Activation of small molecules by cationic rhenium complexes

Abstract

Thermolysis of ReX(CO)$\sb5$ (X = CH$\sb3$ or H) with PPh$\sb3$ and P$\rm\sp{i}PrPh\sb2$ in toluene generates trans-mer-Re(X)(PR$\rm\sb3)\sb2(CO)\sb3$ complexes. Protonation of trans-mer-Re(X)(PR$\rm\sb3)\sb2(CO)\sb3$ with (H(Et$\rm\sb2O)\sb2\rbrack B(Ar\sp\prime)\sb4\ (Ar\sp\prime=3,5(CF\sb3)\sb2C\sb6H\sb3)$ under an H$\sb2$ atmosphere generates stable dihydrogen complexes, ($\rm Re(H\sb2)(PR\sb3)\sb2(CO)\sb3\rbrack B(Ar\sp\prime)\sb4\ (PR\sb3=PPh\sb3$ (4a), $\rm P\sp{i}PrPh\sb2$ (4b)). The large $J\sb{\rm HD}$ values (4a = 32 Hz, 4b = 30 Hz) and short T$\rm\sb{1min}$ values (4a = 10.3 ms, 4b = 10.5 ms) at 300 MHz are consistent with a dihydrogen formulation. The hydrogen ligand can be removed in solution or the solid state by exposing to vacuum or argon to generate a ligand deficient product, (Re(PR$\rm\sb3)\sb2(CO)\sb3\rbrack B(Ar\sp\prime)\sb4$ (5). Complexes 4 and 5 react with a variety of small molecules to form (ReL(PR$\rm\sb3)\sb2(CO)\sb3\rbrack B(Ar\sp\prime)\sb4\ (L=H\sb2O,\ NH\sb3,\ C\sb2H\sb4,\ N\sb2,\ CO, Cl\sp-,\ PPh\sb3,\ THF).$ ($\rm Ph\sb3C\rbrack B(Ar\sp\prime)\sb4$ reacts with $\rm Cp\sb2ReCH\sb3$ and $\rm Cp\sb2ReCH\sb2CH\sb3$ to abstract an $\alpha$-hydride from the alkyl ligand to generate carbene complexes, ($\rm Cp\sb2$Re=CH$\rm\sb2\rbrack B(Ar\sp\prime)\sb4$ (1) and (Cp$\sb2$Re=CH(CH$\rm\sb3)\rbrack B(Ar\sp\prime)\sb4$ (3). Both complexes 1 and 3 decompose to $\rm\lbrack Cp\sb2Re(C\sb2H\sb4)\rbrack\sp+$ and $\rm\lbrack Cp\sb2Re(NCCD\sb3)\rbrack\sp+$ in acetonitrile upon addition of BF$\sb{4\sp-}$ salts or thermolysis of the solutions at 50$\sp\circ$C for two weeks. $\rm\lbrack Cp\sb2Re(CH\sb3)H\rbrack B(Ar\sp\prime)\sb4$ eliminates methane at 0$\sp\circ$C in $\rm CH\sb2Cl\sb2$ to generate $\rm\lbrack Cp\sb2Re(CH\sb2Cl)Cl\rbrack B(Ar\sp\prime)\sb4.$ Addition of (Me$\rm\sb3O\rbrack BF\sb4$ to $\rm Cp\sb2ReR\ (R=CH\sb3,\ CH\sb2CH\sb3,\ CH\sb2SiMe\sb3)$ in acetonitrile forms stable bis-alkyl complexes, $\rm\lbrack Cp\sb2Re(CH\sb3)R\rbrack BF\sb4.$ (Cp$\sb2$Re=CH$\rm\sb2\rbrack B(Ar\sp\prime)\sb4$ (1) reacts with triphenylphosphine and pyridine to generate ylide complexes. Complex 1 reacts with Cl$\rm\sb2,\ Br\sb2,\ I\sb2$ by 1,2-addition across the Re-C double bond to form halomethyl halide complexes. Complex 1 has also been shown to react with oxygen, sulfur and carbene donor reagents to form $\eta\sp2$-formaldehyde, $\eta\sp2$-thioformaldehyde and $\eta\sp2$-olefin complexes.The addition of $\rm Me\sb2SiCl\sb2$ or $\rm(Me\sb2Si)\sb2Cl\sb2$ to a THF solution of ($\eta\sp5$-C$\rm\sb5H\sb4Li)\sb2ReCH\sb3$ gives ansa-bridged complexes with a single or double silicon linker. A X-ray diffraction study was undertaken to confirm the structure of ($\eta\sp5$-$\rm C\sb5H\sb4$-SiMe$\sb2$-$\eta\sp5$-$\rm C\sb5H\sb4)ReCH\sb3.$ Substituted derivatives of $\rm Cp\sb2ReX\ (X=H,\ CH\sb3)$ have also been synthesized with Me or SiMe$\sb3$ groups on each cyclopentadienyl ring. Several methyl hydride rhenocene complexes have been generated by protonation and characterized at low temperature by NMR spectroscopy. Methane elimination from these complexes occurs at ambient temperature, although (($\eta\sp5$-$\rm C\sb5H\sb4$-SiMe$\sb2$-$\eta\sp5$-$\rm C\sb5H\sb4)Re(CH\sb3)H\rbrack B(Ar\sp\prime)\sb4$ has been observed to be more stable at room temperature then analogous complexes.