Controlled Reactivity of Terminal Cyaphide Complexes: Isolation of the 5-Coordinate [Ru(dppe)2(C≡P)].

The novel cyaphide complex trans-[Ru(dppe)2Me(C≡P)] is obtained in excellent yields and exhibits the first instance of controlled reactivity of any terminal cyaphide complex. Its treatment with ZnX2/PPh3 effects selective metathesis of the methyl moiety to afford the unprecedented halocyaphide complexes trans-[Ru(dppe)2(X)(C≡P)] (X = Cl, Br, I), which are structurally characterized (X = Cl, Br). Exemplified with the trans-bromide, these compounds are susceptible to substitution of the halides by nucleophilic reagents-illustrated with Me2Mg-and also readily undergo halide abstraction by TlOTf to afford the first hypocoordinate cyaphide complex, viz., [Ru(dppe)2(C≡P)]·OTf, which is isolable in bulk and exhibits good stability. NMR spectroscopic and crystallographic data reveal the latter to adopt a square-pyramidal geometry with an accessible coordinate vacancy, which is susceptible to the addition of nucleophiles. This is illustrated analytically by reactions with Me2Mg and LiC≡CPh and with its facile bulk carbonylation to afford trans-[Ru(dppe)2(CO)(C≡P)]+.