The First-Row Transition Metal Interstitial Hydride Anion [{PhP(CH₂)₃Fe}₄(μ₄-H)]⁻

Abstract

The metal-exchange reaction of the lithium complex [{PhP(CH 2 ) 3 } 2 (Li 3 thf) 4 ] (1) with FeI 2 gives the tetranuclear Fe II compound [Li(thf) 4 ] þ [{PhP(CH 2 ) 3 Fe} 4 (μ 4 -H)] -(2), a rare example of a first-row transition metal interstitial hydride.In the past decade or so there has been considerable interest in the coordination chemistry of main group element-based anionic ligands containing nitrogen donor functionality. 1-4 Most well studied are the series of isoelectronic tripodal anions [RE-(NR) 3 ] x-(E=main group element) (Figure 1a,b,c), which exhibit a rich coordination chemistry with a broad range of transition and main group metals. Our interest in these species has been renewed by the realization that isovalent phosphorus-based group 13 anions of this class, [MeE(PPh) 3 ] 4-(E=Al, Ga, In, Figure 1d), have the remarkable ability to form supramolecular ionic cages. 5 This feature is seen in the series of isostructural anions [{MeE(PPh) 3 Li 4 } 4 (μ 4 -Cl)] -, composed of a supramolecular, tetrahedral arrangement of four [MeE(PPh) 3 ] 4-anions that surround a Li 16 core. The inverse coordination of the Clanion by a Li 4 unit at the center of the [{MeE(PPh) 3 Li 4 } 4 (μ 4 -Cl)] -anion effectively templates this structure. 6 We showed recently that deprotonation of the commercially available phosphonium salt [PhP(CH 3 ) 3 ] þ I -with t BuLi results in a new carbon-based representative of this class of ligands, [PhP(CH 2 ) 3 ] 2-(Scheme 1). 7 This novel phospholide arrangement offers new opportunities in organometallic chemistry, being a strong σ-donor (via the lone pairs of the CH 2 groups) and a σ-acceptor (via the σ* orbital of the Ph-P bond). 8 We present here the first study of the coordination chemistry of this type of ligand with a transition metal; the tetranuclear anion [{PhP(CH 2 ) 3 Fe} 4 (μ 4 -H)] -(2) reported is a rare example of a first-row transition metal interstitial hydride.The 1:1 stoichiometric reaction of the lithium precursor 1 with FeI 2 in thf produces a dark brown solution, from which dark brown crystals of [Li(thf) 4 ] þ [{PhP(CH 2 ) 3 Fe} 4 (μ 4 -H)] -(2) were isolated in 44% yield. 9 The 1 H and 31 P{ 1 H} NMR spectra of the complex at room temperature show sharp resonances, strongly suggesting that it is diamagnetic in solution. In addition, 2 is also EPR silent at room temperature in thf solution and in the solid state. This provides key evidence that the Fe II centers in the anion of 2 are low-spin (t 2 g 6 eg 0 ). It also provides indirect evidence of the presence of the H -ion within the [{PhP(CH 2 ) 3 Fe} 4 (μ 4 -H)] -anion, which would otherwise have to possess a single, unpaired electron to balance the charge in 2, i.e., paramagnetic (Fe II ) 3 (Fe I ) rather than diamagnetic (Fe II ) 4 (μ 4 -H). In addition to the Ph and CH 2 resonances for the [PhP(CH 2 ) 3 ] 2-ligands, the room-temperature 1 H NMR spectrum shows a broad resonance at δ -11.2, which we assign to the μ 4 -H atom. 10 Although the reaction producing 2 can be reproduced easily, the origin of th...

Phosphorus‐Bearing Lithium Compounds in Modern Synthesis

“…Complex 52 is a rare example of a first-row transition metal interstitial hydride. Each PhP(CH 2 ) 3 moiety of 52 is attached to three iron ions as expected for a tripodal ligand and these metal ions define a cage that contains an ''encapsulated'' hydride ion [21]. The source of the hydride ion was assigned to the ligand.…”

Chelate Effects in Glyme/Lithium Bis(trifluoromethanesulfonyl)amide Solvate Ionic Liquids. I. Stability of Solvate Cations and Correlation with Electrolyte Properties

“…The previous reports suggested the formation of stable solvates in a 3(T m : not reported) for G2-Li[TFSA] mixtures 28,29. In crystalline solvates with THF reported in the literature,30,31 Li + ions are mostly solvated by four THF molecules (4-fold coordination) in the form of [Li(THF) 4 ] + complex cations.Whereas a favorable coordination number for Li + ions is known to be 4−5 in solution,32 complexes with 6-fold coordination via the oxygen atoms of ether solvents, as observed in [Li(G1) 3 ][TFSA], [Li(G2) 2 ][TFSA], and [Li-(G5) 1 ][TFSA], seem to be more stable in the crystalline state. Indeed, they generally possess a higher melting point than other solvates which exhibit 4-or 5-fold coordination.…”

Hydride Migration from a Triangular Face to a Tetrahedral Cavity in Tetranuclear Iron Carbonyl Clusters upon Coordination of [AuPPh3]+ Fragments

“…Concerning fully interstitial hydrides, for very long-time only molecular clusters containing six-coordinate hydrogen in an octahedral cavity were known, [16][17][18] and it was only in 2008 that the first molecular species containing a four-coordinate hydrogen in the tetrahedral cavity of [(C 5 Me 4 SiMe 3 )YH 2 ] 4 (thf) was fully characterized. [19] Some other examples of tetrahedral m 4 -H are also known, [20,21] including [{PhP(CH 2 ) 3 Fe} 4 (m 4 -H)] À , [22] but they are all compounds containing metals in positive oxidation states.…”