Alkylplatinum complexes

On the other hand, H—Pt(ll) complexes are the only group VIll transition metal species for which the anti-Markownikoff insertion of 1-olefins does not clearly prevail 74-76) Thus, rrans[HPt (acetone) (PR3)2]" PF6 [PR3 = CH3P(C6H5)2] inserts pro-pene and butene-1 giving n-propyl- and n-butylplatinum(Il) complexes Attempts to prepare sec-alkylplatinum compounds by an independent route resulted in the formation of the platinum-hydiido bond It was concluded that sec-alkylplatinum complexes are generally unstable. A reason for this behavior of Pt(II), which evidently contrasts with Co(I), Ni(II), Rh(III), Ir(III), and Pd(II) (Table 6) is not known. 

The aminometallation reaction is of special relevance to the key step involved in metal-catalyzed amination of alkenes and alkynes [4b,d,41]. The reversible attack of aliphatic amines at the monoalkene ligand shown in Eq. 8.6 may proceed in stereospecific trans addition and elimination [42]. For example, diethylamine was reacted with 1-butene, which coordinated to Pt using only one enantioface of the olefin ((S)-l-butene-Pt bond) (Scheme 8.24) [42a]. Alkylplatinum complex thus formed was subjected to acidic work-up to give optically active amine salt having the S-configuration at the asymmetric carbon. This result unambiguously demon-... 

Most of the preparative reactions of arylplatinum complexes, such as oxidative addition of organic halides, trans-metallation, and exchange of the auxiliary ligands, are common to those of alkylplatinum complexes. Aromatic C-H bond activation promoted by Pt(0) and Pt(n) complexes is the unique preparation method of arylplatinum complexes. Cationic methylplatinum(ll) complexes with A -ligands promote C-H activation of aromatic hydrocarbons to form cationic arylplatinum complexes, as mentioned in Section 8.08.3.1.3. 

A 4-methylanilidoplatinum(ii) complex with a PGP pincer-type ligand 615 reacts with acrylonitrile to form an alkylplatinum complex 616 via insertion of the G=G bond into the Pt-N bond (Scheme 86). Protonation of the complex releases A-(2-cyanoethyl)-4-methylaniline. The Pt complex also catalyzes addition of the aniline to the G=G bond of acrylonitrile. 

Alkylplatinum(IV) complexes exhibit considerable stability. When /ac-trimethyl-platinum(IV) species are heated, however, they eliminate ethane cleanly ... 

Oxidation and H-D exchange reactions apparently begin with the attack by the reactive form of the platinum(II) complex on the hydrocarbon molecule, RH, which results in the formation of an alkylplatinum(II) a-complex ... 

The CT-alkylplatinum(rV) complex reacts with nucleophiles X (H2O, CE) to afford an alcohol ROH and an alkyl chloride RCl, respectively. Complexes VI-5 and VII-7 (R = CH3 or CH2CH2OH) in aqueous solutions containing excess chloride have been shown [29b] to exist in equilibrium with X = 0.9 mol dm at 25 °C. Rapid dissociative exchange of ligand trans to the alkyl substituent was proposed to occur via the five-coordinate intermediate VII-6. 

Reductive Eliminations to Form C-X Bonds from Aryl and Alkylplatinum(IV) Complexes... 

Studies of the reaction in Equation 8.57 show that reductive elimination of methyl iodide from alkylplatinum iodide complexes also occurs after dissociation of halide. - These reductive eliminations occur between groups originally located in mutually trans positions. This result is consistent with the stereochemistry of the Pt(IV) product from oxidative addition by an S 2 path. The selectivity of the cationic intermediate for reductive... 

Following this oxidative addition, insertion of the olefin or alkyne occurs into the platinum-hydride bond to form an alkyl or vinyl hydride complex. The regioselectivity of the insertion step and the chemistry of the alkyl silyl complexes control the overall regioselectivity of the hydrosilylation of olefins. Recall that these platinum catalysts form terminal alkylsilane products. This regioselectivity indicates that insertions of terminal olefins occur in order to generate a linear alkylplatinum intermediate. Apparently, the insertions of styrene and acrylic acid derivatives into the platinum hydride in these catalysts occur with the same regiochemistry. 

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