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ci~-RuClz(PhzPCHzPPh2)2 (1) reacts with pentadiynes XCWC'CCPhz(OSiMe3) [2 (X = H) and 3 (X = BusSn)], but in the presence of NaPFs, to afford trans-(PhzPCHzPPhZ)z(Cl)-RuCZCCECCPhz(0SiMes) (4). On protonation with HBF4 complex 4 in methanol leads to allenylidene ~~u~~-[(P~zPCHZPP~Z)~(CI)RU=C=C=C(OM~)CH=CP~ZIX (5a) (a: X = BFd and in dichloromethane to ~~~~~-[ ( P~~P C H Z P P~Z ) Z ( C~) R~= C = C = C C H = C~P~~(~-C~H (6a) via electrophilic ortho-substitution within the metallacumulene intermediate LnRu=C=C=C=C= CPhzlX (A). Alternatively, complex 1 and diyne 2 with NaPF6 afford in one step allenylidenes 5b (b: X = PF6) in methanol and 6b in dichloromethane. Bis(diyny1) derivative truns-(Phz-P C H~P P~~) Z R U [ ( C = C C~! C ( O S~M~~) P~Z ] ) Z (7), obtained by reaction of 2 with 1 and HN'PrZ, on protonation with HBF4 in methanol offered a direct route to the first bis(alleny1idene) complex ~~U~~-[(P~ZPCH~PP~Z)ZR~(=C=C=C(OM~)CH=CP~Z)Z~(BF~)Z (8). The X-ray diffraction studies of two allenylidene complexes 6b and 8 are reported. The structure of 6bconsists of two different allenylidene cations. That of 8 shows coplanar allenylidene ligands with a strong contribution of a ynyl resonance structure.

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