Transition Metal Complexes with Sterically Demanding Ligands, 3.¹Synthetic Access to Square-Planar Terdentate Pyridine−Diimine Rhodium(I) and Iridium(I) Methyl Complexes:  Successful Detour via Reactive Triflate and Methoxide Complexes

Abstract

The synthesis of novel square-planar, terdentate, aryl-substituted pyridine-diimine Rh(I) and Ir(I) chloro complexes from the free ligands and the bis(µ-chloro) ethylene-bridged dimers [(C 2 H 4 )RhIrCl] 2 is reported. Since attempts to achieve direct conversion to the corresponding hydride and methyl complexes through metathesis of the chloro ligand in these compounds were unsuccessful, synthetic access to more reactive methoxy-and triflate-substituted starting materials was developed. The methoxy and triflate complexes could be successfully converted to the Rh(I) η 2 -BH 4 and Rh,Ir(I) methyl complexes. The structure and bonding and thermodynamics of the methoxy and η 2 -BH 4 species were analyzed by DFT methods. X-ray crystal structures of selected Rh,Ir(I,III) representatives are reported.

Transition‐Metal Complexes with Sterically Demanding Ligands: Facile Thermal Intermolecular CH Bond Activation in a Square‐Planar IrI Complex

“…[1] In the course of this study, we noticed facile intermolecular CÀH activation in benzene leading quantitatively to the phenyl complex 2 and methane [Eq. as square-planar complexes by their X-ray crystal structures ( Figure 1).…”

“…The intermolecular activation of CÀH bonds is a highly desirable process [1][2][3][4][5][6][7][8] and is part of many catalytic systems, [9][10][11] for example, the dehydrogenation of alkanes to alkenes. [12][13][14] Detailed studies by various groups clearly established that the CÀH activation process is under kinetic rather than thermodynamic control in most cases.…”

“…[2,4,16] Herein, we describe a novel square-planar iridium(i) system 1, which undergoes facile thermal intermolecular CÀH activation in benzene at ambient temperature [Eq. (1)]. The observed unusual low barrier is analyzed and traced by DFT methods providing guidelines for the design of novel systems, which would allow the activation of methane under mild conditions.…”

“…as square-planar complexes by their X-ray crystal structures ( Figure 1). [17] Compound 2 was also obtained by independent synthesis from the corresponding methoxy complex [1] and phenylmagnesium chloride in 38 % yield.…”

“…Monitoring the CÀH activation process shown in Equation (1) by 1 H NMR spectroscopy indicated a clean conversion from 1!2 without detectable traces of intermediates. In neat [D 6 ]benzene under pseudo first-order conditions, a firstorder decay of the starting material 1 with a free enthalpy of activation, DG 313 = 23 kcal mol À1 was measured.…”