C-H bond activation reactions in π-allene-osmium-triisopropylphosphine complexes with cyclopentadienyl or hydridotris(pyrazolyl)borate ligands: Formation of isopropenyldiisopropylphosphine versus hydride-alkenylcarbyne derivatives

摘要

The reactions of the bis(solvento) complexes [OsCp(MeCN)_2(P ~iPr_3)]PF_6 (1; Cp = cyclopentadienyl) and [OsTp(κ~1-OCMe_2)_2(P~iPr _3)]BF_4 (1a; Tp = hydridotris(pyrazolyl)borate) with allenes have been investigated. Complex 1 reacts with 1-methyl-1- (trimethylsilyl)allene and 1,1-dimethylallene to give the π-allene derivatives [OsCp(ν~2-CH_2=C=CRMe)(MeCN)(P ~iPr_3)]PF_6 (R = SiMe_3 (2), Me (3)). In fluorobenzene at 80 °C, complexes 2 and 3 are moderately stable and evolve into the isopropenyldiisopropylphosphine derivative [OsCp{κ ~3P,C,C-P~iPr_2[C(Me)=CH_2]}(MeCN)] PF_6 (4) by hydrogen transfer from an isopropyl substituent of the phosphine to the coordinated double bond of the allene. Under an ethylene atmosphere the acetonitrile ligand of 4 is displaced by the olefin. The resulting π-ethylene derivative [OsCp(ν~2-CH_2=CH _2){κ~3P,C,C-P~iPr_2[C(Me)=CH _2]}]PF_6 (5) is obtained through a one-pot synthesis procedure by the stirring of 3 in fluorobenzene at 80 °C under 2 atm of ethylene. Treatment of 2 and 3 with dimethyl acetylenedicarboxylate gives [OsCp{ν~2-CH(CO_2Me)=CH(CO_2Me)} {κ~3P,C,C-P~iPr_2[C(Me)=CH _2]PF_6 (6). The reaction of 1a with 1,1-dimethylallene leads to [OsTp(ν~2-CH_2=C=CMe_2) (κ~1-OCMe_2)(P~iPr_3)]BF _4 (7). In contrast to its Cp counterpart, complex 7 evolves into the hydride-alkenylcarbyne derivative [OsHTp(=CCH=CMe_2)(P ~iPr_3)]BF_4 (8), by means of a double migration of the hydrogen atoms of the terminal CH_2 group of the allene. One of them migrates to the central carbon atom of the allene, and the other one goes to the metal center. The alkenylcarbyne group of 8 is selectively deprotonated in the presence of the hydride ligand to afford the hydride-alkenylvinylidene OsHTp{=C=CHC(Me)=CH_2}(P~iPr_3) (9). The X-ray structures of 2, 5, 8, and 9 are also reported.