Synthesis, characterization, and reactivity of rhenium polyhydride complexes and their precursors

Salts of the complex cation ($\rm Re\sb2 H\sb6(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$ can be synthesized from the reactions of $\rm ReH\sb4(mq)(PPh\sb3)\sb2$ with an electrophile. The acid-base and redox chemistry of these salts have been explored. By reacting trimethylphosphine or 4-methylpyridine with ($\rm Re\sb2H\sb6(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$, a single deprotonation is achieved and the species ($\rm Re\sb2H\sb5(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp+$ is formed. If the base 1,8-diazabicyclo(5.4.0) undec-7-ene (DBU) is employed, ($\rm Re\sb2H\sb6(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$ is doubly deprotonated to form $\rm Re\sb2H\sb4(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4$. Both $\rm \lbrack Re\sb2H\sb5(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp+$ and $\rm Re\sb2H\sb4(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4$ can be reprotonated to obtain the original dicationic hexahydridodirhenium species. When exposed to O$\sb2$, the complex $\rm Re\sb2H\sb4(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4$ undergoes a two-electron oxidation to form ($\rm Re\sb2H\sb4(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$. The structures of ($\rm Re\sb2H\sb6(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$ and ($\rm Re\sb2H\sb4(\mu$-$\rm mq)\sb2(PPh\sb3)\sb4\rbrack\sp{2+}$ were established by X-ray crystallography. The reaction of mer-trans-ReOCl$\rm\sb3(PPh\sb3)\sb2$ with PMe$\sb3$ resulted in the formation of fac-cis-ReOCl$\rm\sb3(PMe\sb3)\sb2$ and mer-trans-ReOCl$\rm\sb3(PMe\sb3)\sb2$ which were characterized by X-ray crystallography. A high-yield route to the synthesis of $\rm ReH\sb7(PMe\sb3)\sb2$ is afforded by the reactions of fac-cis-$\rm ReOCl\sb3(PMe\sb3)\sb2$ and mer-trans-$\rm ReOCl\sb3(PMe\sb3)\sb2$ with LiAlH$\sb4$. the synthesis of fac-cis-$\rm Re(NEt)Cl\sb3(PMe\sb3)\sb2$ and mer-trans-$\rm Re(NEt)Cl\sb3(PMe\sb3)\sb2$ have been accomplished and their X-ray crystal structures determined. These imido complexes are the first pair of isomers of the type $\rm Re(NR)Cl\sb3(PR\sp\prime\sb3)\sb2$ to have been structurally characterized by X-ray crystallography