Electronic Structure of Bispentalene Complexes of Titanium, Zirconium, and Hafnium:  A Photoelectron Spectroscopic Study

Abstract

The geometrical parameters of the bis(pentalene) complexes of titanium, zirconium, and hafnium (3a-c) have been calculated by applying the RHF method. For 3a a structure with C 1 symmetry results, whereas for 3b,c D 2 symmetry is predicted. The torsional angles between the two pentalene ligands are calculated to be 56°(3a), 51°(3b), and 50°(3c). The orbital sequence of the six highest occupied molecular orbitals agrees very well with the ionization energies measured by PE spectroscopy of 3a-c. These measurements support a structure with D 2 or closely related symmetry.

Bonding in pentalene complexes and their recent applications

“…Ti is found to have a C1 global minimum lying only 2 kcal•mol −1 below a nearby D2 conformation. [24] DFT calculations (BP86/TZP) are in agreement with a predicted θ of 55°. [3] The 20 valence electron (VE) count of the Group 4 pentalene sandwiches aroused theoretical interest.…”

“…[20,21] The d-block Group 4 M(η 8 -Pn)2 compounds lack X-ray structural data but low temperature NMR studies suggest a D2 structure. [24] Calculations employing the…”

“…4). The HOMO, an out of phase combination of the two π5 orbitals ( Reproduced with permission from [24] DFT calculations (BP86/TZP) were carried out on the parent unsubstituted compounds ThPn2 and UPn2. [28] For ThPn2 a D2 conformation was found to be 3 kJ•mol −1 more stable than a D2h conformation.…”

“…Pentalene numbering system and geometric parameters for an η 8 -bound pentalene complex (a) fold angle, FA (b) twist angle, θ, for bis(pentalene) complexes. Correlation diagram of the six highest occupied orbitals of Pn2Ti as function of θ. Reproduced with permission from[24] Frontier orbitals of ZrPn2 and ThPn2 with D2d and D2 symmetry [10]…”

Binuclear Pentalene Iron Carbonyl Complexes

“…The resulting pentalene metal complexes exhibit a diverse array of coordination modes, thereby showing great flexibility in adapting to the electronic requirements of the metal center. [18] Examples of such complexes include the mononuclear transition metal derivatives (C 8 H 6 )V(C 9 H 7 ), (η 8 -C 8 H 6 )M(η 5 -C 5 H 5 ) (M = V, Ti, Zr), (η 8 -C 8 H 6 ) 2 M (M = Ti, Zr, Hf) and (η 3 -C 3 H 5 ) 2 Zr(η 8 -C 8 H 6 ) having a pentalene ligand bonded to a single metal atom as an octahapto ligand, [19][20][21][22] as well as the binuclear pentalene metal carbonyl derivatives cis-(η 5 ,η 5 -C 8 H 6 )Fe 2 (CO) 5 , [6] trans-(η 5 ,η 5 -C 8 H 6 )[M(CO) 3 ] 2 (M = Mn, Re), [7] and Ru 2 (MMe 3 ) 2 (CO) 4 (C 8 H 6 ). [5] Within the last few years the chemistry of pentalene metal complexes has expanded with the development by O'Hare and co-workers of methods for the synthesis of permethylpentalene precursors in quantity.…”