Activation of Carbon-Hydrogen Bonds Mediated by Ru(II) Complexes

heteroaromatic compounds;C-H Activation

Pittard, Karl A. ; David A. Shultz, Committee Member,James D. Martin, Committee Member,Edmond F. Bowden, Committee Member,T. Brent Gunnoe, Committee Chair,Pittard, Karl A. ; David A. Shultz ; Committee Member ; James D. Martin ; Committee Member ; Edmond F. Bowden ; Committee Member ; T. Brent Gunnoe ; Committee Chair

University:North Carolina State University

关键词: heteroaromatic compounds;    C-H Activation;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/4638/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

The RuII complex TpRu(CO)(NCMe)Me (Tp = hydridotris(pyrazolyl)borate) initiates carbon-hydrogen bond activation at the 2-position of furan and thiophene to produce methane and TpRu(CO)(NCMe)Ar (Ar = 2-furyl or 2-thienyl). Solid-state structures have been determined for TpRu(CO)(NCMe)(2-thienyl) and [TpRu(CO)(-C,S-thienyl)]2. The complex TpRu(CO)(NCMe)(2-furyl) serves as a catalyst for the formation of 2-ethylfuran from ethylene and furan.Similar catalytic reactivity was observed with TpRu(CO)(NCMe)(2-thienyl) for the production of 2-ethylthiophene.Density functional theory (DFT) calculations of the C-H activation of furan by {(TAB)Ru(CO)Me} (TAB = tris(azo)borate) indicate that the C-H activation sequence does not proceed through a RuIV oxidative addition intermediate. The reaction of TpRu(CO)(NCMe)Me and pyrrole forms TpRu(CO){ 2-N,N-(H)N=C(Me)(NC4H3)}. The formation of complex TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)} involves the cleavage of the N-H bond and 2-position C-H bond of pyrrole as well as a C-C bond forming step between pyrrole and the acetonitrile ligand of {TpRu(CO)(NCMe)}. Mechanistic studies indicate that the most likely reaction pathway involves initial metal-mediated N-H activation of pyrrole to produce TpRu(CO)(NCMe)(N-pyrrolyl) followed by C-C bond formation and proton transfer. Complex TpRu(CO)(NCMe)(N-pyrrolyl) has been independently prepared. At elevated temperatures, TpRu(CO)(NCMe)(N-pyrrolyl) converts to TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)}.Single crystal X-ray analysis has been achieved for TpRu(CO)(NCMe)(N-pyrrolyl), [TpRu(CO)(NCMe)(1-O-OC4H8) and TpRu(CO){2-N,N-(H)N=C(Me)(NC4H3)}.Computational studies support the suggested selectivity for initial N-H bond cleavage in preference to C-H bond activation. Rational design for a more electron-poor hydroarylation catalyst was discussed.Synthesis of Mp (Mp = tris(pyrazolyl)methane) complexes of the type [MpRu(PPh3)(CO)H]BAr'4, [MpRu(PPh3)(CO)Cl]BAr'4, [MpRu(PPh3)(PMe3)Cl]Cl, [MpRu(PPh3)(PMe3)Cl]BAr'4, [MpRu(PPh3)2Cl]BAr'4, [MpRu(PPh3){P(OMe)3}Cl]Cl, [MpRu(PPh3)(NCMe)Cl]BAr'4, [MpRu(PPh3)(NCMe)Cl]BAr'4 and [MpRu(PPh3)(CO)Cl]BAr'4 accomplished.A single-crystal X-ray diffraction study was carried out on the complex [MpRu(PPh3)(PMe3)Cl]Cl.[MpRu(PPh3)2Me]BAr'4 was prepared and examined by Cyclic Voltammetry (CV) where the E1/2= 1.19 V.C-H activation was observed when [MpRu(PPh3)2Me]BAr'4 was heated in neat C6D6.Orthometalation appears to dominate reactivity via intramolecular C-H activation of a PPh3 ligand, however CH3D was produced at elevated temperatures.A series of Ep (Ep = tris(pyrazolyl)ethane) complexes of the type MpRu(Cl)2PR3 (R = Ph, OMe, or Me) were also synthesized.The [EpRu(PPh3)(NCMe)(Cl)]Cl and [EpRu(PPh3)(PMe3)(Cl)]Cl complexes were observed spectroscopically as intermediates in these syntheses. Improved synthesis of [MpRu(PPh3)2Cl]Cl was also accomplished by improving the yield by 23%, over the previously reported yield of 53%.