881998-40-9Relevant academic research and scientific papers
Competition studies of oxidative addition of aryl halides to the (PNP)Rh fragment
Puri, Mayank,Gatard, Sylvain,Smith, Dan A.,Ozerov, Oleg V.
, p. 2472 - 2482 (2011/06/21)
The (PNP)Rh fragment (2) can be conveniently accessed by dissociation of L from the four-coordinate complexes (PNP)Rh(L) (L = SPri2, 3; L = H2C - CHBut, 10), which contain the tridentate PNP pincer ligand (2-iPr2P-4-Me-C6H 4)2N-. A new and a more straightforward synthesis of 10 is reported, yielding 65% of 10 based on RhCl3(H 2O)x. A number of new aryl halide oxidation addition products (AHOAP) of the general formula (PNP)Rh(Ar)(Hal) (Hal = Cl, Br, I) have been synthesized through oxidative addition (OA) reactions of meta- and para-substituted aryl halides with 3 or 10. The rotation about the Rh-C aryl bond is restricted, resulting in rotamers for the meta-substituted aryls that are distinct on the NMR spectroscopy time scale. Reactions of some aryl halides containing a p-NO2 or p-CO 2Me with 3 or 10 led to the observation of products of C-H OA that are ostensibly stabilized by coordination to the NO2 or CO 2Me group. Analogous C-H OA products were observed for the halide-free nitrobenzene and ethyl benzoate, as well. However, the C-H OA products are thermodynamically unstable with respect to the isomeric AHOAP, to which they convert upon thermolysis. A Hammett-style analysis of the relative electronic effects of the para substituents X in the OA reactions of p-HalC 6H4X with 10 was carried out. The positive values of ρ obtained (ρ = 1.51(15) for Ar-Cl, ρ = 0.70(9) for Ar-Br, and ρ = 0.92(9) for Ar-I) illustrate the increase in the OA rate with increasing electron-withdrawing effect of X. Issues relating to the usefulness of the Hammett parameters in comparing various OA reactions are discussed. Comparison with analogous studies on the OA of aryl halides to Pd(0) complexes leads to the notion that the electronic effects have an impact on the rate similar to, but less pronounced than, that of the (PNP)Rh system, possibly indicative of an earlier transition state for the OA of aryl halides with (PNP)Rh.
Oxidative addition reactions of silyl halides with the (PNP)Rh fragment
Gatard, Sylvain,Chen, Chun-Hsing,Foxman, Bruce M.,Ozerov, Oleg V.
, p. 6257 - 6263 (2009/04/13)
The (PNP)Rh fragment, where PNP is the bis(o-diisopropylphosphinophenyl) amide pincer ligand, has been shown to undergo a series of silicon-halogen oxidative addition reactions. (PNP)Rh(SPri 2) (1) reacted with certain silyl halides with formation of (PNP)Rh(Silyl)(Hal) and release of SPr2i. The reactions with 1.1 equiv of Me3Si-I, Cl3Si-Cl, or MeCl 2Si-Cl proceeded to completion, the reactions with 1.1 equiv of Me2ClSi-Cl or Me3Si-Br produced an equilibrium mixture of (PNP)Rh(Silyl)(Hal) and (PNP)Rh(SPri2) (1), and the reaction with Me3Si-Cl did not proceed at all. (PNP)Rh(SiMe 3)(Cl) was instead prepared via the reaction of (PNP)Rh(Me)(CH 2Ph) with Me3Si-Cl, which proceeds with concomitant elimination of ethylbenzene. The reaction of (PNP)Rh(SPri 2) (1) with Me2SiHCl led to the exclusive formation of (PNP)Rh(SiMe2Cl)(H) (14), containing a borderline Si...H contact. (PNP)Rh(SPr2i) (1) and (PNP)Rh(SiMe 2Cl)(Cl) (7) displayed similar rates in the reaction with PhBr that results in (PNP)Rh(Ph)(Br), presumably via the rate-limiting elimination of either SPr2i or Me2SiCl2.
Thioether, dinitrogen, and olefin complexes of (PNP)Rh: Kinetics and thermodynamics of exchange and oxidative addition reactions
Gatard, Sylvain,Guo, Chengyun,Foxman, Bruce M.,Ozerov, Oleg V.
, p. 6066 - 6075 (2008/10/09)
A variety of (PNP)Rh-L complexes (where L = organic sulfide or sulfoxide, dinitrogen, or tertbutylethylene) have been synthesized by trapping transient (PNP)Rh (1) in situ. Equilibrium studies established the relative affinity of the (PNP)Rh fragment (1) for various L in the following ofder (of decreasing affinity): Ph2SO > SBu2n > SPhMe > dibenzothiophene > SPh2 > benzothiophene > SPr 21 > thiophene ≈ SButMe > SBu 2s ≈ H2C=CHCMe3 ? SBu 2t. Dinitrogen reacted with 1 to yield a mixture of terminal and bridging N2 complexes and was found to bind more strongly than SPr2i. Reaction of (PNP)Rh(SPr 2i) (10) with PhHal led to the corresponding oxidative addition products (PNP)Rh(Ph)(Hal) (Hal = Cl, 18a; Hal = Br, 18b; Hal = I, 18c). The relative rates of oxidative addition of PhHal to 10 were found to be in the order PhI > PhBr > PhCl. Kinetic studies of the reaction of 10 with PhBr were consistent with the reaction proceeding via reversible dissociation of SPr2i, followed by irreversible addition of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph2) in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh]2(N2) (19a) and (PNP)Rh(H2C=CHCMe3) (21) were determined using X-ray crystallography. Approximately squareplanar geometry about Rh was registered.
Carbon-halide oxidative addition and carbon-carbon reductive elimination at a (PNP)Rh center
Gatard, Sylvain,Celenligil-Cetin, Remle,Guo, Chengyun,Foxman, Bruce M.,Ozerov, Oleg V.
, p. 2808 - 2809 (2007/10/03)
An unsaturated (PNP)Rh fragment can be generated by means of C-C reductive elimination from (PNP)Rh(Me)(Ar) or (PNP)Rh(Ar)(Ar). This fragment undergoes carbon-halogen oxidative addition with aryl chlorides, bromides, and iodides at room temperature. The C-H oxidative addition products in reactions with haloarenes are not observed, and evidence is presented that carbon-halogen oxidative addition is thermodynamically preferred. C-C reductive elimination from (PNP)Rh(Me)(Ar) and (PNP)Rh(Ar)(Ar) proceeds near quantitatively as a clean, first-order reaction. Copyright
