Stereoselective formation and catalytic activity of hydrido(acylphosphane)(chlorido)(pyrazole)rhodium(iii) complexes. Experimental and DFT studiesElectronic supplementary information (ESI) available: Cartesian coordinates of optimized DFT structures, images generated from those coordinate files, computationally obtained energy values associated with each structure, and crystallographic data file of complexes 2-Hpz, 3a-Hdmpz and 7-Hpz. CCDC 1062495-1062497. For ESI and crystallographic data in CI
The reaction of [{RhCl(COD)} 2 ] (COD = 1,5-cyclooctadiene) with L = pyrazole (Hpz), 3(5)-methylpyrazole (Hmpz) or 3,5-dimethylpyrazole (Hdmpz) and PPh 2 ( o -C 6 H 4 CHO) (Rh : L : P = 1 : 2 : 1) gives hydridoacyl complexes [RhHCl{PPh 2 ( o -C 6 H 4 CO)}(L) 2 ] ( 1 ). Stereoselective formation of 1...
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| Main Authors | , , , , , , , |
|---|---|
| Format | Journal Article |
| Language | English |
| Published |
14.07.2015
|
| Online Access | Get full text |
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| Summary: | The reaction of [{RhCl(COD)}
2
] (COD = 1,5-cyclooctadiene) with L = pyrazole (Hpz), 3(5)-methylpyrazole (Hmpz) or 3,5-dimethylpyrazole (Hdmpz) and PPh
2
(
o
-C
6
H
4
CHO) (Rh : L : P = 1 : 2 : 1) gives hydridoacyl complexes [RhHCl{PPh
2
(
o
-C
6
H
4
CO)}(L)
2
] (
1
). Stereoselective formation of
1-Hpz
and
1-Hmpz
with pyrazoles
trans
to hydrido and phosphorus and hydrogen bond formation with
O
-acyl and chlorido occur.
1-Hmpz
is a mixture of two linkage isomers in a 9 : 1 ratio, with two 5-methylpyrazole ligands or with one 3- and one 5-methylpyrazole ligand, respectively. Fluxional
1-Hdmpz
undergoes metallotropic tautomerization and is a mixture of equal amounts of
1a-Hdmpz
and
1b-Hdmpz
, with hydrido
trans
to pyrazole or chlorido, respectively. Complexes
1
readily exchange hydrido by chlorido to afford [RhCl
2
{PPh
2
(
o
-C
6
H
4
CO)}(L)
2
] (
2-Hpz
,
2-Hmpz
and
2-Hdmpz
) as single isomers with
cis
chloridos and two N-H Cl hydrogen bonds. The reaction of
1
with PPh
3
or PPh
2
OH affords static [RhHCl{PPh
2
(
o
-C
6
H
4
CO)}(PPh
3
)L] (
3
) or [RhHCl{PPh
2
(
o
-C
6
H
4
CO)}(PPh
2
OH)L] (
4
) respectively with
trans
P-atoms and pyrazoles forming N-H Cl hydrogen bonds.
3-Hpz
and
3-Hmpz
contain single species with hydrido
cis
to chlorido, while
3-Hdmpz
is a mixture of equal amounts of
3a-Hdmpz
and
3b-Hdmpz
. Complexes
4
, with an additional O-H O hydrogen bond, selectively contain only the
cis
-H,Cl species with all the three ligands. The reaction of [{RhCl(COD)}
2
] with L and PPh
2
(
o
-C
6
H
4
CHO) (Rh : L : P = 1 : 1 : 2) led to complexes with
trans
P-atoms, [RhHCl{PPh
2
(
o
-C
6
H
4
CO)}{PPh
2
(
o
-C
6
H
4
CHO)-κ
P
}L] (
5-Hpz
,
5a-Hdmpz
and
5b-Hdmpz
), at room temperature, and to [RhCl{PPh
2
(
o
-C
6
H
4
CO)}{PPh
2
(
o
-C
6
H
4
CHOH)}(Hmpz)] (
6-Hmpz
) or [RhCl{PPh
2
(
o
-C
6
H
4
CO)}
2
L] (
7
) with hydrogen evolution in refluxing benzene. DFT calculations were used to predict the correct isomers, their ratios and the particular intramolecular hydrogen bonds in these complexes. Single crystal X-ray diffraction analysis was performed on
2-Hpz
,
3a-Hdmpz
and
7-Hpz
. Complexes
1
are efficient homogeneous catalysts (0.5 mol% loading) in the hydrolysis of amine- or ammonia-borane (AB) to generate up to 3 equivalents of hydrogen in the presence of air.
Stereoselectivity assisted by hydrogen bond formation, inhibited by steric hindrance, predicted by DFT calculations. |
|---|---|
| Bibliography: | 7-Hpz CCDC 2-Hpz For ESI and crystallographic data in CIF or other electronic format see DOI 3a-Hdmpz and 10.1039/c5dt01705j 1062495-1062497 , Electronic supplementary information (ESI) available: Cartesian coordinates of optimized DFT structures, images generated from those coordinate files, computationally obtained energy values associated with each structure, and crystallographic data file of complexes |
| ISSN: | 1477-9226 1477-9234 |
| DOI: | 10.1039/c5dt01705j |