Alkyls platinum

Table 3.11 Bond lengths (A) in palladium and platinum alkyls and aryls M(PR3)2R X...

The structures of the series trans-Pt(PMePh2)2 RC1 (R = Me, CF2CF3) show Pt-C bonds of 2.081 and 2.013 A, respectively, with the electron-withdrawing fluoroalkyl leading to a shorter and stronger bond. (Data for some other platinum alkyls are discussed in section 3.8.10.)... 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

At this point it should be noted that this mechanism is unexpected. Simple platinum alkyls decompose by 3-elimination whenever possible and there are no well-established examples of a-elimination [10]. All previous studies have indicated that metallacyclobutanes decompose by 3-elimination, even for tantalum and titanium derivatives for which a-elimination is a frequent mechanism for decomposition of the simple alkyls [11, 12]. There is even a labelling study which appears to prove the 3-elimination mechanism for decomposition of platinacyclobutanes (equation 3) [13]. 

Many transition metal alkyls react with carbon monoxide to give acyl compounds. In all these cases the acyl derivatives can be detected at least by infrared methods and in most cases isolated. Molybdenum, manganese, rhenium, iron, cobalt, rhodium, nickel, palladium, and platinum alkyls, Grignard reagents, and boranes, all react with carbon monoxide, and one can explain the products from these on the basis of carbon monoxide inserting into the metal alkyl. 

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

Alkene complexes of platinum(O) react with strong acids to undergo protonation at th< alkene and yield the alkyl complex (equation 263).803 Since platinum alkyl complexes having n< electron-withdrawing groups on carbon are frequently unstable to electrophiles, the products o HX on platinum(O) alkene complexes are often dihaloplatinum(II) complexes (equatioi 264). 

S-bonded alkyl and aryl sulfinato complexes can be prepared by the reaction of sulfonyl chlorides with Pt(C2H4)(PPh3)2,1633 the phase-catalyzed reaction of PtCl with NaS02R, 4 or the insertion of S02 into a platinum-alkyl bond1635 as shown in equations (481)-(483). When PtCl(S02R)L2 is treated with silver ion the 0,0 -bonded chelate complex (173) is formed (equation 484). 

Attempts to find an Sh2 chain reaction between a platinum alkyl and a thiol or disulfide. 

Nucleophilic addition (see Nucleophilic Addition Rules for Predicting Direction) of the hgands represents a major methodology for organometalhc functional transformation. In order to discern how alkane functionahzation fakes place in aqueous PfP systems, a water-soluble platinum alkyl, [PtCl5(CH2R)]2 (R = H, CH2OH), is allowed to react with chloride and water. Both kinetics and inversion of stereochemistry support an Sn2 mechanism. Treatment... 

The X-ray diffractometric studyof a product resulting from insertion of an alkyl-isocyanide into a platinum-alkyl bond has shown the compound to have the expected square-planar geometry with a Pt—C bond distance of 2.027(11) A. 

Various other compounds containing metal alkyl bonds have been studied by He(I) P.E.S., and in most cases reasonable assignments of the M—C ionization have proved possible. In the case of some platinum alkyls, only a preliminary communication has appeared with no spectra or evidence for the assignments given, so these must be regarded as tentative30). 

In the case of propane it is necessary to take into account the possibility of the formation of the n- and i-propyl platinum complexes. An analysis of deuteropropane distribution makes it possible to determine the relative rates of platinum(II) reactions with primary and secondary carbon atoms. For this purpose the distribution of deuteropropanes in the case of platinum alkylation with n-PrHgBr and -prHgBr was investigated. The distribution of the deuteropropanes obtained by the H-D exchange of propane coincides with that detected for n-PrPt- and f-PrPt-derivatives if we accept that they are initially formed with a relative probability of 0.75 and 0.25, respectively. Taking into consideration that the propane molecule contains six primary and two secondary C-H bonds, it may be concluded that the selectivity... 

Chlorohydridobis(trialkylphosphine)pIatinum(II) complexes are useful as precursors to a variety of platinum hydrides " and platinum alkyls,as... 

Cleavage of the C-C bond to the 3-carbon of late-metal-alkyl complexes is slower and less common than that of d early metal complexes. However, a few examples of 3-aU yl elimination from late metal complexes are known. The reversible intramolecular insertion of an olefin into the platinum-alkyl complex described in Chapter 9 involves an early example of 3-alkyl elimination from a late-metal-alkyl complex. In addition, mild 3-aIkyl elimination has been reported to occur from a ruthenacylobutane complex. In this case the product is a stable alkyl allyl species. - ... 

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. ... 

In 16e complexes, a 2e site is usually available, except for Pd(II), and especially for Pt(II), which tend to avoid the 18e configuration. Yamamoto found that frani-[PdL2Et2] complexes (L = 3° phosphine), tend to decompose by reductive elimination via an 18e transition state, but Whitesides found that phosphine dissociation is required for p elimination of the corresponding platinum alkyls [PtL2Bu2] (7.7). The related metalacycle 7.8 -eliminates 10 -fold more slowly than 7.7, presumably because a coplanar M—C—C—H arrangement is harder to achieve ... 

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