Bis(cycloheptatrienyl) Derivatives of the First‐Row Transition Metals: Variable Hapticity of the Cycloheptatrienyl Ring

Abstract

Extrapolation from ferrocene and dibenzenechromium suggests the currently unknown 18‐electron sandwich compound (η7‐C7H7)2Ti as a possible stable molecule. However, density functional theory (DFT) methods using the B3LYP and BP86 functionals predict (η7‐C7H7)2Ti to distort by ring slippage to give a singlet 16‐electron complex (η7‐C7H7)Ti(η5‐C7H7) having an uncomplexed C=C double bond in one of the C7H7 rings but otherwise closely related to the known (η7‐C7H7)Ti(η5‐C5H5). The situation is similar with (C7H7)2V except that the corresponding structures have doublet spin multiplicity. However, an analogous (η7‐C7H7)Cr(η5‐C7H7) structure is not found for chromium. Instead the most stable (C7H7)2Cr structure is a singlet d0 six‐coordinate formally CrVI complex with two tridentate cyclopropyldivinyl C7H7 ligands. The latter rearrangement of the C7H7 rings bonded to chromium can involve initially a (η6‐C7H7)2Cr diradical sandwich compound followed by a bis(η5‐norcaradienyl)Cr intermediate. For the later first‐row transition metals the lowest energy (C7H7)2M structures are predicted to be doublet (η7‐C7H7)Mn(η3‐C7H7) rather than (η5‐C7H7)2Mn for manganese, singlet cis and trans structures (η5‐C7H7)2Fe for iron, doublet (η3‐C7H7)2Co for cobalt, and two singlet (η3‐C7H7)2Ni stereoisomers for nickel.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Formal chromium–chromium triple bonds and bent rings in the binuclear cycloheptatrienylchromium carbonyls (C7H7)2Cr2(CO)n (n=6,5,4,3,2,1,0): A density functional theory study

“…One of its C 7 H 7 rings (the ''lower" one in Fig. 6) has undergone a transannular rearrangement to give a tridentate cyclopropyl divinyl ligand similar to that predicted in previous work [46] to be present in the lowest energy structure of (C 7 H 7 ) 2 Cr. The other C 7 H 7 ring (the ''upper" one in Fig.…”

A Half-Century of Cycloheptatrienylmetal Chemistry: Experiment and Theory

“…MPW1PW91: This newer-generation functional combines the modified Perdew-Wang exchange functional with the Perdew-Wang 91 gradient-correlation functional. [22] The DFT studies on the first row transition metal derivatives (C 7 H 7 ) 2 M (M ¼ Ti, V, Cr, Mn, Fe, Co, Ni) [23] used the B3LYP and BP86 methods. All three methods were used for the study of the (C 7 H 7 ) 2 Mo 2 (CO) n (n ¼ 6, 5, 4, 3, 2, 1) derivatives.…”

Heptahapticity in Binuclear (Cycloheptatrienyl)molybdenum Carbonyl Derivatives: The Interplay between Ring Hapticity/Planarity and Metal–Metal Multiple Bonding

“…Two energetically low-lying structures are predicted for [(C 7 H 7 ) 2 Mo 2 (CO) 5 ], namely, one singlet and one triplet ( Figure 2 and Table 3). The optimized singlet structure (IIA-s) is the global minimum with all real vibrational frequencies.…”

“…The remaining three carbonyl groups are terminal carbonyl groups. One of these is bonded to the (h 5 -C 7 H 7 )Mo moiety and the remaining two are bonded to the (h 3 - 5 ] structure IIB-t ( Figure 2 and Table 3) A total of four structures were found for [(C 7 H 7 ) 2 Mo 2 (CO) 4 ] within 35 kcal mol À1 of the global minimum IIIA-s ( Figure 3 and Table 4). This global minimum is [(h 7 -C 7 H 7 ) 2 Mo 2 (CO) 4 ] with no bridging carbonyl groups and two heptahapto C 7 H 7 rings.…”

“…In most such reactions, the transition-metal compound simply reduced the tropylium ion to bicycloheptatrienyl, C 7 H 7 À C 7 H 7 . Furthermore, the sandwich compound bis(cycloheptatrienyl)titanium, (h 7 -C 7 H 7 ) 2 Ti, strictly analogous to ferrocene and dibenzenechromium, has remained elusive for reasons clarified in a recent theoretical study [5] from our group.Success was achieved by Dauben and Honnen in 1958 [6,7] in the synthesis of cycloheptatrienyl transition-metal compounds when the neutral hydrocarbon 1,3,5-cyclohepta- [a] Prof.…”