Iminophosphorane-based nucleophilic ruthenium(II) carbene complexes:: Unusual C-C coupling and C-H activation promoted by the addition of alkynes to the Ru=C bond

Treatment of the nucleophilic carbene complexes [Ru(eta(6)-p-cymene)(kappa(2)(C,N)-C[P{=NP(= C)(OR)(2)}Ph-2](2))] (R = Et (1), Ph (2)) with an excess of terminal alkynes HC equivalent to CR'(R' = Ph, p-Tol, CPh2(OH), CHPh(OH), C6H9, C(Me)=CH2), in THF at room temperature, results in the chemo- and stereoselective formation of complexes 3a-f and 4a-f, via coupling of the carbenic Ru=C carbon with the C equivalent to C triple bond of the alkyne and concomitant phenyl ortho metalation. Under the same reaction conditions the carbene derivative [Ru(eta(6)-p-cymene)(kappa(2)(C,N)-C[P{=NP(=O)(OEt)(2)}Ph-2] [P{=NP(=O)(OPh)(2)}Ph-2])] (5) reacts with phenylacetylene to afford a nonseparable mixture of the complexes 6 and 7 resulting from the ortho metalation of both N-phosphoryl iminophosphoranyl fragments -Ph2P=NP(=O)(OR)2 (R = Et, Ph). The structure of complex 3c has been unambiguously confirmed by a single-crystal X-ray diffraction study. The reaction of complex 1 with deuterated phenylacetylene suggests that these C-C coupling processes involve transient (eta(2)-alkyne)-Ru(II) species rather than their eta(1)-vinylidene tautomers [Ru]=C=CHR'. Protonation of complexes 3a and 4a with HBF4 generates the cationic derivatives [Ru(eta(6)-p-cymene)(kappa(4)(C,C,C,N)-C[P{=NP(=O)(OR)(2)}Ph-2](2)-{(E)-C(H)=C(H)Ph})] [BF4] (R = Et (8), Ph (9)) via selective cleavage of the Ru-C-aryl bond in 3a and 4a.