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

• Main Authors: San Nacianceno, Virginia, Azpeitia, Susan, Ibarlucea, Lourdes, Mendicute-Fierro, Claudio, Rodríguez-Diéguez, Antonio, Seco, José M, San Sebastian, Eider, Garralda, María A
• Format: Journal Article
• Language: English
• Published: 14.07.2015
• DOI: 10.1039/c5dt01705j
• ISSN: 1477-9226

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.