C–H activation of 2,4,6-triphenylphosphinine: unprecedented formation of cyclometalated [(P⁁C)Ir(iii)] and [(P⁁C)Rh(iii)] complexes

Abstract

An unprecedented C-H activation of 2,4,6-triphenylphosphinine by Ir(III) and Rh(III) has been observed. Time-dependent (31)P{(1)H} NMR spectroscopy gave insight into the cyclometalation reaction and the corresponding coordination compounds were characterized by means of X-ray crystallography. In contrast, 2,4,6-triphenylpyridine does not show any ortho-metalation, demonstrating a remarkable difference in reactivity between these two structurally related aromatic heterocycles.

Cyclometalation of Aryl‐Substituted Phosphinines through CH‐Bond Activation: A Mechanistic Investigation

“…Treatment of 7 with [Cp*IrCl 2 ] 2 and NaOAc in a ratio of 2:1:2 leads initially to the quantitative formation of a new species at room temperature. This compound shows a broad signal at δ =132.4 ppm and can be assigned to the monomeric P‐coordinated neutral adduct [Cp*IrCl 2 ( 7 )] (Ir(PCH), Scheme and Figure 5) as verified before for the reaction of 1 with [Cp*IrCl 2 ] 2 and NaOAc 20…”

“…Despite the fact that the large opening of this ∢C(1)‐P(1)‐C(5) angle reflects a significant disruption of the aromaticity and consequently a high reactivity of the PC double bond is expected, all compounds can easily be isolated, handled, and characterized. We assume that the non‐metalated aryl‐substituent in the 6‐position of the heterocyclic framework might contribute to a steric protection of the PC double bond as we have observed before for the phosphinine‐Rh III and Ir III complexes of the type [Cp*M(P^C)Cl], containing a cyclometalated 2,4,6‐triphenylphosphinine ligand ( 1 ) 20…”

“…Because 2‐(2′‐pyridyl)‐4,6‐diphenylphosphinine is isoelectronic with the formally anionic 2,4,6‐triphenylphosphinine ligand, these encouraging results motivated us to study the cyclometalation of 2,4,6‐triphenylphosphinine as a phosphorus derivative of 2‐phenylpyridine. Thus, we recently demonstrated for the first time that the base‐assisted cyclometalation of 2,4,6‐triphenylphosphinine with [Cp*IrCl 2 ] 2 and [Cp*RhCl 2 ] 2 (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) as metal precursors in the presence of NaOAc is indeed possible (Figure 1, type C ) 20. 21 This new reactivity pattern of 2‐aryl‐phosphinines towards new phosphinine‐based metallacycles might consequently open up new perspectives for the application of phosphinines in molecular materials and homogeneous catalysis.…”

Pyridyl‐Functionalised 3H‐1,2,3,4‐Triazaphospholes: Synthesis, Coordination Chemistry and Photophysical Properties of Low‐Coordinate Phosphorus Compounds

“…From the chemical shift differenceo fDd = 23.8 ppm it is, however, not conclusive whether the triazaphosphole moiety coordinates through the phosphorus or nitrogen lone pairs to the metal centre because s-coordinated phosphinines show asimilar chemical shift difference upon coordination to am etal centre ( Figure 10). [21] Crystals of 7a,s uitable for X-ray crystal-structure analysis, were obtained from cooling ah ot saturated solution of the compound in dichloromethane slowly to T = À21 8C. Compound 7a crystallises in the space group P1 and the molecular structure of the crystal, along with selected bond lengths and angles, is depicted in Figure 11;t his shows the expected facial geometry of the [L 2 Re(CO) 3 Br] complex.…”

Reactivity of Aromatic Phosphorus Heterocycles – Differences Between Nonfunctionalized and Pyridyl‐Substituted 2,4,6‐Triarylphosphinines

“…For example, we have shown that 1 can undergo base-assisted C-H activation in the presence of [Cp*IrCl 2 ] 2 to form the neutral Ir III complex [(1)Cp*IrCl] (Figure 2). [13] In line with the isoelectronic principle, it was further demonstrated that 2-(2Ј-pyridyl)-4,6-diphenylphosphinine (2) forms the cationic Ir In several cases, however, the transition metal complexes of phosphinines are reactive towards nucleophiles. This is especially true for coordination compounds with metal centers in higher oxidation states and less-substituted phosphinines.…”