Platinum amides from platinum nitriles: X-ray crystal structure of trans-dichloro-bis(1-imino-1-hydroxy-2,2-dimethylpropane)platinum(II)

The bisamide complex trans-[PtCl2{HN=C(OH)Bu-t}(2)] (1) has been prepared by hydrolysis of dichlorobis(tertiary-butylnitrile)platinum(II) and characterized via single crystal X-ray diffraction. The complex crystallizes in the Pbcn (No. 60) space group with the cell parameters a = 11.692(2), b = 22.214(3) and c = 18.515(2) Angstrom. Twelve complex molecules are present in the cell where triplets of them are stabilized by intermolecular hydrogen bonds involving N, Cl and O atoms. The structure has a strict similarity with that previously reported (D.B. Brown, R.D. Burbank and M.B. Robin, J. Am. Chem. Soc., 91 (1969) 2895) (the refinement, however, showed all the non-H atoms and converged to R = 0.0471 for 1003 observed reflections (F-0 > 6 sigma(F-0)) in the present work, whereas the structure analysis of the previous work did not show most of the atoms of a molecule in the asymmetric unit and the refinement converged to R = 0.107 for 2047 observed reflections) and proposed to contain, besides the yellow bisamide (I, similar to 70%), also a second yellow material (II, similar to 20%) and a third blue material (III, similar to 10%). The latter two had an analytical composition similar to that of the first one and were formulated as isomeric dichlorobis(amidato)platinum(IV) species, The mixed amidenitrile species trans-[PtCl2{HN=C(OH)Bu-t)}(N=CBut)] (2) has also been characterized. It has NMR signals coincident with those of compound II, its space group and cell parameters are very close to those of 1, and it has a tendency to cocrystallize with 1 in the molar ratio 2:1 in favor of 2, The geometry of the amide ligands in the enol tautomeric form appears to be ideal for favoring the face-to-face association of platinum units stabilized by interfacial hydrogen bonds. In the case of cis geometry (corresponding cis isomer of 1), platinum dimers with an intermetallic distance of 3.165(1) Angstrom were formed; in contrast, in the case of trans geometry (compound 1 presently investigated) platinum triplets with an intermetallic distance of 3.668(1) Angstrom were established. In both cases the preferred conformation is staggered and the shortest distance between platinum atoms in different dimers (cis isomer) or triplets (trans isomer) is in excess of 4.17 Angstrom. Therefore, a special role of the coordination geometry appears to be in determining the mode of association of platinum monomers in oligomers. (C) 1997 Elsevier Science S.A.