. (2014) A theoretical study of the activity in Rh-catalyzed hydroformylation: the origin of the enhanced activity of the π-acceptor phosphinine ligand. Catalysis Science and Technology, 4 . pp. 979-987. ISSN 2044-4753 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/29468/1/post_print_final.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Journal Name The factors governing the activity in Rh-catalyzed hydroformylation were investigated using a set of computational tools. We performed DFT calculations on the phosphinine-modified Rh catalyst [HRh(CO) 3 (PC 5 H 2 R 3 )] and compared it to the phosphane-modified HRh(CO) 3 (PR 3 ) and HRh(CO) 2 (PR 3 ) 2 complexes. The -acceptor phosphinine ligand coordinates preferentially at the equatorial site of 10 pentacoordinated Rh complex with the heterocycle perpendicular to the equatorial plane, although the ligand freely rotates around the Rh-P bond. The overall energy barrier can be divided into the following contributions: alkene complex formation, alkene rotation and alkene insertion. In the absence of steric effects (model systems), the overall barrier correlates with the computed barrier for alkene rotation. This proves that -acceptor ligands reduce backdonation to the alkene, leading to a lower rotational barrier, 15 and consequently, to a higher activity. The Rh-P donor-acceptor interactions were quantified using a modified version of energy decomposition analysis (EDA). In Rh-phosphinine systems, the efficient directionality of the -backdonation, rather than the overall acceptor ability, is responsible for the high catalytic activity. Introducing steric effects increases the energy required to coordinate the alkene, increasing the overall barrier. The factors governing the activity in Rh-monophosphane catalysts seem to 20 be related to those derived for Rh-diphosphane during the development of a QSAR model (Catal. Sci. Technol. 2012¸ 2, 1694). To investigate whether the findings for mono-can be extrapolated to diphosphane ligands, we re-examine our previous QSAR model using the Topological Maximum Cross Correlation (TMACC) method based on easy-to-interpret 2D-descriptors. The TMACC descriptors highlight heteroatoms close to phosphorus as activity-increasing atoms, whereas highly substituted carbon 2...