Reversal of polarization in amidophosphines: Neutral- and anionic-κP coordination vs. anionic-κP,N coordination and the formation of nickelaazaphosphiranes

Article abstract of DOI:10.1039/b507040f

Nickel(II) chloride reacts with the bis(tert-butylamino) diazadiphosphetidine {Bu^t(H)NP(μ-NBu¹) ₂PN(H)Bu^t} to form trans-[{Bu^t(H)NP(μ- NBu^t)₂PN(H)Bu^t}₂NiCl₂]. In solution and the solid-state each heterocyclic ligand coordinates nickel through one phosphorus atom only. For comparison the solid-state structure of the known trans-[NiCl₂(PEt₃)₂] was also determined and it was found that the two complexes have almost identical bond parameters about nickel. The nickel-amidophosphine complexes [{Bu _tOP(μ-NBu^t)₂PNBu^t}NiCl(PBu ⁿ₃)], [(PBu₃ⁿ)ClNi{Bu ^tNP(μ-NBu^t)₂/PNBu^t}NiCl(PBu ₃ⁿ)], and [{Me₂Si(μ-NBu^t) ₂PNBu^t}NiCl(PBu₃ⁿ)] were synthesized and X-ray structurally characterized. In these mono- and di-nuclear nickel complexes the nickel ions are coordinated in pseudo square-planar fashions, by one trialkylphosphine ligand, one chloride ligand and one κP,N-coordinated amidophosphine moiety from tert-butylamido-substituted heterocycles. Attempts to create nickel complexes chelated in a κ²P fashion by the o-phenylenediamine-tethered mono- and di-anionic 1-{Me₂Si(μ- NBu^t)₂PN} 2-{Me₂Si(μ-NBu^t) ₂PNH}C₆H₄ and 1,2-{Me₂Si(μ- NBu^t)₂PN}C₆H₄, respectively, afforded instead [1,2-{Me₂Si(μ-NBu^t) ₂PN{Me₂Si(n-NBu^t)₂PN}C ₆H₄NiCl] and [1,2-{Me₂Si(μ-NBu ^t)₂PN}-{Me₂Si(μ-NBu^t) ₂PN}C₆H₄Ni{PEt₃}], each complex having κP,N and κP coordinated amidophosphine ligands. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b507040f

View Article Online / Journal Homepage / Table of Contents for this issue
F U L L P A P E R
Reversal of polarization in amidophosphines: neutral- and anionic-jP
coordination vs. anionic-jP,N coordination and the formation of
nickelaazaphosphiranes
Ingo Schranz,a Graham R. Lief,a Christopher J. Carrow,a Dana C. Haagenson,a
Luke Grocholl,a Lothar Stahl,*a Richard J. Staples,b Ramamoorthy Boomishankarc and
Alexander Steinerc
a Department of Chemistry, University of North Dakota, Grand Forks, ND, 58202-9024, USA.
E-mail: lstahl@chem.und.edu
b Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA,
02138, USA
c Department of Chemistry, University of Liverpool, Liverpool, UK L69 7ZD
Received 18th May 2005, Accepted 22nd July 2005
First published as an Advance Article on the web 16th August 2005
Nickel(II) chloride reacts with the bis(tert-butylamino)diazadiphosphetidine {But(H)NP(l-NBut)2PN(H)But}
to form trans-[{But(H)NP(l-NBut)2PN(H)But}2NiCl2]. In solution and the solid-state each heterocyclic ligand
coordinates nickel through one phosphorus atom only. For comparison the solid-state structure of the known
trans-[NiCl2(PEt3)2] was also determined and it was found that the two complexes have almost identical bond
parameters about nickel. The nickel–amidophosphine complexes [{ButOP(l-NBut)2PNBut}NiCl(PBun )],
3
[(PBun )ClNi{ButNP(l-NBut)2PNBut}NiCl(PBun )], and [{Me2Si(l-NBut)2PNBut}NiCl(PBun )] were
3
3
3
synthesized and X-ray structurally characterized. In these mono- and di-nuclear nickel complexes the nickel
ions are coordinated in pseudo square-planar fashions, by one trialkylphosphine ligand, one chloride ligand
and one jP,N-coordinated amidophosphine moiety from tert-butylamido-substituted heterocycles. Attempts
to create nickel complexes chelated in a j2P fashion by the o-phenylenediamine-tethered mono- and di-anionic
1-{Me2Si(l-NBut)2PN} 2-{Me2Si(l-NBut)2PNH}C6H4 and 1,2-{Me2Si(l-NBut)2PN}C6H4, respectively,
afforded instead [1,2-{Me2Si(l-NBut)2PN}{Me2Si(l-NBut)2PN}C6H4NiCl] and [1,2-{Me2Si(l-NBut)2PN}-
{Me2Si(l-NBut)2PN}C6H4Ni{PEt3}], each complex having jP,N and jP coordinated amidophosphine ligands.
Introduction
The Group 15 elements nitrogen and phosphorus form com-
pounds of an unusual structural variety and exhibit more bond-
ing modes than any other pair of congeners in the periodic table.1
Among the most common phosphorus–nitrogen compounds are
tris(amino)phosphines, e.g., P(NR2)3, the isoelectronic analogs
of tertiary phosphines. As neutral molecules, these ambidentate
ligands, with their adjacent hard- and soft-donor elements, coor-
dinate transition metals almost exclusively via their phosphorus
atoms. Their structural, and even their electronic, properties thus
mirror those of tertiary phosphines in most respects.
Chart 1
coordination of both phosphorus atoms of one diazadiphosphe-
tidine ring to one nickel center was proposed,13 because the
nearly planar structure of the P2N2 heterocycle made this seem
impossible. As a neutral tetraamine ligand, 1 may be expected to
chelate metal atoms through two or more of its nitrogen atoms,
but we are unaware of any example of a metal coordinated by a
neutral diazadiphosphetidine solely through nitrogen.
In the following we describe nickel complexes in which
amino- and amido-phosphines coordinate metals through either
phosphorus alone or through phosphorus and nitrogen simulta-
neously. We also attempt to shed some light on the chameleonic
behavior of the anionic amidophosphines as ligands in coordina-
tion chemistry and offer suggestions on how these ambidentate
ligands may be tuned to favor one coordination mode over
another.
Aminophosphines bearing at least one primary amine can
be deprotonated to furnish amidophosphines.2 Although such
anions are usually depicted with the negative charge localized
on the nitrogen atom, this is not only an oversimplification,
but often an incorrect representation of the true nature of
these species. Supporting evidence has come from both the
reaction- and the coordination-chemistry of these anions.
Thus, amidophosphines react with electrophiles via nitrogen or
phosphorus,3 depending upon the electrophile and the reaction
conditions. The ambidentate amidophosphines have been shown
to chelate metals through either nitrogen (jN),4 phosphorus
(jP)5 or through both atoms simultaneously (jP,N).6–8
Depending on one’s inclination the bis(tert-butylamino)-
diazadiphosphetidine 1 (Chart 1) may be regarded as either
a cyclic diphosphine or a cyclic tetraamine.9 In the former
role this heterocycle had garnered some attention as neutral
phosphorus-donor ligand for transition metals.10–12 A number
of nickel complexes of such neutral diazadiphosphetidines had
also been claimed, but to our knowledge, none of these was
fully characterized nor had a crystal structure determination
appeared. We were particularly intrigued by reports in which the
Results
The interaction of nickel(II) chloride with two equivalents
of cis-{But(H)NP(l-NBut)2PN(H)But} in refluxing toluene
(Scheme 1) furnished dark-red 2, which crystallized with one
molecule of toluene per complex. Both the H and 31P NMR
1
spectra immediately showed that the diazadiphosphetidine
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 0 7
©

View Article Online
ꢀ
phorus atom ( N–P–N) is 310.3◦, making this phosphorus atom
significantly less pyramidal than the uncoordinated phosphorus
atom (289◦). This flattening of the phosphorus atoms is due to
the conversion of the lone pair of electrons to a bond pair and, as
will be seen below, it increases with increasing metal–phosphorus
interaction. The isolation of 2 is further evidence that neutral
bis(1◦-amino)diazadiphosphetidines act as phosphorus, rather
than nitrogen, donors towards late transition metals, and that
they coordinate these in a monodentate fashion.
Scheme 1
To compare the bond parameters of 2 with those of a
bis(trialkylphosphine)nickel dichloride complex, we synthesized
trans-[NiCl2(PEt3)2] (3) according to a published procedure
and conducted a single-crystal X-ray analysis of the cherry-
red crystals.15 Crystal and refinement data are summarized
in Table 1, while Fig. 2 is a perspective view of this classic
nickel complex. The partially-refined structure of the bromide
analogue, trans-[NiBr2(PEt3)2], had appeared previously,16 but
to our knowledge a single-crystal X-ray analysis of 3 has
not been reported. These bromide and chloride complexes are
isomorphous, but we chose a different unit cell for the refinement
˚
of 3. In trans-[NiBr2(PEt3)2 the nickel–bromide (2.26 A) and
Fig. 1 Thermal ellipsoid (30%) plot and partial labeling scheme of
2. The solvent molecule (toluene) and the hydrogen atoms have been
omitted and the tert-butyl groups are drawn as sticks. The atoms with
primed labels are related to those with plain labels by the symmetry
˚
nickel–triethylphosphine (2.30 A) bonds, enclose angles of
almost exactly 90◦.
˚
operation 1 − x, 1 − y, −z. Selected bond lengths (A) and angles
(◦): Ni1–Cl1 2.1661(13), Ni1–P1 2.2763(13), P1–N4 1.644(3), P2–N3
1.669(4); Cl1–Ni1–P1 86.45(5), Cl1–Ni1–P1ꢀ 93.55(5).
ligands were coordinated through one phosphorus atom only.
Thus there were two signals, at 71.8 and 30.1 ppm, respectively,
in the 31P NMR spectrum, indicative of free and coordinated
phosphorus atoms, as well as two sets of signals for the tertiary
butyl groups and the two amino hydrogen atoms of the ligands.
A single-crystal X-ray analysis of 2 (Fig. 1) showed that the
diazadiphosphetidine ligands were indeed not chelating, but
that they served as monodentate aminophosphines instead. The
crystal data and refinement parameters are listed in Table 1.
Complex 2 is located on a crystallographic inversion center
and thus has trans geometry. The nickel atom lies on the inver-
sion center and heterocycles are orthogonal to the coordination
plane, placing the tert-butylamino groups in the plane of the
metal and the endocyclic nitrogen atoms and their tert-butyl
substituents perpendicular to it. The tert-butylamino groups
attached to the coordinated phosphorus atom have an endo
conformation, while those on the free phosphorus atom are
exo. Due to inductive effects exerted by the metal atom, the
Fig. 2 Thermal ellipsoid (30%) plot and partial labeling scheme of
˚
3. Hydrogen atoms have been omitted. Selected bond lengths (A) and
angles (◦): Ni1–Cl1 2.1628(5), Ni1–P1 2.2329(5); Cl1–Ni1–P1 87.29(2),
Cl1–Ni1–P1ꢀ 92.71(2). The atoms with primed labels are related to those
with plain labels by the symmetry operation −x, 2 − y, −z.
It is fortuitous that both 2 and 3 are trans isomers, because
this makes the comparison of their structural parameters more
meaningful. Although the diazadiphosphetidine is much bulkier
than triethylphosphine, the structural similarities of both com-
plexes are immediately apparent. Just as in 2, the nickel ion, the
chloride ligands and the phosphorus atoms of 3, together with
their central ethyl substituents, all lie in the coordination plane.
The Cl–Ni–Cl and P–Ni–P bonds angles in both complexes are
rigorously 180◦, but the Cl–Ni–P bond angles deviate slightly
from 90◦, the acute angles being 86.45(5)◦ in 2 and 87.29(2)◦
endocyclic and exocyclic P–N bonds are contracted to 1.644(3)
14
˚
˚
and 1.694(4) A, respectively, from 1.664(2) and 1.725(2) A in 1.
The sum of the N–P–N bond angles of the coordinated phos-
Table 1 Crystal and refinement data for 2, 3 and 8
Compound
2
3
8
Formula
C39H76Cl2N8NiP4
910.57
Monoclinic
P21/n (no. 14)
9.541(2)
10.730(2)
25.185(6)
95.92(2)
2564.7(10)
2
C12H30Cl2NiP2
365.91
C26H60ClN3NiP2Si
598.96
Formula weight
Crystal system
Space group
Monoclinic
P21/n (no. 14)
7.3453(10)
11.4847(15)
10.8061(14)
90.990(2)
911.5(2)
Monoclinic
P21/c (no. 14)
10.8581(13)
21.494(3)
15.1459(17)
93.934(2)
3526.6(7)
4
˚
a/A
˚
b/A
˚
c/A
b/◦
3
˚
U/A
Z
2
l/mm−1
0.641
1.515
0.768
Reflections collected
Independent reflections (Rint
R(F),a (I > 2rI)
12945
4389 (0.0671)
0.0561
0.1450
1.192, −0.384
5935
3311 (0.0336)
0.0291
0.1058
0.355, −0.225
25345
8743 (0.0467)
0.0517
0.1660
0.840, −0.444
)
wR2(F2),b all data
−3
˚
q/e A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a R = |Fo − Fc|/ |Fo|. b wR2 = {[ w(Fo − Fc)2]/[ w(Fo2)2]}2/2; w = 1/[ 2(Fo)2 + (xP)2 + yP] where P = (Fo + 2Fc2)/3.
2
2
3 3 0 8
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8

View Article Online
◦
˚
˚
Table 2 Selected bond lengths (A) and angles ( ) for 5, 6 and 8
in 3. The nickel–chloride bond lengths in 2 (2.1662(13) A)
˚
and 3 (2.1628(5) A) are equal within experimental errors, but
the Ni–P bond to the heterocyclic phosphine is somewhat
longer (2.2763(13) A) than that to triethylphosphine (2.2329(5)
A). Despite this slight discrepancy, the almost identical bond
parameters about nickel in these two square-planar complexes
are nonetheless remarkable. Our data thus seem to confirm that,
at least when coordinated to nickel(II) ions, aminophosphines
and trialkylphosphines have similar ligating properties.
5
6
8
˚
Ni–Cl
Ni–N
Ni–P(ring)
Ni–PR3
P–N(exo)
P–N(endo) av.
Si–N av.
2.2175(10)
1.925(3)
2.0796(9)
2.1522(12)
1.559(3)
1.699(2)
n.a.
2.1998(16) av.
1.942(4) av.
2.0749(14) av.
2.1567(17) av.
1.554(4) av.
1.692(4)
2.2209(7)
1.939(2)
2.0693(7)
2.1399(8)
1.560(2)
1.680(2)
1.747(2)
˚
n.a.
A significant difference between aminophosphines and tri-
alkylphosphines is that the former can be readily con-
verted to anionic ligands, provided that at least one primary
amino group is present. We, therefore, chose to investigate
the coordination chemistry of nickel with anionic bis(1◦-
amido)diazadiphosphetidines, which had proven to be a fertile
ground for unusual coordination modes and molecular struc-
tures in both main group and transition metal chemistry.17–20
Deprotonation of the bis(tert-butylamino)diazadiphosphetidine
1 with strong bases (e.g., BunLi) and subsequent treatment
with metal halides had furnished the corresponding metal
derivatives. Most of these adopted one of two structure types,
namely A or B (Chart 2), demonstrating that anionic bis(tert-
butylamido)diazadiphosphetidines show a strong preference to
coordinate metals through nitrogen.
P–Ni–Cl
PR3–Ni–Cl
N–Ni–Cl
P–Ni–PR3
N–Ni–P
Ni–P–N
Ni–N–P
151.17(4)
92.95(5)
105.55(9)
115.88(5)
45.62(9)
61.93(11)
72.45(12)
150.71(6) av.
95.44(7) av.
105.50(13) av.
113.84(6) av.
45.36(12) av.
62.78(15) av.
71.87(15) av.
153.06(3)
96.86(3)
107.42(6)
110.08(3)
45.66(6)
62.74(8)
71.60(9)
Chart 2
Fig. 3 Thermal ellipsoid (30%) plot and partial labeling scheme of
5. The hydrogen atoms and the tert-butyl group on N2ꢀ have been
omitted to enhance clarity. N2ꢀ was generated from N2 by the symmetry
operation x, −y + 0.5, z.
For applications in catalysis we attempted to synthesize
a mono-amido diazadiphosphetidine with an oxygen-donor
functionality (Scheme 2). To this end we modified 1 by replacing
one tert-butylamino group with a tert-butoxy group to obtain
the asymmetric diazadiphosphetidine (4). Deprotonation of 4
adopt a standard coordination geometry, but the structure is
closest to square planar. Due to the very acute endocyclic
nickelaazaphosphirane angle 45.62(9)◦ at nickel only the Cl1–
Ni1–P3 angle (92.95(5)◦) has a value that is close to ideal
square-planar geometry. The N1–Ni1–Cl1 (105.55(9)◦) and P1–
Ni1–P3 (115.88(5)◦) angles, in turn, are intermediate between
square planar and trigonal planar. The nickel–P3 (2.1522(12)
with BunLi and subsequent treatment with trans-[NiCl2(PBun )2]
3
(Scheme 2), however, did not afford the expected N,O-chelated
nickel complex C. Instead, we isolated a dark-red crystalline
compound that was shown by NMR spectroscopy and X-
ray techniques to be the nickelaazaphosphirane 5; that is, a
complex in which the ligand coordinated the metal laterally
in a jP,N fashion. Apparently the late transition metal nickel
preferred the formation of a three-membered Ni–P–N ring over
the more conventional chelation by oxygen and nitrogen above
the heterocycle. The solid-state structure of 5 is shown in Fig. 3;
selected bond parameters are collected in Table 2.
Complex 5 has crystallographic m symmetry and thus
features a rigorously planar nickel(II) coordination environ-
ment, which is composed of the amidophosphine moiety of a
cis-configured P(tert-butoxy)-Pꢀ(tert-butylamido)diazadiphos-
phetidine, one tri(n-butyl)phosphine molecule and one chloride
ligand. The tertiary butyl group attached to the oxygen atom
is exo with respect to the P2N2 heterocycle, while that on
N1 has an endo conformation. This nickel complex does not
˚
˚
A) and the nickel–chloride (2.2175(10) A) bonds have normal
˚
lengths, but the bond to N1 (1.925(3) A) is slightly elongated.
The nickel bond to the phosphorus atom of the heterocycle
˚
(P1), by contrast, is only 2.0796(9) A long, and the coordinated
phosphorus–nitrogen bond (P1–N1) has undergone an even
˚
greater contraction to 1.559(3) A, indicative of a change to
ꢀ
double-bond order. Here
at P1 has increased to 334.0◦,
N–P–N
which is another reflection of the much stronger metal–ligand
interaction in this complex vs. that in 2.
Three-membered rings are highly strained, and there is a
bias against proposing such structures even though in tran-
sition metal chemistry three-membered rings are not uncom-
mon. Nickel, in particular, seems to have a propensity to
from three-membered metalacycles as exemplified by numerous
Scheme 2
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 0 9

View Article Online
Scheme 3
metalacyclopropanes,21 metalacyclopropenes22 and three-
membered nickelacycles involving main group atoms other than
carbon.23 The isolation and stability of 5 further supported this
notion, because the P-amidodiazadiphosphetidine complexes of
nickel form exceptionally strong and symmetrical M–P and M–
N bonds,24 and we therefore decided to study these systems in
more detail. The obvious starting point for this investigation
was the di(tert-butylamino)diazadiphosphetidine 1, which in
its dianionic form had produced only bis(amido) complexes
of structure types A or B. The dianion of 1 reacted with two
Scheme 4
Crystal and refinement data for 8 are collected in Table 1
and selected bond parameters are listed in Table 3. With the
exception of the dimethylsilyl group which now caps one corner
of the heterocycle, the solid-state structure of 8 (Fig. 5) mirrors
that of 5. All bonds to nickel are almost identical to those
in 5 and 6, indicating that the inclusion of silicon into the
heterocycle has had no effect on the bonding parameters of
the nickelaazaphosphirane moiety.
equivalents of trans-[NiCl2(PBun )2], as shown in Scheme 3, to
3
furnish the bis(nickelaazaphosphirane) 6. Because no metal had
previously been coordinated by this ligand in this manner, the
reaction confirmed that nickel has an inherent preference to
coordinate amidophosphines based on heterocyclic scaffolds in
a jP,N fashion. The solid-state structure of 6 is shown in Fig. 4;
selected bond parameters are given in Table 2.
Fig. 4 Thermal ellipsoid (30%) plot and partial labeling scheme of 6.
The hydrogen atoms and the tert-butyl group attached to N2 have been
omitted.
Fig. 5 Thermal-ellipsoid (30%) plot and partial labeling scheme of 8.
Hydrogen atoms and the tertiary butyl group on N1 have been omitted.
The dispirocyclic complex has non-crystallographic C2 sym-
metry and features two nickelaazaphosphirane rings which
cap the diazadiphosphetidine laterally. Overall, the structure is
dominated by the two bulky C3-symmetric tri(n-butyl)phosphine
ligands. For steric reasons both tert-butyl groups of the amido
nitrogen atoms (N3 and N4) have endo conformations, that
is, they are tipped towards the P2N2 heterocycle. The bond
parameters of the nickel ions are isometric and almost identical
to those of the nickel ion in 5. Only the nickel–chloride bonds,
The metalacyclic structures of 5, 6 and 8 are reflected in
their 31P NMR spectra. Thus, for example, the signals for
the phosphorus atoms incorporated in these three-membered
rings appear at −53.6, −82.4 and −53.9 ppm, respectively,
while those for the free ligands cis-{But(H)NP(l-NBut)2POBut},
cis-{But(H)NP(l-NBut)2PN(H)But} and {Me2Si(l-NBut)2PN-
(H)But} appear at 103.9, 88.5 and 114.8 ppm, respectively. These
coordination upfield shifts of about 157–170 ppm far exceed
those of neutral diazadiphosphetidines or trialkylphosphines,
which typically move ca. 50 ppm to higher field or ca. 40 ppm
to lower field, respectively, upon metal coordination.
These findings on 5, 6 and 8 confirmed that heterocyclic
amidophosphines have a strong preference to coordinate
nickel through both phosphorus and nitrogen. To test just
how strong the preference for this coordination mode was,
we deliberately tried to prevent it. We anticipated that a
bis(amidodiazaphosphasiletidine), connected by a suitable
organic linker, would introduce sufficient bond strain in a
j2P,j2N boding mode (D, Chart 3) to make such a chelation
all but impossible. It appeared more likely that a dianionic
ligand would prefer to bind nickel in a less strained j2P
fashion (E). For the synthesis of such a chelating ligand we
treated dilithium o-phenylenediamide with two equivalents
of the P-chlorodiazaphosphasiletidine (Scheme 5). Similar
˚
which average 2.1998(16) A, are somewhat shorter than in the
mono-nickel complex.
Syntheses and structures of 5 and 6 were previously
communicated.25 The difunctional ligands in these complexes
can create both structural and analytical problems and to
simplify the coordination chemistry of these heterocycles we
replaced one of the PN(H)But groups of 1 with a Me2Si group to
obtain the diazaphosphasiletidine {Me2Si(l-NBut)2PN(H)But}
(7).26 This silicon-phosphorus–nitrogen compound retains the
essential structure of the phosphorus–nitrogen ligands, namely a
phosphorus(III) atom incorporated in a heterocycle and flanked
by two sp2-hybridized nitrogen atoms. Deprotonation of 7 and
subsequent treatment of the anion with trans-[NiCl2(PBun )2]
3
(Scheme 4) produced the red, diamagnetic nickel complex 8,
whose NMR spectra identified it as a structural analogue of 5
and 6.
3 3 1 0
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8

View Article Online
to the dilithio-ortho-phenylenediamine, the dianion is in excess
until the reaction is completed and a high concentration of
the monosubstituted, monoanion 9 is present at all times. This
monoanion has sufficient time to undergo a 1,4-proton shift
to furnish an amidophosphine and an NH2 group before it is
trapped by the second equivalent of chlorophosphine, producing
9b. This mechanism implies that the PNH moiety is more acidic
than the NH2 moiety, and given the charge delocalization in the
anionic PN group discussed below, this is not an unreasonable
suggestion. If the dianion is added to a solution of Me2Si(l-
NBut)2PCl (Scheme 5), the dianion is trapped by two equivalents
of the chlorophosphine, before the proton transfer can occur,
and only the symmetric product 9a is formed.
Chart 3
Single-crystal X-ray analyses of 9a and 9b revealed the
expected structures. Crystal and refinement data are listed in
Table 3, while selected bond parameters for 9a are given in
Table 4. Fig. 6 shows a perspective view of 9a that emphasizes
the perpendicular orientation of the almost parallel inorganic
heterocycles with respect to the aromatic ring. The conforma-
tions about the exocyclic P–N bonds are exo, i.e., the lone-pairs
of electrons on the phosphorus atoms are pointing outward
Scheme 5
o-phenylenediamine-based bis(aminophosphines), bearing
diphenylphosphino moieties, are well known.27
Although this ligand synthesis seemed straightforward, the
manner in which the dianion and the chlorophosphine were
combined was crucial for the outcome of the reaction. Thus, the
addition of 1,2-(LiNH)2C6H4 to Me2Si(l-NBut)2PCl (Scheme 5)
afforded only the targeted symmetrical disubstitution-product
9a in 86% yield, while the reverse order of addition (Scheme 6)
produced a mixture of symmetrical (9a) and asymmetrical
disubstitution (9b) products in an overall yield of 69%. This latter
compound, an N,N-diphosphinoamine, has applications in its
own right and although both isomers can be cleanly separated
by fractional crystallization, the former route is obviously
preferable for the ligand synthesis.
The formation of the asymmetric product 9b in Scheme 6,
can be rationalized in terms of the intermolecular 1,4-proton
shift shown in Scheme 7. When the chlorophosphine is added
Fig. 6 Thermal ellipsoid (30%) plot and partial labeling scheme of 9a.
All but the amino hydrogen atoms have been omitted, and the tert-butyl
groups are drawn as sticks only.
Scheme 6
Scheme 7
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 1 1

View Article Online
Table 3 Crystal and refinement data for 9a–11
Compound
9a
9b
10
11
Formula
C26H54N6P2Si2
568.87
Monoclinic
P21/c (no. 14)
9.2122(13)
33.045(5)
C26H54N6P2Si2
568.87
Orthorhombic
Pbca (no. 61)
12.225(3)
16.738(4)
32.714(7)
C33H61ClN6NiP2Si2
754.16
C32H67N6NiP3Si2
743.72
Formula weight
Crystal system
Space group
Monoclinic
P21/n (no. 14)
10.6331(13)
15.7716(15)
25.212(2)
Triclinic
¯
P1 (no. 2)
˚
a/A
11.4153(15)
12.2457(16)
16.145(2)
79.259(2)
79.351(2)
69.353(2)
2057.4(5)
2
˚
b/A
˚
c/A
12.3486(16)
a/◦
b/◦
c /◦
109.808(10)
93.343(8)
3
˚
U/A
3536.7(8)
4
0.214
6712(2)
8
0.228
4220.8(8)
4
0.685
Z
l/mm−1
0.675
Reflections collected
Independent reflections (Rint
R(F),a (I > 2rI)
5826
4593 (0.0221)
0.0588
0.1772
0.455, −0.299
5433
4355 (0.0468)
0.0548
0.1536
0.357, −0.402
7138
5506 (0.0238)
0.0520
0.1444
0.586, −0.372
10494
7116 (0.0556)
0.0505
0.1297
0.987, −0.407
)
wR2(F2),b all data
−3
˚
q/e A
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a R = |Fo − Fc|/ |Fo|. b wR2 = {[ w(Fo − Fc)2]/[ w(Fo2)2]}1/2; w = 1/[ 2(Fo)2 + (xP)2 + yP] where P = (Fo + 2Fc2)/3.
2
2
◦
˚
Table 4 Selected bond lengths (A) and angles ( ) for 9a, 10 and 11
9a
10
11
Ni1–Cl1/P3
Ni–N1
Ni–P1
Ni–P2
P1–N1
2.1640(13)
1.835(3)
2.1783(12)
2.1456(11)
1.603(4)
1.668(3)
1.682(3)
1.679(3)
1.738(3)
1.733(3)
1.389(6)
1.400(5)
1.393(6)
2.1383(11)
1.856(3)
2.1603(11)
2.1756(11)
1.592(3)
1.605(3)
1.684(3)
1.714(3)
1.730(3)
1.729(3)
1.398(4)
1.360(5)
1.432(5)
1.704(3)
1.694(3)
1.712(3)
1.712(3)
1.715(3)
1.716(3)
1.405(4)
1.404(4)
1.391(5)
P2–N2
P1–N(endo) av.
P2–N(endo) av.
Si1–N(endo) av.
Si2–N(endo) av.
N1–C1
N2–C6
C1–C6
Fig. 7 Thermal ellipsoid (30%) plot and partial labeling scheme of
9b. Only one of the two locations of the amino nitrogen atom (6B)
is shown. All hydrogen atoms have been omitted and the tert-butyl
˚
groups are drawn as sticks only. Selected bond lengths (A) and angles
(◦): P1–N5 1.758(3), P2–N5 1.752(3), P1–N(endocyclic, mean) 1.730(3),
P2–N(endocyclic, mean) 1.729(3), P1–N5–P2 108.97(15).
P1–Ni1–Cl1/P3
P1–Ni1–N1
N1–Ni1–P2
P2–Ni1–Cl1/P3
Ni1–N1–P1
Ni1–P1–N1
119.20(5)
46.10(11)
95.46(11)
99.24(5)
78.30(15)
55.60(12)
108.52(12)
117.01(4)
45.93(9)
92.57(10)
104.48(4)
77.16(13)
56.91(11)
112.53(12)
Ni1–P2–N2
and away from each other. A similar structure was recently re-
ported for a macrocycle composed of two diazadiphosphetidine
molecules connected by two o-phenylenediamine linkers, where
geometric constraints dictate an exo conformation.28 The six
crystallographically unique phosphorus–nitrogen bonds of 9a
Scheme 8
˚
are almost isometric, ranging from 1.694(3) to 1.715(3) A, while
˚
the silicon-nitrogen bonds are rigorously isometric (1.715(3) A).
the presence of a nickelaazaphosphirane, while the low field
signal was typical of diazadiphosphetidines coordinated through
phosphorus only. Both doublets were shifted to high field by
about 25 and 148 ppm, respectively, the latter shift difference
being quite similar to those for the metalacyclic phosphorus
atoms in 5, 6 and 8. Even more intriguing than the chemical-
shift differences of the two signals was the unusually large
phosphorus–phosphorus coupling constant of 667 Hz, which
is as large, or larger, than those in compounds with direct
phosphorus–phosphorus bonds.1
In 9b (Fig. 7) the diazaphosphasiletidine rings are both
attached to the same nitrogen atom of the o-phenylenediamine,
making it a diphosphinoamine. The molecule exhibits a rota-
tional disorder in the solid state, with the NH2 group of the
aromatic diamine occupying two positions, which are related to
each other by a non-crystallographic C2 axis coinciding with the
N5–C50 bond. The greater steric crowding in 9b is reflected
˚
in elongated phosphorus–nitrogen (1.740(3) A) and silicon–
˚
nitrogen (1.735(3) A) bonds compared to those in 9a.
For the synthesis of the targeted nickel complex, we treated 9a
with two equivalents of n-butyllithium, and added the ensuing
dilithium derivative to a suspension of anhydrous nickel(II)
chloride, as outlined in Scheme 8. The 31P NMR spectrum of the
maroon product, however, showed an AB pattern of doublets at
94.7 and −28.3 ppm, respectively, which was inconsistent with
a symmetrical structure. The doublet at −28.3 ppm suggested
To obtain conclusive structural information on 10 we analyzed
it by single-crystal X-ray methods. A thermal ellipsoid plot
of the solid-state structure of 10 is shown in Fig. 8. Crystal
and refinement data are collected in Table 3, while selected
bond parameters are listed in Table 4. The presence of the
chloride ligand in 10 immediately indicated that the chelating
bis(diazaphosphasiletidine) ligand was only monoanionic. Our
3 3 1 2
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8

View Article Online
Fig. 8 Thermal ellipsoid (30%) plot and partial labeling scheme of 10.
All hydrogen atoms have been omitted and the tert-butyl groups are
drawn as sticks only.
Fig. 9 Thermal ellipsoid (30%) plot and partial labeling scheme of 11.
All hydrogen atoms have been omitted and the tert-butyl groups are
drawn as sticks only.
failure to obtain the dianion may have been the result of
the incomplete deprotonation of the chelating ligand or the
presence of adventitious water in the nickel(II) chloride, but the
latter scenario is more likely. While the complex is structurally
more elaborate than 5, 6 and 8, the coordination environment
about nickel is rather similar. It is convenient to consider 10 a
nickelaazaphosphirane in which the nickel ion is coordinated by
an amido nitrogen atom (N1), bearing an aromatic, rather than
a tert-butyl, substituent. Tethered to the ortho position of this
aromatic ring is a second aminodiazaphosphasiletidine which
binds the nickel center as a neutral, heterocyclic phosphine.
Due to the chelating nature of 9a, the amido nitrogen (N1)
is now trans (165.29(12)◦) to the chloride ligand, while the two
phosphorus atoms have pseudo-trans (141.56(5)◦) geometry. The
nickel atom and the ligand donor atoms are again in a planar
coordination environment, but there is significant folding of the
molecule along the N1–N2 vector. Thus, the plane defined by
nickel and its nearest atomic neighbors (N1, P1, P2, Cl1) and
that defined by N1, N2, C1 and C6 enclose an angle of ca.
while selected bond parameters are juxtaposed to those of the
corresponding bonds for 9a and 10 in Table 4. Although here the
chelating ligand is dianionic, only one amidophosphine moiety
is coordinated in a jP,N fashion, while the second one is bound
through phosphorus only. This raises the question whether the
negative charge is localized on N2 or delocalized. The notion
that the additional negative charge is substantially delocalized
over the entire molecule is supported by the perfect planarity
of the plane defined by almost all the heavy atoms. Only the
nitrogen atoms of the diazaphosphasiletidines (N3 through N6),
their tert-butyl substituents and the two lateral ethyl groups
of the triethylphosphine ligand do not lie in this plane. The
presumed charge delocalization in 11 is further revealed by the
bond parameters involving nitrogen atom N2. For example,
˚
˚
the P2–N2 (1.605(3) A) and N2–C6 (1.360(5) A) bonds are
significantly shorter than those in 10, while the aromatic bond
◦
˚
˚
14 . The Ni1–P1 (2.1783(12) A) and N1–P1 (1.603(4) A) bonds
˚
from C1 to C6 has lengthened from 1.392(4) to 1.432(5) A.
are somewhat longer than those in 5, 6 and 8, but the Ni1–N1
˚
Also elongated are the nickel–P2 bond (2.1756(11) A) and
˚
˚
bond is ca. 0.1 A shorter (1.835(3) A). The nickel–chloride bond
the endocyclic P2–N5 and P2–N6 bonds, which now average
˚
(2.1640(13) A) is also shorter than those in 5, 6 and 8. These bond
˚
1.714(4) A. The nickel bond to triethylphosphine (2.1383(11)
differences are likely at least partially due to different atoms
being in a trans configuration to each other.
For electron-counting purposes, and using a covalent bonding
model, the P–N moiety is a three-electron donor, while P2
and Cl1 are two- and one-electron donors, respectively. This
makes 10 a 16-electron species–a reasonable electron count for
a diamagnetic, pseudo-square planar nickel complex.
To synthesize a chloride-free nickel complex of 9a, we repeated
the reaction (Scheme 9), but with trans-[NiCl2(PEt3)2] as a
soluble and more reliable source of anhydrous nickel(II). This
reaction produced a visibly different, almost black, solution.
The 31P NMR spectrum of the product exhibited three signals,
namely two doublets of doublets at 78.1 and −6.3 ppm,
respectively, but with a reduced coupling constant of 413 Hz. An
unresolved multiplet at 20.5 ppm for coordinated triethylphos-
phine suggested the absence of the chloride ligand.
˚
A), by contrast, has the same length as the nickel bond to the
tri(n-butyl)phosphine ligand in 8.
Despite the almost identical structures of 10 and 11, the
covalent bonding model yields an electron count of seventeen for
the nickel center in 11. From the NMR data it is clear, however,
that this is a diamagnetic complex, and this shows that, just like
for previously reported anionic phosphine complexes,29 only the
ionic bonding model provides a correct electron count. This
electron-count discrepancy arises from the fact that a coordi-
nated trivalent phosphorus(III) center, such as P2, is assumed
to donate two electrons to the metal in both the ionic- and the
neutral-bonding model. Using the ionic model, the nickel(II)
center has eight electrons, while the anionic jP,N moiety is
assigned four electrons. The anionic jP amidophosphine moiety
contributes only two electrons, as does the neutral PEt3 ligand.
This yields a 16-electron count on the nickel center, just as in 10,
where both counting models yield this answer.
Discussion
The neutral bis(tert-butylamino)diazadiphosphetidine, 1, co-
ordinates nickel in a monodentate fashion through phospho-
rus, rather than nitrogen. Although similar P-coordinated di-
azadiphosphetidine complexes had previously been obtained for
somewhat softer rhodium(I)10 and molybdenum(0) species,11 our
results confirm that even divalent nickel prefers a monodentate
coordination through phosphorus over a potential chelation by
up to four amino nitrogen atoms. Despite its steric bulk 1 forms
a square-planar, rather than a tetrahedral, nickel complex with
identical stereochemistry and almost identical bond parameters
as the much more compact triethylphosphine. These findings
Scheme 9
The solid-state structure of 11, shown in Fig. 9, confirmed
this suspicion as it is essentially identical to that of 10, but
with a triethylphosphine moiety in place of the chloride ion.
Crystal and data collection parameters are provided in Table 2,
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 1 3

View Article Online
seem to support the commonly held belief that aminophos-
phines and trialkylphosphines have similar donor/acceptor
properties.30
amidophosphine with a weak (but real) Li–P interaction and a
phosphorus–nitrogen single bond. The reaction of Li(PhNPPh2)
with zirconium and lanthanide chlorides furnished the eight-
coordinate neutral zirconium complex (G, Chart 4) and the
eight-coordinate anionic lanthanide complexes H, respectively.
A comparison of the metric parameters in the three-membered
rings of G and H shows that the bonding is also decidedly differ-
ent from that in the title compounds. That is, the Zr–N (2.175(5)
In its anionic form, however, 1 and related amidophosphines
based on inorganic-heterocyclic platforms, do not coordinate
nickel through nitrogen alone, as they had done in all previously
characterized metal complexes of these ligands, but they do so
through nitrogen and phosphorus simultaneously. This jP,N
coordination creates three-membered rings composed of nickel,
phosphorus and nitrogen, so-called nickelaazaphosphiranes.
That the thermodynamic driving force for the formation of these
three-membered rings is strong is indicated by the absence of
any dissociation of the phosphorus atoms in solution and by the
unusual shortness of all metalacyclic bonds.
˚
˚
A) and Zr–P (2.742(2) A) bonds are comparatively short and
long, respectively, while the metalacyclic P–N bond has almost
4
˚
single-bond value, namely 1.666(5) A. This asymmetric bond
pattern—short M–N bonds but long M–P bonds—is rather
similar to that for the lithium derivative and not unexpected
for the hard zirconium. The bond asymmetry is also reflected by
the solution behavior of the zirconium complex which shows two
In all three complexes, namely 5, 6 and 8, the three-membered
metalacycles are almost isometric. Thus, the phosphorus–
“free” and two coordinated phosphorus atoms according to 31
P
nitrogen bonds range from 1.554(4) to 1.560(2) A, the nickel–
NMR spectra. An anionic lutetium complex [(Ph2PNPh)4Lu]−
˚
˚
nitrogen bonds range from 1.925(3) to 1.942(4) A and the
(H) exhibited an almost identical bond pattern with short Lu–N
˚
bonds (2.252(7)–2.272(8) A) but long Lu–P (2.886(3)–3.040(3)
8
nickel–phosphorus bonds range from 2.0693(7) to 2.0796(9)
˚
˚
˚ ˚
A) and P–N (1.673(8) A) bonds.
A. Importantly, the phosphorus–nitrogen bonds (1.557 A) are
˚
˚
0.16 A shorter than the formal single bonds (1.725(2) A)
found in pristine 1 indicating double bond character.14 The
nickel–nitrogen bonds are somewhat longer than for related
terminal nickel–organoamido bonds, which range from 1.82 to
31
˚
1.93 A. By contrast, the endocyclic nickel–phosphorus bonds
˚
˚
(av. 2.075 A) are 0.2 A shorter than the nickel–phosphorus
˚
bonds (2.2763(13) A) to the neutral diazadiphosphetidine in 2.
Despite the apparent angle strain in these rings, the metalacyclic
nickel–phosphorus bonds in 5, 6 and 8 are among the shortest
nickel–phosphorus bonds listed in the CCDC Registry for four-
coordinate phosphorus(III) species.32
Although 10 and 11 bear the chelating bis(diazaphos-
phasiletidine) ligand 9a, which we specifically designed to
discourage the jP,N coordination in favor of a jP coordination,
both complexes exhibit a mixture of these two bonding modes.
Thus, in each complex one nickelaazaphosphirane moiety
and one neutral (10) or anionic (11) heterocyclic phosphine,
respectively, are present. The retention of the jP,N coordination
in these chelate complexes is further evidence of the favorability
of the metalacycle formation. Owing to the fact that the ligand
is monoanionic in 10 but dianionic in 11, the metric parameters
of their nickelaazaphosphiranes are not as similar as those
in 5, 6 and 8. Interestingly, however, the formally anionic
phosphine in 11 forms a longer bond with nickel than the
neutral phosphine in 10. Most equivalent bonds of these two
latter nickelaazaphosphiranes are almost equidistant, as shown
Chart 4
˚
by the phosphorus–nitrogen bonds in 10 (1.603(4) A) and 11
Nickel is both smaller and chemically softer than zirco-
nium and the lanthanides, and a comparison of the title
compounds with metalaazaphosphiranes of smaller and later
transition metals is clearly more appropriate. Indeed, the
˚
(1.592(3) A) and the nickel–nitrogen bonds in 10 (1.835(3)
˚
˚
A) and 11 (1.856(3) A). It is significant, that the metalacyclic
˚
P–N bonds are ca. 0.05 A longer than those in 5, 6 and 8,
while the Ni–N1 bonds are substantially shorter (ca. 0.1 A).
5
˚
metalaazaphosphirane moiety in the 18-electron complex [(g -
The bond differences of the nickelaazaphosphirane moieties
between the two groups (5, 6 and 8) and (10 and 11) are due
to a number of factors. The latter complexes feature a chelating
ligand which imposes certain bond constraints and also places
different atoms and groups in cis/trans geometries. In 10 and
11 the amidophosphine nitrogen is substituted with an aromatic
group, and such electron-withdrawing substituents on the N
terminus tend to weaken the phosphorus–nitrogen double bonds
of amidophosphines.33
C5H5)(CO)2Mo(Ph2PNC6F5)], F, is closer to those of the ti-
tle compounds.7 For example, the phosphorus–nitrogen bond
˚
is 1.640(3) A long, while the molybdenum–phosphorus and
˚
molybdenum–nitrogen bonds are 2.362(2) and 2.239(3) A long,
respectively. But even if corrections are made for the approx-
˚
imately 0.15 A larger covalent radius of molybdenum, versus
˚
nickel, the endocyclic bonds in F are still almost 0.1 A longer.
To determine whether the very symmetrical bonding in the
three-membered rings in 5, 6, 8, 10 and 11 are mainly due to the
metal or the uncommon ligand(s), it would of course have been
best to compare our data to those of nickelaazaphosphiranes
based on acyclic amidophosphines. Unfortunately the reaction
of [NiCl2(PPh3)2] with Li(PhNPPh2) did nor furnish a three-
membered ring, but produced instead a dinuclear nickel–nickel
Metalaazaphosphiranes
Metalaazaphosphiranes had been reported previously, but most
were complexes of anilidodiphenylphosphines with a decidedly
unsymmetrical bonding pattern between metal and ligand.
Thus, in one of the simplest conceivable metalaazaphosphirane,
bonded species with a bridging anionic PhNPPh2 moiety.34
A
better structure match for the title compounds is the pseudo
square-planar nickel complex I,35 although here the nickelaaza-
phosphirane is composed of a nickel(0) center and a neutral
amino(imino)phosphine ligand. Not unexpectedly, the three
namely the dimeric [(Et2O)Li(PhNPPh2)]2 reported by Ashby
2
˚
and Li, the relevant bond parameters (Li–N 2.023(4) A, Li–
˚
˚
P 3.004(4) A, P–N 1.672(2) A) define essentially a metal–
3 3 1 4
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8

View Article Online
bonds of this metalacycle, namely, Ni–P 2.231(1), Ni–N 1.908(2),
P–N 1.646(2) A, are somewhat different from those in the title
has been invoked previously and which also has theoretical
support, places the negative charge on the more electropositive
phosphorus atom.33 The accumulation of negative charge and
concomitant shielding of the phosphorus atoms is reflected
in the significant upfield shifts of their signals in the 31P
NMR spectra. There is also ample evidence, from reactivity
and structural studies, that anionic amidophosphines act as P-
centered anions.11
˚
complexes. Notably, it is the nickel–phosphorus bond of I, which
shows the greatest discrepancy, being substantially longer than
those in the title compounds. In addition, the phosphorus–
˚
nitrogen bond has lengthened significantly from 1.545(2) A in
˚
the free iminophosphine to 1.674(1) A in the complex. Because
iminophosphines are valence-isoelectronic with alkenes, I may
be considered a phosphorus–nitrogen analogue of a zerovalent
nickel olefin complex.
In this context it is worth noting that phosphaalkenes often
exhibit a similar reversal of polarization with the negative charge
residing on phosphorus, rather than carbon.37 For amidophos-
phines, where such a charge reversal would seem less likely,
it should be aided by electron-releasing groups on the amido
nitrogen and electron withdrawing groups on the phosphorus
atom and result in a formal phosphorus–nitrogen double bond.
One would expect amidophosphines of this type to bind to
metals as shown in M, namely with a covalent bond between the
metal and phosphorus, a donor bond between the metal and the
nitrogen atom and with a double bond between phosphorus and
nitrogen. Our structural data bear this out, because the anionic
P,N moieties of all seven nickelaazaphosphiranes reported here
have double-bond lengths, while the nickel–phosphorus bonds,
are among the shortest dozen such bonds reported.32 There are
also inductive and resonance effects, which are both due to the
aromatic ring, the inductive effects being evident in the longer
P–N bonds of 10 and 11, while the resonance effects are reflected
in the significantly shortened N2–C6 and C1–C6 bonds of 11.
In its limit the resonance form L may be expected to force
the j2P coordination of a dianionic ligand like 9a. Such
j2P coordinations has been observed for the monoanionic
bis(diphenylphosphino)amide [Ph2PNPPh2]− where this bond-
ing mode is favored over a jP,N coordination in most cases.11
The partial realization of the j2P coordination mode in 11
suggests that, given a suitable linker and substituents, it should
be possible to isolate metal complexes featuring chelating j2P-
coordinated amidophosphines for ligands that are structurally
more complex than [Ph2PNPPh2]−. This will likely require a
linker with a wider span than the o-phenylenediamine used in
9a, namely an m-phenylenediamine, or an aliphatic linker of
similar size. The role of the metal should be considered as well,
and it stands to reason that soft metals which prefer phosphorus
coordination in neutral aminophosphines, such as in 2, should
also favor the jP coordination of anionic amidophosphines.
The bonding in metalaazaphosphiranes
Three-membered rings are comparatively rare in main-group
chemistry, because their substantial angle strain renders them
unstable with respect to their acyclic analogues. Whenever such
rings are encountered, however, they tend to contain nitrogen
or phosphorus, or both elements. In transition-metal chemistry,
by contrast, three-membered rings are much more common,
although this is in part due to the ambiguity of assigning
formal bonds in such compounds. The best-known examples
of transition-metal-containing three-membered heterocycles are
metalacyclopropanes, which are formed when alkenes coordi-
nate to low-valent metal centers. To account for the bonding
of these neutral ligands to the often neutral metal fragments,
Dewar and Chatt proposed that the metal receives electron
density from the p bond into an empty r-type orbital, which
is then synergistically back-donated from an occupied p-type d-
orbital into the p* orbital of the alkene.36 This net electron flow
from a bonding to an antibonding orbital is accompanied by a
diagnostic carbon–carbon bond lengthening. For the bonding of
the iminophosphine in I the Dewar–Chatt model is appropriate,
=
as underscored by the substantial lengthening of the P N bond
upon coordination, although here back donation probably plays
only a minor role.
Most amidophosphines are satisfactorily written as shown
in J (Chart 5), and to account for the bonding of such an
anion to transition metals it is not necessary to invoke the
Dewar–Chatt model. Instead, the interaction of LX-type ligands
with a metal is typically represented as shown in K, namely
with a covalent bond from nitrogen and a donor bond from
phosphorus. This mesomeric form describes the bonding for
amidophosphines to lanthanides, main-group metals, and hard
transition metals well, because it predicts metal–nitrogen and
phosphorus–nitrogen single bonds and a (presumably weak)
donor bond from phosphorus to the metal.
Conclusion
The coordination chemistry of the PN moiety in its neu-
tral and anionic form with nickel species was investigated.
Neutral bis(tert-butylamino)diazadiphosphetidines coordinate
nickel through phosphorus and thus shows a similar coor-
dination behavior as trialkylphosphines. Anionic mono- and
bis(amido)phosphines based on diazadiphosphetidines and re-
lated heterocycles, in contrast, bind nickel species in a much less
predictable manner. Most commonly, these ligands coordinate
nickel through both nitrogen and phosphorus simultaneously
to yield remarkably stable three-membered Ni–P–N rings—
nickelaazaphosphiranes. Unlike previously-studied metalaaza-
phosphiranes, these complexes feature strong bonds between
both, nickel and nitrogen and nickel and phosphorus, and
formal double-bonds between phosphorus and nitrogen. Our
attempts to force a new chelating dianionic bis(amidophosphine)
to bind nickel exclusively in a j2P fashion, succeeded only
partially, leading to jP,N;jP-bound ligands instead. When
such anionic amidophosphines coordinate a metal through
phosphorus alone, only the anionic model provides a correct
electron count on the metal. In the hands of Peters et al. anionic
phosphines have been remarkably useful in the elucidation of
steric and electronic phenomena of late first-row transition
metals, and amidophosphines, suitably modified, may prove to
have similar utility.
Chart 5
For late transition metals, and in particular for the title
compounds, the resonance structure K neither describes the
bonding pattern within the ligand nor the metal–ligand in-
teraction properly, because it fails to account for the short
nickel–phosphorus bond and the phosphorus–nitrogen double
bond. The Dewar-Chatt model can also be discounted because
the phosphorus–nitrogen bonds in the nickelaazaphosphiranes
shorten, rather than lengthen, upon coordination.
The distinguishing features of the nickelaazaphosphiranes
reported herein are the highly contracted phosphorus–nitrogen
and phosphorus–nickel bonds; a bond pattern that is almost
exactly opposite from that observed in all previously reported
metalaazaphosphiranes. It thus appears that the amidophos-
phines based on heterocycles in their “free” anionic form are
best represented as shown in L. This resonance structure, which
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 1 5

View Article Online
JPP = 24.7 Hz), 15.2 (d, JPP = 85.3 Hz), −53.6 (dd, JPP = 84.2,
Experimental
24.7 Hz).
All operations were performed under an atmosphere of argon
or pre-purified nitrogen on conventional Schlenk lines or
in a glove box. The hydrocarbon or ethereal solvents were
pre-dried over molecular sieves or CaH2 and distilled under
nitrogen from sodium or potassium immediately before use.
[(PBun )ClNi{ButNP(l-NBut)2PNBut}NiCl(PBun )]
(6).
3
3
trans-NiCl2[PBun ]2 (0.710 g, 1.33 mmol), dissolved in 10 mL
3
of toluene, was treated dropwise with a toluene solution
of {(Li·THF)(ButN)P(l-NBut)2P(NBut)(Li·THF)} (0.746 g,
1.48 mmol) at RT. The resulting dark-red solution was kept at
50 ◦C for 16 h, filtered through a medium porosity frit, and
concentrated in vacuo to a volume of ca. 15 mL. The solution
was then kept at −12 ◦C to afford several crops of small,
red-brown crystals. The yield was 0.332 g (53.1%), based on
trans-[NiCl2(PEt3)2] and trans-[NiCl2(PBun )2] were synthesized
3
according to published procedures.15 {(Li·THF)(ButN)P(l-
NBut)2P(NBut)(Li·THF)},14 and Me2Si(l-NBut)2PCl38 were
prepared as previously reported. The synthesis of {Me2Si(l-
NBut)2PN(H)But}, 7, via a thermolysis reaction, had been
reported previously;26 a modified version appears below.
NMR spectra were recorded on Varian VXR-300 or Bruker
trans-[NiCl2(PBun )2].
3
Mp 164 ◦C. Found: C, 51.29; H, 10.16; N, 5.97.
C40H90Cl2N4Ni2P4 requires C, 51.15; H, 9.66; N, 5.96%. dH
(C6D6) 1.88 (18 H, s, NBut), 1.67 (12 H, m, NBun), 1.52 (12
H, m, NBun), 1.46 (18 H, s, NBut), 1.35 (12 H, q, JHH = 7.2 Hz,
NBun), 0.89 (18 H, t, JHH = 7.3 Hz, Bun); dC (C6D6) 54.97 (s,
NBut), 53.84 (t, JPC = 14.1 Hz, NBut), 32.95 (s, NBut), 32.70
(t, JPC = 4.6 Hz, NBut), 27.21 (s, Bun), 25.05 (d, JPC = 11.9 Hz,
Bun), 24.45 (d, JPC = 25.0 Hz, Bun), 14.12 (s, Bun); dP (C6D6)
12.19 (dm, JPP = 84.5 Hz), −82.43 (dt, JPP = 85.4, 21.6 Hz).
Avance-500 spectrometers. H, 13C, 31P and 29Si NMR spectra
1
are referenced relative to C6D5H (7.15 ppm), C6H6 (128.0 ppm),
P(OEt)3 (137.0 ppm) and TMS (0.0 ppm), respectively. Melting
points were recorded on a Mel-Temp melting point apparatus;
they are uncorrected. E & R Microanalytical Services, Parsip-
pany, N. J. performed the elemental analyses.
Syntheses
Me2Si(l-NBut)2PN(H)But (7). n-Butyllithium (16.2 mL,
40.5 mmol) was added dropwise to a toluene (25 mL) solution of
tert-butylamine (4.25 mL, 40.4 mmol) at 0 ◦C, and the solution
was refluxed for 1 h. In a separate flask, Me2Si(l-NBut)2PCl
(10.79 g, 40.4 mmol) was dissolved in 25 mL of toluene. This
solution was cooled to 0 ◦C and treated dropwise with the
lithium tert-butylamide solution. The ice-bath was removed and
the mixture was stirred for 18 h at RT, during which time it turned
a light tan color and a white precipitate formed. The mixture
was filtered through a medium porosity frit and concentrated
in vacuo. The brownish liquid was distilled under vacuum (46–
49 ◦C, 0.1 mmHg) to give 9.66 g (78.7%) of a viscous colorless
liquid. Bp 46–49 ◦C, 0.1 mmHg. dH (C6H6) 2.16 (1 H, d, J =
5.5 Hz, NH), 1.26 (18 H, d, J = 0.5 Hz, NtBu), 1.25 (9 H, d,
J = 1.3 Hz, NHtBu), 0.37 (3 H, s, SiMe), 0.33 (s, 3 H, SiMe).
trans-[{But(H)NP(l-NBut)2PN(H)But}2NiCl2]·C6H5CH3 (2).
In a 100 mL two-necked flask, anhydrous NiCl2 (0.229 g,
1.77 mmol) and 1 (1.29 g, 3.90 mmol) were combined in
toluene (25 mL). The initially orange suspension became dark-
red during a 20 h reflux. The solution was filtered warm on
a medium-porosity frit to remove metallic nickel and kept at
60 ◦C for 5 days, while dark red crystals formed (1.43 g, 87.9%).
Mp 250 ◦C (decomp.). Found: C, 50.48; H, 10.19; N, 12.67.
C39H84Cl2N8NiP4 requires C, 50.99; H, 9.22; N, 12.20%. dH
(C6D6) 1.939 (18 H, s), 1.283 (9 H, s), 1.194 (9 H, s); dC (C6D6)
54.42 (d), 53.55 (m), 51.58 (d, JPC = 14.5 Hz), 33.45 (d, JPC
=
11.3 Hz), 33.03 (m, JPC = 7.7 Hz), 32.27 (s); dP (C6D6) 71.76 (s);
30.13 (s).
cis-{But(H)NP(l-NBut)2POBut} (4). In a 100-mL two-neck
flask, cis-[But(H)NP(l-NBut)2PCl] (0.27 g, 0.88 ◦mmol) was
dissolved in 15 mL hexanes, and the cooled (−78 C) solution
was treated with 0.88 mL of a 1.0 M LiOBut solution (hexanes).
The mixture was allowed to warm to RT, then kept at 40 ◦C
for 48 h, filtered on a medium-porosity frit and concentrated
in vacuo to ca. 5 mL. After the solution had been stored in
a freezer (−21 ◦C) for several days, colorless crystals formed.
Yield: 0.27 g, 88%.
dC (C6H6) 51.3 (d, JPC = 12.9 Hz, NH(CMe3)), 50.6 (d, JPC
=
10.4 Hz, N(CMe3)), 33.3 (d, JPC = 10.1 Hz, NH(CMe3)), 33.1
(d, JPC = 6.8 Hz, N(CMe3)), 9.0 (d, JPC = 2.6 Hz, SiMe), 5.8 (s,
SiMe); dP (C6H6) 114.8 (s); dSi (C6H6) 5.1 (s).
[{Me2Si(l-NBut)2PNBut}NiCl(PBun )] (8). A 100-mL two-
3
necked flask, equipped with inlet, stirbar and funnel was charged
with 7 (0.300 g, 0.988 mmol) and toluene (10 mL). The solution
was treated dropwise with n-butyllithium (0.40 mL, 1.0 mmol)
and refluxed (1 h). This solution was added dropwise at RT to
Mp 59–62 ◦C. Found: C, 55.07; H, 11.03; N, 11.81.
C16H37N3OP2 requires C, 55.01; H, 10.60; N, 12.03%. dH (C6D6)
1.45 (18 H, s, NBut), 1.41 (9 H, s, NBut), 1.13 (9 H, s, OBut). dC
(C6D6) 75.45 (d, JPC = 8.5 Hz), 51.82 (t, JPC = 12.4 Hz), 51.27
(s), 32.65 (d, JPC = 9.5 Hz), 31.68 (d, JPC = 10.1 Hz). dP (C6D6)
132.2 (s), 103.9 (s).
a solution of [{Bun P}2NiCl2] (0.540 g, 1.01 mmol) in hexanes
3
(10 mL) and the ensuing reaction mixture was refluxed for 16 h.
The solution was then taken to dryness in vacuo, extracted with
hexanes (20 mL) and the extract was filtered on a medium-
porosity frit. The filtrate was concentrated in vacuo (10 mL)
and stored in a freezer (−21 ◦C) until orange–brown crystals
had formed (0.415 g, 70%). Mp 128 ◦C. Found: C, 52.55; H,
10.13; N, 6.96. C26H60ClN3NiP2Si requires C, 52.14; H, 10.10;
N, 7.02%. dH (C6D6) 1.65 (6 H, m, CH2), 1.59 (6 H, m, CH2),
1.55 (9 H, s, NHBut), 1.45 (18 H, s, NHBut), 1.37 (6 H, m, CH2),
0.90 (9 H, m), 0.20 (3 H, s, SiMe), 0.17 (3 H, s, SiMe); dC (C6D6)
52.9 (dd, JPC = 28.8, 1.6 Hz), 51.9 (s, JPC = 1.6 Hz), 33.0 (d,
JPC = 28.8, 5.8 Hz), 32.4 (dd, JPC = 4.5, 1.5 Hz), 27.0 (s, CH2),
[{ButOP(l-NBut)2PNBut}Ni(PBun )Cl] (5). A solution of
3
the lithium salt of 4, prepared by treating 4 (1.30 g, 3.72 mmol)
with n-butyllithium (1.49 mL, 3.72 mmol), was added to a
suspension of [NiCl2(PBun )2] (1.35 g, 3.72 mmol) in hexanes
3
(15 mL). The reaction mixture was refluxed overnight and
the lithium chloride removed by filtration through a medium-
porosity frit. After the solution had been allowed to cool, it
was concentrated in vacuo to ca. 5 mL, and placed in a freezer
25.3 (dd, JPC = 24.2, 2.1 Hz, CH2), 13.9 (s, Me), 3.7 (d, JPC
=
◦
(−21 C) to afford several crops of well-developed orange–red
3.8 Hz, SiMe), 3.1 (d, JPC = 7.1 Hz, SiMe); dP (C6D6) 14.1 (d,
JPP = 80.2 Hz), −53.9 (d, JPP = 80.2 Hz); dSi (C6D6) −1.4 (s).
crystals. Yield: 1.27 g, 53.6%.
Mp 176–179 ◦C. Found: C, 52.46; H, 9.96; N, 6.64.
C28H63ClN3NiOP3 requires C, 52.15; H, 9.85; N, 6.52%. dH
1,2-{Me2Si(l-NBut)2PNH}2C6H4 (9a). In a 100 mL two-
necked flask, 1,2-diaminobenzene (1.1 g, 10 mmol), dissolved
in THF (20 mL), was treated with n-butyllithium (8.5 mL,
21 mmol) at RT. After the completion of the addition, the
solution was refluxed for 2 h while it became deep blue. In a 250-
mL flask, equipped with a dropping funnel, Me2Si(l-NBut)2PCl
(5.6 g, 21 mmol) was dissolved in toluene (100 mL) and then
(C6D6) 1.626 (9 H, s), 1.592 (30 H, s), 1.349 (6 H, m, JHH
=
7.0 Hz), 1.200 (s, 9 H, NBut), 0.918 (9 H, t, JHH = 7.4 Hz). dC
(C6D6) 76.82 (d, JPC = 8.8 Hz), 54.25 (d, JPC = 27.5 Hz), 53.06
(dd, JPC = 7.6, 3.1 Hz), 32.79 (d, JPC = 4.1 Hz), 32.33 (t, JPC
=
5.6 Hz), 31.30 (d, JPC = 8.8 Hz), 27.09 (s), 25.94 (dd, JPC = 25.5,
1.7 Hz), 25.01 (d, JPC = 12.9 Hz), 14.03 (s); dP (C6D6) 109.6 (d,
3 3 1 6
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8

View Article Online
treated dropwise with the dilithio salt. The reaction mixture
was stirred overnight and the solvents were removed in vacuo.
The remaining solid was redissolved in toluene (40 mL) and
the ensuing extract was filtered on a medium-porosity frit and
concent◦rated to ca. 15 mL in vacuo. It was stored for several days
at −17 C to produce colorless crystals (5.2 g, 86%). Mp 186–
188 ◦C Found: C, 54.90; H, 9.70; N, 14.74. C26H54N6P2Si2
requires C, 54.90; H, 9.57; N, 14.77%. dH (C6D6) 7.57 (2 H,
m, Ph), 6.86 (2 H, m), 4.65 (2 H, s, NH), 1.22 (18 H, s, But), 0.44
(6 H, s, Me), 0.37 (6 H, s, Me); dC (C6D6) 134.2 (d, JPC = 7.8 Hz),
121.1 (s), 119.26 (d, JPC = 17.6 Hz), 50.51 (d, JPC = 10.4 Hz),
32.96 (d, JPC = 6.8 Hz), 8.85 (d, JPC = 1.8 Hz), 5.34 (s); dP (C6D6)
119.16 (s); dSi (C6D6) 10.13 (s).
to remove LiCl, concentrated in vacuo and stored at −21 ◦C to
afford a dark green (almost black) solid (0.617 g, 82.1%). Mp
98–101 ◦C. Found: C, 52.07; H, 9.21; N, 10.86. C32H67N6NiP3Si2
requires C, 51.68; H, 9.08; N, 11.30%. dH (C6D6) 7.52 (2 H, m,
JHH = 7.8 Hz), 7.09 (1 H, m, Ph), 6.86 (2 H, m, Ph), 1.69 (6 H,
t, JPH = 7.8 Hz), 1.50 (18 H, s, NBut), 1.25 (18 H, s, NBut), 0.96
(9 H, m), 0.68 (3 H, s, Me), 0.47 (6 H, s, Me); dC (C6D6) 146.8
(d, JPC = 8.7 Hz), 125.0 (d, JPC = 18.6 Hz), 121.7 (s), 117.9
(s), 115.3 (t, JPC = 19.8 Hz), 114.4 (s), 52.0 (d, JPC = 15.1 Hz),
51.3 (d, JPC = 3.7 Hz), 33.4 (d, JPC = 6.1 Hz), 32.5 (d, JPC
5.8 Hz), 17.8 (dd, JPC = 8.4, 24.7 Hz), 7.99 (m), 7.35 (t, JPC
=
=
6.3 Hz), 4.56 (d, JPC = 3.9 Hz), 4.31 (d, JPC = 6.7 Hz), 3.96 (m);
dP (C6D6) 78.1 (dd, JPP = 413.9, 39.3 Hz), 20.5 (m), −6.3 (dd,
JPP = 413.8, 70.0 Hz); dSi (C6D6) 7.7 (s), 1.7 (s).
1-{Me2Si(l-NBut)2P}2N-2-NH2(C6H4) (9b). In a 250 mL
two-necked flask, 1,2-diaminobenzene (3.94, 36.4 mmol), dis-
solved in THF (50 mL), was treated with n-butyllithium (30 mL,
72 mmol) at RT. Upon completion of the addition, the solution
was refluxed for 2 h, during which time it became deep-blue.
The solution was then treated dropwise at RT with a solution
of Me2Si(l-NBut)2PCl (19.4 g, 72.8 mmol), dissolved in toluene
(50 mL). The reaction mixture was stirred overnight and the
solvents were removed in vacuo. The remaining solid was
extracted with hexanes (40 mL), and the ensuing extract was
filtered on a medium-porosity frit and concentrated to ca. 15 mL
in vacuo to yield 9a and 9b in a 3 : 1 ratio by NMR. After storing
the solution at −17 ◦C a crop of colorless, trapezoidal crystals of
9b was isolated (5.3 g, 25%). Further cooling of the supernatant
afforded 9a (9.3 g, 44%). Mp 166–170 ◦C. dH (C6D6) 7.74 (1 H,
X-Ray crystallography
Compounds 2, 3 and 8. All crystals were grown from
supersaturated solutions at the indicated temperatures. Suitable,
single crystals were coated with oil, affixed to a glass capillary,
and centered on the diffractometer in a stream of cold nitrogen.
Reflection intensities were collected with a Bruker SMART
CCD diffractometer, equipped with an LT-2 low-temperature
apparatus, operating at 213 K. Data were measured using x
scans of 0.3◦ per frame for 30 s until a complete hemisphere had
been collected. The first 50 frames were recollected at the end of
the data collection to monitor for decay. Cell parameters were
retrieved using SMART39 software and refined with SAINT40 on
all observed reflections. Data were reduced with SAINT, which
corrects for Lorentz and polarization effects and decay. An
empirical absorption correction was applied with SADABS.41
The structures were solved by direct methods with the SHELXS-
9042 program and refined by full-matrix least squares methods
on F2 with SHELXL-97,43 incorporated in SHELXTL Version
5.10.44
d, JHH = 7.5 Hz), 6.94 (1 H, t, JHH = 7.5 Hz), 6.71 (1 H, t, JHH
(18 H, s, But), 1.27 (18 H, s, But), 0.40 (6 H, Me), 0.35 (6 H,
=
7.8 Hz), 6.50 (1 H, d, JHH = 7.8 Hz Ph), 4.89 (2 H, s, NH2), 1.31
Me); dC (C6D6) 145.2 (s), 131.6 (t, JHH = 2.9 Hz), 129.5 (t, JHH
=
6.2 Hz), 125.3 (s), 116.0 (s), 114.8 (s), 51.6 (t, JPC = 5.8 Hz), 51.4
(t, JPC = 6.2 Hz), 33.2 (t, JHH = 3.7 Hz) 32.8 (t, JPC = 3.8 Hz),
8.1 (s), 7.4 (s); dP (C6D6) 141.7 (s); dSi (C6D6) 8.1 (s).
Compounds 9a, 9b and 10. The crystals were sealed inside
argon-filled glass capillaries, and the intensity data were col-
lected on a Bruker P4 diffractometer. Three reflections were
monitored after every 97 reflections, and the appropriate inten-
sity corrections were applied during data reduction. Reflection
data were reduced with XDISK of the SHELXTL-PC program
suite, Version 4.1,45 and the structure was solved by direct-
methods with SHELXL-NT, Version 5.10,46 and refined as
described above.
[1-{Me2Si(l-NBut)2PN}-2-{Me2Si(l-NBut)2PNH}C6H4NiCl]
(10). A sample of 9a (0.555 g, 0.976 mmol) was dissolved
in THF (15 mL) and the ensuing solution was treated with
n-butyllithium (2.0 mmol). The mixture was refluxed for 2 h,
allowed to cool to RT and then added dropwise to a suspension
of NiCl2 (0.128 g, 0.987 mmol) in THF (10 mL). After it had
been stirred for a few minutes, the initially colorless mixture
turned green and after 12 h of refluxing, it became maroon.
The THF was removed in vacuo and the residue was extracted
with toluene (30 mL), filtered and concentrated in vacuo to
ca. 15 mL. After the solution had been stored at −22 ◦C for
several days, rod-shaped, maroon crystals (0.508 g) formed.
Yield: 76.7%. Mp 226–228 ◦C. Found: C, 52.60; H, 8.18; N,
11.32. C33H61ClN6NiP2Si2 requires C, 52.56; H, 8.15; N, 11.14%.
Compound 11. Crystal data were collected at 100 K
on a Bruker Smart Apex CCD instrument, using graphite-
˚
monochromated Mo-Ka radiation (k = 0.71069 A). The struc-
ture was solved with Direct Methods and refined by full-matrix
least squares against F2 using the SHELXTL, Version 5.10,
program.
dH (C6D6) 7.19 (2 H, d, JHH = 7.8 Hz); 6.79 (1 H, t, JHH
=
7.7 Hz), 6.63 (1 H, t, JHH = 7.6 Hz), 6.72 (2 H, d, JHH = 7.3 Hz),
6.08 (1 H, d, JHH = 7.9 Hz), 4.09 (1 H, t, JPH = 8.7 Hz), 1.62 (18
H, s, NBut), 1.45 (18 H, s, NBut), 0.63 (3 H, s, Me), 0.30 (6 H, d,
JPH = 1.5 Hz, Me), 0.20 (3 H, s, Me); dC (C6D6) 137.8 (s), 132.6
(d, JPC = 8.7 Hz), 125.6 (s), 121.2 (d, JPC = 11.6 Hz), 120.0 (s),
119.0 (s), 51.8 (d, JPC = 3.7 Hz), 51.7 (d, JPC = 4.9 Hz), 33.5 (d,
JPC = 29.4 Hz), 32.2 (d, JPC = 6.1 Hz), 6.1 (s), 3.9 (m), 3.8 (d,
CCDC reference numbers 272420–272426.
See http://dx.doi.org/10.1039/b507040f for crystallographic
data in CIF or other electronic format.
Acknowledgements
We thank the Chevron Phillips Chemical Company for Research
Assistantships to I. S. and L. G., and the National Science
Foundation for a GAANN fellowship to G. R. L.
JPC = 3.0 Hz), 3.6 (d, JPC = 3.0 Hz); dP (C6D6) 94.7 (d, JPP
=
667 Hz), –28.3 (d, JPP = 667 Hz); dSi (C6D6) 13.8 (s), 8.7 (s).
[1,2-{Me2Si(l-NBut)2PN}{Me2Si(l-NBut)2PN}C6H4Ni{PEt3}]
(11). To a 100 mL two-necked flask, equipped with a stir
bar and dropping funnel was added 9a (0.508 g, 0.900 mmol)
and hexanes (10 mL). The ensuing solution was treated with
n-butyllithium (1.80 mmol) and refluxed for 2 h. It was then
added dropwise at RT to a hexanes (10 mL) solution of
trans-[NiCl2(PEt3)2] (0.328 g, 0.900 mmol). The initially red
mixture was refluxed for 12 h, during which time it turned
green–brown. After the solution had cooled to RT, it was filtered
References
1 D. E. C. Corbridge, Phosphorus, Elsevier, Amsterdam, 5th edn, 1995.
2 M. T. Ashby and Z. Li, Inorg. Chem., 1992, 31, 1321.
3 Z. Fei, R. Scopelliti and P. J. Dyson, Inorg. Chem., 2003, 42, 2125; Z.
Fei, R. Scopelliti and P. J. Dyson, Dalton Trans., 2003, 2772; Z. Fei,
R. Scopelliti and P. J. Dyson, Eur. J. Inorg. Chem., 2004, 530; L. E.
Anagho, J. F. Bickley, A. Steiner and L. Stahl, Angew. Chem., Int.
Ed., 2005, 44, 3271.
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8
3 3 1 7

View Article Online
4 O. Ku¨hl, T. Koch, F. B. Somoza, Jr., P. C. Junk, E. Hey-Hawkins, D.
Plat and M. Eisen, J. Organomet. Chem., 2000, 604, 116.
5 H. Schmidbaur, S. Lauteschla¨ger and B. Milewski-Mahrla,
J. Organomet. Chem., 1983, 254, 59.
6 J. Ellermann, J. Sutter, F. A. Knoch and M. Moll, Angew. Chem.,
Int. Ed. Engl., 1993, 32, 700; J. Ellermann, J. Sutter, C. Schelle, F. A.
Knoch and M. Moll, Z. Anorg. Allg. Chem., 1993, 619, 2006; A.
Winkler, W. Bauer, F. W. Heinemann, V. Garcia-Montalvo, M. Moll
and J. Ellermann, Eur. J. Inorg. Chem., 1988, 437; J. Ellermann, W.
Bauer, M. Schutz, F. W. Heinemann and M. Moll, Monatsh. Chem.,
1998, 129, 547.
7 E. Lindner, M. Heckmann, R. Fawzi and W. Hiller, Chem. Ber., 1991,
124, 2171.
8 T. G. Wetzel, S. Dehnen and P. W. Roesky, Angew. Chem., Int. Ed.,
1999, 38, 1086.
9 R. R. Holmes and J. A. Forstner, Inorg. Chem., 1963, 2, 380.
10 J. C. T. R. Burckett St. Laurent, P. B. Hitchcock and J. F. Nixon,
J. Organomet. Chem., 1983, 249, 243.
26 O. J. Scherer, M. Pu¨ttmann, C. Kru¨ger and G. Wolmersha¨user, Chem.
Ber., 1982, 115, 2076.
27 T. Q. Ly, A. M. Z. Slawin and J. D. Woollins, J. Chem. Soc., Dalton
Trans., 1997, 1611; P. A. Bella, O. Crespo, E. J. Ferna´ndez, A. K.
Fischer, P. G. Jones, A. Laguna, J. M. Lo´pez-de-Luzuriaga and M.
Monge, J. Chem. Soc., Dalton Trans., 1999, 4009.
28 F. Garcia, R. A. Kowenicki, I. Kuzu, L. Riera, M. McPartlin and
D. S. Wright, Dalton Trans., 2004, 2904.
29 J. C. Thomas and J. C. Peters, Inorg. Chem., 2003, 42, 5055; T. A.
Betley and J. C. Peters, Inorg. Chem., 2003, 42, 5074; T. A. Betley and
J. C. Peters, Angew. Chem., Int. Ed., 2003, 42, 2385; C. E. MacBeth,
J. C. Thomas, T. A. Betley and J. C. Peters, Inorg. Chem., 2004, 43,
4645; T. A. Betley and J. C. Peters, J. Am. Chem. Soc., 2004, 126,
6252.
30 R. H. Crabtree, The Organometallic Chemistry of the Transition
Metals, Wiley, New York, 3rd edn, 2001, p. 92.
31 D. J. Mindiola and G. L. Hillhouse, J. Am. Chem. Soc., 2001, 123,
4623, and references cited therein.
11 V. S. Reddy, S. S. Krishnamurthy and M. Nethaji, J. Chem. Soc.,
Dalton Trans., 1994, 2661; V. S. Reddy, S. S. Krishnamurthy and M.
Nethaji, J. Chem. Soc., Dalton Trans., 1995, 1993.
12 H. J. Chen, A. Tarassoli, R. C. Haltiwanger, V. S. Allured and A. D.
Norman, Inorg. Chim. Acta, 1982, 65, L69.
13 N. Kuhn and M. Winter, J. Organomet. Chem., 1983, 243, C47; N.
Kuhn and M. Winter, J. Organomet. Chem., 1983, 243, C42.
14 I. Schranz, L. Stahl and R. J. Staples, Inorg. Chem., 1998, 37, 1493.
15 K. A. Jensen, Z. Anorg. Allg. Chem., 1936, 229, 265.
16 V. Scatturin and A. Turco, J. Inorg. Nucl. Chem., 1958, 8, 447.
17 G. Linti, H. No¨th, E. Schneider and W. Storch, Chem. Ber., 1993,
126, 619.
18 L. Grocholl, L. Stahl and R. J. Staples, Chem. Commun., 1997, 1465;
D. F. Moser, I. Schranz, M. C. Gerrety, L. Stahl and R. J. Staples,
J. Chem. Soc., Dalton Trans., 1999, 751.
19 J. K. Brask, T. Chivers, M. L. Krahn and M. Parvez, Inorg. Chem.,
1998, 38, 290; G. G. Briand, T. Chivers and M. Krahn, Coord. Chem.
Rev., 2002, 233–234, 237.
20 K. V. Axenov, V. V. Kotov, M. Klinga, M. Leskela¨ and T. Reppo,
Eur. J. Inorg. Chem., 2004, 695; K. V. Axenov, M. Klinga, M. Leskela¨,
V. V. Kotov and T. Reppo, Eur. J. Inorg. Chem., 2004, 4702.
21 W. Deissig and H. Dietrich, Acta Crystallogr., Sect. B, 1968, 24, 108.
22 J. Koch, I. Hyla-Kryspin, R. Gleiter, T. Klettke and D. Walther,
Organometallics, 1999, 18, 4942.
23 C. E. MacBeth, J. C. Thomas, T. A. Betley and J. C. Peters, Inorg.
Chem., 2004, 43, 4645; H. Scha¨fer, D. Binder and D. Fenske, Angew.
Chem., Int. Ed. Engl., 1985, 24, 522; M. Aresta, C. F. Nobile, V. C.
Albano, E. Forni and M. Manaserro, J. Chem. Soc., Chem. Commun.,
1975, 636.
24 We define symmetrical M–P and M–N bonds to mean that both
bonds have normal bond lengths.
32 Based on a CSD (version 5.26, November 2004) search of 1703 such
compounds.
33 G. Trinquier and M. T. Ashby, Inorg. Chem., 1994, 33, 1306; W. W.
Schoeller, T. Busch and E. Niecke, Chem. Ber., 1990, 123, 272; W. W.
Schoeller, in Multiple Bonds and Low Coordination in Phosphorus,
ed. M. Regitz and O. J. Scherer, Thieme, Stuttgart, 1990, pp. 5–32.
34 D. Fenske, B. Maczek and K. Maczek, Z. Anorg. Allg. Chem., 1997,
623, 1113.
35 O. J. Scherer, R. Walter and W. S. Sheldrick, Angew. Chem., Int. Ed.
Engl., 1985, 24, 525.
36 M. J. S. Dewar, Bull. Soc. Chim. Fr., 1951, C71–79; J. Chatt and L. A.
Duncanson, J. Chem. Soc., 1953, 2939.
37 L. Weber, Eur. J. Inorg. Chem., 2000, 2425.
38 M. Veith, M. Grosser and V. Huch, Z. Anorg. Allg. Chem., 1984, 513,
89.
39 SMART V 4.043 Software for the CCD Detector System, Bruker
Analytical X-ray Systems, Madison, WI, 1995.
40 SAINT V 4.035 Software for the CCD Detector System, Bruker
Analytical X-ray Systems, Madison, WI, 1995.
41 SADABS program for absorption corrections using the Bruker CCD
Detector System, Based on: R. Blessing, Acta Crystallogr., Sect. A,
1995, 51, 33.
42 G. M. Sheldrick, SHELXS-90, Program for the Solution of Crystal
Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1990.
43 G. M. Sheldrick, SHELXL-97, Program for the Solution of Crystal
Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
44 SMART Version 4.043 Software for the CCD Detector System, Bruker
Analytical X-ray Systems, Madison, WI, 1995.
45 SHELXTL 5.10 (PC-Version), Siemens Analytical X-Ray Instru-
ments, Inc., Madison, WI, 1998.
46 SHELXTL NT Version 5.10, Program Library for Structure Solution
and Molecular Graphics, Bruker Analytical X-ray Systems, Madison,
WI, 1999.
25 G. R. Lief, C. J. Carrow, L. Stahl and R. J. Staples, Chem. Commun.,
2001, 1562.
3 3 1 8
D a l t o n T r a n s . , 2 0 0 5 , 3 3 0 7 – 3 3 1 8