Structures, Bonding, Infrared Spectroscopy, and Two-Electron Reduction Potentials of the Coordinated Metallopnictanes Fe₃(CO)₉(μ₃-EML_n)₂(E = P, As, Sb; ML_n= Cr(CO)₅, MnCp(CO)₂)

Abstract

The triiron clusters Fe3(CO)9(μ3-EML n )2 (1 - E, ML n = MnCp(CO)2, E = P, As, Sb; 2 - E, ML n = Cr(CO)5, E = P, As, Sb) can be considered cluster analogues of organopnictane (ER3) ligands, in which the triply bridging E ligands are coordinated to 16-electron capping metal groups, ML n . Structural parameters, infrared CO stretching frequencies, and reduction potentials for this metallopnictane series are reported. Analysis of structural, spectroscopic, and electrochemical data reveal systematic variations as a function of the capping heteroatom and the metal fragment coordinated to the heteroatom. The covalent radius of the capping heteroatom dictates the structure of the Fe3(CO)9(μ3-E)2 bonding framework, and both Fe−E and Fe−Fe distances increase linearly with increasing heteroatom covalent radius. The electronegativity of the capping heteroatom (E) influences the frequencies of the Fe3-core carbonyl stretching modes (νCO(Sb) < νCO(As) < νCO(P)), while the two-electron reduction potentials for the series 1 and series 2 clusters (E 1/2(Sb) > E 1/2(As) > E 1/2(P)) correlate with the covalent radius of E. Clusters with capping Cr(CO)5 groups are reduced at potentials ∼400 mV more positive than the MnCp(CO)2-capped analogues. On the basis of the frequencies of the CO stretching modes for the capping ML n group and the E−ML n distance, the metallopnictance ligands are classified as intermediate between organopnictanes and halopnictanes in terms of their net electronic impact (the sum of σ-donating and π-accepting properties). Results of Fenske−Hall molecular orbital calculations provide a qualitative description of the Fe3−E2 bonding as a function of heteroatom (E). Trends in Mulliken populations and a Walsh analysis suggest the Fe−E bonds are strongest for the most electronegative E, phosphorus. The Fe−Fe overlap populations are nearly constant with E, despite the increase in Fe−Fe distance attendant upon incorporation of larger heteroatoms. Two-electron reduction of the metallopnictane Fe3-core changes the donor and acceptor characteristics of the metallopnictane ligand, as demonstrated by a structure determination for [(PhCH2)Me3N]2(1 - P). The Mn−P distance in (1 - P)2- is 0.1 Å longer than in the neutral analogue, 1 - P. Single-crystal X-ray structure determinations for 1 - As, 1 - Sb, 2 - P, 2 - As, 2 - Sb, and [(PhCH2)Me3N]2(1 - P) are reported.

The Parent Diarsene HAs=AsH as Side‐on Bound Ligand in an Iron Carbonyl Complex

“…Besides crystals of 4 , very few crystals of [Fe 3 (CO) 9 {μ 3 ‐AsCr(CO) 5 } 2 ] ( 5 ) were obtained and identified by single crystal X‐ray diffractions and by mass spectrometry. The structure of the latter compound 5 was already reported …”

“…Ah ydrogen atom is attached to each arsenic atom, which additionally coordinates to aW(CO) 5 (5)w ere obtained and identified by single crystal X-ray diffractions and by mass spectrometry.T he structure of the latter compound 5 was already reported. [25] Theinfrared spectrum of 4 shows 5stretches at 1940, 2034, 2054, 2065, and 2114 cm À1 for the CO and AsÀHvibrations.In the 1 HNMR spectrum of 4,asinglet at 3.9 ppm can be attributed to the Hatom of the AsH unit. In order to clearly attribute the As À Hstretches and hence to prove the presence of the AsH unit, we performed the reaction of 2D with [Cr(CO) 5 (thf)].T oo ur surprise,t he same reaction product 4 was isolated instead of the expected deuterated complex [{Fe 2 (CO) 8 }AsD{Cr(CO) 5 }].…”

Transition metal complexes of the naked pnictide elements

“…Molecules shown in Figure 30 all bind 16-electron metal fragments to the lone pairs of either As or Sb. The molecules containing Fe3(CO)9E2 cores have six skeletal electron pairs, 49 but CpCp*(CO)4(µ-O)MoW2{PW(CO)5}2 is more complicated to explain. It has a short Mo-W distance suggestive of multiple bonding.…”

Crystallographic and Structural Analysis of Iron Heterometallic Compounds Part IV: Heteropentameric Compounds

“…ex.- There are three coloured Fe 3 Cr 2 clusters [55,56] for which structural data are available (Table 2B). X-ray analysis of brown green [(CO^Fej^-S^Fe^-S^Q^-CSMesXcp^ shows [55] that the peripheral binuclear Cr 2^-SCMe 3 )Oi 5 -cp)2 and Fe 2 (CO) 6 9 Fe 3^4 -E) 2 {Cr(CO) 5 } 2 (E = Ρ or As) [56] which are isostructural.…”

“…X-ray analysis of brown green [(CO^Fej^-S^Fe^-S^Q^-CSMesXcp^ shows [55] that the peripheral binuclear Cr 2^-SCMe 3 )Oi 5 -cp)2 and Fe 2 (CO) 6 9 Fe 3^4 -E) 2 {Cr(CO) 5 } 2 (E = Ρ or As) [56] which are isostructural. The cluster consists of a triangle of Fe atoms, each with three terminal CO ligands.…”