The first 1,3-digermyla-2-nickela-carboranylene and the Ni-catalyzed double germylation of unsaturated organic substrates

Article abstract of DOI:10.1039/b105026p

The reaction of o-bis(dimethylgermyl)carborane with Ni(PEt₃)₄ in pentane affords the reactive intermediate, [o-(GeMe₂)₂C₂B₁₀H ₁₀]Ni(PEt₃)₂ 2: the facile dou

Full text of DOI:10.1039/b105026p

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The first 1,3-digermyla-2-nickela-carboranylene and the Ni-catalyzed
double germylation of unsaturated organic substrates
Junghyun Lee,a Chongchan Lee,a Shim Sung Lee,b Sang Ook Kanga and Jaejung Ko*a
a Department of Chemistry, Korea University, Chochiwon, Chungnam 339-700, Korea.
E-mail: jko@tiger.korea.ac.kr
b Department of Chemistry, and Institute of Natural Science, Gyeong-sang University, Chinju 660-701,
Korea
Received (in Cambridge, UK) 7th June 2001, Accepted 23rd July 2001
First published as an Advance Article on the web 29th August 2001
The reaction of o-bis(dimethylgermyl)carborane with
Ni(PEt3)4 in pentane affords the reactive intermediate, [o-
(GeMe2)2C2B10H10]Ni(PEt3)2 2: the facile double germyla-
tion of unsaturated organic substrates catalyzed by 2 is
reported.
Although the transition metal-catalyzed double silylation of
unsaturated organic substrates has been well documented for
three decades,1 metal-catalyzed double germylation is quite
limited.2–5 Reactions were carried out mainly in the presence of
[Pd(PPh3)4] as a catalyst. In the catalytic cycle, bis(germyl)-
complexes have been implicated as important intermediates.
However, there are only a few precedents for such species6 and
only bis(chlorogermyl)platinum has been structurally charac-
terized by Tanaka and coworkers.7 However, the reactivity
towards unsaturated organic substrates was not studied. We
found that the bis(germyl)nickel complex is the most efficient
and reactive catalyst for the double germylation reaction. We
now describe (i) the isolation of the most reactive intermediate
cyclic bis(germyl)nickel compound with a bulky o-carborane
unit; (ii) the facile double germylation of alkyne catalyzed by
the intermediate under mild conditions; and (iii) the double
germylation of an alkene, aldehyde and nitrile by stoichiometric
reacion with the intermediate.
Fig. 1 Molecular structure of 2. Selected bond lengths (Å) and angles (°):
Ge(1)–C(1) 2.028(3), Ge(2)–C(2) 2.035(3), Ge(1)–Ni 2.3316(5), Ge(2)–Ni
2.3264(5), Ni–P(1) 2.2146(10), Ni–P(2) 2.2230(10); C(1)–Ge(1)–Ni
116.01(10), C(2)–Ge(2)–Ni 116.52(9), P(1)–Ni–P(2) 103.10(4), P(1)–Ni–
Ge(2) 146.73(3), P(2)–Ni–Ge(2) 92.08(3), Ge(2)–Ni–Ge(1) 84.231(8).
product 3 in 62% yield. All the spectral data of 3 were consistent
with the proposed formulation.§ A key feature in the 1H NMR
spectrum includes a singlet at d 6.24 assigned to the vinyl
proton. A characteristic high-field 13C NMR signal at d 142.82
provides evidence for a tethered carbon atom of the two
germanium moieties. Formation of the digermyl ring compound
3 can be related to nickel-catalyzed double silylation.9
The reaction of 2 with 1 equiv. of 4-vinylanisole takes place
at room temperature and affords a moderate yield of the five-
membered digermyl ring compound 4 (Scheme 1). One doublet
(d 2.80) in the 1H NMR spectrum of 4 is assigned to the methine
proton. A low-frequency 13C NMR resonance at d 55.41
provides evidence for the tethered carbon atom of the two
germanium moieties. The structure of 4 has been determined by
X-ray crystallography (Fig. 2).‡ The formation of 4 may
Addition of 1.1 equiv. of o-bis(dimethylgermyl)carborane,
prepared from 1,2-Li2C2B10H10 and 2 equiv. of GeMe2Cl2,
followed by reduction by NaB(CN)H3, to Ni(PEt3)4 in pentane
gave a red solution. Standard work-up and crystallization from
toluene–pentane gave [o-(GeMe2)2C2B10H10]Ni(PEt3)2 2 as a
spectroscopically pure, red crystalline solid very sensitive to air
and water in 60% yield [eqn. (1)].†
(1)
1
The H, 13C and 31P NMR spectra for 2 support the proposed
structure. The structure of 2 was unambiguously established by
a single-crystal X-ray analysis (Fig. 1).‡ Complex 2 has a
distorted tetrahedral geometry with the dihedral angle between
Ge(1)–Ni–Ge(2) and P(1)–Ni–P(2) being 84.60°. This bis(ger-
myl)nickel complex is the first as indicated by a search of the
Cambridge Crystallographic Database. As expected, the aver-
age Ni–Ge bond length [2.3290(5) Å] is slightly longer than that
of 2.248(1) Å in CpNi(PPh3)GeCl3.8 The Ni–P bond distance
[2.2188(10) Å] is consistent with those observed in other
phosphine nickel compounds.
Intermediate 2 was found to be an efficient reactant for the
double germylation reaction under mild conditions. The
reaction of o-bis(dimethylgermyl)carborane 1 with hex-1-yne
(1 equiv.) in the presence of a catalytic amount of 2 (0.03 equiv.)
at room temperature for 14 h afforded the double-germylated
Scheme 1 Reagents and conditions: i, HCCC4H9 (1 equiv.), 1 (0.5 equiv.),
2 (0.03 equiv.), toluene, 25 °C; ii, H2CCHC6H4OMe (1 equiv.), 2 (1 equiv.),
toluene, 80 °C.
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Chem. Commun., 2001, 1730–1731
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b105026p

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hydes and nitriles, generating a new class of heterocyclic
compounds. This potential has been further exploited in a series
of novel chemical transformations with this system.
We are grateful to KOSEF (2001) for generous financial
support.
Notes and references
† Experimental procedure: for 2: compound 1 (0.14 g, 0.38 mmol) in 5 ml
of pentane was added to a stirred solution of Ni(PEt3)4 (0.1 g, 0.37 mmol)
in 10 ml of pentane at 215 °C. The solution was warmed to room
temperature and stirred for 2 h. The solution was then evaporated in vacuo
and the residue extracted with toluene (8 ml) and then the solution was
covered with a layer of pentane (10 ml) at 25 °C. Red crystals of 2 were
formed over a period of several days (0.14 g, 60% yield). 1H NMR (C6D6):
d 1.14 (dq, JHP 7.42, JHH 5.48 Hz, CH2), 0.86 (dt, JHP 7.04, JHH 5.48 Hz,
CH3) and 0.21 (s, GeCH3). 31P{1H} NMR (C6D6): d 6.18.
‡ Crystal data: for 2: C18H52B10P2Ge2Ni, M = 641.52, monoclinic, space
group P21/n, a = 11.28880(10), b = 14.2049(3), c = 20.6930(4) Å, b =
104.7760(10)°, V = 3208.52(10) Å3, Z = 4, Dc = 1.328 g cm23, m(Mo-Ka)
= 2.550 mm21, 5038 reflections observed [I > 2s(I)], 338 parameters,
final R, Rw on [I > 2s(I)] data were 0.0339, 0.0809, goodness of fit on F2
= 1.059.
For 4: C15H32B10Ge2O, M = 481.69, orthorhombic, space group Pbca, a
= 16.6363(9), b = 15.3576(8), c = 18.9404(10) Å, V = 4839.2(4) Å3, Z
= 8, Dc = 1.322 g cm23, m(Mo–Ka) = 2.488 mm21, 5992 reflections
observed [I > 2s(I)], 253 parameters, final R, Rw on [I > 2s(I)] data were
0.0378, 0.0781, goodness of fit on F2 = 0.951. CCDC reference numbers
166073 and 168186. See http://www.rsc.org/suppdata/cc/b1/b105026p/ for
crystallographic data in CIF or other electronic format.
§ 3: 1H NMR (CDCl3): d 6.24 (s, CNCH), 2.13 (t, JHH 9.40 Hz, CH2),
1.59–1.27 (m, CH2CH2), 0.92 (t, JHH 4.46 Hz, CH3), 0.48 (s, GeCH3) and
0.45 (s, GeCH3). 13C{1H} NMR (CDCl3): d 159.20 (CNCH), 142.82 (Si-
CNCH), 41.00, 31.49, 22.69, 14.22, 20.68 and 20.84.
Fig. 2 Molecular structure of 4. Selected bond lengths (Å) and angles (°):
Ge(1)–C(1) 1.990(3), Ge(2)–C(2) 1.997(3), Ge(1)–C(7) 1.967(3), Ge(2)–
C(7) 1.954(3), C(1)–C(2) 1.679(3); Ge(1)–C(7)–Ge(2) 110.04(14), Ge(1)–
C(1)–C(2) 112.30(16).
involve an initial oxidative addition reaction of an olefinic C–H
bond to the nickel center, followed by the shift of a phenyl group
from the nickel atom to one of two germanium atoms. Such a C–
H activation has been observed in Ni-catalyzed double
silylation.10 Treatment of 2 with 1 equiv. of trans-cinnamalde-
hyde at room temperature gave the 1,2-double germylation
product 5 (Scheme 2). The 1H NMR spectrum of 5¶ contained
a distinguishing low-field methine resonance (d 4.61) as a
doublet of doublets which was used to monitor its formation.
This result is in contrast with that of double silylation which
gave the insertion product of two carbonyl ligands into the C–Si
bond.11
¶ 5: 1H NMR (CDCl3): d 7.34–7.25 (m, Ph), 6.52 (dd, JHH 15.88, JHH 1.82
Hz, CNCHPh), 6.22 (dd, JHH 15.88, JHH 5.44 Hz, CHNC), 4.61 (dd, JHH 5.44
Hz, JHH 1.82 Hz, OCH), 0.75 (s, GeCH3), 0.73 (s, GeCH3), 0.44 (s, GeCH3)
and 0.42 (s, GeCH3). 13C{1H} NMR (CDCl3): d 137.04, 131.64, 128.74,
128.43, 127.44, 127.21, 126.26, 70.01, 20.07, 21.85, 23.63 and 26.91.
∑ 6: 1H NMR (CDCl3): d 7.35–7.06 (m, Ph), 4.75 (s, CH), 0.64 (s, GeCH3)
and 0.61 (s, GeCH3). 13C{1H} NMR (CDCl3): d 143.54, 132.86, 130.22,
128.58, 128.34, 128.22, 125.92, 54.59, 5.85 and 1.29.
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Scheme 2 Reagents and conditions: i, PhCHNCHCHO (1 equiv.), 2 (1
equiv.), toluene, 25 °C, 70%; ii, Ph2CHCN (1.3 equiv.), 2 (1 equiv.),
toluene, 25 °C, 66%.
When diphenylacetonitrile is employed in the reaction with 1,
the six-membered digermyl ring compound 6 is isolated as
colorless crystals in 74% yield. All the spectral data of 6 were
consistent with the proposed formulation.∑
In summary, we have isolated a reactive intermediate, a
cyclic bis(germyl)nickel complex, which readily reacts with
unsaturated organic substrates such as alkynes, alkenes, alde-
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Chem. Commun., 2001, 1730–1731
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