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Xantphite: A New Family of Ligands for Catalysis. Applications in the Hydroformylation of Alkenes
Author(s) -
Dieleman Cedric B.,
Kamer Paul C. J.,
Reek Joost N. H.,
van Leeuwen Piet W. N. M.
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20011017)84:10<3269::aid-hlca3269>3.0.co;2-g
Subject(s) - hydroformylation , chemistry , aldehyde , denticity , catalysis , medicinal chemistry , styrene , rhodium , organic chemistry , crystal structure , polymer , copolymer
The novel bulky diphosphite (P∩P) ligands ( 3 and 4 ) based on the 2,7,9,9‐tetramethyl‐9 H ‐xanthene‐4,5‐diol ( 2 ) backbone were investigated in the Rh‐catalyzed hydroformylation of oct‐1‐ene, styrene, and ( E )‐oct‐2‐ene. These diphosphites gave rise to very active and selective catalysts for the hydroformylation of oct‐1‐ene to nonanal with average rates>10000 (mol aldehyde)(mol Rh) −1 h −1 ( P (CO/H 2 )=20 bar, T =80°, [Rh]=1 m M ) 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) −1 h −1 ) were observed for the hydroformylation of styrene in the presence of these bidentate ligands ( P (CO/H 2 )=2 – 10 bar, T =120°, [Rh]=0.2 m M ). Remarkable activities (up to 980 (mol aldehyde)(mol Rh) −1 h −1 ) 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 =120°, [Rh]=1 m M ). 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 bis‐equatorial ( ee ) coordination is not a prerequisite for highly selective catalysts.