Activation of Small Molecules by the Metal–Amido Bond of Rhodium(III) and Iridium(III) (η⁵-C₅Me₅)M-Aminopyridinate Complexes

Abstract

We report the synthesis and structural characterization of five-coordinate complexes of rhodium and iridium of the type [(η-CMe)M(N^N)] (3-M), where N^N represents the aminopyridinate ligand derived from 2-NH(Ph)-6-(Xyl)CHN (Xyl = 2,6-MeCH). The two complexes were isolated as salts of the BAr anion (BAr = B[3,5-(CF)CH]). The M-N bond of complexes 3-M readily activated CO, CH, and H. Thus, compounds 3-M reacted with CO under ambient conditions, but whereas for 3-Rh, CO migratory insertion was fast, yielding a carbamoyl carbonyl species, 4-Rh, the stronger Ir-N bond of complex 3-Ir caused the reaction to stop at the CO coordination stage. In contrast, 3-Ir reacted reversibly with CH, forming adduct 5-Ir, which subsequently rearranged irreversibly to [Ir](H)(═C(Me)N(Ph)-) complex 6-Ir, which contains an N-stabilized carbene ligand. Computational studies supported a migratory insertion mechanism, giving first a β-stabilized linear alkyl unit, [Ir]CHCHN(Ph)-, followed by a multistep rearrangement that led to the final product 6-Ir. Both β- and α-H eliminations, as well as their microscopic reverse migratory insertion reactions, were implicated in the alkyl-to-hydride-carbene reorganization. The analogous reaction of 3-Rh with CH originated a complex mixture of products from which only a branched alkyl [Rh]C(H)(Me)N(Ph)- (5-Rh) could be isolated, featuring a β-agostic methyl interaction. Reactions of 3-M with H promoted a catalytic isomerization of the Ap ligand from classical κ-N,N' binding to κ-N plus η-pseudoallyl coordination mode.

Coordinatively Unsaturated [RhCp*Rf2] (Cp* = C5Me5; Rf = C6F3Cl2-3,5), General Precursor to Cp*-Diaryl and Cp*-Halo-Aryl RhIII Complexes. Observing and Testing the Effect of Cp* as Electronic Buffer

“…Both complexes, 2 and 20 , have their octahedral partners with the ligands Cl – (chloride) or CNXylyl. The N–Rh distance in 20 (1.98 Å) elongates to 2.11 Å (a single N–Rh bond distance) in 21 and 22 upon ligand coordination. , In contrast, L coordination to 2 scarcely affects the Rf–Rh bond distances in 10 and 11 : the most different Rf–Rh distances, 2.06 and 2.11 Å, are found in the octahedral complex 10 , while the distances in the pentacoordinated 2 are 2.06 and 2.07 Å. All of these Rh–C distances are consistent with single bonds as reported for fluoroaryl-Rh III complexes. , …”

“…For instance, pentacoordinated MCp* (M = Rh, Ir) complexes with chelate ligands combining amido-amino or amido-pyridyl groups (Figure 1, B) have been thoroughly studied in the group of Carmona, both structurally and in their interesting reactivity towards small molecules (CO, H 2 , ethylene). 11,12,13,14 The reactions start by coordination of the small molecule (while the amido group retracts its lone electron pair) to give an octahedral intermediate. 15 A similar analysis had been applied earlier to explain the stability of a T-shaped tricoordinated [Pd II (amido)XL], formally 14e but in fact closer to 16e complex.…”

Expanding the Concepts Trans Influence and Back-Donation: Hybrid and Side Donations in [Cp*MIII(L)XY] (M = Rh, Ir) Complexes with CO, CN–, and CNR Ligands. A Window to Cis Influence

“…However, the same procedure using the iridium analogue (μ-Cl) 2 [IrCp*Cl] 2 ( 1b ) leads to a mixture of [IrCp*Rf 2 ] ( 2b ) and [IrCp*Rf 2 (NCMe)] ( 2b -NCMe), not explicit in Scheme . The acetonitrile (MeCN) ligand in 2b -NCMe can be removed by prolonged heating under vacuum at 353 K, yielding quantitative formation of 2b . For the subsequent reactions in Scheme , mixtures of 2b / 2b -NCMe can be used indistinctly as MeCN is fully displaced.…”

16-Electron Half-Sandwich Rhodium(III), Iridium(III), and Ruthenium(II) Complexes as Lysosome-Targeted Anticancer Agents

“…It should be noted that hydrolysis of M–Cl bonds, i.e., Cl – /H 2 O exchange, usually represents an activation step for these 18-electron complexes, since M–H 2 O aqua were usually more reactive than the corresponding chloride analogues . Nevertheless, stable five-coordinated (16-electron, without the leaving group Cl – , Scheme , II ) half-sandwich platinum group metal (Rh, Ir, Ru, and Os) complexes are rarely synthesized, − and their biological evaluation has not been explored.…”