Activation of carbon-hydrogen bonds in saturated hydrocarbons on photolysis of (.eta.5-C5Me5)(PMe3)IrH2. Relative rates of reaction of the intermediate with different types of carbon-hydrogen bonds and functionalization of the metal-bound alkyl groups

Abstract

3929sealed at -196 OC. In preparation for each run, the tube was warmed to -78 OC in a C02/2-propanol bath with shaking to assure the complete formation of Sa. The tube was then warmed to room temperature and placed in the probe of an NMR spectrometer maintained at 28.0 f 0.5 OC. Data sets were collected over 3 half-lives of the reaction. A typical data set consisted of 12 acquisitions at 201.947 MHz with a SW = f1113.58 Hz, a pulse width of 20°, and a 5-s delay between pulses. The progress of the reaction was monitored by integrating the Cp resonances of 5a and 6e at 6 5.4 and 5.15, respectively, vs. the ferrocene resonance at 6 4.1. Acknowledgment.Abstract: The full details of experiments on a homogeneous system which successfully converts completely saturated alkanes into hydridoalkylmetal complexes (M + RH -R-M-H) are reported. Irradiation of (~s-CSMe5)(PMe3)IrH2 (5) in saturated hydrocarbons (R-H) using a 500-W Oriel focused-beam mercury lamp leads to extrusion of H2 and production of the hydrido alkyl complexes (7'-C,Me,)(PMe,)Ir(R)(H). Competition experiments have allowed measurement of the relative rates at which the intermediate formed on H2 loss (presumably the coordinatively unsaturated complex (q5-C5Me5)(PMe3)Ir) reacts with different types of C-H bonds. Relative to cyclohexane (l.O), these are as follows: benzene (4.0), cyclopropane (2.65), cyclopentane (1.6), neopentane (1.14), cyclodecane (0.23), and cyclooctane (0.09). Reductive elimination of hydrocarbon occurs at elevated temperature, regenerating (qS-CsMes)(PMe3)Ir, which may then react with another hydrocarbon acting as solvent; thus the C-H activation process can also be induced thermally. C-H bonds having high bond energies react relatively rapidly; this fact, along with crossover experiments, suggests that radical intermediates are not involved in the C-H activation reaction. Treatment of the hydrido neopentyl complex 8 with CHBr, converts it to the corresponding bromo neopentyl complex 10. This material reacts with HgClz to give neopentylmercuric chloride, which forms neopentyl bromide on reaction with Brz. Thus overall stoichiometric conversion of hydrocarbons to functionalized organic molecules is feasible in this system. The factors which have been presumed to influence the rates of reaction of transition-metal complexes with saturated C-H bonds-notably the need for electron-rich metals and close proximity of reacting centers-are discussed in detail.

Intermolecular versus intramolecular C–H activation reaction in the thermolysis of [Ru(Me)Cp*(PMe2Ph)2] (Cp*=η5-C5Me5): formation and crystallographic characterisation of [Ru(Ph)Cp*(PMe2Ph)2]

“…As early as 1983 Bergman and Janowicz [7] found an approximate 1:1 ratio of the intra-and inter-molecular products in the reaction of [IrCp*(PR 3 )H 2 ] with hydrocarbons. Later Jones and Feher [8] investigated the selectivity of the phosphine cyclometallation vs. benzene activation by the [RhCp*(PCH 2 PhMe 2 )] system (this phosphine was chosen in order to have similar steric constraints for the inter-and intra-molecular pathways) finding out a moderately high thermodynamic preference for the intramolecular activation and a kinetic selectivity for the intermolecular reaction (in neat solvent).…”

Rh(III)- and Ir(III)-Catalyzed C–C Bond Cross Couplings from C–H Bonds

“…Further investigations enabled the discovery of a "second generation" of this CDC reaction. It was found that polyhalogenated aromatics, such as hexabromobenzene, can be used as additives hence enabling the desired coupling with non-halogenated simple arenes and heteroaromatics (12) [141]. A closely related twofold C-H activation between one aromatic partner bearing a directing group and a second, heteroaromatic partner was discovered independently by You [142] and Kambe [143].…”

“…The reactivity of these pseudooctahedral complexes toward various ligands has been investigated enabling isolation and characterization of many interesting organometallic structures. Moreover, following the Maitlis work [11] and since the potential of [Cp*IrPR 3 X 2 ] and [Cp*RhPR 3 X 2 ] complexes to cleave C-H bonds [12,13] had been known already in the 1980s, an extensive study of the stoichiometric reactions between the dicationic [Cp*M(III)] precatalysts (M¼Rh, Ir) and aromatic substrates bearing coordinating substituents (such as imines, ketones, amines, etc.) was undertaken.…”

CH bond activation in functionalized organic compounds with Cp∗ (PMe3)IrMe(OTf): generation, structural characterization and metal-based rearrangement of the acetone activation product Cp∗ (PMe3)Ir(η3-CH2C(OH)CH2)+OTf−

“…The first involves the oxidative addition of the C-H bond to an unsaturated metal fragment, and is typical of electron-rich late metal systems [5][6][7][8][9][10][11][12][13]. The second takes place by a 1,2-R-H addition, in which the C-H bond adds across a highly electrophilic d o metal M-X bond [14][15][16][17][18][19][20][21][22][23][24].…”