PLATINUM AMIDES FROM PLATINUM NITRILES - X-RAY CRYSTAL-STRUCTURES OF THE UNBRIDGED DINUCLEAR COMPOUNDS BIS[BIS(1-IMINO-1-HYDROXY-2,2-DIMETHYLPROPANE)DICHLOROPLATINUM(II)] AND BIS[BIS(1-IMINO-1-HYDROXY-2,2-DIMETHYLPROPANE)(1-AMINO-1-OXO-2,2-DIMETHYLPROPANE)-DICHLOROPLATINUM(II)]

Mono- and bisnitrile platinum complexes, [PtCl3(NCR)]- and cis- and trans-[PtCl2(NCR)2] (R = Bu(t), Me and Ph), hydrolyze to amidate amide and mixed amide-nitrile complexes. The amide ligands generally adopt the enol tautomeric form and coordinate to platinum through nitrogen. The presence of two amides cis to one another plays a critical role in favoring the association of platinum units in dimers. For example, molecules of cis-PtCl2{HN=C-(OH)But}2]2, 7b, comprise two monomeric units, placed face to face, with a Pt-Pt distance of 3.165(l) A and four interplanar N-H...Cl hydrogen bonds. Although hydrogen bonding interactions would place the dimer in the eclipsed conformation, the compound adopts the staggered conformation which minimizes interligand steric interactions allowing a closer approach of the two platinum subunits. The driving force to shortening the intermetallic distance stems from a direct intermetallic bonding interaction. Addition of two extra amides to axial sites of 7b gave [PtCl2{HN=C(OH)Bu(t)}2{H2NC(=O)Bu(t)}]2, 7c. The axial amides differ from the equatorial ones, in both tautomeric form (keto instead of enol) and donor atom (oxygen instead of nitrogen). In spite of a very long Pt-O distance [3.229(5) angstrom] the axial coordination causes a considerable lengthening of the intermetallic distance (0.23 angstrom) and, furthermore, conversion from the staggered to the eclipsed conformation. The solution chemistry of both 7b and 7c is in accord with their dimeric structure. A fast rate of proton exchange, between the hydroxyl group of the amide ligands and water present in the solvent, was observed whenever two amide ligands are cis to one another. Such an exchange process could be favored by the hydrogen bonding interaction of the two cis amides with a molecule of water. Mixed amide nitrile complexes have also been prepared; one trans- [PtCl2{HN=C(OH)Bu(t)}(NCBu(t))] proved to be the complex previously formulated as a platinum(IV) dichlorobisamidate derivative having the two amidate ligands in different tautomeric forms. The structure of 7b.C2H4Cl2 and 7c have been solved by single-crystal X-ray diffraction. 7b crystallizes as 1,2-dichloroethane solvate (1:1) in the space group P1BAR (n-degrees 2) with a = 11.292(3), b = 13.618(3), c = 14.069(4) angstrom, alpha = 62.12(2), beta = 83.58(2), gamma = 76.47(2)degrees, V = 1859(1) angstrom3, Z = 2. 7c crystallizes in the space group P1BAR (n-degrees 2) with a = 10.279(l), b = 10.772(1), c = 11.099(3) angstrom, alpha = 90.66(1), beta = 89.58(1), gamma = 114.27(1)degrees, V = 1120(1) angstrom3, Z = 1.