Efficient synthesis of novel N-substituted bulky diphosphinoamines

Article abstract of DOI:10.1055/s-2007-990868

A convenient procedure for the facile preparation of electron-rich bulky diphosphinoamines from alkylamines and chlorodiphenylphosphine has been developed. The choice of solvent proved to be critical to the successful synthesis of the diphosphinoamine (PNP) products. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-990868

PAPER
3863
Efficient Synthesis of Novel N-Substituted Bulky Diphosphinoamines
S
ynthesis of Bulky Dip
u
hosphinoam
n
ines aka C. Maumela,*a Kevin Blann,a Henriëtte de Bod,a John T. Dixon,a William F. Gabrielli,a
D. Bradley G. Williamsb
a
Sasol Technology (Pty) Ltd, R & D Division, 1 Klasie Havenga Road, Sasolburg 1947, South Africa
Fax +27(11)5220784; E-mail: chris.maumela@sasol.com
University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa
b
Received 2 August 2007
spective alkylamines and chlorodiphenylphosphine. The
synthetic methodology developed also provides access to
a bulky P-substituted PNP, which thus far has been inac-
cessible via the conventional synthetic methods reported
in the literature.8The most convenient procedure7 for the
preparation of phosphinoamines [R¢2PN(H)R] 3 and
diphosphinoamines (PNP) 4 involves the reaction of aryl-
or alkylamines with chlorophosphines in the presence of
an organic base such as triethylamine (Scheme 1).
Abstract: A convenient procedure for the facile preparation of
electron-rich bulky diphosphinoamines from alkylamines and chlo-
rodiphenylphosphine has been developed. The choice of solvent
proved to be critical to the successful synthesis of the diphosphi-
noamine (PNP) products.
Key words: alkylamines, ethylene oligomerisation catalysis, sol-
vent effects, diphoshinoamine ligands, steric hindrance
Since its first commercial application in 1966, ethylene
oligomerisation has become a major industrial route to-
wards the preparation of linear a-olefins.1 The first indus-
trial oligomerisation process based on transition metal
catalysis was the Shell Higher Olefin Process (SHOP),
wherein a neutral nickel catalyst containing a bidentate P–
O chelating ligand effects the oligomerisation of ethylene
to linear C4–C20 olefins.2 Following the success of the
SHOP process, transition metal complexes containing
novel phosphine ligands have received much attention
both in academia and industry.3 We recently reported an
ethylene trimerisation system, as well as the unprecedent-
ed ethylene tetramerisation reaction using aluminoxane
activated catalysts comprising chromium precursors and
diphosphinoamine (Ph2PN[R]PPh2, Figure 1) ligands.4
These catalyst systems produce mainly hex-1-ene and oct-
1-ene, which are important co-monomers used in the pro-
duction of linear low-density polyethylene.5
RNH2
R'2PN(R)H or R'2PN(R)PR'2
+
HCl salt
2
3
4
R,R' = aryl,alkyl
Scheme 1
The most commonly used organic solvents for this reac-
tion include THF, diethyl ether, benzene and toluene.7e–j
The HCl by-product reacts with the base, forming a salt
which is often insoluble in these solvents and is thus readi-
ly separated from the product by filtration. Unexpectedly,
when we adopted this well-established methodology for
the use of tert-butylamine (5, Figure 2), the reaction with
two equivalents of chlorodiphenylphoshine (Ph2PCl) in
the above-mentioned solvents yielded exclusively the
phosphinoamine Ph2PNH(t-Bu) (11) as was evident from
the single peak at d = 22 ppm in the 31P NMR spectrum.
The structure was further confirmed by 1H NMR spectros-
copy.9
R
N
R = alkyl, aryl, silyl
Ph2P
PPh2
Figure 1 Diphosphinoamine ligands
NH2
It has been demonstrated that the nature of the N-substit-
uent has a profound effect on both catalytic activity and
selectivity towards C6 and C8 alk-1-enes, with the best
systems containing bulky groups on the N-atom.4a,b,6 Al-
though a large number of PNP compounds have been re-
ported in the literature,7 to the best of our knowledge the
synthesis of diphosphinoamine compounds containing
very bulky N-alkyl groups, such as tert-butyl or 1-ada-
mantyl, has not been reported. We describe herein the
synthesis of such bulky diphosphinoamines from their re-
NH2
NH2
5
6
7
NH2
NH2
NH2
8
9
10
Figure 2 Bulky alkyl- and arylamines used in the synthesis of di-
phosphinoamine ligands
The use of bulky alkylamines 6–10 (Figure 2) also failed
to afford the target PNP ligands. In all these instances only
the respective phosphinoamines [Ph2PNH(R)] 3 were
formed. It became evident that the reaction of sterically
SYNTHESIS 2007, No. 24, pp 3863–3867
Advanced online publication: 31.10.2007
DOI: 10.1055/s-2007-990868; Art ID: P09307SS
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x
.
2
0
0
7

3864
M. C. Maumela et al.
PAPER
hindered aminesand an excess of Ph2PCl, in solvents such Not satisfied with this multi-step approach to the product
as ethers, paraffins and aromatics, which are typically 15, a more efficient synthetic procedure was sought. We
used for such reactions is not a feasible route to the target- had noted that 3-methyl-2-butylamine (16) (Figure 3) re-
ed PNP ligands. The limitations of this methodology, and acted with Ph2PCl in CH2Cl2 as solvent to produce the
the absence of suitable procedures for the preparation of PNP product N,N-bis(diphenylphosphanyl)-3-methyl-2-
Ph2PN(t-Bu)PPh2 (15) and related N-bulky PNP com- butylamine, in greater than 95% yield within two hours. In
pounds, prompted us to investigate in finding alternative contrast, the analogous reactions in toluene and diethyl
synthetic routes to such systems. We envisaged that the ether proved to be less effective and resulted only in ap-
lithium amide nucleophile 12, generated from the reaction proximately 50% conversion of 3 to 4 over the same peri-
of n-butyllithium and Ph2PNH(t-Bu) (11), would afford od.
the PNP ligand 15, upon reaction with Ph2PCl
(Scheme 2).
n-BuLi
NH2
toluene
N
N
Ph2P
Li
N
16
Ph2P
H
Ph2P
Li
Figure 3 3-Methyl-2-butylamine (16)
11
12
13
Dyson and co-workers10,11 have also reported faster reac-
tion rates with aniline substrates when using CH2Cl2 as
solvent. We believe that the variance in reaction rates may
be explained by considering the likely equilibrium at-
tained between the reaction of triethylammonium chloride
and diphenylphosphonium chloride in CH2Cl2 as shown
in Scheme 4. It is conceivable that the protonated diphe-
nylphosphonium chloride is more electrophilic than its
neutral counterpart and hence more reactive. The afore-
said equilibrium presumably lies far to the left in toluene,
THF, diethyl ether, dioxane, hexane, and pentane, due to
the low solubility of the triethylammonium chloride salt in
these solvents, while it has a higher solubility in CH2Cl2.
X
Ph2PCl
Ph2PCl
cat. Ph2PCl
N
Ph2P
PPh2
14
N
Ph2P
PPh2
15
Scheme 2
However, this reaction yielded the iminobisphosphine
product, Ph2PPPh2=N(t-Bu) (14), as confirmed by two di-
agnostic doublets resonating at –7 and –22 ppm in the 31P
NMR spectrum (Scheme 2). Dyson and co-workers10
have recently reported similar reactions of aniline-derived
amines with Ph2PCl in the presence of Et3N or n-BuLi that
yield predominantly Ph2PPh2P=NAr (Ar = aniline deriva-
tives) together with PNP product. Interestingly, we ob-
served that the kinetically controlled product,
Ph2PPPh2=N(t-Bu) (14), rearranges to the desired isomer-
ic diphosphinoamine (PNP) 15 upon interaction with a
catalytic amount of Ph2PCl. The reaction is fairly slow, as
monitored by 31P NMR spectroscopy and the rearrange-
ment of 14 to 15 requires approximately 15 hours at room
temperature for complete conversion. The role of Ph2PCl
as an isomerisation catalyst has previously been proposed
to reside in its ability to react with the nitrogen atom of the
iminobiphosphine 14, as proposed in Scheme 3.8
Cl–
Cl–
Cl
P
Et
N
Cl
P
Et
N
H
H
+
+
Ph
Ph
Et
Et
Ph
Ph
Et
Et
Scheme 4
Consequently, we set out to prepare PNP derivative 15 us-
ing similar reaction conditions (i.e., with CH2Cl2 as sol-
vent). Gratifyingly, the formation of 15 was achieved in
approximately 50% yield (by 31P NMR spectroscopy)
when two equivalents of Ph2PCl were reacted overnight
with t-BuNH2 in the presence of two equivalents of Et3N
in CH2Cl2 [conducted as a solution (10%; v/v) of this pri-
mary amine in the solvent]. Increasing the concentration
(from 10% to 20%; v/v), led to a significant improvement
in the yield (from 51 to 89%) of 15 as determined by 31
P
Ph
Cl
Ph
NMR analysis. Furthermore, the amount of Et3N present
in the reaction also influenced the yield and the rate of for-
mation of 15. Reactions performed with an excess of Et3N
led to significantly lower yields as compared to when only
two equivalents of base were used. Reactions at even
higher concentrations were not carried out due to the high
viscosity of the reaction mixture thereby resulting in inef-
ficient stirring. This newly developed protocol was ex-
tended to include the use of other bulky amines 6–10,
affording the desired corresponding products, which in-
P
N
14
+ Ph2PCl
Ph2P PPh2
15
+ Ph2PCl
Scheme 3
Synthesis 2007, No. 24, 3863–3867 © Thieme Stuttgart · New York

PAPER
Synthesis of Bulky Diphosphinoamines
3865
affording only 24% of the desired PNP product, whereas
CCl4 and nitropropane failed altogether to produce the de-
sired products, instead producing by-products. As expect-
ed, mixtures of toluene–MeCN (1:1) as well as toluene–
CH2Cl2 (1:1) were found to be effective combinations of
solvents giving 62% and 52% yield, respectively of the
desired PNP ligands (entries 10, 11). Similar trends were
observed with the 1-adamantanamine PNP formation
(68% yield in acetonitrile compared to 50% yield in
CH2Cl2).
Table 1 Formation of PNP 4 at 20% (v/v) Solution of a Reactant Pri-
mary Amine in CH2Cl2
RNH2 Solvent
Ph2PNRPPh2 4
Yield (%)
Ph2PNRPPh2 4
Isolated yield (%, ≥20 h)
(31P NMR, ≥20 h)
5
6
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
89
50
38
92
54
55
61
38
25
66
38
39
7
8
Table 2 Reaction of t-Butylamine and Ph2PCl in Various Solventsa
9
Entry Solvent
Ph2PN(t-Bu)Hb
Yield of 15
(%; determined
10
by 31P NMR)
1
2
3
4
5
6
7
8
9
toluene
Et2O
quant
quant
quant
quant
n.d.
0
cluded two chiral products, in yields of 38–92% (by 31P
NMR monitoring, Table 1).
0
Although the reactions with amines 9 and 10 gave excel-
lent conversion of the phosphinoamines, it was accompa-
nied by the simultaneous formation of by-products,
including tetraphenylbiphosphine (Ph2PPPh2) in amounts
varying between 18% and 25%. The material loss (vari-
ance in yields, isolated vs 31P NMR analysis in Table 1)
was mainly due to oxidation of the PNP products during
filtration through an alumina column. Ironically it was
also noted that the oxidised by-product could be effective-
ly removed from the desired PNP compound by this sim-
ple alumina filtration workup procedure. The present
THF
0
Et3N
0
CH2Cl2
CHCl3
89 (61)c
n.d.
24
CCl4
0
0
DIPK
n.d.
43
MeCN
toluene–MeCN (1:1)
n.d.
91 (85)c
work represents the first account of the synthesis of bulky 10
n.d.
66
52
60
0
N-substituted diphosphinoamines. It is noteworthy that
the synthesis of N,N-bis(diisopropylphosphanyl)methyl-
amine [i-Pr2PN(Me)Pi-Pr2] (17) (Figure 4) and its N-pro-
pyl derivative has been reported by means of a method
similar to that described in Scheme 2.8
12
toluene–CH2Cl2 (1:1) n.d.
13
14
15
16
NMP
n.d.
quant
0
dioxane
nitropropane
EtOAc
0
Me
N
quant
0
(i-Pr)2P
P(i-Pr)2
a Reaction carried out for 20 h.
b n.d. = not determined.
17
c Yield in parenthesis refers to isolated yield.
Figure 4 N,N-Bis(diisopropylphosphanyl)methylamine (17)
In summary, we have established an efficient direct proto-
col for the preparation of a range of bulky N-substituted
diphosphinoamines. This methodology also proved to be
applicable to the preparation of P-alkyl analogues. The
solvent is critical to the success of the reaction, with
CH2Cl2 and acetonitrile being the solvents of choice in the
presence of triethylamine as base.
Using our new protocol we prepared ligand 178 and its N-
ethyl derivative12 in a single step using CH2Cl2 as solvent
in 88% and 54% yield, respectively, as observed by the
31P NMR analysis. Since these reactions had shown such
sensitivity to the solvent being used, a range of other sol-
vents was investigated for the synthesis of 15. The results
are summarised in Table 2, which clearly demonstrate the
profound influence of the solvents on the outcome of
these reactions. The progresses of the reactions were mon-
itored by 31P NMR analysis. Diisopropyl ketone (DIPK),
N-methylpyrrolidinone (NMP), and acetonitrile were all
found to be effective solvents for this reaction. Acetoni-
trile proved to be even more effective than CH2Cl2 afford-
ing 91% of the PNP compound 15 (Table 2, entries 5, 9).
Unexpectedly, CHCl3 was less effective for the process,
All reactions were carried out under dry argon using standard
Schlenk-tube techniques. Chemicals were purchased from either
Aldrich Chemical Co., Lancaster, or Merck, and were used as re-
ceived. Anhydrous, oxygen-free solvents were prepared according
to standard procedure. The NMR spectra were recorded in CDCl3
on a Bruker 600 MHz or 500 MHz and a Varian 400 MHz spectrom-
eter. Elemental analyses were performed on a Carlo Erba 1108
(CE1108) elemental analyser. MS (EI, 70 eV) spectra were record-
ed using MicroMass Autospec-TOF (Magnetic sector used for anal-
Synthesis 2007, No. 24, 3863–3867 © Thieme Stuttgart · New York

3866
M. C. Maumela et al.
PAPER
yses). Melting points were determined on an Electrothermal Digital
Melting Point apparatus and are uncorrected. Yields in tables refer
to 31P NMR yield (average of at least three runs) unless otherwise
stated. Isolated yields refer to yields of pure compounds.
N,N-Bis(diphenylphosphanyl)-1-(1-methylcyclopropyl)ethan-
amine
Prepared according to the Typical Procedure from 1-(1-methyl-
cyclopropyl)ethanamine hydrochloride (8·HCl; 0.37 g, 2.7 mmol)
and Ph2PCl (1.1 mL, 6.1 mmol) in CH2Cl2 (2.0 mL); white powder
(0.85 g, 66%); mp 112–115 °C.
1H NMR (400 MHz, CDCl3,): d = 0.02–0.32 (m, 4 H, cyclopropyl 2
× CH2), 1.06 (s, 3 H, CCH3), 1.42 (d, J = 6.4, CHCH3, 3 H), 3.26–
3.34 (m, 1 H, NCH), 7.20–7.40 (m, 20 H, ArH).
13C NMR (150 MHz, CDCl3): d = 12.2 (d, JP,C = 3 Hz), 14.6, 21.24
(t, JP,C = 9 Hz), 22.1, 23.0 (t, JP,C = 4 Hz), 61.2 (t, JP,C = 7 Hz), 127.8
(d, JP,C = 12.4 Hz), 128.6, 133.3 (very br s), 140.1 (d, JP,C = 14.8
Hz).
N,N-Bis(diphenylphosphanyl)tert-butylamine (15); Typical
Procedure
To a stirred solution of tert-butylamine (5; 2.0 mL, 19.0 mmol) in
MeCN (10.0 mL) was added Et3N (5.8 mL, 41.6 mmol). Ph2PCl
(7.7 mL, 42.9 mmol) was then added in portions. After the addition,
the mixture was stirred overnight at r.t. The mixture was concentrat-
ed and the residue was slurried with Et2O or THF (~100 mL). The
Et3N·HCl salt was filtered by passing through a short activated alu-
mina column. Filtration was repeated until a pure compound was
obtained. The solvent was evaporated to give the desired ligand as
a white solid (7.15 g, 85%); mp 134–135 °C.
1H NMR (400 MHz, CDCl3): d = 1.41 (s, 9 H, t-C4H9), 7.22–7.46
(m, 20 H, ArH).
13C NMR (100 MHz, CDCl3): d = 32.6, 63.6, 127.7, 128.1, 132.6,
140.6 (broad signals with unresolved coupling).
31P NMR (162 MHz, CDCl3): d = 55.0 (very br s).
MS (EI, 70 eV): m/z (%) = 468 (10, [M + H]+), 467 (30, [M]+), 452
(14, [M – CH3]+), 384 (100, [M – C6H11]+), 306 (26, [M – C6H11
– Ph]+), 262 (34, [PPh3]+), 185 (51, [PPh2]+).
Anal. Calcd for C30H31NP2: C, 77.07; H, 6.68; N, 3.00. Found: C,
76.94; H, 6.74; N, 2.97.
31P NMR (162 MHz, CDCl3,): d = 57.8 (very br s).
MS (EI, 70 eV): m/z (%) = 442 (6, [M + H]+), 441 (21, [M]+), 384
(100, [M – t-Bu]+), 306 (39, [M – t-Bu – Ph]+), 262 (44, [PPh3]+),
256 (50, [M – PPh2]+), 185 (59, [PPh2]+).
N,N-(R)-Bis(diphenylphosphanyl)-3,3-dimethyl-2-butylamine
Prepared according to the Typical Procedure from (R)-3,3-dimeth-
yl-2-butylamine (9; 1.00 g, 9.9 mmol) and Ph2PCl (4.0 mL, 22.3
mmol) in CH2Cl2 (5.0 mL); white solid (1.76 g, 38%); mp 105–106
°C.
1H NMR (400 MHz, CDCl3): d = 0.80 (s, 9 H, t-C4H9), 1.54 (d, J =
6.7 Hz, 3 H, NCHCH3), 3.60–3.68 (m, 1 H, NCH), 7.00–7.86 (m,
20 H, ArH).
Anal. Calcd for C28H29NP2: C, 76.18; H, 6.62; N, 3.17. Found: C,
76.07; H, 6.70; N, 3.15.
N,N-Bis(diphenylphosphanyl)-1-adamantanamine
Prepared according to the Typical Procedure from 1-adamantan-
amine (6; 0.50 g, 3.3 mmol) and Ph2PCl (1.3 mL, 7.4 mmol) in
CH2Cl2 (2.5 mL); white solid (0.65 g, 38%); mp 174–175 °C.
1H NMR (400 MHz, CDCl3): d = 1.42–1.60 (6 H, m), 2.02–2.10 (3
H, m), 2.22–2.29 (6 H, m), 7.20–7.80 (20 H, m, ArH).
13C NMR (125 MHz, CDCl3): d = 30.5, 36.0, 44.4 (t, JP,C = 7.0 Hz),
64.6 (t, JP,C = 7.2 Hz), 127.7, 128.0, 132.8 (very br s), 140.9 (d,
JP,C = 17 Hz).
31P NMR (162 MHz, CDCl3): d = 53.3 (br s).
13C NMR (125 MHz, CDCl3): d = 20.0 (JP,C = 17 Hz), 28.4 (t, JP,C
=
3 Hz), 36.4, 64.1 (dd, JP,C = 21.0, 8.8 Hz), 127.3–129.5 (m, 12 C),
132.3–133.9 (m, 8 C), 134.2–135.7 (m, 4 C, unresolved multiplet
signals in the aromatic region).
31P NMR (CDCl3, 162 MHz): d = 52.2 (d, JP,P = 21.3 Hz), 58.6 (d,
JP,P = 21.2 Hz).
MS (EI, 70 eV): m/z (%) = 470 (8, [M + H]+), 469 (22, [M]+), 412
(36, [M – C6H13]+), 384 (100, [M – C6H13]+), 306 (9, [M – C6H13
Ph]+), 262 (36, [PPh3]+), 185 (94, [PPh2]+).
–
MS (EI, 70 eV): m/z (%) = 520 (25, [M + H]+), 519 (48, [M]+), 384
Anal. Calcd for C30H33NP2: C, 76.74; H, 7.08; N, 2.98. Found: C,
76.60; H, 6.98; N, 2.91.
(100, [M – adamantyl]+), 334 (29, [M – PPh2]+), 185 (34, [PPh2]+).
Anal. Calcd for C34H35NP2: C, 78.59; H, 6.79; N, 2.70. Found: C,
78.42; H, 6.65; N, 2.63.
N,N-(S)-Bis(diphenylphosphanyl)-3,3-dimethyl-2-butylamine
Prepared according to the Typical Procedure from (S)-3,3-dimeth-
yl-2-butylamine (10; 1.00 g, 9.9 mmol) and Ph2PCl (4.0 mL, 22.3
mL) in CH2Cl2 (5.0 mL); white solid (1.81 g, 39%); mp 109–111
°C.
1H NMR (400 MHz, CDCl3): d = 0.72 (s, 9 H, t-C4H9), 1.45 (d, J =
6.8 Hz, 3 H, NCHCH3), 3.45–3.61 (m, 1 H, NCH), 6.99–7.80 (m,
20 H, ArH).
13C NMR (125 MHz, CDCl3): d = 20.0 (d, JP,C = 17 Hz), 28.6 (t,
JP,C = 3 Hz), 36.6, 64.4 (dd, JP,C = 21.2, 8.9 Hz), 127.2–130.5 (m, 12
C), 132.0–133.7 (m, 8 C), 135.0–136.0 (m, 4 C, unresolved multi-
plet in the aromatic region).
31P NMR (162 MHz, CDCl3): d = 52.3 (d, JP,P = 21.5 Hz), 58.5 (d,
JP,P = 21.3 Hz).
N,N-Bis(diphenylphosphanyl)-2-adamantanamine
Prepared according to the Typical Procedure from 2-adamantan-
amine hydrochloride (7·HCl; 2.00 g, 10.6 mmol) and Ph2PCl (4.3
mL, 23.9 mmol) in CH2Cl2 (10.0 mL); white solid (1.40 g, 25%);
mp 138–140 °C.
1H NMR (400 MHz, CDCl3): d = 1.49–1.61 (m, 8 H), 1.69 (br s, 3
H), 1.89 (br s, 1 H), 3.03 [d, J = 12 Hz, 2 H, NCH(CH)2], 3.65 (t,
J = 13 Hz, 1 H, NCH), 7.24–7.86 (m, 20 H, ArH).
13C NMR (150 MHz, CDCl3): d = 27.6 (d, JP,C = 56.8 Hz), 29.7,
31.63 (t, JP,C = 8 Hz), 35.8, 38.6 39.6, 65.2 (t, JP,C = 6 Hz), 127.8 (d,
JP,C = 5 Hz), 128.4, 132.8 (d, JP,C = 21.4 Hz), 140.1.
31P NMR (162 MHz, CDCl3): d = 56.9 (br s), 60.2 (br s).
MS (EI, 70 eV): m/z (%) = 520 (25, [M + H]+), 519 (42, [M]+), 384
(100, [M – adamantyl]+), 334 (43, [M – PPh2]+), 262 (40, [PPh3]+),
185 (52, [PPh2]+).
MS (EI, 70 eV): m/z (%) = 470 (20, [M + H]+), 469 (45, [M]+), 412
(52, [M – C6H13]+), 384 (100, [M – C6H13]+), 306 (20, [M – C6H13
Ph]+), 262 (52, [PPh3]+), 185 (90, [PPh2]+).
–
Anal. Calcd for C34H35NP2: C, 78.59; H, 6.79; N, 2.70. Found: C,
78.71; H, 6.80; N, 2.64.
Anal. Calcd for C30H33NP2: C, 76.74; H, 7.08; N, 2.98. Found: C,
76.66; H, 7.07; N, 2.83.
Synthesis 2007, No. 24, 3863–3867 © Thieme Stuttgart · New York

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Synthesis of Bulky Diphosphinoamines
3867
N,N-Bis(diisopropylphosphanyl)methylamine (17)8
Prepared according to the Typical Procedure from MeNH2 (0.49 g,
15.8 mmol) and (i-Pr)2PCl (5.7 mL, 35.8 mmol) in CH2Cl2 (2.5 mL).
1H NMR (400 MHz, CDCl3): d = 1.00–1.12 [m, 24 H, CH(CH3)2],
1.88–1.94 [m, 4 H, PCH(CH3)2] 2.58–2.61 (3 H, m, NCH3).
31P NMR (162 MHz, CDCl3): d = 92.7 (s).8
Killian, E.; Maumela, H.; Morgan, D. H.; Neveling, A.; Otto,
S. Chem. Commun. 2005, 622. (g) Walsh, R.; Morgan, D.
H.; Bollmann, A.; Dixon, J. T. App. Catal. A: Gen. 2006,
306, 184. (h) Kuhlmann, S.; Dixon, J. T.; Haumann, M.;
Morgan, D. H.; Ofili, J.; Spuhl, O.; Taccardi, N.;
Wasserscheid, P. Adv. Synth. Catal. 2006, 348, 1200.
(5) An excellent general overview is provided by: Vogt, D. In
Applied Homogeneous Catalysis with Organometallic
Compounds, Vol. 1; Cornils, B.; Herrmann, W. A., Eds.;
Wiley-VCH: New York, 2002, 240.
Acknowledgment
(6) (a) Blann, K.; Bollmann, A.; de Bod, H.; Dixon, J. T.;
Killian, E.; Klaas, P.; Maumela, M. C.; Maumela, H.;
McConnell, A. E.; Morgan, D. H.; Overett, M. J.; Prétorius,
M.; Kuhlmann, S.; Wasserscheid, P. J. Catal. 2007, 249,
242. (b) Kuhlmann, S.; Blann, K.; Bollmann, A.; Dixon, J.
T.; Killian, E.; Maumela, M. C.; Maumela, H.; Morgan, D.
H.; Prétorius, M.; Taccardi, N.; Wasserscheid, P. J. Catal.
2007, 245, 277. (c) Killian, E.; Blann, K.; Bollmann, A.;
Dixon, J. T.; Kuhlmann, S.; Maumela, M. C.; Maumela, H.;
Morgan, D. H.; Nongodlwana, P.; Overett, M. J.; Pretorius,
M.; Höfener, K.; Wasserscheid, P. J. Mol. Catal. A: Chem.
2007, 270, 214.
The authors would like to express their gratitude to Sasol Techno-
logy (Pty) Ltd., R & D Division for permission to publish this work.
We also like to thank Drs Ann McConnell, Dave Morgan, Marie
Pretorius, and Des Young for valuable discussions.
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(9) 1H NMR (CDCl3): d = 1.35 (s, 9 H, t-C4H9), 2.10 (d, J = 11.6
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(12) N,N-Bis(diisopropylphosphanyl)ethylamine: 31P NMR (162
MHz, CDCl3): d = 83.9 (s).
Synthesis 2007, No. 24, 3863–3867 © Thieme Stuttgart · New York