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

The direct reaction between [{Pd(mu-AcO)(C boolean AND P)}(2)] 1 and cyclic imides to yield new dinuclear cyclometallated palladium(II) complexes containing -NCO- bridging imidates of general formula [{Pd(mu-NCO)(C boolean AND P)}(2)] (C boolean AND P = 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.