Palladium(II) Complexes of 1‐Phosphaisoprene Molecules and Polymers: Reversible Cross‐Linking of a Phosphorus‐Containing Polymer

Abstract The anionic polymerization of 1‐phosphaisoprene [Mes*P=C(Me)−CH=CH 2 ( E ‐ 1 )] affords poly(1‐phosphaisoprene) 2 in high yield (75 %). Concentrated solutions of polymer 2 ( M n =21,800 g mol −1 ; Đ =1.02) a P‐analogue of natural rubber, undergo gelation upon treatment with [Pd(cod)Cl 2 ] (0.15 P equiv). Evidence for P‐coordination of 2 to Pd II was obtained by 31 P and 1 H NMR spectroscopy. The gelation is reversed by the addition of PMe 3 and the reformation of recoverable 2 along with [Pd II −PMe 3 ] complexes were confirmed by 31 P NMR spectroscopy. The use of labile metal‐ligand bonds to reversibly form gels is unprecedented and has relevance to self‐healing materials. In contrast, coordination of 2 to [Pd(η 3 ‐C 3 H 5 )(μ‐Cl)] 2 affords the well‐defined complex 2 ⋅ [Pd(η 3 ‐C 3 H 5 )Cl] which was characterized by 31 P, 1 H, 13 C{ 1 H} NMR spectroscopy and GPC. This polymer chemistry was complemented by detailed molecular model studies of the coordination chemistry of monomer 1‐phosphaisoprene E ‐ 1 with [Pd(cod)Cl 2 ] and [Pd(η 3 ‐C 3 H 5 )(μ‐Cl)] 2 ].