Chemistry of dirhenium(II) and dimolybdenum(II) complexes containing sigma-donor, pi-acceptor and bridging ligands

Jusheng Qi, Purdue University

Abstract

The triply bonded complexes Re$\sb2$X$\sb4$(dppm)$\sb2$ (X = Cl or Br; dppm = Ph$\sb2$PCH$\sb2$PPh$\sb2$) react with tertiary phosphine and phosphite ligands to afford the 1:1 adducts Re$\sb2$X$\sb4$(dppm)$\sb2$(L) (L = PR$\sb3$ or P(OR)$\sb3$; R = Me, Et or Ph) which may have the A-frame-like structure X$\sb2$Re($\mu$-X) ($\mu$-dppm)$\sb2$ReX(L). Re$\sb2$Cl$\sb4$(dppm)$\sb2$(PMe$\sb3$) reacts with nitrile ligands R$\sp\prime$CN (R$\sp\prime$ = Me, Et, Ph or CH$\sb2$Ph) in the presence of TlPF$\sb6$ to yield the complexes (Re$\sb2$Cl$\sb3$(dppm)$\sb2$(NCR$\sp\prime$)$\sb2$) PF$\sb6$. Reactions of Re$\sb2$X$\sb4$(dppm)$\sb2$ with CO and R$\sp{\prime\prime}$NC (R$\sp{\prime\prime}$ = Bu$\sp{\rm t}$ or xylyl) give the complexes Re$\sb2$X$\sb4$(dppm)$\sb2$(CO)$\sb{\rm n}$ (n = 1 or 2) and Re$\sb2$X$\sb4$(dppm)$\sb2$(CO)(CNR$\sp{\prime\prime}$), respectively. Re$\sb2$X$\sb4$(dppm)$\sb2$(CO) reacts with PR$\sb3$ and P(OR)$\sb3$ to form the complexes (Re$\sb2$X$\sb3$(dppm)$\sb2$(CO)(PR$\sb3$)$\sb2$) $\sp+$(A)$\sp-$ (A = Cl, BPh$\sb4$ or PF$\sb6$) or $\{$Re$\sb2$X$\sb3$(dppm)$\sb2$(CO)(P(OR)$\sb3$) $\sb2\}$PF$\sb6$, whereas Re$\sb2$X$\sb4$(dppm)$\sb2$(CO)(CNR$\sp{\prime\prime}$) reacts further with PR$\sb3$ in the presence of TlPF$\sb6$ to form the complexes (Re$\sb2$X$\sb3$(dppm)$\sb2$(CO)(CNR$\sp{\prime\prime}$)(PR$\sb3$)) PF$\sb6$. Re$\sb2$X$\sb4$(dppm)$\sb2$(CO)$\sb2$ reacts with PR$\sb3$ or P(OR)$\sb3$ to form the unsymmetrical $\mu$-CO complexes (Re$\sb2$X$\sb3$(dppm)$\sb2$(CO)$\sb2$(L)) PF$\sb6$ (L = PR$\sb3$ or P(OR)$\sb3$) in the presence of TlPF$\sb6$. (Re$\sb2$Cl$\sb3$(dppm)$\sb2$(CO)$\sb2$(PMe$\sb3$)) PF$\sb6$ can be reduced by Cp$\sb2$Co to yield a neutral paramagnetic species (Re$\sb2$X$\sb3$(dppm)$\sb2$(CO)(PMe$\sb3$)$\sb2$) $\sp0$. The complexes (Re$\sb2$Cl$\sb3$(dppm)$\sb2$(CO)(PMe$\sb3$)$\sb2$) Cl $\cdot$ 1/2CH$\sb2$Cl$\sb2$, (Re$\sb2$Cl$\sb3$(dppm)$\sb2$(CO)$\sb2$(PMe$\sb3$)) PF$\sb6$ and $\{$Re$\sb2$Cl$\sb3$(dppm)$\sb2$(CO)$\sb2$(P(OEt)$\sb3$) $\}$PF$\sb6$ were characterized by X-ray crystallography. Reactions of Re$\sb2$X$\sb4$(dppm)$\sb2$ with neat CS$\sb2$ produce complexes of stoichiometry Re$\sb2$X$\sb4$(dppm)$\sb2$(CS$\sb2$). An X-ray crystallographic study of Re$\sb2$Cl$\sb4$(dppm)$\sb2$(CS$\sb2$) has revealed the presence of $\mu$-Cl and $\mu$-S bridges and a CS ligand within the dirhenium unit; the Re-Re distance $\approx$2.9 A. Re$\sb2$($\mu$-X)($\mu$-S)(dppm)$\sb2$X$\sb3$(CS) react further with nitriles, isocyanides and CO in the presence of TlPF$\sb6$ to give complexes (Re$\sb2$($\mu$-X)($\mu$-S)(dppm)$\sb2$X$\sb2$(CS)(L$\sp\prime$)) PF$\sb6$(L$\sp\prime$ = NCR$\sp\prime$, CNR$\sp{\prime\prime}$, CO). The complexes Re$\sb2$X$\sb4$(dppm)$\sb2$ react with 2-mercaptoquinoline (2-mqH) to afford the 1:1 adducts Re$\sb2$X$\sb4$(dppm)$\sb2$(2-mqH). These complexes undergo a reversible one-electron transfer to give (Re$\sb2$X$\sb4$(dppm)$\sb2$(2-mqH)) PF$\sb6$. This oxidation is followed by the slow elimination of HX to give paramagnetic (Re$\sb2$X$\sb3$($\mu$-dppm)$\sb2$(2-mq)) PF$\sb6$. The X-ray crystal structure of (Re$\sb2$Cl$\sb3$($\mu$-dppm)$\sb2$(2-mq)) PF$\sb6$ were determined. The quadruply bonded dimolybdenum(II) complex Mo$\sb2$(O$\sb2$CCH$\sb3$)$\sb4$ reacts with 2-mqH to form Mo$\sb2$(2-mq)$\sb4$ whereas Mo$\sb2$X$\sb4$(PR$\sb3$)$\sb4$ (PR$\sb3$ = PMePh$\sb2$, PMe$\sb2$Ph or PEt$\sb3$) react with Hmhp or Hdmhp (Hmhp = 2-hydroxy-6-methylpyridine; Hdmhp = 2,4-dimethyl-6-hydroxypyrimidine) to form the series of mixed-ligand complexes Mo$\sb2$X$\sb{\rm n}$(mhp)$\sb{\rm 4-n}$(PR$\sb3$)$\sb{\rm n}$ (n = 1-3) and Mo$\sb2$X$\sb2$(dmhp)$\sb2$(PEt$\sb3$)$\sb2$, respectively.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry|Chemical engineering

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