Bis-cyclometalated complexes of Pd(II) and Pd(IV) from iminophosphoranes: Synthesis, structure and reactivity

The mononuclear bis-orthopalladated complexes [Pd(CˆN){C6H4(PPh2double bond; length as m-dashNPh)-2}] [CˆN = (2-(pyridin-2-yl)phenyl) 3a, (2-((dimethylamino)methyl)phenyl) 3b, (S)-(2-(1-(dimethylamino)ethyl)phenyl) 3c, (quinolin-8-ylmethyl) 3d, (4-methoxy-2-((triphenyl-λ5-phosphanylidene)carbamoyl)phenyl) 3e] have been synthesized as single isomers by reaction of the corresponding chloride dimers [Pd(μ-Cl)(CˆN)]2 (1a–1e) with the lithium derivative [Li{C6H4(PPh2double bond; length as m-dashNPh)-2}] (2) in Et2O. Spectroscopic data show that the two palladated C atoms are in cis disposition, which is confirmed by the X-ray structure of 3a. Oxidation of 3a with PhI(OAc)2 affords the corresponding Pd(IV) derivative (OC-6-32)[Pd(OAc)2{C6H4(PPh2double bond; length as m-dashNPh)-2}{C6H4-(2′-NC5H4)-2}] 4a also as a single isomer. 4a undergoes reductive elimination through C–O coupling to give the dimer [Pd(μ-OAc){C6H4(PPh2double bond; length as m-dashNPh)-2}]25 and the ortho-acetoxylated phenylpyridine 6. The reactivity of 3b–3e towards oxidants is also discussed.