Half-sandwich halide, alkyl, hydride, and related complexes of iron containing the bulky diphosphine 1,2-bis(diisopropylphosphino)ethane. Crystal structure of [FeH2(C5Me5)(dippe)][BPh4]

Article abstract of DOI:10.1021/om00020a052

The four-coordinate iron phosphine complex [FeCl₂(dippe)] (dippe = 1,2-bis(diisopropylphosphino)ethane) reacts with LiC₅H₅ or LiC₅Me₅ in thf, yielding the corresponding half-sandwich derivatives [FeCl(C₅H₅)(dippe)] (1) or [FeCl(C₅Me₅)(dippe)] (2), respectively. These complexes react with Grignard reagents RMgCl to give [FeR(C₅H₅)(dippe)] (R = Me (3) or CH₂SiMe₃ (4)) or [FeR(C₅Me₅)(dippe)] (R = Me (5)). If ⁱPrMgCl is used, the monohydrides [FeH(C₅H₅)(dippe)] (6) and [FeH(C₅Me₅)(dippe)] (7) are obtained, presumably through a β-elimination reaction. These hydrides are also prepared by reaction between the corresponding chloro complexes and Li[HBEt₃] in thf. The monohydrides 6 and 7 undergo a one-electron oxidation by reaction with [Fe(C₅H₅)₂][PF₆], yielding the 17-electron hydrides [FeH(C₅H₅)(dippe)]⁺ and [FeH(C₅Me₅)(dippe)]⁺, isolable as tetraphenylborate salts, [FeH(C₅H₅)(dippe)][BPh₄] (8) and [FeH(C₅Me₅)(dippe)][BPh₄] (9). The reaction of 1 or 2 with dihydrogen in methanol, followed by addition of Na[BPh₄] yielded the dihydrides [FeH₂(C₅H₅)(dippe)][BPh₄] (10) and [FeH₂(C₅Me₅)(dippe)][BPh₄] (11), respectively. No equilibrium dihydride ? dihydrogen has been detected in these complexes, and therefore, they must be regarded as organoiron(IV) species. The crystal structure of 11 has been determined. Crystal data: monoclinic system, space group P2₁/n, cell parameters a = 14.277(4) A?, b = 21.388(6) A?, c = 14.619(6) A?, β = 101.07(3)°, and Z = 4. It suggests a transoid arrangement of hydride ligands consistent with the formulation as an iron(IV) dihydride. The vinylidene complexes [Fe=C=CHPh(C₅H₅)(dippe)][BPh₄] (12) and [Fe=C=CHPh(C₅Me₅)(dippe)][BPh₄] (13) were also prepared and characterized. Deprotonation of these vinylidene complexes yielded the alkynyl derivatives [Fe(C≡CPh)(C₅H₅)(dippe)] (14) and [Fe(C≡CPh)(C₅H₅)(dippe)] (15). All the compounds were characterized by NMR, IR, and microanalysis.