The first co-ordinatively unsaturated Group 8 allenylidene complexes:: insights into Grubbs' vs. Dixneuf-Furstner olefin metathesis catalysts

The reactions of [MCl2(PPh3)(3)] with HC=CCPh2OH provided [MCl2(=C=C=CPh2)(PPh3)(2)] (M = Ru 1a or Os 1b) the first examples of co-ordinatively unsaturated allenylidene complexes of Group 8 metals. The phosphine ligands of la are labile and readily replaced by PCy3 to give [RuCl2(=C=C=CPh2)(PCy3)(2)] Ic. Heating ist with NaPF6, in chloroform gave the known bimetallic salt [Ru-2(mu-Cl)(3)(=C=C=CPh2)(2)(PPh3)(4)]PF6 2 . PF6. The reaction of la with carbon monoxide provided [RuCl2(=C=C=Ph-2)(CO)(PPh3)(2)] 3 which may also be prepared from [RuCl2(CO)(dmf)(PPh3)(2)] and HC=CCPh2OH. The first macrocycle coligated allenylidene complex [RuCl(=C=C=CPh2)(PPh3)([9]aneS(3))]Cl 4 . Cl ([9]aneS(3) = 1,4,7-trithiacyclononane) was obtained from the reaction of la with [9]aneS(3),. Alternatively 4 PF, is also obtained by treating [RuCl2(PPh3)([9]aneS(3))] sequentially with NaPF6, in acetonitrile followed by HC=CCPh2OH. The reaction of la with dppe and NaPF6, yielded the known salt trans-[RuCl(=C=C=CPh2)(dppe)(2)]PF6 5 . PF6. The complex [RuCl(=C=C=CPh2)(PCy3){HB(pz)(3)}] 6 (pz = pyrazol-1-yl) was obtained from the reaction of Ic with K[HB(pz)(3)], whilst the related benzylidene complex [RuCl(=CHPh)(PCy3){HB(pz)(3)}] 7 was obtained similarly from [RuCl2(=CHPh)(PCy3)(2)] and K[HB(pz)(3)]. Heating [Ru-2(mu-Cl)(2)Cl-2(eta-cym)(2)] (cym = (PrC6H4Me)-Pr-i-4) with PCy3 and HC=CPh2OH in refluxing benzene provided a mixture of Ic and the bimetallic complex [Ru-2(mu-Cl-2)Cl-2(=C=C=CPh2)(eta-cym)] 8 and other unidentified products. The complex 8 may however be obtained quantitatively from the reaction of Ic with [Ru-2(mu-Cl)(2)Cl-2(eta-cym)(2)]. These results suggest that the active species in ring-closure olefin metathesis processes mediated by the allenylidene pre-catalyst [RuCl(C=C=CPh2)(PCy3)(eta-cym)](+) in non-polar arene solvents may be allenylidene analogues of the Grubbs' alkene metathesis catalyst, viz. Ic and 8.