86196-70-5Relevant academic research and scientific papers
Chemistry of multisite-bound ligands. Addition of amines to μ-η2-acetylides: Dipolar, electron-rich μ-η1- and μ-η2-alkylidene and μ-η1-vinylidene diiron hexacarbonyl complexes
Mott, Graham N.,Carty, Arthur J.
, p. 2726 - 2736 (2008/10/08)
As part of a major effort to explore and establish patterns of reactivity for multisite-bound unsaturated ligands, the reactions of the μ-η2-acetylides Fe2(CO)6(C2R)[P(C6H 5)2] (1) (R = C6H5, p-MeOC6H4, p-BrC6H4, C6H11, C(CH3)3) toward primary, secondary, and tertiary amines have been investigated. Three types of addition products have been isolated and characterized by microanalysis and infrared, 1H and 31P NMR, and Mo?ssbauer spectroscopy. Solid-state structures by X-ray crystallography are available for several of the adducts. Attack at the β-carbon of the acetylide affords zwitterionic μ-vinylidene compounds Fe2(CO)6[C=C{NHR1R2}R][P(C 6H5)2] (4); attack at the β-carbon atom by primary or secondary amines with hydrogen transfer yields dipolar μ-alkylidene derivatives Fe2(CO)6[CHC{NR1R2}R][P(C 6H5)2] (3) with a single carbon atom bridge between iron atoms. Attack at the α-carbon atom of the μ-η2-acetylide with hydrogen migration gives the μ-η2-alkylidene derivatives Fe2(CO)6[C{NR1R2}CR][P(C 6H5)2] (2) where a two-carbon three-electron ligand is present. 31P NMR and Mo?ssbauer studies permit facile differentiation of the three structural types; in particular δ(31P) shifts show a systematic variation with M-P-M angle and M - M bond length, with larger, downfield shifts corresponding to greater Fe-P-Fe angles. Factors affecting the electrophilicity of the multisite-bound acetylides in 1 and the regiospecificity of nucleophilic attack have been probed via 13C NMR studies of the precursors and variable-temperature 31P studies of reactions of 1 with a variety of nucleophiles. Multisite coordination confers enhanced reactivity toward nucleophihc attack with the site of attachment of the nitrogen nucleophile determined principally by polarization in the μ triple bond, the steric bulk of the substituent R in 1, and the incoming nucleophile.
