Bridged by dppm or Related Ligands

The chemistry of complexes containing dppm or related bifunctional ligands has flourished over the last 15 years. A number of articles reviewing this area have appeared 41-44), and a report describing the development of tripalladium and triplatinum systems bridged by dppm ligands has been published recently 45). We concentrate on diplatinum species here. 

Molecular structure of [Pt2(/ -dppm)3] illustrating the manxane structure. [Reproduced with permission from Manojlovic-Muir et al. (46)  

Platinum-Platinum Bond Distances in dppm-BRiDCED Platinum(I) Dimers 

A versatile approach to dppm-bridged platinum(II) species is via i -dppm intermediates. A series of equilibrium constants has been established for the process 

Whether the cis,cis or trans.trans isomer, or the corresponding monomeric species, is favored thermodynamically has been shown to depend on the steric requirements of the ligands involved. Increasing steric bulk favors monomeric species and is primarily responsible for determining the ground state conformations of the dimeric complexes. Thus, dppm, depm, and dippm (bis(diisopropylphosphino)methane) form monomeric dichlorides. On the other hand, dmpm, dtbpm (Bu HPCHjPHBu ), 

Isolation of the neutral, face-to-face dimers with dmpm, but the ionic, A-frame species with dppm, may be rationalized in terms of steric congestion. Ionization of the halide diminishes the crowding in the molecule, and this becomes more important for the laiger dppm ligand (90). 

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The synthesis of [(cod)PtBr(mes)] has been described it, and the related [PtR(Cl)(cod)] (R = Me, Et, Ph) react with two equivalents of dppm to give [PtR(Ti -dppm)(dppm)]+ or with one equivalent to give [Pt2R2()i-Cl)( i-dppm)2] ". The former can be used to make unsymmetrical dimers with different R groups by reaction with [PtR (Cl)(cod)] the halide from this complex becomes the bridging ligand. Mixed Pd-Pt complexes were also prepared.527,528 Thg complex [Pt2(p-S)(p-dppm)(q -dppm)2] can be used as a tridentate ligand towards [PtR(Cl)(cod)] (R = Me,... 

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