Phosphaalkenes, diphosphenes, and phospha -Wittig reagents: Synthesis, characterization, and applications as novel building blocks for oligomeric materials

The synthesis of the new diphosphenes DmpP=PDmp (Dmp = 2,6dimesitylphenyl), DmtP=PDmt (Dmt = 2,6-dimesityl-para-tolyl), and DxpP=PDxp (Dxp = 2,6-di-(meta-xylyl)phenyl) indicates that sterically encumbering meta-terphenyl ligands are suitable for kinetically stabilizing low-coordinate phosphorus centers. Systematic studies of the diphosphenes and corresponding radical anions by CV and EPR spectroscopy lead to several unexpected and novel results when compared to previously described diphosphenes such as Mes*P=PMes* (Mes* = 2,4,6-tri-tert-butylphenyl).;The stable and isolable phosphanylidene-sigma4-phosphoranes DmpP=PMe3, Mes*P=PMe3, and 2,6-Trip2C 6H3P=PMe3 have been synthesized. Phosphanylidene-sigma 4-phosphoranes, which represent the direct phosphorus analogs of Wittig reagents R2C=PR3, undergo phospha-Wittig reactions with aldehydes to produce phosphaalkenes ArP=C(H)R in high yields. The crystal structure of DmpP=PMe3 has been obtained and displays a short P--P bond length of 2.084(2) A.;Reactions of DmpP=PMe3 with electrophiles EX produce new diphosphanium salts [DmpP(E)PMe3]X and/or phosphines DmpP(E)X. The photolysis of phosphanylidene-sigma4-phosphoranes ArP=PMe3 generates free phosphinidenes "ArP" which subsequently adopt differing pathways culminating in a product of intramolecular CH bond insertion, net dimerization to a diphosphene, or novel CC bond insertion.;Routes to sterically demanding ligands that provide access to materials having two low-coordinate phosphorus centers spanning a phenylene unit have been developed. The new sterically demanding ligand 2,3,5,6-(para-tert -butyl)phenyl has been used to synthesize bis-phosphaalkenes and bis-diphosphenes. UV-vis spectroscopy data for bis-phosphaalkenes and bis-diphosphenes suggest that in solution, the steric forces do not completely isolate the two P=C or P=P units from electronic communication.