1σ4,2σ(x)-diphosphetes (x = 2-6): On the persistence of the P-P bond

Article abstract of DOI:10.1021/ja971821f

Irradiation of [bis(diisopropylamino)phosphino](trimethylsilyl) diazomethane at 254 nm in the presence of tert-butylphosphaalkyne leads to 1σ⁴,2σ²-diphosphete 1 in 90% yield. Derivative 1 reacts with Fe₂(CO)₉ and W(CO)₅(THF) giving rise to the corresponding η¹-complexes 2 (48% yield) and 3 (75% yield), respectively. When 1 equiv of methyl trifluoromethanesulfonate and elemental selenium is added to derivative 1, the cationic and neutral 1σ⁴,2σ³-diphosphetes ⁴ and 5 are isolated in 95 and 66% yields, respectively. Addition of 2 equiv of elemental selenium and bis(trimethylsilyl)peroxide to diphosphete 1 gave rise to 1σ⁴,2σ⁴-diphosphetes 6 (43% yield) and 7 (84% yield), respectively. η¹-(1σ⁴,2σ²-Diphosphete)tungsten complex 3 reacted with bis(trimethylsilyl)peroxide affording heterocyclic complex 8 (68% yield). Addition of 1 equiv of tetrachloro-o-benzoquinone (TCBQ) to the cationic 1σ⁴,2σ³-diphosphete ⁴ and of 2 equiv to the 1σ⁴,2σ²-diphosphete 1 affords the 1σ⁴,2σ⁵- and 1σ⁴,2σ⁶-diphosphetes 9 (86% yield) and 10 (92% yield), respectively. Addition of TCBQ to the η¹-(1σ⁴,2σ²-diphosphete)-tungsten complex 3 affords the η¹-(1σ⁴,2σ⁴-diphosphete)complex 11 (88% yield), which reacts with 2 equiv of trimethylphosphine leading to the zwitterionic 1σ⁴,2σ³-diphosphete 12 (46% yield). Cleavage of the Si-C bond of complex 3 with 1 equiv of tetrabutylammonium fluoride hydrate gives η¹-(1σ⁴,σ²-diphosphete)complex 13 (61% yield), which reacts with TCBQ leading to the cis-1,2-diphosphino alkene complex 14 (77% yield). These results demonstrate that the unsaturated four-membered ring skeleton is a remarkable template for inducing unusual P-P interactions. However, the presence of two very bulky substituents on the ethylenic moiety is necessary for the persistence of the cyclic structure, when the two phosphorus atoms feature a high coordination state. Single crystal X-ray diffraction on studies of derivatives 7 and 11-14 have been carried out.