| Abstract
| - The global minima for Cp2Re2(CO)n (n = 5, 4, 3, 2) are predicted by density functional theory to be the singly bridged structure Cp2Re2(CO)4(μ-CO), the doubly semibridged structure Cp2Re2(CO)4, the triply bridged structure Cp2Re2(μ-CO)3, and the doubly bridged structure Cp2Re2(μ-CO)2, respectively. In addition, structures Cp2Re−Re(CO)n having agostic hydrogen atoms in C−H−Re bridges (n = 4, 3, 2) are also found but at energies above the global minima.
- The cyclopentadienylrhenium carbonyls Cp2Re2(CO)n (Cp = η5-C5H5; n = 5, 4, 3, 2) have been studied by density functional theory. The global minima for the Cp2Re2(CO)n (n = 5, 4, 3, 2) derivatives are predicted to be the singly bridged structure Cp2Re2(CO)4(μ-CO) with a formal Re−Re single bond; the doubly semibridged structure Cp2Re2(CO)4 with a formal ReRe double bond; the triply bridged structure Cp2Re2(μ-CO)3 with a formal ReRe triple bond; and the doubly bridged structure Cp2Re2(μ-CO)2, respectively. The first three of these predicted structures have been realized experimentally in the stable compounds (η5-C5H5)2Re2(CO)4(μ-CO), (η5-Me5C5)2Re2(CO)4 and (η5-Me5C5)2Re2(μ-CO)3. In addition, structures of the type Cp2Re−Re(CO)n with both rings bonded only to one metal and unknown in manganese chemistry are also found for rhenium but at energies significantly above the global minima. The unsaturated Cp2Re−Re(CO)n structures (n = 4, 3, 2) have agostic Cp hydrogen atoms forming C−H−Re bridges to the unsaturated Re(CO)n group with a Re−H distance as short as 2.04 Å.
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