The 'one-pot' syntheses of α,α′-diphosphino-substituted imines: A unique reaction of bulky bis(dialkylamino)chlorophosphines

Article abstract of DOI:10.1039/b009867l

The reaction between various bis(dialkylamino)chlorophosphines and N-isopropyl-substituted lithium amides afforded bis(α,α′-phosphino)imines in a 'one-pot' procedure. These compounds react with sulfur to generate intramolecularly hydrogen-bonded ylide derivatives. The molecular structure of (Pr₂ⁱN)₂PCH₂C(=NBu^t) CH₂P(NPrⁱ)₂ has been determined by X-ray crystallography.

Full text of DOI:10.1039/b009867l

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The “one-potÏ syntheses of a,aº-diphosphino-substituted imines: a
unique reaction of bulky bis(dialkylamino)chlorophosphines
Antoine Baceiredo,a Guy Bertrand,a Philip W. Dyer,*b John Fawcett,b Nina Griep-Raming,b
Olivier Guerret,a Martin J. Hanton,b David R. Russellb and Anna-Maria Williamsonc
a Universite Paul Sabatier, L aboratoire dÏHeterochimie Fondamentale et Appliquee,
ESA 5069ÈBat. 2R1, 118 route de Narbonne, 31062 T oulouse cedex, France
b Chemistry Department, University of L eicester, University Road, L eicester, UK L E1 7RH.
E-mail: p.dyer=le.ac.uk
c Chemistry Department, Imperial College of Science, T echnology and Medicine, South
Kensington, L ondon, UK SW 7 2AY
Received (in Cambridge, UK) 7th December 2000, Accepted 22nd January 2001
First published as an Advance Article on the web 14th March 2001
The reaction between various bis(dialkylamino)chlorophosphines and N-isopropyl-substituted lithium amides
a†orded bis(a,a@-phosphino)imines in a “one-potÏ procedure. These compounds react with sulfur to generate
intramolecularly hydrogen-bonded ylide derivatives. The molecular structure of
(Pri N) PCH C(2NBut)CH P(NPri) has been determined by X-ray crystallography.
2
2
2
2
2
Introduction
Results and discussion
Currently there is a considerable resurgence of interest in the
use of heteroatom substituents at phosphorus to “tuneÏ both
the steric requirements and basicity of phosphine-containing
ligands. This is due, in part, to the ease and considerable
scope associated with the synthesis of phosphorusÈheteroatom
bonds, exempliÐed by PÈO and PÈN bond formation.1 It is
therefore somewhat surprising that despite both the continued
use of bidentate P,P@-ligands in many industrially important
catalytic processes,2 and the on-going development of so-
called “hemi-labileÏ phosphorus-containing systems (e.g.
bidentate P,O-3 P,N-4 and P,S-ligands5),6 there remain few
examples of chelating ligands which possess a diaminophos-
phine component.1a,c
Treating a solution of LDA (lithium diisopropylamide) with a
solution of bis(dialkylamino)chlorophosphines 1 (Et O, 0 ¡C)
2
in a 1 : 1 molar ratio cleanly a†ords bis(a,a@-phosphino)imines
2 and the corresponding secondary phosphines 3,7 in equi-
molar amounts [31P NMR spectroscopy] (Scheme 1, Table
1).8 The addition of less than stoichiometric amounts of LDA
leads to the formation of mixtures of 2, 3 and unchanged
1. Similarly, the reaction of the phosphenium salt
[(Pri N) P][CF SO ] 5 with LDA (Et O) also forms 2a in
2
2
3
3
2
good yield (73%) with concomitant formation of secondary
phosphine 3a and elimination of lithium triÑate. It is note-
worthy that although a number of phosphorus-containing
products were generated from the reaction between 5 and
HNPri in the presence of NEt or 1,4-diazabicyclo[2.2.2]
As the application of phosphorus-based donors in catalysis
continues apace, simple, high-yielding preparative routes to
novel, easily tailored ligand systems are of growing com-
mercial importance. During studies into the use of
bis(dialkylamino)phosphino substituents, the simple “one-potÏ
synthesis of bis(a,a@-phosphino)-substituted imines has been
studied in detail, while the basis of a more general route to
compounds containing the R PCH C2NR@ motif has been
2
3
octane (dabco), none was readily identiÐable. This suggests
that the formation of 2 does not necessitate the generation of
an intermediate [(Pri N) P]` moiety, but favours a concerted
2
2
mechanism as outlined below.
It seems most likely that the imine Me C2NPri 4 is gener-
2
ated during the reaction between 1 and LDA via an N-
analogue of the MeerweinÈPonndorfÈVerley reaction (Scheme
2
2
established.
2), similar reactions having been reported previously for
Table 1 Selected 31P NMR and IR spectroscopic data
Product
R1
R2
R3
d 31P (4J /Hz)a
Yieldb (%)
IRc
PP
2a
2b
2c
NPri
NPri
Pri
Pri
Pri
45.4, 52.9 (11.0)
53.9, 59.3 (25.0)
49.6, 56.6 (13.0)d
49.8, 56.1 (20.0)d
46.5, 53.5 (12.0)
47.6, 55.8 (37.0)
80
75
e
1625
1621
1625f
2
2
NCy
NCy
NCy
2
2
2
NPri
2
2d
2e
NPri
NPri
Cy
But
70
83
1619
1629
2
2
NPri
NPri
2
2
a In CDCl , 300 MHz. b Isolated yield after work-up. c Solution cell, KBr windows, CH Cl , cm~1. d In Et O. e Product isolated as a mixture of
3
2
2
2
two inseparable diastereomers, formed quantitatively according to 31P NMR spectroscopy. f In Et O, severely broadened.
2
DOI: 10.1039/b009867l
New J. Chem., 2001, 25, 591È596
591
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001

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followed by the addition of two equivalents of
diaminochlorophosphine 1a (hexane, 0 ¡C) [Scheme 1]. An
extension to this methodology can be used to prepare
variously substituted a-phosphino-imines, e.g. 7, from
R(Me)C2NR@ and the appropriate chlorophosphine (Scheme
3).11 A variation on this procedure has recently been utilised
for the synthesis of unsymmetrical b-diimines.12
It has proved straightforward to introduce other alkyl sub-
stituents at the imine terminus of diphosphines 2 using the
“one-potÏ methodology. For example, treatment of
diaminochlorophosphine 1a with unsymmetrical lithium N-
alkyl-N-isopropyl amides [LiNPri(R3)] (Et O, 0 ¡C) cleanly
2
a†ords the corresponding bis(phosphino)imines 2d,2e
(Scheme 4, Table 1). In each case, the “sacriÐcialÏ role of one
N-isopropyl group is readily apparent, further supporting the
intermediacy of an imine such as Me C2NR (e.g. R \ Pri, 4).
2
Scheme 1 Reagents and conditions: i, 0 ¡C to r.t., Et O, 12 h; ii,
These ideas are endorsed by the observation that the reaction
2
R1 \ R2 \ NPri , 0 ¡C to r.t., Et O, 12 h; iii, R1 \ R2 \ NPri , BunLi/
2
2
2
of LiN(Pri)(Me) with 1a a†ords H C2NPri (GC-MS, IR l(CN)
tmeda, [78 ¡C, 40 min, hexane; iv, 1a [78 ¡C to r.t., hexane. OTf \
2
1649 cm~1)13 and (Pri N) PH (GC-MS/31P NMR)7 rather
O SCF (triÑate).
2
2
3
3
than M(Pri N) PCH N C2NMe, as
abstraction from the more hydridic NCH group.
Overall, it would appear that the initial hydride transfer
a result of hydride
2
2
2 2
certain transformations involving this amide base.9 It would
appear that imine 4 is then rapidly deprotonated by LDA to
generate an intermediate aza-allyl anion, which subsequently
undergoes substitution by chlorophosphines 1, a process that
is repeated to form 2.
3
between compound 1a and LDA outlined in Scheme 2 occurs
because simple substitution, which would lead to formation of
(Pri N) P 6, is blocked due to unfavourable steric interactions
2
3
Low temperature 31P NMR spectroscopic studies (Et O) of
between the bulky amide substituents. Despite an unveriÐed
report of the 31P NMR spectrum of 6 (vide supra) and two
brief accounts of its generation, little convincing data have
been reported which support the existence of what would be
an extremely sterically encumbered tris(amino)phosphine.8,14
Notably, phosphino-imine formation only occurs when
bulky dialkylamino substituents (e.g. NPri or NCy ) are
2
the reaction between LDA and compound 1a indicate that the
secondary phosphine 3a and phosphino-imine 2a are formed
simultaneously in a 1 : 1 molar ratio as the only phosphorus-
containing products, on the NMR timescale at 243 K (no
reaction is observed below this temperature). There was no
evidence to support the claim that (Pri N) P 6 is involved in
2
3
2
2
the formation of 2a from LDA and 1a, despite a previous
report to the contrary.8¤
present on the chlorophosphines 1. The less bulky derivatives,
(R@ N) PCl (R@ \ Me or Et), react with LDA to a†ord
2
2
Attempts to identify compound 4 directly during reactions
of 1a and LDA by GC-MS were unsuccessful. However, its
intermediacy is supported by the observation that 2a can also
be synthesized (30% yield) by treating an authentic sample of
4 with two equivalents of BunLi/tmeda (hexane, [78 ¡C)
intractable mixtures of phosphorus-containing products,
which include trace amounts of the corresponding
tris(amino)phosphines, (R@ N) PNPri , according to 31P NMR
2
2
2
spectroscopy, but show no evidence of imine formation.15
Similarly, the direct reaction between Ph PCl and LDA, irre-
2
spective of the nature of the solvent, a†ords a mixture of the
product from reductive coupling, Ph PPPh (d [14.2),16 and
2
2
Scheme 3 Reagents and conditions: i, BunLi/tmeda, [78 ¡C to r.t.,
hexane, 12 h (R \ H, Me or Ph; R@ \ Ph, C H Pri -2,6); ii, RAPCl
6
3
2
2
(RA \ NPri or Ph), 0 ¡C, reÑux, 3 h.
2
Scheme 2
¤ It is important to note the coincidence between the reported
31P NMR chemical shift for (Pri N) P 6, d ]133.6 (solvent not
2
3
speciÐed),8,10 and that for its most convenient precursor, namely 1a
M31P NMR (Et O, 273 K): d ]133.6N, suggesting a previously
2
incorrect assignment of the former.
Scheme 4
592
New J. Chem., 2001, 25, 591È596

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the aminophosphine Ph P(NPri ) (d ]37.1),17 resulting from
2
2
substitution, in an approximately 1 : 2 ratio (Scheme 4).”
It is noteworthy that when the reaction between compound
1a and LDA is undertaken in THF instead of Et O the major
2
product becomes (Pri N) PÈP(NPri ) ,18 with only trace
2
2
2 2
amounts of
2 being detectable (\5% by 31P NMR
spectroscopy). This solvent dependency is presumed to reÑect
small changes in the degree of chloride dissociation from 1a
that occurs in each of the solvents.19,20,° The formation of
products resulting from reductive coupling is perhaps not sur-
prising since LDA is known to act as a one-electron donor to
species with favourable reduction potentials.21 However, as
expected neither nucleophilic substitution nor imine formation
was observed to occur when the corresponding r4k5-
thioxophosphine (Pri N) P(S)Cl was treated with LDA in
2
2
Et O, presumably due to a combination of steric hindrance
2
and the lack of a vacant orbital at phosphorus to accommo-
date initial hydride transfer (as required by the mechanism
outlined in Scheme 2).
All the phosphino-imine derivatives 2 (with the exception of
2c) are readily isolated after appropriate work-up as colour-
less solids. Crystals of 2e suitable for an X-ray crystallo-
graphic study were grown from a concentrated hexane
solution at [30 ¡C.Ò The structural parameters associated
with the planar imine moiety (sum of angles about
C(2) \ 360.0¡) are typical for this type of functional group
(Fig. 1).22 The phosphorus atom P(1) is orientated such that
its lone pair is directed away from both the lone pair on the
imine nitrogen N(1) and the second phosphorus P(2). This
induces a staggered conformation along the PCCCP back-
bone such that P(2) and P(1) lie, respectively, 1.5447 A above
and [0.8824 A below the plane deÐned by [N(1)ÈC(3)ÈC(2)È
C(1)]. Changes in the extent of this “twistÏ are believed to be
Fig. 1 Molecular structure of compound 2e. Displacement ellipsoids
are drawn at the 30% probability level. Selected bond distances (A)
and angles (¡): P(1)ÈN(2) 1.698(4), P(1)ÈN(3) 1.689(4), P(2)ÈN(4)
1.699(4), P(2)ÈN(5) 1.704(4), N(1)ÈC(2) 1.274(5), C(1)ÈP(1) 1.871(4),
C(1)ÈC(2) 1.530(6), C(2)ÈC(3) 1.498(6), and C(3)ÈP(2) 1.861(5); C(2)È
N(1)ÈC(4) 127.9(4), N(1)ÈC(2)ÈC(3) 116.5(4), N(1)ÈC(2)ÈC(1) 127.2(4),
C(1)ÈP(1)ÈN(2) 100.03(19), C(1)ÈP(1)ÈN(3) 102.04(19), N(2)ÈP(1)ÈN(3)
109.1(2), C(3)ÈP(2)ÈN(4) 100.05(19), C(3)ÈP(2)ÈN(5) 102.4(2), N(4)È
P(2)ÈN(5) 110.2(2).
13C NMR spectra) and NÈH fragments. Unlike previous
examples of this type of tautomerisation,24 structure 9 is
believed to be favoured over the CÈH acid form as a result of
the formation of an intramolecular SÈHÈN hydrogen bond,
a†ording a six-membered ring system. The stability of this
arrangement is demonstrated by the lack of reactivity of 9
towards strong bases MNaN(SiMe ) in C D or LDA É tmeda
the cause of the considerable variation in the 4J coupling
PP
constants observed (2aÈ2e, Table 1), although no signiÐcant
di†erence in this parameter was observed for 2a at either
reduced or elevated temperatures. The bond distances P(2)È
C(3) and P(1)ÈC(1) are unremarkable and consistent with PÈC
single bonds.1f As is observed for many aminophosphines, the
four PÈN bond distances are signiÐcantly shorter than that
associated with a true PÈN single bond, while the sums of
angles about nitrogen atoms N(2) to N(5) [358.4, 359.9, 360.0,
360.0¡, respectively] indicate signiÐcant sp2 character.23
3 2
6 6
in Et ON and to transition metals MMo(CO) (pip)
2
4
2
(pip \ piperidine) or RhCl(PPh ) N.
3 3
Conclusion
It has been shown that sterically encumbered bis(dialkyl-
amino)chlorophosphines exhibit unusual, yet understandable
reactivity towards isopropyl-substituted lithium amides
undergoing hydride transfer rather than nucleophilic substi-
tution. This observation has led to the synthesis of a family of
bulky phosphino-imines 2 in good yields. Compounds 2 make
interesting bulky ligands for transition metals. They present
both hard imino- and soft phosphino-donor sites making
these species potentially “hemi-labileÏ. Furthermore, the pres-
Diphosphino-imine 2a readily reacts with sulfur, initially
forming the corresponding bis(r4k5-thiophosphoryl)imine 8
[AB system: d ]70.9 and ]72.6 (4J 10.0 Hz)] (Scheme 5)
PP
which rearranges on standing (D12 hours, 25 ¡C) to a†ord the
new hydrogen-bonded ylide tautomer 9. This can be isolated
after recrystallisation from dichloromethane ([30 ¡C) as an
almost colourless solid in 61% yield. Its identity is clearly
apparent from NMR spectroscopy with characteristic signals
observed for the C2N, P2CH (conÐrmed from J-modulated
” These two phosphines were isolated as their sulÐdes following treat-
ment of the reaction mixture with an excess of sulfur and subsequent
separation and puriÐcation by Ñash column chromatography on silica
gel using toluene as eluent.
° The 31P NMR chemical shift for chlorophosphine 1a exhibits a sig-
niÐcant solvent dependency (162.0 MHz, 300 K): d ]133.6 (Et O),
2
]135.8 (THF) and ]140.0 (CDCl ).
3
Ò Crystal data for compound 2e: C
H
N P , M \ 573.85, orthor-
31 69 5 2
hombic, space group Pbca, a \ 17.676(6), b \ 18.784(8), c \ 22.185(11)
A, V \ 7366(5) AŽ 3, Z \ 8, k(Mo-Ka) \ 0.143 mm~1, T \ 200(2) K;
clear colourless plate, Siemens P4 di†ractometer, u scans, 6459 mea-
sured, 6032 independent reÑections (R \ 0.0304). The structure was
int
solved by direct methods and the non-hydrogen atoms were reÐned
anisotropically using full matrix least squares based on F2 to give
R1 \ 0.0776, wR2 \ 0.2000 (all data) for 3052 independent observed
reÑections [I [ 2p(I)] and 343 parameters. CCDC reference number
156002. See http://www.rsc.org/suppdata/nj/b0/b009867l/ for crystal-
lographic data in CIF or other electronic format.
Scheme 5 Reagents and conditions: i, S , CH Cl , r.t., 1 h; ii,
8
2 2
CH Cl , r.t., 12 h.
2
2
New J. Chem., 2001, 25, 591È596
593

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ence of r-electron withdrawing and p-electron donating sub-
stituents at phosphorus could have signiÐcant implications in
catalysis.1g A study of the coordination chemistry of ligands 2
has been initiated and preliminary results will be reported
elsewhere;25 their coordination geometry should contrast with
the many examples of related ortho-phenylene-bridged PÈN
ligands that have been reported.4
12.1; N, 12.5%); 1H NMR (270.0 MHz; C D ) d 3.98 (1 H,
6
6
sept., 3J 6.0, CNCH(CH ) ), 3.35 (8 H, sept. d, 3J
7.0,
HH
3J 12.0, PNCH), 3.10 (2 H, s, CH ), 3.08 (2 H, s, CH ), 1.37
PH
(6 H, d, 3J 6.0, C2NCH(CH ) ), 1.26 (24 H, dd, 3J 7.0,
HH 3 2 HH
4J 12.0, PNCH(CH ) ) and 1.19 (24 H, d, 3J 7.0 Hz,
PH 3 2 HH
PNCH(CH ) ); 13C NMR (62.9 MHz; CDCl ) d 166.0 (dd,
3 2
2J 15.0 and 9.5, C2N), 50.2 (s, C2NCH), 46.6 (d, 2J 11.0,
3 2
HH
2
2
3
PC
PNCH), 46.5 (d, 2J 11.0, PNCH), 44.4 (dd, 1J 12.0, 3J
PC PC
6.0, CH ), 33.7 (dd, 1J 19.0, 3J 8.0, CH ), 24.3 (br d, 3J
PC PC
PC
PC
PC
Experimental
2
2
6.0, PNCH(CH ) ), 24.0 (br d, 3J 6.0, PNCH(CH ) ), 23.7 (d,
3J 7.0 Hz, PNCH(CH ) ) and 23.6 (s, C2NCHMe ); m/z (EI)
PC 3 2
245 (9.3%, [Pri N] PCH ).
3 2
PC
3 2
All manipulations were performed under an atmosphere of
dry argon or nitrogen. Solvents were distilled from the appro-
priate drying agent and stored under argon or nitrogen prior
to use. 1H, 13C and 31P NMR spectra were recorded on
Bruker AC200, WM250, ARX 300 or JEOL 270 spectrometers
at ambient probe temperatures. C D and CDCl were dis-
2
2
2
2
From imine 4. BunLi (23.0 cm3, 1.6 M, 36.6 mmol) was
added dropwise to a cooled ([78 ¡C) solution of imine 4 (2.05
g 18.3 mmol) and tmeda (5.6 cm3, 37.0 mmol) in hexane (20
cm3) and subsequently stirred at this temperature for 40 min.
A suspension of compound 1a (9.76 g, 36.6 mmol) in hexane
(50 cm3) was then added dropwise at [78 ¡C over a period of
5 min. The mixture was stirred at room temperature over-
night, the volatiles were removed under reduced pressure and
the product was extracted with hexane (3 ] 10 cm3). Prolong-
ed cooling of a concentrated pentane solution ([30 ¡C)
a†orded 2a as a colourless solid (3.0 g, 30%).
6
6
3
tilled from P O and degassed prior to use. 1H and 13C
2
5
chemical shifts in ppm were referenced using the partially deu-
teriated solvent as internal reference. 31P downÐeld shifts are
expressed with a positive sign, in ppm, relative to external
85% H PO ; where appropriate a sealed capillary tube con-
3
4
6
taining C D ÈPPh or C D CD ÈPPh was placed inside a
6
3
6
5
3
3
normal 5 mm NMR tube to provide a deuterium lock and an
internal reference. Coupling constants and linewidths are
reported in Hertz. Infrared spectra were obtained in a solution
cell with KBr windows on either a Perkin-Elmer FT-IR1725X
or Mattson Research Series 1 spectrometer, mass spectra on a
Ribermag R10 10E, Kratos Concept, or AutospecQ instru-
ment. GC-MS were performed using a Perkin-Elmer Turb-
omass spectrometer/Perkin-Elmer Autosystem XL gas
chromatograph. Satisfactory elemental analyses have been
obtained for all isolated products. Melting points are uncor-
rected.
From compound 5. An ether solution (10 cm3) of compound
5 (0.25 g, 0.66 mmol) was treated with a solution of LDA (0.66
mmol) in ether (10 cm3) at 0 ¡C, allowed to warm to room
temperature and stirred overnight. Subsequent removal of
solvent in vacuo and extraction of the product with hexane
(3 ] 2 cm3) followed by removal of solvent a†orded 2a as a
white solid (0.09 g, 73% yield).
(Cy N) PCH C(2NPri)CH P(NCy ) (2b). An analogous
2
2
2
2
2 2
1a,26 1c,27 4,28 and 529 were prepared according to liter-
ature procedures, or minor modiÐcations thereof. BunLi (1.6
M, hexanes) was obtained from Aldrich. Amines (Aldrich and
Lancaster) used in the preparation of the lithium amides were
pre-dried over KOH pellets and subsequently stored under
nitrogen over activated 4 A molecular sieves.
procedure to that used for the preparation of compound 2a
was employed using 1b (0.5 g, 1.17 mmol) suspended in ether
(30 cm3) and LDA (1.17 mmol) in ether (10 cm3). After extrac-
tion and removal of volatile components in vacuo,
diphosphine-imine 2b was isolated as an o†-white solid after
washing with CH CN (3 ] 10 cm3) (0.26 g, 75%), mp 185È
3
188 ¡C (Found: C, 73.1; H, 11.0; N, 7.9. C
H N P requires
54 99 5 2
Preparations
C, 74.0; H, 11.4; N, 8.0%); m/z (FAB]) 877 ([M [ H]`).
Lithium amides. These reagents were prepared by treating a
solution of the appropriate amine in diethyl ether with a stoi-
chiometric amount of BunLi at [78 ¡C and used without
further puriÐcation.
Reaction of (Pri N)(Cy N)PCl 1c with LDA. A similar
2
2
experimental procedure to that used for the preparation of
compound 2a was employed, using (Pri N)(Cy N)PCl 1c (5.91
2
2
g, 17.04 mmol) in ether (20 cm3) and LDA (17.04 mmol) in
ether (50 cm3) at 0 ¡C. After stirring overnight at r.t. the
solvent was removed in vacuo and the product extracted o†
the inorganic salts using pentane (3 ] 20 cm3). On removal of
the solvent under reduced pressure an intractable mixture of
diastereomeric products (2c) was isolated as a waxy orange
solid. Direct attempts at puriÐcation via column chromatog-
(Pri N) P(S)Cl. A Schlenk was charged with compound 1a
2
2
(1.0 g, 3.7 mmol) and CH Cl (10 cm3). An excess of sulfur
2
2
(0.15 g, 4.6 mmol) was added slowly as a solid under a Ñow of
nitrogen. The solution was stirred at r.t. for 48 h. Volatile
components were removed under reduced pressure and the
product extracted from any unchanged sulfur using pentane
(3 ] 10 cm3). Removal of pentane in vacuo a†orded
(Pri N) P(S)Cl as a white solid which was sufficiently pure for
raphy (silica) or thiolation with S followed by chromatog-
8
raphy (silica) led to decomposition, while recrystallisation
from a variety of solvents was unsuccessful.
2
2
further use (0.99 g, 98%). 31P NMR (109.4 MHz, CH Cl ): d
2
2
]68.7 (pent., 3J 22.0 Hz).
(Pri N) PCH C(2NCy)CH P(NPri)
2
2d. An identical
PH
2
2
2
2
experimental procedure to that used for the preparation of
compound 2a was employed. A suspension of 1a (2.0 g, 7.5
mmol) in ether (30 cm3) was added to a cold (0 ¡C) solution of
LiN(Pri)(Cy) [prepared as above using BunLi (1.6 M, 7.5
mmol, 4.7 cm3) and HN(Pri)(Cy) (7.5 mmol, 1.2 cm3)]. After
stirring at r.t. for 12 h, removal of all volatile components
under vacuum followed by extraction with hexane (20 cm3)
and its subsequent removal in vacuo gave a viscous yellow oil.
(Pri N) PCH C(2NPri)CH P(NPri ) 2a. A suspension of
2 2
2
2
2
2
compound 1a (10 g, 37.0 mmol) in ether (20 cm3) was added to
a cold (0 ¡C) solution of LDA (prepared as above). The
mixture was allowed to warm to room temperature, where it
became progressively pale yellow and the formation of a white
precipitate occurred. Subsequently, the reaction was stirred for
12 h at room temperature. Removal of volatiles in vacuo
a†orded an orange solid. Extraction with pentane (3 ] 20
cm3) a†orded a clear pale yellow solution. Concentration and
recrystallisation from the pentane solution at [30 ¡C a†orded
colourless crystals of 2a (5.52 g, 80%), mp 130È132 ¡C (Found:
Washing the oil with CH CN (3 ] 10 cm3) followed by drying
3
in vacuo a†orded 2d as a white solid (3.2 g, 70%), mp 114È
118 ¡C (Found: C, 65.0; H, 12.1; N, 11.2. C
H N P
33 71 5 2
requires C, 66.1; H, 11.9; N, 11.7%); 1H NMR (250.1 MHz;
C, 62.1; H, 12.5; N, 12.1. C
H
N P requires C, 64.3; H,
CDCl ) d 3.41 (9 H, m, C2NCH and PNCH), 2.92 (2 H, s,
30 67 5 2
3
594
New J. Chem., 2001, 25, 591È596

View Article Online
PCH ), 1.74 (2 H, br s, PCH ), 1.45È1.08 (58 H, m, CH and
CDCl ) d 7.00 (3H, m, C H ), 3.46 (4 H, d. sept., 3J 7.0, 3J
HH
11.0, PNCH), 2.99 (2 H, s, PCH ), 2.79 (2 H, sept., 3J 7.0,
HH
2
2
2
3
6
3
PH
CH ); 13C NMR (62.9 MHz; CDCl ) d 166.4 (dd, 2J 15.0
PC
and 9.0, C2N), 59.8 (d, 4J 4.0, C2NCH), 47.0 (d, 2J 11.0,
PC PC
PNCH), 46. 8 (d, 2J 11.0, PNCH), 45.0 (dd, 1J 12.0, 3J
PC PC PC
5.0, CH ), 34.5 (s, CH ), 34.3 (dd, 1J 20.0, 3J 8.0, CH ),
PC PC
26.1 (s, CH ), 25.5 (s, CH ), 24.7 (pseudo t, 3J
3
3
2
CCHMe ), 1.75 (3 H, s, CH ), 1.14 (24 H, dd, 3J 7.0, 4J
2
3
PH
PH
17.0, PNCH(CH ) ) and 1.04 (12 H, d, 3J
7.0 Hz,
3 2
HH
CCHMe ); 13C NMR (75.8 MHz, CDCl ) d 171.0 (s, C2N),
2
2
2
2
3
7.0,
146.9 (s, C
of C H ), 137.2 (s, o-C of C H ), 123.3 (s, p-C of
2
2
PC
ipso
C H ), 123.3 (s, m-C of C H ), 47.6 (d, 2J 11.0, PNCH), 45.6
PC
(d, 1J 15.5, CH ), 28.0 (s, CCHMe ), 24.5 (d, 3J 7.0,
PC PC
PNCMe ), 24.2 (s, CCHMe ), 23.8 (s, CCHMe ) and 21.9 (d,
6
3
6 3
PNCH(CH ) ), 24.4 (d, 3J 7.0, PNCH(CH ) ) and 24.1 (d,
3 2
3J 7.0 Hz, PNCH(CH ) ).
PC 3 2
PC
3 2
6
3
6 3
2
2
2
2
2
(Pri N) PCH C(2NBut)CH P(NPri)
2e. An identical
3J 10.0 Hz, CH ); 31P NMR (122.1 MHz): d ]47.5 (s).
PC
2
2
2
2
2
3
experimental procedure to that used for the preparation of
compound 2a was employed. A suspension of 1a (2 g, 7.5
mmol) in ether (10 cm3) was added to a cold (0 ¡C) solution of
LiN(Pri)(But) [prepared as above using BunLi (1.6 M, 7.5
mmol, 4.7 cm3) and HN(Pri)(But) (7.5 mmol, 1.2 cm3)]. Rec-
rystallisation from pentane at [30 ¡C a†orded a Ðrst batch of
colourless crystals of 2e (1.0 g); subsequent concentration and
cooling to [30 ¡C gave a further 0.2 g (total yield 1.2 g, 83%),
mp 142È144 ¡C (Found: C, 64.8; H, 12.0; N, 12.1.
1,3-Bis[bis(diisopropylamino)thiophosphoryl]-2-isopropyl-
iminopropane 8. To a solution of compound 2a (0.10 g, 0.18
mmol) in CDCl (0.5 cm3) was added an excess of sulfur (13.0
3
mg, 0.40 mmol). The solution was monitored by 31P NMR
spectroscopy until complete conversion into 8 had occurred.
l
(KBr, CDCl )/cm~1 1620; 1H NMR (301.5 MHz, CDCl )
max
d 3.90 (13H, m, PNCH and CNCH(CH ) ), 3.73 (2H, s, CH ),
3 2
3.68 (2H, s, CH ), 1.41 (12H, d, 3J 7.0, PNCH(CH ) ), 1.40
HH 3 2
(12H, d, 3J 7.0, PNCH(CH ) ) and 1.14 (6H, d, 3J 6.0 Hz,
HH 3 2 HH
CNCH(CH ) ); 13C NMR (50.3 MHz; CDCl ) d 156.5
3 2
(pseudo triplet, 2J 7.0), 51.2 (br t, 4J 2.0, C2NCH), 46.8 (d,
3
3
2
2
C
H
N P requires C, 65.0; H, 12.2; N, 12.2%); 1H NMR
31 69 5 2
(270.0 MHz; C D ) d 3.36 (8 H, m, PNCH), 3.14 (2 H, s, CH ),
6
6
2
3
3.07 (2 H, s, CH ), 1.54 (9 H, s, CNC(CH ) ), 1.27 (24 H, dd,
3 3
3J 7.0, 3J 17.0, PCH(CH ) ) and 1.21 (24 H, dd, 3J 7.0,
HH PH 3 2 HH
2
PC
PC
2J 5.0, PNCH), 46.2 (d, 2J 5.0, PNCH), 45.2 (d, 1J 79.0,
PC
PC
PC
PC
4J 3.2 Hz, PNCH(CH ) ); 13C NMR (100.6 MHz; C D ) d
CH ), 41.3 (d, 1J
79.0, CH ), 24.0 (d, 3J
2.5,
PH
3 2
6 6
2
PC
2
163.1 (dd, 2J 17.0 and 10.0, C2N), 55.6 (s, C2NC), 47.1 (m,
PNCH(CH ) ), 23.6 (d, 3J 5.0, PNCH(CH ) ) and 23.3 (d,
PC
3 2
PC
3 2
PNCH), 45.9 (dd, 1J 14.0, 3J 6.0, CH ), 37.5 (dd, 1J 21.0,
3J 3.0 Hz, PNCH(CH ) ); 31P NMR (81.0 MHz; CDCl ) d
PC 3 2
]70.9 (4J 10.0, 3J 16.0) and ]72.6 (4J 10.0, 3J 16.0
PP PH PP PH
PC
PC
2
PC
PC
3
3J
4.5, CH ), 31.7 (s, C(CH ) ), 24.8 (d, 3J
8.0,
PC
2
3 3
PNCH(CH ) ), 24.8 (d, 3J 8.0, PNCH(CH ) ), 24.6 (d, 3J
Hz).
3 2
PC
3 2
PC
6.0, PNCH(CH ) ) and 24.0 (d, 3J 6.0 Hz, PNCH(CH ) );
3 2 PC 3 2
m/z (EI) 573 (M`).
Hydrogen-bonded thio tautomer 9. An excess of elemental
sulfur (0.03 g, 0.94 mmol) was added directly to a stirred
dichloromethane solution (10 cm3) of compound 2a (0.20 g,
0.36 mmol) at room temperature. The solution became yellow
almost immediately and gradually turned red upon stirring for
approximately 12 h. After 24 h at room temperature the
mixture was Ðltered to remove unchanged sulfur, concentrated
and placed at [30 ¡C. Pale yellow cubic crystals of 9 (0.14 g,
61%) were isolated after prolonged cooling, mp 132È134 ¡C
Reaction of Ph PCl with LDA. To a cold (0 ¡C) ether solu-
2
tion (20 cm3) of LDA (5.6 mmol) was added a cold ether solu-
tion (10 cm3) of Ph PCl (1.0 cm3, 5.6 mmol). The mixture was
2
allowed to warm to room temperature and stirred overnight.
Volatiles were removed in vacuo and the mixture extracted
with pentane (3 ] 10 cm3) that was subsequently removed
under reduced pressure. Ether (10 cm3) and an excess of sulfur
(0.25 g) were added before stirring overnight. Volatiles were
removed in vacuo and the mixture was separated by column
chromatography on silica gel using toluene as eluent to a†ord
Ph P(S)NPri (R 0.5; 0.88 g, 52%) and Ph P(S)2P(S)Ph (R
(Found: C, 56.9; H, 8.9; N, 11.0. C
H N P S requires C,
30 67 5 2 2
57.8; H, 10.9; N, 11.2%); l
(KBr, CDCl solution)/cm~1
max
3
3264mbr, 2475w, 1610wsh, 1584m and 1538m; 1H NMR (270
MHz; C D ) d 8.21 (1 H, br t, 4J 6.0, NH), 4.35 (2 H, br d,
2
2
f
2
2
f
6
6
PH
PH
0.3; 0.61 g, 25%).
Reaction of (Pri N) PCl with LiN(Me)(Pri). A suspension of
2J 17.0, PCH ), 4.18 (1 H, dd, 2J 7.0, 4J 2.5, PCH), 3.93
PH
2
PH
(8 H, m, PNCH), 3.39 (1 H, sept., 3J
6.0, CNCH(CH ) ),
HH
3 2
2
2
1.45 (24 H, d, 3J 7.0, PNCH(CH ) ), 1.39 (24 H, d, 3J 7.0,
compound 1a (2.0 g, 7.5 mmol) in ether (10 cm3) was added to
an ether solution (10 cm3) of LiN(Me)(Pri) (7.5 mmol) at 0 ¡C.
After stirring at room temperature overnight a 31P NMR
spectrum of the mixture showed a single resonance corre-
sponding to (Pri N) PH (31P: d ]42.1M1J 254.0 HzN). All
HH
3 2
HH
PNCH(CH ) ) and 1.13 (6 H, d, 3J 6.0 Hz, CNCH(CH ) );
3 2 HH 3 2
13C NMR (67.9 MHz; C D ) d 152.2 (dd, 2J 18.0, 7.0, CN),
PC
6
6
83.1 (dd, 1J
152.0, 3J
8.0, PCH), 47.9 (d, 2J
5.0,
PC
PC
PC
P(S)NCH), 46.3 (d, 2J 6.0, P(S)NCH), 43.8 (s, C2NCH), 37.2
PC
2
2
PH
(dd, 1J
85.0, 3J
4.0, PCH ), 24.1 (d, 3J
5.0,
volatile components were isolated by vacuum distillation and
PC
PC
2
PC
PNCH(CH ) ), 24.0 (d, 3J 6.0, PNCH(CH ) ), 23.9 (d, 3J
subjected to analysis by GC-MS. m/z (EI) 71 (M`) and 132
3 2
PC
3 2
PC
2.0, PNCH(CH ) ), 23.5 (d, 3J 3.0 Hz, PNCH(CH ) ) and
(M` [ NPri ).
3 2 PC 3 2
2
22.0 (s, CNCH ); 31P NMR (81.0 MHz; CDCl ) d ]66.7 (s)
3
3
and ]66.6 (s); m/z (EI) 623 (M`), 523 (M [ NMPri N ) and 262
(Pri N) PCH C(2NC H Pri -2,6)CH 7.
A solution of
BunLi (2.4 mmol) was added dropwise from a syringe to a cold
2 2
2
2
2
6
3
2
3
([MPri NN P2S]`).
2
2
([78 ¡C) solution of Me C2N(C H Pri -2,6) (2.4 mmol, 0.52 g)
2
6
3
2
and tmeda (2.5 mmol, 0.4 cm3) in hexane (10 cm3) to a†ord a
clear solution and a bright yellow precipitate which was
stirred at r.t. for 16 h. A solution of compound 1a (2.4 mmol,
0.64 g) in hexane was then added slowly at 0 ¡C. On warming
to r.t. the mixture was heated to reÑux for 3 h. The resulting
clear yellow solution was isolated by Ðltration. The white solid
was washed with hexane (3 ] 5 cm3) and the washings were
combined. A dark yellow viscous oil was obtained on remo-
ving all volatiles in vacuo. Recrystallisation from the minimum
of hot acetonitrile a†orded colourless crystals of 7 (0.49 g);
subsequent concentration and cooling to [30 ¡C a†orded a
further 0.4 g, a total yield of 0.89 g, 83% (Found: C, 72.0; H,
Acknowledgements
The Royal Society is thanked for a European Science
Exchange Fellowship (PWD), The Nuffield Foundation for
both an Undergraduate Summer Bursary (MJH) and an
Award to Newly Appointed Science Lecturers (PWD). Finan-
cial and equipment support from the CNRS, the Departments
of Chemistry at Imperial College and the University of Leices-
ter, and The Royal Society are gratefully acknowledged.
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N P requires C, 72.4; H, 11.3; N, 9.4%);
27 50
3
l
(KBr, CH Cl )/cm~1 1635 (C2N); 1H NMR (301.5 MHz,
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New J. Chem., 2001, 25, 591È596
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596
New J. Chem., 2001, 25, 591È596