Synthesis and characterization of rhodium complexes with phosphine-stabilized germylenes

Article abstract of DOI:10.1021/ic300600c

The reaction of phosphine-stabilized germylenes (1a,b) with dimer complex [Rh₂(μ-Cl)₂(COD)₂] leads to the corresponding phosphine-germylene-Rh(I) complexes (2a,b). Interestingly, the stability of these complexes depends strongly on the nature of the substituent of the germylene fragment. Indeed, the complex (2a) with the chloro-germylene ligand isomerizes into a metallacycle rhodium complex (3a) via germylene insertion into the Rh-Cl bond, while the complex with the phenyl-substituted germylene (2b) was isolated and represents the first stable Rh(I)-germylene complex with a Rh-Cl bond.

Full text of DOI:10.1021/ic300600c

Article
pubs.acs.org/IC
Synthesis and Characterization of Rhodium Complexes with
Phosphine-Stabilized Germylenes
Juan M. García,‡ Edgar Ocando-Mavarez,*,‡ Tsuyoshi Kato,† David Santiago Coll,§ Alexander Briceno,∥
́
̃
Nathalie Saffon-Merceron,⊥ and Antoine Baceiredo*,†
†Universite
‡Laboratorio de Fisico-Química Organ
§Laboratorio de Fisico-Química Teor
ica de Materiales, IVIC, Caracas 1020-A, Venezuela
de Nuevos Materiales, IVIC, Caracas 1020-A, Venezuela
de Toulouse, UPS and CNRS, ICT FR 2599, F-31062 Toulouse, France
́
de Toulouse, UPS and CNRS, LHFA UMR 5069, F-31062 Toulouse, France
ica, IVIC, Caracas 1020-A, Venezuela
́
́
∥Laboratorio de Síntesis y Caracterizacion
́
⊥Universite
́
S
* Supporting Information
ABSTRACT: The reaction of phosphine-stabilized germy-
lenes (1a,b) with dimer complex [Rh2(μ-Cl)2(COD)2] leads
to the corresponding phosphine−germylene−Rh(I) complexes
(2a,b). Interestingly, the stability of these complexes depends
strongly on the nature of the substituent of the germylene
fragment. Indeed, the complex (2a) with the chloro-germylene
ligand isomerizes into a metallacycle rhodium complex (3a)
via germylene insertion into the Rh−Cl bond, while the complex with the phenyl-substituted germylene (2b) was isolated and
represents the first stable Rh(I)−germylene complex with a Rh−Cl bond.
INTRODUCTION
■
In past decades, germylene compounds have attracted growing
interest not only as synthetic tools in organic chemistry but also
for their potential use as ligands for transition metals.1,2
Usually, germylenes are highly reactive derivatives and tend to
oligomerize or polymerize; however, they can be stabilized
kinetically by sterically demanding substituents1 and/or
thermodynamically by inter- or intramolecular coordination
of Lewis base ligands.3 Therefore, numerous four-, five-, and
six-membered N-heterocyclic germylenes have been isolated by
using nitrogen-containing bulky ligands.3−5 The stabilization
strategy using neutral donor ligands led to the formation of
three-coordinate Ge(II) species,3 which remain capable of
binding to transition metals.6
Figure 1. Phosphine-stabilized germylenes.
Scheme 1. Synthesis of Phosphine-Stabilized Germylenes
Despite phosphines being considered excellent ligands in
organometallic chemistry, few phosphine-stabilized germylenes
have been isolated to date. The first one, A, was prepared by Du
Mont et al. in 1981,7 and more recently some Ge(II)halide
complexes, B, with diphosphine ligands were isolated.8 An
original complex, C, featuring two Ge centers in two formal
oxidation states was characterized in the solid state,9 and the
intramolecular phosphine-stabilized germylene D was isolated
two years ago (Figure 1).10 To the best of our knowledge, the
ligand properties of these stabilized germylenes were not
studied, and since we have recently prepared a phosphine-
stabilized chloro-germylene 1a (Scheme 1),11 we were
interested in testing its potential as a ligand for transition
metals. Indeed, the peculiar structure of 1a, featuring a chloro
substituent (easy to substitute) and a phosphine ligand
(versatile soft Lewis base), should allow an easy modulation
of the electronic and steric properties of this original ligand.
Herein, we report the reactivity of [Rh2(μ-Cl)2(COD)2] with
two different phosphine-stabilized germylenes 1a,b.
EXPERIMENTAL SECTION
■
General Procedures. All reactions and manipulations were carried
out under an inert atmosphere of argon by using standard Schlenk
techniques. Dry, oxygen-free solvents were employed. Phosphine-
stabilized chloro-germylene 1a was prepared according to a published
method.11 Dimer complex [Rh2(μ-Cl)2(COD)2] was purchased from
Received: March 22, 2012
Published: July 25, 2012
© 2012 American Chemical Society
8187
dx.doi.org/10.1021/ic300600c | Inorg. Chem. 2012, 51, 8187−8193

Inorganic Chemistry
Article
3
Strem Chemicals. The elemental analysis was performed (C, H, N) on
= 1.1 Hz, PNCH2), 39.4 (s, PNCH2), 40.9 (d, JPC = 8.0 Hz,
NCCHbridgehead), 43.9 (d, 2JPC = 12.0 Hz, PCCHbridgehead), 44.9 (d, 2JPC
1
a model EA1108 Fisons elemental analyzer. H, 13C, and 31P NMR
spectra were recorded with either Bruker Avance-300 or Avance-500
= 7.8 Hz, PNCHiPr), 44.6 (d, 2JPC = 12.1 Hz, PNCHiPr), 46.9 (d, 3JPC
=
1
spectrometers. H and 13C NMR chemical shifts are reported in parts
4.2 Hz, CH2bridge), 91.0 (d, JPC = 28.2 Hz, PCCN), 123.4, 123.4,
per million relative to Me4Si as an external standard. 31P NMR
chemical shifts are expressed in parts per million relative to 85%
H3PO4.
124.1 (3s, 3C, CHAr2), 140.7 (d, JPC = 2.5 Hz, NCipso), 146.6, 147.3
3
(NCortho), 185.0 (d, JPC = 39.4 Hz, PCCN). 31P{1H} NMR (121.5
1
MHz, C6D6, 25 °C): δ = 85.6. Minor diastereomer (40%), H NMR
Synthesis of Phosphine-Stabilized Phenyl-Germylene 1b. To
a THF solution (20 mL) of 1a (1.5 g, 2.73 mmol), at −80 °C, was
slowly added phenyl lithium (1.58 mL, 1.8 M in hexane, 2.86 mmol).
The solution was slowly warmed to room temperature and stirred for
2 h. The 31P NMR spectroscopy indicated the quantitative formation
of the new phenyl-substituted germylene 1b as a mixture of two
diastereomers (75/25; δ 80.5 and 75.6). All volatiles were removed in
vacuo, and the product was extracted twice with pentane. The major
diastereomer of 1b was obtained in pure form as pale yellow crystals,
suitable for an X-ray diffraction analysis, from a concentrated pentane
solution at −30 °C (0.72 g, 45%). 1H NMR (300 MHz, C6D6, 25 °C):
(300 MHz, C6D6, 25 °C): δ 0.81 (d, 3JHP = 18.4 Hz, 3H, GeCH3), 0.87
3
3
(d, JHH = 6.5 Hz, 3H, CH3PNiPr), 0.92 (d, JHH = 6.6 Hz, 3H,
CH3PNiPr), 1.01 (d, JHH = 6.5 Hz, 3H, CH3PNiPr), 1.11 (d, JHH = 5.8
3
3
3
Hz, 3H, CH3iPr), 1.12 (d, JHH = 6.9 Hz, 3H, CH3PNiPr), 1.17
(overlapped with the methyl signal, 1H, 1/2 CH2bridge), 1.19 (d, 3JHH
=
3
6.7 Hz, 3H, CH3iPr), 1.20 (d, JHH = 6.8 Hz, 3H, CH3PNiPr), 1.36 (m,
2H, 1/2 CH2CbridgeheadCN, 1/2 CH2CbridgeheadCP), 1.42 (d, 3JHH = 6.8 Hz,
3H, CH3iPr), 1.43 (overlapped with the methyl signal, 2H, 1/2
CH2CbridgeheadCN, 1/2 CH2CbridgeheadCP), 1.69 (m, 1H, 1/2 CH2bridge),
2.33 (brs, 1H, PCCHbridgehead), 2.44−2.67 (m, 4H, 2 PNCH2), 2.78
3
(brs, 1H, NCCHbridgehead), 3.21 (sept, JHH = 6.8 Hz, 1H, CHiPr), 3.38
3
3
δ 0.56 (d, JHH = 6.7 Hz, 3H, CH3PNiPr), 0.90 (d, JHH = 6.2 Hz, 3H,
(m, 1H, PNCHiPr), 3.46 (sept, 3JHH = 6.8 Hz, 1H, CHiPr), 3.94 (m, 1H,
PNCHiPr), 7.06−7.09 (m, 3H, HAr). 13C{1H} NMR (75.5 MHz, C6D6,
CH3PNiPr), 0.91 (overlapped with the methyl signal, 1H, 1/2 CH2bridge),
3
3
2
3
0.92 (d, JHH = 6.6 Hz, 3H, CH3PNiPr), 0.93 (d, JHH = 6.1 Hz, 3H,
CH3PNiPr), 1.04 (d, 3JHH = 6.5 Hz, 3H, CH3iPr), 1.09 (d, 3JHH = 6.8 Hz,
3H, CH3iPr), 0.91 (brs, 1H, 1/2 CH2bridge), 1.17 (d, 3JHH = 6.9 Hz, 3H,
CH3iPr), 1.32−1.41 (m, 2H, 1/2 CH2CbridgeheadCP, 1/2 CH2CbridgeheadCN),
1.46 (d, 3JHH = 6.7 Hz, 3H, CH3iPr), 1.55 (m, 1H, 1/2 CH2CbridgeheadCP),
1.69 (m, 1H, 1/2 CH2CbridgeheadCN), 2.48−2.69 (m, 5H, 2 PNCH2,
25 °C): δ 4.2 (d, JPC = 2.7 Hz, GeCH3), 19.8 (d, JPC = 1.5 Hz,
3 3
CH3PNiPr), 21.2 (d, JPC = 1.7 Hz, CH3PNiPr), 21.2 (d, JPC = 1.1 Hz,
3
CH3PNiPr), 21.8 (d, JPC = 4.1 Hz, CH3PNiPr), 24.2 (s, CH3iPr), 24.9 (s,
CH3iPr), 25.0 (s, CH3iPr), 26.0 (s, CH3iPr), 26.2 (d, JPC = 1.4 Hz,
CH2CbridgeheadCN), 27.43 (s, CHiPr), 28.3 (s, CHiPr), 30.2 (s,
4
2
CH2CbridgeheadCP), 38.9 (s, PNCH2), 39.1 (d, JPC = 1.9 Hz, PNCH2),
3
3
2
PCCHbridgehead), 2.88 (m, 1H, NCCHbridgehead), 3.00 (sept, JHH = 6.8
40.7 (d, JPC = 7.2 Hz, NCCHbridgehead), 43.3 (d, JPC = 13.5 Hz,
Hz, 1H, CHiPr), 3.41 (m, 1H, PNCHiPr), 3.78 (sept, 3JHH = 6.8 Hz, 1H,
PCCHbridgehead), 43.9 (d, 2JPC = 7.4 Hz, PNCHiPr), 44.4 (d, 2JPC = 11.1
CHiPr), 3.95 (m, 1H, PNCHiPr), 6.96−7.36 (m, 3H, HAr). 13C{1H}
Hz, PNCHiPr), 48.6 (d, JPC = 2.7 Hz, CH2bridge), 91.5 (d, JPC = 23.5
3
3
3
NMR (75.5 MHz, C6D6, 25 °C): δ 19.9 (d, JPC = 0.5 Hz, CH3PNiPr),
Hz, PCCN), 123.8, 125.9, 126.0 (CHAr2), 141.6 (d, JPC = 4.7 Hz,
3
3
20.4 (d, JPC = 0.93 Hz, CH3PNiPr), 20.7 (d, JPC = 4.5 Hz, CH3PNiPr),
NCipso), 146.0, 146.3 (NCortho), 187.3 (d, JPC = 41.2 Hz, PCCN).
31P{1H} NMR (121.5 MHz, C6D6, 25 °C): δ 81.0.
3
21.3 (d, JPC = 7.7 Hz, CH3PNiPr), 23.4 (s, CH3iPr), 24.4 (s, CH3iPr),
24.8 (s, CH3iPr), 25.5 (d, 4JPC = 1.6 Hz, CH2CbridgeheadCN), 26.0 (d, JPC
=
Synthesis of Phosphine-Stabilized Butyl-Germylene 1d. To a
THF solution (20 mL) of 1a (1.0 g, 1.82 mmol), at −80 °C, was
slowly added n-butyl lithium (1.20 mL, 1.6 M in hexane, 1.92 mmol).
The solution was slowly warmed to room temperature and stirred for
2 h. All volatiles were removed in vacuo, and the product was extracted
twice with pentane. Butyl-germylene 1d was obtained as a yellow
powder from a saturated pentane solution at −30 °C (0.36 g, 35%).
The 31P NMR spectroscopy indicated the formation of 1d as a mixture
of two diastereomers (84/16; δ 85.7 and 80.9). Major diastereomer
(84%), H NMR (300 MHz, C6D6, 25 °C): δ 0.86 (t, JHH = 6.9 Hz,
3H, CH3Bu), 0.98 (d, 3JHH = 6.7 Hz, 3H, CH3PNiPr), 1.06 (d, 3JHH = 6.6
Hz, 3H, CH3PNiPr), 1.13 (d, 3JHH = 6.6 Hz, 3H, CH3PNiPr), 1.15 (d, 3JHH
= 6.7 Hz, 3H, CH3PNiPr), 1.21 (d, JHH = 6.8 Hz, 3H, CH3iPr), 1.24
(overlapped with the methyl signal, 2H, GeCH2CH2 Bu), 1.25
2.5 Hz, CH3iPr), 27.8 (s, CHiPr), 28.5 (s, CHiPr), 30.2 (d, 3JPC = 2.3 Hz,
2
2
CH2CbridgeheadCP), 38.9 (d, JPC = 3.0 Hz, PNCH2), 38.9 (d, JPC = 2.8
Hz, PNCH2), 41.1 (d, JPC = 7.9 Hz, NCCHbridgehead), 43.9 (d, JPC
3
2
=
2
5.8 Hz, PNCHiPr), 44.1 (d, JPC = 11.1 Hz, PCCHbridgehead), 44.3 (d,
2JPC = 12.5 Hz, PNCHiPr), 46.3 (d, JPC = 4.0 Hz, CH2bridge), 93.4 (d,
3
J
PC = 31.3 Hz, PCCN), 123.5, 124.0, 126.0 (CHAr), 126.3 (d, 3JPC
=
=
3
1.68 Hz, 2C, GeCHortho), 137.2, 134.6, 134.8 (CHAr), 140.8 (d, JPC
2
1.4 Hz, NCipso), 145.7, 147.1 (NCortho), 152.0 (d, JPC = 6.8 Hz,
GeCipso), 183.8 (d, JPC = 37.2 Hz, PCCN). 31P{1H} NMR (121.5
2
1
3
MHz, C6D6, 25 °C): δ 80.5. Anal. calcd for C33H48N3PGe: C, 67.16;
H, 8.20; N, 7.12. Found: C, 67.47; H, 8.23; N, 7.10.
3
Synthesis of Phosphine-Stabilized Methyl-Germylene 1c. To
a THF solution (20 mL) of 1a (1.0 g, 1.82 mmol), at −80 °C, was
slowly added methyl magnesium bromide (0.64 mL, 3.0 M in dibutyl
ether, 1.92 mmol). The solution was slowly warmed to room
temperature and stirred for 2 h. All volatiles were removed in vacuo,
and the product was extracted twice with pentane. Methyl-germylene
1c was obtained as a yellow powder from a saturated pentane solution
at −30 °C (0.28 g, 30%). The 31P NMR spectroscopy indicated the
formation of 1c as a mixture of two diastereomers (60/40; δ 85.6 and
n
3
(overlapped with the methyl signal, 1H, 1/2 CH2bridge), 1.26 (d, JHH
= 6.9 Hz, 3H, CH3iPr), 1.33 (d, 3JHH = 6.8 Hz, 3H, CH3iPr), 1.38−1.45
n
(m, 3H, 1/2 CH2CbridgeheadCN, CH2CH3 Bu), 1.51 (d, 3JHH = 6.7 Hz, 3H,
CH3iPr), 1.52 (overlapped with the methyl signal, 2H, 1/2
n
CH2CbridgeheadCN, 1/2 GeCH2 Bu), 1.54−1.64 (m, 3H, 1/2 CH2bridge
,
n
1/2 CH2CbridgeheadCP, 1/2 GeCH2 Bu), 1.77 (m, 1H, 1/2
CH2CbridgeheadCP), 2.54−2.65 (m, 3H, PNCH2, PCCHbridgehead), 2.69−
2.80 (m, 2H, PNCH2), 2.96 (brs, 1H, NCCHbridgehead), 3.29 (sept, 3JHH
1
81.0). Major diastereomer (60%), H NMR (300 MHz, C6D6, 25
3
3
°C): δ 0.61 (d, JHP = 18.2 Hz, 3H, GeCH3), 0.91 (d, JHH = 6.7 Hz,
= 6.6 Hz, 1H, CHiPr), 3.56−3.65 (m, 1H, PNCHiPr), 3.76 (sept, 3JHH
=
3
3
3H, CH3PNiPr), 0.95 (d, JHH = 6.6 Hz, 3H, CH3PNiPr), 1.02 (d, JHH
=
6.9 Hz, 1H, CHiPr), 3.91−4.00 (m, 1H, PNCHiPr), 7.13−7.17 (m, 3H,
n
6.8 Hz, 3H, CH3PNiPr), 1.05 (d, 3JHH = 6.6 Hz, 3H, CH3PNiPr), 1.13 (d,
HAr). 13C{1H} NMR (75.5 MHz, C6D6, 25 °C): δ 13.9 (s, CH3 Bu),
2
n
3
3JHH = 6.0 Hz, 3H, CH3iPr), 1.15 (d, JHH = 6.9 Hz, 3H, CH3iPr), 1.16
3
19.1 (d, JPC = 4.1 Hz, GeCH2 Bu), 20.1 (d, JPC = 1.5 Hz, CH3PNiPr),
20.4 (d, JPC = 1.5 Hz, CH3PNiPr), 20.7 (d, JPC = 4.2 Hz, CH3PNiPr),
21.7 (d, JPC = 7.1 Hz, CH3PNiPr), 24.3 (s, CH3iPr), 24.4 (s, CH3iPr),
24.8 (s, CH3iPr), 25.5 (d, JHP = 1.3 Hz, 3H, GeCH2CH2 Bu), 26.1 (d,
JPC = 2.7 Hz, CH3iPr), 26.4 (s, CH2CbridgeheadCN), 27.5 (s, CHiPr), 28.2
3
3
(overlapped with the methyl signal, 1H, 1/2 CH2bridge), 1.17 (d, 3JHH
=
=
3
6.8 Hz, 3H, CH3PNiPr), 1.36 (m, 2H, CH2CbridgeheadCN), 1.43 (d, 3JHH
3
n
6.7 Hz, 3H, CH3iPr), 1.57 (m, 1H, 1/2 CH2bridge), 1.69 (m, 2H,
CH2CbridgeheadCP), 2.44−2.67 (m, 5H, 2 PNCH2, PCCHbridgehead), 2.88
4
n
3
3
(s, CHiPr), 30.1 (d, JHP = 10.2 Hz, 3H, CH2CH3 Bu), 30.3 (d, JPC
=
(brs, 1H, NCCHbridgehead), 3.20 (sept, JHH = 6.8 Hz, 1H, CHiPr),
1.8 Hz,CH2CbridgeheadCP), 39.0 (d, 2JPC = 2.5 Hz, PNCH2), 39.2 (d, 2JPC
3.53−3.64 (m, 2H, CHiPr, PNCHiPr), 3.77 (m, 1H, PNCHiPr), 7.06−
7.09 (m, 3H, HAr). 13C{1H} NMR (75.5 MHz, C6D6, 25 °C): δ 2.9 (d,
2JPC = 4.6 Hz, GeCH3), 20.2 (d, 3JPC = 1.6 Hz, CH3PNiPr), 20.4 (d, 3JPC
3
= 1.5 Hz, PNCH2), 40.9 (d, JPC = 7.8 Hz, NCCHbridgehead), 43.8 (d,
2JPC = 10.7 Hz, PCCHbridgehead), 43.8 (d, 2JPC = 7.2 Hz, PNCHiPr), 44.6
(d, 2JPC = 12.8 Hz, PNCHiPr), 48.73 (d, 3JPC = 3.8 Hz, CH2bridge), 90.1
(d, JPC = 29.4 Hz, PCCN), 123.3, 124.1, 125.8 (CHAr), 141.0 (d,
3JPC = 2.1 Hz, NCipso), 146.1, 146.5 (NCortho), 183.8 (d, 2JPC = 38.6 Hz,
PCCN). 31P{1H} NMR (121.5 MHz, C6D6, 25 °C): δ 85.7. Minor
= 1.7 Hz, CH3PNiPr), 20.8 (d, 3JPC = 4.3 Hz, CH3PNiPr), 21.7 (d, 3JPC
=
0.9 Hz, CH3PNiPr), 24.4 (s, CH3iPr), 24.6 (s, CH3iPr), 24.7 (s, CH3iPr),
25.5 (d, 4JPC = 1.6 Hz, CH2CbridgeheadCN), 26.3 (d, JPC = 2.6 Hz, CH3iPr),
27.6 (s, CHiPr), 28.2 (s, CHiPr), 30.2 (s, CH2CbridgeheadCP), 39.1 (d, 2JPC
8188
dx.doi.org/10.1021/ic300600c | Inorg. Chem. 2012, 51, 8187−8193

Inorganic Chemistry
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1
diastereomer (16%), H NMR (300 MHz, C6D6, 25 °C): δ 0.87 (t,
indicated the quantitative formation of the new Rh(I) complex 2b
(broad signal at δ 60.3), and the diastereomeric ratio was estimated
from the 13C NMR spectrum (65/35). All volatiles were removed in
vacuo, and yellow crystals suitable for an X-ray diffraction analysis were
obtained from a CH2Cl2−Et2O solution at −30 °C. Major
3JHH = 7.3 Hz, 3H, CH3Bu), 0.98 (d, 3JHH = 6.7 Hz, 3H, CH3PNiPr), 1.06
(d, JHH = 6.6 Hz, 3H, CH3PNiPr), 1.13 (d, JHH = 6.6 Hz, 3H,
CH3PNiPr), 1.15 (d, JHH = 6.7 Hz, 3H, CH3PNiPr), 1.22 (d, JHH = 6.7
Hz, 3H, CH3iPr), 1.24 (overlapped with the methyl signal, 2H,
GeCH2CH2Bu), 1.25 (overlapped with the methyl signal, 1H, 1/2
CH2bridge), 1.26 (d, 3JHH = 6.9 Hz, 3H, CH3iPr), 1.33 (d, 3JHH = 6.8 Hz,
3H, CH3iPr), 1.38−1.45 (m, 3H, 1/2 CH2CbridgeheadCN, CH2CH3Bu),
1.51 (d, 3JHH = 6.7 Hz, 3H, CH3iPr), 1.52 (overlapped with the methyl
3
3
3
3
1
diastereomer (65%), H NMR (300 MHz, CDCl3, 25 °C): δ 0.94
(d, 3JHH = 6.8 Hz, 3H, CH3iPr), 1.03 (d, 3JHH = 6.5 Hz, 6H, CH3PNiPr),
1.14 (d, 3JHH = 6.7 Hz, 3H, CH3iPr), 1.15 (overlapped with the methyl
3
signal, 1H, 1/2 CH2CbridgeheadCP), 1.18 (d, JHH = 6.6 Hz, 3H,
n
CH3PNiPr), 1.44 (m, 4H, CH2bridge, 1/2 CH2CbridgeheadCP, 1/2
signal, 2H, 1/2 CH2CbridgeheadCN, 1/2 GeCH2 Bu), 1.54−1.64 (m, 2H,
3
CH2CbridgeheadCN), 1.69 (d, JHH = 6.8 Hz, 12H, CH3PNiPr, 2CH3iPr),
1/2 CH2CbridgeheadCP, 1/2 GeCH2Bu), 1.76−185 (m, 2H, 1/2
CH2CbridgeheadCP, 1/2 CH2bridge), 2.44 (brs, 1H, PCCHbridgehead), 2.54−
2.65 (m, 2H, PNCH2), 2.69−2.80 (m, 2H, PNCH2), 2.88 (brs, 1H,
NCCHbridgehead), 3.29 (sept, 3JHH = 6.6 Hz, 1H, CHiPr), 3.56−3.65 (m,
1.70 (overlapped with the methyl signal, 1H, 1/2 CH2CbridgeheadCN),
1.98 (m, 4H, PNCH2), 2.28 (m, 4H, PNCH2), 2.62 (br s, 1H,
PCCHbridgehead), 2.70 (m, 1H, CHiPr), 2.93 (brs, 1H, NCCHbridgehead),
2.98−3.09 (m, 4H, 2 PNCH2), 3.17−3.23 (m, 2H, PNCHiPr), 3.29 (m,
1H, CHiPr), 4.96, 5.07 (2xbrs, 4H, CHCHCOD), 6.96 (m, 5H, HAr),
7.22 (m, 3H, HAr). 13C{1H} NMR (75.5 MHz, CDCl3, 25 °C): δ 20.3
(s, CH3PNiPr), 21.1 (d, 3JPC = 2.5 Hz, CH3PNiPr), 21.4 (d, 3JPC = 8.6 Hz,
3
1H, PNCHiPr), 3.76 (sept, JHH = 6.9 Hz, 1H, CHiPr), 3.91−4.00 (m,
1H, PNCHiPr), 7.13−7.17 (m, 3H, HAr). 13C{1H} NMR (75.5 MHz,
2
C6D6, 25 °C): δ 13.9 (s, CH3 Bu), 19.3 (d, JPC = 2.1 Hz, GeCH2Bu),
3
3
19.8 (d, JPC = 1.4 Hz, CH3PNiPr), 20.1 (d, JPC = 1.5 Hz, CH3PNiPr),
3
3
3
CH3PNiPr), 21.8 (d, JPC = 1.7 Hz, CH3PNiPr), 22.5 (s, CH3iPr), 25.2 (s,
21.2 (d, JPC = 6.4 Hz, CH3PNiPr), 21.4 (d, JPC = 3.1 Hz, CH3PNiPr),
3
CH3iPr), 25.5 (s, CH3iPr), 25.7 (s, CH3iPr), 26.8 (s, CH2COD), 27.4 (s,
CH2COD), 27.5 (s, CHiPr), 27.8 (s, CHiPr), 29.0 (s, CH2COD), 29.4 (s,
CH2COD), 32.3 (s, CH2CbridgeheadCN), 34.8 (s, CH2CbridgeheadCP), 39.0
24.4 (s, CH3iPr), 24.7 (s, CH3iPr), 24.6 (s, CH3iPr), 25.6 (d, JHP = 1.3
n
Hz, 3H, GeCH2CH2 Bu), 26.2 (d, JPC = 2.7 Hz, CH3iPr), 26.8 (s,
3
CH2CbridgeheadCN), 27.4 (s, CHiPr), 28.26 (s, CHiPr), 30.1 (d, JPC = 0.9
(brs, PNCH2), 40.9 (d, 3JPC = 4.6 Hz, NCCHbridgehead), 43.9 (d, 2JPC
6.3 Hz, PNCHiPr), 44.1 (d, JPC = 9.6 Hz, PNCHiPr), 45.2 (d, JPC
=
=
n
Hz,CH2CbridgeheadCP), 30.6 (d, 4JHP = 9.8 Hz, 3H, CH2CH3 Bu), 39.0 (d,
2
2
2JPC = 2.5 Hz, PNCH2), 39.2 (d, 2JPC = 1.5 Hz, PNCH2), 40.9 (d, 3JPC
2
9.1 Hz, PCCHbridgehead), 46.4 (brs, CH2bridge), 63.2 (brs, HCCHCOD),
65.1 (brs, HCCHCOD), 91.5 (d, JPC = 51.4 Hz, PCCN), 98.8 (m,
HCCHCOD), 99.6 (d, JRhC = 7.3 Hz, HCCHCOD), 123.5, 124.5,
126.3, 126.9, 127.6 (CHAr), 134.3 (d, 3JPC = 6.4 Hz, GeCHortho), 139.7
= 7.8 Hz, NCCHbridgehead), 43.4 (d, JPC = 13.5 Hz, PCCHbridgehead),
43.9 (d, JPC = 6.4 Hz, PNCHiPr), 44.7 (d, JPC = 11.3 Hz, PNCHiPr),
2
2
3
48.9 (d, JPC = 3.0 Hz, CH2bridge), 92.0 (d, JPC = 30.2 Hz, PCCN),
3
123.4, 123.9, 126.1 (CHAr), 141.6 (d, JPC = 5.2 Hz, NCipso), 145.9,
(s, NCipso), 140.2 (brs, GeCipso), 147.4, 147.9 (NCortho),190.7 (d, 2JPC
=
147.3 (NCortho), 186.8 (d, JPC = 40.2 Hz, PCCN). 31P{1H} NMR
2
32.4 Hz, PCCN). 31P{1H} NMR (121.5 MHz, CDCl3, 25 °C): δ
60.3 (br). Minor diastereomer (35%), 13C{1H} NMR (75.5 MHz,
CDCl3, 25 °C): δ 19.4 (d, 3JPC = 3.0 Hz, CH3PNiPr), 20.1 (d, 3JPC = 6.3
Hz, CH3PNiPr), 20.9 (s, 2C, CH3PNiPr), 22.3 (s, CH3iPr), 25.0 (s,
CH3iPr), 26.0 (s, CH3iPr), 26.1 (s, CH3iPr), 28.0 (s, CHiPr), 28.1 (s,
CHiPr), 29.4 (s, CH2COD), 29.7 (s, CH2COD), 30.5 (s, CH2COD), 31.0 (s,
CH2CbridgeheadCN), 31.1 (s, CH2COD), 35.9 (s, CH2CbridgeheadCP), 37.0 (d,
2JPC = 7.1 Hz, PNCH2), 37.9 (d, 2JPC = 6.2 Hz, PNCH2), 39.5 (d, 3JPC
= 3.7 Hz, NCCHbridgehead), 45.0 (d, 2JPC = 8.1 Hz, PNCHiPr), 46.4 (brs,
(121.5 MHz, C6D6, 25 °C): δ 80.9. Anal. calcd for C31H52N3PGe: C,
65.28; H, 9.19; N, 7.37. Found: C, 65.60; H, 9.21; N, 7.40.
Synthesis of Metallacycle 3a. To a THF solution (7 μL) of
[Rh2(μ-Cl)2(COD)2] (30.0 mg, 0.062 mmol) was added, at RT, 1a
(66 mg, 0.121 mmol), and the reaction mixture was stirred for 2 h.
Crystals suitable for an X-ray diffraction analysis were obtained from a
1
saturated THF solution at −30 °C (62.0 mg, 65%). H NMR (300
MHz, C6D6, 25 °C): δ 0.71 (d, JHH = 8.2 Hz, 1H, 1/2 CH2bridge), 1.15
(d, JHH = 6.5 Hz, 3H, CH3PNiPr), 1.18 (d, JHH = 6.7 Hz, 3H, CH3PNiPr),
1.17 (overlapped with the methyl signal, 1H, 1/2 CH2bridge), 1.27 (d,
JHH = 6.9 Hz, 3H, CH3iPr), 1.29 (d, JHH = 6.9 Hz, 3H, CH3iPr), 1.33 (d,
JHH = 6.4 Hz, 3H, CH3PNiPr), 1.45 (d, JHH = 6.8 Hz, 3H, CH3iPr), 1.48
(d, JHH = 6.4 Hz, 3H, CH3PNiPr), 1.55 (m, 3H, CH2CbridgeheadCP, 1/2
CH2CbridgeheadCN), 1.69 (d, JHH = 6.6 Hz, 3H, CH3iPr), 1.68 (overlapped
with the methyl signal, 1H, 1/2 CH2CbridgeheadCN), 1.76−2.11 (m, 8H,
4CH2COD), 2.53 (m, 1H, PCCHbridgehead), 2.58−2.66 (m, 2H, PNCH2),
2.77−2.85 (m, 3H, NCCHbridgehead, PNCH2), 3.26 (m, 1H, PNCHiPr),
3.70 (sept, JHH = 6.8 Hz, 1H, CHiPr), 4.13 (sep, JHH = 6.7 Hz, 1H,
CHiPr), 4.30 (m, 1H, PNCHiPr), 4.80, 4.91 (2xbrs, 2H, CHCHCOD),
5.45, 5.79 (2xbrs, 2H, CHCHCOD), 7.17−7.28 (m, 3H, HAr).
2
2
CH2bridge), 47.2 (d, JPC = 9.2 Hz, PCCHbridgehead), 47.5 (d, JPC = 7.7
Hz, PNCHiPr), 60.2 (d, JRhC = 13.3 Hz, HCCHCOD), 67.2 (d, JRhC
=
13.7 Hz, HCCHCOD), 90.0 (d, JPC = 52.6 Hz, PCCN), 97.1 (d,
JRhC = 8.1 Hz, HCCHCOD), 97.5 (d, JRhC = 6.1 Hz, HCCHCOD),
123.9, 124.1, 128.0, 128.1, 128.6 (CHAr), 134.3 (d, 3JPC = 6.4 Hz, 2C,
GeCHortho), 139.7 (s, NCipso), 140.0 (brs, GeCipso), 146.2, 146.6
2
(NCortho), 192.6 (d, JPC = 32.4 Hz, PCCN). 31P{1H} NMR (121.5
MHz, CDCl3, 25 °C): δ 60.3 (br).
Synthesis of Dimethylbutadiene Cycloadduct 4. To a C6D6
solution (0.5 mL) of 1c (50 mg, 0.095 mmol), at room temperature,
was added 2,3-dimethyl-1,3-butadiene (21.4 μL, 0.189 mmol). The
solution was warmed at 65 °C for 72 h. All volatiles were removed in
vacuo, and the product was obtained as yellow oil and was analyzed
13C{1H} NMR (75.5 MHz, C6D6, 25 °C): δ 21.6 (d, JPC = 5.4 Hz,
3
3
3
CH3PNiPr), 22.0 (d, JPC = 5.5 Hz, CH3PNiPr), 22.4 (d, JPC = 2.5 Hz,
1
3
without any further purification. H NMR (300 MHz, C6D6, 25 °C):
CH3PNiPr), 22.9 (d, JPC = 6.0 Hz, CH3PNiPr), 24.6 (s, CH3iPr), 24.8 (s,
CH3iPr), 25.8 (s, CH3iPr), 26.1 (d, 4JPC = 1.2 Hz, CH2CbridgeheadCN), 28.0
the most representative signals δ 0.48 (brs, 3H, GeCH3), 1.47 (brs,
3H, CH3vinyl), 1.47 (brs, 1H, 1/2CH2vinyl), 1.66 (brs, 3H,
CH3vinyl), 1.70 (brs, 3H, 3/2CH2vinyl). 13C{1H} NMR (75.5 MHz,
C6D6, 25 °C): δ 1.1 (s, GeCH3), 19.2 (s, 2C, CH3vinyl), 22.0 (d, 3JPC
= 15.2 Hz, 2C, CH3PNiPr), 22.2 (d, 3JPC = 10.6 Hz, CH3PNiPr), 22.8 (d,
3JPC = 11.8 Hz, CH3PNiPr), 23.1 (s, CH3iPr), 23.3 (s, CH3iPr), 23.4 (s,
CH3iPr), 23.5 (s, CH3iPr), 25.9 (s, CH2CbridgeheadCN), 27.6 (s, CHiPr),
2
(s, CHiPr), 28.2 (s, CHiPr), 28.3 (s, CH2CbridgeheadCP), 29.1 (d, JRhC
=
=
2
2
2.1 Hz, CH2COD), 29.7 (d, JRhC = 1.8 Hz, CH2COD), 30.6 (d, JRhC
3.2 Hz, CH2COD), 30.9 (d, 2JRhC = 1.4 Hz, CH2COD), 39.9 (d, 2JPC = 1.7
3
2
Hz, PNCH2), 42.7 (d, JPC = 3.6 Hz, CH2bridge), 44.9 (d, JPC = 13.4
Hz, PNCHiPr), 45.8 (d, 3JPC = 1.7 Hz, NCCHbridgehead), 45.9 (d, 2JPC
=
1.2 Hz, PNCH2), 47.2 (d, 2JPC = 6.3 Hz, PNCHiPr), 48.2 (d, 2JPC = 8.2
Hz, PCCHbridgehead), 94.7 (d, JRhC = 8.2 Hz, HCCHCOD), 96.2 (t,
JRhC = 2.7 Hz, HCCHCOD), 96.4 (d, JRhC = 5.9 Hz, HCCHCOD),
100.3 (dd, JRhC = 6.2 Hz, 2JPC = 10.2 Hz, HCCHCOD), 105.2 (dd, JPC
27.7 (s, CHiPr), 28.6 (s, 3C, CH2CbridgeheadCP, CH2vinyl), 43.7 (d, 2JPC
=
1.6 Hz, PCCHbridgehead), 44.3 (d, 3JPC = 3.7 Hz, CH2bridge), 44.8 (d, 2JPC
= 22.6 Hz, PNCHiPr), 49.4 (d, 2JPC = 8.7 Hz, PNCH2), 49.7 (d, 2JPC
=
=
2
3
2
15.0 Hz, PNCHiPr), 50.1 (d, JPC = 6.7 Hz, PNCH2), 51.4 (d, JPC
= 40.3 Hz, JRhC = 7.3 Hz, PCCN), 123.3, 124.2, 126.9 (CHAr),
140.3 (NCipso), 147.2, 148.8 (NCortho), 174.6 (d, 2JPC = 17.8 Hz, PC
22.1 Hz, NCCHbridgehead), 106.6 (d, JPC = 33.0 Hz, PCCN), 123.1,
CN). 31P{1H} NMR (121.5 MHz, C6D6, 25 °C): δ 61.7 (d, JPRh
=
123.3, 126.3 (CHAr), 129.9, 130.0 (brs, 2C, CC), 137.1 (s, 2C,
2
NCortho), 147.2 (brs, NCipso), 158.9 (d, JPC = 5.5 Hz, PCCN).
153.9 Hz).
31P{1H} NMR (121.5 MHz, C6D6, 25 °C): δ 84.5.
Synthesis of Rh(I) Complex 2b. To a THF solution (7 μL) of
[Rh2(μ-Cl)2(COD)2] (30.0 mg, 0.062 mmol) was added, at RT,
phenyl-substituted germylene 1b (71 mg, 0.121 mmol), and the
reaction mixture was stirred for 2 h at RT. The 31P NMR spectroscopy
Crystallographic Studies. Data for compounds 1a and 1b were
collected on a Bruker-AXS SMART APEX II diffractometer at 193(2)
K, with graphite-monochromated Mo Kα radiation (wavelength =
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Table 1. Crystallographic Parameters
1a
1b
2b
3a
empirical formula
fw/g mol−1
cryst size/mm
cryst system
space group
a (Å)
C27H43ClGeN3P
548.65
C33H48GeN3P
590.30
C41H60ClGeN3PRh·0.5(CH2Cl2)
879.30
C35H54Cl2GeN3PRh
794.18
0.42 × 0.26 × 0.20
orthorhombic
Fdd2
0.25 × 0.10 × 0.08
monoclinic
P21/c
0.25 × 0.15 × 0.10
monoclinic
P21/c
0.34 × 0.26 × 0.16
monoclinic
C2/c
10.3296(5)
18.4260(9)
15.6319(7)
90
18.7398(3)
16.2976(2)
10.7861(2)
90
40.324(10)
10.852(2)
20.025(5)
90
32.830(8)
39.870(7)
11.240(3)
90
b (Å)
c (Å)
α (deg)
β (deg)
98.601(3)
90
101.610(1)
90
105.206(6)
90
90
γ (deg)
90
temperature (K)
Mo Kα (Å)
vol (Å3)
193
193
293
293
0.71073
2941.8(2)
4
0.71073
3226.82(9)
4
0.7107
0.7107
14712(6) Å3
16
8456(4)
8
Z
ρcalc (g cm−3
)
1.239
1.215
1.381
1.434
F(000)
μ (mm−1
1160.0
1256.0
6576
)
1.205
1.024
1.30
1.48
reflns collected
29957
56460
47358
7927
42901
unique reflns
5537
6542
7482
Rint
0.1458
0.0678
0.056
1.08
0.037
GOF on F2
0.997
1.021
1.18
R1 [I > 2σ(I)]
0.0621
0.0363
0.060
0.135
0.66/−0.75
0.031
wR2
0.1999
0.0908
0.080
residual electron density peaks (eÅ−3
)
0.418/−0.436
0.543/−0.238
0.60/−0.42
Figure 2. Molecular structure of 1a (left) and 1b (right). Thermal ellipsoids represent 30% probability, and H atoms have been omitted for clarity.
Selected bond lengths (Å) and bond angles (deg) for 1a: Ge−Cl 2.266(3), N1−Ge 1.989(4), Ge−P 2.474(2), P−C1 1.718(6), C1−C2 1.386(7),
C2−N1 1.341(7), Cl−Ge−P 95.23(11), Cl−Ge−N1 96.28(16), N1−Ge−P 83.29(13), Ge−P−C1 95.43(19), P1−C1−C2 116.8(4), C1−C2−N1
126.2(5); for 1b: Ge−P 2.434(1), Ge−N1 1.993(2), Ge−C3 2.003(2), P−C1 1.724(2); C1−C2 1.387(3), C2−N1 1.343(3), N1−Ge−P 84.69(5),
C3−Ge−P 104.43(7), N1−Ge−C3 99.55(9), C2−N1−Ge 114.01(14), N1−C2−C1 124.7(2), C2−C1−P 118.06(17), C1−P−Ge 92.32(8).
0.71073 Å) by using phi and omega scans (see Table 1). The data
were integrated with SAINT, and an empirical absorption correction
with SADABS was applied.12,13 The structures were solved using direct
methods, using SHELXS-97,14 and refined using the least−squares
method on F2.15 All non-H atoms were treated anisotropically. The H
atoms were located by difference Fourier maps and refined with a
riding model. Data for complexes 2b and 3a were recorded at room
temperature on a Rigaku AFC-7S diffractometer equipped with a with
a Mercury CCD detector using monochromated Mo (Kα) radiation (λ
= 0.71070 Å). An empirical absorption correction (multiscan) was
applied using the package CrystalClear.16 The structures were solved
using direct methods and refined by full-matrix least-squares on F2
using the SHELXTL-PLUS package.17 Hydrogen atoms on C and N
atoms were placed at fixed positions using the HFIX instruction. All of
the H atoms were refined with isotropic displacement parameters set
to 1.2−1.5 × Ueq of the attached atom. In the crystal structure of 2b a
dichloromethane molecule was found disordered. Attempts were made
to model this disorder or split it into two positions but were
unsuccessful. A PLATON/SQUEEZE routine was used to correct the
data for the presence of disordered solvent.18 A potential solvent
volume of 582.7 Å3 was found. The stoichiometry of the solvent was
calculated to be approximately 0.5 molecule of dichloromethane per
formula unit, which results in a total of 179 electrons per unit cell. This
molecule was used to calculate expected molecular weight, DXcalc and
F(000).
Theoretical Calculations. All structures were optimized using
DMol3.19 This DFT based program allows us to determine the relative
stability of all studied species on the basis of their electronic structure.
The calculations were performed using the Kohn−Sham Hamiltonian
with the Perdew−Wang 1991 gradient correction20 and the double-ζ
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plus (DNP) numerical basic set.19 The utilization of the numerical
basics sets combined with DFT allows the program to obtain a high
accuracy by keeping a relatively low computational cost, compared
with ab initio methods. DMol3 calculates variational self-consistent
solutions to the density functional theory (DFT) equations. The
solutions to these equations provide the molecular electron densities,
which can be integrated among the atomic volume (defined by the
interatomic surfaces and/or the van der Waals envelope) in order to
obtain the Bader charge on each atom of the system.21
those reported in the case of silicon analogue [4 +1]
cycloadduct.22
Phosphine−Germylene−Rhodium Complexes. The
reaction of chloro-germylene derivative 1a with dimer complex
[Rh2(μ-Cl)2(COD)2] in THF at room temperature, monitored
by 31P NMR spectroscopy, leads, after 1 h of reaction, to the
formation of a mixture of three rhodium complexes: 2a (δ 49.3,
d, JPRh = 24.2 Hz), 2a′ (δ 51.8, d, JPRh = 28.4 Hz), and 3a (δ
61.9, d, JPRh = 153.8 Hz). After 2 h at RT, complexes 2a and 2a′
quantitatively transform into the corresponding rhodium
metallacycle 3a (Scheme 3).
RESULTS AND DISCUSSION
■
Phosphine-Stabilized Germylenes. Phosphine-stabilized
chloro-germylene 1a (mixture of two diastereomers, 65:35)
reacts with phenyllithium to yield the new phenyl-substituted
germylene 1b as a mixture of two diastereomers (75:25).
Indeed, the 31P NMR spectrum showed two singlet resonances
at δ 80.5 and 75.6. Similarly, methyl- and butyl-substituted
germylenes 1c and 1d were prepared by the reaction of 1a with
one equivalent of MeMgBr or nBuLi, respectively. Both were
obtained as mixtures of diastereomers as indicated by the 31P
NMR spectroscopy: 1c (δ 85.6 and 81.0, 60:40), 1d (δ 85.7
and 80.9, 84:16) (Scheme 1).
Scheme 3. Reaction of 1a,b with [Rh2(μ-Cl)2(COD)2]
A diastereoselective crystallization led to the isolation of the
major diastereomer of 1b, which was obtained as yellow crystals
from a saturated n-pentane solution, at −30 °C. Its structure,
unambiguously established by an X-ray diffraction analysis,
showed a strongly pyramidalized germanium center (ΣGeα° =
288.6°) and coordination of the phosphine ligand to the
germanium atom with a P−Ge distance of 2.434 Å, similar to
that observed for phosphine-stabilized chlorogermylene 1a
[2.474(2) Å] and in the range of the previously reported
phosphine−germylene compounds (Figure 2).8−10
Crystals of complex 3a, suitable for an X-ray diffraction
analysis, were obtained from a concentrated THF solution at
−30 °C. The molecular structure of 3a clearly exhibits a six-
membered cycle, in agreement with the migration of a chlorine
atom from the rhodium to the germanium center. Complex 3a
shows slightly distorted square planar geometry around the
rhodium atom, which may result from the steric bulk of the
phosphino-dichlorogermyl ligand. The Rh−P bond length
[2.287 Å] compares well with the Rh−P bonds of metallacycle
Rh(I) cyclooctadiene phosphine−carbene complexes.23 More-
over, the structure of 3a showed a strongly distorted tetrahedral
geometry around the germanium atom, as shown by the Cl2−
Ge−Cl1 bond angle [98.3°], which is considerably more acute
than the N3−Ge−Rh angle [119.9°]. A similar distortion was
previously observed in several trichlorogermyl tungsten
complexes.24 The Ge−Rh bond length (2.358) Å) is much
shorter than that observed for Rh(CO)4−(GePh3) [2.506 Å]25
probably due to a strong rhodium−dichlorogermyl π-back-
bonding.
Upon heating a toluene solution of the isolated isomer of 1b
at 50 °C for 15 min, a slow and clean isomerization was
observed leading to the initial mixture of diastereomers (75:25)
as indicated by the 31P NMR analysis (Scheme 2). The
Scheme 2. Isomerization of 1b
In the case of the phenyl-substituted germylene ligand 1b,
the corresponding Rh(I) complex 2b is thermally stable, and
was isolated, as yellow air-sensitive crystals from a CH2Cl2−
Et2O solution at −30 °C. The 31P NMR spectrum of 2b
showed only one broad singlet resonance at δ 60.3, shifted
toward higher field than that observed for the free ligand 1b (δ
80.5), probably as consequence of the direct coordination of
the germylene fragment. Variable temperature 31P NMR
measurements (−80 °C − 35 °C) showed no change in the
resolution of the spectrum preventing the evaluation of the
diastereomeric ratio. In contrast, the 13C NMR spectrum clearly
indicated that this Rh(I) complex 2b was obtained as a mixture
of two diastereomers (estimated ratio: 65/35).
The structure of 2b was unambiguously confirmed by an X-
ray diffraction analysis, which clearly shows the σ-coordination
of the germylene to rhodium center (Figure 3). Complex 2b
presents a strongly distorted tetrahedral geometry around the
germanium atom with a slightly larger N1−Ge−C3 angle
(102.64°) than that in 1b (99.6°), probably due to the change
inversion at the trigonal pyramidal germanium center could be
rationalized either by a vertex-inversion mechanism or more
likely by a P−Ge bond dissociation−Ge−N bond rotation. In
order to check the lability of this bond, phosphine-stabilized
germylene 1c was reacted with two equivalents of 2,3-
dimethylbutadiene, leading to the formation of the correspond-
ing [4 + 1] cycloadduct 4, which was obtained as only one
diastereomer in good agreement with the occurrence of a
dynamic kinetic resolution. The NMR data are very similar to
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Inorganic Chemistry
Article
Figure 3. Molecular structure of 3a (left) and 2b (right). Thermal ellipsoids represent 30% probability, and H atoms have been omitted for clarity.
Selected bond lengths (Å) and bond angles (deg) for 3a: Rh−P 2.2865(12), Rh−Ge 2.3575(6), Ge−Cl1 2.2114(13), Ge−Cl2 2.2316(12), Ge−N1
1.882(3), N1−C2 1.372(5), C1−C2 1.395(6), P−C1 1.764(4); Cl1−Ge−Cl2 98.32(6), N1−Ge−Rh 119.93(10), N1−Ge−Cl2 100.65(11), N1−
Ge−Cl1 101.56(10), Cl2−Ge−Rh 119.65(4), Cl1−Ge−Rh 113.19(4), P−Rh−Ge 87.46(3); for 2b: Ge−Rh 24499(8), Ge−P 2.3943(14), Ge−C3
1.967(5), Ge−N1 1.956(4), N1−C2 1.348(6), C1−C2 1.379(7), P−C1 1.733(5); Cl−Rh−Ge 93.09(5), C3−Ge−Rh 117.75(14), N1−Ge−C3
102.64(19), C3−Ge−P 109.04(15).
of coordination number of the germanium atom. The Ge−P
and Ge−C3 bond lengths [2.3943 and 1.967 Å] in 2b are
slightly shorter than in 1b [Ge−P = 2.434 and Ge−C3 = 2.003
Å ]; these differences may be ascribable to the decreasing p
character of these bonds as a consequence of the coordination
of Rh on the germanium atom. The Ge−Rh bond length in 2b
[2.4499 Å] is slightly longer than that observed for 3a.
Theoretical Studies. As already mentioned, 2b is thermally
stable compared to 2a, and no isomerization was observed
upon heating at 50 °C for 4 h. With the aim to better explain
the experimental results and to gain more information on the
electronic properties of both free germylenes and rhodium
complexes, DFT calculations have been performed (Table 2).
which isomerizes into complex 3, via the migration of the
chlorine atom from the rhodium to the germanium.
SUMMARY
■
We have successfully synthesized the first Ge(II)−Rh(I)
complexes featuring a Rh−Cl bond using the original
phosphine-stabilized germylene ligands. Of particular interest,
the stability of the resulting complexes depends strongly on the
electron donating character of germylene fragment, which can
be modulated by the nature of the germylene substituent.
ASSOCIATED CONTENT
■
S
* Supporting Information
Theoretical calculation data. This material is available free of
charge via the Internet at http://pubs.acs.org.
Table 2. Selected Bond Lengths (Å), Atomic Charge (q), and
Electron Density (ρ) at the BCP (in a.u.) Calculated for 1a,b
and 2a,b
AUTHOR INFORMATION
■
qGe
qP
qRh
ρGe−P
dGe−P
Corresponding Author
*E-mail: baceired@chimie.ups-tlse.fr, eocando@ivic.gob.ve.
1a
1b
2a
2b
+0.56
+0.75
+0.71
+0.91
+1.96
+1.90
+1.99
+1.97
0.067
0.068
0.076
0.075
2.518
2.459
2.460
2.448
Notes
+0.81
+0.37
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The structures of 1a,b and 2a,b were optimized using
Dmol3.19 Calculations reproduce the same trend experimentally
observed, showing a P−Ge bond length slightly shorter for 1b
and 2b compared with 1a and 2a. A Bader’s topological analysis
of the electron density showed that the density values at the
bond critical points (BCP) of the Ge−P bonds are similar in all
cases, indicating a similar covalent character of these bonds.
Nevertheless, the calculated charges on the P, Ge, and Rh
atoms show that the charge deficiency on the Ge atom in 1a
and 2a is almost 0.2 au lower compared to 1b and 2b,
respectively, while the electron deficiency for the rhodium atom
in 2a is around 0.5 au higher than that for 2b. Thus, the high
electron deficiency at the rhodium atom in 2a probably induces
the phosphine migration from Ge to Rh center to generate a
highly reactive pentacoordinated rhodium−germylene complex,
We thank the Venezuelan Minister for Sciences and
Technology (FONACIT G-2005000433, G-2005000447,
grant LAB-97000821 and PCP-2007001996), the CNRS, and
the ANR (NOPROBLEM, and LEGO) for financial support of
this work. Yosslen Aray from Centro de Quimica-IVIC is also
thanked for helpful discussions.
́
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