Reactivity studies of a corrole germanium hydride complex with aldehydes, olefins and alkyl halides

Article abstract of DOI:10.1039/c1cc15076f

The tris(pentafluorophenyl) corrole germanium hydride complex (TPFC)Ge-H was prepared by the reduction of (TPFC)Ge-OCH₃ with NaBH₄. The reactivity of (TPFC)Ge-H with series of aldehydes, olefins and alkyl halides to produce α-hydroxy alkyl and alkyl complexes was studied.

Full text of DOI:10.1039/c1cc15076f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 11677–11679
www.rsc.org/chemcomm
COMMUNICATION
Reactivity studies of a corrole germanium hydride complex with
aldehydes, olefins and alkyl halidesw
Huayi Fang,a Zhen Ling,a Penelope J. Brothersb and Xuefeng Fu*a
Received 16th August 2011, Accepted 19th September 2011
DOI: 10.1039/c1cc15076f
The tris(pentafluorophenyl) corrole germanium hydride complex
(TPFC)Ge-H was prepared by the reduction of (TPFC)Ge-OCH3
with NaBH4. The reactivity of (TPFC)Ge-H with series of
aldehydes, olefins and alkyl halides to produce a-hydroxy alkyl
and alkyl complexes was studied.
The discoveries of facile syntheses of meso-aryl substituted
corroles in 19991 triggered the revival of the chemistry of
corroles. A variety of main group and transition metal
elements were inserted into the corrole ring2 and some of the
complexes showed similar or superior properties to the related
porphyrin complexes. Despite the broad scope of metallo-
corroles and the unique reactivity of porphyrin metal
hydrides,3 the preparation and the reactivity of corrole metal
Scheme 1 The reactivity pattern of (TPFC)Ge-H.
hydrides have not yet been reported.
precursors to prepare corrole derivatives functionalized on the
Transition metal hydrides play a central role in many of the
ligand periphery by bromo, nitro and amino groups.10a–c This
most important catalytic processes including hydrogenation,
article reports on the reactivity studies of germanium hydride
hydroformylation, and related transformations. The rhodium
corrole complexes with aldehydes, olefins and alkyl halides to
porphyrin hydrides, (por)Rh-H, typical of late transition metal
form corrole germanium a-hydroxy alkyl and alkyl complexes
(Scheme 1).
hydrides, display unique reactivity patterns towards an excep-
tional breadth of substrates including alkyl halides, olefins,4
aldehydes,4,5 and carbon monoxide.3c,4,6 However, analogous
reactivity studies of main group metal hydride complexes are
quite rare.7
The H3(TPFC) free base corrole and (TPFC)Ge-X (X = Cl,
OH) complexes were prepared following the methods reported
by Gross et al.1,10d The labile chloro or hydroxo axial ligand
was rapidly substituted by ꢀOCH3 or ꢀOCH2CH3 at room
temperature when (TPFC)Ge-X was dissolved in methanol or
ethanol, respectively. After dissolution of (TPFC)Ge-OCH3
(1) in ethanol, a new triplet and quartet (at ꢀ1.69 and ꢀ1.01
ppm) assigned to the methyl and methylene, respectively, of
ꢀOCH2CH3 in (TPFC)Ge-OCH2CH3 (2) appeared and the
ꢀOCH3 singlet at ꢀ1.01 ppm disappeared (Table S1, ESIw).
Organo-germanium complexes show unique structures and
fascinating chemical reactivity compared to both their lighter
and heavier group 14 element congeners. Power et al. reported
a
series of novel organogermanium compounds and
transition-metal hybrid organogermanium compounds.8
Roesky et al. studied the reactivity of germanium(II) hydrides
stabilized by bulky b-diketiminate ligands.9 Fully-characterized
germanium corrole complexes are limited to Ge(Cor)OH,
Ge(Cor)OMe and the m-oxo dimer [Ge(Cor)]2O.10 The
Ge(Cor)X (X = OCH3, Cl) corroles have also been used as
1
This diagnostic change in the H NMR spectrum implied the
quantitative formation of complex 2 via a ligand exchange
reaction. Complex 2 was further characterized by molecular
structure determination (Fig. S1, ESIw).
a Beijing National Laboratory for Molecular Sciences, State Key Lab
of Rare Earth Materials Chemistry and Applications, College of
Chemistry and Molecular Engineering, Peking University, Beijing,
100871, China. E-mail: fuxf@pku.edu.cn; Fax: +86 10-6275-1708;
Tel: +86 10-6275-6035
The (TPFC)Ge-H (3) was obtained by reduction of
(TPFC)Ge-OCH3 with NaBH4 in methanol/benzene solution
(1 : 30) (eqn (1)). Because of the large ring-current effect of the
corrole ligand, the resonance of metal-bound hydrogen shifted
upfield and appeared at d = ꢀ2.14 ppm. The IR spectrum of
(TPFC)Ge-H showed an absorption at 2085 cmꢀ1 corres-
ponding to the absorption of Ge-H,11 nearly identical to the
Ge-H absorption at 2086 cmꢀ1 for H2Ge[3,5-(CF3)2C6H3]2.11a
The electronic structure of (TPFC)Ge-H is envisioned as
b School of Chemical Sciences, The University of Auckland, Private
Bag 92019, Auckland 1142, New Zealand
w Electronic supplementary information (ESI) available: The general
procedure details of the reactions and spectral data for related com-
plexes. CCDC 839547–839549. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1cc15076f
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11677–11679 11677

View Article Online
[(TPFC)Ge(II)]H where the electron-withdrawing ligand
TPFC stabilizes the electron rich metal center.
NaBH4;R: T:;4h
ðTPFCÞGe-OCH3
ðTPFCÞGe-H
ð1Þ
ƒƒƒƒƒƒƒƒƒƒ!
C6H6:CH3OH¼30:1
The unusual a-hydroxyalkyl metal complexes are proposed to
be key intermediates in many important catalytic processes12
which are thermodynamically unstable and prone to dissociation
to form a metal hydride complex and an aldehyde.13 Reports
on the reactivity studies of transition metal hydrides with
aldehydes to form a-hydroxyalkyl metal complexes remain
limited and representative complexes are rhodium hydride4,5
Fig. 1 1H NMR spectra of (TPFC)Ge-H and (TPFC)Ge-CH2CH2CO2CH3
at high field. (a) (TPFC)Ge-H; (b) (TPFC)Ge-H plus methyl acrylate at 60 1C
for 12 h without addition of KOH. (TPFC)Ge-H plus methyl acrylate at 60 1C
with addition of KOH: (c) after 8 h, (d) after 16 h, and (e) after 24 h.
and manganese hydride.14 Satge
´
et al. reported that the main
group metal hydride R2GeH2 (R = phenyl, mesityl) can be
deprotonated by tert-butyllithium to form R2GeHLi which
functioned as a strong nucleophile and reacted with benzaldehyde
to form the a-hydroxy benzyl germanium complex.11b We
observed that in the presence of a catalytic amount of KOH,
the reaction of (TPFC)Ge-H with paraformaldehyde at 70 1C
in benzene led to the exclusive formation of the a-hydroxy
methyl germanium corrole complex (TPFC)Ge-CH2OH (4)
(Scheme 1). Addition of D2O to the benzene solution of
(TPFC)Ge-CH2OH resulted in the disappearance of the resonance
at d = ꢀ3.72 ppm and the doublet at d = ꢀ2.20 ppm collapsed
into a singlet, consistent with assignment of the OH and CH2
protons, respectively. The hemiacetal (TPFC)Ge-CH2OCH2OH
was formed through the reaction of (TPFC)Ge-CH2OH with
excess formaldehyde when the reaction was performed lower than
70 1C (eqn (2)). The hemiacetal dissociated nearly quantitatively at
70 1C to form (TPFC)Ge-CH2OH (eqn (2)). The enthalpy and
entropy changes for eqn (2) were obtained from variable-temperature
1H NMR experiments using C6D6 as the solvent where DH2 =
57.8 kJ molꢀ1 and DS2 = 1.92 ꢁ 102 J (Kꢂmol)ꢀ1. The reaction of
(TPFC)Ge-H with benzaldehyde under similar reaction conditions
formed the a-hydroxyalkyl product (TPFC)Ge-CH(OH)C6H5 (5)
(Scheme 1) in 84% yield within 24 hours.
Fig. 2 The structure of 6 illustrated by one of the two independent
molecules. Some atom labels are omitted for clarity.
corroles through the reaction of (TPFC)Ge-H with alkyl
halides in methanol to form (TPFC)Ge-R (R = CH3 (8),
CH2C6H5 (9)) (Scheme 1). Details of the method are described
in ESI.w The (TPFC)Ge-R complexes were easily identified by
(TPFC)Ge-CH2OH + HCHO
1
the characteristic H NMR spectra of the alkyl groups. The
" (TPFC)Ge-CH2OCH2OH
(2)
resonances of axial alkyl hydrogens were shifted to high field
positions due to shielding by the ring-current effect of the
corrole ligand. Hydrogen atoms on the a-carbon atoms appear
at high field ranging from ꢀ3.0 to ꢀ5.2 ppm (Table S1, ESIw)
and the phenyl hydrogens of the benzyl group in 9 were split
and shifted upfield of their normal diamagnetic positions to
3.60 ppm, 6.16 ppm, and 6.41 ppm. The complex 8 was further
characterized by X-ray crystal structure determination and its
molecular structure is illustrated in Fig. 3.
The reaction of (TPFC)Ge-H with olefins CH2QCHR
(R = ꢀCO2CH3 and ꢀCH2CH2CH3) was also investigated
(Scheme 1). Although no alkyl germanium corrole was
observed upon mixing (TPFC)Ge-H with excess of methyl
acrylate at 60 1C for 12 hours (Fig. 1a–b), the complex
(TPFC)Ge-CH2CH2CO2CH3 (6) was formed in over 95%
yield upon the addition of a catalytic amount of KOH
(Fig. 1b–d). Complex 6 was further characterized by molecular
structure determination (Fig. 2). A similar result was also
observed for the unactivated olefin 1-pentene which formed
the corresponding product (TPFC)Ge-CH2CH2CH2CH2CH3
(7) in 50% yield within 24 hours (Scheme 1). The electron-
withdrawing ligand TPFC stabilized the carbanion intermediate.
The stereo-selectivity is determined by steric hindrance of the
ligand where nucleophilic attack occurred at the less crowded
terminal olefinic carbon.
The (TPFC)Ge-H is proposed to be rapidly deprotonated in
basic solution to form a corrole Ge(II) anion intermediate
which subsequently reacts with aldehydes, olefins and alkyl
halides to form a-hydroxyalkyl and alkyl germanium products
(Scheme 2). When the reaction of (TPFC)Ge-H with methyl
acrylate was performed in CD3OD, the deuterated alkyl
germanium product (TPFC)Ge-CH2CHDCO2CH3 was
formed while (TPFC)Ge-CH2CH2CO2CH3 was the main product
in CD3OH. These observations indicate that the hydrogen atom
on the b-carbon is obtained via the protonation of the nucleo-
philic-addition reaction intermediate by the hydroxyl proton of
There is no reported method for the synthesis of alkyl
germanium corrole complexes. Here we demonstrate a simple
one-pot synthesis method for preparation of alkyl germanium
c
11678 Chem. Commun., 2011, 47, 11677–11679
This journal is The Royal Society of Chemistry 2011

View Article Online
(c) M. D. Farnos, B. A. Woods and B. B. Wayland, J. Am. Chem.
Soc., 1986, 108, 3659; (d) J. P. Collman, P. J. Brothers, L. McElwee-
White and E. Rose, J. Am. Chem. Soc., 1985, 107, 6110.
4 X. Fu and B. B. Wayland, J. Am. Chem. Soc., 2005, 127, 16460.
5 B. B. Wayland, B. A. Woods and V. M. Minda, J. Chem. Soc.,
Chem. Commun., 1982, 634.
6 H. W. Bosch and B. B. Wayland, J. Chem. Soc., Chem. Commun.,
1986, 900.
7 (a) G. F. Bradley and S. R. Stobart, J. Chem. Soc., Dalton Trans.,
1974, 264; (b) R. D. Adams, F. A. Cotton, W. R. Cullen,
D. L. Hunter and L. Mihichuk, Inorg. Chem., 1975, 14, 1395;
(c) J. A. Connor, P. D. Rose and R. M. Turner, J. Organomet.
Chem., 1973, 55, 111; (d) S. Aldridge and A. J. Downs, Chem. Rev.,
2001, 101, 3305; (e) A. J. Downs, Coord. Chem. Rev., 1999, 189, 59;
(f) E. C. Ashby, J. Organomet. Chem., 1980, 200, 1.
Fig. 3 The structure of 8ꢂacetone.
8 (a) M. Stender, A. D. Phillips, R. J. Wright and P. P. Power,
Angew. Chem., Int. Ed., 2002, 41, 1785; (b) L. Pu, A. D. Phillips,
A. F. Richards, M. Stender, R. S. Simons, M. M. Olmstead and
P. P. Power, J. Am. Chem. Soc., 2003, 125, 11626; (c) G. H. Spikes,
Y. Peng, J. C. Fettinger and P. P. Power, Z. Anorg. Allg. Chem.,
2006, 632, 1005; (d) R. S. Simons, L. Pu, M. M. Olmstead and
P. P. Power, Organometallics, 1997, 16, 1920; (e) X. Wang,
Y. Peng, M. M. Olmstead, J. C. Fettinger and P. P. Power,
J. Am. Chem. Soc., 2009, 131, 14164; (f) X. Wang, Y. Peng,
M. M. Olmstead, H. Hope and P. P. Power, J. Am. Chem. Soc.,
2010, 132, 13150; (g) R. S. Simons and P. P. Power, J. Am. Chem.
Soc., 1996, 118, 11966; (h) X. Wang, Y. Peng, Z. Zhu,
J. C. Fettinger, P. P. Power, J. Guo and S. Nagase, Angew. Chem.,
Int. Ed., 2010, 49, 4593; (i) G. H. Spikes, J. C. Fettinger and
P. P. Power, J. Am. Chem. Soc., 2005, 127, 12232; (j) C. Cui,
M. M. Olmstead and P.P. Power, J. Am. Chem. Soc., 2004,
126, 5062; (k) C. Cui, M. Brynda, M. M. Olmstead and
P. P. Power, J. Am. Chem. Soc., 2004, 126, 6510; (l) X. Wang,
Z. Zhu, Y. Peng, H. Lei, J. C. Fettinger and P. P. Power, J. Am.
Chem. Soc., 2009, 131, 6912; (m) Y. Peng, J.-D. Guo, B. D. Ellis,
Z. Zhu, J. C. Fettinger, S. Nagase and P. P. Power, J. Am. Chem.
Soc., 2009, 131, 16272.
Scheme 2 Reaction pathways of (TPFC)Ge-H with formaldehyde,
1-pentene and methyl iodide.
9 (a) A. Jana, G. Tavcar, H. W. Roesky and M. John, Dalton Trans.,
2010, 9487; (b) A. Jana, D. Ghoshal, H. W. Roesky, I. Objartel,
G. Schwab and D. Stalke, J. Am. Chem. Soc., 2009, 131, 1288;
(c) A. Jana, H. W. Roesky and C. Schulzke, Dalton Trans., 2010,
132; (d) A. Jana, S. S. Sen, H. W. Roesky, C. Schulzke, S. Dutta
and S. K. Pati, Angew. Chem., Int. Ed., 2009, 48, 4246.
methanol. Previously, the porphyrin rhodium hydride complex
(Por)Rh-H was reported to be deprotonated to form the RhI
porphyrin anion [(Por)Rh]ꢀ which functioned as a nucleophile to
react with organic halides, olefins and alkynes to produce metal
alkyl complexes.15
10 (a) S. Nardis, F. Mandoj, R. Paolesse, F. R. Fronczek,
K. M. Smith, L. Prodi, M. Montalti and G. Battistini, Eur. J.
Inorg. Chem., 2007, 2345; (b) M. Mastroianni, W. Zhu,
M. Stefanelli, S. Nardis, F. R. Fronczek, K. M. Smith, Z. Ou,
K. M. Kadish and R. Paolesse, Inorg. Chem., 2008, 47, 11680;
(c) M. Stefanelli, F. Mandoj, M. Mastroianni, S. Nardis,
P. Mohite, F. R. Fronczek, K. M. Smith, K. M. Kadish,
X. Xiao, Z. Ou, P. Chen and R. Paolesse, Inorg. Chem., 2011,
50, 8281; (d) L. Simkhovich, A. Mahammed, I. Goldberg and
Z. Gross, Chem.–Eur. J., 2001, 7, 1041.
Reactions of late transition metal hydride complexes with
unsaturated substrates play a crucial role in many important
catalytic processes. We have observed that a main group hydride
complex demonstrates parallel reactivity to transition metal
hydrides with aldehydes, olefins and alkyl halides to form
a-hydroxyalkyl and alkyl complexes. This research demonstrates
that the cheaper main-group metal complexes can emulate the
reactivity of transition metal complexes although their electronic
structures, orbitals and bonding properties are quite different.
The main group metal hydrides may function like transition
metal hydrides and find wide application in hydrogenations,
hydroformylation, and related transformations. Further research
focused on the mechanistic study of the substrate reactions of
corrole germanium hydrides is under investigation.
11 Typical IR absorption of Ge-H falls in the range of 1953–2175 cmꢀ1
.
(a) J. E. Bender IV, K. E. Litz, D. Giarikos, N. J. Wells,
M. M. Banaszak Holl and J. W. Kampf, Chem.–Eur. J., 1997,
3, 1793; (b) A. Castel, P. Riviere, J. Satge and H. Y. Ko, Organo-
´
metallics, 1990, 9, 205; (c) F. Riedmiller, G. L. Wegner, A. Jockisch
and H. Schmidbaur, Organometallics, 1999, 18, 4317;
(d) E. J. Kupchik, in Organotin Compounds, ed. A. K. Sawyer, Marcel
Dekker, New York, vol 1, 1971, pp. 7.
12 (a) R. Whyman, A. P. Wright, J. A. Iggo and B. T. Heaton,
J. Chem. Soc., Dalton Trans., 2002, 771; (b) D. R. Fahey, J. Am.
Chem. Soc., 1981, 103, 136; (c) J. A. Roth and M. Orchin,
J. Organomet. Chem., 1978, 172, C27.
We are grateful for support by NSFC Grant 20801002.
Notes and references
13 (a) J. A. Gladysz, J. C. Selover and C. E. Strouse, J. Am. Chem.
Soc., 1978, 100, 6766; (b) D. L. Johnson and J. A. Gladysz, Inorg.
Chem., 1981, 20, 2508.
14 (a) G. D. Vaughn, C. E. Strouse and J. A. Gladysz, J. Am. Chem.
Soc., 1986, 108, 1462; (b) G. D. Vaughn and J. A. Gladysz, J. Am.
Chem. Soc., 1981, 103, 5608.
1 (a) Z. Gross, N. Galili and I. Saltsman, Angew. Chem., Int. Ed.,
1999, 38, 1427; (b) Z. Gross, N. Galili, L. Simkhovich, I. Saltsman,
M. Botoshansky, D. Blaser, R. Boese and I. Goldberg, Org. Lett.,
1999, 1, 599.
¨
2 (a) I. Aviv-Harel and Z. Gross, Chem.–Eur. J., 2009, 15, 8382;
(b) I. Aviv-Harel and Z. Gross, Coord. Chem. Rev., 2011, 255, 717.
3 (a) P. J. Brothers, Adv. Organomet. Chem., 2001, 48, 289;
(b) P. J. Brothers, Adv. Organomet. Chem., 2000, 46, 223;
15 H. Ogoshi, J. Setsune, T. Omura and Z. Yoshida, J. Am. Chem.
Soc., 1975, 97, 6461.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11677–11679 11679