Solution Equilibria in Trialkyl‐Phosphite Derivatives of [Ir₄(CO)₁₂]. Crystal Structure of [Ir₄(CO)₁₁{P(OCH₂)₃CEt}]

Abstract

The monosubstituted [Ir4(CO)IIL] clusters (L = P(OPh),, 1; L = (P(OMe),, 2; L = P(OCH2),CEt, 3) were obtained in good yields by the reaction of [Ir4(C0), ,I]-with the corresponding phosphite. In the solid state, cluster 3 has a C, geometry with all terminal ligands as shown by an X-ray analysis. Three isomers are present in solution: one with terminal ligands (A) and two with three edge-bridging CO's and with L in axial (B) or radial (C) position (see Scheme). The thermodynamic and kinetic parameters of isomerisations B p A and A$C were determined by simulation of the variable-temperature "P-NMR spectra. The three isomers correspond to three minima on the kinetic pathway of CO scrambling, whose relative energies vary independently within a small range (1-9 kJ mol-' at 298 K). At low temperature, isomer C is always the least stable and is not observed for 1 which bears the most bulky phosphite ligand. The isomerisations are due to two intramolecular merry-go-rounds of CO groups about two unequivalent faces of the unbridged species A.Introduction. - . We report here on a thermodynamic and kinetic study of the solution equilibria involving the monosubstituted derivatives of [1r4(CO),J with three different trialkyl phosphites, and on the crystal structure of [Ir,(CO),,{P(OCH,),CEt)].

Energy-dependent Electrospray Ionisation Mass Spectrometry of Carbonyl Clusters

“…The clusters Ru 6 C(CO) 16 (PPh 3 ) [19], Ir 4 (CO) 11 (PR 3 ) (PR 3 =PPh 3 , P(p-C 6 H 4 OMe) 3 , P(p-C 6 H 4 NMe 2 ) 3 , P(p-C 6 H 4 Cl) 3 , P(OPh) 3 , P(OMe) 3 , PO 3 C 5 H 9 [20] ) ions. EDESI-MS/ MS data were collected on a Micromass QTof micro using the following settings.…”

First evidence for two different mu-eta¹-eta¹- and mu-eta¹-eta²- co-ordination modes of the P3C2Bu t2 ring of [Fe(eta5-P3C2Bu t2)(eta5-C5H5)] to a same cluster fragment: synthesis and characterisation of [Ir4(CO)10{[Fe(eta5-P3C2Bu t2)(eta5-C5H5)}] and x-ray molecular structure of the mu-eta¹-eta²- isomer

“…Solvents were dried, degassed and redistilled before use, CH 2 Cl 2 was dried over CaH 2 , hexane over sodium wire and thf over sodium and benzophenone. The compound [Ir 4 [Ir 4 (CO) 11 Br] 21 , were used for the 13 C NMR experiments. All Ir 4 -clusters were stored under an inert atmosphere to avoid decomposition observed in some of the compounds stored for long time in the solid state.…”

“…Chemical shifts are given in ppm and coupling constants (J) in Hz. Deuterated solvents were used as lock and reference ( 1 H NMR relative to the proton resonance resulting from incomplete deuteration of the CD 2 Cl 2 (5.32); 13 C NMR relative to the carbon of the CD 2 Cl 2 (53.7) and for 31 P NMR external 85 % H 3 PO 4 ). Infrared spectra were recorded on a Bomen (FT-IR Michelson) spectrophotometer scanning between 2200 and 1600 cm -1 (ν CO ) using a CaF 2 liquid cell.…”

“…clusters (L-L = diphosphine ligands) known to date exhibit the alternative ground state geometry with three edge bridging COs defining the basal plane of the metal tetrahedron 13,19 . As has been pointed out before 12 , the derivatives with unbridged structure always exhibit shorter Ir-Ir bonds than those with bridged structure.…”

“…Ring size is certainly not the only determining factor in the stabilisation of one of these structures over the other. Indeed, although co-ordination of L-L = Ph 2 PC(H)MePPh 2 and MeSC(H)MeSMe in [Ir 4 (CO) 10 (µ-L-L)] generates fivemembered rings in both cases, X-ray diffraction and VT 13 C NMR studies have established that the diphosphine compound exhibits the bridged structure, whereas the dithioethane derivative has the alternative unbridged structure, both in solution and in the solid state 14 .…”