Heterolytic H2 activation by rhodium thiolato complexes bearing the hydrotris(pyrazolyl)borato ligand and application to catalytic hydrogenation under mild conditions

Abstract

Thiolato complexes of Rh(III) bearing a hydrotris(3,5-dimethylpyrazolyl)borato ligand (Tp(Me2)) have been prepared, and their reactivity toward H(2) has been investigated. The bis(thiolato) complex [Tp(Me2)Rh(SPh)(2)(MeCN)] (1) reacted with 1 atm H(2) at 20 degrees C to produce the hydrido-thiolato complex [Tp(Me2)RhH(SPh)(MeCN)] (2) and PhSH via heterolytic cleavage of H(2). This process is reversible and in equilibrium in THF and benzene. The bis(selenolato) complex [Tp(Me2)Rh(SePh)(2)(MeCN)] (4) was also converted to [Tp(Me2)RhH(SePh)(MeCN)] and PhSeH under 1 atm H(2), but the equilibrium largely shifted to 4. Reaction of the dithiolato complex [Tp(Me2)Rh(bdt)(MeCN)] (3; bdt = 1,2-C(6)H(4)S(2)) with H(2) occurred in the presence of amine, giving the anionic hydrido complex [Tp(Me2)RhH(bdt)](-) and an equimolar amount of ammonium cations. Catalytic activity for hydrogenation has been examined under 1 atm H(2) at 20-50 degrees C. While 1, 2, and 4 slowly hydrogenated styrene at similar rates at 50 degrees C, activities for the hydrogenation of N-benzylideneaniline increased in the order, 2 < 1 < 4. Complex 3 was found to be the most active and selective catalyst for hydrogenation of imines, and thus a variety of imines were reduced at 20 degrees C under 1 atm H(2), with the C=C and C=O bonds in the substrate molecules completely preserved. An ionic mechanism was involved to explain such high chemoselectivity.

Organoselenium ligands in catalysis

“…In 60, the bis( phenylselenolate)Rh(III) unit is coordinated with tris(3,5-dimethylpyrazol-1-yl)borate (Tp Me2 ) coligand resulting in [Tp Me2 Rh(SePh) 2 (MeCN)]. 110,111 Complex 60 has been used in catalytic hydrogenation. Reactions of the Rh(I) complex [Tp Me2 Rh(coe)(MeCN)] (coe = cyclooctene) with one equiv.…”

“…of diphenyldiselenide PhSeSePh afforded 60 (Scheme 7). [110][111][112][113] Chart 9 Methylselenolate bridged diruthenium complexes.…”

“…223 The term "heterolytic dihydrogen cleavage" is used tentatively to describe simple reaction formalism where two hydrogen atoms in a dihydrogen molecule end up bonding to discrete electronically opposite elements. The bis(selenolate)Rh(III) complex having a tris(3,5-dimethylpyrazolyl)borate (Tp Me2 ) as co-ligand, [Tp Me2 Rh(SePh) 2 (MeCN)] (60), 110,111 has been found to react reversibly with H 2 to form the hydrido-selenolato complex [Tp Me2 RhH(SePh)(MeCN)] ( 149) and PhSeH, as shown in Scheme 36. On the basis of this heterolysis of H 2 , a hydrogenation catalyst that operates under ambient temperature and pressure with high chemoselectivity toward imines (PhCHvNPh) has been developed.…”

Ir−Sn Tetrazole Complexes with Proton‐Responsive P−OH Groups and an Ir−Ir Tetrazole Complex for CO2 Hydrogenation

“…Such H 2 activation by metalÀ thiolato complexes have been reported in literature. [33][34][35] Ohki et al [36] reported on the facile heterolysis of H 2 by Ir and Rh half-sandwich complexes for which a sulfur atom bonded to the metal served as a site for H 2 cleavage resulting in SÀ H and metal hydride groups. As such the structure of the resulting metal hydride obtained from 7 may exist as F (Scheme 3 cycle 1).…”

Catalytic activity in transfer hydrogenation using ruthenium (II) carbonyl complexes containing two 1,8-naphthyridine as N-monodentate ligands

“…Transition metal complexes containing a coordinative unsaturated metal center and a Brønsted basic π-donor ligand have been reported in homogeneous transfer hydrogenation. Ligands with different transition metals such as amido [19][20][21][22], thiolate [23][24][25][26][27][28], phosphido [29], imido [30][31][32][33][34][35][36][37][38][39][40], oxo [41][42][43][44][45][46], and sulfido [47] have been investigated for this reaction. The most active and selective catalysts for the transfer hydrogenation reactions are ruthenium [48], iridium [49] and rhodium [50] complexes containing nitrogen, oxygen and N,O-donor ligands [51][52][53][54][55][56][57][58].…”