Reactions of acyl(carbonyl)ruthenium(II) and acyl(carbonyl)iron(II) complexes with amines. Preparation of novel propionyl(carbamoyl)ruthenium(II) complexes

Abstract

Treatment of Ru(COEt)Cl(CO)(PPh 3) 2 ( 1) with secondary amines (R 2NH) under pressure of CO and / or ethylene gives propionyl-carbamoyl complexes Ru(COEt)(CONR 2)(CO)(PPH 3) 2 (NR 2 = NEt 2 ( 4a), N(CH 2) 4CH 2 ( 4b), NMe, ( 4c)) together with the ammonium salt R 2NH 2Cl. Complexes 4a–c have been isolated as pale yellow crystals and characterized by means of NMR and IR spectroscopy and elemental analysis. Reactions of Fe(COMe)I(CO) 2(PMe 3) 2 and [Fe(COMe)(CO) 3(PMe 3) 2]BF 4 with nucleophiles (HNEt 2, LiNMe 2, EtOH (in conjunction with Et 3N) and NaOMe) give the corresponding acetamides and acetic acid esters. The carbonyl(propionyl)ruthenium complex 1 in solution under CO pressure was found to undergo nucleophilic attack of secondary amines on the coordinated CO ligand to give isolable acyl(carbamoyl)ruthenium complexes 4 in a parallel behavior with the previously reported acyl(carbonyl) palladium complexes [4g,h]. However, the isolated acyl(carbamoyl)ruthenium complexes differ in their behavior from the palladium analogs in their inactivity to release α-keto amide. The exact reason for the different behavior is not clear. A possible explanation for the reluctance of reductive elimination from the acyl(carbamoyl)ruthenium complex is that the acyl and the carbamoyl ligands are situated at unfavorable sites for a concerted reductive elimination to occur. In a theoretical treatment of reductive elimination of two organic groups from a five-coordinated nickel complex, it has been discussed that (i) the organic ligands both situated at equatorial positions in a trigonal-bipyramidal complex are symmetrically forbidden to undergo the reductive elimination process, and (ii) kinetic barriers for pseudorotation to bring the concerned organic ligands to axial and equatorial sites are very high [13]. A similar argument might be advanced in the present case but we would rather defer from advancing the discussion further until more bis-acyl type complexes are prepared and their behavior examined.