Platinum phosphorus ligand

Platinum complexes with chiral phosphorus ligands have been extensively used in asymmetric hydroformylation. In most cases, styrene has been used as the substrate to evaluate the efficiency of the catalyst systems. In addition, styrere was of interest as a model intermediate in the synthesis of arylpropionic acids, a family of anti-inflammatory drugs.308,309 Until 1993 the best enantio-selectivities in asymmetric hydroformylation were provided by platinum complexes, although the activities and regioselectivities were, in many cases, far from the obtained for rhodium catalysts. A report on asymmetric carbonylation was published in 1993.310 Two reviews dedicated to asymmetric hydroformylation, which appeared in 1995, include the most important studies and results on platinum-catalogued asymmetric hydroformylation.80,81 A report appeared in 1999 about hydrocarbonylation of carbon-carbon double bonds catalyzed by Ptn complexes, including a proposal for a mechanism for this process.311... 

According to reaction (a) mixed substituted platinum(0)complexes of the hitherto unknown type Ptl L1 and PtLL 2 (where L and L are phosphorus ligands) can be isolated and characterized by nmr spectroscopy. Instead of Ph3P other R3P derivatives and Ph3As can be used. Complex D is very labile. IR data give evidence for a a-coordination of the CS2ligands. With the double ylide RR N-P(S)=NR (reaction (c) ) the four-membered chelate complex E with pentavalent phosphorus of coordination number four is formed. Compound F is an example of the well characterized alkyne complexes (here with the phospha(III)azene ligand L). 

The two metals that have been found to give encouraging conversions and selectivities for the hydroformylation of styrene are platinum and rhodium. The platinum-based catalytic system uses tin chloride as a promoter. It also uses triethyl orthoformate as a scavenger that reacts with the aldehyde to form the acetal. By removing it as soon as it is formed, any further degradative reactions of the aldehyde are avoided. The chirality in these reactions is induced by the use of optically active phosphorus ligands. With the best platinum catalyst, branched and linear aldehydes are produced in about equal proportion, but the former has an e.e. of >96%. 

With respect to platinum group metals, the phosphorus ligands behave as strong <7-donors rather than w-acceptors (cf, 19). 

Chemical shifts in the palladium (127) and platinum (131) mono-(hexafluoroacetone) complexes [256] are almost independent of the metal or of the other ligands, and very similar values are reported for the hexafluoroisopropylidineimine complex [257]. (131) The difference between the coupling of the CF3 groups to phosphorus ligands in the cis and trans positions, however, is notably larger for the platinum complexes than for those of palladium. 

Platinum(II)-phosphorus distances in phosphine and phosphite complexes are usually between 2.2 and 2.4 A. The distances are affected by the ligand trans to phosphorus in the square plane. For a complete listing of platinum-phosphorus distances in such structures the reader is directed to Molecular Structures and Dimensions for structures from 1935-1976, and to the BIDICS series for structures published up through 1981. A list of representative structures and Pt—P bond distances is shown in Table 7. The Pt—Cl distance of 2.344(2) A in cis-PtCl2(PEt3) P(OPh)3 for the chloride trans to P(OPh)3 is shorter than that (2.355(2) A) for the chloride trans to PEts, implying a weaker trans influence of P(OPh)3 than of PEt3. ... 

A related example concerns a platinum complex with phosphine and thiolate ligands that reacts via activation of a C6Fs substituent on phosphorus to couple a phosphorus ligand to a sulfur ligand forming a PtSCCP metallacycle. ... 

Paulusse JMJ, Huijbers JPJ, Sijbesma FkP. Reversible, high molecular weight palladium and platinum coordination polymers based on phosphorus ligands. Macromolecules. 2005 38 6290-6298. 

---