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

Article abstract of DOI:10.1002/ejic.201600722

A series of SN_nmixed-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*M^IIIunits (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). Reactions of [Cp*MCl₂]₂with 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.