Reaction of [(tmeda)NiMe2] with 2-pyridylmethylamine and (2-pyridylmethyl)(diphenylphosphanyl)amine

Article abstract of DOI:10.1016/j.inoche.2008.02.006

2-Aminomethylpyridine (Amp) substitutes the bis(dimethylamino)ethane ligand (TMEDA) of [(tmeda)NiMe₂] leading to the formation of N,N′-(2-aminomethylpyridine)dimethylnickel (1). The reaction of bulkier N-diphenylphosphanyl-2-aminomethylpyridine with [(tmeda)NiMe₂] yields tetrakis(N-diphenylphosphanyl-2-aminomethylpyridine)nickel(0) (2), ethane and TMEDA. The nickel(II) complex 1 shows a distorted square planar environment for the metal center, whereas nickel(0) in 2 displays a distorted tetrahedral coordination sphere with an average Ni-P bond length of 217.35 pm.

Full text of DOI:10.1016/j.inoche.2008.02.006

Available online at www.sciencedirect.com
Inorganic Chemistry Communications 11 (2008) 612–615
www.elsevier.com/locate/inoche
Reaction of [(tmeda)NiMe2] with 2-pyridylmethylamine
and (2-pyridylmethyl)(diphenylphosphanyl)amine
Astrid Malassa, Helmar Go¨rls, Matthias Westerhausen *
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-Universita¨t Jena, August-Bebel-Street 2, D-07743 Jena, Germany
Received 21 January 2008; accepted 12 February 2008
Available online 20 February 2008
Abstract
2-Aminomethylpyridine (Amp) substitutes the bis(dimethylamino)ethane ligand (TMEDA) of [(tmeda)NiMe2] leading to the forma-
tion of N,N0-(2-aminomethylpyridine)dimethylnickel (1). The reaction of bulkier N-diphenylphosphanyl-2-aminomethylpyridine with
[(tmeda)NiMe2] yields tetrakis(N-diphenylphosphanyl-2-aminomethylpyridine)nickel(0) (2), ethane and TMEDA. The nickel(II) com-
plex 1 shows a distorted square planar environment for the metal center, whereas nickel(0) in 2 displays a distorted tetrahedral coordi-
nation sphere with an average Ni–P bond length of 217.35 pm.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Nickel; Dimethylnickel; Phosphane complexes; Amine complexes
The synthesis of many late transition metal bis[(2-pyri-
dylmethyl)(trialkylsilyl)amides] succeeds via a transamina-
tion starting from [M{N(SiMe3)2}2] [1]. However, nickel
bis[bis(trimethylsilyl)amide] decomposes very fast [2] and
therefore, another starting material has to be employed.
The metallation of N-trialkylsilyl-8-aminoquinoline with
nickelocene yields the corresponding paramagnetic com-
plex with the nickel(II) atom in a distorted tetrahedral envi-
ronment [3]. The metallation of 8-aminoquinoline with
[(tmeda)NiMe2] leads to the formation of diamagnetic
nickel di(8-amidoquinoline) with a distorted square planar
metal center [4].
Strongly related N-trialkylsilyl-2-pyridylmethylamides
can easily undergo an oxidative C–C coupling reaction
according to Eq. (1) with dimethylzinc at elevated temper-
atures [5,6]. Without protecting trialkylsilyl groups, the
reaction of H2N–CH2–Py with ZnMe2 at elevated temper-
atures does lead to oxidative C–C coupling reactions, but a
variety of compounds are obtained [7]. This C–C coupling
of 2-pyridylmethylamines strongly depends on the redox
potential E0 of the employed reagents: Initiation of the
coupling with ZnMe2 [E0(Zn/Zn2+) = ꢀ0.763 V] requires
elevated temperatures, whereas this reaction can be per-
formed at room temperature with [Sn{N(SiMe3)2}2]
[E0(Sn/Sn2+) = ꢀ0.137 V] and no coupling was observed
with MgR2 [E0(Mg/Mg2+) = ꢀ2.356 V]. Taking these
observations into account nickel(II) compounds [E0(Ni/
Ni2+) = ꢀ0.257 V] seem to be a suitable reagent for a
CꢀC coupling of 2-pyridylmethylamines.
N
N
N
R'R2Si
Me
N
Zn Me
N SiR'R2
+ ZnMe2
- 2 MeH
- Zn
Zn
R'R2Si
N
N
SiR'R2
ð1Þ
N
Zn
Zn
Me
Me
B
A
The nickel(II) complex [(tmeda)NiMe2] shows several
reaction pathways [8]: addition of bipyridine and bidentate
phosphanes give an exchange of the tmeda ligand and the
formation of LNiMe2 whereas strong p-acceptor molecules
*
Corresponding author. Tel.: +49 3641 948110; fax: +49 3641 948102.
E-mail address: m.we@uni-jena.de (M. Westerhausen).
1387-7003/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2008.02.006

A. Malassa et al. / Inorganic Chemistry Communications 11 (2008) 612–615
613
lead to reductive elimination of ethane and the formation
of [(tmeda)Ni(p-ligand)n] (n = 1, 2). The reaction of terpyr-
idine (tpy) with [(tmeda)NiMe2] yields the nickel(I) com-
plex [(tpy)NiMe] as shown in Eq. (2) [9,10] via a
nonradical reaction mechanism [10]. This complex shows
a Ni–C distance of 195 pm [9].
ric unit, distinguished by the letters ‘‘A” and ‘‘B” [14].
Molecular structure and numbering scheme of molecule
A are represented in Fig. 1. The metal atom of this diamag-
netic complex is in a distorted square planar environment
with average Ni–C and Ni–N bond lengths of 192.6 and
197.2 pm.
The molecular structure of molecule A of 2 is shown in
Fig. 2. The asymmetric unit contains two half molecules
distinguished by ‘‘A” and ‘‘B” [15]. The structure of this
aminophosphane complex is rather similar to the complex
of tetrakis(anilino-diphenylphosphane)nickel(0) [20] which
was prepared from the appropriate phosphane, nickel(II)
chloride and zinc. The nickel atoms of 2 are in slightly dis-
torted tetrahedral environments with an average Ni–P
bond length of 216.9 pm. The P–N distances show an aver-
age value of 169.5 pm which is comparable to the P–N
bonds of [MeZn–N(CH2Py)PPh2]2 but smaller than
observed for Py–CH2–N(PPh2)2 [12].
N
N
N
N
N
N
2
NiMe2
+ 2
ð2Þ
N
N
Ni-Me
2
- C2H6
The reaction of [(tmeda)NiMe2] with 2-aminomethylpyr-
idine (Amp) leads to an exchange of the tmeda ligand and to
the formation of (Amp)NiMe2 1 [11]. This complex is poorly
soluble in toluene and therefore, it precipitates immediately
giving a yield of more than 70%. A reaction in THF gives
lower yields of approximately 20% due to accompanying
decomposition reactions. The bulkier N-diphenylphospha-
nyl-2-aminomethylpyridine [12] reacts with [(tmeda)NiMe2]
yielding tetrakis(N-diphenylphosphanyl-2-aminomethyl-
pyridine)nickel(0) 2 [13]. Rather poor yields of 2 were
obtained due to the fact that also decomposition takes place
during this reaction yielding ethane and nickel(0). A higher
yield was obtained starting from [(cod)2Ni] (cod = 1,5-
cyclooctadiene) and Ph2P–N(H)–CH2–Py. The soft
nickel(0) atom prefers the coordination to the soft phospho-
rus rather than to the harder nitrogen bases.
The organometallic chemistry of [(tmeda)NiMe2] is
rather complex because this compound offers a variety of
different reaction pathways:
(i) Substitution of the neutral coligand TMEDA: 2-Ami-
nomethylpyridine substitutes the TMEDA molecule
giving the nickel(II) complex (2-aminomethylpyri-
dine-N,N0)dimethylnickel 1. Similar observations
were made for 2,20-bipyridine and 1,2-bis(dim-
ethylphosphino)ethane [8].
(ii) Metallation of H-acidic substrates: the metallation
force of (tmeda)NiMe2 was shown in the reaction
with 8-aminoquinoline leading to the formation of
square planar bis(8-amidoquinoline)nickel(II) [4].
N
N
N
N
N
N
NiMe2
+ 4
H
P
H
P
Ni
- C2H6
- TMEDA
4
2
ð3Þ
The crystal structure determinations of 1 [14] and 2 [15]
were performed on a Nonius KappaCCD diffractometer,
using graphite-monochromated Mo–Ka radiation. Data
were corrected for Lorentz and polarization effects, and
not for absorption effects [16,17]. The structures were
solved by direct methods (SHELXS [18]) and refined by
full-matrix least squares techniques against F 2o (SHELXL-
97 [19]). The hydrogen atoms of the four amine groups
of 2 were located by difference Fourier synthesis and
refined isotropically. All other hydrogen atoms were
included at calculated positions with fixed thermal param-
eters. All nonhydrogen, non solvent atoms were refined
anisotropically [19]. XP (SIEMENS Analytical X-ray
Instruments, Inc.) was used for structure representations.
The nickel(II) complex 1 crystallizes in the shape of
extremely thin needles with two molecules in the asymmet-
Fig. 1. Molecular structure of molecule A of (amp)NiMe2 1. The
ellipsoids represent a probability of 40%. Selected bond lengths (pm):
NiA–C7A 192.1(9), NiA–C8A 193.6(9), NiA–N1A 196.8(7), NiA–N2A
198.1(7); angles (°): C7A–NiA–C8A 88.2(5), N1A–NiA–N2A 82.2(3),
C7A–NiA–N1A 98.3(4), C7A–NiA–N2A 179.5(4), C8A–NiA–N1A
172.2(4), C8A–NiA–N2A 91.3(4).

614
A. Malassa et al. / Inorganic Chemistry Communications 11 (2008) 612–615
the Deutsche Forschungsgemeinschaft (DFG, Bonn-Bad
Godesberg, Germany) for generous funding. We also
acknowledge the support by the Fonds der Chemischen
Industrie (Frankfurt/Main, Germany). A. Malassa thanks
the Carl-Zeiss-Stiftung (Germany) for a generous Ph.D.
scholarship.
References
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(1988) 525–532.
Fig. 2. Molecular structure of molecule A of Ni[P(Ph2)–N(H)–CH2Py]4 2.
The ellipsoids represent a probability of 40%. Symmetry equivalent atoms
are marked with an apostrophe. The H atoms are omitted for clarity
reasons. Selected bond lengths (pm): NiA–P1A 217.12(7), NiA–P2A
217.58(7), P1A–N1A 170.0(2), P1A–C7A 185.3(3), P1A–C13A 183.9(3),
P2A–N3A 169.3(2), P2A–C25A 184.3(3), P2A–C31A 184.8(3), N1A–C1A
145.9(4), N3A–C19A 146.2(4); angles (°): P1A–NiA–P2A 105.51(3), P1A–
NiA–P1A0 114.55(4), P1A–NiA–P2A0 108.04(3), P2A–NiA–P2A0
115.49(4), P1A–N1A–C1A 123.9(2), P2A–N3A–C19A 126.3(2).
[9] T.J. Anderson, G.D. Jones, D.A. Vicic, J. Am. Chem. Soc. 126 (2004)
8100–8101 (Erratum: J. Am. Chem. Soc. 126 (2004) 11113).
[10] G.D. Jones, J.L. Martin, C. McFarland, O.R. Allen, R.E. Hall, A.D.
Haley, R.J. Brandon, T. Konovalova, P.J. Desrochers, P. Pulay, D.A.
Vicic, J. Am. Chem. Soc. 128 (2006) 13175–13183.
(iii) Reductive elimination of ethane yields nickel(0)
complexes.
[11] (2-Aminomethylpyridine-N,N0)dimethylnickel 1: A solution of 84 mg
of 2-aminomethylpyridine (0.78 mmol) in 7 ml of toluene was layered
on a toluene solution of 92 mg of [(TMEDA)NiMe2] (0.45 mmol).
Diffusion at r.t. leads to the formation of red needles which were
collected and washed with toluene. Recrystallization from THF gave
single crystals of 1 suitable for X-ray diffraction experiments. Yield:
62 mg (0.31 mmol, 70%). M.p. 136 °C (dec.). 1H NMR (THF-d8): 8.31
(d, 1H, Py1), 7.62 (t, 1H, Py3), 7.07 (m, 2H, Py4, Py2), 3.91 (t, 2H,
CH2), 2.91 (s, br, 2H, NH2), ꢀ0.83 (s, 3H, CH3), ꢀ1.01 (s, 3H, CH3).
13C{1H} NMR (THF-d8): 163.7 (Py5), 147.6 (Py1), 135.1 (Py3), 135.6
(Py3), 123.3 (Py4/2), 120.7 (Py2/4), 48.2 (CH2), ꢀ9.2 (CH3), ꢀ15.1
(CH3). IR (Nujol, KBr windows, cmꢀ1): 3331 s, 3160 w, 3085 m br,
1604 m, 1446 s, 1275 m, 1154 m, 1063 s, 1027 m, 932 w, 750 vs, 667 m,
526 m. MS (DEI, m/z): 181 ([amp-NiCH3]+, 4%), 166 ([amp-Ni]+,
46%), 108 ([amp]+, 100%). Elemental analysis (C8H14N2Ni, 196,90):
calc.: C, 48.80; H, 7.17, N, 14.23; found: C, 47.78; H, 7.12, N, 14.16.
[12] D. Olbert, A. Kalisch, N. Herzer, H. Go¨rls, P. Mayer, L. Yu, M.
Reiher, M. Westerhausen, Z. Anorg. Allg. Chem. 633 (2007) 893–902.
[13] Tetrakis(N-diphenylphosphanyl-2-aminomethylpyridine)nickel(0) 2:
Method A (from [(tmeda)NiMe2]): A solution of 0.43 g of N-
diphenylphosphanyl-2-aminomethylpyridine (1.46 mmol) in 14 ml of
THF was dropped into a solution of 75 mg of [(tmeda)NiMe2]
(0.36 mmol) in 6 ml of THF. Ethane gas was liberated from this
mixture immediately. Yellow cuboid crystals were obtained during
storage at ꢀ20 °C which were washed with THF. A second crop of
crystals can be isolated after concentration of the motherliquor and
cooling again to ꢀ20 °C. Yield: 0.18 g (0.15 mmol, 40%). Method B
(from [Ni(cod)2]): At r.t. a solution of 0.51 g of N-diphenylphospha-
nyl-2-aminomethylpyridine (1.7 mmol) in 10 ml of toluene was added
dropwise to a solution of 124 mg (0.45 mmol) of [Ni(cod)2] in 10 ml of
toluene. All solids were removed by filtration. Then the volume of the
filtrate was reduced and the remaining solution was stored at ꢀ20 °C.
After a week the product was collected and washed with toluene.
Yield: 0.30 g (0.25 mmol, 54%). Physical properties: M.p. 192 °C
(dec.). 1H NMR (benzene-d6): 8.37 (d, 3J(HH) = 4.0 Hz, 4H, Py1),
(iv) Comproportionation of Ni(0) and Ni(II) compounds:
occasionally, comproportionation of nickel(0) and
nickel(II) complexes can lead to nickel(I) compounds
as observed for the reaction of [(tmeda)NiMe2] with
terpyridine [9,10].
Often these reactions are competitive and many side reac-
tions can occur leading to low yields. 2-Pyridylmethylami-
no-diphenylphosphane initiates the formation of nickel(0)
yielding tetrakis(N-diphenylphosphanyl-2-aminomethyl-
pyridine)nickel(0) 2, TMEDA and ethane. Even though
the redox potential E0(Ni/Ni2+) should allow the oxidative
C–C coupling of 2-aminomethylpyridine derivatives similar
to Eq. (1), this reaction was not observed in our case. The
reductive elimination of ethane is favoured instead.
Supplementary material
CCDC 669029 and 669030 contain the supplementary
crystallographic data for 1 and 2. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
Acknowledgements
This work was supported in the collaborative research
initiative of the DFG (SFB 436) and we are grateful to

A. Malassa et al. / Inorganic Chemistry Communications 11 (2008) 612–615
615
˚
7.56 (s, br, 16H, Ph), 6.97 (m, br, 28H, Py3, Ph), 6.73 (d,
3J(HH) = 7.8 Hz, 4H, Py4), 6.60 (t, 3J(HH) = 6.0 Hz, 4H, Py2),
3.78 (m, 8H, CH2), 3.37 (m, br, 4H, NH). 13C{1H} NMR (benzene-
d6): 161.1 (Py5), 149.3 (Py1), 141.6 (br, Ph), 135.6 (Py3), 131.5 (br,
Ph), 128.3 (Ph), 121.8 (Py4), 121.2 (Py2), 50.3 (CH2). 31P{1H} NMR
(benzene-d6): 69.3 (PPh2). IR (Nujol, KBr windows, cmꢀ1): 3400 m,
3382 s, 3365 s, 3051 m, 1964 w, 1903 w, 1586 s, 1569 m, 1432 vs, 1402
m, 1336 w, 1308w, 1276 w, 1207 m, 1154 m, 1102 s, 1075 vs, 1027 m,
994 m, 911 m, br, 836 m, br, 802 m, br, 750 s, 707 s, 696 vs, 680 m, 630
w, 620 w, 596 m, 543 m, 518 s, 486 m, 463 s. MS (DEI, m/z):
292 ([amp-PPh2]+, 100%), 215 ([amp-PPh]+, 100%), 200 ([amp-
PPh2 ꢀ C6H6N]+, 100%). Elemental analysis (C72H68N8P4Ni,
1227.95): calc.: C, 70.42; H, 5.58; N, 9.13; found: C, 69.20; H, 6.21;
N, 7.87.
ꢀ1.377 e Aꢀ3. The crystals of 1 were extremely thin and of low quality
resulting in a substandard data set and a rather high final wRall2 value.
[15] Crystal data for 2: C72H68N8NiP4 ꢂ 1.5 C4H8O, Mr = 1332.06 g molꢀ1
,
yellow prism, size 0.05 ꢁ 0.05 ꢁ 0.04 mm3, monoclinic, space group
˚
P2/c, a = 26.9743(4), b = 11.7894(1), c = 25.1820(4) A, b =
3
˚
116.626(1)°, V = 7158.9(2) A , T = ꢀ90 °C, Z = 4, qcalcd. = 1.236
g cmꢀ3, l (Mo-Ka) = 4.11 cmꢀ1, F(000) = 2800, 81,216 reflections in
h(ꢀ33/34), k(ꢀ14/15), l(ꢀ32/32), measured in the range 1.73° 6
H 6 27.41°, completeness Hmax = 99.4%, 16,214 independent reflec-
tions, Rint = 0.0720, 11,459 reflections with Fo > 4r(Fo), 843 parame-
ters, 0 restraints, R1,obs = 0.0577, wRobs2 = 0.1464, R1,all = 0.0925,
wRall2 = 0.1667, GOOF = 1.021, largest difference peak and hole:
ꢀ3
˚
1.091/ꢀ0.475 e A
.
[16] COLLECT, Data Collection Software, Nonius B.V., Netherlands,
1998.
[14] Crystal data for 1: C8H14N2Ni, Mr = 196.92 g molꢀ1, red prism, size
0.05 ꢁ 0.05 ꢁ 0.05 mm3,
monoclinic,
space
group
P21/c,
[17] Z. Otwinowski, W. Minor, Processing of X-ray diffraction data
collected in oscillation mode. in: C.W. Carter, R.M. Sweet (Eds.),
Methods in Enzymology, vol. 276, Macromolecular Crystallography,
Part A, Academic Press, 1997, pp. 307–326.
[18] G.M. Sheldrick, Acta Crystallogr. A46 (1990) 467–473.
[19] G.M. Sheldrick, SHELXL-97 (Release 97-2), University of Go¨ttin-
gen, Germany, 1997.
˚
a = 12.8428(4), b = 7.2276(4), c = 18.9577(9) A, b = 91.159(3)°,
3
q , l
calcd. = 1.487 g cmꢀ3
˚
V = 1759.34(14) A , T = ꢀ90 °C, Z = 8,
(Mo-Ka) = 21.42 cmꢀ1, F(000) = 832, 11,960 reflections in h(ꢀ16/
16), k(ꢀ9/9), l(ꢀ24/24), measured in the range 1.59° 6 H 6 27.49°,
completeness
Hmax = 99.4%, 4008 independent reflections,
Rint = 0.0668, 2642 reflections with Fo > 4r(Fo), 203 parameters, 0
restraints, R1,obs = 0.0880, wRobs2 = 0.2420, R1,all = 0.1266, wRall2
0.2633, GOOF = 1.051, largest difference peak and hole: 2.168/
=
[20] O. Kuhl, P.C. Junk, E. Hey-Hawkins, Z. Anorg. Allg. Chem. 626
¨
(2000) 1591–1594.