Dual-Unsaturated Transition Metal-Main Group (TM-M’) Heterometallic Complexes for Cooperative Reactivity

Abstract

This thesis describes the synthesis and reactivity of a series of Ru-Zn and Ir-Zn
heterometallic complexes. Efforts to prepare Ru-Zn complexes featuring the bis{(ortho-diphenylphosphino)phenyl}zinc (ZnPhos) ligand through reaction of Ru(PPh3)(C6H4PPh2)2(ZnMe)2 (1.14) with N-heterocyclic carbenes (NHCs), resulted in extensive phosphine
cyclometallation and Zn-NHC bond formation to give Ru(C6H4PPh2)2(IEt2Me2)'(Zn{IEt2Me2})H (2.1a) and Ru(PPh3)(C6H4PPh2)((C6H4)2PPh)(Zn{IiPr2Me2})H (2.2). Use of the free ZnPhos ligand proved slightly more successful in yielding Ru(ZnPhos)(IMe4)(CO)(μ-H)2 (2.8) from Ru(PPh3)2(IMe4)CO)H2, although reaction with Ru(PPh3)3(CO)H2 led to
formation of the tetrametallic Ru-Zn3 product, Ru(ZnPhos)(ZnC6H4PPh2)2(CO) (2.7), via Zn-C bond cleavage.
An alkane elimination strategy was employed to prepare heterometallic Ir-Zn compounds. Treatment of [Ir(IPr)2H2][BArF4] (1.18) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, BArF4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) with ZnMe2 gave the cyclometallated salt [Ir(IPr)IPr)'(ZnMe)2H][BArF4] (3.1a), which added to give the highly fluxional, tetrahydride salt [Ir(IPr)2(ZnMe)2H4][BArF4] (3.2). H/D exchange of 3.2 with D2, as well as elimination of H2 to yield the dihydride salt [Ir(IPr)2(ZnMe)2H2][BArF4] (3.3), proved significantly more challenging. The Ir-Cd analogues [Ir(IPr)(IPr)'(CdMe)2H][BArF4] (3.4a), [Ir(IPr)2(CdMe)2H4][BArF4] (3.5) and [Ir(IPr)2(CdMe)2H2][BArF4] (3.6) were prepared and the JHCd coupling constants used to establish the terminal versus bridging nature of the hydride ligands. Treatment of 1.18 with H2 gave the Hexahydride complex [Ir(IPr)2H6][BArF4] (3.7), which was formulated as the bis-dihydrogen dihydride salt [Ir(IPr)2(η2-H2)2H2][BArF4].
Reaction of 1.18 with ZnPh2 gave two products, the dehydrogenated IPr salt [Ir(IPr)(IPr)''(ZnPh)H][BArF4] (4.2a) and the tetrahydride [Ir(IPr)2(ZnPh)2H4][BArF4] (4.3). These could be prepared independently by repeating the reaction in the presence of an alkene (4.2a) or in the presence of H2 (4.3). The former approach gave the ZnMe, ZnEt and CdMe derivatives 4.2b-c and 4.4a. Addition of H2 gave a mix of the trihydrides [Ir(IPr)(IPr)''(M'R)H3][BArF4] (M'R = ZnMe (4.5b), ZnEt (4.5c), CdMe (4.7) and the pentahydrides [Ir(IPr)2(M'R)H5][BArF4] (M'R = ZnMe (4.6b), ZnEt (4.6c), CdMe (4.8), whereas H2 addition to 4.2a gave [Ir(IPr)2(Zn{THF})H4][BArF4] (4.9, in THF) and [Ir(IPr)(IPr'Zn)Hx][BArF4] (4.10, in C6H5F). Elimination of [ZnR]+ from 4.6a-c gave the neutral pentahydride Ir(IPr)2H5 (4.11), which reacted with ZnR2 reagents and CdMe2 to form the bimetallic, tetrahydride complexes
Ir(IPr)2(ZnR)H4 (M'R = ZnPh (4.14a), ZnMe (4.14b), ZnEt (4.14c), CdMe (4.15)).

Date of Award	25 Jun 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	Michael Whittlesey (Supervisor) & Michael Hill (Supervisor)