room temperature and was
characterized further by an X-ray structural study.1 The
other adduct (Me3SiCH2)3Ga‚P(H)Ph2 melted at 23.5-
24.2 °C but was not characterized in the solid state.
Four other adducts of homoleptic organogallium com-
pounds, Me3Ga‚PMe3,2 Me3Ga‚PPh2C2H4PPh2‚GaMe3,3
Ph3Ga‚P(SiMe3)3,4 and (Me3SiCH2)3Ga‚P(SiMe3)3,5 have
been structurally characterized, but no data permitted
a determination of the extent of dissociation of the first
three of these adducts in solution. The last adduct,
(Me3SiCH2)3Ga‚P(SiMe3)3,5 was investigated by 1H and
13C NMR spectroscopy and was concluded to be undis-
sociated in benzene solution.
1
1
> GaEt3 >> Ga(CH2CMe3)3 > Ga(CH2SiMe3)3
>
Ga(CH2CMe2Ph)3 >> Ga(C6H2Me3)3.
A comparison of the 31P NMR spectroscopic data
revealed significant differences between the chemical
shifts and coupling constants of resonances for solutions
of the adducts at the same concentration in comparison
to the value observed for a solution of pure HPPh2.
Furthermore, as the concentration of the adduct in-
creased, the chemical shift of the observed 31P NMR line
moved downfield or away from the chemical shift of the
line for pure HPPh2 in benzene solution (∆δ increased)
1
as the coupling constant J PH increased (Table 2). Thus,
the NMR and cryoscopic molecular weight data indicate
that Me3Ga‚P(H)Ph2 and Et3Ga‚P(H)Ph2 are only slightly
dissociated in benzene solution but GaMe3 is a stronger
Lewis acid than is GaEt3 toward HPPh2. These obser-
vations may be correlated with the decreased steric
effcts of methyl groups. In contrast, the diphenylphos-
phine adducts of Ga(CH2CMe3)3,1 Ga(CH2SiMe3)3,1 and
Ga(CH2CMe2Ph)3 are significantly dissociated in solu-
tion with ∼0.05 M solutions being more than 50%
dissociated. Trimesitylgallium, Ga(C6H2Me3)3, is so
weak a Lewis acid that it does not appear to form
significant concentrations of adduct even when the
concentrations of the Lewis acid and base are 0.138 M,
the highest concentrations studied.
The Lewis basicities of the phosphines HPPh2,1 HP-
(C6H11)2, HPEt2, and HP(H)(C6H11) toward the common
Lewis acid Ga(CH2CMe3)3 were investigated. The cryo-
scopic molecular weight data were used to calculate an
equilibrium constant for dissociation of each adduct (Kd,
eq 1) and the percent dissociation of the adduct (R) as a
function of concentration. All data (Table 3) confirm the
existence of an equilibrium for each adduct and the
following order of relative Lewis basicity for the phos-
phine: HPEt2 (strongest base) > HP(C6H11)2 ≈ HP(H)-
The Lewis acidities of the series of triorganogallium-
(III) compounds GaR3 (R ) Me, Et, CH2CMe3,1 CH2-
SiMe3,1 CH2CMe2Ph, C6H2Me3) toward the common
X Abstract published in Advance ACS Abstracts, August 1, 1997.
(1) Banks, M. A.; Beachley, O. T., J r.; Maloney, J . D.; Rogers, R. D.
Polyhedron 1990, 9, 335.
(2) (a) Coates, G. E. J . Chem. Soc. 1951, 2003. (b) Burns, J . A.;
Pennington, W. T.; Robinson, G. H. Organometallics 1995, 14, 1533.
(3) Bradley, D. C.; Chudzynska, H.; Faktor, M. M.; Frigo, D. M.;
Hursthouse, M. B.; Hussain, B.; Smith, L. M. Polyhedron 1988, 7, 1289.
(4) Wells, R. L.; Aubuchon, S. R.; Self, M. F.; J asinski, J . P.;
Woudenberg, R. C.; Butcher, R. J . Organometallics 1992, 11, 3370.
(5) Wells, R. L.; Baldwin, R. A.; White, P. S. Organometallics 1995,
14, 2123.
S0276-7333(97)00296-3 CCC: $14.00 © 1997 American Chemical Society

Notes
Organometallics, Vol. 16, No. 18, 1997 4017
Ta ble 1. Cr yoscop ic Molecu la r Weigh t Stu d ies of R3Ga ‚P (H)P h 2 Ad d u ct System s in Ben zen e Solu tion
adduct system
Me3Ga‚P(H)Ph2
calcd mol wt
obsd mol wt
R
Kd(av)
0.0644
0.0525
0.0672
0.0550
4.3
4.8
1 × 10-4
Et3Ga‚P(H)Ph2
0.0580
0.0422
0.0649
0.0478
12
13
8 × 10-4
4 × 10-2
5 × 10-2
5 × 10-2
1
(Me3CCH2)3Ga‚P(H)Ph2
0.0522
0.0415
0.0828
0.0668
58
61
1
(Me3SiCH2)3Ga‚P(H)Ph2
0.0492
0.0376
0.0794
0.0629
62
67
(PhMe2CCH2)3Ga‚P(H)Ph2
(C6H2Me3)3Ga‚P(H)Ph2
0.0495
0.0371
0.0823
0.0690
66
67
0.0415
0.0371
0.0832
0.739
100
99
Ta ble 2. 31P NMR Sp ectr a l Da ta for R3Ga ‚P (H)P h 2
sterically demanding monocyclohexylphosphine. Since
HP(H)(C6H11) would have been expected to be more
basic than HP(C6H11)2, steric effects cannot be the only
important factor influencing the Lewis basicity of these
two phosphines. One possible explanation for the
observation of similar base strengths of HP(C6H11)2 and
of HP(H)(C6H11) might be related to solvation effects.
If the solvation of free HP(H)(C6H11) is more favorable
than is the solvation of the adduct, dissociation of the
adduct would be favored. Molecular models suggest
that the P-H protons in the adduct might be protected
by the three neopentyl groups on gallium from an
interaction with the π-cloud of benzene, whereas such
hindrance would not occur for the free phosphine. It is
also noteworthy that although (Me3CCH2)3Ga‚P(H)-
(C6H11)2 is significantly dissociated in benzene solution
(∼50%), the adduct has been isolated as a colorless
crystalline solid with a sharp melting point (42-43 °C).
A partial elemental (C,H) analysis of a sublimed sample
was consistent with the empirical formula of the adduct.
This observation is consistent with the existence of a
pure, single compound in the solid state. It is regret-
table that attempts to characterize this adduct in the
solid state by an X-ray structural study were unsuc-
cessful.
Ad d u ct System s in Ben zen e Solu tion
adduct
system
concn
(M)
δ
∆δ
1J PH
(ppm) (Hz)
(ppm)
PPh2H
-40.40
215
Me3Ga‚P(H)Ph2
0.0689
0.138
-33.40
-33.17
7.00
7.23
290
292
Et3Ga‚P(H)Ph2
0.0689
0.138
-35.84
-34.00
4.56
6.40
272
296
1
(Me3CCH2)3Ga‚P(H)Ph2
0.0689
0.138
-37.83
-36.48
2.57
3.92
232
241
1
(Me3SiCH2)3Ga‚P(H)Ph2
0.0689
0.138
-38.45
-37.74
1.95
2.66
232
240
(PhMe2CCH2)3Ga‚P(H)Ph2
(C6H2Me3)3Ga‚P(H)Ph2
0.689
0.138
-39.17
-38.40
1.23
2.00
224
230
0.0689
0.138
-40.40
-40.40
0.00
0.00
217
217
Ta ble 3. Cr yoscop ic Molecu la r Weigh t Stu d ies for
(Me3CCH2)3Ga ‚P (H)RR′ Ad d u ct System s in
Ben zen e Solu tion
adduct
system
calcd
mol wt mol wt
obsd
R
Kd(av)
(Me3CCH2)3Ga‚P(H)Et2
0.0541 0.0584
0.0460 0.0507 10
7.9 5 × 10-4
(Me3CCH2)3Ga‚P(H)(C6H11
)
0.0526 0.0785 49
0.0413 0.0639 55
2 × 10-2
3 × 10-2
4 × 10-2
All of the phosphines used in these investigations
have acidic protons with the potential to eliminate the
hydrocarbon6 RH and form a phosphide of the type (R2-
GaPR′2)n.
2
(Me3CCH2)3Ga‚P(H)2(C6H11
)
0.0552 0.0828 52
0.0430 0.0663 54
1
(Me3CCH2)3Ga‚P(H)Ph2
0.0522 0.0828 58
0.0415 0.0668 61
GaR3 + HPR′2 f (1/n)(R2GaPR′2)n + RH
(2)
Ta ble 4. 31P NMR Sp ectr a l Da ta for
(Me3CCH2)3Ga ‚P (H)RR Ad d u ct System s in Ben zen e
Available 31P NMR spectral data were used to study the
relative order of reactivity of different organogallium
compounds with HPPh2 and of different phosphines
with Ga(CH2CMe3)3, all as benzene solutions of the
same concentration. The following order was observed
for decreasing ease of elimination in benzene solution
when the phosphine was HPPh2: GaEt3 (most reactive)
Solu tion
concn
(M)
δ
∆δ
1J PH
compd
(ppm)
(ppm) (Hz)
PEt2H
-55.13
192
(Me3CCH2)3Ga‚P(H)Et2
0.0689
0.138
-38.29 16.84
-37.87 17.26
-27.40
271
272
193
219
230
189
226
227
P(C6H11)2H
(Me3CCH2)3Ga‚P(H)(C6H11
> GaMe3 > Ga(CH2SiMe3)3 >> Ga(CH2CMe3)3
≈
)
0.0689
0.138
-25.02
-25.80
-111.4
-98.3
2.38
3.60
2
Ga(C6H2Me3)3 (no reaction). It should be noted that this
order is not the same order as was observed for the
relative Lewis acidities toward HPPh2, as the order for
GaEt3 and GaMe3 are reversed. Both GaEt3 and GaMe3
eliminated an alkane and formed the organogallium
phosphide (R2GaPPh2)n in benzene solution at room
temperature, but both reactions were very slow. The
NMR data demonstrated that approximately 45% of the
Et3Ga‚P(H)Ph2 as a 0.138 M solution was converted to
P(C6H11)H2
(Me3CCH2)3Ga‚P(H)2(C6H11
)
0.0689
0.138
13.1
15.5
-95.9
(C6H11) > HPPh2. Thus, the least sterically demanding
base HPEt2 is the strongest, as expected. The one
surprise from our data is that HP(C6H11)2 and HP(H)-
(C6H11) have similar basicities.
The bulky dicyclohexylphosphine has an apparent
base strength which is comparable to that of the less
(6) Beachley, O. T., J r.; Coates, G. E. J . Chem. Soc. 1965, 3241.

4018 Organometallics, Vol. 16, No. 18, 1997
Notes
Et2GaPPh2 after 12 days, whereas a benzene solution
of Me3Ga‚P(H)Ph2 eliminated methane much more
slowly. It is noteworthy that Robinson, Burns, and
Pennington7 described the use of a toluene (10 mL)
solution of GaMe3 (5 mmol) and HPPh2 (5 mmol) to
prepare (Me2GaPPh2)3 for an X-ray structural study.
When no solvent was used, temperatures of 90-110 °C
were reported by Coates and Graham8 to be necessary
to initiate the elimination of methane from the adduct
Me3Ga‚P(H)Ph2 in a sealed tube. When the elimination
of SiMe4 from a benzene solution of (Me3SiCH2)3Ga‚P-
(H)Ph2 was investigated,1,9 heating to reflux was neces-
sary to initiate a very slow reaction. In constrast,
(Me3CCH2)3Ga‚P(H)Ph2 did not eliminate CMe4, even
upon refluxing a solution for 3 weeks.1,10 Reactivity
studies of Ga(CH2CMe3)3 with HP(H)(C6H11) demon-
strated that approximately 90% of the CMe4 was
eliminated after a solution of Ga(CH2CMe3)3 and HP-
(H)(C6H11) in benzene had been heated in a 70 °C oil
bath for 7 days. However, heating for 18 days was
necessary for complete reaction. The two phosphines
sociation of these adducts might be required for the
elimination of SiMe4 with formation of [R2GaP(SiMe3)2]n.
The reagents GaMe3 and P(SiMe3)3 reacted smoothly in
toluene solution to form [Me2GaP(SiMe2)2]2.13 In con-
trast, Ga(CH2SiMe3)3 reacted with P(SiMe3)3 in pentane
solution to form only the adduct5 (Me3SiCH2)3Ga‚P-
(SiMe3)3. 1H and 13C NMR spectra demonstrated that
the adduct did not dissociate in benzene solution. The
product of the elimination reaction [(Me3SiCH2)2Ga‚P-
(SiMe3)2]2 was not formed.5
Exp er im en ta l Section
All compounds described in this section were extremely
sensitive to oxygen and water and were manipulated in a
standard vacuum line or under a purified argon atmosphere.
The compounds Ga(CH2CMe3)3,14 Ga(CH2SiMe3)3,15 Ga(C6H2-
Me3)3,16 Ga(CH2CMe2Ph)3,17 (Me3CCH2)3Ga‚P(H)Ph2,1 and (Me3-
SiCH2)3Ga‚P(H)Ph21 were prepared and purified by literature
methods. Dicyclohexylphosphine, cyclohexylphosphine, and
diethylphosphine were purchased from Alfa Products, whereas
diphenylphosphine, trimethylgallium, and triethylgallium were
purchased from Strem Chemicals, Inc. All phosphines were
purified by distillation prior to use. Solvents were dried by
conventional procedures. Elemental analyses were performed
by E + R Microanalytical Laboratory, Inc., Corona, NY. 1H
NMR spectra were recorded at 300 MHz by using a Varian
Gemini-300 spectrometer. Proton chemical shifts are reported
in δ units (ppm) and are referenced to SiMe4 at 0.00 ppm (δ)
and C6D6 at 7.15 ppm. The 31P NMR spectra were recorded
at 161.9 MHz by using a Varian VXR-400 spectrometer.
Proton-decoupled 31P NMR chemical shifts are referenced to
85% H3PO4 at δ 0.00 ppm. All samples for NMR spectra were
contained in tubes sealed by fusion of the glass. Melting points
were observed in sealed capillaries and are uncorrected.
In a typical NMR spectroscopic study, the volatile compo-
nent, either the phosphine or the triorganogallium compound,
was vacuum-distilled into a tared tube equipped with a Teflon
valve and a standard tapered joint and weighed. Then, a
stoichiometric quanity of the nonvolatile component and a
known amount of C6D6 were placed into a reaction tube which
was equipped with a magnetic stirbar and attached to an NMR
tube and a Teflon valve adapter. After the volatile component
was vacuum-distilled into the reaction tube, the reaction
mixture was stirred for 20 min at room temperature. The
resulting solution was then poured into the NMR tube, the
tube was cooled to -196 °C and flame-sealed.
HP(C6H11)2 and HPEt2 did not undergo elimination
reactions with Ga(CH2CMe3)3, even upon heating ben-
zene solutions at 70 °C for 3 weeks.
These observations of the relative rates of elimination
reactions in gallium phosphorus chemistry are consis-
tent with the mechanism proposed for the elimination
reaction in aluminum nitrogen chemistry.11,12 Kinetic
studies for the HMe2Al‚N(H)(Me)(Ph) system supported
a bimolecular reaction between the Lewis acid and
base.11 Formation of the adduct was suggested to be a
“dead-end path” for elimination. Furthermore, studies
of the HMe2Al‚N(H)2(CH2Ph) system12 provided ad-
ditional support for the conclusion that dissociation of
the adduct was needed for the elimination reaction to
occur. When HMe2Al‚N(H)2(CH2Ph) was present as a
solution in toluene, elimination of H2 was observed.
However, when the adduct precipitated from toluene
solution, H2 was not formed. The temperature was
constant for these observations for the HMe2Al‚N(H)2-
(CH2Ph) system. Similarly, a benzene or toluene8
solution of Me3Ga‚P(H)Ph2 eliminated methane at room
temperature, whereas the pure adduct without solvent7
required 90-110 °C. If the adduct had been the active
species for elimination, the solution would have been
expected to be less reactive. Second, the elimination of
ethane from a benzene solution of Et3Ga‚P(H)Ph2 was
faster than was the elimination of methane from a
solution of Me3Ga‚P(H)Ph2, even though GaMe3 is the
stronger Lewis acid. Lastly, the extended times neces-
sary for complete reactions for Et3Ga‚P(H)Ph2 and (Me3-
CCH2)3Ga‚P(H)2(C6H11) are also consistent with the
occurrence of bimolecular reactions.
The adduct systems for cryoscopic molecular weight studies
were prepared by using a procedure similar to that described
previously for the NMR studies. Freezing point depressions
were measured by using an instrument similar to that
described by Shriver and Drezdzon.18 Since the error typical
of these types of measurements is approximately 10%, the data
in the experimental section for each compound give the actual
calculated result, whereas the corresponding values for Kd in
the tables have been rounded off to one significant figure to
avoid misinterpretation or overinterpretation.
(Me3CCH2)3Ga ‚P (H)Et2. (a) 1H NMR (0.0689 M, C6D6,
δ): 0.75 (m, -CH3), 0.92 (s, Ga-CH2-), 1.18 (m, P-CH2-),
13
The observed reactivity patterns of GaMe3 and
5
Ga(CH2SiMe3)3 with P(SiMe3)3 also suggest that dis-
1
1.21 (s, -CMe3), 3.04 (dm, J PH ) 273 Hz, -PH). 1H NMR
(0.138 M, C6D6, δ): 0.76 (m, -CH3), 0.91 (s, Ga-CH2-), 1.18
(m, P-CH2-), 1.21 (s, -CMe3), 3.05 (dm, 1J PH ) 273 Hz, -PH).
(7) Coates, G. E.; Graham, J . J . Chem. Soc. 1963, 233.
(8) Robinson, G. H.; Burns, J . A.; Pennington, W. T. Main Group
Chem. 1995, 1, 153.
1
31P NMR (0.0689 M, C6D6, δ): -38.29 (dp, J PH ) 271 Hz,
(9) Beachley, O. T., J r.; Kopasz, J . P.; Zhang, H.; Hunter, W. E.;
Atwood, J . L. J . Organomet. Chem. 1987, 325, 69.
(10) Banks, M. A.; Beachley, O. T., J r.; Buttrey, L. A.; Churchill,
M. R.; Fettinger, J . C. Organometallics 1991, 10, 1901.
(11) Beachley, O. T., J r.; Tessier-Youngs, C. Inorg. Chem. 1979, 18,
3188.
(12) Beachley, O. T., J r. Inorg. Chem. 1981, 20, 2825.
(13) Dillingham, M. D. B.; Burns, J . A.; Byers-Hill, J .; Gripper, K.
D.; Pennington, W. T.; Robinson, G. H. Inorg. Chim. Acta 1994, 216,
267.
(14) Beachley, O. T., J r.; Pazik, J . C. Organometallics 1988, 7, 1516.
(15) Beachley, O. T., J r.; Simmons, R. G. Inorg. Chem. 1980, 19,
1021.
(16) Beachley, O. T., J r.; Churchill, M. R.; Pazik, J . C.; Ziller, J . W.
Organometallics 1986, 5, 1814.
(17) Beachley, O. T., J r.; Noble, M. J .; Churchill, M. R.; Lake, C. H.
Organometallics 1992, 11, 1051.
(18) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds; Wiley: New York, 1986; p 38.

Notes
Organometallics, Vol. 16, No. 18, 1997 4019
3J PCCH ) 13.4 Hz). 31P NMR (0.138 m, C6D6, δ): -37.87 (dp,
1J PH ) 272 Hz, 3J PCCH ) 13.4 Hz). Cryoscopic molecular weight
(measured upon mixing reagents; formula weight 373.1; calcd
mol wt, obsd mol wt, R or percent dissociation, Kd): 0.0541,
an elimination reaction. Initial 31P NMR spectrum (0.14 m,
20 °C, δ): -25.02 (d, J PH ) 219 Hz, (Me3CCH2)3Ga‚P(H)-
(C6H11)2). No change in the spectrum occurred after heating
the sample for 3 weeks at 70 °C.
1
0.0584, 7.95%, 3.71 × 10-4; 0.0460, 0.0507, 10.2%, 5.35 × 10-4
;
Me3Ga ‚P (H)P h 2: 1H NMR (0.0689 m, C6D6, δ): 0.10 (s,
0.0376, 0.0422, 12.2%, 6.41 × 10-4
.
1
-CH3), 5.19 (d, J PH ) 293 Hz, -PH), 6.8-7.4 (m, Ph). 1H
(b) A solution to study the elimination reaction was
prepared by mixing 0.19 g (0.66 mmol) of Ga(CH2CMe3)3, 0.060
g (0.67 mmol) of HPEt2, and 4.82 g of C6D6. 31P NMR (0.14
1
NMR (0.138 m, C6D6, δ): 0.99 (s, -CH3), 5.20 (d, J PH ) 290
Hz, -PH), 6.8-7.4 (m, Ph). 31P NMR (0.0.0689 M, C6D6, δ):
1
3
-33.40 (dt, J PH ) 290 Hz, J PCCH ) 9.0 Hz). 31P NMR (0.138
1
M, 20 °C, δ): initial spectrum, -37.87 (dp, J PH ) 272 Hz,
1
3
M, C6D6, δ): -33.17 (dp, J PH ) 292 Hz, J PCCH ) 9.2 Hz).
Cryoscopic molecular weight (measured upon mixing reagents;
formula weight 301.02; calcd mol wt, obsd mol wt, R or percent
dissociation, Kd): 0.0644, 0.0672, 4.34%, 1.27 × 10-4; 0.0542,
3J PCCH ) 13.4 Hz, (Me3CCH2)3Ga‚P(H)Et2). No change in the
spectrum occurred after heating the sample for 3 weeks at an
oil bath temperature of 70 °C.
(Me3CCH2)3Ga ‚P (H)2(C6H11). (a) 1H NMR (0.0689 M,
C6D6, δ): 0.90 (s, -C6H11), 0.94 (s, -C6H11), 1.00 (s, -CMe3),
1.07 (s, Ga-CH2-), 1.12 (s, -CMe3), 1.15 (s, -C6H11), 1.18-
1.7 (br, C6H11), 2.75 (dm, 1J PH ) 225 Hz, -PH). 1H NMR (0.138
M, C6D6, δ): 0.90 (s, -C6H11), 0.93 (s, -C6H11), 1.01 (s, -CMe3),
1.06 (s, Ga-CH2-), 1.10 (s, -CMe3), 1.20-1.7 (br, -C6H11),
0.0567, 4.61%, 1.21 × 10-4; 0.0525, 0.0550, 4.76%, 1.25 × 10-4
.
Et3Ga ‚P (H)P h 2: 1H NMR upon mixing reagents (0.0689 M,
C6D6, δ): 0.76 (s, -CH2-), 1.41 (t, 2J HCH ) 8.0 Hz, -CH3), 5.31
(d, 1J PH ) 276 Hz, -PH), 6.8-7.4 (m, Ph). 1H NMR (0.138 M,
C6D6, δ): 0.75 (s, -CH2-), 1.40 (t, 2J HCH ) 8.0 Hz, -CH3), 5.31
(d, 1J PH ) 294 Hz, -PH), 6.8-7.4 (m, Ph). 31P NMR (1 h after
1
2.76 (dm, J PH ) 225 Hz, -PH). 31P NMR (0.0689 M, C6D6,
1
mixing reagents; 0.0689 M, C6D6, δ): -35.84 (dp, J PH ) 272
1
δ): -98.3 (t, J PH ) 227 Hz). 31P NMR (0.138 M, C6D6, δ):
3
Hz, J PCCH ) 9.4 Hz, 4.3 Et3Ga‚P(H)Ph2), -46.32 (s, 1.0, Et2-
1
-95.9 (t, J PH ) 227 Hz). Cryoscopic molecular weight
Ga‚PPh2). 31P NMR (1 h after mixing reagents; 0.138 M, C6D6,
(measured upon mixing reagents; formula weight 399.3; (calcd
1
3
δ): -34.00 (dp, J PH ) 296 Hz, J PCCH ) 9.4 Hz, 4.4, Et3Ga‚P-
mol wt, obsd mol wt, R or percent dissociation, Kd): 0.0552,
(H)Ph2), -46.33 (s, 1.0, Et2Ga‚PPh2). 31P NMR (3 days after
0.0828, 51.8%, 2.76 × 10-2; 0.0430, 0.0663, 54.2%, 2.76 × 10-2
.
1
mixing reagents; 0.0689 M, C6D6, δ): -35.83 (dp, J PH ) 272
(b) A solution to study the elimination reaction was
prepared by using 0.10 g (0.36 mmol) of Ga(CH2CMe3)3, 0.042
g (0.36 mmol) of H2P(C6H11), and 2.69 g of C6D6. 31P NMR
3
Hz, J PCCH ) 8.4 Hz, 3.9, Et3Ga‚P(H)Ph2), -46.24 (s, 1.0, Et2-
Ga‚PPh2). 31P NMR (3 days after mixing reagents, 0.138 M,
1
3
1
C6D6, δ): -33.98 (dp, J PH ) 294 Hz, J PCCH ) 9.6 Hz, 2.7,
Et3Ga‚P(H)Ph2), -46.23 (s, 1.0, Et2Ga‚PPh2). 31P NMR (12
days after mixing reagents, 0.0689 M, C6D6, δ): -36.05 (dp,
(0.13 M, 20 °C, δ): initial spectrum, -95.9 (t, J PH ) 227 Hz,
(Me3CCH2)3Ga‚P(H)2(C6H11)); 3 weeks after mixing reagents,
-63.63 (s, 3.9, (Me3CCH2)2GaP(H)(C6H11)), -73.29 (s, 4.1, (Me3-
CCH2)2GaP(H)(C6H11)), -105.3 (s, 1.0, (Me3CCH2)3Ga‚P(H)2-
(C6H11)). A second solution was prepared by combining 0.13
g (0.47 mmol) of Ga(CH2CMe3)3, 0.054 g (0.47 mmol) of H2P-
(C6H11), and 7.2 g of C6D6. 31P NMR, (0.065 m, 20 °C, δ): initial
1J PH ) 278 Hz, J PCCH ) 8.0 Hz, 2.6, Et3Ga‚P(H)Ph2), -46.39
3
(s, 1.0, Et2Ga‚PPh2). 31P NMR (12 days after mixing reagents,
1
3
0.138 M, C6D6, δ): -34.14 (dp, J PH ) 295 Hz, J PCCH ) 9.1
Hz, 1.2, Et3Ga‚P(H)Ph2), -46.39 (s, 1.0, Et2Ga‚PPh2). Cryo-
scopic molecular weight (measured upon mixing reagents;
formula weight 343.10; calcd mol wt, obsd mol wt, R or percent
dissociation, Kd): 0.0720, 0.0785, 9.03%, 6.45 × 10-4; 0.0580,
1
spectrum, -98.3 (t, J PH ) 227 Hz, (Me3CCH2)3Ga‚P(H)2-
(C6H11)); 7 days at 70 °C, -63.58 (s, 4.3, (Me3CCH2)2GaP(H)-
(C6H11)),-73.27 (s, 5.3, (Me3CCH2)2GaP(H)(C6H11)), -104.8 (s,
1.0, (Me3CCH2)3Ga‚P(H)2(C6H11)); 14 days at 70 °C, -63.83 (s,
5.3, (Me3CCH2)2GaP(H)(C6H11)), -73.10 (s, 8.2, (Me3CCH2)2-
GaP(H)(C6H11)), -107.3 (s, 1.0, (Me3CCH2)3Ga‚P(H)2(C6H11));
18 days at 70 °C, -63.60 (s, 1.0, (Me3CCH2)2GaP(H)(C6H11)),
-73.31 (s, 1.2, (Me3CCH2)2GaP(H)(C6H11)).
0.0649, 11.9%, 9.32 × 10-4; 0.0422, 0.0478, 13.3%, 8.57 × 10-4
.
(P h Me2CCH2)3Ga ‚P (H)P h 2. 1H NMR (0.0689 M, C6D6,
1
δ): 0.83 (s, Ga-CH2-), 1.23 (s, -CMe2-), 5.15 (d, J PH ) 219
Hz, -PH), 6.80-7.40 (m, Ph). 1H NMR (0.138 M, C6D6, δ):
0.84 (s, Ga-CH2-), 1.24 (s, -CMe2-), 5.13 (d, 1J PH ) 231 Hz,
-PH), 6.82-7.42 (m, Ph). 31P NMR (0.0689 M, C6D6, δ):
-39.17 (dp, 1J PH ) 224 Hz, 3J PCCH ) 7.3 Hz). 31P NMR (0.138
Syn th esis of (Me3CCH2)3Ga ‚P (H)(C6H11)2. (a) The re-
agents 0.524 g (1.85 mmol) of Ga(CH2CMe3)3 and 0.367 g (1.85
mmol) of HP(C6H11)2, contained in screw-cap vials, were
transferred quantitatively to a Schlenk flask with repeated
washing with dry pentane. After the solution was stirred for
2 h, the pentane was removed by vacuum distillation to leave
a colorless solid, which was purified by sublimation (0.995 g
of (Me3CCH2)3Ga‚P(H)(C6H11)2, 1.69 mmol, 91.6% yield). Mp:
42-43 °C. 1H NMR (0.0689 M, C6D6, δ): 0.82 (s, -C6H11), 1.05
(s, Ga-CH2-), 1.11 (s, -C6H11), 1.17 (s, -CMe3), 1.37 (s,
-C6H11), 1.54 (s, -C6H11), 1.60 (s, -C6H11), 1.73 (s, -C6H11),
2.98 (dt, 1J PH ) 215 Hz, 2J HCH ) 5.3 Hz, -PH). 1H NMR (0.138
M, C6D6, δ): 0.90 (s, -C6H11), 1.00 (s, -C6H11), 1.07 (s, Ga-
CH2-), 1.08 (s, -C6H11), 1.14 (s, -C6H11), 1.20 (s, -CMe3), 1.41
(s, -C6H11), 1.55 (s, -C6H11), 1.61 (s, -C6H11), 1.74 (s, -C6H11),
1.75 (s, -C6H11), 3.02 (dt, 1J PH ) 231 Hz, 2J HCH ) 4.5 Hz, -PH).
1
3
M, C6D6, δ): -38.40 (dp, J PH ) 230 Hz, J PCCH ) 7.4 Hz).
Cryoscopic molecular weight (formula weight 655.56; calcd mol
wt, obsd mol wt, R or percent dissociation, Kd): 0.0495, 0.0823,
66.3%, 6.44 × 10-2; 0.0414, 0.0690, 66.7%, 5.52 × 10-2; 0.0315,
0.0518, 64.4%, 3.68 × 10-2
.
Rea ction of Ga (C6H2Me3)3 w ith HP P h 2. 1H NMR (0.0689
M of each reagent, C6D6, δ): 2.13 (s, p-Me), 2.32 (s, o-Me), 5.17
1
(d, J PH ) 216 Hz, -PH), 6.73 (s, m-H), 6.9-7.4 (m, Ph). 1H
NMR (0.138 m, C6D6, δ): 2.13 (s, p-Me), 2.32 (s, o-Me), 5.17
1
(d, J PH ) 216 Hz, -PH), 6.73 (s, m-H), 6.9-7.4 (m, Ph). 31P
1
3
NMR (0.0689 M, C6D6, δ): -40.40 (dp, J PH ) 217 Hz, J PCCH
) 6.9 Hz). 31P NMR (0.138 M, C6D6, δ): -40.40 (dp, J PH
217 Hz, J PCCH ) 7.6 Hz). Cryoscopic molecular weight
(formula weight 613.46; calcd mol wt, obsd mol wt, R or percent
dissociation): 0.0415, 0.0832, 100%; 0.0371, 0.0739, 99.2%.
)
1
3
1
31P NMR (0.0689 M, C6D6, δ): -25.02 (d, J PH ) 219 Hz). 31P
1
NMR (0.138 M, C6D6, δ): -23.80 (d, J PH ) 230 Hz). Anal.
Calcd: C, 67.35; H, 11.72. Found: C, 67.27; 11.57. Cryoscopic
molecular weight (formula weight 481.50; calcd mol wt, obsd
mol wt, R or percent dissociation, Kd): 0.0638, 0.0918, 43.8%,
2.18 × 10-2; 0.0528, 0.0785, 48.8%, 2.46 × 10-2; 0.0413, 0.0639,
Ack n ow led gm en t. This work was supported in part
by the Office of Naval Research. We thank Matthew J .
Noble for preparing the Ga(CH2CMe2Ph)3 which was
used in this study.
54.6%, 2.71 × 10-2
.
(b) Equal molar quantities of Ga(CH2CMe3)3 and HP(C6H11
)
2
were combined in C6D6 in order to test for the occurrence of
OM970296Q