Dinuclear Ortho-Metalated Palladium(II) Compounds with N,N- and N,O-Donor Bridging Ligands. Synthesis of New Palladium(III) Complexes

New dinuclear ortho-metalated palladium(II) compounds with N,N′-diarylformamidinates,
Pd2[(C6H4)PPh2]2[R′NC(H)NR′]2 (R′ = C6H5, 3a; R′ = p-CH3C6H4, 3b; R′ = p-CH3OC6H4, 3c) and N,O-donor ligands, Pd2[(C6H4)PPh2]2[N,O]2 (N,O = succinimidate (5), phtalimidate (6), 2-hydroxypyridinate (7), acetanilidate (8)) have been synthesized and characterized by NMR spectroscopy
and X-ray diffraction methods. The oxidation with iodobenzene dichloride
gave new and rare Pd26+ compounds, Pd2[(C6H4)PPh2]2[R′NC(H)NR′]2Cl2 (R′ = C6H5, 4a; R′ = p-CH3C6H4, 4b). DFT calculations on the Pd24+ → Pd26+ oxidation reaction
show that the substituents on the amidinate N atoms have a greater
effect on the reaction energy than the substituents on the C atom.
DFT calculations also confirm that for Pd2[(C6H4)PPh2]2[N,O]2 compounds the symmetric isomers with N atoms trans to O atoms
are the most stable complexes. The palladium dimers were tested as
precursors of catalysts in tandem diboration/arylation/oxidation reactions.

新型双核正金属化钯(II)化合物，包括N,N'-二芳基甲酰胺基钯(II)配合物Pd2[(C6H4)PPh2]2[R′NC(H)NR′]2 (R′ = C6H5, 3a; R′ = p-CH3C6H4, 3b; R′ = p-CH3OC6H4, 3c)以及N,O-供体配体Pd2[(C6H4)PPh2]2[N,O]2 (N,O = succinimidate (5), phtalimidate (6), 2-hydroxypyridinate (7), acetanilidate (8))，已通过核磁共振波谱和X射线衍射技术进行合成与表征。碘苯二氯化物氧化反应产生了新的且罕见的Pd26+化合物，Pd2[(C6H4)PPh2]2[R′NC(H)NR′]2Cl2 (R′ = C6H5, 4a; R′ = p-CH3C6H4, 4b)。对Pd24+ → Pd26+氧化反应的DFT计算表明，取代基对甲酰胺基氮原子的作用比对碳原子的作用更大。DFT计算还证实，对于Pd2[(C6H4)PPh2]2[N,O]2化合物，N原子相对于O原子处于反式位置的对称异构体是最稳定的配合物。这些钯二聚体被作为串联二硼化/芳基化/氧化反应催化剂前体的候选物质进行了测试。