Drastic Acceleration of Phosphine/Phosphite Incorporation into a Tetrahydrido Ruthenium/Osmium Complex, and One‐way Ruthenium to Osmium Migration of a Phosphorus Ligand

Abstract

Cluster complexes form an attractive class in the reactions of transition metal complexes, owing to their capability of activating substrates effectively through the cooperative effects of multiple metal centers. [1] To date, we have demonstrated several examples of cooperative activation by treating various substrates, including unsaturated hydrocarbons, with [Cp*Ru(m-H) 4 RuCp*] (1, Cp* = h 5 -C 5 Me 5 ) and [(Cp*Ru) 3 (m-H) 3 (m 3 -H) 2 ]. [2] Heterometallic cluster complexes that contain different metals may exhibit electronic anisotropic characters stemming from polarized metal-metal bonds. [3] Therefore, significant heterometallic effects, such as marked regioselectivity and remarkable acceleration, could occur in the reaction in addition to the typical effects of cluster complexes resulting from multiple coordination and multielectron transfer.We synthesized a series of heterometallic dinuclear polyhydrido complexes, such as [Cp*Ru(m-H) 4 and demonstrated their heterometallic effects through reactions with unsaturated hydrocarbons, phosphines, amines, and acetylacetone. For example, the reaction of heterometallic Ru-Os complex [Cp*Ru(m-H) 4 OsCp*] (2) with ethylene exclusively afforded [Cp*Os(CH 2 = CH 2 )(m-h 1 ,h 2 -CH = CH 2 ) 2 RuCp*] in which the vinyl groups are h 1 -bonded to Os. [4a] In this reaction, CÀH bond activation selectively occurred at the Os center because Os and Ru atoms served as activation and binding sites, respectively, indicating sharing of functions between the two metal atoms in the reactions of the heterometallic dinuclear polyhydrido clusters. However, the aforementioned reactions, particularly reactions with unsaturated hydrocarbons, involved multiple elementary steps, and the complexity of the reaction often obscured the heterometallic effect in each elementary step. To evaluate the heterometallic effect, this study focused on the addition of a phosphorus ligand to the dinuclear tetrahydrido complex [Cp*M(m-H) 4 M'Cp*] (2: M = Ru, M' = Os; 3: M = M' = Os [5] ) to produce a dihydrido-phosphine or dihydrido-phosphite complex [Cp*(X 3 P)M(m-H) 2 M'Cp*] (X = OMe, Me). Through these reactions, we obtained positive evidence for a kinetic heterometallic effect (KHE) and a thermodynamic heterometallic effect (THE), namely, remarkable acceleration of the incorporation of phosphine or phosphite groups into the heterodinuclear tetrahydride 2 and intramolecular migration of P(OMe) 3 from the ruthenium center to the osmium center in one direction in [Cp*{(MeO) 3 P}Ru(m-H) 2 OsH 2 Cp*] (4), respectively. We have reported the formation of dinuclear dihydridophosphine and dihydrido-phosphite complexes [Cp*-(R 3 P)Ru(m-H) 2 RuCp*] (R = Me (5 a), Et (5 b), iPr (5 c), Bn (5 d), OMe (5 e), and OPh (5 f)) in the reaction of diruthenium tetrahydrido complex 1 with various phosphorus ligands [Eq. ( 1)]. We also demonstrated that the phosphorus ligand reversibly migrated between the two ruthenium atoms. [6] Similarly, diosmium tetrahydrido complex 3 reacted with P(OMe) 3 to generate a dinuclear phos...

Hydroxyl Migration in Heterotrimetallic Clusters: An Assessment of Fluxionality Pathways

“…For example, Suzuki and co-workers have noticed that a remarkable acceleration in phosphine/phosphite incorporation and migration of the ligand happens when the core is changed from dinuclear homometallic Cp*Ru(μ-H) 4 RuCp* (Cp* = pentamethylcyclopentadienyl) to heterometallic Cp*Ru(μ-H) 4 OsCp*. 30 In another relevant work they also showed a notable and distinct "heterometallic effect" for nitrogen− hydrogen bond cleavage in a trinuclear heterometallic polyhydrido cluster containing ruthenium and osmium. 31,32 As an explanation for the distinguishable heterometallic effect, they propose that introduction of the heterometal atom into a cluster causes structural changes, polarizing the metal−metal bond, and leading to electronic anisotropy.…”

Reversible Insertion of 1,3‐Di‐tert‐butylimidazol‐2‐ylidene into a RuH Bond and Bimetallic Activation of a NC Bond of Imidazoline

“…We previously reported the reactions of dinuclear homo‐ and heterometallic tetrahydrido complexes, [Cp*Ru(μ‐H) 4 RuCp*] and [Cp*Ru(μ‐H) 4 OsCp*], with tert ‐phosphorus ligand that do not contain aryl substituents 5. 6…”

Towards Reagents for Bimetallic Activation Reactions: Polyhydride Complexes with Ru2H3, Ru2ZnH6, and Cu2Ru2H6 Cores

“…Current investigations are limited to a small family of compounds that typically contain pentamethylcyclopentadienyl (Cp*) ligands 2. Oligonuclear hydridoruthenium complexes based on other ligand types or containing a second transition metal are scarce even though the combination of two different metal atoms may exert a pronounced effect on the reactivity 5…”