Platinum complexes alkyl transfer

Synthetic organic chemistry applications employing alkane C-H functionalizations are now well established. For example, alkanes can be oxidized to alkyl halides and alcohols by the Shilov system employing electrophilic platinum salts. Much of the Pt(ll)/Pt(rv) alkane activation chemistry discussed earlier has been based on Shilov chemistry. The mechanism has been investigated and is thought to involve the formation of a platinum(ll) alkyl complex, possibly via a (T-complex. The Pt(ll) complex is oxidized to Pt(iv) by electron transfer, and nucleophilic attack on the Pt(iv) intermediate yields the alkyl chloride or alcohol as well as regenerates the Pt(n) catalyst. This process is catalytic in Pt(ll), although a stoichiometric Pt(rv) oxidant is often required (Scheme 6).27,27l 2711... 

Platinum alkyl complexes can be prepared by alkyl transfer from a second alkyl transition metal complex. 

Organomercurials can also be used for the synthesis of alkyl complexes. Organomercurials have stable alkyl-mercury bonds, and the alkyl groups can be transferred to transition metal complexes (alkylation of the transition metal complexes). Thus diphenylmercury reacts with one equivalent of dichloroplat-inum complex to produce phenylmercuric chloride and monosubstituted platinum complex in good yield 73). 

The crystal structure of bis(NN-di-isobutyldithiocarbamato)nickel(ii). [Ni(S2-CNBu 2)2], shows that nickel is approximately square planar and co-ordinated by two symmetric bidentate ligands (Ni—S = 2.20 A) the ligand symmetry approximates to 2- The reduction mechanism of a series of nickel(ii) dithiocarbamates has been investigated in DMSO at the mercury electrode it is claimed to involve a dissociation to a nickel species which is more easily reduced than the nickel(ii) dithiocarbamate. An e.p.r. study of the reversible electrochemical reduction of nickel(ii) diethyldithio-carbamates in the presence of 2,2 -bipyridyl show that a bipy radical anion is formed initially. Ligand alkylation occurs when ao -dibromo-o-xylene is added to bis-(NiV-diethyldithiocarbamato)nickel(ii). The electron-transfer properties of 16 nickel(ii) dithiocarbamate complexes have been studied in acetone at a platinum electrode. Their oxidation is difficult and irreversible the overall process is ... 

It may be assumed, that the reaction of the chloroaquoplatinum(ll) complex with atkanes begins as oxidative addition, proceeds through a three-center transition state, and terminates by the synchronous formation of a platinum-carbon bond with elimination of a proton (which can be transferred to a molecule of water). A similar mechanism has been proposed [35a] for the cyclometalation of 8-alkylquinolines by palladium(II). It has also been suggested that the reverse process (the protolysis of the platinum-carbon bond in alkyl complexes) involves a three-center transition state [35b], and the concerted oxidative addition to Ir(I) complex has been proposed [35c]. 

Much less information has been gained on the oxidation of the Pt(II) alkyl to Pt(IV). In one elegant study, oxidation of the chloroplatinum-mettiyl complex by Pt-labeled Pt(IV) chloride formed a Pt(IV) methyl complex without Tt enrichment (Equation 18.14). This result shows that oxidation of the Pt(II) alkyl complexes by Pt(IV) occurs by transfer of chlorides from the Pt(IV) to the platinum alkyl complex, not by transfer of the alkyl group to the Pt(IV) center. ... 

---