Structural and mechanistic aspects of orthoplatination of acetophenone and benzaldehyde oximes by the platinum(II) sulfoxide and sulfide complexes [PtCl
2L
2] (
2, L = SOMe
2 (
a),
rac-SOMePh (
b),
R-SOMe(C
6H
4Me-4) (
c), andSMe
2 (
d)) to afford the corresponding platinacycles
cis-(
C,S)-[Pt
II(C
6H
3-2-CR'=NOH-5-R)Cl(L)] (
3, R, R' = H, Me)have been investigated. The reaction of acetophenone oxime with sulfoxide complex
2a in methanol solvent occursnoticeably faster than with sulfide complex
2d due to the fact that the sulfoxide is a much better platinum(II)leaving ligand than the sulfide. Evidence is presented that the orthoplatination is a multistep process. The formationof unreactive dichlorobis(
N-oxime)platinum(II) cations accounts for the rate retardation by excess acetophenoneoxime and suggests the importance of pseudocoordinatively unsaturated species for the C-H bond activation byPt
II. A comparative X-ray structural study of dimethyl sulfoxide platinacycle
3b (R = R' = Me) and its sulfideanalogue
3e (R = H, R' = Me), as well as of SOMePh complex
3c (R = H, R' = Me), indicated that they arestructurally similar and a sulfur ligand is coordinated in the cis position with respect to the
![](/images/gifchars/sigma.gif)
-bound phenyl carbon.The differences concern the Pt-S bond distance, which is notably longer in the sulfide complex
3e (2.2677(11) Å)as compared to that in sulfoxide complexes
3b (2.201(2)-2.215(2) Å) and
3c (2.2196(12) Å). Whereas the metalplane is practically a plane of symmetry in
3b due to the H-bonding between the sulfoxide oxygen and the protonat carbon ortho to the Pt-C bond, an
S-bonded methyl of SOMePh and SMe
2 is basically in the platinum(II) planein complexes
3c and
3e, respectively. There are intra- and intermolecular hydrogen bond networks in complex
3b.An interesting structural feature of complex
3c is that the two independent molecules in the asymmetric unit of thecrystal reveal an extremely short Pt-Pt contact of 3.337 Å.