Trans-isomers platinum complexes

Alkenes which have no symmetry planes perpendicular to the plane of the double bond such as Pmr-butene-2 or propene can coordinate to platinum in two enantiomorphous ways (77) and (78). If an optically active ligand is also bound to platinum(H), then two diastereoisomers are found which can be separated by fractional crystallization657,658 or by HPLC.659 Both cis and trans isomers of complexes PtCl(N—0)(alkene) have beenprepared, where N—O is an anion derived from an amino add (equations 235a and 235b).660-664 Epimerization cannot occur by simple rotation of the alkene about its bond axis, but only by a mechanism involving cleavage of the platinum(II)-alkene bond. 

For complexes like PtL2X2 (X = halogen L = NH3, PR3, etc.) where cis-and trans-isomers exist, the trans-isomer is usually thermodynamically more stable. The c/s-isomer may be formed first in a reaction and, in the case of platinum, may be relatively inert to substitution. (Thermodynamic data are relatively scarce trans-Pt(NH3)2Cl2 is some 13kJmol-1 more stable than the cis-isomer.)... 

C20-0004. Platinum forms a large collection of square planar complexes. Draw ball-and-stick models similar to those in Example for the cis and trans Isomers of [Pt (NH3)2 CI2 ]. 

The affinity of platinum(II) for N-donor ligands is well established. There are numerous examples in the literature of mono-, di-, and trinuclear platinum(II)-ammine and alkylamine complexes, most of which are structural analogues of the anticancer agent, mplatin (cis- PtCl2(NH3)2]), and the corresponding trans isomer. Selected novel complexes and synthetic methods are presented below. 

Tertiary phosphine complexes of platinum and palladium M(PR3)2X2 are important [95]. The cis- and trans-isomers are readily obtained for platinum,... 

Isomerization involving a square planar complex is also known. Because of the trans effect, it is easier to synthesize the trans isomer of many complexes than it is to prepare the cis complex. The following reactions lead to the formation of an unusual platinum complex ... 

Heretofore, the most common method for the preparation of the useful platinum(II) complexes of the type [PtCl2L3], where L is a tertiary phosphine, consisted of the reaction between potassium tetrachloroplatinate(II) and tertiary phosphines.1 When trialkylphosphines are used, the reaction usually leads to a mixture of cis- and trans isomers,2 3 and when triaiylphosphines are employed4 only the cis isomers are obtained. The preparation of pure trans complexes by a simple, convenient procedure is highly desirable. 

In the same way, the existence of two isomers, yellow and orange, of Pt(NH3)2Cl2 showed that these complexes are square planar, rather than tetrahedral (Fig. 13.2) the yellow one has no electric dipole moment and therefore is the trans isomer, whereas the orange does and is cis. A tetrahedral Pt(NH3)2Cl2 would have just one isomer (with a dipole moment). Four-coordinate complexes of platinum(II), palladium(II), and gold(III) are virtually always square planar, but tetrahedral complexes such as the purple... 

The trinuclear complex trans-Pt[Mo(CO)3( /5-C5H5)]2(PhCN)2 is prepared by the reaction of two equivalents of sodium carbonylmetallate with the square planar platinum(II) complex PtCl2(PhCN)2.3 Both cis and trans isomers afford the trans trinuclear chain complex. The lability of the benzonitrile ligand in the latter can be used advantageously for cluster synthesis this will be described in the next section. 

Green Salt. The two salts are also so-called polymerization isomers of the cis and trans isomers of the dichlorodiammine complexes of the corresponding metals, which for platinum are cis- and fra/2s-[PtCl2(NH3)2] (see Section 1.1.2.8). 

Strukul and co workers recently prepared a series of cis and trans isomers of the platinum- t-butyl peroxide complexes Pt(R)(OOBu )L2 (R = CF3, Ph, etc. L = tertiary phosphine). The X-ray crystal structure of the franx-[Pt(Ph)(OOBu )(PPh5)2] (88) revealed a square-planar arrangement with... 

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