Synthesis and study of monomeric and dimeric amidine complexes of nickel(II) and platinum(II). Crystal structure of bis(N,N′-diphenylbenzamidino)platinum(II), [Pt{PhNC(Ph)NPh}2]

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Abstract
Amidino-complexes, [{M[R′NC(R)NR′]2}n](M = Ni or Pt, R,R′= allyl or aryl), have been synthesised from NiCl2·0.3C4H10O2 or [Pt(PhCN)2Cl2]. The nickel complexes are dimeric in the solid state, but monomeric with chelating amidino-groups in solution. In contrast, for the platinum complexes, monomeric structures are indicated both in the solid state and solution. This is confirmed by the X-ray crystal structure determination of [Pt{PhNC(Ph)NPh}2][space group C2/c; unit-cell dimensions a= 25.413(7), b= 6.031(2), c= 20.586(3)Å, β= 109.89(2)°, and Z= 4], which shows both amidino-groups to have electron delocalisation [C–N 1.334(7), 1.340(7)Å] and to be symmetrically σ,σ-bonded through nitrogen atoms [Pt–N 2.040(5) and 2.025(5)Å]. The NCN skeletal angle [106.7(5)°] is similar to the angle in other related complexes. 13C N.m.r. studies of selected nickel and platinum complexes in solution are reported, and using the skeletal NCN 13C n.m.r. signal as the criterion of bond type, bidentate chelate and not bridging amidino-groups are shown to occur in solution, indicating monomeric species. Interestingly two sets of signals of equal intensity, but differing by only 1 p.p.m. are observed for [Ni2{PhNC(Ph)NPh}4] at 25 °C; amidino-structural types in solution are discussed.

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