Sterically Encumbered Systems for Two Low-Coordinate Phosphorus Centers

Abstract

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) A. 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) A is ascertained.

Phospha‐Organic Chemistry: Panorama and Perspectives

“…(8)]. [34] The severe limitation put on this process by the low stability of phospha-Wittig reagents bearing non-sterically demanding substituents can be circumvented by complexation of the phosphinidene group, for which, pentacarbonyltungsten is the species of choice. It stabilizes both the starting phospha-ylid and the final phosphaalkene [Eq.…”

Synthesis and characterisation of a diphosphaalkene, a diphosphaalkyne and the first diphosphavinyl lithium complex

“…Its P-C distances (1.703 Å avge. ) are slightly longer than those in related diphosphaalkenes [4] and the mean for all crystallographically characterised phosphaalkenes (1.69 Å ) [5]. These distances are, however, still suggestive of largely localised double bonds.…”

Expanding the Analogy Between P=C and C=C Bonds to Polymer Science

“…This suggests that the presence of the bulky 2,3,5,6-tetraaryl-substituted phenylene spacer might partially disrupt the p-conjugation. X-ray crystallographic data for the model compound 39 seems to support a moderate degree of p-conjugation [110]. For a fully conjugated system the phenylene and P=C bonds should be coplanar.…”