Reaction of [η5:σ-Me2C(C5H4)(C2B10H10)]Ru(NH2Prn)2 with Alkynes. Synthesis and Structural Characterization of Ruthenium Aminocarbene and Enamine Complexes

Syntheses of ruthenium aminocarbene and enamine complexes were achieved by tuning the electronic properties of alkynes. Reaction of [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru(NH 2 Pr n ) 2 ( 1 ) with 2 equiv of phenylacetylene gave the aminocarbene [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[ C(NHPr n )CH(Ph)-η 2 -CH CHPh] ( 2a ) in 45% isolated yield in CH 2 Cl 2 and the enamine complex [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[η 4 -CH(Ph) C(NHPr n )CH CHPh] ( 2b ) in 30% isolated yield in toluene. Treatment of 1 with the electron-rich alkynes 4-ethynyltoluene and 1-hexyne produced only the aminocarbene complexes [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[ C(NHPr n )CH( p -tolyl)-η 2 -CH CH( p -tolyl)] ( 3a ) and [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[ C(NHPr n )CH(Bu n )-η 2 -CH CH(Bu n )] ( 4a ), regardless of the solvents used. In contrast, the reaction of 1 with the electron-deficient alkynes 1-chloro-4-ethynylbenzene and 1-bromo-4-ethynylbenzene afforded only the enamine complexes [η 5:σ-Me 2 C(C 5 H 4 )(C 2 B 10 H 10 )]Ru[η 4 -CH(XC 6 H 4 ) C(NHPr n )CH CH(XC 6 H 4 )] (X = Cl ( 5b ), Br ( 6b )). All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Their molecular structures (except for 4a) were further confirmed by single-crystal X-ray analyses.