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.