Reactions at the coordinated trichloromethyl isocyanide. Part VII. α-Chloroalkenylisocyanide versus oxazolin-2-ylidene(ato) complex formation

• Published in: Journal of organometallic chemistry Vol. 692; no. 14; pp. 2936 - 2948
• Main Authors: Langenhahn, Volker, Beck, Gerhard, Zinner, Gerhard, Lentz, Dieter, Herrschaft, Bernhard, Fehlhammer, Wolf Peter
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.06.2007
• Subjects: Carbene ligands; Chromium complexes; Functional Isocyanides; Organometallic [3+2] cycloadditions; Organometallic Wittig reactions; X-ray structures; Chromium complexes; Carbene ligands; Functional Isocyanides; Organometallic [3+2] cycloadditions; Organometallic Wittig reactions; X-ray structures
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/j.jorganchem.2007.03.005

The one-pot reactions of Cr 0(CO) 5CCl 3, phosphines and ketones proceed via intermediates which due to their double nature as phosphorus and metallo-nitrile ylids either cause Wittig carbonyl-(isocyano)methyleneation of or undergo [3+2] cycloaddition with the ketone. Which course is adopted depends on the phosphine (PPh 3 versus P(NMe 2) 3) [or the metal as demonstrated for the related system [Pt II]–CN–CH–PPh 3/RR′C O]. Under aprotic conditions, Cr(CO) 5CNCCl 3 ( 1) reacts with triphenylphosphine in the presence of aromatic aldehydes or ketones to give the α-chloroalkenylisocyanide complexes cis( Z)- and trans( E)-Cr(CO) 5CNCCl CRR′ {R = H, R′ = 4-C 6H 4F ( 7), 4-C 6H 4-CH C(Cl)NCCr(CO) 5 ( 8)} and Cr(CO) 5CNCCl CR 2 {CR 2 = fluorenylidene ( 9)}. Two further representatives of this class of compounds, Cr(CO) 5CNCCl CCl 2 ( 10) and Cr(CO) 5CN–CCl CCl-NCCr(CO) 5 ( 11), have been obtained in low yields by reduction of 1 with zinc. Reactions with pyrrolidine of the isomeric mixtures 7 and 8 afford the alkylideneamino(pyrrolidino)carbene complexes 13 and 14. An X-ray study of 13 shows the two π-systems within the amino(imino)carbene ligand to be approximately orthogonal to one another. With tris(dimethylamino)phosphine in the place of triphenylphosphine, complex 1, 9-fluorenone plus a secondary amine combine to the 4-amino-Δ 3-oxazolin-2-ylidene chromium complexes 17 and 19, the latter of which has been protonated, alkylated and subject to an X-ray structure analysis. Reasons for the different modes of reaction in the system 1/PR 3/RR′C O are discussed and compared with the “dependence on the metal” of reactions in the system L n MCN–CH–PPh 3/RR′C O {L n M = (OC) 5Cr, (OC) 5W versus Cl(Ph 3P) 2Pt +}.