Ligand Exchange Reactions of [(tmeda)NiR2] (R = CH2CMe3, CH2SiMe3, CH2CMe2Ph) with N-Heterocyclic Carbenes and Bidentate Phosphines

Article abstract of DOI:10.1021/acs.organomet.0c00262

Bis(alkyl)nickel(II) complexes [(tmeda)NiR2] (R = CH2SiMe3 (1a), CH2CMe3 (1b), CH2CMe2Ph (1c)) can be prepared from [(tmeda)Ni(acac)2] and MgR2. This approach is equivalent to and, in some cases, even superior to the frequently employed reaction of [(py)4NiR2] with Grignard reagents. With [(tmeda)NiR2] as the starting material, ligand exchange reactions with N-heterocyclic carbenes and bidentate phosphines were explored. The reaction of [(tmeda)NiR2] with IiPr2Me2 (IiPr2Me = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) yields three different classes of products: (a) [cis-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-cis) derived from NHC by tmeda replacement, (b) [(IiPr2Me2)(κ-C:C-IiPr2MeCH2)Ni(CH2SiMe3)] (3a) as a result of C-H bond activation of one iPr group of the NHC ligand, and (c) [cis-(IiPr2Me2)2Ni(κ-C:C-CH2CMe2C6H4)] (4c-cis), in which an o-C-H bond of the neophyl ligand has been activated. Addition of depe (depe = Et2PCH2CH2PEt2) to 1a,c results in a clean tmeda replacement to give the corresponding complexes [(dppe)NiR2] (R = CH2SiMe3 (5a), CH2CMe2Ph (5c)). All compounds have been fully characterized by various spectroscopic methods and in most cases by single-crystal X-ray diffraction.

Full text of DOI:10.1021/acs.organomet.0c00262

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Article
Ligand Exchange Reactions of [(tmeda)NiR2] (R = CH2CMe3,
CH2SiMe3, CH2CMe2Ph) with N‑Heterocyclic Carbenes and Bidentate
Phosphines
Andreea Enachi, Matthias Freytag, Jan Raeder, Peter G. Jones, and Marc D. Walter*
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ABSTRACT: Bis(alkyl)nickel(II) complexes [(tmeda)NiR2] (R =
CH2SiMe3 (1a), CH2CMe3 (1b), CH2CMe2Ph (1c)) can be
prepared from [(tmeda)Ni(acac)2] and MgR2. This approach is
equivalent to and, in some cases, even superior to the frequently
employed reaction of [(py)4NiR2] with Grignard reagents. With
[(tmeda)NiR2] as the starting material, ligand exchange reactions
with N-heterocyclic carbenes and bidentate phosphines were
explored. The reaction of [(tmeda)NiR2] with IiPr2Me2 (IiPr2Me =
1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) yields three differ-
ent classes of products: (a) [cis-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-
cis) derived from NHC by tmeda replacement, (b) [(IiPr2Me2)(κ-
C:C-IiPr2MeCH2)Ni(CH2SiMe3)] (3a) as a result of C−H bond activation of one iPr group of the NHC ligand, and (c) [cis-
(IiPr2Me2)2Ni(κ-C:C-CH2CMe2C6H4)] (4c-cis), in which an o-C−H bond of the neophyl ligand has been activated. Addition of
depe (depe = Et2PCH2CH2PEt2) to 1a,c results in a clean tmeda replacement to give the corresponding complexes [(dppe)NiR2] (R
= CH2SiMe3 (5a), CH2CMe2Ph (5c)). All compounds have been fully characterized by various spectroscopic methods and in most
cases by single-crystal X-ray diffraction.
synthetic methodology to the preparation of compounds
[(tmeda)NiR2] (R = CH2SiMe3, CH2CMe3, CH2CMe2Ph).
Moreover, their reactivity toward N-heterocyclic carbenes and
a bidentate phosphine is described.
INTRODUCTION
■
Nickel complexes containing Ni−C bonds are key inter-
mediates in many catalytic processes such as olefin oligo- and
copolymerization, CO insertion, C−H bond activation, and
cross-coupling reactions.1 It is therefore unsurprising that the
synthesis and reactivity of bis(alkyl) Ni(II) complexes of the
type [L2NiR2] have been extensively investigated, along with
the intrinsic reactivity of the σ-Ni−C bond toward the
insertion of small molecules.2−16 Many important contribu-
tions can be traced back to the pioneering work of Carmona
and co-workers.9−16 In their original investigations of [L2NiR2]
(L = monodentate or bidentate ligands), [(py)2NiR2] served as
a useful starting material, being in turn prepared from
[(py)4NiCl2] and the corresponding Grignard reagents,
RMgX.9,17 Alternatively, [(tmeda)NiMe2] is accessible from
the reaction of [(tmeda)MgMe2] and [(tmeda)Ni(acac)2].5,18
The nickel precursor [(tmeda)Ni(acac)2] combines many
advantages; it can be prepared on a multigram scale, and it is
readily purified by crystallization or sublimation.19 In a recent
study we have demonstrated that [(tmeda)CoR2] complexes
can be isolated in good yield and excellent purity when
[(tmeda)Co(acac)2] is treated with dialkylmagnesium re-
agents, MgR2.20 Furthermore, the coordinated tmeda is readily
displaced by bidentate phosphines or N-heterocyclic carbenes
(NHC)21 to form four- and three-coordinate complexes,
respectively.20 In this contribution we extend this general
RESULTS AND DISCUSSION
■
Preparation of [(tmeda)NiR2]. When [(tmeda)Ni-
(acac)2] is treated with dialkylmagnesium reagents (MgR2)
in Et2O at 0 °C, the dialkylnickel compounds [(tmeda)NiR2]
(R = CH2SiMe3 (1a), CH2CMe3 (1b) and CH2CMe2Ph (1c))
are isolated in moderate to good yields (Scheme 1 and Table
1; see the Experimental Section for details).
Complex 1a may also be prepared from [(py)4NiCl2] and
Mg(CH2SiMe3)Cl to yield [(py)2Ni(CH2SiMe3)2] followed by
tmeda addition.9 Nevertheless, Carmona and co-workers
explicitly stated, in the same publication in which 1a was
described, that the reaction of [(py)4NiCl2] with Mg-
(CH2CMe2Ph)Cl in the presence of excess tmeda yielded a
Received: April 16, 2020
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whereas 1b,c should be kept at low temperature (−30 °C) for
long-term storage. Table 1 gives some physical properties of
these compounds, including their decomposition points in the
solid state.
Scheme 1. Synthesis of [(tmeda)2NiR2] Compounds (1a−c)
and Subsequent Ligand Exchange Reactions with IiPr2Me2
(IiPr2Me = 1,3-Diisopropyl-4,5-dimethylimidazol-2-ylidene)
Considering the low thermal stability of 1b in solution and
the reported difficulties associated with the synthesis of 1c,9 we
decided to probe their thermal stability and to identify the
decomposition products formed in solution. In a C6D6 solution
compounds 1b,c slowly decompose to form a nickel mirror and
organic byproducts, which were identified by GC/MS
investigations and NMR spectroscopy. For 1b tmeda, 2,2,5,5-
tetramethylhexane, and neopentane are found in a ratio of ca.
4:3:1 (see the Supporting Information for details), whereas 1c
degrades in solution to tmeda and 2-methyl-2-phenylpropane
in an approximate ratio of 3:1 (see the Supporting Information
for details).
Nevertheless, 1a,b can be crystallized from hexane at −30
°C, whereas THF is required for the crystallization of 1c. This
allowed X-ray diffraction data for 1a−c to be collected (Table
S1 in the Supporting Information). Compounds 1a,b
crystallize in the monoclinic space groups C2/c and P21/n,
respectively, while the orthorhombic space group Pbcn was
adopted by 1c; 1a,c display crystallographic 2-fold symmetry.
The molecular structure of 1b is shown in Figure 1, while the
Table 1. Selected Physical Properties
complex
color
mp/°C
79 (dec)
yield/%
80
tmeda Adducts
yellow-
brown
brown
red-brown
red
[(tmeda)NiMe2] (1Me)
a
1a
1b
1c
87−88 (dec)
57−61 (dec)
81 [61]
56
51
102−104
(dec)
IiPr2Me2 (cis Adducts)
Figure 1. Molecular structure of 1b (thermal ellipsoids drawn with
50% probability). Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ni−C6 1.9505(16), Ni−C1
1.9550(16), Ni−N1 2.1066(15), Ni−N2 2.1194(16); C6−Ni−C1
89.60(7), C6−Ni−N1 159.10(7), C1−Ni−N1 97.22(7), C6−Ni−N2
97.06(6), C1−Ni−N2 159.71(7), N1−Ni−N2 83.31(6); τ4 = 0.29.
[cis-(IiPr2Me2)2NiMe2] (2Me- orange
cis)
141−143
68
49
33
45
(dec)
2a-cis
brown
brown
brown
117−119
(dec)
3a
145−147
(dec)
4c-cis
207 (dec)
ORTEP representations of 1a,c are available in the Supporting
Information. Selected bond distances for complex 1b are
provided in the figure caption, while those for compounds 1a,b
are given in the Supporting Information. All bond distances
and angles are within the typical range observed for
diamagnetic square-planar Ni(II, d8) complexes. Compounds
1a−c feature only slight deviations from an ideal square-planar
arrangement, as expressed by the τ4 parameter,22 which can be
readily computed using the equation τ4 = [360° − (α + β)]/
141°, in which α and β are defined as the largest angles within
the four-coordinate species. Therefore, the values of τ4 are 1.0
and 0 for ideal tetrahedral and square-planar coordinations,
respectively. The crystallographic studies on 1a,b complement
those on the related iron and cobalt derivatives [(tmeda)M-
(CH2SiMe3)2] (M = Fe,23 Co24) and [(tmeda)M-
(CH2CMe3)2] (M = Fe,25 Co24).
IiPr2Me2 (trans Adduct)
2a-trans
yellow
154−156
37
(dec)
depe Adducts
brown
5a
5c
98−99
52
68
yellow
116−119
(dec)
a
Two alternative synthetic protocols were used (see the Experimental
Section for details).
solid tentatively assigned as 1c, which however rapidly
decomposed on attempted recrystallization.9 This problem
was not encountered using our synthetic approach; further-
more, we also succeeded in isolating the so far unknown Ni
neopentyl derivative 1b. Nevertheless, the thermal stability of
[(tmeda)NiR2] varies significantly depending on the alkyl
substituent, with 1b being the least stable within this series.
Thus, complex 1a can be stored at ambient temperature,
Ligand Exchange Reactions of [(tmeda)NiR2] (1a−c).
In an initial screening, various NHC ligands (including ItBu
B
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(ItBu = 1,3-di-tert-butylimidazol-2-ylidene) and IMes (IMes =
1,3-dimesitylimidazol-2-ylidene)) and sterically demanding
phosphines (such as P(C6H2(OMe)3-2,4,6)3 and PtBu3)
were added to 1a, resulting either in decomposition
(P(C6H2(OMe)3-2,4,6)3) or the isolation of unreacted starting
materials (PtBu3) (see the Supporting Information for details).
This is in contrast with the observations for the methyl
derivative [(tmeda)NiMe2] (1Me), which forms Ni(0)
compounds [(NHC)2Ni] upon treatment with various steri-
cally encumbered NHC ligands (IMes, IDipp = 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene, SIiPr = 1,3-bis(2,6-
diisopropylphenyl)imdiazolin-2-ylidene, SItBu = 1,3-di-tert-
butyl-4,5-imidazolin-2-ylidene) as a result of tmeda decoordi-
nation and reductive elimination.26 Only in the case of the
sterically less encumbered IiPr2Me2 (IiPr2Me2 = 1,3-
diisopropyl-4,5-dimethylimidazol-2-ylidene) was [cis-
(IiPr2Me2)2NiMe2] (2Me-cis) isolated.26 This along with two
examples containing chelating di-N-heterocyclic carbene
systems27 constitute the only characterized Ni(II) complexes
with two cis-positioned NHC ligands. Nevertheless, when
2Me-cis is heated in C6D6 solution at 50 °C, it converts to
[(IiPr2Me2)2Ni] and organic byproducts (methane and
ethane).26 In contrast to the facile degradation of 2Me-cis in
solution (vide supra),26 decomposition in the solid state occurs
at much higher temperatures (141−143 °C) (see the
Supporting Information for details).
On the basis of the successful synthesis of 2Me-cis, we
decided to study the ligand exchange reactions of 1a,c with
IiPr2Me2 in more detail (Scheme 1). The reactivity patterns of
1a,c, however, are significantly different from those observed
for 2Me-cis.26,28 For example, the more sterically encumbered
derivative 1a forms two different products depending on the
1a:IiPr2Me2 ratio employed in the ligand exchange reaction. A
1:2 mixture of 1a and IiPr2Me2 yields the expected product
[cis-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-cis) in 49% crystallized
yield (Scheme 1). In contrast, the C−H bond activation
product, the metallacycle [(IiPr2Me2)(κ-C:C-IiPr2MeCH2)Ni-
(CH2SiMe3)] (3a), is isolated in 33% yield from a 1:1
1a:IiPr2Me2 mixture under otherwise identical reaction
conditions (Scheme 1). C−H bond activation of an iPr
group of the IiPr2Me2 ligand is not a common phenomenon
but has been previously observed for Ru,29−33 Ir,34 and Fe35
complexes. To establish whether 2a-cis can thermally be
converted to 3a, a C6D6 solution of 2a-cis was heated at 65 °C
for 7 h, forming a mixture containing 2a-trans, 3a, and SiMe4
in an approximate ratio of 1:1.2:1.5 (see the Supporting
Information for details). However, a clean isomerization from
2a-cis to 2a-trans can be achieved when 1 equiv of IiPr2Me2 is
added to a C6D6 solution of 2a-cis and the reaction mixture is
heated to 70 °C for 14 h (see the Supporting Information for
details).36
metallacycle in the presence of PMe3 was traced to the ability
of phosphine ligands to induce δ-H abstraction processes.38
This can also be demonstrated for 1a,c. Addition of PMe3 to a
C6D6 solution of 1a results in the formation of the known cis-
and trans-[(Me3P)2Ni(CH2SiMe3)2] adducts in a ratio of ca.
2:1. It should be noted that this ratio is different from that
observed when [(py)2Ni(CH2CMe2Ph)2] is used as the
starting material; in this case a ratio of ca. 4:1 for the
formation of cis- and trans-[(Me3P)2Ni(CH2SiMe3)2] adducts
was established.9 Nevertheless, when 1c is exposed to PMe3,
the metallacycle [(tmeda)Ni(κ-C:C-CH2CMe2C6H4)] is iso-
lated (Figure 2).
Figure 2. Molecular structure of [(tmeda)Ni(κ-C:C-
CH2CMe2C6H4)] (thermal ellipsoids drawn with 50% probability).
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni−C1 1.9303(10), Ni−C6 1.9120(10), Ni−N1
2.0648(9), Ni−N2 2.0527(9); C6−Ni−C1 81.56(4), C6−Ni−N2
173.96(4), N1−Ni−N2 85.94(4)°; τ4 = 0.07.
Overall, the isolation of complexes 2a-cis, 3a, and 4c-cis
nicely illustrates how subtle changes in steric properties and
bond dissociation energies can significantly modulate the
reaction outcome.
All NHC adducts were fully characterized, including their X-
ray structures. Single crystals were obtained from hexane or
Et2O solutions at −30 °C (see the Experimental Section and
the Supporting Information for details). The molecular
structures of 2a-cis, 3a, and 4c-cis are shown in Figures 3−5,
respectively, and selected bond distances and angles are
included in the respective figure captions.
In contrast to 2a-cis, 3a, and 4c-cis, in which two NHC
ligands are cis-positioned, several examples of thermally very
robust Ni compounds with NHC ligands in a trans
arrangement are known.39,40 Furthermore, complexes of the
type [trans-(NHC)2NiR2] constitute interesting starting
materials in Ni(II) chemistry and are readily prepared from
[trans-(NHC)2NiBr2] and suitable alkyl transfer reagents.39 So
far only [trans-(IiPr2)2NiR2] (R = Me, CH2SiMe3, butyl)
derivatives are known.39,41 We have now extended this
approach to the IiPr2Me2 derivative [trans-(IiPr2Me2)2NiR2]
(R = CH2SiMe3 (2a-trans) (Scheme 2). It is noteworthy that
the trans isomer (2a-trans) is significantly more thermally
stable than the corresponding cis isomer (2a-cis) (Table 1).
The molecular structure of 2a-trans is shown in Figure 6 with
selected bond distances and angles given in the figure caption.
While in the cis isomer 2a-cis the Ni−C bonds to the IiPr2Me2
and neosilyl ligands are essentially identical (ca. 1.952(2) Å),
they differ significantly in the trans isomer 2a-cis (Ni−
C(NHC) 1.905 Å vs Ni−C(neosilyl) 2.032 Å). These metric
values are in good agreement with other structurally
An alternative C−H bond activation product is observed for
1c on treatment with IiPr2Me2 (2 equiv). In this case, no C−H
bond activation of the NHC ligand occurs; instead, the
aromatic C−H bond on the neophyl (=CH2CMe2Ph) moiety
is activated to yield [cis-(IiPr2 Me2 )2 Ni(κ-C:C-
CH2CMe2C6H4)] (4c-cis) (Scheme 1). In group 10 chemistry,
ortho activation of a neophyl ligand has previously been
reported for [L2M(CH2CMe2Ph)2] (where M = Pt, Ni and L2
= bipy, Me2bipy, tBu2bipy),37 [L2M(CH2CMe2Ph)(OC6H3-
2,6-Me2] (L2 = iPr2P(CH2)nPiPr2 (n = 2, 3)),38 and
[(py)2M(CH2CMe2Ph)2] (in the presence of catalytic
amounts of PMe3).11 In these studies the formation of a
C
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Figure 3. Molecular structure of 2a-cis (thermal ellipsoids drawn with
50% probability). Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ni−C1 1.9524(15), Ni−C12
1.9541(15), Ni−C23 2.0027(15), Ni−C27 2.0046(15); C1−Ni−C12
98.54(6), C1−Ni−C23 172.59(6), C12−Ni−C23 87.57(6), C1−Ni−
C27 89.08(6), C12−Ni−C27 171.84(6), C23−Ni−C27 85.05(7); τ4
= 0.11. The molecule displays noncrystallographic 2-fold symmetry
(rms deviation 0.07 Å).
Figure 5. Molecular structure of 4c-cis (thermal ellipsoids drawn with
50% probability). Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ni−C23 1.9238(17), Ni−C1
1.9273(16), Ni−C12 1.9444(16), Ni−C30 1.9720(17); C23−Ni−C1
167.10(7), C23−Ni−C12 92.21(7), C1−Ni−C12 97.40(7), C23−
Ni−C30 82.12(7), C1−Ni−C30 90.01(7), C12−Ni−C30 167.51(7);
τ4 = 0.18.
Scheme 2. Synthesis of [trans-(IiPr2Me2)2Ni(CH2SiMe3)2]
(2a-trans)
Figure 4. Molecular structure of 3a (thermal ellipsoids drawn with
50% probability). Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ni−C1 1.9081(11), Ni−C12
1.9215(11), Ni−C5 1.9786(12), Ni−C23 2.0004(11); C1−Ni−C12
98.83(5), C1−Ni−C5 81.27(5), C12−Ni−C5 171.88(5), C1−Ni−
C23 170.74(5), C12−Ni−C23 88.85(5), C5−Ni−C23 90.39(5); τ4 =
0.12.
Figure 6. Molecular structure of 2a-trans (thermal ellipsoids drawn
with 50% probability). Hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): Ni−C1 1.9071(11),
Ni−C12 1.9019(11), Ni−C23 2.0349(11), Ni−C27 2.0317(11);
C1−Ni−C12 171.79(5), C12−Ni−C27 87.70(4), C1−Ni−C27
93.38(4), C12−Ni−C23 91.77(4), C1−Ni−C23 86.28(4), C23−
Ni−C27 173.73(5); τ4 = 0.10.
characterized Ni-NHC complexes27,39,42−45 and can be
attributed to the different trans-influence of alkyl and NHC
ligands, respectively.
To establish that the tmeda ligand can also be displaced by
the bidentate phosphine ligands, a THF solution of depe (depe
= Et2P(CH2)2PEt2) was added to 1a,c to yield the expected
derivatives 5a,c, respectively (Scheme 3). Both compounds
were characterized by NMR spectroscopy and elemental
analyses and in addition by X-ray diffraction for 5c (Table
S1 in the Supporting Information). The NMR data for 5a are
in good agreement to those obtained for [(dippe)Ni-
( C H 2 Si Me 3 ) 2 ] a n d [ ( d i p p p ) N i ( C H 2 S i M e3 ) 2 ]
(iPr2(CH2)nPiPr2; n = 2 (dippe) and n = 3 (dippp)).38 The
molecular structure of 5c is shown in Figure 7, with selected
bond distances and angles given in the figure caption.
However, as ligand substitution reactions are not limited to
NHC and bidentate phosphine ligands, we also briefly explored
D
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chemical shifts are reported in δ units with reference to the residual
protons of the deuterated solvents, which served as internal standards
for proton chemical shifts.
Scheme 3. Synthesis of [(dppe)NiR2] (R = CH2SiMe3 (5a),
CH2CMe2Ph (5c))
Single crystals were examined under inert oil. Data collection was
performed at 100 K on various Oxford Diffraction or Rigaku-Oxford
diffractometers with monochromated Mo Kα or mirror-focused Cu
Kα radiation. Further details, including crystal and data collection
parameters, are provided in the Supporting Information, in particular
Tables S1 and S2. Anisotropic refinement was performed on F2 using
SHELXL-2017.46
[(tmeda)Ni(acac)2],5 MgR2,47,48 IiPr2Me2,49 and [trans-
(IiPr2Me2)2NiBr2]40 were prepared according to literature proce-
dures. MgMe2 was prepared from the MeMgBr Grignard to avoid
contamination by traces of halides.
[(tmeda)Ni(CH2SiMe3)2] (1a). Method A. To a cooled solution
(−30 °C) of [(tmeda)Ni(acac)2] (500 mg, 1.34 mmol) in Et2O (20
mL) was added dropwise a cold solution (−30 °C) of [Mg-
(CH2SiMe3)2] (267 mg, 1.34 mmol) in Et2O (20 mL). The reaction
mixture was stirred for 4 h at −30 °C and for an additional 1 h at
room temperature. During this time a colorless precipitate formed.
The solvent was removed under dynamic oil pump vacuum; the
brown residue was extracted with n-hexane (30 mL) and the solution
centrifuged (30 min, 4500 rpm, 10 °C). The filtrate was collected, and
the solvent was removed under dynamic vacuum. The brown residue
was dissolved in a minimum amount of n-hexane (5 mL) and cooled
to −30 °C for 2 days. The product was isolated as a brown crystalline
material, which was stable at ambient temperature. Yield: 61% (287
mg, 0.82 mmol).
Method B. To a cooled solution (0 °C) of [(tmeda)Ni(acac)2]
(300 mg, 0.8 mmol) in Et2O (6 mL) was added dropwise a solution
of [(tmeda)Mg(CH2SiMe3)2] (254 mg, 0.81 mmol) in Et2O (6 mL).
The reaction mixture was stirred for 2 h at 0 °C and an additional 20
min at room temperature. The solvent was removed under dynamic
vacuum, the brown residue was extracted with n-hexane (20 mL), and
the solution was filtered through a pad of Celite. The solvent was
removed under dynamic oil pump vacuum; the brown crude product
was redissolved in a minimum amount of n-hexane (2 mL) and cooled
to −30 °C for 2 days. The product was isolated as a brown crystalline
material. Yield: 81% (226 mg, 647 mmol).
Figure 7. Molecular structure of 5c (thermal ellipsoids drawn with
50% probability). Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Ni−C1 2.0079(19), Ni−P
2.1944(6); C1#−Ni−C1 91.32(11), C1−Ni−P# 170.06(5), C1−Ni−
P 92.12(5), P#−Ni−P 86.05(3); τ4 = 0.14. The molecule displays
crystallographic 2-fold symmetry.
the reactivity of 1a with mono- and bidentate amine ligands
such as DMAP (=4-(dimethylamino)pyridine) and tBu2bipy
(=4,4′-di-tert-butyl-2,2′-dipyridyl) (see the Supporting Infor-
mation for details). After moderate heating (1 h, 50 °C) of 1a
in the presence of these amine ligands, partial tmeda
substitution could be achieved for the monodentate DMAP
ligand to yield [cis-(dmap)2Ni(CH2SiMe2)2], whereas smooth
tmeda exchange for tBu2bipy can be realized to form
[(tBu2bipy)Ni(CH2SiMe2)2].
Mp: 87−88 °C (dec). Anal. Calcd for C14H38N2NiSi2 (349.34 g/
mol): C, 48.14; H, 10.96; N, 8.02. Found: C, 48.36; H, 11.07; N,
7.77. 1H NMR (300 MHz, C6D6, 300 K): δ −1.52 (s, 4H, 2
CH2SiMe3), 0.60 (s, 18H, SiMe3), 1.23 (s, 4H, 2 CH2), 1.86 (s, 12H,
4 CH3) ppm. No exchange on the NMR time scale was observed
when free tmeda was added to C6D6 solutions of 1a. 13C{1H} NMR
(75 MHz, C6D6, 300 K): δ −15.14 (s, CH2SiMe3), 5.47 (s, SiMe3),
47.66 (s, CH3), 58.34(s, CH2-CH2) ppm. UV/vis (THF, 22 °C, nm):
250 (ε = 23677 L mol−1 cm−1), 453 (ε = 560 L mol−1 cm−1).
[(tmeda)Ni(CH2CMe3)2] (1b). To a cooled solution (0 °C) of
[(tmeda)Ni(acac)2] (160 mg, 0.43 mmol) in Et2O (5 mL) was added
a mixture of [Mg(CH2CMe3)2] (79 mg, 0.47 mmol) and tmeda (54.8
mg, 0.47 mmol) in Et2O (8 mL) dropwise. The reaction mixture was
stirred for 2 h at 0 °C and an additional 30 min at ambient
temperature. The solvent was removed under dynamic vacuum, and
the red-brown residue was kept under dynamic high vacuum for an
additional 6 h. The crude product was extracted with n-hexane (3
mL) and the solution cooled to −30 °C for 2 days. The product was
isolated as a red-brown crystalline material. Yield: 56% (76 mg, 0.239
mmol). The product had to be stored at −30 °C to avoid degradation.
Mp: 57−61 °C (dec). Anal. Calcd for C16H38N2Ni (317.19 g/mol):
C, 60.59; H, 12.08; N, 8.83. Found: C, 58.99; H, 11.78; N, 8.44.
Despite repeated efforts, the low melting point and the high air and
moisture sensitivity of 1b prevented us from obtaining better
CONCLUSIONS
■
[(tmeda)Ni(acac)2] serves as a convenient starting material for
the bis(alkyl) Ni(II) complexes [(tmeda)NiR2] in acceptable
yields. It therefore represents an alternative to the well-
established [(py)4NiCl4] route. Ligand exchange reactions in
[(tmeda)NiR2] toward NHC ligands were studied, establishing
a delicate balance between steric properties and C−H
dissociation energies of the NHC and alkyl ligands. We are
currently exploring the potential of [(tmeda)NiR2] as starting
materials in other ligand exchange reactions and as precursors
for the synthesis of catalytically active species. Preliminary
catalytic applications of precatalyst 3a such as in the
dehydrocoupling of organosilanes are currently under inves-
tigation.
EXPERIMENTAL SECTION
■
General Considerations. All experiments were performed under
an atmosphere of dry nitrogen by using standard Schlenk and
glovebox techniques. Solvents were dried and deoxygenated by
distillation under a nitrogen atmosphere from sodium benzophenone
ketyl (THF, pentane, diethyl ether, hexane, toluene). Elemental
analyses were performed by combustion and gas chromatographic
analyses with an elementar varioMICRO or elementar varioMICRO
CUBE instrument. NMR spectra were recorded on a Bruker AVII300,
Bruker AVIIIHD300N, or Bruker AVIII400 spectrometer. All
1
elemental analysis data. H NMR (300 MHz, C6D6, 300 K): δ 0.00
(s, 4H, CH2), 1.29 (s, 4H, NCH2), 1.63 (s, 18H, CMe3), 2.00 (s, 12H,
NCH3) ppm. 13C{1H} NMR (75 MHz, C6D6, 300 K): δ 13.26 (s,
CH2), 35.73 (s, CMe3), 36.65 (s, CMe3), 47.91 (s, NCH3), 58.12 (s,
NCH2) ppm. UV/vis (THF, 22 °C, nm): 282 (ε = 16083 L mol−1
cm−1), 466 (sh, ε = 1216 L mol−1 cm−1).
E
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Organometallics XXXX, XXX, XXX−XXX

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Article
[(tmeda)Ni(CH2CMe2Ph3)2] (1c). To a cooled solution (0 °C) of
[(tmeda)Ni(acac)2] (150 mg, 0.4 mmol) in Et2O (5 mL) was added a
mixture of (tmeda) (51 mg, 0.44 mmol) and [Mg(CH2CMe2Ph)2]
(128.5 mg, 0.44 mmol) in Et2O (10 mL) dropwise. The reaction
mixture was stirred for 2 h at 0 °C and an additional 30 min at
ambient temperature. The solvent was removed under dynamic
vacuum, and the red-brown residue was kept under dynamic high
vacuum for an additional 6 h. The product was washed with Et2O (5
mL) and filtered through Celite. The dark red solid thus isolated was
dissolved in THF (2 mL) and cooled to −30 °C for 2 days. The
product was isolated as a dark red crystalline material. Yield: 51% (90
mg, 0.204 mmol). To avoid degradation, the product was stored at
−30 °C. Mp: 102−104 °C (dec). Anal. Calcd for C26H42N2Ni
(441.33 g/mol): C, 70.76; H, 9.59; N, 6.35. Found: C, 70.63; H, 9.63;
(s, CHCH3), 124.57 (s, CCH3), 197.64 (s, NCN) ppm. UV/vis
(Et2O, 22 °C, nm): 422 (br, ε = 957 L mol−1 cm−1), 266 (ε = 15758
L mol−1 cm−1), 222 (ε = 22091 L mol−1 cm−1).
[(IiPr2Me2)(κ-C:C-IiPr2MeCH2)Ni(CH2SiMe3)] (3a). An oven-
dried sealable Schlenk flask was charged with [(tmeda)Ni-
(CH2SiMe3)2] (1a; 380 mg, 1.088 mmol), IiPr2Me2 (196 mg, 1.087
mmol), and 15 mL of toluene. The vessel was sealed, and the contents
were stirred for 4 h on an oil bath (50 °C). After this time, the volatile
material was removed under dynamic oil pump vacuum and the dark
brown residue extracted with 4 mL of n-hexane. The resulting
solution was filtered through a pad of Celite and cooled for 5 days at
−30 °C. The product was isolated as a brown crystalline material.
Yield: 33% (90 mg, 0.178 mmol). Mp: 145−147 °C (dec). Anal.
Calcd for C26H50N4NiSi (505.49 g/mol): C, 61.78; H, 9.97; N, 11.08.
Found: C, 61.41; H, 9,93; N, 10.88. 1H NMR (400 MHz, C6D6, 300
1
N, 6.20. H NMR (300 MHz, C6D6, 300 K): δ 0.3 (br s, 4H, CH2),
2
2
1.25 (br s, 4H, CH2), 1.62 (br s, 12H, CH3), 1.73 (s, 12H, CH3), 7.10
(t, 2H, JHH = 7.2 Hz, HAr‑p), 7.21 (t, 4H, J = 7.4 Hz, HAr‑m), 8.3 (d,
4H, JHH = 7.6 Hz, HAr‑o) ppm. 13C{1H} NMR (75 MHz, C6D6, 300
K): δ 14.82 (s, CH2), 35.3 (s, CH3), 42.1 (s, Cq), 47.51 (s, NCH3),
58.12 (NCH2), 124.75, 127.7, 128.1, 154.77 (s, CAr‑q) ppm. UV/vis
(THF, 22 °C, nm): 258 (ε = 10455 L mol−1 cm−1), 372 (sh, ε = 1592
L mol−1 cm−1), 463 (sh, ε = 587 L mol−1 cm−1).
K): δ −0.55 (d, 1H, J = 11 Hz, CH2SiMe3), −0.35 (d, 1H, J = 11
Hz, CH2SiMe3), 0.62 (s, 9 H, CH2SiMe3), 0.81 (d, 3H, JHH = 7 Hz,
CHCH3), 1.03 (d, 3H, JHH = 7 Hz, CHCH3), 1.1 (d, 3H, JHH = 7 Hz,
CHCH3), 1.26 (d, 3H, JHH = 7 Hz, CHCH3), 1.5−1.56 (m, 7H, 2
CHCH3 + H-CH2Ni), 1.64 (d, 3H, JHH = 6.2 Hz, CHCH3), 1.68 (s,
3H, CCH3), 1.71 (s, 3H, CCH3), 1.73 (s, 3H, CCH3), 1.74 (s, 3H,
CCH3), 2.28 (m, 1H, H-CH2Ni), 4.08 (sept, 1H, JHH = 7.14 Hz,
[cis-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-cis). An oven-dried sealable
Schlenk flask was charged with [(tmeda)Ni(CH2SiMe3)2] (1a; 127
mg, 0.364 mmol), IiPr2Me2 (131 mg, 0.727 mmol), and 15 mL of
toluene. The vessel was sealed and stirred for 4 h on an oil bath (50
°C). After this time, the volatile material was removed under dynamic
oil pump vacuum, the dark brown residue was extracted with 2 mL of
n-hexane, and the solution was filtered through a pad of Celite and
cooled for 2 days at −30 °C. The product was isolated as a brown
crystalline material. Yield: 49% (105 mg, 0.176 mmol). Mp: 117−119
°C (dec). Anal Calcd for C30H62N4NiSi2 (593.72 g/mol): C, 60.69;
H, 10.53; N, 9.44. Found: C, 60.51; H, 10.33; N, 9.38. 1H NMR (300
MHz, C6D6, 300 K): δ −0.5 (br s, 4 H, CH2), 0.5 (s, 18H, SiMe3),
1.41 (br.s, 12H, CH3), 1.69 (br s, 12H, CH3), 5.54 (br s, 2H, CH),
7.06 (br.s, 2H, CH) ppm. 13C{1H} NMR (75 MHz, C6D6, 300 K): δ
0.56 (s, CH2), 5.73 (s, SiMe3), 10.78 (s, CCH3), 21.7 (br. s, ν1/2= 26.5
Hz, CHCH3), 23.59 (br s, ν1/2 = 35 Hz, CHCH3), 52.44 (s,
CH(CH3)2), 195.83 (NCN) ppm. UV/vis (Et2O, 22 °C, nm): 223 (ε
= 18189 L mol−1 cm−1), 268 (ε = 19611 L mol−1 cm−1), 319 (sh, ε =
3618 L mol−1 cm−1), 380 (sh, ε = 1028 L mol−1 cm−1).
[trans-(IiPr2Me2)2Ni(CH2SiMe3)2] (2a-trans). Method A. To a
cooled suspension (0 °C) of [trans-(IiPr2Me2)2NiBr2] (57 mg, 0.096
mmol) in Et2O (3 mL) was added [Mg(CH2SiMe3)2] (19.3 mg,
0.097 mmol) in Et2O (4 mL) dropwise. The mixture changed from
red to brown and then to yellow. The reaction mixture was stirred for
30 min in an ice bath and 1 h at rt. The volatiles were removed under
dynamic high vacuum; the brown residue was extracted with n-hexane
(2 mL) and the solution filtered through a pad of Celite. Storage at
−30 °C for 2 days afforded the product as a yellow crystalline
material. Yield: 37% (21 mg, 0.035 mmol). Anal. Calcd for
C30H62N4NiSi2 (593.72 g/mol): C, 60.69; H, 10.53; N, 9.44.
Found: C, 61.49; H, 10.97; N, 9.49.
CHCH3), 4.27 (q, 1H, JHH = 6.7 Hz, CHCH3), 6.06 (sept, 1H, JHH =
7 Hz, CHCH3), 6.9 (sept, 1H, JHH = 7.2 Hz, CHCH3) ppm. 13C{1H}
NMR (100 MHz, C6D6, 300 K): δ −4.4 (s, CH2SiMe3), 6.4 (s,
CH2Si(CH3)3), 9.79 (s, CCH3), 10.66 (s, CCH3), 10.68 (s, CCH3),
11.45 (s, CCH3), 22.02 (s, CHCH3), 22.43 (s, CHCH3), 22.53 (s,
CHCH3), 23.2 (s, CHCH3), 23.48 (s, CHCH3), 24.04 (s, CHCH3),
27.21 (s, CHCH3), 31.47 (s, NiCH2), 50.72 (s, CHCH3), 52.34 (s,
CHCH3), 52.6 (s, CHCH3), 60.12 (s, CHCH3), 121.93 (s, CCH3),
123.24 (s, CCH3), 123.94 (s, CCH3), 124.73 (s, CCH3), 188.54 (s,
NCN), 200.46 (s, NCN) ppm. UV/vis (Et2O, 22 °C, nm): 365 (sh, ε
= 4251 L mol−1 cm−1), 333 (sh, ε = 5219 L mol−1 cm−1), 231 (ε =
22079 L mol−1 cm−1).
[cis-(IiPr2Me2)2Ni(κ-C:C-CH2CMe2C6H4)] (4c-cis). Method A. To
a cooled (−35 °C) solution of [Mg(CH2CMe2Ph)2] (78 mg, 0.268
mmol) in Et2O (3 mL) was added a solution of [(tmeda)Ni(acac)2]
(100 mg, 0.268 mmol) in Et2O (6 mL). The brown reaction mixture
was stirred at −35 °C for 20 min. After the dropwise addition of 2
equiv of IiPr2Me2 (97 mg, 0.546 mmol) in Et2O (4 mL), the reaction
mixture was stirred for an additional 3 h at −35 °C. The volatiles were
removed under dynamic oil pump vacuum, and the brown residue was
extracted with n-hexane (2 mL). The resulting solution was filtered
through a pad of Celite and stored for 2 days at −30 °C. The product
was isolated as a brown crystalline material. Yield: 11% (16 mg, 0.03
mmol).
Method B. To a solution of [(tmeda)Ni(CH2CMe2Ph)2] (27 mg,
0.06 mmol) in C6D6 (0.6 mL) was added IiPr2Me2 (22 mg, 0.122
mmol). The brown reaction mixture was stored at rt for 6 h. The
volatiles were removed under dynamic oil pump vacuum, the brown
residue was extracted with Et2O (2 mL), and the solution was filtered
through a pad of Celite and stored for 2 days at −30 °C. The product
was isolated as a brown crystalline material. Yield: 45% (15 mg, 0.027
mmol).
Method C. To a cooled suspension (0 °C) of [trans-
(IiPr2Me2)2NiBr2] (79 mg, 0.133 mmol) in THF (3 mL) was
added dropwise [Mg(CH2CMe2Ph)2] (39 mg, 0.134 mmol) in THF
(4 mL). A color change from red to brown and then yellow was
observed. Then the reaction mixture was warmed to room
temperature and was stirred at ambient temperature overnight. The
volatiles were removed under dynamic high vacuum, the yellow-
brown residue was extracted with Et2O (2 mL), and the solution was
filtered through a pad of Celite. Storage at −30 °C for 2 days allowed
the isolation of a pale brown crystalline material. Yield: 17% (16 mg,
0.023 mmol).
Mp: 207 °C (dec). Anal. Calcd for C32H52N4Ni (551.49 g/mol): C,
69.69; H, 9.50; N, 10.16. Found: C, 69.47; H, 9.74; N, 9.46. 1H NMR
(600 MHz, C6D6, 300 K): δ: 1.01 (d, 6H, JHH = 7.2 Hz, CHCH3),
1.06 (d, 6H, JHH = 7.2 Hz, CHCH3), 1.21 (d, 6H, JHH = 7.1 Hz,
CHCH3), 1.31 (d, 6H, JHH = 7.1 Hz, CH3), 1.57 (s, 2H, NiCH2), 1.71
Method B. To a solution of [trans-(IiPr2Me2)2NiBr2] (170 mg,
0.287 mmol) in n-hexane (3 mL) was added a solution of
[Li(CH2SiMe3)] (54 mg, 0.573 mmol) in n-hexane (5 mL) dropwise
at ambient temperature. After the addition was complete, a white
suspension had formed. The reaction mixture was stirred at rt for 1 h
and then filtered through a pad of Celite. The solvent from the filtrate
was removed under dynamic high vacuum, and the yellow residue was
extracted with Et2O (2 mL). The product was isolated as a yellow
crystalline material after cooling the solution for 3 days at −30 °C.
Yield: 63% (110 mg, 0.165 mmol). Anal. Calcd for C30H62N4NiSi2
(593.72 g/mol): C, 60.69; H, 10.53; N, 9.44. Found: C, 61.01; H,
10.66; N, 9.15.
1
Mp: 154−156 °C (dec) H NMR (500 MHz, C6D6, 300 K): δ
−1.185 (s, 4H, NiCH2), 0.11 (s, 18H, SiMe3), 1.5 (d, 24H, JHH = 7
i
i
Hz, Pr-CH3), 1.8 (s, 12H, CH3), 6.63 (sept, 4H, JHH = 7.2 Hz, Pr-
CH) ppm. 13C{1H} NMR (125.8 MHz, C6D6, 300 K): δ −7.67 (s,
NiCH2), 4.35 (s, SiMe3), 10.84 (s, CCH3), 23.51 (s, CHCH3), 52.68
F
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Article
(s, 6H, CCH3), 1.74 (s, 6H, CCH3), 1.95 (s, 6H, C(CH3)2), 6.1 (sept,
2H, JHH = 7.1 Hz, CH(CH3)2), 6.23 (sept, 2H, JHH = 7.1 Hz,
CH(CH3)2), 6.78 (dd, 1H, JHH = 7.1 Hz, J = 1.4 Hz, HAr‑o), 7.04 (td,
1H, JHH = 7.2 Hz, JHH = 1.4 Hz, HAr‑p), 7.24 (td, 1H, JHH = 7.2 Hz,
[(depe)Ni(CH2CMe2Ph)2] (5c). To a solution of [(tmeda)Ni-
(CH2CPhMe2)2] (33 mg, 0.075 mmol; dissolved in thf-d8 (0.6 mL))
was added depe (17 mg, 0.08 mmol) at ambient temperature. The
dark red solution turned brown, and a yellow microcrystalline solid
precipitated. The mother liquor was removed by decantation and the
yellow solid dried under dynamic oil pump vacuum. The product is
insoluble in many common solvents (n-hexane, Et2O, THF, benzene)
and only slightly soluble in dichloromethane. Yield: 68% (27 mg, 0.05
JHH = 1.4 Hz, HAr‑m), 7.33 (dd, 1H, JHH = 7.4 Hz, JHH = 1.4 Hz, HAr‑m)
ppm. 13C{1H} NMR (150 MHz, C6D6, 300 K): δ 10.77 (s, CCH3),
10.89 (s, CCH3), 21.99 (s, CHCH3), 22.02 (s, CHCH3), 23.33 (s,
CHCH3), 36.27 (s, C(CH3)2), 46.49 (s, NiCH2), 52.65 (s, CHCH3),
52.81 (s, CHCH3), 121.67 (s, CAr‑m), 122.67 (s, CAr‑m), 123.34 (s,
1
mmol). Mp: 116−119 °C (dec). H NMR (500 MHz, CD2Cl2, 300
K): δ 1.07 (dt, 12H, JHP = 13 Hz, JHH = 7.6 Hz, PCH2CH3), 1.32−
1.44 (m, 12H, NiCH2, PCH2CH3), 1.45 (s, 12H, CCH3), 1.67 (m,
4H, PCH2CH2P), 7.03 (m, 2H, HAr‑p), 7.18 (m, 4H, HAr‑m), 7.52 (m,
4H, HAr‑o) ppm. 13C{1H} NMR (125 MHz, CD2Cl2, 300 K): δ 8.65
(s, PCH2CH3), 16.46 (dd, JCP= 7.3 Hz, JCP= 3.8 Hz, PCH2), 21.62 (t,
C
Ar‑p), 124.22 (s, CCH3), 124.41 (s, CCH3), 140.82 CAr‑o), 169.31 (s,
Cq‑1), 173.72 (s, NiCAr‑o), 197.47 (s, NCN),197.98 (s, NCN) ppm.
UV/vis (Et2O, 22 °C, nm): 360 (sh, ε = 3436 L mol−1 cm−1), 322 (ε
= 5746 L mol−1 cm−1), 258 (sh, ε = 15159 L mol−1 cm−1).
[(tmeda)Ni(κ-C:C-CH2CMe2C6H4)]. Method A. To a solution of
[(tmeda)Ni(CH2CMe2Ph)2] (47 mg, 0.106 mmol) in toluene (10
mL) was added at ambient temperature a solution of PMe3 (2.5 μL,
ca. 2 mg) in toluene (3 mL). The mixture changed from red to brown.
The reaction mixture was stirred at rt for 1 h. After this time, the
volatile material was removed under dynamic oil pump vacuum, the
residue was extracted with Et2O (2 mL), and the solution was filtered
through a pad of Celite. Storage at −30 °C for 4 days afforded the
product as an orange crystalline material. Yield: 46% (15 mg, 0.049
mmol).
Method B. To a cooled solution (0 °C) of [(tmeda)Ni(acac)2]
(150 mg, 0.402 mmol) in Et2O (10 mL) was added dropwise a
mixture of [Mg(CH2CMe2Ph)2] (129 mg, 0.444 mmol) and tmeda
(52 mg, 0.447 mmol) in Et2O (15 mL). The mixture changed from
blue to orange. The reaction mixture was stirred at 0 °C for 2.5 h at
ambient temperature. PMe3 (ca. 5 μL) diluted in Et2O (5 mL) was
added dropwise at ambient temperature. The brown homogeneous
mixture was stirred for 1 h. After this time, the volatile material was
removed under dynamic high vacuum. The pale brown residue was
extracted first with toluene (2 mL) and then with THF (2 mL); both
solutions were filtered through a pad of Celite and stored for 3 days at
−30 °C. The product was isolated as a brown-orange crystalline
material from both crystallizations. Yield: 43% (53 mg, 0.173 mmol).
Mp: 152−155 °C. Anal. Calcd for C16H28N2Ni (307.11 g/mol): C,
62.58; H, 9.19; N, 9.12. Found: C, 61.82; H, 8.91; N, 8.81. The C
value remained low even after addition of V2O5 or WO3, as a
J
CP= 19.5 Hz, PCH2), 27.9 (dd, JCP= 75 Hz, JCP= 18.5 Hz, NiCH2),
35.00 (s, C(CH3)2), 43.28 (s, C(CH3)2), 124.56 (s, CAr‑p), 126.78 (s,
Ar‑o), 127.94 (s, CAr‑m), 157.76 (s, Cq‑Ar) ppm. 31P{1H} NMR (202.5
C
MHz, CD2Cl2, 300 K): δ 41.57 (s) ppm. The EI mass spectrum
showed a molecular ion at m/z 530 amu. The parent ion isotopic
cluster was simulated (calcd %, obsd %): 530 (100, 100), 532 (43,
36), 533 (15, 3).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00262.
■
sı
Experimental details, crystallographic details, UV/vis
spectra, NMR spectra, and ligand exchange studies
(PDF)
Accession Codes
CCDC 1996992−1997007 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
consequence of incomplete combustion. H NMR (600 MHz, THF,
AUTHOR INFORMATION
Corresponding Author
■
300 K): δ 0.64 (br. s, 2H, NiCH2), 1.39 (s, 6H, C(CH3)2), 2.40 (br. s,
4H, tmeda-CH2), 2.50 (s, 6H, tmeda-CH3), 2.66 (s, 6H, tmeda-CH3),
6.50 (m, 2H, HAr‑o,‑m), 6.64 (t, 1H, J = 7.15 Hz, HAr‑m), 7.06 (d, 1H, J
= 7.5 Hz, HAr‑o) ppm. 13C{1H} NMR (150 MHz, THF, 300 K): δ
35.53 (br. s, C(CH3)2), 38.90 (s, NiCH2), 48.16 (s, C(CH3)2), 49.11
(s, tmeda-CH3), 49.63 (s, tmeda-CH3), 61.01 (s, tmeda-CH2), 61.92
(s, tmeda-CH2), 121.41 (s, CAr‑o), 122.62 (s, CAr‑m), 122.98 (s, CAr‑m),
136.92 (s, CAr‑o), 160.28 (s, CAr‑q), 170.59 (s, CAr‑q) ppm. UV/vis
(THF, 22 °C, nm): 403 (sh, ε = 520 L mol−1 cm−1), 325 (ε = 6998 L
mol−1 cm−1), 243 (sh, ε = 12703 L mol−1 cm−1).
[(depe)Ni(CH2SiMe3)2] (5a). To a solution of [(tmeda)Ni-
(CH2SiMe3)2] (1a; 66.5 mg, 0.19 mmol) in n-hexane (6 mL) was
added a solution of depe (39 mg, 0.19 mmol) in n-hexane (4 mL)
dropwise at ambient temperature. The dark brown reaction mixture
was stirred at ambient temperature for 2 h. The solvent was removed
under dynamic vacuum; the dark residue was extracted with a
minimal amount of n-hexane (2 mL), and the solution was stored at
−30 °C for 2 days. The product was isolated as a brown crystalline
material. Yield: 52% (44 mg, 0.10 mmol). Mp: 98−99 °C. Anal. Calcd
for C18H46NiP2Si2 (439.38 g/mol): C, 49.21; H, 10.55. Found: C,
49.51; H, 10.55. 1H NMR (300 MHz, C6D6, 300 K): δ 0.21 (dd, 4H,
Marc D. Walter − Institut fur Anorganische und Analytische
̈
̈
Chemie, Technische Universitat Braunschweig, 38106
Braunschweig, Germany; orcid.org/0000-0002-4682-8749;
Email: mwalter@tu-bs.de
Authors
Andreea Enachi − Institut fu
̈
r Anorganische und Analytische
̈
Chemie, Technische Universitat Braunschweig, 38106
Braunschweig, Germany
Matthias Freytag − Institut fur Anorganische und Analytische
̈
̈
Chemie, Technische Universitat Braunschweig, 38106
Braunschweig, Germany
Jan Raeder − Institut fur Anorganische und Analytische Chemie,
̈
̈
Technische Universitat Braunschweig, 38106 Braunschweig,
Germany
Peter G. Jones − Institut fur Anorganische und Analytische
̈
̈
Chemie, Technische Universitat Braunschweig, 38106
Braunschweig, Germany
JHH = 6 Hz, JHP = 15 Hz, CH2), 0.45 (s, 18H, SiMe3), 0.84 (m, 16H,
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00262
CH2, CH3), 1.39 (m, 8H, CH2CH3) ppm. 13C{1H} NMR (75 MHz,
C6D6, 300 K): δ 1.51 (m, NiCH2, JCP = 17, 64 Hz), 6.01 (s, SiMe3,),
9.12 (s, CH3), 17.78 (d, CH2Me, JCP = 19 Hz), 22.74 (t, CH2CH2, JCP
= 21 Hz) ppm. 31P{1H} NMR (121.49 MHz, C6D6, 300 K): δ 54.79
(s) ppm. UV/vis (THF, 22 °C, nm): 368 (sh, ε = 4412 L mol−1
cm−1), 324 (sh, ε = 5537 L mol−1 cm−1), 249 (ε = 34064 L mol−1
cm−1).
Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
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Article
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Deutsche Forschungsgemeinschaft (DFG) for
financial support within the Heisenberg program (WA 2513/
8) (M.D.W.) and financial support and the Lower-Saxonian
graduate student program Catalysis for Sustainable Synthesis
(CaSuS) for a Ph.D. fellowship (A.E.). This paper is dedicated
to Professor F. Ekkehardt Hahn on the occasion of his 65th
birthday.
(16) Peloso, R.; Carmona, E. Non-heteroatom-substituted alkylidene
complexes of groups 10 and 11. Coord. Chem. Rev. 2018, 355, 116−
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