Synthesis of differently substituted N- and P-aminodiphosphinoamine PNPN-H ligands

Article abstract of DOI:10.1080/10426507.2013.807257

On the basis of the known aminodiphosphinoamine ligand Ph ₂PN(i-Pr)P(Ph) N(i-Pr)-H (3a), differently substituted aminodiphosphinoamine PNPN-H ligands (3) were prepared. By using different synthetic methods, the N-substituted ligands Ph₂

Full text of DOI:10.1080/10426507.2013.807257

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Synthesis of Differently Substituted N-
and P-Aminodiphosphinoamine PNPN-H
Ligands
Marc Gongoll a , Bernd H. Müller a , Stephan Peitz a , Bhaskar R.
Aluri a , Normen Peulecke a , Anke Spannenberg a , Uwe Rosenthal a ,
Mohammed H. Al-Hazmi b , Anina Wöhl c & Wolfgang Müller c
a Leibniz-Institut für Katalyse, an der Universität Rostock e.V.,
Albert-Einstein-Str. 29 A , D-18059 , Rostock , Germany 1
b Saudi Basic Industries Corporation, P.O. Box 42503 , Riyadh ,
11551 , Saudi Arabia
c Linde Engineering Division, Linde AG, Dr.-Carl-von-Linde-Str. 6-14 ,
D-82049 , Pullach , Germany
Accepted author version posted online: 02 Jul 2013.Published
online: 03 Oct 2013.
To cite this article: Marc Gongoll , Bernd H. Müller , Stephan Peitz , Bhaskar R. Aluri , Normen
Peulecke , Anke Spannenberg , Uwe Rosenthal , Mohammed H. Al-Hazmi , Anina Wöhl & Wolfgang
Müller (2013) Synthesis of Differently Substituted N- and P-Aminodiphosphinoamine PNPN-H
Ligands, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:12, 1845-1854, DOI:
10.1080/10426507.2013.807257
To link to this article: http://dx.doi.org/10.1080/10426507.2013.807257
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Phosphorus, Sulfur, and Silicon, 188:1845–1854, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.807257
SYNTHESIS OF DIFFERENTLY SUBSTITUTED N- AND
P-AMINODIPHOSPHINOAMINE PNPN-H LIGANDS
Marc Gongoll,1 Bernd H. Mu¨ller,1 Stephan Peitz,1
Bhaskar R. Aluri,1 Normen Peulecke,1 Anke Spannenberg,1
∗
Uwe Rosenthal,1, Moh∗ammed H. Al-Hazmi,2 Anina Wo¨hl,3
and Wolfgang Mu¨ller3,
1Leibniz-Institut fu¨r Katalyse, an der Universita¨t Rostock e.V., Albert-Einstein-Str.
29 A, D-18059 Rostock, Germany 1
2Saudi Basic Industries Corporation, P.O. Box 42503, Riyadh 11551, Saudi Arabia
3Linde Engineering Division, Linde AG, Dr.-Carl-von-Linde-Str. 6-14, D-82049
Pullach, Germany
GRAPHICAL ABSTRACT
Abstract On the basis of the known aminodiphosphinoamine ligand Ph2PN(i-Pr)P(Ph)
N(i-Pr)-H (3a), differently substituted aminodiphosphinoamine PNPN-H ligands (3)
were prepared. By using different synthetic methods, the N-substituted ligands Ph2PN
(i-Pr)P(Ph)N(c-Hex)-H (3b), Ph2PN(c-Hex)P(Ph)N(i-Pr)-H (3g), and Ph2PN(i-Pr)P(Ph)
N[(CH2)3Si(OEt)3]-H (3c), in addition to the formerly described Ph2PN(n-Hex)P (Ph)N
Received 7 February 2013; accepted 28 April 2013.
The authors thank Linde Engineering and SABIC for the permission to publish this work. Furthermore, they
wish to thank Linde Engineering’s R&D Chemistry Department for their valuable contributions as well as the
analytical service and the technical staff at LIKAT.
Address correspondence to Uwe Rosenthal, Leibniz-Institut fu¨r Katalyse, an der Universita¨t Rostock e.V.,
Albert-Einstein-Str. 29 A, D-18059 Rostock, Germany 1 or Wolfgang Mu¨ller, Linde AG, Linde Engineering
Division, Dr.-Carl-von-Linde-Str. 6-14, D-82049 Pullach, Germany. E-mail: uwe.rosenthal@catalysis.de
1845

1846
M. GONGOLL ET AL.
(i-Pr)-H (3h), Ph2PN(i-Pr)P(Ph)N(Et)-H(3d), Ph2PN(i-Pr)P(Ph)N(Me)-H (3e), and Ph2PN(c-
Hex)P(Ph)N(c-Hex)-H (3f), were obtained. In addition, Ph2PN(i-Pr)P(Me)N(i-Pr)-H (3i),
(cyclopentyl)2PN(i-Pr)P(Ph)N(i-Pr)-H (3j), (-O-CH2-CH2-O-)PN(i-Pr)P(Ph)N(i-Pr)-H
(3k), and (1-Ad)2PN(i-Pr)P(Ph)N(i-Pr)-H (3l) were prepared with different P-substitutions.
All compounds were characterized and the molecular structures of the intermediates
Ph2PN(i-Pr)P(Ph)Cl (1a) and (cyclopentyl)2PN(i-Pr)P(Ph)Cl (1e) and the ligand
(1-Ad)2PN(i-Pr)P(Ph)N(i-Pr)-H (3l) were investigated by single-crystal X-ray diffraction.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Synthesis; ligand design; N,P ligands; substituent effects
INTRODUCTION
Mixed P and N donor ligand systems were developed and successfully applied for a
variety of catalytic reactions, mostly in the field of olefin oligomerization.1–5 Earlier, we have
shown the utilization of novel PNPN-H donor ligands in homogeneous chromium-based
selective trimerization reaction for 1-hexene. In particular for the Ph2PN(i-Pr)P(Ph)N(i-
Pr)-H (3a) ligand as the best example, we published detailed kinetic experiments and
modeling.6–10,12–15 Also, the coordination behavior of this ligand and some organometallic
chemistry with relevance toward the activation and deactivation of the catalyst were in-
vestigated.7 Now, it is interesting to synthesize such compounds with varying substituents
at phosphorus and nitrogen and characterize them by using different analytical techniques
including single-crystal X-ray diffraction.
The obtained compounds are interesting ligands for many purposes. In this context,
a fine-tuning of electronic and steric properties by introducing different substituents is
inevitable for the optimization of the performance of the respective metal complexes.
RESULTS AND DISCUSSION
The synthesis of the PNPN-H ligand can be carried out following two different routes
(Scheme1). Thesynthesis of Ph2PN(i-Pr)P(Ph)Cl (1a),11a Ph2PN(i-Pr)P(Ph)N(i-Pr)H (3a),6
Ph2PN(c-Hex)P(Ph)N(c-Hex)H (3f),15 Ph2PN(c-Hex)H (3h),11b Ph2PN(n-Hex)P(Ph)N(i-
Pr)H (3f),15 Ph2PN(i-Pr)P(Ph)N(Et)H,7 Ph2PN(i-Pr)H (3d),11c and (1-Ad)2PCl11d,e was
described earlier. Additionally, it is worth mentioning that Ph2PN(i-Pr)P(Ph)Cl (1a) and 3c
were useful in immobilization of the ligand.11f
Following a two-step process, dichlorophenylphosphine reacts with an excess
of a primary amine to the diaminophenylphosphine (2).11g,h Further reaction with
chlorodiphenylphosphine results in the formation of 3 or 4 depending on the sub-
stituent at the nitrogen R2. Compounds 2b, 2c, and 2d could be transformed to the
N,Nꢁ-bis(diphenylphosphino)diaminophenylphosphines 4a, 4b, and 4c.11g,i In contrast, the
reaction of bis(isopropylamino)phenylphosphine (2a) yields Ph2PN(i-Pr)P(Ph)N(i-Pr)-H
(3a), even if a 10-fold excess of chlorodiphenylphosphine was used.11g
The formation either of 3 or 4 depends on the incorporated substituents. In some cases,
the transformation of the PNPN-H ligand 3 into a PNPN-P ligand 4 seems possible.1–5
The two-step approach to the desired ligand type 3 (upper pathway, Scheme 1) is
limited to the availability of the starting material 2. Only compounds with equal substituents

SUBSTITUTED N- AND P-AMINODIPHOSPHINOAMINE LIGANDS
1847
Scheme 1 Different methods for synthesizing R12PN(R2)P(R3)N(R4)H (3)6.
at the nitrogen are accessible. To overcome these limitations, a three-step process was ap-
plied. Starting from a primary amine, the reaction with a chlorophosphine R1 PCl produces
2
R1 PN(R2)H. Further reaction with a dichlorophosphine R3PCl2 results in the intermediates
2
R1 PN(R2)P(R3)Cl 1a–1g, which yield the title compounds R1 PN(R2)P(R3)N(R4)H (3) by
2
2
aminolysis with a primary amine (lower pathway, Scheme 1). The ligands 3a and 3k were
proven to be accessible by both methods.
The 31P NMR data of 3a–3l at room temperature are presented in Table 1. Only
the aminodiphosphino-amine PNPN-H ligands 3g (R2 = c-Hex), 3h (R2 = n-Hex), and 3l
(R2 = i-Pr) show the expected pattern of two sets of sharp doublets. The ligands (3a–3e,
3j, 3k) (R2 = i-Pr) give spectra with two rather broad singlets. Variable temperature 31P
NMR spectroscopy was performed in the case of 3a.11g Different conformers of 3a, which
interconvert on the NMR time scale at room temperature, were postulated. Restricted
rotation about the P N bonds caused by the bulkiness of the i-Pr group is given as reason
for this observation.
2
The JPP coupling constants presented in Table 1 show some interesting features
as they cover a broad range from 14 Hz to 280 Hz. Not all are observable due to line
broadening, which indicates dynamic behavior. For the NPNP compound 3a, this has been
evaluated by dynamic 31P NMR spectroscopy and several conformational isomers were
found that differ with respect to this 2JPP coupling constant.11g Restricted rotation about the
P−N bond was made responsible for this observation. Moreover, Keat and co-workers11a
reported strongly differing coupling constants for triphosphazanes (Ph2PNR)2PPh (25.1 Hz
for R = Et, 4a; 280 Hz for R = Et, 4b) and also for diphosphinoamines Ph2P-NR-PPhCl
(−35 Hz to +334 Hz, depending on the alkyl substituent R). They discussed steric factors
(bulkiness of R) and the resulting different conformations about the P−N bonds as the
reason. In line with these observations, we may assume that the observed variations in
2JPP reflect the differences in population of the possible conformational isomers, which
naturally depend on the substituents.
It is worth mentioning that the 31P chemical shifts for the ligands 3h, 3i, 3k, and 3l
without phenyl substituents at the phosphorus atoms differ expectedly more from the other

1848
M. GONGOLL ET AL.
Table 1 31P NMR data of intermediates and compounds 1–4. Solvent: C6D6, exceptions: [a] CD2Cl2, [b] CDCl3,
and [c] toluene-d8
1a 42.1 d; 132.0 d
2JPP = 29 Hz5
2a 5711h,j,k
3a 41.4 br; 68.7 br
11k
1b 48.2 br; 135.1 br
1c 66.0 d; 139.4 d
2JPP = 147 Hz
2b
3b 40.6 br; 69.3 br
3cb 40.6 br; 72.4 br
2c 6911h,j,k
1d 44.2 br; 144.6 d
2JPP = 23 Hz
3d 41.0 br; 72.6 br
3e 40.5 br; 76.6 br
1e 58.0 d; 133.5 d
2JPP = 35 Hz
1f 121.9 br; 144.5 br
3f 42.1 d; 68.2 br
2JPP = 18 Hz
1gb 84.3; 143.1
2JPP = 40 Hz
3g 42.1 d; 68.2 d
2JPP = 18 Hz
4aa 52.8 d; 104.3 t11a
2JPP = 25 Hz
3h 49.6 d; 80.4 d
2JPP = 60 Hz
4ba 62.3 d; 119.5 t11a
2JPP = 280 Hz
3i 34.1 d; 58.8 br
2JPP = 14 Hz
3j 51.3 br; 70.7 br
3k 61.1 br; 147.7br
3lc 77.95 d, 87.7 d
2JPP = 35.0 Hz
examples with phenyl substituents at P1 and P2. A detailed prediction of the relevance of
these spectroscopic data with respect to the general reactivity of the PNPN-H compounds
is highly desirable. For example, in catalytic oligomerization of ethylene, a deprotonation
of N-H occurs during catalysis.7–10
Figure 1 Molecular structure of Ph2PN(i-Pr)P(Ph)Cl (1a) in the crystal with thermal ellipsoids set at 30% prob-
ability level. All hydrogen atoms have been omitted for clarity. Selected atom distances [Å] and bond angles [◦]:
P1−N1 1.7246(9), P2−N1 1.6843(10), P2−Cl1 2.1052(10), N1−P1−C16 105.4(1), N1−P1−C10 103.0(1),
C16−P1−C10 102.5(1), N1−P2−C1 101.4(1), N1−P2−Cl1 102.0(1), C1−P2−Cl1 99.1(1), C7−N1−P2
122.2(1), C7−N1−P1 116.4(1), P2−N1−P1 121.0(1). (Color figure available online).

SUBSTITUTED N- AND P-AMINODIPHOSPHINOAMINE LIGANDS
1849
Figure 2 Molecular structure of (cyclopentyl)2PN(i-Pr)P(Ph)Cl (1e) in the crystal with thermal ellipsoids
set at 30% probability level. All hydrogen atoms have been omitted for clarity. Selected atom distances [Å]
and bond angles [◦]: P1−N1 1.7534(13), P2−N1 1.6663(12), P2−Cl1 2.1284(6), N1−P1−C15 102.7(1),
N1−P1−C10 103.7(1), C15−P1−C10 100.7(1), C7−N1−P2 122.0(1), C7−N1−P1 116.7(1), P2−N1−P1
120.4(1), N1−P2−C1 102.8(1), N1−P2−Cl1 104.3(1), C1−P2−Cl1 97.7(1). (Color figure available online).
The molecular structures of the intermediates Ph2PN(i-Pr)P(Ph)Cl (1a) (Figure 1) and
(cyclopentyl)2PN(i-Pr)P(Ph)Cl (1e) (Figure 2) and of the ligand (1-Ad)2PN(i-Pr)P(Ph)N(i-
Pr)-H (3l) (Figure 3) were determined by singly-crystal X-ray diffraction.
The molecular structures of other PNPN-H ligands like Ph2PN(iPr)P(Ph)N(iPr)-H
(3a)6a and Ph2PN(i-Pr)P(Ph)N(Et)-H (3d)7 were published before so that a comparison of
all structural data of the intermediates and the ligands is now possible (Table 2).
The atoms N1 are in a distorted trigonal planar environment, whereas the atoms P1
and P2 with their substituents are in a distorted trigonal pyramidal shape. The structural
Figure 3 Molecular structure of (1-Ad)2PN(i-Pr)P(Ph)N(i-Pr)-H (3l) in the crystal with thermal ellipsoids set
at 30% probability level. All hydrogen atoms (except of hydrogen attached to nitrogen) have been omitted for
clarity. Selected atom distances [Å] and angles [◦]: P1−N1 1.7380(13), N1−P2 1.7168(13), P2−N2 1.6785(14),
N1−P1−C11 103.8(1), N1−P1−C1 108.4(1), C11−P1−C1 109.4(1), C21−N1−P2 117.7(1), C21−N1−P1
117.5(1), P2−N1−P1 123.4(1), N2−P2−N1 108.1(1), N2−P2−C24 99.6(1), N1−P2−C24 103.0(1). (Color
figure available online).

1850
M. GONGOLL ET AL.
Table 2 Comparison of structural data for Ph2PN(i-Pr)P(Ph)Cl (1a), (cyclopentyl)2PN(i-Pr)P(Ph)Cl (1e), (1-
Ad)2PN(i-Pr)P(Ph)N(i-Pr)-H (3l), Ph2PN(iPr)P(Ph)N(iPr)-H (3a),6a and Ph2PN(i-Pr)P(Ph)N(Et)-H (3d).7
Atom distances [Å]
P1−N1
1.7246(9)
1.6843(10)
2.1052(10)
1.7554(13)
1.6663(12)
2.1284(6)
1.7380(13)
1.7168(13)
1.708(2)
1.720(2)
1.7092(15)
1.7155(14)
N1−P2
P2−Cl
P2−N2
1.6785(14)
123.4(1)
108.1(1)
1.666(2)
121.5(1)
106.8(1)
1.678(2)
123.1(1)
107.7(1)
Angles [◦]
P1−N1−P2
N1−P2−Cl
N1−P2−N2
Torsion angles [◦]
(P1−N1)−(P2−Cl)
(P1−N1)−(P2−N2)
121.0(1)
102.0(1)
120.4(1)
104.3(1)
−132.0(1)
−108.6(1)
−122.8(1)
136.9(1)
−125.5(1)
Table 3 Crystal structure and data refinement parameters
Compound
1a
1e
3l
Empirical Formula
Formula Weight
C21H22ClNP2
385.79
C19H30ClNP2
369.83
C39H58N2P2
616.81
Crystal System/Space Group
a/Å
b/Å
P-1 Triclinic
10.118(2)
10.153(2)
11.622(2)
73.97(3)
65.70(3)
65.83(3)
984.5(3)
2
P-1 Triclinic
10.2037(5)
10.2286(5)
11.3823(6)
67.053(4)
67.230(4)
76.754(4)
982.40(0)
2
P-1 Triclinic
10.7235(4)
11.0167(4)
15.0329(6)
82.176(3)
82.062(3)
84.878(3)
1738.06(11)
2
c/Å
α/◦
β/◦
γ /◦
V/Å3
Z
Dcalc (g/cm3)
1.301
0.360
1.250
0.357
1.179
0.155
μ (mm−1
)
Crystal size (mm)
Color/Shape
Temp (K)
0.50 × 0.48 × 0.45
Colorless
150(2)
0.60 × 0.50 × 0.22
Colorless prism
150(2)
0.45 × 0.42 × 0.19
Colorless plate
200(2)
Theta range for collection
Reflections collected
Independent reflections
Restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
13, 13, 15
16327
4521
0/228
1.046
13, 14, 15
18881
5292
12/209
1.041
13, 14, 19
28888
7989
10/366
0.873
0.0298
0.0736
0.0391
0.1015
0.0398
0.0976
Largest difference peak/hole
0.390/−0.230
0.669/−0.512
0.648/−0.340

SUBSTITUTED N- AND P-AMINODIPHOSPHINOAMINE LIGANDS
1851
parameters of ligand 3l are in the expected usual range as found in the earlier reported
examples 3a and 3d. Only a significantly longer P1–N1 distance of 1.7380(13) compared
to the phenyl analogues 3a and 3d is observed, caused by the steric and electronic influence
of the two adamantyl substituents.
CONCLUSIONS
Synthesis of a series of aminodiphosphinoamine PNPN-H (3) compounds with
varying substituents on phosphorus and nitrogen atoms is possible by using two dif-
ferent synthetic methods. Following a two-step process, dichlorophenylphosphine reacts
with an excess of a primary amine to give diaminophenyl-phosphines H-PNPN-H (2).
Depending on the used substituent at the nitrogen atom in the further reaction with
chlorodiphenylphosphine either the aminodiphosphinoamines PNPN-H (3) or the N,Nꢁ-
bis(diphenylphosphino)diaminophenylphosphines PNPNP (4) are formed.
The alternative three-step process consists of the reaction of a primary amine with
chlorophosphines R2PCl to give the corresponding aminophosphines, which give in re-
actions with dichlorophosphines RPCl2 the compounds PNP-Cl (1) as intermediates and
by further aminolysis with a primary amine the title compounds PNPN-H (3). General
possibilities of synthesis and yields for the considered compounds and single steps strongly
depend on the substituents used and the intermediates, which are described in detail. The
described compounds are very potent ligands for various catalytic applications, including
ethylene oligomerization.
EXPERIMENTAL
General
All operations were carried out under argon with standard Schlenk techniques or in a
glove box. Prior to use, nonhalogenated solvents (including benzene-d6) were freshly dis-
tilled from sodium tetraethylaluminate and stored under argon. All other chemical reagents
and solvents were obtained from commercial sources and used without further purifica-
tion. The following spectrometers were used: NMR spectra: Bruker AV 300, AV 400, and
AMX 400 (Sigma-Aldrich Co. LLC., St. Louis, Missouri, USA). Chemical shifts (1H, 13C)
are given relative to SiMe4 and are referenced to signals of the used solvent: benzene-d6
(δH = 7.16, δC = 128.0). Chemical shifts for 31P are given relative to 85% H3PO4. The
spectra were assigned with the help of DEPT. —Melting points: sealed capillaries, Bu¨chi
535 apparatus. — Elemental analyses: Leco CHNS-932 elemental analyzer. Mass spectra
were obtained with a MAT 95XP (Thermo) instrument at an ionizing voltage of 70 eV or
for ESI mass spectrometry with an ESI-TOF-MS 6210 (Agilent). A general synthesis of
aminophosphines as educts, the synthesis of the PNP-Cl intermediate 1, and the synthesis
of ligand 3 are given here. Detailed procedures of the individual compounds along with
their analytical data can be found in the Supplemental Materials (available online).
Crystallographic Details
Diffraction data for compounds 1a, 1e, and 3l were collected with a STOE-IPDS
II diffractometer using graphite-monochromated Mo-Kα radiation. The structures were

1852
M. GONGOLL ET AL.
solved by direct methods (SHELXS-9716) and refined by full-matrix least-squares proce-
dures on F2 (SHELXL-9716). DIAMOND was used for graphical representations.17 The
data collection and refinement parameters are given collected in Table 1 of the supplemen-
tal Materials. CCDC 912129 (1a), CCDC 912129 (1e), and CCDC 912131 (3l) contain
supplementary crystallographic data (available online) for the structures presented in this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/retrieving.html
(or from the Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge, B2
1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
General Synthesis of Compounds 3 and 4
Aminophosphines as Educts for the Synthesis of Compounds 1a, 1d,
1e, 1f, and 1g. Chlorophosphine R2PCl was added slowly to an excess amount of
isopropylamine, dissolved either in toluene or in THF at −78◦C. The reaction mixture was
stirred overnight while bringing it slowly from −78◦C to room temperature to give a pale
yellow–white suspension. Excess amine was removed under reduced pressure, the solid
was filtered off, and the solvent was removed from the solution till dryness. If necessary,
the product was washed with n-hexane or alternatively crystallized from n-hexane at −78◦C
to afford a colorless oil or powder.
Aminophosphines as Educts for the Synthesis of Compounds 1b and 1c.
Triethylamine and the required amine were dissolved either in toluene or in THF and cooled
to −78◦C. An equimolar (with respect to the amine) amount of diphenylchlorophosphine
was added slowly to the solution and the reaction mixture was stirred overnight warming
from −78◦C to room temperature to give a pale yellow–white suspension. The workup was
as described earlier for the educts for 1a, 1d, 1e, 1f, and 1g.
Synthesis of PNP-Cl Intermediates 1a–1g. The aminophosphine products as
discussed earlier were dissolved in a mixture of toluene with triethylamine and cooled to
−78◦C. An equimolar amount of dichlorophenylphosphine or dichloromethylphosphine
was added dropwise with stirring. The suspension was allowed to warm up to room tem-
perature overnight. The excess of unreacted amine was removed under reduced pressure,
the suspension was filtrated, and the toluene was removed till dryness. Pale-yellow oil was
obtained and crystallization from n-hexane gave the pure product.
Synthesis of Ligands 3a–3l. The PNP-Cl intermediates (1a–1g) were dissolved
in a mixture of toluene with triethylamine and cooled to −78◦C. The equimolar amount
of the required amine was added slowly to the solution and the reaction mixture was
stirred overnight warming from −78◦C to room temperature giving a pale yellow–white
suspension. The unreacted amine was removed under reduced pressure and the suspension
was filtrated. Toluene was removed till dryness to yield the pure product after washing with
n-hexane at −78◦C.
Synthesis of the NPN Intermediate 2a for the Alternative Synthesis of
3a and 3k. An excess of isopropylamine was dissolved in toluene and cooled to −78◦C.
Dichlorophenylphosphine was added slowly to the solution and the reaction mixture was
stirred overnight warming from −78◦C to room temperature to give a pale yellow–white
suspension. The unreacted amine was removed under reduced pressure, the suspension was
filtered, and the toluene was removed till dryness. If necessary, the product was washed
with n-hexane at −78◦C to yield the pure product.

SUBSTITUTED N- AND P-AMINODIPHOSPHINOAMINE LIGANDS
1853
Synthesis of the Ligands 3a and 3k from 2a. Compound 2a was dissolved in
toluene and triethylamine, the solution was cooled to −78◦C, and an equimolar amount of
the chlorophosphine R2PCl was added slowly to the solution. After stirring overnight and
warming from −78◦C to room temperature, a pale yellow–white suspension was obtained.
Triethylamine was removed under reduced pressure, the suspension was filtered off, and
the toluene was removed till dryness. Washing the product with n-hexane at −78◦C yielded
the pure products.
Compounds 3a,6a 3d,7 3f,15 and 3h,15 were prepared according to published literature
procedures.
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