Silyl platinum complexes

The preparation of various platinum-silyl complexes, including a platinum(II), platinum(IV), and mixed-valence platinum(II)-(IV) species, has been described.59 The treatment of one equivalent of 1,2-disilylbenzene with [Pt(PEt3)3] in toluene solution at 0°C affords [Pt(C6H4Si2H4)-(PEt3)2] (25) as a white powder the use of excess 1,2-disilylbenzene in the reaction leads to the formation of various platinum(IV) derivatives. 

Metal chemical shifts have not found extensive use in relation to structural problems in catalysis. This is partially due to the relatively poor sensitivity of many (but not all) spin 1=1/2 metals. The most interesting exception concerns Pt, which is 33.7% abundant and possesses a relatively large magnetic moment. Platinum chemistry often serves as a model for the catalytically more useful palladium. Additionally, Pt NMR, has been used in connection with the hydrosilyla-tion and hydroformylation reactions. In the former area, Roy and Taylor [82] have prepared the catalysts Pt(SiCl2Me)2(l,5-COD) and [Pt()i-Cl)(SiCl2Me)(q -l,5-COD)]2 and used Pt methods (plus Si and NMR) to characterize these and related compounds. These represent the first stable alkene platinum silyl complexes and their reactions are thought to support the often-cited Chalk-Harrod hydrosilylation mechanism. 

Recently, a new class of platinum silyl complexes was reported (89-91). The complexes of type 49, formed from LPtfQH (L = bulky phosphine) and trialkylsilanes, are extremely efficient hydrosilation catalysts. Upon heating, 49 is converted into 50 via an ill-defined a-elimination process. In all examples of redistributions, the presence of at least one hydro-... 

Arii H, Takahashi M, Takahashi H, Mochida K, Kawashima T (2012) Formation of unique platinum-silyl complexes by the reactimis of a zero-valent platinum complex with various... 

Mono- and bis(silyl)platinum(II) complexes are believed to play important catalytic roles in hydrosilylation, dehydrocoupling, and double silylation reactions with disilanes and hydrosilanes. A stable, mono(silyl)platinum(II) complex has been prepared by the oxidative addition reaction of the sterically hindered, primary arylsilane 2,6-Mes2C6H3SiH3 (Mes = 2,4,6-trimethylbenzene) to the platinum(O) species [Pt(PPr3)3] in hexane solution at room temperature.133 The colorless product m-[PLl 1(2,6-Mes2C6II3(11 )2Si)(PPr3)2] (21) was isolated as the OPPr3 adduct, and its... 

In relation to the mechanistic proposal, an interesting reactivity of (boryl)(silyl)platinum(n) complex has been reported.223 The complex is prepared by the reaction of silylborane with Pt(cod)2 complex via oxidative addition (Scheme 46). The (boryl)(silyl)platinum complex undergoes insertion of alkynes at the B-Pt bond to give (/3-borylalkenyl)(silyl)platinum(n) complex in high yield. Importantly, the insertion takes place regioselectively, with Pt-G bond formation at the internal. -carbon atom. This result may indicate that the boron-transition metal bond is more prone to undergo insertion of unsaturated molecules. 

A platinum(H) complex has been prepared with a phosphine ligand chelated with a silyl. The complex (141) is formed by treating Pt(cod)2 with Ph2PCH2CH2SiHR R" (equation 423).1412 When R = R", racemic and meso diasteromers are formed in varying ratios consistent with asymmetric induction during stepwise chelation. The complexes can be used for asymmetric hydrosilylation.1413... 

Although it is now almost fifty years since Speier and his colleagues first announced the chloroplatinic acid-catalyzed hydrosilation of olefins, we are still far from complete control of the chemistry. A particular problem is the suppression of double bond migration. A solution of this problem will require a more detailed understanding of the factors affecting the relative rates of P-hydride elimination from an alkyl group and of the reductive elimination of Si-H from a platinum silyl hydride complex. Another factor which is poorly understood is suppression of the irreversible reduction of the platinum catalyst to Pt° metal. Both of these problems can greatly increase costs of production of certain products. 

Keywords Silyl Complexes / Platinum / Rhenium / Chelate / Heterobimetallics... 

Ishikawa found the Ni(PEt3)4-catalyzed silylation of aromatic compounds with 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene, providing the l-(di-ethylarylsilyl)-2-(diethylsilyl)benzene in high yields (Eq. 44) [89]. In the case of the reaction of mesitylene, interestingly, the sp3 C-H bond adds to the disilacy-clobutene, albeit in low yield (28% yield) [89]. Platinum(O) complexes are also applicable to this silylation reaction as the catalyst [90]. 

Siloxycyclopropanes are also opened by platinum(II) complexes such as Zeise s dimer. - While 1-aryl-1-siloxycyclopropanes are transformed into P-platinum ketone complexes, 2-alkyl-substituted siloxycyclopropanes are isomerized cleanly to allyl silyl ethers in good yields. The reaction is quite general and proceeds with catalytic amounts of Zeise s dimer (2-10mol%) in many different suitable solvents (chloroform, dichloromethane, ethyl acetate, ethers, benzene) at ambient temperature with 100% inversion of configuration at the siloxy carbon and provides only silyl ethers of 2-methylene alkanols without contamination of doublebond isomers. ... 

Keywords platinum complexes, silyl complexes, catalysis, exchange reactions... 

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