Binuclear dimethylaminoborole iron carbonyls: iron–iron multiple bonding versus nitrogen → iron dative bonding

Abstract

Theoretical studies show that pendant dimethylamino groups can play a significant role in the chemistry of unsaturated binuclear dimethylaminoborole iron carbonyls. For [C 4 H 4 BN(CH 3 ) 2 ] 2 Fe 2 (CO) 5 , the lowest energy structures have single CO bridges and Fe-Fe single bonds of lengths *2.8 Å . The lowest energy [C 4 H 4 BN (CH 3 ) 2 ] 2 Fe 2 (CO) n (n = 4, 3) structures have two bridging CO groups with Fe=Fe double bonds of lengths *2.5 Å for n = 4 and three bridging CO groups with Fe:Fe triple bonds of lengths *2.2 Å for n = 3. These structures are similar to structures previously found for the corresponding methylborole derivatives (C 4 H 4 BCH 3 )Fe 2 (CO) n . However, slightly higher energy [C 4 H 4 BN(CH 3 ) 2 ] 2 Fe 2 (CO) n (n = 4, 3) structures are found in which dimethylaminoborole is a six-electron donor bridging ligand using electron pairs from the nitrogen atom as well as from the two C=C double bonds. For the more highly unsaturated [C 4 H 4 BN (CH 3 ) 2 ] 2 Fe 2 (CO) n (n = 2, 1), low energy singlet (n = 2) and triplet (n = 1) perpendicular structures are also found with similar bridging six-electron donor dimethylaminoborole ligands. In addition, highly unsaturated [C 4 H 4 BN(CH 3 ) 2 ] 2 Fe 2 (CO) n (n = 3, 2, 1) structures are found with agostic hydrogen atoms bridging an iron-carbon bond.Keywords Iron Á Boroles Á Metal carbonyls Á Dimethylaminoborole Á Metal-metal bonding Á Nitrogen-iron dative bonding Á Density functional theory Dedicated to Professor Eluvathingal Jemmis and published as part of the special collection of articles celebrating his 60th birthday. This paper is dedicated to Professor Eluvathingal Jemmis on the occasion of his 60th birthday in recognition of his major contributions to theoretical chemistry, especially those related to boron compounds. Particularly inspiring to us has been Professor Jemmis' work on electron counting as a means to qualitatively understand electronic structures.Electronic supplementary material The online version of this article (

Metal–Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc

“…The dimethylaminoborole carbonyl series Fe 2 (C 4 H 4 BNMe 2 ) 2 (CO) n ( n = 5, 4, 3, 2, and 1) exhibits many examples of N→Fe dative bonds and some structures in which where the aminoborole ligand bridges the central Fe 2 unit (Table ). The Fe 2 (C 4 H 4 BNMe 2 ) 2 (CO) 5 system 04 has three singlet minima with long Fe–Fe single bonds of lengths ranging from 2.786 to 2.839 Å.…”

“…The methylborole (C 4 H 4 BCH 3 )­Fe 2 (CO) n series gives the following length ranges for iron–iron bonds: 2.71 ± 0.10 Å for Fe–Fe single bonds, 2.45 ± 0.06 Å for FeFe double bonds, 2.21 ± 0.03 Å for FeFe triple bonds, and 2.12 ± 0.03 Å for Fe–Fe quadruple bonds. The dimethylaminoborole (C 4 H 4 NBMe 2 ) 2 Fe 2 (CO) n series exhibits the following length ranges for iron–iron bonds: 2.77 ± 0.08 Å for Fe–Fe single bonds, 2.49 ± 0.14 Å for FeFe double bonds, and 2.26 ± 0.04 Å for FeFe triple bonds. The methylborabenzene (C 5 H 5 BCH 3 ) 2 Fe 2 (CO) n series shows the following length ranges for iron–iron bonds: 2.59 ± 0.01 Å for Fe–Fe single bonds and 2.38 ± 0.10 Å for FeFe double bonds.…”

Bridging hydrogen atoms versus iron–iron multiple bonding in binuclear borole iron carbonyls

“…1 (C 1 , 0.0) 1T -1 (C 1 , 7.3) In determining these dissociation energies, the fragments were allowed to relax. [26] were reported using the B3LYP and BP86 methods. However, as discussed above, the B3LYP* method is expected to predict more reliable relative energies for the different electronic spin states [38,39,40].…”