Metallacumulenes: Activation of Diynes and Formation of New Allenylideneruthenium Complexes. Crystal Structures of trans-[(Ph2PCH2PPh2)2(Cl)Ru:C:C:CR1R2]+ and trans-[(Ph2PCH2PPh2)2Ru(:C:C:C(OMe)CH:CPh2)2]2+ Derivatives