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

The dialkylcyanamide complexes cis-[PtCl(NCNR2)(PPh3)2][BF4] 1 and cis-[Pt(NCNR2)2(PPh3)2][BF4]2 2 (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, HONCR‘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)(HONCR‘R‘ ‘)(PPh3)2][BF4]2 3, 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]2 5 (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 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.

二烷基氰胺配合物顺式-[PtCl(NCNR₂)(PPh₃)₂][BF₄] 1 与顺式-[Pt(NCNR₂)₂(PPh₃)₂][BF₄]₂ 2（R=甲基（Me）或乙基（Et）），可分别通过将顺式-[PtCl₂(PPh₃)₂]的二氯甲烷(CH₂Cl₂)溶液与相应的二烷基氰胺，以及1或2当量的四氟硼酸银(Ag[BF₄])反应制得。化合物2亦可通过以类似方法处理1得到。该类配合物与肟HON=CR'R''（R'R''=二甲基（Me₂）或四亚甲基（C₄H₈））在二氯甲烷中、且存在四氟硼酸银或乙酸铜(Cu(CH₃COO)₂)时发生反应，经由前所未有的有机氰胺与肟的偶联过程，生成新型氮杂金属环化合物4；该反应的中间体为混合配体的肟-有机氰胺配合物cis-[Pt(NCNR₂)(HON=CR'R'')(PPh₃)₂][BF₄]₂ 3，且可被Ag+或Cu2+催化——这两种路易斯酸通过向酰胺基团发生路易斯酸加成来活化配位的有机氰胺。与之相对，采用类似制备2的方法（但以腈NCR替代氰胺）得到的有机腈配合物cis-[Pt(NCR)₂(PPh₃)₂][BF₄]₂ 5（R=对甲氧基苯基(C₆H₄OMe-4)或乙基（Et））中，配位的NCR并不会被路易斯酸活化，也无法与肟发生偶联反应。本研究报道了上述所有配合物的光谱性质，以及通过X射线晶体衍射(X-ray crystallography)确定的配合物2b（R=Et）、4a1（R=Me，R'R''=Me₂）和4b1（R=Et，R'R''=Me₂）的分子结构。结构分析结果显示：在配合物2b中，酰胺氮原子呈平面三角形配位构型；而在4a1与4b1中，五元环为平面结构，且存在定域化的N=C双键（该双键源自氰胺的亚胺基团）；此外，4b1中的环外酰胺与亚烷基基团，与环上氧原子形成了两个分子内氢键。