MECHANISTIC AND STEREOCHEMICAL INVESTIGATION OF IMINO ETHERS FORMED BY ALCOHOLYSIS OF COORDINATED NITRILES - X-RAY CRYSTAL-STRUCTURES OF CIS-BIS(1-IMINO-1-METHOXYETHANE)DICHLOROPLATINUM(II) AND TRANS-BIS(1-IMINO-1-METHOXYETHANE)DICHLOROPLATINUM(II)

Addition of alcohols (HOR') to the coordinated nitriles (NCR) in the platinum complexes [PtCl3(NCR)](-) and cis-and trans-[PtCl2(NCR)(2)] (R = Me, Pt, Ph, Bu(1) takes place readily under basic conditions. The Z isomer, corresponding to a trans addition of the alcohol to the C=N triple bond, is the first reaction product, subsequently undergoing isomerization to the E form. An increase of the steric bulk of the R group stabilizes the Z isomer with respect to the E isomer; in contrast, an increase of the steric bulk of the R' group stabilizes the E over the Z isomer. The structures of trans- and cis-[PtCl2{E-HN=C(OMe)Me}(2)] (5EE and 9EE, respectively) have been solved by single-crystal X-ray diffraction. 5EE crystallizes in the space group P $($) over bar$$ 1 (No. 2) with a = 8.491(6) Angstrom, b = 8.603(2) Angstrom, c = 8.973(2) Angstrom, alpha = 75.56(1)degrees, beta = 67.52(2)degrees, gamma = 85.62(2)degrees, V = 586.4(2) Angstrom(3), and Z = 2. 9EE crystallizes in the space group C2/c (No. 15) with a = 15.854(3) Angstrom, b = 8.123(2) Angstrom, c = 9.471(2) Angstrom, beta 93.72(3)degrees, V = 1217.1(4) Angstrom(3), and Z = 4. In each complex, the Pt atom is linked to two Cl- anions and two imino ether N atoms, the coordination geometry is strictly planar, and the Pt-Cl and Pt-N bond distances have normal values. An unexpected feature resulting from the crystallographic data was the ''quasi-planarity'' of the imino ether moiety and electron charge delocalization over the N-C-O moiety. As a consequence, all the groups attached to the N-C-O skeleton share the same plane, causing considerable steric strain, as indicated by deviations (5 degrees or even more) of some bond angles from canonical values.