Rigid N-phosphino guanidine P,N ligands and their use in nickel-catalyzed ethylene oligomerization

Article abstract of DOI:10.1021/om8005933

The rigid bidentate P,N-ligands 3a-d (phosphino substituent: a, Ph; b, mes; c, N-i-Pr₂; d, NPh₂), each with a 7-phosphino-1,5,7- triazabicyclo[4.4.0]dec-5-ene skeleton, are readily prepared in high yields and have been used in the preparation of the nickel complexes [NiBr ₂(3a-d)] (4a-d). The derivatives 4a,d are both diamagnetic, while their counterparts 4b,c are paramagnetic with values of μ_eff(300 K) of 2.05 and 2.10 μ_B, respectively. The structure of 4a has been determined in the solid state by X-ray diffraction, which confirmed the κ²P,N coordination of 3a and the essentially square-planar geometry about Ni. In combination with EtAlCl₂ the Ni(II) complexes of 4b-d are active ethylene oligomerization initiators (C₂H ₄, 1 bar; Ni:Al = 1:14; toluene), affording varying mixtures of butenes, hexenes, and octenes (trace), depending on the nature of the P-donor, but with a reasonable selectivity toward C₄ with complex 4c. In contrast, under identical reaction conditions complex 4a gives rise to products resulting from a sequence of ethylene oligomerization and subsequent Friedel-Crafts alkylation of the toluene solvent. Notably, no activity toward ethylene (1 bar) was observed for 4/MAO (Ni:Al = 1:15 or 1:500).

Full text of DOI:10.1021/om8005933

5082
Organometallics 2008, 27, 5082–5087
Rigid N-Phosphino Guanidine P,N Ligands and Their Use in
Nickel-Catalyzed Ethylene Oligomerization
Philip W. Dyer,*,†,‡ John Fawcett,‡ and Martin J. Hanton‡
Department of Chemistry, Durham UniVersity, South Road, Durham DH1 3LE, U.K., and Department of
Chemistry, UniVersity of Leicester, UniVersity Road, Leicester LE1 7RH, U.K.
ReceiVed June 26, 2008
The rigid bidentate P,N-ligands 3a-d (phosphino substituent: a, Ph; b, mes; c, N-i-Pr2; d, NPh2), each
with a 7-phosphino-1,5,7-triazabicyclo[4.4.0]dec-5-ene skeleton, are readily prepared in high yields and
have been used in the preparation of the nickel complexes [NiBr2(3a-d)] (4a-d). The derivatives 4a,d
are both diamagnetic, while their counterparts 4b,c are paramagnetic with values of µeff(300 K) of 2.05
and 2.10 µB, respectively. The structure of 4a has been determined in the solid state by X-ray diffraction,
which confirmed the κ2P,N coordination of 3a and the essentially square-planar geometry about Ni. In
combination with EtAlCl2 the Ni(II) complexes of 4b-d are active ethylene oligomerization initiators
(C2H4, 1 bar; Ni:Al ) 1:14; toluene), affording varying mixtures of butenes, hexenes, and octenes (trace),
depending on the nature of the P-donor, but with a reasonable selectivity toward C4 with complex 4c. In
contrast, under identical reaction conditions complex 4a gives rise to products resulting from a sequence
of ethylene oligomerization and subsequent Friedel-Crafts alkylation of the toluene solvent. Notably,
no activity toward ethylene (1 bar) was observed for 4/MAO (Ni:Al ) 1:15 or 1:500).
bination of neutral chelating P,N-ligands with Ni(II) has been
shown to be very effective for the catalytic oligomerization of
ethylene, exploiting the electronic and steric asymmetry these
ligands impose to control reactivity and selectivity.14-21
Despite the potential structural diversity of chelating P,N-
metal scaffolds, the majority of structure/property correlation
investigations for ethylene polymerization have focused on the
influence of the N-donor moiety, with comparatively few studies
having probed the role of the P-donor component in any
systematic fashion.16,17 Here we report the “one-pot” synthesis
of a family of readily prepared P,N ligands that exploit the ease
of P-N bond formation to facilitate introduction of a range of
variously substituted R2P fragments onto a bicyclic guanidine
skeleton.22 This approach gives metal scaffolds that are rigid
and predisposed to afford κ2P,N binding with an encumbered
P donor and a “tied-back” imine donor, reminiscent of the steric
demands imposed by the [P,O] chelates employed by Keim.
Introduction
Since the pioneering work of Keim and co-workers,1 nick-
el(II)-based initiators have been instrumental in the development
of alkene oligomerization processes. This is an area that has
been driven by the industrial significance of the resulting
synthetically versatile short-chain alkenes (C4-C10), used as
comonomers and as precursors to plasticizers, detergents, etc.2
Over the past decade there has been a gradual move away from
the use of monoanionic heteroditopic chelate ligands (e.g.,
[P,O],1,3-6 [N,O],7 and [N,S]8) that were used traditionally,
following the discovery that neutral bidentate scaffolds afford
Ni(II) initiators that efficiently oligomerize ethylene at consider-
ably lower temperatures and pressures.9-13 Notably, the com-
* To whom correspondence should be addressed. E-mail: p.w.dyer@
durham.ac.uk. Fax: +44(0)191 384 4737. Tel: +44(0)191 334 2150.
† Durham University.
‡ University of Leicester.
Results and Discussion
(1) Keim, W.; Kowaldt, F. H.; Goddard, R.; Kru¨ger, C. Angew. Chem.,
Int. Ed. Engl. 1978, 17, 466–467.
(2) Vogt, D. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. A., Eds.; Wiley-VCH: Weinheim,
Germany, 2002; Vol. 1, p 240.
The desired N-phosphino guanidine P,N ligands 3a-d were
prepared in a two-step process from commercially available
(3) Braunstein, P.; Chauvin, Y.; Mercier, S.; Saussine, L.; De Cian, A.;
Fischer, J. J. Chem. Soc., Chem. Commun. 1994, 2203–2204.
(4) Matt, D.; Huhn, M.; Fischer, J.; De Cian, A.; Kla¨ui, W.; Tkatchenko,
I.; Bonnet, M. C. J. Chem. Soc., Dalton Trans. 1993, 1173–1178.
(5) Kermagoret, A.; Braunstein, P. Dalton Trans. 2008, 822–831.
(6) Kuhn, P.; Se´meril, D.; Matt, D.; Chetcuti, M. J.; Lutz, P. Dalton
Trans. 2007, 515–528.
(7) Desjardins, S. Y.; Cavell, K. J.; Jin, H.; Skelton, B. W.; White, A. H.
J. Organomet. Chem. 1996, 515, 233–243.
(8) Behr, A.; Falbe, V.; Freudenberg, U.; Keim, W. Isr. J. Chem. 1986,
27, 277–279.
(13) Malinoski, J. M.; Brookhart, M. Organometallics 2003, 22, 5324–
5335.
(14) Daugulis, O.; Brookhart, M. Organometallics 2002, 21, 5926–5934.
(15) Speiser, F.; Braunstein, P.; Saussine, L. Dalton Trans. 2004, 1539–
1545.
(16) Speiser, F.; Braunstein, P.; Saussine, L. Acc. Chem. Res. 2005, 38,
784–793, and references therein.
(17) Braunstein, P. Chem. ReV. 2006, 106, 134–159.
(18) Chen, H.-P.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Organometallics
2003, 22, 4893–4899.
(9) Bonnet, M. C.; Dahan, F.; Ecke, A.; Keim, W.; Schulz, R. P.;
Tkatchenko, I. J. Chem. Soc., Chem. Commun. 1994, 615–616.
(10) Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.;
Redshaw, C.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; Elsegood,
M. R. J. Chem. Eur. J. 2000, 6, 2221–2231.
(11) Svejda, S. A.; Brookhart, M. Organometallics 1999, 18, 65–74.
(12) Laine, T. V.; Klinga, M.; Maaninen, A.; Aitola, E.; Leskela¨, M.
Acta Chem. Scand. 1999, 53, 968–973.
(19) de Souza, R. F.; Bernardo-Gusma˜o, K.; Cunha, G. A.; Loup, C.;
Leca, F.; Re´au, R. J. Catal. 2004, 226, 235–239.
(20) Anderson, C. E.; Batsanov, A. S.; Dyer, P. W.; Fawcett, J.; Howard,
J. A. K. Dalton Trans. 2006, 5362–5378.
(21) Buchard, A.; Auffrant, A.; Klemps, C.; Vu-Do, L.; Boubekeur, L.;
Le Goff, X. F.; Le Floch, P. Chem. Commun. 2007, 1502–1504.
(22) Dyer, P. W.; Fawcett, J.; Hanton, M. J.; Kemmitt, R. D. W.; Padda,
R.; Singh, N. Dalton Trans. 2003, 104–113.
10.1021/om8005933 CCC: $40.75
2008 American Chemical Society
Publication on Web 09/06/2008

Rigid N-Phosphino Guanidine P,N Ligands
Organometallics, Vol. 27, No. 19, 2008 5083
Scheme 1. Synthesis of N-Phosphino Guanidines 3
Scheme 2. Synthesis of Ni(II) N-Phosphino Guanidine
Complexes 4
Figure 1. Molecular structure of 4a · 1/2CD2Cl2 (showing 50%
thermal ellipsoids). The hydrogen atoms and solvent molecule are
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Ni(1)-P(1) ) 2.1054(8), Ni(1)-N(1) ) 1.912(2), Ni(1)-Br(1) )
2.3283(5), Ni(1)-Br(2) ) 2.3483(5), P(1)-N(3) ) 1.698(2),
C(1)-N(1) ) 1.322(4), C(1)-N(2) ) 1.338(4), C(1)-N(3) )
1.390(4); P(1)-Ni(1)-N(1) ) 85.32(8), P(1)-Ni(1)-Br(1) )
84.63(2), Br(1)-Ni(1)-Br(2) ) 92.225(16), N(1)-Ni-Br(2)
) 97.87(8), P(1)-Ni(1)-Br(2) ) 175.66(3), N(1)-Ni(1)-Br(1)
) 169.89(8), N(1)-C(1)-N(2) ) 125.5(3), N(1)-C(1)-N(3) )
116.8(3), N(2)-C(1)-N(3) ) 117.7(3).
1,5,7-triazabicyclo[4.4.0]dec-5-ene (1) via the intermediate
lithium salt 2 and isolated in excellent yield as moderately air
stable crystalline solids (Scheme 1). Each of the ligands presents
a single resonance by 31P NMR spectroscopy, with chemical
shifts consistent with mono- and tris-aminophosphines for 3a,b
and 3c,d, respectively.22
the solid24,25 and solution states24,26 was undertaken. Complexes
4a,d are both diamagnetic, consistent with the square-planar
nickel geometry observed crystallographically for 4a. In contrast,
complexes 4b,c are paramagnetic, with magnetic moments
µeff(300 K) of 2.05 and 2.10 µB, respectively, in both solution
and the solid state. These values are lower than the predicted
spin-only magnetic moments for tetrahedral d8 species, but are
comparable to those measured for other P,N-chelated Ni(II)
complexes.27 Since the cryoscopically determined molecular
weight data for 4b,c are consistent with monometallic struc-
tures,28 the anomalously low magnetic moments are believed
to result from moderate distortions away from square planarity,
caused by geometric and steric constraints imposed by the rigid
scaffolds 3b,c.29
Despite their rather low solubility, 4a-d were all sufficiently
soluble in toluene at room temperature (1 × 10-3 M solutions)
to permit their screening for homogeneous ethylene oligomer-
ization activity. Toluene solutions of each of the nickel
complexes were treated with either MAO (15 or 500 equiv) or
EtAlCl2 (14 equiv) as activator, aged, and subsequently allowed
to contact ethylene.
The desired nickel(II) derivatives [NiBr2(3a-d)] (4a-d) were
prepared by reacting equimolar quantities of the appropriate
ligand with NiBr2(DME) (DME ) 1,2-dimethoxyethane) in
CH2Cl2 at reflux for 24 h (Scheme 2). During this time the
complexes 4a-d precipitated from the reaction medium and
were obtained as air-stable red-purple solids in excellent yields.
For each complex, satisfactory elemental analyses were obtained.
Using mass spectrometry (FAB), an [M - Br]+ ion was
observed in each case, with no evidence for higher molecular
weight species. All the complexes have rather low solubility in
common solvents and react with DMSO to form as yet
unidentified paramagnetic products.
The structure of 4a (CD2Cl2 solvate) was confirmed in the
solid state by an X-ray diffraction study (Figure 1). This revealed
an essentially square-planar geometry about nickel with only a
small (ca. 3°) pseudotetrahedral twist between the NiPN and
NiBr2 planes. Ligand 3a binds in a κ2P,N fashion as expected,
with a moderately acute P(1)-Ni(1)-N(1) bite angle of
85.32(8)°, which is compensated for by a slight opening of the
Br(1)-Ni(1)-Br(2) angle (92.225(16)°). The electronic asym-
metry imposed by ligand 3a is reflected in a small difference
between the two Ni-Br bond distances (0.02 Å), with the longer
of the two being trans to phosphorus, as expected. The
phosphino guanidine presents a planar CN3 core with delocalized
bonding across the N(1)C(1)N(2) moiety. The Ni(1)-N(1) bond
distance (1.912(2) Å) is comparatively short (cf. 1.983(2) Å in
NiCl2(1)2),23 something that reflects the tight binding of the P,N
chelate.21 Despite repeated attempts, crystals of 4b-d suitable
for study by X-ray diffraction could not be obtained.
No reaction with ethylene (1 bar) was detected upon activating
any of the complexes 4a-d with MAO. However, in contrast,
the initiators generated from treatment of 4b-d with EtAlCl2
in toluene react in a very exothermic manner, spontaneously
reaching ca. 80 °C after approximately 5 min, temperatures that
were maintained for the remainder of the test period (ca. 25
min) without the need for external heating. Similar aluminum
(24) Evans, D. F. J. Chem. Soc. 1959, 2003–2005.
(25) Evans, D. F.; Jakubovic, D. A. J. Chem. Soc., Dalton Trans. 1988,
2927–2933.
(26) Sur, S. K. J. Magn. Reson. 1989, 82, 169–173.
(27) Kermagoret, A.; Braunstein, P. Organometallics 2008, 27, 88–99.
(28) Clark, E. P. Ind. Eng. Chem., Anal. Ed. 1941, 13, 820–821.
(29) Kermagoret, A.; Pattacini, R.; Vasquez, P. C.; Rogez, G.; Welter,
R.; Braunstein, P. Angew. Chem., Int. Ed. 2007, 46, 6438–6441.
In order to probe the structures of the various Ni(II)
complexes 4, an investigation of their magnetic properties in
(23) Oakley, S. H.; Soria, D. B.; Coles, M. P.; Hitchcock, P. B.
Polyhedron 2006, 25, 1247–1255.

5084 Organometallics, Vol. 27, No. 19, 2008
Dyer et al.
Table 1. Ethylene Oligomerization Studies Employing Proinitiators 4a-d and EtAlCl2 as Activatora
mass of all
productsb (g)
C4 [1-C4]c (mass %)
C6 [1-C6]c (mass %)
C8 [1-C8]c (mass %)
Kd
5e (mass %)
productivityf
TONg
4a
4b
4c
4d
8.9
4.4
6.3
2.2
9.0 [62.5]
73.5 [13.3]
85.4 [4.1]
54.5 [5.8]
1.1 [13.6]
24.9 [2.8]
14.2 [0.5]
42.0 [0.52]
0
0.1
0.3
0.2
0.8
89.9
6066
2981
4299
1513
6345
3118
4497
1582
1.6 [13.6]
0.4 [18.1]
3.5 [18.3]
0
0
0
a Reaction conditions: 4 (5.00 × 10-5 mol), toluene (50 mL), ambient temperature, 1 bar C2H4 constant pressure, EtAlCl2 (14 equiv), in a Schlenk,
30 min. b Mass [(liquid phase) - (50 mL of C7H8)]. c Determined by quantitative GC; data are an average of three runs. d K ) hexenes (mol)/butenes
(mol). e Friedel-Crafts alkylated products. f In units of g of C2H4 (g of Ni)-1 h-1 g In units of mol of C2H4 (mol of Ni)-1 h-1
. .
Table 2. Distribution of Friedel-Crafts Products Obtained from the
Reaction between Ethylene and Toluene in the Presence of
Proinitiator 4a and EtAlCl2 as Activatora
activator dependence has been reported for a number of related
nickel-based ethylene oligomerization systems.16,20,30,31
Analysis of the resulting organic products (quantitative GC/
GC-MS) revealed the formation of C4, C6, and C8 alkenes as
isomeric mixtures of products (no polymer was obtained) with
reasonably modest productivities (1513-4299 g of C2H4 (g of
Ni)-1 h-1) that are comparable with those for other Ni/ligand-
based oligomerization systems (Table 1).27,32-36 However, the
mild reaction conditions (1 bar, Ni:Al ) 1:14) are a notable
feature of proinitiators 4b-d, especially as the selectivity toward
butenes is retained, despite low regioselectivity.16
compound
R
product distribution (%)b
a
b
c
C4H9
39.5
19.7
25.4
14.1
C6H13
C8H17
C10H21
d
It is evident that for proinitiators 4b-d there is a clear
dependence of oligomerization productivity and selectivity upon
the nature of the P-donor components. Although there is no
discernible relationship between the catalytic outcomes and the
basicity of the P-donor fragment,22 proinitiator 4d, which
possesses the weakest σ-donating P-center, exhibits the lowest
productivity and selectivity (Table 1), suggesting that the P,N-
chelate is displaced during catalysis. In contrast, 4c displays
both the best activity and 1-C4 selectivity; not only is its P center
significantly more Lewis basic but it also provides considerable
steric bulk.22
a Reaction conditions: 4a (5.00 × 10-5 mol), toluene (50 mL),
ambient temperature, 1 bar C2H4 constant pressure, EtAlCl2 (14 equiv),
in a Schlenk, 30 min. b Determined by quantitative GC; data are an
average of three runs.
Scheme 3. Proposed Pathway for the Formation of
Compounds 5
In contrast, exposure of toluene solutions of 4a/EtAlCl2 (Ni:
Al ) 1:14) to ethylene under identical conditions led to a quite
different set of products. Here, only very small amounts of
alkene products (<1 wt %) were observed after 30 min. Instead,
GC-MS analysis revealed the presence of C4, C6, C8, and C10
alkyl-substituted toluenes (5a-d), each as a mixture of regioi-
somers, as the only products (Table 2). Notably, in the absence
of either 4a or EtAlCl2, or on replacing 4a by NiBr2(PPh3)2, no
organic products could be detected. Furthermore, reactions of
4a/EtAlCl2/C2H4 undertaken in CH2Cl2 or chlorobenzene af-
forded only trace quantities of butenes and hexenes, while
reactions undertaken in CH2Cl2 with 100 equiv of toluene
present resulted in complete conversion of the aromatic hydro-
carbon to 5a-d in a ratio comparable to those observed for
runs undertaken in neat toluene.
1:6 ratio, respectively, with the remainder being higher molec-
ular weight alkylated phenyl products analogous to 5b-d.
Careful fractional distillation allowed 7 to be isolated, with
subsequent NMR and mass spectrometric analyses identifying
a mixture of n-butyl- and sec-butylbenzene (1:10 ratio, respec-
tively) by comparison with authentic samples.
To simplify the task of identifying the organic products
resulting from this transformation, a benzene solution of 4a was
treated with EtAlCl2 (Ni:Al ) 1:14) and allowed to contact
ethylene (1 bar), as above; again, this afforded a mixture of
products (GC-MS). Here, the predominant species (ca. 65%)
were o-/p-C6H4(C2H5)2 (6) and C6H5(C4H9) (7), present in a
In order to verify the origins of the ethyl groups observed in
6, both benzene and toluene solutions of 4a were treated with
MeAlCl2 (Ni:Al ) 1:14) and exposed to ethylene (1 bar). In
both cases, products and product ratios were obtained identical
with those from the analogous reactions employing EtAlCl2,
ruling out direct alkylation from the alkylaluminum reagent.
Together, these observations are consistent with a two-stage
process for the formation of 5 and 7 (Scheme 3). Step 1 is 4a/
R′AlCl2-promoted (R′ ) Me, Et) oligomerization of ethylene,
generating C4 to C10 alkenes (as observed with 4b-d). Step 2
is a Friedel-Crafts alkylation of the aromatic solvent by the
olefins generated in step 1, a process that accounts for the
saturated side chains of the alkyl-substituted benzenes obtained
and for the predominance of sec-butyl- over n-butylbenzene, a
result of rearrangement of the carbocation intermediate.
(30) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391–1434.
(31) Sauthier, M.; Leca, F.; De Souza, R.; Bernardo-Gusma˜o, K.;
Queiroz, L. F. T.; Toupet, L.; Re´au, R. New J. Chem. 2002, 26, 630–635.
(32) Reagan, W. K.; Freeman, J. W.; Conroy, B. K.; Pettijohn, T. M.;
Benham, E. A. (Phillips Petroleum Company) U.S. Patent 5,451,645, 1995.
(33) Ban, K.; Hayashi, T.; Suzuki, Y. (Mitsui Chemicals Inc.) Jpn. Patent
JP 10101587, 1998.
(34) Sugimura, K.; Nitabara, T. S.; Fujita, T. (Mitsui Chemicals Inc.)
Jpn. Patent JP 10324710, 1998.
(35) Ban, K.; Hayashi, T.; Suzuki, Y. (Mitsui Chemicals Inc.) Jpn. Patent
JP 11060627, 1999.
Although the origins of this unusual preference toward
aromatic alkylation behavior with 4a/EtAlCl2 remain unclear,
(36) Speiser, F.; Braunstein, P.; Saussine, L. Inorg. Chem. 2004, 43,
1649.

Rigid N-Phosphino Guanidine P,N Ligands
Organometallics, Vol. 27, No. 19, 2008 5085
literature.38 Ethylene was obtained from BOC. Gases were passed
through a drying column (silica/CaCO3/P2O5) prior to use. Melting
points were obtained in sealed glass tubes under nitrogen, using a
Gallenkamp melting point apparatus, and are uncorrected.
a number of scenarios are possible. The most likely is that the
oligomerization initiator generated from the reaction between
4a and the aluminum alkyl is extremely active, but with a very
short lifetime. This would generate significant concentrations
of short-chain alkenes rapidly at the start of a run, prior to the
loss of the active Ni species. Subsequently, the unsaturated
hydrocarbons undergo slower Friedel-Crafts alkylation. No-
tably, it has been disclosed previously that ethyl- and butyl-
substituted benzenes are alkylated by ethylene in the presence
Bis(diphenylamino)chlorophosphine ((Ph2N)2PCl). A three-
necked round-bottom flask fitted with a reflux condenser and
pressure-equalizing dropping funnel was charged with DABCO
(13.55 g, 0.121 mol) and placed under vacuum. After back-filling
with N2, PCl3 (10 mL, 0.115 mol) and DME (50 mL) were added
and the vessel was stirred and cooled to 0 °C. The dropping funnel
was charged with a DME (150 mL) solution of Ph2NH (39.76 g,
0.235 mol), which was added dropwise over 2 h to the cooled
reaction vessel. A further aliquot of DME (50 mL) was washed
through the dropping funnel, before replacing it with a stopper.
The reaction vessel was warmed to room temperature over 4 h and
then heated at reflux for 6 days to give a yellow solution with a
voluminous white precipitate. The solution was filtered using a glass
frit and the precipitate washed with DME (50 mL). The DME was
removed in vacuo to leave a brown oil. Unreacted/excess DABCO,
Ph2NH, and some (Ph2N)PCl2 were removed under high vacuum
(0.01 mmHg) at 150 °C. The resulting viscous orange oil was shown
by 31P{1H} NMR spectroscopy to be a mixture of (Ph2N)PCl2
(11%) and (Ph2N)2PCl (89%) (76.99 g, 72%, combined yield).
Further attempts at purification failed to separate the two products.
Data for the desired product only: 1H NMR (250.13 MHz, CDCl3)
δ 7.10 (8H, m, o-C6H5), 7.00 (4H, m, p-C6H5), 6.87 (8H, m,
m-C6H5); 13C{1H} (62.90 MHz, CDCl3) δ 145.35 (d, 2JPC ) 10.2,
i-C6H5), 129.24 (s, m-C6H5), 126.30 (d, 3JPC ) 8.6, o-C6H5), 125.15
(s, p-C6H5); 31P{1H} (101.26 MHz, CDCl3) δ +123.1 (s); MS (EI+)
402 M+, 234 (M - NPh2)+, 198 (M - NPh2 - Cl)+.
of catalytic quantities of MoCl5/EtAlCl2/ROH (Mo:Al:H+
1:4:3), through what is assumed to be a similar pathway.37
)
Conclusion
The readily prepared, easily derivatized N-phosphino guanidines
are attractive scaffolds for Ni(II), with the resulting complexes
being active ethylene oligomerization initiators in the presence
of EtAlCl2 whose selectivity may be be altered through variation
of the steric and electronic demands of the P-donor component.
Notably, these initiators operate at ambient temperature and 1
bar of ethylene, using a low Ni:Al ratio (1:14), a feature of
particular current industrial relevance. In contrast, in either
benzene or toluene, the Ph2P-substituted system in combination
with EtAlCl2 (Ni:Al ) 1:14) gives rise to an unusual ethylene
oligomerization/Friedel-Crafts alkylation reaction sequence.
This is believed to occur due to the formation of a highly active
yet very short-lived Ni-based initiator that generates higher
alkenes, which act as substrates for a classical Al-catalyzed
alkylation of the aromatic solvents. Studies are ongoing to
enhance the selectivity of proinitiators 4b-d and to better
understand the origins of the Friedel-Crafts chemistry.
Dimesitylphosphine Oxide (Mes2P(dO)H). We used a modified
literature procedure:39 to a cooled (0 °C), stirred solution of PCl3
(8.5 mL, 9.70 × 10-2 mol) in diethyl ether (600 mL) was added
a solution of MesMgBr (1.0 M, diethyl ether, 200 mL, 0.200 mol)
dropwise over 2 h. The resultant mixture was stirred and warmed
to room temperature and then heated at reflux overnight. After the
mixture was recooled (0 °C), deoxygenated, distilled water (150
mL) was added dropwise with vigorous stirring and the mixture
warmed to room temperature overnight. The diethyl ether was
removed in vacuo and the aqueous solution extracted with deoxy-
genated DCM and then dried over MgSO4. The DCM was removed
in vacuo to leave a yellow solid, which was then dissolved in hot
toluene and the solution filtered. Prolonged cooling at -30 °C gave
the product as white crystals (14.31 g, 52%). 1H NMR (250.13
MHz, CDCl3): δ 8.55 (1H, d, 1JPH ) 476.1, PH), 6.86 (4H, d, 4JPH
) 3.9, C6H2(CH3)3), 2.40 (12H, s, o-C6H2(CH3)3), 2.29 (6H, s,
p-C6H2(CH3)3). 13C{1H} NMR (62.90 MHz, CDCl3): δ 142.11 (d,
4JPC ) 2.5, p-C6H2(CH3)3), 141.92 (d, 2JPC ) 10.2, o-C6H2(CH3)3),
Experimental Section
General Considerations. All manipulations of air- and/or water-
sensitive materials were performed under an atmosphere of nitrogen
using standard Schlenk and cannula techniques or in a conventional
nitrogen-filled glovebox (Saffron Scientific) (unless stated other-
wise). Solvents were freshly distilled under nitrogen from sodium/
benzophenone (diethyl ether, toluene, DME), from calcium hydride
(dichloromethane), from sodium (hexane), or from P2O5 (CD2Cl2,
C6D6, and CDCl3) and degassed prior to use. Elemental analyses
were performed by S. Boyer at London Metropolitan University.
NMR spectra were recorded on Bruker AM 250, AMX 300, and
AMX 400 spectrometers; chemical shifts were referenced to residual
protio impurities in the deuterated solvent (1H), to the deuterated
solvent (13C), or to external aqueous 85% H3PO4 (31P). Chemical
shifts are reported in ppm and coupling constants in Hz. All spectra
were obtained at ambient probe temperature (298 K) unless stated
otherwise. For 1H NMR spectra, 31P-coupled resonances were
verified by obtaining 1H{31P} spectra. 13C NMR spectra were
assigned with the aid of DEPT 135. Infrared spectra were recorded
(Nujol mulls (KBr windows), KBr disks, or solution (KBr
windows)) on a Perkin-Elmer 1600 spectrophotometer; Nujol was
dried over sodium wire. FAB (3-nitrobenzyl alcohol matrix) and
EI mass spectra were recorded on a Kratos Concept 1H instrument
and are reported in m/z. GC-MS measurements were performed
either using a Perkin-Elmer Autosystem XL GC (PE-5MS 30 m
coil, internal diameter 0.25 mm, film thickness 0.25 µm) coupled
to a Perkin-Elmer Turbomass mass spectrometer or using a Thermo
Finnegan Trace instrument (Agilent HP-5MS 30 m column, internal
diameter 0.25 mm, film thickness 0.25 µm). NiBr2(DME), DABCO,
EtAlCl2 (1 M, toluene), and PCl3 were purchased from Aldrich
and used as received. (Pri2N)2PCl was prepared according to the
3
1
130.67 (d, JPC ) 10.7, m-C6H2(CH3)3), 126.59 (d, JPC ) 100.2,
i-C6H2(CH3)3), 21.35 (d, 5JPC ) 1.0, p-C6H2(CH3)3), 20.97 (d, 3JPC
) 8.1, o-C6H2(CH3)3). 31P NMR (101.26 MHz, CDCl3): δ 10.0 (d,
1JPH ) 476). MS (FAB+): 287 (MH)+, 167 (M - Mes)+, 119
Mes+. Anal. Calcd for C18H23OP: C, 75.50; H, 8.09. Found: C,
75.40; H, 8.21.
Dimesitylchlorophosphine (Mes2PCl). We used a modified
literature procedure:39 in a thick-walled Young’s tap ampule,
Mes2P(O)H (14.31 g, 5.00 × 10-2 mol) was dissolved in neat PCl3
(85 mL), the system was heated to 60 °C, and the ampule was
sealed. After 3 weeks of stirring at this temperature the solution
was cooled and filtered through a glass frit to remove the orange
solid that had formed. Excess PCl3 was then removed in vacuo to
leave a yellow oil. Repeated addition of diethyl ether (3 × 20 mL)
and removal in vacuo, followed by exposure to vacuum for 12 h,
(38) King, R. B.; Sadanani, N. D. Synth. React. Org. Met.-Org. Chem.
1985, 15, 149–153.
(37) Olechowski, J. R. (Cities Service Company) U.S. Patent 3,720,725,
1973.
(39) Bokanov, A. I.; Rozanel’skaya, N. A.; Steanov, B. I. J. Gen. Chem.
USSR 1978, 48, 1732–1733.

5086 Organometallics, Vol. 27, No. 19, 2008
Dyer et al.
1
left the product as a pale yellow solid (13.07 g, 86%). H NMR
n-BuLi (1.6 M, hexanes, 18.6 mL, 2.98 × 10-2 mol), and the vessel
was warmed to room temperature for 1 h, to give an opaque white
solution. After the solution was recooled (-78 °C), an ethereal
solution (100 mL) of (i-Pr2N)2PCl (7.95 g, 2.98 × 10-2 mol) was
added via cannula. The mixture was stirred at -78 °C for 1 h before
being warmed to room temperature and then stirred for 18 h,
resulting in a pale yellow solution with a white precipitate. Removal
of solvent in vacuo left a white powder. Addition and subsequent
removal of DCM (50 mL) gave a white solid. Addition of toluene
gave a pale yellow solution and white precipitate, which was
removed by glass frit filtration. Concentration and crystallization
at -30 °C gave colorless crystals of 3c (8.77 g, 80%, mp 90-92
(301.24 MHz, C6D6): δ 6.60 (4H, d, 4JPH ) 3.2, C6H2(CH3)3), 2.38
4
(12H, d, JPH ) 2.0, o-C6H2(CH3)3), 2.01 (6H, s, p-C6H2(CH3)3).
13C{1H} NMR (62.90 MHz, C6D6): δ 142.28 (d, JPC ) 18.3,
2
o-C6H2(CH3)3), 140.05 (s, p-C6H2(CH3)3), 133.61 (d, 1JPC ) 46.3,
3
i-C6H2(CH3)3), 131.10 (d, JPC ) 2.0, m-C6H2(CH3)3), 23.31 (d,
3JPC ) 15.8, o-C6H2(CH3)3), 21.20 (s, p-C6H2(CH3)3). 31P{1H}
NMR (101.26 MHz, C6D6): δ 85.0 (s). MS (FAB+): 269 (M -
Cl)+. Anal. Calcd for C18H22PCl: C, 70.93; H, 7.27. Found: C,
68.67; H, 7.99.
7-(Diphenylphosphino)-1,5,7-triazabicyclo[4.4.0]dec-5-ene (3a).
To a stirred, cooled (-78 °C) suspension of 1 (5.10 g, 3.66 × 10-2
mol) in Et2O (200 mL) was added n-BuLi (1.6 M, hexanes, 22.9
mL, 3.66 × 10-2 mol). The vessel was warmed to room temperature
over 1 h, affording a white suspension. After the mixture was
recooled (-78 °C), Ph2PCl (6.6 mL, 3.66 × 10-2 mol) in Et2O
(80 mL) was added and the mixture stirred at -78 °C for 1 h before
being warmed to room temperature and then stirred for 18 h.
Removal of solvents in vacuo followed by addition of toluene and
filtration through a glass frit gave a transparent yellow solution.
Concentration and crystallization at -30 °C gave colorless crystals
of 3a (9.23 g, 78%, mp 120-123 °C). 1H NMR (250.13 MHz,
°C). 1H NMR (250.13 MHz, CDCl3): δ 3.26 (8H, m, CH2
+
3
NCH(CH3)2), 3.02 (4H, m, CH2), 1.80 (2H, ps-quin, JHH ) 6.0,
3
3
CH2), 1.71 (2H, ps-quin, JHH ) 5.7, CH2), 1.18 (12H, d, JHH
)
6.6, NCH(CH3)2), 1.13 (12H, d, 3JHH ) 6.7, NCH(CH3)2); 13C{1H}
NMR (62.90 MHz, CDCl3): δ 149.86 (d, 2JPC ) 14.2, CdN), 48.78
(s, CH2), 48.44 (s, CH2), 46.88 (d, 2JPC ) 15.3, NCH(CH3)2), 43.42
2
3
(s, CH2), 41.36 (d, JPC ) 3.6, CH2), 24.51 (d, JPC ) 6.6,
3
NCH(CH3)2), 24.30 (s, CH2), 23.44 (d, JPC ) 7.1, NCH(CH3)2),
23.30 (s, CH2). 31P{1H} NMR (101.26 MHz, CDCl3): δ 89.6 (s).
MS (FAB+): 370 (MH)+, 269 (M - N-i-Pr2)+, 231 (M - TBD)+.
MS (EI): 369 (M)+, 326 (M - i-Pr)+, 269 (M - N-i-Pr2)+. IR
(KBr, CDCl3 solution): ν(CdN) cannot be assigned unambiguously.
Anal. Calcd for C19H40N5P: C, 61.76; H, 10.91; N, 18.95. Found:
C, 61.69; H, 10.99; N, 19.03.
3
CDCl3): δ 7.36 (10H, m, C6H5), 3.44 (2H, t, JHH ) 5.7, CH2),
3.16 (2H, t, 3JHH ) 6.1, CH2), 3.08 (2H, t, 3JHH ) 6.4, CH2), 2.99
3
3
(2H, t, JHH ) 5.7, CH2), 1.86 (2H, ps-quin, JHH ) 5.9, CH2),
1.69 (2H, ps-quin, 3JHH ) 5.3, CH2). 13C{1H} NMR (75.78 MHz,
2
1
CDCl3): δ 151.9 (d, JPC ) 20.5, CdN), 138.2 (d, JPC ) 20.5,
7-(Bis(diphenylamino)phosphino)-1,5,7-triazabicyclo[4.4.0]dec-
5-ene (3d). To a stirred, cooled (-78 °C) suspension of 1 (6.90 g,
4.96 × 10-2 mol) in diethyl ether (100 mL) was added dropwise
n-BuLi (2.0 M, pentane, 24.8 mL, 4.96 × 10-2 mol), and the vessel
was warmed to room temperature for 1 h. After the mixture was
recooled (-78 °C), an ethereal solution (100 mL) of (Ph2N)2PCl
(15.33 g, 3.80 × 10-2 mol) and (Ph2N)PCl2 (1.56 g, 5.78 × 10-3
mol) (total 16.89 g of mixture) was added via cannula. The mixture
was stirred at -78 °C for 1 h before being warmed to room
temperature and then stirred for 18 h, resulting in an orange solution
with a white precipitate. Removal of solvent in vacuo left a pale
orange powder. Addition and subsequent removal of DCM (50 mL)
gave a brown oil. Addition of toluene (100 mL) gave an orange
solution and a white precipitate, which was removed by filtration.
The precipitate was washed with DCM (30 mL) and filtered. The
toluene and DCM solutions were combined, and the solvent was
removed. The resultant orange solid was dissolved in a minimum
amount of DCM; recrystallization at -30 °C gave colorless crystals
2
i-C6H5), 132.3 (d, JPC ) 21.0, o-C6H5), 128.5 (s, p-C6H5), 128.2
(d, 3JPC ) 5.5, m-C6H5), 48.8 (s, CH2), 48.6 (s, CH2), 44.2 (s, CH2),
42.9 (d, JPC ) 10.0, CH2), 24.2 (s, CH2), 23.1 (s, CH2). 31P{1H}
2
NMR (101.26 MHz, CDCl3): δ 41.6 (s). MS (FAB+): 322 (M -
H)+, 247 (MH - Ph)+, 186 (MH - TBD)+. Anal. Calcd for
C19H22N3P: C, 70.57; H, 6.86; N, 12.99. Found: C, 70.44; H, 6.95;
N, 12.43.
7-(Dimesitylphosphino)-1,5,7-triazabicyclo[4.4.0]dec-5-ene (3b).
To a stirred, cooled (-78 °C) suspension of 1 (2.74 g, 1.97 × 10-2
mol) in diethyl ether (100 mL) was added n-BuLi (2.0 M, pentane,
9.9 mL, 1.97 × 10-2 mol), and the vessel was warmed to room
temperature over 1 h. After the mixture was recooled (-78 °C),
an ethereal solution (50 mL) of Mes2PCl (6.00 g, 1.97 × 10-2
mol) was added via cannula. The mixture was stirred at -78 °C
for 1 h before being warmed to room temperature and then stirred
for 18 h, resulting in a pale yellow solution with a white precipitate.
Removal of solvent in vacuo left a beige powder. Addition and
subsequent removal of DCM (50 mL) gave a beige foam, which
was dissolved in toluene and filtered through a glass frit to give an
orange solution. Concentration and crystallization at -30 °C gave
colorless crystals of 3b (5.94 g, 74%, mp 189-190 °C). 1H NMR
(301.24 MHz, CDCl3): δ 6.73 (4H, d, 4JPH ) 2.9, m-C6H2(CH3)3),
3.42 (2H, t, 3JHH ) 5.5, CH2), 3.13 (2H, t, 3JHH ) 6.0, CH2), 3.05
(4H, ps-t, 3JHH ) 6.0, CH2), 2.22 (6H, s, p-C6H2(CH3)3), 2.16 (12H,
d, 4JPH ) 1.2, o-C6H2(CH3)3), 1.81 (2H, ps-quin, 3JHH ) 5.7, CH2),
1.60 (2H, ps-quin, 3JHH ) 6.0, CH2). 13C{1H} NMR (100.61 MHz,
CDCl3): δ 151.56 (d, 2JPC ) 21.5, CdN), 141.32 (d, 2JPC ) 19.0,
o-C6H2(CH3)3), 137.41 (s, p-C6H2(CH3)3), 134.14 (d, 1JPC ) 33.1,
1
of 3d (7.93 g, 45%, mp 181-184 °C). H NMR (250.13 MHz,
C6D6): δ 7.44 (16H, m, o- + m-C6H5), 7.23 (4H, m, p-C6H5), 3.80
(2H, t, 3JHH ) 5.6, CH2), 3.18 (2H, t, 3JHH ) 5.8, CH2), 2.91 (2H,
3
3
t, JHH ) 6.0, CH2), 2.65 (2H, t, JHH ) 6.1, CH2), 1.86 (2H, ps-
3
3
quin, JHH ) 5.8, CH2), 1.50 (2H, ps-quin, JHH ) 5.9, CH2).
13C{1H} NMR (75.75 MHz, C6D6): δ 149.18 (d, JPC ) 16.9,
2
CdN), 148.19 (d, 2JPC ) 11.4, i-C6H5), 129.52 (s, m-C6H5), 125.78
(d, 3JPC ) 9.0, o-C6H5), 123.77 (s, p-C6H5), 48.53 (s, CH2), 48.03
4
2
(s, CH2), 44.66 (d, JPC ) 3.0, CH2), 41.13 (d, JPC ) 6.6, CH2),
24.03 (s, CH2), 23.89 (s, CH2). 31P{1H} NMR (101.26 MHz, C6D6):
δ 92.3 (s). MS (FAB+): 506 (MH)+, 367 (M - 1 - H)+, 337 (M
- NPh2)+. IR (KBr, C6D6 solution): ν(CdN) cannot be assigned
unambiguously. Anal. Calcd for C31H32N5P: C, 73.64; H, 6.38; N,
13.85. Found: C, 73.76; H, 6.29; N, 13.75.
3
i-C6H2(CH3)3), 129.86 (d, JPC ) 2.1, m-C6H2(CH3)3), 48.85 (d,
4JPC ) 1.8, CH2), 48.45 (s, CH2), 44.53 (d, JPC ) 12.2, CH2),
2
4
44.16 (d, JPC ) 1.5, CH2), 24.16 (s, CH2), 23.35 (s, CH2), 22.07
(d, 3JPC ) 16.6, o-C6H2(CH3)3), 20.88 (s, p-C6H2(CH3)3). 31P{1H}
NMR (121.94 MHz, CDCl3): δ 27.7 (s). MS (FAB+): 408 (MH)+,
392 (M - Me)+, 288 (M - Mes)+, 269 (M - TBD)+. IR (KBr,
CDCl3 solution): ν(CdN) cannot be assigned unambiguously. Anal.
Calcd for C25H34N3P: C, 73.68; H, 8.41; N, 10.31%. Found: C,
73.78; H, 8.52; N, 10.19.
[7-(Diphenylphosphino)-1,5,7-triazabicyclo[4.4.0]dec-5-ene]-
nickel Dibromide (4a). To a mixture of 3a (311 mg, 9.61 × 10-4
mol) and NiBr2(DME) (288 mg, 9.33 × 10-4 mol) was added cold
(-78 °C) CH2Cl2 (200 mL). The solution was warmed to room
temperature and then heated at reflux for 24 h. The resulting purple
precipitate was recovered by filtration, washed with Et2O (4 × 50
mL), and dried in vacuo to afford 4a as a dark purple powder (499
mg, 99%, mp 220 °C dec). Deep red crystals, suitable for an X-ray
structure determination, were grown from a CD2Cl2 solution layered
7-(Bis(diisopropylamino)phosphino)-1,5,7-triazabicyclo[4.4.0]-
dec-5-ene (3c). To a stirred, cooled (-78 °C) suspension of 1 (4.15
g, 2.98 × 10-2 mol) in diethyl ether (100 mL) was added dropwise

Rigid N-Phosphino Guanidine P,N Ligands
Organometallics, Vol. 27, No. 19, 2008 5087
with hexane. MS (FAB+): 461 (M - Br)+. IR (KBr): ν(CN) 1587
cm-1. Anal. Calcd for C19H22N3PBr2Ni: C, 42.11; H, 4.09; N, 7.75.
Found: C, 42.21; H, 4.17; N, 7.83.
at room temperature for a period of 10 min, during which time it
was degassed and left under a partial vacuum. Subsequently, it was
allowed to contact ethylene (1 bar), with rapid stirring, for a period
of 30 min. At the end of the run, the Schlenk was cooled in an ice
bath and the reaction quenched by slow addition of HCl (1 M, 10
mL); nonane (1 mL) was added as an internal GC standard. Aliquots
of the resulting organic phase were rapidly transferred to precooled
GC vials and sealed; GC analyses were undertaken immediately.
[7-(Dimesitylphosphino)-1,5,7-triazabicyclo[4.4.0]dec-5-ene]-
nickel Dibromide (4b). To a mixture of 3b (235 mg, 5.77 × 10-4
mol) and NiBr2(DME) (173 mg, 5.61 × 10-4 mol) was added cold
(-78 °C) CH2Cl2 (200 mL). The mixture was stirred and warmed
to room temperature over 18 h and then heated to reflux for 24 h.
The resultant purple solution was filtered through a glass frit, and
the volatiles were removed in vacuo to leave 4b as a purple powder,
which was washed with diethyl ether (4 × 20 mL) and dried in
vacuo (287 mg, 82%). MS (FAB+): 546 (M - Br)+, 465 (M -
2Br)+. IR (KBr, CH2Cl2 solution): ν(CdN) 1595 cm-1. Anal. Calcd
for C25H34N3PBr2Ni: C, 47.96; H, 5.47; N, 6.71. Found: C, 47.98;
H, 5.33; N, 6.61.
[7-(Bis(diisopropylamino)phosphino-1,5,7-triazabicyclo[4.4.0]-
dec-5-ene]nickel Dibromide (4c). To a mixture of 3c (273 mg,
7.38 × 10-4 mol) and NiBr2(DME) (221 mg, 7.16 × 10-4 mol)
was added cold (-78 °C) CH2Cl2 (200 mL). The mixture was stirred
and warmed to room temperature over 18 h, and then heated to
reflux for 24 h. The resultant purple solution was filtered through
a glass frit, and the volatiles were removed in vacuo to leave 4c as
a lilac powder, which was washed with pentane (5 × 30 mL) and
dried in vacuo (303 mg, 72%). MS (FAB+): 508 (M - Br)+, 427
(M - 2Br)+, 408 (M - Br - N-i-Pr2)+. IR (KBr, CH2Cl2 solution):
ν(CdN) 1591 cm-1. Anal. Calcd for C19H40N5PBr2Ni: C, 38.81;
H, 6.86; N, 11.91. Found: C, 38.74; H, 7.01; N, 12.06.
[7-(Bis(diphenylamino)phosphino)-1,5,7-triazabicyclo[4.4.0]dec-
5-ene]nickel Dibromide (4d). A mixture of 3d (255 mg, 5.04 ×
10-4 mol) and NiBr2(DME) (151 mg, 4.89 × 10-4 mol) was
transferred to a Schlenk line. The vessel was cooled to -78 °C,
and the solids were stirred, as DCM (60 mL) was added dropwise.
The mixture was stirred and warmed to room temperature over 18 h
and then heated to reflux for 24 h. The product 3d precipitated as
a purple powder and was recovered via filtration. Washing with
diethyl ether (5 × 50 mL) and drying in vacuo left a light purple
powder (321 mg, 91%). MS (FAB+): 644 (M - Br)+, 562 (M -
2Br)+. IR (KBr, CH2Cl2 solution): ν(CdN) 1600 cm-1. Anal. Calcd
for C31H32N5PBr2Ni: C, 51.42; H, 4.45; N, 9.67. Found: C, 51.52;
H, 4.51; N, 9.61.
X-ray Data Collection, Structure Solution and Refinement
for 4a. X-ray diffraction data were collected on a Bruker Apex 2K
CCD area detector diffractometer equipped with an Oxford Cry-
ostream N2 cooling device. Data collection and reduction were
conducted using the SMART and SAINT programs, respectively.41
All further calculations were performed using the SHELXTL
package42 and programs therein. The structure was solved using
Patterson methods and was refined using full-matrix least squares
based on F2. An empirical absorption correction was applied to all
data using SADABS.43 All non-hydrogen atoms were refined
anisotropically, and then hydrogen atoms were included at idealized
positions and refined as rigid groups. Crystal data:
C19.50H22DBr2ClN3NiP, Mr ) 584.36, monoclinic, a ) 24.4597(15)
Å, b ) 13.0822(8) Å, c ) 17.0457(11) Å, ꢀ ) 127.244(1)°, V )
4342.1(5) Å3, Z ) 8, µ(Mo KR) ) 4.782 mm-1, T ) 150(2) K,
crystal size 0.49 × 0.29 × 0.21 mm3, space group C2/c, 16 335
reflections collected, 4264 independent reflections (Rint ) 0.0338),
R1 ) 0.0346 and wR2 ) 0.0986 for I > 2σ(I), R1 ) 0.0396 and
wR2 ) 0.1002 for all data. CCDC reference number 653161
contains the supplementary crystallographic data for this paper,
which can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/dat_arequest/
cif.
Acknowledgment. The Lubrizol Corporation, EPSRC, and
Durham and Leicester Universities are thanked for financial
support; Mr. Lauchlan is thanked for assistance with GC and
Dr. M. Jones for mass spectrometry measurements.
Supporting Information Available: A CIF file giving crystal
data for 4a. This material is available free of charge via the Internet
at http://pubs.acs.org.
Generalized Catalyst Testing Procedure. In order to provide
ready/reliable comparison of the catalytic outcomes, the catalyst
test procedure adopted is a modification of that described by
Braunstein and co-workers.40 A large Schlenk equipped with an
efficient magnetic stirrer bar was charged with 4 (5.00 × 10-5 mol)
and dry toluene (50 mL) under nitrogen, prior to addition of EtAlCl2
(1 M, toluene; Ni:Al ) 1:14) via syringe. This solution was aged
OM8005933
(41) Bruker SMART (v 5.622) and SAINT-Plus (v 6.02); Bruker AXS
Inc., Madison, WI, 2001 and 1999.
(42) Sheldrick, G. M. SHELXTL (v 6.1); Bruker AXS Inc., Madison,
WI, 2000.
(43) Sheldrick, G. M. SADABS, Program for the Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen, Go¨ttingen,
Germany, 1996.
(40) Kermagoret, A.; Braunstein, P. Dalton Trans. 2008, 1564–1573.