Ligand-Induced Conversion of π to σ C₆₀−Metal Cluster Complexes: Full Characterization of the μ₃-η¹:η²:η¹-C₆₀ Bonding Mode

Abstract

The reaction of Os3(CO)9(μ 3-η 2:η 2:η 2-C60) (1) with PhCH2NPPh3 in chlorobenzene affords the benzyl isocyanide substituted product Os3(CO)8(CNR)(μ 3-η 2:η 2:η 2-C60) (2a, R = CH2Ph) in 76% yield. Photolysis of 1 in the presence of an excess of benzyl isocyanide gives the isocyanide-inserted product Os3(CO)9(μ 3-CNR)(μ 3-η 1:η 2:η 1-C60) (2b) in 11% yield. Thermal reaction of 2a with an excess of RNC in chlorobenzene at 80 °C produces two isocyanide-inserted, isomeric products, Os3(CO)8(CNR)(μ 3-CNR)(μ 3-η 1:η 2:η 1-C60) (3a, 22%; 3b, 27%). The two isomers 3a and 3b can be selectively prepared by photolysis of 2a in the presence of excess isocyanide in 49% yield and by decarbonylation of 2b with Me3NO/MeCN and subsequent reaction with isocyanide in 56% yield, respectively. Compounds 2a,b and 3a,b have been characterized by microanalytical and spectroscopic methods. In particular, the sp3 carbons of M−C(C60) σ-interactions in μ 3-η 1:η 2:η 1-C60 complexes exhibit unique upfield resonances around 39 ppm in the 13C NMR spectra, compared to the π-bonded sp3 carbon resonances observed in the range of 95−65 ppm. The X-ray crystallographic studies for 2a,b and 3a,b reveal that μ 3-η 2:η 2:η 2-C60 ligands in 1 and 2a transform into new σ-type μ 3-η 1:η 2:η 1-C60 ligands in 2b and 3a,b by insertion of the isocyanide ligand concomitant with Os−Os bond cleavage, forming a bent triosmium framework. In compounds 2b and 3b, a boat-shaped 1,4-cyclohexadiene-like C6 ring in the C60 molecule is clearly observed and the M−C60 σ-bond distances (average 2.24 Å) are shorter than the π-bond lengths (average 2.41 Å). This study represents a novel ligand-induced conversion of π to σ C60−metal complexes.

Structural Aspects of Fullerene ChemistryA Journey through Fullerene Chirality

“…New bonding modes of C 60 , corresponding to a cis -1-type noninherently chiral functionalization pattern involving cage atoms C(1), C(2), C(9), and C(12) (for the numbering of C 60 , see Figure ), were discovered by Park and co-workers in their attempts to convert existing bonding patterns of C 60 −metal cluster complexes into new ones by modifying the coordination sphere of the metal centers. , By doing so, they discovered that C 60 can act as a multifunctional ligand exhibiting various π- and σ-bonding modes. Thus, when [Os 3 (CO) 8 (CNBn)(μ 3 -η 2 :η 2 :η 2 -C 60 )] ((±)- 354 , Scheme , obtained from the reaction between C 3 v -symmetric [Os 3 (CO) 9 (μ 3 -η 2 :η 2 :η 2 -C 60 )] and BnNPPh 3 ) was treated with benzyl isonitrile at 80 °C in chlorobenzene, two constitutional isomers of [Os 3 (CO) 8 (CNBn)(μ 3 -CNBn)(μ 3 -η 2 :η 2 :η 2 -C 60 )], (±)- 355 and (±)- 356 , with one isonitrile ligand inserted into an Os−Os bond were obtained and characterized by X-ray crystallography. , Adduct (±)- 355 was the first structurally characterized complex exhibiting σ-bonding between the fullerene and a metal center. The coordination of one isonitrile ligand to three Os centers in a four-electron-donor μ 3 -η 2 (C):η 1 (N) mode and the equatorial bonding of another isonitrile to one of the outer Os atoms lead to an unsymmetric trimetallic framework and, thus, to a noninherently chiral fullerene functionalization pattern.…”

“…The functionalized cyclohexa-1,4-diene-type ring of the fullerene thus adopts a boat conformation with the σ-bonded C(sp 3 )-atoms located at the bow and stern positions. The thermally (80 °C) noninterconvertible complexes (±)- 355 and (±)- 356 differ only in the coordination site of the terminal isonitrile ligand. ,

31 Chemical Transformations between Triosmium Cluster Complexes Bonded in Various Ways to a C 60 Ligand, Which Displays a Noninherently Chiral C(1),C(2),C(9),C(12)-Addition Pattern 764 a a Carbonyl ligands are not shown explicitly but indicated by free valences departing from the metal atoms.

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Where to bind in buckybowls? The dilemma of a metal ion

“…The synthesis of C 60 Pt(PPh 3 ) 2 by Fagan, Calabrese, and Malone paved the way for exohedral organometallic chemistry and now there exists a plethora of reports on the transition metal complexes of fullerenes. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Equally interesting is the study of metal interaction to the open geodesic polyaromatic molecules often referred to as ''fullerene fragments'' or ''buckybowls''.…”

[60]Fullerene–Metal Cluster Complexes: Understanding Novel η1 and η2[6:5] Bonding Modes of Metallofullerenes

“…It should be mentioned that the metallofullerene complexes containing Os metal atoms have been the most widely investigated in experiments. [11,14,32,33,35,37,[52][53][54][55] The nature of M-C 60 bonding has been investigated through energy partitioning analysis (EPA); the results are given in Table 3. The three top entries in Table 3 give the values of the dissociation energy D e , ∆E prep , ∆E ster , and ∆E orb .…”