Carbodiphosphoranes revised: innovative synthetic strategies for versatile preparation & determination of specific parameters

• Applicant: Dr. Istemi Kuzu
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 438201253

In this project we present various synthetic approaches towards novel carbodiphosphoranes (CDPs) and selected specific parameters for the characterisation of CDPs. Our superiour goal is to analyse, charaterise and synthesise novel CDPs for specific applications (e.g. homogeneous catalysis, deposition on surfaces). Our intermediate goals are the synthesis of CDP based Grubbs-catalysts and the deposition of CDPs on gold surfaces; the long-term goal is to establish CDPs in vast areas of chemistry and to offer CDPs as a good alternative to NHCs. The proposal is divided in two parts, in which both sub-projects are described in detail. In the first part, we show our facile and practicable synthetic approaches towards a broad range of different and new CDPs. In this course we pick up old synthetic routes and refine them. We also want to develop new pathways which should lead to a new type of CDPs. From this different approaches we will use the most successful and effective syntheses for further CDP studies. In the second part we introduce selected specific parameters which we think are the most useful and pragmatic ones. We will use them for the characterisation and description of properties of CDPs. We distinguish between intrinsic and extrinsic properties. The intrinsic properties of CDPs are physical-chemistry-based which can be determined directly. Besides the proton affinity (PA) it is the basicity and nucleophilicity, respectively, the thermodynamic basicity (pKa), the kinetic basicity (proton self-exchange rate), and the one-electron-oxidation (oxidation potential EOx) of CDP. We will determine these parameters with methods and techniques from spectroscopy and physical chemistry. From EOx and pKa the homolytic bond dissociation energy for the acidic CH bonds in [HCDP]+ bzw. [H2CDP]2+ can be calculated. The extrinsic properties can be obtained after reaction of the CDP with a selected electrophile. The electrophiles are established spectroscopic testing probes, delivering informations of the steric and electronic properties of the corresponding CDPs: %Vbur (percent buried volume) via [CDP-Ni(CO)3] and [CDP-MCl], TEP (Tolman electronic parameter) via [CDP-Ni(CO)3] and sigma donor and pi acceptor strength via [CDP-Se] and [CDP-PPh]. In addition, we will also test the catalytic activity of CDPs in a selected benchmark reaction (Au catalysed hydroamination via [CDP-AuCl]). And for the first time, we will deploy chiral CPD ligands in asymmetric catalysis. We will calibrate all data with the values obtained by quantum chemical calculations to provide a model which can deliver a good predictability of properties of newly synthesised CDPs.

• DFG Programme: Research Grants