Synthesis, spectral characterization and crystal structures of organophosphonic diamides: Pyramidal nitrogen centers and hydrogen bonding in [PhP(O)(NHtBu)2], [PhP(O)(NHDipp)2] (Dipp = 2,6-iPr2C6H3) and [tBuP(O)(NHiPr)2]

Article abstract of DOI:10.1039/b300035d

Organophosphonic diamides of general formula [R¹P(O)(NHR²)₂] (1-8; R¹ = Ph, Cy or ^tBu and R² = Cy, ⁱPr, ^tBu or Dipp) have been prepared by the addition of P,P′-dichloro(alkyl/aryl)phosphine oxide, R¹P(O)Cl₂, to a solution of primary amine in toluene. The synthesis of PhP(O)(NH^tBu)₂ (1) in high yield was achieved by slow oxidation of PhP(NH^tBu)₂ in air over several days. All new compounds have been characterized by elemental analysis and by IR, EI mass and NMR (¹H and ³¹P) spectroscopy. The molecular structures of [PhP(O)(NH^tBu)₂] (1), [PhPO(NHDipp)₂] (2) and [^tBuP(O)(NHⁱPr)₂] (7) have been determined by single crystal X-ray diffraction studies. The amido nitrogen atoms in 1, 2 and 7 show considerable deviation from the expected trigonal-planar geometry. The observed dihedral angles and the orientation of the nitrogen lone pair (l.p.) in these compounds point to the role of l.p.(N) → σ*(P-X) type negative hyperconjugative interactions in P-N multiple bonding. Compounds 1 and 7 form interesting polymeric structures in the solid state with the aid of N-H...O=P hydrogen bonding interactions while the presence of the very bulky Dipp substituent on nitrogen in 2 prevents the participation of the N-H protons in hydrogen bonding with phosphoryl oxygen atoms.

Full text of DOI:10.1039/b300035d

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Synthesis, spectral characterization and crystal structures of
organophosphonic diamides: pyramidal nitrogen centers and hydrogen
bonding in [PhP(O)(NHtBu)2], [PhP(O)(NHDipp)2]
(Dipp = 2,6-iPr2C6H3) and [tBuP(O)(NHiPr)2]y
Ramaswamy Murugavel* and Ramasamy Pothiraja
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400 076,
India. E-mail: rmv@iitb.ac.in; Fax: +91 22 2572 3480 or 2576 7152; Tel: +91 22 2576 7163
Received (in Toulouse, France) 2nd January 2003, Accepted 24th January 2003
First published as an Advance Article on the web 14th May 2003
t
Organophosphonic diamides of general formula [R1P(O)(NHR2)2] (1–8; R1 ¼ Ph, Cy or Bu and R2 ¼ Cy,
iPr, tBu or Dipp) have been prepared by the addition of P,P’-dichloro(alkyl/aryl)phosphine oxide, R1P(O)Cl2 ,
to a solution of primary amine in toluene. The synthesis of PhP(O)(NHtBu)2 (1) in high yield was achieved
by slow oxidation of PhP(NHtBu)2 in air over several days. All new compounds have been characterized by
elemental analysis and by IR, EI mass and NMR (1H and 31P) spectroscopy. The molecular structures of
[PhP(O)(NHtBu)2] (1), [PhPO(NHDipp)2] (2) and [tBuP(O)(NHiPr)2] (7) have been determined by single crystal
X-ray diffraction studies. The amido nitrogen atoms in 1, 2 and 7 show considerable deviation from the
expected trigonal-planar geometry. The observed dihedral angles and the orientation of the nitrogen lone pair
(l.p.) in these compounds point to the role of l.p.(N) ! s*(P–X) type negative hyperconjugative interactions in
P–N multiple bonding. Compounds 1 and 7 form interesting polymeric structures in the solid state with the aid
=
of N–Hꢀ ꢀ ꢀO P hydrogen bonding interactions while the presence of the very bulky Dipp substituent on
nitrogen in 2 prevents the participation of the N–H protons in hydrogen bonding with phosphoryl oxygen
atoms.
Renewed interest in organophosphonic diamide chemistry is
Introduction
due to the isoelectronic relation of this class of compounds to the
extensively investigated organophosphonic acids10,11 (Chart 2).
In particular, recent work has demonstrated the use of phos-
phonic acids in the synthesis of several novel cage-like10 and
layered metal phosphonates.11 Similarly, phosphonic diamides
are expected to serve as useful ligands in building aggregates
that simultaneously contain both M–N–P and M–O–P lin-
kages. In this context, we wish to report herein on the synthesis
of a series of organophosphonic diamides and their character-
ization data. We also report on the first crystal structures of
free organophosphonic diamides, establishing the solid-state
conformation and hydrogen-bonding pattern in these ligands.
The discovery of metallocene catalysts for alkene polymeriza-
tion has received considerable attention owing to their role
in stereoselective/specific polymerization.1 While the use of
mixed cyclopentadienyl amide and amidine complexes for cat-
alysis has been reported,2 the interest in synthesis and the
application of diimide precursors is only just emerging.3,4 Since
electron deficient, usually d0, metal centers are required for
efficient catalytic systems, the somewhat poorer donation abil-
ity of amide ligands might be expected to offer enhanced activ-
ity over the analogous ansa-metallocene complexes. In this
context, the groups of Brookhart and Gibson have recently
prepared complexes based on chelating bis(imido) ligands,
which polymerize olefins with excellent activities.5 Organopho-
sphonic amides [R1P(O)(NHR2)2] could serve as very useful
chelating ligands in this regard and may have a marked influ-
ence in the activity of the resulting complex due to the presence
of a phosphorus center adjacent to the ligating nitrogen atoms.
While Kuchen et al. have investigated the coordination chem-
istry of diorganophosphonic amides [R12P(O)(NHR2)] in detail
and have shown that these ligands stabilize transition metal
ions in unusual geometries,6 a recent report by Chivers and
co-workers has demonstrated the use of [P(O)(NHR)3] in
synthesizing amido analogs of aluminophosphates (Chart 1).7
However, there are no studies on the utilization of
[R1P(O)(NHR2)2] as chelating ligands although there have
been reports on the synthesis and mechanism of formation
of these compounds.8,9
Results and discussion
Synthesis
Although several examples of phosphonic diamides have been
described in the literature, they have been poorly character-
ized, with no spectroscopic or structural studies being
y Electronic supplementary information (ESI) available: representa-
tive IR and NMR spectra. See http://www.rsc.org/suppdata/nj/b3/
b300035d/
Chart 1
968
New J. Chem., 2003, 27, 968–974
DOI: 10.1039/b300035d
This journal is # The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2003

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Table 1 Selected characterization data for 1–8
Compound
% Yield M.p./ꢁC m/z+ (EIMS %) d (31P)/ppm
[PhP(O)(NHtBu)2] (1)
80
181–182 268 (5)
210–211 476 (5)
15.3
9.1
Chart 2
[PhP(O)(DippNH)2] (2) 18a
[CyP(O)(NHCy)2] (3)
[CyP(O)(NHtBu)2] (4)
[CyP(O)(NHiPr)2] (5)
[tBuP(O)(NHCy)2] (6)
[tBuP(O)(NHiPr)2] (7)
[tBuP(O)(NHtBu)2] (8)
67
50
52
58
90
65
230–235
236–237
137–138
197–198
164–165
181–182
326(3)
274(2)
247(2)
300(2)
221(5)
249(5)
30.9
28.1
30.1
37.4
35.5
32.6
reported8 More importantly, the use of these functional mole-
cules in further reactions to yield metal derivatives has not
been studied at all. To investigate these points, the synthesis
of a series of phosphonic diamides was carried out by varying
the bulkiness and nature of the substituents on both phos-
phorus and nitrogen atoms.
a
Yield of the twice re-crystallized sample.
The phosphonic diamides 1–8 have been synthesized essen-
tially by following the reaction procedure shown in Scheme 1
although some variations in reaction conditions were neces-
sary, depending on the relative bulkiness of the amines used.
Typically alkyl/arylphosphonic dichlorides R1P(O)Cl2 (R ¼
or aromatic amine R2NH2 in boiling toluene. For the prepara-
tion of [PhP(O)(NHDipp)2] (2), only 2 equiv. of high-boiling
DippNH2 was used while 2 equiv. of Et3N was added in the
reaction mixture as an HCl scavenger. The reaction proceeded
with the formation of amine hydrochloride. Since phosphonic
amides are freely soluble in toluene, the amine hydrochloride
formed was separated by simple filtration.
due to the respective molecular ions, even at 70 eV. The frag-
mentation pattern of the products under EI conditions is con-
sistent with the proposed structures. The IR spectral data of
1–8 display the vibrational bands for all structural linkages
expected for these compounds.12 For example, the characteris-
t
Ph, Bu, Cy) were reacted with 4 equiv. of a primary aliphatic
=
tic P O absorption for all compounds was observed around
1200 cmꢂ1. The N–H stretching vibration in 1–8 results in a
strong absorption in the range 3200–3300 cmꢂ1
.
1
The H NMR spectral data obtained for 1–8 are suggestive
of the expected structure of these molecules. A description of
the spectrum of [PhP(O)(NHDipp)2] (2) is presented here as
a representative example. Compound 2 shows two doublets
(d 0.9 and 1.1 ppm) of equal intensity (3JHH ¼ 6.96 Hz) corre-
sponding to the methyl groups of two inequivalent isopropyl
groups and a septet for the methine protons at d 3.3 ppm.
The resonance appearing at d 4.1 ppm (doublet) is due to the
N–H protons. This resonance could be interpreted either as
two separate peaks for two non-equivalent N–H protons or
as a phosphorus-coupled doublet (2JPH ¼ 10 Hz). This ambi-
guity could, however, be resolved by recording the spectrum
at three different spectral frequencies (60, 300, and 400
MHz), which clearly showed that this resonance is a phos-
phorus-coupled doublet. This strong coupling of phosphorus
to the N–H protons can be attributed to the presence of fairly
strong N–H bonds in 2 due to the absence of hydrogen bond-
ing involving these protons (vide infra).
Synthesis of [tBuP(O)(NHtBu)2] (8) could not be accom-
plished under the conditions described above owing to the pre-
sence of bulky tert-butyl groups in both reactants. Hence this
reaction was carried out under solvothermal conditions in an
autoclave at 140 ꢁC using acetonitrile as described by Quast
et al.8a Work-up in this case was carried out by pouring the
reaction mixture ino ice-cold water and stirring for 30 min to
extract the amine hydrochloride formed. For the synthesis of
1, compared to following the reaction shown in Scheme 1,
crystallization of tervalent phosphorus amide [PhP(NHtBu)2]
in air over prolonged time from a CH2Cl2–hexane solution
results in better yields of [PhP(O)(NHtBu)2] (90%). Although
there has been some variations in the reaction times (typically
5 to 9 days), this reaction is highly reproducible with high iso-
lated yields of 1. While air seems to act as a convenient oxidiz-
ing agent in the present case, the earlier reported method for
the preparation of this compound involves the use of ozone
as the oxidizing agent.8b
The observed 31P NMR chemical shift values for all the
compounds fall in the range d 9.1 to 37.4 ppm (Table 1).
The nature of the R1 group attached directly to phosphorus
has a more pronounced effect on the observed chemical shift
than the R2 group on the nitrogen atoms. For example, the
tert-butyl phosphonic amides show resonances in the range d
32.6 to 37.4 ppm while the chemical shifts of cyclohexyl phos-
phonic amides fall in the range d 28.1 to 30.9 ppm. The most
upfield shifts are observed for the phenyl phosphonic diamides
1 and 2. In particular, the presence of the bulky Dipp group on
the nitrogen in 2 causes the highest upfield shift among the
phosphonic diamides reported herein (d 9.1 ppm).
Characterization
Compounds 1–8 were found to have good solubility in most
organic solvents and hence could be purified by repeated crys-
tallization. The isolated yield of analytically pure [PhP(O)-
(NHDipp)2] (2) is comparatively low due to the substitution
of two very bulky DippNH groups at the phosphorus. Charac-
terization of all the compounds was carried out with the aid of
IR, mass and NMR (1H and 31P NMR) spectroscopic techn-
iques. Selected analytical and spectroscopic data for the new
products are listed in Table 1.
Molecular structures
The re-crystallized samples of all new compounds were ana-
lytically pure with fairly sharp melting points. The electron
impact mass spectra (EI MS) of all compounds yielded peaks
The relative disposition of the acidic N–H protons (Chart 3) in
phosphonic diamides is of interest for their subsequent reac-
tions with metal precursors to generate metallophosphon-
amides. The predominance of one of the forms over other
forms shown in Chart 3 will be dictated by both the bulkiness
of the substituents R1and R2 and the maximization of P–N
multiple bonding effects. Hence, in order to glean structural
insights into the conformations of these molecules, single crys-
tal X-ray diffraction studies were carried out for the represen-
tative examples 1, 2, and 7.13
The ORTEP of the final refined structures of compound 1, 2
and 7 are shown in Fig. 1. Selected bond lengths, bond angles
and dihedral angles found in these compounds are listed in
Tables 2–4, respectively. A comparison of the key structural
Scheme 1
New J. Chem., 2003, 27, 968–974
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˚
Table 2 Selected bond lengths (A), bond angles and dihedral angles
(ꢁ) in 1
P(1)–O(1)
P(1)–N(2)
N(1)–H(1)
1.477(2)
1.644(2)
0.71(3)
117.8(1)
111.7(1)
100.2(1)
129.8(2)
112(3)
P(1)–N(1)
P(1)–C(11)
N(1)–H(2)
1.646(2)
1.811(2)
0.78(3)
104.6(1)
110.5(1)
111.3(1)
125.7(2)
111(2)
O(1)–P(1)–N(1)
O(1)–P(1)–N(2)
N(1)–P(1)–C(11)
P(1)–N(1)–C(1)
P(1)–N(1)–H(1)
C(1)–N(1)–H(1)
C(1)–N(1)–P(1)–O(1)
C(1)–N(1)–P(1)–N(2)
C(1)–N(1)–P(1)–C(11)
H(1)–N(1)–P(1)–N(2)
H(1)–N(1)–P(1)–O(1)
H(1)–N(1)–P(1)–C(11)
N(1)–P(1)–N(2)
O(1)–P(1)–C(11)
N(2)–P(1)–C(11)
P(1)–N(2)–C(5)
Chart 3
C(5)–N(2)–H(2)
P(1)–N(2)–H(2)
C(5)–N(2)–P(1)–O(1)
C(5)–N(2)–P(1)–C(11)
C(5)–N(2)–P(1)–N(1)
H(2)–N(2)–P(1)–O(1)
H(2)–N(2)–P(1)–N(1)
H(2)–N(2)–P(1)–C(11)
features is presented in Table 5. It has been possible to locate
the N–H hydrogen atoms in each of the three compounds from
the difference Fourier maps and subsequently refine them to
convergence.14 This allows a meaningful interpretation of the
nature of the bonding and conformations around the imino
nitrogen atoms. Compounds 1 and 7 form interesting poly-
117(3)
114(2)
ꢂ59.8(3)
65.0(2)
ꢂ179.6(2)
ꢂ124(3)
111(3)
ꢂ43.4(2)
80.7(2)
ꢂ171.9(2)
173(2)
45(2)
ꢂ63(2)
ꢂ9(3)
=
meric structures in the solid state with the aid of N–Hꢀ ꢀ ꢀO P
hydrogen-bonding interactions (Fig. 2). Although both 1 and 7
=
form a one-dimensional polymeric chain through N–Hꢀ ꢀ ꢀO P
interactions, in the case of 1 only one of the N–H groups par-
ticipates in polymer formation. On the other hand, the pre-
=
sence of a mirror symmetry running through the P O axis in
7 imposes the participation of both the N–H groups in hydro-
gen bonding, thus forming PN2H2O rings along the polymeric
chain (Fig. 2). However, in both the cases, no inter-chain
hydrogen bonds are observed. On the other hand, the presence
of the very bulky Dipp groups on nitrogen in 2 does not allow
the formation of hydrogen bonds by this compound and the
molecules of 2 are largely held in the crystal through van der
Waals forces.
=
The observed P O and P–N distances are consistent with
the expected values for these linkages.15 The angles observed
around the central phosphorus are largely tetrahedral. The
most interesting structural feature observed for these mole-
cules is the presence of significantly pyramidalized nitrogen
atoms (Table 5). Barring a few exceptions, a tricoordinate
nitrogen atom that is attached to a phosphorus16 (or silicon17)
is expected to exhibit a perfect trigonal-planar geometry. The
literature examples with non-planar nitrogen atoms attached
to a phosphorus center were proven to be a result of geometric
constraints (e.g., an aziridinyl phosphazene,18 a chelate com-
plex of a l3-cyclotriphosphazane16 or a bridging nitrogen atom
of a bicyclophosphazene,19 etc.) rather than electronic effects.
These well-known exceptions to planar nitrogen atoms in the
literature are normally from constrained cyclic systems of the
above type and are not commonplace among acyclic P–NR2
type compounds. Hence the observed pyramidal geometry
for the nitrogen centers of unconstrained acyclic phosphonic
diamides 1, 2 and 7 is quite unique.
It is important to note, however, that in spite of the appreci-
able pyramidalization of the nitrogen atoms, the observed P–N
˚
distances (1.64–1.65 A) are shorter than the corresponding dis-
tances found in acyclic and cyclic phosphazanes that contain
˚
Table 3 Selected bond lengths (A), bond angles and dihedral angles
(ꢁ) in 2
P(1)–O(1)
P(1)–N(2)
N(1)–H(1)
1.476(2)
1.653(2)
0.82(3)
121.1(1)
111.1(1)
101.7(1)
123.2(2)
114(2)
P(1)–N(1)
P(1)–C(25)
1.658(2)
1.799(3)
0.77(2)
100.4(1)
111.1(1)
110.7(1)
128.0(2)
114(2)
N(1)–H(2)
N(1)–P(1)–N(2)
O(1)–P(1)–N(1)
O(1)–P(1)–N(2)
N(1)–P(1)–C(25)
P(1)–N(1)–C(1)
P(1)–N(1)–H(1)
C(1)–N(1)–H(1)
O(1)–P(1)–N(1)–C(1)
N(2)–P(1)–N(1)–C(1)
C(25)–P(1)–N(1)–C(1)
O(1)–P(1)–N(1)–H(1)
N(2)–P(1)–N(1)–H(1)
C(25)–P(1)–N(1)–H(1)
O(1)–P(1)–C(25)
N(2)–P(1)–C(25)
P(1)–N(2)–C(13)
P(1)–N(2)–H(2)
118(2)
C(13)–N(2)–H(2)
O(1)–P(1)–N(2)–C(13)
N(1)–P(1)–N(2)–C(13)
C(25)–P(1)–N(2)–C(13)
O(1)–P(1)–N(2)–H(2)
N(1)–P(1)–N(2)–H(2)
C(25)–P(1)–N(2)–H(2)
114(2)
ꢂ64.6(2)
58.0(2)
171.8(2)
91(2)
ꢂ32.6(3)
ꢂ161.9(2)
91.3(2)
169(2)
Fig. 1 ORTEP plots (50% probability level) of [PhP(O)(NHtBu)2] (1)
(top), [PhP(O)(NHDipp)2] (2) (middle) and [tBuP(O)(NHiPr)2] (7)
(bottom). The hydrogen atoms on carbon atoms in 2 are omitted for
clarity.
ꢂ147(2)
ꢂ33(2)
40(2)
67(2)
970
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˚
Table 4 Selected bond lengths (A), bond angles and dihedral angles
(ꢁ) in 7
P(1)–O(1)
P(1)–C(1)
1.489(2)
1.823(2)
114.3(1)
107.0(1)
123.5(1)
116(1)
P(1)–N(1)
N(1)–H(1)
1.641(1)
0.80(3)
109.0(1)
104.7(1)
114(2)
O(1)–P(1)–N(1)
N(1)–P(1)–C(1)
P(1)–N(1)–C(4)
C(4)–N(1)–H(1)
O(1)–P(1)–N(1)–C(4)
O(1)–P(1)–C(1)
N(1)–P(1)–N(1)a
P(1)–N(1)–H(1)
ꢂ13.9(2)
C(1)–P(1)–N(1)–C(4)
106.8(1)
137(2)
N(1)a–P(1)–N(1)–C(4) ꢂ139.8(1) O(1)–P(1)–N(1)–H(1)
C(1)–P(1)–N(1)–H(1)
ꢂ103(2)
N(1)a–P(1)–N(1)–H(1) 11(2)
perfectly planar nitrogen atoms.15 The short P–N distances,
largely planar nitrogen coordination and poor amine basicity
have been attributed for a long time to the involvement of
the nitrogen lone pair in multiple bonding with the phosphorus
atom through pp ! dp interactions.17 The importance of this
mode of multiple bonding has been questioned both from a
theoretical and experimental standpoint for the last two dec-
ades.20 It is now believed that the P–N multiple bonding in
these kinds of systems involve l.p.(N) ! s*(P–X) negative
hyperconjugation rather than l.p.(N) ! d(P) interactions.21
Application of the l.p.(N) ! s*(P–X) model to compounds
1, 2, and 7 would require a knowledge of the dihedral angles
involved in the core. For example, if these interactions are
really indeed responsible for the short P–N bonds, then either
the C–P–N–H or O–P–N–H dihedral angle should be close to
90ꢁ (Chart 4), since only such arrangements would allow the
nitrogen lone pair to align itself parallel to the P–O or P–C
s* orbital. The observed dihedral angles listed in Tables 2–5
indeed show that this is true in all three molecules. For exam-
ple, the observed O–P–N–H angles in both 1 and 2 (111ꢁ and
91ꢁ, respectively) indicate that the lone pair on N1 is involved
in multiple bonding through interaction with the P–O s* orbi-
tal while the C–P–N–H dihedral angles involving N2 (ꢂ63ꢁ
and ꢂ67ꢁ, respectively) are indicative of this nitrogen interact-
ing with the P–C s* orbital. In 7, the lone pairs of both nitro-
gen atoms are almost parallel to the P–C bonds. Hence, it
appears that, in spite of the small pyramidalization, the nitro-
gen lone pairs in these molecules prefer a P–X s* orbital to a
dp-orbital.
Fig. 2 Ball-and-stick model showing the hydrogen bonding in
[PhP(O)(NHtBu)2] (1) (top) and [tBuP(O)(NHiPr)2] (7) (bottom). Only
core atoms are shown for the sake of clarity.
=
trans to the P O group. Thus, there appears to be a large flex-
ibility for P–N bond rotation in these molecules in spite of the
geometrical constraints posed by the maximization of negative
hyperconjugative interactions. Hence these compounds should
prove to be useful multidentate and chelate ligands after
deprotonation of the N–H groups.
Conclusion
It has been shown in this contribution that organophosphonic
diamides, which have an isoelectronic relationship with orga-
nophosphonic acids, can be synthesized in good yields using
a simple synthetic methodology. Although the bulkiness of
the amines used in the present study has a marked effect on
the reaction conditions employed to synthesize the phosphonic
amides, the resultant molecules essentially have common struc-
tural features such as short P–N bonds and appreciably pyra-
midalized nitrogen atoms. It appears that the pyramidalization
of the nitrogen atoms is not driven by the packing effects in the
solid state since this phenomenon is observed in all three com-
pounds 1, 2 and 7, which have nitrogen substituents of varying
sizes. Even the alternative explanation that the pyramidal
coordination can be observed in the presence of a low inver-
sion barrier because of the lower steric congestion cannot be
applied to these systems bearing bulky R2 groups. Since the
magnitude of the pyramidalization in the present molecules
is relatively low, the observed non-planar nitrogen coordina-
tion can be accounted for in terms of minimized inductive
effects due to the presence of just one phosphorus substituent
on nitrogen.
Another structural feature of interest in these molecules is
the relative disposition of the N–H protons (Fig. 3), which is
likely to have an influence on the reactivity of these molecules
with metal alkyls and halides. The Hꢀ ꢀ ꢀH distance between the
two N–H protons provides useful information on whether the
molecule has an approximate cis or trans orientation or a
twisted conformation. The calculated Hꢀ ꢀ ꢀH distances (Table
5) indicate that the N–H proton in 7 is in a cis conformation
˚
(2.251 A) while a considerable twist is observed in the relative
˚
N–H orientation in compounds 1 and 2 (3.071 and 3.221 A,
=
The presence of two N–H groups and one P O linkage and
respectively). The molecular core of 1, 2 and 7 viewed along
the C–P axis (Fig. 3) also clearly shows the observed disposi-
tion of the N–H groups as discussed above. Interestingly, as
Fig. 3 also shows, the N–H protons prefer to orient themselves
the observed flexibility of the P–N bonds make these systems
very attractive chelating and bridging ligands for metal amido
chemistry. Our current work in this area is concentrated in
developing medium to large cluster molecules based on these
ligands that will have structural similarities to those reported
for organophosphonic acids.
Table 5 Comparison of structural features of phosphonic diamides 1,
2 and 7
1
2
7
˚
P–O/A
1.477(2)
1.645(2)
358.8
1.476(2)
1.656(2)
355.2
1.489(2)
1.641(1)
353.5
˚
P–N/A
P
cN/ꢁ
350.7
356.0
91(2)
O(1)–P(1)–N(1)–H(1)/ꢁ
O(1)–P(1)–N(2)–H(2)/ꢁ
111(3)
173(2)
3.017
137(2)
–
2.251
169(2)
3.221
˚
Hꢀ ꢀ ꢀH/A
Chart 4
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Toluene from the filtrate was completely removed in vacuo and
the resulting material was crystallized from a petroleum ether–
CH2Cl2 mixture (1:1). Yield: 1.0 g (12%).
Route 2: PhPCl2 (6.4 g, 36 mmol) in benzene (25 mL) was
added dropwise, with stirring, to tert-butylamine (17.4 g, 238
mmol) in benzene (400 mL) under a stream of nitrogen at
0 ꢁC. The amine hydrochloride was removed by filtration
under nitrogen. Removal of benzene by distillation left a vis-
cous yellow oil of [PhP(NHtBu)2]. This oil was dissolved in
benzene and left for crystallization in air. After a week, the
precipitated white solid of 1 was crystallized from a petroleum
ether–CH2Cl2 mixture (1:1). Yield: 8.6 g (90%).
Data for 1: m.p. 181–182 ꢁC. Anal. calcd: C, 62.66; H, 9.39;
N, 10.44%; found: C, 62.6; H, 9.4; N, 10.5%. IR (KBr, cmꢂ1):
3237 s, 2973 s, 2924 m, 2868 m, 1432 w, 1387 m, 1235 s, 1196 s,
1123 m, 1245 s, 1196 s, 1123 w, 1012 s, 873 w, 709 m. 1H NMR
(60 MHz, CDCl3) d 1.3 (s, tBu, 18H), 7.4 (m, Ph, 5H) ppm. 31
P
NMR (120 MHz, CDCl3) d 15.3 ppm. EI-MS (70 eV): m/z
(%): 268 (M+, 5), 57 (tBu, 100).
[PhP(O)(NHDipp)2] (2). To a solution of DippNH2 (7.5 mL,
40 mmol) and Et3N (5.6 mL, 40 mmol) in toluene (70 mL),
PhP(O)Cl2 (2.8 mL, 20 mmol) in toluene (30 mL) was added
through a dropping funnel. The reaction mixture was heated
under reflux for 3 days and filtered through filter paper.
Toluene from the filtrate was completely removed in vacuo
and the resulting solid material was twice crystallized from a
petroleum ether–CH2Cl2 mixture (5:2). Yield: 1.7 g (18%).
M.p. 210–211 ꢁC. Anal. calcd: C, 75.60; H, 8.67; N, 5.88%;
found: C, 74.9; H, 8.5; N, 5.4%. IR (KBr, cmꢂ1): 3412 s,
3353 s, 2954 vs, 2927 vs, 2866 s, 1461 m, 1440 m, 1360 s,
1333 m, 1253 w, 1220 s, 928 m, 910 m, 795 m, 743 m, 695 m.
1H NMR (300 MHz, CDCl3) d 0.9 (d, Me, 12H), 1.1 (d, Me,
12H), 3.3 (sep, CH, 4H), 4.1 (d, NH, 2H), 7.0–8.1 (m, Ph,
11H) ppm. 31P NMR (120 MHz, CDCl3) d 9.1 ppm. EI-MS
(70 eV): m/z (%): 476 (M+, 5), 177 (DippNH2 , 100).
Preparation of 3–7. Compounds 3–7 were prepared by fol-
lowing essentially the same experimental procedure. In a typi-
cal experiment, to a solution of R2NH2 (175 mmol) in toluene
(50 mL), R1P(O)Cl2 (25 mmol) in toluene (50 mL) was added
through dropping funnel. The reaction mixture was heated
under reflux for 24 h and filtered. The volume of the solution
was reduced in vacuo and the compound was crystallized from
toluene at room temperature.
Fig. 3 The molecular core of phosphonic amides 1 (top), 2 (middle)
and 7 (bottom) viewed along the C–P axis showing the relative disposi-
tion of N–H groups with respect to the phosphoryl oxygen.
Experimental
[CyP(O)(NHCy)2] (3). Yield: 5.5 g (67%). M.p. 230–235 ꢁC.
Anal. calcd: C, 66.22; H, 10.81; N, 8.58%; found: C, 61.1; H,
11.0; N, 7.5%. IR (KBr, cmꢂ1): 3210 s, 2921 s, 2855 s, 1460
s, 1163 s, 1131 s, 1032 m, 933 w, 900 w. 1H NMR (300
MHz, CDCl3) d 1.0–2.0 (m, Cy) ppm. 31P NMR (120 MHz,
CDCl3) d 30.9 ppm. EI-MS (70 eV): m/z (%): 326 (M+, 3),
98 (CyNH, 100).
Materials and methods
All reactions were carried out under an atmosphere of purified
nitrogen using standard Schlenk line techniques. Manipula-
tions of all compounds were carried out in a M-Braun glove
box. Elemental analyses were performed on a Carlo Erba
(Italy) Model 1106 Elemental Analyzer at IIT-Bombay. The
EI-MS data for all compounds were obtained on a Perkin–
Elmer GC-MS system. All other spectral measurements were
carried out as described previously.22
[CyP(O)(NHtBu)2] (4). Yield: 3.4 g (50%). M.p. 236–
237 ꢁC. Anal. calcd: C, 61.28; H, 11.39; N, 10.21%; found: C,
61.3; H, 11.5; N, 8.5%. IR (KBr, cmꢂ1): 3237 s, 2967 s, 2927
s, 2855 s, 1453 m, 1394 m, 1242 m, 1170 s, 1012 s, 861
Dichloromethane, petroleum ether, acetonitrile, and toluene
were purified and dried by conventional procedures and freshly
1
t
t
m. H NMR (300 MHz, CDCl3) d 1.3 (s, Bu, 18H), 1.0–2.1
(m, Cy, 11H) ppm. 31P NMR (120 MHz, CDCl3) d 28.1
ppm. EI-MS (70 eV): m/z (%): 274 (M+, 1), 58 (tBuH, 100).
[CyP(O)(NHiPr)2] (5). Yield: 3.2 g (52%). M.p. 137–138 ꢁC.
Anal. calcd: C, 58.51; H, 11.05; N, 11.37%; found: C, 56.6; H,
11.0; N, 10.1%. IR (KBr, cmꢂ1): 3233 s, 2967 s, 2927 s, 2861 m,
distilled prior to use. PCl3 (Thomas Baker), BuOH (SRL),
conc. HCl (Merck), AlCl3 (S.D. Fine), tBuNH2 (Merck),
iPrNH2 (Merck), cyclohexylamine (S.D. Fine), PhP(O)Cl2
(Lancaster), CyP(O)Cl2 (Aldrich) and 2,6-diisopropylaniline
t
(Aldrich) were obtained from commercial sources. BuP(O)Cl2
was prepared using a previously reported procedure.23
1
2730 m, 1473 m, 1440 m, 1381 w, 1163 s, 1012 m, 908 m. H
NMR (300 MHz, CDCl3) d 1.1 (d, Me, 6H), 1.2 (d, Me,
6H), 1.3–1.9 (m, Cy, 11H), 3.4 (sep, CH, 2H) ppm. 31P
NMR (120 MHz, CDCl3) d 30.1 ppm. EI-MS (70 eV): m/z
(%): 247 (M+, 2), 106 (P(O)(NHiPr), 100).
Syntheses
[PhP(O)(NHtBu)2] (1). Route 1: To a solution of tBuNH2 (20
mL, 190 mmol) in toluene (30 mL), PhP(O)Cl2 (5 g, 26 mmol)
in toluene (50 mL) was added through a dropping funnel. The
reaction mixture was heated under reflux for 24 h and filtered.
[tBuP(O)(NHCy)2] (6). Yield: 5.0 g (58%). M.p. 197–
198 ꢁC. Anal. calcd: C, 63.96; H, 11.92; N, 9.32%; found: C,
64.2; H, 11.2; N, 10.7%. IR (KBr, cmꢂ1): 3289 s, 2934 s,
972
New J. Chem., 2003, 27, 968–974

View Article Online
2861 m, 1479 m, 1453 m, 1216 s, 1111 s, 940 s, 834 m, 670 s. 1H
NMR (300 MHz, CDCl3) d 1.2 (d, Bu, 9H), 1.4 (d, CH, 2H),
atoms were refined anisotropically and the hydrogen atoms
isotropically. Other details pertaining to data collection, struc-
ture solution, and refinement are given in Table 6.
CCDC reference number 200563–200565. See http://
www.rsc.org/suppdata/nj/b3/b300035d/ for crystallographic
files in CIF or other electronic format.
t
1.6 (d, CH, 2H), 1.7 (d, CH, 2H), 2.0 (d, CH, 2H), 2.1 (d, CH,
2H), 2.3 (s, CH, H) ppm. 31P NMR (120 MHz, CDCl3) d 37.4
ppm. EI-MS (70 eV): m/z (%): 300 (M+, 2), 98 (CyNH, 100).
[tBuP(O)(NHiPr)2] (7). Yield: 5.8 g (90%). M.p. 164–
165 ꢁC. Anal. calcd: C, 54.52; H, 11.44; N, 12.72%; found: C,
53.8; H, 11.3; N, 11.7%. IR (KBr, cmꢂ1): 3256 s, 2973 s,
2920 m, 2661 m, 1420 m, 1301 m, 1189 s, 1137 s, 887 s. 1H
NMR (300 MHz, CDCl3) d 1.1 (d, Me, 12H), 1.2 (s, Me,
9H), 3.5 (sept, CH, 2H) ppm. 31P NMR (120 MHz, CDCl3)
d 35.5 ppm. EI-MS (70 eV): m/z (%): 221 (M+, 5), 106 (tBu-
P(O)H2 , 100).
Acknowledgements
This work was supported by the DST, New Delhi. We thank
RSIC for NMR measurements and DST funded Single Crystal
X-ray Diffractometer Facility, IIT-Bombay, for the diffraction
data of 2. R. M. also thanks the DST for the award of a Swarna-
jayanti Fellowship.
t
[tBuP(O)(NHtBu)2] (8). BuNH2 (20 mL, 189 mmol) was
added to an autoclave containing BuP(O)Cl2(5 g, 28.6 mmol)
t
in acetonitrile (50 mL). Then the closed autoclave was kept in
an oven at 140 ꢁC for 24 h. After the reaction was completed,
ice cold water (100 mL) was added at room temperature. The
reaction mixture was stirred for 1 h, then filtered. The precipi-
tate was washed with 40 mL of ice cold water. The precipitate
was recovered and crystallized from petroleum ether. Yield:
4.5 g (65%). M.p.181–182 ꢁC. Anal. calcd: C, 58.03; H,
11.77; N, 11.28%; found: C, 58.0; H, 12.1; N, 11.9. IR (KBr,
cmꢂ1): 3289 s, 2967 s, 2900 m, 2868 m, 1486 w, 1387 m,
1368 m, 1249 s, 1178 s, 999 s, 841 s. 1H NMR (60 MHz,
References
1
(a) H. G. Alt and A. Ko¨ppl, Chem. Rev., 2000, 100, 1205; (b) J. P.
Mitchell, S. Hajela, S. K. Brookhart, K. I. Hardcastle, L. M.
Henling and J. E. Bercaw, J. Am. Chem. Soc., 1996, 118, 1045;
(c) F. T. Edelmann, Top Cur. Chem., 1996, 179, 247; (d ) P. W.
Roesky, C. L. Stern and T. J. Marks, Organometallics, 1997, 16,
4705
2
3
J. Klosin, W. J. Kruper, J. P. N. Nickias, G. R. Roof, P. D. Waele
and K. A. Abboud, Organometallics, 2001, 20, 2663.
(a) J. T. Patton, S. G. Feng and K. A. Abboud, Organometallics,
2001, 20, 3399; (b) F. G. N. Cloke, T. J. Geldbach, P. B.
Hitchcock and J. B. Love, J. Organomet. Chem., 1996, 506, 343;
(c) R. Baumann and R. R. Schrock, J. Organomet. Chem., 1998,
557, 69.
t
t
CDCl3) d 1.2 (d, Bu, 9H), 1.4 (s, Bu, 18H), 1.9 (m, NH,
1H) ppm. 31P NMR (120 MHz, CDCl3) d 32.6 ppm. EI-MS
(70 eV): m/z (%): 249 (M+, 5), 57 (tBu, 100).
4
5
V. C. Gibson, B. S. Kimberley, A. J. P. White, D. J. Williams and
P. Howard, Chem. Commun., 1998, 313.
X-Ray structure determination
(a) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev.,
2000, 100, 1169; (b) V. C. Gibson, B. S. Kimberley, A. J. P. White,
D. J. Williams and P. Howard, Chem. Commun., 1998, 313; (c) G.
J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem. Int.
Ed., 1999, 38, 428.
(a) T. Fro¨mmel, W. Peters, H. Wunderlich and W. Kuchen,
Angew. Chem., Int. Ed. Engl., 1992, 31, 612; (b) W. Peters, M.
Fuchs, H. Sicius and W. Kuchen, Angew. Chem., Int. Ed. Engl.,
1985, 24, 231; (c) A. Bruck, U. Englert, W. Kuchen and W. Peters,
Chem. Ber., 1996, 129, 551; (d ) T. Frommel, W. Peters, H.
Wunderlich and W. Kuchen, Angew. Chem., Int. Ed. Engl.,
1993, 32, 907; (e) K. Diemert, U. Englert, W. Kuchen and F.
Sandt, Angew. Chem., Int. Ed. Engl., 1997, 36, 241; ( f ) K.
Diemert, W. Kuchen, W. Poll and F. Sandt, Eur. J. Inorg. Chem.,
1998, 361.
(a) P. Blais, T. Chivers, G. Schatte and M. Krahn, J. Organomet.
Chem., 2002, 646, 107; (b) J. K. Brask and T. Chivers, Angew.
Chem., Int., 2001, 40, 3960; (c) G. G. Briand, T. Chivers, M.
Krahn and M. Parvez, Inorg. Chem., 2002, 41, 6808.
(a) H. Quast, M. Heuschmann and M. O. Abdel-Rahman, Liebigs
Ann. Chem., 1981, 943; (b) A. P. Lane, D. A. Morton-Blake and
D. S. Payne, J. Chem. Soc. A., 1967, 1492.
(a) S. Freeman and M. J. P. Harger, J. Chem. Soc., Chem. Com-
mun., 1985, 1394; (b) S. Freeman and M. J. P. Harger, J. Chem.
Soc., Perkin Trans. 1, 1988, 2737.
Single crystals of 1 and 2 for X-ray structure analysis were
obtained from a petroleum ether–CH2Cl2 solution. Single crys-
tals of 7 for X-ray structure analysis were obtained from
toluene solution by slow evaporation over a period of 5 days.
A suitable crystal of each compound was used for the diffrac-
tion studies (Siemens STOE AED2 diffractometer for 1 and 7
and Nonius MACH-3 diffractometer for 7). The cell para-
meters were derived from well-centered reflections chosen over
a wide 2y range. The structure solution was achieved by direct
methods as implemented in SHELXS-97.24 The final refine-
ment of the structures was carried using full-matrix least-
squares methods on F2 using SHELXL-97.25 The positions
of hydrogen atoms attached to nitrogen atoms were identified
from the successive difference Fourier maps and were included
in further calculations and refinement. All non-hydrogen
6
7
8
9
Table 6 Crystal data and experimental details for 1, 2 and 7
1
2
7
Empirical formula
Formula weight
T/K
C14H25N2OP
268.33
200(2)
C30H41N2OP
476.62
293(2)
C10H25N2OP
220.30
200(2)
0.71073
Orthorhombic
Pnma
10 M. G. Walawalkar, H. W. Roesky and R. Murugavel, Acc. Chem.
Res., 1999, 32, 117.
11 (a) G. Cao, H. G. Hong and T. E. Mallouk, Acc. Chem. Res.,
1992, 25, 420; (b) A. Clearfield, Prog. Inorg. Chem., 1998, 47, 371.
12 L. C. Thomas, Interpretation of the Infrared Spectra of Organo-
phosphorus Compounds, Heyden and Son Ltd., Chichester, U.K.,
1974.
13 Although it has been possible to obtain X-ray quality crystals for
all the compounds, examples 1, 2, 7 were chosen for diffraction
studies in view of the different bulkiness of the R2 group in the
molecules. Diffraction data for 4 were also obtained; however,
the structure of this compound could not be refined to a satisfac-
tory level due to a 3-fold rotational disorder between the cyclo-
˚
l/A
Crystal system
0.71073
Monoclinic
P21/n
0.71073
Monoclinic
P21/n
Space group
˚
a/A
˚
8.268(1)
10.527(1)
18.297(3)
98.20(1)
1576.3(4)
4
12.7979(6)
11.285(1)
20.121(1)
99.745(4)
2864.0(4)
4
9.642(2)
15.934(3)
8.982(2)
–
b/A
˚
c/A
b/ꢁ
U/A
3
˚
1380(1)
4
0.177
Z
m/mmꢂ1
Total reflections
Unique reflections
Rint
0.167
2873
0.119
5183
=
hexyl and tert-butyl groups about the P O axis.
2007
1267
14 At the convergence of refinement, all hydrogen atoms attached to
nitrogen atoms displayed acceptable N–H distances and very
good thermal (Uiso) parameters.
15 (a) R. Keat, Top. Curr. Chem., 1982, 102, 89; (b) N. N.
Greenwood and A. Earnshaw, Chemistry of the Elements, Perga-
mon, Oxford, 1984, pp. 619–633.
2777
0.0368
5033
0.0328
0.0443
0.0366
0.0980
R1 [I > 2s(I)]
wR2 [I > 2s(I)]
0.0507
0.1288
0.0494
0.1015
New J. Chem., 2003, 27, 968–974
973

View Article Online
16 R. Murugavel, S. S. Krishnamurthy and M. Nethaji, J. Chem.
Soc., Dalton Trans., 1993, 3635.
17 K. Ruhlandt-Sange, R. A. Bartlett, M. Olmstead and P. P. Power,
Angew. Chem., Int. Ed. Engl., 1993, 32, 425.
18 (a) K. C. K. Swamy, D. M. Poojary, S. S. Krishnamurthy and
H. Manohar, J. Chem. Soc., Dalton Trans., 1985, 1881; (b) J. F.
Labarre, Top. Curr. Chem., 1982, 102, 1.
19 S. S. Krishnamurthy, Phosphorus Sulfur Silicon Relat. Elem.,
1989, 41, 375.
20 (a) R. Murugavel, S. S. Krishnamurthy, J. Chandrasekhar and
M. Nethaji, Inorg. Chem., 1993, 32, 5447; (b) R. Murugavel,
S. S. Kumaravel, S. S. Krishnamurthy, M. Nethaji and J.
Chandrasekhar, J. Chem. Soc., Dalton Trans., 1994, 847.
21 B. T. Luke, J. A. Pople, M. -B. Krogh-Jespersen, Y. Apeloig, J.
Chandrasekhar and P. V. R. Schleyer, J. Am. Chem. Soc., 1986,
108, 260.
22 (a) R. Murugavel, M. G. Walawalkar, G. Prabusankar and P.
Davis, Organometallics, 2001, 20, 2639; (b) R. Murugavel, V. V.
Karambelkar, G. Anantharaman and M. G. Walawalkar, Inorg.
Chem., 2000, 39, 1381; (c) R. Murugavel, G. Prabusankar and
M. G. Walawalkar, Inorg. Chem., 2001, 40, 1084; (d ) R.
Murugavel, M. Sathiyendiran and M. G. Walawalkar, Inorg.
Chem., 2001, 40, 427; (e) R. Murugavel, K. Baheti and G.
Anantharaman, Inorg. Chem., 2001, 40, 6870; ( f ) M.
Sathiyendiran and R. Murugavel, Inorg. Chem., 2002, 41, 6404;
(g) R. Murugavel, D. Krishnamurthy and M. Sathiyendiran,
J. Chem. Soc., Dalton Trans., 2002, 34.
23 A. M. Kinnear and E. A. Perren, J. Chem. Soc., 1952, 3437.
24 G. M. Sheldrick, SHELXS-97, Program for Crystal Structure
Solution, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
25 G. M. Sheldrick, SHELXL-97, Program for Crystal Structure
Refinement, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
974
New J. Chem., 2003, 27, 968–974