Cationic and Neutral Heterometallic Ir-Group 12 Element Polyhydride Compounds: Synthesis, Structure and Reactivity

The preparation and reactivity of some Ir–Zn and Ir–Cd heterometallic hydride complexes are described. Treatment of [Ir­(IPr)2H2]­[BArF4] (1; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene; ArF = 3,5-C6H3(CF3)2) with M′R2 (M′ = Zn; R = Ph, Me, Et; M′ = Cd, R = Me) and Me3SiCH=CH2 results in dehydrogenation of an IPr isopropyl substituent, along with R–H elimination, to form square-pyramidal [Ir­(IPr)­(IPr″)­(M′R)­H]­[BArF4] (M′R = ZnPh (4a); ZnMe (4b); ZnEt (4c); CdMe (8); IPr″ = dehydrogenated IPr) featuring apical M′R ligands. Heating 1 with 2 equiv ZnPh2 under H2 forms [Ir­(IPr)2(ZnPh)2H4]­[BArF4] (5) featuring trans ZnPh ligands. Exposure of 4b-c and 8 to H2 yields [Ir­(IPr)­(IPr″)­(M′R)­H3]­[BArF4] (9b-c, 10) as intermediates to highly fluxional [Ir­(IPr)2(M′R)­(η2-H2)­H3]­[BArF4] (11b-c, 12). Reacting 11b–c with Lewis bases (L) effects [ZnR]+ abstraction to give pentahydride Ir­(IPr)2H5 (13); with 11c and L = IMes (1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene), [L2ZnEt]­[BArF4] was characterized, whereas with L = PMe3, both 13 and [Ir­(IPr)2(ZnEt)­(PMe3)­H3]­[BArF4] (14c) were formed. Reactions of 13 with M′R2 similarly proceed with R–H elimination to form Ir­(IPr)2(M′R)­H4 (15a-c, 16). Crystallographic and computational analyses characterize a range of hydride ligands, the nature of which depends subtly on the surrounding coordination environment. The new polyhydride complexes reported here add to the small number of such species featuring N-heterocyclic carbene ligands.