Metal-alkyne complexes platinum

The simplest alkyne complexes, the metal acetylenes, resemble those of ethylene. For example, there are analogues of Zeise s salt in which an acetylene molecule ts bound to platinum(l)) and occupies a position like that of ethylene in Zeise s salt. In addition, there are L,Pt(RC=CR) complexes that have structures paralleling that of LjWHjC CHj) (Fig. 15.24). For both of these PtfO) complexes, an approximate square planar arrangement around the metal is found. Alkynes are more electronegative than ulkenes and are therefore better it acceptors. Thus it is appropriate to view them as metal lacyclopropenes 79... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

As outlined in previous volumes, the chemistry of ylides coordinated to noble metals, particularly palladium, platinum and gold continues to attract most attention. Refluxing (dppm)palladium(II) dichloride [dppm = bis(diphenylphosphino)methane] with alkynes in mixtures of 1,2-dichloro-ethane/l,4-dioxane provides a novel route to palladium-bound alkenyl phosphorus ylide complexes (53) (Scheme 1)P The reaction represents the... 

New Applications of TCNE in Organometallic Chemistry, A. J. Fatiadi (1987). Selected reactions used in organometallic synthesis are reviewed. 311 references are given. Structure and bonding of metal-TCNE complexes as well as reactions of TCNE with main-group organometallics, with transition-metal complexes, with metal-coordinated alkenes and alkynes, and reactions of platinum-family complexes are discussed. 

Insertion into metal boryl bonds is represented by two examples described for a late and an early transition metal complexes. Platinum diboryl complexes react with alkynes to give the diborylated alkene (Scheme 6.61, a) [191]. A titanium(II) metallocene with a coordinated ethylene reacts with borane to give, via insertion of the alkene into a M-B bond and subsequent j6-H ehmination, a complex with a coordinated vinylborane (Scheme 6.61, b) [192]. Both processes can be made catalytic. 

The insertions of olefins into metal-silyl complexes is an important step in the hydrosi-lylation of olefins, and the insertions of olefins and alkynes into metal-boron bonds is likely to be part of the mechanism of the diborations and sUaborations of substrates containing C-C multiple bonds. Other reactions, such as the dehydrogenative sUylation of olefins can also involve this step. Several studies imply that the rhodium-catalyzed hydrosilylations of olefins occur by insertion of olefins into rhodium-silicon bonds, while side products from palladium- and platinum-catalyzed hydrosilylations are thought to form by insertion of olefins into the metal-sihcon bonds. In particular, vinylsilanes are thought to form by a sequence involving olefin insertion into the metal-silicon bond, followed by p-hydrogen elimination (Chapter 10) to form the metal-hydride and vinylsilane products. 

Cationic platinum(II) acetylene complexes react with a variety of nucleophiles. Chisholm and Clark showed that the reaction of methanol with coordinated disubsti-tuted acetylenes (generated in situ) affords trans u-bonded vinyl ether complexes (Equation 11.35). The trans stereochemistry of the cr-vinyl group of the product suggests that the nucleophilic attack occurs external to the metal and does not involve prior coordination of methanol, Reger has shown that stable cationic iron-alkyne complexes undergo reaction with a wide variety of nucleophiles to give stable cr-alkenyl complexes resulting from trans attack of the nucleophile on the coordinated acetylene (Equation 11.36). A variety... 

Very few rr-bonded alkyne complexes of palladium(ll) have been reported in recent years. Except for two examples of monomeric complexes, most of them are polymetallic derivatives where a metal alkynyl acts as a liquid, as discussed above for some Pd(0) derivatives. These complexes adopt interesting stmctures that conform to the types shown below. They have been synthesized by reaction of a metal alkynyl with [PdCl(7/ -C3H5)]2 or Pd(C6Fs)2(THF)2. Platinum alkynyl complexes are the most common ligand frame used, as shown in structures 76-79, but other metal alkynyls can play the same role, such as the Rh and Ir alkynyls depicted 80 and 81. The 7 -alkyne moieties bound to palladium are rotated out of the Pd-coordination plane. The angles of the vectors and the normal to the... 

The reactions of zerovalent platinum-alkyne complexes with adds have been studied by several groups (Barlex et ai, 1969 Mann et aU 1971 Tripathy and Roundhill, 1970 Kemmitt et al, 1973). When one equivalent of acid is employed, it is possible to isolate the vinyl derivatives. Nmr studies have generally indicated a cis arrangement about the double bond (Mann et ai, 1971), presumably resulting from initial protonation of the metal, followed by cis M—H addition. The yields for this first step were uniformly good. Shaw and co-workers have reported that addition to ter-... 

Few reports on the reactions of alkyne complexes with electrophiles other than protic acids have appeared. Bromine has been found to react with a few systems to afford vicinal dibromoalkenes [e.g., Eqs. (41) and (42)] (Kruerke and Hubei, 1961 Hiibel and Merenyi, 19M). These reactions may, in fact, involve bromine addition subsequent to oxidative release of the ligand from the metal. The platinum dicyanoacetylene complex behaves differently in forming a product in which addition has occurred but the complex has remained intact (McClure and Baddley, 1970). 

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. 

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