Addition of Carbon Nucleophiles to the Allenylidene Ligand of [Ru(η5-C5H5)(CCCPh2)(CO)(PiPr3)]BF4: Synthesis of New Organic Ligands by Formal C−C Coupling between Mutually Inert Fragments
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Abstract
EHT-MO Calculations on the model cation [Ru(η5-C5H5)(CCCH2)(CO)(PH3)]+ (1a) suggest that 23% and 31% of the LUMO and 26% of the HOMO of [Ru(η5-C5H5)(CCCPh2)(CO)(PiPr3)]BF4 (1) are located on Cα, Cγ, and Cβ of the allenylidene ligand, respectively. On the basis of these results, we report a new synthetic strategy for the preparation of compounds resulting from the formal addition of phenylacetylene, acetone, and methane to the allenylidene of 1. Treatment of 1 with LiC⋮CPh leads to the allenyl complex Ru(η5-C5H5){C(C⋮CPh)CCPh2}(CO)(PiPr3) (2) and the alkynyl derivative Ru(η5-C5H5){C⋮C−C(Ph)2C⋮CPh}(CO)(PiPr3) (3). The reaction of 2 with HBF4 affords the substituted carbene compound [Ru(η5-C5H5){C(C⋮CPh)CHCPh2}(CO)(PiPr3)]BF4 (4), which is a result from the formal addition of phenylacetylene to the Cα−Cβ double bond of the allenylidene of 1. The molecular structure of 4 has been determined by X-ray crystallography. The geometry around the ruthenium center is close to octahedral with the cyclopentadienyl ligand occupying three sites of a face. The RuC bond length is 2.004(5) Å. In the presence of KOH, complex 1 reacts with acetone to give Ru(η5-C5H5){C⋮C−C(Ph)2CH2C(O)CH3}(CO)(PiPr3) (5). The reaction of 5 with HBF4 leads to the unsaturated cyclic carbene Complex 5 also reacts with 2 equiv of CF3CO2D to and CF3CO2H, and the reaction of Ru(η5-C5H5){C⋮C−C(Ph)2CD2C(O)CD3}(CO)(PiPr3) (5-d5) with 2 equiv of HBF4 and DBF4. On the basis of these isotope labeling experiments, the mechanism for the addition of acetone to the allenylidene ligand of 1 is discussed. Complex 1 also reacts with Na(acac) and CH3Li. The reaction with Na(acac) leads to Ru(η5-C5H5){C⋮C−C(Ph)2CH[C(O)CH3]2}(CO)(PiPr3) (7), while the treatment of 1 with CH3Li gives a mixture of Ru(η5-C5H5){C(CH3)CCPh2}(CO)(PiPr3) (8) and Ru(η5-C5H5){C⋮C−C(Ph)2CH3}(CO)(PiPr3) (9). Complex 9 reacts with HBF4 to afford [Ru(η5-C5H5){CCHC(Ph)2CH3}(CO)(PiPr3)]BF4 (10), which is a result of the formal addition of a C−H bond of methane to the Cβ−Cγ double bond of the allenylidene of 1.
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