Studies of catalytic benzene alkenylation using different diimine ligated Rh­(I) acetate complexes and Cu­(OAc)2 as the oxidant revealed statistically identical results in terms of activity and product selectivity. Under ethylene pressure, two representative diimine ligated rhodium­(I) acetate complexes were demonstrated to exchange the diimine ligand with ethylene rapidly to form [Rh­(μ-OAc)­(η2-C2H4)2]2 and free diimine. Thus, it was concluded that diimine ligands are not likely coordinated to the active Rh catalysts under catalytic conditions. At 150 °C under catalytic conditions using commercial Cu­(OAc)2 as the oxidant, [Rh­(μ-OAc)­(η2-C2H4)2]2 undergoes rapid decomposition to form catalytically inactive and insoluble Rh species, followed by gradual dissolution of the insoluble Rh to form the soluble Rh, which is active for styrene production. Thus, the observed induction period under some conditions is likely due to the formation of insoluble Rh (rapid), followed by redissolution of the Rh (slow). The Rh decomposition process can be suppressed and the catalytically active Rh species maintained by using soluble Cu­(II) oxidants or Cu­(OAc)2 that has been preheated. In such cases, an induction period is not observed.

This work focuses on the synthesis of supported Rh materials and study of their efficacy as pre‐catalysts for the oxidative alkenylation of arenes. Rhodium particles supported on silica (Rh/SiO2; ∼3.6 wt% Rh) and on nitrogen‐doped carbon (Rh/NC; ∼1.0 wt% Rh) are synthesized and tested. Heating mixtures of Rh/SiO2 or Rh/NC with benzene and ethylene or α‐olefins and CuX2 {X=OPiv (trimethylacetate) or OHex (2‐ethyl hexanoate)} to 150 °C results in the production of alkenyl arenes. When using Rh/SiO2 or Rh/NC as catalyst precursor, the conversion of benzene and propylene or toluene and 1‐pentene yields a ratio of anti‐Markovnikov to Markovnikov products that is nearly identical to the same ratios as the molecular catalyst precursor [Rh(μ‐OAc)(η2‐C2H4)2]2. These results and other observations are consistent with the formation of active catalysts by leaching of soluble Rh from the supported Rh materials.

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C–C bond formation. In this study, we investigate C–C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ], [Au 2 (μ-CH 3 )(XPhos) 2 ][NTf 2 ], and [Au 2 (μ-CH 3 )( t BuXPhos) 2 ][NTf 2 ] {Ar′ = C 6 H 3 -2,6-(C 6 H 3 -2,6-Me) 2 , C 6 H 3 -2,6-(C 6 H 2 -2,4,6-Me) 2 , C 6 H 3 -2,6-(C 6 H 3 -2,6- i Pr) 2 , or C 6 H 3 -2,6-(C 6 H 2 -2,4,6- i Pr) 2 ; XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; t BuXPhos = 2-di- tert -butylphosphino-2′,4′,6′-triisopropylbiphenyl; NTf 2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH 3 )L and Au(L)(NTf 2 ) {L = phosphines listed above}. For [Au 2 (μ-CH 3 )(XPhos) 2 ][NTf 2 ] and [Au 2 (μ-CH 3 )( t BuXPhos) 2 ][NTf 2 ], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ] increases as the steric bulk of the phosphine substituent Ar′ decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C–C coupling likely involves (1) cleavage of [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ] to form Au(PR 2 Ar′)(NTf 2 ) and Au(CH 3 )(PMe 2 Ar′), (2) phosphine migratio...

The compounds Os 5 (CO) 15 (µ 3 -AuPPh 3 ) 2 , 2 and Os 5 (CO) 14 [µ 4 -Au 3 (PPh 3 ) 3 ](µ 3 -AuPPh 3 ), 3 were obtained from the reaction of [PPN] 2 [Os 5 (CO) 15 ] using [Au(PPh 3 )][NO 3 ]. Compound 2 contains two triply-bridging Au(PPh 3 ) groups. Compound 3 contains one triply-bridging Au(PPh 3 ) group and a quadruply-bridging Au 3 (PPh 3 ) 3 group. When the same reaction was performed in the presence of CH 3 Au(PPh 3 ), the new trigold compound Os 5 (CO) 14 (CH 3 )(µ 3 -AuPPh 3 ) 3 , 4 was obtained. Compound 4 contains three triply-bridging Au(PPh 3 ) groups and one methyl group coordinated to one of the apical osmium atoms of the trigonal bipyramidal pentaosmium cluster. Compound 4 was not obtained by the direct reaction of 2 with CH 3 Au(PPh 3 ) but it was obtained when [Au(PPh 3 )][NO 3 ] was added to the reaction solutions. Cationic digold species such as [CH 3 Au 2 (PPh 3 ) 2 ] + have been proposed as a possible mechanism for the activation of CH 3 Au(PPh 3 ) by [Au(PPh 3 )][NO 3 ]. Compound 4 was also obtained albeit in a lower yield from the reaction of Os 6 (CO) 18 with MeAu(PPh 3 ) following treatment with Me 3 NO. Each of the pentaosmium products was characterized structurally by a single-crystal X-ray diffraction analysis.

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Silica-supported Pd, Rh and Pt metal nanoparticles catalyze the hydrogenolysis of the PtÀ OPh bond of ( t bpy)Pt(OPh)Cl to release PhOH. Based on kinetic studies monitored by 1 H NMR spectroscopy, the reactivity trend is Pd > Rh > Pt. Kinetic studies with Pd/SiO 2 are consistent with a first-order dependence on the catalyst and the molecular Pt(II) complex ( t bpy)Pt(OPh)Cl. Using TEM-EDS mapping and ICP-OES measurements of a recovered Pd catalyst, after 1 hour of hydrogenolysis of ( t bpy)Pt-(OPh)Cl, approximately 10-16 % Pt deposition (relative to Pd mol %) on the Pd/SiO 2 surface was quantified.