2‐(2′‐Pyridyl)‐4,6‐diphenylphosphinine versus 2‐(2′‐Pyridyl)‐4,6‐diphenylpyridine: Synthesis, Characterization, and Reactivity of Cationic Rh^III and Ir^III Complexes Based on Aromatic Phosphorus Heterocycles

Abstract

The bidentate P,N hybrid ligand 1 allows access for the first time to novel cationic phosphinine-based Rh(III) and Ir(III) complexes, broadening significantly the scope of low-coordinate aromatic phosphorus heterocycles for potential applications. The coordination chemistry of 1 towards Rh(III) and Ir(III) was investigated and compared with the analogous 2,2'-bipyridine derivative, 2-(2'-pyridyl)-4,6-diphenylpyridine (2), which showed significant differences. The molecular structures of [RhCl(Cp*)(1)]Cl and [IrCl(Cp*)(1)]Cl (Cp*=pentamethylcyclopentadienyl) were determined by means of X-ray diffraction and confirm the mononuclear nature of the λ(3) -phosphinine-Rh(III) and Ir(III) complexes. In contrast, a different reactivity and coordination behavior was found for the nitrogen analogue 2, especially towards Rh(III) as a bimetallic ion pair [RhCl(Cp*)(2)](+) [RhCl3 (Cp*)](-) is formed rather than a mononuclear coordination compound. [RhCl(Cp*)(1)]Cl and [IrCl(Cp*)(1)]Cl react with water regio- and diastereoselectively at the external PC double bond, leading exclusively to the anti-addition products [MCl(Cp*)(1H⋅OH)]Cl as confirmed by X-ray crystal-structure determination.

Recent Developments in the Chemistry of Pyridyl-functionalized, Low-coordinate Phosphorus Heterocycles

“…44 The molecular structures of 27 and 28 in the crystal show unambiguously that the H 2 O molecule has been added selectively in an anti fashion to the P(1)=C(1) double bond, rather than in a syn fashion. Moreover, the H 2 O molecule has been added selectively to only one side of the heterocycle in such a way that the OH group is pointing away from the Cl ligand.…”

“…They can be prepared and isolated easily starting from the corresponding [MCp*Cl 2 ] 2 metal precursors and the P,N-hybrid ligand. 44 Both the chelate effect of the bidentate ligand and the aryl groups in the 2-and 6-positions of the heterocyclic framework are anticipated to contribute significantly to the formation and stabilization of such complexes. These results demonstrate that the bidentate P,N-hybrid ligand has allowed access to novel cationic Rh(III) and Ir(III) complexes for the first time, broadening significantly the scope of low-coordinate aromatic phosphorus heterocycles for potential applications.…”

Reactions of Pyridyl‐Functionalized, Chelating λ3‐Phosphinines in the Coordination Environment of RhIII and IrIII

“…In contrast, we found that treatment of the cationic phosphinine-M III complexes [(1)Cp*RhCl]Cl and [(1)Cp*IrCl]Cl with water leads quantitatively and selectively to the anti-addition products 2 (Rh) and 3 (Ir), respectively (type C, Figure 2), as confirmed by crystal structure determinations. [16] Additionally, hydrogen bonding between the À OH hydrogen atom and the Cl À counteranion was observed.…”

“…The P(1)ÀC(1) and P(1)ÀC (5) (2) ), whereas the C À C bond lengths in the phosphinine moiety of 6 are essentially identical compared to the ones in [(1)Cp*RhCl]Cl. [16] The À OH group at the phosphorus atom forms an intramolecular hydrogen-bond to the metal-coordinated chloride. It should be noted here that an inversion of configuration had apparently occurred during the proton-transfer step, either at the phosphorus atom or the Rh center.…”

“…[16] The starting material for 3, [(1)Cp*IrCl]Cl, is illustrated as well (spectrum 1) for comparison reasons (see also Scheme 1). [16] Crystals of 4 suitable for X-ray diffraction were isolated in 54 % yield by slow diffusion of Et 2 O into a diluted solution of 4 in CD 2 Cl 2 . The compound crystallizes as a racemate in the orthorhombic space group Pna2 1 with one metal complex molecule in the asymmetric unit.…”