Homo‐ and Heterodinuclear Rh and Ir Complexes Supported by SN_n Mixed‐Donor Ligands (n = 2–4): Stereochemistry and Coordination‐Site‐Exchange Reactions of Cp*M (M = Rh, Ir) Units

Abstract

A series of SNn mixed‐donor ligands [n = 2: H2NC2H4SCH2‐2‐pyridyl (2‐NSpy) (1a), H2NC2H4SCH2‐4‐pyridyl (4‐NSpy) (1b), n = 3: 2‐pyridylCH2NHC2H4SCH2‐2‐pyridyl (2‐pyNSpy) (2), n = 4: (2‐pyridylCH2)2NC2H4SCH2‐2‐pyridyl (2‐py2NSpy) (3)] was utilized to support homo‐ and heterodinuclear complexes including Cp*MIII units (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). Reactions of [Cp*MCl2]2 with 2‐pyNSpy (2), 2‐py2NSpy (3), and 4‐NSpy (1b) afforded homodinulear complexes, [(Cp*MCl)(2‐pyNSpy)(Cp*MCl)](PF6)2 [M = Rh (5a), Ir (5b)], [(Cp*M)(2‐py2NSpy)(Cp*MCl)](PF6)3 [M = Rh (6a), Ir (6b)], [(Cp*MCl)(4‐NSpy)(Cp*MCl2)]Cl [M = Rh (8a), Ir (8b)]. Heterodinuclear complexes [(Cp*MCl)(4‐NSpy)(Cp*M′Cl2)]Cl [M, M′ = Rh, Ir (8c), Ir, Rh (8d)] were prepared using mononuclear complexes [(Cp*MCl)(4‐NSpy)]Cl [M = Rh (7a), Ir (7b)] reacted with [Cp*MCl2]2 (M = Ir, Rh), respectively. Complexes 5–8 were characterized by X‐ray crystallography to determine the configurations around the M, M′, S, and N centers. The solid‐state structures of 6 are retained in acetonitrile solution whereas four diastereomers are generated in the case of 5 due to low stereoselectivity around the coordinated amine nitrogen atom, in contrast to the sulfur atom. Heterodinuclear complexes 8c,d are unstable in solution at 55 °C, readily affording mixtures of 8a–d via intra‐ and intermolecular coordination‐site‐exchange reactions of Cp*M fragments between the SN moiety and the py site. In order to evaluate the selectivity of Cp*M fragments for the SN and py coordination sites, several competitive reactions of [Cp*MCl2]2 (M = Rh, Ir) with H2NC2H4SCH2C6H5 (NSph) (4) and/or 4‐methylpyridine (4‐Mepy) were carried out to demonstrate predominant formation of iridium complexes 9b and 10b among [(Cp*MCl)(NSph)]Cl [M = Rh (9a), Ir (9b)] and [(Cp*MCl)(4‐Mepy)]Cl [M = Rh (10a), Ir (10b)]. These reactions indicated higher affinity of the Cp*Ir fragment to both the NS and py sites relative to the rhodium analogue.

Multidentate Pyridyl‐Aminophosphinite and Pyridyl‐Phosphoramidite Ruthenium(II) Complexes: Synthesis, Structure and Application as Levulinic Acid Hydrogenation Pre‐Catalysts

“…In general, multidentate mixed‐donor ligands that have been reported comprise of phosphorus, nitrogen, sulfur and oxygen donor atoms in different binding arrangements such as P ^ N ^ S and P ^ N ^ N ^ P systems . An example of the latter is the iminophosphorane‐phosphine reported by Le Floch and co‐workers , .…”