Syntheses and structural characterizations of the unsymmetrical diphosphene DmpP=PMes* (Dmp =2,6-Mes(2)C(6)H(3), Mes* = 2,4,6-(t)Bu(3)C(6)H(2)) and the cyclotetraphosphane [DmpPPPh](2).

The new diphosphene DmpP=PMes* (Dmp = 2,6-Mes(2)C(6)H(3); Mes* = 2,4,6-(t)Bu(3)C(6)H(2), 1) having two different classes of sterically demanding aryls has been prepared and structurally characterized. This structure appears to be the first featuring both types of sterically demanding groups (a meta-terphenyl and Mes*) in a single molecule about a multiply bonded unit. Compound 1 features a P=P bond length of 2.024(13) A. The structure of 1 also allows comparisons to the two previously structurally characterized symmetric diphosphenes DmpP=PDmp and MesP=PMes. The crystal structure of the cyclotetraphosphane DmpPPPh (3), the product of self-dimerization of the unstable diphosphene DmpP=PPh (2), has been determined. The structure of 3 demonstrates that a single bulky Dmp group is insufficient to prevent dimerization of 2. (31)P NMR data for all three compounds are also reported.