Synthesis, Molecular Structure, and Reactivity of Neutral and Cationic Areneosmium(II) Complexes with Diarylcarbenes as Ligands

Abstract

While the dinuclear compounds [(η 6 -mes)Os{κ 1 -OC(O)CF 3 }(μ-Cl)] 2 ( 2 ) and [(η 6 -mes)Os{κ 1 -OS(O) 2 CF 3 }(μ-Cl)] 2 ( 3 ), prepared from [(η 6 -mes)OsCl(η 3 -C 3 H 5 )] ( 1 ) and CF 3 CO 2 H or CF 3 SO 3 H by elimination of propene, are not suitable precursors for the synthesis of osmium carbenes, the bis(trifluoroacetato) derivatives [(η 6 -arene)Os{κ 1 -OC(O)CF 3 }(κ 2 -O 2 CCF 3 )] ( 4, 9, 10 ) are useful starting materials. They react with diaryldiazomethanes R 2 CN 2 to give the half-sandwich-type complexes [(η 6 -arene)Os{κ 1 -OC(O)CF 3 } 2 ( CR 2 )] ( 11 − 17 ) in good to excellent yields. The bis(tosylato)osmium(II) compounds [(η 6 -arene)Os{κ 1 -OS(O) 2 R}{κ 2 -O 2 S(O)R}] ( 20, 21; R = p -C 6 H 4 CH 3 ) behave differently and upon treatment with Ph 2 CN 2 and PhCHN 2 afford tetraphenylethene and a mixture of ( E )- and ( Z )-stilbene. The reaction of 12 − 15 and 17 with either Me 3 SiX or NH 4 X (X = Cl, Br, I) leads to the replacement of the trifluoroacetato ligands and the formation of the corresponding carbene complexes [(η 6 -arene)OsX 2 ( CR 2 )] ( 22 − 31 ) in 67−91% yield. An exchange of trifluoroacetate for chloride or bromide by using HCl or HBr is also possible. Treatment of [(η 6 -mes)OsCl 2 ( CPh 2 )] ( 28 ) with M(acac-[F n ]) (M = Na, Tl; n = 0, 3, or 6) affords the chelate compounds [(η 6 -mes)OsCl(κ 2 -acac-[F n ])] ( 33 − 35 ) via elimination of the carbene ligand. Compounds 33 − 35 are also accessible from [(η 6 -mes)OsCl 2 ] 2 ( 19 ) and Hacac/NEt 3 or Na(acac-[F n ]) ( n = 3 or 6), respectively. While 14 (arene = mes; R = Ph) and 28 react with C 6 H 5 MgBr and CH 3 MgI only by displacement of trifluoroacetate or chloride for bromide or iodide, the reaction of 14 with CH 2 CHMgBr gives the η 3 -allyl complex [(η 6 -mes)OsBr(η 3 -CH 2 CHCPh 2 )] ( 36 ). A C−C coupling also takes place upon treatment of 14 with CH 2 CHOEt, resulting in the formation of the metallacyclic compound [(η 6 -mes)Os{κ 2 ( C, O )-Ph 2 C CH CH O Et}{κ 1 -OC(O)CF 3 }] ( 38 ). The bis(trifluoroacetato) derivatives 14, 15, and 17 react in acetone with water to afford the diaryl(carbonyl)osmium(II) complexes [(η 6 -mes)OsR 2 (CO)] ( 39 − 41 ). On the basis of a labeling experiment, a mechanism for this unusual C−C cleavage reaction is proposed. The reaction of the dichloro compounds 28 and 29 with PPh 3 in the presence of AgPF 6 gives the cationic carbene complexes [(η 6 -mes)OsCl(PPh 3 )( CR 2 )]PF 6 ( 45, 46 ) in nearly quantitative yields. The molecular structures of 2, 15, 28, 35, and 46 were determined crystallographically.