Journal of Molecular Catalysis A: Chemical 182–183 (2002) 99–105 Phosphine-containing carbosilane dendrimers based on polyhedral silsesquioxane cores as ligands for hydroformylation reaction of oct-1-ene Lo¨ ıc Ropartz a , Russell E. Morris a , Douglas F. Foster b , David J. Cole-Hamilton a,∗ a School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK b Catalyst Evaluation and Optimisation Service (CATS), School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK Received 2 July 2001; accepted 4 October 2001 Abstract Radical additions of diethyl- and diphenylphosphine have been used to prepare 1st and 2nd generation dendrimers based on polyhedral oligosilsesquioxane cores by a divergent synthetic method. The 1st generation dendrimer is built on either 16 and 24 vinyl or allyl arms formed by successive hydrosilation and vinylation or allylation of vinyl-functionalised polyhedral silsesquioxanes. Successive hydrosilation/allylation followed by hydrosilation/vinylation and addition of phosphine produce the 2nd generation dendrimer. The dendrimers have been used as ligands for the hydroformylation of oct-1-ene catalysed by [Rh(acac)(CO) 2 ]. Using the alkylphosphine-containing dendrimers as ligands, alcohols (nonan-1-ol and 2-methyloctanol) are obtained, whilst the diphenylphosphine counterparts lead to the formation of aldehydes (nonan-1-al and 2-methyloctanal). Linear to branched ratios of 3/1 are obtained for the diethylphosphine compounds while ratios of 12 to 14/1 are given by the diphenylphosphine dendritic molecules. © 2002 Published by Elsevier Science B.V. Keywords: Silsesquioxane; Dendrimer; Hydroformylation; Rhodium; Phosphine 1. Introduction In the last decade, dendritic molecules have stirred a lot of interest in chemistry and more particu- larly in the field of catalysis (for a recent review, see [1]). As they are well-defined macromolecules with potentially numerous functionalisable sites, they have the potential to bridge the gap between homo- geneous and heterogeneous catalysis by acting as soluble macromolecular ligand(s). Numerous applica- tions in catalysis, ranging from C–C coupling [2–4] to hydrogenation [5–7], have already demonstrated their ability to act as efficient ligand(s)/catalyst(s). ∗ Corresponding author. E-mail address: djc@st-andrews.ac.uk (D.J. Cole-Hamilton). Ultra-filtration techniques were successfully applied to this new catalytic system giving high expectations for future industrial applications [2,8,9]. In addition, their preparation allows the tuning of substituents and the diversity of branching patterns, size and crowd- ing of the molecule, which may affect the activity or selectivity of the catalyst. These ‘dendrimer effects’ vary from total inhibition of the reaction [10] to enhanced reactivity [2,3,11,12] and selectivity [13]. The use of bidentate ligands in hydroformylation reactions is often useful in obtaining high selectiv- ity catalysts [14,15]. The incorporation of phosphine moieties (possibly acting as bidentate ligands) into the structure of a dendrimer is therefore of great interest [16,17]. We have previously synthesised a dendrimer structure based on a polyhedral octaoligosilsesquiox- 1381-1169/02/$ – see front matter © 2002 Published by Elsevier Science B.V. PII:S1381-1169(01)00502-7