Coordination of ortho and para quinones and oxidation reduction processes in trimethylphosphine complexes of cobalt and nickel

Article abstract of DOI:10.1016/S0020-1693(99)00008-0

The ortho-quinones 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 3,5-di-tert-butyl-benzoquinone-1,2 oxidatively substitute trimethylphosphine into Ni(PMe₃)₄ affording molecular compounds containing chelating dioxo ligands of the catecholate type. Using CoMe(PMe₃)₄ as a substrate the synthesis was extended to tetrachlorobenzoquinone-1,2 and dibenzoyl with retention of the CoMe group. Formally omitting the methyl group, odd-electron complexes were obtained from Co(cyclopentene)(PMe₃)₃ by reaction with 9,10-phenanthrenequinone or dibenzoyl. The para-quinones 2,5-di-tert-butyl-benzoquinone-1,4 and 2-tert-butyl-naphthoquinone-5,10 displace two trimethylphosphines in Ni(PMe₃)₄ to form diene complexes of zerovalent nickel. X-ray crystal structures establish the presence of O:O coordinated catecholato ligands for nickel(II) and cobalt(III) and reveal an η⁴-diene type quinone ligand coordinated to nickel(0).

Full text of DOI:10.1016/S0020-1693(99)00008-0

Inorganica Chimica Acta 287 (1999) 167–172
Coordination of ortho and para quinones and oxidation reduction
processes in trimethylphosphine complexes of cobalt and nickel
Hans-Friedrich Klein a,*, Emmanuel Auer a, Attila Dal a, Ute Lemke a,
Mathias Lemke a, Thomas Jung a, Caroline Ro¨hr b, Ulrich Flo¨rke c,
Hans-Ju¨rgen Haupt c
a Institut fu¨r Anorganische Chemie der Technischen Uni6ersita¨t Darmstadt, Petersenstraße 18, D-64287 Darmstadt, Germany
b Institut fu¨r Anorganische und Analytische Chemie der Uni6ersita¨t Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany
c Anorganische und Analytische Chemie der Uni6ersita¨t/GH Paderborn, Warburger Strasse 100, D-33098 Paderborn, Germany
Received 2 September 1998; accepted 16 December 1998
Abstract
The ortho-quinones 9,10-phenanthrenequinone, 1,2-naphthoquinone, and 3,5-di-tert-butyl-benzoquinone-1,2 oxidatively substi-
tute trimethylphosphine into Ni(PMe3)4 affording molecular compounds containing chelating dioxo ligands of the catecholate
type. Using CoMe(PMe3)4 as a substrate the synthesis was extended to tetrachlorobenzoquinone-1,2 and dibenzoyl with retention
of the CoMe group. Formally omitting the methyl group, odd-electron complexes were obtained from Co(cyclopentene)(PMe3)3
by reaction with 9,10-phenanthrenequinone or dibenzoyl. The para-quinones 2,5-di-tert-butyl-benzoquinone-1,4 and 2-tert-butyl-
naphthoquinone-5,10 displace two trimethylphosphines in Ni(PMe3)4 to form diene complexes of zerovalent nickel. X-ray crystal
structures establish the presence of O:O coordinated catecholato ligands for nickel(II) and cobalt(III) and reveal an h4-diene type
quinone ligand coordinated to nickel(0). © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Oxidation/reduction; Cobalt complexes; Nickel complexes; Quinone complexes
1. Introduction
Presently there is renewed interest in transition metal
coordination of 1,2-benzoquinones, because molecular
complex units of certain types can switch their elec-
Among these are compounds which serve as homoge-
tronic ground states as a function of temperature [1].
neous catalysts [3], and some are regarded as models
The concept of valence tautomerism has been applied
for biological transport reactions [4].
to the electronic switching in molecules containing
1,4-Benzoquinones are known to act as p-diene lig-
quinone acceptor (A) and metal donor (D) functions
ands [5] towards zerovalent nickel and even in the
and may be described by an equilibrium.
presence of trialkylphosphine donors are incompletely
reduced [6].
D–A+
X
+(D)–A
Competition with monodentate ligands in equilibria
of ligand dissociation is favourable for quinones in
cases where metals are readily oxidised. Two oxo func-
tions and a diene system, in 1,2 and 1,4 positions,
respectively, or vice versa, provide either p-donating or
p-accepting chelate functions which can be utilised by
the metal.
The majority of quinone complexes are found in only
one coordination mode involving either benzoquinone
(B), semiquinone (S), or catecholato (C) ligands [2].
We chose the metal–ligand fragments Ni(PMe3)2
* Corresponding author. Tel.: +49-6151-16 2173; fax: +49-6151-
16 4173.
(d10, 14 valence electrons), Co(PMe3)2 (d9, 13 valence
0020-1693/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00008-0

168
H.-F. Klein et al. / Inorganica Chimica Acta 287 (1999) 167–172
electrons), and CoMe(PMe3)3 (d8, 16 valence electrons)
in order to explore metal-to-ligand charge transfer and
the role of chelating properties of quinones and their
reduced forms.
in 50 ml of THF at 20°C within 16 h formed a dark
green solution. The volatiles were removed in vacuo
and the residue was washed with ether. Crystallisation
from 30 ml THF at −20°C afforded a dark green
solid. Yield 403 mg (89%), m.p. 205–207°C.
Anal. Calc. for C20H38NiO2P2 (431.2): C, 55.71; H,
8.88; P, 14.37. Found: C, 55.29; H, 8.75; P, 14.62%.
1H NMR (300 MHz, THF-d8, 298 K): l=1.19 (s,
9H, CCH3), 1.34 (s, 9H, CCH3), 1.41 (m, 18H, PCH3),
2. Experimental
2.1. General procedures and materials
3
6.20 (d, 3J=2.3 Hz, 1H, 3-H), 6.28 (d, J=2.3 Hz, 1H,
6-H). 13C{1H} NMR (75.4 MHz, THF-d8, 298 K):
l=12.73 (d, 1J(PC)=24.3 Hz, PCH3), 13.39 (d,
1J(PC)=24.9 Hz, PCH3), 28.47 (CCH3), 30.94
(CCH3), 32.60 (CCH3), 33.04 (CCH3), 106.43, 108.09
(CH); 130.34, 134.12 (CO). 31P{1H} NMR (81 MHz,
THF-d8, 223 K): l PA 3.3, l PB 3.9 (2J(PAPB)=90.5
Hz).
All air-sensitive and volatile materials were handled
by standard vacuum techniques and kept under argon.
Details have been given elsewhere [7]. Literature meth-
ods were used in the preparation of the metal com-
plexes Ni(PMe3)4 [8], CoMe(PMe3)4 [9], and Co(C2H4)-
(PMe3)3 [10], quinones (Merck-Schuchardt) were used
as purchased.
2.2.4. 9,10-Phenanthrenequinone(methyl)tris(trimethyl-
phosphine)cobalt (4)
2.2. Preparations
A sample of CoMe(PMe3)4 (800 mg, 2.12 mmol) and
460 mg of 9,10-phenanthrenequinone (2.20 mmol) were
combined in 50 ml of ether and formed an orange
solution which after stirring for 15 h at 20°C became
intensely red. The volatiles were removed in vacuo, and
the residue was extracted with pentane. Crystallisation
at −27°C afforded bunches of red–brown crystals
which were dried in vacuo. Yield 370 mg (34%), dec.
\107°C.
Anal. Calc. for C24H38CoO2P3 (510.4): C, 56.48; H,
7.50; P, 18.20. Found: C, 55.48; H, 7.44; P, 17.62%.
1H NMR (200 MHz, THF-d8, 298 K): l=0.10 (s,
3H, CoCH3), 1.30 (s, 27H, PCH3), 7.24–8.41 (m, 8H,
CH). 31P{1H} NMR (81 MHz, THF-d8, 233 K): l=
11.0 (s).
2.2.1. 9,10-Phenanthrenequinonebis(trimethylphosphine)-
nickel (1)
A sample of Ni(PMe3)4 (400 mg, 1.10 mmol) and 230
mg of 9,10-phenanthrenequinone (1.10 mmol) were
combined in 50 ml of THF at −70°C to form a dark
green mixture. After stirring for 24 h at 20°C the
volatiles were removed in vacuo and the residue was
washed with ether. Crystallisation from THF at
−27°C afforded dark green rhombs which were dried
in vacuo. Yield 340 mg (34%), dec. \217°C.
Anal. Calc. for C20H26NiO2P2 (419.1): C, 57.32; H,
6.25; P, 14.78. Found: C, 58.30: H, 6.35; P, 14.31%.
1H NMR (300 MHz, acetone-d8, 298 K): l=1.61 (m,
18H, PCH3), 7.18 (m, 2H, CH), 7.35 (m, 2H, CH), 8.04
(m, 2H, CH), 8.53 (m, 2H, CH).
2.2.5. 3,5-Di-tert-butyl-1,2-benzoquinone(methyl)-
tris(trimethylphosphine)cobalt (5)
2.2.2. 1,2-Naphthoquinonebis(trimethylphosphine)nickel
(2)
A sample of CoMe(PMe3)4 (330 mg, 0.93 mmol) and
200 mg of 3,5-di-tert-butyl-benzoquinone-1,2 (0.93
mmol) in 50 ml of ether at 20°C formed an orange
solution which within 5 min changed to violet. After 5
h the volatiles were removed in vacuo and the residue
was extracted with pentane over a glass-sinter disc(G
3). Crystallisation at −20°C afforded dark violet
cubes. Yield 300 mg (62%), m.p. 127–129°C.
A sample of Ni(PMe3)4 (1180 mg, 3.25 mmol) and
514 mg of 1,2-naphthoquinone (3.25 mmol) in 50 ml of
THF were constantly stirred at 20°C for 24 h to afford
a dark green solution. The volatiles were removed in
vacuo and the residue was washed with ether and
dissolved in 30 ml of THF. Crystallisation at −20°C
afforded a dark green solid. Yield 785 mg (40%), m.p.
187–189°C.
Anal. Calc. for C29H39NiO4P3 (603.2): C, 57.74; H,
6.52; P, 15.40. Found: C, 57.70; H, 6.20; P, 14.77%.
1H NMR (300 MHz, acetone-d8, 298 K): l=1.45 (m,
27H, PCH3), 6.75 (m, 3H, CH), 6.84 (m, 2H, CH), 7.44
(m, 2H, CH), 7.79 (m, 2H, CH).
Anal. Calc. for C24H50CoO2P3 (522.5): C, 55.17; H,
9.64; P, 17.78. Found: C, 55.09; H, 9.76; P, 17.27%.
1H NMR (300 MHz, THF-d8, 298 K): l= −0.10 (s,
3H, CoCH3), 1.23 (s, 9H, CCH3), 1.30 (d, 27H,
2J(PH)=7.9 Hz, PCH3), 1.41 (s, 9H, CCH3), 6.18 (m,
1H, CH), 6.35 (m, 1H, CH). 13C{1H} NMR (75.4 MHz,
1
THF-d8, 298 K): l=14.7 (d, J(PC)=20.0 Hz, PCH3),
13.39 (d, 1J(PC)=24.9 Hz, PCH3), 30.5 and 32.7
(CCH3), 30.94 (CCH3), 34.5 and 35.3 (CCH3), 33.04
(CCH3), 108.8, 110.4 (CH); 133.0, 135.3 (C), 161.3 and
163.7 (CO).
2.2.3. 3,5-Di-tert-butyl-1,2-benzoquinone)bis(trimethyl-
phosphine)nickel (3)
A sample of Ni(PMe3)4 (380 mg, 1.05 mmol) and 231
mg of 3,5-di-tert-butyl-benzoquinone-1,4 (1.05 mmol)

H.-F. Klein et al. / Inorganica Chimica Acta 287 (1999) 167–172
169
Table 1
Crystal data for compounds 1, 5 and 11
1
5
11
Formula
C20H26NiO2P2
419.1
C24H50CoO2P3
522.5
0.52×0.38×0.47
monoclinic
P21/n
13.253(1)
16.618(2)
13.887(2)
96.304(8)
3039.9(5)
4
C
468.4
22H43NiO2.5P2
Molecular mass
Crystal size (mm)
Crystal system
Space group
0.15×0.20×0.29
orthorhombic
P212121
10.470(2)
11.959(3)
16.422(4)
90
2056.2(8)
4
1.354
0.28×0.17×0.15
monoclinic
P21/c
10.705(1)
18.430(5)
14.276(2)
111.648(8)
2617.8(8)
4
˚
a (A)
˚
b (A)
˚
c (A)
i (°)
V (A )
3
˚
Z
Dcalc (g cm−3
)
1.142
0.738
293(2)
1.188
0.879
293(2)
v(Mo Ka) (mm−1
)
1.11
293(2)
Temperature (K)
Data collection range (°)
h
k
l
No. reflections measured
No. unique data
Parameters
GOF on F2
R1 (I]2|(I))
wR2 (all data)
4.652q554
−105h513
05k515
05l521
4699
4387 (Rint=0.028)
224
0.994
3.852q550
−15h55
−195k519
−165l516
6057
2411(Rint=0.0858)
271
1.006
3.852q555
−15h513
−15k 523
−185l517
7268
5881(Rint=0.0393)
238
1.027
0.061
0.143
0.0526
0.1582
0.0571
0.1632
2.2.6. 3,4,5,6-Tetrachloro-1,2-benzoquinone(methyl)-
tris(trimethylphosphine)cobalt (6)
7.00–7.97 (m, 10H, CH). 13C{1H} NMR (75.4 MHz,
THF-d8, 298 K): l= −8.4 (CoCH3), 13.4 (m, PCH3),
123.3, 125.8, and 126.2 (CH), 140.4 (C), 153.5 (CO).
CoMe(PMe3)4 (700 mg, 1.85 mmol) in 50 ml of ether
upon addition of 470 mg of 3,4,5,6-tetrachlorobenzo-
quinone (1.91 mmol) turned from orange to red–brown
within 2 min. After stirring for 15 h at 20°C a yellow–
green solid was filtered off and the filtrate was evapo-
rated to dryness. Extraction with ether and crys-
tallisation at −27°C afforded dark red crystals which
were dried in vacuo. Yield 440 mg (22%), dec. \
119°C.
2.2.8. 9,10-Phenanthrenequinonetris(trimethyl-
phosphine)cobalt (8)
A sample of Co(C2H4)(PMe3)3 (720 mg, 2.28 mmol)
and 450 mg of 9,10-phenanthrenequinone (2.16 mmol)
were combined in 120 ml of THF and constantly stirred
for 18 h at 20°C. The volatiles were removed in vacuo,
and the greenish–brown residue was extracted with 80
ml of ether. From a volume of 50 ml at 0°C dark green
crystals were collected and dried in vacuo. Yield 500
mg (45%), dec. \120°C.
Anal. Calc. for C16H30Cl4CoO2P3 (548.1): C, 35.06;
H, 5.52. Found: C, 35.65; H, 5.76%.
1H NMR (300 MHz, THF-d8, 298 K): l=0.13 (s,
3H, CoCH3), 1.28 (s, 27H, PCH3). 31P{1H} NMR (81
MHz, THF-d8, 233 K): l=15.0 (s).
Anal. Calc. for C23H35CoO2P3 (495.4): C, 55.75; H,
7.07; P, 18.78. Found: C, 54.83; H, 7.04; P, 19.29%.
2.2.7. 1,2-Diphenylethanedione(methyl)bis(trimethyl-
phosphine)cobalt (7)
2.2.9. 1,2-Diphenylethanedionetris(trimethylphosphine)-
cobalt (9)
A sample of CoMe(PMe3)4 (380 mg, 1.00 mmol) and
200 mg of benzil (0.95 mmol) were combined in 90 ml
of ether to form a blue–green solution. Crystallisation
at −20°C afforded dark green crystals with black
shining faces. Yield 280 mg (66%), dec. \153°C.
Anal. Calc. for C21H31CoO2P2 (436.2): C, 57.81; H,
7.11; P, 14.22. Found: C, 57.57; H, 7.65; P, 14.22%.
1H NMR (300 MHz, THF-d8, 297 K): l=0.65 (s,
A sample of Co(C2H4)(PMe3)3 (890 mg, 2.82 mmol)
and 590 mg of benzil (2.81 mmol) were combined in 90
ml of ether to form a blue–green solution. Crystallisa-
tion from a volume of 70 ml at −20°C gave bunches of
dark green needles which were isolated by decantation
and drying in vacuo. Yield 1150 mg (82%), dec.
\130°C.
Anal. Calc. for C23H37CoO2P3 (497.4): C, 55.53; H,
7.44; P, 18.71. Found: C, 55.20; H, 7.64; P, 17.83%.
2
3H, CoCH3), 1.36 (d, J(PH)=8.1 Hz, 18H, PCH3),

170
H.-F. Klein et al. / Inorganica Chimica Acta 287 (1999) 167–172
2.2.10. 2-tert-Butyl-anthraquinonebis(trimethyl-
phosphine)nickel (10)
A sample of Ni(PMe3)4 (400 mg, 1.10 mmol) and 247
mg of 2-tert-butyl-anthraquinone (0.94 mmol) in 50 ml
of THF after 16 h at 20°C gave a dark red solution.
The volatiles were removed in vacuo, and the residue
was dissolved in ether.
factors of 0.57 and 0.43 for C31–C33 and C41–C43,
respectively. The cell of 11 contains two molecules of
diethyl ether showing disordered ethyl groups.
3. Results and discussion
3.1. 1,2-Dioxo systems
At −20°C dark red crystals were formed. Yield 377
mg (84%), m.p. 65–66°C.
Combining Ni(PMe3)4 with phenanthrenequinone,
1,2-naphthoquinone or 3,5-di-tert-butylbenzoquinone
in a solvent of low polarity induces characteristic
changes of color indicating fast, medium and slow
reactions, respectively. The same order of reactivities
was observed with CoMe(PMe3)4 and phenanthrene-
quinone or 3,5-di-tert-butylbenzoquinone.
Anal. Calc. for C24H34NiO2P2 (475.2): C, 60.67; H,
7.21; P, 13.04. Found: C, 59.85; H, 7.21; P, 13.37%.
1H NMR (300 MHz, benzene-d6, 298 K): l=0.51 (s,
18H, PCH3), 1.32 (s, 9H, CCH3), 7.35 (m, 3H, CH),
8.48 (m, 2H, CH), 8.87 (m, 2H, CH). 13C{1H} NMR
1
(75.4 MHz, THF-d8, 298 K): l=13.48 (d, J(PC)=
22.9 Hz, PCH3), 29.84 (CCH3), 33.98 (CCH3), 117.57,
120.15, 121.56, 125.79, 127.72, 128.62, 129.34 (CH),
146.68 (CO).
(1)
(2)
2.2.11. 2,5-Di-tert-butyl-1,4-benzoquinonebis(trimethyl-
phosphine)nickel (11)
A sample of Ni(PMe3)4 (700 mg, 1.92 mmol) and 425
mg of 2,5-di-tert-butyl-1,4-benzoquinone (1.92 mmol)
in 60 ml of THF after 16 h gave a dark red solution.
Workup as with 2 and crystallisation from 30 ml of
THF gave red–brown rhombs. Yield 538 mg (65%),
m.p. 220–222°C. (Crystals obtained from ether at
−27°C were subjected to an X-ray diffraction analy-
sis.)
Anal. Calc. for C20H38NiO2P2 (431.2): C, 55.71; H,
8.88; P, 14.37. Found: C, 56.70; H, 9.13; P, 14.58%.
1H NMR (300 MHz, THF-d8, 298 K): l=1.28 (d,
2J(PH)=6.4 Hz, 18H, PCH3), 1.33 (s, 18H, CCH3),
5.19 (s, 2H, CH). 13C{1H} NMR (75.4 MHz, THF-d8,
1
298 K): l=14.67 (t%, ꢀ J(PC)+3J(PC)ꢀ=13.2 Hz,
PCH3), 28.93 (CCH3), 32.32 (CCH3), 96.24 (CH).
2.3. X-ray data
2.3.1. Crystal structure analyses
Pertinent crystal data are presented in Table 1.
2.3.2. Data collection
Single crystals of 1, 5 and 11 were sealed in glass
capillaries under argon. Data were collected using
monochromated Mo Ka radiation on a Siemens R3
diffractometer for 1 and on a Siemens P4 diffractome-
ter for 5 and 11. Absorption corrections were applied
via psi-scans for 1 only.
The products 1–5 formed according to Eqs. 1 and 2
are soluble in hydrocarbon or ether solvents as is
expected of molecular compounds. Crystalline materials
have a better air-stability than would be anticipated for
complexes of Ni(0) and Co(I). IR data show a
bathochromic shift of w(CO) bands consistent with the
presence of chelating catecholato ligands [1,2].
2.3.3. Solution and refinement
Structures were solved by direct methods. Non-hy-
drogen atoms were refined anisotropically on F2. Hy-
drogen atoms were fixed at idealised positions with
isotropic displacement parameters. The methyl groups
at P1 of 1 are disordered over two sites with occupation

H.-F. Klein et al. / Inorganica Chimica Acta 287 (1999) 167–172
171
confirmed by X-ray crystallography for nickel and
cobalt metal centers of complexes 1 and 5.
The structure of the nickel complex 1 (Fig. 1) con-
tains planar molecules with no intermolecular contacts.
Bond distances NiO and NiP are as expected for Ni(II),
and the chelate-bite O1–Ni–O2 is almost rectangular
(87.9(2)°).
The molecular structure of complex 5 (Fig. 2) shows
an octahedrally surrounded cobalt atom in a meridional
configuration. A mirror plane of the molecule contains
all the ring atoms of the catecholato ligand and one C
and one P donor atom. One of the Co,O bonds which
experiences the trans influence of the CoMe group is 3
pm longer than the other while both exceed the value
˚
known of semiquinone ligands (1.29 A) [11]. The
chelate-bite angle in
5 (O1–Co–O2=85.5(3)°) is
smaller than in 1.
An effective oxidative addition of the quinones is
indicated in both structures by a shortening of the bond
˚
Fig. 1. Molecular structure of 1; selected distances (A) and angles (°):
Ni–O1 1.875(4), Ni–O2 1.875(4), Ni–P1 2.172(2), Ni–P2 2.168(2),
O1–C13 1.347(6), O2–C14 1.343(6), C13–C14 1.366(8), C12–C13
1.432(7); O1–Ni–O2 87.9(2), O1–Ni–P1 174.6(1), O1–Ni–P2
83.1(1), O2–Ni–P1 87.3(1), O2–Ni–P2 170.8(1), P1–Ni–P2
101.71(8), Ni–O1–C13 108.3(4), Ni–O2–C14 109.1(4), O1–C13–
C14 118.0(5), O2–C14–C13 116.7(5).
˚
distance C(O)–C(O) upon coordination (1.541 A in
˚
ortho-benzoquinone [12]) to 1.366(8) A in 1 and
˚
˚
˚
1.447(14) A in 3 while CO distances (1.216 A in ortho-
benzoquinone) are elongated to 1.345(6) A in 1 and
1.35(2) A in 3 and fall in the range of single bonds.
˚
The cobalt d8 system even reduces stabilised tetra-
chlorobenzoquinone as well as diketones like diphenyl-
ethanedione according to Eq. (2) to afford the
enediolato(methyl)cobalt(III) complexes 6 and 7. The
reaction can also be transferred to the cobalt (d9“d7)
system according to Eq. (3) starting from ethene-
tris(trimethylphosphine)cobalt(0) and yielding the para-
magnetic catecholatocobalt(II) compounds 8 and 9.
In the NMR experiment the 3,5-di-tert-butyl sub-
stituents in 3 render the two 31P nuclei anisochronic.
The AB spin system (J(PP)=90.5 Hz) represents two
trimethylphosphine ligands in cis positions of a square
planar nickel complex. The two oxidation equivalents
for the conversion of nickel from d10 to d8 appear to
arise from a reduction of the quinone to a catecholato
ligand. The presence of catecholato chelate rings is
(3)
˚
Fig. 2. Molecular structure of 5; selected distances (A) and angles (°):
Co–C1 2.022(6), Co–O1 1.961(6), Co–O2 1.932(7), Co–P1 2.180(4),
Co–P2 2.236(3), Co–P3 2.249(3), O1–C2 1.33(2), O2–C15 1.37(2),
C2–C3 1.409(14), C2–C15 1.446(14), C3–C8 1.38(2), C8–C9
1.404(13), C9–C14 1.39(2), C14–C15 1.33(3); O1–Co–C1 177.8(4),
O2–Co–C1 92.3(3), O1–Co–O2 85.5(3), C1–Co–P1 97.6(3), O1–
Co–P1 84.6(3), O2–Co–P1 170.1(2), C1–Co–P2 86.1(2), O1–Co–P2
93.6(2), O2–Co–P2 83.8(2), C1–Co–P3 85.9(2), O1–Co–P3 93.9(3),
O2–Co–P3 83.7(2), P1–Co–P2 96.32(13), P1–Co–P3 97.47(10), P2–
Co–P3 164.85(13), C2–O1–Co 110.2(6), C15–O2–Co 111.2(7), O1–
C2–C3 126.1(9), O1–C2–C15 117.9(11), C3–C2–C15 116.0(14),
O2–C15–C2 115(2), C14–C15–C2 122(2), C14–C15–O2 122.9(11).

172
H.-F. Klein et al. / Inorganica Chimica Acta 287 (1999) 167–172
Physical properties and spectroscopic data are in line
with molecular catecholato or enediolato compounds.
3.2. 1,4-Dioxo systems
1,4-Quinones under the same conditions replace two
of the phosphine ligands in Ni(PMe3)4 according to Eq.
(4) affording (quinone)Ni(PMe3)2 complexes 10 and 11.
(4)
˚
Fig. 3. Molecular structure of 11; selected distances (A) and angles
(°): Ni–C 2.263(4), Ni–C3 2.153(4), Ni–C5 2.257(4), Ni–C6 2.144(4),
Ni–P1 2.200(1), Ni–P2 2.187(1), Ni–C1 2.389(4), Ni–C4 2.399(4),
O1–C1 1.249(4), O2–C4 1.247(4), C1–C2 1.461(5), C2–C3 1.389(5),
C3–C4 1.465(6), C4–C5 1.462(5), C5–C6 1.398(5); P1–Ni–P2
100.81(5), O1–C1–C2 124.0(3), O1–C1–C6 120.3(3), O2–C4–C3
120.2(4), O2–C4–C5 125.3(4), C2–C1–C6 115.5(3), C1–C2–C3
115.4(3), C2–C3–C4 126.9(3), C3–C4–C5 114.4(3), C4–C5–C6
116.4(3), C1–C6–C5 125.4(3).
(Fax: +44-1223-336-033; e-mail: teched@chemcrys.
cam.ac.uk).
Acknowledgements
Strong IR absorptions at 1628 cm−1 (10) or 1579
cm−1 are assigned to w(CꢀO) vibrations of a coordi-
nated 1,4-quinone [5,6]. With smaller substituents in the
position of the tert-butyl group of 11 (Me: w(CꢀO) at
1618 (m), 1599 (s) cm−1, H: w(CꢀO) at 1672 (m), 1614
(s) cm−1) the anthraquinone complexes decompose at
ambient temperature.
Financial support of this work by the Fonds der
Chemischen Industrie and the Deutsche Forschungsge-
meinschaft is gratefully acknowledged.
References
The molecular structure of the thermally most stable
complex 11 (Fig. 3) shows the well-known 1,4-diene
type p-coordination of nickel [5]. NMR spectra are as
expected for a diamagnetic compound and do not
indicate ligand reduction to the semiquinone state or
beyond. All our attempts to obtain the corresponding
methylcobalt(I) or cobalt(0) complexes have failed so
far.
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4. Supplementary material
The crystallographic data (without structure factors)
of the structures described in this publication have been
submitted as supplementary publications no. CCDC-
102648 (1), CCDC-102775 (5), and CCDC-102774 (11)
to the Cambridge Crystallographic Data Centre. Copies
of the data can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ
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