Methylnickel compounds containing 2-phosphinylethanolato ligands - Syntheses, properties, and ethene coupling reactions

Article abstract of DOI:10.1016/j.ica.2005.07.030

Combining dimethylphosphinylethanols HO(R¹R²)CCH ₂PMe₂ (1: R¹ = R² = C ₆H₅; 2: R¹ = R² = 4-OMe-C ₆H₄; 5: R¹ = R² = 4-NMe ₂-C₆H₄) with methyl(methoxo) (trimethylphosphine)nickel gave mononuclear methyl(trimethylphosphine) nickel(chelate) compounds 7-9. Ligand 6 (R¹ = Me, R² = 4-OMe-C₆H₅) afforded a dinuclear methylnickel compound 14. By reacting (TMEDA)lithium-dimethylphosphinylmethanide with ketones OC(R ¹R²), the dimethylphosphinylethanols HO(R ¹R²)CCH₂PMe₂ (3: R¹R ² = 9-fluorenyl; 4: R¹ = H, R² = C ₆H₅) were synthesized as prechelate ligands. Under otherwise similar conditions, the fluorenyl substituted anion in 3 gave rise to a mononuclear complex 10 which was found to act as a source of trimethylphosphine forming dinuclear 11 and at the same time to act as an acceptor of trimethylphosphine forming pentacoordinate 10·PMe ₃. Ni(COD)(PMe₃)₂ was used as a scavenger of PMe₃ in converting 8 or 9 to the dinuclear methylnickel compounds 12 and 13, respectively. Modifying the P,O chelating unit of a methyl nickel compound by introducing 2-phosphinylethanolato ligands leads to novel single-component catalysts for ethene oligomerization showing moderate reactivity and thermal stability.

Full text of DOI:10.1016/j.ica.2005.07.030

Inorganica Chimica Acta 358 (2005) 4394–4402
www.elsevier.com/locate/ica
Methylnickel compounds containing 2-phosphinylethanolato ligands
– Syntheses, properties, and ethene coupling reactions
a,
a
a
b
Hans-Friedrich Klein *, Mengzhen He , Olaf Hetche , Alexander Rau ,
b
b
b
Dirk Walther , Thomas Wieczorek , Gerhard Luft
a
Eduard-Zintl-Institut fu¨r Anorganische und Physikalische Chemie der Technischen Universita¨t Darmstadt, Petersenstraße 18,
D-64285 Darmstadt, Germany
b
Ernst-Berl-Institut fu¨r Technische und Makromolekulare Chemie der Technischen Universita¨t Darmstadt, Petersenstraße 20,
D-64285 Darmstadt, Germany
Received 25 June 2005; accepted 16 July 2005
Available online 30 August 2005
Dedicated to Professor H. Schmidbaur.
Abstract
Combining dimethylphosphinylethanols HO(R1R2)CCH2PMe2 (1: R1 = R2 = C6H5; 2: R1 = R2 = 4-OMe–C6H4; 5: R1 = R2 =
4-NMe2–C6H4) with methyl(methoxo)(trimethylphosphine)nickel gave mononuclear methyl(trimethylphosphine)nickel(chelate)
compounds 7–9. Ligand 6 (R1 = Me, R2 = 4-OMe–C6H5) afforded a dinuclear methylnickel compound 14. By reacting
(TMEDA)lithium-dimethylphosphinylmethanide with ketones O@C(R1R2), the dimethylphosphinylethanols HO(R1R2)CCH2PMe2
(3: R1R2 = 9-fluorenyl; 4: R1 = H, R2 = C6H5) were synthesized as prechelate ligands. Under otherwise similar conditions, the flu-
orenyl substituted anion in 3 gave rise to a mononuclear complex 10 which was found to act as a source of trimethylphosphine form-
ing dinuclear 11 and at the same time to act as an acceptor of trimethylphosphine forming pentacoordinate 10 Æ PMe3.
Ni(COD)(PMe3)2 was used as a scavenger of PMe3 in converting 8 or 9 to the dinuclear methylnickel compounds 12 and 13, respec-
tively. Modifying the P,O chelating unit of a methyl nickel compound by introducing 2-phosphinylethanolato ligands leads to novel
single-component catalysts for ethene oligomerization showing moderate reactivity and thermal stability.
ꢀ 2005 Published by Elsevier B.V.
Keywords: (2-Phosphinyl)ethanolates; Methylnickel compounds; Solution dynamics; Ethene coupling reactions
1. Introduction
In order to shed more light on the mechanism of the C,C-
coupling reaction, we set out to isolate and characterize
some catalyst precursors containing a non-conjugated
backbone of a P,O-metallacycle and showing increased
bond flexibility. In this contribution, we describe some
Among the late transition-metal compounds with
bidentate (P,O) ligands effecting the oligomerization of
ethene, complexes of nickel have been extensively studied
[1]. In catalytically active compounds of nickel(II), these
monoanionic ligands form five- or six-membered metal-
locycles. When equipped with alkyl or hydride nickel
functions, the molecular complexes are regarded as mod-
els for the active species in olefin coupling reactions [2–6].
novel
(2-dimethylphosphinylethanolato)methylnickel
complexes with supporting trimethylphosphine and
some dinuclear methylnickel complexes containing O-
bridging 2-dialkylphosphinylethanolato ligands without
an auxiliary phosphine ligand. The molecular structure
of the latter complex is presented and the catalytic prop-
erties in C,C-coupling reactions of ethene under moder-
ate conditions are discussed.
*
Corresponding author.
E-mail address: hfklein@ac.chemie.tu-darmstadt.de (H.-F. Klein).
0020-1693/$ - see front matter ꢀ 2005 Published by Elsevier B.V.
doi:10.1016/j.ica.2005.07.030

H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
4395
2. Experimental
phenone (10.6 mmol) was added under stirring to give a
blue solution. After 1 h, 8 ml of water was added and the
mixture was stirred at 20 ꢁC for 14 h. The volatiles were
removed in vacuo, and the yellow residue was extracted
with 70 ml of diethyl ether. Crystallization at ꢀ25 ꢁC
afforded colorless crystals of 2 (2.34 g, 71%), m.p.
103–104 ꢁC.
2.1. General procedures and materials
All air-sensitive and volatile materials were han-
dled by standard vacuum techniques and kept under
argon. The chemicals (Merck/Schuchardt) were used
as purchased, but liquids were degassed in vacuo by a
freeze–thaw procedure. Literature methods were fol-
lowed in the preparation of LiCH2PMe2 [16], LiCH2P-
Me2 Æ TMEDA [7], [NiMe(OMe)PMe3]2 [11], and
Ni(COD)(PMe3)2 [17]. Microanalyses were carried out
Anal. Calc. for C18H23O3P (318.4): C, 67.91; H, 7.28;
P, 9.73. Found: C, 68.03; H, 7.19; P, 9.82%.
1
IR (Nujol mull, 4000–1700 cmꢀ1): 3291m m(OH). H
NMR (200 MHz, THF-d8, 298 K): d 0.83 (d, 6H,
2J(PH) = 3.6 Hz, PCH3), 2.36 (d, 2H, 2J(PH) = 2.6
Hz, PCH2), 3.71 (s, 3H, OCH3), 4.71 (d, 1H,
4J(PH) = 7 Hz, OH), 6.72–6.79 (m, 4H, 3,5-H), 7.28–
7.35 (m, 4H, 2,6-H). 13C NMR (75 MHz, THF-d8, 298
K): d 13.9 (d, 1J(PC) = 10.6 Hz, PCH3), 48.8 (d,
1J(PC) = 31.8 Hz, PCH2), 55.1 (s, OCH3), 75.4 (d,
2J(PC) = 10.0 Hz, COH), 111.4 (4-C), 126.4 (2-C),
129.9 (3-C), 157.4 (1-C). 31P NMR (81 MHz, THF-d8,
298 K): d ꢀ54.9 (s).
by Kolbe, Microanalytical Laboratory, Mulheim/Ruhr,
¨
FRG. Melting points or decomposition temperatures
were determined in sealed glass capillaries on a Buchi
¨
Model 510 apparatus and are uncorrected. Infrared
spectra (4000–400 cmꢀ1), as obtained from Nujol mulls
between KBr windows, were recorded on a Bruker
Model FRA 106 spectrophotometer. NMR spectra
(300 and 75 MHz for H and 13C, respectively) were re-
1
corded with Bruker ARX-300, 31P NMR spectra (81
MHz) with a Bruker AM-200 instrument. 13C and 31P
resonances were obtained with broad-band proton
decoupling.
2.2.3. Synthesis of (9-dimethylphosphinyl)methylen-
fluorenol (3)
To a sample of 1.00 g of LiCH2PMe2 Æ TMEDA (12.2
mmol) in 30 ml of THF at ꢀ20 ꢁC, 2.20 g of 9-fluore-
none (12.2 mmol) was added rapidly under stirring in
40 ml of THF. The mixture was allowed to warm up
and at 20 ꢁC formed a solution with a green fluores-
cence. After quenching with 15 ml of water and stirring
for 14 h, the volatiles were removed in vacuo and the
yellow residue was dried at 40 ꢁC in vacuo for 2 h.
Extraction with 30 ml of toluene and crystallization at
4 ꢁC afforded colorless crystals of 3 (1.93 g, 62%), m.p.
103–104 ꢁC.
2.2. Procedures
2.2.1. Synthesis of 2-dimethylphosphinyl-1,1-
diphenylethanol (1)
Upon a sample of 2.65 g of LiCH2PMe2 Æ TMEDA
(13.5 mmol) at ꢀ78 ꢁC, 60 ml of pentane was condensed
in vacuo, and 2.45 g of benzophenone (13.5 mmol) in
50 ml of pentane was added rapidly under stirring.
The blue solution was stirred for 1 h and was then taken
to dryness in vacuo. The residue was dissolved in 50 ml
of THF containing 3 ml of water and kept stirring over-
night. The volatiles were removed in vacuo and the res-
idue was extracted with diethyl ether affording colorless
crystals of 1 (2.58 g, 74%), m.p. 84–85 ꢁC.
Anal. Calc. for C16H19OP (258.2): C, 75.02; H, 6.64;
P, 12.09. Found: C, 75.36; H, 6.75; P, 11.87%.
1
IR (Nujol mull, 4000–1700 cmꢀ1): 3298m m(OH). H
NMR (200 MHz, THF-d8, 298 K): d 0.84 (d, 6H,
2J(PH) = 3.3 Hz, PCH3), 2.09 (d, 2H, 2J(PH) = 2.7
Hz, PCH2), 4.73 (s, 1H, OH), 7.23–7.79 (m, 4H, 3,4-
H), 7.58–7.68 (m, 4H, 2,5-H). 31P NMR (81 MHz,
THF-d8, 298 K): d ꢀ54.4 (s).
Anal. Calc. for C16H19OP (258.2): C, 74.43; H, 7.36;
P, 12.01. Found: C, 75.23; H, 7.10; P, 11.76%.
IR (Nujol mull, 4000–1700 cmꢀ1): 3451 m m(OH). 1H
NMR (200 MHz, THF-d8, 298 K): d 0.84 (d, 6H,
2J(PH) = 3.6 Hz, PCH3), 2.42 (d, 2H, 2J(PH) = 2.6
Hz, PCH2), 4.71 (s, 1H, OH), 7.08–7.26 (m, 6H, 3-H,
4-H), 7.43–7.52 (m, 4H, 2-H). 13C NMR (75 MHz,
2.2.4. Synthesis of 2-dimethylphosphinyl-1-phenylethanol
(4)
To a sample of 1.05 g of benzaldehyde (9.9 mmol) in
20 ml of pentane at 20 ꢁC, 1.95 g of LiCH2PMe2 Æ TME-
DA (9.9 mmol) was added dropwise in 40 ml of pentane.
After quenching with 4 ml of water, the volatiles were
removed in vacuo and the white residue was dried at
40 ꢁC in vacuo for 1 h. Extraction with pentane and
crystallization at 4 ꢁC afforded a colorless oil of 4. Crude
yield 1.67 g (99%).
1
THF-d8, 298 K): d 15.9 (d, J(PC) = 14.3 Hz, PCH3),
49.2 (d, 1J(PC) = 16.3 Hz, PCH2), 77.8 (d,
2J(PC) = 10.6 Hz, COH), 126.9 (4-C), 128.3 (3-C),
128.6 (2-C), 149.9 (1-C). 31P NMR (81 MHz, THF-d8,
298 K): d ꢀ54.0 (s).
2.2.2. Synthesis of 2-dimethylphosphinyl-1,1-
di(4-methoxyphenyl)ethanol (2)
1
IR (Nujol mull, 4000–1700 cmꢀ1): 3361m m(OH). H
To a sample of 0.85 g of LiCH2PMe2 (10.4 mmol) in
50 ml of THF at ꢀ78 ꢁC, 2.58 g of 4,40-dimethoxybenzo-
NMR (300 MHz, THF-d8, 298 K): d 0.83 (d, 6H,
2J(PH) = 3.0 Hz, PCH3), 1.02 (d, 2H, 2J(PH) = 2.8

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H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
Hz, PCH2), 5.36 (s, br, 1H, OH), 7.13–7.37 (m, 5H,
C6H5). 31P NMR (81 MHz, THF-d8, 298 K): d ꢀ55.0 (s).
Anal. Calc. for C20H30NiOP2 (407.1): C, 59.01; H,
7.43; P, 15.22. Found: C, 60.15; H, 7.12; P, 15.05%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ1.22 (s, 3
H, NiCH3), 0.97 (s, br, 6H, PCH3), 1.37 (s, br, 9H,
PCH3), 2.57 (s, br, 2H, PCH2), 6.98–7.16 (m, 6H,
3,4,5-H), 7.65–7.69 (m, 4H, 2,6-H). 13C NMR (75
MHz, THF-d8, 298 K): d 9.4 (d, 1J(PC) = 20.8 Hz,
PCH3), 10.6 (d, 1J(PC) = 18.9 Hz, PCH2), 47.2 (d,
1J(PC) = 29.3 Hz, PCH3), 83.6 (CO), 123.7 (4-C),
125.5 (2-C), 125.7 (3-C), 154.3 (1-C). 31P NMR (81
MHz, THF-d8, 233 K): d ꢀ7.0 (m, 0.95 P, trans-
2.2.5. Synthesis of 2-dimethylphosphinyl-1,1-
di(4-N,N0-dimethylaminophenyl)ethanol (5)
To a sample of 2.07 g of LiCH2PMe2 (10.5 mmol) in
50 ml of diethyl ether at ꢀ78 ꢁC, 2.82 g of 4,40-bis(dim-
ethylamino)benzophenone (10.5 mmol) was added un-
der stirring to give a blue solution which rapidly
turned colorless. After 1 h, 3 ml of water was added
and the mixture was stirred at 20 ꢁC for 14 h. The vol-
atiles were removed in vacuo and the yellow residue
was extracted with 70 ml of diethyl ether. Crystallization
at ꢀ25 ꢁC afforded colorless crystals of 5. (3.00 g, 83%)
m.p. 112–114 ꢁC.
2
PMe3), 3.0 (d, 0.05 P, J(PP) = 18 Hz, cis-PMe3), 15.0
2
(d, 0.05 P, J(PP) = 18 Hz, cis-PMe2), 22.0 (m, 0.95 P,
trans-PMe2); 193 K: d ꢀ5.0 (d, 0.97 P, 2J(PP) = 338
2
Hz, trans-PMe3), 4.0 (d, 0.03 P, J(PP) = 19 Hz, cis-
PMe3), 17.0 (d, 0.03 P, 2J(PP) = 19 Hz, cis-PMe2),
Anal. Calc. for C20H29ON2P (344.4): C, 69.74; H,
8.49; N, 8.13; P, 8.99. Found: C, 70.06; H, 8.19; N,
8.59; P, 9.50%.
2
23.0 (d, 0.97 P, J(PP) = 338 Hz, trans-PMe2).
1
IR (Nujol mull, 4000–1700 cmꢀ1): 3298m m(OH). H
2.2.8. Synthesis of [2-dimethylphosphinyl-1,1-
di(4-methoxyphenyl)ethanolato]-[O,P]-
methyl(trimethylphosphine)nickel (8)
NMR (200 MHz, THF-d8, 298 K): d 0.80 (s, 6H, PCH3),
2.31 (s, 2H, PCH2), 2.86 (s, 12H, NCH3), 4.15 (s, 1H,
OH), 6.54–6.68 (m, 4H, 3,5-H), 7.19–7.25 (m, 4 H, 2,6-
H). 31P NMR (81 MHz, THF-d8, 298 K): d ꢀ55.0 (s).
A brown solution of 0.41 g of [NiMe(OMe)PMe3]2
(1.1 mmol) in 30 ml of THF when combined with 0.72
g of 2 (2.3 mmol) under stirring at 20 ꢁC attained a light-
er color. The volatiles were evaporated to give a yellow
residue which was recrystallized from pentane at 4 ꢁC to
afford as a first fraction colorless crystals of unreacted 2
(IR), which were removed by decantation. From the
mother liquor, a second fraction of light brown crystals
of 8 was obtained (0.73 g, 69%), m.p. 99–101 ꢁC (dec.).
Anal. Calc. for C22H34NiO3P2 (467.1): C, 56.57; H,
7.33; P, 13.26. Found: C, 56.55; H, 7.33; P, 13.29%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ1.25 (s, 3
H, NiCH3), 0.97 (s, 6H, PCH3), 1.34 (s, 9H, PCH3),
2.50 (s, 2H, PCH2), 3.67 (s, 3H, OCH3), 6.64 (m, 4H,
3,5-H), 7.53 (m, 4H, 2,6-H). 13C NMR (75 MHz,
2.2.6. Synthesis of 2-dimethylphosphinyl-1-methyl-1-
(4-methoxyphenyl)ethanol (6)
To a sample of 1.49 g of (4-methoxy)acetophenone
(9.9 mmol) in 20 ml of pentane at 20 ꢁC, 1.95 g of
LiCH2PMe2 Æ TMEDA (9.9 mmol) was added dropwise
in 40 ml of pentane. After 2 h, 8 ml of water was added
and the mixture was stirred at 20 ꢁC for 2 h. The vola-
tiles were removed in vacuo at 40 ꢁC and the white res-
idue was extracted with 70 ml of pentane to give 1.95 g
of a colorless oil (crude yield 99%). Distillation at 131–
133 ꢁC/0.3 mbar afforded a colorless viscous liquid of 2.
Yield 1.78 g (85%).
1
1
IR (Nujol mull, 4000–1700 cmꢀ1): 3361m m(OH). H
THF-d8, 298 K): d 11.3 (d, J(PC) = 21.5 Hz, PCH3),
12.6 (d, 1J(PC) = 18.0 Hz, PCH2), 48.8 (d,
1J(PC) = 31.8 Hz, PCH3), 55.1 (OCH3), 112.9 (CO),
128.1 (4-C), 128.4 (2-C), 147.5 (3-C), 158.3 (1-C). 31P
NMR (81 MHz, THF-d8) 233 K: d ꢀ5.0 (m, 0.96 P,
NMR (200 MHz, acetone-d6, 298 K): d 0.79 (d, 3H,
2J(PH) = 2.9 Hz, PCH3), 0.82 (d, 3H, 2J(PH) = 3.1
Hz, PCH3), 1.63 (s, 3H, CH3), 1.95 (d, 2H,
2J(PH) = 2.9 Hz, PCH2), 3.75 (s, 3H, OCH3), 4.21 (s,
br, 1H, OH), 6.82–6.87 (m, 2H, 3,5-H), 7.39–7.44 (m,
2H, 2,6-H). 31P NMR (81 MHz, acetone-d6, 298 K): d
ꢀ54.0 (s).
2
trans-PMe3), 3.0 (d, 0.04 P, JP,P = 18 Hz, cis-PMe3),
2
16.0 (d, 0.04 P, JP,P = 18 Hz, cis-PMe2), 2.0 (m, 0.96
2
P, trans-PMe2); 193 K: d ꢀ5.0 (d, 0.96 P, J(PP) = 339
2
Hz, trans-PMe3), 4.0 (d, 0.04 P, J(PP) = 20 Hz, cis-
PMe3), 16.0 (d, 0.04 P, 2J(PP) = 20 Hz, cis-PMe2),
2.2.7. Synthesis of (2-dimethylphosphinyl-1,1-
diphenylethanolato)-[O,P]-methyl-
(trimethylphosphine)nickel (7)
2
22.0 (d, 0.96 P, J(PP) = 339 Hz, trans-PMe2).
A brown solution of 0.44 g of [NiMe(OMe)PMe3]2
(1.5 mmol) in 30 ml of THF at ꢀ78 ꢁC when combined
with 0.88 g of 1 (3.0 mmol) under stirring turned rapidly
to yellow. The mixture was warmed to 20 ꢁC and evap-
orated to give an orange oil, which was recrystallized
from pentane at 4 ꢁC to give bunches of light brown nee-
dles of 7 (0.67 g, 55%), m.p. 90–92 ꢁC (dec.).
2.2.9. Synthesis of [2-dimethylphosphinyl-1,1-
di(4-N,N-dimethylaminophenyl)ethanolato]-[O,P]-
methyl(trimethylphosphine)nickel (9)
Upon samples of 0.51 g of [NiMe(OMe)PMe3]2 (1.3
mmol) and 0.81 g of 5 (2.6 mmol), respectively, 30 ml
of THF was condensed in vacuo. After warming to
20 ꢁC, the mixture was stirred for 1 h. The volatiles were

H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
4397
then evaporated and the yellow residue was extracted
with pentane at 50 ꢁC. Crystallization from pentane at
20 ꢁC gave yellow microcrystals of 9 (0.56 g, 44%),
m.p. 140–143 ꢁC (dec.).
Anal. Calc. for C24H40N2NiOP2 (492.2): C, 58.56; H,
8.18; N, 5.69; P, 12.59. Found: C 60.79; H, 7.73; N, 5.85;
P, 13.05%.
Anal. Calc. for C17H21NiOP (331.1): C, 61.69; H,
6.39; P, 9.36. Found: C, 61.52; H, 6.40; P, 8.55%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ2.27 (d, 3
H, 3J(PH) = 5.0 Hz, NiCH3), 0.68 (d, 6H,
2J(PH) = 10.4 Hz, PCH3), 2.33 (d, 2H, 2J(PH) = 9.7
Hz, PCH2), 7.08–7.21 (m, 2H, 4-H), 7.31–7.49 (m, 3,5-
H), 8.27–8.31 (m, 4H, 2,6-H). 13C{1H} NMR (75
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ1.27 (s, br,
3H, NiCH3), 0.92 (s, br, 6H, PCH3), 1.33 (s, 9H, PCH3),
2.47 (s, 2H, PCH2), 2.81 (s, 12H, NCH3), 6.51–6.55 (m,
4H, 3,5-H), 7.41–7.45 (m, 4H, 2,6-H). 31P NMR (81
MHz, THF-d8) 233 K: d ꢀ15.0 (s, 0.06 P, PMe3), ꢀ6.0
MHz, THF-d8, 298 K): d ꢀ21.5 (d, J(PC) = 43.9 Hz,
1
NiCH3), 11.6 (d, 1J(PC) = 30.6 Hz, PCH3), 52.5 (d,
1J(PC) = 26.7 Hz, PCH2), 81.7 (C–O), 126.6 (4-C),
127.4 (2-C), 129.3 (3-C), 149.4 (1-C). 31P NMR (81
MHz, THF-d8, 298 K): d 20.0 (s, PCH3).
2
(m, 0.94 P, trans-PMe3), 2.0 (d, 0.03 P, J(PP) = 223
Hz, cis-PMe3), 15.0 (d, 0.03 P, 2J(PP) = 23 Hz, cis-
PMe2), 22.0 (m, 0.94 P, trans-PMe2); 193 K: d ꢀ14.0
(s, 0.17 P), ꢀ5.0 (d, 0.97 P, 2J(PP) = 342 Hz, trans-
PMe3), 4.0 (m, 0.03 P, cis-PMe3), 17.0 (m, 0.03 P, cis-
2.2.12. Synthesis of trans-bis{l-(2-dimethylphosphinyl-
1,1-di(4-methoxyphenyl)ethanolato-[O,P])
methylnickel} (13)
Method (a): A solution of 0.24 g of 8 (0.50 mmol) in
30 ml of cyclopentene was held at 20 ꢁC for 2 h. The
solution was filtered and and kept at 4 ꢁC to afford yel-
low crystals of 13 suitable for X-ray diffraction. Yield
0.10 g (51%). Method (b): 0.17 g of 8 (0.36 mmol)
and 0.12 g of Ni(COD)(PMe3)2 (0.37 mmol) were com-
bined in 30 ml of diethyl ether at 20 ꢁC to give a yellow
solution which after 2 h was filtered and kept at 4 ꢁC
to yield a yellow solid of 13 (0.90 g, 64%), m.p. 193–
195 ꢁC.
Anal. Calc. for C19H25NiO3P (391.1): C, 58.35; H,
6.44 ; Ni, 15.01. Found: C, 58.35; H, 6.40; Ni, 14.88%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ2.25 (d,
3H, 3J(PH) = 5.0 Hz, NiCH3), 0.69 (d, 6H,
2J(PH) = 10.4 Hz, PCH3), 2.27 (d, 2H, 2J(PH) = 9.7
Hz, PCH2), 3.80 (s, 6H, OCH3), 6.88–6.93 (m, 4H,
3,5-H), 8.14–8.19 (m, 4H, 2,6-H). 31P NMR (81 MHz,
THF-d8, 298 K): d 19.0 (s, PCH3).
2
PMe2), 23.0 (d, 0.97 P, J(PP) = 342 Hz, trans-PMe2).
2.2.10. Synthesis of [9-dimethylphosphinylmethylen-9-
fluorenolato]-[O,P]-methyl(trimethylphosphine)nickel
(11)
A brown solution of 0.33 g of [NiMe(OMe)PMe3]2
(0.9 mmol) in 50 ml of THF at 20 ꢁC was combined with
0.58 g of 3 (2.3 mmol) and stirred for 3 h. The mixture
was evaporated to afford a yellow solid which was
washed with pentane and recrystallized from toluene
to give yellow microcrystals of 7 (0.55 g, 76%), m.p.
82–84 ꢁC (dec.).
Anal. Calc. for C20H28NiOP2 (405.1): C, 59.32; H,
6.92; P, 15.30. Found: C, 58.29; H, 6.65; P, 15.68%.
1H NMR (300 MHz, THF-d8, 298 K): d ꢀ2.44 (d,
0.57H, 3J(PH) = 5.1 Hz, NiCH3), ꢀ1.16 (d, 3H,
3J(PH) = 7.1 Hz, NiCH3), 0.85 (d, 9H, 2J(PH) = 5.0
2
Hz, PCH3), 1.27 (d, 6H, J(PH) = 6.5 Hz, PCH3), 1.93
(d, 2H, 2J(PH) = 7.8 Hz, PCH2), 6.96–7.03 (m, 4H,
3,4,5,6-H), 7.27–7.38 (m, 2H, 2,7-H), 7.86–7.89 (m,
2H, 1,8-H). 13C NMR (75 MHz, THF-d8, 298 K): d
24.6 (s, NiCH3), 12.1 (d, 1J(PC) = 16.2 Hz, PCH3),
2.2.13. Synthesis of trans-bis{l-(2-dimethylphosphinyl-1-
methyl-1-(4-methoxyphenyl)ethanolato)-
[O,P]methylnickel} (14)
Upon 0.57 g of [NiMe(OMe)PMe3]2 (1.6 mmol) and
0.63 g of 6 (3.2 mmol), 60 ml of THF was condensed in
vacuo. After warming to 20 ꢁC, the mixture was stirred
for 2 h. The volatiles were then evaporated and the yel-
low residue was extracted with pentane at 50 ꢁC. From
pentane at ꢀ30 ꢁC an orange oil was obtained, which
was dissolved in diethyl ether to give at ꢀ30 ꢁC yellow
microcrystals of 14 (0.69 g, 62%), m.p. 189–193 ꢁC.
Anal Calc. for C13H25NiO4P (335.0): C, 46.61; H,
7.52; P 9.25. Found: C, 47.39; H, 6.57; P, 9.36%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ1.74 (d, 3
H, 3J(PH) = 5.4 Hz, NiCH3), ꢀ1.69 (d, 3H,
13.2
(d,1J(PC) = 22.1
Hz,
PCH3),
48.0
(d,
1J(PC) = 25.4 Hz, PCH2), 91.5 (CO), 120.8 (5-C),
123.9 (2-C), 127.4 (3-C), 157.2 (4-C). 31P NMR (81
MHz, THF-d8, 193 K): d ꢀ11.0 (s, PMe3), 20 (s, PMe2).
2.2.11. Synthesis of trans-bis{l-(2-dimethylphosphinyl-
1,1-diphenylethanolato[O,P])methylnickel} (12)
Samples of 0.4 g of 7 (1.20 mmol) and 0.20 g of
Ni(COD)(PMe3)2 (2.86 mmol) were combined in 60 ml
of diethyl ether at 20 ꢁC to give a yellow solution, which
after 2 h attained a brown color. The volatiles were re-
moved in vacuo, and the brown residue was dried in va-
cuo at 20 ꢁC for 1 h and washed with pentane. The solid
was then dissolved in THF, the orange solution was fil-
tered and kept at 4 ꢁC to yield orange prisms of 7 (0.21
g, 53%), m.p. 196–197 ꢁC.
2
3J(PH) = 5.2 Hz, NiCH3), 0.59 (d, 3H, J(PH) = 10.4
Hz, PCH3), 0.68 (d, 3H, 2J(PH) = 10.8 Hz, PCH3),
1.09 (d, 3H, 2J(PH) = 8.3 Hz, PCH3), 1.10 (d, 3H,
2J(PH) = 7.9 Hz, PCH3), 1.48 (s, 3H, CCH3), 1.62 (s,
3H, CCH3), 1.78–1.93 (m, 4H, PCH2), 3.78 (s, 3 H,

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H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
Table 1
OCH3), 3.82 (s, 3H, OCH3), 6.87–7.01 (m, 4H, 3,5-H),
8.24–8.45 (m, 4H, 2,6-H). 31P NMR (81 MHz, THF-
d8, 298 K): d 20.0 (s, PMe2), 20.1 (s, PMe2).
Crystal data for compound 13
Formula
C19H25NiO3P
391.1
Molecular mass
Crystal size (mm)
Crystal system
Space group
0.11 · 0.05 · 0.04
monoclinic
C21/c (Nr.15)
1.39600(4)
1.250100(2)
1.631000(3)
105.4030(1)
3.761521(10)
8
2.2.14. Synthesis of (2-isopropyl(phenyl)phosphinyl)-
4,6-di-tert-butylphenolato(methyl)nickel (15)
˚
Upon 0.46 g of [NiMe(OMe)PMe3]2 (1.3 mmol) and
0.90 g of (2-isopropyl(phenyl)phosphinyl)-4,6-di-tert-
butylphenol (2.54 mmol), 60 ml of THF was condensed
in vacuo. After warming to 20 ꢁC, the mixture turned
orange and was stirred for 12 h. The volatiles were then
evaporated and the yellow residue was extracted with
pentane at 50 ꢁC. From pentane at ꢀ30 ꢁC yellow
microcrystals were obtained. The mother liquor was
evaporated to dryness to give a yellow solid, which
was identical with the first fraction (IR). Combined yield
0.94 g of 15 (69%), m.p. 88–90 ꢁC.
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
1.039
0.812
293(2)
l (Mo Ka) (mmꢀ1
)
Temperature (K)
Data collection range (ꢁ)
4.3 6 2H 6 55
ꢀ18 6 h 6 18, ꢀ12 6 k 6 12,
ꢀ15 6 l 6 15
1746
1746
217
1.015
0.0593
0.1347
Limiting indices
Number of reflections measured
Number of unique data
Parameters
Goodness-of-fit on F2
R1 (I > 2r(I))
Anal. Calc. for C27H44NiOP2 (505.3): C, 64.18; H,
8.77; P, 12.26. Found: C, 63.64; H, 8.55; P, 12.56%.
1H NMR (200 MHz, THF-d8, 298 K): d ꢀ0.93 (d, 3
H, 3J(PH) = 1.8 Hz, NiCH3), 0.98–1.24 (m, 12H,
CCH3), 1.30–1.45 (m, 21H, CCH3, PCH3), 2.61–2.72
(m, 1H, CH), 6.90–6.95 (m, 1H, 3-H), 7.13 (d, 1H,
3J(PH) = 2.4 Hz, 5-H), 7.38–7.40 (m, 3H, 9,10-H),
7.59–7.68 (m, 2H, 8-H). 13C NMR (75 MHz, THF-d8,
298 K): d ꢀ22.2 (m, NiCH3), 10.8 (d, 1J(PC) = 22.2
Hz, PCH3), 16.0 (s, CH3), 17.6 (s, CH3), 24,2 (d,
1J(PC) = 37.2 Hz, PCMe), 27.8, 30.3 (all CCH3), 32.6,
33.8 (all CMe3), 113.6 (2-C), 124.9 (5-C), 125.2 (3-C),
wR2 (all data)
were collected (x-scan) using graphite-monochromated
Mo Ka radiation; Lorentz polarization corrections but
no absorption corrections were applied. The structure
was solved by Patterson and conventional Fourier meth-
ods. All non-hydrogen atoms were treated anisotropi-
cally, hydrogen atoms were treated with a riding
model in idealized positions.
2
127.2 (d, J(PC) = 9.0 Hz, 8-C), 128.1 (10-C), 131.2 (d,
3J(PC) = 9.0 Hz, 7-C), 131.9 (6-C), 133.1 (4-C), 135.6
3
2
(d, J(PC) = 9.0 Hz, 9-C), 174.3 (d, J(PC) = 23.4 Hz,
1-C). 31P NMR (81 MHz, THF-d8, 298 K): d ꢀ8.0
(d,trans2J(PP) = 310 Hz, PMe3), 0.3 (d,cis2J(PP) = 24
Hz, PMe3), 40.0 (d,trans2J(PP) = 308 Hz, PPh), 40.5
(d,cis2J(PP) = 24 Hz, PPh).
3. Results and discussion
3.1. Synthesis of (2-dimethylphosphinyl)ethanols
A synthetic route as given by Lappert et al. [7] was
modified to generate (2-dimethylphosphinyl)ethanols
according to Eq. (1)
2.2.15. Ethene oligomerization/polymerization tests
Method (a): A 75 ml stainless steel autoclave
equipped with magnetic stirring was charged with 0.1
mmol of the nickel complexes 7, 10, 15, or 16 in 12 ml
of toluene under argon. Ethene pressure was applied
and the reactor was closed. After a time of precatalysis
extending from 30 to 40 min the drop of pressure was
recorded. Method (b): A 500 ml stainless steel autoclave
was charged with 130 ml of toluene under 70 bar of eth-
ene. 0.5 mmol of the nickel complexes 8 or 9 in 5 ml of
toluene was added under pressure, which was kept at 70
bar by continuous feeding of ethene until showing no
further uptake.
1
1. O=CR R2
2. H2O
2
Me2
N
1
R
R
OH
Me2PCH2Li
N
Me2
P
Me2
1
2
3
4
5
6
R1 = R2 = C6H5
ð1Þ
R1 = R2 = 4-OMe–C6H4
R1 + R2 = 9-fluorenyl
R1 = H, R2 = C6H5
R1 = R2 = 4-NMe2–C6H4
2.2.16. X-ray crystal measurements
Crystal structure analyses: A summary of crystal data
and refinement for 13 is given in Table 1. A yellow spec-
imen was sealed under argon in a glass capillary and
mounted on a Siemens P4 diffractometer. The data sets
R1 = Me, R2 = 4-OMe–C6H4
The products 1–3 and 5 were isolated as white or yellow-
ish crystals which are air-stable for more than two

H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
4399
hours, while 4 and 6 were obtained as colorless oils. All
materials are freely soluble in diethyl ether or toluene,
and their infrared and NMR spectra contain all features
expected from known data [8]. Strong infrared bands
between 3291 (2) and 3661 cmꢀ1 (3) are assigned to
m(OH) vibrations, and 31P resonances contain a sin-
glet around ꢀ54 ppm which is close to the value of
trimethylphosphine [9]. Proton resonances of the aniso-
chronic PMe2 groups in 4 and 6 appear as doublets of
doublets, and CH2 groups are split accordingly as ex-
pected for a center of chirality at C1. This type of mol-
ecule has not yet been investigated as a ligand for late
transition metals.
ing the two P nuclei in cis positions. A cis isomer in
an equilibrium of configurations in methylnickel P,O-
chelates [2a] has been observed for the first time. A sim-
ilar pattern of resonances at variable temperature was
observed with samples of 8 and 9 (see Section 2). The
underlying dynamic process appears to be based on a
reversible dissociation of trimethylphosphine, which is
supported by the known properties of 16-electron
methylnickel compounds acting as a source and as an
acceptor of trimethylphosphine [11]. A broad singlet at
ꢀ15 ppm in the 193 K spectrum could be assigned to
an 18-electron bis(trimethylphosphine)methylnickel
complex. In order to test this possibility, a sample of 7
containing one mole equivalent of trimethylphosphine
was measured under the same conditions. In the 233 K
spectrum, two 31P singlets at 21 and ꢀ15 ppm and
a third one at 55 ppm of equal intensities were assigned
to 7 and free trimethylphosphine, respectively. At 193 K,
only two singlets at d 22 and ꢀ14 ppm were observed in
a 1:2 ratio as expected for pentacoordinate 7 Æ PMe3 still
indicating rapid exchange of ligands.
3.2. Methylnickel compounds of (1,1-diaryl-2-
dimethylphosphinyl)ethanol
After combining the (2-phosphinyl)ethanols 1, 2, and
5
with dimeric methyl(methoxo)(trimethylphos-
phine)nickel in THF according to Eq. (2), the mixture
turned from brown to yellow.
1 R2
1 R2
R
R
3.3. Methylnickel compounds of
(9-dimethylphosphinyl)methylenefluorenol
OH
O
PMe3
Me
+
1 2 [NiMe(OMe)PMe ]
/
3 2
Ni
-MeOH
P
Me2
P
Me2
The observed ligand mobility in compounds 7–9 sug-
gested an attempt at steric fixation of the chelating li-
gand. Attaching the fluorenyl group to the C1 atom of
a 2-phosphinylethanol ties the aromatic substituents to-
gether and reduces the steric shielding of the O-donor
function. Under conditions of the previous synthesis,
(9-dimethylphosphinyl)methylen-fluorenol (3) was com-
bined with methyl(trimethylphosphine)nickel methoxide
according to Eq. (2) to afford yellow microcrystals of 10
which under argon decompose above 82 ꢁC. The crystals
are only slightly soluble in pentane and moderately sol-
uble in diethyl ether or toluene. The infrared spectrum
1
2
5
7
8
9
ð2Þ
From pentane yellowish brown twinned crystals of 7
and yellow microcrystals of 8 and 9 were obtained,
respectively, which under argon decompose above
90 ꢁC and are oxidized in air within less than five min-
utes. In the infrared spectrum, the region of m(OH)
bands is empty and methoxo groups are absent. 1H
and 13C NMR spectra are consistent with a square-
planar coordination geometry around nickel effected
by methyl and trimethylphosphine groups and a chelat-
ing phosphinylethanolato ligand. Further details of
solution configurations were revealed in 31P NMR
measurements.
At 297 K a broad signal at 22 ppm is assigned to a
coordinated Me2P group, while at ꢀ8 ppm a singlet is
observed as typical for coordinated trimethylphosphine
under conditions of rapid exchange. At 233 K, these res-
onances are still broad but are accompanied by two dou-
blets at 16 and 4 ppm (2J(P,P) = 16 Hz) containing 5%
of total peak intensity. At 193 K the coupling attains
19 Hz, while the intensity of the doublets drops to 3%.
97% of the total intensity is then present in an AB-type
pattern of resonances (2J(P,P) = 339 Hz) which is char-
acteristic for P nuclei in trans positions [10]. The second
doublet of doublets was assigned to an isomer contain-
1
closely resembles that of 7, while H NMR signals are
observed as expected for a chelating monoanionic
ligand.
An additional NiMe doublet at ꢀ2.4 ppm (apparent
intensity 0.57 H) as the only novel feature was assigned
to a second species. In the 31P NMR spectrum (193 K), a
corresponding singlet resonance at d 20 ppm (apparent
intensity 0.18 P) was observed besides the singlet reso-
nances of the rapidly exchanging trans isomer of 10
(cis isomer below 3% and not detected). Upon addition
of one mole equivalent of trimethylphosphine the yellow
solution turned orange, and both extra NMR signals
disappeared. Evaporation of the solution at ꢀ10 ꢁC re-
moved all excess trimethylphosphine with the solvent
leaving a solid residue of 10. The transition from yellow
to orange is reminiscent of the pair of dimethylnickel
compounds containing either two trimethylphosphine
ligands (16 electrons, yellow) or three (18 electrons,

4400
H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
orange), suggesting excessive ligand dissociation from
orange 10 Æ PMe3.
Under argon the orange yellow prisms of 12 (from THF)
and the yellow microcrystals of 13 (from ether) melt
above 190 ꢁC. Both materials tolerate handling in air
at room temperature remaining unaltered for at least
three hours. Spectroscopic data are consistent with
the presence of a methylnickel group and a chelating
(2-diarylphosphinyl)ethanolato ligand. The dinuclear
nature of 13 was established by a single-crystal X-ray
diffraction analysis.
The molecular structure (Fig. 1) contains two nickel
atoms at a non-bonding distance of 293.9(0) pm held
in a distorted square planar environment by two bridg-
ing O-atoms, a phosphinyl-P atom and a methyl group.
The dinuclear complex molecule has a center of inver-
sion based on a transoid arrangement of ligands. The
central Ni2O2 metallocycle is folded in a cyclobutane-
like fashion forming a dihedral angle of 12.86ꢁ along
the O1–O1* axis. The five-membered chelate ring with
a sum of internal angles of 522.57ꢁ, including the usual
chelate-bite angle P1–Ni1–O1 = 87.62(18)ꢁ, shows slight
bending. While the bond distances Ni–C1, Ni–O1* and
Ni–P1 lie in the expected range, the bond Ni–O1 is nota-
bly longer due to the strong trans-influence of the
methylnickel group.
From the mother liquor of 10, some dark brown crys-
tals of a by-product (<1%) were collected. The brown
compound was reproducibly obtained in high yields
when toluene solutions of 10 were slowly evaporated
at 60 ꢁC. Eventually, from a deep brown solution dark
brown prisms of 11 were grown which upon removal
of liquor and drying in vacuo lost their lustrous surface.
Elemental analyses were consistent with continuous loss
of toluene under these conditions. Solvent-free 11
decomposes under argon above 118 ꢁC turning black
but remains unaltered at 20 ꢁC in air for three hours,
while solutions in THF, toluene, or acetone under air
are oxidatively decomposed within seconds. The extra
1H doublet and 31P singlet resonances in the spectrum
of 10 coincide with the peaks of added 11.
The propensity of methylnickel alkoxides and phen-
oxides to form bis(l-oxo)-bridged dinickel compounds
[11] suggests that thermal dissociation of trimethylphos-
phine from 10 establishes an equilibrium with dinuclear
11 according to Eq. (3). Dinuclear methylnickel com-
plexes containing (2-diphenylphosphinyl)phenolato li-
gands are believed to take part in equilibria of ligand
dissociation [15] but have not been characterized to date.
The action of Ni(COD)(PMe3)2 on a (2-isopro-
pyl(phenyl)phosphinyl-phenolato)methylnickel complex
[2a] according to Eq. (5) confirms the role of the nickel(0)
reagent as a rapid scavenger of trimethylphosphine.
PMe3
O
Ni
Me
P
Me2
PMe
+
3
-
PMe3
10
PMe
- PMe3
+
3
Me2
P
Me
PMe3
Ni
Ni
Ni
O
PMe3
Me
O
O
P
Me2
Me
P
Me2
.
10 PMe3
11
ð3Þ
When toluene solutions of 7 or 8 were evaporated at 60–
100 ꢁC, a spontaneous decomposition occurred forming
trimethylphosphine oxide among unidentified products.
However, addition of Ni(COD)(PMe3)2 as a scavenger
of trimethylphosphine to a diethyl ether solution of 7
or 8 under milder conditions afforded the desired meth-
ylnickel compounds 12 and 13, respectively (Eq. (4)).
Me2
P
Me
O
R1
R2
PMe3
Me
R1
Ni
Ni
Ni(COD)(PMe )
O
+
-
3 2
2
Ni
R1
R2
2
O
R
COD, Ni(PMe3)4
Fig. 1. Molecular structure of 13 (ORTEP plot without hydrogen
atoms). Selected bond lengths (A) and angles (ꢁ): Ni–C1 1.928(9), Ni–
P1 2.063(3), Ni–O1 1.953(6), Ni–O1* 1.984(6), Ni–Ni* 2.939, O1–C18
1.436(10), P1–C2 1.852(9), C2–C18 1.540(10); C1–Ni–P1 89.4(3), C1–
Ni–O1* 101.0(3), C1–Ni–O1 177.1(3), O1–Ni–O1* 82.0(3), P1–Ni–O1
87.62(18), Ni–O1–Ni* 96.6(2), P1–Ni–O1* 169.5(2), C18–O1–Ni
120.2(5).
P
˚
Me2
Me
P
Me2
7, 8
12, 13
ð4Þ

H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
4401
affording trimethylphosphine oxide among other
products.
PMe3
Me
Ni(COD)(PMe )
+
-
O
P
3 2
Ni
(decomp.)
COD, Ni(PMe3)4
ð5Þ
3.5. Oligomerization of ethene
Complexes 7–10 contain all features required for cat-
alyst activity in C,C-coupling reactions of ethene [1,2]: a
methylnickel group in square planar geometry as a
model of a growing hydrocarbon chain, a P,O-chelating
anion serving as a steering device, and a reversibly
dissociating neutral ligand indicating a site for substr-
ate binding. [2-Isopropyl(phenyl)-phosphinyl]phenolato-
(methyl)nickel (15) was included for comparison as
well as a freely dissociating complex [2-butyl(phenyl)-
phosphinyl]phenolato(methyl)nickel (16) [12] bearing
one or two trimethylphosphine ligands in solution and
mixtures of these with Ni(COD)2 which represent cata-
lyst entities without trimethylphosphine.
However, besides the expected soluble products a
dark brown solid resulted which proved insoluble in
ether, acetone, or acetonitrile and was not further char-
acterized. Steric hindrance in the vicinity of the pheno-
lato-O donor appears to cause side reactions. In spite
of this finding, mixtures of methyl(trimethylphos-
phine)nickel complexes and Ni(COD)2 as a scavenger
[6b] of trimethylphosphine ligands were tested as cata-
lysts for ethene reactions (see below).
3.4. Methylnickel compounds of
(1-aryl-2-dimethylphosphinyl)ethanols
R2
Both dissociation of ligands and access to a vacant
coordination site at the nickel atom depend on steric ef-
fects in the vicinity of an available site. As seen in the
molecular structure of 12, the substituents in the C1-po-
sition (C18 in Fig. 1) should have a marked steric influ-
ence on the coordination of ligands and the binding of
substrates. On replacing one of the aryl substituents by
a methyl group, for instance introducing 6 by reaction
with methylnickel methoxide according to Eq. (6), all
trimethylphosphine was eventually removed with the
solvent.
1
O
P
R
O
PMe3
(PMe )
Ni
3n
Ni
ð7Þ
Me
3
P
Me2
Me
R
15, 16
7 -10
In a typical preparative-scale test reaction with the cat-
alysts 7, 10, 15, 16, or 16 + Ni(COD)2, toluene solutions
were placed in an autoclave (A) under a given pressure
of ethene and kept stirring. Consumption of olefin was
followed as the pressure dropped [13]. A technical auto-
clave (B), in a total volume of 1 dm3 containing toluene,
was held at a given temperature under constant pressure
by continuous feeding of ethene [14]. Measuring the flow
rate gave the rate of ethene conversion in catalytic runs
with complexes 8 and 9. Table 2 gives the conditions and
turnover numbers (TON). In view of the moderate TON
the low-density polyethylene (LDPE) samples were not
further characterized.
Me2
P
MeO
Me
Me
Ni
Ni
O
O
[NiMe(OMe)PMe3]2
+ 2 6
- 2 MeOH
- 2
Me
PMe3
P
Me2
Me
OMe
14
ð6Þ
The yellow microcrystals of 14 are air-sensitive although
stable under argon up to 189 ꢁC. They are sparingly sol-
uble in pentane and freely so in toluene or THF. Spec-
While no explanation suggests itself for the inactivity
of 9 and 10, the low activity of 7 and 8 can be connected
with their preference to form dimers as a reservoir of the
catalytically active species. In the absence of trimethyl-
phosphine a mononuclear 14-electron species would be
1
tral features are those of a dinickel complex, but H,
13C, and 31P NMR spectra contain twice the number
of resonances in equal intensities (see Section 2). This
pattern is best explained by the presence of optical iso-
mers in solution. The possible orientations of two 4-
MeO-C6H4 substituents generate pairs of enantiomers
and pairs of diastereoisomers.
Table 2
Test runs for catalytic conversion of ethene
Complex
T (ꢁC) p (bar) Ethene (g) TON Product
7
100
70
70
80
80
80
80
50
70
70
35
35
35
42
8.5
7.6
294
398
LDPE
LDPE
A methyl substituent replacing an aryl group at the
C1 atom of 2 favors molecular aggregation by bridging
alkoxo groups in 14 over coordination of trimethylphos-
phine. With a hydrogen atom in the C1 position, i.e.,
using 4 in a reaction according to Eq. (6), the expected
fragmentation of the ethanolato ligand [16] proceeds
8
9
10
15
16
7.7
7.7
8.2
257
2220
1470
C4–C24
C4–C14
LDPE
16 + Ni(COD)2

4402
H.-F. Klein et al. / Inorganica Chimica Acta 358 (2005) 4394–4402
be turned onto polymerization by Ni(COD)2 acting as
scavenger of uncoordinated trimethylphosphine.
Me2
P
Me
O
R1
R2
Ni
Ni
R1
R2
O
5. Supplementary material
Me
P
Crystallographic data (without structure factors) for
the structure reported in this paper have been deposited
as supplementary publication with the Cambridge Crys-
tallographic Data Centre. Deposition number is CCDC-
151228 for 13. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (Fax: (internat.) +44 1223 336
033, e-mail: deposit@ccdc.cam.ac.uk).
R1
R2
O
Me2
Ni
Me
P
Me2
C H
+
2
4
R1
R2
O
C H
+
2
4
Ni
P
Me2
Me
C H
+ 2
2 4
1
O
R
R2
Ni
References
Me
P
Me2
14 VE
[1] (a) D. Vogt, in: B. Cornils, W.A. Herrmann (Eds.), Applied
Homogeneous Catalysis with Organometallic Compounds, vol. 1,
VCH, New York, 1996, 245ff;
Scheme 1. Equlibria of dissociation and substrate binding.
(b) G.W. Parshall, S.D. Ittel, Homogeneous Catalysis, Wiley,
New York, 1992, 68ff.
expected to be generated in low equilibrium concentra-
tion, which however could be rapidly converted by sub-
strate binding (Scheme 1).
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16 (1997) 2005;
Comparing the last two experiments in Table 2 is of
particular interest. Dissociation of PMe3 from the 18-
electron complex 16, which must be excessive under
the reaction conditions, raises the catalytic activity
for ethene oligomerization while in the presence of
Ni(COD)2 as a scavenger of PMe3 the catalyst activity
is turned onto polymerization. This clearly confirms
the notion [2a,4b] that coordination of trimethylphos-
phine suppresses ethene binding at the available coordi-
nation sites (h), while elimination of 1-olefin from a
growing chain in the position of NiMe is enhanced by
coordination of trimethylphosphine.
(c) G.J.P. Britovsek, S. Mastroianni, G.A. Solan, S.P.D. Baugh,
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4. Conclusion
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Gautheron, P. Meunier, P. Kalck, Coord. Chem. Rev. 236 (2003)
143.
Dimethylphosphinylethanols without C–H bonds at
the C1-atom are smoothly transformed to stable anionic
[P,O]-ligands forming five-membered nickelacycles in
square planar geometry. When bearing a Ni–CH3 func-
tion the complexes can act as single-component catalysts
in the polymerization of ethene with moderate activity.
Supporting trimethylphosphine ligands are dissociated
by switching to the bridging [P,l-O]-coordination mode
in dinickel compounds which is most effectively con-
trolled by the steric bulk of the substituents at C1. Dinu-
clear compounds are likely to form a reservoir for the
catalytically active chelate(methyl)nickel species (14 me-
tal-valence electrons) and could give rise to the induc-
tion periods observed in the catalysis test runs.
Catalytic activity in the oligomerization of ethene can
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