Oxidation-reduction exchange of 2-acylenolato and trimethylphosphane ligands between d6 and d8 complexes of nickel and cobalt

Article abstract of DOI:10.1016/S0020-1693(99)00331-X

A series of five (C:O)-dianionic 1-acyl-2-enolato ligands C(O)-C=C-O in a transmetallation reaction between 18-electron metal-d⁶ complexes mer-trans-NiMe(X)[C(O)-C=C-O](PMe₃)₂ [C=C=C₆H₄, X = I (1); C=C=3-CMe₃-5-Me-C₆H₂, X = I (2); C=C=5,6-benzo-C₆H₂, X = I (3); C=C=3,4-benzo-cyclohexene, X = Br (4); C=C=1,2-diphenylethene, X = I (5)] and the 18-electron metal-d⁸ compound CoMe(PMe₃)₄ (1:2), undergo a reductive coupling of acyl and methylnickel functions involving the C(O)-C=C-O ligands. Subsequent migration of methyl groups between cobalt intermediates generates three products: mer-trans-CoMe₂[MeC(O)-C=C-O](PMe₃)₂ (6-10), Ni(PMe₃)₄, and CoX(PMe₃)₃. The X-ray crystal structure of compound 7 has been determined. The methyl ligands are found in positions opposite to the O-donor functions. Upon replacing the aromatic rings in salicylaldehyde derivatives C(O)-C=C-O by more flexible cyclohexene rings or acyclic systems the reduction of Ni(IV) complexes follows a different course. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00331-X

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Inorganica Chimica Acta 298 (2000) 63–69
Oxidation–reduction exchange of 2-acylenolato and
trimethylphosphane ligands between d6 and d8 complexes
of nickel and cobalt
Hans-Friedrich Klein a,*, Xiaoyan Li a, Hongjian Sun a, Robert Beck a, Ulrich Flo¨rke b,
Hans-Ju¨rgen Haupt b
a Institut fu¨r Anorganische Chemie der Technischen Uni6ersita¨t Darmstadt, Petersenstraße 18, D-64287 Darmstadt, Germany
b Anorganische und Analytische Chemie der Uni6ersita¨t-GH Paderborn, Warburger Straße 100, D-33098 Paderborn, Germany
Received 25 March 1999; accepted 2 July 1999
Dedicated to H. Schmidbaur on the occasion of his 65th birthday
Abstract
A series of five (C:O)-dianionic 1-acyl-2-enolato ligands C(O)ꢀCꢁCꢀO in a transmetallation reaction between 18-electron
metal-d6 complexes mer-trans-NiMe(X)[C(O)ꢀCꢁCꢀO](PMe3)2 [CꢁCꢁC6H4, X=I (1); CꢁCꢁ3-CMe3-5-Me-C6H2, X=I (2);
CꢁCꢁ5,6-benzo-C6H2, X=I (3); CꢁCꢁ3,4-benzo-cyclohexene, X=Br (4); CꢁCꢁ1,2-diphenylethene, X=I (5)] and the 18-electron
metal-d8 compound CoMe(PMe3)4 (1:2), undergo a reductive coupling of acyl and methylnickel functions involving the
C(O)ꢀCꢁCꢀO ligands. Subsequent migration of methyl groups between cobalt intermediates generates three products: mer-trans-
CoMe2[MeC(O)ꢀCꢁCꢀO](PMe3)2 (6–10), Ni(PMe3)4, and CoX(PMe3)3. The X-ray crystal structure of compound 7 has been
determined. The methyl ligands are found in positions opposite to the O-donor functions. Upon replacing the aromatic rings in
salicylaldehyde derivatives C(O)ꢀCꢁCꢀO by more flexible cyclohexene rings or acyclic systems the reduction of Ni(IV) complexes
follows a different course. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Oxidation/reduction; Cobalt complexes; Nickel complexes; 2-Acylenolato complexes; Transmetallation reaction
1. Introduction
We have been looking for low-valent trimethylphos-
phine complexes of cobalt that would similarly act as
one-electron reductants and serve as catalysts for the
C,C-coupling. In terms of reductive power, CoMe-
(PMe3)4 would be close to Ni(PMe3)4. However, due to
the presence of the methyl function a catalytic cycle is
difficult to close. In stoichiometric reactions an ex-
change of 2-acetylphenolate ions is then envisaged to
occur between the two metals.
Octahedral methyl(acylphenolato)nickel(IV) halide
complexes in the presence of Ni(PMe3)4 as a catalyst
undergo a reductive C,C-coupling reaction [1] accord-
ing to Eq. (1). In a subsequent ligand dismutation
reaction two of the resulting 2-acetylphenolate ions
become coordinated as bidentate ligands to the same
nickel centre.
When reacting nickel (d6) with cobalt (d8) com-
pounds, we discovered a new type of bidentate ligand
transfer which proceeds as an inequivalent exchange
process [2] and effects a transmetallation reaction by
multistep oxidation/reduction processes.
If odd-electron species are ruled out, an inequivalent
exchange of chelating acylenolato ligands and tri-
methylphosphines between d8 complexes of nickel
and cobalt can be described by oxidation/reduction
(1)
* Corresponding author.
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00331-X

64
H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
reactions of the metals according to the schematic Eq.
(a).
isolated by filtration and washed with ether. Extraction
with 60 ml of THF over a glass-sinter disc (G4) and
evaporation of the solvent yielded a light yellow pow-
der (460 mg, 36%), dec. \230°C.
dianionic: Ni (d8)+Co (d8)=Co (d6)+Ni (d10)
CNiC (d6)=Ni (d8)+CC
(a)
(b)
Anal. Calc. for C14H25INiO2P2 (472.8): C, 35.35; H,
5.33. Found: C, 34.73; H, 5.25%.
monoanionic: Ni (d8)+2Co (d8)
=Co (d6)+Ni (d10)+Co (d8)
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1725vs.
1H NMR (200 MHz, THF-d8, 296 K): l 1.25 (t,
(c)
2
3J(PH)=7.9 Hz, 3H, NiCH3), 1.49 (t%, ꢀ J(PH)+
4J(PH)ꢀ=7.7 Hz, 18H, PCH3), 6.35 (t, 3J(HH)=7.3
When combined with the reductive coupling (Eq. (b))
an inequivalent exchange of monoanions requires a 1:2
stoichiometry (Eq. (c)) because a total of four anionic
functions have to be accommodated in the products:
2-acetylphenolate, halide and two methyl groups. Pre-
diction of preferential coordination would place an
O:O-coordinated 2-acetylphenolato ligand at a Co (d6)
site but would not be strict for the remaining groups.
Experiments were designed in order to test this predic-
tion and to learn more about preferential coordination
of trimethylphosphine and chelating monoanionic and
dianionic ligands containing hard and soft donor atoms
in metal coordination numbers five and six.
3
Hz, 1H, CH), 7.2 (m, 2H, CH), 7.76 (d, J(HH)=8.6
Hz, 1H, CH). 31P{1H} NMR (81.0 MHz, THF-d8, 296
K): l 14.3 (s).
2.2.2. Synthesis of mer-trans-iodo(methyl)-
(2-oxo-1-naphthoyl)bis(trimethylphosphine)nickel (3)
A sample containing 820 mg of (2-oxonaphthoyl)-
tris(trimethylphosphine)nickel (1.79 mmol) and 560 mg
of iodomethane (3.94 mmol) in 40 ml of acetonitrile at
−30°C turned olive–green within 20 min, depositing
first a white and finally a yellow solid. After 40 min
workup as for 1 a yellow powder was obtained (480
mg, 51%), dec. \250°C.
Anal. Calc. for C18H27INiO2P2 (522.8): C, 41.32; H,
5.20. Found: C, 41.58; H, 5.24%.
2. Experimental
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1697vs.
1H NMR (200 MHz, THF-d8, 296 K): l 1.26 (t,
2.1. General procedures and materials
2
3J(PH)=8.0 Hz, 3H, NiCH3), 1.48 (t%, ꢀ J(PH)+
3
4J(PH)ꢀ=8.4 Hz, 18H, PCH3), 6.96 (d, J(HH)=9.2
Standard vacuum techniques were used in manipula-
tions of volatile and air-sensitive material. Details of
characterisation and spectroscopic instrumentation
have been given elsewhere [3].
3
Hz, 1H, CH), 7.16 (t, J(HH)=7.6 Hz, 1H, CH), 7.43
3
(t, J(HH)=7.6 Hz, 1H, CH), 7.6 (m, 2H, CH), 8.33
3
(d, J(HH)=8.3 Hz, 1H, CH). 13C{1H} NMR (75.4
1
MHz, CDCl3, 296 K): l 13.6 (t%, ꢀ J(PC)+3J(PC)ꢀ=
2-Formyl-4-phenyl-cyclohexanone, 2-formyl-4-tert-
butyl-cyclohexanone, and 3-hydroxy-2,3-diphenyl-pro-
penal were obtained by literature methods [4]. (2-
Oxobenzoyl)tris(trimethylphosphine)nickel [5], (2-oxo-
naphthoyl)tris(trimethylphosphine)nickel [5], [(1,2-di-
phenyl - 2 - oxoethene - 1 - yl)carbonyl]tris(trimethylphos-
phine)nickel [2], Co(CCPh)(PMe3)4 [6], CoMe(PMe3)4
[6], Co(PMe3)4 [6], mer-CoMe3(PMe3)3 [7], (3-carbonyl-
4 - oxo - 1,2 - dihydro - naphthalenyl)tris(trimethylphos-
phine)nickel [2], [(5-tert-butyl-2-oxocyclohexen-1-yl) car-
bonyl]tris(trimethylphosphine)nickel [2], and the methyl-
nickel(IV) complexes 2 [1] and 11 [2] were prepared by
published procedures. Other chemicals (Aldrich) were
used as purchased.
33.4 Hz, PCH3), 27.1 (C(O)CH3), 122.4, 122.9, 128.2,
129.4, 137.8 (CH). 31P{1H} NMR (81 MHz, THF-d8,
296 K): l 14.5 (s).
2.2.3. Synthesis of mer-trans-bromo(methyl)-
(3-carbonyl-4-oxo-1,2-dihydronaphthalenyl)-
bis(trimethylphosphine)nickel (4)
A sample containing 6.04 g of (3-carbonyl-4-oxo-
1,2-dihydronaphthalenyl)tris(trimethylphosphine)nickel
(13.2 mmol) and 3.7 g of bromomethane (39.0 mmol) in
50 ml of acetonitrile at −30°C turned red–brown
within 15 min, depositing first a white and finally a
yellow solid. Washing with 20 ml of cold ether followed
by 30 ml of water left a yellow solid which was recrys-
tallised from ether (4.50 g, 71%), dec. \104°C.
Anal. Calc. for C18H29BrNiO2P2 (478.0): C, 45.23; H,
6.12. Found: C, 45.01; H, 6.57%.
2.2. Procedures
2.2.1. Synthesis of mer-trans-iodo(methyl)-
(2-oxobenzoyl)bis(trimethylphosphine)nickel (1)
A sample containing 1110 mg of (2-oxobenzoyl)-
tris(trimethylphosphine)nickel (1.70 mmol) and 842 mg
of iodomethane (5.94 mmol) in 40 ml of acetonitrile
at 0°C turned dark brown within 20 min, depositing
first a white and finally a yellow solid. The solids were
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1686vs.
1H NMR (300 MHz, THF-d8, 243 K): l 1.10 (t,
2
3J(PH)=8.3 Hz, 3H, NiCH3), 1.43 (t%, ꢀ J(PH)+
4J(PH)ꢀ=8.3 Hz, 18H, PCH3), 2.48 (t, 3J(HH)=7.3
Hz, 2H, CH2), 2.82 (m, 2H, CH2), 7.3 (m, 3H, CH2),
3
7.88 (d, J(HH)=6.5 Hz, 1H, CH).

H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
65
2.2.4. Synthesis of mer-trans-iodo(methyl)-
(1-carbonyl-2-oxo-1,2-diphenyl-diyl)-
Workup as above (method a) afforded red–brown
platelets (1320 mg, 65%), dec. \151°C.
bis(trimethylphosphine)nickel (5)
Anal. Calc. for C21H41CoO2P2 (446.4): C, 56.50; H,
9.26; P, 13.88. Found: C, 56.68; H, 8.91; P, 13.71%.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1619w,
A sample containing 4.40 g of [(1,2-diphenyl-2-
oxo-ethene-1-yl)carbonyl]tris(trimethylphosphine)nickel
(8.64 mmol) and 3.50 g of iodomethane (24.7 mmol) in
40 ml of acetonitrile at −30°C turned brown within 15
min, depositing first a white and finally a yellow solid.
Workup as with 4 produced a yellow powder (4.36 g,
88%), dec. \101°C.
1
1580s. H NMR (200 MHz, THF-d8, 296 K): l −0.81
3
3
(t, J(PH)=9.2 Hz, 3H, CoCH3), −0.47 (t, J(PH)=
9.0 Hz, 3H, CoCH3), 1.12 (s, 18H, PCH3), 1.26 (s, 9H,
C(CH3)3), 2.05 (s, 3H, CCH3), 2.24 (s, 3H, C(O)CH3),
6.9–7.0 (m, 2H, CH). 13C{1H} NMR (50.3 MHz, THF-
1
Anal. Calc. for C22H31INiO2P2 (575.0): C, 45.95; H,
5.43. Found: C, 45.52; H, 6.10%.
d8, 296 K): l −15.4 (s, br, CoCH3), 11.6 (t%, ꢀ J(PC)+
3J(PC)ꢀ=20.2 Hz, PCH3), 20.9 (CCH3), 28.2
(C(O)CH3), 30.6 (C(CH3)3), 35.6 (C(CH3)3), 120.8,
134.0, 144.8 (C), 118.2, 130.0 (CH), 173.1 (CO), 197.3
(C(O)CH3). 31P{1H} NMR (121.5 MHz, THF-d8, 233
K): l 19.7 (s, br).
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1696vs,
1678m. 1H NMR (200 MHz, THF-d8, 296 K): l 1.15 (t,
3J(PH)=8.2 Hz, 3H, NiCH3), 1.60 (t%, ꢀ J(PH)+
2
4J(PH)ꢀ=8.3 Hz, 18H, PCH3), 7.20 (m, 10H, CH).
2.2.5. Synthesis of (2-acetylphenolato-O:O)-cis-
dimethyl-trans-bis(trimethylphosphine)cobalt (6)
2.2.7. Synthesis of (1-acetyl-2-naphtholato-O:O)-cis-
dimethyl-trans-bis(trimethylphosphine)cobalt (8)
A sample containing 1000 mg of 3 (1.91 mmol) and
1450 mg of CoMe(PMe3)4 (3.84 mmol) in 50 ml of ether
slowly formed a red–brown mixture. After 18 h at 20°C
workup as above (method a) afforded bunches of dark
red needles (550 mg, 67%), dec. \123°C.
Method a: A total of 930 mg 1 (1.97 mmol) and 1520
mg CoMe(PMe3)4 (4.03 mmol) in 60 ml of ether
formed a red–brown mixture within 20 h at 20°C,
from which a blue solid of CoI(PMe3)3 (IR) was
removed by filtration. The filtrate was taken to dry-
ness in vacuo, and the brown residue was extracted
with pentane to afford bunches of red needles (200
mg, 27%).
Method b: A sample containing 800 mg of 2-
acetylphenol (5.88 mmol) and 1430 mg of mer-
CoMe3(PMe3)3 (4.31 mmol) in 40 ml of ether at
20°C, formed a red solution which turned brown,
within 1 h, under slow evolution of gas. After 2 h the
mixture was filtered and the filtrate was kept at
−27°C to yield red platelets which were dried in
vacuo (1090 mg, 62%), dec. \135°C.
Anal. Calc. for C20H33CoO2P2 (426.4): C, 56.34; H,
7.80. Found: C, 56.02; H, 8.11%.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1614s,
1
1577s. H NMR (300 MHz, THF-d8, 297 K): l −0.72
3
3
(t, J(PH)=9.5 Hz, 3H, CoCH3), −0.66 (t, J(PH)=
9.5 Hz, 3H, CoCH3), 1.13 (s, 18H, PCH3), 2.36 (s, 3H,
C(O)CH3), 6.6–7.1 (m, 6H, CH). 13C{1H} NMR (75.4
MHz, THF-d8, 297 K): l 10.9 (t%, ꢀ J(PC)+3J(PC)ꢀ=
1
21.0 Hz, PCH3), 31.0 (C(O)CH3), 117.3 (CC(O)CH3),
121.8, 125.3, 127.2, 128.9, 129.5, 135.1 (CH), 127.7,
136.6 (C), 177.3 (CO), 193.9 (C(O)CH3). 31P{1H}
NMR (81.0 MHz, THF-d8, 233 K): l 20.6 (s, br).
Anal. Calc. for C16H31CoO2P2 (376.3): C, 51.07; H,
8.30; P, 16.46. Found: C, 51.11; H, 8.26; P, 16.63%.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1611s,
2.2.8. Synthesis of (3-acetyl-4-oxo-1,2-
dihydronaphthalenyl-O:O)-cis-dimethyl-
trans-bis(trimethylphosphine)cobalt (9)
A sample containing 940 mg of 4 (1.97 mmol) and
1520 mg of CoMe(PMe3)4 (4.02 mmol) in 50 ml of ether
formed a red–brown mixture, within 18 h at 20°C.
Workup as above (method a) afforded (besides a blue
solid of CoBr(PMe3)3 [8], IR) bunches of dark red
crystals (470 mg, 56%), dec. \145°C.
1
1588s. H NMR (200 MHz, THF-d8, 296 K): l −0.77
3
3
(t, J(PH)=8.9 Hz, 3H, CoCH3), −0.61 (t, J(PH)=
9.5 Hz, 3H, CoCH3), 1.12 (t%, ꢀ J(PH)+4J(PH)ꢀ=6.5
2
Hz, 18H, PCH3), 1.73 (s, 3H, C(O)CH3), 6.0–7.3 (m,
4H, CH). 13C{1H} NMR (75.4 MHz, THF-d8, 297 K):
l −16.6 (s, br, CoCH3), 10.8 (t%, ꢀ J(PC)+3J(PC)ꢀ=
1
20.3 Hz, PCH3), 27.1 (C(O)CH3), 111.3, 127.9, 132.9,
135.2 (CH), 121.4 (CC(O)CH3), 174.5 (CO), 197.5
(C(O)CH3). 31P{1H} NMR (121.5 MHz, THF-d8, 297
K): l 14.6 (s, br).
Anal. Calc. for C20H35CoO2P2 (428.4): C, 56.08; H,
8.23. Found: C, 55.67; H, 8.40%.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1606s,
1
1584s. H NMR (200 MHz, THF-d8, 296 K): l −0.68
3
3
2.2.6. Synthesis of (2-acetyl-4-methyl-6-tert-
butylphenolato-O:O)-cis-dimethyl-trans-bis-
(trimethylphosphine)cobalt (7)
A sample containing 2480 mg of 2 (4.67 mmol) and
3460 mg of CoMe(PMe3)4 (9.16 mmol) in 80 ml of ether
formed a red–brown mixture, within 20 h at 20°C.
(t, J(PH)=9.4 Hz, 3H, CoCH3), −0.64 (t, J(PH)=
2
9.4 Hz, 3H, CoCH3), 1.36 (t%, ꢀ J(PH)+4J(PH)ꢀ=5.8
Hz, 18H, PCH3), 1.91 (s, 3H, C(O)CH3), 2.50 (m, 2H,
CH2), 2.70 (m, 2H, CH2), 7.4–7.8 (m, 4H, CH).
13C{1H} NMR (75.4 MHz, THF-d8, 296 K): l 10.8 (t%,
1
ꢀ J(PC)+3J(PC)ꢀ=20.0 Hz, PCH3), 26.8 (C(O)CH3),

66
H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
26.1, 30.1 (CH2), 104.2 (CC(O)CH3), 126.8, 126.9,
127.3, 129.8 (CH), 137.2, 140.5 (C), 176.1 (CO), 187.8
(C(O)CH3). 31P{1H} NMR (121.5 MHz, THF-d8, 296
K): l 13.6 (s, br).
2.2.12. Reaction of 11 with CoMe(PMe3)4
A sample containing 1.75 g of 11 (3.33 mmol) and
2.52 g of CoMe(PMe3)4 (6.67 mmol) in 60 ml of ether
turned from red to brown within 10 min. After 20 min
the volatiles were removed in vacuo, and the residue
was extracted with 80 ml of pentane over a glass-sinter
disc (G3). Slowly reducing the volume of the filtrate
gave dark blue crystals (400 mg) of CoI(PMe3)3 [8]
(IR). Subsequent crystallisation from the mother liquor
at −27°C afforded light brown crystals (549 mg, 30%
based on the chelate ligand) of 13 [9] which was iden-
2.2.9. Synthesis of (1-acetyl-2-oxo-1,2-diphenyl-
diyl-O:O)-cis-dimethyl-trans-bis(trimethyl-phosphine)-
cobalt (10)
A sample containing 1030 mg of 5 (1.79 mmol) and
1350 mg of CoMe(PMe3)4 (3.58 mmol) in 60 ml of ether
at 20°C formed a dark brown mixture, within 18 h.
Workup as above (method a) afforded red–brown
needles (600 mg, 70%), dec. \142°C.
1
tified by IR and H NMR spectroscopy. Among the
highly soluble compounds remaining in the mother
liquor Ni(PMe3)4 was detected (IR).
Anal. Calc. for C24H37CoO2P2 (478.4): C, 60.25; H,
7.79. Found: C, 60.41; H, 8.03%.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1582m,
1561m. 1H NMR (300 MHz, acetone-d6, 297 K): l
−0.67 (t, 3J(PH)=9.5 Hz, 3H, CoCH3), −0.65 (t,
2.2.13. Reaction of 12 with CoMe(PMe3)4
In a similar procedure starting with 1.80 g of 12 (3.43
mmol) and 2.59 g of CoMe(PMe3)4 (6.86 mmol) were
obtained dark blue crystals (400 mg) of CoI(PMe3)3 [8]
and yellow crystals (300 mg, 15% based on the chelate
ligand) of 14 [9].
2
3J(PH)=9.5 Hz, 3H, CoCH3), 1.27 (t%, ꢀ J(PH)+
4J(PH)ꢀ=9.2 Hz, 18H, PCH3), 1.63 (s, 3H, C(O)CH3),
7.0–7.1 (m, 10H, CH).
2.2.10. Synthesis of mer-trans-iodo(methyl)-
[(5-tertbutyl-2-oxocyclohexen-1-yl)carbonyl]-
bis(trimethylphosphine)nickel (12)
A sample containing 3.00 g of [(5-tert-butyl-2-oxocy-
clohexen - 1 - yl)carbonyl]tris(trimethylphosphine)nickel
(6.42 mmol) and 2.27 g of iodomethane (16.0 mmol) in
40 ml of acetonitrile at −30°C turned from red to
green within 5 min, depositing first a white and finally
a yellow solid. Workup as with 4 produced a yellow
powder (2.25 g, 66%), dec. \110°C.
2.2.14. Reaction of 11 with Co(PMe3)4
A sample containing 1.23 g of 11 (2.59 mmol) and
0.95 g of Co(PMe3)4 (2.62 mmol) in 50 ml of ether at
−30°C turned from red to brown within 10 min. After
a slight turbidity was removed by filtration the solution
at −27°C afforded light brown crystals (250 mg, 18%)
1
of 13 [9] which were identified by IR and H NMR
spectroscopy.
2.2.15. Reaction of 15 with Co(PMe3)4
Anal. Calc. for C18H37INiO2P2 (533.0): C, 40.56; H,
7.00. Found: C, 39.79; H, 6.83%.
A sample containing 0.92 g of 15 (1.70 mmol) and
0.63 g Co(PMe3)4 (1.74 mmol) in 50 ml of acetone
formed a dark brown solution upon warming from
−30 to 20°C. After evaporation to dryness the residue
was extracted with ether to afford, at −27°C, red
crystals of (1-carbonyl-2-oxo-1,2-diphenyl-diyl)tris-
(trimethylphosphine)nickel (180 mg, 21%) which were
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1688vs.
Solution spectroscopy was not reproducible due to a
fast decomposition in THF-d8 at −60°C which was
recognised from a green colour.
2.2.11. Synthesis of mer-trans-bromo(methyl)-
(1-carbonyl-2-oxo-1,2-diphenyl-diyl)-
1
identified by IR and H NMR spectroscopy. No cobalt
bis(trimethylphosphine)nickel (15)
containing species could be identified.
A sample containing 3.55 g of (1-carbonyl-2-oxo-
1,2-diphenyl-diyl)tris(trimethylphosphine)nickel (6.97
mmol) and 2.00 g of bromomethane (21.1 mmol) in 50
ml of acetonitrile at −30°C turned brown within 15
min, depositing first a white and finally a yellow solid.
The solids were washed with two 5 ml portions of ether
and three times with water to yield, after drying in
vacuo, a yellow powder (3.28 g, 89%), dec. \152°C.
Anal. Calc. for C22H31BrNiO2P2 (528.0): C, 50.04; H,
5.96. Found: C, 49.78; H, 5.92%.
2.2.16. Reaction of 15 with CoCꢂCPh(PMe3)4
A total of 0.99 g of 15 (1.88 mmol) and 0.87 g of
Co(CCPh)(PMe3)4 (1.88 mmol) in 60 ml of ether
formed a brown solution upon warming from −30 to
20°C. After evaporation to dryness the residue was
extracted with pentane to afford, at −27°C, red cubes
of (1-carbonyl-2-oxo-1,2-diphenyl-diyl)tris(trimethyl-
phosphine)nickel (280 mg, 29%) which were identified
as above.
IR (Nujol mull, w(CꢁO), 2600–1600 cm−1): 1693vs,
1
1670s. H NMR (300 MHz, acetone-d6, 243 K): l 1.16
2.2.17. X-ray data
3
2
(t, J(PH)=8.2 Hz, 3H, NiCH3), 1.54 (t%, ꢀ J(PH)+
4J(PH)ꢀ=8.6 Hz, 18H, PCH3), 7.17 (m, 10H, CH).
31P{1H} NMR (81 MHz, THF-d8, 233 K): l 18.5 (s).
2.2.17.1. Crystal structure analysis. Crystal data for
complex 7 are presented in Table 1.

H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
67
Table 1
Crystal data and refinement details for 7
Formula
C21H41CoO2P2
Molecular mass
Crystal size (mm)
Crystal system
Space group
446.4
0.07×0.20×0.65
orthorhombic
Pbca
,
a (A)
17.916(4)
13.734(3)
20.080(3)
4940.9(17)
,
b (A)
,
c (A)
V (A )
3
,
Z
8
Dcalc (g cm−3
)
1.200
0.836
293(2)
v(Mo Ka) (mm−1
)
Temperature (K)
Data collection range (°)
Limiting indices
2.03–27.50
−1BhB23, −17BkB1, −1BlB26
No. reflections measured
No. unique data
Parameters
6866
5675 (Rint=0.0291)
236
0.931
Goodness-of-fit on F2
R1 (I\2|(I))
0.0509
R1 (all data)
0.1669
wR2 (all data)
0.1594
0.336
−0.392
−3
,
Dzmax (e A
)
)
−3
,
Dzmin (e A
2.2.17.2. Data collection. A crystal of suitable shape was
sealed in a glass capillary under argon and mounted on
a diffractometer (Bruker P4). Data were collected using
monochromated Mo Ka radiation. Cell constants were
refined from 25 centred reflections. An absorption cor-
rection based on c-scans was introduced. The structure
was solved by direct methods. Non-hydrogen atoms
were refined anisotropically on F2. Hydrogen atoms
were fixed at idealised positions with isotropic thermal
parameters.
The novel oxidation/reduction transformations of lig-
ands and complexes in ether solutions under ambient
conditions require reaction times of about two days and
are monitored by a slow change from a red to a
red–brown coloration. Workup and separation of the
three products formed by the two metals is best
achieved in pentane. The almost insoluble blue micro-
crystals of CoX(PMe3)3 [8] are easily removed by filtra-
tion, while Ni(PMe3)4 remains in solution when the red
crystals of dimethylcobalt complexes 6–10 are frozen
out. Only in the synthesis of 6 with its exceptionally
meagre yield of 27%, were small amounts of (2-oxoben-
zoyl)tris(trimethylphosphine)nickel [5] detected as a by-
product (IR).
An independent high yield synthesis for 6 proceeds
according to Eq. (3) and appears to provide the most
straightforward route to this type of dimethylcobalt(III)
complex starting from a 2-acylphenol [10]. Chelating
coordination of the acetylic O-donor renders the overall
reaction smoother than with unsubstituted phenol [6].
3. Results and discussion
In a second type of bidentate ligand exchange [2]
following a 1:2 stoichiometry and involving acyl-
(methyl)nickel(IV) complexes and methylcobalt(I) com-
pounds, the total of six anionic ligand functions be-
comes four through a reductive C,C-coupling reaction
according to Eq. (2).
(3)
The molecular structure of 7 is shown in Fig. 1. The
cobalt atom attains an octahedral coordination by two
equatorial cis-methyl groups (C14ꢀCoꢀC15=94.61(18)°
(2)

68
H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
initiated by single-electron transfer from a Ni(0) frag-
ment F to the Ni(IV) educt complex (1–5) along a
NiꢀXꢀNi bridge [1] generating intermediates A and B.
After reductive elimination the resulting Ni(I) interme-
diate and CoMe(PMe3)4 exchange the 2-acetylphenolate
ion for phosphine ligands via ring-opening and bridging
coordination leading to a 17-electron species D and the
16-electron Ni(0) fragment F closing the catalytic cycle
of nickel.
Formation of the Ni(0) product and a second Co(II)
intermediate E is followed by transfer of a methyl
group involving both Co(II) species D and E which in
a dismutation reaction provide the Co(III) and Co(I)
final products. Methyl group transfer reactions involv-
ing odd-electron species have been recently investigated
in (diimine)PtMe2 systems [10].
,
Fig. 1. Molecular structure of 7; selected distances (A) and angles (°):
CoꢀO1 1.985(3), CoꢀO2 1.990(3), CoꢀC14 1.999(4), CoꢀC15 1.986(4),
CoꢀP1 2.2228(17), CoꢀP2 2.2213(17), O1ꢀC1 1.254(4), O2ꢀC7
1.299(4), C1ꢀC2 1.445(5), C1ꢀC13 1.506(5), C2ꢀC7 1.427(5);
O1ꢀCoꢀC15 176.88(15), O1ꢀCoꢀO2 88.53(10), C15ꢀCoꢀO2 88.36(14),
O1ꢀCoꢀC14 88.5(1), C15ꢀCoꢀC14 94.61(18), O2ꢀCoꢀC14 177.03(15),
O1ꢀCoꢀP2 91.67(11), C15ꢀCoꢀP2 88.73(15), O2ꢀCoꢀP2 92.84(10),
C14ꢀCoꢀP2 87.15(16), O1ꢀCoꢀP1 90.20(11), C15ꢀCoꢀP1 89.70(15),
O2ꢀCoꢀP1 92.69(10), C14ꢀCoꢀP1 87.41(16), P2ꢀCoꢀP1 174.21(6),
C1ꢀO1ꢀCo 130.5(3), C7ꢀO2ꢀCo 129.3(2), O1ꢀC1ꢀC2 124.3(3),
O1ꢀC1ꢀC13 114.1(3), C7ꢀC2ꢀC1 123.0(3).
4. Miscellaneous ligand exchange reactions
When cyclohexene-type acylenolato ligands are intro-
duced reactions under conditions of Eq. (2) unexpect-
edly take a different course. Without transforming an
acyl into an acetyl function the anionic ligand is trans-
ferred from nickel to cobalt according to Eq. (4).
opposite to the planar O:O-chelate ring of a 2-
acetylphenolate anion with the usual bite-angle
(O1ꢀCoꢀO2=88.53(10)° and by two axial trimethyl-
phosphines which are slightly bent (P1ꢀCoꢀP2=
174.21(6)°) towards the CoMe groups. CoꢀO and CoꢀC
distances are as expected and fall within the range of
,
three standard deviations (1.99(1) A). While the 2-
acetylphenolato ligand displays a shorter acyl(sp2)C,O
,
distance (C1ꢀO1=1.254(4) A) when compared with the
2
,
phenolato(sp )C,O distance (C7ꢀO2=1.299(4) A), con-
jugational effects upon coordination shorten the origi-
,
nal single bond C1ꢀC2 to 1.445(4) A and lead to similar
angles at the two oxygen atoms (C1ꢀO1ꢀCo=130.5(3),
C7ꢀO2ꢀCo=129.3(2)°).
(4)
Reaction of tetravalent nickel with low-valent cobalt
complexes according to Eq. (5) does not include trans-
fer of the chelating ligand. Any trimethylphosphine
complex of cobalt in a formal oxidation state of +1 or
below appears to be capable of performing a reductive
substitution reaction of 15.
The fate of the NiMe and CoMe groups in the
transmetallation process has been investigated by deu-
terium labelling. Oxidative addition of CD3I in the
preparation of 2 [1] furnishes a NiCD3 group in com-
plex 2(D). Crystals of 7 and 7(D) were shown to be
isotypical (identical lattice parameters). NMR spectra
of the products of the reaction described by Eq. (2)
show all the deuterium of compound 7(D) to be con-
tained in the methylketone group of the bidentate lig-
and. Migration of methyl groups between nickel and
cobalt is thus excluded but is believed to occur between
two intermediate methylcobalt complexes in a subse-
quent step.
(5)
At this stage we find it difficult to predict the stoi-
chiometries and directions of transmetallation reactions
involving dianionic chelate systems. The only general
trend observed here demonstrates that Co(d6) com-
plexes are thermodynamically more stable than Ni(d6)
complexes with a similar set of ligands.
In Scheme 1 a mechanism is suggested for a product-
forming sequence of four bimolecular steps.
A total of six hypothetical intermediates (A–F) is
required to connect the two educts with the three
products of Eq. (2). C,C-coupling is most probably
.

H.-F. Klein et al. / Inorganica Chimica Acta 298 (2000) 63–69
69
Scheme 1.
5. Supplementary material
References
Crystallographic data (excluding structure factors) for
the structure reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre.
Copies of the data (CCDC-127451) can be obtained free
of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336-033,
e-mail: deposit@chemcrys.cam.ac.uk).
[1] H.-F. Klein, A. Bickelhaupt, T. Jung, G. Cordier, Organometallics
13 (1994) 2557.
[2] H.-F. Klein, X. Li, H. Sun, A. Brand, M. Lemke, U. Flo¨rke, H.-J.
Haupt, Inorg. Chim. Acta, in preparation.
[3] H.-F. Klein, A. Bickelhaupt, M. Lemke, H. Sun, A. Brand, T. Jung,
C. Ro¨hr, U. Flo¨rke, H.-J. Haupt, Organometallics 16 (1997) 668.
[4] Houben-Weyl’s Methoden der Organischen Chemie, fourth ed.,
Thieme Verlag, Stuttgart, Germany, vol. 6/1D, 1978, p. 40.
[5] H.-F. Klein, A. Bickelhaupt, B. Hammerschmitt, U. Flo¨rke, H.-J.
Haupt, Organometallics 13 (1994) 2944.
[6] H.-F. Klein, H.H. Karsch, Chem. Ber. 108 (1975) 944.
[7] H.-F. Klein, H.H. Karsch, Chem. Ber. 108 (1975) 956.
[8] H.-F. Klein, H.H. Karsch, Inorg. Chem. 14 (1975) 473.
[9] H.-F. Klein, S. Haller, H. Sun, X. Li, T. Jung, C. Ro¨hr, U. Flo¨rke,
H.-J. Haupt, Z. Naturforsch., Teil B 53 (1998) 856.
[10] L. Johansson, O.B. Ryan, C. Rømming, M. Tilset, Organometallics
17 (1998) 3957.
Acknowledgements
Financial support of this work by the Fonds der
Chemischen Industrie and Deutsche Forschungs-
gemeinschaft is gratefully acknowledged.