Reactions of a phosphido-bridged unsymmetrical diiron complex (η 5-C 5Me 5)Fe 2(CO) 4(μ-CO)(μ-PPh 2) with various alkynes

Abstract

A phosphido-bridged unsymmetrical diiron complex (η 5-C 5Me 5)Fe 2(CO) 4(μ-CO)(μ-PPh 2) ( 1) was synthesized by a new convenient method; photo-dissociation of a CO ligand from (η 5-C 5Me 5)Fe 2(CO) 6(μ-PPh 2) ( 2) that was prepared by the reaction of Li[Fe(CO) 4PPh 2] with (η 5-C 5Me 5)Fe(CO) 2I. The reactivity of 1 toward various alkynes was studied. The reaction of 1 with t BuCCH gave a 1:1 mixture of two isomeric complexes (η 5-C 5Me 5)Fe 2(CO) 3(μ-PPh 2)[μ-CHC( t Bu)C(O)] ( 3) containing a ketoalkenyl ligand. The reactions of 1 with other terminal alkynes RCCH (R=H, CO 2Me, Ph) afforded complexes incorporating one or two molecules of alkynes and a carbonyl group. The principal products were dinuclear complexes bridged by a new phosphinoketoalkenyl ligand, (η 5-C 5Me 5)Fe 2(CO) 3(μ-CO)[μ-CR 1CR 2C(O)PPh 2] ( 4a: R 1=H, R 2=H; 4b: R 1=CO 2Me, R 2=H; 4c: R 1=H, R 2=Ph). In the cases of alkynes RCCH (R=H, CO 2Me), dinuclear complexes having a new ligand composed of two molecules of alkynes, a carbonyl group, and a phosphido group; i.e. (η 5-C 5Me 5)Fe 2(CO) 3[μ-CRCHCHCRC(O)PPh 2] ( 5a: R=H; 5b: R=CO 2Me), were also obtained. In all cases, mononuclear complexes, (η 5-C 5Me 5)Fe(CO)[CR 1CR 2C(O)PPh 2] ( 6a: R 1=H, R 2=H; 6b: R 1=H, R 2=CO 2Me; 6c: R 1=H, R 2=Ph) were isolated in low yields. The structures of 1, 4c, 5b, and 6a were confirmed by X-ray crystallography. The detailed structures of the products and plausible reaction mechanisms are discussed.