Metal-metal multiple bonds in organometallic compounds. I. (Di-tert-butylacetylene)hexacarbonyldiiron and -dicobalt

Abstract

Metal-Metal Multiple Bonds in Organometallic Compounds. I. (Di-ie/-/-butylacetylene)hexacarbonyldiiron and -dicobalt

Formation of a four-electron donor carbonyl group in the decarbonylation of the unsaturated H2C2Fe2(CO)6 tetrahedrane as an alternative to an iron–iron triple bond

“…In 6-1S a small twist of the HC-CH axis relative to the Fe-Fe bond lowers the symmetry of the central Fe 2 C 2 tetrahedrane from C 2v to C 2 , which is in agreement with the structure determined by X-ray diffraction for t-Bu 2 C 2 Fe 2 (CO) 6 [7,8]. Consequently, the three carbonyls on each iron atom are neither strictly in eclipsed positions nor staggered positions to those on another iron atom.…”

“…This suggests that the initially produced R 2 C 2 Co 2 (CO) 5 isomer retains the Co-Co single bond of the H 2 C 2 Co 2 (CO) 6 starting material so that the cobalt atom bearing just two terminal carbonyl groups has only a 16-electron configuration. However, the second and lower energy H 2 C 2 Co 2 (CO) 5 isomer, produced experimentally by heating the original 90 K matrix to 140 K, is predicted to have a Co@Co distance of only 2.36 Å, which is very similar to the experimentally determined Fe@Fe double bond distance [7,8] of 2.316 Å in t-Bu 2 C 2 Fe 2 (CO) 6 . Thus this more stable H 2 C 2 Co 2 (CO) 5 isomer is inferred to have a formal Co@Co double bond so that both cobalt atoms in the Co 2 C 2 tetrahedrane unit have the favored 18-electron configuration.…”

“…t-Bu 2 C 2 Fe 2 (CO) 6 ( Fig. 1), rather than the originally suggested seven carbonyl groups [7,8]. Application of the 18-electron rule suggests a formal Fe@Fe double bond in this tetrahedrane structure.…”

“…The chemistry of acetylene derivatives of metal carbonyls dates back to the 1956 discovery [1] that reactions of Co 2 (CO) 8 with a variety of alkynes lead to stable red (alkyne)Co 2 (CO) 6 derivatives in good yields under mild reaction conditions. Since this original discovery the chemistry of (alkyne)Co 2 (CO) 6 derivatives has developed extensively [2,3].…”

Alkyne transformations at RhMn centres. Facile conversion between parallel and perpendicular alkyne binding modes and conversions to vinyl groups

“…Concomitant with the transformation of this carbonyl from semibridging, to symmetrically bridging, to terminal on Rh, is a change in the metal-metal bonding, from no bond in 3, to a conventional Rh-Mn bond in the symmetrically CO- The minor isomer 5a is proposed to have a perpendicular alkyne binding mode, shown below, as has been previously observed within the Co triad for [ R~, ( c (6), a series of related dicobalt complexes (24)(25)(26)(27)(28)(29)(30), as well as other dirhodium (31,32) and diiridium (33) systems. This proposed structure is based on the spectral data.…”