Sterically encumbered systems for two low-coordinate phosphorus centers

Tetraarylphenyls of the form 2,3,5,6-Ar4C6 (Ar = p-tert-butylphenyl) are in vestigated as sterically demanding ligands for the syntheses of compounds h aving two p-phenylene-bridged phosphorus centers. The precursor to such mat erials, 1,4-diiodo-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (1), is read ily obtained via a one-pot procedure in 68% yield. Compound 1 is then used to provide the bis(dichlorophosphine) 1,4-bis(dichlorophosphino)-2,3,5,6-te trakis(p-tert-butylphenyl)benzene (2) and the derived bis(phosphine) 1,4-bi s(phosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (3) in yields of 5 6 and 94% respectively. These materials provide access to novel materials c ontaining two low-coordinate phosphorus centers bridged by a sterically enc umbered phenylene unit. Compound 2 reacts with benzaldehyde and 2,6-dichlor obenzaldehyde in the presence of excess trimethylphosphine and zinc to prod uce the new pale yellow crystalline bis(phosphaalkenes) (E,E)-PhC(H)=PAr4C6 P=C(H)Ph (4a; 42%) and (E,E)-Ar'C(H)=PAr4C6P=C(H)Ar' (4b; 46%; Ar' = 2,6-di chlorophenyl). The crystal structure of Ja shows a P=C bond length of 1.676 (5) Angstrom. Compound 2 is also used to provide the unusual red-orange bis (diphosphene) DmpP=PAr4C6P=PDmp (5; 55%; Dmp = 2,6-Mes(2)C(6)H(3)). Compoun d 5 is structurally characterized, and a P=P bond length of 2.008(2) Angstr om is ascertained.