1,6-Diene Complexes of Palladium(0) and Platinum(0):  Highly Reactive Sources for the Naked Metals and [L−M⁰] Fragments

Abstract

The complexes (cod)MCl 2 (M = Pd, Pt; cod = cis,cis -1,5-cyclooctadiene) react with Li 2 (cot) (cot = cyclooctatetraene) in a 1,6-diene/diethyl ether mixture (1,6-diene = hepta-1,6-diene, diallyl ether, dvds (1,3-divinyl-1,1,3,3-tetramethyldisiloxane)) to afford the isolated homoleptic dinuclear Pd 0 and Pt 0 compounds Pd 2 (C 7 H 12 ) 3 ( 1 ), Pd 2 (C 6 H 10 O) 3 ·C 6 H 10 O ( 2 ‘; 2: Pd 2 (C 6 H 10 O) 3 ), Pd 2 (dvds) 3 ( 3 ), and Pt 2 (C 7 H 12 ) 3 ( 4 ). When 1 − 4 are treated with additional 1,6-diene the equally homoleptic but mononuclear derivatives of type M(1,6-diene) 2 ( 5 − 8 ) and with ethene the mixed alkene complexes (C 2 H 4 )M(1,6-diene) ( 9 − 12 ) are obtained in solution. Complexes 1 − 12 react with donor ligands such as phosphanes, phosphites, or t BuNC to give isolated complexes of types L−M(1,6-diene) ( 13 − 41 ), which have also been prepared by other routes. In all complexes the metal centers are TP -3 coordinated: complexes 1 − 4 contain chelating and bridging 1,6-diene ligands, whereas the other complexes contain a chelating 1,6-diene ligand and an η 2 -alkene ( 5 − 12 ) or η 1 -donor ligand ( 13 − 41 ). Of the studied 1,6-diene complexes the hepta-1,6-diene derivatives are most reactive, while the diallyl ether complexes are often more convenient to handle. The readily isolable dinuclear hepta-1,6-diene and diallyl ether complexes 1, 2 ‘, and 4, and their mononuclear pure olefin derivatives are among the most reactive sources for naked Pd 0 and Pt 0 . The corresponding L−M(1,6-diene) complexes are equally reactive precursor compounds for the generation of [L−M 0 ] fragments in solution, which for M = Pd are available otherwise only with difficulty. The results are significant for the operation of naked Pd 0 and L−Pd 0 catalysts in homogeneous catalysis.