Unsymmetrical 1,4-Diazabutadiene Complexes of Platinum(II)

Abstract

The new unsymmetrical 1,4-diazabutadiene ligand glyoxal bis(2-(methoxymethyl)-4,6-di-tert-butylphenyl)diimine (L) and its reduced analog (LH 4 ) were synthesized. The reactions of both ligands with bis(benzonitrile) complexes of palladium and platinum, MCl2(PhCN)2, were investigated. Two isomers of formula MCl2 L were isolated from the reaction of L with MCl2(PhCN)2 (1a and 1b for Pd, 2a and 2b for Pt), while only a single product, MCl2(LH 4 ), formed in the reaction with LH 4 (3 for M = Pd, 4 for M = Pt). All new compounds were characterized by elemental analyses and IR and NMR spectroscopies. The molecular structures for L, LH 4 , 2b, 3, and 4 were determined by single-crystal X-ray diffraction. The metal complexes exhibit distorted square-planar geometry. The aryl groups of the L and LH 4 ligands lie out of the coordination plane in a manner that blocks potential axial ligation sites. Ligand L crystallizes in the triclinic space group P1̄ with a = 5.760(1) Å, b = 9.383(2) Å, c = 14.954(3) Å, α = 89.38(2)°, β = 79.67(2)°, γ = 88.14(2)°, and Z = 1. The reduced ligand LH 4 crystallizes in the monoclinic space group P21 with a = 5.9758(1) Å, b = 17.4272(2) Å, c = 15.6222(1) Å, β = 99.063(1)°, and Z = 2. Complex 2b crystallizes in the monoclinic space group P21/c with a = 16.9599(2) Å, b = 18.4985(2) Å, c = 12.4976(0) Å, β = 100.945(0)°, and Z = 4. Complex 3 crystallizes in the monoclinic space group C2/c with a = 36.1506(8) Å, b = 8.0994 (2) Å, c = 15.5671(1) Å, β = 113.988(1)°, and Z = 4. Complex 4 crystallizes in the monoclinic space group C2/c with a = 36.0649(3) Å, b = 8.1787(2) Å, c = 15.7585(3) Å, β = 112.610(1)°, and Z = 4.

Effective binuclear Pd(II) complexes for Suzuki reactions in water

“…The characteristic imine proton resonance of L1 , L2 and L5 shows a sharp singlet between δ 8.36 and 8.52 ppm. Similar resonance shifts have been observed in related divalent compounds before . Compared to those of the free ligands L1 , L2 and L5 , the imine proton resonances for C1 , C2 and C5 are shifted downfield about 0.6–0.8 ppm.…”

Microwave-assisted aqueous Suzuki coupling reactions catalyzed by ionic palladium(II) complexes

“…Diagnostic of chelating ligand coordination in these complexes is the downfield shift in the 1 HNMR spectra of the imine signal by 0.3-0.4 ppm upon coordination to the Pd(II) centre. Similar shifts have been observed in related compounds [18,25,[30][31][32]. The imine signals in the 13 CNMR spectra also show a downfield shift of 10.1-16.3 ppm upon metal coordination.…”

Ligand effects in palladium‐catalyzed Suzuki and Heck coupling reactions

“…Similar resonance shifts have been observed in related complexes. [9] All complexes are stable in air and readily soluble in polar organic compounds such as methanol, DMSO and DMF.…”

“…We used our catalysts in the catalytic cross-coupling of various aryl halides with aryl boronic acids (Suzuki reaction) [7] and methyl acrylate (Heck reaction). [8,9] Results and Discussion…”