[1] Compounds can exhibit localized singlet diradical character (diradicaloid) between the boron atoms in the solution and solid state.
[1] Alternative routes of synthesis utilizing facile leaving groups have also been discovered including hydrogen halide and organylphosphane elimination to obtain the monomer precursors.
[2][6] The diphosphadiboretanediyl derivatives have a wider structural range, adopting planar and bicyclo[1.1.0] geometries, similar to diphosphacylobutanediyls.
Coplanar π-bonding to the boron atom and addition of aromatic groups to the ring favors the bicyclo[1.1.0] structure with a B-B bond length shorten down to 1.83 Å.
[1][8] In the planar, diphosphadiboretanediyl structures, the substantially long B-B bond can be considered to experience homolytic cleavage to form a localized singlet diradicaloid between the boron atoms.
The radical cation is found to exhibit triplet state by electronic paramagnetic resonance, accompanying with a shortening of the B-B bond (2.63 Å) and slight perturbance of planar, square structure.
[8] The compounds have been shown to perform chloride abstraction from deuterated chloroform, trans-addition of trimethyl tin hydride, and formation of bicyclo[1.1.1] structure with selenium.
Reactivity is displayed towards bromotrichloromethane where radical activity induces formation of boron-containing spiro-compound from the tert-butyl group.
Thermolysis of facile silyl halide leaving group forms boraphosphane from silylphosphine and tribromobromide. Boraphosphane dimerizes, leaving diphosphadiboretane.
Formation of singlet diradical diphosphaboretanediyl using 1,2-dichloro-1,2-di(
tert
-butyl)diborane with lithium diisopropylphosphide reagent.
Synthesis of diphosphadiboretane using reactive diboryne precursor with tetraethyldiphosphine (Dep = 2,6-diethyl phenyl).
Structural range of diphosphadiboretanediyl (phosphorus = orange; boron = pink, R = white).
2D contour plot of
electron localization function
of hydrogen-substituted diphosphadiboretanediyl. Displayed plane contains both B-H bonds and is perpendicular to plane of B
2
P
2
ring. Contour lines between B atoms indicates through-space interactions.
Frontier orbitals of hydrogen-substituted diphosphadiboretanediyl compound in square/diradical geometry.
Coordination of diphosphadiboretanetetradyl derivative by chromium(0) pentacarbonyl tetrahydrofuran results in the cycloreversion of the dimer to boraphosphene, stabilized by mono-coordination to the phosphorus atom.
One and two electron oxidation of diphosphadiboretane synthesized from diboryne offers radical cation and dication species. The dication exhibits a butterfly-type structure (Dep = 2,6-diethyl phenyl).
Reaction between di(diisopropylphospha)-di(tert-butyl)boretanediyl with bromotrichloromethane leads to bromine atom addition on a boron atom, boron spiro-complex formation, and trichloromethane byproduct.
