The showcase catalyst for olefin hydrogenations is Wilkinson's complex CIRh
(PPh3)(3) (1). Here, the Wilkinson-type catalyst ClRh[Ph2P(CH2)(3)Si(OEt)(3
)](3) (2), trans-ClRh(CO)CPh2P(CH2)(3)Si(OEt)(3)](2) (3), and the chelate c
omplex ClRh(PPh3)[Ph2PCH2-CHOHCH2PPh2] (4) have been synthesized using the
bifunctional ligands Ph2P(CH2)(3)Si(OEt)(3) (5) and Ph2PCH2CHOHCH2PPh2 (6),
and fully characterized. The dihydride complex 4(H)(2) has been generated
in situ and characterized with NMR. Complexes 2, 3, and 4 have been immobil
ized on silica, giving 2i, 3i, and 4i, respectively, which have been studie
d by solid-state NMR. The catalytic activities of 2i-4i for the hydrogenati
on of 1-dodecene (7), 2-cyclohexen-1-one (8), and 4-bromostyrene (9) are co
mpared with those of the homogeneous analogs 2 and 3, as well as with 1. Wh
ile there are no substantial differences between 1 and 2 concerning TON and
TOF, 2i shows reversed activity for the three test samples: dodecene gives
the lowest TOF, followed by bromostyrene and cyclohexenone. However, TON a
nd maximal yield are the same for 1, 21 and 21. In contrast to 1 and 2, the
immobilized catalyst 21 can be recycled seven times, 4i three times. Catal
ysts 3 and 3i give maximal TOF for the hydrogenation of 7, followed by 8 an
d 9. The yields are below 100% for the homogeneous catalyst 3, but immobili
zation (3i) gives maximum yields for all substrates. (C) 2001 Elsevier Scie
nce B.V. All rights reserved.