Protonolysis and thermolysis reactions of functionalised NHC-carbene boranes and borates.
نویسندگان
چکیده
A set of β-ketoimidazolium and β-ketoimidazolinium salts of the general formula [R(1)C(O)CH2{CH[NCR(3)CR(3)N(R(2))]}]X (R(1) = (t)Bu, naphth; R(2) = (i)Pr, Mes, (t)Bu; R(3) = H, Me, (H)2; X = Cl, Br) show contrasting reactivity with superhydride bases MHBEt3; two are reduced to chiral β-alcohol carbene-boranes R(1)CH(OH)CH2{C(BEt3)[NCR(3)CR(3)N(R(2))]} 2 (R(1) = (t)Bu; R(2) = (i)Pr, Mes; R(3) = H), two with bulky R(2) substituents are reduced to chiral β-borate imidazolium salts [R(1)CH(OBEt3)CH2{CH[NCR(3)CR(3)N(R(2))]}]X 3 (R(1) = (t)Bu, naphth; R(2) = Mes, (t)Bu; R(3) = H, Me; X = Cl, Br), and the two saturated heterocycle derivatives remain unreduced but form carbene-borane adducts R(1)C(O)CH2{C(BEt3)[NCR(3)CR(3)N(R(2))]} 4 (R(1) = (t)Bu, naphth; R(2) = Mes; R(3) = (H)2). Heating solutions of the imidazolium borates 3 results in the elimination of ethane, in the first example of organic borates functioning as Brønsted bases and forming carbene boranes R(1)CH(OBEt2)CH2{C[NCR(3)CR(3)N(R(2))]} 5 (R(1) = naphth; R(2) = Mes; R(3) = Me). The 'abnormal' carbene borane of the form 2 R(1)CH(OH)CH2{CH[NC(BEt3)CR(3)N(R(2))]} (R(1) = (t)Bu; R(2) = (t)Bu; R(3) = H), is also accessible by thermolysis of 3, suggesting that the carbene-borane alcohol is a more thermodynamically stable combination than the zwitterionic imidazolium borate. High-temperature thermolysis also can result in complete cleavage of the alcohol arm, eliminating tert-butyloxirane and forming the B-N bound imidazolium borate 7. The strong dependence of reaction products on the steric and electronic properties of each imidazole precursor molecule is discussed.
منابع مشابه
Protonolysis of a ruthenium-carbene bond and applications in olefin metathesis.
The synthesis of a ruthenium complex containing an N-heterocylic carbene (NHC) and a mesoionic carbene (MIC) is described wherein addition of a Brønsted acid results in protonolysis of the Ru-MIC bond to generate an extremely active metathesis catalyst. Mechanistic studies implicated a rate-determining protonation step in the generation of the metathesis-active species. The activity of the NHC/...
متن کاملFunctionalised [(NHC)Pd(allyl)Cl] Complexes: Synthesis, Immobilisation and Application in Cross-Coupling and Dehalogenation Reactions
A novel NHC–palladium(II) (NHC = N-heterocyclic carbene) complex and its immobilised version have been prepared and fully characterised. Optimisation studies led to good catalytic activities in Suzuki-Miyaura cross coupling and chloroarene dehalogenation reactions. Furthermore, the unexpected palladium-mediated transfer hydrogenation of a carbonyl compound is reported.
متن کاملSynthesis of functionalised N-heterocyclic carbene ligands bearing a long spacer and their use in olefin metathesis.
A synthetic route to backbone functionalised imidazolinium salts-NHC ligand precursors has been developed. These tagged NHC ligands can be used to obtain a homogeneous Hoveyda-type catalyst (19) containing a quaternary ammonium group on a C-8 long spacer. Products of olefin metathesis reactions promoted by complex 19 can be readily purified from Ru-residues by filtration of the reaction mixture...
متن کاملExpanded ring and functionalised expanded ring N-heterocyclic carbenes as ligands in catalysis.
The synthesis of new functionalised 6- and 7-membered NHC (N-heterocyclic carbene) precursors bearing anisidyl or pyridine N-substituents, both symmetrically and non-symmetrically substituted is reported. Their corresponding rhodium(i) and iridium(i) complexes, M(COD)(NHC)Cl, were also prepared and characterised. The unusual Rh(iii)/Rh(i) salt, [Rh(eta(2)-NHC-py)(2)Cl(2)][Rh(COD)Cl(2)], was obt...
متن کاملIndenyl-functionalised triethylborane adduct of N-heterocyclic carbene: stepwise coordination of indenyl and NHC ligands toward molybdenum fragment.
Indenyl-functionalised BEt(3)-adduct NHCs were prepared by the reaction of imidazolium pro-ligands with LiBEt(3)H. This compound was converted into the indenyl-coordinate molybdenum complex dangling the NHC·BEt(3) moiety as a substituent. The stepwise coordination of NHC afforded a chelate-type mononuclear complex as well as a bimetallic complex.
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
برای دانلود متن کامل این مقاله و بیش از 32 میلیون مقاله دیگر ابتدا ثبت نام کنید
ثبت ناماگر عضو سایت هستید لطفا وارد حساب کاربری خود شوید
ورودعنوان ژورنال:
- Dalton transactions
دوره 43 41 شماره
صفحات -
تاریخ انتشار 2014