Syntheses of complexes containing the novel 1,2,3-azadiphosphole and 1,2,5-azadiphosphole ring systems: Crystal and molecular structure of[Ir (η-C5Me5)(η4-(Bu(t)CPNBu(t)PCBu(t)]

Article abstract of DOI:10.1039/b004692m

The first examples of complexes containing the novel 1,2,5-azadiphosphole and 1,2,3-azadiphosphole ring systems are presented, together with the molecular structure of [Ir(η⁵-C₅Me₅)(η⁴-(Bu(t)CPNBu(t)PCBu(t))] as established by a single crystal X-ray diffraction study.

Full text of DOI:10.1039/b004692m

Syntheses of complexes containing the novel 1,2,3-azadiphosphole and
1,2,5-azadiphosphole ring systems: crystal and molecular structure of
[Ir(h5-C5Me5)(h4-(ButCPNButPCBut)]
F. Geoffrey N. Cloke,*a Peter B. Hitchcock,a John F. Nixon,*a Udo Schiemann,b Rainer Streubel*b and
D. James Wilsona
a School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, Sussex, UK BN1 9QJ
b Institut fu¨r Anorganische und Analytische Chemie der Technischen Universita¨t Braunschweig, Postfach 3329,
D-38106 Braunschweig, Germany. E-mail: r.streubel@tu-bs.de
Received (in Cambridge, UK) 13th June 2000, Accepted 21st July 2000
The first examples of complexes containing the novel
1,2,5-azadiphosphole and 1,2,3-azadiphosphole ring systems
are presented, together with the molecular structure of
[Ir(h5-C5Me5)(h4-(ButCPNButPCBut)] as established by a
single crystal X-ray diffraction study.
molecular structures of 3b and 6 were deduced by NMR
spectroscopy‡ (13C, 31P) (vide infra) and confirmed by a single
crystal X-ray diffraction study§ in the case of 6 (Fig. 1). The
31P{1H} NMR spectra of complexes 3 and 4 displayed the
expected AB-type spectra with low-field resonances for the
two-coordinated phosphorus centers and with typical magni-
tudes of phosphorus–phosphorus coupling constants (for 3 ca.
294 Hz; for 4 ca. 34 Hz). Additionally, complex 3b shows
signals in its 13C{1H} NMR spectrum at d 180.3 (m) and 196.5
Transition metal-promoted syntheses of unsaturated P-hetero-
cycles has received considerable attention in recent years in the
quest for sophisticated ligands containing sp2- and/or sp3-
hybridised phosphorus atoms in heterocyclic rings.1 Tungsten
complexes of 2H-1,2-azaphosphole,2 2H-1,3,2-diazaphos-
phole3 and 2H-1,4,2-diazaphosphole3,4 rings can be obtained
using the dual precursor potential of 2H-azaphosphirene
complexes via intermediate terminal phosphanediyl and ni-
trilium phosphane-ylide complexes, the former giving rise to 3-
and 4-membered and the latter to 5-membered P-heterocycles.
The planar, aromatic 1,2,4-azadiphosphole ring systems,
P2C2But2NR5 (R = Pri, Et, Ph, Tol, Prn, Cy, ButCH2) on the
otherhand, have recently been reported via coupling reactions
involving the phospha-alkyne, PCBut, with the imido fragment
of [TiCl2(NR)(py)3] (R = Pri, Et, Ph, Tol) or [VCl3(NR)] (R =
Pri, Prn, Cy, ButCH2) complexes.5 We now describe the
syntheses of complexes containing the previously unknown
1,2,3-azadiphosphole and 1,2,5-azadiphosphole ring systems;
we also provide first evidence for 1,2,4-azadiphosphole com-
plexes.
1
2
(dd, J(PC) 61.1 Hz, J(PC) 9.7, CNP), which were readily
assigned to the imino- and the phosphaalkene-carbon atoms
respectively. The 31P{1H} NMR spectrum of 6 displayed a
singlet (d 0.26) implying a symmetrical environment for the
two P atoms. The three signals (d 1.92, 1.48, 1.07) observed in
the 1H NMR spectrum were readily assigned to C5Me5, PCBut
and NBut respectively. Further insight into the structure of this
molecule was gained from the 13C{1H} NMR spectrum which
3
3
showed two pseudo triples (d 34.7 J(PC) 6.51 Hz, 28.7 J(PC)
7.28 Hz) in an intensity ratio of 2+1 which were assigned to the
methyl resonances of the two sets of non-equivalent tert-butyl
groups, thereby establishing the connectivity of both phospho-
rus nuclei with nitrogen.
The molecular structure of complex 6 which was confirmed
by a single crystal X-ray analysis of crystals grown from a
saturated pentane solution (250 °C), is shown in Fig. 1 together
Extending our three-component reaction concept3 towards
phospha-alkynes, we have now observed that 2H-azaphosphir-
ene complex 16 react with 1-piperidinonitrile (2 equiv.) and an
excess of ButCP7 2a or 1-AdCP8 2b (Ad = adamantyl) in
toluene at elevated temperature to give the 1,2,3-azadiphos-
phole complexes 3a,b and 1,2,4-azadiphosphole complexes
4a,b. Based on observations made earlier, cf. ref. 3 we assume
that a transiently formed C-1-piperidino-substituted nitrilium
phosphane-ylide complex react with the phospha-alkynes in [4
+ 2] cycloaddition reactions to yield the two regioisomers,
which were formed in ratios of 8+1 (3a+4a) and 3+1 (3b+4b)
respectively. Unfortunately, even using low-temperature col-
umn chromatography, only complex 3b could be separated by
extraction and subsequent crystallisation (Scheme 1).
Bergman and co-workers,9 synthesised the monomeric imido
5
5
complex [Ir(h -C5Me5)(NBut)] from [{Ir(h -C5Me5)Cl2}2] and
4 equiv. of LiNHBut in THF and described its cycloaddition
reaction with dimethyl acetylenedicarboxylate to afford the
Scheme 1 Reaction of complex 1 with 1-piperidinonitrile and phospha-
alkynes 2a,b§
structurally characterised compound [Ir(h -C5Me5){NBut-
5
4
(MeO2CCCCO2Me)2}], which contains an h -coordinated
pyrrole ring. Since phospha-alkynes, PCR, are known to behave
very like alkynes,1 we have extended this type of cyclisation
reaction and find that [Ir(h -C5Me5)(NBut)] 5 on treatment with
5
an excess of PCBut 2a in toluene at ambient temperature
4
afforded the h -ligated 1,2,5-azadiphosphole ring complex 6.¶
5
Scheme 2 Reaction of [Ir(h -C5Me5)(NBut)] 5 with the phospha-alkyne
The E.I. mass spectra† exhibited the molecular ions of 3b and
6, which are consistent with the proposed formulations. The
PCBut 2a.¶
DOI: 10.1039/b004692m
Chem. Commun., 2000, 1659–1660
This journal is © The Royal Society of Chemistry 2000
1659

Notes and references
† Satisfactory elemental analysis were obtained for complexes 3b and 6.
NMR data were recorded in [2H6]benzene solutions (295 K) at 75.5 MHz
(
13C) and 81.0 (31P), using TMS and 85% H3PO4 as standard references;
J/Hz. Selected spectroscopic data for 3, 4 and 6. 31P{1H} NMR: 3a: d 340.4
(d, J(PP) 297.1), 91.2 (d, 1J(PP) 297.1, J(PW) 211.0). 4a: d 234.1 (d, J(PP)
1
1
2
2
1
1
34.2), 107.6 (d, J(PP) 34.2). 3b: d 341.8 (d, J(PP) 296.2), 93.3 (d, J(PP)
296.2, 1J(PW) 209.5). 4b: d 232.9 (d, 2J(PP) 34.8), 105.8 (d, 2J(PP) 34.8). 3b:
13C{1H} NMR: d 2.7 [mc, br, (SiCH3)], 21.7 [mc, (CH(SiCH3)2)], 23.9 [s,
NCH2CH2CH2], 25.9 [s, NCH2CH2], 29.4 [s, Ad C3/C5/C7], 36.7 [s, Ada
C4/C6/C10], 42.9 [dd, J(PC) 10.1, J(PC) 11.8, Ad C1], 44.0 [d, 3J(PC) 14.3, Ad
C2/C8/C9], 54.7 [s, NCH2], 180.3 [mc, CNN], 196.5 [dd, 1J(PC) 61.1, 2J(PC)
9.7, CNP], 197.3 [dd, J(PC) 3.5, J(PC) 4.5, cis-CO], 198.6 [d, J(PC) 19.4 Hz,
trans-CO]. EI-MS (pos.-CI, NH3) m/z (%): 802 (80) [M]+. 6: 31P{1H}
NMR: d 0.26. 13C{1H} NMR: d 11.5 [C5(CH3)5], 28.7 [t, NC(CH3)3, 3J(PC)
3
7.28], 34.7 [pseudo-t, PCC(CH3)3, J(PC) 6.51 Hz], 36.2 [pseudo-t,
PCC(CH3)3, 2J(PC) 8.21], 95.2 [m, PCC], 94.0 [C5(CH3)5]. EI-MS m/z (%):
559 (30) [M]+.
‡ Crystal data for 6: C24H42IrNP2, M = 598.73, orthorhombic, space group
Pna21 (no. 33), a = 20.067(2), b = 14.271(3), c = 8.775(5) Å, U =
2513(2) Å3, Z = 4, Dc = 1.58 Mg m23, crystal dimensions 0.2 3 0.2 3 0.2
mm, F(000) = 1200, T = 173(2) K, Mo-Ka radiation, l = 0.71073 Å. Data
were collected on an Enraf-Nonius CAD4 diffractometer and of the total
4635 reflections measured 2151 having I > 2s(I) were used in the
calculations. The final indices (I > 2s(I)) were R1 = 0.022, wR2 = 0.049.
CCDC 182/1727. See http://www.rsc.org/suppdata/cc/b0/b004692m/ for
crystallographic files in .cif format.
5
4
Fig. 1 Molecular structure of [Ir(h -C5Me5)(h -(ButCPNButPCBut)] 6.
Selected distances (Å) and angles (°): P(1)–C(1) 1.846(7), C(2)–P(2)
1.837(11), P(1)–N 1.718(7), P(2)–N 1.733(6), C(2)–C(1) 1.427(12), Ir–
C(2) 2.161(11), Ir–C(1) 2.173(5), Ir–P(2) 2.333(2), Ir–P(1) 2.338(3),
C(18)–C(19) 1.433(14) Å. N–P(2)–C(2) 101.3(4), N–P(1)–C(1) 101.2(3),
P(1)–N–P(2) 98.9(3), C(2)–C(1)–P(1) 108.8(5), C(1)–C(2)–P(2) 109.1(7),
P(2)–N–C(11) 121.8(4), P(2)–C(2)–C(7) 118.6(7), C(1)–C(2)–C(7)
132.0(8)°. Hydrogen atoms are omitted for clarity. Displacement ellipsoids
are shown at the 50% probability level.
§ Experimental: to a solution of 2.15 g (3.5 mmol) 2H-azaphosphirene
complex 1 in 20 ml toluene was added 0.6 mL (5 mmol) 1-piperidinonitrile
and 1.4 g (14 mmol) ButCP or 2.5 g (14 mmol) 1-AdaCP. The solutions
were heated with stirring at 75–80 °C for 3 h and the volatiles removed in
vacuo (0.1 mbar). In the case of 3b, the crude product was separated by
extraction of the brown residue with light petroleum (60+40) and
crystallised from n-pentane/toluene at 220 °C; yield 2.13 g, 19%.
with principal bond lengths and angles. The IrC5Me5 fragment
is h -ligated to the 1,2,5-azadiphosphole ring resulting in the
4
nitrogen atom becoming pyramidalised and it lies out of the
plane formed by P(2)–C(2)–C(1)–P(1), (dihedral angle between
P(2)–C(2)–C(1)–P(1) and P(1)–N–P(2), 44.2(3)°). The longer
Ir–P(1)/Ir–P(2) (av. 2.335 Å) bond lengths compared with Ir–
C(2)/Ir–C(1) (av. 2.167 Å) causes the P(2)–C(2)–C(1)–P(1)
fragment to tilt away from the plane of the C5Me5 ring (dihedral
angle between P(1)–C(1)–C(2)–P(2) and C(15)–C(16)–C(17)–
C(18)–C(19), 7.7°). The C(1)–C(2) bond distance (1.427(12) Å)
5
¶ Experimental: to a stirred solution of [Ir(h -C5Me5)(NBut)] (0.370 g, 0.9
mmol) in toluene (30 ml) was added dropwise, PCBut (0.232 g, 2.3 mmol)
and the resulting black solution was allowed to stir for 24 h. The solvent was
removed in vacuo and the residue sublimed (180 °C, 1025 mbar) yielding a
white waxy solid (yield 0.205 g, 40%). Crystals suitable for X-ray analysis
were grown from a slowly cooled and concentrated pentane solution
(248 °C).
4
lies within the range expected for h -bonded systems, whereas
the P(1)–C(1) and P(2)–C(2) distances (1.846(7), 1.837(11) Å)
are considerably longer than anticipated for PNC double bonds.
This is the first structurally characterised metal complex
containing a 1,2,5-azadiphosphole derivative.
1 K. B. Dillon, F. Mathey and J. F. Nixon, Phosphorus: The Carbon Copy,
John Wiley, Chichester, 1998.
2 R. Streubel, H. Wilkens, A. Ostrowski, C. Neumann, F. Ruthe and P. G.
Jones, Angew. Chem., Int. Ed. Engl., 1997, 36, 1492.
3 H. Wilkens, F. Ruthe, P. G. Jones and R. Streubel, Eur. Chem. J., 1998,
4, 1542.
4 R. Streubel, H. Wilkens, F. Ruthe and P. G. Jones, Chem. Commun.,
1999, 2127.
5 F. G. N. Cloke, P. B. Hitchcock, J. F. Nixon, D. J. Wilson, F. Tabellion,
U. Fishbeck, F. Preuss, M. Regitz and L. Nyulaszi, Chem. Commun.,
1999, 2363.
6 R. Streubel, A. Ostrowski, S. Priemer, U. Rohde, J. Jeske and P. G.
Jones, Eur. J. Inorg. Chem., 1998, 257.
7 G. Becker, G. Gresser and W. Uhl, Z. Naturforsch., Teil B, 1981, 36,
11.
8 T. Allspach, M. Regitz, G. Becker and W. Becker, Synthesis, 1986,
31.
9 D. S. Glueck, J. Wu, F. J. Hollander and R. G. Bergman, J. Am. Chem.
Soc., 1991, 113, 2041.
It is interesting to note that Regitz and co-workers10 recently
proposed, on the basis of 31P{1H} NMR spectroscopic data, the
possible intermediacy of a 1,2,5-azadiphosphole ring system in
the metal-mediated formation of azatetraquadricyclanes from
phosphaalkynes. Complex 1, which has a formal electron count
of 18e, was found to be remarkably stable and column
chromatography (silica gel, pentane) in air resulted in only very
slight decomposition of the sample (1% loss), likewise attempts
to displace the heterocycle from iridium by carbonylation of the
metal centre proved unsuccessful.
R. S. and U. S. are grateful to the Deutsche Forschungsge-
meinschaft and the Fonds der Chemischen Industrie for
financial support. F. G. N. C., J. F. N. and D. J. W. thank the
EPSRC for their continuing support for phospha-organome-
tallic chemistry.
10 F. Tabellion, A. Nachbauer, S. Leininger, C. Peters, F. Preuss and M.
Regitz, Angew. Chem., Int. Ed., 1998, 76, 1223.
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