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Metallaborane

From Wikipedia, the free encyclopedia
Structure of(C5(CH3)5)FeHCo(CO)3B4H7.[1] Color code: yellow = B, blue = Fe & Co, red = O, gray = C.

Inchemistry, ametalloborane is a compound that contains one or more metal atoms and one or moreboron hydride. These compounds are related conceptually and often synthetically to theboron-hydride clusters by replacement of BHn units with metal-containing fragments. Often these metal fragments are derived frommetal carbonyls orcyclopentadienyl complexes. Their structures can often be rationalized bypolyhedral skeletal electron pair theory. The inventory of these compounds is large, and their structures can be quite complex.[2][3]

Examples

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Chemical structure ofB4H8Fe(CO)3. As is customary for boron hydrides, the lines drawn between B and H do not represent 2-center, 2-electron bonds.

Two simple examples areB4H8Fe(CO)3 and B4H8Co(C5H5). The MB4 cores (M = Fe or Co) of these two compounds adopt structures expected for nido 5-vertex clusters. The iron compound is produced by reaction ofdiiron nonacarbonyl withpentaborane.B4H8Fe(CO)3 andcyclobutadieneiron tricarbonyl have similar structures.

Metallacarboranes

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Structure of (Me4N+)2[Fe(C2B9H11)2]2-, showing only one Me4N+.[4]

Even greater in scope than metalloboranes aremetallacarboranes. These cages have carbon vertices, often CH, in addition to BH and M vertices.[2] A well-developed class of metallacarboranes are prepared fromdicarbollides, anions of the formula [C2B9H11]2-. These anions function as ligands for a variety of metals, often formingsandwich complexes.[5]

Some metalloboranes are derived by the metalation of neutralcarboranes. Illustrative are the six-and seven-vertex cages prepared fromcloso-C2B3H5. Reaction of this carborane with iron carbonyl sources givescloso Fe- and Fe2-containing products, according to these idealized equations:[6]

C2B3H5 + Fe2(CO)9 → C2B3H5Fe(CO)3 + Fe(CO)5 + CO
C2B3H5Fe(CO)3 + Fe2(CO)9 → C2B3H5(Fe(CO)3)2 + Fe(CO)5 + CO

A further example of insertion into a closo carborane is the synthesis of the yellow-orange solid closo-1,2,3-(CO)3FeC2B4H6:

closo−C2B4H8 + Fe2(CO)9 → closo−(CO)3FeC2B4H6 + Fe(CO)5 + CO

A closely related reaction involves the capping of an anionic nido carboraneC2B4H−7

closo−C2B4H8 + NaH → Na(nido−B4H7) + H2
Na(nido−B4H7) + CoCl2 + NaC5H5 → closo−(C5H5)CoB4H6 + 2 NaCl + ...

The last reaction is worked up with acid and air.

References

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  1. ^Peldo, Melanie A.; Beatty, Alicia M.; Fehlner, Thomas P. (2002). "Routes to Compounds Containing M−B Bonds. Reaction of [Cp*FeH2]2 with BH3·THF, Yielding the Hydrogen-Rich arachno-Ferrapentaborane 1-Cp*FeB4H11 (Cp* = η5-C5Me5)".Organometallics.21 (14):2821–2823.doi:10.1021/om020273y.
  2. ^abGreenwood, Norman N.; Earnshaw, Alan (1997).Chemistry of the Elements (2nd ed.).Butterworth-Heinemann.ISBN 978-0-08-037941-8.
  3. ^Grimes, Russell N. (1982).Metal Interactions with Boron Clusters. Springer.ISBN 9780306409332.
  4. ^Kang, H. C.; Lee, S. S.; Knobler, C. B.; Hawthorne, M. F. (1991). "Syntheses of Charge-Compensated Dicarbollide Ligand Precursors and Their Use in the Preparation of Novel Metallacarboranes".Inorganic Chemistry.30 (9):2024–2031.doi:10.1021/ic00009a015.
  5. ^Sivaev, I. B.; Bregadze, V. I. (2000). "Chemistry of Nickel and Iron Bis(dicarbollides). A Review".Journal of Organometallic Chemistry.614–615:27–36.doi:10.1016/S0022-328X(00)00610-0.
  6. ^Grimes, R. N. (1982). "Metallacarboranes and Metalloboranes".Comprehensive Organometallic Chemistry. pp. 459–542.doi:10.1016/B978-008046518-0.00009-X.ISBN 9780080465180.
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