Platinum complexes carbon-metalated phosphines

The additions of bimetallic reagents such as the silicon-metal and tin-metal compounds to the carbon-carbon multiple bonds have been extensively studied however, there are few reports concerning the metal-boron compounds as shown above. Miyaura and co-workers have examined the addition reaction of tetraafkoxydiboron to alkynes and found that only the platinum complexes such as Pt(PPh3)4 exhibited excellent catalytic activity (Scheme 24). Pd(PPh3)4 and Pd(OAc)2-isocyanide complexes, which have been the best catalysts for the silyl- and stannyhnetallation, were ineffective because their oxidative addition to palladium(0)-phosphine complexes is very slow. ... 

While hydrosilylation of 1-alkenes and HSiCl3 with platinum catalysts provides linear products (1-trichlorosilylalkanes), palladium chloride modified with phosphines gives products carrying the trichlorosilyl group at the secondary carbon. This is highly remarkable because all other metal complexes studied so far lead to 1-substituted products. This regioselectivity leads to the possibility to carry out asymmetric hydrosilylation. 

On mixed ligated complexes of palladium(II) and platinum(II), the cis coordination of the NHC and a phosphine ligand is thermodynamically favored. i27,261,262 Thermal isomerization was reported for tra i -[(NHC)2Cr(CO)4] (M = Cr, Mo) to the ds-complex. For [(NHC)2Mo(CO)4] this proceeds even in the solid state. A barrier of rotation due to a double-bond character of the metal-NHC bond could not be determined so far. This is in agreement with the single-bond character of the metal-carbon bond. Barriers of rotation determined so far are due to steric hindrance. 

The marked dependence of 7( P—M— P) on stereochemistry for complexes of the platinum group metals has been used in NMR spectroscopy for several years 109,115). For methyl or tert-h xty tertiary phosphines, when the two phosphines are mutually trans then a triplet pattern results, but if the two phosphines are mutually cis, then a doublet pattern results as a consequence of the spectrum being of the AA X X type and the dependence of V( P—M— P) on stereochemistry. Exactly the same behavior is found in NMR spectroscopy with the advantage that the technique is far more versatile and is not normally troubled by resolution problems. Thus for cr-[RhCl3(CO)(PBu"2Ph)2] triplet patterns have been observed for six of the eight different carbon atoms in the tertiary phosphine ligand 164). When —M—is... 

Olefin isomerization has been widely studied, mainly because it is a convenient tool for unravelling basic mechanisms involved in the interaction of olefins with metal atoms (10). The reaction is catalyzed by cobalt hydrocarbonyl, iron pentacarbonyl, rhodium chloride, palladium chloride, the platinum-tin complex, and by several phosphine complexes a review of this field has recently been published (12). Two types of mechanism have been visualized for this reaction. The first involves the preformation of a metal-hydrogen bond into which the olefin (probably already coordinated) inserts itself with the formation of a (j-bonded alkyl radical. On abstraction of a hydrogen atom from a diflFerent carbon atom, an isomerized olefin results. 

A theoretical study of the intermediates involved in the formation of phospha-propyne from pyrolysis of vinylphosphirane has led to a new route to phospha-alkynes. Thus, pyrolysis of trimethylsilyl(l-phosphiranyl)diazomethane has yielded MeaSiC = P, via an intermediate 1-phosphiranylmethylene . Regioselec-tivity in the [3 + 2] cycloaddition reaction between phosphaethyne and diazomethane has been studied by theoretical techniques , and further examples of reactions of this type described . Cycloaddition of phospha-alkynes with silylenes has also been reported. The primary phosphine 324 has been isolated from the addition of diethylphosphite to t-butylphosphaethyne. The chemistry of phospha-alkyne cyclotetramer systems has been reviewed and the first examples of platinum(II) complexes of such cage systems described. Aspects of the reactivity of coordinated phospha-alkynes have received further study, and a remarkable metal-mediated double reduction of t-butylphosphaethyne to the complexed fluorophosphine 325 described Phosphorus-carbon-aluminium cage structures have been isolated from the reactions of kinetically stable phospha-alkynes with trialkylaluminium compounds and new phosphaborane systems have been obtained from the reactions of phospha-alkynes with polyhedral boranes . Further studies of wo-phospha-alkyne coordination chemistry have appeared . The reactivity of the ion 326 has been explored. ... 

There are many carbonyl complexes of nickel, palladium, and platinum containing phosphines (L). Nickel compounds of the type [Ni(CO)4 j,Lj,] are readily formed in substitution reactions of [Ni(CO)4]. Palladium and platinum phosphine carbonyls are prepared by reactions of compounds of these metals with carbon monoxide in the presence of phosphines. The following complexes are known [M(CO)L3], [M3(C0)3L3], [M3(C0)3L4], [Pt(CO)2L2] and [M4(CO)5L4] (M = Pd, Pt). Trinuclear platinum compounds resist oxidation. 

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