Neutral β-diketiminato nickel(II) monoalkyl complexes

Article abstract of DOI:10.1016/S0020-1693(02)01310-5

Reaction of NiCl₂(2,4-lutidine)₂ (1) with Tl[Me₂NN] (3) in THF results in the transmetallation of the β-diketiminate ligand from which the tetrahedral {[Me₂NN]NiCl}₂ (4) was isolated in poor yield. After filtration of the TlCl formed in the reaction between 1 and 3 in THF, addition of Grignard reagents RMgBr results in the isolation of monoalkyl complexes [Me₂NN]Ni(R)(2,4-lutidine) (R=Me (5), Et (6), Pr (7)) in 40-70% yield. X-ray structures 5-7 of show these monoalkyls to be somewhat crowded, square planar species. NMR studies of the diamagnetic monoalkyl complexes show that lutidine dissociation/reassociation occurs on the NMR timescale at room temperature. In ethyl and propyl complexes 6 and 7, an equilibrium between the four coordinate [Me₂NN]Ni(R)(2,4-lutidine) and a lutidine-free species [Me₂NN]Ni(R) (R=Et, Pr) is observed. Broad, high-field ¹H resonances consistent with the presence of β-H agostic alkyl groups are observed for the base-free species. The observation of two broad upfield ¹H NMR signals at δ -2.7 and -7.3 ppm for the base-free Ni-propyl complex suggests a mixture of primary and secondary β-agostic isomers that reversibly interconvert by β-H elimination/reinsertion. Ethylene slowly inserts into monoalkyls 5-7 demonstrate to give highly branched ethylene oligomers.

Full text of DOI:10.1016/S0020-1693(02)01310-5

Inorganica Chimica Acta 345 (2003) 199ꢁ208
/
www.elsevier.com/locate/ica
Neutral b-diketiminato nickel(II) monoalkyl complexes
Heather L. Wiencko, Elzbieta Kogut, Timothy H. Warren *
Department of Chemistry, Georgetown University, Washington, DC 20057, USA
Received 5 June 2002
Dedicated to Professor Richard R. Schrock
Abstract
Reaction of NiCl2(2,4-lutidine)2 (1) with Tl[Me2NN] (3) in THF results in the transmetallation of the b-diketiminate ligand from
which the tetrahedral {[Me2NN]NiCl}2 (4) was isolated in poor yield. After filtration of the TlCl formed in the reaction between 1
and 3 in THF, addition of Grignard reagents RMgBr results in the isolation of monoalkyl complexes [Me2NN]Ni(R)(2,4-lutidine)
(Rꢀ
/
Me (5), Et (6), Pr (7)) in 40ꢁ
/
70% yield. X-ray structures 5ꢁ7 of show these monoalkyls to be somewhat crowded, square planar
/
species. NMR studies of the diamagnetic monoalkyl complexes show that lutidine dissociation/reassociation occurs on the NMR
timescale at room temperature. In ethyl and propyl complexes 6 and 7, an equilibrium between the four coordinate
1
Et, Pr) is observed. Broad, high-field H resonances
[Me2NN]Ni(R)(2,4-lutidine) and a lutidine-free species [Me2NN]Ni(R) (Rꢀ
/
consistent with the presence of b-H agostic alkyl groups are observed for the base-free species. The observation of two broad upfield
1H NMR signals at d ꢂ
2.7 and ꢂ7.3 ppm for the base-free Niꢁpropyl complex suggests a mixture of primary and secondary b-
agostic isomers that reversibly interconvert by b-H elimination/reinsertion. Ethylene slowly inserts into monoalkyls 5ꢁ
/
/
/
/
7
demonstrate to give highly branched ethylene oligomers.
# 2002 Published by Elsevier Science B.V.
Keywords: b-Diketiminato nickel(II) complexes; Monoalkyl complexes; X-ray structures
1. Introduction
work by Ostoja-Starzewski et al. and Klabunde et al.
demonstrated that replacing the phosphine by more
weakly coordinating neutral ligands in SHOP-like
systems lead to similarly heteroatom tolerant catalysts
capable of producing linear, high molecular weight
Later transition metal complexes attract attention as
olefin polymerization catalysts due to their lower
electrophilicity and resulting greater heteroatom toler-
ance as compared to early metal systems [1]. This
significantly decreases the susceptibility of the late-metal
catalysts to poisoning by polar monomers or polar
impurities in the monomer feed [1,2]. An early example
polyethylene [9ꢁ14].
/
Brookhart’s preparation and study of discrete Ni and
Pd monoalkyl cations supported by a-diimine ligands
highlighted key features important in late-metal ethylene
is the Shell Higher Olefin Process (SHOP) [3ꢁ
oped by Keim et al. that employs monoanionic OSP
ligands in [Ph2PC(R)ÄC(R)O]Ni(Ph)L (Lꢀphosphine)
complexes that catalyze the formation of linear a-olefins
(C6ꢁC20) from ethylene in 1,4-butanediol [6]. Only
under forcing conditions [7] or in the presence of a
phosphine scavenger [8], however, did these complexes
polymerize ethylene to high molecular weight. Later
/
5] devel-
polymerization catalysts [15ꢁ26]. While electrophilic,
/
cationic metal centers that possess an accessible coordi-
nation site for an incoming olefin facilitate rapid olefin
insertion, the use of bulky N-aryl groups slows associa-
tive chain transfer resulting in high molecular weight
polymers [1]. Both the molecular weight and the degree
of branching in the resulting polyethylenes can be
controlled by choice of a-diimine substituents
[15,17,21]. Furthermore, detailed NMR studies have
identified the solution structures and dynamics of
catalytically important species in the olefin polymeriza-
/
/
/
* Corresponding author. Tel.: ꢃ
6209.
E-mail address: thw@georgetown.edu (T.H. Warren).
/
1-202-687 6362; fax: ꢃ1-202-687
/
tion catalytic cycle [19,20,22,24ꢁ26].
/
0020-1693/02/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 3 1 0 - 5

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H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ208
/
Benefiting from these insights are new families of
M[Me2NN] (MꢀLi, K). Furthermore, the reaction
/
heteroatom tolerant, single-component neutral Ni(II)
complexes possessing bulky OSN and NSN monona-
nionic ligands that are capable of polymerizing ethylene
to high molecular weights [27,28]. Grubbs’ family of
neutral nickel complexes based on OSN salicylaldimi-
nato ligands produces highly linear ethylene at rates that
rival the highly active metallocenes [2,28,29]. Related
OSN complexes based on anilinotroponates also show
high activity but produce branched polyethylene whose
branching numbers may be controlled by polymeriza-
with the potassium salt resulted in the formation of a
nickel mirror, indicating reduction of the metal center.
We then explored the use of a less reducing thallium
derivative Tl[Me2NN] (3) [41] to encourage chloride
removal from 1.
While the reaction of 3 with 1 in THF results in the
ready precipitation of TlCl, only in one solitary case
were we able to unambiguously identify a reaction
product.
A
few black crystals of dimeric
{[Me2NN]NiCl}2 (4) were once isolated in very low
yield (less than 5%) from THF after filtration of TlCl
and we obtained its crystal structure (Scheme 1; Fig. 2).
The b-diketiminate ligand symmetrically chelates the
tion temperature and pressure [30]. Klaui et al. have
¨
developed a new family of OSN ligands that copoly-
merize ethylene and carbon monoxide at high rates and
are also stable in the presence of excess CO [31].
Furthermore, he has shown that neutral NSN com-
plexes based on bidentate, sterically hindered h2-
tris(pyrazolyl)borate [32] and semicorrine-type [31]
monoanionic ligands are also competent ethylene and
CO copolymerization catalysts.
nickel center with bond distances of 1.913(3) and
˚
N bond distances in 4
1.915(3) A (Table 1). The NiÃ
/
are slightly shorter than those reported for the related
tetrahedral bis(b-diketiminato) complexes Ni(h2-
˚
1.97(1) A) [42]
PhNC(Me)CHC(Me)NPh)2 (1.95(1)ꢁ
/
and Ni(h2-ArNC(H)CPhC(H)NAr)2 (Arꢀ
/p-ClC6H5)
While b-diketiminates ([NN]ꢂ) have been investi-
gated as ancillary ligands in cationic, early transition
˚
(1.943(2) and 1.947(2) A) [43] perhaps due to greater
steric crowding in the homoleptic Ni(II) complexes. The
metal olefin polymerization catalysts [33ꢁ38], we sought
/
N1Ã
93.1(5)ꢁ
complexes. The lengthened ketiminate NÃ
/
NiÃ
95.0(5) observed for the bis(b-diketiminato)
C bond dis-
/
N2 angle of 94.69(11)8 in 4 is in the range of
the synthesis of well defined neutral monoalkyl com-
plexes [NN]Ni(R)(L) that could be stabilized by an
additional neutral base L (Fig. 1). Our initial efforts
focused on the use of the mononanionic b-diketiminate
ligand [Me2NN]ꢂ derived from 2,4-bis(2,6-dimethyl-
phenyllimido)pentane (H[Me2NN]) [39,40]. Herein we
describe the synthesis and X-ray structures of monoalkyl
complexes [Me2NN]Ni(R)(L) along with NMR studies
outlining their solution dynamics and alkene insertion
behavior.
/
/
˚
tances of 1.330(4) and 1.338(4) A in 4 are consistent with
delocalization throughout the b-diketiminate fragment
when compared to the shorter ketimine NÄ
/
C distances
of 1.280(8) and 1.269(8) A found in the b-diketimine
complex C(Me)CH2C(Me)ÄNAr]NiBr2
[h2-ArNÄ
(Arꢀ
2,6-iPr2C6H3) [43]. The tetrahedral nickel centers
˚
/
/
/
˚
in 5 are separated by 3.2966(8) A and are essentially
symmetrically bridged by two chlorides as shown by the
˚
Cl distances of 2.2997(9) and 2.3127(9) A
similar NiÃ
/
that form a ClÃ
/
NiÃCl? angle of 88.76(3)8.
/
2. Results
While our inability to reproducibly prepare 4 pre-
cluded its use as a synthetic intermediate, filtration of
the TlCl formed during the reaction of 1 and 3 followed
by addition of Grignard reagents RMgCl provides the
2.1. Synthesis and X-ray structures of b-diketiminato
Ni(II) complexes
monoalkyl complexes [Me2NN]NiR(2,4-lutidine) (Rꢀ
/
Aiming to prepare a b-diketiminate complex with a
halide handle for alkylation, we explored the use of
known NiCl2(2,4-lutidine)2 (1) with several derivatives
of [Me2NN]ꢂ. Reactions between 1 and the b-diketi-
mine H[Me2NN] (2) as well as related b-diketiminato
lithium and potassium salts in a variety of organic
solvents did not lead to the isolation of any new Ni(II)
complexes. Surprisingly, we did not observe the pre-
cipitation of insoluble LiCl or KCl, expected transme-
tallation products of reactions between
1
and
Fig. 1. Target b-diketiminato complexes.
Scheme 1.

H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ
/
208
201
Fig. 3. ORTEP diagram of [Me2NN]Ni(Me)(2,4-lutidine) (5).
Fig. 2. ORTEP diagram of {[Me2NN]NiCl}2 (4).
Table 1
˚
Bond distances (A) and angles (8) in 4
Bond distances
NiÃ
NiÃ
NiÃ
NiÃ
/
N1
N2
Cl
1.913(3)
1.915(3)
2.3127(9)
2.2997(9)
/
/
/Cl?
Bond angles
N1ÃNiÃN2
ClÃNiÃCl?
N1ÃNiÃ
N1ÃNiÃ
N2ÃNiÃ
N2ÃNiÃ
/
/
94.69(11)
88.76(3)
/
/
/
/Cl
110.50(8)
132.08(8)
120.61(8)
112.97(9)
/
/Cl?
Fig. 4. ORTEP diagram of [Me2NN]Ni(Et)(2,4-lutidine) (6).
/
/Cl
/
/Cl?
˚
N1 1.970(3) A) compared to that
alkyl group (NiÃ
/
˚
N2 1.906(4) A)
opposite the 2,4-lutidine ligand (NiÃ
/
may be a result of a stronger trans influence for the alkyl
ligand. Alternatively, this may be a reflection of the
greater steric demands of the 2,4-lutidine ligand (NiÃ
/
N3
1.914(4) A) perhaps amplified by the somewhat tight
N3 84.55(17)8) flanked
˚
coordination pocket (C29Ã
/
NiÃ
/
by the b-diketiminate N-aryl rings. The NiÃ
/
Ca distances
Table 2
Bond distances (A) and angles (8) in 5ꢁ
˚
/7
5
6
7
Scheme 2.
Bond distances
NiÃ
NiÃ
NiÃ
NiÃ
/
N1
N2
N3
C29
1.970(3)
1.906(4)
1.914(4)
1.937(4)
1.987(3)
1.915(3)
1.916(3)
1.965(4)
1.497(7)
1.9716(17)
1.9190(17
1.9179(16)
1.997(3)
Me (5), Et (6), Pr (7)) as red crystals from ether in 40ꢁ
70% yield (Scheme 2).
In contrast to 4, the X-ray structures of 5ꢁ
5) reveal a square planar geometry about the nickel
center as observed in other neutral four-coordinate
/
/
/
/
7 (Figs. 3ꢁ
/
/
C29Ã
Bond angles
N2
/C30
1.518(6)
Ni(II)-alkyl complexes [29,30,44ꢁ
metrical parameters are observed in each complex 5ꢁ
(Table 2). Similar to tetrahedral 4, the [Me2NN]ꢂ ligand
forms a ‘bite’ angle of 93.87(15)8 in 5. The longer NiÃ
distance for the b-diketiminate donor opposing the NiÃ
/47]. Nearly identical
N1Ã
C29Ã
N3ÃNiÃ
N1ÃNiÃ
NiÃ
/
NiÃ
NiÃ
/
93.87(15)
84.55(17)
169.83(15)
168.4(2)
93.16(12)
86.74(14)
163.19(14)
157.95(17)
119.9(3)
93.57(7)
81.01(10)
167.76(8)
172.60(10)
107.1(3)
/
/
N3
/
7
/
/N2
/
/C29
/
N
/
C29Ã
/
C30
/

202
H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ208
/
Fig. 5. ORTEP diagram of [Me2NN]Ni(Pr)(2,4-lutidine) (7). The propyl group (C29ÃC31) is disordered over two sets of positions; only the major
/
(60%) occupancy is shown.
Fig. 6. Variable temperature1H NMR spectra of 5 (500 MHz, toluene-d8).
increase with the length of the alkyl group (1.937(4),
˚
square plane of the complex. Low temperature 1H NMR
spectra in toluene-d8 reveal upfield signals for the NiÃ
alkyl a-H atoms. The NiÃCH3 resonance in 5 appears as
a singlet d ꢂ1.64 ppm while the NiÃCH2 resonances for
6 and 7 consist of two diastereotopic multiplets each at
d 0.13 and 0.06 ppm and d ꢂ0.04 and ꢂ0.50 ppm,
respectively, consistent with the C1 symmetry of 5ꢁ7.
1.965(4), 1.997(3) A for 5, 6, 7, respectively) and the NiÃ
/
/
C29Ã
/
C30 angles in the ethyl and propyl complexes 7
/
and 8 of 119.9(3) and 107.1(3)8 do not indicate the
presence of b-agostic interactions in these four-coordi-
nate species.
/
/
/
/
/
2.2. Solution behavior probed by NMR spectroscopy
1H and 13C NMR spectra of 5ꢁ
temperature (approximately ꢂ40 8C) are consistent
/7 taken at low
/
with their structures in the solid state. Six diastereotopic
b-diketiminate methyl signals are observed as a conse-
quence of the o-Me group of the lutidine being out the
Scheme 3.

H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ
/
208
203
Fig. 7. Room temperature 1H NMR spectrum of 6 (300 MHz, toluene-d8).
Variable temperature 1H NMR spectra of these
monoalkyls demonstrate that 2,4-lutidine is labile in
these complexes. Gradually warming a toluene-d8 solu-
tion of 5 results in the broadening of all b-diketiminate
While unbound lutidine also appears in the room
1
temperature H NMR spectrum of Niꢁ
7 in toluene-d8, two broad upfield signals at d ꢂ
7.3 ppm are observed (Fig. 8) suggesting the presence
of two different b-H agostic Niꢁpropyl species at room
/propyl complex
/
2.7 and
ꢂ
/
/
signals except for the backbone CÃ
/
H group (Fig. 6).
temperature. While these upfield resonances have not
been unequivocally assigned due to their broad nature,
both a primary (linear) and a secondary (branched) b-H
agostic propyl group would be expected if b-H elimina-
tion followed by reinsertion readily occurs upon disas-
sociation of lutidine [24]. This process is reversible;
cooling regenerates the four-coordinate primary alkyl
[Me2NN]Ni(Pr)(2,4-lutidine) (Scheme 5).
This behavior is consistent with the reversible dissocia-
tion/reassociation of 2,4-lutidine (Scheme 3). Identifying
the exact coalescence temperature for the backbone Me
groups (16(2) 8C at 300 MHz) allowed us to establish
an activation barrier DG" ꢀ
/
12.1(3) kcal molꢂ1 at this
temperature. An associative mechanism for exchange
was ruled out as there is no change in the coalescence
temperature in the presence of added 2,4-lutidine.
The variable temperature behavior of the b-H con-
taining monoalkyls 6 and 7 is markedly different than
that observed for 5. At room temperature in toluene-d8,
ethyl complex 6 exhibits new aromatic resonances
corresponding to free lutidine as well as a broad
2.3. Ethylene reactivity
Addition of approximately 3 equiv. of ethylene to
methyl and ethyl complexes 5 and 6 in benzene-d6 at 1
atm and room temperature results in the observation of
resonance at d ꢂ5.3 ppm of area 3 relative to the
/
1
broad upfield H NMR signals at d ꢂ
/
2.7 and ꢂ7.3
/
released lutidine (Fig. 7). These new resonances increase
in intensity as the temperature is raised to 40 8C. These
observations are consistent with the reversible loss of
lutidine to produce an observable concentration of the
lutidine-free [Me2NN]NiEt (8). Due to the significantly
ppm after 2ꢁ
observed for the propyl complex 7, suggesting the
presence of both linear and branched NiÃalkyl chains
/3 min. These signals are similar to those
/
formed by the insertion of ethylene into the original NiÃ
/
1
C bonds present in 5 and 6. While both the ethylene H
upfield-shifted NiÃ
suggest that the ethyl group in 8 assumes a b-agostic
structure [19,20,24,26,48] in which a b-CÃH bond
/CH2CH3 resonance observed, we
NMR signal at d 5.24 ppm and the upfield 1H resonance
of base-free 8 at d ꢂ
after approximately 10 min, the NiÃ
at d ꢂ1.64 ppm could still be observed after complete
/
5.3 ppm were completely consumed
/
/Me resonance of 5
interacts with the coordination site left vacant by the
2,4-lutidine (Scheme 4). The observation of a single b-H
resonance of area 3 indicates that rotation about the
/
consumption of ethylene. This suggests that the extent
of lutidine dissociation may be an important factor in
determining the rate of ethylene insertion. Exposure of 6
to 100 psi ethylene in toluene at room temperature for
ethyl CÃ/C bond is rapid at these temperatures. The
temperature dependence of the equilibrium constant for
1
lutidine dissociation measured by H NMR allows the
10 min followed cleavage of all NiÃ
/
alkyl chains by an
determination of DHꢀ
/
8.3 (3) kcal molꢂ1 and DSꢀ
/20
acidic workup results in a distribution of C8ꢁ
/C18
(3) cal molꢂ1 K for this process.
oligomers in which each C2nꢃ2 fraction consists of
several resolved isomers. The presence of highly
branched oligomers is consistent with the above NMR
studies and indicate that isomerization via b-H elimina-
tion/reinsertion is fast compared to insertion [24].
Initiation with Niꢁpropyl complex 7 under identical
/
conditions leads to the exclusive production of C2nꢃ1
oligomers, showing that each Ni center produces only
one alkyl chain.
Scheme 4.

204
H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ208
/
Fig. 8. Variable temperature 1H NMR spectra of upfield region of 7 (300 MHz, toluene-d8).
have been suggested on the basis of spectroscopic data
for Sc [50], Ti [51], and Ta [52] as well as demonstrated
in the X-ray structures of TiCl3(dmpe)Et [53,54] and
[P2N2]Ta(CH2CH2)Et
Me2CH2)2PPh) [55]. The more electron-rich, b-diketi-
minato Niꢁethyl and Niꢁpropyl complexes discussed
([P2N2]Ä/PhP(CH2SiMe2NSi-
/
/
herein may favor b-agostic interactions due to a more
compact coordination wedge as compared to neutral
OSP and OSN systems due to the presence of two b-
diketiminato N-aryl substituents, favoring loss of a
neutral base. Chemical removal of 2,4-lutidine from 6
and 7 would allow a more detailed investigation into
these neutral, base-free b-agostic alkyls [Me2NN]NiR
(RꢀEt (8), Pr) and will be reported elsewhere shortly.
/
Scheme 5.
4. Experimental
3. Discussion and conclusion
4.1. General experimental details
We were originally attracted to 2,4-lutidine as a
potentially labile base in our targeted four-coordinate
monoalkyl complexes by Schrock’s finding that 2,4-
lutidine can serve as a stabilizing, yet labile base in the
molybdenum imido alkylidene complex Mo(CHC-
All experiments were carried out in a dry nitrogen
atmosphere using an MBraun glovebox and/or standard
Schlenk techniques. 4A molecular sieves were activated
in vacuo at 180 8C for 24 h. Dry C6H5CH3 was
purchased from Aldrich and was stored over activated
4A molecular sieves. Benzene, Et2O, tetrahydrofuran
(THF) and C5H12 were distilled before use from sodium/
benzophenone and CH2Cl2 was distilled from CaH2. All
deuterated solvents were sparged with nitrogen, dried
over activated 4A molecular sieves and stored under
nitrogen. 1H and 13C NMR spectra were recorded either
on a Mercury Varian 300 MHz spectrometer (300 and
75.4 MHz, respectively) or a Varian Unity 500 MHz
spectrometer (500 and 125.6 MHz) at 25 8C unless
otherwise noted. The NMR spectra were indirectly
referenced to TMS using residual solvent signals as
internal standards. 2,4-Lutidine was obtained from
Aldrich and stored over 4A molecular sieves prior to
use. Anhydrous NiCl2 was obtained from Strem and
ethylene from MG industries; all were used as received.
All Grignard reagents were obtained from Aldrich and
titrated directly before use. 2,4-Bis(2,6-dimethylphenyl-
limido)pentane, (H[Me2NN]) (3) [39,40] and Tl[Me2NN]
Me2Ph)(NAd)[OCH(CF3)2]2(2,4-lutidine) (Adꢀ1-ada-
/
mantyl) that catalyzes the polymerization of (o-
(trimethylsilyl)phenyl)acetylene [49]. The use of 2,4-
lutidine results in the crystalline, easily isolable four-
coordinate [Me2NN]Ni(R)(2,4-lutidine) complexes 5ꢁ7
/
that readily dissociate the lutidine base in solution. In
the case of the b-H containing ethyl and propyl
complexes 6 and 7, H NMR data indicate a reversible,
1
temperature dependent equilibrium between lutidine-
bound and lutidine-free species. b-H elimination/reinser-
tion is a facile, reversible process that is rapid relative to
ethylene insertion and results in the formation of highly
branched short chain oligomers.
While b-agostic interactions in cationic late-metal
systems are well established and play an important
role in the branching of metalÃalkyl chains via b-H
/
elimination/reinsertion, these interactions are far less
commonly observed in neutral systems. b-H agostic
interactions in neutral, early transition metal complexes

H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ
/
208
205
(4) [41] were synthesized according to literature proce-
dures.
124.93, 123.78, 123.49, 122.16, 97.12 (backbone C),
27.61, 25.38, 23.96, 20.49, 19.58, 18.12, 15.96, ꢂ4.10
CH3); Anal. Calc. for C29H37N3: C, 71.59; H, 7.68;
/
(NiÃ
/
4.2. Preparation of NiCl2(2,4-lut)2 (1)
N, 8.64. Found: C, 71.42; H, 7.65; N, 8.15%.
Adapted from a literature procedure [56]: anhydrous
NiCl2 (1.87 g, 14.4 mmol) was suspended in 11 ml 2,4-
lutidine (neat) and heated to 80 8C. The suspension
turned from yellow to bright purple in approximately 7
min. The resulting solution was filtered hot through
Celite. Purple crystals of NiCl2(2,4-lut)2 began to form
immediately. The crystals that formed were isolated and
washed with pentane to afford a total yield of 3.13 g
(91.8%) of purple crystals.
4.5. Preparation of [Me2NN]NiEt(2,4-lut) (7)
Tl[Me2NN] (3.00 g, 5.90 mmol) was dissolved in 5 ml
THF and added to a stirring suspension of 1 (2.02 g 5.90
mmol) in 10 ml THF at room temperature (r.t.). The
purple solution immediately turned deeper purple and
became cloudy. Thallium chloride was removed by
filtration through Celite. A chilled (ꢂ
of CH3CH2MgCl (2.58 ml, 5.90 mmol, 2.29 M in Et2O)
in 5 ml THF was added with stirring to the chilled (ꢂ
/
30 8C) solution
/
4.3. Isolation of {[Me2NN]NiCl}2 (4)
30 8C) filtrate. The purple solution turned red quickly,
deepening in color over 3 min. The THF was removed
under vacuum and the remaining solids were extracted
with 15 ml ether. Magnesium salts were precipitated by
the addition of dioxane (0.52 g, 5.9 mmol) with stirring.
The mixture was filtered through Celite, and the filtrate
was concentrated to 7 ml under vacuum. Crystallization
occurred as the solution was concentrated, and the
Tl[Me2NN] (1.00 g, 1.96 mmol) in 2 ml THF was
added to a stirring suspension of 1 (0.465 g, 1.96 mmol)
in approximately 5 ml THF. A white precipitate formed
quickly. After stirring for 1 h, the solution was filtered
through Celite to remove TlCl, concentrated, and left to
stand for 2 days at ꢂ30 8C. A few black crystals
/
formed and one was characterized by X-ray.
solution was left to stand at ꢂ
crystals that formed were collected and dried under
vacuum to afford a total yield of 2.024 g (69%) of redꢁ
orange crystals in two crops. 1H NMR (C6H5CH3-d8, ꢂ
/
35 8C overnight. The
4.4. Preparation of [Me2NN]NiMe(2,4-lut) (6)
/
/
[Me2NN]Tl (2.51 g, 4.93 mmol) was dissolved in 5 ml
THF and added with stirring to a suspension of
NiCl2(2,4-lut)2 (1.69 g, 4.93 mmol) in 15 ml THF.
Over 5 min, the solution turned deeper purple and
became cloudy. The precipitate was then allowed to
settle and the solution was filtrated through Celite. After
40 8C): d 7.47 (d, 1, lut), 7.13, 7.11, 7.09, 7.05, 7.04,
7.01, 6.99, 6.95 (aromatic), 6.65 (t, 1, lut), 6.31 (d, 1, lut),
5.87 (s, 1, lut), 5.59 (d, 1, lut), 5.03 (s, 1, H-backbone),
3.79 (s, 3, lut-CH3), 3.25 (s, 3, ArÃ
CH3), 2.54 (s, 3, ArÃCH3), 1.61, 1.55, 1.49, 1.45 (s, 3,
CH3; 1 ArÃMe, 1 lutÃMe, 2 backbone Me), 0.13 (q, 1,
NiCH2CH3), 0.06 (q, 1, NiCH2CH3), ꢂ0.43 (t, 3,
NiCH2CH3); 13C NMR (THF-d8, ꢂ
40 8C): d 159.66,
/
CH3), 2.81 (s, 3, ArÃ
/
/
/
/
chilling the filtrate to ꢂ
(1.44 ml, 4.93 mmol, 3.42 M in Et2O) in 5 ml THF was
added with stirring. The purple solution turned orangeꢁ
/
35 8C, a solution of MeMgBr
/
/
/
158.81, 158.77, 151.98, 151.41, 150.38, 146.73, 133.75,
133.50, 132.58, 131.71, 128.54, 128.26, 128.01, 127.91,
124.94, 123.95, 123.46, 121.79, 97.28 (backbone C),
27.42, 23.80, 20.73, 20.45, 19.76, 19.36, 17.83, 13.84
red immediately, becoming deeper in color over 5 min.
The volatiles were removed in vacuo and the remaining
solids were dissolved in 20 ml ether. The Mg salts were
precipitated by addition of dioxane (0.434 g, 4.93 mmol)
with stirring. After the solids were allowed to settle, the
solution was filtered through Celite and the filtrate was
concentrated leading to partial crystallization. The
(Cb), 8.84 (Ca); JCaÃH
ꢀ
/
128.07 Hz, JCbÃH
Anal. Calc. for C30H39N3: C, 72.01; H, 7.87; N,
ꢀ124.68;
/
8.40%. Found: C, 71.71; H, 7.92; N, 8.20.
solution was left to further crystallize at ꢂ
/
35 8C
4.6. Preparation of [Me2NN]NiPr(2,4-lut) (8)
overnight. Redꢁorange crystals were collected on a
/
frit, washed with ether (5 ml), and dried by vacuum to
1
afford 1.052 g (44% yield) of the product. H NMR
Tl[Me2NN] (0.714 g, 1.40 mmol) was dissolved in 2 ml
THF and added to a stirring suspension of 1 (0.481g
1.40 mmol) in 5 ml THF at r.t. The purple solution
immediately turned deeper purple and became cloudy.
(THF-d8, ꢂ
6.80, 6.79, 6.77, 6.75 (aromatic), 6.60 (t, 1, Ar), 6.37 (d,
1, Ar), 6.19 (d, 1, ArÃlut), 4.80 (s, 1, H-backbone), 3.78
(s, 3, lutÃCH3), 2.98 (s, 3, ArÃCH3), 2.52 (s, 3, ArÃ
CH3), 2.28 (s, 3, ArÃCH3), 2.05, 1.72, 1.36, 1.32 (s, 3,
CH3; 1 ArÃMe, 1 lutÃMe, 2 backbone Me), ꢂ1.64 (s, 3,
Nià 40 8C): d 159.07,
CH3); 13C NMR (THF-d8, ꢂ
/
40 8C): d 7.68 (d, 1, lut), 6.95, 6.92, 6.91,
/
After removal of the TlCl precipitate, a chilled (ꢂ
/
/
/
/
30 8C) solution of CH3CH2CH2MgCl (0.70 ml, 1.4
mmol, 2.0 M in Et2O) in 2 ml THF was added with
/
/
/
/
stirring to the chilled (ꢂ30 8C) filtrate. The purple
/
/
/
solution turned red quickly, deepening in color over 3
min. The THF was removed under vacuum and the
remaining solids were dissolved in 10 ml ether. Magne-
158.93, 158.55, 152.49, 151.45, 151.02, 146.74, 133.46,
133.16, 132.20, 131.81, 128.14, 128.11, 127.92, 127.86,

206
H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ208
/
sium salts were precipitated by the addition of dioxane
(0.12 g, 1.4 mmol) with stirring. The mixture was filtered
through Celite, and the filtrate was concentrated to 4 ml
under vacuum. Crystallization occurred as the solution
was being concentrated, and the solution was left to
4.9. Addition of ethylene to 6
Complex 6 (0.030 g, 0.059 mmol) was placed into an
NMR tube and dissolved in C6D6. One equiv. of
1
ethylene at 1 atm was added by syringe and H spectra
stand at ꢂ
/
35 8C overnight. The crystals that formed
were taken. After 2 min, new b-agostic signals at d ꢂ
and ꢂ7.3 ppm appeared. The signals at d 5.24 ppm
(C2H4) and ꢂ5.27 ppm (NiÃCH2CH3) had disappeared
/
2.7
were collected and dried under vacuum to afford 0.423 g
1
(62%) of red crystals in one crop. H NMR (C6H5CH3-
/
/
/
d8, ꢂ
/
50 8C): d 7.47 (d, 1, lut), 7.13, 7.11, 7.09, 7.05,
after 30 min, suggesting propagation and initiation
7.04, 7.01, 6.99, 6.96 (aromatic), 6.65 (t, 1, lut), 6.30 (d,
1, lut), 5.84 (s, 1, lut), 5.57 (d, 1, lut), 5.02 (s, 1, H-
occur at comparable rates.
backbone), 3.79 (s, 3, lutÃ
2.82 (s, 3, ArÃCH3), 2.53 (s, 3, ArÃ
1.47, 1.44 (s, 3, CH3; 1 ArÃMe, 1 lutÃ
Me), 1.85 (m, 1, NiCH2CHAHB), 0.91 (m, 1, NiCH2-
CHAHB), 0.56 (t, 3, NiCH2CH2CH3), ꢂ0.037 (m, 1,
NiCHAHB), ꢂ
0.502 (m, 1, NiCHAHB); 13C NMR
(THF-d8): d 159.29, 158.47, 158.41, 151.76, 151.13,
150.13, 146.49, 133.59, 133.24, 132.28, 131.38, 128.09,
127.81, 124.72, 123.74, 123.29, 121.66, 123.46, 97.22
(backbone C), 27.54, 24.04, 23.12, 20.98, 20.59, 20.02,
19.58, 17.94 (Cb), 16.33 (Cg), 16.08 (Ca); Anal. Calc. for
C31H41N3Ni: C, 72.39; H, 8.03; N, 8.17. Found: C,
72.54; H, 8.18; N, 7.82%.
/
CH3), 3.28 (s, 3, ArÃ
CH3), 1.62, 1.55,
Me, 2 backbone
/
CH3),
4.10. Structure determinations and crystal data for 4ꢁ7
/
/
/
/
/
Single crystals of each compound were mounted
under mineral oil on glass fibers and immediately placed
/
in a cold nitrogen stream at ꢂ
SMART CCD system. Full spheres of data were
collected (0.38 v-scans; 2umax 568; monochromatic
/
100(2) 8C on a Bruker
/
ꢀ
/
˚
0.7107 A) and integrated with
Mo Ka radiation, lꢀ
the Bruker SAINT program. Structure solutions were
performed using the SHELXTL/PC suite and XSEED [57ꢁ
/
/
59]. Intensities were corrected for Lp effects and an
empirical absorption correction was applied using
Blessing’s method as incorporated into the program
SADABS [60]. Non-hydrogen atoms were refined with
aniostropic thermal parameters and hydrogen atoms
were included in idealized positions. Positional disorder
was observed in the propyl group of 7 and was modeled
4.7. Determination of DH and DS for [Me2NN]Ni(2,4-
lut)Et
using a 60/40 ratio of two different orientations (C29AÃ
/
A sample of [Me2NN]Ni(2,4-lut)Et (0.047 g, 0.094
mmol) was dissolved in 1 ml of C6H5CH3-d8 in a
1
volumetric flask and transferred in to NMR tube. H
C30AÃC31A/C29BÃC30BÃC31B).
/
/
/
4.10.1. Crystal/refinement details for 4
C21H25ClN2Ni, Mꢀ399.59, black crystal 0.32ꢄ
0.20ꢄ0.12 mm, monoclinic, space group P2(1)/c, aꢀ
12.8726(15), bꢀ
103.535(2)8, Vꢀ
NMR spectra were acquired every 10 8C over the range
/
/
of temperatures ꢂ
nances corresponding to free (d 8.38 ppm) and bound
lutidine (d 7.47 ppm) as well as b-agostic species (d ꢂ
/
30ꢁ
/
60 8C. The integration of reso-
/
/
˚
/
8.9541(10), cꢀ
1948.1(4) A , Zꢀ
/
17.384(2) A, bꢀ
4, mꢀ
1.138 mmꢂ1
T 51.00),
100 8C, 4759 indepen-
0.0829), 3352 reflections ob-
/
/
3
˚
/
/
/
,
5.26 ppm) against an internal standard (C5H12) allowed
the calculation of the equilibrium constants at different
temperatures using the following dependence:
empirical absorption correction (0.755
21 627 reflections collected at ꢂ
dent reflections (Rint
served [I ꢀ2s(I)], 233 refined parameters, R1ꢀ
wR2ꢀ0.1380 (observed reflections), R1ꢀ
wR2ꢀ
/
/
/
ꢀ
/
Keq ꢀf[free lutidine][b-agostic]=[bound lutidine]g
ꢄ[initial concentration]
/
/
0.0600,
0.0968,
/
/
/
0.1505 (all data), max. residual electron density
A van’t Hoff plot of ln K versus 1/T allowed the
calculation of DH (slope) and DS (intercept).
ꢂ3
˚
0.756 and ꢂ
/
1.236 e A
.
4.10.2. Crystal/refinement details for 5
C29H37CN3Ni, Mꢀ486.33, orange plate 0.20ꢄ
0.18ꢄ0.08 mm, monoclinic, space group P2(1)/n, aꢀ
7.759(4), bꢀ
104.137(14)8, Vꢀ
empirical absorption correction (0.795
25 917 reflections collected at ꢂ100 8C, 5132 indepen-
dent reflections (Rint 0.1605), 2228 reflections ob-
served [I ꢀ2s(I)], 308 refined parameters, R1ꢀ
wR2ꢀ0.1104 (observed reflections), R1ꢀ
wR2ꢀ
4.8. Addition of ethylene to 5
/
/
/
/
˚
Complex 5 (0.030 g, 0.060 mmol) was placed into an
NMR tube and dissolved in C6D6. One equiv. of
1
ethylene at 1 atm was added by syringe and H spectra
/
21.837(10), cꢀ
/
15.861(7) A, bꢀ
2606(2) A , Zꢀ4, mꢀ
0.765 mmꢂ1
T 51.00),
/
3
˚
/
/
/
,
/
/
were taken. After 2 min, new b-agostic signals at d ꢂ
and ꢂ7.3 ppm appeared. Although the signal at d 5.24
ppm (C2H4) disappeared after 30 min, the signal at d ꢂ
CH3) remained throughout the experi-
/
2.7
/
/
ꢀ
/
/
/
/
0.0536,
0.1615,
1.64 ppm (NiÃ
/
/
/
ment, suggesting propagation occurs more readily than
initiation.
/
0.1284 (all data), max. residual electron density
ꢂ3
˚
0.487 and ꢂ0.441 e A
/
.

H.L. Wiencko et al. / Inorganica Chimica Acta 345 (2003) 199ꢁ
/
208
207
4.10.3. Crystal/refinement details for 6
C30H39N3Ni, Mꢀ500.35, red chunk 0.38ꢄ
0.45 mm, orthorhombic, space group P2(1)2(1)2(1),
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/
/
0.44ꢄ
/
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2713.6(7) A , Zꢀ
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/
9.8201(15), bꢀ
/
10.8194(10), cꢀ
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/
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˚
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/
4.10.4. Crystal/refinement details for 7
C31H41N3Ni, Mꢀ514.38, red chunk 0.36ꢄ
0.56 mm, orthorhombic, space group P2(1)2(1)2(1),
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aꢀ
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/
10.0300(6), bꢀ
/
11.1256(7), cꢀ
4, mꢀ
0.712 mmꢂ1, empirical absorp-
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/
25.2157(16) A, Vꢀ
/
3
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˚
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/
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/
it@ccdc.cam.ac.uk or www: http://www.cam.ac.uk).
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