Cyclo-Dipnictadialanes

Using the AlI precursor Cp3t Al in conjunction with triphosphiranes (PAr)3 (Ar=Mes, Dip, Tip) we have succeeded in preparing Lewis base-free cyclic diphosphadialanes with both the Al and P atoms bearing three substituents. Using the sterically more demanding Dip and Tip substituents the first 1,2-diphospha-3,4-dialuminacyclobutanes were obtained, whereas with Mes substituents [Cp3t Al(μ-PMes)]2 is formed. This divergent reactivity was corroborated by DFT studies, which indicated the thermodynamic preference for the 1,2-diphospha-3,4-dialuminacyclobutane form for sterically more demanding groups on phosphorus. Using Cp*Al we could extend this concept to the corresponding cyclic diarsadialanes [Cp*Al(μ-AsAr)]2 (Ar=Dip, Tip) and additionally add the phosphorus variants [Cp*Al(μ-PAr)]2 (P=Mes, Dip, Tip). The reactivity of one variant [Cp3t Al(μ-PPh)]2 towards NHCs was tested and resulted in double NHC-stabilised [Cp3t (IiPr2 )Al(μ-PPh)]2 .

Isolation of Neutral, Mono-, and Dicationic B2 P2 Rings by Diphosphorus Addition to a Boron-Boron Triple Bond

The NHC-stabilised diboryne (B₂ (SIDep)₂ ; SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P-P bond activation with tetraethyldiphosphine at room temperature to form a B₂ P₂ heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B-B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B₂ P₂ rings, with their diradicaloid, planar-ring isomers lying close in energy.