Reactivity of Diaryloxy Palladium Complex with TMEDA (N,N,N‘,N‘-Tetramethylethylenediamine) Ligand toward Carbon Monoxide and Carbon Dioxide

Abstract

The reactivity of the diaryloxy palladium complex toward carbon monoxide was investigated relevant to the mechanism of the palladium-catalyzed oxidative carbonylation of phenol to produce diphenyl carbonate (DPC). (TMEDA)Pd(OC 6 H 4 -p-t-Bu) 2 (1) reacted at high CO pressures (10-80 atm) at 100 °C to give the di(p-tert-butyl)phenyl carbonate. The yield of the carbonate increased with the increase in the CO pressure and with the addition of triphenylphosphine. The 13 C{ 1 H} NMR and IR spectroscopic studies at room temperature under high CO pressure (50 atm) revealed that CO inserts into one of the Pd-O bonds in 1. Thus, the formation of palladium phenoxide followed by carbonylation and subsequent reductive elimination is considered to be one of the possible DPC formation routes in the oxidative carbonylation of phenol; the reductive elimination is slower than the carbonylation. The reactivity of 1 with carbon dioxide was also examined relating to the DPC synthesis from carbon dioxide and phenol. The reaction of 1 with CO 2 led to the formation of a palladium carbonate complex, (TMEDA)Pd(η 2 -CO 3 ) (2), whose molecular structure was determined by X-ray crystallography.

Reaction of carbon dioxide with a palladium–alkyl complex supported by a bis-NHC framework

“…The solid state IR spectrum obtained for (MDC Mes )Pd(CO 3 ) shows an intense stretching frequency at 1601 cm −1 , which matches that reported for similar complexes. 47,44,48–49 …”

Aspects of carbon dioxide utilization

“…Therefore, it is required to find highly reactive metal catalysts. The investigations of the reaction between carbon dioxide and metal compounds, as transition elements, e.g., Ni [5][6][7][8][9], Pd [10,11], Pt [22], Co [12,55], Rh [13,14,22,34], Ir [15][16][17][18], Fe [19][20][21]34,53], Ru [22][23][24][25][26]34,53], Mn [27][28][29], Re [27,[30][31][32][33][34], Cr [35], Mo [35][36][37][38][39], W [35,[38][39][40][41], V …”

Unusual Reactivity Patterns of 1,3,6,8-Tetraazatricyclo-[4.4.1.13,8]-dodecane (TATD) Towards Some Reducing Agents: Synthesis of TMEDA

“…This diamine is a versatile bidentate ligand and a chelating Lewis base [7]. Many of these complexes have shown catalytic activity in oxidative coupling reactions [8], olefin polymerizations [9], oxidative carbonylation of phenol to produce diphenyl carbonate (DPC) [10], and alkyl-alkyl cross-coupling reactions [11]. In the same way, TMEDA has been used as an initiator of anionic polymerization in the synthesis of high vinyl copolymers containing styrene and butadiene [12], lithiation by alkylLi/TMEDA [13], reductive ring opening of many oxygen-, nitrogen-, or sulfur-containing heterocycles [14], synthesis of asymmetric hydroborating reagents [15] and diastereoselective dihydroxylation of olefins [16].…”