The Ansa-Effect in Zirconocene Chemistry:  The Syntheses and Interconversions of the Hydride Complexes {[Me₂Si(C₅Me₄)₂]Zr(H)(μ-H)}₂, [Me₂Si(C₅Me₄)₂]ZrH₂(PMe₃), and [Me₂Si(C₅Me₄)₂]Zr(Ph)H

Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

“…The violet solid product was washed with 30 mL of pentane, diethyl ether (2 Â 20 mL), and dried under vacuum. Yield: 1.12 g (1.32 mmol, 80% Synthesis of Fe(DPPEPM)Br 2 (2). rac-DPPEPM (0.27 g, 0.40 mmol) was dissolved in 15 mL of THF.…”

“…The reaction between Fe(CH 3 CN) 2 (OTf) 2 and DPPEPM might have been expected to generate a product with reduced coordination number because steric constraints should make it difficult for two triflate anions to bind cis to each other and because the labile triflate and acetonitrile ligands could readily dissociate. We anticipated that a five-coordinate iron center containing an outersphere triflate would have different substitution chemistry than 1.…”

“…20 Notably, the linear, ethylene-bridged, tetraphosphine ligand Ph 2 CH 2 CH 2 PPhCH 2 -CH 2 PPhCH 2 CH 2 PPh 2 (DPPEPE, Chart 1) typically provides trans compounds with Group 8 metal centers 21,22 with structures similar to those of complexes with two bidentate ligands such as trans-FeCl 2 (dmpe) 2 (dmpe = bis(dimethylphosphino)ethane, 23 [FeH(H 2 )(dmpe) 2 ][BPh 4 ], 24 and FeCl 2 (DHPePE) 2 (DHPePE = 1,2-bis(bis(hydroxypropyl)phosphino)ethane). 25 The trans geometry in these compounds may limit their reactivity by suppressing processes that require cis-disposed valencies, although cis-iron(II) complexes of bidentate and meso isomers of linear tetradentate phosphines are also formed on occasion.…”

“…One approach involves replacing the central ethylene unit in DPPEPE with a methylene to shorten the ligand backbone and provide the ligand Ph 2 PCH 2 CH 2 PPhCH 2 PPhCH 2 -CH 2 PPh 2 (DPPEPM, Chart 1). 31 Monometallic rhodium(III) compounds of the related tetraphosphine-containing diethylphosphino groups, Et 2 Our interest in phosphine complexes of group 8 metals arises from their potential in nitrogen activation and reduction. 22,24,36 In a recent example, an iron complex containing two bidentate phosphine ligands has been shown to react with molecular hydrogen and nitrogen through a series of intermediates to generate measurable amounts of ammonia and hydrazine.…”

Silicon–Carbon bond cleavage reactions of Ansa tungstenocene compounds: The [Me 2 Si] bridge as a site for metallocene functionalization

“…For example, we have recently described how a [Me 2 Si] ansa bridge modulates the reactivity of permethylated metallocene complexes (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). In each of these examples, the [Me 2 Si] ansa bridge is merely a substituent that modifies the chemistry of the system due to (i) an inductive effect and (ii) a structural effect that displaces the cyclopentadienyl groups from their natural positions.…”