Thermal reactions of Mes*-substituted triphospha[3]radialene (Mes*: 2,4,6-tri-t-butylphenyl) with [M(CO)(5)center dot(thf)] (M = Cr, W) resulted in the formation of the corresponding group 6 metal pentacarbonyl complexes bearing the triphospha[3]radialene ligand, where one of the P=C bond moiety of the triphospha[3]radialene was a-coordinating to the metal moiety in eta'-fashion. The noncoordinating P=C bonds in the obtained complexes were found to undergo photochemical (E)-(Z) isomerization.