An investigation of the fluxionality of [Fe3(CO)11(CNBut)] and [Fe3(CO)10(CNBut){P(OMe)3}], and the X-ray structure of [Fe3(CO)10(CNBut){P(OMe)3}]

Mechanism of the low-energy fluxional process in [Fe3(CO)12−nL n] (n = 0–2): a perspective

“…The crystal structures described in this paper were downloaded from the Cambridge Crystallographic Database at Daresbury or taken from in-house data. 26, 36 The structures were manipulated using CSC Chem3D TM from Cambridge Scientific Computing, Inc., Cambridge, Massachusetts.…”

“…An axial Bu t NC ligand does not slow the mechanism sufficiently to produce even a broadening 13 C NMR spectrum at 9.4 T at Ϫ100 ЊC, as the ligand can go into the equatorial and/or bridge position. 36 For example, in the crystal structure of [Fe 3 (CO) 10 (CNBu t ) 2 ] 9, one isocyanide ligand adopts an axial position and the other an equatorial one. 37 A little broadening is observed in the 13 C NMR spectrum of [Fe 3 (CO) 10 {P(OMe) 3 }(CNBu t )] 10 at Ϫ100 ЊC and this could indicate ∆G ‡ = ca.…”

“…41 The 31 C NMR spectrum of [Fe 3 (CO) 11 (CNBu t )] at Ϫ100 ЊC consists of three signals at δ 242.2, 215.6 and 207.6, with intensities 1 : 5 : 5. 36 There are two pathways for carbonyl exchange by the concerted bridgeopening bridge-closing mechanism in [Fe 3 (CO) 11 (CNBu t )]. Scheme 7 shows a mechanism involving the isocyanide ligand moving into an equatorial position.…”

“…This is shown in Fig. 4, where the position of the carbon, oxygen and iron atoms derived from the crystal structures of [Fe 3 (CO) 45 [Fe 3 (CO) 10 (CN-Bu t ) 2 ], 37 [Fe 3 (CO) 10 (CNBu t ){P(OMe) 3 }], 36 [Fe 3 (CO) 10 (µ-CNCF 3 )(PMe 3 )], 13 [Fe 3 (CO) 10 (µ-CNCF 3 ){P(OMe) 3 }] (both isomers), 13 4(a) shows the iron atoms and carbonyl ligand positions plotted for all the compounds in Table 4. The molecules have been aligned so that the S 10 axis through ligands 6 and 10 is orthogonal to the paper and the Fe 2 atoms are coincident.…”

“…Scheme 7The application of the concerted-bridge-opening bridge-closing mechanism to [Fe 3 (CO) 11 (CNBu t )] 11 36. Firstly there is rotation of the carbonyls and the isocyanide around the Fe 1 ᎐Fe 2 and Fe 3 ᎐Fe 2 edges of the Fe 3 triangle to move the isocyanide into the equatorial position.…”