A. Extending the chemistry of Carbones
The reactivity of nucleophilic carbodiphosphorane (C(PPh3)2) and carbodicarbene (C(NHC)2) ligands (L) towards various dichlorophosphines has been explored. In most cases the expected carbone-for-chloride ligand exchange was observed. However, the use of MeN(PCl2)2 resulted in a unique P–N bond cleavage that, according to computational studies, occurred via an SN2′-like mechanism (Chem. Commun. 2015, 51, 10762).
Figure 1. Carbone induced P-N bond cleavage.
B. Bis(carbodicarbene)phosphenium trication: the case against hypervalency
The first example of a phosphenium trication has been prepared by using the exceptional nucleophilic properties of a carbodicarbene ligand. According to theoretical investigations the trication contains quite polarized P–C bonds suggesting a substantial contribution from the dative bond model. As one of the resonance forms for the title compound depicted a hypervalent phosphoranide we also showed that phosphoranides, in general, do not contain a hypervalent P centre (Chem. Commun. 2016, 52, 9789).
Figure 2. Bis(carbodicarbene)phosphenium trication.
C. Small Molecule Activation
Our work reflects efforts to increase the Lewis acidity of two-coordinate phosphorus(III)-based compounds for the purpose of small molecule activation. In this view, we tuned the electronic properties of phosphenium ions by increasing their overall positive charge and by varying the extent of p-donation from the neighboring substituents to the central P atom. This enabled the activation of enthalpically strong C-F bond of trifluorotoluene and [BArF4]- (ArF = (CF3)2-C6H3) anion (Inorg. Chem. 2015, 54, 4180). Furthermore, implemented structural modifications enabled activation of E-H bonds (E = B, Si, and C), resulting in the formation of formal E-H insertion and/or hydride abstraction products (Chem. Commun. 2017, accepted). Described chemical reactivity, although well established for transition metals, has no precedent in P(III)-based chemistry.
Figure 3. Small molecule activation by Phosphenium cations.
D. Ortho Metalation of Carbone Ligands directed by Ir(I)-center
C-H activation of phenyl rings was observed when carbodiphosphorane was mixed with Ir(I) dimer. The corresponding carbone-Ir complex was isolated in good yield and its identity was confirmed by multinuclear NMR and X-ray methods. If Ph group was replaced by methyl, the corresponding C(sp3)-H bonds remained inert towards ortho metalation. Preliminary results indicated that newly prepared Ir(I)-complex is capable of activating aromatic C-F bonds (unpublished results).
Figure 4. Ortho metalation of carbone ligands at Iridium(I)-center.