1σ4,2σx-Diphosphetes (x = 2−6): On the Persistence of the P−P Bond

Irradiation of [bis(diisopropylamino)phosphino](trimethylsilyl)diazomethane at 254 nm in the presence of tert -butylphosphaalkyne leads to 1σ 4,2σ 2 -diphosphete 1 in 90% yield. Derivative 1 reacts with Fe 2 (CO) 9 and W(CO) 5 (THF) giving rise to the corresponding η 1 -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 1σ 4,2σ 3 -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 1σ 4,2σ 4 -diphosphetes 6 (43% yield) and 7 (84% yield), respectively. η 1 -(1σ 4,2σ 2 -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 1σ 4,2σ 3 -diphosphete 4 and of 2 equiv to the 1σ 4,2σ 2 -diphosphete 1 affords the 1σ 4,2σ 5 - and 1σ 4,2σ 6 -diphosphetes 9 (86% yield) and 10 (92% yield), respectively. Addition of TCBQ to the η 1 -(1σ 4,2σ 2 -diphosphete)tungsten complex 3 affords the η 1 -(1σ 4,2σ 4 -diphosphete)complex 11 (88% yield), which reacts with 2 equiv of trimethylphosphine leading to the zwitterionic 1σ 4,2σ 3 -diphosphete 12 (46% yield). Cleavage of the Si−C bond of complex 3 with 1 equiv of tetrabutylammonium fluoride hydrate gives η 1 -(1σ 4,2σ 2 -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 studies of derivatives 7 and 11 − 14 have been carried out.