A novel oxidative addition product from [Pt2(dba)3]: synthesis and spectroscopic characterization of a bimetallic Pt-eta2-tetracyanoethylene complex containing 2,3,5,6-tetrakis(alpha-pyridyl)pyrazine

Abstract

{[Pt(η 2 -TCNE)] 2 (μ-TPP)} (1) foi preparado a partir da reação entre o composto de Pt(0) [Pt 2 (dba) 3 ] (dba = dibenzilidenoacetona), tetracianoetileno (TCNE) e 2,3,5,6-tetraquis(α-piridil)pirazina (TPP) na razão estequiométrica 1:2:1, respectivamente. 1 foi caracterizado por análise elementar, espectroscopia no infravermelho, RMN de 1 H em solução e RMN de 13 C no estado sólido (CP/MAS). De acordo com os espectros de RMN, o ligante TPP em 1 se coordena a cada centro metálico por dois átomos de nitrogênio piridínicos, segundo um modo de coordenação bis-bidentado já relatado em outros complexos de TPP com Pt II . Além dos sinais atribuídos aos átomos de carbono do TPP (δ 128-155) e aos átomos de carbono dos grupos nitrila (δ 115,1), o espectro de RMN de 13 C-CP/MAS de 1 exibe na região de menor freqüência um duplo dupleto [δ 1 -2,6; 1 J( 195 Pt-13 C) = 223 Hz e δ 2 1,6; 1 J( 195 Pt-13 C) = 188 Hz]. Estes últimos sinais são atribuídos aos átomos de carbono etilênicos do TCNE ligados a platina e confirmam que a ligação nos fragmentos Pt-η 2 -TCNE é melhor descrita segundo o modelo metalaciclopropano.{[Pt(η 2 -TCNE)] 2 (μ-TPP)} (1) has been prepared from the Pt(0) compound [Pt 2 (dba) 3 ] (dba = dibenzylideneacetone), tetracyanoethylene (TCNE), and 2,3,5,6-tetrakis(α-pyridyl)pyrazine (TPP) in the 1:2:1 stoichiometric ratio, respectively. 1 has been characterized by elemental analysis, infrared spectroscopy, solution 1 H NMR and solid-state 13 C (CP/MAS) NMR spectroscopy. According to the NMR spectra of 1, TPP binds to each metal through two pyridine nitrogen atoms. In addition to the signals assigned to the TPP carbon atoms (δ 128-155) and to the nitrile carbon atoms (δ 115.1), the 13 C-CP/MAS NMR spectrum of 1 exhibits a double doublet [δ 1 -2.6, 1 J( 195 Pt-13 C) = 223 Hz and δ 2 1.6, 1 J( 195 Pt-13 C) = 188 Hz] in the low frequency region. These signals are assigned to the ethylenic TCNE carbon atoms attached to platinum and confirm that the bonding at the Pt-η 2 -TCNE moieties is best described according to the metalacyclopropane model.

2,3,5,6-Tetra(pyrazin-2-yl)pyrazine: a novel bis-bidentate, bis-tridentate chelator

“…This compound will have 10 nitrogen atoms: six in a potential bis-tridentate binding system and four in a bis-bidentate binding system, significantly increasing the amount of coordination modes, compared to the seven modes shown by 1. 6 To put this idea into practice 1,2-di(pyrazin-2-yl)ethene-1,2-diol (7) was prepared in 73% yield by benzoin coupling of pyrazine-2-carbaldehyde (6) in water with 10 mol % potassium cyanide 7 (Scheme 1). An increase in the catalyst loading in this reaction led to invariably lower yields.…”