μ‐Carbonyl‐bis(cyclobutadiencarbonyleisen), ein Komplex mit Eisen‐Eisen‐Dreifachbindung ‐ Ein Modell für das ungewöhnliche Verhalten von Fe(CO)₄ in Lösung?

Iron–iron bonding versus iron–phosphorus bonding in binuclear diphosphacyclobutadiene iron carbonyl complexes

“…The known iron complex (g 4 -Bu t 2 C 2 P 2 )Fe(CO) 3 might be expected to undergo decarbonylation upon photolysis to form binuclear derivatives of the general type (g 4 -Bu t 2 C 2 P 2 ) 2 Fe 2 (CO) n similar to the reported [10,11], formation of (g 4 -C 4 H 4 ) 2 Fe 2 (l-CO) 3 from the photolysis of (g 4 -C 4 H 4 )Fe(CO) 3 . Previous theoretical studies on the (g 4 -C 4 H 4 ) 2 Fe 2 (CO) n derivatives, [12] potentially obtainable from (g 4 -C 4 H 4 )Fe(CO) 3 , predict mainly structures having tetrahapto C 4 H 4 rings and iron-iron bonds with formal orders predicted by the 18-electron rule.…”

“…7) have three bridging carbonyl groups and very short Fe"Fe distances of 2.15-2.18 Å suggesting the formal triple bonds required to give both iron atoms the favored 18-electron configuration. Such structures are related to those of the experimentally known cyclobutadiene derivatives (g 4 -R 4 C 4 ) 2 Fe 2 (l-CO) 3 (R = H, [10] Me [11]) as well as the predicted (g 5 -C 4 H 4 P) 2 Mn 2 (l-CO) 3 structure for the related phospholyl manganese carbonyl derivative [43].…”

“…The tricarbonyl (Me 2 C 2 P 2 ) 2 Fe 2 (CO) 3 differs from the tetracarbonyl and pentacarbonyl by having low energy structures with only terminal g 4 -Me 2 C 2 P 2 ligands and thus resemble the experimentally known [9,10] cyclobutadiene analogues (g 4 -R 4 C 4 ) 2 Fe 2 (-l-CO) 3 (R = H, Me). In such structures all three carbonyl groups bridge the Fe 2 unit and the Fe"Fe distance of $2.16 Å is short enough to suggest the formal triple bond required to give the iron atoms the favored 18-electron configuration.…”

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

“…1832 1810 1775 1922 1795 1809 1775 1816 1837 1870 1943 1925 1807 1815 1799 1936 1941 1949 1951 1964 1934 1949 1934 1951 1950 1983 1998 1971 1943 1976 1969 Bridging m(CO) frequencies are in bold The global minimum of [C 4 H 4 BN(CH 3 ) 2 ] 2 Fe 2 (CO) 3 depends upon the DFT method. In fact, structure 3S-1 is related to the experimentally known structure for the essentially isoelectronic (g 5 -C 5 H 5 ) 2 Mn 2 (l-CO) 3 and (g 4 -C 4 H 4 ) 2 Fe 2 (CO) 3 , likewise, formulated with formal metal-metal triple bonds [13][14][15][16]. Like [C 4 H 4 BN(CH 3 ) 2 ] 2 Fe 2 (CO) 4 discussed above, the B3LYP method favors the high-spin state and the BP86 method favors the low-spin state as noted by Reiher et al [47].…”

“…These are isoelectronic with both cymantrene [11,12] (g 5 -C 5 H 5 )Mn(CO) 3 and the very stable cyclobutadiene-iron tricarbonyl (g 4 -C 4 H 4 )Fe(CO) 3 . Among such derivatives, the binuclear tricarbonyls [13][14][15][16] (g 5 -C 5 H 5 ) 2 Mn 2 (CO) 3 and (g 4 -C 4 H 4 ) 2 Fe 2 (CO) 3 with formal metal-metal triple bonds appear to be the most stable and are readily synthesized. Among such derivatives, the binuclear tricarbonyls [13][14][15][16] (g 5 -C 5 H 5 ) 2 Mn 2 (CO) 3 and (g 4 -C 4 H 4 ) 2 Fe 2 (CO) 3 with formal metal-metal triple bonds appear to be the most stable and are readily synthesized.…”