Describing Polytopal Rearrangement Processes of Octacoordinate Structures. I. Renewed Insights into Fluxionality of the Rhenium Polyhydride Complex ReH₅(PPh₃)₂(Pyridine)

Abstract

Hydride ligands of transition metal polyhydride complexes with a high coordination number are prone to fluxionality leading to interesting structural dynamics. However, the underlying polytopal rearrangement pathways have been rarely studied. Based on quantum chemical calculations carried out in this work with density functional theory and coupled-cluster theory, two new fluxional mechanisms have been identified for the rhenium polyhydride complex ReH 5 (PPh 3 ) 2 (pyridine) to jointly account for two consecutive coalescence events in the variable-temperature NMR spectra upon heating: lateral and basal three-arm turnstile rotation. The frequently cited pseudorotation in ReH 5 (PPh 3 ) 2 (pyridine) (Lee et al. Inorg. Chem. 1996, 35, 695) turns out to be a three-step process including two lateral three-arm turnstile steps and one basal turnstile step in between. The new fluxional mechanisms discovered in this work may also exist in other transition metal polyhydrides.

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The HÀ H contacts are between 2.4 Å and 2.8 Å for compound 3 and 2.6 Å and 3.1 Å for compound 2. They are consistent with the assignment of both compounds as classical hydrido complexes and, thus, with the information derived from the room temperature 1 H NMR relaxation parameters of their respective hydrido resonances (see Supporting Information for details).…”

“…This becomes even more evident, when looking at the IR spectra of the polymorphs, which show significant differences in the complexity pattern of their Re‐H valence vibrational bands. These results suggest that the frequently discussed fluxionality of the hydrido ligands in rhenium polyhydrides [1–9,11–15,18−23,68] may also play a role in the solid state.…”

“…The immediate addition of methanol to the formed, clear reaction mixture results in the precipitation of bright yellow crystals of the mono-substituted complexes [ReH 3 (PPh 3 ) 3 (PMe 3 )] ( 2) and [ReH 3 (PPh 3 ) 3 (PBu 3 )] (3). The single substitution is readily verified by the doublet of quartets splitting pattern of the respective hydrido 1 H NMR resonances and the doublet splitting for the PPh 3 phosphorus atom resonance alongside the quartet splitting of the PR 3 (R = Me, Bu) phosphorus atom resonances with a 3 : 1 integral ratio in their 31 P{ 1 H} NMR spectra. The observation of single resonances indicates that the structures of the products are fluxional at room temperature and equalize the PPh 3 phosphorus nuclei as well as the hydrido ligands.…”

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The HÀ H contacts are between 2.4 Å and 2.8 Å for compound 3 and 2.6 Å and 3.1 Å for compound 2. They are consistent with the assignment of both compounds as classical hydrido complexes and, thus, with the information derived from the room temperature 1 H NMR relaxation parameters of their respective hydrido resonances (see Supporting Information for details).…”

“…This becomes even more evident, when looking at the IR spectra of the polymorphs, which show significant differences in the complexity pattern of their Re‐H valence vibrational bands. These results suggest that the frequently discussed fluxionality of the hydrido ligands in rhenium polyhydrides [1–9,11–15,18−23,68] may also play a role in the solid state.…”

“…The immediate addition of methanol to the formed, clear reaction mixture results in the precipitation of bright yellow crystals of the mono-substituted complexes [ReH 3 (PPh 3 ) 3 (PMe 3 )] ( 2) and [ReH 3 (PPh 3 ) 3 (PBu 3 )] (3). The single substitution is readily verified by the doublet of quartets splitting pattern of the respective hydrido 1 H NMR resonances and the doublet splitting for the PPh 3 phosphorus atom resonance alongside the quartet splitting of the PR 3 (R = Me, Bu) phosphorus atom resonances with a 3 : 1 integral ratio in their 31 P{ 1 H} NMR spectra. The observation of single resonances indicates that the structures of the products are fluxional at room temperature and equalize the PPh 3 phosphorus nuclei as well as the hydrido ligands.…”

Generalized Turnstile Rotation: Formulation, Visualization, Workflow Implementation, and Application for Modeling Polytopal Rearrangements

“…Beyond these prototypical systems, turnstile‐like motions have been identified in a broad range of fluxional processes. Our recent theoretical studies of rhenium polyhydride complexes ReH$$$ {}_5 $$$(PPh$$$ {}_3 $$$)$$$ {}_2 $$$(py) and ReH$$$ {}_9^{2-} $$$ revealed turnstile rotation mechanisms operative in both solution and crystalline environments [6, 7]. Similar fluxional behavior was later observed in related Re–NHC polyhydride systems by Grieco and co‐workers [8].…”

Dynamic Processes of Rhenium Polyhydride Complexes

“…Some practical aspects of the dynamic properties of rhenium polyhydride complexes that relate to the entire set of inner coordination sphere atoms are apparent from the literature. These practical aspects include: (1) when the ligand set makes it feasible to test, all rhenium polyhydride complexes supported by monodentate ligands participate in a pseudorotation or pseudorotation-like rearrangement of all inner coordination sphere atoms in solution at room temperature [1,23,24,30,33,34,35,36,37,49,51,53,54,65,66,68]; (2) the pseudorotation or pseudorotation-like rearrangement of inner sphere atoms can sometimes be slowed or stopped, in room-temperature solutions, by chelating ligands with larger-than-usual ring sizes (>6 member ring), tridentate ligands, or relatively rigid bidentate ligands [8,34,73]; (3) when pseudorotation or pseudorotation-like rearrangement occurs (given an appropriate ligand set and overall symmetry or lack thereof), it can be observed by NMR spectroscopy for both the hydrogen atoms and the heavier atoms [34,35,37,59]; and (4) the characteristics associated with heavy atom rearrangement by a pseudorotation or pseudorotation-like rearrangement should match the characteristics of one of the modes of hydride ligand rearrangement [34,37,59]. For investigators of the chemical properties associated with rhenium polyhydride complexes, the most important aspect related to heavy atom rearrangement is the ability of certain chelating ligands to slow or arrest the room-temperature rearrangement of such complexes.…”

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The HÀ H contacts are between 2.4 Å and 2.8 Å for compound 3 and 2.6 Å and 3.1 Å for compound 2. They are consistent with the assignment of both compounds as classical hydrido complexes and, thus, with the information derived from the room temperature 1 H NMR relaxation parameters of their respective hydrido resonances (see Supporting Information for details).…”

“…This becomes even more evident, when looking at the IR spectra of the polymorphs, which show significant differences in the complexity pattern of their Re‐H valence vibrational bands. These results suggest that the frequently discussed fluxionality of the hydrido ligands in rhenium polyhydrides [1–9,11–15,18−23,68] may also play a role in the solid state.…”

“…The immediate addition of methanol to the formed, clear reaction mixture results in the precipitation of bright yellow crystals of the mono-substituted complexes [ReH 3 (PPh 3 ) 3 (PMe 3 )] ( 2) and [ReH 3 (PPh 3 ) 3 (PBu 3 )] (3). The single substitution is readily verified by the doublet of quartets splitting pattern of the respective hydrido 1 H NMR resonances and the doublet splitting for the PPh 3 phosphorus atom resonance alongside the quartet splitting of the PR 3 (R = Me, Bu) phosphorus atom resonances with a 3 : 1 integral ratio in their 31 P{ 1 H} NMR spectra. The observation of single resonances indicates that the structures of the products are fluxional at room temperature and equalize the PPh 3 phosphorus nuclei as well as the hydrido ligands.…”

Generalized Turnstile Rotation: Formulation, Visualization, Workflow Implementation, and Application for Modeling Polytopal Rearrangements

“…Beyond these prototypical systems, turnstile‐like motions have been identified in a broad range of fluxional processes. Our recent theoretical studies of rhenium polyhydride complexes ReH$$$ {}_5 $$$(PPh$$$ {}_3 $$$)$$$ {}_2 $$$(py) and ReH$$$ {}_9^{2-} $$$ revealed turnstile rotation mechanisms operative in both solution and crystalline environments [6, 7]. Similar fluxional behavior was later observed in related Re–NHC polyhydride systems by Grieco and co‐workers [8].…”

Dynamic Processes of Rhenium Polyhydride Complexes

“…Some practical aspects of the dynamic properties of rhenium polyhydride complexes that relate to the entire set of inner coordination sphere atoms are apparent from the literature. These practical aspects include: (1) when the ligand set makes it feasible to test, all rhenium polyhydride complexes supported by monodentate ligands participate in a pseudorotation or pseudorotation-like rearrangement of all inner coordination sphere atoms in solution at room temperature [1,23,24,30,33,34,35,36,37,49,51,53,54,65,66,68]; (2) the pseudorotation or pseudorotation-like rearrangement of inner sphere atoms can sometimes be slowed or stopped, in room-temperature solutions, by chelating ligands with larger-than-usual ring sizes (>6 member ring), tridentate ligands, or relatively rigid bidentate ligands [8,34,73]; (3) when pseudorotation or pseudorotation-like rearrangement occurs (given an appropriate ligand set and overall symmetry or lack thereof), it can be observed by NMR spectroscopy for both the hydrogen atoms and the heavier atoms [34,35,37,59]; and (4) the characteristics associated with heavy atom rearrangement by a pseudorotation or pseudorotation-like rearrangement should match the characteristics of one of the modes of hydride ligand rearrangement [34,37,59]. For investigators of the chemical properties associated with rhenium polyhydride complexes, the most important aspect related to heavy atom rearrangement is the ability of certain chelating ligands to slow or arrest the room-temperature rearrangement of such complexes.…”

[ReH3(PPh3)4] – A Key Compound in the Rhenium Hydride Chemistry

“…The HÀ H contacts are between 2.4 Å and 2.8 Å for compound 3 and 2.6 Å and 3.1 Å for compound 2. They are consistent with the assignment of both compounds as classical hydrido complexes and, thus, with the information derived from the room temperature 1 H NMR relaxation parameters of their respective hydrido resonances (see Supporting Information for details).…”

“…This becomes even more evident, when looking at the IR spectra of the polymorphs, which show significant differences in the complexity pattern of their Re‐H valence vibrational bands. These results suggest that the frequently discussed fluxionality of the hydrido ligands in rhenium polyhydrides [1–9,11–15,18−23,68] may also play a role in the solid state.…”

“…The immediate addition of methanol to the formed, clear reaction mixture results in the precipitation of bright yellow crystals of the mono-substituted complexes [ReH 3 (PPh 3 ) 3 (PMe 3 )] ( 2) and [ReH 3 (PPh 3 ) 3 (PBu 3 )] (3). The single substitution is readily verified by the doublet of quartets splitting pattern of the respective hydrido 1 H NMR resonances and the doublet splitting for the PPh 3 phosphorus atom resonance alongside the quartet splitting of the PR 3 (R = Me, Bu) phosphorus atom resonances with a 3 : 1 integral ratio in their 31 P{ 1 H} NMR spectra. The observation of single resonances indicates that the structures of the products are fluxional at room temperature and equalize the PPh 3 phosphorus nuclei as well as the hydrido ligands.…”

Generalized Turnstile Rotation: Formulation, Visualization, Workflow Implementation, and Application for Modeling Polytopal Rearrangements

“…Beyond these prototypical systems, turnstile‐like motions have been identified in a broad range of fluxional processes. Our recent theoretical studies of rhenium polyhydride complexes ReH$$$ {}_5 $$$(PPh$$$ {}_3 $$$)$$$ {}_2 $$$(py) and ReH$$$ {}_9^{2-} $$$ revealed turnstile rotation mechanisms operative in both solution and crystalline environments [6, 7]. Similar fluxional behavior was later observed in related Re–NHC polyhydride systems by Grieco and co‐workers [8].…”

Dynamic Processes of Rhenium Polyhydride Complexes

“…Some practical aspects of the dynamic properties of rhenium polyhydride complexes that relate to the entire set of inner coordination sphere atoms are apparent from the literature. These practical aspects include: (1) when the ligand set makes it feasible to test, all rhenium polyhydride complexes supported by monodentate ligands participate in a pseudorotation or pseudorotation-like rearrangement of all inner coordination sphere atoms in solution at room temperature [1,23,24,30,33,34,35,36,37,49,51,53,54,65,66,68]; (2) the pseudorotation or pseudorotation-like rearrangement of inner sphere atoms can sometimes be slowed or stopped, in room-temperature solutions, by chelating ligands with larger-than-usual ring sizes (>6 member ring), tridentate ligands, or relatively rigid bidentate ligands [8,34,73]; (3) when pseudorotation or pseudorotation-like rearrangement occurs (given an appropriate ligand set and overall symmetry or lack thereof), it can be observed by NMR spectroscopy for both the hydrogen atoms and the heavier atoms [34,35,37,59]; and (4) the characteristics associated with heavy atom rearrangement by a pseudorotation or pseudorotation-like rearrangement should match the characteristics of one of the modes of hydride ligand rearrangement [34,37,59]. For investigators of the chemical properties associated with rhenium polyhydride complexes, the most important aspect related to heavy atom rearrangement is the ability of certain chelating ligands to slow or arrest the room-temperature rearrangement of such complexes.…”