Ten Years of Metallocarboranes

Callahan, Kenneth P.; Hawthorne, M. Frederick

doi:10.1016/s0065-3055(08)60651-6

Cited by 115 publications

(63 citation statements)

References 92 publications

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“…In the event it was shown that B 6 H 10 reacted essentially quantitatively with i -B 9 H 15 to form the new conjuncto-borant B 15 H 23 with the loss of one mole of H 2 (38,39), and subsequent X-ray analysis showed (40) that the structure was indeed composed of a B 6 H 10 unit bonded by η 2 donation to a B 9 H 13 unit as shown in Figure 4. Similarly, the novel conjuncto-borme B 14 Figure 6, is a structural analogue of nido-B 6 H 10 with one basal {BH t H^ group replaced by the Ir(HI) center (44).…”

Section: B-h-m Interactions Involving Higher Boranesmentioning

confidence: 99%

“…Numerous other reviews of various aspects of the subject have appeared during the ensuing 15 years, of which the following are representative (7,. A parallel literature exists on carbaborane species as ligands (e.g., [13][14][15][16][17][18][19]. Indeed, an important harbinger of the evolving idea of binary boranes as ligands was M. Frederick Hawthorne's seminal recognition in 1965 that the /wdodicarbaborane anion, C^BçH!…”

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confidence: 99%

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Electron-Deficient Boranes as Novel Electron-Donor Ligands

Greenwood

1994

ACS Symposium Series

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The history of the concept of "boranes as ligands" will be traced from its origins in the mid-1960s to the present day. Polyhedral boranes and their anions are often classified as electron deficient species but, in fact, many can act as excellent polyhapto ligands to metal centers, thereby forming coordination complexes that are often more stable than the parent borane species. Furthermore, many of the binary boranes and their anions can themselves usefully be regarded as coordination complexes of a borane ligand and a borane acceptor, i.e., a borane -borane adduct. The exciting synthetic, structural, and bonding implications of these ideas will be outlined by referring to key compounds and reactions in the literature.Boron is the element immediately preceding carbon in the periodic table and so has one less electron than orbitals available for bonding. As a consequence, many of its molecular compounds are "electron deficient" in the sense that there are insufficient electrons to form two-center two-electron bonds between each contiguous pair of atoms. The classic examples of this situation are the binary boron hydrides and the carbaboranes, which relieve their so-called electron deficiency by forming polyhedral cluster molecules in which pairs of electrons simultaneously bond more than two atoms by means of three-center or polycenter bonds (1). In diagrams depicting the structure of these compounds it is important to note that straight lines between the atoms do not necessarily indicate pairs of electrons but merely delineate the geometrical shape of the cluster. Another way of relieving the electron deficiency is for the borane species to act as an electron-pair acceptor by interaction with a Lewis base, L, e.g., LBH 3 where L = CO, Me 2 0, Me 2 S, Me 3 N, H", etc.About 30 years ago, in the mid-1960s, we began to realize that, far from being deficient in electrons, many boranes and their anions could act as very effective

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Section: B-h-m Interactions Involving Higher Boranesmentioning

confidence: 99%

mentioning

confidence: 99%

Electron-Deficient Boranes as Novel Electron-Donor Ligands

Greenwood

1994

ACS Symposium Series

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“…Hawthorne and coworkers 4 were the first to show that boron vertices in 10-to 12-vertex borane deltahedra can be replaced by isolobal transition metal vertices to give stable metallaboranes synthesized using decaborane-14, B 10 H 14 , as the boron hydride starting material for their syntheses. Shortly thereafter, Grimes and co-workers 5 showed that similar metallaboranes could be synthesized based on smaller polyhedra using pentaborane-9, B 5 H 9 , as the boron hydride starting material.…”

Section: Introductionmentioning

confidence: 99%

Dimetallaborane analogues of pentaborane

2015

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The structures of five-vertex dimetallaboranes Cp2M2B3H7 (Cp = η(5)-C5H5) of the second and third row transition metals, including the experimentally known Cp*2Rh2B3H7 (Cp* = η(5)-Me5C5), have been investigated by density functional theory. The predicted low-energy structures for Cp2M2B3H7 (M = Rh, Ir) are tetragonal pyramids similar to Cp*2Rh2B3H7 and pentaborane-9 B5H9 and consistent with their 14 Wadean skeletal electrons. Two Cp*2Rh2B3H7 structures with the same central Rh2B3 tetragonal prism are found with energies within ∼1 kcal mol(-1) of each other, consistent with the experimental observation of two isomers in solution. The electron-richer Cp2M2B3H7 (M = Pd, Pt) systems having 16 Wadean skeletal electrons are predicted to exhibit more open structures analogous to the known structure for the valence isoelectronic pentaborane-11 B5H11. Trigonal bipyramids with the metal atoms at equatorial vertices are typically found to be low-energy structures for the hypoelectronic Cp2M2B3H7 systems (M = Ru, Os, Re, Mo, W, Ta). In addition, the low-energy Cp2Re2B3H7 structures of the rhenium derivatives Cp2Re2B3H7 provide examples of structures based on a central Re2B2 tetrahedron with the Re-Re edge bridged by the third boron atom. Such structures can be derived from a trigonal bipyramid by the rupture of one of the axial-equatorial edges.

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“…Metallacarborane chemistry originated in the 1960s when Hawthorne and co-workers [1,2] discovered that the vertices in closo dicarbaboranes obtained from decaborane and alkynes [3,4] can be replaced by isolobal transition metal vertices. Subsequent work by Grimes and co-workers [5] used pentaborane as a starting material to synthesize a variety of metallaboranes and metallacarboranes based on smaller polyhedra.…”

Section: Introductionmentioning

confidence: 99%