Tetranuclear Complexes Containing Quadruply Bonded Dimolybdenum Units Joined by μ-Hydride Ions

Abstract

Two tetranuclear complexes of the type [Mo2(DArF)3]2(μ-H)2, DArF = N,N‘-diarylformamidinate, Ar = p-tolyl (1) and p-anisyl (2), have been prepared by reaction of Mo2(DArF)3Cl2 and NaHBEt3. The cores are similar and show two quadruply bonded dimolybdenum units joined by two hydrogen atoms. These are the first structurally characterized tetranuclear molecules with localized quadruple bonds and also the first molecules with two independent M−(μ-H)−M units, in which each metal atom is also bonded to another M atom. It is remarkable that in each case the compound resists hydrolysis by water but will react with HCl. The δ → δ* transitions, which are normally the lowest energy bands in the visible region of the electronic absorption spectra, appear as shoulders at 449 and 444 nm for 1 and 2. However, each compound also shows two more transitions at lower energy (ca. 505 and 728 nm). These bands have been assigned to transitions involving the three center−two electron Mo−H−Mo bridges.

Experimental and Computational Studies on Quadruply Bonded Dimolybdenum Complexes with Terminal and Bridging Hydride Ligands

“…Subsequently, however, it was noted that its two three‐centered, two‐electron (3c‐2e) Mo‐H‐Mo interactions were more in accordance with a Mo=Mo formulation [17] . Some tetranuclear complexes comprising two Mo≣Mo units bridged by hydride ligands and stabilized by coordination to p ‐aryl substituted formamidinate groups were reported by Cotton, Murillo, and co‐workers [18–21] . A few dimolybdenum hydride complexes with lower Mo−Mo bond orders have also been described [22–25] …”

Nitrile Hydrolysis Promoted by Rhenium(III) Metal-Metal Bonded Systems

“…[59] The use of less than two equivalents of the silver salt in the reaction results in diminished yields, less than the optimal 21%, and supports the proposed reaction mechanism in which both OH -or H 2 O and CH 3 CN are coordinated at the Re 2 (III, III) core. [58,59] The ability to form conjugated systems containing multiple metal-metal bonds has been confirmed, [78][79][80][81][82][83][84][85][86][87][88] and the potential to form extended systems based on the [N( [58] building block through linkage of the dirhenium core via weak axial chlorides demonstrated. With the ability to hydrolyze nitriles to amides, the potential exists to link two or more of the Re 2 (III, III) units by the use of an arene bearing two nitrile functionalities.…”

Anionic Oligomerization as a Route to Chain Clusters

“…For instance, the reaction of the quadruply bonded complex [Mo 2 (DArF) 3 Cl 2 ] (DArF N,N'-diarylformamidinate) with NaHBEt 3 does not result in H À addition but rather in reductive substitution, leading to the cyclic oligomer [Mo 2 (DArF) 3 ] 2 (m-H) 2 , containing Mo 2 units that still retain the quadruple bond. [44] However, other types of addition reactions do occur: for instance the addition of bifunctional ligands in the axial positions of various multiply bonded M 2 L 8 dimers (see Scheme 10 a) leads to one-dimensional coordination polymers, without M ± M bonds connecting M 2 units. [9,45] If these bifunctional ligands could be replaced by some suitable organometallic fragment, copolymers made of -M 2 -M'-M 2 -chains would be obtained (Scheme 10 b).…”