Stabilization of nickel(O) by hemilabile P,N-ferrocene ligands and their ethylene oligomerization activities

Article abstract of DOI:10.1021/om060607+

Ligand displacement reactions of Ni(COD)₂ with a ferrocenediyl iminophosphine, viz., [C₅H₄CH= N(C₆F ₅)]Fe[η-C₅H₄PPh₂] (1) or [C ₅H₄CH=NC(H)(CH

Full text of DOI:10.1021/om060607+

4878
Organometallics 2006, 25, 4878-4882
Stabilization of Nickel(0) by Hemilabile P,N-Ferrocene Ligands and
Their Ethylene Oligomerization Activities
Zhiqiang Weng,†,‡ Shihui Teo,† and T. S. Andy Hor*,†
Department of Chemistry, National UniVersity of Singapore, 3 Science DriVe 3, Kent Ridge, Singapore
117543, and Institute of Chemical and Engineering Sciences, No. 1, Pesek Road,
Jurong Island, Singapore 627833
ReceiVed July 5, 2006
Ligand displacement reactions of Ni(COD)2 with a ferrocenediyl iminophosphine, viz., [C5H4CHd
N(C6F5)]Fe[η-C5H4PPh2] (1) or [C5H4CHdNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2] (2), in the presence of
t-BuNC, CO, or PhCtCPh give the appropriate mixed-ligand Ni(0) complexes, viz., [C5H4CHd
N(C6F5)]Fe[η-C5H4PPh2]Ni0(CNt-Bu)3 (3), [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0(CO)2 (4a), {[C5H4-
CHdN(C6F5)]Fe[η-C5H4PPh2]}2Ni0(CO)2 (4b), and [C5H4CHdNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2]Ni0(η2-
PhCtCPh) (5). The X-ray crystal and molecular structures of 4b and 5 are described. The hemilability
of iminophosphine is illustrated by the formation of both P,N-chelating and imine-pendant functions. All
the complexes examined are catalytically active toward ethylene oligomerization at 30 °C, with 5 showing
the best activity, followed by 3 and 4.
Our interest in the coordination12 and catalytic13 chemistry
of dppf [1,1′-bis(diphenylphosphino)ferrocene] stems from its
coordinative variance.14 Such ligand adaptability tends to
complement and support the metal geometric and coordinative
changes along the catalytic path. To maximize this advantage,
we need to design hemilabile ligands with suitable heterodi-
functional donors that could match the need of the metal and
Introduction
Ethylene oligomerization developed at Shell, BP Amoco, and
Chevron Phillips has provided the industry with highly desirable
linear R-olefins in the C6-C20 range. These oligomers are
important precursors for detergents, plasticizer alcohols, syn-
thetic lubricants, and fine chemicals and as comonomers in the
production of linear low-density polyethylene.1,2 They also
provided good incentives for catalytic research in nickel
coordination complexes, especially those of Ni(II). For example,
the SHOP-type [P,O] system developed by Keim3 and Ostoja4
affords highly linear R-olefins (C6-C20). Brookhart used Ni-
(II) diimine [N,N] complexes with a large excess of methyl-
aluminoxane (MAO) to produce highly active R-olefin catalysts
for ethylene oligomerization with high selectivity.5 [N,O]
chelating neutral nickel catalysts have been reported by DuPont,6
Grubbs,7 Brookhart,8 etc.,9 whereas [P,N] chelating nickel
ethylene oligomerization catalysts have been studied by Braun-
stein10 and others.11
(5) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169. (b) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414. (c) Killian, C. M.; Tempel, D. J.; Johnson, L. K.;
Brookhart, M. J. Am. Chem. Soc. 1996, 118, 11664. (d) Killian, C. M.;
Johnson, L. K.; Brookhart, M. Organometallics 1997, 16, 2005.
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rathy, A.; Hauptman, E.; Simpson, R. D.; Feldman, J.; Coughlin, E. B.
WO 98/30609, 1998.
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H.; Bansleben, D. A.; Day, M. W. Organometallics 1998, 17, 3149. (b)
Younkin, T. R.; Connor, E. F.; Henderson, J. I.; Friedrich, S. K.; Grubbs,
R. H.; Bansleben, D. A. Science 2000, 287, 460.
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25, 1868. (b) Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22, 250.
(c) Hicks, F. A.; Jenkins, J. C.; Brookhart, M. Organometallics 2003, 22,
3533. (d) Hicks, F. A.; Brookhart, M. Organometallics 2001, 20, 3217. (e)
Rachita, M. J.; Huff, R. L.; Bennett, J. L.; Brookhart, M. J. Polym. Sci.,
Part A: Polym. Chem. 2000, 38, 4627-4640.
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946. (b) Walther, D.; Dohler, T.; Theyssen, N.; Gorls, H. Eur. J. Inorg.
Chem. 2001, 2049-2060.
(10) Speiser, F.; Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005, 38,
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23, 2625. (c) Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R. Organo-
metallics 2004, 23, 2613. (d) Speiser, F.; Braunstein, P.; Saussine, L.; Welter,
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(11) (a) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schulz, R. P.;
Tkatchenko, I. J. Chem. Soc., Chem. Commun. 1994, 615. (b) Ecke,
A.; Keim, W.; Bonnet, M. C.; Tkatchenko, I.; Dahan, F. Organometallics
1995, 14, 5302.
(12) See for example: (a) Fong, S.-W. A.; Vittal, J. J.; Hor T. S. A.
Organometallics 2000, 19, 918. (b) Neo, Y. C.; Vittal, J. J.; Hor. T. S. A.
Dalton Trans. 2002, 337. (c) Xu, X.-L.; Fong, S. W. A.; Li, Z.-H.; Loh,
Z.-H. Zhao, F.; Vittal, J. J.; Henderson, W.; Khoo, S. B.; Hor, T. S. A.
Inorg. Chem. 2002, 41, 6838.
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1988, 1345. (b) Ohe, T.; Miyaura, N.; Suzuki, A. J. Org. Chem. 1993, 58,
2201. (c) Hughes, O. R.; Unruh, J. D. J. Mol. Catal. 1981, 12, 71.
(14) Gan, K.-S.; Hor, T. S. A. Ferrocenes-Homogeneous Catalysis,
Organic Synthesis, Materials Science; Togni, A., Hayashi, T., Eds.; VCH:
Weinheim, 1995; Chapter 1, p 3.
* To whom correspondence should be addressed. E-mail: andyhor@
nus.edu.sg.
† National University of Singapore.
‡ Institute of Chemical and Engineering Sciences.
(1) (a) Chauvin, Y.; Olivier, H. In Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH:
Weinheim, Germany, 1996; Vol. 1, pp 258-268. (b) Vogt, D. In Applied
Homogeneous Catalysis with Organometallic Compounds; Cornils, B.,
Herrmann, W. A., Eds.; VCH: Weinheim, Germany, 1996; Vol. 1, pp 245-
256. (c) Parshall, G. W.; Ittel, S. D. In Homogeneous Catalysis: The
Applications and Chemistry of Catalysis by Soluble Transition Metal
Complexes; Wiley: New York, 1992; pp 68-72.
(2) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. J. Orgamomet.
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Int. Ed. Engl. 1978, 17, 466. (b) Keim, W.; Hoffmann, B.; Lodewick, R.;
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Chem., Int. Ed. Engl. 1990, 29, 235. (d) Hirose, K.; Keim, W. J. Mol. Catal.
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2000, 431.
(4) (a) Ostoja Starzewski, K. A.; Born, L. Organometallics 1992, 11,
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In Transition Metals and Organometallics as Catalysts for Olefin Polym-
erization; Kaminsky, W., Sinn, H., Eds.; Springer: Berlin, 1987; p 349.
10.1021/om060607+ CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/30/2006

Stabilization of Nickel(0) by Hemilabile P,N-Ferrocene Ligands
Scheme 1
Organometallics, Vol. 25, No. 20, 2006 4879
Scheme 2
system of interest. A notable example is the recent use of an
iminophosphine, [η-C5H4CHdN(C6H5)]Fe[η-C5H4P(t-Bu)2], to
promote Suzuki coupling15 and ethylene oligomerization,16 the
latter of which is catalyzed by Ni(I). These results, coupled with
the landmark findings of Wilke et al. that Ni(0) complexes, such
as Ni(COD)2, could catalyze olefin oligomerization,17 encour-
aged us to explore the complementary use of new Ni(0) with
hemilabile P,N-ferrocene ligands to promote ethylene oligo-
merization. The catalytic chemistry of zerovalent organonickel
complexes18 is poorly understood compared to that of Ni(II).
C-N stretching frequency does not conclusively support
π-imine complexation. There is also no spectroscopic evidence
to propose imine coordination in 4b. Complex 4a is related to
the established Ni(CO)2(η2-R2PAPR2)21 except that the former
carries a heterofunctionality of iminophosphine.
Surprisingly, a similar reaction of 1 with Ni(COD)2 and
diphenylacetylene does not give the expected (PN)Ni0(η2-PhCt
CPh). Instead, the known dinuclear [(COD)Ni0]2(µ2,η2-PhCt
CPh)22 was detected after product crystallization from the
reaction mixture. This may be attributed to the weak binding
ability and steric hindrance of 1. This problem can be solved
by changing to 2 as a supporting ligand. Under argon and excess
diphenylacetylene, a new Ni(0) alkyne complex, [C5H4CHd
NC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2]Ni0(η2-PhCtCPh) (5), can
be isolated. Spectroscopic evidence points to a chelating
iminophosphine (Scheme 2).
All the products were isolated and spectroscopically charac-
terized. All products in solid form are stable in air for a few
hours except 5, which is extremely air- and moisture-sensitive.
It decomposes easily in NMR solution in the presence of trace
O2 or H2O, giving unknown paramagnetic species. Satisfactory
elemental analytical and mass spectroscopic data were hence
not obtainable. The solutions of 3 and 4 also readily decompose
upon extended (>30 min) exposure to air. Under argon, all of
them can be kept for a prolonged period (weeks).
Results and Discussion
We focus on the design of hemilabile ligands on Ni(0) that
are stabilized by π-acids such as carbonyl (CO) and isocyanide
(RNC). Although RNC is known to be a better σ-donor but
weaker π-acceptor than CO,19,20 their relative effects on the
efficacy of Ni(0) in promoting ethylene oligomerization are less
clear. Our first target, therefore, was to synthesize a range of
related Ni(0) complexes for direct comparison. Ferrocendiyl
iminophosphines are our choice ligands, as they are coordina-
tively and electronically adaptive. Their inherent hemilability
would give extra structural flexibility to the associated catalytic
metal center. Two representative iminophosphines of different
coordinative abilities are chosen as models, viz., [C5H4CHd
N(C6F5)]Fe[η-C5H4PPh2] (1) and C5H4CHdNC(H)(CH3)-
(C6H5)]Fe[η-C5H4PCy2] (2). Ni(COD)2 reacts with 1 and a
3-fold excess of t-BuNC under argon to give a Ni(0) tris-
isocyanide complex, [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0-
(CNt-Bu)3 (3). Its structure, with a pendant imine, has been
described.16 Under atmospheric CO, a mixture of Ni(COD)2 and
a molar equivalence of 1 gives two Ni(0) dicarbonyl complexes,
[C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0(CO)2 (4a) and {[C5H4-
CHdN(C6F5)]Fe[η-C5H4PPh2]}2Ni0(CO)2 (4b) (Scheme 1). The
IR and mass spectral data of 4a suggest that it is mononuclear
with bidentate iminophosphine and terminal carbonyls. The
Structures. The solution data of 4b point to a mononuclear
Ni(0) dicarbonyl complex with two dangling imine moieties. It
thus belongs to the general class of Ni0(CO)2(PR3)2,23 but, to
our knowledge, there is no structural precedence of the
(15) Weng, Z.; Teo, S.; Koh, L. L.; Hor, T. S. A. Organometallics 2004,
23, 4342.
(16) Weng, Z.; Teo, S.; Koh, L. L.; Hor, T. S. A. Angew. Chem., Int.
Ed. 2005, 44, 7560.
(17) Wilke, G.; Bogdanovic, B.; Hardt, P.; Heimbach, P.; Keim, W.;
Kro¨ner, M.; Oberkirch, W.; Tanaka, K.; Steinbru¨cke, E.; Walter, D.;
Zimmermann, H. Angew. Chem., Int. Ed. 1966, 5, 151.
(18) (a) Munshieva, M. K. Azerb. Khim. Zh. 1999, 104; 2003, 171. (b)
Barnett, K. W. U.S. Patent 4628139 A 19861209, 1986.
(19) Ugi, I., Ed. Isonitrile Chemistry; Academic Press: New York, 1971.
(20) (a) Tanabiki, M.; Tsuchiya, K.; Kumanomido, Y.; Matsubara, K.;
Motoyama, Y.; Nagashima, H. Organometallics 2004, 23, 3976. (b) Veya,
P.; Floriani, C. Organometallics 1993, 12, 4899. (c) Otsuka, S.; Nakamura,
A.; Yoshida, T.; Naruto, M.; Ataka, K. J. Am. Chem. Soc. 1973, 95, 3180.
(21) (a). Van Hecke, G. R.; Horrocks, W. D., Jr. Inorg. Chem. 1966, 5,
1960. (b) Kawata, Y.; Tanaka, T. Chem. Lett. 1974, 7, 831.
(22) Day, V. W.; Abdel-Meguid, S. S.; Dabestani, S.; Thomas, M. G.;
Pretzer, W. R.; Muetterties, E. L. J. Am. Chem. Soc. 1976, 98, 8289.
(23) See for examples: (a) Kru¨ger, C.; Tsay, Y.-H. Cryst. Struct.
Commun. 1974, 3, 455. (b) Del Pra, A.; Zanotti, G.; Pandolfo, L.; Segala,
P. Cryst. Struct. Commun. 1981, 10, 7. (c) Meichel, E.; Stein, T. Kralik, J.;
Lang, R. H. J. Organomet. Chem. 2002, 649, 191. (d) Lesueur, W.; Solari,
E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg. Chem. 1997, 36, 3354.

4880 Organometallics, Vol. 25, No. 20, 2006
Weng et al.
Figure 1. Molecular structure of complex 4b (H atoms are
omitted). Thermal ellipsoids are drawn at the 40% probability level.
Table 1. Selected Bond Lengths (Å) and Angles (deg) of 4b
Bond Lengths
Ni(1)-C(1)
Ni(1)-P(1)
N(1)-C(3)
N(2)-C(10)
C(1)-O(1)
1.777(5)
2.2096(11)
1.277(5)
1.283(6)
1.133(5)
Ni(1)-C(2)
Ni(1)-P(2)
N(1)-C(4)
N(2)-C(11)
C(2)-O(2)
1.764(5)
2.2145(11)
1.410(5)
1.395(6)
1.145(5)
Figure 2. Molecular structure of complex 5 (H atoms are omitted).
Thermal ellipsoids are drawn at the 40% probability level.
Bond Angles
C(1)-Ni(1)-C(2)
C(1)-Ni(1)-P(1)
C(1)-Ni(1)-P(2)
C(3)-N(1)-C(4)
116.9(2)
C(2)-Ni(1)-P(1)
C(2)-Ni(1)-P(2)
P(1)-Ni(1)-P(2)
C(10)-N(2)-C(11)
104.80(15)
106.24(14)
112.52(4)
118.3(4)
Table 2. Selected Bond Lengths (Å) and Angles (deg) of 5
109.69(14)
106.81(14)
119.0(4)
Bond Lengths
Ni(1)-C(20)
Ni(1)-N(1)
N(1)-C(1)
1.900(7)
1.945(6)
1.287(10)
1.480(13)
Ni(1)-C(21)
Ni(1)-P(1)
N(1)-C(2)
1.902(7)
2.202(2)
1.464(17)
1.275(9)
analogous Ni0(CO)2(η1-R2PAPR2)2 or other heterodifunctional
analogues such as Ni0(CO)2(η1-R2PAXRn) with dangling donor
units. It is rare to have two donor pendants on a single metal
since they tend to collapse as a chelate or dimerize as a bridge.
We hence had to conduct a single-crystal X-ray crystallographic
analysis to confirm if this unusual structure can be sustained in
the solid state (Figure 1, Table 1). It indeed shows a tetrahedral
Ni(0) with two extended side-arms represented by the imine-
phosphine ferrocene ligands monocoordinating through its P site.
The variable torsional twist of the C5 rings allows the dangling
imine N atom to move to an anti position. The two Ni-P bonds
are comparable (2.2096(11) 2.2145(11) Å) and similar to those
in 3 (2.2001(10) Å) and (PPh3)2Ni(CO)2 (2.221 Å).23a The two
Ni-C bonds (1.777(5) and 1.764(5) Å) are comparable to that
of (PPh3)2Ni(CO)2 (1.763 Å)23a but significantly shorter, and
presumably stronger, than those found in the isonitrile complex
3 (1.821(4), 1.842(4), and 1.843(4) Å). This is consistent with
the expected stronger π-acidity of CO, and hence stronger M-C,
compared to RNC.
We have not detected the tricarbonyl derivative of 4, viz.,
[C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0(CO)3, which would be
the carbonyl analogue of 3. In this preparation, 4a is the major
product, whereas 4b is a minor byproduct. The yield of 4b can
be improved by the use of excess 1, but the formation of 4a is
inevitable. This is understood in terms of the more favorable
entropy effect of a chelate, despite a much weaker imino ligating
ability. In solution upon addition of excess 1, complex 4a can
convert (not quantitatively) to 4b. The co-formation of 4a and
4b demonstrates the hemilability of 1 and its ability to stabilize
an exposed metal through additional coordination. This would
lend support to an active catalyst that is susceptible to
decomposition through ligand loss.
N(1)-C(2A)
C(20)-C(21)
Bond Angles
C(20)-Ni(1)-C(21)
C(21)-Ni(1)-N(1)
C(21)-Ni(1)-P(1)
C(1)-N(1)-C(2)
39.2(3) C(20)-Ni(1)-N(1)
141.3(3) C(20)-Ni(1)-P(1)
113.1(2) N(1)-Ni(1)-P(1)
113.6(9) C(21)-C(20)-Ni(1)
144.1(6) C(20)-C(21)-Ni(1)
103.7(3)
149.4(2)
105.51(19)
70.5(5)
C(22)-C(20)-Ni(1)
C(28)-C(21)-Ni(1)
70.3(5)
150.4(6) C(21)-C(20)-C(22) 145.3(8)
C(20)-C(21)-C(28) 138.9(7)
Ni-C bonds (1.900(7) and 1.902(7) Å), which are slightly
longer, and presumably weaker, than other donor-stabilized
diphenylacetylene complexes, e.g., (dippe)Ni(η2-PhCtCPh) (av
1.879(2) Å),24b (t-BuNC)2Ni(η2-PhCtCPh) (av 1.884(9) Å),25a
and (2,2-bipyridyl)Ni(η2-PhCtCPh) (av 1.846(2) Å).25b The
weaker CtC bond (1.275(9) Å) and bent CtC-C angles
(145.3(8)° and 138.9(7)°), compared to free diphenylacetylene
(CtC 1.198(4) Å),26 are in agreement with the expected π*
back-donation27 and consistent with other L2Ni(η2-PhCtCPh)
complexes.24,25 Further comparisons in detail would not be
justified since the crystallographic data are of marginal quality.
Catalytic Oligomerization of Ethylene. Some preliminary
results on catalytic oligomerization of ethylene using complexes
3, 4a, 4b, and 5 are summarized in Table 3. Using MAO as the
cocatalyst with Al/Ni ) 1000, the ethylene oligomerization
activity (TOF) decreases in the order 5 (alkyne) > 3 (isocyanide)
. 4b (carbonyl, excess iminophosphine) > 4a (carbonyl,
limiting iminophosphine). This order follows the decreasing
Ni-C bond lengths in these complexes (alkyne > isocyanide
> carbonyl). The weaker metal-ligand contacts could lead to
(24) (a) Mu¨ller, C.; Lachicotte, R. J.; Jones, W. D. Organometallics 2002,
21, 1975. (b) Edelbach, B. L.; Lachicotte, R. J.; Jones, W. D. Organome-
tallics 1999, 18, 4040.
(25) (a) Dickson, R. S.; Ibers, J. A. J. Organomet. Chem. 1972, 36, 191.
(b) Eisch, J. J.; Ma, X.; Han, K. I. Eur. J. Inorg. Chem. 2001, 77. (c)
Po¨rschke, K. R.; Mynott, R.; Angermund, K.; Kru¨ger, C. Z. Naturforsch.
1995, 40b, 199. (d) Goddard, R.; Apotecher, B.; Hoberg, H. Acta
Crystallogr. 1987, C43, 1290.
(26) Mavriris, A.; Moustakali-Mavridis, I. Acta Crystallogr. 1977, B33,
3612.
(27) See for examples: (a) Rosenthal, U.; Nauck, C.; Amdt, P.; Pulst,
S.; Baumann, W.; Burlakov, V. V.; Gorls, H. J. Organomet. Chem. 1994,
484, 81. (b) Rosenthal, U.; Schulz, W. J. Organomet. Chem. 1987, 321,
103. (c) Bartik, T.; Happ, B.; Iglewsky, M.; Bandmann, H.; Boese, R.;
Heimbach, P.; Hoffmann, T.; Wenschuh, E. Organometallics 1992, 11, 1235.
X-ray single-crystal structural analysis of 5 revealed an
unusual combination of a chelating iminophosphine with a side-
on alkyne attachment at nickel. The two sterically demanding
and contrasting ligands are fused at a distorted planar (mean
plane deviation 0.1003 Å) Ni(0) center (Figure 2, Table 2). The
Ni-P bond (2.202(2) Å) is comparable to those in 3 and 4b,
but longer than in the Ni(I) complex [η-C5H4CHdN(C6H5)]-
Fe[η-C5H4P(t-Bu)2-CN,P]NiICl (2.169(2) Å)16 and Ni(0) com-
plex [(i-Pr)2PCH2CH2NMe2)]Ni(η2-PhCtCPh) (2.1565(10) Å).24
The alkyne ligand is symmetrically bound with two identical

Stabilization of Nickel(0) by Hemilabile P,N-Ferrocene Ligands
Organometallics, Vol. 25, No. 20, 2006 4881
Table 3. Activities toward Oligomerization of Ethylenea,b
and used as received. [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2] and
[C5H4CHdNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2] were synthesized
by a literature procedure.29
oligomerd
time
C4/∑C C6/∑C R-olefin
Synthesis of [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0(CNt-Bu)3
(3). To a red solution of [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2] (41
mg, 0.073 mmol) in n-hexane (5 mL) was added Ni(COD)2 (20
mg, 0.073 mmol), and the mixture was stirred at rt for 20 min to
give an orange solution. CNt-Bu (18 mg, 0.217 mmol) in hexane
(1 mL) was added and the reaction mixture further stirred at rt for
2 h. The resultant red-orange solution was filtered through a layer
of Celite. The solvent was removed to afford a red-orange solid of
3 (52 mg, 0.060 mmol, 82% yield). IR [KBr, cm-1]: νCtN 2105
entry cat. activator Al/Ni (h)
TOFc
%
%
% (C4)
1e
2e
3
4
5
3
3
MAO
EtAlCl2
1000
146
1000
1000
1000
3
3
3
3
1
1
75 000
91 600
476
2000 100
88 000
64 000
87.1
69.9
80.7
12.9
30.1
19.3
0
17.8
30.2
16.5
45.9
52.5
59.2
76.6
53.3
4a MAO
4b MAO
5
5
MAO
EtAlCl2 1000
82.2
69.7
6
a Optimized by Endeavor catalyst screening system. b Conditions: 0.25
µmol of catalyst, 4 mL of toluene, 30 °C, 300 psi of ethylene. c TOF )
1
mol of ethylene consumed/mol of Ni‚h-1 d mol %. e Given in ref 16.
.
(w), 2027 (w). νCN 1623 (m), 1516 (m, sh), 1504 (s). H NMR
(C6D6): δ 7.77 (s, 1 H, CHdN), 7.89 (t, J ) 7.2 Hz, 4 H, phenyls),
7.18-7.03 (m, 6 H, phenyls), 4.95 (t, J ) 1.6 Hz, 2 H, Cp),
4.78 (q, J ) 1.6 Hz, 2 H, Cp), 4.65 (t, J ) 1.62 Hz, 2 H, Cp), 4.44
(t, J ) 1.6 Hz, 2 H, Cp), 1.07 (s, 27 H, CNt-Bu). 13C NMR
(C6D6): δ 171.44 (NC(CH3)3), 168.48 (CHdN), 144.45 (Ph),
144.15 (Ph), 134.45 (Ph), 134.28 (Ph), 128.10 (Ph), 128.00 (Ph),
80.43 (Cp), 76.90 (Cp), 76.73 (Cp), 75.15 (Cp), 73.20 (d, Cp), 71.90
(Cp), 31.54 (NC(CH3)3). 31P NMR (C6D6): δ 20.56. Anal. Calcd
for C44H46F5N4PFeNi: C 60.65, H 5.32, N 6.43. Found: C 60.85,
H 5.07, N 6.55.
higher ligand lability and make the metal more receptive to the
incoming ethylene and hence higher catalytic activity. We are
not aware of any prior report on Ni(0) alkyne molecular
complexes in ethylene oligomerization. It is intriguing that 5 is
generally superior among the complexes that we examined. Its
combinative chelating protection and alkyne stabilization could
suppress catalyst decomposition or conversion to its inactive
dimeric form. The 1-butene selectivity for 5 is much higher
than that of 3. EtAlCl2 is a better activator than MAO for
complex 3 (entry 2) but poorer for 5 (entry 6). Nevertheless,
both 3 and 5 perform substantially better than other heteroge-
neous Ni(0) catalysts,18 such as Ni0(COD)2 on zeolite [TOF
(ethylene) ca. <4000 h-1].18b They (3 and 5) are also able to
maintain their activities within a reasonable lifetime (a few
hours), which is an important consideration in catalyst design.
Synthesis of [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]Ni0(CO)2 (4a)
and {[C5H4CHdN(C6F5)]Fe[η-C5H4PPh2]}2Ni0(CO)2 (4b). To a
red solution of [C5H4CHdN(C6F5)]Fe[η-C5H4PPh2] (44 mg, 0.078
mmol) in n-hexane (5 mL) was added Ni(COD)2 (21.5 mg, 0.078
mmol), and the mixture was stirred at rt for 10 min to give an
orange solution. An atmosphere of carbon monoxide was introduced
to the reaction vessel, and the reaction mixture was further stirred
at rt for 5 h. The resultant red-orange solution was filtered through
a layer of Celite. The filtrate was evaporated under vacuum, leaving
a red-orange solid. This solid was redissolved in hexane and cooled
at -30 °C for 2 days to precipitate 4b as a dark red powder (ca. 5
mg, 0.004 mmol, 5% yield). The mother liquid was dried to yield
4a as a red-orange powder (ca. 32 mg, 0.047 mmol, 61% yield).
4a: IR [KBr, cm-1]: νCO 2067 (s), 1989 s. νCN 1623 (m), 1515
(m, sh), 1504 (s). 1H NMR (C6D6): δ 7.23 (s, 1 H, CHdN), 7.39-
7.32 (m, 4 H, phenyls), 6.62-6.90 (m, 6 H, phenyls), 4.53 (t, J )
2 Hz, 2 H, Cp), 4.25 (t, J ) 1.2 Hz, 2 H, Cp), 4.22 (t, J ) 2 Hz,
2 H, Cp), 4.19 (t, J ) 1.6 Hz, 2 H, Cp). 13C NMR (C6D6): δ 196.3
(CO), 169.1 (CHdN), 132.4, 132.2, 129.2, 128.4, 128.3, 128.2,
128.1, 127.7, 127.4 (Ph), 75.2, 75.1, 73.4, 73.3, 73.2, 70.5 (Cp).
31P NMR (C6D6): δ 22.92. MS (FAB+): m/z 650 [M - CO]+,
621 [M - 2CO]+. Anal. Calcd for C31H19F5NO2PFeNi: C 54.92,
H 2.82, N 2.07. Found: C 54.67, H 2.81, N 2.65. 4b: IR [KBr,
cm-1]: νCO 1997 (s), 1939 (s), νCN 1617 (s), 1516 (s, sh), 1504
(s). 1H NMR (C6D6): δ 7.38-7.31 (m, 5 H, CHdN and phenyls),
6.91-6.88 (m, 6 H, phenyls), 4.57 (t, J ) 1.6 Hz, 2 H, Cp), 4.22
(t, J ) 2 Hz, 4 H, Cp), 4.20 (t, J ) 2 Hz, 2 H, Cp). 13C NMR
(C6D6): δ 200.5 (CO), 169.5 (CHdN), 132.8, 132.7, 132.4, 132.2,
131.3, 131.2, 129.7, 129.3, 128.4, 128.1, 128.2 (Ph), 81.2 (d), 80.8
(d), 79.3, 75.3, 75.1, 73.7, 73.4, 72.7, 72.6, 71.1, 70.6 (Cp). 31P
NMR (C6D6): δ 23.99. MS (FAB+): m/z 1185 [M - 2CO]+, 621
[((C5H4CHdN(C6F5))Fe(η-C5H4PPh2))Ni]+. Anal. Calcd for
C60H38F10N2O2P2Fe2Ni: C 58.06, H 3.08, N 2.26. Found: C 58.33,
H 3.10, N 2.09.
Conclusions
We have demonstrated herein that appropriately stabilized
Ni(0) complexes can be prepared, isolated, structurally char-
acterized, and activated for ethylene oligomerization. The use
of Ni(II)28 complexes is much more popular, and they remain
probably the catalyst of choice because they are generally much
more stable and easier to prepare. However, the results described
herein suggested that suitably designed Ni(0) can be prepared
and used in one-pot reactions, as it may have an advantage in
high activity and oligomeric selectivity. The combinative use
of an adaptive hemilabile ligand and a supporting π-accepting
ligand would meet these requirements. The use of an alkyne-
stabilized catalyst can be viewed as a mimic for olefin entry to
Ni-promoted olefin oligomerization. Our next target is to tune
the hemilability by adjusting the substituents at the phosphine
and imine sites. Such variation would provide a handle to
balance the delicate interrelationship between coordinative
ability, complex stability, and catalytic activity.
Experimental Section
General Procedures. All reactions were carried out using
conventional Schlenk techniques under an inert atmosphere of
nitrogen or argon with an M. Braun Labmaster 130 inert gas system.
NMR spectra were measured on Bruker ACF300 300 MHz FT
NMR spectrometers (1H at 300.14 MHz, 13C at 75.43 MHz, and
31P at 121.49 MHz). Mass spectra were obtained on a Finnigan
Mat 95XL-T spectrometer. Elemental analyses were performed by
the microanalytical laboratory in-house. Ni(COD)2 and pentafluo-
roaniline were used as supplied by Fluka Chemical Co. and
Lancaster, respectively. MAO (methylaluminoxane) (10 wt % in
toluene solution), EtAlCl2 (25 wt % in toluene solution), diphen-
ylacetylene, and tert-butyl isocyanide were purchased from Aldrich
Synthesis of [C5H4CHdNC(H)(CH3)(C6H5)]Fe[η-C5H4PCy2]-
Ni0(η2-PhCtCPh) (5). To a red solution of [C5H4CHdNC(H)-
(CH3)(C6H5)]Fe[η-C5H4PCy2] (34 mg, 0.06 mmol) in n-hexane (5
mL) was added Ni(COD)2 (17 mg, 0.06 mmol), and the mixture
was stirred at rt for 20 min to give an orange solution. Diphenyl-
acetylene in hexane (1 mL) was added, and the reaction mixture
was further stirred at rt for 2 h. The resultant red-orange solution
was filtered through a layer of Celite. The solvent was removed to
afford a red-orange solid of 5 (ca. 18 mg, 0.026 mmol, 43% yield).
(28) de Souza, R. F.; Bernardo-Gusma˜o, K.; Cunha, G. A.; Loup, C.;
Leca, F.; Re´au, R. J. Catal. 2004, 226, 235.
(29) Wright, M. E. Organometallics 1990, 9, 853.

4882 Organometallics, Vol. 25, No. 20, 2006
Weng et al.
1H NMR (C6D5CD3): δ 8.55, 8.15, 7.56-7.00 (m, phenyls), 4.23-
4.20 (m, Cp), 4.18 (s, Cp), 4.14 (s, Cp), 4.06 (s, Cp), 3.93-3.90
(m), 3.61, 3.59, 1.53 (d, Cy), 0.91 (t, Cy). 13C NMR (C6D6): δ
161.1, 160.1, 139.9 (t, J ) 5.0 Hz, tC-Ph), 134.9 (t, J ) 4.4 Hz,
tC-Ph), 134.4, 133.4, 128.8, 128.5, 128.3, 128.0, 127.7, 127.4,
124.4, 124.3, 124.0 (Ph), 79.4-75.9 (m), 71.4 (d), 71.0 (d), 70.8
(d), 70.4 (d), 70.2 (d), 69.4, 69.1 (d), 67.5 (d) (Cp), 39.5 (d), 38.2
(d), 36.0 (d), 35.8 (d), 31.5, 30.1 (d), 29.7 (d), 29.3, 29.0-22.6
(m) (Cy). 31P NMR (C6D5CD3): δ 26.13, 24.87. IR [KBr, cm-1]:
Table 4. Selected Crystal Data, Data Collection, and
Refinement Parameters of Compounds 4b and 5
4b‚C6H14
5‚C6H14
formula
C66H52F10Fe2N2NiO2P2
1327.45
C51H64FeNNiP
836.56
fw
cryst size/mm
temperature/K
crystal syst
space group
a/Å
0.30 × 0.20 × 0.12
0.30 × 0.12 × 0.08
223(2)
295(2)
triclinic
P1h
triclinic
P1h
11.0651(8)
15.2100(11)
17.6504(12)
86.609(2)
80.427(2)
83.410(2)
2907.4(4)
2
9.7577(10)
12.6044(14)
18.6464(19)
94.371(3)
94.356(3)
96.860(3)
2261.9(4)
2
νCN 1633 (s), 1600 (w). Anal. Calcd for C45H50NPFeNi: C 72.03,
b/Å
c/Å
H 6.72, N 1.87. Found: C 69.95, H 7.04, N 1.73. This compound
is highly air- and moisture-sensitive, resulting in unsatisfactory
elemental analytical data.
R/deg
â/deg
γ/deg
Oligomerization of Ethylene. The catalytic activities of com-
plexes 3, 4a, 4b, and 5 were screened by Endeavor parallel pressure
reactor, following recommended procedures. (1) Prepare a stock
solution of catalyst (0.001 M, 5 mL). (2) Prepare 8 glass liners
with 4 mL of toluene as solvent. (3) Inject the catalyst solution
(250 µL, 0.25 µmol) and activator solution. (4) Secure stirrer top
with impellers to reactor block. (5) Program reaction temperature,
pressure, volume 4 mL, run time, and reaction sequence by using
Endeavor Advanced software. (6) Start Endeavor software on PC.
(7) Click “Start” on Endeavor software on PC. (8) At the end of
each test, the reaction mixture was cooled to 0 °C and terminated
by addition of 1 mL of H2O. The upper-layer solution was filtered
through a layer of Celite and analyzed by GC. The individual
products of oligomerization were identified by GC-MS.
V/Å3
Z
Dc/g cm-3
radiation used
µ/mm-1
1.516
Mo KR
0.948
1.228
Mo KR
0.806
θ range/deg
no. of unique
reflns measd
max., min.
transmn
1.75 to 27.50
38 590
1.63 to 25.00
13 226
0.8947 and 0.7641
0.9383 and 0.7940
final R indices
[I > 2σ(I)]a,b
R indices
(all data)
goodness-of-fit
on F2 c
R1 ) 0.0652,
wR2 ) 0.1586
R1 ) 0.0978,
wR2 ) 0.1741
1.032
R1 ) 0.0999,
wR2 ) 0.1957
R1 ) 0.1436,
wR2 ) 0.2125
1.160
large diff peak
1.081 and -0.524
0.455 and -0.450
Crystal Structure Analyses. Diffraction-quality single crystals
were obtained at -30 °C as follows: 4b as dark red prisms after
4 days from solution in toluene layered with hexane; 5 as dark red
polyhedra after 5 days from solution in hexane. Crystals were
mounted on quartz fibers and X-ray data collected on a Bruker
AXS APEX diffractometer, equipped with a CCD detector, using
Mo KR radiation (λ 0.71073 Å). The data were corrected for
Lorentz and polarization effect with the SMART suite of programs30
and for absorption effects with SADABS.31 Structure solution and
refinement were carried out with the SHELXTL suite of programs.32
The structures were solved by direct methods to locate the heavy
atoms, followed by difference maps for the light non-hydrogen
atoms. The asymmetric unit of 5 contains one titled molecule and
one disordered hexane solvent. The hexane is disordered into two
positions at 50:50 occupancies. In the titled molecule, the C6H5-
CHCH3 group is also disordered into two positions at 50:50
and hole, e Å-3
2 1/2
a R ) (∑|Fo| - |Fc|)∑|Fo|. b wR2 ) [(∑w|Fo| - |Fc|)2/∑w|Fo| ]
.
c GoF
) [(∑w|Fo| - |Fc|)2/(Nobs - Nparam)]1/2
.
occupancies. The data collection and processing parameters are
given in Table 4.
Acknowledgment. We are grateful to the Agency for
Science, Technology & Research (Singapore), the Institute of
Chemical and Engineering Sciences (Singapore) (Grant No. 012-
101-0035), and the National University of Singapore for support.
We are indebted to Dr. L. L. Koh and Ms. G. K. Tan for
assistance in the crystallographic analysis.
Supporting Information Available: For structures of 4b and
5: complete listing of bond lengths and angles, ORTEP diagrams,
tables of atomic coordinates and equivalent isotropic displacement
parameters, anisotropic displacement parameters, hydrogen coor-
dinates, and isotropic displacement parameters. This material is
available free of charge via the Internet at http://pubs.acs.org.
(30) SMART version 5.1; Bruker Analytical X-ray Systems: Madison,
WI, 2000.
(31) Sheldrick, G. M. SADABS, a program for Empirical Absorption
Correction; Go¨ttingen: Germany, 2000.
(32) SHELXTL version 5.03; Bruker Analytical X-ray Systems: Madison,
WI, 1997.
OM060607+