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Chromium–Chromium Bonding in Binuclear Azulene Chromium Carbonyl Complexes
Author(s) -
Wang Hongyan,
Sun Zhonghua,
Xie Yaoming,
King R. Bruce,
Schaefer Henry F.
Publication year - 2010
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201000737
Subject(s) - chemistry , disproportionation , chromium , cyclopentadienyl complex , singlet state , decarbonylation , metal carbonyl , azulene , density functional theory , crystallography , triple bond , chromium compounds , medicinal chemistry , photochemistry , stereochemistry , double bond , computational chemistry , polymer chemistry , excited state , catalysis , organic chemistry , metal , physics , nuclear physics
The experimentally known cis ‐[(η 5 ,η 5 ‐C 10 H 8 )Cr 2 (CO) 6 ] structure with a rather long formal Cr–Cr single bond of about 3.3 Å is predicted by density functional theory to be the lowest energy C 10 H 8 Cr 2 (CO) 6 structure. However, a trans ‐[(η 7 ,η 5 ‐C 10 H 8 )Cr 2 (CO) 6 ] structure lies in energy within ca. 4 kcal/mol of this global minimum. The lowest energy structures for the unsaturated derivatives C 10 H 8 Cr 2 (CO) n ( n = 5, 4, 3, 2) are all related structures with cis stereochemistry of the two chromium atoms, a chromium‐chromium bond, and a single bridging carbonyl group. Such structures include singlet cis ‐[(η 5 ,η 5 ‐C 10 H 8 )Cr 2 (CO) 4 (μ‐CO)], singlet cis ‐[(η 7 ,η 5 ‐C 10 H 8 )Cr 2 (CO) 3 (μ‐CO)], triplet cis ‐[(η 7 ,η 5 ‐C 10 H 8 )Cr 2 (CO) 2 (μ‐CO)], and triplet cis ‐[(η 7 ,η 5 ‐C 10 H 8 )Cr 2 (CO)(η 2 ‐μ‐CO)], for n = 5, 4, 3, and 2, respectively. The C 10 H 8 Cr 2 (CO) 5 structure is thermodynamically viable with respect to disproportionation into C 10 H 8 Cr 2 (CO) 6 and C 10 H 8 Cr 2 (CO) 4 , in contrast to its cyclopentadienyl analogue [(η 5 ‐C 5 H 5 ) 2 Cr 2 (CO) 5 ]. However, the C 10 H 8 Cr 2 (CO) 4 structure is thermodynamically unfavorable with respect to disproportionation into C 10 H 8 Cr 2 (CO) 5 and C 10 H 8 Cr 2 (CO) 3, in contrast to its very stable and experimentally known cyclopentadienyl analogue [(η 5 ‐C 5 H 5 ) 2 Cr 2 (CO) 4 ]. The lowest energy structure cis ‐[(η 7 ,η 5 ‐C 10 H 8 )Cr 2 (μ‐CO)] for the monocarbonyl C 10 H 8 Cr 2 (CO) is a triplet structure with an unsymmetrical bridging carbonyl group and a Cr≡Cr distance of about 2.4 Å, suggesting a formal triple bond. The qualitatively assigned Cr–Cr formal bond orders (one through five) are remarkably consistent with the Wiberg bond indices obtained from the Weinhold natural bond order analysis.