496856-95-2Relevant academic research and scientific papers
A zwitterionic phosphonio-1,2,4-diazaphospholide and neutral 1,2,4-diazaphosphole - A comparative study of molecular structures and co-ordination properties
Szarvas, Laszlo,Bajko, Zoltan,Fusz, Stefan,Burck, Sebastian,Daniels, Joerg,Nieger, Martin,Gudat, Dietrich
, p. 2303 - 2310 (2008/10/08)
The bis-phosphonio-1,2,4-diazaphospholide salt (1[Cl]) reacts with complex boron hydrides under selective extrusion of one PPh3 moiety to give borane adducts of a novel zwitterionic phosphonio-1,2,4-diazaphospholide. Both the Et3B adduct 2b and the free zwitterionic heterocycle 3, which was liberated by further reaction of 2b with NEt3, were characterized by spectroscopic data and 2b, as well, by a single crystal X-ray diffraction study. The comparison of the structural data with those of a neutral 1,2,4-diazaphosphole and a lithium-1,2,4-diazaphospholide which was formed by deprotonation of the parent 1,2,4-diazaphosphole 4a discloses trends in endocyclic bonding distances which can be rationalized in terms of a charge dependent shift in the π-electron distribution. First studies of the co-ordination properties reveal for both 2b and 4a a marked preference to bind two M(CO)5-fragments (M = Cr, W) via the lone-pairs of the phosphorus and one nitrogen atom; mononuclear complexes with P-co-ordinated heterocycles are formed as intermediates. A single crystal X-ray diffraction study of the dinuclear complex [Cr2(CO)10(μ2-C2H 3N2P-κP,κN)] (10a) together with spectroscopic studies (including 183W NMR studies of tungsten complexes) suggests that M→L back donation is more efficient for P- than for N-bound metal fragments. No evidence for π-co-ordination of the 1,2,4-diazaphosphole ring to a Cr(CO)3 fragment was obtained.
