The activation of small molecules by dirhenium complexes

Keng-Yu Shih, Purdue University

Abstract

The reactions of cis-Re$\sb2(\mu$-O$\sb2$CC$\sb2$H$\sb5)\sb2$Cl$\sb2(\mu$-dppm)$\sb2$ with RCN ligands in the presence of strong acid afford salts of the cis- ($\rm Re\sb2Cl\sb2(\mu$-$\rm dppm)\sb2(NCR)\sb4\rbrack \sp{2+}$ cations. Attempts to grow crystals of cis- ($\rm Re\sb2Cl\sb2(\mu$-$\rm dppm)\sb2(NCC\sb2H\sb5)\sb4\rbrack (PF\sb6)\sb2$ led to its conversion to ($\rm Re\sb2Cl\sb3(\mu$-$\rm dppm)\sb2(NCC\sb2H\sb5)\sb2\rbrack PF\sb6$. The reaction of cis-$\rm Re\sb2(\mu$-$\rm O\sb2CCH\sb3)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$ with NaBH$\sb3$CN in THF gives cis-$\rm Re\sb2(\mu$-$\rm O\sb2CCH\sb3)\sb2(NCBH\sb3)\sb2(\mu$-$\rm dppm)\sb2$. Another example of a (BH$\sb3$CN) $\sp-$ containing complex is the conversion of $\rm Re\sb2Cl\sb4(\mu$-$\rm dppm)\sb2$ to $\rm Re\sb2(NCBH\sb3)\sb4(\mu$-$\rm dppm)\sb2(H\sb2O)\sb2$ upon its reaction with Na (BH$\sb3$CN) in methanol. The compounds $\rm Re\sb2X\sb4(\mu$-$\rm dppm)\sb2$ (X = Cl or Br) react with H$\sb2$S in THF with resulting oxidative addition at the dimetal core to afford the complexes of stoichiometry $\rm Re\sb2(\mu$-$\rm H)(\mu$-$\rm SH)X\sb4(\mu$-$\rm dppm)\sb2$. This can be contrasted with non-redox reaction of cis-$\rm Re\sb2(\mu$-$\rm O\sb2CR)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$ with H$\sb2$S in the presence of strong acid which leads to the generation of cis-$\rm Re\sb2(\mu$-$\rm SH)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$. When a similar type of reaction between H$\sb2$S and cis-$\rm Re\sb2(\mu$-$\rm O\sb2CR)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$ is carried out in ketone or aldehyde solution under acidic conditions a different product $\rm Re\sb2(\mu$-$\rm S\sb2CRR\sp\prime)Cl\sb2(\mu$-$\rm dppm)\sb2$ is isolated. This type of gem-dithiolato complex can also be generated by the reaction of $\rm Re\sb2(\mu$-$\rm SH)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$ in the ketone solution under acidic conditions. The activation of O$\sb2$ is accomplished by using $\rm Re\sb2X\sb4(\mu$-$\rm dppm)\sb2$ (1) to afford $\rm Re\sb2(\mu$-$\rm O)(\mu$-$\rm X)(O)X\sb3(\mu$-$\rm dppm)\sb2$ (2) and $\rm Re\sb2(\mu$-$\rm O)(O)\sb2X\sb4(\mu$-$\rm dppm)\sb2$ (3) in which the $\rm Re\sb2X\sb4(\mu$-$\rm dppm)\sb2$ entity is preserved and net 4- and 6-electron oxidations of the dirhenium unit have occurred. Complex 2 can be derivatized by reaction with isocyanide ligands and acetonitrile to give complex of the type $\rm Re\sb2(\mu$-$\rm O)(O)Cl\sb4(\mu$-$\rm dppm)\sb2$(L) (L = RNC or MeCN). The conversion of 3 to the closely related tetraoxo dirhenium(V) species $\rm Re\sb2(\mu$-$\rm O)\sb2(O)\sb2(\mu$-$\rm dppm)\sb2$ occurs in the presence of amines such as NEt$\sb3$ and pyridine. This reaction can be reversed upon reacting $\rm Re\sb2(\mu$-$\rm O)\sb2(O)\sb2Cl\sb2(\mu$-$\rm dppm)\sb2$ with SOCl$\sb2$. Further oxidation of the complexes 2 and 3 with O$\sb2$ or peroxide leads to complex of the type ReOCl$\sb3$(dppmO). Treatment of complex 2 with SOCl$\sb2$ gives $\rm Re\sb2(\mu$-$\rm O)Cl\sb6(\mu$-$\rm dppm)\sb2$. The complex $\rm Re\sb2(\mu$-$\rm Cl)Cl\sb3(\mu$-$\rm dppm)\sb2(CO)$ reacts with alkynes in the presence of TlPF$\sb6$ to afford salts of the type ($\rm Re\sb2Cl\sb3(\mu$-$\rm dppm)\sb2(CO)(\eta\sp2$-$\rm R\sp1CCR\sp2)\rbrack PF\sb6$. Complexes of the type $\rm Re\sb2(\mu$-$\rm Cl)(\mu$-$\rm CO)Cl\sb3(L)(\mu$-$\rm dppm)\sb2$ (L = CO or CNxyl) have been shown to undergo reductive coupling reactions with 1-alkynes in the presence of TlPF$\sb6$ at room temperature to yield products of the type ($\rm Re\sb2(\mu$-$\rm Cl)(\mu$-$\rm CPC(R)=CH)Cl\sb2(L)(\mu$-$\rm dppm)\sb2\rbrack PF\sb6$. Interestingly, the dirhenium alkylidyne complexes $\rm Re\sb2(\mu$-$\rm Cl) ({\equiv}CCH\sb2R)Cl\sb2(CO)(L)(\mu$-$\rm dppm)\sb2$, as well as their oxidized congeners, can be generated from these reductively coupled products via ring-opening reactions.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS