823202-50-2Relevant academic research and scientific papers
Aromatic and aldehyde carbon-hydrogen bond activation at cationic Rh(III) centers. Evaluation of electronic substituent effects on aldehyde binding and C-H oxidative addition
Corkey, Britton K.,Taw, Felicia L.,Bergman, Robert G.,Brookhart, Maurice
, p. 2943 - 2954 (2008/10/09)
Cationic rhodium methyl complexes, [Cp*(L)Rh(Me)(CH 2Cl2)]+ (L = PMe3, P(OMe) 3) react with benzene to yield the corresponding phenyl complexes, [Cp*(L)Rh(Ph)(CH2Cl2)]+. Reactions of [Cp*(L)Rh(Me)(CH2Cl2)]+ with p-X-substituted benzaldehydes (X = -CF3, -CH3, and -OMe) produce acyl aldehyde adducts, [Cp*(L)Rh(C(O)C6H 4X)(p-XC6H4CHO)]+. In the case of L = PMe3, decarbonylation of the aldehyde adducts occurs cleanly to form [Cp*(PMe3)Rh(C6H4X)(CO)] +. For L = P(OMe)3, decarbonylation is a more complicated process. Cationic rhodium methyl complexes, [Cp(PMe3)Rh(Me)(CH2Cl2)] BAr4′(1) and [Cp(P(OMe)3)Rh(Me)(CH2Cl2)]BAr4′(3), react with benzene to yield the corresponding phenyl complexes, [Cp(PMe3)Rh(Ph)(CH2Cl2)] BAr4′(6) and [Cp(P(OMe)3)Rh(Ph)(CH2Cl2)]BAr4′(7). First-order rate constants observed in 1.1 M benzene in CD2Cl2 at 25°C are (2.1 ± 0.2) × 10-5 s-1 and (1.9 ± 0.2) × 10-5 s-1, respectively. Reactions of 1 and 3 with p-X-substituted benzaldehydes (X = -CF3, -CH3, and -OMe) initially produce the σ-aldehyde adducts, [Cp(L)Rh(Me)(p-XC6H4CHO)] BAr4′ (L = PMe3 (15), P(OMe)3 (16)). Exchange of free with bound aldehyde occurs via a dissociative process and quantitative NMR rate measurements show that complexes of 1 exchange faster than those of 3 and that less basic aldehydes exchange faster than more basic aldehydes (p-CF 3C6H4CHO > p-CH3C 6H4CHO > p-CH3OC6H 4CHO). The aldehyde adducts undergo C-H bond activation to produce initially methane plus acyl aldehyde adducts, [Cp(L)Rh(C(O)C6H4X)(p-XC6H4CHO)] BAr4′ (L = PMe3 (17), P(OMe)3 (18)). Rates of C-H activation are correlated with aldehyde exchange rates; activation barriers of weakly bound aldehydes are lower than more strongly bound aldehydes. In the case of L = PMe3, decarbonylation of the aldehyde adducts occurs cleanly to form aryl carbonyl complexes, [Cp(PMe3)Rh(C6H4X)(CO)]BAr4′. For L = P(OMe)3, decarbonylation is a more complicated process; some intermediates and products have been identified by NMR spectroscopy.
