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]

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 [FeCI(C5H5)(dip pe)] (1) or [FeCI(C5Me5)(dippe)] (2), respectively. These complexes re act with Grignard reagents RMgCl to give [FeR(C5H5)(dippe)] (R = Me (3 ) or CH2SiMe3 (4)) or [FeR(C5Me5)(dippe)] (R = Me (5)). If (i)PrMgCl i s used, the monohydrides [FeH(C5H5)(dippe)] (6) and [FeH(C5Me5)(dippe) ] (7) are obtained, presumably through a beta-elimination reaction. Th ese hydrides are also prepared by reaction between the corresponding c hloro 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), re spectively. No equilibrium dihydride reversible dihydrogen has been de tected in these complexes, and therefore, they must be regarded as org anoiron(IV) species. The crystal structure of 11 has been determined. Crystal data: monoclinic system, space group P2(1)/n, cell parameters a = 14.277(4) angstrom, b = 21.388(6) angstrom, c = 14.619(6) angstrom , beta = 101.07(3)-degrees, and Z = 4. It suggests a transoid arrangem ent of hydride ligands, consistent with the formulation as an iron(IV) dihydride. The vinylidene complexes [Fe=C=CHPh(C5H5)(dippe)][BPh4] (1 2) and [Fe=C=CHPh(C5Me5)(dippe)][BPh4] (13) were also prepared and cha racterized. Deprotonation of these vinylidene complexes yielded the al kynyl derivatives [Fe(C=CPh)(C5H5)(dippe)] (14) and [Fe(C=CPh)(C5H5)(d ippe)] (15). All the compounds were characterized by NMR, IR, and micr oanalysis.