Dichloro(pentamethylcyclopentadienyl)ruthenium—Novel Dichotomy in a Molecular Structure

Abstract

The title complex [fCp*RuCI,},], 1 (Cp* = q5-C,Me,),['.21 is a much-used reagent in the preparation of Cp*Ru sandwich and, in particular, half-sandwich complexes.I3-'] Although the solubility of the complex in halogenated hydrocarbons and the molar mass in chloroform (as determined by osmometric speaks against the existence of a polymer, the compound is always seen as such. ' In the preparation from RuCI,(,,, and Cp*H in methanol ['] or ethanol,[21 1 precipitates as a red-brown, microcrystalline powder, which for some time thwarted attempts at crystallization. Crystals suitable for X-ray crystallography were finally obtained by diffusion of ether into a concentrated dichloromethane solution of 1, after purification of an ether/dichloromethane solution by chromatography on silylated silicaFor compounds 2 and 3 the chromatographic procedure is unnecessary.showed that all three compounds were dimers, as anticipated. A pecularity of the crystals of 1 was the equal distribution of forms l a and lb (Fig. l) (3.712 wI1']). This isomer should thus be paramagpetic. This interpretation is supported by solid-state CP/MAS NMR spectroscopy on 1.'''] The 'H and 13C NMR spectra each show two resonance signals (6 = 2 and 18, and 6 = 13 and 246, respectively), which can be attributed to the deformational isomers. The low-field signals show the temperature proportionality characteristic of NMR signals of paramagnetic compounds. In contrast to the IR spectrum of 4, in the case of 1 (CsT pellet) the bands assigned to the M-CI vibrational modes at 292/309 and 260/275 cm-' are split. This correlates with the different distances between the Ru atoms and the terminal chloro ligands in l a and l b (Table 1). Ru-CI-Ru angles, and Ru-Ru distances of 2.93 and 3.75 A (Fig. 2), and are located at positions 000 and 0% (la) and and 9 0 (lb) of the monoclinic unit cell. The bonding parameters of l a and l b differ enough to justify the term "deformational isomerism". The molecular geometries of the compounds 2 and 3, where crystals consist of only one form, correspond to isomer l a ( Table 1). The different Ru-Ru distances in the isomers suggest a strong exchange interaction between the unpaired spins of the d5 low-spin Ru centers['61 in la, but not in lb, where the metal-metal distance is similar to the nonbonding Rh-Rh distance in the analogous Rh complex [{Cp*RhCl,},] 4

Crystallographic Snapshots of the Bond‐Breaking Isomerization Reactions Involving Nickel(II) Complexes with Hemilabile Ligands

“…Each exhibits a n CN stretch diagnostic of non-bridging N-bound thiocyanate (Supporting Information, Figure S3, Table S2). [33,34] Importantly, when these crystals of 2 a or 2 b were dissolved in CD 2 Cl 2 and characterized by 31 P{ 1 H} NMR spectroscopy, only a single broad resonance at d = 32.6 ppm was observed, which is consistent with the 31 P{ 1 H} NMR data for the mixture of isomers in solution. Based on the characterization of three distinct isomers in the solid state, we decided to determine if the three structures exist in solution as well.…”

“…[28,29] The solid-state structure of 4 a consists of a square-planar nickel center with two equivalents of N-bound SCN À ligands and two equivalents of P-bound monodentate P,S À Ph ligands arranged in trans configurations. Importantly, the room temperature 31 P{ 1 H} NMR spectrum of 4 a in CD 2 Cl 2 exhibits a broad resonance at d = 10.9 ppm, which sharpens with decreasing temperature ( Supporting Information, Figure S1 B), consistent with a monodentate coordination mode for the phosphine ligand. [28] Similarly, model compound 4 b, which contains a non-chelating phosphine ligand, was synthesized from complex 3 b under nearly identical chloride abstraction conditions to those used for 3 a (see the Supporting Information; Scheme 2, Figure 2 a).…”

“…[30] The solid-state structure of 4 b showed a square-planar nickel center, much like 4 a, with two equivalents of N-bound SCN À ligands and two equivalents of the non-chelating phosphine each arranged in a trans configuration. Significantly, room-temperature 31 P{ 1 H} NMR spectroscopy of 4 b in CD 2 Cl 2 showed a single sharp resonance at d = 16.7 ppm that remains unchanged with decreasing temperature. This complex, Figure 2.…”

“…In solution at room temperature, these complexes are rapidly interconverting, as evidenced by a single broad 31 P{ 1 H} NMR resonance observed at d = 32.6 in CD 2 Cl 2 . Variable-temperature (VT) 31 P{ 1 H} NMR spectroscopy confirmed that this broadening is a result of rapid exchange between multiple complexes. When the temperature of the solution was lowered to 213 K in a stepwise manner, the spectrum changed significantly.…”

“…Compound 1 (which has two chloride ligands) serves as a model complex for octahedral compounds with trans phosphine and trans thioether ligands, such as 2 a and 2 b. Indeed, in CD 2 Cl 2 , complex 1 [29] exhibits a downfield resonance at d = 32 ppm in its 31 P{ 1 H} NMR spectrum, which is highly diagnostic of structures with five-membered P-containing chelates and remarkably close to the second resonance at d = 32.6 ppm observed for the mixture of 2 a-c at low temperature. [28] We have not observed a third resonance at low temperature, and therefore speculate that 2 a and 2 b rapidly interconvert, even at 213 K on the NMR spectroscopic timescale.…”