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(η6-p-cymene)(κ2(C,N)-C[P{NP(O)(OR)2}Ph2]2)] (R = Et (1), Ph (2)) with an excess of terminal alkynes HC⋮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⋮C triple bond of the alkyne and concomitant phenyl ortho
metalation. Under the same reaction conditions the carbene derivative [Ru(η6-p-cymene)(κ2(C,N)-C[P{NP(O)(OEt)2}Ph2][P{NP(O)(OPh)2}Ph2])] (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 (η2-alkyne)−Ru(II) species rather than their
η1-vinylidene tautomers [Ru]CCHR‘. Protonation of complexes 3a and 4a with HBF4
generates the cationic derivatives [Ru(η6-p-cymene)(κ4(C,C,C,N)-C[P{NP(O)(OR)2}Ph2]2{(E)-C(H)C(H)Ph})][BF4] (R = Et (8), Ph (9)) via selective cleavage of the Ru−Caryl bond in
3a and 4a.