Synthesis and solid-state structure of a metal complex of a diphosphineimine

Article abstract of DOI:10.1002/anie.200462588

(Figure Presented) A stabilizing influence: Heterocyclic diaminophosphines can stabilize diphosphineimines sufficiently to allow the preparation of metal complexes. A kinetically stable diphosphineimine is isolated and its coordination chemistry investiga

Full text of DOI:10.1002/anie.200462588

Angewandte
Chemie
Phosphazanes
Synthesis and Solid-State Structure of a Metal
Complex of a Diphosphineimine**
Leonard E. Anagho, Jamie F. Bickley,
Alexander Steiner,* and Lothar Stahl*
Dedicated to Professor Michael Veith
on the occasion of his 60th birthday
Diphosphineimine compounds of the general structure R2P-
[1]
=
PR2 NR [A; Eq. (1)] have been known for some time, but
the pronounced tendency of these molecules to rearrange to
the isomeric diphosphinoamines B has hampered the devel-
opment of their chemistry and relegated them to structural
=
curiosities. For example, the diphosphineimine iPr2P( N-
Ph)PEt2 was reported to completely rearrange to diphosphi-
noamine iPr2P-NPh-PEt2 in the presence of electrophiles or
nucleophiles.[1d] Similarly, the attempted synthesis of a
=
palladium dichloride complex of Ph2P-PPh2 N{C6H4(o-CN)}
only furnished the diphosphinoamine complex cis-[PdCl2{(o-
CN)C6H4N(PPh2)2}].[2b] Diphosphinoamines, of course, have a
[*] J. F. Bickley, Dr. A. Steiner
Department of Chemistry
University of Liverpool
Crown Street, Liverpool, L697ZD (UK)
Fax: (+44)151-794-3588
E-mail: a.steiner@liverpool.ac.uk
L. E. Anagho, Professor Dr. L. Stahl
Department of Chemistry
University of North Dakota
Grand Forks, ND 58202 (USA)
Fax: (+1)701-777-2331
E-mail: lstahl@chem.und.edu
[**] The Chevron Phillips Chemical Company (L.S.) and the EPSRC
(A.S.) are acknowledged for financial support.
Angew. Chem. Int. Ed. 2005, 44, 3271 –3275
DOI: 10.1002/anie.200462588
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3271

Communications
long history as ligands for transition metals and as stable
molecules in their own right.[3] They have been used in late-
transition-metal homogeneous polyolefin catalysis because
they impart a greater stability to the complexes than the more
conventional diimines.[4,5] The asymmetric diphosphineimines
have both electron-donating imine and electron-accepting
phosphine functionalities, as exemplified in the ylidic form C,
which may combine the best features of diimines and
diphosphines and, thus, be superior ligands. Furthermore,
these hemilabile phosphorus(iii)/phosphorus(v) molecules
should have applications in other important catalytic trans-
formations, such as hydroformylation
and hydrogenation reactions,[6] thus
making the search for stable diphos-
phineimines an area of interest.
Herein, we report the synthesis
and solid-state structure of the first
diphosphineimine that is kinetically
stable enough to allow the isolation of
Figure 1. Solid-state structure of 1 (hydrogen atoms have been omit-
ted). Selected bond lengths [ꢀ] and angles [8]: P(1)-P(2) 2.2092(7),
P(1)-N(1) 1.5568(15), P(1)-N(2) 1.6761(15), P(1)-N(3) 1.6804(16);
N(1)-P(1)-P(2) 97.12(6), N(2)-P(1)-N(3) 86.67(8), C(61)-P(2)-P(1)
104.01(6), C(51)-P(2)-P(1) 106.44(7), C(51)-P(2)-C(61) 102.84(8).
a transition-metal complex. Our investigations also furnished
the first solid-state structure of a diphosphineimine sulfide
and of a metal complex in which the diphosphineimine has
isomerized to the corresponding diphosphinoamine, thereby
providing the rare opportunity to compare coordination
compounds of both structural isomers.
Diphosphineimines are occasionally formed when amido-
phosphines are treated with halophosphines in the attempted
synthesis of diphosphinoamines.[1,2] Symmetrical diphosphi-
nediimines can also be synthesized by the oxidative coupling
of amidophosphines.[7] The addition of {Me2Si(m-NtBu)2PN-
Ph}Li to Ph2PCl in THF resulted in the nucleophilic attack of
{Me2Si(m-NtBu)2PNPh}À on the phosphorus atom of Ph2PCl
ranged from 2.2379(16) to 2.2498(18) ꢀ and from 1.571(3) to
1.578(3) ꢀ, respectively.[2] These bond-length contractions
may be a reflection of the greater stability of 1, which proved
to be unusually thermally robust: it exhibited no tendency to
decompose or rearrange to the corresponding diphosphino-
amine on heating to reflux in toluene (24 hours).
Diphosphineimines are normally kinetic products that
isomerize to the corresponding diphosphinoamines during
attempted chemical transformations and metal coordina-
tion.[1d,2] In notable contrast, the reaction of 1 with elemental
sulfur produced the colorless compound 2 as the only product
[Eq. (3)]. To the best of our knowledge, this diphosphine-
=
to afford Me2Si(m-NtBu)2P( NPh)PPh2 (1) as the only
phosphorus-containing product [Eq. (2)]. Treatment of
(Ph2PNPh)Li with Me2Si(m-NtBu)2PCl,[8] in contrast, gave
only an intractable mixture.
imine sulfide is only the second of its kind to have been
reported and the first to have been characterized by X-ray
structural analysis.[1c]
À
A direct P P bond in 1 was suggested by an AB pattern of
doublets in the 31P NMR spectrum at d = 49.9 and 44.9 ppm,
respectively (J(P,P) = 182 Hz), but later findings showed that
coupling constants of this magnitude are not diagnostic for
À
The solid-state structure of 2 confirmed that the P P bond
had remained intact during the reaction (Figure 2). The
molecule adopted a staggered conformation to minimize
nonbonding interactions: the bulkiest substituent on one
phosphorus atom is in a gauche conformation with the
smallest substituents on the opposite phosphorus atom. This
conformation renders 2 almost perfectly mirror-symmetric,
with the phosphorus, sulfur, silicon, and nitrogen (imino)
atoms all lying in a noncrystallographic mirror plane. The
À
direct P P bonds in these systems (see below). A single-
crystal X-ray analysis of the colorless product confirmed the
assumed structure of 1.
Figure 1 shows one of the two independent molecules,
whose metric parameters are identical within experimental
À
=
uncertainties. The P P and P N bonds (2.2092(7) and
1.5568(15) ꢀ, respectively) are somewhat shorter than those
of the previously characterized diphosphineimine of the type
=
=
comparatively short P S and P N(imino) bonds (1.9563(8)
and 1.5507(19) ꢀ, respectively) form a torsion angle of
=
(o-X)C6H4N PPh2-PPh2 (X = CF3, Ph, CN) in which they
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Figure 2. Solid-state structure of 2 (hydrogen atoms have been omit-
ted). Selected bond lengths [ꢀ] and angles [8]: P(1)-P(2) 2.2332 (7),
P(1)-N(1) 1.5507(19), P(2)-S(1) 1.9563(8), P(1)-N(2) 1.6684(18), P(1)-
N(3) 1.6677(17); N(1)-P(1)-P(2) 99.72(7), P(1)-P(2)-S(1) 110.71(3),
N(2)-P(1)-N(3) 87.54(9), C(41)-P(2)-C(51) 103.19(10).
Figure 3. Solid-state structure of 3. (Only one of the two independent
molecules is shown; the toluene molecule and the hydrogen atoms
have been omitted.) Selected bond lengths [ꢀ] and angles [8]: Mo(1)-
P(2) 2.4915(9), Mo(1)-N(1) 2.321(2), Mo(1)-C(1) 2.032(3), Mo(1)-C(2)
1.946(3), Mo(1)-C(3) 1.976(3), Mo(1)-C(4) 2.042(3), P(1)-P(2)
2.2362(11), P(1)-N(1) 1.599(2), P(1)-N(2) 1.661(2), P(1)-N(3)
1.669(2); N(1)-P(1)-P(2) 91.29(9), Mo(1)-N(1)-P(1) 111.16(11), Mo(1)-
P(2)-P(1) 86.99(3).
À
approximately 1798 about the slightly elongated P P bond
(2.2332(7) ꢀ).
Compound 1 did not isomerize on heating and oxidation,
which encouraged us to explore its coordination chemistry.
Treatment of 1 with cis-[Mo(CO)4(piperidine)2] in THF and
heating to reflux afforded the light-yellow molybdenumte-
tracarbonyldiphosphineimine [3; Eq. (4)]. The infrared spec-
the axial bonds are significantly longer than the equatorial
À
ones. Notably, the Mo CO bond trans to the best electron
donor, namely the imino nitrogen atom, is the shortest one of
À
the four Mo CO bonds. The bond parameters within the
diazasilaphosphetidine are unremarkable and similar to those
in related compounds.[11]
À
À
Despite the direct P P bond, the P P coupling constant of
3 is only a third of the magnitude (ca. 69 Hz) as that of 1, for
reasons that are not yet clear.
Although the surprising thermal and chemical stabilities
of 1 suggested that this diphosphineimine might be thermo-
dynamically stable with respect to its isomer, its interaction
with nickel salts proved otherwise. Compound 1 was treated
with
cis-[NiBr2(diglyme)]
(diglyme = diethyleneglycol
dimethyl ether) to furnish the diphosphinoaminenickel
dibromide complex 4 as the only product, even at room
temperature [Eq. (5)].
trum exhibited three n(CO) bands at 2010, 1890, and
1850 cmÀ1, respectively, as is common for many molybde-
numtetracarbonyl complexes with local C2v symmetry. These
carbonyl stretching vibrations are lower than for most
complexes of the cis-[Mo(CO)4(PP)] type (PP refers to
alkanediyl- or amine-bridged bisphosphines),[9] thus suggest-
ing that 1 is the expected electron-rich chelating ligand.
Complex 3, which crystallizes as a monotoluene solvate
with two independent molecules in the asymmetric unit, was
analyzed by single-crystal X-ray analysis. The spirocyclic
molecule is composed of two almost-planar four-membered
rings (Figure 3), but the trapezoidal Mo-P-P-N ring is much
more irregular than the rhombus of the diazasilaphospheti-
À
À
dine. Thus, the cis-configured Mo P and Mo N bonds are
The diamagnetism of the compound had indicated a
square-planar coordination geometry about the nickel ion,
and this arrangement was confirmed by the solid-state
structure of 4 (Figure 4). The two planes defined by the
nickel and phosphorus and the nickel and bromide atoms,
respectively, are nearly coplanar (dihedral angle = 68) and
perpendicular to the diazasilaphosphetidine ring. Despite the
À
=
2.4915(9) and 2.321(2) ꢀ, respectively, while the P P and P
N bond lengths are 2.2362(11) and 1.599(2) ꢀ, respectively.
À
The Mo P bond length is similar to those in the related cis-
[Mo(CO)4(PP)] and cis-[Mo(CO)4(PN)] complexes,[9,10] but
2
À
=
the Mo N and P N bonds are rather long for an sp -
hybridized nitrogen atom,[10] possibly because of ring strain.
À
À
There is a distinct asymmetry in the Mo CO bond lengths as
dissimilar substituents on both phosphorus atoms, the Ni P
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diazasilaphosphetidine give this particular diphosphineimine
its unique stability remains to be seen. The potential rewards
for finding stable diphosphineimines are clear, and we are
currently exploring the reaction chemistry of 1 to understand
the properties of these intriguing molecules.
Experimental Section
1: A solution of Me2Si(m-NtBu)2PN(H)Ph[11a] (11.2 mmol) in hexanes
(20 mL) was treated dropwise at 08C with nBuLi (11.3 mmol) in
hexanes (15 mL). The reaction mixture was heated at reflux for 1 h,
cooled to RT, and then treated dropwise with a solution of Ph2PCl
(11.2 mmol) in hexanes. This caused a white precipitate to form. The
mixture was stirred overnight and then filtered to afford a colorless,
clear solution from which colorless, rectangular crystals separated
upon cooling; yield: 3.69 g (64.9%). M.p. 170–1728C; elemental
analysis (%) calcd for C28H39N3P2Si: C 66.24, H 7.74, N 8.28; found: C
Figure 4. Solid-state structure of 4 (the THF molecule and the hydro-
gen atoms have been omitted). Selected bond lengths [ꢀ] and angles
[8]: Ni(1)-P(1) 2.1270(10), Ni(1)-P(2) 2.1151(10), Ni(1)-Br(1)
2.3481(6), Ni(1)-Br(2) 2.3302(6), P(1)-N(1) 1.714(3), P(2)-N(1)
1.714(3), P(1)-N(2) 1.658(3), P(1)-N(3) 1.670(3); P(1)-N(1)-P(2)
97.17(14), P(1)-Ni(1)-P(2) 74.62(4), Br(1)-Ni(1)-Br(2) 98.07(2), N(2)-
P(1)-N(3) 87.67(15).
1
66.01, H 7.84, N 8.11; H NMR (500.1 MHz, CD2Cl2, 218C): d = 7.94
(m, 4H, Ph), 7.37 (m, 6H, Ph), 7.15 (t, J = 7.1 Hz, 2H, Ph), 7.06 (d, J =
8.1 Hz, 2H, Ph), 6.72 (t, J = 7.1 Hz, 1H, Ph), 1.13 (s, 18H, tBu), 0.56 (s,
3H, Me), 0.20 ppm (s, 3H, Me); 31P[1H] NMR (202.5 MHz, CD2Cl2,
218C): d = 2.66 (d, J(P,P) = 182.4 Hz), À30.82 ppm (d, J(P,P) =
182.8 Hz).
À
À
bonds are almost equidistant (the Ni P1 and Ni P2 bond
lengths are 2.1270(10) and 2.1151(10) ꢀ) and are slightly
shorter than those in the related cis-[NiBr2{Ar2PN(Me)PAr2}]
2: Compound 1 (0.235 g, 0.486 mmol) and elemental sulfur
(0.016 g, 0.50 mmol) were dissolved in THF (20 mL), and the mixture
was heated at reflux for 3 h. Following removal of THF, the ensuing
white powder was dissolved in toluene to afford colorless crystals
upon cooling; yield: 0.213 g (81.2%). M.p. 202–2068C; elemental
analysis (%) calcd for C28H39N3P2SSi: C 62.31, H 7.28, N 7.79; found:
C 61.94, H 7.35, N 7.72; 1H NMR (500.1 MHz, C6D6, 218C): d = 9.178
(dd, J = 12.4, 8.0 Hz, 4H, Ph), 7.43 (d, J = 8.3 Hz, 2H, Ph), 7.34 (t, J =
7.5 Hz, 2H, Ph), 7.11 (td, J = 8.0, 3.2 Hz, 2H, Ph), 6.99 (t, J = 7.4 Hz,
2H, Ph), 6.95 (t, J = 7.3 Hz, 1H, Ph), 0.94 (s, 18H, tBu), 0.83 (s, 3H,
Me), 0.38 ppm (s, 3H, Me); 31P[1H] NMR (202.5 MHz, CD2Cl2,
218C): d = 10.94 (d, J(P,P) = 238.8 Hz), À8.40 ppm (d, J(P,P) =
238.8 Hz).
À
(Ar= o-tBuC6H4), which features symmetrical Ni P bonds
(2.1611(6) ꢀ).[4a] This latter nickel complex, with its bulky
bis(diphenylphosphine)amine ligand, was shown to be a very
good polyolefin catalyst, and the more electron-rich 4 may
exhibit a similar reactivity.
The 31P NMR spectrum gave no indication that the
isomerization of 1 had occurred as it showed two doublets
at d = 55.8 and 43.9 ppm for the P1 and P2 atoms, respectively,
with larger coupling constants (J(P,P) = 137 Hz) than those
seen in 3. Thus, 31P NMR spectroscopy, which is usually
considered a diagnostic tool, was neither reliable for predict-
ing the connectivity in these phosphorus–nitrogen compounds
nor did it show a correlation between the coupling constants
3: Compound 1 (0.250 g, 0.500 mmol) and cis-[Mo(CO)4(piper-
idine)2] (0.195 g, 0.500 mmol) were dissolved in THF (50 mL) and the
mixture was heated at reflux for 3 h. A yellow powder precipitated
upon cooling, which was recrystallized from toluene to afford light-
yellow crystals; yield: 0.263 g (65.1%). M.p. 1768C (decomp);
elemental analysis (%) calcd for C39H47MoN3O4P2Si: C 57.99, H
À
and the P P bond lengths. These results are in keeping with
earlier studies that showed large and variable two-bond P P
coupling constants in diphosphinoamines that ranged from 15
À
1
to 665 Hz.[12]
5.86, N 5.20; found: C 58.04, H 5.98, N 5.34; H NMR (500.1 MHz,
CD2Cl2, 218C): d = 8.09 (m, 4H, Ph), 7.52 (s, 6H, Ph), 7.39 (t, J =
7.6 Hz, 2H, Ph), 7.22 (m, 4H, Ph), 6.91 (t, J = 7.3 Hz, 1H, Ph), 2.34 (s,
3H, Me), 0.84 (s, 21H, tBu, Me), 0.66 ppm (s, 3H, Me); 31P[1H] NMR
(202.5 MHz, CD2Cl2, 218C): d = 49.93 (d, J(P,P) = 69.5 Hz),
44.97 ppm (d, J(P,P) = 69.0 Hz); 13C[1H] NMR (CD2Cl2),
121.5 MHz, 218C): d = 221.4 (s, COeq), 218.3 (d, J = 32.9 Hz, COeq),
210.2 (d, J = 8.5 Hz, COax), 132.8 (d, J = 26.4 Hz, Ph), 131.9 (s, Ph),
129.6 (s, Ph), 128.9 (s, Ph), 126.1 (s, Ph), 122.4 (s, Ph), 32.4 (s, tBu), 5.0
(s, Me), 4.4 ppm (s, Me); IR (nujol): n˜ = 2010.4 (s), 1889.9 (vs),
1850.4 cmÀ1 (vs).
4: A suspension of cis-[NiBr2(diglyme)] (0.321 g, 0.912 mmol) in
THF (10 mL) was treated dropwise with a solution of 1 (0.398 g,
0.816 mmol) in THF (25 mL) at RT. The ensuing orange mixture
slowly turned red and was stirred overnight. The dark red–brown
solution was filtered through a medium-porosity frit and stored in a
freezer. Several crops of red–brown, needle-shaped crystals formed
upon cooling; yield: 0.369 g (59.0%). M.p. 273–2828C; elemental
analysis (%) calcd for C32H47 Br2N3NiOP2Si: C 48.15, H 5.93, N 5.26;
found: C 47.91, H 5.98, N 5.23; 1H NMR (500.1 MHz, CD2Cl2, 218C):
d = 8.11 (dd, J = 12.4, 7.9 Hz, 4H, Ph), 7.77 (s, 2H, Ph), 7.49 (s, 4H,
Ph), 7.23 (s, 4H, Ph), 7.01 (s, 3H, Ph), 3.58 (s, 4H, THF), 1.85 (s, 4H,
THF) 1.50 (s, 18H, tBu) 0.78 (s, 3H, Me), 0.401 ppm (s, 3H, Me);
Given the catalytic activity of nickel and the inertness of
the [Mo(CO)4] moiety, it is not surprising that 1 isomerized in
the presence of NiBr2 even at room temperature, although it
was unaffected by [Mo(CO)4] when they were heated
together to reflux in THF. However, it is surprising that the
soft {Mo(CO)4} fragment is coordinated by the hard nitrogen
atom, although the harder NiBr2 moiety is coordinated by the
soft phosphorus atoms. This disparity further underlines the
kinetic control demonstrated in Equations (4) and (5). Our
results also suggest that attempts to stabilize diphosphine-
imines with certain Group 10 metal compounds, as had been
done previously, may cause isomerization instead.[2a] The ease
with which 1 isomerizes in the presence of NiBr2 clearly rules
out its use as a diphosphineimine ligand in Group 10 metal
catalysis.
In summary, the syntheses and solid-state structures of a
kinetically stable diphosphineimine, its molybdenum com-
plex, and its sulfide analogue have been reported. Whether
the electronic properties or the cyclic structure of the
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Chemie
31P{1H} NMR (202.5 MHz, CD2Cl2, 218C): d = 55.81 (d, J(P,P) =
137.0 Hz), 43.88 ppm (d, J(P,P) = 137.0 Hz).
Brunner in Applied Homogeneous Catalysis with Organometallic
Compounds (Eds.: B. Cornils, W. A. Herrmann), VCH, Wein-
heim, 1996, pp. 201 – 216.
Crystal data for 1, 3, and 4 were collected on a Bruker Smart
Apex CCD and those for 2 on a Stoe IPDS diffractometer using
graphite monochromated MoKa radiation (l = 0.71069 ꢀ). The struc-
tures were solved with direct methods and refined by full-matrix least-
squares against F2 using the SHELXTL program.
[7] a) J. Ellermann, P. Gabold, F. A. Knoch, M. Moll, A. Schmidt, M.
Schꢃtz, Z. Naturforsch. B 1996, 51, 201; b) P. Braunstein, R.
Hasselbring, A. Tiripicchio, F. Ugozzoli, J. Chem. Soc. Chem.
Commun. 1995, 37.
[8] a) M. Veith, M. Grosser, V. Huch, Z. Anorg. Allg. Chem. 1984,
513, 89; b) M. Veith, B. Bertsch, V. Huch, Z. Anorg. Allg. Chem.
1988, 599, 73.
¯
Crystal data for 1: C28H39N3P2Si, triclinic, space group P1 (no. 2),
a = 12.1274(7), b = 15.3090(9), c = 16.1150(9) ꢀ, a = 81.0053(11), b =
72.7523(10), g = 82.8704(10)8, V= 2812.6(3) ꢀ3, Z = 4, 1calcd
=
1.199 gcmÀ3, T= 100 K, 2qmax = 508, m = 0.218 mmÀ1, 13774 reflec-
tions measured, of which 9783 were unique (Rint = 0.0632), final
R indices: R1 = 0.0365, (I > 2s(I)), wR2 = 0.0904 (all data).
Crystal data for 2: C28H39N3SiP2S, monoclinic, space group P21/n
(no. 14), a = 9.0459(10), b = 9.7581(9), c = 33.246(4) ꢀ, b =
93.604(13)8, V= 2928.8(5) ꢀ3, Z = 4, 1calcd = 1.224 gcmÀ3, T= 200 K,
2qmax=488, m = 0.282 mmÀ1, 18452 reflections measured, of which 4522
were unique (Rint = 0.0502), final R indices: R1 = 0.0370 (I > 2s(I)),
wR2 = 0.0997 (all data).
[9] a) S. L. Mukerjee, S. P. Nolan, C. D. Hoff, R. Lopez de la Vega,
Inorg. Chem. 1988, 27, 81; b) M. S. Balakrishna, T. K. Prakasha,
S. S. Krishnamurthy, U. Siriwardane, N. S. Hosmane, J. Organo-
met. Chem. 1990, 390, 203; c) I. Bernal, G. M. Reisner, G. D.
Dobson, C. B. Dobson, Inorg. Chim. Acta 1986, 121, 199.
[10] D. Walther, S. Liesicke, L. Bꢂttcher, R. Fischer, H. Gꢂrls, G.
Vaughan, Inorg. Chem. 2003, 42, 625.
[11] a) D. C. Haagenson, D. F. Moser, L. Stahl, R. J. Staples, Inorg.
Chem. 2002, 41, 1245; b) O. J. Scherer, M. Pꢃttmann, C. Krꢃger,
G. Wolmershꢁuser, Chem. Ber. 1982, 115, 2076.
Crystal data for 3: C39H47MoN3O4P2Si, monoclinic, space group
P21/n (no. 14), a = 19.2663(16), b = 11.4770(10), c = 36.889(3) ꢀ, b =
[12] I. J. Colquhoun, W. McFarlane, J. Chem. Soc. Dalton Trans. 1977,
1674.
103.3213(14)8, V= 7937.3(12) ꢀ3, Z = 8, 1calcd = 1.352 gcmÀ3
, T=
100 K, 2qmax = 508, m = 0.483 mmÀ1, 40213 reflections measured, of
which 13998 were unique (Rint = 0.0500), final R indices: R1 = 0.0401
(I > 2s(I)), wR2 = 0.1006 (all data).
Crystal data for 4: C32H47Br2N3NiOP2Si, monoclinic, space group
P21/c (no. 14), a = 18.3666(13), b = 12.1328(8), c = 16.1095(11) ꢀ, b =
90.4750(14)8, V= 3589.7(4) ꢀ3, Z = 4, 1calcd = 1.477 gcmÀ3, T= 100 K,
2qmax=508, m = 2.918 mmÀ1, 18367 reflections measured, of which 6325
were unique (Rint = 0.0375), final R indices: R1 = 0.0351 (I > 2s(I)),
wR2 = 0.0859 (all data).
CCDC-254120–254123 (1–4, respectively) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Received: November 12, 2004
Published online: April 21, 2005
Keywords: heterocycles · molybdenum · N,P ligands · nickel ·
.
phosphazanes
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