Bernard D. Santarsiero

Bio: Bernard D. Santarsiero is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Hydrogen bond & Resonance (chemistry). The author has an hindex of 2, co-authored 2 publications receiving 661 citations.

.sigma.-Bond metathesis for carbon-hydrogen bonds of hydrocarbons and Sc-R (R = H, alkyl, aryl) bonds of permethylscandocene derivatives. Evidence for noninvolvement of the .pi. system in electrophilic activation of aromatic and vinylic C-H bonds

Abstract: The authors report herein synthetic and structural studies of hydride and hydrocarbyl derivatives of permethylscandocene, together with investigations of their reactivities with H/sub 2/ and hydrocarbons. Experiments designed to probe the mechanism of these processes have been carried out, and the possibility of involvement of the ..pi.. system in electrophilic activation of aromatic and vinylic C-H bonds has been examined. A picture of the transition state for such sigma-bond metathesis reactions is developed, which accounts for the relative reactivities of sp-, sp/sup 2/-, and sp/sup 3/-hybridized C-H bonds with Cp*/sub 2/Sc-R (R = H, alkyl, aryl).

Activation of c-h bonds by metal complexes

Abstract: ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Understanding and exploiting C–H bond activation

Abstract: The selective transformation of ubiquitous but inert C–H bonds to other functional groups has far-reaching practical implications, ranging from more efficient strategies for fine chemical synthesis to the replacement of current petrochemical feedstocks by less expensive and more readily available alkanes. The past twenty years have seen many examples of C–H bond activation at transition-metal centres, often under remarkably mild conditions and with high selectivity. Although profitable practical applications have not yet been developed, our understanding of how these organometallic reactions occur, and what their inherent advantages and limitations for practical alkane conversion are, has progressed considerably. In fact, the recent development of promising catalytic systems highlights the potential of organometallic chemistry for useful C–H bond activation strategies that will ultimately allow us to exploit Earth's alkane resources more efficiently and cleanly.

C−H Activation for the Construction of C−B Bonds

Abstract: A number of studies were conducted to demonstrate C-H activation for the construction of C-B bonds. Investigations revealed that the conversion of C-H bonds to C-B bonds was both thermodynamically and kinetically favorable. The reaction at a primary C-H bond of methane or a higher alkene B 2(OR)4 formed an alkylboronate ester R' -B(OR)2 and the accompanying borane H-B(OR2. The ester and the borane were formed on the basis of calculated bond energies for methylboronates and dioaborolanes. The rates of key steps along the reaction pathway for the conversion of a C-H bond in an alkane or arene to the C-B bond in an alkyl or arylboronate ester were favorable. These studies also highlighted the accessible barriers for C-H bond cleavage and B-C bond formation during the borylation of alkanes and arenes.

3d Transition Metals for C-H Activation.

Abstract: C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.