118275-50-6Relevant articles and documents
Chromium, molybdenum, and tungsten zerovalent complexes of the nitrogen chelating ligand 2-(phenylazo)pyridine (2-PAP), including air-stable cis-M(CO)2(2-PAP)2 and M(2-PAP)3
Ackermann, Martin N.,Barton, Carolyn R.,Deodene, Charles J.,Specht, Elizabeth M.,Keill, Sarah C.,Schreiber, William E.,Kim, Hidong
, p. 397 - 403 (2008/10/08)
The reaction of 2-(phenylazo)pyridine (2-PAP) with M(CO)4(norbornadiene), M(CO)3(CH3CN)3, or M(CO)6 provides M-(CO)4(2-PAP) (M = Cr, Mo, W), cis-M(CO)2(2-PAP)2 (M = Mo, W), and M(2-PAP)3 (M = Cr, Mo, W) as air-stable solids. All compounds are diamagnetic except Cr(2-PAP)3, for which μeff is ～ 1.1 μB at ambient temperature. In M(CO)4(2-PAP) and cis-M(CO)2(2-PAP)2 the CO stretching frequencies are unusually high for complexes of a chelating nitrogen ligand. Compared to the frequency for uncoordinated 2-PAP, the N=N stretching frequency is lowered by 61-136 cm-1 in the complexes with the magnitude of the decrease following the order M(CO)4(2-PAP) > cis-M(CO)2(2-PAP)2 > M(2-PAP)3. Cyclic voltammetry shows that the first oxidation occurs at relatively high potentials in these complexes. 1H and 13C NMR data suggest that the cis-M-(CO)2(2-PAP)2 and M(2-PAP)3 complexes may each exist in a single isomeric form. The 95Mo chemical shifts increase by 900-1200 ppm for each pair of CO's replaced by 2-PAP in Mo(CO)6; the shift of + 1502 ppm for Mo(2-PAP)3 is over 1000 ppm more positive than any previously reported for a Mo(0) compound. The complexes are compared to those of other chelating nitrogen ligands. It is concluded that 2-PAP is a poor σ donor but a very good π acceptor toward low-valent metal centers.
