Preparation, X-ray structure, and reactivity of an olefin-carbene-osmium complex:: α-alkenylphosphine to α-allylphosphine transformation via an osmaphosphabicyclopentane intermediate

The isopropenyldi(isopropyl)phosphine complex Os(eta(5)-C5H5)Cl{[eta(2)-CH2=C(CH3)](PPr2)-Pr-i} (1) reacts at room temperature with phenyldiazomethane to give the olefin-carbene derivative Os(eta(5)-C5H5)Cl(=CHPh){(PPr2)-Pr-i[C(CH3)=CH2]} (2), which has been characterized by X-ray diffraction analysis. In toluene at 70 degreesC, complex 2 evolves into the osmaphosphabicyclo- pentane compound Os(eta(5)-C5H5)Cl{(PPr2)-Pr-i[C(CH3)CH2CHPh]} (3). Treatment of 3 with TIPF6 at room temperature leads to a 1:1 mixture of the alpha-allylphosphine complex OsH(eta(5)-C5H5)Cl{[eta(3)-CHPhCHC(CH3)] (PPr2)-Pr-i}]PF6 (4) and its alpha-alkenyl-gamma-(eta(3)-benzyl)phosphine isomer [OsH-(eta(5)-C5H5){[eta(3)-C6H6CHCH=C(CH3)] (PPr2)-Pr-i}]PF6 (5). The heating of the mixture in tetrahydrofuran at 66 degreesC gives rise to the isomerization of 5 into 4, which has been also characterized by X-ray diffraction analysis. The hydride ligand of 4 is fairly acidic. Its deprotonation with NaOCH3 leads to an equilibrium mixture of the neutral osmium(II) alpha-allylphosphine OsH-(eta(5)-C5H5)Cl{[eta(3)-CHPhCHC(CH3)] (PPr2)-Pr-i} (6), alpha-alkenyl-gamma-(eta(3)-benzyl)phosphine OsH(eta(5)-C5H5)- Cl{[eta(3)-CHPhCHC(CH3)(PPr2)-Pr-i} (7), and alpha-alkenyl-gamma-carbenephosphine OsH(eta(5)-C5H5){[=C(Ph)-CH=C(Cl{[ (PPr2)-Pr-i} (8) isomers. Complex 2 also reacts with TIPF6. The reaction affords the -C5H5)(=CPh){(PPr2)-Pr-i[C(CH3)=CH2]}]PF6 (9), which evolves hydride-carbyne derivative [OsH(eta(5) into 4. The isomerization is a first-order process with activation parameters of DeltaH(double dagger) = 23 3 kcal.mol(-1) and DeltaS(double dagger) = -4 +/- 4 cal.K-1.mol(-1). The hydride ligand of 9 is also fairly acidic. Its deprotonation with NaOCH3 leads to the neutral carbyne Os(eta(5)-C5H5)(dropCPh){(PPr2)-Pr-i[C(CH3)=CH2]} (10), which reacts with methanol to give the hydride-alkoxycarbene derivative OsH(eta(5)-C5H5){=C(OMe)Ph}{(PPr2)-Pr-i[C(CH3)=CH2]} (11). The carbene carbon atom of 2 has amphiphilic character, reacting with electrophiles and nucleophiles. The reaction with HBF4 leads to the hydride-benzylcyclopentadienyl derivative OsH(eta(5)-C5H4CH2Ph)Cl{[eta(2)-CH2=C(CH3)+Pr-2}]PF6 (14) via eta(1)-benzyl intermediates, whereas the reaction with CH3Li gives the hydride-styrene compound OsH(eta(5)-C5H5)(eta(2)-CH2=CHPh){(PPr2)-Pr-i[C(CH3)=CH2]} (15).