Unusual ligand design: A platinum(II) mediated [2+2] photocycloaddition followed by a nickel(II) induced methoxyactivation

Article abstract of DOI:10.1016/j.ica.2009.03.009

The novel dimer of the composition [Pt₂Cl₄(μ-(κP¹:κP²-o-MeO-trans-dppen))₂] (1) (o-MeO-trans-dppen = 1,2-(bis(o-methoxyphenyl)phosphanyl)ethylene) has been prepared and characterized by a single crystal X-ray structure analysis, NMR spectroscopy, mass spectrometry and elemental analysis. This latter compound undergoes a [2+2] photocycloaddition reaction yielding the tetraphosphane all-trans-1,2,3,4-tetrakis(di(o-methoxyphenyl)phosphanyl)cyclobutane (o-MeO-dppcb). The X-ray structure of the dimeric Ni(II) complex that contains the latter ligand, of the formula [Ni₂Cl₄(μ-(κP¹:κP²:κP³:κP⁴-o-MeO-dppcb))] (2) reveals that the apical coordination sites of both square pyramidal Ni(II) coordination spheres are occupied by methoxy-oxygen atoms of the ligand. As a consequence, this dimeric Ni(II) complex 2 is prone to a thermally induced regio- and diastereoselective metal-assisted methoxy-group cleavage. The stepwise formed new mono- and bis-phenolate complexes [Ni₂Cl₃(μ-(κO¹,κP¹:κP²:κP³:κP⁴-o-MeO-O-dppcb))] (3) and [Ni₂Cl₂(μ-(κO¹,κP¹:κP²:κO²,κP³:κP⁴-o-MeO-O,O′-dppcb))] (4), respectively, contain the novel chiral tetraphosphane ligands all-trans-1,2,3-tris((di-o-methoxyphenyl)phosphano)-4-((o-methoxy-phenyl)(o-phenolate)phosphano)cyclobutane (o-MeO-O-dppcb) and all-trans-1,2-bis((di-o-methoxyphenyl)phosphano)-3,4-bis((o-methoxyphenyl)(o-phenolate)phosphano)cyclobutane (o-MeO-O,O′-dppcb). Compounds 3 and 4 have been synthesized independently and are also fully characterized by both single crystal X-ray structure analyses, NMR spectroscopy, mass spectrometry and elemental analyses. The conversion of 2 into 3 and then further into 4 has been followed by a variable-temperature ³¹P{¹H} NMR experiment with compound 2 in DMF-d⁷, revealing that the cleavage of the second methoxy group is kinetically disfavoured. This is in agreement with the X-ray structure analysis of 3, indicating the lack of any methoxy-oxygen atom coordination that could easily induce a further methoxy-group cleavage. o-MeO-O-dppcb and o-MeO-O,O′-dppcb are rare P-stereogenic tetraphosphine ligands and contribute to the synthetic field of new κ³-P,P,O-coordinating phosphanylphenolate ligands that are believed to be important for the SHOP process (SHOP, Shell Higher Olefin Process).

Full text of DOI:10.1016/j.ica.2009.03.009

Inorganica Chimica Acta 363 (2010) 2001–2008
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Unusual ligand design: A platinum(II) mediated [2+2] photocycloaddition
followed by a nickel(II) induced methoxyactivation
Markus Fessler a, Georg Czermak a, Sylvia Eller a, Barbara Trettenbrein a, Stephan Haringer a,
Werner Oberhauser b, Peter Brüggeller a,
*
a Institut für Allgemeine, Anorganische und Theoretische Chemie der Universität Innsbruck, Innrain 52a, 6020 Innsbruck, Austria
b Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
a r t i c l e i n f o
a b s t r a c t
The novel dimer of the composition [Pt2Cl4(l-(j j
P1: P2-o-MeO-trans-dppen))2] (1) (o-MeO-trans-
Article history:
Received 18 December 2008
Accepted 8 March 2009
Available online 16 March 2009
dppen = 1,2-(bis(o-methoxyphenyl)phosphanyl)ethylene) has been prepared and characterized by a sin-
gle crystal X-ray structure analysis, NMR spectroscopy, mass spectrometry and elemental analysis. This
latter compound undergoes a [2+2] photocycloaddition reaction yielding the tetraphosphane all-trans-
1,2,3,4-tetrakis(di(o-methoxyphenyl)phosphanyl)cyclobutane (o-MeO-dppcb). The X-ray structure of
Dedicated to Prof. Umberto Belluco
the dimeric Ni(II) complex that contains the latter ligand, of the formula [Ni2Cl4(l-(j j j j
P1: P2: P3: P4-o-
MeO-dppcb))] (2) reveals that the apical coordination sites of both square pyramidal Ni(II) coordination
spheres are occupied by methoxy-oxygen atoms of the ligand. As a consequence, this dimeric Ni(II)
complex 2 is prone to a thermally induced regio- and diastereoselective metal-assisted methoxy-group
Keywords:
Nickel(II) complexes
Tetraphosphane
Methoxy-group cleavage
X-ray crystallography
Phosphanophenolate
P-chirality
cleavage. The stepwise formed new mono- and bis-phenolate complexes [Ni2Cl3(
l-(j j
O1, P1:
j
P2: P3: P4-o-MeO-O-dppcb))] (3) and [Ni2Cl2( O1, P1: P2: O2, P3: P4-o-MeO-O,O0-dppcb))] (4),
j
j
l
-(
j
j
j
j
j
j
respectively, contain the novel chiral tetraphosphane ligands all-trans-1,2,3-tris((di-o-methoxy-
phenyl)phosphano)-4-((o-methoxy-phenyl)(o-phenolate)phosphano)cyclobutane (o-MeO-O-dppcb) and
all-trans-1,2-bis((di-o-methoxyphenyl)phosphano)-3,4-bis((o-methoxyphenyl) (o-phenolate)phosphan-
o)cyclobutane (o-MeO-O,O0-dppcb). Compounds 3 and 4 have been synthesized independently and are
also fully characterized by both single crystal X-ray structure analyses, NMR spectroscopy, mass spec-
trometry and elemental analyses. The conversion of 2 into 3 and then further into 4 has been followed
by a variable-temperature 31P{1H} NMR experiment with compound 2 in DMF-d7, revealing that the
cleavage of the second methoxy group is kinetically disfavoured. This is in agreement with the X-ray
structure analysis of 3, indicating the lack of any methoxy-oxygen atom coordination that could easily
induce a further methoxy-group cleavage. o-MeO-O-dppcb and o-MeO-O,O0-dppcb are rare P-stereogenic
tetraphosphine ligands and contribute to the synthetic field of new
j
3-P,P,O-coordinating phosphanyl-
phenolate ligands that are believed to be important for the SHOP process (SHOP, Shell Higher Olefin
Process).
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
oligomerization reaction [1a]. In this context, a complex with the
general formula [Ni(j
2-P,O-L)Ph(PPh3)] (L = 2-phenyl-diphenyl-
Catalytic systems, that are obtained by the combination of Ni(II)
phosphanoenolate) (Scheme 1, a) has been synthesized and suc-
cessfully applied by Keim et al. for the oligomerization of
ethylene [1b].
with a
the SHOP process (SHOP, Shell Higher Olefin Process) [1].
Among the
2-P,O-chelating ligands used for this latter impor-
j
2-P,O-chelating ligand were found to be very efficient for
j
Since then, a great deal of synthetic protocols appeared in the lit-
erature aimed at synthesizing phosphanoenolates and 2-phosphan-
ophenolates. Among them are of particular synthetic importance
the reaction of 2-lithio-lithiumphenolates with chlorophosphanes
[2], the metallation of 2-bromo-phenylphosphanites with sodium
[3] and the ortho-metalation of phenylmethoxymethylethers and
the subsequent reaction with chlorophosphanes [4]. Furthermore,
also metal-assisted synthetic methods are known like nickel cata-
lyzed arylations of triarylphosphanes and subsequent cleavage of
tant industrial process, phosphanoenolates are particular attrac-
tive, since the negatively charged oxygen atom efficiently
coordinates to the metal center, stabilizing various metallorganic
species that take part in the catalytic cycle of the
a-olefin
* Corresponding author. Fax: +43 512 5072934.
E-mail address: Peter.Brueggeller@uibk.ac.at (P. Brüggeller).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.03.009

2002
M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
2. Experimental
2.1. General procedures, methods and materials
Allsyntheseshavebeenperformedundera dryargonatmosphere
applying standard Schlenk techniques. Solvents have been dried
over suitable activated molecular sieves and deaerated prior to
use. Bis(o-methoxyphenyl)phosphane [10], compound 2 [11], o-
MeO-trans-dppen [11], and o-MeO-dppcb [11] were synthesized
according to literature methods, while all other reagents were used
as purchased from Aldrich or Strem. Deuterated solvents for routine
NMR measurements were used as purchased from EuroIsotop. 1H,
13C{1H}, and 31P{1H} NMR spectra were obtained on a Bruker Avance
DPX300 spectrometer, measuringat 300.13, 75.48, and 121.50 MHz,
respectively. Chemical shifts (d) are reported in ppm relative to TMS
(1H and 13C{1H} NMR) or 85% H3PO4 (31P{1H} NMR). Elemental anal-
yses were performed using a Perkin–Elmer Model 2400 elemental
analyser. FAB mass spectrometry measurements have been carried
out on a Finnigan MAT-95 spectrometer, using 3-nitrobenzylalcohol
(NOBA) as matrix. The 31P{1H} NMR spectrum of compound 4 has
been simulated using the INSIM-GUI V 1.0 program [12].
2.2. Synthesis of [Pt2Cl4(
l-(j j
P1: P2-o-MeO-trans-dppen))2] (1)
Scheme 1.
[PtCl2(g
4-COD)] (3.74 g, 10.0 mmol) was added to a deaerated
solution of o-MeO-trans-dppen (5.16 g, 10.0 mmol) in CH2Cl2
(200 ml) at room temperature. The reaction mixture was allowed
to stir overnight. The solid formed was then separated by filtration,
washed with CH2Cl2 (3 ꢁ 50 ml) and dried under vacuum. Yield
7.22 g (92.2%). Mp >350 °C. Anal. Calc. for C60H60Cl4O8P4Pt2
(1564.92): C, 46.05; H, 3.86. Found: C, 45.97; H, 3.93%. 1H NMR
(CD2Cl2, 25 °C): d 2.68–2.90 (br m, 12H, OCH3), 3.63–3.78 (br m,
12H, OCH3), 5.01 (m, 2H, CH@CH), 5.60 (m, 2H, CH@CH), 6.98–
7.61 (br m, 32H, Ar–H). 31P{1H} NMR (CD2Cl2, 25 °C): d ꢂ5.9 (s,
1JPtP = 3640.0 Hz). MS (FAB+) m/z: 1529.71 (M++H).
an aryl group [5,6]. The reaction of o-benzochinone-2-ylidene-tri-
phenylphosphorane with [Ni(
4-COD)2] (COD = 1,5-cyclooctadi-
g
ene) [7] also resulted to be one of the most applied synthesis paths.
In the past decade P-stereogenic diphosphane ligands have
played a pivotal role in the creation of a strictly defined asymmet-
ric environment around the metal center [8]. In this context, chiral
phosphanylphenolate ligands, capable of coordinating metals in a
j
3-P,P,O-mode, are much less studied compared to 2-P,O-coordi-
j
nating phosphanylphenolates. In fact, only (2-((2-bis(o-methoxy-
phenyl)phosphano)ethyl)(o-methoxyphenyl)phosphano)phenolate
[9] that coordinates in a j
3-P,P,O-fashion to Ru(II) is known up to
2.3. Synthesis of [Ni2Cl3(l-(j j j j j
O1, P1: P2: P3: P4-o-MeO-O-dppcb))]
now (Scheme 1, b). The simultaneous coordination of two soft do-
nor atoms such as phosphorus and a negatively charged hard phe-
nolate oxygen atom may give rise to a rich coordination chemistry
of this kind of ligands endowing the metal center with unique elec-
tronic properties.
(3)
A deaerated solution of compound 2 (40.0 mg, 0.031 mmol) in
DMF (15.0 mL) was placed into a Schlenk tube. The red solution
was heated at 80 °C for 1.5 h under nitrogen. The red solution
was then cooled to room temperature and the solvent removed
by means of a vacuum pump. The crude product was suspended
in diethyl ether (25 ml), stirred for 10 min, separated by filtration
and dried under vacuum. Yield 23.8 mg (61.8%). Mp = 174 °C dec.
Anal. Calc. for C59H57Cl3Ni2O8P4 (1241.705): C, 57.07; H, 4.63.
Found: C, 56.95; H, 4.49%. 1H NMR (CD2Cl2, 25 °C): d 2.60–3.62
(br m, 21H, OCH3), 4.33 (br s, 4H, PCH), 6.20–8.20 (m, 30H, Ar–
H), 9.60 (br s, 1H, o-Ar–H), 10.82 (br s, 1H, o-Ar–H). 31P{1H} NMR
(CD2Cl2, 25 °C): d 9.43 (br s), 21.80 (br s), 29.25 (br s), 36.70 (br
s). MS (FAB+) m/z: 1205.5 (M+ꢂCl).
In order to contribute in this field of synthetic chemistry,
especially of new
j
3-P,P,O-coordinating phosphanophenolate
ligands, we report the synthesis of the two novel bridging phos-
phanylphenolate ligands all-trans-1,2,3- tris((di-o-methoxy-
phenyl)phosphano)-4-((o-methoxyphenyl)(o-phenolate)phosphano)
cyclobutane
(o-MeO-O-dppcb)
and
all-trans-1,2-bis((di-o-
methoxyphenyl)phosphano)-3,4-bis((o-methoxyphenyl)(o-pheno-
late)phosphano)cyclobutane (o-MeO-O,O0-dppcb) coordinated to
Ni(II). Thus, these ligands yield [Ni2Cl3(
l
-(
j
j
O1,
P1:
j
j
P1:
P2:
j
j
P2:
O2,
j
j
P3:
P3:
j
j
P4-o-
P4-o-
MeO-O-dppcb))] (3) and [Ni2Cl2( -(
l
j
O1,
MeO-O,O0-dppcb))] (4), respectively (Scheme 1, c). The key steps
for the synthesis of both latter complexes are an intramolecular
[2+2] photocycloaddition reaction of the new binuclear complex
2.4. Synthesis of [Ni2Cl2(l-(j j j j j j
O1, P1: P2: O2, P3: P4-o-MeO-O,O0-
dppcb)] (4)
[Pt2Cl4(l-(
j
P1:
j
P2-o-MeO-trans-dppen))2]
(1)
(o-MeO-trans-
A deaerated solution of compound 3 (35.0 mg, 0.028 mmol) in
DMF (10.0 ml) was placed into a Schlenk tube under nitrogen.
The clear red solution was heated at 100 °C for 1.5 h. Afterwards
the solution was cooled to room temperature, followed by the
evaporation of the solvent to dryness by means of a vacuum pump.
The obtained red-brown powder was suspended in diethyl ether
(20 ml) and stirred for 10 min. The solid product was separated
by filtration and dried under vacuum. Yield 35.4 mg (95.9%). Mp
>350 °C. Anal. Calc. for C58H54Cl2Ni2O8P4 (1191.22): C, 58.48; H,
4.57. Found: C, 58.33; H, 4.64%. 1H NMR (CD2Cl2, 25 °C): d 2.41
dppen = 1,2-(bis(o-methoxyphenyl) phosphanyl)ethylene), that
yields all-trans-1,2,3,4-tetrakis(di(o-methoxyphenyl)phosphanyl)
cyclobutane (o-MeO-dppcb), upon a cyanolysis reaction of the pho-
tochemically obtained Pt-intermediate and a thermally induced
methoxy-group cleavage in the dimeric Ni(II) complex of the latter
ligand of the formula [Ni2Cl4(l-(j j j j
P1: P2: P3: P4-o-MeO-dppcb))]
(2). This reaction represents a unique regio- and diastereoselective
metal-assisted methoxy-group cleavage. The single crystal X-ray
structures of 1 ꢀ 4CH2Cl2, 2 ꢀ 2.5C2H4Cl2 ꢀ H2O, 3 ꢀ 3DMF and
4 ꢀ 2CH3CN are reported and discussed.

M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
2003
2
(d, JPH = 14 Hz, 2H, PCH), 2.80 (s, 3H, OCH3), 2.89 (s, 3H, OCH3),
ature within seconds, were obtained retrosynthetically via a li-
quid–liquid diffusion of deaerated CH2Cl2 solutions of [PtCl2(g4
2
3.06 (s, 6H, OCH3), 3.39 (s, 6H, OCH3), 4.58 (br d, JPH = 12 Hz, 2H,
-
PCH), 6.3–7.7 (br m, 30H, Ar–H), 9.26 (br s, 1H, o-Ar–H), 9.57 (dd,
COD)] and trans-o-MeO-dppen, respectively, into each other at
room temperature. Single crystals of 2 ꢀ 2.5C2H4Cl2 ꢀ H2O,
3 ꢀ 3DMF and 4 ꢀ 4CH3CN suitable for X-ray structure analyses were
obtained by the evaporation of the corresponding C2H4Cl2, DMF
and CH3CN solutions of 2, 3 and 4 at room temperature. Crystallo-
graphic data and structure refinement details for all four com-
pounds are summarized in Table 1. Diffraction data were
3
3JPH = 8 Hz, JHH = 8 Hz, 1H, o-Ar–H). 13C{1H} NMR (CD2Cl2, 25 °C):
1
1
d 31.55 (d, JPC = 28 Hz, PCH), 38.65 (d, JPC = 22 Hz, PCH), 54.22
(s, OCH3), 55.24 (s, OCH3), 110.32–142.66 (s, Ar–C), 158.61 (s, C–
2
OCH3), 159.87 (s, C–OCH3), 175.23 (d, JPC = 20 Hz, Ar–C–O).
2
3
31P{1H} NMR (CD2Cl2, 25 °C): d 22.70 (dd, JPP = 83 Hz, JPP = 29 Hz,
Pachiral), 39.37 (br s, Pchiral). MS (FAB+) m/z: 1157.2 (M+ꢂCl).
collected on a Nonius Kappa CCD diffractometer using u–
x-scans
2.5. Variable-temperature NMR study of 2 in DMF-d7
and graphite-monochromated Mo K radiation (k = 0.71073 Å).
a
Cell refinement, data reduction, and the empirical absorption cor-
rection were done by the DENZO and SCALEPACK programs [13]. All
structure determination calculations were performed using SHELXTL
NT V6.1 including SHELXS-97 and SHELXL-97 [14]. Final refinements on
F2 were carried out applying anisotropic thermal parameters for
all non-hydrogen atoms, while all hydrogen atoms were included
in the refinement using a riding model with isotropic U-values
depending on the Ueq of the adjacent carbon atoms. The hydrogen
atoms on O(9) of the water solvent molecule in structure 2, on
C(18), C(19) and C(20) of one DMF solvent molecule in structure
3, and on C(9) of one MeCN solvent molecule in structure 4 have
been omitted due to substantial disorder in these solvent
molecules.
Compound 2 (6.0 mg, 0.005 mmol) was dissolved in deaerated
DMF-d7 (1.5 ml) and the obtained red solution was transferred into
a 5 mm NMR tube under nitrogen and sealed. The NMR tube was
then transferred into a NMR probe at room temperature, followed
by the acquisition of a 31P{1H} NMR spectrum. Then the NMR probe
was heated to 40 °C for half an hour, followed by the acquisition of a
31P{1H} NMR spectrum. Afterwards the NMR probe was cooled to
room temperatureand a 31P{1H} NMR spectrum at thelatter temper-
ature was acquired. This heating and cooling cycle was repeated un-
til a temperature of 80 °C was reached, increasing the temperature
from cycle to cycle in 10 °C steps. Once the conversion of 2 into 3
was completed, the NMR probe was heated to 100 °C and 31P{1H}
NMR spectra were acquired at the latter temperature in time inter-
vals of half an hour. As soon as no further changes of the 31P{1H}
NMR peak intensities were observed and hence the conversion of 3
into 4 was completed, the NMR probe was cooled to room tempera-
ture followed by the acquisition of a final 31P{1H} NMR spectrum.
3. Results and discussion
3.1. Synthesis and crystal structure of [Pt2Cl4(l-(j j
P1: P2-o-MeO-
trans-dppen))2] (1)
The synthesis of o-MeO-dppcb has been achieved following the
synthetic protocol as shown in Scheme 2. Although basic informa-
tion about the synthesis of the latter ligand has already been re-
ported [11], no explanation of the observed all-trans-
2.6. X-ray crystal structure determination
Single crystals of 1 ꢀ 4CH2Cl2 suitable for an X-ray diffraction
study, that easily released the solvent molecules at room temper-
Table 1
Crystallographic data and structure refinement details for compounds 1 ꢀ 4CH2Cl2, 2 ꢀ 2.5C2H4Cl2 ꢀ H2O, 3 ꢀ 3DMF and 4 ꢀ 4CH3CN.
1 ꢀ 4CH2Cl2
2 ꢀ 2.5C2H4Cl2 ꢀ H2O
3 ꢀ 3DMF
4 ꢀ 4CH3CN
Empirical formula
Formula weight
Crystal shape
Crystal dimensions (mm)
Colour
C60H60Cl4O8P4Pt2 ꢀ 4CH2Cl2
C60H60Cl4Ni2O8P4 ꢀ 2.5C2H4Cl2 ꢀ H2O
C59H57Cl3Ni2O8P4 ꢀ 3DMF
C58H54Cl2Ni2O8P4 ꢀ 4CH3CN
1904.63
1557.58
1460.99
needle
1355.43
prism
rod
needle
0.25 ꢁ 0.15 ꢁ 0.025
0.3 ꢁ 0.1 ꢁ 0.05
0.25 ꢁ 0.2 ꢁ 0.1
0.25 ꢁ 0.1 ꢁ 0.05
colourless
red
red
red
Crystal system
Space group
a (Å)
b (Å)
c (Å)
triclinic
P1
14.2262(3)
15.3145(3)
18.0654(4)
89.674(1)
81.425(1)
73.415(1)
3727.1(1)
293
monoclinic
P2(1)/n
12.2978(4)
12.2633(3)
46.560(2)
triclinic
P1
monoclinic
P2(1)/c
16.4460(2)
17.6790(2)
23.4653(3)
ꢀ
ꢀ
12.2709(1)
12.8065(2)
23.1120(3)
79.2779(7)
85.8389(8)
77.1085(8)
3476.80(8)
243
a
(°)
b (°)
91.024(1)
110.5541(7)
c
(°)
V (Å3)
7020.7(4)
243
6388.2(1)
243
T (K)
Z
2
4
2
4
Dcalc (Mg/m3)
1.697
4.315
1872
1.474
1.024
3204
1.389
0.809
1510
1.406
0.831
2804
Absorption coefficient (mmꢂ1
F(000)
)
h range for data collection (°)
Limiting indices
1.51–26.41
ꢂ14 6 h 6 17
ꢂ19 6 k 6 19
ꢂ22 6 l 6 22
24853
2.13–25.12
ꢂ14 6 h 6 14
ꢂ14 6 k 6 14
ꢂ55 6 l 6 55
13622
1.79–27.55
ꢂ15 6 h 6 15
ꢂ16 6 k 6 16
ꢂ30 6 l 6 30
30555
1.48–26.04
ꢂ20 6 h 6 20
ꢂ21 6 k 6 21
ꢂ28 6 l 6 25
42124
Reflections collected
Independent reflections (Rint
Absorption correction
Refinement method
)
15307 (0.0426)
multi-scan
full-matrix least-squares on F2
14963/0/811
1.037
12550 (0.0420)
15883 (0.0414)
12598 (0.0377)
Data/restraints/parameters
8506/2/829
1.030
15883/0/835
1.037
12598/5/780
1.033
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I), 1, 3, 4; I > 3
r
(I), 2]
R1 = 0.0311, wR2 = 0.0807
R1 = 0.0414, wR2 = 0.0984
0.810 and ꢂ0.680
R1 = 0.0510, wR2 = 0.1238
R1 = 0.0691, wR2 = 0.1644
0.620 and ꢂ0.470
R1 = 0.0379, wR2 = 0.1085
R1 = 0.0530, wR2 = 0.1371
0.650 and ꢂ0.360
R1 = 0.0347, wR2 = 0.0909
R1 = 0.0465, wR2 = 0.1093
0.340 and ꢂ0.350
Largest difference in peak and hole (e Åꢂ3
)

2004
M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
Scheme 2.
Fig. 1. ORTEP diagram of 1 ꢀ 4CH2Cl2. Hydrogen atoms and solvent molecules are
omitted for clarity and thermal ellipsoids are shown at the 30% probability level.
configuration in o-MeO-dppcb has been provided so far due to the
fact that 1 is extremely difficult to crystallize and highly air sensi-
tive single crystals loosing CH2Cl2 within seconds can only be ob-
tained retrosynthetically. In this regard, we report here the
synthesis (Scheme 2, step c) and full characterization of 1, that rep-
resents the key compound in the synthesis of o-MeO-dppcb
(Scheme 2, steps a–d).
Table 2
Selected bond lengths (Å) and bond angles (°) for 1 ꢀ 4CH2Cl2.
Bond lengths (Å)
Bond angles (°)
Pt(1)–P(1)
Pt(1)–P(3)
Pt(1)–Cl(1)
Pt(1)–Cl(2)
Pt(2)–P(2)
Pt(2)–P(4)
Pt(2)–Cl(3)
Pt(2)–Cl(4)
C(1)–C(2)
C(3)–C(4)
2.2498(15)
2.2458(16)
2.3470(16)
2.3597(17)
2.2430(16)
2.2476(15)
2.3444(17)
2.3514(16)
1.301(7)
P(1)–Pt(1)–P(3)
P(3)–Pt(1)–Cl(1)
P(1)–Pt(1)–Cl(1)
P(3)–Pt(1)–Cl(2)
P(1)–Pt(1)–Cl(2)
Cl(1)–Pt(1)–Cl(2)
P(2)–Pt(2)–P(4)
P(2)–Pt(2)–Cl(3)
P(4)–Pt(2)–Cl(3)
P(2)–Pt(2)–Cl(4)
P(4)–Pt(2)–Cl(4)
Cl(3)–Pt(2)–Cl(4)
99.94(5)
87.03(6)
171.58(5)
172.41(5)
86.14(6)
87.31(6)
100.56(6)
169.30(6)
87.53(6)
85.57(6)
170.85(6)
87.28(6)
The reaction of trans-o-MeO-dppen with [PtCl2(
1:1 molar ratio selectively yielded the dinuclear trans-o-MeO-
dppen bridged compound [Pt2Cl4( -(
P1: P2-o-MeO-trans-
g
4-COD)] in a
l
j
j
dppen))2] (1), that has been isolated with 92.2% yield. The
31P{1H} NMR spectrum of the latter compound, acquired in CD2Cl2,
exhibited one singlet centered at ꢂ5.9 ppm and a 1JPtP parameter of
3640 Hz, that is comparable to the corresponding value of 3550 Hz
1.309(7)
found for the phenyl-counterpart [Pt2Cl4(
dppen))2] [15].
l-(j j
P1: P2-trans-
Compound 1 has been characterized by multinuclear NMR spec-
troscopy, mass spectrometry (FAB, using 3-nitrobenzylalcohol as
matrix), elemental analysis, and by a single crystal X-ray structure
analysis (vide infra). An ORTEP plot of 1 ꢀ 4CH2Cl2 is presented in
Fig. 1, while crystallographic data and selected bond distances
and angles are shown in Tables 1 and 2, respectively.
The crystal structure of 1 ꢀ 4CH2Cl2 contains four molecules of
CH2Cl2 per asymmetric unit. Both metal centers show a square-pla-
nar coordination sphere that is built up by two cis-coordinating
phosphorus donor atoms of two different bridging phosphane li-
gands. The coordination sphere of both metal centers is completed
by two chloride atoms. Both P–Pt–P coordination angles of
99.94(5)° and 100.56(6)° (Table 2) are significantly larger when
trans-dppen))2] produces a cis,trans,cis orientation of the phospha-
nyl groups in dppcb, where dppcb is cis,trans,cis-1,2,3,4-tetrakis(di-
phenylphosphanyl)cyclobutane [15]. Since [2+2] cycloaddition
reactions where both reacting C@C double bonds are perpendicular
to each other are photochemically forbidden, according to the
Woodward and Hoffmann rules of orbital symmetry [16,17], we
are not in the condition to either confirm or rule out a radical
mechanism that might be operative in the intramolecular forma-
tion of the cyclobutane carbon ring of o-MeO-dppcb. A similar sit-
uation has been found to occur for the synthesis of 1,2-
bis(diphenylphosphanyl)-3,4-diphenylcyclobutane [18].
The relative all-trans configuration of the o-methoxyphenyl-
phosphanyl groups with respect to the cyclobutane carbon ring
in o-MeO-dppcb has been confirmed by several single crystal X-
ray structure analyses of dimeric Pt(II) [11], Pd(II) [11] and Ni(II)
complexes (vide infra). Though 1,2-bis(diphenylphosphanyl)-3,4-
diphenylcyclobutane also shows an all-trans arrangement [18], to
the best of our knowledge o-MeO-dppcb is the first example of a
cyclobutane derivative with four phosphorus substituents in this
all-trans configuration. Unlike the cis,trans,cis orientation of the
diphenylphosphanyl substituents in dppcb [19], the all-trans con-
figuration of the substituted phosphanyl groups in o-MeO-dppcb
implies two possible coordination modes of the ligand, that com-
prise an 1,2-cis, or 1,3-cis coordination of the phosphorus donor
atoms to the same metal center. As a result, either two five-mem-
compared to that observed for the related complex [Pt2Cl4(
l-
(j
P1: P2-trans-dppen))2] of 94.77(14)° and 95.08(14)° [15]. The
j
most striking structural difference between the latter compound
and 1 ꢀ 4CH2Cl2 is the relative orientation of the adjacent C@C dou-
ble bonds of the coordinating trans-o-MeO-dppen ligands in the
dinuclear complexes. This has a crucial effect on the outcome of
the photochemically induced [2+2] cycloaddition reaction. In this
regard, a Newman projection along the carbon atoms C(1) and
C(3) in 1 ꢀ 4CH2Cl2 (Fig. 1) shows a dihedral angle of 68.1(4)°,
whereas the analogous projection for the phenyl-counterpart
[Pt2Cl4(l-(j j
P1: P2-trans-dppen))2] exhibited only a value of 34.8°
[15]. This significant difference in the relative orientation of the
C@C double bonds to each other in both latter Pt-complexes selec-
tively leads to an all-trans orientation of the phosphanyl groups in
o-MeO-dppcb (see Scheme 2). By contrast, [Pt2Cl4(l-(j j
P1: P2-

M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
2005
bered or two six-membered metallacycles are obtained (Scheme 3)
[11].
different Ni–P distances of 2.186(2) and 2.174(2) Å (Table 3), while
the P–Ni–P bite angles of 94.86(7)° (P(1)–Ni(1)–P(3)) and 95.01(8)°
(P(2)–Ni(2)–P(4)) are identical within statistical significance.
It is important to emphasize at this point, that the inequiva-
lence of the phosphorus donor atoms observed in the solid state
persists also in solution. Accordingly, the 31P{1H} NMR spectrum
of 2 showed at room temperature two doublets at 7.37 and
25.55 ppm (2JPP = 94.0 Hz), while the 1H NMR spectrum exhibited
two broad down-field shifted singlets centered at 9.60 and
10.48 ppm, evidencing Ni(II) ortho-methoxy-oxygen interactions
that occur in solution [11]. Similar metal–oxygen interactions have
been also observed in other complexes containing ortho-methoxy-
modified phosphanes [11,20].
Intrigued by the fact that two methoxy-oxygen atoms are very
close to both Ni(II) centers in 2 ꢀ 2.5C2H4Cl2 ꢀ H2O, we studied the
thermal behavior of 2 in solution in order to gain information on
a possible intramolecular methoxy C–O cleavage, obtaining thus
a phenolate moiety, that coordinates to Ni(II). For this purpose, a
variable-temperature 31P{1H} NMR spectroscopic study was car-
ried out with 2 dissolved in DMF-d7 and a sequence of selected
31P{1H} NMR spectra of this study are shown in Fig. 3.
3.2. Single crystal X-ray structure of [Ni2Cl4(
MeO-dppcb)] (2) and its stepwise methoxy-group cleavage
l-(j j j j
P1: P2: P3: P4-o-
Unlike the reaction of o-MeO-dppcb with Pt(II) and Pd(II), the
reaction with NiCl2 ꢀ 6H2O selectively yielded the dimeric complex
2, that is characterized by two six-membered metallacycles shar-
ing a folded cyclobutane carbon ring, as shown in the ORTEP plot
of the single crystal X-ray structure of 2 ꢀ 2.5C2H4Cl2 ꢀ H2O (Fig. 2).
The crystal structure of compound 2 ꢀ 2.5C2H4Cl2 ꢀ H2O shows
for both Ni(II) centers square pyramidal coordination spheres.
While the basal coordination sites are occupied by two 1,3-cis-
coordinating phosphorus donor atoms of o-MeO-dppcb (Scheme
3) and two chloride atoms, the apical coordination sites are occu-
pied by methoxy-oxygen ato0ms of the ligand (Ni(1)–O(6)
0
2.604(6) ÅA, Ni(2)–O(3) 2.621(5) ÅA, Fig. 2 and Table 3). As a result,
the two phosphorus donor atoms coordinating to the same Ni(II)
center are not equivalent, showing at least at Ni(2) significantly
The 31P{1H} NMR spectrum of a deaerated solution of 2 in DMF-
d7 showed two doublets centered at 6.50 and 24.80 ppm
(2JPP = 94.0 Hz (Fig. 3, trace a)). This latter NMR solution was then
gradually heated from room temperature to 80 °C (Fig. 3, trace b)
at a temperature interval of 10 °C. Since 31P{1H} NMR spectra ac-
quired at temperatures higher than 40 °C showed no signal, the
NMR probe always has been cooled back to room temperature, fol-
lowed by the acquisition of a 31P{1H} NMR spectrum, before it has
been heated to a temperature that was 10 °C higher compared to
the previous one. From this heating and cooling sequence of the
DMF-d7 solution of 2 turned out that the latter compound was con-
verted into the unsymmetrical mono-phenolate complex of the
formula [Ni2Cl3(l-(j j j j j
O1, P1: P2: P3: P4-o-MeO-O-dppcb))] (3)
(Scheme 4) at 80 °C in a time interval of 1.5 h.
Accordingly, the 31P{1H} NMR spectrum showed for 3 four
broad humps centered at 7.80, 20.70, 28.10 and 36.10 ppm
(Fig. 3, trace c), due to the asymmetry of the molecule and in accor-
Scheme 3.
dance with a fluxional structure. However, in contrast to [Ni2Cl2(
l-
(j
O1, P1: P2: O2, P3: P4-o-MeO-o-O,O0-dppcb)] (4) this fluxional
j
j
j
j
j
behavior could not be resolved by cooling the NMR solution to
ꢂ90 °C (vide infra). The 31P{1H} NMR signal at 36.10 ppm has been
assigned to the phosphorus atom bearing the phenolate moiety.
After the conversion of 2 into 3 had been completed, the NMR solu-
tion was heated to 100 °C. The first 31P{1H} NMR spectrum at that
temperature showed the occurrence of two broad humps centered
at 23.10 and 38.80 ppm (Fig. 3, trace d). Prolonged heating (i.e. for
1.5 h) of the NMR solution at this latter temperature brought about
the complete conversion of 3 into the bis-phenolate complex of
the formula [Ni2Cl2(l-(j j j j j j
O1, P1: P2: O2, P3: P4-o-MeO-o-O,O0-
dppcb)] (4) (Scheme 4 and Fig. 3, trace e). A successively acquired
31P{1H} NMR spectrum at room temperature confirmed the quan-
titative conversion of 3 into 4 (Fig. 3, trace f). In accordance with
the symmetric structure of 4, the 31P{1H} NMR spectrum shows a
multiplet at 22.80 and a hump at 39.90 ppm, that have been as-
signed to the couple of achiral and chiral phosphorus atoms,
respectively.
In the light of the experimental results obtained from the vari-
able-temperature NMR experiment of 2, compounds 3 and 4 have
been synthesized independently, following a synthetic protocol as
shown in Scheme 4. The isolated compounds 3 and 4 were ob-
tained as micro-crystalline powders with 61.8% and 95.9% yield,
respectively. Both latter complexes have been characterized by
multinuclear NMR spectroscopy, mass spectrometry (FAB, using
3-nitrobenzylalcohol as matrix), elemental analyses, and by single
crystal X-ray structure analyses (vide infra).
Fig. 2. ORTEP diagram of 2 ꢀ 2.5C2H4Cl2 ꢀ H2O. Hydrogen atoms and solvent
molecules are omitted for clarity and thermal ellipsoids are shown at the 30%
probability level.

2006
M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
Table 3
Selected bond lengths (Å) and bond angles (°) for 2 ꢀ 2.5C2H4Cl2 ꢀ H2O, 3 ꢀ 3DMF and 4 ꢀ 4CH3CN.
Bond lengths (Å)
Bond angles (°)
2
3
4
2
3
4
Ni(1)–P(1)
Ni(1)–P(3)
Ni(1)–Cl(1)
Ni(1)–Cl(2)
Ni(1)–O(1)
Ni(1)–O(2)
Ni(1)–O(5)
Ni(1)–O(6)
Ni(2)–P(2)
Ni(2)–P(4)
Ni(2)–Cl(3)
Ni(2)–Cl(4)
Ni(2)–Cl(2)
Ni(2)–O(3)
Ni(2)–O(4)
Ni(2)–O(7)
Ni(2)–O(8)
2.182(2)
2.182(2)
2.206(2)
2.244(2)
3.787(6)
5.169(5)
5.194(5)
2.604(6)
2.186(2)
2.174(2)
2.226(2)
2.208(2)
2.1691(11)
2.1783(10)
2.2005(12)
2.2058(10)
3.517(2)
5.095(3)
5.176(2)
3.340(2)
2.1477(9)
2.1291(10)
2.1993(9)
P(1)–Ni(1)–P(3)
P(1)–Ni(1)–Cl(1)
P(1)–Ni(1)–Cl(2)
P(3)–Ni(1)–Cl(1)
P(3)–Ni(1)–Cl(2)
Cl(1)–Ni(1)–Cl(2)
P(1)–Ni(1)–O(6)
P(3)–Ni(1)–O(6)
O(6)–Ni(1)–Cl(1)
P(2)–Ni(2)–P(4)
P(2)–Ni(2)–Cl(2)
P(2)–Ni(2)–Cl(3)
P(2)–Ni(2)–Cl(4)
P(2)–Ni(2)–O(3)
P(4)–Ni(2)–Cl(2)
P(4)–Ni(2)–Cl(3)
P(4)–Ni(2)–Cl(4)
P(4)–Ni(2)–O(3)
Cl(4)–Ni(2)–Cl(3)
Cl(3)–Ni(2)–O(3)
O(3)–Ni(2)–Cl(2)
94.86(7)
86.46(8)
173.73(10)
178.68(9)
86.55(8)
92.15(8)
95.00(4)
177.12(3)
86.14(4)
87.87(4)
178.12(3)
90.98(4)
94.59(4)
90.28(4)
170.71(3)
5.098(2)
3.226(2)
5.004(3)
1.891(2)
2.1313(10)
2.1585(10)
169.77(7)
84.44(7)
92.14(7)
91.95(3)
168.82(4)
2.1217(9)
2.1578(9)
2.2045(10)
95.01(8)
92.07(4)
164.12(4)
87.02(7)
92.17(4)
162.46(8)
93.45(8)
88.42(8)
179.66(9)
2.1953(10)
1.905(2)
2.861(2)
5.144(2)
3.275(3)
2.621(5)
5.221(5)
5.136(5)
3.583(5)
1.906(2)
2.949(2)
5.155(3)
3.470(3)
86.52(7)
92.86(4)
173.35(9)
85.26(8)
164.43(8)
91.50(7)
91.29(8)
The 31P{1H} NMR spectrum of the independently synthesized
compound 3, acquired in CD2Cl2, showed analogously to that ac-
quired in DMF-d7 (Fig. 3, trace c) four broad humps centered at
9.43, 21.80, 29.25 and 36.70 (i.e. chiral phosphorus) ppm, while
the corresponding 1H NMR spectrum exhibited for the methoxy-
group hydrogen atoms very broad and poorly resolved singlets in
the chemical shift range from 2.60 to 3.62 ppm, indicating a com-
pletely asymmetric molecule. A FAB-spectrum of the latter com-
pound showed a peak at m/z of 1205.5 that has been assigned to
the [MꢂCl]+ fragment.
The 31P{1H} NMR spectrum of compound 4, acquired in CD2Cl2,
exhibited at room temperature
a broad hump centered at
39.50 ppm and multiplet of higher order centered at
a
23.30 ppm. Upon cooling the latter NMR solution to ꢂ80 °C, the
hump in the 31P{1H} spectrum at 39.50 ppm, that has been as-
signed to the couple of chiral phosphorus atoms, has been resolved
very nicely into a multiplet, while the multiplet at 23.30 ppm only
experienced a slight shift upon cooling the NMR solution. Since the
31P{1H} NMR spectrum of 4 is of higher order, it has been success-
fully simulated employing the following NMR parameters:
d1 = 41.39, d2 = 41.45, d3 = d4 = 23.98 ppm, 2JPP = 83.0 Hz and
3JPP = 29.0 Hz [12].
3.3. Single crystal X-ray structures of [Ni2Cl3(
l
j
-(
j
O1,
j
j
P1:
j
j
P2:
j
j
P3:
j
j
P4-
o-MeO-o-O-dppcb))] (3) and [Ni2Cl2(
l-(
j
O1,
P1:
P2:
O2,
P3:
P4-o-
MeO-o-O,O0-dppcb)] (4)
Fig. 3. Variable-temperature 31P{1H} NMR study of 2 (DMF-d7, 121.50 MHz): (a)
under nitrogen at room temperature; (b) after heating the NMR solution to 80 °C;
(c) after cooling the NMR solution (1.5 h at 80 °C) to room temperature; (d) after
heating the NMR solution to 100 °C; (e) after heating the NMR solution at 100 °C for
1.5 h and (f) after cooling the NMR solution to room temperature.
A single crystal X-ray structure analysis of 3 ꢀ 3DMF unambigu-
ously confirmed the occurrence of a phosphanylphenolate ligand
bearing one coordinating phenolate unit bonded to a chiral phos-
Scheme 4.

M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
2007
phorus donor atom. As a result the ligand acts as a bridging
and
3-P,P,O ligand. An ORTEP drawing of the molecular structure
j
2-P,P
j
is shown in Fig. 4, while selected bond distances and angles are re-
ported in Table 3.
The crystal structure of compound 3 ꢀ 3DMF shows for both
Ni(II) centers two different square-planar coordination spheres.
While Ni(1) is 1,3-cis coordinated by two phosphorus donor atoms
(see Scheme 3) and two chloride atoms, Ni(2) binds to two 2,4-cis-
coordinating phosphorus atoms, to one chloride atom, and to a
phenolate oxygen atom. As a consequence, one of the phosphorus
atoms (i.e. P(2)) that bears the phenolate unit and the cyclobutane
carbon atom C(2) (see Fig. 4) constitutes a center of chirality. The
coordination of the phenolate oxygen atom O(3) to Ni(2) leads to
a completely asymmetric molecule that is clearly evidenced by
0
four different Ni–P distances ranging from 2.1217(9) ÅA for Ni(2)–
0
P(2) to 2.1783(10) ÅA for Ni(1)–P(3) (see Table 3). In accordance
with this, also the P–Ni–P bite angles are significantly different,
showing for P(1)–Ni(1)–P(3) 95.00(4)° and for P(2)–Ni(2)–P(4)
92.07(4)°. A further consequence of the phenolate coordination
to Ni(2) is that unlike 2 ꢀ 2.5C2H4Cl2 ꢀ H2O, 3 ꢀ 3DMF shows no sig-
nificant methoxy-oxygen interactions at Ni(1) (see Table 3), due to
a slight conformational change of the ligand upon the coordination
of the phenolate unit to Ni(2). As a consequence, the energy barrier
for the second methoxy-cleavage that occurred at Ni(1) has to be
significantly higher compared to the first one. Accordingly, the var-
iable-temperature 31P{1H} NMR experiment showed that the con-
version of 3 into 4 occurs at a temperature that is 20 °C higher
compared to that found for the conversion of 2 into 3 (i.e. 100 ver-
sus 80 °C) (Fig. 3).
Fig. 5. ORTEP diagram of 4 ꢀ 4CH3CN. Hydrogen atoms and solvent molecules are
omitted for clarity and thermal ellipsoids are shown at the 30% probability level.
ties attached to phosphorus atoms that belong to different Ni-coor-
dination spheres, in 4 ꢀ 4CH3CN two phosphorus atoms (i.e. P(2)
and P(3)) and the cyclobutane carbon atoms represent centers of
chirality. Additionally, the latter compound exhibits a chiral axis
due to the rigid folding of the cyclobutane ring that is perpendicu-
lar to the best plane defined by the cyclobutane carbon atoms.
However, since only one pair of diastereomers is formed, these
centers of chirality are obviously related to each other as a conse-
quence of seven fused rings (see Fig. 5). All Ni–P bonding distances
in 4 ꢀ 4CH3CN are significantly shorter compared to those observed
in 2 ꢀ 2.5C2H4Cl2 ꢀ H2O (Table 3). Like 3 ꢀ 3DMF, 4 ꢀ 4CH3CN shows
significantly shorter Ni–P bonds for the chiral phosphorus atoms
(i.e. P(2) and P(3), Fig. 5), due to the fact that the latter atoms share
two five- and six-membered metallacycles, respectively. Impor-
tantly, the two coordination moieties of 4 ꢀ 4CH3CN are not identi-
cal, clearly evidenced by the significantly different P–Ni–P bite
angles of 94.59(4)° and 91.95(3)°.
A single crystal structure analysis of compound 4 ꢀ 4CH3CN
(Fig. 5) confirmed the occurred double methoxy-group cleavage
and the formation of a symmetrical j
3-P,P,O-coordinating bis-phe-
nolate ligand, leading to one coordinating phenolate unit at each
metal center (see Scheme 4 and Fig. 5).
The crystal structure of 4 ꢀ 4CH3CN shows for both Ni(II) centers
a square-planar coordination geometry with two 1,3-cis-coordinat-
ing phosphorus atoms (see Scheme 3), a phenolate oxygen atom
and a chloride atom. Due to the presence of two phenolate moie-
4. Conclusions
The dinuclear Pt-complex (1) that represents the key compound
in the synthesis of o-MeO-dppcb by an intramolecular [2+2] photo-
cycloaddition, exploiting the template effect of 1, has been synthe-
sized and completely characterized. The single crystal X-ray
structure analysis of the latter complex gives a convincing clue
for the selective formation of the all-trans configuration regarding
the bis(o-methoxyphenylphosphanyl) groups attached to the
cyclobutane carbon ring in o-MeO-dppcb. Obviously,
p-stacking
interactions between adjacent o-methoxyphenyl groups in 1 that
are clearly visible in Fig. 1, occur as a consequence of ‘‘steric pres-
sure” [21]. Thus, the orientations of the bridges in 1 change due to
this ‘‘steric pressure”, compared with the phenyl-counterpart
[Pt2Cl4(l-(j j p-stack-
P1: P2-trans-dppen))2], where no analogous
ing interactions between adjacent phenyl groups are present [15].
The single crystal structure analysis of the dinuclear Ni(II) com-
plex 2 that contains all-trans-o-MeO-dppcb in the 1,3-cis-coordi-
nating mode (Scheme 3), exhibits one Ni(II)–o-MeO–oxygen
Fig. 4. ORTEP diagram of 3 ꢀ 3DMF. Hydrogen atoms and solvent molecules are
omitted for clarity and thermal ellipsoids are shown at the 30% probability level.

2008
M. Fessler et al. / Inorganica Chimica Acta 363 (2010) 2001–2008
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(f) W. Keim, R.P. Schulz, J. Mol. Catal. 92 (1994) 21;
interaction in both coordination spheres. These latter interactions
have been exploited to convert 2, upon a thermal reaction, first into
the mono-phenolate complex 3 and then into the bis-phenolate
complex 4. This intramolecular methoxy-group cleavage occurring
step by step is due to a slight conformational change of the ligand
(g) F.M. Bauer, S. Mecking, Macromolecules 34 (2001) 1165;
(h) R. Soula, J.P. Broyer, M.F. Llauro, A. Tomov, R. Spitz, J. Claverie, X. Drujon, J.
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2-P,P and 3-P,P,O-coor-
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dination modes of this ligand to the Ni(II) centers. Compounds 3
and 4 have been isolated and fully characterized in solution and
in the solid state. Their single crystal X-ray diffraction analyses
have been reported and discussed.
Attempts to de-coordinate and isolate the new phosphanophen-
olate ligands o-MeO-O-dppcb and o-MeO-O,O0-dppcb from 3 and 4,
respectively, are in progress in our laboratory.
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Acknowledgments
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of Innsbruck, Innsbruck, Austria, 1998.
The authors thank the Fonds zur Förderung der wissenschaftli-
chen Forschung (FWF) and the Forschungsförderungsgesellschaft
(FFG), Vienna, Austria, the Tiroler Wissenschaftsfonds, Innsbruck,
Austria, and the companies D. Swarovski and Co. and VERBUND –
Austrian Renewable Power GmbH for financial support.
[13] Z. Otwinowski, W. Minor, in: C.W. Carter Jr., R.M. Sweet (Eds.), Methods in
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Appendix A. Supplementary material
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