New phospha-palladacycles: efficient catalysts in the formylation of aryl chlorides

Abstract

The direct reaction between [{Pd(μ-AcO)(CˆP)}₂] 1 and cyclic imides to yield new dinuclear cyclometallated palladium(II) complexes containing –NCO– bridging imidates of general formula [{Pd(μ-NCO)(CˆP)}₂] (CˆP = CH₂C₆H₄P(o-tolyl)₂; –NCO– = succinimidate (suc) 2, maleimidate (mal) 3, phthalimidate (phthal) 4 or saccharinate (sacc) 5 is described. Spectroscopic techniques and structural characterisation by X-ray diffraction of complex 2 confirmed the proposed formulae. The new dimeric complexes are shown to be excellent catalysts for the selective formylation of aryl halides under CO-free conditions to obtain synthetically important aromatic aldehydes. Yields are diminished by steric hindrance around the aryl halides.