Lori Beth Anderson

The isolation and characterization of the first examples of pairs of α- and β-isomers of dirhenium(II) of type Re2X4(LL)2 (X = Cl or Br, LL = bidentate phosphine ligand)

Abstract The complexes Re2Br4(depe)2 and Re2X4(dppee)2 (X = Cl or Br, depe = Et2PCH2CH2PEt2, dppee = cis-Ph2PCHCHPPh2) have been prepared in their α- (eclipsed rotational geometry, chelating phosphine ligands) and β- (staggered rotational geometry, bridging phosphine ligands) isomeric forms. The chloro complex β-Re2Cl4(depe)2 has also been isolated. In the case of α- and β- Re2Br4(depe)2, the preparations involve the reactions of Re2Br4(P-n-Pr3)4 with depe in toluene-ethanol. While α-Re2X4(dppee)2 are prepared from the reactions of (n-Bu4N)2Re2X8 with dppee in various solvents, the β-isomers are obtained upon reacting Re2X4(PR3)4 (R = Et or n-Pr) with dppee in benzene. These are the first examples of triply bonded dirhenium(II) complexes that have been isolated in both their α- and β-forms. β-Re2X4(dppee)2 (X = Cl or Br) constitute the first examples of complexes of this structural type which contain both CC and MM units within the same fused decalin-like ring system. The isomers β-Re2Cl4(depe)2 and β-Re2X4(dppee)2 (X = Cl or Br) are oxidized by NOPF6 in acetonitrile to give paramagnetic β-[Re2Cl4(depe)2]PF6 and β-[Re2X4(dppee)2]PF6. These oxidized complexes in turn react with CH3CN in the presence of T1PF6 to afford β-[Re2Cl3(depe)2(NCMe)](PF6)2 and β-[Re2X3(dppee)2(NCMe)](PF6)2, respectively. The cleavage of the ReRe bonds of α- and β-Re2Cl4(dppee)2 occurs upon their reaction with CCl4-CH2Cl2 to give cis-ReCl4(dppee). The related bromo complex cis-ReBr4(dppee) is formed when β-Re2Br4(dppee)2 is reacted with CH2Cl2-Br2.

Reactions of the dirhenium(II) complexes [Re2X4(dppm)2](X = Cl or Br, dppm = Ph2PCH2PPh2) with isocyanides. Part 2. The A-frame-like monoisocyanide species [Re2(µ-X)(µ-dppm)2X3(CNR)]n+(R = Me, But, or C6H3Me2-2,6; n= 0 or 1)

The triply bonded complexes [Re2X4(dppm)2](X = Cl or Br, dppm = Ph2PCH2PPh2) react with RNC (R = Me, But, or C6H3Me2-2,6) to yield the monoisocyanide adducts [Re2X4(dppm)2(CNR)]. The spectroscopic properties of these species are in accord with the presence of isomers in solution. Chemical oxidation of the neutral complexes to their corresponding paramagnetic monocations produces a single isomer in each instance. The solid-state structure of [Re2Cl4(dppm)2(CNBut)] has been shown to be that of the A-frame-like molecule [Cl2Re(µ-Cl)(µ-dppm)2ReCl(CNBut)]. The retention of a Re–Re multiple bond is supported by both structural work (Re–Re = 2.30 A) and a qualitative treatment of the bonding which is consistent with the presence of a slightly weakened triple bond.

Reactions of the multiply bonded dirhenium complexes [Re2X4(L–L)2]n+(X = Cl or Br, L–L = Ph2PCH2CH2PPh2 or Ph2PCH2CH2AsPh2; n= 0 or 1) with isocyanides and nitriles. Reaction without metal–metal bond disruption

The reaction of paramagnetic [Re2X4(L–L)2] PF6 with RNC (X = CI or Br, L–L = Ph2PCH2CH2PPh2 or Ph2PCH2CH2AsPh2, R = Pri or But) proceeds with reduction of the dirhenium core to yield the diamagnetic complexes [Re2X3(L–L)2(CNR)] PF6. These isocyanide-containing compounds can be oxidized to the paramagnetic dications using NOPF6 as the oxidant. The reactions of complexes [Re2X4(L–L)2] PF6 with nitriles RCN (R = Me or Et) in the presence of TIPF6 yield the paramagnetic complexes [Re2X3(L–L)2(NCR)][PF6]2, which can be reduced to the corresponding monocations using LiBEt3H or cobaltocene as the reductants. The staggered rotational geometry of the parent complexes [Re2X4(L–L)2]n+(n= 0 or 1) is believed to be retained in [Re2X3(L–L)2(CNR)]n+ and [Re2X3(L-L)2(NCR)]n+(n= 1 or 2).