Xantphite: A New Family of Ligands for Catalysis. Applications in the Hydroformylation of Alkenes

Abstract

Dedicated to the memory of Professor Luigi M. VenanziThe novel bulky diphosphite (P P) ligands (3 and 4) based on the 2, 7,9,9-tetramethyl-9H-xanthene-4,5diol (2) backbone were investigated in the Rh-catalyzed hydroformylation of oct-1-ene, styrene, and (E)-oct-2ene. These diphosphites gave rise to very active and selective catalysts for the hydroformylation of oct-1-ene to nonanal with average rates b 10000 (mol aldehyde)(mol Rh) À1 h À1 (P(CO/H 2 ) 20 bar, T 808, [Rh] 1 mm) and maximum selectivities of 79% for the linear product. Relatively high selectivities towards the linear aldehyde (up to 70%, linear/branched up to 2.3) but very high activities (up to 39000 (mol aldehyde)(mol Rh) À1 h À1 ) were observed for the hydroformylation of styrene in the presence of these bidentate ligands (P(CO/ H 2 ) 2 ± 10 bar, T 1208, [Rh] 0.2 mm). Remarkable activities (up to 980 (mol aldehyde)(mol Rh) À1 h À1 ) were achieved with these diphosphites for the hydroformylation of (E)-oct-2-ene with selectivities for the linear product of 74% (l/b up to 2.8, P(CO/H 2 ) 2 bar, T 1208, [Rh] 1 mm). A detailed study of the solution structure of the catalyst under catalytic conditions was performed by NMR and high-pressure FT-IR. The spectroscopic data revealed that under hydroformylation conditions, the bidentate ligands rapidly formed stable, well-defined catalysts with the structure [RhH(CO) 2 (P P)]. All the ligands showed a preference for an equatorial-apical (ea) coordination mode in the trigonal bipyramidal Rh-complexes, indicating that a bisequatorial (ee) coordination is not a prerequisite for highly selective catalysts.

Synthesis, characterization and coordination chemistry of a new phosphite–ether ligand: The effects of alkali metal salts and the ligand/Rh molar ratio on the catalytic activity and regioselectivity of a Rh(I) complex of this ligand in the hydroformylation of styrene

“…To gain more insight into this effect, we have studied Rh(I) complexes of the monodentate phosphite polyether ligand (2,2 0 -C 12 hydroformylation [16][17][18][19][20][21][22]. It is also similar to monodentate phosphite ligands [23][24][25][26] that have been used in Rh(I) catalysts for the hydroformylation of styrene and to phosphine/ether ligands that have been used in a variety of catalytic reactions such as alkene and CO 2 hydrogenation, alkene oligomerization and polymerization, methanol and methyl acetate carbonylation by Lindner et al [27].…”

New Rhodium Complexes Coordinated by Bidentate Imine Ligands with Benzothiazolyl Functionalities

“…The most successful hydroformylation catalysts in recent studies contain bidentate phosphine ligands [12], and the discovery that the hydroformylation of propene is accelerated by the addition of N-containing compounds like amines, amino acids, heterocycles, and urea derivatives [13] influenced our decision to focus on the preparation and characterization of rhodium(I) complexes with bidentate imine-coordinating benzothiazolyl-containing ligands for future use in hydroformylation reactions.…”

“…In the 1 H-NMR spectrum of 4, two sets of broad s are observed for the four olefinic protons at d 4.69, for HÀC (12) and HÀC(12') (deshielded by the anisotropic effect of the pseudoaromatic benzothiazole rings) and at d 4.48 for HÀC (13) and HÀC(13')-facing the CH 2 CH 2 bridge (less deshielded by the benzothiazole rings) 1 ). Five signals for the cod ligand and no 13 C-NMR data have been reported for the cod ligand in [Rh(cod){2-[(4,5-dihydro-4-isopropyl)oxazol-2-yl)methyl]pyridine}]PF 6 [9].…”

“…Five signals for the cod ligand and no 13 C-NMR data have been reported for the cod ligand in [Rh(cod){2-[(4,5-dihydro-4-isopropyl)oxazol-2-yl)methyl]pyridine}]PF 6 [9]. The signals in the 13 C-NMR of 4 at d 87.33 for C (12) and C(12') and at d 83.86 for C (13) and C(13') are coupled to Rh and the coupling constants are 11.69 Hz. Similar Rh,C coupling constants have been described for the olefinic cod C-atoms in the 13 [6].…”