X-ray structures of the first platinum complexes with Z configuration iminoether ligands: trans-dichlorobis(1-imino-1-methoxy-2,2 '-dimethylpropane)platinum(II) and trans-tetrachlorobis(1-imino-1-methoxy-2,2 '-dimethylpropane)platinum(IV)

摘要

Platinum complexes with Z configuration iminoether ligands (trans-[PtCl2{ HN=C(OMe)BUt}(2)], 1, and trans-[PtCl4-{HN=C(OMe)Bu-t}(2)], 2) have been structurally characterized for the first time. The nearly planar Pt-N-C-O-C chain, all atoms being in gauche conformation, brings the terminal Pt and C atoms very close to one another. The steric clash is released by considerably increasing the Pt-N-C, N-C-O, and C-O-C bond angles (133, 124, and 1210 for 1, respectively; 147, 129, and 1270 for 2, respectively), which are well above the expected values (1200 for Pt-N-C and N-C-O; less than 120degrees for C-O-C owing to the repulsive effect exerted by the lone pair of electrons on the oxygen atom). In the platinum(II) case the smaller increase of bond angles is accompanied by a greater value of the Pt-N-C-O torsion angle (27.3 and 15.6degrees for 1 and 2, respectively). The stabilization of the Z configuration, notwithstanding the steric clashes described above, has been achieved by a careful choice of the R substituent in the iminoether moiety (a bulky tert-buy group). The reactions of the platinum(IV) species (2) in basic and acidic conditions and with triphenylphosphine have been investigated. Bases and acids both interact with the coordinated ligand in such a way to weaken the coordinative bond and promote the release of the iminoether ligands. The phosphine promotes a ready and complete reduction of the platinum(IV) complex to the corresponding platinum(II) species (1). Compound 1 reacts with a stoichiometric amount of phosphine (1:1 molar ratio) to form cis-[PtCl2(PPh3){Z-HN=C(OMe)Bu-t}] and with excess phosphine to form [PtCl2(PPh3)(2)] and free iminoether. The latter two reactions leading to formation of a mixed phosphine/iminoether platinum species and to free iminoether, which can be used as a synthon for further organic transformations, can be of synthetic utility. [References: 30]