Amidino-complexes of rhenium. Bidentate NN′- and ortho-metallated derivatives

Abstract

[Re(CO)₄{R′NC(R)NR′}] complexes (I; R = Me or Ph; R′= Ph or C₆H₄Me-p), containing delocalised bidentate NN′-chelated amidino-groups, have been prepared by reactions of (i)[{Re(CO)₄X}₂](X = Cl or Br) with R′N(Li)C(R)NR′, (ii)[Re(CO)₄{R′NC(R)NHR′}X] with LiBuⁿ, (iii)[Re₂(CO)₁₀] with R′NHC(R)NR′, and (iv) by decarbonylation of [Re(CO)₄{CON(R′)C(R)NR′}] complexes. Triphenylphosphine displaces CO from (I) to form [Re(CO)₃(PPh₃){R′NC(R)NR′}](II), which are more conveniently prepared by the reactions of [Re(CO)₄L′Br](L′= PPh₃ or AsPh₃) with amidines in refluxing toluene. This reaction stops at the intermediate compound [Re(CO)₃(PPh₃){R′NC(R)N(Me)R′}Br] when a NNN′-trisubstituted amidine is used. Related complexes [Re(CO)₃(PPh₃){R′NC(R)NHR′}Br] are formed when (II) are treated with hydrobromic acid. [Re(CO)₅X](X = Cl or Br) and [{Re(CO)4Br}2] react with amidines to form o-metallated [[graphic omitted]H₃R″-p}{R′NC(R)NHR′}](R = H, R′= Ph; R″= H; R = Me or Ph, R′= C₆H₄Me-p, R″= Me; R = Me or Ph, R′= Ph, R″= H) complexes which contain a six-membered o-metallated ring. Benzamidines (R = Ph) produce in addition an isomeric complex in which o-metallation of the R substituent occurs to give complexes having five-membered o-metallated rings. Intermediate [Re(CO)₃{R′NC(R)NHR′}₂X] complexes were isolated for R′= C₆H₄Me-p, R = Me, and X = Cl or Br. A 1,3-proton-shift mechanism for the o-metallation reaction is eliminated by the formation of the complex [[graphic omitted]C₆H₃Me-p}{R′NC(Me)N(Me)R′}](R′= C₆H₄Me-p) from R′N(Me)C(Me)NR′. Reaction schemes are suggested for the course of the reactions, and structures for the new complexes are proposed on the basis of spectroscopic data.