Palladium complexes hydrocarbyl

Recently, we [53] and others [54] simultaneously reported an example of a complex in which the transition metal dictates the coordination mode, viz. urea-functionalized phosphine 20, which forms a trans palladium complex, complemented by hydrogen bonding ofthe urea fragments (Figure 10.6). Bear in mind that any monophosphine, and even wide bite angle diphosphines, give trans complexes with a hydrocarbyl palladium halide. More interestingly, the urea moieties can function as a host for another halide ion. 

Following the synthesis of the first methyl-palladium NHC complexes it was subsequently found that the complexes undergo a facile thermal decomposition process in which the NHC is lost as 2-methylimidazolium salt and the Pd is rednced to Pd(0) (Scheme 13.1) [15-17]. In ensuing studies investigating the reaction behavionr of a range of hydrocarbyl Pd and Ni carbene complexes, it was found that the decomposition reaction is ubiquitous. It occurs with varying ease, for mono-NHC, bis-NHC and donor functionalised-NHC complexes [16-23]. 

Imido dialkyl complexes, with tantalum, 5, 120 Imido-dicarbenes, with palladium, 8, 228-229 Imido groups, in Ru-Os mixed-metal clusters, 6, 1078 Imido hydrocarbyl complexes, with Re(VII), 5, 945 Imido ligands... 

Simpler p-halide eliminations occur from late transition metal catalysts for olefin polymerization (Equations 10.25 and 10.26). Reactions of the cationic palladium-alkyl complexes occur in a similar fashion to the reactions of the cationic group 4 complexes, despite the softer nature of these species. In this case, propylene and the metal chloride are formed. Even a neutral nickel-hydrocarbyl complex (the salicaldimine complex in Equation 10.26) undergoes reactions with vinyl chloride that involve insertion followed by P-chloride elimination. 

Abstract Square-planar palladium(II) and platinum(II) complexes with a high-lying filled d 2 orbital can act as metalloligands for Lewis-acidic metal centers such as d ° and s cations. This behavior is promoted by hard ligands such as a-bound hydrocarbyl ligands. A wide diversity of structural motifs based on this kind of donor-acceptor metal-metal bonds has been discovered in the last decades. This chapter reviews the coordination chemistry of metalloligands derived from alkyl, aryl, alkynyl, and carbene complexes of palladium(II) and platinum(II). The specific reactivity of the resulting bimetallic complexes is also addressed. 

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