1-SIGMA(4),2-SIGMA(X)-DIPHOSPHETES (X=2-6) - ON THE PERSISTENCE OF THE P-P BOND

Irradiation of [bis(diisopropylamino)phosphino] (trimethylsilyl)diazom ethane at 254 nm in the presence of tert-butylphosphaalkyne leads to 1 sigma(4),2 sigma(2)-diphosphete 1 in 90% yield. Derivative 1 reacts w ith Fe-2(CO)(9) and W(CO)(5)(THF) giving rise to the corresponding eta (1)-complexes 2 (48% yield) and 3 (75% yield), respectively. When 1 eq uiv of methyl trifluoromethanesulfonate and elemental selenium is adde d to derivative 1, the cationic and neutral 1 sigma(4),2 sigma(3)-diph osphetes 4 and 5 are isolated in 95 and 66% yields, respectively. Addi tion of 2 equiv of elemental selenium and bis(trimethylsilyl)peroxide to diphosphete 1 gave rise to 1 sigma(4),2 sigma(4)-diphosphetes 6 (43 % yield) and 7 (84% yield), respectively. eta(1)-(1 sigma(4),2 sigma(2 )-Diphosphete)tungsten complex 3 reacted with bis(trimethylsilyl)perox ide affording heterocyclic complex 8 (68% yield). Addition of 1 equiv of tetrachloro-o-benzoquinone (TCBQ) to the cationic 1 sigma(4),2 sigm a(3)-diphosphete 4 and of 2 equiv to the 1 sigma(4),2 sigma(2)-diphosp hete 1 affords the 1 sigma(4),2 sigma(5)- and 1 sigma(4),2 sigma(6)-di phosphetes 9 (86% yield) and 10 (92% yield), respectively. Addition of TCBQ to the eta(1)-(1 sigma(4),2 sigma(2)-diphosphete)tungsten comple x 3 affords the eta(1)-(1 sigma(4),2 sigma(4)-diphosphete)complex 11 ( 88% yield), which reacts with 2 equiv of trimethylphosphine leading to the zwitterionic 1 sigma(4),2 sigma(3)-diphosphete 12 (46% yield). Cl eavage of the Si-C bond of complex 3 with 1 equiv of tetrabutylammoniu m fluoride hydrate gives eta(1)-(1 sigma(4),2 sigma(2)-diphosphete)com plex 13 (61% yield), which reacts with TCBQ leading to the cis-1,2-dip hosphino 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 ve ry bulky substituents on the ethylenic moiety is necessary for the per sistence of the cyclic structure, when the two phosphorus atoms featur e a high coordination state. Single crystal X-ray diffraction studies of derivatives 7 and 11-14 have been carried out.