Synthesis, Solid-State Structure, Solution Dynamics, and Reactivity of the Trinuclear Open Cluster Anion [Re₂(CO)₉{(μ-H)ReH(CO)₄}]^-

Abstract

The addition of [M(CO) 5 ] -anions (M ) Re, Mn) to the electronically unsaturated [Re 2 (µ-H) 2 (CO) 8 ] complex rapidly and selectively gives the trinuclear anions [ReM(CO) 9 {(µ-H)ReH-(CO) 4 }] -(M ) Re, 2; M ) Mn, 3). The single-crystal X-ray analysis of [NEt 4 ]2 has revealed a fully staggered L-shaped structure. The anion 2 has been obtained with good selectivity also by reacting (i) [Re 2 (CO) 9 (THF)] with [H 2 Re(CO) 4 ] -and (ii) [HRe 2 (CO) 9 ] -with [HRe-(CO) 5 ]. The last reaction can be reversed upon treatment with CO. The reaction of the trinuclear open cluster [Re 2 (CO) 9 {(µ-H)Re(CO) 5 }] with [H 2 Re(CO) 4 ] -affords 2 as well, evenif not quantitatively. 1 H and 13 C NMR spectra of 2 show conformational freedom around both the Re-Re interactions and a dynamic process exchanging the two hydrides and the carbonyls trans to them (E a ) 67(2) kJ/mol). This last is attributable to a windshield-wiper motion of the H 2 Re(CO) 4 fragment around the two trans diaxial carbonyls. The exchange of the hydrides with comparable ∆G q has been observed also for 3, suggesting that the same type of motion is occurring. 13 C-NMR studies of the related [Re 2 (CO) 9 {(µ-H)Re(CO) 5 }] complex have shown the facile mobility of the bridging hydride between the two metal-metal interactions (at variance with the anion 2), resulting in a "dynamic" C 2v symmetry of the molecule in solution. Upon heating, the anion 2 looses CO and gives irreversibly the previously known triangular cluster anion [Re 3 (µ-H) 2 (CO) 12 ] -. The addition of a strong acid (CF 3 SO 3 H) results in fragmentation of the trinuclear skeleton of 2, affording [HRe(CO) 5 ] and [Re 2 (µ-H) 2 (CO) 8 ].

[Re5(μ-H)4(CO)20]− and [Re5(μ-H)5(CO)20], Two Isolobal Analogues of Cyclopentane

“…In addition, spacers (for example, polyphenyls, [6] alkenes, [7] or alkynes [5,8] ) can also be selected to serve as electron-conducting active components to promote long-range electronic coupling between terminal subunits or (for example, saturated hydrocarbons [9] ) to serve as passive connecting components. Systems with unsaturated sp carbon chains (C n ) between two subunits constitute one of the most fundamental classes of one-dimensional molecular wires, however, intense studies in numerous laboratories have focused on the systems with alkynes or acetylenyl bridges.…”

“…tetranuclear clusters, [6,7] by allowing hydrido ± carbonyl rhenates to react with [Re 2 (CO) 9 L], where L is a very labile ligand such as THF or H 2 O (the otherwise labile MeCN ligand is not labile enough to be substituted by neutral [8] or anionic [6] hydride complexes). Recently the di-substituted complex 1,2-eq,eq-[Re 2 (CO) 8 8 ] with diazomethane.…”

“…We have prepared one such species, the 8 ]. [6] The treatment of 1 with a stoichiometric amount of 2 afforded the novel cyclic pentanuclear cluster anion [Re 5 (m-H) 4 …”

Anionic Oligomerization as a Route to Chain Clusters

“…shown that replacement of X À with isolobal carbonylmetalates affords trinuclear L-shaped cluster anions, [19,33] due to the formation of MÀRe bonds (Scheme 8). More recently we proved that also carbonylates containing terminal hydrido ligands can add to 1, [22,18] through M-H-Re interactions (Scheme 8).…”

“…[18,19] On the other hand, ring opening by the addition of electron donors [20] is penalized by the fact that the number of ring clusters of nuclearity higher than 3 is very limited.…”