Azametallacycles from Ag(I)- or Cu(II)-Promoted Coupling Reactions of Dialkylcyanamides with Oximes at Pt(II)

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Abstract
The dialkylcyanamide complexes cis-[PtCl(NCNR2)(PPh3)2][BF4] 1 and cis-[Pt(NCNR2)2(PPh3)2][BF4]22 (R = Me or Et) have been prepared by treatment of a CH2Cl2 solution of cis-[PtCl2(PPh3)2] with the appropriate dialkylcyanamide and one or two equivalents of Ag[BF4], respectively. Compounds 2 can also be obtained from 1 by a similar procedure. Their reaction with oximes, HONCR‘R‘ ‘ (R‘R‘ ‘ = Me2 or C4H8), in CH2Cl2 and in the presence of Ag[BF4] or Cu(CH3COO)2, leads to the novel type of azametallacycles 4 upon an unprecedented coupling of the organocyanamides with oximes, in a process that proceeds via the mixed oxime−organocyanamide species cis-[Pt(NCNR2)(HONCR‘R‘ ‘)(PPh3)2][BF4]23, and is catalyzed by either Ag+ or Cu2+ which activate the ligating organocyanamide by Lewis acid addition to the amide group. In contrast, in the organonitrile complexes cis-[Pt(NCR)2(PPh3)2][BF4]25 (R = C6H4OMe-4 or Et), obtained in a similar way as 2 (but by using NCR instead of the cyanamide), the ligating NCR is not activated by the Lewis acid and does not couple with the oximes. The spectroscopic properties of those complexes are reported along with the molecular structures of 2b (R = Et), 4a1 (R = Me, R‘R‘ ‘ = Me2), and 4b1 (R = Et, R‘R‘ ‘ = Me2), as established by X-ray crystallography which indicates that in the former complex the amide-N-atoms are trigonal planar, whereas in the latter (4a1 and 4b1) the five-membered rings are planar with a localized NC double bond (imine group derived from the cyanamide) and the exocyclic amide and alkylidene groups (in 4b1) are involved in two intramolecular H-bonds to the oxygen atom of the ring.

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