Ring Expansion of a Platinacyclopropane to a Platinacyclopentane by Double Insertion of Isocyanides into Pt−C Bonds

Abstract

A platinum isocyanide complex bearing a η2-TCNE ligand, (η2-TCNE)Pt(η-CNC6H3-2,6-Me2)2 (1), was synthesized, and its crystallographic study revealed the coordination mode of the η2-TCNE ligand to be a typical metallacyclopropane extreme, in which back-donation from metal to TCNE contributes primarily to the stabilization of 1. Treatment of 1 with 2 equiv of CNC6H3-2,6-Me2 resulted in ring expansion of the platinacyclopropane by insertion of CNC6H3-2,6-Me2 into each Pt−C bond of the metallacycle, leading to formation of a new complex having a platinacyclopentane structure, (TCNE)Pt(η-CNC6H3-2,6-Me2)4 (4). Although the molecular structures of palladium and nickel homologues of 1 were close to the corresponding metallacyclopropane, no metallacyclopentane complex was obtained under similar conditions. Studies on variable-temperature NMR spectroscopy and spin-saturation transfer measurement of 4 showed exchange of the imidoyl CNC6H3-2,6-Me2 group and the coordinated CNC6H3-2,6-Me2 ligand in solution, suggesting the ring expansion to be reversible.

Substitution of Tetracyanoethene by Ethynyl–Metal Complexes Gives Tricyanovinylethynyl (Tricyanobutenynyl) Derivatives: Syntheses, Protonation, and Addition of Metal–Ligand Fragments

“…Recent examples include Ru­(η 1 -tcne)­{NBu t C­(mes)­NBu t }­Cp*, trans -[{Ru­(PPh 3 ) 2 Cp} 2 (μ-tcne)] 2+ , and [{Fe­(CO) 2 Cp} 4 (μ 4 -tcne)] n + ( n = 3, 4) . Metal π complexes were first reported by Baddley, who prepared Pt­{η 2 -C 2 (CN) 4 }­(PPh 3 ) 2 and showed conversion of this complex to trans -Pt­(CN)­{C­(CN)C­(CN) 2 }­(PPh 3 ) 2 . , Many related compounds have since been prepared, especially for the later transition metals, such as M­(CO) 5 (η 2 -tcne) (M = Cr, W), Ru­(η 2 -tcne)­(NRCR′NR)­Cp*, and M­(η 2 -tcne)­(L) 2 (M = Ni, Pd, Pt, L = CNAr), and aspects of the coordination chemistry of tcne and physical properties of the resulting complexes have also been reviewed. − …”

Palladium-Catalyzed Synthesis of 5-Iminopyrrolones through Isocyanide Double Insertion Reaction with Terminal Alkynes and Water

“…Isocyanides have been widely applied to construct various nitrogen heterocyclic compounds due to their superior capability to rapidly create molecular diversity, however, most reported achievements mainly focus on the utility of isocyanides single insertion for the synthesis of nitrogen-containing compounds . Only a few examples of metal-catalyzed double isocyanides insertion have been reported . For example, in 2015, Tu and Jiang disclosed a palladium-catalyzed double isocyanide insertion–cyclization between 2-haloanilines and isocyanides to form 3-iminoindol-2-amines (Scheme a).…”

Theoretical Characterizations of the Ring Expansion of a Metallacyclopropane to a Metallacyclopentane

“…The principal motivation for this research is a remarkable recent experimental discovery in the laboratory of Nagashima . Via a variable-temperature NMR spectroscopy and several other probe techniques, the Japanese group reported that the group 10 metal isocyanide complexes bearing a η 2 -TCNE ligand, (η 2 -TCNE)Ni(η-CNC 6 H 3 -2-6-Me 2 ) 2 ( 1 ), (η 2 -TCNE)Pd(η-CNC 6 H 3 -2-6-Me 2 ) 2 ( 2 ), and (η 2 -TCNE)Pt(η-CNC 6 H 3 -2-6-Me 2 ) 2 ( 3 ), were synthesized and characterized structurally . In particular, they found that the coordination mode of the η 2 -TCNE ligand is a typical metallacyclopropane extreme, in which back-donation from Pt to TCNE contributes primarily to the stabilization of 3 .…”