Reactions of alkenyl and alkynyl ruthenium(II) complexes with isocyanides: Synthesis of α, β-unsaturated η1-acylruthenium(II) complexes and X-ray structure of [Ru(CCPh)(CN+Bu)3(PPh3)2]PF6

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Abstract Reaction of (E)-alkenyl complexes Ru(CO)Cl(CHCHR)(PPh3)2 and Ru(CO)Cl(CHCHR) (PPh3)2L (L  Me2Hpz, py) with an excess of an isocyanide R′NC (R′tBu or cyclohexyl (Cy)) gives (E)-α,β-unsaturated-η1-acyl complexes [Ru(COCHCHR)(CNR′)3(PPh3)2]Cl in good yield. The corresponding reactions with 1 equivalent of isocyanide give the hexacoordinate complexes Ru(CO)Cl(CHCHR)(CNR′)(PPh3)2. The reaction of [Ru(CO)(CHCHR)(NCMe)2(PPh3)2]PF6 with tBuNC also affords η1-acyl complexes [Ru(COCHCHR)(CNtBu)3(PPh3)2]PF6. On the other hand, treatment of alkynyl complexes [Ru(CO)(CCR)(py)2(PPh3)2]PF6 with an excess of tBuNC under forcing conditions promotes substitution of CO and pyridine ligands by the isocyanide, yielding alkynyl derivatives [Ru(CCR)CNtBu)3(PPh3)2]PF6. An X-ray diffraction study of one of the complexes (R  Ph) confirmed the proposed structure. Similarly, reaction of the alkynyl complexes with CO gives only the ligand-substitution products [Ru(CO)2(CCR)(py)(PPh3)2][PF6]. The reaction of (E)-alkenyl ruthenium(II) complexes with alkyl isocyanides proceeds under mild conditions to yield (E)-α,β-unsaturated-η1-acyl ruthenium(II) complexes. Although these complexes are obtained from intermediates with both CO and isocyanide ligands, exclusive migratory insertion of the alkenyl ligand into the RuCO bond is observed. The related alkynyl carbonyl ruthenium(II) complexes do not undergo insertion, reacting sluggishly with the isocyanides to yield new alkynyl ruthenium complexes in which the carbonyl ligand has been replaced by an isocyanide ligand. The corresponding reaction with CO leads to dicarbonyl alkynyl complexes by substitution of the pyridine trans to the alkynyl ligand.