Olefins, complexes with platinum coordination compounds

Some attempts which I had made in 1946 to obtain PtPh2 or [PtPhJ from the reaction of phenylmagnesium bromide with [ PtCl2(C2H4)2 2] in ether had yielded biphenyl as the only pure solid product, and this served to confirm in my mind the belief that transition metals had no normal organometallic chemistry. I decided then to concentrate on the platinum(II)-olefin complexes. The first question was whether the olefin-metal bond used the d electrons normally involved in the oxidation of platinum(II) to platinum(IV) (valence d electrons) to bind the olefin, as required by such structures as (I), or whether, as was then generally believed, they were olefin coordination compounds formed independently of the presence of d electrons, even by Main Group element ions. 

Complexes of Pt can be tetrahedral, planar three-coordinate, or hnear two-coordinate. Soft ligands and n-acceptor ligands are required to stabilize this low oxidation state. Acetylenes ([Pt(/ -PhC=CPh)2]), olefines (([Pt() -PhCH=CH2)3)]), and especially phosphines are the most common ligands found in zerovalent complexes of platinum. Compounds with mixed ligands, including p-block elements donor ligands, are also known. 

Several compounds analogous to IV have been reported, and X-ray crystallographic studies have established that in each case the coordination environment at platinum is similar to that in Zeise s salt, e.g., square-planar platinum coordination by three chlorides and the olefin tf-system ). We have prepared complexes having structure IV by the direct reaction of the N-substituted allyl amine with potassium tetrachloroplatinite in acidic aqueous solution. Analytical data establish the formulation, and infrared spectra demonstrate that the olefin is coordinated to platinum. 

From a practical point of view, isocyanates, together with carbamates and ureas (Chapter 3), are the most important organic products discussed in this book. Their synthesis from nitroarenes has indeed been the subject of many patents. There are also limited examples of aliphatic isocyanates obtained by this route. Organic mono- and diisocyanates may be prepared in a continues liquid phase method by treating the appropriate amine with phosgene. However, the reaction is rather complex [6] and, besides the use of the dangerous phosgene, the formation of the corrosive hydrochloric acid creates several problems. Aliphatic isocyanates can also be obtained from olefins with isocyanate ion in the presence of a salt of a coordination compound of palladium or platinum [7], from olefins with isocyanic acid in the vapour phase over Pt/ALOs [8], and from formamides, by oxidation over a silver catalyst [9]. Apparently only the last reaction seems to have some potential practical applications [10]. 

Potassium trichloro(ethene)platinate(II), also known as Zeise s salt, has the formula K[PtCl3(C2H4)]H20 and contains rj -ethylene ligand. The compound is a yeUow-coloured coordination complex that is stable in air. The platinum atom has a square planar geometry. While reacting K2PtCl4 with ethanol in 1827, a Danish chemist Zeise synthesized this metal olefin complex containing a platinum-bound ethylene moiety, which incidentally represented the first metal—olefin complex. 

Divalent and tetravalent Pt probably form as many complexes as any other metal. The platinum(II) complexes are numerous with IV. S, halogens, and C. The letranitritoplatinum complexes are soluble in basic solution. Tetranitntoplatinum(II) ion is formed when a solution of plat-inum(II) chloride is boiled, at about neutral pH, with an excess of NaNO f. The ammonium salt may explode when heated. Generally, platinum-metal nitrites should be destroyed in solution. They never should be heated in the dry form. Pladnum(II) complexes most often have a coordination number of 4. Many compounds have been prepared with olefins, cyanides, nitriles, halides, isonitnles, amines, phosphines, arsines, and nitro compounds. 

Laboratory in Oxford, and Geoffrey Ozin at the University of Toronto in the early 1970s. With the metal atom cocondensation technique (which as described in Chaps. 6 and 7 was also used to prepare a series of zerovalent arene and olefin metal complexes), they reported simultaneously that the elusive palladium and platinum tetracarbonyls, Pd(CO)4 and Pt(CO)4, as well as the coordinatively unsaturated fragments M(CO)3, M(CO)2, and M(CO) (M = Pd, Pt) were formed by cocondensation reactions of Pd and Pt atoms with CO in inert gas matrices at 4-10 K [119-122]. The comparison of the CO bond stretching force constants for Pd(CO)ra and Pt(CO)ra (n - 1-4) revealed that, in analogy to Ni(CO) , the most stable compounds were the tetracarbonyls. In a xenon matrix, Pd(CO)4 existed up to about 80 K [120]. Ozin s group as well as others... 

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