Entrapment of THF‐Stabilized Iridacyclic Ir^III Silylenes from Double H−Si Bond Activation and H₂ Elimination

Abstract

The reaction of H SiR (R=Ph, nBu) with cationic η -C Me - (Cp*) and benzo[h]quinolinyl-based iridacycle [1 b] gives rise to new [(IrH)→SiRH ] adducts. In the presence of THF these adducts readily undergo elimination of H gas at subambient temperature to form THF-stabilized metallacyclic Ir silylene complexes, which were characterized in situ by NMR spectroscopy, trapped in minute amounts by reactive crystallization, and structurally characterized by XRD. Theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) support the promoting role of THF in the H elimination step and the consolidation of the Ir-to-Si interaction in the spontaneous (ΔG<0) formation of Ir silylenes in the presence of THF. Mechanistic insights indicate that the Ir silylene species arising from the [1 b] /phenylsilane system are relevant catalytic species in the hydrodefluorination of fluoroalkanes.

An H‐Substituted Rhodium Silylene

“…While Rh→CO backbonding interactions of π‐symmetry were observed, our DFT analyses do not support the presence of substantial Rh→Si π bonding, such as those reported previously for iridium silylenes . Notably, Djukic and co‐workers found that coordination of THF to an Ir=SiHPh moiety resulted in a 30 % reduction of the π character in the Ir−Si interaction . We therefore reason that the stronger σ‐donor abilities of the phosphinimine in 3 , compared to THF, may account for the diminished double bond character in this system.…”

“…Examination of the 1 H NMR spectrum revealed a sharp singlet at δ =4.47, which disappeared upon exposure to reduced pressure, suggesting the evolution of H 2 gas. Cases in which silylene formation occurs with spontaneous H 2 loss are rare; a recent example from Djukic and co‐workers highlighted the role of an exogeneous donor (THF) in promoting such H 2 extrusion (Scheme b) . A diagnostic silicon‐bound hydrogen was identified as a doublet of doublets ( 2 J H−Rh =5.4 Hz, 3 J H−P =5.8 Hz) at δ= 5.90.…”

“…[13,14] Notably,D jukic and co-workers found that coordinationo fT HF to an Ir = SiHPh moietyr esulted in a3 0% reduction of the p characteri nt he IrÀSi interaction. [16] We therefore reason that the stronger s-donora bilities of the phosphinimine in 3,c ompared to THF,m ay account for the diminished double bond character in this system.Acomparisono ft he natural atomic charge on Si in 3-SiHPh, with that in the base-free (PNP)Ir(H) = SiHMes (PNP = [N(2-PiPr 2 -4-Me-C 6 H 3 ) 2 ] À ), reported by Tilley, [10] indicated similar values (+ 1.19 cf. + 1.03, respectively), whichi sp erhaps at odds with this hypothesis.…”

“…Cases in which silylene formation occurs with spontaneous H 2 loss are rare; [15] ar ecent example from Djukica nd coworkers highlighted the role of an exogeneousd onor (THF) in promoting such H 2 extrusion (Scheme1b). [16] Ad iagnostics ilicon-boundh ydrogen was identified as ad oublet of doublets ( 2 J HÀRh = 5.4 Hz, 3 J HÀP = 5.8 Hz) at d = 5.90. When decoupled from 31 P, this resonance collapses into ad oublet with well-resolved 29 Si satellites ( 1 J HÀSi = 183 Hz).…”

Effect of Enhanced Electron Withdrawal on the Cohesion of Cr‐Pd Hemichelates

“…This fragment‐based method of analysis breaks down orbital contributions of bonds consisting of multiple contributions into associated orbital interaction energy terms. In simple cases it is capable of readily decompose coordinative bonds into their σ, π and δ components , …”