Selective phosphoramidite cleavage as a route to novel chiral and achiral pentacoordinated nickel(II) PNP pincer complexes

Article abstract of DOI:10.1002/ejic.200600498

Treatment of NiBr₂(DME) (DME = 1,2-dimethoxyethane) or anhydrous NiBr₂ with 2 equiv. of PNP pincer ligands featuring phosphoramidites in CH₂Cl₂ yields the novel neutral pentacoordinate complexes [Ni(PNP){κ¹

Full text of DOI:10.1002/ejic.200600498

FULL PAPER
DOI: 10.1002/ejic.200600498
Selective Phosphoramidite Cleavage as a Route to Novel Chiral and Achiral
Pentacoordinated Nickel(II) PNP Pincer Complexes
David Benito-Garagorri,[a] Kurt Mereiter,[b] and Karl Kirchner*[a]
Keywords: Nickel complexes / Tridentate ligands / Square-pyramidal complexes / Hydrolysis
Treatment of NiBr2(DME) (DME = 1,2-dimethoxyethane) or
ite ligand [R2P=O]–, while a second PNP ligand remains in-
anhydrous NiBr2 with 2 equiv. of PNP pincer ligands featur- tact and is coordinated in a κ3-(P,N,P) fashion. The X-ray
ing phosphoramidites in CH2Cl2 yields the novel neutral
pentacoordinate complexes [Ni(PNP){κ1(P)-R2P=O}Br]. Over
the course of this reaction the P–N bonds of the phosphoram-
idite units of one PNP ligand are selectively cleaved due to
hydrolysis affording an anionic κ1-(P)-coordinated phosphin-
structure of one [Ni(PNP){κ1(P)-PR2=O}Br] complex has been
determined.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
recently designed an alternative and versatile modular ap-
proach for the high-yield synthesis of a new generation of
tridentate PNP pincer-type ligands based on 2,6-diami-
nopyridine and R2PCl. The latter may contain both bulky
and/or electron-rich dialkylphosphanes as well as various
Tridentate PNP ligands in which the central pyridine-
based ring donor contains –CH2PR2 substituents in the two
ortho positions are widely utilized ligands in transition
metal chemistry (e.g., Fe, Ru, Rh, Ir, Pd, Pt).[1–10] We have
Scheme 1.
[a] Institute of Applied Synthetic Chemistry, Vienna University of P–O bond containing achiral and chiral phosphite units de-
rived from diols or amino alcohols (Scheme 1).[11] With this
Technology,
Getreidemarkt 9, 1060 Vienna, Austria
synthetic route it is possible to modify both electronic, ste-
ric, and stereochemical parameters of the PNP ligands in a
simple and straightforward manner avoiding tedious multi-
step syntheses and expensive starting materials.
Fax: +43-1-58801-16399
E-mail: kkirch@mail.zserv.tuwien.ac.at
[b] Institute of Chemical Technologies and Analytics, Vienna Uni-
versity of Technology,
Getreidemarkt 9, 1060 Vienna, Austria
4374
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Nickel(II) PNP Pincer Complexes
FULL PAPER
Several of these new PNP ligands have recently been suc-
cessfully applied to the synthesis of square-planar NiII,
PdII, and PtII PNP complexes as shown in Scheme 2.[11]
While in the case of palladium and platinum there were no
limitations as to the nature of the PNP ligands, surprisingly
with nickel the synthesis of square-planar PNP complexes
was limited to the alkyl- and aryl-substituted phosphane
ligands 1a–c, which lack P–O bonds. In the particular case
of phosphite ligands hydrolysis of the P–N bond(s) took
place presumably because of the presence of small amounts
of water in the solvents leading to the formation of decom-
position products. It has to be noted that indeed in some
instances PIII–N bonds turned out to be sensitive towards
Scheme 3.
All complexes have been characterized by a combination
acid- or base-catalyzed hydrolysis during complexation re- of elemental analysis and H, 13C{1H}, and 31P{1H} NMR
actions.[12] In this paper we utilize one such decomposition spectroscopy. Most diagnostic is the 31P{1H} NMR spec-
pathway as a selective high-yield synthetic route to obtain trum exhibiting an A2X pattern with a doublet in the range
novel pentacoordinated Ni PNP complexes featuring chiral of δ = 116–147 ppm, assignable to the intact PNP ligand,
and achiral PNP ligands together with κ1-(P)-coordinated and a triplet in the range of δ = 74–87 ppm, assignable to
1
phosphinite ligands R2P=O–.
the κ1-(P)-coordinated phosphinite ligand R2P=O–. The JPP
coupling constant ranges from 90 to 115 Hz.
In order to unequivocally establish the ligand arrange-
ment around the metal center, the structure of 2i (in the
form of 2i·MeOH) has been determined by X-ray crystal-
lography. A structural view is depicted in Figure 1 with se-
lected bond lengths and angles given in the caption. The
nickel atom exhibits a square-pyramidal coordination with
the Br atom in the apical position. The diphenylphosphinite
ligand is clearly coordinated through the lone-pair at the P
atom rather than through the oxygen lone-pairs. The PNP
ligand is coordinated in the typical meridional κ3-(P,N,P)
fashion. Nickel pentacoordination is rare in organometallic
chemistry and only about 9% of all complexes adopt this
coordination number of which about half belong to the tri-
gonal-bipyramidal and the rest to the square-pyramidal
type (Cambridge Structural Data base, CSD, version 5.27,
release 2006).[14] Only one compound was found in this
Scheme 2.
Results and Discussion
Treatment of NiBr2(DME) (DME = 1,2-dimethoxy- database with a square-pyramidal Ni(PNP)(P)Br coordina-
ethane)[13] with 1 equiv. of the PNP ligands 1e, (S,S)-1g, tion, however, with the Br atom in the basal and the N
(R,R)-1h, (S,S)-1i, and (S,R)-1j (see Scheme 1) in CH2Cl2 atom in the apical position.[15] Another example with a co-
at room temperature for 16 h afforded the novel neutral ordination related to 2i·MeOH is dibromo{bis[2-(diphenyl-
pentacoordinate complexes [Ni(PNP){κ1(P)-PR2=O}Br] phosphanyl)ethyl]amine}nickel(II)[16] having a Ni(PNP)Br2
(2e,g–j) (Scheme 3). The isolated yields were typically less square pyramid with a basal Ni–Br bond of 2.33 Å and an
than 50%. There was no evidence for the formation of other apical Ni–Br bond of 2.70 Å, whereas in 2i·MeOH the latter
products such as square-planar complexes of the type measures 2.54 Å on average for the two independent com-
[Ni(PNP)Br]Br. The isolated yields of 2e,g–j could be signif- plexes.
icantly improved up to 89% when NiBr2(DME) was treated
Over the course of this reaction, the P–N bonds of one
with Ն1.5 equiv. of PNP ligand in CH2Cl2 as the solvent PNP ligand were selectively cleaved to afford a complex
for 16 h. The same reaction took place if anhydrous NiBr2 with one anionic phosphinite ligand PR2=O– and one intact
was treated with 2 equiv. of the respective PNP ligands in κ3-(P,N,P)-coordinated PNP ligand. Only a few examples
CH2Cl2 in the presence of 1 equiv. of DMSO (or DMF). of mononuclear complexes with a single PR2=O– ligand are
The addition of these solvents resulted in immediate dissol- reported in the literature including [RuCp{=C(CH2Ph)-
ution of the otherwise insoluble nickel precursor ac- NHPh}(PPh2NHPh){κ1(P)-PPh2=O}],[17]
companied by a color change of the solution from colorless (NC-9-anthracenyl){κ1(P)-PPh2=O}],[18]
[Pt(PPh3)(Ph)-
and HNEt3-
to bright orange indicating the formation of 2e,g–j. It has [W(CO)5{κ1(P)-PPh2=O}].[19] However, in many cases phos-
to be emphasized that DMSO does not participate in the phinite ligands are found in conjunction with the corre-
reaction as an oxygen-transfer agent but merely increases sponding phosphinous acids PR2OH to form R2P–O–
the solubility of the stated materials. Under these condi- H···O=PR2 moieties with very strong and almost symmetric
tions the reaction time could be reduced to 1 h.
hydrogen bonds of O···O distances as low as 2.40 Å.[20–22]
Eur. J. Inorg. Chem. 2006, 4374–4379
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D. Benito-Garagorri, K. Mereiter, K. Kirchner
FULL PAPER
Figure 1. Structural view of [Ni(PNP-HBz){κ1(P)-HBz-P=O}Br] (2i·CH3OH) (second independent Ni complex, C-bonded H atoms and
CH3OH omitted for clarity). Selected bond lengths [Å] and bond angles [°]: Ni(1)–N(1) 1.913(8), Ni(1)–P(1) 2.144(3), Ni(1)–P(2) 2.114(3),
Ni(1)–P(3) 2.132(6), Ni(1)–Br(1) 2.535(4); P(1)–Ni(1)–P(2) 157.6(3), N(1)–Ni(1)–P(3) 163.6(4), Br(1)–Ni(1)–N(1) 97.1(4), Br(1)–Ni(1)–
P(1) 98.7(2), Br(1)–Ni(1)–P(2) 101.8(2), Br(1)–Ni(1)–P(3) 99.2(2).
A proposed and plausible mechanism for the formation aminopyridine are 2.16 and 2.90 (NH2 protonation), and
of 2e,g–j supported by 1H and 31P{1H} NMR spectroscopic 7.22 (protonation of the pyridine nitrogen atom)].[24]
studies is depicted in Scheme 4. NMR monitoring of the
In line with the observed stoichiometry (2 equiv. of nickel
reaction of NiBr2(DME) with varying amounts of PNP- salt requires 3 equiv. of PNP ligand for quantitative conver-
BIPOL (1e) ranging from 0.8 to 4 equiv. in CD2Cl2 revealed sion), despite the absence of other detectable intermediates,
in all cases the formation of an intermediate species that the reaction may be initiated by the formation of the cat-
exhibits a characteristic A2X pattern in the 31P{1H} NMR ionic square-planar [Ni(PNP)Br]+ complex A. Nucleophilic
spectrum with a doublet centered at δ = 145.7 ppm and a attack of water at one of the two electrophilic phosphorus
triplet centered at δ = 122.4 ppm (JPP = 109.8 Hz). This atoms of the coordinated PNP ligand leads to P–N bond
pattern is consistent with a square-pyramidal five-coordi- cleavage affording B. This compound reacts readily with an-
nate species D where, in contrast to the final product 2e, other PNP ligand to afford D. Thereby the monophosphan-
the phosphinite ligand is coordinated in the apical position ylated 2,6-diaminopyridine ligand C is released, which in
and the Br atom in a basal position. This intermediate turn reacts with NiBr2(DME) to give complex E adopting
isomerizes at room temperature within 16 h to afford quan- either a square-planar or tetrahedral geometry. The latter
titatively the final product 2e exhibiting a doublet centered reacts again with water to give F. The 2,6-diaminopyridine
at δ = 145.8 ppm and a triplet centered at δ = 95.4 ppm (JPP ligand is readily replaced by the tridentate PNP ligand to
= 104.2 Hz). Surprisingly, in all cases there was no evidence yield D with concomitant release of 2,6-diaminopyridine in
for the formation of any additional phosphorus-containing the form of its pyridinium cation G.
species as a result of PNP decomposition. In fact, if
Additional evidence for intermediate B comes from the
NiBr2(DME) was treated with 0.8 equiv. of 1e, complex 2e fact that a similar square-planar palladium chloride com-
was cleanly formed after 16 h but the conversion was not plex, viz. [Pd{κ2(P,N)-NH2-PN-BIPOL}{κ1(P)-BIPOL-
quantitative and substantial amounts of the unreacted P=O}Cl] (4), was obtained during an attempt to obtain
poorly soluble nickel precursor remained in the NMR tube. crystals of [Pd(PNP-BIPOL)Cl]Cl (3) (Scheme 5). Small
If NiBr2(DME) was treated with 1.5 equiv. of 1e, complete amounts of pale-yellow crystals of 4 were repeatedly formed
consumption of both NiBr2(DME) and 1e took place, while by slow solvent evaporation of a DMF solution of 3 at
with an excess of 1e (Ͼ1.5 equiv.) NiBr2(DME) was com- room temperature over a period of 10 d. The molecular
pletely converted to afford 2e but unreacted PNP ligand structure of this compound (in the form of 4·DMF) is
was still present. In the course of all these experiments a shown in Figure 2 with selected bond lengths and angles
white precipitate was formed, which was removed by fil- reported in the caption. The Pd center adopts a distorted
tration. Upon dissolution in CD3CN this compound was square-planar geometry defined by two phosphorus atoms,
unequivocally identified as the 2,6-diaminopyridinium salt the central nitrogen atom of the PNP ligand, and a chlorine
G giving rise to signals at δ = 7.46 (t, J = 7.5 Hz, 1 H, H5) atom. The PdNP2Cl coordination deviates significantly
and 5.92 (d, J = 7.5 Hz, 2 H, H3,4) ppm and broad signals from planarity most likely because of a short intramolecu-
at δ = 13.4 (1 H, pyN-H) and 7.2 (4 H, NH2) ppm, which lar contact between C(28)H and Cl (Figure 1). Moreover,
is in agreement with an authentic sample[23] of the 2,6-di- there is a stabilizing short intramolecular hydrogen bond
aminopyridinium cation [cf. the three pKa values of 2,6-di- N(3)–H···Cl with N···Cl = 3.15 Å. It has to be mentioned
4376
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Eur. J. Inorg. Chem. 2006, 4374–4379

Nickel(II) PNP Pincer Complexes
FULL PAPER
Scheme 4.
that structurally related “one-armed” pincer-type platinum 16 h leading to the formation of several intractable materi-
complexes have been reported recently.[25]
als giving rise to signals in the range of δ = 6–20 ppm in the
31P{1H} NMR spectrum [cf. BIPOL-P(OH)=O, a possible
decomposition product, gives rise to a signal at δ =
5.71 ppm].[26]
Experimental Section
General: All manipulations were performed under argon by using
Schlenk techniques. The solvents were purified according to stan-
dard procedures. The starting materials (4S,5S)-2-chloro-4,5-di-
phenyl-1,3,2-dioxaphospholane,[27] (4S,5R)-2-chloro-3,4-dimethyl-
5-phenyl-1,3,2-oxazaphospholidine,[28] PNP-BIPOL (1e), PNP-
TARMe (1g), PNP-TARPr (1h), and [Pd(PNP-BIPOL)Cl]Cl (3) were
prepared according to literature procedures.[11] The deuterated sol-
vents were purchased from Aldrich and dried with molecular sieves
(4 Å). 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded with
a Bruker AVANCE-250 spectrometer and were referenced to SiMe4
Scheme 5.
1
and H3PO4 (85%), respectively. H and 13C{1H} NMR signal as-
signments were confirmed by 1H-COSY, 135-DEPT, and
HMQC(1H-13C) experiments.
N,NЈ-Bis[(4S,5S)-4,5-diphenyl-1,3,2-dioxaphospholan-2-yl]-2,6-di-
aminopyridine (PNP-HBz) (1i): (4S,5S)-2-Chloro-4,5-diphenyl-
1,3,2-dioxaphospholane (500 mg, 1.8 mmol) was dissolved in tolu-
ene (5 mL) and added to a mixture of 2,6-diaminopyridine (98 mg,
0.9 mmol) and triethylamine (0.25 mL, 1.8 mmol) dissolved in tolu-
ene (15 mL). The reaction mixture was stirred at 80 °C for 16 h and
insoluble materials were removed by filtration. After removal of the
solvent under reduced pressure, 1i was obtained in an analytically
pure form as a white solid. Yield: 363 mg (68%). C33H29N3O4P2
(593.56): calcd. C 66.78, H 4.92, N 7.08; found C 66.81, H 4.89, N
7.15. 1H NMR (CDCl3, 20 °C): δ = 7.38–7.11 (m, 21 H, Ph and
py4), 6.43 (d, J = 8.0 Hz, 2 H, py3,5), 6.05 (d, J = 8.2 Hz, 2 H,
NH), 5.24–5.15 (m, 2 H, CH), 5.00–4.81 (m, 2 H, CH) ppm.
13C{1H} NMR (CDCl3, 20 °C): δ = 157.6 (py2,6), 140.2 (py4), 136.5
(Ph1), 129.0 (Ph2,6), 128.5 (Ph4), 126.7 (Ph3,5), 100.7 (py3,5), 87.2
(CH) ppm. 31P{1H} NMR (CDCl3, 20 °C): δ = 130.0 ppm.
Figure 2. Structural view of [Pd{κ2(P,N)-NH2-PN-BIPOL}{κ1(P)-
BIPOL-P=O}Cl]·DMF (4·DMF) (C-bonded H atoms omitted for
clarity). Selected bond lengths [Å] and bond angles [°]: Pd–N(1)
2.171(2), Pd–P(1) 2.1787(5), Pd–P(2) 2.2276(6), Pd–Cl 2.3505(5);
P(1)–Pd–P(2) 91.78(2), Cl–Pd–P(2) 86.76(2), N(1)–Pd–P(2)
173.51(5), Cl–Pd–P(1) 165.39(2).
Finally, it has to be noted that phosphoramidite PNP
ligands are very stable in CH2Cl2 and comparatively stable
also in neat DMSO. In the case of PNP-BIPOL (1e) about
N,NЈ-Bis[(4S,5R)-3,4-dimethyl-5-phenyl-1,3,2-oxazaphos-
pholidin-2-yl]-2,6-diaminopyridine (PNP-Ephe) (1j): This ligand was
prepared analogously to 1i with (4S,5R)-2-chloro-3,4-dimethyl-5-
50% decomposition is observed at room temperature after phenyl-1,3,2-oxazaphospholidine (500 mg, 2.2 mmol), 2,6-diami-
Eur. J. Inorg. Chem. 2006, 4374–4379
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D. Benito-Garagorri, K. Mereiter, K. Kirchner
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nopyridine (118 mg, 1.1 mmol), and triethylamine (0.30 mL,
[Ni(PNP-Ephe){κ1(P)-Ephe-P=O}Br] (2j): This complex was pre-
2.2 mmol). Yield: 283 mg (52%). C25H31N5O2P2 (495.50): calcd. C pared analogously to 2e with NiBr2 (175 mg, 0.40 mmol), 1j
1
60.60, H 6.31, N 14.13; found C 60.54, H 6.42, N 14.25. H NMR (400 mg, 0.80 mmol), and DMSO (29 µL, 0.40 mmol) as the start-
(CDCl3, 20 °C): δ = 7.37–7.15 (m, 13 H, Ph, py3,5 and py4), 5.86
ing materials. Yield: 213 mg (63%). C35H44BrN6NiO4P3 (844.31):
(d, J = 7.8 Hz, 2 H, NH), 4.71–4.60 (m, 2 H, CHPh), 3.77–3.60 calcd. C 49.79, H 5.25, N 9.95; found C 49.69, H 5.09, N 10.05.
(m, 2 H, CHCH3), 2.84–2.63 (m, 6 H, NCH3), 0.84–0.63 (m, 6 H, 1H NMR ([D6]DMSO, 20 °C): δ = 7.40–7.02 (m, 18 H, Ph, py4 and
CHCH3) ppm. 13C{1H} NMR (CDCl3, 20 °C): δ = 157.0 (py2,6),
py3,5), 5.60 (s, 2 H, NH), 4.90–4.74 (m, 3 H, CHPh), 3.64–3.47 (m,
3 H, CHCH3), 3.22–3.11 (m, 9 H, NCH3), 0.94–0.72 (m, 9 H,
140.1 (py4), 139.6 (Ph1), 128.5 (Ph2,6), 126.8 (Ph4), 125.8 (Ph3,5),
99.7 (py3,5), 81.7 (CHPh), 60.2 (CHCH3), 29.1 (NCH3), 14.6 CHCH3) ppm. 13C{1H} NMR ([D6]DMSO, 20 °C): δ = 155.7
(CHCH3) ppm. 31P{1H} NMR (CDCl3, 20 °C): δ = 119.0 ppm.
(py2,6), 143.9 (py4), 141.3 (Ph), 128.6–126.1 (Ph), 99.7 (py3,5), 84.5
(CHPh), 81.6 (CHPh), 65.2 (CHCH3), 59.2 (CHCH3), 30.9
(NCH3), 28.8 (NCH3), 15.5 (CHCH3), 9.5 (CHCH3) ppm. 31P{1H}
NMR ([D6]DMSO, 20 °C): δ = 116.8 (d, J = 114.1 Hz, PNP-Ephe),
74.5 (t, J = 114.1 Hz, Ephe-P=O) ppm.
[Ni(PNP-BIPOL){κ1(P)-BIPOL-P=O}Br] (2e): NiBr2 (150 mg,
0.46 mmol) was suspended in a solution of 1e (500 mg, 0.93 mmol)
in CH2Cl2 (5 mL). Upon addition of DMSO (33 µL, 0.46 mmol),
the solution turned deep orange. The mixture was stirred at room
temperature for 1 h and the volume of the solution was reduced
under vacuum. The orange product was precipitated with Et2O and
dried under vacuum. Yield: 371 mg (89%). C41H29BrN3NiO7P3
(907.23): calcd. C 54.28, H 3.22, N 4.63; found C 54.24, H 3.16, N
X-ray Structure Determination: Crystals of 2i were obtained as
2i·CH3OH from diethyl ether diffusion into a saturated CH3OH
solution of 2i. Crystals of 4 were obtained as 4·DMF by slow con-
centration of a DMF solution. X-ray data were collected with a
Bruker Smart APEX CCD area detector diffractometer using
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) and
0.3° ω-scan frames. Corrections for absorption, λ/2 effects, and
crystal decay were applied.[29] The structures were solved by direct
methods using the program SHELXS97.[30] Structure refinement
on F2 was carried out with the program SHELXL97.[27] Non-hy-
drogen atoms were refined anisotropically (for 2i·MeOH iso-
tropically for C, N, and O atoms). Hydrogen atoms were inserted
in idealized positions and were refined riding with the atoms to
which they are bonded, except for N-bound hydrogen atoms, which
were refined in x,y,z if permitted by data quality. Salient crystallo-
1
3.35. H NMR ([D6]DMSO, 20 °C): δ = 7.33–7.09 (m, 20 H, Ph),
6.93–6.88 (m, 4 H, Ph), 6.70 (t, J = 7.3 Hz, 1 H, py4), 6.36 (d, J =
7.3 Hz, 2 H, py3,5), 5.80 (d, J = 8.0 Hz, 2 H, NH) ppm. 13C{1H}
NMR ([D6]DMSO, 20 °C): δ = 155.1 (Ph), 154.3 (py2,6), 142.2
(py4), 132.3–124.4 (Ph), 100.8 (py3,5) ppm. 31P{1H} NMR ([D6]-
DMSO, 20 °C): δ = 147.7 (d, J = 98.6 Hz, BIPOL-PNP), 86.6 (t,
J = 98.6 Hz, BIPOL-PO) ppm.
[Ni(PNP-TARMe){κ1(P)-TARMe-P=O}Br] (2g): This complex was
prepared analogously to 2e with NiBr2 (205 mg, 0.94 mmol), 1g
(980 mg, 1.87 mmol), and DMSO (68 µL, 0.94 mmol) as the start-
ing materials. Yield: 672 mg (81%). C35H53BrN3NiO19P3 (1051.35):
1
graphic data are: 2i·CH3OH: C48H45BrN3NiO8P3, Mr
=
=
calcd. C 39.99, H 5.08, N 4.00; found C 40.09, H 5.00, N 4.10. H
1023.40 gmol–1, orthorhombic, space group P212121,
a
NMR ([D6]DMSO, 20 °C): δ = 7.44 (t, J = 8.0 Hz, 1 H, py4), 6.40
(d, J = 8.0 Hz, 2 H, py3,5), 5.83 (d, J = 8.3 Hz, 2 H, NH), 5.03–
4.89 (m, 4 H, CH), 4.80–4.61 (m, 2 H, CH), 1.23–1.14 (m, 18 H,
CH3) ppm. 13C{1H} NMR ([D6]DMSO, 20 °C): δ = 170.2 (CO),
166.3 (CO), 159.6 (py2,6), 142.1 (py4), 100.8 (py3,5), 95.1 (CH), 76.7
(CH), 45.9 (CH3), 45.3 (CH3) ppm. 31P{1H} NMR ([D6]DMSO,
20 °C): δ = 146.2 (d, J = 104.2 Hz, TARMe-PNP), 85.3 (t, J =
104.2 Hz, TARMe-P=O) ppm.
15.043(12), b = 19.159(12), c = 33.21(3) Å, V = 9572(12) Å3, Z
= 8, µ = 1.396 mm–1, T = 173 K. 11282 independent reflections,
reflections were collected up to θmax = 23.1°; final R indices: R1 =
0.131 [5725 reflections with IϾ2σ(I)], wR1 = 0.365 (all data). All
available crystals were thin and bent blades (Ͻ0.03 mm), giving
broad reflection profiles and poor intensities. Therefore, aniso-
tropic displacement parameters were used only for Ni, Br, and P,
and the phenyl rings were refined as idealized rigid groups. Despite
the relatively large R values, the structure is sound and hydrogen
bonding as well as absolute structure [Flack absolute structure pa-
rameter = 0.00(3)] could safely be clarified. The asymmetric unit of
the structure contains two independent Ni complexes and methanol
molecules mutually linked through hydrogen bonds with N–H and
O–H as donors and the Br and phosphinite O atoms as acceptors.
Only one of the two independent Ni complexes is shown in Fig-
ure 1. 4·DMF: C32H29ClN4O6P2Pd, Mr = 769.38 gmol–1, mono-
clinic, space group P21/c, a = 9.4778(4), b = 13.7127(6), c =
24.2252(10) Å, β = 94.642(1)°, V = 3138.1(2) Å3, Z = 4, µ =
0.831 mm–1, T = 173 K. 9147 independent reflections, reflections
were collected up to θmax = 30.0°; final R indices: R1 = 0.0330 [7211
reflections with IϾ2σ(I)], wR1 = 0.0768 (all data). A view of the
molecular structure with all hydrogen bonds is shown in Figure
2. CCDC-608245 (2i·CH3OH) and -608246 (4·DMF) contain the
supplementary 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.
[Ni(PNP-TARPr){κ1(P)-TARPr-PO}Br] (2h): This complex was pre-
pared analogously to 2e with NiBr2 (290 mg, 1.33 mmol), 1h (1.6 g,
2.7 mmol), and DMSO (96 µL, 1.33 mmol) as the starting materi-
als. Yield: 979 mg (70%). C23H29BrN3NiO19P3 (883.03): calcd. C
31.28, H 3.31, N 4.76; found C 31.21, H 3.40, N 4.66. 1H NMR
([D6]DMSO, 20 °C): δ = 7.42 (t, J = 7.8 Hz, 1 H, py4), 6.41 (d, J
= 7.8 Hz, 2 H, py3,5), 5.81 (d, J = 8.2 Hz, 2 H, NH), 5.06–4.40 [m,
12 H, CH and CH(CH3)2], 1.23–1.12 (m, 36 H, [CH(CH3)2] ppm.
13C{1H} NMR ([D6]DMSO, 20 °C): δ = 170.2 (CO), 168.3 (CO),
159.8 (py2,6), 145.1 (py4), 100.8 (py3,5), 95.2 (CH), 80.0 (CH), 69.1
[CH(CH3)2], 68.8 [CH(CH3)2], 21.9 [CH(CH3)2], 21.7 [CH(CH3)2]
ppm. 31P{1H} NMR ([D6]DMSO, 20 °C): δ = 146.1 (d, J =
100.8 Hz, TARPr-PNP), 85.5 (t, J = 100.8 Hz, TARPr-P=O) ppm.
[Ni(PNP-HBz){κ1(P)-HBz-P=O}Br] (2i): This complex was pre-
pared analogously to 2e with NiBr2 (54 mg, 0.24 mmol), 1i
(300 mg, 0.49 mmol), and DMSO (18 µL, 0.24 mmol) as the start-
ing materials. Yield: 132 mg (55%). C47H41BrN3NiO7P3 (991.39):
1
calcd. C 56.94, H 4.17, N 4.24; found C 57.04, H 4.19, N 4.31. H
NMR ([D6]DMSO, 20 °C): δ = 7.29–7.00 (m, 33 H, Ph, py4 and
py3,5), 5.70 (d, J = 8.0 Hz, 2 H, NH), 5.24–4.90 (m, 6 H, CH) ppm.
13C{1H} NMR ([D6]DMSO, 20 °C): δ = 152.6 (py2,6), 144.3 (Ph),
142.5 (py4), 130.1–127.3 (Ph), 98.8 (py3,5), 95.1 (CH), 87.0 (CH)
Acknowledgments
ppm. 31P{1H} NMR ([D6]DMSO, 20 °C): δ = 143.4 (d, J = Financial support by the “Fonds zur Förderung der wissen-
107.2 Hz, PNP-HBz), 87.8 (t, J = 107.2 Hz, HBz-P=O) ppm. schaftlichen Forschung” is gratefully acknowledged (Project No.
4378
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Eur. J. Inorg. Chem. 2006, 4374–4379

Nickel(II) PNP Pincer Complexes
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Received: May 29, 2006
Published Online: September 18, 2006
Eur. J. Inorg. Chem. 2006, 4374–4379
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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