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

Abstract

The dialkylcyanamide complexes cis-[PtCl(NCNR(2))(PPh(3))(2)][BF(4)] 1 and cis-[Pt(NCNR(2))(2)(PPh(3))(2)][BF(4)](2) 2 (R = Me or Et) have been prepared by treatment of a CH(2)Cl(2) solution of cis-[PtCl(2)(PPh(3))(2)] with the appropriate dialkylcyanamide and one or two equivalents of Ag[BF(4)], respectively. Compounds 2 can also be obtained from 1 by a similar procedure. Their reaction with oximes, HON=CR'R' ' (R'R' ' = Me(2) or C(4)H(8)), in CH(2)Cl(2) and in the presence of Ag[BF(4)] or Cu(CH(3)COO)(2), leads to the novel type of azametallacycles cis-[Pt(NH=C(ON=CR'R")-NR2)(PPh3)2][BF4]2 4 upon an unprecedented coupling of the organocyanamides with oximes, in a process that proceeds via the mixed oxime-organocyanamide species cis-[Pt(NCNR(2))(HON=CR'R' ')(PPh(3))(2)][BF(4)](2) 3, and is catalyzed by either Ag(+) or Cu(2+) which activate the ligating organocyanamide by Lewis acid addition to the amide group. In contrast, in the organonitrile complexes cis-[Pt(NCR)(2)(PPh(3))(2)][BF(4)](2) 5 (R = C(6)H(4)OMe-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' ' = Me(2)), and 4b1 (R = Et, R'R' ' = Me(2)), 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 N=C 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.

Highly Reactive NiII‐Bound Nitrile–Oxime Coupling Intermediates Stabilized by Substituting Conventional Nitriles with a Dialkylcyanamide

“…It was recognized earlier that in many instances ligated Alk 2 NCN compounds exhibit different behavior from the coordinated conventional nitriles RCN. These differences were recognized not only at the quantitative,17f,30 but also at the qualitative level2e,3a,3b,3e when conventional nitrile and dialkylcyanamide ligands react with the same reagent in different ways to give, consequently, different products. The distinctions in the reaction routes are accounted for by a special role of the NR 2 group in dialkylcyanamides.…”

Pop-the-Cork Strategy in Synthetic Utilization of Imines: Stabilization by Complexation and Activation via Liberation of the Ligated Species

“…Thus, imines with very close structural characteristics being ligated to a metal center can exhibit even the opposite reactivity modes, for example, stabilization vs activation toward hydrolysis. 2 Recently we (see reviews 3 ) and others 4 found explicit evidence that platinum group metals, [5][6][7][8][9] rhenium, 10 gold, 11a,b or silver 11c centers provide enormous stabilization of the potentially unstable imines RR′CdNH, and these ligands can be "stored" without changes in the coordinated form under normal conditions for a prolonged time. Moreover, it appears that the formation of imines is one of the major driving forces for some reactions, e.g., condensation of complexed ammonia with ketones, 11 reductions of oximes, 12 oxidative dehydration of amines (e.g., at Fe, 13 Ru, 14,15 Os, 16 Re, 17 and Pt 18 centers), and nucleophilic additions to metal-bound nitriles.…”

trans-Dichlorobis(piperidine-1-carbonitrile)platinum(II)

“…It has previously been observed that some push-pull nitrilecontaining complexes, in particular dialkylcyanamide metal species, display unusual reactivity patterns unknown for conventional RCN compounds (Bokach et al, 2003;Cunha et al, 2002;Ferreira et al, 2001;Guedes da Silva et al, 1997;Pombeiro et al, 1989). This difference, in view of our general interest in the reactions of metal-activated nitriles (Kukushkin et al, 2002;Kukushkin et al, 2005;Bokach et al, 2005), prompted us to verify some structural differences between push-pull and conventional nitrile species ligated to a Pt II centre.…”