Synthesis of P-bridged, planar bis(NHC) BCl3 adducts.

Planar PV- or PIII-bridged bis(NHCs), which have only been employed in transition metal complex chemistry so far, were subjected to BCl3-containing solutions targeting the corresponding bis(NHC) BCl3 adducts. While the P(O)NEt2-bridged bis(NHC) showed the expected adduct formation, the PNEt2-bridged bis(NHC) reacted not only at the carbene moiety but also at the P-NEt2 functional group. The latter enabled access to the first 1,4-diphosphinine bis(NHC) main group adduct; its formation and properties were investigated by DFT calculations. Through the same route, a 1,4-diphosphinine bis(imidazolium) scaffold was generated and explored theoretically and experimentally. The new 1,4-diphosphinines are shown to possess high global aromaticity and a unique P-centred reactivity, allowing the formation of hitherto inaccessible [4 + 2]-cycloaddition products, thus suggesting potential new applications compared to previously known 1,4-diphosphinine derivatives.

Tapping into the coordinative potential of a C-functional 1,4-diphosphabarrelene using two sets of complementary ligand centres.

7,8-Dihydro-1,4-diphosphabarrelene diselones and bis(NHCs) were synthesised and employed as multitopic P,Se and P,C ligands in coordination chemistry, benefitting from a unique bent, P-bridged topology, thus being promising new building blocks.

Elimination reactions in 1,4-diphosphinine chemistry: mixed-valence intermediates and 1,1- vs. 1,4-elimination pathways.

Reactions of tricyclic 1,4-diphosphinines 1,4 with LiOH, followed by protonation are reported. 1,3-Thiazole-2-thione-derived 1 enabled only observation of the first anionic addition product 2/3. On the other hand, imidazole-2-selone-annelated derivative 4 enabled the identification of the first (5) and second product (6) at low temperature. As water was eliminated upon warming in both cases, DFT calculations were performed to gain more insight into the reaction pathway(s).

Application of phosphorus-bridged rigid, bent bis(NHCs) as dipodal ligands in main group and transition metal chemistry.

Phosphorus-bridged rigid, bent bis(N-heterocyclic) carbenes have not been reported, so far, despite having structural features that could make them interesting ligands in coordination and main group element chemistry. In previous reports, we had demonstrated that tuning of σ3- and σ4-phosphorus environments in planarised bis(NHCs) affects electronic properties and can provide additional coordination sites. Herein, we report on first examples of synthesis and conversion of 1,4-diphosphabarrelene-related compounds into rigid bent, doubly P-bridged bis(NHCs). The formation of main group element adducts with substrates from group 13, 14 and 15 illustrates opportunities to access novel scaffolds and to create nonplanar branching points. DFT calculations reveal the new bis(NHCs) to be good candidates as novel soft/hard ligands with up to four coordination sites. The synthesis of a dinuclear Fe(CO)4 complex is demonstrated. The thermal retro-[4 + 2] cycloaddition was theoretically and experimentally explored for a variety of ionic and zwitterionic 1,4-diphosphabarrelenes, and the generation and trapping of a dinuclear Fe(0) bis(NHC) complex with a tricyclic 1σ2,4 σ2-diphosphinine scaffold is presented.

A homonuclear π-system with a singlet carbene-type α and a nucleophilic ß phosphorus - the first use in P-heterocyclic synthesis.

A µ2-(η1,η2)-dinuclear diphosphene complex having two W(CO)5 groups with dimethyl acetylenedicarboxylate, 4-phenyl-1,2,4-triazoline-3,5-dione and diethyl azodicarboxylate was applied to P-heterocyclic synthesis, i.e., using a singlet carbene-type reactivity of a homonuclear π-system assisted by a haptotropic shift thus rendering a more nucleophilic ß phosphorus and, hence, a subsequent ring expansion.