Elian M & Hoffmann R. Bonding Capabilities of Transition Metal
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CC/NUMBER 44 This Week’s Citation Classic OCTOBER31 1988 Elian M & Hoffmann R. Bonding capabilities of transition metal carbonyl fragments. Inorg. Chem. 14:1058-76, 1975. [Department of Chemisuy, Cornell University, Ithaca, NY] The energy ordering, symmetry, and extent in had limitations, but it was extraordinarily space of the valence molecular orbitals of a transparent and lent itself well to a perturba- range of geometries of M(CO) , M(CO) , and tion theory analysis. Explanations were easy M(CO) fragments, where M3is a transition4 metal center,5 are analyzed in detail. The prop- to extract from it, couched in simple terms, erties of the fragment orbitals are then used to based on bonding, symmetry, and overlap. examine the ability of the fragments to inter- In the early 1970s the Hoffmanngroup be- act with other ligands as well as the geometri- came interested in inorganic chemistry. Their cal preferences of the isolated fragments. [The entry point was the chemistry of sulfur and SCI® indicates that this paper has been cited phosphorus, and they were greatly aided by in over 505 publications.] Earl Muetterties, who had just joined the Cor- nell faculty. He helped the group appreciate the beauties of inorganic stereochemistry and introduced them to transition metal chemistry. Roald Hoffmann Inorganic chemistry, especially organometalhic Department of Chemistry chemistry, was in the air. It was high time to Cornell University learn it, to overcome barriers to drawing d Ithaca, NY 14853-1301 electrons and to counting electrons (what triv- and ial obstacles we create for ourselves!). Mihai Elian The Hoffmann group began, gingerly at first~, Centrul de Chimie Organica to look at transition metal complexes, It was Spi lndependentei 202 B helped by the programming of a new interpre- Bucharest tative tool, the fragment molecular orbital Romania analysis, 1brought2 to the group by Hiroshi Fujimoto. ’ This method seemed ideally suited to typical problems in organometalhic July 5, 1988 chemistry: for instance, the nature of the bond- ing in (cyclooctadiene)-Cr(CO) vs. Fe(CO) . 4 3 The coauthors of this article came to inor- Obviously, one should divide the molecule into ganic chemistry, and specifically to organome- an organic piece (cyclooctadiene) and an in- tallic chemistry, in different ways. Mihai Elian organic one (Cr(CO) , Fe(CO) j. Any differ- 8 3 began his studies in physical organic chemistry ences in bonding would emerge fromarecon- with the late Costin Nenitzescu in Bucharest. stitution of the composite molecule from its In 1969 [han visited the group of [.0. Fisher fragments. That’s, in fact, carried out in part .5-. in München, and there was introduced to the of this paper. joys of organometallic chemistry. Roald Hoff- Elian came to Cornell as a postdoctoral as- mann began as a theoretical inorganic chemist sociate just at the time the inorganic worktook with W.N. Lipscomb, butfrom the time ofhis off. We worked hard together, building piece collaboration with LB. Woodward he concen- by piece a library of most of the important trated on organic molecules. At Cornell Uni- fragments ofinorganic chemistry, in every con- versity, his group developed an approach to ceivable geometry. After this library was in organic molecules and reaction intermediates place, it was simple to implement the recon- that was based on the extended HückeI meth- struction of the bonding in most any inorganic od, butmore importantly on a frontier orbital or organometalhic molecule. And in the course 8~ perspective, a singling out of the higher oc- ofthis analysis we grew aware of a remarkable cupied and lower unoccupied orbitals of a similarity between the orbitals of inorganic molecule as controlling electronic structure and organic molecular building blocks.3 In time and reactivity. The extended Hückel method this became the isohobal analogy -- V.. I. Homnann R, Fujinacto H, Swenaoa ,J R & Wan C-C. Theoretical aspects of the bonding in some three-membered rings containing sulfur. J. Amer. Chem. Soc. 95:7644-50, 1973. (cited 95 times.) 2. Fujimoto H & Hoefla.nn R. A naclecular orbital study of the addition of singlet methylene to buradiene. I. J~jys.Chem. 78:1167-73. 1974. (Cited 70 times.) 3. Hoffinasm H. Building bridges between inorganic and organicchemisuy (Nobel Lecture). Angew. Chcm. Inc Ed. 21:711-24, 1982. (Cited 275 times.) (Also published as Angew. diem. 94:725.38, 1982. ]cited 135 times.]) 3~r~ 18 @1988 by SI® CURRENT CONTENTS®.