Photochemistry of Dihydrido(hydrotris(3,5-dimethylpyrazolyl)borato)(Z-cyclooctene)iridium. Synthetic Intermediates and Mechanism of the Photochemical Formation of Hydridophenyl(hydrotris(3,5-dimethylpyrazolyl)borato)(trimethyl phosphite)iridium

Abstract

The photolysis of a benzene solution of [Tp(Me2)IrH(2)(COE)], 1 (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate, COE = Z-cyclooctene), in the presence of P(OMe)(3), gives the stable novel complex [Tp(Me2)IrH(C(6)H(5))(P(OMe)(3))], 3a. The photochemical syntheses of [Tp(Me2)IrH(2)(P(OMe)(3))], from 1 and P(OMe)(3) in diethyl ether, and [Tp(Me2)IrH(2)(CH(2)=CHCOO(t)Bu)], from 1 in tert-butyl acrylate, are also reported. The above reactions and several experiments using C(6)D(6) and P(OCD(3))(3) show that, in all cases, the primary photoproduct is the 16-electron, five-coordinate iridium(III) intermediate {Tp(Me2)IrH(2)}, 6a, produced by loss of COE from 1. The above experiments also allow the postulation of a mechanistic pathway for the formation of 3a which involves the oxidative addition of an aromatic C-H bond by 6a. Furthemore, the photochemical reaction of 1 in the presence of P(OCD(3))(3) shows that, under the reaction conditions used, oxidative addition of C-H bonds of P(OMe)(3) and of coordinated Tp(Me2)-ligands, presumably, to the intermediates 6a and {Tp(Me2)IrH(C(6)H(5))}, also occurs. Thus, coordinatively unsaturated iridium(III) species readily activate C-H bonds.

Photochemistry of Transition Metal Hydrides

“…The photochemical reactivity of Tp′Ir­(H) 2 (cyclooctene) with phosphites was also investigated; cyclooctene was shown to be the photolabile ligand with H 2 still bound to the metal center in the products. The [Tp′Ir­(H) 2 ] intermediate formed initially underwent a complex series of reactions with incoming ligands and with benzene solvent . The vinyl complex Ir­(H) 2 (CHCHPh)­(triphos) isomerized photochemically to two isomers of IrH­(triphos)­(η 2 -CH 2 CHPh); the H 2 -loss product Ir­(H) 2 (CCPh)­(triphos) was also formed.…”

Photochemistry of tris(pyrazolyl)borate titanium(IV) complexes

“…Since 1 and 2 are formally complexes of the d 0 Ti(IV), the observed bands must represent charge transfer transitions. The longest wavelength p-p* absorption of free and coordinate Tp À and Tp* À ligands appears in the 210-230 nm region [6][7][8]. As the Tp was changed to Tp*, the band showed a red shift, reflecting the increased p donation of the Tp* to the metal d orbitals.…”

C−H Bond Activation of Benzene and Cyclic Ethers by TpIrIII Species

“…[41] In systems with very bulky environments (for example when R and R' are hydrocarbon groups), direct transfer from the coordinated substrate to R or R' (s-bond metathesis) would seem a more reasonable mechanistic pathway. It is evident that further work is needed on these and related systems in order to clarify this important question.…”