Platinum tetrahalides

Addition of a boron-boron bond across a carbon-carbon triple bond is known for some 40 years since the finding that diboron tetrahalides add to alkenes and alkynes in the absence of catalysts.36 Although the reaction seemed to be potentially attractive, the instability of diboron tetrahalides was the critical drawback for the practical use in synthesis. In 1993, much more stable pinacol ester derivative of diboron was found to add to alkynes in the presence of platinum catalysts such as Pt(PPh3)4, Pt(CH2=CH2)(PPh3)2, and Pt(CO)2(PPh3)2 (Figure 1, Scheme 2).37,38 Other... 

Chlorofluoro compounds were electroreductivelv added to aldehydes to give the corresponding fluorinated alcohols (231) (equation 124)214. In this process platinum or lead are employed as the cathode, under constant-current conditions. The starting dihalides or trihalides (halogen = F, Cl or Br) can be prepared on an industrial scale by the reaction of the corresponding tri- or tetrahalide at a sacrificial anode (Zn, A1 or Mg)220. 

Platinum alone forms all 4 tetrahalides and these vary in colour from the light-brown Ptp4 to the very dark-brown PtLi- Ptp4 is obtained by the action of BrFs on PtCH at 200°C and is violently hydrolysed by water. The others are obtained directly from the elements, the chloride being recrystallizable from water but the bromide and iodide being more soluble in alcohol and in ether. The only other tetrahalide is the red Pdp4 which is similar to its platinum analogue. 

Dihalides of uncertain purity are prepared by the disproportionation of the trihalides. Alternate routes have also been reported. Swaroop and Flengas (549) prepared ZrCU of 95-99% purity by heating the trichloride and metallic zirconium at 675°C for 30-35 hours in an evacuated quartz tube lined with platinum foil. There is also a reference to the production of liquid dihalides by the reaction of the gaseous tetrahalides with loosely packed zirconium at 700°C for the chloride and 400°C for the bromide and iodide (270). The difluoride has been prepared (357) by the reaction of atomic hydrogen on thin layers of zirconium tetrafluoride at 350°C. New data on hafnium are lacking, although Corbett (542) has concluded that hafnium diiodide does not exist. 

In some cases the use of homoleptic solvento-complexes as starting materials in non-aqueous solvents involves a diversion fiom the common reaction pathway. The interaction between platinum(II) and palladium(II) complexes with potentially tetradentate thioether ligands,8-n Figure 4.2, has been studied. The reactions of the tetrahalide complexes [MX4P-, where M = Pt, Pd X = Cl, Br, I, with the thioether ligands in an ethanol-dichloromethane... 

---