ORTHOMETALLATED AMIDINE COMPLEXES OF PALLADIUM, PLATINUM AND NICKEL(II) - CRYSTAL-STRUCTURE OF [PD(P-CH3C6H4NC-(CH3)NHC6H3CH3-P)(ETA-5-C5H5)]

In aqueous methanol K2[MCl4] (M = Pd or Pt) react with formamidines, acetamidines and benzamidines [R'NHC(R)NR'] having aryl substituents to form sparingly soluble orthometallated complexes. N,N'-Diaryl-formamidines and -acetamidines form six-membered metallocycles, [{M[R'NC(R)NH-C6H3R"]Cl}n], whereas for N,N'-diarylbenzamidines having both N- and C-aryl substituents five-membered metallocycles [{M[R'NC(C6H4)NHR']Cl}n] are also produced. Related complexes form from the reactions of N-p-tolylacetamide and acetanilide with K2[PdCl4]. The adducts [M{R'NC(R)-NHR'}Cl2] on heating in solution also yield orthometallated complexes. The chloride bridges of the oligomeric/polymeric materials are cleaved to give pyridine and dimethyl sulphoxide adducts, whereas displacement of the chloro-ligand leads to eta-5-cyclopentadienyl, acetylacetonato, aceto-, benzamidino-, and allyl complexes, which retain the orthometallated amidino-group. Treatment of the chloride-bridged platinum complexes with CO under pressure causes carbonylation to form [Pt{R'NC(R)C6H3R"}(CO)Cl], whereas for palladium cleavage of the orthometallated ligand from the metal occurs with formation of the corresponding quinazolin-4-one. The six-membered nature of the metallocycle is confirmed by the crystallographic structure of [Pd{p-CH3C6H4NC(CH3)NHC6H3CH3}(eta-5-C5H5)] [a = 9.0267(2), b = 9.8949(8), c = 12.1519(3) angstrom, alpha = 89.855(3), beta = 121.278(2), gamma = 99.199(3)-degrees, space group P1BAR, Z = 2]. The structure was refined to a discrepancy index R of 0.054 for 2390 reflections. The amidino-group forms a six- rather than a four-membered ring which is also feasible. The ring, which has a shallow boat configuration, contains C-N bonds with different distances [1.285(9), 1.350(9), 1.434(10) angstrom] indicating little delocalisation of electrons within the ring. The palladium does not lie directly over the centroid of the planar cyclopentadienyl ring but is displaced by 0.25 angstrom towards one of the ring carbon atoms, though the ring C-C bond distances do not vary significantly from the mean [1.386(17) angstrom].