Sterically encumbered acyclic diphosphazanes: Synthesis, conformations and coordination behavior

Article abstract of DOI:10.1039/b516316a

The reaction between λ³-diphosphazane [EtN(PCl ₂)₂] and the sodium salts of substituted phenols affords sterically encumbered diphosphazanes [EtN{P(OR)₂}₂] (R = -C₆H₃ⁱ

Full text of DOI:10.1039/b516316a

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www.rsc.org/dalton | Dalton Transactions
Sterically encumbered acyclic diphosphazanes: synthesis, conformations and
coordination behavior†
Ganesan Prabusankar,a Nallasamy Palanisami,a Ramaswamy Murugavel*a and Ray J. Butcherb
Received 17th November 2005, Accepted 3rd February 2006
First published as an Advance Article on the web 21st February 2006
DOI: 10.1039/b516316a
The reaction between k3-diphosphazane [EtN(PCl2)2] and the sodium salts of substituted phenols
i
affords sterically encumbered diphosphazanes [EtN{P(OR)2}2] (R = –C6H3 Pr2-2,6 (1), –C6H3Me2-2,6
(2) and –C6H2Me3-2,4,6 (3)). When the same reaction was carried out with bulky sodium
2,4-di-tert-butyl-4-methylphenoxide, only a monosubstitution takes place to result in the formation of
t
[EtN{PCl(OR)}2] (R = –C6H2 Bu2-2,6-Me-4) (4). Further reaction of 2 with [Mo(CO)4(NBD)]
produces cis-[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5). Diphosphazanes 1–4 and the metal derivative 5
have been characterized by means of their analytical data and EI-MS, IR and multinuclear NMR (1H
and 31P) spectral data. The solid-state structure of the diphosphazanes 1, 2 and 4, and the molybdenum
complex 5 have been determined by X-ray diffraction studies. Irrespective of the size of substituent, the
bulky groups on the phosphorus and nitrogen are on the same side of the P–N–P skeleton with a local
C2v symmetry. The central nitrogen remains almost trigonal planar in all the compounds.
with very bulky substituents on phosphorus centers have not been
Introduction
investigated in detail. While the introduction of such large sub-
Metal–phosphine complexes have played an important role in
stituents is expected to have a major influence in determining the
homogeneous catalysis since the discovery of Wilkinson’s catalyst.
conformation of the diphosphazane ligand, their steric bulkiness
Studies on metal–phosphine complexes have continued to be a
around the donor phosphorus centers also will have a crucial
fertile area of research due to discoveries such as Heck reaction.1
role to play while using these compounds as ligands towards low
Among the diphosphine ligands, diphenylphosphinomethane
valent metals. Thus, in order to get more insight into the role
(dppm) has occupied a special place in view of its ability to
of sterically encumbered groups on conformational changes, we
have carried out the systematic study on a series of o,oꢀ-substituted
form very stable chelate rings and provide enough stability
around the low-valent metal centers.2,3 Substitution of nitrogen in
place of central carbon bridge of dppm to form diphosphazanes
diphosphazanes, [EtN{P(OR)2}2].
(e.g. X2PN(R)PX2) can result in significant changes in their
Synthesis and spectral characterization of k3-[EtN{P(OR)2}2] (1–3)
coordination behavior and the structural features of the resulting
The reaction between one equivalent of k3-diphosphazane
complexes.4–12 Electronic and steric factors of diphosphazanes can
also be altered in a systematic way by varying the substituents
on phosphorus and nitrogen centers.9,13 These suitably substituted
diphosphazanes can also stabilize multiple bonds between main-
group or transition-metal elements,11 and such type of compounds
have usually been isolated with sterically encumbered organic
groups.14 Besides, the study of the reaction between bulky arylox-
ides and [EtN(PCl2)2] can unravel the conformational preferences
of sterically encumbered acyclic diphosphazanes. Thus, we report
herein the reaction of [EtN(PCl2)2] with o,oꢀ-disubstituted phenols
and the ability of the reaction products to function as ligands in
low-valent transition-metal organometallic chemistry.
[EtN(PCl2)2] and four equivalents of the corresponding sodium
aryloxide produces the k3-diphosphazanes [EtN{P(OC6H3 Pr2-
i
2,6)2}2] (1), k3-[EtN{P(OC6H3Me2-2,6)2}2] (2) and k3-
[EtN{P(OC6H2Me3-2,4,6)2}2] (3) in good yields (Scheme 1).
Results and discussion
Although the chemistry of diphosphazanes has gone through a
period of intense activity in the last few decades, diphosphazanes
aDepartment of Chemistry, Indian Institute of Technology-Bombay, Powai,
Mumbai, 400 076, India. E-mail: rmv@chem.iitb.ac.in; Fax: +(22) 2572
3480; Tel: +(22) 2576 7163
bDepartment of Chemistry, Howard University, Washington DC, 20059, USA
† Dedicated to Professor S. S. Krishnamurthy on the occasion of his 65th
birthday.
Scheme 1
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Table 1 31P NMR chemical shifts for diphosphazanes
spectrum of 1–3 and their relative intensities are consistent
with the formulation of each of the derivative. In the 31P NMR
spectrum, a single sharp signal is observed for all the three
derivatives indicating magnetic equivalence both the phosphorus
centers. The observed 31P NMR chemical shifts (d 151.5 for 1,
141.8 for 2, 141.8 for 3) are comparable with those for reported
acyclic diphosphazanes (Table 1).
Compound
d (ppm)
Ref.
EtN(PCl2)2
MeN(PCl2)2
MeN(PBr2)2
MeN(PBrCl)2
PhN(PCl2)2
MeN(PF2)2
EtN(PF2)2
164.6
159.5
157.7
159.7
155.5
144.5
141.3
149.9
140.3
135.1
127.7
133.8
145.3
149.9
28.9, 155.8
27.9, 148.6
145.7
134.7
130.5
48.8
13b
13b
13b
13b
9
9
9
10c
10c
10c
10c
13b
6
i
Molecular structure of k3-[EtN{P(OC6H3 Pr2-2,6)2}2] (1)
[MeN{P(OCH2CF3)2} ]
[PhN{P(OCH2CF3)2}22]
[MeN{P(OPh)2} ]
[PhN{P(OPh)2}22]
Colorless crystals of 1 suitable for X-ray structure analysis were
grown from dichloromethane–hexane (1 : 1, v/v) at 0 ◦C (Table 2).
Compound 1 crystallizes in the monoclinic space group C2/c. A
perspective view of the final refined structure of 1 is shown in
Fig. 1. The molecule of 1 is built around a P–N–P skeleton. Each
[tBuN{P(OMe)2} ]
[MeN{P(OMe)2}22]
[iPrN{P(O2C6H4)}2]
[Ph2PN(iPr)P(O2C6H4)]
[Ph2PN(iPr)P(O2C12H8)]
PhN(PCl)2{OC6H2(tBu)(l-S)(tBu)2C6H2O)}
PhN(PF)2{OC6H2(tBu)(l-S)(tBu)2C6H2O)}
[PhN{P(OC6H4Br-p)}2]
[iPrN(PPh2)2]
9
9
9
i
phosphorus center in the molecule has two OC6H3 Pr2-2,6 groups.
10a
10a
10c
10c
10e
The ethyl group on nitrogen and substituents on phosphorus are
occupying one side of the P–N–P backbone. The phosphorus
and nitrogen atoms occupy planes which are orthogonal to the
plane formed by the O–P–O fragment. Thus, the molecule can be
considered to posses C2v point group symmetry. Selected bond
lengths and angles in 1 are listed in Table 3. The P–N bond
[MeN{P(OCH(CH3)2)2}2]
139.4
140.6
151.5
141.8
141.8
166.8
[MeN{P(OCH2CH2O}2]
10e
i
a
[EtN{P(OC6H3 Pr2-2,6)2}2] (1)
a
a
a
[EtN{P(OC6H3Me2-2,6)2}2] (2)
[EtN{P(OC6H2Me3-2,4,6)2}2] (3)
˚
length (1.674(5) A) suggests that these bonds have a considerable
t
[EtN{PCl(OC6H2 Bu2-2,6-Me-4)}2] (4)
double bond character (normal P–N single bond length, 1.75–
a This work.
15
˚
1.80 A ) and suggests a certain degree of multiple bonding in the
P–N–P skeleton.16 Two types of P–O distances are observed in
˚
the molecule (1.642(5) and 1.658(5) A). The observed P–O bond
Analytically pure samples of 1–3 were crystallized from hexane–
dichloromethane (1 : 1, v/v) mixture at 0 ◦C and characterized by
CHN analysis and EI-MS, IR, NMR (1H and 31P) spectroscopic
techniques. In the EI-MS spectrum molecular ion peak of each
of the new diphosphazane was observed (m/z 813 for 1, 590
length is however in agreement with those observed in the case of
k3-acyclic diphosphazanes9,17 The P–N–P angle (109.5◦) also falls
in the expected range.9 A distorted tetrahedral geometry (angle
range: 95.8–103.9◦) is retained around the phosphorus atoms while
the geometry around the central nitrogen atom is trigonal-planar
ꢀ
N 360.1◦).
1
for 2 and 645 for 3). The resonances observed in the H NMR
(
Table 2 Crystal data for 1, 2, 4 and 5
1
2
4
5
Empirical formula
Mr
C50H76NO4P2
817.06
293(2)
C34H41NO4P2
589.62
293(2)
C32H51Cl2NO2P2
614.58
293(2)
Nonius-MACH3
0.71073
Triclinic
¯
P1
9.348(1)
12.216(1)
15.424(1)
97.828(6)
96.701(7)
90.327(7)
1732.7(3)
2
C38H41NP2O8Mo
797.60
293(2)
T/K
Diffractometer
STOE-AED2
0.71073
Monoclinic
C2/c
25.910(5)
8.8881(2)
22.878(5)
—
106.65(3)
—
5047.5(18)
4
Nonius-MACH3
0.71073
Monoclinic
P21/n
12.1004(7)
10.9409(9)
12.6202(13)
—
102.384(7)
—
1631.9(2)
2
Bruker CCD
0.71073
Monoclinic
P21/c
12.4493(8)
14.503(1)
21.609(2)
—
102.087(1)
—
3815.0(4)
4
˚
k/A
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
Dc/Mg m−3
1.075
0.126
1.200
0.170
1.178
0.307
1.389
0.478
l/mm−1
F(000)
1780
628
660
1648
Crystal size/mm
0.4 × 0.4 × 0.3
3.52–20.00
2291/0/264
1.061
0.0985
0.2365
0.5 × 0.4 × 0.3
1.86–24.95
2855/0/267
1.033
0.0481
0.1297
0.4 × 0.3 × 0.2
1.34–24.98
6088/0/367
1.054
0.0485
0.1207
0.15 × 0.2 × 0.6
1.67–29.14
9679/0/460
1.130
0.0475
0.1002
h Range/◦
Data/restraints/params
Goodness-of-fit on F2
R1 [I > 2r(I)]
wR2 [I > 2r(I)]
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i
Table 3 Selected structural parameters for cis-k3-[EtN{P(OC6H3 Pr2-
Table 4 Selected structural parameters for cis-k3-[EtN{P(OC6H3Me2-
2,6)2}2] (2)
2,6)2}2] (1)
˚
˚
Bond lengths (A)
Bond lengths (A)
P(1)–N(1)
P(1)–O(1)
1.674(5) P(1)–O(2)
1.642(5)
1.658(5)
P(1)–N(1)
1.693(2)
1.693(2)
P(1)–O(1)
P(1)–O(2)
1.643(2)
1.651(2)
N(1)–P(1)a
Bond angles (◦)
P(1)–N(1)–P(1)a
C(7)–N(1)–P(1)
C(7)–N(1)–P(1)a
O(1)–P(1)–N(1)
Bond angles (◦)
P(1)–N(1)–P(1)a
C(1)–N(1)–P(1)
C(1)a–N(1)–P(1)
C(1)a–N(1)–P(1)a
C(1)–N(1)–P(1)a
109.5(5) O(2)–P(1)–N(1)
125.3(2) O(2)–P(1)–O(1)
125.3(2) C(1)–O(1)–P(1)
103.9(3) C(11)–O(2)–P(1)
97.5(3)
95.8(3)
118.8(5)
114.5(5)
113.1(2)
118.2(3)
124.9(3)
118.2(3)
124.9(3)
O(1)–P(1)–N(1)
O(2)–P(1)–N(1)
O(2)–P(1)–O(1)
C(3)–O(1)–P(1)
C(9)–O(2)–P(1)
95.7(1)
103.78(9)
96.7(1)
120.8(2)
119.0(2)
Dihedral angles (◦)
C(7)–N(1)–P(1)–O(1)
48.02
C(7)–N(1)–P(1)–O(2)
−49.84
Dihedral angles (◦)
C(1)–N(1)–P(1)–O(1)
−22.92
C(1)–N(1)–P(1)–O(2)
75.38
a
Symmetry transformations used to generate equivalent atoms: −x, y,
−z + 3/2.
Symmetry transformations used to generate equivalent atoms: a −x + 3/2,
y, −z + 3/2.
i
Fig. 1 Molecular structure of cis-[EtN{P(OC6H3 Pr2-2,6)2}2] (1) (hydro-
gen atoms are omitted for clarity).
Fig. 2 Molecular structure of cis-[EtN{P(OC6H3Me2-2,6)2}2] (2) (hydro-
gen atoms are omitted for clarity).
Molecular structure of k3-[EtN{P(OC6H3Me2-2,6)2}2] (2)
4 was obtained in good yield by treatment of k3-diphosphazane
[EtN(PCl2)2] with two equivalents of sodium 2,6-di-tert-butyl-
4-methylphenoxide (Scheme 1). Compound 4 is fairly stable
towards moisture and readily soluble in common organic solvents.
Compound 4 has been characterized by various analytical and
spectroscopic techniques, and a single-crystal X-ray diffraction
study. The EI-MS spectrum of 4 shows the expected isotopic
Compound 2 crystallizes in the monoclinic space group P21/n
(Table 2). The solid-state structure of 2 (Fig. 2) is analogous to
that of molecule 1. The core of 2 is a P–N–P skeleton which
consists of two aryloxy substituents (–OC6H3Me2-2,6) on the each
phosphorus centers. In view of the positions of substituents present
on the P–N–P skeleton, molecule 2 can be considered as a cis
isomer with C2v point group symmetry. Selected bond lengths and
angles are listed in Table 4. The average P–N (1.693(3) A)
1
pattern for the molecular ion at m/z 614. The H and 31P NMR
15,16
˚
spectra of 4 were recorded in CDCl3. The methyl protons of
CH3CH2N in 4 resonate as a triplet at d 1.64 ppm and the
CH2 group appears as a multiplet at d 4.05–4.10. The 31P NMR
spectrum of 4 shows a single resonance at d 166.8 ppm which
is downfield shifted compared to compounds 1–3, due to the
incomplete substitution at phosphorus (Table 1).
16,17
˚
and P–O (1.647(2) A)
bond distances are consistent with the
literature reports. The P–N–P bond angle (113.1◦) also falls in the
expected range.9 The sum of bond angles around the nitrogen gives
ꢀ
a trigonal-planar geometry for the nitrogen atom ( N 356.2◦)
and phosphorus atom have distorted tetrahedral geometry (angle
range: 95.7–103.78◦).
Molecular structure of k3-[EtN{PCl(OC6H2 Bu2-2,6-Me-4)}2] (4)
t
Synthesis and spectral characterization of
The molecular structure of compound 4 has been determined
by single-crystal X-ray diffraction studies (Table 2). Selected bond
lengths and angles are listed in Table 5. Compound 4 crystallizes
k3-[EtN{PCl(OC6H2 Bu2-2,6-Me-4)}2] (4)
t
Owing to the bulkiness of the 2,6-di-tert-butyl-4-methylphenol,
treatment of [EtN(PCl2)2] with four equivalents of sodium 2,6-di-
tert-butyl-4-methylphenoxide led only to an incomplete substitu-
tion to yield the diaryloxydichlorodiphosphazane. Diphosphazane
¯
in the triclinic space group P1. A perspective view of the molecular
structure of 4 is depicted in Fig. 3. The molecular structure of 4 is
built around a puckered P–N–P skeleton. Each phosphorus center
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t
Table 5 Selected structural parameters for cis-k3-[EtN{PCl(OC6H2 Bu2-
CH3 and CH2 group of the CH3CH2N moiety, respectively. The
aryl protons of compound 5 appear as a singlet at d 6.99 ppm. The
31P NMR spectrum of 5 shows a single resonance at d 144.3 ppm
and it is downfield shifted (Ddp + 2) upon complexation to the
metal compared to 2 (Table 1).
2,6-Me-4)}2] (4)
˚
Bond lengths (A)
P(1)–N(1)
P(2)–N(1)
P(1)–Cl(1)
1.677(2)
1.678(2)
2.097(1)
P(2)–Cl(2)
P(1)–O(1)
P(2)–O(2)
2.091(1)
1.633(2)
1.636(2)
Molecular structure of [(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5)
Bond angles (◦)
P(1)–N(1)–P(2)
P(2)–N(1)–C(31)
P(1)–N(1)–C(31)
O(1)–P(1)–N(1)
O(1)–P(1)–Cl(1)
N(1)–P(1)–Cl(1)
110.3(1)
123.2(2)
123.0(2)
100.7(1)
100.22(8) C(16)–O(2)–P(2)
101.4(1)
N(1)–P(2)–Cl(2)
O(2)–P(2)–N(1)
O(2)–P(2)–Cl(2)
C(1)–O(1)–P(1)
101.6(1)
100.3(1)
100.05(8)
113.2(2)
113.6(2)
Pale yellow crystals of 5 suitable for X-ray structure analysis
were obtained from dichloromethane–n-hexane (1 : 1, v/v) at
0
◦C (Table 2). A perspective view of the molecule with the
atom numbering scheme is shown in Fig. 4. Selected bond
lengths and bond angles are listed in Table 6. Compound 5
crystallizes in the monoclinic space group, P21/c with a two-
fold axis of symmetry. The solid-state structure of 5 reveals a
typical octahedral environment around the molybdenum center
with four carbonyl groups and two phosphorus centers of the P–
N–P skeleton. Two carbonyl ligands, P–N–P chain and the central
molybdenum atom are in the same plane. The remaining two
carbonyls are occupying the axial positions. There is no significant
difference between the equatorial and axial Mo–C bond lengths;
Dihedral angles (◦)
C(31)–N(1)–P(1)–Cl(1) 32.75
C(31)–N(1)–P(1)–O(1) −70.08
C(31)–N(1)–P(2)–Cl(2) 71.88
C(31)–N(1)–P(2)–O(2) −30.74
˚
the average Mo–C bond length is 2.024(3) A. The P–N–P bond
angle is (103.7(1)◦) considerably smaller than that observed for
2, which clearly indicates the consequences of chelation. The sum
ꢀ
of the angles around the nitrogen ( N 359.3◦) shows a trigonal-
planar geometry for the central nitrogen atom.
t
Fig. 3 Molecular structure of cis-[EtN{PCl(OC6H2 Bu2-2,6-Me-4)}2] (4)
(hydrogen atoms are omitted for clarity).
t
in the molecule has one –OC6H2 Bu2-2,6-Me-4 unit and one free
chloride moiety. All the substituents are present on one side of
the P–N–P backbone with a C2v point group symmetry. The P–N
˚
bond lengths are found to be 1.677(2) and 1.678(2) A, with a P–N–
P angle of 110.3◦. The chloride on each of the phosphorus centers
10
˚
has a trans orientation with a P–Cl bond distance of 2.094 A.
˚
The average P–O bond distance (1.635 A) is in agreement with the
ꢀ
literature precedents.16,17 A trigonal-planar geometry ( N 356.5◦)
is retained around the nitrogen atom and phosphorus atom is in
distorted tetrahedral geometry (angle range: 100.22–101.4◦ for
P(1) and 100.05–101.6◦ for P(2)).
Fig. 4 Molecular structure of cis-[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4]
(5) (hydrogen atoms are omitted for clarity).
Synthesis and spectral characterization of
[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5)
Comparison and summary
To study the coordination ability of sterically crowded aryloxy
diphosphazanes, compound 2 was reacted with [Mo(CO)4(NBD)]
(NBD = norbornadiene) in light petroleum (bp 60–80 ◦C),
yielding [(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5) (Scheme 1).
Analytically pure 5 has been characterized with the aid of
CHN analysis and EI-MS, IR, NMR (1H and 31P) spectroscopic
techniques and a single-crystal X-ray diffraction study.
The solid-state structures of 1, 2 and 4 reveal that the molecules
are in the cis isomeric form. The presence of bulky groups
on phosphorus atoms seems to have no major effect on their
conformational preferences and all isolated diphosphazanes prefer
to exist as a C2v conformer. When the sterically more crowded
group like 2,6-di-tert-butyl-4-methylphenol was used as the aryl-
oxide, only partial substitution takes place at phosphorus, still
preserving the C2v symmetry. The observed P–N bond lengths
and P–N–P angles found in 1, 2 and 4 are almost comparable
to each other (Table 7). As expected, for the chelate complex 5,
the P–N–P angle decreases, enhancing the planarity of nitrogen
compared to 2. The observed bond lengths and angles of 5 agree
well with the known molybdenum carbonyl complexes of acyclic
diphosphazanes (Table 8).
The elemental percentages found for 5 fit well with the calculated
values. The molecular ion peak of 5 was observed at m/z 799
(M+) in the EI-MS spectrum. The IR spectrum of 5 shows four
intense bands in the metal carbonyl region (mC=O, 2037, 1944, 1925,
1866 cm−1) indicating the presence of a Mo(CO)4 moiety with an
1
approximate local C2v symmetry. The H NMR spectrum of 5
shows resonances at d 1.73–1.78 (t) and 4.04–4.14 (m) ppm for
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Table 6 Selected structural parameters for cis-[(EtN{P(OC6H3Me2-
2,6)2}2)Mo(CO)4] (5)
Thus, it would be both interesting and beneficial to investigate
the coordination chemistry of these ligands with metals such as
rhodium, palladium and platinum, and investigate the utility of
resultant products as homogeneous catalysts.
˚
Bond lengths (A)
P(1)–N
P(2)–N
P(1)–O(11)
P(1)–O(12)
P(2)–O(21)
P(2)–O(22)
P(1)–P(2)
1.687(2)
1.688(2)
1.623(2)
1.626(2)
1.622(2)
1.620(2)
2.653(1)
Mo–C(1)
Mo–C(2)
Mo–C(3)
Mo–C(4)
Mo–P(1)
Mo–P(2)
2.000(3)
2.009(3)
2.034(3)
2.054(3)
2.4841(7)
2.4815(7)
Experimental
Apparatus and chemicals
All reactions were carried out under an atmosphere of purified
nitrogen using standard Schlenk-line techniques and in a nitrogen-
filled M-BRAUN glove-box. Dichloromethane, hexane, light
Bond angles (◦)
O(11)–P(1)–O(12)
O(11)–P(1)–N
O(12)–P(1)–N
O(11)–P(1)–Mo
O(12)–P(1)–Mo
N–P(1)–Mo
O(11)–P(1)–P(2)
O(12)–P(1)–P(2)
N–P(1)–P(2)
Mo–P(1)–P(2)
O(22)–P(2)–O(21)
O(22)–P(2)–N
O(21)–P(2)–N
O(22)–P(2)–Mo
O(21)–P(2)–Mo
N–P(2)–Mo
O(22)–P(2)–P(1)
O(21)–P(2)–P(1)
N–P(2)–P(1)
97.8(1)
107.7(1)
96.9(1)
122.71(7) C(121)–O(12)–P(1)
130.84(8) C(211)–O(21)–P(2)
95.83(8) C(221)–O(22)–P(2)
125.72(8) C(1)–Mo–C(2)
121.24(7) C(1)–Mo–C(3)
38.19(7) C(2)–Mo–C(3)
57.65(2) C(1)–Mo–C(4)
96.9(1)
106.4(1)
98.1(1)
123.68(7) C(2)–Mo–P(2)
130.74(8) C(3)–Mo–P(2)
95.90(8) C(4)–Mo–P(2)
126.50(8) C(1)–Mo–P(1)
121.01(8) C(2)–Mo–P(1)
38.16(7) C(3)–Mo–P(1)
57.75(2) C(4)–Mo–P(1)
C(11)–N–P(1)
C(11)–N–P(2)
C(111)–O(11)–P(1)
129.2(2)
126.4(2)
124.6(2)
127.7(2)
125.8(2)
125.2(2)
93.6(1)
85.8(1)
86.3(1)
85.7(1)
85.3(1)
167.6(1)
165.8(1)
100.6(1)
95.17(9)
95.31(9)
101.2(1)
165.2(1)
93.81(8)
96.6(1)
◦
petroleum (bp 40–60 C) and tetrahydrofuran were purified and
dried by conventional procedures and freshly distilled prior to
use.21 Ethylamine hydrochloride (Aldrich), phosphorus trichlo-
ride (Spectrochem), sodium (Rankem), 2,6-diisopropylphenol
(Aldrich), 2,4,6-trimethylphenol (Lancaster), 2,6-dimethylphenol
(Merck) and 2,6-di-tert-butyl-4-methylphenol (Spectrochem) were
used as purchased. The precursor complex [Mo(CO)4(NBD)] was
synthesized as described in the literature.22 The 1H (Me4Si internal
standard) and 31P (85% H3PO4 external standard) NMR spectra
were recorded on a Varian VXR 300S spectrometer. The chemical
shifts downfield from the standard are assigned positive values.
Infrared spectra were obtained from Nicolet Impact-400 FT-IR
spectrometer. Microanalyses were performed onaCarlo Erba 1106
microanalyser. The EI-MS spectra were obtained on a Perkin–
Elmer, Clarus 500 GC-MS mass spectrometer in CHCl3. Moisture-
sensitive k3-diphosphazane [EtN(PCl2)2] has been synthesized as
described previously and stored under a nitrogen atmosphere.23
C(2)–Mo–C(4)
C(3)–Mo–C(4)
C(1)–Mo–P(2)
Mo–P(2)–P(1)
P(1)–N–P(2)
103.7(1)
P(2)–Mo–P(1)
64.60(2)
In conclusion, sterically encumbered diphosphazanes have been
synthesized and characterized by multinuclear NMR spectroscopy
and single-crystal X-ray diffraction studies. The diphosphazanes
exist in cis isomeric form with C2v point group symmetry. The
increase in the size of the aryl group has no or very little effect on
their conformational preferences. The extremely crowded 2,6-di-
tert-butyl-4-methylphenol does not undergo full substitution of
the four P–Cl bonds. Further, in spite of high steric congestion
around the P(III) centers, these diphoshazanes show a tendency
to form sufficiently stable low-valent metal carbonyl complexes.
k3-[EtN{P(OC6H3 Pr2-2,6)2}2] (1). Compounds 1–4 were syn-
i
thesized using a similar procedure. A mixture of sodium (0.42 g,
18 mmol) and 2,6-diisopropylphenol (1.07 g, 6 mmol) was heated
under reflux in tetrahydrofuran (50 mL) for 24 h and filtered
to remove the unreacted sodium metal. [EtN(PCl2)2] (0.37 g,
1.5 mmol) was added dropwise to the above stirred solution
at 0 ◦C. The reaction mixture was slowly brought to room
temperature and heated under reflux for 12 h. The mixture was
allowed to stand for 2 h and the precipitated sodium chloride
Table 7 Comparative structural data for cis-diphosphazanes
ꢀ
ꢀ
˚
˚
Compound
av. P–N/A
av. P–O/A
P–N–P/◦
N/◦
P/◦
i
[EtN{P(OC6H3 Pr2-2,6)2}2] (1)
[EtN{P(OC6H3Me2-2,6)2}2] (2)
1.674(5)
1.693(2)
1.678(2)
1.688(2)
1.65(5)
109.5(5)
113.1(2)
110.3(1)
103.7(1)
360.1
356.2
356.5
359.3
297.2
296.2
302.2
—
1.647(2)
1.635(2)
1.623(2)
t
[EtN{PCl(OC6H2 Bu2-2,6-Me-4)}2] (4)
[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5)
Table 8 Comparative structural data for molybdenum carbonyl complexes of diphosphazanes
P–N–P/◦
Ref.
˚
˚
˚
Compound
av. P–N/A
av. Mo–P/A
av. Mo–CO/A
a
[(EtN{P(OC6H3Me2-2,6)2}2)Mo(CO)4] (5)
[{EtN(PPh2)2}Mo(CO)4]
1.688(2)
1.72
1.71
1.69
1.70
1.70
1.69
2.4828(7)
2.50
2.48
2.43
2.49
2.51
2.37
2.024(3)
1.90
2.03
2.03
2.00
1.99
2.00
103.7(1)
103.8
104.0
101.3
—
113.2
98.8
18
19
10c
20
9
[(PhN{P(NHPh)2}2)Mo(CO)4]
[(PhN{P(OPh)2}2)Mo(CO)4]
[(meso-iPrN{P(Ph)(NHiPr)}2)Mo(CO)4]
[{Ph2P(iPrN)P(O)Ph2}Mo(CO)4]
3
[jP,jP,jS-{g -PhN(PF)2{-OC6H2(tBu)2)2(l-S)}Mo(CO)4]
10a
a This work.
2144 | Dalton Trans., 2006, 2140–2146
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was removed by filtration. Removal of solvent under reduced
pressure gave an oily product, which was dissolved in hexane
(50 mL) and filtered and the solvent was removed completely
to obtain as a waxy solid. Crystallization of this solid from
hexane–dichloromethane mixture (1 : 1, v/v) at 0 ◦C yielded single
crystals of 1. Yield: 0.84 g (69% based on EtN(PCl2)2). Mp 207–
209 ◦C. Anal. Calc. for C50H73NP2O4 (mol wt: 814.07): C, 73.36; H,
9.04; N, 1.74. Found: C, 72.95; H, 9.17; N, 1.67%. Mass spectrum
(EI, 70 eV): m/z 813 (M+), 637 (M+ − OR), 460 (M+ − (OR)2),
429 (M+ − P(OR)2), 385 (M+ − EtNP(OR)2). IR (KBr, cm−1): m˜
2967(s), 2927(m), 2875(m), 1453(m), 1335(w), 1262(w), 1177(m),
were obtained from by crystallization of this solid from hexane–
dichloromethane (1 : 1, v/v) mixture at 0 ◦C. Yield: 0.13 g
(49% based on 2). Mp 158–160 ◦C (decomp.). Anal. Calc. for
C38H41NP2O8Mo (mol wt: 799.0): C, 57.07; H, 5.13; N, 1.75.
Found: C, 57.35; H, 5.08; N, 1.55%. Mass spectrum (EI, 70 eV):
m/z 799 (M+), 771 (M+ − CO), 715 (M+ − 3CO), 687 (M+ − 4CO),
273 (M+ − Mo(CO)4 − P(OR)2NEt, 100%). IR (KBr, cm−1): m˜
3094(w), 3012(w), 3000(w), 2964(w), 2924(w), 2851(w), 2037(vs),
1944(vs), 1925(vs), 1866(vs), 1589(w), 1473(s), 1435(s), 1377(w),
1306(w), 1263(s), 1191(s), 1166(vs), 1091(s), 1027(w), 911(w),
892(w), 854(vs), 765(vs), 723(m), 646(w), 622(w), 570(w), 551(w),
508(w), 435(w). 1H NMR (300 MHz, CDCl3): d 1.73–1.78 (t, 3H,
1
1111(m), 861(vs), 775(s), 736(w), 440(w). H NMR (300 MHz,
i
3
3
CDCl3): d 0.98 (dd, 48H, CH3 of Pr, JHH = 7 Hz), 1.83 (t, 3H,
CH2CH3, JHH = 7 Hz), 2.24 (s, 24H, CH3), 4.04–4.14 (m, 2H,
3
CH2CH3, JHH = 7 Hz), 3.19–3.23 (m, 2H, CH2CH3), 4.15–4.16
CH2) and 6.99 (s, 12H, aryl protons) ppm. 31P NMR (121 MHz,
(m, 8H, CH of iPr) and 7.26 (s, 12H, aryl protons) ppm. 31P NMR
CDCl3): d 144.3 (s) ppm.
(121 MHz, CDCl3): d 151.5 (s) ppm.
Single-crystal X-ray solution and refinement
k3-[EtN{P(OC6H3Me2-2,6)2}2] (2). Yield: 0.68 g (77% based
on EtN(PCl2)2). Mp 165–167 ◦C. Anal. Calc. for C34H41NP2O4
(mol wt: 589.64): C, 69.26; H, 7.01; N, 2.38. Found: C, 68.57;
H, 7.44; N, 2.43%. Mass spectrum (EI, 70 eV): m/z 590 (M+),
469 (M+ − OR), 346 (M+ − (OR)2), 318 (M+ − P(OR)2), 273
(M+ − EtNP(OR)2). IR (KBr, cm−1): m˜ 3015(w), 2955(m), 2919(m),
2854(w), 1585(w), 1464(vs), 1261(s), 1192(vs), 1160(vs), 1089(m),
911(m), 857(vs), 757(vs), 722(s), 643(m), 550(m), 504(m). 1H NMR
Molecular structures of 1, 2, 4 and 5 were unambiguously
determined by single-crystal X-ray diffraction technique. Crys-
tals suitable for X-ray diffraction were grown from a hexane–
dichloromethane mixture of 1, 2, 4 and 5 at 0 ◦C. Intensity
data were collected on a STOE AED-2 four-circle diffractometer
for 1, Nonius MACH-3 four-circle diffractometer for 2 and
4, and Bruker CCD area detector for 5. All calculations were
carried out using the programs available in WinGX suite.24 The
structure solution was achieved in each case by direct methods as
implemented in SIR-92.25 The final refinement of the structure was
carried out using full least-squares methods on F2 using SHELXL-
97.26 The crystallographic data collection, structure solution and
refinement for 1, 2, 4 and 5 are accumulated in Table 2.
CCDC reference numbers 289830 (1), 289832 (2), 289831 (4)
and 289829 (5).
3
(300 MHz, CDCl3): d 1.75–1.80 (t, 3H, CH2CH3, JHH = 7 Hz),
2.15 (s, 24H, CH3), 4.17–4.24 (m, 2H, CH2) and 6.84–6.95 (m,
12H, aryl protons) ppm. 31P NMR (121 MHz, CDCl3): d 141.8 (s)
ppm.
k3-[EtN{P(OC6H2Me3-2,4,6)2}2] (3). Yield: 0.68 g (70% based
on EtN(PCl2)2). Mp 156–158 ◦C. Anal. Calc. for C38H49NP2O4
(mol wt: 645.75): C, 70.68; H, 7.65; N, 2.17. Found: C, 70.35;
H, 8.01; N, 1.97%. Mass spectrum (EI, 70 eV): m/z 645 (M+),
510 (M+ − OR), 375 (M+ − (OR)2), 344 (M+ − P(OR)2), 301
(M+ − EtNP(OR)2). IR (KBr, cm−1): m˜ 2953(m), 2920(m), 2856(w),
1479(vs), 1309(w), 1209(s), 1135(vs), 1077(m), 1022(s), 824(vs),
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b516316a
1
764(s), 674(m), 564(w). H NMR (300 MHz, CDCl3): d 1.74 (t,
References
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ppm. 31P NMR (121 MHz, CDCl3): d 141.8 (s) ppm.
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2146 | Dalton Trans., 2006, 2140–2146
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The Royal Society of Chemistry 2006
©