Some aspects of organonitrogen transition metal complexes

Abstract

Attempts to introduce amidino ligands into Transition metal carbonyl and non carbonyl systems are described, and a new synthetic route to transition metal methyleneamino complexes is explored. Reaction of lithiodiaryl -acetamidines and -benzamidines with Re(CO) (_5)X (X = C1,Br) produced carbamoyl type complexes, Re(CO)(_4)(CONR-CR'-NR) containing a bidentate carbamoyl-amidino ligand. These complexes could be decarbonylated, forming the chelated amidino complexes Re(CO)(_4)(RN-CR'-NR) by heating. The chelated amidino complexes were also prepared by the direct action of lithioamidines on the rhenium carbonyhalide dimer [Re(CO)(_4)X](_2), and by the reaction of n-butyllithium with the simple two electron donor monodentate amidine complexes, Re(CO)(_4)(Amidine)X. Complexes containing ortho-metallated diaryl -formamidino, -acetamidino and -benzamidino ligands were prepared by the action of the parent amidine on Re(CO)(_5)X or Re(CO)(_4)(Amidine)X in refluxing monoglyme. These complexes also contained a simple two electron donor monodentate amidine. The acetamidine and formamidine derivatives formed six membered ortho-metallate rings, the benzamidines forming either five or six membered ring complexes. In contrast, refluxing Re(CO)(_4)(Amidine)X with PPh(_3) in monoglyme produced a chelated amidino species, Re(C0)(_3)(PPh(_3))(RN-CR'-NR). The reaction mechanisms for the formation of the above complexes, and their probable bonding modes are discussed. Interconversions between many of the species were possible. FeCl(_2) reacts with lithiodiarylamidines to produce [Fe(amidino)(_3)](_n) type complexes. The acetamidines and formamidines form monomeric complexes (with a probable tris chelate structure), and the benzamidine forms both a monomeric and an oligomeric/polymeric complex. FeCl reacts similarly with lithiumdi-p-tolylacetamidine, both monomeric and oligomeric/polymeric [Fetamidine)(_2)](_n) species being produced. The complexes are paramagnetic, the Fe(III) species have magnetic moments that suggest they contain five unpaired electrons. Nucleophilic attack by n-butyllithium at the carbon atom of [CpMo(CO)(AsPh(_3)) (NCPh) ](^+) did not produce a methyleneamino complex. Free nitrile was liberated in the reaction, and dimeric molybdenum complexes were produced.