Synthesis and coordination properties of new σ2,λ3-P/N switchable chelators based on [1,2,3]-diazaphosphole

Abstract

Novel hybrid ligands based on [1,2,3]-diazaphosphole (dap) were prepared and their coordination behaviour toward selected transition metals has been studied. The syntheses and spectroscopic properties of polydentate bis(5-t-butyl-[1,2,3]-diazaphosphol-2-yl)-dimethylsilane (Bdaps^H,tBu) and bis(4-methyl-5-ethyl-[1,2,3]-diazaphosphol-2-yl)-dimethylsilane (Bdaps^Me,Et) are reported. In zerovalent compounds of the type [M(CO)₄(κ²-P,P′-Bdaps^R1,R2)] (R1 = Me, R2 = Et, M = Cr, Mo and W; R1 = H, R2 = t-Bu, M = W) and [Ni(κ²-P,P′-Bdaps^H,tBu)₂] the ligand serves as a P,P′-donor, giving rigid six-membered chelate rings. Bdaps^Me,Et is also capable of behaving as an N,N′-chelator as confirmed by isolation of high-spin chelate complex [CoBr₂(κ²-N,N′-Bdaps^Me,Et)]. The reaction of parent 2H-4-methyl-5-ethyl-[1,2,3]-diazaphosphole with NiBr₂·DME yielded paramagnetic compound [NiBr₂(κ-N-dap)₂], where the dap heterocycle bonds with the nickel(II) centre via a 1-nitrogen donor atom in a distorted tetrahedral environment. All the studied complexes showing different coordination modes of the new ligands were fully characterized, including single-crystal X-ray diffraction analysis.