Lithioalkynyl iron(II) or ruthenium(II) complexes as precursors of novel alkynyl and vinylidene derivatives: heterobimetallic complexes containing a bridging ethynediyl system

Abstract

Deprotonation of ethynyl complexes [Fe(CCH)(η⁵-C₅H₅)(dppm)]1a(dppm = Ph₂PCH₂PPh₂) and [Ru(CCH)(η⁵-C₉H₇)L₂][L₂= 2PPh₃1b, Ph₂PCH₂CH₂PPh₂(dppe)1c or (PMe₃)(PPh₃)1d] with LiBu^t at –78 °C gave the lithiated complexes [Fe(CCLi)(η⁵-C₅H₅)(dppm)]2a and [Ru(CCLi)(η⁵-C₉H₇)L₂]2b–2d, respectively. These species have been used in situ as precursors of novel alkynyl and vinylidene complexes by reactions with electrophiles. Treatment of complexes 2a–2d with MeOSO₂CF₃ at –78 °C gave vinylidene complexes [Fe(CCMe₂)(η⁵C₅H₅)(dppm)][CF₃SO₃]3a and [Ru(CCMe₂)(η⁵-C₉H₇)L₂][CF₃SO₃][L₂= 2PPh₃3b, dppe 3c or (PPh₃)(PMe₃)3d]. Iodoalkynyl complexes [Ru(CCl)(η⁵-C₉H₇)L₂](L₂= 2PPh₃4b or dppe 4c) have been obtained by reaction of [I(py)₂][BF₄](py = pyridine) with 2b and 2c, respectively. Reaction of 2a–2d with SnPh₃Cl yielded the ethynediyl bridging bimetallic complexes [(η⁵-C₅H₅)(dppm)Fe–CC–SnPh₃]5a and [(η⁵-C₉H₇)L₂Ru–CC–SnPh₃][L₂= 2PPh₃5b, dppe 5c or (PPh₃)(PMe₃)5d]. Similar heterobimetallic complexes [(η⁵-C₅H₅)(dppm)Fe–CC–Au(PPh₃)]6a and [(η⁵-C₉H₇)L₂Ru–CC–Au(PPh₃)]6b–6d have been obtained by treatment of ethynyl complexes 1a–1d with [AuCl(PPh₃)] and TI(acac)(acac = acetylacetonate) in dichloromethane. Complexes 6a and 6b can alternatively be obtained by reaction of 5a and with 5b with [AuCl(PPh₃)] in the presence of [PdCl₂(MeCN)₂]. The crystal structure of 5a has been determined by X-ray diffraction methods. It shows a typical three-legged piano-stool geometry. The iron atom is bonded to the cyclopentadienyl ring, the two phosphorus atoms of a chelating dppm ligand, with a narrow bite angle [74.90(5)°] and the terminal carbon of the triphenyltin acetylide group. The ethynyl bridge is bound to the iron and tin forming an CC–Sn angle of 162.8(4)° and an almost linear Fe–CC arrangement [178.0(3)°].