Premium
Unsaturation in binuclear iron carbonyl complexes of the split (3 + 2) five‐electron donor hydrocarbon ligand bicyclo[3.2.1]octa‐2,6‐dien‐4‐yl: Role of agostic hydrogen atoms
Author(s) -
Wan Di,
Li Huidong,
Shi Liming,
Wu Xueke,
Fan Qunchao,
Feng Hao,
King Robert Bruce,
Schaefer Henry F.
Publication year - 2019
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26010
Subject(s) - agostic interaction , chemistry , ligand (biochemistry) , crystallography , singlet state , cyclopentadienyl complex , metal , density functional theory , electron donor , electron deficiency , stereochemistry , computational chemistry , excited state , biochemistry , physics , receptor , organic chemistry , nuclear physics , catalysis
The experimentally known split (3 + 2) five‐electron donor bicyclo[3.2.1]octa‐2,6‐dien‐4‐yl (bcod) ligand provides a flexible alternative to the rigid planar cyclopentadienyl (Cp) ligand. In this connection, the structures and energetics of the binuclear iron carbonyl complexes (bcod) 2 Fe 2 (CO) n (n = 4, 3, 2, 1) have been investigated by density functional theory for comparison with the corresponding Cp 2 Fe 2 (CO) n derivatives. The cis and trans doubly CO‐bridged (bcod) 2 Fe 2 (μ‐CO) 2 (CO) 2 structures are the lowest energy tetracarbonyl structures, similar to the Cp 2 Fe 2 (CO) 4 system. However, an unbridged (bcod) 2 Fe 2 (CO) 4 isomer lies only ~1 kcal/mol in energy above the doubly bridged isomers. The flexibility of the bcod ligand leads to low‐energy singlet and triplet spin state structures with agostic hydrogen atoms for the unsaturated (bcod) 2 Fe 2 (CO) n (n = 3, 2, 1) systems. Analogous structures are not found in the corresponding Cp 2 Fe 2 (CO) n systems with the rigid Cp ligand. Such structures, effectively involving donation of an electron pair from an olefinic C‐H bond to an iron atom through three‐center two‐electron C‐H‐Fe bonding, are energetically competitive with isomeric structures with metal‐metal multiple bonds.