Better Understanding of the Species with the Shortest Re26+ Bonds and Related Re27+ Species with Tetraguanidinate Paddlewheel Structures

Expanding the Chemistry of Rhenium Metal-Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes

Quadruply bonded rhenium(III) dimers with the stoichiometry Re₂L₄F₂ (1, L = hexahydro-2H-pyrimido[1,2a]pyrimidinate (hpp^-); 2, L = diphenyl formamidinate (dpf^-)) were prepared from the solid-state melt reactions (SSMRs) between (NH₄)₂[Re₂F₈]·2H₂O and HL. Those compounds were characterized in the solid state by single-crystal X-ray diffraction and in solution by UV-visible spectroscopy and cyclic voltammetry. The compound [Re₂(hpp)₄F₂]PF₆ (3) was prepared from the one-electron oxidation of Re₂(hpp)₄F₂ with [Cp₂Fe]PF₆. Compounds 1-3 are isostructural with the corresponding chloro derivatives. In solution, compound 1 undergoes two one-electron oxidations. Comparison with its higher halogen homologues reveals that Re₂(hpp)₄F₂ (1) is more easily oxidized than its chloro and bromo analogues.

Unprecedented spin localisation in a metal–metal bonded dirhenium complex

[N(n-Bu)₄]₃[Re₂(mnt)₅] is the first class I, valence localized dirhenium(iii,iv) compound, with a metal–metal bond.

A Magic Equation: Delta Bonds Plus Bicyclic Guanidinates Equals Strong Reducing Agents

Reactions of bicyclic guanidinates with dimolybdenum and ditungsten precursors having quadruple bonded units with a σ2π4δ2 (Q) electronic configuration have generated the most easily ionized, chemically stable species and very strong reducing agents. Analogous rhenium compounds have led to the formation of species having dimetal units in unusually high oxidation states. Here we review this chemistry and the accounts that explain such behaviour that has been attributed to the interaction of the π electrons of the guanidinate C(N)3 core with the electrons that give rise to the delta bond of the dimetal units.

The usefulness of EPR spectroscopy in the study of compounds with metal–metal multiple bonds

A discussion of how EPR spectroscopy has contributed to the understanding of the electronic structure of paddlewheel compounds with multiple bonds between metal atoms is presented while commemorating the 50th anniversary of the paper describing the quadruple bond and the identification of the delta bond in the Re₂Cl₈²⁻ anion.

Direct evidence from electron paramagnetic resonance for additional configurations in uncommon paddlewheel Re2(7+) units surrounded by an unsymmetrical bicyclic guanidinate

Three rare compounds have been synthesized and structurally characterized; these species have paddlewheel structures and Re(2)(7+) cores surrounded by four bicyclic guanidinates and two axial ligands along the Re-Re axis. Each possesses a formal bond order of 3.5 and a σ(2)π(4)δ(1) electronic configuration that entails the presence of one unpaired electron for each compound. The guanidinate ligands characterized by having CH(2) entities and a central C(N)(3) unit that joins two cyclic units--one having two fused 6-membered rings (hpp) and the other having a 5- and a 6-membered ring fused together (tbn)--allowed the isolation of [Re(2)(tbn)(4)Cl(2)]PF(6), 1, [Re(2)(tbn)(4)Cl(2)]Cl, 2, and [Re(2)(hpp)(4)(O(3)SCF(3))(2)](O(3)SCF(3)), 3. Because of the larger bite angle of the tbn relative to the hpp ligand, the Re-Re bond distances in 1 and 2 (2.2691(14) and 2.2589(14) Å, respectively) are much longer than that in 3 (2.1804(8) Å). Importantly, electron paramagnetic resonance (EPR) studies at both X-band (~9.4 GHz) and W-band (112 GHz) in the solid and in frozen solution show unusually low g-values (~1.75) and the absence of zero-field splitting, providing direct evidence for the presence of one metal-based unpaired electron for both 1 and 3. These spectroscopic data suggest that the unsymmetrical 5-/6-membered ligand leads to the formation of isomers, as shown by significantly broader EPR signals for 1 than for 3, even though both compounds possess what appears to be similar ideal crystallographic axial symmetry on the X-ray time scale.

Synthesis and structure of a dinuclear gold(II) complex with terminal fluoride ligands

The potential for reductive elimination of fluorine from dinuclear gold(II) for catalysis has prompted our efforts to synthesize a dinuclear gold(II) fluoride complex. This has been achieved with bis(2,6-dimethylphenyl)formamidinate bridging ligands. In order to obtain this product, it was necessary first to synthesize the corresponding dinuclear gold(II) nitrate, which reacts readily with KF in a metathesis reaction. The nitrate complex and fluoride complexes have been structurally characterized. The Au-Au distance in the dinuclear fluoride, 2.595 Å, is longer than the distance found in the analogous chloride complex, 2.567 Å. This result is consistent with the presence of a fluoride "π electron effect" on the filled Au 5d orbitals. The Raman spectrum shows an Au-Au stretch at 206 cm(-1), which agrees with Woodruff's rules and the density functional theory computational model used for modeling the complex.