Synthesis and characterization of pentanuclear Fe–Ir carbonyl clusters. Solid-state structures of [N(PPh₃)₂]₂[FeIr₄(CO)₁₅] and [PPh₄][Fe₂Ir₃(CO)₁₄]

Abstract

The dianion [ Felr,( C0),,l2-can be obtained b y reduction of an equimolar mixture of [ Fe( CO),] and [Ir,(CO),,] in alcoholic NaOH and under 1 atm of carbon monoxide. The salt [N( PPh,),], [Felr,( CO),,] (1) crystallizes in the triclinic space group P i with unit-cell dimensions The mean values of the Fe-lr and Ir-lr distances are 2.648 and 2.708 A, respectively. In the derivative (1) the trigonal bipyramid is considerably elongated in the direction of the apical atoms, when compared with that in (2). This elongation is consistent with the increased number of cluster valence electrons: 76 in (1 ) and 7 2 in (2).Transition-metal clusters are attracting a great deal of interest with respect to their potential as catalysts. Particularly mixedmetal clusters are extensively studied because adjacent metal centres formed by different elements offer the possibility for co-operative reactions leading to new, more active, or more selective catalysts.' -3 Moreover, they should act as potential precursors of bimetallic heterogeneous catalysts of well defined st~icheiometry.~ The lack of an extensive work on Fe-Ir bimetallic clusters5 and recent reports on Fe-lr traditional catalysts, very selective for the production of MeOH from C O and H2,6--8 prompted us to investigate this field. In this paper we describe the synthesis, the chemical characterization, and the solid-state structures of the two new clusters [N(PPh,),], [Felr,(CO),,] (1) and(2), the first examples of Fe-lr mixedmetal carbonyl clusters. Results and DiscussionPi-epurutioi? I?f' [FeIr,(CO), 5]2 -(l).

The Interpretation of the Terminal ν(CO) Spectra of Some Tetranuclear Carbonyl Clusters

“…In particular, the tangential modes will already been reported. [8] The similarity of the spectra of 1e have significant infrared intensity, a feature that serves to with those of the C 3v complexes is clearly evident. The speccharacterise the THM; it is to be noted that a P mode split-tra of 1f suffer from the poor quality of the Raman specting occurs in both the SHM and the THM, although it trum and of the broadness of the infrared; however, the seems to be larger in the latter.…”

“…Moreover, the complex 1g, structurally derived gression from almost pure SHM behaviour through to from 1e with an AuPPh 3 unit bridging the basal FeIr 2 trisomething that shows characteristics which surely indicate angle, [8] does not show any significant changes in the speca transition to something closer to the THM limit. For this tra (Figure 6) Ϫ the splitting of the P and D modes is simreason we do not regard the evident E, A 1 , E splitting of ply more evident.…”

“…It is convenient to start by a study of the spectra of bonyls. [8] ref. [9] 1f [FeIr 3 (CO) 12 ] Ϫ C 3v C s ca.…”

Gold–Heterometal Interactions and Bonds

“…A structural diversity of heterodimetallic and -trimetallic cores was observed for the pentanuclear species containing Au-Fe [296][297][298][299][300][301][302][303][304][305][306][307][308][309], Au-Ru [267,272,[310][311][312][313][314][315][316][317][318][319][320][321][322][323][324][325] and Au-Os [326][327][328][329][330][331][332][333][334][335]. A (Ph 3 P)Au unit can bridge in a m 3 -fashion a face of a tetrahedral heterodimetallic (Fe 2 Ir 2 , Fe 2 Rh 2 , Ru 2 Rh 2 , Ru 3 Rh, Ru 3 Co) core [296,297,310,311,315] [311]…”

“…A (Ph 3 P)Au unit can bridge in a m 3 -fashion a face of a tetrahedral heterodimetallic (Fe 2 Ir 2 , Fe 2 Rh 2 , Ru 2 Rh 2 , Ru 3 Rh, Ru 3 Co) core [296,297,310,311,315] [311]. For Ru and Os clusters a common pattern is the edge-bridging of a (R 3 P)Au fragment to a homonuclear M 4 (M ¼ Ru [312], Os [326][327][328][329][330]) or heteronuclear M 3 W (M ¼ Ru [313], Os [331]), Ru 3 Co [315] and Os 3 Ni [332], for example, in (Ph 3 P)AuRu 3 W(h 5 -Cp)(m 3 -H)(m-H) (CO) 11 [327].…”