Reactions of palladium(ii) and platinum(ii) bis(azido) complexes with isocyanides: synthesis and structural characterization of palladium(ii) and platinum(ii) complexes containing carbodiimido (or bis(carbodiimido)) and bis(tetrazolato) ligands

Abstract

2 , 4) containing a carbodiimido ligand and a C-coordinated 5-membered tetrazolato ligand. X-Ray structures of 1 and 2 identified the formation of palladium() complexes with a carbodiimido group, in which a nitrogen of the linear N᎐ ᎐ C᎐ ᎐ N moiety is bonded to the metal center, and with a tetrazolato ring formed via 1,3-dipolar cycloaddition of the isocyanide to the coordinated azido bond. Heating the isolated complexes 1 and 3 at 60 ЊC for 5 h converted them into the bis(carbodiimido)palladium() complexes,). The reactions of 2,6-dimethylphenyl isocyanide with Pd(N 3 ) 2 L 2 (L = PMe 3 , PEt 3 ) also gave the same complexes directly. Reaction of Pd(N 3 ) 2 (dppe) with 2,6-dimethylphenyl isocyanide also caused the formation of the bis(carbodiimido) complex Pd[N᎐ ᎐ C᎐ ᎐ N-2,6-Me 2 C 6 H 3 ] 2 (dppe), 7 in 75% yield. However, reactions of M(N 3 ) 2 (PMe 3 ) 2 (M = Pd or Pt) with tert-butyl isocyanide resulted in the formation of bis(tetrazolato) compounds, M[CN 4 (R)] 2 (PMe 3 ) 2 (R = tert-butyl, M = Pd, 8; Pt, 9) by the cycloaddition of isocyanide to the coordinated azido bond. The same reactions with other isocyanides such as cyclohexyl and n-butyl isocyanides afforded bis(tetrazolato) complexes, trans-M[CN 4 (R)] 2 L 2 (M =

Substituent-Dependent Azide Addition to Isocyanides Generates Strongly Luminescent Iridium Complexes

“…The crystal structures clearly show the five-membered π-conjugated tetrazolato bound through carbon, with the aryl ring on the tetrazolato directed toward one of the cyclometalating ligands. We presume that, for the aryl cyanamido products described above (Scheme and Figure ), the corresponding tetrazolato is formed as an intermediate, which then expels N 2 as described in other related chemistry . When electron-donating groups are present, the tetrazolato is apparently more stable, and even prolonged heating of tetrazolato products 3 F2ppy‑xyl and 3 F2ppy‑OMe in ambient atmosphere does not lead to formation of aryl cyanamido complexes.…”

“…From the standpoint of organometallic synthesis, the results described above are significant. While both tetrazolato and cyanamido products have been previously observed upon reaction of azides and isocyanides, − in some cases with the tetrazolato converting to the cyanamido by thermolysis, this is the first study to show that the preference for tetrazolato or cyanamido can be controlled by the electronic nature of the isocyanide. All reactions involving isocyanides with electron-withdrawing groups formed aryl cyanamido products, whereas tetrazolato complexes are usually observed with electron-donating groups.…”

“…Two important insights emerge from this study: (1) From the standpoint of fundamental reactivity and organometallic synthesis, we show that the outcome of the azide functionalization reaction depends on the electronic nature of the isocyanide. It has previously been shown, almost exclusively on square-planar d 8 metal complexes, that azides and isocyanides can react to form either tetrazolato or cyanamido products. − The work presented here is the first to show that this reactivity can be controlled by varying substituents on the isocyanide. Moreover, we also introduce a new ligand structure type that emerges when both cis -oriented isocyanides react with an equivalent of azide and couple.…”

“…We presume that, for the aryl cyanamido products described above (Scheme 1 and Figure 1), the corresponding tetrazolato is formed as an intermediate, which then expels N 2 as described in other related chemistry. 36 When electron-donating groups are present, the tetrazolato is apparently more stable, and even prolonged heating of tetrazolato products 3 F2ppy-xyl and 3 F2ppy-OMe in ambient atmosphere does not lead to formation of aryl cyanamido complexes. We also note that, despite using a large excess of sodium azide and long reaction times, we never observed products where both isocyanides were converted to cyanamidos, tetrazolatos, or a combination of the two.…”