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

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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.

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