Stabilization of η³-indenyl compounds by sterically demanding N,N-chelating ligands in the molybdenum coordination sphere

Abstract

A series of h 3 -indenyl molybdenum compounds [(h 3 -4,7-Me 2 C 9 H 5 )Mo(CO) 2 ( N,N L)Cl] ( N,N L ¼ bpy, phen, pyma), isostructural with well-known h 3 -allyl compounds, was synthesized from the recently established halide synthon [{(h 5 -4,7-Me 2 C 9 H 5 )Mo(CO) 2 (m-Cl)} 2 ]. The low stability of the hexacoordinated h 3 -indenyl molybdenum species in solution has been overcome by a modification of the chelating ligand. Hence, the dissociation of the compounds bearing ligands with methyl groups beside nitrogen donor atoms (e.g. 6,6 0 -Me 2 -bpy, 2,9-Me 2 -phen; 2,9-Me 2 -4,7-Ph 2 -phen) is strongly disfavored due to the steric requirements of the substituents. The considerable discrimination of the pentacoordinated species enables the use of [(h 5 -4,7-Me 2 C 9 H 5 )Mo(CO) 2 (2,9-Me 2 -phen)][BF 4 ] for the assembly of derivatives bearing other halides and pseudohalides in the coordination sphere of molybdenum. The current study further describes some other new indenyl complexes accessible from [{(h 5 -4,7-Me 2 C 9 H 5 )Mo(CO) 2 (m-Cl)} 2 ]. All structural types presented in this experimental study were supported by X-ray crystallographic data.Scheme 1 Molecular formula of 1.Scheme 3 Reaction of 2 with two equivalents of bpy, phen and pyma.This journal is Fig. 3 ORTEP drawing of [(h 3 -C 3 H 5 )Mo(CO) 2 (pyma)Cl] (6-allyl). The labeling for all non-hydrogen atoms is shown. Thermal ellipsoids are drawn at the 30% probability level. Scheme 4 Synthesis of cationic molybdenum compounds. This journal isScheme 9 Reaction of 2 with two equivalents of 3,4,7,8-Me 4 -phen and 4,4 0 -Me 2 -bpy.Scheme 10 Syntheses of complexes bearing 2,9-Me 2 -4,7-Ph 2 -phen and 6,6 0 -Me 2 -bpy.This journal is

Indenyl Compounds with Constrained Hapticity: The Effect of Strong Intramolecular Coordination

“…Infrared and Raman spectra of the neutral chloride complex 13 show the CO stretching bands at considerably lower wavenumbers than cationic analogues bearing acetonitrile (11) or pyridine ligand (12). It is due to higher electron density on metal that enhances back donation into π*-orbitals of carbonyl ligands.…”

“…Due to short intramolecular bridge, the pyridine arm and indenyl are in The indenyl ligand takes configuration with C6-ring above carbonyls that is common for the hexacoordinated molybdenum compounds without intramolecular coordination. [12,13,20] The η 3 :κN-coordination mode of the s functionalized indenyl ligand is unprecedented. Hence, the more conventional η 5 :κN was reported for number of lanthanide [21] and group IV metal compounds.…”

“…From mechanistic point of view, one may expect formation of pentacoordinated species with coordination sphere resembling the recently described chloride complex [(η 5 -4,7-Me2C9H5)Mo(CO)2(py)Cl]. [12] The unusual stability of the compound 16 is probably not only a result of constrained geometry but also due to high energetic barrier of the η 3 :η 5 -indenyl ring slippage as will be discussed in detail later on compound 14. :κN-1-(C5H4NCH2)C9H6}Mo(CO)2 (phen)] + present in crystal structure of 15. The labeling scheme for all non-hydrogen atoms is shown.…”

“…Since the compound 14 gives one set of sharp signals at room, consistent with C1 molecular symmetry, fluxional behavior is not expected in solution. According to previous studies on indenyl compounds without substituents in five-membered ring, [10,12,13] 3 . This experiment unambiguously revealed η 3 -coordination mode of the indenyl ligand that was confirmed in solid state by X-ray diffraction analysis (Fig.…”

“…[9] The molybdenum(II) compounds were found to be very suitable for the investigation of η 5 -η 3 rearrangements due to pronounced stability of η 3 -indenyl species. Hence, they are often accessible from η 5 -species by simple association of 2e donor into the coordination sphere of molybdenum(II) [10][11][12][13] or 2e reduction of molybdenum(IV) compounds. [14] The aim of the present work is to demonstrate the effect of annulated benzene ring on reactivity of cyclopentadienyl molybdenum compounds bearing strong N-donor in the side chain.…”