Energetics of Metal−Ligand Multiple Bonds. A Combined Solution Thermochemical and ab Initio Quantum Chemical Study of MO Bonding in Group 6 Metallocene Oxo Complexes

Abstract

In this paper, we report a synthetic, molecular structure, thermochemical, and ab initio Hartree−Fock/Moller−Plesset level study of bonding and bonding energetics in the group 6 metallocene oxo series Cp2Mo/(MeCp)2MO, M = Cr, Mo, W. Efficient, high-yield syntheses of the pairs Cp2MH2/(MeCp)2MH2, Cp2MCl2/(MeCp)2MCl2, and Cp2MO/(MeCp)2MO where M = Mo or W are reported. The molecular structure of (MeCp)2WO features a “bent sandwich” geometry with a WO distance of 2.04(1) Å and an average WC(Cp) distance of 2.371(8) Å. Thus, WC(Cp) exhibits a ∼0.07 Å elongation over the corresponding distance in typical Cp2WX2 complexes and a WO distance which appears to be elongated versus what might be expected for a formal triple bond. D(MO) values obtained from (MeCp)2MO silanolytic (Me3SiCl, Me3SiI) batch titration calorimetry are very large: 110(11) kcal/mol (M = Mo) and 132(10) kcal/mol (M = W). The corresponding D(WOTMS) value is determined to be 65(18) kcal/mol. Ab initio relativistic core potential calculations reveal significantly weakened MCp bonding versus that in the corresponding Cp2MCl2 compounds, weakened MO bonding due to population of MO π antibonding levels, and a pronounced accumulation of negative charge on the oxo ligand (consistent with observed nucleophilicity of these complexes). Calculated Cp2MCl2 and Cp2MO molecular geometries and D(MO) values at the MP2 level are in favorable agreement with experiment. The D(MO) and D(MO) data provide significant insight into the chemistry of Cp2MO complexes, especially in regard to constraints on oxo transfer as well as oxametallacycle formation and scission processes.

“Bent Bonds” between Bismuth and Carbon Atoms as a Result of CH Activation in MoBi Complexes

“…However, at no stage did a detectable concentration of 3 or 2 or any other intermediate build up. In conclusion, the methyl substituents on the Cp rings of molybdocenedihydride have a pronounced effect on 1) the course of its reaction with [Bi(OtBu) 3 ], 2) the solubilities of the products and 3) on the nature of the products-an observation that had not really been expected in advance (a decrease of the solubilities is commonly observed on going from Me Cp to Cp, [7] but usually to a smaller extent). Naturally the question arose, why in the case of unmethylated molybdocenedihydride was 3 formed and not an isomer 4 corresponding to IV.…”

“…[Cp 2 MoH 2 ] and [Bi(OtBu) 3 ] were prepared as described. [7,17,18] 1: Synthesis and spectroscopic data: see reference [2]. 9152, Dm = 6.0 mm).…”

Catalytic Degenerate and Nondegenerate Oxygen Atom Transfers Employing N2O and CO2 and a MII/MIV Cycle Mediated by Group 6 MIV Terminal Oxo Complexes

“…While these bonds are significantly longer than the tungsten-oxygen bond of 1.684 determined for [W(O)Cl 4 ] [13] and of 1.689(6) for [W(O)(CO)Cl 2 (PMePh 2 ) 2 ], [10] of two has been proposed. [14][15][16] Accordingly, based on these simple bond-length comparisons, we currently favor the assignment of a MÀO bond order for 7 and 8 that lies somewhere between two and three. [17] This bond order formalization for 7 and 8 further implies a lower nucleophilicity for the terminal oxo group, as compared to that experimentally determined for [(MeCp) 2 M(O)] and related metallocene terminal oxo complexes, such as […”

Synthese und Koordinationseigenschaften von Molybdocenalkoxiden – das erste Heterodimetallalkoxid mit Molybdän und Bismut

“…Im Hinblick auf die Antitumoreigenschaften von [Cp 2 MoCl 2 ], deren Grundlagen zur Zeit intensiv untersucht werden, [18] erscheint die Verwendung von Verbindungen wie 1 ebenfalls reizvoll. [11] in 20 mL THF wird tropfenweise zu einer Lösung von 0.20 g (0.82 mmol) [Cp 2 MoO] [10] in 40 mL THF gegeben. Nach 1 h Rühren wird das Lösungsmittel von der resultierenden braunen Lösung entfernt und der zurückbleibende braune Feststoff mit Toluol extrahiert.…”

“…20 mL eingeengt und bei À 40 8C gelagert, wobei 0.32 g (0.58 mmol, 70 % Ausbeute) analysenreines 1 erhalten werden. 2: 0.74 g (2.5 mmol) [Cp 2 MoCl 2 ] [10] werden in 30 mL EtOH suspendiert und zu 2.15 g (5.0 mmol) [Bi(OtBu) 3 ] I gelöst in 30 mL EtOH gegeben. 2 h Rühren liefert eine braune Lösung, die 40 min auf 70 8C erhitzt wird.…”