Synthesis and characterization of mixed-substituent P-n-propyl-N-trimethylsilylphosphoranimines

Article abstract of DOI:10.1080/10426500307867

One approach to the synthesis of polyphosphazenes is the condensation polymerization of phosphoranimines. In this work, several novel P-n-propyl-N-trimethylsilylphosphoranimines have been synthesized and characterized. Modifications to the literature synt

Full text of DOI:10.1080/10426500307867

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Phosphorus, Sulfur, and Silicon and the Related
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Synthesis and Characterization of Mixed-Substituent P-
n -Propyl-N-trimethylsilylphosphoranimines
John R. Klaehn a , Thomas A. Luther a , Mason K. Harrup a & Frederick F. Stewart a
a Idaho National Engineering and Environmental Laboratory , Idaho Falls, Idaho
Published online: 27 Oct 2010.
To cite this article: John R. Klaehn , Thomas A. Luther , Mason K. Harrup & Frederick F. Stewart (2003) Synthesis and
Characterization of Mixed-Substituent P- n -Propyl-N-trimethylsilylphosphoranimines, Phosphorus, Sulfur, and Silicon and the
Related Elements, 178:7, 1587-1603, DOI: 10.1080/10426500307867
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Phosphorus, Sulfur, and Silicon, 178:1587–1603, 2003
C
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390213004
SYNTHESIS AND CHARACTERIZATION
OF MIXED-SUBSTITUENT P-n-PROPYL-N-
TRIMETHYLSILYLPHOSPHORANIMINES
John R. Klaehn, Thomas A. Luther, Mason K. Harrup,
and Frederick F. Stewart
Idaho National Engineering and Environmental Laboratory,
Idaho Falls, Idaho
(Received December 1, 2002; accepted February 3, 2003)
One approach to the synthesis of polyphosphazenes is the conden-
sation polymerization of phosphoranimines. In this work, several
novel P-n-propyl-N-trimethylsilylphosphoranimines have been syn-
thesized and characterized. Modifications to the literature synthetic
routes were required to obtain the precursor phosphines. The N-
trimethylsilylphosphoranimines were obtained though oxidation of the
phosphine with bromine and then subsequent nucleophilic displace-
ment using lithium phenoxide. These phosphoranimines were stable
for long periods of time under dry inert conditions. NMR analyses re-
vealed complex splitting patterns beyond typical coupling due to the
stereocenter at phosphorus. We report several approaches to the n-propyl
containing phosphines and phosphoranimines.
Keywords: Characterization; phosphines; phosphoranimines; stereo-
center; synthesis
Polyphosphazenes can have a wide variety of properties depending
on the substituents on the P-N backbone, and this versatility gives
polyphosphazenes potential advantages over other polymer systems
4
for a variety of applications.1 Two general methods are employed
for polyphosphazene synthesis: ring opening polymerization (ROP) and
condensation polymerization.
The most recognized process for polyphosphazene synthesis is the
ROP route developed by Allcock and coworkers.5 The cyclic trimer,
This work was supported by the United States Department of Energy through con-
tract DE-AC07-99ID13727. Technical discussions with Dr. Robert H. Neilson at Texas
Christian University were greatly appreciated.
Address correspondence to John R. Klaehn, Idaho National Engineering and Environ-
mental Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2208. E-mail: klaejr@inel.gov
1587

1588
J. R. Klaehn et al.
hexachlorocyclotriphosphazene, is thermally ring opened to produce hy-
drolytically unstable poly(dichlorophosphazene). Stable polymers are
generated through nucleophilic displacement of chlorine, mainly with
amines, aryloxides, and alkoxides. This synthetic order is immutable as
a fully substituted cyclic phosphazene will not polymerize, hence substi-
tution at phosphorus must be carried out after polymerization. To form
polyphosphazenes via the ROP route with direct P-C linkages requires
reactions using organometallic reagents, such as Grignards, but these
reactions give only partial substitution at the phosphorus center.6 Even
under forcing conditions, the alkyl or aryl substitutions are incomplete,
and in some cases polymer degradation or undesired side reactions oc-
cur. Therefore, alkyl and aryl substitution must be accomplished by a
different technique.
The other well-known process for polyphosphazene synthesis is the
condensation polymerization developed by Neilson and Wisian-Neilson
10
(Scheme 1).7
The condensation polymerization method provides a
useful alternative route to stable alkyl and aryl polyphosphazenes
where the functional groups are incorporated prior to polymerization. A
further advantage of the condensation route is that mixed substituent
homopolymers can be synthesized readily. Whereas, nucleophilic sub-
stitution of the ROP derived polydichlorophosphazene with two sub-
stituents results only in the synthesis of random terpolymers.
SCHEME 1
A wide variety of alkyl and aryl N,N-bis(trimethylsilyl)aminopho-
sphines, (Me3Si)2NP(R)(R0), have been prepared using the Wilburn
17
method (Scheme 2).11
The first step in producing phosphazenes
via the condensation route is the synthesis of (Me3Si)2NP(R)(R0)
which generally proceeds through a one-pot reaction where reagents
are added sequentially. Conversion of (Me3Si)2NP(R)(R0) to halo-
N-trimethylsilylphosphoranimines, (Me3Si)N P(R)(R0)(Br), is accom-
plished by using oxidizing agents, such as Br2.16,17 Displacement
of bromine with oxo-nucleophiles yields potential mixed substituent
homopolymer precursors.7
Neilson and Wisian-Neilson developed a successful method for
synthesizing many types of dialkyl and alkyl/aryl polyphosphazenes.7

Synthesis and Characterization of Mixed-Substituent
1589
SCHEME 2
Their route yielded several symmetrical and unsymmetrical
N-trimethylsilylphosphoranimines containing either methyl or
phenyl groups.11,12 Other synthetic pathways have synthesized
(Me3Si)2NP(R)(Cl), (Me3Si)2NP(R)(Br) and the corresponding
(Me3Si)N P(R)(Br)2 where R is an alkyl or aryl. Previously, these
products were obtained only through the attachment of sterically bulky
groups, such as t-butyl.19 Later, others have isolated and characterized
some monoalkylated chlorophosphines,20 yet many of these compounds
18
were intermediates for other reactions.11,12,14
In this contribution,
we report the synthesis of mixed-substituent phosphoranimines
containing n-propyl groups.
RESULTS AND DISCUSSION
P-n-Propyl-N,N-bis(trimethylsilyl)aminophosphines, 1–9
The Wilburn method13 was utilized for the synthesis of 1 and 2,
(Me3Si)2NP(n-Pr)(Cl) and (Me3Si)2NP(i-Pr)(Cl), respectively.18,20 The
key step in these reactions is the addition of only one equivalent
of Grignard in the final step of the reaction sequence (Scheme 3).
The reaction yielded nearly pure 2, however, the synthesis of 1 af-
forded a slight mixture of products with its analogous dialkylated
SCHEME 3

1590
J. R. Klaehn et al.
product. Integration of the resonances obtained by 31P NMR spec-
troscopy showed an 83% conversion to 1 was achieved with the bal-
ance comprised of the dialkylated phosphine side-product. Vacuum
distillation with a fractionation column failed to separate these two
products.
1
31P{ H} NMR spectroscopic analyses of 1 and 2 gave the expected
phosphorus(III) downfield shifts at 160 and 164 ppm respectively.
1
The H NMR spectrum of 1 shows multiplets at 2.48–2.60 and 1.68–
1
1.82 ppm, and a triplet at 1.28 ppm. The 13C{ H} NMR spectrum re-
veals C-P spin-coupling with the (44 Hz), (26 Hz), and (15 Hz)
carbon nuclei.
The NMR spectral properties of 2 are significantly different from 1.
Compound 2 has diastereotopic i-propyl methyl groups that are clearly
1
1
evident in the H and 13C{ H} NMR spectra (Figure 1). The i-propyl
methyl groups are unique regardless of the rotation around the phos-
phorus carbon bond (Figure 2). As a result, the NMR spectra of the
i-propyl methyl groups became more complicated with two sets of dou-
1
blet of doublets in the H NMR spectrum and two sets of doublets in
1
1
the 13C{ H} NMR spectrum. In addition, the H NMR spectrum of 2
with phosphorus decoupling reduces the resonance for the protons of
the i-propyl methyl groups to two doublets.
(Me3Si)2NP(n-Pr)2, 3, and (Me3Si)2NP(n-Pr)(Me), 4, were syn-
thesized according to reported literature procedures.11,12 The
(Me3Si)2NP(n-Pr)(n-Hex), 5, was obtained through addition of the larger
alkyl Grignard to generate the corresponding chlorophosphine in situ,
followed by the addition of the smaller alkyl Grignard (Scheme 4). Se-
quential addition was found to limit the amount of di-n-propyl phos-
phine through simple steric hindrance created by the larger alkyl
nucleophile.
SCHEME 4
The 31P NMR spectra for 3 and 4 are consistent with data reported
in the literature.11 The 31P NMR resonance of 5 was slightly upfield
1
as compared to signals for 3 and 4 (Table I). The H NMR spectrum
of 5 exhibited the resonance for the phosphorus bound n-propyl CH2
group further downfield with respect to the other methylene groups.

Synthesis and Characterization of Mixed-Substituent
1591
1
FIGURE 1 1H (upper) and 13C{ H} (lower) NMR spectra of (Me3Si)2NP(i-
Pr)(Cl) (2) (CDCl3).
The terminal methyl groups of the n-hexyl and n-propyl alkyl chains
are clearly evident by separate triplets.
Compound 6, (Me3Si)2NP(n-Pr)(i-Pr), could not be synthesized using
the one-pot Wilburn method. It was found that the n-propyl Grignard

1592
J. R. Klaehn et al.
FIGURE 2 Newman Projections of (Me3Si)2NP(n-Pr)(Cl), 2, across the P C
bond.
did not react with (Me3Si)2NP(i-Pr)(Cl) in diethyl ether or THF us-
ing the previous reaction conditions. Application of vigorous reflux
conditions gave multiple products that were not separable through
vacuum distillation. It was determined that 2 had to be isolated first to
produce 6. The rate of reaction between n-propyl Grignard and 2 is al-
most non-existent at room temperature. The temperature was elevated
to a light reflux in THF, affording 6 (Scheme 5).
SCHEME 5
The 31P NMR resonance for 6 (63.9 ppm) is downfield with respect
to the other dialkyl phosphines possibly due to steric interactions
1
with the two side groups. The H NMR spectrum of 6 is similar to 2,
in which there is additional splitting of the i-propyl methyl protons
resulting from the diastereotopic nature of their environment. Further
complicating this region of the spectrum are the n-propyl methyl
protons that gave a coincidental triplet with the diastereotopic doublet
1
of doublets (Figure 3). The 13C{ H} NMR spectrum of 6 also exhibits
resonances that are consistent with the diastereotopic methyls on the
i-propyl group. In addition, the signals for the n-propyl group were
consistent with 3.
The nucleophilic displacement of chlorine from 1 was performed
with lithium 2,2,2-trifluoroethoxide or lithium phenoxide to form 7 and
8 (Scheme 6). The chemical shift of the resonance of the 31P NMR
spectrum of 7 was downfield relative to its chlorophosphine analog
(166 ppm) whereas 8 was slightly upfield (155 ppm). These values were
consistent with the previous examples (Table I).20 The methylene pro-
tons of the CF3CH2O- group in 7 displayed a pentet at 3.96 ppm in

1593

1594
J. R. Klaehn et al.
FIGURE 3 1H NMR spectrum of (Me3Si)2NP(n-Pr)(i-Pr) (6) (CDCl3).
SCHEME 6
1
the H NMR spectrum due to the coupling with fluorine and the CH2
group of 8, to the phosphorus, exhibited diastereotopic hydrogens.
Phosphorus coupling was observed at the phenoxy substituent as addi-
1
tional splitting patterns in the aromatic region of the 1H and 13C{ H}
NMR spectra of 8.
The reaction method for the formation of 9 was similar to the pre-
vious synthesis, however, phenyldichlorophosphine was used to gen-
erate (Me3Si)2NP(Ph)(Cl) (Scheme 7). The addition of the n-propyl
Grignard went to completion at room temperature using THF as the
solvent. The 31P NMR spectrum of 9 was comparable to the other
1
1
bis-alkylphosphines (Table I). Additionally, the H and 13C{ H} NMR
spectra were consistent with the proposed structure.

Synthesis and Characterization of Mixed-Substituent
1595
SCHEME 7
P-n-Propyl-P-phenoxy-N-
trimethylsilylphosphoranimines, 10–16
Oxidation of phosphines 3 through 9 with bromine has been ac-
complished using the method of Neilson and Wisian-Neilson.7 In
their method, benzene was employed as the solvent, however, in this
study, toluene was successfully used without difficulty. Bromine was
added slowly to each phosphine at 0 C (Scheme 8). Although the
bromophosphoranimine intermediates were not isolated, the phenoxide
readily displaces the bromine to yield the corresponding phosphoran-
imines, 10–16.
SCHEME 8
Isolation of products was performed using a flash vacuum distillation
process. It was found that the salt coproducts could not be entirely sepa-
rated by simple washing of the phosphoranimine with hexanes without
creating an intractable residue. Even common techniques using frac-
tional amounts of hexanes could not separate the residue. However,
the product was separated from the residue by vacuum distillation,
utilizing heated glassware to minimize decomposition of the product.
Special precautions were taken because the products have distillation
temperatures close to their decomposition temperatures, especially 11,
15, and 16. Overall, these phosphoranimines were stable under dry,
inert conditions for extended periods.
Most of the 31P NMR spectra for the dialkyl phosphoranimines, 10–
13, exhibit similar chemical shifts, 32–38 ppm, while 16 was slightly
upfield at 23 ppm. In contrast, the 2,2,2-trifluoroethoxy, 14, and the phe-
noxy, 15, clearly showed an upfield shift (16 and 10 ppm respectively) in

1596
J. R. Klaehn et al.
FIGURE 4 1H NMR spectrum of (Me3Si)N P(n-Pr)(OCH2CF3)(OPh) (14)
(CDCl3).
the 31P NMR spectra due to the attachment through oxygen rather than
a carbon linkage. The 1H NMR spectra for compounds 10–16 were more
difficult to categorize. The chemical shifts and coupling constants were
fairly consistent for the phenoxy group on all of the isolated phosphora-
1
nimines. However, the H NMR spectrum of 14 showed diastereotopic
hydrogens on the methylene group on CF3CH2O- (Figure 4) and 13 dis-
played diastereotopic methyl groups as seen before with its analogous
phosphine, 6. The 13C NMR spectra of 10–16 did not show the same
trend in coupling constants as for the phosphines 1–9. The J1CP for the
alkyl chains were determined to be 90–145 Hz, 2–8 Hz for J2CP, and
20–25 Hz for J3CP, consistent with a trend found with other alkylphos-
phorus(V) compounds.11
CONCLUSIONS
A facile route to new mixed-substituent phosphines has been de-
vised where few undesirable side products are produced. Initially at-
tached substituents that are sterically demanding, such as i-propyl
or phenyl, appear to inhibit further substitution with larger alkyl
Grignard reagents in diethyl ether. Overall, many of the previ-
ous reported synthetic pathways were modified to provide better

Synthesis and Characterization of Mixed-Substituent
1597
routes for a diverse array of mixed-substitutent phosphines and
phosphoranimines.
Several of the NMR spectra for the phosphines and phosphoran-
imines revealed diastereotopic carbons that complicate the 1H and
1
13C{ H} NMR spectra because of the phosphorus stereocenter. Sev-
eral trends in the 31P NMR spectra are apparent. Inductive electron
withdrawing effects were clearly seen with the 2,2,2-trifluoroethoxy
and the phenoxy groups giving a downfield shift with respect to the
alkyl substituents (Table I). However, in the phosphoranimines, these
substituents clearly showed an upfield shift in the 31P NMR spectra.
Another trend observed in the 31P NMR spectra among the alkyl-n-
propylphosphines and the alkyl-n-propylphosphoranimines is a down-
field shift of the 31P NMR signal with increased steric bulk around the
phosphorus.
EXPERIMENTAL
Materials and General Procedures
The following reagents were obtained from Aldrich and used without
further purification: (Me3Si)2NH, PCl3, PhPCl2, methyl MgBr (3.0 M in
ether), n-propyl MgCl (2.0 M in ether), i-propyl MgCl (2.0 M in ether),
n-hexyl MgCl (2.0 M in ether), n-butyl lithium (2.5 M in hexanes),
CF3CH2OH, and phenol. Solvents employed were anhydrous diethyl
ether, anhydrous tetrahydrofuran (THF), anhydrous toluene, and hex-
anes, and they were used as received from the manufacturer. Proton,
1
1
13C{ H}, and 31P{ H} NMR spectra were recorded on a Bruker DMX
300 WB spectrometer operating at 7.04T: 300 MHz (1H), 75 MHz (13C)
and 121 MHz (31P).
Preparation of P-n-propyl-P-chloro-N,N-
bis(trimethylsilyl)aminophosphine (1) and
P-i-propyl-P-chloro-N,N-bis(trimethylsilyl)-
aminophosphine (2)
These materials were prepared according to literature procedures.20
(Me3Si)2NP(n-Pr)(Cl) (1); [83% yield, bp = 65–75 C at 0.5–0.6 mmHg,
31P NMR (CDCl3) = (s) 159.8, 1H NMR (CDCl3) = (m, 2H) 2.48–2.60,
(m, 2H) 1.68–1.82, (t, 3H, JHH = 7.3 Hz) 1.28, (s, 18H) 0.32, 13C NMR
(CDCl3) = (d, CH2, JPC = 43.9 Hz) 41.5, (d, CH2, JPC = 25.7 Hz)
18.6, (d, CH3, JPC = 15.2 Hz) 15.2, (d, Si(CH3)3, JPC = 8.7 Hz) 4.4].
(Me3Si)2NP(i-Pr)(Cl) (2); [71% yield, bp = 63–65 C at 0.5–0.6 mmHg,
31P NMR (CDCl3) = (s) 164.2,1H NMR (CDCl3) = (H, doublet of

1598
J. R. Klaehn et al.
septets, JHH = 7.1 Hz, JPH = 2.8 Hz) 2.54, (diastereotopic methyls) (3H,
dd, (CH3)A, JHH = 7.0 Hz, JPH = 19.9 Hz) 1.12, (3H, dd, (CH3)B, JHH
=
7.3 Hz, JPH = 16.9 Hz) 1.03, (18H, s) 0.34, 13C NMR (CDCl3) = (d, CH,
JPC = 36.8 Hz) 35.5, (d, (CH3)A, JPC = 29.0 Hz) 18.6, (d, (CH3)B, JPC
21.4 Hz) 18.4, (d, Si(CH3)3, JPC = 8.1 Hz) 5.0].
=
Preparation of P,P-bis-n-propyl-N,N-bis(trimethylsilyl)-
aminophosphine (3); P-n-propyl-P-methyl-N,N-
bis(trimethylsilyl)aminophosphine (4); and
P-n-propyl-P-n-hexyl-N,N-bis(trimethylsilyl)-
aminophosphine (5)
These materials were prepared according to literature procedures.11
However, the larger alkyl chain Grignard reagent (1 equivalent) is
added first, followed by the smaller alkyl chain Grignard reagent (1
equivalent). (Me3Si)2NP(n-Pr)2(3); [73% yield, bp = 63–70 C at 0.3–
0.35 mmHg, 31P NMR (CDCl3) = (s) 49.6, 1H NMR (CDCl3) = (m, 4H)
1.78–1.88, (m, 4H) 1.34–1.55, (t, 6H, JHH = 7.0 Hz) 1.02, (d, 18H, JPH
=
1.0 Hz) 0.22, 13C NMR (CDCl3) = (d, CH2, JPC = 18.6 Hz) 35.2, (d,
CH2, JPC = 19.0 Hz) 19.6, (d, CH3, JPC = 13.3 Hz) 16.2, (s, Si(CH3)3) 5.0].
(Me3Si)2NP(n-Pr)(Me) (4); [60% yield, bp = 58–68 C at 0.25 mmHg,
31P NMR (CDCl3) = (s) 40.3, 1H NMR (CDCl3) = (m, 2H) 1.78–1.87,
(m, 2H) 1.39–1.50, (d, 3H, JPH = 5.8 Hz) 1.31, (t, 3H, JHH = 7.0 Hz)
1.02, (s, 18H) 0.22]. (Me3Si)2NP(n-Pr)(n-Hex) (5); [60% yield, bp =
1
76–82 C at 0.07–0.09 mmHg, 31P NMR (CDCl3) = (s) 50.1 ppm, H
NMR (CDCl3) = (m, 2H) 1.78–1.87, (m, 8H) 1.32–1.55, (m, 4H) 1.25–
1.37, (t, 3H, JHH = 7.0 Hz) 1.03, (t, 3H, JHH = 6.9 Hz) 0.91, (s, 18H)
0.22, 13C NMR (CDCl3) = (d, CH2, JPC = 18.6 Hz) 35.8, (d, CH2, JPC
18.4 Hz) 33.4, (s, CH2) 32.5, (d, CH2, JPC = 12.6 Hz) 31.9, (d, CH2, JPC
=
=
18.2 Hz) 26.8, (s, CH2) 23.4, (d, CH2, JPC = 19.0 Hz) 20.2, (d, CH3,
JPC = 13.3 Hz) 16.8, (s, CH3) 14.9, (s, Si(CH3)3) 5.5].
Preparation of P-n-propyl-P-i-propyl-N,N-
bis(trimethylsilyl)aminophosphine (6)
A 250 mL three-neck, round bottom flask, equipped with a gas inlet,
two rubber septa, and a magnetic stir bar was purged with nitrogen.
Compound 2 (13.5 g, 0.050 mmol) was introduced into the flask via sy-
ringe with 100 mL of THF. This solution was cooled to 0 C, and n-propyl
magnesium chloride (25.0 mL, 0.050 mmol) was slowly transferred to
the 250 mL flask with the aid of a syringe. The reaction mixture was
placed under a light reflux with stirring, overnight. After cooling to
room temperature, 75% of the ether was removed by reduced pressure
leaving behind a salt slurry. The slurry was washed three times with

Synthesis and Characterization of Mixed-Substituent
1599
100 mL of distilled hexane and filtered each time. The hexane was re-
moved at reduced pressure leaving behind an oil. Fractional distillation
under vacuum gave a colorless, clear liquid. (Me3Si)2NP(n-Pr)(i-Pr)
(6); [50% yield, bp = 80–95 C at 0.6–0.8 mmHg, 31P NMR (CDCl3) =
1
(s) 63.9, H NMR (CDCl3) = (H, doublet of septets, JHH = 7.1 Hz,
JPH = 2.8 Hz) 2.03, (m, 2H) 1.78–1.87, (m, 2H) 1.25–1.50, (diastereotopic
methyls) (3H, dd, (CH3)A, JHH = 7.0 Hz, JPH = 14.1 Hz) 1.06, (3H, dd,
(CH3)B, JHH = 6.9 Hz, JPH = 18.0 Hz) 0.92, (t, 3H, JHH = 7.0 Hz) 1.03, (s,
18H) 0.23, 13C NMR (CDCl3) = (d, CH2, JPC = 21.3 Hz) 33.4, (d, CH,
JPC = 15.0 Hz) 28.9, (d, (CH3)A, JPC = 18.1 Hz) 20.2, (d, (CH3)B, JPC
=
15.8 Hz) 20.1 (d, CH2, JPC = 29.3 Hz) 18.8, (d, CH3, JPC = 12.9 Hz) 16.3,
(two broaden peaks, Si(CH3)3) 3.2–6.0].
Preparation of P-n-propyl-P-2,2,2-trifluoroethoxy-
N,N-bis(trimethylsilyl)aminophosphine (7) and
P-n-propyl-P-phenoxy-N,N-
bis(trimethylsilyl)aminophosphine (8)
These materials were prepared according to literature procedures.20
(Me3Si)2NP(n-Pr)(OCH2CF3) (7); [67% yield, bp = 60–70 C at 0.3–
0.35 mmHg, 31P NMR (CDCl3) = (s) 166.7, 1H NMR (CDCl3) =
(pent, 2H, JFH = 8.8 Hz) 3.96, (diastereotopic hydrogens) (H, m, HA)
1.83–1.96, (H, m, HB) 1.55–1.68, (m, 2H) 1.37–1.54, (t, 3H, JHH
=
7.2 Hz) 1.03, (s, 18H) 0.22, 13C NMR (CDCl3) = (doublet of quartets,
CF3, JPC = 11.4 Hz, JFC = 278.4 Hz) 124.1, (doublet of quartets, CH2,
JPC = 20.4 Hz, JFC = 35.3 Hz) 66.0, (d, CH2, JPC = 19.5 Hz) 36.2, (d,
CH2, JPC = 25.7 Hz) 18.6, (d, CH3, JPC = 14.5 Hz) 15.2, (d, Si(CH3)3,
JPC = 8.7 Hz) 4.0]. (Me3Si)2NP(n-Pr)(OPh) (8); [50% yield, bp = 95–
1
115 C at 0.3–0.5 mmHg, 31P NMR (CDCl3) = (s) 154.7, H NMR
(CDCl3) = (t, meta, JHH = 7.4 Hz) 7.31, (d, ortho, JHH = 8.3 Hz) 7.10, (t,
para, JHH = 7.0 Hz) 7.05, (diastereotopic hydrogens) (H, m, HA) 2.05–
2.18, (H, m, HB) 1.72–1.90, (m, 2H) 1.53–1.72, (t, 3H, JHH = 7.2 Hz)
1.13, (s, 18H) 0.31, 13C NMR (CDCl3) = (d, ipso, JPC = 8.5 Hz) 158.0,
(s, meta) 130.0, (s, para) 122.8, (d, ortho, JPC = 10.1 Hz) 120.2, (d, CH2,
JPC = 21.1 Hz) 39.9, (d, CH2, JPC = 22.5 Hz) 18.4, (d, CH3, JPC = 14.0 Hz)
16.6, (d, Si(CH3)3, JPC = 3.4 Hz) 4.1].
Preparation of P-n-propyl-P-phenyl-N,N-
bis(trimethylsilyl)aminophosphine (9)
A 500 mL three-neck, round bottom flask, equipped with a gas inlet,
a 125 mL addition funnel, magnetic stir bar, and a rubber septum was
charged with nitrogen, (Me3Si)2NH (20.9 mL, 0.100 mmol), and THF
(100 mL). The solution was cooled to 0 C, and n-butyl lithium (40 mL,
0.100 mmol) was added to the addition funnel via syringe. The n-butyl

1600
J. R. Klaehn et al.
lithium was then slowly added to the cooled solution and the addition
funnel was washed with THF (30 mL). The ice bath was removed and
the mixture was allowed to warm to room temperature for 1 h. The so-
lution was cooled to 78 C in a dry ice/acetone bath for 10 min. PhPCl2
(13.5 mL, 0.100 mmol) was injected via syringe into the addition fun-
nel and slowly added to the cooled solution. THF (30 mL) was used to
rinse the addition funnel. The dry ice/acetone bath was removed and the
mixture was allowed to warm to room temperature for 1.5 h. The mix-
ture was then cooled to 0 C for 10 min. The n-propyl Grignard reagent
(50 mL, 0.100 mmol) solution was added to the addition funnel via sy-
ringe and slowly added to the reaction mixture. After warming to room
temperature and stirring overnight, 75% of the THF was removed under
reduced pressure, leaving behind a slurry. The slurry was washed three
times with 200 mL of distilled hexanes to precipitate the salts. The su-
pernatant was decanted into a nitrogen purged, 1000 mL round bottom
flask equipped with a magnetic stir bar. The hexanes were removed at
reduced pressure, leaving an oil. Fractional distillation under vacuum
gave a colorless, clear liquid. (Me3Si)2NP(n-Pr)(Ph) (9); [85% yield,
1
bp = 115–120 C at 0.2–0.3 mmHg, 31P NMR (CDCl3) = (s) 47.8, H
NMR (CDCl3) = (d, ortho, JHH = 6.0 Hz) 7.41, (t, meta, JHH = 7.1 Hz)
7.34, (t, para, JHH = 7.0 Hz) 7.22, (m, 2H) 2.05–2.18, (m, 2H) 1.72–1.90,
(m, 2H) 1.53–1.72, (t, 3H, JHH = 7.2 Hz) 1.13, (s, 18H) 0.31, 13C NMR
(CDCl3) = (d, ipso, JPC = 22.8 Hz) 147.7, (d, meta, JPC = 14.9 Hz) 129.4,
(d, ortho, JPC = 2.6 Hz) 128.8, (s, para) 127.5, (d, CH2, JPC = 22.0 Hz)
35.2, (d, CH2, JPC = 21.8 Hz) 20.5, (d, CH3, JPC = 14.7 Hz) 16.9, (d,
Si(CH3)3, JPC = 6.7 Hz) 4.1].
Preparation of P-n-propyl-P-phenoxy-N-
trimethylsilylphosphoranimines (10–16)
The procedure is similar to previous literature with the substitution
of toluene as the solvent.16 A 250 mL three-neck, round bottom flask,
equipped with a gas inlet, 60 mL addition funnel, magnetic stir bar, and
a rubber septum, was purged with nitrogen. The appropriate phosphine
(0.035 mmol) was added by syringe to the flask containing 150 mL of
anhydrous toluene. The flask was cooled to 0 C, and bromine (2.0 mL,
0.039 mmol) was introduced to the addition funnel by syringe and mixed
with 10 mL of toluene. The bromine solution was added slowly to the
cooled flask with constant stirring. The addition was stopped when a
yellow color persisted in the flask. The ice bath was removed, and the
solution was slowly warmed to room temperature for 1.5 h. The sol-
vent was removed at reduced pressure leaving a red-brown viscous liq-
uid. The viscous liquid was dissolved in 100 mL of diethyl ether with
stirring. A separate 100 mL three-neck, round bottom flask, equipped

Synthesis and Characterization of Mixed-Substituent
1601
with a gas inlet, 60 mL addition funnel, magnetic stir bar, and a rub-
ber septum was purged with nitrogen. Phenol (3.7 g, 0.038 mmol) was
added to that flask along with 75 mL of diethyl ether. The flask was
cooled to 0 C for 10 min, and n-butyl lithium (15 mL, 0.038 mmol) was
added to the addition funnel via syringe and slowly added to the phe-
nol/ether solution. The solution was allowed to warm to room temper-
ature for about one hour. The brominated phosphoranimine solution
was cooled to 0 C for 10 min, and the lithium phenoxide solution was
transferred to the phosphoranimine solution by cannula, directed by ni-
trogen flow. The solution was warmed to room temperature overnight.
Reduced pressure was used to remove 75% of the ether leaving behind a
salt slurry. The salt slurry was “flash” distilled under vacuum yielding
a colorless, clear liquid. (Me3Si)N P(n-Pr)2(OPh) (10); [50% yield,
1
bp = 90 C at 0.2 mmHg, 31P NMR (CDCl3) = (s) 35.6, H NMR
(CDCl3) = (t, meta, JHH = 8.0 Hz) 7.31, (d, ortho, JHH = 7.7 Hz) 7.15, (t,
para, JHH = 6.6 Hz) 7.14, (m, 4H) 1.70–1.85, (m, 4H) 1.55–1.70, (t, 6H,
JHH = 7.0 Hz) 1.04, (s, 9H) 0.05]. (Me3Si)N P(n-Pr)(Me)(OPh) (11);
[53% yield, bp = 85–95 C at 0.1–0.3 mmHg, 31P NMR (CDCl3) = (s)
32.0, 1H NMR (CDCl3) = (t, meta, JHH = 8.0 Hz) 7.22, (d, ortho,
JHH = 7.7 Hz) 6.88, (t, para, JHH = 6.6 Hz) 6.85, (m, 4H) 1.55–
1.85, (d, 2H, JPH = 11.6 Hz) 1.51, (m, 3H) 0.93–1.12, (s, 18H) 0.28].
(Me3Si)N P(n-Pr)(n-Hex)(OPh) (12); [42% yield, bp = 140–150 C
at 0.25 mmHg, 31P NMR (CDCl3) = (s) 36.2, 1H NMR (CDCl3) = (t,
meta, JHH = 8.0 Hz) 7.31, (d, ortho, JHH = 7.7 Hz) 7.15, (t, para, JHH
=
6.6 Hz) 7.14, (m, 4H) 1.69–1.87, (m, 4H) 1.50–1.69, (m, 6H) 1.25–1.50,
(t, 3H, JHH = 7.3 Hz) 1.04, (t, 3H, JHH = 6.5 Hz) 0.91, (s, 9H) 0.06, 13
C
NMR (CDCl3) = (d, ipso, JPC = 9.1 Hz) 152.5, (s, meta) 130.0, (s, para)
124.6, (d, ortho, JPC = 4.2 Hz) 122.2, (d, CH2, JPC = 90.5 Hz) 33.4, (s,
CH2) 32.2, (d, CH2, JPC = 16.1 Hz) 31.4, (d, CH2, JPC = 90.4 Hz) 31.3,
(d, CH2, JPC = 3.2 Hz) 23.6, (s, CH2) 23.3, (d, CH2, JPC = 3.1 Hz) 17.3,
(d, CH3, JPC = 17.3 Hz) 16.4, (s, CH3) 14.9, (d, Si(CH3)3, JPC = 3.3 Hz)
4.3]. (Me3Si)N P(n-Pr)(i-Pr)(OPh) (13); [53% yield, bp = 95–105 C
at 0.2–0.3 mmHg, 31P NMR (CDCl3) = (s) 37.7, 1H NMR (CDCl3) =
(t, meta, JHH = 8.3 Hz) 7.31, (d, ortho, JHH = 8.6 Hz) 7.18, (t, para, JHH
=
7.0 Hz) 7.11, (H, septet, JHH = 7.1 Hz) 2.01, (m, 2H) 1.70–1.84, (m, 2H)
1.57–1.73, (diastereotopic methyls) (3H, dd, (CH3)A, JHH = 7.1 Hz, JPH
=
17.1 Hz) 1.25, (3H, dd, (CH3)B, JHH = 7.1 Hz, JPH = 18.0 Hz) 1.23, (t,
3H, JHH = 7.2 Hz) 1.03, (s, 9H) 0.05, 13C NMR (CDCl3) = (d, ipso,
JPC = 9.6 Hz) 153.0, (s, meta) 130.0, (s, para) 124.4, (d, ortho, JPC
=
4.3 Hz) 122.2, (d, CH2, JPC = 86.6 Hz) 31.3, (d, CH, JPC = 95.0 Hz) 30.1,
(d, (CH3)A, JPC = 4.0 Hz) 17.2, (d, CH2, JPC = 1.2 Hz) 17.1, (d, (CH3)B,
JPC = 3.3 Hz) 16.9 (d, CH3, JPC = 16.7 Hz) 16.6, (d, Si(CH3)3, JPC
=
2.8 Hz) 4.4]. (Me3Si)N P(n-Pr)(OCH2CF3) (OPh) (14); [67% yield,

1602
J. R. Klaehn et al.
1
bp = 70 C at 0.15 mmHg, 31P NMR (CDCl3) = (s) 16.1, H NMR
(CDCl3) = (t, meta, JHH = 7.4 Hz) 7.34, (t, para, JHH = 7.0 Hz) 7.17,
(d, ortho, JHH = 8.3 Hz) 7.11, (diastereotopic hydrogens) (H, m, HA)
4.33–4.51, (H, 0 m, HB) 4.09–4.25, (m, 2H) 1.84–1.95, (m, 2H) 1.62–
1.80, (t, 3H, JHH = 7.3 Hz) 1.06, (s, 9H) 0.03, 13C NMR (CDCl3) =
(d, ipso, JPC = 9.7 Hz) 151.6, (s, meta) 130.2, (s, para) 125.4, (d, ortho,
JPC = 4.5 Hz) 121.9, (doublet of quartets, CF3, JPC = 11.4 Hz, JFC
=
99.5 Hz) 121.6, (doublet of quartets, CH2, JPC = 5.8 Hz, JFC = 36.9 Hz)
61.5, (d, CH2, JPC = 141.5 Hz) 31.2, (d, CH2, JPC = 5.4 Hz) 16.6, (d, CH3,
JPC = 19.3 Hz) 15.4, (s, Si(CH3)3) 3.2]. (Me3Si)N P(n-Pr)(OPh)2(15);
[67% yield, bp = 130–140 C at 0.25–0.3 mmHg, 31P NMR (CDCl3) =
1
(s) 10.7, H NMR (CDCl3) = (t, meta, JHH = 7.4 Hz) 7.34, (d, ortho,
JHH = 8.3 Hz) 7.17, (t, para, JHH = 7.0 Hz) 7.15, (m, 2H) 1.90–2.07, (m,
2H) 1.70–1.87, (t, 3H, JHH = 7.2 Hz) 1.09, (s, 9H) 0.19 ppm, 13C NMR
(CDCl3) = (d, ipso, JPC = 9.2 Hz) 152.1, (s, meta) 130.2, (s, para) 125.2,
(d, ortho, JPC = 4.5 Hz) 122.1, (d, CH2, JPC = 144.6 Hz) 31.9, (d, CH2,
JPC = 5.2 Hz) 17.5, (d, CH3, JPC = 19.3 Hz) 16.1, (d, Si(CH3)3, JPC
=
3.3 Hz) 3.6]. (Me3Si)N P(n-Pr)(Ph)(OPh) (16); [37% yield, bp =
1
140–150 C at 0.25 mmHg, 31P NMR (CDCl3) = (s) 22.5, H NMR
(CDCl3) = (m, 2H) 7.51–7.90, (m, 3H) 7.51–7.90, (t, meta, JHH = 8.1 Hz)
7.28, (d, ortho, JHH = 7.3 Hz) 7.09, (t, para, JHH = 7.3 Hz) 7.08, (m,
2H) 1.97–2.10, (m, 2H) 1.40–1.75, (t, 3H, JHH = 7.3 Hz) 0.99, (s, 9H)
0.00, 13C NMR (CDCl3) = (d, ipso, JPC = 9.0 Hz) 151.9, (d, ipso,
JPC = 183.1 Hz) 133.4, (d, meta, JPC = 10.2 Hz) 131.9, (s, meta) 129.4,
(d, ortho, JPC = 2.6 Hz) 128.4, (s, para) 123.9, (s, ortho) 121.3, (d, CH2,
JPC = 98.9 Hz) 35.6, (d, CH2, JPC = 2.7 Hz) 16.4, (d, CH3, JPC = 18.2 Hz)
15.6, (d, Si(CH3)3, JPC = 3.4 Hz) 3.6].
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Synthesis and Characterization of Mixed-Substituent
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