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Iminoacylation. 3. Formation of Platinum(IV)-Based Metallaligands Due to Facile One-End Addition of vic-Dioximes to Coordinated Organonitriles1-3

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posted on 05.01.2000, 00:00 by Vadim Yu. Kukushkin, Tatyana B. Pakhomova, Nadezhda A. Bokach, Gabriele Wagner, Maxim L. Kuznetsov, Markus Galanski, Armando J. L. Pombeiro
The reaction of vic-dioximes with the organonitrile platinum(IV) complexes trans-[PtCl4(RCN)2] (R = Me, CH2Ph, Ph, vic-dioxime = dimethylglyoxime; R = Me, vic-dioxime = cyclohexa-, cyclohepta-, and cyclooctanedione dioximes) proceeds rapidly under relatively mild conditions and affords products of one-end addition of the dioximes to the nitrile carbon, i.e. [PtCl4(NHC(R)ON{spacer}NOH)2] (16) (R = Me, CH2Ph, Ph, spacer = C(Me)C(Me) for dimethylglyoxime; R = Me, spacer = C{C4H8}C, C{C5H10}C, C{C6H12}C for the other dioximes), giving a novel type of metallaligand. All addition compounds were characterized by elemental analyses (C, H, N, Cl, Pt), FAB mass spectrometry, and IR and 1H, 13C{1H}, and 195Pt NMR spectroscopy. X-ray structure determination of the dimethylformamide bis-solvate [PtCl4(NHC(Me)ONC(Me)C(Me)NOH)2]·2DMF (1a) disclosed its overall trans geometry with the dimethylglyoxime part in anti configuration and the amidine one-end (rather than N,N-bidentate) coordination mode of the N-donor ligands. When a mixture of cis- and trans-[PtCl4(MeCN)2] in MeCN was treated with dimethylglyoxime, the formation of, correspondingly, cis- and trans-[PtCl4(NHC(Me)ONC(Me)C(Me)NOH)2] (1) was observed and cis-to-trans isomerization in DMSO-d6 solution was monitored by 1H, 2D [1H,15N] HMQC, and 195Pt NMR spectroscopies. Although performed ab initio calculations give evidence that the trans geometry is the favorable one for the iminoacylated species [PtCl4(ligand)2], the platinum(IV) complex [PtCl4(NHC(Me)ONC{C4H8}CNOH)2] (4) was isolated exclusively in cis configuration with the two metallaligand “arms” held together by intramolecular hydrogen bonding between the two peripheral OH groups, as it was proved by single-crystal X-ray diffractometry. The classic substitution products, e.g. [PtCl2(N,N-dioximato)2] (1215), are formed in the addition reaction as only byproducts in minor yield; two of them, [PtCl2(C7H11N2O2)2] (14) and [PtCl2(C8H13N2O2)2] (15), were structurally characterized. Complexes (1215) were also prepared by reaction of the vic-dioximes with [PtCl4L(Me2SO)] (L = Me2SO, MeCN), but monoximes (Me2CNOH, {C4H8}CNOH, {C5H10}CNOH, PhC(H)NOH, (OH)C6H4C(H)NOH) react differently adding to [PtCl4(MeCN)(Me2SO)] to give the corresponding iminoacylated products [PtCl4(NHC(Me)ONCRR‘)(Me2SO)] (711).