Mechanistic studies of oxidative addition to low-valent metal complexes. Stereochemistry at carbon in addition of alkyl halides to iridium(I)

The Photolysis of Chlorocarbonylbis(triphenylphosphine)iridium(I) in Chloroform

“…Despite the similarities, the oxidative addition reported here displays obvious differences from the oxidative addition investigated by Labinger and Osborn. The photoreaction of [IrCl(CO)(PMe 3 ) 2 ] with chloroform proceeded with addition of the entire CHCl 3 molecule to yield [IrCl 2 (CO)(CHCl 2 )(PMe 3 ) 2 ] (26), whereas we find the product with the triphenylphosphine complex to be [IrCl 2 (CO)H(PPh 3 ) 2 ]. Of particular interest, though, is the fact that Labinger and Osborn reported no reaction when CH 2 Cl 2 was substituted for CHCl 3 (26).…”

“…The photoreaction of [IrCl(CO)(PMe 3 ) 2 ] with chloroform proceeded with addition of the entire CHCl 3 molecule to yield [IrCl 2 (CO)(CHCl 2 )(PMe 3 ) 2 ] (26), whereas we find the product with the triphenylphosphine complex to be [IrCl 2 (CO)H(PPh 3 ) 2 ]. Of particular interest, though, is the fact that Labinger and Osborn reported no reaction when CH 2 Cl 2 was substituted for CHCl 3 (26). The reason lies presumably in the greater C–Cl bond strength in dichloromethane, and in the fact that the oxidative addition of CCl 4 , in which the C–Cl bond is even weaker, took place instantaneously (26).…”

“…Labinger and Osborn studied a number of systems involving the thermal and photochemical oxidative addition of chloromethanes and other alkyl halides to [IrCl(CO)(PR 3 ) 2 ] complexes, primarily the trimethylphosphine complex, which was considerably more reactive than complexes that had any phenyl groups on the phosphine (26). There was considerable evidence that the reaction proceeded through a radical pathway in which alkyl radicals served as chain propagators (26).…”

“…Of particular interest, though, is the fact that Labinger and Osborn reported no reaction when CH 2 Cl 2 was substituted for CHCl 3 (26). The reason lies presumably in the greater C–Cl bond strength in dichloromethane, and in the fact that the oxidative addition of CCl 4 , in which the C–Cl bond is even weaker, took place instantaneously (26).…”

Near-UV photolysis of μ-dibromotetrabromo- dipalladate(II) in chloroform

“…Chlorine abstraction from chloroalkanes by metal complexes has been seen in other systems [49,50], but the feasibility of chlorine atom transfer in this case clearly depends on the relative bond strengths for homolytic cleavage of the Pd-Cl and C-Cl bonds. In chloroform, the latter is 339 kJ M À1 [51], while the Pd-Cl bond energy in PdCl 2À 4 has been estimated to lie between 339 and 351 kJ M À1 [52].…”