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Sterically Encumbered Systems for Two Low-Coordinate Phosphorus Centers

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journal contribution
posted on 25.07.2000, 00:00 by Shashin Shah, Tom Concolino, Arnold L. Rheingold, John D. Protasiewicz
Tetraarylphenyls of the form 2,3,5,6-Ar4C6 (Ar = p-tert-butylphenyl) are investigated as sterically demanding ligands for the syntheses of compounds having two p-phenylene-bridged phosphorus centers. The precursor to such materials, 1,4-diiodo-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (1), is readily 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-tetrakis(p-tert-butylphenyl)benzene (2) and the derived bis(phosphine) 1,4-bis(phosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (3) in yields of 56 and 94% respectively. These materials provide access to novel materials containing two low-coordinate phosphorus centers bridged by a sterically encumbered phenylene unit. Compound 2 reacts with benzaldehyde and 2,6-dichlorobenzaldehyde in the presence of excess trimethylphosphine and zinc to produce the new pale yellow crystalline bis(phosphaalkenes) (E,E)-PhC(H)PAr4C6PC(H)Ph (4a; 42%) and (E,E)-Ar‘C(H)PAr4C6PC(H)Ar‘ (4b; 46%; Ar‘ = 2,6-dichlorophenyl). The crystal structure of 4a shows a PC bond length of 1.676(5) Å. Compound 2 is also used to provide the unusual red-orange bis(diphosphene) DmpPPAr4C6PPDmp (5; 55%; Dmp = 2,6-Mes2C6H3). Compound 5 is structurally characterized, and a PP bond length of 2.008(2) Å is ascertained.