Insertion of CO and Strained Olefins into Organometallic (Ferrocenylmethyl)phosphane Palladium Complexes

The reaction of [Pd(cod)(CH3)Cl] (cod = 1,5-cyclooctadiene) with the primary phosphane (ferrocenylmethyl)phosphane (PH2CH 2Fc, 1, 2 equiv.) affords trans-[Pd(PH2CH 2Fc)2(CH3)-Cl] (2) in 95% yield. The intermediate chlorido-bridged dinuclear complex [Pd(PH2CH 2Fc)(CH3)(μ-Cl)]2 (3) is traversed along the formation of 2. Complex 3 may be isolated as a mixture of anti-3a and syn-3b isomers by treating [Pd(cod)-(CH3)Cl] with 1 (1 equiv.). For comparison, the analogous reactions of 1 with [Pt(COd)(CH3)Cl] gives [Pt(PH2CH2Fc)2(CH3)-Cl] as a mixture of cis-4a and trans-4b geometric isomers, regardless of the P/Pt molar ratio used. The insertion (at 1 atm and 253 K) of CO into the methyl-Pd bonds of either 2 or 3 gives the acetyl Pd complexes trans- [Pd(PH2CH 2Fc)2-(COCH3)Cl] (5) and anri-[Pd(PH 2CH2Fc)(COCH3)(μ-Cl)]2 (6), respectively. The process leading from 3 to 6 occurs without fragmentation of the dinuclear core of the complexes, lending support to an associative mechanism with CO binding to the metal. Complex 6 undergoes facile insertion of strained olefins, such as norbornadiene or norbornene, into the acetyl-palladium bond, giving the complexes [Pd(κ2C, O-C7H 8C(O)CH3)(Cl)(PH2CH2Fc)] (7) and [Pd(κ2CO-C7H10C-(O)CH3)(Cl) (PH2CH2Fc)] (8), respectively. Complexes 3 were tested as precatalysts for the vinylic polymerization of norbornene at 253 K, as well as for the alternate copolymerization of carbon monoxide with norbornene.