Synthesis, Electrochemistry, and Spectroscopic Characterization of Bis-dirhodium Complexes Linked by Axial Ligands

Abstract

The synthesis and electrochemical and spectroscopic properties of bis-dirhodium complexes containing ap or dpf bridging ligands, (ap)(4)Rh(2)(C triple bond C)(2)Rh(2)(ap)(4) (2) and (dpf)(4)Rh(2)(CNC(6)H(4)NC)Rh(2)(dpf)(4) (4), were investigated (where ap and dpf are the 2-anilinopyridinate and N,N'-diphenylformamidinate ions, respectively). The related "simple" dirhodium species, (ap)(4)Rh(2)(C triple bond C)(2)Si(CH(3))(3) (1) and (dpf)(4)Rh(2)(CNC(6)H(5)) (3), with the same set of bridging ligands were also synthesized and their properties compared to those of the analogous bis-dirhodium complexes. Compound 1 was obtained by mixing (ap)(4)Rh(2)Cl and Li(C triple bond C)(2)Si(CH(3))(3) in refluxing THF for 16 h under vacuum while compound 2 was prepared by a reaction between (ap)(4)Rh(2)(C triple bond C)(2)Li and (ap)(4)Rh(2)Cl under similar conditions. The reaction between (CF(3)COO)(4)Rh(2) and molten Hdpf under vacuum for 24 h leads to the generation of compound 3 with a yield of 65%. The red-orange compound 4 was obtained upon addition of 0.5 equiv of CNC(6)H(4)NC at room temperature to a CH(2)Cl(2) solution containing (dpf)(4)Rh(2) which was synthesized according to a method described previously in the literature. Compound 1 crystallizes in the triclinic space group P1, with a = 10.164(3) A, b = 13.881(3) A, c = 18.805(4) A, alpha = 73.55(2) degrees, beta = 77.89(2) degrees, gamma = 84.85(2) degrees, and Z = 2. Crystals of 2 were not good enough to collect adequate data for X-ray analysis, but the identity of this compound was confirmed, along with its P1; space group. Crystals of 3 and 4 belong to the monoclinic, P2(1)/c space group and the triclinic, P1; space group, respectively, with a = 13.5254(5) A, b = 13.7387(4) A, c = 27.2011(12) A, beta = 102.637(2) degrees, and Z = 4 for 3 and a = 13.866(8) A, b = 14.756(7) A, c = 15.008(6) A, alpha = 79.91(3) degrees, beta = 87.72(4) degrees, gamma = 89.19(4) degrees, and Z = 1 for 4. Compound 1 exhibits a single reversible oxidation at E(1/2) = 0.66 V and a single reversible reduction at E(1/2) = -0.44 V vs SCE in THF, 0.2 M TBAP. Both processes involve a one-electron transfer. Compound 2 undergoes a reversible oxidation at E(1/2) = 0.60 V and two separate one-electron-transfer reductions at E(1/2) = -0.52 and -0.65 V in THF, 0.2 M TBAP. The oxidation involves two overlapped one-electron-transfer processes. Compounds 3 and 4 undergo two reversible oxidations in CH(2)Cl(2), 0.1 M TBAP located at E(1/2) = 0.23 and 1.22 V (3) or 0.22 and 1.20 V (4). Each redox reaction of 3 involves a one-electron-transfer step while each redox reaction of 4 involves two overlapping one-electron transfers. Compound 2 shows interaction between the two dirhodium cores upon reduction, while 4 gives no evidence of electronic interaction between the two dirhodium units during either reduction or oxidation. An ESR signal with axial symmetry was obtained for the neutral compounds 1 and 2, and a similar spectrum was obtained for the singly oxidized products of compounds 3 and 4, thus sug...

Structures and Properties of 4-phpy, pyz, and 4,4′-bpy Adducts of Lantern-Type Dirhodium Complexes with µ-Formamidinato and µ-Carboxylato Bridges

“…Only a bidentate ligand 1,4-diisocyanobenzene (1,4-dib) with longer NC ligating arms from a benzene ring (Scheme 3) can coordinate to the Rh ion through the axial crowded space, giving a polymer complex [Rh 2 (4-Me-pf) 4 (1,4-dib)] n , which was isolated from the benzene and toluene solution [28,29]. A hexanuclear complex [{Rh 2 (4-Mepf) 4 } 3 (1,4-dib) 2 ] was isolated from the dichloromethane solution [28], while a tetranuclear complex [{Rh 2 (dpf) 4 } 2 (1,4-dib)] (dpf -= N,N'-diphenylformamidinate anion) was also isolated from dichloromethane solution [30]. We preliminarily showed that pyz could work as a linker ligand for cis-[Rh 2 (R-pf) 2 (O 2 CCF 3 ) 2 ] with less crowded axial sites compared with [Rh 2 (R-pf) 4 ] based on the crystal structure of [Rh 2 (4-Et-pf) 2 (O 2 CCF 3 ) 2 (pyz)] n •n(toluene) (4-Et-pf -= N,N'-bis(4-ethylphenyl)formamidinate anion), such a study has not been performed since then [31].…”

Synthesis, characterization, and substituent effects of mononuclear ruthenium complexes [RuCl(CO)(PMe3)3(CHCH-C6H4-R-p)] (R=H, CH3, OCH3, NO2, NH2, NMe2)

“…Highly unsaturated, rigid -(C"C) n -and -(C@C) n -bridges offer an extended p-system and have been recognized as being particularly efficient in mediating electronic transfer [5][6][7][8][9][10]. In this context, a vast number of mono-and bimetallic complexes with polyynediyl or polyacetylene bridges have been extensively studied [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. For example, as model complexes to aid understanding of the influence of substituents on the bonding properties within the metal-acetylide backbone, mononuclear metal r-arylacetylides [(g 2 -dppe)(g 5 -C 5 Me 5 )M(C"C)-1,4-(C 6 H 4 )X] (M = Fe or Ru) have recently been reported by Paul and Bruce et al [4].…”

NMR studies on interaction of rhodium(II) tetratrifluoroacetate with the ligands containing nitrile, isonitrile, isothiocyanate or isocyanate functional groups

“…X-ray studies revealed the formation of a CARh bond, a structural analog of rhodium carbenoids [21][22][23]. For example, rhodium(II) tetraacetate forms with phenylisonitrile an 1:2 adduct, appearing as yellow crystals [22].…”